Caustic soda evaporation and concentration system

Abstract

The utility model relates to the technical field of chlor-alkali chemical industry, and particularly discloses a caustic soda evaporation and concentration system. The system comprises a first-effect falling-film evaporator, a second-effect falling-film evaporator and a third-effect falling-film evaporator which are connected in sequence, and a condensate outlet of a heat exchanger of the third-effect falling-film evaporator is provided with a first flash tank. A second flash tank is arranged between a condensate outlet of the second-effect falling film evaporator heat exchanger and an inlet of the first-effect falling film evaporator heat exchanger, the first-effect falling film evaporator, the second-effect falling film evaporator and the third-effect falling film evaporator are combined, secondary steam generated by the previous stage is used as a heating heat source of the next stage, the steam utilization rate is increased, and the energy consumption is reduced. A flash tank is additionally arranged at a condensate outlet of a heat exchanger of a second-effect falling film evaporator, condensate generated by second-effect is subjected to secondary flash evaporation in a negative-pressure state of second-effect secondary steam and then used for third-effect alkali liquor heat exchange, and latent heat of the condensate is fully utilized.

Description

Technical fields:

[0002] This utility model relates to the field of chlor-alkali chemical technology, and in particular to a caustic soda evaporation and concentration system. Background technology:

[0004] Caustic soda (sodium hydroxide) is an important product in the chlor-alkali industry. The chlor-alkali industry often uses the electrolysis of sodium chloride to produce caustic soda. The concentration of liquid caustic soda produced by the electrolysis process is about 30%, which needs to be further concentrated to 50%. Increasing the concentration of liquid caustic soda can significantly reduce the storage tank space required for liquid caustic soda storage and save storage and transportation costs. In addition, other related subsequent by-products also require liquid caustic soda with higher concentrations. Therefore, it is necessary to concentrate the 30% liquid caustic soda produced by the electrolysis process.

[0005] Existing caustic soda evaporation and concentration equipment uses multi-effect falling film evaporation, which uses steam as a heat source to evaporate the water in the liquid caustic soda and achieve the effect of concentration. In order to ensure the evaporation efficiency of the tubes, the temperature required for the falling film evaporator must be increased, resulting in a higher exhaust temperature. The latent heat of the steam in the exhaust is not effectively released, which leads to a decrease in the utilization efficiency of the steam. Therefore, concentrating liquid caustic soda requires a large amount of heat source and has high energy consumption. Utility model content:

[0007] The purpose of this invention is to provide a caustic soda evaporation and concentration system to solve the problems existing in the prior art.

[0008] This utility model is implemented by the following technical solution: a caustic soda evaporation and concentration system, comprising a first-effect falling film evaporator, a second-effect falling film evaporator, and a third-effect falling film evaporator. The outlet of the first-effect falling film evaporator is connected to the inlet of the second-effect falling film evaporator via a first-effect caustic soda pump. The outlet of the second-effect falling film evaporator is connected to the inlet of the third-effect falling film evaporator via a second-effect caustic soda pump. The outlet of the third-effect falling film evaporator is connected to the inlet of the third-effect caustic soda pump. The condensate outlet of the heat exchanger of the third-effect falling film evaporator is connected to the inlet of the first flash tank. The secondary steam outlet of the third-effect falling film evaporator is connected to the inlet of the heat exchanger of the second-effect falling film evaporator. The condensate outlet of the membrane evaporator heat exchanger is connected to the inlet of the second flash tank. The steam recovery port of the second flash tank is connected to the inlet of the first-effect falling film evaporator heat exchanger. The bottom drain port of the second flash tank is connected to the inlet of the condensate recovery tank. The secondary steam outlet of the second-effect falling film evaporator is connected to the inlet of the first-effect falling film evaporator heat exchanger. The condensate outlet of the first-effect falling film evaporator heat exchanger is connected to the inlet of the condensate recovery tank. The secondary steam outlet of the first-effect falling film evaporator is connected to the inlet of the air condenser. The air condenser vent is connected to the inlet of the vacuum pump. The condensate outlet of the air condenser is connected to the inlet of the condensate recovery tank.

[0009] Furthermore, it also includes a double-effect alkali heat exchanger, a double-effect steam heat exchanger, and the outlet of the triple-effect alkali pump is connected to the heat source inlet of the double-effect alkali heat exchanger. The condensate outlet of the first flash tank is connected to the heat source inlet of the double-effect steam heat exchanger. The outlet of the double-effect alkali pump is connected to the medium inlet of the double-effect alkali heat exchanger and the medium inlet of the double-effect steam heat exchanger, respectively. The medium outlet of the double-effect alkali heat exchanger and the medium outlet of the double-effect steam heat exchanger are connected to the liquid inlet of the triple-effect falling film evaporator, respectively.

[0010] Furthermore, it also includes a first-effect alkali heat exchanger and a first-effect steam heat exchanger. The heat source outlet of the second-effect alkali heat exchanger is connected to the heat source inlet of the first-effect alkali heat exchanger. The heat source outlet of the second-effect steam heat exchanger is connected to the heat source inlet of the first-effect steam heat exchanger. The outlet of the first-effect alkali pump is connected to the medium inlet of the first-effect alkali heat exchanger and the medium inlet of the first-effect steam heat exchanger, respectively. The medium outlet of the first-effect alkali heat exchanger and the medium outlet of the first-effect steam heat exchanger are connected to the liquid inlet of the second-effect falling film evaporator, respectively.

[0011] Furthermore, it also includes a triple-effect alkaline heat exchanger, with the condensate outlet of the first flash tank connected to the heat source inlet of the triple-effect alkaline heat exchanger, the heat source outlet of the triple-effect alkaline heat exchanger connected to the heat source inlet of the second-effect alkaline heat exchanger, the medium outlet of the second-effect alkaline heat exchanger connected to the medium inlet of the triple-effect alkaline heat exchanger, and the medium outlet of the triple-effect alkaline heat exchanger connected to the liquid inlet of the triple-effect falling film evaporator.

[0012] Furthermore, the outlet of the condensate recovery tank is connected to the inlet of the condensate recovery pump.

[0013] Furthermore, it also includes a finished product cooler, with the heat source outlet of the first-effect alkali heat exchanger connected to the heat source inlet of the finished product cooler.

[0014] The advantages of this invention are as follows: It adopts a combination of single-effect, double-effect, and triple-effect falling film evaporators, using the secondary steam generated in the previous stage as the heating heat source for the next stage, realizing the step-by-step utilization of heat, which greatly improves the steam utilization rate and reduces the energy consumption per unit product. A flash tank is added to the condensate outlet of the heat exchanger of the double-effect falling film evaporator, and the condensate generated in the double-effect is flashed again under the negative pressure of the secondary steam in the double-effect and then used for the alkaline heat exchange in the triple-effect, making full use of the latent heat of the condensate. At the same time, it is also equipped with multi-stage alkaline heat exchangers of single-effect, double-effect, and triple-effect, which can fully recover the waste heat of the product alkaline solution generated by the triple-effect falling film evaporator and improve the utilization efficiency of the steam heat source. Attached image description:

[0016] Figure 1 This is a schematic diagram of the system of this utility model.

[0017] In the diagram: 1. Single-effect falling film evaporator; 2. Double-effect falling film evaporator; 3. Triple-effect falling film evaporator; 4. First flash tank; 5. Second flash tank; 6. First-effect alkali pump; 7. Second-effect alkali pump; 8. Triple-effect alkali pump; 9. Condensate recovery tank; 10. Air condenser; 11. Vacuum pump; 12. Double-effect alkali heat exchanger; 13. Double-effect steam heat exchanger; 14. First-effect alkali heat exchanger; 15. First-effect steam heat exchanger; 16. Triple-effect alkali heat exchanger; 17. Condensate recovery pump; 18. Finished product cooler. Detailed implementation method:

[0019] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0020] like Figure 1The diagram shows a caustic soda evaporation and concentration system, comprising a single-effect falling film evaporator 1, a second-effect falling film evaporator 2, and a third-effect falling film evaporator 3, arranged sequentially according to the concentration of the produced caustic soda solution. The single-effect falling film evaporator 1 has the lowest concentration, and the third-effect falling film evaporator 3 has the highest concentration. The inlet of the single-effect falling film evaporator 1 is connected to 30% concentration liquid caustic soda from the electrolysis process. The outlet of the single-effect falling film evaporator 1 is connected to the inlet of the second-effect falling film evaporator 2 via a single-effect caustic soda solution pump 6. The outlet of the second-effect falling film evaporator 2 is connected to the inlet of the third-effect falling film evaporator 3 via a second-effect caustic soda solution pump 7. The outlet of the third-effect falling film evaporator 3 is connected to the inlet of a third-effect caustic soda solution pump 8. The 30% concentration is then concentrated by each stage of the falling film evaporator. The final concentration delivered from the triple-effect falling film evaporator 3 is approximately 50%. The inlet of the triple-effect falling film evaporator 3 heat exchanger is connected to an external steam pipeline. Its steam source can utilize surplus recovered steam from the plant area or a separate steam generator. The condensate outlet of the triple-effect falling film evaporator 3 heat exchanger is connected to the inlet of the first flash tank 4. The steam exiting the triple-effect falling film evaporator 3 heat exchanger has a relatively high temperature and pressure, and still possesses significant latent heat. It can be further fed into the first flash tank 4 for pressure regulation and temporary storage, used for preheating various alkaline solutions. The secondary steam outlet of the triple-effect falling film evaporator 3 is connected to the inlet of the second-effect falling film evaporator 2 heat exchanger. The secondary steam of the triple-effect falling film evaporator 3 has a relatively high temperature and pressure, and still possesses significant latent heat. The large latent heat can serve as a heat source for the double-effect falling film evaporator 2, improving steam utilization efficiency. The condensate outlet of the double-effect falling film evaporator 2 is connected to the inlet of the second flash tank 5, and the steam recovery port of the second flash tank 5 is connected to the inlet of the first-effect falling film evaporator 1. Conventionally, the condensate from the double-effect falling film evaporator 2 is recovered after condensation, but the heat is not utilized by the next stage, the first-effect falling film evaporator 1. In this invention, the second flash tank 5 can depressurize and vaporize the condensate from the double-effect falling film evaporator 2 again. The steam contains a large amount of latent heat, which, when fed back into the first-effect falling film evaporator 1, can improve steam utilization efficiency. The bottom of the second flash tank 5... The drain outlet of the first-effect falling film evaporator 2 is connected to the inlet of the condensate recovery tank 9. The liquid from the second flash tank 5 can be directly sent into the condensate recovery tank 9 through the bottom drain outlet. The secondary steam outlet of the second-effect falling film evaporator 2 is connected to the inlet of the heat exchanger of the first-effect falling film evaporator 1. The condensate outlet of the heat exchanger of the first-effect falling film evaporator 1 is connected to the inlet of the condensate recovery tank 9. The secondary steam outlet of the first-effect falling film evaporator 1 is connected to the inlet of the air condenser 10. The vent of the air condenser 10 is connected to the inlet of the vacuum pump 11. The condensate outlet of the air condenser 10 is connected to the inlet of the condensate recovery tank 9. The vacuum pump 11 and the air condenser 10 provide a vacuum for the falling film evaporators connected to each stage, so that the heat exchange, evaporation and concentration of each stage can proceed normally.

[0021] To improve steam utilization efficiency, a multi-stage heat exchanger is installed to preheat the condensate from the triple-effect evaporator and the product alkali solution. The outlet of the triple-effect alkali pump 8 is connected to the heat source inlet of the second-effect alkali heat exchanger 12 and the second-effect steam heat exchanger 13. The outlet of the first flash tank 4 is connected to the heat source inlet of the second-effect steam heat exchanger 13. The outlet of the second-effect alkali pump 7 is connected to the medium inlet of the second-effect alkali heat exchanger 12 and the medium inlet of the second-effect steam heat exchanger 13, respectively. The medium outlets of the second-effect alkali heat exchanger 12 and the second-effect steam heat exchanger 13 are connected to the liquid inlet of the triple-effect falling film evaporator 3, respectively. The heat source outlet of the first-effect alkali heat exchanger 14 and the first-effect steam heat exchanger 15 are connected to the heat source inlet of the first-effect alkali heat exchanger 14. The heat source outlet of the second-effect steam heat exchanger 13 is connected to the heat source inlet of the first-effect steam heat exchanger 15. The outlet of the first-effect alkali pump 6 is connected to the medium inlet of the first-effect alkali heat exchanger 14 and the medium inlet of the first-effect steam heat exchanger 15, respectively. The medium outlet of the first-effect alkali heat exchanger 14 and the medium outlet of the first-effect steam heat exchanger 15 are connected to the liquid inlet of the second-effect falling film evaporator 2, respectively. The condensate outlet of the first flash tank 4 is connected to the heat source inlet of the triple-effect alkaline heat exchanger 16. The heat source outlet of the triple-effect alkaline heat exchanger 16 is connected to the heat source inlet of the second-effect alkaline heat exchanger 12. The medium outlet of the second-effect alkaline heat exchanger 12 is connected to the medium inlet of the triple-effect alkaline heat exchanger 16. The medium outlet of the triple-effect alkaline heat exchanger 16 is connected to the liquid inlet of the triple-effect falling film evaporator 3.

[0022] The outlet of the condensate recovery tank 9 is connected to the inlet of the condensate recovery pump 17. The condensate is discharged through the condensate recovery pump 17 to maintain a stable liquid level in the condensate recovery tank 9.

[0023] After passing through the first-effect alkali heat exchanger 14, the second-effect alkali heat exchanger 12, and the third-effect alkali heat exchanger 16, the temperature of the finished alkali solution gradually decreases. However, the finished alkali solution is still at a relatively high room temperature and needs to be cooled again during storage and transportation. Therefore, a finished product cooler 18 is installed. The heat source outlet of the first-effect alkali heat exchanger 14 is connected to the heat source inlet of the finished product cooler 18. The cooling water of the finished product cooler 18 is supplied from outside the system. After being heated by the finished product cooler 18, this cooling water can be used as a heat source for winter antifreeze, further improving the waste heat utilization efficiency and saving costs.

[0024] In the description of this utility model, it should be noted that the terms "center", "upper", "lower", "front", "rear", "top", "bottom", "left", "right", "vertical", "horizontal", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

Claims

1. A caustic soda evaporation and concentration system, characterized in that, The system includes a single-effect falling film evaporator (1), a double-effect falling film evaporator (2), and a triple-effect falling film evaporator (3). The outlet of the single-effect falling film evaporator (1) is connected to the inlet of the double-effect falling film evaporator (2) via a single-effect alkali pump (6). The outlet of the double-effect falling film evaporator (2) is connected to the inlet of the triple-effect falling film evaporator (3) via a double-effect alkali pump (7). The outlet of the triple-effect falling film evaporator (3) is connected to the inlet of the triple-effect alkali pump (8). The condensate outlet of the triple-effect falling film evaporator (3) is connected to the inlet of the first flash tank (4). The secondary steam outlet of the triple-effect falling film evaporator (3) is connected to the inlet of the double-effect falling film evaporator (2). The condensate outlet of the double-effect falling film evaporator (2) is connected to the inlet of the double-effect falling film evaporator (2). The second flash tank (5) is connected to the inlet of the second flash tank (5), the steam recovery port of the second flash tank (5) is connected to the inlet of the heat exchanger of the first-effect falling film evaporator (1), the bottom drain port of the second flash tank (5) is connected to the inlet of the condensate recovery tank (9), the secondary steam outlet of the second-effect falling film evaporator (2) is connected to the inlet of the heat exchanger of the first-effect falling film evaporator (1), the condensate outlet of the heat exchanger of the first-effect falling film evaporator (1) is connected to the inlet of the condensate recovery tank (9), the secondary steam outlet of the first-effect falling film evaporator (1) is connected to the inlet of the air condenser (10), the vent of the air condenser (10) is connected to the inlet of the vacuum pump (11), and the condensate outlet of the air condenser (10) is connected to the inlet of the condensate recovery tank (9).

2. The caustic soda evaporation and concentration system according to claim 1, characterized in that, It also includes a double-effect alkaline heat exchanger (12) and a double-effect steam heat exchanger (13). The outlet of the triple-effect alkaline pump (8) is connected to the heat source inlet of the double-effect alkaline heat exchanger (12). The condensate outlet of the first flash tank (4) is connected to the heat source inlet of the double-effect steam heat exchanger (13). The outlet of the double-effect alkaline pump (7) is connected to the medium inlet of the double-effect alkaline heat exchanger (12) and the medium inlet of the double-effect steam heat exchanger (13), respectively. The medium outlet of the double-effect alkaline heat exchanger (12) and the medium outlet of the double-effect steam heat exchanger (13) are connected to the liquid inlet of the triple-effect falling film evaporator (3), respectively.

3. The caustic soda evaporation and concentration system according to claim 2, characterized in that, It also includes a first-effect alkali heat exchanger (14) and a first-effect steam heat exchanger (15). The heat source outlet of the second-effect alkali heat exchanger (12) is connected to the heat source inlet of the first-effect alkali heat exchanger (14). The heat source outlet of the second-effect steam heat exchanger (13) is connected to the heat source inlet of the first-effect steam heat exchanger (15). The outlet of the first-effect alkali pump (6) is connected to the medium inlet of the first-effect alkali heat exchanger (14) and the medium inlet of the first-effect steam heat exchanger (15), respectively. The medium outlet of the first-effect alkali heat exchanger (14) and the medium outlet of the first-effect steam heat exchanger (15) are connected to the liquid inlet of the second-effect falling film evaporator (2), respectively.

4. The caustic soda evaporation and concentration system according to claim 3, characterized in that, It also includes a triple-effect alkaline heat exchanger (16), the condensate outlet of the first flash tank (4) is connected to the heat source inlet of the triple-effect alkaline heat exchanger (16), the heat source outlet of the triple-effect alkaline heat exchanger (16) is connected to the heat source inlet of the second-effect alkaline heat exchanger (12), the medium outlet of the second-effect alkaline heat exchanger (12) is connected to the medium inlet of the triple-effect alkaline heat exchanger (16), and the medium outlet of the triple-effect alkaline heat exchanger (16) is connected to the liquid inlet of the triple-effect falling film evaporator (3).

5. The caustic soda evaporation and concentration system according to claim 1, characterized in that, The outlet of the condensate recovery tank (9) is connected to the inlet of the condensate recovery pump (17).

6. The caustic soda evaporation and concentration system according to claim 4, characterized in that, It also includes a finished product cooler (18), and the heat source outlet of the first-effect alkaline heat exchanger (14) is connected to the heat source inlet of the finished product cooler (18).

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