GB2381573A

GB2381573A - Controlling the outlet temperature when incinerating waste and sludge

Info

Publication number: GB2381573A
Application number: GB0304005A
Authority: GB
Inventors: Akira Nakamura; Takashi Noto; Hajime Akiyama; Seiji Kinoshita; Yoshinari Fujisawa; Seiichi Noguchi
Original assignee: NKK Corp; Nippon Kokan Ltd
Current assignee: JFE Engineering Corp
Priority date: 1998-11-24
Filing date: 1999-11-19
Publication date: 2003-05-07
Anticipated expiration: 2019-11-19
Also published as: GB2381572B; GB2381573B; GB0304005D0; GB0304004D0; GB2381572A

Abstract

In an incinerator 901 waste and sludge combusts together and a cooler 902 cools the exhaust gas temperature, measured at the inlet to an electrostatic precipitator (fig 35,904) to less than 230 degrees Celsius, to reduce the emission of dioxins. Cooler 902 comprises a water spray cooler with the rate of water spray being controlled to effect control of the exhaust gas temperature. Incinerator 901 is further equipped with a waste hopper 901a, a sludge supply hopper 901b, a temperature sensor 907, temperature controller 908, an exhaust gas treating device 903, a fan 905 and a stack 906.

Description

238 1 573

Specification..DTD: WASTE DISPOSAL INCINERATION METHOD AND APPARATUS TEHREOF

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus for incinerating a waste.

BACKGROUND OF THE INVENTION

.... ... ....DTD: : Most ova municipal refuse and an industrial waste (when Hi ystateclas awaste,bothoranyoneofthem-willbedesignated hereafter) are incinerated and disposed of by landfill. Many or the waste incinerating facilities are provided with fire grate incinerators, and some of them are provided with fluidized bed incinerators. -. i..: A waste incineration in an incinerating facility provided with the fire grate incinerator is.carried out as follows. At first, the waste is chargedintotheincinerator, its temperature is raisedwhile being cried by the combustionairblown from below the fire grate and by the radiant heat inside of the incinerator, andit catches fire.Subsequently, the wasteis burned end reduced to an ash, and discharged as an incineration ash outside of the incinerator. On the other hand, slice an exhausting gas contains a combustible gas such as H2, CO, and CH. generated in a drying ,. step, in a temperature-raising step and in an initial co bustion-s.ep, an air is blown in a secondary combus ion

2 - chamber for burning a combustible gas. The exhausting gas from the secondary combustion chamber is subjected to heat recovery by a boiler or to cooling in a gas cooling device such as a gas cooler, and sent to an exhausting gas treating step. After the harmful gas removal treatment and the dust removal one, it is released from a stack.

As shown in FIG.2, the waste incineration in the incineration facility provided with a fluidized bed incinerator is carried out as follows. The waste is charged into the ......

fluidized bed incinerator 1 by a non-indust'rial waste charger .... 2, 'and'-then, its temperature is raised while being dried in a fluidized layer 9 on the fluidized bed 4, and the waste is burnt.

However, since the exhausting gas generated in the fluidized bed contains a combustible gas such as He, CO, and CH4, an air is blown into a freeboard section of the incinerator for burning ' the combustible gas. After that, the exhausting gas is subjected to cooling in a gas cooling facility and sent to a exhausting gas treating facility5, whereit issub} ectedto a harmful gas removal treatment and a dust removal treatment, and released into the atmosphere from a stack 6. The fluidized bed incinerator shown in Patent Laid Open No. 9-303743 is one example in this way.

In a fluidized bed incinerator as above, RDF is sometimes burnt. RDF (Refuse Derived Fuel) means a waste converted into a fuel; that is, a fuel made by adding calcium compound to an industrial waste, a municipal refuse and has a lower calorific value of 3000 to 6000 kcal/kg with a water content of 1 to 20 at%. There happens one problem when burning RDF; that is to say, men tit _ _4,} 41 | | ||_11-lil_lllll I_al_ llllllll

i - 3 much chlorine is contained in the RD., and the reaction thereof with aromatic compounds is likely to generate a sort OI dioxins such as dioxin or furan.

Recently it has been found that an exhausting gas generated in a waste incinerating facilities containssomesortsoLdioxins such as chlorodibenzodioxan and chlorodibenzofuran, or other organic chlorine compounds, and it causes a serious problem against protecting an environmental conditions. Therefore, I regulations over dioxins emissions are being tightened.

Under these circumstances, various technological ' . developments are being carried out '' or' reducing dioxins in an exhausting gas. However, many of them intend to catch dioxins . together with a fly ash, and a treatments of making a fly ash nontoxic needs to be independently carried out. By that reason, they result in no fundamental solution. In addition, a technology for decomposing dioxi'ns accompanies a large-scale' treating apparatusf and when applying to the present waste incinerating facilities, a substantial facility renovation is required, and hit is difficult to implement that renovation. For example, the technology disclosedinPatentLaidOpenNo.5-161822 requires to install a ceramic filter for treating an exhausting gas. DISCLOSURE OF TRE INVENTION

The present invention has been realized to solve these problems, and accordingly one of the objects of the present invention is to provide a waste incineration me hod for an -

r _ g incinerator by introducing a relatively simple combustion method which does not cause problems as mentioned above. It maintains a constant combustion in an incinerator, thereby suppressing emissions o a harmful gas and an unburnt gas.

The present invention is to further solve the above-

menlioned problems, and one of the objects of the present inventionis to provide a waste incineration method and a facility thereof by equipping a very simple apparatus and just by adding cheap substances, thereby enabling to reduce the amount of generated dioxins itself.

In order toaccomplishthe above-mentioned objects, firstly, the present invention is to provide a waste incineration method, which means; preparing a sludge which has the water content of 65 to 90 wit, the sulfur content of 0.1 to 2.0 wit in a drying condition, and a nitrogen content of 1 to 10 wt%; preparing one selected from the group consisting of RDF, which has a lower calorific value of 3,000 to 6,000 koal/kg and the water content of 1 to 20 wt%, and a non-industrial waste including a municipal refuse which has the lower calorific value of 1,500 to 4,000 kcal/kg and the water content of 30 to 70 wt%; and - I performing a mixed fuel combustion of the sludge and one selected from the group consisting of the RDF and the non-industrial waste including the municipal refuse in a waste incinerator., - ---iF4 1ilW ii 1 18 10B 1 1 B,R;I N lI-III8-IIR- 11 11 1llll ll I -15 1

f - _ _ Secondly, the present invention is to provide a waste incineration method, as follows: preparing a sludge and a waste plastic of a lower calorific value of 4,500 kcal/kg or more; performing a mixed fuel combustion of the sludge and the waste plastic in a waste incinerator; and controlling an outlet temperature of the waste I incinerator at 900-1,200 C and an oxygen concentration at 3 12 wt%.

Thirdly, the present invention is to provide a waste incineration method, as follows: performing a mixed fuel combustion of the waste and a sludge in a waste incinerator; measuring a SOx concentration in an exhausting gas in the waste incinerator; and, controlling at least one selected from the group consisting of the sludge supply amount end the waste supply amount in accordance with a measured value of the SOx concentration.

Fourthly, the present invention is to provide a waste incineration method, as follows: .... performing a mixed fuel combustion of a waste and a sulfur contained material; and measuring a SOx concentration in an exhausting gas in a waste incinerator; and controlling at least one selected from the group

i coasisting of a supply amount or the sulfur contained material and the supply amount of the waste in accordance with a measured ma He of the SOx concentration.

Fifthly, the present invention is to provide a waste incineration method, as follows: performing a mixed fuel combustion of a sulfur contained material and RDF in a waste incinerator; measuring the SON concentration in an exhausting gas in the waste incinerator; controlling at least one selected from the group consisting of the supply amount of the sulfur contained material and RDF in accordance with the measured value of the SOx concentration. Sixthly, the present invention is to provide a waste incineration method, as follows: supplying a sulfur contained powder to a waste incinerator by way;of at least one selected from the group consisting of a sludge-supply line and a waste-supply line; and, performing a mixed fuel combustion of the sludge and waste in waste incinerator; and measuring a SOx concentration in an exhausting gas in the waste incinerator; and controlling a supply amount of the sulfur contained powder in accordance with a measured value of the SOx concentration. tr _ r' _ R * HIllll Il;_UlIl 111 l - 8 At l 51_1; | 111 1

l' Seventhly, the present invention is to provide a waste incineration method, as follows: supplying dispersedly at least one selected from the group consisting of a sludge and a sulfur contained material and supplying it to a dust hopper of the waste incinerator; and performing a mixed fuel combustion of the waste and at least one selected from the group consisting of the sludge and the sulfur contained material.

Eighthly, the present invention is to provide a waste incineration method, as follows: supplying dispersedly at least one selected from the Group consisting ofa sludge and a sulfur contained materialonto a fire grate in a drying stage of a waste incinerator land, performing a mixed fuel combustion of the waste and, at least one selected from the group consisting of the sludge and the sulfur contained material.

Ninthly, the present invention is to provide a waste incineration method, as follows: adding a nitrogen compound to a waste; charging a waste into the incinerator; and incinerating the waste in the incinerator.

lOthly, the present invention is to provide a waste; incineration method, as follows:

feeding a waste into a drying zone of a fire grate incinerator; adding a nitrogen compound to the fed waste; and, incinerating the waste to which the nitrogen compound is added.

llthly, the present invention is to provide a waste incineration method, as follows: charging a waste into a fluidized bed incinerator; incinerating a waste in a incinerator; and, blowing a nitrogen compound into a zone prior to secondary combustion in a freeboard section positioned above the fluidized bed.

12thly, the present invention is to provide a waste incineration method, as follows: adding a nitrogen compound to the waste; charging the waste into an incinerator; incinerating the waste, and, blowing the nitrogen compound to an exhausting gas flow path through which the exhausting gas having 650 C or lower temperature flows.

13thly, the present invention is to provide a waste inci e ation method, as follows: preparing a waste incineration device having an incinerator, a temperature reducing device and an electrostatic _,4. _.,.,,,,_',,,.,.!, _,.:, '.= e''

r - 9 - l precipitator; performing a mixed fuel combustion of the waste and a sludge; and controlling the temperature reducing device so that an exhausting gas temperature is 230 C or lower at an inlet of the electrostatic precipitator.

14thly, the present invention is to provide a waste incineration apparatus, as follows: an incinerator locatedin a waste incineration device; a waste feeding device and a sludge feeding device for performing a mixed fuel combustion of the waste and the sludge in the waste incinera or; a SOx concentration meter for measuring the SOx concentration inside of the incinerator or at the outlet of the incinerator; and a control device for controlling a supply amounts of at least one selected from the group consisting of the sludge and the waste in accordance with the SOxconcentration.

15thly, the present invention is to provide a waste incineration apparatus, as follows: an incinerator located in a waste incineration device; a sulfur-contained material feeding device and a waste feeding device for performing a mixed fuel combustion of the sulfur-contained material and the waste n the incinerato'.

r - 10 a SOx concentration meter for measuring the SOx concentration in or at the outlet of the incinera or; and, a control apparatus for controlling the supply amount of at leas, one of the sulfur-containing substance and waste in accordance with the SOx concentration.

16thly, the present invention is to provide a waste incineration apparatus, an incinerator located in a waste incineration device; a sulfur-contained material feeding device and a RDF feeding device for performing a mixed fuel combustion of a sulfur-contained material and a RDF in the incinerator; a SOx concentration meter for measuring a SOx concentration in or at an outlet of the incinerator or in a stack; and a control device for controlling a supply amounts of at least one selected from the group consisting of a sulfur contained material and the RDF.

17th y, the present invention is to provide a waste incineration apparatus, as follows: an incinerator located in a waste incineration device) a sludge feeding device and a waste feeding device to the incir. eratori and a sulfur-contained powder feeding device provided in a reed line of the sludge and the waste into the incinerator.

_ I, _ _ H __ it I _1_11: 1-111 1111_ _11 18

f J 18thly, the present invention is to provide a waste incineration apparatus, as follows: an incinerator for performing a mixed fuel combustion of a waste and at least one selected from the group consisting of a sludge and a sulfur-contained material. substance; a waste hopper attached to the incinerator; and a lance for dispersing at least one of the sludge and sulfur-containing substance and feeding to the waster hopper.

l9thly, the present invention is to provide a waste incineration apparatus, as follows: -

an incinerator for performing a mixed fuel combustion of the waste and at least one selected from the group consisting of a sludge and a sulfurcontained material: a fire grate in the drying stage located in the incinerator; and.

a lance for dispersing at least one of the sludge and sulfur-containing substance and feeding it on the|fire grate|of the dry step.

20thly, the present invention is to provide a waste incineration apparatus, as follows: an device for adding the nitrogen compound to Haste to be charged into an incinerator; and an device for blowing the nitrogen compound into a flow path of an exhausting gas.

- r - 12 21stly, the present invention is to provide a waste incineration apparatus, as follows: an incinerator having a fire grate; and, a nitrogen compound adding device for supplying a nitrogen compound to a drying zone above a fire grate provided in an incinerator.

22ndly, the present invention is to provide a waste incineration apparatus, as follows: an incinerator having a fluidized bed; and, a nitrogen compound adding device for supplying the nitrogen compound to a zone prior to secondary combustion in a freeboard section located above the fluidized bed.

23rdly, the present invention is to provide a waste incineration apparatus, as follows: an incinerator locatedina waste incineration device; a nitrogen compound adding device for adding the nitrogen compound to the waste.obe charged into heincinerator; a heat recovery boiler located behind the incinerator along a gas flow direction; and . a device for blowing the nitrogen compound into a flow path of an exhausting gas at the outlet of the boiler.

24thly, the present invention is to provide a waste inc Aeration apparatus, as folios: Err__ i_ i: Em:: 45;_ 11_ 1 _118RlIII

r - 13 an incineratorlocated ins wasteincineration device; a nitrogen compound adding device for adding a nitrogen compound Lo the waste to be chargedintotheincinerator; a gas cooler loca ed behind the incinerator along the gas flow direction; and a device or blowing the nitrogen compound into a flow path of an exhausting gas at the outlet of the Has cooler.

25thly, the present invention is to provide a waste incineration device/ as follows; a waste incineration device, structured by connecting in series, via a flue, an incinerator, temperature reducing device, an exhausting gas treating device, an electrostatic precipitator, an induced draft fan, and a stack; a waste supply hopper provided to the incinerator; a sludge supply hopper provided to the incinerator; an exhausting gas temperature control device at the inlet of the electrostatic precipitator, connecting with the temperature reducing device and the electrostatic precipitator; and, a temperature sensor for sensing a temperature of the exhausting gas at an inlet of the electrostatic precipitator, which is located inside of a temperature control device for the islet exhausting gas of the electrostatic precipitator.

lo F BRIEF DESCRIPTION OF THE WOWINGS

FIG. 1 is a cross sectional view showing a schematic stricture of a fluidized bed incinerator, used in embodiments of the present invention; r IG. 2 is a view showing a schematic structure of a prior art fluidized bed incinerator; FIG.3 is a cross sectional view showing a schematic structure of a fire grate incinerator used in embodiments of the present invention; FIG.4 is a cross sectional view showing a schematic structure of the fluidized bed incinerator used in embodiments of the present invention; FIG.5 is a flow chart showing one form o: embodiment of the present invention;.

rIG. 6 is a graph illustrating one form of embodiment of the present invention and shows the relationship between the SOx concentration and the dioxins and poisonous substance ('. 2S + S03) concentration at the outlet of the incinerator; FIG. 7 is a schematic view showing one example of the fluidized bed incinerator of the present invention; FIG. 8 is a flow chart showing one form of embodiment of the present invention; rIG. 9 is a flow chart showing one form of embodimen-t-c f-the-

present invention; FIG.10 is a schematic v ew showing one example of a waste incineration apparatus of he present invention; FIG.11 is a schematic chart showing another example _, _ _ I,., I__ __ Ned _ 11111111 i __ 11 111 i8111 1 111 _1

of the incinerating apparatus of the present invention; FIG.12 is a schematic chart showing a structure of one example of the incinerating apparatus of the present invention; FIG.13 is a schematic chart showing a structure of another example of the incinerating apparatus of the present invention; FIG.14 is a schematic view showing a structure of a further example of a waste incinerating apparatus of the present invention) FIG. 15 is an explanatory view showing the first example of one form of embodiment of the present invention) FIG.16 is an explanatory view showing the second example of one form of embodiment of the present invention; FIG.17 is an explanatory view showing the third example of one form of embodiment of the present invention; FIG.18 is an explanatory view showing the fourth example of one form of embodiment of the present invention; FIG.l9 is an explanatory view showing the first example of another form of embodiment of the present.invention; FIG.20 is.an explanatory view showing the second example of another form of embodiment of the.present invention; FIG.21 is an explanatory view showing the third example of another form of embodiment of the present invention; FIG.22 is an explanatory view showing the fourth example of another form of embodiment of the present invention; FIG.23 is an explanatory view showing she first example of another form of embodiment of the present invention; FIG.24 is an explanatory view showing the second example

- - - 16 of another form of embodiment of the present invention; FIG.25 is an explanatory view showing the third example of another form of embodiment of the present invention) FIG.26 is an explanatory view showing the fourth example of another form of embodiment of the present invention; FIG.27 is an explanatory view showing the first example of another form of embodiment of the present invention; FIG.28 is an explanatory view showing the second example of another form of embodiment of the.present invention; FIG.29 is an explanatory view showing the third example of another form of embodiment of the present invention; FIG.30 is an explanatory view showing the fourth example of another form of embodiment of the present invention; FIG.31 is a view showing one example of an exhausting gas treating step in a waste incineration facility of the present invention, where a boiler is installed; FIG.32 is a view showing one example of an exhausting gas Creating step in a waste incineration facility of the present invention, where a gas cooler is installed; FIG.33 is a system configuration chart of a waste incineration facility in one form of embodiment of the present invention; FIG 34 is a graph OI the present invention, showing the relationship between the operating temperature of an electrostatic precipitator and the ra e of increase or dioxin; and FIG. 35 is a system configuration chart of a prior art waste

_ 1; _110 01518 1_1 1 151 1l

l incinera ion facility.

BEST MODE OF EMBODIMENT IN THE INVENTION

Detailed explanation will be made one by one for best mode of embodiment of the invention.

BEST MODE 1

This best mode 1 has accomplished the object oftheinvention by a Haste incineration method in a waste incinerator which is characterized by a mixed fuel combustion at a mixed fuel combustion ratio of 10-70% of sludge, which has the water content or 65-90 wit, dry sulfur content of 0. 1-2.0 wt%, and nitrogen content of 1-10 wt%, and RDF, which has the lower calorific value of 3,000-6,000 kcal/kg and water content of 1-20 wt%.

Herein, a mixed fuel combustion ratio is defined by sludge supply weight /(sludge supply weight + RDF supply weight).

This method of embodiment is charac erized by addition of sludge to RDF for combustion, and the sulfur content in sludge stays in the incinerator as H2S, CS2, COS, SO2 or SO3 during the combustion process. These substances have a poisoning effect to copper and similar substances which act as catalysts for the generation of di oxins, and can effectively restrain dioxins in the waste gas line from the high temperature combustion field

in the incinerator to behind the outlet of the incinerator. The nitrogen content in sludge generates ammonia in the combustion process, particularly in the reducing atmosphere of the primary combustion field, and by reacting with chloride compounds,

- 18 ammonia suppresses the dioxin generating reaction by C1 in the course of generating dioxins. Further, by controlling the concentration of water in sludge and restraining the combustion reaction rate of combustible matters, soot generation can be lowered. If the soot generation amount is able to be restrained, the concentration ofaroma ic organic compounds derived from soot is reduced, resulting in lowering the concentration of dioxins, which are products of incomplete combustion.

The current mode of embodiment can be applied to any type of waste incinerators. However, in order to raise the mixing property of RDF and sludge and increase the combustibility of sludge, it is preferable to carry out combustion by fluidizing the burning materials; in particular a fluidized bed incinerator is preferable.

RDF is as mentioned above a fuel formed by adding a calcium compound to industrial waste, municipal refuse, and other types of waste. Municipal waste is a mixture of household garbage, lef_over ood, plastic containers, waste papers, and wood chips.

Calcium carbonate or calcium hydroxide is used as a calcium compound. RDF thus produced has the lower calorific value of around 3000 to 6000 kcal/kg and the water content of around l to 20 wit.

Sludge is discharged from a wastewater treatment facility.

Any type of sludge is applicable, including sewage sludge, night soil slu ge,sludge Generated when performing an act -:a.edsludge treatment o organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing i-- 11 1 1 i Hi I I I_. It 14 _ -; 11, 1-

r - 19 organic materials, sludge generated in closed water areas as in river dredging, and other sludge generated in the course of treating wastewater. Sludge preferable for the method of this invention is one which has the nitrogen content of around 1 'o TO wt%, sulfur content of around 0.1 to 2.0 wt%, both in dry contents, and the water content of around 65 to 90 wt%. If the sulfur and nitrogen contents in sludge are lower than 0.1% and 1% respectively, the absolute concentrations of H2S, CS2, COS, SO2, SO3or similar components become toolow, and effects thereof become weak. Conversely, if the S and N contents in sludge are higher than 2.0% and 10% respectively, the concentrations of SO and NO from a stack become too high, and there-arises a possibility that regulated values may not be accomplished.

Further, if the concentration of water in sludge is lower than 65%, it is difficult to effectively control the combustion reaction rate of combustible materials. Conversely, if the concentration of water in sludge is higher than 90%, it is difficult to maintain the temperature in the incinerator.

The mixed combustion ratio of sludge and RDF is 10 to 70.

This is because the S content of 10 plus ppm and the N content of several 10 ppm at the lowest respectively are necessary for expecting he above mentioned effects, and the mixed combustion ratio needs to be more than 10% at the lowest. Conversely, if the mixed fuel combustion Ma io exceeds 70%, the water content becomes too high, and even i'- operated by squeezing down the air ratio, i is difficult to maintain the temperature at the outlet of the incinerator at 300 C.

- ( - 20 I: is sufficient to perform mixed fuel combustion of sludge and RDF in the incinerator. They may be mixed before charging, or charged into the incinerator separately.

The adequate combustion temperate e (in the fluidized bed type, the temperature at the freeboard section) is usually around 850 to 1000 C.

FIG.1 shows a structure of the incinerator used in an example of embodiment.

This incineratorlisafluidized bed type. In the interior, a sand layer to form the fluidized layer 9 is prevented from moving down by a dispersing plate. Under the dispersing plate, there is a wind box into which combustion air is blown. This incinerator 1 is separately provided with a RDF charger 2 and a sludge charger 3. For the combustion treatment, sludge and RDF are charged from the respective chargers into the incinerator, dried in the sand layer fluidized by the air sent from the wind box under the dispersing plate, their temperatures are raised and they catch fire. Sludge and RDF are burned in the fluidized layer above the fluidized bed 4 and in the freeboard section further above, and complete the combustion by the time they reach the outlet of the incinerator. After combustion, the waste gas is discharged outside hroush the outlet of the incinerator, goes through the waste gas treating facility, and released from a stack. By using the above me.itioncd incinerator, mixed fuel combustion of RDF and sludge was performed, where RDF was made from municipal refuse and has the value of 4000 kcal/kg and the 4, _.., _ il, _' I_ I; I; 11:: -

r t - 21 water concentration of8t, end sludge has the wafer concentration of 30%, N content of 7%, and S content of 0.6%. Combustion was carried out by maintaining the temperature in the incinerator at 850 C and changing the temperature in the fluidized layer between 500 and 850 C and that at the freeboard section between 850 and 1000 C. In the case of burning merely RDF, the average value of the dioxins concentrations was 2. 1 ng/Nm3-teq, but when RDF of 1 t/h and sludge of 0.5 t/h were burned at the mixed combustion ratio of 33.3%, the average value was able to be suppressed down to 0.2 ng/Nm3-teq.

Further, RDF, which was made from municipal refuse and has the value of 6000 kcal/kg and the water concentration of 5%, and sludge' which has the water concentration of 90%, N content of 7%, and S content of 0.6%, were burnt. At first, only RDF was burnt and the temperature in the incinerator was controlled merely by water spraying inside the incinerator. RDF of 0.6t/h and sludge of 1.4 t/h were burnt at the mixed fuel combustion ratio of 70%. At this time, the temperature at the outlet of the incinerator was controlled to be the same as when burning merely RDF. Comparing with the combustion of just RDF, the dioxins concentration at mixed fuel combustion with sludge was brought down by about half in average. As seen from the above, the present mode is characterized by mixed fuel

combustion et the ratio between 10 to70% o' sludge, which has the S content of 0.1 to 2.0%, water concentration of 65 to 90S, and N content of 1 to 10%, and RDF. By carrying out mixed fuel combustion of sludge, which has the high wafer content

- 22 and reduced lower caloriZic value, and RDF, which has the high lower calorific value, stable combustionismadepossibleso that the generation of poisonous gas or unburnt gas can be suppressed.

Further, by carrying out mixed combustion of sludge having the above concentration, the S. N and water contents in sludge can effectively restrain the generation of dioxins.

When incinerating sludge, sludge of the high wafer consent has the reduced lower calorific value, so that it is difficult.

to keep the burning conditions in the incinerator constant, and the temperature in the combustion chamber or the distribution of concentrations in the combustion gas inevitably becomes non-uniform both over time and space. This not only makes the control difficult but also causes a problem that poisonous gas is likely to be generated.

However, sludge, which is so difficult to burn, can be burnt smoothly by this mode.

BEST MODE

This mode of embodiment has accomplished the object o' the invention by a waste incineration method in a waste incinerator characterized by mixed fuel combustion at a mixed combustion ratio of 10-40% of sludge, which has the water content of 65-90 wt%, dry sulfur content of 0.1-2.0 wit and nitrogen content l-10 wt%, and non-_ndustrial waste such as municipal refuse, which has the lower caiorific value of 1500-4000 keal/ka and water content 30-70 wt%.

Herein, a m xed combustion rations defined by sludge supply - i''n I" B. l Illll_.R I" ' _ -.

( F - 23 weight /(sludge supply weight + supply weight of non-industrial waste such as municipal refuse).

This method of embodiment is characterized by addition of sludge to nonindustrial waste such as municipal refuse for combustion, and the sulfur content in sludge stays in the incinerator as H2S, CS2, COS, SO2 or SO3 during the combustion process. These substances have a poisoning effect to copper and similar substances which act as catalysts for the generation of dioxins, and can effectively restrain dioxins in the waste gas line from the high temperature combustion field in the

incinerator to behind the outlet of the incinerator. The nitrogen content in sludge generates ammonia in the combustion process, particularly in the reducing atmosphere of the primary combustion field, and by reacting with chloride compounds, i

ammonia suppresses the dioxin generating reaction or C1 in the course of generating dioxins. Further, by controlling the concentration of water in sludge and restraining the combustion reaction rate of combustible matters, soot generation can be lowered. If the soot generation amount is able to be restrained, the concentration of aromatic organic compound derived from soot is reduced, resulting in lowering the concentration of dioxins, which are products of incomplete combustion.

The current mode o' embodiment can be applied to any type oLwaste incinerators, and the fire grate type incinerator or the luidized bed incinerator can be used.

Municipal waste is a mixture o household garbage, lertover food, plastic containers, waste papers, and wood chips, and the

r - 24 lower calorific value is aroundlOOO to 3000 koal/kg end the water content is around 30 to 70 we%.

The mixed fuel combustion ratio of sludge and municipal waste is to to 40%. This is because the S content of 10 plus ppm and the N content of several lOppm at the lowest respectively are necessary for expecting the above mentioned effects and the mixed combustion ratio needs to be more than lOt at the lowest.

Conversely, if the mixed fuel combustion ratio exceeds 40%, the water content becomes too high, and even if operated by squeezing down the air ratio, it is difficult to keep the temperature at the outlet of the incinerator at 800 C.

It issuf icient toperformamixed fuel combustion of sludge and municipal waste in the incinerator. They may be mixed before charging, or charged into the incinerator separately.

The adequate combustion temperature (in the fluidized bed type, the temperature is at the freeboard section) is usually around BSO to lOOODC.

FIG.3 shows a structure of the incinerator used in an example Of embodiment.

This incinerator is the fire grate type, and the fire grate of the furnace bed of the main combustion chamber, that is, a drying stage ll, combustion stage 12, and post combustion stage 13, has a structure inclined downward in three steps. The main combustion chamber is equipped with a waste chute 10 at the uppermost par. of the,.re grate, and at the end of the lowest part of the fire grate is a main ash chute 15. Above the main combustion chamber, a secondary combustion chamber 14 is . I,,_ Al ail I8 BIRIllil ll:lil -II ill-_ if 1

( - 25 urnished for carrying out the secondary combustion of an exhausting gas. Sludge and waste are charged into the incinerator from the waste chute 10, sent to a drying stoker, where they are dried by the air from below and radiant heat in the incinerator, their temperatures are raised, and they catch fire. Sludge and waste which caught fire and started to burn are led to a combustion stoker, and are burnt by the combustion air sent from below, and the unburnt portion completes the combustion in the post combustion step. Ash left after combustion is taken out through the main ash chute 15. The combustion is performed in the main combustion chamber, and exhausting gas (gas staying in the furnace) is mixed in the secondary combustion chamber 14, where the secondary combustion takes place and the unburnt portion completes the combustion, and is sent to the exhausting gas treating facility.

By using the above mentioned incinerator, mixed fuel combustion of municipal refuse and sludge was performed, where municipal refuse has the value of 2300 kcal/kg, and sludge has the water concentration of 80%, N content of 7%, and S content of 0.6%, and the combustion was carried out by keeping the temperature in the incinerator at 850: and changing the temperature in the fluidized layer between 650 and 850 C and that at the freeboard section between 900 and 1000 C. In the case of burning merely municipal refuse, the average value of the dioxins concentrations was 1.6 ng/Nm3-teg, but when urban refuse OI 2,/h and sludge of 1 t/h were burned at the mixed fuel combustion ratio of 33.3%, the average -value was able to be

- 26 suppressed down to 0.25 ng/Nm3-teq.

Further, municipal refuse, which has the value of 2800 keel/kg, and sludge, which has the water concentration of 90 wti r N content or 7 wt%, and S content of 0.6 wt%, were burnt in the luidized bed incinerator. Comparing the combustion of merely municipal refuse with the mixed fuel combustion of municipal refuse and sludge, the dioxins concentration was reduced by about 60% in average when mixed combustion was carried out. Both experiments were carried out at the equal temperature at the outlet of the incinerator.

As seen from the above, the present embodiment is characterized by mixed fuel combustion at the ratio between 10 to 40% of sludge, which has the S content of 0.1 to 2.0%, water concentration of 65 to 90%, and N content of 1 to 10%, and non-industrial waste such as urban refuse. By carrying out mixed fuel combustion of sludge, which has the high water content and reduced lower calorific value, and the urban waste, which has the relatively high lower calorific value, stable combustion is made possible so that the generation of poisonous gas or unburnt gas can be suppressed. Eurther, with the above concentration, the S. N and water contents in sludge can effectively restrain the generation ol dioxins.

Sludge of the high water content has the reduced lower calorific value is low, so that it is difficult to decrease the temperature in the incinerator and maintain the burning conditions constant. Deriving therefrom, the emperature in the combustion chamber or the distribution of concentrations in

f - 27 combustion gas becomes non-uniform over time and space. This makes the control difficult, and also causes a problem that unburnt gas and poisonous gas are likely to be generated. In addition, in a fire grate type incinerator widely used as the waste incinerator, sludge drops down from the fire grate, and complete combustion is not carried out, and the blowing air path under the fire grate is often choked, so that in general it is not used for sludge incineration.

However, sludge, which is so difficult toburn, can be burnt smoothly by this best mode.

BEST MODE 3

When incinerating waste plastics in a fluidized bed incinerator, there is a problem that chlorine contained in waste plastics reacts with aromatic compound and islikely to generate dioxins such as dioxin and luran. Since waste plastic has a high lower calorific value, the temperatureintheincineratorbecomes high, and the combustion reaction rapidly progresses, which generates soot or unburnt portion. Thus, the concentration of aromatic organic compounds, which contribute to dioxins generation, becomes high and as a result, dioxins concentration becomes high.

As resolution of this problem, various combustion control and air blowing methods have been proposed es prior technologies.

10wever, depending upon properties oLwas.e Plastic charged, the e perature and -low rate of waste gas are largely varied, and it is difficult to effectively control poisonous gas such as

- 28 dioxins. This mode is to solve the above problem, and i s object -s to provide a waste plastic incineration method which introduces a comparatively simple combustion method without causing the above problem, keeps the combustion condition in the incinerator stable, and thus restrain the emission of poisonous gas and unburnt gas.

The present mode of embodiment is to achieve the above object by a waste plastic combustion method characterized by mixed fuel combustion of waste plastic, of which combustible matters have the lower calorific value of 4500 keel/kg or more, with sludge at the temperature at the outlet of the incinerator of 900 to 1200DC and the oxygen concentration at the outlet of 3 to 12.

By carrying out mixed fuelcombustion of sludge of high wafer content and reduced lower calorific value and waste plastic of high lower calorific value, it is possible to control the temperature of the fluidized bed to a low level and keep that of the freeboard section at a high level. As the burning conditions in the incinerator is made stable, poisonous gas or unburnt gas can be prevented from releasing.

Dioxins generation can be more suppressed by mixed combustion of waste plastic and sludge than combustion of waste plastics only.

The S content in sludge stays in the incinerator as H-S, CS, COS, SON or SO3 during the combustion process. These subs ances have a poisoning effect to copper and similar substances which _ 'at_ B_ I've it_ Bell il I 151! 1 1 1 818Bi 1: 11811 1 1:! 1 1 1

- 29 ac as catalysts for the generation of dioxins, and can effectively restrain dioxins in the waste gas line from the high temperature combustion field in the incinerator to behind the

outlet of the incinerator. Nitrogen content in sludge generates ammonia in the combustion step, particularly in the reducing atmosphere of the primary combustion field, and by reacting with

chloride compounds, ammonia suppresses the dioxin generating reaction of C1 in the course of generating dioxins. Further, by controlling the concentration of water in sludge and restraining the combustion reacting rate of combustible matters, soot generation can be lowered. If the soot generation amount is able to be restrained, the concentration of aromatic organic compound derived from soot is reduced, resulting in lowering the concentration of dioxins, which are products of incomplete combustion. Further, by lowering the temperature of the sand layer to 380-450 C, the reaction speed of waste plastics in the fluidized layer is lowered. Thereby, gasification of sold waste plastic issloweddown, end the balancein mixing agitation is kept between combustible gas, whichis generated from waste plastics, and air.

As a result, generation of soot, which is unburnt matter, can be suppressed and also, generation of dioxins, which is an incomplete combustionsubstanceinbroad sense, can tee suppressed.

Gasified plastics and combustible content in sludge are burnt in the freeboard section maintained at a high temperature, and poisonous gas generation is u-therrestrained. The temperature at the exit becomes to be 900 to 1200 . As air is supplied into

- 30 the inclne-ator so as to keep the outlet oxygen concentration at 3 to 12t, combustion is completed before the gas reaches the exit of the incinerator.

The current mode of embodiment can be applied to any type of waste incinerators including the fire grate type. However, in order to raise the mixing property of waste plastic and sludge and increase the combustibility of sludge, it is preferable to carry out combustion by fluidizing the burning materials; in particular a fluidized bed incinerator is preferable.

Preferable waste plastic is those of which the combustible matter has the low calorific value of more than 4500 kcal/kg, preferably around 4500 to 12000 kcal/kg, more preferably around 4500 to 8000 kcal/kg. The chlorine content shall be 20 wit or less, preferably 0.1 to 10 wt%.

The mixed combustion ratio of waste plastics and sludge is 10 to 70%. This is because the S content of 10 plus ppm and the N content of several 10 ppm at the lowest respectively are necessary for expecting the above mentioned effects, and the mixed combustion ratio needs to be more than 10% at the lowest.

Conversely, if the mixed combustion ratio exceeds 70%, the water content becomes too high, and even if operated by squeezing down the air ratio, it is difficult to keep the temperature at the outlet of the incinerator at 900 C. It is sufficient to perform mixed combustion of sludge and waste plastics in the incinerator. They may be mixed before charging, or charged into the incinerator separately.

Desirable burning conditions are that the tempera Are at l .,_

the outlet of the incinerator is around 900 to 1200 C, the oxygen concentration at the outlet is around 3 to 10%, and when a fluidized bed type incinerator is used, the temperature of the sand layer is around 380 to4500C. When sorely burning municipal refuse or waste plastic, it is usually difficult to keep the temperature of the sand layer at 450 C orless, but by performing mixed fuel combustion with sludge, the temperature of the sand layer can be kept at 380 to 450 C due to the contribution of the solid carbon content in the sludge. Waste plastic and sludge are slowly gasified in the fluidized layer and burn. Desirable conditions are that the fluidizing magnification is 2 to 8, the air ratioin the fluidizedlayer isO.1 to1.0,andthetemperature of fluidizing air sent into the fluidized layer is 20 to 500 C.

Subsequently, combustion is completed in the freeboard section kept at a high temperature, and the temperature becomes 900 to 1200 C at the outlet. After combustion, the exhausting gas is discharged outside through the exit of the incinerator, where the oxygen content is maintained at 3 to 12%, goes through the exhausting gas treating facility, and released from a stack.

FIG.4 shows a structure of the incinerator used in an example of the embodiment.

The incinerator is a fluidized bed type. In the interior, a sand layer to form the fluidized bed is prevented from moving down by a dispersing plate. Under the dispersing plate, there is a wind box into which combustion air is blown. This incinerator is separately provided with a waste plastics charger 20 and a sludge charger 3. For the combustion treatment, sludge

l K - 32 and waste plastics are charged from the respective chargers into the incinerator, dried in the sand layer fluidized by the air sent from the wind box under the dispersing plate, their temperature are raised, and they catch fire. Sludge and waste plastic are burned in the fluidized layer 4 and at the freeboard section above, and complete the combustionby the time they reach the exit of the incinerator. After the combustion, the waste gas is discharged outside through the exit of the incinerator, goes through the waste gas beating facility, end released from a smoke stack. A thermometer 21 of the sand layer, a thermometer 22 of the exit of the incinerator, and a sensor 23 of the oxygen concentration of the exit are respectively equipped. It is sufficient to control those values so as to fall into predetermined ranges. In case of automatic control, it is sufficient to incorporate them into operation parameters. In place of the sensor of oxygen concentration at the exit, it is also sufficient to provide a concentration sensor in the vicinity of the smoke stack and estimate the oxygen concentration at the exit from its value.

By using the above mentioned incinerator, mixed combustion was performed by supplying waste plastic, which is mainly composed of polyethylene and have the lower calori ic value or 8500 kcal/kg, and sewage sludge, which has the chlorine content of 1 wt , water content o 88wt%, N content of 6. 0 wt%, and S content of 1.0 we%, each in the amount or 500 kg/in. The temperature of the sand layer was maintained at 380 to 450 C, 11111111 111 _11111 l lll rlBlllllll_ 11111111 Illml_rlllnllnns-_ll_ 11B 1-ll

- 33 temperature of the fluidizing air at 20 to 280 , temperature at the exit at 900 to 1200 C, and the oxygen concentration at the exit at 3 to 12%. As a result, the concentration of dioxins was reduced about by half in average in comparison with combustion of waste plastics only. In particular, when combustion was carried out at the sand layer temperature of 440 C, fluidized air temperature of 200 C, freeboard temperature of 950 C, exit temperature of 920 C, and oxygen concentration at the exit of 8 + 2%, the concentration of dioxins at the exit was able to be suppressed to 0.06 ng/Nm3-teq.

As explained above, the present invention is a combustion method characterized by mixed combustion of waste plastics, of which combustible matter has the lower calorific value of 4500 kealikg or more, with sludge, maintaining the temperature at the exit of the incinerator and the oxygen concentration at the exit of the incinerator within specific ranges.

Stable combustion is effected by performing the mixed combustion of sludge of the high water content and reduced lower calorific value and plastic of high lower calorific value, so that emission of poisonous gas or unburnt part is restrained.

In addition, by bringing down the temperature of the sand layer to 380450 C, the reacting rate otp imary combustion is lowered, thereby the balance between mixing agitation with air and the reaction therewith is fully maintained, so that the generating amount of soot and dioxins can be restrained. Gasified waste plastics and combustible matter in sludge are burned at the freeboard section maintained at a high temperature and DOW SOnOUS

i gas is Further restrained, and the temperature becomes 900 Lo 1200 C an the exit. Oxygen concentration at the exit is kept at 3 to 12t, and by this time, combustion is completed. In case of automatic control, it is sufficient to incorporate the values of each thermometer and oxygen concentration meter in the parameters. BEST MODE 4

In this mode, the inventors diligently made investigations on efficient suppression of Toxins in waste treatment by mixed combustion of waste and sludge in an incinerator, and have obtained following findings from the present mode.

Namely, for controlling the charging ratio of sludge and waste and the charging amount of sludge so as to realize stable burning conditions in the waste treatment, the concentration of SOX in the incinerator or at the outlet of the same shall be used as a parameter for judging burning conditions in the incinerator, and be kept within a predetermined range, thereby enabling to effectively suppress generation of dioxins.

The dioxins suppressing effect is further improved by setting the S content, N content, and water content in sludge within predetermined ranges.

The present mode has been built based on such findings, and is characterized by the following structure.

This mode provides a waste treating method characterized by mixed fuel combustion of waste and sludge in an incinerator, where the SOD concentration in the incinerator or at the outlet 14 1- e1 111 111555 1 11! I I 111 1 11111 1;11 1 lI_lli_1181 1 11_1 1111

f of the same is measured, and the supply amounts of sludge and/or waste are controlled in accordance with the measured values.

In the current mode, it is preferable that the incinerator is a fluidized bed type, and the supply amounts of sludge and/or waste are controlled so that the SOx concentration is 100 to 2000 ppm. Further preferably, the above sludge shall have, by dry weight percent, the S content of 0.1 to 2 0%, N content of 1 to 10\, and water content of 65 to 90 wit.

Further, this embodiment provide a waste treating apparatus characterized by mixed combustion of waste and sludge in an incinerator, which equips aSOx concentration meter for measuring the SO concentration in the incinerator or at the outlet of the same, and a control apparatus for controlling the supply amounts of sludge and/or waste in accordance with the measured values.

- In this mode, it is preferable that the incinerator is a fluidized bed type, and the supply amounts of sludge and/or waste are controlled so that the SOx concentration is 100 to 2000 ppm.

Further preferably, the apparatus of this embodiment shall treat the sludge which has, by dried weight percentage, the S content of 0.1 to 2. 0%, N content of 1 to 10%, and water content of 65 to 90 wt%.

In waste treatment by mixed fuel combustion of waste and sludge using the incinerator of this mode, by monitoring the SOx concentration in the incinerator or at the outlet of the same, dioxins emissions can be effectively reduced.

The SO concentration in the incinerator a- at the outlet

- 36 of he same can be used as an index of burning reactions in the incinerator. Further, since SOx is mostly derived from the S content in sludge, the SOx concentration can also be used as an index for the charge amount of sludge. In other words, it can be used as an index to judge at what ratio sludge is to be charged relative to waste, and in what extent combustion is progressing in the incinerator. Therefore, by adjusting the SOx concentration in the incinerator or at the outlet of the same within a predetermined range, it is possible to determine the charge ratio of sludge and waste for realizing a stable burning condition and effectively restrain dioxins.

For accomplishing this object, it is sufficient to install a SOx concentration meter in the incinerator or at the outlet of the same, and for automatic control, it is sufficient to incorporate values thereof into operating parameters. It can be realized at a relatively low cost without special renovation.

If it is difficult to install a SOx concentration meter in the incinerator or at the exit of the same, the effect of this mode can be obtained by installing a SOx concentration meter in the stack so as to adjust the SOx concentration in the stack in a predetermined range.

Detailed explanation will be made referring to FIG.5.

FIG.5 shows one example of a waste treating apparatus in the present mode. This treating apparatus is provided with a l 'dized bed incinerator 101, a waste charger 102, and a sludge charger 103. The incinerator 101 is connected to an exhausting gas treating apparatus 110 which is connected to a stack 112.

_.,,.,.. ___ _ _ q l _! IlIIIIl IIa_ l ll_l l

Fir fit he outlet 10o of he incinerator 101, a Soy concentration me e-106 is provided/ from which a concentration sensing signal is input to a control apparatus, or a gauge, 107.

Sludge and waste charged into the fluidized bed incinerator 101 from the respective chargers 102 and 103 contact a sand layer fluidized by a fluidizing gas (e.g., air) sent from below a dispersing plate 104, are dried, and catch fire. The sludge and waste which caught fire burn within the incinerator 101. While doing so, for suppressing generation of soot which causes the increase the dioxins concentration, the residence time shall desirously be more than three seconds, and the temperature of the exhausting gas shall preferably be less than 700 C at the outlet. In FIG. 5, charge amounts of sludge and/or waste is determined so that measured values of the SOx concentration meter 106 provided at the outlet 105 of the incinerator fall within predetermined ranges. Namely, a concentration sensing signal is input from the concentrationmeterlO6 to the controlapparatus or gauge 107, and based on this signal the charge amounts of sludge and/or waste are determined so that the measured values of the SOX concentration meter 106 provided at the outlet 105 of the incinerator are within the predetermined ranges. If the SOx concentration is low, the charge amount of sludge is increased and/or the charge amount of waste is increased, on the other hand, i,- the SOx concentration is high, the charge amount of sludge is decreased and/or the charge amount of waste is decreased.

In the present mode, the appropriate SOx concentration at

- 38 the outlet is 100 to 9000 ppm. If the SOx concentration at the outlet is less than 100 ppm, the effect of suppressing dioxins is not sufficient, and if it exceeds 2000 pcm, the concentration of H2S or SO3 in waste gas goes up, and much consideration on operating environments becomes necessary.

In this mode, the same effect as mentioned above can also be brought about when a concentration meter 106 is provided in the incinerator 101, end the charge amounts of sludge and/or waste are controlled so that the SOx concentration in the incinerator 101 falls into the predetermined range, preferably 100 to 2000 ppm. If it is difficult to provide the SON concentration meter in the incinerator or at its exit, the SOx concentration meter may be provided in the stack. In such a case, white smoke prevention air may join in the waste gas line at the upstream of the stack es shown in FIG.5, and influence theSOx concentration in the stack. In this case, the concentration may be converted for consideration using, forexample, the oxygen-12% conversion.

The type of ir,cinerator for the present mode is not especially limited, but the fluidized bed type is particularly preferable, which carries out the combustion by fluidizing the materials to burnt in the incinerators, and provides excellent combustibility of sulfur containing substances. This type includes the fluidized bed incinerator and the fluidized bed thermal decomposition incinerator.

In addition, in the trea mer.. o' waste relating to the present mode, dioxins can be more effectively decreased by adjusting the S. N. and water conten in sludge to be supplied

o the incinerator.

Sludge is discharged from a wastewater treatment facility.

Any type of sludge is applicable, including sewage sludge, night soil sludge, sludge generated when performing en activated sludge treatment of organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging, and other sludge generated in the course of treating wastewater.

With respect to waste treatment in the fluidized bed incinerator, examples of the present mode will be explained, but the present mode is not limited to these.

In the fluidized bed incinerator, the sludge, which has, by dried weight, the S content of 0.7%, N content of 6% and water content of 75 wit, endurban refuse, which has the lower calorific value of 2300 kcal/kg, were burnt by adjusting temperature in the incinerator to 650-700 C. FIG.6 is a graph showing the relation of the SO concentration with the dioxins concentration at the outlet of the incinerator and the concentration of poisonous substance (H S+SO3). Fromthis result, when the sludge supply amount is controlled so that the SOx concentration at the outlet is 100 to 2000 ppm, dioxins can be effectively removed and the concentration of poisonous or corrosive substances can be suppressed.

FIG.7 shows one example or performing mixed combustion of waste and sludge without controlling the sludge supply amount based on the SO concen ration. FIG.7 shows a waste charger 102,

- do sludge charger 103, fluidized bed incinerator 104, outlet 105, exhausting treating apparatus 110, and stack 112.

As explained in FIG.5, the present mode measures the SOL concentration in the incinerator or the outlet of the same as indexes for judging burning conditionsin the incinerator. Based on the measured values, the charge ratio of sludge and waste is determined for realizing stable burning conditions, and is is possible to efficiently restrain generation of dioxins and emission of poisonous gas together with realizing the stable combustion. It can be realized at a relatively low cost without requiring any large scale renovation.

BEST MODE 5

In this mode, the inventors diligently made investigations on efficient suppression of dioxins in waste treatment by an incinerator, and have obtained the following findings.

Namely, dioxins can be reduced by performing mixed fuel combustion of waste and sulfur containing substance. Further, the SOx concentration in the incinerator or at the outlet off the same can be used as an index for judging burning conditions in the incinerator, and by keeping it in a predetermined range, it is possible to effectively suppress generation of dioxins.

This mode provides a waste treating method characterized by mixed fuel combustion of sulfur contained material and waste in an ncinerator, where the SOxconcen ration in the incinerator _,,__,,,.' ill" ' 1 l _il '.18 1 _11. e IL

- or at the outlet of the same is measured, and the supply amounts of the sulfur contained material and/or waste are controlled in accordance with the measured values.

In the current mode, it is preferable that the incinerator is a fluidized bed type, and the supply amounts of sulfur contained material and/or waste are controlled so that the SOx concentration is 100 to 2000 ppm.

Further, this mode provide a waste treating apparatus characterized by combustion of waste in an incinerator, which equips a sulfur contained material charger, a waste charger, a SOX concentration meter for measuring the SOx concentration in the incinerator or at the outlet of the same, and a control apparatus for controlling the supply amounts of sulfur contained material and/or waste in accordance with the measured values.

In this mode, it is preferable that the incinerator is a fluidized bed type, and the supply amounts of sulfur contained material-and/or waste are controlled so that the SOx concentration is 100 to 2000 ppm.

In the waste treating technology of this mode, by performing mixed fuel combustion of sulfur contained material and waste in the incinerator, and observing the Sol concentration in the incinerator or at the outlet of the same, dioxins can be effectively reduced.

The S content in sludge stays in the incinerator as H2S, CS2, COS, SO2 or SO3 during the combustion step. These substances have a poisoning effect to copper and similar substances which act as catalysts for the generation of dioxins, and can effectively

- - 42 restrain dioxins in the exhausting gas line from the high temperature combustion field within the incinerator to behind

the outlet of the incinerator.

The SOx concentration in the incinerator or at the outlet of the same can be used as an index of burning reactions in the incinerator. Further, since SOx is mostly derived from the S content in the sulfur contained material, the SOy concentration can also tee an index for the charge amount of the sulfur contained substance. In other words, it can be used as an index to judge at what ratio sulfur contained material is to be charged relative to waste, and in what extent combustion is progressing in the incinerator. Therefore, by adjusting the SOx concentration in the incinerator or et the outlet of the samewithina predetermined range, it is possible to determine the charge amount of sulfur contained material for realizing a stable burning condition and more effectively restrain dioxins.

For accomplishing this object, it is sufficient to install a SON concentration meter in the ncinerator or the outlet of the same, and for automatic control, it is sufficient to incorporate values thereof into operating parameters. It can be realized at a relatively low cost without special renovation.

if it is difficult to install the SOx concentration meter in the incinerator or at the outlet of the same, the effect of this mode can be obtained by installing the SO concertration in the stack so as to adjus the SON concentration in the stack in a predetermined range.

Detailed explanation will be made referring to Fig. 8.

_e _ ____ 4 _ __ 51 11_ 1 1_1 1

- - 43 - FIG.8 shows one example of a waste treating apparatus in the present mode. This treating apparatus is provided with a fluidized bed incinerator 101, a sulfur contained material charger 103 and a waste charger 102, and the incinerator 101 is connected to an exhausting gas treating apparatus 110, which is connected to a stack112. At the outlet 105 oftheincinerator 101, a SOx concentration meter 106 is provided from which a concentration sensing signal is input to a control apparatus, or a gauge, 107.

Sulfur contained material and waste charged in the incinerator 101 from the respective chargers 102 and 103 contact a sand layer fluidized by a fluidizing gas (e.g., air) sent from below a dispersing plate 104, are dried, and catch fire. The sulfu- contained material and waste which caught fire burn in the incinerator 101. While doing so, for suppressing generation of soot which causes the increase of the dioxins concentration, the residence time shall desirously be more than three seconds, and the temperature of the waste gas shall preferably be less than 700 C at the outlet. Subsequently,the exhausting gas is discharged from the outlet 105, goes through the exhausting gas treating apparatus 110, and is released outside from the stack 112. In FIG.8, the charged amounts of sulfa' contained material and/or waste are determined so that measured values of the SOy concentration meter 106 provided a the exit 105 of the incinerator 101 fall within the predetermined ranges. Namely, a concentration sensing signal is input from he concentration

me'er 106 to the control apparatus or gauge 107, and based on this signal, the charged amounts of sulfur contained material andJor waste are determined so that the measured values of the SOx concentration meter 106 provided at the outlet 105 of the incinerator are within the predetermined ranges. If the SOx concentration is low, the charged amounts of sulfur contained material is increased and/or the charged amounts Of waste is decreased, on the other hand, if the SOx concentration is high, the charged amount of sulfur contained material is decreased and/or the charge amounts of waste is increased.

In the present mode, the appropriate SOx concentration at the outlet is 100 to 2000 ppm. If the SOx concentration at the outlet is less than 100 ppm, the effect or suppressing dioxins is not sufficient, and if it exceeds 2000 ppm, the concentration ofH2SorSO3in waste gas goes up, and much consideration on safety and health becomes necessary.

In this mode, by providing the SOx concentration meter 106 in the incinerator 101, it is possible to control the charged amounts of sulfur contained material and/or waste so that the SOX concentration in the incinerator 101 falls within the predetermined range, preferably 100 to 2000 ppm. If it is difficult to provide the SOx concentration meter in the incinerator or at its outlet, the SOx concentration meter may be provided in the stack. In such a case, white smoke prevention air may join. 'n the exhausting gas line as shown in FIG.8, and influence the SO concentration in the stock. In this case, the concentration may be converted for consideration using, _or . ___r __À H111. IRI. _ IR all! _. r

- 45 example, the oxygen-12% conversion.

The type of incinerator for the present mode is not especially limited, but the fluidized bed type is particularly preferable, wh ch carries out the combustion by fluidizing the materiels to beburntin the incinerators, and provides excellent combustibilityo. sulfur contained material. This typeincludes the fluidized bed incinerator and the fluidized bed thermal decomposition incinerator.

As explained above, based on the SOx concentration values measured in the incinerator or at the outlet of the same, it is possible to determine the charged ratio of sulfur contained material and waste and to efficiently restrain generation of dioxins. It can be realized at a relatively low cost without requiring any large scale renovation.

BEST MODE 6

The present mode provides a ROF treatment method and a apparatus thereof by introducing a relatively simple apparatus, which keeps the burning condition in the incinerator constant, thereby suppresses the emission of poisonous gas or unburnt gas and efficiently reduces dioxins.

In this mode,the inventors diligently mace investigations on efficient suppression of dioxins in the RDF treatment by an incinerator, and have obtained the following findings.

Namely, d oxins can be reduced by performing mixed combustion o_ RDF and sul_ur contained material. Further, the SOy concentration in the incinerator, at _hG outlet of the same

- or at a stack can be used as an index for judging burning conditions in the incinerator, and by keeping it in a predetermined range, it is possible to effectively suppress generation of dioxins.

This mode provides a RDF treating method characterized by mixed fuel combustion of sulfur contained material and RDF, where the SOx concentration in the incinerator, at the outlet of the same, or at the stack, is measured, and the supply amounts of the sulfur contained material and/or RDF are controlled in accordance with the measured values.

In the current mode, it is preferable that the incinerator is a fluidizedbedtype, and the supplyamounts of sulfur contained material and/or RDF are controlled so that the SOx concentration at the stack is 50 to 400 ppm.

Further, this embodiment provides a RDF treating apparatus characterized by mixed fuel combustion of sulfur contained substance and RDF in the incinerator, which equips a sulfur contained material charger, a RDF charger, a SOx concentration meter for measuring the SOx concentration in the incinerator, at the outlet of the same, or at the stack, and a control apparatus for controlling the supply amounts of sulfur contained material and/or RDF in accordance with the measured values.

In th s mode, it is preferable that the incinerator is a fluidized bed type and a control apparatus is provided for cc ntrolling the supply amounts of sulfur contained ma erial

f - 47 and/or RDF so hat the SOx concentration at the stack is 50 to 400 ppm.

In the RDF treating technology of this mode, by performing the mixed fuel combustion of RDE and sulfur contained material in the incinerator, and observing the concentration of SOxin the incinerator, at the outlet of the same, or at the stack, dioxins can be effectively reduced.

The sulfur content stays in the incinerator as H2S, CS2, COS, SO2 or SO3 during the combustion process. These substances have a poisoning effect to copper and similar substance which act as catalysts for the generation of dioxins, and can effectively restrain dioxins in the exhasutingline from the high temperature combustion field in the incinerator to behind the outlet of the

incinerator. Some of these substances restrain the reaction for generating dioxins of C1 in the course of generating dioxins.

As a result, the generation of dioxins in the combustion step and its downstream is restrained.

The SOx concentration in the incinerator, at the outlet of the same, or in the stack can be used as an index of burning reactions in the incinerator. Further, since SOx is mostly derived from the S content in the sulfur contained material, the SO concentration can also be an index for charge amounts of the sulfur contained material. In other words, i can be used as an index to judge at what ratio sulfur contained material is to be charged relative to waste, and in what extend combustion is progressing in the incinerator. Tha. is, this is to be an index for efficient reaction to contribute to the reduction of dioxins.

- - 43 For accomplishing this realization, it is sufficient to install a SOy concentration meter in the incinerator, the outlet of the some or in the stack, and for automatic control, it is enough to incorporate values thereof into operating parameters.

Detailed explanation will be made referring to Fig. 9.

FIG.9 shows one example of a RDF treating apparatus in the present mode. This treating apparatus is provided with a fluidized bed incinerator 101, a RDF charger 130 and a sulfur contained material charger 132, and the incinerator lO1 is connected to a exhausting gas treating apparatus llO which is connected to a stack 112. The stack 112 is provided with a SOx concentration meterl27 fromwhicha concentration sensing signal is input to a control apparatus or a gauge 128.

RDF and sulfur containedmaterial charged in theincinerator 101 from the respective chargers 130 and 132 contact a sand layer fluidized by fluidizing gas (e.g., air) sent from below a dispels ng plate 104 and catch fire. RDF and sulfur contained material which caught fire burn in the incinerator lO1. The exhausting gas is discharged from the exit 106, goes though the exhausting gas facility 110, and is released outside from the stack 112.

In Fig.9, charged amounts of RDF and/or sulfur contained material are determined so that measured values of the SOx concentration meter 127 provided in the stack fall within predetermined ranges. Namely, a concentration sensing signal is input from the SOx concentration meter 127 o the control apparatus or gauge 107 connected to the concentration meter 127 l l l l l l _ I! nell ell_d

-. - 49 provided in the stack 112, and based on this signal, the charged amounts of RDF and/or sulfur contained material are determined so that the measured values of the Sol concentration meter 106 provided in the stack are within the predetermined ranges. If the SOx concentration is low, the charged amounts of sludge is increased and/or the charge amounts of RDF are decreased. On the othe- hand, if the SOx concentration is high, the charged amounts of sludge are decreased and/or the charged amounts of RDF are increased.

White smoke prevention air may join in the exhausting gas line at the upstream of the stack as shown in FIG.9, and influence the SOx concentration in the stock. In this case, the concentration may be converted for consideration using, for example, the oxygen-12% conversion. For automatic control, values of SON concentration may be added to operation parameters.

In the present mode, the appropriate concentration at the outlet is 50 to 400 ppm. If the Sol concentration at the outlet isless then 50ppm, the reaction by the S consent cannot be carried out el iciently, and if it exceeds 400 ppm, a corrosion possibility deriving from sulfur oxide in a down stream becomes large. In this mode, the SOx concentration meter 106may be provided in the incinerator or at the outlet thereof, and the charged amounts of RDF and/or sulfur contained material may be controlled so that the SO concentration in the incinerator or at the outlet thereof falls into the predetermined range, preferably 60 to 600 opm. Also in this case, the same effect as mentioned above can

- 50 be obtained.

The type ofincineratorin the present models not especially limited, but the fluidized bed incinerator, which carries out the combustion by fluidizing the materials to be burnt, is particularly preferable for providing excellent combustibility of sulfur contained material.

As explained above, by this mode for the treatment of refuse solid fuel in the incinerator, it became possible to determine the charged ratio of sulfur contained material and RDF for realizing stable burning conditions and to efficiently restrain generation of dioxins. It can be realized at a relatively low cost without requiring any large scale renovation.

BEST MODE 7

The present mode is to provide a waste treating method and an apparatus thereof, which keep burning conditions in an incinerator constant by performing mixed fuel combustion of sludge and waster thereby to efficiently reduce dioxins The inventors diligently made investigations on effective suppression of dioxins in the waste treatment by an incinerator, and have obtained the following findings.

In the waste treating technology of carrying out the mixed fuel combustion of sludge and waste, by supplying sulfur contained material into feeding lines of sludge or waste to the incinerator, it is possible to supply, under stable conditions, the S content which has he effect of reducing the concentration of dioxins.

1 11_Ài.1111 11iill i. Bilili l _lll ll;llll1 g 1__1Ill 8l

f i Further, for controlling the charged amounts of sulfur contained powder to realize stable burning conditions, by using the SOx concentration in the incinerator, at the outlet of the same Grin the stack asanindex for judging the burning condition, and keeping it within a predetermined range, the effect of suppressing dioxins is more improved.

The present mode is based on such findings, and characterized by the following structure.

This mode is to provide the waste treating method characterized by supplying sulfur contained material into the feed line of sludge or waste to an incinerator when performing waste treatment by mixed fuel combustion of sludge and waste in an incinerator.

In this mode, the SOx concentration is measured in the incinerator, at the outlet of the same or in the stack, and based on the measured value, the supply amount of the sulfur contained powder is controlled. The supply amount is preferably controlled so that the SOx concentration in the stack is 50 to 400 Pam, and the incinerator is preferably a fluidized bed type.

Further, the modeisto provide the waste treating apparatus characterized by provision of an apparatus for supplying sulfur contained material into the feeding line of sludge or waste to tL.e incinerator when performing waste treatment by mixed fuel combustion of sludge and waste in an incinerator.

* In addition, this mode is to provide the waste treating apparatus characterized by provision of a SOx concentration meter or measuring the SOx concentration in the incinerator, at the

- 52 outlet of the same or in the stack, and a control apparatus for controlling based on the measured value, the supply amount of the sulfur contained powder. The supply amount is preferably controlled so that the SGK concentration in the stack is 50 to 400 ppm, and the incinerator is preferably a fluidized bed type.

Herein, the above mentioned"apparatus for supplying sulfur contained powder" means a sulfur powder storage bin and a sulfur powder supply line connected with a sludge supplyline r or a sulfur powder storage bin and a waste supply line.

In the waste treating technology relating to this mode, by supplying the sulfur contained powder into the sludge or waste supply line to the incinerators it is possible to supply the S content, efficiently and in a stable condition, when it is in shortage for effectively reducing dioxins.

By connecting the sulfur supply line for supplying sulfur containing powder to the sludge supply line or the waste supply line to the incinerator and supplying the sulfur contained powder mixed with the sludge or waste, the mixture composed of the sulfur powder and the sludge o' waste can be supplied, in uniform properties, into the incinerator. In this way, it is also possible to avoid non-uniformity in the incinerator caused by directly supplying the sulfur containing powder into the incinerator, or danger of waste explosion. In the operation, since the supply of the S content can be started or ended together with starting or ending of the sludge or waste supply, operational simplicity and safety can be established. Further, enough S. N and water contents are supplied into the incinerator, and so _._,.,..,.,_.__._,,-__,,,, ( F I] _ llell _ 1 B

f-- dioxins can be effectively reduced due to the above mentioned reasons. The SOx concentration in waste gas in the incinerator, at the outlet of the same or in the stack is determined by burning conditions such as the temperature in the incinerator and the amount of S powder supplied through the sludge supply line or waste supply line, and it can be used as an index for the generation of dioxins. In other words, by observing the value of SOx concentration and adjusting the combustion so that the SOx concentration in the incinerator, at the outlet of the same or in the stack is within a predetermined range, it is possible to determine the amount of the sulfur powder required for realizing a stable burning condition and to efficiently restrain the generation of poisonous gas such as dioxins.

For realizing this, it is sufficient to install a SOx concentration meter in the incinerator, at the outlet of the same or in the stack. It can be realized at a low cost without requiring any special renovation.

Detailed explanation will be made referring to FIG. 10.

However, this mode is not limited thereto.

FIG.10 shows one example of the waste treating apparatus of this invention. This treating apparatus is equipped with a waste storage bin 201, sludge storage bin 202, S powder storage bin 203 and an incinerator 204. The waste storage bin 201 and the incinerator 204 are connected by a waste supply line 205 for supplying waste in the waste storage bin 201 to the incinerator 204. The sludge storage bin 202 and the incinerator 204 ae

- 54 connected by a sludge supply line 206 for supplying sludge in the sludge storage bin 202 to the incinerator 204. The sulfur powder storage bin203 and the sludge supply line206are connected by a sulfur powder supply line 207 for supplying sulfur powder in the sulfur powder storage bin 203 to the incinerator 204.

In the present example, the sludge in the sludge storage bin 202 is sent under pressure by a pump (not shown) to the incinerator 204 via the sludge storage line 206. The sulfur powder sent under pressure from the sulfur powder storage bin 203 is supplied into the sludge supply line 206, mixed with the sludge, made into a uniform property while being transferred downstream, and supplied to the incinerator 204.

By such an arrangement, it is possible to avoid non-

uniformity in the incinerator caused by directly supplying the sulfur containing powderinto theincinerator, or danger of waste explosion, and efficiently reduce dioxins while maintaining a balance among the S. N and water contents in the incinerator.

In the operation, since the supply of the S content can be started or ended together with starting or ending of the sludge or waste supply, operational simplicity and safety can be established.

In this embodiment, the S content to be supplied into the sludge supply line is not limited to powder, and any forms, e.g., slurry, may be suitably used.

FIG.10 shows an example of connecting the sulfur power line to the sludge supply line. However, it also is possible to connect the sulfur powder supply line to the waste supply line, and also in this case the waste and the sulfur powder are mixed -,._, it-,.,,,,,._ ma.,,_, I'llell lli I _i III I. I Illl _'1 11111111_ 1 15 1 1

F - 55 and sect to the incinerator in a uniform property, and the same effect as mentioned above can tee brought about. The same effect is obtained by a more simple method than the one exemplified here such es sulfur powder supply to a wafer supplyline for controlling the temperature of the incinerator or a wastewater supply line.

FIG.llshowsanotherexampleofthe waste beating apparatus of this invention. This treating apparatus is equipped with a waste storage bin 211, sludge storage bin 212, sulfur powder I storage bin 213 and a fluidized bed incinerator 214 to which a waste gas treating apparatus 222 is connected, and a smoke stack 224 is connected to the waste gas treating apparatus 222. The waste storage bin 211 and the incinerator 214 are connected by a waste supply line 215 for supplying waste in the waste storage bin 211 to the incinerator 214. The sludge storage bin 212 and the incinerator 214 are connected by a sludge supply line 216 for supplying sludge in the sludge storage bin 212 to the incinerator214. The sulfurpowder storage bin213 and the sludge supply line 216 are connected by a sulfur powder supply line 217 for supplying sulfur powder in the sulfur powder storage bin 213 to the incinerator 214. The smoke stack 224 is provided with a SOx concentration meter 220from which a concentration sensing signal is input to a control apparatus or a gauge 221.

In this example, the sulfur contained powder supplied to the sludge supply line 216 is completely mixed with sludge in the line 216 and is sent to the incinerator 214 in a uniform property. This sludge and the waste sent via the waste supply line 215 from the waste storage bin 211 are dried in the sand

- -: - - - 56 layer luidized by the air from the wind box 22 5 under the dispersing plate 218, their temperature being raised, and catch fire. The waste which caught fire bums in the freeboard section, and the combustion is perfectly completed. The exhausting gas is released outside from the stack 224 via the exhausting gas treating apparatus 222. Based on the concentration sensing signal from the SOx concentration meter installed in the stack 224, the supply amount of the sulfur powder is determined by the control apparatus or the gauge 221 so that the SOx concentration in the stack is within the predetermined range. More concretely, if the SOx concentration is too low, the sulfur powder supply amount is increased, and conversely if it is too high, the amount is decreased.

In this embodiment, the appropriate SOx concentration in the stack is 50 to 400 ppm. If it is less than 50 ppm, the effect of suppressing dioxins is not sufficient, while if it exceeds 400 ppm, the SOx concentration cannot achieve a regulated value.

White smoke prevention air may join in the exhausting gas fine et the upstreamof the stack es shown in Fig.11, and influence the Sol concentration in The stack, In this case, the concentration may be converted for consideration using, for example, the oxygen-12% conversion. For automatic control, values of Sol concentration may be incorporated into operation parameters. Further, in this example, the SON concentration meter is installed at the smoke stack, but the SOx concentration meter may be installed in the incinerate 214 or at the outlet 219, and _...,.,..,,.,,_ i11 1011 11i _1;4i111111 11 11111_11 Of

- - 57 the supply amount of the sulfur contained powder is controlled so that the SOx concentration in the incinerator or at the outlet o the same is within the predetermined range, preferably 60-600 ppm in either case. This drawing shows the fluidized bed incinerator, not limiting thereto, and it is applicable to a fire grate type incinerator. As explained above, by this mode, in the waste treatment performing mixed

fuel combustion of the waste and sludge, the sulfur powder can be efficiently supplied in a stable condition, which supplements the S concentration to obtain the effect of reducing dioxins.

The burning condition can be judged in accordance with the SOX concentration in the incinerator, at the outlet of the same or the stack, so that the supply amount of the sulfur powder can be decided for realizing the stable burning condition so as to efficiently reduce dioxins.

BEST MODE

The present mode is to provide a waste treating method performing mixed fuel combustion of waste and sludge and/or sulfur contained material in the waste incinerator, characterized by dispersed supply of the sludge and/or sulfur containing substance into a waste hopper.

This mode is to further provide a waste treating apparatus performing the mixed fuel combustion of waste and sludge and/or sulfur contained material in the waste incinerator, characterized by pro-vision of a dispersed supply means for

-. S8 per orming the dispersed supply of the sludge and/or sulfur contained material into a waste hopper.

Below, detailed explanation will be made on this mode.

In this mode, sludge and/or sulfur contained material a-e dispersed and supplied into the waste chute by a dispersed supply apparatus which has the function of performing dispersed supply.

No limitation isespeciallymade to a dispersed supply apparatus, and any type is applicable as far as it has a function of uniformly dispersing sludge and/or sulfur containedmaterial into the waste chute. Forexample, screw conveyor or sliding conveyor, or their combination will be enumerated.

It is desirable that waste has been supplied in the waste hopper prior to dispersed supply of sludge and/or sulfur containing substance.

When sludge is dispersed and supplied, it penetrates into the waste in the waste hopper due to its own weight, and the combustible matter and water content are dispersed evenly and mixed uniformly with the waste In the case of sulfur contained material, it is evenly dispersed over the waste and mixed uni ormlytherewith. Since mixed sludge and/or sulfur contained material are supplied in company with the supply of the waste into the incinerator, sections which have extremely low calorific value or extremely high water content are not formed, and stable combustion takes place over a wide range, and soot generation is avoided.

As the apparatus of dispersed supply of sludge and/or sulfur containing substance, it is preferably to employ a lance which Alp__- R-I: hi; l - _

- 59 mixes them with gas and perform dispersed supply into the waste hopper. By using a lance which uses air or CON as a transferring ! gas, sludge and/or sulfur contained material can be dispersed more uniformly end affectively in the waste hopper together with the transferring gas.

The dispersed supply o' sludge and/or sulfur containing substance into the waste hopper from the dispersed supply apparatuses preferably carried out by meeting the timing of waste charging into the waste hopper by the waste crane. Ordinarily, the waste stored in a waste pit is supplied by the waste crane to the waste hopper at appropriately determined intervals. If sludge and/or sulfur containing substances are continued to be supplied when the amount of waste in the waste hopper is small, only these are fedlnto the incinerator. If sludge and/or sulfur containing substances are continued Lo tee supplied when the waste crane is supplying wasteinto the waste hopper, sulfur containing substance and waste are considered to be scattered around the waste hopper. If the dispersed supply apparatus is, therefore, operated meeting the charge timing of waste into the hopper, appropriate amounts of sludge and/or sulfur containing substances can be efficiently supplied.

For example, the dispersed supply apparatus is operated in the following manners.

(1) After waste is supplied into the hopper by the crane, the sludge and/or sulfur containing substances of fixed amount are dispersed and supplied.

(2) The amount of waste in he hopper is sensed by a sensor, and

- 60 sludge and/or sulfur contained material of the most appropriate amount relative to the amount of the waste staying in the waste hopper et that time is dispersed end supplied so that sludge and/or sulfur containing substances are uniformly mixed.

(3) When the crane is charging the waste into the hopper, sludge and/or sulfur contained material are stopped to be supplied.

(4) The weight of waste charged into the hopper by the crane is sensed by a weight sensor, and sludge and/or sulfur contained material of the appropriate amount relative to the waste weight are dlapersed and supplied after waste charging.

These manners may be carried out in combination. Manners are not limited to the above four, and other manners may be employed for dispersed supply otwaste, meeting the charge timing at the hopper.

The dispersed supply of sludge and/or sulfur contained material by the above mentioned manners should be preferably stopped at latest one hour prior to stopping the operation of the incinerator. Usually, the incinerator enters the operation adjustment several hours prior to stopping the operation, and begins to reduce charge amounts ofwaste. If sludge and/or sulfur containing substances are continued Lo be suppliedinthls period, troubles will occur as follows. If the supply of sludge is continued, it is foreseen that the whole calorific value goes down so that a burning condition becomes unstable. If sulfur corralled material is continued to be supplied, the combustion rate thereoLgoes up in the incinerator, so that Sol concentration increases in the exhausting gas.

t'ó '1 L 1 __5115_ 11 ll_11851 1 1 1 11 1:1 1 181 _1 18_1111

J - 61 By stopping the supply of sludge and/or sulfur contained material by using the dispersed supply apparatus at latest one hour prior to stopping the operation of the incinerator, the above mentioned troubles can be avoided, and the burning condition can be prevented from becoming unstable during the perioUto stopping the operation.

The invention will be explained more in detail referring to the drawing.

FIG.12 is a schematic view showing one example of the waste treating apparatus of this invention, illustrating the waste hopper section of the waste incinerator. Waste is charged into the waste hopper 302 from the waste crane 301, and on the other hand, sludge and/or sulfur contained material are transferred from an introducing inlet 305 of sludge and/osulfur contained material onto the conveyor 304 and are dispersed over waste in the hopper.

Sludge subsequently penetrates into the waste in the hopper 302 due to its own weight, and the combustible matter and water content are mixed evenly. Sulfur contained material is also dispersed evenly over the wastein the hopper andmixed uniformly.

In certain circumstances, mixed sulfur contained material is subsequently supplied along with the supply of the waste into the incinerator. Thus, sludge and/or sulfur contained material are supplied together with waste into the incinerator (not shown) from the waste chute 303.

FIG.13 is a schematic view showing another example of the waste treating apparatus of this invention, illustrating a waste

- hopper section of the waste incinerator. In the same manner as in FIG. 12, waste is chargedinto ire waste hopper302 by the waste crane 301. On the other hand, sludge and/or sulfur contained material are introduced from the introducing inlet 305 of sludge and/or sulfur contained material and are transferred from the lance 306 together with the transferring gas sent from a transferring gas outlet 307, dispersed and supplied into the waste hopper 302. Thus, sludge and/or sulfur contained material are dispersed widely over the waste in the hopper 302. As the transferring gas, other than the air, CO2 or nitrogen, re-

circulating waste gas may be employed. A flow rate thereof is not especially limited as far as it is in a range enabling to disperse sludge and/or sulfur containing substance.

Sludge subsequently penetrates into the waste in the hopper 302 due to its own weight, and the combustible matter and water content are mixed evenly. Sulfur containing substance is also dispersed evenly over the waste in the hopper end mixed uniformly.

Thus, sludge and/or sulfur containing substance are supplied together with waste into the incinerator (not shown) from the waste chute 303.

As sludge for mixed fuelcombustion with waste in the present mode, any type of sludge is applicable, including sewage sludge, night soil sludge, sludge generated when performing an activated sludge treatment of organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging, and other sludge genera ed in the course OI _. _._....,.. _,._,.____ 11 154511111 1111_116 111111111 All 18 I_ 1 1 1 1 1 1 Awl_

- 63 treating wastewater. No special limitation is made to the water content in sludge, and those with the water content in a usual range such as 10 to 90% can be used.

As sulfur contained material, sulfur powder, industrial wastewater (because it contains sulfur), waste rubber such as waste tires can be used. When using waste rubber such as waste tires, the operation should be carried out taking the calorific value into consideration.

In addition, the above mentioned sludge may be used in combination with sulfur containing substance.

This mode does not limit the type of incinerator, and any type of incinerator such as a fluidized bet incinerator, fire grate incinerator or kiln incinerator may be applied for performing the mixed fuel combustion of waste and sludge and/or sulfur contained material. The temperature in the combustion chamber may be in an ordinary range.

Below, this invention will be explained more in detail, showing actual examples.

(Example 1)

The fire grate incinerator was employed as the waste incinerator, and municipal refuse and sludge were mixed and incinerated, according to the method of this invention.

Firstly, sludge and air were mixed, and using a lance which has the function of dispersing the sludge, supplied into the waste hopper in which Haste had previously been charged. The transferring gas for sludge was CO2. Municipal refuse was with

(. - - 64 the value of 2300 kcal/kg and the sludge ratio was 80%. The mixed fuel combustion of municipal refuse and sludge was carried out by changing the temperature of the drying stage from 700 to 850 C and the temperature in the combustion chamber from 850 to lOOOQC.

As a result, comparing with a case of charging municipal refuse and sludge into the incinerator from separate chutes, the CO concentration was reduced to less than half, and the concentration of dioxins was also reduced by BOO. During the corrbustion, the incinerator could be operated under stable conditions, and no abnormality was seen in the waste gas concentration or conditions of ashes.

(Example 2)

Firstly, sulfur powder was used as sulfur contained material and using a lance which has the function of dispersing the sulfur contained material, supplied into the waste hopper in which waste had previously been charged. The transferring gas for sulfur contained material was CO2. Municipal refuse was with the value of 2300 kcal/kg and the sulfur contained material ratio was 80.

The mixed fuel combustion of municipal refuse and sulfur powder was carried out by changing the temperature of the drying stage from 700 to 850 C and the temperature in the combustion chamber from 850 to 1000 C.

As a result, comparing with a case of charging municipal ,ll,ll,ll._.'.,., ,,, _,_

ref_se and sulfur powder into the incinerator from separate chutes, the CO concentration was reduced to less than half, and the concentration of dioxins was also reduced by 20%. During the combustion, the incinerator could be operated under stable conditions, and no abnormality was seen in the waste gas concentration or conditions of ashes.

As mentioned above, the present mode provides a waste treating method and an apparatus which keep burning conditions constant, and efficiently perform the mixed combustion of sludge and/or sulfur contained material and waste such as municipal refuse so as to reduce the concentration of dioxins in an exhausting gas.

By using the present mode, it is possible to uniformly supply sludge and/or sulfur contained materiel and waste into the waste hopper and therefore it is possible to supply these in the incinerator. Accordingly, a stable combustion progresses without generating any range of extremely low calorific value in the incinerator, and consequently, generation of dioxins in the exhausting gas can be effectively reduced.

By this mode, the mixed fuel combustion of sludge and/or sulfur contained material can be applied not only to a conventional fluidi-zed bed incinerator but also to a fire grate ir.clnerator, bringing about great industrial value.

BEST MODE 9

The present mode is to offer a waste treating method pe- orm ng he mixed fuel combustion of waste and sludge and/or

f t - 66 sulfur contained material in a waste incinerator using a fire grate, characterized by dispersed supply of the sludge and/or sulfur contained material onto the fire grate of a drying stage.

The present mode is to further provide a waste treating apparatus performing the mixed _uel combustion of waste and sludge and/or sulfur contained material in the waste incinerator using the fire grate, characterized by providing a dispersed supply means of dispersing the sludge and/or sulfur contained material and supply them onto the fire grate of the drying stage Below, detailed explanation will be made on this mode.

In this mode, sludge and/or sulfur contained material are dispersed and supplied onto the fire grate of the drying stage of the fire grate incinerator by a dispersed supply apparatus which has the function oLperforming the dispersed supply of these.

As a dispersed supply apparatus, nolimitationis especially made as far as it has a function of uniformly dispersing sludge and/or sulfur contained material onto the fire grate ofthedrying stage, and arbitrary types can be used.

When sludge is dispersed and supplied, as it mixes into the waste being dried on the fire grate due to its own weight, it is cried end soon catches fire. Alsoin a ease of sulfur contained material, it is evenly dispersed over the waste being dried on the fire grate, dried together with waste, and startscombustion.

A stable combustion takes place without partially forming ranges where the temperature is low. As sludge evenly mixes with waste, sludge before burning does not fall onto an ash chute under the fire grate through openings of the fire grate such es holes formed

t - 67 by being pushed by blowing air.

As an apparatus for dispersed supply ofaludge and/or sulfur contained material, it is preferably to employ a lance which performs dispersed supply onto the fire grate of the drying step by mixing them with gas. This type of lance, using air or CON as a transferring gas, can disperse sludge and/or sulfur contained material uniformly and effectively on the fire grade of the drying stage. In the present invention, sludge and/or sulfur contained material are dispersed and supplied on the fire grate, and in case the surface temperature of the lance becomes high, a cooling mechanism is desired to be installed outside of the lance.

The dispersed supply of sludge and/or sulfur contained material onto the fire grate of the drying step should be preferably stopped at latest one hour before the operation of the incinerator is stopped. Usually, the incinerator enters the operation adjustment severalhours before slopping the operation, and begins to reduce charge amounts. If sludge and/or sulfur contained material, are continued to be supplied in this period, troubles may occur as follows. If the supply of sludge goes on, it is foreseen that the whole calorific value goes down so that a burning condition becomes unstable. When sulfur contained material is continued to be supplied, the combustion fuel ratio thereof goes up in the incinerator, so that the SO,concentration increases in an exhausting gas.

When the dispersed supply of sludge and/or sulfur contained material a-e stopped at latest one hour before the operation of

- 68 the incinerator is stopped, the above mentioned troubles can be avoided, and the burning condition can tee preventedlrom becoming unstable before the operation is stopped.

The invention will be explained more in detail referring to the drawing.

FIG.14 is a schematic view showing one example of fire grate waste incinerators of this invention. Waste charged into the waste hopper 401 is sent to the fire grate of the drying stage 401 through the waste chute 402.

On the other hand, sludge and/or sulfur contained material are introduced from an introducing inlet 408 of sludge and/or sulfur contained material, sent through the lance 407 together with the transferring gas supplied from a transferring gas inlet 409 and are dispersed over the firegrate403. Thus, sludge and/or sulfur contained material are dispersed efficiently and widely over the waste on the fire grate. As the transferring gas, other than air, CO^or nitrogen, a re-circulating waste gas may be employed.

It is preferable that a flow rate thereof is enough to disperse sludge and/or sulfur contained material without influencing the combustion in the incinerator.

In the illustrated incinerator, the lance 407 for dispersed supply of sludge and/or s containing substance on the fire grate of the drying stage 403 is provided along a moving direction of waste, but it is not limited thereto. It is also possible to provide the lance in a direction perpendicular thereto for dispersed supply of sludge and/or sulfur containing substance on the -ire grate 403.

ease I__ troth! 1] Il1 1 1l 1_ I _ 1llilllil 1l 1l ll

J - 63 Sludge penetrates subsequently into the waste on the fire grate 403 due to its own weight, and the combustible matter and water content mix evenly. Sulfur contained material is also dispersed evenly overthewasteonthefiregrateandmixeduniformly. Thus, sludge and/or sulfur contained materiaal are dried together with waste by the air 406 blown from below and by the radiant heat in the incinerator, their temperature is raised and catch fire.

When the combustion starts, sludge and/or sulfur contained material are transferred together with waste to the fire grate of the combustion step 404 and burnt by the combustion air 306 sent from below the fire grate 403. Unburnt parts are sent to the fire grate 405 of a post combustion step andcompletely burnt, and ashes remaining after the combustion are taken out outside from a main ash chute 410.

The combustion takes place in a main combustion chamber 411, and exhausting gas (gas in the incinerator) is subjected to secondary combustion in a secondary combustion chamber 412, so that the unburnt parts are perfectly burnt. The exhausting gas is discharged outside of the incinerator and sent to downstream steps such as a waste gas treating facility (not shown).

As sludge for mixed combustion with waste in the present mode, any type of sludge is applicable, including sewage sludge, night soil sludge, sludge generated when performing en activated sludge treatment of organic wastewater, sludge generated when performing a solid-licuid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging, and other sludge generated in the course of

70 treating wastewater. A special limitation is not made to the water content in sludge, and those containing the usual water content such as 10 to 90% can be used.

As sulfur contained material, arbitrary sulfur contained material maybe employed such as in powder, liquid, solid or other states, and preferable are those easy to be transferred and without the dangers such as explosion.

In addition, the above mentioned sludge and sulfur contained material may be used in combination.

This mode does not especially limit the temperature in the drying stage and temperature in the combustion chamber. The mixed fuel combustion of sludge and/or sulfur contained material and waste can be efficiently carried out at temperature in the drying stage and at temperature in the combustion chamber within ordinary ranges.

More detailed explanation will be made to the present mode, showing actual examples.

(Example 1)

The fire grate incinerator as shown in FIG.14 was used, and municipal refuse end sludge were treated by mixed fuel combustion, according to the present mode.

Firstly, sludge and nitrogen were mixed, and supplied onto the fire grate by means of a lance which has the function of dispersing the sludge. A transferring gas of sludge was CO?.

Municipal refuse was with the value of 2000 kcal/kg and the sludge ration was 80%. The mixed fuel combustion of municipal refuse .,. _ -e Illlllll _ 11_1 1 i 110151_ 1 111 11_1 1 11 118111: _111 1

l - and sludge was carried out by changing the temperature of the drying stage from 700 to 850 C and that in the combustion chamber from 850 to 1000 C.

As a result, comparing with the case of not performing the mixed fuel combustion of municipal refuse and sludge, the average CO concentration was reduced to less than one half, and the concentration of dioxins was also reduced by 70% on average.

During the combustion, the incinerator was able to be operated under stable conditions, and any abnormalities were not seen in waste gas concentration or conditions of ashes.

(Example 2)

The sire grate incinerator as shown in FIG.14 was used, and municipal refuse and sludge were treated by mixed fuel combustion, according to the method of this invention.

Firstly, sulfurpowder was employed es sulfur containedmaterial, and was supplied onto the fire grate by means of a lance which has the function of dispersing the sulfur contained material.

A transferring gas of sludge was CO2. Municipal refuse had general composition. The mixed fuel combustion or municipal refuse end sulfur powder was carried out et usual testconditions.

As a result, comparing with a case of not performing the mixed fuel combustion of municipal refuse and sulfur contained material, the average CO concentration was reduced to less than one half, a-d the concentration of dioxins was also reduced by 50% on average. During the combustion, the incinerator was able to be operated under stable conditions, and any abnormalities

- 72 were no. seen in waste gas concentration or conditions of ashes.

As explained above r by the present invention, the waste treating method and apparatus are provided, which keep the combustion condition in the fire grateincineratorconstantr end efficiently carry out the mixed fuel combustion of waste such as municipal refuse with sludge and/or sulfur contained material, so that the concentration of dioxins in the exhausting gas can be effectively reduced. By using this mode, along with sludge and/or sulfur contained material, waste can be evenly supplied onto the fire grate of the drying stage without creating ranges where the calorific value is extremely low' resulting in efficient reduction of dioxins generation.

By thismode, it became possible to apply themixedfuelcombustion with sludge and/or sulfur contained material to the fire grate incinerator bringing about great industrial value.

BEST MODE 10

In this mode, the inventors made various experiments of incineration treatment of waste, and found that by performing mixed fuel combustion of waste with sludge such as sewage sludge, the dioxins content in combustion waste gas is lowered.

Therefore, the inventors carried out various investigations as to how the effect of reducing dioxins was brought about by mixed ue1 combustion with sludge.

Ore or the causes generating dioxins in combustion o_ waste is known to be that waste is burnt in an oxygen-poor atmosphere.

_,a,,,,,,,.,_. _ i,__ _ _., i' ___UU11111:1 11111 11111111 1115111_ _

i - 73 The burning conditions under such a state correspond to the conditions at the early stage of combustion where waste charged in the incinerator is heated audits temperature is raised. From this, it is considered that substances produced by thermal decomposition of sludge in the early stage of combustion restrains the generation of dioxins.

Therefore, as general sludge contains the N content of 2 to 10 weight % (dried), substances suppressing the generation of dioxins are considered to be those produced by thermal decomposition of N containing substances in sludge, and experiments were carried out. In the experiments, N compounds were added to waste and combustion was performed, and reduction of dioxins in the combustion waste gas was acknowledged. From this fact, it is supposed that the substance suppressing the generation of dioxins is ammonia (NH3) and compounds having a NH radical generated at thermal decomposition of N containing substances in sludge.

A mechanism that thermally decomposed products of N containing substances suppresses the generation of dioxins is not clear, but it isconsideredthat such products have a poisoning effect to copper and other substances which act as catalysts for generating dioxins. This poisoning effect is assumed to be one cause of bringing about the effect of suppressing the generation of dioxins.

As above, since N compounds produced by thermal decomposition of sludge restrains the generation of dio>ins when burning waste, it has been found that if waste is combusted after

N compounds are added to it, the generation of dioxins is suppressed. Further, in the present mode, studies were made on problems that dioxins are also generated in an exhausting gas flow path behind the outlet of the incinerator, and a method of restraining such generation of dioxins was found. It is assumed that in 'he waste gas flow path, certain components in fly ash act as catalysts, and reaction between unburnt aromatic compounds and chlorine progresses, and dioxins are generated. Therefore, experiments were carried out for blowing N compounds into the exhausting gas flow path following the outlet of the incinerator, and reduction of dioxins in the exhausting gas was acknowledged. This is considered that N compounds blown into the exhausting gas flow path suppress the generation of dioxins similarly to charging of compounds into the incinerator.

Thus, when N compounds are charged into the incinerator and further into the waste gas flow path, the amount of dioxins to be generated in these two locations are reduced respectively, and dioxins in the exhausting gas are more lowered. The present mode has been realized on the ground of the these experiments and investigations.

Of the present mode, the 1st is the waste combustion method characterized by adding N compounds to waste to be charged into the incinerator, and blowing N compounds in the r-low path of combustion waste gas behind the outlet of the incir erator.

In this mode, the generation of dioxins is suppressed at the two locations as mentioned above by charging N compounds into _ - '''''_ n.' _ _ 1

- 75 waste to be charged to the incinerator and into waste gas in the exhausting gas path. Accordingly, dioxins in an exhausting gas are substantially reduced.

In this mode' the outlet of the incinerator means the outlet Of the secondary combustion chamber.

Sludge herein means sludge such as sewage sludge, night soil sludge, sludge generated when performing an activated sludge treatment of organicwastewater, sludge generated when performing a solid-liquid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging.

N compounds means organic and inorganic compounds containing nitrogen. Examples of preferable N compounds are low-cost compounds such as ammonia or urea. N compounds may be used in a form O' gas, liquid, solid, or water solution, and depending on locations to be added at, an appropriate form may be selected.

Of the present embodiments, the 2nd is the waste combustion method characterized by charging sludge together with waste into the incinerator, and blowing N compounds into the combustion waste gas path behind the exit of the incinerator.

In this invention, combustion of sludge is carried out together with waste. By combustion of sludge, an effect of suppressing the generation of dioxins can be provided. By blowing N compounds into the path of combustionwaste gas, dioxins generation in the incinerator and the combustion waste gas path can tee suppressed. Tngeneral, waste and sludge areincinerated independent ly by di bereft incineration facilities, by_ by

- 76 concurrent incineration of waste and sludge, additional merits can be enjoyed such as saving in capital cost end operationcost.

Of the present mode, the 3rd is the waste combustion method characterized by adding N compounds to waste and/or sludge when charging waste and sludge into the incinerator.

In thismode, N compounds are added toeitherwasteor sludge, or to both before charging them into the incinerator. Sludge to be burn' such as sewage sludge are clay-like matter, and contains much water (65 to 90 wit) even if it is dewatered. If those dewatered sludge are charged in a large amount, combustion conditions in the incinerator becomes deteriorated. Therefore, there occurs a ease where enough sludge for supplying the N content of a required amount cannot be charged. In such a case, the invention adds separately N compounds for supplementing the shortage in the N content, thereby enabling to substantially decrease dioxins generation in the incinerator while maintaining the normal combustion.

When mixed combustion of waste and sludge is carried out in the waste incineration facility, the merit of saving costs as mentioned above is brought about.

Of the present mode, the 4th is the waste incineration facility characterized by provision of a means for adding N compounds to waste to be charged into the incinerator and provision of a means for blowing N compounds into the exhausting gas path.

By this mode, N compounds can be added to waste, and the generating amount of dioxins in the incinerator can be decreased.

If - 77 Further, as N compounds can beblowninto the exhausting gas path, the generating amount of dioxins in the waste gas path can be decreased. Of the present embodiments, the 5th is the waste incinerating characterized by provision of a means for charging sludge into the incinerator, and addition, to this means for charging sludge, ofa means for blowingNcompoundsinthe sludge, and further provision of a means for blowing N compounds into the combustion waste gas path.

By this mode, as sludge can be charged into the incinerator, generation of dioxins in the incinerator is restrained. Further, as N compounds can be added to sludge, if the effect of restraining dioxins generation isinsufficient only by the N content in the sludge to be charged, the N content to be charged in the incinerator can be supplemented. The merit of saving costs is brought about by mixed combustion of waste and sludge.

In each of the above mode, the position for blowing the N compoundsintothecombustionwastegastlowpathmaybe anywhere in the range from the exit of the incinerator to the stack.

However, preferably it should be done before collecting fly ash which contains a catalyst component, that is, at the position upstream of the dust collector.

FIG.15 is an explanatory view showing the 1st example for carrying out the embodiment. Ashown, the incineration facility is provided with the fire grate incinerator, and in the drawing, 510 is the Fire grate incinerator, 511 is a waste hopper for

- 78 charging was e such as urban refuse into the incinerator, 515 is a was e gas renting process which carries out gas cooling, acid gas removal, and dust collection.

As an auxiliary facility of the incinerator 510, a means 550 for adding N compounds to waste to be charged into the incinerator 510 is provided. The N compound adding means 550 is composed of storage bin 551 of urea solution, which is one kind of N compounds, a urea supply pump 552, and a urea spraying nozzle 553. As an auxiliary facility of the waste gas treating process 515, a means 570 for blowing N compounds into the combustion waste gas path is provided. The N compound blowing means 570 is composed of an ammonia gas holder 571, a flow rate controller 572, and a spray nozzle (not shown).

A combustion chamber 512 of the incinerator is stepwise and provided with a fire gate 513a of the drying step, a fire grate 513b Of the combustion step, and a fire grate 513c of the post combustion step. Thus, the interior of the combustion chamber 512 is sectioned into an area for mainly drying charged waste (drying zone), an area for burning the dried waste (combustion zone) and an zone for reducing those sent in a combustion state into ash.

In the waste incinerating facility composed as above, waste is charged into the waste hopper 511 and over this waste, the urea solution is sprayed from the urea spray nozzle 553. The waste to which urea is added is sent from the hopper 511 to the combustion chamber 512. In the combustion chamber 512, the charged waste is sent on the respective fire grates and changed _ _r 8- - t i I | | 41 | I I 111_ 1lilililll_l llIlBll l

- - - 79 into ash while going through the drying, combustion and the post combustion steps, and discharged. Since the operation is performed where the supply amount of the combustion air is restrained at the upstream side, combustion proceedsin an oxygen poor state in the drying step fire grate 513a (drying zone) and part of the combustion step fire grate 513b (combustion zone).

At such incomplete combustion, in the prior art, aromatic

compound/and chlorine easily react and generate d oxins, but in the present embodiment, urea added to waste is thermally decomposed to generate compounds having the ammonia (NH3) or NH2 radical, so that the dioxins generating reaction is suppressed.

Ascombustionwasteg s generated in the combustion chamber 512 contains combustible gas generated in the drying step fire grate 513a and part of the combustion step fire grate 513b, by blowing the air into the secondary combustion chamber 514, secondary combustion treatment takes place for combusting the combustible gas.

The combustion waste gas exhausted from the secondary combustion chamber 514 is sent to the waste treating process 515, subjected to the cooling treatment, the poisonous gas removing treatment and the dust removing treatment, and is released from the smoke stack 516. Ammonia gas supplied from gas holder 571 is blown into these apparatuses of performing the waste gas treatment or into flues connecting each apparatus, and dioxins genera ion in the combustion waste gas flow path is reduced.

As above, by supplying N compounds into the incinerator and the waste gas flow oath, it is possible to reduce dioxins

t - 80 ger,eration in the incinerator and the waste gas flow path.

FIG.16is an explanatory view showing the2ndexample for carrying out the embodiment. With respect to the same structural parts asFig.15, the same numerals are given end explanationis omitted.

In this embodiment, a new sludge supply means is provided as a. auxiliary facility for charging sludge together with waste into the waste hopper 511. Numeral 540 designates a sludge charger. Further, a N compound blowing means 570 for blowing N compounds into the combustion waste gas flow path is provided as an auxiliary facility of a waste gas treating process.

In the waste incinerating facility composed as above, waste and sludge charged in the waste hopper 511 are sent to the combustion chamber 512. In the incinerator512,waste and sludge are reduced into ash while going through the drying, combustion, and post combustion steps, and exhausted. As mentioned above, in the drying process and in the early period of the combustion process, N containing components in sludge charged with waste is thermally decomposed to generate compounds having the ammonia (NH3) or NH' radical so that the dioxins generating reaction is suppressed. Accordingly, the amount of dioxins contained in the combustion waste gas generated in the combustion chamber 512 is decreased. - The exhausting gas generated in the combustion chamber 512 is sent to the waste gas treating step 515 through the secondary combustion chamber 514 in a similar manner to the facility of rIG.15, into which ammonia gas supplied from a gas holder 571 is blown, so that dioxins generation in the combustion waste gas __ _ A,._._ a. I._ IRIll I I I I I 11111111 1 1 11'1 1l lillllil lilllIII IIIII. Gil_

flow path is decreased.

As above, by charging sludge into the incinerator together with waste, and blowing N compounds into the waste gas flow path, the generation of dioxins is restrained at two locations of the incinerator and the waste gas flow path.

FIG.17 is an explanatory view showing the 3rd example for carrying out the embodiment. With respect to the same structural parts as FIG.15 and 16, the same numerals are given and explanation is omitted. In this mode, in addition to the structure of FIG.16, a N compound adding means 560 for adding N compounds to the sludge charger 540 is equipped, which is composed of a hopper561 for storing urea powder end a urea charger 562. As an auxiliary facility of the waste gas treating process, a N compound blowing means 570 for blowing N compound into the combustion waste gas flow path is provided.

In the waste incinerating facility composed as above, waste is charged into the waste hopper 511, and sludge is supplied from the sludge charger 540. When supplying sludge, urea powder is supplied from the urea charger 552 to the sludge charger 540.

The sludge mixed with urea is charged into the waste hopper 511.

Subsequently, the sludge and waste to which urea is added are sent into the combustion chamber 512.

In the incinerator 512, waste and sludge are reduced into ash while going through the drying, combustion, post combustion processes, and exhausted. As mentioned above, in The drying process and in the early period of the combustion process, the N containing component in sludge charged with waste and urea

- 82 separately added a-e thermally decomposed to generate compounds having the ammonia (NH3) or NH2 radical, so that the dioxins generating reaction is suppressed. Accordingly, the amount of dioxins contained in the combustion waste gas generated in the combustion chamber 512 is decreased.

The combustion waste gas Generated in the combustion chamber 512 is sent to the waste gas treating process 515 through the secondary combustion chamber 514 in a similar manner to the facility of Fig. 15, into which ammonia gas is blown from a gas holder 571, so that dioxins generation in the combustion waste gas flow path is decreased.

As above, by adding urea when sludge is charged into the incinerator to increase the N content to be charged into the incinerator 510, dioxins generation in the incinerator can be further reduced.

FIG.18 is an explanatory view showing the 4th example for carrying out the embodiment. The incinerating facility shown in the figure is provided with the fluidized bed incinerator, numeral 520 is the fluidized bed incinerator, and 540 is a sludge charger. 526 designates a exhausting gas treating process for carrying out the gas cooling, acid gas removal and dust collection. The luidized bed incinerator 520 is sectioned into a fluidized layer section 523 where a fluidized layer is formed by the airblownlromawindbox52latoperation, and the freeboard section 524, which is furnished with a nozzle 525 for blowing a secondary combustion air.

Il_ll _ l.'l' l I I l call_ it lea - - laxly a: lit l

t - 83 As an auxiliary facility of the waste gas treating process 526, a means 570 for blowing N compounds into the combustion waste gas flow path is provided, which is composed of an ammonia gas holder 571, a flow rate controller 572 and a spray nozzle (not shown). In the waste incinerating facility composed as above, waste is charged into the incinerator from the waste charger 530, and sludge is charged from the sludge charger 540. The charged waste and sludge are dried in the fluidized bed, heated, and burnt.

Since the air blowing amount is suppressed in the fluidized bed, it is in a state where dioxins is easily generated when applying the prior art. But in this practice, the N containing substance

in sludge charged with waste is thermally decomposed to generate compounds haying theammonia (NH3) orNH2 radical, and the dioxins generating reaction is suppressed.

The exhausting gas generated in the fluidized layer section 523 contains combustible gas such as H2, CO or CH, and so the air is blown from the nozzle 525 at the freeboard section 524 so as to perform the secondary combustion of the combustible gas.

The exhausted gas from the incinerator 520 is sent to the waste gas treating process 526, subjected to the cooling treatment, poisonous gas removal and dust removal, and released from the stack 527. Ammonia gas supplied from the gas holder 571 is blown into these apparatuses of performing the waste gas treatment or into flues connecting each apparatus, and dioxins generation in the combustion waste gas flow path is reduced.

As above, dioxins in exhausting gas are substantially

decreased by charging sludge together with waste into the incinerator and blowing N compounds into the zone prior to secondary combustion in the freeboard section.

FIG.15 to 18 show the waste incinerating facilities equipped with the fire gate incinerator or the fluidized bed incinerator, but incinerators to which the present embodiment is applicable are not limitedLotheabove two, but also applicable, for example, to a kiln type.

FIG. 15 to 18 show the fire grate incinerators which are provided with the stepwise fire grate, but application of the mode is not limited to these stepwise structures, and it also is applicable to these which have the section functioning as a drying zone in the incinerator.

In the facility of FIG.15, urea is added to materials to be charged into the incinerator in a solution state, and in the facility of FIG.17, it is added to sludge in a powder state, but the invention does not limit stases of the N compound to be added.

When adding N compounds to waste, for dispersing a small amount of N compounds to a large amount of bulky waste as uniformly as possible, solution is desirable. When adding N compounds to sludge, for lessening water content, powder is desirable.

In the facilities of FIG.15 tots, the N compound to be blown into the waste gas flow path is ammonia gas, but it is not limited to a gaseous state, and solution of ammonium or urea is also applicable. (Example l)

._ 81 11111 51111111 _131111 1le111e 1 11 11111111 111111111111 1 -_ 5111 11 1_ 11_ 1 111110 111 1101_ 81

l - 85 Explanation will be made to results of burning waste, using the fire grate testing apparatus. Waste tested was urban refuse, and sludge tested was sewage sludge(water content = 77% and N = 6% in dry weight). Ammonia gas was used as the N compound to be charged into the waste gas flow path. Urban refuse of 2000 kg/H end sewage sludge of200kg/H were charged. Aftercombustion waste gas was cooled, ammonia gas was blown loto the waste gas duct at the rate of 0.35 Nm3/H. Temperature within the waste gas duct was around 300 C.

The concentration of dioxins in the released combustion waste gas was measured during waste incineration by the above condition, and average values of dioxins concentration in 2, 3, 7, 8-TCDD toxicity equivalent were as low as around 25% in comparison with the values in a case where only urban refuse was burns end only ordinary waste gas treatment was carried out. Thus, when burning waste, it is confirmed that the amount of dioxins contained in the combustion waste gas is substantially decreased by charging sludge together with waste and blowing ammonia gas into the waste gas flow path.

By the present mode, sludge or N compounds are charged together with waste into the incinerator, and the N containing component is thermally decomposed to generate the N compound serving to suppress generation of dioxins. Further, the N compound is blown into the combustion waste gas flow path behind the exit oftheincineratorso es to restrain generation o dioxins in the combustion waste gas flow path, so that generation of dioxins is greatly reduced at the two sections of the interior

- 86 o_ the incinerator and the combustion waste gas flow path. In addition, by the waste incinerating facility installed with N compound supply apparatuses at two sections of the incinerator and the combustion waste gas treating process, N compound can be supplied to the two sections of the incinerator and the exhausting gas treating process, and the above effect can be brought about.

BEST MODE 11

In this mode, through various tests of burning treatments oLwaste, it was found that, by carrying out mixedfuelcombustion oLwaste and sludge such as sewage sludge, the amount of dioxins contained in exhausting gas is lowered. The inventors made studies as to how the effect o_ reducing dioxins is brought about by mixed fuel combustion.

It is known that one of main causes of dioxins generation by combustion of waste is to burn waste in an oxygen-poor atmosphere, and the burning condition under this state corresponds to the condition in the stage where waste charged in the incinerator is heated and its temperature is raised. From this fact, it is considered that materials generated by thermal decomposition of sludge in the early stage of combustion serves to suppress the generation of dioxins.

Therefore, since general sludge contains the N content of 2 to 10 weight% (in dry weight), it is assumed that materials suppressing the generation or dioxins are those generated by thermal decomposition of the N containing substance in sludge, it I -115

( - 87 and tests were carried out. In the tests, when a N compound was added to waste to be burnt, it was acknowledged that dioxins in thecombustion waste gas were decreased. Fromthis, it isassumed that a substance suppressing the generation of dioxins is a compound having an ammonia (NH3) or NH2 radical generated when the N containing substance is thermally decomposed.

A mechanism that N compounds generated by thermal decomposition suppresses the generation of dioxins is not clear, but such substances are considered to have a poisoning effect to copper and other substances which act as catalysts for generating dioxins. This poisoning effect is assumed to be one cause bringing about the effect of suppressing the generation of dioxins.

As above, when burning waste, by charging N compounds together with waste, the generation ofbioxinsis also restrained.

The present invention has been realized based on the findings from the above mentioned tests and investigations. Accordingly, the above mentioned problems are solved by the invention as follows. Of this mode, the 1st is the waste incineration method characterized by adding N compounds to waste and charging it into the incinerator.

In this mode, ifN compounds are charged together with waste, the formation of dioxins is controlled, and it is possible to decrease dioxins in combustion waste gas by installing a very simple apparatus.

The And or this mode is the waste incineration method of

t - 38 charging sludge ogethe with waste into the incinerator, characterized by adding N compounds before charging the waste and/or sludge.

Incineration of waste and sludge is in general performed by separate incinerating facilities respectively, but by burning the waste and sludge together, there occurs a merit of saving equipment cost and operation cost and an effect of controlling the formation of dioxins by combustion of sludge. But sludge to be incinerated such as sewage sludge is clay- like matter containing much water (65 to 90 weight%) even if it is dewatered.

If those dewatered sludge is charged in a large amount, the combustion conditions in the incinerator becomes deteriorated.

Therefore, there occurs a case where enough sludge for supplying the N content o'- a required amount cannot be charged. The invention deals with such cases by adding N compounds to waste and/or sludge before charging into the incinerator and supplementing the shortage of the N content.

The 3rd of this mode is the waste incineration method Of charging sludge together with waste into the incinerator, characterized by adding N compounds to waste and sludge charged in the waste hopper of the incinerator.

In this mode, as N compounds are added to both of waste and sludge, N compounds are uniformly dispersed over the charged materials, so that the formation ofdioxinsis evenly suppressed.

The tth of this mode is the waste incinerating of burning sludge together with waste, characterized in that a N compound addition means is provided for adding N compounds to waste to admit-B_ 1 1 ll- t iIIHlilil k1 1 B1 1111:ii; IIll li I;;;11, 15 1151 1 1, fIIG:,111B,1:,::11:! 11lC 11111 11

- 89 be charged into the incinerator.

In this mode, as N compounds are added to waste, it is possible to uniformly add a smallamount of N compounds to a large amount of bulky waste, so that the formation of dioxins is evenly suppressed. The 5th of this mode is the waste incinerating of burning sludge together with waste, characterized in that a N compound addition means is provided to a sludge charger, so that sludge and N compounds are mixed and charged into the incinerator.

This mode is useful in particular when a N compound in powder is added. If a N compound is added in a powder state and the wa er content of materials to be charged in the incinerator is lessened, the combustion efficiency can be heightened.

In the above respective mode, sludge means sewage sludge, night soil sludge, sludge generated when performing an activated sludge treatment of organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging, and other sludge.

The N compounds mean organic or inorganic compounds containing nitrogen. Preferable examples of N compounds are low-cost compounds such as ammonia or urea. The N compound may be gaseous, liquid, solid or solution, and suitable forms are selected by position at which it is added.

FIG.19 is an explanatory view showing the 1st example -or carrying out this mode. The incinerating facility shown is provided with the fire grate incinerator. 610 designates the

9o fire grate incinerator, 611 is a waste hopper for charging waste such as urban refuse into the incinerator, and 615 is a waste gas treating process which carries out the gas cooling, acid gas removing reatment and dust collection by means of a boiler and gas cooler. As an auxiliary facility of the incinerator 610, a means 650 for adding N compounds to waste is provided. 651 designates a storage bin of urea solution, which is one kind of N compounds. 652 is a urea supplypump, 653 is a urea spray nozzle, and 670 is waste such as urban refuse.

In the interior of the combustion chamber 612 of the incinerator, a drying step fire grate 613a, combustion step fire grate 613b and post combustion step fire grate 613c are provided stepwise, each having the transfer function. Thus, the combustion chamber is sectioned into an area for drying the charged waste 670 (drying zone), an area for burning the dried waste (combustion zone) and an area for reducing materials sent in a combusting state into ash (post combustion zone).

In the waste incinerating facility composed as above, waste is charged into the waste hopper 611, and the urea solution is sprayed over the waste from the urea spray nozzle 653. The waste to which urea is added is sent into the combustion chamber 612 from the waste hopper 611.

In the combustion chamber 612, the charged waste is transferred through the respective fire grates and is reduced to ash by going through the drying, combustion end postcombustion steps, and exhausted. As the operation is carried out wild the supply amount of combustion air lessened at the upstream fire _ - _! I_ I I__ Il _ 1 _

grate, the combustion is carried out under an oxygen-poor state in the drying stage fire grate 613a (drying zone) and part of the combustion stage fire grate 613b (combustion zone). If such incomplete combustion takes place, reaction between aromatic compound and chlorine easily forms dioxins, but in this mode, urea added Lo waste is thermally decomposed Lo generate compounds having an ammonia (NH3) or NH2 radical, so that the progress of dioxins generating reaction is restrained.

The exhausting gas generated in the combustion chamber 612 contains combustible gas generated in the drying stage fire grate 613a and part of the combustion stage fire grate 613b, and the combustible gas is burnt by blowing the air into the secondary combustion chamber 614. The exhausting gas exhausted from the secondary combustion chamber 614 is sent to the exhausting treating process 615, subjected to the cooling treatment, poisonous gas removing treatment and dust removing treatment, and is released from the stack 616.

As above, when waste to which urea is added is burnt, the forming amount of dioxins in the incinerator is decreased, so that the amount of dioxins contained in the combustion waste gas is substantially lowered.

FIG.20 is an explanatory view showing the 2nd example for carrying out the present mode. With respect to the same parts as hose in Fig. 19, the same numerals are given and explanation is omitted. In addition to the structure of r IG. 19, a sludge supply means is provided 'or supplying sludge together with waste into the waste hopper 611. 640 is a sludge charge- which is

- 92 equipped with a N compound addition means 660 for mixing the N compound with sludge. 661 is a storage bin of urea powder, and 669 is a urea powder charger.

In the waste incinerating facility composed as above, waste and sludge charged into the waste hopper 611 are sent to the combustion chamber 612 where waste and sludge pass through the drying, combustion, post combustion processes, reduced to ash and are exhausted. In the drying process and in the early period of the combustion process, the N compound in sludge and urea added to sludge are thermally decomposed to generate compounds having the ammonia (NH3) or NHz radical, so that the forming reaction of dioxins is restrained, and the amount of dioxins contained in exhausting gas is substantially decreased.

Exhausting gas generated in the combustion chamber 612 is, as in the facility of FIG.15, subjected to the secondary combustion treatment, gas cooling treatment, poisonous gas removing treatment, and dust removing treatment, and then is released from the stack 616.

FIG.21 is an explanatory view showing the 3rd example for carrying out the present embodiment. With respect to the same structure as in FIG.19, the same numerals are given, and explanation is omitted.

In this mode, a means 650 for adding the N compound to waste and sludge charged into the waste hopper 611 is provided. 651 is a storage bin of urea solution, 652 is a urea supply pump and 653 is a urea spray nozzle.

In the waste incinerating facility composed as above, the _, _ _, a_ __ l _

urea solution is sprayed over waste and sludge ' rom the spray nozzle 652.The waste and sludge over which urea is sprayed are sent into a combustion chamber 612 from the waste hopper 611.

In a incinerator 612, waste and sludge are reduced into ash while going through the drying, combustion and post combustion processes, and are exhausted. Similarly to the facility of FIG. 20, the N compound in sludge and urea separately added are thermally decomposed to generate compounds having the ammonia (NH3) or NH2 radical and suppress the forming reaction of dioxins, so that the amount of dioxins contained in combustion waste gas is substantially decreased.

Exhausting gas generated in the combustion chamber 612 is treated in a similar manner to the case in the facility of FIG. 19, and is released from the stack 616.

FIG.22 is an explanatory view showing the 4th of this mode for carrying out the present mode. 630 is a waste charger, 640 is a sludge charger, and 620 is a fluidized bed incinerator. 626 is a waste gas treating process for gas cooling, acid gas removing and dust removing.

The interior of the fluidized bed incinerator.620 is sectioned into a fluidized layer section 623 forming a fluidized layer by air supplied from a wind box 621 and a freeboard section 624 which is provided with an air blowing nozzle 625. 622 is a dispersing plate for rectifying the air to be blown into the fluidized layer rom the wind box 621. The sludge charger 640 is provided with an addition means or the N compound For mixing the N compound into sludge. 661 is a storage bin of urea powder

- 94 and 662 is a urea powder charger.

In the wasteincinerating facility composed as above, waste is charged into the incinerator 620 from the waste charger 630, and sludge is charged from the sludge charger 640. Then, urea powder is supplied into the sludge charger 640 from the urea charger 662, and the sludge mixed with urea is charged. The charged waste end sludge are dried in the fluidized layer, their temperature raised, and are burnt.

As the amount of air blown into the fluidized layer is suppressed, it is in a combustion state likely to form dioxins.

In this invention, the N compound in sludge and urea added into sludge are thermallydecomposed to generate compounds haying the ammonia (NH3) or NO radical and suppress the dioxins forming reaction. Unburnt materials in waste are taken out from the bottom of the incinerator.

As combustible gas such as Hz' CO or CH4 is included in combustion waste gas generated in the fluidized layer section, air is blown from the nozzle 625 at the freeboard section 624 so as to perform the secondary combustion of the combustiblegas.

Combustion waste gas exhausted from the secondary combustion chamber 614 is sent to the waste gas treating process 626, subjected to the cooling treatment, poisonous gas removal and dust removal, and released from the stack 627.

By charging waste together with sludge to which urea, one kind of N compounds, is added, and combusting them, the amount o_ dioxins containedin exhausting gas is substantially lowered.

FIG.19 to 22 show waste incinerating facilities furnished _,_ _ _ __ -'' 'ea'-a_-.

* with the fire grateincineracor or the fluidized bedincinerator, but applicability of the present embodiment is not limit to these

two types.

FIG.l9 to 21 show the fire grate incinerators provided with the overwise fire grates, but applicability of the present mode

is not limit to the stepwise type and it is applicable to a type with fire grates arranged horizontally.

In the facilities of FIG.19 to 22, two cases are described; in one case, urea is added as a N compound in a powder state and in another, in a solution state. However, no limitation is made to its state when added. When adding a N compound to bulky waste, it is preferable to add it in a solution state and make it adhere to waste for adding as uniformly as possible. When adding a N compound to sludge, it is preferable to add it in a powder state and make it mix with sludge in the sludge charger for preventing the water content of charged material from becoming too high.

(Example 1)

Below, explanation will be made on results of burning waste, using a testing apparatus of the similar composition to the fire grate incinerator shown in FIG.20. Municipal refuse was used as testing material of waste and sewage (water content = 77% and N = 6% (in dry)3 was used as testing materiel ofsludge. Municipal refuse of 2000 kg/H, sewage of 200 kg/H and urea of 1 kg/H were charged. The concentration of dioxins in the released exhausting gas was measured during combustion by the above condition, and average values of dioxins concentration in 2, 3, 7, 8-TCDD

toxicity equivalent were as low as around 20% in comparison with values in a case where only municipal refuse was burnt and only ordinary waste gas treatment was carried out.

Thus, when burning waste, it is confirmed that the amount of dioxins contained in the combustionwastegasissubs.antially decreased by charging sludge or further by adding a N compound.

By this mode, the N compound or the sludge and N compound are added when waste is charged into the incinerator, and the sludge and N compound are thermally decomposed to suppress dioxins generation, so that the generating amount of dioxins in the incinerator is decreased and the amount of dioxins contained in the exhausting gas is substantially reduced. Further, by means of the waste incinerating facility equipped with the N compound adding apparatus, it becomes possible to add the N compound to waste to be charged into the incinerator so as to bring about the above mentioned effect.

BEST MODE 12

The present mode is to provide the waste incineration method and the facility thereof, which make it possible to reduce the generated amount of dioxins only by installing a very simple apparatus and adding low-cost substances.

In the course of carrying ouLvarious tests of burning waste with this embodiment, iLwas found that, by carrying out the mixed fuel combustion of waste and sludge such as sewage sludge, the amount of dioxins contained in exhausting gas was lowered.

Therefore, the inventors carried out various studies as to how _.,,,,,_, ___, - a__ l,,l,, Il.,,, l,',,,! I!

- 7 - the effect of reducing dioxinsis brought about by the mixed fuel combustion with sludge.

It is known that one of main causes generating dioxins by burningwasteis combustion ofwasteinan oxygen-poor atmosphere.

The combustion condition under such state corresponds to a condition in the early period of the combustion step where waste chargedin the incineratoris treated anditstemperature is raised.

From this fact, it is considered that substances by generated by thermal decomposition of sludge acts to suppress dioxins generation. Since general sludge contains a N content as high as 2 to 10 wtt (in dry), it is assumed that substances suppressing the generation of dioxins are those that are generated by thermal decomposition or the N containing substances in sludge, and tests were carried out. In the tests, when waste is burnt with a N compound added to it, it was acknowledged that dioxins in the exhausting gas were decreased. From this, it is assumed that substances suppressing the generation of dioxins are compounds having ammonia (NH3) or NH2 radicals generated by thermal decomposition of N containing substances.

A mechanism than thermally decomposed products of N contained substance suppresses the generation of dioxins is not clear, but it is considered that such products have a poisoning action to copper and other substances which act as catalysts for generating dioxins. This poisoning effect is assumed to be one cause of bringing about Ohm effect of suppressing the generation of dioxins.

As above, when burning waste, by charging N compounds togetherwithwaste, thegeneration oLdioxinsis also restrained.

The present invention has been realized based on the findings from the above mentioned tests and investigations. Accordingly, the above mentioned problems are solved by the invention as follows. The 1st of the present mode is the waste incineration method by the incinerating facility equipped with the fire grate incinerator, characterized by adding N compounds to waste charged in the incinerator and sent to the drying zone, and burning it.

As mentioned above, at the early combustion step, the combustion is carried out under the condition likely to generate dioxins. Therefore, by adding N compounds to waste heated and dried, or to waste in the drying zone and started to be thermally decomposed, it is possible to decrease the amount of dioxins to be generated by thermal decomposition in this drying zone and by combustion in the following combustion zone.

The 2nd of the present mode is the waste incineration method by the incinerating facility equipped with the fire grate incinerator, characterized by charging sludge together with waste, adding N compounds to waste sent in the drying zone of the incinerator, and burning it.

The combustion of waste and sludge is in general performed by separate incinerating facilities respectively, but by burning the waste and sludge together, there occur a merit of saving equipment cost and operation cost and further, an effect o_ controlling the formation or dioxins by the combustion of sludge.

___ __ r _ l l all alll 1 1111 1111111111__111111 11 lllll l

! Bu' sludge such es sewage sludgeis clay-likematter, and contains much water (65 to 90 wt%) even if it is dewatered. If these dewatered sludge is charged in a large amount, combustion conditions in the incinerator becomes deteriorated. Therefore, there occurs a ease where enough sludge for supplying the N content of a required amount cannot be charged. This invention deals with such cases by adding N compounds to waste and sludge in the drying zone of the incinerator, and supplementing the shortage of the N content.

The 3rd of the present mode is the waste incineration method by the incinerating facility equipped with the fluidized bed incinerator, characterized by charging waste into the incinerator for combustion and blowing N compounds into a zone prior to secondary combustion in the freeboard section. In this embodiment, the zone prior to secondary combustion in the freeboard section means a zone between the upper end of the fluidized layer and the position where secondary combustion air is blown in.

Waste charged in the fluidized bed incinerator is burnt in the fluidized layer. However, in particular, the early period of combustion, where charged waste is dried and starts to burn, is in a state which is likely to generate dioxins. Accordingly, the zone to which the combustion gas generated in the fluidized laye- rises and preceding the section where air is blown in for secondary combustion in the freeboard is also in a state which is likely to generate dioxins. By adding a N compound into this zone, the dioxins generating amount can be decreased.

i The 4th of the present mode is the waste incineration method as set forth in the 3rd or the present mode, characterized by charging sludge together with waste into the incinerator.

In this mode, sludge is charged into the incinerator, and N compounds are blowninto the zone prior to secondary combustion in the freeboard, so that the dioxins generating amount can be decreased. The 5th of the present mode is the waste incinerating facility equipped with the fire grate incinerator, characterized by provision of a N compound adding means for supplying N compounds into the drying zone of the incinerator.

In this mode, the N compound is supplied into the drying zone where dioxins are started to be generated, thereby to decrease the generating amount of dioxins in the drying zone and the combustion zone.

The 6th of the present mode is the waste incinerating facility equipped with the fire grate incinerator, characterized by provision OI ameansforsupplyingsludgeinto theincinerator, and a N compound adding means for supplying a N compound into the drying zone of the incinerator.

In this mode, sludge is charged together with waste, and waste and sludge are treated concurrently, resulting in saving in the equipment cost and operation cost in addition to suppression of dioxins generation. Further, the N compound is supplied into he drying zone of the incinerator, supplementing the shortage of nitrogen in sludge.

The 7th or the present mode is the waste incinerating __,.,- ,, Ida, it,., ['ii, e _ 'ci' i ma;;;_:: =L,

r - 101 facility equipped with the fluidized bed incinerator, characterized by provision of a N compound adding means for blowing a N compoundinto the zone prior to secondary combustion in the freeboard of the incinerator.

By this mode, the N compound is supplied to the zone prior to secondary combustion in the freeboard, decreasing the amount of dioxins generated downstream of the freeboard section.

The 8th of the present mode is the waste incinerating i facility equipped with the fluidized bed incinerator, characterized by provision of a means for supplying sludge into the incinerator and a N compound adding means for blowing the N compound into the zone prior to secondary combustion in the freeboard section of the incinerator.

In this mode, sludge is charged into the incinerator, and the NcompoundisUlowninto the zone prior to secondary combustion in the freeboard section, decreasing the amount of dioxins to be generated downstream of the fluidized layer and the freeboard section. In each mode above, sludge means sewage sludge, night soil sludge, sludge generated when performing an activated sludge treatment of organic wastewater, sludge generated when performing a solid-liqu d separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging, and other sludge.

The N compounds means organic or inorganic compounds containing nitrogen. Examples of preferable N compounds are low-cost compounds such as ammonia or urea. The N compound may

- 102 be gaseous, liquid, solid or solution, and suitable r-orms are selected by position at which it is added.

FIG.23 is an explanatory view showing the 1st example for carrying out this mode. The incinerating facility shown is provided with the fire grate incinerator. 710 designates the fire grate incinerator, 711 is a waste hopper for charging waste such as municipal refuse into the incinerator, and 715 is a waste gas treating process which carries out the gas cooling, acid gas removing treatment and dust collection by means of a boiler and gas cooler.

In the interior 712 of the incinerator, a drying stage fire grate 713, combustion stage fire grate 713b and post combustion stage fire grate 713c are provided stepwise. Thus, the combustion chamber is sectioned into an area for drying the charged waste (drying zone), an area for burning the dried waste (combustion zone) and an area for reducing these sent in a combustion state into ash (post combustion zone).

As an auxiliary facility of the incinerator 710, a means 750 for adding N compound to waste in the combustion chamber 712 is provided, which is composed of a storage bin 751 of urea solution as one kind of N compounds, a urea supply pump 752 and a urea spray nozzle 753. The urea spray nozzle753passesthrough a wall of the incinerator 710 above the drying step fire grate 713a. The urea spray nozzle 753 may be plural if required, and scatter the urea solution allover in the width direction of the drying stage fire grate 713a.

In the waste incinerating composed as above, waste is i I! 1 111_5111111_1 11_81181 1111'1111

( I - 103 charged into the waste trooper 711 and sent onto the drying step fire grate 713a in the combustion chamber, and the urea solution is sprayed over the waste from the urea spray nozzle 753.

In the combustion chamber 712, the charged waste is transferred on the respective fire grates as above andis reduced to ash while going through the drying, combustion and post co bustionprocesses, end exhausted. As the operationis carried out with the supply amount of combustion air lessened at the upstream fire grates, the combustion is carried out under an oxygen-poor state in the drying stage fire grate 713a (drying zone? end pert of the combustionstagefiregrate713b (combustion zone). If such incomplete combustion takes place, reaction between aromatic compound and chlorine easily generates dioxins, but in this embodiment, urea added to waste in the drying step fire grate 713a (drying zone) isthermallydecomposedLo generate compounds having ammonia (NH3) or NH2 radicals, so that the progress of dioxins generating reaction of is restrained.

Thecombustion waste gas generated in the combustionchamber 712 contains combustible gas generated in the drying step fire grate 713a and part of the combustion step fire grate 713b, and the combustible gas is burnt by blowing the air into the secondary combustion chamber 714. The combustion waste gas exhausted from the secondary combustion chamber 714 is sent to the waste gas treating process 715, subjected to the cooling treatment, poisonous gas removing Treatment and dust removing treatment, and is released from the stack 716.

As above, by burning the waste with urea added to it, the

f - 104 amount ofdioxinsto begeneratedin the incinerator is decreased, so that the amount of dioxins contained in the combustion waste gas is substantially lowered.

FIG.24 is an explanatory view showing the 2nd example for carrying out the present mode. With respect to the same parts as those in FIG.23, the same numerals are given and explanation is omitted. In addition to the structure of FIG.23, a sludge supply means is provided for supplying sludge together with waste into the waste hopper 711. 740 is a sludge charger.

In the waste incinerating facility composed as above, waste and sludge chargedin the waste hopper 711 are sent onto the drying step fire grate 713a in the combustion chamber 712 on which the urea solution is sprayed from the urea spray nozzle 753. In the incinerator 712, waste and sludge pass through the drying, combustion, post combustion processes, reduced to ash and are exhausted. In the drying process and the early period of the combustion process, the N compound in sludge and urea added to sludge are thermally decomposed to generate compounds having ammonia (Nib) or NH2radicals,sothat the dioxins forming reaction is restrained, and the amount of dioxins contained in combustion waste gas is substantially decreased.

Exhausting gas generated in the combustion chamber 712 is, as in the facility of FIG.23, subjected to the secondary combustion treatment, gas cooling treatment, poisonous gas removing treatment, and dust removing treatment, and then is released from the smoke stack 716.

FIG.23 is an explanatory vied showing the 3rd example to' I ll il lie_-_ 1 7 1: 1;111 1111:181_ 11 1 118 111_1 _114

carrying out the present embodiment. The incinerating facility is provided with the fluidized bed incinerator, and 720 is the fluidized bed incinerator, and 730 is a waste charger. 726 is a waste gas treating process of gas cooling, acid gas removing and dust removing.

The interior of the fluidized bed incinerator 720 is sectioned into a fluidized layer section 723 forming a fluidized layer by the air supplied from a wind box 721 and a freeboard section 724 which is provided with an air blowing nozzle 725 for secondary combustion.

As an auxiliary facility of the fluidized bed incinerator 720, is provided for blowing the N compound to the freeboard section 724 of the incinerator. The N compound adding means 750 is composed of a storage bin 751 of urea solution as one kind of N compounds, a urea supply pump 752 and a urea spray nozzle 753. The urea spray nozzle 753 is furnished at a level lower than a position of the air blowing nozzle 725 so that the urea solution is blown into combustion waste gas which is in an incomplete combustion state.

In the operation of the waste incinerating facility composed as above, wasteis chargedinto the incinerator 720 from the waste charger 730, and the charged waste is heated up while being dried in the fluidized layer 723. As the blowing amount of the air to the fluidized laye' 723 is restrained, the freeboard section 724, where combustion waste gas goes up, is in a combustion state which is likely to form dioxins in the prior art. But in this

mode, the urea blown in is thermally decomposed to generate

- 106 compounds having ammonia (NH3) or NH2 radicals, so that the progress OI dioxins generating reaction is restrained.

As combustible gas such as H2, CO or CHIP is included in exhausting gas generated in the fluidized layer section 723, air is blown in from the nozzle 725 so as to perform secondary combustion of the combustible gas. Exhausting gas exhaustedfrom the incinerator 720 is sent to the exhausting gas beating process 726, subjected to the cooling treatment, poisonous gas removal and dust removal, and released from the stack 727.

As above, the amount of dioxins contained in combustion waste gas is reduced by blowing the N compound into the zone prior to secondary combustion in the freeboard section.

FIG.26 is an explanatory view showing the 4th example for carrying out the present mode. The incinerating facility shown is equipped with the fluidized bed incinerator. With respect to the same parts as those in FIG. 25, the same numerals are given and explanation is omitted. In addition to the structure of FIG. 25, a sludge supply means is provided for supplying sludge together with waste into the incinerator 720. 740 is a sludge charger. In the waste incinerating facility composed as above, waste is charged into the incinerator 720 from the waste charger 730, and sludge is charged from the sludge charger 740. The charged waste and sludge is heated up while being dried. IS the air blowing amount is lessened in The luidized layer 723, dioxins a-e easily generated in the prior art. But in this mode of

practice, sludge is charged, and the generation of dioxins is it_ _ =!!!_ IN Illl Iti-!: C;

suppressed in the fluidized layer 723 by the N compound generated by thermal decomposition of sludge.

Further, at the freeboard section 724, urea solution is sprayed into combustion waste gas arising from the rluidized layer 723. By the N compound formed by thermal decomposition of the urea blown in, the formation of dlaxins is restrained downstream of the freeboard section 724.

As mentioned above, by charging sludgeinto the incinerator, and blowing the N compound into the zone prior to secondary combustion in the freeboard section, the generation of dioxins is suppressed at the two parts of the fluidized layer and the freeboard section. Accordingly, theamountof dioxins contained in exhausting gas can be lowered.

FIG.23 and 24 show the fire grate incinerator of stepwise structure, but applicability of this mode is not limited to such

structure, and it is applicable to those with the function of the drying zone incorporated in them.

In the waste incinerating facility shown in FIG.25, the N compound is blown into the zone prior to secondary combustion in the freeboard section, thereby decreasing dioxins generation downstream of the freeboard section. When there is added a structure for charging sludge together with waste, the generation of dioxins is further decreased. Tha. is, N compounds are formed by thermal decomposition of the N content in sludge, so that the generation of dioxins in the fluidized lays- 723 is restrained, and the amount of dioxins contained in the exhausting gas can be substantially reduced.

- 108 In the facilities of FIG.23 to 25/ urea as a N compound is described to be added in a solution state, but the state in which it is added is not limited to solution. When adding it to waste on the drying zone of a fire grate incinerator, urea powder is applicable, and when blowing it into the freeboard section of the fluidized bed incinerator, ammonia gas is applicable.

(Example 1)

Explanation will be made on results of burning waste using the fire grate type testing apparatus. Testing material oLwaste was a municipal refuse and testing materiel of sludge was a sewage sludge (water content = 77 wt. and N = 6 wt. (in dry)). A nitrogen compound to be blown into the incinerator was urea in solution. Municipal refuse of 2000 kg/H and sewage of 200 kg/H were charged. Urea solution was sprayed over waste on the drying stage of the incinerator. For blowing urea in, the flow rate was set at l kg/H.

The concentration of dioxins in the exhausting gas was measured during combustion by the above condition, and average values of dioxins concentration in 2, 3, 7, 8-TCDD toxicity equivalent were as low as around 20t in comparison with values in a case where only municipal refuse was burnt and only ordinary waste gas treatment was carried out.

Thus, when incinerating waste, by charging sludge containing nitrogen or adding a N compound, it is confirmed that the amount of dioxins contained in the combustion waste gas is substantially decreased.

_ mu__ Ill lL If_ 1 11 _11 1 11 11 1 11 515 111L

- 109 By the present example, the N compound is added to waste or waste and sludge sent into the dry zone of the incinerator so as to generate substances suppressing the generated dioxins by thermally decomposing/he sludge and added N compound, so that the amount of dioxins to be generated in the incinerator can be substantially decreased. Further, by the waste incinerating facility equipped with the nitrogen supply apparatus, it is possible to supply the N compound to be added to waste, bringing about the above mentioned ef'-ect.

BEST MODE 13

In this mode, in the course of carrying out various tests of incinerating waste, by carrying out the mixed fuel combustion of waste and sludge such as sewage sludge, it was found that the amount of dioxins contained in combustion waste gas was lowered.

The inventors made various studies as to how the effect of reducing dioxins is brought about by the mixed fuel combustion of sludge.

It is known that one of main causes generating dioxins by incinerating waste is combustion of waste in an oxygen-poor atmosphere. The combustion condition under such state corresponds to a condition in the early period of the combustion step where waste in the incineratoris heated and its temperature is raised. From this fac, it is considered that substances genera edby.hermal decomposi iono sludge acts for suppressing the formation of dioxins.

Since general sludge con sins the N content of 2 to 10 wt%

- 110 (in dry)/ it is assumed that substances suppressing the generation of dioxins are those generated by thermal decomposition of N containing substances in sludge, and tests were carried out. In the tests, when waste is burnt with N compounds added to it, dioxins in the combustion waste gas were decreased. From this, it is assumed that substances suppressing the generation of dioxins are compounds having ammonia (NH3) or NH radicals generated when N containing substances are thermally decomposed. A mechanism that N compounds generated by thermal decomposition of N containing substances suppress the generation of dioxins is not clear, but such substances are considered to have a poisoning effect to copper and other substances which act as catalysts for generating dioxins. This poisoning effect is assumed to be one cause bringing about suppression of the generation of dioxins.

As above, since N compounds generated by thermal decomposition of sludge works to suppress the generation of dioxins when incinerating waste, it has been found that the generation of dioxins can be suppressed by adding N compounds to waste.

Further, in this mode, investigations were also made on generating dioxins in combustion waste gas exhausted from the incinerator, and a method of restraining their generation was round. In the flow path of exhausting gas, certa n ki,lds of fly ash work as catalysts, so that the reaction between unburnt aromatic compounds and chlorine progresses and dioxidesa-e ,,,,_ i t _ _ 11 1 _; 1111_11111 11111_Rlllllllllllll_Uel

- 111 generated. Also in this case, tests were carried out by blowing N compounds in combustionwaste gas exhausted from the incinerator, and it was confirmed that dioxins in exhausting gas decreased.

It is considered that N compounds blown into the waste gas flow path decreases the generation of dioxins in a similar manner to the case where N compounds are charged into the incinerator.

It is said that the temperature range likely to generate dioxins is from 200 to 800 C. When N compounds are blown into the exhausting gas of more than 700 C, the N compounds blown in are consumed in a reducing reaction of NOX and suppression of dioxins generation is not efficiently performed.

Accordingly, when blowing N compounds into combustion waste gas, the temperature of combustion waste gas should be 700 C or lower, preferably around 650 C or lower. Therefore, in this invention, positions at which the N compounds are blown in is limited to those of the waste gas flow path cooled to below 650 C The exhausting gas exhausted from the secondary combustion chamber of the incinerator is generally 850 to 950 C, and after itis cooled to below 650 C, N compounds are blownin. Forexample, in a facility equipped with a boiler, when N compounds are blown in at an appropriate position of the boiler which is cooled to below 650 C or at the exhausting gas flow path ofa boiler outlet, the generation of dioxins can be efficiently suppressed. In a facility equipped with a gas cooler, the generation of dioxins can be efficiently suppressed by blowing N compounds into the gas cooler or its outlet.

- 112 The present mode has been realized based on the findings from the results of the above tests and investigations.

The 1st of this mode is the waste incinerating method characterized by adding N compounds to waste to be charged into the incinerator, and blowing N compounds into the exhausting gas flow path at a position where the temperature is 650 C or lower.

In this mode, the generation of dioxins is suppressed at the two positions, that is, in the incinerator and in the exhausting gas flow path, by charging N compounds in waste to be charged into the incinerator, and in the exhausting gas path.

Thus, dioxins in exhausting gas are substantially decreased.

Blowing of N compounds into the exhausting gas path is carried out by selecting a position of below 650 C where N cc mpounds effectively works, so that the formation ofdioxins is decreased.

The 2nd of this mode is the waste incinerating method characterized by charging sludge together with waste into the incinerator, and blowing N compounds into the 3 exhausting gas flow path at a position where the temperature is 650 C or lower.

In this mode, sludge is burnt together with waste. The generation of dioxins is effectively restrained by N compounds generated by combustion of sludge. Further, by blowing N compounds into the exhausting gas path, the formation of dioxins in the incinerator and in the exhausting gas path is restrained.

In general, waste and sludge are burnt by separate facilities respectively, but by burning waste and sludge at the same time, further merits of saving in equipment cost and operation cost can be enjoyed.

__ t.' 11 I!11111__ _ 11 AIL

- 113 The 3rd of this mode is the waste incinerating method as set forth in the 2nd mode, characterized by adding N compounds to waste and/or sludge when charging waste and sludge into the incinerator In this mode, N compounds are added to waste or sludge or to both before charging into the incinerator. Sludge such as sewage sludge to be burnt are clay-like matter containing much water (65to 90wt%) even ifit is dewatered, and if such dewatered sludge is charged in a large amount, the combustion state in the incinerator becomes deteriorated. There may be a case where enough sludge for supplying the N content of a required amount cannot be charged.

In such a case, the N compound is separately added to supplement the shortage of the nitrogen content, thereby substantially reducing dioxins generated in the incinerator while maintaining the combustion state normal. By performing the mixed combustion of waste and sludge, the merit of saving in costs is effected.

The 4th of this mode is the waste incinerating facility equipped with a boiler recovering heat of waste gas after secondary combustion, characterized by provision of a means for adding N compounds to waste to be charged into the incinerator and a means for blowing N compounds into the combustion waste gas flow path of the boiler outlet.

According to this mode, as N compounds can be added to waste, the formingamount ofdioxinsin theincinerator can tee decreased.

There is provided the means of blowing N compounds into exhausting

gas in the combustion waste gas path, so that N compounds can be blown in at a position of 6503C or lower where dioxins are efficiently reduced.

The 5th of this mode is the waste incinerating facility equipped with a gas cooler for cooling waste gas after secondary combustion, characterized by provision of a means for adding N compounds to waste to be charged into the incinerator and a means for blowing N compounds into the exhausting gas flow path of the gas cooler outlet.

According to this mode, N compounds can be added to waste, and in addition, N compounds can be blown into the gas cooler outlet of 650 C or lower where dioxins are efficiently reduced.

The 6th of this mode is the waste incinerating facility as set forth in the 4th or 5th mode, characterized by provision of a means for charging sludge into the incinerator in place of a means of adding N compounds to waste to be charged into the incinerator. According to this mode, as sludge is charged into the incinerator in place of N compounds, the formation of dioxins in the incinerator is restrained by combustion of sludge' and the effects of the 4th and 5th mode are brought about.

The 7th of this mode is the waste incineration facility as set forth in the 6th mode, characterized by addition, to the sludge charging means, of a means for adding N compounds.

According to this mode, when charging sludge, N compounds can be added, and in case the dioxins restraining effect is insufficient with only the nitrogen content in sludge to be aree._ __ _ i s s A_-B _ I__ IB! Il!! AIRY __ deli

charged, it is possible to supplement the nitrogen content to be charged into the incinerator.

In each mode, the exhausting gas flow path means devices such as a heat recovery device, gas cooling device and waste gas treating device, and flues connecting them, through which exhausting gas after secondary combustion treatment flows.

Sludge means sewage sludge, night soil sludge, sludge generated when performing an activated sludge treatment of organic wastewater, sludge generated when performing a solid-liquid separation of wastewater containing organic materials, sludge generated in closed water areas as in river dredging, and other sludge. The N compound means organic or inorganic compounds containing nitrogen. Preferable examples of N compounds are low-cost compounds such as ammonia or urea. N compounds may be gaseous, liquid, solid or solution, and suitable forms are selected by position at which it is added.

FIG. 27 is an explanatory view showing the 1st one for carrying out this mode. The incinerating facility shown is provided with a fire grate incinerator. The incinerating facility shown is also equipped with a boiler. 810 designates the fire grate incinerator, 811 is a waste hopper for charging waste 880 such as municipal refuse into the incinerator' and 815 is the boiler and 816 is the dust collected such as a bag filter.

As an auxiliary facility of the incinerator 810, there is provided a means 850 for adding N compounds to waste to be charged in the incinerator 810, which is composed of a storage bin 851 of urea solution as one kind of N compounds, a urea supply pump

- 116 852 and a urea spray nozzle 853.

As the auxiliary facility of the waste gas beating process, there is provided a means 870 for blowing N compounds into the exhausting gas flow path. This means 870 for blowing N compounds in comprises an ammonia gas holder 871, a flow rate regulator 872 and a not shown spray nozzle. The ammonia gas spray nozzle is inserted in the exhausting gas path at the outlet of the boiler 815. At the combustion chamber 812 of the incinerator, a drying stage fire grate 813a, combustion stage fire grate 613b and post combustion stage fire grate 613c are provided stepwise. Thus, the combustion chamber 812 is sectioned into an area for drying the charged waste 880 (drying zone), an area for burning the dried waste (combustion zone) and an area for reducing materials sent in a combusting state into ash (post combustion zone).

In the waste incinerating composed as above, waste is chargedinto the wastehopper811, end the urea solutionis sprayed over the waste from the urea spray nozzle 853. The waste to which urea is added is sent into the combustion chamber 812 from the waste hopper 811.

In the combustion chamber 812, the charged waste is transferred onto the respective fire grates and is reduced to ash while going through the drying, combustion and post combustlonstases, end exhausted. Since the operationis carried out with the supply amount of the combustion air is lessened at the upstream fire grate, the combustion is carried out under an oxygen-poor state at the drying stage fire grate 813a (drying an, __ r __ _ _ H 8-Ill _ l Aim

117 zone) and part of the combustion stage firegrate813b (combustion zone). If such incomplete combustion takes place, reaction between aromatic compound and chlorine easily forms dioxins in the prior art, but in this mode, urea added to waste isthermallydecomposed to generate compounds having ammonia (NH3) or NH2 radicals, so that the progress of dioxins generating reaction is restrained.

The exhausting gas generated in the combustion chamber 812 contains combustible gas generated at the crying stage fire grate 813a and part of the combustion stage fire grate 813b, and the combustible gas is burnt byblowing the air in the secondary combustion chamber 814.

The exhausting gas exhausted from the secondary combustion chamber 814 is thermally recovered at the boiler 815, cooled to around 200 to 300 C, sent to the dust collector forremoving dust, and is released into the atmosphere. At that time, ammonia gas is blown into the exhausting gas flow path at the outlet of the boiler 814 from the N compound blowing-in means 870. By blowing ammonia gas in, dioxins to be generated in the exhausting flow path is decreased.

As above, the amount of dioxins generation can be decreased at the two positions, that is, in the incinerator and in the exhausting gas path, by charging N compounds into the incinerator and the combustion waste gas path.

FIG.28 is an explanatory view showing the 2nd example for carrying out the present mode. With respect to the same parts as those in Fig. 27, the same numerals are given and explanation

- 118 is omitted. As the auxiliary facility of the incinerator, a sludge supply means is provided for supplying sludge together with waste into the waste hopper 811. 840 is a sludge charger.

As the auxiliary facility of the waste gas treating process, a N compound blowing-in means 870 is installed for the exhausting gas flow path.

In the above waste incinerating facility, waste and sludge charged in the wastehopper811 are sent to the combustion chamber 812 where waste and sludge pass through the drying, combustion, post combustion processes, reduced to ash and are exhausted. In the drying step and in the early period of the combustion step, the N compound in sludge and urea added to sludge are thermally decomposed to generate compounds having ammonia (NH3) or NH2 radicals, so that the dioxins forming reaction is restrained, and the amount of dioxins contained in exhausting gas generated in the combustion chamber 812 is decreased.

Exhausting gas generated in the combustion chamber 812 is, as in the facility of Fig. 27, is exhausted from the secondary combustion chamber 814, and is released into the atmosphere via the boiler 815 and the dust collector B16. At that time, ammonia gas is blown into the combustion waste gas flow path at the outlet of the boiler 814 from the N compound blowing-in means 870. By blowing ammonia gasin, dioxins to be generated in the exhausting gas flow path is decreased.

As above, the amount of dioxins generation can be decreased at the two positions, that is, in the incinerator and in the exhausting gas path, by charging N compounds into the incinerator l,. _ ''lelllelle _ 11111___11_ ___ 1 111

and the exhausting gas path.

FIG.29 is an explanatory view showing the 3rd one for carrying out the present mode. With respect to the same parts as those in FlG.27-or 28, the same numerals are given and explanation is omitted.

This mode is equipped with a N compound adding means 860 for adding N compounds to the sludge charger 840 in addition to the structure of FIG 28. The N compound adding means 860 comprises ahopper861 for storingureapowderand the urea charger 862. As the auxiliary facility of the exhausting gas treating process, a N compound blowing-in means870is provided for blowing N compound into the exhausting gas path.

In the waste incinerating facility composed as above, waste is charged into the waste hopper 811, and sludge is supplied from the sludge charger 840. When supplying sludge, urea powder is supplied to the sludge charger 840 from the urea charger 862, and sludge mixed with urea is charged into the waste hopper 811, and subsequently, sludge and waste to which urea is added are sent into the combustion chamber 812.

In the incinerator 812, waste and sludge pass through the drying, combustion, post combustion processes, reduced to ash and are exhausted. As mentioned before, in the drying step and in the early period of the combustion step, the N compound in sludge and urea added to sludge are thermally decomposed to generate compounds having ammonia (NH3) or NH2 radicals, so that the forming reaction of dioxins is restrained, and the amount of dioxins contained in combustion waste gas is substantially

- 120 decreased. The exhausting gas generated in the combustion chamber B12 is exhausted from the secondary combustion chamber 314 in a similar manner to the facility of FIG.27, and is released into the atmosphere through the boiler 815 and the dust collector 816.

At that time, ammonia is blown into the exhausting gas flow path of the exit of the boiler 815 from the N compound blowing-in means 870, thereby decreasing the formation of dioxins in the exhausting gas flow path.

As mentioned above, when sludge is charged in the incinerator, urea is added to increase the nitrogen content to be charged in the incinerator 810, whereby dioxins to be generated in the incinerator are further decreased.

E IG.30 is an explanatory view showing the 4th one for carrying out the present mode. In the drawing, 820 is the fluidized bed incinerator, 830 is a waste charger, 840 is a sludge charger, and 825 is a gas cooler for directly cooling combustion waste gas by spraying water, and 826 is a electrostatic precipitator. The interior of the fluidized bed incinerator 820 is sectioned into a fluidized layer section 823 forming a fluidized layer by the air supplied from a wind box 621 and a freeboard section 824 which is provided with an air blowing nozzle for secondary combustion.

As the auxiliary facility of the waste gas treating step, there is provided a means 870 for blowing the N compound into the exhausting gas path. This blowing-in means 870 comprises _ __ _ _ 111 _ 11

- 121 the ammonia gas holder 871, the flow rate regulator 872 and a not shown spray nozzle which is inserted into the exhausting gas path at the outlet of the gas cooler 825.

In the waste incinerating facility composed as above, waste is charged into the incinerator 820 from the waste charger 830, and sludge is charged from the sludge charger 840. The charged waste and sludge is heated up while being dried in the fluidized layer, and burn. As the air blowing amount is lessened in the fluidized layer, dioxins are easily generated in the prior art.

But in the present mode of practice, the N content in the sludge charged with waste is thermally decomposed to generate compounds having ammonia (NH3) or NH2 radicals, so that the dioxins generating reaction is suppressed.

Combustible gas such as H2, CO or CHg is included in combustion waste gas generated in the fluidized layer section 823, and so the air is blown in at the freeboard section 824 so as to perform the secondary combustion of the combustible gas.

Combustion waste gas exhausted from the incinerator 820 is cooled to around 200 to 400DC, is sent to the dust collector 826 for removing dust, and is released into the atmosphere. At that time, ammonia is blown into the combustion waste gas flow path at the exit of the gas cooler 825 from the N compound blowing-in means 870, thereby decreasing the formation of dioxins in the combustion waste gas flow path.

FIG.27 to 30 show waste incinerating facilities furnished with the fire grate incinerator or the fluidized bedincinerator, but applicability of the present mode is not limited to these

two types, and it is applicable to, for example, a kiln type.

FIG.27 to 30 show the fire grate incinerators provided with stepwise fire grates, but applicability of the present mode is

not limited to a stepwise type, and it also is applicable to those which have the section functioning as a drying zone in the incinerator In FIG. 27 to 30, the spray nozzle of the N compound blowing-in means 870 installed to the waste gas treating process is inserted into the outlet of the boiler 815 for blowing the N compound to the outlet of the boiler 815, but this is one example for a ease where a boilerisequipped, end the position for blowing the N compound in is not limited toe boiler outlet. In a facility equipped with a gas cooler,the position for blowing the N compound in is not limited to a gas cooler outlet. Thus, the N compound blowing-in position is not limited to the outlet of the boiler or the gas cooler, and the N compound may be blown in at an appropriate position of a boiler cooled to below 630 C or in the gas cooler.

In the facility of FIG.27, urea is added to material before charging into the incinerator in a solution state, and in FIG. 29, it is in a powder state, but the invention does not limit states of the N compound to be added. When adding N compounds to waste, for dispersing a small amount of N compounds to a large amount of bulky waste as uniformly as possible, solution is desirable. When adding N compounds to sludge, for 'essenir,g water content, powder is desirable.

In the facilities of FIG.27 to30, the N compound to be blown _.,

- 123 into the combustion waste gas flow path is ammonia gas, but the N compound to be blown into the exhausting gas flow path is not limited to a gaseous state, and solution of ammonia or urea is also applicable.

(Example 1)

Explanation will be made to results ofLurning waste, using the fire grate testing apparatus. Testing material of waste was municipal refuse and testing material of sludge is sewage sludge(water content = 77 weight. % and N = 6 weight.% (in dry)j.

The N compound to be blown into the incinerator was a onia in solution. Municipal refuse of 2000 kg/H and sewage of 200 kg/H and were charged. Urea was added to sludge at a rate of 1 kg/H.

The generated exhausting gas was cooled by the gas cooler, and ammonia gas was blown at a flow rate of 0.35 Nm3/H into the exhausting gas duct. The temperature in the exhausting gas duct was around 300 C.

The concentration of dioxins in the released exhausting gas was measured during combustion by the above condition, and average values of dioxins concentration in 2, 3, 7, 8-TCDD toxicity equivalent were as low as around 10t in comparison with the values in a case where only municipal refuse was burnt and only ordinary waste gas treatment was carried out. Thus, when burning waste, it was confirmed that the amount of dioxins contained in the combustion waste gas is substantially decreased by charging sludge JO which urea is added together with waste, and ammonia gas is blown into the combustion waste gas path.

- 124 By the present mode, sludge and N compounds are charged together with waste into the incinerator, and the N containing component is thermally decomposed to generate the N compound working to suppress generation of dioxins. Further, the N compoundisblowninto the exhausting gas path, so that the forming amount ofbioxins is substantially decreased at the two positions of in the incinerator and in the exhausting gas path. Further, as the N component is blown into the exhausting gas path where the temperature of the exhausting gas is below 650 C, de-

nitrification reaction is difficult to occur so that the formation of dioxins is effectively restrained.

There is provided an apparatus for charging sludge or N compounds in the incinerator, and by using the waste incinerating facility equipped with the N compound blowing-in apparatus at the outlet of the boiler or the gas cooler, it becomes possible to charge sludge or N compounds into the incinerator for suppressing the generation of dioxins and to blow N compounds into the combustion waste gas path at a position where the generation of dioxins is effectively restrained, thereby obtaining the above mentioned effect.

BEST MODE 14

The present mode relates to a waste incineration method and an apparatus thereof which hum waste in an incinerator, releases generated waste gas into the atmosphere after treatment, while efficiently decreasing dioxins generation.

FIG. 35 shows the structure of the waste incinerating ...,,,,,_ a_

- 125 system, inwhich901isanincinerator having a waste supply hopper 9Ola, 902 is a temperature reducing device comprising, e.g., a temperature reducing tower, boiler, or heat exchanger, 903 is a waste gas treating facility for removing acid gas such as HCl or SO<from the waste gas cooled down in the temperature reducing device 902. 904 is an electric precipitator, 905 is an induction fan, and 906 is a stack. Those are connected in series by flues.

In this system, waste charged into the incinerator by the crane from a waste pit is dried and burnt in the incinerator 901, and unburnt parts are completely burnt. After combustion, exhausting gas is discharged outside, goes through the temperature reducing device 902, waste gas treating facility 903 and electrostatic precipitator 904, and exhausted from the stack 906.

The electric precipitator 904 has, as is well known, the characteristics that it is not influenced by properties of gas or dust and can catch fine particles. But, in this waste incinerating system, the waste gas from the outlet of the incinerator 901 first goes through the temperature reducing device 902 and the waste gas treating facility 903, and is introduced at about 300 C into the electrostatic precipitator 904 for dust collection. The temperature of about 300 C is the one where dioxins are easily generated, and if exhausting gas is passed at about 300 Cthrough the electrostatic precipitator, a problem arises that the high concentration of dioxins is exhausted from the stack 906.

A technological problem to be addressed by the present mode

126 is to keep the combustion conditions in the incinerator constant by introducing a relatively simple apparatus, so that the concentration of dioxins in the incinerator is lowered, and also the formation of dioxins in the electrostatic precipitator is suppressed. The waste incineration method in the present mode is to use a waste incineration system composed of an incinerator, temperature reducing device, waste gas treating facility, electrostatic precipitator, induced fan, and stack connected in series, where the incinerator is provided with a waste supply hopper end a sludge supplyhopper,wasteis burntmixedwithsludge, and a temperature controller is provided at the inlet of the dust collector for controlling the electric dust collector to operate at a temperature below 230 C.

The present waste incinerating method is characterized by control of the temperature reducing device so that the temperature of the exhausting gas at the inlet of the electrostatic precipitator is below 230 C.

Further, the electrostatic precipitator is provided at its inlet with a temperature sensor for sensing the temperature of exhausting gas so as to control the temperature reducing device for keep the temperature at the inlet of the electrostatic precipitator below 230 C.

Explanation will be provided on the waste incinerating method and apparatus for carrying out the present mode/ referring to FIG.33. FIG.33 is the system configuration of the waste incinerating apparatus of the present mode. For the same -,.,._,, By,.,l,,'l.., _. _

- 127 sections as in the prior example (FIG.35), the same numerals are given. In the waste incinerating apparatus of the present mode, the incinerator 901 is provided with not only the waste supply hopper 901a but also the sludge supply hopper 901b, as well as the temperature sensor 907 installed for sensing the waste gas temperature at the inlet of the electrostatic precipitator 904, and further the electrostatic precipitator inlet temperature controller 908 is furnished for operating the electrostatic precipitator 904 at the temperature below 230 C by controlling the temperature reducing device 902 so as to make the rate of temperature reduction of the high temperature exhausting gas larger when the temperature sensed by the temperature sensor 907 exceeds 230 C or when the temperature sensed by the temperature sensor 907 does not exceed 230 C yet, but is rising too quickly.

In this system, the temperature reducer 902 comprises the temperature reducing tower which lowers the temperature of the high temperature waste gas by passing it through the water spray atmosphere, and when a command is issued from the electrostatic precipitatorinlet temperature controller 908 forincreasing the water spray amount, the temperature reducing device increase the water spray amount.

Further explanation will be provided on the method of burning waste by this system. First, waste is transferred by the crane from the waste pit and is charged into the incinerator 901 from the supply hopper 901a, while organic sludge generated at sewage treating, for example, is charged by the sludge supply

- 128 hopper 901b. Sludge and waste charged in the incinerator 901 are dried in the incinerator, catch fire, and is subjected to mixed combustion, end waste basis sent downstream from the outlet of the incinerator. Thereby, the concentration of dioxins is lowered in comparison with a case of burning only waste.

The reason of dioxins suppression has been mentioned for other mode, and is omitted.

By the present mode, it has been found that, when carrying out the mixed combustion of waste and sludge, by using the electrostatic precipitator 904 and lowering its operating temperature, the concentration of dioxins is decreased. It is assumedthat, by carrying out the operation at a temperature lower then the range ofaround300 Cwhere dioxins are easily generated, dioxins generation is restrained. FIG.34 shows the findings obtained from the inventors' experimental studies. This is a graph showing the relation of the rate of increase of dioxins between the inlet and outlet of the electrostatic precipitator.

The axis of ordinate is the rate of increase of dioxins and the axis of abscissa is the temperature at the inlet of the electrostatic precipitator.

From this result, it is seen that when the temperature of the electrostatic precipitator is below 230 C, preferably below 210 C, the concentration of dioxins does not increase in the electrostaticprecipitator Bed, and the concentration of dioxins is efficiently lowered.

Accordingly, observing the waste gas temperature by the temperature sensor 907 installed at the inlet of the 51111_ 1 11 1 115 - 111111_ _185 1 _

electrostatic precipitator and by the temperature controller 908, when the temperature sensed by the temperature sensor exceeds 230 C or when the temperature sensed by the temperature sensor does not exceed 230 C yet, but is rising too quickly, a command for increasing the water spray amount is issued from the electrostatic precipitator inlet temperature controller 908 to the temperature reducer 902 so as to increase the water spray amount in the temperature reducing device, increase the rate of temperature reduction of high temperature exhausting gas. In this way, by controlling the operating temperature of the electrostatic precipitator 90g to below 230 C, dioxins can be decreased. By the synergistic effect of this effect end the effect of decreasing dioxins due to supply of sludge, the concentration of dioxins can be more effectively decreased.

When the whole system is automatically controlled, it is sufficient to incorporate a sensed value of the temperature sensor 907 as one of the operating parameters.

The air made clean by the electrostatic precipitator 904 removing fine particles is released into the atmosphere from the stack 906.

In order to confirmthe effect of this mode, municipal refuse and waste were burns by a fire grate incinerator, the temperature of the exhausting gas was lowered to 210 C by a temperature reducing tower, and dust was removed by an electrostatic precipitator. The resultant concentration of dioxins was compared with that obtained when only municipal refuse was burnt and the electrostatic precipitator was operated at 270 C. It

- 130 was confirmed that in the former case of the present mode, the concentration of dioxins is lowered by about 90% in comparison with the latter case.

As mentioned above, by the present mode, in the waste incinerating system composed of an incinerator, temperature reducing device, waste gas treating facility, electrostatic precipitator, induced fan, and stack connected in series, the generation of dioxins can be efficiently decreased, due to mixed combustion with sludge and operation of the electrostatic precipitator at a temperature below 230 C.

INDUSTRIAL APPLICABILITY

As above, the waste incineration method and apparatus thereof relating to this invention provides the effect of suppressing the generated dioxins by performing the mixed fuel combustion of waste, sludge, plastic, RDF, sulfur contained material, and others in a fire grate incinerator or a fluidized bed incinerator, and controlling the combustion in accordance with the Sol concentration, and further by generating N compounds, thereby bringing about very large industrial effects.

_.,.__., _À, n-it,-_; 1 1 1 1IC111-

Claims

-131 Claims:

1. A method for incinerating a waste comprising the steps of: preparing a waste incineration device having an incinerator, a temperature reducing device, and an electrostatic precipitator; performing a mixed fuel combustion of a waste and a sludge; and controlling the temperature reducing device so that an exhausting gas temperature is 230 C or lower at an inlet of the electrostatic precipitator.

2. An apparatus for incinerating a waste, the apparatus comprising: a waste incineration device, structured by connecting in series, via a flue, an incinerator, temperature reducing device, an exhausting gas treating device, an electrostatic precipitator, an induced draft fan, and a stack; a waste supply hopper provided to the incinerator; a sludge supply hopper provided to the incinerator; an exhausting gas temperature control device at the inlet of the electrostatic precipitator, connecting with the temperature reducing device and the electrostatic precipitator; and, a temperature sensor for sensing a temperature of the exhausting gas at an inlet of the electrostatic precipitator, which is located inside of a temperature control device for the inlet exhausting gas of the electrostatic precipitator.