System for recovering HF gas in anode of process for preparing NF3 through electrolytic method

Abstract

The utility model discloses a system for recovering HF gas in a process anode for preparing NF3 through an electrolytic method. A gas compressor (2), a heat exchanger (3), a buffer tank (5) and a water scrubber (7) are sequentially connected through pipelines; the bottom of the water washing tower (7) is connected with a water washing tank (8); the bottom of the alkaline washing tower (10) is connected with an alkaline washing tank (11); the water washing tank (8) is communicated with the upper space of the alkali washing tank (11); the upper part of the alkaline washing tower (10) is connected with the lower part of the alkaline washing tank (11) through an alkaline liquid pump (12) to form a loop; the tower top of the water washing tower (7) is connected with the lower part of the water washing tank (8) through an alkali circulating pump (12) to form a loop; and a hydrofluoric acid storage tank removing branch is arranged on a connecting pipeline of the water washing tower and the acid circulating pump. According to the system, HF gas can be recycled, and the raw material cost in the electrolysis process is reduced; and meanwhile, the subsequent HF treatment process is simplified, the use of equipment and pipelines is reduced, the frequency of pipeline blockage is reduced, the occupied area is reduced, the labor cost is reduced, manual disposal is reduced, and the safety risk is reduced.

Description

Technical Field

[0001] The utility model relates to a HF recovery system in a process of preparing NF3 by NH4F·nHF molten salt electrolysis. Background Art

[0002] Anhydrous hydrogen fluoride (HF) is an important chemical raw material, which is widely used in the preparation of fluoride salts, halogenated fluoroalkanes, fluorine refrigerants, etching glass, impregnating wood, electrolyzing elemental fluorine, etc. In industry, NF3 gas is prepared by electrolysis of NH4F·nHF molten salt. NH4F·nHF molten salt is usually prepared by mixing anhydrous HF and ammonia. In addition to HF contained in the raw materials, HF will be generated as a by-product during the electrolysis reaction. During the electrolysis process, a large amount of HF gas will be entrained to the subsequent water washing and alkali washing section, increasing the processing load of the water washing tower.

[0003] The reaction formula for the formation of byproduct HF during electrolysis is:

[0004] NH4F·HF+3F2→NF3+5HF

[0005] 2NH4F·HF+3F2→N2+10HF

[0006] NH4F·HF+NF3→N2+5HF

[0007] At present, the conventional operation is to directly pass the anode gas in the NF3 electrolysis process through a multi-stage water washing section, absorb the HF entrained in the gas to a certain concentration, and then extract it as a by-product, and then use the multi-stage alkali washing section to absorb the HF gas not absorbed in the water washing section. There are some problems with this process. For example, although the HF entrained in the electrolysis process is absorbed and produced and sold as a by-product, it causes waste of NF3 production raw materials and increases production costs; because the HF content entrained in the anode gas is relatively high (the HF content is generally around 8%), the processing load of the subsequent water washing section is increased, wasting energy consumption; the multi-stage water washing and alkali washing process is relatively complicated, involving more equipment and pipelines, and the manual operation is cumbersome, which increases production safety hazards. Therefore, it is necessary to recover the HF in the anode gas before water washing and alkali washing. Utility Model Content

[0008] In view of the problems existing in the prior art, the purpose of the utility model is to provide a HF gas recovery system in the anode of the NF3 electrolytic process. The system can realize the recovery and utilization of HF gas, reduce the cost of raw materials in the electrolytic process; at the same time, it can simplify the subsequent HF treatment process, reduce the use of equipment and pipelines, reduce the frequency of pipeline blockage, reduce the floor space, reduce labor costs, reduce manual disposal, and reduce safety risks.

[0009] In order to solve the problems existing in the prior art, the technical scheme adopted by the utility model is: a HF gas recovery system in the anode of the NF3 process of electrolysis preparation, a gas compressor 2, a heat exchanger 3, a buffer tank 5, and a water washing tower 7 are connected in sequence through pipelines; the bottom of the water washing tower 7 is connected to the water washing tank 8; the bottom of the alkali washing tower 10 is connected to the alkali washing tank 11; the water washing tank 8 is communicated with the upper space of the alkali washing tank 11; the upper part of the alkali washing tower 10 is connected to the lower part of the alkali washing tank 11 through an alkali liquid pump 12 to form a loop; the top of the water washing tower 7 is connected to the lower part of the water washing tank 8 through an alkali circulation pump 12 to form a loop; a dehydrofluoric acid storage tank branch is provided on the connecting pipeline between the water washing tower and the acid circulation pump.

[0010] Furthermore, a first ball valve 101 is installed on the gas compressor inlet pipeline, and a second ball valve 102 is installed on the gas outlet pipeline.

[0011] Furthermore, a regulating valve 4 is installed on the connecting pipeline between the heat exchanger 3 and the middle of the buffer tank 5; a check valve 6, a fourth ball valve 104, and a fifth ball valve 105 are installed in sequence on the connecting pipeline between the top of the buffer tank 5 and the upper part of the water washing tower 7; and a third ball valve 103 is installed at the bottom of the buffer tank.

[0012] Furthermore, a sixth ball valve 106 and a seventh ball valve 107 are installed on the pipeline connecting the water washing tower 7 and the acid circulation pump 9; an acid conversion pneumatic valve 13 is installed on the branch pipeline of the dehydrofluoric acid storage tank; and an eighth ball valve 108 is installed on the pipeline connecting the water washing tank 8 and the acid circulation pump 9.

[0013] Furthermore, a pure water branch is provided on the connecting pipeline between the water washing tower 7 and the acid circulation pump 9 , and a water supply valve 16 is installed on the pure water branch pipeline.

[0014] Furthermore, a tenth ball valve 110 is installed on the connecting pipeline between the alkali washing tower 10 and the alkali liquid pump 12; a ninth ball valve 109 is installed on the connecting pipeline between the alkali liquid pump 12 and the alkali liquid tank 11; an alkali liquid three-way valve 14 is installed on the connecting pipeline between the ninth ball valve 109 and the alkali liquid tank 11; a sewage treatment system branch is provided on the connecting pipeline between the alkali liquid three-way valve 14 and the alkali washing tank 11, and an alkali transfer pneumatic valve 15 is provided on the branch.

[0015] Furthermore, a bypass is provided between the inlet pipeline of the gas compressor 2 and the inlet pipeline of the heat exchanger 3 , and an eleventh ball valve 111 is provided on the bypass.

[0016] Furthermore, a bypass is provided between the inlet pipeline of the heat exchanger 3 and the outlet pipeline at the top of the buffer tank 5 , and the bypass is provided between the fourth ball valve 104 and the fifth ball valve 105 ; a twelfth ball valve 112 is provided on the bypass.

[0017] Furthermore, a first liquid level gauge 17 is provided on the alkali liquid tank 11;

[0018] Furthermore, an online concentration meter 18 is provided on the alkali solution tank 11 .

[0019] Furthermore, a second liquid level gauge 19 is provided on the water washing tank 8 .

[0020] Furthermore, an online acidity meter 20 is provided on the water washing tank 8 .

[0021] Furthermore, the first liquid level meter 17 , the online concentration meter 18 and the alkali transfer pneumatic valve 15 are interlocked.

[0022] Furthermore, the second liquid level meter 19 , the online acidity meter 20 and the acid conversion pneumatic valve 13 are interlocked.

[0023] Furthermore, the material of the pipeline containing HF gas is preferably a fluorine-lined carbon steel pipeline, and stainless steel and other materials may also be used.

[0024] Furthermore, the buffer tank is preferably made of carbon steel, and stainless steel, fluorocarbon steel and other materials may also be selected; the water washing tower, alkali washing tower, water washing tank and alkali washing tank are preferably made of polytetrafluoroethylene, and first-grade stainless steel and other materials may also be selected, and acid and alkali resistant fillers may be installed inside.

[0025] Furthermore, the heat exchanger is preferably a coil heat exchanger.

[0026] When recovering and treating HF in the anode gas of the NF3 electrolysis process, the utility model adopts the process of first compression and condensation, then water washing and alkali washing, and transfers it to the hydrofluoric acid storage tank system in time after absorption to reduce pollution and reduce costs. It can effectively recover HF in the NF3 finished gas for electrolyte configuration, reduce the waste of HF raw materials, and use a primary water washing and alkali washing system to treat the uncondensed HF gas, which not only avoids the workload caused by the acid and alkali liquid conversion operations, but also reduces the leakage risk caused by the investment in equipment and pipelines. The system can realize efficient recovery and treatment of HF-containing gas, effectively reduce the consumption of HF raw materials, and is suitable for industrial production applications. The utility model can be applied to the recovery and utilization of HF in the product gas in the NF3 electrolysis process, can meet the requirements of the process, is simple to operate, reduces costs, and improves production quality and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to clearly illustrate the examples of the utility model, the drawings required for use will be further described below. The drawings in the following description are only partial embodiments of the utility model.

[0028] Figure 1 This is a schematic diagram of an embodiment provided by the utility model.

[0029] In the schematic diagram:

[0030] 101. the first ball valve, 102. the second ball valve, 103. the third ball valve, 104. the fourth ball valve, 105. the fifth ball valve, 106. the sixth ball valve, 107. the seventh ball valve, 108. the eighth ball valve, 109. the ninth ball valve, 110. the tenth ball valve, 111. the eleventh ball valve, 112. the twelfth ball valve.

[0031] 2. Gas compressor, 3. Heat exchanger, 4. Regulating valve, 5. Buffer tank, 6. Check valve, 7. Water washing tower, 8. Water washing tank, 9. Acid circulation pump, 10. Alkali washing tower, 11. Alkali washing tank, 12. Alkali liquid pump, 13. Acid transfer pneumatic valve, 14. Alkali liquid three-way valve, 15. Alkali transfer pneumatic valve, 16. Water supply valve, 17. First liquid level meter, 18. Online concentration meter, 19. Second liquid level meter, 20. Online acidity meter. DETAILED DESCRIPTION

[0032] In order to introduce the technical solution provided by the utility model in more detail, it is described in conjunction with the embodiments below. The following description of the embodiments of the utility model is for illustration only and does not limit the utility model and its application or use. Based on the embodiments mentioned in the utility model, other embodiments obtained by those skilled in the art without making creative work all belong to the protection scope of the utility model. The techniques, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be regarded as part of the authorization specification.

[0033] Example 1

[0034] like Figure 1 As shown, a HF gas recovery system in a process of preparing NF3 by electrolysis, a gas compressor 2, a heat exchanger 3, a buffer tank 5, and a water washing tower 7 are connected in sequence through pipelines; the bottom of the water washing tower 7 is connected to the water washing tank 8; the bottom of the alkali washing tower 10 is connected to the alkali washing tank 11; the water washing tank 8 is connected to the upper space of the alkali washing tank 11, and the gas absorbed by water reaches the alkali washing tower 10 through the connecting area, and the alkali liquid is circulated by the alkali liquid pump 12 in the alkali washing tower 10 for alkali washing; the upper part of the alkali washing tower 10 is connected to the lower part of the alkali washing tank 11 through the alkali liquid pump 12 to form a loop; the top of the water washing tower 7 is connected to the lower part of the water washing tank 8 through the acid circulation pump 9 to form a loop; a branch for dehydrofluoric acid storage tank is arranged on the connecting pipeline between the water washing tower and the acid circulation pump.

[0035] A first ball valve 101 is installed on the air inlet pipeline of the gas compressor, and a second ball valve 102 is installed on the air outlet pipeline; a regulating valve 4 is installed on the connecting pipeline between the heat exchanger 3 and the middle of the buffer tank 5; a check valve 6, a fourth ball valve 104, and a fifth ball valve 105 are installed in sequence on the connecting pipeline between the top of the buffer tank 5 and the upper part of the water washing tower 7; a third ball valve 103 is installed on the bottom of the buffer tank; a sixth ball valve 106 and a seventh ball valve 107 are installed on the connecting pipeline between the water washing tower 7 and the acid circulation pump 9; an acid transfer pneumatic valve 13 is installed on the branch pipeline of the dehydrofluoric acid storage tank; an eighth ball valve 108 is installed on the connecting pipeline between the water washing tank 8 and the acid circulation pump 9; there is a pure water branch on the connecting pipeline between the water washing tower and the acid circulation pump, and a water supply valve 16 is installed on the pure water branch pipeline; a tenth ball valve 110 is installed on the connecting pipeline between the alkali washing tower 10 and the alkali liquid pump 12; a ninth ball valve is installed on the connecting pipeline between the alkali liquid pump 12 and the alkali liquid tank 11 109; an alkali three-way valve 14 is installed on the pipeline connecting the ninth ball valve 109 and the alkali liquid tank 11; a sewage treatment system branch is provided on the pipeline connecting the alkali liquid three-way valve 14 and the alkali washing tank 11, and an alkali transfer pneumatic valve 15 is provided on the branch; a branch is provided between the inlet pipeline of the gas compressor 2 and the inlet pipeline of the heat exchanger 3, and an eleventh ball valve 111 is provided on the branch; a branch is provided between the inlet pipeline of the heat exchanger 3 and the top outlet pipeline of the buffer tank 5, and the branch is provided between the fourth ball valve 104 and the fifth ball valve 105; a twelfth ball valve 112 is provided on the branch; a first liquid level gauge 17 and an online concentration meter 18 are provided on the alkali liquid tank 11; a second liquid level gauge 19 and an online acidity meter 20 are provided on the water washing tank 8; the first liquid level gauge 17, the online concentration meter 18 are interlocked with the alkali transfer pneumatic valve 15; the second liquid level gauge 19, the online acidity meter 20 are interlocked with the acid transfer pneumatic valve 13. The heat exchanger is preferably a coil heat exchanger. The water washing tank 8 is provided with a liquid level and acidity interlock; the alkali washing tank 11 is provided with a liquid level and concentration interlock.

[0036] The water washing tower 7, the alkali washing tower 10, the water washing tank 8 and the alkali washing tank 11 are all made of hard polyvinyl chloride, and the pipeline through which the HF-containing gas passes is made of fluorocarbon lined steel.

[0037] The refrigerant of the heat exchanger is preferably the residual cold of liquid nitrogen in the fine workshop, and the temperature is preferably -15 to -10°C; the flow rate of the heat exchanger is preferably 30L / min.

[0038] The content of NF3 in the anode gas of the electrolytic cell is 55%, the content of N2 is 37%, and the content of HF is 8%.

[0039] In this embodiment, HF in the anode gas is recovered by compression followed by condensation; and the unrecovered HF is then treated by primary water washing and primary alkali washing.

[0040] The operating liquid level of the water washing tank 8 is preferably 800-1000mm. When the mass concentration of hydrofluoric acid in the water washing tank reaches 40%-45%, start to transfer the hydrofluoric acid in the water washing tank 8 to the hydrofluoric acid storage tank; when the liquid level in the water washing tank 8 is as low as 200mm, stop transferring the acid solution to the hydrofluoric acid storage tank, and start to add pure water to the water washing tank 8 until the liquid level in the water washing tank returns to the preferred liquid level.

[0041] The operating liquid level of the alkali washing tank 11 is preferably 800-1000mm, and the alkali solution in the alkali washing tank is preferably a KOH aqueous solution with a mass concentration of 10%-15%. When the mass concentration of KOH in the alkali washing tank 11 is lower than 5%, the alkali solution in the alkali washing tank 11 is started to be transferred to the sewage treatment system; when the liquid level of the alkali washing tank 11 drops to 200mm, the transfer of the alkali solution to the sewage treatment system is stopped, and the alkali washing tank 11 is started to be supplemented with a KOH aqueous solution with a mass concentration of 15% until the liquid level of the alkali washing tank returns to the preferred liquid level.

[0042] HF gas recovery process: connect the HF gas inlet pipeline to the inlet of the gas compressor 2, open the gas compressor 2 and the heat exchanger 3 in sequence, and compress the HF gas pressure to 2MPa through the gas compressor 2 at a flow rate of 30L / min before entering the heat exchanger 3. The temperature is controlled at -10 to -15°C. The material outlet flow rate after the heat exchanger is controlled at 10L / min by the regulating valve 4 to ensure that the liquid nitrogen residual cooling liquefies the HF. The liquefied HF flows into the bottom of the buffer tank 5. When the HF in the buffer tank 5 reaches a certain weight, open the third ball valve 103 for transfer, so that the liquid phase HF is used for electrolyte configuration in the batching system; the remaining gas passes through the check valve 6, the fourth ball valve 104 and the fifth ball valve 105 from the top of the buffer tank 5 to the water washing tower 7, open the water supply valve 16 to add water to the water washing tank 8, and open the acid circulation pump 9 at a flow rate of 15L / min. During the absorption process, when the mass concentration of the acid solution in the online acidity meter 20 reaches more than 40%, the acid circulation pump 9 is turned off and the acid transfer pneumatic valve 13 is opened; when the liquid level value of the second liquid level meter 19 of the water washing tank 8 drops to 200mm, the acid transfer pneumatic valve 13 is turned off and the water supply valve 16 is opened; when the water washing tank 8 is replenished, the water supply valve 16 is closed after the liquid level value of the second liquid level meter 19 reaches 800mm. The water washing tank 8 is connected to the top of the alkali liquid tank 11 (the overflow direction is as follows Figure 1As shown), the gas after water absorption reaches the alkali washing tower 10 through the connecting area, and the alkali liquid is circulated in the alkali washing tower 10 by the alkali liquid pump 12 for alkali washing. The gas discharge valve at the top of the alkali washing tower is normally open and connected to the gas cabinet system through a pipeline. The alkali liquid in the alkali liquid tank 11 is a KOH aqueous solution with a mass concentration of 10% to 15%. The normal operating liquid level is controlled at 800mm. The alkali liquid pump 12 is turned on, and the alkali liquid three-way valve 14 adjusts the valve position to open the alkali liquid circulation, and the escaped HF gas is sprayed and absorbed. The alkali liquid tank 11 is provided with a first liquid level meter 17, an online concentration meter 18 and an alkali transfer pneumatic valve 15 interlocked. During the absorption process, the measured value of the online concentration meter 18 is lower than 5% or the liquid level of the first liquid level meter 17 is higher than 8. 00mm, the position of the alkali solution three-way valve 14 is adjusted, the circulation valve position is closed, the alkali solution pump 12 is stopped, and the alkali transfer pneumatic valve 15 is opened to transfer the alkali solution to the sewage treatment system; when the liquid level value of the first liquid level gauge of the alkali washing tank 11 drops to 200mm, the alkali transfer pneumatic valve 15 is closed, the valve position of the alkali solution three-way valve 14 is adjusted to the alkali replenishment valve position, and when the liquid level of the alkali solution tank 11 reaches 800mm, the valve position of the alkali solution three-way valve 14 is adjusted to the circulation valve position, and the alkali solution pump 12 is opened. When the alkali solution is added to the alkali washing tank 11, after the liquid level value of the first liquid level gauge 17 reaches 800mm, the valve position of the alkali solution three-way valve 14 is adjusted to the circulation valve position, the replenishment of alkali solution to the alkali washing tank 11 is stopped, and the circulation is reopened to absorb HF gas.

[0043] The description of the embodiments of the present invention is given for the purpose of illustration and description, and is not intended to be exhaustive or to limit the present invention to the disclosed form. Many modifications and variations are obvious to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention and to enable those of ordinary skill in the art to understand the present invention and design various embodiments with various modifications suitable for specific purposes.

Claims

1. A HF gas recovery system in the anode of the NF3 electrolytic production process, characterized in that: The gas compressor (2), the heat exchanger (3), the buffer tank (5), and the water washing tower (7) are connected in sequence through pipelines; the bottom of the water washing tower (7) is connected to the water washing tank (8); the bottom of the alkali washing tower (10) is connected to the alkali washing tank (11); the water washing tank (8) is communicated with the upper space of the alkali washing tank (11); the upper part of the alkali washing tower (10) is connected to the lower part of the alkali washing tank (11) through an alkali liquid pump (12) to form a loop; the top of the water washing tower (7) is connected to the lower part of the water washing tank (8) through an acid circulation pump (9) to form a loop; and a dehydrofluoric acid storage tank branch is provided on the connecting pipeline between the water washing tower and the acid circulation pump.

2. The HF gas recovery system in the anode of the electrolytic preparation of NF3 process according to claim 1, characterized in that: A first ball valve (101) is installed on the gas compressor inlet pipeline, and a second ball valve (102) is installed on the gas outlet pipeline; a regulating valve (4) is installed on the pipeline connecting the heat exchanger (3) and the middle of the buffer tank (5); a check valve (6), a fourth ball valve (104), and a fifth ball valve (105) are installed in sequence on the pipeline connecting the top of the buffer tank (5) and the upper part of the water washing tower (7); a third ball valve (103) is installed on the bottom of the buffer tank; a sixth ball valve (106) and a seventh ball valve (107) are installed on the pipeline connecting the water washing tower (7) and the acid circulation pump (9); an acid conversion pneumatic valve (13) is installed on the branch pipeline of the dehydrofluoric acid storage tank; and an eighth ball valve (108) is installed on the pipeline connecting the water washing tank (8) and the acid circulation pump (9).

3. The HF gas recovery system in the anode of the electrolytic preparation of NF3 process according to claim 1, characterized in that: A pure water branch is provided on the connecting pipeline between the water washing tower (7) and the acid circulation pump (9), and a water supply valve (16) is installed on the pure water branch pipeline.

4. The HF gas recovery system in the anode of the electrolytic preparation of NF3 process according to claim 1, characterized in that: A tenth ball valve (110) is installed on the pipeline connecting the alkali washing tower (10) and the alkali liquid pump (12); a ninth ball valve (109) is installed on the pipeline connecting the alkali liquid pump (12) and the alkali washing tank (11); an alkali liquid three-way valve (14) is installed on the pipeline connecting the ninth ball valve (109) and the alkali washing tank (11); a sewage treatment system branch is provided on the pipeline connecting the alkali liquid three-way valve (14) and the alkali washing tank (11), and an alkali transfer pneumatic valve (15) is provided on the branch.

5. The HF gas recovery system in the anode of the electrolytic preparation of NF3 process according to claim 1, characterized in that: A bypass is provided between the inlet pipeline of the gas compressor (2) and the inlet pipeline of the heat exchanger (3), and an eleventh (111) is provided on the bypass.

6. The HF gas recovery system in the anode of the electrolytic preparation of NF3 process according to claim 1, characterized in that: A bypass is provided between the inlet pipeline of the heat exchanger (3) and the outlet pipeline at the top of the buffer tank (5), and the bypass is provided between the fourth ball valve (104) and the fifth ball valve (105); a twelfth ball valve (112) is provided on the bypass.

7. The HF gas recovery system in the anode of the electrolytic preparation of NF3 according to claim 1, characterized in that: The alkali washing tank (11) is provided with a first liquid level meter (17) and an online concentration meter (18).

8. The HF gas recovery system in the anode of the electrolytic preparation of NF3 process according to claim 1, characterized in that: The water washing tank (8) is provided with a second liquid level meter (19) and an online acidity meter (20).

9. The HF gas recovery system in the anode of the electrolytic preparation of NF3 process according to claim 1, characterized in that: The first liquid level meter (17) and the online concentration meter (18) are interlocked with the alkali conversion pneumatic valve (15); the second liquid level meter (19) and the online acidity meter (20) are interlocked with the acid conversion pneumatic valve (13).

10. The HF gas recovery system in the anode of the electrolytic preparation of NF3 process according to claim 1, characterized in that: The material of the pipeline containing HF gas is fluorine-lined carbon steel or stainless steel; the material of the buffer tank is carbon steel, stainless steel or fluorine-lined carbon steel; the water washing tower, alkali washing tower, water washing tank and alkali washing tank are made of polytetrafluoroethylene or first-grade stainless steel, and are equipped with acid and alkali resistant fillers; the heat exchanger is a coil heat exchanger.

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