Poly-generation acid gas removal method and device 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 device matched with the coal water slurry gasification device. The method has the characteristics of classified flash evaporation, series washing and secondary full utilization of washing liquid by optimally setting a medium-pressure flash evaporation process; the reabsorption process is optimized, low-sulfur methanol is generated and reutilized, and the low-temperature methanol washing device has the characteristic of low comprehensive energy consumption; by optimizing the gas stripping process, the semi-barren solution methanol, the first H2S-rich methanol and the low-sulfur methanol perform series absorption on the gas stripping gas generated by gas stripping, and the method has the characteristic of low comprehensive energy consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-temperature methanol washing, in particular to a multi-production acid gas removal method matched with a coal water slurry gasification device and a multi-production acid gas removal device matched with a coal water slurry gasification device. BACKGROUND

[0002] H2 and CO in the synthesis gas produced by the coal water slurry gasification technology are called effective gas, and the synthesis gas also contains a large amount of CO2 and a small amount of H2S, COS, NH3, HCN and other components. The acid gas H2S is generally a poison of the synthesis catalyst, so it must be removed before the synthesis process.

[0003] The low-temperature methanol washing process is the mainstream process technology matched with the coal water slurry gasification for removing acid gas. In the low-temperature methanol washing process, the CO2-rich methanol can be recycled by pressure reduction flash evaporation, but the H2S-containing methanol must be recycled by heat regeneration, which is the main source of energy consumption of the low-temperature methanol washing. Therefore, reducing the total amount of H2S-containing methanol and strengthening the use efficiency of H2S-containing methanol is the key to technical innovation. Specifically, it is to achieve the upper limit of the absorption of H2S gas in the synthesis gas before the heat regeneration of the H2S-containing methanol, so as to improve the concentration of H2S in the H2S-rich methanol and reduce the total amount of H2S-rich methanol and the subsequent heat regeneration amount. At the same time, the setting of the medium-pressure flash evaporation process is also particularly important, which not only ensures the recovery of effective gas with less compression work, but also ensures that the washing liquid of the flash evaporation gas has the least influence on the flashed liquid, and also ensures that the washing liquid can be used twice to reduce the comprehensive energy consumption of the low-temperature methanol washing. SUMMARY

[0004] The present application aims to overcome the problems of low use efficiency of non-shift CO2-rich methanol and H2S-rich methanol after non-shift gas purification and unreasonable setting of the medium-pressure flash evaporation process in the existing multi-production low-temperature methanol washing technology, and provides a multi-production acid gas removal method matched with a coal water slurry gasification device and a multi-production acid gas removal device matched with a coal water slurry gasification device. The method has the characteristics of classified flash evaporation, series washing and twice full use of the washing liquid by optimizing the setting of the medium-pressure flash evaporation process. The method has the characteristics of low comprehensive energy consumption of the low-temperature methanol washing device by optimizing the setting of the reabsorption process to generate low-sulfur methanol and perform secondary use. The method has the characteristics of low comprehensive energy consumption by optimizing the setting of the gas stripping process to perform series absorption of the gas stripping gas generated by the gas stripping by the semi-lean liquid methanol, the first H2S-rich methanol and the low-sulfur methanol.

[0005] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a multi-production acid gas removal method matched with a coal water slurry gasification device, which comprises:

[0006] (1) the synthesis gas is subjected to two-stage H2S absorption to obtain primary H2S-rich methanol, secondary H2S-rich methanol and desulfurized gas; the desulfurized gas is subjected to three-stage CO2 absorption to obtain primary CO2-rich methanol, secondary CO2-rich methanol in two streams, tertiary CO2-rich methanol and purified gas; wherein the non-shift H2S-rich methanol in three streams and the non-shift CO2-rich methanol in two streams from a non-shift gas purification process are obtained;

[0007] (2) the first stream of secondary CO2-rich methanol is subjected to CO2 flashing to obtain CO2 flashing liquid and CO2 flashing gas; the secondary H2S-rich methanol and the third stream of non-shift H2S-rich methanol are subjected to H2S flashing respectively to obtain H2S flashing liquid and H2S flashing gas;

[0008] (3) the CO2 flashing liquid is subjected to first flashing to obtain semi-lean liquid methanol in three streams; the second stream of semi-lean liquid methanol and the H2S flashing liquid are subjected to second flashing and third flashing respectively to obtain low-sulfur methanol and first H2S-rich methanol;

[0009] (4) the first H2S-rich methanol, the low-sulfur methanol and the second H2S-rich methanol are subjected to gas stripping respectively to obtain gas stripping gas; the gas stripping gas and the third stream of semi-lean liquid methanol are subjected to first washing to obtain the second H2S-rich methanol;

[0010] wherein the first stream of semi-lean liquid methanol is divided into a stream of semi-lean liquid methanol and a stream of semi-lean liquid methanol; the stream of semi-lean liquid methanol and the CO2 flashing gas are subjected to second washing and then subjected to third washing with the H2S flashing gas to obtain low-sulfur carbon-rich methanol;

[0011] wherein the first stream of non-shift H2S-rich methanol, the primary CO2-rich methanol and the low-sulfur carbon-rich methanol are returned to the two-stage H2S absorption respectively; the second stream of non-shift H2S-rich methanol and the second stream of non-shift CO2-rich methanol are returned to the non-shift gas purification process respectively; the second stream of secondary CO2-rich methanol, the tertiary CO2-rich methanol, the first stream of non-shift CO2-rich methanol and the a stream of semi-lean liquid methanol are returned to the three-stage CO2 absorption respectively.

[0012] The second aspect of the present application provides a multi-production acid gas removal device matched with a coal water slurry gasification device, wherein the device comprises a non-shift gas purification tower, an H2S absorption tower, a CO2 absorption tower, a CO2 medium-pressure flashing tower, an H2S medium-pressure flashing tower and a reabsorption tower connected;

[0013] The non-reforming gas purification tower is used for three-stage purification of non-reforming gas, to obtain pre-purified non-reforming H2S-rich methanol, three streams of non-reforming H2S-rich methanol, two streams of non-reforming CO2-rich methanol and purified non-reforming gas; the H2S absorption tower is used for two-stage H2S absorption of synthesis gas, to obtain first-stage H2S-rich methanol, second-stage H2S-rich methanol and desulfurized gas; the CO2 absorption tower is used for three-stage CO2 absorption of the desulfurized gas, to obtain first-stage CO2-rich methanol, two streams of second-stage CO2-rich methanol, third-stage CO2-rich methanol and purified gas;

[0014] The CO2 medium-pressure flash tower comprises a CO2 flash section arranged at the lower part and a CO2 washing section arranged at the upper part, and the CO2 flash section is used for CO2 flash of the first stream of second-stage CO2-rich methanol, to obtain CO2 flash liquid and CO2 flash gas; the H2S medium-pressure flash tower comprises an H2S flash section arranged at the lower part and an H2S washing section arranged at the upper part, and the H2S flash section is used for H2S flash of the second-stage H2S-rich methanol and the third stream of non-reforming H2S-rich methanol, respectively, to obtain H2S flash liquid and H2S flash gas;

[0015] The reabsorption tower comprises an upper tower and a lower tower, wherein the upper tower is divided into a first flash section, a second flash section and a third flash section from top to bottom, and is used for first flash, second flash and third flash of the CO2 flash liquid, the second stream of semi-lean liquid methanol and the H2S flash liquid, respectively, to obtain three streams of semi-lean liquid methanol, low-sulfur methanol and first H2S-rich methanol; the lower tower is divided into a washing section and a gas stripping section from top to bottom, and the gas stripping section is used for gas stripping of the first H2S-rich methanol, the low-sulfur methanol and the second H2S-rich methanol, respectively, to obtain gas stripping gas which is sent to the washing section through a rising hole, and the third stream of semi-lean liquid methanol is subjected to first washing to obtain the second H2S-rich methanol;

[0016] The first stream of semi-lean liquid methanol is divided into a stream of semi-lean liquid methanol and a stream of semi-lean liquid methanol, which are sent to the CO2 absorption tower and the CO2 washing section, respectively; the CO2 washing section is used for second washing of the stream of semi-lean liquid methanol and the CO2 flash gas, and the obtained post-washing CO2-rich methanol is sent to the H2S washing section, and the H2S flash gas is subjected to third washing to obtain low-sulfur carbon-rich methanol which is returned to the H2S absorption tower;

[0017] The first stream of non-reforming H2S-rich methanol and the first-stage CO2-rich methanol are returned to the H2S absorption tower, respectively; the second stream of non-reforming H2S-rich methanol and the second stream of non-reforming CO2-rich methanol are returned to the non-reforming gas purification tower, respectively; the second stream of second-stage CO2-rich methanol, the third-stage CO2-rich methanol and the first stream of non-reforming CO2-rich methanol are returned to the CO2 absorption tower, respectively.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] (1) the method provided by the application optimizes the medium-pressure flash process, absorbs CO2 flash gas by introducing semi-lean liquid methanol, and obtains washed CO2-rich methanol which is used to absorb H2S flash gas in series, compared with the prior art, the first secondary CO2-rich methanol and the secondary H2S-rich methanol are respectively flashed and washed in series, and the generated low-sulfur carbon-rich methanol is returned to the two-stage H2S absorption, which is beneficial to reducing the energy consumption of the device;

[0020] (2) the method provided by the application divides the non-shift H2S-rich methanol from the non-shift gas purification process into three streams, wherein the first non-shift H2S-rich methanol and the second non-shift H2S-rich methanol are used for pretreating the synthesis gas and the non-shift gas respectively, under the premise of obtaining the same washing effect, the use amount of the first CO2-rich methanol is reduced, which is positive for reducing the energy consumption of the low-temperature methanol washing device;

[0021] (3) the method provided by the application optimizes the reabsorption process, realizes the absorption of the sulfur-containing gas generated by the flash of the H2S flash liquid by the flash liquid of the second semi-lean liquid methanol, and does not mix with the first H2S-rich methanol after flashing;

[0022] (4) the method provided by the application adopts a three-stage tail gas washing technology, selectively sets three streams of methanol with different H2S contents according to the different H2S contents in the tail gas, and sequentially washes from high to low, so as to use the least semi-lean liquid methanol under the premise of ensuring that the tail gas emission meets the standard, thereby reducing the heat regeneration energy consumption of the whole low-temperature methanol washing. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The application provides a structure schematic diagram of a multi-cogeneration acid gas removal device matched with a coal water slurry gasification device.

[0024] BRIEF DESCRIPTION OF DRAWINGS

[0025] T-1, non-shift gas purification tower; T-2, H2S absorption tower; T-3, CO2 absorption tower; T-4, CO2 medium-pressure flash tower; T-5, H2S medium-pressure flash tower; T-6, reabsorption tower;

[0026] E-1, first cooler; E-2, second cooler; E-3, third cooler; E-4, fourth cooler; E-5, fifth cooler; P-1, first pump; P-2, second pump; P-3, third pump; Q-1, first heat exchanger; Q-2, second heat exchanger;

[0027] 1. non-shifted gas; 2. non-shifted H2S rich methanol; 2-i. first stream of non-shifted H2S rich methanol; 2-ii. second stream of non-shifted H2S rich methanol; 2-iii. third stream of non-shifted H2S rich methanol; 3. lean methanol; 3-i. first stream of lean methanol; 3-ii. second stream of lean methanol; 4. pre-purified non-shifted H2S rich methanol; 5. purified non-shifted gas; 6. synthesis gas; 7. primary H2S rich methanol; 8. non-shifted CO2 rich methanol; 8-i. first stream of non-shifted CO2 rich methanol; 8-ii. second stream of non-shifted CO2 rich methanol; 9. primary CO2 rich methanol; 10. secondary H2S rich methanol; 11. sweetened gas; 12. secondary CO2 rich methanol; 12-i. first stream of secondary CO2 rich methanol; 12-ii. second stream of secondary CO2 rich methanol; 13. semi-lean liquid methanol; 13-i. first stream of semi-lean liquid methanol; 13-i-a. a stream of semi-lean liquid methanol; 13-i-b. b stream of semi-lean liquid methanol; 13-ii. second stream of semi-lean liquid methanol; 13-iii. third stream of semi-lean liquid methanol; 14. purified gas; 15. tail gas; 16. second H2S rich methanol; 17. H2S rich methanol after gas stripping; 18. H2S flash gas after washing; 19. H2S flash liquid; 20. first H2S rich methanol; 21. low sulfur methanol; 22. CO2 product gas; 23. CO2 flash gas after washing; 24. CO2 flash liquid; 25. low sulfur carbon rich methanol; 26. nitrogen gas; 27. CO2 rich methanol after washing; 28. tertiary CO2 rich methanol. DETAILED DESCRIPTION

[0028] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as implicitly split by the language of the specification. The described ranges should be construed as being encompassing both the specific values recited and values close thereto. For values which are less than one, one of ordinary skill in the art will appreciate that the value is intended to mean less than one unit, and that the specific value represents the exact point. For values which are greater than one, one of ordinary skill in the art will contemplate that the value is intended to mean greater than one unit, and that the specific value represents the exact point.

[0029] In the present invention, unless otherwise specifically indicated, "first", "second", "third", "fourth" and "fifth" do not indicate that a sequence or order of importance, but are used only to distinguish or refer back to a step or material.

[0030] In the present invention, unless otherwise specifically indicated, "top" of a vessel refers to 0-10% of the height of the vessel from top to bottom; "upper" of a vessel refers to 10-40% of the height of the vessel from top to bottom; "middle" of a vessel refers to 40-60% of the height of the vessel from top to bottom; "lower" of a vessel refers to 60-90% of the height of the vessel from top to bottom; and "bottom" of a vessel refers to 90-100% of the height of the vessel from top to bottom.

[0031] The application provides a method for removing acid gas in a multiple production system matched with a coal water slurry gasification device.

[0032] (1) performing two-stage H2S absorption on the synthesis gas to obtain first-stage H2S-rich methanol, second-stage H2S-rich methanol and desulfurized gas; performing three-stage CO2 absorption on the desulfurized gas to obtain first-stage CO2-rich methanol, second-stage CO2-rich methanol in two groups, third-stage CO2-rich methanol and purified gas; wherein non-shift H2S-rich methanol in three groups and non-shift CO2-rich methanol in two groups from a non-shift gas purification process are obtained;

[0033] (2) performing CO2 flashing on the first group of second-stage CO2-rich methanol to obtain CO2 flashing liquid and CO2 flashing gas; performing H2S flashing on the second-stage H2S-rich methanol and the third group of non-shift H2S-rich methanol respectively to obtain H2S flashing liquid and H2S flashing gas;

[0034] (3) performing first flashing on the CO2 flashing liquid to obtain semi-lean liquid methanol in three groups; performing second flashing and third flashing on the second group of semi-lean liquid methanol and the H2S flashing liquid respectively to obtain low-sulfur methanol and first H2S-rich methanol;

[0035] (4) performing gas stripping on the first H2S-rich methanol, the low-sulfur methanol and the second H2S-rich methanol respectively to obtain gas stripping gas; and performing first washing on the third group of semi-lean liquid methanol with the gas stripping gas to obtain the second H2S-rich methanol;

[0036] wherein the first group of semi-lean liquid methanol is divided into a group of semi-lean liquid methanol and a group of semi-lean liquid methanol; the group of semi-lean liquid methanol and the CO2 flashing gas are subjected to second washing, and then the third washing with the H2S flashing gas to obtain low-sulfur carbon-rich methanol;

[0037] wherein the first group of non-shift H2S-rich methanol, the first-stage CO2-rich methanol and the low-sulfur carbon-rich methanol are returned to the two-stage H2S absorption respectively; the second group of non-shift H2S-rich methanol and the second group of non-shift CO2-rich methanol are returned to the non-shift gas purification process respectively; the second group of second-stage CO2-rich methanol, the third-stage CO2-rich methanol, the first group of non-shift CO2-rich methanol and the a group of semi-lean liquid methanol are returned to the three-stage CO2 absorption respectively.

[0038] In the application, the synthesis gas and the non-shift gas are both from the coal water slurry gasification device without special conditions.

[0039] In the present application, preferably, the mole content of H2S in the synthesis gas is 0.9-1.2%, the mole content of CO2 is 40-50%; the temperature is -15 to -5℃, and the pressure is 5.4-5.6 MPa(G); the mole content of H2S in the non-shift gas is 0.9-1.2%, the mole content of CO2 is 5-10%; the temperature is -35 to -25℃, and the pressure is 5.6-6 MPa(G).

[0040] In some embodiments of the present application, preferably, the non-shift gas purification process comprises: performing three-stage purification on the non-shift gas to obtain pre-purified non-shift H2S-rich methanol, non-shift H2S-rich methanol, non-shift CO2-rich methanol, and purified non-shift gas.

[0041] In some embodiments of the present application, preferably, the three-stage purification comprises: first purification, second purification, and third purification; wherein the second stream of non-shift H2S-rich methanol returns to the first purification; and the second stream of non-shift CO2-rich methanol returns to the second purification.

[0042] In the present application, the first purification aims to remove HCN, NH3, and other impurities, as well as a small amount of H2S and CO2, in the non-shift gas; the second purification aims to further remove H2S in the non-shift gas; and the third purification aims to further remove CO2 in the non-shift gas.

[0043] In some embodiments of the present application, further preferably, the non-shift gas and the second stream of non-shift H2S-rich methanol are contacted and subjected to the first purification to obtain the pre-purified non-shift H2S-rich methanol and pre-desulfurized non-shift gas; the pre-desulfurized non-shift gas and the second stream of non-shift CO2-rich methanol are contacted and subjected to the second purification to obtain the non-shift H2S-rich methanol and desulfurized non-shift gas; and the desulfurized non-shift gas and the first stream of methanol-lean are contacted and subjected to the third purification to obtain the non-shift CO2-rich methanol and purified non-shift gas.

[0044] In the present application, preferably, the mole flow ratio of the non-shift gas to the second stream of non-shift H2S-rich methanol is 52-62:1; the mole content of H2S in the pre-purified non-shift H2S-rich methanol is 2.1-2.6%, and the mole content of CO2 is 3-7%, which is sent to subsequent processes.

[0045] In the present application, preferably, the mole flow ratio of the second stream of non-shift CO2-rich methanol to the non-shift gas is 1:1-2.

[0046] In some embodiments of the present application, preferably, the non-shift H2S-rich methanol has a H2S molar content of 1.2-1.6%, a CO2 molar content of 4-9%; a temperature of -30 to -26℃; and a pressure of 5.6-6 MPa(G).

[0047] In the present application, the non-shift H2S-rich methanol is divided into three streams, the first stream is subjected to the first H2S absorption, the second stream is subjected to the first purification, and the third stream is subjected to the H2S flashing. Further preferably, the molar flow ratio of the first stream of non-shift H2S-rich methanol, the second stream of non-shift H2S-rich methanol, and the third stream of non-shift H2S-rich methanol is 5-7:1:32-35.

[0048] In the present application, preferably, the molar flow ratio of the first stream of methanol-lean and non-shift gas is 1-2.5:1-2.

[0049] In some embodiments of the present application, preferably, the non-shift CO2-rich methanol has a H2S molar content of 0.5-1 ppm, a CO2 molar content of 5-8%; a temperature of -35 to -30℃.

[0050] In the present application, the non-shift CO2-rich methanol is divided into two streams, the first stream is subjected to the third CO2 absorption, and the second stream is subjected to the second purification. Further preferably, the molar flow ratio of the first stream of non-shift CO2-rich methanol and the second stream of non-shift CO2-rich methanol is 1:1-2.

[0051] In some embodiments of the present application, preferably, the purified non-shift gas has a H2S molar content of ≤0.1 ppm, a CO2 molar content of ≤20 ppm; a temperature of -55 to -45℃, and a pressure of 5.5-5.9 MPa(G).

[0052] In some embodiments of the present application, preferably, the two-stage H2S absorption comprises a first H2S absorption and a second H2S absorption; wherein the first stream of non-shift H2S-rich methanol is returned to the first H2S absorption; and the low-sulfur carbon-rich methanol and the primary CO2-rich methanol are returned to the second H2S absorption, respectively.

[0053] In the present application, the first H2S absorption aims to remove impurities such as HCN, NH3, and a small amount of H2S and CO2 in the synthesis gas; and the second H2S absorption aims to further remove H2S and CO2 in the synthesis gas.

[0054] In some embodiments of the present application, further preferably, the synthesis gas and the first stream of non-shift H2S-rich methanol are contacted and the first H2S absorption is carried out to obtain the primary H2S-rich methanol and pre-desulfurized gas; the pre-desulfurized gas, low-sulfur carbon-rich methanol and primary CO2-rich methanol are contacted and the second H2S absorption is carried out to obtain the desulfurized gas and secondary H2S-rich methanol.

[0055] In the present application, preferably, the molar flow ratio of the synthesis gas and the first stream of non-shift H2S-rich methanol is 60-70:1; further preferably, the molar content of H2S in the primary H2S-rich methanol is 2.4-2.9%, and the molar content of CO2 is 66-71%, which is sent to subsequent processes for treatment.

[0056] In the present application, preferably, the molar flow ratio of the low-sulfur carbon-rich methanol and synthesis gas is 1:12-18; and the molar flow ratio of the primary CO2-rich methanol and synthesis gas is 5-8:12-18.

[0057] In some embodiments of the present application, preferably, the molar content of H2S in the lean methanol is 0%, and the molar content of CO2 is 0%. In the present application, the lean methanol is selected from subsequent processes. In the present application, without special circumstances, the lean methanol is divided into a first stream of lean methanol and a second stream of lean methanol; the present application does not limit the molar flow ratio of the first stream of lean methanol and the second stream of lean methanol.

[0058] In some embodiments of the present application, preferably, the molar content of H2S in the secondary H2S-rich methanol is 1.5-2%, and the molar content of CO2 is 40-45%; the temperature is -12 to -8℃.

[0059] In some embodiments of the present application, preferably, the molar content of H2S in the desulfurized gas is 0.5-1 ppm, and the molar content of CO2 is 40-44%; the temperature is -20 to -10℃; and the pressure is 5.35-5.55 MPa(G).

[0060] In some embodiments of the present application, preferably, in the order of material flow direction, the primary CO2-rich methanol is first pressurized to 5.6-6 MPa(G) and then cooled to -36 to -33℃ to carry out the second H2S absorption.

[0061] In some embodiments of the present application, preferably, in the order of material flow direction, the low-sulfur carbon-rich methanol is second pressurized to 5.6-6 MPa(G) to carry out the second H2S absorption.

[0062] In some embodiments of the present application, preferably, the three-stage CO2 absorption comprises: a first CO2 absorption, a second CO2 absorption and a third CO2 absorption; wherein the second-stage CO2-rich methanol is returned to the first CO2 absorption, and the third-stage CO2-rich methanol is returned to the second CO2 absorption; the first non-shift CO2-rich methanol and the a semi-lean methanol are returned to the third CO2 absorption.

[0063] In some embodiments of the present application, further preferably, the desulfurized gas and the second-stage CO2-rich methanol are contacted and subjected to the first CO2 absorption to obtain the first-stage CO2-rich methanol and a first pre-purified gas; the first pre-purified gas and the third-stage CO2-rich methanol are contacted and subjected to the second CO2 absorption to obtain the second-stage CO2-rich methanol and a second pre-purified gas; the second pre-purified gas, the first non-shift CO2-rich methanol, the a semi-lean methanol and the second lean methanol are contacted and subjected to the third CO2 absorption to obtain the third-stage CO2-rich methanol and a purified gas.

[0064] In the present application, preferably, the molar flow ratio of the desulfurized gas and the second-stage CO2-rich methanol is 2-3:1.

[0065] In some embodiments of the present application, preferably, the first-stage CO2-rich methanol has a molar content of H2S of 0.1-0.5 ppm, a molar content of CO2 of 38-42%, a temperature of -12 to -5℃ and a pressure of 5.35-5.55 MPa(G).

[0066] In some embodiments of the present application, preferably, the second-stage CO2-rich methanol has a molar content of H2S of 0.1-0.5 ppm, a molar content of CO2 of 28-33%, a temperature of -10 to -5℃ and a pressure of 5.3-5.4 MPa(G); further preferably, the molar flow ratio of the first second-stage CO2-rich methanol and the second second-stage CO2-rich methanol is 2-3:1.

[0067] In some embodiments of the present application, further preferably, the second-stage CO2-rich methanol is cooled to -20 to -18℃ in a second cooling process to be subjected to the first CO2 absorption.

[0068] In some embodiments of the present application, preferably, the third-stage CO2-rich methanol is cooled to -36 to -33℃ in a third cooling process to be subjected to the second CO2 absorption.

[0069] In some embodiments of the present application, preferably, the first non-shift CO2-rich methanol is cooled to -50 to -48℃ in a fourth cooling process to be subjected to the third CO2 absorption.

[0070] In the present application, preferably, the molar flow ratio of the first non-shifted CO2-rich methanol and the purified gas is 1:7-9; the molar flow ratio of the a semi-lean liquid methanol and the purified gas is 1:1-3; the molar flow ratio of the second lean methanol and the purified gas is 1-1.3:1.

[0071] In some embodiments of the present application, preferably, the molar content of H2S in the purified gas is ≤0.1 ppm, the molar content of CO2 is ≤20 ppm; the temperature is -55 to -50℃, and the pressure is 5.25-5.45 MPa(G).

[0072] In the present application, the first secondary CO2-rich methanol is subjected to CO2 flashing to obtain CO2 flashing gas and CO2 flashing liquid; the secondary H2S-rich methanol and the third non-shifted H2S-rich methanol are subjected to H2S flashing respectively to obtain H2S flashing gas and H2S flashing liquid.

[0073] In some embodiments of the present application, preferably, the first secondary CO2-rich methanol is cooled to -36 to -33℃ by the fifth cooling to be subjected to the CO2 flashing.

[0074] In some embodiments of the present application, preferably, the pressure of the CO2 flashing and the H2S flashing is 1.6-2 MPa(G) respectively.

[0075] In some embodiments of the present application, preferably, the molar content of H2S in the CO2 flashing liquid is 0.1-0.5 ppm, the molar content of CO2 is 27.5-32.5%, and the temperature is -37 to -34℃.

[0076] In some embodiments of the present application, preferably, the molar content of H2S in the H2S flashing liquid is 1.5-1.8%, the molar content of CO2 is 34-38%, and the temperature is -18 to -13℃.

[0077] In some embodiments of the present application, preferably, the process of the second washing comprises: contacting the b semi-lean liquid methanol and the CO2 flashing gas and subjecting to the second washing to obtain washed CO2-rich methanol and washed CO2 flashing gas.

[0078] In some embodiments of the present application, further preferably, the molar content of H2S in the washed CO2 flashing gas is 0.1-0.5 ppm, the molar content of CO2 is 12-16%, the molar content of CO is 0.1-0.5%, the molar content of H2 is 82-86%, the temperature is -65 to -55℃, and the pressure is 1.6-2 MPa(G).

[0079] In some embodiments of the present application, preferably, the H2S molar content in the washed CO2-rich methanol is 0.1-0.5 ppm, the CO2 molar content is 28-33%, and the temperature is -38 to -33℃.

[0080] In some embodiments of the present application, preferably, the third washing process comprises: contacting the washed CO2-rich methanol and H2S flash gas and performing the third washing to obtain low-sulfur carbon-rich methanol and washed H2S flash gas.

[0081] In some embodiments of the present application, further preferably, the H2S molar content in the low-sulfur carbon-rich methanol is 0.3-0.5%, the CO2 molar content is 33-38%, and the temperature is -22 to -18℃.

[0082] In some embodiments of the present application, further preferably, the CO2 molar content in the washed H2S flash gas is 38-43%, the CO molar content is 18-23%, the H2 molar content is 33-38%, the temperature is -40 to -35℃, and the pressure is 1.6-2 MPa (G).

[0083] In some embodiments of the present application, preferably, the CO2 flash liquid is subjected to the first flash to obtain the semi-lean liquid methanol and a first CO2 product gas; the second semi-lean liquid methanol is subjected to the second flash to obtain a second flash liquid and a second CO2 product gas; and the H2S flash liquid is subjected to the third flash to obtain the first H2S-rich methanol and a sulfur-containing gas phase; wherein the second flash liquid and the sulfur-containing gas phase are contacted and subjected to a fourth washing to obtain low-sulfur methanol and a third CO2 product gas; and wherein the first CO2 product gas, the second CO2 product gas, and the third CO2 product gas are mixed to obtain a CO2 product gas.

[0084] In some embodiments of the present application, preferably, the H2S molar content in the semi-lean liquid methanol is 0.1-0.5 ppm; the CO2 molar content is 18-23%, the temperature is -65 to -60℃, and the pressure is 0.05-0.08 MPa (G).

[0085] In some embodiments of the present application, further preferably, the molar flow ratio of the a semi-lean liquid methanol, the b semi-lean liquid methanol, the second semi-lean liquid methanol, and the third semi-lean liquid methanol is 5-7: 1: 3-5: 3.5-5.5.

[0086] In some embodiments of the present application, further preferably, the first semi-lean liquid methanol is pressurized to 5.6-6 MPa (G) to divide into the a semi-lean liquid methanol and the b semi-lean liquid methanol.

[0087] In some embodiments of the present application, preferably, the low-sulfur methanol has a H2S molar content of 1.1-1.4%, a CO2 molar content of 18-23%, a temperature of -60 to -55℃, and a pressure of 0.12-0.16 MPa (G).

[0088] In some embodiments of the present application, preferably, the first H2S-rich methanol has a H2S molar content of 1.5-1.8%, a CO2 molar content of 17-21%, a temperature of -63 to -58℃, and a pressure of 0.13-0.17 MPa (G).

[0089] In some embodiments of the present application, preferably, the CO2 product gas has a H2S molar content of ≤1 ppm, a CO2 molar content of 99.4-99.7%, a temperature of -65 to -60℃, and a pressure of 0.05-0.08 MPa (G).

[0090] In some embodiments of the present application, preferably, the first H2S-rich methanol, the low-sulfur methanol, and the second H2S-rich methanol are respectively contacted with nitrogen and subjected to gas stripping to obtain a stripping gas and a post-stripping H2S-rich methanol.

[0091] In some embodiments of the present application, further preferably, the first H2S-rich methanol is subjected to a first heat exchange to a temperature of -30 to -28℃ before the gas stripping.

[0092] In some embodiments of the present application, further preferably, the second H2S-rich methanol is subjected to a second heat exchange to a temperature of -20 to -18℃ before the gas stripping.

[0093] In some embodiments of the present application, further preferably, the post-stripping H2S-rich methanol has a H2S molar content of 1.3-1.6%, a CO2 molar content of 1-3%, a temperature of -48 to -40℃, and a pressure of 0.12-0.16 MPa (G), and is sent to a subsequent process.

[0094] In some embodiments of the present application, preferably, the third semi-lean methanol and the stripping gas are contacted and subjected to the first washing to obtain a tail gas and a second H2S-rich methanol.

[0095] In some embodiments of the present application, further preferably, the second H2S-rich methanol has a H2S molar content of 1.4-1.8%, a CO2 molar content of 17-22%, a temperature of -65 to -60℃, and a pressure of 0.06-0.09 MPa (G).

[0096] In some embodiments of the present invention, preferably, the molar content of H2S in the tail gas is 0.5 - 1 ppm, the molar content of CO2 is 80 - 84%; the temperature is -68 to -63 °C, and the pressure is 0.12 - 0.16 MPa(G).

[0097] The second aspect of the present invention provides a structural schematic diagram of a polygeneration acid gas removal device supporting a water coal gasification device as Figure 1 shown, from Figure 1 it can be seen that the device includes: a connected non-shift gas purification tower T-1, H2S absorption tower T-2, CO2 absorption tower T-3, CO2 medium-pressure flash tower T-4, H2S medium-pressure flash tower T-5, and reabsorption tower T-6;

[0098] The non-shift gas purification tower T-1 is used to purify the non-shift gas 1 in three stages to obtain pre-purified non-shift H2S-rich methanol 4, non-shift H2S-rich methanol 2 in three streams, non-shift CO2-rich methanol 8 in two streams, and purified non-shift gas 5; the H2S absorption tower T-2 is used to absorb H2S in the syngas 6 in two stages to obtain first-stage H2S-rich methanol 7, second-stage H2S-rich methanol 10, and desulfurized gas 11; the CO2 absorption tower T-3 is used to absorb CO2 in the desulfurized gas 11 in three stages to obtain first-stage CO2-rich methanol 9, second-stage CO2-rich methanol 12 in two streams, third-stage CO2-rich methanol 28, and purified gas 14;

[0099] The CO2 medium-pressure flash tower T-4 includes a CO2 flash section arranged at the bottom and a CO2 washing section arranged at the top. The CO2 flash section is used to flash CO2 in the first-stage second-stage CO2-rich methanol 12-i to obtain CO2 flash liquid 24 and CO2 flash gas; the H2S medium-pressure flash tower T-5 includes an H2S flash section arranged at the bottom and an H2S washing section arranged at the top. The H2S flash section is used to flash the second-stage H2S-rich methanol 10 and the third-stage non-shift H2S-rich methanol 2-iii respectively to obtain H2S flash liquid 19 and H2S flash gas;

[0100] The reabsorption tower T-6 includes an upper tower and a lower tower. Among them, the upper tower is divided into a first flash section, a second flash section, and a third flash section from top to bottom, which are respectively used to flash the CO2 flash liquid 24, the second semi-lean methanol 13-ii, and the H2S flash liquid 19 to obtain semi-lean methanol 13 in three streams, low-sulfur methanol 21, and first-stage H2S-rich methanol 20; the lower tower is divided into a washing section and a stripping section from top to bottom. The stripping section is used to strip the first-stage H2S-rich methanol 20, low-sulfur methanol 21, and second-stage H2S-rich methanol 16 respectively to obtain stripping gas, which is sent to the washing section through the lifting holes and is first washed with the third semi-lean methanol 13-iii to obtain the second-stage H2S-rich methanol 16;

[0101] wherein the first stream of semi-lean methanol 13-i is divided into a stream of semi-lean methanol 13-i-a and a stream of semi-lean methanol 13-i-b, which are sent to the CO2 absorption tower T-3 and the CO2 washing section, respectively; the CO2 washing section is used for second washing of the stream of semi-lean methanol 13-i-b and the CO2 flash gas, and the obtained washed CO2-rich methanol 27 is sent to the H2S washing section to perform third washing with the H2S flash gas, and the obtained low-sulfur carbon-rich methanol 25 is returned to the H2S absorption tower T-2;

[0102] wherein the first stream of non-shift H2S-rich methanol 2-i and the first-stage CO2-rich methanol 9 are returned to the H2S absorption tower T-2, respectively; the second stream of non-shift H2S-rich methanol 2-ii and the second stream of non-shift CO2-rich methanol 8-ii are returned to the non-shift gas purification tower T-1, respectively; the second stream of second-stage CO2-rich methanol 12-ii, the third-stage CO2-rich methanol 28 and the first stream of non-shift CO2-rich methanol 8-i are returned to the CO2 absorption tower T-3, respectively.

[0103] In the present application, as shown in Figure 1 the non-shift gas purification tower T-1 is divided into a first purification section, a second purification section and a third purification section from bottom to top, which are communicated by a gas lift hole; wherein the second stream of non-shift H2S-rich methanol 2-ii is returned to the first purification section; the second stream of non-shift CO2-rich methanol 8-ii is returned to the second purification section.

[0104] In the present application, as shown in Figure 1 the non-shift gas purification tower T-1, wherein the first purification section is used for contacting the non-shift gas 1 and the second stream of non-shift H2S-rich methanol 2-ii and performing first purification to obtain pre-purified non-shift H2S-rich methanol 4 and pre-desulfurized non-shift gas; the second purification section is used for contacting the pre-desulfurized non-shift gas and the second stream of non-shift CO2-rich methanol 8-ii and performing second purification to obtain the non-shift H2S-rich methanol 2 and desulfurized non-shift gas; the third purification section is used for contacting the desulfurized non-shift gas and the first stream of lean methanol 3-i and performing third purification to obtain the non-shift CO2-rich methanol 8 and purified non-shift gas 5.

[0105] In the present application, as shown in Figure 1 the H2S absorption tower T-2 is divided into a first H2S absorption section and a second H2S absorption section from bottom to top, which are communicated by a gas lift hole; wherein the first stream of non-shift H2S-rich methanol 2-i is returned to the first H2S absorption section; the first-stage CO2-rich methanol 9 and the low-sulfur carbon-rich methanol 25 are returned to the second H2S absorption section, respectively.

[0106] In the present application, as shown in Figure 1As shown, in the H2S absorption tower T-2, a first H2S absorption section is used for contacting the synthesis gas 6 and the first non-shift H2S-rich methanol 2-i and performing first H2S absorption to obtain the first H2S-rich methanol 7 and a pre-desulfurized gas; a second H2S absorption section is used for contacting the pre-desulfurized gas, the first CO2-rich methanol 9 and the low-sulfur carbon-rich methanol 25 and performing second H2S absorption to obtain the desulfurized gas 11 and the second H2S-rich methanol 10.

[0107] In the present application, as shown in Figure 1 As shown, the CO2 absorption tower T-3 is divided into a first CO2 absorption section, a second CO2 absorption section and a third CO2 absorption section from bottom to top, which are communicated by a gas lift hole; wherein the second stream of the second CO2-rich methanol 12-ii returns to the first CO2 absorption section, and the third CO2-rich methanol 28 returns to the second CO2 absorption section; the a stream of the semi-lean liquid methanol 13-i-a and the first non-shift CO2-rich methanol 8-i return to the third CO2 absorption section.

[0108] In the present application, as shown in Figure 1 As shown, in the CO2 absorption tower T-3, the first CO2 absorption section is used for contacting the desulfurized gas 11 and the second stream of the second CO2-rich methanol 12-ii and performing first CO2 absorption to obtain the first CO2-rich methanol 9 and a first pre-purified gas; the second CO2 absorption section is used for contacting the first pre-purified gas and the third CO2-rich methanol 28 and performing second CO2 absorption to obtain the second CO2-rich methanol 12 and a second pre-purified gas; the third CO2 absorption section is used for contacting the second pre-purified gas, the first non-shift CO2-rich methanol 8-i, the a stream of the semi-lean liquid methanol 13-i-a and the second lean methanol 3-ii and performing third CO2 absorption to obtain the third CO2-rich methanol 28 and the purified gas 14.

[0109] In the present application, as shown in Figure 1 As shown, the CO2 medium-pressure flash tower T-4 includes a CO2 flash section arranged at the lower part and a CO2 washing section arranged at the upper part, wherein the CO2 flash section is used for performing CO2 flash on the first stream of the second CO2-rich methanol 12-i to obtain a CO2 flash liquid 24 and a CO2 flash gas; and the CO2 washing section is used for contacting the b stream of the semi-lean liquid methanol 13-i-b and the CO2 flash gas and performing second washing to obtain a washed CO2-rich methanol 27 and a washed CO2 flash gas 23.

[0110] In the present application, as shown in Figure 1As shown, the H2S medium-pressure flash evaporator T-5 includes an H2S flash evaporation section at the bottom and an H2S washing section at the top. The H2S flash evaporation section is used to flash evaporate the secondary H2S-rich methanol 10 and the third non-conversion H2S-rich methanol 2-iii to obtain H2S flash liquid 19 and H2S flash vapor. The H2S washing section is used to contact the washed CO2-rich methanol 27 and the H2S flash vapor and perform a third washing to obtain low-sulfur carbon-rich methanol 25 and washed H2S flash vapor 18.

[0111] According to the present invention, such as Figure 1 As shown, the upper column of the reabsorption tower T-6 is divided into a first flash section, a second flash section, and a third flash section from top to bottom. The first flash section is used to perform a first flash evaporation on CO2 flash liquid 24 to obtain semi-lean methanol 13 and a first stream of CO2 product gas. The second flash section is used to perform a second flash evaporation on the second stream of semi-lean methanol 13-ii to obtain a second flash liquid and a second stream of CO2 product gas. The third flash section is used to perform a third flash evaporation on H2S flash liquid 19 to obtain a first H2S-rich methanol 20, and the resulting sulfur-containing gas phase is contacted with the second flash liquid through the riser and subjected to a fourth wash to obtain low-sulfur methanol 21 and a third stream of CO2 product gas. The first, second, and third streams of CO2 product gas are mixed to obtain CO2 product gas 22.

[0112] According to the present invention, such as Figure 1 As shown, the lower column of the reabsorption tower T-6 is divided into a washing section and a stripping section from top to bottom. The stripping section is used to contact the first H2S-rich methanol 20, low-sulfur methanol 21, and second H2S-rich methanol 16 with nitrogen 26 and perform stripping to obtain stripped gas and stripped H2S-rich methanol 17. The washing section is used to contact the third semi-lean methanol 13-iii with the stripping gas and perform a first washing to obtain tail gas 15 and second H2S-rich methanol 16.

[0113] 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 second H2S absorption section and the first CO2 absorption section. These are used to sequentially pressurize and cool the first-stage CO2-rich methanol 9 before it undergoes the second H2S absorption.

[0114] According to the present invention, preferably, such as Figure 1 As shown, a second pump P-2 is installed on the pipeline connecting the H2S washing section and the second H2S absorption section according to the material flow direction. This pump is used to pressurize the low-sulfur, carbon-rich methanol 25 before absorbing the second H2S.

[0115] According to the present invention, preferably, such as Figure 1As shown, a second cooler E-2 is arranged on the pipeline connecting the second CO2 absorption section and the first CO2 absorption section, for cooling the second CO2-rich methanol stream 12-ii before the first CO2 absorption.

[0116] According to the present application, preferably, as shown in Fig. 1, a third cooler E-3 is arranged on the pipeline connecting the third CO2 absorption section and the second CO2 absorption section, for cooling the third CO2-rich methanol stream 28 before the second CO2 absorption. Figure 1

[0117] According to the present application, preferably, as shown in Fig. 1, a fourth cooler E-4 is arranged on the pipeline connecting the third purification section and the third CO2 absorption section, for cooling the first non-shift CO2-rich methanol stream 8-i before the third CO2 absorption. Figure 1

[0118] According to the present application, preferably, as shown in Fig. 1, a fifth cooler E-5 is arranged on the pipeline connecting the second CO2 absorption section and the CO2 flashing section, for cooling the first second CO2-rich methanol stream 12-i before the CO2 flashing. Figure 1

[0119] According to the present application, preferably, as shown in Fig. 1, a third pump P-3 is arranged on the pipeline connecting the first flashing section, the third CO2 absorption section and the CO2 washing section, for pressurizing the first semi-lean methanol stream 13-i into the a semi-lean methanol stream 13-i-a and the b semi-lean methanol stream 13-i-b. Figure 1

[0120] According to the present application, preferably, as shown in Fig. 1, a first heat exchanger Q-1 is arranged on the pipeline connecting the third flashing section and the stripping section, for heat exchanging the first H2S-rich methanol stream 20 before the stripping. Figure 1 According to the present application, preferably, as shown in Fig. 1, a second heat exchanger Q-2 is arranged on the pipeline connecting the washing section and the stripping section, for heat exchanging the second H2S-rich methanol stream 16 before the stripping.

[0121] Figure 1 The present application will be described in detail by way of examples.

[0122] In the present application, the synthesis gas and the non-shift gas are both derived from the coal slurry gasification device, unless otherwise specified.

[0123] Example 1

[0124] Example 1

[0125] ​​​​​Devices such as Figure 1 Figure 1 Figure 1 Figure 1 Figure 1 Figure 1 Figure 1 Figure 1 Figure 1 Figure 1 Figure 1 Figure 1 Figure 1 As shown, the device includes: a non-shift gas purification tower T-1, an H2S absorption tower T-2, a CO2 absorption tower T-3, a CO2 medium-pressure flash tower T-4, an H2S medium-pressure flash tower T-5, a reabsorption tower T-6, a first cooler E-1, a second cooler E-2, a third cooler E-3, a fourth cooler E-4 and a fifth cooler E-5, a first pump P-1, a second pump P-2 and a third pump P-3, and a first heat exchanger Q-1 and a second heat exchanger Q-2;

[0126] The method is carried out in the above-described apparatus and includes:

[0127] 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)) and a second non-shift H2S-rich methanol 2-ii are contacted at a molar flow ratio of 52-62:1 for the first purification, resulting in pre-purified non-shift H2S-rich methanol 4 (H2S molar content 2.1-2.6%, CO2 molar content 3-7%) and pre-desulfurized non-shift gas; the above pre-desulfurized non-shift gas is then contacted with a second non-shift CO2-rich methanol 8-ii for the second purification, resulting in non-shift H2S-rich methanol 2 (H2S molar content 0.9-1.2%, CO2 molar content 5-10%; temperature -35 to -25℃, pressure 5.5-6MPa(G)) for the first purification, resulting in pre-purified non-shift H2S-rich methanol 4 (H2S molar content 2.1-2.6%, CO2 molar content 3-7%) and pre-desulfurized non-shift gas; The process involves: 1.2-1.6% molar H2S content, 4-9% molar CO2 content; -30 to -26°C temperature; 5.6-6 MPa (G) pressure); and desulfurized non-shift gas. The desulfurized non-shift gas is then contacted with the first lean methanol stream 3-i and subjected to a third purification process to obtain non-shift CO2-rich methanol 8 (H2S molar content 0.5-1 ppm, CO2 molar content 5-8%; -35 to -30°C temperature) and purified non-shift gas 5 (H2S molar content ≤0.1 ppm, CO2 molar content ≤20 ppm; -55 to -45°C temperature; 5.5-5.9 MPa (G) pressure).

[0128] The non-conversion H2S-rich methanol 2 is divided into a first non-conversion H2S-rich methanol 2-i, a second non-conversion H2S-rich methanol 2-ii, and a third non-conversion H2S-rich methanol 2-iii with a molar flow ratio of 5-7:1:32-35; the non-conversion CO2-rich methanol 8 is divided into a first non-conversion CO2-rich methanol 8-i and a second non-conversion CO2-rich methanol 8-ii with a molar flow ratio of 1:1-2.

[0129] The molar flow ratio of the second non-conversion CO2-rich methanol 8-ii and the non-conversion gas 1 is 1:1-2; the molar flow ratio of the first lean methanol 3-i and the non-conversion gas 1 is 1.5-2.5:1-2.

[0130] The above synthesis gas 6 (molar content of H2S is 0.9-1.2%, molar content of CO2 is 40-50%; temperature is -15 to -5°C, pressure is 5.4-5.6 MPa(G)) and the first non-shift H2S-rich methanol 2-i are contacted at a molar flow ratio of 60-70:1 and a first H2S absorption is carried out to obtain a pre-desulfurization gas and a first H2S-rich methanol 7 (molar content of H2S is 2.4-2.9%, molar content of CO2 is 66-71%); the above pre-desulfurization gas, low-sulfur carbon-rich methanol 25 (second pressurized to 5.6-6 MPa(G)), and the first CO2-rich methanol 9 (first pressurized to 5.6-6 MPa(G) and first cooled to -36 to -33°C) are contacted and the second H2S absorption is carried out to obtain a desulfurization gas 11 (molar content of H2S is 0.5-1 ppm, molar content of CO2 is 40-44%; temperature is -20 to -10°C; pressure is 5.35-5.55 MPa(G)) and a second H2S-rich methanol 10 (molar content of H2S is 1.5-2%, molar content of CO2 is 40-45%; temperature is -12 to -8°C);

[0131] wherein the molar flow ratio of the above low-sulfur carbon-rich methanol 25 and the synthesis gas 6 is 1:12-18; the molar flow ratio of the first CO2-rich methanol 9 and the synthesis gas 6 is 5-8:12-18;

[0132] The above desulfurization gas 11 and the second second CO2-rich methanol 12-ii (second cooled to -20 to -18°C) are contacted at a molar flow ratio of 2-3:1 and a first CO2 absorption is carried out to obtain the first CO2-rich methanol 9 (molar content of H2S is 0.1-0.5 ppm, molar content of CO2 is 38-42%, temperature is -12 to -5°C, pressure is 5.35-5.55 MPa(G)) and a first pre-purification gas; the above first pre-purification gas and the third CO2-rich methanol 28 (third cooled to -36 to -33°C) are contacted and a second CO2 absorption is carried out to obtain the second CO2-rich methanol 12 (molar content of H2S is 0.1-0.5 ppm, molar content of CO2 is 28-33%, temperature is -10 to -5°C, pressure is 5.3-5.4 MPa(G)) and a second pre-purification gas; the above second pre-purification gas, the first non-shift CO2-rich methanol 8-i (fourth cooled to -50 to -48°C), the a stream of semi-lean liquid methanol 13-i-a, and the second lean methanol 3-ii are contacted and a third CO2 absorption is carried out to obtain the third CO2-rich methanol 28 and a purified gas 14 (molar content of H2S is ≤0.1 ppm, molar content of CO2 is ≤20 ppm; temperature is -55 to -50°C, pressure is 5.25-5.45 MPa(G));

[0133] wherein the molar flow ratio of the first non-shifted CO2-rich methanol 8-i and the purge gas is 1:7-9; the molar flow ratio of the a stream of semi-lean liquid methanol 13-i-a and the purge gas is 1:1-3; the molar flow ratio of the second lean methanol 3-ii and the purge gas is 1-1.3:1;

[0134] wherein the secondary CO2-rich methanol 12 is divided into a first secondary CO2-rich methanol 12-i and a second secondary CO2-rich methanol 12-ii with a molar flow ratio of 2-3:1;

[0135] The first secondary CO2-rich methanol 12-i (cooled to -36 to -33°C) is subjected to CO2 flashing (at a pressure of 1.6-2 MPa(G)) to obtain a CO2 flashing gas and a CO2 flashing liquid 24 (H2S molar content of 0.1-0.5 ppm, CO2 molar content of 27.5-32.5%, temperature of -37 to -34°C);

[0136] The secondary H2S-rich methanol 10 and the third non-shifted H2S-rich methanol 2-iii are subjected to H2S flashing (at a pressure of 1.6-2 MPa(G)) to obtain a H2S flashing gas and a H2S flashing liquid 19 (H2S molar content of 1.5-1.8%, CO2 molar content of 34-38%; temperature of -18 to -13°C);

[0137] The CO2 flashing liquid 24 is subjected to first flashing (at a pressure of 0.05-0.08 MPa(G)) to obtain a semi-lean liquid methanol 13 (H2S molar content of 0.1-0.5 ppm; CO2 molar content of 18-23%, temperature of -65 to -60°C; pressure of 0.05-0.08 MPa(G)) and a first CO2 product gas; the second semi-lean liquid methanol 13-ii is subjected to second flashing (at a pressure of 0.06-0.09 MPa(G)) to obtain a second flashing liquid and a second CO2 product gas; the H2S flashing liquid 19 is subjected to third flashing (at a pressure of 0.12-0.16 MPa(G)) to obtain a first H2S-rich methanol 20 (H2S molar content of 1.5-1.8%, CO2 molar content of 17-21%; temperature of -63 to -58°C; pressure of 0.13-0.17 MPa(G)) and a sulfur-containing gas phase; wherein the second flashing liquid and the sulfur-containing gas phase are subjected to fourth washing to obtain a low-sulfur methanol 21 (H2S molar content of 1.1-1.4%, CO2 molar content of 18-23%; temperature of -60 to -55°C, pressure of 0.12-0.16 MPa(G)) and a third CO2 product gas;

[0138] The first, second and third CO2 product gases are mixed to obtain a CO2 product gas 22 (molar content of H2S ≤ 1 ppm, molar content of CO2 99.4-99.7%, temperature -65 to -60℃, pressure 0.05-0.08 MPa (G));

[0139] The semi-lean methanol 13 is divided into a first semi-lean methanol 13-i-a, a second semi-lean methanol 13-i-b, a third semi-lean methanol 13-ii and a fourth semi-lean methanol 13-iii in a molar flow ratio of 5-7:1:3-5:3.5-5.5. The first semi-lean methanol 13-i-a is pressurized to 5.6-6 MPa (G) and divided into a first semi-lean methanol 13-i-a and a second semi-lean methanol 13-i-b;

[0140] The first H2S-rich methanol 20 (-30 to -28℃ after first heat exchange), the low-sulfur methanol 21 and the second H2S-rich methanol 16 (-20 to -18℃ after second heat exchange) are respectively contacted with nitrogen 26 and subjected to gas stripping to obtain a gas stripping gas and a gas-stripped H2S-rich methanol 17 (molar content of H2S 1.3-1.6%, molar content of CO2 1-3%, temperature -48 to -40℃, pressure 0.12-0.16 MPa (G));

[0141] The third semi-lean methanol 13-iii and the gas stripping gas are contacted and subjected to first washing to obtain a tail gas 15 (molar content of H2S 0.5-1 ppm, molar content of CO2 80-84%, temperature -68 to -63℃, pressure 0.12-0.16 MPa (G)) and a second H2S-rich methanol 16 (molar content of H2S 1.4-1.8%, molar content of CO2 17-22%, temperature -65 to -60℃, pressure 0.06-0.09 MPa (G));

[0142] wherein the above b stock semi-lean liquid methanol 13-i-b and CO2 flash gas are contacted and subjected to a second washing to obtain washed CO2-rich methanol 27 (molar content of H2S is 0.1-0.5 ppm, molar content of CO2 is 28-33%; temperature is -38 to -33°C) and washed CO2 flash gas 23 (molar content of H2S is 0.1-0.5 ppm, molar content of CO2 is 12-16%, molar content of CO is 0.1-0.5%, molar content of H2 is 82-86%; temperature is -65 to -55°C, pressure is 1.6-2 MPa (G)); and the above washed CO2-rich methanol 27 and H2S flash gas are contacted and subjected to a third washing to obtain low-sulfur carbon-rich methanol 25 (molar content of H2S is 0.3-0.5%, molar content of CO2 is 33-38%; temperature is -22 to -18°C) and washed H2S flash gas 18 (molar content of CO2 is 38-43%, molar content of CO is 18-23%, molar content of H2 is 33-38%, temperature is -40 to -35°C, pressure is 1.6-2 MPa (G)).

[0143] Comparative Example 1

[0144] Taking a hydrogen production device using a coal water slurry gasification gasification plant as an example, the effective gas (H2+CO) entering the low-temperature methanol washing device is 230000 Nm 3 / h, and the main parameters of the technology of the lean liquid-semi-lean liquid process (i.e., CN201110260570.0 discloses a low-temperature methanol washing process) are compared with the above baseline, as shown in Table 1.

[0145] Table 1

[0146]

[0147] As can be seen from the results in Table 1, taking a hydrogen production device based on a coal water slurry gasification gasification plant as an example, the multi-generation acid gas removal method provided by Example 1 for the supporting coal water slurry gasification device, the lean methanol circulation amount is 88.9% of the lean methanol circulation amount in Comparative Example 1 (lean liquid-semi-lean liquid process), the semi-lean liquid methanol circulation amount is 80% of the semi-lean liquid methanol circulation amount in Comparative Example 1 (lean liquid-semi-lean liquid process), the use amount of CO2-rich methanol in the H2S absorption tower is 85.3% of the use amount of CO2-rich methanol in Comparative Example 1 (lean liquid-semi-lean liquid process), and the cumulative external cold consumption is reduced by 700 KW / h, and the overall energy saving effect is remarkable.

[0148] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that each technical feature is combined in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method for removing acidic gases from a multi-generation coal-water slurry gasification unit, characterized in that, The method includes: (1) The synthesis gas (6) is subjected to two-stage H2S absorption to obtain first-stage H2S-rich methanol (7), second-stage H2S-rich methanol (10) and desulfurized gas (11); the desulfurized gas (11) is subjected to three-stage CO2 absorption to obtain first-stage CO2-rich methanol (9), second-stage CO2-rich methanol (12) divided into two streams, third-stage CO2-rich methanol (28) and purified gas (14); among which, the non-conversion H2S-rich methanol (2) from the non-conversion gas purification process is divided into three streams and the non-conversion CO2-rich methanol (8) is divided into two streams; (2) The first secondary CO2-rich methanol (12-i) is subjected to CO2 flash evaporation to obtain CO2 flash liquid (24) and CO2 flash vapor; the secondary H2S-rich methanol (10) and the third non-conversion H2S-rich methanol (2-iii) are subjected to H2S flash evaporation to obtain H2S flash liquid (19) and H2S flash vapor respectively. (3) The CO2 flash liquid (24) is subjected to a first flash evaporation, and the resulting semi-lean methanol (13) is divided into three streams; the second semi-lean methanol (13-ii) and the H2S flash liquid (19) are subjected to a second flash evaporation and a third flash evaporation, respectively, to obtain low-sulfur methanol (21) and first H2S-rich methanol (20); (4) The first H2S-rich methanol (20), low-sulfur methanol (21) and the second H2S-rich methanol (16) are stripped by gas, and the stripped gas is washed with the third semi-lean methanol (13-iii) to obtain the second H2S-rich methanol (16). The first semi-lean methanol (13-i) is divided into a semi-lean methanol (13-ia) and b semi-lean methanol (13-ib). The b semi-lean methanol (13-ib) and CO2 flash vapor are washed in a second wash and then washed in a third wash with H2S flash vapor to obtain low-sulfur carbon-rich methanol (25). Among them, the first non-conversion H2S-rich methanol (2-i), the first-stage CO2-rich methanol (9), and the low-sulfur carbon-rich methanol (25) are returned to the two-stage H2S absorption, respectively; the second non-conversion H2S-rich methanol (2-ii) and the second non-conversion CO2-rich methanol (8-ii) are returned to the non-conversion gas purification process, respectively; the second-stage CO2-rich methanol (12-ii), the third-stage CO2-rich methanol (28), the first non-conversion CO2-rich methanol (8-i), and the a-seed semi-lean methanol (13-ia) are returned to the third-stage CO2 absorption, respectively.

2. The method according to claim 1, wherein, In step (1), The non-conversion gas purification process includes: subjecting the non-conversion gas (1) to three-stage purification to obtain pre-purified non-conversion H2S-rich methanol (4), non-conversion H2S-rich methanol (2), non-conversion CO2-rich methanol (8), and purified non-conversion gas (5). Preferably, the three-stage purification includes: a first purification, a second purification, and a third purification; wherein, the second non-conversion H2S-rich methanol (2-ii) is returned to the first purification; and the second non-conversion CO2-rich methanol (8-ii) is returned to the second purification. More preferably, the non-conversion gas (1) and the second non-conversion H2S-rich methanol (2-ii) are contacted and subjected to the first purification to obtain the pre-purified non-conversion H2S-rich methanol (4) and the pre-desulfurized non-conversion gas; the pre-desulfurized non-conversion gas and the second non-conversion CO2-rich methanol (8-ii) are contacted and subjected to the second purification to obtain the non-conversion H2S-rich methanol (2) and the desulfurized non-conversion gas; the desulfurized non-conversion gas and the first lean methanol (3-i) are contacted and subjected to the third purification to obtain the non-conversion CO2-rich methanol (8) and the purified non-conversion gas (5); Preferably, the non-conversion H2S-rich methanol (2) has a molar content of 1.2-1.6% for H2S and a molar content of 4-9% for CO2; a temperature of -30 to -26°C; and a pressure of 5.6-6 MPa(G). Preferably, the molar flow ratio of the first non-conversion H2S-rich methanol (2-i), the second non-conversion H2S-rich methanol (2-ii), and the third non-conversion H2S-rich methanol (2-iii) is 5-7:1:32-35; Preferably, the non-conversion CO2-rich methanol (8) has a molar content of H2S of 0.5-1 ppm and a molar content of CO2 of 5-8%; and a temperature of -35 to -30°C. Preferably, the molar flow ratio of the first non-conversion CO2-rich methanol (8-i) and the second non-conversion CO2-rich methanol (8-ii) is 1:1-2; Preferably, the molar content of H2S in the purified non-conversion gas (5) is ≤0.1ppm, the molar content of CO2 is ≤20ppm, the temperature is -55 to -45℃, and the pressure is 5.5-5.9MPa(G).

3. The method according to claim 1 or 2, wherein, In step (1), The two-stage H2S absorption includes: a first H2S absorption and a second H2S absorption; wherein, the first non-conversion H2S-rich methanol (2-i) returns to the first H2S absorption; the low-sulfur carbon-rich methanol (25) and the first-stage CO2-rich methanol (9) return to the second H2S absorption respectively; Preferably, the synthesis gas (6) and the first non-conversion H2S-rich methanol (2-i) are contacted and subjected to the first H2S absorption to obtain the first-stage H2S-rich methanol (7) and pre-desulfurized gas; the pre-desulfurized gas, low-sulfur carbon-rich methanol (25) and first-stage CO2-rich methanol (9) are contacted and subjected to the second H2S absorption to obtain the desulfurized gas (11) and second-stage H2S-rich methanol (10); Preferably, the molar content of H2S in the secondary H2S-rich methanol (10) is 1.5-2%, and the molar content of CO2 is 40-45%; the temperature is -12 to -8℃. Preferably, the desulfurization gas (11) has a molar content of H2S of 0.5-1 ppm and a molar content of CO2 of 40-44%; a temperature of -20 to -10°C; and a pressure of 5.35-5.55 MPa(G). Preferably, according to the material flow direction, the first-stage CO2-rich methanol (9) is sequentially pressurized to 5.6-6 MPa (G) and cooled to -36 to -33°C for the second H2S absorption; Preferably, the low-sulfur, carbon-rich methanol (25) is pressurized to 5.6-6 MPa (G) in the direction of material flow to carry out the second H2S absorption.

4. The method according to any one of claims 1-3, wherein, In step (1), The three-stage CO2 absorption includes: a first CO2 absorption, a second CO2 absorption, and a third CO2 absorption; wherein, the second secondary CO2-rich methanol (12-ii) returns to the first CO2 absorption, and the third CO2-rich methanol (28) returns to the second CO2 absorption; the first non-conversion CO2-rich methanol (8-i) and a semi-lean methanol (13-ia) return to the third CO2 absorption; Preferably, the desulfurized gas (11) and the second secondary CO2-rich methanol (12-ii) are contacted and subjected to the first CO2 absorption to obtain the primary CO2-rich methanol (9) and the first pre-purified gas; the first pre-purified gas and the tertiary CO2-rich methanol (28) are contacted and subjected to the second CO2 absorption to obtain the secondary CO2-rich methanol (12) and the second pre-purified gas; the second pre-purified gas, the first non-conversion CO2-rich methanol (8-i), the a-strand semi-lean methanol (13-ia), and the second lean methanol (3-ii) are contacted and subjected to the third CO2 absorption to obtain the tertiary CO2-rich methanol (28) and the purified gas (14); Preferably, the molar content of H2S in the first-grade CO2-rich methanol (9) is 0.1-0.5 ppm, the molar content of CO2 is 38-42%, the temperature is -12 to -5℃, and the pressure is 5.35-5.55 MPa (G); Preferably, the molar content of H2S in the secondary CO2-rich methanol (12) is 0.1-0.5 ppm, the molar content of CO2 is 28-33%, the temperature is -10 to -5℃, and the pressure is 5.3-5.4 MPa(G); Preferably, the molar flow ratio of the first secondary CO2-rich methanol (12-i) and the second secondary CO2-rich methanol (12-ii) is 2-3:1; Preferably, the second secondary CO2-rich methanol (12-ii) is cooled to -20 to -18°C for the first CO2 absorption. Preferably, the third-stage CO2-rich methanol (28) is cooled to -36 to -33°C in the third stage for the second CO2 absorption. Preferably, the first non-conversion CO2-rich methanol (8-i) is cooled to -50 to -48°C in the fourth stage for the third CO2 absorption.

5. The method according to any one of claims 1-4, wherein, In step (2), The first secondary CO2-rich methanol (12-i) is cooled to -36 to -33°C in a fifth cooling process to perform CO2 flash evaporation; Preferably, the pressures for CO2 flash evaporation and H2S flash evaporation are 1.6-2 MPa(G); Preferably, the CO2 flash liquid (24) has a molar content of H2S of 0.1-0.5 ppm, a molar content of CO2 of 27.5-32.5%, and a temperature of -37 to -34°C; Preferably, the H2S flash liquid (19) has a molar content of 1.5-1.8% for H2S and a molar content of 34-38% for CO2; and a temperature of -18 to -13°C. Preferably, the second washing process includes: contacting the b-strand semi-lean methanol (13-ib) and CO2 flash vapor and performing the second washing to obtain washed CO2-rich methanol (27) and washed CO2 flash vapor (23); Preferably, the third washing process includes: contacting the washed CO2-rich methanol (27) and H2S flash vapor and performing the third washing to obtain low-sulfur carbon-rich methanol (25) and washed H2S flash vapor (18); Preferably, the low-sulfur, carbon-rich methanol (25) contains 0.3-0.5% H2S and 33-38% CO2, and the temperature is -22 to -18°C.

6. The method according to any one of claims 1-5, wherein, In step (3), The CO2 flash liquid (24) is subjected to the first flash evaporation to obtain the semi-lean methanol (13) and the first CO2 product gas; the second semi-lean methanol (13-ii) is subjected to the second flash evaporation to obtain the second flash liquid and the second CO2 product gas; the H2S flash liquid (19) is subjected to the third flash evaporation to obtain the first H2S-rich methanol (20) and the sulfur-containing gas phase; The second flash liquid is contacted with a sulfur-containing gas phase and subjected to a fourth wash to obtain low-sulfur methanol (21) and a third CO2 product gas; the first CO2 product gas, the second CO2 product gas and the third CO2 product gas are mixed to obtain CO2 product gas (22). Preferably, the semi-lean methanol (13) has a molar content of H2S of 0.1-0.5 ppm, a molar content of CO2 of 18-23%, a temperature of -65 to -60°C, and a pressure of 0.05-0.08 MPa(G). Preferably, the molar flow ratio of the a-strand semi-lean methanol (13-ia), b-strand semi-lean methanol (13-ib), second semi-lean methanol (13-ii), and third semi-lean methanol (13-iii) is 5-7:1:3-5:3.5-5.5; Preferably, the first semi-lean methanol (13-i) is pressurized to 5.6-6 MPa (G) and divided into a semi-lean methanol (13-ia) and b semi-lean methanol (13-ib); Preferably, the low-sulfur methanol (21) has a molar content of H2S of 1.1-1.4% and a molar content of CO2 of 18-23%; the temperature is -60 to -55°C and the pressure is 0.12-0.16 MPa(G); Preferably, the first H2S-rich methanol (20) has a molar content of 1.5-1.8% for H2S and a molar content of 17-21% for CO2; a temperature of -63 to -58°C; and a pressure of 0.13-0.17 MPa(G). Preferably, the molar content of H2S in the CO2 product gas (22) is ≤1ppm, the molar content of CO2 is 99.4-99.7%, the temperature is -65 to -60℃, and the pressure is 0.05-0.08MPa(G).

7. The method according to any one of claims 1-6, wherein, In step (4), The first H2S-rich methanol (20), low-sulfur methanol (21), and second H2S-rich methanol (16) are respectively contacted with nitrogen (26) and subjected to the gas stripping to obtain the stripped gas and the stripped H2S-rich methanol (17). Preferably, the first H2S-rich methanol (20) is subjected to a first heat exchange to a temperature of -30 to -28°C for the gas stripping process; Preferably, the second H2S-rich methanol (16) is subjected to a second heat exchange to a temperature of -20 to -18°C for the gas stripping process; Preferably, the third semi-lean methanol (13-iii) is contacted with stripping gas and subjected to the first washing to obtain tail gas (15) and second H2S-rich methanol (16). Preferably, the second H2S-rich methanol (16) has a molar content of 1.4-1.8% for H2S and a molar content of 17-22% for CO2; the temperature is -65 to -60°C and the pressure is 0.06-0.09 MPa (G).

8. A polygeneration acid gas removal device for supporting a water coal slurry gasification device, characterized in that The device includes: a non-shift gas purification tower (T-1), an H2S absorption tower (T-2), a CO2 absorption tower (T-3), a CO2 medium-pressure flash tower (T-4), an H2S medium-pressure flash tower (T-5), and a reabsorption tower (T-6) connected together; The non-shift gas purification tower (T-1) is used to perform three-stage purification of non-shift gas (1) to obtain pre-purified non-shift H2S-rich methanol (4), non-shift H2S-rich methanol (2) split into three streams, non-shift CO2-rich methanol (8) split into two streams, and purified non-shift gas (5); the H2S absorption tower (T-2) is used to perform two-stage H2S absorption of syngas (6) to obtain first-stage H2S-rich methanol (7), second-stage H2S-rich methanol (10), and desulfurized gas (11); the CO2 absorption tower (T-3) is used to perform three-stage CO2 absorption of the desulfurized gas (11) to obtain first-stage CO2-rich methanol (9), second-stage CO2-rich methanol (12) split into two streams, third-stage CO2-rich methanol (28), and purified gas (14); The CO2 medium-pressure flash distillation tower (T-4) includes a CO2 flash distillation section located at the bottom and a CO2 washing section located at the top. The CO2 flash distillation section is used to flash distill the first secondary CO2-rich methanol (12-i) to obtain CO2 flash liquid (24) and CO2 flash vapor. The H2S medium-pressure flash distillation tower (T-5) includes an H2S flash distillation section located at the bottom and an H2S washing section located at the top. The H2S flash distillation section is used to flash distill the secondary H2S-rich methanol (10) and the third non-conversion H2S-rich methanol (2-iii) to obtain H2S flash liquid (19) and H2S flash vapor. The reabsorption tower (T-6) includes an upper tower and a lower tower. The upper tower is divided into a first flash section, a second flash section and a third flash section from top to bottom. These sections are used to perform the first flash, second flash and third flash of the CO2 flash liquid (24), the second semi-lean methanol (13-ii) and the H2S flash liquid (19) respectively, to obtain the semi-lean methanol (13) divided into three streams, low-sulfur methanol (21) and the first H2S rich methanol (20). The lower tower is divided into a washing section and a stripping section from top to bottom. The stripping section is used to strip the first H2S rich methanol (20), low-sulfur methanol (21) and the second H2S rich methanol (16) respectively. The stripped gas is sent to the washing section through the gas riser and is washed with the third semi-lean methanol (13-iii) to obtain the second H2S rich methanol (16). The first semi-lean methanol (13-i) is divided into a semi-lean methanol (13-ia) and b semi-lean methanol (13-ib), which are sent to the CO2 absorption tower (T-3) and the CO2 washing section, respectively. The CO2 washing section is used to wash the b semi-lean methanol (13-ib) and CO2 flash vapor in the second washing process. The washed CO2-rich methanol (27) is sent to the H2S washing section and washed with H2S flash vapor in the third washing process. The resulting low-sulfur carbon-rich methanol (25) is returned to the H2S absorption tower (T-2). Among them, the first non-conversion H2S-rich methanol (2-i) and the first-stage CO2-rich methanol (9) are returned to the H2S absorption tower (T-2); the second non-conversion H2S-rich methanol (2-ii) and the second non-conversion CO2-rich methanol (8-ii) are returned to the non-conversion gas purification tower (T-1); the second secondary CO2-rich methanol (12-ii), the tertiary CO2-rich methanol (28) and the first non-conversion CO2-rich methanol (8-i) are returned to the CO2 absorption tower (T-3).

9. The apparatus according to claim 8, wherein, The non-conversion gas purification tower (T-1) is divided into a first purification section, a second purification section, and a third purification section from bottom to top, which are connected by air risers. Specifically, the second non-converted H2S-rich methanol (2-ii) returns to the first purification section; the second non-converted CO2-rich methanol (8-ii) returns to the second purification section. Preferably, the H2S absorption tower (T-2) is divided into a first H2S absorption section and a second H2S absorption section, which are connected by air risers from bottom to top. The first non-conversion H2S-rich methanol (2-i) returns to the first H2S absorption section; the first-stage CO2-rich methanol (9) and the low-sulfur carbon-rich methanol (25) return to the second H2S absorption section respectively. Preferably, the CO2 absorption tower (T-3) is divided into a first CO2 absorption section, a second CO2 absorption section, and a third CO2 absorption section from bottom to top, which are connected by air risers. The second secondary CO2-rich methanol (12-ii) returns to the first CO2 absorption section, and the tertiary CO2-rich methanol (28) returns to the second CO2 absorption section; the a-series semi-lean methanol (13-ia) and the first non-conversion CO2-rich methanol (8-i) return to the third CO2 absorption section.

10. The apparatus according to claim 9, wherein, According to the material flow direction, a first pump (P-1) and a first cooler (E-1) are sequentially installed on the pipeline connecting the second H2S absorption section and the first CO2 absorption section, which are used to sequentially pressurize and cool the first-stage CO2-rich methanol (9) before absorbing the second H2S. Preferably, a second pump (P-2) is installed on the pipeline connecting the H2S washing section and the second H2S absorption section according to the material flow direction, for the second H2S absorption after the low-sulfur carbon-rich methanol (25) is pressurized. Preferably, a second cooler (E-2) is provided on the pipeline connecting the second CO2 absorption section and the first CO2 absorption section according to the material flow direction, for the second stream of secondary CO2-rich methanol (12-ii) to be cooled before the first CO2 absorption; Preferably, a third cooler (E-3) is provided on the pipeline connecting the third CO2 absorption section and the second CO2 absorption section according to the material flow direction, for cooling the three-stage CO2-rich methanol (28) before the second CO2 absorption. Preferably, a fourth cooler (E-4) is provided on the pipeline connecting the third purification section and the third CO2 absorption section, which is used to cool the first non-conversion CO2-rich methanol (8-i) before the third CO2 absorption. Preferably, a fifth cooler (E-5) is provided on the pipeline connecting the second CO2 absorption section and the CO2 flash evaporation section, for flash evaporation of the first secondary CO2-rich methanol (12-i) after the first stream of secondary CO2-rich methanol (12-i) has been cooled by the fifth cooler; Preferably, a third pump (P-3) is installed on the pipeline connecting the first flash section, the third CO2 absorption section and the CO2 washing section, for dividing the first semi-lean methanol (13-i) into the a semi-lean methanol (13-ia) and the b semi-lean methanol (13-ib) after the first semi-lean methanol (13-i) is pressurized. Preferably, a first heat exchanger (Q-1) is provided on the pipeline connecting the third flash section and the stripping section, for stripping the first H2S-rich methanol (20) after the first heat exchange; Preferably, a second heat exchanger (Q-2) is provided on the pipeline connecting the washing section and the stripping section, for stripping the second H2S-rich methanol (16) after the second heat exchange.

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