Process for recovering HF in cathode tail gas discharged by fluorine-making electrolytic bath

Abstract

The invention relates to a process for recovering HF in cathode tail gas discharged by a fluorine-making electrolytic bath. The process comprises the following steps: S1, putting a NaF filler into an absorption tower; s2, discharging cathode tail gas discharged by the fluorine preparation electrolytic bath into three absorption towers in sequence, and enabling NaF filler in the absorption towers to absorb HF in the cathode tail gas; s3, after the cathode tail gas passes through the three absorption towers to fully absorb HF, discharging the residual cathode tail gas from the top of the tail-end absorption tower, and introducing the residual cathode tail gas into a tail gas absorption tower for subsequent treatment; s4, switching to another group of three-stage HF absorption towers, and absorbing HF in the cathode tail gas; and S5, three absorption towers of the first group of three-stage HF absorption towers are activated and regenerated, the absorbed HF is volatilized, the volatilized HF is cooled through a cooler to obtain condensate, the purity of the HF in the condensate is larger than 98.5%, and the HF is recycled. The NaF filler used in the process can be repeatedly used and is less in consumption, the purity of the HF recovered by the process is as high as 98.5%, and the recovered HF can be directly used without further purification.

Description

Technical Field

[0001] The invention relates to the technical field of waste gas recovery and treatment in electrolytic fluorine production, and in particular to a process for recovering HF in cathode tail gas discharged from a fluorine production electrolytic cell. Background Art

[0002] Fluorine gas is very active in chemical properties and has strong oxidizing properties. It can react with almost all organic and inorganic substances except perfluorinated compounds. In industry, fluorine gas can be used as an oxidant in rocket fuel, a refrigerant, plasma etching, etc. With the development of semiconductor manufacturing processes and the need for environmental protection, there is a trend of using fluorine gas to replace fluorine for etching.

[0003] In the production process of fluorine by electrolysis, the cathode tail gas often contains a certain amount of HF. HF is a highly toxic substance that poses a serious threat to human health. At the same time, its direct emission will also cause serious pollution to the environment. Therefore, it is particularly important to effectively recover and treat the HF in the cathode tail gas. Traditional cathode tail gas treatment processes often have problems such as low recovery efficiency and unsatisfactory treatment effects. For example, although the hydrogen bubbling method can treat some HF, the absorption effect is limited and may introduce new safety issues.

[0004] Chinese patent CN114534453B discloses a process for recovering HF in cathode tail gas discharged from a nitrogen trifluoride electrolyzer, comprising the following steps: preparing a KF solution, and then discharging it into a primary KHF2 tank, a secondary KHF2 tank and a tertiary KHF2 tank in sequence; passing the electrolytic gas cathode gas into a tertiary HF absorption tower, and passing the KF solution in the primary KHF2 tank into the tertiary HF absorption tower to absorb HF; then, the absorbed cathode gas of the electrolyzer is continuously passed into the secondary HF absorption tower and the primary HF absorption tower in sequence, and after a certain amount of HF is absorbed, the solution in the primary KHF2 tank at the lower end of the tertiary absorption tower is discharged, the KHF2 in the solution is crystallized by cooling, the crystallized KHF2 is evaporated and dehydrated, and then heated, and then cooled to obtain HF with a purity of up to 98.5%. The above method adopts an alkali solution circulation spraying method, which can more fully remove the cathode gas, but the alkali solution will generate insoluble salts after the reaction with hydrogen fluoride. These salts will accumulate in the spray absorption tower to form scaling, affecting the spray effect and absorption efficiency; the alkali solution spray absorption method requires a large amount of alkali solution and water resources, and also requires the spray liquid to be circulated and regenerated, which will consume a lot of energy; at the same time, after the spray washing absorption tower absorbs HF, the internal pressure of the container will drop significantly, which may affect the production and operation of the electrolytic cell and even cause safety hazards. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a process for recovering HF in the cathode tail gas emitted by a fluorine-producing electrolytic cell. The recovery process of the present invention can not only ensure the efficient collection of HF in the cathode tail gas and achieve HF emission standards, but also save a lot of energy, reduce costs, and improve the utilization efficiency of the cathode tail gas.

[0006] To achieve the purpose of the present invention, the specific technical solutions provided by the present invention are as follows:

[0007] A process for recovering HF from cathode tail gas discharged from a fluorine production electrolytic cell comprises the following steps:

[0008] S1. Place NaF filler into an absorption tower, wherein the absorption tower comprises at least two groups of HF absorption towers, each group of HF absorption towers is provided with three HF absorption towers, and is divided into three-stage HF absorption towers;

[0009] S2, the cathode tail gas discharged from the fluorine production electrolytic cell is discharged into the first group of three-stage HF absorption towers through a Roots blower, and passes through the three absorption towers in sequence, so that the NaF filler in the absorption tower absorbs HF in the cathode tail gas;

[0010] S3, after the cathode tail gas passes through the three absorption towers to fully absorb HF, the remaining cathode tail gas is discharged from the top of the terminal absorption tower and passed into the tail gas absorption tower for subsequent treatment;

[0011] S4, switching to another set of three-stage HF absorption towers. When the first set of three-stage HF absorption towers reaches saturation in HF adsorption, the cathode tail gas is discharged into another set of three-stage HF absorption towers. The cathode tail gas passes through the three absorption towers in sequence, so that the NaF filler in the absorption tower absorbs HF in the cathode tail gas.

[0012] S5. Activate and regenerate the NaF fillers in the three absorption towers of the first group of three-stage HF absorption towers, heat the absorption towers to volatilize the absorbed HF, discharge the volatilized HF into the HF cooler, and obtain a condensate after cooling in the cooler. The purity of HF in the condensate is greater than 98.5%, and the condensate is transported back to the electrolytic cell for recycling.

[0013] Preferably, in step S1, the pore size of the NaF filler is 15-30 mm, the diameter of the absorption tower is 1200 mm, the height is 8 m, and the filling amount of the NaF filler is 60%-85% of the volume of the absorption tower.

[0014] Preferably, in step S1, the absorption towers include a first group of HF absorption towers and a second group of HF absorption towers, the first group of HF absorption towers includes a first absorption tower, a second absorption tower and a third absorption tower; the second group of HF absorption towers includes absorption tower A, absorption tower B and absorption tower C.

[0015] Preferably, in step S2, the cathode tail gas discharged from the fluorine production electrolytic cell is discharged into the first group of three-stage HF absorption towers through a Roots blower, and the flow rate of the Roots blower is 120-240m 3 / h, pressure is 8000pa.

[0016] Preferably, in step S2, the temperature of the first group of three HF absorption towers is set to 0-80°C.

[0017] Preferably, in step S4, after the adsorption of HF reaches saturation, the adsorption amount of HF is 180-240 kg.

[0018] Preferably, in step S4, the temperature of another group of three HF absorption towers is set to 0-80°C. After the three absorption towers fully absorb HF, the remaining cathode tail gas is discharged from the top of the terminal absorption tower and passed into the tail gas absorption tower for subsequent treatment.

[0019] Preferably, in step S5, the absorption tower is heated at a heating temperature of 280-420°C.

[0020] Preferably, in step S5, the HF cooler is divided into two stages of cooling, including a first cooler and a second cooler, and the cooling temperatures of the first cooler and the second cooler are set to -30 to -15°C.

[0021] Preferably, in step S5, the activated first set of three-stage HF absorption towers can subsequently continue to absorb HF in the cathode tail gas.

[0022] The process for recovering HF from cathode tail gas discharged from a fluorine-producing electrolytic cell of the present invention has the following beneficial effects:

[0023] 1. The purity of HF recovered by this process is as high as 98.5%. This high-purity HF can be directly reused by the electrolytic cell, thus significantly reducing production costs. Compared with other recovery methods, such as making HF acid or other by-products, this method has more advantages in recovery purity, so that the recovered HF can be used directly without further purification;

[0024] 2. This process sets up two groups of HF absorption towers, which can be used alternately for regeneration. The NaF filler used can be reused and consumed less, realizing the closed-loop management of the materials in the entire system, which not only reduces resource waste, but also complies with the clean production principle in chemical production, making this process show excellent performance in environmental protection and resource utilization;

[0025] 3. This process relies on the material absorption principle to absorb HF. Compared with other recovery methods that require high energy consumption, this method has obvious advantages in energy consumption. This low-energy absorption process helps to reduce production costs and also helps to reduce the impact on the environment;

[0026] 4. The industrial waste gas treated by this process meets the emission standards, thus avoiding safety accidents caused by electrolytic fluorine waste gas; at the same time, the emission of waste gas also meets the green environmental protection standards, which not only helps to protect the environment, but also reduces the cost of treating waste gas, making this process have higher application value in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a process flow chart of the HF recovery process of the present invention;

[0028] Explanation of the markings in the figure: 1. fluorine-producing electrolytic cell; 21. first absorption tower; 22. second absorption tower; 23. third absorption tower; 31. absorption tower A; 32. absorption tower B; 33. absorption tower C; 4. tail gas absorption tower; 51. first cooler; 52. second cooler; 61. first valve; 62. second valve; 63. third valve; 64. fourth valve. DETAILED DESCRIPTION

[0029] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation method, structure, characteristics and effects of the present invention are described in detail below in combination with the preferred embodiments.

[0030] Example 1

[0031] like Figure 1 As shown, this embodiment provides a process for recovering HF in cathode tail gas discharged from a fluorine-producing electrolytic cell, comprising the following steps:

[0032] S1. Select spherical NaF filler, the pore size of the NaF filler is 15-30 mm, put the NaF filler into an HF absorption tower, the diameter of the HF absorption tower is 1200 mm, the height is 8 m, the filling amount of the NaF filler is 80% of the volume of the absorption tower, the HF absorption tower includes a first group of HF absorption towers and a second group of HF absorption towers, each group of HF absorption towers is provided with three HF absorption towers, and the HF absorption tower is divided into three stages to absorb HF in the cathode tail gas;

[0033] The first group of HF absorption towers includes a first absorption tower, a second absorption tower and a third absorption tower; the second group of HF absorption towers includes absorption tower A, absorption tower B and absorption tower C;

[0034] S2, the cathode tail gas discharged from the fluorine production electrolytic cell is discharged into the cathode tail gas main pipeline through the Roots blower. The flow rate of the Roots blower is 180m 3 / h, pressure is 8000pa, the first valve is opened, the cathode tail gas enters the first group of HF absorption tower after passing through the main pipeline, the temperature of the first group of HF absorption tower is controlled to be 20°C, and the NaF filler in the first group of HF absorption tower absorbs HF in three stages;

[0035] Specifically, after passing through the main pipeline, the cathode tail gas first enters the first absorption tower in the first group of HF absorption towers to absorb HF in the cathode tail gas; the cathode tail gas that is not completely absorbed is discharged from the top of the first absorption tower and passed into the second absorption tower, and the HF in the cathode tail gas is continuously absorbed in the second absorption tower; the cathode tail gas that is not completely absorbed is discharged from the top of the second absorption tower and passed into the third absorption tower, and the HF in the cathode tail gas is continuously absorbed in the third absorption tower;

[0036] S3, after the cathode tail gas passes through the first group of HF absorption towers to fully absorb HF, the remaining cathode tail gas is discharged from the top of the third absorption tower and passed into the tail gas absorption tower for subsequent treatment;

[0037] S4, after the first group of HF absorption towers adsorb HF to saturation, switch to another group of three-stage HF absorption towers. At this time, the adsorption amount of HF adsorbed by the first group of HF absorption towers is about 200kg. The pipeline connecting the first group of HF absorption towers and the second group of HF absorption towers is operated with pipeline valves, the first valve is closed, and the second valve is opened. At this time, the cathode tail gas passes through the Roots blower, passes through the main pipeline, and enters the absorption tower A, absorption tower B and absorption tower C of the second group of HF absorption towers in sequence. The NaF filler in the second group of HF absorption towers absorbs HF in three stages. The temperature of the HF absorption tower is controlled to be 20°C. After the cathode tail gas fully absorbs HF through the second group of HF absorption towers, the remaining cathode tail gas is discharged from the top of the absorption tower C and passed into the tail gas absorption tower for subsequent treatment;

[0038] S5, activating and regenerating the first group of HF absorption towers, heating the first absorption tower, the second absorption tower and the third absorption tower of the first group of HF absorption towers to volatilize the absorbed HF, the heating temperature is 380° C., and at the same time, opening the third valve to discharge the volatilized HF into a two-stage HF cooler, the two-stage HF cooler includes a first cooler and a second cooler, the volatilized HF is cooled by the first cooler and the second cooler in sequence to obtain a condensate, and the cooling temperature of the first cooler and the second cooler is set to -30° C.;

[0039] The condensate was tested and the purity of HF in the cooled condensate was 98.5%. The condensate containing HF was transported back to the electrolytic cell for recycling. The first set of HF absorption towers after activation could continue to absorb HF in the cathode tail gas.

[0040] Example 2

[0041] This embodiment provides a process for recovering HF from cathode tail gas discharged from a fluorine production electrolytic cell, comprising the following steps:

[0042] S1. Select spherical NaF filler, the pore size of the NaF filler is 15-30 mm, put the NaF filler into an HF absorption tower, the diameter of the HF absorption tower is 1200 mm, the height is 8 m, the filling amount of the NaF filler is 85% of the volume of the absorption tower, the HF absorption tower includes a first group of HF absorption towers and a second group of HF absorption towers, each group of HF absorption towers is provided with three HF absorption towers, and the HF absorption towers are divided into three stages to absorb HF in the cathode tail gas;

[0043] The first group of HF absorption towers includes a first absorption tower, a second absorption tower and a third absorption tower; the second group of HF absorption towers includes absorption tower A, absorption tower B and absorption tower C;

[0044] S2. The cathode tail gas discharged from the fluorine production electrolytic cell is discharged into the cathode tail gas main pipeline through the Roots blower. The flow rate of the Roots blower is 120m 3 / h, pressure is 8000pa, the first valve is opened, the cathode tail gas enters the first group of HF absorption tower after passing through the main pipeline, the temperature of the first group of HF absorption tower is controlled to be 80°C, and the NaF filler in the first group of HF absorption tower absorbs HF in three stages;

[0045] Specifically, after passing through the main pipeline, the cathode tail gas first enters the first absorption tower in the first group of HF absorption towers to absorb HF in the cathode tail gas; the cathode tail gas that is not completely absorbed is discharged from the top of the first absorption tower and passed into the second absorption tower, and the HF in the cathode tail gas is continuously absorbed in the second absorption tower; the cathode tail gas that is not completely absorbed is discharged from the top of the second absorption tower and passed into the third absorption tower, and the HF in the cathode tail gas is continuously absorbed in the third absorption tower;

[0046] S3, after the cathode tail gas passes through the first group of HF absorption towers to fully absorb HF, the remaining cathode tail gas is discharged from the top of the third absorption tower and passed into the tail gas absorption tower for subsequent treatment;

[0047] S4, after the first group of HF absorption towers adsorb HF to saturation, switch to another group of three-stage HF absorption towers. At this time, the adsorption amount of HF adsorbed by the first group of HF absorption towers is about 220kg, and the pipeline valve operation is performed on the connecting pipelines between the first group of HF absorption towers and the second group of HF absorption towers, the first valve is closed, and the second valve is opened. At this time, the cathode tail gas enters the absorption tower A, absorption tower B and absorption tower C of the second group of HF absorption towers in sequence after passing through the main pipeline. The NaF filler in the second group of HF absorption towers absorbs HF in three stages, and the temperature of the HF absorption tower is controlled to be 0°C. After the cathode tail gas fully absorbs HF through the second group of HF absorption towers, the remaining cathode tail gas is discharged from the top of the absorption tower C and passed into the tail gas absorption tower for subsequent treatment;

[0048] S5, activating and regenerating the first group of HF absorption towers, heating the first absorption tower, the second absorption tower and the third absorption tower of the first group of HF absorption towers to volatilize the absorbed HF, the heating temperature is 420° C., and at the same time, opening the third valve to discharge the volatilized HF into a two-stage HF cooler, the two-stage HF cooler includes a first cooler and a second cooler, the volatilized HF is cooled by the first cooler and the second cooler in sequence to obtain a condensate, and the cooling temperature of the first cooler and the second cooler is set to -30° C.;

[0049] The condensate was tested and the purity of HF in the cooled condensate was 98.6%. The condensate containing HF was transported back to the electrolytic cell for recycling. The first set of HF absorption towers after activation could continue to absorb HF in the cathode tail gas.

[0050] Example 3

[0051] like Figure 1 As shown, this embodiment provides a process for recovering HF in cathode tail gas discharged from a fluorine-producing electrolytic cell, comprising the following steps:

[0052] S1. Select spherical NaF filler, the pore size of the NaF filler is 15-30 mm, put the NaF filler into the HF absorption tower, the diameter of the HF absorption tower is 1200 mm, the height is 8 m, the filling amount of the NaF filler is 70% of the volume of the absorption tower, the HF absorption tower includes a first group of HF absorption towers and a second group of HF absorption towers, each group of HF absorption towers is provided with three HF absorption towers, and the HF absorption tower is divided into three stages to absorb HF in the cathode tail gas;

[0053] The first group of HF absorption towers includes a first absorption tower, a second absorption tower and a third absorption tower; the second group of HF absorption towers includes absorption tower A, absorption tower B and absorption tower C;

[0054] S2, the cathode tail gas discharged from the fluorine production electrolytic cell is discharged into the cathode tail gas main pipeline through the Roots blower. The flow rate of the Roots blower is 240m3 / h, pressure is 8000pa, the first valve is opened, the cathode tail gas enters the first group of HF absorption tower after passing through the main pipeline, the temperature of the first group of HF absorption tower is controlled to be 0°C, and the NaF filler in the first group of HF absorption tower absorbs HF in three stages;

[0055] Specifically, after passing through the main pipeline, the cathode tail gas first enters the first absorption tower in the first group of HF absorption towers to absorb HF in the cathode tail gas; the cathode tail gas that is not completely absorbed is discharged from the top of the first absorption tower and passed into the second absorption tower, and the HF in the cathode tail gas is continuously absorbed in the second absorption tower; the cathode tail gas that is not completely absorbed is discharged from the top of the second absorption tower and passed into the third absorption tower, and the HF in the cathode tail gas is continuously absorbed in the third absorption tower;

[0056] S3, after the cathode tail gas passes through the first group of HF absorption towers to fully absorb HF, the remaining cathode tail gas is discharged from the top of the third absorption tower and passed into the tail gas absorption tower for subsequent treatment;

[0057] S4, after the first group of HF absorption towers adsorb HF to saturation, switch to another group of three-stage HF absorption towers. At this time, the adsorption amount of HF adsorbed by the first group of HF absorption towers is about 240kg, and the pipeline valve operation is performed on the connecting pipelines between the first group of HF absorption towers and the second group of HF absorption towers, the first valve is closed, and the second valve is opened. At this time, the cathode tail gas enters the absorption tower A, absorption tower B and absorption tower C of the second group of HF absorption towers in sequence after passing through the main pipeline. The NaF filler in the second group of HF absorption towers absorbs HF in three stages, and the temperature of the HF absorption tower is controlled to be 0°C. After the cathode tail gas fully absorbs HF through the second group of HF absorption towers, the remaining cathode tail gas is discharged from the top of the absorption tower C and passed into the tail gas absorption tower for subsequent treatment;

[0058] S5, activating and regenerating the first group of HF absorption towers, heating the first absorption tower, the second absorption tower and the third absorption tower of the first group of HF absorption towers to volatilize the absorbed HF, the heating temperature is 280° C., and at the same time, opening the third valve to discharge the volatilized HF into a two-stage HF cooler, the two-stage HF cooler includes a first cooler and a second cooler, the volatilized HF is cooled by the first cooler and the second cooler in sequence to obtain a condensate, and the cooling temperature of the first cooler and the second cooler is set to -15° C.;

[0059] The condensate was tested and the purity of HF in the cooled condensate was 98.8%. The condensate containing HF was transported back to the electrolytic cell for recycling. The first group of HF absorption towers after activation could continue to absorb HF in the cathode tail gas.

[0060] Example 4

[0061] like Figure 1 As shown, this embodiment provides a process for recovering HF in cathode tail gas discharged from a fluorine-producing electrolytic cell, comprising the following steps:

[0062] S1. Select spherical NaF filler, the pore size of the NaF filler is 15-30 mm, put the NaF filler into the HF absorption tower, the diameter of the HF absorption tower is 1200 mm, the height is 8 m, the filling amount of the NaF filler is 60% of the volume of the absorption tower, the HF absorption tower includes a first group of HF absorption towers and a second group of HF absorption towers, each group of HF absorption towers is provided with three HF absorption towers, and the HF absorption tower is divided into three stages to absorb HF in the cathode tail gas;

[0063] The first group of HF absorption towers includes a first absorption tower, a second absorption tower and a third absorption tower; the second group of HF absorption towers includes absorption tower A, absorption tower B and absorption tower C;

[0064] S2. The cathode tail gas discharged from the fluorine production electrolytic cell is discharged into the cathode tail gas main pipeline through the Roots blower. The flow rate of the Roots blower is 200m 3 / h, pressure is 8000pa, the first valve is opened, the cathode tail gas enters the first group of HF absorption towers after passing through the main pipeline, the temperature of the first group of HF absorption towers is controlled to be 50°C, and the NaF filler in the first group of HF absorption towers absorbs HF in three stages;

[0065] Specifically, after passing through the main pipeline, the cathode tail gas first enters the first absorption tower in the first group of HF absorption towers to absorb HF in the cathode tail gas; the cathode tail gas that is not completely absorbed is discharged from the top of the first absorption tower and passed into the second absorption tower, and the HF in the cathode tail gas is continuously absorbed in the second absorption tower; the cathode tail gas that is not completely absorbed is discharged from the top of the second absorption tower and passed into the third absorption tower, and the HF in the cathode tail gas is continuously absorbed in the third absorption tower;

[0066] S3, after the cathode tail gas passes through the first group of HF absorption towers to fully absorb HF, the remaining cathode tail gas is discharged from the top of the third absorption tower and passed into the tail gas absorption tower for subsequent treatment;

[0067] S4, after the first group of HF absorption towers adsorb HF to saturation, switch to another group of three-stage HF absorption towers. At this time, the adsorption amount of HF adsorbed by the first group of HF absorption towers is about 180kg, and the pipeline valve operation is performed on the connecting pipelines between the first group of HF absorption towers and the second group of HF absorption towers, the first valve is closed, and the second valve is opened. At this time, the cathode tail gas enters the absorption tower A, absorption tower B and absorption tower C of the second group of HF absorption towers in sequence after passing through the main pipeline. The NaF filler in the second group of HF absorption towers absorbs HF in three stages, and the temperature of the HF absorption tower is controlled to be 30°C. After the cathode tail gas fully absorbs HF through the second group of HF absorption towers, the remaining cathode tail gas is discharged from the top of the absorption tower C and passed into the tail gas absorption tower for subsequent treatment;

[0068] S5, activating and regenerating the first group of HF absorption towers, heating the first absorption tower, the second absorption tower and the third absorption tower of the first group of HF absorption towers to volatilize the absorbed HF, the heating temperature is 400° C., and at the same time, opening the third valve to discharge the volatilized HF into a two-stage HF cooler, the two-stage HF cooler includes a first cooler and a second cooler, the volatilized HF is cooled by the first cooler and the second cooler in sequence to obtain a condensate, and the cooling temperature of the first cooler and the second cooler is set to -25° C.;

[0069] The condensate was tested and the purity of HF in the cooled condensate was 98.5%. The condensate containing HF was transported back to the electrolytic cell for recycling. The first set of HF absorption towers after activation could continue to absorb HF in the cathode tail gas.

[0070] Comparative Example 1

[0071] Compared with Example 1, in the control steps S2 and S4, the temperature of the HF absorption tower is 100° C. After the cathode tail gas passes through the three-stage HF absorption tower to absorb HF, the remaining cathode tail gas is passed into the tail gas absorption tower. At this time, the content of hydrogen fluoride in the remaining cathode tail gas is detected before the tail gas absorption tower. The content of hydrogen fluoride is 0.32%, indicating that the hydrogen fluoride is not completely absorbed.

[0072] Comparative Example 2

[0073] Compared with Example 1, in step S5, the cooling temperature of the first cooler and the second cooler is set to -40°C, and the condensate is tested. The test results show that the purity of HF in the condensate is 97.6%. This indicates that when the absorption tower is activated and regenerated, the volatilized HF is condensed, and other impurities absorbed by the absorption tower are also condensed by the cooler and finally mixed into the condensate, so that the concentration of HF is reduced.

[0074] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A process for recovering HF from cathode tail gas discharged from a fluorine production electrolytic cell, characterized in that: The following steps are involved: S1. Place NaF filler into an absorption tower, wherein the absorption tower comprises at least two groups of HF absorption towers, each group of HF absorption towers is provided with three HF absorption towers, and is divided into three-stage HF absorption towers; S2, discharge the cathode tail gas discharged from the fluorine production electrolytic cell into the first group of three-stage HF absorption towers, and pass through the three absorption towers in sequence, so that the NaF filler in the absorption tower absorbs HF in the cathode tail gas; S3, after the cathode tail gas passes through the three absorption towers to fully absorb HF, the remaining cathode tail gas is discharged from the top of the terminal absorption tower and passed into the tail gas absorption tower for subsequent treatment; S4, switching to another set of three-stage HF absorption towers. When the first set of three-stage HF absorption towers reaches saturation in HF adsorption, the cathode tail gas is discharged into another set of three-stage HF absorption towers. The cathode tail gas passes through the three absorption towers in sequence, so that the NaF filler in the absorption tower absorbs HF in the cathode tail gas. S5. Activate and regenerate the NaF fillers in the three absorption towers of the first group of three-stage HF absorption towers, heat the absorption towers to volatilize the absorbed HF, discharge the volatilized HF into the HF cooler, and obtain a condensate after cooling in the cooler. The purity of HF in the condensate is greater than 98.5%, and the condensate is transported back to the electrolytic cell for recycling.

2. The process for recovering HF from cathode tail gas discharged from a fluorine production electrolytic cell according to claim 1, characterized in that: In step S1, the pore size of the NaF filler is 15-30 mm, the diameter of the absorption tower is 1200 mm, the height is 8 m, and the filling amount of the NaF filler is 60%-85% of the volume of the absorption tower.

3. The process for recovering HF from cathode tail gas discharged from a fluorine production electrolytic cell according to claim 1, characterized in that: In step S1 , the absorption towers include a first group of HF absorption towers and a second group of HF absorption towers. The first group of HF absorption towers includes a first absorption tower, a second absorption tower and a third absorption tower; the second group of HF absorption towers includes absorption tower A, absorption tower B and absorption tower C.

4. The process for recovering HF from cathode tail gas discharged from a fluorine production electrolytic cell according to claim 1, characterized in that: In step S2, the cathode tail gas discharged from the fluorine production electrolytic cell is discharged into the first group of three-stage HF absorption towers through a Roots blower. The flow rate of the Roots blower is 120-240m 3 / h, pressure is 8000pa.

5. The process for recovering HF from cathode tail gas discharged from a fluorine production electrolytic cell according to claim 1, characterized in that: In step S2, the temperature of the first group of three HF absorption towers is set to 0-80°C.

6. The process for recovering HF from cathode tail gas discharged from a fluorine production electrolytic cell according to claim 1, characterized in that: In step S4, after HF adsorption reaches saturation, the adsorption amount of HF is 180 to 240 kg.

7. The process for recovering HF from cathode tail gas discharged from a fluorine production electrolytic cell according to claim 1, characterized in that: In step S4, the temperature of another group of three HF absorption towers is set to 0-80°C. After the three absorption towers fully absorb HF, the remaining cathode tail gas is discharged from the top of the terminal absorption tower and passed into the tail gas absorption tower for subsequent treatment.

8. The process for recovering HF from cathode tail gas discharged from a fluorine production electrolytic cell according to claim 1, characterized in that: In step S5, the absorption tower is heated at a temperature of 280-420°C.

9. The process for recovering HF from cathode tail gas discharged from a fluorine production electrolytic cell according to claim 1, characterized in that: In step S5, the HF cooler is divided into two stages of cooling, including a first cooler and a second cooler, and the cooling temperatures of the first cooler and the second cooler are set to -30 to -15°C.

10. The process for recovering HF from cathode tail gas discharged from a fluorine production electrolytic cell according to claim 1, characterized in that: In step S5, the activated first set of three-stage HF absorption towers can continue to absorb HF in the cathode tail gas.

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