TW202239461A - Combustion exhaust gas treatment method and combustion exhaust gas treatment apparatus - Google Patents

Abstract

This combustion exhaust gas treatment method comprises: a dry-mode treatment step for adding an alkali agent to an untreated combustion exhaust gas containing an acidic gas to neutralize the acidic gas, thereby producing an alkali-treated combustion exhaust gas; a dust collection step for supplying the alkali-treated combustion exhaust gas to a dust collector to collect fly ash; and a heavy metal fixation step for discharging the fly ash from the dust collector and adding a heavy metal fixing agent to the fly ash to fix a heavy metal in the fly ash. In the method, the concentration of the acidic gas in the untreated combustion exhaust gas is measured, the amount of the alkali agent to be added to the untreated combustion exhaust gas is calculated on the basis of a measurement value of the concentration of the acidic gas, and the alkali agent is added in the calculated amount, and the concentration of the unreacted alkali agent in the fly ash discharged from the dust collector is calculated, the amount of the heavy metal fixing agent to be added to the fly ash is calculated on the basis of a calculation value of the concentration of the unreacted alkali agent, and the heavy metal fixing agent is added in the calculated amount.

Description

Combustion exhaust treatment method and combustion exhaust treatment device

The present invention relates to a combustion exhaust gas including harmful acid gases such as hydrogen chloride and sulfur oxides generated from combustion facilities such as urban waste incinerators, industrial waste incinerators, power generation boilers, carbonization furnaces, and private factories. The treatment method and the treatment device of combustion exhaust gas.

Since the combustion exhaust gas discharged from waste incinerators such as municipal garbage or industrial waste, thermal power plants and other combustion facilities contains carbon dioxide or water vapor, oxygen, nitrogen, hydrogen chloride, sulfur oxides (SO _x ), nitrogen oxides ( NO _x ), heavy metal compounds, and coal ash, so from the viewpoint of preventing air pollution, it is necessary to remove these substances before releasing them into the atmosphere. Combustion exhaust containing harmful hydrogen chloride or sulfur oxides As described in Patent Document 1, the combustion exhaust is usually sprayed with an alkali agent such as slaked lime (calcium hydroxide) near the dust collector of the incinerator to oxidize hydrogen chloride and sulfur After neutralizing the acid gas such as dust, use a dust collector such as a filter bag to remove dust, and discharge it from the chimney. On the other hand, the fly ash collected by the dust collector contains harmful heavy metals such as lead and cadmium, and these harmful heavy metals are stabilized before landfill disposal.

As an efficient neutralization treatment method for acid gas, for example, Patent Document 2 proposes a method of using calcium hydroxide having a specific specific surface area and apparent density based on the concentration of hydrogen chloride and sulfur oxides in the combustion exhaust near the dust collector, or Patent Document 3 proposes a method of adjusting the supply amount of the alkali agent based on the gas analysis measurement results on either or both sides of the upstream side or the downstream side of the dust collecting mechanism.

On the other hand, as a treatment method for heavy metals in fly ash that has been dedusted by a dust collector, in addition to using chelate-based heavy metals such as piperazine dithiocarbamate, diethyldithiocarbamate, etc. In addition to the method of insolubilizing the chemical agent, from the viewpoint of preventing the re-elution of heavy metals in the final disposal site, in recent years, as in Patent Document 4, a method using hydroxyapatite that changes heavy metals into inorganic minerals has been disclosed. Phosphoric acid and other phosphoric acid compounds are used as heavy metal fixatives. In addition, the following methods are known: a method of adding acid neutralizers such as hydrochloric acid and aluminum sulfate; In the case of elution of heavy metals such as mercury, it is a method to prevent the elution of these heavy metals by adding iron-containing compounds such as ferrous chloride and polyferric sulfate. [Prior art literature] [Patent Document]

Patent Document 1: Japanese Patent Laid-Open No. 9-99215 Patent Document 2: Japanese Patent No. 4194001 Patent Document 3: Japanese Patent Laid-Open No. 2002-361040 Patent Document 4: Japanese Patent Application Publication No. 4-61710

[Problem to be Solved by the Invention] Since the method of neutralizing the acid gas in the combustion exhaust gas with the alkaline agent is the reaction of the gaseous acid gas and the solid alkaline agent, the reaction efficiency is poor. Therefore, in order to neutralize the acid gas, an alkaline agent more than the neutralization reaction equivalent is added to the combustion exhaust gas as the regulations on the acid gas are strengthened. Therefore, after the neutralization process, the fly ash collected by the dust collector contains unreacted alkali components. In the case of heavy metal treatment of the fly ash with a heavy metal fixative, in order to optimize the effect of the heavy metal treatment, it is necessary to analyze the concentration of the alkali component in the fly ash, and calculate the heavy metal fixative according to the concentration of the alkali component. and add the required amount of heavy metal fixative to the fly ash. However, in the case of analyzing the concentration of the alkali component in the fly ash as described above, the analysis takes time and effort, and the analysis needs to be performed at an analysis frequency matching the change of the fly ash, and it is not suitable for real-time fly ash. deal with.

The present invention is completed in view of the above actual situation, and its purpose is to provide a treatment method of combustion exhaust gas and a treatment device of combustion exhaust gas, which can immediately grasp the concentration of alkali components in fly ash without analyzing The concentration of unreacted alkali components in fly ash can be safely and easily processed with higher precision. [Means to solve the problem]

As a result of intensive research by the inventors of the present invention, it was found that the concentration of unreacted alkali agent in the fly ash was calculated by calculation based on the measurement result of the acid gas concentration before the dry treatment of the combustion exhaust gas. , so that it is not necessary to analyze the concentration of the alkali component in the fly ash, the concentration of the unreacted alkali agent in the fly ash can be grasped in real time, and the heavy metal treatment of the fly ash can be performed with higher precision. That is, the present invention provides the following [1] to [11]. [1] A method for treating combustion exhaust gas, comprising: a dry treatment step of adding an alkali agent to untreated combustion exhaust gas containing acid gas, neutralizing the acid gas, and obtaining alkali-treated combustion exhaust gas. exhaust; a dust collecting step of supplying the alkali-treated combustion exhaust gas to a dust collector to collect fly ash; and a heavy metal fixation step, discharging the fly ash from the dust collector, adding a heavy metal fixative to the fly ash to fix the heavy metal in the fly ash, measuring the concentration of said acid gases in said untreated combustion exhaust, Based on the measured value of the concentration of the acid gas, the amount of the alkali agent to be added to the untreated combustion exhaust gas is calculated and added, and the unreacted alkali agent in the fly ash discharged from the dust collector is calculated. concentration, Based on the calculated value of the concentration of the unreacted alkali agent, the amount of the heavy metal fixing agent to be added to the fly ash is calculated and added. [2] The method for treating combustion exhaust as described in [1], wherein the heavy metal immobilization step includes: a storage step of storing the fly ash discharged from the dust collector in a storage bin; and a kneading step, The fly ash in the storage bin is extracted and supplied to a mixer, and the heavy metal fixing agent is added to the fly ash in the mixer to fix the heavy metal in the fly ash. [3] The combustion exhaust gas treatment method according to [2] above, wherein the gas supplied from the dust collector to the storage unit calculated based on the measured value of the acid gas concentration in the untreated combustion exhaust gas is memorized. time-lapse data on the concentration of unreacted alkaline agent in the fly ash in the silo, Based on the time-lapse data and the supply flow rate when the fly ash is extracted from the storage bin and supplied to the kneader, the concentration of unreacted alkali agent in the fly ash supplied to the kneader and processed is calculated. changes over time, Based on the change over time, the addition amount of the heavy metal fixing agent is controlled over time to fix the heavy metal in the fly ash. [4] The method for treating combustion exhaust gas according to [2] or [3] above, wherein in the kneading step, an acid neutralizer is further added to the kneader. [5] The method for treating combustion exhaust as described in any one of [1] to [4] above, wherein the acid gas concentration in the combustion exhaust before the dry treatment is measured, and based on the As a measured value, in the dry processing step, an alkali agent is added so as to be 1 equivalent to 3 equivalents with respect to the acid gas concentration. [6] The method for treating combustion exhaust gas according to any one of [1] to [5], wherein the acid gas contains hydrogen chloride and sulfur oxides, and the total concentration of the hydrogen chloride and sulfur oxides is measured amount as acid gas concentration. [7] The method for treating combustion exhaust gas according to any one of [1] to [6] above, wherein the alkali agent contains at least one kind of alkali salt of an alkali metal or an alkaline earth metal. [8] The method for treating combustion exhaust gas according to any one of [1] to [7], wherein the heavy metal fixing agent is an inorganic heavy metal fixing agent.

[9] A treatment device for combustion exhaust, comprising: a dry treatment device for adding an alkali agent to untreated combustion exhaust containing acid gas to neutralize the acid gas to obtain alkali-treated combustion exhaust gas; a dust collector connected to the dry processing device to collect the fly ash in the alkali-treated combustion exhaust; A heavy metal fixing device, connected to the dust collector, adding a heavy metal fixing agent to the fly ash to fix the heavy metal in the fly ash; a measuring device for measuring the concentration of the acid gas in the untreated combustion exhaust; The calculation device has: an alkali agent addition amount calculation unit for calculating the addition amount of the alkali agent added to the untreated combustion exhaust gas based on the measured value of the acid gas concentration; calculating the concentration of the unreacted alkali agent a part that calculates the concentration of unreacted alkali agent in the fly ash discharged from the dust collector; added amount; an alkali agent addition device for adding the alkali agent to the untreated combustion exhaust gas in the dry processing device based on the calculated value of the addition amount of the alkali agent calculated by the calculation device; and The adding device of the heavy metal fixing agent adds the heavy metal fixing agent based on the calculated value of the addition amount of the heavy metal fixing agent to the fly ash. [10] The treatment device for combustion exhaust as described in [9], wherein the heavy metal fixing device has: a storage bin, connected to the dust collector, for storing the fly ash discharged from the dust collector; a mixing machine connected to the storage bin; a supply device for extracting the fly ash in the storage bin and supplying it to the kneader; and A device for adding a heavy metal fixing agent, adding the heavy metal fixing agent to the mixer. [11] The combustion exhaust gas treatment device as described in [10] above, comprising: a computing device including a memory unit for storing a value calculated based on the measured value of the acid gas concentration in the untreated combustion exhaust gas; The time-lapse data of the concentration of unreacted alkali agent in the fly ash supplied from the dust collector to the storage bin; The supply flow rate during the kneading machine is used to calculate the time-dependent change in the unreacted alkali agent concentration in the fly ash supplied to the kneader and processed; and the calculation unit is based on the time-dependent change in the unreacted alkali agent concentration, Calculate the addition amount of the heavy metal fixative to the fly ash; and The adding device of the heavy metal fixing agent adds the heavy metal fixing agent based on the calculated value of the addition amount of the heavy metal fixing agent to the fly ash. [Effect of the invention]

According to the combustion exhaust gas treatment method and treatment device of the present invention, without analyzing the concentration of alkali components in fly ash, the concentration of unreacted alkali components in fly ash can be grasped in real time, and the Safe and easy heavy metal handling of fly ash with precision.

[How to deal with combustion exhaust] The method for treating combustion exhaust gas of the present invention has: a dry treatment step, adding an alkali agent to the untreated combustion exhaust gas containing acid gas, neutralizing the acid gas, and obtaining alkali-treated combustion exhaust gas ; dust collection step, the combustion exhaust gas that has been subjected to alkali treatment is supplied to a dust collector, and fly ash is collected; heavy metal fixing step, the fly ash is discharged from the dust collector, and a heavy metal fixative is added to the fly ash , and fix the heavy metals in the fly ash, The concentration of the acid gas in the untreated combustion exhaust gas is measured, and the addition of the alkali agent to be added to the untreated combustion exhaust gas is calculated based on the measured value of the concentration of the acid gas. and adding, and calculate the unreacted alkali agent concentration in the fly ash discharged from the dust collector, based on the calculated value of the unreacted alkali agent concentration, calculate the addition amount of the heavy metal fixing agent to the fly ash and Add to. Hereinafter, the method of treating combustion exhaust gas according to the present invention may be simply referred to as "the method of treating the present invention". According to the treatment method of the present invention, by measuring the concentration of the acid gas before the dry treatment of the combustion exhaust gas, and based on the measurement result, the concentration of the non-reversed alkali agent in the fly ash is calculated by calculation, thereby eliminating the need to treat the fly ash In the case of analyzing the concentration of alkali components in the fly ash, the concentration of unreacted slaked lime in the fly ash can be grasped in real time, and the heavy metal treatment of the fly ash can be performed with higher accuracy.

In the treatment method of the present invention, as the heavy metal immobilization step, it is suitable to have: a storage step, storing the fly ash discharged from the dust collector in a storage bin; and a mixing step, extracting the fly ash in the storage bin and The mixture is supplied to a kneader, and the heavy metal fixing agent is added to the fly ash in the kneader to fix the heavy metal in the fly ash. As mentioned above, by storing the fly ash in the storage bin and extracting the fly ash in the storage bin to carry out the heavy metal fixation treatment in the fly ash, the heavy metal fixation treatment can be stopped, or the fly ash in the storage bin can be stored to a certain extent before proceeding. Heavy metal immobilization treatment, or concentrate fly ash for heavy metal immobilization treatment at a faster speed than fly ash flows into the storage bin, or adjust the timing of heavy metal immobilization treatment.

In addition, in the treatment method of the present invention, it is preferable to memorize the unreacted alkali agent in the fly ash supplied from the dust collector to the storage bin calculated based on the measured value of the acid gas concentration in the untreated combustion exhaust gas. Concentration over time data, based on the time-lapse data and the supply flow rate when the fly ash is extracted from the storage bin and supplied to the kneader, the concentration in the fly ash supplied to the kneader and processed is calculated. Based on the change over time of the concentration of the unreacted alkali agent, the addition amount of the heavy metal fixing agent is controlled over time based on the change over time, thereby fixing the heavy metal in the fly ash. In this way, even if the fly ash in the storage bin is stored to a certain extent, the heavy metal fixation treatment is carried out, or the fly ash is concentrated for heavy metal fixation treatment at a faster speed than the fly ash flowing into the storage bin, or the heavy metal fixation treatment is adjusted. In the case of timing, since an appropriate amount of heavy metal fixative can be added according to the time-dependent change of the unreacted alkali concentration in the fly ash extracted from the storage bin, it is not necessary to analyze the concentration of the alkali component in the fly ash. The concentration of unreacted slaked lime in the fly ash can be grasped in real time, and the heavy metal treatment of the fly ash can be performed with higher precision.

[Combustion Exhaust Treatment Device] FIG. 1 is a schematic view showing an embodiment of a combustion exhaust gas treatment device for carrying out the treatment method of the present invention. In the combustion exhaust gas treatment device 100 of FIG. 1 , the combustion exhaust gas including the acid gas generated by the incinerator 11 is cooled by the gas cooling tower 13 via the pipe 1, the boiler 12 utilizing the heat of the combustion exhaust gas, and the pipe 2, and It is introduced into the dust collector 14 via the flue 3 . The alkali agent is supplied from the alkali agent adding device 51 , and the combustion exhaust gas containing acid gas is mixed with the alkali agent in the middle of the flue 3 . Through the gas discharge passage 4 , the combustion exhaust gas treated with alkali is sucked out from the dust collector 14 by the exhaust fan 15 , and discharged from the chimney 16 . On the other hand, the fly ash collected in the storage bin 21 is discharged from the dust collector 14 through the fly ash discharge passage 5, and the fly ash in the storage bin 21 is extracted by the fly ash supply device 22, and is supplied to the kneader through the pipe 6. The fly ash is discharged into the ash pit 24 after the heavy metal fixing agent is supplied from the heavy metal fixing agent adding device 52 directly in front of the mixer 23 to the fly ash.

The combustion exhaust treatment device 100 of FIG. 1 according to the embodiment of the present invention further includes an acid gas concentration measuring device 30 installed in the flue 3 in order to process the acid gas in the combustion exhaust discharged from the incinerator 11, and The computing device 40 constitutes a dry processing device together with the alkali agent adding device 51 . Here, the acid gas concentration measuring device 30 includes a hydrogen chloride concentration measuring device 30a and a sulfur oxide concentration measuring device 30b. The hydrogen chloride concentration measuring device 30a continuously measures the hydrogen chloride concentration in the untreated combustion exhaust gas flowing through the flue 3, while the sulfur oxide concentration measuring device 30b measures the concentration of hydrogen chloride in the untreated combustion exhaust gas flowing in the flue 3. The sulfur oxide concentration is continuously measured, and output to the computing device 40 in the form of the hydrogen chloride concentration signal S1 from the hydrogen chloride concentration measuring device 30a and the sulfur oxide concentration signal S2 from the sulfur oxide concentration measuring device 30b. In addition, the form of the hydrogen chloride concentration measuring device 30a and the sulfur oxide concentration measuring device 30b is not limited as long as they are measuring devices capable of measuring the hydrogen chloride concentration and the sulfur oxide concentration respectively. The concentration of hydrogen chloride gas can be measured by ion electrode method, single absorption line absorption spectrometry using laser, etc., and the concentration of sulfur oxide gas can be measured by non-dispersive infrared absorption method, ultraviolet fluorescence method, etc.

The computing device 40 includes: an alkali agent addition amount calculation unit 41; an unreacted alkali agent concentration calculation unit 42, based on the alkali dose signal S4 including the total value of the hydrogen chloride concentration and the sulfur oxide concentration and the added alkali dose output from the calculation unit 41 , and the amount of fly ash produced, calculate the concentration of unreacted alkali agent in the fly ash; Addition amount of the heavy metal fixing agent to the kneader 23. Here, the fly ash includes the ash content from the incinerated waste and the alkaline agent added to the incinerated waste, and the amount of fly ash generated can be calculated as a constant value (approximately 3% by mass) relative to the amount of waste .

The alkali agent addition amount calculation unit 41 calculates the acid gas concentration for neutralizing the acidity in the combustion exhaust gas based on the measured value of the acid gas concentration which is the total value of the hydrogen chloride concentration and the sulfur oxide concentration based on the hydrogen chloride concentration signal S1 and the sulfur oxide concentration signal S2. The amount of alkali agent added per unit time that should be added for gas is output in the form of alkali agent addition signal S3. The alkali agent addition device 51 is a device for adding an alkali agent to the untreated combustion exhaust gas flowing through the flue 3 based on the alkali agent addition signal S3.

The unreacted alkali agent concentration calculation unit 42 includes: a calculation unit, based on the signal S4 calculated by the alkali agent addition amount calculation unit 41, calculates the unreacted alkali agent concentration in the fly ash discharged from the dust collector 14 and supplied to the storage bin 21 The memory unit memorizes the concentration of the unreacted alkali agent; and the calculation unit calculates the supply flow to the mixer 23 based on the concentration of the unreacted alkali agent and the supply flow rate when the fly ash is extracted from the storage bin 21 and supplied to the mixer 23. And the concentration of unreacted alkaline agent in the fly ash being treated. In the unreacted alkali agent concentration calculation unit 42, the unreacted alkali agent concentration in the fly ash supplied to the storage bin 21 is preferably stored in the memory unit as time-lapse data of the unreacted alkali agent concentration. In addition, the concentration of unreacted alkali agent in the fly ash supplied to the kneader 23 and processed is suitably calculated as the amount of change over time of the concentration of unreacted alkali agent.

The heavy metal fixing agent addition amount calculation unit 43 calculates the addition amount of the heavy metal fixing agent to be added to the fly ash based on the signal S5 including the calculated value of the unreacted alkali agent concentration in the fly ash supplied to the mixer 23 and processed. . The heavy metal fixing agent addition calculation unit 43 preferably calculates the addition amount of the heavy metal fixing agent to be added to the fly ash based on the signal S5 based on the concentration of the unreacted alkali agent in the fly ash supplied to the storage bin 21. Time-lapse data and the supply flow rate when the fly ash is extracted from the storage bin 21 and supplied to the mixer 23, including the calculated value of the change over time of the unreacted alkali agent concentration in the fly ash supplied to the mixer 23 and processed . Furthermore, it is appropriate to use the time-lapse data of the concentration of the unreacted alkali agent, the amount of fly ash produced per unit time (that is, the amount of fly ash stored in the storage bin), the capacity of the storage bin, and the supply flow rate (per unit time Fly ash processing capacity of the mixing machine), based on the time-lapse data of the concentration of the unreacted alkali agent, and also considering the fly ash processing capacity and operating conditions of the heavy metal fixing device, calculate the amount of heavy metal fixing agent that should be added to the fly ash Add amount.

The heavy metal fixing device in the combustion exhaust gas treatment device of the embodiment of the present invention includes the storage bin 21, the fly ash supply device 22, the mixer 23, the computing device 40, and supplies the heavy metal fixing device directly in front of the mixer 23. The heavy metal fixing agent adding device 52 of the agent. The heavy metal fixing agent adding device 52 is a device that adds a heavy metal fixing agent to the fly ash right in front of the mixer 23 based on the heavy metal fixing agent addition signal S6 from the heavy metal fixing agent addition amount calculation unit 43 constituting the computing device 40 .

[Dry treatment step] In the treatment method of the present invention, firstly, a dry treatment step is performed, that is, an alkali agent is added to the untreated combustion exhaust gas containing acid gas to neutralize the acid gas to obtain the alkali-treated combustion exhaust. The combustion exhaust gas to which the treatment method of the present invention can be applied is not particularly limited. For example, combustion exhaust gas containing acid gases such as hydrogen chloride, sulfur oxides, and nitrogen oxides generated in combustion facilities such as municipal waste incinerators, industrial waste incinerators, power generation boilers, carbonization furnaces, and private factories can be cited. The alkaline agent for removing acid gas in the combustion exhaust gas preferably contains at least one alkaline salt of an alkali metal or an alkaline earth metal. Examples of the alkaline agent include slaked lime (calcium hydroxide), sodium hydroxide, potassium hydroxide, magnesium hydroxide, sodium bicarbonate, sodium carbonate, calcium carbonate, calcium oxide, dolomite hydroxide [Ca(OH) ₂ -Mg(OH) ₂ ], or a mixture of these.

From the viewpoint of ensuring reactivity with acid gases such as hydrogen chloride and sulfur oxides, and avoiding a reduction in collection efficiency or an increase in differential pressure in the dust collector, the alkali agent preferably has a specific surface area of 20 m ² /g or more, a medium The compound is in powder form with a diameter (d50) of 5 μm to 30 μm. These alkaline agents can be formulated into other components within the range that does not hinder the effect of the present invention, such as activated carbon for treating combustion exhaust gas with dioxin, or diatomaceous earth used as a filter aid for filter bags.

The alkali agent is preferably added from the incinerator body to the dust collector, near the dust collector such as a filter bag after the combustion exhaust gas is cooled by a cooling tower and the acid gas concentration is measured. The method of adding alkali agent in the combustion exhaust is not particularly limited, for example, the alkali agent loaded into the chemical storage tank of the alkali agent adding device 51 is blown to the combustion exhaust gas of the flue 3 from the nozzle provided in the flue 3 . The alkali agent may be used in the form of powder, or may be used in the form of a dispersion liquid by dispersing the powder of the alkali agent in a dispersion medium in which the alkali agent does not dissolve, such as ethanol or isopropanol. The alkaline agent can be added intermittently or continuously. The temperature of the combustion exhaust gas when the alkali agent is added is not particularly limited. The temperature of the combustion exhaust directly in front of the dust collector is preferably 100°C to 300°C, more preferably 130°C to 230°C in terms of the reaction of the alkali agent with the acid gas in the dust collector.

In the treatment method of the present invention, the acid gas concentration in the untreated combustion exhaust gas is measured, preferably the total amount of the concentration of hydrogen chloride and sulfur oxide is used as the acid gas concentration, and based on the measured value of the acid gas concentration, The addition amount of the alkali agent to be added to the untreated combustion exhaust gas is calculated, and the alkali agent is added. It is excellent that the amount of the alkali agent added is an amount capable of reaching the treatment target value of the acid gas, and in such a manner that the concentration of the unreacted alkali agent in the fly ash discharged from the dust collector described below can be reduced, according to the amount of the acid gas (Hydrogen chloride and sulfur oxides) changes over time in the measured value of the concentration, and control it to a constant equivalent. More specifically, the amount of the alkali agent to be added is preferably 1 to 3 equivalents based on the measured values of the concentrations of acid gases in the combustion exhaust, especially hydrogen chloride and sulfur oxides, relative to the total concentration. The alkali agent is more preferably 1.5 to 2.5 equivalents. If the alkali agent is added in such an amount, it is easy to reduce the amount of the heavy metal fixing agent and reduce the amount of fly ash that is finally disposed of.

[Dust collection procedure] The treatment method of the present invention has a dust collection step of collecting fly ash in the alkali-treated combustion exhaust gas. The fly ash can be collected using a known dust collector such as a filter bag connected to the dry processing device. The dust collector is connected to a heavy metal fixing device that fixes heavy metals in the fly ash by adding a heavy metal fixing agent to the fly ash.

[Heavy metal fixing procedure] The treatment method of the present invention has a heavy metal fixing step of adding a heavy metal fixing agent to the fly ash collected in the dust collection step to fix the heavy metal in the fly ash. The treatment method of the present invention is characterized in that the alkali agent to be added to the untreated combustion exhaust gas is calculated based on the measured value of the concentration of the acid gas in the untreated combustion exhaust gas in the dry treatment step. and adding the added amount, and calculating the unreacted alkali agent concentration in the fly ash discharged from the dust collector, based on the calculated value of the unreacted alkali agent concentration, calculating the addition of the heavy metal fixing agent to the fly ash Measure and add. The amount of alkali agent added to the untreated combustion exhaust is calculated based on the measured value of the concentration of the acid gas in the untreated combustion exhaust, and the amount based on the concentration of the acid gas is subtracted from the added amount Calculate the unreacted alkali agent concentration in the fly ash discharged from the dust collector. That is, without analyzing the concentration of the alkali component in the fly ash, it is possible to perform fly ash treatment in real time with high accuracy, safely and simply.

Lead is a typical example of the heavy metal in the collected fly ash, and other examples include cadmium, chromium, arsenic, selenium, mercury, and the like. As heavy metal fixing agents, inorganic heavy metal fixing agents and chelate heavy metal fixing agents are known, and in the treatment method of the present invention, it is preferable to use inorganic heavy metal fixing agents. The heavy metal fixing agent may be used in a powder form, or may be used in a liquid form by dissolving or dispersing the powder in water or the like. Examples of the inorganic heavy metal fixing agent include phosphoric acid-based compounds, silica-based compounds, and iron-containing compounds.

Phosphoric acid-based compounds exhibit a long-term elution prevention effect of heavy metals in disposal sites, and are effective materials from the viewpoint of environmental protection. The phosphoric acid-based compound reacts with lead, which is a heavy metal, for example, to form phosphopyronite or phosphofenite, and fixes lead in a mineral form to prevent lead elution. As the phosphoric acid-based compound, as long as it contains phosphoric acid, it can be used without particular limitation, and may be a phosphate or a mineral. Examples of phosphoric acid-based compounds include orthophosphoric acid (orthophosphoric acid), polyphosphoric acid, metaphosphoric acid, hypophosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, superphosphoric acid, sodium dihydrogenphosphate, disodium hydrogenphosphate, triphosphate Sodium, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, calcium dihydrogen phosphate, dicalcium hydrogen phosphate, magnesium dihydrogen phosphate, dimagnesium hydrogen phosphate, first ammonium phosphate, diammonium hydrogen phosphate, superphosphate, Sodium tripolyphosphate, potassium tripolyphosphate, sodium hexametaphosphate, potassium hexametaphosphate, sodium pyrophosphate, potassium pyrophosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, potassium hypophosphite, etc. Among them, minerals in the form of orthophosphoric acid, dihydrogenphosphate, dihydrogenphosphate, triphosphate, tripolyphosphate, hexametaphosphate, pyrophosphate, hydroxyapatite, especially apatite (phosphorus Limestone compound) exhibits a good heavy metal elution prevention effect. Among heavy metals, phosphoric acid compounds are particularly useful for preventing the leaching of lead.

Compounds containing silica are considered to have the following effects: the calcium component in fly ash reacts with silica to form calcium silicate mineral (3CaO-2SiO ₂ -3H ₂ O), and heavy metals are enclosed in the mineral; and Silicon oxide directly acts on heavy metals to form insoluble heavy metal silicates (PbSiO ₃ , etc.), thereby preventing the dissolution of heavy metals. Compounds containing silicon dioxide are susceptible to the alkali content of the fly ash, and in the case of extremely high alkali contents in the fly ash, the required addition to form the reaction product increases. Therefore, by means of the treatment method of the present invention, the required addition amount can also be greatly reduced in the compound containing silicon dioxide.

The silicon dioxide-containing compound can be used without particular limitation as long as it is a compound containing a SiO ₂ component, and may be silicon dioxide itself, or may be a salt or a mineral. Compounds containing silicon dioxide include: sodium silicate, potassium silicate and other silicates containing alkali metals or alkaline earth metals, fumed silicon, silica gel, attapulgite, zeolite, bentonite, kaolin, and chalite, antigorite, biological Rock, talc, montmorillonite, saponite, vermiculite, muscovite, orange glass, illite, phlogopite, biotite, pearl mica, green brittle mica, splenite, aluminochlorite, clinochlorite Oolitic chlorite, sepiolite, palygorskite, filiform allophane, allophane and black silica and other silicate minerals. Among heavy metals, compounds containing silicon dioxide are particularly useful for preventing the elution of lead.

As an iron-containing compound, what is necessary is just to contain iron, and ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, polyferric sulfate, iron powder, etc. are mentioned. Among heavy metals, iron-containing compounds are particularly useful for preventing the dissolution of hexavalent chromium, arsenic, selenium, and mercury.

An acidic neutralizing agent may be added to the inorganic heavy metal fixing agent and used in the treatment method of the present invention. The acid neutralizing agent has the effect of reducing the elution amount of heavy metals. Therefore, from the viewpoint of further suppressing the elution of heavy metals, it is preferable to further add an acid neutralizing agent to the inorganic heavy metal fixing agent, that is, to use both together. The acid neutralizer will also be affected by the residual alkali content in the fly ash. When the alkali content in the residual fly ash is extremely high, the required addition amount will increase. Therefore, with the present invention, the required addition amount of the acid neutralizer can also be greatly reduced. Examples of the acid neutralizer include hydrochloric acid, sulfuric acid, nitric acid, aluminum chloride, polyaluminum chloride, aluminum sulfate, ferric sulfate, and ferric chloride. When the inorganic heavy metal fixing agent and the acid neutralizing agent are used together, it is preferable in that the usage-amount of an expensive inorganic heavy metal fixing agent can be reduced.

The heavy metal immobilization step suitably includes: a storage step of storing the fly ash discharged from the dust collector in a storage bin; The heavy metal fixing agent is added to the fly ash in the machine to fix the heavy metal in the fly ash. In the treatment method of the present invention, it is preferable to memorize the unreacted alkaline agent concentration in the fly ash supplied from the dust collector to the storage bin calculated based on the measured value of the acid gas concentration in the untreated combustion exhaust gas. Based on the time-lapse data and the supply flow rate when the fly ash is extracted from the storage bin and supplied to the kneader, the unreacted amount in the fly ash supplied to the kneader and processed is calculated. Based on the change over time of the alkali agent concentration, the addition amount of the heavy metal fixing agent is controlled over time based on the change over time, thereby fixing the heavy metal in the fly ash.

The method of adding the heavy metal fixative to the fly ash is not limited, and the components in the liquid state can also be mixed and added to the water as described below. When further adding an acidic neutralizer to the inorganic heavy metal fixing agent, both may be mixed and added to water. In addition, a quantitative supply device may be installed at the fly ash inlet of the kneading device, and the components in a powder state may be injected together with the fly ash. As the kneader, known kneaders such as a biaxial table top kneader mixer, a disk granulator mixer, and a vibration mixer can be used. The fly ash handling capacity per unit time of the kneader is usually designed to be greater than the fly ash production, so the state of operation and stop can be controlled according to the amount of fly ash generated from the continuously operating incinerator stored in the storage bin.

Preferably, heavy metal fixative and water are added to the kneader. In addition to the function of dissolving the heavy metal fixing agent, water also has the following functions: making mixing easier, making the heavy metal fixing agent evenly spread throughout the fly ash, and reacting with calcium chloride or calcium oxide in the fly ash exhibit heat of hydration. The amount of water added is preferably 5 to 40 parts by mass, more preferably 10 to 30 parts by mass, relative to 100 parts by mass of fly ash. If it is set at 5 parts by mass or more, the above-mentioned effects are easily exhibited, and if it is set at 40 parts by mass or less, it is possible to prevent the fly ash from becoming muddy or increasing its weight, resulting in reduced handling properties, and it is also possible to prevent excessive water absorption. The heat of hydration hinders the temperature rise.

As described above, the amount of unreacted alkali agent in the collected and discharged fly ash was calculated based on the measured value of the acid gas (hydrogen chloride and sulfur oxide) concentration in the untreated combustion exhaust, and based on the unreacted alkali The calculated value of the concentration of the heavy metal fixative can be used to calculate the amount of the heavy metal fixative added to the fly ash, thereby reducing the amount of heavy metal fixative used, reducing the amount of fly ash discharged to the final disposal site, and prolonging the use of the final disposal site period.

[Example of Calculation Method of Adding Amount of Heavy Metal Fixing Agent] First, based on the measured value of the acid gas concentration, calculate and add the amount of alkali agent to be added to the untreated combustion exhaust gas, and at the same time calculate the amount of alkali agent discharged from the dust collector Concentration of unreacted alkaline agent in ash. For example, the amount of hydrogen chloride in the untreated combustion exhaust gas is A mol/m ³ , and the amount of sulfur oxides is B mol/m ³ , and the sum of these is measured as the acid gas concentration, and the acid gas is completely neutralized. In the same way, when slaked lime equivalent to 3 times the acid gas is added as the alkali agent, the amount of alkali agent added to the combustion exhaust gas is 3×(1/2A+B) mol/m ³ , and, among them, there is no The amount of reaction alkali agent is 2×(1/2A+B) mol/m ³ . Furthermore, when the amount of coal ash in the combustion exhaust gas is C kg/m ³ , the unreacted alkali agent concentration X [molar /kg-fly ash] can be calculated by the following. X={2×(1/2A+B)}/{C+2×(1/2A+B)}[mol/kg-fly ash] Furthermore, the amount of acid gas in the untreated combustion exhaust depends on the upstream combustion facilities The operating conditions of the dust collector change, so the unreacted alkali agent concentration X [mol/kg-fly ash] in the fly ash discharged from the dust collector also changes over time.

Then, the time-lapse data of the unreacted alkali agent concentration in the fly ash supplied from the dust collector to the storage bin calculated based on the measured value of the acid gas concentration in the untreated combustion exhaust gas is memorized. For example, supply the fly ash with the unreacted alkali agent concentration of X [mol/kg-fly ash] obtained in the above manner to the storage bin, and memorize the time-lapse data of the unreacted alkali agent concentration in the supplied fly ash .

Then, based on the time-lapse data α of the concentration of unreacted alkali agent in the fly ash supplied from the dust collector to the storage bin and the supply flow rate when the fly ash is extracted from the storage bin and supplied to the kneader , the time-dependent change β of the unreacted alkali agent concentration in the fly ash supplied to the kneader and processed was calculated. For example, when the flow rate of the fly ash extracted from the storage bin is Y times the flow rate of the fly ash supplied to the storage bin, the concentration of the unreacted alkali agent in the fly ash supplied to the mixer and processed The change β is Y times the time-lapse data α of the unreacted alkali agent concentration in the fly ash supplied from the dust collector to the storage bin. As described above, even when the flow rate of the fly ash extracted from the storage bin is Y times the flow rate of the fly ash supplied to the storage bin, since the unreacted alkali in the fly ash supplied to the kneader and processed is grasped The time-dependent change β of the agent concentration, and according to the time-dependent change β, an appropriate amount of the heavy metal fixing agent can be added to the fly ash supplied to the mixer, so it is possible to add an appropriate amount of the heavy metal fixing agent to the fly ash over time. In fly ash.

For example, assume as follows. Fly ash generation (feed flow of fly ash to the storage bin): G _FA kg/hr (regular generation) Fly ash handling capacity of the mixer: M _FA kg/hr Low level to high level of the level sensor of the storage bin Capacity: V kg Also, assume that the following steps are repeated: stop the mixer (stop step) before the level of the storage bin reaches a high level from a low level, and after the level of the storage bin reaches a high level, extract fly ash from the storage bin and supply To the mixer, fly ash processing starts, and if the level returns to a low level, fly ash processing is stopped (fly ash processing step). In this case, the time T _S (hr) required for the stop step is expressed by the following formula. T _S (hr)=V/G _FA Also, the time T _M (hr) required for the fly ash treatment step is expressed by the following formula. T _M (hr) = V/(M _FA - G _FA ) In other words, T _S is also the time from the end of the fly ash treatment in the mixer to the start (the time when the mixer is stopped), and T _M is also It is the time required from the start of the fly ash treatment in the mixer to the end (the time when the mixer is running). Here, if the total of one stop step and one fly ash processing step is set as one interval, the time required for one interval is T _S + _TM (hr). Also, the fly ash stored in the storage bin during the interval ( _TS + _TM (hr)) is processed by the kneader for _TM (hr) time. That is, it takes T _S +T _M (hr) to store fly ash in the storage bin (fly ash produced between T _S and T _M ) to be processed by the mixer for _TM (hr) time. That is, the time for processing the fly ash by the kneader becomes _TM /(T _S + _TM ) of the time for storing the fly ash in the storage bin. Also, the analysis of the processing time _TM (hr) of the kneader is as follows. Processing time for fly ash generated between stop steps: T _M ×{T _M /(T _S +T _M )} Processing time for fly ash generated between fly ash processing steps: T _M ×{T _S /(T _S +T _M )} In other words, the time-lapse data α of the concentration of unreacted alkali agent in the fly ash supplied from the dust collector to the storage bin memorized in the above manner is compressed into T _M /(T _S +T _M ) times, and can be used to control the amount of weight fixative added to the fly ash supplied to the mixer. [Example]

Next, the present invention will be described in further detail by way of examples, but the present invention is not limited by these examples.

[Example 1] In a fully continuous incinerator (processing capacity 160 t/day), hydrogen chloride was installed in the flue before adding slaked lime (specific surface area 45m ² /g, median diameter (d50) 10 μm) as an alkali agent Measuring equipment (manufactured by Kyoto Electronics Industry Co., Ltd., HL-22) and sulfur oxide concentration measuring equipment (Horiba Manufacturing Co., Ltd., PG-337) to measure the concentration of hydrogen chloride and sulfur oxide in the untreated combustion exhaust gas, and record the measurement Values are taken as 30-min moving average concentrations. The temporal changes of the hydrogen chloride concentration and the sulfur oxide concentration within 24 hours are shown in FIG. 2 .

The total of the recorded hydrogen chloride concentration and sulfur oxide concentration was used as the acid gas concentration, and the amount of slaked lime added was calculated so as to be 3 equivalents of the acid gas concentration, and slaked lime was added to the flue near the filter bag as a dust collector. Here, the combustion exhaust temperature near the filter bag is 170°C, and the amount of fly ash generated (G _FA ) is 200 kg/h. The generated fly ash is collected by filter bags and discharged to a storage bin with a storage capacity (V) of 3600 kg. The time-lapse data of the unreacted hydrated lime concentration in the fly ash was calculated based on the added amount of the slaked lime and the measured value of the acid gas concentration in the untreated combustion exhaust gas. The temporal change of the unreacted slaked lime concentration in the fly ash is shown in FIG. 3 .

Then, the fly ash in the storage bin was extracted, and the fly ash was supplied to a mixer with a fly ash processing capacity (M _FA ) of 800 kg/h, and a heavy metal fixative (Kurita Industries Co., Ltd.) was added near the mixer Manufactured, trade name "Ashnite R303", phosphoric acid (acidic) compound) and water (the amount of water added to 100 parts by mass of fly ash: 20 parts by mass). The addition amount of the heavy metal fixing agent to the kneader was calculated as follows, and the heavy metal fixing agent adding device was controlled.

First, according to the amount of fly ash generated G _FA , the storage capacity V of the storage bin, and the fly ash processing capacity M _FA of the mixer per unit time, the time for storing the fly ash in the storage bin to the capacity V, that is, the mixing time is determined. The time from the end of the fly ash treatment in the refinery to the start (T _S ). On the other hand, the time (T _M ) required from the start to the end of the fly ash treatment in the mixer is determined. Next, after the heavy metal fixation step of the fly ash of the kneader starts, the time-lapse data of the unreacted slaked lime concentration in the fly ash between _TS and _TM is output, and using the time-lapse data, the unreacted slaked lime in the fly ash is The concentration of the reacted _slaked lime is processed in the form of time conversion of TS ( _TM / ( _TS + _TM )) and _TM ( _TM / ( _TS + _TM )), converted into the added amount of heavy metal fixative and calculated, And continuously control the amount of heavy metal fixative added to the mixer. Furthermore, the fly ash stored in the storage bin is naturally accumulated in the storage bin without stirring, and the added amount of the heavy metal fixing agent is calculated assuming that there is a concentration distribution along the vertical direction.

FIG. 4 shows the change over time of the concentration of unreacted slaked lime in the fly ash and the change over time of the amount of the heavy metal fixing agent added to the kneader. In addition, Fig. 5 shows that in the heavy metal immobilization step, the time-dependent change of the unreacted hydrated lime concentration in the fly ash accumulated in the storage bin is converted into the fly ash discharged from the storage bin to the mixer by compressing the time axis. The concept map calculated by converting the concentration of unreacted slaked lime into the added amount of heavy metal fixative.

1, 2, 6: Piping 3: flue 4: Gas discharge path 5: Fly ash discharge path 11: Incinerator 12: Boiler 13: Gas cooling tower 14: Dust collector 15: Exhaust fan 16: chimney 21: storage bin 22: Fly ash supply device 23: Kneader 24: Ash Pit 30: Acid gas concentration detector 30a: hydrogen chloride concentration detector 30b: Sulfur oxide concentration detector 40: computing device 41: Alkali agent addition amount calculation department 42: Unreacted alkali agent concentration calculation unit 43: Heavy Metal Fixative Addition Calculation Department 51: Alkali agent adding device 52: Heavy metal fixative adding device 100: Combustion exhaust treatment device S1: Hydrogen chloride concentration signal S2: Sulfur oxide concentration signal S3: Alkaline agent addition signal S4: Alkali dose signal S5: Unreacted alkali agent concentration signal S6: Heavy metal fixative addition signal

FIG. 1 is a schematic diagram showing an embodiment of a combustion exhaust gas treatment method and a combustion exhaust gas treatment apparatus according to the present invention. Fig. 2 is a graph showing changes over time in the concentration of hydrogen chloride and the concentration of sulfur oxides in untreated combustion exhaust near the dust collector. Fig. 3 is a graph showing changes over time in the concentration of unreacted slaked lime in fly ash. 4 is a graph showing changes over time of the concentration of unreacted slaked lime in fly ash added to the kneader and changes over time of the amount of heavy metal fixing agent added to the kneader. 5 is a conceptual diagram calculated by converting the time-dependent change in the concentration of unreacted slaked lime in the fly ash accumulated in the storage bin into the added amount of the heavy metal fixing agent in the heavy metal fixing step.

1, 2, 6: Piping

3: flue

4: Gas discharge path

5: Fly ash discharge path

11: Incinerator

12: Boiler

13: Gas cooling tower

14: Dust collector

15: Exhaust fan

16: chimney

21: storage bin

22: Fly ash supply device

23: Kneader

24: Ash Pit

30: Acid gas concentration detector

30a: hydrogen chloride concentration detector

30b: Sulfur oxide concentration detector

40: computing device

41: Alkali agent addition amount calculation department

42: Unreacted alkali agent concentration calculation unit

43: Heavy Metal Fixative Addition Calculation Department

51: Alkali agent adding device

52: Heavy metal fixative adding device

100: Combustion exhaust treatment device

S1: Hydrogen chloride concentration signal

S2: Sulfur oxide concentration signal

S3: Alkaline agent addition signal

S4: Alkali dose signal

S5: Unreacted alkali agent concentration signal

S6: Heavy metal fixative addition signal

Claims (11)

A method for treating combustion exhaust, comprising: A dry treatment step, adding an alkali agent to the untreated combustion exhaust gas containing acid gas, neutralizing the acid gas, and obtaining alkali-treated combustion exhaust gas; a dust collecting step of supplying the alkali-treated combustion exhaust gas to a dust collector to collect fly ash; and a heavy metal fixation step, discharging the fly ash from the dust collector, adding a heavy metal fixative to the fly ash to fix the heavy metal in the fly ash, measuring the concentration of said acid gases in said untreated combustion exhaust, Based on the measured value of the concentration of the acid gas, the amount of the alkali agent to be added to the untreated combustion exhaust gas is calculated and added, and the unreacted alkali agent in the fly ash discharged from the dust collector is calculated. concentration, Based on the calculated value of the concentration of the unreacted alkali agent, the amount of the heavy metal fixing agent to be added to the fly ash is calculated and added. The method for treating combustion exhaust as claimed in claim 1, wherein the heavy metal fixing step has: a storing step of storing the fly ash discharged from the dust collector in a storage bin; and In the mixing step, the fly ash in the storage bin is extracted and supplied to a mixer, and the heavy metal fixing agent is added to the fly ash in the mixer to fix the heavy metal in the fly ash. The combustion exhaust gas treatment method according to claim 2, wherein the fly ash supplied from the dust collector to the storage bin calculated based on the measured value of the acid gas concentration in the untreated combustion exhaust gas is memorized Time-lapse data of the concentration of unreacted alkaline agent in Based on the time-lapse data and the supply flow rate when the fly ash is extracted from the storage bin and supplied to the kneader, the concentration of unreacted alkali agent in the fly ash supplied to the kneader and processed is calculated. changes over time, Based on the change over time, the addition amount of the heavy metal fixing agent is controlled over time to fix the heavy metal in the fly ash. The method for treating combustion exhaust gas according to claim 2 or 3, wherein in the kneading step, an acid neutralizer is further added to the kneader. The method for treating combustion exhaust gas according to any one of claims 1 to 4, wherein the acid gas concentration in the combustion exhaust gas before the dry treatment is measured, and based on the measured value, in the dry treatment In the treatment process, an alkali agent is added so as to be 1 equivalent to 3 equivalents with respect to the concentration of the acidic gas. The method for treating combustion exhaust gas according to any one of claims 1 to 5, wherein the acid gas includes hydrogen chloride and sulfur oxides, and the total amount of the concentrations of the hydrogen chloride and sulfur oxides is measured as the acid gas concentration. The method for treating combustion exhaust gas according to any one of claims 1 to 6, wherein the alkali agent contains at least one kind of alkali salt of an alkali metal or an alkaline earth metal. The method for treating combustion exhaust gas according to any one of claims 1 to 7, wherein the heavy metal fixing agent is an inorganic heavy metal fixing agent. A treatment device for combustion exhaust, comprising: A dry treatment device, adding an alkali agent to the untreated combustion exhaust containing acid gas to neutralize the acid gas to obtain alkali-treated combustion exhaust; a dust collector connected to the dry processing device to collect the fly ash in the alkali-treated combustion exhaust; A heavy metal fixing device, connected to the dust collector, adding a heavy metal fixing agent to the fly ash to fix the heavy metal in the fly ash; a measuring device for measuring the concentration of the acid gas in the untreated combustion exhaust; The calculation device has: an alkali agent addition amount calculation unit for calculating the addition amount of the alkali agent added to the untreated combustion exhaust gas based on the measured value of the acid gas concentration; calculating the concentration of the unreacted alkali agent a part that calculates the concentration of unreacted alkali agent in the fly ash discharged from the dust collector; added amount; an alkali agent addition device for adding the alkali agent to the untreated combustion exhaust gas in the dry processing device based on the calculated value of the addition amount of the alkali agent calculated by the calculation device; and The adding device of the heavy metal fixing agent adds the heavy metal fixing agent based on the calculated value of the addition amount of the heavy metal fixing agent to the fly ash. The treatment device for combustion exhaust as claimed in item 9, wherein the heavy metal fixing device has: a storage bin, connected to the dust collector, for storing the fly ash discharged from the dust collector; a mixing machine connected to the storage bin; a supply device for extracting the fly ash in the storage bin and supplying it to the kneader; and A device for adding a heavy metal fixing agent, adding the heavy metal fixing agent to the mixer. The combustion exhaust treatment device as described in claim 10, has: The calculation device includes a memory unit storing the unreacted alkaline agent concentration in the fly ash supplied from the dust collector to the storage bin calculated based on the measured value of the acid gas concentration in the untreated combustion exhaust gas. The calculation unit calculates the fly ash supplied to the kneader and processed based on the time-lapse data and the supply flow rate when the fly ash is extracted from the storage bin and supplied to the kneader the change over time of the concentration of the unreacted alkali agent in the fly ash; and the calculation unit calculates the addition amount of the heavy metal fixing agent to the fly ash based on the change over time of the concentration of the unreacted alkali agent; and The adding device of the heavy metal fixing agent adds the heavy metal fixing agent based on the calculated value of the addition amount of the heavy metal fixing agent to the fly ash.

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