Method for using calcium-containing calcined fine powder and method for producing acid gas treatment composition

Abstract

To reduce carbon dioxide emissions during production of an acidic gas treatment material composition.SOLUTION: Provided is a method of using a calcium-containing burned pulverized powder, wherein the calcium-containing burned pulverized powder generated in a process of producing a calcium oxide product by burning calcium carbonate is used as a component of an acidic gas treatment material composition. It is preferable that the acidic gas treatment material composition contains at least one selected from the group consisting of calcium hydroxide, calcium carbonate, and sodium bicarbonate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for using calcium-containing calcined fine powder that is a by-product when calcium oxide is produced by calcining calcium carbonate, and also to a method for producing an acidic gas treatment composition. [Background technology]

[0002] Calcium compounds such as quicklime and slaked lime are industrially produced through a calcination process of calcium carbonate such as limestone. Calcination of calcium carbonate requires the combustion of fuel, which generates carbon dioxide. Furthermore, the reaction of producing quicklime or slaked lime from calcium carbonate also generates carbon dioxide. Thus, when calcium compounds such as quicklime or slaked lime are produced using calcium carbonate as a raw material, a large amount of carbon dioxide is generated.

[0003] Therefore, from the viewpoint of environmental protection, there have been proposed a method of reusing collected dust recovered from the gas emitted when calcium oxide is produced by calcining calcium carbonate (Patent Document 1), and a method of mixing dust recovered from the exhaust gas of a calcination furnace with water-washed sludge produced in the limestone washing process, drying the mixture, and then reusing the mixture as a raw material for lime calcination (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-090130 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-114029 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, efforts to prevent global warming by reducing carbon dioxide emissions have become an urgent issue in the industrial sector, and there is an increasing need to reduce carbon dioxide emissions through the effective use of by-products derived from the limestone calcination process, as described above. The object of the present invention is to propose an effective method for utilizing by-products derived from the limestone calcination process, thereby reducing carbon dioxide emissions. [Means for solving the problem]

[0006] The present invention provides a method for using calcium-containing calcined fine powder, which is generated in the process of producing a calcium oxide product by calcining calcium carbonate, as one component of an acidic gas treatment composition.

[0007] The present invention also provides a method for producing an acidic gas treatment composition, which comprises mixing calcium-containing calcined fine powder generated in the process of producing a calcium oxide product by calcining calcium carbonate with at least one member selected from the group consisting of calcium hydroxide, calcium carbonate, and sodium bicarbonate. [Effects of the Invention]

[0008] According to the present invention, a by-product generated in the manufacturing process of calcium oxide products is utilized as one component of the composition for treating acidic gas, thereby reducing the amount of carbon dioxide emitted during the manufacturing of the composition for treating acidic gas. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing one embodiment of a kiln used to produce calcium oxide products from calcium carbonate. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below based on preferred embodiments thereof. The present invention relates to the use of calcium-containing calcined fine powder generated during the calcination of calcium carbonate to produce calcium oxide products. Because calcium-containing calcined fine powder contains a high percentage of elemental calcium, its effective use in various applications can reduce carbon dioxide emissions, thereby helping to prevent global warming.

[0011] In the present invention, various types of calcination furnaces can be used to calcinate calcium carbonate. Examples of calcination furnaces include vertical calcination furnaces such as a Maerz furnace, a Beckenbach furnace, a co-firing furnace, a shaft kiln, and a top-type kiln, as well as horizontal calcination furnaces such as a rotary kiln. Among these, a vertical calcination furnace is preferred, and a Beckenbach furnace is particularly preferred, from the viewpoints of excellent thermal efficiency, enabling uniform calcination, and excellent energy saving. The firing conditions can be appropriately set depending on the type of firing furnace used. For example, in the case of a Beckenbach furnace, when the maximum production capacity is 200 to 400 t / day, the firing conditions include a maximum temperature of 1000°C and a residence time of 24 hours. However, the firing conditions are not limited to these.

[0012] Fig. 1 shows a schematic diagram of one embodiment of a vertical kiln used for calcining calcium carbonate. The vertical kiln 10 shown in the figure has a furnace body 11 extending vertically. The furnace body 11 has a raw material charging section 12 at the top of the furnace. Raw materials are charged into the furnace body 11 from the raw material charging section 12. If necessary, in addition to the raw materials, a solid fuel, such as anthracite coal or oil coke, is also charged into the furnace body 11 from the raw material charging section 12. The calcium carbonate to be fired can be any calcium carbonate-containing ore such as limestone, known as heavy calcium carbonate, or synthetic calcium carbonate, known as light calcium carbonate, without any particular limitations. Of these calcium carbonates, heavy calcium carbonate is suitable for the vertical firing furnace 10. In addition, since an ascending air current is generated within the furnace body 11 during firing in the vertical firing furnace 10, it is preferable to use calcium carbonate in a lump form. An example using lump calcium carbonate will be described below.

[0013] The furnace body 11 has a liquid fuel inlet 13 on its side. The liquid fuel is injected into the furnace body 11 from the inlet 13 and burned to calcine the raw materials. Heavy oil is generally used as the liquid fuel.

[0014] Exhaust gas is generated when calcium carbonate, which is the raw material, is fired in the furnace body 11. The generated exhaust gas is discharged to the outside through an exhaust pipe 14 provided at the top of the furnace body 11. The exhaust gas discharged to the outside contains not only gas components but also solid components originating from the raw materials. The solid components consist of fine powder containing calcium components. In the following explanation, this fine powder is also referred to as "calcium-containing calcined fine powder A." The calcium-containing calcined fine powder A is separated into solid and gas and collected by a dust collector 15, such as a cyclone or bag filter, connected to a discharge pipe 14.

[0015] The particle size of the recovered calcium-containing calcined fine powder A can be adjusted by selecting the type of dust collector 15. The dust collector can be selected from known devices such as a cyclone, a scrubber, a bag filter, and an electrostatic precipitator. From the viewpoint of simplifying the process for utilizing the recovered calcium-containing calcined fine powder A, it is preferable to use a dry device. One or more of these dust collectors can be used in parallel or in series, and the type of device can be selected depending on the particle size to be recovered. For example, if a relatively large particle size of calcium-containing calcined fine powder A is desired, the powder separated and recovered by a cyclone dust collector can be used. In this case, the particle size of the recovered calcium-containing calcined fine powder A is approximately 50 μm to 1000 μm. In addition, by combining a cyclone and a bag filter, it is possible to obtain a calcium-containing calcined fine powder A having a relatively small particle size from the bag filter. In this case, the particle size of the recovered calcium-containing calcined fine powder A is approximately 0.1 μm or more and less than 50 μm. In this way, the calcium-containing calcined fine powder A has already been classified when it passes through the dust collector 15, and is therefore easy to use. In this specification, the term "particle size" refers to the volume cumulative particle size D at 50% cumulative volume measured by a laser diffraction scattering particle size distribution measurement method. 50 This means that...

[0016] The recovered calcium-containing calcined fine powder A contains calcium components such as calcium carbonate, calcium oxide, calcium hydroxide, and calcium sulfate, depending on the calcination conditions. The calcium-containing calcined fine powder A may also contain components other than the calcium component derived from the fuel or raw materials, such as silicon dioxide and unburned carbon. When calcium-containing calcined fine powder A contains unburned carbon, the proportion of unburned carbon is preferably 30 mass % or less, more preferably 20 mass % or less, and even more preferably 10 mass % or less, calculated as carbon element. The proportion of unburned carbon contained in calcium-containing calcined fine powder A can be measured by the following method.

[0017] [Method for measuring the proportion of unburned carbon] Hydrochloric acid (1 + 1) is added dropwise to approximately 10 g of sample until the reaction is complete, and then another 10 ml is added dropwise after the reaction is complete. The sample is then heated for 1 hour in a boiling water bath. After heating is complete, the sample is suction filtered while being washed with water using a pre-weighed glass filter paper (1 μm mesh). The glass filter paper is then dried at 105°C, and the ratio of the recovered residue to the sample mass is taken as the insoluble residue (mass%). The total carbon content (mass%) in the insoluble residue is measured using an EMIA-Step carbon / sulfur analyzer (manufactured by Horiba, Ltd.). The measurement conditions are a temperature of 1250°C and a measurement time of 120 seconds. The product of the insoluble residue fraction and the total carbon content in the insoluble residue is taken as the percentage of unburned carbon (mass%).

[0018] The proportion of elemental calcium contained in calcium-containing calcined fine powder A is affected by the raw fuel and calcination conditions, but in use in the present invention, it is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more, calculated as CaO by fluorescent X-ray measurement. There is no particular upper limit to the proportion of elemental calcium contained in calcium-containing calcined fine powder A, and the higher the proportion, the more useful the calcium-containing calcined fine powder A becomes.

[0019] One of the uses of calcium-containing calcined fine powder A is as a component of a composition for treating acidic gases. Because calcium-containing calcined fine powder A recovered by a dust collector has excellent air transportability, the composition for treating acidic gases containing calcium-containing calcined fine powder A can be used without any problems, for example, by adding it to flue gas.

[0020] As described above, calcium-containing calcined fine powder A contains substances capable of neutralizing acidic gases, such as calcium carbonate, calcium oxide, and calcium hydroxide. Therefore, by using calcium-containing calcined fine powder A as one component of an acidic gas treatment composition, the acidic gas to be treated can be successfully neutralized. For this purpose, the total proportion of calcium carbonate, calcium oxide, and calcium hydroxide relative to the total amount of calcium compounds in calcium-containing calcined fine powder A is preferably 60% by mass or more, more preferably 60% by mass or more, and even more preferably 75% by mass or more. There is no upper limit to the total proportion of calcium carbonate, calcium oxide, and calcium hydroxide contained in calcium-containing calcined fine powder A; the higher the proportion, the more useful the calcium-containing calcined fine powder A becomes. This proportion can be determined by X-ray diffraction measurement of calcium-containing calcined fine powder A.

[0021] Calcium oxide is produced in the furnace by firing the raw material calcium carbonate. The produced calcium oxide is discharged from the bottom of the furnace body 11 to the outside of the furnace. The discharged calcium oxide is affected by the shape of the raw material calcium carbonate. For example, when using agglomerated calcium carbonate, the calcium oxide obtained is mainly agglomerated. Therefore, hereinafter, the calcium oxide discharged to the outside of the furnace will also be referred to as "agglomerated calcium oxide." Because the particle size of agglomerated calcium oxide is not uniform, it is desirable to crush it to produce a calcium oxide product with a uniform particle size. In other words, it is desirable to crush the agglomerated calcium oxide to a predetermined particle size and produce the desired calcium oxide product.

[0022] In the process of producing calcium oxide products by pulverizing lump calcium oxide, fine powder is generated by the pulverization. This fine powder contains calcium components. In the following description, this fine powder is also referred to as "calcium-containing calcined fine powder B." The calcium-containing calcined fine powder B is collected by dust collector 16. Although it depends on the grinding conditions of the lump calcium oxide, the particle size of the calcium-containing calcined fine powder B collected by the dust collector 16 can be adjusted by the configuration of the dust collector, similar to the above-mentioned calcium-containing calcined fine powder A. For example, when a cyclone dust collector is used, the particle size is about 50 μm or more and 1000 μm or less, and when a cyclone and a bag filter are combined, the particle size is about 0.1 μm or more and less than 50 μm.

[0023] The recovered calcium-containing calcined fine powder B contains calcium components such as calcium carbonate, calcium oxide, calcium hydroxide, and calcium sulfate, depending on the calcination conditions. Because calcium-containing calcined fine powder B is derived from a portion of the lump calcium oxide, calcium oxide accounts for almost the entire amount of calcium-containing calcined fine powder B. Although calcium-containing calcined fine powder B may contain calcium carbonate or calcium hydroxide, these calcium components are generally thought to be generated when moisture or carbon dioxide in the environment reacts with calcium oxide during storage of calcium-containing calcined fine powder B, etc. Furthermore, calcium-containing calcined fine powder B contains, for example, silicon dioxide as a component other than calcium.

[0024] One of the uses of calcium-containing calcined fine powder B is as a component of a composition for treating acidic gas, similar to calcium-containing calcined fine powder A. As described above, calcium-containing calcined fine powder B contains a large amount of calcium oxide, which is a substance capable of neutralizing acidic gases. Therefore, by using calcium-containing calcined fine powder B as a component of a composition for treating acidic gases, the acidic gases to be treated can be successfully neutralized.

[0025] As described above, in the present invention, calcium-containing calcined fine powder A and calcium-containing calcined fine powder B are generated in the process of producing a calcium oxide product by calcining calcium carbonate (hereinafter, for convenience, calcium-containing calcined fine powder A and calcium-containing calcined fine powder B are also collectively referred to as "calcium-containing calcined fine powders"). In the present invention, either calcium-containing calcined fine powder A or calcium-containing calcined fine powder B can be used alone, or both can be used in combination. In either case, it is advantageous to use the calcium-containing calcined fine powder as one component of an acidic gas treatment composition. Thus, the present invention provides a method for using the calcium-containing calcined fine powder.

[0026] As used herein, the term "acidic gas treatment composition" refers to a composition used to neutralize gases containing acidic components. Examples of gases containing acidic components include hydrogen chloride (HCl); sulfur oxides (SOx), such as sulfur monoxide, sulfur dioxide, and sulfur trioxide. Acidic gases containing these components may be, for example, exhaust gases generated from waste incineration plants that incinerate municipal waste and industrial waste, or exhaust gases generated from thermal power plants that burn fossil fuels. Alternatively, the acidic gas may be a purge gas emitted when cleaning the inside of a vacuum chamber used in semiconductor manufacturing.

[0027] The acidic gas treatment composition is preferably produced by mixing calcium-containing calcined fine powder and an acidic gas treatment material as components of the composition. That is, the present invention provides a method for producing an acidic gas treatment composition. Mixing of the two components can be performed using a mixing device commonly used in the art. For example, a ribbon mixer, a paddle mixer, a Nauta mixer, or the like can be used. The acidic gas treatment material is a compound capable of neutralizing gases containing the above-mentioned acidic components. It is preferable to use at least one selected from the group consisting of calcium hydroxide, calcium carbonate, and sodium bicarbonate as the acidic gas treatment material because it has a high ability to neutralize acidic components. It is particularly preferable to use calcium hydroxide as the acidic gas treatment material, since it can more effectively neutralize gases containing acidic components.

[0028] When calcium hydroxide is used as the acidic gas treatment agent, it is preferable to use calcium hydroxide produced from a calcium oxide product obtained by the process shown in Fig. 1, i.e., a calcium oxide product produced by calcining calcium carbonate, as a raw material. This has the advantage that both the acidic gas treatment agent and the calcium-containing calcined fine powder that constitute the acidic gas treatment agent composition can be produced simultaneously using the same production equipment.

[0029] To produce calcium hydroxide using calcium oxide products as raw materials, for example, the calcium oxide products are fed into a digester, and 1.3 to 2 times the theoretical amount of water required to hydrate the calcium oxide to calcium hydroxide is added. The calcium oxide and water are vigorously stirred to digest, and the mixture is further stirred in a maturing machine to eliminate uneven digestion and evaporate excess water. After discharge, the mixture is crushed and classified as necessary.

[0030] As described above, calcium-containing calcined fine powder contains a high proportion of substances with a high acid gas neutralizing effect, such as calcium carbonate and calcium oxide. Therefore, the content of calcium-containing calcined fine powder in the acid gas treatment composition produced by mixing calcium-containing calcined fine powder with an acid gas treatment material can be relatively high. Specifically, the content of calcium-containing calcined fine powder in the acid gas treatment material composition can be 1% by mass or more, preferably 3% by mass or more, and even more preferably 5% by mass or more. Furthermore, from the viewpoint of ensuring acid gas neutralization, the content of calcium-containing calcined fine powder in the acid gas treatment material composition is preferably 80% by mass or less, more preferably 60% by mass or less, and even more preferably 40% by mass or less.

[0031] In addition to the calcium-containing calcined fine powder and the acid gas treatment material, the acid gas treatment composition may further contain additives to enhance various performance properties of the acid gas treatment composition. Examples of such additives include porous substances such as activated carbon, activated clay, and zeolite, metal salts of silicic acid such as orthosilicic acid and metasilicic acid, and hardening components such as cement powder and calcium aluminate. The necessity and amount of additives to be added are preferably determined based on the results of preliminary tests.

[0032] When the additive is used, (a) the calcium-containing calcined fine powder, the acidic gas treatment material, and the additive can be simultaneously added to the acidic gas, or (b) the additive can be added when the calcium-containing calcined fine powder and the acidic gas treatment material are mixed to produce the acidic gas treatment material composition. The amount of additive added is preferably 5% by mass or more, and more preferably 10% by mass or more, of the acidic gas treatment material composition, from the viewpoint of suppressing the release of dioxins and heavy metals from the flue. In the case of (b), the amount of additive added is preferably 15% by mass or less of the acidic gas treatment material composition, from the viewpoint of not impairing the acidic gas treatment performance relative to the amount added.

[0033] The acidic gas treatment composition can be used in a method for treating flue gas, for example, by contacting the composition with flue gas containing acidic gases. According to this method, flue gas containing acidic gases and heavy metals is contacted with the acidic gas treatment composition, thereby effectively neutralizing and insolubilizing both the acidic gases and heavy metals in the flue gas. Typically, flue gas is a mixture of only gases containing acidic gases or the like, or of the gases and fine fly ash. Such flue gas is generated, for example, from municipal waste incineration plants, industrial waste incineration plants, or coal-fired thermal power plants.

[0034] Examples of methods for contacting the acidic gas treatment composition with flue gas include passing the flue gas through a container containing the acidic gas treatment composition, or blowing the acidic gas treatment composition into the flue gas flow path (flue). [Example]

[0035] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0036] Example 1 A calcium oxide product was produced using limestone as a raw material in a vertical calcination furnace 10 shown in Figure 1. Calcination conditions were 1000°C and 24 hours. The exhaust gas generated during calcination of the limestone was passed through a dust collector consisting of a cyclone and a bag filter to separate the solid and gas, and calcium-containing calcined fine powder A was recovered from the bag filter. The particle size of calcium-containing calcined fine powder A was 4.3 μm. X-ray fluorescence measurement using the briquette method revealed that calcium-containing calcined fine powder A contained 69 mass% calcium elemental calcium, calculated as CaO. X-ray diffraction measurement also revealed that calcium-containing calcined fine powder A contained calcium oxide, calcium hydroxide, calcium carbonate, and calcium sulfate as calcium compounds. The total proportion of calcium oxide, calcium hydroxide, and calcium carbonate was 97 mass% (relative to the total amount of calcium compounds).

[0037] Fluorescent X-ray measurements were performed using the glass bead method with lithium tetraborate as the flux, using an X-ray fluorescence analyzer (Rigaku Supermini 200). Quantitative analysis of the detected characteristic X-rays was performed using the fundamental parameter method, and the CaO content was calculated by converting the detected components into oxides, with the total content taken as 100%.

[0038] X-ray diffraction measurements were performed using a Bruker AXS NEW D8 ADVANCE X-ray analyzer. The X-ray source was CuKα (with a Ni filter). The tube voltage was 40 kV and the tube current was 40 mA. The detector was a one-dimensional semiconductor high-speed LynxEye detector. The entrance / receiving slit was 0.30°, the step width was 0.02°, and the counting time was 1 s / step. Rietveld analysis was performed based on the obtained X-ray diffraction data, and the total of calcium oxide, calcium hydroxide, calcium carbonate, and calcium sulfate (anhydrous) was set as 100% to calculate the total percentage of calcium oxide, calcium hydroxide, and calcium carbonate (relative to the total amount of calcium compounds). When calcium sulfate was gypsum hemihydrate or gypsum dihydrate, it was converted to anhydrous calcium sulfate.

[0039] The calcium-containing calcined fine powder A thus obtained was mixed with an acidic gas treatment material to obtain an acidic gas treatment material composition. The acidic gas treatment material used was calcium hydroxide produced using a calcium oxide product produced using the vertical calcination furnace shown in Figure 1 and water. The content of calcium-containing calcined fine powder A in the acidic gas treatment material composition was 30%, and the content of calcium hydroxide was 70%. The acidic gas treatment composition thus obtained was subjected to an acidic gas treatment test, the details of which are as follows.

[0040] The acidic gas treatment composition was formed into a φ20 mm compact by uniaxial molding, and then crushed and sieved to obtain granules with a diameter of 500 μm to 710 μm. 4.0 g of these granules were uniformly packed onto a stack of glass filters and glass fiber filter paper placed in a vertically installed glass column (inner diameter 36 mm). The gas line and column were heated to 180°C, which is a temperature simulating the temperature of a flue, and acidic gas was supplied into the column under these conditions. The flow rate of the acidic gas was 4750 mL / min, and the space velocity was 50,000 h -1 This space velocity is the same as the space velocity assumed in the flue of an incineration plant (approximately 5000 h -1 The acid gas composition was HCl: 1000 ppm, SO2: 100 ppm, O2: 10 vol%, CO2: 10 vol%, H2O: 15 vol%, and the balance was N2.

[0041] The removal rates of acidic gases were measured for HCl and SO2. A 0.3% aqueous solution of hydrogen peroxide was used as the absorption solution, and acidic gases were collected at the inlet and outlet of the column. The chloride ion and sulfate ion concentrations in the absorption solution after collection were measured using an ion chromatograph, and the removal rate (%) was calculated using the formula (inlet concentration - outlet concentration) / inlet concentration x 100. The results are shown in Table 1 below.

[0042] Example 2 In Example 1, the content of calcium-containing calcined fine powder A in the acidic gas treatment composition was 50%, and the content of calcium hydroxide was 50%. Except for this, the acidic gas treatment composition was prepared in the same manner as in Example 1, and the acidic gas removal rate of this acidic gas treatment composition was measured in the same manner as in Example 1. The results are shown in Table 1.

[0043] Comparative Example 1 In Example 1, only calcium hydroxide was used, without using calcium-containing calcined fine powder A. Except for this, the removal rate of acidic gases was measured in the same manner as in Example 1. The results are shown in Table 1.

[0044] [Table 1]

[0045] As is clear from the results shown in Table 1, the acidic gas treatment composition containing calcium-containing calcined fine powder A obtained in each example can remove acidic gases to the same extent as calcium hydroxide (Comparative Example 1). Thus, according to the present invention, by-products generated in the manufacturing process of calcium oxide products are utilized as one component of the acidic gas treatment material composition, and at the same time, the consumption of conventionally used acidic gas treatment materials is reduced, thereby contributing to a comprehensive reduction in carbon dioxide emissions. [Explanation of symbols]

[0046] 10 Vertical kiln 11 Furnace body 12 Raw material input section 13 Liquid fuel input 14 Discharge pipe 15 Dust collector 16 Dust collector

Claims

1. A method for using calcium-containing calcined fine powder, in which calcium hydroxide obtained from a calcium oxide product produced by calcining calcium carbonate and calcium-containing calcined fine powder produced in the process of producing the calcium oxide product are used as one component of an acidic gas treatment material composition, comprising: the calcium-containing calcined fine powder contains calcium carbonate, calcium oxide, and calcium hydroxide; the proportion of calcium element contained in the calcium-containing calcined fine powder as determined by fluorescent X-ray measurement is 65% by mass or more in terms of CaO; The calcium-containing calcined fine powder is used, and the total amount of calcium carbonate, calcium oxide, and calcium hydroxide is 75% by mass or more based on the total amount of calcium compounds in the calcium-containing calcined fine powder as determined by X-ray diffraction measurement, and A method for using the calcium-containing calcined fine powder, comprising using the calcium-containing calcined fine powder so that the content of the calcium-containing calcined fine powder in the acidic gas treatment material composition is 5% by mass or more and 60% by mass or less.

2. 2. The method for using the acidic gas treatment composition according to claim 1, wherein the acidic gas treatment composition further comprises at least one selected from the group consisting of calcium carbonate and sodium bicarbonate.

3. 3. The method according to claim 1, wherein the calcium-containing calcined fine powder is separated from gas produced by calcining the calcium carbonate.

4. 3. The method according to claim 1, wherein the calcium-containing calcined fine powder is produced in the process of producing the calcium oxide product by calcining calcium carbonate in a vertical calcination furnace.

5. A method for producing an acidic gas treatment composition, comprising mixing calcium hydroxide obtained from a calcium oxide product produced by calcining calcium carbonate as a raw material with calcium-containing calcined fine powder produced in the process of producing the calcium oxide product, the calcium-containing calcined fine powder contains calcium carbonate, calcium oxide, and calcium hydroxide; the proportion of calcium element contained in the calcium-containing calcined fine powder as determined by fluorescent X-ray measurement is 65% by mass or more in terms of CaO; The total amount of calcium carbonate, calcium oxide, and calcium hydroxide in the calcium-containing calcined fine powder is 75% by mass or more as determined by X-ray diffraction measurement, and A method for producing an acidic gas treatment composition, comprising mixing the calcium-containing calcined fine powder with calcium hydroxide so that the content of the calcium-containing calcined fine powder in the acidic gas treatment composition is 5% by mass or more and 60% by mass or less.

6. The method according to claim 5, wherein the calcium-containing calcined fine powder is separated from gas produced by calcining the calcium carbonate.

7. 7. The method according to claim 5, wherein the calcium oxide product is produced by calcining calcium carbonate in a vertical calcination furnace.

Images