Silane and chlorosilane mixed gas treatment process and control system and method

Abstract

The invention discloses a silane and chlorosilane mixed gas treatment process and a control system and method, and relates to the technical field of waste gas treatment in polycrystalline silicon production, and the process comprises the following steps: S1, mixed gas pretreatment; s2, deep removal of chlorosilane; s3, silane is removed, after three-stage treatment, the content of silane in tail gas is smaller than or equal to 1.0 mg / m < 3 >, the content of chlorosilane is smaller than or equal to 1.0 mg / m < 3 >, and then the tail gas is emptied, meanwhile, the control system and the control method suitable for the process are disclosed, optimization treatment of mixed process gas containing chlorosilane, silane, nitrogen and hydrogen generated in polycrystalline silicon production is achieved, use of alkali liquor is reduced, and the production cost is reduced. The emission is reduced, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of waste gas treatment technology in polysilicon production, specifically to a process, control system, and method for treating a mixed gas of silane and chlorosilane. Background Technology

[0002] In high-end manufacturing fields such as semiconductors and photovoltaics, silane gas (SiH4) is a core electronic-grade raw material. Its production process requires the reduction or disproportionation reaction of chlorosilanes (such as SiCl4, SiHCl3, SiH2Cl2, etc.). This process is accompanied by the emission of a large amount of mixed waste gas. The chlorosilane components are not only highly corrosive (reacting with water to form hydrochloric acid and silicon dioxide), but may also undergo secondary reactions with silane gas to generate solid impurities. Direct emission of these components will not only cause equipment corrosion and pipeline blockage, but also lead to serious environmental risks and waste of raw materials. Therefore, the efficient removal of chlorosilanes / silanes from the waste gas has become a key environmental protection and process assurance link in the silane gas production process.

[0003] Traditional industries commonly use sodium hydroxide (NaOH) alkaline scrubbing to purify this type of waste gas. The core process route is "three-tower series countercurrent scrubbing": the first tower (primary absorption tower) uses a concentrated alkaline solution of 20-30% to initially absorb the high concentration of chlorosilanes (usually 5-15% by volume) in the waste gas. This is achieved through the neutralization reaction of chlorosilanes with NaOH (e.g., SiHCl3 + 3NaOH → Si). The process (OH)3Na+3NaCl+H2O converts most of the chlorosilanes into soluble sodium silicate and sodium chloride. The second tower (secondary purification tower) reduces the alkali concentration to 10-15%, deeply capturing residual low-concentration chlorosilanes (0.5-2% by volume) while suppressing side reactions between silane gas and high-concentration alkali. The third tower (tail gas control tower) uses 5-8% dilute alkali to further remove trace amounts of chlorosilanes (targeting a volume fraction below 0.1%), ensuring that the outlet tail gas meets the emission standard of GB37822-2019 "Emission Standard for Pollutants from Electronic Industry" which specifies an emission concentration of chlorosilanes ≤10 mg / m³. 3 The requirement of "".

[0004] From the perspective of treatment effectiveness, this process, with its "gradient concentration alkali solution + multi-tower series" design, can achieve a chlorosilane / silane removal rate of over 99%, effectively avoiding subsequent equipment corrosion and environmental compliance issues. It has been used in the industry for decades. However, with the expansion of silane gas production capacity (single unit capacity increasing from thousands of tons to tens of thousands of tons) and the upgrading of cost control requirements, the inherent defects of this process have gradually become apparent: the core problem lies in the high content of chlorosilanes, which leads to a significant increase in the alkali consumption rate—when the volume fraction of chlorosilanes in the waste gas is maintained at the conventional level of 8-12%, the alkali consumption rate increases dramatically for every 1000 m³ treated. 3The waste gas needs to consume about 80-120 kg of NaOH solution with a concentration of 30-50%, and in order to maintain the pH stability of the alkali liquor of each tower (the pH needs to be kept greater than or equal to 11 to ensure the absorption efficiency), the concentrated alkali liquor needs to be added once every 2-4 hours. The annual average NaOH consumption of a single set of 10,000-ton-level silane gas device can reach 800-1200 tons, accounting for more than 60% of the total cost of the waste gas treatment link, which significantly increases the raw material procurement and storage pressure of the production enterprises.

[0005] Based on the above status, the existing waste gas treatment process is still being optimized by the technical personnel in the industry to achieve the purpose of energy saving and emission reduction and reducing production cost. SUMMARY

[0006] The purpose of the present application is to provide a silane and chlorosilane mixed gas treatment process, control system and method, which realizes the optimized treatment of the mixed process gas containing chlorosilane, silane, nitrogen and hydrogen generated in the production of polysilicon, reduces the use of alkali liquor, and reduces emissions and production cost.

[0007] The present application is realized by the following technical solutions: A silane and chlorosilane mixed gas treatment process, which realizes the staged purification of the mixed gas by using three-stage washing towers in series, specifically comprising the following steps: S1, mixed gas pretreatment: introducing the collected silane and chlorosilane mixed gas into the first-stage washing tower, and spraying the mixed gas with recycled water generated in the chlorosilane manufacturing plant; the recycled water is a product obtained by neutralizing the acidic waste residue and acidic waste water discharged from the chlorosilane manufacturing plant, and the pH value of the recycled water is 8-9; by the contact between the recycled water and the mixed gas, most of the chlorosilane in the mixed gas is absorbed; S2, chlorosilane deep removal: introducing the mixed gas treated by the first-stage washing tower into the second-stage washing tower, and continuing to spray with the recycled water as described in step S1; by prolonging the contact time and optimizing the spraying coverage, the remaining chlorosilane in the mixed gas is further absorbed, so that the content of chlorosilane in the mixed gas is reduced to 10 mg / m 3 Below; S3, silane removal: introducing the mixed gas treated by the second-stage washing tower into the third-stage washing tower, spraying the mixed gas with alkali liquor, and controlling the alkali liquor temperature in the third-stage washing tower to be 45-55℃, the alkali liquor pH value to be 10-12, until the content of silane in the tail gas is ≤1.0 mg / m 3 , the content of chlorosilane is ≤1.0 mg / m 3 , and the tail gas is vented.

[0008] Further, in step S1, the recycled water contains Ca 2+ , Cl - , Na + , and Cl -The content is 15000-25000ppm.

[0009] Further, in step S1, the reclaimed water is generated from a wastewater treatment system in polysilicon production, after the wastewater in the wastewater treatment system is neutralized with quicklime, calcium chloride is precipitated, and after filtration by a filter press, the supernatant is the reclaimed water.

[0010] Further, in steps S1 and S2, the spraying amount of the reclaimed water is controlled to be 110-130m 3 / h; the first-stage washing tower and the second-stage washing tower are respectively provided with a spraying mechanism, the spraying mechanism comprises 2-8 layers of spraying pipes, a plurality of spiral nozzles are arranged on each layer of the spraying pipes, and the spraying amount of each spiral nozzle is 2-3m 3 / h.

[0011] Further, in steps S1, S2 and S3, the first-stage washing tower, the second-stage washing tower and the third-stage washing tower all adopt a washing method of spraying the washing liquid in a circulating manner, each stage of the washing tower is connected with a corresponding storage tank through a pipeline, when the pH value of the reclaimed water or the lye in the storage tank is lower than a preset value, new reclaimed water or lye is supplemented through a connected reclaimed water supplement pipeline or lye supplement pipeline.

[0012] Further, in steps S1 and S2, the pressure in the first-stage washing tower and the second-stage washing tower is controlled to be 9-11kPa, and the temperature in the tower is controlled to be 25-35℃.

[0013] Further, in step S3, the pressure in the third-stage washing tower is controlled to be 9-11kPa, and the temperature in the tower is controlled to be 40-60℃.

[0014] A control system for the silane / chlorosilane mixed gas treatment process as described above, comprising a DCS, a first-stage washing tower, a first-stage wastewater storage tank, a second-stage washing tower, a second-stage wastewater storage tank, a third-stage washing tower and a third-stage lye storage tank, the first-stage wastewater storage tank, the second-stage wastewater storage tank and the third-stage lye storage tank are respectively provided with a liquid level meter I, a liquid level meter II and a liquid level meter III for detecting the liquid level in the tank, and the third-stage lye storage tank is provided with a temperature sensor; The first-stage washing tower is connected with a silane / chlorosilane mixed gas pipeline, the liquid outlet of the first-stage washing tower is connected with the first-stage wastewater storage tank through a pipeline, the first-stage wastewater storage tank is connected with the spraying pipe inlet of the first-stage washing tower through a circulating pipeline I, the circulating pipeline I is provided with a booster pump I, the first-stage wastewater storage tank is connected with a reclaimed water supplement pipeline, and the booster pump I is connected with the liquid level meter I in control; The liquid outlet of the second-stage washing tower is connected with the second-stage wastewater storage tank through a pipeline, the second-stage wastewater storage tank is connected with the spraying pipe inlet of the second-stage washing tower through a circulating pipeline II, the circulating pipeline II is provided with a booster pump II, the second-stage wastewater storage tank is connected with a reclaimed water supplement pipeline, and the booster pump II is connected with the liquid level meter II in control; The liquid outlet of the third-stage elution tower is connected to a third-stage lye storage tank through a pipeline, the third-stage lye storage tank is connected to the inlet of the spray pipe of the third-stage elution tower through a circulating pipeline III, a booster pump III is arranged on the circulating pipeline III, the third-stage lye storage tank is connected to a high-concentration lye supply pipeline, and the booster pump III is connected to a liquid level meter III. A heat exchanger for heating the lye in the tank is connected to the outside of the third-stage lye storage tank, and the heat exchanger is connected to a heat exchange medium inlet pipe. Preferably, the heat exchange medium in the heat exchange medium inlet pipe is steam or circulating water with a temperature of 80-90°C.

[0015] Further, the second-stage wastewater storage tank is connected to the first-stage wastewater storage tank through a circulating pipeline IV, and a booster pump IV is arranged on the circulating pipeline IV, which delivers the elution liquid in the second-stage wastewater storage tank to the first-stage wastewater storage tank.

[0016] A control method of the control system, wherein a pH sensor is arranged on the third-stage lye storage tank, and an adjusting valve I is arranged on the high-concentration lye supply pipeline, the content of silane and chlorosilane in the exhaust gas treated by the third-stage elution tower is controlled by controlling the pH value and the temperature of the elution liquid in the third-stage elution tower. a. The pH signal of the elution liquid in the third-stage lye storage tank is collected by the pH sensor arranged on the third-stage lye storage tank and uploaded to the DCS, the DCS processes the received signal, determines the real-time pH value of the elution liquid according to the corresponding signal, and compares the real-time pH value with the preset pH value: When the real-time pH value is equal to the preset pH value, the DCS sends a signal to the adjusting valve I to maintain the current opening degree; When the real-time pH value is less than the preset pH value, the DCS sends a signal to the adjusting valve I to increase the flow, and controls the opening degree of the adjusting valve I, the adjusted pH value signal is returned to the DCS again for comparison until the real-time pH value is equal to the preset pH value; When the real-time pH value is greater than the preset pH value, the DCS sends a signal to the adjusting valve I to decrease the flow, and controls the opening degree of the adjusting valve I, the adjusted pH value signal is returned to the DCS again for comparison until the real-time pH value is equal to the preset pH value; b. The adjusting valve II is arranged on the heat exchange medium inlet pipe connected to the heat exchanger, the temperature signal of the elution liquid in the third-stage lye storage tank is collected by the temperature sensor III arranged on the third-stage lye storage tank and uploaded to the DCS, the DCS processes the received signal, determines the real-time temperature of the elution liquid according to the corresponding signal, and compares the real-time temperature value with the preset temperature value: When the real-time temperature value is equal to the preset temperature value, the DCS sends a signal to the adjusting valve II to maintain the current opening degree; When the real-time temperature is less than the preset temperature, the DCS sends a signal to the temperature regulating valve II to increase the flow of the heat exchange medium, and controls the opening of the regulating valve II, and the adjusted temperature value signal is returned to the DCS again for comparison until the real-time temperature value is equal to the preset temperature value. When the real-time temperature is greater than the preset temperature, the DCS sends a signal to the temperature regulating valve II to reduce the flow of the heat exchange medium, and controls the opening of the regulating valve II, and the adjusted temperature value signal is returned to the DCS again for comparison until the real-time temperature value is equal to the preset temperature value.

[0017] Further, the heat exchange medium is steam or circulating water with a temperature of 80-90 DEG C.

[0018] Compared with the prior art, the present application has the following advantages and beneficial effects: I. In the present application, a silane and chlorosilane mixed gas treatment process is proposed, which is a three-stage washing and grading purification process. The reuse water (made by neutralizing acid waste residue and acid wastewater, which needs to be treated and discharged) of a silane manufacturing plant is used as the spraying liquid of steps S1 and S2 (i.e. first-stage washing and second-stage washing) to replace industrial water to absorb chlorosilane, thereby directly reducing the equipment, reagents and operation and maintenance costs of the reuse water discharge treatment. Moreover, the reuse water has a stable alkaline pH value of 8-9, and has a more excellent absorption capacity for acidic chlorosilane than neutral industrial water, so that most of the chlorosilane in the mixed gas can be efficiently removed. In step S3, by controlling the process parameters of the pH value of the alkali solution to be 10-12 and the temperature to be 45-55 DEG C, the final purification target of the tail gas silane and chlorosilane content being less than or equal to 1.0 mg / m 3 is achieved, which meets the production requirements.

[0019] II. In the present application, the first-stage washing and the second-stage washing in the silane and chlorosilane mixed gas treatment process use the product (high-chlorine wastewater) of the wastewater treatment system in the polysilicon production, which continues to replace the use of industrial water, thereby reducing the discharge treatment cost and ensuring the sustainability of the absorption effect due to the fact that the ion does not weaken the absorption advantage of the industrial water. In addition, the reuse water can be treated according to the requirements of the system to meet the reuse water requirement standard (the reuse water contains Ca 2+ , Cl - , Na + , wherein the Cl - content is 15000-25000 ppm, and the pH value is 8-9) of the present process, without the need for further deep purification. In this way, the treatment pressure of the wastewater treatment system is reduced, and the reuse water with high alkalinity and high-chlorine ion content has a more excellent waste gas treatment effect than industrial water, thereby ensuring that the waste gas after three-stage treatment meets the index requirements of venting.

[0020] Thirdly, in the silane and chlorosilane mixed gas treatment process, the reuse water is further defined as the industrial wastewater that is "to be treated and discharged", which is directly used for spraying and then the terminal treatment process of the part of wastewater is omitted, thereby significantly reducing the overall water treatment cost; the lime neutralization process ensures that the reuse water is stable alkaline, and after the removal of calcium chloride by precipitation, the purity meets the spraying requirements, avoids the blockage of the nozzle by impurities, and the alkalinity is stronger than that of ordinary industrial water, and the chlorosilane absorption capacity is more prominent.

[0021] Fourthly, in the silane and chlorosilane mixed gas treatment process, the design of the multi-layer spraying pipe and the spiral nozzle increases the contact area of the reuse water and the mixed gas, and the spraying amount (110~130 m 3 / h) is set, so that the alkaline reuse water fully contacts the chlorosilane, and the absorption efficiency is improved; the stable spraying amount parameter provides a flow basis for "reverse step-by-step water replenishment", avoids the decrease of the reuse water transportation efficiency of the first-stage and second-stage elution towers due to flow fluctuation, and guarantees the maximum utilization of water resources.

[0022] Fifthly, in the silane and chlorosilane mixed gas treatment process, each elution tower is respectively connected with a corresponding storage tank through a pipeline, the storage tank is used for temporarily storing the corresponding reuse water or alkali liquor, and is connected with the corresponding elution tower through a circulating pipeline, so as to realize the recycling use of the elution liquid; when the pH value of the elution liquid in the storage tank decreases to the minimum limit value (which means that the OH - in the elution liquid is close to complete consumption, if the recycling use continues, the expected washing effect will not be achieved within the preset washing time), fresh reuse water or high-concentration alkali liquor is supplied, so that the maximum water resource utilization rate is realized on the basis of reducing the supply amount of fresh reuse water and alkali liquor.

[0023] Sixthly, in the silane and chlorosilane mixed gas treatment process, the tower pressure and tower temperature of the first-stage elution tower, the second-stage elution tower and the third-stage elution tower are controlled, the stable working condition can avoid the insufficient contact time of the waste gas and the elution liquid due to pressure fluctuation, and at the same time, the washing process of the waste gas is continuously ensured, so as to ensure that the absorption efficiency of the alkaline reuse water or alkali liquor on the chlorosilane is not disturbed. Through a large number of test verifications, the temperature control temperature of the third-stage elution tower is 40~60℃, the washing effect of the alkali liquor on the waste gas is best (short time and complete washing), the stable tower pressure can also ensure that the mixed gas has sufficient residence time, so that the silane has sufficient time to react with the alkali liquor with stable pH, and the pH control forms a double protection, thereby improving the silane removal effect.

[0024] Seven, in the application, a new silane, chlorosilane mixed gas treatment process control system is provided, the system is designed with DCS, storage tank, sensor, booster pump, heat exchanger and other hardware devices, the corresponding booster pump connected with the first-stage waste water storage tank and the second-stage waste water storage tank provides power for the first-stage and second-stage waste gas washing, and is linked with the DCS and the temperature sensor to control, so that the first-stage and second-stage waste gas washing effect is ensured, and the water efficiency is maximized. The third-stage lye storage tank provides hardware support for lye temperature control through the heat exchanger, and cooperates with the DCS and the temperature sensor III to create stable temperature conditions for the pH automatic lye supplement system.

[0025] Eight, in the application, a new silane, chlorosilane mixed gas treatment process control system is provided, which adopts a reverse step-by-step water supplementing mode for comprehensive utilization of water, and the recycled water first enters the second-stage leaching tower for spraying washing, and the water of the second-stage leaching tower enters the first-stage leaching tower through the booster pump IV, so that the water resources can be maximized.

[0026] Nine, in the application, the silane and chlorosilane content in the waste gas treated by the third-stage leaching tower is controlled by controlling the pH value and the temperature of the leaching liquid of the third-stage leaching tower, the pH closed-loop control (the DCS compares the real-time pH with a preset value, and adjusts the adjusting valve I) realizes the function of the 'pH automatic lye supplement system', the lye pH used by the third-stage leaching tower is maintained at 10-12 in real time, the silane reaction is ensured to be sufficient, and the absorption efficiency is prevented from being reduced due to pH deviation; the temperature closed-loop control (the adjusting valve II controls the heat exchange medium) cooperates with the pH control to maintain the lye temperature at 45-55 DEG C, and the optimal reaction condition is further ensured; the DCS controls the booster pump in linkage, so that the stability is synchronously ensured, and the water resource utilization and the purification effect are double optimized.

[0027] Ten, in the application, the heat exchange medium is steam or circulating water with a temperature of 80-90 DEG C, which can stably provide heat exchange energy for the third-stage lye storage tank, ensures that the lye temperature is accurately maintained at 45-55 DEG C, avoids that the medium temperature fluctuation affects the silane absorption, forms the double protection of 'pH stability + temperature stability', and ensures that the silane absorption reaction is always in the best state. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a device diagram (one) of the application.

[0029] Figure 2 It is a schematic view of the third-stage lye storage tank.

[0030] Figure 3 It is a device diagram (two) of the application.

[0031] Figure 4 It is a diagram (one) of the control system of the application.

[0032] Figure 5Fig. 2 is a schematic diagram of the control system of the present application (II).

[0033] Figure 6 Fig. 1 is a logic control diagram of the control system of the present application (I).

[0034] Figure 7 Fig. 3 is a logic control diagram of the control system of the present application (II).

[0035] Wherein, 1, first-stage washing tower; 2, first-stage wastewater storage tank; 3, second-stage washing tower; 4, second-stage wastewater storage tank; 5, third-stage washing tower; 6, third-stage lye storage tank; 7, liquid level meter I; 8, liquid level meter II; 9, liquid level meter III; 10, temperature sensor; 11, silane / chlorosilane mixed gas pipeline; 12, circulating pipeline I; 13, booster pump I; 14, recycled water supply pipeline; 15, circulating pipeline II; 16, booster pump II; 17, circulating pipeline III; 18, booster pump III; 19, high-concentration lye supply pipeline; 20, heat exchanger; 21, heat exchange medium inlet pipeline; 22, circulating pipeline IV; 23, booster pump IV; 24, pH sensor; 25, regulating valve I; 26, regulating valve II; 27, spraying mechanism; 28, vent pipeline; 29, discharge pipeline; 5.1, air inlet I; 5.2, liquid outlet I; 27.1, spraying pipe; 27.2, spiral nozzle. DETAILED DESCRIPTION

[0036] The present application will be further described in detail below in conjunction with examples, but the embodiments of the present application are not limited thereto.

[0037] Example 1 A silane / chlorosilane mixed gas treatment process, which realizes the staged purification of mixed gas by using three-stage washing towers in series, relates to a system device as shown in Figure 1 .

[0038] The treatment process specifically comprises the following steps: S1, mixed gas pretreatment: collect and introduce the silane / chlorosilane mixed gas generated in the process of preparing silane gas (SiH4) into the first-stage washing tower 1, and use the recycled water generated in the chlorosilane manufacturing plant for spraying treatment of the mixed gas; the recycled water is the product obtained after neutralization treatment of the acidic waste residue and acidic wastewater discharged by the chlorosilane manufacturing plant, and the pH value of the recycled water is 8-9; through the contact of the recycled water and the mixed gas, most of the chlorosilane in the mixed gas is absorbed, and the content of chlorosilane in the mixed gas is treated to be less than 100 mg / m 3 ; S2, deep removal of chlorosilane: the mixed gas treated by the first stage of the washing tower 1 is introduced from the pipeline at the top into the second stage of the washing tower 3, and the reuse water described in step S1 is continued to be sprayed; by prolonging the contact time and optimizing the spraying coverage, the remaining chlorosilane in the mixed gas is further absorbed, so that the content of chlorosilane in the mixed gas is reduced to 10 mg / m 3 Below; S3, removal of silane: the mixed gas treated by the second stage of the washing tower 3 is introduced from the pipeline at the top into the third stage of the washing tower 5, and the mixed gas is sprayed with lye, and the temperature of the lye (i.e. the third stage of the washing liquid) in the third stage of the washing tower 5 is controlled to be 45~55℃, in the specific implementation, the lye can be heated by using an external heat exchanger, or a jacket is arranged outside the third stage of the washing tower 5, and the lye is heated by using steam or high-temperature jacket water as a heat exchange medium, so that a better reaction temperature environment is provided for the reaction between the lye and the silane and the chlorosilane in the tower, and the pH value of the lye is preferably controlled to be 10~12, so that the content of silane in the tail gas is ≤1.0 mg / m 3 , the content of chlorosilane is ≤1.0 mg / m 3 , and the tail gas is vented.

[0039] Example 2 Compared with Example 1, the difference is that in step S1, the reuse water contains Ca 2+ , Cl - , Na + , and the content of Cl - is 15000~25000ppm, and the reuse water is the wastewater generated by the wastewater treatment system in the production of polysilicon, which is treated to meet the reuse water requirement standard of the process: the reuse water contains Ca 2+ , Cl - , Na + , and the content of Cl - is 15000~25000ppm, and the pH value is 8~9, so no further purification is required. At the same time, such reuse water with high alkalinity and high chloride ion content has a more excellent waste gas treatment effect than industrial water, and ensures that the waste gas after three-stage treatment meets the index requirements of venting.

[0040] Further, the reuse water is generated by the wastewater treatment system in the production of polysilicon, and after the wastewater in the wastewater treatment system is neutralized with quicklime, calcium chloride is precipitated, and then the upper clear liquid obtained after filtration by a filter press is the reuse water.

[0041] Example 3 Compared with Examples 1~2, the difference is that in steps S1 and S2, the spraying amount of the reuse water is controlled to be 110~130 m 3 / h; the first-stage washing tower 1, the second-stage washing tower 3 and the third-stage washing tower 5 are respectively provided with a spraying mechanism 27, the spraying mechanism 27 comprises 2-8 layers of spraying pipes 27.1, a plurality of spiral nozzles 27.2 are arranged on each layer of the spraying pipes 27.1, and the spraying amount of each spiral nozzle 27.2 is 2-3 m 3 / h, and the reference Figure 2 , Figure 2 The structure of the third-stage washing tower 5 is shown, the third-stage washing tower 5 is supplied with high-concentration lye through the high-concentration lye supply pipe 19, so as to ensure that the pH value of the third-stage washing liquid is within an expected range. The waste gas washed by the second-stage washing tower 3 enters the third-stage washing tower 5 from the gas inlet Ⅰ5.1 of the third-stage washing tower 5, the washed gas is discharged from the vent pipe at the top of the third-stage washing tower 5, and the used washing liquid is discharged from the liquid discharge port Ⅰ5.2.

[0042] In the embodiment, in order to investigate the washing effect of each process condition on the waste gas, the structure shown in FIG. 1 is adopted, the volume of the first-stage washing tower 1, the second-stage washing tower 2 and the third-stage washing tower 3 is about 30 m 3 The time consumed when the washing of the gas is up to the emission standard is counted, and the results are shown in Table 1. The initial waste gas of each group is from the same source, and is from a silicon material preparation unit. The first-stage and second-stage washing of the comparison groups 1 and 2 uses pure water to wash the mixed gas, and the first-stage and second-stage washing of the comparison group 3 still uses the reused water to wash the mixed gas.

[0043] Table 1

[0044] As shown in Table 1, when the reused water or the pure water is used to wash the mixed gas containing silane and chlorosilane, the washing effect on the silane is poor, and the silane content in the gas stream after the second-stage washing is slightly different from the silane content in the initial mixed gas. However, the washing effect on the chlorosilane is good when the reused water is used, and most of the chlorosilane can be removed.

[0045] As compared with the comparison group 6, the flow rate of the nozzles of the comparison groups 1 and 7 is reduced from 3 m 3 / h to 2.43 m 3 / h, and the silane contents after the first-stage and second-stage washing for 100 s are 1.05 mg / m 3 and 1.0 mg / m 3 , respectively, which are slightly higher than that of the comparison group 6 (0.94 mg / m 3 ), the chlorosilane content has reached the emission requirement, and it is necessary to continue washing for a certain time to control the silane content to be 1.0 mg / m 3 and below, and the time is slightly longer than that of the comparison group 6.

[0046] Compared to Group 1, Group 2 only washed for 50 seconds during rinsing, which was clearly insufficient. The content of silane and chlorosilane in Group 2 was higher, which did not meet the emission requirements.

[0047] Compared to group 1, group 3 had a nozzle flow rate of 2.4 m³ / s during rinsing. 3 / h reduced to 2m 3 / h, but the washing time increased by 20s, and the content of silane and chlorosilane was slightly lower than in Group 1. Experiments showed that when the nozzle flow rate was too low (below 2m), 3 When the washing time is / h), the washing time will increase significantly.

[0048] Compared to group 6, group 4 had a nozzle flow rate of 3m³ / h during rinsing. 3 / h reduced to 2m 3 / h, the pH value of the alkaline solution decreased from 12 to 11. After washing for the same amount of time, the silane content in the exhaust gas was relatively high, reaching 1.44 mg / m³. 3 This does not meet emission requirements.

[0049] Compared to Group 1, in Group 5, the alkaline solution temperature was reduced from 50℃ to 40℃ during rinsing. After the same washing time, the silane content in the exhaust gas was significantly higher, reaching 2.68 mg / m³. 3 It can be seen that the temperature of the alkaline solution has a significant impact on the washing effect of the exhaust gas, and the gas after washing for 100 seconds does not meet the emission requirements.

[0050] In summary, the process conditions employed in this scheme can achieve exhaust gas washing to meet emission standards in a relatively short time. A comparison of groups 1-7 with control groups 1 and 2 shows that using recycled water to wash the exhaust gas results in a silane content ≤1.0 mg / m³. 3 Silyl chloride content ≤1.0mg / m³ 3 Compared to using pure water to wash the exhaust gas, the time consumed is significantly reduced (comparison group 1 requires 100 seconds more time than group 1). When the first and second stages of the comparison group and the implementation group have the same washing time, it means that the content of silane and chlorosilane in the exhaust gas is relatively high, and the third stage will consume more alkaline solution and the washing time will be longer.

[0051] A comparison of groups 1-7 with control group 3 shows that the spray volume of the spiral nozzle is too small, resulting in poor washing effect and significantly increased washing time.

[0052] Example 4 The embodiment is different from the embodiments 1-3 in that in the steps S1, S2 and S3, the first-stage washing tower 1, the second-stage washing tower 3 and the third-stage washing tower 5 are all washed by the spray method of the circulating washing liquid, and each washing tower is connected with a corresponding storage tank through a pipeline, and when the pH value of the recycled water or the lye in the storage tank is lower than the preset value, the new recycled water or lye is supplemented through the connected recycled water supplement pipeline 14 or the high-concentration lye supplement pipeline 19.

[0053] Reference Figure 3 , Figure 3 The figure shows that the first-stage washing tower 1, the second-stage washing tower 3 and the third-stage washing tower 5 are respectively connected with the first-stage wastewater storage tank 2, the second-stage wastewater storage tank 4 and the third-stage wastewater storage tank 6, the first-stage wastewater storage tank 2 and the second-stage wastewater storage tank 4 are connected with the recycled water supplement pipeline 14, and the third-stage wastewater storage tank 6 is connected with the high-concentration lye supplement pipeline 19. The bottoms of the first-stage wastewater storage tank 2, the second-stage wastewater storage tank 4 and the third-stage wastewater storage tank 6 are connected with the external discharge pipeline 29.

[0054] Embodiment 5 The embodiment is different from the embodiments 1-4 in that in the steps S1 and S2, the pressure in the first-stage washing tower 1 and the second-stage washing tower 3 is controlled to be 9-11 kPa, and the temperature in the towers is controlled to be 25-35℃.

[0055] Embodiment 6 The embodiment is different from the embodiments 1-5 in that in the step S3, the pressure in the third-stage washing tower 5 is controlled to be 9-11 kPa, and the temperature in the tower is controlled to be 40-60℃.

[0056] Embodiment 7 The embodiment provides a preferred control system for the process of treating the silane / chlorosilane mixed gas, which is used to realize the process as described in the embodiment 1.

[0057] Reference Figure 2 , 4 The control system comprises a DCS, the first-stage washing tower 1, the first-stage wastewater storage tank 2, the second-stage washing tower 3, the second-stage wastewater storage tank 4, the third-stage washing tower 5 and the third-stage lye storage tank 6, and the first-stage wastewater storage tank 2, the second-stage wastewater storage tank 4 and the third-stage lye storage tank 6 are respectively provided with a liquid level meter I 7, a liquid level meter II 8 and a liquid level meter III 9 for detecting the liquid level in the tanks, and the third-stage lye storage tank 6 is provided with a temperature sensor 10. The first-stage washing tower 1 is connected with a silane / chlorosilane mixed gas pipeline 11, the liquid outlet of the first-stage washing tower 1 is connected with the first-stage wastewater storage tank 2 through a pipeline, the first-stage wastewater storage tank 2 is connected with the spray pipe inlet of the first-stage washing tower 1 through a circulating pipeline I 12, the circulating pipeline I 12 is provided with a booster pump I 13, the first-stage wastewater storage tank 2 is connected with the recycled water supplement pipeline 14, and the DCS is connected with the booster pump I 13 and the liquid level meter I 7 in control. The liquid outlet of the second-stage elution tower 3 is connected to the second-stage wastewater storage tank 4 through a pipeline, the second-stage wastewater storage tank 4 is connected to the spray pipe inlet of the second-stage elution tower 3 through a circulation pipeline II 15, a booster pump II 16 is arranged on the circulation pipeline II 15, the second-stage wastewater storage tank 4 is connected to the reclaimed water supply pipeline 14, and the DCS is connected to the booster pump II 16 and the liquid level meter II 8 for control; The liquid outlet of the third-stage elution tower 5 is connected to the third-stage lye storage tank 6 through a pipeline, the third-stage lye storage tank 6 is connected to the spray pipe inlet of the third-stage elution tower 5 through a circulation pipeline III 17, a booster pump III 18 is arranged on the circulation pipeline III 17, the third-stage lye storage tank 6 is connected to the high-concentration lye supply pipeline 19, and the booster pump III 18 is connected to the liquid level meter III 9 for control; The third-stage lye storage tank 6 is externally connected to a heat exchanger 20 for heating the elution liquid, i.e., lye, and the heat exchanger 20 is connected to a heat exchange medium inlet pipe 21. An adjusting valve II 26 is arranged on the heat exchange medium inlet pipe 21, and the DCS is connected to the temperature sensor 10 and the adjusting valve II 26 for control. The temperature sensor 10 and the adjusting valve II 26 are interlocked to stabilize the temperature of the lye within an optimal temperature range.

[0058] Example 8 Compared with Example 7, the difference is that the second-stage wastewater storage tank 4 is connected to the first-stage wastewater storage tank 2 through a circulation pipeline IV 22, as shown in Figure 2 , 5 A booster pump IV 23 is arranged on the circulation pipeline IV 22, and the booster pump IV 23 delivers the elution liquid in the second-stage wastewater storage tank 4 to the first-stage wastewater storage tank 2.

[0059] Based on the control system, the control method of the above process is as follows: a pH sensor 24 is arranged on the third-stage lye storage tank 6, and an adjusting valve I 25 is arranged on the high-concentration lye supply pipeline 19. The content of silane and chlorosilane in the exhaust gas treated by the third-stage elution tower 5 is controlled by controlling the pH value and the temperature of the elution liquid of the third-stage elution tower 5.

[0060] Specifically: a. The pH signal of the elution liquid in the third-stage lye storage tank 6 is collected by the pH sensor 24 arranged on the third-stage lye storage tank 6, as shown in Figure 6 , and the pH signal is uploaded to the DCS. The DCS processes the received signal, determines the real-time pH value of the elution liquid according to the corresponding signal, and compares the real-time pH value with the preset pH value: When the real-time pH value is equal to the preset pH value, the DCS sends a signal to the adjusting valve I 25 to maintain the current opening degree; When the real-time pH value is less than the preset pH value, the DCS sends a signal to increase the flow to the regulating valve 125, and controls the opening of the regulating valve 125, and the adjusted pH value signal is returned to the DCS again for comparison until the real-time pH value is equal to the preset pH value; When the real-time pH value is greater than the preset pH value, the DCS sends a signal to decrease the flow to the regulating valve 125, and controls the opening of the regulating valve 125, and the adjusted pH value signal is returned to the DCS again for comparison until the real-time pH value is equal to the preset pH value; b. The heat exchange medium inlet pipe 21 connected with the heat exchanger 20 is provided with a regulating valve 126, and the reference Figure 7 The temperature signal of the elution liquid in the third lye storage tank 6 is collected by the temperature sensor 10III arranged on the third lye storage tank 6, and the temperature signal is uploaded to the DCS, the DCS processes the received signal, determines the real-time temperature of the elution liquid according to the corresponding signal, and compares the real-time temperature value with the preset temperature value: When the real-time temperature value is equal to the preset temperature value, the DCS sends a signal to maintain the current opening to the regulating valve 126; When the real-time temperature is less than the preset temperature, the DCS sends a signal to increase the flow of the heat exchange medium to the temperature regulating valve 126, and controls the opening of the regulating valve 126, and the adjusted temperature value signal is returned to the DCS again for comparison until the real-time temperature value is equal to the preset temperature value; When the real-time temperature is greater than the preset temperature, the DCS sends a signal to decrease the flow of the heat exchange medium to the temperature regulating valve 126, and controls the opening of the regulating valve 126, and the adjusted temperature value signal is returned to the DCS again for comparison until the real-time temperature value is equal to the preset temperature value.

[0061] The control system and the control method are used to process 1000 Nm 3 / h of the mixed gas containing silane and chlorosilane, compared with the traditional scheme of “three-stage washing tower (pure water+pure water+alkali)”, 2600 m 3 of pure water and 500 square meters of 30wt% concentration of lye can be saved every month, and the processing time can be shortened by 10%; in addition, 2600 m 3 of high-chlorine wastewater generated by the waste gas treatment system can be consumed every month, and the treatment cost of about 15000 yuan of high-chlorine wastewater is reduced.

[0062] The above is only a preferred embodiment of the present application, and does not limit the present application in any form, and any simple modification and equivalent change made on the basis of the technical essence of the present application to the above embodiment falls within the protection scope of the present application.

Claims

1. A process for treating a mixed gas of silane and chlorosilane, characterized in that, A three-stage scrubbing tower connected in series is used to achieve staged purification of the mixed gas, specifically including the following steps: S1. Pretreatment of mixed gas: The collected silane and chlorosilane mixed gas is introduced into the first-stage scrubbing tower (1), and the mixed gas is sprayed with recycled water generated from the chlorosilane manufacturing plant. The recycled water is the product obtained by neutralizing acidic waste residue and acidic wastewater discharged from the chlorosilane manufacturing plant. The pH value of the recycled water is 8-9. Through the contact between the recycled water and the mixed gas, most of the chlorosilane in the mixed gas is absorbed. S2. Deep removal of chlorosilanes: The mixed gas treated by the first-stage scrubbing tower (1) is introduced into the second-stage scrubbing tower (3) and continues to be sprayed with the recycled water described in step S1; by extending the contact time and optimizing the spray coverage, the remaining chlorosilanes in the mixed gas are further absorbed, reducing the chlorosilane content in the mixed gas to 10 mg / m³. 3 the following; S3, Silane Removal: The mixed gas treated by the second-stage scrubbing tower (3) is introduced into the third-stage scrubbing tower (5). The mixed gas is sprayed with alkaline solution, and the temperature of the alkaline solution in the third-stage scrubbing tower (5) is controlled at 45~55℃, and the pH value of the alkaline solution is 10~12, until the silane content in the tail gas is ≤1.0mg / m³. 3 Silyl chloride content ≤1.0mg / m³ 3 Then release the exhaust fumes.

2. The process for treating a silane and chlorosilane mixed gas according to claim 1, characterized in that: In step S1, the recycled water contains Ca. 2+ Cl - Na + Cl - The content is 15,000~25,000 ppm.

3. The process for treating a silane and chlorosilane mixed gas according to claim 2, characterized in that: In step S1, the recycled water is generated by the wastewater treatment system in polysilicon production. After the wastewater in the wastewater treatment system is neutralized with quicklime, calcium chloride is precipitated out through precipitation. After being filtered by a filter press, the clear liquid obtained is the recycled water.

4. The process for treating a silane and chlorosilane mixed gas according to claim 1, characterized in that: In steps S1 and S2, the spray volume of the recycled water is controlled at 110~130m³. 3 / h; The first-stage scrubbing tower (1) and the second-stage scrubbing tower (3) are respectively equipped with a spraying mechanism (27), which includes 2 to 8 layers of spray pipes (27.1). Each layer of spray pipes (27.1) is equipped with multiple spiral nozzles (27.2), and the spray volume of each spiral nozzle (27.2) is 2 to 3 m. 3 / h.

5. The process for treating a mixed gas of silane and chlorosilane according to claim 4, characterized in that: In steps S1, S2, and S3, the first-stage scrubbing tower (1), the second-stage scrubbing tower (3), and the third-stage scrubbing tower (5) all use a scrubbing liquid circulation spray method to wash the waste gas. Each scrubbing tower is connected to a corresponding storage tank through a pipeline. When the pH value of the recycled water or alkali in the storage tank is lower than the preset value, new recycled water or alkali is added through the connected recycled water supply pipe (14) or alkali supply pipe.

6. The process for treating a silane and chlorosilane mixed gas according to claim 1, characterized in that: In steps S1 and S2, the pressure inside the first-stage scrubbing tower (1) and the second-stage scrubbing tower (3) is controlled at 9~11 kPa, and the temperature inside the tower is controlled at 25~35℃.

7. The process for treating a silane and chlorosilane mixed gas according to claim 1, characterized in that: In step S3, the pressure inside the third-stage scrubbing tower (5) is controlled at 9~11 kPa and the temperature inside the tower is controlled at 40~60℃.

8. A control system for the treatment process of a silane and chlorosilane mixed gas as described in claim 1, characterized in that: It includes a DCS, a first-stage scrubbing tower (1), a first-stage wastewater storage tank (2), a second-stage scrubbing tower (3), a second-stage wastewater storage tank (4), a third-stage scrubbing tower (5), and a third-stage alkali storage tank (6). The first-stage wastewater storage tank (2), the second-stage wastewater storage tank (4), and the third-stage alkali storage tank (6) are respectively equipped with level gauge I (7), level gauge II (8), and level gauge III (9) for detecting the liquid level of the material in the tank. The third-stage alkali storage tank (6) is equipped with a temperature sensor (10). The first-stage scrubbing tower (1) is connected to a silane / chlorosilane mixed gas pipeline (11). The drain outlet of the first-stage scrubbing tower (1) is connected to the first-stage wastewater storage tank (2) through a pipeline. The first-stage wastewater storage tank (2) is connected to the inlet of the spray pipe (27.1) of the first-stage scrubbing tower (1) through a circulation pipeline I (12). A booster pump I (13) is installed on the circulation pipeline I (12). The first-stage wastewater storage tank (2) is connected to a recycled water supply pipe (14). The booster pump I (13) is connected to the level gauge I (7) for control. The drain outlet of the second-stage scrubbing tower (3) is connected to the secondary wastewater storage tank (4) through a pipeline. The secondary wastewater storage tank (4) is connected to the inlet of the spray pipe (27.1) of the second-stage scrubbing tower (3) through the circulation pipeline II (15). A booster pump II (16) is installed on the circulation pipeline II (15). The secondary wastewater storage tank (4) is connected to the recycled water supply pipe (14). The booster pump II (16) is connected to the level gauge II (8) for control. The drain outlet of the third-stage scrubbing tower (5) is connected to the third-stage alkali storage tank (6) through a pipeline. The third-stage alkali storage tank (6) is connected to the inlet of the spray pipe (27.1) of the third-stage scrubbing tower (5) through the circulation pipeline III (17). A booster pump III (18) is installed on the circulation pipeline III (17). The third-stage alkali storage tank (6) is connected to the high-concentration alkali supply pipe (19). The booster pump III (18) is connected to the level gauge III (9) for control. The three-stage alkali storage tank (6) is externally connected to a heat exchanger (20) for heating the alkali solution inside the tank, and the heat exchanger (20) is connected to the heat exchange medium inlet pipe (21).

9. The control system for a silane and chlorosilane mixed gas treatment process according to claim 8, characterized in that: The secondary wastewater storage tank (4) is connected to the primary wastewater storage tank (2) through the circulation pipeline IV (22). The circulation pipeline IV (22) is equipped with a booster pump IV (23), which transports the rinsing liquid in the secondary wastewater storage tank (4) to the primary wastewater storage tank (2).

10. A control method for the control system as claimed in claim 8, characterized in that: The three-stage alkaline storage tank (6) is equipped with a pH sensor (24), and the high-concentration alkaline supply pipe (19) is equipped with a regulating valve I (25). By controlling the pH value and temperature of the rinsing liquid in the third-stage rinsing tower (5), the content of silane and chlorosilane in the exhaust gas after treatment by the third-stage rinsing tower (5) can be controlled. a. The pH signal of the rinsing solution in the three-stage alkali storage tank (6) is collected by the pH sensor (24) installed on the three-stage alkali storage tank (6), and the pH signal is uploaded to the DCS. The DCS processes the received signal, determines the real-time pH value of the rinsing solution according to the corresponding signal, and then compares the real-time pH value with the preset pH value: When the real-time pH value equals the preset pH value, the DCS sends a signal to the regulating valve I (25) to maintain the current opening degree; When the real-time pH value is less than the preset pH value, the DCS sends a signal to the regulating valve I (25) to increase the flow rate and controls the opening of the regulating valve I (25). The pH value signal after adjustment and control is returned to the DCS for comparison again until the real-time pH value is equal to the preset pH value. When the real-time pH value is greater than the preset pH value, the DCS sends a signal to the regulating valve I (25) to reduce the flow rate and controls the opening of the regulating valve I (25). The pH value signal after adjustment and control is returned to the DCS for comparison again until the real-time pH value is equal to the preset pH value. b. A regulating valve II (26) is provided on the heat exchange medium inlet pipe (21) connected to the heat exchanger (20). The temperature signal of the rinsing liquid in the three-stage alkali storage tank (6) is collected by the temperature sensor (10) installed on the three-stage alkali storage tank (6), and the temperature signal is uploaded to the DCS. The DCS processes the received signal, determines the real-time temperature of the rinsing liquid according to the corresponding signal, and then compares the real-time temperature value with the preset temperature value: When the real-time temperature value equals the preset temperature value, the DCS sends a signal to the regulating valve II (26) to maintain the current opening degree. When the real-time temperature is lower than the preset temperature, the DCS sends a signal to the temperature regulating valve II (26) to increase the flow rate of the heat exchange medium and controls the opening of the regulating valve II (26). The temperature value signal after adjustment and control is returned to the DCS for comparison again until the real-time temperature value is equal to the preset temperature value. When the real-time temperature is greater than the preset temperature, the DCS sends a signal to the temperature regulating valve II (26) to reduce the flow rate of the heat exchange medium and controls the opening of the regulating valve II (26). The temperature value signal after adjustment and control is returned to the DCS for comparison again until the real-time temperature value is equal to the preset temperature value.

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