Method and system for recovering hydrogen and nitrogen from polysilicon off-gas

Abstract

The application provides a method and system for recovering hydrogen and nitrogen in polysilicon venting waste gas, and relates to the technical field of polysilicon. The method for recovering hydrogen and nitrogen in polysilicon venting waste gas comprises the following steps: waste gas filtration; deep cooling and adsorption to remove chlorosilane and hydrogen chloride; gas membrane separation; PSA adsorption on the permeated gas and purification on the non-permeated gas; non-permeated gas dehydrogenation, gas-water separation and drying; and nitrogen purification through a rectifying column. The system for recovering hydrogen and nitrogen in polysilicon venting waste gas comprises sequentially connected waste gas filtration device, deep cooling device, adsorption device and gas membrane separation device. The permeated gas and the non-permeated gas output by the gas membrane separation device enter the pressure swing adsorption device and the nitrogen purification device respectively. The nitrogen purification device comprises sequentially connected dehydrogenator, cooling condenser, gas-water separator, drying assembly, filter assembly, nitrogen storage tank and purification assembly. The application recycles hydrogen and nitrogen, and avoids direct discharge and waste.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polysilicon, in particular to a method and system for recycling hydrogen and nitrogen in polysilicon venting waste gas. BACKGROUND

[0002] Polysilicon is a form of elemental silicon. When molten elemental silicon solidifies under supercooling conditions, silicon atoms arrange in a diamond lattice form to form many crystal nuclei. If these crystal nuclei grow into grains with different crystal plane orientations, these grains combine to form polysilicon.

[0003] In the prior art, the whole plant waste gas includes dust-containing waste gas and dust-free waste gas. The dust-containing waste gas contains solid silicon powder. The whole plant waste gas is vented after treatment. The composition of the venting gas is hydrogen and nitrogen, wherein the hydrogen content fluctuates between 10% and 55% (V). The emission of hydrogen and nitrogen causes waste, and only the amount of fresh hydrogen and nitrogen produced by the electrolytic hydrogen device and the air separation nitrogen device of the public auxiliary can be increased to supplement the system to maintain hydrogen balance and nitrogen balance. SUMMARY

[0004] The purpose of the present application is to develop a method and system for recycling hydrogen and nitrogen in polysilicon venting waste gas, avoiding direct emission and waste.

[0005] The present application is realized by the following technical scheme:

[0006] The method for recycling hydrogen and nitrogen in polysilicon venting waste gas comprises the following steps:

[0007] S1. The dust-containing waste gas is filtered to remove solid silicon powder, and then mixed with the dust-free waste gas to form a mixed gas;

[0008] S2. The mixed gas is pressurized, then deep-cooled by circulating water and -70℃ dichloromethane to remove chlorosilane in the mixed gas;

[0009] S3. The mixed gas is adsorbed by a waste gas adsorption column to remove hydrogen chloride and chlorosilane not deep-cooled, and becomes venting gas;

[0010] S4. The venting gas is pressurized and subjected to gas membrane separation. After the gas membrane separation, the permeate gas is hydrogen, and the non-permeate gas is nitrogen;

[0011] S5. A small amount of nitrogen in the permeate gas is removed by PSA adsorption to purify hydrogen, and a small amount of hydrogen in the non-permeate gas is removed to purify nitrogen;

[0012] S6. The non-permeate gas passes through a dehydrogenation catalyst to make hydrogen in the nitrogen react with excess oxygen to generate water. The gaseous water is condensed into liquid water, and after gas-water separation and drying by a dryer, the water is fully removed to obtain dry nitrogen and residual oxygen not reacted, which is then filtered and stored.

[0013] S7. The nitrogen gas and residual oxygen are cooled to saturation temperature after heat exchange, and then are subjected to rectification in a rectification tower to obtain high-purity nitrogen gas at the top of the rectification tower;

[0014] In the step S3, the hydrogen chloride in the vent gas is less than or equal to 30 ppm, and the total amount of chlorosilanes is less than or equal to 30 ppm.

[0015] In the step S5, the permeate gas is pressurized to 0.9 MPa and then is subjected to PSA adsorption.

[0016] Optionally, in the steps S2 and S3, when the deep cooling or adsorption process is abnormal, the mixed gas is subjected to water spray absorption in a water wash tower, and then is vented after passing through a water seal tank and a flame arrester.

[0017] Optionally, in the step S3, the waste adsorption column is activated carbon; and in the step S6, the oxygen gas is vented oxygen gas from the oxygen separation side of a plant electrolytic hydrogen production device.

[0018] Optionally, in the step S7, part of the high-purity nitrogen gas is used as product nitrogen gas, is reheated and pressurized, and then is sent to a user end; and another part of the high-purity nitrogen gas is condensed and liquefied in a condenser evaporator to obtain liquid nitrogen, part of which is output as a product for storage, and another part of which is re-input into the rectification tower as reflux liquid.

[0019] Optionally, in the step S7, part of the liquid oxygen extracted from the bottom of the rectification tower is throttled and then is sent to the condenser evaporator as a cold source thereof after passing through a cold device, evaporates in the condenser evaporator, and then is sent to a dryer as regeneration gas of the dryer after being cooled, expanded and reheated.

[0020] Optionally, in the step S7, the product nitrogen gas and the oxygen evaporated in the condenser evaporator are heat-exchanged with the nitrogen gas and residual oxygen produced in the step S6, in the process of which the product nitrogen gas and the oxygen are reheated, and the nitrogen gas and residual oxygen produced in the step S6 are cooled to saturation temperature.

[0021] A system for recovering hydrogen gas and nitrogen gas from a vented waste gas of a polysilicon production device, comprising:

[0022] a waste gas filtering device, a deep cooling device, an adsorption device, a gas membrane separation device connected in sequence; and

[0023] a pressure swing adsorption device and a nitrogen gas purification device connected with the gas membrane separation device;

[0024] The permeate gas output from the gas membrane separation device is input into the pressure swing adsorption device, and the non-permeate gas output from the gas membrane separation device is input into the nitrogen gas purification device.

[0025] The nitrogen gas purification device comprises a dehydrogenation device, a cooling condenser, a gas-water separator, a drying assembly, a filtering assembly, a nitrogen gas storage tank and a purification assembly connected in sequence.

[0026] Optionally, the drying assembly comprises at least two parallel nitrogen gas dryers, and the filtering assembly comprises at least two parallel nitrogen gas filters.

[0027] Optionally, the purifying assembly comprises a main heat exchanger, an expander, a subcooler, a rectifying tower, a liquid nitrogen storage tank and a buffer tank, the buffer tank is communicated with a nitrogen gas use end, the rectifying tower is provided with a condenser evaporator at the top, the liquid nitrogen storage tank is communicated with a rectifying tower bottom pipeline and the pipeline passes through the main heat exchanger, the rectifying tower top is communicated with a condenser evaporator inlet pipeline, the condenser evaporator outlet is communicated with the liquid nitrogen storage tank pipeline, and a branch pipe communicated with the rectifying tower top is further arranged on the pipeline between the condenser evaporator outlet and the liquid nitrogen storage tank, a pipeline communicated with the buffer tank through the main heat exchanger and the expander is further arranged on the pipeline between the rectifying tower top and the condenser evaporator inlet, the liquid nitrogen storage tank is communicated with the buffer tank pipeline and a gasifier is arranged on the pipeline.

[0028] Optionally, the condenser evaporator is provided with a pipeline communicated with a plurality of nitrogen gas dryers through a cooler, an expander, a subcooler and a main heat exchanger.

[0029] The present application has the following beneficial effects:

[0030] The dust-containing waste gas and dust-free waste gas in the factory are treated to obtain a nitrogen-hydrogen mixed gas, the mixed gas is separated and purified to realize the recycling of nitrogen and hydrogen, not only avoiding the explosion and fire of hydrogen in the mixed gas during emptying, improving the safety of the factory area, but also the purity of the purified nitrogen and hydrogen is high, which can be directly used, reducing energy waste, reducing the amount of hydrogen and nitrogen produced by the electrolytic hydrogen production device and the air separation nitrogen production device of the public auxiliary, and reducing energy consumption and capital consumption. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0032] Figure 1 It is a structure schematic diagram of the gas film separation device.

[0033] Figure 2 It is a structure schematic diagram of the nitrogen gas purification device.

[0034] Reference: 1, emptying waste gas buffer tank; 2, emptying waste gas compressor; 3, filtering mechanism; 301, first filter; 302, second filter; 4, heat exchanger; 5, primary membrane separation; 6, hydrogen buffer tank; 7, secondary membrane separation; 8, nitrogen buffer tank; 9, dehydrogenator; 10, cooling condenser; 11, gas-water separator; 12, nitrogen dryer; 13, nitrogen filter; 14, nitrogen storage tank; 15, main heat exchanger; 16, expander; 17, subcooler; 18, condensation evaporator; 19, rectification column; 20, liquid nitrogen storage tank; 21, gasifier; 22, buffer tank. DETAILED DESCRIPTION

[0035] In the following, certain example embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the drawings and the description are considered to be exemplary in nature rather than limiting.

[0036] In the present invention, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature can include that the first and second features are in direct contact, or can include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the first feature is "on", "above" and "over" the second feature includes that the first feature is directly above and obliquely above the second feature, or only means that the first feature is horizontally higher than the second feature. The first feature is "under", "below" and "underneath" the second feature includes that the first feature is directly below and obliquely below the second feature, or only means that the first feature is horizontally lower than the second feature.

[0037] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0038] The present invention discloses a method for recycling hydrogen and nitrogen in the emptying waste gas of polysilicon, comprising the following steps:

[0039] S1. After the dust-containing waste gas is filtered to remove solid silicon powder, it is mixed with dust-free waste gas to form a mixed gas;

[0040] S2. After the mixed gas is pressurized, it is subjected to deep cooling by circulating water and -70℃ dichloromethane to remove chlorosilane in the mixed gas;

[0041] S3. The mixed gas is subjected to adsorption in a waste gas adsorption column to remove uncooled hydrogen chloride and trace amounts of chlorosilane to become emptying gas;

[0042] S4. The emptying gas is pressurized and subjected to gas membrane separation, after which the permeate gas is hydrogen and the non-permeate gas is nitrogen;

[0043] S5. Purification of hydrogen by adsorption of small amount of nitrogen in permeate gas by PSA (pressure swing adsorption), and purification of nitrogen by removing small amount of hydrogen in non-permeate gas;

[0044] S6. Reaction of hydrogen in nitrogen with excess oxygen to produce water by passing non-permeate gas through dehydrogenation catalyst, condensation of gaseous water into liquid water, separation of water and drying by dryer, removal of moisture to obtain dry nitrogen and residual oxygen, and storage after filtration;

[0045] S7. Cooling of nitrogen and residual oxygen to saturation temperature by heat exchange, rectification in rectification column, and obtaining of high purity nitrogen with purity of 99.9% at top of rectification column;

[0046] In which, the dust-containing waste gas contains solid silicon powder, chlorosilane (SiHCl3, SiCl4, SiH2Cl2), hydrogen, nitrogen, hydrogen chloride, and the dust-free waste gas contains chlorosilane (SiHCl3, SiCl4, SiH2Cl2), hydrogen, nitrogen, hydrogen chloride;

[0047] In steps S2 and S3, when the deep cooling or adsorption process is abnormal, the mixed gas is sprayed and absorbed by water in the elution tower, and then discharged after water seal tank and fire arrestor;

[0048] In step S3, the waste adsorption column is activated carbon;

[0049] In step S3, the hydrogen chloride in the discharged gas is below 30 ppm, and the total amount of chlorosilane is below 30 ppm;

[0050] In step S5, the permeate gas is pressurized to 0.9 MPa and then subjected to PSA adsorption for further purification of hydrogen, and the purity of hydrogen after purification is 99.9%;

[0051] In step S6, the oxygen comes from the discharged oxygen of the oxygen separation side of the on-site electrolytic hydrogen production device;

[0052] In step S7, part of the high purity nitrogen is used as product nitrogen, and after reheating and pressurization, it is sent to the user end; another part of the high purity nitrogen is condensed and liquefied by a condenser evaporator to obtain liquid nitrogen, part of which is output as product for storage, and another part is re-entered into the rectification column as reflux liquid;

[0053] In step S7, a part of the liquid oxygen is throttled and sent to the condenser evaporator as its cooling source after being cooled by a cold device; the liquid oxygen is evaporated in the condenser evaporator, and then after being cooled, expanded and reheated, it is sent to the dryer as the regeneration gas of the dryer;

[0054] In step S7, the product nitrogen and the oxygen evaporated in the condenser evaporator are heat exchanged with the nitrogen and residual oxygen produced in step S6; in this process, the product nitrogen and oxygen are reheated, and the nitrogen and residual oxygen produced in step S6 are cooled to saturation temperature.

[0055] This invention also discloses a system for recovering hydrogen and nitrogen from polycrystalline silicon vent gas, comprising a gas filtration device, a cryogenic device, an adsorption device, and a gas membrane separation device connected in sequence, and further comprising a pressure swing adsorption device and a nitrogen purification device connected to the gas membrane separation device. The permeate gas output from the gas membrane separation device enters the pressure swing adsorption device, and the non-permeate gas output from the gas membrane separation device enters the nitrogen purification device.

[0056] The exhaust gas filtration device includes a silicon powder filter and an exhaust gas buffer tank connected together. The exhaust gas buffer tank is connected to the cryogenic device. A compressor is installed on the pipeline between the exhaust gas buffer tank and the cryogenic device. A dust-laden exhaust gas pipe is connected to the silicon powder filter, and a dust-free exhaust gas pipe is connected to the exhaust gas buffer tank. After the dust-laden exhaust gas enters the silicon powder filter to filter silicon powder, it is sent to the exhaust gas buffer tank to mix with the dust-free exhaust gas and then pressurized and input into the cryogenic device.

[0057] The cryogenic device uses circulating water and -70℃ dichloromethane to cryogenically cool the waste gas, removing chlorosilanes from it. The waste gas is then passed into an adsorption device, where activated carbon adsorption columns adsorb uncryogenically cooled hydrogen chloride and trace amounts of chlorosilanes.

[0058] The exhaust gas filtration device also includes a venting mechanism. When the cryogenic device or adsorption device malfunctions, the exhaust gas in the exhaust gas buffer tank is vented by the venting mechanism. The venting mechanism includes a scrubbing tower, a water seal tank, and a flame arrester that are connected in sequence with the exhaust gas buffer tank. The flame arrester is connected to the outside.

[0059] like Figure 1 As shown, the gas film separation device includes a vented waste gas buffer tank 1, a vented waste gas compressor 2, a filter mechanism 3, a heat exchanger 4, and a separation membrane mechanism connected in sequence. The vented waste gas buffer tank 1 is connected to the adsorption device. The filter mechanism 3 includes two sets of parallel filter components. The filter components include a first filter 301 and a second filter 302 connected in sequence. The filtration accuracies of the first filter 301 and the second filter 302 are 1µm and 0.01µm, respectively. The two sets of filter components are used in one and standby in the other to ensure that the system does not stop operating when the filter element is replaced.

[0060] The separation membrane mechanism includes a primary membrane separator 5 and a secondary membrane separator 7. The primary membrane separator 5 is connected to the heat exchanger 4, the hydrogen buffer tank 6 and the secondary membrane separator 7. The secondary membrane separator 7 is connected to the nitrogen buffer tank 8 and the vented waste gas buffer tank 1. The hydrogen buffer tank 6 is connected to the pressure swing adsorption device. The nitrogen buffer tank 8 is connected to the nitrogen purification device. The primary membrane separator 5 uses a high-selectivity membrane module, and the secondary membrane separator 7 uses a high-flux membrane module.

[0061] The exhaust gas in the vent gas buffer tank 1 is pressurized, filtered, and heat-exchanged before being fed into the primary membrane separator 5. The permeate from the primary membrane separator 5 is fed into the hydrogen buffer tank 6, and the stagnant gas from the primary membrane separator 5 is fed into the secondary membrane separator 7. The permeate from the secondary membrane separator 7 is returned to the vent gas buffer tank 1, and the non-permeate from the secondary membrane separator 7 is fed into the nitrogen buffer tank 8.

[0062] A compressor is installed between the hydrogen buffer tank 6 and the pressure swing adsorption device. The compressor pressurizes the hydrogen in the hydrogen buffer tank 6 to 0.9 MPa and then sends it to the pressure swing adsorption device for further purification of the hydrogen, so that the hydrogen reaches a usable purity.

[0063] like Figure 2 As shown, the nitrogen purification device includes a dehydrogenator 9, a cooling condenser 10, a gas-liquid separator 11, a drying assembly, a filtering assembly, a nitrogen storage tank 14, and a purification assembly connected in sequence. Nitrogen from the nitrogen buffer tank 8 is fed into the dehydrogenator 9, which contains a dehydrogenation catalyst. Excess oxygen is introduced into the dehydrogenator 9, where residual hydrogen reacts with the excess oxygen to produce gaseous water. The dehydrogenated nitrogen is then fed into the cooling condenser 10, where the gaseous water is condensed into liquid water. The nitrogen containing liquid water passes sequentially through the gas-liquid separator 11, the drying assembly, and the filtering assembly to remove water and impurities. The nitrogen and any remaining oxygen (which has not reacted with hydrogen) are then fed into the nitrogen storage tank 14. At this point, a small amount of oxygen remains in the nitrogen in the storage tank 14, which is further purified by the purification assembly.

[0064] The drying assembly includes two nitrogen dryers 12 connected in parallel, with one dryer in operation and the other on standby. The filtration assembly includes two nitrogen filters 13 connected in parallel, with one filter in operation and the other on standby.

[0065] The purification components include a main heat exchanger 15, an expander 16, a subcooler 17, a distillation column 19, a liquid nitrogen storage tank 20, and a buffer tank 22. The buffer tank 22 is connected to the nitrogen usage end, and the top of the distillation column 19 is equipped with a condenser-evaporator 18.

[0066] The nitrogen storage tank 14 is connected to the bottom pipeline of the distillation column 19 and the pipeline passes through the main heat exchanger 15. The top of the distillation column 19 is connected to the inlet pipeline of the condenser evaporator 18. The outlet of the condenser evaporator 18 is connected to the liquid nitrogen storage tank 20. A branch pipe connected to the top of the distillation column 19 is also provided on the pipeline between the outlet of the condenser evaporator 18 and the liquid nitrogen storage tank 20. A pipeline connected to the buffer tank 22 after passing through the main heat exchanger 15 and the expander 16 is also provided on the pipeline between the top of the distillation column 19 and the inlet of the condenser evaporator 18. The liquid nitrogen storage tank 20 is connected to the buffer tank 22 and a vaporizer 21 is provided on the pipeline.

[0067] The rectification tower 19 is provided with a pipeline communicated with the condenser 18 through the cooler 17 at the bottom, and the condenser 18 is provided with a pipeline communicated with the two nitrogen dryers 12 through the cooler 17, the expander 16, the supercooler 17 and the main heat exchanger 15.

[0068] The flow track of nitrogen in the purification assembly is as follows:

[0069] The nitrogen in the nitrogen storage tank 14 is cooled to saturation temperature through the main heat exchanger 15, and then enters the rectification tower 19 for rectification, and high-purity nitrogen is obtained at the top of the rectification tower 19, during which a part of the high-purity nitrogen is sent to the main heat exchanger 15 to exchange heat with the nitrogen output from the nitrogen storage tank 14 to realize reheating, and then is pressurized by the expander 16 and sent to the buffer tank 22 and finally reaches the nitrogen use end, and another part of the high-purity nitrogen is sent to the condenser 18 to be condensed and liquefied to obtain liquid nitrogen, a part of which is sent to the liquid nitrogen storage tank 20 for storage, and the other part of which is sent to the buffer tank 22 after being gasified by the gasifier 21, and the other part of the liquid nitrogen reenters the rectification tower 19 as reflux liquid.

[0070] The flow track of oxygen in the purification assembly is as follows:

[0071] A part of the liquid oxygen at the bottom of the rectification tower 19 is throttled and sent to the condenser 18 as a cooling source through the cooler 17, and the liquid oxygen is evaporated by exchanging heat with nitrogen in the condenser 18, enters the supercooler 17 for the first time, then enters the expander 16 for expansion, then enters the supercooler 17 again, and finally enters the main heat exchanger 15 to exchange heat with the nitrogen output from the nitrogen storage tank 14 to realize reheating, and is sent to the corresponding nitrogen dryer 12 as regenerated gas.

[0072] The beneficial effects of the present application are as follows:

[0073] The dust-containing waste gas and dust-free waste gas in the factory are treated to obtain a nitrogen-hydrogen mixed gas, the mixed gas is separated and purified to realize the recycling of nitrogen and hydrogen, which not only avoids the explosion and fire that may occur when the hydrogen in the mixed gas is exhausted, improves the safety of the factory area, but also the purified nitrogen and hydrogen have high purity and can be directly used, reduces energy waste, reduces the amount of hydrogen and nitrogen produced by the electrolytic hydrogen production device and the air separation nitrogen production device of the public auxiliary, and reduces energy consumption and capital consumption.

[0074] The above embodiments are only the preferred embodiments of the present application, and are not a limitation on the technical solutions of the present application, and any technical solutions that can be realized on the basis of the above embodiments without creative labor should be considered to fall within the protection scope of the present application.

Claims

1. A method for recovering hydrogen and nitrogen from a polysilicon off-gas, characterized in that, The method comprises the following steps: S1. The dust-containing waste gas is filtered to remove solid silicon powder, and then mixed with dust-free waste gas to form mixed gas; S2. The mixed gas is pressurized, then deep-cooled by circulating water and -70℃ dichloromethane to remove chlorosilane in the mixed gas; S3. The mixed gas is adsorbed by a waste gas adsorption column to remove hydrogen chloride and chlorosilane not deep-cooled, and then becomes venting gas; S4. The venting gas is pressurized and subjected to gas membrane separation, and after the gas membrane separation, the permeate gas is hydrogen and the non-permeate gas is nitrogen; S5. A small amount of nitrogen in the permeate gas is removed by PSA adsorption to purify hydrogen, and a small amount of hydrogen in the non-permeate gas is removed to purify nitrogen; S6. The non-permeate gas passes through a dehydrogenation catalyst to make hydrogen in the nitrogen react with excess oxygen to generate water, the gaseous water is condensed into liquid water, and after gas-water separation and drying by a dryer, the water is fully removed to obtain dry nitrogen and residual oxygen not reacted, and then the nitrogen and the residual oxygen are filtered and stored; S7. The nitrogen and the residual oxygen are cooled to saturation temperature after heat exchange, then subjected to rectification in a rectification tower, and high-purity nitrogen is obtained at the top of the rectification tower; In the step S3, the hydrogen chloride in the venting gas is less than 30ppm, and the total amount of chlorosilane is less than 30ppm; In the step S5, the permeate gas is pressurized to 0.9Mpa and then subjected to PSA adsorption; In the step S7, a part of the high-purity nitrogen is used as product nitrogen, reheated and pressurized, and then sent to a user end; another part of the high-purity nitrogen is condensed and liquefied by a condensing evaporator to obtain liquid nitrogen, a part of the liquid nitrogen is output as product and stored, and another part of the liquid nitrogen is returned to the rectification tower as reflux liquid; In the step S7, a part of liquid oxygen is extracted from the bottom of the rectification tower, throttled, and then sent to the condensing evaporator as a cold source, the liquid oxygen is evaporated in the condensing evaporator, then subjected to cooling, expansion and reheating, and sent to the dryer as regeneration gas of the dryer.

2. The method of claim 1, wherein, In the steps S2 and S3, when the deep-cooling or adsorption process is abnormal, the mixed gas is sprayed and absorbed by water in a washing tower, then sealed by a water seal tank and a fire arrester, and then vented.

3. The method of claim 1, wherein the method further comprises: In the step S3, the waste adsorption column is activated carbon; in the step S6, the oxygen comes from venting oxygen of an oxygen separation side of a plant electrolytic hydrogen production device.

4. The method of claim 1, wherein the method further comprises: In the step S7, the product nitrogen and oxygen evaporated in the condensing evaporator are heat-exchanged with the nitrogen and residual oxygen produced in the step S6, in this process, the product nitrogen and oxygen are reheated, and the nitrogen and residual oxygen produced in the step S6 are cooled to saturation temperature.

5. A system for recovering hydrogen and nitrogen from polycrystalline silicon vent gas, characterized in that, The method comprises the following steps: sequentially connected waste gas filtering device, deep-cooling device, adsorption device, gas membrane separation device; and pressure swing adsorption device and nitrogen purification device connected with the gas membrane separation device; In the method, the permeate gas output by the gas membrane separation device enters the pressure swing adsorption device, and the non-permeate gas output by the gas membrane separation device enters the nitrogen purification device; The nitrogen purification device comprises sequentially connected dehydrogenation device, cooling condenser, gas-water separator, drying assembly, filtering assembly, nitrogen storage tank and purification assembly; The drying assembly comprises at least two parallel nitrogen dryers, and the filtering assembly comprises at least two parallel nitrogen filters. The purification assembly comprises a main heat exchanger, an expander, a subcooler, a rectifying tower, a liquid nitrogen storage tank and a buffer tank, the buffer tank is communicated with a nitrogen use end, the rectifying tower is provided with a condensation evaporator at the top, the nitrogen storage tank is communicated with a rectifying tower bottom pipeline and the pipeline passes through the main heat exchanger, the rectifying tower top is communicated with a condensation evaporator inlet pipeline, the condensation evaporator outlet is communicated with the liquid nitrogen storage tank pipeline, a branch pipe communicated with the rectifying tower top is further arranged on the pipeline between the condensation evaporator outlet and the liquid nitrogen storage tank, a pipeline communicated with the buffer tank through the main heat exchanger and the expander is further arranged on the pipeline between the rectifying tower top and the condensation evaporator inlet, the liquid nitrogen storage tank is communicated with the buffer tank pipeline and a gasifier is arranged on the pipeline, the rectifying tower bottom is provided with a pipeline communicated with the condensation evaporator after passing through the cold cooler; The condensation evaporator is provided with a pipeline communicated with a plurality of nitrogen dryers after passing through the cold cooler, the expander, the subcooler and the main heat exchanger.

Images