A novel material coupling column method for cold hydrogenation

Abstract

The present application belongs to the technical field of polysilicon production, and discloses a new material coupling tower method for cold hydrogenation. The process adopts a vertical pressurized material coupling tower, which is provided with a tank storage section, a bubbling dust removal section, a packing coupling heat exchange section and a tower top defoaming section. The tank is connected with a side line flash vaporization system. Raw material liquid silicon tetrachloride is fed in several streams, and the gaseous phase at the top of the quenching tower is fed from the lower part of the tower. After bubbling dust removal, the gaseous phase is in countercurrent contact with the liquid silicon tetrachloride in the packing section to realize dust removal and heat exchange. The liquid phase in the tank is extracted through a side line, throttled and depressurized, then enters a flash tank for vaporization, and then is reused after being controlled by a gas-liquid balance separation tank. The present application avoids fouling and plugging of the heat exchange surface, prolongs the operation cycle, reduces external heating energy consumption through direct coupling recovery of latent heat of phase change, ensures the component stability of the reused material, and improves the system operation stability.

Description

Technical Field

[0001] This invention belongs to the field of polycrystalline silicon production technology, specifically relating to a novel cold hydrogenation material coupling tower method. Background Technology

[0002] Cold hydrogenation is a key step in polysilicon production, converting the byproduct silicon tetrachloride into trichlorosilane, thus enabling the recycling of silicon resources. Currently, in cold hydrogenation, the high-temperature, high-pressure gas phase discharged from the top of the quench tower typically exchanges heat with the raw material via a partitioned heat exchanger, and then is cooled in stages by circulating water, 7°C water, and -45°C Freon to finally separate hydrogen from chlorosilanes. However, silicon powder, metal chlorides, and high-boiling-point polychlorosilanes entrained in the gas phase easily deposit on the tube walls during the cooling process of the partitioned heat exchanger, forming a dense scale layer. This leads to a rapid decline in heat exchange efficiency, an increase in system pressure drop, and frequent shutdowns for cleaning. Simultaneously, the latent heat of phase change released by the condensation of chlorosilanes in the gas phase is not effectively recovered, and the vaporization of the raw material silicon tetrachloride before entering the reactor still heavily relies on external steam, making it difficult to further reduce overall energy consumption. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a novel cold hydrogenation material coupling tower method that uses high-pressure direct contact heat exchange to replace the indirect heat exchanger, thus eliminating the metal heat exchanger tube wall as a carrier for scale deposition.

[0004] The technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a method for a cold hydrogenation material coupling tower, used to process the high-temperature, high-pressure gas phase at the top of a quench tower and vaporize the raw material silicon tetrachloride, comprising the following steps: Step 1: The high-temperature and high-pressure gas phase at the top of the quench tower is introduced from the bottom of the vertical pressurized material coupling tower. The interior of the coupling tower is arranged from bottom to top as follows: high-pressure liquid storage section at the bottom of the tower, coarse dust removal section with bubbling, fine coupling heat exchange section with packing and defoaming discharge section at the top of the tower. Step 2: The raw material liquid silicon tetrachloride is divided into main spray feed and tower bottom feed. The main spray feed is sprayed evenly from the top of the packing fine coupling heat exchange section, and the tower bottom feed is directly added to the tower bottom liquid phase. Step 3: The high-temperature and high-pressure gas phase passes through the bubbling coarse dust removal section and the packing fine coupling heat exchange section from bottom to top in the coupling tower, and comes into direct countercurrent contact with the liquid silicon tetrachloride sprayed from top to bottom. After the gas phase is cooled and dusted, it is discharged from the top of the tower, and the liquid phase absorbs heat and collects in the bottom of the tower. Step 4: The high-pressure liquid phase in the tower bottom is drawn out from the side stream, and after being throttled and depressurized, it enters the flash tank for vaporization. The gas phase at the top of the flash tank enters the gas-liquid balance separator. The operating temperature and pressure of the separator are controlled so that the low-boiling-point trichlorosilane is preferentially condensed and refluxed. The silicon tetrachloride-enriched gas phase is drawn out from the top of the separator and superheated by the heat exchanger before being sent to the hydrogenation reactor feed system.

[0005] Preferably, the coupling tower is designed with a pressure of 2.5 MPa to 3.0 MPa and a design temperature of 200°C; an anti-vortex baffle is installed inside the high-pressure liquid storage section of the tower bottom.

[0006] Preferably, the bubbling coarse dust removal section is equipped with a gas distributor, which is a bubbling tube distributor with small holes of 4mm to 6mm in diameter on the bubbling tube; a self-circulating liquid distributor is installed at the upper part of the bubbling coarse dust removal section to circulate and spray part of the liquid phase from the bottom of the tower to the top of the bubbling area to form a liquid curtain.

[0007] Preferably, the packed fine-coupling heat exchange section is filled with stainless steel wire mesh corrugated structured packing with a specific surface area of ​​not less than 500 m². 2 / m 3 It is filled in two to three layers, with liquid redistributors installed between the layers.

[0008] Preferably, the side-line flash vaporization system includes a high-pressure liquid phase extraction pipe led out from the upper side wall of the tower, a throttling flash valve, a flash tank, a gas-liquid balance separator, a superheater, and a defoaming filter component installed at the gas phase outlet at the top of the flash tank and / or the inlet of the separator. The high-pressure liquid phase in the tower bottom enters the throttling flash valve through the extraction pipe, where it is depressurized to 0.4MPa to 0.5MPa before entering the flash tank. The gas phase at the top of the flash tank enters the gas-liquid equilibrium separator. The temperature of the separator is controlled at 115℃ to 125℃ and the pressure at 0.4MPa to 0.5MPa, so that the trichlorosilane content in the silicon tetrachloride-enriched gas phase is less than 10%. The silicon tetrachloride-enriched gas phase is then superheated by a heater and sent to the hydrogenation reactor feed system. Part of the unvaporized liquid phase at the bottom of the flash tank is returned to the tower bottom of the coupling tower, and the other part is sent to the downstream process.

[0009] Preferably, the raw material liquid silicon tetrachloride is divided into two fresh feed streams, including a main spray feed and a reboiler supplement feed; the main spray feed accounts for 70% of the total fresh feed and is sprayed from the upper part of the packing fine coupling heat exchange section after being pressurized by a high-pressure pump; the reboiler supplement feed accounts for 20% of the total fresh feed and is directly added to the reboiler liquid phase; a portion of the liquid phase inside the reboiler is extracted by a circulation pump and returned to the upper part of the bubbling coarse dust removal section to form a self-circulating washing liquid, the volume of which is 25% to 35% of the total liquid phase volume in the reboiler.

[0010] Preferably, the operating pressure of the coupling tower is 2.0 MPa to 2.2 MPa, the gas phase temperature at the top of the tower is 85°C to 95°C, the liquid phase temperature at the bottom of the tower is 145°C to 160°C, the side flash vaporization rate is 35% to 45%, the mass ratio of the gas phase to the main spray liquid phase is 1:1.0 to 1:1.5, and the residence time of the liquid phase at the bottom of the tower is 50 min to 70 min.

[0011] Preferably, the side-stream flash vaporization system adopts a two-stage flash structure, including a first-stage throttling flash valve, a first-stage flash tank, a second-stage throttling flash valve, and a second-stage flash tank. The high-pressure liquid phase in the tower bottom is depressurized to 0.8MPa to 1.2MPa by the first-stage throttling flash valve and then enters the first-stage flash tank. The liquid phase at the bottom of the first-stage flash tank is then depressurized to 0.4MPa to 0.5MPa by the second-stage throttling flash valve and then enters the second-stage flash tank. The total vaporization rate of the two stages is 35% to 45%.

[0012] Preferably, the packed fine coupling heat exchange section adopts a combination of 316L stainless steel wire mesh corrugated structured packing and polytetrafluoroethylene wire mesh corrugated structured packing. The lower layer is filled with 316L stainless steel wire mesh corrugated structured packing, and the upper layer is filled with polytetrafluoroethylene wire mesh corrugated structured packing. The height ratio of the two layers is 1.5:1, and the gas phase temperature at the top of the tower does not exceed 140℃.

[0013] Preferably, the raw material liquid silicon tetrachloride is divided into two fresh feed streams, including a main spray feed and a reboiler supplement feed; the main spray feed accounts for 80% of the total fresh feed, of which 20% is diverted to the upper part of the bubbling coarse dust removal section to form a liquid curtain washing, and the remainder enters the upper part of the packed fine coupling heat exchange section; the reboiler supplement feed accounts for 20% of the total fresh feed and is directly added to the reboiler liquid phase.

[0014] The beneficial effects of this invention are as follows: (1) The present invention uses high-pressure direct contact heat exchange to replace the indirect wall heat exchanger, eliminating the metal heat exchange tube wall as a carrier for scale deposition. At the same time, through the three-stage synergistic purification mechanism of bubbling coarse dust removal, packing fine washing and self-circulating liquid curtain, particulate and dissolved impurities in the gas phase are deeply captured by the liquid phase, reducing the scaling rate of the subsequent cooling equipment and extending the continuous operation cycle of the device. (2) The present invention uses a side-line flash vaporization system and a gas-liquid balance separator to convert the latent heat of condensation of the high-pressure gas phase into the latent heat of vaporization in the low-pressure flash vaporization after the high-pressure liquid phase heat storage. The content of trichlorosilane in the gas phase returned to the reactor is controlled by the boiling point difference. Under the premise of avoiding the disruption of the reaction balance, the direct material coupling of condensation heat release and vaporization heat absorption is achieved, reducing the intermediate heat exchange medium and heat transfer links, and reducing the external steam consumption of the cold hydrogenation process. (3) The present invention integrates deep dust removal, high-efficiency heat exchange and raw material vaporization into a single coupled tower, which reduces the number of indirect heat exchangers, pre-washing equipment and independent vaporizers, thus reducing the equipment footprint and maintenance frequency. (4) By distributing multiple feed streams and adjusting the opening of the side flash valve, the vaporization rate and tower top temperature can be flexibly controlled under different production loads and raw material compositions, thus improving the system's operational stability. Detailed Implementation

[0015] The present invention will be further explained below with reference to specific embodiments.

[0016] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0017] This embodiment discloses a novel cold hydrogenation material coupling tower process to solve the technical problems of scaling and clogging of the indirect heat exchanger during the cold hydrogenation production process due to the entrainment of silicon powder, metal chlorides and high-boiling substances in the gas phase, as well as the technical problem that the latent heat of condensation phase change of chlorosilanes in the high-temperature and high-pressure gas phase cannot be effectively recovered for the vaporization of raw materials. The specific solution is as follows. Example

[0018] The core equipment of this process is a vertical pressurized material coupling tower. The tower is designed to withstand pressures of 2.5 MPa to 3.0 MPa and temperatures of 200°C. The tower body is made of 316L stainless steel. The tower's interior, from bottom to top, consists of a high-pressure storage section at the bottom, a bubbling coarse dust removal and self-circulating washing section, a packing fine coupling heat exchange section, and a defoaming and discharge section at the top. A side-stream flash vaporization system is connected to the bottom of the tower.

[0019] The high-pressure liquid storage section is located at the bottom of the tower body, forming a high-pressure liquid storage chamber. The operating pressure is maintained between 2.0 MPa and 2.2 MPa, and it is used to store the high-pressure liquid phase material after heat exchange and washing. This liquid storage section is equipped with a liquid level control valve, a high-pressure liquid phase outlet, a side flash evaporation extraction port, and a bottom periodic drain port. It is equipped with two anti-vortex baffles arranged in a cross shape, with a baffle height of 300 mm and a distance of 150 mm between the bottom of the baffle and the bottom plate of the tower reboiler.

[0020] The bubbling coarse dust removal and self-circulating washing section is located above the liquid layer in the column bottom. It is equipped with a bubbling tube distributor, with small holes of 4mm to 6mm in diameter on the bubbling tubes, and the opening rate controlled at 8% to 12%. After the gas phase is dispersed through the small holes, it forms microbubbles of 4mm to 6mm in diameter. A self-circulating liquid distributor is installed at the top of this section, circulating and spraying a portion of the liquid phase from the column bottom onto the bubbling zone to form a liquid curtain. The self-circulating liquid distributor is a tubular distributor with spray holes of 5mm in diameter, spraying downwards.

[0021] The packed fine-coupling heat exchange section is located in the middle of the tower body and is filled with 316L stainless steel wire mesh corrugated structured packing with a specific surface area of ​​500 m². 2 / m 3 up to 600m 2 / m 3The material is packed in three layers, each layer with a height of 1000 mm, with a trough-type liquid redistributor installed between the layers. The raw material, liquid silicon tetrachloride, is evenly sprayed from the top of this section through the liquid distributor, ensuring full contact with the rising gas phase in a counter-current flow.

[0022] The demister discharge section at the top of the tower is located at the top of the tower body and is equipped with a double-layer wire mesh demister. The lower layer is made of 316L stainless steel wire mesh with a wire diameter of 0.25mm, a mesh density of 120 mesh, and a thickness of 120mm; the upper layer is made of 316L stainless steel wire mesh with a wire diameter of 0.18mm, a mesh density of 180 mesh, and a thickness of 100mm. A gas phase outlet is provided at the top of the tower.

[0023] The side-stream flash vaporization system includes a high-pressure liquid phase extraction pipe leading from the upper side wall of the column reboiler, a throttling flash valve, a flash tank, a gas-liquid equilibrium separator, and a superheater. The high-pressure, high-temperature liquid phase in the column reboiler enters the throttling flash valve through the extraction pipe, where it is depressurized to 0.4 MPa to 0.5 MPa before entering the flash tank. The gas phase at the top of the flash tank enters the gas-liquid equilibrium separator, which maintains a temperature of 120°C and a pressure of 0.5 MPa. This causes the low-boiling-point trichlorosilane in the gas phase to preferentially condense and reflux, while the silicon tetrachloride-enriched gas phase is drawn from the top of the separator and superheated to 150°C to 170°C before being sent to the hydrogenation reactor feed system. The unvaporized liquid phase at the bottom of the flash tank is partially returned to the reboiler of the coupling column as supplementary feed, and the other part is sent to the rectification section.

[0024] The raw material, liquid silicon tetrachloride, is fed in three streams. The main spray feed accounts for 70% of the total feed volume. After being pressurized to 2.2 MPa by a high-pressure pump, it is evenly sprayed from the liquid distributor at the top of the packed fine coupling heat exchange section. The bottom replenishment feed accounts for 20% of the total feed volume and is directly added to the bottom liquid phase. The self-circulating washing feed accounts for 25% to 35% of the total bottom liquid phase volume. This circulation volume is equivalent to 12% to 18% of the total fresh raw material feed volume. It is drawn from the high-pressure bottom liquid phase by a circulation pump and returned to the self-circulating liquid distributor at the top of the bubbling coarse dust removal and self-circulating washing section.

[0025] The high-temperature, high-pressure gas phase at the top of the quench tower has a temperature of 170°C and a pressure of 2.1 MPa. Its main components are hydrogen, trichlorosilane, and silicon tetrachloride, along with impurities such as silicon powder and metal chlorides. This gas phase enters the bubbling coarse dust removal and self-circulating washing section from the bottom of the coupling tower. After being dispersed by the bubbling tube distributor, it passes through the liquid layer in the tower bottom, completing primary coarse dust removal and preliminary heat exchange, reducing its temperature to 130°C to 150°C. Subsequently, the gas phase continues to rise into the packed fine coupling heat exchange section, where it comes into full countercurrent contact with the liquid silicon tetrachloride sprayed from top to bottom. The gas phase continues to cool to 85°C to 95°C, during which some of the chlorosilane components condense, releasing sensible heat and latent heat of phase change. The liquid silicon tetrachloride feedstock absorbs heat and heats up to 140°C to 160°C. Due to the maintained high pressure inside the tower, the liquid phase does not undergo significant vaporization in this section, and collects in the tower bottom as a high-pressure, high-temperature liquid phase.

[0026] The high-pressure, high-temperature liquid phase inside the column bottom is at 150℃ and 2.1MPa. After being drawn from the side stream, it is depressurized to 0.5MPa via a throttling flash valve. Inside the flash tank, the high-pressure, high-temperature liquid phase flashes due to the sudden pressure drop, with the vaporization rate controlled at 40%. The vapor phase at the top of the flash tank enters a gas-liquid equilibrium separator. After separation, the trichlorosilane content in the silicon tetrachloride-enriched vapor phase is controlled below 10%, and after being superheated by a heater, it is sent to the reactor. The unvaporized liquid phase at the bottom of the flash tank is partially returned to the column bottom of the coupling column and partially sent to the distillation section.

[0027] The liquid phase at the bottom of the column contains captured silicon powder and impurities. After periodic sludge discharge into the settling filter tank to remove solid impurities, part of it is sent to the quench tower as quench spray liquid, and the other part is sent to the distillation section for component separation.

[0028] The low-temperature clean gas phase discharged from the top of the tower enters the hydrogen preheater, circulating water cooler, 7℃ water cooler and -45℃ cryocooler in sequence, and the temperature is reduced in stages to achieve complete separation of hydrogen and chlorosilane.

[0029] This process replaces indirect heat exchangers with high-pressure direct contact heat exchange, eliminating the metal heat exchanger tube walls as a carrier for scale deposition. Simultaneously, it utilizes countercurrent liquid-phase washing to deeply capture particulate and dissolved impurities in the gas phase. Through a side-stream flash vaporization system and a gas-liquid equilibrium separator, the latent heat of condensation in the high-pressure gas phase is stored in the high-pressure liquid phase and then converted into latent heat of vaporization in low-pressure flash vaporization. The boiling point difference is then used to separate trichlorosilane and silicon tetrachloride, allowing silicon tetrachloride to be enriched in the gas phase for reuse, thus avoiding disruption of the reaction equilibrium. Example

[0030] Based on the scheme determined in Example 1, this embodiment optimizes and limits the specific structure and size of the material coupling tower. For a cold hydrogenation unit with an annual production capacity of 5,000 tons of polysilicon, the gas phase processing capacity at the top of the quench tower is approximately 5,000 standard cubic meters per hour.

[0031] The coupling tower body is made of 316L stainless steel, with an inner diameter of 1000mm and a total height of 8000mm. The high-pressure liquid storage section in the tower bottom has a storage chamber height of 2000mm, and the operating liquid level is controlled at 70% of the storage chamber height. Two anti-vortex baffles are installed inside the storage chamber, with a baffle height of 400mm and a distance of 150mm between the bottom of the baffle and the bottom plate of the tower bottom.

[0032] The bubbling coarse dust removal and self-circulating washing section is equipped with a bubbling tube distributor. The bubbling tube has small holes with a diameter of 5mm, resulting in an opening rate of 10%. The gas phase is dispersed through these holes to form tiny bubbles with a diameter of 5mm. A self-circulating liquid distributor is located 400mm above the bubbling tube and is a tubular distributor with spray holes of 5mm diameter. The spray direction is downwards, and the spray coverage angle is 150 degrees.

[0033] The packed, finely coupled heat exchange section is filled with 316L stainless steel wire mesh corrugated structured packing with a specific surface area of ​​550 m² / m³, arranged in three layers, each layer with a height of 1000 mm. A trough-type liquid distributor is installed above each layer of packing, with 8 mm diameter distribution holes at the bottom of the trough. The distance between the trough-type distributor and the packing layer is 200 mm. Inclined-plate liquid redistributors are installed between adjacent layers of packing.

[0034] A double-layer wire mesh demister is installed at the top of the tower's demister discharge section. The lower layer is made of 316L stainless steel wire mesh with a wire diameter of 0.25mm, a mesh density of 120 mesh, and a thickness of 120mm. The upper layer is made of 316L stainless steel wire mesh with a wire diameter of 0.18mm, a mesh density of 180 mesh, and a thickness of 100mm. The total height of the double-layer wire mesh demister is 250mm.

[0035] The high-pressure liquid phase extraction pipe of the side-stream flash vaporization system is led out from the upper side wall of the column bottom, located 150 mm above the normal operating liquid level. The extraction pipe diameter is 80 mm. A high-pressure angle regulating valve with a hard alloy core and an adjustable ratio of 30:1 is used for the throttling flash valve. The flash tank is a vertical cylindrical container with a design pressure of 0.8 MPa, a design temperature of 180℃, an inner diameter of 800 mm, and a straight section height of 2000 mm. A gas phase outlet is located at the top of the flash tank, equipped with a wire mesh demister. After demisting, the gas phase is connected to a gas-liquid balance separator. A precision filter is installed at the inlet of the separator to intercept trace droplets and solid impurities entrained in the flash vapor. A liquid phase outlet is located at the bottom of the flash tank, branching into two paths: one path returns to the column bottom of the coupling column via a circulating pump, and the other path sends the liquid to downstream processes.

[0036] The gas-liquid balance separator is designed with a pressure of 0.6 MPa and a temperature of 150℃. It has an inner diameter of 600 mm, a straight section height of 1500 mm, and is equipped with a two-layer inclined plate condensation reflux structure to control the operating temperature at 120℃.

[0037] Under this preferred structure, the operating gas velocity is 0.1 m / s to 0.2 m / s, the pressure drop in the packing section is 200 Pa / m to 300 Pa / m, and the system operates stably. Example

[0038] Based on the scheme determined in Example 1, this embodiment optimizes and limits the key process parameters.

[0039] The preferred ratio of the three feed streams for the raw material liquid silicon tetrachloride is as follows: the main spray feed accounts for 70% of the total feed, the reboiler feed accounts for 20% of the total feed, and the self-circulating washing feed accounts for 25% to 35% of the total liquid phase in the reboiler. At this ratio, the main spray feed is sufficient to form a uniform liquid film in the packed fine-coupling heat exchange section, the reboiler feed can maintain a stable reboiler liquid level, and the self-circulating washing feed can form an effective liquid curtain above the bubbling zone.

[0040] The preferred operating pressure for the coupling tower is 2.0 MPa to 2.2 MPa. This pressure range matches the top gas phase pressure of the cold hydrogenation quench tower, eliminating the need for additional pressurization energy consumption. Simultaneously, it ensures that the boiling point of silicon tetrachloride in the bottom liquid phase is above 195°C at this pressure (approximately 195°C at gauge pressure 2.0 MPa and approximately 200°C at gauge pressure 2.2 MPa), preventing premature vaporization of the liquid phase within the tower and thus avoiding flooding.

[0041] The preferred mass ratio of gas phase to main spray liquid phase is 1:1.0 to 1:1.5. Within this range, the liquid phase is sufficient to fully cover the packing surface to form a liquid film, ensuring sufficient contact between the gas and liquid phases, resulting in high heat exchange efficiency. At the same time, excessive liquid phase will not cause excessive pressure drop or flooding in the packing section.

[0042] The gas phase temperature at the top of the column is preferably controlled between 85°C and 95°C. This temperature range ensures that the chlorosilane components are fully condensed, impurities are deeply captured by the liquid phase, and sufficient temperature is reserved for subsequent hydrogen preheating.

[0043] The reboiler liquid temperature is preferably controlled between 140°C and 160°C. This temperature range ensures that the liquid phase fully absorbs the sensible heat and latent heat of phase change released by the gas phase, forming a high-pressure, high-temperature liquid phase, providing sufficient superheat for subsequent side-stream flash vaporization. If the reboiler liquid temperature is below 140°C, the superheat of the high-pressure liquid phase after depressurization flash vaporization is insufficient, and the vaporization rate is difficult to reach more than 30%; if it is above 160°C, it approaches the boiling point of silicon tetrachloride under high pressure, posing a risk of localized vaporization within the column.

[0044] The side flash vaporization rate is preferably controlled between 35% and 45%. At this vaporization rate, 45% to 55% of the external steam energy consumption required for the vaporization of the raw material silicon tetrachloride can be covered, while ensuring that the unvaporized liquid phase at the bottom of the flash tank still has a sufficient flow rate to return to the coupling tower to maintain system balance. When the vaporization rate is below 30%, the energy-saving effect is not significant; when it is above 50%, the amount of liquid phase returned to the coupling tower is insufficient, which may lead to a drop in the tower bottom liquid level and interruption of the self-circulating washing feed.

[0045] The optimal feed rate for self-circulating washing is 25% to 35% of the total liquid phase in the reboiler. At this ratio, the liquid curtain density above the bubbling zone is moderate, effectively capturing fine silica powder and dissolved metal chlorides with particle sizes of 1μm to 10μm. When the ratio is below 20%, the liquid curtain density is insufficient, resulting in high penetration of fine particles; when it is above 40%, the excessively dense liquid curtain leads to increased pressure drop in the bubbling section, and excessive liquid phase return may cause fluctuations in the reboiler liquid level.

[0046] The optimal liquid-to-gas ratio in the packing section is between 15 m³ / 1000 m³ and 25 m³ / 1000 m³. Within this range, the liquid film renewal rate on the packing surface is moderate, the gas-liquid mass transfer efficiency is high, and the system pressure drop is controlled within a reasonable range.

[0047] The preferred residence time for the liquid phase in the column bottom is 50 to 70 minutes. This residence time ensures that silicon powder and impurities have sufficient time to settle and separate in the column bottom, while avoiding excessive accumulation of high-boiling substances due to excessive residence time.

[0048] The preferred operating temperature for the gas-liquid equilibrium separator is 115°C to 125°C, and the pressure is 0.4 MPa to 0.5 MPa. This temperature is higher than the boiling point of trichlorosilane at the corresponding pressure (approximately 95°C to 105°C) and lower than the boiling point of silicon tetrachloride at the corresponding pressure (approximately 125°C to 135°C), causing trichlorosilane to preferentially condense and reflux, while silicon tetrachloride remains in the gas phase, thereby ensuring that the trichlorosilane content in the silicon tetrachloride-enriched gas phase at the top of the separator is less than 10%. Example

[0049] This embodiment, as another implementation of Embodiment 1, provides an alternative configuration for the side-line flash vaporization system.

[0050] In this embodiment, the side-stream flash vaporization system adopts a two-stage flash structure. A first-stage high-pressure liquid phase extraction pipe is installed at the top of the reboiler, connected to a first-stage throttling flash valve. This reduces the pressure of the high-pressure liquid phase from 2.0 MPa to 2.2 MPa to 0.8 MPa to 1.2 MPa before it enters the first-stage flash tank. In the first-stage flash tank, approximately 15% to 25% of the liquid phase vaporizes, with the vaporization temperature controlled at 130°C to 150°C. The liquid phase at the bottom of the first-stage flash tank is further depressurized to 0.4 MPa to 0.5 MPa via a second-stage throttling flash valve before entering the second-stage flash tank, where another 15% to 25% vaporizes. The total vaporization rate of the two stages is controlled at 35% to 45%.

[0051] The vapor phase from the top of the first-stage flash tank enters the first-stage gas-liquid equilibrium separator, where the temperature is controlled at 135°C to 145°C. After separation, the silicon tetrachloride-enriched vapor phase is directly fed into the hydrogenation reactor feed system. The vapor phase from the top of the second-stage flash tank enters the second-stage gas-liquid equilibrium separator, where the temperature is controlled at 115°C to 125°C. After separation, the silicon tetrachloride-enriched vapor phase is also superheated in a heat exchanger before being fed into the hydrogenation reactor feed system. The unvaporized liquid phases at the bottom of the two flash tanks are combined; part of them are returned to the bottom of the coupling tower, and the other part is sent to downstream processes.

[0052] This two-stage flash evaporation structure is suitable for operating conditions where the liquid phase temperature in the tower bottom is high or the vaporization rate requirement is high. By reducing the pressure in stages, the intensity of a single flash evaporation is reduced, thereby lowering the risk of liquid phase entrainment in the flash tank. Example

[0053] This embodiment, as another implementation of Embodiment 1, provides an alternative configuration for the feeding method.

[0054] In this embodiment, the independent self-circulating washing feed is eliminated. Instead, a portion of the main spray feed is diverted to the upper part of the bubbling coarse dust removal and self-circulating washing section. Specifically, 20% of the total main spray feed is drawn from the liquid distributor at the upper part of the packing fine coupling heat exchange section and transported via a bypass pipeline to the liquid distributor at the upper part of the bubbling coarse dust removal and self-circulating washing section to form a liquid curtain washing. The remaining 80% of the main spray feed still enters the packing fine coupling heat exchange section.

[0055] This alternative reduces the number of circulating pumps and independent piping, simplifying system configuration. However, the liquid phase temperature in the bubbling zone's liquid curtain scrubbing is the same as the main spray feed temperature, typically room temperature or slightly above room temperature, resulting in a slightly less effective cooling and scrubbing effect on the gas phase compared to the high-temperature liquid phase circulation method used in Example 1. Therefore, this approach is more suitable for applications with lower fine particle content in the gas phase or where system simplification is a higher priority. Example

[0056] This embodiment, as another implementation of Embodiment 1, provides an alternative configuration for the packing material of the packed fine coupling heat exchange section.

[0057] In this embodiment, the packed fine-coupling heat exchange section uses a combination of 316L stainless steel wire mesh corrugated structured packing and polytetrafluoroethylene (PTFE) wire mesh corrugated structured packing. The lower packing layer, located near the bubbling coarse dust removal and self-circulating washing section, is filled with 316L stainless steel wire mesh corrugated structured packing. This layer primarily contacts the gas phase containing a high amount of silica powder; the stainless steel material has high mechanical strength and is resistant to particle erosion. The upper packing layer, located near the top demister discharge section, is filled with PTFE wire mesh corrugated structured packing. This layer primarily contacts the relatively clean gas phase after the lower coarse dust removal layer; the PTFE material is resistant to chlorosilane corrosion.

[0058] The height ratio of the two packing layers is 1.5:1. The height of the 316L stainless steel wire mesh corrugated packing layer is 900mm, and the height of the PTFE wire mesh corrugated packing layer is 600mm. A liquid collection and redistribution device is installed between the two packing layers.

[0059] This combined packing method is suitable for special operating conditions where the silica content in the gas phase is high and the corrosiveness of chlorosilanes is strictly required. However, it should be noted that the mechanical strength of PTFE material decreases above 150°C, and this alternative solution is only applicable to operating conditions where the gas phase temperature at the top of the tower does not exceed 140°C. Example

[0060] This embodiment verifies the effectiveness of the processes described in Embodiments 1 to 6. By setting up comparative and single-variable control experiments, it explains the reasons for the range of key parameter values ​​and the technical effects.

[0061] Baseline conditions: All verification experiments were conducted on a cold hydrogenation unit with an annual production capacity of 5,000 tons of polysilicon. The quench tower top gas phase throughput was 5,000 standard cubic meters per hour. The gas phase composition was 55% hydrogen, 30% trichlorosilane, and 14% silicon tetrachloride, with the remainder being trace impurities. The gas phase temperature was 170°C, the pressure was 2.1 MPa, the silicon powder content in the gas phase was 150 mg / m³, and the metal chloride content was 20 mg / m³. The feed rate of liquid silicon tetrachloride was 12 tons per hour.

[0062] Comparative Example: Traditional Craftsmanship A shell-and-tube heat exchanger made of 316L stainless steel is used for vapor-phase cooling. The heat exchanger has a heat exchange area of ​​180 m². A circulating water cooler is connected in series with a -45°C cryogenic cooler. The raw material silicon tetrachloride is vaporized using an external steam vaporizer at a steam pressure of 1.0 MPa.

[0063] Verification 1: Comparison of operating cycle and scaling rate The scheme determined in Example 1 (operating pressure 2.1 MPa gauge pressure, bottom liquid phase temperature 150°C, self-circulation washing ratio 30%, vaporization rate 40%) was used and operated continuously for 18 months. In contrast, the comparative unit operated for 3 months, and the heat transfer coefficient of the indirect heat exchanger decreased from the initial 320 W / (m²·K) to 175 W / (m²·K), a decrease of 45%. The system pressure drop increased from the initial 0.05 MPa to 0.12 MPa, forcing a shutdown for cleaning. In Example 1, after 18 months of continuous operation, the heat transfer coefficients of the subsequent hydrogen preheater and cooler decreased by only 7% from their initial values, and the system pressure drop stabilized within 108% of the initial value, eliminating the need for shutdown for cleaning. These results indicate that high-pressure direct contact heat exchange combined with a liquid phase washing mechanism can extend the continuous operation period of the unit from 3 months to more than 18 months.

[0064] Verification 2: Energy Consumption Comparison and Flash Vaporization Rate Range Verification Based on baseline heat balance calculations, the sensible heat released by the vapor phase at the top of the quench tower as it cools from 170°C to 90°C is approximately 1.2 × 10⁻⁶. 6 kJ / h, of which the latent heat of phase change released by the condensation of chlorosilane is approximately 2.8 × 10 kJ / h. 6 kJ / h, total recoverable heat is approximately 4.0 × 10 kJ / h. 6 The heat absorbed by the liquid feedstock during heating and vaporization, calculated at a 40% vaporization rate, is approximately 3.2 × 10 kJ / h. 6 The flash evaporation system has a heat recovery efficiency of approximately 85%, corresponding to a steam capacity that can be replaced by 3.6 tons / h to 4.2 tons / h, which is consistent with the experimental results below.

[0065] Under baseline conditions, the comparative example has an hourly steam consumption of 8.5 tons (all used for feedstock vaporization). Using the scheme of Example 1, the side-stream flash vaporization rate was controlled at 25%, 35%, 45%, and 55%, respectively, and the overall steam consumption change was tested.

[0066] Test results show that: at a vaporization rate of 25%, 2.1 tons of steam are replaced per hour, resulting in a 22% reduction in overall steam consumption, but the energy-saving effect is not significant; at a vaporization rate of 35%, 3.5 tons of steam are replaced, resulting in a 33% reduction in overall steam consumption; at a vaporization rate of 45%, 4.2 tons of steam are replaced, resulting in a 38% reduction in overall steam consumption, but the amount of liquid phase returned to the bottom of the tower is close to the lower limit, and the self-circulation washing ratio needs to be reduced from 30% to 22% to maintain the liquid level; at a vaporization rate of 55%, the liquid level in the bottom of the tower continues to drop, the self-circulation washing ratio cannot be maintained, the dust removal efficiency in the bubbling zone decreases, the content of fine particles in the gas phase increases, and the system operation becomes unstable. Therefore, a vaporization rate range of 35% to 45% can achieve the best balance between energy-saving effect and system stability.

[0067] Verification 3: Verification of Self-Circulating Washing Ratio Under the baseline conditions and with other parameters fixed in Example 1 (vaporization rate 40%, bottom liquid phase temperature 150℃), the gas phase dust removal effect and system stability were tested when the self-circulating washing feed rate was 15%, 25%, 35%, 45%, and 50% of the total liquid phase in the bottom of the tower.

[0068] Test results show that: at a concentration of 15%, the removal rate of fine silica powder with a particle size of 1μm to 5μm in the gas phase is 93%, but the heat transfer coefficient decreases by 22% after 6 months of operation of the subsequent hydrogen preheater; at a concentration of 25%, the removal rate of fine silica powder is 98%, but the heat transfer coefficient decreases by 7% after 18 months of operation of the subsequent heat exchanger; at a concentration of 35%, the removal rate of fine silica powder is 99.5%, but the heat transfer coefficient decreases by 5% after 20 months of operation of the subsequent heat exchanger; at a concentration of 45%, the removal rate of fine silica powder is 99.6%, but the pressure drop in the bubbling section increases by 28%, and the liquid level fluctuation in the tower bottom exceeds ±15%; at a concentration of 50%, the pressure drop in the bubbling section increases by 45%, and flooding occurs, making the system unstable. Therefore, a self-circulating scrubbing ratio range of 25% to 35% can achieve the best balance between dust removal efficiency and system pressure drop.

[0069] Verification 4: Verification of the liquid phase temperature in the column bottom Under the baseline conditions and with other parameters fixed in Example 1 (vaporization rate 40%, self-circulation washing ratio 30%), the side-stream flash vaporization effect and system safety were tested at bottom liquid phase temperatures of 130℃, 145℃, 150℃, 160℃, and 170℃.

[0070] Test results show that at 130℃, the superheat of the high-pressure liquid phase after depressurization to 0.5MPa is insufficient, resulting in a flash vaporization rate of only 22% and poor energy-saving effect. At 145℃, the flash vaporization rate is 34%; at 150℃, it is 40%; at 160℃, it is 47%; and at 170℃, it is 54%. However, in some areas of the column bottom, the liquid phase temperature has reached 95% of the boiling point of silicon tetrachloride under high pressure, resulting in slight vaporization and a significant increase in the risk of flooding in the packed section. Therefore, a column bottom liquid phase temperature range of 145℃ to 160℃ can ensure sufficient superheat of the high-pressure liquid phase for flash vaporization while preventing premature vaporization within the column.

[0071] Verification 5: Gas-Liquid Mass Ratio Verification Under the baseline conditions and with other parameters fixed in Example 1, the heat exchange and dust removal effects were tested when the mass ratio of gas phase to main spray liquid phase was 1:0.6, 1:1.0, 1:1.5, 1:2.0, and 1:2.5, respectively.

[0072] Test results show that: at a gas-liquid mass ratio of 1:0.6, the liquid film coverage on the packing surface is insufficient, the gas phase temperature at the top of the tower reaches as high as 108℃, chlorosilane condensation is incomplete, the impurity removal rate is 94%, and the scaling rate of the subsequent cooler is rapid; at a gas-liquid mass ratio of 1:1.0, the gas phase temperature at the top of the tower drops to 95℃, and the impurity removal rate is 98%; at a gas-liquid mass ratio of 1:1.5, the gas phase temperature at the top of the tower drops to 88℃, the impurity removal rate is 99.5%, and the system pressure drop is normal; at a gas-liquid mass ratio of 1:2.0, the gas phase temperature at the top of the tower drops to 85℃, the impurity removal rate is 99.6%, but the pressure drop in the packing section increases by 18%; at a gas-liquid mass ratio of 1:2.5, flooding occurs in the packing section, the system pressure drop increases sharply, and the gas phase carryover phenomenon is obvious. Therefore, a gas-liquid mass ratio range of 1:1.0 to 1:1.5 can achieve the best balance between heat exchange efficiency, dust removal effect, and system stability.

[0073] Verification 6: Coupling Tower Operating Pressure Verification Under baseline conditions, the system operation was tested at coupling tower operating pressures of 1.6 MPa, 2.0 MPa, 2.1 MPa, 2.2 MPa, and 2.6 MPa, respectively.

[0074] Test results show that: at a pressure of 1.6 MPa, which is lower than the pressure of the gas phase at the top of the quench tower, the gas phase cannot smoothly enter the coupling tower, requiring an additional compressor for pressurization, increasing energy consumption and posing a risk of compression condensation; at a pressure of 2.0 MPa, the gas phase enters smoothly, and the boiling point of the liquid phase at the bottom of the tower is approximately 195℃ at 2.0 MPa, far below the boiling point of 150℃, eliminating the risk of vaporization within the tower; at a pressure of 2.1 MPa, operation is stable and perfectly matches the system pressure; at a pressure of 2.2 MPa, operation is stable, and the boiling point of the liquid phase at the bottom of the tower is approximately 200℃, providing sufficient safety margin; at a pressure of 2.6 MPa, additional pressurization of the gas phase at the top of the quench tower is required, increasing energy consumption by more than 15%, and requiring increased equipment wall thickness, thus raising investment costs. Therefore, the operating pressure range of 2.0 MPa to 2.2 MPa achieves the best balance between system compatibility, safety, and economy.

[0075] Verification 7: Temperature Verification of the Gas-Liquid Balance Separator Under the baseline conditions and with other parameters fixed in Example 1 (flash tank pressure 0.5 MPa gauge pressure), the gas phase components were tested at operating temperatures of 105°C, 115°C, 120°C, 125°C, and 135°C.

[0076] Test results show that at 105℃, the temperature of the separator is below the boiling point of trichlorosilane, and the trichlorosilane content in the gas phase is as high as 35%. Direct return to the reactor will significantly inhibit the conversion rate of silicon tetrachloride. At 115℃, the trichlorosilane content in the gas phase decreases to 12%; at 120℃, it decreases to 8%; at 125℃, it decreases to 6%; and at 135℃, it decreases to 5%, but the condensation loss of silicon tetrachloride increases, and the total vaporization recovery rate decreases by 8%. Considering both the reaction equilibrium effect and the vaporization recovery rate, the separator operating temperature of 115℃ to 125℃ can control the trichlorosilane content in the gas phase returned to the reactor to below 10%, with an impact of less than 3% on the single-pass conversion rate of silicon tetrachloride, which is within an acceptable range.

[0077] The above verification results show that the core parameter ranges defined in Example 1, including the coupling tower operating pressure of 2.0 MPa to 2.2 MPa, the tower bottom liquid phase temperature of 145°C to 160°C, the side stream flash vaporization rate of 35% to 45%, the self-circulation washing ratio of 25% to 35% (based on the total liquid phase volume in the tower bottom), the gas-liquid mass ratio of 1:1.0 to 1:1.5, the tower bottom liquid phase residence time of 50 min to 70 min, and the gas-liquid equilibrium separator temperature of 115°C to 125°C, have all been verified by comparative proportions and multiple sets of single-variable control experiments. Only this range can simultaneously meet the comprehensive requirements of deep dust removal, efficient heat exchange, stable flash vaporization, controllable reactor feed composition, and long-term safe operation of the system.

Claims

1. A novel cold hydrogenation material coupling tower method for processing the high-temperature, high-pressure gas phase at the top of a quench tower and vaporizing the raw material silicon tetrachloride, characterized in that, Includes the following steps: Step 1: The high-temperature and high-pressure gas phase at the top of the quench tower is introduced from the bottom of the vertical pressurized material coupling tower. The interior of the coupling tower is arranged from bottom to top as follows: high-pressure liquid storage section at the bottom of the tower, coarse dust removal section with bubbling, fine coupling heat exchange section with packing and defoaming discharge section at the top of the tower. Step 2: The raw material liquid silicon tetrachloride is divided into main spray feed and tower bottom feed. The main spray feed is sprayed evenly from the top of the packing fine coupling heat exchange section, and the tower bottom feed is directly added to the tower bottom liquid phase. Step 3: The high-temperature and high-pressure gas phase passes through the bubbling coarse dust removal section and the packing fine coupling heat exchange section from bottom to top in the coupling tower, and comes into direct countercurrent contact with the liquid silicon tetrachloride sprayed from top to bottom. After the gas phase is cooled and dusted, it is discharged from the top of the tower, and the liquid phase absorbs heat and collects in the bottom of the tower. Step 4: The high-pressure liquid phase in the tower bottom is drawn out from the side stream, and after being throttled and depressurized, it enters the flash tank for vaporization. The gas phase at the top of the flash tank enters the gas-liquid balance separator. The operating temperature and pressure of the separator are controlled so that the low-boiling-point trichlorosilane is preferentially condensed and refluxed. The silicon tetrachloride-enriched gas phase is drawn out from the top of the separator and superheated by the heat exchanger before being sent to the hydrogenation reactor feed system.

2. The method for a cold hydrogenation material coupling tower according to claim 1, characterized in that, The coupling tower is designed with a pressure of 2.5MPa to 3.0MPa and a design temperature of 200℃; the high-pressure liquid storage section in the tower bottom is equipped with an anti-vortex baffle.

3. The method for a cold hydrogenation material coupling tower according to claim 1, characterized in that, The bubbling coarse dust removal section is equipped with a gas distributor, which is a bubbling tube distributor with small holes of 4mm to 6mm in diameter on the bubbling tube; a self-circulating liquid distributor is installed at the upper part of the bubbling coarse dust removal section to circulate and spray part of the liquid phase from the bottom of the tower to the top of the bubbling area to form a liquid curtain.

4. The novel cold hydrogenation material coupling tower method according to claim 1, characterized in that, The fine-coupling heat exchange section is filled with stainless steel wire mesh corrugated structured packing with a specific surface area of ​​not less than 500 m². 2 / m 3 It is filled in two to three layers, with liquid redistributors installed between the layers.

5. The novel cold hydrogenation material coupling tower method according to claim 1, characterized in that, The side-line flash vaporization system includes a high-pressure liquid phase extraction pipe led out from the upper side wall of the tower, a throttling flash valve, a flash tank, a gas-liquid balance separator, a superheater, and a defoaming filter component installed at the gas phase outlet at the top of the flash tank and / or the inlet of the separator. The high-pressure liquid phase in the tower bottom enters the throttling flash valve through the extraction pipe, where it is depressurized to 0.4MPa to 0.5MPa before entering the flash tank. The gas phase at the top of the flash tank enters the gas-liquid equilibrium separator. The temperature of the separator is controlled at 115℃ to 125℃ and the pressure at 0.4MPa to 0.5MPa, so that the trichlorosilane content in the silicon tetrachloride-enriched gas phase is less than 10%. The silicon tetrachloride-enriched gas phase is then superheated by a heater and sent to the hydrogenation reactor feed system. Part of the unvaporized liquid phase at the bottom of the flash tank is returned to the tower bottom of the coupling tower, and the other part is sent to the downstream process.

6. The method for a cold hydrogenation material coupling tower according to claim 1, characterized in that, The raw material, liquid silicon tetrachloride, is divided into two fresh feed streams: a main spray feed and a reboiler feed. The main spray feed accounts for 70% of the total fresh feed and is sprayed from the top of the packing fine coupling heat exchange section after being pressurized by a high-pressure pump. The reboiler feed accounts for 20% of the total fresh feed and is directly added to the reboiler liquid phase. A portion of the liquid phase inside the reboiler is pumped out by a circulation pump and returned to the upper part of the bubbling coarse dust removal section to form a self-circulating washing liquid. The volume of this self-circulating washing liquid is 25% to 35% of the total liquid phase in the reboiler.

7. The method for a cold hydrogenation material coupling tower according to claim 1, characterized in that, The operating pressure of the coupling tower is 2.0 MPa to 2.2 MPa, the gas phase temperature at the top of the tower is 85°C to 95°C, the liquid phase temperature at the bottom of the tower is 145°C to 160°C, the side flash vaporization rate is 35% to 45%, the mass ratio of the gas phase to the main spray liquid phase is 1:1.0 to 1:1.5, and the residence time of the liquid phase at the bottom of the tower is 50 min to 70 min.

8. The method for a cold hydrogenation material coupling tower according to claim 1, characterized in that, The side-stream flash vaporization system adopts a two-stage flash structure, including a first-stage throttling flash valve, a first-stage flash tank, a second-stage throttling flash valve, and a second-stage flash tank. The high-pressure liquid phase in the tower bottom is depressurized to 0.8MPa to 1.2MPa by the first-stage throttling flash valve and then enters the first-stage flash tank. The liquid phase at the bottom of the first-stage flash tank is then depressurized to 0.4MPa to 0.5MPa by the second-stage throttling flash valve and then enters the second-stage flash tank. The total vaporization rate of the two stages is 35% to 45%.

9. The method for a cold hydrogenation material coupling tower according to claim 4, characterized in that, The packed fine coupling heat exchange section adopts a combination of 316L stainless steel wire mesh corrugated structured packing and polytetrafluoroethylene wire mesh corrugated structured packing. The lower layer is filled with 316L stainless steel wire mesh corrugated structured packing, and the upper layer is filled with polytetrafluoroethylene wire mesh corrugated structured packing. The height ratio of the two layers is 1.5:1, and the gas phase temperature at the top of the tower does not exceed 140℃.

10. The method for a cold hydrogenation material coupling tower according to claim 1, characterized in that, The raw material, liquid silicon tetrachloride, is divided into two fresh feed streams, including a main spray feed and a reboiler feed. The main spray feed accounts for 80% of the total fresh feed, of which 20% is diverted to the upper part of the bubbling coarse dust removal section to form a liquid curtain for washing, and the remainder enters the upper part of the packed fine coupling heat exchange section. The reboiler feed accounts for 20% of the total fresh feed and is directly added to the reboiler liquid phase.