A trichlorosilane synthesis gas washing method and control system applicable to high and low loads, and a method

Abstract

The invention discloses a trichlorosilane synthesis gas scrubbing method and control system applicable to high and low loads, belonging to the technical field of trichlorosilane synthesis process. Synthesis gas discharged from the tops of at least two trichlorosilane synthesis furnaces is sent to a scrubbing unit for scrubbing and then sent to a condenser for treatment. The non-condensable gas obtained after the condensation treatment is sent to a regenerated hydrogen system; the liquid phase obtained after the condensation treatment is collected in a product liquid storage tank; the scrubbing unit comprises a large scrubbing tower and a small scrubbing tower connected in parallel. When the scrubbing unit is in operation, either the large scrubbing tower or the small scrubbing tower is selectively opened. The processing capacity of the large scrubbing tower can meet the scrubbing of gas generated by all trichlorosilane synthesis furnaces connected thereto in simultaneous operation. The invention solves the problem in the prior art that high-temperature synthesis gas discharged from the tops of multiple trichlorosilane synthesis furnaces enters a scrubbing tower for scrubbing, resulting in a mismatch between the actual processing capacity of the scrubbing tower and the designed processing capacity of the equipment, poor scrubbing effect, and excessively high content of metal impurities in the obtained product liquid.

Description

Technical Field

[0001] The present invention relates to the technical field of trichlorosilane synthesis technology, and in particular to a trichlorosilane synthesis gas washing method and control system applicable to high and low loads. Background Art

[0002] In the production of polysilicon, the synthesis gas discharged from the top of the trichlorosilane synthesis furnace has a temperature of about 300°C. The synthesis gas contains chlorosilane, hydrogen, silicon powder, metal chlorides and high-boiling substances. The conventional treatment method is to filter the synthesis gas through a silicon powder filter to remove most of the large particles of silicon powder, and then send it to a washing tower for washing.

[0003] In actual production, to reduce equipment layout space and lower equipment investment, a single scrubber is generally used to connect multiple trichlorosilane synthesis furnaces to treat synthesis gas. However, during actual equipment operation, equipment load mismatch can easily lead to poor scrubbing results. Taking one of our company's trichlorosilane synthesis production lines as an example, the scrubber's processing capacity was designed based on the gas output of four trichlorosilane synthesis furnaces operating simultaneously. However, when only one or two trichlorosilane synthesis furnaces are in operation, the overall heat load of the high-temperature mixed gas entering the scrubber is relatively low, and the corresponding required spray volume of spray liquid is also relatively small. However, since the scrubber specifications have been determined, adjusting the spray volume to too low will result in poor scrubbing results and easy clogging of the tower trays. To ensure normal operation of the equipment and avoid clogging of the tower trays, the spray volume is usually increased, and the product liquid is continuously extracted from the bottom of the scrubber into the product tank for processing.

[0004] Although this method of increasing the amount of spray liquid can avoid the purpose of tower plate clogging, the washed silicon powder, metal chlorides and high-boiling substances are easy to enter the product liquid tank. When only 1 to 2 trichlorosilane synthesis furnaces are in operation, the metal impurity content in the product liquid is relatively high, reaching more than 10,000 ppbw, resulting in the problem of low product liquid quality. That is, the scrubber does not achieve the role of a scrubber, but only achieves the effect of cooling the synthesis gas. Summary of the Invention

[0005] The present invention aims to provide a trichlorosilane synthesis gas scrubbing method applicable to both high and low loads. The method is based on further optimization of an existing scrubbing system and solves the problems in the prior art whereby high-temperature synthesis gas discharged from the top of multiple trichlorosilane synthesis furnaces enters a scrubbing tower for scrubbing, but the scrubbing effect fails to achieve the desired effect due to a mismatch between the actual gas processing capacity of the scrubbing tower and the designed gas processing capacity of the equipment. Furthermore, the scrubbing method wastes energy, causes difficulty in handling washed silicon powder, metal chlorides, and high-boiling substances that enter a product liquid tank, and results in high costs.

[0006] The present invention is achieved through the following technical solutions:

[0007] A trichlorosilane synthesis gas scrubbing method applicable to high and low loads, wherein the synthesis gas discharged from the top of at least two trichlorosilane synthesis furnaces is sent to a scrubbing unit for scrubbing, the gas phase obtained after treatment in the scrubbing unit is sent to a condenser for treatment through a pipeline at the top of the scrubbing unit, and the non-condensable gas obtained after condensation treatment is sent to a regenerated hydrogen system in a recovery process;

[0008] The liquid phase obtained after condensation treatment is collected into the product liquid storage tank for standby use;

[0009] The slurry obtained after being processed by the washing unit is discharged from the lower part of the washing unit to the slurry processing unit for processing;

[0010] The washing unit includes a large washing tower and a small washing tower connected in parallel. When the washing unit is working, either the large washing tower or the small washing tower is selectively opened. The processing capacity of the large washing tower can meet the needs of washing the gas generated when all trichlorosilane synthesis furnaces connected to the large washing tower are running simultaneously.

[0011] Furthermore, the processing capacity of the small washing tower can meet the needs of washing the gas generated when half the number of trichlorosilane synthesis furnaces connected to the small washing tower are running simultaneously.

[0012] That is, in the present invention, the layout of the original trichlorosilane synthesis tower is almost unchanged. Only a small scrubbing tower needs to be added to the original treatment system. Relatively speaking, the changes to the equipment and pipeline layout are relatively small, the equipment investment is small, and it is easy to promote. In addition, the impurity content in the obtained product liquid is stable and reduced to 5000 ppbw or less.

[0013] Furthermore, the large washing tower and the small washing tower are provided with a jacket for passing steam.

[0014] When the gas volume entering the scrubbing unit from the front-end trichlorosilane synthesis furnace is small and matches the load of the small scrubber at 60% to 120%, start the small scrubber and shut down the large scrubber. If it is lower than 60% of the load of the small scrubber, pass steam into the jacket of the small scrubber to keep the load of the small scrubber between 60% and 120%.

[0015] When the gas volume entering the scrubbing unit from the front-end trichlorosilane synthesis furnace is large, and the load of the small scrubber exceeds 120% without steam being introduced, the large scrubber is started and the small scrubber is shut down. If the large scrubber is operating at a load of 60% to 120%, there is no need to pass steam into the jacket of the large scrubber. If the load is lower than 60%, steam needs to be passed into the jacket of the large scrubber to achieve the minimum normal operating load of the large scrubber, which can further improve the problem of mismatch between the actual operating load and the design load of the scrubber.

[0016] Furthermore, the present invention also proposes a washing tower structure with a more optimal structure, which specifically includes a tower body, which is a hollow cylinder. The lower part of the tower body is provided with an air inlet, and the air inlet is connected to a gas distributor extending into the interior of the tower body. The gas distributor is provided with a number of short sections with openings facing downwards. The middle and upper part of the tower body is provided with a number of tower plates, and sieve holes are distributed on the tower plates. The aperture of the sieve holes on the lower tower plate is larger than the aperture of the sieve holes on the upper tower plate. A bubble breaker is provided above the gas distributor. Preferably, the large washing tower and the small washing tower in this scheme both adopt the above-mentioned tower body structure. The optimized tower body structure can significantly reduce the impurity content in the product tank, which can be reduced from the original impurity content of 10,000 ppbw to below 5,000 ppbw.

[0017] Furthermore, the trays inside the tower body are divided into trays with multiple levels of apertures.

[0018] Furthermore, a packing layer is provided above the tower tray at the top of the tower body. The washing tower provided with the packing layer can significantly reduce the impurity content in the product liquid.

[0019] Furthermore, the outlet weir of the tower tray is an inclined plate, and the tail of the inclined plate is connected to a vertical plate.

[0020] Furthermore, the angle between the inclined plate and the tower tray is ɵ, 90°<ɵ≤150°.

[0021] Furthermore, the arched area of ​​the tower plate is provided with guide holes and / or guide plates. The further optimized washing tower can not only significantly reduce the impurity content in the product liquid, but also significantly increase the operating cycle of the washing tower, reduce the maintenance frequency of the equipment, and reduce the labor intensity of workers who maintain the equipment.

[0022] A trichlorosilane synthesis gas scrubbing control system suitable for high and low loads includes a DCS, and a large scrubbing tower with a high throughput and a small scrubbing tower with a low throughput connected in parallel. The small scrubbing tower is connected to a discharge pipeline I, a spray liquid inlet pipe I, an air inlet pipe I, a slag discharge pipeline I, and a steam inlet pipe I. The air inlet pipe I is provided with a shut-off valve I, and the steam inlet pipe I is provided with a regulating valve I. A pressure sensor II is provided in the middle of the small scrubbing tower, and the regulating valve I is controllably connected to the pressure sensor I and the pressure sensor II, respectively. The spray liquid inlet pipe I is provided with a regulating valve II and a flowmeter I, and the regulating valve II is controllably connected to the flowmeter I.

[0023] The large washing tower is connected to a discharge pipeline II, a spray liquid inlet pipe II, an air intake pipeline II, a slag discharge pipeline II and a steam inlet pipe II. The air intake pipeline II is provided with a shut-off valve II, the steam inlet pipe II is provided with a regulating valve III, a pressure sensor III is provided in the middle of the large washing tower, and the regulating valve III is respectively controlled and connected with the pressure sensor I and the pressure sensor III; the spray liquid inlet pipe II is provided with a regulating valve IV and a flowmeter II, and the regulating valve IV is controlled and connected with the flowmeter II.

[0024] A control method for the aforementioned scrubbing control system, wherein all the synthesis gas in the trichlorosilane synthesis tower is connected to the large scrubbing tower and the small scrubbing tower respectively through a synthesis gas main pipe, and a pressure sensor 1 is provided on the synthesis gas main pipe.

[0025] a. Pressure sensor I, located on the syngas main, and pressure sensor II, located in the middle of the small scrubber, collect the inlet and mid-tower pressure signals, respectively, and upload these signals to the DCS. The DCS processes the received signals and determines the real-time liquid level in the small scrubber based on the difference between the inlet and mid-tower pressures. This level is then compared with the preset level.

[0026] When the real-time liquid level is equal to the preset liquid level value, the regulating valve I on the steam inlet pipe I is not opened;

[0027] When the real-time liquid level is lower than the preset level, the regulating valve I on the steam inlet pipe I is not opened. At the same time, the DCS sends a flow increase signal to the flow meter I and controls the opening of the regulating valve II connected to the flow meter I. The adjusted pressure signal is then returned to the DCS for comparison again until the real-time liquid level reaches the preset level. At the same time, the flow meter I uploads the flow signal to the DCS, which controls the opening of the regulating valve II connected to the flow meter I. When the flow signal uploaded by the flow meter I reaches 120% of the load of the design value of the flow meter I, the system switches to the large scrubber.

[0028] When the real-time liquid level is higher than the preset liquid level value, the DCS sends a signal to the control valve I to increase the steam pressure and adjust the opening of the control valve I. The adjusted pressure signal is then returned to the DCS for comparison again until the real-time liquid level is equal to the preset liquid level value.

[0029] b. The pressure sensor I set on the syngas main and the pressure sensor III in the middle of the large scrubber collect the inlet pressure signal and the pressure signal in the middle of the tower respectively, and upload the pressure signal to the DCS. The DCS processes the received signal and determines the real-time liquid level in the large scrubber, and then compares the real-time liquid level with the preset liquid level value;

[0030] When the real-time liquid level is equal to the preset liquid level value, the regulating valve III on the steam inlet pipe II is not opened;

[0031] When the real-time liquid level is lower than the preset level, the regulating valve III on the steam inlet pipe II will not be opened. At the same time, the DCS will send a flow increase signal to the flow meter II and adjust the opening of the regulating valve IV connected to the flow meter II. The adjusted pressure signal will be returned to the DCS for comparison again until the real-time liquid level is equal to the preset level. At the same time, the flow meter II will upload the flow signal to the DCS, and the DCS will adjust the opening of the regulating valve II connected to the flow meter II.

[0032] When the real-time liquid level is higher than the preset liquid level value, the DCS sends a signal to the control valve III to increase the steam pressure and control the opening of the control valve III. The adjusted pressure signal is then returned to the DCS for comparison again until the real-time liquid level equals the preset liquid level value. If the control valve on the steam inlet pipe II is fully open and the liquid level in the large scrubber is still too high, the small scrubber is switched to scrub the synthesis gas.

[0033] Furthermore, a shut-off valve III is provided on the discharge pipeline I of the small washing tower, and a shut-off valve IV is provided on the slag discharge pipeline I of the small washing tower; a shut-off valve V is provided on the discharge pipeline II of the large washing tower, and a shut-off valve VI is provided on the slag discharge pipeline II of the large washing tower.

[0034] The method of switching from a small scrubber to a large scrubber is:

[0035] I. Replenish the large scrubber through the spray liquid inlet pipe II;

[0036] II and then open the shut-off valve II on the inlet line connected to the large scrubber I, and then open the shut-off valve V on the discharge line connected to the large scrubber II;

[0037] III and then close the small washing tower connected to the spray liquid inlet pipe I on the regulating valve II, stop replenishing the small washing tower;

[0038] IV. Close the shut-off valve I on the air inlet line I connected to the small washing tower, then close the shut-off valve III on the discharge line I connected to the small washing tower, and periodically open the shut-off valve VI on the slag discharge line II to discharge the slag.

[0039] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0040] First, this invention proposes an optimized trichlorosilane synthesis gas scrubbing method suitable for both high and low loads. This method utilizes a scrubbing unit comprising a large scrubber and a small scrubber connected in parallel. When all of the trichlorosilane synthesis furnaces connected to the scrubbing unit are operating, the large scrubber can be activated to process the synthesis gas. When only a small number (e.g., half or less) of the trichlorosilane synthesis furnaces are operating, the small scrubber can be activated to process the synthesis gas. This minimizes scrubber blockage and incomplete scrubbing caused by a mismatch between the scrubber's actual gas processing capacity and its rated design capacity. This solution results in low metallic impurities in the resulting product liquid, potentially as low as 10 ppbw or less.

[0041] 2. In the present invention, in order to reduce the equipment investment cost and the equipment occupied area in actual production, a set of trichlorosilane synthesis furnaces connected to one washing unit may be as large as 4 to 5 trichlorosilane synthesis furnaces. Even if two sizes of washing towers, large and small, are provided for selection, it is still easy for the actual gas processing capacity of the equipment to not match the designed rated processing capacity, resulting in clogging of the washing tower or incomplete washing. Without adding washing towers of other sizes, a steam jacket is provided on the outside of the large and small washing towers. Of course, steam jackets can also be provided on some washing towers according to actual needs to increase the heat load, ensure the washing effect, and ensure that the tower tray is not blocked; the silicon powder, metal chloride and high boiling point discharged from the washing tower are discharged from the system in a timely manner to achieve effective separation from the product liquid.

[0042] 3. The present invention also proposes a structurally optimized washing tower. By optimizing the material inlet components, tower trays and other structures in the washing tower, impurities such as silicon powder and metal chlorides in the synthesis gas can be effectively washed away, and the impurities can be discharged from the system through the slag discharge pipeline of the tower kettle to the slurry treatment system for further treatment, thereby avoiding scaling and clogging of the equipment.

[0043] 4. The present invention also proposes a better control system and control method. By detecting the pressure on the synthesis gas main pipe and the pressure in the middle of the large and small washing towers, and judging the liquid level of the fluid in the tower by the pressure difference between the two places, the valve opening on the corresponding steam inlet pipe of the washing tower and the valve opening on the spray liquid inlet pipe are adjusted according to the liquid level in the tower, or the large and small washing towers are switched, so that the real-time liquid level in the tower matches the liquid level at the design value, thereby achieving the expected treatment effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic diagram of the system structure of Example 1.

[0045] Figure 2 It is a schematic diagram of the system structure of another embodiment.

[0046] Figure 3It is a schematic diagram of the system structure of another embodiment.

[0047] Figure 4 It is a structural diagram of the washing tower.

[0048] Figure 5 It is a structural schematic diagram of a washing tower in another preferred embodiment.

[0049] Figure 6 yes Figure 5 Magnified view of part A.

[0050] Figure 7 It is a schematic diagram of a tower plate structure provided with guide holes and guide plates.

[0051] Figure 8 It is a structural schematic diagram of a washing tower in another preferred embodiment.

[0052] Figure 9 It is a structural diagram of the scrubbing control system of trichlorosilane synthesis gas.

[0053] Figure 10 This is a schematic structural diagram of the washing system in Comparative Example 1.

[0054] Among them, 1. trichlorosilane synthesis furnace; 2. condenser; 3. regeneration hydrogen system; 4. product liquid storage tank; 5. large scrubber; 6. small scrubber; 7. slurry treatment unit; 8. tower body; 9. DCS; 10. discharge pipeline I; 11. spray liquid inlet pipe I; 12. air inlet pipeline I; 13. slag discharge pipeline I; 14. steam inlet pipe I; 15. shut-off valve I; 16. pressure sensor I; 17. regulating valve I; 18. pressure sensor II; 19. regulating valve II; 20. flow meter I; 21. discharge pipeline II; 22. spray liquid inlet pipe II; 23. air inlet pipeline II; 24. slag discharge pipeline II; 2 5. Steam inlet pipe II; 26. Shut-off valve II; 27. Pressure sensor III; 28. Control valve III; 29. ​​Synthesis gas main; 30. Control valve IV; 31. Flowmeter II; 32. Shut-off valve III; 33. Shut-off valve IV; 34. Shut-off valve V; 35. Shut-off valve VI; 36. Jacket; 37. Pump; 7.1. Slurry buffer tank; 8.1. Air inlet; 8.2. Gas distributor; 8.3. Pup joint; 8.4. Tower tray; 8.5. Sieve hole; 8.6. Bubble breaker; 8.7. Packing layer; 8.8. Inclined plate; 8.9. Vertical plate; 8.10. Guide hole; 8.11. Guide plate. DETAILED DESCRIPTION

[0055] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0056] Example 1

[0057] This embodiment is the most basic implementation method, which is a trichlorosilane synthesis gas washing method applicable to high and low loads, belonging to the technical field of trichlorosilane synthesis. The synthesis gas discharged from the top of at least two trichlorosilane synthesis furnaces 1 is sent to a set of washing units for washing.

[0058] refer to Figure 1 This solution is further illustrated by taking a system in which the synthesis gas discharged from the tops of two trichlorosilane synthesis furnaces 1 is sent to a set of scrubbing units for scrubbing as an example. The scrubbing unit includes a large scrubber 5 and a small scrubber 6 connected in parallel. The processing capacity of the large scrubber 5 is sufficient to scrub the gas generated when two trichlorosilane synthesis furnaces 1 are operating simultaneously, while the small scrubber 6 is sufficient to scrub the gas generated when one trichlorosilane synthesis furnace 1 is operating. When the scrubbing unit is operating, either the large scrubber 5 or the small scrubber 6 is selectively activated.

[0059] The gas phase obtained after treatment in the washing unit is sent to the condenser 2 through the pipeline at the top of the washing unit for treatment, and the non-condensable gas obtained after condensation treatment is sent to the regeneration hydrogen system 3 of the recovery process;

[0060] The liquid phase obtained after condensation treatment is collected into product liquid storage tank 4 for standby use;

[0061] The slurry obtained after being processed by the washing unit is discharged from the lower part of the washing unit to the slurry processing unit 7 for further processing.

[0062] Example 2

[0063] This embodiment is another preferred embodiment, which is a further optimization of embodiment 1. Figure 2 In this embodiment, a structure in which a washing unit is connected to four trichlorosilane synthesis furnaces 1 is taken as an example to further illustrate this solution.

[0064] Among them, the processing capacity of the small washing tower 6 can meet the washing of gas generated when two trichlorosilane synthesis furnaces 1 connected to the small washing tower 6 are running at the same time, and the large washing tower 5 can meet the washing of gas generated when four trichlorosilane synthesis furnaces 1 are running at the same time.

[0065] Example 3

[0066] The difference between this embodiment and embodiment 1-2 is that, Figure 3 The large washing tower 5 and the small washing tower 6 are provided with a jacket 36 for passing steam outside.

[0067] When the gas volume entering the scrubbing unit from the front trichlorosilane synthesis furnace 1 is small and matches the load of the small scrubbing tower 6 at 60% to 120%, the small scrubbing tower 6 is started and the large scrubbing tower 5 is shut down; if it is less than 60% of the load of the small scrubbing tower 6, steam is passed into the jacket 36 of the small scrubbing tower 6 to keep the load of the small scrubbing tower 6 between 60% and 120%;

[0068] When the gas volume entering the scrubbing unit from the front trichlorosilane synthesis furnace 1 is large and exceeds 120% of the load of the small scrubbing tower 6 without steam being introduced, the large scrubbing tower 5 is started and the small scrubbing tower 6 is shut down. If the large scrubbing tower 5 is operating at a load of 60% to 120%, there is no need to introduce steam into the jacket 36 of the large scrubbing tower 5. If the load is lower than 60%, steam needs to be introduced into the jacket 36 of the large scrubbing tower 5 to achieve the minimum normal operating load of the large scrubbing tower 5.

[0069] Of course, it is also possible to provide a steam-permeable jacket 36 on some of the scrubbing towers (small scrubbing tower 6 or large scrubbing tower 5) according to actual production needs, such as the number of trichlorosilane synthesis furnaces connected.

[0070] Example 4

[0071] The difference between this embodiment and embodiments 1-3 is that the large washing tower 5 and the small washing tower 6 both include a tower body 8, which is a hollow cylinder. Figure 4 The lower part of the tower body 8 is provided with an air inlet 8.1, connected to the air inlet 8.1 and extending into the interior of the tower body 8. The gas distributor 8.2 is provided with a plurality of short sections 8.3 with downward openings. The middle and upper part of the tower body 8 is provided with a plurality of tower trays 8.4, each having sieve holes 8.5 distributed on the tower trays 8.4. The aperture of the sieve holes 8.5 on the lower tower tray 8.4 is larger than the aperture of the sieve holes 8.5 on the upper tower tray 8.4. A bubble breaker 8.6 is provided above the gas distributor 8.2.

[0072] In this embodiment, a gas distributor 8.2 is used, extending into the interior of the tower body 8. Gas distributor 8.2 is equipped with several downwardly opening short sections 8.3. Alternatively, several downwardly opening holes may be directly provided in gas distributor 8.2. This disperses a large airflow into several smaller streams, increasing the gas-liquid contact area. Furthermore, the mixed gas entering the tower body 8 first fully contacts the slurry at the bottom of the tower in a "bubbling" state, providing preliminary scrubbing and cooling of the process gas. This removes more impurities such as silicon powder and metal chlorides, reduces the amount of impurities entering the tower body 8 between trays 8.4, and minimizes the chance of clogging trays 8.4. Furthermore, metal chlorides and chlorosilanes are prone to scaling when not flowing or flowing too slowly. Since the lower gas phase contains more impurities, the probability of clogging is greater. Therefore, the sieve holes 8.5 on the lower tray 8.4 are designed to have a larger diameter than the sieve holes 8.5 on the upper tray 8.4, minimizing the chance of clogging.

[0073] Using the large scrubber 5 and small scrubber 6 of the tower body 8 structure of this embodiment, with only one trichlorosilane synthesis furnace in operation, the small scrubber 6 had an operating cycle of 140 days (i.e., blockage first occurred on the 140th day); with only two trichlorosilane synthesis furnaces in operation, the small scrubber 6 had an operating cycle of 180 days (i.e., blockage first occurred on the 180th day); with three trichlorosilane synthesis furnaces in operation simultaneously, the large scrubber 6 had an operating cycle of 190 days; and with four trichlorosilane synthesis furnaces in operation simultaneously, the large scrubber 6 had an operating cycle of 210 days. It was found that the arched area of ​​the upper tray of the scrubber first developed significant scaling. The resulting product liquid after treatment contained metallic impurities at or below 1500 ppbw.

[0074] Example 5

[0075] Compared with Examples 1-4, this embodiment differs in that the tower tray 8.4 inside the tower body 8 is divided into tower trays 8.4 with multiple levels of aperture. According to the specifications of the designed washing tower, the tower trays 8.4 with multiple levels of aperture can be designed. The apertures of the tower trays 8.4 at the same level are equal, and the aperture of the tower tray 8.4 at the lower level is larger than the aperture of the sieve hole 8.5 on the tower tray 8.4 at the upper level.

[0076] Example 6

[0077] The difference between this embodiment and embodiments 1-5 is that, Figure 5 A packing layer 8.7 is provided above the tower tray 8.4 at the top of the tower body 8.

[0078] Example 7

[0079] The difference between this embodiment and embodiment 1-6 is that, Figure 5-6 The outlet weir of the tower tray 8.4 is an inclined plate 8.8, and the tail of the inclined plate 8.8 is connected to a vertical plate 8.9.

[0080] Preferably, the angle between the inclined plate 8.8 and the tower tray 8.4 is ɵ, and the washing effect is better when the angle ɵ is in the range of 90°<ɵ≤150°.

[0081] Example 8

[0082] The difference between this embodiment and embodiments 1-7 is that the arcuate area of ​​the tray 8.4 is provided with guide holes 8.10 and / or guide plates 8.11, which can effectively prevent the arcuate area from being blocked.

[0083] refer to Figure 7 The arcuate area of ​​the tower plate 8.4 is provided with a guide hole 8.10 and a guide plate 8.11.

[0084] In actual applications, "blank" areas where fluid flows are likely to appear on both sides of tray 8.4. That is, the amount of fluid flowing through the two sides is very small, which can easily form "flow dead zones" and thus easily cause scaling. In this embodiment, guide plates are provided on both sides of the flow channel of tray 8.4 to guide the fluid to both sides, so that the fluid at all positions on tray 8.4 flows, avoiding the formation of "flow dead zones" and solving the scaling problem.

[0085] The large scrubber 5 and small scrubber 6 of the tower body 8 structure of this embodiment were tested. The only difference between this test tower and the scrubber used in Example 4 was that the arched areas of the trays 8.4 of the large scrubber 5 and small scrubber 6 were equipped with guide holes 8.10 and guide plates 8.11. When only one trichlorosilane synthesis furnace was in operation, the small scrubber 6 had an operating cycle of 180 days (i.e., blockage first occurred on the 180th day); when only two trichlorosilane synthesis furnaces were in operation, the small scrubber 6 had an operating cycle of 220 days (i.e., blockage first occurred on the 220th day); when three trichlorosilane synthesis furnaces were in operation simultaneously, the large scrubber 6 had an operating cycle of 230 days; and when four trichlorosilane synthesis furnaces were in operation simultaneously, the large scrubber 6 had an operating cycle of 260 days. It was found that scaling was relatively uniform across all areas of the scrubber's upper trays, and the metallic impurity content in the resulting product liquid after treatment was controlled to 1000 ppbw or less.

[0086] Example 9

[0087] This embodiment provides a preferred embodiment of the washing tower structure. Compared with Examples 4-8, the difference is that, with reference to the attached Figure 6 、 7 , 8, including tower body 8,

[0088] The tower body 8 is a hollow cylinder with an air inlet 8.1 provided at its lower portion. Connected to the air inlet 8.1 is a gas distributor 8.2 extending into the interior of the tower body 8. The gas distributor 8.2 is provided with a number of short sections 8.3 with downwardly facing openings. A number of trays 8.4 are provided in the upper and middle portion of the tower body 8. Each tray has sieve holes 8.5 distributed thereon. The sieve holes 8.5 on the lower tray 8.4 have a larger aperture than the sieve holes 8.5 on the upper tray 8.4. A bubble breaker 8.6 is provided above the gas distributor 8.2.

[0089] In this embodiment, the trays 8.4 inside the tower body 8 are divided into five levels of aperture trays 8.4, such as Figure 8In the tower body 8, there are 12 layers of tower trays 8.4 from bottom to top. The bottom two layers of tower trays 8.4 are preferably provided with sieve holes 8.5 of 20-25 mm. The 3rd to 4th layers of tower trays 8.4 from bottom to top are provided with sieve holes 8.5 of 18 mm, the 5th to 6th layers of tower trays 8.4 are provided with sieve holes 8.5 of 16 mm, and the 7th to 12th layers of tower trays 8.4 are all provided with sieve holes 8.5 of 12 mm. A packing layer 8.7 is provided above the tower tray 8.4 at the top of the tower body 8 to further reduce the metal chloride content of the product.

[0090] The outlet weir of tray 8.4 is formed by an inclined plate 8.8, with a vertical plate 8.9 connected to its rear end. The angle between inclined plate 8.8 and tray 8.4 is 120°. The arcuate area of ​​tray 8.4 is equipped with guide holes 8.10 and guide plates 8.11. These guide holes 8.10 and guide plates 8.11 align with the direction of liquid flow, allowing gas passing through sieve holes 8.5 to propel liquid flow and reduce the possibility of blockage in the arcuate area.

[0091] Example 10

[0092] This embodiment is based on the aforementioned trichlorosilane synthesis gas scrubbing method, applicable to both high and low loads, and a control system designed to match it. This scheme is further illustrated using a trichlorosilane synthesis production line of our company as an example. This trichlorosilane synthesis gas scrubbing control system, applicable to both high and low loads, includes a DCS 9, along with a large, high-throughput scrubber 5 and a small, low-throughput scrubber 6 connected in parallel. These large and small scrubbers 5 and 6 are collectively connected to four trichlorosilane synthesis furnaces 1.

[0093] refer to Figure 9 The small washing tower 6 is connected to a discharge pipeline I10, a spray liquid inlet pipe I11, an air intake pipeline I12, a slag discharge pipeline I13 and a steam inlet pipe I14. The air intake pipeline I12 is provided with a shut-off valve I15, and the steam inlet pipe I14 is provided with a regulating valve I17. A pressure sensor II18 is provided in the middle of the small washing tower 6, and the regulating valve I17 is respectively controlled and connected with the pressure sensor I16 and the pressure sensor II18; the spray liquid inlet pipe I11 is provided with a regulating valve II19 and a flow meter I20, and the regulating valve II19 is controlled and connected with the flow meter I20;

[0094] The large washing tower 5 is connected to a discharge pipeline II21, a spray liquid inlet pipe II22, an air intake pipeline II23, a slag discharge pipeline II24 and a steam inlet pipe II25. The air intake pipeline II23 is provided with a shut-off valve II26, and the steam inlet pipe II25 is provided with a regulating valve III28. A pressure sensor III27 is provided in the middle of the large washing tower 5, and the regulating valve III28 is controlled and connected to the pressure sensor III27 respectively; the spray liquid inlet pipe II22 is provided with a regulating valve IV30 and a flowmeter II31, and the regulating valve IV30 is controlled and connected to the flowmeter II31.

[0095] Furthermore, a shut-off valve III32 is provided on the discharge pipeline I10 of the small washing tower 6, and a shut-off valve IV33 is provided on the slag discharge pipeline I13 of the small washing tower 6; a shut-off valve V34 is provided on the discharge pipeline II21 of the large washing tower 5, and a shut-off valve VI35 is provided on the slag discharge pipeline II24 of the large washing tower 5.

[0096] In this embodiment, the large washing tower 5 and the small washing tower 6 are selected from the anti-blocking washing towers with the better structure in Example 9. Figure 6-8 The tower body 8 comprises a hollow cylindrical structure with an air inlet 8.1 at its lower portion. Connected to air inlet 8.1 is a gas distributor 8.2 extending into the tower body 8. Gas distributor 8.2 is provided with several downwardly opening short sections 8.3. A plurality of trays 8.4 are provided in the upper and middle portion of the tower body 8. Each tray 8.4 has sieve holes 8.5. The sieve holes 8.5 on the lower trays 8.4 have larger diameters than those on the upper trays 8.4. A bubble breaker 8.6 is provided above the gas distributor 8.2. The trays 8.4 within the tower body 8 have multiple apertures. A packing layer 8.7 is provided above the top tray 8.4 within the tower body 8. The outlet weir of each tray 8.4 is an inclined plate 8.8, forming a 120° angle with the trays 8.4. The arcuate area of ​​the tray 8.4 in this embodiment is provided with guide holes 8.10 and guide plates 8.11.

[0097] Furthermore, a control method for a trichlorosilane synthesis gas scrubbing control system applicable to high and low loads comprises the following steps:

[0098] The synthesis gas in all the trichlorosilane synthesis towers is connected to the large scrubber 5 and the small scrubber 6 respectively through the synthesis gas main pipe 29. The synthesis gas main pipe 29 is provided with a pressure sensor 116.

[0099] a. The pressure sensor I16 provided on the synthesis gas main pipe 29 and the pressure sensor II18 in the middle of the small scrubber 6 respectively collect the inlet pressure signal and the pressure signal in the middle of the small scrubber 6, and upload the pressure signal to the DCS9. The DCS9 processes the received signal and determines the real-time liquid level in the small scrubber 6 based on the difference between the inlet pressure and the middle pressure of the tower, and then compares the real-time liquid level with the preset liquid level value.

[0100] When the real-time liquid level is equal to the preset liquid level value, the regulating valve I17 on the steam inlet pipe I14 is not opened;

[0101] When the real-time liquid level is lower than the preset liquid level value, the regulating valve I17 on the steam inlet pipe I14 is not opened. At the same time, the DCS9 sends a signal to the flow meter I20 to increase the flow rate and controls the opening of the regulating valve II19 connected to the flow meter I20. The adjusted pressure signal is then returned to the DCS9 for comparison again until the real-time liquid level equals the preset liquid level value. At the same time, the flow meter I20 uploads the flow signal to the DCS9, which controls the opening of the regulating valve II19 connected to the flow meter I20. When the flow signal uploaded by the flow meter I20 reaches 120% of the load of the design value of the flow meter I20, the system switches to the large scrubber 5.

[0102] When the real-time liquid level is higher than the preset liquid level value, DCS9 sends a signal to the control valve I17 to increase the steam pressure and adjust the opening of the control valve I17. The adjusted pressure signal is then returned to DCS9 for comparison again until the real-time liquid level is equal to the preset liquid level value.

[0103] b. The pressure sensor I16 provided on the synthesis gas main pipe 29 and the pressure sensor III27 in the middle of the large scrubber 5 respectively collect the inlet pressure signal and the pressure signal in the middle of the scrubber 5, and upload the pressure signal to the DCS9. The DCS9 processes the received signal and determines the real-time liquid level in the large scrubber 5, and then compares the real-time liquid level with the preset liquid level value.

[0104] When the real-time liquid level is equal to the preset liquid level value, the regulating valve III28 on the steam inlet pipe II25 is not opened;

[0105] When the real-time liquid level is lower than the preset liquid level value, the regulating valve III28 on the steam inlet pipe II25 is not opened. At the same time, the DCS9 sends a signal to the flow meter II31 to increase the flow rate and adjusts the opening of the regulating valve IV30 connected to the flow meter II31. The adjusted pressure signal is then returned to the DCS9 for comparison again until the real-time liquid level equals the preset liquid level value. At the same time, the flow meter II31 uploads the flow signal to the DCS9, and the DCS9 adjusts the opening of the regulating valve II19 connected to the flow meter II31.

[0106] When the real-time liquid level is higher than the preset liquid level value, DCS9 sends a signal to the regulating valve III28 to increase the steam pressure and controls the opening of the regulating valve III28. The adjusted pressure signal is then returned to DCS9 for comparison again until the real-time liquid level equals the preset liquid level value. If the regulating valve on the steam inlet pipe II25 is fully open and the liquid level in the large scrubber 5 is still too high, the small scrubber 6 is switched to scrub the synthesis gas.

[0107] The method of switching from the small scrubbing tower 6 to the large scrubbing tower 5 is as follows:

[0108] I. replenishing the large scrubber 5 through the spray liquid inlet pipe II22;

[0109] II then open the shut-off valve II26 on the inlet line I12 of the large scrubber 5, and then open the shut-off valve V34 on the discharge line II21 of the large scrubber 5;

[0110] III and then close the small washing tower 6 connected to the spray liquid inlet pipe I11 regulating valve II19 on the stop to the small washing tower 6 replenishment;

[0111] IV and then close the shut-off valve I15 on the inlet line I12 connected to the small washing tower 6, after closing the shut-off valve III32 on the discharge line I10 connected to the small washing tower 6, and regularly open the shut-off valve VI35 on the slag discharge line II24 for slag discharge,

[0112] The method of switching from the large scrubbing tower 5 to the small scrubbing tower 6 is similar to the above method.

[0113] Comparative Example 1

[0114] This comparative example is a washing unit previously used by our company, that is, a large washing tower with the same structure as in Example 9 is connected to the same four trichlorosilane synthesis furnaces. Figure 10 , other equipment is the same as Example 9.

[0115] Comparative Example 2

[0116] The difference between this comparative example and comparative example 1 is that the large scrubber before optimization is used, and the specifications of the large scrubber are the same as those in comparative example 1, that is, the gas processing capacity of the equipment is the same.

[0117] The large washing tower in this comparative example is different from that in Example 9 in that a gas inlet pipe is provided in the tower body, and a plurality of tower plates are provided in the middle and upper part of the tower body. Sieve holes of the same size and a diameter of 12 mm are evenly distributed on the tower plates. No guide holes or guide plates are provided in the arched area of ​​the tower plates, and the outlet weir of the tower plates is a vertical plate.

[0118] test

[0119] 1. Select monitoring points on the slag discharge pipelines of Examples 2, 3, and 10, and Comparative Examples 1-2, and detect the metal impurity content of the fluid at the monitoring points, or sample the slurry buffer tank connected at the rear end to detect its metal impurity content, and simultaneously detect the metal impurity content in the product tank. The changes in the metal impurity content at each monitoring point when 1, 2, 3, and 4 trichlorosilane synthesis towers are respectively operated in each embodiment are investigated.

[0120] In addition, the scrubber operation period (i.e., the time when the scrubber first becomes clogged) during the treatment of high-temperature trichlorosilane synthesis gas containing chlorosilane, hydrogen, silicon powder, metal chloride, and high-boiling substances in each embodiment was examined. The results are shown in Table 1.

[0121] Table 1

[0122]

[0123] According to the aforementioned embodiments and Table 1, Embodiment 2 is a scheme in which only one small washing tower 6 of the original structure is added to the original scheme, and the original equipment is still used. This scheme can reduce the impurity content in the product liquid from 10,000 ppbw to 5,000 ppbw. The investment cost of the equipment is relatively small, but the continuous operation cycle of the equipment is relatively short. Compared with the original system process, the equipment operation cycle is significantly improved when only a small number (1 to 2) trichlorosilane synthesis towers are in operation.

[0124] Example 3 is a further optimization of the system of Example 2. Steam jackets 36 are provided on the large scrubber 5 and the small scrubber 6. This further improves the mismatch between the actual operating load and the designed operating load of the scrubbers, further controls the impurity content in the product liquid to around 1000 ppbw, and significantly increases the continuous operation cycle of the scrubbers. Regardless of how many trichlorosilane synthesis towers are in operation, the continuous operation cycle can reach more than 120 days.

[0125] Example 9, based on Example 3, utilizes a preferred scrubber structure. This optimized scrubber features improvements to the air inlet 8.1 and tray 8.4, along with the addition of a packing layer 8.7 and a bubble breaker 8.6. This significantly improves scrubbing efficiency, reducing impurity levels in the product liquid to 10 ppbw or below. However, the significant component changes and the use of packing layer 8.7 result in a relatively high capital investment. Furthermore, guide holes 8.10 and guide plates 8.11 are incorporated into tray 8.4, significantly improving scaling in the bowed area of ​​tray 8.4 and significantly extending the equipment's continuous operation cycle.

[0126] Comparative Examples 1 and 2 show that replacing the original scrubber with the optimized one significantly reduces the impurity content in the product liquid and significantly extends the equipment's continuous operation cycle, even without adding a small scrubber 6. However, the maintenance cost of the optimized scrubber is significantly higher than that of the original scrubber. When only one or two trichlorosilane synthesis towers are in operation, the scrubber's continuous operation time is only 320 to 400 days. The investment costs due to material and component replacement and cleaning are also relatively high.

[0127] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for washing trichlorosilane synthesis gas applicable to high and low loads, characterized in that: The synthesis gas discharged from the top of at least two trichlorosilane synthesis furnaces (1) is sent to a scrubbing unit for scrubbing. The gas phase obtained after the scrubbing unit treatment is sent to a condenser (2) through a pipeline at the top of the scrubbing unit for treatment. The non-condensable gas obtained after the condensation treatment is sent to a regeneration hydrogen system (3) of a recovery process. The liquid phase obtained after condensation is collected into the product liquid storage tank (4) for future use; The slurry obtained after being processed by the washing unit is discharged from the lower part of the washing unit to the slurry processing unit (7) for processing; The scrubbing unit comprises a large scrubbing tower (5) and a small scrubbing tower (6) connected in parallel. When the scrubbing unit is in operation, either the large scrubbing tower (5) or the small scrubbing tower (6) is selectively opened. The processing capacity of the large scrubbing tower (5) is sufficient to scrub the gas generated when all trichlorosilane synthesis furnaces (1) connected to the large scrubbing tower (5) are in operation simultaneously. The processing capacity of the small washing tower (6) is sufficient to wash the gas generated when half the number of trichlorosilane synthesis furnaces (1) connected to the small washing tower (6) are in operation simultaneously.

2. The washing method according to claim 1, wherein: The large washing tower (5) and the small washing tower (6) are provided with a jacket (36) for passing steam outside. When the amount of gas entering the scrubbing unit from the front trichlorosilane synthesis furnace (1) is small and matches the load of the small scrubbing tower (6) between 60% and 120%, the small scrubbing tower (6) is started and the large scrubbing tower (5) is shut down; if it is lower than 60% of the load of the small scrubbing tower (6), steam is passed through the jacket (36) of the small scrubbing tower (6) to keep the load of the small scrubbing tower (6) between 60% and 120%; When the gas volume entering the scrubbing unit from the front trichlorosilane synthesis furnace (1) is large, and exceeds 120% of the load of the small scrubbing tower (6) without introducing steam, the large scrubbing tower (5) is started and the small scrubbing tower (6) is closed. If the large scrubbing tower (5) is operating at a load of 60% to 120%, it is not necessary to introduce steam into the jacket (36) of the large scrubbing tower (5); if the load is lower than 60%, it is necessary to introduce steam into the jacket (36) of the large scrubbing tower (5) to achieve the minimum normal operating load of the large scrubbing tower (5).

3. The washing method according to claim 1, wherein: The large scrubbing tower (5) and the small scrubbing tower (6) both include a tower body (8), the tower body (8) being a hollow cylinder, an air inlet (8.1) being provided at the lower portion of the tower body (8), a gas distributor (8.2) extending into the interior of the tower body (8) being connected to the air inlet (8.1), the gas distributor (8.2) being provided with a plurality of short sections (8.3) with downward openings, a plurality of tower trays (8.4) being provided at the middle and upper portion of the tower body (8), sieve holes (8.5) being distributed on the tower trays (8.4), the aperture of the sieve holes (8.5) on the lower tower tray (8.4) being larger than the aperture of the sieve holes (8.5) on the upper tower tray (8.4), guide plates being provided on both sides of the flow channel of the tower tray (8.4), and a bubble breaker (8.6) being provided above the gas distributor (8.2).

4. The washing method according to claim 3, wherein: The tower tray (8.4) inside the tower body (8) is divided into tower trays (8.4) with multiple levels of aperture.

5. The washing method according to claim 3, wherein: A packing layer (8.7) is provided above the tower tray (8.4) at the top of the tower body (8).

6. The washing method according to claim 3, wherein: The outlet weir of the tower tray (8.4) is an inclined plate (8.8), and the tail of the inclined plate (8.8) is connected to a vertical plate (8.9).

7. The washing method according to claim 6, wherein: The angle between the inclined plate (8.8) and the tower tray (8.4) is ɵ, 90°<ɵ≤150°.

8. The washing method according to claim 3, wherein: The arcuate area of ​​the tower tray (8.4) is provided with guide holes (8.10) and / or guide plates (8.11).

9. A scrubbing control system for trichlorosilane synthesis gas applicable to high and low loads, characterized by: The invention comprises a DCS (9), a large washing tower (5) with a high processing capacity and a small washing tower (6) with a low processing capacity connected in parallel, wherein the small washing tower (6) is connected with a discharge pipeline I (10), a spray liquid inlet pipe I (11), an air inlet pipe I (12), a slag discharge pipeline I (13) and a steam inlet pipe I (14), wherein the air inlet pipe I (12) is provided with a shut-off valve I (15), and the steam inlet pipe I (14) is provided with a regulating valve I (17). A pressure sensor II (18) is provided in the middle of the small washing tower (6), and the regulating valve I (17) is respectively connected to the pressure sensor I (16) and the pressure sensor II (18) for control; the spray liquid inlet pipe I (11) is provided with a regulating valve II (19) and a flow meter I (20), and the regulating valve II (19) is connected to the flow meter I (20) for control; The large washing tower (5) is connected to a discharge pipeline II (21), a spray liquid inlet pipe II (22), an air inlet pipe II (23), a slag discharge pipeline II (24) and a steam inlet pipe II (25). A shut-off valve II (26) is provided on the air inlet pipe II (23). A regulating valve III (28) is provided on the steam inlet pipe II (25). A pressure sensor III (27) is provided in the middle of the large washing tower (5). The regulating valve III (28) is control-connected to the pressure sensor I (16) and the pressure sensor III (27) respectively. The spray liquid inlet pipe II (22) is provided with a regulating valve IV (30) and a flow meter II (31). The regulating valve IV (30) is control-connected to the flow meter II (31). The processing capacity of the large scrubber (5) is sufficient to scrub the gas generated when all trichlorosilane synthesis furnaces (1) connected to the large scrubber (5) are in operation simultaneously; The processing capacity of the small washing tower (6) is sufficient to wash the gas generated when half the number of trichlorosilane synthesis furnaces (1) connected to the small washing tower (6) are in operation simultaneously.

10. A control method of a washing control system according to claim 9, characterized in that: The synthesis gas in all trichlorosilane synthesis towers is connected to the large scrubber (5) and the small scrubber (6) through the synthesis gas main pipe (29). The synthesis gas main pipe (29) is provided with a pressure sensor I (16). a. The pressure sensor I (16) provided on the synthesis gas main pipe (29) and the pressure sensor II (18) provided in the middle of the small washing tower (6) respectively collect the inlet pressure signal and the pressure signal of the middle part of the small washing tower (6), and upload the pressure signals to the DCS (9). The DCS (9) processes the received signals, determines the real-time liquid level in the small washing tower (6) based on the difference between the inlet pressure and the middle part of the tower pressure, and then compares the real-time liquid level with the preset liquid level value; When the real-time liquid level is equal to the preset liquid level value, the regulating valve I (17) on the steam inlet pipe I (14) is not opened; When the real-time liquid level is lower than the preset liquid level value, the regulating valve I (17) on the steam inlet pipe I (14) is not opened, and at the same time, the DCS (9) sends a signal to the flow meter I (20) to increase the flow rate, and controls the opening of the regulating valve II (19) connected to the control of the flow meter I (20). The pressure signal after adjustment is returned to the DCS (9) and compared again until the real-time liquid level is equal to the preset liquid level value; at the same time, the flow meter I (20) uploads the flow signal to the DCS (9), and the DCS (9) controls the opening of the regulating valve II (19) connected to the control of the flow meter I (20). When the flow signal uploaded by the flow meter I (20) reaches 120% of the load of the design value of the flow meter I (20), the flow is switched to the large washing tower (5); When the real-time liquid level is higher than the preset liquid level value, the DCS (9) sends a signal to the regulating valve I (17) to increase the steam pressure and controls the opening of the regulating valve I (17). The pressure signal after the adjustment is returned to the DCS (9) and compared again until the real-time liquid level is equal to the preset liquid level value. b. The pressure sensor I (16) provided on the synthesis gas main pipe (29) and the pressure sensor III (27) in the middle of the large scrubber (5) are used to collect the inlet pressure signal and the pressure signal in the middle of the scrubber (5), respectively, and the pressure signals are uploaded to the DCS (9). The DCS (9) processes the received signals and determines the real-time liquid level in the large scrubber (5), and then compares the real-time liquid level with the preset liquid level value; When the real-time liquid level is equal to the preset liquid level value, the regulating valve III (28) on the steam inlet pipe II (25) is not opened; When the real-time liquid level is lower than the preset liquid level value, the regulating valve III (28) on the steam inlet pipe II (25) is not opened, and at the same time, the DCS (9) sends a signal to increase the flow rate to the flow meter II (31), and controls and adjusts the opening of the regulating valve IV (30) connected to the control of the flow meter II (31). The pressure signal after adjustment is returned to the DCS (9) and compared again until the real-time liquid level is equal to the preset liquid level value; at the same time, the flow meter II (31) uploads the flow signal to the DCS (9), and the DCS (9) controls and adjusts the opening of the regulating valve II (19) connected to the control of the flow meter II (31); When the real-time liquid level is higher than the preset liquid level value, the DCS (9) sends a signal to the regulating valve III (28) to increase the steam pressure and controls the opening of the regulating valve III (28). The pressure signal after adjustment is returned to the DCS (9) and compared again until the real-time liquid level is equal to the preset liquid level value. If the regulating valve on the steam inlet pipe II (25) is fully opened and the liquid level in the large scrubber (5) is still too high, the small scrubber (6) is switched to scrub the synthesis gas.

11. The control method according to claim 10, characterized in that: The discharge pipeline I (10) of the small washing tower (6) is provided with a shut-off valve III (32), and the slag discharge pipeline I (13) of the small washing tower (6) is provided with a shut-off valve IV (33); the discharge pipeline II (21) of the large washing tower (5) is provided with a shut-off valve V (34), and the slag discharge pipeline II (24) of the large washing tower (5) is provided with a shut-off valve VI (35). The method of switching from the small scrubber (6) to the large scrubber (5) is as follows: I. replenishing the large scrubber (5) through the spray liquid inlet pipe II (22); II. Then open the shut-off valve II (26) on the inlet pipeline I (12) connected to the large scrubber (5), and then open the shut-off valve V (34) on the discharge pipeline II (21) connected to the large scrubber (5); III. Then close the regulating valve II (19) on the spray liquid inlet pipe I (11) connected to the small washing tower (6), and stop replenishing the liquid to the small washing tower (6); IV. Then close the shut-off valve I (15) on the air inlet pipeline I (12) connected to the small washing tower (6), and then close the shut-off valve III (32) on the discharge pipeline I (10) connected to the small washing tower (6), and periodically open the shut-off valve VI (35) on the slag discharge pipeline II (24) to discharge the slag.

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