Method for producing potassium nitrate and system for treating waste discharged from cement plant

Abstract

To provide a method for producing potassium nitrate by which the potassium nitrate can efficiently and easily be obtained by effectively utilizing waste discharged from a cement plant, and to provide a system for treating the waste discharged from the cement plant.SOLUTION: A method for producing potassium nitrate, comprising a step of bringing chlorine bypass dust discharged from a cement plant into contact with a saturated aqueous solution of potassium chloride at normal temperature to extract potassium chloride from the chlorine bypass dust, a step of bringing potassium chloride obtained in the step of extracting potassium chloride into contact with nitric acid obtained from nitrogen oxides contained in a combustion exhaust gas discharged from the cement plant, and a step of heating a fluid obtained in the step of bringing into contact at 75 °C or higher and 175 °C or lower to obtain potassium nitrate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing potassium nitrate and a system for treating waste discharged from a cement factory. [Background technology]

[0002] In cement manufacturing, flue gas generated by burning coal, heavy oil, and recycled fuel is used to dry the raw materials, then discharged after a dust collection process. In addition to carbon dioxide and trace amounts of chlorides, flue gas contains large amounts of nitrogen oxides (hereinafter referred to as NOx) from fuel combustion. The nitrogen dioxide (hereinafter referred to as NO2) contained in NOx causes environmental impacts such as acid rain and has adverse effects on the human body. In light of these issues, cement plants are making ongoing efforts to reduce NOx emissions, for example by selecting fuels with low nitrogen content and removing NOx using denitrifiers.

[0003] Currently, a catalytic reduction method (SNCR method) using urea or alcohol is used as a NOx denitrification technology in cement plants (for example, Patent Document 1). Furthermore, at cement plants, excess chlorides generated during the burning of recycled fuels are known to have a negative effect on the physical properties of cement, and so companies are working to control the quality of cement by recovering chlorides as chlorine bypass dust using cooled probes. The chlorine bypass dust is washed with water and reused as a cement raw material. Meanwhile, the water after washing is adjusted to a composition that complies with municipal wastewater standards and is sufficiently diluted before being discharged, but it still contains a large amount of potassium chloride. Furthermore, a method for producing potassium chloride salt from chlorine bypass dust has been proposed (for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-189989 [Patent Document 2] Japanese Patent Application Publication No. 2019-26521 Summary of the Invention [Problem to be solved by the invention]

[0005] The SNCR method described above requires an optimum temperature of 800°C or higher for the denitrification reaction, which requires operation in an extremely high-temperature environment, making it difficult to say it is a simple method. Furthermore, the hot gas that passes through the urea spray zone is not denitrified, and it is estimated that approximately 400 ppm of NOx is emitted into the atmosphere. Therefore, denitrification in cement plants can only be performed within a limited temperature range, and it is difficult to effectively reuse the captured NO2.

[0006] As mentioned above, the water obtained after washing chlorine bypass dust contains a large amount of potassium chloride. However, since it also contains heavy metals, it cannot be used for food, and since it also contains chlorine, its use as fertilizer is also limited. In addition, in the above-mentioned method for producing potassium chloride salt, flue gas desulfurization effluent is added to chlorine bypass dust to obtain a slurry, and then the slurry is subjected to solid-liquid separation to obtain a filtrate containing potassium chloride and selenium. However, a reducing agent (heavy metal remover) must be added to remove selenium from the filtrate, which increases the number of production steps.

[0007] For these reasons, NOx and chlorine bypass dust emitted from cement plants are not currently being used effectively.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing potassium nitrate that can effectively utilize waste discharged from cement factories and can produce potassium nitrate highly efficiently and easily, and a system for treating waste discharged from cement factories. [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 of contacting chlorine bypass dust discharged from a cement plant with a saturated aqueous solution of potassium chloride at room temperature to extract potassium chloride from the chlorine bypass dust; a step of contacting the potassium chloride obtained in the step of extracting potassium chloride with nitric acid obtained from nitrogen oxides contained in combustion exhaust gas discharged from a cement factory; A method for producing potassium nitrate, comprising the step of heating the fluid obtained in the contacting step at a temperature of 75°C or higher and 175°C or lower to obtain potassium nitrate. [2] The method for producing potassium nitrate according to [1] above, wherein the chlorine bypass dust is contacted with the saturated aqueous potassium chloride solution by reflux. [3] The method for producing potassium nitrate according to [1] or [2], wherein a fluid obtained by contacting the chlorine bypass dust with the saturated aqueous potassium chloride solution is subjected to a first solid-liquid separation at a temperature of 80°C or higher and 150°C or lower. [4] The method for producing potassium nitrate according to [3] above, wherein the saturated aqueous potassium chloride solution recovered by the first solid-liquid separation is cooled to room temperature and then subjected to a second solid-liquid separation to obtain potassium chloride as a solid content. [5] The method for producing potassium nitrate according to [4] above, wherein the potassium chloride obtained by the second solid-liquid separation is used in the contacting step. [6] The method for producing potassium nitrate according to [4] above, wherein the saturated aqueous potassium chloride solution recovered by the second solid-liquid separation is reused for contact with the chlorine bypass dust. [7] The method for producing potassium nitrate according to any one of [1] to [6], wherein the content of the nitric acid is more than 1.0 molar equivalent and not more than 2.0 molar equivalents relative to 1.0 molar equivalent of the potassium chloride. [8] The method for producing potassium nitrate according to any one of [1] to [7] above, wherein the concentration of the nitric acid is 10% by mass or more and 60% by mass or less. [9] The method for producing potassium nitrate according to any one of [1] to [8], further comprising heating to dryness at 100°C or higher in the step of obtaining potassium nitrate.

[10] The method for producing potassium nitrate according to [9], wherein nitric oxide and chlorine produced by the heating and drying are recovered.

[11] A chlorine bypass dust receiving facility for receiving chlorine bypass dust discharged from a cement plant; Flue gas receiving facilities that receive flue gas emitted from cement factories; a potassium chloride extraction facility for extracting potassium chloride from the chlorine bypass dust by bringing the chlorine bypass dust into contact with a saturated aqueous potassium chloride solution at room temperature; a facility for contacting the potassium chloride obtained in the potassium chloride extraction facility with nitric acid obtained from nitrogen oxides contained in the combustion exhaust gas; and A system for treating waste discharged from a cement factory, comprising a potassium nitrate production facility for heating the fluid obtained in the contacting facility to a temperature of 75°C or higher and 175°C or lower to obtain potassium nitrate. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a method for producing potassium nitrate that can effectively utilize waste discharged from cement factories and easily obtain potassium nitrate, and a system for treating waste discharged from cement factories. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a method for producing potassium nitrate according to an embodiment of the present invention. [Figure 2] 1 is a diagram showing an example of a system for treating waste discharged from a cement factory according to an embodiment of the present invention. [Figure 3] FIG. 1 is a schematic diagram showing a potassium chloride extraction apparatus used in Reference Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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.

[0014] [Method of producing potassium nitrate] The method for producing potassium nitrate according to the present embodiment includes the steps of: a step of contacting chlorine bypass dust discharged from a cement plant with a saturated aqueous solution of potassium chloride at room temperature to extract potassium chloride from the chlorine bypass dust; a step of contacting the potassium chloride obtained in the step of extracting potassium chloride with nitric acid obtained from nitrogen oxides contained in combustion exhaust gas discharged from a cement factory; The method further comprises a step of heating the fluid obtained in the contacting step at a temperature of 75°C or higher and 175°C or lower to obtain potassium nitrate.

[0015] In the method for producing potassium nitrate of the present embodiment, chlorine bypass dust and combustion exhaust gas are used as waste materials discharged from a cement factory, potassium chloride contained in the chlorine bypass dust is brought into contact with nitric acid obtained from nitrogen oxides contained in the combustion exhaust gas, and the resulting fluid is heated within a temperature range of 75°C or higher and 175°C or lower. This simple method makes it possible to obtain potassium nitrate with high purity and high yield.

[0016] Fig. 1 is a schematic diagram showing an example of a method for producing potassium nitrate according to the present embodiment. As shown in Fig. 1, the method for producing potassium nitrate according to the present embodiment includes a step of extracting potassium chloride, a step of contacting potassium chloride with nitric acid, and a step of obtaining potassium nitrate.

[0017] [Step of extracting potassium chloride] This step is a step of extracting potassium chloride from chlorine bypass dust discharged from a cement plant by bringing the dust into contact with a saturated aqueous solution of potassium chloride at room temperature. 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.

[0018] 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 %. The content of other substances (for example, metal oxides other than calcium, potassium, and sodium) is usually 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.

[0019] The contact of the chlorine bypass dust with the saturated aqueous potassium chloride solution at room temperature (25° C.) is not particularly limited, but is preferably carried out by reflux from the viewpoint of further increasing the purity and yield of the extracted potassium chloride. The reflux is carried out, for example, by a method in which a contact tower into which the chlorine bypass dust and the saturated aqueous potassium chloride solution have been introduced is heated, and a part of the generated gas is cooled in a cooler from the top of the tower and returned to the contact tower.

[0020] From the viewpoint of further increasing the solubility of potassium chloride, the liquid temperature during reflux is preferably 100° C. or higher, more preferably 110° C. or higher, and even more preferably 120° C. or higher. There is no particular upper limit, but it is 350° C. or lower. The reflux time is preferably 0.1 to 5 hours, more preferably 0.3 to 2 hours, and even more preferably 0.4 to 1 hour.

[0021] For heating during reflux, it is preferable to use combustion exhaust gas discharged from a cement factory as a heat source, from the viewpoint of further demonstrating the effects of the present invention (see FIG. 1). The temperature of the combustion exhaust gas cannot be generalized because it varies depending on the source of the exhaust gas used, but is usually 30° C. or higher and 250° C. or lower, preferably 50° C. or higher and 200° C. or lower, more preferably 70° C. or higher and 180° C. or lower, and even more preferably 80° C. or higher and 150° C. If the temperature of the combustion exhaust gas is within the above range, it is easy to adjust the liquid temperature to a desired temperature range.

[0022] From the viewpoint of further increasing the solubility of potassium chloride in the fluid obtained by contacting the chlorine bypass dust with the saturated aqueous potassium chloride solution and increasing the amount of potassium chloride extracted, it is preferable to perform the first solid-liquid separation at a temperature of 80°C or higher and 150°C or lower. From the above viewpoint, the temperature of the fluid when the first solid-liquid separation is carried out is preferably 90°C or higher and 130°C or lower, more preferably 90°C or higher and 110°C or lower.

[0023] The first solid-liquid separation method is not particularly limited, 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 separation device that settles solids by leaving the mixture to stand. Among these, the method using a centrifugal separator is preferred because it is necessary to separate the mixed liquid (fluid) at a high temperature in a short time.

[0024] The solid content (for example, potassium chloride) recovered by the first solid-liquid separation may be desalted and used in a cement factory.

[0025] Furthermore, it is preferable to cool the saturated aqueous potassium chloride solution recovered as a liquid by the first solid-liquid separation to room temperature (25°C) and then subject the solution to a second solid-liquid separation, from the viewpoint of further increasing the purity and yield of the extracted potassium chloride. The higher the purity and yield of the potassium chloride, the higher the purity and yield of potassium nitrate that can be obtained in the step of obtaining potassium nitrate, which will be described later. The second solid-liquid separation allows potassium chloride to be obtained as a solid content, which is used in the step of contacting potassium chloride with nitric acid, which will be described later, as shown in FIG. The second solid-liquid separation method can be any of the methods described above for the first solid-liquid separation method. Among these, a method using a sedimentation separation device is preferred because the particle size of the potassium chloride produced can be very small depending on the conditions.

[0026] As shown in FIG. 1, the saturated aqueous potassium chloride solution recovered as a liquid by the second solid-liquid separation is preferably reused for contact with the chlorine bypass dust.

[0027] [Step of contacting potassium chloride with nitric acid] This step is a step of contacting the potassium chloride obtained in the potassium chloride extraction step with nitric acid obtained from nitrogen oxides contained in combustion exhaust gas discharged from a cement factory. By bringing the potassium chloride into contact with the nitric acid, potassium nitrate is produced, and a fluid containing the potassium nitrate is obtained. The temperature during the contact cannot be generally defined because it varies depending on the concentration of nitric acid, but is usually preferably less than 75° C., more preferably 70° C. or less, and even more preferably 60° C. or less. There is no particular lower limit, but it is preferably 20° C. or more.

[0028] The method for producing the nitric acid is not particularly limited, but an example thereof is a wet recovery method in which nitrogen oxides (NOx) contained in combustion exhaust gas are absorbed into water using a gas purification device described in JP 2017-51899 A to obtain nitric acid.

[0029] Examples of a method for contacting the potassium chloride obtained in the potassium chloride extraction step with the nitric acid include a method in which the potassium chloride and the nitric acid are introduced into a reaction device capable of mixing the potassium chloride and the nitric acid, and then mixed.

[0030] The reaction equipment is not particularly limited, but is preferably a stirring equipment from the viewpoint of more efficiently proceeding the reaction and obtaining potassium nitrate as a product. 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 potassium chloride and the nitric acid.

[0031] The content of the nitric acid is preferably more than 1.0 molar equivalent and not more than 2.0 molar equivalents, more preferably more than 1.1 molar equivalents and not more than 1.8 molar equivalents, and even more preferably more than 1.2 molar equivalents and not more than 1.6 molar equivalents, relative to 1.0 molar equivalent of the potassium chloride. When the content of the nitric acid is within the above range, potassium nitrate can be obtained with higher purity and higher yield.

[0032] The concentration of the nitric acid is preferably 10% by mass or more and 60% by mass or less, more preferably 15% by mass or more and 50% by mass or less, even more preferably 15% by mass or more and 45% by mass or less, and even more preferably 18% by mass or more and 42% by mass or less. When the concentration of the nitric acid is within the above range, potassium nitrate can be obtained with higher purity and higher yield.

[0033] [Step for obtaining potassium nitrate] This step is a step of obtaining potassium nitrate by heating the fluid obtained in the contacting step at 75°C or higher and 175°C or lower. When the heating temperature for heating the fluid is within the above range, potassium nitrate can be obtained with high purity and high yield. From this viewpoint, the heating temperature is preferably 75°C or higher and 170°C or lower, more preferably 80°C or higher and 160°C or lower, and even more preferably 80°C or higher and 150°C or lower.

[0034] From the viewpoint of further demonstrating the effects of the present invention, it is preferable to use, as a heat source for the heating, combustion exhaust gas discharged from a cement factory, as shown in Figure 1. The temperature of the combustion exhaust gas is as described in the step of extracting potassium chloride.

[0035] The reaction equipment used when heating the fluid is not particularly limited, but from the viewpoint of more efficiently progressing the reaction, a stirring equipment is preferred. Examples of the stirring equipment include the stirring equipment exemplified as the stirring equipment that can be used in the step of contacting potassium chloride with nitric acid, and among them, a Henschel mixer is preferred. The stirring device may be the same as that used in the step of contacting potassium chloride with nitric acid, or a different stirring device may be used.

[0036] For example, it is preferable to heat the fluid from the temperature in the contacting step to the heating temperature (hereinafter also referred to as "post-heating temperature") and then stir the fluid. From the viewpoint of obtaining potassium nitrate with higher purity and higher yield, it is preferable that the post-heating temperature is not lower than 75°C. The stirring time is preferably 0.1 to 5 hours, more preferably 0.1 to 2 hours, and even more preferably 0.2 to 1 hour.

[0037] This step preferably further comprises heating to dryness at 100°C or higher, from the viewpoint of further increasing the purity and yield of the potassium nitrate obtained. Furthermore, a portion of the nitric acid reacts with chloride ions in the solution to produce nitrosyl chloride (NOCl), which is difficult to separate from the solution. However, the nitrosyl chloride decomposes at temperatures above 100°C to produce nitric oxide (NO) and chlorine (Cl). Therefore, by carrying out the heating and drying process at temperatures above 100°C, the produced nitrosyl chloride is decomposed, allowing it to be recovered as nitric oxide and chlorine.

[0038] The generated gas containing nitric oxide and chlorine is subjected to, for example, a heat exchanger to remove moisture, and then zeolite (e.g., N114) is used to adsorb and recover the nitric oxide, followed by appropriate recovery of chlorine gas. The moisture removed by the heat exchanger may be reused in the above-mentioned reaction.

[0039] The recovered nitrogen monoxide can be used to produce nitric acid, as shown in Figure 1. Chlorine can also be used as a raw material for vinyl chloride, bleaching powder, pickling agents, pH adjusters, etc.

[0040] The heating temperature is preferably 110°C or higher and 160°C or lower, more preferably 115°C or higher and 155°C or lower, and even more preferably 120°C or higher and 150°C or lower. The heating time is preferably 0.1 to 5 hours, more preferably 0.2 to 2 hours, and even more preferably 0.4 to 1 hour. In order to further enhance the effects of the present invention, it is preferable to use combustion exhaust gas discharged from a cement factory as a heat source for the heating (see FIG. 1). The temperature of the combustion exhaust gas is as described in the step of extracting potassium chloride. According to the production method of this embodiment, combustion exhaust gas emitted from a cement factory can be used as a heat source in the step of extracting potassium chloride, the step of contacting potassium chloride with nitric acid, and the step of obtaining potassium nitrate, and can also be used as a NOx source for producing nitric acid.

[0041] The potassium nitrate thus obtained is recovered. Since the potassium nitrate may adhere to the wall surface of the reaction equipment, it may be recovered by appropriately spraying water on it and drying it. Alternatively, the reaction liquid obtained by the above reaction may be naturally cooled, and the precipitated potassium nitrate may be recovered by solid-liquid separation and dried. Since the purity of the obtained potassium nitrate depends on the purity of the potassium chloride, it is preferable to recrystallize the potassium nitrate as necessary.

[0042] The purity of the potassium nitrate is preferably 80% or more, more preferably 85% or more, and even more preferably 95% or more. The yield of potassium nitrate is preferably 75% or more, more preferably 85% or more, and even more preferably 95% or more.

[0043] [Waste treatment system from cement factories] The system for treating waste discharged from a cement factory according to this embodiment includes: Chlorine bypass dust receiving facility that receives chlorine bypass dust discharged from cement plants; Flue gas receiving facilities that receive flue gas emitted from cement factories; a potassium chloride extraction facility for extracting potassium chloride from the chlorine bypass dust by bringing the chlorine bypass dust into contact with a saturated aqueous potassium chloride solution at room temperature; a facility for contacting the potassium chloride obtained in the potassium chloride extraction facility with nitric acid obtained from nitrogen oxides contained in the combustion exhaust gas; and The system is equipped with a potassium nitrate production facility that heats the fluid obtained in the contacting facility to a temperature of 75°C or higher and 175°C or lower to obtain potassium nitrate.

[0044] Fig. 2 is a diagram showing an example of a treatment system for waste discharged from a cement factory according to this embodiment. As shown in Fig. 2, the treatment system 100 for waste discharged from a cement factory according to this embodiment includes a chlorine bypass dust receiving facility 10, a combustion exhaust gas receiving facility 20, a potassium chloride extraction facility 30, a facility 40 for contacting potassium chloride with nitric acid, and a potassium nitrate production facility 50. Between the combustion exhaust gas receiving facility 20 and the facility 40 for contacting potassium chloride with nitric acid, a nitric acid production facility 21 for obtaining nitric acid from nitrogen oxides contained in the combustion exhaust gas may be provided.

[0045] The chlorine bypass dust is supplied to a chlorine bypass dust receiving facility 10 from a probe located at the end of the cement kiln (not shown). The chlorine bypass dust supplied to the chlorine bypass dust receiving facility 10 is supplied to a potassium chloride extraction facility 30 through a supply line (1), and is brought into contact with a saturated aqueous solution of potassium chloride at room temperature supplied from another line in the potassium chloride extraction facility 30, where potassium chloride (solid) is extracted. The extracted potassium chloride is fed through a feed line (2) to a facility 40 for contacting potassium chloride with nitric acid.

[0046] From the viewpoint of further exerting the effects of the present invention, the potassium chloride extraction equipment 30 preferably includes a contact tank 31 for bringing the chlorine bypass dust into contact with the saturated aqueous potassium chloride solution, a first solid-liquid separation device 32 for performing a first solid-liquid separation on the fluid obtained in the contact tank 31 within a desired temperature range, a cooling tank 33 for cooling the saturated aqueous potassium chloride solution recovered by the first solid-liquid separation to room temperature, and a second solid-liquid separation device 34 for performing a second solid-liquid separation on the saturated aqueous potassium chloride solution cooled to room temperature (see FIG. 2 ).

[0047] The combustion exhaust gas is supplied from the cement plant to a combustion exhaust gas receiving facility 20 through a supply line (not shown). The combustion exhaust gas supplied to the combustion exhaust gas receiving facility 20 is then supplied through a supply line (3) to a nitric acid production facility 21, where nitric acid is produced from the nitrogen oxides contained in the combustion exhaust gas. The produced nitric acid is supplied through a supply line (4) to a facility 40 that brings potassium chloride and nitric acid into contact with each other, where potassium nitrate is produced by contact with the potassium chloride, and a fluid containing the potassium nitrate is obtained. The obtained fluid is supplied through a supply line (5) to a potassium nitrate production facility 50, where it is heated at a temperature of 75°C to 175°C, whereby potassium nitrate is produced as a solid. In FIG. 2, the equipment 40 for bringing potassium chloride into contact with nitric acid and the potassium nitrate manufacturing equipment 50 are separate equipment, but the equipment 40 for bringing potassium chloride into contact with nitric acid and the potassium nitrate manufacturing equipment 50 may be the same equipment.

[0048] The reactions, raw materials, equipment (devices), etc. used in the potassium chloride extraction equipment 30, nitric acid production equipment 21, equipment 40 for contacting potassium chloride with nitric acid, and potassium nitrate production equipment 50 are the same as those described in the potassium nitrate production method. In addition, in the potassium chloride extraction equipment 30, equipment 40 for contacting potassium chloride with nitric acid, and potassium nitrate production equipment 50, combustion exhaust gas from the combustion exhaust gas receiving equipment 20 may be used as a heat source for heating. [Example]

[0049] 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.

[0050] 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). [nitric acid] Nitric acid was obtained by absorbing NOx contained in exhaust gas (carbon dioxide concentration: 10-30% by mass, water concentration: 5-20% by mass, NOx concentration: 50-800 ppm by mass) generated in a cement factory using a gas purification device (MKN, manufactured by Pollution Prevention Equipment Laboratory Co., Ltd.) to obtain a nitric acid concentration of 60-61% by mass.

[0051] (Reference example 1) The following procedure was carried out using the potassium chloride extraction apparatus shown in FIG. An excess amount of potassium chloride (Kanto Chemical Co., Ltd., 32326-00) was added to the ultrapure water and mixed thoroughly. Since the mixture cooled due to endothermic heat immediately after mixing, it was mixed again after returning to room temperature (25°C) and left to stand for at least one day. 80 mL of the supernatant of the resulting saturated potassium chloride solution was collected and placed in a round-bottom flask equipped with a Liebig tube (see Figure 3). 20 g of chlorine bypass dust was added and stirred. The saturated potassium chloride solution containing the chlorine bypass dust was heated to 120 °C using a mantle heater and refluxed for 30 minutes. After that, the solution was placed in a centrifuge (H-112, manufactured by Kokusan Co., Ltd.) equipped with a filter cloth (TR84385, manufactured by Kokusan Co., Ltd.) at a high temperature and subjected to solid-liquid separation (first solid-liquid separation) at a peripheral speed of 800 m / s while maintaining the temperature at 80 °C or higher. The separated dehydrated cake (solid content) can be used as a cement raw material by desalination. The treated water used in the desalination process can be returned to the round-bottom flask and reused as the saturated potassium chloride solution. The filtrate obtained by the first solid-liquid separation was left to stand for 8 hours or more and returned to room temperature (25°C), causing potassium chloride crystals to precipitate. These crystals were recovered by solid-liquid separation (second solid-liquid separation) and then dried for 1 day or more in a dryer at 105°C. The potassium chloride (crystals) after drying were analyzed using an X-ray diffractometer (manufactured by PANalytical, trade name: X'Pert Pro), and the result was that the purity was 99% and the yield was 6.4 g (86 mmol).

[0052] Table 1 shows the amounts of water, potassium chloride (KCl), and sodium chloride (NaCl) in the saturated aqueous potassium chloride solution before the first and second solid-liquid separations, the amounts of the filtrate, crystals, and deposits on the equipment after the first and second solid-liquid separations, and the changes therein. The change in Table 1 is (total amount after the first and second solid-liquid separations) - (total amount before the first and second solid-liquid separations) for each component in the saturated aqueous potassium chloride solution.

[0053] [Table 1]

[0054] From Table 1, it can be seen that there are losses of each component in the saturated potassium chloride aqueous solution due to wall adhesion 1 and 2, but these losses do not need to be taken into consideration during continuous operation of an actual plant. Furthermore, since the potassium chloride in the saturated potassium chloride aqueous solution (filtrate) reaches equilibrium with the potassium chloride in the raw material when the filtrate is recycled, it is presumed that a certain amount of potassium chloride will be produced during continuous operation.

[0055] (Reference example 2) The filtrate (saturated aqueous potassium chloride solution) recovered by the second solid-liquid separation in Reference Example 1 was returned to the round-bottom flask for reuse, and potassium chloride crystals were obtained by the same operation as in Reference Example 1. This operation was repeated three times. The obtained potassium chloride crystals were analyzed using an energy dispersive X-ray fluorescence analyzer (Epsilon3 XLE, manufactured by Malvern PANalytical). The results are shown in Table 2.

[0056] [Table 2]

[0057] Table 2 shows that when the saturated aqueous potassium chloride solution (filtrate) recovered by the second solid-liquid separation is recycled, high-purity potassium chloride with few impurities is obtained in the first, second, and third runs.

[0058] Example 1 6.4 g of potassium chloride crystals (purity: 99%) obtained in the same manner as in Reference Example 1 and 24.3 mL of nitric acid diluted to a concentration of 20% by mass (1.0 molar equivalent of nitric acid per 1.0 molar equivalent of potassium chloride) were placed in a round-bottom flask and thoroughly stirred at room temperature (25°C) to dissolve. The mixture was then heated to 70°C while aerating at 0.5 m / s and stirred for 1 hour, then further heated to 120°C and heated to dryness for 0.5 hours. After heating to dryness, the solid matter obtained by further heating was recovered and dried in a dryer at 105°C for at least one day. Meanwhile, the gas in the round-bottom flask was subjected to a heat exchanger to remove water vapor, and nitric oxide was recovered using zeolite (N114). Analysis using a gas detector tube (Gastec Corporation, detector tube: 8HH) revealed that approximately 3-5% chlorine gas was constantly detected. The dried solid was analyzed using an X-ray diffractometer (manufactured by PANalytical, trade name: X'Pert Pro), and it was found that potassium nitrate with a purity of 83% (8.2 g, yield: 79%) was obtained. The results are shown in Table 3.

[0059] Examples 2 to 4 Potassium nitrate was obtained in the same manner as in Example 1, except that the amount (molar equivalent) of nitric acid relative to 1.0 molar equivalent of potassium chloride and the heating temperature [temperature after heating (°C)] were changed to the values ​​shown in Table 3. The results are shown in Table 3.

[0060] Example 5 6.4 g of potassium chloride crystals (purity: 99%) obtained in the same manner as in Reference Example 1 and 24.3 mL of nitric acid diluted to a concentration of 20% by mass (1.0 molar equivalent of nitric acid per 1.0 molar equivalent of potassium chloride) were placed in a round-bottom flask and thoroughly stirred at room temperature (25°C) to dissolve. The mixture was then heated to 110°C while aerating at 0.5 m / s, stirred for 0.2 hours, and then heated to dryness at 110°C for 1 hour to obtain a solid. Potassium nitrate was obtained in the same manner as in Example 1. The results are shown in Table 3.

[0061] (Examples 6 to 16 and Comparative Examples 1 and 2) Potassium nitrate was obtained in the same manner as in Example 5, except that the nitric acid concentration (% by mass), the amount of nitric acid (molar equivalent) relative to 1.0 molar equivalent of potassium chloride, and the heating temperature [temperature after heating (°C) and heating to dryness (°C)] were changed to the values ​​shown in Table 3. The results are shown in Table 3.

[0062] [Table 3]

[0063] Table 3 shows that all of the potassium nitrates obtained by the production method of this embodiment were highly pure and in high yield (Examples 1 to 16). [Industrial Applicability]

[0064] The method for producing potassium nitrate according to the present embodiment effectively utilizes waste materials discharged from cement factories to produce potassium nitrate with high efficiency and ease. The potassium nitrate thus obtained is suitable for use as compost for agricultural cultivation, microalgae cultivation, and the like, and as explosives. [Explanation of symbols]

[0065] 100: Treatment system for waste generated from cement factories 10: Chlorine bypass dust receiving facility 20: Combustion exhaust gas receiving facility 21: Nitric acid production equipment 30: Potassium chloride extraction equipment 31: Contact tank 32: First solid-liquid separation device 33: Cooling tank 34: Second solid-liquid separation equipment 40: Equipment for contacting potassium chloride with nitric acid 50: Potassium nitrate manufacturing equipment 1: Supply line (1) 2: Supply line (2) 3: Supply line (3) 4: Supply line (4) 5: Supply Line (5)

Claims

1. a step of contacting chlorine bypass dust discharged from a cement plant with a saturated aqueous solution of potassium chloride at room temperature to extract potassium chloride from the chlorine bypass dust; a step of contacting the potassium chloride obtained in the step of extracting potassium chloride with nitric acid obtained from nitrogen oxides contained in combustion exhaust gas discharged from a cement factory; A method for producing potassium nitrate, comprising a step of heating the fluid obtained in the contacting step at a temperature of 75°C or higher and 175°C or lower to obtain potassium nitrate.

2. 2. The method for producing potassium nitrate according to claim 1, wherein the chlorine bypass dust is contacted with the saturated aqueous potassium chloride solution by reflux.

3. 2. The method for producing potassium nitrate according to claim 1, wherein a fluid obtained by contacting the chlorine bypass dust with the saturated aqueous potassium chloride solution is subjected to a first solid-liquid separation at a temperature of 80°C or higher and 150°C or lower.

4. 4. The method for producing potassium nitrate according to claim 3, wherein the saturated aqueous potassium chloride solution recovered by the first solid-liquid separation is cooled to room temperature and then subjected to a second solid-liquid separation to obtain potassium chloride as a solid content.

5. 5. The method for producing potassium nitrate according to claim 4, wherein the potassium chloride obtained by the second solid-liquid separation is used in the contacting step.

6. 5. The method for producing potassium nitrate according to claim 4, wherein the saturated aqueous potassium chloride solution recovered by the second solid-liquid separation is reused for contact with the chlorine bypass dust.

7. 2. The method for producing potassium nitrate according to claim 1, wherein the content of the nitric acid is more than 1.0 molar equivalent and not more than 2.0 molar equivalents relative to 1.0 molar equivalent of the potassium chloride.

8. 2. The method for producing potassium nitrate according to claim 1, wherein the concentration of the nitric acid is 10% by mass or more and 60% by mass or less.

9. 2. The method for producing potassium nitrate according to claim 1, further comprising heating to dryness at 100°C or higher in the step of obtaining potassium nitrate.

10. The method for producing potassium nitrate according to claim 9, wherein nitric oxide and chlorine produced by the heating to dryness are recovered.

11. Chlorine bypass dust receiving facility that receives chlorine bypass dust discharged from cement plants; Flue gas receiving facilities that receive flue gas emitted from cement factories; a potassium chloride extraction facility for extracting potassium chloride from the chlorine bypass dust by bringing the chlorine bypass dust into contact with a saturated aqueous potassium chloride solution at room temperature; a facility for contacting the potassium chloride obtained in the potassium chloride extraction facility with nitric acid obtained from nitrogen oxides contained in the combustion exhaust gas; and A system for treating waste discharged from a cement factory, comprising a potassium nitrate production facility for heating the fluid obtained in the contacting facility to a temperature of 75°C or higher and 175°C or lower to obtain potassium nitrate.

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