A crystallization apparatus and a method for continuously producing large particles of baking soda using the apparatus

Abstract

The application discloses a crystallization device and a method for continuously preparing large-particle baking soda by using the device. The crystallization device comprises a shell, a stirrer module and a driving device for driving the rotation of the stirrer module. The method for continuously preparing large-particle baking soda by using the above crystallization device comprises the following steps: (1) preparing a saturated baking soda solution with a temperature of 25-40 DEG C as a crystallization mother liquor; (2) closing a crystal slurry outlet, inputting the crystallization mother liquor into the shell of the crystallization device, and making the crystallization mother liquor flow circularly between the shell of the crystallization device and a buffer tank; (3) preparing a baking soda melting liquid with a temperature of 50-80 DEG C and a density of 1.580-1.590 g / cm 3 ; (4) opening a heat exchanger and the stirrer module, adding the baking soda melting liquid and initial crystal seeds into the shell of the crystallization device under stirring during a crystallization period; (5) after the time limit of the crystallization period is reached, opening the crystal slurry outlet to discharge the crystal slurry and filter, the obtained filtrate is used for maintaining the liquid level of the material liquid in the shell constant, and the obtained crystal is dried to obtain a large-particle baking soda product.

Description

Technical Field

[0001] This invention belongs to the field of crystallization technology and relates to crystallization equipment (devices) and a method for preparing large-particle sodium thiosulfate using crystallization equipment. Background Technology

[0002] Sodium thiosulfate, chemically known as thiosulfate, is a widely used inorganic salt. In the leather industry, it can be used to tan leather, thereby giving it superior properties; in aquaculture, it can be used to disinfect fishponds, reducing mortality rates; and in the pharmaceutical industry, it can be used as a drug to treat skin pruritus, urticaria, drug rash, cyanide poisoning, thallium poisoning, and arsenic poisoning.

[0003] Sodium thiocyanate is typically produced using cooling crystallization. Commonly used crystallizers are the DTB crystallizer (drip tube and baffle crystallizer) and the Oslo crystallizer (Oslo-type crystallizer). The DTB crystallizer places the agitator inside a cylindrical drip tube, using a low rotation speed to push the liquid upwards for internal circulation. This type of crystallizer lacks particle size classification; large and small crystals collide with the agitator, resulting in excessive secondary nucleation and hindering crystal growth. Furthermore, scaling easily occurs at the connection between the drip tube and the shell, and the W-shaped bottom of the shell requires complex cutting processes. The Oslo crystallizer uses an external circulation pump to remove material, relying on a high flow rate for material circulation. This crystallizer can achieve particle size classification while avoiding crystal breakage by the agitator. However, when crystal production is high, the circulation pump alone cannot achieve suspension, limiting the application of the Oslo crystallizer. Additionally, the Oslo crystallizer is prone to blockage due to pipe scaling during operation, and sodium thiocyanate has a narrow metastable region during cooling crystallization, meaning that the sodium thiocyanate solution is more likely to precipitate crystals during cooling, leading to pipe blockage.

[0004] Existing technologies typically produce sodium thiosulfate with small particle sizes. For example, the sodium thiosulfate prepared using the Oslo continuous crystallizer in patent application CN 104609377A has a particle size of only 2mm to 3mm. Sodium thiosulfate has a melting point of 48°C, meaning it can only be slowly dried at low temperatures. The fine crystals tend to carry more mother liquor, and the slow drying process easily forms crystal bridges, leading to product agglomeration, which significantly affects product quality. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a crystallization device and a method for continuously preparing large-particle sodium thiosulfate using the device, so as to produce large-particle sodium thiosulfate with uniform particle size, and to make the crystallization device easier to process, easier to maintain, disassemble and assemble, reduce energy consumption during operation, avoid scaling at the connection between the guide tube and the shell, and avoid blockage of heat exchangers and pipelines due to crystal precipitation.

[0006] The crystallization apparatus of the present invention includes a shell, a stirrer module, and a drive device for driving the stirrer module to rotate;

[0007] The shell, from top to bottom, consists of an upper end cap, a first cylindrical section, a conical section, a second cylindrical section, and a lower end cap. The first cylindrical section, the conical section, and the second cylindrical section are an integrated structure with an insulation layer on the outer wall. The upper end cap is detachably connected to the first cylindrical section, and the lower end cap is either fixedly connected to or detachably connected to the second cylindrical section. The ratio of the height H1 of the first cylindrical section to its inner diameter D1 is 0.1 to 0.5. The inner diameter D2 of the second cylindrical section is 0.25D1 to 0.5D1, and the height H3 of the second cylindrical section is 0.2D2 to 0.8D2. The inner diameter of the upper end of the conical section is the same as the inner diameter D1 of the first cylindrical section. The inner diameter of the lower end of the conical section is the same as the inner diameter D2 of the second cylindrical section. The height H2 of the conical section is 2D2 to 4D2, and the inclination angle α of the sidewall relative to the vertical direction is 5° to 20°. The upper end cap is provided with a through hole, a first liquid inlet, and a seed crystal inlet. The through hole is located at the center of the upper end cap. The distance between the first liquid inlet and the through hole is L2, and the distance between the seed crystal inlet and the through hole is L1. The upper end of the conical section is provided with a liquid outlet on its sidewall, the upper end of the second cylindrical section is provided with a second liquid inlet on its sidewall, and the bottom of the lower end cap is provided with a slurry outlet. The size of the slurry outlet should allow large crystal particles contained in the slurry to be released.

[0008] The stirrer module consists of a guide tube, a stirring rod, a first stirring paddle, a second stirring paddle, and a third stirring paddle. The stirring rod is coaxially mounted with the guide tube, and its upper and lower ends are located outside the guide tube. The first and second stirring paddles are installed at a distance from each other in the section of the stirring rod located inside the guide tube and are connected to the inner wall of the guide tube. The third stirring paddle is installed at the lower end of the stirring rod. The inner diameter of the guide tube is d = 0.5D2 ~ 0.9D2, and its height h is the same as the height of the conical section of the shell. The distance h3 between the third stirring paddle and the lower end face of the guide tube is 0.5H3 ~ 0.7H3.

[0009] Assembly method of shell, stirrer module and drive device: The stirrer module is located in the inner cavity of the shell, the center line of the guide tube in the stirrer module coincides with the center line of the shell, and the upper end face of the guide tube is flush with the upper end of the conical section in the shell; the upper end of the stirring rod in the stirrer module passes through the through hole provided in the upper end cap of the shell and is connected to the drive device.

[0010] In the above assembly method, the distance L2 between the first liquid inlet and the through hole on the shell end cap is 0 < L2 < 1 / 2d, and the distance L1 between the seed crystal inlet and the through hole is 1 / 2d < L1 < 1 / 2D1.

[0011] The crystallization device of the present invention has a first and second stirring blade in its stirring module, which are three-bladed blades, and the blades of the three-bladed blades are preferably tilted at an angle of 45° relative to the stirring rod; the third stirring blade in its stirring module is a flat blade with a diameter of 0.5D2 to 0.9D2, and the flat blade is wrapped with polytetrafluoroethylene.

[0012] In the crystallization device of the present invention, the distance h1 between the first stirring blade and the upper end face of the guide tube in the stirring module is preferably h1 = 0.2h, and the distance h2 between the second stirring blade and the lower end face of the guide tube is preferably h2 = 0.2h.

[0013] The crystallization equipment of the present invention has a lower end cap that is concave upwards in an arc shape, and an upper end cap that is convex upwards in an arc shape or a flat plate.

[0014] In the crystallization equipment of the present invention, the inner diameter D1 of the first cylindrical section is determined according to experimental or production needs, the wall thickness of the guide tube is less than 3mm, and the wall thickness of the shell is determined according to the relationship between product density, chemical properties, yield, etc.

[0015] Depending on the production scale, the method for continuous preparation of large-particle sodium thiosulfate described in this invention has the following two process flows:

[0016] 1. First process flow

[0017] The method for continuous preparation of large-particle sodium thiosulfate according to the present invention uses the above-mentioned crystallization equipment and is equipped with a buffer tank, a circulating pump, a heat exchanger and a feed pump. The process steps are as follows:

[0018] (1) Prepare a saturated sodium thiosulfate solution at 25℃~40℃ as the crystallization mother liquor. The amount of crystallization mother liquor should be such that the crystallization mother liquor can circulate between the buffer tank and the shell of the crystallization equipment under the action of the circulating pump.

[0019] (2) Close the crystal slurry outlet at the bottom of the lower head in the crystallization equipment shell, add the crystallization mother liquor to the buffer tank, and then turn on the circulation pump to input the crystallization mother liquor into the crystallization equipment shell through the heat exchanger and the second liquid inlet of the crystallization equipment shell. When the liquid level of the crystallization mother liquor in the crystallization equipment shell is higher than the upper end face of the guide tube, the crystallization mother liquor overflows from the liquid outlet of the crystallization equipment shell and enters the buffer tank through the pipeline, realizing the circulation flow of the crystallization mother liquor between the crystallization equipment shell and the buffer tank; the temperature of the crystallization equipment shell and the temperature of the buffer tank are controlled at the same temperature as the crystallization mother liquor.

[0020] (3) The preparation temperature is 50℃~80℃ and the density is 1.580g / cm³. 3 ~1.590g / cm 3The amount of molten sodium thiosulfate is controlled such that after it is fed into the crystallization equipment shell, the volume of the liquid inside the crystallization equipment shell is less than the volume of the crystallization equipment shell.

[0021] (4) With a crystallization cycle of 1h to 3h, turn on the stirrer module and heat exchanger. During the crystallization cycle, under stirring, the sodium thiosulfate melt is fed into the guide tube located in the inner cavity of the crystallization equipment shell through the first liquid inlet set in the upper end of the crystallization equipment shell by the feed pump. The initial seed crystal is added into the annular interval formed by the inner wall of the crystallization equipment shell and the outer wall of the guide tube through the seed crystal inlet set in the upper end of the crystallization equipment shell. The temperature control of the heat exchanger should ensure that during the addition of the sodium thiosulfate melt, the material liquid cooled by the heat exchanger is input into the inner cavity of the crystallization equipment shell through the second liquid inlet so that the temperature of the material liquid in the inner cavity of the crystallization equipment shell is the same as the temperature of the crystallization mother liquor.

[0022] (5) After the crystallization cycle is completed, the crystal slurry outlet at the bottom of the lower head in the crystallization equipment shell is opened to release the crystal slurry. The volume of the released crystal slurry is the same as the volume of the second cylindrical section of the shell. The collected crystal slurry is filtered, and the filtrate obtained is returned to the buffer tank to maintain the constant liquid level in the crystallization equipment shell. The filtered crystals are dried to obtain large particle sodium thiosulfate product (Na2S2O3·5H2O).

[0023] Repeating steps (3) to (5) above can achieve continuous preparation of large-particle sodium thiosulfate; however, when repeating step (4) above, only sodium thiosulfate melt needs to be added under stirring during the crystallization cycle, and no seed crystals need to be added.

[0024] The above process flow is applicable to laboratory and small-scale pilot production.

[0025] 2. Second process flow

[0026] The method for continuous preparation of large-particle sodium thiosulfate according to the present invention uses the above-mentioned crystallization equipment and is equipped with a buffer tank, a circulating pump, a heat exchanger and a feed pump. The process steps are as follows:

[0027] (1) Prepare a saturated sodium thiosulfate solution at 25℃~40℃ as the crystallization mother liquor. The amount of crystallization mother liquor should be such that the crystallization mother liquor can circulate between the buffer tank and the shell of the crystallization equipment under the action of the circulating pump.

[0028] (2) Close the crystal slurry outlet at the bottom of the lower head in the crystallization equipment shell, add the crystallization mother liquor to the buffer tank, and then turn on the circulation pump to input the crystallization mother liquor into the crystallization equipment shell through the heat exchanger and the second liquid inlet of the crystallization equipment shell. When the liquid level of the crystallization mother liquor in the crystallization equipment shell is higher than the upper end face of the guide tube, the crystallization mother liquor overflows from the liquid outlet of the crystallization equipment shell and enters the buffer tank through the pipeline, realizing the circulation flow of the crystallization mother liquor between the crystallization equipment shell and the buffer tank; the temperature of the crystallization equipment shell and the temperature of the buffer tank are controlled at the same temperature as the crystallization mother liquor.

[0029] (3) The preparation temperature is 50℃~80℃ and the density is 1.580g / cm³. 3 ~1.590g / cm 3 Melt sodium thiosulfate; turn on the stirrer module and heat exchanger, and under stirring, feed the melt sodium thiosulfate into the guide tube located in the inner cavity of the crystallization equipment shell through the first inlet set in the upper end of the crystallization equipment shell by the feed pump. Add the initial seed crystals into the annular area formed by the inner wall of the crystallization equipment shell and the outer wall of the guide tube through the seed crystal feeding port set in the upper end of the crystallization equipment shell. The temperature control of the heat exchanger should ensure that during the addition of the melt sodium thiosulfate, the liquid cooled by the heat exchanger is input into the inner cavity of the crystallization equipment shell through the second inlet so that the temperature of the liquid in the inner cavity of the crystallization equipment shell is the same as the temperature of the mother liquor.

[0030] After the sodium thiosulfate melt is added and the operation is stable, open the crystal slurry outlet set at the bottom of the lower head in the crystallization equipment shell and adjust the addition rate of sodium thiosulfate melt to match the crystal slurry release rate, so that the crystal slurry is released at the same time as the sodium thiosulfate melt is added.

[0031] (4) The collected crystal slurry is filtered, and the filtrate is returned to the buffer tank to maintain a constant liquid level in the crystallization equipment shell. The filtered crystals are dried to produce large-particle sodium thiosulfate (Na2S2O3·5H2O).

[0032] The above process flow is suitable for industrial production.

[0033] In the first process flow described above, the initial seed crystal is sodium thiosulfate with a particle size of less than 1 mm, and the amount of initial seed crystal added is 1 / 150 to 1 / 120 of the amount of sodium thiosulfate melt added in the first crystallization cycle.

[0034] In the second process flow described above, the initial seed crystal is sodium thiosulfate with a particle size of less than 1 mm. The amount of initial seed crystal added is 1 / 150 to 1 / 120 of the amount of sodium thiosulfate melt added within 1 to 3 hours, starting from the time the sodium thiosulfate melt is added.

[0035] In the above method, the stirring rate setting of the stirrer module should ensure that the sodium thiosulfate crystals can be suspended in the crystallization equipment shell during the crystallization process when the sodium thiosulfate melt is added, but will not flow out from the liquid outlet set in the crystallization equipment shell.

[0036] In the above method, the drying temperature of the filtered crystals is 25℃~30℃.

[0037] In the above method, the temperature control of the heat exchanger is achieved by the temperature and flow rate of the cooling water. The temperature of the cooling water should be 3℃ to 5℃ lower than the temperature of the mother liquor. After the temperature of the cooling water is determined, the flow rate of the cooling water needs to be verified by experiments.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. Due to the special design of the shell shape and structure in the crystallization equipment described in this invention, as well as the modular structure of the guide tube and the stirring paddle and the installation method of the stirrer module, compared with the existing DTB crystallizer, it not only has the function of particle size classification, but also avoids the stirring paddle from breaking the crystals, which is conducive to the preparation of large particles with uniform particle size. At the same time, the stirring module is relatively independent from the shell, making the processing simpler and the maintenance, disassembly and assembly more convenient.

[0040] 2. Because the crystallization equipment of the present invention is equipped with a stirrer module consisting of a guide tube, a stirring rod and a stirring paddle, it can achieve crystal suspension in the liquid even with a large crystal production volume compared with the existing Oslo crystallizer.

[0041] 3. Because the method described in this invention uses a crystallization device with the structure described in this invention and directly adds the molten sodium thiosulfate into the shell of the crystallization device before heat exchange, the amount of water entering the sodium thiosulfate crystallization system is reduced, thus lowering the energy consumption for subsequent evaporation and concentration. At the same time, the lower heat exchange temperature difference can effectively prevent blockage of the heat exchanger and pipelines due to crystal precipitation.

[0042] 4. Using the method described in this invention, sodium thiosulfate products with a particle size of 8mm were continuously produced. Compared with commercially available small-particle sodium thiosulfate, the mother liquor entrainment was significantly reduced, and it did not clump after drying, exhibiting excellent anti-caking properties. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the crystallization equipment described in this invention;

[0044] Figure 2 This is a schematic diagram of the shell structure in the crystallization device described in this invention;

[0045] Figure 3 This is a schematic diagram of the stirrer module in the crystallization equipment of the present invention;

[0046] Figure 4 This is a schematic diagram showing the tilt angle of the blades of the first and second agitators relative to the agitator rod in the agitator module.

[0047] Figure 5 This is a process flow diagram of the method for continuous preparation of large-particle sodium thiosulfate according to the present invention;

[0048] Figure 6 These are optical photographs of the large-particle sodium thiosulfate prepared in Example 2 of the present invention and the commercially available small-particle sodium thiosulfate, wherein (a1) is the commercially available small-particle sodium thiosulfate and (a2) is the large-particle sodium thiosulfate prepared in Example 2.

[0049] Figure 7 These are optical photographs of the large-particle sodium thiosulfate prepared in Example 3 of the present invention and the commercially available small-particle sodium thiosulfate, wherein (b1) is the commercially available small-particle sodium thiosulfate and (b2) is the large-particle sodium thiosulfate prepared in Example 3.

[0050] Figure 8 These are optical photographs of the large-particle sodium thiosulfate prepared in Example 4 of the present invention and the commercially available small-particle sodium thiosulfate, wherein (c1) is the commercially available small-particle sodium thiosulfate and (c2) is the large-particle sodium thiosulfate prepared in Example 4.

[0051] Figure 9 These are optical photographs of the products obtained by thoroughly wetting the large-particle sodium thiosulfate and commercially available small-particle sodium thiosulfate prepared in Example 2 of this invention in a saturated sodium thiosulfate solution at 25°C and then filtering them. (a1) shows the large-particle sodium thiosulfate prepared in Example 2. ,2 It is commercially available small-particle sodium thiosulfate;

[0052] Figure 10 These are optical photographs of the products obtained after filtering and drying the large-particle sodium thiosulfate and commercially available small-particle sodium thiosulfate prepared in Example 2 of this invention, which were fully moistened in a saturated sodium thiosulfate solution at 25°C. (b1) is the large-particle sodium thiosulfate prepared in Example 2, and (b2) is the commercially available small-particle sodium thiosulfate.

[0053] In the diagram, 1—shell, 1-1—first liquid inlet, 1-2—seed crystal inlet, 1-3—upper head, 1-4—first cylindrical section, 1-5—liquid outlet, 1-6—conical section, 1-7—second liquid inlet, 1-8—second cylindrical section, 1-9—lower head, 1-10—crystal slurry outlet, 1-11—insulation layer, 2—stirrer module, 2-1—stirring rod, 2-2—guide tube, 2-3—first stirring paddle, 2-3-1—first stirring paddle blade, 2-4—second stirring paddle, 2-4-1—second stirring paddle blade, 2- 5—Third stirring paddle, 3—Drive device, D1—Inner diameter of the first cylindrical section, H1—Height of the first cylindrical section, H2—Height of the conical section, D2—Inner diameter of the second cylindrical section, H3—Height of the second cylinder, L1—Distance between the seed inlet and the through hole, L2—Distance between the first liquid inlet and the through hole, d—Inner diameter of the guide tube, h—Height of the guide tube, h1—Distance between the first stirring paddle and the upper end face of the guide tube, h2—Distance between the second stirring paddle and the lower end face of the guide tube, h3—Distance between the third stirring paddle and the lower end face of the guide tube. Detailed Implementation

[0054] The crystallization apparatus of the present invention and the method for continuously preparing large-particle sodium thiosulfate using the apparatus will be further described below through examples and in conjunction with the accompanying drawings.

[0055] Example 1

[0056] In this embodiment, the crystallization equipment for producing large-particle crystals is as follows: Figure 1 As shown, it includes a housing 1, a stirrer module 2, and a drive device 3 for driving the stirrer module to rotate.

[0057] The housing 1 is as follows Figure 2As shown, from top to bottom, it consists of an upper end cap 1-3, a first cylindrical section 1-4, a conical section 1-6, a second cylindrical section 1-8, and a lower end cap 1-9. The first cylindrical section 1-4, the conical section 1-6, and the second cylindrical section 1-8 are an integrated structure with an insulation layer 1-11 on the outer wall. The upper end of the first cylindrical section 1-4 has a threaded section, and the lower end of the second cylindrical section 1-8 has a threaded section. The upper side wall of the conical section 1-6 has a liquid outlet 1-5. A second liquid inlet 1-7 is provided on the side wall of the upper end of the cylindrical section 1-8; the upper end cap 1-3 consists of an upwardly convex arc surface and a threaded ring at the lower end of the arc surface, and is threadedly connected to the first cylindrical section 1-4. A through hole, a first liquid inlet 1-1, and a seed crystal inlet 1-2 are provided on the arc surface of the upper end cap. The through hole is located at the center of the arc surface, the distance between the first liquid inlet 1-1 and the through hole is L2, and the distance between the seed crystal inlet 1-2 and the through hole is L1; the lower end cap 1-9 consists of an upwardly convex arc surface... The first cylindrical section consists of a concave arc surface and a threaded ring at the upper end of the arc surface, which is threadedly connected to the second cylindrical section 1-8. A crystal slurry outlet 1-10 is provided at the bottom of the arc surface of the lower end cap. The diameter of this outlet is 20mm, allowing large crystal particles with a diameter of approximately 8mm contained in the slurry to be released. The inner diameter D1 of the first cylindrical section is 300mm, and the height H1 is 100mm (0.33D1). The inner diameter D2 of the second cylindrical section is 120mm (0.4D1), and the height H3 is 5mm. 0mm (0.42D2); the inner diameter of the upper end of the conical section 1-6 is the same as the inner diameter D1 of the first cylindrical section, and the inner diameter of the lower end of the conical section 1-6 is the same as the inner diameter D2 of the second cylindrical section. The height H2 of the conical section 1-6 is 350mm (2.92D2), and the inclination angle α of the side wall relative to the vertical direction is 14°; the wall thickness of the upper end cap 1-3, the first cylindrical section 1-4, the conical section 1-6, the second cylindrical section 1-8, and the lower end cap 1-9 is 3mm.

[0058] The stirrer module 2 is as follows Figure 3 As shown, it consists of a guide tube 2-2, a stirring rod 2-1, a first stirring paddle 2-3, a second stirring paddle 2-4, and a third stirring paddle 2-5. The guide tube 2-2 is a cylindrical shape with open ends, an inner diameter d of 80 mm (0.67D2), a height h of 350 mm (the same height as the conical section 1-6), and a wall thickness of 2.5 mm. The stirring rod 2-1 is coaxially mounted with the guide tube, with its upper and lower ends located outside the guide tube. The first stirring paddle 2-3 is a three-bladed paddle installed on the section of the stirring rod inside the guide tube, with a distance h1 of 70 mm (0.2h) between it and the upper end face of the guide tube. The blades of the first stirring paddle 2-3-1 are welded to the inner wall of the guide tube, and the angle of inclination relative to the stirring rod is 45° (see...). Figure 4The second impeller 2-3 is also a three-bladed impeller, installed in the section of the stirring rod located inside the guide tube, with a distance h2 of 70mm (0.2h) between it and the lower end face of the guide tube. The blades of the second impeller 2-3-1 are fixedly connected to the inner wall of the guide tube by welding, and the inclination angle relative to the stirring rod is 45° (see...). Figure 4 The third stirring paddle 2-5 is a flat paddle, wrapped with polytetrafluoroethylene, with a diameter of 80mm (0.67D2), installed at the lower end of the stirring rod, and the distance h3 between it and the lower end face of the guide tube is 35mm (0.7H3).

[0059] The drive device 3 consists of a motor and a reducer, and the motor shaft is connected to the power input shaft of the reducer through a coupling.

[0060] The assembly method of the shell 1, the stirrer module 2 and the drive device 3 is as follows: Figure 1 As shown: The stirrer module 2 is located in the inner cavity of the shell 1. The center line of the guide tube 2-2 in the stirrer module coincides with the center line of the shell. The upper end face of the guide tube 2-2 is flush with the upper end of the conical section 1-6 in the shell. The upper end of the stirring rod 1-1 in the stirrer module passes through the through hole provided in the upper end cap 1-3 of the shell and is connected to the reducer power output shaft in the drive device 3 through a coupling.

[0061] In the above assembly method, the distance L2 between the first liquid inlet 1-1 and the through hole on the shell end cap is 20mm (0<L2<1 / 2d), and the distance L1 between the seed crystal inlet 1-2 and the through hole is 75mm (1 / 2d<L1<1 / 2D1).

[0062] Examples 2, 3, and 4 below describe methods for the continuous preparation of large-particle sodium thiosulfate, using the crystallization equipment described in Example 1, and equipped with a buffer tank, circulating pump, heat exchanger, and feed pump to form... Figure 5 The process flow is shown. The buffer tank is equipped with an insulation layer, a feed inlet, and a discharge outlet. The circulating pump, heat exchanger, and feed pump are conventional equipment purchased from the market.

[0063] Example 2

[0064] The process steps in this embodiment are as follows:

[0065] (1) Prepare 14 L of saturated sodium thiosulfate solution at 25 °C as crystallization mother liquor;

[0066] (2) Close the crystal slurry outlet 1-10 at the bottom of the lower end cap 1-9 in the crystallization equipment shell, add the crystallization mother liquor to the buffer tank, and then turn on the circulation pump to input the crystallization mother liquor into the crystallization equipment shell through the heat exchanger from the second liquid inlet 1-7 of the crystallization equipment shell. When the liquid level of the crystallization mother liquor in the crystallization equipment shell is higher than the upper end face of the guide tube, the crystallization mother liquor overflows from the liquid outlet 1-5 of the crystallization equipment shell and enters the buffer tank through the pipeline, realizing the circulation flow of the crystallization mother liquor between the crystallization equipment shell and the buffer tank; the temperature of the crystallization equipment shell and the temperature of the buffer tank are controlled at 25℃.

[0067] (3) The preparation temperature is 55℃ and the density is 1.589 g / cm³. 3 1500g of molten sodium thiosulfate;

[0068] (4) With a crystallization cycle of 2 hours, turn on the stirrer module and heat exchanger, and set the speed of the stirrer module to 180 rpm. During the crystallization cycle, under stirring, 1500 g of sodium thiosulfate melt is fed into the guide tube 2-2 located in the inner cavity of the crystallization equipment shell through the first inlet 1-1 set in the upper end cap 1-3 of the crystallization equipment shell at a uniform speed. 10 g of initial seed sodium thiosulfate with a particle size of less than 1 mm is added into the annular area formed by the inner wall of the crystallization equipment shell and the outer wall of the guide tube through the seed inlet 1-2 set in the upper end cap 1-3 of the crystallization equipment shell. The temperature control of the heat exchanger should ensure that during the addition of sodium thiosulfate melt, the material liquid cooled by the heat exchanger is input into the inner cavity of the crystallization equipment shell through the second inlet 1-7 so that the temperature of the material liquid in the inner cavity of the crystallization equipment shell is 25°C, which is the same as the temperature of the crystallization mother liquor. The temperature control of the heat exchanger is achieved by setting the temperature of its cooling water to 22°C and the flow rate of the cooling water to 10 L / min.

[0069] (5) After the crystallization cycle is completed, open the crystal slurry outlet 1-10 at the bottom of the lower end cap 1-9 in the crystallization equipment shell to release the crystal slurry. The released volume of the crystal slurry is the same as the volume of the second cylindrical section 1-8 of the shell. Filter the collected crystal slurry, and return the filtrate to the buffer tank to maintain a constant liquid level in the crystallization equipment shell. Dry the filtered crystals at 25℃ to obtain 1185g of sodium thiosulfate product with a particle size of approximately 8mm. See [link to product details]. Figure 6 (a2) in the middle;

[0070] Repeating steps (3) to (5) above can achieve continuous preparation of large-particle sodium thiosulfate; however, when repeating step (4) above, only 1500g of sodium thiosulfate melt needs to be added under stirring during the crystallization cycle. After the first cycle of discharge, there are enough crystals remaining, so no more seed crystals need to be added.

[0071] This embodiment ran for four cycles. The second cycle yielded 1476g of sodium thiosulfate product, the third cycle yielded 1490g of sodium thiosulfate product, and the fourth cycle yielded 1483g of sodium thiosulfate product.

[0072] Example 3

[0073] The process steps in this embodiment are as follows:

[0074] (1) Prepare 14 L of saturated sodium thiosulfate solution at 35 °C as crystallization mother liquor;

[0075] (2) Close the crystal slurry outlet 1-10 at the bottom of the lower end cap 1-9 in the crystallization equipment shell, add the crystallization mother liquor to the buffer tank, and then turn on the circulation pump to input the crystallization mother liquor into the crystallization equipment shell through the heat exchanger from the second liquid inlet 1-7 of the crystallization equipment shell. When the liquid level of the crystallization mother liquor in the crystallization equipment shell is higher than the upper end face of the guide tube, the crystallization mother liquor overflows from the liquid outlet 1-5 of the crystallization equipment shell and enters the buffer tank through the pipeline, realizing the circulation of the crystallization mother liquor between the crystallization equipment shell and the buffer tank; the temperature of the crystallization equipment shell and the temperature of the buffer tank are controlled at 35℃;

[0076] (3) The preparation temperature is 50℃ and the density is 1.590 g / cm³. 3 1200g of molten sodium thiosulfate;

[0077] (4) With a crystallization cycle of 1 hour, turn on the stirrer module and heat exchanger, and set the speed of the stirrer module to 160 rpm. During the crystallization cycle, under stirring, 1200 g of sodium thiosulfate melt is fed into the guide tube 2-2 located in the inner cavity of the crystallization equipment shell through the first inlet 1-1 set in the upper end cap 1-3 of the crystallization equipment shell at a uniform speed. 10 g of initial seed sodium thiosulfate with a particle size of less than 1 mm is added into the annular area formed by the inner wall of the crystallization equipment shell and the outer wall of the guide tube through the seed inlet 1-2 set in the upper end cap 1-3 of the crystallization equipment shell. The temperature control of the heat exchanger should ensure that during the addition of sodium thiosulfate melt, the material liquid cooled by the heat exchanger is input into the inner cavity of the crystallization equipment shell through the second inlet 1-7 so that the temperature of the material liquid in the inner cavity of the crystallization equipment shell is 35°C, which is the same as the temperature of the crystallization mother liquor. The temperature control of the heat exchanger is achieved by setting the temperature of its cooling water to 30°C and the flow rate of the cooling water to 8 L / min.

[0078] (5) After the crystallization cycle is completed, open the crystal slurry outlet 1-10 located at the bottom of the lower end cap 1-9 in the crystallization equipment shell to release the crystal slurry. The released volume of the crystal slurry is the same as the volume of the second cylindrical section 1-8 of the shell. Filter the collected crystal slurry, and return the filtrate to the buffer tank to maintain a constant liquid level in the crystallization equipment shell. Dry the filtered crystals at 30℃ to obtain 985g of sodium thiosulfate product with a particle size of approximately 8mm. See [link to product details]. Figure 7(b2) in the middle;

[0079] Repeating steps (3) to (5) above can achieve continuous preparation of large-particle sodium thiosulfate; however, when repeating step (4) above, only 1200g of sodium thiosulfate melt needs to be added under stirring during the crystallization cycle. After the first cycle of discharge, there are enough crystals remaining, so no more seed crystals need to be added.

[0080] This embodiment ran for five cycles. The second cycle yielded 1176g of sodium thiosulfate product, the third cycle yielded 1191g of sodium thiosulfate product, the fourth cycle yielded 1170g of sodium thiosulfate product, and the fifth cycle yielded 1188g of sodium thiosulfate product.

[0081] Example 4

[0082] The process steps in this embodiment are as follows:

[0083] (1) Prepare 14 L of saturated sodium thiosulfate solution at 40 °C as crystallization mother liquor;

[0084] (2) Close the crystal slurry outlet 1-10 at the bottom of the lower end cap 1-9 in the crystallization equipment shell, add the crystallization mother liquor to the buffer tank, and then turn on the circulation pump to input the crystallization mother liquor into the crystallization equipment shell through the heat exchanger from the second liquid inlet 1-7 of the crystallization equipment shell. When the liquid level of the crystallization mother liquor in the crystallization equipment shell is higher than the upper end face of the guide tube, the crystallization mother liquor overflows from the liquid outlet 1-5 of the crystallization equipment shell and enters the buffer tank through the pipeline, realizing the circulation flow of the crystallization mother liquor between the crystallization equipment shell and the buffer tank; the temperature of the crystallization equipment shell and the temperature of the buffer tank are controlled at 40℃.

[0085] (3) The preparation temperature is 80℃ and the density is 1.580 g / cm³. 3 2400g of molten sodium thiosulfate;

[0086] (4) With a crystallization cycle of 1 hour, turn on the stirrer module and heat exchanger, and set the speed of the stirrer module to 220 rpm. During the crystallization cycle, under stirring, 2400 g of sodium thiosulfate melt is fed into the guide tube 2-2 located in the inner cavity of the crystallization equipment shell through the first inlet 1-1 set in the upper end cap 1-3 of the crystallization equipment shell at a uniform speed. 20 g of initial seed sodium thiosulfate with a particle size of less than 1 mm is added into the annular interval formed by the inner wall of the crystallization equipment shell and the outer wall of the guide tube through the seed inlet 1-2 set in the upper end cap 1-3 of the crystallization equipment shell. The temperature control of the heat exchanger should ensure that during the addition of sodium thiosulfate melt, the material liquid cooled by the heat exchanger is input into the inner cavity of the crystallization equipment shell through the second inlet 1-7 so that the temperature of the material liquid in the inner cavity of the crystallization equipment shell is 40°C, which is the same as the temperature of the crystallization mother liquor. The temperature control of the heat exchanger is achieved by setting the temperature of its cooling water to 35°C and the flow rate of the cooling water to 19 L / min.

[0087] (5) After the crystallization cycle is completed, open the crystal slurry outlet 1-10 at the bottom of the lower end cap 1-9 in the crystallization equipment shell to release the crystal slurry. The released volume of the crystal slurry is the same as the volume of the second cylindrical section 1-8 of the shell. Filter the collected crystal slurry, and return the filtrate to the buffer tank to maintain a constant liquid level in the crystallization equipment shell. Dry the filtered crystals at 25°C to obtain 1895g of sodium thiosulfate product with a particle size of approximately 8mm. See [link to product details]. Figure 8 (c2) in the middle;

[0088] Repeating steps (3) to (5) above can achieve continuous preparation of large-particle sodium thiosulfate; however, when repeating step (4) above, only 2400g of sodium thiosulfate melt needs to be added under stirring during the crystallization cycle. After the first cycle of discharge, there are enough crystals remaining, so no more seed crystals need to be added.

[0089] This embodiment was run for three cycles. The second cycle yielded 2381g of sodium thiosulfate product, and the third cycle yielded 2393g of sodium thiosulfate product.

[0090] Example 5

[0091] This embodiment compares the mother liquor entrainment and anti-caking performance of large-particle sodium thiosulfate prepared in Examples 2, 3, and 4 with commercially available sodium thiosulfate.

[0092] (1) Comparison experiment on the amount of mother liquor carried over

[0093] Take 50g each of the large-particle sodium thiosulfate prepared in Examples 2, 3, and 4, and commercially available sodium thiosulfate. Soak each in a mother liquor (saturated sodium thiosulfate solution) at 25°C for 0.5h to fully wet them. Then filter and weigh them, and record the weight as m1. Dry each type of sodium thiosulfate obtained from filtration at 25°C and weigh them, and record the weight as m2. Then calculate the entrainment rate of the mother liquor using the following formula:

[0094]

[0095] The experimental results are shown in Table 1 below.

[0096] Table 1. Weight and mother liquor entrainment rate of different sodium bicarbonate before and after drying

[0097]

[0098] The experimental results above show that the large-particle sodium thiosulfate prepared in Examples 2, 3 and 4 has a significantly lower mother liquor entrainment rate compared with commercially available sodium thiosulfate.

[0099] (2) Comparative experiment on anti-caking performance

[0100] Take 10g each of the large-particle sodium thiosulfate prepared in Example 2 and commercially available sodium thiosulfate, and soak them separately in a 25°C mother liquor (saturated sodium thiosulfate solution) for 0.5h to fully wet them. Then filter and take pictures. The resulting pictures are shown below. Figure 9 The various sodium thiosulfate solutions obtained after filtration were then dried at 25°C and photographed. The resulting photos are shown below. Figure 10 .

[0101] from Figure 9 (a1) It can be seen that the large-particle sodium thiosulfate prepared in Example 2 basically did not contain any mother liquor. Figure 9 (a2) It can be seen that commercially available sodium thiosulfate contains a large amount of mother liquor in clumps.

[0102] from Figure 10 (b1) It can be seen that the large-particle sodium thiosulfate prepared in Example 2 remained distinct after drying. Figure 10 (b2) It can be seen that commercially available sodium thiosulfate completely clumps after drying. Therefore, the large-particle sodium thiosulfate prepared in Example 2 has excellent anti-caking properties, which are significantly improved compared with commercially available sodium thiosulfate.

Claims

1. A crystallization apparatus for producing large-particle crystals, comprising a housing (1), a stirrer module (2), and a drive device (3) for driving the stirrer module to rotate, characterized in that: The shell (1) is composed of an upper end cap (1-3), a first cylindrical section (1-4), a conical section (1-6), a second cylindrical section (1-8), and a lower end cap (1-9) from top to bottom. The first cylindrical section (1-4), the conical section (1-6), and the second cylindrical section (1-8) are an integrated structure with an insulation layer (1-11) on the outer wall. The upper end cap (1-3) is detachably connected to the first cylindrical section (1-4), and the lower end cap (1-9) is either fixedly connected to or detachably connected to the second cylindrical section (1-8). The ratio of the height H1 of the first cylindrical section to its inner diameter D1 is 0.1~0.

5. The inner diameter D2 of the second cylindrical section is 0.25D1~0.5D1, and the height H3 of the second cylindrical section is 0.2D2. ~0.8D2; The inner diameter of the upper end of the conical cylinder section (1-6) is the same as the inner diameter D1 of the first cylinder section, and the inner diameter of the lower end of the conical cylinder section (1-6) is the same as the inner diameter D2 of the second cylinder section. The height H2 of the conical cylinder section (1-6) is 2D2. ~4D2, and the sidewall is inclined at an angle α of 5°~20° relative to the vertical direction; the upper end cap (1-3) is provided with a through hole, a first liquid inlet (1-1) and a seed crystal inlet (1-2), the through hole is located at the center of the upper end cap (1-3), the distance between the first liquid inlet (1-1) and the through hole is L2, and the distance between the seed crystal inlet (1-2) and the through hole is L1; the upper end of the conical section (1-6) is provided with a liquid outlet (1-5) on the sidewall, the upper end of the second cylindrical section (1-8) is provided with a second liquid inlet (1-7) on the sidewall, and the bottom of the lower end cap (1-9) is provided with a crystal slurry outlet (1-10), the size of which should allow large crystal particles contained in the crystal slurry to be released; The stirrer module (2) consists of a guide tube (2-2), a stirring rod (2-1), a first stirring paddle (2-3), a second stirring paddle (2-4), and a third stirring paddle (2-5). The stirring rod (2-1) is coaxially mounted with the guide tube, and its upper and lower ends are located outside the guide tube. The first stirring paddle (2-3) and the second stirring paddle (2-4) are installed at a distance from each other in the section of the stirring rod (2-1) inside the guide tube and are connected to the inner wall of the guide tube. The third stirring paddle (2-5) is installed at the lower end of the stirring rod (2-1). The inner diameter of the guide tube (2-2) is d=0.5D2~0.9D2, and its height h is the same as the height of the conical section (1-6) of the shell. The distance h3 between the third stirring paddle (2-5) and the lower end face of the guide tube (2-2) is 0.5 H3~0.7 H3. The stirrer module (2) is located inside the shell (1). The center line of the guide tube (2-2) in the stirrer module coincides with the center line of the shell. The upper end face of the guide tube (2-2) is flush with the upper end of the conical section (1-6) in the shell. The upper end of the stirring rod (2-1) in the stirrer module passes through the through hole provided in the upper end cap (1-3) of the shell and is connected to the drive device (3). The distance L2 between the first liquid inlet (1-1) and the through hole on the shell cap is 0 < L2 < 1 / 2d, and the distance L1 between the seed crystal inlet (1-2) and the through hole is 1 / 2d < L1 < 1 / 2D1.

2. The crystallization equipment for producing large-particle crystals according to claim 1, characterized in that... The first and second impellers (2-3 and 2-4) in the agitator module are three-bladed impellers, and the third impeller (2-5) in the agitator module is a flat impeller with a diameter of 0.5D2 to 0.9D2.

3. The crystallization equipment for producing large-particle crystals according to claim 2, characterized in that... The blades (2-3-1, 2-4-1) of the three-bladed paddle are tilted at an angle of 45° relative to the stirring rod (2-1), and the paddle is wrapped with polytetrafluoroethylene.

4. The crystallization apparatus for producing large-particle crystals according to any one of claims 1 to 3, characterized in that... The distance between the first stirring blade (2-3) and the upper end face of the guide tube (2-2) in the stirrer module is h1=0.2h, and the distance between the second stirring blade (2-4) and the lower end face of the guide tube (2-2) is h2=0.2h.

5. The crystallization apparatus for producing large-particle crystals according to any one of claims 1 to 3, characterized in that... The lower end cap (1-9) in the shell is an upwardly concave arc-shaped end cap.

6. A method for continuous preparation of large-particle sodium thiosulfate, characterized in that... Using the crystallization equipment for producing large-particle crystals as described in any one of claims 1 to 5, and equipped with a buffer tank, a circulating pump, a heat exchanger, and a feed pump, the process steps are as follows: (1) Prepare a saturated sodium thiosulfate solution at 25℃~40℃ as the crystallization mother liquor. The amount of crystallization mother liquor should be such that it can circulate between the buffer tank and the shell of the crystallization equipment under the action of the circulating pump. (2) Close the crystal slurry outlet (1-10) at the bottom of the lower end cap (1-9) in the crystallization equipment shell, add the crystallization mother liquor to the buffer tank, and then turn on the circulation pump to input the crystallization mother liquor into the crystallization equipment shell through the heat exchanger from the second liquid inlet (1-7) of the crystallization equipment shell. When the liquid level of the crystallization mother liquor in the crystallization equipment shell is higher than the upper end face of the guide tube, the crystallization mother liquor overflows from the liquid outlet (1-5) of the crystallization equipment shell and enters the buffer tank through the pipeline, realizing the circulation flow of the crystallization mother liquor between the crystallization equipment shell and the buffer tank; the temperature of the crystallization equipment shell and the temperature of the buffer tank are controlled at the same temperature as the crystallization mother liquor. (3) The preparation temperature is 50℃~80℃ and the density is 1.580 g / cm³. 3 ~1.590 g / cm 3 The amount of molten sodium thiosulfate is controlled such that after it is fed into the crystallization equipment shell, the volume of the liquid inside the crystallization equipment shell is less than the volume of the crystallization equipment shell. (4) With a crystallization cycle of 1h to 3h, turn on the stirrer module and heat exchanger. During the crystallization cycle, under stirring, the sodium thiosulfate melt is fed into the guide tube (2-2) located in the inner cavity of the crystallization equipment shell through the first inlet (1-1) set in the upper end cap (1-3) of the crystallization equipment shell by the feed pump. The initial seed crystal is added into the annular interval formed by the inner wall of the crystallization equipment shell and the outer wall of the guide tube through the seed crystal feeding port (1-2) set in the upper end cap (1-3) of the crystallization equipment shell. The temperature control of the heat exchanger should ensure that during the addition of the sodium thiosulfate melt, the material liquid cooled by the heat exchanger is input into the inner cavity of the crystallization equipment shell through the second inlet (1-7) so that the temperature of the material liquid in the inner cavity of the crystallization equipment shell is the same as the temperature of the crystallization mother liquor. (5) After the crystallization cycle time is reached, open the crystal slurry outlet (1-10) set at the bottom of the lower end cap (1-9) in the crystallization equipment shell to release the crystal slurry. The volume of the released crystal slurry is the same as the volume of the second cylindrical section (1-8) of the shell. Filter the collected crystal slurry and return the filtrate obtained from the filtration to the buffer tank to maintain a constant liquid level in the crystallization equipment shell. After drying, the filtered crystals are large-particle sodium thiosulfate products. Repeating steps (3) to (5) above can achieve continuous preparation of large-particle sodium thiosulfate; however, when repeating step (4) above, only sodium thiosulfate melt needs to be added under stirring during the crystallization cycle, and no seed crystals need to be added.

7. The method for continuous preparation of large-particle sodium thiosulfate according to claim 6, characterized in that... The initial seed crystals are sodium thiosulfate with a particle size of less than 1 mm. The amount of initial seed crystals added is 1 / 150 to 1 / 120 of the amount of sodium thiosulfate melt added in the first crystallization cycle.

8. The method for continuous preparation of large-particle sodium thiosulfate according to claim 6 or 7, characterized in that... The stirring rate setting of the stirrer module should ensure that the sodium thiosulfate crystals can be suspended in the crystallization equipment shell during the crystallization process when the sodium thiosulfate melt is added, but will not flow out from the liquid outlet (1-5) set in the crystallization equipment shell; the drying temperature of the filtered crystals is 25℃~30℃.

9. A method for continuous preparation of large-particle sodium thiosulfate, characterized in that... Using the crystallization equipment for producing large-particle crystals as described in any one of claims 1 to 5, and equipped with a buffer tank, a circulating pump, a heat exchanger, and a feed pump, the process steps are as follows: (1) Prepare a saturated sodium thiosulfate solution at 25℃~40℃ as the crystallization mother liquor. The amount of crystallization mother liquor should be such that it can circulate between the buffer tank and the shell of the crystallization equipment under the action of the circulating pump. (2) Close the crystal slurry outlet (1-10) at the bottom of the lower end cap (1-9) in the crystallization equipment shell, add the crystallization mother liquor to the buffer tank, and then turn on the circulation pump to input the crystallization mother liquor into the crystallization equipment shell through the heat exchanger from the second liquid inlet (1-7) of the crystallization equipment shell. When the liquid level of the crystallization mother liquor in the crystallization equipment shell is higher than the upper end face of the guide tube, the crystallization mother liquor overflows from the liquid outlet (1-5) of the crystallization equipment shell and enters the buffer tank through the pipeline, realizing the circulation flow of the crystallization mother liquor between the crystallization equipment shell and the buffer tank; the temperature of the crystallization equipment shell and the temperature of the buffer tank are controlled at the same temperature as the crystallization mother liquor. (3) The preparation temperature is 50℃~80℃ and the density is 1.580 g / cm³. 3 ~1.590 g / cm 3 The sodium thiocyanate melt is fed into the crystallizing equipment housing through the first inlet (1-1) set in the upper end cap (1-3) of the crystallizing equipment housing via a feed pump into the guide tube (2-2) located in the inner cavity of the crystallizing equipment housing. The initial seed crystals are added into the annular interval formed by the inner wall of the crystallizing equipment housing and the outer wall of the guide tube through the seed crystal feeding port (1-2) set in the upper end cap (1-3) of the crystallizing equipment housing. The temperature control of the heat exchanger should ensure that during the addition of the sodium thiocyanate melt, the liquid cooled by the heat exchanger is input into the inner cavity of the crystallizing equipment housing through the second inlet (1-7) so that the temperature of the liquid in the inner cavity of the crystallizing equipment housing is the same as the temperature of the crystallizing mother liquor. After the sodium thiosulfate melt is added and the operation is stable, open the crystal slurry outlet (1-10) set at the bottom of the lower head in the crystallization equipment shell and adjust the addition rate of sodium thiosulfate melt to match the crystal slurry release rate, and release the crystal slurry at the same time as adding sodium thiosulfate melt. (4) The collected crystal slurry is filtered, and the filtrate obtained is returned to the buffer tank to maintain a constant liquid level in the shell of the crystallization equipment. The filtered crystals are dried to produce large-particle sodium thiosulfate products.

10. The method for continuous preparation of large-particle sodium thiosulfate according to claim 9, characterized in that... The initial seed crystals are sodium thiosulfate with a particle size of less than 1 mm. The amount of initial seed crystals added is 1 / 150 to 1 / 120 of the amount of sodium thiosulfate melt added within 1 to 3 hours, starting from the time the sodium thiosulfate melt is added.

11. The method for continuous preparation of large-particle sodium thiosulfate according to claim 9 or 10, characterized in that... The stirring rate setting of the stirrer module should ensure that the sodium thiosulfate crystals can be suspended in the crystallization equipment shell during the crystallization process when the sodium thiosulfate melt is added, but will not flow out from the liquid outlet (1-5) set in the crystallization equipment shell; the drying temperature of the filtered crystals is 25℃~30℃.

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