Poly-generation synthesis gas purification device and method matched with pulverized coal gasification device

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to a poly-generation synthesis gas purification device matched with a pulverized coal gasification device and a poly-generation synthesis gas purification method matched with the pulverized coal gasification device. According to the method, a two-stage flash evaporation process is optimally configured, first-stage CO2 flash evaporation steam, second-stage CO2 flash evaporation steam and first-stage H2S flash evaporation steam are washed with non-conversion CO2-rich methanol, second-stage H2S flash evaporation steam is washed with non-conversion H2S-rich methanol, and reasonable use of the non-conversion CO2-rich methanol and the non-conversion H2S-rich methanol is achieved; the gas stripping process is optimized, and the gas stripping gas generated by the first gas stripping is subjected to multi-stage series absorption, so that the device has the characteristic of low comprehensive energy consumption.

Description

Technical Field

[0001] This invention relates to the field of low-temperature methanol washing technology, specifically to a multi-product syngas purification device and a multi-product syngas purification method for a pulverized coal gasification unit. Background Technology

[0002] The syngas produced using pulverized coal gasification technology contains H2 and CO, which are referred to as effective gases. The syngas also contains a large amount of CO2 and trace amounts of H2S, COS, NH3, HCN, and other components. After the hydrogen-to-carbon ratio is adjusted in a shift converter, the H2 and CO become the feedstock gases for synthesizing chemical products such as methanol and ammonia. Acidic gases CO2 and H2S are generally poisons to synthesis catalysts and must be removed before the synthesis process.

[0003] Low-temperature methanol washing technology uses low-temperature methanol as the absorbent solvent to absorb and remove acidic gases such as H2S and CO2 from the synthesis gas, while also removing trace components such as HCN and NH3. In the low-temperature methanol washing process of multi-generation plants, the non-conversion CO2-rich methanol solution is characterized by the absence of H2S gas and low CO2 content, while the non-conversion H2S-rich methanol solution is characterized by low CO2 content and relatively high CO gas content. How to rationally reuse these two rich methanol streams is a key consideration in the design of the low-temperature methanol washing process of multi-generation plants.

[0004] CN201110260570.0 discloses a low-temperature methanol washing process. However, this process has several drawbacks: First, it uses CO2-rich methanol to wash the syngas in the H2S absorption tower, increasing the amount of H2S-rich methanol produced. This H2S-rich methanol requires thermal regeneration before recycling, resulting in high energy consumption. Second, in the CO2 flash evaporation section of the reabsorption tower, the CO2-rich methanol directly mixes with the H2S-rich methanol while washing the flash vapor, becoming contaminated itself. The resulting low-concentration H2S methanol is also not fully utilized, further increasing energy consumption. Third, the tail gas washing setup is inadequate; it does not selectively use methanol with different H2S contents based on the H2S content in the tail gas to reduce the overall thermal regeneration energy consumption of the low-temperature methanol washing process. Fourth, the medium-pressure flash evaporation process is simplistic, using only a single-stage flash evaporation, resulting in low flash vapor pressure and requiring significant compression power for recovery.

[0005] CN201810994082.4 discloses a low-temperature methanol washing system and a method for providing syngas. This technology makes secondary use of non-shift H2S-rich methanol after non-shift gas washing, but it is only used as flash steam washing methanol after medium-pressure flash evaporation of H2S-rich methanol. Its use is not sufficient and efficient, and there is still room for technological improvement and energy consumption reduction. Summary of the Invention

[0006] The object of the present invention is to overcome the problems in the existing polygeneration low-temperature methanol washing technology, such as the unreasonable process settings of the medium-pressure flash tower and the reabsorption tower, and the unreasonable use of the carbon-rich methanol after washing and absorbing the non-shifted gas. A polygeneration syngas purification device supporting a pulverized coal gasification device and a polygeneration syngas purification method supporting a pulverized coal gasification device are provided. By optimizing the configuration of the two-stage flash process, the non-shifted CO2-rich methanol is used to wash the first-stage CO2 flash gas, the second-stage CO2 flash gas and the first-stage H2S flash gas, and the non-shifted H2S-rich methanol is used to wash the second-stage H2S flash gas, realizing the reasonable use of the non-shifted CO2-rich methanol and the non-shifted H2S-rich methanol; by optimizing the stripping process and performing multi-stage series absorption on the stripping gas generated by the first stripping, it has the characteristics of low comprehensive energy consumption.

[0007] To achieve the above object, in the first aspect of the present invention, a polygeneration syngas purification device supporting a pulverized coal gasification device is provided. The device includes: a non-shifted gas scrubbing tower, an absorption tower, a first-stage medium-pressure flash tower, a second-stage medium-pressure flash tower, a reabsorption tower and a low-carbon methanol stripping tower connected in sequence;

[0008] Among them, the non-shifted gas scrubbing tower is divided into a first purification section, a second purification section and a third purification section from bottom to top, which are respectively used to purify the non-shifted gas in sequence for the first purification, the second purification and the third purification, obtaining pre-purified non-shifted H2S-rich methanol, the non-shifted H2S-rich methanol is divided into two streams, the non-shifted CO2-rich methanol is divided into three streams and purified non-shifted gas; the absorption tower is divided into a first H2S absorption section, a second H2S absorption section, a first CO2 absorption section and a second CO2 absorption section from bottom to top, which are respectively used to perform the first-stage H2S absorption, the second-stage H2S absorption, the first-stage CO2 absorption and the second-stage CO2 absorption on the syngas in sequence, obtaining first-stage H2S-rich methanol, the second-stage H2S-rich methanol is divided into two streams, the first-stage CO2-rich methanol is divided into two streams, the second-stage CO2-rich methanol and purified gas;

[0009] Among them, the first-stage medium-pressure flash tower is divided into a first-stage CO2 flash section and a first-stage H2S flash section from top to bottom; the second-stage medium-pressure flash tower is divided into a second-stage CO2 flash section and a second-stage H2S flash section from top to bottom; the first-stage CO2 flash section is connected to the second-stage CO2 flash section, and is used to perform two-stage CO2 flashing on the second stream of the first-stage CO2-rich methanol, obtaining first-stage CO2 flash gas, second-stage CO2 flash gas and the second-stage CO2 flash liquid divided into two streams; the first-stage H2S flash section is connected to the second-stage H2S flash section, and is used to perform two-stage H2S flashing on the second stream of the second-stage H2S-rich methanol, obtaining first-stage H2S flash gas, second-stage H2S flash gas and the second-stage H2S flash liquid;

[0010] The first and second non-conversion CO2-rich methanol streams are sent to the second H2S absorption section and the second purification section, respectively. The third non-conversion CO2-rich methanol stream is divided into stream a and stream b, which are sent to the upper part of the first-stage H2S flash evaporation section and the upper part of the second-stage CO2 flash evaporation section for first and second washing, respectively. The first and second non-conversion H2S-rich methanol streams are sent to the upper part of the second-stage H2S flash evaporation section and the first purification section, respectively, for third washing and first purification, respectively.

[0011] The upper section of the reabsorption tower is divided into a first flash section, a second flash section, and a third flash section from top to bottom. These sections are used to flash the first secondary CO2 flash liquid, the second secondary CO2 flash liquid, and the secondary H2S flash liquid, respectively, to obtain two streams of semi-lean methanol, low-sulfur methanol, first H2S-rich methanol, and CO2 product gas. The lower section of the reabsorption tower is divided into a washing section and a stripping section from top to bottom. The stripping section connects the upper parts of the second flash section, the third flash section, the washing section, and the secondary H2S flash section. It is used to strip the low-sulfur methanol, first H2S-rich methanol, second H2S-rich methanol, and washed non-conversion H2S-rich methanol, respectively, to obtain the first stripping. The stripped gas is sent to the washing section for a fourth washing with the second stream of semi-lean methanol to obtain the second H2S-rich methanol. The low-carbon methanol stripping tower is used to strip the first stream of semi-lean methanol to obtain the second CO2 absorption section.

[0012] A second aspect of the present invention provides a method for purifying syngas produced by a combined coal gasification unit, the method comprising:

[0013] The non-shift gas is subjected to first purification, second purification and third purification in sequence to obtain pre-purified non-shift H2S rich methanol, non-shift H2S rich methanol split into two streams, non-shift CO2 rich methanol split into three streams and purified non-shift gas.

[0014] Syngas is subjected to first-stage H2S absorption, second-stage H2S absorption, first-stage CO2 absorption and second-stage CO2 absorption in sequence to obtain first-stage H2S-rich methanol, second-stage H2S-rich methanol in two streams, first-stage CO2-rich methanol in two streams, second-stage CO2-rich methanol and purified gas.

[0015] The second stream of primary CO2-rich methanol is subjected to two-stage CO2 flash evaporation to obtain primary CO2 flash vapor, secondary CO2 flash vapor, and secondary CO2 flash liquid in two separate streams; the second stream of secondary H2S-rich methanol is subjected to two-stage H2S flash evaporation to obtain primary H2S flash vapor, secondary H2S flash vapor, and secondary H2S flash liquid.

[0016] Specifically, the first and second non-conversion CO2-rich methanol streams are returned to the secondary H2S absorption and secondary purification processes, respectively. The third non-conversion CO2-rich methanol stream is divided into stream a and stream b. Stream a undergoes a first wash with primary CO2 flash vapor and primary H2S flash vapor, while stream b undergoes a second wash with secondary CO2 flash vapor. The first non-conversion H2S-rich methanol stream undergoes a third wash with secondary H2S flash vapor, and the second non-conversion H2S-rich methanol stream is returned to the first purification process.

[0017] The first secondary CO2 flash liquid, the second secondary CO2 flash liquid, and the secondary H2S flash liquid are subjected to first flash evaporation, second flash evaporation, and third flash evaporation, respectively, to obtain two semi-lean methanol streams, low-sulfur methanol, first H2S-rich methanol, and CO2 product gas. The low-sulfur methanol, first H2S-rich methanol, second H2S-rich methanol, and washed non-conversion H2S-rich methanol are then subjected to a first gas stripping. The resulting stripped gas is then washed with the second semi-lean methanol stream in a fourth wash to obtain the second H2S-rich methanol. The first semi-lean methanol stream is subjected to a second gas stripping, and the resulting low-carbon methanol is returned to the secondary CO2 absorption.

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

[0019] (1) The method provided by the present invention adopts a two-stage medium-pressure flash evaporation technology. The first-stage flash evaporation pressure is higher and more effective gas is flashed out. The first-stage flash gas 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 flash evaporation pressure is lower, ensuring that the effective gas in the first-stage CO2 flash liquid and the first-stage H2S flash liquid is recovered. At the same time, the intake air volume of the first-stage cylinder of the compressor in the compression process can be reduced, which can also reduce the power consumption of the compressor.

[0020] (2) The method provided by the present invention optimizes the medium-pressure flash evaporation process by introducing non-conversion rich CO2 methanol to wash the primary CO2 flash vapor, primary H2S flash vapor and secondary CO2 flash vapor, and introduces non-conversion rich H2S methanol to wash the secondary H2S flash vapor. The washing liquid and the washed liquid do not mix. Compared with the prior art, this avoids the reduction of the concentration of the secondary CO2 flash liquid and the secondary H2S flash liquid, and can generate a lower temperature through desorption in the reabsorption tower, which is beneficial to reducing the energy consumption of the device.

[0021] (3) The present invention adopts a four-stage tail gas washing technology. According to the different H2S contents in the first tail gas, four different methanol streams with different H2S contents, namely the second semi-lean methanol, low-sulfur methanol, post-washing non-shifted H2S-rich methanol, and the first H2S-rich methanol, are selectively set up and washed in sequence from high to low. On the premise of ensuring that the first tail gas meets the emission standards, the least amount of the second semi-lean methanol is used to reduce the heat regeneration energy consumption of the entire low-temperature methanol washing process;

[0022] (4) The method provided by the present invention optimizes the reabsorption process, enabling the flash liquid obtained by the second flash of the second-stage CO2 flash liquid of the second stream to absorb the sulfur-containing gas phase (such as H2S) generated by the third flash of the second-stage H2S flash liquid, resulting in low-sulfur methanol and creating conditions for the reuse of this low-sulfur methanol. Brief Description of the Drawings

[0023] Figure 1 It is a schematic structural diagram of a polygeneration syngas purification device supporting a pulverized coal gasification device provided by the present invention.

[0024] Description of the Reference Numerals in the Drawings

[0025] T-1, non-shifted gas washing tower; T-2, absorption tower; T-3, first-stage medium-pressure flash tower; T-4, second-stage medium-pressure flash tower; T-5, reabsorption tower; T-6, low-carbon methanol stripping tower;

[0026] E-1, first cooler; E-2, second cooler; E-3, third cooler; E-4, fourth cooler; E-5, fifth cooler; E-6, sixth cooler; E-7, seventh cooler; P-1, first pump; P-2, second pump; Q-1, first heat exchanger; Q-2, second heat exchanger; Q-3, third heat exchanger;

[0027] 1. Non-shift gas; 2. Non-shift H2S-rich methanol; 2-i. First non-shift H2S-rich methanol; 2-ii. Second non-shift H2S-rich methanol; 3. Lean methanol; 3-i. First lean methanol; 3-ii. Second lean methanol; 4. Pre-purified non-shift H2S-rich methanol; 5. Purified non-shift gas; 6. Syngas; 7. Primary H2S-rich methanol; 8. Non-shift CO2-rich methanol; 8-i. First non-shift CO2-rich methanol; 8-ii. Second... Non-conversion CO2-rich methanol; 8-iii, third non-conversion CO2-rich methanol; 8-iii-a, a-share non-conversion CO2-rich methanol; 8-iii-b, b-share non-conversion CO2-rich methanol; 9, primary CO2-rich methanol; 9-i, first-share primary CO2-rich methanol; 9-ii, second-share primary CO2-rich methanol; 10, secondary CO2-rich methanol; 11, secondary H2S-rich methanol; 11-i, first-share secondary H2S-rich methanol; 11-ii, second... 12. Primary CO2 flash liquid; 13. Semi-lean methanol; 13-i. First semi-lean methanol; 13-ii. Second semi-lean methanol; 14. Purified gas; 15. Primary CO2 flash vapor; 16. Primary flash vapor; 17. Primary H2S flash liquid; 18. Secondary CO2 flash vapor after washing; 19. Secondary H2S flash vapor after washing; 20. Secondary CO2 flash liquid; 20-i. First secondary CO2 flash liquid; 20- ii. Secondary CO2 flash liquid; 21. Low-sulfur CO2-rich methanol; 22. Low-sulfur methanol; 23. Secondary H2S flash liquid; 24. First H2S-rich methanol; 25. Second H2S-rich methanol; 26. H2S-rich methanol after stripping; 27. Second tail gas; 28. Nitrogen; 28-i. First nitrogen stream; 28-ii. Second nitrogen stream; 29. ​​Low-carbon methanol; 30. CO2 product gas; 31. First tail gas; 32. Non-conversion H2S-rich methanol after washing. Detailed Implementation

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] In this invention, unless otherwise specified, "first", "second", "third", "fourth" and "fifth" do not indicate a sequence or limit the various materials or steps, but are used only to distinguish or indicate that they are not the same step or material.

[0030] In the present invention, unless otherwise specified, 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.

[0031] The first aspect of the present invention provides a structural schematic diagram of a polygeneration syngas purification device for supporting a pulverized coal gasification device as Figure 1 shown, and it can be seen from Figure 1 that the device includes: a connected non-shift gas scrubbing tower T-1, an absorption tower T-2, a first-stage medium-pressure flash tower T-3, a second-stage medium-pressure flash tower T-4, a reabsorption tower T-5, and a low-carbon methanol stripping tower T-6;

[0032] Among them, the non-shift gas scrubbing tower T-1 is divided into a first purification section, a second purification section, and a third purification section from bottom to top, which are respectively used to perform the first purification, the second purification, and the third purification on the non-shift gas 1 in sequence, obtaining pre-purified non-shift H2S-rich methanol 4, non-shift H2S-rich methanol 2 in two streams, non-shift CO2-rich methanol 8 in three streams, and purified non-shift gas 5; the absorption tower T-2 is divided into a first H2S absorption section, a second H2S absorption section, a first CO2 absorption section, and a second CO2 absorption section from bottom to top, which are respectively used to perform the first-stage H2S absorption, the second-stage H2S absorption, the first-stage CO2 absorption, and the second-stage CO2 absorption on the syngas 6 in sequence, obtaining first-stage H2S-rich methanol 7, second-stage H2S-rich methanol 11 in two streams, first-stage CO2-rich methanol 9 in two streams, second-stage CO2-rich methanol 10, and purified gas 14;

[0033] Among them, the first-stage medium-pressure flash tower T-3 is divided into a first-stage CO2 flash section and a first-stage H2S flash section from top to bottom; the second-stage medium-pressure flash tower T-4 is divided into a second-stage CO2 flash section and a second-stage H2S flash section from top to bottom; the first-stage CO2 flash section is connected to the second-stage CO2 flash section, which is used to perform two-stage CO2 flashing on the second stream of first-stage CO2-rich methanol 9-ii, obtaining first-stage CO2 flash gas 15, second-stage CO2 flash gas, and second-stage CO2 flash liquid 20 in two streams; the first-stage H2S flash section is connected to the second-stage H2S flash section, which is used to perform two-stage H2S flashing on the second stream of second-stage H2S-rich methanol 11-ii, obtaining first-stage H2S flash gas, second-stage H2S flash gas, and second-stage H2S flash liquid 23;

[0034] Specifically, the first non-conversion CO2-rich methanol 8-i and the second non-conversion CO2-rich methanol 8-ii are sent to the second H2S absorption section and the second purification section, respectively. The third non-conversion CO2-rich methanol 8-iii is divided into a non-conversion CO2-rich methanol 8-iii-a and b non-conversion CO2-rich methanol 8-iii-b, which are sent to the upper part of the first-stage H2S flash evaporation section and the upper part of the second-stage CO2 flash evaporation section for the first and second washing, respectively. The first non-conversion H2S-rich methanol 2-i and the second non-conversion H2S-rich methanol 2-ii are sent to the upper part of the second-stage H2S flash evaporation section and the first purification section, respectively, for the third washing and the first purification, respectively.

[0035] The upper section of the reabsorption tower T-5 is divided into a first flash section, a second flash section, and a third flash section from top to bottom. These sections are used to flash the first secondary CO2 flash liquid 20-i, the second secondary CO2 flash liquid 20-ii, and the secondary H2S flash liquid 23, respectively, to obtain semi-lean methanol 13 (divided into two streams), low-sulfur methanol 22, first H2S-rich methanol 24, and CO2 product gas 30. The lower section of the reabsorption tower T-5 is divided into a washing section and a stripping section from top to bottom. The stripping section connects to the second flash section. The upper parts of the third flash evaporation section, the washing section, and the secondary H2S flash evaporation section are used to perform the first gas stripping on the low-sulfur methanol 22, the first H2S-rich methanol 24, the second H2S-rich methanol 25, and the washed non-conversion H2S-rich methanol 32, respectively. The resulting stripped gas is sent to the washing section and subjected to a fourth washing with the second semi-lean methanol 13-ii to obtain the second H2S-rich methanol 25. The low-carbon methanol stripping tower T-6 is used to perform the second gas stripping on the first semi-lean methanol 13-i, and the resulting low-carbon methanol 29 is returned to the second CO2 absorption section.

[0036] In this invention, such as Figure 1 As shown, in the non-shifting gas scrubbing tower T-1, the first purification section, the second purification section, and the third purification section are connected through air risers.

[0037] In this invention, such as Figure 1 As shown, preferably, in the non-shift gas scrubbing tower T-1,

[0038] The first purification section is connected to the bottom of the second purification section and is used to perform the first purification on the non-conversion gas 1 and the second stream of non-conversion H2S-rich methanol 2-ii to obtain pre-purified non-conversion H2S-rich methanol 4 and pre-desulfurized non-conversion gas; the second purification section is connected to the bottom of the third purification section and is used to perform the second purification on the pre-desulfurized non-conversion gas and the second stream of non-conversion CO2-rich methanol 8-ii to obtain the non-conversion H2S-rich methanol 2 and desulfurized non-conversion gas; the third purification section is used to perform the third purification on the desulfurized non-conversion gas and the first stream of lean methanol 3-i to obtain the non-conversion CO2-rich methanol 8 and purified non-conversion gas 5.

[0039] In this invention, such as Figure 1 As shown, in the absorption tower T-2, the first H2S absorption section, the second H2S absorption section, the first CO2 absorption section, and the second CO2 absorption section are connected through the gas riser.

[0040] In this invention, such as Figure 1 As shown, preferably, in the absorption tower T-2,

[0041] The first H2S absorption section is connected to the bottom of the second H2S absorption section and is used to absorb the synthesis gas 6 and the first stream of secondary H2S-rich methanol 11-i through the first-stage H2S absorption to obtain the first-stage H2S-rich methanol 7 and pre-desulfurized gas. The second H2S absorption section is connected to the upper part of the first-stage H2S flash evaporation section, the third purification section, and the bottom of the first CO2 absorption section and is used to absorb the pre-desulfurized gas, low-sulfur CO2-rich methanol 21, the first stream of non-conversion CO2-rich methanol 8-i, and the first stream of first-stage CO2-rich methanol 9-i through the second-stage H2S absorption. H2S absorption yields desulfurized gas and the secondary H2S-rich methanol 11; the first CO2 absorption section is connected to the bottom of the second CO2 absorption section and is used to perform the primary CO2 absorption on the desulfurized gas and the secondary CO2-rich methanol 10 to obtain the primary CO2-rich methanol 9 and pre-purified gas; the second CO2 absorption section is connected to the low-carbon methanol stripping tower T-6 and is used to perform the secondary CO2 absorption on the pre-purified gas, low-carbon methanol 29 and the second lean methanol 3-ii to obtain the secondary CO2-rich methanol 10 and purified gas 14.

[0042] According to the present invention, preferably, such as Figure 1 As shown, in accordance with the material flow direction, a first pump P-1 is installed on the pipeline connecting the upper part of the first-stage H2S flash section and the second H2S absorption section. This pump is used to pressurize the low-sulfur, CO2-rich methanol 21 before it undergoes the second-stage H2S absorption.

[0043] According to the present invention, preferably, such as Figure 1As shown, a first cooler E-1 is installed on the pipeline connecting the second H2S absorption section and the first CO2 absorption section according to the material flow direction. This cooler is used to cool the first primary CO2-rich methanol 9-i before it undergoes the secondary H2S absorption.

[0044] According to the present invention, preferably, such as Figure 1 As shown, a second cooler E-2 is installed on the pipeline connecting the first CO2 absorption section and the second CO2 absorption section according to the material flow direction. This cooler is used to cool the secondary CO2-rich methanol 10 before it undergoes the primary CO2 absorption.

[0045] According to the present invention, preferably, such as Figure 1 As shown, in the primary medium-pressure flash evaporator T-3,

[0046] The first-stage CO2 flash evaporation section is connected to the first-stage CO2 absorption section and is used to perform first-stage CO2 flash evaporation on the second-stage CO2-rich methanol 9-ii. The resulting first-stage CO2 flash vapor 15 is sent to the upper part of the first-stage H2S flash evaporation section via a pipeline, and the resulting first-stage CO2 flash liquid 12 is sent to the second-stage CO2 flash evaporation section via a pipeline.

[0047] The lower part of the primary H2S flash evaporation section is connected to the second H2S absorption section, which is used to perform primary H2S flash evaporation on the second secondary H2S-rich methanol 11-ii. The resulting primary H2S flash vapor is sent to the upper part of the primary H2S flash evaporation section through the riser, and the resulting primary H2S flash liquid 17 is sent to the lower part of the secondary H2S flash evaporation section through the pipeline. The upper part of the primary H2S flash evaporation section is connected to the third purification section, which is used to perform the first washing on the non-conversion CO2-rich methanol 8-iii-a, the primary CO2 flash vapor 15, and the primary H2S flash vapor to obtain primary flash vapor 16 and the low-sulfur CO2-rich methanol 21.

[0048] According to the present invention, preferably, such as Figure 1 As shown, in the secondary medium-pressure flash evaporator T-4,

[0049] The secondary CO2 flash evaporation section is used to perform secondary CO2 flash evaporation on the primary CO2 flash liquid 12 to obtain secondary CO2 flash liquid 20. The obtained secondary CO2 flash vapor is then subjected to a second wash with b streams of non-conversion rich CO2 methanol 8-iii-b to obtain washed secondary CO2 flash vapor 18. The second wash liquid is mixed into the secondary CO2 flash liquid 20. The lower part of the secondary H2S flash evaporation section is used to perform secondary H2S flash evaporation on the primary H2S flash liquid 17 to obtain secondary H2S flash liquid 23. The obtained secondary H2S flash vapor is sent to the upper part of the secondary H2S flash evaporation section through the riser hole and subjected to a third wash with the first stream of non-conversion rich H2S methanol 2-i to obtain washed secondary H2S flash vapor 19 and washed non-conversion rich H2S methanol 32.

[0050] According to the present invention, preferably, such as Figure 1 As shown, a third cooler E-3 is installed on the pipeline connecting the upper part of the first-stage H2S flash evaporation section and the second-stage CO2 flash evaporation section in the third purification section. This cooler is used to separate the third non-conversion CO2-rich methanol 8-iii into two streams: stream a, non-conversion CO2-rich methanol 8-iii-a, and stream b, non-conversion CO2-rich methanol 8-iii-b, after the third cooling process.

[0051] According to the present invention, preferably, such as Figure 1 As shown, in the upper section of the reabsorption tower T-5, the first flash evaporation section is used to perform the first flash evaporation on the first secondary CO2 flash liquid 20-i to obtain semi-lean methanol 13 and the first CO2 product gas; the second flash evaporation section is used to perform the second secondary CO2 flash liquid 20-ii to obtain flash liquid and the second CO2 product gas; the third flash evaporation section is used to perform the third flash evaporation on the secondary H2S flash liquid 23 to obtain the first H2S-rich methanol 24, and the sulfur-containing gas phase is contacted with the flash liquid through the riser to obtain low-sulfur methanol 22 and the third CO2 product gas; wherein, the CO2 product gas 30 includes the first CO2 product gas, the second CO2 product gas and the third CO2 product gas.

[0052] According to the present invention, preferably, such as Figure 1As shown, a fourth cooler E-4 is installed on the pipe connecting the secondary CO2 flash section, the first flash section, and the second flash section, for dividing the secondary CO2 flash liquid 20 into a first secondary CO2 flash liquid 20-i and a second secondary CO2 flash liquid 20-ii after the fourth cooling; more preferably, a fifth cooler E-5 is installed on the pipe connecting the fourth cooler E-4 and the first flash section, for performing the first flash evaporation after the first secondary CO2 flash liquid 20-i has undergone the fifth cooling; a sixth cooler E-6 is installed on the pipe connecting the fourth cooler E-4 and the second flash section, for performing the second flash evaporation after the second secondary CO2 flash liquid 20-ii has undergone the sixth cooling.

[0053] According to the present invention, preferably, such as Figure 1 As shown, a seventh cooler E-7 is installed on the pipeline connecting the secondary H2S flash section and the third flash section, which is used to cool the secondary H2S flash liquid 23 in the seventh stage before performing the third flash evaporation.

[0054] According to the present invention, preferably, such as Figure 1 As shown, in the lower column of the reabsorption tower T-5, the stripping section is used to independently strip the low-sulfur methanol 22, the first H2S-rich methanol 24, the second H2S-rich methanol 25, the washed non-conversion H2S-rich methanol 32, and the first nitrogen gas 28-i to obtain stripped gas and stripped H2S-rich methanol 26; the washing section is used to perform the fourth washing on the second semi-lean methanol 13-ii and the stripped gas to obtain the first tail gas 31 and the second H2S-rich methanol 25.

[0055] According to the present invention, preferably, such as Figure 1 As shown, the low-carbon methanol stripping tower T-6 is used to perform the second stripping of the first semi-lean methanol 13-i and the second nitrogen 28-ii to obtain the second tail gas 27 and the low-carbon methanol 29.

[0056] According to the present invention, preferably, such as Figure 1 As shown, a first heat exchanger Q-1 is installed on the pipeline connecting the third flash section and the stripping section, which is used to perform the first stripping of the first H2S-rich methanol 24 after the first heat exchange.

[0057] According to the present invention, preferably, such as Figure 1 As shown, a second heat exchanger Q-2 is installed on the pipeline connecting the washing section and the stripping section, which is used to perform the first stripping of the second H2S-rich methanol 25 after passing through the second heat exchanger.

[0058] According to the present invention, preferably, such as Figure 1As shown, a third heat exchanger Q-3 is installed on the pipeline connecting the first flash section and the low-carbon methanol stripping tower T-6. This heat exchanger is used to transfer the first semi-lean methanol 13-i through the third heat exchanger to the second stripping process.

[0059] According to the present invention, preferably, such as Figure 1 As shown, a second pump P-2 is installed on the pipeline connecting the low-carbon methanol stripping tower T-6 and the second CO2 absorption section, which is used to pressurize the low-carbon methanol 29 for the secondary CO2 absorption.

[0060] A second aspect of the present invention provides a method for purifying syngas produced by a combined coal gasification unit, the method comprising:

[0061] The non-shift gas is subjected to first purification, second purification and third purification in sequence to obtain pre-purified non-shift H2S rich methanol, non-shift H2S rich methanol split into two streams, non-shift CO2 rich methanol split into three streams and purified non-shift gas.

[0062] Syngas is subjected to first-stage H2S absorption, second-stage H2S absorption, first-stage CO2 absorption and second-stage CO2 absorption in sequence to obtain first-stage H2S-rich methanol, second-stage H2S-rich methanol in two streams, first-stage CO2-rich methanol in two streams, second-stage CO2-rich methanol and purified gas.

[0063] The second stream of primary CO2-rich methanol is subjected to two-stage CO2 flash evaporation to obtain primary CO2 flash vapor, secondary CO2 flash vapor, and secondary CO2 flash liquid in two separate streams; the second stream of secondary H2S-rich methanol is subjected to two-stage H2S flash evaporation to obtain primary H2S flash vapor, secondary H2S flash vapor, and secondary H2S flash liquid.

[0064] Specifically, the first and second non-conversion CO2-rich methanol streams are returned to the secondary H2S absorption and secondary purification processes, respectively. The third non-conversion CO2-rich methanol stream is divided into stream a and stream b. Stream a undergoes a first wash with primary CO2 flash vapor and primary H2S flash vapor, while stream b undergoes a second wash with secondary CO2 flash vapor. The first non-conversion H2S-rich methanol stream undergoes a third wash with secondary H2S flash vapor, and the second non-conversion H2S-rich methanol stream is returned to the first purification process.

[0065] The first secondary CO2 flash liquid, the second secondary CO2 flash liquid, and the secondary H2S flash liquid are subjected to first flash evaporation, second flash evaporation, and third flash evaporation, respectively, to obtain two semi-lean methanol streams, low-sulfur methanol, first H2S-rich methanol, and CO2 product gas. The low-sulfur methanol, first H2S-rich methanol, second H2S-rich methanol, and washed non-conversion H2S-rich methanol are then subjected to a first gas stripping. The resulting stripped gas is then washed with the second semi-lean methanol stream in a fourth wash to obtain the second H2S-rich methanol. The first semi-lean methanol stream is subjected to a second gas stripping, and the resulting low-carbon methanol is returned to the secondary CO2 absorption.

[0066] In this invention, unless otherwise specified, both the non-shift gas and the syngas originate from the pulverized coal gasification unit, wherein the syngas is obtained from the non-shift gas through a shift process.

[0067] In some embodiments of the present invention, preferably, the non-shift gas originates from a pulverized coal gasification unit; wherein the molar content of H2S in the non-shift gas is 0.4-0.6%, the molar content of CO2 is 5-10%, the temperature is -35 to -25°C, and the pressure is 3.5-3.6 MPa(G).

[0068] In this invention, the first purification aims to remove impurities such as HCN and NH3, as well as small amounts of H2S and CO2, from the non-shifted gas; the second purification aims to further remove H2S from the non-shifted gas; and the third purification aims to further remove CO2 from the non-shifted gas.

[0069] In some embodiments of the present invention, preferably, the non-conversion gas and the second stream of non-conversion H2S-rich methanol are subjected to the first purification to obtain pre-purified non-conversion H2S-rich methanol and pre-desulfurized non-conversion gas; the pre-desulfurized non-conversion gas and the second stream of non-conversion CO2-rich methanol are subjected to the second purification to obtain the non-conversion H2S-rich methanol and desulfurized non-conversion gas; the desulfurized non-conversion gas and the first stream of lean methanol are subjected to the third purification to obtain the non-conversion CO2-rich methanol and purified non-conversion gas.

[0070] In this invention, preferably, the molar flow ratio of the non-conversion gas and the second non-conversion H2S-rich methanol is 52-62:1; more preferably, the molar content of H2S in the pre-purified non-conversion H2S-rich methanol is 0.8-1.2%, and the molar content of CO2 is 3-6%; the temperature is -35 to -25°C, and it is sent to subsequent processing steps.

[0071] In some embodiments of the present invention, preferably, the molar content of H2S in the non-conversion H2S-rich methanol is 0.5-0.9%, the molar content of CO2 is 3-7%, the temperature is -32 to -28°C, and the pressure is 3.49-3.59 MPa(G).

[0072] In some embodiments of the present invention, more preferably, the molar flow ratio of the first non-conversion H2S-rich methanol and the second non-conversion H2S-rich methanol is 37-42:1.

[0073] In some embodiments of the present invention, preferably, the molar content of H2S in the non-conversion CO2-rich methanol is 0.5-1 ppm, the molar content of CO2 is 3-8%, and the temperature is -40 to -33°C.

[0074] In some embodiments of the present invention, more preferably, the molar flow ratio of the first non-conversion CO2-rich methanol, the second non-conversion CO2-rich methanol, the a-share non-conversion CO2-rich methanol, and the b-share non-conversion CO2-rich methanol is 20-23:27-30:5-7:1.

[0075] In this invention, preferably, the molar flow ratio of the second non-conversion CO2-rich methanol and the non-conversion gas is 1:1-2; and the molar flow ratio of the first lean methanol and the non-conversion gas is 1.5-2.5:1-2.

[0076] In some embodiments of the present invention, preferably, the molar content of H2S and the molar content of CO2 in the lean methanol are 0%. In the present invention, the lean methanol is selected from subsequent processes. In the present invention, unless otherwise specified, the lean methanol is divided into a first lean methanol stream and a second lean methanol stream; the present invention does not limit the molar flow ratio of the first lean methanol stream and the second lean methanol stream.

[0077] In this invention, preferably, the molar content of H2S in the purified non-conversion gas is ≤0.1ppm, the molar content of CO2 is ≤20ppm, the temperature is -55 to -45℃, and the pressure is 3.4-3.5MPa(G).

[0078] In this invention, the primary H2S absorption aims to remove impurities such as HCN and NH3, as well as small amounts of H2S and CO2, from the synthesis gas; the secondary H2S absorption aims to further remove H2S and CO2 from the synthesis gas.

[0079] In some embodiments of the present invention, preferably, the syngas originates from a pulverized coal gasification unit, and the syngas contains 0.3-0.35% H2S and 40-50% CO2; the temperature is -25 to -15°C, and the pressure is 3.1-3.2 MPa(G).

[0080] In some embodiments of the present invention, preferably, the synthesis gas and the first stream of secondary H2S-rich methanol are subjected to the primary H2S absorption to obtain the primary H2S-rich methanol and pre-desulfurized gas; the pre-desulfurized gas, low-sulfur CO2-rich methanol, the first stream of non-conversion CO2-rich methanol and the first stream of primary CO2-rich methanol are subjected to the secondary H2S absorption to obtain desulfurized gas and the secondary H2S-rich methanol; the desulfurized gas and the secondary CO2-rich methanol are subjected to the primary CO2 absorption to obtain the primary CO2-rich methanol and pre-purified gas; the pre-purified gas, low-carbon methanol and the second stream of lean methanol are subjected to the secondary CO2 absorption to obtain the secondary CO2-rich methanol and purified gas.

[0081] In this invention, preferably, the molar flow ratio of the syngas and the first secondary H2S-rich methanol is 47-57:1; more preferably, the molar content of H2S in the primary H2S-rich methanol is 0.6-0.8%, and the molar content of CO2 is 30-36%; the temperature is -25 to -15°C, and it is sent to subsequent processing steps.

[0082] In this invention, preferably, the molar flow ratio of the low-sulfur CO2-rich methanol to the syngas is 1:26-30; the molar flow ratio of the first non-conversion CO2-rich methanol to the syngas is 1:8-10; and the molar flow ratio of the first primary CO2-rich methanol to the syngas is 3-5:8-10.

[0083] In some embodiments of the present invention, preferably, the molar content of H2S in the secondary H2S-rich methanol is 0.4-0.6%, the molar content of CO2 is 27-31%, and the temperature is -20 to -16°C.

[0084] In some embodiments of the present invention, more preferably, the molar flow ratio of the first secondary H2S-rich methanol to the second secondary H2S-rich methanol is 1:32-36.

[0085] In some embodiments of the present invention, preferably, the low-sulfur, CO2-rich methanol is pressurized to 3.6-4 MPa(G) before the secondary H2S absorption is performed.

[0086] In this invention, both the primary CO2 absorption and the secondary CO2 absorption are intended to further remove CO2 from the desulfurized gas. Preferably, the molar flow ratio of the synthesis gas to the secondary CO2-rich methanol is 1:1-2; the molar flow ratio of the purified gas to the low-carbon methanol is 1-1.2:1; and the molar flow ratio of the purified gas to the second lean methanol stream is 1:1.5-1.7.

[0087] In some embodiments of the present invention, preferably, the molar content of H2S in the primary CO2-rich methanol is 0.1-0.5 ppm, the molar content of CO2 is 18-23%, the temperature is -20 to -15°C, and the pressure is 3.05-3.15 MPa(G).

[0088] In some embodiments of the present invention, more preferably, the molar flow ratio of the first primary CO2-rich methanol stream and the second primary CO2-rich methanol stream is 1:2-4.

[0089] In some embodiments of the present invention, preferably, the first primary CO2-rich methanol is cooled to -46 to -43°C before the secondary H2S absorption is performed.

[0090] In some embodiments of the present invention, preferably, the secondary CO2-rich methanol is cooled to -36 to -33°C before the primary CO2 absorption is performed.

[0091] In some embodiments of the present invention, preferably, the low-carbon methanol is pressurized to 3.6-4 MPa(G) before the secondary CO2 absorption is performed.

[0092] In some embodiments of the present invention, preferably, the molar content of H2S in the purified gas is ≤0.1ppm, the molar content of CO2 is ≤20ppm, the temperature is -55 to -50°C, and the pressure is 3-3.1MPa(G).

[0093] In some embodiments of the present invention, preferably, the two-stage CO2 flash evaporation includes a first-stage CO2 flash evaporation and a second-stage CO2 flash evaporation; wherein, the second stream of first-stage CO2-rich methanol is subjected to first-stage CO2 flash evaporation to obtain first-stage CO2 flash vapor and first-stage CO2 flash liquid; the first-stage CO2 flash liquid is subjected to second-stage CO2 flash evaporation to obtain second-stage CO2 flash vapor and second-stage CO2 flash liquid.

[0094] In some embodiments of the present invention, preferably, the pressure of the first-stage CO2 flash evaporation is 1.5-1.8 MPa(G), and the pressure of the second-stage CO2 flash evaporation is 0.8-1 MPa(G).

[0095] In this invention, preferably, the molar content of H2S in the primary CO2 flash liquid is 0.1-0.5 ppm, the molar content of CO2 is 17.5-22.5%, and the temperature is -20.5 to -15.5℃.

[0096] In some embodiments of the present invention, preferably, the molar content of H2S in the secondary CO2 flash liquid is 0.1-0.5 ppm, the molar content of CO2 is 17-22%, and the temperature is -22 to -16°C; more preferably, the molar flow ratio of the first secondary CO2 flash liquid and the second secondary CO2 flash liquid is 3-5:1.

[0097] In some embodiments of the present invention, preferably, the two-stage H2S flash evaporation includes a first-stage H2S flash evaporation and a second-stage H2S flash evaporation; wherein, the second stream of secondary H2S-rich methanol is subjected to a first-stage H2S flash evaporation to obtain a first-stage H2S flash vapor and a first-stage H2S flash liquid; the first-stage H2S flash liquid is subjected to a second-stage H2S flash evaporation to obtain a second-stage H2S flash vapor and a second-stage H2S flash liquid.

[0098] In some embodiments of the present invention, preferably, the pressure of the first-stage H2S flash evaporation is 1.5-1.8 MPa(G), and the pressure of the second-stage H2S flash evaporation is 0.8-1 MPa(G).

[0099] In this invention, preferably, the molar content of H2S in the primary H2S flash liquid is 0.35-0.55%, the molar content of CO2 is 23.5-28.5%, and the temperature is -20.5 to -16.5℃.

[0100] In some embodiments of the present invention, preferably, the molar content of H2S in the secondary H2S flash liquid is 0.35-0.55%, the molar content of CO2 is 23-28%, and the temperature is -25 to -21°C.

[0101] In some embodiments of the present invention, preferably, the first washing process includes: subjecting the non-conversion CO2-rich methanol, primary CO2 flash vapor and primary H2S flash vapor to the first washing to obtain primary flash vapor and the low-sulfur CO2-rich methanol.

[0102] In some embodiments of the present invention, more preferably, the molar content of H2S in the primary flash vapor is 1-5 ppm, the molar content of CO2 is 32-36%, the molar content of CO is 5-9%, and the molar content of H2 is 56-60%; the temperature is -32 to -22°C, and the pressure is 1.5-1.8 MPa(G).

[0103] In some embodiments of the present invention, preferably, the molar content of H2S in the low-sulfur, CO2-rich methanol is 0.04-0.08%, the molar content of CO2 is 18-25%, the temperature is -20 to -13°C, and the pressure is 1.5-1.8 MPa(G).

[0104] In some embodiments of the present invention, preferably, the second washing process includes: subjecting b strands of non-conversion CO2-rich methanol and secondary CO2 flash vapor to the second washing to obtain washed secondary CO2 flash vapor, and mixing a second washing liquid into the secondary CO2 flash vapor.

[0105] In some embodiments of the present invention, more preferably, the molar content of CO2 in the secondary CO2 flash vapor after washing is 85-90%, the molar content of CO is 4-7%, the molar content of H2 is 4-8%, the temperature is -25 to -15°C, and the pressure is 0.8-1 MPa(G), before being sent to subsequent processes.

[0106] In some embodiments of the present invention, preferably, the third washing process includes: subjecting the first stream of non-conversion H2S-rich methanol and secondary H2S flash vapor to the third washing to obtain washed secondary H2S flash vapor and washed non-conversion H2S-rich methanol.

[0107] In some embodiments of the present invention, more preferably, the molar content of H2S in the secondary H2S flash vapor after washing is 0.6-1%, the molar content of CO2 is 20-25%, the molar content of CO is 68-72%, the molar content of H2 is 3-7%, the temperature is -35 to -25°C, and the pressure is 0.8-1 MPa(G).

[0108] In some embodiments of the present invention, more preferably, the molar content of H2S in the washed non-conversion H2S-rich methanol is 0.5-0.8%, the molar content of CO2 is 13-18%, and the temperature is -12 to -8°C.

[0109] In some embodiments of the present invention, preferably, the third non-conversion CO2-rich methanol is cooled to -53 to -47°C and then divided into the a-share non-conversion CO2-rich methanol and the b-share non-conversion CO2-rich methanol.

[0110] In some embodiments of the present invention, preferably, the first secondary CO2 flash liquid is subjected to the first flash evaporation to obtain semi-lean methanol and a first CO2 product gas; the second secondary CO2 flash liquid is subjected to the second flash evaporation to obtain a flash liquid and a second CO2 product gas; the secondary H2S flash liquid is subjected to the third flash evaporation to obtain the first H2S-rich methanol and a sulfur-containing gas phase; wherein, the flash liquid and the sulfur-containing gas phase are contacted to obtain low-sulfur methanol and a third CO2 product gas; wherein, the CO2 product gas includes the first CO2 product gas, the second CO2 product gas, and the third CO2 product gas.

[0111] In some embodiments of the present invention, preferably, the secondary CO2 flash liquid is cooled to -36 to -33°C in a fourth step and divided into a first secondary CO2 flash liquid and a second secondary CO2 flash liquid; more preferably, the first secondary CO2 flash liquid is cooled to -40 to -38°C in a fifth step and then subjected to the first flash evaporation; the second secondary CO2 flash liquid is cooled to -52 to -50°C in a sixth step and then subjected to the second flash evaporation.

[0112] In some embodiments of the present invention, preferably, the secondary H2S flash liquid is cooled to -55 to -52°C in a seventh step before the third flash evaporation is performed.

[0113] In some embodiments of the present invention, preferably, the molar content of H2S in the semi-lean methanol is 0.1-0.5 ppm; the molar content of CO2 is 11-16%; the temperature is -58 to -53°C; and the pressure is 0.05-0.08 MPa(G).

[0114] In some embodiments of the present invention, preferably, the molar flow ratio of the first semi-lean methanol stream and the second semi-lean methanol stream is 1-2:1.

[0115] In some embodiments of the present invention, preferably, the molar content of H2S in the low-sulfur methanol is 0.1-0.25%, the molar content of CO2 is 15-19%, the temperature is -60 to -50°C, and the pressure is 0.12-0.16 MPa(G).

[0116] In some embodiments of the present invention, preferably, the molar content of H2S in the first H2S-rich methanol is 0.3-0.7%, the molar content of CO2 is 11.5-17.5%, the temperature is -60 to -59°C, and the pressure is 0.13-0.17 MPa(G).

[0117] In some embodiments of the present invention, preferably, the molar content of H2S in the CO2 product gas is ≤1ppm, the molar content of CO2 is 99.4-99.7%; the temperature is -65 to -55°C, and the pressure is 0.05-0.08MPa(G);

[0118] In some embodiments of the present invention, preferably, the low-sulfur methanol, the first H2S-rich methanol, the second H2S-rich methanol, the washed non-conversion H2S-rich methanol, and the first stream of nitrogen are each subjected to a first gas stripping independently to obtain stripped gas and stripped H2S-rich methanol.

[0119] In some embodiments of the present invention, preferably, the first H2S-rich methanol is subjected to a first heat exchange to a temperature of -40 to -36°C before the first gas stripping is performed; the second H2S-rich methanol is subjected to a second heat exchange to a temperature of -40 to -36°C before the first gas stripping is performed.

[0120] In some embodiments of the present invention, preferably, the molar content of H2S in the H2S-rich methanol after gas stripping is 0.2-0.5%, the molar content of CO2 is 2-3%, the temperature is -65 to -55°C, and the pressure is 0.22-0.24 MPa(G).

[0121] In some embodiments of the present invention, preferably, the second semi-lean methanol and stripping gas are subjected to the fourth washing to obtain the first tail gas and the second H2S-rich methanol; more preferably, the molar content of H2S in the first tail gas is ≤1ppm, the molar content of CO2 is 68-72%, the temperature is -63 to -58°C, and the pressure is 0.16-0.18MPa(G).

[0122] In some embodiments of the present invention, preferably, the molar content of H2S in the second H2S-rich methanol is 0.2-0.5%, the molar content of CO2 is 10-14%, the temperature is -60 to -55°C, and the pressure is 0.2-0.22 MPa(G).

[0123] In some embodiments of the present invention, preferably, the first semi-lean methanol and the second nitrogen are subjected to the second gas stripping to obtain the second tail gas and the low-carbon methanol; more preferably, the molar content of H2S in the second tail gas is 0.1-0.5ppm, the molar content of CO2 is 86-92%; the temperature is -50 to -40°C, the pressure is 0.12-0.14MPa(G), and it is sent to the subsequent process.

[0124] In some embodiments of the present invention, preferably, the molar content of H2S in the low-carbon methanol is 0.1-0.5 ppm, the molar content of CO2 is 4-6%, and the temperature is -56 to -52°C;

[0125] In some embodiments of the present invention, preferably, the first semi-lean methanol stream is subjected to a third heat exchange to a temperature of -45 to -42°C before the second gas stripping is performed.

[0126] The present invention will be described in detail below through embodiments.

[0127] In this invention, unless otherwise specified, both the non-shift gas and the syngas originate from the pulverized coal gasification unit.

[0128] Example 1

[0129] Devices such as Figure 1 As shown, the apparatus includes: a non-shift gas scrubbing tower T-1, an absorption tower T-2, a primary medium-pressure flash tower T-3, a secondary medium-pressure flash tower T-4, a reabsorption tower T-5, and a low-carbon methanol stripping tower T-6; a first cooler E-1, a second cooler E-2, a third cooler E-3, a fourth cooler E-4, a fifth cooler E-5, a sixth cooler E-6, and a seventh cooler E-7; a first pump P-1, a second pump P-2; and a first heat exchanger Q-1, a second heat exchanger Q-2, and a third heat exchanger Q-3.

[0130] The method is carried out in the above-described apparatus and includes:

[0131] Non-shift gas 1 (H2S molar content 0.4-0.6%, CO2 molar content 5-10%; temperature -35 to -25℃, pressure 3.5-3.6 MPa(G)) and a second non-shift H2S-rich methanol 2-ii are contacted at a molar flow ratio of 52-62:1 for the first purification, resulting in pre-purified non-shift H2S-rich methanol 4 (H2S molar content 0.8-1.2%, CO2 molar content 3-6%; temperature -35 to -25℃) and pre-desulfurized non-shift gas. The above pre-desulfurized non-shift gas is then contacted with a second non-shift CO2-rich methanol 8-ii for the second purification, resulting in non-shift H2S-rich methanol. 2 (H2S molar content 0.5-0.9%, CO2 molar content 3-7%; temperature -32 to -28℃; pressure 3.49-3.59MPa(G)) and desulfurized non-shift gas; the above desulfurized non-shift gas is contacted with the first lean methanol 3-i and subjected to third purification to obtain non-shift CO2-rich methanol 8 (H2S molar content 0.5-1ppm, CO2 molar content 3-8%; temperature -40 to -33℃) and purified non-shift gas 5 (H2S molar content ≤0.1ppm, CO2 molar content ≤20ppm; temperature -55 to -45℃, pressure 3.4-3.5MPa(G));

[0132] Among them, the above-mentioned non-conversion H2S-rich methanol 2 is divided into two streams, and the molar flow ratio of the first stream of non-conversion H2S-rich methanol 2-i and the second stream of non-conversion H2S-rich methanol 2-ii is 37-42:1.

[0133] Among them, the above-mentioned non-conversion CO2-rich methanol 8 is divided into the first non-conversion CO2-rich methanol 8-i, the second non-conversion CO2-rich methanol 8-ii, the a-strand non-conversion CO2-rich methanol 8-iii-a and the b-strand non-conversion CO2-rich methanol 8-iii-b with a molar flow ratio of 20-23:27-30:5-7:1.

[0134] The molar flow ratio of the second non-conversion CO2-rich methanol 8-ii and the non-conversion gas 1 is 1:1-2; the molar flow ratio of the first lean methanol 3-i and the non-conversion gas 1 is 1.5-2.5:1-2.

[0135] The above-mentioned synthesis gas 6 (H2S molar content 0.3-0.35%, CO2 molar content 40-50%; temperature -25 to -15℃, pressure 3.1-3.2 MPa(G)) and the first secondary H2S-rich methanol 11-i are contacted at a molar flow ratio of 47-57:1 for primary H2S absorption, yielding pre-desulfurized gas and primary H2S-rich methanol 7 (H2S molar content 0.6-0.8%, CO2 molar content 30-36%; temperature - The pre-desulfurized gas, low-sulfur CO2-rich methanol 21 (after first pressurization to 3.6-4 MPa(G)), first non-conversion CO2-rich methanol 8-i, and first primary CO2-rich methanol 9-i (after first cooling to -46 to -43°C) are contacted and subjected to secondary H2S absorption to obtain desulfurized gas and secondary H2S-rich methanol 11 (H2S molar content is 0.4-0.6%, CO2 molar content is 27-31%; temperature is -20 to -14°C).

[0136] The above-mentioned desulfurized gas and secondary CO2-rich methanol 10 (after a second cooling to -36 to -33°C) are subjected to primary CO2 absorption to obtain primary CO2-rich methanol 9 (H2S molar content of 0.1-0.5ppm, CO2 molar content of 18-23%, temperature of -20 to -15°C, pressure of 3.05-3.15MPa(G)) and pre-purified gas; the above-mentioned pre-purified gas, low-carbon methanol 29 (after a second pressurization to 3.6-4MPa(G)) and a second stream of lean methanol 3-ii are subjected to secondary CO2 absorption to obtain secondary CO2-rich methanol 10 and purified gas 14 (H2S molar content ≤0.1ppm, CO2 molar content ≤20ppm; temperature of -55 to -50°C, pressure of 3-3.1MPa(G));

[0137] The molar flow ratio of low-sulfur CO2-rich methanol 21 to syngas 6 is 1:26-30; the molar flow ratio of the first non-conversion CO2-rich methanol 8-i to syngas 6 is 1:8-10; the molar flow ratio of the first primary CO2-rich methanol 9-i to syngas 6 is 3-5:8-10; the molar flow ratio of syngas 6 to secondary CO2-rich methanol 10 is 1:1-2; the molar flow ratio of the above-mentioned purified gas 14 to low-carbon methanol 29 is 1-1.2:1; and the molar flow ratio of purified gas 14 to the second lean methanol 3-ii is 1:1.5-1.7.

[0138] Specifically, the above-mentioned secondary H2S-rich methanol 11 is divided into a first secondary H2S-rich methanol 11-i and a second secondary H2S-rich methanol 11-ii with a molar flow ratio of 1:32-36; the above-mentioned primary CO2-rich methanol 9 is divided into a first primary CO2-rich methanol 9-i and a second primary CO2-rich methanol 9-ii with a molar flow ratio of 1:2-4.

[0139] The second primary CO2-rich methanol 9-ii was subjected to primary CO2 flash evaporation (pressure 1.5-1.8 MPa(G)) to obtain primary CO2 flash vapor 15 (H2S molar content 0.1-0.5 ppm, CO2 molar content 17.5-22.5%; temperature -20.5 to -15.5℃) and primary CO2 flash liquid 12; the primary CO2 flash liquid 12 was subjected to secondary CO2 flash evaporation (pressure 0.8-1 MPa(G)) to obtain secondary CO2 flash vapor and secondary CO2 flash liquid 20 (H2S molar content 0.1-0.5 ppm, CO2 molar content 17-22%; temperature -22 to -16℃);

[0140] The second secondary H2S-rich methanol 11-ii was subjected to primary H2S flash evaporation (pressure 1.5-1.8 MPa(G)) to obtain primary H2S flash vapor and primary H2S flash liquid 17 (H2S molar content 0.35-0.55%, CO2 molar content 23.5-28.5%; temperature -20.5 to -16.5℃); the primary H2S flash liquid 17 was subjected to secondary H2S flash evaporation (pressure 0.8-1 MPa(G)) to obtain secondary H2S flash vapor and secondary H2S flash liquid 23 (H2S molar content 0.35-0.55%, CO2 molar content 23-28%; temperature -25 to -21℃).

[0141] Specifically, the above-mentioned non-conversion CO2-rich methanol 8-iii-a, primary CO2 flash vapor 15, and primary H2S flash vapor are subjected to a first wash to obtain primary flash vapor 16 (H2S molar content of 1-5 ppm, CO2 molar content of 32-36%, CO molar content of 5-9%, H2 molar content of 56-60%; temperature of -32 to -22℃, pressure of 1.5-1.8 MPa(G)) and the above-mentioned low-sulfur CO2-rich methanol 21 (H2S molar content of 0.04-0.08%, CO2 molar content of 18-25%, temperature of -20 to -13℃, pressure of 1.5-1.8 MPa(G)).

[0142] Specifically, the above-mentioned non-conversion CO2-rich methanol 8-iii-b and secondary CO2 flash vapor are subjected to a second wash to obtain washed secondary CO2 flash vapor 18 (CO2 molar content 85-90%, CO molar content 4-7%, H2 molar content 4-8%, temperature -25 to -15℃, pressure 0.8-1MPa(G)), and the second wash liquid is mixed into the secondary CO2 flash liquid 20; the above-mentioned first non-conversion H2S-rich methanol 2-i and secondary H2S flash vapor are subjected to a third wash to obtain washed secondary H2S flash vapor 19 (H2S... The content of methanol is 0.6-1%, the molar content of CO2 is 20-25%, the molar content of CO is 68-72%, and the molar content of H2 is 3-7%); and the washed non-conversion H2S-rich methanol 32 (H2S molar content is 0.5-0.8%, CO2 molar content is 13-18%; temperature is -12 to -8℃); wherein, the above-mentioned third non-conversion CO2-rich methanol 8-iii is cooled to -53 to -47℃ and then divided into the a-strand non-conversion CO2-rich methanol 8-iii-a and the b-strand non-conversion CO2-rich methanol 8-iii-b;

[0143] After the above-mentioned secondary CO2 flash liquid 20 is cooled to -36 to -33°C in the fourth stage, it is divided into a first secondary CO2 flash liquid 20-i and a second secondary CO2 flash liquid 20-ii with a molar flow ratio of 3-5:1. After the first secondary CO2 flash liquid 20-i is cooled to -40 to -38°C in the fifth stage, it undergoes a first flash evaporation to obtain a semi-lean methanol 13 (H2S molar content of 0.1-0.5ppm; CO2 molar content of 11-16%, temperature of -58 to -53°C; pressure of 0.05-0.08MPa(G)) and a first CO2 product gas. After the second secondary CO2 flash liquid 20-ii is cooled to -52 to -50°C in the sixth stage, it undergoes a second flash evaporation to obtain a flash liquid and a second CO2 product gas.

[0144] The above-mentioned secondary H2S flash liquid 23 (cooled to -55 to -52°C after a seventh cooling) is subjected to a third flash evaporation to obtain the first H2S-rich methanol 24 (H2S molar content of 0.3-0.7%, CO2 molar content of 11.5-17.5%; temperature of -64 to -59°C; pressure of 0.13-0.17 MPa(G)) and a sulfur-containing gas phase; wherein, the flash liquid and the sulfur-containing gas phase are contacted to obtain low-sulfur methanol 22 (H2S molar content of 0.1-0.25%, CO2 molar content of 11.5-17.5%). The first, second, and third CO2 product gases are mixed to obtain CO2 product gas 30 (H2S molar content ≤1ppm, CO2 molar content 99.4-99.7%; temperature -65 to -55℃, pressure 0.05-0.08MPa(G)).

[0145] Among them, the above-mentioned semi-lean methanol 13 is divided into a first semi-lean methanol 13-i and a second semi-lean methanol 13-ii with a molar flow ratio of 1-2:1;

[0146] The low-sulfur methanol 22, the first H2S-rich methanol 24 (first heat exchange at -40 to -36°C), the second H2S-rich methanol 25 (second heat exchange at -40 to -36°C), the washed non-conversion H2S-rich methanol 32, and the first nitrogen stream 28-i were each independently subjected to a first gas stripping process to obtain stripped gas and stripped H2S-rich methanol 26 (H2S molar content 0.2-0.5%, CO2 molar content 2-3%; temperature -65 to -55°C, pressure 0.22-0.24 MPa(G)).

[0147] The second semi-lean methanol 13-ii and stripping gas were subjected to a fourth wash to obtain the first tail gas 31 (H2S molar content ≤1ppm, CO2 molar content 68-72%; temperature -63 to -58℃, pressure 0.16-0.18MPa(G)) and the second H2S-rich methanol 25 (H2S molar content 0.2-0.5%, CO2 molar content 10-14%; temperature -60 to -55℃, pressure 0.2-0.22MPa(G)).

[0148] The first semi-lean methanol 13-i (after a third heat exchange to -45 to -42°C) and the second nitrogen 28-ii are subjected to a second gas stripping to obtain a second tail gas 27 (H2S molar content of 0.1-0.5ppm, CO2 molar content of 86-92%; temperature of -50 to -40°C, pressure of 0.12-0.14MPa(G)) and the low-carbon methanol 29 (H2S molar content of 0.1-0.5ppm, CO2 molar content of 4-6%; temperature of -56 to -52°C, pressure of 0.15-0.25MPa(G)).

[0149] Comparative Example 1

[0150] Taking a hydrogen production unit using pulverized coal gasification as an example, the effective gas (H2+CO) entering the low-temperature methanol washing unit is 161,000 Nm³. 3 / h, the main technical parameters of the process are compared with those of the lean-semi-lean process (i.e., a low-temperature methanol washing process disclosed in CN201110260570.0) under this benchmark, as shown in Table 1.

[0151] Table 1

[0152]

[0153] As can be seen from the results in Table 1, taking the hydrogen production unit based on pulverized coal gasification as an example, the polygeneration syngas purification method of the pulverized coal gasification unit provided in Example 1 has a lean methanol circulation rate of 84.6% of that in Comparative Example 1 (lean liquid-semi-lean liquid process), a semi-lean / low-carbon methanol circulation rate of 66.7% of that in Comparative Example 1 (lean liquid-semi-lean liquid process), and a CO2-rich methanol usage in the H2S absorption tower of 80% of that in Comparative Example 1 (lean liquid-semi-lean liquid process). This results in a cumulative reduction of 1300 KW / h in external cooling energy consumption, demonstrating a significant overall energy-saving effect.

[0154] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A polygeneration syngas purification device supporting a pulverized coal gasification device, characterized in that, The apparatus includes: a non-shift gas scrubbing tower (T-1), an absorption tower (T-2), a primary medium-pressure flash evaporator (T-3), a secondary medium-pressure flash evaporator (T-4), a reabsorption tower (T-5), and a low-carbon methanol stripping tower (T-6) connected together; The non-shift gas scrubbing tower (T-1) is divided into a first purification section, a second purification section, and a third purification section from bottom to top. These sections are used to sequentially purify the non-shift gas (1) to obtain pre-purified non-shift H2S-rich methanol (4), non-shift H2S-rich methanol (2) split into two streams, non-shift CO2-rich methanol (8) split into three streams, and purified non-shift gas (5). The absorption tower (T-2) is divided into a first H2S absorption section, a second H2S absorption section, a first CO2 absorption section, and a second CO2 absorption section from bottom to top. These sections are used to sequentially purify the syngas (6) to obtain first-stage H2S-rich methanol (7), second-stage H2S-rich methanol (11) split into two streams, first-stage CO2-rich methanol (9) split into two streams, second-stage CO2-rich methanol (10), and purified gas (14). The first-stage medium-pressure flash tower (T-3) is divided into a first-stage CO2 flash section and a first-stage H2S flash section from top to bottom; the second-stage medium-pressure flash tower (T-4) is divided into a second-stage CO2 flash section and a second-stage H2S flash section from top to bottom; the first-stage CO2 flash section is connected to the second-stage CO2 flash section and is used to perform two-stage CO2 flash evaporation on the second stream of first-stage CO2-rich methanol (9-ii) to obtain first-stage CO2 flash vapor (15), second-stage CO2 flash vapor and second-stage CO2 flash liquid (20) in two streams; the first-stage H2S flash section is connected to the second-stage H2S flash section and is used to perform two-stage H2S flash evaporation on the second stream of second-stage H2S-rich methanol (11-ii) to obtain first-stage H2S flash vapor, second-stage H2S flash vapor and second-stage H2S flash liquid (23); Specifically, the first non-conversion CO2-rich methanol (8-i) and the second non-conversion CO2-rich methanol (8-ii) are sent to the second H2S absorption section and the second purification section, respectively. The third non-conversion CO2-rich methanol (8-iii) is divided into a non-conversion CO2-rich methanol (8-iii-a) and b non-conversion CO2-rich methanol (8-iii-b), which are sent to the upper part of the first-stage H2S flash evaporation section and the upper part of the second-stage CO2 flash evaporation section for the first and second washing, respectively. The first non-conversion H2S-rich methanol (2-i) and the second non-conversion H2S-rich methanol (2-ii) are sent to the upper part of the second-stage H2S flash evaporation section and the first purification section, respectively, for the third washing and the first purification, respectively. The upper section of the reabsorption tower (T-5) is divided into a first flash section, a second flash section, and a third flash section from top to bottom. These sections are used to flash the first secondary CO2 flash liquid (20-i), the second secondary CO2 flash liquid (20-ii), and the secondary H2S flash liquid (23) through the first, second, and third flashes, respectively, to obtain semi-lean methanol (13) in two streams, low-sulfur methanol (22), first H2S-rich methanol (24), and CO2 product gas (30). The lower section of the reabsorption tower (T-5) is divided into a washing section and a stripping section from top to bottom. The stripping section connects to the second flash section. The upper parts of the third flash section, the washing section, and the secondary H2S flash section are used to perform the first gas stripping on the low-sulfur methanol (22), the first H2S-rich methanol (24), the second H2S-rich methanol (25), and the washed non-conversion H2S-rich methanol (32), respectively. The stripped gas is sent to the washing section and washed with the second semi-lean methanol (13-ii) for the fourth washing to obtain the second H2S-rich methanol (25). The low-carbon methanol stripping tower (T-6) is used to perform the second gas stripping on the first semi-lean methanol (13-i), and the low-carbon methanol (29) is returned to the second CO2 absorption section.

2. The apparatus according to claim 1, wherein, In the non-shift gas scrubbing tower (T-1), The first purification section is connected to the bottom of the second purification section and is used to perform the first purification on the non-conversion gas (1) and the second stream of non-conversion H2S-rich methanol (2-ii) to obtain pre-purified non-conversion H2S-rich methanol (4) and pre-desulfurized non-conversion gas; the second purification section is connected to the bottom of the third purification section and is used to perform the second purification on the pre-desulfurized non-conversion gas and the second stream of non-conversion CO2-rich methanol (8-ii) to obtain the non-conversion H2S-rich methanol (2) and desulfurized non-conversion gas; the third purification section is used to perform the third purification on the desulfurized non-conversion gas and the first stream of lean methanol (3-i) to obtain the non-conversion CO2-rich methanol (8) and purified non-conversion gas (5); In the absorption tower (T-2), The first H2S absorption section is connected to the bottom of the second H2S absorption section and is used to absorb the syngas (6) and the first stream of secondary H2S-rich methanol (11-i) through the first-stage H2S absorption to obtain the primary H2S-rich methanol (7) and pre-desulfurized gas; the second H2S absorption section is connected to the upper part of the primary H2S flash section, the third purification section and the bottom of the first CO2 absorption section, and is used to absorb the pre-desulfurized gas, low-sulfur CO2-rich methanol (21), the first stream of non-conversion CO2-rich methanol (8-i) and the first stream of primary CO2-rich methanol (9-i) through the secondary H2S absorption. S absorption yields desulfurized gas and the secondary H2S-rich methanol (11); the first CO2 absorption section is connected to the bottom of the second CO2 absorption section and is used to perform the first-stage CO2 absorption on the desulfurized gas and the secondary CO2-rich methanol (10) to obtain the primary CO2-rich methanol (9) and pre-purified gas; the second CO2 absorption section is connected to the low-carbon methanol stripping tower (T-6) and is used to perform the secondary CO2 absorption on the pre-purified gas, low-carbon methanol (29) and the second stream of lean methanol (3-ii) to obtain the secondary CO2-rich methanol (10) and purified gas (14); Preferably, a first pump (P-1) is installed on the pipeline connecting the upper part of the first-stage H2S flash section and the second H2S absorption section, according to the material flow direction; Preferably, a first cooler (E-1) is installed on the pipe connecting the second H2S absorption section and the first CO2 absorption section according to the material flow direction; Preferably, a second cooler (E-2) is installed on the pipe connecting the first CO2 absorption section and the second CO2 absorption section, according to the material flow direction.

3. The apparatus according to claim 1 or 2, wherein, In the first-stage medium-pressure flash evaporator (T-3), The first-stage CO2 flash evaporation section is connected to the first-stage CO2 absorption section and is used to perform first-stage CO2 flash evaporation on the second-stage CO2-rich methanol (9-ii). The resulting first-stage CO2 flash vapor (15) is sent to the upper part of the first-stage H2S flash evaporation section via a pipeline, and the resulting first-stage CO2 flash liquid (12) is sent to the second-stage CO2 flash evaporation section via a pipeline. The lower part of the first-stage H2S flash evaporation section is connected to the second H2S absorption section, which is used to perform first-stage H2S flash evaporation on the second stream of secondary H2S-rich methanol (11-ii). The resulting first-stage H2S flash vapor is sent to the upper part of the first-stage H2S flash evaporation section through the riser hole, and the resulting first-stage H2S flash liquid (17) is sent to the lower part of the secondary H2S flash evaporation section through the pipeline. The upper part of the first-stage H2S flash evaporation section is connected to the third purification section, which is used to perform the first washing on a stream of non-conversion CO2-rich methanol (8-iii-a), first-stage CO2 flash vapor (15) and first-stage H2S flash vapor to obtain first-stage flash vapor (16) and the low-sulfur CO2-rich methanol (21). Preferably, in the secondary medium-pressure flash evaporator (T-4), The secondary CO2 flash evaporation section is used to perform secondary CO2 flash evaporation on the primary CO2 flash liquid (12) to obtain the secondary CO2 flash liquid (20), and the obtained secondary CO2 flash vapor is subjected to a second wash with b strands of non-conversion rich CO2 methanol (8-iii-b) to obtain washed secondary CO2 flash vapor (18), and the second wash liquid is mixed into the secondary CO2 flash liquid (20); the lower part of the secondary H2S flash evaporation section is used to perform secondary H2S flash evaporation on the primary H2S flash liquid (17) to obtain the secondary H2S flash liquid (23), and the obtained secondary H2S flash vapor is sent to the upper part of the secondary H2S flash evaporation section through the riser hole to perform the third wash with the first strand of non-conversion rich H2S methanol (2-i) to obtain washed secondary H2S flash vapor (19) and washed non-conversion rich H2S methanol (32); Preferably, a third cooler (E-3) is provided on the pipe connecting the upper part of the first-stage H2S flash evaporation section and the second-stage CO2 flash evaporation section of the third purification section.

4. The apparatus according to any one of claims 1-3, wherein, In the upper column of the reabsorption tower (T-5), The first flash evaporation section is used to perform the first flash evaporation on the first secondary CO2 flash liquid (20-i) to obtain semi-lean methanol (13) and the first CO2 product gas; the second flash evaporation section is used to perform the second flash evaporation on the second secondary CO2 flash liquid (20-ii) to obtain flash liquid and the second CO2 product gas; the third flash evaporation section is used to perform the third flash evaporation on the secondary H2S flash liquid (23) to obtain the first H2S-rich methanol (24), and the sulfur-containing gas phase is contacted with the flash liquid through the riser hole to obtain low-sulfur methanol (22) and the third CO2 product gas; wherein the CO2 product gas (30) includes the first CO2 product gas, the second CO2 product gas and the third CO2 product gas; Preferably, a fourth cooler (E-4) is provided on the pipe connecting the secondary CO2 flash section, the first flash section and the second flash section; more preferably, a fifth cooler (E-5) is provided on the pipe connecting the fourth cooler (E-4) and the first flash section, and a sixth cooler (E-6) is provided on the pipe connecting the fourth cooler (E-4) and the second flash section. Preferably, a seventh cooler (E-7) is installed on the pipe connecting the secondary H2S flash section and the third flash section; Preferably, in the lower column of the reabsorption tower (T-5), The gas stripping section is used to independently perform the first gas stripping on the low-sulfur methanol (22), the first H2S-rich methanol (24), the second H2S-rich methanol (25), the washed non-conversion H2S-rich methanol (32), and the first stream of nitrogen (28-i) to obtain stripped gas and stripped H2S-rich methanol (26); the washing section is used to perform the fourth washing on the second stream of semi-lean methanol (13-ii) and the stripped gas to obtain the first tail gas (31) and the second H2S-rich methanol (25); Preferably, the low-carbon methanol stripping tower (T-6) is used to perform a second stripping of the first semi-lean methanol (13-i) and the second nitrogen (28-ii) to obtain a second tail gas (27) and the low-carbon methanol (29); Preferably, a first heat exchanger (Q-1) is installed on the pipeline connecting the third flash section and the stripping section; Preferably, a second heat exchanger (Q-2) is installed on the pipe connecting the washing section and the air-lift section; Preferably, a third heat exchanger (Q-3) is installed on the pipeline connecting the first flash section and the low-carbon methanol stripping tower (T-6); Preferably, a second pump (P-2) is installed on the pipeline connecting the low-carbon methanol stripping tower (T-6) and the second CO2 absorption section.

5. A method for purifying syngas from a multi-product coal gasification unit, characterized in that, The method includes: The non-conversion gas (1) is subjected to first purification, second purification and third purification in sequence to obtain pre-purified non-conversion H2S rich methanol (4), non-conversion H2S rich methanol (2) split into two streams, non-conversion CO2 rich methanol (8) split into three streams and purified non-conversion gas (5). Syngas (6) is subjected to first-stage H2S absorption, second-stage H2S absorption, first-stage CO2 absorption and second-stage CO2 absorption in sequence to obtain first-stage H2S-rich methanol (7), second-stage H2S-rich methanol (11) split into two streams, first-stage CO2-rich methanol (9) split into two streams, second-stage CO2-rich methanol (10) and purified gas (14). The second primary CO2-rich methanol (9-ii) is subjected to two-stage CO2 flash evaporation to obtain primary CO2 flash vapor (15), secondary CO2 flash vapor and secondary CO2 flash liquid (20) in two streams; the second secondary H2S-rich methanol (11-ii) is subjected to two-stage H2S flash evaporation to obtain primary H2S flash vapor, secondary H2S flash vapor and secondary H2S flash liquid (23); Specifically, the first non-conversion CO2-rich methanol (8-i) and the second non-conversion CO2-rich methanol (8-ii) are returned to the secondary H2S absorption and secondary purification processes, respectively. The third non-conversion CO2-rich methanol (8-iii) is divided into a non-conversion CO2-rich methanol (8-iii-a) and b non-conversion CO2-rich methanol (8-iii-b). The a non-conversion CO2-rich methanol (8-iii-a) is subjected to a first wash with the primary CO2 flash vapor (15) and the primary H2S flash vapor, respectively. The b non-conversion CO2-rich methanol (8-iii-b) is subjected to a second wash with the secondary CO2 flash vapor. The first non-conversion H2S-rich methanol (2-i) is subjected to a third wash with the secondary H2S flash vapor, and the second non-conversion H2S-rich methanol (2-ii) is returned to the first purification process. The first secondary CO2 flash liquid (20-i), the second secondary CO2 flash liquid (20-ii), and the secondary H2S flash liquid (23) are subjected to first flash evaporation, second flash evaporation, and third flash evaporation, respectively, to obtain semi-lean methanol (13) which is divided into two streams, low-sulfur methanol (22), first H2S-rich methanol (24), and CO2 product gas (30); wherein, the low-sulfur methanol (22), the first H2S-rich methanol (24), the second H2S-rich methanol (25), and the washed non-conversion-rich H2S methanol (32) are subjected to first gas stripping, and the obtained stripped gas is subjected to fourth washing with the second semi-lean methanol (13-ii) to obtain the second H2S-rich methanol (25); the first semi-lean methanol (13-i) is subjected to second gas stripping, and the obtained low-carbon methanol (29) is returned to the secondary CO2 absorption.

6. The method according to claim 5, wherein, The non-shift gas (1) originates from a pulverized coal gasification unit; wherein, the molar content of H2S in the non-shift gas (1) is 0.4-0.6%, the molar content of CO2 is 5-10%, the temperature is -35 to -25℃, and the pressure is 3.5-3.6 MPa(G); Preferably, the non-conversion gas (1) and the second non-conversion H2S-rich methanol (2-ii) are subjected to the first purification to obtain pre-purified non-conversion H2S-rich methanol (4) and pre-desulfurized non-conversion gas; the pre-desulfurized non-conversion gas and the second non-conversion CO2-rich methanol (8-ii) are subjected to the second purification to obtain the non-conversion H2S-rich methanol (2) and desulfurized non-conversion gas; the desulfurized non-conversion gas and the first lean methanol (3-i) are subjected to the third purification to obtain the non-conversion CO2-rich methanol (8) and purified non-conversion gas (5); Preferably, the non-conversion H2S-rich methanol (2) has a molar content of 0.5-0.9% for H2S and a molar content of 3-7% for CO2; a temperature of -32 to -28°C; and a pressure of 3.49-3.59 MPa(G). Preferably, the molar flow ratio of the first non-conversion H2S-rich methanol (2-i) and the second non-conversion H2S-rich methanol (2-ii) is 37-42:1; Preferably, the non-conversion CO2-rich methanol (8) has a molar content of H2S of 0.5-1 ppm and a molar content of CO2 of 3-8%; and a temperature of -40 to -33°C. Preferably, the molar flow ratio of the first non-conversion CO2-rich methanol (8-i), the second non-conversion CO2-rich methanol (8-ii), the a-strand non-conversion CO2-rich methanol (8-iii-a), and the b-strand non-conversion CO2-rich methanol (8-iii-b) is 20-23:27-30:5-7:1; Preferably, the molar content of H2S in the purified non-conversion gas (5) is ≤0.1ppm, the molar content of CO2 is ≤20ppm, the temperature is -55 to -45℃, and the pressure is 3.4-3.5MPa(G).

7. The method according to claim 5 or 6, wherein, The syngas (6) originates from a pulverized coal gasification unit. The syngas (6) contains 0.3-0.35% H2S and 40-50% CO2. The temperature is -25 to -15°C and the pressure is 3.1-3.2 MPa(G). Preferably, the synthesis gas (6) and the first secondary H2S-rich methanol (11-i) are subjected to the primary H2S absorption to obtain the primary H2S-rich methanol (7) and pre-desulfurized gas; the pre-desulfurized gas, low-sulfur CO2-rich methanol (21), the first non-conversion CO2-rich methanol (8-i) and the first primary CO2-rich methanol (9-i) are subjected to the secondary H2S absorption to obtain desulfurized gas and the secondary H2S-rich methanol (11); the desulfurized gas and the secondary CO2-rich methanol (10) are subjected to the primary CO2 absorption to obtain the primary CO2-rich methanol (9) and pre-purified gas; The pre-purified gas, low-carbon methanol (29), and second lean methanol (3-ii) are subjected to the secondary CO2 absorption to obtain the secondary CO2-rich methanol (10) and purified gas (14). Preferably, the molar content of H2S in the secondary H2S-rich methanol (11) is 0.4-0.6%, the molar content of CO2 is 27-31%, and the temperature is -20 to -16°C. Preferably, the molar flow ratio of the first secondary H2S-rich methanol (11-i) to the second secondary H2S-rich methanol (11-ii) is 1:32-36; Preferably, the low-sulfur, CO2-rich methanol (21) is pressurized to 3.6-4 MPa (G) before the secondary H2S absorption is performed; Preferably, the molar content of H2S in the first-grade CO2-rich methanol (9) is 0.1-0.5 ppm, the molar content of CO2 is 18-23%, the temperature is -20 to -15℃, and the pressure is 3.05-3.15 MPa (G); Preferably, the molar flow ratio of the first primary CO2-rich methanol (9-i) and the second primary CO2-rich methanol (9-ii) is 1:2-4; Preferably, the first primary CO2-rich methanol (9-i) is cooled to -46 to -43°C before the secondary H2S absorption is performed; Preferably, the secondary CO2-rich methanol (10) is subjected to a second cooling to -36 to -33°C before the primary CO2 absorption is performed; Preferably, the low-carbon methanol (29) is pressurized to 3.6-4 MPa (G) before the secondary CO2 absorption is performed; Preferably, the purified gas (14) has a molar content of H2S ≤0.1ppm and a molar content of CO2 ≤20ppm; the temperature is -55 to -50℃ and the pressure is 3-3.1MPa(G).

8. The method according to any one of claims 5-7, wherein, The two-stage CO2 flash evaporation includes a first-stage CO2 flash evaporation and a second-stage CO2 flash evaporation; The second primary CO2-rich methanol (9-ii) is subjected to primary CO2 flash evaporation to obtain primary CO2 flash vapor (15) and primary CO2 flash liquid (12); the primary CO2 flash liquid (12) is subjected to secondary CO2 flash evaporation to obtain secondary CO2 flash vapor and secondary CO2 flash liquid (20). Preferably, the pressure of the first-stage CO2 flash evaporation is 1.5-1.8 MPa(G), and the pressure of the second-stage CO2 flash evaporation is 0.8-1 MPa(G); Preferably, the molar content of H2S in the secondary CO2 flash liquid (20) is 0.1-0.5 ppm, the molar content of CO2 is 17-22%, and the temperature is -22 to -16°C; Preferably, the molar flow ratio of the first secondary CO2 flash liquid (20-i) and the second secondary CO2 flash liquid (20-ii) is 3-5:1; Preferably, the two-stage H2S flash evaporation includes a first-stage H2S flash evaporation and a second-stage H2S flash evaporation; The second secondary H2S-rich methanol (11-ii) is subjected to primary H2S flash evaporation to obtain primary H2S flash vapor and primary H2S flash liquid (17); the primary H2S flash liquid (17) is subjected to secondary H2S flash evaporation to obtain secondary H2S flash vapor and secondary H2S flash liquid (23). Preferably, the pressure of the first-stage H2S flash evaporation is 1.5-1.8 MPa(G), and the pressure of the second-stage H2S flash evaporation is 0.8-1 MPa(G). Preferably, the molar content of H2S in the secondary H2S flash liquid (23) is 0.35-0.55%, the molar content of CO2 is 23-28%, and the temperature is -25 to -21℃.

9. The method according to any one of claims 5-8, wherein, The first washing process includes: subjecting the a-strand non-conversion CO2-rich methanol (8-iii-a), primary CO2 flash vapor (15) and primary H2S flash vapor to the first washing to obtain primary flash vapor (16) and the low-sulfur CO2-rich methanol (21); Preferably, the low-sulfur, CO2-rich methanol (21) has a molar content of H2S of 0.04-0.08%, a molar content of CO2 of 18-25%, a temperature of -20 to -13°C, and a pressure of 1.5-1.8 MPa (G). Preferably, the second washing process includes: subjecting b strands of non-conversion CO2-rich methanol (8-iii-b) and secondary CO2 flash vapor to the second washing to obtain washed secondary CO2 flash vapor (18), and mixing the second washing liquid into the secondary CO2 flash vapor liquid (20); Preferably, the third washing process includes: subjecting the first non-conversion H2S-rich methanol (2-i) and the secondary H2S flash vapor to the third washing to obtain washed secondary H2S flash vapor (19) and washed non-conversion H2S-rich methanol (32); More preferably, the molar content of H2S in the washed non-conversion H2S-rich methanol (32) is 0.5-0.8%, and the molar content of CO2 is 13-18%; the temperature is -12 to -8℃. Preferably, the third non-conversion CO2-rich methanol (8-iii) is cooled to -53 to -47°C and then divided into the a-strand non-conversion CO2-rich methanol (8-iii-a) and the b-strand non-conversion CO2-rich methanol (8-iii-b).

10. The method according to any one of claims 5-9, wherein, The secondary CO2 flash liquid (20) is cooled to -36 to -33°C in the fourth stage and divided into the first secondary CO2 flash liquid (20-i) and the second secondary CO2 flash liquid (20-ii); More preferably, the first secondary CO2 flash evaporator (20-i) is cooled to -40 to -38°C in a fifth cooling process before the first flash evaporation is performed; the second secondary CO2 flash evaporator (20-ii) is cooled to -52 to -50°C in a sixth cooling process before the second flash evaporation is performed. Preferably, the secondary H2S flash liquid (23) is cooled to -55 to -52°C in the seventh stage before the third flash evaporation is performed; Preferably, the semi-lean methanol (13) has a molar content of H2S of 0.1-0.5 ppm, a molar content of CO2 of 11-16%, a temperature of -58 to -53°C, and a pressure of 0.05-0.08 MPa(G). Preferably, the molar flow ratio of the first semi-lean methanol (13-i) and the second semi-lean methanol (13-ii) is 1-2:1; Preferably, the low-sulfur methanol (22) has a molar content of H2S of 0.1-0.25% and a molar content of CO2 of 15-19%; the temperature is -60 to -50°C and the pressure is 0.12-0.16 MPa(G); Preferably, the first H2S-rich methanol (24) has a molar content of H2S of 0.3-0.7% and a molar content of CO2 of 11.5-17.5%; a temperature of -64 to -59°C; and a pressure of 0.13-0.17 MPa(G). Preferably, the molar content of H2S in the CO2 product gas (30) is ≤1ppm, the molar content of CO2 is 99.4-99.7%; the temperature is -65 to -55℃, and the pressure is 0.05-0.08MPa(G); Preferably, the low-sulfur methanol (22), the first H2S-rich methanol (24), the second H2S-rich methanol (25), the washed non-conversion H2S-rich methanol (32), and the first nitrogen gas (28-i) are each subjected to a first gas stripping independently to obtain stripped gas and stripped H2S-rich methanol (26). Preferably, the first H2S-rich methanol (24) is subjected to a first heat exchange to a temperature of -40 to -36°C before the first gas stripping is performed; the second H2S-rich methanol (25) is subjected to a second heat exchange to a temperature of -40 to -36°C before the first gas stripping is performed. Preferably, the second semi-lean methanol (13-ii) and stripping gas are subjected to the fourth washing to obtain the first tail gas (31) and the second H2S-rich methanol (25); Preferably, the molar content of H2S in the second H2S-rich methanol (25) is 0.2-0.5%, the molar content of CO2 is 10-14%, the temperature is -60 to -55°C, and the pressure is 0.2-0.22 MPa(G); Preferably, the first semi-lean methanol (13-i) and the second nitrogen (28-ii) are subjected to the second gas stripping to obtain the second tail gas (27) and the low-carbon methanol (29); Preferably, the low-carbon methanol (29) has a molar content of H2S of 0.1-0.5 ppm and a molar content of CO2 of 4-6%; the temperature is -56 to -52°C and the pressure is 0.15-0.25 MPa(G); Preferably, the first semi-lean methanol (13-i) is subjected to a third heat exchange to a temperature of -45 to -42°C before the second gas stripping is performed.

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