JP2000001349A - How to treat municipal garbage incineration ash - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method for treating municipal garbage incineration ash for recovering useful materials from municipal garbage incineration ash. A municipal waste incineration ash is supplied to a cement kiln as a part of a cement raw material, and components volatilized at a temperature of 900 ° C. or more are bled and collected, and a heavy metal component, a potassium component, and bromine are sequentially recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel method for treating incinerated ash from municipal waste. Specifically, the present invention provides a processing method for safely recycling a large amount of municipal waste incineration ash.

[0002]

2. Description of the Related Art Municipal refuse incineration ash is characterized by a large amount of generation, a high chlorine content, a heavy metal content, a dioxin content, and a large change in components depending on the source. Is not yet developed. On the other hand, in recent years, landfills have become smaller, and dioxins and heavy metals have become more difficult to landfill due to concerns about elution into the environment. The development of technology for safely recycling is awaited. One of the candidates is the alternative use of raw materials in the cement industry.

[0003] Recent cement kilns are provided with a pre-heater for the purpose of recovering the heat of the kiln exhaust gas, and heat is exchanged with the input raw materials. Therefore, when municipal waste incineration ash as described above is used as a part of the cement raw material, halogens such as chlorine introduced into the sintering process (kiln) by the incineration ash easily react with alkali components and heavy metal components at a high temperature to volatilize. It becomes a metal halide or the like and usually starts to evaporate at temperatures up to 900 ° C. Further, the combustion gas flows at a considerable flow rate in the kiln, and the volatiles from the municipal waste incineration ash are discharged mixed with the kiln exhaust gas, but exchange heat with the raw material newly supplied by the preheater. When the temperature drops below the dew point,
It returns to the kiln again because it is absorbed by the raw material. Therefore, alkali metal halides and the like circulate between the kiln and the preheater and are concentrated. This alkali metal halide shows tackiness in the pre-heater, fuses to the inner wall, grows and agglomerates the raw material powder, which causes blockage of the pre-heater duct, etc., and hinders stable operation. There is also. Another problem in using municipal waste incineration ash containing a large amount of chlorine as a part of the cement raw material is that the chlorine concentration of the cement product is high. When cement containing a large amount of chlorine is used in a reinforced concrete structure, it causes corrosion of the reinforcing steel and causes concrete deterioration such as cracking and chipping. For this reason, the JIS standard also regulates that the chlorine content in cement is 200 ppm or less. Thus, chlorine has many adverse effects in cement production.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to effectively utilize municipal garbage incineration ash by recycling it as a resource, rather than simply discarding it for landfill. The present invention provides a series of systems that use so-called ash as part of a cement raw material and that recovers heavy metals, highly useful alkali metal compounds, such as potassium chloride or bromine, from incinerated ash from municipal waste.

Conventionally, in a cement kiln with a preheater, a phenomenon has been known in which volatile alkali compounds and halogen compounds introduced from cement raw materials and fuels circulate between the kiln and the preheater and are concentrated. I was However, it has also been known that when a certain concentration is reached, an equilibrium is reached with the amount taken out of cement clinker and exhaust gas.

[0006] In this case, if the amount of alkali component and halogen component brought into the cement kiln increases, the quality of the obtained clinker deteriorates. For this reason, kiln gas is extracted from the joint between the preheater and the kiln or the kiln butt,
A method has been proposed in which volatile components are condensed and then collected by a bag filter (Japanese Patent Application Laid-Open No. 9-227184). However, in these methods, the so-called ash is used as a part of the cement raw material. However, useful components such as heavy metals, potassium, and bromine contained in the incinerated ash of the municipal waste are not collected. It could not be said that the incineration ash could be completely recycled.

[0007]

Means for Solving the Problems The present inventors have intensively studied to solve the above-mentioned problems. As a result, chlorine,
Municipal waste incineration ash containing a large amount of bromine, alkali metals and heavy metals is used as a raw material substitute in the cement manufacturing process, and these components are concentrated in a kiln preheater for cement manufacturing, and this is extracted and cooled, and useful components are removed. The present invention has been completed, which aims at efficiently separating and recovering.

That is, according to the present invention, in a cement burning process in which municipal waste incineration ash is used as a part of a cement burning raw material, (a) gas in the kiln is extracted from a portion in the kiln where the gas temperature becomes 900 ° C. or more. (B) cooling the extracted gas to 300 ° C. or lower to separate the gas into condensate, and contacting the condensate with water to separate a soluble salt solution mainly composed of an alkali halide from a solid;
(C) adjusting the acidity of the solid suspension to near neutrality;
Producing a soluble calcium salt and separating and removing it, (d) dissolving the heavy metal salt by adding an acid to a suspension of the remaining solid matter, and recovering the solution;
(E) A method for treating municipal waste incineration ash comprising a step of precipitating and recovering heavy metal compounds by neutralizing the recovered solution.

The present invention also includes a step of concentrating the solution mainly composed of an alkali halide obtained in the step (b) to precipitate potassium chloride and recovering the same.

[0010] The present invention further includes recovering bromine from the mother liquor from which the potassium chloride has been recovered.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, municipal waste incineration ash used as a raw material substitute in a cement production process is not particularly limited as long as it is incineration ash of general waste. Stalker method,
There is no distinction between incineration systems such as fluidized bed systems, and no distinction between ash types such as hearth ash and fly ash.

In general, incinerated ash contains chlorine as high as 3 to 20%, and heavy metals as high as 0.1 to 2.0% for Zn and 0.05 to 1.5% for Pb. In the present invention, it is preferable that the incinerated municipal garbage ash is washed with water to remove soluble halogen substances such as sodium chloride and other deposits.

In the present invention, the useful component is concentrated while producing cement by using municipal incineration ash as a raw material. Further, there is also an advantage that organic substances such as dioxin adsorbed on the municipal waste incineration ash are substantially eliminated due to high heat in the cement kiln.

The cement sintering furnace used in the present invention is not particularly limited. A cement kiln with a pre-heater for producing ordinary Portland cement or the like can be used.

The bleeding step, which is the step (a) in the present invention, is performed from a zone where the gas temperature in the kiln is 900 ° C. or higher. As a result, the useful components contained in the municipal waste incineration ash are substantially in the form of gas or suspended as mist or fine dust in the combustion gas, and they are concentrated. It is. The means for bleeding is not particularly limited, but may have the same structure as conventionally used alkali bypass or chlorine bypass equipment.
Of course, when the suction port of the alkali bypass or the chlorine bypass is open to a zone of 900 ° C. or higher in the cement kiln, it can also be used.

In the present invention, in the step (b), the bleed gas is cooled to 300 ° C. or less to concentrate and solidify volatiles of useful components, and separate the solids from the combustion gas in the kiln and the solids extracted therefrom. Then, the solid matter is further brought into contact with water to separate into a soluble matter mainly composed of an alkali metal halide and a solid matter. These separation means are not particularly limited. For example, after the temperature of the extracted gas is once cooled to about 300 ° C., preferably to 300 ° C. or less by a heat exchanger, the suspended solids are collected by a bag filter or the like. This solid is supplied to a dissolution tank and separated into water-soluble and insoluble components. Although the type of the dissolving tank is not particularly limited, it is preferable to use stirring.

In this method, the solid content collected from the bleed gas is temporarily stored in a storage tank or the like, mixed uniformly, and then supplied to the dissolving tank to stabilize the composition of the solid content. It is preferable because it can be performed.

As another means, the bleed gas can be brought into direct contact with water to dissolve soluble components simultaneously with cooling of the gas.

The gas-liquid contact means in this case is not particularly limited, but gas-liquid contact devices such as a packed tower, a column tower, a spray tower, a scrubber, a bubble tower, a bubble stirring tank, an irrigation tower, a jet condenser, etc. Or a combination of two or more of such contact type coolers.

The water for dissolving the soluble components is desirably at a high temperature in order to accelerate the dissolution rate. Normal 3
0 to 100 ° C, preferably about 40 to 80 ° C. One means of obtaining these temperatures is to utilize the temperature of the bleed gas. That is, it can also be obtained by exchanging the extracted gas at 900 ° C. or higher with water for dissolution.

Further, the solid content in the bleed gas contains a large amount of calcium oxide, and when brought into contact with water, the solution shows a very high alkalinity. For this reason, when brought into contact with water, heavy metals, especially amphoteric metals such as lead, may be dissolved together with the alkali metal halide. Therefore, it is desirable to use as little water as possible. It is also preferable to adjust the pH as needed and keep it in the range of 5 to 14, especially 8 to 13.

In general, complete dissolution of soluble components such as alkali metals may take a certain amount of time. Therefore, in any of the above methods, stirring may be further performed in a tank-type dissolving tank as necessary. In some cases, it is preferable to dissolve the alkali metal salt sufficiently for several minutes to several hours.

The separation of the aqueous solution mainly containing an alkali metal halide and the insoluble residue mainly containing silica, alumina, lime and heavy metal compounds is performed by a decantation method such as filtration or a centrifuge.

Next, in the step (c), the insoluble residue separated in the step of bringing the solid matter into contact with water is neutralized with an acid such as hydrochloric acid and the like and neutralized (pH 5 to 10, preferably pH 6 to 10).
To 9) to produce a solution mainly composed of a soluble calcium salt such as calcium chloride, which is separated and removed. This step is a part of the step of removing the acid-soluble matter in the insoluble residue to increase the concentration of heavy metals. The remaining insoluble solid matter from which the calcium salt soluble near neutrality has been removed is further added to the suspension of the insoluble solid matter in the step (c) in the step (d) by adding an acid to the acidic state, preferably in the step (d). Is pH
3 or less, heavy metals are dissolved. Since the dissolved residue is an inorganic compound mainly composed of silicon dioxide and aluminum oxide, it can be used as a cement raw material if necessary after washing and dehydration. The solution is neutralized with an alkaline solution in step (e) to precipitate a heavy metal salt and recover as a heavy metal compound having a high concentration.

The precipitation of heavy metals in the step (e) may be performed by adding hydrogen sulfide or alkali sulfides to precipitate as heavy metal sulfides instead of neutralizing the solution with an alkali solution, or by using carbon dioxide gas or alkali metal carbonate. In addition, a method of precipitating it as a heavy metal carbonate may be used, but it is preferable to recover the heavy metal as a hydroxide from the viewpoint of reuse.

In the step (b), the aqueous solution mainly containing an alkali halide, especially potassium chloride and sodium chloride, is subjected to evaporation and removal of water using a multiple evaporator or the like to precipitate potassium chloride and recover it. I do.
Usually, the solution is concentrated to a saturated concentration of potassium chloride at a temperature of 80 ° C. or higher, and then cooled to precipitate and recover potassium chloride. To increase collection efficiency,
Cooling is preferably reduced to 10 ° C. or less. The cooling rate is slow, and potassium chloride crystals having high purity are recovered by sufficiently growing the crystals of the precipitated potassium chloride. Thus, the recovered potassium chloride is reused as a raw material such as fertilizer.

The residual solution in the step (e) is generally an aqueous solution mainly containing sodium chloride containing 3,000 mg / l or more of bromine. Therefore, bromine gas can be recovered with high efficiency by a known bromine production method such as a commonly used seawater direct method. The bromine gas can be recovered by electrolysis of the solution.

[0028]

According to the present invention, in the treatment of municipal garbage incineration ash, the useful components are concentrated in a cement sintering furnace, and this is subjected to bleeding, water washing, acid dissolving and other treatments.
It can systematically recover useful substances such as high-concentration heavy metal compounds, cement raw materials, high-concentration potassium chloride, and high-concentration bromine gas. Therefore, in the treatment of municipal garbage incineration ash, it is safe to solve the problems of processing, such as the large amount of generation, the high chlorine content, the heavy metals, the dioxins, and the components that greatly change depending on the source. Thus, it is possible to effectively recycle useful materials and to provide a process which does not affect the production process and quality of cement.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

Example 1 Municipal garbage incineration ash (an example of composition is shown in Table 1) was used as a cement raw material substitute by the treatment process shown in FIG. 1, and a chlorine bypass device attached to the cement kiln bottom was used. Concentrates chlorine, bromine, alkali metals and heavy metals and collects them as chlorine bypass dust along with some cement raw materials.

The incinerated ash generated in the municipal waste incineration plant (1) is stored in the receiving tank (2), and is uniformly mixed by an air mixing device. The incinerated ash is dissolved in a water washing facility (3) comprising a dissolving tank equipped with a stirrer and a centrifugal filter with 10 times the weight of the ash to dissolve soluble salts, and insolubles are filtered. Insoluble incineration ash is supplied to the cement firing furnace (4) at a rate of 20 kg per 1 t of cement. Concentrates chlorine, alkali metals and heavy metals at 1050 ° C and a bleed rate of about 2% using a chlorine bypass device consisting of a coarse-grained separation cyclone with a bleed port at the kiln bottom and a bag filter, and 150 ° C as chlorine bypass dust.
Recover with a bag filter at a temperature of. This chlorine bypass dust (the composition is shown in Table 1) is stored in the silo (6).

The useful substances are recovered from the chlorine bypass dust by the processing steps shown in FIG.

First, the collected chlorine bypass dust is extracted from the silo (6), and the same washing equipment (1) as in FIG.
In step 01), water (W) in an amount 5 times the weight of the chlorine bypass dust is added and dissolved at room temperature for 5 minutes to mainly dissolve soluble salts such as alkali halides. The dissolved residue is dehydrated, and the dehydrated cake is placed in a dissolving equipment (102) having the same structure as in FIG. 1 (3), and 10% hydrochloric acid (E) is neutralized (pH 5.5).
To 8.5), and mainly calcium hydroxide and calcium carbonate are dissolved out as soluble chlorides such as calcium chloride. Calcium chloride can be easily recovered from the filtrate by concentration. The dissolved residue is dehydrated, and the dehydrated cake is put into a dissolving equipment (103) having the same structure as in FIG. 1 (3), and hydrochloric acid (F) having a concentration of 3% is added thereto, and the heavy metal is mainly acidified (pH 3 or less). Are dissolved out as soluble heavy metal chlorides. The dissolved residue is mainly silica and clay mineral and can be used as a cement raw material (A). The filtrate is put into a sedimentation facility (104) having the same structure as that of FIG. 1 (3), and caustic soda (G) is added thereto and neutralized (pH 7-9.
In the state of 3), mainly heavy metals are converted to heavy metal hydroxides (B)
To be precipitated.

The filtrate coming out of the washing equipment (101) is put into a sedimentation equipment (112) having the same structure as that of FIG. 1 (3), and carbon dioxide gas (H) is blown from below (pH 7 to 9.3). Calcium and heavy metals are precipitated in the form of carbonate. The filtration residue is sent to a dissolution facility (102). The solution is sent to a multi-stage evaporator (113) to increase the concentration until crystals start to precipitate, and then cooled to 0 ° C. in a cooling bath (114) to precipitate potassium chloride crystals. After that, filtration equipment (115)
The potassium chloride crystals (C) are filtered with. After adjusting the pH to 3 by adding sulfuric acid (I) to the filtrate, the multi-stage reaction column (11
5) Spraying is carried out to oppose the chlorine gas (J) to obtain a crude bromine gas (D).

Table 1 shows the components of the recovered material obtained in each step. According to this embodiment, it can be seen that the municipal waste incineration ash can be effectively recycled.

[0037]

[Table 1]

[Brief description of the drawings]

Fig. 1 Use of municipal waste incineration ash in the cement manufacturing process and an example of chlorine bypass dust extraction

[Explanation of symbols]

 1 Incineration plant 2 Municipal garbage incineration ash storage silo 3 Incineration ash washing equipment 4 Cement firing furnace 5 Chlorine bypass equipment 6 Chlorine bypass dust storage silo

FIG. 2 is a block diagram of a useful component recovery process from chlorine bypass dust.

[Explanation of symbols]

 101 chlorine bypass dust washing equipment 102 acid dissolution equipment 1 103 acid dissolution equipment 2 104 sedimentation equipment 1 112 sedimentation equipment 2 113 evaporator 114 cooling equipment 115 reaction tower A cement raw material B heavy metal hydroxide C potassium chloride crystal D crude bromine gas E 10% hydrochloric acid F 3% hydrochloric acid G 5% caustic soda H 20% carbon dioxide I 5% sulfuric acid J 100% chlorine gas W water

Claims (3)

[Claims] 1. A cement burning process using municipal waste incinerated ash as a part of a cement burning raw material, wherein (a)
A step of extracting gas in the kiln from a portion where the gas temperature in the kiln becomes 900 ° C. or more; (b) extracting the extracted gas at 300 ° C.
A step of cooling and separating into a gas and a condensate, and contacting the condensate with water to separate into a soluble salt solution mainly composed of an alkali halide and a solid; (c) a suspension of the solid Adjusting the acidity to near neutrality to form a soluble calcium salt and separating and removing it; (d) adding the acid to the suspension of the remaining solids to dissolve the heavy metal salt and to dissolve the solution. A method for treating municipal waste incineration ash, comprising: a step of collecting; and (e) a step of precipitating and collecting heavy metal compounds by neutralizing the recovered solution. 2. A method for treating municipal waste incineration ash according to claim 1, wherein the solution mainly consisting of an alkali halide obtained in the step (b) is concentrated, and potassium chloride is precipitated and recovered. . 3. The method according to claim 2, wherein bromine gas is recovered from a residual solution from which potassium chloride has been recovered.