Cooling and stirring apparatus and method for producing crystals

Abstract

To provide a cooling and stirring apparatus capable of obtaining potassium chloride-containing crystals having a large particle diameter, and to provide a method for producing the crystals.SOLUTION: A cooling and stirring apparatus 1 includes: a stirring tank 3 in which a liquid L is to be stored; a stirring blade 5 which is disposed inside the stirring tank 3 and rotates around a rotation axis to suck the liquid L from an axial direction and discharges the liquid L in a radial direction; a cylindrical body 4 which is disposed between the stirring blade 5 and a bottom surface L2 of the stirring tank 3 and has a cylindrical shape opening toward the stirring blade 5 and the bottom surface L2; and a cooling body 6 for cooling the liquid L. The method for producing crystals includes: a step of storing the liquid L in which a predetermined crystallization object is dissolved in the stirring tank 3 of the cooling and stirring apparatus 1; and a step of stirring the liquid by rotating the stirring blade 5 while lowering the temperature of the liquid L by the cooling body 6.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cooling and stirring apparatus and a method for producing crystals using the cooling and stirring apparatus. [Background technology]

[0002] A known method for producing salt using seawater as a raw material is to obtain brine by subjecting the raw seawater to ion exchange membrane electrodialysis, and then subject the brine to heating, evaporation and crystallization to precipitate sodium chloride, thereby recovering sodium chloride. The liquid remaining after recovering sodium chloride from the brine is called bittern. This bittern contains various inorganic ions (e.g., potassium ions, etc.), and conventionally, these inorganic ions have been further recovered from the bittern. For example, one method for recovering potassium chloride from salt bittern is to cool the bittern to precipitate and recover potassium ions as potassium chloride (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 55-56014 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional potassium chloride recovery method as described above, it is generally difficult to increase the particle size of the precipitated crystals, and therefore it is difficult to separate water from the solid-liquid mixture (i.e., the mixture of potassium chloride-containing crystals and depotashed bittern) after the potassium chloride precipitation treatment to obtain potassium chloride-containing crystals. Furthermore, as can be understood from this description, not only when producing potassium chloride-containing crystals from salt-making bittern, but also when producing crystals from a liquid containing a crystallization target that is difficult to increase the particle size of the precipitated crystals, it is difficult to separate water from the solid-liquid mixture after the precipitation treatment to obtain crystals, as described above.

[0005] An object of the present invention is to provide a cooling and stirring apparatus capable of obtaining crystals with a large particle size, and a method for producing crystals. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the cooling and stirring device and the crystal manufacturing method according to the present invention have the following features.

[0007] [1] A cooling and stirring device that cools and stirs a liquid, A stirring tank in which the liquid is to be contained; a stirring blade disposed inside the stirring tank, the stirring blade rotating about a rotation axis to suck in the liquid in an axial direction and discharge the liquid in a radial direction; a cylindrical body disposed between the agitating blade and a bottom surface of the agitation tank and having a cylindrical shape opening toward the agitating blade and the bottom surface; A cooling body that cools the liquid. It is a cooling and stirring device. [2] In the cooling and stirring apparatus described in the above [1], The cylindrical body is The opening has a cylindrical shape in which the opening area of ​​the opening that opens toward the stirring blade is larger than the opening area of ​​the opening that opens toward the bottom surface. It is a cooling and stirring device. [3] A method for producing a crystal, comprising the steps of: A step of placing a liquid containing a predetermined crystallization target in the stirring tank of the cooling and stirring apparatus described in [1] or [2] above; The liquid is stirred by rotating the stirring blade while lowering the temperature of the liquid by the cooling body. It is a method for producing crystals. [4] In the manufacturing method according to the above [3], The liquid is bittern obtained when seawater is subjected to a salt production process, The crystal is a potassium chloride-containing crystal. It is a method for producing crystals. Effect of the Invention

[0008] According to the cooling stirring device and the method for producing crystals of the present invention, a cylindrical body (so-called draft tube) is arranged between the stirring blade arranged inside the stirring tank and the bottom surface of the stirring tank. Therefore, when the stirring tank is filled with liquid to the extent that the stirring blade is submerged in the liquid, the stirring blade is arranged at a position closer to the liquid surface than the cylindrical body. When the stirring blade arranged in this way is rotated, the liquid discharged in the radial direction by the rotation of the stirring blade flows downward toward the bottom surface of the stirring tank along the inner wall surface of the stirring tank, joins near the center of the bottom surface of the stirring tank, flows upward toward the stirring blade, is sucked into the stirring blade, and is discharged from the stirring blade again. Furthermore, the downward flow and the upward flow are separated by the cylindrical wall of the cylindrical body, so that the downward flow and the upward flow are prevented from mixing, and the formation of a stronger upward flow is promoted compared to the case where the cylindrical body is not present. This allows a rectified liquid flow circulating inside the stirring tank to be generated.

[0009] When liquid (e.g., bittern for salt making) is cooled and stirred using this cooling and stirring device, crystals (e.g., potassium chloride-containing crystals) precipitated as the temperature of the liquid drops gather near the center of the bottom of the stirring tank along the flow of the liquid circulating inside the stirring tank. This reduces the distance between the crystals compared to when simply stirring the liquid (e.g., when the stirring blades are placed near the bottom of the stirring tank), promoting the aggregation of the crystals. Furthermore, by exposing the aggregated crystals to the flow of the liquid, it is possible to selectively leave strongly aggregated crystals. In addition, since the formation of an upward flow is promoted as described above, the generation of excessive crystal nuclei is suppressed by separating the crystals with a small degree of aggregation from the bottom of the stirring tank (i.e., by allowing them to overflow from the cylindrical body) and cooling them again. By promoting the aggregation of the crystals in this way, crystals with a large apparent particle size can be obtained.

[0010] Therefore, the cooling and stirring device and the crystal manufacturing method according to the present invention make it possible to obtain crystals with large grain sizes. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of a cooling and stirring device according to an embodiment of the present invention. [Diagram 2] FIG. 2 shows a schematic diagram of a cooling and stirring apparatus and a graph showing the particle size distribution of the potassium chloride-containing crystals obtained, in which (A1) is a schematic diagram of a conventional cooling and stirring apparatus, (A2) is a graph showing the particle size distribution of the potassium chloride-containing crystals obtained by the conventional cooling and stirring apparatus, (B1) is a schematic diagram of a cooling and stirring apparatus according to an embodiment of the present invention, and (B2) is a graph showing the particle size distribution of the potassium chloride-containing crystals obtained by the cooling and stirring apparatus according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a graph showing the relationship between the rotation speed of the stirring blade of the cooling stirring device, the shape of the draft tube, and the 50% particle size of the obtained potassium chloride-containing crystals. [Figure 4] FIG. 4 is a graph showing the relationship between the rotation speed of the impeller of the cooling and stirring device, the shape of the draft tube, and the uniform number calculated when the particle size distribution of the obtained potassium chloride-containing crystals is approximated to the Rosin-Rammla distribution (RR distribution). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a cooling and stirring apparatus 1 according to an embodiment of the present invention and a method for producing potassium chloride-containing crystals using the cooling and stirring apparatus 1 will be described with reference to the drawings.

[0013] 1 is a schematic diagram of a cooling and stirring apparatus 1 according to an embodiment. The cooling and stirring apparatus 1 is an apparatus for precipitating a crystallization target by cooling and stirring a liquid L in which the crystallization target is dissolved, thereby obtaining crystals S. In this embodiment, salt-making bittern obtained after seawater is subjected to a salt-making process to recover sodium chloride (NaCl) is used as the liquid L contained in the cooling and stirring apparatus 1, and potassium chloride-containing crystals (crystals containing KCl) are recovered from the salt-making bittern.

[0014] The cooling and stirring device 1 according to the embodiment includes a stirring tank 3, a draft tube 4, a stirring blade 5, and a cooling body 6. The stirring tank 3 is a member for accommodating the liquid L and the precipitated crystals S therein. The stirring tank 3 has a cylindrical shape with a bottom surface L2. The cylindrical shape of the stirring tank 3 makes it easier to form a circulating flow of the liquid L as described below.

[0015] The draft tube 4 is disposed between the agitator blade 5 and the bottom surface L2 of the agitator vessel 3 inside the agitator vessel 3. The draft tube 4 has a tubular shape (for example, a cylindrical shape or a conical shape) that opens upward and downward toward the agitator blade 5 and the bottom surface L2 of the agitator vessel 3. Of the upper and lower openings 4a and 4b of the draft tube 4, the opening area of ​​the upper opening 4a that opens toward the agitator blade 5 is larger than the opening area of ​​the opening 4b that opens toward the bottom surface L2. That is, the draft tube 4 has a tubular shape (hereinafter referred to as an inverted cone shape) that is obtained by removing a portion near the apex of a cone with an apex at the bottom and making the inside hollow. The draft tube 4 is supported and fixed to the wall of the agitator vessel 3 by a support member not shown. As described later, the draft tube 4 is a member for arranging (i.e., rectifying) the flow of the liquid L inside the agitator vessel 3.

[0016] The agitator blade 5 is disposed inside the agitator tank 3. Specifically, when the liquid L is contained in the agitator tank 3, the agitator blade 5 is disposed at a position closer to the liquid surface of the liquid L than the draft tube 4. The agitator blade 5 is fixed to the tip of the rotating shaft 10 and rotates with the rotation of the rotating shaft 10. In other words, the agitator blade 5 is disposed so as to rotate around the cylindrical axis of the draft tube 4. The rotating shaft 10 is rotated by a power source such as a motor (not shown). The agitator blade 5 has a so-called turbine blade type structure configured to suck in the liquid L from the axial direction and discharge it in the radial direction by rotating around the rotating shaft 10. As described later, the agitator blade 5 rotates, and the liquid L is agitated while circulating in the tank of the agitator tank 3.

[0017] The cooling body 6 is a member that cools the liquid L, and is disposed so as to surround the periphery of the stirring tank 3. The cooling body 6 is composed of, for example, a pipe or the like through which a liquid (e.g., seawater) that is lower in temperature than the liquid L passes, and a plate-shaped heat transfer body that incorporates the pipe or the like.

[0018] As shown in FIG. 1, when the impeller 5 of the cooling and stirring device 1 is rotated, the liquid L discharged in the radial direction by the rotation of the impeller 5 flows downward along the inner wall surface of the stirring tank 3 toward the bottom surface of the stirring tank 3 (see the downward flow F2 in the figure), joins with the liquid L near the center of the bottom surface L2 of the stirring tank 3, and then flows upward toward the impeller 5 (see the upward flow F1 in the figure), is sucked into the impeller 5, and is discharged from the impeller 5 again. Furthermore, the cylindrical wall of the draft tube 4 isolates the above-mentioned upward flow F1 and downward flow F2, suppressing the upward flow F1 and downward flow F2 from mixing, and promoting the formation of a stronger upward flow F1 than when there is no draft tube 4. In this way, in the cooling and stirring device 1, a rectified liquid flow circulating in the stirring tank 3 can be generated in the stirring tank 3.

[0019] When the liquid L (in this example, bittern for salt making) is cooled and stirred using the cooling and stirring device 1, the crystals S (in this example, potassium chloride-containing crystals) precipitated as the temperature of the liquid L decreases gather near the center of the bottom surface L2 of the stirring tank 3 along the flow of the liquid L circulating in the stirring tank 3. This reduces the distance between the crystals S, promoting the aggregation of the crystals S. Furthermore, by exposing the aggregated crystals S to the flow of the liquid L circulating in the tank, it is possible to selectively leave and grow the strongly aggregated crystals S (i.e., the crystals S with strong aggregation strength). In addition, since the formation of the upward flow F1 is promoted as described above, the crystals S with a small degree of aggregation are separated from the bottom surface L2 of the stirring tank 3 (i.e., are allowed to overflow from the opening 4a of the draft tube 4 together with the upward flow F1) and are cooled again by the cooling body 6, which can suppress the generation of excessive crystal nuclei.

[0020] In this way, the cooling and stirring apparatus 1 can promote the aggregation of the crystals S, thereby obtaining crystals S with a large apparent particle size. This facilitates solid-liquid separation in which the aggregated crystals S are separated from the liquid L using a filter or the like. When salt-making bittern as the liquid L is cooled and stirred using the cooling and stirring apparatus 1, crystals S containing potassium chloride as a main component (i.e., potassium chloride-containing crystals) are obtained.

[0021] Next, with reference to Fig. 2, the relationship between the configuration of the cooling and stirring device and a graph showing the particle size distribution of potassium chloride-containing crystals S when salt-making bittern is used as liquid L will be described. The test conditions were as follows: the amount of liquid L was 0.5 L, the inner diameter of the stirring tank 3 was 74 mm, the number of blades (inclined blades) of the stirring impeller 5 was 4, the rotation speed of the stirring impeller 5 was 200 rpm (200 revolutions per minute), and the temperature of liquid L was cooled from 80°C to 25°C over 6 hours. The salt-making bittern was the residual liquid remaining after recovery of sodium chloride by a well-known salt-making method using seawater as a raw material.

[0022] Figures 2(A1) and 2(A2) show test results of a comparative example for comparison with the embodiment of the present invention. Specifically, Figure 2(A1) is a schematic diagram of a cooling and stirring apparatus in which a stirring blade 5 is installed near the bottom surface of a stirring tank 3 and there is no draft tube, and Figure 2(A2) is a particle size distribution graph of potassium chloride-containing crystals S obtained by this cooling and stirring apparatus. It can be seen that the particle size of the potassium chloride-containing crystals obtained by this cooling and stirring apparatus has a peak at around 500 μm.

[0023] In contrast, Fig. 2 (B1) and Fig. 2 (B2) will explain the test results of the embodiment of the present invention. Specifically, Fig. 2 (B1) is a schematic diagram of the cooling and stirring device 1 according to the embodiment, and Fig. 2 (B2) is a particle size distribution graph of the potassium chloride-containing crystals S obtained by the cooling and stirring device 1 according to the embodiment. It can be seen that the particle size of the potassium chloride-containing crystals S obtained by the cooling and stirring device 1 has a peak at about 800 μm, and potassium chloride-containing crystals S having a larger particle size can be obtained compared to the above-mentioned conventional cooling and stirring device.

[0024] This is because, when the liquid L (salt-making bittern) is cooled and stirred using the cooling and stirring device 1, the crystals S (potassium chloride-containing crystals) precipitated as the temperature of the liquid L drops gather near the center of the bottom of the stirring tank 3 along the flow of the liquid L circulating in the stirring tank 3, and the distance between the crystals S becomes smaller than when the liquid is simply stirred (for example, when the stirring blades 5 are placed near the bottom L2 of the stirring tank 3 as shown in Figure 2 (A1)), which promotes the aggregation of the crystals S. Furthermore, it is considered that the strongly aggregated crystals S can be selectively left by exposing the aggregated crystals S to the flow of the liquid L. In addition, it is considered that the formation of the upward flow F1 is promoted, and the crystals S with a low degree of aggregation are separated from the bottom L2 of the stirring tank 3 (i.e., overflowed from the draft tube 4) and cooled again, thereby suppressing the generation of excessive crystal nuclei.

[0025] Next, the relationship between the rotation speed of the stirring blade 5 of the cooling stirring device 1 and the 50% particle size (median size, average particle size) of the obtained potassium chloride-containing crystals S will be described with reference to Fig. 3. Furthermore, the relationship between the rotation speed of the stirring blade 5 of the cooling stirring device 1 and the degree of particle size distribution of the obtained potassium chloride-containing crystals S (the uniform number calculated when the particle size distribution of the potassium chloride-containing crystals is approximated to a rosin-Rammler distribution (RR distribution), hereinafter referred to as the uniform number of the RR distribution) will be described with reference to Fig. 4.

[0026] The test conditions were the same as those in FIG. 2, with the amount of liquid L being 0.5 L, the inner diameter of the stirring tank 3 being 74 mm, the number of blades (inclined blades) of the stirring impeller 5 being 4, and the temperature of the liquid L being cooled from 80°C to 25°C over 6 hours. Furthermore, the rotation speed of the stirring impeller 5 was changed from 100 rpm to 300 rpm. Samples 1 to 3 shown in FIG. 3 were the same in other test conditions, except that the shape of the draft tube 4 used in the cooling and stirring device 1 was different. Details of Samples 1 to 3 are described below.

[0027] The cooling and stirring apparatus 1 according to Samples 1 to 3 has the following structure. Sample 1: The stirring blade 5 is placed near the liquid surface. A cylindrical draft tube 4 (with a uniform inner diameter of 50 mm) is used. Sample 2: The stirring blade 5 is placed near the liquid surface. An inverted cone-shaped draft tube 4 (the inner diameter of the upper opening 4a is 55 mm, and the inner diameter of the lower opening 4b is 35 mm) is used. Sample 3: The stirring blade 5 is placed near the liquid surface. An inverted cone-shaped draft tube 4 (the inner diameter of the upper opening 4a is 60 mm, and the inner diameter of the lower opening 4b is 30 mm) is used.

[0028] From the test results shown in FIG. 3, it can be seen that the 50% particle size of the potassium chloride-containing crystals S obtained is larger when the inverted cone-shaped draft tube 4 is used (samples 2 and 3) than when a simple cylindrical draft tube 4 is used (sample 1). Furthermore, from a comparison between sample 2 and sample 3, it can be seen that the larger the difference between the inner diameter of the upper opening 4a and the inner diameter of the lower opening 4b of the inverted cone-shaped draft tube 4 (in other words, the apex angle when the draft tube 4 is considered to have a conical shape), the larger the 50% particle size of the potassium chloride-containing crystals S obtained becomes. In addition, it can be seen that regardless of the shape of the draft tube 4, when the rotation speed of the stirring blade 5 is a specific rotation speed (200 rpm in this example), the effect of increasing the 50% particle size of the potassium chloride-containing crystals S is maximized.

[0029] This is believed to be because, as described above, excessive nucleation of the potassium chloride-containing crystals S is suppressed while promoting aggregation of the potassium chloride-containing crystals S by arranging the stirring blades 5 near the liquid surface and using the draft tube 4. Furthermore, when the rotation speed of the stirring blades 5 is low (in this example, 100 rpm), the degree of stirring of the liquid L is too low, resulting in a small effect of suppressing nucleation, whereas when the rotation speed of the stirring blades 5 is high (in this example, 300 rpm), the degree of stirring of the liquid L is too high, resulting in the aggregation of the potassium chloride-containing crystals S being hindered.

[0030] From the test results shown in Fig. 4, it can be seen that in both cases where a cylindrical draft tube 4 is used (sample 1) and where an inverted cone-shaped draft tube 4 is used (samples 2 and 3), when the rotation speed of the stirring blade 5 is a specific rotation speed (in this example, when it is 200 rpm or 300 rpm), the distribution width of the particle size of the obtained potassium chloride-containing crystals S is at a preferable level (the uniform number of the RR distribution shown by the dashed line in the figure is "3" or more). Note that the larger the uniform number of the RR distribution, the narrower the particle size distribution of the potassium chloride-containing crystals S and the more uniform the particle size is.

[0031] This is thought to be because, similar to the test results shown in Figure 3, by placing the stirring blade 5 near the liquid surface and using the draft tube 4, excessive nucleation of the potassium chloride-containing crystals S is suppressed while promoting the aggregation of the potassium chloride-containing crystals S.

[0032] 3 and 4, it is understood that it is possible to control the 50% particle size of the obtained potassium chloride-containing crystals S and the particle size distribution of the obtained potassium chloride-containing crystals S by adjusting the shape of the draft tube 4 and the rotation speed of the stirring blade 5. Specifically, in this example, it is understood that it is preferable to use an inverted cone-shaped draft tube 4 and set the rotation speed of the stirring blade 5 to 150 rpm or more and 250 rpm or less, and it is more preferable to set the rotation speed of the stirring blade 5 to 200 rpm.

[0033] <Actions and Effects> As described above, according to the cooling stirring device 1 and the manufacturing method of the potassium chloride-containing crystal S according to this embodiment, the draft tube 4 is disposed between the stirring blade 5 disposed inside the stirring tank 3 and the bottom surface L2 of the stirring tank 3. Therefore, when the stirring tank 3 is filled with liquid L to the extent that the stirring blade 5 is submerged in the liquid L, the stirring blade 5 is disposed at a position closer to the liquid surface of the liquid L than the draft tube 4. When the stirring blade 5 disposed in this manner is rotated, the liquid L discharged in the radial direction by the rotation of the stirring blade 5 flows downward toward the bottom surface L2 of the stirring tank 3 along the inner wall surface of the stirring tank 3, joins with the liquid L near the center of the bottom surface L2 of the stirring tank 3, flows upward toward the stirring blade 5, is sucked into the stirring blade 5, and is discharged from the stirring blade 5 again. Furthermore, the upward flow F1 and the downward flow F2 are isolated by the cylindrical wall of the draft tube 4, so that the upward flow F1 and the downward flow F2 are prevented from mixing with each other, and the formation of a stronger upward flow F1 is promoted compared to the case where the draft tube 4 is not present. This allows a rectified flow of the liquid L circulating within the stirring tank 3 to be generated within the stirring tank 3.

[0034] When the liquid L (salt bittern) is cooled and stirred using this cooling and stirring device 1, the crystals S (potassium chloride-containing crystals S) precipitated as the temperature of the liquid L drops gather near the center of the bottom surface L2 of the stirring tank 3 along the flow of the liquid L circulating in the stirring tank 3. This reduces the distance between the crystals S, promoting the aggregation of the crystals S. Furthermore, the aggregated crystals S are exposed to the flow of the liquid L circulating in the tank, so that the strongly aggregated crystals S can be selectively left. In addition, since the formation of the upward flow F1 is promoted as described above, the crystals S with a small degree of aggregation are separated from the bottom surface L2 of the stirring tank 3 (overflowing from the draft tube 4) and cooled by a cooling body, and the generation of excess crystal S nuclei is suppressed. By promoting the selective aggregation of the crystals S in this way, crystals S with a large apparent particle size can be obtained.

[0035] Furthermore, by using an inverted cone-shaped draft tube 4, the above-mentioned flocculation effect can be further improved.

[0036] <Other forms> The present invention is not limited to the above-described embodiments, and various modifications can be adopted within the scope of the present invention. For example, the present invention is not limited to the above-described embodiments, and appropriate modifications, improvements, etc. are possible. In addition, the material, shape, size, number, arrangement location, etc. of each component in the above-described embodiments are arbitrary as long as the present invention can be achieved, and are not limited.

[0037] For example, in the above-described embodiment, potassium chloride-containing crystals are produced from bittern used in salt production using the cooling and stirring apparatus 1. In contrast, the cooling and stirring apparatus 1 according to the present invention is not limited to the production of potassium chloride-containing crystals, and can be used in various processes for producing crystals from liquids containing crystallization targets that are unlikely to produce large crystal grains.

[0038] Here, the features of the embodiments of the cooling and stirring apparatus 1 and the method for producing crystals S according to the present invention will be briefly summarized and listed below in [1] to [4].

[0039] [1] A cooling and stirring device (1) for cooling and stirring a liquid (L), comprising: A stirring tank (3) in which the liquid (L) is to be contained; an agitating blade (5) disposed inside the agitating tank (3) and rotating about a rotation axis to suck in the liquid (L) from an axial direction and discharge it in a radial direction; a cylindrical body (4) that is disposed between the stirring blade (5) and a bottom surface (L2) of the stirring tank (3) and has a cylindrical shape that opens toward the stirring blade (5) and the bottom surface (L2); A cooling body (6) for cooling the liquid (L), Cooling and stirring device (1). [2] In the cooling and stirring apparatus (1) described in the above [1], The cylindrical body (4) is The mixing blade (5) has an opening (4a) having a larger opening area than the opening (4b) having a bottom surface (L2). Cooling and stirring device (1). [3] A method for producing a crystal, comprising the steps of: A step of placing a liquid (L) containing a predetermined crystallization target in the stirring tank (3) of the cooling and stirring apparatus (1) described in the above [1] or [2]; and a step of rotating the stirring blade (5) to stir the liquid (L) while lowering the temperature of the liquid (L) by the cooling body (6). Method for producing crystals. [4] In the manufacturing method according to the above [3], The liquid (L) is bittern obtained when seawater is subjected to a salt production process, The crystal (S) is a potassium chloride-containing crystal. Method for producing crystals. [Explanation of symbols]

[0040] 1 Cooling and stirring device 3 Mixing tank 4 Draft tube (cylindrical body) 4a Opening on the liquid surface side 4b Bottom opening 5 Mixing blade 6 Cooling body

Claims

1. A cooling and stirring device that cools and stirs a liquid, A stirring tank in which the liquid is to be contained; a stirring blade disposed inside the stirring tank, the stirring blade rotating about a rotation axis to suck in the liquid in an axial direction and discharge the liquid in a radial direction; a cylindrical body disposed between the agitating blade and a bottom surface of the agitation tank and having a cylindrical shape opening toward the agitating blade and the bottom surface; A cooling body that cools the liquid. Cooling and stirring device.

2. The cooling and stirring device according to claim 1, The cylindrical body is The opening has a cylindrical shape in which the opening area of ​​the opening that opens toward the stirring blade is larger than the opening area of ​​the opening that opens toward the bottom surface. Cooling and stirring device.

3. A method for producing a crystal, comprising the steps of: A step of storing a liquid containing a predetermined crystallization target in the stirring tank of the cooling and stirring apparatus according to claim 1 or 2; The liquid is stirred by rotating the stirring blade while lowering the temperature of the liquid by the cooling body. Method for producing crystals.

4. The method according to claim 3, The liquid is bittern obtained when seawater is subjected to a salt production process, The crystal is a potassium chloride-containing crystal. Method for producing crystals.

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