JP4617934B2 - Reduction method of dioxins in fly ash of garbage incineration equipment - Google Patents

Description

  The present invention relates to a method for reducing dioxins in fly ash generated in a garbage incineration facility.

The sources of dioxins in garbage incineration equipment are exhaust gas and solid residues such as fly ash and main ash. Here, advanced exhaust gas treatment can reduce emissions associated with exhaust gas, and main ash can be reduced by high-temperature incineration, but the amount of dioxins contained in the solid residue, especially fly ash, that occupies most of the dioxins overall. There are still many. In fact, when the exhaust gas from the garbage incineration facility is treated with a chemical mixed with activated carbon in slaked lime, the dioxins in the exhaust gas are as low as 0.1 ng-TEQ / Nm ³ , but the dioxins in the fly ash are 1 ng-TEQ. / G is present. If the concentration of fly ash in the exhaust gas is 5 to 10 g / Nm ³ , 5 to 10 ng-TEQ / Nm ³ dioxins must be captured together with the fly ash. Therefore, in order to reduce the total amount of dioxins generated from garbage incineration facilities, it is important not only to reduce dioxins in exhaust gas but also to reduce dioxins in fly ash.

  For example, in the adsorption method using activated carbon or the like, which is mainly used for the removal of dioxins from exhaust gas, the dioxins in solid waste such as fly ash are eventually removed even if dioxins in exhaust gas are highly removed. This will not contribute to the reduction of the total amount of dioxins discharged from garbage incineration facilities. The reason why the concentration of dioxins in the fly ash is high is that not only the dioxins are adsorbed but also re-synthesized from the precursor. Therefore, it is an important problem that resynthesis can be suppressed. In addition, the production conditions for dioxins in fly ash are different from exhaust gas, and the residence time is long and the contact time with copper chloride or the like, which is a catalyst for producing dioxins, is also long. Therefore, even if the method for reducing dioxins in exhaust gas is applied as it is, the effect is small. Thus, basically, the method for reducing dioxins in exhaust gas and the method for reducing dioxins in fly ash are different methods.

  Patent Documents 1 to 3 describe a method for reducing dioxins and hydrogen chloride in exhaust gas. However, these are not inventions aimed at reducing dioxins in fly ash, but the selection of suitable drug types for reducing dioxins in fly ash and the porosity, average particle size, and fineness of the drug. There is no disclosure of important physical properties such as pore structure. Moreover, since the thing using activated carbon together like patent document 3 capture | acquires dioxins by activated carbon, the quantity of dioxins in fly ash does not fall.

JP-A-3-224618 (Claim 1) Japanese Patent Laid-Open No. 11-104439 (Claims 1, 2, and 7) JP 2000-354735 A (Claims 1 and 3)

  An object of the present invention is to provide a method for easily reducing dioxins in fly ash at a low temperature of less than 300 ° C.

The present invention finds that there is a specific range in average particle diameter, specific surface area and pore structure when using potassium carbonate for the purpose of reducing dioxins in fly ash, and provides the following method. is there.
(1) flying an average particle size of 1 to 50 [mu] m, a specific surface area of the drug containing potassium carbonate porous is 1.0~3.0m2 / g, at 100 ° C. exceeding 260 ℃ less, generated from refuse incinerators A method for reducing dioxins in fly ash, which comprises contacting with ash.
(2) The method according to (1), wherein the potassium carbonate has a total pore volume of pores having a pore diameter of 0.1 to 1.0 μm of 0.08 mL / g or more.
(3) The reduction method according to (1) or (2), wherein the drug contains sodium hydrogen carbonate having an average particle size of 20 μm or less.
(4) The said chemical | medical agent contains 0.1 to 5% of fumed silica with respect to the sum total of potassium carbonate and fumed silica, The reduction method of the dioxins in the fly ash in any one of (1)-(3) .
(5) The reduction method according to any one of (1) to (4), wherein the chemical is sprayed into a flue of a garbage incineration facility and then collected together with fly ash.
(6) The reduction method according to (5), wherein porous potassium carbonate having an average particle size of 60 to 500 μm is sprayed on the flue while being pulverized to an average particle size of 1 to 50 μm.
(7) Potassium carbonate having an average particle size of 60 to 500 μm and sodium hydrogen carbonate having an average particle size of 60 to 500 μm are mixed and sprayed onto the flue while pulverizing the potassium carbonate to an average particle size of 1 to 50 μm (5) The reduction method described.
(8) The reduction method according to (5), wherein the chemical is sprayed into a flue between the cooling device and the dust collecting device in a garbage incineration facility including a cooling device on the upstream side of the dust collecting device for collecting fly ash.

  Due to the use of the drug according to the present invention, the dioxins in the fly ash are 0.1 ng-TEQ / g or less, further 0.05 ng-TEQ / g or less, further 0.02 ng-TEQ / g or less. It can be reduced to a low concentration. Dioxins in fly ash can be easily reduced at a low temperature of 300 ° C. or lower. In addition, waste incineration equipment that does not have a melting furnace or heating furnace can be implemented without additional equipment. In addition, since the reaction product and the unreacted product of the drug according to the present invention are water-soluble, it can be drained if it is dissolved in water to remove heavy metals and the like, and it does not increase solid waste during disposal. it can.

  In the present specification, unless otherwise specified,% represents mass%.

  In measuring each physical property value, the average particle size is measured using a laser scattering diffraction type particle size distribution measuring device for the pulverized product. The apparatus used in the present invention is “Microtrac FRA9220” (trade name, manufactured by Nikkiso Co., Ltd.). The average particle size of the unground product is measured by low-tap sieving measurement. The apparatus used in the present invention is “SIEVE SHAKER” (trade name, manufactured by Iida Seisakusho). The specific surface area is measured by a nitrogen substitution method. The apparatus used in the present invention is “rapid surface area measuring apparatus SA-1000” (trade name, manufactured by Shibata Kagaku Co.). The pore volume is measured by a mercury intrusion method. The apparatus used in the present invention is “Micromeritics Pore Sizer 9310 type” (trade name, manufactured by Shimadzu Corporation, measurement range: pore diameter 0.0071 to 609.5 μm).

First, the chemical | medical agent (henceforth this chemical | medical agent) containing the porous potassium carbonate whose average particle diameter which concerns on this invention is 1-50 micrometers and whose specific surface area is 1.0-3.0 m < ² > / g is demonstrated. The average particle diameter of the porous potassium carbonate contained in this drug is 1 to 50 μm. Here, the larger the average particle size, the smaller the number of potassium carbonate per unit mass of fly ash, even if the fly ash contains the same content of potassium carbonate, and the dispersion of potassium carbonate in the fly ash In order to decrease, the upper limit is 50 μm or less. More preferably, it is 20 micrometers or less, More preferably, it is 10 micrometers or less. On the other hand, regarding the lower limit, the smaller the average particle diameter, the larger the number and the higher the degree of dispersion in the fly ash, but if it is too small, the production by pulverization becomes difficult or the particles tend to aggregate. On the contrary, the dispersibility is lowered, the hygroscopic property is strong, and it is easy to deliquesce. Therefore, the lower limit is 1 μm or more. More preferably, it is 2 micrometers or more, More preferably, it is 5 micrometers or more.

The specific surface area of potassium carbonate in 1.0~3.0m ² / g, more preferably the upper limit is 2.5 m ² / g, the lower limit is 1.5 m ² / g. The larger the specific surface area, the more part contributes to the reaction. On the other hand, the large specific surface area means that the pore diameter of one pore and the pore volume of one pore are small. Since it contradicts with increasing the pore volume of one pore and leads to a decrease in performance in this application, 3.0 m ² / g or less is preferable. When the specific surface area is less than 1.0 m ² / g, the area contributing to the reaction is reduced, and the effect of reducing dioxins is lowered. Even with the same pore structure, the specific surface area increases as the average particle size decreases. However, as described above, if the average particle size is too small, there are problems from the viewpoints of dispersibility, hygroscopicity, and industrial productivity. Therefore, the specific surface area is 3.0 m ² / g or less due to the limitation of the average particle size. Range is preferred. Here, when potassium carbonate is not porous, the specific surface area remains below 1.0 m ² / g even if the average particle size is reduced to 10 μm.

  In the porous potassium carbonate, the total pore volume of pores having a pore diameter of 0.1 to 1.0 μm is preferably 0.08 mL / g or more. In order to increase the reactivity, potassium carbonate preferably has a large number of pores having a pore diameter of 0.1 to 1 μm, and the total pore volume of pores having a pore diameter of 0.1 to 1.0 μm is It is preferably 0.08 mL / g or more, and more preferably 0.1 mL / g or more. Here, the pore diameter refers to the diameter of the pore. The inventors have developed a pore having a pore diameter of 0.1 to 1 μm, which facilitates mass transfer within the potassium carbonate pores of the precursor of dioxins as a reaction partner. It is estimated that the dioxin reduction effect in ash is improved. That is, the presence of porous potassium carbonate in contact with fly ash in the present invention suppresses the reaction between the precursors of dioxins such as chlorobenzenes and chlorophenols, and chlorine gas, bromine gas or hydrogen chloride gas. Therefore, it is speculated that the resynthesis of dioxins by heavy metals in fly ash is also suppressed. Presumably, fine pores with a pore diameter of less than 0.1 μm have a slow mass transfer rate within the potassium carbonate pores of the dioxin precursor, which is the reaction partner, even if the specific surface area is large, resulting in a decrease in reaction activity. is doing.

In relation to the size of the specific surface area, the mechanism of reduction of hydrogen chloride gas in exhaust gas and dioxins in fly ash is estimated as follows. Since the molecule of hydrogen chloride gas is smaller than the molecule of the precursor of dioxins, the reactivity with hydrogen chloride gas is good even if the pore size of the drug is small, and the larger the specific surface area of the drug is better. On the other hand, with regard to the reduction of dioxins in fly ash, since the gaseous dioxin precursor diffuses in the pores of potassium carbonate and must be dechlorinated there, the pore size of this drug is the same as that of dioxins. It needs to be large compared to the precursor. That is, the smaller the pore diameter, the larger the specific surface area. However, since the pore diameter has a lower limit, an upper limit appears in the specific surface area. For this reason, it is estimated that the value of a specific surface area is preferably 1.0 to 3.0 m ² / g.

The drug preferably contains sodium hydrogen carbonate having an average particle size of 20 μm or less. Sodium hydrogen carbonate becomes porous sodium carbonate when sprayed on the flue, and the specific surface area measured by the BET method is 4 m ² / g or more. This sodium carbonate has high reactivity with acidic gas components such as hydrogen chloride, and suppresses the consumption of porous potassium carbonate due to the reaction with acidic gas components such as hydrogen chloride in the exhaust gas. That is, it is considered that sodium hydrogen carbonate is mainly involved in the removal of acidic gas components such as hydrogen chloride in the exhaust gas, and porous potassium carbonate is mainly involved in the reduction of dioxins in the fly ash.

  The average particle size of sodium hydrogen carbonate is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably less than 10 μm. The lower limit is preferably 1 μm or more. Finer sodium bicarbonate increases the number per unit mass in the exhaust gas and shortens the diffusion distance of acidic gas such as hydrogen chloride to sodium bicarbonate. Although excellent in the reaction, sodium hydrogen carbonate having a size of less than 1 μm is expensive to produce industrially and more easily aggregates.

  The amount of sodium bicarbonate mixed is 10 to 99% with respect to the total of potassium carbonate and sodium bicarbonate, although it depends on the concentration of acidic gas components such as hydrogen chloride in the exhaust gas. More preferably, it is 50 to 95%. If it is less than 10%, the effect of adding sodium bicarbonate is small, and if it is more than 99%, the effect of potassium carbonate is not remarkable.

  Sodium bicarbonate may be sprayed after mixing with potassium carbonate, or may be sprayed separately, such as spraying sodium bicarbonate first on the upstream portion of the flue.

  Another advantage of using sodium bicarbonate instead of slaked lime for removal of acidic gas components such as hydrogen chloride in the exhaust gas is that sodium bicarbonate is water soluble and does not increase solid waste that is not water soluble. In addition, there is an effect of lowering pH when fly ash is dissolved in water. In slaked lime, the pH when fly ash is dissolved in water is high, and the elution amount of lead from the fly ash increases. If this chemical | medical agent containing potassium carbonate and sodium hydrogencarbonate is used, the elution amount of the lead from fly ash can be reduced. This is because sodium bicarbonate is baked in exhaust gas to form sodium carbonate, but the pH of the sodium carbonate and potassium carbonate is lower than that of slaked lime. The pH of potassium carbonate is about the same as that of sodium carbonate. This prevents elution of lead, which is an amphoteric metal, in the high pH range, thus reducing the amount of chelating agent used for fly ash treatment and reducing the elution concentration of lead, facilitating management and disposal costs for landfills. Can be further reduced.

  It is preferable that this chemical | medical agent contains 0.1 to 5% of fumed silica with respect to the sum total of potassium carbonate and fumed silica. An anti-caking agent can be used to improve dispersibility when pulverized into fine powder. In particular, fumed silica can be preferably used. Although fumed silica can be used for both hydrophilicity and hydrophobicity, it is preferable to use hydrophilic fumed silica in the case of wet treatment such as dissolving fly ash in water. Further, fumed silica is not only mixed with potassium carbonate having an average particle diameter of 1 to 50 μm, but can also be used by mixing with potassium carbonate having an average particle diameter of 60 to 500 μm before pulverization in an on-site pulverization method described later. As a result, powder can be stably charged into the pulverizer, aggregation during pulverization can be suppressed, dispersibility of the fine powder after pulverization can be improved, and the drug can be uniformly added to the fly ash.

  The amount of fumed silica added is 0.1 to 5%, preferably 0.3 to 2%, based on the total amount of potassium carbonate and fumed silica. If the addition amount of fumed silica is less than 0.1%, the addition effect is small. On the other hand, since fumed silica is expensive, it is not economical to add more than 5%.

  It is preferred that the drug is substantially free of activated carbon. This is because activated carbon increases solid waste as a water-insoluble component, and it is flammable, which limits its use at high temperatures. Furthermore, from the viewpoint of reducing dioxins in fly ash, which is the object of the present invention, activated carbon only adsorbs dioxins and is unnecessary because it does not contribute to the reduction of dioxins in fly ash.

The present invention is a method for reducing dioxins in fly ash by bringing the above-mentioned drug into contact with fly ash generated from garbage incineration equipment at 100 ° C. or more and less than 300 ° C.
The temperature which makes this chemical | medical agent contact with fly ash is 100 degreeC or more and less than 300 degreeC. If the lower limit is less than 100 ° C., the reactivity of the drug may be reduced, dust incineration gas may be condensed to absorb moisture, or the acid dew point may be lowered and equipment corrosion may occur. In addition, at 300 ° C. or higher, the specific surface area decreases due to the gradual change of the pore structure of the drug, and the equipment corrodes with alkali. More preferably, the lower limit is 120 ° C and the upper limit is 260 ° C.
The garbage incineration equipment refers to equipment that burns municipal waste, industrial waste, and RDF (solidified product obtained by compressing and molding waste containing thermoplastic resin).

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an outline of a preferred example in which the present invention is applied to dioxin reduction in fly ash generated from garbage incineration equipment. The embodiment of the present invention is not limited to the description using this drawing, and includes an embodiment in which fly ash is taken out from the garbage incineration facility, and then mixed with the present drug and heated to 100 to 300 ° C.

  As an embodiment of the method for reducing dioxins in fly ash according to the present invention, it is preferable to spray the chemical on a flue of a garbage incinerator and then collect the dust together with fly ash. For example, the second flue 4 sprays the exhaust gas generated from the waste incineration facility 1 of FIG. When spraying this drug, use it in powder form without using aqueous solution or slurry. The sprayed medicine is collected together with fly ash by a dust collector such as a bag filter or an electric dust collector. For example, it is removed by the dust collector 5 of FIG. 1, and the exhaust gas is further discharged from the chimney 7 through the third flue 6.

As an aspect of spraying the drug on the flue, it is preferable to spray the flue gas while pulverizing porous potassium carbonate having an average particle diameter of 60 to 500 μm to an average particle diameter of 1 to 50 μm. The average particle size before pulverization is preferably 60 to 500 μm so that the input to the pulverizer is stable. More preferably, it is 100-400 micrometers. If it exceeds 500 μm, the pulverizer becomes large, and if it is less than 60 μm, the fluidity as a powder decreases and the charging to the pulverizer becomes unstable. The average particle diameter of the pulverized potassium carbonate is 1 to 50 μm, more preferably 1 to 20 μm, and still more preferably 1 to 10 μm. A method in which a fine powder having an average particle diameter of 50 μm or less is prepared in advance and is not sprayed, and a coarse powder having an average particle diameter of 60 to 500 μm is sprayed while being ground to an average particle diameter of 1 to 50 μm is hereinafter referred to as an on-site grinding method. The specific surface area of porous potassium carbonate having an average particle size of 60 to 500 μm is preferably 1 m ² / g or more. That is, the specific surface area needs to be 1.0 to 3.0 m ² / g after being pulverized to an average particle diameter of 1 to 50 μm.

  As another aspect of spraying the drug on the flue, potassium carbonate having an average particle size of 60 to 500 μm and sodium hydrogen carbonate having an average particle size of 60 to 500 μm are mixed, so that the average particle size of potassium bicarbonate is 1 to 50 μm. It is preferable to spray the flue while being pulverized. For potassium carbonate and sodium hydrogen carbonate, the average particle size before pulverization is preferably 60 to 500 μm so that the charging to the pulverizer is stable. More preferably, it is 100-400 micrometers. If the size is larger than 500 μm, the pulverizer becomes large, and if it is finer than 60 μm, the fluidity as powder decreases, and the charging into the pulverizer is not stable. The average particle diameter of the pulverized potassium carbonate is 1 to 50 μm, preferably 1 to 20 μm, more preferably 1 to 10 μm. On the other hand, the average particle size after pulverization of sodium bicarbonate is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably less than 10 μm, for the reasons described above.

  It is preferable to mix 50% to 99% of sodium hydrogen carbonate with respect to the total of potassium carbonate having an average particle diameter of 60 to 500 μm and sodium hydrogen carbonate having an average particle diameter of 60 to 500 μm. This is because it is possible to prevent potassium carbonate from adhering to the hammer of the pulverizer or the impeller of the classifier because of the presence of sodium hydrogen carbonate having low hygroscopicity.

  As another aspect, it is possible to employ a method in which porous potassium carbonate or sodium hydrogen carbonate previously pulverized is mixed or separately stored in a reservoir and a certain amount is sequentially used. This method is advantageous when the present invention is adopted in a small-scale waste incineration facility because fine pulverization can be efficiently performed on a large scale in another line.

  For the above-described pulverization, an impact pulverizer having a built-in wind classification function, for example, “ACM Pulverizer” (trade name, manufactured by Hosokawa Micron Co., Ltd.) can be preferably used. Since potassium carbonate has strong hygroscopicity, it is pulverized in dry air having a dew point of 0 ° C. or lower, more preferably −10 ° C. or lower.

[Example 1 (Example)]
In a batch furnace garbage incineration facility, 3000 kg of paper was incinerated in 20 hours. The temperature control of the waste incineration part is 400 to 480 ° C. In the initial stage of combustion, the primary burner burns using natural gas as auxiliary fuel, and after 8 hours, the auxiliary fuel is stopped and changes by self-combustion. Further, the temperature of the exhaust gas generated here was controlled to 800 to 900 ° C. with a secondary burner. Thereafter, the exhaust gas is cooled to 180 ° C. by the cooling device 3 which is a spray-type cooling tower, and then the chemical of the present invention is sprayed to collect the dust collecting device 5 which is a bag filter. In the following examples, the waste quality and the amount of incineration were the same.

  Average particles prepared in advance by pulverizing porous potassium carbonate having an average particle diameter of 290 μm in dry air having a dew point of −15 ° C. using ACM Pulverizer ACM-5 (trade name, manufactured by Hosokawa Micron) 5.7 kg / h of this drug prepared by previously mixing 10% potassium carbonate having a diameter of 12 μm and 90% sodium hydrogen carbonate having an average particle diameter of 9 μm prepared in advance (containing 1% hydrophilic fumed silica) in advance. Sprayed. A spraying place is the 2nd flue 4 between the cooling device 3 which is a water spray type cooling tower, and the dust collector 5 which is a bag filter. Table 1 shows the physical properties of the sprayed potassium carbonate.

  Two hours after the start of incineration when the combustion state was stabilized, analysis of exhaust gas and fly ash at the outlet of the dust collector 5 as a bag filter was started. The analysis results were as shown in Table 2. The concentration of dioxins in the exhaust gas was good even though no activated carbon was used.

  Table 2 shows the lead concentration in the fly ash. In addition, the lead concentration measured according to the dissolution test stipulated in the Environmental Agency Notification No. 13 of 1973 was 0.08 mg / L as shown in Table 2, which is a concentration that can be safely discarded. Furthermore, fly ash discharged from the bag filter is not ignitable and does not contain activated carbon, so it is effective in reducing solid waste.

[Example 2 (comparative example)]
The same equipment as in Example 1 was used, and under the same incineration conditions, the only chemical sprayed was sodium bicarbonate. As the sodium hydrogen carbonate, sodium hydrogen carbonate having an average particle diameter of 9 μm used in Example 1 was used. The spray amount was 5.7 kg / h.

For confirmation, the same amount of sodium bicarbonate is added to a gas that does not contain acidic gas components such as hydrogen chloride and sulfur oxide that react with sodium bicarbonate at the same gas flow rate and gas temperature. Sprayed. It was 5.7 m < ² > / g when it extract | collected with the bag filter and the specific surface area was measured.

[Example 3 (comparative example)]
Using the same equipment as in Example 1, the sprayed chemical was only slaked lime under the same incineration conditions. The slaked lime used was a special slaked lime number from Ube Materials Co., Ltd., and the average particle size was 6.5 μm. The spray amount was 5.7 kg / h.

  According to the present invention, dioxins in fly ash can be reduced to a very low concentration of 0.01 ng-TEQ / g or less. Compared with Example 1 and Example 2 regarding the effect of the potassium carbonate of the present invention, Example 1 was obtained by replacing only 10% of the same sodium hydrogen carbonate with Example 2 with the potassium carbonate of the present invention. Regarding dioxins, Example 1 was 0.01 / 0.15 = 1/15 compared to Example 2. On the other hand, with respect to the concentration of hydrogen chloride gas, Example 1 was 1.2 / 1.8 = 1 / 1.5 compared to Example 2, so that the potassium carbonate of the present invention was a solution of dioxins in fly ash. It can be seen that selective reduction was effective. Moreover, about the density | concentration of dioxins in waste gas, Example 1 did not reach 0.29 / 0.46, ie, 1/2 with respect to Example 2. This indicates that the drug was effective in reducing dioxins in fly ash.

  The concentration of lead in the fly ash of Example 1 and the concentration of lead eluted in the dissolution test are very low compared to Example 3. high.

  The present invention can be used to reduce dioxins in fly ash generated from garbage incineration facilities.

The figure which shows the outline | summary of the garbage incineration equipment which uses the chemical | medical agent which concerns on this invention.

Explanation of symbols

1. Garbage incineration equipment,
2. The first flue,
3. Cooling system,
4). The second flue,
5. Dust collector,
6). The third flue,
7). chimney,
8). Drugs (reducing agents for dioxins in fly ash),
9. Fly ash.

Claims (8)

A chemical containing porous potassium carbonate having an average particle diameter of 1 to 50 μm and a specific surface area of 1.0 to 3.0 m ² / g, fly ash generated from a garbage incineration facility at 100 ° C. or more and 260 ° C. or less A method for reducing dioxins in fly ash, which is characterized by contacting.   The reduction method according to claim 1, wherein the potassium carbonate has a total pore volume of pores having a pore diameter of 0.1 to 1.0 μm of 0.08 mL / g or more.   The reduction method according to claim 1 or 2, wherein the drug contains sodium hydrogen carbonate having an average particle size of 20 µm or less.   The said chemical | medical agent contains 0.1 to 5% of fumed silica with respect to the sum total of potassium carbonate and fumed silica, The reduction method of the dioxins in fly ash in any one of Claims 1-3.   The reduction method according to any one of claims 1 to 4, wherein the chemical is sprayed into a flue of a garbage incineration facility and then collected together with fly ash.   6. The reduction method according to claim 5, wherein porous potassium carbonate having an average particle size of 60 to 500 [mu] m is sprayed on the flue while being pulverized to an average particle size of 1 to 50 [mu] m.   6. Reduction according to claim 5, wherein potassium carbonate having an average particle size of 60 to 500 [mu] m and sodium hydrogen carbonate having an average particle size of 60 to 500 [mu] m are mixed and sprayed onto the flue while pulverizing potassium carbonate to an average particle size of 1 to 50 [mu] m. Method. The reduction method according to claim 5, wherein the chemical is sprayed into a flue between the cooling device and the dust collector in a garbage incineration facility provided with a cooling device on the upstream side of the dust collector that collects fly ash.

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