Poly-generation acid gas removal technology matched with coal water slurry gasification device

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to a poly-generation acid gas removal method matched with a coal water slurry gasification device and a poly-generation acid gas removal system matched with the coal water slurry gasification device. According to the method, the two-stage medium-pressure flash evaporation process is optimally arranged, so that the method has the advantage of saving subsequent compression power consumption; according to the low-temperature methanol washing device, the reabsorption process is optimized, low-H2S methanol is generated, meanwhile, the low-H2S methanol is reutilized, and the low-temperature methanol washing device has the advantage of being low in comprehensive energy consumption; the gas stripping process is optimized, and the H2S-rich gas generated by gas stripping is subjected to series absorption by using the low H2S methanol, the second H2S-rich methanol and the third H2S-rich methanol, so that the method has the characteristic of low comprehensive energy consumption.

Description

Technical Field

[0001] This invention relates to the field of low-temperature methanol washing technology, specifically to a method for removing acidic gases produced by a coal-water slurry gasification unit and a system for removing acidic gases produced by a coal-water slurry gasification unit. Background Technology

[0002] The syngas produced using coal-water slurry gasification technology contains H2 and CO, which are referred to as effective gases. Syngas also contains a large amount of CO2 and trace amounts of H2S, COS, NH3, HCN, and other components. Acidic gas H2S is generally a poison to the synthesis catalyst and must be removed before the synthesis process.

[0003] In the low-temperature methanol washing process, CO2-rich methanol can be recycled through reduced-pressure flash evaporation, but H2S-containing methanol requires thermal regeneration for recycling, making it the main energy-consuming source of the process. Therefore, improving the utilization efficiency of H2S-containing methanol is crucial for technological innovation. Specifically, this means ensuring that the H2S-containing methanol absorbs the maximum amount of H2S from the syngas before thermal regeneration, thereby increasing the H2S concentration in the H2S-rich methanol and reducing the total amount of H2S-rich methanol and the subsequent thermal regeneration workload. Simultaneously, the design of the medium-pressure flash evaporation process is also critical. It must ensure sufficient recovery of the effective gas, minimize compression work during recovery, and minimize the impact of the washing liquid from the flash evaporation on the flashed liquid.

[0004] CN201110260570.0 discloses a low-temperature methanol washing process. However, this process has several drawbacks. First, in the H2S absorption tower, CO2-rich methanol is used entirely to wash the syngas. This CO2-rich methanol becomes contaminated while absorbing H2S gas, increasing the amount of H2S-rich methanol produced. Furthermore, the H2S-rich methanol requires thermal regeneration before it can be recycled, resulting in high energy consumption. Second, the medium-pressure flash evaporation process is simple, but the compression work consumed during effective gas recovery is significant. Additionally, the CO2 gas flashed from the upper tower of the medium-pressure flash evaporator is sent to the lower tower for washing and absorption with H2S-rich methanol. The washing solution selection is not optimal, and the rich liquid cannot be reused, hindering the reduction of overall energy consumption in the low-temperature methanol washing unit. Third, in the CO2 flash evaporation section of the reabsorption tower, the CO2-rich methanol directly mixes with the H2S-rich methanol while washing the flash vapor, becoming contaminated itself. The resulting low-concentration H2S methanol is also not fully utilized, leading to high energy consumption.

[0005] CN201810994082.4 discloses a low-temperature methanol washing system and a method for providing syngas. This technology reuses the non-shift H2S-rich methanol after non-shift gas washing as washing methanol for the flash vapor produced by medium-pressure flash evaporation of H2S-rich methanol. Therefore, there is still room for technological improvement and energy consumption reduction. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low utilization efficiency of non-shift H2S-rich methanol after non-shift gas washing and unreasonable setting of medium-pressure flash evaporation process in existing low-temperature methanol washing technology for combined heat and power generation. This invention provides a method for removing acidic gases from combined heat and power generation systems for coal-water slurry gasification units. This method optimizes the two-stage medium-pressure flash evaporation process, saving power consumption in subsequent compression. Optimizing the reabsorption process generates low-H2S methanol, which is then reused, resulting in low overall energy consumption for the low-temperature methanol washing unit. Optimizing the gas stripping process, using low-H2S methanol, second-stage H2S-rich methanol, and third-stage H2S-rich methanol in series to absorb the H2S-rich gas generated from gas stripping, also results in low overall energy consumption.

[0007] The first aspect of this invention provides a method for removing acidic gases from a multi-generation coal-water slurry gasification unit, the method comprising:

[0008] The CO2-rich methanol from the syngas CO2 absorption process is divided into two streams. The first stream of CO2-rich methanol is returned to the syngas H2S absorption process, and the second stream of CO2-rich methanol is subjected to first-stage CO2 flash evaporation and second-stage CO2 flash evaporation in sequence to obtain first-stage CO2 flash vapor, second-stage CO2 flash vapor and second-stage CO2 flash liquid.

[0009] The first H2S-rich methanol from the syngas H2S absorption process is subjected to first-stage H2S flash evaporation and second-stage H2S flash evaporation to obtain first-stage H2S flash vapor, second-stage H2S flash vapor and second-stage H2S flash liquid.

[0010] The secondary CO2 flash liquid is subjected to a first flash evaporation, and the resulting semi-lean methanol is divided into five streams. The fifth stream of semi-lean methanol and the secondary H2S flash liquid are subjected to a second flash evaporation and a third flash evaporation, respectively. The resulting low-H2S methanol and second-rich H2S methanol are contacted with nitrogen gas and stripped. The stripped gas is then washed with the first stream of semi-lean methanol to obtain the third-rich H2S methanol.

[0011] Specifically, the second semi-lean methanol stream is returned to the syngas CO2 absorption process; the third semi-lean methanol stream and primary CO2 flash vapor undergo a second wash; the fourth semi-lean methanol stream and secondary CO2 flash vapor undergo a third wash; the non-shift H2S-rich methanol from the non-shift gas purification process is divided into five streams: the first non-shift H2S-rich methanol stream is returned to the non-shift gas purification process; the second and third non-shift H2S-rich methanol streams are both returned to the syngas H2S absorption process; the fourth non-shift H2S-rich methanol stream and primary H2S flash vapor undergo a fourth wash; and the fifth non-shift H2S-rich methanol stream and secondary H2S flash vapor undergo a fifth wash.

[0012] A second aspect of the present invention provides a multi-generation acid gas removal system for a coal-water slurry gasification unit. The system includes: a non-shift gas scrubbing tower, an H2S absorption tower, a CO2 absorption tower, a medium-pressure flash tower, and a reabsorption tower connected in series. The medium-pressure flash tower is divided from top to bottom into a two-stage CO2 flash section, a first-stage CO2 flash section, a two-stage H2S flash section, and a first-stage H2S flash section. The reabsorption tower is divided from top to bottom into a first flash section, a second flash section, a third flash section, a scrubbing section, and a gas stripping section.

[0013] The H2S absorption tower is used for the H2S absorption process of syngas. The first H2S-rich methanol obtained is sent to the first-stage H2S flash evaporation section for first-stage H2S flash evaporation to obtain first-stage H2S flash vapor and first-stage H2S flash liquid. The second-stage H2S flash evaporation section is connected to the bottom of the first-stage H2S flash evaporation section and is used to perform second-stage H2S flash evaporation on the first-stage H2S flash liquid to obtain second-stage H2S flash vapor and second-stage H2S flash liquid.

[0014] The CO2 absorption tower is used for the synthesis gas CO2 absorption process. The resulting CO2-rich methanol is divided into two streams. The first stream of CO2-rich methanol is returned to the H2S absorption tower, and the second stream of CO2-rich methanol is sent to the lower part of the primary CO2 flash evaporation section for primary CO2 flash evaporation to obtain primary CO2 flash vapor and primary CO2 flash liquid. The secondary CO2 flash evaporation section is connected to the bottom of the primary CO2 flash evaporation section and is used to perform secondary CO2 flash evaporation on the primary CO2 flash liquid to obtain secondary CO2 flash liquid and secondary CO2 flash vapor.

[0015] The first flash section, the second flash section, and the third flash section are connected by a gas riser. The first flash section is used to perform the first flash evaporation of the secondary CO2 flash liquid. The resulting semi-lean methanol is divided into five streams. The fifth stream of semi-lean methanol and the secondary H2S flash liquid are sent to the second flash section and the third flash section respectively for the second flash evaporation and the third flash evaporation, respectively, to obtain low H2S methanol and second H2S rich methanol.

[0016] The washing section and the stripping section are connected by a gas lift hole. The stripping section connects the lower part of the second flash section, the third flash section and the washing section. It is used to contact the low H2S methanol, the second H2S rich methanol and the third H2S rich methanol with nitrogen and perform stripping. The stripped gas is sent to the washing section and is washed with the first semi-lean methanol to obtain the third H2S rich methanol.

[0017] Specifically, the second semi-lean methanol stream is returned to the CO2 absorption tower; the third semi-lean methanol stream is sent to the upper part of the first-stage CO2 flash evaporation section for a second wash with the first-stage CO2 flash vapor; and the fourth semi-lean methanol stream is sent to the upper part of the second-stage CO2 flash evaporation section for a third wash with the second-stage CO2 flash vapor.

[0018] The non-shift gas scrubbing tower is used for non-shift gas purification process. The resulting non-shift H2S-rich methanol is divided into five streams. The first stream of non-shift H2S-rich methanol is returned to the non-shift gas scrubbing tower. The second and third streams of non-shift H2S-rich methanol are returned to the H2S absorption tower. The fourth stream of non-shift H2S-rich methanol is sent to the upper part of the first-stage H2S flash evaporation section for a fourth wash with the first-stage H2S flash vapor. The fifth stream of non-shift H2S-rich methanol is sent to the upper part of the second-stage H2S flash evaporation section for a fifth wash with the second-stage H2S flash vapor.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The method provided by the present invention adopts a two-stage medium-pressure flash evaporation technology. The first stage adopts a higher flash evaporation pressure, and the effective gas flashed out can be directly sent to the second stage of the compressor in the compression process, which reduces the power consumption of the compressor. The second stage adopts a lower flash evaporation pressure to ensure that the effective gas in the first stage CO2 flash liquid and the first stage H2S flash liquid is fully recovered. At the same time, it can reduce the air intake of the first stage cylinder of the compressor in the compression process, and correspondingly reduce the power consumption of the compressor.

[0021] (2) The method provided by the present invention optimizes the medium-pressure flash evaporation process by introducing non-conversion H2S-rich methanol to absorb H2S flash vapor (i.e., the fourth and fifth non-conversion H2S-rich methanol streams absorb the first-stage and second-stage H2S flash vapors respectively), and introduces semi-lean methanol to absorb CO2 flash vapor (i.e., the third and fourth semi-lean methanol streams absorb the first-stage and second-stage CO2 flash vapors respectively). Compared with the prior art, it realizes the separate flash evaporation and separate washing of the second CO2-rich methanol stream and the first H2S-rich methanol stream, avoids the technical problem of CO2 gas being transferred to H2S-rich methanol, and is conducive to reducing the energy consumption of the device.

[0022] (3) The method provided by the present invention divides the non-conversion H2S-rich methanol from the non-conversion gas purification process into five streams. The second and third streams of non-conversion H2S-rich methanol are returned to the synthesis gas H2S absorption process. Compared with the prior art using CO2-rich methanol, the amount of CO2-rich methanol used is reduced while achieving the same washing effect, which is of positive significance for reducing the energy consumption of the low-temperature methanol washing device. At the same time, the fourth and fifth streams of non-conversion H2S-rich methanol are used as washing solvents for H2S flash vapor.

[0023] (4) The method provided by the present invention optimizes the reabsorption process and realizes the absorption of sulfur-containing gas generated by the flash evaporation of the secondary H2S flash liquid by the flash liquid of the fifth semi-lean methanol, but without mixing with the second H2S rich methanol after flash evaporation.

[0024] (5) The method provided by the present invention adopts a three-stage tail gas washing technology. According to the different H2S content in the tail gas, three methanols with different H2S contents are selectively set and washed in order from high to low. Under the premise of ensuring that the tail gas emission meets the standards, the minimum amount of semi-lean methanol is used, thereby reducing the heat regeneration energy consumption of the entire low temperature methanol wash. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of a multi-generation acid gas removal system for a coal-water slurry gasification unit provided by the present invention.

[0026] Explanation of reference numerals in the attached figures

[0027] T-1, Non-shift gas scrubbing tower; T-2, H2S absorption tower; T-3, CO2 absorption tower; T-4, Medium-pressure flash evaporator; T-5, Reabsorption tower;

[0028] E-1, First cooler; E-2, Second cooler; E-3, Third cooler; E-4, Fourth cooler; P-1, First pump; P-2, Second pump;

[0029] Q-1, First heat exchanger; Q-2, Second heat exchanger; Q-3, Third heat exchanger;

[0030] 1. Non-shift gas; 2. Lean methanol; 2-i. First lean methanol stream; 2-ii. Second lean methanol stream; 3. Non-shift H2S-rich methanol; 3-i. First non-shift H2S-rich methanol stream; 3-ii. Second non-shift H2S-rich methanol stream; 3-iii. Third non-shift H2S-rich methanol stream; 3-iv. Fourth non-shift H2S-rich methanol stream; 3-v. Fifth non-shift H2S-rich methanol stream; 4. Pre-purified non-shift H2S-rich methanol; 5. Purified non-shift gas; 6. Syngas; 7. Fourth H2S-rich methanol; 9. CO2-rich methanol; 9-i. First CO2-rich methanol stream; 9-ii. Second CO2-rich methanol stream; 10. First H2S-rich methanol; 11. Desulfurized gas; 12. CO2-containing methanol; 14. Purified gas; 15. First-stage flash vapor; 15-i. First-stage scrubber 15-ii, H2S flash vapor after primary washing; 16, secondary flash vapor; 16-i, CO2 flash vapor after secondary washing; 16-ii, H2S flash vapor after secondary washing; 17, H2S-rich methanol after stripping; 18, nitrogen; 19, third H2S-rich methanol; 20, tail gas; 21, primary H2S flash liquid; 22, secondary H2S flash liquid; 23, primary CO2 flash liquid; 24, secondary CO2 flash liquid; 25, CO2 product gas; 26, second H2S-rich methanol; 27, semi-lean methanol; 27-i, first semi-lean methanol; 27-ii, second semi-lean methanol; 27-iii, third semi-lean methanol; 27-iv, fourth semi-lean methanol; 27-v, fifth semi-lean methanol; 28, low H2S methanol. Detailed Implementation

[0031] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0032] In this invention, unless otherwise specified, the terms "first," "second," "third," and "fourth" do not indicate a sequential order, nor do they limit the specific materials or steps; they are merely used to distinguish that these are not the same material or step. For example, in "first H2S-rich methanol," "second H2S-rich methanol," "third H2S-rich methanol," and "fourth H2S-rich methanol," the terms "first," "second," "third," and "fourth" are used only to indicate that these are not the same H2S-rich methanol.

[0033] In this invention, unless otherwise specified, the “top” of the container refers to 0-10% of the container’s height from top to bottom; the “upper part” of the container refers to 10-40% of the container’s height from top to bottom; the “middle part” of the container refers to 40-60% of the container’s height from top to bottom; the “lower part” of the container refers to 60-90% of the container’s height from top to bottom; and the “bottom” of the container refers to 90-100% of the container’s height from top to bottom.

[0034] The first aspect of this invention provides a method for removing acidic gases from a multi-generation coal-water slurry gasification unit, the method comprising:

[0035] The CO2-rich methanol from the syngas CO2 absorption process is divided into two streams. The first stream of CO2-rich methanol is returned to the syngas H2S absorption process, and the second stream of CO2-rich methanol is subjected to first-stage CO2 flash evaporation and second-stage CO2 flash evaporation in sequence to obtain first-stage CO2 flash vapor, second-stage CO2 flash vapor and second-stage CO2 flash liquid.

[0036] The first H2S-rich methanol from the syngas H2S absorption process is subjected to first-stage H2S flash evaporation and second-stage H2S flash evaporation to obtain first-stage H2S flash vapor, second-stage H2S flash vapor and second-stage H2S flash liquid.

[0037] The secondary CO2 flash liquid is subjected to a first flash evaporation, and the resulting semi-lean methanol is divided into five streams. The fifth stream of semi-lean methanol and the secondary H2S flash liquid are subjected to a second flash evaporation and a third flash evaporation, respectively. The resulting low-H2S methanol and second-rich H2S methanol are contacted with nitrogen gas and stripped. The stripped gas is then washed with the first stream of semi-lean methanol to obtain the third-rich H2S methanol.

[0038] Specifically, the second semi-lean methanol stream is returned to the syngas CO2 absorption process; the third semi-lean methanol stream and primary CO2 flash vapor undergo a second wash; the fourth semi-lean methanol stream and secondary CO2 flash vapor undergo a third wash; the non-shift H2S-rich methanol from the non-shift gas purification process is divided into five streams: the first non-shift H2S-rich methanol stream is returned to the non-shift gas purification process; the second and third non-shift H2S-rich methanol streams are both returned to the syngas H2S absorption process; the fourth non-shift H2S-rich methanol stream and primary H2S flash vapor undergo a fourth wash; and the fifth non-shift H2S-rich methanol stream and secondary H2S flash vapor undergo a fifth wash.

[0039] In this invention, unless otherwise specified, the non-shift gas purification process refers to purifying the non-shift gas and the first lean methanol stream to obtain non-shift H2S-rich methanol and purified non-shift gas.

[0040] In some embodiments of the present invention, preferably, the non-conversion gas purification process includes: subjecting the non-conversion gas to primary purification and secondary purification in sequence to obtain the non-conversion H2S-rich methanol.

[0041] In some embodiments of the present invention, preferably, the first stream of non-conversion H2S-rich methanol is returned and subjected to the first-stage purification.

[0042] In some embodiments of the present invention, more preferably, the non-conversion gas and the first stream of non-conversion H2S-rich methanol are contacted and subjected to the first-stage purification to obtain pre-purified non-conversion H2S-rich methanol and pre-purified non-conversion gas; the pre-purified non-conversion gas and the first stream of lean methanol are contacted and subjected to the second-stage purification to obtain non-conversion H2S-rich methanol and purified non-conversion gas.

[0043] The non-conversion H2S-rich methanol is divided into a first stream of non-conversion H2S-rich methanol, a second stream of non-conversion H2S-rich methanol, a third stream of non-conversion H2S-rich methanol, a fourth stream of non-conversion H2S-rich methanol, and a fifth stream of non-conversion H2S-rich methanol with a molar flow ratio of 1:5-7:38-42:9-11:9-11.

[0044] In some embodiments of the present invention, preferably, the molar content of H2S in the non-shift gas is 0.9-1.2%, and the molar content of CO2 is 5-10%; the temperature is -35 to -25°C, and the pressure is 5.5-6 MPa(G). In the present invention, the source of the non-shift gas has a wide range of selection, as long as the above limitations are met. The non-shift gas includes, but is not limited to, the upstream non-shift gas cooling process.

[0045] In this invention, the primary purification aims to remove impurities such as HCN and NH3, as well as small amounts of H2S and CO2, from the non-shift gas to obtain pre-purified non-shift gas. Preferably, the molar flow ratio of the non-shift gas to the first non-shift H2S-rich methanol stream is 50-60:1.

[0046] In this invention, the pre-purified non-conversion H2S-rich methanol has a molar content of 2.1-2.6% for H2S and a molar content of 3-7% for CO2; the temperature is -33 to -27°C. In this invention, it is then sent to subsequent processing steps.

[0047] In this invention, the secondary purification aims to further remove H2S and CO2 from the non-shift gas, obtaining non-shift H2S-rich methanol and purified non-shift gas. Preferably, the molar flow ratio of the first lean methanol stream to the non-shift gas is 1-1.1:1; the molar content of H2S in the purified non-shift gas is ≤0.1ppm, and the molar content of CO2 is ≤20ppm; the temperature is -55 to -50℃, and the pressure is 5.4-6MPa(G).

[0048] In some embodiments of the present invention, preferably, the molar content of H2S in the non-conversion H2S-rich methanol is 0.6-1.1%, the molar content of CO2 is 4-9%, the temperature is -32 to -27°C, and the pressure is 5.5-6 MPa(G).

[0049] In some embodiments of the present invention, preferably, the syngas H2S absorption process includes: sequentially subjecting the syngas from the coal-water slurry gasification unit to primary H2S absorption and secondary H2S absorption to obtain desulfurized gas.

[0050] In some embodiments of the present invention, more preferably, the second non-conversion H2S-rich methanol stream is returned and subjected to the first-stage H2S absorption; the third non-conversion H2S-rich methanol stream and the first CO2-rich methanol stream are each independently returned and subjected to the second-stage H2S absorption.

[0051] In some embodiments of the present invention, more preferably, the synthesis gas and the second non-conversion H2S-rich methanol are contacted and subjected to the first-stage H2S absorption to obtain the fourth H2S-rich methanol and pre-desulfurized gas; the pre-desulfurized gas, the third non-conversion H2S-rich methanol and the first CO2-rich methanol are contacted and subjected to the second-stage H2S absorption to obtain the first H2S-rich methanol and desulfurized gas.

[0052] In this invention, unless otherwise specified, the syngas originates from a coal-water slurry gasification unit. Preferably, the syngas contains 0.9-1.2% H2S and 40-50% CO2; the temperature is -15 to -5°C; and the pressure is 5.3-5.7 MPa(G).

[0053] In this invention, the primary H2S absorption is intended to remove impurities such as HCN and NH3, as well as small amounts of H2S and CO2, from the synthesis gas. Preferably, the molar content of H2S in the fourth H2S-rich methanol is 2.4-2.9%, and the molar content of CO2 is 66-71%; the temperature is -9 to -5°C.

[0054] In some embodiments of the present invention, preferably, the molar flow ratio of the syngas and the second non-conversion H2S-rich methanol is 60-70:1, for example, 60:1, 65:1, 70:1, and any value within the range of any two values.

[0055] In this invention, the secondary H2S absorption is intended to further remove H2S from the syngas, as well as a small amount of CO2. Preferably, the first H2S-rich methanol contains 1.4-1.8% H2S and has a CO2 molar content of 34-38%; the temperature is -20 to -13°C.

[0056] In this invention, the molar flow ratio of the syngas to the third non-conversion H2S-rich methanol is 9-11:1; the molar flow ratio of the syngas to the first CO2-rich methanol is 2-3:1.

[0057] In some embodiments of the present invention, preferably, the molar content of H2S in the desulfurization gas is 0.5-1 ppm, and the molar content of CO2 is 37-41%; more preferably, the temperature of the desulfurization gas is -20 to -13°C, and the pressure is 5.3-5.4 MPa(G).

[0058] In some embodiments of the present invention, preferably, the first stream of CO2-rich methanol is subjected to a first pressurization to 5.8-6 MPa(G) and a first cooling to -46 to -43°C in the direction of material flow before the secondary H2S absorption is carried out.

[0059] In some embodiments of the present invention, preferably, the syngas CO2 absorption process includes: sequentially subjecting the desulfurized gas from the syngas H2S absorption process to primary CO2 absorption and secondary CO2 absorption to obtain purified gas.

[0060] In some embodiments of the present invention, it is further preferred that the second semi-lean methanol stream is returned and subjected to the secondary CO2 absorption.

[0061] In some embodiments of the present invention, more preferably, the desulfurized gas and CO2-containing methanol are subjected to the first-stage CO2 absorption to obtain the CO2-rich methanol and pre-purified gas; the pre-purified gas, the second stream of semi-lean methanol and the second stream of lean methanol are subjected to the second-stage CO2 absorption to obtain the purified gas and CO2-containing methanol.

[0062] In this invention, the primary CO2 absorption is intended to further remove CO2 from the desulfurized gas. Preferably, the molar content of H2S in the CO2-rich methanol is 0.1-0.5 ppm, the molar content of CO2 is 29-34%, the temperature is -10 to -6°C, and the pressure is 5.3-5.4 MPa(G).

[0063] In some embodiments of the present invention, more preferably, the CO2-rich methanol is divided into a first CO2-rich methanol stream and a second CO2-rich methanol stream with a molar flow ratio of 1:2-3.

[0064] In some embodiments of the present invention, preferably, the molar flow ratio of the desulfurized gas and the CO2-containing methanol is 1:1.1-1.5, for example, 1:1.1, 1:1.3, 1:1.5, and any value within the range of any two values.

[0065] In some embodiments of the present invention, more preferably, the CO2-containing methanol is subjected to a second cooling to -36 to -33°C before the first-stage CO2 absorption is performed.

[0066] In some embodiments of the present invention, preferably, the molar flow ratio of the purified gas and the second semi-lean methanol is 1.4-1.6:1; the molar flow ratio of the purified gas and the second lean methanol is 1:1-1.2.

[0067] In some embodiments of the present invention, preferably, the molar content of H2S and the molar content of CO2 in the lean methanol are 0%.

[0068] In some embodiments of the present invention, preferably, the molar content of H2S in the purified gas is ≤0.1ppm, the molar content of CO2 is ≤20ppm, the temperature is -55 to -50°C, and the pressure is 5.2-5.3MPa(G).

[0069] In this invention, the primary and secondary CO2 flash evaporations are intended to remove CO2 flash vapor from the second CO2-rich methanol stream. Preferably, the pressure of the primary CO2 flash evaporation is 3.5-3.7 MPa(G); and the pressure of the secondary CO2 flash evaporation is 1.6-2 MPa(G).

[0070] In some embodiments of the present invention, preferably, the second stream of CO2-rich methanol is subjected to the first-stage CO2 flash evaporation to obtain the first-stage CO2 flash vapor and the first-stage CO2 flash liquid; the first-stage CO2 flash liquid is subjected to the second-stage CO2 flash evaporation to obtain the second-stage CO2 flash vapor and the second-stage CO2 flash liquid.

[0071] In some embodiments of the present invention, preferably, the molar content of H2S in the primary CO2 flash liquid is 0.1-0.5 ppm, the molar content of CO2 is 28.5-33.5%, and the temperature is -38.5 to -34.5°C.

[0072] In some embodiments of the present invention, preferably, the molar content of H2S in the secondary CO2 flash liquid is 0.1-0.5 ppm, the molar content of CO2 is 28-33%, and the temperature is -40 to -35°C.

[0073] In some embodiments of the present invention, more preferably, the second CO2-rich methanol stream is cooled to -36 to -33°C in a third step before the first-stage CO2 flash evaporation is performed.

[0074] In this invention, the primary and secondary H2S flash evaporations are intended to remove H2S flash vapor from the first H2S-rich layer. Preferably, the pressure of the primary H2S flash evaporation is 3.5-3.7 MPa(G); and the pressure of the secondary H2S flash evaporation is 1.6-2 MPa(G).

[0075] In some embodiments of the present invention, preferably, the first H2S-rich methanol is subjected to the first-stage H2S flash evaporation to obtain the first-stage H2S flash vapor and the first-stage H2S flash liquid; the first-stage H2S flash liquid is subjected to the second-stage H2S flash evaporation to obtain the second-stage H2S flash vapor and the second-stage H2S flash liquid.

[0076] In some embodiments of the present invention, preferably, the molar content of H2S in the primary H2S flash liquid is 1.4-1.9%, the molar content of CO2 is 32-37%, and the temperature is -10 to -6°C.

[0077] In some embodiments of the present invention, preferably, the molar content of H2S in the secondary H2S flash liquid is 1.35-1.85%, the molar content of CO2 is 31-35%, and the temperature is -12 to -8°C.

[0078] In some embodiments of the present invention, preferably, the molar content of H2S in the semi-lean methanol is 0.1-0.5 ppm; the molar content of CO2 is 20-24%; the temperature is -66 to -61°C; and the pressure is 0.05-0.08 MPa(G).

[0079] In some embodiments of the present invention, it is further preferred that the semi-lean methanol is divided into a first semi-lean methanol stream, a second semi-lean methanol stream, a third semi-lean methanol stream, a fourth semi-lean methanol stream, and a fifth semi-lean methanol stream with a molar flow ratio of 14-16:13-15:1:1-2:7-9.

[0080] In this invention, the semi-lean methanol solution is divided into five streams. The first stream undergoes the first washing, the second stream undergoes secondary CO2 absorption, the third stream undergoes the second washing, the fourth stream undergoes the third washing, and the fifth stream undergoes the second flash evaporation.

[0081] In some embodiments of the present invention, more preferably, the second, third, and fourth semi-lean methanol streams are pressurized to 5.8-6 MPa(G) and returned to the secondary CO2 absorption, second washing, and third washing processes, respectively.

[0082] In some embodiments of the present invention, preferably, the fifth semi-lean methanol is subjected to a second flash evaporation to obtain a flash liquid and a second CO2 product gas; the H2S flash liquid is subjected to a third flash evaporation to obtain a second H2S-rich methanol and a sulfur-containing gas; the flash liquid and the sulfur-containing gas are contacted to obtain the low-H2S methanol and a third CO2 product gas; wherein the second CO2 product gas and the third CO2 product gas are mixed with the first CO2 product gas obtained from the first flash evaporation to obtain CO2 product gas.

[0083] In this invention, preferably, the pressure of the first flash evaporation is 0.05-0.08 MPa(G); the pressure of the second flash evaporation is 0.06-0.09 MPa(G); and the pressure of the third flash evaporation is 0.12-0.16 MPa(G).

[0084] In some embodiments of the present invention, more preferably, the secondary H2S flash liquid is cooled to -34 to -30°C in the fourth stage before the third flash evaporation is performed.

[0085] In some embodiments of the present invention, preferably, the molar content of H2S in the low-H2S methanol is 0.6-0.9%, the molar content of CO2 is 19.5-23.5%, the temperature is -63 to -57°C, and the pressure is 0.12-0.16 MPa(G).

[0086] In some embodiments of the present invention, preferably, the molar content of H2S in the second H2S-rich methanol is 1.2-1.6%, the molar content of CO2 is 20-24%, the temperature is -66 to -62°C, and the pressure is 0.13-0.17 MPa(G).

[0087] In some embodiments of the present invention, preferably, the molar content of H2S in the CO2 product gas is ≤1ppm, the molar content of CO2 is 99.4-99.7%, the temperature is -66 to -62°C, and the pressure is 0.05-0.08MPa(G).

[0088] In some embodiments of the present invention, preferably, the gas stripping process includes: sequentially contacting the second H2S-rich methanol, the third H2S-rich methanol, and the low H2S methanol with nitrogen and performing the gas stripping to obtain stripped gas and stripped H2S-rich methanol.

[0089] In some embodiments of the present invention, more preferably, the molar content of H2S in the H2S-rich methanol after gas stripping is 1-2%, the molar content of CO2 is 2-5%, and the temperature is -52 to -48°C.

[0090] In some embodiments of the present invention, preferably, the second H2S-rich methanol is subjected to a first heat exchange to a temperature of -40 to -36°C before the gas stripping is performed.

[0091] In some embodiments of the present invention, preferably, the third H2S-rich methanol is subjected to a second heat exchange to a temperature of -40 to -36°C before the gas stripping is performed.

[0092] In some embodiments of the present invention, preferably, the low-H2S methanol is subjected to a third heat exchange to a temperature of -40 to -36°C before the gas stripping is performed.

[0093] In one specific embodiment of the present invention, the second H2S-rich methanol is subjected to a first heat exchange at -40 to -36°C, the third H2S-rich methanol is subjected to a second heat exchange at -40 to -36°C, and the low H2S methanol is subjected to a third heat exchange at -40 to -36°C, and then contacted with nitrogen and stripped to obtain stripped H2S-rich methanol and stripped gas.

[0094] In some embodiments of the present invention, preferably, the stripped gas is subjected to the first washing with a first semi-lean methanol stream to obtain the third H2S-rich methanol and tail gas.

[0095] In some embodiments of the present invention, preferably, the molar content of H2S in the third H2S-rich methanol is 1-3%, the molar content of CO2 is 17-22%, and the temperature is -63 to -58°C.

[0096] In some embodiments of the present invention, more preferably, the molar content of H2S in the exhaust gas is ≤1ppm, the molar content of CO2 is 82-86%, and the temperature is -67 to -63°C.

[0097] In this invention, the second washing process includes: performing the second washing with a third semi-lean methanol solution and a first-stage CO2 flash vapor to obtain first-stage washed CO2 flash vapor and a first-stage CO2 washing liquid; the third washing process includes: performing the third washing with a fourth semi-lean methanol solution and a second-stage CO2 flash vapor to obtain second-stage washed CO2 flash vapor and a second-stage CO2 washing liquid.

[0098] The primary CO2 washing liquid is mixed with the primary CO2 flash liquid; the secondary CO2 washing liquid is mixed with the secondary CO2 flash liquid.

[0099] In this invention, unless otherwise specified, the primary CO2 flash liquid contains a primary CO2 scrubbing liquid; the secondary CO2 flash liquid contains a secondary CO2 scrubbing liquid.

[0100] In some embodiments of the present invention, preferably, the molar content of H2 in the CO2 flash vapor after the first-stage washing is 88-92%, the molar content of CO2 is 6-11%, the temperature is -63 to -60°C, and the pressure is 3.5-3.7 MPa(G).

[0101] In some embodiments of the present invention, preferably, the molar content of H2 in the CO2 flash vapor after the secondary washing is 82-87%, the molar content of CO2 is 12-16%, the temperature is -65 to -62°C, and the pressure is 1.6-2 MPa(G).

[0102] In this invention, the fourth washing process includes: performing the fourth washing on a fourth stream of non-conversion H2S-rich methanol and a first-stage H2S flash vapor to obtain H2S flash vapor after first-stage washing and a first-stage H2S washing liquid; the fifth washing process includes: performing the fifth washing on a fifth stream of non-conversion H2S-rich methanol and a second-stage H2S flash vapor to obtain H2S flash vapor after second-stage washing and a second-stage H2S washing liquid;

[0103] The primary H2S washing liquid is mixed with the primary H2S flash evaporator; the secondary H2S washing liquid is mixed with the secondary H2S flash evaporator.

[0104] In this invention, unless otherwise specified, the primary H2S flash liquid contains a primary H2S washing liquid; the secondary H2S flash liquid contains a secondary H2S washing liquid.

[0105] In some embodiments of the present invention, preferably, the molar content of H2 in the H2S flash vapor after the first-stage washing is 60-65%, the molar content of CO2 is 9-14%, the temperature is -30 to -25°C, and the pressure is 3.5-3.7 MPa(G).

[0106] In some embodiments of the present invention, preferably, the molar content of H2 in the H2S flash vapor after the secondary washing is 7-11%, the molar content of CO2 is 72-77%, the temperature is -8 to -4°C, and the pressure is 1.6-2 MPa(G).

[0107] In this invention, unless otherwise specified, the CO2 flash vapor and H2S flash vapor after primary washing are mixed to obtain primary flash vapor; the CO2 flash vapor and H2S flash vapor after secondary washing are mixed to obtain secondary flash vapor.

[0108] A second aspect of the present invention provides a schematic diagram of a multi-generation acid gas removal system for a coal-water slurry gasification unit, as shown in the figure below. Figure 1 As shown, by Figure 1It is known that the system includes: a non-shift gas scrubbing tower T-1, an H2S absorption tower T-2, a CO2 absorption tower T-3, a medium-pressure flash tower T-4, and a reabsorption tower T-5 connected together; wherein, the medium-pressure flash tower T-4 is divided into a two-stage CO2 flash section, a one-stage CO2 flash section, a two-stage H2S flash section, and a one-stage H2S flash section from top to bottom; the reabsorption tower T-5 is divided into a first flash section, a second flash section, a third flash section, a scrubbing section, and a gas stripping section from top to bottom;

[0109] The H2S absorption tower T-2 is used for the H2S absorption process of syngas. The first H2S-rich methanol 10 obtained is sent to the first-stage H2S flash evaporation section for first-stage H2S flash evaporation to obtain first-stage H2S flash vapor and first-stage H2S flash liquid 21. The second-stage H2S flash evaporation section is connected to the bottom of the first-stage H2S flash evaporation section and is used to perform second-stage H2S flash evaporation on the first-stage H2S flash liquid 21 to obtain second-stage H2S flash vapor and second-stage H2S flash liquid 22.

[0110] The CO2 absorption tower T-3 is used for the synthesis gas CO2 absorption process. The resulting CO2-rich methanol 9 is divided into two streams. The first CO2-rich methanol 9-i is returned to the H2S absorption tower T-2, and the second CO2-rich methanol 9-ii is sent to the lower part of the primary CO2 flash evaporation section for primary CO2 flash evaporation, resulting in primary CO2 flash vapor and primary CO2 flash liquid 23. The secondary CO2 flash evaporation section is connected to the bottom of the primary CO2 flash evaporation section and is used to perform secondary CO2 flash evaporation on the primary CO2 flash liquid 23, resulting in secondary CO2 flash liquid 24 and secondary CO2 flash vapor.

[0111] The first flash section, the second flash section, and the third flash section are connected by a gas riser. The first flash section is used to perform the first flash evaporation of the secondary CO2 flash liquid 24, and the resulting semi-lean methanol 27 is divided into five streams. The fifth stream of semi-lean methanol 27-v and the secondary H2S flash liquid 22 are respectively sent to the second flash section and the third flash section for the second flash evaporation and the third flash evaporation, respectively, to obtain low H2S methanol 28 and second H2S rich methanol 26.

[0112] The washing section and the stripping section are connected by a gas lift hole. The stripping section connects the lower part of the second flash section, the third flash section and the washing section. It is used to contact the low H2S methanol 28, the second H2S rich methanol 26 and the third H2S rich methanol 19 with nitrogen 18 and perform stripping. The stripped gas is sent to the washing section and performs a first washing with the first semi-lean methanol 27-i to obtain the third H2S rich methanol 19.

[0113] Specifically, the second semi-lean methanol 27-ii stream is returned to the CO2 absorption tower T-3; the third semi-lean methanol 27-iii stream is sent to the upper part of the primary CO2 flash evaporation section for a second wash with the primary CO2 flash vapor; and the fourth semi-lean methanol 27-iv stream is sent to the upper part of the secondary CO2 flash evaporation section for a third wash with the secondary CO2 flash vapor.

[0114] The non-shift gas scrubbing tower T-1 is used for non-shift gas purification. The resulting non-shift H2S-rich methanol 3 is divided into five streams. The first stream of non-shift H2S-rich methanol 3-i is returned to the non-shift gas scrubbing tower T-1. The second and third streams of non-shift H2S-rich methanol 3-ii and non-shift H2S-rich methanol 3-iii are returned to the H2S absorption tower T-2. The fourth stream of non-shift H2S-rich methanol 3-iv is sent to the upper part of the first-stage H2S flash evaporation section for a fourth wash with the first-stage H2S flash vapor. The fifth stream of non-shift H2S-rich methanol 3-v is sent to the upper part of the second-stage H2S flash evaporation section for a fifth wash with the second-stage H2S flash vapor.

[0115] According to the present invention, preferably, such as Figure 1 As shown, the non-shift gas scrubbing tower T-1 is divided into a primary purification section and a secondary purification section connected by air risers from bottom to top. The primary purification section is used to contact non-shift gas 1 and the first stream of non-shift H2S-rich methanol 3-i for primary purification to obtain pre-purified non-shift H2S-rich methanol 4 and pre-purified non-shift gas. The secondary purification section is used to contact the pre-purified non-shift gas and the first stream of lean methanol 2-i for secondary purification to obtain non-shift H2S-rich methanol 3 and purified non-shift gas 5.

[0116] According to the present invention, preferably, such as Figure 1 As shown, the H2S absorption tower is divided into a primary H2S absorption section and a secondary H2S absorption section connected by air risers from bottom to top. The primary H2S absorption section is used to contact the synthesis gas 6 and the second non-conversion H2S-rich methanol 3-ii for primary H2S absorption, resulting in the fourth H2S-rich methanol 7 and pre-desulfurized gas. The secondary H2S absorption section is used to contact the pre-desulfurized gas, the third non-conversion H2S-rich methanol 3-iii, and the first CO2-rich methanol 9-i for secondary H2S absorption, resulting in the first H2S-rich methanol 10 and desulfurized gas 11.

[0117] According to the present invention, preferably, such as Figure 1As shown, the CO2 absorption tower T-3 is divided into a primary CO2 absorption section and a secondary CO2 absorption section connected by air risers from bottom to top. The primary CO2 absorption section is used to contact the desulfurized gas 11 and CO2-containing methanol 12 for primary CO2 absorption to obtain CO2-rich methanol 9 and pre-purified gas. The secondary CO2 absorption section is used to contact the pre-purified gas, the second semi-lean methanol 27-ii and the second lean methanol 2-ii for secondary CO2 absorption to obtain purified gas 14 and CO2-containing methanol 12.

[0118] According to the present invention, such as Figure 1 As shown, in the medium-pressure flash tower T-4, the middle part of the primary CO2 flash section is used to perform primary CO2 flash evaporation on the second stream of CO2-rich methanol 9-ii, obtaining primary CO2 flash vapor and primary CO2 flash liquid 23; the upper part of the primary CO2 flash section is used to perform a second washing on the third stream of semi-lean methanol 27-iii and the primary CO2 flash vapor, obtaining primary washed CO2 flash vapor 15-i and primary CO2 washing liquid; wherein, the primary CO2 flash liquid 23 contains primary CO2 washing liquid.

[0119] According to the present invention, such as Figure 1 As shown, in the medium-pressure flash tower T-4, the middle part of the secondary CO2 flash section is used to perform secondary CO2 flash evaporation on the primary CO2 flash liquid 23 to obtain secondary CO2 flash vapor and secondary CO2 flash liquid 24; the upper part of the secondary CO2 flash section is used to perform a third wash on the fourth semi-lean methanol 27-iv and the secondary CO2 flash vapor to obtain secondary washed CO2 flash vapor 16-i and secondary CO2 wash liquid; wherein, the secondary CO2 flash liquid 24 contains the secondary CO2 wash liquid.

[0120] According to the present invention, such as Figure 1 As shown, in the medium-pressure flash tower T-4, the middle part of the first-stage H2S flash evaporation section is used to flash the first H2S-rich methanol 10 to obtain first-stage H2S flash vapor and first-stage H2S flash liquid 21; the upper part of the first-stage H2S flash evaporation section is used to wash the fourth non-conversion H2S-rich methanol 3-iv and the first-stage H2S flash vapor to obtain first-stage washed H2S flash vapor 15-ii and first-stage H2S washing liquid; wherein, the first-stage H2S flash liquid 21 contains the first-stage H2S washing liquid.

[0121] According to the present invention, such as Figure 1As shown, in the medium-pressure flash tower T-4, the middle part of the secondary H2S flash section is used to flash the primary H2S flash liquid 21 to obtain secondary H2S flash vapor and secondary H2S flash liquid 22; the upper part of the secondary H2S flash section is used to wash the fifth non-conversion H2S-rich methanol 3-v and the secondary H2S flash vapor to obtain secondary washed H2S flash vapor 16-ii and secondary H2S washing liquid; wherein, the secondary H2S flash liquid 22 contains secondary H2S washing liquid.

[0122] According to the present invention, such as Figure 1 As shown, in the reabsorption tower T-5, the first flash evaporation section is used to perform a first flash evaporation on the secondary CO2 flash liquid 24 to obtain semi-lean methanol 27 and a first CO2 product gas; the second flash evaporation section is used to perform a second flash evaporation on the fifth semi-lean methanol 27-v to obtain a flash liquid and a second CO2 product gas; the third flash evaporation section is used to perform a third flash evaporation on the secondary H2S flash liquid 22 to obtain a second H2S-rich methanol 26 and a sulfur-containing gas; wherein, the flash liquid and the sulfur-containing gas are contacted to obtain low-H2S methanol 28 and a third CO2 product gas; wherein, the first CO2 product gas, the second CO2 product gas and the third CO2 product gas are mixed to obtain CO2 product gas 25.

[0123] According to the present invention, such as Figure 1 As shown, in the reabsorption tower T-5, the stripping section is used to contact the second H2S-rich methanol 26, the third H2S-rich methanol 19, and the low H2S methanol 28 with nitrogen 18 and perform stripping to obtain stripped gas and stripped H2S-rich methanol 17; the washing section is used to perform a first washing on the first semi-lean methanol 27-i and the stripped gas to obtain the third H2S-rich methanol 19 and tail gas 20.

[0124] According to the present invention, preferably, such as Figure 1 As shown, the secondary purification section is connected to the primary purification section, the primary H2S absorption section, and the secondary H2S absorption section via pipelines, and is used to divide the non-conversion H2S-rich methanol into five streams. The first stream of non-conversion H2S-rich methanol 3-i, the second stream of non-conversion H2S-rich methanol 3-ii, and the third stream of non-conversion H2S-rich methanol 3-iii are returned to the primary purification, primary H2S absorption, and secondary H2S absorption, respectively.

[0125] According to the present invention, preferably, such as Figure 1 As shown, in accordance with the material flow direction, a first pump P-1 and a first cooler E-1 are sequentially installed on the pipeline connecting the primary CO2 absorption section and the secondary H2S absorption section. These are used to sequentially pressurize and cool the first stream of CO2-rich methanol 9-i before it undergoes the secondary H2S absorption.

[0126] According to the present invention, preferably, such as Figure 1 As shown, a second cooler E-2 is installed on the pipeline connecting the primary CO2 absorption section and the secondary CO2 absorption section according to the material flow direction. This cooler is used to cool the CO2-containing methanol 12 before it undergoes primary CO2 absorption.

[0127] According to the present invention, preferably, such as Figure 1 As shown, a third cooler E-3 is installed on the pipeline connecting the first-stage CO2 absorption section and the first-stage CO2 flash evaporation section. This cooler is used to cool the second stream of CO2-rich methanol 9-ii before it undergoes the first-stage CO2 flash evaporation.

[0128] According to the present invention, preferably, such as Figure 1 As shown, a second pump P-2 is installed on the pipeline connecting the first flash section to the secondary CO2 absorption section, the primary CO2 flash section and the secondary CO2 flash section. This pump is used to pressurize the second semi-lean methanol 27-ii, the third semi-lean methanol 27-iii and the fourth semi-lean methanol 27-iv respectively, and then perform secondary CO2 absorption, second washing and third washing respectively.

[0129] According to the present invention, preferably, such as Figure 1 As shown, a fourth cooler E-4 is installed on the pipeline connecting the secondary H2S flash section and the third flash section, which is used to cool the secondary H2S flash liquid 22 in the fourth way before performing the third flash evaporation.

[0130] According to the present invention, preferably, such as Figure 1 As shown, a first heat exchanger Q-1 is installed on the pipeline connecting the third flash section and the stripping section, which is used to strip the second H2S-rich methanol 26 after the first heat exchange.

[0131] According to the present invention, preferably, such as Figure 1 As shown, a second heat exchanger Q-2 is installed on the pipeline connecting the washing section and the stripping section, which is used to strip the third H2S-rich methanol 19 after passing through the second heat exchanger.

[0132] According to the present invention, preferably, such as Figure 1 As shown, a second heat exchanger Q-3 is installed on the pipeline connecting the second flash section and the stripping section, which is used to strip the low-H2S methanol 28 after the third heat exchange.

[0133] The present invention will be described in detail below through embodiments.

[0134] Example 1

[0135] The system includes: a non-shift gas scrubbing tower T-1, an H2S absorption tower T-2, a CO2 absorption tower T-3, a medium-pressure flash evaporator T-4, and a reabsorption tower T-5 connected together;

[0136] Among them, the non-shift gas scrubbing tower T-1 is divided into a primary purification section and a secondary purification section connected by air risers from bottom to top; the H2S absorption tower T-2 is divided into a primary H2S absorption section and a secondary H2S absorption section connected by air risers from bottom to top; the CO2 absorption tower T-3 is divided into a primary CO2 absorption section and a secondary CO2 absorption section connected by air risers from bottom to top; the medium-pressure flash evaporator T-4 is divided into a secondary CO2 flash evaporator section, a primary CO2 flash evaporator section, a secondary H2S flash evaporator section, and a primary H2S flash evaporator section from top to bottom; and the reabsorption tower T-5 is divided into a first flash evaporator section, a second flash evaporator section, a third flash evaporator section, a scrubbing section, and a stripping section from top to bottom.

[0137] The methods include:

[0138] Non-shift gas 1 (H2S molar content 0.9-1.2%, CO2 molar content 5-10%; temperature -35 to -25℃, pressure 5.5-6MPa(G)) from the upstream non-shift gas cooling process is sent to the primary purification section. It is purified with the first non-shift H2S-rich methanol 3-i at a molar flow ratio of 50-60:1 to obtain pre-purified non-shift H2S-rich methanol 4 (H2S molar content 2.1-2.6%, CO2 molar content 3-7%; temperature -33 to -27℃) which is then sent to the subsequent processes. The pre-purified non-shifted gas is processed and sent to the secondary purification section through the riser. It undergoes secondary purification with the first lean methanol 2-i from the subsequent process to obtain purified non-shifted gas 5 (H2S molar content ≤0.1ppm, CO2 molar content ≤20ppm; temperature -55 to -50℃, pressure 5.4-6MPa(G)) and non-shifted H2S-rich methanol 3 (H2S molar content 0.6-1.1%, CO2 molar content 4-9%; temperature -32 to -27℃; pressure 5.5-6MPa(G)).

[0139] Among them, the molar flow ratio of the first lean methanol 2-i and the non-conversion gas 1 is 1-1.1:1;

[0140] The above-mentioned non-conversion H2S-rich methanol 3 is divided into the first non-conversion H2S-rich methanol 3-i, the second non-conversion H2S-rich methanol 3-ii, the third non-conversion H2S-rich methanol 3-iii, the fourth non-conversion H2S-rich methanol 3-iv, and the fifth non-conversion H2S-rich methanol 3-v with a molar flow ratio of 1:5-7:38-42:9-11:9-11.

[0141] Syngas 6 (H2S molar content 0.9-1.2%, CO2 molar content 40-50%; temperature -15 to -5℃, pressure 5.3-5.7 MPa(G)) from the coal-water slurry gasification unit is sent to the primary H2S absorption section, where it contacts the second non-conversion H2S-rich methanol 3-ii at a molar flow ratio of 60-70:1 for primary H2S absorption, yielding the fourth H2S-rich methanol 7 (H2S molar content 2.4-2.9%, CO2 molar content 66-71%; temperature -9 to -5℃) which is then sent to subsequent processes. The resulting pre-desulfurized gas is also sent to the secondary H2S absorption section via a riser. The methanol is then contacted with a third non-conversion H2S-rich methanol 3-iii and a first CO2-rich methanol 9-i (which are sequentially pressurized to 5.8-6 MPa(G) by a first pump P-1 and cooled to -46 to -43°C by a first cooler E-1) and undergoes secondary H2S absorption to obtain a first H2S-rich methanol 10 (H2S molar content of 1.4-1.8%, CO2 molar content of 34-38%; temperature of -20 to -13°C) and desulfurized gas 11 (H2S molar content of 0.5-1 ppm, CO2 molar content of 37-41%; temperature of -20 to -13°C; pressure of 5.3-5.4 MPa(G)).

[0142] The molar flow ratio of the above-mentioned syngas 6 and the third non-conversion H2S-rich methanol 3-iii is 9-11:1; the molar flow ratio of the above-mentioned syngas 6 and the first CO2-rich methanol 9-i is 2-3:1.

[0143] The desulfurized gas 11 is sent to the primary CO2 absorption section, where it is contacted with CO2-containing methanol 12 (cooled to -36 to -33°C by the second cooler E-2) at a molar flow ratio of 1:1.1-1.5 for primary CO2 absorption, yielding CO2-rich methanol 9 (H2S molar content of 0.1-0.5 ppm, CO2 molar content of 29-34%, temperature of -10 to -6°C, pressure of 5.3-5.4 MPa(G)), which is then divided into fractions with a molar flow ratio of 1:2-3. The first CO2-rich methanol 9-i and the second CO2-rich methanol 9-ii, along with the resulting pre-purified gas, are sent to the secondary CO2 absorption section through the riser. They come into contact with the second semi-lean methanol 27-ii and the second lean methanol 2-ii and undergo secondary CO2 absorption to obtain purified gas 14 (H2S molar content ≤0.1ppm, CO2 molar content ≤20ppm; temperature -55 to -50℃, pressure 5.2-5.3MPa(G)) and the aforementioned CO2-containing methanol 12.

[0144] The molar flow ratio of the above-mentioned purified gas 14 and the second semi-lean methanol 27-ii is 1.4-1.6:1, and the molar flow ratio of the above-mentioned purified gas 14 and the second lean methanol 2-ii is 1:1-1.2.

[0145] The second CO2-rich methanol stream 9-ii is cooled to -36 to -33°C by the third cooler E-3, and then sent to the middle of the first-stage CO2 flash evaporation section for first-stage CO2 flash evaporation (pressure 3.5-3.7 MPa(G)) to obtain first-stage CO2 flash vapor. The resulting first-stage CO2 flash liquid 23 (H2S molar content 0.1-0.5 ppm, CO2 molar content 28.5-33.5%; temperature -38.5 to -34.5°C) is then sent through pipeline to the middle of the second-stage CO2 flash evaporation section for second-stage CO2 flash evaporation (pressure 1.6-2 MPa(G)) to obtain second-stage CO2 flash vapor and second-stage CO2 flash liquid 24 (H2S molar content 0.1-0.5 ppm, CO2 molar content 28-33%; temperature -40 to -35°C).

[0146] The first H2S-rich methanol 10 is sent to the middle section of the first-stage H2S flash evaporation for first-stage H2S flash evaporation (pressure 3.5-3.7 MPa(G)) to obtain first-stage H2S flash vapor and the resulting first-stage H2S flash liquid 21 (H2S molar content 1.4-1.9%, CO2 molar content 32-37%; temperature -10 to -6℃); the first-stage H2S flash liquid 21 is sent to the middle section of the second-stage H2S flash evaporation for second-stage H2S flash evaporation (pressure 1.6-2 MPa(G)) to obtain second-stage H2S flash vapor and second-stage H2S flash liquid 22 (H2S molar content 1.35-1.85%, CO2 molar content 31-35%; temperature -12 to -8℃);

[0147] The above-mentioned secondary CO2 flash liquid 24 is sent to the first flash section for first flash evaporation (pressure 0.05-0.08 MPa(G)) to obtain semi-lean methanol 27 (H2S molar content 0.1-0.5 ppm; CO2 molar content 20-24%, temperature -66 to -61℃; pressure 0.05-0.08 MPa(G)) and the first CO2 product gas;

[0148] Among them, the above-mentioned semi-lean methanol 27 is divided into the first semi-lean methanol 27-i, the second semi-lean methanol 27-ii, the third semi-lean methanol 27-iii, the fourth semi-lean methanol 27-iv and the fifth semi-lean methanol 27-v with a molar flow ratio of 14-16:13-15:1:1-2:7-9.

[0149] The fifth semi-lean methanol 27-v is sent to the second flash evaporation section for a second flash evaporation (pressure 0.06-0.09 MPa(G)) to obtain flash liquid and second CO2 product gas; the second-stage H2S flash liquid 22 (cooled to -34 to -30°C by the fourth cooler E-4) undergoes a third flash evaporation (pressure 0.12-0.16 MPa(G)) to obtain second H2S-rich methanol 26 (H2S molar content 1.2-1.6%, CO2 molar content 20-24%; temperature -66 to -62°C; pressure 0.13-0.17 MPa(G)) and... Sulfur gas; wherein, the above flash liquid and sulfur-containing gas are contacted to obtain low-H2S methanol 28 (H2S molar content of 0.6-0.9%, CO2 molar content of 19.5-23.5%; temperature of -63 to -57℃) and a third CO2 product gas; wherein, the above first CO2 product gas, second CO2 product gas and third CO2 product gas are mixed to obtain CO2 product gas 25 (H2S molar content ≤1ppm, CO2 molar content of 99.4-99.7%; temperature of -66 to -62℃, pressure of 0.05-0.08MPa(G));

[0150] Specifically, the aforementioned second H2S-rich methanol 26 (heated to -40 to -36°C via the first heat exchanger Q-1), third H2S-rich methanol 19 (heated to -40 to -36°C via the second heat exchanger Q-2), and low H2S methanol 28 (heated to -40 to -36°C via the third heat exchanger Q-3) are respectively sent to the stripping section, where they are sequentially contacted with nitrogen 18 and stripped to obtain stripped gas and stripped H2S-rich methanol 17 (H2S molar content 1-2%, CO2 molar content 1-2%). The content is 2-5%; the temperature is -52 to -48℃); the above stripped gas is sent to the washing section through the gas riser, and is washed with the first semi-lean methanol 27-i to obtain the above third H2S-rich methanol 19 (H2S molar content is 1-3%, CO2 molar content is 17-22%; temperature is -63 to -58℃) and tail gas 20 (H2S molar content ≤1ppm, CO2 molar content is 82-86%; temperature is -67 to -63℃);

[0151] Among them, the second semi-lean methanol 27-ii, the third semi-lean methanol 27-iii, and the fourth semi-lean methanol 27-iv are pressurized to 5.8-6 MPa(G) by the second pump P-2 and sent to the upper part of the secondary CO2 absorption section, the primary CO2 flash section, and the secondary CO2 flash section, respectively.

[0152] In this process, the third semi-lean methanol 27-iii and the first-stage CO2 flash vapor are subjected to a second wash to obtain the first-stage washed CO2 flash vapor 15-i (H2 molar content of 88-92%, CO2 molar content of 6-11%, temperature of -63 to -60℃, pressure of 3.5-3.7MPa(G)), and the obtained first-stage CO2 washing liquid is mixed into the above-mentioned first-stage CO2 flash vapor 23; the fourth semi-lean methanol 27-iv and the second-stage CO2 flash vapor are subjected to a third wash to obtain the second-stage washed CO2 flash vapor 16-i (H2 molar content of 82-87%, CO2 molar content of 12-16%, temperature of -65 to -62℃, pressure of 1.6-2MPa(G)), and the obtained second-stage CO2 washing liquid is mixed into the above-mentioned second-stage CO2 flash vapor 24;

[0153] Specifically, the fourth non-conversion H2S-rich methanol 3-iv and the first-stage H2S flash vapor are subjected to a fourth wash to obtain first-stage washed H2S flash vapor 15-ii (H2 molar content of 60-65%, CO2 molar content of 9-14%, temperature of -30 to -25℃, pressure of 3.5-3.7MPa(G)), and the obtained first-stage H2S washing liquid is mixed into the first-stage H2S flash vapor 21; the fifth non-conversion H2S-rich methanol 3-v and the second-stage H2S flash vapor are subjected to a fifth wash to obtain second-stage washed H2S flash vapor 16-ii (H2 molar content of 7-11%, CO2 molar content of 72-77%, temperature of -8 to -4℃, pressure of 1.6-2MPa(G)), and the obtained second-stage H2S washing liquid is mixed into the second-stage H2S flash vapor 22;

[0154] Specifically, the CO2 flash vapor 15-i and H2S flash vapor 15-ii after primary washing are mixed to obtain primary flash vapor 15; the CO2 flash vapor 16-i and H2S flash vapor 16-ii after secondary washing are mixed to obtain secondary flash vapor 16.

[0155] Comparative Example 1

[0156] Taking a hydrogen production unit that uses coal-water slurry gasification as an example, the effective gas (H2+CO) entering the low-temperature methanol washing unit is 230,000 Nm³. 3 / h, the main technical parameters of the process are compared with those of the lean-semi-lean process (i.e., a low-temperature methanol washing process disclosed in CN201110260570.0) under this benchmark, as shown in Table 1.

[0157] Table 1

[0158]

[0159] As can be seen from the results in Table 1, taking the hydrogen production unit based on coal-water slurry gasification as an example, the acid gas removal method of the coal-water slurry gasification unit provided in Example 1 has a lean methanol circulation rate of 88.9% in Comparative Example 1 (lean liquid-semi-lean liquid process), a semi-lean liquid methanol circulation rate of 93.3% in Comparative Example 1 (lean liquid-semi-lean liquid process), and a CO2-rich methanol usage in the H2S absorption tower of 84.2% in Comparative Example 1 (lean liquid-semi-lean liquid process). This results in a cumulative reduction of 500 KW / h in external cooling consumption, demonstrating a significant overall energy-saving effect.

[0160] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for removing acidic gases from a multi-generation coal-water slurry gasification unit, characterized in that, The method includes: The CO2-rich methanol (9) from the synthesis gas CO2 absorption process is divided into two streams. The first stream of CO2-rich methanol (9-i) is returned to the synthesis gas H2S absorption process, and the second stream of CO2-rich methanol (9-ii) is subjected to first-stage CO2 flash evaporation and second-stage CO2 flash evaporation in sequence to obtain first-stage CO2 flash vapor, second-stage CO2 flash vapor and second-stage CO2 flash liquid (24). The first H2S-rich methanol (10) from the syngas H2S absorption process is subjected to first-stage H2S flash evaporation and second-stage H2S flash evaporation to obtain first-stage H2S flash vapor, second-stage H2S flash vapor and second-stage H2S flash liquid (22). The secondary CO2 flash liquid (24) is subjected to a first flash evaporation, and the resulting semi-lean methanol (27) is divided into five streams. The fifth stream of semi-lean methanol (27-v) and the secondary H2S flash liquid (22) are subjected to a second flash evaporation and a third flash evaporation, respectively, to obtain low H2S methanol (28) and second rich H2S methanol (26). The third rich H2S methanol (19) is then contacted with nitrogen (18) and stripped. The stripped gas is then washed with the first stream of semi-lean methanol (27-i) to obtain the third rich H2S methanol (19). The process involves: returning the second semi-lean methanol stream (27-ii) to the syngas CO2 absorption process; performing a second wash on the third semi-lean methanol stream (27-iii) and the first-stage CO2 flash vapor; performing a third wash on the fourth semi-lean methanol stream (27-iv) and the second-stage CO2 flash vapor; dividing the non-conversion H2S-rich methanol (3) from the non-conversion gas purification process into five streams, with the first non-conversion H2S-rich methanol (3-i) returning to the non-conversion gas purification process, the second non-conversion H2S-rich methanol (3-ii) and the third non-conversion H2S-rich methanol (3-iii) both returning to the syngas H2S absorption process; performing a fourth wash on the fourth non-conversion H2S-rich methanol (3-iv) and the first-stage H2S flash vapor; and performing a fifth wash on the fifth non-conversion H2S-rich methanol (3-v) and the second-stage H2S flash vapor.

2. The method according to claim 1, wherein, The non-conversion gas purification process includes: subjecting the non-conversion gas (1) to primary purification and secondary purification in sequence to obtain the non-conversion H2S-rich methanol (3); Preferably, the first non-conversion H2S-rich methanol (3-i) is returned and subjected to the first-stage purification; More preferably, the non-conversion gas (1) and the first non-conversion H2S-rich methanol (3-i) are contacted and subjected to the first-stage purification to obtain pre-purified non-conversion H2S-rich methanol (4) and pre-purified non-conversion gas; the pre-purified non-conversion gas and the first lean methanol (2-i) are contacted and subjected to the second-stage purification to obtain non-conversion H2S-rich methanol (3) and purified non-conversion gas (5); The non-conversion H2S-rich methanol (3) is divided into five streams of non-conversion H2S-rich methanol (3-i), non-conversion H2S-rich methanol (3-ii), non-conversion H2S-rich methanol (3-iii), non-conversion H2S-rich methanol (3-iv), and non-conversion H2S-rich methanol (3-v) with a molar flow ratio of 1:5-7:38-42:9-11:9-11. Preferably, the non-conversion H2S-rich methanol (3) has a molar content of 0.6-1.1% for H2S and a molar content of 4-9% for CO2; a temperature of -32 to -27°C; and a pressure of 5.5-6 MPa (G).

3. The method according to claim 2, wherein, The syngas H2S absorption process includes: sequentially subjecting the syngas (6) from the coal-water slurry gasification unit to primary H2S absorption and secondary H2S absorption to obtain desulfurized gas (11); Preferably, the second non-conversion H2S-rich methanol (3-ii) is returned and subjected to the first-stage H2S absorption; the third non-conversion H2S-rich methanol (3-iii) and the first CO2-rich methanol (9-i) are each independently returned and subjected to the second-stage H2S absorption. More preferably, the synthesis gas (6) and the second non-conversion H2S-rich methanol (3-ii) are contacted and subjected to the first-stage H2S absorption to obtain the fourth H2S-rich methanol (7) and pre-desulfurized gas; the pre-desulfurized gas, the third non-conversion H2S-rich methanol (3-iii) and the first CO2-rich methanol (9-i) are contacted and subjected to the second-stage H2S absorption to obtain the first H2S-rich methanol (10) and desulfurized gas (11); Preferably, the molar content of H2S in the first H2S-rich methanol (10) is 1.4-1.8%, the molar content of CO2 is 34-38%, and the temperature is -20 to -13°C; Preferably, the desulfurization gas (11) has a molar content of H2S of 0.5-1 ppm and a molar content of CO2 of 37-41%; a temperature of -20 to -13°C; and a pressure of 5.3-5.4 MPa(G). Preferably, in accordance with the material flow direction, the first stream of CO2-rich methanol (9-i) is sequentially pressurized to 5.8-6 MPa (G) and cooled to -46 to -43°C before undergoing the secondary H2S absorption; Preferably, the synthesis gas CO2 absorption process includes: sequentially performing primary CO2 absorption and secondary CO2 absorption on the desulfurized gas (11) from the synthesis gas H2S absorption process to obtain purified gas (14); More preferably, the second semi-lean methanol stream (27-ii) is returned and subjected to the secondary CO2 absorption; More preferably, the desulfurized gas (11) and CO2-containing methanol (12) are subjected to the first-stage CO2 absorption to obtain the CO2-rich methanol (9) and pre-purified gas; the pre-purified gas, the second semi-lean methanol (27-ii) and the second lean methanol (2-ii) are subjected to the second-stage CO2 absorption to obtain the purified gas (14) and CO2-containing methanol (12); Preferably, the molar content of H2S in the CO2-rich methanol (9) is 0.1-0.5 ppm, the molar content of CO2 is 29-34%, the temperature is -10 to -6℃, and the pressure is 5.3-5.4 MPa(G); Preferably, the CO2-rich methanol (9) is divided into a first CO2-rich methanol (9-i) and a second CO2-rich methanol (9-ii) with a molar flow ratio of 1:2-3; More preferably, the CO2-containing methanol (12) is subjected to a second cooling to -36 to -33°C before the first-stage CO2 absorption is performed.

4. The method according to any one of claims 1-3, wherein, The pressure of the first-stage CO2 flash evaporation is 3.5-3.7 MPa(G); the pressure of the second-stage CO2 flash evaporation is 1.6-2 MPa(G); Preferably, the second stream of CO2-rich methanol (9-ii) is subjected to the first-stage CO2 flash evaporation to obtain the first-stage CO2 flash vapor and the first-stage CO2 flash liquid (23); the first-stage CO2 flash liquid (23) is subjected to the second-stage CO2 flash evaporation to obtain the second-stage CO2 flash vapor and the second-stage CO2 flash liquid (24); Preferably, the molar content of H2S in the primary CO2 flash liquid (23) is 0.1-0.5 ppm, the molar content of CO2 is 28.5-33.5%, and the temperature is -38.5 to -34.5℃. Preferably, the molar content of H2S in the secondary CO2 flash liquid (24) is 0.1-0.5 ppm, the molar content of CO2 is 28-33%, and the temperature is -40 to -35°C. More preferably, the second CO2-rich methanol (9-ii) is cooled to -36 to -33°C in a third step before undergoing the first-stage CO2 flash evaporation.

5. The method according to any one of claims 1-4, wherein, The pressure of the first-stage H2S flash evaporation is 3.5-3.7 MPa(G); the pressure of the second-stage H2S flash evaporation is 1.6-2 MPa(G); Preferably, the first H2S-rich methanol (10) is subjected to the first-stage H2S flash evaporation to obtain the first-stage H2S flash vapor and the first-stage H2S flash liquid (21); the first-stage H2S flash liquid (21) is subjected to the second-stage H2S flash evaporation to obtain the second-stage H2S flash vapor and the second-stage H2S flash liquid (22). Preferably, the molar content of H2S in the primary H2S flash liquid (21) is 1.4-1.9%, the molar content of CO2 is 32-37%, and the temperature is -10 to -6℃. Preferably, the molar content of H2S in the secondary H2S flash liquid (22) is 1.35-1.85%, the molar content of CO2 is 31-35%, and the temperature is -12 to -8℃.

6. The method according to any one of claims 1-5, wherein, The semi-lean methanol (27) contains 0.1-0.5 ppm H2S, 20-24% CO2, at a temperature of -66 to -61°C, and at a pressure of 0.05-0.08 MPa(G). Preferably, the semi-lean methanol (27) is divided into a first semi-lean methanol (27-i), a second semi-lean methanol (27-ii), a third semi-lean methanol (27-iii), a fourth semi-lean methanol (27-iv), and a fifth semi-lean methanol (27-v) with a molar flow ratio of 14-16:13-15:1:1-2:7-9. More preferably, the second semi-lean methanol stream (27-ii), the third semi-lean methanol stream (27-iii), and the fourth semi-lean methanol stream (27-iv) are respectively pressurized to 5.8-6 MPa(G) and returned to the secondary CO2 absorption, the second washing, and the third washing, respectively; Preferably, the fifth semi-lean methanol (27-v) is subjected to the second flash evaporation to obtain a flash liquid and a second CO2 product gas; the secondary H2S flash liquid (22) is subjected to the third flash evaporation to obtain a second H2S-rich methanol (26) and a sulfur-containing gas; the flash liquid and the sulfur-containing gas are contacted to obtain the low-H2S methanol (28) and a third CO2 product gas; wherein the second CO2 product gas and the third CO2 product gas are mixed with the first CO2 product gas obtained from the first flash evaporation to obtain CO2 product gas (25); More preferably, the secondary H2S flash liquid (22) is cooled to -34 to -30°C in the fourth stage before the third flash evaporation is performed; Preferably, the low-H2S methanol (28) has a molar content of H2S of 0.6-0.9% and a molar content of CO2 of 19.5-23.5%; a temperature of -63 to -57°C and a pressure of 0.12-0.16 MPa(G); Preferably, the second H2S-rich methanol (26) has a molar content of 1.2-1.6% for H2S, a molar content of 20-24% for CO2, a temperature of -66 to -62°C, and a pressure of 0.13-0.17 MPa(G). Preferably, the molar content of H2S in the CO2 product gas (25) is ≤1ppm, the molar content of CO2 is 99.4-99.7%, the temperature is -66 to -62℃, and the pressure is 0.05-0.08MPa(G).

7. The method according to any one of claims 1-6, wherein, The gas stripping process includes: sequentially contacting the second H2S-rich methanol (26), the third H2S-rich methanol (19), and the low H2S methanol (28) with nitrogen (18) and performing the gas stripping to obtain stripped gas and stripped H2S-rich methanol (17). Preferably, the molar content of H2S in the stripped H2S-rich methanol (17) is 1-2%, and the molar content of CO2 is 2-5%; the temperature is -52 to -48°C. Preferably, the second H2S-rich methanol (26) is subjected to a first heat exchange to a temperature of -40 to -36°C before the gas stripping is performed; Preferably, the third H2S-rich methanol (19) is subjected to a second heat exchange to a temperature of -40 to -36°C before the gas stripping is performed; Preferably, the low-H2S methanol (28) is subjected to a third heat exchange to a temperature of -40 to -36°C before the gas stripping is performed; Preferably, the stripping gas is subjected to the first washing with the first semi-lean methanol (27-i) to obtain the third H2S-rich methanol (19) and tail gas (20); Preferably, the molar content of H2S in the third H2S-rich methanol (19) is 1-3%, the molar content of CO2 is 17-22%, and the temperature is -63 to -58°C.

8. The method according to any one of claims 1-7, wherein, The second washing process includes: performing the second washing with a third semi-lean methanol stream (27-iii) and a first-stage CO2 flash vapor to obtain a first-stage washed CO2 flash vapor (15-i) and a first-stage CO2 washing liquid; the third washing process includes: performing the third washing with a fourth semi-lean methanol stream (27-iv) and a second-stage CO2 flash vapor to obtain a second-stage washed CO2 flash vapor (16-i) and a second-stage CO2 washing liquid; The primary CO2 washing liquid is mixed with the primary CO2 flash liquid (23); the secondary CO2 washing liquid is mixed with the secondary CO2 flash liquid (24); Preferably, the fourth washing process includes: performing the fourth washing with a fourth stream of non-conversion H2S-rich methanol (3-iv) and primary H2S flash vapor to obtain primary-washed H2S flash vapor (15-ii) and primary H2S washing liquid; the fifth washing process includes: performing the fifth washing with a fifth stream of non-conversion H2S-rich methanol (3-v) and secondary H2S flash vapor to obtain secondary-washed H2S flash vapor (16-ii) and secondary H2S washing liquid; The primary H2S washing liquid is mixed with the primary H2S flash liquid (21); the secondary H2S washing liquid is mixed with the secondary H2S flash liquid (22).

9. A multi-generation acid gas removal system for a coal-water slurry gasification unit, characterized in that, The system includes: a non-shift gas scrubbing tower (T-1), an H2S absorption tower (T-2), a CO2 absorption tower (T-3), a medium-pressure flash tower (T-4), and a reabsorption tower (T-5) connected together; wherein, the medium-pressure flash tower (T-4) is divided into a two-stage CO2 flash section, a one-stage CO2 flash section, a two-stage H2S flash section, and a one-stage H2S flash section from top to bottom; the reabsorption tower (T-5) is divided into a first flash section, a second flash section, a third flash section, a scrubbing section, and a gas stripping section from top to bottom; The H2S absorption tower (T-2) is used for the H2S absorption process of syngas. The first H2S-rich methanol (10) obtained is sent to the first-stage H2S flash evaporation section for first-stage H2S flash evaporation to obtain first-stage H2S flash vapor and first-stage H2S flash liquid (21). The second-stage H2S flash evaporation section is connected to the bottom of the first-stage H2S flash evaporation section and is used to perform second-stage H2S flash evaporation on the first-stage H2S flash liquid (21) to obtain second-stage H2S flash vapor and second-stage H2S flash liquid (22). The CO2 absorption tower (T-3) is used for the synthesis gas CO2 absorption process. The resulting CO2-rich methanol (9) is divided into two streams. The first stream of CO2-rich methanol (9-i) is returned to the H2S absorption tower (T-2), and the second stream of CO2-rich methanol (9-ii) is sent to the lower part of the primary CO2 flash section for primary CO2 flash evaporation to obtain primary CO2 flash vapor and primary CO2 flash liquid (23). The secondary CO2 flash section is connected to the bottom of the primary CO2 flash section and is used to perform secondary CO2 flash evaporation on the primary CO2 flash liquid (23) to obtain secondary CO2 flash liquid (24) and secondary CO2 flash vapor. The first flash section, the second flash section and the third flash section are connected by a gas riser. The first flash section is used to perform the first flash evaporation of the secondary CO2 flash liquid (24). The resulting semi-lean methanol (27) is divided into five streams. The fifth stream of semi-lean methanol (27-v) and the secondary H2S flash liquid (22) are sent to the second flash section and the third flash section respectively for the second flash evaporation and the third flash evaporation to obtain low H2S methanol (28) and second rich H2S methanol (26). The washing section and the stripping section are connected by a gas lift hole. The stripping section is connected to the lower part of the second flash section, the third flash section and the washing section. It is used to contact the low H2S methanol (28), the second H2S rich methanol (26) and the third H2S rich methanol (19) with nitrogen (18) and perform stripping. The stripped gas is sent to the washing section and is washed with the first semi-lean methanol (27-i) to obtain the third H2S rich methanol (19). Specifically, the second semi-lean methanol stream (27-ii) is returned to the CO2 absorption tower (T-3); the third semi-lean methanol stream (27-iii) is sent to the upper part of the primary CO2 flash evaporation section for a second wash with the primary CO2 flash vapor; and the fourth semi-lean methanol stream (27-iv) is sent to the upper part of the secondary CO2 flash evaporation section for a third wash with the secondary CO2 flash vapor. The non-shift gas scrubbing tower (T-1) is used for non-shift gas purification process. The obtained non-shift H2S-rich methanol (3) is divided into five streams. The first stream of non-shift H2S-rich methanol (3-i) is returned to the non-shift gas scrubbing tower (T-1). The second stream of non-shift H2S-rich methanol (3-ii) and the third stream of non-shift H2S-rich methanol (3-iii) are returned to the H2S absorption tower (T-2). The fourth stream of non-shift H2S-rich methanol (3-iv) is sent to the upper part of the first-stage H2S flash evaporation section for fourth washing with the first-stage H2S flash vapor. The fifth stream of non-shift H2S-rich methanol (3-v) is sent to the upper part of the second-stage H2S flash evaporation section for fifth washing with the second-stage H2S flash vapor.

10. The system according to claim 9, wherein, The non-shift gas scrubbing tower (T-1) is divided into a primary purification section and a secondary purification section connected by air risers from bottom to top; The H2S absorption tower (T-2) is divided into a primary H2S absorption section and a secondary H2S absorption section connected by air risers from bottom to top. The CO2 absorption tower (T-3) is divided into a primary CO2 absorption section and a secondary CO2 absorption section connected by air risers from bottom to top; Preferably, the secondary purification section is connected to the primary purification section, the primary H2S absorption section, and the secondary H2S absorption section via pipelines. Preferably, a first pump (P-1) and a first cooler (E-1) are sequentially installed on the pipeline connecting the primary CO2 absorption section and the secondary H2S absorption section, according to the material flow direction; Preferably, a second cooler (E-2) is installed on the pipeline connecting the primary CO2 absorption section and the secondary CO2 absorption section, according to the material flow direction; Preferably, a third cooler (E-3) is provided on the pipeline connecting the primary CO2 absorption section and the primary CO2 flash section; Preferably, a second pump (P-2) is installed on the pipeline connecting the first flash section to the secondary CO2 absorption section, the primary CO2 flash section and the secondary CO2 flash section; Preferably, a fourth cooler (E-4) is provided on the pipe connecting the secondary H2S flash section and the third flash section; Preferably, a first heat exchanger (Q-1) is installed on the pipeline connecting the third flash section and the stripping section; Preferably, a second heat exchanger (Q-2) is installed on the pipe connecting the washing section and the air-lift section; Preferably, a third heat exchanger (Q-3) is provided on the pipe connecting the second flash section and the stripping section.

Images