Exhaust gas treatment method

Abstract

The present invention provides an exhaust gas treatment method that is capable of inhibiting the elution of arsenic, selenium, and compounds of these from fly ash.　An exhaust gas treatment method for neutralizing, by dry processes, an exhaust gas containing an acidic component, wherein: a neutralizer containing sodium hydrogen carbonate is brought into contact with the exhaust gas; a mixture comprising a gas component, which has been obtained by bringing the neutralizer into contact with the exhaust gas, and a fly ash component is separated by a dry filter into the gas component and the fly ash component; and arsenic, selenium, and compounds of these which are contained in the fly ash component are insolubilized in the presence of calcium carbonate.

Description

[Technical field]

[0001] The present invention relates to an exhaust gas treatment method. [Background technology]

[0002] Fly ash collected from combustion facilities such as municipal waste incinerators, industrial waste incinerators, power generation boilers, carbonization furnaces, and private factories may contain harmful substances such as mercury, lead, arsenic, selenium, or their compounds. Insolubilization treatment is carried out to prevent these harmful substances from leaching out of the fly ash.

[0003] Patent Document 1 describes a method for preventing the elution of heavy metals from fly ash collected from combustion exhaust gas sprayed with a carbonate-containing alkaline compound, which is characterized by adding a calcium compound having calcium elution properties to the fly ash, adjusting the pH of the eluate shown in the Environment Agency Notification No. 13 test (L / S=10) to 8.0 to 11, and adjusting the calcium ion concentration in the eluate to 50 mg / L or more. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-56495 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method for preventing the elution of heavy metals described in Patent Document 1 does not consider the insolubilization of arsenic, selenium, and their compounds, and there are cases in which the insolubilization of harmful substances is insufficient.

[0006] An object of the present invention is to provide an exhaust gas treatment method capable of suppressing the elution of arsenic, selenium and their compounds from fly ash. [Means for solving the problem]

[0007] [1] A method for treating exhaust gas containing acidic components by dry neutralization, comprising: contacting the exhaust gas with a neutralizing agent containing sodium bicarbonate; A mixture containing a gas component and a fly ash component obtained by contacting the neutralizing agent with the exhaust gas is separated into the gas component and the fly ash component by a dry filter; The method for treating exhaust gas comprises insolubilizing arsenic, selenium and compounds thereof contained in the fly ash component in the presence of calcium carbonate. [2] The method for treating an exhaust gas according to [1], further comprising the steps of: separating the gas component and the fly ash component; and mixing the fly ash component with calcium carbonate. [3] The method for treating an exhaust gas according to [1], further comprising contacting a mixture containing a gas component and a fly ash component obtained by contacting the neutralizing agent with the exhaust gas with calcium carbonate. [4] The flue gas treatment method according to [1], wherein the flue gas is contacted with calcium carbonate before the neutralizing agent is contacted with the flue gas. [5] The flue gas treatment method according to [1], wherein when the neutralizing agent is brought into contact with the flue gas, the flue gas is brought into contact with a mixture containing the neutralizing agent and calcium carbonate. [6] The method for treating an exhaust gas according to any one of [1] to [5], wherein a calcium concentration when arsenic, selenium, and compounds thereof contained in the fly ash component are insolubilized in the presence of calcium carbonate is 3 to 20 mass% of a total mass of the fly ash component and calcium carbonate. [7] The method for treating an exhaust gas according to any one of [1] to [6], wherein the neutralizing agent is particles containing sodium hydrogen carbonate. Effect of the Invention

[0008] According to the present invention, there is provided an exhaust gas treatment method capable of suppressing the elution of arsenic, selenium and their compounds from fly ash. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 is a schematic diagram of an exhaust gas treatment facility for carrying out a first embodiment of the exhaust gas treatment method of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of an exhaust gas treatment facility for carrying out the second embodiment of the exhaust gas treatment method of the present invention. [Diagram 3] FIG. 3 is a schematic diagram of an exhaust gas treatment facility for carrying out the third embodiment of the exhaust gas treatment method of the present invention. [Figure 4] FIG. 4 is a schematic diagram of an exhaust gas treatment facility for carrying out the fourth embodiment of the exhaust gas treatment method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Below, a form for implementing the present invention will be described, but the present invention is not limited to the embodiments described below, and various modifications are possible as long as they do not change the gist of the present invention.

[0011] A numerical range expressed using "~" is intended to include the numerical values ​​on both sides of the "~". "Arsenic, selenium and their compounds" refers to arsenic as an element and compounds, and selenium as an element and compounds. "Mercury, lead, arsenic, selenium and their compounds" means mercury and its compounds, lead and its compounds, arsenic and its compounds, and selenium and its compounds. The method for measuring the amount of eluted mercury, lead, arsenic, selenium and their compounds in fly ash shall be in accordance with the "Testing Method for Metals, etc. Contained in Industrial Waste" (Notification No. 13 of the Environment Agency of Japan, promulgated on February 17, 1973, hereinafter sometimes abbreviated as "Environmental Notification No. 13").

[0012] [First embodiment] <Exhaust gas treatment equipment> The configuration of an exhaust gas treatment facility 1 shown in FIG. 1 for carrying out a first embodiment of the exhaust gas treatment method of the present invention will be described. The exhaust gas treatment equipment 1 includes an exhaust gas supply pipe 101, a neutralizing agent supplying device 20 connected midway through the exhaust gas supply pipe 101, a bag filter 32 connected to an exhaust gas supply pipe outlet 101b of the exhaust gas supply pipe 101, a fly ash component supplying pipe 103 connected to a dust discharge device 33 arranged at the lower end of the bag filter 32, an insolubilization treatment tank 41 to which the fly ash component supplying pipe 103 is connected, and a calcium carbonate supplying device 10, a chelating agent supplying device 50, a humidification water supplying pipe 42, and a post-insolubilization treatment dust discharge pipe 104, which are connected to the insolubilization treatment tank 41.

[0013] The exhaust gas supply pipe 101 connects an exhaust gas supply pipe inlet 101a and an exhaust gas supply pipe outlet 101b. Exhaust gas is supplied to the exhaust gas treatment facility 1 from an exhaust gas supply pipe inlet 101a. A mixture of gas components and fly ash components is supplied into the bag filter 32 from the exhaust gas supply pipe outlet 101b.

[0014] The neutralizing agent supply device 20 is composed of a neutralizing agent silo 22 which is the main body, a quantitative feeder 23 arranged at the lower end of the neutralizing agent silo 22, a neutralizing agent supply pipe 24 which connects the quantitative feeder 23 to the exhaust gas supply pipe 101, and a neutralizing agent 21 contained inside the neutralizing agent silo 22. The neutralizing agent supplying device 20 supplies (sprays) a neutralizing agent into the inside of the exhaust gas supply pipe 101.

[0015] The bag filter 32 is provided therein with a filter cloth 31. The filter cloth 31 separates the mixture of gas components and fly ash components supplied from the exhaust gas supply pipe outlet 101b into the inside of the bag filter 32, into the gas components and the fly ash components. The separated gas components are discharged to the outside of the exhaust gas treatment facility 1 through a gas component discharge pipe 102 connected to the bag filter 32 . The separated fly ash component is supplied to the insolubilization treatment tank 41 through the fly ash component supply pipe 103 by the dust discharge device 33.

[0016] The insolubilization tank 41 is a device for insolubilizing arsenic, selenium and their compounds contained in the fly ash component separated by the bag filter 32 . To the insolubilization treatment tank 41, a chelating agent supplying device 50, a calcium carbonate supplying device 10, a humidification water supplying pipe 42, and a post-insolubilization treatment dust discharge pipe 104 are connected. The insolubilization tank 41 is a mixer that mixes the fly ash components with a chelating agent, calcium carbonate, and water. In many cases, ribbon, screw, or paddle type horizontal axis rotating mixers are used as the mixer, but the type and scale of the mixer are not important as long as it can mix the powder and liquid as described above.

[0017] The chelating agent supply device 50 is composed of a chelating agent supply pipe 54 having one end connected to the insolubilization treatment tank 41, a metering pump 53 arranged midway along the chelating agent supply pipe 54, a chelating agent storage tank 52 having the other end connected to the chelating agent supply pipe 54, and a chelating agent 51 contained in the chelating agent storage tank 52. The chelating agent supplying device 50 supplies a chelating agent to the inside of the insolubilization treatment tank 41 .

[0018] The calcium carbonate supplying device 10 is composed of a calcium carbonate hopper 12 which is the main body, a quantitative feeder 13 arranged at the lower end of the calcium carbonate hopper 12, a calcium carbonate supplying pipe 15 having one end connected to the quantitative feeder 13 and the other end connected to an insolubilization treatment tank 41, and calcium carbonate particles 11 accommodated in the calcium carbonate hopper 12. The calcium carbonate supplying device 10 supplies calcium carbonate particles into the insolubilization treatment tank 41 .

[0019] The humidification water supply pipe 42 is a pipe for supplying humidification water to the inside of the insolubilization treatment tank 41 . The post-insolubilization treatment dust discharge pipe 104 is a pipe for discharging the fly ash (post-insolubilization treatment dust) after the insolubilization treatment to the outside of the exhaust gas treatment facility 1 .

[0020] Next, a first embodiment of the exhaust gas treatment method of the present invention will be described with reference to FIG.

[0021] <Exhaust gas treatment method> The flue gas treatment method of the present invention is a flue gas treatment method in which flue gas containing acidic components is neutralized in a dry manner. The exhaust gas treatment method of the present embodiment includes the following steps 1 to 3.

[0022] Step 1 Step 1 is a step of contacting the exhaust gas with a neutralizing agent containing sodium bicarbonate. The neutralizing agent supplying device 20 supplies the neutralizing agent 21 contained inside the neutralizing agent silo 22 through the quantitative feeder 23 and the neutralizing agent supplying pipe 24 to the inside of the exhaust gas supplying pipe 101 . When supplying the neutralizing agent 21 into the exhaust gas supply pipe 101, it is preferable to spray the neutralizing agent 21 into the exhaust gas supply pipe 101. By spraying the neutralizing agent 21 into the exhaust gas supply pipe 101, the particles of the neutralizing agent 21 are more likely to diffuse into the exhaust gas supply pipe 101, and the chances of the particles of the neutralizing agent 21 coming into contact with the exhaust gas are increased.

[0023] The neutralizing agent 21 is a particle containing sodium bicarbonate. The component contained in the neutralizing agent 21 other than sodium bicarbonate is, for example, hydrophilic fumed silica used as an anti-caking agent and fluidizing agent for powder. When the neutralizing agent 21 contains sodium bicarbonate and hydrophilic fumed silica, it is more preferable that most of the hydrophilic fumed silica is uniformly dispersed in the form of primary particles on the surfaces of the particles made of sodium bicarbonate. By dispersing most of the hydrophilic fumed silica in the form of primary particles, the fluidity of the neutralizing agent can be made more appropriate compared to when the hydrophilic fumed silica is present in the form of secondary particles, and clumping due to aggregation can be prevented. The powder anti-caking agent and fluidizing agent are not limited to fumed silica, and examples thereof include precipitated silica, salts of fatty acids such as stearic acid, zeolite, diatomaceous earth, silicates, and talc.

[0024] The average particle size of the neutralizing agent 21 is preferably 3 to 20 μm, and more preferably 5 to 10 μm. When the average particle size is within this range, the neutralizing agent is appropriately supported on the filter cloth surface of the dry filter (bag filter) to form a filtration layer, and the neutralizing agent passes through the dry filter (bag filter), reducing the risk of being included in the gas components and clogging the filter cloth. In addition, better fluidity and dispersibility are obtained, allowing the acidic components in the exhaust gas to be removed more efficiently.

[0025] The average particle size of the neutralizing agent 21 is a volume-based average particle size measured using a laser diffraction scattering type particle size distribution measuring device with ethanol as a medium. In this specification, the average particle size is measured using a Microtrac FRA9220 (trade name) manufactured by Nikkiso Co., Ltd.

[0026] The average particle size of the primary particles of the hydrophilic fumed silica is preferably 5 to 50 nm. When the average particle size of the primary particles of the hydrophilic fumed silica is within this range, it is easy to disperse in the neutralizing agent 21. Here, the primary particle of the hydrophilic fumed silica is the smallest unit of the constituent particles as determined by visual inspection of an image observed with a SEM (scanning electron microscope).

[0027] The average particle size of the primary particles of the hydrophilic fumed silica is actually measured by a scanning electron microscope (SEM), specifically, the particle sizes of 100 primary particles are measured and the measured values ​​are calculated as the arithmetic average.

[0028] The exhaust gas is preferably a combustion exhaust gas generated in combustion facilities such as municipal waste incinerators, industrial waste incinerators, power generation boilers using coal, heavy oil, residual oil, biomass, etc. as fuel, carbonization furnaces, and private factories. Examples of acidic components contained in the exhaust gas include sulfur oxides (SOx) and hydrogen chloride (HCl).

[0029] When the neutralizing agent 21 is brought into contact with exhaust gas, the high-temperature exhaust gas causes the sodium bicarbonate contained in the neutralizing agent 21 to thermally decompose, releasing carbon dioxide and water, and becoming porous particles with a large surface area. In an ideal state, 2 moles of sodium bicarbonate (NaHCO3) produce 1 mole of carbon dioxide (CO2), 1 mole of sodium carbonate (Na2CO3), and 1 mole of water (H2O). The acidic components in the exhaust gas are mainly neutralized by the sodium carbonate.

[0030] Step 2 Step 2 is a step in which a mixture of gas components and fly ash components obtained by contacting the neutralizing agent 21 with the exhaust gas is separated into the gas components and the fly ash components by a dry filter (bag filter 32).

[0031] In this embodiment, a bag filter 32 is used as the dry filter. The bag filter has a filter cloth 31 disposed therein, and separates gas components that pass through the filter cloth 31 from fly ash components that cannot pass through the filter cloth.

[0032] The gas components are discharged to the outside of the exhaust gas treatment facility 1 through a gas component discharge pipe 102 installed near the upper end of the bag filter 32 . The gas components are gases in which acidic components such as SOx and HCl have been neutralized by contacting the exhaust gas with the neutralizing agent 21, and no problems will arise even if the gas components are discharged into the environment.

[0033] The fly ash component is supplied to the insolubilization treatment tank 41 through the fly ash component supply pipe 103 by the dust discharge device 33 installed at the lower end of the bag filter 32. The fly ash may contain arsenic, selenium, and compounds thereof, and therefore, these components are subjected to an insolubilization treatment.

[0034] Step 3 Step 3 is a step in which arsenic, selenium and their compounds contained in the fly ash are insolubilized in the presence of calcium carbonate.

[0035] The fly ash component is supplied into the insolubilization treatment tank 41, and then mixed with a chelating agent 51 supplied into the insolubilization treatment tank 41 from a chelating agent supplying device 50, calcium carbonate particles 11 supplied into the insolubilization treatment tank 41 from a calcium carbonate supplying device 10, and humidification water supplied into the insolubilization treatment tank 41 through a humidification water supplying pipe 42, to perform insolubilization treatment of arsenic, selenium, and their compounds.

[0036] The chelating agent 51 is preferably one capable of insolubilizing at least one of the metals and the like listed in Environmental Notification No. 13, which may be contained in the fly ash component, more preferably one capable of insolubilizing at least one of mercury, lead, arsenic, and selenium, and further preferably one capable of insolubilizing arsenic and selenium. Examples of the chelating agent 51 include piperazine dithiocarbamic acid, diethyl dithiocarbamic acid, dimethyl dithiocarbamic acid, dibutyl dithiocarbamic acid, polyamine dithiocarbamic acid, tetraethylene pentamine, and salts thereof. The salts are preferably sodium salts or potassium salts. However, the chelating agent 51 is not limited to these organic chelating compounds and their salts, and inorganic insolubilizers such as iron salts may also be used.

[0037] The calcium carbonate particles 11 are particles containing calcium carbonate, and the calcium carbonate content in the calcium carbonate particles 11 is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. As the calcium carbonate, either heavy calcium carbonate produced by crushing and classifying limestone or light calcium carbonate chemically synthesized by a carbon dioxide gas reaction method or a soluble salt reaction method can be used. From the viewpoint of stable quality and less impurities, light calcium carbonate is preferred.

[0038] The calcium carbonate particles 11 are preferably secondary particles of calcium carbonate, and the average particle size of the secondary particles is preferably 1 to 10 μm, and more preferably 1 to 5 μm. When the average particle size of the secondary particles of calcium carbonate is within this range, the particles do not become too cohesive and do not easily adhere to each other. Also, the particles are easily dispersed uniformly in the fly ash component during the insolubilization treatment. The average particle size of the calcium carbonate particles 11 as secondary particles is a volume-based average particle size (MV) measured by a laser diffraction scattering type measuring device.

[0039] The calcium concentration during the insolubilization treatment in step 3 is preferably 3 to 20 mass% of the total mass of the fly ash component and calcium carbonate, more preferably 5 to 17 mass%, and even more preferably 7 to 12 mass%. When the calcium concentration is within this range, the insolubilization treatment effect of arsenic, selenium, and mixtures thereof is further improved. If too much calcium carbonate particles are added, the total mass of the fly ash component and calcium carbonate increases, which may increase the cost of post-treatment such as landfill disposal. The calcium concentration can be determined by applying the analysis method of JIS K0102 (2019)-50.3. Calcium carbonate is not a strong alkaline compound like calcium hydroxide, so it can be handled very safely. Also, unlike calcium chloride, it is not highly corrosive to iron-based materials, so it is preferable for equipment made of iron-based materials that is installed in the process after the insolubilization treatment tank 41.

[0040] Tap water, deionized water, distilled water, etc. are used as the humidification water supplied from the humidification water supply pipe 42 to the inside of the insolubilization treatment tank 41. Supplying humidification water to the inside of the insolubilization treatment tank 41 suppresses scattering of fly ash components to the surroundings and facilitates mixing of the fly ash components with the calcium carbonate particles 11 and the chelating agent 51, thereby improving the efficiency of the insolubilization treatment.

[0041] After insolubilization treatment, the fly ash components have arsenic, selenium and mixtures thereof insolubilized, and the amount of arsenic, selenium and their compounds eluted is below the standard value as specified by the test method of Environmental Notification No. 13. Arsenic: 0.3 mg / L Selenium: 0.3 mg / L

[0042] The fly ash components after the insolubilization treatment are discharged as dust after the insolubilization treatment from the dust after insolubilization treatment discharge pipe 104 to the outside of the flue gas treatment facility 1 .

[0043] [Second embodiment] <Exhaust gas treatment equipment> An exhaust gas treatment facility 2 shown in FIG. 2 is an exhaust gas treatment facility for carrying out a second embodiment of the exhaust gas treatment method of the present invention. The difference from the exhaust gas treatment equipment 1 shown in FIG. 1 is that a calcium carbonate supplying device 10′ connected between the position of the exhaust gas supply pipe 101 to which the neutralizing agent supplying device 20 is connected and the bag filter 32 is used, instead of the calcium carbonate supplying device 10 connected to the insolubilization treatment tank 41.

[0044] The calcium carbonate supplying device 10′ is composed of a calcium carbonate hopper 12 which is a main body, a quantitative feeder 13 arranged at the lower end of the calcium carbonate hopper 12, a calcium carbonate supplying pipe 14 which is connected at one end to the quantitative feeder 13 and at the other end to an exhaust gas supplying pipe 101, and calcium carbonate particles 11 accommodated in the calcium carbonate hopper 12. In the calcium carbonate supplying device 10', a calcium carbonate supplying pipe 14 is connected between the part of the exhaust gas supplying pipe 101 to which the neutralizing agent supplying device 20 is connected and the exhaust gas supplying pipe outlet 101b. Calcium carbonate particles 11 are supplied (sprayed) from the calcium carbonate supplying device 10' into the exhaust gas supply pipe 101, and the calcium carbonate particles 11 are brought into contact with a mixture obtained by contacting the neutralizing agent 21 with the exhaust gas.

[0045] Other points are the same as those of the exhaust gas treatment facility 1 shown in FIG.

[0046] <Exhaust gas treatment method> The exhaust gas treatment method of this embodiment includes the following steps 1a to 4a.

[0047] Step 1a Step 1a is a step of supplying a neutralizing agent 21 containing sodium hydrogen carbonate into the inside of the exhaust gas supply pipe 101 and bringing the neutralizing agent 21 into contact with the exhaust gas.

[0048] Step 1a is similar to step 1 in the first embodiment of the exhaust gas treatment method of the present invention, and a description thereof will be omitted.

[0049] Step 2a Step 2a is a step of contacting the mixture obtained by contacting the neutralizing agent obtained in step 1a with the exhaust gas with calcium carbonate particles supplied (sprayed) from the calcium carbonate supplying device 10′ into the inside of the exhaust gas supply pipe 101.

[0050] The calcium carbonate supplying device 10 ′ has the same configuration as the calcium carbonate supplying device 10 . The calcium carbonate particles 11 supplied from the calcium carbonate supplying device 10′ and the mixture obtained by contacting the neutralizing agent obtained in step 1a with the exhaust gas are mixed together to form a mixture containing a gas component and a fly ash component.

[0051] Step 3a Step 3a is a step of separating the mixture of gas components and fly ash components obtained in step 2a into the gas components and the fly ash components using a dry filter (bag filter 32).

[0052] Step 3a is similar to step 2 in the first embodiment of the flue gas treatment method of the present invention, except that the fly ash component obtained in step 3a has already been mixed with calcium carbonate particles 11, and therefore further description thereof will be omitted.

[0053] Step 4a Step 4a is a step of insolubilizing arsenic, selenium and their compounds contained in the fly ash component in the presence of calcium carbonate.

[0054] Since the fly ash component obtained in step 3a and supplied to the inside of the insolubilization treatment tank 41 already contains calcium carbonate particles 11, it is not necessary to further add calcium carbonate particles 11 to the fly ash component in step 4a. Except for this point, step 4a is similar to step 3 in the first embodiment of the exhaust gas treatment method of the present invention, and further description will be omitted.

[0055] [Third embodiment] <Exhaust gas treatment equipment> An exhaust gas treatment facility 3 shown in FIG. 3 is an exhaust gas treatment facility for carrying out a third embodiment of the exhaust gas treatment method of the present invention. The difference from the flue gas treatment equipment 2 shown in FIG. 2 is that the calcium carbonate supplying device 10′ is connected between the flue gas supply pipe inlet 101a of the flue gas supply pipe 101 and the point where the neutralizing agent supplying device 20 is connected to the flue gas supply pipe 101. Other points are the same as those of the exhaust gas treatment facility 2 shown in FIG.

[0056] <Exhaust gas treatment method> The exhaust gas treatment method of this embodiment includes the following steps 1b to 4b.

[0057] Step 1b Step 1b is a step of supplying (spraying) calcium carbonate particles 11 from a calcium carbonate supplying device 10' into the inside of the exhaust gas supply pipe 101, and bringing the calcium carbonate particles 11 into contact with the exhaust gas.

[0058] The calcium carbonate supplying device 10 ′ has the same configuration as the calcium carbonate supplying device 10 . When calcium carbonate particles 11 are supplied (sprayed) into the exhaust gas supply pipe 101, a mixture of the calcium carbonate particles 11 and the exhaust gas is obtained.

[0059] Step 2b Step 2b is a step of contacting the mixture of calcium carbonate particles 11 and exhaust gas obtained in step 1b with the neutralizing agent 21 supplied (sprayed) from the neutralizing agent supply device 20 into the exhaust gas supply pipe 101. The mixture of calcium carbonate particles 11 and exhaust gas obtained in step 1b is mixed with the neutralizing agent 21 to form a mixture of gas components and fly ash components.

[0060] Step 3b Step 3b is a step of separating the mixture of gas components and fly ash components obtained in step 2b into the gas components and the fly ash components using a dry filter (bag filter 32).

[0061] Step 3b is similar to step 3a in the second embodiment of the exhaust gas treatment method of the present invention, and further description will be omitted.

[0062] Step 4b Step 4b is a step of insolubilizing arsenic, selenium and their compounds contained in the fly ash component in the presence of calcium carbonate.

[0063] Step 4b is similar to step 4a in the second embodiment of the exhaust gas treatment method of the present invention, and further description will be omitted.

[0064] [Fourth embodiment] <Exhaust gas treatment equipment> An exhaust gas treatment facility 4 shown in FIG. 4 is an exhaust gas treatment facility for carrying out the fourth embodiment of the exhaust gas treatment method of the present invention. The difference from the exhaust gas treatment facility 1 shown in FIG. 1 is that the neutralizing agent and calcium carbonate particles are supplied by a neutralizing agent / calcium carbonate mixture supply device 60 connected to the exhaust gas supply pipe 101.

[0065] The neutralizing agent / calcium carbonate mixture supplying device 60 is composed of a neutralizing agent / calcium carbonate mixture silo 62 which is the main body, a quantitative feeder 63 installed at the lower end of the neutralizing agent / calcium carbonate mixture silo 62, a neutralizing agent / calcium carbonate mixture supplying pipe 64 which connects the quantitative feeder 63 with the exhaust gas supply pipe 101, and a mixture 61 containing the neutralizing agent and calcium carbonate particles contained in the neutralizing agent / calcium carbonate mixture silo 62.

[0066] A mixture 61 containing a neutralizing agent and calcium carbonate particles is supplied (sprayed) from a neutralizing agent / calcium carbonate mixture supplying device 60 into the exhaust gas supply pipe 101, and the mixture 61 containing a neutralizing agent and calcium carbonate particles is brought into contact with the exhaust gas.

[0067] <Exhaust gas treatment method> The exhaust gas treatment method of this embodiment includes the following steps 1c to 3c.

[0068] Step 1c Step 1c is a step of supplying a mixture 61 containing a neutralizing agent and calcium carbonate particles into the inside of the exhaust gas supply pipe 101, and bringing the neutralizing agent and the calcium carbonate particles into contact with the exhaust gas.

[0069] The neutralizing agent is the same as neutralizing agent 21 described above. The calcium carbonate particles are the same as the calcium carbonate particles 11 described above. The content of the neutralizing agent and the calcium carbonate particles in the mixture 61 containing the neutralizing agent and the calcium carbonate particles is preferably 1 to 10 parts by mass, more preferably 2 to 7 parts by mass, and even more preferably 2 to 5 parts by mass of the calcium carbonate particles per 100 parts by mass of the neutralizing agent.

[0070] In step 1c, a mixture 61 containing a neutralizing agent and calcium carbonate particles is brought into contact with the flue gas to obtain a mixture of a gas component and a fly ash component.

[0071] Step 2c Step 2c is a step of separating the mixture of gas components and fly ash components obtained in step 1c into the gas components and the fly ash components using a dry filter (bag filter 32).

[0072] Step 2c is similar to step 3a in the second embodiment of the exhaust gas treatment method of the present invention, and further description will be omitted.

[0073] Step 3c Step 3c is a step of insolubilizing arsenic, selenium and their compounds contained in the fly ash component in the presence of calcium carbonate.

[0074] Step 3c is similar to step 4a in the second embodiment of the exhaust gas treatment method of the present invention, and further description will be omitted. EXAMPLES

[0075] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the examples described below, and various modifications are possible without departing from the gist of the present invention. Example 1 corresponds to a comparative example, and Examples 2 to 4 correspond to working examples.

[0076] [Example 1] A neutralizing agent (Acrecia (registered trademark), manufactured by AGC Corporation; sodium bicarbonate particles, average particle size 9 μm) was sprayed into the exhaust gas from a general waste (municipal waste) incinerator, and then the fly ash component and the gas component were separated using a bag filter. A chelating agent (Arcite L-105, manufactured by Fuji Sash Corporation) was added in an amount of 0 to 6 mass % of the fly ash component. Using 100 g of the treated dust, the amounts of arsenic, selenium, mercury, lead, and their compounds eluted were measured using a test method in accordance with Environmental Notification No. 13. The measurement results are shown in Table 1.

[0077] The amounts of arsenic, selenium, mercury, lead and their compounds eluted from the treated dust did not exceed the standard values, but they tended to leach out easily.

[0078] [Example 2] A neutralizing agent (Acrecia (registered trademark), manufactured by AGC Corporation; sodium bicarbonate particles, average particle size 9 μm) was sprayed into the exhaust gas from a general waste (municipal waste) incinerator, and then calcium carbonate particles (average particle size 2 μm) were sprayed into the exhaust gas, and the fly ash component and gas component were separated using a bag filter. A chelating agent (Arcite L-105, manufactured by Fuji Sash Corporation) was added in an amount of 0 to 6 mass% of the fly ash component. The calcium concentration in the dust after the insolubilization treatment was 10.4 mass%. Using 100 g of the treated dust, the amount of eluted arsenic, selenium, mercury, lead, and their compounds was measured using a test method based on Environmental Notification No. 13. The measurement results are shown in Table 1.

[0079] The amounts of arsenic, selenium, mercury, lead and their compounds eluted from the treated dust did not exceed the standard values. Compared to Example 1, the tendency for elution was suppressed.

[0080] [Example 3] A neutralizing agent (Acrecia (registered trademark), manufactured by AGC; sodium bicarbonate particles, average particle size 9 μm) was sprayed into the exhaust gas from a general waste (municipal waste) incinerator, and then the fly ash component and the gas component were separated using a bag filter. A chelating agent (Alcite L-105, manufactured by Fuji Sash Co., Ltd.) was added to the fly ash component at 0-6 mass %. In addition, calcium carbonate particles (average particle size 2 μm) were added to the fly ash component. The calcium content in the dust after the insolubilization treatment was 7.2 mass %. Using 100 g of the treated dust, the amount of eluted arsenic, selenium, mercury, lead, and their compounds was measured using a test method based on Environmental Notification No. 13. The measurement results are shown in Table 1.

[0081] [Example 4] A neutralizing agent (Acrecia (registered trademark), manufactured by AGC Corporation; sodium bicarbonate particles, average particle size 9 μm) was sprayed into the exhaust gas from a general waste (municipal waste) incinerator, and then the fly ash component and the gas component were separated using a bag filter. A chelating agent (Alcite L-105, manufactured by Fuji Sash Corporation) was added at 0-6% by mass to the fly ash component. Calcium carbonate particles (average particle size 2 μm) were also added to the fly ash component. The calcium content in the dust after the insolubilization treatment was 18.6% by mass. The amount of eluted arsenic, selenium, mercury, lead, and their compounds was measured using 100 g of the treated dust by a test method based on Environmental Notification No. 13. The measurement results are shown in Table 1.

[0082] The amounts of arsenic, selenium, mercury, lead and their compounds eluted from the treated dust did not exceed the standard values, and the ease of elution was reduced compared to Example 1.

[0083] [Table 1]

[0084] The contents and elution amounts in the columns for arsenic, selenium, mercury, and lead include values ​​for compounds of each element. [Industrial Applicability]

[0085] The flue gas treatment method of the present invention can be carried out by simply making small changes to conventional flue gas treatment equipment, and can suppress the elution of arsenic, selenium, and their compounds from fly ash through simple operations. Therefore, the method is suitable for treating fly ash collected in combustion facilities such as municipal waste incinerators, industrial waste incinerators, power generation boilers, carbonization furnaces, and private factories. The entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2019-193439, filed on October 24, 2019, are hereby incorporated by reference as the disclosure of the specification of the present invention. [Explanation of symbols]

[0086] 1,2,3,4 Exhaust gas treatment equipment 10,10' Calcium carbonate supply device 11 Calcium carbonate particles 12 Calcium carbonate hopper 13 Quantitative Feeder 14,15 Calcium carbonate supply pipe 20 Neutralizing agent supply device 21 Neutralizer 22 Neutralizer Silo 23 Quantitative Feeder 24 Neutralizer supply pipe 31 Filter cloth 32 Bag filter 33 Dust exhaust device 41 Insolubilization tank 42 Humidification water supply pipe 50 Chelating agent supply device 51 Chelating Agents 52 Chelating agent storage tank 53 Metering pump 54 Chelating agent supply pipe 60 Neutralizer / Calcium Carbonate Mixture Supply Device 61 Mixtures containing neutralizing agents and calcium carbonate particles 62 Neutralizer / Calcium Carbonate Mixture Silo 63 Fixed quantity feeder 64 Neutralizer / calcium carbonate mixture supply pipe 101 Exhaust gas supply pipe 101a Exhaust gas supply pipe inlet 101b Exhaust gas supply pipe outlet 102 Gas component exhaust pipe 102a Gas component exhaust pipe inlet 102b Gas component exhaust pipe outlet 103 Fly ash component supply pipe 104 Dust discharge pipe after insolubilization treatment A Exhaust gas B Gas component C Fly ash component D. Dust after insolubilization treatment E Humidifying water

Claims

1. An exhaust gas treatment method for dry neutralizing exhaust gas containing acidic components, comprising: contacting the exhaust gas with a neutralizing agent containing sodium bicarbonate; A mixture of a gas component and a fly ash component obtained by contacting the neutralizing agent with the exhaust gas is separated into the gas component and the fly ash component by a dry filter; Arsenic, selenium and compounds thereof contained in the fly ash component are insolubilized in the presence of calcium carbonate, The method for treating an exhaust gas, wherein a calcium concentration when the arsenic, selenium and compounds thereof contained in the fly ash component are insolubilized in the presence of calcium carbonate is 5 to 20 mass % of a total mass of the fly ash component and calcium carbonate.

2. 2. The method for treating an exhaust gas according to claim 1, further comprising the steps of: separating the gas component and the fly ash component; and mixing the fly ash component with calcium carbonate.

3. 2. The method for treating an exhaust gas according to claim 1, further comprising contacting a mixture containing a gas component and a fly ash component obtained by contacting the neutralizing agent with the exhaust gas with calcium carbonate.

4. The method for treating an exhaust gas according to claim 1 , further comprising contacting the exhaust gas with calcium carbonate before contacting the exhaust gas with the neutralizing agent.

5. The method for treating an exhaust gas according to claim 1 , wherein when the neutralizing agent is brought into contact with the exhaust gas, the exhaust gas is brought into contact with a mixture containing the neutralizing agent and calcium carbonate.

6. The exhaust gas treatment method according to any one of claims 1 to 5, wherein the neutralizing agent is particles containing sodium bicarbonate.

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