Method for producing nitrate, method for treating combustion exhaust gas, and method for producing carbon dioxide

Abstract

To provide a method for producing a nitrate, a method for treating a combustion exhaust gas and a method for producing carbon dioxide by which wastes discharged from a cement factory or the like can effectively be utilized.SOLUTION: A step (1) of bringing calcium hydroxide, ammonium chloride, and carbon dioxide into contact with each other, a step (2) of bringing calcium hydroxide and ammonium chloride into contact with each other, a step (3) of bringing calcium carbonate obtained in the step (1) and nitric acid into contact with each other, a step (4) of bringing calcium nitrate obtained in the step (3), ammonia, and carbon dioxide into contact with each other, and a step (5) of bringing ammonium nitrate obtained in the step (4) and an alkali metal chloride into contact with each other, wherein at least one of the calcium hydroxide in the step (1) and the step (2), the carbon dioxide in the step (1) and the step (4), and the nitric acid in the step (3) is derived from waste discharged from a cement plant.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing nitrates, a method for treating combustion exhaust gas, and a method for producing carbon dioxide. [Background technology]

[0002] In recent years, various methods for reducing carbon dioxide emissions have been investigated due to the effects of global warming. Meanwhile, in the agricultural sector, environmentally friendly methods for improving productivity have been explored in response to concerns about food shortages due to population growth. Addition of nutrients (fertilizers) is a common method for improving productivity. Typical examples of fertilizers include nitrates and bicarbonates, which are produced by processes such as the conversion method described in Patent Document 1 and the ammonia soda method described in Patent Document 2. In these processes, ammonium chloride, which is produced as a by-product, reacts with calcium hydroxide, obtained by calcining and hydrating calcium carbonate, to produce calcium chloride and ammonia. The ammonia can be recovered, for example, by a stripping method (see, for example, Patent Document 3). The recovered ammonia can be used, for example, to produce ammonium nitrate by neutralizing it with nitric acid. Thus, in the series of processes from the production of fertilizers such as nitrates to the treatment of by-products, a large amount of carbon dioxide is generated by calcining calcium carbonate during the production of calcium hydroxide.

[0003] Furthermore, since the combustion exhaust gas generated by burning coal, heavy oil, and recycled fuels in cement plants contains a large amount of carbon dioxide, various methods for reducing carbon dioxide emissions are being considered. A common method for capturing carbon dioxide is the chemical absorption method, in which carbon dioxide is chemically absorbed into an absorbing liquid such as aqueous ammonia or an aqueous solution of an amine compound (for example, Patent Document 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 1-163286 [Patent Document 2] Special Publication No. 36-7725 [Patent Document 3] Japanese Patent Publication No. 2023-150325 [Patent Document 4] Japanese Patent Application Laid-Open No. 2009-160565 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in the series of processes from the production of fertilizers such as nitrates to the treatment of by-products using the methods described in Patent Documents 1 to 3, a large amount of carbon dioxide is generated by calcining calcium carbonate during the production of calcium hydroxide. Therefore, there is a demand for a reduction in carbon dioxide emissions during fertilizer production.

[0006] Furthermore, in the chemical absorption method described in Patent Document 4, ammonia is difficult to store because it is a toxic and flammable gas, and there is also concern about the consumption of ammonia during thermal regeneration, which increases the procurement costs of ammonia used to capture carbon dioxide at cement plants.

[0007] For these reasons, it is necessary to consider methods that take into account both the reduction of carbon dioxide emissions in fertilizer production and the reduction of carbon dioxide emissions in cement production.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a method for producing nitrates, a method for treating combustion exhaust gas, and a method for producing carbon dioxide, which can effectively utilize waste materials discharged from cement factories and the like. [Means for solving the problem]

[0009] As a result of extensive research into solving the above problems, the present inventors have found that the above problems can be solved by the following invention.

[0010] That is, the present invention relates to the following: [1] a step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; Step (2) of contacting calcium hydroxide with ammonium chloride; Step (3) of contacting the calcium carbonate obtained in step (1) with nitric acid; Step (4) of contacting the calcium nitrate obtained in step (3) with ammonia and carbon dioxide; and and a step (5) of contacting the ammonium nitrate obtained in the step (4) with an alkali metal chloride. A method for producing nitrate, wherein at least one of the calcium hydroxide in the steps (1) and (2), the carbon dioxide in the steps (1) and (4), and the nitric acid in the step (3) is derived from waste discharged from a cement factory. [2] The method for producing nitrate according to [1] above, wherein the calcium hydroxide in the steps (1) and (2) is obtained from calcium hydroxide contained in waste or calcium oxide contained in chlorine bypass dust discharged from cement plants. [3] The method for producing nitrates according to [1] or [2] above, wherein the nitric acid in the step (3) is obtained from nitrogen oxides contained in combustion exhaust gas discharged from a cement factory. [4] The method for producing nitrate according to any one of [1] to [3] above, wherein the carbon dioxide in the steps (1) and (4) is carbon dioxide contained in combustion exhaust gas emitted from a cement factory. [5] The method for producing a nitrate according to any one of [1] to [4] above, wherein the alkali metal chloride in the step (5) is potassium chloride or sodium chloride. [6] The method for producing a nitrate according to any one of [1] to [5] above, wherein the ammonia obtained in the step (2) is used in the step (4). [7] The method for producing a nitrate according to any one of [1] to [6] above, wherein the ammonium chloride obtained in the step (5) is used in the steps (1) and (2). [8] The method for producing a nitrate according to any one of [1] to [7] above, wherein the nitrate obtained in the step (5) contains calcium carbonate.

[0011] [9] Step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; Step (2) of contacting calcium hydroxide with ammonium chloride; Step (3) of contacting the calcium carbonate obtained in step (1) with nitric acid; Step (4) of contacting the calcium nitrate obtained in step (3) with ammonia and carbon dioxide; and and a step (5) of contacting the ammonium nitrate obtained in the step (4) with an alkali metal chloride. A method for treating combustion exhaust gas, wherein at least one of the carbon dioxide in the steps (1) and (4) and the nitric acid in the step (3) is derived from combustion exhaust gas emitted from a cement plant.

[10] The method for treating combustion exhaust gas according to [9] above, wherein the calcium hydroxide in the steps (1) and (2) is obtained from calcium hydroxide contained in waste or calcium oxide contained in chlorine bypass dust discharged from a cement factory.

[0012]

[11] A step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; Step (2) of contacting calcium hydroxide with ammonium chloride; Step (3) of contacting the calcium carbonate obtained in step (1) with nitric acid; Step (4) of contacting the calcium nitrate obtained in step (3) with ammonia and carbon dioxide; and A step (R) of recovering the carbon dioxide obtained in the step (3), The method for producing carbon dioxide, wherein the carbon dioxide in the steps (1) and (4) is carbon dioxide contained in combustion exhaust gas emitted from a cement plant. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a method for producing nitrates, a method for treating combustion exhaust gas, and a method for producing carbon dioxide, which can effectively utilize waste materials discharged from cement factories and the like. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating a method for producing nitrates according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. The present invention is not limited to the following embodiment, and can be implemented with any modifications within the scope that does not impair the effects of the invention. In this specification, the notation of a numerical range as "AA to BB" means "at least AA and at most BB." In addition, in this specification, the numbers associated with "at least," "at most," and "to" in describing a numerical range are numbers that can be arbitrarily combined. For example, when a certain numerical range is described as "CC to DD" and "EE to FF," the numerical ranges "CC to FF" and "EE to DD" are also included.

[0016] [Method of producing nitrates] The method for producing nitrate according to the present embodiment includes the steps of: Step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; Step (2) of contacting calcium hydroxide with ammonium chloride; Step (3) of contacting the calcium carbonate obtained in step (1) with nitric acid; Step (4) of contacting the calcium nitrate obtained in step (3) with ammonia and carbon dioxide; and and a step (5) of contacting the ammonium nitrate obtained in the step (4) with an alkali metal chloride. At least one of the calcium hydroxide in the steps (1) and (2), the carbon dioxide in the steps (1) and (4), and the nitric acid in the step (3) is derived from waste materials discharged from cement factories.

[0017] In the method for producing nitrate of the present embodiment, at least one of calcium hydroxide in the steps (1) and (2), carbon dioxide in the steps (1) and (4), and nitric acid in the step (3) is derived from waste materials discharged from cement factories, and therefore, the waste materials can be effectively utilized. Examples of waste materials discharged from cement factories include chlorine bypass dust, concrete-containing waste materials (waste concrete), and combustion exhaust gas.

[0018] Fig. 1 is a schematic diagram illustrating a method for producing nitrate according to one embodiment of the present invention. Fig. 1 illustrates an example in which calcium hydroxide used in step (1) described below is obtained from calcium oxide contained in chlorine bypass dust discharged from a cement factory, and an example in which the alkali metal chloride used in step (5) described below is potassium chloride.

[0019] [Step (1)] Step (1) is a step of contacting calcium hydroxide, ammonium chloride, and carbon dioxide. In this step, from the viewpoint of further exerting the effects of the present invention, it is preferable that at least one of the calcium hydroxide and the carbon dioxide is derived from waste discharged from a cement factory, and it is more preferable that both the calcium hydroxide and the carbon dioxide are derived from waste discharged from a cement factory.

[0020] The calcium hydroxide may be calcium hydroxide contained in waste discharged from cement plants, or may be calcium hydroxide obtained from calcium oxide contained in chlorine bypass dust discharged from cement plants. In this specification, "chlorine bypass dust" refers to particulate matter with a high chlorine content contained in exhaust gas extracted from a probe located at the end of a cement kiln. Chlorine bypass dust includes oxides of metals such as calcium, potassium, and sodium, and halides such as chlorides.

[0021] The proportions of substances contained in chlorine bypass dust cannot be generalized because they can vary depending on the cement factory, etc., but for example, calcium oxide is usually 15 to 45 mass%, preferably 20 to 40 mass%, and more preferably 25 to 35 mass%. The content of potassium oxide is usually 5 to 40 mass %, preferably 20 to 40 mass %, and more preferably 25 to 40 mass %. The content of sodium oxide is usually 0 to 40% by mass, preferably 0.5 to 40% by mass, and more preferably 1 to 40% by mass. The chloride (for example, calcium chloride, potassium chloride, sodium chloride, etc.) is usually 10 to 30 mass %, preferably 15 to 28 mass %, more preferably 18 to 25 mass %. Other substances (for example, metal oxides other than calcium, potassium, and sodium) are generally 10 to 25 mass %, preferably 12 to 22 mass %, and more preferably 15 to 20 mass %. The proportion of the substance contained in the chlorine bypass dust can be measured, for example, using an energy dispersive X-ray fluorescence analyzer (XRF analyzer). Specifically, it can be measured by the method described in the Examples.

[0022] When the calcium hydroxide is obtained from calcium oxide contained in chlorine bypass dust, the method for producing the calcium hydroxide is not particularly limited. For example, calcium hydroxide can be obtained by adding chlorine bypass dust to water, stirring and mixing the mixture for preferably 4 hours or more, subjecting the resulting fluid to solid-liquid separation, and dissolving the calcium oxide obtained as a solid content in water. There are no particular limitations on the method for solid-liquid separation of a fluid containing calcium oxide, and examples thereof include a method using a pressure separation device that separates solids and liquids by applying pressure or squeezing using a filter, a method using a centrifugal separator that separates solids and liquids by the action of centrifugal force, and a method using a sedimentation separator that allows the solids to settle by leaving the mixture to stand. Among these, the method using a sedimentation separator is preferred from the viewpoint of recovering as much calcium hydroxide as possible that has eluted around the solids. The fluid from which calcium oxide has been recovered as a solid may be used as a cement raw material after chlorine removal.

[0023] In order to further exert the effects of the present invention, the carbon dioxide is preferably carbon dioxide contained in combustion exhaust gas emitted from a cement factory. Since the combustion exhaust gas contains dust and nitrogen oxides (NOx), it is preferable to remove the dust and recover the NOx before using the combustion exhaust gas in the production method of this embodiment. The dust can be removed by, for example, recovering the dust in the combustion exhaust gas using a bag filter or an electrostatic precipitator, and then cooling the combustion exhaust gas to about 30°C. The NOx can be recovered by, for example, contacting the cooled combustion exhaust gas after dust removal with water to absorb the NOx into the water, and recovering the NOx as a nitrate-nitrogen-containing liquid or a nitrite-nitrogen-containing liquid.

[0024] From the viewpoint of more efficiently progressing the reaction, the content of carbon dioxide contained in the combustion exhaust gas is preferably 5 to 30 mass %, more preferably 5 to 25 mass %, and even more preferably 10 to 20 mass %. The NOx content in the combustion exhaust gas (after NOx recovery) varies depending on the equipment and cannot be generalized, but is usually 400 ppm by mass or less, further 100 ppm by mass or less, or 90 ppm by mass or less. There is no particular lower limit, and it is, for example, about 50 ppm by mass or more.

[0025] Although a commercially available product may be used as the ammonium chloride, it is preferable to recycle and reuse the ammonium chloride produced in the step (5) described below in order to further enhance the effects of the present invention (see FIG. 1).

[0026] In step (1), it is preferable to first mix the calcium hydroxide and ammonium chloride in order to more efficiently proceed with the reaction. Normally, the carbonation reaction of calcium hydroxide is slow, but adding ammonium chloride makes the reaction proceed more efficiently. The method for mixing the calcium hydroxide and the ammonium chloride is not particularly limited, and the calcium hydroxide and the ammonium chloride may be mixed by being charged into a reaction device capable of mixing the calcium hydroxide and the ammonium chloride. When mixing the calcium hydroxide and the ammonium chloride, a solvent such as water may be added. The order in which these compounds are added to the reaction device is not particularly limited.

[0027] The calcium hydroxide and the ammonium chloride may be mixed using a stirring device. The stirring device is not particularly limited, but examples thereof include a Henschel mixer, a mixing shaker, a tumbler mixer, a V-type mixer, a double-cone type mixer, a ribbon type mixer, a Nauta mixer, a Super Mixer, etc. Among these, a Henschel mixer is preferred from the viewpoint of more efficiently carrying out the reaction between the calcium hydroxide and the ammonium chloride.

[0028] The mixing ratio of the calcium hydroxide to the ammonium chloride is preferably 2:1 to 2:3 by mass, more preferably 3:2 to 4:5, and even more preferably 3:2 to 1:1. When the mixing ratio is within the above range, the reaction can proceed more efficiently.

[0029] The reaction temperature when mixing the calcium hydroxide and the ammonium chloride is preferably 5 to 70°C, more preferably 5 to 30°C, and even more preferably 5 to 15°C, from the viewpoint of more efficiently progressing the reaction. The reaction time is preferably 0.1 to 5 hours, more preferably 0.3 to 2 hours, and even more preferably 0.4 to 1 hour.

[0030] The fluid obtained by stirring and mixing is subjected to solid-liquid separation, and a fluid containing calcium chloride and ammonia is recovered as a liquid fraction. The calcium hydroxide recovered as a solid fraction may be used as a cement raw material, may be reused in this step, or may be supplied to step (2) described below. As the method for the solid-liquid separation, the method described above for the method for solid-liquid separation of a fluid containing calcium oxide can be used.

[0031] Next, the fluid containing calcium chloride and ammonia is brought into contact with carbon dioxide. There are no particular limitations on the method for contacting the fluid containing calcium chloride and ammonia with carbon dioxide. For example, carbon dioxide may be supplied so as to be blown into a reactor into which the fluid containing calcium chloride and ammonia has been introduced. The reaction equipment is not particularly limited, but from the viewpoint of more efficiently proceeding with the reaction, a stirring equipment is preferable. As the stirring equipment, any of the stirring equipments exemplified as stirring equipment that can be used in mixing the calcium hydroxide and the ammonium chloride can be used.

[0032] The carbon dioxide is supplied until the pH of the fluid containing calcium chloride and ammonia reaches preferably about 5 to 7, more preferably 6 to 7. When the pH of the fluid is within the above range, the reaction proceeds more efficiently, and calcium carbonate is obtained as a product. In this specification, pH is a value measured by a pH measuring device capable of measuring the hydrogen ion exponent of a fluid.

[0033] The temperature of the fluid containing calcium chloride and ammonia when the carbon dioxide is brought into contact with the fluid is preferably 5 to 70° C., more preferably 5 to 30° C., and even more preferably 5 to 15° C. When the temperature of the fluid is within the above range, the reaction proceeds more efficiently, and calcium carbonate is obtained as a product.

[0034] Carbon dioxide is supplied to the fluid containing calcium chloride and ammonia until the pH of the fluid falls within the above range, and then the resulting fluid is subjected to solid-liquid separation. As the method for the solid-liquid separation, the method described above for the method for solid-liquid separation of a fluid containing calcium oxide can be used. The calcium carbonate recovered as a solid content is supplied to the step (3) described below either as it is or after drying. When the calcium carbonate is dried, the drying temperature is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher. The upper limit is preferably 150°C or lower, more preferably 130°C or lower, and even more preferably 120°C or lower. The drying time is preferably 6 to 48 hours, more preferably 10 to 36 hours, and even more preferably 12 to 30 hours.

[0035] The fluid recovered as the liquid component contains ammonium chloride produced as a by-product. This ammonium chloride may be reused in this process or may be supplied to the process (2) described below (see FIG. 1).

[0036] [Step (2)] Step (2) is a step of contacting calcium hydroxide with ammonium chloride. In this step, the calcium hydroxide is preferably derived from waste materials discharged from cement factories, in order to further exert the effects of the present invention.

[0037] The calcium hydroxide used can be the same as that described in step (1). Although a commercially available product may be used as the ammonium chloride, it is preferable to recycle and reuse the ammonium chloride produced in the step (5) described below in order to further enhance the effects of the present invention. In addition, the ammonium chloride produced as a by-product in the step (1) may also be reused (see FIG. 1).

[0038] An example of a method for contacting the calcium hydroxide with the ammonium chloride is mixing the calcium hydroxide with the ammonium chloride. The mixing method described in step (1) above can be used for mixing the calcium hydroxide with the ammonium chloride. The reaction equipment and agitation equipment used for mixing the calcium hydroxide with the ammonium chloride can be the reaction equipment and agitation equipment described in step (1) above.

[0039] The mixing ratio of the calcium hydroxide to the ammonium chloride is preferably 2:1 to 2:3 by mass, more preferably 3:2 to 4:5, and even more preferably 3:2 to 1:1. When the mixing ratio is within the above range, the reaction can proceed more efficiently.

[0040] The reaction temperature when mixing the calcium hydroxide and the ammonium chloride is preferably 5 to 70°C, more preferably 5 to 30°C, and even more preferably 5 to 15°C, from the viewpoint of more efficiently progressing the reaction. The reaction time is preferably 0.1 to 5 hours, more preferably 0.3 to 2 hours, and even more preferably 0.4 to 1 hour.

[0041] The mixing produces a fluid containing calcium chloride and ammonia. The resulting fluid is heated to a temperature of preferably 70°C or higher but lower than 100°C, more preferably 72°C or higher but lower than 95°C, and even more preferably 74°C or higher but lower than 90°C, thereby allowing the ammonia to evaporate more efficiently. The evaporation of ammonia is preferably carried out until the pH of the fluid reaches 7 to 8. The evaporated ammonia is supplied to step (4) described below (see FIG. 1).

[0042] The fluid (calcium chloride-containing liquid) obtained after evaporating the ammonia may be discharged after desalination treatment, or may be reused for the reaction with carbon dioxide in the step (1) above.

[0043] [Step (3)] Step (3) is a step of contacting the calcium carbonate obtained in step (1) with nitric acid. The nitric acid may be a commercially available product, but from the viewpoint of further exerting the effects of the present invention, it is preferably derived from waste materials discharged from cement factories, and more preferably derived from nitrogen oxides contained in combustion exhaust gas discharged from cement factories.

[0044] When the nitric acid is obtained from nitrogen oxides (NOx) contained in combustion exhaust gas, the method for producing it is not particularly limited. For example, a method of obtaining nitric acid by absorbing NOx into water using a gas purification device described in JP 2017-51899 A can be mentioned.

[0045] From the viewpoint of more efficiently progressing the reaction, the concentration of the nitric acid is preferably 6 to 30% by mass, more preferably 8 to 25% by mass, and even more preferably 10 to 20% by mass.

[0046] An example of a method for contacting the calcium carbonate obtained in the step (1) with the nitric acid is to mix the calcium carbonate and the nitric acid by adding them to a reactor capable of mixing them. When mixing the calcium carbonate and the nitric acid, a solvent such as water may be added.

[0047] The reaction equipment is not particularly limited, but is preferably a stirring equipment from the viewpoint of more efficiently proceeding the reaction and obtaining calcium nitrate as a product. As the stirring equipment, the stirring equipment described in the step (1) can be used.

[0048] The calcium nitrate produced by the neutralization reaction between the calcium carbonate and the nitric acid is supplied to step (4) described later (see FIG. 1). The heat of neutralization of the calcium nitrate may be circulated and used for heating when evaporating ammonia in step (2) or for heating when evaporating and drying ammonium nitrate obtained in step (4) described later.

[0049] Furthermore, carbon dioxide is generated as a by-product of the neutralization reaction (see Figure 1). Because the carbon dioxide does not contain impurities, high-purity carbon dioxide can be obtained by recovering it. Carbon dioxide can be recovered by applying various well-known methods, such as physical adsorption, physical absorption, chemical absorption, and cryogenic separation. The captured carbon dioxide can be used for CCUS (Carbon dioxide Capture, Utilization and Storage), such as methanation and calcium carbonate production.

[0050] [Step (4)] Step (4) is a step of contacting the calcium nitrate obtained in step (3) with ammonia and carbon dioxide. In order to further exert the effects of the present invention, it is preferable to use the ammonia obtained in the step (2) (see FIG. 1). From the viewpoint of further exerting the effects of the present invention, the carbon dioxide is preferably derived from waste discharged from a cement factory, and more preferably carbon dioxide contained in combustion exhaust gas discharged from a cement factory.

[0051] There is no particular limitation on the method for bringing the calcium nitrate obtained in the step (3), ammonia, and carbon dioxide into contact with each other. For example, the ammonia obtained in the step (2) may be supplied to a reactor containing the calcium nitrate in a blown manner, the ammonia may be dissolved, and then carbon dioxide may be supplied to the reactor in a blown manner.

[0052] The reaction equipment is not particularly limited, but is preferably a stirring equipment from the viewpoint of more efficiently proceeding with the reaction. As the stirring equipment, the stirring equipment described in the step (1) can be used.

[0053] The amount of ammonia supplied is preferably 2.2 to 3.0 equivalents, more preferably 2.3 to 2.8 equivalents, and even more preferably 2.4 to 2.6 equivalents, from the viewpoint of allowing the reaction with calcium nitrate to proceed sufficiently.

[0054] The carbon dioxide is supplied until the pH of the fluid containing calcium nitrate and ammonia reaches preferably about 5 to 7, more preferably 6 to 7. When the pH of the fluid is within the above range, the reaction proceeds more efficiently, and ammonium nitrate is obtained as a product.

[0055] The temperature of the fluid containing calcium nitrate and ammonia when the carbon dioxide is brought into contact with the fluid is preferably 5 to 70° C., more preferably 5 to 30° C., and even more preferably 5 to 15° C. When the temperature of the fluid is within the above range, the reaction proceeds more efficiently, and ammonium nitrate is obtained as a product.

[0056] Carbon dioxide is supplied to the fluid containing calcium nitrate and ammonia until the pH of the fluid falls within the above range, and then the resulting fluid is subjected to solid-liquid separation. As the method for the solid-liquid separation, the method described above for the method for solid-liquid separation of a fluid containing calcium oxide can be used.

[0057] The ammonium nitrate recovered as a liquid is evaporated to dryness and then supplied to step (5) described below.

[0058] The calcium carbonate recovered as a solid content may be recycled as it is or after drying and reused in the above-mentioned step (3). When the calcium carbonate is dried, the drying temperature and drying time are as described in the step (1).

[0059] [Step (5)] Step (5) is a step of contacting the ammonium nitrate obtained in step (4) with an alkali metal chloride. As the alkali metal chloride, potassium chloride or sodium chloride is preferred, and potassium chloride is more preferred, from the viewpoint of further exerting the effects of the present invention. Although commercially available potassium chloride and sodium chloride may be used, in order to further enhance the effects of the present invention, potassium chloride and sodium chloride derived from chlorine bypass dust discharged from cement plants are preferred. Potassium chloride and sodium chloride can be obtained, for example, by washing chlorine bypass dust with water.

[0060] The ammonium nitrate obtained in step (4) can be brought into contact with an alkali metal chloride by, for example, introducing the ammonium nitrate and the alkali metal chloride into a reactor capable of mixing them. When mixing the ammonium nitrate and the alkali metal chloride, a solvent such as water may be added.

[0061] The reaction equipment is not particularly limited, but is preferably a stirring equipment from the viewpoint of more efficiently proceeding the reaction and obtaining nitrate as a product. As the stirring equipment, the stirring equipment described in the step (1) can be used.

[0062] The reaction between the ammonium nitrate and the alkali metal chloride produces a nitrate and ammonium chloride (see FIG. 1). The nitrate can be separated from the ammonium chloride by crystallization. The crystallization conditions cannot be generalized because they may vary depending on the amount of nitrate produced, the amount of alkali metal chloride added, the amount of solvent added, etc., but it is preferable to raise the liquid temperature to 80°C and then cool it to 10°C, and it is more preferable to raise the liquid temperature to 60°C and then cool it to 10°C. The nitrate precipitated by the crystallization is recovered as a solid by solid-liquid separation. As the method for the solid-liquid separation, the method described above for the method for solid-liquid separation of a fluid containing calcium oxide can be used.

[0063] The ammonium chloride recovered as a liquid by the solid-liquid separation may be crystallized and recovered as needed. The crystallization conditions may be appropriately adjusted depending on the amount of ammonium chloride recovered. The recovered ammonium chloride is preferably used in the steps (1) and (2) in order to further exert the effects of the present invention (see FIG. 1).

[0064] The nitrate obtained by the production method of this embodiment may contain calcium carbonate.

[0065] [Method of treating combustion exhaust gas] The method for treating combustion exhaust gas according to the present embodiment includes the steps of: Step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; Step (2) of contacting calcium hydroxide with ammonium chloride; Step (3) of contacting the calcium carbonate obtained in step (1) with nitric acid; Step (4) of contacting the calcium nitrate obtained in step (3) with ammonia and carbon dioxide; and and a step (5) of contacting the ammonium nitrate obtained in the step (4) with an alkali metal chloride. At least one of the carbon dioxide in the steps (1) and (4) and the nitric acid in the step (3) is derived from combustion exhaust gas emitted from a cement plant.

[0066] The method for producing nitrate according to the present embodiment not only produces nitrate as described above, but also enables efficient treatment of combustion exhaust gas emitted from cement plants. Thus, the present invention also provides a method for treating combustion exhaust gas.

[0067] Steps (1) to (5), as well as the raw materials and equipment used in these steps, such as calcium hydroxide, ammonium chloride, carbon dioxide, and nitric acid, are the same as those explained in the method for producing nitrate.

[0068] [Method of producing carbon dioxide] The method for producing carbon dioxide of this embodiment includes: Step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; Step (2) of contacting calcium hydroxide with ammonium chloride; Step (3) of contacting the calcium carbonate obtained in step (1) with nitric acid; Step (4) of contacting the calcium nitrate obtained in step (3) with ammonia and carbon dioxide; and A step (R) of recovering the carbon dioxide obtained in the step (3), The carbon dioxide used in the steps (1) and (4) is carbon dioxide contained in combustion exhaust gas emitted from a cement factory.

[0069] Combustion exhaust gas emitted from cement factories and other plants contains impurities other than carbon dioxide, making it difficult to utilize the carbon dioxide in the combustion exhaust gas. According to the method for producing nitrate of the present embodiment, not only can nitrate be produced as described above, but also high-purity carbon dioxide can be recovered. Therefore, according to the method for producing carbon dioxide of the present embodiment, high-purity carbon dioxide can be obtained, and the carbon dioxide can be used for CCUS (Carbon dioxide Capture, Utilization, and Storage) such as methanation and production of calcium carbonate.

[0070] Steps (1) to (4), as well as the raw materials and equipment used in these steps, such as calcium hydroxide, ammonium chloride, carbon dioxide, and nitric acid, are the same as those explained in the method for producing nitrate.

[0071] The carbon dioxide used in the steps (1) and (4) is carbon dioxide contained in the combustion exhaust gas emitted from a cement factory. The carbon dioxide content in the combustion exhaust gas is preferably 5 to 30 mass %, more preferably 5 to 25 mass %, and even more preferably 10 to 20 mass %. When the carbon dioxide content is within the above range, the reaction proceeds more efficiently, making it easier to obtain high-purity carbon dioxide.

[0072] [Process (R)] Step (R) is a step of recovering the carbon dioxide obtained in the step (3). Carbon dioxide can be recovered by applying various well-known methods such as physical adsorption, physical absorption, chemical absorption, and cryogenic separation. [Example]

[0073] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples in any way.

[0074] A laboratory-scale test simulating the present invention was carried out as follows. The raw materials used are shown below. [Chlorine bypass dust] Chlorine bypass dust recovered from a cement plant: calcium oxide (CaO): 31.5 mass%, potassium oxide (KO): 28.4 mass%, sodium oxide (NaO): 1.0 mass%, chlorides: 20.5 mass% (including chlorides such as calcium chloride), other substances: 18.6 mass% The proportion of substances contained in the chlorine bypass dust is a value measured using an energy dispersive X-ray fluorescence analyzer (XRF analyzer) (Epsilon3 XLE, manufactured by Malvern PANalytical). [Combustion exhaust gas] Exhaust gas generated during N clinker burning in a cement factory is subjected to dust removal, cooling, moisture removal, and NOx recovery (gas temperature: 35°C, moisture concentration in gas: 0.3 mass%, carbon dioxide concentration in gas: 10-15 mass%, NOx amount in gas: 60-80 mass ppm). [Ammonium chloride] Manufactured by Kanto Chemical Co., Ltd. For research and testing purposes, JIS K8116:2006. Reagent purity: 99.5% by mass. [nitric acid] Manufactured by Kanto Chemical Co., Ltd., for testing and research purposes, JIS K8541:2015. Nitric acid concentration: 60-61% by mass. [Potassium chloride] It is obtained by washing chlorine bypass dust recovered from cement plants.

[0075] Example 1 [Step (1)] 353.7 g of chlorine bypass dust (calcium oxide content: 31.5% by mass) was added to a stirring device containing 1.4 L of ultrapure water, and the mixture was stirred at room temperature (25°C) for approximately 18 hours. The resulting fluid was then subjected to solid-liquid separation by filtration. 1.8 L of ultrapure water and 52.6 g of ammonium chloride were added to 111.4 g of the solid calcium hydroxide, and the mixture was stirred for 10 minutes. The resulting fluid was then subjected to solid-liquid separation by filtration. Carbon dioxide (carbon dioxide concentration in the gas: 10-15% by mass) simulating combustion exhaust gas was blown into the resulting filtrate (fluid containing calcium chloride and ammonia) until the liquid temperature reached 20°C and the pH reached 5-6, precipitating calcium carbonate. The calcium carbonate-containing fluid was then subjected to solid-liquid separation by filtration. The resulting solid was placed in a dryer and dried overnight at 105°C, yielding 57.3 g of calcium carbonate (yield: 56%). The obtained calcium carbonate was analyzed using an energy dispersive X-ray fluorescence analyzer (Epsilon3 XLE, manufactured by Malvern PANalytical), and as a result, it was confirmed that the calcium carbonate had a purity of 99.0%.

[0076] [Step (2)] 353.7 g of chlorine bypass dust (calcium oxide content: 31.5% by mass) was added to a stirrer containing 1.4 L of ultrapure water, and the mixture was stirred at room temperature (25°C) for approximately 18 hours. The resulting fluid was then subjected to solid-liquid separation by filtration. 1.8 L of ultrapure water and 52.6 g of ammonium chloride were added to 111.4 g of calcium hydroxide obtained as a solid content, and the mixture was stirred for 10 minutes. The resulting fluid was then subjected to solid-liquid separation by filtration. The resulting filtrate (fluid containing calcium chloride and ammonia) was heated at a heating temperature of 90°C using a mantle heater. When the liquid temperature reached 76°C, ammonia began to evaporate, and the filtrate was recovered and supplied to step (4) described below.

[0077] [Step (3)] 717 mL of nitric acid (concentration: 10% by mass) and 4.1 L of ultrapure water were added to 57.3 g of the calcium carbonate obtained in the above step (1) and stirred. The carbon dioxide generated by the reaction was recovered by chemical absorption, and the concentration of the recovered carbon dioxide was 99.0% or more.

[0078] [Step (4)] After the temperature of the fluid obtained in step (3) returned to room temperature (25°C), the ammonia obtained in step (2) was blown into the fluid. Thereafter, carbon dioxide simulating combustion exhaust gas (carbon dioxide concentration in the gas: 10 to 15% by mass) was blown into the fluid until the liquid temperature of the fluid reached 25°C and the pH reached 5 to 6, thereby precipitating calcium carbonate. The fluid containing the calcium carbonate was then subjected to solid-liquid separation by filtration. The obtained solid matter was placed in a dryer and dried overnight at a heating temperature of 105°C, yielding 52.6 g of calcium carbonate (yield: 91%). The obtained calcium carbonate was analyzed using an energy dispersive X-ray fluorescence analyzer (Epsilon3 XLE, manufactured by Malvern PANalytical) and was confirmed to be calcium carbonate with a purity of 99.8%. Meanwhile, the separated ammonium nitrate aqueous solution was evaporated to dryness, yielding 86.0 g of ammonium nitrate (yield: 95%).

[0079] [Step (5)] 48.0 g of the ammonium nitrate obtained in step (4) and 74.6 g of potassium chloride were added to a stirrer containing 100 mL of ultrapure water, and the mixture was stirred until the liquid temperature was raised to 60° C. After that, the mixture was left to stand until the liquid temperature reached 10° C. The precipitated crystals were separated into solid and liquid by filtration, and the obtained crystals were placed in a dryer and dried at a heating temperature of 105° C. for 16 hours to obtain 37.9 g of potassium nitrate. The obtained potassium nitrate was analyzed using an energy dispersive X-ray fluorescence analyzer (Epsilon3 XLE, manufactured by Malvern PANalytical), and as a result, it was confirmed that the potassium nitrate had a purity of 99.1%.

[0080] Next, 37.3 g of ammonium nitrate and 40.0 g of potassium chloride were added to the filtrate after solid-liquid separation and stirred. The liquid temperature was raised to 80° C., and then the liquid was allowed to stand until the temperature reached 45° C. The precipitated crystals were separated into solid and liquid by filtration, and the obtained crystals were placed in a dryer and dried at a heating temperature of 105° C. for 16 hours to obtain 10.3 g of ammonium chloride. The obtained ammonium chloride was analyzed using an energy dispersive X-ray fluorescence analyzer (Epsilon3 XLE, manufactured by Malvern PANalytical), and as a result, it was confirmed that the purity of the ammonium chloride was 98.8%. The obtained ammonium chloride can be recycled and used in the above steps (1) and (2).

Claims

1. Step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; Step (2) of contacting calcium hydroxide with ammonium chloride; a step (3) of contacting the calcium carbonate obtained in the step (1) with nitric acid; a step (4) of contacting the calcium nitrate obtained in the step (3) with ammonia and carbon dioxide; and and a step (5) of contacting the ammonium nitrate obtained in the step (4) with an alkali metal chloride, A method for producing nitrate, wherein at least one of the calcium hydroxide in the steps (1) and (2), the carbon dioxide in the steps (1) and (4), and the nitric acid in the step (3) is derived from waste discharged from a cement factory.

2. 2. The method for producing nitrate according to claim 1, wherein the calcium hydroxide in the steps (1) and (2) is obtained from calcium hydroxide contained in waste or calcium oxide contained in chlorine bypass dust discharged from a cement plant.

3. 3. The method for producing nitrates according to claim 1 or 2, wherein the nitric acid in the step (3) is obtained from nitrogen oxides contained in combustion exhaust gas discharged from a cement factory.

4. 3. The method for producing nitrates according to claim 1 or 2, wherein the carbon dioxide in the steps (1) and (4) is carbon dioxide contained in combustion exhaust gas emitted from a cement factory.

5. 3. The method for producing nitrates according to claim 1 or 2, wherein the alkali metal chloride in step (5) is potassium chloride or sodium chloride.

6. The method for producing nitrates according to claim 1 or 2, wherein the ammonia obtained in the step (2) is used in the step (4).

7. The method for producing nitrates according to claim 1 or 2, wherein the ammonium chloride obtained in the step (5) is used in the steps (1) and (2).

8. The method for producing nitrates according to claim 1 or 2, wherein the nitrates obtained in the step (5) contain calcium carbonate.

9. Step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; Step (2) of contacting calcium hydroxide with ammonium chloride; a step (3) of contacting the calcium carbonate obtained in the step (1) with nitric acid; a step (4) of contacting the calcium nitrate obtained in the step (3) with ammonia and carbon dioxide; and and a step (5) of contacting the ammonium nitrate obtained in the step (4) with an alkali metal chloride, The method for treating combustion exhaust gas, wherein at least one of the carbon dioxide in the step (1) and the step (4) and the nitric acid in the step (3) is derived from combustion exhaust gas emitted from a cement factory.

10. 10. The method for treating a combustion exhaust gas according to claim 9, wherein the calcium hydroxide in the steps (1) and (2) is obtained from calcium hydroxide contained in waste or calcium oxide contained in chlorine bypass dust discharged from a cement plant.

11. Step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; Step (2) of contacting calcium hydroxide with ammonium chloride; a step (3) of contacting the calcium carbonate obtained in the step (1) with nitric acid; a step (4) of contacting the calcium nitrate obtained in the step (3) with ammonia and carbon dioxide; and A step (R) of recovering the carbon dioxide obtained in the step (3), The method for producing carbon dioxide, wherein the carbon dioxide in the steps (1) and (4) is carbon dioxide contained in combustion exhaust gas emitted from a cement plant.

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