Acid gas 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 an acid gas flash evaporation and reabsorption method matched with a pulverized coal gasification device and an acid gas flash evaporation and reabsorption device matched with the pulverized coal gasification device. According to the method, the two-stage medium-pressure flash evaporation process is optimized, so that the method has the advantage of saving flash evaporation gas compression power consumption; by optimizing the flow of the re-absorption tower, low-H2S methanol is generated, and meanwhile, the low-H2S methanol is reutilized, so that the low-temperature methanol washing device has the characteristic of low comprehensive energy consumption; the gas stripping process is optimized, CO2-rich methanol subjected to three-stage CO2 flash evaporation is used for carrying out series absorption on H2S gas in gas stripping gas generated by gas stripping, and the method 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 an acid gas flashing and reabsorption method matched with a pulverized coal gasification device and an acid gas flashing 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 flashing process is a process of flashing and recovering the effective gas in the CO2-rich methanol and the H2S-rich methanol sent from the previous process, and in order to reduce the total amount of CO2 gas in the flashing gas, the flashing gas needs to be washed and absorbed. Therefore, the selection of the washing methanol is particularly critical, which needs to ensure the washing and absorption effect of the flashing gas and avoid the adverse effects of the washing liquid on the subsequent system.

[0003] CN201110260570.0 discloses a low-temperature methanol washing process, which has two problems. One is that the CO2 gas flashed from the upper tower of the medium-pressure flashing tower is sent to the lower tower to be washed and absorbed by using the H2S-rich methanol, the washing solution is not selected reasonably, the rich liquid after washing cannot be used twice, and it is not conducive to reducing the comprehensive energy consumption of the low-temperature methanol washing device. The other is that in the CO2 flashing section of the reabsorption tower, the CO2-rich methanol is directly mixed with the H2S-rich methanol while washing the H2S-rich methanol flashing gas, and the CO2-rich methanol is polluted by the H2S-rich methanol, and the low-concentration H2S methanol generated is not fully used, which has high energy consumption. SUMMARY

[0004] The present application aims to overcome the above technical problems, and provides an acid gas flashing and reabsorption method matched with a pulverized coal gasification device and an acid gas flashing and reabsorption device matched with the pulverized coal gasification device. The method has the advantages of saving the compression power consumption of the flashing gas by optimizing the two-stage medium-pressure flashing process, generating low-H2S methanol by optimizing the setting of the reabsorption tower process, and having the characteristics of low comprehensive energy consumption of the low-temperature methanol washing device by twice using the low-H2S methanol, and has the characteristics of low comprehensive energy consumption by using the CO2-rich methanol (i.e. the three-stage CO2 flashing liquid) after the three-stage CO2 flashing to absorb the H2S gas in the stripping gas generated by the stripping process.

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

[0006] (1) the CO2-rich methanol is subjected to two-stage CO2 flashing to obtain a first-stage CO2 flashing gas, a second-stage CO2 flashing gas and a second-stage CO2 flashing liquid; the first H2S-rich methanol is subjected to two-stage H2S flashing to obtain a first-stage H2S flashing gas, a second-stage H2S flashing gas and a second-stage H2S flashing liquid;

[0007] (2) the second-stage CO2 flashing liquid is divided into three streams, the first stream of the second-stage CO2 flashing liquid is subjected to third-stage CO2 flashing to obtain a third-stage CO2 flashing liquid; the second stream of the second-stage CO2 flashing liquid, the third stream of the second-stage CO2 flashing liquid and the second-stage H2S flashing liquid are subjected to first flashing, second flashing and third flashing respectively to obtain a semi-lean liquid methanol, a low-H2S methanol and a second H2S-rich methanol;

[0008] (3) the semi-lean liquid methanol is divided into two streams, the second stream of the semi-lean liquid methanol and the first-stage CO2 flashing gas are subjected to first washing, and then the low-H2S methanol, the second-stage CO2 flashing gas and the second-stage H2S flashing gas are subjected to second washing and third washing respectively to obtain a low-sulfur carbon-rich methanol;

[0009] (4) the second H2S-rich methanol, the low-sulfur carbon-rich methanol and a third H2S-rich methanol are subjected to gas stripping respectively to obtain gas stripping gas and H2S-rich methanol after gas stripping, and the third H2S-rich methanol is obtained from the third-stage CO2 flashing liquid by fourth flashing, and then the gas stripping gas is subjected to fifth washing.

[0010] The second aspect of the present application provides an acid gas 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, and the device comprises: connected first-stage medium-pressure flashing towers, second-stage medium-pressure flashing towers, reabsorption towers, low-pressure flashing towers and H2S concentration towers;

[0011] The first-stage medium-pressure flashing towers are divided into a first CO2 washing section, a first-stage CO2 flashing section, a first H2S washing section and a first-stage H2S flashing section from top to bottom; the second-stage medium-pressure flashing towers are divided into a second CO2 washing section, a second-stage CO2 flashing section, a second H2S washing section and a second-stage H2S flashing section from top to bottom; and the reabsorption towers are divided into a first flashing section, a second flashing section and a third flashing section connected by a gas lift hole from top to bottom;

[0012] The first-stage CO2 flashing section and the second-stage CO2 flashing section are connected by a pipeline, and the second-stage CO2 flashing section is connected with the low-pressure flashing towers, the first flashing section and the second flashing section; the first-stage H2S flashing section and the second-stage H2S flashing section are connected by a pipeline, and the second-stage H2S flashing section is connected with the third flashing section;

[0013] The first CO2 washing section is connected with the first flash section, the first CO2 washing section, the second CO2 washing section and the second H2S washing section are connected in series through pipelines, and the second CO2 washing section is further connected with the second flash section; the first H2S washing section and the secondary H2S flash section are connected through pipelines.

[0014] The H2S concentration tower is divided into a flash washing part and a gas stripping part connected through a gas lifting hole from top to bottom, the flash washing part is connected with the low-pressure flash tower, and the gas stripping part is connected with the third flash section, the second H2S washing section and the flash washing part.

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

[0016] (1) The present application adopts a three-stage tail gas washing technology, and according to the different H2S contents in the tail gas, three different H2S content methanols are selectively set, i.e., the second H2S-rich methanol, the low-sulfur carbon-rich methanol and the third CO2 flash liquid, which are sequentially washed from high to low, so as to ensure that the tail gas emission meets the standard and the least third CO2 flash liquid is used, thereby reducing the heat regeneration energy consumption of the whole low-temperature methanol washing;

[0017] (2) The present application adopts a two-stage medium-pressure flash technology, the first stage adopts a higher flash 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 pressure, which ensures that the effective gas in the first CO2 flash liquid and the first H2S flash liquid is fully recovered, and at the same time, the gas cylinder inlet amount of the first stage of the compressor in the compression process is reduced, and the power consumption of the compressor is correspondingly reduced;

[0018] (3) The present application optimizes the medium-pressure flash process, and in the process of the first CO2 flashing and the second CO2 flashing, the semi-lean liquid methanol and the low-H2S methanol are respectively 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 without being polluted by the H2S-rich methanol; at the same time, the second H2S flash gas is washed in series, which realizes the separate flashing and classified washing of the CO2-rich methanol and the H2S-rich methanol, creates a prerequisite for the secondary use of the low-H2S methanol, and is beneficial to reducing the energy consumption of the device;

[0019] (4) The present application optimizes the reabsorption process, realizes the absorption of the sulfur component in the CO2 product gas generated by the flashing of the second H2S flash liquid by the flash liquid, but does not mix with the H2S-rich methanol at the bottom of the tower after flashing; therefore, compared with the prior art, the low-H2S methanol obtained after the flash liquid absorbs the H2S gas flashed out is used for the series washing of the second CO2 flash gas and the second H2S flash gas. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1is a structural schematic diagram of an acid gas flash and reabsorption device of a complete pulverized coal gasification device provided by the present application.

[0021] Reference numerals

[0022] T-1, first-stage medium-pressure flash tower; T-2, second-stage medium-pressure flash tower; T-3, reabsorption tower; T-4, low-pressure flash tower; T-5, H2S concentration tower;

[0023] E-1, first cooler; E-2, second cooler; E-3, third cooler; E-4, fourth cooler; Q-1, first heat exchanger; Q-2, second heat exchanger; P-1, first pump; P-2, second pump; P-3, third pump;

[0024] 1, CO2-rich methanol; 2, semi-lean liquid methanol; 2-i, first semi-lean liquid methanol; 2-ii, second semi-lean liquid methanol; 3, first-stage CO2 flash liquid; 4, fourth washing liquid; 5, first-stage flash gas; 5-i, first-stage CO2 flash gas after washing; 5-ii, first-stage H2S flash gas after washing; 6, first H2S-rich methanol; 7, non-shift H2S-rich methanol; 8, first-stage H2S flash liquid; 9, mixed H2S flash liquid; 10, second-stage CO2 flash liquid; 10-i, first second-stage CO2 flash liquid; 10-ii, second second-stage CO2 flash liquid; 10-iii, third second-stage CO2 flash liquid; 11, second-stage flash gas; 11-i, second-stage CO2 flash gas after washing; 11-ii, second-stage H2S flash gas after washing; 12, second-stage H2S flash liquid; 13, low-H2S methanol; 14, second H2S-rich methanol; 15, first CO2 product gas; 16, second CO2 product gas; 17, third-stage CO2 flash liquid; 18, third H2S-rich methanol; 19, nitrogen; 20, low-sulfur carbon-rich methanol; 21, H2S-rich methanol after stripping; 22, tail gas; 23, first-stage H2S flash gas; 24, first-stage CO2 flash gas; 25, first washing liquid; 26, second washing liquid. DETAILED DESCRIPTION

[0025] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges and values should be construed to be approximations that allow for significant variation. Various ranges of values that are stated herein are considered to be approximate values that can vary by a small amount. Endpoints of various ranges of values, endpoints of various ranges of values and individual point values, and individual point values can be combined with each other to create one or more new ranges of values that are considered to be specifically disclosed herein.

[0026] In the present application, "first", "second", "third", "fourth" and "fifth" do not indicate the order of precedence, nor do they limit the various materials or steps, but are only used to distinguish that they are not the same material or step. For example, "first", "second", "third", "fourth" and "fifth" in "first washing", "second washing", "third washing", "fourth washing" and "fifth washing" are only used to indicate that they are not the same washing.

[0027] The first aspect of the present application provides an acid gas flashing and reabsorption method for a complete pulverized coal gasification device, the method comprising the following steps:

[0028] (1) performing two-stage CO2 flashing on the CO2-rich methanol to obtain first-stage CO2 flashing gas, second-stage CO2 flashing gas and second-stage CO2 flashing liquid; and performing two-stage H2S flashing on the first H2S-rich methanol to obtain first-stage H2S flashing gas, second-stage H2S flashing gas and second-stage H2S flashing liquid;

[0029] (2) dividing the second-stage CO2 flashing liquid into three streams, performing third-stage CO2 flashing on the first stream of second-stage CO2 flashing liquid to obtain third-stage CO2 flashing liquid; and performing first flashing, second flashing and third flashing on the second stream of second-stage CO2 flashing liquid, the third stream of second-stage CO2 flashing liquid and the second-stage H2S flashing liquid, respectively, to obtain semi-lean liquid methanol, low-H2S methanol and second H2S-rich methanol;

[0030] (3) dividing the semi-lean liquid methanol into two streams, performing first washing on the second stream of semi-lean liquid methanol and the first-stage CO2 flashing gas, and then performing second washing on the low-H2S methanol and the second-stage CO2 flashing gas, respectively, and then performing third washing on the second-stage H2S flashing gas, to obtain low-sulfur carbon-rich methanol;

[0031] (4) performing gas stripping on the second H2S-rich methanol, low-sulfur carbon-rich methanol and third H2S-rich methanol, respectively, to obtain gas stripping gas and H2S-rich methanol after gas stripping, and the third H2S-rich methanol is obtained by performing fourth flashing on the third-stage CO2 flashing liquid, and then performing fifth washing on the gas stripping gas.

[0032] In the present application, preferably, in step (1), the two-stage CO2 flashing comprises first-stage CO2 flashing and second-stage CO2 flashing; wherein the CO2-rich methanol is subjected to the first-stage CO2 flashing to obtain the first-stage CO2 flashing gas and first-stage CO2 flashing liquid; and the first-stage CO2 flashing liquid is subjected to the second-stage CO2 flashing to obtain the second-stage CO2 flashing gas and second-stage CO2 flashing liquid.

[0033] In the present application, the pressure of the first CO2 flash is greater than the pressure of the second CO2 flash. Preferably, the pressure of the first CO2 flash is 1.5-1.8 MPa (G), and the pressure of the second CO2 flash is 0.8-1 MPa (G).

[0034] In the present application, preferably, the first H2S-rich methanol is derived from a synthesis gas H2S absorption process, i.e., H2S absorption of synthesis gas to obtain the first H2S-rich methanol and desulfurized gas, and the synthesis gas is derived from a pulverized coal gasification device; and the CO2-rich methanol is derived from a synthesis gas CO2 absorption process, i.e., CO2 absorption of the desulfurized gas to obtain the CO2-rich methanol and purified gas.

[0035] In the present application, preferably, the first H2S-rich methanol is derived from a synthesis gas H2S absorption process, i.e., H2S absorption of synthesis gas to obtain the first H2S-rich methanol and desulfurized gas, and the synthesis gas is derived from a pulverized coal gasification device; and the CO2-rich methanol is derived from a synthesis gas CO2 absorption process, i.e., CO2 absorption of the desulfurized gas to obtain the CO2-rich methanol and purified gas.

[0036] In the present application, preferably, the first H2S-rich methanol is derived from a synthesis gas H2S absorption process, i.e., H2S absorption of synthesis gas to obtain the first H2S-rich methanol and desulfurized gas, and the synthesis gas is derived from a pulverized coal gasification device; and the CO2-rich methanol is derived from a synthesis gas CO2 absorption process, i.e., CO2 absorption of the desulfurized gas to obtain the CO2-rich methanol and purified gas.

[0037] In the present application, preferably, the first H2S-rich methanol is derived from a synthesis gas H2S absorption process, i.e., H2S absorption of synthesis gas to obtain the first H2S-rich methanol and desulfurized gas, and the synthesis gas is derived from a pulverized coal gasification device; and the CO2-rich methanol is derived from a synthesis gas CO2 absorption process, i.e., CO2 absorption of the desulfurized gas to obtain the CO2-rich methanol and purified gas.

[0038] In the present application, preferably, in step (1), the two-stage H2S flashing includes a first H2S flashing and a second H2S flashing, wherein the first H2S-rich methanol is subjected to the first H2S flashing to obtain the first H2S flashing gas and the first H2S flashing liquid; and the first H2S flashing liquid is subjected to the second H2S flashing to obtain the second H2S flashing gas and the second H2S flashing liquid.

[0039] In the present application, the pressure of the first H2S flashing is greater than the pressure of the second H2S flashing. Preferably, the pressure of the first H2S flashing is 1.5-1.8 MPa (G), and the pressure of the second H2S flashing is 0.8-1 MPa (G).

[0040] In the present application, preferably, the first H2S-rich methanol has a CO2 molar content of 24-30%, a H2S molar content of 0.3-0.7%, a temperature of -20 to -15℃, and a pressure of 3-3.05 MPa (G).

[0041] In the present application, further preferably, after the first H2S-rich methanol is cooled to -36 to -33℃, the primary H2S flashing is performed.

[0042] In the present application, preferably, the mole content of H2S in the primary H2S flashing liquid is 0.3-0.7%, the mole content of CO2 is 23.5-29.5%, and the temperature is -36.5 to -33.5℃.

[0043] In the present application, preferably, the mole content of H2S in the secondary H2S flashing liquid is 0.4-0.6%, the mole content of CO2 is 22.5-28.5%, and the temperature is -38 to -35℃.

[0044] In the present application, the secondary CO2 flashing liquid is divided into three streams, the first stream is subjected to tertiary CO2 flashing, the second stream is subjected to first flashing, and the third stream is subjected to third flashing. Preferably, in step (2), the secondary CO2 flashing liquid is divided into a first stream of secondary CO2 flashing liquid, a second stream of secondary CO2 flashing liquid, and a third stream of secondary CO2 flashing liquid, with a molar flow ratio of 1-2:2-4:1.

[0045] In the present application, preferably, the pressure of the tertiary CO2 flashing is 0.4-0.6 MPa(G). In the present application, the first stream of secondary CO2 flashing liquid is subjected to the tertiary CO2 flashing to obtain a tertiary CO2 flashing liquid and a second CO2 product gas.

[0046] In the present application, preferably, the mole content of H2S in the tertiary CO2 flashing liquid is 0.1-0.5 ppm, the mole content of CO2 is 14-19%, and the temperature is -36 to -30℃.

[0047] In the present application, preferably, the mole content of H2S in the second CO2 product gas is ≤0.1 ppm, the mole content of CO2 is 92-96%, the temperature is -40 to -35℃, and the pressure is 0.4-0.6 MPa(G).

[0048] In the present application, preferably, the second stream of secondary CO2 flashing liquid is subjected to the first flashing to obtain a semi-lean liquid methanol and a first stream of CO2 product gas; the third stream of secondary CO2 flashing liquid is subjected to the second flashing to obtain a flashing liquid and a second stream of CO2 product gas; and the secondary H2S flashing liquid is subjected to the third flashing to obtain a sulfur-containing gas and a second H2S-rich methanol; wherein the sulfur-containing gas and the flashing liquid are contacted 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.

[0049] In the present application, preferably, the pressure of the first flash is 0.05-0.08 MPa (G); the pressure of the second flash is 0.06-0.09 MPa (G); and the pressure of the third flash is 0.12-0.16 MPa (G).

[0050] In the present application, preferably, the molar content of H2S in the semi-lean liquid methanol is 0.1-0.5 ppm, the molar content of CO2 is 11-14%, the temperature is -60 to -50℃, and the pressure is 0.05-0.08 MPa (G).

[0051] In the present application, preferably, the molar content of H2S in the low-H2S methanol is 0.1-0.4%, the molar content of CO2 is 15-23%, the temperature is -60 to -50℃, and the pressure is 0.12-0.16 MPa (G).

[0052] In the present application, preferably, the molar content of H2S in the second H2S-rich methanol is 0.35-0.55%, the molar content of CO2 is 15-19%, and the temperature is -65 to -59℃.

[0053] In the present application, further preferably, the molar content of H2S in the first CO2 product gas is ≤1 ppm, the molar content of CO2 is 99.4-99.7%, the temperature is -60 to -50℃, and the pressure is 0.05-0.08 MPa (G).

[0054] In the present application, the semi-lean liquid methanol is divided into two streams, the first stream is sent to subsequent processes, and the second stream is returned and subjected to the first washing. Preferably, in step (3), the semi-lean liquid methanol is divided into a first stream of semi-lean liquid methanol and a second stream of semi-lean liquid methanol, with a molar flow ratio of 1:30-40.

[0055] In the present application, further preferably, after the semi-lean liquid methanol is pressurized to 2-2.4 MPa (G), it is divided into the first stream of semi-lean liquid methanol and the second stream of semi-lean liquid methanol.

[0056] In the present application, preferably, the second stream of semi-lean liquid methanol and the first-stage CO2 flash gas are subjected to the first washing to obtain a first-washed CO2 flash gas and a first washing liquid; the first washing liquid and the low-H2S methanol are respectively subjected to the second washing with the second-stage CO2 flash gas to obtain a second-washed CO2 flash gas and a second washing liquid; and the second washing liquid and the second-stage H2S flash gas are subjected to the third washing to obtain the low-sulfur carbon-rich methanol and a second-washed H2S flash gas.

[0057] In the present application, further preferably, the molar content of CO2 in the CO2 flash gas after the first washing is 15-25%, the molar content of H2 is 35-45%, and the molar content of CO is 35-45%; the temperature is -45 to -40℃.

[0058] In the present application, further preferably, the molar content of CO2 in the CO2 flash gas after the first washing is 15-25%, the molar content of H2 is 35-45%, and the molar content of CO is 35-45%; the temperature is -45 to -40℃.

[0059] In the present application, further preferably, the molar content of CO2 in the CO2 flash gas after the first washing is 15-25%, the molar content of H2 is 35-45%, and the molar content of CO is 35-45%; the temperature is -45 to -40℃.

[0060] In the present application, preferably, the molar content of H2S in the low-sulfur carbon-rich methanol is 0.1-0.3%, and the molar content of CO2 is 22-26%; the temperature is -46 to -40℃.

[0061] In the present application, preferably, the non-shift H2S-rich methanol and the first-stage H2S flash gas are subjected to a fourth washing to obtain a fourth washing liquid and a first-stage H2S flash gas after the washing.

[0062] In the present application, unless otherwise specified, the non-shift H2S-rich methanol is derived from a non-shift gas purification process, i.e., the non-shift gas derived from a pulverized coal gasification device is contacted with lean methanol (the molar content of H2S in the lean methanol is 0%, and the molar content of CO2 is 0%) and purified to obtain the non-shift H2S-rich methanol. In the present application, the molar content of H2S in the non-shift H2S-rich methanol is 0.1-0.6%, the molar content of CO2 is 3-7%, the temperature is -36 to -31℃, and the pressure is 3.5-3.55 MPa(G).

[0063] In the present application, further preferably, the molar content of CO2 in the CO2 flash gas after the first washing is 15-25%, the molar content of H2 is 35-45%, and the molar content of CO is 35-45%.

[0064] In the present application, further preferably, the CO2 flash gas after the first washing and the H2S flash gas after the first washing are mixed to obtain a first-stage flash gas, and the CO2 flash gas after the second washing and the H2S flash gas after the second washing are mixed to obtain a second-stage flash gas.

[0065] In the present application, more preferably, the fourth washing liquid and the primary H2S flash liquid are mixed to obtain a mixed H2S flash liquid, and the secondary H2S flashing is performed on the mixed H2S flash liquid; the molar content of CO2 in the mixed H2S flash liquid is 23-29%, the molar content of H2S is 0.45-0.55%, and the temperature is -35 to -32℃.

[0066] In the present application, preferably, in step (4), the pressure of the fourth flashing is 0.15-0.25 MPa (G).

[0067] In the present application, preferably, the molar content of H2S in the third H2S-rich methanol is 0.1-0.4%, the molar content of CO2 is 11-15%, and the temperature is -62 to -56℃.

[0068] In the present application, the fifth washing process includes: after the third CO2 flash liquid is subjected to fourth flashing, the fourth flashing liquid is contacted with the stripping gas to perform the fifth washing, thereby obtaining a third H2S-rich methanol and a tail gas. Preferably, the fifth washing also obtains a tail gas, in which the molar content of H2S is ≤1 ppm; the molar content of CO2 is 70-80%; and the molar content of N2 is 20-30%.

[0069] In the present application, the stripping process includes: the second H2S-rich methanol, the low-sulfur carbon-rich methanol, and the third H2S-rich methanol are respectively contacted with nitrogen to perform the stripping, thereby obtaining a post-stripping H2S-rich methanol and a stripping gas. Preferably, the post-stripping H2S-rich methanol has a molar content of H2S of 0.1-0.5%; a molar content of CO2 of 2-4%; and a temperature of -55 to -48℃.

[0070] In the present application, preferably, after the second stream of the secondary CO2 flash liquid is cooled to -36 to -33℃, the first flashing is performed.

[0071] In the present application, preferably, after the third stream of the secondary CO2 flash liquid is cooled to -52 to -48℃, the second flashing is performed.

[0072] In the present application, preferably, after the third stream of the secondary CO2 flash liquid is cooled to -52 to -48℃, the second flashing is performed.

[0073] In the present application, preferably, in the order of material flow direction, the second H2S-rich methanol is subjected to the second pressurization to 0.5-1 MPa (G) and the first heat exchange to -36 to -33℃, and then the stripping is performed.

[0074] In the present application, preferably, after the third H2S-rich methanol is subjected to the second heat exchange to -36 to -33℃, the stripping is performed.

[0075] In the present invention, preferably, the low-H2S methanol is pressurized to 1-1.2 MPa(G) for the third time, and the second washing is carried out.

[0076] A schematic structural diagram of an acid gas flashing and reabsorption device for a pulverized coal gasification device provided by the second aspect of the present invention is as follows Figure 1 shown, and it can be seen from Figure 1 that the method provided by the first aspect is carried out in this device. The device includes a connected first-stage medium-pressure flash tower T-1, a second-stage medium-pressure flash tower T-2, a reabsorption tower T-3, a low-pressure flash tower T-4, and a H2S concentration tower T-5;

[0077] The first-stage medium-pressure flash tower T-1 is divided from top to bottom into a first CO2 washing section, a first-stage CO2 flash section, a first H2S washing section, and a first-stage H2S flash section; the second-stage medium-pressure flash tower T-2 is divided from top to bottom into a second CO2 washing section, a second-stage CO2 flash section, a second H2S washing section, and a second-stage H2S flash section; the reabsorption tower T-3 is divided from top to bottom into a first flash section, a second flash section, and a third flash section connected by lift holes;

[0078] Among them, the first-stage CO2 flash section and the second-stage CO2 flash section are connected by a pipeline, and the second-stage CO2 flash section is respectively connected to the low-pressure flash tower T-4, the first flash section, and the second flash section; the first-stage H2S flash section and the second-stage H2S flash section are connected by a pipeline, and the second-stage H2S flash section is connected to the third flash section;

[0079] Among them, the first CO2 washing section is connected to the first flash section, the first CO2 washing section, the second CO2 washing section, and the second H2S washing section are connected in series by a pipeline, and the second CO2 washing section is also connected to the second flash section; the first H2S washing section and the second-stage H2S flash section are connected by a pipeline;

[0080] Among them, the H2S concentration tower T-5 is divided from top to bottom into a flash washing section and a stripping section connected by lift holes. The flash washing section is connected to the low-pressure flash tower T-4, and the stripping section is connected to the third flash section, the second H2S washing section, and the flash washing section.

[0081] In the present invention, as shown in Figure 1As shown, the first-stage medium-pressure flash distillation tower T-1 includes a first-stage CO2 flash distillation section for CO2-rich methanol 1, with the resulting first-stage CO2 flash vapor 24 being piped to the first CO2 washing section, and the resulting first-stage CO2 flash liquid 3 being piped to the second-stage CO2 flash distillation section; the first CO2 washing section for first-stage washing of the second semi-lean methanol 2-ii and the first-stage CO2 flash vapor 24, resulting in first-stage washed CO2 flash vapor 5-i, and the resulting first-stage washing liquid 25 being piped to the second CO2 washing section; and a first-stage H2S flash distillation section for first-stage H2S-rich methanol 6, resulting in... The first-stage H2S flash vapor 23 is sent to the first H2S washing section via pipeline, and the obtained first-stage H2S flash liquid 8 is sent to the second H2S flash section via pipeline; the first H2S washing section is used to perform a fourth wash on the non-conversion H2S-rich methanol 7 and the first-stage H2S flash vapor 23, and the obtained fourth washing liquid 4 is sent to the second H2S flash section via pipeline, and the first-stage washed H2S flash vapor 5-ii is obtained; wherein, the first-stage washed CO2 flash vapor 5-i and the first-stage washed H2S flash vapor 5-ii are mixed to obtain the first-stage flash vapor 5; the first-stage H2S flash liquid 8 and the fourth washing liquid 4 are mixed to obtain the mixed H2S flash liquid 9.

[0082] In this invention, such as Figure 1 As shown, the two-stage medium-pressure flash tower T-2 includes a two-stage CO2 flash section for flashing the primary CO2 flash liquid 3. The resulting secondary CO2 flash vapor is sent to the second CO2 washing section via a riser. The resulting secondary CO2 flash liquid 10 is divided into three streams: a first secondary CO2 flash liquid 10-i, a second secondary CO2 flash liquid 10-ii, and a third secondary CO2 flash liquid 10-iii, which are respectively sent to the low-pressure flash tower T-4, the first flash section, and the second flash section via pipelines. The second CO2 washing section uses the first washing liquid 25 and low-H2S methanol 13 to perform a second washing on the secondary CO2 flash vapor, resulting in secondary washed CO2 flash vapor 11-i and the obtained second washing liquid. 26 is sent to the second H2S washing section via pipeline; the second-stage H2S flash evaporation section is used to perform second-stage H2S flash evaporation on the mixed H2S flash evaporation liquid 9 obtained by mixing the first-stage H2S flash evaporation liquid 8 and the fourth washing liquid 4, and the resulting second-stage H2S flash vapor is sent to the second H2S washing section via the riser, and the resulting second-stage H2S flash evaporation liquid 12 is sent to the third flash evaporation section via pipeline; the second-stage H2S washing section is used to perform third washing on the second washing liquid 26 and the second-stage H2S flash vapor to obtain low-sulfur carbon-rich methanol 20, which is sent to the gas stripping section via pipeline, and to obtain second-stage washed H2S flash vapor 11-ii; wherein, the above-mentioned second-stage washed CO2 flash vapor 11-i and second-stage washed H2S flash vapor 11-ii are mixed to obtain second-stage flash vapor 11.

[0083] In this invention, such as Figure 1 As shown, in the reabsorption tower T-3, the first flash evaporation section is used to perform a first flash evaporation on the second secondary CO2 flash liquid 10-ii to obtain semi-lean methanol 2 and a first CO2 product gas; the second flash evaporation section is used to perform a second flash evaporation on the third secondary CO2 flash liquid 10-iii to obtain flash liquid and a second CO2 product gas; the third flash evaporation section is used to perform a third flash evaporation on the secondary H2S flash liquid 12 to obtain a second H2S-rich methanol 14 and a sulfur-containing gas; wherein, the sulfur-containing gas and the flash liquid are contacted to obtain low-H2S methanol 13, and the obtained third CO2 product gas is mixed with the first CO2 product gas and the second CO2 product gas to obtain a first CO2 product gas 15.

[0084] In this invention, such as Figure 1 As shown, the low-pressure flash tower T-4 is used to perform tertiary CO2 flash evaporation on the first secondary CO2 flash liquid 10-i, and the resulting tertiary CO2 flash liquid 17 is sent to the flash washing section through a pipeline; and to obtain the second CO2 product gas 16.

[0085] In this invention, such as Figure 1 As shown, in the H2S concentration tower T-5, the stripping section is used to contact the second H2S-rich methanol 14, low-sulfur carbon-rich methanol 20, and third H2S-rich methanol 18 with nitrogen 19 and perform stripping, so that the stripped gas is sent to the flash washing section through a pipeline, and the stripped H2S-rich methanol 21 is obtained; the flash washing section is used to contact the third-stage CO2 flash liquid 17 with the above-mentioned stripped gas after the fourth flash and perform a fifth washing, so that the third H2S-rich methanol 18 is sent to the stripping section through a pipeline, and the tail gas 22 is obtained.

[0086] In this invention, preferably, as follows: Figure 1 As shown, a first pump P-1 is installed on the pipeline connecting the first flash evaporation section and the first CO2 washing section. It is used to divide the semi-lean methanol 2 into a first semi-lean methanol 2-i and a second semi-lean methanol 2-ii after the semi-lean methanol 2 is pressurized.

[0087] In this invention, preferably, as follows: Figure 1 As shown, in accordance with the material flow direction, a second pump P-2 and a first heat exchanger Q-1 are sequentially installed on the pipeline connecting the third flash section and the stripping section, for stripping the second H2S-rich methanol 14 after passing it through the second pressurization and the first heat exchange.

[0088] In this invention, preferably, as follows: Figure 1 As shown, a second heat exchanger Q-2 is installed on the pipeline connecting the flash washing section and the stripping section, which is used to strip the third H2S-rich methanol 18 after passing through the second heat exchanger.

[0089] In the present application, preferably, as shown in Figure 1 A third pump P-3 is arranged on the pipeline connecting the second flash section and the second CO2 washing section, for performing the second washing after the low H2S methanol 13 is pressurized by the third pump.

[0090] In the present application, preferably, as shown in Figure 1 A first cooler E-1 is arranged on the pipeline connecting the first H2S flash section, for performing the first-stage H2S flash after the first H2S-rich methanol 6 is cooled by the first cooler.

[0091] In the present application, preferably, as shown in Figure 1 A second cooler E-2 is arranged on the pipeline connecting the second-stage CO2 flash section and the first flash section, for performing the first flash after the second stream of the second-stage CO2 flash liquid 10-ii is cooled by the second cooler; and a third cooler E-3 is arranged on the pipeline connecting the second-stage CO2 flash section and the second flash section, for performing the second flash after the third stream of the second-stage CO2 flash liquid 10-iii is cooled by the third cooler.

[0092] In the present application, preferably, as shown in Figure 1 A fourth cooler E-4 is arranged on the pipeline connecting the low-pressure flash tower T-4 and the flash washing section, for performing the fourth flash and the fifth washing in sequence after the third-stage CO2 flash liquid 17 is cooled by the fourth cooler.

[0093] The present application will be described in detail below through examples.

[0094] Example 1

[0095] As shown in Figure 1 The device comprises a first-stage medium-pressure flash tower T-1, a second-stage medium-pressure flash tower T-2, a reabsorption tower T-3, a low-pressure flash tower T-4, and an H2S concentration tower T-5, which are connected;

[0096] The first-stage medium-pressure flash tower T-1 is divided into a first CO2 washing section, a first-stage CO2 flash section, a first H2S washing section, and a first-stage H2S flash section from top to bottom; the second-stage medium-pressure flash tower T-2 is divided into a second CO2 washing section, a second-stage CO2 flash section, a second H2S washing section, and a second-stage H2S flash section from top to bottom; the reabsorption tower T-3 is divided into a first flash section, a second flash section, and a third flash section which are communicated through a riser from top to bottom; and the H2S concentration tower T-5 is divided into a flash washing section and a gas stripping section which are communicated through a riser from top to bottom;

[0097] wherein the first H2S-rich methanol 6 (H2S molar content of 0.3-0.7%, CO2 molar content of 24-30%; temperature of -20 to -15°C) derived from the synthesis gas H2S absorption process is sent to the first H2S flashing section after the first cooler E-1 (temperature of -36 to -33°C) to perform the first H2S flashing (pressure of 1.5-1.8 MPa(G)) to obtain the first H2S flashing gas 23 and the first H2S flashing liquid 8 (H2S molar content of 0.3-0.7%, CO2 molar content of 23.5-29.5%, temperature of -36.5 to -33.5°C);

[0098] wherein the first H2S-rich methanol 6 (H2S molar content of 0.3-0.7%, CO2 molar content of 24-30%; temperature of -20 to -15°C) derived from the synthesis gas H2S absorption process is sent to the first H2S flashing section after the first cooler E-1 (temperature of -36 to -33°C) to perform the first H2S flashing (pressure of 1.5-1.8 MPa(G)) to obtain the first H2S flashing gas 23 and the first H2S flashing liquid 8 (H2S molar content of 0.3-0.7%, CO2 molar content of 23.5-29.5%, temperature of -36.5 to -33.5°C);

[0099] wherein the first H2S flashing gas 23 is sent to the first H2S washing section via a pipe to perform the fourth washing with the non-shift H2S-rich methanol 7 (H2S molar content of 0.1-0.6%, CO2 molar content of 3-7%; temperature of -36 to -31°C; pressure of 3.5-3.55 MPa(G)) derived from the non-shift gas purification process to obtain the fourth washing liquid 4 and the first washing post-H2S flashing gas 5-ii (CO2 molar content of 15-25%, H2 molar content of 35-45%; CO molar content of 35-45%);

[0100] The fourth washing liquid 4 is mixed with the first H2S flash liquid 8 to obtain a mixed H2S flash liquid 9 (H2S molar content: 0.45-0.55%, CO2 molar content: 23-29%, temperature: -35 to -32°C) which is sent to the second H2S flash section through a pipe to perform the second H2S flashing (pressure: 0.8-1 MPa (G)), and the second H2S flash gas is sent to the second H2S washing section through a riser, and the second H2S flash liquid 12 (H2S molar content: 0.4-0.6%, CO2 molar content: 22.5-28.5%, temperature: -38 to -35°C) is obtained;

[0101] The reabsorption tower T-3 is divided into a first flash section, a second flash section and a third flash section which are communicated through risers from top to bottom;

[0102] The second H2S flash liquid 12 is sent to the third flash section to perform the third H2S flashing (pressure: 0.12-0.16 MPa (G)) to obtain a sulfur-containing gas and a second H2S-rich methanol 14 (H2S molar content: 0.35-0.55%, CO2 molar content: 15-19%, temperature: -65 to -59°C, pressure: 0.13-0.17 MPa (G)) ; wherein the flash liquid and the sulfur-containing gas are contacted to obtain a low H2S methanol 13 (H2S molar content: 0.1-0.4%, CO2 molar content: 15-23%, temperature: -60 to -50°C, pressure: 0.12-0.16 MPa (G)), 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 a first CO2 product gas 15 (H2S molar content: ≤1 ppm, CO2 molar content: 99.4-99.7%, temperature: -60 to -50°C, pressure: 0.05-0.08 MPa (G)) ;

[0103] The above semi-lean methanol 2 is sent to the first pressurization to 2.2-2.4 MPa (G) through a pipeline, and then divided into a first semi-lean methanol 2-i and a second semi-lean methanol 2-ii with a molar flow ratio of 1:30-40;

[0104] The above second semi-lean methanol 2-ii and primary CO2 flash gas 24 are subjected to first washing to obtain a primary washed CO2 flash gas 5-i (the molar content of CO2 is 15-25%, the molar content of H2 is 35-45%, and the molar content of CO is 35-45%; the temperature is -45 to -40°C) and a first washing liquid 25; the above first washing liquid 25 and low H2S methanol 13 (subjected to third pressurization to 1-1.2 MPa (G)) are subjected to second washing with the above secondary CO2 flash gas to obtain secondary washed CO2 flash gas 11-i (the molar content of CO2 is 21-27%, the molar content of H2 is 67-74%, and the molar content of CO is 3-5%; the temperature is -60 to -53°C) and a second washing liquid 26; the above second washing liquid 26 and secondary H2S flash gas are subjected to third washing to obtain low-sulfur carbon-rich methanol 20 (the molar content of H2S is 0.1-0.3%, and the molar content of CO2 is 22-26%; the temperature is -46 to -40°C) and secondary washed H2S flash gas 11-ii (the molar content of CO2 is 38-44%, the molar content of H2 is 50-56%, and the molar content of CO is 3-7%; the temperature is -48 to -40°C);

[0105] The above first secondary CO2 flash liquid 10-i is sent to the low-pressure flash tower T-4 to perform third CO2 flashing (the pressure is 0.4-0.6 MPa (G)) to obtain third CO2 flash liquid 17 (the molar content of H2S is 0.1-0.5 ppm, the molar content of CO2 is 14-19%, and the temperature is -36 to -30°C) and second CO2 product gas 16 (the molar content of H2S is ≤0.1 ppm, the molar content of CO2 is 92-96%, the temperature is -40 to -35°C, and the pressure is 0.4-0.6 MPa (G));

[0106] The above third CO2 flash liquid 17 is sent to the flash washing part after fourth cooler E-4 (the temperature is -52 to -48°C), and first subjected to fourth flashing (the pressure is 0.15-0.25 MPa (G)), and then subjected to fifth washing with stripping gas from the stripping part to obtain third H2S-rich methanol 18 (the molar content of H2S is 0.1-0.4%, the molar content of CO2 is 11-15%, and the temperature is -62 to -56°C) and tail gas 22 (the molar content of H2S is ≤1 ppm, the molar content of CO2 is 70-80%, and the molar content of N2 is 20-30%; the temperature is -65 to -55°C);

[0107] The second H2S-rich methanol 14 is sequentially pressurized to 0.5-1 MPa (G), the first heat exchanger Q-1 (temperature is -36 to -33℃), the third H2S-rich methanol 18 is sequentially passed through the second heat exchanger Q-2 (temperature is -36 to -33℃), the low-sulfur carbon-rich methanol 20 is respectively sent to the gas stripping part, contacted with nitrogen 19 and subjected to gas stripping, the obtained gas stripping gas is sent to the flash washing part through the gas lifting hole, and the obtained post-gas stripping H2S-rich methanol 21 (molar content of H2S is 0.1-0.5%, molar content of CO2 is 12-4%; temperature is -55 to -48℃).

[0108] Comparative Example 1

[0109] Taking a hydrogen production device using a pulverized coal gasification gasification device 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 liquid process (i.e., CN201110260570.0 discloses a low-temperature methanol washing process) are compared with the above-mentioned baseline, as shown in Table 1.

[0110] Table 1

[0111]

[0112] As can be seen from the results in Table 1, taking a hydrogen production device based on a pulverized coal gasification gasification device as an example, the acid gas flash and reabsorption process provided by Example 1 for the supporting pulverized coal gasification device adopts two-stage medium-pressure flash and classified washing technology, and the reabsorption tower adopts three-stage tail gas washing technology, which accumulatively reduces the external cold consumption by 500 KW / h, and the overall energy-saving effect is remarkable.

[0113] The above describes the preferred embodiments of the present application in detail, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions 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 flash evaporation and reabsorption of acidic gas in a pulverized coal gasification unit, characterized in that, The method includes the following steps: (1) CO2-rich methanol (1) is subjected to two-stage CO2 flash evaporation to obtain first-stage CO2 flash vapor (24), second-stage CO2 flash vapor and second-stage CO2 flash liquid (10); first H2S-rich methanol (6) is subjected to two-stage H2S flash evaporation to obtain first-stage H2S flash vapor (23), second-stage H2S flash vapor and second-stage H2S flash liquid (12); (2) The secondary CO2 flash liquid (10) is divided into three streams. The first stream of secondary CO2 flash liquid (10-i) is subjected to tertiary CO2 flash evaporation to obtain tertiary CO2 flash liquid (17). The second stream of secondary CO2 flash liquid (10-ii), the third stream of secondary CO2 flash liquid (10-iii) and the secondary H2S flash liquid (12) are subjected to first flash evaporation, second flash evaporation and third flash evaporation respectively to obtain semi-lean methanol (2), low H2S methanol (13) and second rich H2S methanol (14). (3) The semi-lean methanol (2) is divided into two streams. The second stream of semi-lean methanol (2-ii) and the first-stage CO2 flash vapor (24) are washed for the first time, and then washed with the low-H2S methanol (13) and the second-stage CO2 flash vapor respectively for the second time, and then washed with the second-stage H2S flash vapor for the third time to obtain low-sulfur carbon-rich methanol (20). (4) The second H2S-rich methanol (14), the low-sulfur carbon-rich methanol (20) and the third H2S-rich methanol (18) are stripped by gas to obtain stripped gas and stripped H2S-rich methanol (21). The third H2S-rich methanol (18) is obtained by the third-stage CO2 flash liquid (17) after the fourth flash evaporation and the stripped gas after the fifth washing.

2. The method according to claim 1, wherein, In step (1), The two-stage CO2 flash evaporation includes a first-stage CO2 flash evaporation and a second-stage CO2 flash evaporation; wherein, the CO2-rich methanol (1) is subjected to the first-stage CO2 flash evaporation to obtain the first-stage CO2 flash vapor (24) and the first-stage CO2 flash liquid (3); the first-stage CO2 flash liquid (3) is subjected to the second-stage CO2 flash evaporation to obtain the second-stage CO2 flash vapor and the second-stage CO2 flash liquid (10); 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 CO2-rich methanol (1) is 0.1-0.5 ppm, the molar content of CO2 is 18-23%, the temperature is -24 to -18°C, and the pressure is 3.6-4 MPa(G). Preferably, the molar content of H2S in the secondary CO2 flash liquid (10) is 0.1-0.5 ppm, the molar content of CO2 is 17-22%, and the temperature is -25 to -19℃.

3. The method according to claim 1 or 2, wherein, In step (1), The two-stage H2S flash evaporation includes a first-stage H2S flash evaporation and a second-stage H2S flash evaporation. The first-stage H2S-rich methanol (6) is subjected to the first-stage H2S flash evaporation to obtain the first-stage H2S flash vapor (23) and the first-stage H2S flash liquid (8). The first-stage H2S flash liquid (8) is subjected to the second-stage H2S flash evaporation to obtain the second-stage H2S flash vapor and the second-stage H2S flash liquid (12). 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 first H2S-rich methanol (6) has a CO2 molar content of 24-30%, an H2S molar content of 0.3-0.7%, a temperature of -20 to -15°C, and a pressure of 3-3.05 MPa(G); More preferably, the first H2S-rich methanol (6) is cooled to -36 to -33°C before the first-stage H2S flash evaporation is performed; Preferably, the molar content of H2S in the secondary H2S flash liquid (12) is 0.4-0.6%, the molar content of CO2 is 22.5-28.5%, and the temperature is -38 to -35℃.

4. The method according to any one of claims 1-3, wherein, In step (2), The secondary CO2 flash liquid (10) is divided into a first secondary CO2 flash liquid (10-i), a second secondary CO2 flash liquid (10-ii), and a third secondary CO2 flash liquid (10-iii) with a molar flow ratio of 1-2:2-4:1; Preferably, the pressure of the three-stage CO2 flash evaporation is 0.4-0.6 MPa(G); Preferably, the molar content of H2S in the tertiary CO2 flash liquid (17) is 0.1-0.5 ppm, the molar content of CO2 is 14-19%, and the temperature is -36 to -30°C; Preferably, the second secondary CO2 flash liquid (10-ii) is subjected to the first flash evaporation to obtain semi-lean methanol (2) and the first CO2 product gas; the third secondary CO2 flash liquid (10-iii) is subjected to the second flash evaporation to obtain flash liquid and the second CO2 product gas; the secondary H2S flash liquid (12) is subjected to the third flash evaporation to obtain sulfur-containing gas and the second H2S-rich methanol (14); wherein, the sulfur-containing gas and the flash liquid are contacted to obtain the low H2S methanol (13), 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 (15); Preferably, the semi-lean methanol (2) contains 0.1-0.5 ppm H2S, 11-14% CO2, at a temperature of -60 to -50°C, and at a pressure of 0.05-0.08 MPa (G). Preferably, the low-H2S methanol (13) has a molar content of H2S of 0.1-0.4%, a molar content of CO2 of 15-23%, and a temperature of -60 to -50°C; Preferably, the second H2S-rich methanol (14) has a molar content of 0.35-0.55% for H2S, a molar content of 15-19% for CO2, and a temperature of -65 to -59°C. More preferably, the molar content of H2S in the first CO2 product gas (15) 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).

5. The method according to any one of claims 1-4, wherein, In step (3), The semi-lean methanol (2) is divided into a first semi-lean methanol (2-i) and a second semi-lean methanol (2-ii) with a molar flow ratio of 1:30-40; Preferably, the semi-lean methanol (2) is pressurized to 2-2.4 MPa (G) and then divided into a first stream of semi-lean methanol (2-i) and a second stream of semi-lean methanol (2-ii); Preferably, the second semi-lean methanol (2-ii) and the first-stage CO2 flash vapor (24) are subjected to the first wash to obtain CO2 flash vapor (5-i) after the first wash and the first wash liquid (25); the first wash liquid (25) and the low-H2S methanol (13) are subjected to the second-stage CO2 flash vapor for the second wash to obtain CO2 flash vapor (11-i) after the second wash and the second wash liquid (26); the second wash liquid (26) and the second-stage H2S flash vapor are subjected to the third wash to obtain the low-sulfur carbon-rich methanol (20) and H2S flash vapor (11-ii) after the second wash. More preferably, the molar content of CO2 in the CO2 flash vapor (5-i) after the first-stage washing is 15-25%, the molar content of H2 is 35-45%, and the molar content of CO is 35-45%; the temperature is -45 to -40°C. More preferably, the molar content of CO2 in the CO2 flash vapor (11-i) after the secondary washing is 21-27%, the molar content of H2 is 67-74%, and the molar content of CO is 3-5%; the temperature is -60 to -53°C. More preferably, the molar content of CO2 in the H2S flash vapor (11-ii) after the secondary washing is 38-44%, the molar content of H2 is 50-56%, and the molar content of CO is 3-7%; the temperature is -48 to -40°C. Preferably, the low-sulfur, carbon-rich methanol (20) contains 0.1-0.3% H2S and 22-26% CO2; and the temperature is -46 to -40°C. Preferably, the non-conversion H2S-rich methanol (7) and the first-stage H2S flash vapor (23) are subjected to a fourth wash to obtain a fourth wash liquid (4) and the first-stage washed H2S flash vapor (5-ii); More preferably, the molar content of CO2 in the H2S flash vapor (5-ii) after the first-stage washing is 15-25%, the molar content of H2 is 35-45%, and the molar content of CO is 35-45%. More preferably, the CO2 flash vapor (5-i) after primary washing and the H2S flash vapor (5-ii) after primary washing are mixed to obtain primary flash vapor (5); the CO2 flash vapor (11-i) after secondary washing and the H2S flash vapor (11-ii) after secondary washing are mixed to obtain secondary flash vapor (11); More preferably, the fourth washing liquid (4) and the first-stage H2S flash liquid (8) are mixed, and the resulting mixed H2S flash liquid (9) is used for the second-stage H2S flash evaporation; the mixed H2S flash liquid (9) has a CO2 molar content of 23-29%, an H2S molar content of 0.45-0.55%, and a temperature of -35 to -32°C.

6. The method according to any one of claims 1-5, wherein, In step (4), The pressure of the fourth flash evaporation is 0.15-0.25 MPa(G); Preferably, the molar content of H2S in the third H2S-rich methanol (18) is 0.1-0.4%, the molar content of CO2 is 11-15%, and the temperature is -62 to -56°C; Preferably, the molar content of H2S in the exhaust gas (22) obtained by the fifth washing is ≤1ppm; the molar content of CO2 is 70-80%; and the molar content of N2 is 20-30%. Preferably, the H2S molar content in the stripped H2S-rich methanol (21) is 0.1-0.5%; the CO2 molar content is 2-4%; and the temperature is -55 to -48°C.

7. The method according to any one of claims 1-6, wherein, The second secondary CO2 flash liquid (10-ii) is cooled to -36 to -33°C before the first flash evaporation is performed; Preferably, the third secondary CO2 flash liquid (10-iii) is cooled to -52 to -48°C before the second flash evaporation is performed; Preferably, the third-stage CO2 flash liquid (17) is cooled to -52 to -48°C before the fourth flash evaporation is performed; Preferably, the second H2S-rich methanol (14) is subjected to a second pressurization to 0.5-1 MPa (G) and a first heat exchange to -36 to -33°C in the direction of material flow before the gas stripping is performed; Preferably, the third H2S-rich methanol (18) is subjected to a second heat exchange to a temperature of -36 to -33°C before the gas stripping is performed; Preferably, the low-H2S methanol (13) is subjected to a third pressurization to 1-1.2 MPa (G) for the second washing.

8. An acid gas 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), a reabsorption tower (T-3), a low-pressure flash distillation tower (T-4), and an H2S concentration tower (T-5) connected together. The first-stage medium-pressure flash evaporator (T-1) is divided into a first CO2 washing section, a first-stage CO2 flash evaporation section, a first H2S washing section, and a first-stage H2S flash evaporation section from top to bottom; the second-stage medium-pressure flash evaporator (T-2) is divided into a second CO2 washing section, a second-stage CO2 flash evaporation section, a second H2S washing section, and a second-stage H2S flash evaporation section from top to bottom; the reabsorption tower (T-3) is divided into a first flash evaporation section, a second flash evaporation section, and a third flash evaporation section connected by air risers from top to bottom; The primary CO2 flash section and the secondary CO2 flash section are connected by pipelines, and the secondary CO2 flash section is connected to the low-pressure flash tower (T-4), the first flash section and the second flash section respectively; the primary H2S flash section and the secondary H2S flash section are connected by pipelines, and the secondary H2S flash section is connected to the third flash section. The first CO2 washing section is connected to the first flash evaporation section. The first CO2 washing section, the second CO2 washing section, and the second H2S washing section are connected in series through pipelines, and the second CO2 washing section is also connected to the second flash evaporation section. The first H2S washing section and the second H2S flash evaporation section are connected through pipelines. The H2S concentration tower (T-5) is divided into a flash washing section and a stripping section from top to bottom, which are connected by air risers. The flash washing section is connected to the low-pressure flash tower (T-4), and the stripping section is connected to the third flash section, the second H2S washing section, and the flash washing section.

9. The apparatus according to claim 8, wherein, A first pump (P-1) is installed on the pipeline connecting the first flash section and the first CO2 washing section; Preferably, a second pump (P-2) and a first heat exchanger (Q-1) are sequentially installed on the pipeline connecting the third flash section and the air stripping section, according to the material flow direction; Preferably, a second heat exchanger (Q-2) is provided on the pipe connecting the flash washing section and the air stripping section; Preferably, a third pump (P-3) is installed on the pipeline connecting the second flash section and the second CO2 washing section.

10. The apparatus according to claim 8 or 9, wherein, A first cooler (E-1) is installed on the pipe connecting the first H2S flash section; Preferably, a second cooler (E-2) is provided on the pipe connecting the secondary CO2 flash section and the first flash section; a third cooler (E-3) is provided on the pipe connecting the secondary CO2 flash section and the second flash section. Preferably, a fourth cooler (E-4) is provided on the pipe connecting the low-pressure flash tower (T-4) and the flash washing section.

Images