Polycrystalline silicon waste gas recycling system

Abstract

The utility model provides a polycrystalline silicon waste gas recycling system, and aims to solve the technical problem that the cost is increased due to the fact that waste gas cannot be recycled in the conventional polycrystalline silicon cold hydrogenation system. The system comprises a silicon powder filtering unit, a pressurization condensation unit, an adsorption unit, a nitrogen recycling unit and a reverse blowing unit which are sequentially connected through pipelines, the nitrogen-containing waste gas passes through the silicon powder filtering unit to remove silicon powder, passes through the pressurization condensation unit to remove chlorosilane, passes through the adsorption unit to further remove chlorosilane, and then pure nitrogen is obtained. And further recycling the chlorosilane gas into a cold hydrogenation system through the nitrogen recycling unit, desorbing the saturated chlorosilane gas in the adsorption tower through the blowback unit, and further refluxing the saturated chlorosilane gas into the pressurized condensation unit to be purified again. According to the waste gas recycling system disclosed by the utility model, nitrogen in waste gas discharged in a drying link of the waste silicon powder tank is recycled, so that the nitrogen consumption of the system is reduced, and the purposes of reducing the purchase consumption of liquid nitrogen and reducing the production cost are achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of tail gas recovery in polysilicon preparation, in particular to a polysilicon waste gas recycling system. Background Art

[0002] Cold hydrogenation technology is an important technology in the preparation of polysilicon. Its main principle is to reduce the impurities in the single crystal silicon grains with hydrides first, and then cool the operating chamber under a certain hydrogen partial pressure to obtain polysilicon with low impurity concentration and high crystal order. At present, a large amount of waste gas is generated in the process of producing polysilicon by cold hydrogenation. The main components of the waste gas are nitrogen, hydrogen, silicon tetrachloride, trichlorosilane, dichlorosilane, hydrogen chloride and trace silicon powder. At present, the waste gas treatment method in the polysilicon industry is mainly through leaching, that is, using water to react with chlorosilane, absorbing hydrogen chloride at the same time, and discharging harmful gases in the waste gas. The remaining nitrogen and hydrogen are discharged into the atmosphere at high points. However, there are the following problems with using this method to treat waste gas: (1) Nitrogen needs to be introduced into both the chlorosilane storage tank and the distillation tower for purifying trichlorosilane from chlorosilane to maintain a stable gas pressure. Nitrogen usually needs to be provided from outside, and the purchase of liquid nitrogen will increase production costs; (2) The venting of process waste gas causes trace amounts of silicon powder to be contained in the waste gas, which pollutes surrounding equipment.

[0003] Therefore, it is of great significance to study a polysilicon waste gas recycling system that can effectively recover nitrogen from the waste gas and prevent silicon powder pollution. Utility Model Content

[0004] The purpose of the utility model is to solve the technical problem that nitrogen cannot be effectively recovered during waste gas treatment in the prior art polysilicon cold hydrogenation technology, by collecting and reusing nitrogen in the waste gas discharged from the drying process of the waste silicon powder tank: using silicon powder filtration, pressurized condensation, and activated carbon adsorption technology to remove silicon powder and chlorosilane in the waste gas; and solving the problem of hydrogen enrichment in the waste gas by automatically controlling the venting through the system.

[0005] In order to solve the above technical problems, the utility model adopts the following technical solutions:

[0006] A polysilicon waste gas recycling system comprises a silicon powder filtering unit, a pressurized condensing unit, an adsorption unit and a nitrogen recycling unit which are sequentially connected by pipelines;

[0007] The silicon powder filtration unit comprises a silicon powder filter for removing silicon powder from nitrogen-containing waste gas in a polysilicon cold hydrogenation system;

[0008] The pressurized condensation unit comprises an exhaust gas compressor, a post-condenser and a heat exchanger connected in sequence, and is used to perform deep cooling condensation on the nitrogen-containing exhaust gas after silicon removal to remove chlorosilane in the nitrogen-containing exhaust gas;

[0009] The adsorption unit comprises an adsorption tower, in which an adsorption column is arranged, and the adsorption column is filled with activated carbon, which is used to further adsorb chlorosilane in the nitrogen-containing waste gas through the activated carbon;

[0010] The nitrogen recycling unit includes a reflux pipeline connected to the top of the adsorption tower, which is used to return the purified nitrogen after adsorption by the adsorption column to the polysilicon cold hydrogenation system through the reflux pipeline for continued use in cold hydrogenation;

[0011] It also includes a back-blowing unit, which includes a back-blowing pipeline and a back-blowing filter pipeline;

[0012] The back-blowing gas pipeline is connected to the reflux pipeline, and is connected to a nitrogen heater I, which is used to heat part of the purified nitrogen and then back-blow it into the adsorption tower under a slight positive pressure when the chlorosilane enriched in the activated carbon reaches saturation;

[0013] The back-blowing gas filter pipeline is connected to the bottom of the adsorption tower, and a back-blowing gas filter is connected thereto. The back-blowing gas back-blown into the adsorption tower desorbs chlorosilane from the adsorption column, and then is filtered by the back-blowing gas filter and re-delivered to the pressurized condensation unit.

[0014] As the preferred technical solution:

[0015] Optionally, control valves are installed on both the back-blowing air pipeline and the back-blowing air filtering pipeline, and the control valves are closed before the activated carbon reaches a saturated state.

[0016] Optionally, an organic pre-buffer tank is provided between the silicon powder filtration unit and the pressurized condensation unit for mixing and buffering the chlorosilane desorbed from the back-blowing unit and the nitrogen-containing waste gas in the polysilicon cold hydrogenation system.

[0017] Optionally, the polysilicon cold hydrogenation system includes a nitrogen heater II, a waste silicon powder dechlorination drying tank and a waste silicon powder tank. The nitrogen-containing waste gas generated in the system is first heated by the nitrogen heater II and then passed into the waste silicon powder dechlorination drying tank and the waste silicon powder tank in sequence and then into the silicon powder filtration unit.

[0018] Optionally, the purified nitrogen gas is refluxed into the crystalline silicon cold hydrogenation system through the reflux pipeline to continue to be used for cold hydrogenation, which means that the purified nitrogen gas is refluxed into the waste silicon powder dechlorination drying tank and the waste silicon powder tank through the reflux pipeline.

[0019] Optionally, the pipeline connecting the post-machine condenser and the heat exchanger in the pressurized condensing unit is also connected with a post-machine buffer tank and a precision filter for cooling and buffering the pressurized gas in the pressurized condensing unit and further removing impurities.

[0020] Optionally, a Freon heat exchanger is connected behind the heat exchanger to recover the condensed chlorosilane after heat exchange.

[0021] Optionally, the adsorption unit further comprises a product filter a and a product filter b connected in parallel, which are connected to the gas outlet pipeline at the top of the adsorption tower and are used for further filtering the gas to obtain purified nitrogen.

[0022] Optionally, a waste gas venting pipeline is further provided after the product filter a and the product filter b. By regularly checking the hydrogen content in the adsorbed product nitrogen, the system automatically controls the venting and replacement when the hydrogen content is high, thereby solving the difficulty of hydrogen enrichment in the product gas.

[0023] Optionally, the adsorption tower comprises an adsorption tower a, an adsorption tower b and an adsorption tower c connected in parallel; the back-blowing filter comprises a back-blowing filter a and a back-blowing filter b connected in parallel.

[0024] Compared with the prior art, the beneficial effects of the utility model are:

[0025] 1. The polycrystalline waste gas recycling system of the utility model removes silicon powder and chlorosilane in the waste gas through silicon powder filtration, pressurized condensation, and activated carbon adsorption technology, and reuses the purified nitrogen to the polycrystalline silicon cold hydrogenation system, thereby realizing efficient nitrogen recycling, avoiding the need to purchase additional liquid nitrogen, and greatly reducing production costs;

[0026] 2. The polycrystalline waste gas recycling system of the utility model solves the problem of hydrogen enrichment in the waste gas by automatically controlling the venting of the system;

[0027] 2. The polycrystalline waste gas recycling system of the utility model is different from the flushing process of the prior art. It effectively recovers nitrogen and avoids the pollution of the surrounding environment by silicon powder in the waste gas during the waste gas venting treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 This is the PID diagram of the polycrystalline waste gas recycling system of the utility model;

[0030] Reference numerals:

[0031] 1-silicon powder filtration unit; silicon powder filter 10; 11-pre-machine buffer tank;

[0032] 2-pressurized condensing unit; 21-exhaust gas compressor; 22-rear condenser; 23-heat exchanger; 24-rear buffer tank; 25-precision filter; 26-Freon heat exchanger;

[0033] 3-adsorption unit; 31-adsorption tower a; 32-adsorption tower b; 33-adsorption tower c; 34-product filter a; 35-product filter b;

[0034] 4-nitrogen recycling unit; 41-nitrogen heater II; 42-waste silicon powder dechlorination drying tank; 43-waste silicon powder tank;

[0035] 5-backflush unit; 51-nitrogen heater I; 521-backflush filter a; 522-backflush filter b;

[0036] 100-air outlet pipeline; 200-waste gas venting pipeline; 300-reflux pipeline; 400-back-blowing pipeline; 500-back-blowing gas filtration pipeline; 600-chlorosilane recovery pipeline. DETAILED DESCRIPTION

[0037] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0038] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the products of the present invention are conventionally placed when in use, or are the orientations or positional relationships conventionally understood by those skilled in the art, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0039] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present utility model, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0040] In the present invention, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] In the present utility model, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0042] The disclosure below provides many different embodiments or examples for realizing different structures of the utility model. In order to simplify the disclosure of the utility model, the components and settings of specific examples are described below. Of course, they are merely examples, and the purpose is not to limit the utility model. In addition, the utility model may repeat reference numbers and / or reference letters in different examples, and such repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the utility model provides various specific examples of processes and materials, but those of ordinary skill in the art may be aware of the application of other processes and / or the use of other materials.

[0043] The embodiments of the present utility model are described in detail below with reference to the accompanying drawings.

[0044] The embodiment of the utility model provides a polycrystalline waste gas recycling system, comprising a silicon powder filtering unit 1, a pressurized condensing unit 2, an adsorption unit 3 and a nitrogen recycling unit 4, and a back-blowing unit 5 which are sequentially connected by pipelines.

[0045] The silicon powder filtering unit 1 includes a silicon powder filter 10, which is used to remove silicon powder from nitrogen-containing waste gas in the polysilicon cold hydrogenation system;

[0046] The pressurized condensing unit 2 includes an exhaust gas compressor 21, a post-condenser 22 and a heat exchanger 23 which are connected in sequence, and is used to deep-cold and condense the nitrogen-containing exhaust gas after silicon removal by the silicon powder filtration unit to remove chlorosilanes in the nitrogen-containing exhaust gas; the pipeline connecting the post-condenser 22 and the heat exchanger 23 is also connected to an organic post-buffer tank 24 and a precision filter 25; the back of the heat exchanger 23 is also connected to a Freon heat exchanger 26, to which a chlorosilane recovery pipeline 600 is connected, so as to recover the chlorosilanes condensed by heat exchange in the Freon heat exchanger 26.

[0047] The adsorption unit 3 includes an adsorption tower, an adsorption column is arranged in the adsorption tower, and the adsorption column is filled with activated carbon, which is used to further adsorb chlorosilane in the nitrogen-containing waste gas through the activated carbon, wherein the adsorption tower includes an adsorption tower a 31, an adsorption tower b 32 and an adsorption tower c 33 connected in parallel; the adsorption unit 3 also includes a product filter a 34 and a product filter b 35 connected in parallel, which are connected to the gas outlet pipeline 100 at the top of the adsorption tower, and are used to further filter the gas to obtain purified nitrogen. A waste gas venting pipeline 200 is also arranged behind the product filter a 34 and the product filter b 35.

[0048] The nitrogen recycling unit 4 includes a reflux pipeline 300 connected to the top of the adsorption tower in the adsorption unit 3, which is used to reflux the purified nitrogen after adsorption by the adsorption column to the polysilicon cold hydrogenation system through the reflux pipeline 300 for continued use in cold hydrogenation, wherein the polysilicon cold hydrogenation system includes a nitrogen heater II 41, a waste silicon powder dechlorination drying tank 42 and a waste silicon powder tank 43, and the waste gas generated in the polysilicon cold hydrogenation system is first heated by the nitrogen heater II 41 and then sequentially passed into the waste silicon powder dechlorination drying tank 42 and the waste silicon powder tank 43 and then passed into the silicon powder filtration unit 1;

[0049] The nitrogen purified by the adsorption tower in the adsorption unit 3 is refluxed to the waste silicon powder dechlorination drying tank 42 and the waste silicon powder tank 43 through the reflux pipeline 300;

[0050] The back-blowing unit 5 includes a back-blowing gas pipeline 400 and a back-blowing gas filtering pipeline 500, wherein the back-blowing gas pipeline 400 is connected to the reflux pipeline 300, to which a nitrogen heater Ⅰ51 is connected, and is used to heat a portion of the purified nitrogen and then back-blow it into the adsorption tower under a slight positive pressure after the chlorosilane enriched in the activated carbon reaches saturation; the back-blowing gas filtering pipeline 500 is connected to the bottom of the adsorption tower, to which a back-blowing gas filter 52 is connected, and the back-blowing gas (i.e., the purified nitrogen) back-blown into the adsorption tower desorbs the chlorosilane from the adsorption column and is then filtered by the back-blowing gas filter 52 and re-delivered to the pressurized condensing unit 2, wherein the back-blowing filter 52 includes a back-blowing filter a 521 and a back-blowing filter b 522 connected in parallel.

[0051] Control valves are installed on the back-blowing gas pipeline 400 and the back-blowing gas filter pipeline 500. Before the activated carbon in the adsorption column in the adsorption tower adsorbs chlorosilane to a saturated state, the control valve is closed, and the entire system filters silicon powder in the exhaust gas and purifies and reuses nitrogen. When the activated carbon in the adsorption column adsorbs chlorosilane to a saturated state, the control valve is opened automatically or manually, and part of the purified nitrogen flowing out of the adsorption tower is heated to 180°C, and then heated and back-blown under a slightly positive pressure condition, and back-blown from the top of the adsorption tower into the adsorption tower again, so that chlorosilane is desorbed from the surface of the activated carbon, filtered from the bottom of the adsorption tower through the back-blowing gas filter pipeline 500, and then sent back to the pressurized condensation unit 2, and pressurized and condensed together with the nitrogen-containing exhaust gas from the cold hydrogenation, so as to achieve the purpose of removing all chlorosilane in the nitrogen and recovering them separately.

[0052] An organic pre-buffer tank 11 is arranged between the silicon powder filtering unit 1 and the pressurized condensing unit 2, for mixing and buffering the chlorosilane desorbed from the back-blowing unit 5 and the nitrogen-containing silane waste gas from the polysilicon cold hydrogenation system.

[0053] The polysilicon waste gas recycling system of the utility model recycles nitrogen in the waste gas discharged from the drying link of the waste silicon powder tank in the polysilicon cold hydrogenation system, thereby reducing the nitrogen consumption of the system, achieving the purpose of reducing liquid nitrogen procurement consumption and reducing production costs.

[0054] By using pressurized condensation, activated carbon adsorption and other process technologies, chlorosilane in the waste gas is removed (recovered). Through automatic system control, the difficulty of hydrogen enrichment is solved, achieving overall process innovation. At the same time, the problem of trace silicon powder in the waste gas discharged from the original process polluting the surrounding equipment is solved, achieving environmental protection improvement and innovation.

Claims

1. A polysilicon waste gas recycling system, characterized in that: It includes a silicon powder filtration unit, a pressurized condensation unit, an adsorption unit and a nitrogen recycling unit which are sequentially connected by pipelines; The silicon powder filtration unit comprises a silicon powder filter for removing silicon powder from nitrogen-containing waste gas in a polysilicon cold hydrogenation system; The pressurized condensation unit comprises an exhaust gas compressor, a post-condenser and a heat exchanger connected in sequence, and is used to perform deep cooling condensation on the nitrogen-containing exhaust gas after silicon removal to remove chlorosilane in the nitrogen-containing exhaust gas; The adsorption unit comprises an adsorption tower, in which an adsorption column is arranged, and the adsorption column is filled with activated carbon, which is used to further adsorb chlorosilane in the nitrogen-containing waste gas through the activated carbon; The nitrogen recycling unit includes a reflux pipeline connected to the top of the adsorption tower, which is used to return the purified nitrogen after adsorption by the adsorption column to the polysilicon cold hydrogenation system through the reflux pipeline for continued use in cold hydrogenation; It also includes a back-blowing unit, wherein the back-blowing unit includes a back-blowing pipeline and a back-blowing filter pipeline; The back-blowing gas pipeline is connected to the reflux pipeline, and is connected to a nitrogen heater I, which is used to heat part of the purified nitrogen and then back-blow it into the adsorption tower under a slight positive pressure after the chlorosilane enriched in the activated carbon reaches saturation; The back-blowing gas filter pipeline is connected to the bottom of the adsorption tower, and a back-blowing gas filter is connected thereto. The back-blowing gas back-blown into the adsorption tower desorbs chlorosilane from the adsorption column, and then is filtered by the back-blowing gas filter and re-delivered to the pressurized condensation unit.

2. A polysilicon waste gas recycling system according to claim 1, characterized in that: Control valves are installed on both the back-blowing air pipeline and the back-blowing air filtering pipeline, and the control valves are closed before the activated carbon reaches a saturated state.

3. A polysilicon waste gas recycling system according to claim 1, characterized in that: An organic pre-buffer tank is arranged between the silicon powder filtering unit and the pressurized condensing unit, for mixing and buffering the chlorosilane desorbed from the back-blowing unit and the nitrogen-containing waste gas in the polysilicon cold hydrogenation system.

4. A polysilicon waste gas recycling system according to claim 1, characterized in that: The polysilicon cold hydrogenation system includes a nitrogen heater II, a waste silicon powder dechlorination drying tank and a waste silicon powder tank. The nitrogen-containing waste gas generated in the system is first heated by the nitrogen heater II and then sequentially passed into the waste silicon powder dechlorination drying tank and the waste silicon powder tank and then into the silicon powder filtration unit.

5. A polysilicon waste gas recycling system according to claim 4, characterized in that: The purified nitrogen gas is respectively refluxed into the polysilicon cold hydrogenation system through the reflux pipeline to continue to be used for cold hydrogenation, which means that the purified nitrogen gas is refluxed into the waste silicon powder dechlorination drying tank and the waste silicon powder tank through the reflux pipeline.

6. A polysilicon waste gas recycling system according to claim 1, characterized in that: The pipeline connecting the post-machine condenser and the heat exchanger in the pressurized condensing unit is also connected to a post-machine buffer tank and a precision filter.

7. A polysilicon waste gas recycling system according to claim 6, characterized in that: The heat exchanger is also connected to a Freon heat exchanger behind it for recovering the condensed chlorosilane after heat exchange.

8. The polysilicon waste gas recycling system according to claim 1, characterized in that: The adsorption unit further comprises a product filter a and a product filter b connected in parallel, which are connected to the gas outlet pipeline at the top of the adsorption tower and are used for further filtering the gas to obtain purified nitrogen.

9. A polysilicon waste gas recycling system according to claim 8, characterized in that: A waste gas venting pipeline is also arranged behind the product filter a and the product filter b.

10. The polysilicon waste gas recycling system according to claim 1, characterized in that: The adsorption tower comprises an adsorption tower a, an adsorption tower b and an adsorption tower c connected in parallel; the back-blowing gas filter comprises a back-blowing filter a and a back-blowing filter b connected in parallel.

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