Gradient cooling falling film dynamic crystallizer and falling film crystallization separation method for mixture

Abstract

The object of the present invention is to provide a gradient cooling falling-film dynamic crystallizer and a falling-film crystallization separation method for mixtures in view of the problems existing in the existing dynamic crystallization devices, belonging to the technical field of chemical engineering equipment. The gradient cooling falling-film dynamic crystallizer of the present invention comprises, from top to bottom, a feeding unit, a falling-film crystallization unit and a discharging unit; the upper part of the feeding unit is a flow-smoothing tank and the lower part is a raw material tank; several falling-film tubes are arranged inside the falling-film crystallization unit, a jacket tube is sleeved on the outer wall of the falling-film tube, and a circulating water inlet and an outlet are arranged on the side wall; the base of the falling-film crystallization unit is fixedly connected to the top of the discharging unit, and a material outlet is arranged on the side wall of the lower part of the falling-film crystallization unit. The present invention solves the stability and uniformity of the material entering the dynamic crystallizer by setting a flow-smoothing tank; avoids the accumulation of crystallization scale in the initial stage by improving the uniformity of the material spraying on the inner wall of the falling-film tube; and improves the crystallization efficiency of the tube side by improving the heat exchange efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical equipment, and particularly relates to a purification device and a purification method for easily crystallizable substances in petrochemical and coal chemical industries. Background Art

[0002] In the production of products such as refined naphthalene and refined anthracene in the petrochemical industry and the coal chemical industry, substances such as benzothiophene, methylindene, and phenanthrene have similar boiling points, and it is difficult to obtain products with high purity by distillation. Therefore, the common method is to use the crystallization method according to the difference in crystallization points.

[0003] At present, the static crystallization process technology is mostly used in China. The static crystallizer technology is mainly as follows: the cooling and temperature-lowering medium flows through the tube side, and the material flows through the shell side. Most of the inner tube walls of the shell side are provided with fins to increase the heat transfer area. After the material fills the shell side and stands still, the tube side gradually cools down through the cooling medium, and the uncrystallized material is discharged after a certain time. After repeated static crystallization, a purified product is obtained. However, the problems of the static crystallization process are: the crystallization process is uneven, there are many non-crystalline impurities entrained, high energy consumption, low efficiency, and poor quality control. When discharging, due to the specific gravity difference of the crystallized substances in the shell side, as the uncrystallized material falls off and is discharged, there is a phenomenon of pipeline blockage.

[0004] With the opening of China's market, in the 1990s, the double-falling film dynamic crystallization technology of Sulzer in Switzerland entered the Chinese market and was applied by a few large enterprises. The double-falling film dynamic crystallization process technology has well solved many deficiencies of the static crystallization process technology. The double-falling film dynamic crystallization process technology is mainly that the material flows downward along the inner tube wall in the form of a falling film in the tube side, the cooling medium is outside the tube wall, and the cooling and temperature-lowering medium in the shell side overflows from the top and flows downward in the form of a falling film along the outer tube wall, gradually exchanging heat to obtain crystals on the inner tube wall. This form can avoid the temperature non-uniformity during the flow process when the tube side is filled with the cooling and temperature-lowering medium. However, the problems of this process technology are: the raw material is pumped into the high-level tank. Due to the action of the pump pressure, turbulence will be generated when the raw material enters the raw material tank, causing fluctuations in the downward flow due to the head difference. The high-level raw material tank is connected to the falling film heat exchange tube side through a flexible hose. The purpose is to evenly distribute the raw material to each falling film heat exchange in the tube side. Since a flexible hose is used to connect the high-level raw material tank and the falling film heat exchange tube side, there must be a certain installation space, resulting in material waste. The flexible hose connection will also have a certain degree of bending. In the initial stage of production, there will be phenomena of different pressure differences and uneven flow velocities, which will have a certain impact on production. The bending degree of the flexible hose is also very easy to cause crystallization blockage. The cooling medium flows downward in the form of a falling film on the outer wall of the tube side through overflow. Due to the process, the tube bundle is relatively long, generally more than 10 meters. It is difficult for the falling film cooling medium to achieve the balance of square cooling. Another is that the heat exchanged out by the falling film cooling heat exchange from top to bottom accumulates and flows downward, resulting in unevenness up and down in the tube side, with thick crystals on the upper part and thin crystals on the lower part, forming an inverted cone phenomenon. These two factors will greatly reduce the production efficiency. Summary of the Invention

[0005] The object of the present invention is to provide a gradient cooling falling film dynamic crystallizer and a falling film crystallization separation method for mixtures in view of the problems existing in the existing dynamic crystallization devices. The present invention solves the stability and uniformity of the material entering the dynamic crystallizer by setting a slow flow tank; avoids the accumulation of crystallization scale in the initial stage by improving the uniformity of the material jet on the inner wall of the falling film tube; and improves the crystallization efficiency of the tube by improving the heat exchange efficiency.

[0006] One of the technical solutions of the present invention is a gradient cooling falling film dynamic crystallizer, which successively includes a feeding unit, a falling film crystallization unit, and a discharging unit from top to bottom;

[0007] The upper part of the feeding unit is a slow flow tank, and the lower part is a raw material tank; the upper part of the side wall of the slow flow tank is provided with a material inlet, and the bottom of the tank is provided with several outlets, and a cofferdam plate is arranged around each outlet; a sieve plate, a grid plate, and a flange hole plate are successively arranged in the raw material tank from top to bottom. The sieve holes of the sieve plate are equidistant holes, several through holes are uniformly distributed on the flange hole plate, and several spray pipes are inserted into the through holes;

[0008] The falling film crystallization unit is a cavity sealed up and down. The top cover of the cavity is fixedly connected to the flange hole plate of the feeding unit. The upper part of the side wall of the cavity is provided with a circulating water inlet, and the lower part is provided with a circulating water outlet. Two sealing plates are arranged in the cavity, respectively below the circulating water inlet and above the circulating water outlet. Several falling film tubes are arranged inside the cavity. The falling film tubes respectively open at the top cover and the bottom of the cavity. The spray pipes of the feeding unit are inserted into the upper openings of the corresponding falling film tubes. There is an annular gap between the spray pipes and the falling film tubes of the falling film unit. A jacket pipe is sleeved on the outer wall of the falling film tube. The falling film tube passes through the upper and lower sealing plates. The upper end of the jacket pipe opens at the upper sealing plate, and the lower end of the jacket pipe opens at the lower sealing plate;

[0009] Preferably, several cooling water inlets and a cooling water outlet are successively arranged from top to bottom on the side wall of the falling film unit between the upper and lower sealing plates. A sealing and fixing partition plate is arranged below each cooling water inlet. The falling film tube and the jacket pipe pass through the sealing and fixing partition plate. There is a gap between the sealing and fixing partition plate and the jacket pipe, so that a secondary cooling cavity is formed between the sealing plate, the inner side of the side wall of the falling film crystallization unit, and the outer side of the jacket pipe;

[0010] The discharging unit is a cavity with a base. The base of the falling film crystallization unit is fixedly connected to the top of the discharging unit. A material outlet is arranged on the side wall of the lower part of the falling film crystallization unit.

[0011] Another technical solution of the present invention is a falling film crystallization separation method for mixtures, which adopts the above-mentioned gradient cooling falling film dynamic crystallizer, and includes the following steps:

[0012] 1) Open the circulating water inlet, circulating water outlet, cooling water inlet and cooling water outlet to fill the jacketed pipe and the secondary cooling cavity with the cooling medium;

[0013] 2) The mixture material is pumped into the uppermost slow-flow tank by the feeding pump, overflows from the periphery of the slow-flow tank weir plate into the raw material tank; the mixture material flows through the sieve holes of the sieve plate into the lower grid plate, and enters the falling film tube pass through the spray pipe installed on the flange orifice plate at the bottom of the grid plate;

[0014] 3) The insertion depth of the spray pipe is 10 - 15 mm, there is a 2 - 5 mm annular gap between the spray pipe and the inner wall of the falling film tube, the mixture material is ejected by the head pressure, the spraying angle is 20 - 30°, and it is evenly sprayed on the inner wall of the falling film tube pass in an umbrella shape, and then flows downward in a falling film manner; the crystallization of the tube pass adopts jacketed pipe falling film cooling heat exchange. In addition, there is a 3 - 6 mm gap between the sealing fixed partition plate and the jacketed pipe, and the cooling medium enters the secondary cooling cavity from several cooling water inlets and flows downward along the outer wall of the jacketed pipe around the periphery to form a secondary gradient falling film heat exchange; the mixture is cooled by the falling film tube to crystallize one of the compounds, thereby separating the mixture.

[0015] Compared with the prior art, the advantages of the present invention are as follows:

[0016] 1. The present invention sets a raw material tank and a slow-flow tank at the material feeding stage to solve the stability and uniformity of the material before entering the falling film tube pass.

[0017] 2. The present invention sets a direct current spray pipe for the material. When the material is ejected from the direct current spray pipe, it has a certain power to evenly spray the ejected material on the inner wall of the falling film tube pass, and then flows downward in a falling film manner to avoid the accumulation of crystallization scale in the initial stage of crystallization.

[0018] 3. The present invention sets a secondary cooling cavity outside the jacketed pipe to form a secondary gradient falling film heat exchange, re-extract the heat exchanged by the cooling medium from top to bottom in the primary falling film heat exchange to improve the crystallization efficiency of the tube pass, and at the same time, it can also meet the crystallization process requirements at different temperatures. Brief Description of the Drawings

[0019] Figure 1 The schematic diagram of the crystallizer of the present invention.

[0020] Among them, 1. Slow-flow tank, 2. Raw material tank, 3. Material inlet, 4. Falling film crystallization unit, 5. Discharge unit, 6. Material outlet, 11. Weir plate, 21. Grid plate, 22. Flange orifice plate, 23. Spray pipe, 41. Falling film tube, 42. Jacketed pipe, 43. Circulating water inlet, 44. Circulating water outlet, 45. Upper sealing plate, 46. Lower sealing plate, 47. Cooling water inlet, 48. Cooling water outlet, 49. Sealing fixed partition plate, 491. Secondary cooling cavity. Detailed Embodiment

[0021] Example 1

[0022] A gradient cooling falling-film dynamic crystallizer, which successively includes a feeding unit, a falling-film crystallization unit and a discharging unit from top to bottom;

[0023] The upper part of the feeding unit is a slow-flow tank 1, and the lower part is a raw material tank 2; a material inlet 3 is arranged on the upper part of the side wall of the slow-flow tank, and several outlets are arranged at the bottom of the tank, and a cofferdam plate 11 is arranged around each outlet; a sieve plate, a grid plate 21 and a flange orifice plate 22 are successively arranged from top to bottom in the raw material tank. The sieve holes of the sieve plate are equidistant holes, several through holes are evenly distributed on the flange orifice plate, and several spray pipes 23 are inserted into the through holes;

[0024] The falling-film crystallization unit 4 is a cavity sealed up and down. The top cover of the cavity is fixedly connected to the flange orifice plate of the feeding unit. Several falling-film tubes 41 are arranged inside the cavity. The number of falling-film tubes is selected according to the processing capacity. The falling-film tubes are respectively opened at the top cover and the bottom of the cavity. The spray pipe 23 is inserted into the upper opening of the corresponding falling-film tube, and the insertion depth of the spray pipe is 10 - 15 mm, and there is an annular gap between the spray pipe and the falling-film tube, and the annular gap spacing is 2 - 5 mm. A jacket tube 42 is sleeved on the outer wall of the falling-film tube. A circulating water inlet 43 is arranged on the upper part of the side wall, and a circulating water outlet 44 is arranged on the lower part. Two sealing plates are arranged in the cavity, respectively below the circulating water inlet and above the circulating water outlet. The falling-film tubes pass through the upper and lower sealing plates. The upper end of the jacket tube is opened at the upper sealing plate 45, and the lower end of the jacket tube is opened at the lower sealing plate 46;

[0025] Several cooling water inlets 47 and one cooling water outlet 48 are successively arranged from top to bottom on the side wall of the falling-film unit between the upper and lower sealing plates. A sealing and fixing partition plate 49 is arranged below each cooling water inlet. The falling-film tubes and the jacket tubes pass through the sealing and fixing partition plate. There is a gap between the sealing and fixing partition plate and the jacket tube, and the gap spacing is 3 - 6 mm, so that a secondary cooling cavity 491 is formed between the sealing plate, the inner side of the side wall of the falling-film crystallization unit and the outer side of the jacket tube;

[0026] The discharging unit 5 is a cavity with a bottom. The bottom of the falling-film crystallization unit is fixedly connected to the top of the discharging unit. A material outlet 6 is arranged on the side wall below the falling-film crystallization unit.

[0027] A falling-film crystallization separation method for a mixture, using the gradient cooling falling-film dynamic crystallizer of this embodiment, includes the following steps:

[0028] 1) Open the circulating water inlet, the circulating water outlet, the cooling water inlet and the cooling water outlet to make the jacket tube and the secondary cooling cavity filled with a cooling medium;

[0029] 2) The mixture material is pumped into the uppermost slow-flow tank by a feed pump and overflows inward from the periphery of the slow-flow tank weir plate into the raw material tank; the mixture material flows into the following grid plate through the equidistant holes of the sieve plate and enters the falling film tube pass through the spray pipe installed on the flange orifice plate at the bottom of the grid plate; the main purpose is to solve the stability and uniformity of the material.

[0030] 3) The insertion depth of the spray pipe is 10 - 15 mm, there is a 2 - 5 mm annular gap between the spray pipe and the inner wall of the falling film tube, the mixture material is ejected using the head pressure, the spraying angle is 20 - 30 degrees °, and it is evenly sprayed in an umbrella shape on the inner wall of the falling film tube pass, and then flows downward in a falling film manner. When the material is ejected from the direct current spray pipe, it will carry a certain amount of power, which can preferably avoid the crystallization scale accumulation in the initial stage; the mixture is cooled by the falling film tube to crystallize one of the compounds, thereby separating the mixture.

[0031] The crystallization in the tube pass mainly adopts falling film cooling heat transfer, and the flow rate and the uniformity of the heat transfer area during falling film are controlled by the jacket tube; there is a 3 - 6 mm gap between the sealed fixed partition plate and the jacket tube, the cooling medium enters the secondary cooling cavity from several cooling water inlets and flows downward along the outer wall periphery of the jacket tube through the gap, forming a secondary gradient falling film heat transfer to secondarily transfer the heat transferred out by the cooling medium of the primary falling film heat transfer, improving the crystallization efficiency of the tube pass, and at the same time, it can also meet the crystallization process requirements at different temperatures.

Claims

1. A gradient cooling falling-film dynamic crystallizer, which successively comprises a feeding unit, a falling-film crystallization unit and a discharging unit from top to bottom; The upper part of the feeding unit is a flow-slowing tank, and the lower part is a raw material tank; the upper part of the side wall of the flow-slowing tank is provided with a material inlet, and the bottom of the tank is provided with several outlets, and a cofferdam plate is arranged around each outlet; a sieve plate, a grid plate and a flange orifice plate are successively arranged in the raw material tank from top to bottom, several through holes are evenly distributed on the flange orifice plate, and several spray pipes are inserted into the through holes; The falling-film crystallization unit is a cavity sealed up and down. The top cover of the cavity is fixedly connected with the flange orifice plate of the feeding unit. The upper part of the side wall of the cavity is provided with a circulating water inlet, and the lower part is provided with a circulating water outlet. Two sealing plates are arranged in the cavity, respectively below the circulating water inlet and above the circulating water outlet. Several falling-film pipes are arranged inside the cavity. The falling-film pipes respectively open at the top cover and the bottom of the cavity. The spray pipes of the feeding unit are inserted into the upper openings of the corresponding falling-film pipes. A jacket pipe is sleeved on the outer wall of the falling-film pipe. The falling-film pipe passes through the upper and lower sealing plates. The upper end of the jacket pipe opens at the upper sealing plate, and the lower end of the jacket pipe opens at the lower sealing plate; The discharging unit is a cavity with a bottom. The bottom of the falling-film crystallization unit is fixedly connected with the top of the discharging unit. A material outlet is arranged on the side wall below the falling-film crystallization unit; It is characterized in that Several cooling water inlets and a cooling water outlet are successively arranged from top to bottom on the side wall of the falling-film unit between the upper and lower sealing plates. A sealing and fixing partition plate is arranged below each cooling water inlet. The falling-film pipe and the jacket pipe pass through the sealing and fixing partition plate. A gap is arranged between the sealing and fixing partition plate and the jacket pipe, so that a secondary cooling cavity is formed between the sealing plate, the inner side of the side wall of the falling-film crystallization unit and the outer side of the jacket pipe.

2. The gradient cooling and falling film dynamic crystallizer according to claim 1, characterized in that The sieve holes of the sieve plate are equidistant holes.

3. The gradient cooling and falling film dynamic crystallizer according to claim 1, wherein There is an annular gap between the spray pipe and the falling-film pipe of the falling-film unit.

4. A falling film crystallization separation method for a mixture, which uses the gradient cooling falling film dynamic crystallizer described in claim 1, is characterized in that It includes the following steps: 1) Open the circulating water inlet, the circulating water outlet, the cooling water inlet and the cooling water outlet to make the jacket pipe and the secondary cooling cavity filled with a cooling medium; 2) The mixture material is pumped into the uppermost flow-slowing tank by a feeding pump, and overflows from the periphery of the cofferdam plate of the flow-slowing tank into the raw material tank; the mixture material flows through the sieve holes of the sieve plate into the lower grid plate, and enters the falling-film tube pass through the spray pipes installed on the flange orifice plate at the bottom of the grid plate; 3) The mixture material is ejected by using the head pressure, and is sprayed evenly on the inner wall of the falling-film pipe in an umbrella shape, and then flows downward in a falling-film manner; the crystallization of the tube pass adopts the falling-film cooling heat exchange of the jacket pipe. In addition, a gap is arranged between the sealing and fixing partition plate and the jacket pipe. The cooling medium enters the secondary cooling cavity from several cooling water inlets, and flows downward along the outer wall of the jacket pipe through the gap around the periphery to form a secondary gradient falling-film heat exchange; the mixture is cooled by the falling-film pipe, so that one of the compounds crystallizes, thereby separating the mixture.

5. The falling film crystallization separation method of the mixture according to claim 4, characterized in that, In the step 3), the spraying angle of the mixture material ejected is 20-30°.

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