Waste gas treatment system for polycrystalline silicon production

Abstract

The utility model discloses a waste gas treatment system for polycrystalline silicon production, relates to the technical field of polycrystalline silicon, and aims to reduce the escape probability of chlorosilane waste gas. According to the main technical scheme, the waste gas treatment system for polycrystalline silicon production is characterized in that the lower end side of an acid liquor buffer tank, an acid liquor conveying pump and the side wall of a first-stage washing tower are sequentially connected, a tower kettle of the first-stage washing tower is connected to the top wall of the acid liquor buffer tank, and the side wall of the first washing tower is connected to a waste gas input pipe; the lower end side of the alkali liquor buffer tank, the alkali liquor delivery pump and the side wall of the secondary washing tower are sequentially connected, a tower kettle of the secondary washing tower is connected to the top wall of the alkali liquor buffer tank, the upper end of the primary washing tower is connected to the side wall of the secondary washing tower, and an outlet of the alkali liquor delivery pump is connected to the water seal tank; the side wall of the water-sealed tank is connected to the upper end side and the lower end side of the secondary washing tower, and the upper end of the water-sealed tank is connected to the blow-down pipe; and the outlet of the acid liquor delivery pump and the outlet of the alkali liquor delivery pump are respectively connected to the neutralization regulating tank.

Description

Technical Field

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

[0002] During the production of polysilicon using the Siemens process, waste gas containing chlorosilane is generated.

[0003] Since chlorosilane-containing waste gas needs to be treated in time before it can be discharged, in September 2019, Tang Weibo, Xu Liqiang and Wang Feixing of Shaanxi Nonferrous Tianhong Ruike Silicon Materials Co., Ltd. published an article in the journal Chemical Management titled "Treatment of Silane Waste Gas in Polysilicon Production". The article states the following:

[0004] like Figure 2 As shown, the silane waste gas discharged from the upstream first enters the Venturi scrubber together with the 5%wt sodium hydroxide solution, and the gas-liquid two-phase reaction absorption is accelerated through the "throat" of the Venturi scrubber, mainly generating soluble Na2SiO3 accompanied by H2, consuming more than 90% of the silane gas. Then, the gas-liquid mixture enters the silane elution tank at the bottom, and the water flows to the spray tower equipped with a packing layer at the top of the tank, fully reacting with the 5%wt sodium hydroxide solution in countercurrent, consuming the remaining silane gas, and pure nitrogen needs to be input. Other components in the tail gas include nitrogen, hydrogen, water vapor and silane gas.

[0005] However, the high internal pressure of the silane waste gas washing tank and the spray tower will inevitably lead to a faster gas flow rate, which will shorten the residence time of the silane waste gas in the spray tower, increase the risk of silane waste gas escape, and cause the risk of not being able to completely treat the silane waste gas. Utility Model Content

[0006] In view of this, an embodiment of the utility model provides a waste gas treatment system for polysilicon production, the main purpose of which is to reduce the probability of chlorosilane waste gas escape and efficiently treat the chlorosilane waste gas.

[0007] In order to achieve the above purpose, the utility model mainly provides the following technical solutions:

[0008] The utility model embodiment provides a waste gas treatment system for polysilicon production, the system comprising: an acid washing section, an alkali washing section and a solid waste removal section;

[0009] The acid washing part includes a primary washing tower, an acid buffer tank and an acid delivery pump, the lower end side of the acid buffer tank, the acid delivery pump and the side wall of the primary washing tower are connected in sequence, the tower kettle of the primary washing tower is connected to the top wall of the acid buffer tank, and the side wall of the first washing tower is connected to the exhaust gas input pipe;

[0010] The alkali solution washing part includes a secondary washing tower, an alkali solution buffer tank, an alkali solution delivery pump and a water seal tank, the lower end side of the alkali solution buffer tank, the alkali solution delivery pump and the side wall of the secondary washing tower are connected in sequence, the tower kettle of the secondary washing tower is connected to the top wall of the alkali solution buffer tank, the upper end of the primary washing tower is connected to the side wall of the secondary washing tower, the outlet of the alkali solution delivery pump is connected to the water seal tank, the side wall of the water seal tank is connected to the upper end and the lower end side of the secondary washing tower, and the upper end of the water seal tank is connected to the vent pipe;

[0011] The solid waste removal unit comprises a neutralization regulating tank, a plate and frame filter press and a neutral wastewater tank which are connected in sequence, and the outlet of the acid solution delivery pump and the outlet of the alkali solution delivery pump are respectively connected to the neutralization regulating tank.

[0012] The purpose of the utility model and the solution to its technical problems can also be further achieved by adopting the following technical measures.

[0013] Optionally, a plurality of acid spray plates are vertically arranged in sequence in the first-stage washing tower, and an output pipe of the acid delivery pump passes through a side wall of the first-stage washing tower and is respectively connected to the plurality of acid spray plates.

[0014] Optionally, a plurality of alkali solution spray plates are vertically arranged in sequence in the secondary washing tower, and an output pipe of the alkali solution delivery pump passes through a side wall of the secondary washing tower and is respectively connected to the plurality of alkali solution spray plates.

[0015] Optionally, it also includes a water supply pipe, which is respectively connected to the upper end side of the first-level washing tower and the upper end side of the second-level washing tower.

[0016] Optionally, it also includes a wastewater delivery pump, the inlet of which is connected to the lower end side of the neutral wastewater tank, and the outlet of which is connected to the water replenishment pipe and the evaporation crystallization mechanism respectively.

[0017] Optionally, the output pipe of the acid solution delivery pump is connected to the first circulating water heat exchanger.

[0018] Optionally, the output pipe of the alkali solution delivery pump is connected to the second circulating water heat exchanger.

[0019] Optionally, the output pipe of the wastewater delivery pump is connected to the third circulating water heat exchanger.

[0020] By means of the above technical solution, the utility model has at least the following advantages:

[0021] The acid in the acid buffer tank is transported to the primary washing tower by the acid delivery pump, and the chlorosilane-containing waste gas enters the first washing tower from the waste gas inlet pipe. The chlorosilane-containing waste gas and the acid are reversely contacted, and the chlorosilane therein is hydrolyzed, and a large amount of HCL and SiO2 are generated in the bottom of the washing tower. The acid in the bottom of the tower enters the acid buffer tank and is then transported to the primary washing tower by the acid delivery pump. The acid circulates and contacts the chlorosilane-containing waste gas to hydrolyze the chlorosilane.

[0022] The mixed gas of HCL gas, hydrogen and inert gas that is not absorbed in the waste gas is discharged from the top of the first-level scrubber and enters the second-level scrubber. The alkali in the alkali buffer tank is sprayed into the second-level scrubber by the alkali delivery pump. The alkali and the mixed gas are in countercurrent contact to remove the HCL gas. The hydrogen and inert gas that cannot be absorbed are discharged from the upper end of the second-level scrubber to the water seal tank, and finally discharged to the outside from the vent pipe at the upper end of the water seal tank.

[0023] In the above process, the alkali solution delivery pump also outputs the alkali solution to the water seal tank, and then flows back to the kettle of the secondary washing tower, thereby reducing the proportion of the HCL component in the gas discharged from the water seal tank.

[0024] The acid (containing SiO2) output by the acid delivery pump and the alkali solution output by the alkali delivery pump are mixed in the neutralization adjustment tank, the pH value is adjusted to neutral, SiO2 and sodium hydroxide react to generate Na2SiO3, the waste liquid in the neutralization adjustment tank is pressurized by the filter press feed pump and transported to the plate and frame filter press, the solid waste such as Na2SiO3 is filtered and transported away by a dump truck, and the neutral high-salt waste liquid enters the neutral wastewater tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the structure of a waste gas treatment system for polysilicon production provided by an embodiment of the utility model;

[0026] Figure 2 This is a schematic diagram of the treatment method of silane waste gas in the prior art.

[0027] The figure marks in the drawings of the specification include: a primary washing tower 1, an acid buffer tank 2, an acid delivery pump 3, a waste gas input pipe 4, a secondary washing tower 5, an alkali buffer tank 6, an alkali delivery pump 7, a water seal tank 8, a vent pipe 9, a neutralization adjustment tank 10, a plate and frame filter press 11, a neutral wastewater tank 12, a filter press feed pump 13, an exhaust pipe 14, a reflux pipe 15, a first regulating valve 16, a second regulating valve 17, an acid spray plate 18, an alkali spray plate 19, a water supply pipe 20, a wastewater delivery pump 21, a first circulating water heat exchanger 22, a second circulating water heat exchanger 23, a third circulating water heat exchanger 24, a water supply spray plate 25, a guide cap 26, and an annular plate 27. DETAILED DESCRIPTION

[0028] In order to further explain the technical means and effects adopted by the utility model to achieve the predetermined utility model purpose, the specific implementation methods, structures, features and effects of the utility model application are described in detail below in conjunction with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures, or characteristics in one or more embodiments may be combined in any suitable form.

[0029] The utility model is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0030] like Figure 1 As shown, an embodiment of the utility model provides a waste gas treatment system for polysilicon production, which includes: an acid washing part, an alkali washing part and a solid waste removal part;

[0031] The acid washing part includes a primary washing tower 1, an acid buffer tank 2 and an acid delivery pump 3, the lower end side of the acid buffer tank 2, the acid delivery pump 3 and the side wall of the primary washing tower 1 are connected in sequence, the tower bottom of the primary washing tower 1 is connected to the top wall of the acid buffer tank 2, and the side wall of the first washing tower is connected to the exhaust gas input pipe 4;

[0032] The alkali solution washing part includes a secondary washing tower 5, an alkali solution buffer tank 6, an alkali solution delivery pump 7 and a water seal tank 8, the lower end side of the alkali solution buffer tank 6, the alkali solution delivery pump 7 and the side wall of the secondary washing tower 5 are connected in sequence, the tower kettle of the secondary washing tower 5 is connected to the top wall of the alkali solution buffer tank 6, the upper end of the primary washing tower 1 is connected to the side wall of the secondary washing tower 5, the outlet of the alkali solution delivery pump 7 is connected to the water seal tank 8, the side wall of the water seal tank 8 is connected to the upper end and the lower end side of the secondary washing tower 5, and the upper end of the water seal tank 8 is connected to the vent pipe 9;

[0033] The solid waste removal unit includes a neutralization adjustment tank 10, a plate and frame filter press 11 and a neutral wastewater tank 12 which are connected in sequence. The outlet of the acid delivery pump 3 and the outlet of the alkali delivery pump 7 are respectively connected to the neutralization adjustment tank 10.

[0034] The working process of the waste gas treatment system for polysilicon production is as follows:

[0035] The acid in the acid buffer tank 2 is transported to the primary washing tower 1 by the acid delivery pump 3, and the chlorosilane-containing waste gas enters the first washing tower from the waste gas inlet pipe 4. The chlorosilane-containing waste gas and the acid are reversely contacted, and the chlorosilane therein is hydrolyzed, and a large amount of HCL and SiO2 are generated in the bottom of the washing tower. The acid in the bottom of the tower enters the acid buffer tank 2, and then is transported to the primary washing tower 1 by the acid delivery pump 3. The acid circulates and contacts the chlorosilane-containing waste gas, so that the chlorosilane is hydrolyzed.

[0036] The mixed gas of HCL gas, hydrogen and inert gas that is not absorbed in the waste gas is discharged from the top of the primary washing tower 1 and enters the secondary washing tower 5. The alkali liquid in the alkali liquid buffer tank 6 is sprayed into the secondary washing tower 5 through the alkali liquid delivery pump 7. The alkali liquid and the mixed gas are in countercurrent contact to remove the HCL gas therein, and the hydrogen and inert gas that cannot be absorbed are discharged from the upper end of the secondary washing tower 5 to the water seal tank 8, and finally discharged to the outside from the vent pipe 9 at the upper end of the water seal tank 8.

[0037] In the above process, the alkali solution delivery pump 7 also outputs the alkali solution to the water seal tank 8, and then refluxes to the kettle of the secondary washing tower 5, thereby further reducing the proportion of the HCL component in the gas discharged from the water seal tank 8.

[0038] The acid (containing SiO2) output by the acid delivery pump 3 and the alkali solution output by the alkali delivery pump 7 are mixed in the neutralization adjustment tank 10, and the pH value is adjusted to neutral. SiO2 reacts with sodium hydroxide to generate Na2SiO3. The waste liquid in the neutralization adjustment tank 10 is pressurized by the filter press feed pump 13 and transported to the plate and frame filter press 11. The solid waste such as Na2SiO3 therein is filtered and transported away by a dump truck. The neutral high-salt waste liquid therein enters the neutral wastewater tank 12.

[0039] In the technical solution of the utility model, the hydrolysis of chlorosilane is carried out in the primary washing tower 1, and the neutralization of the acidic gas by alkali solution is carried out in the secondary washing tower 5. The internal space of the primary washing tower 1 and the internal space of the secondary washing tower 5 are sealed by the water sealing effect of the water sealing tank 8 to prevent the entry of external air, and no nitrogen input is required, thereby ensuring the residence time of chlorosilane gas or acidic gas in the washing tower, thereby preventing the escape of chlorosilane gas or acidic gas and efficiently treating chlorosilane waste gas.

[0040] Specifically, the inlet of the filter press feed pump 13 is connected to the lower end side of the neutralization adjustment tank 10 , and the outlet of the filter press feed pump 13 is connected to the plate and frame filter press 11 .

[0041] Specifically, the exhaust pipe 14 at the upper end of the secondary washing tower 5 penetrates the side wall of the water seal tank 8 and extends below the liquid level of the water seal tank 8. The output pipe of the alkali solution delivery pump 7 is connected to the upper end side of the water seal tank 8, and the lower end side of the water seal tank 8 is connected to the lower end side of the secondary washing tower 5 through the return pipe 15. The output pipe of the alkali solution delivery pump 7 is installed with a first regulating valve 16, and the return pipe 15 is installed with a second regulating valve 17. By adjusting the opening of the first regulating valve 16 and the opening of the second regulating valve 17, on the one hand, the liquid level of the water seal tank 8 is guaranteed to form a liquid seal on the exhaust pipe 14; on the other hand, a pressure balance is formed between the water seal tank 8 and the secondary washing tower 5.

[0042] like Figure 1As shown, in a specific embodiment, a plurality of acid spray plates 18 are vertically arranged in sequence in the primary washing tower 1, and the output pipe of the acid delivery pump 3 passes through the side wall of the primary washing tower 1 and is respectively connected to the plurality of acid spray plates 18.

[0043] In this embodiment, specifically, the acid solution is pressurized by the acid solution delivery pump 3, and then delivered to a plurality of acid solution spray plates 18 along the output pipe, and sprayed downward uniformly, and the acid solution and the exhaust gas are uniformly contacted in reverse, thereby promoting the hydrolysis of chlorosilane.

[0044] Specifically, the number of the acid spray trays 18 is three.

[0045] like Figure 1 As shown, in a specific embodiment, a plurality of alkali solution spray plates 19 are vertically arranged in sequence in the secondary washing tower 5, and the output pipe of the alkali solution delivery pump 7 passes through the side wall of the secondary washing tower 5 and is respectively connected to the plurality of alkali solution spray plates 19.

[0046] In this embodiment, specifically, after being pressurized by the alkali solution delivery pump 7, the alkali solution is delivered to a plurality of alkali solution spray plates 19 along the output pipe and sprayed downward uniformly, so that the alkali solution and the exhaust gas are in uniform reverse contact, thereby improving the efficiency of the alkali solution in capturing acidic gases.

[0047] Specifically, the number of the alkali solution spraying plates 19 is three.

[0048] like Figure 1 As shown, in a specific embodiment, a water supply pipe 20 is also included, and the water supply pipe 20 is connected to the upper end side of the primary washing tower 1 and the upper end side of the secondary washing tower 5 respectively.

[0049] In this embodiment, specifically, during daily operation, fresh water can be added to the primary washing tower 1 and the secondary washing tower 5 through the water supply pipe 20 .

[0050] Specifically, the water replenishment pipe 20 passes through the upper side wall of the primary washing tower 1 and the upper side wall of the secondary washing tower 5 respectively, and is connected to the water replenishment spray plate 25, which is located above the acid spray plate 18 or the alkali spray plate 19.

[0051] It also includes a guide cap 26 and an annular plate 27. The annular plate 27 is fixedly arranged between the water replenishment spray plate 25 and the acid spray plate 18 (alkali spray plate 19). The guide cap 26 covers the central hole of the annular plate 27 and is used to allow the rising air flow in the primary washing tower 1 and the secondary washing tower 5 to pass over the periphery of the guide cap 26, so that fresh water and the rising air flow are fully in contact.

[0052] like Figure 1As shown, in a specific embodiment, it also includes a wastewater delivery pump 21, the inlet of the wastewater delivery pump 21 is connected to the lower end side of the neutral wastewater tank 12, and the outlet of the wastewater delivery pump 21 is respectively connected to the water replenishment pipe 20 and the evaporation crystallization mechanism.

[0053] In this embodiment, specifically, during daily operation, the neutral wastewater after removing solid wastes such as Na2SiO3 is pressurized by the wastewater delivery pump 21, a part of the neutral wastewater enters the evaporation crystallization mechanism, and the other part flows back to the primary washing tower 1 and the secondary washing tower 5 respectively, thereby realizing wastewater reuse and reducing the amount of fresh water required to be supplemented by the water supply pipe 20.

[0054] like Figure 1 As shown, in a specific implementation, the output pipe of the acid solution delivery pump 3 is connected to the first circulating water heat exchanger 22 .

[0055] In the present embodiment, specifically, because the hydrolysis reaction of chlorosilane releases heat, the primary washing tower 1 and the acid buffer tank 2 are connected, and the temperature of the acid in the acid buffer tank 2 increases. However, after the acid flowing through the output pipe of the acid delivery pump 3 is cooled by the first circulating water heat exchanger 22, the temperature drops again, thereby ensuring the circulating spraying effect of the primary washing tower 1.

[0056] like Figure 1 As shown, in a specific implementation, the output pipe of the alkali solution delivery pump 7 is connected to the second circulating water heat exchanger 23 .

[0057] In the present embodiment, specifically, because the acid-base neutralization reaction is exothermic, the secondary washing tower 5 and the alkali solution buffer tank 6 are connected, and the temperature of the alkali solution in the alkali solution buffer tank 6 increases. However, after the alkali solution flowing through the output pipe of the alkali solution delivery pump 7 is cooled by the second circulating water heat exchanger 23, the temperature drops again, thereby ensuring the circulating spraying effect of the secondary washing tower 5.

[0058] like Figure 1 As shown, in a specific implementation, the output pipe of the wastewater delivery pump 21 is connected to the third circulating water heat exchanger 24 .

[0059] In this embodiment, specifically, the neutral wastewater is pressurized by the wastewater delivery pump 21, cooled by the third circulating water heat exchanger 24, and then supplied to the primary washing tower 1 and the secondary washing tower 5 to ensure the effect of spray washing.

[0060] This system reuses neutral high-salt wastewater, so that the high-salt wastewater generated in polysilicon production is recycled to the first and second level leaching towers for circulating spraying, reducing the treatment discharge of wastewater and the use of fresh water, reducing economic losses, greatly reducing environmental pressure, and realizing wastewater recycling.

[0061] The water supply pipe stops replenishing fresh water (the temperature of fresh water is 25℃ and the pressure is 0.3Mpa). After the neutral high-salt wastewater passes through the third circulating water heat exchanger for heat exchange and cooling, the temperature drops to 32℃ and the pressure is 0.55Mpa, which meets the use requirements. After spraying the washing tower with fresh water and neutral high-salt wastewater, the sample data in the neutral wastewater tank are compared:

[0062]

[0063] Through the above data results and the operating conditions of the device, it is confirmed that after using neutral high-salt wastewater, the total salt content of the wastewater in the neutral wastewater tank increased by up to 80,000 mg / L, the operation of the primary washing tower and the secondary washing tower was not affected, and the pipeline was not blocked due to the increase in total salt content, chloride ions and total hardness, and the production operation was not affected. The production requirements for recycling and utilization were met, and the purpose of recycling the wastewater generated in the polysilicon production process was achieved.

[0064] The operating parameters of the primary scrubber and the secondary scrubber are compared as follows:

[0065]

[0066]

[0067] In summary, the above scheme can achieve the following effects:

[0068] 1. By analyzing and comparing the data of neutral wastewater tank samples, it is accurately inferred that the method can achieve the operating effect;

[0069] 2. The spray volume of neutral high-salt wastewater in the primary and secondary washing towers should be no less than 1.5m 3 / h, and no crystallization occurred in the pipeline, which confirmed the feasibility of the scheme.

[0070] The above is only a specific implementation of the utility model, but the protection scope of the utility model is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the utility model, which should be included in the protection scope of the utility model. Therefore, the protection scope of the utility model should be based on the protection scope of the claims.

Claims

1. A waste gas treatment system for polysilicon production, characterized in that: include: An acid washing section, the acid washing section comprising a primary washing tower, an acid buffer tank and an acid delivery pump, the lower end side of the acid buffer tank, the acid delivery pump and the side wall of the primary washing tower are connected in sequence, the tower kettle of the primary washing tower is connected to the top wall of the acid buffer tank, and the side wall of the primary washing tower is connected to the exhaust gas inlet pipe; An alkali solution washing section, the alkali solution washing section comprises a secondary washing tower, an alkali solution buffer tank, an alkali solution delivery pump and a water seal tank, the lower end side of the alkali solution buffer tank, the alkali solution delivery pump and the side wall of the secondary washing tower are connected in sequence, the tower kettle of the secondary washing tower is connected to the top wall of the alkali solution buffer tank, the upper end of the primary washing tower is connected to the side wall of the secondary washing tower, the outlet of the alkali solution delivery pump is connected to the water seal tank, the side wall of the water seal tank is connected to the upper end and the lower end side of the secondary washing tower, and the upper end of the water seal tank is connected to the vent pipe; The solid waste removal part comprises a neutralization regulating tank, a plate and frame filter press and a neutral waste water tank which are connected in sequence, and the outlet of the acid delivery pump and the outlet of the alkali delivery pump are respectively connected to the neutralization regulating tank.

2. The waste gas treatment system for polysilicon production according to claim 1, characterized in that: A plurality of acid liquid spraying plates are arranged vertically in sequence in the first-stage washing tower, and the output pipe of the acid liquid delivery pump passes through the side wall of the first-stage washing tower and is respectively connected to the plurality of acid liquid spraying plates.

3. The waste gas treatment system for polysilicon production according to claim 1, characterized in that: A plurality of alkali solution spray plates are arranged vertically in sequence in the secondary washing tower, and the output pipe of the alkali solution delivery pump passes through the side wall of the secondary washing tower and is respectively connected to the plurality of alkali solution spray plates.

4. The waste gas treatment system for polysilicon production according to claim 2 or 3, characterized in that: It also includes a water supply pipe, which is respectively connected to the upper end side of the first-level washing tower and the upper end side of the second-level washing tower.

5. The waste gas treatment system for polysilicon production according to claim 4, characterized in that: It also includes a wastewater delivery pump, the inlet of which is connected to the lower end of the neutral wastewater tank, and the outlet of which is connected to the water replenishment pipe and the evaporation crystallization mechanism respectively.

6. The waste gas treatment system for polysilicon production according to claim 2, characterized in that: The output pipe of the acid solution delivery pump is connected to the first circulating water heat exchanger.

7. The waste gas treatment system for polysilicon production according to claim 3, characterized in that: The output pipe of the alkali solution delivery pump is connected to the second circulating water heat exchanger.

8. The waste gas treatment system for polysilicon production according to claim 5, characterized in that: The output pipe of the wastewater delivery pump is connected to the third circulating water heat exchanger.

Images