Crystallization reaction apparatus and crystallization reaction method

Abstract

The purpose of the present invention is to provide a crystallization reaction apparatus and a crystallization reaction method capable of stably measuring a slurry concentration in a crystallization reaction tank and maintaining an efficient crystallization reaction. A crystallization reaction apparatus (1) for crystallizing calcium fluoride by adding a calcium agent to water to be treated which contains fluorine comprises: a crystallization reaction tank (10); a calcium agent addition means for adding a calcium agent into the crystallization reaction tank (10); a stirring device (12) provided in the crystallization reaction tank (10); a gas supply device (16) for supplying a gas into the crystallization reaction tank (10); a gas discharge unit (58) for discharging the supplied gas into the crystallization reaction tank (10); a pressure measurement device (18) for measuring the pressure of the discharged gas; a liquid level conversion device (14) for calculating the slurry concentration in the crystallization reaction tank (10) from a measured value of the pressure of the gas; and a slurry concentration calculation device (24).

Description

Crystallization reaction apparatus and crystallization reaction method

[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.

[0002] A widely known method for treating hydrofluoric acid-containing wastewater discharged from semiconductor factories and other plants is to comply with fluorine discharge standards or to reuse the hydrofluoric acid as a valuable resource by using a technology that produces 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 extracted and the amount of seed crystals added.

[0004] As described in

[0004] of Patent Document 1, it is important to maintain the slurry concentration in the crystallization reaction tank as constant as possible in a 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, high-concentration slurries such as those in crystallization reaction tanks may exceed the measurement concentration range, or the sensor may need to be frequently cleaned due to scale formation caused by calcium or the like. Furthermore, Patent Document 1 also describes a method of measuring the sedimentation volume of crystals by sampling the slurry solution in the crystallization reaction tank by some method, but this requires sampling of the slurry solution containing hydrofluoric acid, and the measurement takes time, so it may not be possible to appropriately follow the amount of slurry withdrawn or the amount of seed crystals added 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 pressure of the exhaust gas or atmospheric pressure, and converting the measured 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.

[0007] Japanese Patent No. 5941329 Japanese Patent Application Laid-Open No. 2021-166955

[0008] An object of the present invention is to provide 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.

[0009] The present invention provides a crystallization reaction apparatus for crystallizing calcium fluoride by adding a calcium agent to fluoride-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 unit 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 unit; and a calculating means for calculating a slurry concentration in the crystallization reaction tank from the measured value of the gas pressure measured by the pressure measuring means.

[0010] The crystallization reaction apparatus preferably further comprises a liquid level measuring means for measuring the liquid level in the crystallization reaction tank.

[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 addition means for adding acid into the crystallization reaction tank, a seed crystal addition means for adding seed crystals into the crystallization reaction tank, and a slurry withdrawal 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 is a crystallization reaction method for crystallizing calcium fluoride by adding a calcium agent to fluoride-containing water to be treated, which comprises 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 port, measuring the pressure of the gas discharged from the gas discharge port, and calculating the slurry concentration in the crystallization reaction tank from the measured value of the gas pressure.

[0014] In the crystallization reaction method, it is preferable to measure the liquid level in the crystallization reaction tank.

[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, based on the calculated slurry concentration, 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.

[0017] According to the present invention, it is possible to provide 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.

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

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is 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 fluorine-containing water to be treated. The crystallization reaction apparatus 1 comprises 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 equipped with an agitator blade or the like as 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 unit 58 for discharging the gas supplied from the gas supply device 16 into the crystallization reaction tank 10; a pressure measurement device 18 as pressure measurement means for measuring the pressure of the gas discharged from the gas discharge unit 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 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 into the crystallization reaction tank 10; a pump 44 and a seed crystal addition pipe 48 as seed crystal addition means for adding seed crystals into 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 be equipped with a draft tube 64 described below. The crystallization reaction apparatus 1 may be equipped with 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 be equipped with 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 Figure 1, a water-to-be-treated supply pipe 30 is connected to the water-to-be-treated inlet of the crystallization reaction tank 10 via a pump 28, an acid addition pipe 36 is connected to the acid inlet via a pump 32 and a valve 34, a calcium agent addition pipe 42 is connected to the calcium agent inlet via a pump 38 and a valve 40, and a seed crystal addition pipe 48 is connected to the seed crystal inlet via a pump 44 and a valve 46. A slurry withdrawal pipe 54 is connected to the slurry outlet of the crystallization reaction tank 10 via an withdrawal pump 50 and a valve 52. An inner peripheral wall is disposed opposite the peripheral wall of the crystallization reaction tank 10, and a crystallized water discharge channel 62 is formed between the inner and outer peripheral walls. A crystallized water pipe 60 is connected to the crystallized water outlet at the top of the crystallized water discharge channel 62.

[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 on 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 via 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 via 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 so as to be able to communicate each other via 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 via 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 via 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 by pump 28 through the water-to-be-treated supply pipe 30 to the crystallization reaction tank 10. With valve 46 open, seed crystals are added to the water to be treated by pump 44 through the seed crystal addition pipe 48. With valve 40 open, a calcium agent is added to the water to be treated by pump 38 through the calcium agent addition pipe 42. In the crystallization reaction tank 10, fluorine contained in the water to be treated reacts with the calcium agent to produce calcium fluoride, which precipitates on the surfaces of the seed crystals, producing poorly soluble calcium fluoride crystals (crystallization reaction process). During this process, the inside of the crystallization reaction tank 10 is stirred by the agitator 12. With valve 34 open, an acid serving as a pH adjuster is added to the crystallization reaction tank 10 through the acid addition pipe 36 by pump 32, thereby adjusting the pH in the crystallization reaction tank 10. The calcium agent is preferably added near the agitator blades of the agitator 12.

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

[0030] The crystallization reaction method and crystallization reaction apparatus according to this embodiment enable stable measurement of the slurry concentration in the crystallization reaction tank 10 during the crystallization reaction. The inventors have newly discovered that when a gas such as air is supplied from the gas supply device 16 to the crystallization reaction liquid 66 in the crystallization reaction tank 10 and discharged from the gas discharge port 58, and the back pressure (air supply pressure) is measured, the back pressure varies with the slurry concentration (changes in the specific gravity of the slurry) even when the distance between the liquid level in the crystallization reaction tank 10 and the gas discharge port 58 is constant, and that there is a proportional relationship between the back pressure and the slurry concentration. By utilizing this proportional relationship, the slurry concentration can be measured accurately and stably on-site without sampling the slurry. This facilitates management of the amount of slurry withdrawn from the crystallization reaction tank 10 and the amount of seed crystals replenished, and enables the calcium fluoride recovery rate, which is susceptible to fluctuations depending on the slurry concentration, to be maintained at a high level. 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, the method for measuring the slurry concentration involves installing a crystal concentration meter in the crystallization reaction tank, or sampling the slurry solution in the crystallization reaction tank and measuring the settling volume of the crystals. In contrast, the crystallization reaction method and crystallization reaction apparatus according to this embodiment installs a gas supply pipe 56 for discharging a gas such as air into the crystallization reaction tank 10, and delivers gas from a gas supply device 16. By utilizing the correlation between the back pressure and the specific gravity of the slurry, which varies depending on the slurry concentration, the slurry concentration can be measured without sampling the slurry. This eliminates the risk of scale buildup due to contact of the sensor with the liquid, and eliminates the need for sampling the slurry liquid. Furthermore, it is possible to measure the slurry concentration even for high-concentration slurries, for example, in the range of 0 to 60% v / v, as the settling volume of the crystals.

[0032] In Patent Document 2, the concentration of gypsum slurry produced 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. In contrast, the crystallization reaction method and crystallization reaction apparatus according to this 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) rather than simply pressure (water pressure), and is located outside the crystallization reaction tank, eliminating the risk of scale.

[0033] The crystallization reaction tank 10 is a tank for storing the crystallization reaction liquid 66 and performing the crystallization reaction. 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 agitator 12 is not particularly limited as long as it can agitate the crystallization reaction liquid 66 in the crystallization reaction tank 10, but for example, it may have an agitator blade, and the agitator blade is rotated by rotational force generated by a driving means such as a motor transmitted via an agitator 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 below the water surface in the crystallization reaction tank 10 so that the agitating blades of the agitator 12 are positioned inside a cylindrical or other tube. When the draft tube 64 is installed and the agitating blades are placed inside the draft tube 64, a downward flow is generated toward the bottom of the draft tube 64, forming a zone with a relatively high diffusion flow rate. This allows the treated water, calcium agent, etc. to be diffused more quickly, and it is thought that it is possible to minimize contact between areas where the concentrations of the treated water or calcium agent are locally high, resulting in the direct generation of calcium fluoride particles.

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

[0037] Furthermore, the crystals whose particle size has increased as the crystallization reaction progresses 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 sizes and to an improvement in 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 agitating blades be located somewhere in the lower half of the tube. More preferably, they should be located slightly above the lower end of the tube. With this arrangement, a zone with a high agitation flow rate is formed like a vortex near the lower end of the tube, and from there, a stable upward flow is formed along the outer periphery of the tube. This effectively promotes the diffusion of the treated water and calcium additives, as well as the classification of particles.

[0039] When the draft tube 64 is provided, the injection point for the water to be treated and the calcium agent is preferably located inside the draft tube 64 so that they are carried along with the downward flow inside the draft tube 64 and diffused quickly and effectively. A more preferable position is inside the draft tube 64 and above the stirring blades.

[0040] In order to make the slurry concentration in the crystallization reaction tank 10 as uniform as possible, the rotation speed of the stirring blades of the stirrer 12 may be set, 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 set, 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 stirring blades, 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 a withdrawal pump 50, a valve 52, and a slurry withdrawal pipe 54 as a slurry withdrawal means.

[0042] The calcium agent may be added to the crystallization reaction tank 10 by calcium addition means such as a pump 38, a valve 40, and a calcium agent addition 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, or calcium carbonate, or a slurry may be used. One type of calcium agent may be used alone, or two or more types may be used in combination.

[0043] The amount of calcium agent added may be, for example, in the range of 0.8 to 2 times the chemical equivalent of calcium as that of fluorine, 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 form as fine particles without precipitating on seed crystals, and calcium fluoride may be contaminated into the crystallization treatment water. If the chemical equivalent of calcium is less than 0.8 times, a large proportion of the fluorine in the water to be treated does not become calcium fluoride, and fluorine may be contaminated 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, the other end has a gas discharge port 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 port 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 port 58 can be measured by the pressure measuring device 18. The gas discharge port 58 is preferably located at a water level between the upper and lower ends of the draft tube 64. To prevent the gas supply pipe 56 from being entangled in the stirring rod or stirring blades of the stirrer 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 the gas supply piping 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] The gas supply device 16 may be an air-type level meter in which the pressure measuring device 18 and the liquid level conversion device 14 are integrated.

[0048] There are no particular restrictions on the materials of the gas supply pipe 56 and the gas discharge part 58, but from the viewpoint of lifespan, it is preferable that the materials be resistant to hydrofluoric acid and strong acids, such as polytetrafluoroethylene (Teflon (registered trademark)) or polyvinyl chloride.

[0049] The crystallization reaction tank 10 may be equipped with a liquid level measuring device 22 such as a liquid level meter 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 measuring device 22 is capable of measuring the liquid level without coming into contact with the crystallization reaction liquid in the crystallization reaction tank 10, and for example, an ultrasonic level meter may be used.

[0050] The gas supply pressure from the gas supply device 16 may be, for example, 30 kPa or more, and from the viewpoint of power consumption, it 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 be any device capable of detecting the gas supply pressure, and is not particularly limited. 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 that can calculate 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 measurement device 18.

[0053] The slurry concentration calculation device 24 may be a personal computer (PC) or a programmable logic controller (PLC) that can calculate the slurry concentration from the analog or digital signal from the liquid level conversion device 14 .

[0054] The control device 26 is composed of, for example, a microcomputer and electronic circuitry, which are made up of a calculation means such as a CPU that executes a program and storage means such as a ROM and RAM that store the program and calculation results. The control device 26 may be a programmable controller (also called a programmable logic controller) (PLC) that incorporates a microprocessor and controls equipment using a program. The control device 26 has the 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 valve 40 to control the amount of calcium agent added; controlling the pump 32 or valve 34 to control the amount of acid added; controlling the pump 44 or valve 46 to control the amount of seed crystals added; and controlling the withdrawal pump 50 or valve 52 to control the amount of slurry withdrawn.

[0055] The water to be treated is water containing fluorine, such as wastewater containing fluorine, and may be water of any origin. However, from the viewpoints of impurities and recovery efficiency, 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 addition means, such as a pump 32, a valve 34, and an acid addition pipe 36, for adding an acid to the crystallization reaction tank 10. Examples of the acid to be added include strong acids such as hydrochloric acid, nitric acid, and sulfuric acid. One type of acid may be used alone, or two or more types may be used in combination.

[0059] The crystallization reaction apparatus 1 may be equipped with a seed crystal addition means, such as a pump 44, a valve 46, or a seed crystal addition pipe 48, for adding seed crystals to the crystallization reaction tank 10. The seed crystals may be made of any material that can precipitate crystals of a poorly soluble calcium salt formed on their surfaces. Examples of the seed crystals 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 Sakulandum (trade 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 in the form of 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 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.

[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 each have an inverter.

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

[0065] (Creating an Approximate Formula) First, an approximate 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 unit, gas discharge unit 58, as in the crystallization reaction apparatus 1 of Figure 1. At this time, a liquid level conversion value (referred to 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 unit 58 to the liquid level as constant as possible while creating the approximate formula.

[0066] An approximate equation (y = ax + b, where x is the slurry concentration, y is the liquid level conversion value, a is a proportional constant, and b is the distance from the gas discharge port 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. To create 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 port becomes as uniform as possible, a liquid level conversion value is obtained using the liquid level conversion device 14, and this value is designated as y'. The slurry concentration is calculated by substituting y' for y in the approximate formula y = ax + b, substituting the proportionality constant obtained in creating the approximate formula for a, and substituting the value of the distance from the gas discharge port 58 to the liquid level obtained in creating the approximate formula for b.

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

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

[0070] The crystallization reaction apparatus 3 shown in Figure 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 the gas discharge unit 58. A gas supply pipe 70 branches off from the gas supply pipe 56, and one end of the gas supply pipe 70 is connected via a valve 76 to the upstream side of the valve 74 in the gas supply pipe 56, and the other end has the 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 necessarily have to include a liquid level measuring device 22 as in the crystallization reaction apparatus 1 of Figure 1. Other than these, the crystallization reaction apparatus has the same configuration as that of the crystallization reaction apparatus 1 in FIG.

[0071] In the crystallization reaction apparatus 3, the depths of the gas discharge ports 58, 72 from the water surface may be different. In the crystallization reaction tank 10, if the water level from the liquid surface to the upper end of the draft tube increases due to liquid level fluctuations, there may be a portion of the phase from the liquid surface to the upper end of the draft tube where the agitation flow does not reach, resulting in a concentration gradient. In this case, by providing two or more gas discharge ports in a portion where the concentration is approximately uniform due to agitation, the slurry concentration can be calculated from the difference in pressure between them. Because the concentration is maintained approximately uniform at the water level from the upper end to the lower end of the draft tube 64 in the crystallization reaction tank 10, the two or more gas discharge ports 58, 72 are preferably located at a water level between the upper and lower ends of the draft tube 64. To prevent the gas supply pipes 56, 70 from becoming entangled in the agitator rod or agitator blades of the agitator 12, it is more preferable to provide the gas supply pipes 56, 70 on the outer periphery of the draft tube 64 rather than inside the draft tube 64.

[0072] 2 , the crystallization reaction apparatus 3 has one gas supply device, the gas supply device 16, and the gas supply pipe 56 branches into the gas supply pipe 70 to provide two or more gas discharge ports, the gas discharge ports 58 and 72. However, two or more gas supply devices may be provided, each equipped with a gas supply pipe, with one end of the gas supply pipe connected to the gas supply device and the gas discharge port at the other end immersed to a predetermined depth in the crystallization reaction solution 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 locations by switching the valves using a timer or the like. For example, with the valve 74 open and the valve 76 closed, 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. Thereafter, valve 74 is switched to a closed state and 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. The order in which the valves are opened and closed is not particularly limited. Alternatively, two or more gas supply devices and pressure measurement devices may be provided, each equipped with a gas supply pipe, with one end of the gas supply pipe connected to the gas supply device and the gas discharge port at the other end immersed to a predetermined depth in the crystallization reaction solution 66 in the crystallization reaction tank 10. In this case, a valve may be provided in the gas supply pipe of each line, but switching between valves according to the measurement is not particularly required, and the back pressure of each line may be measured. The pressure of the gas discharged from the gas discharge port may be measured anywhere between the gas supply device and the gas discharge port. The back pressure near the gas supply device (i.e., the air supply pressure) may be measured, or the pressure near the gas discharge port, such as the tip of the gas discharge port of the gas supply pipe, may be measured.

[0073] <Method for Calculating Slurry Concentration> (Creating Approximate Formula) First, an approximate formula is created. While stirring a slurry solution adjusted to a predetermined slurry concentration, two gas discharge units, gas discharge units 58 and 72, are installed at different locations to achieve a predetermined water level difference (denoted as c), as in the crystallization reaction apparatus 3 of FIG. 2. With valve 74 or valve 76 open, gases such as air (denoted as gas 1 and gas 2) are supplied from the gas supply device 16 into the slurry solution through the respective gas discharge units 58 and 72. At this time, liquid level conversion values ​​(denoted as y1 and y2) are calculated using the liquid level conversion device 14 from the discharge pressure detected by the pressure measurement device 18. During the creation of the approximate formula, it is preferable to maintain the water level difference between the respective gas discharge units 58 and 72 at a predetermined value.

[0074] An approximate 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, and 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. To create 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%.

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

[0076] Separate devices may be used for "creating the approximation formula" and "calculating the concentration using the approximation formula." In that case, it is desirable to make the water level difference at the gas discharge unit installation position as similar 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] (Calculation of Slurry Concentration) 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) at that time is detected by the pressure measuring device 18. (A2) The value detected by the pressure measuring device 18 is sent as a signal to the liquid level conversion device 14. (A3) A liquid level conversion value is calculated using the signal received by the liquid level conversion device 14 and a pre-programmed equation relating the pressure value and the liquid level. For example, if the pressure during gas discharge is ΔP, an arbitrary value ρ is ρ, the gravitational acceleration is g, and the distance from the gas discharge port to the liquid level is h, then ΔP = ρgh and the calculation can be made as h = ΔP / ρ / g. ρ can be set to the specific gravity of the solvent (e.g., 1 for water). (A4) The liquid level conversion value calculated by the liquid level conversion device 14 is sent 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 part 58 to the liquid level, measured by a liquid level measuring device 22 such as a liquid level meter, is also sent as a signal to the slurry concentration calculation device 24. (A6) The slurry concentration calculation device 24 calculates the slurry concentration using the signal received by the slurry concentration calculation device 24 and an approximate equation that has been created and programmed in advance.

[0079] (Operation Control) Operation is controlled according to the following flow: (B1) The value of the slurry concentration is sent as a signal from the slurry concentration calculation device 24 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 crystal added, the amount of slurry extracted, and the like, which are set in advance 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 to be extracted may be adjusted by controlling the opening time of the valve 52 of the slurry extraction means, the driving time of the extraction pump 50, etc., 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, if 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, the flow rate of the pump 28 of the treated water supply means may be controlled to be reduced in order to avoid risks such as overflow, and the amount of calcium agent or 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, comprising: a crystallization reaction tank, 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 unit 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 unit, and a calculating means for calculating a slurry concentration in the crystallization reaction tank from the measured value of the gas pressure measured by the pressure measuring means.

[0086] [2] The crystallization reaction apparatus according to [1], further comprising 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], wherein 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.

[0088] [4] The crystallization reaction apparatus according to any one of [1] to [3], further comprising at least one of: a water-to-be-treated supply means for supplying water-to-be-treated into the crystallization reaction tank; an acid addition means for adding acid into the crystallization reaction tank; a seed crystal addition means for adding seed crystals into the crystallization reaction tank; and a slurry withdrawal means for withdrawing a slurry from the crystallization reaction tank; and 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 withdrawn, 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: 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 part; measuring the pressure of the gas discharged from the gas discharge part; and calculating a slurry concentration in the crystallization reaction tank from the measured value of the gas pressure.

[0090] [6] The crystallization reaction method according to [5], wherein the liquid level in the crystallization reaction tank is measured.

[0091] [7] The crystallization reaction method according to [5] or [6], wherein the crystallization reaction method has at least two or more gas discharge ports, and the pressure of the gas discharged from the at least two or more gas discharge ports is measured.

[0092] [8] The crystallization reaction method according to any one of [5] to [7], wherein 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.

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

[0094] The crystallization reaction tank 10 was a stirred polyvinyl chloride crystallization reaction tank with an effective volume of 10 L. A pneumatic level gauge (EK series, manufactured by Fuji Control Co., Ltd.) was used as the gas supply device 16 and pressure measurement device 18, and a φ6 x 4 mm Teflon (registered trademark) tube was used as the gas supply pipe 56. The slurry solution was prepared by adding calcium fluoride to a hydrofluoric acid solution with a fluorine concentration of 10,000 ppm or less to achieve a predetermined slurry concentration of 0 to 60 v / v%. The slurry concentration was measured by sampling the slurry solution in the crystallization reaction tank 10 and measuring the ratio of the settled volume of the crystals to the total volume of the slurry solution. The rotation speed of the stirring blades of the stirring device 12 was adjusted to 300 rpm so that the slurry layer concentration at the gas outlet 58 at the tip of the gas supply pipe 56 was as uniform as possible. The experimental conditions are shown in Table 1.

[0095]

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

[0097]

[0098] An approximate equation was obtained in which each slurry concentration and the liquid level at that time were proportional (y = ax + b, where x is the slurry concentration, y is the liquid level equivalent, a is the proportionality constant, and b is the distance from the gas discharge port to the liquid level). The results are shown in Figure 4.

[0099] (Concentration Calculation Using Approximation Formula) Next, for a calcium fluoride slurry solution whose slurry concentration was unknown, a liquid level equivalent value was obtained using an air-type level meter, 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 proportionality constant obtained in creating 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' = 0.25 m and b = 0.21 m was 21.1 v / v %. On the other hand, the actual measured value was 20.5 v / v %, and the calculated value and the actual measured value were almost the same.

[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 a slurry solution of calcium fluoride that had been stirred as uniformly as possible in a measuring cylinder having a volume of 100 mL.

[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 (Creation of Approximation Formula) While stirring a 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 c = 0.1 m. Liquid level equivalent values ​​(referred to as y1 and y2) were obtained by converting the discharge pressure when air (referred to as air 1 and air 2) was supplied as gas from gas supply device 16 into the slurry solution. The results are shown in Table 3.

[0104]

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

[0106] (Concentration Calculation Using Approximation Formula) Next, for a calcium fluoride slurry solution whose slurry concentration was unknown, a liquid level equivalent value was obtained using an air-type level meter, 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 proportionality constant obtained in creating the approximate formula for a', and the value of the water level difference at the installation position of the gas discharge port for c in the approximate formula y1-y2=a'x+c. The calculated value when y1' = 0.33 m, y2' = 0.19 m, and c = 0.10 m was 42.1 v / v%. On the other hand, the actual measured value was 41.3 v / v%, and the calculated value and the actual measured value were almost the same.

[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 a slurry solution of calcium fluoride that had been stirred as uniformly as possible in a measuring cylinder having a volume of 100 mL.

[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)=0.00095xx(v / v%)+0.10(m) x≈42.1(v / v%)

[0110] As described above, the method of the present invention enabled stable measurement of the slurry concentration in the crystallization reaction tank, thereby enabling stable and efficient crystallization reaction to be maintained.

[0111] 1 Crystallization reaction apparatus, 10 Crystallization reaction tank, 12 Agitator, 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 section. 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 fluoride-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 gas into the crystallization reaction tank; a gas discharge section 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 section; and a calculating means for calculating a slurry concentration in the crystallization reaction tank from the measured value of the gas pressure measured by the pressure measuring means.

2. The crystallization reaction apparatus according to claim 1, further comprising a liquid level measuring means for measuring the liquid level in said crystallization reaction tank.

3. A crystallization reaction apparatus according to claim 1 or 2, comprising at least two or more of the gas discharge ports, and wherein the pressure measuring means measures the pressure of the gas discharged from at least two or more of the gas discharge ports.

4. A crystallization reaction apparatus according to any one of claims 1 to 3, further comprising 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 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 withdrawn, 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: 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 port; measuring the pressure of the gas discharged from the gas discharge port; and calculating a slurry concentration in the crystallization reaction tank from the measured value of the gas pressure.

6. The crystallization reaction method according to claim 5, further comprising measuring the liquid level in the crystallization reaction tank.

7. A crystallization reaction method according to claim 5 or 6, comprising: at least two or more of the gas discharge ports; and measuring the pressure of the gas discharged from at least two or more of the gas discharge ports.

8. A crystallization reaction method according to any one of claims 5 to 7, 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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