Medium-pressure flash evaporation and reabsorption process matched with pulverized coal gasification device

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to a medium-pressure flash evaporation and reabsorption method matched with a pulverized coal gasification device and the medium-pressure flash evaporation and reabsorption device matched with the pulverized coal gasification device. According to the method, a two-stage medium-pressure flash evaporation process is optimally arranged, and a washing solvent is reasonably used; by optimizing the flow of the re-absorption tower, low H2S methanol is generated, and meanwhile, the low H2S methanol is reutilized; the gas stripping process is optimized, so that the CO2 content in the semi-barren solution methanol is further reduced, the CO2 absorption capacity of the semi-barren solution methanol is improved, and the low-temperature methanol washing device has the characteristic of low comprehensive energy consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-temperature methanol washing, in particular to a medium-pressure flash evaporation and reabsorption method matched with a pulverized coal gasification device and a medium-pressure flash evaporation and reabsorption device matched with the pulverized coal gasification device. BACKGROUND

[0002] The low-temperature methanol washing technology is to remove H2S and CO2 and other acid gases in the synthesis gas by using the large solubility of the low-temperature methanol to the acid gases, and to remove HCN and NH3 and other trace components. In the low-temperature methanol washing process, the medium-pressure flash evaporation process is to flash evaporate and recover the effective gas in the CO2-rich methanol and the H2S-rich methanol sent from the upstream. At the same time, in order to reduce the total amount of CO2 gas in the flash evaporation gas and reduce the compression power consumption of the flash evaporation gas, it is necessary to optimize the flash evaporation pressure and to wash and absorb the CO2 gas in the flash evaporation gas. Therefore, the selection of the methanol for washing the flash evaporation gas is particularly crucial, which needs to ensure the washing and absorption effect of the flash evaporation gas and to avoid the adverse effects of the washing liquid on the downstream system.

[0003] CN201110260570.0 discloses a low-temperature methanol washing process. First, the CO2 gas flashed out of the upper tower of the medium-pressure flash evaporation tower is sent to the lower tower to be washed and absorbed by using the H2S-rich methanol, and the washing solution is not selected reasonably. The rich liquid after washing cannot be used twice, which is not conducive to reducing the comprehensive energy consumption of the low-temperature methanol washing device. Second, in the CO2 flash evaporation section of the reabsorption tower, the CO2-rich methanol is directly mixed with the H2S-rich methanol while washing the H2S-rich methanol flash evaporation gas, and the CO2-rich methanol is polluted by the H2S-rich methanol. The low-concentration H2S methanol produced is not fully used, and the energy consumption is high. Third, the semi-lean liquid methanol containing a high carbon content in the CO2 absorption tower has a weak absorption capacity for CO2 gas, and the circulation amount of the semi-lean liquid is large, which is not conducive to reducing the comprehensive energy consumption of the low-temperature methanol washing device as a whole. SUMMARY

[0004] The present application aims to overcome the above technical problems, and provides a medium-pressure flash evaporation and reabsorption method matched with a pulverized coal gasification device and a medium-pressure flash evaporation and reabsorption device matched with the pulverized coal gasification device. The method optimizes the two-stage medium-pressure flash evaporation process and reasonably uses the washing solvent. The method optimizes the reabsorption tower process to generate low-H2S methanol and to use the low-H2S methanol twice. The method optimizes the gas stripping process to further reduce the CO2 content in the semi-lean liquid methanol, to improve the CO2 absorption capacity of the semi-lean liquid methanol, and to have the characteristics of low comprehensive energy consumption of the low-temperature methanol washing device.

[0005] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a medium-pressure flash evaporation and reabsorption method matched with a pulverized coal gasification device, which comprises the following steps:

[0006] The CO2-rich methanol from the CO2 absorption process of the synthesis gas is sequentially subjected to first CO2 flashing, second CO2 flashing to obtain three streams of first CO2 flashing gas, second CO2 flashing gas and second CO2 flashing liquid; the first H2S-rich methanol from the H2S absorption process of the synthesis gas is sequentially subjected to first H2S flashing, second H2S flashing to obtain first H2S flashing gas, second H2S flashing gas and second H2S flashing liquid;

[0007] The second stream of second CO2 flashing liquid, the third stream of second CO2 flashing liquid and the second H2S flashing liquid are sequentially subjected to first flashing, second flashing and third flashing to obtain semi-lean liquid methanol, low H2S methanol and second H2S-rich methanol;

[0008] The semi-lean liquid methanol is subjected to first gas stripping to obtain two streams of low carbon methanol, and the first stream of low carbon methanol is sequentially subjected to first washing with the first CO2 flashing gas, the second CO2 flashing gas and the second H2S flashing gas to obtain low-sulfur carbon-rich methanol; the non-shift H2S-rich methanol from the non-shift gas purification process is subjected to second washing with the first H2S flashing gas, and the washed H2S-rich methanol is subjected to the second H2S flashing;

[0009] The low-sulfur carbon-rich methanol, the low H2S methanol, the second H2S-rich methanol and the washed carbon-rich methanol are subjected to second gas stripping to obtain gas stripping gas and gas-stripped H2S-rich methanol; the washed carbon-rich methanol is obtained by fourth flashing of the first stream of second CO2 flashing liquid, and the flashed CO2-rich methanol is subjected to third washing with the gas stripping gas.

[0010] The second aspect of the present application provides a medium-pressure flashing and reabsorption device matched with a pulverized coal gasification device, and the method provided in the first aspect is carried out in the device; the device comprises: a first medium-pressure flashing tower, a second medium-pressure flashing tower and a reabsorption tower connected in sequence, and a flashing tower and a low-carbon methanol gas stripping tower;

[0011] The first medium-pressure flashing tower is divided into a first CO2 washing section, a first CO2 flashing section, a first H2S washing section and a first H2S flashing section from top to bottom, and the first CO2 washing section and the first CO2 flashing section are connected by a pipeline, and the first H2S washing section and the first H2S flashing section are connected by a pipeline;

[0012] The second medium-pressure flashing tower is divided into a second CO2 washing section, a second CO2 flashing section, a second H2S washing section and a second H2S flashing section from top to bottom, and the second CO2 washing section and the second CO2 flashing section are communicated by a riser, and the second H2S washing section and the second H2S flashing section are communicated by a riser;

[0013] The reabsorption tower is divided into an upper tower and a lower tower, the upper tower is divided into a first flash evaporation section, a second flash evaporation section and a third flash evaporation section from top to bottom and communicated by riser holes, and the lower tower is divided into a washing section and a gas stripping section from top to bottom and communicated by riser holes;

[0014] The first CO2 flash evaporation section and the second CO2 flash evaporation section are connected by a pipeline, and the second CO2 flash evaporation section, the flash evaporation tower, the first flash evaporation section and the second flash evaporation section are connected by a pipeline; the first H2S flash evaporation section, the first H2S washing section and the second H2S flash evaporation section are connected by a pipeline, and the second H2S flash evaporation section and the third flash evaporation section are connected by a pipeline; the first CO2 washing section, the second CO2 washing section and the second H2S washing section are connected by a pipeline;

[0015] The flash evaporation tower and the washing section are connected by a pipeline; the second H2S washing section, the second flash evaporation section, the third flash evaporation section and the washing section are each independently connected with the gas stripping section by a pipeline;

[0016] The low-carbon methanol gas stripping tower is connected with the first flash evaporation section and the first CO2 washing section by a pipeline.

[0017] The application provides a medium-pressure flash evaporation and reabsorption method and device matched with a pulverized coal gasification device, and has the following advantages:

[0018] (1) The application adopts a four-stage tail gas washing technology, and selectively sets four groups of methanol with different H2S contents, i.e., second H2S-rich methanol, low-sulfur carbon-rich methanol, low-H2S methanol and CO2-rich methanol after flash evaporation, which are sequentially washed from high to low, so that the least CO2-rich methanol after flash evaporation is used under the premise that the second tail gas emission meets the standard, thereby reducing the heat regeneration energy consumption of the entire low-temperature methanol washing;

[0019] (2) The application adopts a two-stage medium-pressure flash evaporation technology, the first stage adopts a higher flash evaporation pressure, and the effective gas flashed out can be directly sent to the second stage of the compressor in the compression process, thereby reducing the power consumption of the compressor; the second stage adopts a lower flash evaporation pressure, so that the effective gas in the first CO2 flash evaporation liquid and the mixed H2S-rich methanol is fully recovered, and the gas cylinder inlet gas amount of the first stage of the compressor in the compression process is reduced, and the power consumption of the compressor is correspondingly reduced;

[0020] (3) The present application optimizes the two-stage medium-pressure flash process, and in the process of the first CO2 flash and the second CO2 flash, low-carbon methanol is introduced to absorb the first CO2 flash gas and the second CO2 flash gas; compared with the prior art, the CO2 component in the first CO2 flash gas and the second CO2 flash gas is reduced at the same time without being polluted by H2S-rich methanol; at the same time, the second H2S flash gas is subjected to cascade washing to obtain low-sulfur carbon-rich methanol, the H2S-rich methanol and the CO2-rich methanol are separately flashed and classified washed, a prerequisite for secondary utilization of the low-carbon methanol is created, and the device energy consumption is reduced;

[0021] (4) The present application optimizes the reabsorption process, realizes the absorption of the third second CO2 flash liquid to the second H2S flash liquid to produce a sulfur-containing gas, and obtains low-H2S methanol for second tail gas washing, but the low-H2S methanol is not mixed with the second H2S-rich methanol after flashing;

[0022] (5) In the method provided by the present application, in order to further reduce the CO2 content in the semi-lean liquid methanol and maximize the CO2 absorption capacity of the semi-lean liquid, the optimized reabsorption process is used to perform nitrogen stripping on the semi-lean liquid methanol again, so that the CO2 content in the semi-lean liquid methanol is further reduced to 3-7%, and low-carbon methanol is obtained, which can produce two positive effects: first, with the increase of the absorption capacity of the low-carbon methanol and the decrease of the circulation amount, the pump operation cost can be reduced by 15%; second, the low-carbon methanol can replace part of the lean methanol, so that the circulation amount of the lean methanol in the CO2 absorption tower is also reduced, the reduction of the lean methanol flow will be transmitted to the CO2-rich methanol, and the flow of the rich methanol that needs to be heat regenerated will also be reduced, and the energy consumption of the heat regeneration system will also be reduced accordingly. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The present application provides a medium-pressure flash and reabsorption device for a complete pulverized coal gasification device.

[0024] BRIEF DESCRIPTION OF DRAWINGS

[0025] T-1, first-stage medium-pressure flash tower; T-2, second-stage medium-pressure flash tower; T-3, reabsorption tower; T-4, flash tower; T-5, 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; Q-1, first heat exchanger; Q-2, second heat exchanger; P, pump;

[0027] 1. CO2-rich methanol; 2. first CO2 flash liquid; 3. first CO2 flash gas; 4. first flash gas; 4-i. first CO2 flash gas after washing; 4-ii. first H2S flash gas after washing; 5. first CO2 wash liquid; 6. second CO2 flash liquid; 6-i. first stream of second CO2 flash liquid; 6-ii. second stream of second CO2 flash liquid; 6-iii. third stream of second CO2 flash liquid; 7. second CO2 wash liquid; 8. second flash gas; 8-i. second CO2 flash gas after washing; 8-ii. second H2S flash gas after washing; 9. first H2S-rich methanol; 10. first H2S flash liquid; 11. first H2S flash gas; 12. non-shift H2S-rich methanol; 13. washed H2S-rich methanol; 14. mixed H2S-rich methanol; 15. second H2S flash liquid; 16. low-sulfur carbon-rich methanol; 17. semi-lean liquid methanol; 18. low-H2S methanol; 19. second H2S-rich methanol; 20. nitrogen; 20-i. first stream of nitrogen; 20-ii. second stream of nitrogen; 21. stripped H2S-rich methanol; 22. washed carbon-rich methanol; 23. flashed CO2-rich methanol; 24. second CO2 product gas; 25. first CO2 product gas; 26. second tail gas; 27. first tail gas; 28. low-carbon methanol; 28-i. first stream of low-carbon methanol; 28-ii. second stream of low-carbon methanol. DETAILED DESCRIPTION

[0028] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are provided as approximate descriptions of the ranges and are understood to be open-ended. Each range is a continuous range including each and every value subsumed therein. For ranges comprising values of a parameter, the endpoints of the ranges are included in the ranges. The endpoints of the ranges and any values are not to be construed as limiting the range or value. The ranges and values are understood to be approximate.

[0029] In the present disclosure, "first", "second", "third", "fourth" and "fifth" do not indicate any order or limitation on the materials or steps, but are used to distinguish the materials or steps from each other, unless otherwise specified. For example, "first CO2 flash" and "second CO2 flash" are used to distinguish the two CO2 flashes from each other, and similarly, "first heat exchange" and "second heat exchange" are used to distinguish the two heat exchanges from each other.

[0030] In the present application, the "top" of the container refers to the 0-10% height from the top down of the container; the "upper part" of the container refers to the 10-40% height from the top down of the container; the "middle part" of the container refers to the 40-60% height from the top down of the container; the "lower part" of the container refers to the 60-90% height from the top down of the container; and the "bottom" of the container refers to the 90-100% height from the top down of the container.

[0031] The present application provides a medium-pressure flash evaporation and reabsorption method for a complete pulverized coal gasification device, which comprises the following steps:

[0032] The CO2-rich methanol from the CO2 absorption process of the synthesis gas is sequentially subjected to first CO2 flash evaporation and second CO2 flash evaporation to obtain three streams of first CO2 flash evaporation gas, second CO2 flash evaporation gas and second CO2 flash evaporation liquid; and the first H2S-rich methanol from the H2S absorption process of the synthesis gas is sequentially subjected to first H2S flash evaporation and second H2S flash evaporation to obtain first H2S flash evaporation gas, second H2S flash evaporation gas and second H2S flash evaporation liquid.

[0033] The second CO2 flash evaporation liquid, the third CO2 flash evaporation liquid and the second H2S flash evaporation liquid are sequentially subjected to first flash evaporation, second flash evaporation and third flash evaporation to obtain semi-lean liquid methanol, low-H2S methanol and second H2S-rich methanol.

[0034] The semi-lean liquid methanol is subjected to first gas stripping to obtain two streams of low-carbon methanol, and the first stream of low-carbon methanol is sequentially subjected to first washing with the first CO2 flash evaporation gas, the second CO2 flash evaporation gas and the second H2S flash evaporation gas to obtain low-sulfur carbon-rich methanol; the non-shift H2S-rich methanol from the non-shift gas purification process is subjected to second washing with the first H2S flash evaporation gas, and the washed H2S-rich methanol is subjected to the second H2S flash evaporation.

[0035] The low-sulfur carbon-rich methanol, the low-H2S methanol, the second H2S-rich methanol and the washed carbon-rich methanol are subjected to second gas stripping to obtain gas stripping gas and gas-stripped H2S-rich methanol; and the washed carbon-rich methanol is obtained by subjecting the first stream of second CO2 flash evaporation liquid to fourth flash evaporation, and the flash-evaporated CO2-rich methanol is subjected to third washing with the gas stripping gas.

[0036] In the present application, the H2S absorption process of the synthesis gas refers to the H2S absorption of the synthesis gas, and the CO2 absorption process of the synthesis gas refers to the CO2 absorption of the synthesis gas.

[0037] In the present application, the synthesis gas H2S absorption process aims to remove HCN, NH3, H2S and a small amount of CO2 from the synthesis gas. Preferably, the synthesis gas H2S absorption process comprises: absorbing H2S from the synthesis gas to obtain the first H2S-rich methanol and desulfurized gas.

[0038] In some embodiments of the present application, preferably, the H2S content in the first H2S-rich methanol is 0.35-0.55%, the CO2 content is 23-30%, and the temperature is -20 to -14℃.

[0039] In some embodiments of the present application, the synthesis gas comprises, but is not limited to, the synthesis gas cooling process of the pulverized coal gasification device. Preferably, the H2S content in the synthesis gas is 0.3-0.35%, the CO2 content is 40-50%, the temperature is -25 to -15℃, and the pressure is 3.12-3.15 MPa (G).

[0040] In some embodiments of the present application, preferably, the H2S content in the desulfurized gas is 0.5-1 ppm, the CO2 content is 34-38%, the temperature is -30 to -20℃, and the pressure is 3.05-3.1 MPa (G).

[0041] In the present application, the synthesis gas CO2 absorption process aims to remove CO2 from the synthesis gas, i.e., remove CO2 from the desulfurized gas. Preferably, the synthesis gas CO2 absorption process comprises: absorbing CO2 from the desulfurized gas to obtain CO2-rich methanol and purified gas.

[0042] In some embodiments of the present application, preferably, the H2S content in the CO2-rich methanol is 0.1-0.5 ppm, the CO2 content is 16-21%, the temperature is -22 to -17℃, and the pressure is 3.05-3.09 MPa (G).

[0043] In some embodiments of the present application, preferably, the H2S content in the purified gas is <0.1 ppm, the CO2 content is <20 ppm, the temperature is -55 to -50℃, and the pressure is 3-3.05 MPa (G).

[0044] In some embodiments of the present application, preferably, the non-shift gas purification process comprises: purifying the non-shift gas and lean methanol to obtain the non-shift H2S-rich methanol and purified non-shift gas. In the present application, unless otherwise specified, the H2S content in the lean methanol is 0%, and the CO2 content is 0%.

[0045] In some embodiments of the present application, preferably, the non-converted H2S-rich methanol has a H2S molar content of 0.1-0.6%, a CO2 molar content of 3-7%, a temperature of -36 to -31℃, and a pressure of 3.5-3.55 MPa (G).

[0046] In the present application, the non-converted gas refers to, but is not limited to, the non-converted gas cooling process in the upstream, in particular, the non-converted gas cooling process in the pulverized coal gasification device. Preferably, the non-converted gas has a H2S molar content of 0.4-0.6%, a CO2 molar content of 5-10%, a temperature of -35 to -25℃, and a pressure of 3.5-3.6 MPa (G); preferably, the purified non-converted gas has a H2S molar content of ≤0.1 ppm and a CO2 molar content of ≤20 ppm.

[0047] In the present application, the first and second CO2 flashings are intended to remove the CO2 effective gas in the CO2-rich methanol; and the first and second H2S flashings are intended to remove the H2S effective gas in the first H2S-rich methanol.

[0048] In some embodiments of the present application, preferably, the first CO2 flashing is performed at a pressure greater than that of the second CO2 flashing; and the first H2S flashing is performed at a pressure greater than that of the second H2S flashing; further preferably, the first CO2 flashing and the first H2S flashing are each independently performed at a pressure of 1.5-1.8 MPa (G); and the second CO2 flashing and the second H2S flashing are each independently performed at a pressure of 0.8-1 MPa (G).

[0049] In some embodiments of the present application, preferably, the CO2-rich methanol is subjected to the first CO2 flashing to obtain the first CO2 flashing gas and the first CO2 flashing liquid; and the first CO2 flashing liquid is subjected to the second CO2 flashing to obtain the second CO2 flashing gas and the second CO2 flashing liquid.

[0050] In some embodiments of the present application, preferably, the first CO2 flashing liquid has a H2S molar content of 0.1-0.5 ppm, a CO2 molar content of 15.5-20.5%, and a temperature of -22 to -18℃.

[0051] In some embodiments of the present application, preferably, the second CO2 flashing liquid has a H2S molar content of 0.1-0.5 ppm, a CO2 molar content of 15-20%, and a temperature of -36.5 to -33.5℃.

[0052] In the present application, the second CO2 flash liquid is divided into three streams. Preferably, the molar flow ratio of the first stream of the second CO2 flash liquid, the second stream of the second CO2 flash liquid and the third stream of the second CO2 flash liquid is 1-2:1-3:1.

[0053] In some embodiments of the present application, further preferably, the first CO2 flash liquid is cooled to -36 to -33°C before the second CO2 flash.

[0054] In some embodiments of the present application, preferably, the first H2S flash is performed on the first H2S-rich methanol to obtain the first H2S flash gas and the first H2S flash liquid; the first H2S flash liquid and the H2S-rich methanol after washing are mixed to obtain the mixed H2S-rich methanol, and the second H2S flash is performed on the mixed H2S-rich methanol to obtain the second H2S flash gas and the second H2S flash liquid.

[0055] In some embodiments of the present application, further preferably, the molar content of H2S in the first H2S flash liquid is 0.4-0.5%, the molar content of CO2 is 24-28%, and the temperature is -20 to -15°C.

[0056] In some embodiments of the present application, further preferably, the molar content of H2S in the H2S-rich methanol after washing is 0.2-0.5%, the molar content of CO2 is 11-16%, and the temperature is -18 to -15°C.

[0057] In some embodiments of the present application, further preferably, the molar content of H2S in the mixed H2S-rich methanol is 0.3-0.5%, the molar content of CO2 is 22-28%, and the temperature is -20 to -15°C.

[0058] In the present application, compared with directly performing the second H2S flash on the first H2S flash liquid, the present application performs the second H2S flash on the mixed H2S-rich methanol obtained by mixing the first H2S flash liquid and the H2S-rich methanol after washing, which optimizes the heat exchange efficiency of the cooler and reduces the investment cost of the heat exchange equipment.

[0059] In some embodiments of the present application, further preferably, the molar content of H2S in the second H2S flash liquid is 0.25-0.55%, the molar content of CO2 is 18-22%, and the temperature is -36.5 to -33.5°C.

[0060] In some embodiments of the present application, more preferably, the mixed H2S-rich methanol is cooled to -36 to -33°C before the second H2S flash.

[0061] In some embodiments of the present application, preferably, the second stream of the second CO2 flash liquid is subjected to the first flash to obtain the semi-lean liquid methanol and a first stream of CO2 product gas; the third stream of the second CO2 flash liquid is subjected to the second flash to obtain a flash liquid and a second stream of CO2 product gas; the second H2S flash liquid is subjected to the third flash to obtain a sulfur-containing gas and the second H2S-rich methanol; wherein the flash liquid and the sulfur-containing gas are subjected to a fourth washing to obtain the low-H2S methanol, and the third stream of CO2 product gas obtained is mixed with the first stream of CO2 product gas and the second stream of CO2 product gas to obtain a first CO2 product gas.

[0062] In some embodiments of the present application, preferably, the second stream of the second CO2 flash liquid is subjected to a third cooling to -36 to -33°C before the first flash.

[0063] In some embodiments of the present application, preferably, the third stream of the second CO2 flash liquid is subjected to a fourth cooling to -52 to -48°C before the first flash.

[0064] In some embodiments of the present application, preferably, the first flash is carried out at a pressure of 0.05-0.08 MPa (G), the second flash is carried out at a pressure of 0.06-0.09 MPa (G), and the third flash is carried out at a pressure of 0.12-0.16 MPa (G).

[0065] In some embodiments of the present application, preferably, the semi-lean liquid methanol has a molar content of H2S of 0.1-0.5 ppm, a molar content of CO2 of 9-13%, and a temperature of -56 to -51°C.

[0066] In some embodiments of the present application, preferably, the low-H2S methanol has a molar content of H2S of 0.1-0.4%, a molar content of CO2 of 15-19%, and a temperature of -60 to -50°C.

[0067] In some embodiments of the present application, preferably, the second H2S-rich methanol has a molar content of H2S of 0.2-0.5%, a molar content of CO2 of 14-17%, and a pressure of 0.13-0.17 MPa (G).

[0068] In some embodiments of the present application, preferably, the first CO2 product gas has a molar content of H2S of ≤1 ppm, a molar content of CO2 of 99.4-99.7%, a temperature of -60 to -50°C, and a pressure of 0.05-0.08 MPa (G).

[0069] In some embodiments of the present application, preferably, the first stripping process comprises: contacting the semi-lean methanol with a first nitrogen gas stream and performing the first stripping to obtain the low-carbon methanol and a first tail gas.

[0070] In some embodiments of the present application, preferably, the low-carbon methanol has a H2S molar content of 0.1-0.5 ppm and a CO2 molar content of 3-7%, a temperature of -70 to -66℃, and a pressure of 0.15-0.2 MPa (G).

[0071] In the present application, the low-carbon methanol is divided into two streams, a first stream is returned and subjected to the first washing, and a second stream is returned to the synthesis gas CO2 absorption process. Preferably, the molar flow ratio of the first low-carbon methanol stream to the second low-carbon methanol stream is 1:33-37, for example, 1:33, 1:35, 1:37, and any value within the range of any two values.

[0072] In some embodiments of the present application, preferably, the second low-carbon methanol stream is returned to the synthesis gas CO2 absorption process.

[0073] In some embodiments of the present application, preferably, the first tail gas has a H2S molar content of 0.1-0.5 ppm and a CO2 molar content of 62-66%, a temperature of -62 to -57℃, and a pressure of 0.12-0.14 MPa (G). In the present application, the first tail gas is sent to a subsequent process.

[0074] In some embodiments of the present application, preferably, the low-carbon methanol is divided into the first low-carbon methanol stream and the second low-carbon methanol stream after being pressurized to 1.8-2 MPa (G).

[0075] In the present application, the first low-carbon methanol stream is sequentially subjected to the first washing with a first CO2 flash gas, a second CO2 flash gas, and a second H2S flash gas to obtain the low-sulfur carbon-rich methanol. Preferably, the first washing process comprises: performing a first washing of the first low-carbon methanol stream with a first CO2 flash gas to obtain a first CO2 flash gas after washing and a first CO2 washing liquid; performing a second washing of the first CO2 washing liquid with a second CO2 flash gas to obtain a second CO2 flash gas after washing and a second CO2 washing liquid; and performing a third washing of the second CO2 washing liquid with a second H2S flash gas to obtain the low-sulfur carbon-rich methanol and a second H2S flash gas after washing.

[0076] In some embodiments of the present application, preferably, the low-sulfur carbon-rich methanol has a H2S molar content of 50-60 ppm, a CO2 molar content of 18-22%, and a temperature of -32 to -24℃.

[0077] In some embodiments of the present application, it is further preferred that the temperature of the first CO2 flash gas after the first washing is -35 to -25℃, and the pressure is 1.5-1.8 MPa (G); the molar content of H2S in the first CO2 washing liquid is ≤0.1 ppm, and the molar content of CO2 is 19-23%; and the temperature is -28 to -22℃.

[0078] In some embodiments of the present application, it is further preferred that the temperature of the second CO2 flash gas after the second washing is -30 to -20℃, and the pressure is 0.8-1 MPa (G); the molar content of H2S in the second CO2 washing liquid is ≤0.1 ppm, and the molar content of CO2 is 18-22%; and the temperature is -30 to -25℃.

[0079] In some embodiments of the present application, it is further preferred that the temperature of the second H2S flash gas after the second washing is -30 to -24℃, and the pressure is 0.8-1 MPa (G).

[0080] In some embodiments of the present application, it is preferred that the process of the second washing comprises: subjecting the non-shifted H2S-rich methanol and the first H2S flash gas to the second washing to obtain washed H2S-rich methanol and first H2S flash gas after the first washing; and it is further preferred that the temperature of the first H2S flash gas after the first washing is -30 to -24℃, and the pressure is 0.8-1 MPa (G).

[0081] In some embodiments of the present application, it is further preferred that the first H2S flash gas after the first washing and the first H2S flash gas after the first washing are mixed to obtain a first flash gas, in which the molar content of H2 is 60-65%, the molar content of CO is 6-11%, and the molar content of CO2 is 25-30%; the temperature is -35 to -30℃, and the pressure is 1.5-1.8 MPa (G).

[0082] In some embodiments of the present application, it is further preferred that the second H2S flash gas after the second washing and the second H2S flash gas after the second washing are mixed to obtain a second flash gas, in which the molar content of H2 is 30-34%, the molar content of CO is 1-4%, and the molar content of CO2 is 63-67%; the temperature is -28 to -24℃, and the pressure is 0.5-0.8 MPa (G).

[0083] In some embodiments of the present application, it is preferred that the process of the second stripping comprises: sequentially contacting the second H2S-rich methanol, the washed carbon-rich methanol, the low-sulfur carbon-rich methanol, and the low-H2S methanol with a second nitrogen gas and subjecting them to the second stripping to obtain the stripping gas and the H2S-rich methanol after the stripping.

[0084] In some embodiments of the present application, it is further preferred that the H2S-rich methanol after the stripping has a H2S molar content of 0.2-0.4%, a CO2 molar content of 1-4%, a temperature of -50 to -44℃, and a pressure of 0.22-0.24 MPa (G). In the present application, the H2S-rich methanol after the stripping is sent to a subsequent process.

[0085] In some embodiments of the present application, it is further preferred that the second H2S-rich methanol is subjected to the second stripping after being cooled to -36 to -33℃ by the first heat exchange.

[0086] In some embodiments of the present application, it is preferred that the fourth flash has a pressure of 0.2-0.5 MPa (G).

[0087] In some embodiments of the present application, it is further preferred that the CO2-rich methanol after the flashing has a H2S molar content of 0.1-0.5 ppm, a CO2 molar content of 14.5-19.5%, and a temperature of -40 to -35℃.

[0088] In some embodiments of the present application, it is further preferred that the fourth flashing further obtains a second CO2 product gas having a H2S molar content of ≤1 ppm, a CO2 molar content of 92-95%, a temperature of -40 to -35℃, and a pressure of 0.2-0.5 MPa (G).

[0089] In some embodiments of the present application, it is further preferred that the CO2-rich methanol after the flashing is cooled to -52 to -48℃ by the fifth cooling before being subjected to the third washing.

[0090] In some embodiments of the present application, it is preferred that the third washing process comprises: after the CO2-rich methanol after the flashing is cooled by the fifth cooling, contacting the CO2-rich methanol with the stripping gas and performing the third washing to obtain the carbon-rich methanol after the washing and a second tail gas.

[0091] In some embodiments of the present application, it is further preferred that the carbon-rich methanol after the washing has a H2S molar content of 0.1-0.5%, a CO2 molar content of 15-19%, a temperature of -57 to -53℃, and a pressure of 0.2-0.22 MPa (G).

[0092] In some embodiments of the present application, it is further preferred that the carbon-rich methanol after the washing is subjected to the second stripping after being cooled to -36 to -33℃ by the second heat exchange.

[0093] In some embodiments of the present invention, further preferably, the molar content of H2S in the second tail gas is ≤1 ppm, and the molar content of CO2 is 72 - 77%; the temperature is -63 to -58 °C, and the pressure is 0.16 - 0.18 MPa(G).

[0094] The second aspect of the present invention provides a structural schematic diagram of a medium-pressure flash and reabsorption device for supporting a pulverized coal gasification device as Figure 1 shown, from Figure 1 which it can be seen that the method provided in the first aspect is carried out in this device. The device includes a first-stage medium-pressure flash tower T-1, a second-stage medium-pressure flash tower T-2, and a reabsorption tower T-3 connected in sequence, as well as a flash tower T-4 and a low-carbon methanol stripper T-5;

[0095] The first-stage medium-pressure flash tower T-1 is divided into a first CO2 washing section, a first CO2 flash section, a first H2S washing section, and a first H2S flash section from top to bottom. The first CO2 washing section and the first CO2 flash section are connected by a pipeline, and the first H2S washing section and the first H2S flash section are connected by a pipeline;

[0096] The second-stage medium-pressure flash tower T-2 is divided into a second CO2 washing section, a second CO2 flash section, a second H2S washing section, and a second H2S flash section from top to bottom. The second CO2 washing section and the second CO2 flash section are connected by a riser hole, and the second H2S washing section and the second H2S flash section are connected by a riser hole;

[0097] The reabsorption tower T-3 is divided into an upper tower and a lower tower. The upper tower is divided into a first flash section, a second flash section, and a third flash section connected by riser holes from top to bottom. The lower tower is divided into a washing section and a stripping section connected by riser holes from top to bottom;

[0098] Among them, the first CO2 flash section and the second CO2 flash section are connected by a pipeline, and the second CO2 flash section, the flash tower T-4, the first flash section, and the second flash section are connected by a pipeline; the first H2S flash section, the first H2S washing section, and the second H2S flash section are connected by a pipeline, and the second H2S flash section and the third flash section are connected by a pipeline; the first CO2 washing section, the second CO2 washing section, and the second H2S washing section are connected by a pipeline;

[0099] Among them, the flash tower T-4 and the washing section are connected by a pipeline; the second H2S washing section, the second flash section, the third flash section, and the washing section are each independently connected to the stripping section by a pipeline;

[0100] Among them, the low-carbon methanol stripper T-5 is connected to the first flash section and the first CO2 washing section by a pipeline.

[0101] In the present invention, as Figure 1As shown, preferably, in the primary medium pressure flash tower T-1,

[0102] The first CO2 flash section is used for first CO2 flash of the CO2-rich methanol 1 from the synthesis gas CO2 absorption process, to obtain a first CO2 flash gas 3 and a first CO2 flash liquid 2;

[0103] The first CO2 washing section is used for first washing of the first CO2 flash gas 3 and a first low-carbon methanol 28-i, to obtain a first washed CO2 flash gas 4-i and a first CO2 washing liquid 5;

[0104] The first H2S flash section is used for first H2S flash of the first H2S-rich methanol 9 from the synthesis gas H2S absorption process, to obtain a first H2S flash gas 11 and a first H2S flash liquid 10;

[0105] The first H2S washing section is used for second washing of the non-shift H2S-rich methanol 12 from the non-shift gas purification process with the first H2S flash gas 11, to obtain a washed H2S-rich methanol 13 and a first washed H2S flash gas 4-ii.

[0106] In the present application, as shown, Figure 1 As shown, preferably, in the secondary medium pressure flash tower T-2,

[0107] The second CO2 flash section is used for second CO2 flash of the first CO2 flash liquid 2, to obtain a second CO2 flash gas and a second CO2 flash liquid 6 in three streams;

[0108] The second CO2 washing section is used for second washing of the second CO2 flash gas and the first CO2 washing liquid 5, to obtain a second washed CO2 flash gas 8-i and a second CO2 washing liquid 7;

[0109] The second H2S flash section is used for mixing the first H2S flash liquid 10 and the washed H2S-rich methanol 13, and second H2S flash of the obtained mixed H2S-rich methanol 14, to obtain a second H2S flash gas and a second H2S flash liquid 15;

[0110] The second H2S washing section is used for third washing of the second CO2 washing liquid 7 and the second H2S flash gas 11, to obtain a low-sulfur carbon-rich methanol 16 and a second washed H2S flash gas 8-ii.

[0111] In the present application, as shown, Figure 1As shown, preferably, in the upper tower of the reabsorption tower T-3, the first flash section is used for first flashing the second second CO2 flash liquid 6-ii to obtain the semi-lean liquid methanol 17 and the first CO2 product gas; the second flash section is used for second flashing the third second CO2 flash liquid 6-iii to obtain the flash liquid and the second CO2 product gas; the third flash section is used for third flashing the second H2S flash liquid 15 to obtain the sulfur-containing gas and the second H2S-rich methanol 19; wherein the flash liquid and the sulfur-containing gas are subjected to fourth washing to obtain the low-H2S methanol 18, and the third CO2 product gas obtained is mixed with the first CO2 product gas and the second CO2 product gas to obtain the first CO2 product gas 25.

[0112] In the present application, as shown in Figure 1 As shown, preferably, the low-carbon methanol stripping tower T-5 is used for first stripping the semi-lean liquid methanol 17 and the first nitrogen gas 20-i to obtain the first tail gas 27 and the low-carbon methanol 28 in two streams.

[0113] In the present application, as shown in Figure 1 As shown, preferably, the flash tower T-4 is used for fourth flashing the first second CO2 flash liquid 6-i to obtain the second CO2 product gas 24 and the CO2-rich methanol after flashing 23.

[0114] In the present application, as shown in Figure 1 As shown, preferably, in the lower tower of the reabsorption tower T-3, the washing section is used for third washing the CO2-rich methanol after flashing 23 and the stripping gas to obtain the carbon-rich methanol after washing 22 and the second tail gas 26; the stripping section is used for sequentially contacting the second H2S-rich methanol 19, the carbon-rich methanol after washing 22, the low-sulfur carbon-rich methanol 16, and the low-H2S methanol 18 with the second nitrogen gas 20-ii and performing second stripping to obtain the stripping gas and the H2S-rich methanol after stripping 21.

[0115] In the present application, as shown in Figure 1 As shown, preferably, the device further comprises a first cooler E-1 arranged on a pipeline connecting the first CO2 flash section and the second CO2 flash section, which is used for performing the second CO2 flashing after first cooling the first CO2 flash liquid 2.

[0116] In the present application, as shown in Figure 1 As shown, preferably, the device further comprises a second cooler E-2 arranged on a pipeline connecting the first H2S flash section, the first H2S washing section, and the second H2S flash section, which is used for performing the second H2S flashing after second cooling the mixed H2S-rich methanol 14 obtained by mixing the first H2S flash liquid 10 and the H2S-rich methanol after washing 13.

[0117] In the present application, as shown in Figure 1 Preferably, the device further comprises a third cooler E-3 arranged on the pipeline connecting the second CO2 flash section and the first flash section, for performing the first flash after the third cooling of the second CO2 flash liquid 6-ii.

[0118] In the present application, as shown in Figure 1 Preferably, the device further comprises a fourth cooler E-4 arranged on the pipeline connecting the second CO2 flash section and the second flash section, for performing the second flash after the fourth cooling of the third CO2 flash liquid 6-iii.

[0119] In the present application, as shown in Figure 1 Preferably, the device further comprises a fifth cooler E-5 arranged on the pipeline connecting the flash tower T-4 and the washing section, for performing the third washing after the fifth cooling of the flash CO2-rich methanol 23.

[0120] In the present application, as shown in Figure 1 Preferably, the device further comprises a first heat exchanger Q-1 arranged on the pipeline connecting the third flash section and the stripping section, for performing the second stripping after the first heat exchange of the second H2S-rich methanol 19.

[0121] In the present application, as shown in Figure 1 Preferably, the device further comprises a second heat exchanger Q-2 arranged on the pipeline connecting the washing section and the stripping section, for performing the second stripping after the second heat exchange of the washed carbon-rich methanol 22.

[0122] In the present application, as shown in Figure 1 Preferably, the device further comprises a pump P arranged on the pipeline connecting the low-carbon methanol stripping tower T-5 and the first CO2 washing section, for pressurizing the low-carbon methanol 28 into a first low-carbon methanol 28-i and a second low-carbon methanol 28-ii, and returning the first low-carbon methanol 28-i to perform the primary washing.

[0123] The present application will be described in detail below through examples.

[0124] Example 1

[0125] As shown in Figure 1 The device comprises a primary medium-pressure flash tower T-1, a secondary medium-pressure flash tower T-2, and a reabsorption tower T-3 connected in sequence, as well as a flash tower T-4 and a low-carbon methanol stripping tower T-5.

[0126] The first medium-pressure flash tower T-1 is divided into a first CO2 washing section, a first CO2 flash section, a first H2S washing section and a first H2S flash section from top to bottom; the second medium-pressure flash tower T-2 is divided into a second CO2 washing section, a second CO2 flash section, a second H2S washing section and a second H2S flash section from top to bottom;

[0127] The CO2-rich methanol 1 (the molar content of H2S is 0.35-0.55%, the molar content of CO2 is 23-30%, and the temperature is -20 to -14°C) from the synthesis gas CO2 absorption process is sent to the first CO2 flash section to perform the first CO2 flash (the pressure is 1.5-1.8 MPa(G)), to obtain the first CO2 flash gas 3 which is sent to the first CO2 washing section through a pipeline, and the first CO2 flash liquid 2 (the molar content of H2S is 0.1-0.5 ppm, the molar content of CO2 is 15.5-20.5%, and the temperature is -22 to -18°C) which is sent to the second CO2 flash section to perform the second flash (the pressure is 0.8-1 MPa(G)) through a first cooler E-1 (the temperature is -36 to -33°C) and a pipeline, the second CO2 flash gas is sent to the second CO2 washing section through a riser, and the second CO2 flash liquid 6 (the molar content of H2S is 0.1-0.5 ppm, the molar content of CO2 is 15-20%, and the temperature is -36.5 to -33.5°C) is divided into the first second CO2 flash liquid 6-i, the second second CO2 flash liquid 6-ii and the third second CO2 flash liquid 6-iii with a molar flow ratio of 1-2:1-3:1;

[0128] The first H2S-rich methanol 9 (the molar content of H2S is 0.35-0.55%, the molar content of CO2 is 23-30%, and the temperature is -20 to -14°C) from the synthesis gas H2S absorption process is sent to the first H2S flash section to perform the first H2S flash (the pressure is 1.5-1.8 MPa(G)), to obtain the first H2S flash gas 11 and the first H2S flash liquid 10 (the molar content of H2S is 0.4-0.5%, the molar content of CO2 is 24-28%, and the temperature is -20 to -15°C);

[0129] The first H2S flash gas 11 is sent to the first H2S washing section through a pipeline, and the non-shift H2S-rich methanol 12 (the molar content of H2S is 0.1-0.6%, the molar content of CO2 is 3-7%, the temperature is -36 to -31°C, and the pressure is 3.5-3.55 MPa(G)) from the non-shift gas purification process is sent to the first H2S washing section to perform the second washing, to obtain the washed H2S-rich methanol 13 (the molar content of H2S is 0.2-0.5%, the molar content of CO2 is 11-16%, and the temperature is -18 to -15°C) and the first washed H2S flash gas 4-ii;

[0130] The H2S-rich methanol 13 after washing is mixed with the first H2S flash liquid 10 to obtain a mixed H2S-rich methanol 14 (the molar content of H2S is 0.3-0.5%, the molar content of CO2 is 22-28%, and the temperature is -20 to -15°C), which is sent to the second H2S flash section through the second cooler E-2 (the temperature is -36 to -33°C) after cooling, and the second H2S flash gas is sent to the second H2S washing section through the riser, and the second H2S flash liquid 15 (the molar content of H2S is 0.25-0.55%, the molar content of CO2 is 18-22%, and the temperature is -36.5 to -33.5°C) is obtained;

[0131] The reabsorption tower T-3 is divided into an upper tower and a lower tower, the upper tower is divided into a first flash section, a second flash section, and a third flash section from top to bottom and connected by a riser, and the lower tower is divided into a washing section and a gas stripping section from top to bottom and connected by a riser;

[0132] The second CO2 flash liquid 6-ii is sent to the first flash section through the third cooler E-3 (the temperature is -36 to -33°C) to perform the first flash (the pressure is 0.05-0.08 MPa (G)), to obtain the semi-lean liquid methanol 17 (the molar content of H2S is 0.1-0.5 ppm, the molar content of CO2 is 9-13%, and the temperature is -56 to -51°C), and the first CO2 product gas is obtained; the third CO2 flash liquid 6-iii is sent to the second flash section through the fourth cooler E-4 (the temperature is -52 to -48°C) to perform the second flash (the pressure is 0.06-0.09 MPa (G)), to obtain the flash liquid and the second CO2 product gas; the second H2S flash liquid 15 is sent to the third flash section to perform the third flash (the pressure is 0.12-0.16 MPa (G)), to obtain the sulfur-containing gas and the second H2S-rich methanol 19 (the molar content of H2S is 0.2-0.5%, the molar content of CO2 is 14-17%, and the pressure is 0.13-0.17 MPa (G)); the flash liquid and the sulfur-containing gas are subjected to the fourth washing to obtain the low-H2S methanol 18 (the molar content of H2S is 0.1-0.4%, the molar content of CO2 is 15-19%, and the temperature is -60 to -50°C) which is sent to the gas stripping section, and the third CO2 product gas is obtained, which is mixed with the first CO2 product gas and the second CO2 product gas to obtain the first CO2 product gas 25 (the molar content of H2S is ≤1 ppm, the molar content of CO2 is 99.4-99.7%, the temperature is -60 to -50°C, and the pressure is 0.05-0.08 MPa (G));

[0133] The semi-lean liquid methanol 17 is sent to a low-carbon methanol stripping column T-5 via a pipeline, and is subjected to first stripping with a first nitrogen gas stream 20-i to obtain low-carbon methanol 28 (molar content of 0.1-0.5 ppm, molar content of CO2 of 3-7%; temperature of -70 to -66°C; pressure of 0.15-0.2 MPa (G)) and first tail gas 27 (molar content of H2S of 0.1-0.5 ppm, molar content of CO2 of 62-66%; temperature of -62 to -57°C, pressure of 0.12-0.14 MPa (G));

[0134] The low-carbon methanol is pressurized to 1.8-2 MPa (G) by a pump P, and is divided into a first low-carbon methanol stream 28-i and a second low-carbon methanol stream 28-ii at a molar flow ratio of 1:33-37;

[0135] The first low-carbon methanol stream 28-i is sent to a first CO2 washing section, and is subjected to first washing with a first CO2 flash gas to obtain first-washed CO2 flash gas 4-i, and the obtained first CO2 washing liquid 5 (molar content of H2S of ≤0.1 ppm, molar content of CO2 of 19-23%; temperature of -28 to -22°C) is sent to a second CO2 washing section via a pipeline, and is subjected to second washing with a second CO2 flash gas to obtain second-washed CO2 flash gas 8-i, and the obtained second CO2 washing liquid 7 (molar content of H2S of ≤0.1 ppm, molar content of CO2 of 18-22%; temperature of -30 to -25°C) is sent to a second H2S washing section via a pipeline, and is subjected to third washing with the second H2S flash gas to obtain low-sulfur carbon-rich methanol 16 (molar content of H2S of 50-60 ppm, molar content of CO2 of 18-22%, temperature of -32 to -24°C) and second-washed H2S flash gas 8-ii;

[0136] The first-washed CO2 flash gas 4-i and the first-washed H2S flash gas 4-ii are mixed to obtain first flash gas 4 (molar content of H2 of 60-65%, molar content of CO of 6-11%, molar content of CO2 of 25-30%; temperature of -35 to -30°C, pressure of 1.5-1.8 MPa (G)); and the second-washed CO2 flash gas 8-i and the second-washed H2S flash gas 8-ii are mixed to obtain second flash gas 8 (molar content of H2 of 30-34%, molar content of CO of 1-4%, molar content of CO2 of 63-67%; temperature of -28 to -24°C, pressure of 0.5-0.8 MPa (G)).

[0137] The first stream of the second CO2 flash liquid 6-i is sent to the flash tower T-4 for fourth flash (pressure is 0.2-0.5 MPa (G)) to obtain the flash CO2-rich methanol 23 (molar content of H2S is 0.1-0.5 ppm, molar content of CO2 is 14.5-19.5%, temperature is -40 to -35℃) and the second CO2 product gas 24 (molar content of H2S is ≤1 ppm, molar content of CO2 is 92-95%; temperature is -40 to -35℃, pressure is 0.2-0.5 MPa (G));

[0138] The flash CO2-rich methanol 23 is sent to the washing section after the fifth cooler E-5 (temperature is -52 to -48℃) to perform third washing with the stripping gas from the stripping section to obtain the washed carbon-rich methanol 22 and the second tail gas 26 (molar content of H2S is ≤1 ppm, molar content of CO2 is 72-77%; temperature is -63 to -58℃, pressure is 0.16-0.18 MPa (G));

[0139] The second H2S-rich methanol 19, the washed carbon-rich methanol 22, the low-sulfur carbon-rich methanol 16 and the low-H2S methanol 18 are sent to the stripping section to be sequentially contacted with the second nitrogen gas 20-ii and to perform second stripping to obtain the stripping gas sent to the washing section through the riser and the stripped H2S-rich methanol 21 (molar content of H2S is 0.2-0.4%, molar content of CO2 is 1-4%; temperature is -50 to -44℃, pressure is 0.22-0.24 MPa (G)).

[0140] Comparative Example 1

[0141] Taking a hydrogen production device based on pulverized coal gasification as an example, the effective gas (H2+CO) entering the low-temperature methanol washing device is 161000 Nm 3 / h, and the main technical parameters of the lean-liquid-semi-lean process (i.e., CN201110260570.0 discloses a low-temperature methanol washing process) are compared with the above baseline, as shown in Table 1.

[0142] Table 1

[0143]

[0144] As can be seen from the results in Table 1, taking a hydrogen production device based on pulverized coal gasification as an example, the method provided in Example 1 adopts two-stage medium-pressure flash and classification washing technology, and four-stage tail gas washing technology in the reabsorption tower, and the low-carbon methanol circulation amount is 58.3% of the semi-lean methanol circulation amount in Comparative Example 1 (lean-liquid-semi-lean process), and the overall energy-saving effect is remarkable.

[0145] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method for medium pressure flash evaporation and reabsorption of a coal gasification plant, characterized in that, The method includes: The CO2-rich methanol (1) from the synthesis gas CO2 absorption process is subjected to a first CO2 flash evaporation and a second CO2 flash evaporation in sequence to obtain a first CO2 flash vapor (3), a second CO2 flash vapor and a second CO2 flash liquid (6) in three streams; the first H2S-rich methanol (9) from the synthesis gas H2S absorption process is subjected to a first H2S flash evaporation and a second H2S flash evaporation in sequence to obtain a first H2S flash vapor (11), a second H2S flash vapor and a second H2S flash liquid (15); The second CO2 flash liquid (6-ii), the third CO2 flash liquid (6-iii), and the second H2S flash liquid (15) were subjected to first flash evaporation, second flash evaporation, and third flash evaporation in sequence to obtain semi-lean methanol (17), low H2S methanol (18), and second H2S rich methanol (19). In this process, the semi-lean methanol (17) is subjected to a first gas stripping process, and the resulting low-carbon methanol (28) is divided into two streams. The first stream of low-carbon methanol (28-i) is sequentially washed with the first CO2 flash vapor (3), the second CO2 flash vapor, and the second H2S flash vapor to obtain low-sulfur carbon-rich methanol (16). The non-shift H2S-rich methanol (12) from the non-shift gas purification process is washed with the first H2S flash vapor (11) and the resulting washed H2S-rich methanol (13) is subjected to the second H2S flash evaporation. The low-sulfur carbon-rich methanol (16), low-H2S methanol (18), second H2S-rich methanol (19), and washed carbon-rich methanol (22) are subjected to a second gas stripping to obtain stripped gas and stripped H2S-rich methanol (21); wherein the washed carbon-rich methanol (22) is obtained by the fourth flash distillation of the first second CO2 flash liquid (6-i) and the resulting flash distilled CO2-rich methanol (23) is subjected to a third washing with the stripped gas.

2. The method of claim 1, wherein, The synthesis gas H2S absorption process includes: absorbing H2S from the synthesis gas to obtain the first H2S-rich methanol (9) and desulfurized gas; the synthesis gas CO2 absorption process includes: absorbing CO2 from the desulfurized gas to obtain CO2-rich methanol (1) and purified gas. Preferably, the molar content of H2S in the first H2S-rich methanol (9) is 0.35-0.55%, the molar content of CO2 is 23-30%, and the temperature is -20 to -14°C. Preferably, the molar content of H2S in the CO2-rich methanol (1) is 0.1-0.5 ppm, the molar content of CO2 is 16-21%, the temperature is -22 to -17°C, and the pressure is 3.05-3.09 MPa(G); Preferably, the non-shift gas purification process includes: purifying the non-shift gas and lean methanol to obtain the non-shift H2S-rich methanol (12) and purified non-shift gas; Preferably, the non-conversion H2S-rich methanol (12) has a molar content of 0.1-0.6% for H2S and a molar content of 3-7% for CO2; a temperature of -36 to -31°C; and a pressure of 3.5-3.55 MPa (G).

3. The method of claim 1 or 2, wherein, The pressure of the first CO2 flash evaporation is greater than the pressure of the second CO2 flash evaporation; the pressure of the first H2S flash evaporation is greater than the pressure of the second H2S flash evaporation; Preferably, the pressures of the first CO2 flash evaporation and the first H2S flash evaporation are each independently 1.5-1.8 MPa(G); the pressures of the second CO2 flash evaporation and the second H2S flash evaporation are each independently 0.8-1 MPa(G); Preferably, the CO2-rich methanol (1) is subjected to the first CO2 flash evaporation to obtain the first CO2 flash vapor (3) and the first CO2 flash liquid (2); the first CO2 flash liquid (2) is subjected to the second CO2 flash evaporation to obtain the second CO2 flash vapor and the second CO2 flash liquid (6); Preferably, the molar content of H2S in the first CO2 flash liquid (2) is 0.1-0.5 ppm, the molar content of CO2 is 15.5-20.5%, and the temperature is -22 to -18°C; Preferably, the molar content of H2S in the second CO2 flash liquid (6) is 0.1-0.5 ppm, and the molar content of CO2 is 15-20%. The temperature ranges from -36.5 to -33.5℃; Preferably, the molar flow ratio of the first second CO2 flash liquid (6-i), the second second CO2 flash liquid (6-ii), and the third second CO2 flash liquid (6-iii) is 1-2:1-3:1; More preferably, before performing the second CO2 flash evaporation, the first CO2 flash liquid (2) is cooled to -36 to -33°C; Preferably, the first H2S-rich methanol (9) is subjected to the first H2S flash evaporation to obtain the first H2S flash vapor (11) and the first H2S flash liquid (10); the first H2S flash liquid (10) is mixed with washed H2S-rich methanol (13) to obtain the mixed H2S-rich methanol (14) and subjected to the second H2S flash evaporation to obtain the second H2S flash vapor and the second H2S flash liquid (15); More preferably, the first H2S flash liquid (10) has a molar content of H2S of 0.4-0.5%, a molar content of CO2 of 24-28%, and a temperature of -20 to -15°C; More preferably, the molar content of H2S in the washed H2S-rich methanol (13) is 0.2-0.5%, the molar content of CO2 is 11-16%, and the temperature is -18 to -15°C; More preferably, the H2S molar content in the mixed H2S-rich methanol (14) is 0.3-0.5%, the CO2 molar content is 22-28%, and the temperature is -20 to -15°C; More preferably, the molar content of H2S in the second H2S flash liquid (15) is 0.25-0.55%, the molar content of CO2 is 18-22%, and the temperature is -36.5 to -33.5℃; More preferably, before the second H2S flash evaporation, the mixed H2S-rich methanol (14) is subjected to a second cooling to -36 to -33°C.

4. The method of any of claims 1-3, wherein, The second CO2 flash liquid (6-ii) is subjected to the first flash evaporation to obtain the semi-lean methanol (17) and the first CO2 product gas; the third CO2 flash liquid (6-iii) is subjected to the second flash evaporation to obtain the flash liquid and the second CO2 product gas; the second H2S flash liquid (15) is subjected to the third flash evaporation to obtain the sulfur-containing gas and the second H2S-rich methanol (19); wherein the flash liquid and the sulfur-containing gas are subjected to the fourth washing to obtain the low H2S methanol (18), and the obtained third CO2 product gas is mixed with the first CO2 product gas and the second CO2 product gas to obtain the first CO2 product gas (25); Preferably, before the first flash evaporation, the second stream of second CO2 flash liquid (6-ii) is cooled to -36 to -33°C in a third cooling process; Preferably, before the first flash evaporation, the third stream of the second CO2 flash liquid (6-iii) is cooled to -52 to -48°C in a fourth cooling process; Preferably, the pressure of the first flash evaporation is 0.05-0.08 MPa(G), the pressure of the second flash evaporation is 0.06-0.09 MPa(G), and the pressure of the third flash evaporation is 0.12-0.16 MPa(G); Preferably, the semi-lean methanol (17) contains 0.1-0.5 ppm of H2S and 9-13% of CO2, and is prepared at a temperature of -56 to -51°C. Preferably, the low-H2S methanol (18) has a molar content of H2S of 0.1-0.4% and a molar content of CO2 of 15-19%; and the temperature is -60 to -50°C. Preferably, the second H2S-rich methanol (19) has a molar content of H2S of 0.2-0.5% and a molar content of CO2 of 14-17%; and a pressure of 0.13-0.17 MPa(G). Preferably, the molar content of H2S in the first CO2 product gas (25) is ≤1ppm, the molar content of CO2 is 99.4-99.7%, the temperature is -60 to -50℃, and the pressure is 0.05-0.08MPa(G); Preferably, the first gas stripping process includes: contacting the semi-lean methanol (17) and the first stream of nitrogen (20-i) and performing the first gas stripping to obtain the low-carbon methanol (28) and the first tail gas (27); Preferably, the low-carbon methanol (28) has a molar content of H2S of 0.1-0.5 ppm and a molar content of CO2 of 3-7%; a temperature of -70 to -66°C; and a pressure of 0.15-0.2 MPa(G). Preferably, the molar flow ratio of the first low-carbon methanol (28-i) and the second low-carbon methanol (28-ii) is 1:33-37; Preferably, the low-carbon methanol (28) is pressurized to 1.8-2 MPa (G) and then divided into a first stream of low-carbon methanol (28-i) and a second stream of low-carbon methanol (28-ii).

5. The method of any of claims 1-4, wherein, The first washing process includes: washing the first stream of low-carbon methanol (28-i) and the first CO2 flash vapor (3) once to obtain CO2 flash vapor (4-i) after the first wash and the first CO2 washing liquid (5); washing the first CO2 washing liquid (5) and the second CO2 flash vapor a second time to obtain CO2 flash vapor (8-i) after the second wash and the second CO2 washing liquid (7); washing the second CO2 washing liquid (7) and the second H2S flash vapor a third time to obtain the low-sulfur carbon-rich methanol (16) and the second H2S flash vapor (8-ii) after the second wash; Preferably, the low-sulfur, carbon-rich methanol (16) has a molar content of H2S of 50-60 ppm, a molar content of CO2 of 18-22%, and a temperature of -32 to -24°C. Preferably, the second washing process includes: subjecting the non-conversion H2S-rich methanol (12) and the first H2S flash vapor (11) to the second washing to obtain washed H2S-rich methanol (13) and first washed H2S flash vapor (4-ii); More preferably, the first washed CO2 flash vapor (4-i) and the first washed H2S flash vapor (4-ii) are mixed to obtain the first flash vapor (4) with a molar content of H2 of 60-65%, a molar content of CO of 6-11%, and a molar content of CO2 of 25-30%; the temperature is -35 to -30°C and the pressure is 1.5-1.8 MPa(G); More preferably, the second washed CO2 flash vapor (8-i) and the second washed H2S flash vapor (8-ii) are mixed to obtain the second flash vapor (8) with a molar content of H2 of 30-34%, a molar content of CO of 1-4%, and a molar content of CO2 of 63-67%; the temperature is -28 to -24°C and the pressure is 0.5-0.8 MPa (G).

6. The method of any of claims 1-5, wherein, The second gas stripping process includes: sequentially contacting the second H2S-rich methanol (19), washed carbon-rich methanol (22), low-sulfur carbon-rich methanol (16), and low-H2S methanol (18) with a second stream of nitrogen (20-ii) and performing the second gas stripping to obtain the stripping gas and the stripped H2S-rich methanol (21). Preferably, the molar content of H2S in the stripped H2S-rich methanol (21) is 0.2-0.4%, and the molar content of CO2 is 1-4%; the temperature is -50 to -44℃, and the pressure is 0.22-0.24 MPa(G); Preferably, the second H2S-rich methanol (19) is subjected to a first heat exchange to a temperature of -36 to -33°C before the second gas stripping is performed.

7. The method according to any one of claims 1-6, wherein, The pressure of the fourth flash evaporation is 0.2-0.5 MPa(G); Preferably, the molar content of H2S in the flash-evaporated CO2-rich methanol (23) is 0.1-0.5 ppm, the molar content of CO2 is 14.5-19.5%, and the temperature is -40 to -35°C; Preferably, the second CO2 product gas (24) obtained by the fourth flash evaporation has a molar content of H2S ≤1ppm and a molar content of CO2 of 92-95%; the temperature is -40 to -35℃ and the pressure is 0.2-0.5MPa(G); Preferably, the flash-evaporated CO2-rich methanol (23) is cooled to -52 to -48°C in the fifth stage before the third washing is performed; Preferably, the third washing process includes: after the flash-evaporated CO2-rich methanol (23) is cooled in the fifth stage, it is contacted with the stripping gas and subjected to the third washing to obtain the washed carbon-rich methanol (22) and the second tail gas (26). Preferably, the molar content of H2S in the washed carbon-rich methanol (22) is 0.1-0.5%, and the molar content of CO2 is 15-19%; the temperature is -57 to -53°C, and the pressure is 0.2-0.22 MPa(G); Preferably, the washed carbon-rich methanol (22) is subjected to a second heat exchange to a temperature of -36 to -33°C before the second gas stripping is performed.

8. A medium-pressure flash evaporation and reabsorption device for a pulverized coal gasification unit, characterized in that, The method described in any one of claims 1-7 is carried out in the apparatus, which includes a primary medium-pressure flash distillation tower (T-1), a secondary medium-pressure flash distillation tower (T-2), and a reabsorption tower (T-3) connected in sequence, as well as a flash distillation tower (T-4) and a low-carbon methanol stripping tower (T-5); The first-stage medium-pressure flash tower (T-1) is divided into a first CO2 washing section, a first CO2 flash evaporation section, a first H2S washing section and a first H2S flash evaporation section from top to bottom. The first CO2 washing section and the first CO2 flash evaporation section are connected by pipes, and the first H2S washing section and the first H2S flash evaporation section are connected by pipes. The two-stage medium-pressure flash tower (T-2) is divided into a second CO2 washing section, a second CO2 flash evaporation section, a second H2S washing section and a second H2S flash evaporation section from top to bottom. The second CO2 washing section and the second CO2 flash evaporation section are connected through a gas riser, and the second H2S washing section and the second H2S flash evaporation section are also connected through a gas riser. The reabsorption tower (T-3) is divided into an upper tower and a lower tower. The upper tower is divided into a first flash section, a second flash section and a third flash section connected by air risers from top to bottom. The lower tower is divided into a washing section and a stripping section connected by air risers from top to bottom. The first CO2 flash evaporation section and the second CO2 flash evaporation section are connected by pipelines, and the second CO2 flash evaporation section, the flash tower (T-4), the first flash evaporation section and the second flash evaporation section are connected by pipelines; the first H2S flash evaporation section, the first H2S washing section and the second H2S flash evaporation section are connected by pipelines, and the second H2S flash evaporation section and the third flash evaporation section are connected by pipelines; the first CO2 washing section, the second CO2 washing section and the second H2S washing section are connected by pipelines. The flash tower (T-4) and the washing section are connected by pipelines; the second H2S washing section, the second flash section, the third flash section and the washing section are each independently connected to the air stripping section by pipelines. The low-carbon methanol stripping tower (T-5) is connected to the first flash evaporation section and the first CO2 washing section via pipelines.

9. The apparatus according to claim 8, wherein, In the first-stage medium-pressure flash evaporator (T-1), The first CO2 flash evaporation section is used to perform first CO2 flash evaporation on CO2-rich methanol (1) from the synthesis gas CO2 absorption process to obtain first CO2 flash vapor (3) and first CO2 flash liquid (2); The first CO2 washing section is used to wash the first CO2 flash vapor (3) and the first stream of low-carbon methanol (28-i) once to obtain the first washed CO2 flash vapor (4-i) and the first CO2 washing liquid (5); The first H2S flash evaporation section is used to perform first H2S flash evaporation on the first H2S-rich methanol (9) from the synthesis gas H2S absorption process to obtain first H2S flash vapor (11) and first H2S flash liquid (10); The first H2S washing section is used to wash the non-conversion H2S-rich methanol (12) from the non-conversion gas purification process with the first H2S flash vapor (11) to obtain washed H2S-rich methanol (13) and first washed H2S flash vapor (4-ii). Preferably, in the secondary medium-pressure flash evaporator (T-2), The second CO2 flash evaporation section is used to perform a second CO2 flash evaporation on the first CO2 flash liquid (2) to obtain a second CO2 flash vapor and a second CO2 flash liquid (6) which are divided into three streams; The second CO2 washing section is used to perform a second washing of the second CO2 flash vapor and the first CO2 washing liquid (5) to obtain the second washed CO2 flash vapor (8-i) and the second CO2 washing liquid (7); The second H2S flash evaporation section is used to mix the first H2S flash liquid (10) and washed H2S-rich methanol (13), and the resulting mixed H2S-rich methanol (14) is subjected to second H2S flash evaporation to obtain second H2S flash vapor and second H2S flash liquid (15). The second H2S washing section is used to wash the second CO2 washing liquid (7) and the second H2S flash vapor three times to obtain low-sulfur carbon-rich methanol (16) and the second washed H2S flash vapor (8-ii); Preferably, in the upper column of the reabsorption tower (T-3), the first flash evaporation section is used to perform a first flash evaporation on the second stream of second CO2 flash liquid (6-ii) to obtain semi-lean methanol (17) and a first stream of CO2 product gas; the second flash evaporation section is used to perform a second flash evaporation on the third stream of second CO2 flash liquid (6-iii) to obtain flash liquid and a second stream of CO2 product gas; the third flash evaporation section is used to perform a third flash evaporation on the second H2S flash liquid (15) to obtain sulfur-containing gas and second H2S-rich methanol (19); wherein, the flash liquid and sulfur-containing gas are subjected to a fourth wash to obtain the low H2S methanol (18), and the obtained third stream of CO2 product gas is mixed with the first stream of CO2 product gas and the second stream of CO2 product gas to obtain the first CO2 product gas (25); Preferably, the low-carbon methanol stripping tower (T-5) is used to perform a first stripping of the semi-lean methanol (17) and the first stream of nitrogen (20-i) to obtain a first tail gas (27) and low-carbon methanol (28) in two streams; Preferably, the flash tower (T-4) is used to perform a fourth flash evaporation on the first stream of second CO2 flash liquid (6-i) to obtain second CO2 product gas (24) and flash-enriched CO2 methanol (23); Preferably, in the lower column of the reabsorption tower (T-3), the washing section is used to perform a third washing on the flash-evaporated CO2-rich methanol (23) and the stripping gas to obtain washed carbon-rich methanol (22) and a second tail gas (26); the stripping section is used to sequentially contact the second H2S-rich methanol (19), washed carbon-rich methanol (22), low-sulfur carbon-rich methanol (16), and low-H2S methanol (18) with a second stream of nitrogen gas (20-ii) and perform a second stripping to obtain stripping gas and stripped H2S-rich methanol (21).

10. The apparatus according to claim 9, wherein, The device further includes: a first cooler (E-1) is installed on the pipe connecting the first CO2 flash section and the second CO2 flash section; Preferably, the device further includes a second cooler (E-2) installed on the pipe connecting the first H2S flash evaporation section, the first H2S washing section and the second H2S flash evaporation section; Preferably, the device further includes a third cooler (E-3) installed on the pipe connecting the second CO2 flash section and the first flash section; Preferably, the device further includes a fourth cooler (E-4) installed on the pipe connecting the second CO2 flash section and the second flash section; Preferably, the device further includes a fifth cooler (E-5) installed on the pipe connecting the flash tower (T-4) and the washing section; Preferably, the device further includes a first heat exchanger (Q-1) installed on the pipe connecting the third flash section and the stripping section; Preferably, the device further includes a second heat exchanger (Q-2) installed on the pipe connecting the washing section and the air-lift section; Preferably, the apparatus further includes a pump (P) installed on the pipeline connecting the low-carbon methanol stripping tower (T-5) and the first CO2 washing section.

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