Low-temperature low-sulfur low-carbon methanol washing process matched with pulverized coal gasification device

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to a low-temperature low-sulfur low-carbon methanol washing method matched with a pulverized coal gasification device and a device thereof.The method has the advantages that low-carbon methanol is high in CO2 gas absorption energy, low-H2S methanol is high in synthesis gas absorption energy and high in use efficiency, a medium-pressure flash evaporation process is advanced and reasonable in arrangement, and low-sulfur low-carbon methanol is obtained. And the low-temperature methanol washing device is low in comprehensive energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of low-temperature methanol washing, and particularly relates to a low-temperature, low-sulfur, and low-carbon methanol washing method for supporting a pulverized coal gasification device and a low-temperature, low-sulfur, and low-carbon methanol washing device for supporting a pulverized coal gasification device. Background Art

[0002] In the syngas produced by using the pulverized coal gasification technology, H 2 and CO are called effective gases. At the same time, the syngas also contains a large amount of CO 2 and trace amounts of H 2 S, COS, NH 3 , HCN and other components. Among them, H 2 and CO are the raw material gases for synthesizing chemical products such as methanol and ammonia after adjusting the hydrogen-carbon ratio through the shift unit. The acidic gases CO 2 and H 2 S are generally poisons for synthesis catalysts, so they must be removed before the synthesis process.

[0003] The low-temperature methanol washing technology uses low-temperature methanol as the absorption solvent, and utilizes the excellent characteristics of extremely high solubility of low-temperature methanol in acidic gases to physically absorb and remove H 2 S and CO 2 and other acidic gases in the syngas, and at the same time removes trace components such as HCN and NH 3 . This process has the advantages of high gas purification degree, good selectivity, and large methanol absorption capacity. The rich H 2 S methanol after absorbing acidic gases is regenerated through rectification, and the rich CO 2 methanol realizes cyclic absorption through staged pressure reduction and flashing.

[0004] At present, the innovative research on the low-temperature methanol washing technology mainly focuses on the recycling of the rich CO 2 methanol through pressure reduction and flashing. The typical process is the lean liquid - semi-lean liquid process, which has played a positive role in reducing the comprehensive energy consumption of the low-temperature methanol washing process. In the low-temperature methanol washing process flow, the rich CO 2 methanol can be recycled through flashing, but the H 2 S-containing methanol must be recycled through rectification, which is the main energy-consuming source of the low-temperature methanol washing. Therefore, the direction and key factor of technological innovation are to make the H 2 S-containing methanol reach the absorption limit for the H 2 S gas in the syngas before the rectification regeneration of the H 2 S-containing methanol, so as to reduce the amount of rich H

[0005] CN201110260570.0 discloses a low-temperature methanol washing process. First, in this low-temperature methanol washing process, in H 2The S absorption tower uses rich CO entirely 2 methanol to wash the syngas, increasing the production of rich H 2 S methanol. The rich H 2 S methanol needs to be thermally regenerated before it can be recycled, resulting in high energy consumption. Second, in the CO 2 flashing section of the reabsorption tower, the rich CO 2 methanol directly mixes with the rich H 2 S methanol flash gas while washing the rich H 2 S methanol, and itself is contaminated by the rich H 2 S methanol, producing low-concentration H 2 S methanol that is not fully utilized, resulting in high energy consumption. Third, the CO 2 gas flashed from the upper tower of the medium-pressure flash tower is contaminated while being washed by the rich H 2 S methanol, resulting in high energy consumption. Fourth, the semi-lean liquid methanol has a relatively high CO 2 content, and the circulating absorption capacity is limited, which is not conducive to reducing the comprehensive energy consumption of the low-temperature methanol washing unit. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above technical problems and provide a low-temperature, low-sulfur, and low-carbon methanol washing method for a supporting pulverized coal gasification unit and a low-temperature, low-sulfur, and low-carbon methanol washing unit for a supporting pulverized coal gasification unit. This method has the characteristics that low-carbon methanol has strong absorption energy for CO 2 gas, low H 2 S methanol has strong absorption energy and high utilization efficiency for syngas, the medium-pressure flash process is set up advanced and reasonable, and the comprehensive energy consumption of the low-temperature methanol washing unit is low.

[0007] To achieve the above purpose, the first aspect of the present invention provides a low-temperature, low-sulfur, and low-carbon methanol washing method for a supporting pulverized coal gasification unit, which includes:

[0008] Perform H 2 S absorption on the syngas to obtain the first rich H 2 S methanol and desulfurized gas; sequentially perform primary CO 2 absorption, secondary CO 2 absorption, and tertiary CO 2 absorption on the desulfurized gas to obtain the first rich CO 2 methanol and the second rich CO 2 methanol; divide the second rich CO 2 methanol into two streams. The first stream of rich CO 2 methanol returns and performs the above-mentioned primary CO 2 absorption. The second stream of rich CO 2 methanol, after the first heat exchange, performs CO 2 flashing to obtain CO 2 flashed gas and rich CO 2The methanol undergoes a first flash evaporation to obtain semi-lean methanol in three streams. The second stream of semi-lean methanol undergoes a second flash evaporation to obtain a flash evaporation liquid; the first rich H 2 S methanol is divided into two streams, and the second stream of rich H 2 S methanol undergoes H 2 S flash evaporation to obtain H 2 S flash evaporation gas, and the rich H 2 S methanol after flash evaporation undergoes a third flash evaporation after the second heat exchange, and the sulfur-containing gas phase obtained is subjected to a first washing with the flash evaporation liquid to obtain low H 2 S methanol;

[0009] After the first stream of semi-lean methanol undergoes the first heat exchange, it undergoes a first-stage stripping to obtain first-stage low-carbon methanol. After the first-stage low-carbon methanol undergoes the second heat exchange, it undergoes a second-stage stripping to obtain second-stage low-carbon methanol in two streams. The first stream of low-carbon methanol returns and undergoes the third-stage CO 2 absorption, and the second stream of low-carbon methanol sequentially undergoes a second washing and a third washing with the CO 2 flash evaporation gas and the H 2 S flash evaporation gas respectively to obtain low-sulfur rich-carbon methanol;

[0010] Among them, the first stream of rich H 2 S methanol, the first rich CO 2 methanol, the low H 2 S methanol, and the low-sulfur rich-carbon methanol independently return and undergo the H 2 S absorption.

[0011] In the second aspect of the present invention, a low-temperature, low-sulfur, and low-carbon methanol washing device for supporting a pulverized coal gasification device is provided. The device includes: an H 2 S absorption tower, a CO 2 absorption tower, a CO 2 flash evaporation tower, an H 2 S flash evaporation tower, a reabsorption tower, and a stripping tower; among them, the CO 2 absorption tower is divided into a first-stage CO 2 absorption section, a second-stage CO 2 absorption section, and a third-stage CO 2 absorption section from bottom to top; the CO 2 flash evaporation tower is divided into a CO 2 flash evaporation section and a CO 2 washing section from bottom to top; the H 2 S flash evaporation tower is divided into an H 2 S flash evaporation section and an H 2 S washing section from bottom to top; the stripping tower is divided into a first-stage stripping section and a second-stage stripping section from top to bottom;

[0012] The syngas enters the H 2 S absorption tower for H 2 S absorption to obtain the first rich H2 S methanol and desulfurized gas; the desulfurized gas is successively introduced into the first-stage CO 2 absorption section, the second-stage CO 2 absorption section and the third-stage CO 2 absorption section to obtain the first rich CO 2 methanol and the second rich CO 2 methanol; the second rich CO 2 methanol is divided into two streams. The first stream of rich CO 2 methanol is recycled to the first-stage CO 2 absorption section, and the second stream of rich CO 2 methanol, after passing through the first heat exchanger, enters the CO 2 flashing section for CO 2 flashing to obtain CO 2 flashed gas, and the rich CO 2 methanol after flashing enters the upper part of the reabsorption tower for the first flashing, and the obtained semi-lean methanol is divided into three streams. The second stream of semi-lean methanol is recycled to the middle part of the reabsorption tower for the second flashing to obtain the flashed liquid; the first rich H 2 S methanol is divided into two streams. The second stream of rich H 2 S methanol enters the H 2 S flashing section for H 2 S flashing to obtain H 2 S flashed gas, and the rich H 2 S methanol after flashing, after passing through the second heat exchanger, enters the lower part of the reabsorption tower for the third flashing, and the obtained sulfur-containing gas phase is subjected to the first washing with the flashed liquid to obtain low H 2 S methanol;

[0013] The first stream of semi-lean methanol enters the first-stage stripping section through the first heat exchanger, and the obtained first-stage low-carbon methanol enters the second-stage stripping section after passing through the second heat exchanger. The second-stage low-carbon methanol is divided into two streams. The first stream of low-carbon methanol is recycled to the third-stage CO 2 absorption section, and the second stream of low-carbon methanol successively enters the CO 2 washing section and the H 2 S washing section, and is successively subjected to the second washing and the third washing with the CO 2 flashed gas and the H 2 S flashed gas respectively to obtain low-sulfur rich-carbon methanol;

[0014] Among them, the first stream of rich H 2 S methanol, the first rich CO 2 methanol, the low H 2 S methanol and the low-sulfur rich-carbon methanol are each independently recycled to the H 2 S absorption tower.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) The method provided by the present invention optimizes the H 2 S absorption process. The first rich H 2 S methanol is used to perform primary H 2 S absorption on the syngas, and low H 2 S methanol and low-sulfur rich-carbon methanol are introduced for secondary H 2 S absorption. This not only realizes the recycling of low-sulfur rich-carbon methanol, reduces the usage amount of the first rich CO 2 methanol, which is equivalent to reducing the second rich H 2 S methanol that needs to be thermally regenerated; such a setting correspondingly reduces the working load of the subsequent CO 2 absorption process and reduces the usage amounts of lean methanol and the second low-carbon methanol.

[0017] (2) The method provided by the present invention optimizes the reabsorption process, realizing the absorption of the sulfur-containing gas phase (such as H 2 S) in the third CO 2 product gas generated by the flashing of the rich H 2 S methanol after flashing by the flashing liquid of the second semi-lean liquid methanol, but without mixing with the third rich H 2 S methanol after flashing. Therefore, after the flashing liquid absorbs the flashed H 2 S gas, compared with the prior art, the H 2 S content in the solution is lower, which is called low H 2 S methanol, creating conditions for the reuse of this low H 2 S methanol.

[0018] (3) The method provided by the present invention further reduces the CO 2 content in the semi-lean liquid methanol and maximally improves the CO 2 absorption capacity of the semi-lean liquid methanol. After the optimized reabsorption process, the first semi-lean liquid methanol is subjected to two-stage nitrogen stripping after the first heat exchange, so that the CO 2 content is further reduced to 2-4%, obtaining secondary low-carbon methanol. This can produce two positive effects: one is that with the improvement of the absorption capacity and the reduction of the circulation amount of the secondary low-carbon methanol, the operating cost of the pump can be reduced by about 15%, and the diameter of the CO 2 absorption tower can be reduced by about 5%.

[0019] (4) The method provided by the present invention optimizes the medium-pressure flashing process flow. The second low-carbon methanol is used to perform the second washing on the CO 2 flashed gas flashed from the medium-pressure flashing tower. Compared with the prior art, while reducing the CO 2 component in the CO 2 flashed gas, it does not mix with the rich CO 2 after flashing. 2Methanol mixing; using low CO that has absorbed the flash vapor from the upper column 2 Methanol to H 2 H flashed from the medium-pressure flash column of H 2 S flash vapor is subjected to a third wash. Compared with the prior art, while reducing the rich H 2 CO flashed from the S methanol 2 component, it is not contaminated by the rich H 2 S methanol after flashing; realizing the separate flashing and separate washing of the second rich CO 2 methanol and the second rich H 2 S methanol, avoiding the technical problem of the CO 2 gas in the rich CO 2 methanol after flashing transferring to the rich H 2 S methanol after flashing. At the same time, the low-sulfur rich-carbon methanol after washing is reused, which is beneficial to reducing the energy consumption of the device. Brief Description of the Drawings

[0020] Figure 1 is a schematic structural diagram of a low-temperature, low-sulfur, and low-carbon methanol washing device provided by the present invention for supporting a pulverized coal gasification device.

[0021] Description of the Reference Numerals in the Drawings

[0022] T-1, H 2 S absorption column; T-2, CO 2 absorption column; T-3, CO 2 flash column; T-4, H 2 S flash column; T-5, reabsorption column; T-6, stripping column; Q-1, first heat exchanger; Q-2, second heat exchanger; 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; P-4, fourth pump;

[0023] 1, syngas; 2, low H 2 S methanol; 3, second rich H 2 S methanol; 4, first rich CO 2 methanol; 5, first rich H 2 S methanol; 5-i, first stream of rich H 2 S methanol; 5-ii, second stream of rich H 2 S methanol; 6, desulfurized gas; 7, low-sulfur rich-carbon methanol; 8, semi-lean methanol; 8-i, first stream of semi-lean methanol; 8-ii, second stream of semi-lean methanol; 8-iii, third stream of semi-lean methanol; 9, lean methanol; 10, second rich CO 2 methanol; 10-i, first stream of rich CO 2 methanol; 10-ii, second stream of rich CO2 Methanol; 11. Third CO-rich 2 Methanol; 12. Secondary low-carbon methanol; 12-i. First stream of low-carbon methanol; 12-ii. Second stream of low-carbon methanol; 13. Tertiary purified gas; 14. Low CO 2 Methanol; 15-i. CO after washing 2 Flash gas; 15-ii. H after washing 2 H2S flash gas; 15. Flash gas; 16. CO-rich after flashing 2 Methanol; 17. CO 2 Product gas; 18. H-rich after flashing 2 H2S methanol; 19. Third H-rich 2 H2S methanol; 20. Primary low-carbon methanol; 21. Tail gas; 22. Nitrogen; 23. CO-rich after heat exchange 2 Methanol; 24. Semi-lean liquid methanol after heat exchange; 25. H-rich after heat exchange 2 H2S methanol; 26. Low-carbon methanol after heat exchange. Detailed implementation manners

[0024] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0025] In the present invention, without special circumstances, "first", "second", "third", and "fourth" neither represent the order nor limit each material or step, but are only used to distinguish that these are not the same material or step. For example, "first pressurization", "second pressurization", "third pressurization", and "fourth pressurization" only use "first", "second", "third", and "fourth" to indicate that these are not the same pressurization.

[0026] In the present invention, without special circumstances, the "top" of a container refers to the 0-10% height of the container from top to bottom; the "upper part" of the container refers to the 10-40% height of the container from top to bottom; the "middle part" of the container refers to the 40-60% height of the container from top to bottom; the "lower part" of the container refers to the 60-90% height of the container from top to bottom; the "bottom" of the container refers to the 90-100% height of the container from top to bottom.

[0027] The first aspect of the present invention provides a low-temperature, low-sulfur, and low-carbon methanol washing method for a supporting pulverized coal gasification device, and the method includes:

[0028] Subjecting the syngas to H2 2S is absorbed to obtain the first H-rich 2 S methanol and desulfurized gas; the desulfurized gas is successively subjected to primary CO 2 absorption, secondary CO 2 absorption, and tertiary CO 2 absorption to obtain the first CO-rich 2 methanol and the second CO-rich 2 methanol; the second CO-rich 2 methanol is divided into two streams, the first stream of CO-rich 2 methanol returns and undergoes the above-mentioned primary CO 2 absorption, and the second stream of CO-rich 2 methanol, after the first heat exchange, undergoes CO 2 flashing to obtain CO 2 flash gas, and the CO-rich 2 methanol after flashing undergoes the first flashing to obtain semi-lean methanol which is divided into three streams, and the second stream of semi-lean methanol undergoes the second flashing to obtain the flash liquid; the first H-rich 2 S methanol is divided into two streams, and the second stream of H-rich 2 S methanol undergoes H 2 S flashing to obtain H 2 S flash gas, and the H-rich 2 S methanol after flashing, after the second heat exchange, undergoes the third flashing, and the sulfur-containing gas phase obtained is subjected to the first washing with the flash liquid to obtain low-H 2 S methanol;

[0029] The first stream of semi-lean methanol, after the first heat exchange, undergoes primary stripping, and the primary low-carbon methanol obtained, after the second heat exchange, undergoes secondary stripping. The secondary low-carbon methanol obtained is divided into two streams. The first stream of low-carbon methanol returns and undergoes the above-mentioned tertiary CO 2 absorption, and the second stream of low-carbon methanol successively undergoes the second washing and the third washing with the above-mentioned CO 2 flash gas and H 2 S flash gas respectively to obtain low-sulfur CO-rich methanol;

[0030] Among them, the first stream of H-rich 2 S methanol, the first CO-rich 2 methanol, the low-H 2 S methanol, and the low-sulfur CO-rich methanol each independently return and undergo the above-mentioned H 2 S absorption.

[0031] In some embodiments of the present invention, preferably, the process of the H 2 S absorption includes: primary H 2 S absorption and secondary H 2 S absorption; wherein, the syngas and the first stream of H-rich 2 S methanol are contacted to perform the above-mentioned primary H 2S is absorbed to obtain pre-desulfurized gas and second rich H 2 S methanol; the pre-desulfurized gas, low H 2 S methanol, low-sulfur rich-carbon methanol and first rich CO 2 Methanol are contacted and the secondary H 2 S absorption is carried out to obtain first rich H 2 S methanol and desulfurized gas.

[0032] In the present invention, the molar content of H 2 S in the syngas is 0.3 - 0.4%, and the molar content of CO 2 is 40 - 47%; the temperature is -25 to -15 °C, and the pressure is 3.12 - 3.15 MPa(G). In the present invention, there is a relatively wide selection range for the source of the syngas, as long as the syngas meets the above limitations. Preferably, the syngas is selected from the waste heat boiler process or the quench process of pulverized coal gasification.

[0033] In some embodiments of the present invention, preferably, the molar flow ratio of the syngas and the first stream of rich H 2 S methanol is 60 - 70:1.

[0034] In the present invention, the primary H 2 S absorption aims to remove impurities such as HCN and NH 3 in the syngas, as well as a small amount of H 2 S and CO 2 . Preferably, the molar content of H 2 S in the second rich H 2 S methanol is 0.6 - 0.9%, and the molar content of CO 2 is 30 - 36%. In the present invention, the temperature of the second rich H 2 S methanol is -25 to -15 °C, and the pressure is 3.12 - 3.15 MPa(G).

[0035] In some embodiments of the present invention, preferably, the molar flow ratio of the low H 2 S methanol and the syngas is 1:3 - 4; the molar flow ratio of the low-sulfur rich-carbon methanol and the syngas is 1:7 - 9; the molar flow ratio of the first rich CO 2 methanol and the syngas is 1:1.5 - 2.5.

[0036] In the present invention, the secondary H 2 S absorption aims to further remove H 2 S in the syngas, as well as a small amount of CO 2 . Preferably, the molar content of H 2 S in the first rich H 2 S methanol is 0.3 - 0.5%, and CO2 The molar content is 25 - 30%.

[0037] In the present invention, the first H-rich 2 S methanol is divided into two streams. The first stream returns and undergoes primary H 2 S absorption, and the second stream undergoes H 2 S flash evaporation. Preferably, the first H-rich 2 S methanol is divided into a first stream of H-rich 2 S methanol and a second stream of H-rich 2 S methanol with a molar flow rate ratio of 1:60 - 70.

[0038] In some embodiments of the present invention, preferably, the molar content of H 2 S in the desulfurized gas is 0.5 - 1 ppm, and the molar content of CO 2 is 32 - 36%; the temperature is -27 to -22 °C; the pressure is 3.05 - 3.1 MPa(G).

[0039] In some embodiments of the present invention, preferably, the low H 2 S methanol is first pressurized to 3.5 - 3.6 MPa(G) and then returns to undergo the secondary H 2 S absorption.

[0040] In some embodiments of the present invention, preferably, the process of the primary CO 2 absorption includes: contacting the desulfurized gas and the first stream of CO-rich 2 methanol and performing the primary CO 2 absorption to obtain the first CO-rich 2 methanol and the primary purified gas; the process of the secondary CO 2 absorption includes: contacting the primary purified gas and the third CO-rich 2 methanol and performing the secondary CO 2 absorption to obtain the second CO-rich 2 methanol and the secondary purified gas; the process of the tertiary CO 2 absorption includes: contacting the secondary purified gas, the first stream of low-carbon methanol and the lean methanol and performing the tertiary CO 2 absorption to obtain the third CO-rich 2 methanol and the tertiary purified gas.

[0041] In some embodiments of the present invention, preferably, the molar flow rate ratio of the desulfurized gas and the first stream of CO-rich 2 methanol is 1:1.5 - 2.5.

[0042] In some embodiments of the present invention, preferably, the first stream of CO-rich 2After the methanol is first cooled to -33 to -27 °C, it returns and undergoes the first-stage CO 2 absorption.

[0043] In some embodiments of the present invention, preferably, the CO content in the first rich CO 2 methanol is 20-25% in terms of molar content, and the H 2 S content is 0.1-0.5 ppm in terms of molar content; the temperature is -25 to -20 °C, and the pressure is 3.05-3.1 MPa(G). 2 In some embodiments of the present invention, preferably, the molar flow ratio of the desulfurized gas to the third rich CO

[0044] methanol is 1:2-2.5. 2 In some embodiments of the present invention, preferably, the H

[0045] S content in the second rich CO 2 methanol is 0.1-0.5 ppm in terms of molar content, and the CO 2 content is 16-20% in terms of molar content; the temperature is -20 to -15 °C, and the pressure is 3.05-3.1 MPa(G); more preferably, the second rich CO 2 methanol is divided into the first rich CO 2 methanol and the second rich CO 2 methanol with a molar flow ratio of 1:2.5-3. 2 In the present invention, the second rich CO

[0046] methanol is divided into two streams. The first stream returns and undergoes the first-stage CO 2 absorption, and the second stream undergoes CO 2 flashing. 2 In some embodiments of the present invention, preferably, the molar flow ratio of the three-stage purified gas to the first lean methanol is 1:1-1.2; the molar flow ratio of the three-stage purified gas to the lean methanol is 1:1.4-1.7.

[0047] In some embodiments of the present invention, preferably, the H

[0048] S molar content in the three-stage purified gas is <0.1 ppm, and the CO 2 molar content is <20 ppm; the temperature is -55 to -50 °C, and the pressure is 3-3.1 MPa(G). 2 In some embodiments of the present invention, preferably, after the third rich CO

[0049] methanol is secondarily cooled to -36 to -33 °C, it returns and undergoes the second-stage CO 2 absorption. 2 In some embodiments of the present invention, preferably, the molar flow ratio of the three-stage purified gas to the first lean methanol is 1:1-1.2; the molar flow ratio of the three-stage purified gas to the lean methanol is 1:1.4-1.7.

[0050] In some embodiments of the present invention, preferably, in the direction of material flow, the first CO-rich 2 methanol is pressurized to 3.5 - 4 MPa(G) for the second time, cooled to -50 to -45 °C for the third time, and then returned for the H 2 S absorption.

[0051] In some embodiments of the present invention, preferably, the process of the first heat exchange includes: performing the first heat exchange between the second CO-rich 2 methanol and the first semi-lean methanol, to obtain the heat-exchanged CO-rich 2 methanol transformed from the second CO-rich 2 methanol, and the heat-exchanged semi-lean methanol transformed from the first semi-lean methanol.

[0052] In some embodiments of the present invention, more preferably, the temperature of the heat-exchanged CO-rich 2 methanol is -33 to -30 °C; the temperature of the heat-exchanged semi-lean methanol is -40 to -35 °C.

[0053] In some embodiments of the present invention, preferably, the process of the CO 2 flashing includes: flashing the heat-exchanged CO-rich 2 methanol to obtain the CO 2 flash gas and the flashed CO-rich 2 methanol. 2 methanol.

[0054] In some embodiments of the present invention, preferably, the pressure of the CO 2 flashing is 0.8 - 1 MPa(G); more preferably, the molar content of H 2 S in the flashed CO-rich 2 methanol is 0.1 - 0.5 ppm, and the molar content of CO 2 is 15.5 - 19.5%; the temperature is -33.5 to -30.5 °C.

[0055] In some embodiments of the present invention, preferably, after the second H 2 S-rich methanol is cooled to -42 to -38 °C for the fourth time, the H 2 S flashing is performed.

[0056] In the present invention, the process of the H 2 S flashing includes: flashing the material after the fourth cooling to obtain the H 2 S flash gas and the flashed H 2 S-rich methanol. 2 S-rich methanol.

[0057] In some embodiments of the present invention, preferably, the H 2 S flashing pressure is 0.8 - 1 MPa(G); further preferably, the H 2 in the H 2 S in the rich H 2 S methanol has a molar content of 0.3 - 0.5%, and the CO

[0058] In some embodiments of the present invention, preferably, the second stream of low-carbon methanol and CO 2 are brought into contact with the flashed gas and the second washing is carried out to obtain the washed CO 2 flashed gas and low-CO 2 methanol; the low-CO 2 methanol and H 2 S flashed gas are subjected to a third washing to obtain the washed H 2 S flashed gas and the low-sulfur rich-carbon methanol; wherein, the washed CO 2 flashed gas and the washed H 2 S flashed gas are mixed to obtain the flashed gas.

[0059] In some embodiments of the present invention, preferably, the H 2 in the low-sulfur rich-carbon methanol has a molar content of <100 ppm, and the CO 2 has a molar content of 7 - 11%; the temperature is -40 to -35 °C.

[0060] In some embodiments of the present invention, further preferably, after the low-sulfur rich-carbon methanol is pressurized to 3.3 - 3.5 MPa(G) for the fourth time, it is returned and the H 2 S absorption is carried out.

[0061] In some embodiments of the present invention, preferably, the H 2 in the low-CO 2 methanol has a molar content of 0.1 - 0.5 ppm, and the CO 2 has a molar content of 6 - 9%; the temperature is -43 to -38 °C.

[0062] In some embodiments of the present invention, preferably, the temperature of the flashed gas is -43 °C to -38 °C, and the pressure is 0.8 - 1 MPa(G).

[0063] In some embodiments of the present invention, preferably, after the rich CO 2 methanol after flashing is cooled to -45 °C to -40 °C for the fifth time, the first flashing is carried out.

[0064] In some embodiments of the present invention, preferably, the process of the first flash evaporation includes: subjecting the fifth cooled material to the first flash evaporation to obtain the semi-lean methanol and the first CO 2 product gas; the process of the second flash evaporation includes: subjecting the second stream of semi-lean methanol to the second flash evaporation to obtain the flash liquid and the second CO 2 product gas; the process of the third flash evaporation includes: subjecting the H 2 -rich methanol after flash evaporation to the third flash evaporation after the second heat exchange to obtain the sulfur-containing gas phase and the third H 2 -rich methanol; wherein, mixing the first CO 2 product gas, the second CO 2 product gas and the third CO 2 product gas obtained from the first scrubbing also to obtain the CO 2 product gas.

[0065] In some embodiments of the present invention, preferably, the molar content of H 2 S in the CO 2 product gas is <1 ppm, and the molar content of CO 2 is 99.3-99.7%; the temperature is -55°C to -50°C, and the pressure is 0.05-0.08 MPa(G).

[0066] In some embodiments of the present 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); the pressure of the third flash evaporation is 0.12-0.16 MPa(G).

[0067] In some embodiments of the present invention, preferably, the molar content of H 2 S in the semi-lean methanol is ≤0.5 ppm, and the molar content of CO 2 is 10-14%; the temperature is -55 to -50°C, and the pressure is 0.05-0.08 MPa(G); further preferably, the semi-lean methanol is divided into the first stream of semi-lean methanol, the second stream of semi-lean methanol and the third stream of semi-lean methanol with a molar flow ratio of 2.5-2.8:1.1-1.3:1.

[0068] In the present invention, the semi-lean methanol is divided into three streams. The first stream is subjected to two-stage stripping after the first heat exchange; the second stream is subjected to the second flash evaporation; and the third stream is sent to subsequent processes for treatment.

[0069] In some embodiments of the present invention, preferably, the molar content of H 2 S in the low-H 2 -S methanol is 0.1-0.2%, and the CO 2The molar content is 12 - 17%; the temperature is -52 to -48 °C, and the pressure is 0.12 - 0.16 MPa(G).

[0070] In some embodiments of the present invention, preferably, the third H-rich 2 In the H-rich 2 S in methanol, the molar content of H 2 S is 0.3 - 0.4%, and the molar content of CO

[0071] In some embodiments of the present invention, preferably, the process of the second heat exchange includes: subjecting the flashed H-rich 2 S methanol and the first-stage low-carbon methanol to the second heat exchange to obtain the heat-exchanged H-rich 2 S methanol transformed from the flashed H-rich 2 S methanol, and the heat-exchanged low-carbon methanol transformed from the first-stage low-carbon methanol; more preferably, the temperature of the heat-exchanged H-rich 2 S methanol is -44 to -40 °C; the temperature of the heat-exchanged low-carbon methanol is -40 to -38 °C.

[0072] In some embodiments of the present invention, preferably, after the first semi-lean methanol is subjected to the first heat exchange, it is contacted with nitrogen and subjected to the first-stage stripping. The obtained first-stage low-carbon methanol is subjected to the second heat exchange, contacted with nitrogen, and subjected to the second-stage stripping to obtain the second-stage low-carbon methanol and the tail gas.

[0073] In some embodiments of the present invention, preferably, the second-stage low-carbon methanol is pressurized to 3.3 - 3.5 MPa(G) by the third stage and then divided into two streams.

[0074] In the present invention, the second-stage low-carbon methanol is divided into two streams. The first stream returns and undergoes tertiary CO 2 absorption, and the second stream returns for CO 2 washing. More preferably, the second-stage low-carbon methanol is divided into a first-stage low-carbon methanol and a second-stage low-carbon methanol with a molar flow ratio of 4 - 5:1.

[0075] In some embodiments of the present invention, preferably, the molar content of H 2 S in the second-stage low-carbon methanol is ≤0.5 ppm, and the molar content of CO 2 is 2 - 4%; the temperature is -50 to -45 °C; the pressure is 0.15 - 0.2 MPa(G).

[0076] In some embodiments of the present invention, preferably, the molar content of H 2 S in the tail gas is ≤0.5 ppm, and CO2 The molar content is 75 - 78%; the temperature is -40 to -35 °C; the pressure is 0.1 - 0.15 MPa (G).

[0077] The second aspect of the present invention provides a structural schematic diagram of a low-temperature, low-sulfur, and low-carbon methanol washing device for a coal gasification device, as shown in Figure 1 As can be seen, the device includes: H Figure 1 S absorption tower T-1, CO 2 absorption tower T-2, CO 2 absorption tower T-2, CO 2 flash tower T-3, H 2 S flash tower T-4, reabsorption tower T-5, and stripping tower T-6; wherein, the CO 2 absorption tower T-2 is divided into a first-stage CO 2 absorption section, a second-stage CO 2 absorption section, and a third-stage CO 2 absorption section from bottom to top; the CO 2 flash tower T-3 is divided into a CO 2 flash section and a CO 2 washing section from bottom to top; the H 2 S flash tower T-4 is divided into an H 2 S flash section and an H 2 S washing section from bottom to top; the stripping tower T-6 is divided into a first-stage stripping section and a second-stage stripping section from top to bottom;

[0078] Synthesis gas 1 enters the H 2 S absorption tower T-1 for H 2 S absorption, obtaining first-rich H 2 S methanol 5 and desulfurized gas 6; the desulfurized gas 6 is successively fed into the first-stage CO 2 absorption section, the second-stage CO 2 absorption section, and the third-stage CO 2 absorption section, obtaining first-rich CO 2 methanol 4 and second-rich CO 2 methanol 10; the second-rich CO 2 methanol 10 is divided into two streams. The first stream of rich CO 2 methanol 10-i is recycled to the first-stage CO 2 absorption section, and the second stream of rich CO 2 methanol 10-ii, after passing through the first heat exchanger Q-1, enters the CO 2 flash section for CO 2 flashing, obtaining CO 2 flash gas, and the CO 2Methanol 16 enters the upper part of the reabsorption tower T-5 for the first flash evaporation. The obtained semi-lean methanol 8 is divided into three streams. The second stream of semi-lean methanol 8-ii is recycled to the middle part of the reabsorption tower T-5 for the second flash evaporation to obtain a flash evaporation liquid; the first rich H 2 S methanol 5 is divided into two streams. The second stream of rich H 2 S methanol 5-ii enters the H 2 S flash evaporation section for H 2 S flash evaporation to obtain H 2 S flash evaporation, and the rich H 2 S methanol 18 after passing through the second heat exchanger Q-2 enters the lower part of the reabsorption tower T-5 for the third flash evaporation. The obtained sulfur-containing gas phase is subjected to the first washing with the flash evaporation liquid to obtain low H 2 S methanol 2;

[0079] The first stream of semi-lean methanol 8-i enters the first-stage stripping section through the first heat exchanger Q-1. The obtained first-stage low-carbon methanol 20 enters the second-stage stripping section after passing through the second heat exchanger Q-2. The obtained second-stage low-carbon methanol 12 is divided into two streams. The first stream of low-carbon methanol 12-i is recycled to the third-stage CO 2 absorption section. The second stream of low-carbon methanol 12-ii successively enters the CO 2 washing section and H 2 S washing section, and successively performs the second washing and the third washing with the CO 2 flash evaporation gas and H 2 S flash evaporation gas respectively to obtain low-sulfur rich-carbon methanol 7;

[0080] Among them, the first stream of rich H 2 S methanol 5-i, the first rich CO 2 methanol 4, low H 2 S methanol 2 and low-sulfur rich-carbon methanol 7 are each independently recycled to the H 2 S absorption tower T-1.

[0081] According to the present invention, preferably, as Figure 1 shown, the H 2 S absorption tower T-1 is divided into a first-stage H 2 S absorption section and a second-stage H 2 S absorption section from bottom to top; among them, the first stream of rich H 2 S methanol 5-i is recycled to the first-stage H 2 S absorption section; the first rich CO 2 methanol 4, low H 2 S methanol 2 and low-sulfur rich-carbon methanol 7 are each independently recycled to the second-stage H 2 S absorption section.

[0082] According to the present invention, as Figure 1 shown, the H 2The S absorption tower is divided into a first-stage H 2 S absorption section and a second-stage H 2 S absorption section from bottom to top, and the first-stage H 2 S absorption section and the second-stage H 2 S absorption section are connected through lifting holes; among them, the first-stage H 2 S absorption section is connected to the second-stage H 2 S absorption section of the first rich H 2 S methanol outlet, which is used to bring the synthesis gas 1 into contact with the first stream of rich H 2 S methanol 5-i and carry out the first-stage H 2 S absorption to obtain the second rich H 2 S methanol 3 and pre-desulfurized gas; the first-stage H 2 S absorption section is connected to the low H 2 S methanol outlet of the re-absorption tower T-5, H 2 low-sulfur rich-carbon methanol outlet of the HS washing section and the first rich CO 2 2 methanol outlet of the absorption section, which is used to bring the pre-desulfurized gas into contact with low H 2 S methanol 2, low-sulfur rich-carbon methanol 7 and the first rich CO 2 methanol 4 in sequence and carry out the second-stage H 2 S absorption to obtain the desulfurized gas 6 and the first rich H 2 S methanol 5.

[0083] According to the present invention, preferably, as Figure 1 shown, a first pump P-1 is provided on the pipeline connecting the low H 2 S methanol outlet of the re-absorption tower T-5 and the second-stage H 2 S absorption section, which is used to pressurize the low H 2 S methanol 2 for the first time and then return it to carry out the second-stage H 2 S absorption.

[0084] In the present invention, as Figure 1 shown, the CO 2 absorption tower T-2 is divided into a first-stage CO 2 absorption section, a second-stage CO 2 absorption section and a third-stage CO 2 absorption section from bottom to top, and the first-stage CO 2 absorption section, the second-stage CO 2 absorption section and the third-stage CO 2 absorption section are connected through lifting holes. Among them, the first-stage CO 2 absorption section is used to bring the desulfurized gas 6 and the first stream of rich CO 2 methanol 10-i into contact and carry out the first-stage CO 2 absorption to obtain the first rich CO 2Methanol 4 and primary purified gas; secondary CO 2 The absorption section is used to bring the primary purified gas and the third CO-rich 2 into contact with methanol 11 and perform secondary CO 2 absorption to obtain the second CO-rich 2 methanol 10 and secondary purified gas; tertiary CO 2 The absorption section is used to bring the secondary purified gas, the first low-carbon methanol 12-i and lean methanol 9 into contact and perform tertiary CO 2 absorption to obtain the third CO-rich 2 methanol 11 and tertiary purified gas 13.

[0085] According to the present invention, preferably, as Figure 1 shown, in the direction of material flow, a first cooler E-1 is provided on the pipeline connecting the bottom of the secondary CO 2 absorption section and the primary CO 2 absorption section, for cooling the first CO-rich 2 methanol 10-i. After the first cooling, it returns and performs primary CO 2 absorption.

[0086] According to the present invention, preferably, as Figure 1 shown, in the direction of material flow, a second cooler E-2 is provided on the pipeline connecting the bottom of the tertiary CO 2 absorption section and the secondary CO 2 absorption section, for cooling the third CO-rich 2 methanol 11. After the second cooling, it returns and performs secondary CO 2 absorption.

[0087] According to the present invention, preferably, as Figure 1 shown, in the direction of material flow, a second pump P-2 and a third cooler E-3 are successively provided on the pipeline connecting the outlet of the first CO-rich 2 methanol of the primary CO 2 absorption section and the secondary H 2 S absorption section, for successively subjecting the first CO-rich 2 methanol 4 to second pressurization and third cooling, and then returning it to perform secondary H 2 S absorption.

[0088] In the present invention, as Figure 1 shown, the first heat exchanger Q-1 is used to respectively obtain the heat-exchanged CO-rich 2 methanol 23 and the heat-exchanged semi-lean methanol 24 after heat-exchanging the second CO-rich 2 methanol 10-ii and the first semi-lean methanol 8-i.

[0089] In the present invention, as Figure 1As shown, CO 2 The flash tower T-3 is divided into a CO 2 flash section and a CO 2 washing section from bottom to top, and the CO 2 flash section and the CO 2 washing section are connected through up-vent holes. Among them, the CO 2 flash section is used to flash the rich CO 2 methanol 23 after heat exchange to obtain the CO 2 flash gas and the rich CO 2 methanol 16 after flashing; the CO 2 washing section is used to conduct a second wash on the CO 2 flash gas and the second stream of low-carbon methanol 12-ii to obtain low-CO 2 methanol 14 and the CO 2 flash gas 15-i after washing. 2

[0090] According to the present invention, preferably, as Figure 1 shown, a fourth cooler E-4 is provided on the pipeline connecting the first rich H 2 S methanol outlet of the S absorption section and the H 2 S flash section pipeline, which is used to cool the second stream of rich H 2 S methanol 5-ii and then conduct the H 2 S flash on it. 2 2

[0091] In the present invention, as Figure 1 shown, the H 2 2 S flash tower T-4 is divided into an H 2 S flash section and an H 2 S washing section from bottom to top, and the H 2 S flash section and the H 2 S washing section are connected through up-vent holes. Among them, the H 2 S flash section is used to flash the material after the fourth cooling to obtain the H 2 S flash gas and the rich H 2 S methanol 18 after flashing; the H 2 S washing section is used to conduct a third wash on the H 2 S flash gas and the low-CO 2 methanol 14 to obtain low-sulfur rich-carbon methanol 7 and the H 2 S flash gas 15-ii after washing. 2

[0092] According to the present invention, preferably, as Figure 1 shown, connecting the rich CO 2 2 after flashing of the CO 2A fifth cooler E-5 is provided on the pipeline at the upper part of the methanol export and reabsorption tower T-5, which is used to cool the rich CO 2 After the methanol 16 is cooled by the fifth cooler, it undergoes the first flash evaporation.

[0093] In the present invention, as Figure 1 shown, the upper part and the middle part of the reabsorption tower T-5 are connected by lifting holes, and the middle part and the lower part are also connected by lifting holes. Among them, the upper part is used to flash the rich CO 2 After the methanol 16 is cooled by the fifth cooler, it undergoes the first flash evaporation to obtain semi-lean methanol 8 and the first CO 2 product gas; the middle part is used to flash the second semi-lean methanol 8-ii to obtain the flash liquid and the second CO 2 product gas; the lower part is used to flash the rich H 2 S methanol 18 after the second heat exchange to obtain the sulfur-containing gas phase and the third rich H 2 S methanol 19; among them, the flash liquid and the sulfur-containing gas phase are subjected to the first washing to obtain the low H 2 S methanol 2 and the third CO 2 product gas, and the first CO 2 product gas, the second CO 2 product gas and the third CO 2 product gas are mixed to obtain the CO 2 product gas 17.

[0094] In the present invention, as Figure 1 shown, the second heat exchanger Q-2 is used to perform the second heat exchange between the rich H 2 S methanol 18 after the flash evaporation and the primary low-carbon methanol 20 to obtain the heat-exchanged rich H 2 S methanol 25 and the heat-exchanged low-carbon methanol 26 respectively.

[0095] In the present invention, as Figure 1 shown, the stripping tower T-6 is divided into a primary stripping section and a secondary stripping section from top to bottom, and the primary stripping section and the secondary stripping section are connected by lifting holes. Among them, the primary stripping section is used to contact the semi-lean methanol 24 after the heat exchange with nitrogen 22 and perform the primary stripping to obtain the primary low-carbon methanol 20; the secondary stripping section is used to contact the low-carbon methanol 26 after the heat exchange with nitrogen 22 and perform the secondary stripping to obtain the secondary low-carbon methanol 12 and the tail gas 21.

[0096] According to the present invention, preferably, as Figure 1 shown, a third pump P-3 is provided on the pipeline connecting the secondary low-carbon methanol outlet of the secondary stripping section, the tertiary CO 2 absorption section and the CO 2 washing section, which is used to divide the secondary low-carbon methanol 12 into two streams after the third pressurization and then recycle them respectively.

[0097] According to the present invention, preferably, as Figure 1 shown, the low-sulfur and carbon-rich methanol outlet of the H 2 S washing section and the pipeline of the secondary H 2 S absorption section are provided with a fourth pump P-4, which is used to return the low-sulfur and carbon-rich methanol 7 after being pressurized for the fourth time and perform secondary H 2 S absorption.

[0098] The present invention will be described in detail below through embodiments.

[0099] Embodiment 1

[0100] The device is as Figure 1 shown, and the device includes: H 2 S absorption tower T-1, CO 2 absorption tower T-2, CO 2 flash tower T-3, H 2 S flash tower T-4, reabsorption tower T-5 and stripper T-6, as well as heat exchangers Q-1 to Q-2, coolers E-1 to E-5, and pumps P-1 to P-4;

[0101] Among them, the H 2 S absorption tower T-1 is divided into a primary H 2 S absorption section and a secondary H 2 S absorption section from bottom to top; the CO 2 absorption tower T-2 is divided into a primary CO 2 absorption section, a secondary CO 2 absorption section and a tertiary CO 2 absorption section from bottom to top; the CO 2 flash tower T-3 is divided into a CO 2 flash section and a CO 2 washing section from bottom to top; the H 2 S flash tower T-4 is divided into an H 2 S flash section and an H 2 S washing section from bottom to top; the stripper T-6 is divided into a primary stripping section and a secondary stripping section from top to bottom.

[0102] The method includes:

[0103] Contacting syngas 1 (the molar content of H 2 S is 0.3-0.4%, the molar content of CO 2 is 40-47%; the temperature is -25 to -15 °C, and the pressure is 3.12-3.15 MPa (G)) and the first rich H 2 S methanol 5-i in a molar flow ratio of 60-70:1 and performing primary H 2 S absorption to obtain pre-desulfurized gas and the second rich H 2 S methanol 3 (H2 The molar content of S is 0.6 - 0.9%, and the molar content of CO 2 is 30 - 36%); The above-mentioned pre-desulfurized gas, low-H 2 S methanol 2 (pressurized to 3.5 - 3.6 MPa(G) for the first time), low-sulfur and carbon-rich methanol 7 (pressurized to 3.3 - 3.5 MPa(G) for the fourth time), and the first CO-rich 2 methanol 4 (pressurized to 3.5 - 4 MPa(G) for the second time and cooled to -50 to -45 °C for the third time) are contacted for secondary H 2 S absorption to obtain the first H-rich 2 S methanol 5 (the molar content of H 2 S is 0.3 - 0.5%, and the molar content of CO 2 is 25 - 30%) and desulfurized gas 6 (the molar content of H 2 S is 0.5 - 1 ppm, and the molar content of CO 2 is 32 - 36%; the temperature is -27 to -22 °C; the pressure is 3.05 - 3.1 MPa(G));

[0104] The molar flow ratio of low-H 2 S methanol 2 to syngas 1 is 1:3 - 4; the molar flow ratio of low-sulfur and carbon-rich methanol 7 to syngas 1 is 1:7 - 9; the molar flow ratio of the first CO-rich 2 methanol 4 to syngas 1 is 1:1.5 - 2.5; The above-mentioned first H-rich 2 S methanol 5 is divided into the first H-rich 2 S methanol 5-i and the second H-rich 2 S methanol 5-ii with a molar flow ratio of 1:60 - 70;

[0105] The above-mentioned desulfurized gas 6 and the first CO-rich 2 methanol 10-i (cooled to -33 to -27 °C for the first time) are contacted with a molar flow ratio of 1:1.5 - 2.5 for primary CO 2 absorption to obtain the first CO-rich 2 methanol 4 (the molar content of CO 2 is 20 - 25%, and the molar content of H 2 S is 0.1 - 0.5 ppm; the temperature is -25 to -20 °C, and the pressure is 3.05 - 3.1 MPa(G)) and primary purified gas; The above-mentioned primary purified gas and the third CO-rich 2 methanol 11 (cooled to -36 to -33 °C for the second time) are contacted for secondary CO 2 absorption to obtain the second CO-rich 2 methanol 10 (the molar content of H 2 S is 0.1 - 0.5 ppm, and the molar content of CO 2The molar content is 16 - 20%, the temperature is -20 to -15 °C, the pressure is 3.05 - 3.1 MPa(G)), and the secondary purified gas; contacting the above secondary purified gas, the first stream of low-carbon methanol 12-i and lean methanol 9 and performing tertiary CO 2 absorption to obtain the third CO-rich 2 methanol 11 and tertiary purified gas 13 (H 2 S molar content < 0.1 ppm, CO 2 molar content < 20 ppm; the temperature is -55 to -50 °C, the pressure is 3 - 3.1 MPa(G));

[0106] Among them, the molar flow ratio of the above desulfurized gas 6 and the first stream of CO-rich 2 methanol 10-i is 1:1.5 - 2.5; the molar flow ratio of the desulfurized gas 6 and the third CO-rich 2 methanol 11 is 1:2 - 2.5; the molar flow ratio of the tertiary purified gas 13 and the first stream of low-carbon methanol 12-i is 1:1 - 1.2; the molar flow ratio of the tertiary purified gas 13 and the lean methanol 9 is 1:1.4 - 1.7; dividing the above second CO-rich 2 methanol 10 into the first stream of CO-rich 2 methanol 10-i and the second stream of CO-rich 2 methanol 10-ii with a molar flow ratio of 1:2.5 - 3;

[0107] Contacting the above second stream of CO-rich 2 methanol 10-ii and the first stream of semi-lean methanol 8-i for the first heat exchange to obtain the heat-exchanged CO-rich 2 methanol 23 at a temperature of -33 to -30 °C, and the heat-exchanged semi-lean methanol 24 at a temperature of -40 to -35 °C;

[0108] Subjecting the heat-exchanged CO-rich 2 methanol 23 to CO 2 flashing (pressure is 0.8 - 1 MPa(G)) to obtain CO 2 flash gas and the flashed CO-rich 2 methanol 16 (H 2 S molar content is 0.1 - 0.5 ppm, CO 2 molar content is 15.5 - 19.5%; the temperature is -33.5 to -30.5 °C); subjecting the above second stream of H 2 S methanol 5-ii to the fourth cooling to -42 to -38 °C, and then performing H 2 S flashing (pressure is 0.8 - 1 MPa(G)) to obtain H 2 S flash gas and the flashed H 2 S methanol 18 (H 2 S molar content is 0.3 - 0.5%, CO2 The molar content is 24.5 - 29.5%; the temperature is -42.5 to -38.5 °C);

[0109] After the above-mentioned flash evaporation, the rich CO 2 After the methanol 16 is cooled for the fifth time to -45 °C to -40 °C, the first flash evaporation is carried out (the pressure is 0.05 - 0.08 MPa(G)), and semi-lean methanol 8 (H 2 The molar content of H₂S is ≤0.5 ppm, CO 2 The molar content is 10 - 14%; the temperature is -55 to -50 °C, the pressure is 0.05 - 0.08 MPa(G)) and the first CO 2 product gas, and the semi-lean methanol 8 is divided into a first semi-lean methanol 8-i, a second semi-lean methanol 8-ii and a third semi-lean methanol 8-iii with a molar flow ratio of 2.5 - 2.8:1.1 - 1.3:1; the above-mentioned second semi-lean methanol 8-ii is subjected to a second flash evaporation (the pressure is 0.06 - 0.09 MPa(G)), and a flash liquid and a second CO 2 product gas;

[0110] After the above-mentioned flash evaporation, the rich H₂ 2 After the methanol 18 exchanges heat for the second time, the heat-exchanged rich H₂ 2 S methanol 25 is subjected to a third flash evaporation (the pressure is 0.12 - 0.16 MPa(G)), and a sulfur-containing gas phase and a third rich H₂ 2 S methanol 19 (H 2 The molar content of H₂S is 0.3 - 0.4%, CO 2 The molar content is 18 - 22%; the temperature is -65 to -60 °C; the pressure is 0.13 - 0.17 MPa(G)); the sulfur-containing gas phase and the flash liquid are subjected to the first washing to obtain low H₂ 2 S methanol 2 (H 2 The molar content of H₂S is 0.1 - 0.2%, CO 2 The molar content is 12 - 17%; the temperature is -52 to -48 °C, the pressure is 0.12 - 0.16 MPa(G)) and the third CO 2 product gas; the first CO 2 product gas, the second CO 2 product gas and the third CO 2 product gas are mixed to obtain CO 2 product gas 17 (H 2 The molar content of H₂S is <1 ppm, CO 2 The molar content is 99.3 - 99.7%; the temperature is -55 °C to -50 °C, the pressure is 0.05 - 0.08 MPa(G));

[0111] The semi-lean methanol 24 after heat exchange is brought into contact with nitrogen 22 and the primary stripping is carried out. The resulting primary low-carbon methanol 20 is subjected to a second heat exchange to obtain heat-exchanged low-carbon methanol 26 at a temperature of -40 to -38°C, which is brought into contact with nitrogen 22 and the secondary stripping is carried out to obtain secondary low-carbon methanol 12 (H 2 The molar content of S is ≤0.5 ppm, and the molar content of CO 2 is 2 - 4%; the temperature is -50 to -45°C; the pressure is 0.15 - 0.2 MPa (G)) and tail gas 21 (H 2 The molar content of S is ≤0.5 ppm, and the molar content of CO 2 is 75 - 78%; the temperature is -40 to -35°C; the pressure is 0.1 - 0.15 MPa (G));

[0112] The above-mentioned secondary low-carbon methanol 12 is pressurized to 3.3 - 3.5 MPa (G) for the third time and then divided into a first low-carbon methanol 12-i and a second low-carbon methanol 12-ii with a molar flow ratio of 4 - 5:1;

[0113] The above-mentioned second low-carbon methanol 12-ii is brought into contact with CO 2 flash gas and the second washing is carried out to obtain washed CO 2 flash gas 15-i and low-CO 2 methanol 14 (H 2 The molar content of S is 0.1 - 0.5 ppm, and the molar content of CO 2 is 6 - 9%; the temperature is -43 to -38°C); the above-mentioned low-CO 2 methanol 14 and H 2 S flash gas are subjected to a third washing to obtain washed H 2 S flash gas 15-ii and low-sulfur carbon-rich methanol 7 (H 2 The molar content of S is <100 ppm, and the molar content of CO 2 is 7 - 11%; the temperature is -40 to -35°C); among them, the washed CO 2 flash gas 15-i and the washed H 2 S flash gas 15-ii are mixed to obtain flash gas 15 (the temperature is -43°C to -38°C, and the pressure is 0.8 - 1 MPa (G)).

[0114] Comparative Example 1

[0115] Taking a hydrogen production device using pulverized coal gasification as an example, the effective gas (H 2 +CO) entering the cold methanol wash device is 161000 Nm 3 / h. Under this benchmark, the main technical parameters of the lean solution - semi - lean solution process (i.e., CN201110260570.0 discloses a low - temperature methanol washing process and a syngas purification process for a supporting pulverized coal gasification device) are compared as shown in Table 1.

[0116] Table 1

[0117]

[0118] From the results in Table 1, taking the hydrogen production device based on pulverized coal gasification as an example, for the syngas purification process of the supporting pulverized coal gasification device provided in Example 1, the lean methanol circulation rate is 87.7% of the lean methanol circulation rate in Comparative Example 1 (lean solution - semi - lean solution process), and the low - carbon methanol circulation rate is 58.3% of the semi - lean methanol circulation rate in Comparative Example 1 (lean solution - semi - lean solution process). The amount of rich CO 2 methanol used in the H 2 S absorption tower is 85.7% of the amount of rich CO 2 methanol used in Comparative Example 1 (lean solution - semi - lean solution process), and the cumulative reduction of external cold consumption is 1300 KW / h, with a significant overall energy - saving effect.

[0119] 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 technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A low-temperature, low-sulfur, low-carbon methanol washing method for a pulverized coal gasification device, characterized in that: The method comprises: The synthesis gas is subjected to H2S absorption to obtain a first H2S-rich methanol and a desulfurized gas; the desulfurized gas is subjected to primary CO2 absorption, secondary CO2 absorption, and tertiary CO2 absorption in sequence to obtain a first CO2-rich methanol and a second CO2-rich methanol; the second CO2-rich methanol is divided into two streams, the first stream of CO2-rich methanol is returned and subjected to the primary CO2 absorption, the second stream of CO2-rich methanol is subjected to CO2 flash distillation after a first heat exchange to obtain CO2 flash gas, and the flashed CO2-rich methanol is subjected to a first flash distillation to obtain semi-lean liquid methanol, which is divided into three streams, and the second stream of semi-lean liquid methanol is subjected to a second flash distillation to obtain a flash liquid; the first H2S-rich methanol is divided into two streams, the second stream of H2S-rich methanol is subjected to H2S flash distillation to obtain H2S flash gas, and the flashed H2S-rich methanol is subjected to a third flash distillation after a second heat exchange, and the obtained sulfur-containing gas phase is subjected to a first washing with the flash liquid to obtain low H2S methanol; The first stream of semi-lean liquid methanol is subjected to the first heat exchange and then subjected to the first-stage stripping. The first-stage low-carbon methanol obtained is subjected to the second heat exchange and then subjected to the second-stage stripping. The second-stage low-carbon methanol obtained is divided into two streams. The first stream of low-carbon methanol is returned and subjected to the third-stage CO2 absorption. The second stream of low-carbon methanol is sequentially subjected to the second washing and the third washing with the CO2 flash gas and the H2S flash gas, respectively, to obtain low-sulfur carbon-rich methanol. The first stream of H2S-rich methanol, the first stream of CO2-rich methanol, the low H2S methanol and the low-sulfur carbon-rich methanol are each independently returned and subjected to the H2S absorption.

2. The method according to claim 1, wherein: The H2S absorption process includes: primary H2S absorption and secondary H2S absorption; The synthesis gas is contacted with the first stream of H2S-rich methanol and subjected to the first-level H2S absorption to obtain pre-desulfurized gas and second H2S-rich methanol; the pre-desulfurized gas, low-H2S methanol, low-sulfur carbon-rich methanol and first CO2-rich methanol are contacted and subjected to the second-level H2S absorption to obtain first H2S-rich methanol and desulfurized gas; and / or, the molar content of H2S in the synthesis gas is 0.3-0.4%, the molar content of CO2 is 40-47%; the temperature is -25 to -15°C, and the pressure is 3.12-3.15MPa(G); and / or, the molar content of H2S in the first H2S-rich methanol is 0.3-0.5%, and the molar content of CO2 is 25-30%; and / or, dividing the first H2S-rich methanol into a first stream of H2S-rich methanol and a second stream of H2S-rich methanol at a molar flow ratio of 1:60-70; and / or, the molar content of H2S in the desulfurized gas is 0.5-1ppm, the molar content of CO2 is 32-36%; the temperature is -27 to -22°C; the pressure is 3.05-3.1MPa(G); Preferably, the low H2S methanol is first pressurized to 3.5-3.6 MPa(G) and then returned to undergo the secondary H2S absorption.

3. The method according to claim 1 or 2, wherein: The process of the primary CO2 absorption comprises: contacting the desulfurized gas with the first stream of CO2-rich methanol and performing the primary CO2 absorption to obtain the first CO2-rich methanol and the primary purified gas; The process of the secondary CO2 absorption comprises: contacting the primary purified gas with the third CO2-rich methanol and performing the secondary CO2 absorption to obtain the second CO2-rich methanol and the secondary purified gas; The three-stage CO2 absorption process includes: contacting the second-stage purified gas, the first stream of low-carbon methanol and lean methanol and performing the three-stage CO2 absorption to obtain the third CO2-rich methanol and the three-stage purified gas; and / or, the first stream of CO2-rich methanol is first cooled to -33 to -27°C and then returned to the first-stage CO2 absorption; and / or, the molar content of CO2 in the first CO2-rich methanol is 20-25%, the molar content of H2S is 0.1-0.5 ppm; the temperature is -25 to -20°C, and the pressure is 3.05-3.1 MPa(G); and / or, the molar content of H2S in the second CO2-rich methanol is 0.1-0.5 ppm, the molar content of CO2 is 16-20%, the temperature is -20 to -15°C, and the pressure is 3.05-3.1 MPa(G); and / or, dividing the second CO2-rich methanol into the first CO2-rich methanol and the second CO2-rich methanol at a molar flow ratio of 1:2.5-3; Preferably, the molar content of H2S in the three-stage purified gas is less than 0.1ppm, and the molar content of CO2 is less than 20ppm; the temperature is -55 to -50°C, and the pressure is 3-3.1MPa(G); Preferably, the third CO2-rich methanol is cooled to -36 to -33°C for the second time and then returned to the secondary CO2 absorption; And / or, according to the material flow direction, the first CO2-rich methanol is successively pressurized to 3.5-4 MPa (G) and cooled to -50 to -45°C for a third time, and then returned to perform the H2S absorption.

4. The method according to any one of claims 1 to 3, wherein: The first heat exchange process includes: performing a first heat exchange on the second stream of CO2-rich methanol and the first stream of semi-lean methanol to obtain heat-exchanged CO2-rich methanol converted from the second stream of CO2-rich methanol and heat-exchanged semi-lean methanol converted from the first stream of semi-lean methanol; Preferably, the temperature of the CO2-rich methanol after the heat exchange is -33 to -30°C; the temperature of the semi-lean methanol after the heat exchange is -40 to -35°C; And / or, the pressure of the CO2 flash evaporation is 0.8-1MPa(G); and / or, the molar content of H2S in the CO2-rich methanol after the flash evaporation is 0.1-0.5 ppm, the molar content of CO2 is 15.5-19.5%; the temperature is -33.5 to -30.5°C; and / or, subjecting the second stream of H2S-rich methanol to a fourth cooling process to -42 to -38°C, and then performing the H2S flash evaporation; And / or, the pressure of the H2S flash evaporation is 0.8-1 MPa(G); And / or, the molar content of H2S in the H2S-rich methanol after the flash evaporation is 0.3-0.5%, the molar content of CO2 is 24.5-29.5%; the temperature is -42.5 to -38.5°C.

5. The method according to any one of claims 1 to 4, wherein: The second stream of low-carbon methanol is contacted with CO2 flash gas and subjected to the second washing to obtain washed CO2 flash gas and low-CO2 methanol; the low-CO2 methanol and H2S flash gas are subjected to the third washing to obtain washed H2S flash gas and the low-sulfur and carbon-rich methanol; wherein the washed CO2 flash gas and the washed H2S flash gas are mixed to obtain flash gas; and / or, the molar content of H2S in the low-sulfur, carbon-rich methanol is <100 ppm, the molar content of CO2 is 7-11%; the temperature is -40 to -35°C; And / or, the low-sulfur, carbon-rich methanol is pressurized to 3.3-3.5 MPa(G) for the fourth time and then returned to perform the H2S absorption.

6. The method according to any one of claims 1 to 5, wherein: The CO2-rich methanol after the flash is cooled to -45°C to -40°C for the fifth time, and then the first flash is performed; And / or, the first flash evaporation process includes: performing a first flash evaporation on the fifth cooled material to obtain the semi-lean liquid methanol and the first CO2 product gas; the second flash evaporation process includes: performing a second flash evaporation on the second stream of semi-lean liquid methanol to obtain the flash liquid and the second CO2 product gas; the third flash evaporation process includes: performing a third flash evaporation on the flashed H2S-rich methanol after a second heat exchange to obtain a sulfur-containing gas phase and a third H2S-rich methanol; wherein the first CO2 product gas, the second CO2 product gas and the third CO2 product gas obtained by the first washing are mixed to obtain a CO2 product gas; Preferably, the molar content of H2S in the CO2 product gas is <1ppm, the molar content of CO2 is 99.3-99.7%; the temperature is -55°C to -50°C, and the pressure is 0.05-0.08MPa(G); And / or, 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); the pressure of the third flash evaporation is 0.12-0.16 MPa(G); and / or, the molar content of H2S in the semi-lean methanol is ≤0.5ppm, the molar content of CO2 is 10-14%; the temperature is -55 to -50°C, and the pressure is 0.05-0.08MPa(G); and / or, dividing the semi-lean methanol into the first stream of semi-lean methanol, the second stream of semi-lean methanol and the third stream of semi-lean methanol at a molar flow ratio of 2.5-2.8:1.1-1.3:1; And / or, the molar content of H2S in the low H2S methanol is 0.1-0.2%, the molar content of CO2 is 12-17%; the temperature is -52 to -48°C, and the pressure is 0.12-0.16 MPa(G).

7. The method according to any one of claims 1 to 6, wherein: The second heat exchange process comprises: performing the second heat exchange on the flash H2S-rich methanol and the primary low-carbon methanol to obtain heat-exchanged H2S-rich methanol converted from the flash H2S-rich methanol and heat-exchanged low-carbon methanol converted from the primary low-carbon methanol; Preferably, the temperature of the H2S-rich methanol after the heat exchange is -44 to -40°C; the temperature of the low-carbon methanol after the heat exchange is -40 to -38°C; and / or, the first stream of semi-lean liquid methanol is subjected to the first heat exchange and then contacted with nitrogen and subjected to the first-stage stripping, and the first-stage low-carbon methanol obtained is subjected to the second heat exchange and then contacted with nitrogen and subjected to the second-stage stripping to obtain the second-stage low-carbon methanol and tail gas; and / or, the secondary low-carbon methanol is pressurized to 3.3-3.5 MPa(G) for a third time and then divided into two streams; and / or, dividing the secondary low-carbon methanol into a first stream of low-carbon methanol and a second stream of low-carbon methanol at a molar flow ratio of 4-5:1; And / or, the molar content of H2S in the secondary low-carbon methanol is ≤0.5ppm, the molar content of CO2 is 2-4%; the temperature is -50 to -45°C; and the pressure is 0.15-0.2MPa(G).

8. A low-temperature, low-sulfur, low-carbon methanol washing device supporting a pulverized coal gasification device, characterized in that: The device comprises: an H2S absorption tower, a CO2 absorption tower, a CO2 flash tower, an H2S flash tower, a reabsorption tower and a stripping tower; wherein the CO2 absorption tower is divided into a primary CO2 absorption section, a secondary CO2 absorption section and a tertiary CO2 absorption section from bottom to top; the CO2 flash tower is divided into a CO2 flash section and a CO2 washing section from bottom to top; the H2S flash tower is divided into an H2S flash section and an H2S washing section from bottom to top; the stripping tower is divided into a primary stripping section and a secondary stripping section from top to bottom; The synthesis gas enters the H2S absorption tower for H2S absorption to obtain the first H2S-rich methanol and the desulfurized gas; the desulfurized gas enters the primary CO2 absorption section, the secondary CO2 absorption section and the tertiary CO2 absorption section in sequence to obtain the first CO2-rich methanol and the second CO2-rich methanol; the second CO2-rich methanol is divided into two streams, the first CO2-rich methanol is recycled to the primary CO2 absorption section, the second CO2-rich methanol passes through the first heat exchanger, and then enters the CO2 flash evaporation section for CO2 flash evaporation to obtain CO2 flash gas and the CO2-rich methanol after flash evaporation. The CO2 methanol enters the upper part of the reabsorption tower for the first flash evaporation, and the semi-lean liquid methanol obtained is divided into three streams, and the second stream of the semi-lean liquid methanol is recycled to the middle part of the reabsorption tower for the second flash evaporation to obtain a flash liquid; the first H2S-rich methanol is divided into two streams, and the second stream of the H2S-rich methanol enters the H2S flash evaporation section for H2S flash evaporation to obtain H2S flash gas, and the flashed H2S-rich methanol enters the lower part of the reabsorption tower after passing through the second heat exchanger for the third flash evaporation, and the obtained sulfur-containing gas phase is first washed with the flash liquid to obtain low-H2S methanol; The first stream of semi-lean liquid methanol enters the primary stripping section through the first heat exchanger, and the obtained primary low-carbon methanol enters the secondary stripping section after passing through the second heat exchanger. The obtained secondary low-carbon methanol is divided into two streams. The first stream of low-carbon methanol is recycled to the tertiary CO2 absorption section, and the second stream of low-carbon methanol enters the CO2 washing section and the H2S washing section in sequence, and is washed with CO2 flash steam and H2S flash steam for the second and third washings respectively to obtain low-sulfur carbon-rich methanol; The first stream of H2S-rich methanol, the first stream of CO2-rich methanol, the low H2S methanol and the low-sulfur carbon-rich methanol are independently recycled to the H2S absorption tower.

9. The device according to claim 8, wherein: The H2S absorption tower is divided into a primary H2S absorption section and a secondary H2S absorption section from bottom to top; The first stream of H2S-rich methanol is recycled to the primary H2S absorption section; the first CO2-rich methanol, low H2S methanol and low-sulfur carbon-rich methanol are independently recycled to the secondary H2S absorption section; Preferably, a first pump is provided on the pipeline connecting the low H2S methanol outlet of the reabsorption tower and the secondary H2S absorption section; and / or, a first cooler is provided on the pipeline connecting the bottom of the secondary CO2 absorption section and the primary CO2 absorption section according to the material flow direction; and / or, a second cooler is provided on the pipeline connecting the bottom of the third-stage CO2 absorption section and the second-stage CO2 absorption section according to the material flow direction; Preferably, according to the material flow direction, a second pump and a third cooler are sequentially arranged on the pipeline connecting the first CO2-rich methanol outlet of the primary CO2 absorption section and the secondary H2S absorption section.

10. The device according to claim 9, wherein: A fourth cooler is provided on the pipeline connecting the first H2S-rich methanol outlet of the secondary H2S absorption section and the H2S flash section; And / or, a fifth cooler is provided on the pipeline connecting the outlet of the CO2-rich methanol after flash evaporation of the CO2 flash evaporation section and the upper part of the reabsorption tower; And / or, a third pump is provided on the pipeline connecting the secondary low-carbon methanol outlet of the secondary stripping section, the tertiary CO2 absorption section and the CO2 washing section, for dividing the secondary low-carbon methanol into two streams after the third pressurization, and then reusing them respectively; And / or, a fourth pump is provided on the pipeline connecting the low-sulfur and carbon-rich methanol outlet of the H2S washing section and the secondary H2S absorption section.

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