CN212731614U

CN212731614U - High-efficient solvent regeneration system

Info

Publication number: CN212731614U
Application number: CN202020837864.XU
Authority: CN
Inventors: 徐国栋; 高春海; 毛文茂
Original assignee: SHANDONG CHANGYI PETROCHEMICAL CO Ltd
Current assignee: SHANDONG CHANGYI PETROCHEMICAL CO Ltd
Priority date: 2020-05-19
Filing date: 2020-05-19
Publication date: 2021-03-19
Anticipated expiration: 2030-05-19

Abstract

The utility model discloses a high-efficient solvent regeneration system, including the dry gas desulfurizing tower, the rich solution that the dry gas desulfurizing tower produced communicates the rich solution flash tank through the rich solution pipeline, and the rich solution flash tank communicates the regenerator through the poor rich solution pipeline, and the rich solution pipeline communicates with the feed liquor end of rich solution one-level heat exchanger and rich solution second grade heat exchanger respectively, the lean solution pipeline of regenerator lower part respectively with the heat source import intercommunication of poor rich solution heat exchanger, rich solution one-level heat exchanger and rich solution second grade heat exchanger, and the play liquid end of rich solution one-level heat exchanger is through first branch roadAnd a rich liquid pipeline communicated to the liquid outlet end of the rich liquid secondary heat exchanger, wherein a primary cold and hot flow regulating valve is arranged on the rich liquid pipeline between the rich liquid primary heat exchanger and the rich liquid secondary heat exchanger, and a gate valve is arranged on the first branch. The utility model discloses realize improving and get into flash tank rich liquid heat transfer back final temperature, reinforcing CO₂The flash evaporation effect is realized, and the purity of the acid gas is improved; the load of the regeneration tower is reduced, the steam consumption is reduced, and the cost is reduced; the cooling load is reduced, and the energy consumption of the device is reduced.

Description

High-efficient solvent regeneration system

Technical Field

The utility model relates to a high-efficient solvent regeneration system.

Background

The sulfur-containing dry gas comes from a heavy oil catalytic cracking device under the conditions of 43 ℃ and 1.0MPa, enters a dry gas separating tank to remove liquid drops and mechanical impurities carried by the sulfur-containing dry gas, then enters a dry gas desulfurization tower to be in countercurrent contact with an N-methyl-di-ethanolamine solvent pumped into the top of the tower by a solvent circulating pump, and H in the dry gas₂S is absorbed by the solvent. Ethanol amine absorbs H₂S rate is superior to CO₂However, when the hydrogen sulfide concentration of the absorbed gas is reduced to the ppm level, the excess carbon dioxide is absorbed. CO in dry gas before desulfurization of DCC device₂The average content of the sulfur is 5 percent, and CO in the desulfurized dry gas₂The content is reduced to 0.02 percent. And (3) enabling rich liquid from the bottom of the dry gas desulfurization tower to enter a rich liquid flash tank, enabling gas obtained by flash evaporation to enter the upper part of the packing section to be in countercurrent contact with the lean liquid, and enabling flash hydrocarbon to enter a flare pipe network from the top of the packing section through a pressure regulating valve under the condition that the pressure is 0.25 MPa. The flashed rich solution is pumped out by a rich solution solvent pump, heated by a lean rich solution first-stage heat exchanger and then enters a regeneration tower for regeneration, and the heat required by the regeneration is provided by a reboiler at the bottom of the regeneration tower. The temperature of the rich liquid flash tank can be maximally increased to 65 ℃ under the old process condition, and CO is increased at the temperature₂Is not flashed off but instead follows the rich liquid into the regenerator column. The regeneration temperature is about 120 ℃, and the absorbed H before this time₂S、CO₂Is desorbed (released), whereby the ethanolamine solution itself is regenerated. Final CO₂The acid gas enters the acid gas, so that the purity of the acid gas is only about 70 percent. At the same partial pressure, the temperature increases, H₂S、CO₂All equilibrium solubilities of (A) are reduced, and CO₂The solubility decreases more rapidly, thus increasing the temperature, CO₂Ratio H₂S is more likely to precipitate.

Disclosure of Invention

The to-be-solved technical problem of the utility model is to provide a high-efficient solvent regeneration system to realize improving the final temperature after getting into the rich liquid heat transfer of flash tank, reinforcing CO₂The flash evaporation effect is realized, and the purity of the acid gas is improved to 93 percent; the load of the regeneration tower is reduced, the steam consumption at the bottom of the regeneration tower is reduced, and the production cost is reduced; reduceThe temperature of the air-cooling barren solution is reduced, the cooling load is reduced, and the energy consumption of the device is reduced.

In order to solve the technical problem, the utility model comprises a dry gas desulfurization tower, wherein rich solution generated by the dry gas desulfurization tower is communicated to a rich solution flash tank through a rich solution pipeline at the bottom of the dry gas desulfurization tower, the lower part of the rich solution flash tank is communicated to a regeneration tower through a poor and rich solution pipeline, a poor and rich solution heat exchanger is arranged on the poor and rich solution pipeline, and the lower part of the regeneration tower is communicated to a solvent buffer tank through a poor solution pipeline, which is characterized in that a rich solution primary heat exchanger and a rich solution secondary heat exchanger are sequentially arranged on the rich solution pipeline, the rich solution pipeline is respectively communicated with the liquid inlet ends of the rich solution primary heat exchanger and the rich solution secondary heat exchanger, the lean solution pipeline is respectively communicated with the heat source inlets of the poor and rich solution primary heat exchangers and the rich solution secondary heat exchanger, the liquid outlet end of the rich solution primary heat exchanger is communicated with the rich solution pipeline of the liquid outlet end of the rich, and a primary cold and hot flow regulating valve is arranged on a rich liquid pipeline between the rich liquid primary heat exchanger and the rich liquid secondary heat exchanger, and a gate valve is arranged on the first branch.

After the structure is adopted, because the highest temperature in the rich liquid flash tank is 65 ℃, the temperature of the rich liquid flowing into the rich liquid flash tank is also lower than 65 ℃, carbon dioxide in the rich liquid cannot be flashed away, because the poor liquid with the temperature of 125 ℃ and the pressure of 0.15MPa is generated at the bottom of the regeneration tower, the poor liquid flows into a poor liquid pipeline, the heat in the poor liquid is directly discharged, the working pressure of the subsequent process is increased, and the waste of the heat is caused, so the poor liquid sequentially flows into a poor liquid heat exchanger, a rich liquid primary heat exchanger and a rich liquid secondary heat exchanger on the poor liquid pipeline for heat exchange, the poor liquid is used as a heat source for heating the liquid flowing into the poor liquid heat exchanger, the rich liquid primary heat exchanger and the rich liquid secondary heat exchanger, the heat in the poor liquid is recovered, the energy consumption is reduced, the rich liquid in the rich liquid pipeline flows into the rich liquid primary heat exchanger and the rich liquid secondary heat exchanger and then, reduction of CO in rich liquor₂The solubility of the acid gas is improved, the flash evaporation effect of the rich solution is improved, the purity of the acid gas is effectively improved to more than 93 percent, and the content of inert gas is reduced; reduce the load of the regeneration tower, reduce the steam consumption at the bottom of the regeneration tower and reduceThe production cost is low; simultaneously contributes to increasing H of the sulfur device₂The mass transfer coefficient of S in the tower improves the desulfurization efficiency and reduces the energy consumption; the primary cold and hot flow regulating valve can control the flow according to the temperature of the rich liquid, so that the rich liquid entering the flash tank can be accurately controlled to reach the final temperature of 80-85 ℃; when the temperature of the rich liquid reaches the standard, the primary cold and hot flow regulating valve reduces the flow, the gate valve of the branch is opened, and the rich liquid can be directly conveyed to the rich liquid flash tank through the branch without secondary heating; when the temperature of the rich liquid does not reach the standard, the primary cold and hot flow regulating valve increases the flow, the gate valve of the branch is closed, and the rich liquid is heated by the primary rich liquid heat exchanger and then by the secondary rich liquid heat exchanger, so that the rich liquid entering the flash tank is heated to 80-85 ℃ finally; the lean liquid pipeline is sequentially communicated with the lean-rich liquid heat exchanger, the rich liquid primary heat exchanger and the rich liquid secondary heat exchanger, namely part of heat of the lean liquid is conveyed to the lean-rich liquid heat exchanger, the rich liquid primary heat exchanger and the rich liquid secondary heat exchanger, so that part of heat of the lean liquid is recovered, meanwhile, the temperature of the air-cooled lean liquid is reduced, the cooling load is reduced, and the energy consumption of the device is reduced.

Gate valves are arranged on the lean-rich liquid pipelines at the liquid inlet end and the liquid outlet end of the lean-rich liquid heat exchanger, second branches are connected in parallel on the lean-rich liquid pipelines at the liquid inlet end and the liquid outlet end of the lean-rich liquid heat exchanger, and the second branches are provided with second-stage cold and hot flow regulating valves. When the temperature difference between the temperature of the lean and rich liquid and the temperature inside the regeneration tower is large, the secondary cold and hot flow regulating valve on the second branch is closed, the gate valve on the lean and rich liquid pipeline is opened, the lean and rich liquid flows into the lean and rich liquid heat exchanger for heat exchange, namely, part of heat in the lean liquid generated by the regeneration tower is transferred into the lean and rich liquid, so that the initial temperature of the lean and rich liquid entering the regeneration tower is increased, the steam consumption of the regeneration tower is reduced, the energy is saved, meanwhile, the heat in the lean liquid generated by the regeneration tower is reused, the temperature of the air-cooled lean liquid is reduced, the cooling load is reduced, and the energy consumption of a device is reduced; when the temperature difference between the temperature of the lean and rich liquid and the temperature inside the regeneration tower is small, the secondary cold and hot flow regulating valve on the second branch is opened, the gate valve on the lean and rich liquid pipeline is closed, the lean and rich liquid is directly sent into the regeneration tower for reaction, and the influence of overhigh temperature of the lean and rich liquid on the regeneration reaction in the regeneration tower is avoided.

The upper portion of rich liquid flash tank pass through the return gas pipeline with the upper portion of dry gas desulfurizing tower intercommunication, on the return gas pipeline parallelly connected have two with dry gas desulfurizing tower intercommunication third branch road and fourth branch road, the third branch road with the fourth branch road all is equipped with the gate valve. The positions of the gas return pipeline, the third branch and the fourth branch communicated with the dry gas desulfurization tower are different, so that the feeding position of the dry gas desulfurization tower can be flexibly adjusted, and the absorption rate of carbon dioxide is reduced.

Drawings

The invention will be further explained with reference to the following figures and examples:

FIG. 1 is a schematic diagram of a prior art configuration;

fig. 2 is a schematic structural diagram of the present invention.

In the figure: 1-a dry gas liquid separation tank, 2-a dry gas desulfurization tower, 3-a dry gas amine liquid recoverer, 4-a rich liquid flash tank, 5-a rich liquid pipeline, 6-a rich liquid filter, 7-a rich liquid primary heat exchanger, 8-a rich liquid secondary heat exchanger, 9-a lean rich liquid pipeline, 10-a regeneration tower, 11-a rich solvent pump, 12-a lean liquid heat exchanger, 13-a primary cold and hot flow regulating valve, 14-a secondary cold and hot flow regulating valve, 15-a gate valve, 16-a gas return pipeline, 17-a lean liquid pipeline, 18-a first branch, 19-a second branch, 20-a lean liquid pressurizing pump, 21-a lean liquid air cooler, 22-a lean liquid cooler, 23-a circulation pipeline, 24-a circulation pump solvent, 25-a third branch and 26-a fourth branch, 27-solvent buffer tank.

Detailed Description

In order to clearly understand the design concept and the embodiments based on the design concept of the present invention, it is necessary to briefly introduce the existing solvent regeneration system before describing the embodiments of the present invention. Referring to fig. 1, sulfur-containing dry gas enters a dry gas liquid separation tank 1 to remove liquid drops and mechanical impurities carried by the sulfur-containing dry gas from a heavy oil catalytic cracking device under the conditions of 43 ℃ and 1.0MPa, then enters the lower part of a dry gas desulfurization tower 2 to be in countercurrent contact with N-methyl-di-ethanolamine solvent pumped into the tower top by a solvent circulating pump 24, and H in the dry gas₂S is absorbed by the solvent. Removal of H₂Dry to dry gas amine of SThe liquid recoverer 3 separates the carried solvent through gravity settling and a wire mesh demister. The dry gas is sent out to a dry gas pipe network through an adjusting valve. The rich liquid from the bottom of the dry gas desulfurization tower 2 enters a rich liquid filter 6 after passing through a liquid level regulating valve, the filtered rich liquid enters a rich liquid flash tank 4, the flashed gas enters the upper part of the packing section and is in countercurrent contact with the lean liquid, and the flashed hydrocarbon enters a flare pipe network from the top of the packing section through a pressure regulating valve under the condition of 0.25MPa of pressure. The flashed rich solution is pumped out by a rich solution solvent pump, heated by a lean rich solution heat exchanger 12 and then enters a regeneration tower 10 through a regulating valve for regeneration, and the heat required by the regeneration is provided by a reboiler at the bottom of the regeneration tower 10. The solvent semi-barren solution is led out from the bottom of the tower at about 120 ℃ and is heated by a reboiler to be vaporized and then returns to the regeneration tower 10. The barren liquor from the bottom of the regeneration tower 10 is introduced into a barren and rich liquor heat exchanger 12 at 125 ℃ and 0.15MPa, then is pressurized by a barren liquor pressurizing pump 20, is cooled by a barren liquor air cooler 21 and a barren liquor cooler 22, is sent to a solvent buffer tank 27, and is sent to a dry gas desulfurization tower 2 by a solvent circulating pump 24 for recycling. Ethanol amine absorbs H₂S rate is superior to CO₂But when absorbing H of the gas₂After the S concentration is reduced to the ppm level, the excess CO₂It is absorbed. CO in dry gas before desulfurization of DCC device₂The average content of the sulfur is 5 percent, and CO in the desulfurized dry gas₂The content is reduced to 0.02 percent. The temperature of the rich liquor flash tank 4 under old process conditions can be raised to 65 ℃ at the maximum. At this temperature CO₂And is not flashed off but instead follows the rich liquid into the regenerator column 10. The regeneration temperature is about 120 ℃, and the absorbed H before this time₂S、CO₂Is desorbed (released), whereby the ethanolamine solution itself is regenerated. Final CO₂The acid gas enters the acid gas, so that the purity of the acid gas is only about 70 percent. At the same partial pressure, the temperature increases, H₂S、CO₂All equilibrium solubilities of (A) are reduced, and CO₂The solubility decreases more rapidly, thus increasing the temperature, CO₂Ratio H₂S is more likely to precipitate.

In order to solve the technical problem, referring to fig. 2, the high-efficiency solvent regeneration system comprises a dry gas liquid separation tank 1 (model: V3202), wherein the gas outlet end of the dry gas liquid separation tank 1 is communicated to the middle lower part of a dry gas desulfurization tower 2 (model: T3202) through a pipeline,the dry gas desulfurization tower 2 is communicated with a dry gas amine liquid recoverer 3 through a gas outlet pipeline to remove H₂The method comprises the following steps that (1) dry gas enters a dry gas amine liquid recoverer 3 (model: V3204) and passes through a gravity settling and wire mesh demister, the dry gas is sent out of a dry gas pipe network through a regulating valve, rich liquid generated by a dry gas desulfurization tower 2 is communicated with a rich liquid flash tank 4 through a rich liquid pipeline 5 at the bottom of the dry gas desulfurization tower 2, a rich liquid filter 6, a rich liquid primary heat exchanger 7 and a rich liquid secondary heat exchanger 8 are sequentially arranged on the rich liquid pipeline 5, the rich liquid pipeline 5 is respectively communicated with liquid inlet ends of the rich liquid primary heat exchanger 7 and the rich liquid secondary heat exchanger 8, a liquid outlet end of the rich liquid primary heat exchanger 7 is communicated with the rich liquid pipeline 5 at a liquid outlet end of the rich liquid secondary heat exchanger 8 through a first branch 18, a primary cold and hot flow regulating valve 13 is arranged on the rich liquid pipeline 5 between the rich liquid primary heat exchanger 7 and the rich liquid secondary heat; the upper part of the rich liquid flash tank 4 is communicated with the upper part of the dry gas desulfurization tower 2 through a gas return pipeline 16, the flashed gas enters the upper part of the packing section, the flashed hydrocarbon is sent into a flare pipe network through a pressure regulating valve under the condition of 0.25MPa pressure from the top of the packing section, the lower part of the rich liquid flash tank 4 is communicated with the regeneration tower 10 through a lean rich liquid pipeline 9, namely, the generated lean rich liquid flows into the regeneration tower 10 from the rich liquid flash tank 4, a rich solvent pump 11 and a lean rich liquid heat exchanger 12 are arranged on the lean rich liquid pipeline 9, gate valves 15 are arranged on the lean rich liquid pipelines 9 at the liquid inlet end and the liquid outlet end of the lean rich liquid heat exchanger 12, a second branch 19 is connected in parallel to the lean rich liquid pipelines 9 at the liquid inlet end and the liquid outlet end of the lean rich liquid heat exchanger 12, and a second cold and hot flow regulating. The second branch 19 is provided with a secondary cold and hot flow regulating valve 14; when the temperature difference between the temperature of the lean and rich liquid and the temperature inside the regeneration tower 10 is large, the secondary cold and hot flow regulating valve 14 on the second branch 19 is closed, the gate valve 15 on the lean and rich liquid pipeline 9 is opened, the lean and rich liquid flows into the lean and rich liquid heat exchanger 12 for heat exchange, namely, part of heat in the lean liquid generated by the regeneration tower is transferred into the lean and rich liquid, so that the initial temperature of the lean and rich liquid entering the regeneration tower is increased, the steam consumption of the regeneration tower is reduced, the energy is saved, meanwhile, the heat in the lean liquid generated by the regeneration tower is reused, the temperature of the air-cooled lean liquid is reduced, the cooling load is reduced, and the energy consumption of the device is reduced; when the temperature of the lean and rich liquid is equal to that of the interior of the regeneration tower 10When the temperature difference of the temperature is small, the secondary cold and hot flow regulating valve 14 on the second branch 19 is opened, the gate valve 15 on the lean and rich liquid pipeline 9 is closed, the lean and rich liquid is directly sent into the regeneration tower for reaction, and the influence of overhigh temperature of the lean and rich liquid on the regeneration reaction in the regeneration tower is avoided; the lower part of the regeneration tower 10 is communicated with a solvent buffer tank 27 through a lean liquid pipeline 17, the lean liquid pipeline 17 is respectively communicated with heat source inlets of a lean-rich liquid heat exchanger 12, a rich liquid primary heat exchanger 7 and a rich liquid secondary heat exchanger 8, a lean liquid booster pump 20, a lean liquid air cooler 21 and a lean liquid cooler 22 are sequentially arranged on the lean liquid pipeline 17 between the rich liquid secondary heat exchanger 8 and the solvent buffer tank 27, the lean liquid booster pump 20 can provide power for the transportation of lean liquid, the lean liquid air cooler 21 and the lean liquid cooler 22 can reduce the temperature of the lean liquid, the solvent buffer tank 27 is communicated with a gas return pipeline 16 through a circulation pipeline 23, a solvent circulating pump 24 is arranged on the circulation pipeline 23, two third branches 25 and four branches 26 communicated with a dry gas desulfurization tower 2 are connected on the gas return pipeline 16 in parallel, gate valves 15 are arranged on the third branches 25 and the fourth branches 26, and the positions of the gas return pipeline 16, the third branches 25 and the fourth branches 26 communicated with the dry gas desulfurization tower 2 are different, can realize nimble adjustment 2 feed position of dry gas desulfurizing tower, reduce the carbon dioxide absorptivity.

When the utility model is used, the highest temperature in the rich liquid flash tank 4 is 65 ℃, the temperature of the rich liquid flowing into the rich liquid flash tank 4 is also lower than 65 ℃, so that the carbon dioxide in the rich liquid can not be flashed away; because the lean solution with the temperature of 125 ℃ and the pressure of 0.15MPa is generated at the bottom of the regeneration tower 10, the lean solution flows into the lean solution pipeline 17, the heat in the lean solution is directly discharged to increase the working pressure of the subsequent process and cause heat waste, namely the working pressure of the lean solution air cooler 21 and the lean solution cooler 22 is increased and the energy consumption is wasted, therefore, the lean solution sequentially flows into the lean and rich solution heat exchanger 12, the rich solution primary heat exchanger 7 and the rich solution secondary heat exchanger 8 on the lean solution pipeline 17 for heat exchange, the lean solution is used as a heat source for heating the liquid flowing into the lean and rich solution heat exchanger 12, the rich solution primary heat exchanger 7 and the rich solution secondary heat exchanger 8, the heat in the lean solution is recovered, the energy consumption is reduced, the rich solution in the rich solution pipeline 5 flows into the rich solution primary heat exchanger 7 and the rich solution secondary heat exchanger 8 and is heated, the rich solution after the temperatureCO in low-richness liquid₂The solubility of the acid gas is improved, the flash evaporation effect of the rich solution is improved, the purity of the acid gas is effectively improved to more than 93 percent, and the content of inert gas is reduced; the load of the regeneration tower 10 is reduced, the steam consumption at the bottom of the regeneration tower 10 is reduced, and the production cost is reduced; simultaneously contributes to increasing H of the sulfur device₂The mass transfer coefficient of S in the tower improves the desulfurization efficiency and reduces the energy consumption; the primary cold and hot flow regulating valve 13 can control the flow according to the temperature of the rich liquid, so that the rich liquid entering the flash tank can be accurately controlled to reach the final temperature of 80-85 ℃; when the temperature of the rich liquid reaches the standard, the primary cold and hot flow regulating valve 13 reduces the flow, the gate valve 15 of the branch is opened, and the rich liquid can be directly conveyed to the rich liquid flash tank 4 through the branch without secondary heating; when the temperature of the rich liquid does not reach the standard, the primary cold and hot flow regulating valve 13 increases the flow, the gate valve 15 of the branch is closed, the rich liquid is heated by the primary rich liquid heat exchanger 7 and then heated by the secondary rich liquid heat exchanger 8, and the rich liquid entering the flash tank is heated to the final temperature of 80-85 ℃; the barren liquor pipeline 17 is sequentially communicated with the barren liquor and rich liquor heat exchanger 12, the rich liquor primary heat exchanger 7 and the rich liquor secondary heat exchanger 8, namely, part of heat of barren liquor is conveyed to the barren liquor and rich liquor heat exchanger 12, the rich liquor primary heat exchanger 7 and the rich liquor secondary heat exchanger 8, part of heat of barren liquor is recovered, meanwhile, the temperature of air-cooled barren liquor is reduced, the cooling load is reduced, and the energy consumption of the device is reduced.

Claims

1. The utility model provides a high-efficient solvent regeneration system, includes dry gas desulfurizing tower (2), and the rich liquor that dry gas desulfurizing tower (2) produced communicates rich liquor flash tank (4) through rich liquor pipeline (5) of dry gas desulfurizing tower (2) bottom, and the lower part of rich liquor flash tank (4) communicates regenerator column (10) through lean rich liquor pipeline (9), and be equipped with lean rich liquor heat exchanger (12) on lean rich liquor pipeline (9), and the lower part of regenerator column (10) communicates solvent buffer tank (27) through lean liquor pipeline (17), its characterized in that: the liquid-enriched air conditioner is characterized in that a rich liquid primary heat exchanger (7) and a rich liquid secondary heat exchanger (8) are sequentially arranged on the rich liquid pipeline (5), the rich liquid pipeline (5) is respectively communicated with liquid inlet ends of the rich liquid primary heat exchanger (7) and the rich liquid secondary heat exchanger (8), the lean liquid pipeline (17) is respectively communicated with heat source inlets of the lean and rich liquid heat exchanger (12), the rich liquid primary heat exchanger (7) and the rich liquid secondary heat exchanger (8), a liquid outlet end of the rich liquid primary heat exchanger (7) is communicated with the rich liquid pipeline (5) at a liquid outlet end of the rich liquid secondary heat exchanger (8) through a first branch (18), a primary cold and hot flow regulating valve (13) is arranged on the rich liquid pipeline (5) between the rich liquid primary heat exchanger (7) and the rich liquid secondary heat exchanger (8), and a gate valve (15) is arranged on the first branch (18).

2. The high efficiency solvent regeneration system of claim 1, wherein: the liquid inlet end and the liquid outlet end of the lean and rich liquid heat exchanger (12) are respectively provided with a gate valve (15) on the lean and rich liquid pipeline (9), the liquid inlet end and the liquid outlet end of the lean and rich liquid heat exchanger (12) are connected with a second branch (19) in parallel on the lean and rich liquid pipeline (9), and the second branch (19) is provided with a second-stage cold and hot flow regulating valve (14).

3. The high efficiency solvent regeneration system of claim 1, wherein: the upper portion of the rich liquid flash tank (4) is communicated with the upper portion of the dry gas desulfurization tower (2) through a gas return pipeline (16), the gas return pipeline (16) is connected with a third branch (25) and a fourth branch (26) which are communicated with the dry gas desulfurization tower (2) in parallel, and the third branch (25) and the fourth branch (26) are both provided with gate valves (15).