JP2007260553A - Treatment method of exhaust gas and fly ash of incineration plant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method of an exhaust gas and a fly ash of an incineration plant which surely treats an acidic component in the exhaust gas of the incineration plant to be harmless and also plans to stably fix a heavy metal such as Pb in a final disposal site for a long time and to prevent a corrosion of a material etc. of a fly ash kneader. <P>SOLUTION: The treatment method of the exhaust gas and the fly ash of the incineration plant has a step for treating the acidic component in the exhaust gas by spraying an acidic gas treatment agent containing a Mg-based alkali agent and NaHCO<SB>3</SB>on the exhaust gas generating from a combustion plant, and a step for fixing the heavy metal in the fly ash by adding a phosphoric-acid based heavy-metal fixing agent to the fly ash collected from the exhaust gas, under the condition of pH of 9-11.5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is an exhaust gas containing harmful acidic components such as hydrogen chloride and sulfur oxide (hereinafter referred to as “acid gas”) generated in combustion facilities such as a waste incinerator, a power generation boiler, a carbonization furnace, and an ash melting furnace. In particular, the present invention relates to a method for treating heavy metals in fly ash, and in particular, a treatment method effective for preventing long-term stable elution of lead in fly ash.

  Conventionally, exhaust gases containing harmful acidic components such as hydrogen chloride and sulfur oxides generated in combustion facilities such as waste incinerators, power generation boilers, carbonization furnaces, and ash melting furnaces are treated with acid gas treatment agents such as slaked lime. After that, it is removed by a dust collector such as a bag filter and then discharged from the chimney.

  On the other hand, the fly ash collected by the dust collector contains harmful heavy metals such as Pb and Cd, and thus is subjected to landfill disposal after stabilization of these harmful heavy metals. Conventionally, as a method for treating heavy metals in fly ash, a method of insolubilizing with a chelating agent such as diethyldithiocarbamate (for example, Patent Documents 1 and 2) is generally used. Although the short-term fixing effect by the Notification No. 13 test is high, there remain problems of pH reduction due to acid rain at the final disposal site and re-elution of heavy metals such as Pb due to oxidative self-decomposition of chelates.

  On the other hand, the method of fixing heavy metals with a phosphate-based heavy metal fixing agent such as phosphoric acid (for example, Patent Document 3) changes the heavy metal to the form of hydroxyapatite, which is an inorganic mineral, and thus long-term stability at the final disposal site. It is an excellent treatment method from the viewpoint of environmental protection.

By the way, when processing acidic gas such as hydrogen chloride with slaked lime, there is much necessary amount of slaked lime with respect to acidic gas. As a result, fly ash collected in incineration facilities treating acidic gas with slaked lime is due to slaked lime. It becomes alkaline fly ash (hereinafter sometimes referred to as “alkali fly ash”) in which unreacted alkali remains. In order to treat such alkaline fly ash with an inorganic heavy metal fixing agent such as phosphoric acid, a large amount of addition is required, or in order to lower the fly ash pH, normal phosphoric acid or neutralizer with high acidity It is necessary to use a sulfuric acid band, iron chloride or the like together. Since these acidic chemicals are strong acids, the use of such chemicals may cause problems such as corrosion of the chemical injection piping and kneader materials, and modifications such as material changes are necessary to prevent corrosion. There is.
Japanese Patent Laid-Open No. 3-231921 JP-A-6-15280 Japanese Examined Patent Publication No. 4-61710

  In consideration of the present state of exhaust gas and fly ash treatment in such incineration facilities, the present invention uses phosphoric acid heavy metal fixatives to achieve long-term stable fixation of fly ash lead, etc. at the final disposal site. It is an object of the present invention to provide an optimum treatment method in comprehensive treatment including treatment of acid gas and prevention of corrosion of fly ash kneader materials and the like.

  The method for treating exhaust gas and fly ash in an incineration facility according to the present invention (Claim 1) includes a step of spraying a magnesium-based alkaline agent and sodium bicarbonate to exhaust gas generated from a combustion facility to treat acidic components in the exhaust gas. And a step of immobilizing heavy metals in the fly ash by adding a phosphate heavy metal fixative to the fly ash collected from the exhaust gas under a pH of 9 to 11.5. And

  A method for treating exhaust gas and fly ash in an incineration facility according to claim 2 is characterized in that, in claim 1, the magnesium-based alkaline agent is magnesium oxide and / or magnesium hydroxide.

  A method for treating exhaust gas and fly ash in an incineration facility according to claim 3 is characterized in that, in claim 2, the magnesium oxide and / or magnesium hydroxide is made of ore as a raw material.

  The method for treating exhaust gas and fly ash in an incineration facility according to claim 4 is an aqueous solution in which the phosphoric acid heavy metal fixing agent is blended with normal phosphoric acid and an alkaline agent in any one of claims 1 to 3. The aqueous solution has a pH of 3 or more.

  A method for treating exhaust gas and fly ash in an incineration facility according to claim 5 is characterized in that, in claim 4, the alkaline agent is sodium hydroxide and / or potassium hydroxide.

  A method for treating exhaust gas and fly ash in an incineration facility according to claim 6 is the method according to any one of claims 1 to 5, wherein an acid gas treatment agent containing a magnesium-based alkaline agent and sodium bicarbonate is sprayed on the exhaust gas. It is characterized by.

  A method for treating exhaust gas and fly ash in an incineration facility according to claim 7 is characterized in that, in any one of claims 1 to 6, the acid gas treating agent contains activated carbon.

  According to the present invention, it is possible to reliably treat the acidic components in the exhaust gas and make them harmless, and to stably fix long-term heavy metals such as lead at the final disposal site and to prevent corrosion of fly ash kneader materials and the like. It becomes.

  That is, by spraying the magnesium-based alkaline agent and sodium hydrogen carbonate on the exhaust gas, acidic components such as hydrogen chloride and sulfur oxide in the exhaust gas react with the magnesium-based alkaline agent and sodium hydrogen carbonate to be neutralized and removed. Moreover, when the residue of a magnesium-type alkali agent is contained in fly ash, the pH of the fly ash can be stably adjusted to 9-11.5 unlike the slaked lime by the pH buffer action, lead. And cadmium elution can be suppressed.

  The magnesium-based alkali agent is preferably magnesium oxide and / or magnesium hydroxide (Claim 2), and the magnesium oxide and / or magnesium hydroxide may be made from ore (Claim 3).

  In addition, by using a magnesium-based alkali agent and sodium bicarbonate in combination, the pH, which was unstable in the treatment with sodium bicarbonate alone, can be stably adjusted to 9 to 11.5, and an acidic heavy metal fixing agent Cd elution associated with a drop in fly ash pH during application can be prevented by the pH buffering action of the magnesium-based alkaline agent. Moreover, activated carbon may be blended with the acidic gas treating agent according to the present invention, and in this case, dioxins in the exhaust gas can be adsorbed and removed by the adsorption effect of the activated carbon (claim 7).

  Thus, if fly ash is obtained by treating exhaust gas with magnesium-based alkaline agent and sodium hydrogen carbonate, heavy metal can be fixed stably and reliably over a long period of time with a small amount of phosphate-based heavy metal fixing agent. Since there is no need to use an acidic agent as a neutralizing agent, the problem of corrosion of the material of the kneader is reduced.

  The phosphate heavy metal fixing agent is preferably an aqueous solution containing normal phosphoric acid and an alkali agent such as sodium hydroxide and / or potassium hydroxide (Claims 4 and 5). The problem of corrosion of the agent to the material of the kneader is greatly reduced.

  Embodiments of a method for treating exhaust gas and fly ash in an incineration facility according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a schematic diagram of an incineration facility for explaining an embodiment of a method for treating exhaust gas and fly ash in the incineration facility.

  As shown in FIG. 1, in the incineration facility, after the exhaust gas from the incinerator 1 is cooled by the gas cooling tower 2, the dust is collected by the bag filter (BF) 3 and discharged from the chimney 4. The fly ash collected by the bag filter 3 is stored in the silo 5, and then, after the heavy metal fixing agent is added and kneaded by the kneader 6 to fix the heavy metal, it is disposed of in landfill.

  In the present invention, in such an incineration facility, magnesium-based alkaline agent and sodium hydrogen carbonate are sprayed as an acidic gas treating agent on flue exhaust gas, and a phosphate-based heavy metal fixing agent is added to fly ash as a heavy metal fixing agent. To do.

  As the magnesium-based alkali agent, magnesium hydroxide and / or magnesium oxide is preferable, and it is advantageous to reduce the drug cost to use those derived from minerals such as brucite.

  The magnesium-based alkali agent is preferably in the form of fine particles because it has a large specific surface area and excellent reaction activity. However, an excessively thin one increases the bag filter differential pressure, and specifically, the average particle diameter d50 is 30 μm. Hereinafter, it is particularly preferably 6 to 20 μm.

  Sodium bicarbonate is also preferably in the form of fine particles because of its large specific surface area and excellent reaction activity. Specifically, the average particle diameter d50 is preferably 30 μm or less, particularly preferably 6 to 20 μm.

  The acid gas treatment agent is preferably added to a location upstream of the dust collector such as the bag filter 3 in the incineration facility. For example, the point B that is the inlet of the bag filter 3 in FIG. It is preferable to add to point A which is the inlet of 2).

  As temperature of the location where an acidic gas processing agent is added, about 150-700 degreeC is preferable and especially 160-500 degreeC is more preferable.

  For example, the acidic gas treating agent may be sprayed only at one point A or B point in FIG. 1 or may be sprayed at a plurality of locations such as two points A and B. Moreover, when using 2 or more types of chemical | medical agents as an acidic gas processing agent, these may be mixed beforehand and may be sprayed as one agent, may be sprayed separately in one place, without mixing, and several separately You may spray at a spot. For example, when a magnesium-based alkaline agent and sodium hydrogen carbonate are used in combination, the magnesium-based alkaline agent may be sprayed on point A and sodium hydrogen carbonate may be sprayed on point B. good. In particular, since sodium hydrogen carbonate is a highly reactive agent, it can be sprayed into the exhaust gas in the flue in front of the dust collector on the downstream side of the gas cooling tower or the temperature reducing tower. It is preferable in terms of removal effect.

  The amount of the acid gas treatment agent sprayed is determined according to the concentration of acidic components such as hydrogen chloride and sulfur oxide contained in the exhaust gas discharged from the incinerator. It is preferable to add 1 equivalent or more of magnesium oxide and sodium bicarbonate in total. Further, when the spray amount is controlled by the concentration of the acidic component upstream or downstream from the spray position of the acidic gas treating agent, the neutralization removal of the acidic component can be efficiently performed with the minimum spray amount.

In the usual case, the spray amount of the acidic gas treating agent is preferably sprayed at a ratio of 1:20 to 1 (weight ratio) of the magnesium-based alkaline agent and sodium hydrogen carbonate in a total amount of about 600 to 20000 mg / Nm ³ .

  The magnesium-based alkaline agent may be sprayed as a powder, or may be sprayed as a water slurry of about 0.1 to 45% by weight, preferably about 8 to 20% by weight. If the slurry concentration in this case is thin, the amount of slurry sprayed increases, and if the slurry concentration is high, the drug supply line and nozzle may be blocked.

In the exhaust gas treatment according to the present invention, an acid gas treating agent and activated carbon may be used in combination, and dioxins in the exhaust gas can be adsorbed and removed by using activated carbon in combination. In this case, the activated carbon is preferably sprayed before the bag filter, and the spray amount is preferably about 20 to 300 mg / Nm ³ . The activated carbon may be sprayed separately from the acid gas treating agent, or the activated carbon and the acid gas treating agent previously mixed to form a single agent may be sprayed.

  The fly ash collected from the exhaust gas treated with the magnesium-based alkaline agent and sodium hydrogen carbonate is adjusted to pH 9-11.5 stably by the pH buffering action of the magnesium-based alkaline agent. If it is ash, elution of heavy metals hardly occurs.

  In the present invention, a phosphate heavy metal fixing agent is added to such fly ash under conditions of pH 9 to 11.5 and kneaded to fix the heavy metal in the fly ash. By adding and kneading phosphoric acid heavy metal fixative to fly ash under pH 9 to 11.5 conditions, it is possible to sufficiently obtain the heavy metal fixing effect of the phosphoric acid heavy metal fixing agent, and there is little phosphoric acid heavy metal fixing. Heavy metal can be fixed stably and reliably with the added amount of the agent.

  As described above, the fly ash discharged from the incineration facility sprayed with the magnesium-based alkaline agent and sodium hydrogen carbonate as the acid gas treating agent is in the range of pH 9 to 11.5 as it is, so it is necessary to adjust the pH particularly. However, if the pH exceeds 11.5, a neutralizing agent such as sulfuric acid band, iron sulfate, or iron chloride is added. Moreover, when pH is less than 9, the addition amount of the magnesium-type alkali agent sprayed on waste gas is increased, or the amount of alkali agents, such as NaOH and KOH, mix | blended with phosphoric acid is increased.

  As the phosphoric acid heavy metal fixing agent used here, orthophosphoric acid (orthophosphoric acid), polyphosphoric acid, metaphosphoric acid, hypophosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, superphosphoric acid, primary phosphoric acid Soda, dibasic sodium phosphate, tribasic sodium phosphate, primary potassium phosphate, secondary potassium phosphate, tertiary potassium phosphate, primary calcium phosphate, secondary calcium phosphate, primary magnesium phosphate, secondary phosphate Magnesium, primary ammonium phosphate, secondary ammonium phosphate, lime superphosphate, sodium tripolyphosphate, potassium tripolyphosphate, sodium hexametaphosphate, potassium hexametaphosphate, sodium pyrophosphate, potassium pyrophosphate, sodium phosphite, phosphorous acid Phosphoric acid such as potassium, sodium hypophosphite and potassium hypophosphite and alkali gold of phosphoric acid Salts, and salts such as alkaline earth metal salts. These phosphoric acid heavy metal fixing agents may be used alone or in combination of two or more.

  Of these, orthophosphoric acid is particularly preferred in terms of the heavy metal fixing effect and processing cost.

  A phosphoric acid heavy metal fixing agent such as orthophosphoric acid is usually added to fly ash as an aqueous solution of about 15 to 80% by weight.

  In addition, when using regular phosphoric acid as the phosphoric acid heavy metal fixing agent, it is preferable to add it as an aqueous solution containing normal phosphoric acid and an alkali agent such as sodium hydroxide and / or potassium hydroxide. By adding an alkali agent to the material, it is possible to significantly reduce the influence of corrosion of the kneader material and the like.

  In this case, it is preferable to add 15 to 35% by weight as normal phosphoric acid, and 5 to 35% by weight of an alkaline agent such as NaOH or KOH, and add to fly ash as an aqueous solution having a pH of 2 or more, particularly about 3 to 11. .

  The amount of phosphate heavy metal fixative added varies depending on the type of phosphate heavy metal fixative used, the presence or absence of an alkaline agent, the nature of the fly ash to be treated (pH and amount of residual drug), etc., but usually effective The component amount is preferably 0.1 to 10% by weight in terms of normal phosphoric acid with respect to fly ash.

  Moreover, when using an alkali agent together, 0.1-10 weight% of an active ingredient amount of a phosphoric acid heavy metal fixing agent and 0.1-20 weight% of an active ingredient amount should be added to fly ash. Is preferred.

  The amount of water added to the fly ash during the treatment of the fly ash does not greatly affect the treatment effect, but it is 10 to 40% by weight with respect to the fly ash in terms of kneadability and handleability of the treated ash. % Is preferable. Usually, a phosphate heavy metal fixing agent aqueous solution or a phosphate heavy metal fixing agent aqueous solution at a concentration that can secure such a water addition amount by adding an aqueous solution of a phosphate heavy metal fixing agent and an alkaline agent. Alternatively, an aqueous solution of a phosphate heavy metal fixing agent and an alkali agent is prepared.

  In the exhaust gas treatment in the present invention, other exhaust gas treatment agents may be used in combination with magnesium-based alkaline agent, sodium hydrogen carbonate, and activated carbon. Similarly, in the treatment of fly ash, in addition to the phosphoric acid heavy metal fixing agent and the alkali agent, other fly ash treatment agents such as a dioxin decomposition agent may be added.

  According to such a method of the present invention, it is possible to stably and reliably treat these by selecting and using an optimal chemical in the relationship between exhaust gas treatment and fly ash treatment.

  EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto. In the following, “%” indicates “% by weight”.

Example 1
In the waste incineration facility shown in FIG. 1 (waste treatment amount 8 t / day), magnesium oxide (particle size d50 = 16 μm) made of mineral (brucite) is used as exhaust gas before the gas cooling tower (point A, temperature 600 ° C.). ) 0.6 kg / h (300 mg / Nm ³ ) and sodium bicarbonate (particle size d50 = 10 μm) 1.2 kg / h (600 mg / h) on the exhaust gas before the bag filter (point B, temperature 190 ° C.). Nm ³ ) Sprayed. At this time, the hydrogen chloride concentration of the bag filter outlet exhaust gas was measured at a rate of 3 times / day in the latter stage of the bag filter to evaluate the acid gas removal ability (Example 1 in Table 1).

  In addition, to the fly ash collected at the time of spraying this drug, the phosphate heavy metal fixing agent shown in Table 2 was added in the addition amount shown in Table 2 (addition weight% as an active ingredient with respect to fly ash) and kneaded sufficiently. About the obtained treated ash, the elution amounts of Pb and Cd were measured by the Environmental Agency Notification No. 13 test, and the results are shown in Table 2.

  In Table 2, “fly ash 1”, “fly ash 2”, and “fly ash 3” are “fly ash collected during the first hydrogen chloride concentration measurement” and “second chlorination”, respectively. “Fly ash collected during measurement of hydrogen concentration” and “Fly ash collected during measurement of hydrogen chloride concentration for the third time” are shown.

  Moreover, in Table 2, the measurement result of the raw ash not containing the phosphate heavy metal fixing agent is also shown as a blank.

Example 2
In the same facility as in Example 1, the same mineral as used in Example 1 was mixed with magnesium oxide as a raw material and sodium bicarbonate similar to that used in Example 1 at a weight ratio of 1: 2. The body chemical was sprayed to the exhaust gas before the bag filter (point B) at 1.8 kg / h, and the acid gas removing ability and the effect of fixing heavy metals of fly ash were evaluated in the same manner as in Example 1. Table 1 and Table 2 show the results. This is shown in FIG.

Example 3
In the same facility as in Example 1, the powdered medicine in which the same mineral as used in Example 1 was blended with magnesium oxide and powdered activated carbon in a ratio of 3: 1 (weight ratio) was added to the exhaust gas before the bag filter ( B point) is sprayed with 0.8 kg / h (400 mg / Nm ³ ), and sodium hydrogen carbonate similar to that used in Example 1 is applied to the exhaust gas before the bag filter (point B) at 1.2 kg / h (600 mg / h). Nm ³ ) Sprayed. In the same manner as in Example 1, the acid gas removal ability and the heavy metal fixing effect of fly ash were evaluated, and the results are shown in Tables 1 and 4.

Comparative Example 1
In the same facility as in Example 1, 1.8 kg / h of JIS special slaked lime is sprayed onto the exhaust gas before the bag filter (point B) to evaluate the acid gas removal ability and the effect of fixing heavy metals in fly ash as in Example 1. The results are shown in Tables 1 and 5.

Comparative Example 2
In the same facility as in Example 1, sodium hydrogen carbonate (particle size d50 = 10 μm) was sprayed to the exhaust gas before the bag filter (point B) at 1.8 kg / h, and the acid gas removal ability and fly ash were the same as in Example 1. Table 1 and Table 6 show the results of evaluating the heavy metal fixing effect.

  The following can be understood from the results of Examples 1 to 3 and Comparative Examples 1 and 2.

[Effect of removing hydrogen chloride from exhaust gas]
As is apparent from Table 1, in Examples 1 and 2 sprayed with magnesium oxide and sodium hydrogen carbonate, the hydrogen chloride concentration level could be greatly reduced as compared with Comparative Example 1 sprayed with the same amount of slaked lime. . Moreover, the treatment effect was almost the same level as that of sodium bicarbonate added in the same amount.

[About heavy metal fixing effect of fly ash]
From Tables 2 to 4, the fly ash collected when sprayed with magnesium oxide and sodium bicarbonate (Examples 2 and 3) had a pH of 11.5 or less of the raw ash to which no phosphate heavy metal fixing agent was added. Therefore, the elution of lead and cadmium is small. In the fly ash 2 and fly ash 3 of Example 1, the fly ash 1 of Example 2, and the fly ash 2 of Example 3, the elution of lead is based on the landfill standard (lead: 0.1 mg / L or less, Elution of lead slightly exceeding cadmium (0.1 mg / L or less) was observed, but by adding a small amount of phosphate heavy metal fixative of about 2% and kneading, sufficient elution of lead Can be prevented.

  Compared with Examples 1 to 3, in Comparative Example 1 shown in Table 5, since fly ash contains slaked lime, the pH of fly ash exceeds 12, and the phosphate heavy metal fixing agent is slaked lime in fly ash. In order to prevent elution of fly ash, it is necessary to add a phosphoric acid heavy metal fixing agent in an amount exceeding 10%.

  In Comparative Example 2 shown in Table 6, heavy metals can be fixed with a small amount of a phosphoric acid heavy metal fixing agent, but when the pH is 9 or less as in fly ash 2, Cd is eluted. In this case, elution of Cd cannot be prevented with acidic agents such as normal phosphoric acid having a pH of fly ash and normal phosphoric acid containing 10% sodium hydroxide. Treatment with 30% potassium hydroxide-containing normal phosphoric acid is possible, but a large amount of addition is required.

  As described above, hydrogen chloride can be stably removed by the method of adding magnesium oxide and sodium hydrogen carbonate, and reliable heavy metal fixation can be achieved by using a small amount of a phosphoric acid heavy metal fixing agent.

It is a schematic diagram of the incineration facility explaining the embodiment of the method for treating exhaust gas and fly ash in the incineration facility of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Incinerator 2 Gas cooling tower 3 Bag filter 4 Chimney 5 Silo 6 Kneading machine

Claims (7)

  A process of treating acidic components in the exhaust gas by spraying magnesium-based alkaline agent and sodium hydrogen carbonate as an acid gas treating agent on the exhaust gas generated from the combustion facility, and pH 9 to 11.5 in the fly ash collected from the exhaust gas A process for treating exhaust gas and fly ash in an incineration facility, comprising the step of fixing a heavy metal in the fly ash by adding a phosphoric acid heavy metal fixing agent under the above conditions.   The method for treating exhaust gas and fly ash in an incineration facility according to claim 1, wherein the magnesium-based alkaline agent is magnesium oxide and / or magnesium hydroxide.   The method for treating exhaust gas and fly ash in an incineration facility according to claim 2, wherein the magnesium oxide and / or magnesium hydroxide is made from ore.   The incineration facility according to any one of claims 1 to 3, wherein the phosphate heavy metal fixing agent is an aqueous solution in which normal phosphoric acid and an alkaline agent are blended, and the pH of the aqueous solution is 3 or more. Waste gas and fly ash treatment method.   5. The method for treating exhaust gas and fly ash in an incineration facility according to claim 4, wherein the alkaline agent is sodium hydroxide and / or potassium hydroxide.   6. A method for treating exhaust gas and fly ash in an incineration facility according to claim 1, wherein the exhaust gas is sprayed with a chemical containing a magnesium-based alkaline agent and sodium hydrogen carbonate as the acidic gas treating agent. .   The method for treating exhaust gas and fly ash in an incineration facility according to any one of claims 1 to 6, wherein the acidic gas treating agent contains activated carbon.

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