System and method for treating high-boiling cracking waste liquid in polycrystalline silicon production process

Abstract

The invention discloses a high-boiling cracking waste liquid treatment system and method in a polycrystalline silicon production process, and belongs to the technical field of high-boiling cracking waste liquid treatment.The system comprises a waste liquid buffer tank, a waste liquid hydrolysis tank, a lime milk preparation pool, a waste alkali buffer pool, a drying pool and a tail gas spraying and washing unit; the feeding end of the waste liquid buffer tank is connected with the reaction tank, and the discharging end of the waste liquid buffer tank is connected with the waste liquid hydrolysis tank; an alkali liquor inlet of the waste liquor hydrolysis tank is connected with the waste alkali buffer pool, a lime milk inlet of the waste liquor hydrolysis tank is connected with the lime milk preparation pool, a bottom discharge port of the waste liquor hydrolysis tank is connected with the drying pool through a liquid seal tank drainage pipeline, and a top tail gas phase outlet of the waste liquor hydrolysis tank is connected with the hydrolysis tail gas spraying and washing unit; the drying tank is provided with a water outlet, and the water outlet is connected to the lime milk preparation tank through a trench. According to the method, the sodium hydroxide waste alkali liquor and the lime powder are used for treating the high-boiling cracking waste liquid, the purpose of treating waste with waste is achieved, and meanwhile zero sewage discharge is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of high-boiling pyrolysis waste liquid treatment, and in particular to a system and method for treating high-boiling pyrolysis waste liquid in a polysilicon production process. Background Art

[0002] In the polysilicon production process, whether it is the modified Siemens method or the silane fluidized bed method for preparing polysilicon, there is a cold hydrogenation production process of silicon tetrachloride to prepare trichlorosilane. The preparation of trichlorosilane by silicon tetrachloride also produces high-boiling substances as by-products, which include hexachlorodisilane, hexachlorodisiloxane, and chlorosilanes with 3 or more silicon chains as the main components, as well as metal impurities (Fe, Al, Ca), non-metallic impurities (B, P) and their chlorides. In order to recycle the by-product high-boiling substances, polysilane can be decomposed into trichlorosilane and silicon tetrachloride through the high-boiling substance cracking process.

[0003] At present, the high-boiling product cracking process commonly used by domestic polysilicon manufacturers is mainly through a kettle reactor, using amine substances as high-boiling cracking catalysts. Due to the presence of difficult-to-crack components in high-boiling products, such as polysilane containing silicon-oxygen bonds, and the presence of impurities in high-boiling products, in the actual production process, the catalyst is deactivated and a certain amount of high-boiling cracking waste liquid is generated at the bottom of the reactor during the high-boiling cracking reaction.

[0004] High-boiling pyrolysis waste mainly contains silicon tetrachloride, siloxane, metal impurities (Fe, Al, Ca) and their chlorides. Hydrolysis and neutralization process is usually adopted to treat high-boiling pyrolysis waste. The alkali solution used for neutralization is usually lime milk solution or sodium hydroxide waste alkali solution generated during production maintenance and operation.

[0005] Among them, lime milk solution is used to hydrolyze and neutralize the high-boiling pyrolysis waste, and the main reaction equation is as follows:

[0006] Hydrolysis reaction:

[0007] SiCl 4 (l) + (n+2)H 2 O (l) = SiO 2 ·nH 2 O (s) + 4HCl (g) (1)

[0008] Si 2 OCl 6 (l) + (n+3)H 2 O (l) = 2SiO 2 ·nH 2 O (s) + 6HCl (g) (2)

[0009] Hydrolysis neutralization reaction:

[0010] SiCl 4 (l) + 3Ca(OH) 2 (l) + (n-3)H 2 O (l) = CaSiO 3 ·nH 2 O (s) + 2CaCl 2 (l) (3)

[0011] Si 2 OCl 6 (l) + 5Ca(OH) 2 (l) + (n-5)H 2 O (l) = 2CaSiO 3 ·nH 2 O (s) + 3CaCl 2 (l) (4)

[0012] 2AlCl 3 (s) + 4Ca(OH) 2 (l) + (n-4)H 2 O (l) = 3CaCl 2 (g) + Ca(AlO 2 ) 2 ·nH 2 O(s) (5)

[0013] 2Al(S) + Ca(OH) 2 (l) + (n+2)H 2 O (l) = Ca(AlO 2 ) 2 ·nH 2 O(s) + 3H 2 (g) (6)

[0014] From reaction equations (1) to (2), it can be seen that the main component of chlorosilane in high boiling liquid is SiCl 4 and Si 2 OCl 6 When reacting with water, HCl gas is released. The HCl gas enters the acid mist spray washing from the gas phase pipeline at the top of the hydrolysis tank and is neutralized and absorbed by the lime milk solution. It can be seen from reaction equations (3) to (6) that the main reaction component SiCl in the high-boiling pyrolysis wastewater is 4 、Si 2 OCl 6 、AlCl 3They all react with the lime milk solution to generate solid substances of calcium silicate and calcium aluminate containing crystal water and soluble salt calcium chloride respectively; the components in the high-boiling pyrolysis waste liquid that do not react with the lime milk solution, such as iron, calcium elements and their chlorides, exist in the wastewater after hydrolysis in the form of elemental, soluble salts.

[0015] The sodium hydroxide in the waste alkali liquid is used to hydrolyze and neutralize the high-boiling cracking waste liquid. The main reaction equation is as follows:

[0016] SiCl 4 (l) + 6NaOH (l) + (n-3)H 2 O (l) = Na 2 SiO 3 ·nH 2 O (s) + 4NaCl (l) (7)

[0017] Si 2 OCl 6 (l) + 10NaOH (l) + (n-5)H 2 O (l) = 2Na 2 SiO 3 ·nH 2 O(s) + 6NaCl(l) (8)

[0018] AlCl 3 (s) + 4NaOH (l) + (n-2)H 2 O (l) = 3NaCl (l) + NaAlO 2 ·nH 2 O (s) (9)

[0019] 2Al (s) + 2NaOH (l) + (2n+2)H 2 O (l) = 2NaAlO 2 ·nH 2 O(s) + 3H 2 (g) (10)

[0020] From reaction equations (7) to (10), it can be seen that the main reaction component SiCl 4 、Si 2 OCl 6 、AlCl 3 It can react with sodium hydroxide in waste alkali to produce solid substances such as sodium silicate and sodium aluminate containing crystal water and soluble salt sodium chloride; components in high-boiling cracking waste liquid that do not react with sodium hydroxide in waste alkali, such as iron, calcium and chloride, exist in the wastewater after hydrolysis in the form of simple substances or soluble salts.

[0021] The sodium hydroxide waste alkali liquor can come from the silane waste gas treatment device. The silane waste gas treatment device uses 15wt% sodium hydroxide solution and silane gas (SiH 4 ) reaction, remove silane gas in the tail gas, and produce Na 2 SiO 3 The main reaction equation of the waste alkali solution (containing 12 wt% to 15 wt% of sodium silicate and 3 wt% to 5 wt% of sodium hydroxide) is as follows:

[0022] S H 4 (g) + 2NaOH (l) + (n+1)H 2 O (l) = Na 2 SiO 3 ·nH 2 O(s) + 4H 2 (g) (11)

[0023] From the reaction equation (11), we can see that the silane gas SiH 4 It reacts with sodium hydroxide to generate solid sodium silicate containing crystal water and releases hydrogen. In order to prevent the solid sodium silicate containing crystal water from clogging the spray pump, pipes and nozzles, causing the alkali solution elution system to fail to operate normally, the sodium hydroxide waste alkali solution must be discharged and replaced with new alkali solution.

[0024] In the related art, whether it is the hydrolysis wastewater of high-boiling cracking waste liquid or the high-alkali wastewater containing sodium silicate produced by the silane waste gas treatment device, it is sent to the sewage treatment device through a pipeline for treatment to prevent direct discharge and pollution of the environment. From the above reaction, it can be seen that these sewage contains high silicate and sodium ions, which are easy to form viscous sodium silicate. Viscous sodium silicate will cause the pipeline of the sewage treatment device to be blocked, the equipment failure rate is high, the maintenance frequency is high, the operation stability is poor, and the operation cycle is short. The operating cost and maintenance cost are high, which seriously restricts the treatment speed of high-boiling cracking waste liquid, and then restricts the production balance of the entire company. In addition, since the high-boiling cracking catalyst is an amine-containing hydrocarbon substance, it is easy to produce a large amount of foam after hydrolysis, which not only increases the difficulty of sewage treatment, but also may affect the treatment efficiency. It is usually necessary to add a defoaming agent to reduce the foam, which ultimately leads to a significant increase in the cost of the added agent used.

[0025] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgement or any form of suggestion that the information constitutes the prior art already known to ordinary technicians in this field. Summary of the invention

[0026] Purpose of the invention: The technical problem to be solved by the present invention is to provide a system and method for treating high-boiling cracking waste liquid in the production process of polysilicon in view of the deficiencies in the prior art, which can avoid the blockage of sewage treatment equipment and pipelines by viscous sodium silicate, and is conducive to extending the operation cycle of the sewage treatment equipment and the stability of operation, while achieving zero sewage discharge.

[0027] In order to solve the above technical problems, the first aspect of the present invention discloses a high-boiling cracking waste liquid treatment system in the polysilicon production process, which includes a waste liquid buffer tank, a waste liquid hydrolysis tank, a lime milk preparation tank, a waste alkali buffer tank, a drying tank and a tail gas spray washing unit. The feed end of the waste liquid buffer tank is connected to the reaction tank, and the discharge end is connected to the waste liquid hydrolysis tank. The alkali liquid inlet of the waste liquid hydrolysis tank is connected to the waste alkali buffer tank, the lime milk inlet is connected to the lime milk preparation tank, the bottom discharge port is connected to the drying tank through the hydrolysis tank discharge pipeline, and the top tail gas gas phase outlet is connected to the hydrolysis tail gas spray washing unit. The drying tank is provided with a drain, and the drain is connected to the lime milk preparation tank through a ditch.

[0028] The invention uses sodium hydroxide waste alkali liquid and lime milk solution generated in the polysilicon production process to carry out hydrolysis and neutralization reaction with high-boiling pyrolysis waste liquid, so that the sodium hydroxide remaining as an effective component in the waste alkali liquid is effectively utilized to achieve the purpose of treating waste with waste, and solid-liquid separation is achieved by discharging solid-containing waste water generated by hydrolysis and neutralization into a drying tank for drying treatment. The liquid obtained by solid-liquid separation and slaked lime powder are prepared in a lime milk preparation tank to obtain lime milk solution. The prepared lime milk solution is subjected to hydrolysis and neutralization reaction with the high-boiling pyrolysis waste liquid to consume water in the waste alkali liquid, so that zero discharge of sewage treated with the high-boiling pyrolysis waste liquid is achieved, and finally the difficulty of sewage treatment by a sewage treatment device and the purpose of reducing the operation cost of the device are achieved.

[0029] Furthermore, the system also includes a lime powder adding device, which includes a lime powder silo and a screw conveyor. The bottom discharge port of the lime powder silo is connected to the feed port of the screw conveyor, and the discharge port of the screw conveyor is adapted to the feed port of the lime milk preparation tank.

[0030] In this embodiment, lime powder is added to the lime milk preparation tank through the lime powder adding device, so that the system can achieve continuous processing.

[0031] Specifically, the system comprises a lime milk pump, and the lime milk pump is arranged on a pipeline connecting the lime milk inlet of the waste liquid hydrolysis tank and the lime milk preparation tank.

[0032] In this embodiment, according to the need for hydrolysis of high-boiling cracking waste liquid, the lime milk solution in the lime milk preparation pool is pressurized by a lime milk pump and then sent to the waste liquid hydrolysis tank.

[0033] Specifically, the system comprises a waste alkali liquid pump, and the waste alkali liquid pump is arranged on a pipeline connecting the alkali liquid inlet of the waste liquid hydrolysis tank and the waste alkali buffer tank.

[0034] In this embodiment, according to the need for hydrolysis of high-boiling cracking waste liquid, the waste alkali liquid in the waste alkali buffer tank is pressurized by a waste alkali liquid pump and then sent to the waste liquid hydrolysis tank.

[0035] Specifically, the lime milk inlet of the waste liquid hydrolysis tank and the alkali solution inlet of the waste liquid hydrolysis tank are both located on the side of the waste liquid hydrolysis tank.

[0036] Specifically, the ditch is connected to the side of the lime milk preparation pool.

[0037] Specifically, the system comprises a nitrogen bubbling coil, and the gas outlet end of the nitrogen bubbling coil is arranged at the bottom of the lime milk preparation tank.

[0038] In this embodiment, nitrogen is continuously introduced into the bottom of the lime milk preparation tank through the outlet end of the nitrogen bubbling coil to bubble and stir the lime milk concentrate in the tank, thereby ensuring that the lime milk concentrate is uniform and not prone to sedimentation, thereby facilitating the transportation of the lime milk by a pump.

[0039] Specifically, the system includes a heating coil, and the bottom of the drying tank is provided with the heating coil.

[0040] In winter, by circulating hot water or using steam, the drying pool can also have a good solid-liquid separation effect in the lower temperature winter.

[0041] Specifically, the hydrolysis tail gas spray washing unit includes a spray circulating liquid pool, a spray tower, a liquid seal tank, a spray circulating pump, a venting pipeline, a spray tower drainage pipeline, a liquid seal tank drainage pipeline and a tail gas gas phase outlet pipeline. The spray circulating liquid pool is connected to the input port of the spray circulating pump through a pipeline, and the hydrolysis tank liquid inlet of the waste liquid hydrolysis tank and the spray liquid inlet of the spray tower are respectively connected to the output port of the spray circulating pump. The top tail gas gas phase outlet of the waste liquid hydrolysis tank is connected to the lower gas phase inlet of the spray tower through the tail gas gas phase outlet pipeline, so that the top tail gas gas phase outlet of the waste liquid hydrolysis tank is connected to the hydrolysis tail gas spray washing unit. The gas phase outlet of the spray tower is connected to the air inlet of the liquid seal tank, the vent line is connected to the top of the liquid seal tank, the bottom of the liquid seal tank is connected to the spray circulating liquid pool through the liquid seal tank drain line, and the bottom of the spray tower is connected to the spray circulating liquid pool through the spray tower drain line.

[0042] The second aspect of the present invention provides a method for treating high-boiling pyrolysis waste liquid using the above system, the method comprising the following steps:

[0043] The solid-containing wastewater obtained by the hydrolysis and neutralization reaction of the waste alkali liquid and the high-boiling cracking waste liquid in the waste liquid hydrolysis tank is discharged into the drying tank for drying treatment to achieve solid-liquid separation; the liquid obtained by the solid-liquid separation in the drying tank is discharged into the lime milk preparation tank to participate in the preparation of lime milk solution; the prepared lime milk solution is transported to the waste liquid hydrolysis tank for hydrolysis and neutralization reaction with the high-boiling cracking waste liquid.

[0044] The above steps are repeated to hydrolyze the high-boiling pyrolysis waste liquid by adding lime powder and waste alkali liquid, so as to effectively utilize the sodium hydroxide in the waste alkali liquid and consume the water in the waste alkali liquid by reacting the prepared lime milk solution with the high-boiling pyrolysis waste liquid. While achieving the purpose of treating waste with waste, zero sewage discharge from the treatment of high-boiling pyrolysis waste liquid is realized.

[0045] Beneficial effects:

[0046] 1. The present invention uses the sodium hydroxide waste alkali liquor, lime milk and high-boiling pyrolysis waste generated during production maintenance and operation to perform hydrolysis and neutralization, and uses a drying tank to separate the solid-containing wastewater obtained by the hydrolysis and neutralization reaction into solid and liquid, that is, calcium silicate, sodium silicate, sodium aluminate and calcium aluminate containing crystal water that are easy to block the pipeline are retained in the drying tank, and the soluble salts including calcium chloride, sodium chloride and ferric chloride in the sewage are dissolved in the water of the solid material, and the liquid phase water seeps out from the bottom of the drying tank and is reused for the preparation of the lime milk solution. The prepared lime milk solution reacts with the high-boiling pyrolysis waste liquid to consume water, and the unconsumed water is separated again through the drying tank and reused for the preparation of the lime milk solution. In this way, the cycle is operated, and the water is consumed in the cycle. While utilizing the remaining effective ingredient NaOH in the waste alkali liquor and treating waste with waste, the high-boiling pyrolysis waste liquid is treated to achieve zero discharge of sewage, and finally achieve the purpose of reducing the difficulty of sewage treatment by the sewage treatment device, balancing the production material treatment and reducing the operation cost of the device.

[0047] 2. Compared with the prior art, the treatment system of the present invention uses a drying tank to dry the solid-containing wastewater obtained by the hydrolysis and neutralization reaction, and does not need to be transmitted to the sewage treatment device for treatment through pipelines. This can avoid the problem of easy blockage of existing sewage treatment devices and pipelines, reduce the difficulty of sewage treatment devices in treating sewage, reduce the operation and maintenance costs of the devices, extend the operation cycle of the sewage treatment devices, and improve the operation efficiency of the sewage treatment devices. At the same time, since the effect of the drying treatment in the drying tank is not affected by the foam generated by hydrolysis, the present invention helps to reduce the use of defoaming agents, thereby reducing the cost of chemicals.

[0048] 3. The process route of the present invention is simple, the operation efficiency is high, and the maintenance cost is low. It can greatly improve the processing speed of high-boiling cracking waste, reduce the impurity enrichment degree of the high-boiling cracking system, improve the stability and economy of the operation of the high-boiling cracking system, and to a certain extent improve the overall process stability and superiority of polysilicon. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0050] Figure 1 A schematic diagram of the structure of a high-boiling pyrolysis waste liquid treatment system in a polysilicon production process provided by one embodiment of the present invention;

[0051] Figure 2 for Figure 1 A top view of a drying tank in a high-boiling pyrolysis waste liquid treatment system when a gravel filter layer and a fine sand filter layer are not laid;

[0052] Figure 3 For along Figure 2 Transverse section view along the median section line AA.

[0053] The following are the descriptions of the reference numerals:

[0054] 10. Waste liquid buffer tank; 101. High boiling cracking waste liquid feed pipe; 102. High boiling cracking waste liquid discharge pipe; 103. Nitrogen purge pipeline; 20. Waste liquid hydrolysis tank; 201. Top tail gas gas phase outlet; 202. Hydrolysis tank discharge pipeline; 203. Lime milk inlet; 204. Alkali liquid inlet; 205. Hydrolysis tank inlet; 30. Lime powder silo; 301. Lime powder conveying pipeline; 302. Discharge pipeline; 40. Screw conveyor; 50. Lime milk preparation tank; 501. Ditch; 502. Nitrogen bubbling coil; 503. Lime milk pump; 505. Industrial water inlet pipe; 60. Waste alkali buffer tank; 601. Waste alkali inlet pipe; 602. Waste alkali liquid pump; 70, drying tank; 71, first drying tank; 72, second drying tank; 701, heating coil; 702, drain outlet; 703, drying tank body; 704, tank bottom boss; 705, drainage ditch; 706, grille plate; 707, gravel filter layer; 708, fine sand filter layer; 80, tail gas spray washing unit; 801, spray circulation liquid tank; 802, spray tower; 803, liquid seal tank; 804, spray circulation pump; 805, venting pipeline; 806, recycled water replenishment pipeline; 807, spray tower drainage pipeline; 808, liquid seal tank drainage pipeline; 809, tail gas gas phase outlet pipeline; 810, liquid seal tank overflow pipeline. DETAILED DESCRIPTION

[0055] According to the actual operation of the sewage treatment device, when treating the sewage generated by high-boiling pyrolysis waste liquid, there are problems such as blockage of equipment pipelines, high equipment failure rate, high maintenance frequency, poor operation stability, and short operation cycle, and the operation cost and maintenance fee remain high. The present invention develops a new process path, using the sodium hydroxide waste alkali liquid and lime milk solution generated in the polysilicon production process to hydrolyze and neutralize the high-boiling pyrolysis waste liquid, which not only effectively utilizes the remaining effective component sodium hydroxide in the waste alkali liquid to achieve the purpose of treating waste with waste, but also discharges the solid-containing waste water generated by hydrolysis and neutralization into a drying tank for drying treatment to achieve solid-liquid separation, and the liquid obtained by solid-liquid separation is prepared with slaked lime powder, that is, calcium hydroxide powder with a content of 80% to 90% to obtain a lime milk solution, and the prepared lime milk solution is reacted with the high-boiling pyrolysis waste liquid to consume the water in the waste alkali liquid, so as to achieve zero discharge of sewage treated with high-boiling pyrolysis waste liquid, and finally achieve the purpose of reducing the difficulty of sewage treatment by the sewage treatment device and reducing the operation cost of the device.

[0056] Figure 1 A schematic diagram of the structure of a high-boiling pyrolysis waste liquid treatment system in a polysilicon production process provided by an embodiment of the present invention is shown. Figure 1 The dotted line in the figure indicates the liquid level. The system includes a waste liquid buffer tank 10, a waste liquid hydrolysis tank 20, a lime milk preparation tank 50, a waste alkali buffer tank 60, a drying tank 70 and a tail gas spray washing unit 80. Figure 1 As shown, the waste liquid buffer tank 10 is configured to buffer high-boiling cracking waste liquid, a feed end of which is connected to the reaction tank, and a discharge end of which is connected to the waste liquid hydrolysis tank 20. Figure 1 The reaction tank is not shown. The alkali liquid inlet 204 of the waste liquid hydrolysis tank 20 is connected to the waste alkali buffer tank 60, the lime milk inlet 203 is connected to the lime milk preparation tank 50, the bottom discharge port is connected to the drying tank 70 through the hydrolysis tank discharge pipeline 202, and the top tail gas gas phase outlet 201 is connected to the hydrolysis tail gas spray washing unit 80. The drying tank 70 is provided with a drain 702, and the drain 702 is connected to the lime milk preparation tank 50 through the trench 501.

[0057] The waste liquid hydrolysis tank 20 is also provided with an agitator.

[0058] The waste alkali buffer tank 60 is used to buffer the waste alkali liquid. The waste alkali liquid of the present application comes from the waste alkali liquid generated during the operation or maintenance of the company's internal equipment, for example, from the silane waste gas treatment device. The silane waste gas treatment device uses a 15 wt% sodium hydroxide solution to react with the silane gas (SiH4) in the tail gas generated in the silane gas preparation process to remove the silane gas in the tail gas and generate waste alkali liquid at the same time. The waste alkali liquid contains 12 wt% to 15 wt% of sodium silicate and 3 wt% to 5 wt% of sodium hydroxide.

[0059] A process route that can be implemented in the high-boiling cracking waste liquid treatment system in the polysilicon production process of the present invention is described below.

[0060] First, the high boiling cracking waste liquid generated by the reaction tank is buffered in the waste liquid buffer tank 10. The alkali liquid including the lime milk solution and the waste alkali liquid is sent to the waste liquid hydrolysis tank 20 and the alkali liquid level is controlled to 40 wt% to 50 wt%, and stirring is started at the same time.

[0061] Then, the high-boiling cracking waste liquid in the waste liquid buffer tank 10 can flow into the waste liquid hydrolysis tank 20, and undergo a hydrolysis and neutralization reaction with the alkali solution in the waste liquid hydrolysis tank 20. The acidic hydrolysis tail gas generated during the hydrolysis process flows out from the top tail gas gas phase outlet 201 to the hydrolysis tail gas spray washing unit 80 for treatment. After the hydrolysis and neutralization reaction in the waste liquid hydrolysis tank 20 is completed, the solid-containing waste water obtained by the hydrolysis and neutralization reaction of the alkali solution and the high-boiling cracking waste liquid is discharged into the drying tank 70 for drying treatment. Among them, the solid phase material in the solid waste water is trapped in the drying tank 70, and water seeps out from the bottom of the drying tank 70 to achieve solid-liquid separation. The solid phase material trapped in the drying tank 70 is mainly calcium silicate, sodium silicate, sodium aluminate and calcium aluminate containing crystal water, and the soluble salts including calcium chloride, sodium chloride and ferric chloride in the sewage are dissolved in the water of the solid material, so that they can be taken out of the treatment system together. The solid phase material intercepted by the drying tank 70 is tested, and the test results show that the water content in the solid phase material is 50wt% to 60wt%. The liquid obtained by solid-liquid separation in the drying tank 70, that is, the clean water seeping from the bottom of the drying tank 70, flows out from the drain port 702 and is discharged into the lime milk preparation tank 50 through the ditch 501. In the lime milk preparation tank 50, this part of the clean water and the purchased slaked lime powder, that is, 80wt% to 90wt% of calcium hydroxide powder are prepared to obtain a lime milk solution. The prepared lime milk solution is pressurized and transported to the waste liquid hydrolysis tank 20 according to the need for hydrolysis of high-boiling waste materials. The water in the lime milk solution is consumed due to its reaction with chlorosilane (silicon tetrachloride, siloxane) in the high-boiling cracking waste liquid, and the unconsumed water enters the lime milk preparation tank 50 again after infiltration through the drying tank to prepare the lime milk solution. In this way, the high-boiling pyrolysis waste liquid is hydrolyzed by adding lime powder and waste alkali liquid, which not only makes effective use of the sodium hydroxide in the waste alkali liquid to achieve the purpose of treating waste with waste, but also consumes the water in the waste alkali liquid through the reaction of the prepared lime milk solution with the high-boiling pyrolysis waste liquid, thereby achieving zero sewage discharge from the treatment of high-boiling pyrolysis waste liquid.

[0062] In addition, the present application utilizes the drying pool 70 to intercept solid phase materials that are prone to cause pipeline blockage, so that the system can operate smoothly. This helps to improve the processing efficiency of high-boiling pyrolysis waste. Excavators can be used to clean and transport the dried solid phase materials in the pool.

[0063] In some embodiments, in combination Figure 1As shown, the lime milk preparation tank 50 is connected to an industrial water inlet pipe 505. When the discharge amount of waste alkali liquid is insufficient, industrial water can be added into the lime milk preparation tank 50 through the industrial water inlet pipe 505, so that the amount of water used to prepare the lime milk solution in the lime milk preparation tank 50 meets the use demand, ensuring the water balance of the system operation and the hydrolysis balance of the high-boiling cracking waste liquid.

[0064] In some embodiments, in combination Figure 1 As shown, the waste alkali buffer tank 60 is connected to a waste alkali liquid inlet pipe 601, and the waste alkali liquid in the production process is introduced into and buffered in the waste alkali buffer tank 60 through the waste alkali liquid inlet pipe 601. In some other embodiments, the waste alkali liquid in the production process is discharged to the waste alkali buffer tank 60 by transporting in ton barrels.

[0065] In some embodiments, in order to achieve continuous treatment, the system further includes a lime powder adding device. Figure 1 As shown, the lime powder adding device includes a lime powder silo 30 and a screw conveyor 40. The bottom discharge port of the lime powder silo 30 is connected to the feed port of the screw conveyor 40 through a controllable discharge pipe 302. The discharge port of the screw conveyor 40 is arranged corresponding to the feed port of the lime milk preparation tank 50. The top of the lime powder silo 30 is connected to a lime powder delivery pipe 301. The lime powder can be delivered to the lime powder silo 30 by a tank truck through the lime powder delivery pipe 301. In some embodiments, the lime powder adding device controls the addition of lime powder according to the change of lime milk concentration in the lime milk preparation tank 50. In a specific embodiment, when the lime milk concentration in the lime milk preparation tank 50 is lower than 3 wt%, the system controls the screw conveyor 40 to start to deliver lime powder into the lime milk preparation tank 50; when the lime milk concentration in the lime milk preparation tank 50 reaches 8 wt%, the system controls the screw conveyor 40 to stop to stop replenishing lime powder into the lime milk preparation tank 50.

[0066] Combination Figure 1 As shown, the system includes a lime milk pump 503, which is configured to pump the lime milk solution from the lime milk preparation tank 50 to the lime milk inlet 203 of the waste liquid hydrolysis tank 20. More specifically, the lime milk pump 503 is disposed on a pipeline connecting the lime milk inlet 203 of the waste liquid hydrolysis tank 20 and the lime milk preparation tank 50.

[0067] In this embodiment, according to the need for hydrolysis of high-boiling cracking waste liquid, the lime milk solution is pressurized by the lime milk pump 503 and then sent to the waste liquid hydrolysis tank 20.

[0068] Combination Figure 1As shown, the system includes a waste alkali liquid pump 602, which is configured to pump the waste alkali liquid from the waste alkali buffer tank 60 to the alkali liquid inlet 204 of the waste liquid hydrolysis tank 20. More specifically, the waste alkali liquid pump 602 is disposed on a pipeline connecting the alkali liquid inlet 204 of the waste liquid hydrolysis tank 20 and the waste alkali buffer tank 60.

[0069] In this embodiment, according to the need for hydrolysis of high-boiling cracking waste liquid, the waste alkali liquid is pressurized by the waste alkali liquid pump 602 and then sent to the waste liquid hydrolysis tank 20.

[0070] Combination Figure 1 As shown, the system includes a high-boiling pyrolysis waste liquid feed pipe 101 and a high-boiling pyrolysis waste liquid discharge pipe 102. The feed end of the waste liquid buffer tank 10 is connected to the reaction tank through the high-boiling pyrolysis waste liquid feed pipe 101, and the discharge end of the waste liquid buffer tank 10 is connected to the waste liquid hydrolysis tank 20 through the high-boiling pyrolysis waste liquid discharge pipe 102. A high-boiling pyrolysis waste liquid discharge valve for controlling the high-boiling pyrolysis waste liquid discharge pipe 102 to be opened and closed is provided on the high-boiling pyrolysis waste liquid discharge pipe 102.

[0071] Combination Figure 1 As shown, a hydrolysis tank drain valve for controlling the opening and closing of the hydrolysis tank drain pipeline 202 is provided on the hydrolysis tank drain pipeline 202. In one embodiment, the system is configured to intermittently open the high-boiling cracking waste liquid discharge valve according to the pressure or temperature inside the waste liquid hydrolysis tank 20, so that the waste liquid in the waste liquid buffer tank 10 can be intermittently discharged into the waste liquid hydrolysis tank 20 for hydrolysis treatment. In another embodiment, the system is configured to control the opening and closing of the hydrolysis tank drain valve according to the pH value of the liquid in the waste liquid hydrolysis tank 20 to control the opening and closing of the hydrolysis tank drain pipeline 202. In a specific embodiment, when the pH value of the liquid in the waste liquid hydrolysis tank 20 is set to 8, the hydrolysis and neutralization reaction in the waste liquid hydrolysis tank 20 is completed, and the hydrolysis tank drain valve on the hydrolysis tank drain pipeline 202 is opened to discharge the solid-containing wastewater after hydrolysis in the waste liquid hydrolysis tank 20 into the drying tank 70 for solid-liquid separation; the hydrolysis tank drain valve is closed when emptying.

[0072] Further, combined with Figure 1 As shown, in order to prevent the high-boiling pyrolysis waste liquid discharge pipe 102 from being blocked, the high-boiling pyrolysis waste liquid discharge pipe 102 is also connected to a nitrogen purge pipeline 103, and a nitrogen purge valve is provided on the nitrogen purge pipeline 103. When the high-boiling pyrolysis waste liquid discharge pipe 102 is blocked, the nitrogen purge valve is opened, and nitrogen is introduced through the nitrogen purge pipeline 103 for purge and dredging.

[0073] Combination Figure 1 As shown, the lime milk inlet 203 and the alkali solution inlet 204 are both located on the side of the waste liquid hydrolysis tank 20.

[0074] Combination Figure 1As shown, the ditch 501 is connected to the side of the lime milk preparation tank 50 , and the water seeping out from the bottom of the drying tank 70 enters the lime milk preparation tank 50 through the ditch 501 .

[0075] Combination Figure 1 As shown, the system includes a nitrogen bubbling coil 502 , and the gas outlet end of the nitrogen bubbling coil 502 is arranged at the bottom of the lime milk preparation tank 50 .

[0076] In this embodiment, nitrogen is continuously introduced into the bottom of the lime milk preparation tank 50 through the outlet end of the nitrogen bubbling coil 502 to bubble and stir the lime milk concentrate in the tank, thereby ensuring that the lime milk concentrate is uniform and not easy to precipitate, thereby facilitating transportation by the lime milk pump 503.

[0077] Combination Figure 3 As shown, the system includes a heating coil 701, which is arranged at the bottom of the drying pool 70. In winter, hot water circulation or steam is used to enable the drying pool 70 to have a good solid-liquid separation effect even in winter when the temperature is relatively low.

[0078] Specifically, drainage outlets 702 may be provided at both ends of the drying pool 70 , and water seeping out from the bottom of the drying pool 70 enters the ditch 501 through the drainage outlets 702 .

[0079] Specifically, Figure 2 It is a top view of a drying tank in the high-boiling pyrolysis waste liquid treatment system of this embodiment when the gravel filter layer and the fine sand filter layer are not laid. Figure 3 For along Figure 2 A transverse section view along the median section line AA, and Figure 3 A cross-sectional view of two drying tanks arranged side by side is shown. Figure 2 and Figure 3 As shown, the drying pool 70 includes a drying pool body 703, in which a pool bottom boss 704 is arranged, and the side wall of the pool bottom boss 704 and the pool bottom of the drying pool body 703 form a drainage groove 705, and a grating plate 706 is laid on the drainage groove 705, and the grating plate 706 can be a glass fiber reinforced plastic grating plate. The heating coil 701 is arranged below the grating plate 706, and the heating coil 701 can be a steam heating coil. The grating plate 706 and the pool bottom boss 704 are sequentially laid with a gravel filter layer 707 and a fine sand filter layer 708 from bottom to top. The drain port 702 is opened at the bottom of the pool wall of the drying pool body 703, and the drain port 702 connects the drainage groove 705 and the ditch 501.

[0080] In this example, the drying pool 70 uses gravel and fine sand as filter media, which has the advantages of good penetration effect, fast solid-liquid separation, conducive to improving the processing speed of high-boiling waste, easy replacement, low maintenance cost, etc., and its processing process does not require the addition of any chemicals, which improves the overall process stability and economy of polysilicon to a certain extent.

[0081] In a specific embodiment, the wall height of the drying pool body 703 is 1.5 m, the thickness of the gravel filter layer 707 is 20 cm, and the thickness of the fine sand filter layer 708 is 15 cm. The average particle size of the gravel filter layer 707 is 10 mm to 20 mm, and the average particle size of the fine sand filter layer 708 is 1 mm to 2 mm.

[0082] Specific, combined Figure 1 As shown, two drying tanks 70 are provided and configured to be used alternately. Figure 3 As shown, the two drying tanks 70 are respectively the first drying tank 71 and the second drying tank 72. The first drying tank 71 and the second drying tank 72 can be used alternately. For example, if the first drying tank 71 is in the drying stage, the second drying tank 72 receives the solid-containing wastewater from the waste liquid hydrolysis tank 20. After the solid-containing wastewater is dried in the drying tank, an excavator is used to clean and transport the solid materials in the tank, and the cleaned drying tank is used for standby. By setting up two drying tanks for switching use, the solid-containing wastewater in the waste liquid hydrolysis tank 20 can be continuously discharged, and the system can operate continuously. In a specific embodiment, the drying cycle is about 2 days, and the water content of the solid materials in the tank is less than 60 wt%.

[0083] Combination Figure 1As shown, the hydrolysis tail gas spray washing unit 80 is used for spray washing the hydrolysis tail gas formed in the waste liquid hydrolysis tank 20, so that the residual gas absorbed by washing can be directly discharged into the atmosphere. The hydrolysis tail gas spray washing unit 80 includes a spray circulating liquid pool 801, a spray tower 802, a liquid seal tank 803, a spray circulation pump 804, a venting pipeline 805, a spray tower drainage pipeline 807, a liquid seal tank drainage pipeline 808 and a tail gas gas phase outlet pipeline 809. The spray circulating liquid pool 801 contains a spray circulating liquid. The spray circulating liquid pool 801 is connected to the input port of the spray circulation pump 804 through a pipeline, and the hydrolysis tank liquid inlet 205 of the waste liquid hydrolysis tank 20 and the spray liquid inlet of the spray tower 802 are respectively connected to the output port of the spray circulation pump 804 through corresponding pipelines. The tail gas gas phase outlet 201 at the top of the waste liquid hydrolysis tank 20 is connected to the lower gas phase inlet of the spray tower 802 through the tail gas gas phase outlet pipeline 809, so as to realize that the tail gas gas phase outlet 201 at the top of the waste liquid hydrolysis tank 20 is connected to the hydrolysis tail gas spray washing unit 80. The gas phase outlet of the spray tower 802 is connected to the air inlet of the liquid seal tank 803, the venting pipeline 805 is connected to the top of the liquid seal tank 803, the bottom of the liquid seal tank 803 is connected to the spray circulating liquid pool 801 through the liquid seal tank drainage pipeline 808, and the bottom of the spray tower 802 is connected to the spray circulating liquid pool 801 through the spray tower drainage pipeline 807.

[0084] In the present application, the hydrolysis tail gas formed in the waste liquid hydrolysis tank 20 includes HCl, water vapor and a small amount of chlorosilane, so the spray circulating liquid can be selected from lime milk solution, and the mass concentration of the lime milk solution is preferably 5 wt% to 8 wt%. The liquid in the liquid seal tank 803 also uses the spray circulating liquid. The hydrolysis tail gas enters the lower gas phase inlet of the spray tower 802 from the top tail gas gas phase outlet 201 through the tail gas gas phase outlet pipeline 809, and is washed and absorbed by the lime milk solution sprayed from the spray liquid inlet of the spray tower 802 in the spray tower 802. The residual gas after washing and absorption by the spray tower 802 flows out from the gas phase outlet of the spray tower 802 to the gas inlet of the liquid seal tank 803 and passes below the liquid level of the liquid seal tank 803, and then escapes from the liquid in the liquid seal tank 803 and is discharged into the atmosphere through the venting pipeline 805.

[0085] The spray circulating liquid in the spray circulating liquid pool 801 is pressurized by the spray circulating pump 804 and sent to the spray liquid inlet of the spray tower 802 for spray washing of the hydrolysis tail gas discharged from the waste liquid hydrolysis tank 20; the spray circulating liquid after washing and absorption is discharged from the spray tower discharge pipeline 807 at the bottom of the spray tower 802 and enters the spray circulating liquid pool 801 to form a circulating spray.

[0086] Combination Figure 1As shown, the bottom of the liquid seal tank 803 is also connected to a recycled water replenishment pipeline 806, and the side wall of the liquid seal tank 803 is also connected to a liquid seal tank overflow pipeline 810, and the liquid seal tank overflow pipeline 810 is connected to the liquid seal tank drainage pipeline 808. The recycled water replenishment pipeline 806, the liquid seal tank overflow pipeline 810 and the liquid seal tank drainage pipeline 808 are respectively provided with control valves for controlling the on-off of the pipelines. The control valve corresponding to the liquid seal tank drainage pipeline 808 is located between the bottom of the liquid seal tank 803 and the connection point between the liquid seal tank overflow pipeline 810 and the liquid seal tank drainage pipeline 808. When the liquid level of the liquid seal tank 803 is low, the recycled water is replenished through the recycled water replenishment pipeline 806 to maintain the liquid level of the liquid seal tank 803; when the liquid level of the liquid seal tank 803 is high, the excess liquid is discharged to the spray circulation liquid pool 801 through the liquid seal tank overflow pipeline 810 and the liquid seal tank drainage pipeline 808 in sequence to maintain the liquid level balance of the liquid seal tank 803. When the liquid seal tank 803 needs to be emptied, it is emptied through the liquid seal tank drainage pipeline 808.

[0087] The embodiment of the present invention also provides a method for treating high-boiling pyrolysis waste liquid using the above system, the method comprising the following steps:

[0088] The solid-containing wastewater obtained by the hydrolysis and neutralization reaction of the waste alkali liquid and the high-boiling cracking waste liquid in the waste liquid hydrolysis tank 20 is discharged into the drying tank 70 for drying treatment to achieve solid-liquid separation; the liquid obtained by the solid-liquid separation in the drying tank 70 is discharged into the lime milk preparation tank 50 to participate in the preparation of the lime milk solution, and the prepared lime milk solution is transported to the waste liquid hydrolysis tank 20 for hydrolysis and neutralization reaction with the high-boiling cracking waste liquid, consuming water.

[0089] The above steps are repeated to hydrolyze the high-boiling pyrolysis waste liquid by adding lime powder and waste alkali liquid, so as to effectively utilize the sodium hydroxide in the waste alkali liquid and consume the water in the waste alkali liquid by reacting the prepared lime milk solution with the high-boiling pyrolysis waste liquid. While achieving the purpose of treating waste with waste, zero sewage discharge from the treatment of high-boiling pyrolysis waste liquid is realized.

[0090] The present invention provides a system and method for treating high-boiling cracking waste liquid in the production process of polysilicon. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A system for treating high boiling cracking waste liquid in a polysilicon production process, characterized in that: The invention comprises a waste liquid buffer tank (10), a waste liquid hydrolysis tank (20), a lime milk preparation tank (50), a waste alkali buffer tank (60), a drying tank (70) and a tail gas spray washing unit (80); the feed end of the waste liquid buffer tank (10) is connected to the reaction tank, and the discharge end is connected to the waste liquid hydrolysis tank (20); the alkali liquid inlet (204) of the waste liquid hydrolysis tank (20) is connected to the waste alkali buffer tank (60), the lime milk inlet (203) is connected to the lime milk preparation tank (50), the bottom discharge port is connected to the drying tank (70) through the hydrolysis tank discharge pipeline (202), and the top tail gas gas phase outlet (201) is connected to the hydrolysis tail gas spray washing unit (80); the drying tank (70) is provided with a drain port (702), and the drain port (702) is connected to the lime milk preparation tank (50) through a trench (501).

2. The high boiling cracking waste liquid treatment system in the polysilicon production process according to claim 1, characterized in that: It also comprises a lime powder dosing device, the lime powder dosing device comprising a lime powder silo (30) and a screw conveyor (40), the bottom discharge port of the lime powder silo (30) being connected to the feed port of the screw conveyor (40), and the discharge port of the screw conveyor (40) being adapted to the feed port of the lime milk preparation tank (50).

3. The high boiling cracking waste liquid treatment system in the polysilicon production process according to claim 1, characterized in that: It comprises a lime milk pump (503), wherein the lime milk pump (503) is arranged on a pipeline connecting a lime milk inlet (203) of the waste liquid hydrolysis tank (20) and the lime milk preparation tank (50).

4. The high boiling cracking waste liquid treatment system in the polysilicon production process according to claim 1, characterized in that: It comprises a waste alkali liquid pump (602), wherein the waste alkali liquid pump (602) is arranged on a pipeline connecting an alkali liquid inlet (204) of the waste liquid hydrolysis tank (20) and the waste alkali buffer tank (60).

5. The high boiling cracking waste liquid treatment system in the polysilicon production process according to claim 1, characterized in that: The lime milk inlet (203) of the waste liquid hydrolysis tank (20) and the alkali solution inlet (204) of the waste liquid hydrolysis tank (20) are both located on the side of the waste liquid hydrolysis tank (20).

6. The high boiling cracking waste liquid treatment system in the polysilicon production process according to claim 1, characterized in that: The ditch (501) is connected to the side of the lime milk preparation tank (50).

7. The high boiling cracking waste liquid treatment system in the polysilicon production process according to claim 1, characterized in that: It comprises a nitrogen bubbling coil (502), wherein the gas outlet end of the nitrogen bubbling coil (502) is arranged at the bottom of the lime milk preparation tank (50).

8. The high boiling cracking waste liquid treatment system in the polysilicon production process according to claim 1, characterized in that: It comprises a heating coil (701), and the bottom of the drying pool (70) is provided with the heating coil (701).

9. The high boiling cracking waste liquid treatment system in the polysilicon production process according to claim 1, characterized in that: The hydrolysis tail gas spray washing unit (80) comprises a spray circulating liquid pool (801), a spray tower (802), a liquid seal tank (803), a spray circulating pump (804), a venting pipeline (805), a spray tower drainage pipeline (807), a liquid seal tank drainage pipeline (808) and a tail gas gas phase outlet pipeline (809); the spray circulating liquid pool (801) is connected to the input port of the spray circulating pump (804) through a pipeline, the hydrolysis tank liquid inlet (205) of the waste liquid hydrolysis tank (20) and the spray liquid inlet of the spray tower (802) are respectively connected to the output port of the spray circulating pump (804); the tail gas gas phase outlet (201) at the top of the waste liquid hydrolysis tank (20) is connected to the outlet of the spray circulating pump (804); The lower gas phase inlet of the spray tower (802) is connected through the tail gas gas phase outlet pipeline (809) to realize that the top tail gas gas phase outlet (201) of the waste liquid hydrolysis tank (20) is connected to the hydrolysis tail gas spray washing unit (80); the gas phase outlet of the spray tower (802) is connected to the air inlet of the liquid seal tank (803), the venting pipeline (805) is connected to the top of the liquid seal tank (803), the bottom of the liquid seal tank (803) is connected to the spray circulating liquid pool (801) through the liquid seal tank drain pipeline (808), and the bottom of the spray tower (802) is connected to the spray circulating liquid pool (801) through the spray tower drain pipeline (807).

10. A method for treating high-boiling pyrolysis waste liquid using the system according to claim 1, characterized in that: The steps include: Solid-containing wastewater obtained by hydrolysis and neutralization reaction of waste alkali liquid and high-boiling pyrolysis waste liquid in a waste liquid hydrolysis tank (20) is discharged into a drying tank (70) for drying treatment to achieve solid-liquid separation; the liquid obtained by solid-liquid separation in the drying tank (70) is discharged into a lime milk preparation tank (50) to participate in the preparation of lime milk solution; the prepared lime milk solution is transported to the waste liquid hydrolysis tank (20) to undergo hydrolysis and neutralization reaction with the high-boiling pyrolysis waste liquid.

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