A treatment system for cathode tail gas of nitrogen trifluoride electrolyzer

Abstract

The invention discloses a treatment system for cathode tail gas of a nitrogen trifluoride electrolyzer, comprising: an electrolyzer cathode gas main pipeline, an HF condenser, an HF absorption device, and an HF recovery tank; the cathode chambers of all electrolyzers are connected to the electrolyzer cathode gas main pipeline through a cathode tail gas transmission pipeline; the HF condenser has a gas inlet to be condensed, a condensed liquid outlet, a condensed gas outlet, a condensed medium inlet, and a condensed medium outlet; the gas inlet to be condensed is connected to the electrolyzer cathode gas main pipeline, the condensed liquid outlet is connected to the HF recovery tank through an HF recovery pipeline connected with a drain valve, and the condensed gas outlet is connected to the HF absorption device through a gas supply pipeline; the HF absorption device includes a three-stage absorption tower assembly. The present invention can realize the collection and absorption of HF in the cathode tail gas, and realize the standard emission of HF in the cathode tail gas of the electrolyzer.

Description

Technical Field

[0001] The invention relates to the technical field of cathode tail gas treatment of a nitrogen trifluoride electrolytic cell, and in particular to a treatment system for cathode tail gas of a nitrogen trifluoride electrolytic cell. Background Art

[0002] The chemical formula of nitrogen trifluoride is NF3. It is a colorless, odorless, stable gas at room temperature and a strong oxidant. Nitrogen trifluoride is an excellent plasma etching gas in the microelectronics industry. For etching silicon and silicon nitride, nitrogen trifluoride has a higher etching rate and selectivity than carbon tetrafluoride and a mixture of carbon tetrafluoride and oxygen, and has no pollution to the surface. Especially in the etching of integrated circuit materials with a thickness of less than 1.5um, nitrogen trifluoride has a very excellent etching rate and selectivity, leaving no residue on the surface of the etched object, and is also a very good cleaning agent. With the development of nanotechnology and the large-scale development of the electronics industry, its demand will increase day by day.

[0003] At present, the waste gas generated by nitrogen trifluoride electrolysis is mainly treated by chemical neutralization reaction in China. The treatment of HF in the cathode tail gas generated by nitrogen trifluoride electrolysis also needs to solve the problem of whether the HF in the cathode tail gas meets the emission standards after purification. In the existing technology, the HF in the cathode tail gas is not recycled, but directly purified and discharged to meet the standards, which is a great waste of production resources and increases the cost of industrial production. Summary of the invention

[0004] In view of this, the present invention provides a system and method for treating cathode tail gas of a nitrogen trifluoride electrolyzer, which can collect and absorb HF in the cathode tail gas and achieve standard emission of HF in the cathode tail gas of the electrolyzer.

[0005] In order to solve the above technical problems, the present invention is implemented as follows.

[0006] A system for treating cathode tail gas of a nitrogen trifluoride electrolytic cell, comprising: a cathode gas main pipeline of the electrolytic cell, an HF condenser, an HF absorption device, and an HF recovery tank;

[0007] The cathode chambers of all electrolyzers are connected to the cathode gas main pipeline of the electrolyzer through the cathode tail gas transmission pipeline;

[0008] The HF condenser has a gas inlet to be condensed, a condensed liquid outlet, a condensed gas outlet, a condensed medium inlet and a condensed medium outlet; the gas inlet to be condensed is connected to the cathode gas main pipeline of the electrolyzer, the condensed liquid outlet is connected to the HF recovery tank through an HF recovery pipeline connected to a drain valve, and the condensed gas outlet is connected to the HF absorption device through a gas supply pipeline;

[0009] The HF absorption device comprises a three-stage absorption tower assembly; each stage absorption tower assembly comprises a spray absorption tower and an acid tank: the acid liquid outlet of the acid tank is connected to the circulating liquid adding port of the previous stage acid tank and the absorption liquid inlet of the current stage spray absorption tower through an acid liquid circulation pipeline with a circulation pump; the acid liquid outlet at the bottom of the spray absorption tower is connected to the acid tank of the current stage through an acid liquid recovery pipeline; the top of the spray absorption tower is connected to the bottom of the next stage spray absorption tower through an HF discharge pipeline; wherein, the acid liquid outlet of the first stage acid tank is connected to the absorption liquid inlet of the current stage spray absorption tower only through the acid liquid circulation pipeline with a circulation pump, the acid liquid outlet of the first stage acid tank is used as a finished acid discharge port, the circulating liquid adding port of the tertiary acid tank is connected to an external pure water adding device, and the HF discharge pipeline of the tertiary spray absorption tower is connected to an external discharge tower.

[0010] Preferably, the cathode tail gas transmission pipeline, the acid liquid circulation pipeline, the HF discharge pipeline and the acid liquid recovery pipeline are all provided with valves.

[0011] Preferably, the condensing medium introduced into the HF condenser is cold nitrogen.

[0012] Preferably, the inlet for the gas to be condensed is arranged at the lower part of the HF condenser, the outlet for the condensed liquid is arranged at the bottom of the HF condenser, and the outlet for the condensed gas is arranged at the top of the HF condenser.

[0013] Preferably, there are two HF condensers connected in parallel; valves are provided on the pipelines connected to the gas inlet to be condensed, the condensed liquid outlet, the condensed gas outlet, the condensing medium inlet and the condensing medium outlet of each HF condenser.

[0014] Preferably, the nominal diameter of the cathode gas main pipeline of the electrolytic cell is 150 mm, and the pipeline is made of carbon steel lined with fluorine.

[0015] Preferably, the condensation temperature of the HF condenser is -45±15°C, and the condenser pressure is normal pressure.

[0016] Preferably, a temperature sensor and a heating device are provided in the spray absorption tower to maintain the temperature of the spray absorption tower at 20±5° C.; and the pressure of the spray absorption tower is at normal pressure.

[0017] The present invention provides a method for treating cathode tail gas of a nitrogen trifluoride electrolytic cell, using any one of the above-mentioned devices for treating cathode tail gas of a nitrogen trifluoride electrolytic cell; the method comprises:

[0018] Step 1: The cathode tail gas generated by the electrolytic cell is transported from the cathode gas main pipeline of the electrolytic cell to the HF condenser for condensation treatment;

[0019] Step 2, the HF condenser deeply condenses the cathode tail gas sent, condenses most of the HF gas in the cathode tail gas into HF liquid, and the HF liquid is regularly discharged from the lower drain valve of the HF condenser to the HF recovery tank; the cathode tail gas is condensed by the condenser and sent to the HF absorption device for purification;

[0020] Step 3, the condensed cathode tail gas continuously enters the primary spray absorption tower, the secondary spray absorption tower and the tertiary spray absorption tower in the HF absorption device; the acid liquid produced by the spray absorption tower enters the acid tank of this stage; pure water is pumped into the tertiary acid tank, and the circulating water in the tertiary acid tank is pumped into the secondary acid tank in sequence by a circulating pump, and the circulating water in the secondary acid tank is pumped into the primary acid tank to ensure that the pure water fully absorbs the HF in the cathode gas, and the primary acid tank releases the finished acid with the required concentration through the finished acid discharge port; the circulating water of each acid tank is further pumped into the spray absorption tower of this stage for further absorbing HF.

[0021] Beneficial effects:

[0022] (1) The cathode tail gas of the electrolytic cell mainly consists of hydrogen, hydrogen fluoride and nitrogen. In the case of continuous production of nitrogen trifluoride, the HF in the cathode tail gas produced by the electrolytic cell can be completely collected and absorbed by using a condenser and an HF absorption device, so that the HF in the cathode tail gas of the electrolytic cell can be discharged in compliance with the emission standards.

[0023] (2) By adding a condenser, most of the HF in the tail gas is condensed into HF liquid and recovered. The subsequent HF absorption device only needs to use a three-stage absorption tower to achieve the recovery of almost all HF, which not only ensures that the tail gas meets the emission standards and meets environmental protection requirements, but also reduces a certain cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a block diagram of the composition of the system for treating cathode tail gas of a nitrogen trifluoride electrolyzer. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0026] The present invention provides a system for treating cathode tail gas of a nitrogen trifluoride electrolyzer, such as Figure 1 As shown, it includes an electrolytic cell cathode gas main pipeline, an HF condenser, an HF absorption device, and an HF recovery tank.

[0027] The cathode chambers of all electrolyzers are connected to the cathode gas main pipeline of the electrolyzer through the cathode tail gas transmission pipeline. The nominal diameter of the cathode gas main pipeline of the electrolyzer is preferably 150 mm, and the pipeline material is a carbon steel pipe lined with fluorine to prevent corrosion of the pipeline by the cathode gas. A valve can be set on the cathode tail gas transmission pipeline to control which electrolyzers participate in the tail gas treatment of this system.

[0028] The HF condenser has a gas inlet to be condensed, a condensed liquid outlet, a condensed gas outlet, a condensed medium inlet and a condensed medium outlet. The gas inlet to be condensed is arranged at the lower part of the HF condenser, the condensed liquid outlet is arranged at the bottom of the HF condenser, and the condensed gas outlet is arranged at the top of the HF condenser. The condensed medium inlet and the condensed medium outlet are arranged at the lower part and the upper part of the HF condenser respectively. The condensed medium is cold nitrogen, which flows from bottom to top, so that the condensation temperature of the HF condenser is controlled at -45±15℃. The condenser is in normal pressure.

[0029] The inlet of the gas to be condensed is connected to the cathode gas main pipeline of the electrolyzer, the outlet of the condensed liquid is connected to the HF recovery tank through the HF recovery pipeline connected with a liquid discharge valve, and the outlet of the condensed gas is connected to the HF absorption device through the gas supply pipeline.

[0030] In this embodiment, there are two HF condensers, one is a main device and the other is a standby device, and the two are connected in parallel. Valves are provided on the pipelines connected to the gas inlet to be condensed, the condensed liquid outlet, the condensed gas outlet, the condensed medium inlet and the condensed medium outlet of each HF condenser. The switching of the currently used device is achieved by valve switch control.

[0031] The HF absorption device includes a three-stage absorption tower assembly. Since the condenser has condensed most of the HF into liquid for recovery, the condensed cathode gas only contains a small amount of HF gas, so only three-stage absorption towers are needed to absorb most of the HF and make finished acid for recovery.

[0032] like Figure 1 As shown, each level of absorption tower assembly includes a spray absorption tower and an acid tank: the acid outlet of the acid tank is connected to the circulating liquid addition port of the previous level acid tank and the absorption liquid inlet of the current level spray absorption tower through an acid circulation pipeline with a circulation pump; the acid outlet at the bottom of the spray absorption tower is connected to the current level acid tank through an acid recovery pipeline; the top of the spray absorption tower is connected to the gas inlet at the bottom of the next level spray absorption tower through an HF discharge pipeline; wherein, the acid outlet of the first level acid tank is connected to the absorption liquid inlet of the current level spray absorption tower only through an acid circulation pipeline with a circulation pump, the acid outlet of the first level acid tank is used as the finished acid discharge port, the circulating liquid addition port of the third level acid tank is connected to the pure water installation equipment, and the HF discharge pipeline of the third level spray absorption tower is connected to the external discharge tower. wherein, valves can be set in the acid circulation pipeline, the HF discharge pipeline, and the acid circulation pipeline to achieve closure during equipment maintenance.

[0033] The spray absorption tower is provided with a temperature sensor and a heating device, and the temperature of the spray absorption tower is set to 20±5° C.; the pressure of the spray absorption tower is at normal pressure.

[0034] The cathode tail gas treatment method using the above device comprises the following steps:

[0035] Step 1, cathode tail gas recovery process: the cathode tail gas generated by the electrolytic cell is transported from the cathode gas main pipeline of the electrolytic cell to the HF condenser for condensation treatment.

[0036] Step 2, cathode tail gas condensation process: the HF condenser deeply condenses the cathode tail gas sent from the cathode tail gas recovery process, and condenses most of the HF gas in the cathode tail gas into HF liquid. The HF liquid is regularly discharged from the lower drain valve of the HF condenser to the HF recovery tank; the cathode tail gas is condensed by the condenser and sent to the next process for purification.

[0037] Step 3, cathode tail gas purification process: the condensed cathode tail gas continuously enters the first-stage spray absorption tower, the second-stage spray absorption tower and the third-stage spray absorption tower in the HF absorption device. The acid liquid produced by the spray absorption tower enters the acid tank of this stage; pure water is pumped into the third-stage acid tank, and the circulating water in the third-stage acid tank is pumped into the second-stage acid tank in turn by a circulating pump, and the circulating water in the second-stage acid tank is pumped into the first-stage acid tank to ensure that the pure water fully absorbs the HF in the cathode gas until the first-stage acid tank releases the finished acid with the required concentration through the finished acid discharge port. The circulating water of each first-stage acid tank is further pumped into the spray absorption tower of this stage for further absorption of HF.

[0038] In the treatment process of the present invention, the cathode tail gas of the electrolytic cell mainly comprises hydrogen, hydrogen fluoride and nitrogen. Under the condition of continuously producing nitrogen trifluoride, the HF in the cathode tail gas produced by the electrolytic cell is completely collected and absorbed by using a condenser and an HF absorption device, so that the HF in the cathode tail gas of the electrolytic cell can be discharged in compliance with the emission standards.

[0039] The treatment process of the cathode tail gas of the electrolyzer can reduce the HF content in the tail gas to below 3ppm, and at the same time can recover more than 50% of the anhydrous HF for reuse in production, and the remaining 50% can be made into hydrofluoric acid and sold as a by-product. This can not only ensure that the tail gas meets the emission standards and meets environmental protection requirements, but also reduce certain costs.

[0040] The above specific embodiments only describe the design principle of the present invention. The shapes and names of the components in the description may be different and are not limited. Therefore, those skilled in the art in the field of the present invention may modify or replace the technical solutions recorded in the above embodiments; and these modifications and replacements do not deviate from the creative purpose and technical solutions of the present invention and should all fall within the protection scope of the present invention.

Claims

1. A system for treating cathode tail gas of a nitrogen trifluoride electrolyzer, characterized in that: include: Electrolyzer cathode gas main pipeline, HF condenser, HF absorption device, HF recovery tank; The cathode chambers of all electrolyzers are connected to the cathode gas main pipeline of the electrolyzer through the cathode tail gas transmission pipeline; The HF condenser has a gas inlet to be condensed, a condensed liquid outlet, a condensed gas outlet, a condensed medium inlet and a condensed medium outlet; the gas inlet to be condensed is connected to the cathode gas main pipeline of the electrolyzer, the condensed liquid outlet is connected to the HF recovery tank through an HF recovery pipeline connected to a drain valve, and the condensed gas outlet is connected to the HF absorption device through a gas supply pipeline; The HF absorption device comprises a three-stage absorption tower assembly; each stage absorption tower assembly comprises a spray absorption tower and an acid tank: the acid liquid outlet of the acid tank is connected to the circulating liquid adding port of the previous stage acid tank and the absorption liquid inlet of the current stage spray absorption tower through an acid liquid circulation pipeline with a circulation pump; the acid liquid outlet at the bottom of the spray absorption tower is connected to the acid tank of the current stage through an acid liquid recovery pipeline; the top of the spray absorption tower is connected to the bottom of the next stage spray absorption tower through an HF discharge pipeline; wherein, the acid liquid outlet of the first stage acid tank is connected to the absorption liquid inlet of the current stage spray absorption tower only through the acid liquid circulation pipeline with a circulation pump, the acid liquid outlet of the first stage acid tank is used as a finished acid discharge port, the circulating liquid adding port of the tertiary acid tank is connected to an external pure water adding device, and the HF discharge pipeline of the tertiary spray absorption tower is connected to an external discharge tower; The inlet of the gas to be condensed is arranged at the lower part of the HF condenser, the outlet of the condensed liquid is arranged at the bottom of the HF condenser, and the outlet of the condensed gas is arranged at the top of the HF condenser; the condensation temperature of the HF condenser is -45±15°C, and the condenser pressure is normal pressure; The spray absorption tower is provided with a temperature sensor and a heating device to maintain the temperature of the spray absorption tower at 20±5°C; the pressure of the spray absorption tower is at normal pressure; The treatment process of the cathode tail gas of the nitrogen trifluoride electrolyzer includes: Step 1: The cathode tail gas generated by the electrolytic cell is transported from the cathode gas main pipeline of the electrolytic cell to the HF condenser for condensation treatment; Step 2, the HF condenser deeply condenses the cathode tail gas sent, condenses most of the HF gas in the cathode tail gas into HF liquid, and the HF liquid is regularly discharged from the lower drain valve of the HF condenser to the HF recovery tank; the cathode tail gas is condensed by the condenser and sent to the HF absorption device for purification; Step 3, the cathode tail gas after condensation continuously enters the primary spray absorption tower, the secondary spray absorption tower and the tertiary spray absorption tower in the HF absorption device; the acid liquid produced by the spray absorption tower enters the acid tank of this stage; pure water is pumped into the tertiary acid tank, and the circulating water in the tertiary acid tank is pumped into the secondary acid tank in sequence by a circulating pump, and the circulating water in the secondary acid tank is pumped into the primary acid tank to ensure that the pure water fully absorbs the HF in the cathode gas, and the primary acid tank releases the finished acid with the required concentration through the finished acid discharge port; the circulating water of each acid tank is further pumped into the spray absorption tower of this stage for further absorbing HF.

2. The system according to claim 1, characterized in that The cathode tail gas transmission pipeline, the acid liquid circulation pipeline, the HF discharge pipeline and the acid liquid recovery pipeline are all provided with valves.

3. The system according to claim 1, characterized in that The condensing medium introduced into the HF condenser is cold nitrogen.

4. The system according to claim 1, characterized in that There are two HF condensers connected in parallel; valves are provided on the pipelines connected to the gas inlet to be condensed, the condensed liquid outlet, the condensed gas outlet, the condensed medium inlet and the condensed medium outlet of each HF condenser.

5. The system according to claim 1, wherein: The nominal diameter of the cathode gas main pipeline of the electrolytic cell is 150 mm, and the pipeline material is a carbon steel pipe lined with fluorine.

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