CA1173399A

CA1173399A - Method and device for producing carbon enriched solids from waste materials

Info

Publication number: CA1173399A
Application number: CA000364982A
Authority: CA
Inventors: Franz O. Hug; Hans B. Wiesli
Original assignee: OFAG OFENBAU- und FEUERUNGSTECHNIK AG
Current assignee: OFAG OFENBAU- und FEUERUNGSTECHNIK AG
Priority date: 1979-11-25
Filing date: 1980-11-19
Publication date: 1984-08-28
Also published as: ATE9166T1; EP0029580A1; DE3069079D1; JPS5687484A; EP0029580B1

Abstract

ABSTRACT

In the processing of garbage there is the technical problem of on the one hand exploiting to the fullest the energy content of the garbage whilst on the other hand disposing of the garbage with a minimum of pollution.

In contrast to the usual methods using extensive degasification or gasifica-tion or obtaining oil at low or medium temperature pyrolysis or by obtaining active carbon together with substantial degasification by using medium and high temperature pyrolysis, with low temperature pyrolysis of between approxi-mately 240° and 380°C there is produced 2 garbage containing sufficiently high carbon enrichment and conservation of carbon compound 5 in order to obtain a storable fuel suitable for domestic as well as industrial ovens. This is achieved by directly heating and passing an inert heating gas through the garbage in a continuous reactor (1) provided with temperature control circuit (2,27,28). The heating and flushing gas can preferably be obtained by burning the pyrolysis waste gases at (5) discharged by the reactor (1) in a burner (6) and a heat exchanger (13) for useful heating connected in series with the burner.(6).

Description

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Method and Device for Producing Carbon Enriched Solids from Waste Materials.

The invention relates to a method for producing carbon enriched solids from organic carbon comp~ s, especially waste containing cellulose or cellulose like compounds, particularly cor~munal waste and sewage sludge, wherein the waste is subjected to a pyrolytic treatment and gas rernoval in an air-free atmosphereO The invention furthermore relates to a device for effecting such a method.

A waste converting method of the aforementioned type and the corresponding device is known from a journal entitled "Waste and Garbag~ Processing - Mull -Handbuch", Erich Schmidt Verlag, Berlin, 1964, vol.4, page 15, 16, under the title "Sodete~-Verfahren"~ In this method the garbage is converted into heating gas and a solid residue for use as a filter medium by heating in a continuous retort. Although this method relates to the production of solids, the simultaneous production of gases is of prime importance. This pyrolysis gas i3 also used for heating the retort through an external burner.

oi the The essential feature~ Sodeteg method or the associated device are the indi-rect heating of the waste to be converted, whereby the heat flow must be directed to the material to be treated by heat conduction from the external heater via the wall of the retort and must satisfy the necessary purity re-quirements in the degasification of thee~uct which is determined by theuse~ For such substantial degasification or production of active carbon, it is necessary to useimedium or high temperature pyrolysis, as described in for example/"Schriftreihe Abfallwirtschaft", Bayerisches Landesamt fUr Urnweltschutz, 1975, Vol.3, page 4 (the illustration 1; formation of gas), page 5 (Table 2; the formation of combustible gases and the end of tar forma-tion) and page 20 line 7-9.

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~urthermore, on page 20, line 7 of the aforementioned literature source Erom "Schriftreihe Abfallwir-tschaft" is described the use of low temperature pyrolysis with temperatures between 400 and 600C
for converting garbage. This is used in the so-called "garrett process" for obtaining by pyrolytic means oil from waste material (see page 20, paragraph 6.1, of the aforementioned literature source as well as page 13 of the literature source "Mull - Handbauch", listed a little further up). In other words, this does not relate to a method for obtaining enriched solids with a carbon content as compared to the solids used in the charge, whereby the treating temperature range used corresponds to the aim of this process. For heating the retort the same applies as that used in the Sodeteg process.

Also known from the above mentioned literature source "Mull -Handbuch", page 14 is a medium temperature range pyrolysis method for producing steam from waste and especially under the heading "Landgard process". Similar to the process for producing steam, the formation of combustible heating gases for the series-connected steam generator is of prime importance, whereas the solid residues after separation of the inorganic components "Metals, Glass" is intended for depositing, in other words not for further use. The pyrolytic treating temperature of approximately 800C corresponds to a maximum yield of gases with a high thermal output or carbon content. The heating of the charge takes place counter current to the hot waste gases of an oil burner in a revolving furnace, i.e. through direct application of the heating gas which is obtained by combustion of its own fuel.

To summarise therefore, the state of the art for converting garbage by pyrolytic means without air includes the following:

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1). Production of solids for filter purposes ~essentially active carbon) containing a high concentration of carbon by substant-ial degasification and practically complete degradation of the organic carbon cornpounds, i.e. large losses of combustible substance by using the medium and high temperature hydrolysis with indirect heating of the xetort.

2). Production of oil through low temperature pyrolysis by minimis-ing the solid residue, indirect heating of the retort.

3). Production of heating gas (for steam generation) through medium temperature pyrolysis by minimising the solids residue, direct heating of the garbage used by waste gas flowing counter current in a special burner.

It is th~refore the aim of the invention to produce a garbage processing method for producing solids as the educt having a carbon content which is higher than that of the charge, but by maximising the solids yield whereby the degasiication and therefore the degradation of the organic carbon compound is to be effected only so far as is necessary for achieving a sufficiently conserved carbon content, i.e. one that is sufficient for use as a solid fuel and which will keep in storage and not fer~ent or decompose in any other way. The object therefore is to achieve an optimum compromise between solids yeild on the one hand and conservation or carbon enrichment of the educt on the other hand.

According to one aspect the invention consists o:E a method of pro-ducing carbon enriched solids from solid waste, said method comprising the steps of: introducing a raw material in a reaction chamber; said raw material consisting at least partly of solid "~t ,,.J~ 3 r~

~ ~173399 waste containing cellulose or eellulose-like polyhydrocarbon compounds; moving said solid waste along a processing path through said reaction chamber; exposing said solid waste in said reaction chamber to an inert heating gas flowing through said reaction ehamber eounter-eurrently to the movement of said solid waste;
heating, degasifying and flushing said solid waste so as to establish a pyrolytie carbonization reaetion by means of said inert heating gas to produce processed solid waste and was-te gases; said pyrolytic carbonization reaction being exothermie on a substantial part of said proeessing path; maintaining the maximum temPerature of said solid waste undergoing said pyrolytic carbonization reaetion above about 240C and below 310C.

~ecording to another aspect the invention eonsists of a deviee for effecting the foregoing method, eharaeterized by a temperature eontrol with a pyrolytie treating station for the waste to be eonverted as the eontrol system, havirgat least one measuring probe for recording the maximum treating temperature as the eontrol value, and at least one eontrol member aeting on the heating of the pyrolytie treating s-tation.

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The method according to the invention is based on the understanding that -through pyrolysis in the absence of air li.e. pyrolysis in the narrower sense as opposed to the decomposition with partial com-bustion without air at higher temperatures as described in the literature; also described as "gasification" in contrast to "degasification" through pyrolysis in the narrower sense) at treat~
ment temperatures which are below those of known low temperature pyrolysis at approximately 400C to 600C, it is possible to obtain an educt suitable as a solid fuel and which is sufficiently con-served in the sense of the ai~ of the invention, as follows, thisarea is also referred to as "low temperature pyrolysis". A pre-condition for a successful rocess is the direct heating of the charge through an essentially inert heating and flushing stream in order to achieve at these relatively low treating temperatures a sufficiently even temperature distribution within the goods.

With res ect to the prior art it should be noted that the range of low temperature pyrolysis has already been described in scientific literature (see dissertation of the ETH Zurich "Contribution to the pyrolysis of cellulose for the production of active carbon from cellulose containing waste substances", by Dr. P.H. Brunner, 1976, Diss. ETH 5705) had already been examined in the application of cellulose and garbage, but not with the result corresponding to the present inventive thought and not by using the direct heating gas application - already known rom the Landgard method for medium temperature pyrolysis. According to these experiments (see page 72, 2, second paragraph, oE the aforesaid dissertation) it is far more advantageous for the........................................... ~

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waste processing to optimise the pyrolysis gases, whereby high temperatures or a high rate of heating is aimed for with regard to the hydrogen concen-'r~liS iS
tration and the gas yield. in contrast to the method according to the inven-tion with its low temperature pyrolysis by direct heating and flushing gas application for optimising the yield of sufficiently conserved and for burning purposes sufficiently carbon enriched solids.

The upper marginal temperature of the method according to the invention can be varied fundamentally - but in comparatively narrow bounds - according to the scale of the particular specially required educt properties and nature of the charge~ For average communal garbage, the keeping of a maximum ~al~e of the treating temperature of approximately 350 & has proved suitable for optimising yield at relatively high conservation requirements.

Detailed practical tests with the aim of obtaining even greater optimum yields while still keeping within the necessary conser~ation of the educt have shown that keeping within a range Qf between 265 & and approximately 310C for the treating temperature during pyrolysis or during a substantial part of the process, prove to be particularly advantageous.

~f particular advantage also is the embodiment of the invention whereby the waste is directly subjected to a heating gas which is produced by the combustion of waste gases during pyrolytic degasi~ication. This results in a high degree of energy whereby if necessary heating gas can also be given off for external use.

Further features and advantages of the in~ention are described with the aid of the drawings and the embodiment examples depicted therein. These show:

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Fig.1.
A schematic diagram for the functioning of the plant and a device for low temperature pyrolysis, Fig.2~
A diagram showing the various temperatures (endothermal or exothermal charac-ter of the p~rolysis) regarding the treatment temperatures ~or treated commu-nal garbage, and Fig.3.
A time diagram for the pyrolysis process at various treatment te~peratures for representing the loss in weight of the goods being treated in the course of the process~ ¦

The plant according to Fig.1 comprises a directly heated shaft oven 1 as the pyrolysis treatment station with heating and flushir~ gas supply 2 , raw~
material charge 3 and controllable educt discharge 4 with associated control member 23 for adjusting the discharge or through-put rates. A waste gas outlet 5 is provided ;n an external burner 6 with controllable air supply 8 as well as a similar addltional ~uel supply 9 for starting the process. The associated control members are designated as 10 or 11; they are in controlled contact with the heating gas temperature sensor 7. Connected in series with - 6 ~ ', I
!

the heating gas outlet 12 of burner 6 is a working-gas exchanger 13 which can also be used as cooling device for adding cold inert exhaust gas ~/len subjecting the reactor to hot gases for the purpose of rapid temperature control. For thicpurpose the waste gas outlet of heat exchanger 13 is pro-vided with a fan 14 with by-pass valve 15 which latter is controlled by a temperature sensor 16i n the heating and flushing gas supply in the sense of a controlled circuit for maintaining the aforementioned treatment tempera-ture. The overflow gas outlet 17 with a release valve 18 and co~pressed air blower 19 arranged before it in connection with a temperature sensor 20 con-lO trolling the valve 18 in the gas outlet of the burner 6 enables the heating ¦
and flushing gases flowing to the reactor to be kept within the/forementioned limits. At the same time an inlet valve 21 of the heat exchanger 13 is con-trolled by the temperature sensor 20 in a complimentary sense with respect to the opening position Or the paFticular outlet valve 18.

The aforementioned control and regulator devices act as auxiliary control circuits to a main control circuit with the treatment temperature as the control value which i9 sensed directly on the reactor by a temperature sensor 22 and compared with a given nominal standard value in a control 25.
Thus resulting adjustment control signal in the example given controls the control member 23 of the educt output 4 and the through-put rat~
resultir~ in a process temperature control.

In place of the aforementioned through-put control as the contro~ member for the temperature control or if necessary additional to the through-put control, it is possible to have a further direct process temperature measurement through sensor 27 and associated control 28 for the standard value - nominal value comparison and with a heating gas valve 26 as the control member.

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This generally results in particularly precise and comparatively rapid con-trol of the process temperature.

In the plant according to Fig. 1 there is a further possiblity for addition-ally inactivating or inertisation of the heating gases supplied by the hurner 6 with the aid of a post treating station 24. This for example oan be in the form of an after burner and preferably connected with chemical treatment plants for the binding'undesired waste gas components.

In the endotherm/exotherm diagram accordir~ to Fig.2 the treating temperature ~ of approximately 290C represents the optimum process parameter. This value lies in the starting rarge of the region of exothermal garbage decompo-sition reactions. Experience has shown that these lead to a comparatively rapid decomposition reactlon at a reduced requirement of additionally supp-lied process heat and also provide the desired conservation and carbon en-ric~ent of the educt. The upward limit of the process temperature range ensures a substantial optimising of the educt yield.

The time - temperature diagram according to Fig.3 shows that the process temperature range around 300& leads to a comparatively rapid 105s in weight in the charge and which corresponds to the degasification reaction for the desired conservation and carbon enrichment of the educt, but comes to an end at approximately 5G%. The latter corresponds to the optimum quantity of the educt yield.

The charge or educt data which can be readily understood without having to go into details, in comparison show particularly the increase in the fix-carbon content in the educt which corresponds to the desired conservation, as well as the weight-related heating value which represents a measure for the quality of the educt with regard to the use as a solid fuel L~ ~ 3 3 ~ ~

The analysis data of the samples according to tables I and II were obtain-ed at a mean process temperature of approximately 290& . The educt had a heat~ e, dry consistency which after storage remained unchanged such as for example would meet the re~uir~ments of domestic or industrial fuel.

In the event that the property of the garbage being used does not permit its use for industrial or domestic fuel without special precautions against the emission of noxious substances when being burned, the garbage can be chemically pre-treated to bind the particular components. In consideration of the conditions conducive for the reaction, especially the temperature, these binding reactions in the pyrolysis process can be effected with par-ticular intensity. It is possible that the noxious components are formed only during pyrolysis in the subsequent combustion process so that it may be possible to act on the components forming the noxious substances by addir~ appropriate neutralising additives.

In general the components of the pyrolysls educt forming the noxious sub-stances after combustion are acid in character. This applies particularly to the Chlorine-ccntaining most co~mon plastics components in co~munal gar-bage. For neutralising this it is advantageous to add calcium oxide or calcium hydroxide during pyrolysis and especially by mixing in with the 20 garbage. In general it is necessary to exceed the required dose of the ~ ent alkaline neutralisin~ by 50 to 10~/o above the stoichiometric equilibrium of the quantity corresponding to the binding reaction~ In addition other alkaline reagents are also used for neutralising the acid noxious substances, but lime has the advantage because of its generally low toxidity in the resulting end product and is also cheap. -_ 9_ , .

7 3 3 9 ~ 1 Neutralisation of the aforementioned kind can also be affected independentof the formation and emission of noxious substances during combustion and is therefore useful with regard to ~rotecti~g furnaces against ag~ressive components, especially against acid components which attack metal.

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TABLE I

Sample No. 1: Rawmaterial _ _ . ~
Charged Air Dry Water Water +
Free Ash Free _ _ Water Content %1,5 1,5 Ash %22,6 22,6 23,0 Carbonate- %1,4 1,4 1,4 Carbonic Ac.id CarXbon %14,4 14,4 14,7 19,4 Volatile %60,1 60,1 60,9 80,6 Components Lower Heating J/g 14'885 14'885 15'155 20'030 Value kcal/kg 3'555 3'555 3'6204'784 Upper Heating J/g 16'075 16'075 16'330 21'580 Value kcal/kg 3'839 3'839 3'9005'154 Elementary Analysis Carbon %39,2 39,2 52,7 Hydrogen %5,1 5,1 6,8 Oxygen %28,8 28,8 38,5 Nitrogen ~0,4 0,4 0,6 Sulphur ~0,7 0,7 0,9 Ash %22,6 22,6 Water %1,5 1,5 Chlorine %0,3 0,3 0,5 i At complete combustion without excess air the air requirement per Kilogram fuel: 5,0 kg3resp.
3,9 Nm Melting of ash: Softening point 1100C
Hemispheric point 1160C
Flowpoint 1250C

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TABLE II

Sample No. 2: Educt.
.
ChargedAir dry Water Ash Free Free Water Content % 0,4 0,4 Ash %35,8 35,8 35,9 Carbonate- %1,7 1,7 1,7 Carbonic Acid Fixer Carbon % 22,9 22,9 23,0 37,0 Vola-tile Components %39,2 39,2 39,4 63r0 Lower Heating /g 18'440 18'44018'550 29'725 Value Kcal/kg 4'405 4'405 4'4307'100 Upper Heating /g 19'405 19'40519'490 31'255 Value Kcal/kg 4'635 4'635 4'6557'465 Elementary Analysis Carbon %45,2 45,2 72,8 EIydrogen %4,2 4,2 6,8 Oxyyen %10,7 10,7 17,1 Nitrogen %0,8 0,8 1,3 Sulphur %0,6 0,6 1,0 Ash %35,8 35,8 Water %0,4 0,4 Chlorine %0,6 0,6 1,0 _ At complete combustion without excess air the air requirement per kilogram fuel: 6,2 Kg3resp.

4,8 Nm Melting of the Ash: Softening point 1100C
(according to DIN
51730) Hemispheric point 1170C
Flowpoint 1300C

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of producing carbon enriched solids from solid waste, said method comprising the steps of:
introducing a raw material in a reaction chamber;
said raw material consisting at least partly of solid waste containing cellulose or cellulose-like polyhydrocarbon compounds;
moving said solid waste along a processing path through said reaction chamber;
exposing said solid waste in said reaction chamber to an inert heating gas flowing through said reaction chamber counter-currently to the movement of said solid waste;
heating, degasifying and flushing said solid waste so as to establish a pyrolytic carbonization reaction by means of said inert heating gas to produce processed solid waste and waste gases;
said pyrolytic carbonization reaction being exothermic on a substantial part of said processing path;
maintaining the maximum temperature of said solid waste under-going said pyrolytic carbonization reaction above about 240°C and below 310°C.

2. A method according to claim 1, characterised in maintaining the maximum temperature of said solid waste undergoing said pyrolytic carbonization reaction above about 240°C and below 300°C.

3. A method according to claim 2, characterised in maintaining the maximum temperature of said solid waste undergoing said pyrolytic carbonization reaction within the range of about 265°C to 290°C.

4. A method according to claim 1, characterised in maintaining aid exothermic pyrolytic carbonization reaction within said temperature limits by controlling the movement of said solid waste through said reaction chamber.

5. A method according to claim 4, characterised in that said step of controlling the movement of said solid waste is effected by regulating the rate of output of said processed solid waste drawn from an exit port of said reaction chamber.

6. A method according to claim l, 2 or 3, characterised in that said inert heating gas is produced at least partly by combustion of said waste gas.

7. A method according to claim 1, 2 or 3, characterised in that said heating gas is processed before being introduced in said reaction chamber so as to eliminate oxygen and oxydyzing compounds therefrom.

8. A method according to claim 1, characterised in that at least one noxious-substance neutralising reagent is added in order to effect the pyrolytic process.

9. A method according to claim 8, characterised in that the noxious-substance neutralising reagent is added to the waste to be burned.

10. A method according to claim 8 or 9, characterised in that the noxious-substance neutralising reagent is added in excess by approximately 50 to 100% with respect to the stoichiometric balance of the respective binding reaction.

11. A method according to claim 8 or 9, characterised in that calcium oxide or calcium hydroxide is used as the acid noxious-substance neutralising reagent.

14 2. A device for effecting the method according to claim 1, characterised by a temperature control with a pyrolytic treating station for the waste to be converted as the control system, having at least one measuring probe for recording the maximum treating temperature as the control value, and at least one control member acting on the heating of the pyrolytic treating station.

13. A device according to claim 12, characterised by a pyrolytic waste treatment station comprising heating or heating and flushing gas circulation, which is provided externally of this treating station with a combustion station fed with gas from the treating station and supplied with combustion air or oxygen as well as being connected in series with a controllable branch station for excess combustion gases.

14. A device according to claim 13, characterised by at least one working-heat exchanger device connected in series with the combustion gas branch station.

15. A device according to claim 14, characterised by at least one additional combustion gas inertisation device arranged in series with the combustion station.

16. A device according to claim 13, 14 or 15, characterised by at least one controllable cooling device arranged between the waste-gas combustion station and the heating or heating and flushing gas supply of the pyrolytic treating station.

17. A device according to claim 13, 14 or 15, characterised by at least one controllable cooling gas mixing device arranged before the heating or heating and flushing gas supplies of the pyrolytic treating station.

8. A device according to claim 12, characterised in that the control of the combustion gas branch station, the working-heat exchange device, the cooling device and/or cooling gas mixing device are coupled as the control member with the temperature control of the pyrolytic treating station.

19. A device according to claim 12, characterised by at least one pyrolytic treating station in the form of a directly heated shaft furnace.