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

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to a low-temperature low-sulfur synthesis gas purification method matched with a coal water slurry gasification device and a device of the low-temperature low-sulfur synthesis gas purification method.According to the method, the H2S absorption process is optimally set, low-sulfur carbon-rich methanol is used for washing synthesis gas, and the use amount of CO2-rich methanol is reduced; the reabsorption process is optimized, so that low H2S methanol is generated; the concentration of CO2 in the low-H2S methanol is increased by optimally setting the medium-pressure flash evaporation process, and the obtained low-sulfur carbon-rich methanol is reused for the H2S absorption process, so that the comprehensive energy consumption of the low-temperature methanol washing device can be effectively reduced.

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 device and a device for purifying low-temperature and low-sulfur syngas for a coal water slurry gasification device. 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 in the syngas 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 the 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 . At present, the innovative research on the low-temperature methanol washing technology mainly focuses on the recycling of the pressure-reducing flash evaporation of the CO 2 -rich methanol. The typical process flow mainly includes 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, but there are technical bottlenecks in further optimization and innovation. Therefore, it is necessary to adjust the technical innovation and optimization 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 flash evaporation, but the H 2 S-rich methanol must be recycled through thermal regeneration, which is the main energy-consuming source of the low-temperature methanol washing. Therefore, improving the utilization efficiency of the H 2 S-rich methanol is the direction and key factor of the next technological innovation. Specifically, it is necessary to achieve that before the thermal regeneration of the H 2 S-rich methanol, its absorption of H 2 S gas in the syngas reaches the upper limit, so as to reduce the amount of H 2 S-rich methanol that needs to be thermally regenerated.

[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 fully CO-rich 2 methanol to wash the syngas, increasing the usage amount of CO-rich 2 methanol and generating H-rich 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 CO-rich 2 methanol directly mixes with the H-rich 2 S methanol while washing the H-rich 2 S methanol flash gas, and itself is contaminated by the H-rich 2 S methanol, generating low-concentration H 2 S methanol is not fully utilized either, 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. By optimizing the H 2 S absorption process, using low-sulfur and carbon-rich methanol to wash the syngas, the usage amount of CO-rich 2 methanol is reduced; by optimizing the reabsorption process, low-H 2 S methanol is generated; by optimizing the medium-pressure flashing process, the CO 2 concentration in the low-H 2 S methanol is increased, and the obtained low-sulfur and carbon-rich methanol is recycled to the H 2 S absorption process, which can effectively reduce the comprehensive energy consumption of the cold methanol washing unit.

[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, subjecting the desulfurized gas obtained to CO 2 absorption, and dividing the obtained CO-rich 2 methanol into two streams. The second stream of CO-rich 2 methanol is subjected to CO 2 flashing after the first cooling to obtain the flashed CO-rich 2 methanol divided into two streams. The first stream of the flashed CO-rich 2 methanol is subjected to the first flashing to obtain the semi-lean liquid methanol divided into two streams; the second stream of the flashed CO-rich 2 methanol is subjected to the second flashing after the second cooling;

[0008] Subjecting the first H-rich 2 S methanol obtained from the H 2 S absorption to H 2 S flashing after the third cooling to obtain the flashed H-rich2 The sulfur-containing gas phase obtained by subjecting methanol to a third flash evaporation and the flash evaporation liquid of the second flash evaporation are subjected to a first washing to obtain low-H 2 S methanol;

[0009] Among them, the CO 2 The CO also obtained by flash evaporation 2 The flash evaporation gas and the H 2 The H also obtained by flash evaporation of H 2 S flash evaporation gas are mixed and then subjected to a second washing with the low-H 2 S methanol to obtain low-sulfur carbon-rich methanol;

[0010] Among them, the low-sulfur carbon-rich methanol and the first stream of CO-rich 2 Methanol are each independently returned and subjected to the H 2 S absorption; the first stream of semi-lean liquid methanol is returned and subjected to the CO 2 Absorption.

[0011] 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: an H 2 S absorption tower, a CO 2 Absorption tower, a flash evaporation tower and a reabsorption tower, as well as a first cooler, a second cooler and a third cooler; the flash evaporation tower includes a CO 2 Flash evaporation section provided on the upper part and an H 2 S flash evaporation section provided on the lower part, and the top of the CO 2 Flash evaporation section is connected to the lower part of the H 2 S flash evaporation section;

[0012] The syngas enters the H 2 S absorption tower for H 2 S absorption, and the desulfurized gas obtained enters the CO 2 Absorption tower for CO 2 Absorption, and the CO-rich 2 Methanol is divided into two streams. The second stream of CO-rich 2 Methanol enters the CO 2 Flash evaporation section after passing through the first cooler for CO 2 Flash evaporation, and the flash evaporation gas and the H 2 The CO-rich methanol after flash evaporation is divided into two streams. The first stream of CO-rich 2 Methanol after flash evaporation enters the upper part of the reabsorption tower for the first flash evaporation to obtain semi-lean liquid methanol divided into two streams; the second stream of CO-rich 2 Methanol after flash evaporation enters the middle part of the reabsorption tower for the second flash evaporation after passing through the second cooler;

[0013] The first rich-H 2 S methanol obtained by the H 2 S absorption also enters the H after passing through the third cooler,2 H is carried out at the lower part of the S flash evaporation section 2 S flash evaporation is performed, and the flashed H-rich after flash evaporation 2 S methanol enters the lower part of the reabsorption tower for the third flash evaporation. The sulfur-containing gas phase obtained is subjected to the first washing with the flash evaporation liquid obtained from the second flash evaporation, and the low-H 2 S methanol enters H 2 the upper part of the S flash evaporation section, and reacts with the CO 2 The CO obtained from the flash evaporation 2 The flash evaporation gas and the H 2 The H obtained from the S flash evaporation 2 The S flash evaporation gas is subjected to the second washing, and the low-sulfur carbon-rich methanol obtained is recycled and used in the H 2 S absorption tower;

[0014] The first stream of CO-rich 2 methanol is recycled and used in the H 2 S absorption tower; the first stream of semi-lean liquid methanol is recycled and used in the CO 2 absorption tower.

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

[0016] (1) The method provided by the present invention realizes the absorption of CO in the second stream of CO-rich 2 S methanol for the flash evaporation gas and the first H-rich 2 methanol by optimizing the medium-pressure flash evaporation process, and at the same time avoids the pollution of the low-H 2 S methanol by the flashed H-rich 2 S methanol, and the low-sulfur carbon-rich methanol obtained realizes selective absorption in the H 2 S absorption process; 2 S absorption process; 2 S methanol for the low-H 2 S methanol, and the low-sulfur carbon-rich methanol obtained realizes selective absorption in the H 2 S absorption process;

[0017] (2) In the H 2 S absorption process of the method provided by the present invention, by introducing low-sulfur carbon-rich methanol to absorb H 2 S and CO 2 gases in the synthesis gas, the recycling of low-sulfur carbon-rich methanol is realized, and the usage amount of the first stream of CO-rich 2 methanol in the H 2 S absorption is reduced, which is equivalent to reducing the first H-rich 2 S methanol that needs to be thermally regenerated;

[0018] (3) In the H 2 S flash evaporation process of the method provided by the present invention, by introducing low-H 2 S methanol to absorb CO 2 flash evaporation gas and H2 S flash vapor, with a small increase in low H 2 H in S methanol 2 Under the condition of increasing the concentration of S, the CO 2 gas content is increased. The obtained low-sulfur and carbon-rich methanol has a higher CO 2 mole content. In the H 2 S absorption process, the absorption amount of CO 2 gas is correspondingly reduced, so that as much CO as possible in the syngas 2 gas is absorbed by lean methanol and semi-lean methanol in the CO 2 absorption tower, and the amount of CO 2 gas contaminated by rich H 2 S methanol is reduced, which has a positive significance for reducing the comprehensive energy consumption of the low-temperature methanol washing device. Description of the Drawings

[0019] Figure 1 It is a schematic structural diagram of a low-temperature and low-sulfur syngas purification device supporting a water coal slurry gasification device provided by the present invention.

[0020] Description of the Reference Numerals in the Drawings

[0021] T-1, H 2 S absorption tower; T-2, CO 2 absorption tower; T-3, flash tower; T-4, reabsorption tower; 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;

[0022] 1, syngas; 2, low-sulfur and carbon-rich methanol; 2-i, the first stream of low-sulfur and carbon-rich methanol; 2-ii, the second stream of low-sulfur and carbon-rich methanol; 3, the second rich H 2 S methanol; 4, rich CO 2 methanol; 4-i, the first stream of rich CO 2 methanol; 4-ii, the second stream of rich CO 2 methanol; 5, the first rich H 2 S methanol; 6, desulfurized gas; 7, CO-containing 2 methanol; 8, semi-lean methanol; 8-i, the first stream of semi-lean methanol; 8-ii, the second stream of semi-lean methanol; 9, lean methanol; 10, purified gas; 11, CO 2 flash vapor; 12, flash vapor; 13, flash vapor-rich CO 2 methanol; 13-i, the first stream of flash vapor-rich CO 2 methanol; 13-ii, the second stream of flash vapor-rich CO 2 methanol; 14, flash vapor-rich H 2 S methanol; 15, low H2 S methanol; 16. Third H-rich 2 S methanol; 17. CO 2 Product gas. Detailed implementation manners

[0023] 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, between the endpoint values of each range, between the endpoint values 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.

[0024] 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, the "first", "second", "third", "fourth" and "fifth" in "first cooling", "second cooling", "third cooling", "fourth cooling" and "fifth cooling" are only used to indicate that these are not the same cooling.

[0025] 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.

[0026] The first aspect of the present invention provides a low-temperature and low-sulfur syngas purification method for a supporting coal water slurry gasification device. The method includes: subjecting the syngas to H 2 S absorption, and subjecting the obtained desulfurized gas to CO 2 absorption, and dividing the obtained CO-rich 2 methanol into two streams, and subjecting the second stream of CO-rich 2 methanol to CO 2 flash evaporation after the first cooling to obtain the flash-evaporated CO-rich 2 methanol divided into two streams, subjecting the first stream of flash-evaporated CO-rich 2 methanol to the first flash evaporation to obtain semi-lean liquid methanol divided into two streams; subjecting the second stream of flash-evaporated CO-rich 2 methanol to the second flash evaporation after the second cooling;

[0027] Subjecting the first H-rich 2 S methanol obtained from the H 2 S absorption to H 2S flashing, and the flashed H-rich 2 The sulfur-containing methanol is subjected to a third flashing, and the sulfur-containing gas phase obtained and the flashed liquid of the second flashing are subjected to a first washing to obtain low-H 2 S methanol;

[0028] Among them, the CO 2 The CO obtained by flashing 2 The flashed gas and the H 2 The H obtained by flashing the S 2 The S flashed gas are mixed, and then mixed with the low-H 2 S methanol is subjected to a second washing to obtain low-sulfur carbon-rich methanol;

[0029] Among them, the low-sulfur carbon-rich methanol and the first stream of CO-rich 2 Methanol are each independently returned and subjected to the H 2 S absorption; the first stream of semi-lean liquid methanol is returned and subjected to the CO 2 Absorption.

[0030] In some embodiments of the present invention, preferably, the process of the H 2 S absorption includes: contacting the syngas and the first stream of low-sulfur carbon-rich methanol and performing a first H 2 S absorption to obtain second H-rich 2 S methanol and pre-washed syngas; the pre-washed syngas is sequentially contacted with the second stream of low-sulfur carbon-rich methanol and the first stream of CO-rich 2 Methanol and perform a second H 2 S absorption to obtain the desulfurized gas and the first H-rich 2 S methanol; among them, the low-sulfur carbon-rich methanol is divided into the first stream of low-sulfur carbon-rich methanol and the second stream of low-sulfur carbon-rich methanol.

[0031] In the present invention, without special instructions, the low-sulfur carbon-rich methanol is divided into two streams, the first stream performs the first H 2 S absorption, and the second stream performs the second H 2 S absorption.

[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 upstream syngas cooling process.

[0033] In some embodiments of the present invention, preferably, the molar flow rate ratio of the syngas to the first low-sulfur and carbon-rich 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, CO 2 . Preferably, the molar content of H 2 S in the second H 2 S-rich methanol is 1-2%, and the molar content of CO 2 is 67-73%. In the present invention, the temperature of the second H 2 S-rich methanol is -15 to -5 °C, and the pressure is 5.2-5.7 MPa(G).

[0035] 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 CO 2 in the first H 2 S-rich methanol is 38-42%, and the molar content of H 2 S is 0.6-1%; the temperature is -13 to -8 °C, and the pressure is 5.3-5.5 MPa(G).

[0036] In some embodiments of the present invention, preferably, the molar flow rate ratio of the syngas to the second low-sulfur and carbon-rich methanol is 5-7:1.

[0037] In some embodiments of the present invention, preferably, the molar flow rate ratio of the syngas to the first CO 2 -rich methanol is 2-3:1.

[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 38-42%; the temperature is -20 to -10 °C; the pressure is 5.2-5.4 MPa(G).

[0039] In some embodiments of the present invention, preferably, the method further includes: after the low-sulfur and carbon-rich methanol is pressurized to 5.8-6 MPa(G) for the first time, it is returned and the H 2 S absorption is carried out; more preferably, after the low-sulfur and carbon-rich methanol is pressurized for the first time, it is divided into two streams, which are respectively returned and the first H 2 S absorption and the second H 2 S absorption are carried out.

[0040] In some embodiments of the present invention, preferably, the method further includes: in the direction of material flow, the first rich CO 2 methanol is pressurized to 5.8 - 6 MPa(G) for the second time, cooled to -32 to -28 °C for the fourth time, and then returned to carry out the H 2 S absorption, preferably returned to carry out the second H 2 S absorption.

[0041] In some embodiments of the present invention, preferably, the process of CO 2 absorption includes: contacting the desulfurized gas with CO 2 -containing methanol to carry out the first CO 2 absorption to obtain the rich CO 2 -containing methanol and the pre-purified gas; contacting the pre-purified gas with the first semi-lean methanol and lean methanol in sequence to carry out the second CO 2 absorption to obtain the CO 2 -containing methanol and the purified gas.

[0042] In the present invention, the rich CO 2 -containing methanol is divided into two streams. The first stream is returned to carry out the second H 2 S absorption, and the second stream is subjected to CO 2 flashing. Preferably, the rich CO 2 -containing methanol is divided into a first rich CO 2 -containing methanol and a second rich CO 2 -containing methanol with a molar flow rate ratio of 1:1.8 - 2.3.

[0043] In the present invention, the first CO 2 absorption aims to further remove CO 2 from the desulfurized gas. Preferably, the molar content of CO 2 in the rich CO 2 -containing methanol is 30 - 35%, and the molar content of H 2 S is 0.1 - 0.5 ppm; the temperature is -10 to -5 °C, and the pressure is 5.2 - 5.4 MPa(G).

[0044] In some embodiments of the present invention, preferably, the molar flow rate ratio of the desulfurized gas to the CO 2 -containing methanol is 1:1.1 - 1.4.

[0045] In some embodiments of the present invention, preferably, after the CO 2 -containing methanol is cooled to -36 to -33 °C for the fifth time, it is returned to carry out the first CO 2 absorption.

[0046] In some embodiments of the present invention, preferably, the molar flow rate ratio of the purified gas to the first semi-lean methanol solution is 1.2 - 1.5:1; the molar flow rate ratio of the purified gas to the lean methanol is 1:0.9 - 1.2.

[0047] In some embodiments of the present invention, preferably, the H 2 S molar content in the purified gas < 0.1 ppm, and the CO 2 molar content < 20 ppm; the temperature is -55 to -50 °C, and the pressure is 5.2 - 5.3 MPa(G).

[0048] In the present invention, the first cooling is achieved by reducing the temperature of the second rich CO 2 methanol solution, aiming to reduce the volume of the CO 2 flash gas, and at the same time laying a foundation for obtaining low temperature (high-quality cold energy) for the reabsorption tower. Preferably, the temperature of the material after the first cooling is -36 to -33 °C.

[0049] In some embodiments of the present invention, preferably, the process of the CO 2 flash evaporation includes: subjecting the material after the first cooling to the CO 2 flash evaporation to obtain the rich CO 2 methanol solution after flash evaporation and the CO 2 flash gas.

[0050] In some embodiments of the present invention, preferably, the pressure of the CO 2 flash evaporation is 1.6 - 2 MPa(G); further preferably, the rich CO 2 methanol solution after flash evaporation is divided into the first rich CO 2 methanol solution after flash evaporation and the second rich CO 2 methanol solution after flash evaporation with a molar flow rate ratio of 3.5 - 4.5:1.

[0051] In some embodiments of the present invention, preferably, the H 2 S molar content in the rich CO 2 methanol solution after flash evaporation is 0.1 - 0.5 ppm, and the CO 2 molar content is 29.5 - 34.5%; the temperature is -36.5 to -33.5 °C.

[0052] In the present invention, the second cooling is achieved by reducing the temperature of the second rich CO 2 methanol solution after flash evaporation, generating low temperature through pressure reduction and flash evaporation, improving the absorption capacity of the flash evaporation liquid for H 2 S gas, which is beneficial to washing H 2 in the CO 2Gas S. Preferably, the temperature of the second cooled material is -55 to -50 °C.

[0053] In the present invention, the third cooling is achieved by reducing the temperature of the first H-rich 2 methanol, with the aim of reducing the total amount of medium-pressure flash gas and laying a foundation for obtaining low temperature (high-quality cold energy) for the reabsorption tower. Preferably, the temperature of the material after the third cooling is -32 to -30 °C.

[0054] In some embodiments of the present invention, preferably, the 2 process of H 2 S flashing includes subjecting the material after the third cooling to H 2 S flashing to obtain the flashed H-rich 2 methanol and H

[0055] S flash gas. 2 In some embodiments of the present invention, preferably, the pressure of the H

[0056] S flash is 1.6 - 2 MPa(G). 2 In some embodiments of the present invention, preferably, the molar content of H 2 S in the flashed H-rich 2 methanol is 0.6 - 1%, and the molar content of CO

[0057] is 37.5 - 41.5%; the temperature is -32.5 to -30.5 °C.

[0058] In some embodiments of the present invention, preferably, the pressure of the first flash < the pressure of the second flash < the pressure of the third flash; more preferably, the pressure of the first flash is selected from 0.05 - 0.08 MPa(G); the pressure of the second flash is selected from 0.06 - 0.09 MPa(G); the pressure of the third flash is selected from 0.12 - 0.16 MPa(G). 2 In some embodiments of the present invention, preferably, the process of the first flash includes subjecting the first flashed CO-rich 2 methanol to the first flash to obtain the semi-lean methanol and the first CO 2 product gas; the process of the second flash includes subjecting the material after the second cooling to the second flash to obtain the flashed liquid and the second CO 2 product gas; the process of the third flash includes subjecting the flashed H-rich 2 methanol to the third flash to obtain the sulfur-containing gas phase and the third H-rich

[0059] In some embodiments of the present invention, preferably, the semi-lean methanol is divided into a first stream of semi-lean methanol and a second stream of semi-lean methanol with a molar flow ratio of 1.5 - 2:1.

[0060] In some embodiments of the present invention, preferably, the CO 2 molar content in the semi-lean methanol is 21 - 25%, and the H 2 S molar content is ≤0.5 ppm; the temperature is -66 to -61 °C; the pressure is 0.05 - 0.08 MPa(G).

[0061] In the present invention, the semi-lean methanol is divided into two streams. The first stream is returned for the CO 2 absorption, and the second stream is sent to subsequent processes for use. Preferably, after the first stream of semi-lean methanol is pressurized to 5.6 - 6 MPa(G) by a third stage, it is returned for the CO 2 absorption.

[0062] In some embodiments of the present invention, preferably, the process of the first washing includes: bringing the flash liquid into contact with the sulfur-containing gas phase for the first washing to obtain the low-H 2 S methanol and the third CO 2 product gas.

[0063] In some embodiments of the present invention, preferably, the H 2 S molar content in the low-H 2 S methanol is 3 - 6‰, and the CO 2 molar content is 26 - 32%; the temperature is -65 to -60 °C, and the pressure is 0.12 - 0.16 MPa(G).

[0064] In some embodiments of the present invention, preferably, the H 2 S molar content in the third rich-H 2 S methanol is 0.6 - 1%, and the CO 2 molar content is 27 - 32%; the temperature is -68 to -65 °C.

[0065] In some embodiments of the present invention, preferably, after mixing the first CO 2 product gas, the second CO 2 product gas, and the third CO 2 product gas, the H 2 S molar content in the obtained CO 2 product gas is <1 ppm, and the CO 2 molar content is 99.4 - 99.7%; the temperature is -70 to -60 °C, and the pressure is 0.05 - 0.08 MPa(G).

[0066] In some embodiments of the present invention, preferably, the process of the second washing includes: subjecting the CO 2 flash gas and H 2 S flash gas to mixing, then contacting with the low-H 2 S methanol for the second washing to obtain the low-sulfur carbon-rich methanol and the flash gas.

[0067] In some embodiments of the present invention, preferably, the low-H 2 S methanol is pressurized to 1.6 - 2 MPa(G) in the fourth stage and then subjected to the second washing.

[0068] In some embodiments of the present invention, preferably, the molar content of H 2 S in the low-sulfur carbon-rich methanol is 3 - 6‰, and the molar content of CO 2 is 28 - 32%; the temperature is -60 to -55 °C.

[0069] In some embodiments of the present invention, preferably, the low-sulfur carbon-rich methanol is divided into a first stream of low-sulfur carbon-rich methanol and a second stream of low-sulfur carbon-rich methanol with a molar flow rate ratio of 1:11 - 15, and then they are respectively returned for the first H 2 S absorption and the second H 2 S absorption.

[0070] In some embodiments of the present invention, preferably, the molar content of H 2 in the flash gas is 78 - 84%, the molar content of CO 2 is 14 - 19%, and the molar content of CO is 0.4 - 0.9%. In the present invention, the temperature of the flash gas is -65 to -60 °C, and the pressure is 1.6 - 2 MPa(G), and it is sent to subsequent processes for treatment.

[0071] A schematic structural diagram of a low-temperature and low-sulfur syngas purification device for a coal water slurry gasification device according to the second aspect of the present invention is as shown in Figure 1 and it can be seen from Figure 1 that the device includes: an H 2 S absorption tower T-1, a CO 2 absorption tower T-2, a flash tower T-3, and a reabsorption tower T-4, which are connected in sequence, as well as a first cooler E-1, a second cooler E-2, and a third cooler E-3; the flash tower T-3 includes: a CO 2 flash section provided on the upper part and an H 2 S flash section provided on the lower part, and the top of the CO 2 flash section is connected to the lower part of the H 2 S flash section;

[0072] The syngas 1 enters the H 2 S absorption tower T-1 for H2 S is absorbed, and the desulfurized gas 6 enters CO 2 Absorber T-2 for CO 2 Absorption to obtain rich CO 2 Methanol 4 is divided into two streams, and the second stream of rich CO 2 After passing through the first cooler E-1, methanol 4-ii enters CO 2 Flash section for CO 2 Flash to obtain rich CO after flashing 2 Methanol 13 is divided into two streams, and the first stream of rich CO after flashing 2 Methanol 13-i enters the upper part of the reabsorber T-4 for the first flash to obtain semi-lean methanol 8 divided into two streams; the second stream of rich CO after flashing 2 After passing through the second cooler E-2, methanol 13-ii enters the middle part of the reabsorber T-4 for the second flash to obtain the flash liquid;

[0073] The said H 2 The first rich H obtained by H 2 After passing through the third cooler E-3, methanol 5 of H 2 Enters the lower part of the H 2 Flash section for H 2 Flash to obtain rich H after flashing 2 Methanol 14 of H 2 Enters the upper part of the H 2 Flash also obtains CO 2 Flash gas 11 and the said H 2 Flash also obtains H 2 Flash gas of H 2 Undergoes the second washing to obtain low-sulfur rich-carbon methanol 2 recycled to the H

[0074] Absorber T-1; 2 The first stream of rich CO 2 Methanol 4-i is recycled to the H 2 Absorber T-1; the first stream of semi-lean methanol 8-i is recycled to the CO

[0075] In the present invention, as Figure 1 Shown, the said H 2 Absorber T-1 includes a first H 2 Absorption section provided below and a second H 2 Absorption section provided above. Specifically, the first H 2 Absorption section, the first stream of low-sulfur rich-carbon methanol 2-i to H in synthesis gas 1 2 S, HCN, NH3 Perform pre-washing and absorption; second H 2 S absorption section, by introducing a second stream of low-sulfur, carbon-rich methanol 2-ii to absorb H in the syngas after pre-washing 2 S and CO 2 gas, realizing the recycling of low-sulfur, carbon-rich methanol 2, reducing the usage amount of the first stream of CO-rich 2 methanol 4-i, which is equivalent to reducing the first H-rich that needs to be thermally regenerated 2 S methanol 5; in addition, such a setting correspondingly reduces the working load of the subsequent CO 2 absorption tower, which is also of positive significance for reducing the usage amounts of lean methanol and semi-lean methanol in the CO 2 absorption tower.

[0076] In the present invention, as Figure 1 shown, the low-sulfur, carbon-rich methanol 2 is divided into a first stream of low-sulfur, carbon-rich methanol 2-i and a second stream of low-sulfur, carbon-rich methanol 2-ii and recycled back to the first H 2 S absorption section and the second H 2 S absorption section respectively.

[0077] In the present invention, as Figure 1 shown, the first stream of CO-rich 2 methanol 4-i is recycled back to the second H 2 S absorption section.

[0078] In the present invention, as Figure 1 shown, in the H 2 S absorption tower T-1, the first H 2 S absorption section and the second H 2 S absorption section are connected by lifting holes; the first H 2 S absorption section is connected to the low-sulfur, carbon-rich methanol outlet at the upper part of the H 2 S flash section, for contacting the syngas 1 with the first stream of low-sulfur, carbon-rich methanol 2-i and performing the first H 2 S absorption to obtain the second H-rich 2 S methanol 3 and the pre-washed syngas; the second H 2 S absorption section is connected to the low-sulfur, carbon-rich methanol outlet at the upper part of the H 2 S flash section and the CO 2 absorption tower T-2's CO-rich 2 methanol outlet, for successively contacting the pre-washed syngas with the second stream of low-sulfur, carbon-rich methanol 2-ii and the first stream of CO-rich 2 methanol 4-i and performing the second H 2 S absorption to obtain the desulfurized gas 6 and the first H-rich 2 S methanol 5.

[0079] In the present invention, without special circumstances, the first H 2 In the S absorption section, the contact mode between the syngas and the first low-sulfur and carbon-rich methanol 2-i is preferably countercurrent contact between the syngas 1 and the first low-sulfur and carbon-rich methanol 2-i, that is, the syngas 1 enters from the bottom of the first H 2 S absorption section, and the first low-sulfur and carbon-rich methanol 2-i enters from the upper part of the first H 2 S absorption section.

[0080] In the present invention, as Figure 1 shown, the CO 2 absorption tower T-2 includes a first CO 2 absorption section provided at the lower part and a second CO 2 absorption section provided at the upper part, and the lower part of the second CO 2 absorption section is connected to the upper part of the first CO 2 absorption section.

[0081] In the present invention, as Figure 1 shown, the CO 2 absorption tower T-2 includes a first CO 2 absorption section provided at the lower part and a second CO 2 absorption section provided at the upper part; the first CO 2 absorption section and the second CO 2 absorption section are connected by a riser hole, wherein the upper part of the first CO 2 absorption section is connected to the lower part of the second CO 2 absorption section, for contacting the desulfurized gas 6 with the CO 2 -containing methanol 7 and performing the first CO 2 absorption to obtain the CO 2 -rich methanol 4 and the pre-purified gas; the second CO 2 absorption section is connected to the semi-lean liquid methanol outlet of the re-absorption tower T-4 and the lean methanol 9 from the subsequent process, for successively contacting the pre-purified gas with the first semi-lean liquid methanol 8-i and the lean methanol 9 and performing the second CO 2 absorption to obtain the purified gas 10 and the CO 2 -containing methanol 7.

[0082] In the present invention, without special circumstances, in the CO 2 absorption tower T-2, for the first CO 2 absorption section, the contact mode between the desulfurized gas 6 and the CO 2 -containing methanol 7 is preferably selected from countercurrent contact between the desulfurized gas 6 and the CO 2 -containing methanol 7; that is, the desulfurized gas 6 enters from the bottom of the first CO 2 absorption section, and the CO 2 -containing methanol 7 enters from the first CO 2Enter the upper part of the absorption section.

[0083] In the present invention, if Figure 1 As shown in , the flash tower T-3 includes a CO 2 Flash section and H set below 2 S flash section, and CO 2 Top of flash section and H 2 The upper part of the S flash section is connected by a pipeline; specifically, CO 2 Flash section, used to convert the second stream of CO-rich 2 Methanol 4-ii is first cooled and then CO 2 Flash evaporation to obtain CO 2 Flash gas 11 and rich CO after flash evaporation 2 Methanol 13; H 2 The lower part of the S flash section is used to transfer the first H-rich 2 S methanol 5 is cooled for the third time and then H 2 S flashes to obtain H 2 S flash gas and H-rich after flash evaporation 2 S methanol 14; among which, H 2 S flash steam enters H 2 The upper part of the S flash section, with CO 2 After flash gas 11 is mixed with low H 2 S methanol 15 is contacted and subjected to a second washing to obtain low-sulfur carbon-rich methanol 2 and flash gas 12.

[0084] The present invention optimizes the internal structure of the reabsorption tower to achieve the second stream of CO2-rich after flash evaporation 2 Methanol flash liquid has a positive effect on H-rich after flash evaporation 2 S methanol flash produced by the sulfur component of the sulfur-containing gas phase absorption, but not with the flash after the third H-rich 2 S methanol is mixed with each other. Therefore, compared with the prior art, the low H 2 S H in methanol 2 The S content is lower, which is the reason for the low H of the stock in the future 2 The conditions for the reuse of S methanol have been created.

[0085] In the present invention, if Figure 1 As shown in FIG. 1 , the upper and middle parts of the reabsorption tower T-4 are connected through a gas riser, and the middle and lower parts are also connected through a gas riser. Specifically, the upper part is used to transfer the first stream of flash-evaporated CO-rich 2 Methanol 13-i is subjected to a first flash distillation to obtain semi-lean methanol 8 and the first CO 2 Product gas; the middle part is used to flash the second stream of CO-rich 2 Methanol 13-ii is subjected to a second flash evaporation after a second cooling to obtain a flash liquid and a second CO 2 ​​​​​​​Product gas; the lower part is used to subject the rich H 2 S methanol 14 to a third flash evaporation to obtain a third rich H 2 S methanol 16 and a sulfur-containing gas phase; wherein, the sulfur-containing gas phase and the flash liquid are subjected to a first washing to obtain a low H 2 S methanol 15 and a third CO 2 Product gas; CO 2 Product gas 17 includes a first CO 2 Product gas, a second CO 2 Product gas and a third CO 2 Product gas.

[0086] In the present invention, as Figure 1 shown, preferably, a first pump P-1 is provided on the pipeline connecting the upper part of the H 2 S flash evaporation section and the H 2 S absorption tower T-1 for dividing the low-sulfur rich carbon methanol 2 into two streams after the first pressurization and then recycling them back to the first H 2 S absorption section and the second H 2 S absorption section.

[0087] In the present invention, as Figure 1 shown, preferably, in the direction of material flow, a second pump P-2 and a fourth cooler E-4 are successively provided on the pipeline connecting the rich CO 2 methanol outlet of the absorption tower T-2 and the second H 2 S absorption section for subjecting the first stream of rich CO 2 methanol 4-i to a second pressurization and a fourth cooling in sequence and then recycling it back to the second H 2 S absorption section. 2 S absorption section.

[0088] In the present invention, as Figure 1 shown, preferably, in the direction of material flow, a fifth cooler E-5 is provided on the pipeline connecting the second CO 2 absorption section and the first CO 2 absorption section for subjecting the CO 2 -containing methanol 7 to a fifth cooling and then recycling it back to the first CO 2 absorption section.

[0089] In the present invention, as Figure 1 shown, preferably, a third pump P-3 is provided on the pipeline connecting the semi-lean liquid methanol outlet of the reabsorption tower T-4 and the second CO 2 absorption section for subjecting the first stream of semi-lean liquid methanol 8-i to a third pressurization and then recycling it back to the second CO 2 absorption section.

[0090] In the present invention, as Figure 1As shown, preferably, the low H connected to the reabsorption tower T-4 2 S methanol outlet and H 2 On the pipeline at the upper part of the S flash section, a fourth pump P-4 is provided to pump the low H 2 S methanol 15. After the fourth pressurization, the second washing is carried out.

[0091] The present invention will be described in detail below through embodiments.

[0092] Embodiment 1

[0093] The low-temperature and low-sulfur syngas purification device for a coal water slurry gasification device is as Figure 1 shown. This device includes: H 2 S absorption tower T-1, CO 2 absorption tower T-2, flash tower T-3 and reabsorption tower T-4, first cooler E-1, second cooler E-2, third cooler E-3, fourth cooler E-4 and fifth cooler E-5, and first pump P-1, second pump P-2, third pump P-3 and fourth pump P-4;

[0094] H 2 S absorption tower T-1 includes a first H 2 S absorption section arranged at the lower part and a second H 2 S absorption section arranged at the upper part; CO 2 absorption tower T-2 includes a first CO 2 absorption section arranged at the lower part and a second CO 2 absorption section arranged at the upper part; the flash tower T-3 includes a CO 2 flash section arranged at the upper part and an H 2 S flash section arranged at the lower part, and the top of the CO 2 flash section and the upper part of the H 2 S flash section are connected by a pipeline.

[0095] The low-temperature and low-sulfur syngas purification method for a coal water slurry gasification device includes:

[0096] 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 low-sulfur and carbon-rich methanol 2-i in a molar flow ratio of 70 - 80:1 in countercurrent contact and carrying out the first H 2 S absorption to obtain the second H-rich 2 S methanol 3 (the molar content of H 2 S is 1 - 2%, the molar content of CO 2with a molar content of 67 - 73%) and the syngas after pre - washing; the above - mentioned syngas after pre - washing is successively in counter - current contact with the second low - sulfur and carbon - rich methanol 2 - ii and the first CO - rich 2 methanol 4 - i (successively pressurized to 5.8 - 6 MPa(G) for the second time and cooled to - 32 to - 28 °C for the fourth time) for second H 2 S absorption to obtain desulfurized gas 6 (H 2 with a molar content of H2S of 0.5 - 1 ppm and CO 2 with a molar content of 38 - 42%; temperature of - 20 to - 10 °C; pressure of 5.2 - 5.4 MPa(G)) and the first H2S - rich 2 methanol 5 (CO 2 with a molar content of 38 - 42% and H 2 S with a molar content of 0.6 - 1.0%; temperature of - 13 to - 8 °C and pressure of 5.3 - 5.5 MPa(G));

[0097] The molar flow ratio of the syngas 1 to the second low - sulfur and carbon - rich methanol 2 - ii is 5 - 7:1; the molar flow ratio of the syngas 1 to the first CO - rich 2 methanol 4 - i is 2 - 3:1;

[0098] The above - mentioned desulfurized gas 6 and the CO - containing 2 methanol 7 (cooled to - 36 to - 33 °C for the fifth time) are in counter - current contact at a molar flow ratio of 1:1.1 - 1.4 for first CO 2 absorption to obtain CO - rich 2 methanol 4 (CO 2 with a molar content of 30 - 35% and H 2 S with a molar content of 0.1 - 0.5 ppm; temperature of - 10 to - 5 °C and pressure of 5.2 - 5.4 MPa(G)) and pre - purified gas, where the CO - rich 2 methanol 4 is divided into the first CO - rich 2 methanol 4 - i and the second CO - rich 2 methanol 4 - ii with a molar flow ratio of 1:1.8 - 2.3; the above - mentioned pre - purified gas is successively in counter - current contact with the first semi - lean liquid methanol 8 - i (pressurized to 5.6 - 6 MPa(G) for the third time) and lean methanol 9 (CO 2 with a molar content of 0% and H 2 S with a molar content of 0%) for second CO 2 absorption to obtain purified gas 10 (H 2 S molar content < 0.1 ppm and CO 2 molar content < 20 ppm; temperature of - 55 to - 50 °C and pressure of 5.2 - 5.3 MPa(G));

[0099] Among them, the molar flow rate ratio of the purified gas 10 to the first semi-lean methanol 8-i is 1.2 - 1.5:1; the molar flow rate ratio of the purified gas 10 to the lean methanol 9 is 1:0.9 - 1.2;

[0100] The second rich CO 2 methanol 4-ii is cooled to -36 to -33 °C for the first time and then undergoes CO 2 flash evaporation (pressure: 1.6 - 2 MPa(G)) to obtain the rich CO 2 methanol 13 after flash evaporation (the molar content of H 2 S is 0.1 - 0.5 ppm, and the molar content of CO 2 is 29.5 - 34.5%; the temperature is -36.5 to -33.5 °C) and the CO 2 flash vapor 11; the first rich H 2 S methanol 5 is cooled to -33 to -30 °C for the third time and then undergoes H 2 S flash evaporation (pressure: 1.6 - 2 MPa(G)) to obtain the rich H 2 S methanol 14 after flash evaporation (the molar content of H 2 S is 0.6 - 1%, and the molar content of CO 2 is 37.5 - 41.5%; the temperature is -32.5 to -30.5 °C) and the H 2 S flash vapor;

[0101] The rich CO 2 methanol 13 after flash evaporation is divided into the first rich CO 2 methanol 13-i and the second rich CO 2 methanol 13-ii with a molar flow rate ratio of 3.5 - 4.5:1; the first rich CO 2 methanol 13-i undergoes the first flash evaporation (pressure: 0.05 - 0.08 MPa(G)) to obtain the first CO 2 product gas and semi-lean methanol 8 (the molar content of CO 2 is 21 - 25%, and the molar content of H 2 S is ≤0.5 ppm; the temperature is -66 to -61 °C; the pressure is 0.05 - 0.08 MPa(G)), among which, the above semi-lean methanol 8 is divided into the first semi-lean methanol 8-i and the second semi-lean methanol 8-ii with a molar flow rate ratio of 1.5 - 2:1; the second rich CO 2 methanol 13-ii is cooled to -55 to -50 °C for the second time and then undergoes the second flash evaporation (pressure: 0.06 - 0.09 MPa(G)) to obtain the second CO 2 product gas and the flash liquid; the rich H 2The methanol containing sulfur 14 undergoes a third flash evaporation (at a pressure of 0.12 - 0.16 MPa (G)) to obtain a sulfur-containing gas phase and a third H-rich 2 methanol containing sulfur 16 (H 2 with a molar content of sulfur being 0.6 - 1%, and CO 2 with a molar content of 27 - 32%; at a temperature of -68 to -65 °C); the above sulfur-containing gas phase and flash liquid are subjected to a first washing to obtain a third CO 2 product gas and a low-H 2 methanol containing sulfur 15 (H 2 with a molar content of sulfur being 3 - 6‰, and CO 2 with a molar content of 26 - 32%; at a temperature of -65 to -60 °C and a pressure of 0.12 - 0.16 MPa (G));

[0102] Among them, after mixing the above CO 2 flash gas 11 and H 2 S flash gas, and contacting with the low-H 2 methanol containing sulfur 15 (pressurized to 1.6 - 2 MPa (G) for the fourth time) for a second washing, a low-sulfur carbon-rich methanol 2 (H 2 with a molar content of sulfur being 3 - 6‰, and CO 2 with a molar content of 28 - 32%; at a temperature of -60 to -55 °C) and flash gas 12 (H 2 with a molar content of 78 - 84%, CO 2 with a molar content of 14 - 19%, and a molar content of CO being 0.4 - 0.9%; at a temperature of -65 °C to -60 °C and a pressure of 1.6 - 2 MPa (G)); after pressurizing the above low-sulfur carbon-rich methanol 2 to 5.8 - 6 MPa (G) for the first time, it is divided into the above first low-sulfur carbon-rich methanol 2-i and second low-sulfur carbon-rich methanol 2-ii with a molar ratio of 1:11 - 15;

[0103] Among them, the above first CO 2 product gas, second CO 2 product gas, and third CO 2 product gas are mixed to obtain a CO 2 product gas 17 (H 2 with a molar content of sulfur < 1 ppm, and CO 2 with a molar content of 99.4 - 99.7%; at a temperature of -70 to -60 °C and a pressure of 0.05 - 0.08 MPa (G)).

[0104] Comparative Example 1

[0105] Taking a hydrogen production device using coal water slurry gasification for gas production as an example, the effective gas (H 2 +CO) entering the low-temperature methanol washing device is 230000 Nm 3 / h. Under this benchmark, the main technical parameters are compared with those of the lean solution - semi - lean solution process (i.e., CN201110260570.0 discloses a low - temperature methanol washing process), as shown in Table 1.

[0106] Table 1

[0107]

[0108] From the results in Table 1, taking the hydrogen production unit based on coal - water slurry gasification as an example, for the low - temperature and low - sulfur syngas purification method of the supporting coal - water slurry gasification unit provided in Example 1, the lean methanol circulation rate is 92.6% of that in Comparative Example 1 (lean solution - semi - lean solution process), the semi - lean methanol circulation rate is 93.3% of that in Comparative Example 1 (lean solution - semi - lean solution process), and the amount of rich CO 2 methanol used in the H 2 S absorption tower is 90.5% of that in Comparative Example 1 (lean solution - semi - lean solution process). The cumulative reduction of external cooling consumption is 400 KW / h, and the overall energy - saving effect is significant. 2

[0109] 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 synthesis gas to H2S absorption, subjecting the obtained desulfurized gas to CO2 absorption, obtaining CO2-rich methanol and dividing it into two streams, subjecting the second stream of CO2-rich methanol to CO2 flash distillation after a first cooling, obtaining CO2-rich methanol after flash distillation and dividing it into two streams, subjecting the first stream of CO2-rich methanol after flash distillation to a first flash distillation, obtaining semi-lean liquid methanol and dividing it into two streams; subjecting the second stream of CO2-rich methanol after flash distillation to a second flash distillation after a second cooling, obtaining a flash distillation liquid; The first H2S-rich methanol obtained by the H2S absorption is subjected to a third cooling and then subjected to H2S flash evaporation, the obtained flashed H2S-rich methanol is subjected to a third flash evaporation, and the obtained sulfur-containing gas phase and the flash liquid are subjected to a first washing to obtain low-H2S methanol; wherein the CO2 flash gas obtained by the CO2 flash evaporation and the H2S flash gas obtained by the H2S flash evaporation are mixed and then subjected to a second washing with the low-H2S methanol to obtain low-sulfur and carbon-rich methanol; The low-sulfur carbon-rich methanol and the first stream of CO2-rich methanol are returned independently and subjected to the H2S absorption; the first stream of semi-lean liquid methanol is returned and subjected to the CO2 absorption.

2. The method according to claim 1, wherein: The H2S absorption process comprises: contacting the synthesis gas with a first stream of low-sulfur carbon-rich methanol and performing a first H2S absorption to obtain a second H2S-rich methanol and a pre-washed synthesis gas; contacting the pre-washed synthesis gas with a second stream of low-sulfur carbon-rich methanol and a first stream of CO2-rich methanol in sequence and performing a second H2S absorption to obtain the desulfurized gas and the first H2S-rich methanol; wherein the low-sulfur carbon-rich methanol is divided into the first stream of low-sulfur carbon-rich methanol and the second stream of low-sulfur carbon-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, the molar content of CO2 in the first H2S-rich methanol is 38-42%, the molar content of H2S is 0.6-1%; the temperature is -13 to -8°C, and the pressure is 5.3-5.5MPa(G); And / or, the molar content of H2S in the desulfurized gas is 0.5-1 ppm, the molar content of CO2 is 38-42%; the temperature is -20 to -10°C; and the pressure is 5.2-5.4 MPa(G).

3. The method according to claim 1 or 2, wherein: The method further comprises: after the low-sulfur and carbon-rich methanol is first pressurized to 5.8-6 MPa(G), returning it and performing the H2S absorption; And / or, the method further comprises: according to the material flow direction, the first stream of CO2-rich methanol is sequentially pressurized to 5.8-6 MPa(G) for a second time, cooled to -32 to -28°C for a fourth time, and then returned to perform the H2S absorption.

4. The method according to any one of claims 1 to 3, wherein: The CO2 absorption process includes: contacting the desulfurized gas with CO2-containing methanol and performing a first CO2 absorption to obtain the CO2-rich methanol and pre-purified gas; contacting the pre-purified gas with a first stream of semi-lean liquid methanol and lean methanol in sequence and performing a second CO2 absorption to obtain the CO2-containing methanol and purified gas; and / or, dividing the CO2-rich methanol into a first stream of CO2-rich methanol and a second stream of CO2-rich methanol at a molar flow ratio of 1:1.8-2.3; and / or, the molar content of CO2 in the CO2-rich methanol is 30-35%, the molar content of H2S is 0.1-0.5 ppm; the temperature is -10 to -5°C, and the pressure is 5.2-5.4 MPa(G); Preferably, the CO2-containing methanol is cooled to -36 to -33°C for the fifth time and then returned to the first CO2 absorption process; Preferably, the molar content of H2S in the purified gas is less than 0.1 ppm, and the molar content of CO2 is less than 20 ppm; the temperature is -55 to -50°C, and the pressure is 5.2-5.3 MPa(G).

5. The method according to any one of claims 1 to 4, wherein: The temperature of the material after the first cooling is -36 to -33°C; And / or, the CO2 flash evaporation process comprises: subjecting the first cooled material to the CO2 flash evaporation to obtain the flashed CO2-rich methanol and CO2 flash gas; And / or, the pressure of the CO2 flash evaporation is 1.6-2MPa(G); and / or, dividing the flashed CO2-rich methanol into the first stream of flashed CO2-rich methanol and the second stream of flashed CO2-rich methanol at a molar flow ratio of 3.5-4.5:1; 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 29.5-34.5%; the temperature is -36.5 to -33.5°C; And / or, the temperature of the second cooled material is -55 to -50°C; And / or, the temperature of the material after the third cooling is -32 to -30°C; And / or, the H2S flash evaporation process comprises: subjecting the third cooled material to the H2S flash evaporation to obtain the flashed H2S-rich methanol and H2S flash gas; And / or, the pressure of the H2S flash evaporation is 1.6-2MPa(G); And / or, the molar content of H2S in the H2S-rich methanol after the flash evaporation is 0.6-1%, the molar content of CO2 is 37.5-41.5%; the temperature is -32.5 to -30.5°C.

6. The method according to any one of claims 1 to 5, wherein: The pressure of the first flash vaporization is less than the pressure of the second flash vaporization and less than the pressure of the third flash vaporization; And / or, the pressure of the first flash evaporation is selected from 0.05-0.08 MPa(G); the pressure of the second flash evaporation is selected from 0.06-0.09 MPa(G); the pressure of the third flash evaporation is selected from 0.12-0.16 MPa(G); And / or, the first flash evaporation process includes: subjecting the first flashed CO2-rich methanol to the first flash evaporation to obtain the semi-lean liquid methanol and the first CO2 product gas; the second flash evaporation process includes: subjecting the second cooled material to the second flash evaporation to obtain the flashed liquid and the second CO2 product gas; the third flash evaporation process includes: subjecting the flashed H2S-rich methanol to the third flash evaporation to obtain the sulfur-containing gas phase and the third H2S-rich methanol; and / or, dividing the semi-lean methanol into a first stream of semi-lean methanol and a second stream of semi-lean methanol at a molar flow ratio of 1.5-2:1; and / or, the molar content of CO2 in the semi-lean methanol is 21-25%, the molar content of H2S is ≤0.5ppm; the temperature is -66 to -61°C; the pressure is 0.05-0.08MPa(G); and / or, the first stream of semi-lean methanol is pressurized to 5.6-6 MPa(G) for the third time and then returned to perform the CO2 absorption; And / or, the first washing process includes: contacting the flash liquid with the sulfur-containing gas and performing a first washing to obtain the low-H2S methanol and the third CO2 product gas; and / or, the molar content of H2S in the low H2S methanol is 3-6‰, the molar content of CO2 is 26-32%; the temperature is -65 to -60°C, and the pressure is 0.12-0.16MPa(G); Preferably, after mixing the first CO2 product gas, the second CO2 product gas and the third CO2 product gas, the molar content of H2S in the obtained CO2 product gas is less than 1ppm, and the molar content of CO2 is 99.4-99.7%; the temperature is -70 to -60°C, and the pressure is 0.05-0.08MPa(G).

7. The method according to any one of claims 1 to 6, wherein: The second washing process comprises: mixing the CO2 flash gas and the H2S flash gas, contacting with the low-H2S methanol and performing the second washing to obtain the low-sulfur carbon-rich methanol and the flash gas; and / or, the low H2S methanol is pressurized to 1.6-2 MPa(G) for the fourth time and then subjected to the second washing; and / or, the molar content of H2S in the low-sulfur, carbon-rich methanol is 3-6‰, the molar content of CO2 is 28-32%; the temperature is -60 to -55°C; and / or, dividing the low-sulfur carbon-rich methanol into a first stream of low-sulfur carbon-rich methanol and a second stream of low-sulfur carbon-rich methanol at a molar flow ratio of 1:11-15; Preferably, the molar content of H2 in the flash gas is 78-84%, the molar content of CO2 is 14-19%, and the molar content of CO is 0.4-0.9%; the temperature is -65 to -60°C, and the pressure is 1.6-2MPa(G).

8. A low-temperature, low-sulfur synthesis gas purification device supporting a water-coal slurry gasification device, characterized in that: The device comprises: an H2S absorption tower, a CO2 absorption tower, a flash tower and a reabsorption tower connected in sequence, as well as a first cooler, a second cooler and a third cooler; the flash tower comprises a CO2 flash section arranged on the top and an H2S flash section arranged on the bottom, and the top of the CO2 flash section is connected to the bottom of the H2S flash section; The synthesis gas enters the H2S absorption tower for H2S absorption, and the obtained desulfurized gas enters the CO2 absorption tower for CO2 absorption. The obtained CO2-rich methanol is divided into two streams. The second stream of CO2-rich methanol passes through the first cooler and enters the CO2 flash section for CO2 flash evaporation. The obtained flashed CO2-rich methanol is divided into two streams. The first stream of CO2-rich methanol after flash evaporation enters the upper part of the reabsorption tower for the first flash evaporation to obtain semi-lean liquid methanol divided into two streams. The second stream of CO2-rich methanol after flash evaporation passes through the second cooler and enters the middle part of the reabsorption tower for the second flash evaporation to obtain flash liquid. The first H2S-rich methanol obtained by the H2S absorption passes through the third cooler and enters the lower part of the H2S flash section for H2S flash evaporation. The flashed H2S-rich methanol obtained enters the lower part of the reabsorption tower for the third flash evaporation. The sulfur-containing gas phase obtained is first washed with the flash liquid. The low-H2S methanol obtained enters the upper part of the H2S flash section and is secondly washed with the CO2 flash gas obtained by the CO2 flash evaporation and the H2S flash gas obtained by the H2S flash evaporation. The low-sulfur and carbon-rich methanol obtained is recycled to the H2S absorption tower. The first stream of CO2-rich methanol is recycled back to the H2S absorption tower; the first stream of semi-lean methanol is recycled back to the CO2 absorption tower.

9. The device according to claim 8, wherein: The H2S absorption tower comprises a first H2S absorption section disposed at the bottom and a second H2S absorption section disposed at the top; Preferably, the low-sulfur carbon-rich methanol is divided into a first stream of low-sulfur carbon-rich methanol and a second stream of low-sulfur carbon-rich methanol, which are recycled back to the first H2S absorption section and the second H2S absorption section respectively; Preferably, the first stream of CO2-rich methanol is recycled back to the second H2S absorption stage; And / or, the CO2 absorption tower includes a first CO2 absorption section disposed at the bottom and a second CO2 absorption section disposed at the top, and the lower part of the second CO2 absorption section is connected to the upper part of the first CO2 absorption section.

10. The device according to claim 9, wherein: A first pump is provided on the pipeline connecting the upper part of the H2S flash section and the H2S absorption tower, for dividing the low-sulfur and carbon-rich methanol into two streams after the first pressurization, and then circulating them back to the first H2S absorption section and the second H2S absorption section respectively; And / or, according to the material flow direction, a second pump and a fourth cooler are sequentially arranged on the pipeline connecting the CO2-rich methanol outlet of the CO2 absorption tower and the second H2S absorption section, so as to circulate the first stream of CO2-rich methanol back to the second H2S absorption section after the second pressurization and the fourth cooling; and / or, a fifth cooler is provided on the pipeline connecting the second CO2 absorption section and the first CO2 absorption section according to the material flow direction; And / or, a third pump is provided on the pipeline connecting the semi-lean liquid methanol outlet of the reabsorption tower and the second CO2 absorption section, for circulating the first stream of semi-lean liquid methanol back to the second CO2 absorption section after the third pressurization; And / or, a fourth pump is provided on the pipeline connecting the low H2S methanol outlet of the reabsorption tower and the upper part of the H2S flash section, for performing the second washing after the low H2S methanol is subjected to a fourth pressurization.

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