A circulating treatment system for silane gas decomposition tail gas in polysilicon production

Abstract

The utility model discloses a kind of cyclic treatment systems of silane gas decomposition tail gas in polysilicon production, including at least one group by adsorption tower and analysis tower composition pressure swing adsorption device, the gas inlet end of pressure swing adsorption device is equipped with tail gas compressor, tail gas compressor connects the tail gas outlet of silane gas decomposition device, the product gas outlet end of pressure swing adsorption device is equipped with adsorption product gas tank, adsorption product gas tank is connected to silane gas decomposition device by circulating hydrogen pipe, the pressure relief end of pressure swing adsorption device is connected to cold hydrogenation device.The utility model utilizes the principle of pressure swing adsorption to separate and impurity removal hydrogen in silane gas decomposition tail gas, obtained product hydrogen and pressure relief gas can be used as circulating hydrogen and cold hydrogenation device respectively, without material waste, the setting of tail gas compressor and adsorption product gas tank can guarantee the stability of system control and circulating hydrogen recovery.

Description

Technical Field

[0001] This utility model relates to a recycling system for silane gas decomposition tail gas in polysilicon production, specifically a recycling and treatment system for low-pressure tail gas generated during silane gas decomposition to prepare polysilicon, belonging to the field of polysilicon production technology. Background Technology

[0002] Thermal decomposition of silane gas (SiH4) is a key process in the production of high-purity polycrystalline silicon, widely used in photovoltaic, semiconductor, and electronic device manufacturing. Under certain temperature and pressure conditions, silane gas decomposes into hydrogen (H2) and solid silicon (Si), with silicon being the target product, and its purity directly affecting the performance of downstream devices. Currently, to control the decomposition rate of silane gas, recycled hydrogen is usually introduced as a dilution gas during the reaction. However, if the recycled hydrogen contains high levels of impurities (such as N2, CH4, CO, carbon dioxide, H2O, B / P, and metallic impurities), it will not only reduce the purity of the silicon product but may also trigger side reactions (such as the formation of SiO2 or SiC), thereby affecting the electrical properties of polycrystalline silicon. Therefore, efficient purification of recycled hydrogen is a necessary step to ensure product quality.

[0003] Silane decomposition units typically operate at relatively low pressures (0.01–1 MPa). Under these conditions, traditional hydrogen purification technologies (such as pressure swing adsorption (PSA) and temperature swing adsorption (TSA)) are mainly designed for conventional industrial hydrogen purification. However, there is still a lack of system solutions that balance economic efficiency and stability for the treatment of silane decomposition tail gas and the precise control of circulating hydrogen.

[0004] Existing patent CN209378717U discloses a hydrogen recovery system from silane decomposition tail gas. This system includes at least two adsorption columns, with each column alternating between adsorption and desorption modes. A hydrogen compressor provides pressure differential power to continuously recover hydrogen from the silane decomposition tail gas. Simultaneously, a small amount of silane gas in the tail gas is discharged outside the system for further treatment. An online detector monitors the silane gas content in the hydrogen in real time, providing feedback to the DCS control system, thus achieving effective separation of hydrogen from the silane decomposition tail gas and ensuring the purity of the recovered hydrogen. While this system can separate hydrogen from the tail gas, placing the compressor after the adsorption columns means that the gas pressure entering the adsorption columns is lower. This may lead to unstable compressor intake during adsorption column switching, affecting the stable operation of the equipment. Furthermore, the system does not provide a reasonable arrangement for the specific processing of the separated hydrogen. Utility Model Content

[0005] The purpose of this invention is to provide a recycling system for silane decomposition tail gas in polysilicon production. It utilizes the pressure swing adsorption principle to separate and remove hydrogen from the silane decomposition tail gas. The resulting product hydrogen and depressurized gas can be used as recycled hydrogen and cold hydrogenation devices, respectively, without material waste. The tail gas compressor and the product gas adsorption tank ensure the stability of system control and recycled hydrogen recovery.

[0006] This utility model is achieved through the following technical solution: a circulating treatment system for silane gas decomposition tail gas in polysilicon production, comprising at least one pressure swing adsorption (PSA) device consisting of an adsorption tower and a desorption tower. The PSA device is equipped with a tail gas compressor at its inlet end, which is connected to the tail gas outlet of the silane gas decomposition device. The PSA device is equipped with an adsorbed product gas tank at its product gas outlet end, which is connected to the silane gas decomposition device via a circulating hydrogen pipe. The PSA device is also connected to a cold hydrogenation device at its pressure relief end.

[0007] The circulating hydrogen pipeline is equipped with a circulating hydrogen flow regulating valve and a circulating hydrogen flow detector arranged sequentially along the circulating hydrogen flow direction, and the circulating hydrogen flow detector and the circulating hydrogen flow regulating valve are interlocked.

[0008] Between the pressure swing adsorption device and the cold hydrogenation device, a pressure relief regulating device and a venting hydrogen compressor are sequentially installed. The pressure relief regulating device consists of two sets of pipelines connected in parallel. One set of pipelines is equipped with a pressure relief regulating valve, and the other set of pipelines is equipped with a pressure relief shut-off valve and a vacuum pump.

[0009] The adsorption product gas tank is equipped with a pressure gauge, and a connecting pipeline is provided between the adsorption product gas tank and the venting hydrogen compressor. A product gas pressure regulating valve is provided on the connecting pipeline, and the product gas pressure regulating valve is interlocked with the pressure gauge.

[0010] The adsorption tower and the desorption tower have the same structure. The inlet end of the pressure swing adsorption device is the inlet of the adsorption tower / desorption tower, the product gas outlet end of the pressure swing adsorption device is the product gas outlet of the adsorption tower / desorption tower, and the pressure relief end of the pressure swing adsorption device is the pressure relief port of the adsorption tower / desorption tower.

[0011] The adsorption / desorption tower is equipped with shut-off valves at its inlet, product gas outlet, and pressure relief port.

[0012] Compared with the prior art, this utility model has the following advantages and beneficial effects:

[0013] (1) This utility model can realize the complete recovery and utilization of the tail gas of the silane gas decomposition device. Pressure swing adsorption is used to remove impurities and separate hydrogen in the tail gas. The separated product hydrogen is recycled as circulating hydrogen for the silane gas decomposition device. The gas discharged after depressurization can be used in the cold hydrogenation device.

[0014] (2) This utility model can achieve stable control of the circulating hydrogen flow rate. On the one hand, the circulating hydrogen flow rate detector and the circulating hydrogen flow rate regulating valve can be used to achieve precise control of the gas flow rate on the circulating hydrogen pipeline. On the other hand, the product gas pressure regulating valve can be used to achieve stable adjustment of the pressure of the adsorption product gas tank, thus ensuring the stability of the circulating hydrogen source.

[0015] (3) By setting a tail gas compressor at the inlet end of the pressure swing adsorption device, the present invention forms a “compression-adsorption” treatment method. Compared with the existing structure without a compressor, it can realize the advantages of miniaturization of equipment (such as adsorption column and auxiliary instruments, pipes and valves, etc.) and small overall equipment footprint, which can save equipment cost investment. In addition, the tail gas compressor can effectively control the inlet pressure, making the inlet pressure more stable and the inlet flow rate fluctuation smaller, which significantly improves the stability of system control. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of this utility model.

[0017] Among them, 1—adsorption tower, 2—desorption tower, 3—tail gas compressor, 4—adsorption product gas tank, 5—circulating hydrogen pipe, 6—circulating hydrogen flow regulating valve, 7—circulating hydrogen flow detector, 8—venting hydrogen compressor, 9—pressure relief regulating valve, 10—vacuum pressure relief shut-off valve, 11—vacuum pump, 12—pressure gauge, 13—connecting pipeline, 14—product gas pressure regulating valve. Detailed Implementation

[0018] The utility model's purpose, technical solution, and beneficial effects will be further explained in detail below.

[0019] It should be noted that the following detailed description is exemplary and intended to provide further explanation of the claimed invention. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0020] The silane gas decomposition unit is a key piece of equipment used to pyrolyze silane gas (SiH4) into silicon and hydrogen, and it has important applications in the polycrystalline silicon production process. The exhaust gas emitted by this unit mainly consists of high-purity hydrogen (purity > 99%), while also containing trace impurities, including nitrogen, methane, carbon monoxide, carbon dioxide, moisture, B / P impurities, and metallic impurities. In existing technologies, although high-purity hydrogen can be separated from the exhaust gas using pressure swing adsorption (PSA), there is a lack of systematic planning for the subsequent utilization of the recovered hydrogen. To address this technological gap, this invention proposes a recycling system for the exhaust gas from the silane gas decomposition process in polycrystalline silicon production. This system aims to achieve two core objectives: first, to deeply purify various impurities in the exhaust gas; and second, to reintroduce the recovered high-purity hydrogen into the silane gas decomposition unit for recycling.

[0021] The cyclic processing system provided by this utility model has significant technical value:

[0022] Firstly, considering that adding an appropriate amount of hydrogen to the silane decomposition reaction (SiH4⇌Si+2H2) can effectively regulate the chemical equilibrium and reduce the concentration of SiH4, preventing the reaction from becoming too rapid, the deposition kinetics of silicon particles can be optimized by precisely controlling the hydrogen-to-silane ratio (H2 / SiH4) during silane decomposition, significantly improving the deposition rate and uniformity. This system provides a reliable guarantee for the precise control of this key process parameter by establishing a stable hydrogen circulation channel.

[0023] Secondly, from an economic perspective, this recycling system significantly reduces the consumption of fresh hydrogen during production by recovering and reusing hydrogen from the exhaust gas, effectively saving raw material costs. This design not only aligns with the concept of green manufacturing but also creates considerable economic benefits for the company.

[0024] The specific implementation of this utility model will be described below with reference to the embodiments. Of course, the protection scope of this utility model is not limited to the following embodiments.

[0025] Example 1:

[0026] This embodiment describes a recycling system for the tail gas from the decomposition of silane gas in polysilicon production. Its structure is as follows: Figure 1As shown, it mainly consists of a tail gas compressor 3, an adsorption tower 1, a desorption tower 2, an adsorption product gas tank 4, a vacuum pump 11, and a venting air compressor. Among them, the adsorption tower 1 and the desorption tower 2 form a pressure swing adsorption device. The low-pressure tail gas of the silane gas decomposition device is compressed by the tail gas compressor 3 and sent to the pressure swing adsorption device. After being processed by the adsorption tower 1, the product gas is sent to the adsorption product gas tank 4 for buffering, and then sent to the silane gas decomposition device as mixed hydrogen gas. After the adsorption time is reached, the adsorption tower 1 is depressurized. The depressurized gas is extracted by the vacuum pump 11 and then compressed by the venting air compressor and sent to the cold hydrogenation device.

[0027] This embodiment also includes a process detection and control system, including a circulating hydrogen flow detector 7 (real-time flow monitoring), a circulating hydrogen flow regulating valve 6 (closed-loop control with flow monitoring), a pressure gauge 12 of the adsorption product gas tank 4 (real-time tank pressure monitoring), and a product gas pressure regulating valve 14 (closed-loop control with tank pressure). This ensures the stability of the hydrogen circulation process in the system and the precise adjustability of parameters, thus guaranteeing the accurate control of the hydrogen to silane ratio (H2 / SiH4) in the silane gas decomposition device.

[0028] Specifically, in this embodiment, a circulating hydrogen pipe 5 is installed between the adsorption product gas tank 4 and the silane gas decomposition device. A circulating hydrogen flow regulating valve 6 and a circulating hydrogen flow detector 7 are sequentially installed on the circulating hydrogen pipe 5 along the direction of circulating hydrogen flow. The circulating hydrogen flow detector 7 monitors the flow rate of circulating hydrogen in the pipe in real time. When the circulating hydrogen flow rate fluctuates, it is fed back to the upstream circulating hydrogen flow regulating valve 6 in real time. The opening degree of the circulating hydrogen flow regulating valve 6 is adjusted by a PID controller to achieve precise control of the circulating hydrogen flow rate. In this embodiment, a connecting pipe 13 is installed between the adsorption product gas tank 4 and the venting hydrogen compressor 8, and a product gas pressure regulating valve 14 is installed on this connecting pipe 13. The pressure gauge 12 of the adsorption product gas tank 4 monitors the hydrogen pressure in the tank in real time. When the pressure fluctuates, the opening degree of the product gas pressure regulating valve 14 is adjusted by a PID controller to ensure the stability of the circulating hydrogen source.

[0029] This embodiment enables the recovery and reuse of all tail gas in the silane decomposition device. Hydrogen is used as circulating hydrogen after pressure swing adsorption (PSA), and the depressurized gas after adsorption can be sent to the cold hydrogenation device (to participate in the reaction as a raw material in the hydrogenation furnace). Specifically, in this embodiment, a pressure relief regulating device and a venting hydrogen compressor 8 are sequentially installed between the PSA device and the cold hydrogenation device. The pressure relief regulating device consists of two sets of pipelines connected in parallel. One set of pipelines is equipped with a pressure relief regulating valve 9, and the other set of pipelines is equipped with a pressure relief shut-off valve and a vacuum pump 11.

[0030] In this embodiment, both adsorption tower 1 and desorption tower 2 adopt the same pressure swing adsorption (PSA) tower structure design, and alternately perform the functions of adsorption (hydrogen purification) and desorption (adsorbent regeneration) in the PSA device. Therefore, in this embodiment, adsorption tower 1 refers to the PSA tower that performs the adsorption function, and desorption tower 2 refers to the PSA tower that performs the desorption function.

[0031] Furthermore, the process flow of this embodiment can be summarized as follows:

[0032] (1) Exhaust gas compression

[0033] The silane gas decomposition unit produces low-pressure tail gas (mainly hydrogen, with a pressure of about 10 to 100 kPa), which is then sent to the tail gas compressor 3 for pressurization (about 0.1 to 0.6 MPa) and then sent to the pressure swing adsorption unit.

[0034] (2) Pressure Swing Adsorption

[0035] Open the inlet shut-off valve V1 at the bottom (inlet) of adsorption tower 1 in the pressure swing adsorption unit to pressurize adsorption tower 1. After pressurizing to the set value, open the product gas shut-off valve V2 at the top (product gas outlet) of adsorption tower 1. The tail gas is sent into adsorption tower 1 for adsorption and impurity removal. The product gas after adsorption and impurity removal is sent from the top (product gas outlet) of adsorption tower 1 into the adsorption product gas tank 4 for buffering. After the set adsorption time is reached, close the inlet shut-off valve V1 at the bottom (inlet) of adsorption tower 1 and the product gas shut-off valve V2 at the top (product gas outlet) of adsorption tower 1 in sequence, and then open the adsorption tower 4. The pressure relief shut-off valve V3 and pressure relief regulating valve 9 at the bottom (pressure relief port) of adsorption column 1 are used for pressure relief. When the pressure inside the adsorption column reaches the set value, the pressure relief regulating valve 9 is closed, the vacuum pressure relief shut-off valve 10 is opened, and the vacuum pump 11 is automatically started to perform vacuuming. When the pressure inside the column is evacuated to the set vacuum level, the pressure relief shut-off valve V3 at the bottom (pressure relief port) of adsorption column 1 is closed, the vacuum pressure relief shut-off valve 10 and the vacuum pump 11 are closed, and adsorption column 1 is converted into desorption column 2. After desorption (the desorption process and adsorption process are conventional techniques in this field and will not be described in detail here), it is ready for use. The depressurized tail gas is sent to the venting air compressor for pressurization (about 0.6 to 1.0 MPa), and then sent to the cold hydrogenation unit for recycling.

[0036] (3) Circulating hydrogen regulation

[0037] Most of the product gas (circulating hydrogen) in the product gas tank is sent to the silane gas decomposition unit for recycling through the circulating hydrogen flow regulating valve 6. During this process, the circulating hydrogen flow detector 7 monitors the circulating hydrogen flow in real time. At the same time, the circulating hydrogen flow regulating valve 6 automatically adjusts its opening according to the set circulating hydrogen flow value. In addition, the pressure of the product gas tank is controlled by the product hydrogen pressure regulating valve to adjust the opening, venting to the air venting compressor, and then pressurizing and sending it to the cold hydrogenation unit for recycling.

[0038] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present utility model shall fall within the protection scope of the present utility model.

Claims

1. A system for recycling processing of silane gas decomposition off-gas in polysilicon production, characterized by: It includes at least one pressure swing adsorption device consisting of an adsorption tower (1) and a desorption tower (2). The inlet end of the pressure swing adsorption device is equipped with a tail gas compressor (3), which is connected to the tail gas outlet of the silane gas decomposition device. The product gas outlet end of the pressure swing adsorption device is equipped with an adsorption product gas tank (4), which is connected to the silane gas decomposition device through a circulating hydrogen pipe (5). The pressure relief end of the pressure swing adsorption device is connected to a cold hydrogenation device.

2. The cyclic treatment system of claim 1, wherein: The circulating hydrogen pipe (5) is provided with a circulating hydrogen flow regulating valve (6) and a circulating hydrogen flow detector (7) arranged sequentially along the circulating hydrogen flow direction. The circulating hydrogen flow detector (7) and the circulating hydrogen flow regulating valve (6) are interlocked.

3. The cyclic processing system according to claim 1, characterized in that: The pressure swing adsorption device is connected to the cold hydrogenation device by a pressure relief regulating device and a venting hydrogen compressor (8) in sequence. The pressure relief regulating device consists of two sets of pipelines connected in parallel. One set of pipelines is equipped with a pressure relief regulating valve (9), and the other set of pipelines is equipped with a vacuum pressure relief shut-off valve (10) and a vacuum pump (11).

4. The cyclic processing system according to claim 3, characterized in that: The adsorption product gas tank (4) is equipped with a pressure gauge (12), and a connecting pipeline (13) is provided between the adsorption product gas tank (4) and the venting hydrogen compressor (8). A product gas pressure regulating valve (14) is provided on the connecting pipeline (13), and the product gas pressure regulating valve (14) is interlocked with the pressure gauge (12).

5. The cyclic processing system according to claim 1, characterized in that: The adsorption tower (1) and the desorption tower (2) have the same structure. The inlet end of the pressure swing adsorption device is the inlet of the adsorption tower (1) / desorption tower (2), the product gas outlet end of the pressure swing adsorption device is the product gas outlet of the adsorption tower (1) / desorption tower (2), and the pressure relief end of the pressure swing adsorption device is the pressure relief port of the adsorption tower (1) / desorption tower (2).

6. The cyclic processing system according to claim 5, characterized in that: The adsorption tower (1) / desorption tower (2) is equipped with shut-off valves at the air inlet, product gas outlet and pressure relief port.

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