JP2011127861A - Waste treatment device and waste treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waste treatment device and a waste treatment method, which miniaturize a constitution of the device, in the waste treatment device which reduces a landfill disposal amount of soot, and melts the soot not including a reaction product of alkali chemical. <P>SOLUTION: This waste treatment device 1 includes a gasification melting furnace 2 for thermally decomposing the waste and melting its residue, an alkali chemical supply device 3 supplying the alkali chemical into an exhaust gas from the gasification melting furnace 2, between the gasification melting furnace 2 and a dust collecting device 4 to produce a reaction product of an acid material included in the exhaust gas and the alkali chemical by the supply of alkali chemical, a classifying device 5 for classifying the soot included in the reaction product collected by the dust collecting device 4 into coarse soot and fine soot and separating the reaction product to a fine dust side, and a coarse dust returning means 6 for returning the coarse dust to the gasification melting furnace 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a waste treatment apparatus and a waste treatment method that are most suitable for treating waste such as municipal waste, waste solidified fuel, and industrial waste. The present invention relates to a waste treatment apparatus and a waste treatment method capable of reducing the amount of soot discharged to landfill from a gasification melting furnace or an incinerator equipped with an ash melting furnace.

  In recent years, it has become difficult to construct new landfill sites due to environmental issues, and wastes such as municipal waste and industrial waste are treated to melt and slag the waste to reduce the amount of landfill disposal. Many have been built. There are the following two types of facilities for melting such waste.

1) Form in which waste is pyrolyzed in a gasification melting furnace and the residue is melted 2) Form in which waste is incinerated in an incinerator and then incineration residue and dust are melted in an ash melting furnace However, both forms are landfilled Disposal is not lost, but the dust collected in the exhaust gas from the gasification melting furnace and incinerator is landfilled. In order to further reduce the amount of landfill disposal, dust in exhaust gas is collected and a part thereof is returned to a gasification melting furnace or ash melting furnace to be melted and slagted.

  On the other hand, exhaust gas discharged from gasification melting furnaces and incinerators contains acidic substances such as hydrogen chloride and sulfur oxides. In order to remove these, alkaline chemicals (hereinafter referred to as exhaust gas) are used in front of the dust collector. (Called "alkaline chemicals"). As the alkali chemicals, powder chemicals such as slaked lime and sodium bicarbonate, and liquid chemicals such as aqueous caustic soda and magnesium hydroxide are used, but slaked lime powder is often used because of its low price. Alkaline chemicals react with acidic substances in the exhaust gas to produce reaction products, which are collected by a dust collector together with ash (fly ash) scattered from the furnace. Therefore, the dust collected by the dust collector of the gasification melting furnace or incinerator contains a reaction product of an alkaline agent in addition to fly ash.

  When a part of the dust in the exhaust gas is supplied to a gasification melting furnace or ash melting furnace and melted, if the reaction product of alkaline chemicals is contained in the dust, the reaction product is decomposed when it is melted. Acidic substances are generated and returned to the exhaust gas. In order to avoid this, a measure has been taken in which only the dust containing no reaction product of the alkaline chemical is supplied to the gasification melting furnace or ash melting furnace for melting treatment.

  As a waste treatment apparatus that can reduce the amount of soot disposal to landfill and that does not contain a reaction product of an alkaline chemical, those described in Patent Document 1 and Patent Document 2 are known.

  FIG. 11 is a diagram showing an outline of the configuration of the waste disposal apparatus described in Patent Document 1. In the waste treatment apparatus 100 of Patent Document 1, as a device for treating the exhaust gas discharged from the gasification melting furnace 101, a centrifugal dust collector (cyclone) 102 that collects most of the dust contained in the exhaust gas, There are provided an alkaline chemical supply device 103 for blowing slaked lime as an alkaline chemical into the exhaust gas from the centrifugal dust collector 102, and a filtration dust collector (bag filter) 104 for collecting the remaining soot dust containing the reaction product of slaked lime. Yes.

  Most of the dust collected by the centrifugal dust collector 102 on the upstream side is returned to the gasification melting furnace 101 by the dust return means 105 and subjected to a melting process to become slag. Further, the remaining dust collected by the downstream filter dust collector 104 is subjected to a landfill disposal after being subjected to stabilization processing by the stabilization processing device 106 to prevent elution of heavy metals. In patent document 1, since most of the dust is melt-processed into slag, the amount of landfill disposal can be reduced accordingly.

  FIG. 12 is a diagram showing an outline of the configuration of the waste disposal apparatus described in Patent Document 2. In the waste treatment apparatus 200 of Patent Document 2, as a device for treating the exhaust gas discharged from the incinerator 201, the first bag filter 202 that collects dust contained in the exhaust gas, and the first bag filter 202 are passed. There are provided an alkaline chemical supply device 203 for blowing slaked lime as an alkaline chemical into the exhaust gas, and a second bug filter 204 for collecting dust (fly ash) mainly containing a reaction product of slaked lime.

  The dust collected by the upstream first bag filter 202 is melted in the ash melting furnace 205 together with the incinerated ash generated in the incinerator 201 to be slag. Further, the fly ash mainly containing the reaction product of slaked lime collected by the second bag filter 204 on the downstream side is subjected to a stabilization process for preventing elution of heavy metals by the stabilization processor 206. And then landfilled. In Patent Document 2, since the dust collected by the first bag filter 202 is melted to form slag, the amount of landfill disposal can be reduced accordingly.

JP 10-232007 7-103980

  As described above, in Patent Document 1, a centrifugal dust collector and a filtration dust collector are provided, and in Patent Document 2, a first bag filter and a second bag filter are provided. That is, in Patent Document 1 and Patent Document 2, in order to return soot that does not contain a reaction product of an alkaline agent to a gasification melting furnace or an ash melting furnace, the soot in the exhaust gas is collected by a dust collector provided in two stages. Yes. However, providing the dust collector in two stages in this way has a problem that when a waste disposal facility is newly established, a large installation area is required for the apparatus, and the construction cost increases. In addition, when remodeling an existing waste disposal facility, there is a problem that it is difficult to install on the layout of the equipment.

  In view of such a situation, the present invention is a waste treatment apparatus that can reduce the amount of dust disposed of in landfills and melts soot that does not contain a reaction product of an alkaline agent, and has a compact configuration. It is an object to provide a treatment apparatus and a waste treatment method.

<First invention>
A waste treatment apparatus according to the first invention includes a gasification melting furnace that thermally decomposes waste and melts residues, and a dust collector that collects dust contained in exhaust gas discharged from the gasification melting furnace, An alkaline agent supply device for generating a reaction product of an acidic substance and an alkaline agent contained in the exhaust gas by blowing an alkaline agent into the exhaust gas from the gasification melting furnace between the gasification melting furnace and the dust collector; and A classifier that classifies the dust containing the reaction product collected by the dust collector into coarse dust and fine dust and separates the reaction product into the fine dust side, and the coarse dust into the gasification melting furnace. Coarse grain return means for returning is provided.

  According to the first invention, the coarse dust classified by the classification device is returned to the gasification melting furnace by the coarse particle feedback means and subjected to the melting treatment, so that only the fine dust classified by the classification device is disposed in landfill. The Rukoto. Therefore, compared with the case where coarse dust is not returned to the gasification melting furnace, the amount of soot landfill disposal can be reduced. In the first invention, it is only necessary to provide one dust collecting device and classifying device, and it is not necessary to provide two dust collecting devices as in the prior art, so the waste processing device is made compact accordingly. be able to.

  Moreover, since the alkaline chemical supply device is provided, harmful acidic substances contained in the exhaust gas can be neutralized and removed by blowing the alkaline chemical into the exhaust gas. Furthermore, since the reaction product of the acidic substance and the alkaline chemical is classified to the fine dust side by the classifier, only the soot that does not contain the alkaline chemical reaction product classified to the coarse particle side is returned to the gasification melting furnace. Therefore, it is possible to prevent the reaction product from being decomposed in the gasification melting furnace and generating an acidic substance and returning to the exhaust gas.

<Second invention>
A waste treatment apparatus according to the second invention collects dust contained in an incinerator for incinerating waste, an ash melting furnace for melting incineration residue of the incinerator, and exhaust gas discharged from the incinerator. An alkaline chemical supply device that generates a reaction product of an acidic substance and an alkaline chemical contained in the exhaust gas by blowing an alkaline chemical into the exhaust gas from the incinerator between the dust collector and the incinerator and the dust collector; and A classifier that classifies the dust containing the reaction product collected by the dust collector into coarse and fine dust and separates the reaction product to the fine dust side, and supplies the coarse dust to the ash melting furnace. And a coarse particle supply means.

  According to the second invention, the coarse particles classified by the classification device are supplied to the ash melting furnace by the coarse particle supply means and subjected to the melting treatment, so that only the fine particles classified by the classification device are landfilled. The Rukoto. Therefore, compared with the case where coarse dust is not supplied to the ash melting furnace, the amount of soot landfill disposal can be reduced. In the second invention, it is only necessary to provide one dust collecting device and classifying device, and it is not necessary to provide two dust collecting devices as in the prior art, so the waste processing device is made compact accordingly. be able to.

  Moreover, since the alkaline chemical supply device is provided, harmful acidic substances contained in the exhaust gas can be neutralized and removed by blowing the alkaline chemical into the exhaust gas. Furthermore, since the reaction product of the acidic substance and the alkaline chemical is classified to the fine dust side by the classifier, only the soot that does not contain the alkaline chemical reaction product classified to the coarse particle side is returned to the ash melting furnace. Since the melting treatment can be performed and the reaction product is not supplied to the ash melting furnace, the reaction product can be prevented from being decomposed in the ash melting furnace to generate an acidic substance and return to the exhaust gas.

<Third invention>
A waste treatment method according to a third invention is a waste treatment method in which waste is thermally decomposed in a gasification melting furnace and the residue is melted, and an alkali chemical is blown into the exhaust gas discharged from the gasification melting furnace. An alkaline chemical supply step for generating a reaction product of an acidic substance and an alkaline chemical contained in the exhaust gas; a dust collection step for collecting the soot and dust contained in the exhaust gas after the alkaline chemical supply step; Classifying the dust containing the reaction product collected in the dust collecting step into coarse dust and fine dust and separating the reaction product into the fine dust side; and the coarse dust into the gasification melting furnace The method is characterized by comprising a coarse particle return step for returning to the above and a stabilization treatment step for stabilizing fine particles.

  According to the third invention, since the coarse dust classified in the classification step is returned to the gasification melting furnace in the coarse particle return step and subjected to the melting treatment, only the fine dust classified in the classification step is disposed to the landfill. Will be. Therefore, compared with the case where coarse dust is not returned to the gasification melting furnace, the amount of soot landfill disposal can be reduced. Further, in the third invention, it is sufficient to provide one dust collecting device and classifying device, and it is not necessary to provide two dust collecting devices as in the prior art. The waste disposal apparatus can be made compact. Further, by blowing an alkaline chemical into the exhaust gas discharged from the gasification melting furnace, harmful acidic substances contained in the exhaust gas can be neutralized and removed. Furthermore, since the reaction product of the acidic substance and the alkali chemicals is classified to the fine dust side by the classification process, only the soot that does not contain the reaction product of the alkaline chemicals classified to the coarse particle side is returned to the gasification melting furnace. Therefore, it is possible to prevent the reaction product from being decomposed in the gasification melting furnace and generating an acidic substance and returning to the exhaust gas.

<Fourth Invention>
A waste treatment method according to a fourth invention is a waste treatment method in which waste is incinerated in an incinerator and the incineration residue is melted in an ash melting furnace. An alkaline chemical supply step for generating a reaction product of the acidic substance and the alkaline chemical contained in the dust, a dust collection step for collecting the soot and dust contained in the exhaust gas after the alkaline chemical supply step, and the above Classifying the dust containing the reaction product collected in the dust collection process into coarse dust and fine dust and separating the reaction product to the fine dust side, and supplying the coarse dust to the ash melting furnace A coarse particle supplying process and a stabilizing process for stabilizing fine particles.

  According to the fourth aspect of the invention, since the coarse dust classified in the classification process is supplied to the ash melting furnace in the coarse particle supply process and subjected to the melting treatment, only the fine dust classified in the classification process is landfilled. Will be. Therefore, compared with the case where coarse dust is not supplied to the ash melting furnace, the amount of soot landfill disposal can be reduced. Further, in the fourth invention, it is only necessary to provide one dust collecting device and classifying device, and it is not necessary to provide two dust collecting devices as in the prior art, so that the waste disposal method according to the fourth invention is used. The waste disposal apparatus can be made compact. Further, by blowing an alkaline chemical into the exhaust gas discharged from the incinerator, harmful acidic substances contained in the exhaust gas can be neutralized and removed. Furthermore, since the reaction product of the acidic substance and the alkaline chemical is classified to the fine dust side by the classification process, only the soot that does not contain the reaction product of the alkaline chemical classified to the coarse particle side is returned to the ash melting furnace. Since the melting treatment can be performed and the reaction product is not supplied to the ash melting furnace, the reaction product can be prevented from being decomposed in the ash melting furnace to generate an acidic substance and return to the exhaust gas.

  In the third and fourth inventions, the alkaline agent blown in the alkaline agent supply step is a powdered alkaline agent, and in the classification step, the powdered alkaline agent is based on a classification point set in advance based on the particle size distribution of the powdered alkaline agent. The reaction product is preferably classified to the fine dust side.

  The particle size of the reaction product of the powdered alkaline agent greatly depends on the particle size of the powdered alkaline agent. Therefore, by setting a classification point based on the particle size distribution of the powdered alkaline agent such that the reaction product of the powdered alkaline agent is classified to the fine dust side in the classification step, It can be prevented from being classified to the dust side. As a result, since the reaction product is not supplied to the gasification melting furnace or the ash melting furnace, it can be avoided that the reaction product is melted and decomposed to generate an acidic substance. The classification point is preferably set within a range of 10 to 1200 μm.

  According to the present invention, of the dust contained in the exhaust gas, coarse dust is supplied to the gasification melting furnace or ash melting furnace and subjected to melting treatment to become slag, and only the fine dust is disposed in landfill. The amount of landfill disposal can be greatly reduced. Further, in the present invention, since only one dust collecting device and classification device may be provided, it is possible to make the waste treatment device compact compared to the case where two dust collecting devices are provided as in the prior art. it can. As a result, when a waste disposal facility is newly established, the installation area of the apparatus can be reduced, and an increase in construction costs can be suppressed. In addition, when the existing waste treatment facility is remodeled, installation becomes easy due to the layout of the equipment.

  Further, according to the present invention, when classifying the dust mixed with the reaction product obtained by reacting the acidic substance and the alkali chemicals in the exhaust gas, the reaction product is classified into the fine dust side by classifying the reaction product. Supply to a gasification melting furnace or ash melting furnace is avoided. As a result, it can be avoided that the reaction product is decomposed in the gasification melting furnace or the ash melting furnace and the acidic substance is generated again.

It is a figure which shows the waste processing apparatus which concerns on 1st embodiment. It is a figure which shows the waste processing apparatus which concerns on 2nd embodiment. It is a figure which shows the particle size distribution of slaked lime. It is a figure which shows the relationship between a classification point and Ca content rate in coarse-grained dust. It is a figure which shows the waste disposal apparatus in the past. It is a figure which shows the relationship between a classification point, a coarse-grained dust ratio, and the chlorine content rate in coarse-grained dust. It is a figure which shows the relationship between a classification point and the ratio of coarse-particle dust x chlorine content in coarse-grain dust. It is a figure which shows the relationship between another classification point and Ca content rate in coarse-grained dust. It is a figure which shows the relationship between a classification point and the chlorine content rate in mixed ash. It is a figure which shows the particle size distribution of the soot collected by the dust collector in an Example. It is a figure which shows the other waste disposal apparatus in the past. It is a figure which shows the other waste disposal apparatus in the past.

  Hereinafter, embodiments of a waste treatment apparatus according to the present invention will be described with reference to the accompanying drawings.

<First embodiment>
FIG. 1 is a diagram showing a waste disposal apparatus according to this embodiment. The waste treatment apparatus 1 according to the present embodiment includes a gasification melting furnace 2 that thermally decomposes waste and melts the residue, and an alkali chemical supply unit that blows an alkali chemical into the exhaust gas from the gasification melting furnace 2. The alkaline chemical supply device 3, the dust collector 4 that collects the dust and the reaction product of the alkaline chemical contained in the exhaust gas into which the alkaline chemical is blown, the soot collected by the dust collector 4, and the above A classifier 5 for classifying the reaction product into coarse dust and fine dust, a coarse dust return path 6 as coarse dust return means for returning the coarse dust to the gasification and melting furnace 2, and the fine dust And a stabilization processing device 7 for performing the stabilization processing described later.

  The gasification melting furnace 2 thermally decomposes the input waste to discharge exhaust gas. In addition to soot dust, the exhaust gas contains harmful acidic substances such as hydrogen chloride and sulfur oxides. In addition, the gasification melting furnace 2 melts the residue generated by the thermal decomposition of the waste and the coarse dust classified by the classifier 5, and discharges it as slag to the outside.

  The alkaline chemical supply device 3 blows the alkaline chemical into the exhaust gas discharged from the gasification melting furnace 2 between the gasification melting furnace 2 and the dust collector 4. In the present embodiment, the alkaline agent is, for example, a powdered alkaline agent such as slaked lime or baking soda. When the alkaline chemical is blown into the exhaust gas, the acidic substance contained in the exhaust gas is neutralized and removed. Hereinafter, the reaction product of the alkaline agent and the acidic substance is referred to as “alkaline agent reaction product”.

  The dust collector 4 collects soot contained in the exhaust gas into which the alkaline chemical is blown. Alkaline chemical reaction products are mixed in the dust, and the reaction products are also collected by the dust collector 4. Examples of the dust collector 4 include a filtration dust collector. The exhaust gas that has passed through the dust collector 4 is discharged from the chimney to the outside.

  The classifier 5 classifies the dust collected by the dust collector 4 into coarse dust and fine dust based on a preset classification point. Specifically, the classification point is set in advance based on the particle size distribution of the alkali chemicals as will be described later, and the classification device 5 sets the dust above the classification point as coarse dust, and removes the dust below the classification point. Classify as fine dust. Examples of the classification device 5 include a vibration sieve and an airflow classifier, and various methods can be employed. In the present embodiment, the classification point is set so that the alkaline chemical reaction product is classified so as to be included on the fine dust side.

  The coarse particle return path 6 connects the classifier 5 and the gasification melting furnace 2, and conveys or conveys coarse particle dust by a conveyor, air transportation, etc., and the coarse particle dust enters the gasification melting furnace 2. Supply. The soot dust classified as coarse dust by the classifier 5 is returned to the gasification melting furnace 2 through the coarse dust return path 6. It is desirable to supply the coarse dust to the gasification melting furnace by mixing and blowing it with combustion air in order to suppress scattering of the coarse dust. The coarse dust is mainly fly ash generated by thermal decomposition in the gasification melting furnace 2, is returned to the gasification melting furnace 2, is melted, and is discharged to the outside as slag.

  The stabilization processing device 7 is a stabilization processing for preventing elution of heavy metals by adding, for example, a chelating agent to the soot dust or alkaline chemical reaction product classified as fine dust in the classification device 5 and kneading. Apply. Then, the fine dust that has been subjected to the stabilization treatment is disposed of in landfill.

  In the present embodiment, soot dust contained in the exhaust gas is classified into coarse dust and fine dust by the classifier 5, and the coarse dust is returned to the gasification melting furnace 2 for melting treatment, and the fine dust is disposed in landfill. As a result, the amount of landfill disposal can be reduced.

  Moreover, in this embodiment, since the dust in the exhaust gas is collected by a single dust collecting device 4, the configuration of the device is compact compared to the case where two dust collecting devices are installed in series as in the past. Therefore, the installation area can be reduced, and the same effect as the conventional one can be obtained at a much lower apparatus cost. Moreover, in this embodiment, it is only necessary to install a single dust collecting device 4 and classification device 5, the configuration of the device is compact, and the degree of freedom of installation location is high. Installation and modification are also easy.

  Moreover, according to this embodiment, when classifying the dust mixed with the alkaline chemical reaction product, the reaction product is returned to the gasification melting furnace 2 by classifying the reaction product to the fine dust side. Nothing will happen. As a result, it can be avoided that the reaction product is decomposed and an acidic substance is generated again.

<Second embodiment>
In this embodiment, the waste is incinerated in an incinerator, and the incineration residue and coarse dust are melted in an ash melting furnace, so that the thermal decomposition of the waste and the melting of the residue and coarse dust are in the gasification melting furnace. This is different from the first embodiment performed in the above. In this embodiment, it demonstrates centering on a different point from 1st embodiment, attaches | subjects the same code | symbol to the part same as 1st embodiment, and abbreviate | omits description.

  FIG. 2 is a diagram illustrating the waste disposal apparatus according to the present embodiment. As shown in FIG. 2, in the waste treatment apparatus 1 ′ according to the present embodiment, an incinerator 8 and ash melting are used instead of the gasification melting furnace 2 of the waste treatment apparatus 1 according to the first embodiment. A furnace 9 is provided. The incinerator 8 incinerates the input waste and discharges exhaust gas. In addition to soot dust, the exhaust gas contains acidic substances such as hydrogen chloride and sulfur oxides. The incinerator 8 discharges incineration residues generated by incineration of waste. The incineration residue and coarse dust classified by the classification device 5 are put into the ash melting furnace 9 by a screw conveyor or a pusher (not shown), melted, and discharged as slag to the outside.

  In the present embodiment, soot dust classified as coarse dust by the classifier 5 is supplied to the ash melting furnace 9 through the coarse dust supply passage 10 as coarse dust supply means, and is melted together with the incineration residue to be slag. It becomes. And like 1st embodiment, since dust was classified with the classification apparatus 5 and the fine dust containing an alkaline chemical | medical agent reaction product was landfilled, landfill disposal amount can be reduced. Also in the present embodiment, as in the first embodiment, the configuration of the apparatus is compact and the installation area can be reduced, and the alkaline chemical reaction product is not decomposed and the acidic substance is not generated again. Needless to say.

<Setting classification points>
Hereinafter, setting of classification points of the classification device 5 in the first embodiment and the second embodiment will be described. Since the particle size of the alkaline chemical reaction product is often the same as the particle size of the powdered alkaline agent, if the maximum particle size of the powdered alkaline chemical is set as the classification point, the alkaline chemical reaction product is classified to the fine dust side. Will be.

  Also, when slaked lime powder is used as the alkaline agent, calcium chloride, which is a reaction product of the slaked lime powder and hydrogen chloride in the exhaust gas, is hygroscopic, so that the reaction product particles aggregate to produce large particles. There is. Considering this, if the classification point is set to be twice or more the maximum particle size of the slaked lime powder, the reaction product of the slaked lime powder can be reliably classified to the fine dust side.

  Therefore, the particle size distribution of the powdered alkaline agent actually blown by the alkaline agent supply apparatus 3 is examined in advance, and the alkali agent reaction is generated by setting the maximum particle size or more or twice the maximum particle size as the classification point. Objects can be classified to the fine dust side. The classifying point is set by setting an opening of the sieve when the classifying device 5 is a vibration sieve, and when the classifying device 5 is an airflow classifier, the rotational speed of the airflow classifier. This can be done by setting operating conditions such as the amount of air and the amount of air.

  The case where slaked lime powder is used as the powder alkaline agent will be described in more detail. The particle size distribution of slaked lime powder varies depending on the slaked lime manufacturing company. FIG. 3 is a diagram showing the particle size distribution of slaked lime powders of Company A and Company B as examples of slaked lime manufacturing companies. The slaked lime powder made by Company A is fine and the maximum particle size is 20 μm. The maximum particle size of the slaked lime powder manufactured by B company is 100 μm. Japanese Industrial Standard JIS R 9001 specifies that the maximum particle size of slaked lime powder is 600 μm. Considering these, the maximum particle size of the slaked lime powder is in the range of 20 to 600 μm.

  Considering that the reaction product particles of slaked lime powder can aggregate to form large particles as described above, the maximum particle size of slaked lime powder is in the range of 20 to 600 μm. The classification point for classification to the fine dust side is preferably set within a range of 20 to 1200 μm, which is twice the maximum particle size of the slaked lime powder. Furthermore, in order to reduce the amount of soot classified to the fine particle side and reduce the amount of landfill disposal, the classification point is set within a range of 10 to 1200 μm in consideration of making the classification point as small as possible. It is preferable. Hereinafter, the setting range of the classification points will be described in more detail.

<Upper limit of classification point setting range>
First, the upper limit of the classification point setting range will be described in detail. The dust collected by the dust collector of the incinerator facility using the slaked lime powder manufactured by Company A having a maximum particle size of 20 μm shown in FIG. 3 was analyzed. The classification device was changed to a sieve using a vibrating sieve, and the dust was classified at classification points of 20 μm, 30 μm, 45 μm, 65 μm, and 90 μm, and the calcium content in coarse dust was measured. FIG. 4 shows the relationship between the classification point and the calcium content in the coarse dust. Since slaked lime is calcium hydroxide and the reaction product is a calcium compound such as calcium chloride or calcium sulfite, the amount of calcium content in the coarse dust can be seen. Know the degree of contamination. When the classification point is less than 40 μm, the calcium content of coarse dust is large, indicating that slaked lime and its reaction product are contained on the coarse dust side. When the classification point was 40 μm or more, the calcium content of coarse dust was almost constant, 12%. This indicates that calcium derived from calcium silicate contained in the ash content of coarse dust is contained, not calcium derived from slaked lime.

  As shown in FIG. 4, if classification is performed at a classification point of 40 μm, the calcium content of the coarse dust can be reduced, and the coarse dust side does not contain slaked lime and its reaction product, so that the fine dust side Can be separated to include these. If the maximum particle size of the slaked lime powder manufactured by Company A used in the study is 20 μm and classified by 40 μm, which is twice the maximum particle size of the slaked lime powder, it can be separated so as not to contain the reaction product on the coarse dust side. . That is, by setting the classification point for classifying the dust collected by the dust collector to be twice the maximum particle size of the slaked lime powder, the coarse particle side does not contain slaked lime and its reaction product. It can be separated to include these on the fine particle side. In addition, if the classification point is set to be larger than twice the maximum particle size of the slaked lime powder, it can be separated so as not to contain slaked lime and its reaction product on the coarse dust side, but the amount of fine dust increases and landfill Since the amount of disposal increases, it is not preferable. That is, it is preferable that the upper limit of the range for setting the classification point is a size that is twice the maximum particle size of the slaked lime powder. In Japanese Industrial Standard JIS R 9001, the maximum particle size of slaked lime powder is defined as 600 μm, so the upper limit of the range for setting the classification point is preferably 1200 μm.

<Lower limit of classification point setting range>
If the classification point for classifying the dust collected by the dust collector is set to more than twice the maximum particle size of the alkaline chemical powder (for example, slaked lime powder), the reaction product of the alkaline chemical is reliably classified to the fine dust side. can do. On the other hand, if the classification point is set to a large size, a lot of soot and dust such as fly ash with a fine particle size other than the reaction product is classified to the fine particle side, and the proportion of fine particle increases and the amount of landfill disposal increases. Become. Since the slaked lime produced by Company B shown in FIG. 3 has a maximum particle size of about 100 μm, the reaction product is reliably classified into the fine dust side and returned to the coarse particle dust returned to the gasification melting furnace or ash melting furnace. In order to ensure that it is not included, the classification point is classified at 200 μm or more, but this means that a lot of soot such as fly ash is classified on the fine particle side, and the amount of landfill disposal increases.
Therefore, the allowable range of the ratio of the reaction product contained in the coarse dust returned to the gasification melting furnace is clarified, and the coarse dust mixed with the reaction product within the allowable range is returned to the gasification melting furnace. If the classification point is reduced, the amount of fine dust is reduced, and the landfill disposal amount can be reduced.

  A study for examining the allowable range of the proportion of the reaction product contained in the coarse dust returned to the gasification melting furnace was performed using the conventional waste treatment apparatus shown in FIG. The conventional waste treatment apparatus shown in FIG. 5 supplies alkali chemicals to the exhaust gas discharged from the gasification melting furnace 101, collects dust containing reaction products of the alkaline chemicals by the filter dust collector 104, and collects them. A part of the soot dust is returned to the gasification melting furnace 101 and melted, and the remaining soot dust is stabilized and disposed of in landfill. Since the collected dust contains a reaction product of an alkaline agent, if the amount of returned dust returned to the gasification melting furnace 101 is large, the amount of acidic substances generated by decomposition of the reaction product increases. The concentration of acidic substances in the exhaust gas will increase.

  The slaked lime manufactured by Company B shown in FIG. 3 was used as the alkaline agent. By changing the return ratio of the dust returned to the gasification melting furnace 101 (feedback dust weight / total dust weight), the concentration of hydrogen chloride in the exhaust gas discharged from the gasification melting furnace 101 is measured, and the concentration of hydrogen chloride in the exhaust gas is measured. As a result of investigating an allowable return ratio within a range not increasing the amount of gas, it was found that the return ratio up to 20 wt% can be returned to the gasification melting furnace 101. If the feedback ratio is greater than 20% by weight, the concentration of hydrogen chloride in the exhaust gas increases, which is not preferable.

  In addition, since the chlorine concentration in the dust at this time was 8% by weight, the amount of chlorine contained in the dust that can be returned to the gasification melting furnace is the total dust weight x allowable return ratio 0.2 x in dust The chlorine concentration can be expressed as 0.08, that is, 0.016 × total dust weight.

  When the dust collected by the filter dust collector 104 is classified by a classifier and the coarse dust is returned to the gasification melting furnace, the amount of chlorine contained in the coarse dust is 0.016 × total dust from the above relationship. If it is less than the weight, the concentration of hydrogen chloride in the exhaust gas does not increase and there is no problem. That is, when the coarse dust is returned to the gasification melting furnace, the allowable range of the amount of chlorine contained in the coarse dust is 0.016 × the total dust weight or less.

  Further, the amount of chlorine contained in the coarse dust is determined by the total dust weight × the ratio of the classified coarse dust × the chlorine concentration in the coarse dust. The dust was classified by changing several classification points, and the ratio of the classified coarse dust and the chlorine concentration in the coarse dust were measured. FIG. 6 shows the relationship between the classification point, the ratio of coarse particles, and the chlorine concentration in the coarse particles. ○ is the proportion of coarse dust, and Δ is the chlorine concentration in the coarse dust.

  FIG. 7 shows the relationship between the ratio of the coarse dust and the ratio of the coarse dust determined from the measurement result of the chlorine concentration in the coarse dust × the chlorine concentration in the coarse dust and the classification point. Since the allowable range of the amount of chlorine contained in coarse dust is less than the value of 0.016 x total dust weight, as shown by the dotted line in Fig. 7, the coarse particles classified with a classification point of 10 µm or more are gasified and melted Can be returned to the furnace. That is, in the waste treatment apparatus provided with the gasification melting furnace, the lower limit of the setting range of the classification point is 10 μm. When the classification point is 10 μm, the proportion of coarse particles is 60% by weight as shown in FIG. 6, the fine particles to be disposed of in landfill are 40% by weight, and the dust is returned to the gasification and melting furnace without classification. Compared with landfill disposal of 80% by weight of soot dust, the amount of landfill disposal can be greatly reduced.

  Further, the allowable range of the amount of chlorine contained in the coarse dust supplied to the ash melting furnace in the waste treatment apparatus provided with the ash melting furnace shown in FIG. 2 was examined, and the lower limit of the setting range of the classification point was examined. A mixture of the incineration residue from the incinerator and coarse dust classified from the dust collected by the dust collector is called mixed ash, and the mixed ash is melted in the ash melting furnace. At this time, if the chlorine concentration in the mixed ash is large, a molten salt layer is formed in the furnace, and the molten salt penetrates into the lining refractory, resulting in increased wear and a decrease in the life of the refractory.

  The incineration residue and dust generation weight ratio of this incinerator is 65:35, the chlorine concentration in the incineration residue is 0.6% by weight, and the chlorine concentration in the soot is 15% by weight. When the incineration residue and the total amount of dust are mixed, the chlorine concentration in the mixed ash is (0.6 × 65 + 15 × 35) /100=5.6% by weight. Such chlorine concentration in the large mixed ash causes a problem because a molten salt layer is formed. It has been confirmed that when the chlorine concentration in the mixed ash is about 3.5% by weight or less, formation of a molten salt layer is suppressed and no problem occurs. Therefore, it is necessary to reduce the chlorine concentration in the mixed ash, and it is required to reduce the amount of chlorine contained in the coarse dust to be classified, and studies have been made to clarify the relationship with the classification point.

  Using the slaked lime produced by Company A shown in Fig. 3, the dust collected by the filter dust collector is classified by the classifier, and the coarse dust and the incineration residue from the incinerator are mixed to form mixed ash and melted in the ash melting furnace Considered processing. The classification point was changed to several points, soot dust was classified, and the proportion of classified coarse dust and the chlorine concentration in the coarse dust were measured. FIG. 8 shows the relationship between the classification point, the proportion of coarse particles, and the chlorine concentration in the coarse particles. ○ is the proportion of coarse dust, and Δ is the chlorine concentration in the coarse dust.

  The measurement result of the ratio of the coarse dust and the chlorine concentration in the coarse dust shown in FIG. 8, the generation weight ratio of the incineration residue and the dust is 65:35, and the chlorine concentration in the incineration residue is 0.6. Based on the weight percent, the chlorine concentration in the mixed ash of the classified coarse dust and the incineration residue is obtained, and the relationship with the classification point is shown in FIG.

  Since the allowable range of the chlorine concentration contained in the mixed ash is 3.5% by weight or less, the coarse particles classified with the classification point set to 10 μm or more from FIG. 9 are mixed with the incineration residue and supplied to the ash melting furnace. Can do. That is, in the waste treatment apparatus including the incinerator and the ash melting furnace, the lower limit of the setting range of the classification point is 10 μm.

  When the dust collected by the filter dust collector is classified by the classifier and coarse dust is supplied to the gasification melting furnace or ash melting furnace, the setting range of the classification point is set to 10 to 1200 μm. Or the reaction product of alkaline chemicals decomposes in the ash melting furnace and acidic substances such as hydrogen chloride are generated again, increasing the concentration of acidic substances in the exhaust gas, and forming a molten salt layer in the ash melting furnace In addition, it is possible to reduce the amount of fine dust to be landfilled.

  In the first embodiment and the second embodiment, the alkaline agent is a powder agent such as slaked lime or baking soda. Instead, a liquid agent such as an aqueous caustic soda solution or an aqueous magnesium hydroxide solution is used as the alkaline agent. Is also possible. Since the temperature of the exhaust gas from the gasification melting furnace or incinerator is 150 ° C. or higher, when the liquid chemical is sprayed and supplied to the exhaust gas from the gasification melting furnace or incinerator, the acidic substance contained in the exhaust gas and The reaction product with the mist-like liquid drug evaporates moisture into solid particles and is collected by a dust collector. Since the reaction product of the particulate liquid alkali chemicals is also concentrated on the fine dust side, it is classified by a classifying device in which the setting range of the classification point is set to 10 to 1200 μm, and coarse dust Is preferably supplied to a gasification melting furnace or an ash melting furnace and melt-treated to dispose of fine dust containing a large amount of alkali chemical reaction products in landfill.

  An example in the case where slaked lime powder is used as an alkaline agent in a waste treatment facility equipped with a gasification melting furnace as described in the first embodiment will be described. As the slaked lime powder blown into the exhaust gas, a slaked lime powder having a relatively coarse particle size manufactured by B company shown in FIG. 3 was used.

  FIG. 10 is a view showing the particle size distribution of the soot collected by the dust collector from the exhaust gas discharged from the gasification melting furnace. The particle size distribution of the dust varies greatly depending on the type of furnace, the type of waste, the operating conditions of each furnace, etc., but the dust discharged from the gasification melting furnace according to the present embodiment belongs to a fine particle size category. As shown in FIG. 10, the particle size distribution of the dust has frequency peaks at two locations near 7 μm and 100 μm. When the dust was observed with an electron microscope, it was found that the large particles of about 100 μm were burned out of combustible waste because the fibrous substance was rounded. Moreover, the small particle | grains of about 7 micrometers originated from the reaction product and fume of slaked lime and an acidic substance.

  The classification point was adjusted to 10 μm, and the classified coarse dust was mixed with the combustion air and injected into the gasification melting furnace, but it could be stably melted without increasing the hydrogen chloride concentration in the exhaust gas. Further, when this embodiment is not carried out, that is, the dust collected as in the conventional waste treatment apparatus shown in FIG. 5 is not classified and the amount of 20% by weight or less of the collected dust is returned to the gasification melting furnace. In this case, 80 to 100% by weight of the dust must be landfilled. In this embodiment, the classification point is set to 10 μm, and 60% by weight of the collected dust is coarsely dusted as a gasification melting furnace. Therefore, the amount of landfill disposal can be reduced to 40% by weight of the collected dust.

  The fine dust classified by the classifier was kneaded with a heavy metal stabilizer and water, subjected to stabilization treatment to prevent elution of heavy metal, and then disposed to landfill. Here, the kneaded material after the stabilization treatment satisfied the environmental standards related to landfill disposal.

1, 1 'waste treatment equipment 2 gasification melting furnace 3 alkali chemical supply device (alkali chemical supply means)
4 Dust collector 5 Classification device 6 Coarse dust return path (coarse dust return means)
8 Incinerator 9 Ash melting furnace 10 Coarse dust supply path (Coarse dust supply means)

Claims (6)

A gasification melting furnace that thermally decomposes waste and melts the residue;
A dust collector for collecting dust contained in the exhaust gas discharged from the gasification melting furnace;
An alkali chemical supply device that blows an alkaline chemical into the exhaust gas from the gasification melting furnace between the gasification melting furnace and the dust collector to generate a reaction product of an acidic substance and an alkaline chemical contained in the exhaust gas;
A classifier for classifying the dust containing the reaction product collected by the dust collector into coarse dust and fine dust and separating the reaction product to the fine dust side;
Coarse dust return means for returning coarse dust to the gasification melting furnace,
A waste treatment apparatus comprising: An incinerator to incinerate waste,
An ash melting furnace for melting the incineration residue of the incinerator;
A dust collector for collecting dust contained in the exhaust gas discharged from the incinerator;
An alkaline chemical supply device that blows an alkaline chemical into the exhaust gas from the incinerator between the incinerator and the dust collector to generate a reaction product of an acidic substance and an alkaline chemical contained in the exhaust gas;
A classifier for classifying the dust containing the reaction product collected by the dust collector into coarse dust and fine dust and separating the reaction product to the fine dust side;
Coarse dust supply means for supplying coarse dust to the ash melting furnace,
A waste treatment apparatus comprising: A waste treatment method for thermally decomposing waste in a gasification melting furnace and melting the residue,
An alkali chemical supplying step of blowing an alkali chemical into the exhaust gas discharged from the gasification melting furnace to generate a reaction product of an acidic substance and an alkaline chemical contained in the exhaust gas;
A dust collection step for collecting the dust containing the reaction product contained in the exhaust gas after the alkali chemical supply step;
A classification step of classifying the dust containing the reaction product collected in the dust collection step into coarse dust and fine dust and separating the reaction product to the fine dust side;
A coarse dust return step for returning the coarse dust to the gasification melting furnace,
A stabilization process for stabilizing fine dust,
A waste treatment method comprising: A waste treatment method in which waste is incinerated in an incinerator and the incineration residue is melted in an ash melting furnace,
An alkali chemical supplying step of blowing an alkali chemical into the exhaust gas discharged from the incinerator to generate a reaction product of an acidic substance and an alkaline chemical contained in the exhaust gas;
A dust collection step for collecting the dust containing the reaction product contained in the exhaust gas after the alkali chemical supply step;
A classification step of classifying the dust containing the reaction product collected in the dust collection step into coarse dust and fine dust and separating the reaction product to the fine dust side;
Coarse dust supply process for supplying coarse dust to the ash melting furnace,
A stabilization process for stabilizing fine dust,
A waste treatment method comprising:   The alkaline chemical blown in the alkaline chemical supply step is a powder alkaline chemical, and in the classification step, classification is performed based on a classification point set in advance based on a particle size distribution of the powder alkaline chemical. 4. The waste treatment method according to 4.   The waste classification method according to claim 5, wherein the classification point is set within a range of 10 to 1200 μm.

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