Crystallization reaction apparatus and crystallization reaction method

Abstract

An object of the present invention is to provide a crystallization reaction apparatus and a crystallization reaction method capable of stably measuring the slurry concentration in a crystallization reaction tank and maintaining an efficient crystallization reaction. [Solution] A crystallization reaction apparatus 1 for crystallizing calcium fluoride by adding a calcium agent to fluorine-containing water to be treated, the crystallization reaction apparatus 1 comprising a crystallization reaction tank 10, a calcium agent adding means for adding the calcium agent into the crystallization reaction tank 10, an agitator 12 provided in the crystallization reaction tank 10, a gas supplying device 16 for supplying gas into the crystallization reaction tank 10, a gas discharge section 58 for discharging the supplied gas into the crystallization reaction tank 10, a pressure measuring device 18 for measuring the pressure of the discharged gas, and a liquid level conversion device 14 and a slurry concentration calculation device 24 for calculating the slurry concentration in the crystallization reaction tank 10 from the measured gas pressure value.

Description

[Technical field]

[0001] The present invention relates to a crystallization reaction apparatus and a crystallization reaction method for performing crystallization treatment on fluorine-containing water to be treated. [Background technology]

[0002] A widely known method for treating hydrofluoric acid-containing wastewater discharged from semiconductor factories and the like is to comply with fluorine discharge standards or to achieve goals such as reusing hydrofluoric acid as a valuable resource by using a technique for producing calcium fluoride through a crystallization reaction using a calcium agent.

[0003] In such a method, in order to increase the recovery rate of fluorine, it is required to control the slurry concentration in a crystallization reaction tank in which the crystallization reaction is carried out within a predetermined range by adjusting the amount of calcium fluoride crystals produced to be extracted or the amount of seed crystals to be added.

[0004] As described in

[0004] of Patent Document 1, it is important to keep the slurry concentration in the crystallization reaction tank as constant as possible in the crystallization reaction apparatus. However, when measuring the slurry concentration using, for example, an ultrasonic concentration meter as the crystal concentration meter described in

[0024] of Patent Document 1, a high concentration slurry such as that in the crystallization reaction tank may exceed the measurement concentration range, or the sensor may need to be cleaned frequently due to scale generation caused by calcium or the like. Furthermore, Patent Document 1 also describes a method of sampling the slurry solution in the crystallization reaction tank by some method to measure the sedimentation volume of the crystals, but it is necessary to sample the slurry solution containing hydrofluoric acid, and since it takes time to measure, there are cases where the amount of slurry drawn or the amount of seed crystals added cannot be appropriately tracked in response to fluctuations in the slurry concentration.

[0005] In Patent Document 2, the concentration of gypsum slurry generated in a flue gas desulfurization facility is measured by measuring the pressure using a pressure detector installed at a predetermined height position (water depth) in a reaction tank based on the exhaust gas pressure or atmospheric pressure, and converting the pressure into a slurry concentration. However, even with the method of Patent Document 2, problems may occur in the pressure detector due to scale generation.

[0006] Under these circumstances, there is a demand for a crystallization reaction apparatus and a crystallization reaction method that can stably measure the slurry concentration in a crystallization reaction tank and maintain an efficient crystallization reaction in the crystallization treatment of fluorine-containing water to be treated. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5941329 [Patent Document 2] Patent Publication No. 2021-166955 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a crystallization reaction apparatus and a crystallization reaction method capable of stably measuring the slurry concentration in a crystallization reaction tank and maintaining an efficient crystallization reaction. [Means for solving the problem]

[0009] The present invention is a crystallization reaction apparatus for crystallizing calcium fluoride by adding a calcium agent to fluorine-containing water to be treated, the crystallization reaction apparatus comprising a crystallization reaction tank, a calcium agent adding means for adding the calcium agent into the crystallization reaction tank, a stirring means provided in the crystallization reaction tank, a gas supplying means for supplying gas into the crystallization reaction tank, a gas discharge part for discharging the gas supplied from the gas supplying means into the crystallization reaction tank, a pressure measuring means for measuring the pressure of the gas discharged from the gas discharge part, and a measured value of the pressure of the gas measured by the pressure measuring means. a predetermined liquid level value in the crystallization reaction tank, or a measured liquid level value measured by a liquid level measuring means for measuring the liquid level in the crystallization reaction tank;and a calculation means for calculating the slurry concentration in the crystallization reaction tank from the calculated slurry concentration.

[0010] The present invention involves adding a calcium agent to fluoride-containing water to be treated to crystallize calcium fluoride. Crystallization Reactor a calcium agent adding means for adding the calcium agent into the crystallization reaction tank; an agitation means provided in the crystallization reaction tank; a gas supplying means for supplying a gas into the crystallization reaction tank; a gas discharge portion for discharging the gas supplied from the gas supplying means into the crystallization reaction tank; a pressure measuring means for measuring the pressure of the gas discharged from the gas discharge portion; and a calculation means for calculating a slurry concentration in the crystallization reaction tank from a measured value of the pressure of the gas measured by the pressure measuring means, wherein the gas discharge portion is provided at least in two or more different positions so as to achieve a predetermined water level difference, and the pressure measuring means measures the pressure of the gas discharged from at least two or more of the gas discharge portions. .

[0011] It is preferable that the crystallization reaction apparatus has at least two or more gas discharge ports, and the pressure measuring means measures the pressure of the gas discharged from the at least two or more gas discharge ports.

[0012] The crystallization reaction apparatus preferably further comprises at least one of a water-to-be-treated supply means for supplying water-to-be-treated into the crystallization reaction tank, an acid adding means for adding acid into the crystallization reaction tank, a seed crystal adding means for adding seed crystals into the crystallization reaction tank, and a slurry withdrawing means for withdrawing a slurry from the crystallization reaction tank, and further comprises a control means for controlling at least one of the flow rate of the water to be treated, the amount of the calcium agent added, the amount of the acid added, the amount of the seed crystals added, and the amount of the slurry withdrawn, based on the slurry concentration calculated by the calculation means.

[0013] The present invention relates to a crystallization reaction method for crystallizing calcium fluoride by adding a calcium agent to fluorine-containing water to be treated, comprising the steps of: using a crystallization reaction tank equipped with an agitation means; adding the calcium agent to the water to be treated in the crystallization reaction tank to carry out a crystallization reaction; supplying gas into the crystallization reaction tank from a gas discharge portion; measuring the pressure of the gas discharged from the gas discharge portion; and a predetermined liquid level value in the crystallization reaction tank or a measured liquid level value in the crystallization reaction tank; and calculating the slurry concentration in the crystallization reaction tank from the above.

[0014] The present invention involves adding a calcium agent to fluoride-containing water to be treated to crystallize calcium fluoride. Crystallization reaction method a crystallization reaction tank equipped with an agitation means is used, the calcium agent is added to the water to be treated in the crystallization reaction tank to carry out a crystallization reaction, gas is supplied into the crystallization reaction tank from a gas discharge port, the pressure of the gas discharged from the gas discharge port is measured, and a slurry concentration in the crystallization reaction tank is calculated from the measured value of the pressure of the gas measured, the gas discharge port is provided at least in two or more different positions so as to provide a predetermined water level difference, and the pressure of the gas discharged from the at least two or more gas discharge ports is calculated based on the measured value of the pressure of the gas measured, Measuring , a crystallization reaction method .

[0015] In the crystallization reaction method, it is preferable that the apparatus has at least two or more gas discharge ports, and that the pressure of the gas discharged from the at least two or more gas discharge ports is measured.

[0016] In the crystallization reaction method, it is preferable to control at least one of the flow rate of the water to be treated into the crystallization reaction tank, the amount of the calcium agent added, the amount of acid added into the crystallization reaction tank, the amount of seed crystals added into the crystallization reaction tank, and the amount of slurry withdrawn from the crystallization reaction tank, based on the calculated slurry concentration. Effect of the Invention

[0017] According to the present invention, it is possible to provide a crystallization reaction apparatus and a crystallization reaction method capable of stably measuring the slurry concentration in a crystallization reaction tank and maintaining an efficient crystallization reaction. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram showing an example of a crystallization reaction apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing another example of a crystallization reaction apparatus according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing an outline of an example of calculation of a slurry concentration and operation control in the crystallization reaction method according to an embodiment of the present invention. [Figure 4] 1 is a graph showing the relationship between the slurry concentration (v / v%) and the liquid level equivalent value (m) in Example 1. [Diagram 5] 1 is a graph showing the relationship between the slurry concentration (v / v%) and the liquid level equivalent value (m) in Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is merely an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0020] [Embodiment 1] An example of a crystallization reaction apparatus according to an embodiment of the present invention is outlined in FIG. 1, and its configuration will be described.

[0021] The crystallization reaction apparatus 1 shown in Fig. 1 is an apparatus for crystallizing calcium fluoride by adding a calcium agent to the fluorine-containing water to be treated. The crystallization reaction apparatus 1 includes a crystallization reaction tank 10; a pump 38 and a calcium agent addition pipe 42 as calcium agent addition means for adding the calcium agent to the crystallization reaction tank 10; an agitator 12 having an agitator blade or the like as an agitation means provided in the crystallization reaction tank 10; a gas supply device 16 and a gas supply pipe 56 as gas supply means for supplying gas into the crystallization reaction tank 10; a gas discharge part 58 for discharging the gas supplied from the gas supply device 16 into the crystallization reaction tank 10; a pressure measurement device 18 as a pressure measurement means for measuring the pressure of the gas discharged from the gas discharge part 58; and a liquid level conversion device 14 and a slurry concentration calculation device 24 as calculation means for calculating the slurry concentration in the crystallization reaction tank 10 from the measured value of the gas pressure measured by the pressure measurement device 18.

[0022] The crystallization reaction apparatus 1 may include a pump 28 and a water-to-be-treated supply pipe 30 as water-to-be-treated supply means for supplying water to be treated into the crystallization reaction tank 10; a pump 32 and an acid addition pipe 36 as acid addition means for adding acid to the crystallization reaction tank 10; a pump 44 and a seed crystal addition pipe 48 as seed crystal addition means for adding seed crystals to the crystallization reaction tank 10; and an extraction pump 50 and a slurry extraction pipe 54 as slurry extraction means for extracting slurry from the crystallization reaction tank 10.

[0023] The crystallization reaction apparatus 1 may include a draft tube 64 described later. The crystallization reaction apparatus 1 may include a liquid level measuring device 22 as a liquid level measuring means for measuring the liquid level in the crystallization reaction tank 10. The crystallization reaction apparatus 1 may include a control device 26 as a control means for controlling at least one of the flow rate of the water to be treated, the amount of calcium agent added, the amount of acid added, the amount of seed crystals added, and the amount of slurry extracted, based on the slurry concentration calculated by the calculation means.

[0024] In the crystallization reaction apparatus 1 of FIG. 1, the treated water inlet of the crystallization reaction tank 10 is connected to the treated water supply pipe 30 via the pump 28, the acid inlet is connected to the acid addition pipe 36 via the pump 32 and the valve 34, the calcium agent inlet is connected to the calcium agent addition pipe 42 via the pump 38 and the valve 40, and the seed crystal inlet is connected to the seed crystal addition pipe 48 via the pump 44 and the valve 46. The slurry outlet of the crystallization reaction tank 10 is connected to the slurry withdrawal pipe 54 via the withdrawal pump 50 and the valve 52. An inner peripheral wall is disposed opposite to the peripheral wall of the crystallization reaction tank 10, and the space between the inner and outer peripheral walls forms the crystallization treatment water discharge channel 62. The crystallization treatment water outlet at the top of the crystallization treatment water discharge channel 62 is connected to the crystallization treatment water pipe 60.

[0025] In the crystallization reaction apparatus 1, one end of a gas supply pipe 56 is connected to the gas supply device 16, and the other end of the gas supply pipe 56 has a gas discharge section 58. A pressure measuring device 18 is installed in the gas supply pipe 56. A liquid level measuring device 22 is installed in the crystallization reaction tank 10.

[0026] In the crystallization reaction apparatus 1, the control device 26 is connected to the pump 28 of the water supply means, the pump 32 and valve 34 of the acid addition means, the pump 38 and valve 40 of the calcium agent addition means, the pump 44 and valve 46 of the seed crystal addition means, and the withdrawal pump 50 and valve 52 of the slurry withdrawal means so as to be able to communicate and control each other by wired or wireless electrical connections. The liquid level conversion device 14 and the pressure measurement device 18 are connected to be able to communicate each other by wired or wireless electrical connections. The slurry concentration calculation device 24 is connected to the liquid level conversion device 14 and the pressure measurement device 18 are connected to be able to communicate each other by wired or wireless electrical connections. The slurry concentration calculation device 24 is connected to the liquid level measurement device 22 so as to be able to communicate each other by wired or wireless electrical connections. The control device 26 is connected to the slurry concentration calculation device 24 so as to be able to communicate each other by wired or wireless electrical connections.

[0027] The crystallization reaction method and the operation of the crystallization reaction apparatus 1 according to this embodiment will be described.

[0028] The fluorine-containing water to be treated is pumped to the crystallization reaction tank 10 through the water to be treated supply pipe 30 by the pump 28. The valve 46 is opened to add seed crystals to the water to be treated through the seed crystal addition pipe 48 by the pump 44, and the valve 40 is opened to add a calcium agent to the water to be treated through the calcium agent addition pipe 42 by the pump 38. In the crystallization reaction tank 10, the fluorine contained in the water to be treated reacts with the calcium agent to generate calcium fluoride, which is precipitated on the surface of the seed crystal, and poorly soluble calcium fluoride crystals are generated (crystallization reaction step). At this time, the inside of the crystallization reaction tank 10 is stirred by the stirrer 12. The valve 34 is opened to add an acid, which is a pH adjuster, to the crystallization reaction tank 10 through the acid addition pipe 36 by the pump 32, and the pH in the crystallization reaction tank 10 may be adjusted. The calcium agent is preferably added near the stirring blade of the stirrer 12.

[0029] The slurry containing calcium fluoride crystals produced in the crystallization reaction tank 10 is withdrawn from the slurry withdrawal pipe 54 by the withdrawal pump 50 with the valve 52 opened, and is recovered. The crystallized treated water, the fluorine content of which has been reduced by the crystallization reaction in the crystallization reaction tank 10, is discharged from the crystallized treated water discharge path 62 through the crystallized treated water pipe 60.

[0030] In the crystallization reaction method and crystallization reaction apparatus according to the present embodiment, the slurry concentration in the crystallization reaction tank 10 during the crystallization reaction can be stably measured. The inventors have newly discovered that when a gas such as air is sent from the gas supply device 16 to the crystallization reaction liquid 66 in the crystallization reaction tank 10 and discharged from the gas discharge part 58, and the back pressure (air supply pressure) at that time is measured, even if the distance between the liquid level of the crystallization reaction tank 10 and the gas discharge part 58 is constant, the back pressure changes depending on the slurry concentration (change in specific gravity of the slurry), and further, there is a proportional relationship between the back pressure and the slurry concentration. By utilizing this proportional relationship, the slurry concentration can be measured on-site with high accuracy and stability without sampling the slurry. This makes it easy to manage the amount of slurry drawn out and the amount of seed crystals replenished in the crystallization reaction tank 10, and makes it possible to maintain a high recovery rate of calcium fluoride, which is prone to change depending on the slurry concentration. Therefore, a stable and efficient crystallization reaction can be maintained. A method for calculating the slurry concentration will be described later.

[0031] In Patent Document 1, a method for measuring the slurry concentration is used in which a crystal concentration meter is installed in the crystallization reaction tank, or the slurry solution in the crystallization reaction tank is sampled and the settling volume of the crystals is measured. In contrast, in the crystallization reaction method and crystallization reaction apparatus according to the present embodiment, a gas supply pipe 56 for discharging gas such as air into the crystallization reaction tank 10 is installed, and gas is sent from the gas supply device 16. By utilizing the correlation between the back pressure at that time and the specific gravity of the slurry which varies depending on the slurry concentration, the slurry concentration can be measured without sampling the slurry, so there is no risk of scale due to the contact of the sensor with the liquid, and it is not necessary to sample the slurry liquid. In addition, it is possible to measure the slurry concentration even in a high concentration slurry in the range of, for example, 0 to 60 v / v% as the settling volume of the crystals.

[0032] In Patent Document 2, the concentration of the gypsum slurry generated in the flue gas desulfurization equipment is measured by a pressure detector installed at a predetermined height position (water depth) in the reaction tank based on the exhaust gas pressure or atmospheric pressure, and converted into a slurry concentration. In contrast, the crystallization reaction method and crystallization reaction apparatus according to the present embodiment are characterized in that the crystallization reaction apparatus uses highly corrosive water to be treated such as hydrofluoric acid, measures gas back pressure (air supply pressure) instead of simply pressure (water pressure), and is located outside the crystallization reaction tank, eliminating the risk of scale generation.

[0033] The crystallization reaction tank 10 is a tank in which a crystallization reaction liquid 66 is stored and in which a crystallization reaction is carried out. The crystallization reaction tank 10 is an agitation type crystallization reaction tank having an agitation mechanism such as an agitator 12 inside the tank.

[0034] The stirring device 12 is not particularly limited as long as it is capable of stirring the crystallization reaction liquid 66 in the crystallization reaction tank 10, but may be, for example, a device having a stirring blade, the stirring blade being rotated by a rotational force generated by a driving means such as a motor transmitted via a stirring shaft.

[0035] As one method for making the slurry concentration in the crystallization reaction tank 10 as uniform as possible, it is preferable to install a draft tube 64 so that the stirring blades of the stirring device 12 are located inside a tube such as a cylindrical tube below the water surface in the crystallization reaction tank 10. When the draft tube 64 is installed and the stirring blades are installed inside the draft tube 64, a downward flow is generated toward the bottom of the draft tube 64, and a zone with a relatively high diffusion flow rate is formed. This allows the treated water, calcium agent, etc. to be diffused more quickly, and it is considered possible to minimize the direct generation of calcium fluoride particles caused by contact between areas with locally high concentrations of the treated water or calcium agent.

[0036] A gentle upward flow zone is formed around the outer periphery of the draft tube 64. In this zone, the particles are classified, and the small particles rise along the outer surface of the tube, re-enter the tube from the upper end and fall back inside the tube, and are recirculated to the vicinity of the injection point of the treated water and calcium agent, and to the stirring zone below, where these small crystals act as nuclei to promote the crystallization reaction. This makes it possible to stably form calcium fluoride crystals with large diameters, and improve the recovery rate.

[0037] Furthermore, the crystals whose particle size has increased as a result of the crystallization reaction do not rise due to the upward flow around the outer periphery of the tube, but sink to the bottom and are unlikely to reenter the draft tube 64, which is thought to prevent the grown crystals from being destroyed by collision with the stirring blades. This advantage also contributes to the stable production of calcium fluoride crystals with large particle size, and contributes to the improvement of the recovery rate.

[0038] In order to form a zone with a relatively high agitation flow rate in the lower part of the draft tube 64 and to stably form an upward flow around the outer periphery of the tube, it is preferable that the agitator blade is located somewhere in the lower half of the tube. More preferably, it is located a little above the lower end of the tube. With such an arrangement, it is considered that a zone with a high agitation flow rate is formed like a vortex near the lower end of the tube, and further an upward flow is formed stably from there along the outer periphery of the tube. Therefore, it is possible to effectively diffuse the treated water and calcium agent, and to effectively classify particles.

[0039] When the draft tube 64 is provided, the injection points of the water to be treated and the calcium agent are preferably located inside the draft tube 64 so that they are carried by the downward flow in the draft tube 64 and diffused quickly and effectively. A more preferable position is inside the draft tube 64 and above the stirring blade.

[0040] In order to make the slurry concentration in the crystallization reaction tank 10 as uniform as possible, the rotation speed of the impeller of the stirrer 12 may be, for example, in the range of 100 to 300 rpm when the crystallization reaction tank 10 is equipped with a draft tube 64, and may be, for example, in the range of 300 to 500 rpm when the crystallization reaction tank 10 is not equipped with a draft tube 64. The inside of the crystallization reaction tank 10 is stirred by the stirrer 12, for example, at the rotation speed of the impeller, and it is assumed that the slurry concentration is in a substantially uniform state.

[0041] The slurry outlet of the crystallization reaction tank 10 may be equipped with an extraction pump 50, a valve 52, and a slurry extraction pipe 54 as slurry extraction means.

[0042] The calcium agent may be added to the crystallization reaction tank 10 by calcium adding means such as a pump 38, a valve 40, and a calcium agent adding pipe 42. There are no particular limitations on the calcium agent as long as it contains calcium, and for example, a liquid such as an aqueous solution containing an inorganic salt of calcium such as calcium hydroxide, calcium chloride, calcium carbonate, or a slurry may be used. The calcium agent may be used alone or in combination of two or more kinds.

[0043] The amount of calcium agent to be added may be, for example, 0.8 to 2 times the amount of fluorine in terms of the chemical equivalent of calcium, more preferably 1 to 2 times, and even more preferably 1 to 1.2 times. If the chemical equivalent of calcium is more than twice the chemical equivalent of fluorine in the water to be treated, calcium fluoride is likely to be generated as fine particles without being precipitated on seed crystals, and calcium fluoride may be mixed into the crystallization treatment water. If the amount is less than 0.8 times, the proportion of fluorine in the water to be treated that does not become calcium fluoride increases, and fluorine may be mixed into the crystallization treatment water.

[0044] The gas supply means includes a gas supply device 16 and a gas supply pipe 56. One end of the gas supply pipe 56 is connected to the gas supply device 16, and the other end has a gas discharge part 58, and the gas supply pipe 56 is immersed to a predetermined depth in the crystallization reaction liquid 66 in the crystallization reaction tank 10. The immersion depth (distance from the water surface) of the gas discharge part 58 is not particularly specified as long as it is within a range in which the back pressure of the gas discharged from the gas discharge part 58 can be measured by the pressure measuring device 18. The gas discharge part 58 is preferably located at a water level between the upper end and the lower end of the draft tube 64, and in order to prevent the gas supply pipe 56 from being entangled in the stirring rod or stirring blades of the stirring device 12, the gas supply pipe 56 is more preferably provided on the outer periphery of the draft tube 64.

[0045] The gas supply device 16 supplies gas into the crystallization reaction tank 10 through a gas supply pipe 56, and is not particularly limited as long as it can supply gas, such as a blower, a compressor, a gas cylinder, or compressed air from a factory utility.

[0046] The gas supplied from the gas supply device 16 may be nitrogen, air, or the like, and is not particularly limited, but air is preferred from the viewpoint of cost-effectiveness.

[0047] As the gas supply device 16, a pneumatic level gauge in which the pressure measuring device 18 and the liquid level conversion device 14 are integrated may be used.

[0048] The materials of the gas supply pipe 56 and the gas discharge portion 58 are not particularly limited, but from the viewpoint of life span, it is preferable that the materials are resistant to hydrofluoric acid and strong acids, such as polytetrafluoroethylene (Teflon (registered trademark)) or polyvinyl chloride.

[0049] The crystallization reaction tank 10 may be provided with a liquid level measuring device 22, such as a liquid level gauge for measuring the distance from the gas discharge portion 58 to the liquid level. There are no particular limitations on the liquid level measuring device 22, but it is preferable that the liquid level can be measured without coming into contact with the crystallization reaction liquid in the crystallization reaction tank 10, and for example, an ultrasonic level gauge may be used.

[0050] The air pressure supplied by the gas supply device 16 may be, for example, 30 kPa or more, and from the viewpoint of power consumption, etc., is preferably in the range of 80 to 100 kPa.

[0051] The pressure measuring device 18 is installed in the gas supply pipe 56 and can detect the gas supply pressure. There are no particular limitations on the pressure measuring device 18, but for example, a Bourdon tube pressure gauge, a diaphragm pressure gauge, a bellows pressure gauge, etc. can be used.

[0052] The liquid level conversion device 14 may be any device capable of calculating a liquid level conversion value of the crystallization reaction liquid 66 in the crystallization reaction tank 10 from the pressure value detected by the pressure measuring device 18 .

[0053] The slurry concentration calculation device 24 may be any device capable of calculating the slurry concentration from an analog or digital signal from the liquid level conversion device 14, such as a personal computer (PC) or a programmable logic controller (PLC).

[0054] The control device 26 is composed of, for example, a microcomputer and electronic circuits, which are composed of a calculation means such as a CPU that calculates a program, and storage means such as a ROM and RAM that store the program and the calculation results. The control device 26 may be a programmable controller (also called a programmable logic controller) (PLC) that has a built-in microprocessor and controls the equipment by a program. The control device 26 has a function of controlling at least one of the following based on the slurry concentration calculated by the calculation means: controlling the pump 28 to control the flow rate of the water to be treated, controlling the pump 38 or the valve 40 to control the amount of calcium agent added, controlling the pump 32 or the valve 34 to control the amount of acid added, controlling the pump 44 or the valve 46 to control the amount of seed crystals added, and controlling the withdrawal pump 50 or the valve 52 to control the amount of slurry extracted.

[0055] The water to be treated is water containing fluorine, such as wastewater containing fluorine, and may be water of any origin. From the standpoint of impurities and recovery efficiency, however, it is preferable that the water to be treated is wastewater containing hydrofluoric acid discharged from a semiconductor factory.

[0056] The water to be treated may be supplied into the crystallization reaction tank 10 by means of a water to be treated supply means such as a pump 28 and a water to be treated supply pipe 30 .

[0057] The fluorine concentration of the water to be treated is not particularly limited, but is, for example, 10,000 mg / L or less, and preferably in the range of 1,000 to 10,000 mg / L.

[0058] The crystallization reaction apparatus 1 may be equipped with an acid adding means, such as a pump 32, a valve 34, and an acid adding pipe 36, for adding an acid into the crystallization reaction tank 10. The acid to be added may be a strong acid such as hydrochloric acid, nitric acid, or sulfuric acid. The acid may be used alone or in combination of two or more kinds.

[0059] The crystallization reaction apparatus 1 may be provided with a seed crystal addition means, such as a pump 44, a valve 46, and a seed crystal addition pipe 48, for adding seed crystals to the crystallization reaction tank 10. The seed crystal may be any material capable of precipitating the poorly soluble calcium salt crystals formed on its surface, and may be made of any material. Examples of the seed crystal include, but are not limited to, particles containing an oxide of a metal element, such as filter sand, activated carbon, zircon sand, garnet sand, and Sakurandum (product name, manufactured by Nippon Cartridge Co., Ltd.), and particles containing a poorly soluble salt of calcium fluoride, which is a precipitate produced by a crystallization reaction. From the viewpoint of obtaining a purer poorly soluble salt as pellets or the like, particles containing a poorly soluble salt, which is a precipitate produced by a crystallization reaction (e.g., fluorite in the case of calcium fluoride), are preferred.

[0060] Seed crystals may be present in the crystallization reaction tank 10 before the water to be treated and the calcium agent are added to the crystallization reaction tank 10, or seed crystals may be present in the crystallization reaction tank 10 after the water to be treated and the calcium agent are added to the crystallization reaction tank 10. In order to perform stable treatment, it is preferable that seed crystals are present in the crystallization reaction tank 10 before the water to be treated and the calcium agent are added to the crystallization reaction tank 10.

[0061] The crystallization reaction tank 10 is preferably provided with supply pipes so that the water to be treated, the calcium agent, the acid, and the seed crystals can be added near the stirring blades of the stirring device 12.

[0062] The crystallization reaction tank 10 may be an open type or a closed type. The crystallization reaction tank 10 is preferably an open type. If the crystallization reaction tank 10 is a closed type, the internal pressure may increase due to the gas supplied from the gas supply device 16, which may lead to a decrease in the measurement accuracy of the slurry concentration.

[0063] The pump 28, the pump 32, the pump 38, the pump 44, and the withdrawal pump 50 may have an inverter.

[0064] <Slurry concentration calculation method> The crystallization reaction method and the method for calculating the slurry concentration in the crystallization reaction apparatus according to this embodiment will be described.

[0065] (Creating an approximate formula) First, an approximation formula is created. While stirring a slurry solution adjusted to a predetermined slurry concentration, a gas such as air is supplied from the gas supply device 16 into the slurry solution using a single gas discharge part 58 as in the crystallization reaction apparatus 1 of FIG. 1. At this time, a liquid level conversion value (denoted as y) is calculated using the liquid level conversion device 14 from the discharge pressure detected by the pressure measurement device 18. It is preferable to keep the distance from the gas discharge part 58 to the liquid level as constant as possible during the creation of the approximation formula.

[0066] An approximate equation (y=ax+b, x: slurry concentration, y: liquid level conversion value, a: proportionality constant, b: distance from the gas discharge portion to the liquid level) that shows a proportional relationship is calculated from each slurry concentration and the liquid level conversion value calculated using the liquid level conversion device 14. In creating the approximate equation, it is preferable to use plots of two or more points, preferably five or more points, excluding the slurry concentration of 0%.

[0067] (Concentration calculation using approximate formula) While stirring the calcium fluoride slurry solution with an unknown slurry concentration so that the concentration near the gas discharge part becomes as uniform as possible, a liquid level conversion value is obtained by the liquid level conversion device 14, and the value is designated as y'. The slurry concentration is calculated by substituting y' for y in the approximation equation y=ax+b, the proportional constant obtained in creating the approximation equation for a, and the distance from the gas discharge part 58 to the liquid level obtained in creating the approximation equation for b.

[0068] Different crystallization reaction devices may be used for "creating the approximate formula" and "calculating the concentration using the approximate formula". In that case, it is preferable to make the distance from the gas discharge part 58 to the liquid surface as the same as possible.

[0069] [Embodiment 2] In the crystallization reaction method and crystallization reaction apparatus according to this embodiment, there may be two or more gas discharge parts 58, and two or more air discharge locations. An example of a crystallization reaction apparatus having such a configuration is shown in FIG.

[0070] The crystallization reaction apparatus 3 shown in FIG. 2 includes a gas supply device 16, gas supply pipes 56 and 70, and gas discharge units 58 and 72 that discharge the gas supplied from the gas supply device 16 into the crystallization reaction tank 10 as gas supply means for supplying gas into the crystallization reaction tank 10. In the crystallization reaction apparatus 3, one end of the gas supply pipe 56 is connected to the gas supply device 16 via a valve 74, and the other end has a gas discharge unit 58. A gas supply pipe 70 branches off from the gas supply pipe 56, one end of the gas supply pipe 70 is connected to the upstream side of the valve 74 in the gas supply pipe 56 via a valve 76, and the other end has a gas discharge unit 72. A pressure measuring device 18 is installed upstream of the connection point of the gas supply pipe 70 in the gas supply pipe 56. The crystallization reaction apparatus 3 does not need to include a liquid level measuring device 22 as in the crystallization reaction apparatus 1 in FIG. 1. Other than these, the configuration is the same as that of the crystallization reaction apparatus 1 in FIG.

[0071] In the crystallization reaction apparatus 3, the depths of the gas discharge parts 58, 72 from the water surface may be different. In the crystallization reaction tank 10, when the water level from the liquid surface to the upper end of the draft tube increases due to the liquid level fluctuation, there may be a portion of the phase from the liquid surface to the upper end of the draft tube where the stirring flow does not reach, and a concentration gradient may occur. In this case, by providing two or more gas discharge parts in a portion where the concentration is almost uniform due to stirring, the slurry concentration can be calculated from the difference in pressure between them. Since the concentration is kept almost uniform at the water level from the upper end to the lower end of the draft tube 64 in the crystallization reaction tank 10, it is preferable that the two or more gas discharge parts 58, 72 are located at the water level between the upper end and the lower end of the draft tube 64, and it is more preferable that the gas supply pipes 56, 70 are provided on the outer periphery of the draft tube 64 rather than inside the draft tube 64 in order to prevent the gas supply pipes 56, 70 from being caught in the stirring rod or stirring blade of the stirring device 12.

[0072] In the crystallization reaction apparatus 3 in FIG. 2, the gas supply device is one gas supply device 16, and the gas supply pipe 56 is branched into the gas supply pipe 70 to provide two or more gas discharge parts, namely, the gas discharge parts 58 and 72. However, two or more gas supply devices may be provided, each of which is provided with a gas supply pipe, one end of the gas supply pipe is connected to the gas supply device, and the gas discharge part at the other end may be immersed to a predetermined depth in the crystallization reaction liquid 66 in the crystallization reaction tank 10. In this case, the pressure measuring device 18 may be shared by two or more gas supply devices, and the back pressure may be measured at two or more points by switching the valves using a timer or the like. For example, the valve 74 is opened and the valve 76 is closed, and a gas such as air is supplied from the gas supply device 16 into the slurry solution, and the back pressure after a predetermined time has elapsed is measured. Thereafter, the valve 74 is switched to a closed state and the valve 76 is switched to an open state, and a gas such as air is supplied from the gas supply device 16 into the slurry solution, and the back pressure is measured after a predetermined time has elapsed. There is no particular restriction on the order in which the valves are opened and closed. In addition, two or more gas supply devices and pressure measuring devices are provided, and each is provided with a gas supply pipe, and one end of the gas supply pipe is connected to the gas supply device, and the gas discharge part at the other end is immersed to a predetermined depth in the crystallization reaction liquid 66 in the crystallization reaction tank 10. In this case, a valve may be provided in the gas supply pipe of each series, but it is not particularly necessary to switch according to the measurement, and the back pressure of each series may be measured. The pressure of the gas discharged from the gas discharge part may be measured anywhere between the gas supply device and the gas discharge part, and the back pressure near the gas supply device (i.e., the air supply pressure) may be measured, or the pressure near the gas discharge part, such as the tip of the gas discharge part of the gas supply pipe, may be measured.

[0073] <Slurry concentration calculation method> (Creating an approximate formula) First, an approximation formula is created. While stirring the slurry solution adjusted to a predetermined slurry concentration, the gas discharge parts 58 and 72 are installed at different positions so as to have a predetermined water level difference (c) as in the crystallization reaction apparatus 3 of FIG. 2. With the valve 74 or valve 76 in an open state, gas such as air (gas 1 and gas 2) is supplied from the gas supply device 16 into the slurry solution from the gas discharge parts 58 and 72. At this time, the liquid level conversion value (y1 and y2) is calculated using the liquid level conversion device 14 from the discharge pressure detected by the pressure measurement device 18. During the creation of the approximation formula, it is preferable to maintain the water level difference between the gas discharge parts 58 and 72 at a predetermined value.

[0074] An approximation equation (y1-y2=a'x+c, where x is the slurry concentration, y1 is the liquid level equivalent value when gas is discharged from the gas discharge unit installed at a deep position, y2 is the liquid level equivalent value when gas is discharged from the gas discharge unit installed at a shallow position, a' is a proportionality constant, c is the water level difference at the installation position of the gas discharge unit) is calculated in which the difference between each slurry concentration and the liquid level equivalent value calculated using the liquid level conversion device 14 is proportional to each other. In creating the approximation equation, it is preferable to use plots of two or more points, preferably five or more points, excluding the slurry concentration of 0%.

[0075] (Concentration calculation using approximate formula) While stirring the calcium fluoride slurry solution with an unknown slurry concentration so that the concentration near the gas discharge part becomes as uniform as possible, the liquid level conversion device 14 obtains liquid level conversion values, which are designated as y1' and y2', respectively. The slurry concentration is calculated by substituting y1' for y1, y2' for y2, the proportional constant obtained by creating the approximation formula in a', and the value of the water level difference at the installation position of the gas discharge part in c of the approximation formula y1-y2=a'x+c.

[0076] Separate devices may be used for "creating the approximate formula" and "calculating the concentration using the approximate formula". In that case, it is desirable to make the water level difference at the gas discharge unit installation position as the same as possible.

[0077] <Slurry concentration calculation and operation control> FIG. 3 shows an outline of an example of calculation of the slurry concentration and operation control based on the slurry concentration.

[0078] (Slurry concentration calculation) The slurry concentration is calculated according to the following flow. (A1) Gas is supplied from the gas supply device 16 into the crystallization reaction tank 10 at predetermined intervals, and the back pressure (air supply pressure) during this process is detected by the pressure measuring device 18. (A2) The value detected by the pressure measuring device 18 is transmitted as a signal to the liquid level conversion device 14. (A3) The liquid level conversion device 14 calculates a liquid level conversion value using the signal received and a pre-programmed relational expression between the pressure value and the liquid level. For example, if the pressure during gas ejection is ΔP, an arbitrary value ρ, the gravitational acceleration g, and the distance from the gas ejection part to the liquid level h, then ΔP=ρgh and the calculation can be made as h=ΔP / ρ / g. ρ may be set to the specific gravity of the solvent (for example, 1 for water). (A4) The liquid level converted value calculated by the liquid level conversion device 14 is transmitted as a signal to the slurry concentration calculation device 24. (A5) When there is one gas discharge point, the value of the distance from the gas discharge portion 58 to the liquid level measured by a liquid level measuring device 22 such as a liquid level gauge is also sent to the slurry concentration calculation device 24 as a signal. (A6) The slurry concentration is calculated by the slurry concentration calculation device 24 using the signal received by the slurry concentration calculation device 24 and an approximation equation that has been created and programmed in advance.

[0079] (Operation control) Operation is controlled according to the following flow. (B1) The slurry concentration calculation device 24 transmits the value of the slurry concentration as a signal to the control device 26. (B2) Operation is controlled based on the signal received by the control device 26 and the flow rate of the water to be treated, the amount of calcium agent added, the amount of acid added, the amount of seed crystals added, the amount of slurry extracted, etc., which are preset according to the slurry concentration.

[0080] For example, when the slurry concentration in the crystallization reaction tank 10 is to be maintained within a predetermined range, the amount of slurry extracted may be adjusted by controlling the opening time of the valve 52 of the slurry extraction means and the driving time of the extraction pump 50 based on the calculated value of the slurry concentration.

[0081] For example, when it is desired to increase the slurry concentration in the crystallization reaction tank 10, the open time of the valve 52 and the drive time of the withdrawal pump 50 may be controlled to be shorter so as to reduce the amount of slurry withdrawn, and the open time of the valve 46 of the seed crystal adding means and the drive time of the pump 44 may be controlled to be longer so as to increase the amount of seed crystals added.

[0082] The amount of seed crystals to be added may be adjusted either before or after the slurry is extracted. It is preferable to calculate the slurry concentration after the slurry is extracted and determine the amount of seed crystals to be added based on this value.

[0083] For example, when the rate at which the slurry concentration in the crystallization reaction tank 10 increases is too fast, the operation may be controlled to shorten the interval at which the slurry is withdrawn in order to avoid the risk of overflow or the like.

[0084] For example, if the rate of increase in the slurry concentration in the crystallization reaction tank 10 is too fast, in order to avoid risks such as overflow, the flow rate of the pump 28 of the treated water supply means may be controlled to be reduced, and the amount of calcium agent added or the amount of acid added may also be controlled to be reduced accordingly.

[0085] This specification includes the following embodiments. [1] A crystallization reaction apparatus for crystallizing calcium fluoride by adding a calcium agent to fluoride-containing water to be treated, A crystallization reaction tank; a calcium agent adding means for adding the calcium agent into the crystallization reaction tank; A stirring means provided in the crystallization reaction tank; A gas supplying means for supplying a gas into the crystallization reaction tank; a gas discharge unit that discharges the gas supplied from the gas supply means into the crystallization reaction tank; a pressure measuring means for measuring the pressure of the gas discharged from the gas discharge portion; a calculation means for calculating a slurry concentration in the crystallization reaction tank from a measured value of the gas pressure measured by the pressure measuring means; A crystallization reaction apparatus comprising:

[0086] [2] The crystallization reaction apparatus according to [1], The crystallization reaction apparatus further comprises a liquid level measuring means for measuring a liquid level in the crystallization reaction tank.

[0087] [3] The crystallization reaction apparatus according to [1] or [2], The gas discharge unit has at least two gas discharge portions, The pressure measuring means measures the pressure of the gas discharged from at least two or more of the gas discharge ports.

[0088] [4] The crystallization reaction apparatus according to any one of [1] to [3], a water supply means for supplying water to be treated into the crystallization reaction tank; an acid adding means for adding acid to the crystallization reaction tank; A seed crystal adding means for adding seed crystals into the crystallization reaction tank; a slurry extracting means for extracting the slurry from the crystallization reaction tank; and The crystallization reaction apparatus further comprises a control means for controlling at least one of the flow rate of the water to be treated, the amount of the calcium agent added, the amount of the acid added, the amount of the seed crystals added, and the amount of the slurry extracted, based on the slurry concentration calculated by the calculation means.

[0089] [5] A crystallization reaction method for crystallizing calcium fluoride by adding a calcium agent to fluoride-containing water to be treated, comprising the steps of: A crystallization reaction tank equipped with an agitation means is used, and the calcium agent is added to the water to be treated in the crystallization reaction tank to carry out a crystallization reaction. A crystallization reaction method comprising: supplying a gas into the crystallization reaction tank from a gas discharge port; measuring a pressure of the gas discharged from the gas discharge port; and calculating a slurry concentration in the crystallization reaction tank from a measured value of the gas pressure.

[0090] [6] The crystallization reaction method according to [5], The crystallization reaction method further comprises measuring a liquid level in the crystallization reaction tank.

[0091] [7] The crystallization reaction method according to [5] or [6], The gas discharge unit has at least two gas discharge portions, The crystallization reaction method further comprises measuring pressures of the gas discharged from at least two of the gas discharge ports.

[0092] [8] The crystallization reaction method according to any one of [5] to [7], A crystallization reaction method, comprising controlling at least one of a flow rate of the water to be treated into the crystallization reaction tank, an amount of the calcium agent added, an amount of an acid added into the crystallization reaction tank, an amount of seed crystals added into the crystallization reaction tank, and an amount of slurry withdrawn from the crystallization reaction tank, based on the calculated slurry concentration. EXAMPLES

[0093] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0094] As the crystallization reaction tank 10, a stirring type crystallization reaction tank made of vinyl chloride with an effective volume of 10 L was used. As the gas supply device 16 and the pressure measurement device 18, a pneumatic level gauge (EK series manufactured by Fuji Control Co., Ltd.) was used, and as the gas supply pipe 56, a tube made of Teflon (registered trademark) with a diameter of 6 × 4 mm was used. The slurry solution was prepared by adding calcium fluoride to a hydrofluoric acid solution with a fluorine concentration of 10,000 ppm or less so that the slurry concentration was a predetermined concentration of 0 to 60 v / v%. The slurry concentration at this time was measured by sampling the slurry solution in the crystallization reaction tank 10 and measuring the ratio of the precipitated volume of the crystals to the total volume of the slurry solution. In addition, the rotation speed of the stirring blade of the stirring device 12 was adjusted to 300 rpm so that the slurry layer concentration at the position of the gas discharge part 58 at the tip of the gas supply pipe 56 was as uniform as possible. The experimental conditions are shown in Table 1.

[0095] [Table 1]

[0096] <Example 1> (Creating an approximate formula) While stirring the slurry solution adjusted to a predetermined concentration, the gas discharge part was set to one gas discharge part 58 as shown in Figure 1, and the liquid level equivalent value (denoted as y) was obtained, which was converted from the discharge pressure when air was supplied as gas from the gas supply device 16 into the slurry solution. The results are shown in Table 2.

[0097] [Table 2]

[0098] An approximate equation was obtained in which the liquid level at each slurry concentration is proportional to the concentration (y=ax+b, x: slurry concentration, y: liquid level conversion value, a: proportionality constant, b: distance from the gas outlet to the liquid level). The results are shown in Figure 4.

[0099] (Concentration calculation using approximate formula) Next, for the calcium fluoride slurry solution with an unknown slurry concentration, a liquid level equivalent was obtained using an air-type level gauge, and this value was designated as y'.

[0100] The slurry concentration x was calculated by substituting y' for y in the approximate equation y=ax+b, the proportional constant obtained in the creation of the approximate equation for a, and the distance from the gas discharge port 58 to the liquid surface for b. The calculated value when y'=0.25m and b=0.21m was 21.1v / v%. On the other hand, the actual measured value was 20.5v / v%, and the calculated value and the actual measured value almost matched.

[0101] The actual measured value was calculated from the volume ratio of the crystals to 100 mL after the crystals had settled by placing 100 mL of calcium fluoride slurry solution that had been stirred as uniformly as possible into a 100 mL measuring cylinder.

[0102] The calculation formula for the slurry concentration in Example 1 is as follows: y=ax+b 0.25(m)=0.0019×x(v / v%)+0.21(m) x ≒ 21.1 (v / v%)

[0103] <Example 2> (Creating an approximate formula) While stirring the slurry solution adjusted to a predetermined concentration, two gas discharge units, gas discharge units 58 and 72, were installed at different locations as shown in Figure 2 so that the water level difference was c = 0.1 m. Liquid level conversion values ​​(y1 and y2) converted from the discharge pressure when air (referred to as air 1 and air 2) was supplied as gas from the gas supply device 16 into the slurry solution were obtained. The results are shown in Table 3.

[0104] [Table 3]

[0105] An approximate equation was obtained in which the difference between each slurry concentration and the corresponding liquid level equivalent is proportional (y1-y2=a'x+c, x: slurry concentration, y1: liquid level equivalent when gas is discharged from the gas discharge unit installed at a deep position, y2: liquid level equivalent when gas is discharged from the gas discharge unit installed at a shallow position, a': proportionality constant, c: water level difference at the installation position of the gas discharge unit). The results are shown in Figure 5.

[0106] (Concentration calculation using approximate formula) Next, for the calcium fluoride slurry solution with an unknown slurry concentration, the liquid level conversion value was obtained using an air-type level gauge, and the values ​​were designated as y1' and y2'.

[0107] The slurry concentration x was calculated by substituting y1' for y1, y2' for y2, the proportional constant obtained by creating the above approximation equation for a', and the value of the water level difference at the installation position of the gas discharge unit for c in the approximate equation y1-y2=a'x+c. The calculated value when y1'=0.33m, y2'=0.19m, and c=0.10m was 42.1v / v%. On the other hand, the actual measured value was 41.3v / v%, and the calculated value and the actual measured value almost matched.

[0108] The actual measured value was calculated from the volume ratio of the crystals to 100 mL after the crystals had settled by placing 100 mL of calcium fluoride slurry solution that had been stirred as uniformly as possible into a 100 mL measuring cylinder.

[0109] The calculation formula for the slurry concentration in Example 2 is as follows: y1-y2=a'x+c 0.33(m)-0.19(m)=0.00095×x(v / v%)+0.10(m) x ≒ 42.1 (v / v%)

[0110] In this way, the method of the present embodiment enables the slurry concentration in the crystallization reaction tank to be stably measured, thereby enabling the crystallization reaction to be maintained stably and efficiently. [Explanation of symbols]

[0111] 1 crystallization reaction apparatus, 10 crystallization reaction tank, 12 agitation device, 14 liquid level conversion device, 16 gas supply device, 18 pressure measuring device, 22 liquid level measuring device, 24 slurry concentration calculation device, 26 control device, 28, 32, 38, 44 pump, 30 treated water supply pipe, 34, 40, 46, 52 valve, 36 acid addition pipe, 42 calcium agent addition pipe, 48 seed crystal addition pipe, 50 withdrawal pump, 54 slurry withdrawal pipe, 56, 70 gas supply pipe, 58, 72 gas discharge part. 60 crystallization treatment water pipe, 62 crystallization treatment water discharge channel, 64 draft tube, 66 crystallization reaction liquid.

Claims

1. A crystallization reaction apparatus for crystallizing calcium fluoride by adding a calcium agent to fluorine-containing water to be treated, A crystallization reaction tank; a calcium agent adding means for adding the calcium agent into the crystallization reaction tank; A stirring means provided in the crystallization reaction tank; A gas supplying means for supplying a gas into the crystallization reaction tank; a gas discharge unit that discharges the gas supplied from the gas supply means into the crystallization reaction tank; a pressure measuring means for measuring the pressure of the gas discharged from the gas discharge portion; a calculation means for calculating a slurry concentration in the crystallization reaction tank from a measured value of the pressure of the gas measured by the pressure measuring means and a predetermined liquid level value in the crystallization reaction tank or a measured value of a liquid level measured by a liquid level measuring means for measuring the liquid level in the crystallization reaction tank; A crystallization reaction apparatus comprising:

2. A crystallization reaction apparatus for crystallizing calcium fluoride by adding a calcium agent to fluorine-containing water to be treated, comprising: A crystallization reaction tank; a calcium agent adding means for adding the calcium agent into the crystallization reaction tank; A stirring means provided in the crystallization reaction tank; A gas supplying means for supplying a gas into the crystallization reaction tank; a gas discharge unit that discharges the gas supplied from the gas supply means into the crystallization reaction tank; a pressure measuring means for measuring the pressure of the gas discharged from the gas discharge portion; a calculation means for calculating a slurry concentration in the crystallization reaction tank from a measured value of the gas pressure measured by the pressure measuring means; Equipped with The gas discharge portion has at least two or more gas discharge portions at different positions so as to provide a predetermined water level difference, The crystallization reaction apparatus, wherein the pressure measuring means measures pressures of gases discharged from at least two of the gas discharge ports.

3. The crystallization reaction apparatus according to claim 1, The gas discharge unit has at least two gas discharge portions, The crystallization reaction apparatus, wherein the pressure measuring means measures pressures of gases discharged from at least two of the gas discharge ports.

4. The crystallization reaction apparatus according to claim 1 or 2, a water supply means for supplying water to be treated into the crystallization reaction tank; an acid adding means for adding acid to the crystallization reaction tank; A seed crystal adding means for adding seed crystals into the crystallization reaction tank; a slurry extracting means for extracting the slurry from the crystallization reaction tank; and A crystallization reaction apparatus characterized by further comprising a control means for controlling at least one of the flow rate of the water to be treated, the amount of the calcium agent added, the amount of the acid added, the amount of the seed crystals added, and the amount of the slurry extracted, based on the slurry concentration calculated by the calculation means.

5. A crystallization reaction method for crystallizing calcium fluoride by adding a calcium agent to fluoride-containing water to be treated, comprising the steps of: A crystallization reaction tank equipped with an agitation means is used, and the calcium agent is added to the water to be treated in the crystallization reaction tank to carry out a crystallization reaction. A crystallization reaction method comprising the steps of: supplying a gas into the crystallization reaction tank from a gas discharge port; measuring a pressure of the gas discharged from the gas discharge port; and calculating a slurry concentration in the crystallization reaction tank from a measured value of the measured gas pressure and a predetermined liquid level in the crystallization reaction tank or a measured value of the liquid level in the crystallization reaction tank.

6. A crystallization reaction method for crystallizing calcium fluoride by adding a calcium agent to fluoride-containing water to be treated, comprising the steps of: A crystallization reaction tank equipped with an agitation means is used, and the calcium agent is added to the water to be treated in the crystallization reaction tank to carry out a crystallization reaction. supplying a gas into the crystallization reaction tank from a gas discharge port, measuring a pressure of the gas discharged from the gas discharge port, and calculating a slurry concentration in the crystallization reaction tank from a measured value of the gas pressure; The gas discharge portion has at least two or more gas discharge portions at different positions so as to provide a predetermined water level difference, A crystallization reaction method comprising measuring pressures of gases discharged from at least two of the gas discharge ports.

7. The crystallization reaction method according to claim 5, The gas discharge unit has at least two gas discharge portions, A crystallization reaction method comprising measuring pressures of gases discharged from at least two of the gas discharge ports.

8. The crystallization reaction method according to claim 5 or 6, A crystallization reaction method, characterized in that at least one of the flow rate of the water to be treated into the crystallization reaction tank, the amount of the calcium agent added, the amount of acid added into the crystallization reaction tank, the amount of seed crystals added into the crystallization reaction tank, and the amount of slurry withdrawn from the crystallization reaction tank is controlled based on the calculated slurry concentration.

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