Method for producing nitrate, method for treating flue gas, and method for producing carbon dioxide

Abstract

Provided are: a method for producing nitrate capable of effectively utilizing waste discharged from cement factory, etc. that has a step (1) for bringing calcium hydroxide, ammonium chloride, and carbon dioxide into contact, a step (2) for bringing calcium hydroxide and ammonium chloride into contact, a step (3) for bringing the calcium carbonate obtained in step (1) into contact with nitric acid, a step (4) for bringing the calcium nitrate obtained in step (3) into contact with ammonia and carbon dioxide, and a step (5) for bringing the ammonium nitrate obtained in step (4) into contact with an alkali metal chloride, in which at least one of the calcium hydroxide of steps (1) and (2), the carbon dioxide of steps (1) and (4), and the nitric acid of step (3) is derived from waste discharged from a cement factory; a method for treating flue gas; and a method for producing carbon dioxide.

Description

Nitrate production method, combustion exhaust gas treatment method, and carbon dioxide production method

[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.

[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. Common carbon dioxide capture methods include a chemical absorption method in which carbon dioxide is chemically absorbed into an absorbing liquid such as ammonia water or an aqueous solution of an amine compound (see, for example, Patent Document 4).

[0004] Japanese Patent Laid-Open No. 1-163286 Japanese Patent Publication No. 36-7725 Japanese Patent Laid-Open No. 2023-150325 Japanese Patent Laid-Open No. 2009-160565

[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.

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

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

[10] The method for treating combustion exhaust gas according to [9], wherein the calcium hydroxide in 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.

[0012]

[11] A method for producing carbon dioxide, comprising: a step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; a 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), ammonia, and carbon dioxide; and a step (R) of recovering the carbon dioxide obtained in the step (3), wherein the carbon dioxide in the step (1) and the step (4) is carbon dioxide contained in combustion exhaust gas emitted from a cement plant.

[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.

[0014] FIG. 1 is a schematic diagram illustrating a method for producing nitrates according to one embodiment of the present 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. Note that the notation of a numerical range as "AA to BB" in this specification means "at least AA and at most BB." Furthermore, in this specification, the numerical values ​​associated with "at least," "at most," and "to" in describing a numerical range are values ​​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 for producing nitrate] The method for producing nitrate of this embodiment includes: a step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; a 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), ammonia, and carbon dioxide; and a step (5) of contacting the ammonium nitrate obtained in the step (4) with an alkali metal chloride, 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.

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

[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 vary depending on the cement plant, etc.; however, for example, calcium oxide is typically 15 to 45 mass%, preferably 20 to 40 mass%, and more preferably 25 to 35 mass%. Potassium oxide is typically 5 to 40 mass%, preferably 20 to 40 mass%, and more preferably 25 to 40 mass%. Sodium oxide is typically 0 to 40 mass%, preferably 0.5 to 40 mass%, and more preferably 1 to 40 mass%. Chlorides (e.g., calcium chloride, potassium chloride, sodium chloride, etc.) are typically 10 to 30 mass%, preferably 15 to 28 mass%, and more preferably 18 to 25 mass%. Other substances (e.g., metal oxides other than calcium, potassium, and sodium) are typically 10 to 25 mass%, preferably 12 to 22 mass%, and more preferably 15 to 20 mass%. The proportions of substances contained in the chlorine bypass dust can be measured, for example, using an energy dispersive X-ray fluorescence (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 production method is not particularly limited. For example, calcium hydroxide can be obtained by adding chlorine bypass dust to water, stirring and mixing the resulting fluid, preferably for four hours or more, subjecting the resulting fluid to solid-liquid separation, and dissolving the calcium oxide obtained as a solid component in water. The method for solid-liquid separation of a fluid containing calcium oxide is not particularly limited. Examples of the method include a method using a pressure separation device that separates solids and liquid components by applying pressure or squeezing using a filter, a method using a centrifugal separator that separates solids and liquid components by the action of centrifugal force, and a method using a sedimentation separation device that allows the solid component to settle by standing. Among these, the method using a sedimentation separation device is preferred from the viewpoint of recovering as much calcium hydroxide as possible that has eluted around the solid component. The fluid from which calcium oxide has been recovered as a solid component may be used as a cement raw material after removing chlorine.

[0023] In order to further enhance the effects of the present invention, the carbon dioxide is preferably carbon dioxide contained in combustion exhaust gas emitted from a cement factory. Because 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, for example, by recovering the dust in the combustion exhaust gas using a bag filter or an electrostatic precipitator, and then cooling the combustion exhaust gas to approximately 30°C. The NOx can be recovered, for example, by contacting the cooled combustion exhaust gas after dust removal with water to absorb the NOx into the water, and then recovering the NOx as a nitrate-nitrogen-containing liquid or a nitrite-nitrogen-containing liquid.

[0024] From the viewpoint of more efficient reaction progression, 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%. 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 restriction on the lower limit, and it is, for example, about 50 ppm by mass or more.

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

[0026] In step (1), it is preferable to first mix the calcium hydroxide and the ammonium chloride from the viewpoint of more efficiently proceeding with the reaction. Normally, the carbonation reaction of calcium hydroxide is slow, but adding ammonium chloride allows the reaction to proceed more quickly. There are no particular limitations on the method for mixing the calcium hydroxide and the ammonium chloride; the calcium hydroxide and the ammonium chloride may be mixed by being introduced into a reactor capable of mixing the calcium hydroxide and the ammonium chloride. Furthermore, a solvent such as water may be added when mixing the calcium hydroxide and the ammonium chloride. The order in which these compounds are introduced into the reactor is also not particularly limited.

[0027] The calcium hydroxide and the ammonium chloride may be mixed using a stirring device. Examples of the stirring device include, but are not limited to, a Henschel mixer, a mixing shaker, a tumbler mixer, a V-type mixer, a double-cone mixer, a ribbon mixer, a Nauta mixer, and a Super Mixer. 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] From the viewpoint of more efficiently proceeding with the reaction, 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. 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 a 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 contacted with carbon dioxide. There are no particular limitations on the method for contacting the fluid containing calcium chloride and ammonia with carbon dioxide, and for example, carbon dioxide may be supplied by blowing it into a reactor into which the fluid containing calcium chloride and ammonia has been introduced. The reactor is not particularly limited, but is preferably a stirring device from the viewpoint of more efficiently progressing the reaction. As the stirring device, any of the stirring devices exemplified as stirring devices that can be used for mixing the calcium hydroxide and 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, the pH is a value measured with a pH meter that can measure the hydrogen ion exponent of the 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 is within the above range, and then the resulting fluid is subjected to solid-liquid separation. As a 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 employed. The calcium carbonate recovered as a solid content is supplied to step (3) described below either directly or after drying. When drying the calcium carbonate, 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. The ammonium chloride may be reused in this step or may be supplied to step (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 discharged from a cement factory, from the viewpoint of further exerting the effects of the present invention.

[0037] The calcium hydroxide may be the same as that described in the step (1). The ammonium chloride may be a commercially available product. However, in order to further enhance the effects of the present invention, it is preferable to recycle and reuse the ammonium chloride produced in the step (5) described below. Furthermore, 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 as the method for mixing the calcium hydroxide with the ammonium chloride. The reaction equipment and agitation equipment used when mixing the calcium hydroxide with the ammonium chloride can be the reaction equipment and agitation equipment described in step (1).

[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] From the viewpoint of more efficiently proceeding with the reaction, 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. 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 liquid 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 evaporation of ammonia may be discharged after desalination treatment, or may be reused for the reaction with carbon dioxide in the step (1).

[0043] [Step (3)] Step (3) is a step of contacting the calcium carbonate obtained in step (1) with nitric acid. While a commercially available product can be used as the nitric acid, from the viewpoint of further exerting the effects of the present invention, it is preferable that the nitric acid be derived from waste materials discharged from cement factories, and more preferably, that the nitric acid be obtained 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 the nitric acid is not particularly limited. For example, a method in which NOx is absorbed into water using a gas purification device described in JP 2017-51899 A can be mentioned.

[0045] From the viewpoint of more efficiently proceeding with 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 a method in which the calcium carbonate and the nitric acid are introduced into a reactor capable of mixing the calcium carbonate and the nitric acid, and then mixed. 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 of calcium carbonate with nitric acid is supplied to step (4) described later (see FIG. 1). The heat of neutralization of 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 this 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 recovered carbon dioxide can be used for CCUS (Carbon dioxide Capture, Utilization, and Storage), such as methanation and the production of calcium carbonate.

[0050] [Step (4)] Step (4) is a step of contacting the calcium nitrate obtained in step (3), ammonia, and carbon dioxide. From the viewpoint of further exerting the effects of the present invention, it is preferable to use the ammonia obtained in step (2) (see FIG. 1 ). From the viewpoint of further exerting the effects of the present invention, it is preferable that the carbon dioxide be 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 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 the step (5) described below.

[0058] The calcium carbonate recovered as a solid content may be recycled as it is or after drying in the above-mentioned step (3). When the calcium carbonate is dried, the drying temperature and drying time are the same as those described in the above-mentioned 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, with potassium chloride being more preferred, from the viewpoint of further exerting the effects of the present invention. Commercially available potassium chloride and sodium chloride may be used, but from the viewpoint of further exerting 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 the 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 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 vary depending on the amount of nitrate produced, the amount of alkali metal chloride added, the amount of solvent added, and other factors. However, 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. The method for solid-liquid separation can be the same as that described above for the method for solid-liquid separation of a fluid containing calcium oxide.

[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 for treating combustion exhaust gas] The method for treating combustion exhaust gas of this embodiment includes the steps of: (1) contacting calcium hydroxide, ammonium chloride, and carbon dioxide; (2) contacting calcium hydroxide with ammonium chloride; (3) contacting the calcium carbonate obtained in the step (1) with nitric acid; (4) contacting the calcium nitrate obtained in the step (3), ammonia, and carbon dioxide; and (5) contacting the ammonium nitrate obtained in the step (4) with an alkali metal chloride, 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 factory.

[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 for producing carbon dioxide] The method for producing carbon dioxide of this embodiment includes: a step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; a 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), ammonia, and carbon dioxide; and a step (R) of recovering the carbon dioxide obtained in the step (3), wherein the carbon dioxide in the step (1) and the step (4) is carbon dioxide contained in combustion exhaust gas emitted from a cement factory.

[0069] Combustion exhaust gas emitted from cement plants and the like 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, it is possible not only to produce nitrate as described above, but also to recover high-purity carbon dioxide. 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 the 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 steps (1) and (4) is carbon dioxide contained in combustion exhaust gas discharged 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] [Step (R)] Step (R) is a step of recovering the carbon dioxide obtained in the step (3). Carbon dioxide recovery can be carried out by applying various well-known methods such as physical adsorption, physical absorption, chemical absorption, and cryogenic separation.

[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 as follows: [Chlorine bypass dust] Chlorine bypass dust recovered from a cement factory: calcium oxide (CaO): 31.5 mass%, potassium oxide (K ２ O): 28.4% by mass, sodium oxide (Na ２O): 1.0%, chloride: 20.5% by mass (including chlorides such as calcium chloride), other substances: 18.6% by mass. The proportions of substances contained in the chlorine bypass dust were measured using an energy dispersive X-ray fluorescence (XRF) analyzer (Epsilon3 XLE, manufactured by Malvern PANalytical). [Combustion Exhaust Gas] Exhaust gas generated during N clinker burning in a cement plant was subjected to dust removal, cooling, moisture removal, and NOx recovery (gas temperature: 35°C, moisture concentration in gas: 0.3% by mass, carbon dioxide concentration in gas: 10-15% by mass, NOx content in gas: 60-80 ppm by mass). [Ammonium Chloride] Manufactured by Kanto Chemical Co., Ltd., JIS K8116:2006 for testing and research. Reagent purity: 99.5% by mass. [Nitric Acid] Manufactured by Kanto Chemical Co., Ltd., JIS K8541:2015 for testing and research. Nitric acid concentration: 60-61% by mass. [Potassium chloride] Obtained by washing chlorine bypass dust recovered from cement factories.

[0075] Example 1 [Step (1)] 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. 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 content 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 was found to have 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 90°C using a mantle heater. Ammonia began to evaporate at a liquid temperature of 76°C, and the filtrate was then 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 step (1) and stirred. Carbon dioxide generated by the reaction was recovered by chemical absorption. 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. Carbon dioxide (carbon dioxide concentration in the gas: 10 to 15% by mass) simulating combustion exhaust gas was then blown into the fluid until the fluid temperature reached 25°C and the pH reached 5 to 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 52.6 g of calcium carbonate (yield: 91%). The resulting calcium carbonate was analyzed using an energy-dispersive X-ray fluorescence analyzer (Epsilon3 XLE, manufactured by Malvern PANalytical) and confirmed to be calcium carbonate with a purity of 99.8%. The ammonium nitrate aqueous solution after separation 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 stirred. The liquid temperature was raised to 60°C and then allowed to stand until the liquid temperature reached 10°C. The precipitated crystals were subjected to solid-liquid separation by filtration, and the resulting 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 was confirmed to have 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 allowed to stand until the liquid temperature reached 45°C. The precipitated crystals were separated into solid and liquid by filtration, and the resulting 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 confirmed to have a purity of 98.8%. The obtained ammonium chloride can be recycled and used in the above steps (1) and (2).

Claims

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

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

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

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

5. 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 step (2) is used in step (4).

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

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

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

10. The method for treating combustion exhaust gas according to claim 9, wherein the calcium hydroxide in 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. A method for producing carbon dioxide, comprising: a step (1) of contacting calcium hydroxide, ammonium chloride, and carbon dioxide; a step (2) of contacting calcium hydroxide with ammonium chloride; a step (3) of contacting the calcium carbonate obtained in step (1) with nitric acid; a step (4) of contacting the calcium nitrate obtained in step (3), ammonia, and carbon dioxide; and a step (R) of recovering the carbon dioxide obtained in step (3), wherein the carbon dioxide in steps (1) and (4) is carbon dioxide contained in combustion exhaust gas emitted from a cement factory.

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