Low-temperature low-sulfur synthesis gas purification technology matched with coal water slurry gasification device

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to a low-temperature low-sulfur synthesis gas purification method and device matched with a coal water slurry gasification device.According to the method and technology, the H2S absorption process is optimally set, low H2S methanol is used for washing synthesis gas, and the use amount of a first strand of CO2-rich methanol is reduced; the two-stage medium-pressure flash evaporation process is optimally arranged, so that the advantage that flash evaporation gas generated by flash evaporation is independently washed and does not pollute each other is achieved; the reabsorption process is optimized, so that the low H2S methanol is generated, and meanwhile, the low H2S methanol is prevented from being deeply polluted; the steam stripping process is optimized, so that the CO2 content in the semi-lean solution methanol is further reduced, the CO2 absorption capacity is improved, the use amount of lean methanol in the CO2 absorption section is reduced, and the method has the characteristic of low comprehensive energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of low-temperature methanol washing, and specifically relates to a method for purifying low-temperature and low-sulfur syngas for a coal water slurry gasification unit and a device for purifying low-temperature and low-sulfur syngas for a coal water slurry gasification unit. Background Art

[0002] In the syngas produced by using the coal water slurry 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, ammonia, and ethylene glycol 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 utilizes the characteristic that low-temperature methanol has a great solubility for acidic gases to remove acidic gases such as H 2 S and CO 2 in the syngas, and at the same time removes trace components such as HCN and NH 3 . At present, the innovative research on the low-temperature methanol washing technology mainly focuses on the recycling of the pressure-reduced flash evaporation of CO 2 -rich methanol. The typical process flow mainly has the lean liquid-semi-lean liquid process, but there are technical bottlenecks in further optimizing and innovating the lean liquid-semi-lean liquid process. Therefore, it is necessary to adjust the technical innovation direction of the low-temperature methanol washing process.

[0004] In the low-temperature methanol washing process flow, the CO 2 -rich methanol can be recycled through pressure-reduced flash evaporation, but the H 2 S-containing methanol must be recycled through thermal regeneration, which is the main energy-consuming source of the low-temperature methanol washing. Therefore, how to enhance the utilization efficiency of the H 2 S-containing methanol is the key factor in technological innovation. Specifically, it is necessary to make the H 2 S-containing methanol reach the absorption limit for the H 2 S gas in the syngas before the thermal regeneration of the H 2 S-containing methanol, so as to increase the concentration of H 2 S in the H 2 S-rich methanol, reduce the total amount of the H

[0005] CN201110260570.0 discloses a low-temperature methanol washing process. First, in the H 2The S absorption tower uses rich CO entirely 2 methanol to wash the syngas, and the rich CO 2 methanol is contaminated while absorbing H 2 S gas, 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 flashing gas while washing the rich H 2 S methanol, and is contaminated by the rich H 2 S methanol itself. The resulting low-concentration H 2 S methanol is not fully utilized either, resulting in high energy consumption. Third, the CO 2 gas flashed from the upper tower of the medium-pressure flash tower is sent to the lower tower to be washed and absorbed by the rich H 2 S methanol, and is contaminated while being washed by the rich H 2 S methanol, which is not conducive to reducing the comprehensive energy consumption of the cold methanol washing unit. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above technical problems and provide a method for purifying low-temperature and low-sulfur syngas for a coal water slurry gasification unit and a device for purifying low-temperature and low-sulfur syngas for a coal water slurry gasification unit. Through optimizing the H 2 S absorption process, using low-H 2 S methanol to wash the syngas, the usage amount of the first rich CO 2 methanol is reduced; by optimizing the two-stage medium-pressure flashing process, the flashed gases generated by flashing have the advantage of being washed separately without mutual contamination; by optimizing the reabsorption process, low-H 2 S methanol is generated, and at the same time, the low-H 2 S methanol is prevented from being deeply contaminated; by optimizing the stripping process, the CO 2 content in the semi-lean liquid methanol is further reduced, the CO 2 absorption capacity is improved, and the usage amount of lean methanol in the CO 2 absorption section is reduced, featuring low comprehensive energy consumption.

[0007] To achieve the above purpose, the first aspect of the present invention provides a method for purifying low-temperature and low-sulfur syngas for a coal water slurry gasification unit. The method includes: subjecting the syngas to H 2 S absorption and CO 2 absorption in sequence to obtain the first rich H 2 S methanol and the first rich CO 2 methanol, both of which are divided into two equal parts; the second rich CO 2 methanol and the second rich H2 The methanol is independently subjected to primary flashing to obtain primary CO 2 flash gas and primary H 2 S flash gas, and the obtained primary CO 2 flash liquid and primary H 2 S flash liquid are independently subjected to secondary flashing to obtain secondary CO 2 flash gas and secondary H 2 S flash gas, and secondary CO 2 flash liquid and secondary H 2 S flash liquid; wherein, the primary CO 2 flash gas, primary H 2 S flash gas, secondary CO 2 flash gas and secondary H 2 S flash gas are respectively subjected to the first washing, the second washing, the third washing and the fourth washing to obtain low-sulfur and carbon-rich methanol;

[0008] The secondary CO 2 flash liquid is divided into two streams. The first stream of secondary CO 2 flash liquid is subjected to primary flashing, and the obtained semi-lean liquid methanol is divided into two streams; the second stream of secondary CO 2 flash liquid and the low-sulfur and carbon-rich methanol are independently subjected to secondary flashing to obtain flash liquid; the secondary H 2 S flash liquid is subjected to tertiary flashing, and the obtained sulfur-containing gas phase and the flash liquid are subjected to the fifth washing to obtain low-H 2 S methanol; the first stream of semi-lean liquid methanol is stripped to obtain low-carbon methanol, which is divided into three streams. The first stream of low-carbon methanol returns and undergoes the CO 2 absorption, and the second stream of low-carbon methanol and the third stream of low-carbon methanol respectively return and undergo the first washing and the second washing; wherein, the low-H 2 S methanol, the first stream of CO-rich 2 methanol and the first stream of H-rich 2 S methanol independently return and undergo the H 2 S absorption.

[0009] The second aspect of the present invention provides a low-temperature and low-sulfur syngas purification device for a coal water slurry gasification device. The device includes: a shift gas absorption tower, a primary flash tower, a secondary flash tower, a reabsorption tower and a stripping tower connected in sequence; the shift gas absorption tower is divided into an H 2 S absorption section and a CO 2 absorption section from bottom to top; the primary flash tower is divided into a primary H 2 S flash section and a primary CO 2 flash section from bottom to top; the secondary flash tower is divided into a secondary H 2 S flash section and a secondary CO 2 flash section from bottom to top;

[0010] The shift gas absorption tower is used to allow syngas to enter the H 2 S absorption section and the CO 2 absorption section in sequence, and perform H 2 S absorption and CO 2 absorption respectively to obtain the first rich H 2 S methanol and the first rich CO 2 methanol, each of which is divided into two streams;

[0011] The lower part of the first-stage CO 2 flashing section is connected to the lower part of the second-stage CO 2 flashing section, and the upper part of the first-stage CO 2 flashing section is connected to the upper part of the second-stage CO 2 flashing section, which is used to perform first-stage CO 2 flashing and second-stage CO 2 flashing on the second stream of rich CO 2 methanol in sequence, and the second-stage CO 2 flashing liquid is divided into two streams, and the first-stage CO 2 flashing gas is subjected to the first washing to obtain the first washing liquid, and the second-stage CO 2 flashing gas is subjected to the third washing to obtain the third washing liquid;

[0012] The lower part of the first-stage H 2 S flashing section is connected to the lower part of the second-stage H 2 S flashing section, and the upper part of the first-stage H 2 S flashing section and the upper part of the second-stage CO 2 flashing section are both connected to the upper part of the second-stage H 2 S flashing section, which is used to perform first-stage H 2 S flashing and second-stage H 2 S flashing on the second stream of rich H 2 S methanol in sequence to obtain the second-stage H 2 S flashing liquid, and the first-stage H 2 S flashing gas is subjected to the second washing to obtain the second washing liquid, and the second washing liquid and the third washing liquid are respectively subjected to the fourth washing with the second-stage H 2 S flashing gas to obtain low-sulfur rich-carbon methanol;

[0013] The upper part of the reabsorption tower is used to perform the first flashing on the first stream of the second-stage CO 2 flashing liquid to obtain semi-lean liquid methanol, which is divided into two streams; the middle part of the reabsorption tower is used to perform the second flashing on the second stream of the second-stage CO 2 flashing liquid and the low-sulfur rich-carbon methanol independently to obtain the flashing liquid; the lower part of the reabsorption tower is used to perform the third flashing on the second-stage H 2 S flashing liquid to obtain the sulfur-containing gas phase, and the flashing liquid is subjected to the fifth washing to obtain low-H 2S methanol;

[0014] The stripping column is used to bring the first semi-lean methanol into contact with nitrogen for stripping. The resulting low-carbon methanol is divided into the first low-carbon methanol, the second low-carbon methanol, and the third low-carbon methanol, which are respectively recycled to the 2 absorption section, the first-stage CO 2 upper part of the flash section and the first-stage H 2 upper part of the S flash section;

[0015] Among them, the low-H 2 S methanol, the first rich CO 2 methanol, and the first rich H 2 S methanol are each independently recycled to the 2 S absorption section.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) The present invention adopts a two-stage flash technology. The first stage uses a relatively high flash pressure, and the effective gas flashed out can be directly sent to the second stage of the compressor in the compression process, reducing the power consumption of the compressor; the second stage uses a relatively low flash pressure to ensure that the effective gas in the first-stage CO 2 flash liquid and the first-stage H 2 S flash liquid is fully recovered. At the same time, the intake volume of the first-stage cylinder of the compressor in the compression process can be reduced, correspondingly reducing the power consumption of the compressor; at the same time, the flash gas generated by the two-stage flash is washed separately to avoid mutual contamination;

[0018] (2) The present invention optimizes the first-stage flash process flow. During the first-stage CO 2 flash process, by introducing the second low-carbon methanol to absorb the first-stage CO 2 flash gas, compared with the prior art, while reducing the CO 2 component in the first-stage CO 2 flash gas, it is not contaminated by the first-stage H 2 S flash liquid; the separate flashing and separate washing of the second rich CO 2 methanol and the second rich H 2 S methanol are realized, avoiding the technical problem that the CO 2 gas in the first-stage CO 2 flash liquid is transferred to the first-stage H 2 S flash liquid, which is beneficial to reducing the energy consumption of the device;

[0019] (3) The present invention optimizes the reabsorption process flow, realizing the absorption of the sulfur component in the CO 2 product gas generated by the second-stage H 2 S flash liquid by the flash liquid, but without mixing with the third rich H 2S methanol is mixed with each other; therefore, compared with the prior art, after the flash liquid absorbs the flashed H 2 S gas, the H 2 S content in the solution is lower, which is called low H 2 S methanol; the low H 2 S methanol is sent to the H 2 S absorption process to absorb H 2 S and CO 2 gas in the syngas, realizing the recycling of the low H 2 S methanol, reducing the usage amount of the first rich CO 2 methanol, which is equivalent to reducing the second rich H 2 S methanol that needs thermal regeneration;

[0020] (4) In the method provided by the present invention, to further reduce the CO 2 content in the semi-lean liquid methanol and maximize the CO 2 absorption capacity of the semi-lean liquid methanol, the optimized re-absorption process performs nitrogen stripping on the semi-lean liquid methanol again, so that the CO 2 content in the semi-lean liquid methanol is further reduced to 13 - 17%, becoming low-carbon methanol. This can produce two positive effects: one is that with the improvement of the absorption capacity of the low-carbon methanol and the reduction of the circulation volume, the operation 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%; the other is that the low-carbon methanol can replace part of the lean methanol, so that the circulation amount of the lean methanol in the CO 2 absorption tower also decreases, and the reduction of the lean methanol flow rate will be transmitted to the rich CO 2 methanol, and the flow rate of the second rich CO 2 methanol that needs thermal regeneration will also decrease, and the energy consumption of the corresponding thermal regeneration system will also decrease accordingly. Brief Description of the Drawings

[0021] Figure 1 is a schematic structural diagram of a low-temperature and low-sulfur syngas purification device supporting a water coal gasification device provided by the present invention.

[0022] Description of the Reference Numerals in the Drawings

[0023] T-1, shift gas absorption tower; T-2, first flash tower; T-3, second flash tower; T-4, re-absorption tower; T-5, stripping tower; Q, 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;

[0024] 1, syngas; 2, low H 2 S methanol; 3, second rich H 2 S methanol; 4, first rich CO2 Methanol; 4-i, the first rich CO 2 Methanol; 4-ii, the second rich CO 2 Methanol; 5, the first rich H 2 S Methanol; 5-i, the first rich H 2 S Methanol; 5-ii, the second rich H 2 S Methanol; 6, purified gas; 7, the second rich CO 2 Methanol; 8, semi-lean methanol; 8-i, the first semi-lean methanol; 8-ii, the second semi-lean methanol; 9, lean methanol; 10, primary CO 2 Flash liquid; 11, the first washing liquid; 12, primary flash gas; 12-i, primary CO 2 Washing gas; 12-ii, primary H 2 S Washing gas; 13, the second washing liquid; 14, secondary flash gas; 14-i, secondary CO 2 Washing gas; 14-ii, secondary H 2 S Washing gas; 15, primary H 2 S Flash liquid; 16, secondary CO 2 Flash liquid; 16-i, the first secondary CO 2 Flash liquid; 16-ii, the second secondary CO 2 Flash liquid; 17, low-sulfur carbon-rich methanol; 18, secondary H 2 S Flash liquid; 19, CO 2 Product gas; 20, low-carbon methanol; 20-i, the first low-carbon methanol; 20-ii, the second low-carbon methanol; 20-iii, the third low-carbon methanol; 21, nitrogen; 22, tail gas; 23, the third rich H 2 S Methanol; 24, heat-exchanged secondary CO 2 Flash liquid; 25, heat-exchanged semi-lean methanol; 26, the third washing liquid. Detailed implementation mode

[0025] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the values between the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values 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.

[0026] In the present invention, without special circumstances, "first", "second", "third", "fourth", and "fifth" 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, in "first washing", "second washing", "third washing", "fourth washing", and "fifth washing", "first", "second", "third", "fourth", and "fifth" are only used to indicate that these are not the same washing.

[0027] In the present invention, without special circumstances, the "top" of the 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.

[0028] The first aspect of the present invention provides a method for purifying low - temperature and low - sulfur syngas for a coal - water slurry gasification device, and the method includes: sequentially subjecting the syngas to H 2 S absorption and CO 2 absorption to obtain first H - rich 2 methanol and first CO - rich 2 methanol, both of which are evenly divided into two streams; subjecting the second - stream CO - rich 2 methanol and the second - stream H - rich 2 methanol to primary flashing independently to obtain primary CO 2 flash gas and primary H 2 S flash gas, and subjecting the obtained primary CO 2 flash liquid and primary H 2 S flash liquid to secondary flashing independently to obtain secondary CO 2 flash gas and secondary H 2 S flash gas, and secondary CO 2 flash liquid and secondary H 2 S flash liquid; wherein, subjecting the primary CO 2 flash gas, primary H 2 S flash gas, secondary CO 2 flash gas and secondary H 2 S flash gas to first washing, second washing, third washing, and fourth washing respectively to obtain low - sulfur and carbon - rich methanol;

[0029] Dividing the secondary CO 2 flash liquid into two streams, subjecting the first - stream secondary CO 2 flash liquid to first flashing to obtain semi - lean liquid methanol divided into two streams; the second - stream secondary CO 2The flash liquid and the low-sulfur carbon-rich methanol are each independently subjected to a second flash to obtain a flash liquid; the secondary H 2 S flash liquid is subjected to a third flash, and the sulfur-containing gas phase obtained and the flash liquid are subjected to a fifth washing to obtain low-H 2 S methanol; the first semi-lean liquid methanol is stripped, and the obtained low-carbon methanol is divided into three streams. The first stream of low-carbon methanol is returned and subjected to the above-mentioned CO 2 absorption, and the second and third streams of low-carbon methanol are respectively returned and subjected to the first washing and the second washing; wherein, the low-H 2 S methanol, the first CO-rich 2 methanol and the first H-rich 2 S methanol are each independently returned and subjected to the above-mentioned H 2 S absorption.

[0030] In the present invention, unless otherwise specified, the fact that the first H-rich 2 S methanol and the first CO-rich 2 methanol are each divided into two streams means that the first H-rich 2 S methanol is divided into the first H-rich 2 S methanol and the second H-rich 2 S methanol; the first CO-rich 2 methanol is divided into the first CO-rich 2 methanol and the second CO-rich 2 methanol.

[0031] In some embodiments of the present invention, preferably, the process of the H 2 S absorption includes: bringing the syngas into contact with the first H-rich 2 S methanol and performing the first H 2 S absorption to obtain the second H-rich 2 S methanol and the pre-desulfurized gas; bringing the pre-desulfurized gas, the low-H 2 S methanol, and the first CO-rich 2 methanol into contact and performing the second H 2 S absorption to obtain the desulfurized gas and the first H-rich 2 S methanol.

[0032] In some embodiments of the present invention, preferably, the molar content of H 2 S in the syngas is 0.9-1.2%, and the molar content of CO 2 is 40-50%; the temperature is -15 to -5 °C, and the pressure is 5.2-5.7 MPa(G). In the present invention, the source of the syngas has a relatively wide selection range, as long as the syngas meets the above limitations. Preferably, the syngas is selected from the syngas cooling process upstream of the source.

[0033] In some embodiments of the present invention, preferably, the molar flow rate ratio of the syngas and the first stream of H-rich 2 S methanol is 70 - 80:1.

[0034] In the present invention, the first H 2 S absorption is intended 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 H-rich 2 S methanol is 2 - 3%, and the molar content of CO 2 is 70 - 75%.

[0035] In some embodiments of the present invention, preferably, the first H-rich 2 S methanol is divided into the first stream of H-rich 2 S methanol and the second stream of H-rich 2 S methanol with a molar flow rate ratio of 1:50 - 60. In the present invention, the first H-rich 2 S methanol is divided into two streams. The first stream returns and undergoes the first H 2 S absorption, and the second stream undergoes primary H 2 S flash evaporation.

[0036] In the present invention, the second H 2 S absorption is intended 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 H-rich 2 S methanol is 1.4 - 1.7%, and the molar content of CO 2 is 37 - 43%.

[0037] In some embodiments of the present invention, preferably, after the first stream of CO-rich 2 methanol is cooled to -35 to -25 °C by the third cooler, it returns and undergoes the second H 2 S absorption.

[0038] In some embodiments of the present invention, preferably, the molar flow rate ratio of the syngas and the low H 2 S methanol is 4.5 - 5:1; the molar flow rate ratio of the syngas and the first stream of CO-rich 2 methanol is 2.2 - 2.5:1.

[0039] In some embodiments of the present invention, preferably, the process of CO 2 absorption includes: contacting the desulfurized gas and the second CO-rich 2 methanol and performing the first CO2 Absorb to obtain pre-purified gas and the first CO-rich gas 2 Methanol; contacting the pre-purified gas, the first stream of low-carbon methanol and lean methanol and performing a second CO 2 Absorb to obtain purified gas and the second rich CO 2 Methanol.

[0040] In some embodiments of the present invention, preferably, the desulfurized gas and the second CO-rich 2 The molar flow ratio of methanol is 1:1.1-1.2.

[0041] In the present invention, the first CO 2 Absorption is intended to further remove CO from sweetened gas 2 . Preferably, the first CO-rich 2 CO in methanol 2 The molar content of is 31-36%, H 2 The molar content of S is 0.1-0.5ppm; the pressure is 5.2-5.4MPa(G).

[0042] In the present invention, the first CO-rich 2 Methanol is divided into two streams, the first stream is returned and used for the second H 2 S absorption, the second stream for primary CO 2 Flash evaporation. Preferably, the first CO-rich 2 Methanol is divided into the first stream rich in CO with a molar flow ratio of 1:1.8-2.2 2 Methanol and a second CO-rich stream 2 Methanol.

[0043] In some embodiments of the present invention, preferably, the molar flow ratio of the purified gas to the first stream of low-carbon methanol is 1.8-2:1; the molar flow ratio of the purified gas to lean methanol is 1:1-1.2.

[0044] In some embodiments of the present invention, preferably, the second CO-rich 2 After the methanol is cooled to -36 to -34°C for the fourth time, it is returned and used for the first CO 2 Absorb.

[0045] In some embodiments of the present invention, preferably, the second CO-rich 2 H in methanol 2 The molar content of S is 0.1-0.5ppm, CO 2 The molar content of is 18-22%.

[0046] In some embodiments of the present invention, preferably, the H in the purified gas 2 S molar content <0.1ppm, CO​​​​​​2 Mole content < 20 ppm; temperature is -55 to -50 °C, and pressure is 5.2 - 5.3 MPa(G).

[0047] In some embodiments of the present invention, preferably, the primary flash evaporation includes primary CO 2 flash evaporation and primary H 2 S flash evaporation; wherein, the second CO-rich 2 methanol is subjected to the primary CO 2 flash evaporation to obtain the primary CO 2 flash vapor and primary CO 2 flash liquid; the second H-rich 2 S methanol is subjected to the primary H 2 S flash evaporation to obtain the primary H 2 S flash vapor and primary H 2 S flash liquid.

[0048] In some embodiments of the present invention, more preferably, after the second CO-rich 2 methanol is cooled to -36 to -33 °C by the first cooler, it is subjected to the primary CO 2 flash evaporation. The first cooling reduces the temperature of the second CO-rich 2 methanol, aiming to reduce the total amount of medium-pressure flash gas and lay a foundation for obtaining low temperature (high-quality cold energy) for the reabsorption tower.

[0049] In some embodiments of the present invention, more preferably, after the second H-rich 2 S methanol is cooled to -33 to -30 °C by the second cooler, it is subjected to the primary H 2 S flash evaporation. The second cooling reduces the temperature of the second H-rich 2 S methanol, aiming to reduce the total amount of medium-pressure flash gas and lay a foundation for obtaining low temperature (high-quality cold energy) for the reabsorption tower.

[0050] In some embodiments of the present invention, preferably, the pressure of the primary flash evaporation is 3.5 - 3.7 MPa(G). That is, the pressures of both the primary CO 2 flash evaporation and the primary H 2 S flash evaporation are 3.5 - 3.7 MPa(G).

[0051] In some embodiments of the present invention, preferably, the mole content of H 2 S in the primary CO 2 flash liquid is 0.1 - 0.5 ppm, and the mole content of CO 2 is 30.5 - 35.5%; the temperature is -36.5 to -33.5 °C.

[0052] In some embodiments of the present invention, preferably, the primary H 2 S flash liquid has an H 2 S molar content of 1.4 - 1.7%, and a CO 2 molar content of 36.5 - 42.5%; the temperature is -33.5 to -30.5 °C.

[0053] In some embodiments of the present invention, preferably, the secondary flash includes secondary CO 2 flash and secondary H 2 S flash; wherein, the primary CO 2 flash liquid is subjected to the secondary CO 2 flash to obtain the secondary CO 2 flash gas and the secondary CO 2 flash liquid; the primary H 2 S flash liquid is subjected to the secondary H 2 S flash to obtain the secondary H 2 S flash gas and the secondary H 2 S flash liquid.

[0054] In some embodiments of the present invention, preferably, the pressure of the secondary flash is 1.6 - 2 MPa(G). That is, the pressures of both the secondary CO 2 flash and the secondary H 2 S flash are 1.6 - 2 MPa(G).

[0055] In some embodiments of the present invention, preferably, the secondary CO 2 flash liquid has an H 2 S molar content of 0.1 - 0.5 ppm, and a CO 2 molar content of 29 - 33%; the temperature is -37 to -34 °C.

[0056] In some embodiments of the present invention, preferably, the secondary CO 2 flash liquid is divided into the first stream of secondary CO 2 flash liquid and the second stream of secondary CO 2 flash liquid with a molar flow rate ratio of 3.1 - 3.5:1. In the present invention, the secondary CO 2 flash liquid is divided into two streams, the first stream is subjected to the first flash, and the second stream is subjected to the second flash.

[0057] In some embodiments of the present invention, preferably, the secondary H 2 S flash liquid has an H 2 S molar content of 1.4 - 1.7%, and a CO 2 molar content of 36 - 42%; the temperature is -34 to -31 °C.

[0058] In the present invention, without special circumstances, low-sulfur and carbon-rich methanol is obtained by washing the second low-carbon methanol and the third low-carbon methanol with primary CO 2 flash gas, primary H 2 S flash gas, secondary CO 2 flash gas and secondary H 2 S flash gas respectively.

[0059] In some embodiments of the present invention, preferably, the process of the first washing includes: bringing the second low-carbon methanol into contact with the primary CO 2 flash gas and performing the first washing to obtain primary CO 2 scrubbing gas and a first scrubbing liquid; more preferably, the molar content of H 2 S in the first scrubbing liquid is 0.1 - 0.5 ppm, and the molar content of CO 2 is 13 - 18%; the temperature is -70 to -65 °C.

[0060] In some embodiments of the present invention, preferably, the process of the second washing includes: bringing the third low-carbon methanol into contact with the primary H 2 S flash gas and performing the second washing to obtain primary H 2 S scrubbing gas and a second scrubbing liquid; more preferably, the molar content of H 2 S in the second scrubbing liquid is 0.14 - 0.17%, and the molar content of CO 2 is 20 - 25%; the temperature is -45 to -40 °C.

[0061] In some embodiments of the present invention, preferably, the temperature of the primary CO 2 scrubbing gas is -73 °C to -68 °C, and the pressure is 3.5 - 3.7 MPa(G); the temperature of the primary H 2 S scrubbing gas is -70 °C to -65 °C, and the pressure is 3.5 - 3.7 MPa(G); mixing the primary CO 2 scrubbing gas and the primary H 2 S scrubbing gas, and sending the obtained primary flash gas to subsequent processes for treatment.

[0062] In some embodiments of the present invention, preferably, the process of the third washing includes: bringing the first scrubbing liquid into contact with the secondary CO 2 flash gas and performing the third washing to obtain secondary CO 2 scrubbing gas and a third scrubbing liquid; more preferably, the molar content of H 2 S in the third scrubbing liquid is 0.1 - 0.5 ppm, and the molar content of CO 2 is 14 - 19%.

[0063] In some embodiments of the present invention, preferably, the process of the fourth washing includes: separately contacting the second washing liquid and the third washing liquid with the secondary H 2 S flash gas and performing the fourth washing to obtain secondary H 2 S washing gas and low-sulfur carbon-rich methanol.

[0064] In some embodiments of the present invention, preferably, the molar content of H 2 S in the low-sulfur carbon-rich methanol is <0.1%, and the molar content of CO 2 is 20-23%.

[0065] In some embodiments of the present invention, more preferably, the temperature of the secondary CO 2 washing gas is -68°C to -62°C, and the pressure is 1.6-2 MPa(G); the temperature of the secondary H 2 S washing gas is -63°C to -58°C, and the pressure is 1.6-2 MPa(G). In the present invention, the secondary CO 2 washing gas and the secondary H 2 S washing gas are mixed, and the obtained secondary flash gas is sent to subsequent processes for treatment.

[0066] In the present invention, the first stream of secondary CO 2 flash liquid is subjected to the first flash to obtain semi-lean liquid methanol and the first CO 2 product gas. Preferably, the pressure of the first flash is 0.05-0.08 MPa(G).

[0067] In some embodiments of the present invention, preferably, the molar content of CO 2 in the semi-lean liquid methanol is 20-23%, and the molar content of H 2 S is ≤0.5 ppm; the temperature is -65 to -60°C; the pressure is 0.05-0.08 MPa(G).

[0068] In the present invention, the semi-lean liquid methanol is divided into two streams, the first stream is subjected to stripping, and the second stream is sent to subsequent processes for treatment. Preferably, the semi-lean liquid methanol is divided into the first stream of semi-lean liquid methanol and the second stream of semi-lean liquid methanol with a molar flow ratio of 1.4-1.6:1.

[0069] In some embodiments of the present invention, preferably, the second stream of secondary CO 2 flash liquid and the first stream of semi-lean liquid methanol are heat-exchanged to obtain the heat-exchanged secondary CO 2 flash liquid transformed from the second stream of secondary CO 2 flash liquid, and the heat-exchanged semi-lean liquid methanol transformed from the first stream of semi-lean liquid methanol.

[0070] In some embodiments of the present invention, further preferably, the temperature of the secondary CO 2 flash liquid after heat exchange is -55 to -50 °C; the temperature of the semi-lean methanol after heat exchange is -62 to -60 °C.

[0071] In some embodiments of the present invention, preferably, after cooling the low-sulfur rich-carbon methanol to -48 to -44 °C by the fifth cooler, the second flash evaporation is carried out. By reducing the temperature of the low-sulfur rich-carbon methanol, low temperature is generated by pressure-reducing flash evaporation, and the absorption capacity of the flash liquid for H 2 S gas is improved, which is beneficial to washing H 2 S gas in the CO 2 product gas after flash evaporation.

[0072] In some embodiments of the present invention, preferably, the secondary CO 2 flash liquid after heat exchange and the material after the fifth cooling are each independently subjected to the second flash evaporation to obtain the flash liquid and the second CO 2 product gas.

[0073] In some embodiments of the present invention, preferably, the pressure of the second flash evaporation is 0.06 - 0.09 MPa(G).

[0074] In the present invention, the secondary H 2 S flash liquid is subjected to a third flash evaporation to obtain a sulfur-containing gas phase and a third H 2 S-rich methanol. Preferably, the pressure of the third flash evaporation is 0.12 - 0.16 MPa(G).

[0075] In the present invention, the process of the fifth washing includes bringing the flash liquid into contact with the sulfur-containing gas phase and washing to obtain low-H 2 S methanol and a third CO 2 product gas. Preferably, the molar content of H 2 S in the low-H 2 S methanol is 0.7 - 0.9%, and the molar content of CO 2 is 23 - 28%; the temperature is -63 to -58 °C, and the pressure is 0.12 - 0.16 MPa(G).

[0076] In some embodiments of the present invention, preferably, after the low-H 2 S methanol is pressurized to 5.8 - 6 MPa(G) by the first pressurization, it is returned and subjected to the H 2 S absorption, preferably returned and subjected to the second H 2 S absorption.

[0077] In some embodiments of the present invention, preferably, the third flash evaporation also obtains a third H 2H in methanol 2 The molar content of S is 1.4 - 1.7%, and the molar content of CO 2 is 25 - 29%; the temperature is -70 to -65 °C; the pressure is 0.13 - 0.17 MPa(G).

[0078] In some embodiments of the present invention, further preferably, the first CO obtained by the first flash evaporation 2 product gas, the second CO obtained by the second flash evaporation 2 product gas, and the third CO obtained by the fifth washing 2 product gas are mixed to obtain a CO 2 product gas with the molar content of H 2 S < 1 ppm and the molar content of CO 2 is 99.4 - 99.7%; the temperature is -66 °C to -61 °C, and the pressure is 0.05 - 0.08 MPa(G).

[0079] In some embodiments of the present invention, preferably, the stripping process includes: contacting the first semi-lean methanol with nitrogen and performing the stripping to obtain the low-carbon methanol and the tail gas; further preferably, after the first semi-lean methanol is heat-exchanged, the stripping is performed.

[0080] In some embodiments of the present invention, preferably, the molar content of H 2 S in the low-carbon methanol ≤ 0.5 ppm, and the molar content of CO 2 is 13 - 17%; the temperature is -73 to -68 °C; the pressure is 0.15 - 0.25 MPa(G).

[0081] In some embodiments of the present invention, preferably, the low-carbon methanol is divided into a first low-carbon methanol, a second low-carbon methanol, and a third low-carbon methanol with a molar flow ratio of 40 - 50:3 - 4:1. In the present invention, the low-carbon methanol is divided into three streams. The first stream returns and undergoes the second CO 2 absorption, the second stream returns and undergoes the first washing, and the third stream returns and undergoes the second washing.

[0082] In some embodiments of the present invention, further preferably, after the low-carbon methanol is secondarily pressurized to 5.8 - 6 MPa(G), it is divided into three streams.

[0083] In some embodiments of the present invention, preferably, the molar content of H 2 S in the tail gas ≤ 0.5 ppm, and the molar content of CO 2 is 88 - 92%; the temperature is -65 to -60 °C; the pressure is 0.15 - 0.25 MPa(G).

[0084] The second aspect of the present invention provides a structural schematic diagram of a low-temperature and low-sulfur syngas purification device for a coal water slurry gasification device as shown in Figure 1 shown, and it can be seen from Figure 1 that the device includes: a shift gas absorption tower T-1, a first flash tower T-2, a second flash tower T-3, a reabsorption tower T-4, and a stripping tower T-5, which are connected in sequence; the shift gas absorption tower T-1 is divided into an H 2 S absorption section and a CO 2 absorption section from bottom to top; the first flash tower T-2 is divided into a first-stage H 2 S flash section and a first-stage CO 2 flash section from bottom to top; the second flash tower T-3 is divided into a second-stage H 2 S flash section and a second-stage CO 2 flash section from bottom to top;

[0085] The shift gas absorption tower T-1 is used to allow the syngas 1 to enter the H 2 S absorption section and the CO 2 absorption section in sequence, and perform H 2 S absorption and CO 2 absorption respectively, and the obtained first rich H 2 S methanol 5 and the first rich CO 2 methanol 4 are each divided into two streams;

[0086] The lower part of the first-stage CO 2 flash section is connected to the lower part of the second-stage CO 2 flash section, and the upper part of the first-stage CO 2 flash section is connected to the upper part of the second-stage CO 2 flash section, which is used to perform first-stage CO 2 flash and second-stage CO 2 flash on the second stream of rich CO 2 methanol 4-ii in sequence. The obtained second-stage CO 2 flash liquid 16 is divided into two streams, and the first-stage CO 2 flash gas is subjected to the first washing to obtain the first washing liquid 11, and the second-stage CO 2 flash gas is subjected to the third washing to obtain the third washing liquid 26;

[0087] The lower part of the first-stage H 2 S flash section is connected to the lower part of the second-stage H 2 S flash section, and the upper part of the first-stage H 2 S flash section and the upper part of the second-stage CO 2 flash section are both connected to the upper part of the second-stage H 2 S flash section, which is used to perform first-stage H 2 S flash and second-stage H 2 S flash on the second stream of rich H 2S flashing to obtain secondary H 2 S flashing liquid 18, and subjecting primary H 2 The second washing of the S flashing gas, and the obtained second washing liquid 13 and third washing liquid 26 are respectively combined with secondary H 2 The S flashing gas is subjected to a fourth washing to obtain low-sulfur carbon-rich methanol 17;

[0088] The upper part of the reabsorption tower T-4 is used for the first stream of secondary CO 2 The flashing liquid 16-i is subjected to a first flashing, and the obtained semi-lean liquid methanol 8 is divided into two streams; the middle part of the reabsorption tower T-4 is used for subjecting the second stream of secondary CO 2 The flashing liquid 16-ii and the low-sulfur carbon-rich methanol 17 are each independently subjected to a second flashing to obtain a flashing liquid; the lower part of the reabsorption tower T-4 is used for subjecting the secondary H 2 The S flashing liquid 18 is subjected to a third flashing, and the obtained sulfur-containing gas phase and the flashing liquid are subjected to a fifth washing to obtain low-H 2 S methanol 2;

[0089] The stripping tower T-5 is used for bringing the first stream of semi-lean liquid methanol 8-i into contact with nitrogen 21 and stripping, and the obtained low-carbon methanol 20 is divided into a first stream of low-carbon methanol 20-i, a second stream of low-carbon methanol 20-ii and a third stream of low-carbon methanol 20-iii, and are respectively recycled to the CO 2 absorption section, primary CO 2 the upper part of the flashing section and primary H 2 the upper part of the S flashing section;

[0090] Among them, the low-H 2 S methanol 2, the first stream of CO-rich 2 methanol 4-i and the first stream of H-rich 2 S methanol 5-i are each independently recycled to the H 2 S absorption section.

[0091] In the present invention, as Figure 1 shown, the H 2 S absorption section is divided into a first H 2 S absorption part and a second H 2 S absorption part from bottom to top. Specifically, the first H 2 S absorption part introduces the first stream of H-rich 2 S methanol 5-i to pre-wash and absorb HCN and NH 3 in the syngas 1; the second H 2 S absorption part absorbs H 2 S and CO 2 in the pre-desulfurized gas by introducing low-H 2 S methanol 2, realizing the recycling of low-H 2 S methanol 2 and reducing the first stream of CO-rich2 The usage amount of methanol 4-i is equivalent to reducing the second rich H stream that needs thermal regeneration 2 S methanol 5-ii; in addition, such setting correspondingly reduces the subsequent CO 2 absorption section's working load, and correspondingly also reduces the CO 2 usage amounts of lean methanol 9 and the first low-carbon methanol 20-i in the absorption section.

[0092] In the present invention, as Figure 1 shown, preferably, the first rich H 2 S methanol 5-i is recycled to the first H 2 S absorption section; preferably, the first rich CO 2 methanol 4-i and low H 2 S methanol 2 are each independently recycled to the second H 2 S absorption section.

[0093] In the present invention, as Figure 1 shown, the H 2 S absorption section is divided into a first H 2 S absorption section and a second H 2 S absorption section from bottom to top. The first H 2 S absorption section and the second H 2 S absorption section are connected through lifting air holes. Among them, the first H 2 S absorption section is used to contact the syngas 1 and the first rich H 2 S methanol 5-i and perform the first H 2 S absorption to obtain the second rich H 2 S methanol 3 and the pre-desulfurized gas; the second H 2 S absorption section is used to contact the pre-desulfurized gas, low H 2 S methanol 2 and the first rich CO 2 methanol 4-i and perform the second H 2 S absorption to obtain the desulfurized gas and the first rich H 2 S methanol 5.

[0094] In the present invention, without special instructions, in the first H 2 S absorption section, the contact mode between the syngas 1 and the first rich H 2 S methanol 5-i is preferably the countercurrent contact between the syngas 1 and the first rich H 2 S methanol 5-i, that is, the syngas 1 enters from the bottom of the first H 2 S absorption section, and the first rich H 2 S methanol 5-i enters from the upper part of the first H 2 S absorption section.

[0095] In the present invention, as Figure 1As shown, the CO 2 absorption is divided into a first CO 2 absorption section and a second CO 2 absorption section from bottom to top. Among them, the first CO 2 absorption section is used to bring the desulfurized gas into contact with the second rich CO 2 methanol 7 and conduct the first CO 2 absorption to obtain a pre-purified gas and the first rich CO 2 methanol 4; the second CO 2 absorption section is used to bring the pre-purified gas, the first stream of low-carbon methanol 20-i and lean methanol 9 into contact and conduct the second CO 2 absorption to obtain a purified gas 6 and the second rich CO 2 methanol 7.

[0096] In the present invention, without special instructions, in the CO 2 absorption section, for the first CO 2 absorption section, the contact mode between the desulfurized gas and the second rich CO 2 methanol 7 is preferably selected from the countercurrent contact between the desulfurized gas and the second rich CO 2 methanol 7; that is, the desulfurized gas enters from the bottom of the first CO 2 absorption section, and the second rich CO 2 methanol 7 enters from the upper part of the first CO 2 absorption section.

[0097] In the present invention, as Figure 1 shown, preferably, in the direction of material flow, a third cooler E-3 is provided on the pipeline connecting the first CO 2 absorption section and the second H 2 S absorption section, which is used to cool the first stream of rich CO 2 methanol 4-i and then return it to conduct the second H 2 S absorption.

[0098] In the present invention, as Figure 1 shown, preferably, in the direction of material flow, a fourth cooler E-4 is provided on the pipeline connecting the second CO 2 absorption section and the first CO 2 absorption section, which is used to cool the second rich CO 2 methanol 7 and then return it to conduct the first CO 2 absorption.

[0099] In the present invention, as Figure 1 shown, the first-stage flash tower T-2 is divided into a first-stage H 2 S flash section and a first-stage CO 2 flash section from bottom to top. Specifically, the first-stage CO2 The lower part of the flash evaporation section is used to subject the second stream of CO-rich 2 methanol 4-ii to primary CO 2 flash evaporation to obtain primary CO 2 flash vapor and primary CO 2 flash liquid 10. The primary CO 2 flash vapor enters the upper part of the primary CO 2 flash evaporation section, contacts with the second stream of low-carbon methanol 20-ii and undergoes the first washing to obtain the first washing liquid 11 and primary CO 2 washing gas 12-i; The lower part of the primary H 2 S flash evaporation section is used to subject the second stream of H-rich 2 S methanol 5-ii to primary H 2 S flash evaporation to obtain primary H 2 S flash vapor and primary H 2 S flash liquid 15. The primary H 2 S flash vapor enters the upper part of the primary H 2 S flash evaporation section, contacts with the third stream of low-carbon methanol 20-iii and undergoes the second washing to obtain the second washing liquid 13 and primary H 2 S washing gas 12-ii.

[0100] In the present invention, as Figure 1 shown, the upper and lower parts of the primary CO 2 flash evaporation section are connected by lifting holes; the upper and lower parts of the primary H 2 S flash evaporation section are connected by lifting holes.

[0101] In the present invention, as Figure 1 shown, the secondary flash evaporation tower T-3 is divided into a secondary H 2 S flash evaporation section and a secondary CO 2 flash evaporation section from bottom to top. Specifically, the lower part of the secondary CO 2 flash evaporation section is used to subject the primary CO 2 flash liquid 10 to secondary CO 2 flash evaporation to obtain secondary CO 2 flash vapor and secondary CO 2 flash liquid 16. The secondary CO 2 flash vapor enters the upper part of the secondary CO 2 flash evaporation section, contacts with the first washing liquid 11 and undergoes the third washing to obtain the third washing liquid 26 and secondary CO 2 washing gas 14-i; The lower part of the secondary H 2 S flash evaporation section is used to subject the primary H 2 S flash liquid 15 to secondary H 2 S flash evaporation to obtain secondary H 2 S flash vapor and secondary H 2S Flash Liquid 18, Secondary H 2 S Flash Vapor Enters Secondary H 2 The upper part of the S Flash Section contacts the Second Scrubbing Liquid 13 and the Third Scrubbing Liquid 26 respectively and performs the Fourth Scrubbing to obtain Low-Sulfur Rich-Carbon Methanol 17 and Secondary H 2 S Scrubbed Gas 14-ii.

[0102] In the present invention, as Figure 1 shown, Secondary CO 2 The upper and lower parts of the Flash Section are connected by lifting holes; Secondary H 2 The upper and lower parts of the S Flash Section are connected by lifting holes.

[0103] In the present invention, as Figure 1 shown, the upper and middle parts of the Reabsorption Tower T-4 are connected by lifting holes, and the middle and lower parts are also connected by lifting holes. Specifically, the upper part is used to perform the First Flash on the First Stream of Secondary CO 2 Flash Liquid 16-i to obtain Semi-Poor Liquid Methanol 8 and First CO 2 Product Gas; the middle part is used to perform the Second Flash on the Second Stream of Secondary CO 2 Flash Liquid 16-ii and Low-Sulfur Rich-Carbon Methanol 17 independently to obtain Flash Liquid and Second CO 2 Product Gas; the lower part is used to perform the Third Flash on Secondary H 2 S Flash Liquid 18 to obtain Third H 2 Rich S Methanol 23 and Sulfur-Containing Gas Phase; wherein, the Sulfur-Containing Gas Phase and the Flash Liquid are subjected to the Fifth Scrubbing to obtain Low-H 2 S Methanol 2 and Third CO 2 Product Gas; CO 2 Product Gas 19 includes First CO 2 Product Gas, Second CO 2 Product Gas and Third CO 2 Product Gas.

[0104] In the present invention, as Figure 1 shown, the Stripping Tower T-5 is used to contact the First Stream of Semi-Poor Liquid Methanol 8-i with Nitrogen 21 and perform the Stripping, and Tail Gas 22 is obtained at the top of the tower and Low-Carbon Methanol 20 is obtained at the bottom of the tower.

[0105] In the present invention, as Figure 1 shown, a First Cooler E-1 is provided on the pipeline connecting the First CO 2 Absorption Section and the lower part of the Primary CO 2 Flash Section, which is used to cool the Second Stream of CO 2 Rich Methanol 4-ii and then perform the Primary CO 2 Flash.

[0106] In the present invention, asFigure 1 As shown, connecting the second H 2 S absorption section and the first-stage H 2 A second cooler E-2 is provided on the pipeline at the lower part of the S flash evaporation section for cooling the second rich H 2 S methanol 5-ii. After being cooled by the second cooler, it undergoes the first-stage H 2 S flash evaporation.

[0107] In the present invention, as Figure 1 shown, a heat exchanger Q is provided on the pipelines connecting the lower part of the secondary CO 2 flash evaporation section, the upper part of the reabsorption tower T-4, the middle part of the reabsorption tower T-4, and the stripping tower T-5 for exchanging heat between the second secondary CO 2 flash evaporation liquid 16-ii and the first semi-lean methanol 8-i. The heat-exchanged secondary CO 2 flash evaporation liquid 24 and the heat-exchanged semi-lean methanol 25 respectively undergo the second flash evaporation and stripping.

[0108] In the present invention, as Figure 1 shown, a fifth cooler E-5 is provided on the pipeline connecting the upper part of the secondary H 2 S flash evaporation section and the middle part of the reabsorption tower T-4 for cooling the low-sulfur rich carbon methanol 17. After being cooled by the fifth cooler, it undergoes the second flash evaporation.

[0109] In the present invention, as Figure 1 shown, a first pump P-1 is provided on the pipeline connecting the middle part of the reabsorption tower T-4 and the second H 2 S absorption section for pressurizing the low H 2 S methanol 2. After being pressurized by the first pump, it returns and undergoes the second H 2 S absorption.

[0110] In the present invention, as Figure 1 shown, a second pump P-2 is provided on the pipeline connecting the stripping tower T-5, the second CO 2 absorption section, the upper part of the first-stage CO 2 flash evaporation section, and the upper part of the first-stage H 2 S flash evaporation section. The second pump P-2 is used to pressurize the low-carbon methanol 20 in three streams, which respectively return and undergo the second CO 2 absorption, the first washing, and the second washing.

[0111] The present invention will be described in detail below through embodiments.

[0112] Embodiment 1

[0113] The device is as Figure 1As shown in the figure, it includes: a shift gas absorption tower T-1, a first flash tower T-2, a second flash tower T-3, a reabsorption tower T-4, and a stripping tower T-5 connected in sequence, a heat exchanger Q, coolers E-1 to E-5, and pumps P-1 to P-2;

[0114] Among them, the shift gas absorption tower T-1 is divided into an H 2 S absorption section and a CO 2 absorption section from bottom to top. The H 2 S absorption section is divided into a first H 2 S absorption part and a second H 2 S absorption part from bottom to top; the CO 2 absorption is divided into a first CO 2 absorption part and a second CO 2 absorption part from bottom to top; the first flash tower T-2 is divided into a first H 2 S flash section and a first CO 2 flash section from bottom to top; the second flash tower T-3 is divided into a second H 2 S flash section and a second CO 2 flash section from bottom to top; the lower part of the first CO 2 flash section is connected to the lower part of the second CO 2 flash section, and the upper part of the first CO 2 flash section is connected to the upper part of the second CO 2 flash section; the lower part of the first H 2 S flash section is connected to the lower part of the second H 2 S flash section, and the upper part of the first H 2 S flash section and the upper part of the second CO 2 flash section are both connected to the upper part of the second H 2 S flash section;

[0115] The method is carried out in the above device, and the method includes:

[0116] Mixing syngas 1 (the molar content of H 2 S is 0.9 - 1.2%, the molar content of CO 2 is 40 - 50%; the temperature is -15 to -5 °C, and the pressure is 5.2 - 5.7 MPa(G)) and the first rich H 2 S methanol 5-i in a molar flow ratio of 70 - 80:1, contacting and performing the first H 2 S absorption to obtain the second rich H 2 S methanol 3 (the molar content of H 2 S is 2 - 3%, and the molar content of CO 2 is 70 - 75%) and pre-desulfurized gas; Mixing the above pre-desulfurized gas, low H 2 S methanol 2 (pressurized to 5.8 - 6 MPa(G) for the first time) and the first rich CO 2Methanol 4-i (cooled to -35 to -25 °C in the third cooler) contacts and undergoes a second H 2 S absorption to obtain desulfurized gas and the first rich H 2 S methanol 5 (H 2 The molar content of S is 1.4 - 1.7%, and the molar content of CO 2 is 37 - 43%); the above-mentioned first rich H 2 S methanol 5 is divided into a first rich H 2 S methanol 5-i and a second rich H 2 S methanol 5-ii with a molar flow rate ratio of 1:50 - 60;

[0117] Among them, the molar flow rate ratio of syngas 1 and low H 2 S methanol 2 is 4.5 - 5:1; the molar flow rate ratio of syngas 1 and the first rich CO 2 Methanol 4-i is 2.2 - 2.5:1;

[0118] The above-mentioned desulfurized gas and the second rich CO 2 Methanol 7 (cooled to -36 to -34 °C in the fourth cooler) contacts at a molar flow rate ratio of 1:1.1 - 1.2 and undergoes a first CO 2 Absorption to obtain the first rich CO 2 Methanol 4 (CO 2 The molar content is 31 - 36%, and H 2 The molar content of S is 0.1 - 0.5 ppm; the pressure is 5.2 - 5.4 MPa (G)) and pre-purified gas; the above-mentioned pre-purified gas, the first low-carbon methanol 20-i and lean methanol 9 contact and undergo a second CO 2 Absorption to obtain purified gas 6 (H 2 The molar content of S < 0.1 ppm, and the molar content of CO 2 is < 20 ppm; the temperature is -55 to -50 °C, and the pressure is 5.2 - 5.3 MPa (G)) and the above-mentioned second rich CO 2 Methanol 7 (H 2 The molar content of S is 0.1 - 0.5 ppm, and the molar content of CO 2 is 18 - 22%);

[0119] The above-mentioned first rich CO 2 Methanol 4 is divided into a first rich CO 2 Methanol 4-i and a second rich CO 2 Methanol 4-ii with a molar flow rate ratio of 1:1.8 - 2.2; the molar flow rate ratio of purified gas 6 and the first low-carbon methanol 20-i is 1.8 - 2:1; the molar flow rate ratio of purified gas 6 and lean methanol 9 is 1:1 - 1.2;

[0120] The above-mentioned second rich CO 2After the first cooling of methanol 4-ii to -36 to -33 °C, primary CO 2 flash evaporation (at a pressure of 3.5 - 3.7 MPa(G)) is carried out to obtain primary CO 2 flash vapor and primary CO 2 flash liquid 10 (H 2 The molar content of S is 0.1 - 0.5 ppm, and the molar content of CO 2 is 30.5 - 35.5%; the temperature is -36.5 to -33.5 °C); After the second rich H 2 S methanol 5-ii is cooled to -33 to -30 °C in the second stage, primary H 2 S flash evaporation (at a pressure of 3.5 - 3.7 MPa(G)) is carried out to obtain primary H 2 S flash vapor and primary H 2 S flash liquid 15 (H 2 The molar content of S is 1.4 - 1.7%, and the molar content of CO 2 is 36.5 - 42.5%; the temperature is -33.5 to -30.5 °C);

[0121] The above-mentioned primary CO 2 flash liquid 10 is subjected to secondary CO 2 flash evaporation (at a pressure of 1.6 - 2 MPa(G)) to obtain secondary CO 2 flash vapor and secondary CO 2 flash liquid 16 (H 2 The molar content of S is 0.1 - 0.5 ppm, and the molar content of CO 2 is 29 - 33%; the temperature is -37 to -34 °C); The above-mentioned primary H 2 S flash liquid 15 is subjected to the above-mentioned secondary H 2 S flash evaporation (at a pressure of 1.6 - 2 MPa(G)) to obtain secondary H 2 S flash vapor and secondary H 2 S flash liquid 18 (H 2 The molar content of S is 1.4 - 1.7%, and the molar content of CO 2 is 36 - 42%; the temperature is -34 to -31 °C);

[0122] Among them, the second low-carbon methanol 20-ii and primary CO 2 flash vapor are contacted and subjected to the first washing to obtain primary CO 2 scrubbing gas 12-i (temperature is -73 °C to -68 °C, pressure is 3.5 - 3.7 MPa(G)) and the first scrubbing liquid 11 (H 2 The molar content of S is 0.1 - 0.5 ppm, and the molar content of CO 2The molar content is 13 - 18%; the temperature is -70 to -65 °C); the third low-carbon methanol 20-iii and the first-stage H 2 S flash gas are contacted and subjected to a second washing to obtain the first-stage H 2 S washing gas 12-ii (temperature is -70 °C to -65 °C, pressure is 3.5 - 3.7 MPa(G)) and the second washing liquid 13 (H 2 The molar content of S is 0.14 - 0.17%, and the CO 2 The molar content is 20 - 25%; the temperature is -45 to -40 °C); the above-mentioned first washing liquid 11 and the second-stage CO 2 flash gas are contacted and subjected to a third washing to obtain the second-stage CO 2 washing gas 14-i (temperature is -68 °C to -62 °C, pressure is 1.6 - 2 MPa(G)) and the third washing liquid 26 (H 2 The molar content of S is 0.1 - 0.5 ppm, and the CO 2 The molar content is 14 - 19%); the above-mentioned second washing liquid 13 and the third washing liquid 26 are respectively contacted with the second-stage H 2 S flash gas and subjected to a fourth washing to obtain the second-stage H 2 S washing gas 14-ii (temperature is -63 °C to -58 °C, pressure is 1.6 - 2 MPa(G)) and low-sulfur rich-carbon methanol 17 (H 2 The molar content of S is <0.1%, and the CO 2 The molar content is 20 - 23%);

[0123] The above-mentioned second-stage CO 2 flash liquid 16 is divided into a first-stage second-stage CO 2 flash liquid 16-i and a second-stage second-stage CO 2 flash liquid 16-ii with a molar flow rate ratio of 3.1 - 3.5:1; the first-stage second-stage CO 2 flash liquid 16-i is subjected to a first flash (pressure is 0.05 - 0.08 MPa(G)) to obtain semi-lean liquid methanol 8 (CO 2 The molar content is 20 - 23%, and the H 2 The molar content of S is ≤0.5 ppm; the temperature is -65 to -60 °C; the pressure is 0.05 - 0.08 MPa(G)) and the first CO 2 product gas;

[0124] The above-mentioned semi-lean liquid methanol 8 is divided into the first-stage semi-lean liquid methanol 8-i and the second-stage semi-lean liquid methanol 8-ii with a molar flow rate ratio of 1.4 - 1.6:1; the second-stage second-stage CO 2 flash liquid 16-ii and the first-stage semi-lean liquid methanol 8-i are heat-exchanged to obtain the heat-exchanged second-stage CO 2Flash liquid 24 (temperature -55 to -50 °C) and semi-lean methanol 25 after heat exchange (temperature -62 to -60 °C);

[0125] After heat exchange, secondary CO 2 The flash liquid 24 and the low-sulfur carbon-rich methanol 17 (cooled to -48 to -44 °C in the fifth cooler) each independently undergo a second flash (pressure 0.06 - 0.09 MPa(G)) to obtain a flash liquid and secondary CO 2 Product gas; The secondary H 2 S flash liquid 18 undergoes a third flash (pressure 0.12 - 0.16 MPa(G)) to obtain a sulfur-containing gas phase and a third H 2 S-rich methanol 23 (the molar content of H 2 S is 1.4 - 1.7%, the molar content of CO 2 is 25 - 29%; temperature -70 to -65 °C; pressure 0.13 - 0.17 MPa(G)), and the sulfur-containing gas phase and the above flash liquid are subjected to a fifth wash to obtain low-H 2 S methanol 2 (the molar content of H 2 S is 0.7 - 0.9%, the molar content of CO 2 is 23 - 28%; temperature -63 to -58 °C, pressure 0.12 - 0.16 MPa(G)) and tertiary CO 2 Product gas;

[0126] Among them, the above-mentioned primary CO 2 Product gas, secondary CO 2 Product gas and tertiary CO 2 Product gas are mixed to obtain CO 2 In product gas 19, the molar content of H 2 S < 1 ppm, the molar content of CO 2 is 99.4 - 99.7%; temperature -66 to -61 °C, pressure 0.05 - 0.08 MPa(G);

[0127] The above-mentioned semi-lean methanol 25 after heat exchange is contacted with nitrogen 21 and stripped to obtain low-carbon methanol 20 (the molar content of H 2 S ≤ 0.5 ppm, the molar content of CO 2 is 13 - 17%; temperature -73 to -68 °C; pressure 0.15 - 0.25 MPa(G)) and tail gas 22 (the molar content of H 2 S ≤ 0.5 ppm, the molar content of CO 2 is 88 - 92%; temperature -65 to -60 °C; pressure 0.15 - 0.25 MPa(G));

[0128] After pressurizing the above-mentioned low-carbon methanol 20 to 5.8 - 6 MPa(G) for the second time, it is divided into a first low-carbon methanol, a second low-carbon methanol, and a third low-carbon methanol with a molar flow ratio of 40 - 50:3 - 4:1, and then they are respectively returned and subjected to the above-mentioned second CO 2 absorption, first washing, and second washing.

[0129] Comparative Example 1

[0130] Taking a hydrogen production device using coal water slurry gasification as an example, the effective gas (H 2 +CO) entering the Rectisol unit is 230000 Nm 3 / h. Based on this benchmark, the main technical parameters are compared with those of the lean-rich liquor process (i.e., a Rectisol process disclosed in CN201110260570.0) in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] From the results in Table 1, taking the hydrogen production device based on coal water slurry gasification as an example, for the low-temperature and low-sulfur syngas purification process of the supporting coal water slurry gasification device provided in Example 1, the lean methanol circulation rate is 81.5% of the lean methanol circulation rate in Comparative Example 1 (lean-rich liquor process), the low-carbon methanol circulation rate is 73.3% of the semi-lean methanol circulation rate in Comparative Example 1 (lean-rich liquor process), and the amount of rich CO 2 methanol used in the H 2 S absorption tower is 89.5% of the amount of rich CO 2 methanol used in Comparative Example 1 (lean-rich liquor process), with a cumulative reduction in external cold consumption of 800 KW / h, and the overall energy-saving effect is significant.

[0135] 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 method for purifying low-temperature, low-sulfur syngas from a coal-water slurry gasification device, characterized in that: The method comprises: subjecting the synthesis gas to H2S absorption and CO2 absorption in sequence, and the obtained first H2S-rich methanol and the first CO2-rich methanol are equally divided into two streams; the second CO2-rich methanol and the second H2S-rich methanol are independently subjected to primary flash evaporation to obtain primary CO2 flash gas and primary H2S flash gas, and the obtained primary CO2 flash liquid and primary H2S flash liquid are independently subjected to secondary flash evaporation to obtain secondary CO2 flash gas and secondary H2S flash gas, and secondary CO2 flash liquid and secondary H2S flash liquid; wherein the primary CO2 flash gas, the primary H2S flash gas, the secondary CO2 flash gas and the secondary H2S flash gas are respectively subjected to the first washing, the second washing, the third washing and the fourth washing to obtain low-sulfur carbon-rich methanol; The secondary CO2 flash liquid is divided into two streams, the first stream of the secondary CO2 flash liquid is subjected to the first flash, and the obtained semi-lean liquid methanol is divided into two streams; the second stream of the secondary CO2 flash liquid and the low-sulfur carbon-rich methanol are each independently subjected to the second flash to obtain a flash liquid; the secondary H2S flash liquid is subjected to the third flash, and the obtained sulfur-containing gas phase and the flash liquid are subjected to the fifth washing to obtain low-H2S methanol; the first stream of the semi-lean liquid methanol is stripped, and the obtained low-carbon methanol is divided into three streams, the first stream of the low-carbon methanol is returned for the CO2 absorption, the second stream of the low-carbon methanol and the third stream of the low-carbon methanol are respectively returned for the first washing and the second washing; wherein the low H2S methanol, the first stream of the CO2-rich methanol and the first stream of the H2S-rich methanol are each independently returned for the H2S absorption.

2. The method according to claim 1, wherein: The first-stage flash evaporation includes a first-stage CO2 flash evaporation and a first-stage H2S flash evaporation; The second stream of CO2-rich methanol is subjected to the first-level CO2 flash evaporation to obtain the first-level CO2 flash gas and the first-level CO2 flash liquid; the second stream of H2S-rich methanol is subjected to the first-level H2S flash evaporation to obtain the first-level H2S flash gas and the first-level H2S flash liquid; Preferably, the second stream of CO2-rich methanol is first cooled to -36 to -33°C before the first CO2 flash evaporation is performed; Preferably, the second stream of H2S-rich methanol is subjected to a second cooling to -33 to -30°C before the first-stage H2S flash evaporation is performed; And / or, the pressure of the first-stage flash evaporation is 3.5-3.7 MPa(G); and / or, the molar content of H2S in the primary CO2 flash liquid is 0.1-0.5 ppm, the molar content of CO2 is 30.5-35.5%; the temperature is -36.5 to -33.5°C; And / or, the molar content of H2S in the first-stage H2S flash liquid is 1.4-1.7%, the molar content of CO2 is 36.5-42.5%; and the temperature is -33.5 to -30.5°C.

3. The method according to claim 1 or 2, wherein: The secondary flash evaporation includes secondary CO2 flash evaporation and secondary H2S flash evaporation; Wherein, the first-level CO2 flash liquid is subjected to the second-level CO2 flash to obtain the second-level CO2 flash gas and the second-level CO2 flash liquid; the first-level H2S flash liquid is subjected to the second-level H2S flash to obtain the second-level H2S flash gas and the second-level H2S flash liquid; And / or, the pressure of the secondary flash evaporation is 1.6-2 MPa(G); and / or, the molar content of H2S in the secondary CO2 flash liquid is 0.1-0.5 ppm, the molar content of CO2 is 29-33%; the temperature is -37 to -34°C; and / or, dividing the secondary CO2 flash liquid into the first secondary CO2 flash liquid and the second secondary CO2 flash liquid at a molar flow ratio of 3.1-3.5:1; And / or, the molar content of H2S in the secondary H2S flash liquid is 1.4-1.7%, the molar content of CO2 is 36-42%; and the temperature is -34 to -31°C.

4. The method according to any one of claims 1 to 3, wherein: The first washing process includes: contacting the second stream of low-carbon methanol with the first CO2 flash gas and performing the first washing to obtain the first CO2 washing gas and the first washing liquid; Preferably, the molar content of H2S in the first scrubbing liquid is 0.1-0.5 ppm, the molar content of CO2 is 13-18%; the temperature is -70 to -65°C; And / or, the second washing process comprises: contacting the third stream of low-carbon methanol with the primary H2S flash gas and performing the second washing to obtain the primary H2S washing gas and the second washing liquid; Preferably, the molar content of H2S in the second scrubbing liquid is 0.14-0.17%, the molar content of CO2 is 20-25%; the temperature is -45 to -40°C; Preferably, the temperature of the primary CO2 scrubbing gas is -73°C to -68°C, and the pressure is 3.5-3.7 MPa(G); the temperature of the primary H2S scrubbing gas is -70°C to -65°C, and the pressure is 3.5-3.7 MPa(G); the primary CO2 scrubbing gas and the primary H2S scrubbing gas are mixed to obtain primary flash gas; Preferably, the third washing process comprises: contacting the first washing liquid with the secondary CO2 flash gas and performing the third washing to obtain the secondary CO2 washing gas and the third washing liquid; Further preferably, the molar content of H2S in the third washing liquid is 0.1-0.5 ppm, and the molar content of CO2 is 14-19%; Preferably, the fourth washing process comprises: contacting the second washing liquid and the third washing liquid with the secondary H2S flash gas respectively and performing the fourth washing to obtain secondary H2S washing gas and low-sulfur carbon-rich methanol; And / or, the molar content of H2S in the low-sulfur and carbon-rich methanol is <0.1%, and the molar content of CO2 is 20-23%; Further preferably, the temperature of the secondary CO2 scrubbing gas is -68°C to -62°C, and the pressure is 1.6-2MPa(G); the temperature of the secondary H2S scrubbing gas is -63°C to -58°C, and the pressure is 1.6-2MPa(G); the secondary CO2 scrubbing gas and the secondary H2S scrubbing gas are mixed to obtain secondary flash gas.

5. The method according to any one of claims 1 to 4, wherein: The H2S absorption process includes: contacting the synthesis gas with the first stream of H2S-rich methanol and performing a first H2S absorption to obtain a second H2S-rich methanol and a pre-desulfurized gas; contacting the pre-desulfurized gas, the low-H2S methanol, and the first stream of CO2-rich methanol and performing a second H2S absorption to obtain a desulfurized gas and the first H2S-rich methanol; and / or, the molar content of H2S in the synthesis gas is 0.9-1.2%, the molar content of CO2 is 40-50%; the temperature is -15 to -5°C, and the pressure is 5.2-5.7MPa(G); and / or, dividing the first H2S-rich methanol into the first stream of H2S-rich methanol and the second stream of H2S-rich methanol at a molar flow ratio of 1:50-60; and / or, the molar content of H2S in the first H2S-rich methanol is 1.4-1.7%, and the molar content of CO2 is 37-43%; Preferably, the first stream of CO2-rich methanol is cooled to -35 to -25°C for the third time and then returned to the second H2S absorption process; Preferably, the CO2 absorption process comprises: contacting the desulfurized gas with the second CO2-rich methanol and performing a first CO2 absorption to obtain pre-purified gas and the first CO2-rich methanol; contacting the pre-purified gas, the first stream of low-carbon methanol and lean methanol and performing a second CO2 absorption to obtain purified gas and the second CO2-rich methanol; and / or, the molar content of CO2 in the first CO2-rich methanol is 31-36%, the molar content of H2S is 0.1-0.5 ppm; the pressure is 5.2-5.4 MPa(G); and / or, dividing the first CO2-rich methanol into the first CO2-rich methanol and the second CO2-rich methanol at a molar flow ratio of 1:1.8-2.2; Preferably, the second CO2-rich methanol is cooled to -36 to -34°C for the fourth time and then returned to the first CO2 absorption.

6. The method according to any one of claims 1 to 5, wherein: The pressure of the first flash evaporation is 0.05-0.08 MPa(G); and / or, the molar content of CO2 in the semi-lean methanol is 20-23%, the molar content of H2S is ≤0.5ppm; the temperature is -65 to -60°C; the pressure is 0.05-0.08MPa(G); and / or, dividing the semi-lean methanol into the first stream of semi-lean methanol and the second stream of semi-lean methanol at a molar flow ratio of 1.4-1.6:1; and / or, exchanging heat between the second secondary CO2 flash liquid and the first semi-lean methanol to obtain heat-exchanged secondary CO2 flash liquid converted from the second secondary CO2 flash liquid and heat-exchanged semi-lean methanol converted from the first semi-lean methanol; Preferably, the temperature of the secondary CO2 flash liquid after the heat exchange is -55 to -50°C; the temperature of the semi-lean liquid methanol after the heat exchange is -62 to -60°C; and / or, the low-sulfur and carbon-rich methanol is subjected to a fifth cooling to -48 to -44°C and then subjected to the second flash distillation; Preferably, the second CO2 flash liquid after heat exchange and the material after the fifth cooling are independently subjected to the second flash to obtain the flash liquid; And / or, the pressure of the second flash evaporation is 0.06-0.09 MPa(G); And / or, the pressure of the third flash evaporation is 0.12-0.16 MPa(G); and / or, the molar content of H2S in the low H2S methanol is 0.7-0.9%, the molar content of CO2 is 23-28%; the temperature is -63 to -58°C, and the pressure is 0.12-0.16MPa(G); and / or, the low H2S methanol is first pressurized to 5.8-6 MPa(G) and then returned to perform the H2S absorption; And / or, the third H2S-rich methanol obtained by the third flash has a molar content of H2S of 1.4-1.7%, a molar content of CO2 of 25-29%, a temperature of -70 to -65°C, and a pressure of 0.13-0.17 MPa(G); And / or, the first CO2 product gas obtained by the first flash evaporation, the second CO2 product gas obtained by the second flash evaporation and the third CO2 product gas obtained by the fifth washing are mixed to obtain a CO2 product gas with a molar content of H2S less than 1ppm and a molar content of CO2 of 99.4-99.7%; a temperature of -66 to -61°C, and a pressure of 0.05-0.08MPa(G).

7. The method according to claim 6, wherein: The stripping process comprises: contacting the first stream of semi-lean methanol with nitrogen and performing the stripping to obtain the low-carbon methanol and tail gas; and / or, subjecting the first stream of semi-lean methanol to the stripping after the heat exchange; And / or, the molar content of H2S in the low-carbon methanol is ≤0.5ppm, the molar content of CO2 is 13-17%; the temperature is -73 to -68°C; the pressure is 0.15-0.25MPa(G); and / or, dividing the low-carbon methanol into a first stream of low-carbon methanol, a second stream of low-carbon methanol and a third stream of low-carbon methanol with a molar flow ratio of 40-50:3-4:1; And / or, the low-carbon methanol is pressurized to 5.8-6 MPa(G) for a second time and then divided into three streams.

8. A low-temperature, low-sulfur synthesis gas purification device supporting a water-coal slurry gasification device, characterized in that: The device comprises: a shift gas absorption tower, a primary flash tower, a secondary flash tower, a reabsorption tower and a stripping tower connected in sequence; the shift gas absorption tower is divided into an H2S absorption section and a CO2 absorption section from bottom to top; the primary flash tower is divided into a primary H2S flash section and a primary CO2 flash section from bottom to top; the secondary flash tower is divided into a secondary H2S flash section and a secondary CO2 flash section from bottom to top; The shift gas absorption tower is used to sequentially allow the synthesis gas to enter the H2S absorption section and the CO2 absorption section to absorb H2S and CO2 respectively, and the obtained first H2S-rich methanol and first CO2-rich methanol are respectively divided into two streams; The lower part of the primary CO2 flash section is connected to the lower part of the secondary CO2 flash section, and the upper part of the primary CO2 flash section is connected to the upper part of the secondary CO2 flash section, so as to sequentially perform primary CO2 flash and secondary CO2 flash on the second stream of CO2-rich methanol, and obtain the secondary CO2 flash liquid into two streams, and perform the first washing on the primary CO2 flash gas, and perform the third washing on the obtained first washing liquid and the secondary CO2 flash gas, and obtain the third washing liquid; The lower part of the primary H2S flash section is connected to the lower part of the secondary H2S flash section, and the upper part of the primary H2S flash section and the upper part of the secondary CO2 flash section are both connected to the upper part of the secondary H2S flash section, so as to sequentially perform primary H2S flash evaporation and secondary H2S flash evaporation on the second stream of H2S-rich methanol to obtain secondary H2S flash liquid, and perform a second washing on the primary H2S flash gas, and perform a fourth washing on the obtained second washing liquid and third washing liquid with the secondary H2S flash gas respectively to obtain low-sulfur carbon-rich methanol; The upper part of the reabsorption tower is used for the first flash evaporation of the first secondary CO2 flash liquid, and the obtained semi-lean liquid methanol is divided into two streams; the middle part of the reabsorption tower is used for the second flash evaporation of the second secondary CO2 flash liquid and the low-sulfur carbon-rich methanol, respectively, to obtain a flash liquid; the lower part of the reabsorption tower is used for the third flash evaporation of the secondary H2S flash liquid, and the obtained sulfur-containing gas phase and the flash liquid are subjected to the fifth washing to obtain low-H2S methanol; The stripping tower is used to contact the first stream of semi-lean liquid methanol with nitrogen and perform stripping, and the obtained low-carbon methanol is divided into the first stream of low-carbon methanol, the second stream of low-carbon methanol and the third stream of low-carbon methanol, which are respectively recycled to the CO2 absorption section, the upper part of the first CO2 flash section and the upper part of the first H2S flash section; The low-H2S methanol, the first stream of CO2-rich methanol and the first stream of H2S-rich methanol are independently recycled to the H2S absorption section.

9. The device according to claim 8, wherein: The H2S absorption section is divided into a first H2S absorption section and a second H2S absorption section from bottom to top, wherein the first H2S absorption section is used to contact the synthesis gas with the first stream of H2S-rich methanol and perform the first H2S absorption to obtain the second H2S-rich methanol and the pre-desulfurized gas; the second H2S absorption section is used to contact the pre-desulfurized gas, the low-H2S methanol and the first stream of CO2-rich methanol and perform the second H2S absorption to obtain the desulfurized gas and the first H2S-rich methanol; Preferably, the CO2 absorption is divided into a first CO2 absorption section and a second CO2 absorption section from bottom to top, wherein the first CO2 absorption section is used to contact the desulfurized gas and the second CO2-rich methanol and perform a first CO2 absorption to obtain pre-purified gas and the first CO2-rich methanol; the second CO2 absorption section is used to contact the pre-purified gas, the first stream of low-carbon methanol and the lean methanol and perform a second CO2 absorption to obtain purified gas and the second CO2-rich methanol; Preferably, according to the material flow direction, a third cooler is provided on the pipeline connecting the first CO2 absorption part and the second H2S absorption part, for returning the first stream of CO2-rich methanol after the third cooling and performing the second H2S absorption; Preferably, according to the material flow direction, a fourth cooler is provided on the pipeline connecting the second CO2 absorption part and the first CO2 absorption part, for returning the second CO2-rich methanol after the fourth cooling to the first CO2 absorption.

10. The device according to claim 9, wherein: A first cooler is provided on the pipeline connecting the first CO2 absorption section and the lower part of the first CO2 flash evaporation section, for subjecting the second stream of CO2-rich methanol to the first CO2 flash evaporation after the first cooling; And / or, a second cooler is provided on the pipeline connecting the second H2S absorption section and the lower part of the first H2S flash evaporation section, for subjecting the second stream of H2S-rich methanol to the first H2S flash evaporation after the second cooling; And / or, a heat exchanger is provided on the pipeline connecting the lower part of the secondary CO2 flash section, the upper part of the reabsorption tower, the middle part of the reabsorption tower and the stripping tower, for exchanging heat between the second secondary CO2 flash liquid and the first semi-lean liquid methanol, and the obtained heat-exchanged secondary CO2 flash liquid and heat-exchanged semi-lean liquid methanol are respectively subjected to the second flashing and stripping; And / or, a fifth cooler is provided on the pipeline connecting the upper part of the secondary H2S flash section and the middle part of the reabsorption tower, for cooling the low-sulfur and carbon-rich methanol through the fifth step before performing the second flash; and / or, a first pump is provided on the pipeline connecting the middle part of the reabsorption tower and the second H2S absorption part, for returning the low H2S methanol after the first pressurization and performing the second H2S absorption; And / or, a second pump is provided on the pipeline connecting the stripping tower, the second CO2 absorption section, the upper part of the first CO2 flash section and the upper part of the first H2S flash section, for dividing the low-carbon methanol into three streams after the second pressurization, and returning them to perform the second CO2 absorption, the first washing and the second washing respectively.

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