A multi-stage treatment process for polysilicon slurry

Abstract

The application provides a multi-stage treatment process for polysilicon slurry and relates to the technical field of polysilicon slurry treatment. First, the slurry of a cold hydrogenation section is collected into a collecting tank and cooled to below 30 DEG C, while a certain proportion of diatomite is added to the collecting tank to mix with the slurry to form a clumpy coagulum and is delivered to a vacuum drum filter. The vacuum drum filter adopts a filter screen coated with diatomite of different mesh numbers and two or more layers of filter cloth to intercept silicon powder and high-boiling substances in the slurry to obtain filter cake and clear liquid. The filter cake is delivered to a hydrolysis subsystem after being treated by a drying machine. The clear liquid is treated by various buffer tanks and heat exchangers to recover chlorosilane, remove metal chlorides and deliver tail gas to a tail gas cryogenic subsystem. The vacuum drum filter adopts a filter screen coated with diatomite of different mesh numbers and multiple layers of filter cloth to intercept silicon powder and high-boiling substances in the slurry to prevent high-boiling substances and silicon powder from penetrating and clogging the filter cloth, thereby ensuring normal liquid output.

Description

Technical Field

[0001] This invention relates to the field of polycrystalline silicon slag slurry treatment technology, and in particular to a multi-stage treatment process for polycrystalline silicon slag slurry. Background Technology

[0002] The slurry produced in the cold hydrogen chemical section of polysilicon production mainly consists of chlorosilanes, silicon powder, and metallic impurities, primarily aluminum chloride. After simple filtration, the slurry separates into a clear liquid and a dry slag. The clear liquid is sent to a subsequent process for settling and further treatment, while the dry slag is discharged in an open-loop manner. After settling, the clear liquid yields a supernatant and slag. The supernatant is sent to a high-boiling-point tower for further treatment and recovery, while the slag undergoes hydrolysis. The saturated wastewater generated from the hydrolysis is sent to a subsequent auxiliary process for further treatment.

[0003] Currently, the polysilicon slag slurry treatment process has the following problems: In traditional slurry treatment systems, the composition of the slurry places certain requirements on the filtration accuracy of the filter. If the filter accuracy is too high, it becomes difficult to transport the slurry and the filter needs frequent cleaning; if the accuracy is too low, it cannot perform its filtering function. High-boiling-point substances and silica fume particles are particularly fine and easily penetrate the filter, clogging the filter cloth and causing difficulties in slurry discharge. This affects the normal production operation of subsequent processes and the overall system balance of the company. Summary of the Invention

[0004] To address the problems in the prior art, this invention provides a multi-stage treatment process for polycrystalline silicon slag slurry.

[0005] The technical solution adopted in this invention is: A multi-stage treatment process for polycrystalline silicon slag slurry includes the following steps: S1. The slurry from the cold hydrogen chemical section is transported to a collection tank. After cooling, a certain proportion of diatomaceous earth is added to the collection tank for premixing. The material in the collection tank is then transported to a vacuum drum filter for filtration to obtain filter cake and clear liquid a. The filter cake is sent to a dryer for drying, and clear liquid a is sent to a buffer tank I for temporary storage. The vacuum drum filter uses filter screens with different mesh sizes of diatomaceous earth coated on the inside and outside and two or more layers of filter cloth to intercept silica powder and high-boiling substances in the slurry. S2. After the filter cake is dried by the dryer in step S1, slag and gas phase a are obtained. The slag is transported to the hydrolysis subsystem, and gas phase a is transported to heat exchanger I for cooling treatment to obtain chlorosilane condensate. The chlorosilane condensate is transported to buffer tank II for temporary storage. S3. The slag material in the collection tank, after being cooled by the circulating water jacket, is transported to the slurry settling tank and cooled to below 15°C by 7°C water. After settling, the supernatant and the lower slag material are obtained. The supernatant is transported to the buffer tank III after passing through the liquid phase filter. After being pressurized by the pump, it is transported to the distillation section. The lower slag material is directly sent to the dryer for drying. S4. After pressurizing the chlorosilane condensate in buffer tank II in step S2, it is transported to buffer tank I. A vacuum pump is connected to the rear end of buffer tank I, so that the pressure in buffer tank I is -30kPa to -70kPa and the temperature is 15-25℃. S5. Then, the liquid phase a in buffer tank I is pumped to buffer tank III. The gas phase b in buffer tank I is condensed to obtain liquid phase b and gas phase c. Liquid phase b is transported to buffer tank I. Gas phase c is filtered, pressurized, and condensed by heat exchanger III to obtain liquid phase c. Liquid phase c is transported to tail gas condenser. S6. After being processed by buffer tank Ⅲ in step S5, liquid phase d and gas phase d are obtained. The liquid phase d is pressurized and then sent to the distillation section. The gas phase d is condensed and then liquid phase e is sent to buffer tank Ⅲ. S7. The gas phase e and liquid phase f obtained after treatment by the tail gas condenser are sent to the vacuum drum filter and the liquid phase f is sent to the buffer tank II.

[0006] Furthermore, in step S1, the filter screen of the vacuum drum filter is coated with a coating made of diatomaceous earth and silicon tetrachloride liquid, with a coating thickness of 80-120mm, wherein the proportion of diatomaceous earth is usually 3.7%; the interior is coated with a mixture of 400-mesh diatomaceous earth and silicon tetrachloride, and the exterior is coated with a mixture of 200-300-mesh diatomaceous earth and silicon tetrachloride.

[0007] Furthermore, in step S1, the filter cloth of the vacuum drum filter uses two or more layers of filter cloth, with different pore sizes in each layer. The outer layer of filter cloth has an air permeability of 250-300 L•m2 / s, and the inner layer of filter cloth has an air permeability of 150-200 L•m2 / s.

[0008] Furthermore, in step S1, a circulating water jacket is provided on the outside of the collection tank to ensure that the material temperature transported from the collection tank to the vacuum drum filter does not exceed 30°C.

[0009] Furthermore, the hydrolysis subsystem in step S2 includes a slag storage tank, a hydrolysis pool, a scrubbing tower I, a feed pipeline, a regulating valve I, a water supply pipeline, a venting pipeline, and a regulating valve II. The bottom of the slag storage tank is connected to the hydrolysis pool via the feed pipeline, and the feed pipeline is equipped with a regulating valve I. The hydrolysis pool is connected to a water supply pipeline. Gas a generated after the slag is treated in the hydrolysis pool is transported to the scrubbing tower I for further treatment. The gas b obtained after treatment is discharged through the venting pipeline, and the venting pipeline is equipped with a regulating valve II.

[0010] Furthermore, the gas phase outlets of buffer tanks I, II, and III are all connected to a cryogenic tail gas subsystem. The cryogenic tail gas subsystem includes a scrubbing tower II, a heat exchanger V, a pump II, and a feed pipe. Scrubbing tower II uses chlorosilane liquid as the scrubbing fluid. The scrubbing fluid is transported from the bottom of scrubbing tower II to heat exchanger V for cooling to -5 to -25°C, and then returned to scrubbing tower II for scrubbing the gas entering the cryogenic tail gas subsystem from the feed pipe. The liquid chlorosilane obtained after scrubbing and cooling is recycled, and the resulting non-condensable gas is sent from the top outlet of scrubbing tower II to the waste gas treatment system for further treatment.

[0011] Furthermore, the heat source for the dryer is 2 kg of hot water at a temperature of 80~110℃ for drying the material.

[0012] Furthermore, the vacuum drum filter is modified by adding a spray device inside, which cleans the drum surface.

[0013] Furthermore, in step S5, gas phase b is condensed by heat exchanger II to obtain liquid phase b and gas phase c. The temperature of the material is controlled at 5-15℃ and the pressure is controlled at -40kPa to -60kPa. The obtained liquid phase b is temporarily stored in buffer tank I. Gas phase c is further condensed to obtain liquid phase b, which is also sent to buffer tank I. The gas phase c, which is still in a gaseous state, is sent to an air filter for filtration. Then, pump I draws the vacuum to -40kPa to -65kPa and sends it to heat exchanger III for condensation to obtain liquid phase c. Liquid phase c is then temporarily stored in the tail gas condenser.

[0014] Furthermore, the air filter is a T-type filter with a sintered metal filter element and a filtration accuracy of 50-80 mesh.

[0015] The beneficial effects of this invention are: I. In this invention, compared with the original slurry treatment process, the multi-stage slurry treatment technology further optimizes the existing process, breaks through the bottleneck of the high-boiling-point treatment process in the polycrystalline silicon slurry treatment process, improves the treatment capacity of slurry and high-boiling-point substances, solves the clogging problem, reduces the slurry treatment load of the downstream system, and reduces the slurry treatment cost.

[0016] Second, compared with the prior art, the new process can reduce the frequency of filter cleaning. The original process required cleaning 6 filters per day, and each filter required 4 people to clean. With the new process, only 1 filter needs to be cleaned every 6 months. Therefore, the safety risks and environmental pollution caused by open-loop operation can be reduced, the risk of hydrolysis can be significantly reduced, and the workload of personnel can be reduced.

[0017] Third, in this invention, a certain proportion of diatomaceous earth is added to the collection tank so that some of the silica powder and high-boiling-point substances in the slurry are mixed with the diatomaceous earth to form agglomerated aggregates, which are more easily adsorbed on the drum surface of the vacuum drum filter, while preventing high-boiling-point substances and silica powder from penetrating into the inside of the drum.

[0018] IV. In this invention, the filter screen of the vacuum drum filter is coated with a coating made of chlorosilane and diatomaceous earth, with a coating thickness of 80-120mm, wherein the proportion of diatomaceous earth is usually 3.7%; the inner and outer surfaces of the vacuum drum filter are pre-coated with diatomaceous earth of different mesh sizes, with 400-mesh diatomaceous earth used inside to prevent high-boiling substances and silica powder from penetrating and clogging the filter cloth, and 200-300-mesh diatomaceous earth used outside to facilitate the adsorption of normal residue on the surface, prevent diatomaceous earth from falling off, and ensure normal liquid output.

[0019] Fifth, in this invention, the filter cloth in the vacuum drum filter is changed from a single layer to two or more layers, and the pore size of each layer is different. The outer layer filter cloth has an air permeability of 250-300 L·m2 / s, and the inner layer filter cloth has an air permeability of 150-200 L·m2 / s. Secondly, the PTFE filter cloth is changed to a metal filter cloth, which has better structural strength and ductility, and also has better moisture absorption than PTFE.

[0020] VI. In this invention, by analyzing the solid content in the slurry in advance, the slurry with high solid content is treated by a vacuum drum filter, while the slurry with low solid content is treated by multi-stage cooling and sedimentation and then sent to the downstream process for treatment. The slurry is graded and the problem of high operating cost of slurry treatment equipment is solved.

[0021] VII. In this invention, the use of this process reduces the amount of slag entering the hydrolysis subsystem, increases the recovery rate of chlorosilanes in the slurry (reaching over 97%), reduces the load on downstream slurry treatment, recovers some chlorosilanes to balance the raw material system, reduces the input of purchased TCS, and simultaneously reduces the load on the wastewater treatment system. It effectively reduces the amount of chlorosilane hydrolyzed, lowering the chloride ion concentration in wastewater. Furthermore, it significantly reduces the content of metal impurities in the recovered chlorosilanes, lowering the metal impurity content in the product from 100,000-200,000 ppbm to within 20,000 ppbm, thus improving product quality.

[0022] 8. In this invention, the exhaust gas contains a high content of chlorosilanes. By adopting this process, the original vented exhaust gas can be recycled and reused through the exhaust gas cryogenic system, reducing emissions into the air and lowering environmental pressure. At the same time, the chlorosilanes in the exhaust gas can be recycled and reused, increasing project revenue.

[0023] 9. In the original slurry process of this invention, the slag material is temporarily stored in a slag storage tank after being processed by a dryer, and needs to be manually discharged by staff. This manual discharge process causes some pollution to the site environment, and the discharged slag material needs to be transferred to a hydrolysis tank, where the hydrolysis reaction is relatively vigorous and inefficient, posing certain safety risks. The hydrolysis subsystem in this solution is fully enclosed. The slag material enters the hydrolysis tank directly after passing through the slag storage tank for hydrolysis. Simultaneously, the exhaust gas after hydrolysis is treated by a scrubbing tower I before being vented. The hydrolysis tank is separately connected to a water supply pipeline for water replenishment and an external discharge port for slag discharge, preventing equipment blockage and water saturation.

[0024] 10. In this invention, after the new deep cryogenic subsystem for treating and recovering the exhaust gas, chlorosilane is used as the scrubbing liquid without introducing other substances that may affect the operation of the equipment. The chlorosilane in the exhaust gas is condensed from the gas phase to the liquid phase for recovery. The resulting non-condensable gas is then sent to the downstream exhaust gas compressor for recycling, thereby reducing environmental pollution, lowering the water system load, and recovering the exhaust gas.

[0025] XI. In this invention, the liquid discharge pipelines connecting heat exchangers I, II, and III are straight pipes to prevent problems such as difficulty in liquid discharge due to excessive static pressure difference in U-shaped pipes. The preferred pipe diameter is DN50-DN150. Because the material contains small particles such as silicon powder, the scouring effect on pipe bends and other structures is significant under high temperature and high flow velocity conditions, resulting in severe wear. The dryer discharge pipeline bends in this solution are coated with a wear-resistant layer of silicon carbide or silicon nitride, which solves the aforementioned problems and increases the service life of the corresponding structural components and equipment.

[0026] 12. In this invention, through technical modification, the cleaning of the drum surface of the vacuum drum filter is changed from direct liquid injection cleaning to spray cleaning from the nozzle, which solves the problems of uneven drum surface cleaning and difficulty in controlling the flow rate of the cleaning liquid, and further extends the operating cycle of the vacuum drum filter. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a process flow diagram of the present invention.

[0029] Figure 2 This is a schematic diagram of the exhaust gas cryogenic subsystem.

[0030] Figure 3 This is a schematic diagram of the hydrolysis subsystem.

[0031] Marked in the image: 1. Collection tank; 2. Vacuum drum filter; 3. Dryer; 4. Buffer tank I; 5. Hydrolysis subsystem; 6. Heat exchanger I; 7. Buffer tank II; 8. Buffer tank III; 9. Tail gas condenser; 10. Heat exchanger II; 11. Heat exchanger III; 12. Air filter; 13. Liquid phase filter; 14. Slurry settling tank; 15. Temperature sensor; 17. Tail gas cryogenic subsystem; 5.1. Slag storage tank; 5.2. Hydrolysis tank; 5.3. Scrubber I; 5.4. Feed pipeline; 5.5. Regulating valve I; 5.6. Water supply pipeline; 5.7. Vent pipeline; 5.8. Regulating valve II; 17.1. Scrubber II; 17.2. Heat exchanger V; 17.3. Pump II; 17.4. Feed pipe. Detailed Implementation

[0032] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0033] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, these are merely examples and are not intended to limit the present invention.

[0034] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0035] This invention provides a multi-stage treatment process for polycrystalline silicon slurry, which solves the problem of frequent filter cleaning and safety hazards in existing polycrystalline silicon slurry treatment processes; at the same time, it improves the production system's ability to process silicon powder and high-boiling-point substances in the slurry and increases the recovery rate of chlorosilanes in the slurry.

[0036] Reference Figure 1 A multi-stage treatment process for polycrystalline silicon slag slurry mainly includes the following steps: S1. The slurry from the cold hydrogen chemical section is transported to the collection tank 1 and cooled to 25°C or below by a circulating water jacket. A certain proportion of diatomaceous earth is added to the collection tank 1 according to the slurry volume and premixed with the slurry. The mixture in the collection tank 1 is then transported to the vacuum drum filter 2 for adsorption filtration to obtain filter cake and clear liquid a. The filter cake is sent to the dryer 3 for drying, and the clear liquid a is sent to the buffer tank I6 for temporary storage. The vacuum drum filter 2 uses filter screens with different mesh sizes of diatomaceous earth coated inside and outside and two or more layers of filter cloth to intercept silica powder and high-boiling substances in the slurry. S2. After the filter cake is dried by the dryer 3 in step S1, the residue and gas phase a are obtained. The residue is transported to the hydrolysis subsystem 5 for further processing, and the gas phase a is transported to the heat exchanger I6 for cooling to obtain chlorosilane condensate. The chlorosilane condensate is transported to the buffer tank II7 for temporary storage. S3. The slag material in the collection tank 1, after being cooled by the circulating water jacket, is transported to the slurry settling tank 14 and cooled to below 15°C by water at 7°C. After settling, the supernatant and the lower slag material are obtained. The supernatant is transported to the buffer tank Ⅲ8 after passing through the liquid phase filter 13. After being pressurized by the pump, it is transported to the distillation section for further processing. The lower slag material is directly sent to the dryer 3 for drying. S4. After pressurizing the chlorosilane condensate in buffer tank II 7 in step S2, it is transported to buffer tank I 4. A vacuum pump is connected to the rear end of buffer tank I 4 so that the pressure in buffer tank I 4 is -30kPa to -70kPa and the temperature is 15-25℃. S5. The liquid phase a in buffer tank I4 is then pumped to buffer tank III8 for further processing. The gas phase b in buffer tank I4 is condensed to obtain liquid phase b and gas phase c. Liquid phase b is transported to buffer tank I4. Gas phase c is filtered, pressurized, and condensed by heat exchanger III11 to obtain liquid phase c. Liquid phase c is transported to tail gas condenser 9. S6. After being processed by buffer tank Ⅲ8 in step S5, liquid phase d and gas phase d are obtained. The liquid phase d is pressurized and then sent to the distillation section. The gas phase d is condensed and then liquid phase e is sent to buffer tank Ⅲ8. S7. The gas phase e and liquid phase f obtained after being processed by the tail gas condenser 9 are sent to the vacuum drum filter 2 for further circulation, and the liquid phase f is sent to the buffer tank II 7.

[0037] In this embodiment, the slurry collected from the cold hydrogen chemical section generally has a temperature greater than 40°C. The metal chlorides in it are generally in the gaseous phase mixed with the chlorosilane gaseous phase. Traditional technology usually sends this part of the slurry directly to the vacuum drum filter 2 for treatment. The material containing metal chlorides enters the vacuum drum filter 2 under low pressure and low temperature conditions, where the metal chlorides are cooled into a solid state and aggregate into large particles.

[0038] The filter cloth inside the vacuum drum filter 2 has very small pores, causing metal chloride particles to adhere to it. This leads to frequent equipment failures and requires frequent open-loop cleaning of the filter mechanism (filter cloth, etc.) of the vacuum drum filter 2. This causes the metal chlorides to re-enter the downstream pipeline, resulting in a high content of metal impurities in the recovered chlorosilanes.

[0039] After adopting this solution, the material in collection tank 1 is cooled to 30°C or below, causing the metal chlorides to cool and aggregate into large particles. After being processed by vacuum drum filter 2, most of the metal chlorides are retained to form a filter cake that enters the downstream slag treatment section. This significantly reduces the number of times the vacuum drum filter 2 needs to be cleaned, extends the continuous service life of the equipment, and also significantly reduces the metal impurity content in the recovered chlorosilanes.

[0040] The pressure and temperature in buffer tank I4 are the same as those in vacuum drum filter 2. The pressure in buffer tank I4 is generally stable in the range of -30kPa to -70kPa. If the negative pressure is higher than 70kPa, excessive silica powder and high-boiling substances will adhere to the filter cloth and clog it. At the same time, it may cause severe hardening of the drum surface of vacuum drum filter 2 and obstruction of the scraper operation. If the negative pressure is lower than 30kPa, the diatomaceous earth adsorption force is weak and the drum surface coating is easy to fall off.

[0041] Furthermore, in step S5, after the gas phase b is condensed by heat exchanger II10, the temperature of the material is controlled at 5-15℃ and the pressure is controlled at -40kPa~-60kPa. The obtained liquid phase b is then temporarily stored in buffer tank I4.

[0042] Furthermore, in step S5, the gas phase c is condensed to obtain liquid phase b, which is then transported to buffer tank I4. The gas phase c, which is still in a gaseous state, is transported to air filter 12 for filtration. Then, pump I evacuates the vacuum to -40kPa to -65kPa and transports it to heat exchanger III11 for condensation to obtain liquid phase c. Liquid phase c is then transported to tail gas condenser 9 for temporary storage.

[0043] Furthermore, air filter 12 is a T-type filter with a sintered metal filter element and a filtration precision of 50-80 mesh. When a filter element with a filtration precision higher than 80 mesh is selected, the filter is prone to frequent clogging, resulting in a low vacuum level in the vacuum drum filter 2. Conversely, when a filter element with a filtration precision lower than 50 mesh is selected, the larger pore size prevents the filtration of high-boiling-point substances and other materials, leading to clogging and affecting equipment operation. In this design, to further investigate the impact of the filtration precision of air filter 12 on its filtration effect, filter elements of 50 mesh, 60 mesh, 70 mesh, and 80 mesh were installed on air filter 12, and the solid content in the material flowing through the downstream pipeline was measured. The results are shown in Table 1.

[0044] Table 1

[0045] As shown in Table 1, while the filtration effect is enhanced with the increase of filter precision, it also leads to a shorter filter operating cycle and the need for frequent filter cleaning; if the precision is too low, the filtration effect will be poor.

[0046] Furthermore, in step S1, a circulating water jacket is installed on the outside of the collection tank 1 to ensure that the material temperature transported from the collection tank 1 to the vacuum drum filter 2 does not exceed 30°C. This solves the problem in traditional technology where excessively high temperatures of the slag entering the vacuum drum filter 2 lead to the precipitation of large amounts of high-boiling-point substances, clogging the filter cloth of the vacuum drum filter 2, and affecting the vacuum level and slurry treatment effect. Currently, in the polysilicon production industry, the impact of the temperature in the collection tank 1 at the front end of the vacuum drum filter 2 on the process is almost entirely ignored.

[0047] Furthermore, in step S1, the filter cloth of the vacuum drum filter 2 consists of two or more layers, each with a different pore size. The outer layer filter cloth has a permeability of 250-300 L•m. 2 / s, the inner filter cloth specification is 150-200 L•m air permeability. 2 / s. In this embodiment, after adopting this solution, the recovery rate of chlorosilanes in the slurry can reach 95% or more, which is significantly better than the traditional slurry treatment technology (the recovery rate of chlorosilanes in the traditional process is 85%-90%), an improvement of more than 5%, significantly reducing raw material costs and reducing the pressure of downstream chlorosilane treatment. At the same time, the filter cloth material is changed from PTFE to metal, increasing structural strength and ductility, and improving moisture absorption.

[0048] Furthermore, in step S1, the filter screen of the vacuum drum filter 2 is coated with a coating made of a mixture of diatomaceous earth and silicon tetrachloride solution, with a coating thickness of 80-120mm, of which diatomaceous earth typically accounts for 3.7%. The interior is coated with a mixture of 400-mesh diatomaceous earth and silicon tetrachloride to effectively intercept high-boiling substances and silicon powder from penetrating the filter cloth of the vacuum drum filter 2, preventing clogging. The exterior is coated with a mixture of 200-300-mesh diatomaceous earth and silicon tetrachloride to facilitate the adsorption of normal residue on the surface, ensuring a normal output. In actual production, the raw material ratio can be adjusted appropriately or the coating raw materials can be changed according to specific circumstances.

[0049] Further, see Figure 3In step S2, the hydrolysis subsystem 5 includes a slag storage tank 5.1, a hydrolysis tank 5.2, a scrubbing tower I 5.3, a feed pipeline 5.4, a regulating valve I 5.5, a water supply pipeline 5.6, a venting pipeline 5.7, and a regulating valve II 5.8. The bottom of the slag storage tank 5.1 is connected to the hydrolysis tank 5.2 via the feed pipeline 5.4, which is equipped with a regulating valve I 5.5. The hydrolysis tank 5.2 is connected to the water supply pipeline 5.6. Gas a generated after the slag is treated in the hydrolysis tank 5.2 is transported to the scrubbing tower I 5.3 for further treatment. The resulting gas b is discharged through the venting pipeline 5.7, which is equipped with a regulating valve II 5.8.

[0050] Furthermore, the gas phase outlets of buffer tanks I-4, II-7, and III-8 are all connected to the exhaust gas cryogenic subsystem 17; see [link / reference] Figure 2 The tail gas cryogenic subsystem 17 includes a scrubbing tower II 17.1, a heat exchanger V 17.2, a pump II 17.3, and a feed pipe 17.4. The scrubbing tower II 17.1 uses chlorosilane liquid as the scrubbing fluid. The scrubbing fluid is transported from the bottom of the scrubbing tower II 17.1 to the heat exchanger V 17.2 for cooling to -5~-25℃, and then sent back to the scrubbing tower II 17.1 to scrub the gas entering the tail gas cryogenic subsystem 17 from the feed pipe 17.4. The liquid chlorosilane obtained after scrubbing and cooling is recycled. The obtained non-condensable gas is sent from the top outlet of the scrubbing tower II 17.1 to the waste gas treatment system for further treatment.

[0051] After processing in each buffer tank (including buffer tank I4, buffer tank II7, and buffer tank III8), the resulting gas phase is collected and subjected to cryogenic treatment to further recover the chlorosilanes mixed in this gas phase. This gas is then cooled to -5 to -15°C, the liquid phase (mainly chlorosilanes) is recovered, and the final non-condensable gas (mainly hydrogen) is sent to the waste gas treatment system for further processing.

[0052] Furthermore, the liquid discharge lines connected to heat exchangers I6, II10, and III11 are all straight pipes, and the inner side of the elbow of the feed line of dryer 3 is coated with a wear-resistant layer.

[0053] Furthermore, the heat source for dryer 3 is 2 kg of hot water at a temperature of 80~110℃ for material drying. Due to the special properties of the material, if a heat source with excessively high temperature and pressure is used, it may cause dryer 3 to vent and subsequent condenser to become clogged.

[0054] Furthermore, the vacuum drum filter 2 has been modified by adding a spray device inside. The spray device cleans the drum surface, solving the problems of uneven drum surface cleaning and difficulty in controlling the flow rate of the cleaning liquid, and further extending the operating cycle of the vacuum drum filter 2.

[0055] Furthermore, the sight glasses of the slurry treatment device are prone to becoming clogged and blurred during use. Introducing a low-temperature chlorosilane solution to rinse the sight glasses ensures their cleanliness while preventing the introduction of other substances that could affect the operation of the equipment.

[0056] The above embodiments are merely a more detailed description of the present invention. Those skilled in the art can still modify the technical solutions in the foregoing embodiments or make equivalent substitutions. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the protection scope of this patent.

Claims

1. A multi-stage treatment process for polycrystalline silicon slag slurry, characterized in that, Includes the following steps: S1. The slurry from the cold hydrogen chemical section is transported to a collection tank. After cooling, a certain proportion of diatomaceous earth is added to the collection tank for premixing. The material in the collection tank is then transported to a vacuum drum filter for filtration to obtain filter cake and clear liquid a. The filter cake is sent to a dryer for drying, and clear liquid a is sent to a buffer tank I for temporary storage. The vacuum drum filter uses filter screens with different mesh sizes of diatomaceous earth coated on the inside and outside and two or more layers of filter cloth to intercept silica powder and high-boiling substances in the slurry. S2. After the filter cake is dried by the dryer in step S1, slag and gas phase a are obtained. The slag is transported to the hydrolysis subsystem, and gas phase a is transported to heat exchanger I for cooling treatment to obtain chlorosilane condensate. The chlorosilane condensate is transported to buffer tank II for temporary storage. S3. The slag material in the collection tank, after being cooled by the circulating water jacket, is transported to the slurry settling tank and cooled to below 15°C by 7°C water. After settling, the supernatant and the lower slag material are obtained. The supernatant is transported to the buffer tank III after passing through the liquid phase filter. After being pressurized by the pump, it is transported to the distillation section. The lower slag material is directly sent to the dryer for drying. S4. After pressurizing the chlorosilane condensate in buffer tank II in step S2, it is transported to buffer tank I. A vacuum pump is connected to the rear end of buffer tank I, so that the pressure in buffer tank I is -30kPa to -70kPa and the temperature is 15-25℃. S5. Then, the liquid phase a in buffer tank I is pumped to buffer tank III. The gas phase b in buffer tank I is condensed to obtain liquid phase b and gas phase c. Liquid phase b is transported to buffer tank I. Gas phase c is filtered, pressurized, and condensed by heat exchanger III to obtain liquid phase c. Liquid phase c is transported to tail gas condenser. S6. After being processed by buffer tank Ⅲ in step S5, liquid phase d and gas phase d are obtained. The liquid phase d is pressurized and then sent to the distillation section. The gas phase d is condensed and then liquid phase e is sent to buffer tank Ⅲ. S7. The gas phase e and liquid phase f obtained after treatment by the tail gas condenser are sent to the vacuum drum filter and the liquid phase f is sent to the buffer tank II.

2. The multi-stage treatment process for polycrystalline silicon slag slurry according to claim 1, characterized in that: In step S1, the filter screen of the vacuum drum filter is coated with a coating made of diatomaceous earth and silicon tetrachloride liquid. The coating thickness is 80-120mm, and the proportion of diatomaceous earth is usually 3.7%. The interior is coated with a mixture of 400-mesh diatomaceous earth and silicon tetrachloride, and the exterior is coated with a mixture of 200-300-mesh diatomaceous earth and silicon tetrachloride.

3. The multi-stage treatment process for polycrystalline silicon slag slurry according to claim 1, characterized in that: In step S1, the filter cloth of the vacuum drum filter uses two or more layers, with each layer having a different pore size. The outer layer filter cloth has a permeability of 250-300 L·m. 2 / s, the inner filter cloth specification is 150-200 L•m air permeability. 2 / s.

4. The multi-stage treatment process for polycrystalline silicon slag slurry according to claim 1, characterized in that: In step S1, a circulating water jacket is installed on the outside of the collection tank to ensure that the material temperature of the material transported from the collection tank to the vacuum drum filter does not exceed 30°C.

5. The multi-stage treatment process for polycrystalline silicon slag slurry according to claim 1, characterized in that: The hydrolysis subsystem in step S2 includes a slag storage tank, a hydrolysis pool, a scrubbing tower I, a feed pipeline, a regulating valve I, a water supply pipeline, a venting pipeline, and a regulating valve II. The bottom of the slag storage tank is connected to the hydrolysis pool via a feed pipeline, which is equipped with a regulating valve I. The hydrolysis pool is connected to a water supply pipeline. Gas a generated after the slag is treated in the hydrolysis pool is transported to the scrubbing tower I for further treatment. Gas b obtained after treatment is discharged through the venting pipeline, which is equipped with a regulating valve II.

6. The multi-stage treatment process for polycrystalline silicon slag slurry according to claim 1, characterized in that: The gas phase outlets of buffer tanks I, II, and III are all connected to a cryogenic tail gas subsystem. The cryogenic tail gas subsystem includes a scrubbing tower II, a heat exchanger V, a pump II, and a feed pipe. Scrubbing tower II uses chlorosilane liquid as the scrubbing fluid. The scrubbing fluid is transported from the bottom of scrubbing tower II to heat exchanger V for cooling to -5 to -25°C, and then returned to scrubbing tower II to scrub the gas entering the cryogenic tail gas subsystem from the feed pipe. The liquid chlorosilane obtained after scrubbing and cooling is recycled, and the resulting non-condensable gas is sent from the top outlet of scrubbing tower II to the waste gas treatment system for further treatment.

7. The multi-stage treatment process for polycrystalline silicon slag slurry according to claim 1, characterized in that: The heat source for the dryer is 2 kg of hot water at a temperature of 80~110℃ for drying materials.

8. The multi-stage treatment process for polycrystalline silicon slag slurry according to claim 1, characterized in that: The vacuum drum filter has been modified by adding a spray device inside, which cleans the drum surface.

9. The multi-stage treatment process for polycrystalline silicon slag slurry according to claim 1, characterized in that: In step S5, gas phase b is condensed by heat exchanger II to obtain liquid phase b and gas phase c. The temperature of the material is controlled at 5-15℃ and the pressure is controlled at -40kPa to -60kPa. The obtained liquid phase b is temporarily stored in buffer tank I. Gas phase c is further condensed to obtain liquid phase b, which is also sent to buffer tank I. The gas phase c, which is still in a gaseous state, is sent to an air filter for filtration. Then, pump I evacuates the vacuum to -40kPa to -65kPa and sends it to heat exchanger III for condensation to obtain liquid phase c. Liquid phase c is then temporarily stored in the tail gas condenser.

10. The multi-stage treatment process for polycrystalline silicon slag slurry according to claim 9, characterized in that: The air filter is a T-type filter with a sintered metal filter element and a filtration accuracy of 50-80 mesh.

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