Potassium nitrate manufacturing method and cement factory waste treatment system

Abstract

The present invention provides a method for producing potassium nitrate that can effectively utilize waste materials discharged from cement factories and can produce potassium nitrate highly efficiently and easily, and a system for treating waste materials discharged from cement factories. [Solution] A method for producing potassium nitrate includes 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 potassium chloride extraction step with nitric acid obtained from nitrogen oxides contained in combustion exhaust gas discharged from the cement plant, and 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.

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 plant. [Background technology]

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

[0003] Currently, the catalytic reduction method (SNCR method) using urea or alcohol is used as a NOx denitrification technology in cement plants (for example, Patent Document 1). In addition, in cement plants, excess chlorides generated during the burning of recycled fuels are known to have a detrimental effect on the physical properties of cement, and so cement companies are working to control the quality of cement by recovering chlorides as chlorine bypass dust using a cooling probe. The chlorine bypass dust is washed with water and reused as a cement raw material. On the other hand, 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 lot 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] JP 2009-189989 A [Patent Document 2] JP 2019-26521 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the SNCR method described above, the optimum temperature for the denitration reaction is said to be 800°C or higher, and since operation in an extremely high-temperature environment is required, it is difficult to say that it is a simple method. In addition, it can be assumed that the hot gas that has passed through the urea spray area is not denitrified, and that approximately 400 ppm of NOx is emitted into the atmosphere. Therefore, denitration in cement plants can only be performed in a limited temperature range, and it is difficult to effectively reuse the captured NO2.

[0006] As described above, the water after washing the 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 limited. In the above-mentioned method for producing potassium chloride salt, flue gas desulfurization effluent is added to the 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, in order to remove selenium from the filtrate, it is necessary to add a reducing agent (heavy metal remover), 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 has an object to provide a method for producing potassium nitrate that can effectively utilize waste materials discharged from cement factories and can produce potassium nitrate efficiently and easily, and a system for treating waste materials discharged from cement factories. [Means for solving the problem]

[0009] As a result of intensive research aimed at 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 plant; 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] above, 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 fraction. [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 per 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] above, 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], further comprising recovering nitric oxide and chlorine produced by the heating and drying.

[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 discharged from cement plants; a potassium chloride extraction facility for extracting potassium chloride from the chlorine bypass dust by contacting the chlorine bypass dust 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 from the contacting facility to a temperature of 75°C or higher and 175°C or lower to obtain potassium nitrate. Effect 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 materials discharged from cement factories and can produce potassium nitrate highly efficiently and easily, and a system for treating waste materials discharged from cement factories. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing an example of a method for producing potassium nitrate according to an embodiment of the present invention. [Diagram 2] FIG. 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. [Diagram 3] FIG. 1 is a schematic diagram showing a potassium chloride extraction apparatus used in Reference Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 modification within the scope that does not impair the effects of the invention. In this specification, the expression "AA to BB" for a numerical range means "AA or more and BB or less". In this specification, the numerical values ​​related to "above", "below" and "to" in the description of a numerical range are numerical 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.

[0014] [Method of producing potassium nitrate] The method for producing potassium nitrate according to the present embodiment is as follows: 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 plant; The method further comprises the step of heating the fluid obtained in the contacting step at a temperature of 75° C. or more and 175° C. or less 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 plant, 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 obtained fluid is heated in a temperature range of 75° C. or more and 175° C. or less. This is a simple method by which potassium nitrate can be obtained 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 the chlorine bypass dust discharged from a cement plant by contacting the chlorine bypass dust 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 the exhaust gas extracted from a probe at the bottom 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 plant, 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% by mass, preferably 20 to 40% by mass, and more preferably 25 to 40% by mass. The content of sodium oxide is usually 0 to 40 mass %, preferably 0.5 to 40 mass %, and more preferably 1 to 40 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, by 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 potassium chloride saturated aqueous solution at room temperature (25° C.) is not particularly limited, but is preferably performed by reflux from the viewpoint of further increasing the purity and yield of potassium chloride to be extracted. The reflux is performed, for example, by a method in which a contact tower into which the chlorine bypass dust and the potassium chloride saturated aqueous solution are charged is heated, and a part of the generated gas is cooled by 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 further preferably 0.4 to 1 hour.

[0021] For heating during the reflux, it is preferable to use combustion exhaust gas discharged from a cement factory as a heat source, from the viewpoint of exerting the effects of the present invention more effectively (see FIG. 1). The temperature of the combustion exhaust gas cannot be generally determined because it varies depending on which exhaust gas is used, but is usually from 30° C. to 250° C., preferably from 50° C. to 200° C., more preferably from 70° C. to 180° C., and even more preferably from 80° C. to 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 viewpoints, 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 pressurized 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 them 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 matter (eg, potassium chloride, etc.) recovered by the first solid-liquid separation may be desalted and used in a cement plant.

[0025] In addition, 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 perform a second solid-liquid separation from the viewpoint of increasing the purity and yield of the potassium chloride extracted. 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 described below. The second solid-liquid separation can obtain potassium chloride 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 may be the method described in the first solid-liquid separation method. Among them, 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 fraction 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 the combustion exhaust gas discharged from a cement plant. 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 for example, a wet recovery method can be used in which nitrogen oxides (NOx) contained in combustion exhaust gas are absorbed into water to obtain nitric acid using a gas purification device described in JP 2017-51899 A.

[0029] An example of a method for contacting the potassium chloride obtained in the potassium chloride extraction step with the nitric acid is 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 with the reaction and obtaining potassium nitrate as a product. The stirring device is not particularly limited, and 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 equivalent, more preferably more than 1.1 molar equivalent and not more than 1.8 molar equivalent, and even more preferably more than 1.2 molar equivalent and not more than 1.6 molar equivalent, 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 a temperature of 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 more and 170°C or less, more preferably 80°C or more and 160°C or less, and even more preferably 80°C or more and 150°C or less.

[0034] In order to more effectively achieve the effects of the present invention, it is preferable to use, as a heat source for the heating, a combustion exhaust gas discharged from a cement factory, as shown in Fig. 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 efficient reaction, a stirring equipment is preferable. As the stirring equipment, the stirring equipment exemplified as the stirring equipment that can be used in the step of contacting potassium chloride with nitric acid, among which a Henschel mixer is preferable. 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 "temperature after heating") and stir the fluid. From the viewpoint of obtaining potassium nitrate with higher purity and higher yield, it is preferable that the temperature after heating is not less than 75°C. The stirring time is preferably 0.1 to 5 hours, more preferably 0.1 to 2 hours, and further preferably 0.2 to 1 hour.

[0037] It is preferable that this step further includes heating to dryness at 100° C. or higher, from the viewpoint of further increasing the purity and yield of the potassium nitrate obtained. In addition, a part of the nitric acid reacts with chloride ions in the solution to generate nitrosyl chloride (NOCl), which is difficult to separate from the solution. On the other hand, the nitrosyl chloride decomposes at 100°C or higher to generate nitric oxide (NO) and chlorine (Cl2). Therefore, by carrying out the heating to dryness at 100°C or higher, the generated nitrosyl chloride is decomposed and can be recovered as nitric oxide and chlorine.

[0038] The gas containing nitric oxide and chlorine thus produced is subjected to, for example, a heat exchanger to remove moisture, and then nitric oxide is adsorbed and recovered using zeolite (e.g., N114), and chlorine gas is then appropriately recovered. The moisture removed by the heat exchanger may be reused in the above-mentioned reaction.

[0039] The recovered nitric oxide can be used to produce nitric acid, as shown in Figure 1. In addition, the chlorine can be used as a raw material for vinyl chloride, bleaching powder, pickling agents, pH adjusters, etc.

[0040] The heating to dryness is preferably carried out while ventilating. 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 further preferably 0.4 to 1 hour. In order to achieve the effects of the present invention, it is preferable to use, as a heat source, a combustion exhaust gas discharged from a cement factory (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, the combustion exhaust gas discharged 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 also 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 of the reaction device, it may be recovered by appropriately spraying water and drying. 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 resulting 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 further preferably 95% or more. The yield of the potassium nitrate is preferably 75% or more, more preferably 85% or more, and further preferably 95% or more.

[0043] [Waste treatment system for cement plants] The waste treatment system for waste discharged from a cement factory according to the present embodiment includes: Chlorine bypass dust receiving facility for receiving chlorine bypass dust discharged from cement plants; Flue gas receiving facilities that receive flue gas discharged from cement plants; a potassium chloride extraction facility for extracting potassium chloride from the chlorine bypass dust by contacting the chlorine bypass dust 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 fluid obtained in the contacting facility is heated to 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 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 the potassium chloride (solid) is extracted by contacting the chlorine bypass dust with a saturated aqueous solution of potassium chloride at room temperature supplied from another line in the potassium chloride extraction facility 30. The extracted potassium chloride is fed through a feed line (2) to a unit 40 for contacting the potassium chloride with nitric acid.

[0046] In order to further exert 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 subjecting the fluid obtained in the contact tank 31 to a first solid-liquid separation 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 subjecting the saturated aqueous potassium chloride solution cooled to room temperature to a second solid-liquid separation (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 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 for contacting potassium chloride with nitric acid, where potassium nitrate is produced by contacting 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. or higher and 175° C. or lower, whereby potassium nitrate is obtained 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 in the potassium chloride extraction equipment 30, the nitric acid production equipment 21, the equipment 40 for contacting potassium chloride with nitric acid, and the potassium nitrate production equipment 50, as well as the raw materials, devices (equipment), and the like used are the same as those described in the potassium nitrate production method. In addition, in the potassium chloride extraction equipment 30, the equipment 40 for contacting potassium chloride with nitric acid, and the potassium nitrate production equipment 50, the combustion exhaust gas from the combustion exhaust gas receiving equipment 20 may be used as a heat source for heating. EXAMPLES

[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 collected at a cement plant: Calcium oxide (CaO): 31.5% by mass, potassium oxide (K2O): 28.4% by mass, sodium oxide (Na2O): 1.0% by mass, chlorides: 20.5% by mass (including chlorides such as calcium chloride), other substances: 18.6% by mass The ratio of the substance contained in the chlorine bypass dust is a value measured using an energy dispersive X-ray fluorescence analysis (XRF analysis) device (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.). Nitric acid concentration: 60-61% by mass.

[0051] (Reference example 1) The following operation 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 obtained potassium chloride saturated aqueous solution was collected and put into a round-bottom flask equipped with a Liebig tube as shown in FIG. 3, and 20 g of chlorine bypass dust was added and stirred. The potassium chloride saturated aqueous solution containing the chlorine bypass dust was heated to 120°C with a mantle heater and refluxed for 30 minutes, and then put into a centrifuge (Kokusan Co., Ltd., H-112 type) equipped with a filter cloth (Kokusan Co., Ltd., TR84385) in a high-temperature state, and solid-liquid separation (first solid-liquid separation) was performed 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 performing a desalting treatment. In addition, the treated water used in the desalting treatment can be returned to the round-bottom flask and reused as a potassium chloride saturated aqueous 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), whereby potassium chloride crystals were precipitated, which were then 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 was analyzed using an X-ray diffractometer (manufactured by PANalytical, product name: X'Pert Pro), and as a result, it was found that the purity was 99% and the yield was 6.4g (86mmol).

[0052] Table 1 shows the amounts of water, potassium chloride (KCl) and sodium chloride (NaCl) components 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, for each component in the saturated aqueous potassium chloride solution, (total amount after the first and second solid-liquid separations) - (total amount before the first and second solid-liquid separations).

[0053] [Table 1]

[0054] From Table 1, it can be seen that although there are losses of each component in the saturated potassium chloride aqueous solution due to wall adhesion 1 and 2, there is almost no need to consider these losses during continuous operation of an actual machine. In addition, since the potassium chloride in the saturated potassium chloride aqueous solution (filtrate) is in equilibrium with the potassium chloride in the raw material when the filtrate is recycled, it is presumed that a certain amount of potassium chloride is 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 the same operation as in Reference Example 1 was carried out to obtain potassium chloride crystals. 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] From Table 2, it can be seen 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 put into a round-bottom flask and thoroughly stirred at room temperature (25°C) to dissolve. After that, the mixture was heated to 70°C while being aerated at 0.5 m / s and stirred for 1 hour, and then further heated to 120°C and heated to dryness for 0.5 hours. After heating to dryness, the solid matter obtained by heating sufficiently was collected and dried in a dryer at 105°C for more than one day. Meanwhile, the gas in the round-bottom flask was analyzed using a detector tube type gas measuring instrument (manufactured by Gastec Corporation, detector tube: 8HH) after removing water vapor using a heat exchanger and recovering nitric oxide with zeolite (N114), and the gas was constantly detected at about 3 to 5% of chlorine gas. The solid matter after drying was analyzed using an X-ray diffractometer (manufactured by PANalytical, product name: X'Pert Pro), and 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. Thereafter, the mixture was heated to 110°C while aerating at 0.5 m / s and 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 concentration of nitric acid (% 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] It can be seen from Table 3 that the potassium nitrate obtained by the production method of this embodiment is all of high purity and high yield (Examples 1 to 16). [Industrial Applicability]

[0064] The method for producing potassium nitrate according to the present embodiment makes effective use of waste materials discharged from cement factories, and can produce potassium nitrate easily and efficiently. 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 from cement plants 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 device 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 plant; 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. 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. 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 for receiving chlorine bypass dust discharged from cement plants; Flue gas receiving facilities that receive flue gas discharged from cement plants; a potassium chloride extraction facility for extracting potassium chloride from the chlorine bypass dust by contacting the chlorine bypass dust 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 from the contacting facility at 75°C or more and 175°C or less to obtain potassium nitrate.

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