Crystallization reaction device and crystallization reaction method

Abstract

To provide a crystallization reaction device 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 device 1 which is a crystallization reaction device 1 crystallizing calcium fluoride by adding a calcium preparation to water to be treated including fluorine, comprises a crystallization reaction tank 10, a calcium preparation adding means of adding a calcium preparation into the crystallization reaction tank 10, an agitation device 12 provided in the crystallization tank 10, a gas supply device 16 supplying gas into the crystallization reaction tank 10, a gas injector 58 injecting the supplied gas into the crystallization reaction tank 10, a pressure measurement device 18 measuring the pressure of the gas to be injected, a liquid level conversion device 14 calculating the slurry concentration in the crystallization reaction tank 10 from a measured value of the gas pressure and a slurry concentration calculation device 24.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a crystallization reactor and a crystallization reaction method for performing crystallization treatment of water to be treated containing fluorine.

Background Art

[0002] Regarding hydrofluoric acid-containing waste liquid discharged from semiconductor factories and the like, in order to comply with the discharge standards of fluorine or to achieve the purpose of reusing hydrofluoric acid as a valuable substance, a method of treating by a crystallization reaction using a calcium agent to produce calcium fluoride is widely known.

[0003] In such a method, in order to increase the recovery rate of fluorine, it is required to adjust the amount of extracted calcium fluoride crystals, the amount of added seed crystals, etc., and manage the slurry concentration in the crystallization reaction tank where the crystallization reaction is performed within a predetermined range.

[0004] As described in

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

[0024] of Patent Document 1, a high-concentration slurry such as in a crystallization reaction tank may exceed the measurement concentration range or may require frequent sensor cleaning due to scale generation 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 and measuring the sedimentation volume of crystals, but it is necessary to sample the slurry solution containing hydrofluoric acid, and since it takes time for measurement, the amount of extracted slurry, the amount of added seed crystals, etc. may not be able to appropriately follow the change in slurry concentration.

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

[0006] Against such a background, in the crystallization treatment of water to be treated containing fluorine, there is a demand for a crystallization reaction apparatus and a crystallization reaction method capable of stably measuring the slurry concentration in the crystallization reaction tank and maintaining an efficient crystallization reaction.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems 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 Problems

[0009] The present invention relates to a crystallization reaction apparatus for crystallizing calcium fluoride by adding a calcium agent to water to be treated containing fluorine, comprising a crystallization reaction tank, calcium agent addition means for adding the calcium agent into the crystallization reaction tank, stirring means provided in the crystallization reaction tank, gas supply means for supplying gas into the crystallization reaction tank, a gas discharge part for discharging the gas supplied from the gas supply means into the crystallization reaction tank, pressure measurement means for measuring the pressure of the gas discharged from the gas discharge part, and arithmetic means for calculating the slurry concentration in the crystallization reaction tank from the measured value of the pressure of the gas measured by the pressure measurement means.

[0010] In the crystallization reaction apparatus, it is preferable to further include liquid level measurement means for measuring the liquid level in the crystallization reaction tank.

[0011] In the crystallization reaction apparatus, it is preferable to have at least two or more gas discharge parts, and the pressure measurement means measures the pressure of the gas discharged from at least two or more gas discharge parts.

[0012] In the crystallization reaction apparatus, it further includes at least one of treated water supply means for supplying treated water into the crystallization reaction tank, acid addition means for adding acid into the crystallization reaction tank, seed crystal addition means for adding seed crystals into the crystallization reaction tank, and slurry extraction means for extracting slurry from the crystallization reaction tank, and further includes control means for controlling at least one of the flow rate of the treated water, the addition amount of the calcium agent, the addition amount of the acid, the addition amount of the seed crystals, and the extraction amount of the slurry based on the slurry concentration calculated by the arithmetic means.

[0013] The present invention is a crystallization reaction method for adding a calcium agent to water to be treated containing fluorine to crystallize calcium fluoride. A crystallization reaction tank equipped with stirring means is used, the calcium agent is added to the water to be treated in the crystallization reaction tank to perform a crystallization reaction, gas is supplied from a gas discharge part into the crystallization reaction tank, the pressure of the gas discharged from the gas discharge part is measured, and the slurry concentration in the crystallization reaction tank is calculated from the measured value of the pressure of the measured gas.

[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 to have at least two or more gas discharge parts and measure the pressures of the gases discharged from at least two or more gas discharge parts.

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

Advantages 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

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0019] The embodiments of the present invention will be described below. This embodiment is an example of carrying out the present invention, and the present invention is not limited to this embodiment.

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

[0021] The crystallization reaction apparatus 1 shown in FIG. 1 is an apparatus for adding a calcium agent to the water to be treated containing fluorine to crystallize calcium fluoride. The crystallization reaction apparatus 1 includes a crystallization reaction tank 10; a calcium agent adding means for adding a calcium agent into the crystallization reaction tank 10, including a pump 38 and a calcium agent adding pipe 42; a stirring means provided in the crystallization reaction tank 10, such as a stirring device 12 having stirring blades; a gas supply means for supplying gas into the crystallization reaction tank 10, including a gas supply device 16 and a gas supply pipe 56; a gas discharge part 58 for discharging the gas supplied from the gas supply device 16 into the crystallization reaction tank 10; a pressure measuring means for measuring the pressure of the gas discharged from the gas discharge part 58, such as a pressure measuring device 18; and an arithmetic means for calculating the slurry concentration in the crystallization reaction tank 10 from the measured value of the gas pressure measured by the pressure measuring device 18, such as a liquid level conversion device 14 and a slurry concentration arithmetic device 24.

[0022] The crystallization reaction apparatus 1 may include a pump 28 and a to-be-treated water supply pipe 30 as to-be-treated water supply means for supplying to-be-treated water into the crystallization reaction tank 10; a pump 32 and an acid addition pipe 36 as acid addition means for adding an 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 a withdrawal pump 50 and a slurry withdrawal pipe 54 as slurry withdrawal means for withdrawing 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 measurement device 22 as liquid level measurement means for measuring the liquid level in the crystallization reaction tank 10. The crystallization reaction apparatus 1 may include a control device 26 as control means for controlling at least one of the flow rate of the to-be-treated water, the addition amount of the calcium agent, the addition amount of the acid, the addition amount of the seed crystals, and the withdrawal amount of the slurry based on the slurry concentration calculated by the arithmetic means.

[0024] In the crystallization reaction apparatus 1 of FIG. 1, the to-be-treated water supply pipe 30 is connected to the to-be-treated water inlet of the crystallization reaction tank 10 via the pump 28, the acid addition pipe 36 is connected to the acid inlet via the pump 32 and the valve 34, the calcium agent addition pipe 42 is connected to the calcium agent inlet via the pump 38 and the valve 40, and the seed crystal addition pipe 48 is connected to the seed crystal inlet via the pump 44 and the valve 46. The slurry withdrawal pipe 54 is connected to the slurry outlet of the crystallization reaction tank 10 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 a crystallization-treated water discharge path 62 is formed between the inner and outer peripheral walls. A crystallization-treated water pipe 60 is connected to the crystallization-treated water outlet at the upper part of the crystallization-treated water discharge path 62.

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

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

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

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

[0029] The slurry containing calcium fluoride crystals generated in the crystallization reaction tank 10 is withdrawn from the slurry withdrawal pipe 54 by the withdrawal pump 50 with the valve 52 in the open state and recovered. The crystallization treated water with reduced fluorine by the crystallization reaction in the crystallization reaction tank 10 is discharged from the crystallization treated water discharge passage 62 through the crystallization treated water pipe 60.

[0030] In the crystallization reaction method and the crystallization reaction apparatus according to the present embodiment, the slurry concentration in the crystallization reaction tank 10 in the crystallization reaction can be stably measured. The inventors of the present invention send a gas such as air from the gas supply device 16 to the crystallization reaction liquid 66 in the crystallization reaction tank 10 and discharge it from the gas discharge portion 58, and when measuring the back pressure (air supply pressure) at that time, even if the distance between the liquid level of the crystallization reaction tank 10 and the gas discharge portion 58 is constant, the back pressure changes depending on the slurry concentration (change in the specific gravity of the slurry), and it has been newly found that there is a proportional relationship between the back pressure and the slurry concentration. By utilizing this proportional relationship, it becomes possible to accurately and stably measure the slurry concentration on-site without sampling the slurry. As a result, it becomes easier to manage the amount of slurry withdrawn from the crystallization reaction tank 10, the replenishment amount of seed crystals, etc., and it becomes possible to maintain a high recovery rate of calcium fluoride, which is likely to vary depending on the slurry concentration. Therefore, a stable and efficient crystallization reaction can be maintained. The calculation method of the slurry concentration will be described later.

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

[0032] In Patent Document 2, for measuring the concentration of gypsum slurry generated in a flue gas desulfurization facility, the pressure is measured by a pressure detector installed at a predetermined height position (water depth) in the reaction tank with reference to the pressure of the exhaust gas or the atmospheric pressure, and is converted into the slurry concentration. In contrast, in the crystallization reaction method and the crystallization reaction apparatus according to the present embodiment, it is a crystallization reaction apparatus using a highly corrosive water to be treated such as hydrofluoric acid, the back pressure (air supply pressure) of the gas is measured instead of simply the pressure (water pressure), and the pressure measuring device is outside the crystallization reaction tank and there is no scale risk.

[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 a stirring type crystallization reaction tank having a stirring mechanism such as a stirring device 12 inside the tank.

[0034] The stirring device 12 may be any device that can stir the crystallization reaction liquid 66 in the crystallization reaction tank 10, and is not particularly limited. For example, it has stirring blades and the stirring blades rotate by the rotational force generated by driving means such as a motor transmitted through a stirring shaft.

[0035] As one method of 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 of the crystallization reaction tank 10 so that the stirring blades of the stirring device 12 or the like are located inside a cylinder such as a cylinder. When the draft tube 64 is installed and the stirring blade is installed in the draft tube 64, a downward flow is generated toward the lower part of the draft tube 64, and a zone with a relatively large diffusion flow velocity is formed. Therefore, it is considered that the water to be treated, the calcium agent, etc. can be diffused more quickly, and it is possible to extremely suppress the direct generation of calcium fluoride particles due to the contact of locally concentrated regions of the concentration of the water to be treated and the calcium agent.

[0036] And, a gentle upward flow zone of the flow is formed on the outer peripheral portion of the draft tube 64. In this zone, the particles are classified, and the small-particle-size particles rise along the outer surface of the tube, re-enter the tube from the upper end of the tube and descend, and are recirculated to the vicinity of the injection point of the water to be treated, the calcium agent, etc. and the stirring zone below it. It is considered that the crystallization reaction is promoted with these small-particle-size crystals as nuclei. Therefore, it is possible to stably form calcium fluoride crystals with a large particle size, and the recovery rate can be improved.

[0037] Furthermore, the crystals that have grown in size as the crystallization reaction progresses do not rise due to the upward flow on the outer peripheral portion of the tube and sink downward, making it difficult to enter the draft tube 64 again. Therefore, it is considered that it is possible to suppress the grown crystals from being destroyed by collision with the stirring blades. Such an advantage also contributes to stably obtaining calcium fluoride crystals with a large particle size and can contribute to an improvement in the recovery rate.

[0038] In order to form a zone with a relatively high agitation flow velocity at the lower part of the draft tube 64 and stably form an upward flow on the outer periphery of the tube, it is preferable that the agitation blade is positioned somewhere in the lower half of the tube inside the tube. More preferably, it is at a position slightly above the lower end of the tube. With such an arrangement, it is considered that a zone with a high agitation flow velocity is formed like a vortex near the lower end of the tube, and further an upward flow is stably formed along the outer periphery of the tube from there. Therefore, diffusion of the water to be treated, calcium agent, etc. and classification of particles can be effectively promoted.

[0039] When providing the draft tube 64, the injection points of the water to be treated and the calcium agent are preferably arranged inside the cylinder of the draft tube 64 in order to quickly and effectively diffuse them by riding on the downward flow inside the draft tube 64. A more preferable position is inside the cylinder of the draft tube 64 and above the agitation blade.

[0040] In order to make the slurry concentration in the crystallization reaction tank 10 as uniform as possible, the rotational speed of the agitation blade of the agitation device 12 may be in the range of, for example, 100 to 300 rpm when the crystallization reaction tank 10 is provided with the draft tube 64, and may be in the range of, for example, 300 to 500 rpm when the crystallization reaction tank 10 is not provided with the draft tube 64. It is assumed that the inside of the crystallization reaction tank 10 is agitated by the agitation device 12 at, for example, the rotational speed of the above-mentioned agitation blade, and the slurry concentration is in a substantially uniform state.

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

[0042] Calcium agent may be added into the crystallization reaction tank 10 by means of calcium addition means such as pump 38, valve 40, calcium agent addition pipe 42, etc. As the calcium agent, any substance containing calcium may be used without particular limitation. 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] As the addition amount of the calcium agent, for example, it may be in the range of 0.8 to 2 times the chemical equivalent of calcium to fluorine, more preferably in the range of 1 to 2 times, and even more preferably in the range of 1 to 1.2 times. If the chemical equivalent of calcium is more than 2 times the chemical equivalent of fluorine in the water to be treated, calcium fluoride is likely to be generated as fine particles without precipitating on the seed crystal, and calcium fluoride or the like may be mixed into the crystallized treated water. If it 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 crystallized treated 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, which is immersed in the crystallization reaction liquid 66 in the crystallization reaction tank 10 at a predetermined depth. The immersion depth (distance from the water surface) of the gas discharge part 58 may be within the range where the back pressure of the gas discharged from the gas discharge part 58 can be measured by the pressure measuring device 18, and there is no particular specification. The gas discharge part 58 is preferably located at the water level between the upper end and the lower end of the draft tube 64. In order to prevent the gas supply pipe 56 from being caught by the stirring rod or stirring blade of the stirring device 12, it is more preferable that the gas supply pipe 56 is provided on the outer periphery rather than inside the draft tube 64.

[0045] The gas supply device 16 is for sending gas into the crystallization reaction tank 10 through the gas supply pipe 56. For example, it may be any device that can supply gas such as a blower, a compressor, a gas cylinder, or compressed air from a factory utility, and there is no particular limitation.

[0046] Examples of the gas supplied from the gas supply device 16 include nitrogen, air, etc., and there is no particular limitation, but air is preferred from the viewpoint of cost effectiveness.

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

[0048] The materials of the gas supply pipe 56 and the gas discharge part 58 are not particularly limited, but from the viewpoint of lifespan, etc., it is preferable that the materials are resistant to hydrofluoric acid and strong acids such as polytetrafluoroethylene (Teflon (registered trademark)) and 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 part 58 to the liquid surface. The liquid level measuring device 22 is not particularly limited, but it is preferable that the liquid level can be measured without contacting the crystallization reaction liquid in the crystallization reaction tank 10. For example, an ultrasonic level gauge may be used.

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

[0051] The pressure measuring device 18 may be installed in the gas supply pipe 56 and may be any device that can detect the air supply pressure of the gas, and there is no particular limitation. 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 the 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 that can perform arithmetic processing on the slurry concentration from an analog signal or a 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, an arithmetic means such as a CPU that calculates a program, and a storage means such as a ROM and a RAM that store a program and an arithmetic result, and is composed of a microcomputer and an electronic circuit. The control device 26 may be a programmable controller (or also called a programmable logic controller) (PLC) that incorporates a microprocessor and controls equipment by a program. The control device 26 has a function of controlling at least one of the flow rate of the water to be treated by controlling the pump 28, the addition amount of the calcium agent by controlling the pump 38 or the valve 40, the addition amount of the acid by controlling the pump 32 or the valve 34, the addition amount of the seed crystal by controlling the pump 44 or the valve 46, and the extraction amount of the slurry by controlling the extraction pump 50 or the valve 52, based on the slurry concentration calculated by the arithmetic means.

[0055] The water to be treated is water containing fluorine such as wastewater containing fluorine, and it may be water from any source, but from the viewpoints of impurities and recovery efficiency, etc., it is preferably hydrofluoric acid-containing wastewater discharged from a semiconductor factory.

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

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

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

[0059] The crystallization reaction apparatus 1 may be provided with seed crystal addition means such as a pump 44, a valve 46, and a seed crystal addition pipe 48 for adding seed crystals into the crystallization reaction tank 10. The seed crystal may be any material as long as it can precipitate crystals of a sparingly soluble calcium salt on its surface, and any material can be selected. For example, particles composed of oxides of metal elements such as filter sand, activated carbon, zircon sand, garnet sand, sakuradam (trade name, manufactured by Nippon Cartridge Co., Ltd.), and particles composed of a sparingly soluble salt of calcium fluoride which is a precipitate by the crystallization reaction, etc. may be mentioned, but it is not limited thereto. From the viewpoint that a purer sparingly soluble salt can be obtained as pellets or the like, particles composed of a sparingly soluble salt which is a precipitate by the crystallization reaction (for example, fluorite in the case of calcium fluoride) are preferable.

[0060] Before adding the water to be treated and the calcium agent to the crystallization reaction tank 10, seed crystals may be present in the crystallization reaction tank 10 in advance, or seed crystals may be present in the crystallization reaction tank 10 after adding the water to be treated and the calcium agent 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 in advance before adding the water to be treated and the calcium agent to the crystallization reaction tank 10.

[0061] The crystallization reaction tank 10 preferably has a supply pipe so that the water to be treated, the calcium agent, the acid, and the seed crystals are added in the vicinity of 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 it 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 pumps 28, 32, 38, 44, and the extraction pump 50 may have inverters.

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

[0065] (Creation of Approximation Formula) First, an approximation formula is created. While stirring a slurry solution adjusted to a predetermined slurry concentration, as in the crystallization reaction apparatus 1 of FIG. 1, the gas discharge part is set as one location of the gas discharge part 58, and a gas such as air is supplied from the gas supply device 16 into the slurry solution. At this time, a liquid level conversion value (referred to as y) is calculated from the discharge pressure detected by the pressure measuring device 18 using the liquid level conversion device 14. During the creation of the approximation formula, it is preferable to keep the distance from the gas discharge part 58 to the liquid surface as constant as possible.

[0066] An approximation formula (y = ax + b, where x is the slurry concentration, y is the liquid level conversion value, a is the proportionality constant, and b is the distance from the gas discharge part to the liquid surface) showing a proportional relationship is calculated from each slurry concentration and the liquid level conversion value calculated using the liquid level conversion device 14. For creating the approximation formula, it is preferable to use two or more plots, preferably five or more plots, excluding a slurry concentration of 0%.

[0067] (Concentration Calculation Using the Approximation 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 this value is referred to as y'. The slurry concentration is calculated by substituting y' for y in the approximation formula y = ax + b, the proportionality constant obtained in the creation of the above approximation formula for a, and the value of the distance from the gas discharge part 58 to the liquid surface obtained in the creation of the above approximation formula for b.

[0068] "Creation of the approximation formula" and "concentration calculation using the approximation formula" may use different crystallization reaction apparatuses. In that case, it is preferable to make the distance from the gas discharge part 58 to the liquid surface as identical as possible.

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

[0070] The crystallization reaction apparatus 3 shown in FIG. 2 includes a gas supply means for supplying gas into the crystallization reaction tank 10, a gas supply device 16, gas supply pipes 56 and 70, and gas discharge portions 58 and 72 for discharging the gas supplied from the gas supply device 16 into the crystallization reaction tank 10. In the crystallization reaction apparatus 3, one end side of the gas supply pipe 56 is connected to the gas supply device 16 via a valve 74, and the gas discharge portion 58 is provided at the other end side. The gas supply pipe 70 branches from the gas supply pipe 56. One end side 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 gas discharge portion 72 is provided at the other end side. 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 may not include a liquid level measuring device 22 such as the crystallization reaction apparatus 1 of FIG. 1. Other than these, the configuration is the same as that of the crystallization reaction apparatus 1 of FIG. 1.

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

[0072] In the crystallization reaction apparatus 3 of FIG. 2, the gas supply device is one of the gas supply devices 16, the gas supply pipe 56 is branched into the gas supply pipe 70, and the gas discharge part is two or more gas discharge parts 58 and 72. However, two or more gas supply devices may be provided, each having a gas supply pipe. One end side of the gas supply pipe is connected to the gas supply device, and the gas discharge part on the other end side may be immersed in the crystallization reaction liquid 66 in the crystallization reaction tank 10 at a predetermined depth. 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 valve with 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. Then, the valve 74 is closed and the valve 76 is switched to the open state, and a gas such as air is also supplied from the gas supply device 16 into the slurry solution, and the back pressure after a predetermined time has elapsed is measured. Note that there is no particular limitation on the opening and closing order of the valves. Further, two or more gas supply devices and two or more pressure measuring devices may be provided, each having a gas supply pipe. One end side of the gas supply pipe is connected to the gas supply device, and the gas discharge part on the other end side may be immersed in the crystallization reaction liquid 66 in the crystallization reaction tank 10 at a predetermined depth. In this case, a valve may be provided in each series of gas supply pipes, but it is not particularly necessary to switch according to the measurement, and the back pressure of each series may be measured. Note that 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. The back pressure (i.e., the air supply pressure) near the gas supply device 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> (Creation of Approximation Formula) First, an approximate formula is created. While stirring a slurry solution adjusted to a predetermined slurry concentration, as in the crystallization reactor 3 of FIG. 2, the gas discharge parts are provided at two locations, the gas discharge parts 58 and 72, at different locations so as to have a predetermined water level difference (denoted as c). With the valve 74 or the valve 76 in the open state, gases such as air (denoted as gas 1 and gas 2) are supplied from the gas supply device 16 into the slurry solution from the respective gas discharge parts 58 and 72. At this time, the 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 keep the water level difference between the respective gas discharge parts 58 and 72 at a predetermined value.

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

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

[0076] "Creation of the approximate formula" and "concentration calculation by the approximate formula" may use different devices. In that case, it is desirable to make the water level difference at the installation position of the gas discharge part as identical as possible.

[0077] <Regarding Slurry Concentration Calculation and Operation Control> Fig. 3 shows an outline of an example of slurry concentration calculation and operation control based on the slurry concentration.

[0078] (Slurry Concentration Calculation) The slurry concentration is calculated by 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 (supply gas pressure) at that time 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 received signal and a relational expression between the pre-programmed pressure value and the liquid level. For example, when the pressure at the time of gas discharge is ΔP, an arbitrary value ρ, the gravitational acceleration g, and the distance h from the gas discharge part to the liquid level, ΔP = ρgh, and h = ΔP / ρ / g can be calculated. ρ may be set to the specific gravity of the solvent (for example, 1 if it is water). (A4) The liquid level conversion 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 location, the value of the distance from the gas discharge part 58 to the liquid level measured by the liquid level measuring device 22 such as a liquid level gauge is also transmitted as a signal to the slurry concentration calculation device 24. (A6) The slurry concentration calculation device 24 calculates the slurry concentration using the received signal and an approximation formula created and programmed in advance.

[0079] (Operation Control) The operation is controlled by the following flow. (B1) The value of the slurry concentration is transmitted as a signal from the slurry concentration calculation device 24 to the control device 26. (B2) The control device 26 is controlled based on the received signal and the flow rate of the water to be treated, the addition amount of the calcium agent, the addition amount of the acid, the addition amount of the seed crystal, the slurry withdrawal amount, etc. set in advance according to the slurry concentration.

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

[0081] For example, when it is desired to increase the slurry concentration in the crystallization reaction tank 10, the opening time of the valve 52 and the driving time of the extraction pump 50 may be shortened to control the slurry extraction amount to decrease, and the opening time of the valve 46 of the seed crystal addition means and the driving time of the pump 44 may be controlled to increase, and the addition amount of the seed crystal may be adjusted to increase.

[0082] The adjustment of the addition amount of the seed crystal may be carried out at any timing before or after the extraction of the slurry. It is preferable to calculate the slurry concentration after the extraction of the slurry and determine the addition amount of the seed crystal according to the value.

[0083] For example, when the rising rate of the slurry concentration in the crystallization reaction tank 10 is too fast, for risk avoidance such as overflow, operation control may be performed to advance the extraction interval of the slurry.

[0084] For example, when the rising rate of the slurry concentration in the crystallization reaction tank 10 is too fast, for risk avoidance such as overflow, the flow rate of the pump 28 of the water to be treated supply means may be controlled to decrease, and accordingly, the addition amount of the calcium agent and the addition amount of the acid may also be controlled to decrease.

[0085] This specification includes the following embodiments. [1] A crystallization reaction apparatus for crystallizing calcium fluoride by adding a calcium agent to water to be treated containing fluorine, a crystallization reaction tank, calcium agent addition means for adding the calcium agent into the crystallization reaction tank, stirring means provided in the crystallization reaction tank, gas supply means for supplying gas into the crystallization reaction tank, a gas discharge part for discharging the gas supplied from the gas supply means into the crystallization reaction tank, Pressure measuring means for measuring the pressure of the gas discharged from the gas discharge section, Calculation means for calculating the slurry concentration in the crystallization reaction tank from the measured value of the pressure of the gas measured by the pressure measuring means, A crystallization reaction apparatus comprising:

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

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

[0088] [4][1] ~ [3] Any one of the crystallization reaction apparatus according to, Water to be treated supply means for supplying water to be treated into the crystallization reaction tank, Acid addition means for adding acid into the crystallization reaction tank, Seed crystal addition means for adding seed crystals into the crystallization reaction tank, Slurry extraction means for extracting slurry from the crystallization reaction tank, Further comprising at least one of, Based on the slurry concentration calculated by the calculation means, at least one of the flow rate of the water to be treated, the addition amount of the calcium agent, the addition amount of the acid, the addition amount of the seed crystal, and the extraction amount of the slurry is controlled. A crystallization reaction apparatus further comprising control means.

[0089] [5] A crystallization reaction method for adding a calcium agent to water to be treated containing fluorine to crystallize calcium fluoride, Using a crystallization reaction tank equipped with stirring means, adding the calcium agent to the water to be treated in the crystallization reaction tank to perform a crystallization reaction, A crystallization reaction method, which comprises supplying gas from a gas discharge part into the crystallization reaction tank, measuring the pressure of the gas discharged from the gas discharge part, and calculating the slurry concentration in the crystallization reaction tank from the measured value of the pressure of the measured gas.

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

[0091] The crystallization reaction method according to [7][5] or [6], wherein there are at least two or more of the gas discharge parts, and the pressures of the gases discharged from at least two or more of the gas discharge parts are measured.

[0092] The crystallization reaction method according to any one of [8][5] to [7], wherein 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 addition amount of the calcium agent, the addition amount of the acid into the crystallization reaction tank, the addition amount of the seed crystal into the crystallization reaction tank, and the amount of the slurry withdrawn from the crystallization reaction tank is controlled.

Examples

[0093] Hereinafter, examples and comparative examples will be given to describe the present invention more specifically and in detail, 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 capacity of 10 L was used. As the gas supply device 16 and the pressure measuring device 18, an air level gauge (EK series manufactured by Fujikontrol) was used, and as the gas supply pipe 56, a φ6×4 mm Teflon (registered trademark) tube 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 became 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 calculating the ratio of the sedimentation volume of the crystals to the volume of the entire slurry solution. Also, the rotational speed of the stirring blades of the stirring device 12 was adjusted to 300 rpm so that the slurry layer concentration at the gas discharge part 58 at the tip of the gas supply pipe 56 became as uniform as possible. The experimental conditions are shown in Table 1.

[0095]

Table 1

[0096] <Example 1> (Creation of approximate formula) While stirring the slurry solution adjusted to a predetermined concentration, with the gas discharge part as one location of the gas discharge part 58 as shown in Fig. 1, the liquid level conversion value (referred to as y) converted from the discharge pressure when air was supplied as a gas into the slurry solution from the gas supply device 16 was obtained. The results are shown in Table 2.

[0097]

Table 2

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

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

[0100] The slurry concentration x was calculated by substituting y' for y, the proportionality constant obtained in the creation of the above approximate formula for a, and the value of the distance from the gas discharge part 58 to the liquid level for b into the approximate formula y = ax + b. When y' = 0.25 m and b = 0.21 m, the calculated value was 21.1 v / v%. On the other hand, the measured value was 20.5 v / v%, and the calculated value and the measured value were almost the same.

[0101] The measured value was calculated from the volume ratio of the crystals to 100 mL after crystal sedimentation by collecting 100 mL of the calcium fluoride slurry solution stirred as uniformly as possible into a 100 mL volumetric 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> (Creation of approximate formula) While stirring the slurry solution adjusted to a predetermined concentration, the gas discharge part was set at two different locations, the gas discharge parts 58 and 72 as shown in Fig. 2, so that the water level difference c = 0.1 m. The liquid level conversion values (designated as y1 and y2) converted from the discharge pressure when supplying air (designated as air 1 and air 2) as a gas into the slurry solution from the gas supply device 16 were obtained. The results are shown in Table 3.

[0104]

Table 3

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

[0106] (Concentration calculation by approximate formula) Next, for a 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] By substituting y1' for y1, y2' for y2, the proportionality constant obtained in the creation of the above approximate formula for a', and the value of the water level difference at the installation position of the gas discharge part for c in the approximate formula y1 - y2 = a'x + c, the slurry concentration x was calculated. When y1' = 0.33 m, y2' = 0.19 m, and c = 0.10 m, the calculated value was 42.1 v / v%. On the other hand, the measured value was 41.3 v / v%, and the calculated value and the measured value were almost the same.

[0108] The measured value was calculated from the volume ratio of crystals to 100 mL after crystal precipitation by collecting 100 mL of a calcium fluoride slurry solution stirred as uniformly as possible into a 100 mL volumetric 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, by the method of the example, the slurry concentration in the crystallization reaction tank could be stably measured. As a result, a stable and efficient crystallization reaction could be maintained.

Explanation of symbols

[0111] 1 Crystallization reaction apparatus, 10 Crystallization reaction tank, 12 Stirring device, 14 Liquid level conversion device, 16 Gas supply device, 18 Pressure measurement device, 22 Liquid level measurement device, 24 Slurry concentration calculation device, 26 Control device, 28, 32, 38, 44 Pumps, 30 Treated water supply pipe, 34, 40, 46, 52 Valves, 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 pipes, 58, 72 Gas discharge part. 60 Crystallized treated water pipe, 62 Crystallized treated water discharge path, 64 Draft tube, 66 Crystallization reaction liquid.

Claims

1. A crystallization reactor that adds a calcium agent to water to be treated containing fluorine to crystallize calcium fluoride, comprising: a crystallization reaction tank; calcium agent addition means for adding the calcium agent into the crystallization reaction tank; agitation means provided in the crystallization reaction tank; gas supply means for supplying gas into the crystallization reaction tank; a gas discharge part for discharging the gas supplied from the gas supply means into the crystallization reaction tank; pressure measurement means for measuring the pressure of the gas discharged from the gas discharge part; calculation means for calculating the slurry concentration in the crystallization reaction tank from the measured value of the pressure of the gas measured by the pressure measurement means; A crystallization reactor characterized by comprising the above.

2. The crystallization reactor according to claim 1, further comprising liquid level measurement means for measuring the liquid level in the crystallization reaction tank. A crystallization reactor characterized by the above.

3. The crystallization reactor according to claim 1, having at least two or more of the gas discharge parts, wherein the pressure measurement means measures the pressure of the gas discharged from at least two or more of the gas discharge parts. A crystallization reactor characterized by the above.

4. The crystallization reactor according to claim 1, further comprising at least one of: untreated water supply means for supplying untreated water into the crystallization reaction tank; acid addition means for adding acid into the crystallization reaction tank; seed crystal addition means for adding seed crystals into the crystallization reaction tank; slurry extraction means for extracting slurry from the crystallization reaction tank; and further comprising control means for controlling at least one of the flow rate of the untreated water, the addition amount of the calcium agent, the addition amount of the acid, the addition amount of the seed crystals, and the extraction amount of the slurry based on the slurry concentration calculated by the calculation means. A crystallization reactor characterized by the above.

5. A crystallization reaction method for adding a calcium agent to water to be treated containing fluorine to crystallize calcium fluoride, comprising: using a crystallization reaction tank equipped with agitation means, adding the calcium agent to the untreated water in the crystallization reaction tank to perform a crystallization reaction, supplying gas from a gas discharge part into the crystallization reaction tank, measuring the pressure of the gas discharged from the gas discharge part, and calculating the slurry concentration in the crystallization reaction tank from the measured value of the measured pressure of the gas.

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

7. The crystallization reaction method according to claim 5, wherein there are at least two or more of the gas discharge parts, a crystallization reaction method characterized by measuring the pressures of gases discharged from at least two or more of the gas discharge parts.

8. The crystallization reaction method according to claim 5, wherein 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 addition amount of the calcium agent, the addition amount of the acid into the crystallization reaction tank, the addition amount of the seed crystal into the crystallization reaction tank, and the withdrawal amount of the slurry from the crystallization reaction tank is controlled.

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