A new acrylic acid reaction gas separation system

Abstract

The present application relates to a kind of new acrylic acid reaction gas separation systems, the product gas of the present application is first cooled by primary cooling system, then enters initial fractionating column and is separated, the raw material propylene in initial fractionating column top is cold source, most of acrylic acid in product gas is condensed in initial fractionating column and then enters azeotrope column from bottom, and the remaining product gas in initial fractionating column top enters absorption tower, and is washed and absorbed using desalted water, and acrylic acid absorbing liquid enters azeotrope column from bottom;The present application uses product gas primary cooling system to efficiently recover the heat in acrylic acid product gas, not only increases the preheating temperature of fresh air, but also greatly improves the energy utilization rate of device;Initial fractionating column top condenser uses raw material propylene as cold source to further condense and separate product gas, propylene provides lower temperature level, and most of acrylic acid product is condensed and recovered in initial fractionating column, so that the gas amount in subsequent absorption tower and waste gas treatment device is greatly reduced, and wastewater volume is reduced.

Description

Technical Field

[0001] This invention relates to the field of acrylic acid production technology, specifically to a novel acrylic acid reaction gas separation system. Background Technology

[0002] Acrylic acid, as an important organic chemical raw material, is widely used in the production of adhesives and water-soluble coatings. It plays an important role in fields such as chemical fibers, papermaking, leather, building materials, plastic modification, synthetic rubber, and radiation-cured water treatment agents. It can also be further processed into butyl acrylate, etc.

[0003] Acrylic acid has gone through an era where various preparation methods coexisted. Acrylonitrile hydrolysis, high-pressure Ryp process (high-pressure carbonyl synthesis), modified Ryp process (low-pressure carbonyl synthesis), cyanoethanol process, and ketene process were all major methods for producing acrylic acid and its esters. However, these methods have been largely phased out due to severe equipment corrosion, high energy consumption, low yield, and high cost. Currently, the most commonly used method for producing acrylic acid is the propylene oxidation process. In the propylene oxidation process for producing acrylic acid, the current method for product gas separation generally involves directly feeding the product gas from the acrylic acid plant into a quench tower after passing it through a byproduct low-pressure steam. A quench absorption system with a circulating cooling solution is installed at the bottom of the quench tower. Circulating acetic acid wastewater or fresh demineralized water is used as the absorbent to absorb and separate the acrylic acid product gas. The crude acrylic acid liquid at the bottom of the quench tower enters an azeotropic tower for azeotropic separation. The tail gas at the top of the tower is partially recycled back to the reaction system after oxidation treatment, and partially discharged. For example, Chinese patents CN103193618B and CN10260036B, although differing in their waste gas treatment methods, both employ fresh demineralized water for rapid absorption of the initially cooled acrylic acid product gas. Part of the absorbed tail gas is recycled, and the remainder is treated and sent to the incineration system. Both utilize fresh demineralized water for reabsorption to reduce the organic content in the rapidly cooled acrylic acid tail gas, followed by pressurized recirculation of a portion of the tail gas. This technology suffers from high fresh water consumption and large wastewater volumes during subsequent separation processes. Patent CN105001072B uses a three-in-one absorption tower with circulating acetic acid-containing wastewater as the rapid absorption agent. The tail gas at the top of the tower undergoes catalytic oxidation waste gas treatment, with part compressed and returned to the reaction system, and the remainder emitted. It recycles the acetic acid wastewater as the rapid absorption agent for the acrylic acid product gas, and all the tail gas at the top of the rapid cooling tower is sent to the waste gas treatment system. This not only consumes a large amount of waste gas treatment catalyst but also results in high carbon emissions.

[0004] In the aforementioned mainstream acrylic acid product gas separation technologies, the high temperature of the acrylic acid product gas entering the quench tower means that the bottom liquid circulation quenching method does not efficiently recover the medium- and low-temperature waste heat from the product gas. Furthermore, the large volume of product gas in the quench tower and its high separation temperature necessitate the consumption of a significant amount of fresh demineralized water to ensure acrylic acid recovery and reduce the organic matter content in the acrylic acid tail gas after quenching. Therefore, current mainstream acrylic acid product gas separation technologies suffer from problems such as large wastewater and waste gas treatment volumes and low energy utilization efficiency.

[0005] Therefore, the current separation system for acrylic acid reaction gas needs further optimization. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a novel acrylic acid reaction gas separation system that can improve energy utilization by efficiently recovering the heat of acrylic acid product gas, reduce the amount of fresh demineralized water, the consumption of waste gas treatment catalyst and wastewater by low-temperature condensation and separation of product gas, and reduce steam consumption by absorbing the heat of product gas to complete the raw material vaporization process.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] A novel acrylic acid reaction gas separation system includes:

[0009] The reaction system produces acrylic acid gas.

[0010] A primary cooling system, located downstream of the reaction system, is used to recover energy from the acrylic acid gas produced by the reaction system and to preheat the air; the primary cooling system has a first outlet for returning the gaseous propylene obtained after energy recovery to the reaction system and a second outlet for outputting the obtained product gas.

[0011] The primary separation tower is located downstream of the primary cooling system and is used to condense and separate the product gas. It has an inlet at the bottom for product gas input to the second outlet of the primary cooling system and a first outlet for liquid phase output, and a second outlet at the top for gas phase output.

[0012] An azeotropic column, located downstream of the primary separation column and connected to the first output port of the primary separation column, is used for azeotropic distillation separation of acrylic acid solution. The bottom of the column has an output port for inputting the obtained crude acrylic acid solution.

[0013] An acrylic acid refining system, located downstream of the azeotropic tower and connected to its bottom outlet, is used to refine propylene to obtain acrylic acid products; and

[0014] An absorption tower, located downstream of the primary separator and connected to its second outlet, is used to wash and absorb the residual gas after condensation and separation in the primary separator. A pipeline is installed at the top of the tower to transport a portion of the purified circulating tail gas to the reaction system as circulating gas. The proportion of acrylic acid tail gas recycled as circulating gas is 0.5% to 60.0%.

[0015] Preferably, the upper part of the primary fractionation column is provided with a condensation structure using propylene as the cold source. The primary fractionation column is a distillation column with a condenser, and a condensation section is provided at the top of the distillation column, in which the condensation structure is located. The operating pressure of the primary fractionation column is 0.01–0.2 MPaG; the theoretical number of plates in the primary fractionation column is 5–20.

[0016] Preferably, the primary cooling system includes an air preheater, a hot water heat exchanger, a propylene superheater, and a circulating water cooler connected in series. One inlet of the air preheater is connected to the acrylic acid gas outlet of the reaction system, and the outlet of the circulating water cooler constitutes the second outlet of the primary cooling system and is connected to the primary separation tower.

[0017] Preferably, the air preheater has an inlet on one side for supplying fresh raw material air and an outlet on the other side for supplying preheated fresh raw material air to the reaction system. The operating temperature of the product gas outlet in the air preheater is 140–220°C.

[0018] Preferably, one side of the propylene superheater is connected to the top of the primary separation tower, providing an opening for the input of vaporized propylene, while the other side has a first outlet of the primary cooling system. The operating temperature of the product gas side outlet of the propylene superheater is 50–90°C.

[0019] Preferably, the circulating gas delivery pipeline is equipped with a circulating gas compressor for pressurizing the circulating gas.

[0020] Preferably, the top of the absorption tower is provided with a gas supply pipeline for transporting another portion of the purified circulating tail gas to the waste gas treatment system. Optionally, the downstream pipeline of the waste gas treatment system is provided with a cross-line pipeline for transporting a portion of the purified gas to the circulating gas. The flow rate of the cross-line pipeline is controlled between 0.5% and 60.0% (the flow rate of the cross-line pipeline accounts for 0.5% to 60.0% of the total tail gas flow rate after passing through the waste gas treatment system) to control the organic matter content in the circulating gas.

[0021] Preferably, it also includes a condenser and a reflux tank connected in series at the top of the azeotropic tower, for heterogeneous separation of the material at the top of the azeotropic tower, so that the separated azeotropic agent is returned to the azeotropic tower, the acetic acid-containing wastewater is discharged, and the waste gas is sent to the flare system.

[0022] Preferably, a reboiler is provided at the bottom of the azeotropic column.

[0023] Preferably, the air preheater uses compressed fresh raw material air as the heat exchange medium, the warm water heat exchanger uses warm water as the heat exchange medium, the propylene superheater uses vaporized propylene as the heat exchange medium, and the circulating water cooler uses circulating water as the heat exchange medium to sequentially recover energy from the acrylic acid product gas.

[0024] Preferably, the warm water heat exchanger recovers energy from the heat in the middle section of the product gas, and the preheated warm water is used for heat preservation and tracing of the device. The operating temperature of the product gas side outlet of the warm water heat exchanger is 60-100℃. The operating temperature of the product gas side outlet of the circulating water cooler is 30-50℃.

[0025] Preferably, the absorption tower uses fresh demineralized water as the absorbent to wash and absorb the gas at the top of the initial separation tower, and the liquid-to-gas ratio of fresh demineralized water to circulating tail gas in the absorption tower is 0.01 to 0.1; the operating pressure of the absorption tower is 0.01 to 0.2 MPaG.

[0026] Compared with the prior art, the advantages of this invention are as follows: The product gas of this invention is first cooled by a primary cooling system, and then enters the primary separation tower for separation. The top of the primary separation tower uses the raw material propylene as a cold source. Most of the acrylic acid in the product gas is condensed in the primary separation tower and enters the azeotropic tower from the bottom of the tower. The remaining product gas in the top of the primary separation tower enters the absorption tower, where it is washed and absorbed using demineralized water. The acrylic acid absorbent enters the azeotropic tower from the bottom of the tower. Specifically:

[0027] This invention employs a product gas pre-cooling system to efficiently recover heat from the acrylic acid product gas. This not only increases the preheating temperature of fresh air but also supplies the waste heat from the product gas to the production operation of the warm water system, greatly improving the energy utilization rate of the equipment. The top condenser of the pre-separation tower uses raw material propylene as a cold source to further condense and separate the product gas. Propylene provides a lower temperature, which is more conducive to the absorption of acrylic acid and organic matter. Most of the acrylic acid product is condensed and recovered in the pre-separation tower, which greatly reduces the amount of gas in the subsequent absorption tower and waste gas treatment device, reducing the consumption of fresh demineralized water and waste gas treatment catalyst, and reducing wastewater volume. The raw material liquid propylene absorbs heat from the product gas in the pre-separation tower condenser to complete the vaporization process, replacing the original propylene evaporator, reducing steam consumption, and greatly increasing the economic efficiency of the production equipment.

[0028] This invention employs a product gas primary cooling system and a primary separation tower. Different heat exchange media are used to recover heat from different sections of the product gas based on their temperature levels, thereby improving the energy utilization efficiency of the waste heat. In the primary separation tower, propylene is used as the condenser cold source, which not only lowers the condensation temperature of the product gas and increases the recovery rate of acrylic acid, but also effectively reduces the gas volume in the absorption tower and waste gas treatment system. Therefore, the consumption of fresh demineralized water and waste gas treatment catalyst is effectively reduced, greatly improving the economic and environmental benefits of the device. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention;

[0030] Figure 2 This is a process flow diagram of Embodiment 2 of the present invention;

[0031] Figure 3 This is a process flow diagram of Embodiment 3 of the present invention;

[0032] Figure 4 This is a process flow diagram of Embodiment 4 of the present invention. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0034] Example 1:

[0035] like Figure 1 As shown, the novel acrylic acid reaction gas separation system of this embodiment includes:

[0036] Reaction system 1 produces acrylic acid gas.

[0037] The primary cooling system 2 is located downstream of the reaction system 1 and is used to recover energy from the acrylic acid gas produced by the reaction system 1 and to preheat the air. The primary cooling system 2 has a first outlet for returning the gaseous propylene obtained after energy recovery to the reaction system 1 and a second outlet for outputting the obtained product gas.

[0038] The primary separation tower 3 is located downstream of the primary cooling system 2 and is used to condense and separate the product gas. It has an inlet at the bottom for the product gas to enter the second outlet of the primary cooling system and a first outlet for the liquid phase to exit, and a second outlet at the top for the gas phase to exit.

[0039] Azeotropic column 7 is located downstream of primary column 3 and connected to the first outlet of primary column 3. It is used for azeotropic distillation separation of acrylic acid solution. The bottom of the column has an outlet for input of the obtained crude acrylic acid solution.

[0040] Acrylic acid refining system 12, located downstream of azeotropic tower 7 and connected to its bottom outlet, is used to refine propylene to obtain acrylic acid products; and

[0041] Absorption tower 4, located downstream of primary separator 3 and connected to the second outlet of primary separator 3, is used to wash and absorb the residual gas after condensation and separation in primary separator 3. A pipeline is installed at the top of the tower to transport a portion of the purified circulating tail gas to the reaction system as circulating gas. The proportion of acrylic acid tail gas recycled as circulating gas is 0.5% to 60.0%.

[0042] In this embodiment, the upper part of the primary fractionation column 3 is equipped with a condensation structure that uses propylene as the cold source. The primary fractionation column 3 is a distillation column with a condenser, and a condensation section is provided at the top of the distillation column, in which the condensation structure is located. The operating pressure of the primary fractionation column 3 is 0.01 to 0.2 MPaG; the theoretical number of trays in the primary fractionation column is 5 to 20, and this embodiment uses 10 trays.

[0043] The primary cooling system 2 in this embodiment includes an air preheater 2.1, a hot water heat exchanger 2.2, a propylene superheater 2.3, and a circulating water cooler 2.4 connected in series. One inlet of the air preheater 2.1 is connected to the acrylic acid gas outlet of the reaction system 1. The outlet of the circulating water cooler 2.4 constitutes the second outlet of the primary cooling system 2 and is connected to the primary separation tower 3. The air preheater 2.1 has an inlet for fresh raw material air input on one side and an outlet for preheated fresh raw material air to be transported to the reaction system on the other side. The operating temperature of the product gas outlet in the air preheater 2.1 is 140–220°C. The propylene superheater 2.3 has an opening connected to the top of the primary separation tower 3 for vaporized propylene input on one side and a first outlet of the primary cooling system 2 on the other side. The operating temperature of the product gas outlet in the propylene superheater 2.3 is 50–90°C. Air preheater 2.1 uses compressed fresh feed air as the heat exchange medium; warm water heat exchanger 2.2 uses warm water as the heat exchange medium; propylene superheater 2.3 uses vaporized propylene as the heat exchange medium; and circulating water cooler 2.4 uses circulating water as the heat exchange medium to sequentially recover energy from the acrylic acid product gas. The warm water heat exchanger 2.2 recovers energy from the heat in the middle temperature section of the product gas, and the preheated warm water is used for heat preservation and tracing of the unit. The operating temperature of the product gas side outlet of the warm water heat exchanger 2.2 is 60–100℃. The operating temperature of the product gas side outlet of the circulating water cooler 2.4 is 30–50℃.

[0044] In this embodiment, a circulating gas compressor 6 is installed on the circulating gas delivery pipeline for pressurizing the circulating gas. A gas supply pipeline is installed at the top of the absorption tower 4 to supply another portion of the purified circulating tail gas to the waste gas treatment system 5. Optionally, a cross-line pipeline 5.1 is installed on the downstream pipeline of the waste gas treatment system 5 to supply a portion of the purified gas to the circulating gas delivery pipeline. The flow rate of the cross-line pipeline 5.1 is controlled between 0.5% and 60.0% (cross-line pipeline, flow rate accounts for 0.5% to 60.0% of the total tail gas flow rate after passing through the waste gas treatment system) to control the organic matter content in the circulating gas.

[0045] This embodiment also includes a condenser 8 and a reflux tank 9 connected in series at the top of the azeotropic tower 7, used for heterogeneous separation of the material at the top of the azeotropic tower 7, so that the separated azeotropic agent is returned to the azeotropic tower 7, the acetic acid-containing wastewater is discharged, and the waste gas is sent to the flare system. A reboiler 11 is provided at the bottom of the azeotropic tower 7.

[0046] Absorption tower 4 uses fresh demineralized water as absorbent to wash and absorb the gas from the top of the primary separator. The liquid-to-gas ratio of fresh demineralized water to circulating tail gas in absorption tower 4 is 0.01 to 0.1. The operating pressure of absorption tower 4 is 0.01 to 0.2 MPaG.

[0047] The following explanation uses the product gas separation system of a 200,000-ton / year propylene oxidation to acrylic acid plant as an example:

[0048] The acrylic acid product gas (150-300℃, 0.01-0.20MPaG) with a capacity of 140-190 t / hr first enters the primary cooling system 2, and then sequentially passes through the air preheater 2.1, the hot water heat exchanger 2.2, the propylene superheater 2.3, and the circulating water cooler 2.4 for energy recovery. The product gas temperature is reduced to 40-60℃. The preheated air and gaseous propylene are then sent to the reaction system 1. The primary cooled product gas is directly fed into the primary separator 3 for condensation and separation. The primary separator 3 has a condensation section at the top, using liquefied propylene (12-20℃) as a cold source to cool the reaction gas at the top of the primary separator 3 to 15-35℃. Most of the acrylic acid in the reaction gas condenses in the primary separator 3 and flows out from the bottom of the tower into the azeotropic tower 7, while the remaining gas enters the absorption tower 4. Absorption tower 4 uses fresh demineralized water as the absorbent to wash and absorb the residual gas after condensation and separation in the primary separator 3. The liquid-to-gas ratio of the demineralized water to the product gas is 0.01–0.10. The top of absorption tower 4 yields purified circulating tail gas. A portion of this tail gas (40–100%) undergoes high-temperature catalytic oxidation treatment in the waste gas treatment system 5, achieving emission standards. The remaining portion (0–60%) is pressurized by the circulating gas compressor 6 and returned to the reaction system 1. To ensure the normal operation of the reactor, a cross-line pipe 51 is installed on the tail gas pipeline after the waste gas treatment system, connecting it to the circulating gas. The organic matter content in the circulating gas can be adjusted and controlled by the flow rate ratio (0.0%–60.0%). The bottom of absorption tower 4 contains acrylic acid absorbent, which enters azeotropic tower 7 for separation and purification. In azeotropic tower 7, an azeotropic agent is used at the top to perform azeotropic distillation separation of the acrylic acid solution. The ratio of the azeotropic agent to the acrylic acid solution in the azeotropic tower is 1.0–3.0. The bottom of the tower yields crude acrylic acid liquid, which is sent to the acrylic acid refining system 12 to finally obtain the acrylic acid product. After heterogeneous separation in reflux tank 9, the azeotropic agent is returned to the azeotropic tower, while the acetic acid-containing wastewater is discharged and a small amount of waste gas is sent to the flare system.

[0049] Calculations show that when a 200,000-ton / year propylene oxidation to acrylic acid plant adopts a new product gas separation system, it can reduce fresh water consumption by about 2 to 20 tons / hour, which is about 50% to 85% of the traditional technology; save steam consumption by about 15 to 21 tons / hour, which is about 10% to 15% of the traditional technology; reduce waste gas treatment volume by about 10 to 40 tons / hour, which is about 7% to 30% of the traditional technology; and reduce waste liquid treatment volume by about 1 to 4 tons / hour, which is about 5% to 20% of the traditional technology.

[0050] Example 2:

[0051] The difference between this embodiment and Embodiment 1 is that: Figure 2 As shown, the condensation section at the top of the primary separator 3 is separated from the primary separator 3 and connected between the primary separator 3 and the absorption tower 4 in the form of a primary separator condenser 13 and a separator tank 14.

[0052] Example 3:

[0053] The difference between this embodiment and Embodiment 1 is that: Figure 3 As shown, considering that the number of theoretical plates required for the primary separation column 3 is relatively small, the primary separation column 3 and the azeotropic column 7 are coupled in one column body to reduce the footprint of the equipment.

[0054] Example 4:

[0055] The difference between this embodiment and Embodiment 1 is that: Figure 4 As shown, the heat exchange sequence in the primary cooling system 2 for the product gas has been changed. Considering the low temperature of vaporized propylene, the primary cooling system 2 uses compressed fresh raw material air, warm water, and circulating water to vaporize propylene sequentially as heat exchange media to recover energy from the acrylic acid product gas and reduce its condensation temperature. After passing through the primary cooling system 1, the product gas temperature can be reduced to 30–50°C.

Claims

1. A novel acrylates reaction gas separation system characterized by The application relates to a propylene glycol production system, which comprises the following parts: a reaction system, wherein the reaction produces acrylic acid gas; a primary cooling system, which is arranged downstream of the reaction system and is used for recovering energy of the acrylic acid gas produced by the reaction system and preheating air; the primary cooling system has a first outlet for returning the gas-phase propylene obtained after energy recovery to the reaction system and a second outlet for outputting product gas; a primary separation tower, which is arranged downstream of the primary cooling system and is used for condensing and separating the product gas; the primary separation tower is provided with an inlet for inputting the product gas from the second outlet of the primary cooling system and a first outlet for outputting liquid phase; the primary separation tower is provided with a second outlet for outputting gas phase; an azeotropic tower, which is arranged downstream of the primary separation tower and is connected with the first outlet of the primary separation tower and is used for azeotropically distilling and separating acrylic acid solution; the azeotropic tower is provided with an outlet for inputting the obtained crude acrylic acid liquid; an acrylic acid refining system, which is arranged downstream of the azeotropic tower and is connected with the outlet of the azeotropic tower and is used for refining propylene to obtain acrylic acid product; and an absorption tower, which is arranged downstream of the primary separation tower and is connected with the second outlet of the primary separation tower and is used for washing and absorbing the residual gas after the condensing and separating of the primary separation tower; the absorption tower is provided with a conveying pipeline for conveying a part of the obtained purified circulating tail gas to the reaction system as circulating gas; the proportion of the acrylic acid tail gas circulating back as circulating gas is 0.5% to 60.0%. The upper part of the primary separation tower is provided with a condensing structure using raw propylene as a cold source; the primary separation tower is a distillation tower with a condenser; the condensing structure is arranged in the condensing section of the top of the distillation tower; the operation pressure of the primary separation tower is 0.01 to 0.2 MPaG; the theoretical plate number of the primary separation tower is 5 to 20; the primary cooling system comprises an air preheater, a warm water heat exchanger, a propylene superheater and a circulating water cooler which are connected in series; one inlet of the air preheater is connected with the acrylic acid gas outlet of the reaction system; the outlet of the circulating water cooler constitutes the second outlet of the primary cooling system and is connected with the primary separation tower. The air preheater uses compressed fresh raw air as a heat exchange medium; the warm water heat exchanger uses warm water as a heat exchange medium; the propylene superheater uses raw vaporized propylene as a heat exchange medium; the circulating water cooler uses circulating water as a heat exchange medium to recover the energy of the acrylic acid product gas; the warm water heat exchanger recovers the heat in the warm section of the product gas; the preheated warm water is used for device heat preservation and heating; the outlet operation temperature of the product gas side of the warm water heat exchanger is 60 to 100 DEG C; the outlet operation temperature of the product gas side of the circulating water cooler is 30 to 50 DEG C. One side of the air preheater is provided with an inlet for inputting fresh raw air; the other side is provided with an outlet for outputting the preheated fresh raw air to the reaction system; the outlet operation temperature of the product gas side of the air preheater is 140 to 220 DEG C. One side of the propylene superheater is connected with the top of the primary separation tower and is provided with an opening for inputting vaporized propylene; the other side is provided with the first outlet of the primary cooling system; the outlet operation temperature of the product gas side of the propylene superheater is 50 to 90 DEG C. ​ ​ ​ ​ 2. The novel acrylate reaction gas separation system according to claim 1, characterized in that: ​ 3. The novel acrylic reaction gas separation system according to claim 1, characterized in that: ​ 4. The novel acrylic reaction gas separation system according to any one of claims 1 ~ 3, characterized in that: The conveying pipeline of the circulating gas is provided with a circulating gas compressor for pressurizing the circulating gas.

5. The novel acrylic reaction gas separation system according to any one of claims 1 ~ 3, characterized in that: The top of the absorption tower is provided with a gas delivery pipeline for delivering another part of the obtained purified circulating tail gas to a waste gas treatment system, a cross-pipeline is arranged on a downstream pipeline of the waste gas treatment system for delivering part of the purified gas to the conveying pipeline of the circulating gas, and the flow ratio of the cross-pipeline is controlled at 0.5% to 60.0% to control the content of organic matters in the circulating gas.

6. The novel acrylic reaction gas separation system according to any one of claims 1 ~ 3, characterized in that: The absorption tower is used to wash and absorb the primary fractionation tower overhead gas by taking fresh desalted water as the absorbent, the liquid-gas ratio of the fresh desalted water to the circulating tail gas in the absorption tower is 0.01 to 0.1, and the operation pressure of the absorption tower is 0.01 to 0.2 MPaG.

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