Recycling system and recycling method for polycrystalline silicon slag slurry

Abstract

The invention provides a recovery system and a recovery method of polycrystalline silicon slag slurry. The recovery system of the polycrystalline silicon slag slurry comprises an evaporation condensation unit and a rectification separation unit. The evaporation and condensation unit comprises an evaporation furnace and a first condensation device, and the evaporation furnace is provided with a steam outlet and a dry slag outlet; the steam outlet is connected with an inlet of the first condensing device, and the dry slag outlet is used for discharging dry slag. The rectifying separation unit comprises a rectifying tower, an inlet of the rectifying tower is connected with an outlet of the first condensing device, and the rectifying tower is further provided with a tower top outlet, a side line outlet and a tower kettle outlet; a tower top outlet is used for discharging a gas-phase substance and condensing to obtain a liquid low-boiling-point substance and non-condensable gas; the side line outlet is used for discharging high-boiling-point substances; the tower kettle outlet is used for discharging tower kettle materials. By means of the recovery system, recovery of chlorosilane is improved, and effective separation of low-boiling-point substances and high-boiling-point substances in chlorosilane is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polysilicon production, in particular to a polysilicon slag slurry recovery system and recovery method. BACKGROUND

[0002] The preparation of polysilicon occupies a core position in the photovoltaic industry. The slag slurry produced in the production process of polysilicon mainly includes silicon powder, metal chlorides and chlorosilanes. These substances contain valuable resources and energy. The traditional slag slurry treatment method is often accompanied by a large amount of wastewater and waste gas emission, which pollutes the environment. Therefore, the treatment and recycling of slag slurry is a problem that needs to be solved in the polysilicon industry.

[0003] The prior art cannot effectively separate high-boiling-point substances (such as hexachloroethyldisilane) and completely remove metal impurities (such as aluminum chloride AlCl3) when recovering chlorosilanes, resulting in a decrease in product purity. If you want to remove high-boiling-point impurities (such as hexachloroethyldisilane), distillation or multi-tower rectification technology is usually used, but these methods have high energy consumption and high cost. In addition, the equipment used to treat slag slurry usually operates in a high-temperature, high-corrosion environment, which is prone to blockage and corrosion, requiring frequent maintenance and maintenance, affecting the continuity and efficiency of production. In summary, the recovery process of slag slurry in the prior art is complex, the equipment is more, the operation is difficult, and the equipment investment and operation and maintenance cost are high.

[0004] Therefore, the present application is proposed. SUMMARY

[0005] The main purpose of the present application is to provide a polysilicon slag slurry recovery system and recovery method to solve one of the problems of the prior art, such as complex process, more equipment, difficult operation, and high operating cost.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a polysilicon slag slurry recovery system is provided, which comprises an evaporation condensation unit and a rectification separation unit; wherein the evaporation condensation unit comprises an evaporation furnace and a first condensing device, the evaporation furnace has a steam outlet and a dry slag outlet; the steam outlet is connected with the inlet of the first condensing device, and the dry slag outlet is used for discharging dry slag; the rectification separation unit comprises a rectification tower, the outlet of the first condensing device is connected with the inlet of the rectification tower, and the rectification tower has a tower top outlet, a side line outlet and a tower kettle outlet; the tower top outlet is connected with a second condensing device, the second condensing device is used for condensing the gas phase material discharged from the tower top outlet to obtain liquid low-boiling-point material and non-condensable gas; the side line outlet is used for discharging high-boiling-point material; and the tower kettle outlet is used for discharging tower kettle material.

[0007] Further, the recycling system further comprises a raw material supply unit, the raw material supply unit comprises a raw material supply tank, the raw material supply tank is connected with the inlet of the evaporation furnace, and the raw material supply tank is used for supplying the polysilicon residue slurry.

[0008] Further, the recycling system further comprises a settling tank, the settling tank is arranged on a pipeline between the raw material supply tank and the evaporation furnace.

[0009] Further, the first condensing device comprises a first condenser.

[0010] Further, the second condensing device comprises an overhead reflux condenser and a deep condenser, and the tower top outlet is sequentially connected with the overhead reflux condenser and the deep condenser.

[0011] Further, the rectifying tower is a dividing wall column.

[0012] Further, the tower top outlet is connected with the raw material supply tank.

[0013] Further, the recycling system further comprises a hydrolysis unit, the hydrolysis unit comprises a hydrolysis tower, the hydrolysis tower has a first hydrolysis inlet, a second hydrolysis inlet and a third hydrolysis inlet; the first hydrolysis inlet is connected with the dry residue outlet, the second hydrolysis inlet is connected with the second condensing device, so that the non-condensable gas is introduced into the hydrolysis tower; the third hydrolysis inlet is used for introducing water into the hydrolysis tower; the hydrolysis tower further has a tail gas outlet and a waste outlet; the tail gas outlet is used for discharging tail gas, and the waste outlet is used for discharging waste.

[0014] According to another aspect of the present application, a recycling method of polysilicon residue slurry is provided, comprising the following steps: step S1, sequentially evaporating and first condensing the polysilicon residue slurry to obtain a condensed liquid containing chlorosilane and dry residue; wherein the polysilicon residue slurry comprises chlorosilane, non-condensable gas and solid impurities, the chlorosilane comprises at least one of dichlorodihydrogenosilane, trichlorohydrogenosilane, silicon tetrachloride, hexachloroethylosilane and hexachlorodisiloxane; the non-condensable gas comprises at least one of hydrogen and hydrogen chloride; the solid impurities comprise at least one of aluminum chloride and silicon powder; step S2, rectifying the condensed liquid containing chlorosilane to obtain gas phase material, high boiling material and tower top material; second condensing the gas phase material to obtain liquid low boiling material and non-condensable gas; wherein the liquid low boiling material comprises dichlorodihydrogenosilane, trichlorohydrogenosilane and silicon tetrachloride; the high boiling material comprises hexachlorodisiloxane and hexachloroethylosilane; and the tower top material comprises aluminum chloride and silicon powder.

[0015] Further, step S1 further comprises the following steps: when the temperature of the polysilicon residue slurry is >70℃, evaporating the polysilicon residue slurry; when the temperature of the polysilicon residue slurry is ≤70℃, first performing solid-liquid separation on the polysilicon residue slurry, and then evaporating.

[0016] Further, in step S1, the evaporation temperature is 50-100℃, and the evaporation time is 0.01-1h.

[0017] Further, the evaporation pressure is -20-100 kpa.

[0018] Further, the first condensation temperature is 0-70 DEG C.

[0019] Further, the solid-liquid separation time is 3-24 h, and the solid-liquid separation temperature is 0-70 DEG C.

[0020] Further, the solid-liquid separation is sedimentation.

[0021] Further, rectification is performed by using a rectification tower.

[0022] Further, the rectification tower top pressure is -80-500 kpa, and the rectification tower top temperature is 7-112 DEG C.

[0023] Further, the rectification tower bottom temperature is 112-249 DEG C.

[0024] Further, the second condensation includes reflux condensation and deep condensation.

[0025] Further, the reflux condensation temperature is 1-106 DEG C.

[0026] Further, the deep condensation temperature is -10--40 DEG C.

[0027] Further, the tower bottom material returns to the step S1.

[0028] Further, the recovery method further comprises a step S3, which comprises: mixing the dry residue, non-condensable gas and water to perform hydrolysis treatment, to obtain tail gas and waste; the tail gas is hydrogen, and the waste comprises silicon powder, aluminum chloride, silicon dioxide and hydrochloric acid.

[0029] By using the technical scheme of the present application, the polycrystalline silicon residue slurry is evaporated in the evaporation furnace, the chlorosilane and solid impurities (silicon powder and aluminum chloride) are effectively separated by using the low boiling point of silane, the chlorosilane-containing steam and dry residue are obtained, and the content of chlorosilane in the dry residue is low. The steam outlet of the evaporation furnace is connected with the first condensing device and the rectification tower in sequence, so that the chlorosilane-containing steam is first condensed and liquefied into chlorosilane-containing condensed liquid in the first condensing device, and then is separated by rectification in the rectification tower, the gas phase material is discharged from the top outlet of the rectification tower, the second condensing device is connected with the top outlet, the gas phase material is condensed into liquid low-boiling substance and non-condensable gas, the high-boiling substance is discharged from the side outlet of the rectification tower, and the tower bottom material is discharged from the tower bottom outlet of the rectification tower. The low-boiling substance and the high-boiling substance are effectively separated by using the rectification tower, and the recovery of chlorosilane is improved.

[0030] The polycrystalline silicon slag slurry recovery system provided by the application reduces the number of equipment by optimizing the process design, makes the process more concise, and reduces the equipment investment and operation and maintenance costs. Moreover, only the chlorosilane-containing condensate obtained by evaporating and condensing the polycrystalline silicon slag slurry and dry slag, and the chlorosilane-containing condensate are subjected to single-tower rectification purification, the purposes of solid separation, recovery of low-boiling chlorosilane, and recovery of high-boiling chlorosilane can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0031] The drawings constituting a part of the specification of the application serve to provide further understanding of the application, and the illustrative embodiments of the application and their descriptions serve to explain the application, and do not constitute improper limitations on the application. In the drawings:

[0032] Figure 1 A schematic diagram of a polycrystalline silicon slag slurry recovery system provided in some embodiments of the application is shown.

[0033] Among them, the above drawings include the following reference signs:

[0034] 10, raw material supply tank; 20, evaporation furnace; 21, first condenser; 30, settling tank; 40, rectification tower; 41, overhead reflux condenser; 42, deep condenser; 50, hydrolysis tower. DETAILED DESCRIPTION

[0035] It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict. The application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0036] As analyzed in the background art of the application, when the existing ammonium chloride, liquid ammonia and toluene in the silicon nitride recovery liquid are separated, the obtained liquid ammonia and toluene have low purity, the device is easy to be blocked, the energy consumption is large, and the operation cost is high. In order to solve this problem, the application provides a silicon nitride recovery liquid separation system and a separation method.

[0037] In a typical embodiment of the application, a polycrystalline silicon slag slurry recovery system is provided, as shown in Figure 1 The evaporation and condensation unit includes an evaporation furnace 20 and a first condensing device, the evaporation furnace 20 has a steam outlet and a dry slag outlet; the steam outlet is connected with the inlet of the first condensing device, and the dry slag outlet is used for discharging dry slag; the rectification and separation unit includes a rectification tower 40, the outlet of the first condensing device is connected with the inlet of the rectification tower 40, and the rectification tower 40 has a tower top outlet, a side line outlet and a tower kettle outlet; the tower top outlet is connected with a second condensing device, the second condensing device is used for condensing the gas phase material discharged from the tower top outlet to obtain liquid low-boiling substances and non-condensable gas; the side line outlet is used for discharging high-boiling substances; and the tower kettle outlet is used for discharging tower kettle materials.

[0038] The polysilicon residue slurry is evaporated in the evaporation furnace 20, and the chlorosilane and solid impurities (silicon powder, aluminum chloride) are effectively separated by using the low boiling point of silane, so that the steam containing chlorosilane and dry residue are obtained, and the content of chlorosilane in the obtained dry residue is low. The steam outlet of the evaporation furnace 20 is connected with the first condensing device and the rectifying tower 40 in sequence, so that the steam containing chlorosilane is first condensed and liquefied into condensed liquid containing chlorosilane in the first condensing device, and then is separated by rectification in the rectifying tower 40. The gas phase material is discharged from the overhead outlet of the rectifying tower 40, and the second condensing device is connected with the overhead outlet. The gas phase material is condensed into liquid low-boiling substance and non-condensed gas. The high-boiling substance is discharged from the side outlet of the rectifying tower 40, and the tank material is discharged from the tank outlet of the rectifying tower 40. The effective separation of low-boiling substance and high-boiling substance is realized by the rectifying tower 40, and the recovery of chlorosilane is improved.

[0039] The recovery system of the polysilicon residue slurry provided by the application optimizes the process design, reduces the number of equipment, makes the process more concise, and reduces the equipment investment and operation and maintenance cost. Moreover, only the condensed liquid containing chlorosilane and dry residue obtained by evaporating and condensing the polysilicon residue slurry are needed, and the condensed liquid containing chlorosilane is subjected to single-tower rectification purification, so that the purposes of solid separation, recovery of low-boiling substance in chlorosilane, and recovery of high-boiling substance in chlorosilane are achieved.

[0040] In some embodiments, the recovery system further comprises a raw material supply unit, and the raw material supply unit comprises a raw material supply tank 10 connected with the inlet of the evaporation furnace 20, and the raw material supply tank 10 is used for supplying the polysilicon residue slurry.

[0041] In some embodiments, the recovery system further comprises a settling tank 30 arranged on the pipeline between the raw material supply tank 10 and the evaporation furnace 20. The top of the settling tank 30 is provided with a clear liquid outlet, and the bottom of the settling tank 30 is provided with a slurry outlet. The clear liquid outlet is connected with the inlet of the rectifying tower 40, and the slurry outlet is connected with the inlet of the evaporation furnace 20.

[0042] In some embodiments, the inside of the settling tank 30 is further provided with a first stirrer (not shown in the figure), and the inside of the evaporation furnace 20 is further provided with a second stirrer (not shown in the figure) to uniformly mix the materials.

[0043] In some embodiments, a jacket (not shown in the figure) is arranged outside the evaporation furnace 20 to pass a heating medium into the jacket to heat, and the heating medium is preferably water vapor.

[0044] In some embodiments, a sight glass (not shown in the figure) is further arranged on the pipeline communicating the clear liquid outlet with the rectifying tower 40 to observe the conveying condition of the clear liquid and prevent the slurry from being discharged together with the clear liquid to reduce the product purity.

[0045] In some embodiments, the first condensing device comprises a first condenser 21.

[0046] In some embodiments, the second condensing device comprises an overhead reflux condenser 41 and a deep condenser 42, the overhead outlet is connected to the overhead reflux condenser 41 and the deep condenser 42 in sequence. The overhead reflux condenser 41 has an overhead reflux condensing gas phase outlet and an overhead reflux condensing liquid phase outlet in addition to the reflux, the overhead reflux condensing liquid phase outlet is used to discharge the first liquid phase, and the overhead reflux condensing gas phase outlet is connected to the inlet of the deep condenser 42. The deep condenser 42 also has a deep condensing liquid phase outlet and a deep condensing gas phase outlet, the deep condensing liquid phase outlet is used to discharge the second liquid phase, and the deep condensing gas phase outlet is used to discharge the non-condensable gas.

[0047] In some embodiments, the rectifying column 40 is a divided wall column. The divided wall column in this application is a lower divided wall column, that is, the column body below the feed inlet uses a partition to divide the column body into two parts A and B along the axial direction, the raw material enters one side A and falls into the column, the vapor rising from the column is respectively introduced into the column body A and B on both sides of the partition, the reflux liquid above the feed plate is also introduced into the column body A and B on both sides of the partition, and the bottom product is taken out from the appropriate position of the side B. Compared with other types of rectifying columns, the divided wall column has the following advantages: 1. The solids (silicon powder, etc.) and salts (aluminum chloride, etc.) contained in the condensate liquid containing chlorosilane fall into the column from the side A but do not enter the side B; since the solids and salts cannot be evaporated, the solids and salts in the vapor rising from the column do not enter the side B; similarly, the solids and salts in the liquid falling from the feed inlet also do not enter the side B. This ensures that the product taken out from the side B does not contain solids and salts. 2. The divided wall column essentially combines two rectifying columns, which plays a role in improving the purity of the product on the side B.

[0048] In some embodiments, the column outlet is connected to the raw material supply tank 10 to return the column material to the polysilicon residue slurry recovery system, further improving the recovery rate of components.

[0049] In some embodiments, the recovery system further comprises a hydrolysis unit, the hydrolysis unit comprises a hydrolysis column 50, the hydrolysis column 50 has a first hydrolysis inlet, a second hydrolysis inlet and a third hydrolysis inlet; the first hydrolysis inlet is connected to the dry residue outlet, the second hydrolysis inlet is connected to the second condensing device to introduce the non-condensable gas into the hydrolysis column 50; the third hydrolysis inlet is used to introduce water into the hydrolysis column 50; the hydrolysis column 50 also has a tail gas outlet and a waste outlet; the tail gas outlet is used to discharge the tail gas, and the waste outlet is used to discharge the waste.

[0050] The dry residue discharged from the evaporation furnace 20 only contains a small amount of chlorosilane, and the dry residue can be directly sold or directly hydrolyzed and then treated as harmless solid waste. When hydrolysis treatment is performed, the non-condensable gas discharged from the rectification tower 40 enters the hydrolysis tower 50, and the chlorosilane reacts with water to generate silicon dioxide, hydrogen chloride and hydrogen. The hydrogen chloride is dissolved in water to form hydrochloric acid, the hydrogen is discharged from the tail gas outlet, the silicon dioxide and the hydrochloric acid are discharged from the waste outlet as acidic slurry to a subsequent three-waste treatment device (not shown in the figure) for solid waste treatment, and the obtained water is returned to the hydrolysis leaching tower for repeated use, and the remaining solid is transported out after neutralization and pressure filtration treatment, thereby reducing environmental pollution.

[0051] In another typical embodiment of the present application, a recovery method of polysilicon residue slurry is provided, comprising the following steps: step S1, sequentially evaporating and first condensing the polysilicon residue slurry to obtain a condensate containing chlorosilane and dry residue; wherein the polysilicon residue slurry comprises chlorosilane, non-condensable gas and solid impurities, the chlorosilane comprises at least one of dichlorodihydrogen silicon, trichlorohydrogen silicon, silicon tetrachloride, hexachloroethyldisilane and hexachlorodisiloxane; the non-condensable gas comprises at least one of hydrogen and hydrogen chloride; and the solid impurities comprise at least one of aluminum chloride and silicon powder; step S2, rectifying the condensate containing chlorosilane to obtain gas phase, high-boiling substance and tower bottom material; and second condensing the gas phase to obtain liquid low-boiling substance and non-condensable gas; wherein the liquid low-boiling substance comprises dichlorodihydrogen silicon, trichlorohydrogen silicon and silicon tetrachloride; the high-boiling substance comprises hexachlorodisiloxane and hexachloroethyldisilane; and the tower bottom material comprises aluminum chloride and silicon powder.

[0052] The recovery method of polysilicon residue slurry provided by the present application evaporates the polysilicon residue slurry in the evaporation furnace 20, effectively separates the chlorosilane from the solid impurities (silicon powder and aluminum chloride) by utilizing the low boiling point of silane, and obtains steam containing chlorosilane and dry residue, and the content of chlorosilane in the obtained dry residue is low. The steam outlet of the evaporation furnace 20 is sequentially connected with the first condensing device and the rectification tower 40, so that the steam containing chlorosilane is first condensed and liquefied into a condensate containing chlorosilane in the first condensing device, and then is subjected to rectification separation in the rectification tower 40. The gas phase is discharged from the overhead outlet of the rectification tower 40, the overhead outlet is connected with the second condensing device, the gas phase is condensed into liquid low-boiling substance and non-condensable gas, the high-boiling substance is discharged from the side outlet of the rectification tower 40, and the tower bottom material is discharged from the tower bottom outlet of the rectification tower 40. The effective separation of low-boiling substance and high-boiling substance is realized by the rectification tower 40, and the recovery of chlorosilane is improved.

[0053] The polycrystalline silicon residue slurry recovery method provided by the application optimizes the process, makes the process more concise, and reduces equipment investment and operation and maintenance costs. Moreover, only the condensed liquid containing chlorosilane and dry residue obtained after evaporation and condensation of the polycrystalline silicon residue slurry are needed, and the condensed liquid containing chlorosilane is subjected to single-tower rectification purification, so that the purposes of solid separation, recovery of chlorosilane medium and low boiling point substances, and recovery of chlorosilane high boiling point substances are achieved.

[0054] In some embodiments, the high-boiling residue recovered by side extraction can be sold or further purified by rectification.

[0055] In some embodiments, step S1 further includes the following steps: when the temperature of the polycrystalline silicon residue slurry is > 70℃, the polycrystalline silicon residue slurry is evaporated; unnecessary heat energy loss is avoided. When the temperature of the polycrystalline silicon residue slurry is ≤ 70℃, the polycrystalline silicon residue slurry is first subjected to solid-liquid separation to obtain upper clear liquid and lower slurry. The upper clear liquid is mainly chlorosilane, and the upper clear liquid is directly subjected to rectification separation. The lower slurry is mainly a small amount of clear liquid entraining silicon powder, aluminum chloride and other solid impurities, which is further evaporated to further separate chlorosilane from solid impurities to obtain steam containing chlorosilane and dry residue, and the dry residue mainly includes silicon powder and aluminum chloride and only includes a small amount of chlorosilane. Evaporation of the lower slurry further improves the recovery of chlorosilane and reduces the content of chlorosilane in the dry residue, and the obtained dry residue can be directly sold, avoiding the problem that when the content of chlorosilane in the dry residue is high, it reacts with air and does not meet environmental protection standards.

[0056] In the application, the polycrystalline silicon residue slurry is derived from waste discharged in the process of preparing polycrystalline silicon. In terms of mass percentage, the content of silicon powder in the residue slurry is 0.05-0.5wt%, the content of metal chlorides (such as aluminum chloride) is 0.3-0.7wt%, the content of chlorosilane is 95-99wt%, and the content of other impurities is 1-5wt%. The other impurities are high polymers (components with a boiling point higher than that of hexachloroethyldisilane).

[0057] In some embodiments, the evaporation temperature is 50-100℃, and the evaporation time is 0.01-1h. When the evaporation temperature is too low, chlorosilane cannot be vaporized and separated from the residue slurry, and when the evaporation temperature is too high, too much aluminum chloride in the residue slurry volatilizes, affecting the purity of the chlorosilane product. The evaporation heating mode can be steam or electric heating. According to the composition of the slurry, a suitable heating heat source can be selected, which can be a steam jacket, electric heating winding, or an internal coil. In some specific embodiments, when the temperature in the evaporation furnace 20 is detected to be significantly increased and exceeds the above-mentioned evaporation temperature, heating is stopped, stirring is continued, and the temperature is maintained for no more than 1h until the temperature is reduced to room temperature.

[0058] In some embodiments, the evaporation pressure is -20-100kpa, and the evaporation pressure is maintained within this range to further promote the evaporation of silicon chloride.

[0059] It should be noted that the pressure in the present application is all gauge pressure.

[0060] In order to condense the steam containing chlorosilane into liquid, the temperature of the first condensation is preferably 0-70℃.

[0061] In order to further improve the degree of solid-liquid separation in the slurry, the time of solid-liquid separation is preferably 3-24h, and the temperature of solid-liquid separation is preferably 0-70℃, so as to further improve the efficiency of solid-liquid separation.

[0062] In some embodiments, the solid-liquid separation is preferably sedimentation, and the slurry is placed in the settling tank 30 after entering the settling tank 30, and is cooled to 25-40℃ through natural heat dissipation. As the temperature decreases, aluminum chloride (AlCl3) in the slurry will precipitate as a solid and precipitate to the bottom of the settling tank 30 together with the silicon powder in the slurry, realizing liquid-solid separation.

[0063] In order to further improve the separation effect of low-boiling and high-boiling chlorosilanes and further reduce the content of aluminum chloride and improve the purity of low-boiling and high-boiling chlorosilanes, the top pressure of the rectifying column 40 is preferably -80-500kpa, and the top temperature of the rectifying column 40 is preferably 7-112℃; the column bottom temperature of the rectifying column 40 is preferably 112-249℃; the column bottom pressure of the rectifying column 40 is preferably -60-520kpa, and in actual operation, the pressure drop can be adjusted adaptively according to the column internals, column height, operation, etc. The column bottom temperature is greatly affected by the column pressure and the metal chloride content in the raw material. The higher the pressure and the higher the salt concentration, the higher the column bottom temperature. When the column pressure is low, the energy saving effect is good and the components are easier to separate, but the column pressure is too low, which will lead to high operating difficulty.

[0064] In order to further recover low-boiling chlorosilanes and high-boiling chlorosilanes and improve the purity of each component of chlorosilanes through single-tower purification, the rectifying column 40 is preferably a dividing wall column.

[0065] In order to further promote the condensation of gas phase into liquid low-boiling chlorosilanes and non-condensable gas, the second condensation preferably includes reflux condensation and deep condensation. The gas phase is first subjected to reflux condensation to obtain a first liquid phase, which includes trichlorosilane, silicon tetrachloride and a small amount of dichlorodisilane. The first liquid phase is used for reflux, and the rest is sent to a subsequent processing unit for further separation and purification. The uncondensed dichlorodisilane, hydrogen and hydrogen chloride are subjected to deep condensation to further condense the dichlorodisilane. The first liquid phase obtained by deep condensation is mainly dichlorodisilane, and the non-condensable gas is mainly hydrogen and hydrogen chloride. Further preferably, the temperature of the reflux condensation is 1-106℃, and further preferably, the temperature of the deep condensation is -10--40℃.

[0066] In some embodiments, the recycling method further includes step S3, which includes: mixing the dry residue and non-condensable gas with water for hydrolysis treatment to obtain tail gas and waste; the tail gas is hydrogen, and the waste includes silicon powder, aluminum chloride, silicon dioxide, and hydrochloric acid. The discharged dry residue can be sold directly or directly hydrolyzed and then treated as harmless solid waste. When hydrolysis is performed, it and the non-condensable gas discharged from the distillation tower 40 enter the hydrolysis tower 50. The chlorosilane reacts with water to generate silicon dioxide, hydrogen chloride, and hydrogen. The hydrogen chloride dissolves in the water to form hydrochloric acid, and the hydrogen is discharged as tail gas. The silicon dioxide and hydrochloric acid are discharged together as waste to the subsequent waste treatment device (not shown in the figure) for solid waste treatment. The obtained water is returned to the hydrolysis scrubbing tower for reuse, and the remaining solids are transported off-site after neutralization and pressure filtration, reducing environmental pollution.

[0067] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0068] Example 1

[0069] This embodiment provides a polycrystalline silicon slag slurry recycling system, such as... Figure 1 As shown, the recovery system includes: 10, raw material supply storage tank; 20, evaporator; 21, first condenser; 30, settling tank; 40, distillation column; 41, top reflux condenser; 42, depth condenser; and 50, hydrolysis column.

[0070] The raw material supply tank 10 is connected to the inlet of the evaporator 20, which also has a steam outlet and a dry slag outlet. The steam outlet is connected to the inlet of the first condenser 21, and the dry slag outlet is used to discharge dry slag. A settling tank 30 is installed on the pipeline between the raw material supply tank 10 and the evaporator 20. A clear liquid outlet is provided at the top of the settling tank 30, and a slurry outlet is provided at the bottom of the settling tank 30. The slurry outlet is connected to the inlet of the evaporator 20. A first agitator (not shown in the figure) is also installed inside the settling tank 30, and a second agitator (not shown in the figure) is also installed inside the evaporator 20. A jacket (not shown in the figure) is fitted around the outside of the evaporator 20.

[0071] The inlet of the rectification tower 40 is connected with the outlet of the first condenser 21 and the clean liquid outlet respectively, and a sight glass (not shown in the figure) is arranged on the pipeline connecting the clean liquid outlet with the rectification tower 40. The rectification tower 40 also has a tower top outlet, a side outlet and a tower bottom outlet. The tower top outlet is connected with the tower top reflux condenser 41 and the deep condenser 42 in sequence. The tower top reflux condenser 41 has a tower top reflux condensation gas phase outlet and a tower top reflux condensation liquid phase outlet in addition to the reflux. The tower top reflux condensation liquid phase outlet is used to discharge the first liquid phase, and the tower top reflux condensation gas phase outlet is connected with the inlet of the deep condenser 42. The deep condenser 42 also has a deep condensation liquid phase outlet and a deep condensation gas phase outlet. The deep condensation liquid phase outlet is used to discharge the second liquid phase, and the deep condensation gas phase outlet is used to discharge the non-condensed gas. The side outlet is used to discharge the high-boiling substance, and the tower bottom outlet is connected with the raw material supply tank 10.

[0072] The hydrolysis tower 50 has a first hydrolysis inlet, a second hydrolysis inlet and a third hydrolysis inlet. The first hydrolysis inlet is connected with the dry residue outlet, the second hydrolysis inlet is connected with the deep condensation gas phase outlet, and the third hydrolysis inlet is used to pass water into the hydrolysis tower 50. The hydrolysis tower 50 also has a tail gas outlet and a waste outlet. The tail gas outlet is used to discharge the tail gas, and the waste outlet is used to discharge the waste.

[0073] Example 2

[0074] The present embodiment provides a recovery method of polysilicon residue slurry, which uses the recovery system in Example 1 and specifically includes the following steps:

[0075] (1) The polysilicon residue slurry with a temperature of 70°C (the mass content of silicon powder in the slurry is 0.05-0.5%, the mass content of metal chlorides (such as aluminum chloride) is 0.3-0.7%, the mass content of chlorosilane is 95-99%, and the mass content of other impurities is 1-5%. The other impurities are high polymers, i.e., components with a boiling point higher than that of hexachloroethyisilane) is passed into the settling tank 30. The first stirrer in the settling tank 30 is started to stir at the same time of feeding. After the feeding is completed, the stirring is stopped, and the solid-liquid separation is performed after standing for 24 hours. The upper layer is the clean liquid, and the lower layer is the slurry. The polysilicon residue slurry is naturally cooled to room temperature during the standing process.

[0076] (2) The slurry discharged from the slurry outlet of the settling tank 30 is introduced into the evaporation furnace 20, the second agitator in the evaporation furnace 20 is started to agitate, and 0.4 MPaG water vapor is introduced into the jacket of the evaporation furnace 20 to heat. The polycrystalline silicon residue slurry is evaporated in the evaporation furnace 20 under the conditions of 5 kPa of furnace pressure and 80°C of furnace temperature for 0.5 h. The steam containing chlorosilane generated by evaporation is discharged from the steam outlet and then introduced into the first condenser 21 to condense at 45°C to obtain a condensed liquid containing chlorosilane, which is transported to the rectification tower 40. After the evaporation furnace 20 is cooled, dry residue is discharged from the dry residue outlet, which includes silicon powder, aluminum chloride and a small amount of chlorosilane.

[0077] (3) The clear liquid and the condensed liquid containing chlorosilane are separated by rectification in the rectification tower 40, which is a divided wall column, under the conditions of 50 kPa of tower top pressure, 59°C of tower top temperature, 182°C of tower bottom temperature and 70 kPa of tower bottom pressure. Hexachlorodisilane and hexachlorodisiloxane are obtained from the side outlet, and the tower bottom material including aluminum chloride and silicon powder is obtained from the tower bottom outlet. The gas phase material discharged from the tower top outlet is condensed at 50°C in the tower top reflux condenser 41 to obtain a first liquid phase, which mainly includes trichlorosilane, silicon tetrachloride and a small amount of dichlorodisilane. The first liquid phase is used as reflux, and the remaining liquid phase low-boiling substance is discharged as a recovered product. Hydrogen, hydrogen chloride and the remaining uncondensed dichlorodisilane are introduced into the deep condenser 42 at -20°C for deep condensation. A second liquid phase mainly including dichlorodisilane is obtained from the deep condenser liquid phase outlet, and non-condensable gas mainly including hydrogen and hydrogen chloride is obtained from the deep condenser gas phase outlet.

[0078] (4) The dry residue, the non-condensable gas and water are introduced into the hydrolysis tower 50 for hydrolysis, in which the chlorosilane reacts with water to generate silicon dioxide, hydrogen chloride and hydrogen. The silicon dioxide is a solid insoluble in water, the hydrogen chloride dissolves in water to form hydrochloric acid, and the hydrogen is insoluble in water and discharged from the tail gas outlet. The silicon powder, aluminum chloride, silicon dioxide and hydrochloric acid are discharged from the waste outlet.

[0079] Example 3

[0080] The difference between this example and Example 2 is that the tower top pressure of the rectification tower 40 is 0 kPa, the corresponding tower top temperature is 46°C, the corresponding tower bottom temperature is 166°C, and the tower bottom pressure is 20 kPa.

[0081] Example 4

[0082] The difference between this example and Example 2 is that the tower top pressure of the rectification tower 40 is -40 kPa, the corresponding tower top temperature is 32°C, the corresponding tower bottom temperature is 145°C, and the tower bottom pressure is -30 kPa.

[0083] Comparative Example 1

[0084] The difference between the present comparative example and Example 2 is that the rectification tower 40 is a common plate tower.

[0085] Test Example

[0086] The total mass content of chlorosilane in the first liquid phase, the mass content of polymer in the side-draw, the mass content of chlorosilane in the dry residue, and whether the side-draw contains silicon powder and metal chlorides were tested using the chromatographic analysis method, and the results are shown in Table 1.

[0087] Table 1

[0088]

[0089] As can be seen from the results of Examples 2 to 4 and Comparative Example 1, the recovery system and method of polysilicon residue slurry provided by the present application effectively separates chlorosilane from solid impurities (silicon powder and aluminum chloride), so that the content of chlorosilane in the dry residue is < 5 wt%, and effectively separates low-boiling substances from high-boiling substances through the baffle tower rectification, so that the total content of chlorosilane in the first liquid phase is > 98 wt%, the content of polymer (components with a boiling point higher than that of hexachloroethyisilane) in the side-drawn material is < 0.01 wt%, and no silicon powder and metal chlorides are detected in the side-drawn material.

[0090] In Comparative Example 1, since the common rectification tower has no baffle inside, when the total yield of hexachloroethyisilane and hexachlorodisiloxane in the side-draw reaches the same value, the side-drawn material of the common rectification tower contains silicon powder and metal chlorides, and the content of polymer (components with a boiling point higher than that of hexachloroethyisilane) in the side-drawn material increases to 0.1-1 wt%.

[0091] From the above description, it can be seen that the above-mentioned examples of the present application achieve the following technical effects:

[0092] The recovery system of polysilicon residue slurry provided by the present application optimizes the process design, reduces the number of equipment, makes the process more concise, and reduces the equipment investment and operation and maintenance costs. Moreover, only the condensed liquid containing chlorosilane and dry residue obtained by evaporating and condensing the polysilicon residue slurry are needed, and the condensed liquid containing chlorosilane is subjected to single-tower rectification purification, so as to achieve the purposes of solid separation, recovery of low-boiling substances from chlorosilane, and recovery of high-boiling substances from chlorosilane.

[0093] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A system for recovering polysilicon slurry, characterized by, The recovery system comprises: an evaporation-condensation unit, which comprises an evaporation furnace (20) and a first condensing device, the evaporation furnace (20) having a steam outlet and a dry residue outlet; the steam outlet is connected with an inlet of the first condensing device, and the dry residue outlet is used for discharging dry residue; a rectification separation unit, which comprises a rectification column (40), an outlet of the first condensing device being connected with an inlet of the rectification column (40), the rectification column (40) having a column top outlet, a side outlet and a column bottom outlet; the column top outlet is connected with a second condensing device, which is used for condensing gas phase substances discharged from the column top outlet to obtain liquid low-boiling substances and non-condensable gas; the side outlet is used for discharging high-boiling substances; and the column bottom outlet is used for discharging column bottom materials.

2. The recovery system of polysilicon slurry according to claim 1, characterized in that, The recovery system further comprises a raw material supply unit, which comprises a raw material supply tank (10), the raw material supply tank (10) being connected with an inlet of the evaporation furnace (20) and being used for supplying polysilicon residue slurry. Preferably, the recovery system further comprises a settling tank (30), which is arranged on a pipeline between the raw material supply tank (10) and the evaporation furnace (20).

3. The system for recovering polysilicon slurry according to claim 1, wherein, The first condensing device comprises a first condenser (21); and / or, the second condensing device comprises a column top reflux condenser (41) and a deep condenser (42), the column top outlet being connected with the column top reflux condenser (41) and the deep condenser (42) in sequence; and / or, the rectification column (40) is a dividing wall column; and / or, the column bottom outlet is connected with the raw material supply tank (10).

4. The recovery system of polysilicon slurry according to any one of claims 1 to 3, characterized in that, The recovery system further comprises a hydrolysis unit, which comprises a hydrolysis column (50), the hydrolysis column (50) having a first hydrolysis inlet, a second hydrolysis inlet and a third hydrolysis inlet; the first hydrolysis inlet is connected with the dry residue outlet, the second hydrolysis inlet is connected with the second condensing device so that the non-condensable gas is introduced into the hydrolysis column (50); and the third hydrolysis inlet is used for introducing water into the hydrolysis column (50); the hydrolysis column (50) further has a tail gas outlet and a waste outlet; the tail gas outlet is used for discharging tail gas, and the waste outlet is used for discharging waste.

5. A method for recovering polysilicon slurry, characterized by, The recovery system comprises the following steps: S1. Evaporating and first condensing polysilicon residue slurry to obtain condensed liquid containing chlorosilane and dry residue; wherein the polysilicon residue slurry comprises chlorosilane, non-condensable gas and solid impurities; the chlorosilane comprises at least one of dichlorodihydrogenosilane, trichlorohydrogenosilane, silicon tetrachloride, hexachloroethyldisilane and hexachlorodisiloxane; the non-condensable gas comprises at least one of hydrogen and hydrogen chloride; and the solid impurities comprise at least one of aluminum chloride and silicon powder; Step S2, the condensed liquid containing chlorosilane is subjected to rectification to obtain gas phase material, high-boiling material and tower kettle material; the gas phase material is subjected to second condensation to obtain liquid low-boiling material and the non-condensable gas; wherein the liquid low-boiling material comprises dichlorodihydrogenosilane, trichlorohydrogenosilane and silicon tetrachloride; the high-boiling material comprises hexachlorodisiloxane and hexachlorodisilane; and the tower kettle material comprises aluminum chloride and silicon powder.

6. The method for recovering the polysilicon slurry according to claim 5, characterized in that, The step S1 further comprises the following step: when the temperature of the polysilicon residue slurry is greater than 70 DEG C, the polysilicon residue slurry is subjected to the evaporation. When the temperature of the polysilicon residue slurry is less than or equal to 70 DEG C, the polysilicon residue slurry is subjected to solid-liquid separation first, and then subjected to the evaporation.

7. The recovery method of the polysilicon residue slurry according to claim 5, wherein in the step S1, the temperature of the evaporation is 50-100 DEG C, and the time of the evaporation is 0.01-1 h; and / or the pressure of the evaporation is -20-100 kpa; and / or the temperature of the first condensation is 0-70 DEG C; and / or the time of the solid-liquid separation is 3-24 h, and the temperature of the solid-liquid separation is 0-70 DEG C; and / or the solid-liquid separation is sedimentation. The rectification is performed by using a rectification tower (40). Preferably, the top pressure of the rectification tower (40) is -80-500 kpa, and the top temperature of the rectification tower (40) is 7-112 DEG C. Preferably, the kettle temperature of the rectification tower (40) is 112-249 DEG C. The second condensation comprises reflux condensation and deep condensation.

8. The method of recovering polysilicon slurry according to claim 5, wherein Preferably, the temperature of the reflux condensation is 1-106 DEG C. Preferably, the temperature of the deep condensation is -10--40 DEG C. Preferably, the bottom material returns to the step S1.

9. The method of recovering polysilicon slurry according to claim 5, wherein The recovery method further comprises a step S3, which comprises: mixing the dry residue, the non-condensable gas and water to perform hydrolysis treatment, to obtain tail gas and waste material; the tail gas is hydrogen, and the waste material comprises silicon powder, aluminum chloride, silicon dioxide and hydrochloric acid. ​ ​ ​ 10. The method for recovering the polysilicon slurry according to any one of claims 5 to 9, characterized in that, ​

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