Safe low-carbon polycrystalline silicon waste gas treatment system

Abstract

The utility model discloses a safe low-carbon polycrystalline silicon waste gas treatment system, which is used for optimizing, upgrading and transforming a chlorosilane-containing waste gas alkali washing process on the basis of treating polycrystalline silicon waste gas by a traditional alkali washing method. Chlorosilane-containing waste gas enters a two-stage waste gas alkaline washing tower through a waste gas buffer tank, and slurry jet flow disturbance is arranged at the bottom of the washing tower so as to prevent the tower bottom and a pipeline from being blocked by accumulated materials. Chlorosilane reacts with alkali liquor to generate hydrogen, after alkali washing, gas containing hydrogen and nitrogen enters a hydrogen concentration unit through a liquid seal tank and a flame arrester, the hydrogen can be concentrated to 95% or above, condensed liquid nitrogen serves as a cold source, and self-supply of the cold source of the system is achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of polysilicon production, in particular to a safe and low-carbon polysilicon waste gas treatment system. Background Art

[0002] Waste gas treatment in the polysilicon industry primarily comes from production waste gas from cold hydrogenation units, slurry treatment waste gas, PSA hydrogen purification waste gas, distillation unit and tank farm waste gas, reduction unit waste gas, and tail gas recovery unit waste gas. Currently, the commonly used waste gas treatment processes include alkaline washing, incineration, and dry recovery.

[0003] Among them, the alkaline washing method has a simple process flow, low operating difficulty, and small investment, but it also has the problems of large sludge production, easy pipeline blockage, and the production of a large amount of hydrogen, which causes certain safety risks and waste of resources; the incineration method is generally equipped with corresponding waste heat recovery and is highly economical, but after the waste heat boiler, rapid cooling measures are generally required to prevent the formation of dioxins. The process flow is relatively long and the investment is high; the dry recovery process is more economical, but the investment is higher.

[0004] Therefore, in the actual production and operation process of the polysilicon industry, it is necessary to select appropriate process technology routes according to the source and composition of the waste gas, solve the problems brought about by the above process routes, and ultimately achieve safe, economical, low-carbon and stable operation of polysilicon waste gas treatment. Utility Model Content

[0005] The utility model provides a safe and low-carbon polysilicon waste gas treatment system based on the above-mentioned technical problems.

[0006] The purpose of the utility model can be achieved through the following technical solutions:

[0007] A safe and low-carbon polysilicon waste gas treatment system includes a waste gas buffer tank, the top output end of the waste gas buffer tank is connected to an alkali washing tower, the top output end of the alkali washing tower is connected to a gas-liquid separator via a waste gas liquid seal tank and a buffer tank, the top output end of the gas-liquid separator is connected to a primary heat exchanger and a secondary heat exchanger in sequence, the bottom output end is connected to a flash tank, and the top output of the flash tank is connected to the buffer tank.

[0008] In the technical solution of the utility model: the top of the waste gas buffer tank is also provided with an output end connected to the pipeline liquid separator.

[0009] In the technical solution of the utility model, the top output end of the pipeline liquid distributor is connected to the fire accident pool through a safety measure valve group.

[0010] In the technical solution of the utility model: the bottom of the pipeline liquid separator and the waste gas buffer tank are both connected to the main process device.

[0011] In the technical solution of the utility model: a slurry circulation pump is provided in the middle of the alkali washing tower, one output end of the slurry circulation pump is connected to the upper part of the alkali washing tower, and the other output end is connected to the lower part of the alkali washing tower.

[0012] In the technical solution of the utility model, a flame arrester is further provided on the pipeline connecting the waste gas liquid sealing tank and the buffer tank.

[0013] In the technical solution of the present utility model: a pressure gauge is provided on the top of the exhaust gas buffer tank.

[0014] A method for treating polysilicon waste gas safely and with low carbon content using the above system is described as follows:

[0015] Waste gas from the polysilicon industry typically contains trichlorosilane, silicon tetrachloride, dichlorosilane, hydrogen chloride, hydrogen, silicon powder, and nitrogen. Chlorosilane-containing waste gas (dust-free) enters the caustic scrubber via a waste gas buffer tank. Chlorosilane reacts with lye to produce hydrogen. The hydrogen- and nitrogen-containing gas then passes through a liquid seal tank and flame arrester into the hydrogen enrichment unit. After pressurization, it first enters the primary and secondary heat exchangers, where the temperature is lowered to -196°C, condensing most of the nitrogen into a liquid state. The condensed gas-liquid mixture enters a vapor-liquid separator, which separates the gas-liquid mixture from the two heat exchangers to produce liquid nitrogen and cold hydrogen. The cold hydrogen is then reheated through the secondary and primary heat exchangers, allowing it to be concentrated to over 95%. The condensed liquid nitrogen returns to the system as a cooling source. Excess liquid nitrogen is throttled by a cryogenic valve and then enters the secondary heat exchanger for reheating. It then enters the primary heat exchanger for reheating and is vented at a high point.

[0016] When the volume of accident exhaust gas is high and the pressure in the gas buffer tank is high, the pressure gauge will sound an alarm, and the bursting disc on the pipeline to the accident water pool will open. When the pressure is very high, the interlock opens the shut-off valve on the pipeline to the accident water pool, and the accident exhaust gas will be discharged to the accident water pool. Because chlorosilane-containing exhaust gas is flammable and explosive, it poses a significant safety risk. The accident water pool must be located away from the equipment and separated by a fireproof retaining wall. The accident water pool should not be located under the pipe gallery or framework.

[0017] In the above method: under normal circumstances, the pipeline from the waste gas buffer tank to the bursting disc or cut-off valve is always full of waste gas, a pipeline distributor is set on the accident pipeline, and the condensate is regularly discharged to the chlorosilane condensate tank.

[0018] In the above method: the amount of accident gas containing chlorosilane is large, and there is a certain risk in discharging it into the accident water pool. The accident water pool needs to be away from the device and separated by a fire retaining wall, and the accident water pool should not be set under the pipe gallery or frame.

[0019] In the above method: a slurry jet disturbance is set at the bottom of the alkali washing tower to make the slurry in a suspended state, thereby preventing the tower kettle and pipeline from being blocked by material accumulation.

[0020] In the above method: the chlorosilane-containing waste gas is washed in an alkali washing tower and then enters the hydrogen purification system through a flame arrester.

[0021] In the above method: hydrogen and nitrogen are separated by liquid nitrogen condensation. The cold source for separating hydrogen and nitrogen only needs to use nitrogen source during startup or special working conditions. The liquid nitrogen source under normal working conditions is self-supplied by the system, which can achieve hydrogen concentration of more than 95%.

[0022] In the technical solution of this utility model, the liquid nitrogen condensation method is used to

[0023] Hydrogen and nitrogen are separated, and the cold source for hydrogen purification only needs to use nitrogen source during start-up or special working conditions. The liquid nitrogen source under normal working conditions is self-supplied by the system, which can achieve hydrogen concentration of more than 95%.

[0024] Beneficial effects of the utility model:

[0025] 1) The hydrogen concentration process focuses on solving the problem of a large amount of hydrogen generated during the alkaline washing process of polysilicon waste gas treatment, which causes certain safety risks and waste of resources.

[0026] 2) During the normal operation of hydrogen enrichment, there is no need to add liquid nitrogen, which overcomes the problem of high investment and operating costs of dry recovery process.

[0027] 3) When the amount of accident waste gas is large, the waste gas goes to the accident water pool through the pipeline separator, and the condensate of the pipeline separator is discharged to the chlorosilane condensate tank, preventing the chlorosilane condensate on the accident pipeline from being discharged through the drain pipe and causing explosion or fire.

[0028] 4) Adopting alkaline washing + hydrogen concentration process, the safe, economical, low-carbon and stable operation of polysilicon waste gas treatment is finally achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Attachment Figure 1 This is a flow chart of a system and method for treating waste gas from safe and low-carbon polysilicon.

[0030] In the figure, 1 is the waste gas buffer tank, 2 is the alkali washing tower, 3 is the slurry circulation pump, 4 is the waste gas liquid seal tank, 5 is the flame arrester, 6 is the buffer tank, 7 is the primary heat exchanger, 8 is the secondary heat exchanger, 9 is the gas-liquid separator, 10 is the air compressor, 11 is the flash tank, 12 is the pressure gauge, 13 is the pipeline liquid separator, 14 is the safety measure valve group, 15 is the fire accident pool, and 16 is the low temperature valve. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the following embodiments, but the scope of protection of the present invention is not limited thereto:

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the following content does not limit the scope of protection of the present invention.

[0033] like Figure 1 A safe, low-carbon polysilicon waste gas treatment system, comprising a waste gas buffer tank 1, wherein the top output end of the waste gas buffer tank 1 is connected to an alkali washing tower 2, and the top output end of the alkali washing tower 2 is connected to a gas-liquid separator 9 via a waste gas liquid seal tank 4 and a buffer tank 6. The top output end of the gas-liquid separator 9 is connected to a primary heat exchanger 7 and a secondary heat exchanger 8 in sequence, and the bottom output end is connected to a flash tank 11, and the top output end of the flash tank 11 is connected to a buffer tank 6. The waste gas buffer tank 1 also has an output end at the top connected to a pipe separator 13. The top output end of the pipe separator 13 is connected to a fire accident pool 15 via a safety valve group 14. The bottom of the pipe separator 13 and the waste gas buffer tank 1 are both connected to the main process equipment. A slurry circulation pump 3 is provided in the middle of the alkali washing tower 2, wherein one output end of the slurry circulation pump 3 is connected to the upper part of the alkali washing tower 2, and the other output end is connected to the lower part of the alkali washing tower 2. A flame arrester 5 is also provided on the pipeline connecting the waste gas liquid seal tank 4 and the buffer tank 6. A pressure gauge 12 is provided on the top of the waste gas buffer tank 1.

[0034] A method for treating polysilicon waste gas safely and with low carbon content using the above system comprises:

[0035] In order to ensure the safe and stable operation of the alkaline washing process for polysilicon waste gas, when the amount of accident gas is large, the pressure gauge 12 of the waste gas buffer tank 1 is set to a high alarm value. When the pressure rises further, the bursting disc opens, the pressure gauge 12 is set to a high value, and the interlock opens the shut-off valve.

[0036] Under normal circumstances, the pipeline from the waste gas buffer tank 1 to the bursting disc or shut-off valve 14 is always filled with waste gas. A pipe separator 13 is installed on the emergency pipeline to regularly discharge condensate to the chlorosilane condensate tank and then to the process equipment. Because the volume of accident waste gas containing chlorosilane is large and chlorosilane is flammable and explosive, discharging it into the emergency water pool poses certain risks. Therefore, the emergency water pool 15 must be located away from the equipment and separated by a fireproof retaining wall. The emergency water pool should not be located below the pipe gallery or framework.

[0037] Because alkaline washing of polysilicon waste gas can generate large amounts of sludge and easily cause clogging of the tower and pipelines, a slurry jet disturbance is installed at the bottom of alkaline washing tower 2 to suspend solids in the tower slurry, preventing clogging of the tower and pipelines. Furthermore, the sludge discharge pipeline is sloped and flanged every three meters to facilitate silt removal.

[0038] The gas containing hydrogen and nitrogen enters the hydrogen concentration unit through the liquid seal tank 4 and the flame arrester 5, and after being pressurized by the air compressor 10, it enters the primary heat exchanger 7 and the secondary heat exchanger 8 in sequence, and the temperature is reduced to the nitrogen liquefaction temperature so that most of the nitrogen is condensed into liquid.

[0039] The condensed gas-liquid mixture enters the gas-liquid separator 9, which separates the gas-liquid mixture flowing out of the two-stage heat exchanger to obtain liquid nitrogen and cold hydrogen. The cold hydrogen can be concentrated to more than 95% after being reheated in the secondary heat exchanger 8 and the primary heat exchanger 7.

[0040] The condensed liquid nitrogen returns to the system as a cold source, and the excess liquid nitrogen is throttled by the low-temperature valve 16 and enters the secondary heat exchanger 8 for reheating, and then enters the primary heat exchanger 7 for reheating and then discharged at a high point.

[0041] The cold box condensation process design allows for stable gas concentrations and large fluctuations in feed gas volume. As long as the system temperature and outlet pressure are properly controlled, the system outlet gas concentration will be relatively stable. Furthermore, the cooling source (liquid nitrogen) is only used during the initial system startup; no additional liquid nitrogen is required during operation, thus achieving a low-carbon process.

[0042] Example:

[0043] The waste gas in the polysilicon industry contains trichlorosilane, silicon tetrachloride, dichlorosilane, hydrogen chloride, hydrogen, nitrogen, etc. The process waste gas volume is ~2000Nm 3 / h, trichlorosilane ~8.2%, silicon tetrachloride ~0.5%, dichlorosilane ~0.4%, hydrogen ~19.8%, hydrogen chloride ~0.05%, nitrogen ~66%. After treatment in the alkali washing tower, the hydrogen concentration reaches ~29%. After further hydrogen concentration treatment, the hydrogen concentration is ≥95%.

[0044] Chlorosilane-containing waste gas enters a two-stage waste gas alkaline scrubber via a waste gas buffer tank. Chlorosilane reacts with lye to produce hydrogen. The hydrogen- and nitrogen-containing gas then enters the hydrogen enrichment unit through a liquid seal tank and flame arrester. After pressurization, it enters the primary and secondary heat exchangers, where the temperature is lowered to -196°C, condensing most of the nitrogen into a liquid state. The condensed gas-liquid mixture enters a vapor-liquid separator, where the gas-liquid mixture exiting the two-stage heat exchanger is separated to produce liquid nitrogen and cold hydrogen. The cold hydrogen, after reheating through the secondary and primary heat exchangers, can reach a concentration of over 95%. The condensed liquid nitrogen returns to the system as a cooling source. Excess liquid nitrogen is throttled by a cryogenic valve and then enters the secondary heat exchanger for reheating. It then enters the primary heat exchanger for reheating and is vented at a high point.

[0045] To ensure the safe and stable operation of the polysilicon waste gas alkaline washing process, when the accident gas volume is large and the waste gas buffer tank pressure is high, the pressure gauge alarm is set to ~0.08 MPa. The bursting disc on the pipeline to the accident water pool then opens, and the bursting disc release pressure is set to ~0.09 MPa. When the pressure is very high, an interlock opens the shut-off valve on the pipeline to the accident water pool, and the high-high interlock value is set to ~0.10 MPa, and the waste gas is discharged to the accident water pool. Because chlorosilane waste gas is flammable and explosive, it poses a significant safety risk. The accident water pool must be located away from the equipment and separated by a fireproof retaining wall. The accident water pool must not be located under the pipe gallery or framework.

[0046] Under normal circumstances, the pipeline from the waste gas buffer tank to the bursting disc or shut-off valve is always filled with waste gas. A pipeline separator is installed on the accident pipeline, and the condensate is regularly discharged to the condensate separator tank to prevent the chlorosilane condensate on the accident pipeline from being discharged through the drain pipe and causing explosions or fires.

[0047] Because alkaline washing of polysilicon waste gas can generate large amounts of sludge and easily clog pipelines, a slurry jet disturbance is installed at the bottom of the first and second scrubbers, and a liquid distributor is installed in the tower kettle to suspend solids in the slurry in the tower kettle, preventing material accumulation and clogging in the tower kettle and pipelines. Furthermore, the sludge discharge pipeline is designed with a certain slope and flange connections every 3 meters to facilitate silt removal.

[0048] The mixture of hydrogen and nitrogen is pressurized to 1.0Mpa by the air compressor and then enters the primary heat exchanger and the secondary heat exchanger in sequence, reducing the temperature to -196℃.

[0049] The condensed gas-liquid mixture enters the gas-liquid separator, and the gas-liquid mixture flowing out of the two-stage heat exchanger is separated into liquid nitrogen and cold hydrogen. The cold hydrogen is reheated in the secondary heat exchanger and the primary heat exchanger in turn to obtain 0.6Mpa, high-concentration hydrogen of more than 95%.

[0050] The condensed liquid nitrogen is returned to the hydrogen enrichment system as a source of cryogenic liquid nitrogen. The excess liquid nitrogen is throttled by a cryogenic valve and then enters the secondary heat exchanger for reheating. It then enters the primary heat exchanger for reheating and is vented at a high point.

[0051] This utility model discloses a safe, low-carbon polysilicon waste gas treatment system and method. Based on the characteristics of polysilicon waste gas, this system utilizes an alkali wash + hydrogen purification process. This not only addresses the safety risks and resource waste caused by the large amount of hydrogen generated during the alkali wash process, as well as the blockage of tower reactors and pipelines caused by accumulated material, but also overcomes the high investment and operating costs of dry recovery processes by utilizing condensed liquid nitrogen as the nitrogen source.

[0052] Although the present invention is described and illustrated herein by one or some specific configurations, it is not intended to limit the details, because various modifications and structural changes are possible within the scope of the patent claims without departing from the spirit of the invention.

[0053] The parts not involved in the present invention are the same as the existing technology or can be implemented by using the existing technology.

Claims

1. A safe and low-carbon polysilicon waste gas treatment system, characterized by: The system comprises a waste gas buffer tank (1), wherein the top output end of the waste gas buffer tank (1) is connected to an alkali washing tower (2), the top output end of the alkali washing tower (2) is connected to a gas-liquid separator (9) via a waste gas liquid sealing tank (4) and a buffer tank (6), the top output end of the gas-liquid separator (9) is sequentially connected to a primary heat exchanger (7) and a secondary heat exchanger (8), and the bottom output end is connected to a flash tank (11), and the top output of the flash tank (11) is connected to the buffer tank (6).

2. The safe low-carbon polysilicon waste gas treatment system according to claim 1 is characterized by: The top of the waste gas buffer tank (1) also has an output end connected to the pipeline liquid separator (13).

3. The safe low-carbon polysilicon waste gas treatment system according to claim 2 is characterized by: The top output end of the pipeline liquid distributor (13) is connected to the fire accident pool (15) through a safety measure valve group (14).

4. The safe low-carbon polysilicon waste gas treatment system according to claim 3 is characterized by: The bottom of the pipeline liquid separator (13) and the waste gas buffer tank (1) are both connected to the main process device.

5. The safe low-carbon polysilicon waste gas treatment system according to claim 1 is characterized in that: A slurry circulation pump (3) is provided in the middle of the alkali washing tower (2). One output end of the slurry circulation pump (3) is connected to the upper part of the alkali washing tower (2), and the other output end is connected to the lower part of the alkali washing tower (2).

6. The safe low-carbon polysilicon waste gas treatment system according to claim 1 is characterized by: A flame arrester (5) is also provided on the pipeline connecting the waste gas liquid sealing tank (4) and the buffer tank (6).

7. The safe low-carbon polysilicon waste gas treatment system according to claim 1 is characterized by: A pressure gauge (12) is provided on the top of the waste gas buffer tank (1).

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