Low-temperature methanol washing process matched with pulverized coal gasification device

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to a low-temperature methanol washing method matched with a pulverized coal gasification device and a low-temperature methanol washing device matched with the pulverized coal gasification device. According to the method, the H2S absorption process is optimized, and H2S absorption is performed on the synthesis gas by using low-sulfur methanol, non-conversion CO2-rich methanol and non-conversion H2S-rich methanol, so that the use amount of first-stage CO2-rich methanol is reduced; the technical problem that CO2 flash steam in a medium-pressure flash tower is secondarily polluted is solved by optimally setting a medium-pressure flash evaporation process and using classified flash evaporation and classified washing technologies; and by optimally arranging a reabsorption process, low-sulfur methanol is generated and fully utilized.

Description

TECHNICAL FIELD

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

[0002] H2 and CO in the synthesis gas produced by the pulverized coal gasification technology are called effective gas, and the synthesis gas also contains a large amount of CO2 and a small amount of H2S, COS, NH3, HCN and other components. The acid gases CO2 and H2S generally need to be removed before the synthesis process. The low-temperature methanol washing is used to remove the acid gases H2S and CO2 in the synthesis gas by physical absorption, and also remove the trace components such as HCN and NH3.

[0003] In the poly-generation low-temperature methanol washing process, the CO2-rich methanol can be recycled by pressure reduction flash evaporation, but the H2S-containing methanol must be recycled by heat regeneration, which is the main source of energy consumption of the low-temperature methanol washing. Therefore, when designing the poly-generation low-temperature methanol washing process, it is the key of the technical innovation to strengthen the use efficiency of the non-shift CO2-rich methanol and the non-shift H2S-rich methanol generated by the washing of the non-shift gas, and to reduce the total amount of the lean methanol used in the washing. Specifically, it is required to make the H2S-containing methanol absorb as much H2S gas as possible before heat regeneration, so as to increase the concentration of H2S in the H2S-rich methanol and reduce the amount of the H2S-rich methanol that needs to be regenerated.

[0004] CN201110260570.0 discloses a low-temperature methanol washing process. Firstly, the low-temperature methanol washing process uses the CO2-rich methanol to wash the synthesis gas in the H2S absorption tower, and the CO2-rich methanol is contaminated while absorbing the H2S gas, which increases the amount of the H2S-rich methanol generated, and the H2S-rich methanol can be recycled only after heat regeneration, which is high in energy consumption. Secondly, the CO2 flashed from the CO2 medium-pressure flash evaporation tower is sent to the H2S medium-pressure flash evaporation tower, and the H2S-rich methanol from the bottom of the reabsorption tower is used for washing and absorption, which contaminates the CO2 gas without sulfur and requires a second washing and desulfurization in the reabsorption tower, which is not conducive to reducing the energy consumption of the device. Thirdly, in the CO2 flash evaporation section of the reabsorption tower, the CO2-rich methanol directly mixes with the H2S-rich methanol while washing the H2S-rich methanol flash gas, and the CO2-rich methanol is contaminated by the H2S-rich methanol, and the low-concentration H2S methanol generated is not fully used, which is high in energy consumption.

[0005] CN201810994082.4 discloses a low-temperature methanol washing system and a method for providing synthesis gas. The technology uses part of non-transformed CO2-rich methanol as pre-washing methanol in the desulfurization section of the non-transformed gas washing tower, which is not scientific and reasonable. The non-transformed H2S-rich methanol is used twice, but only as washing methanol for H2S-rich methanol flash gas, which is not efficient enough. There is still room for improvement and energy saving. SUMMARY

[0006] The purpose of the present application is to overcome the above technical problems, provide a low-temperature methanol washing method for a complete pulverized coal gasification device and a low-temperature methanol washing device for a complete pulverized coal gasification device. The method optimizes the H2S absorption process, uses low-sulfur methanol, non-transformed CO2-rich methanol, and non-transformed H2S-rich methanol for H2S absorption of synthesis gas, reducing the use of primary CO2-rich methanol. By optimizing the setting of the medium-pressure flash process, using classification flash and classification washing technology, the technical problem of CO2 flash gas being polluted twice in the medium-pressure flash tower is solved. By optimizing the setting of the reabsorption process, low-sulfur methanol is generated and fully utilized.

[0007] To achieve the above purpose, the first aspect of the present application provides a low-temperature methanol washing method for a complete pulverized coal gasification device, which comprises:

[0008] The non-transformed gas is subjected to primary purification to obtain pre-purified non-transformed H2S-rich methanol and pre-desulfurized non-transformed gas. The pre-desulfurized non-transformed gas is subjected to secondary purification to obtain three groups of non-transformed H2S-rich methanol and desulfurized non-transformed gas. The desulfurized non-transformed gas is subjected to tertiary purification to obtain two groups of non-transformed CO2-rich methanol and purified non-transformed gas.

[0009] The synthesis gas is subjected to primary H2S absorption and secondary H2S absorption in sequence to obtain primary H2S-rich methanol, secondary H2S-rich methanol, and desulfurized gas. The desulfurized gas is subjected to primary CO2 absorption and secondary CO2 absorption to obtain two groups of primary CO2-rich methanol, secondary CO2-rich methanol, and purified gas.

[0010] The secondary H2S-rich methanol is subjected to H2S flashing to obtain H2S flashing liquid and H2S flashing gas for first washing. The second group of primary CO2-rich methanol is subjected to CO2 flashing to obtain two groups of CO2 flashing liquid and CO2 flashing gas for second washing.

[0011] wherein the first stream of CO2 flash liquid, the second stream of CO2 flash liquid and the H2S flash liquid are subjected to first flash, second flash and third flash respectively to obtain three streams of semi-lean liquid methanol, two streams of low-sulfur methanol and first H2S-rich methanol; the first stream of low-sulfur methanol, the first H2S-rich methanol and the second H2S-rich methanol are independently contacted with nitrogen and subjected to gas stripping to obtain a stripping gas, and the stripping gas is subjected to third washing with the first stream of semi-lean liquid methanol to obtain the second H2S-rich methanol;

[0012] wherein the first stream of non-shift H2S-rich methanol, the second stream of non-shift H2S-rich methanol and the third stream of non-shift H2S-rich methanol are subjected to the first H2S absorption, the first purification and the first washing respectively; the first stream of non-shift CO2-rich methanol and the second stream of non-shift CO2-rich methanol are subjected to the second H2S absorption and the second purification respectively; the first stream of first CO2-rich methanol and the second stream of low-sulfur methanol are subjected to the second H2S absorption respectively; the second stream of semi-lean liquid methanol and the third stream of semi-lean liquid methanol are subjected to the second CO2 absorption and the second washing respectively.

[0013] The second aspect of the present application provides a low-temperature methanol washing device matched with a pulverized coal gasification device, and the device comprises: a non-shift gas washing tower, an H2S absorption tower, a CO2 absorption tower, an H2S medium-pressure flash tower, a CO2 medium-pressure flash tower, a reabsorption tower and an H2S concentration tower connected.

[0014] wherein the non-shift gas washing tower is divided into a first purification section, a second purification section and a third purification section from bottom to top; wherein the first purification section is used for purifying the non-shift gas to obtain pre-purified non-shift H2S-rich methanol, and the obtained pre-desulfurized non-shift gas enters the second purification section through a riser hole to be subjected to second purification to obtain three streams of non-shift H2S-rich methanol, and the obtained desulfurized non-shift gas enters the third purification section through a riser hole to be subjected to third purification to obtain two streams of non-shift CO2-rich methanol and purified non-shift gas;

[0015] wherein the H2S absorption tower is used for sequentially subjecting the synthesis gas to first H2S absorption and second H2S absorption to obtain first H2S-rich methanol, second H2S-rich methanol and desulfurized gas; the CO2 absorption tower is used for subjecting the desulfurized gas to first CO2 absorption and second CO2 absorption to obtain two streams of first CO2-rich methanol, second CO2-rich methanol and purified gas;

[0016] wherein the H2S medium-pressure flash tower is used for subjecting the second H2S-rich methanol to H2S flash to obtain H2S flash liquid, and the H2S flash gas is subjected to first washing; the CO2 medium-pressure flash tower is used for subjecting the second stream of first CO2-rich methanol to CO2 flash to obtain two streams of CO2 flash liquid, and the CO2 flash gas is subjected to second washing;

[0017] The reabsorption tower is divided into a first flash section, a second flash section and a third flash section from top to bottom, and is used for respectively performing first flash, second flash and third flash on the first CO2 flash liquid, the second CO2 flash liquid and the H2S flash liquid to obtain three groups of semi-lean liquid methanol, two groups of low-sulfur methanol and first H2S-rich methanol.

[0018] The H2S concentration tower is divided into a stripping section and a washing section from bottom to top; the stripping section is used for respectively contacting the first low-sulfur methanol, the first H2S-rich methanol and the second H2S-rich methanol with nitrogen and performing stripping to obtain stripping gas, which enters the washing section through a gas lifting hole, contacts the first semi-lean liquid methanol and performs third washing to obtain the second H2S-rich methanol.

[0019] The first non-shift H2S-rich methanol, the second non-shift H2S-rich methanol and the third non-shift H2S-rich methanol are returned to the H2S absorption tower, the primary purification section and the H2S medium-pressure flash tower respectively; the first non-shift CO2-rich methanol and the second non-shift CO2-rich methanol are returned to the H2S absorption tower and the secondary purification section respectively; the first primary CO2-rich methanol and the second low-sulfur methanol are returned to the H2S absorption tower respectively; and the second semi-lean liquid methanol and the third semi-lean liquid methanol are returned to the CO2 absorption tower and the CO2 medium-pressure flash tower respectively.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] (1) The method provided by the present application adopts a three-stage tail gas washing technology, selectively sets three groups of methanol with different H2S contents, i.e., the first semi-lean liquid methanol, the first low-sulfur methanol and the first H2S-rich methanol, and sequentially performs washing from high to low, so as to ensure that the tail gas emission meets the standard and the least semi-lean liquid methanol is used, thereby reducing the heat regeneration energy consumption of the whole low-temperature methanol washing device.

[0022] (2) The non-shift H2S-rich methanol obtained by performing secondary purification on the non-shift gas is divided into three groups, the second non-shift H2S-rich methanol performs primary purification on the non-shift gas, and the first non-shift H2S-rich methanol performs primary H2S absorption on the synthesis gas, compared with the prior art which uses CO2-rich methanol for washing, the use amount of the CO2-rich methanol is reduced under the premise of achieving the same washing effect, which is of positive significance for reducing the energy consumption of the low-temperature methanol washing device.

[0023] (3) The method provided by the present application optimizes the non-shift gas purification process, divides the non-shift CO2-rich methanol into two streams, the first stream is subjected to secondary H2S absorption, and the synthesis gas is treated, which can effectively reduce the use amount of the first-stage CO2-rich methanol from the CO2 absorption tower, equivalent to reducing the total amount of the second-stage H2S-rich methanol, and is beneficial to reducing the energy consumption of the device; at the same time, the second stream is subjected to secondary purification, so as to ensure the treatment effect of the non-shift gas;

[0024] (4) The method provided by the present application optimizes the medium-pressure flash evaporation process, introduces the third non-shift H2S-rich methanol to wash the H2S flash evaporation gas, and introduces the third semi-lean liquid methanol to wash the CO2 flash evaporation gas, compared with the prior art, the secondary H2S-rich methanol and the second first-stage CO2-rich methanol are respectively subjected to flash evaporation and washing, the technical problem that the CO2 flash evaporation gas is transferred to the H2S flash evaporation liquid is avoided, and this is beneficial to reducing the energy consumption of the device;

[0025] (5) The method provided by the present application optimizes the reabsorption process, realizes the absorption of the sulfur-containing gas generated by the third flash evaporation of the H2S flash evaporation liquid by the second flash evaporation of the second CO2 flash evaporation liquid, and the low-sulfur methanol is obtained without mixing with the first H2S-rich methanol;

[0026] (6) The method provided by the present application optimizes the H2S absorption process, introduces the second low-sulfur methanol, the first non-shift H2S-rich methanol and the first non-shift CO2-rich methanol to jointly absorb the H2S gas in the synthesis gas, realizes the recycling use of the low-sulfur methanol, and the effective use of the non-shift H2S-rich methanol and the non-shift CO2-rich methanol, reduces the use amount of the first-stage CO2-rich methanol in the H2S absorption, and equivalent to reducing the secondary H2S-rich methanol which needs to be heat regenerated. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a structure schematic view of a low-temperature methanol washing device matched with a pulverized coal gasification device.

[0028] REFERENCE SIGNS

[0029] T-1, non-shift gas washing tower; T-2, H2S absorption tower; T-3, CO2 absorption tower; T-4, H2S medium-pressure flash evaporation tower; T-5, CO2 medium-pressure flash evaporation tower; T-6, reabsorption tower; T-7, H2S concentration tower;

[0030] E-1, first cooler; E-2, second cooler; E-3, third cooler; E-4, fourth cooler; E-5, fifth cooler; P-1, first pump; P-2, second pump; P-3, third pump; P-4, fourth pump; P-5, fifth pump; Q-1, first heat exchanger; Q-2, second heat exchanger;

[0031] 1. non-reformed gas; 2. non-reformed H2S-rich methanol; 2-i. first stream of non-reformed H2S-rich methanol; 2-ii. second stream of non-reformed H2S-rich methanol; 2-iii. third stream of non-reformed H2S-rich methanol; 3. lean methanol; 3-i. first stream of lean methanol; 3-ii. second stream of lean methanol; 4. pre-purified non-reformed H2S-rich methanol; 5. purified non-reformed gas; 6. synthesis gas; 7. primary H2S-rich methanol; 8. non-reformed CO2-rich methanol; 8-i. first stream of non-reformed CO2-rich methanol; 8-ii. second stream of non-reformed CO2-rich methanol; 9. primary CO2-rich methanol; 9-i. first stream of primary CO2-rich methanol; 9-ii. second stream of primary CO2-rich methanol; 10. secondary H2S-rich methanol; 11. sweetened gas; 12. secondary CO2-rich methanol; 13. semi-lean liquid methanol; 13-i. first stream of semi-lean liquid methanol; 13-ii. second stream of semi-lean liquid methanol; 13-iii. third stream of semi-lean liquid methanol; 14. purified gas; 15. tail gas; 16. second H2S-rich methanol; 17. H2S-rich methanol after gas stripping; 18. H2S flash gas after washing; 19. H2S flash liquid; 20. first H2S-rich methanol; 21. low-sulfur methanol; 21-i. first stream of low-sulfur methanol; 21-ii. second stream of low-sulfur methanol; 22. CO2 product gas; 23. CO2 flash gas after washing; 24. CO2 flash liquid; 24-i. first stream of CO2 flash liquid; 24-ii. second stream of CO2 flash liquid; 25. nitrogen. DETAILED DESCRIPTION

[0032] The endpoints of the ranges and any values described herein are not limited to the precise values stated. The ranges and values should be construed to be roughly about the ranges or values. For ranges, the endpoints are included within the range unless specifically stated otherwise. For values, the value is inclusive of the value unless specifically stated otherwise.

[0033] 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 only to distinguish or indicate that this is not the same step or material. For example, "first cooling", "second cooling", "third cooling", "fourth cooling", and "fifth cooling" are used only to indicate that this is not the same cooling.

[0034] In the present application, unless otherwise specified, the "top" of the container refers to the height of 0-10% of the container from top to bottom; the "upper part" of the container refers to the height of 10-40% of the container from top to bottom; the "middle part" of the container refers to the height of 40-60% of the container from top to bottom; the "lower part" of the container refers to the height of 60-90% of the container from top to bottom; and the "bottom" of the container refers to the height of 90-100% of the container from top to bottom.

[0035] The first aspect of the present application provides a method for supporting a coal gasification device, the method comprising:

[0036] The non-shift gas is subjected to primary purification to obtain pre-purified non-shift H2S-rich methanol and pre-desulfurized non-shift gas, the pre-desulfurized non-shift gas is subjected to secondary purification to obtain three streams of non-shift H2S-rich methanol and desulfurized non-shift gas, and the desulfurized non-shift gas is subjected to tertiary purification to obtain two streams of non-shift CO2-rich methanol and purified non-shift gas;

[0037] The synthesis gas is sequentially subjected to primary H2S absorption and secondary H2S absorption to obtain primary H2S-rich methanol, secondary H2S-rich methanol and desulfurized gas, and the desulfurized gas is subjected to primary CO2 absorption and secondary CO2 absorption to obtain two streams of primary CO2-rich methanol, secondary CO2-rich methanol and purified gas;

[0038] The secondary H2S-rich methanol is subjected to H2S flashing to obtain H2S flashing liquid, and the H2S flashing gas is subjected to first washing; the second stream of primary CO2-rich methanol is subjected to CO2 flashing to obtain two streams of CO2 flashing liquid, and the CO2 flashing gas is subjected to second washing;

[0039] The first stream of CO2 flashing liquid, the second stream of CO2 flashing liquid and the H2S flashing liquid are subjected to first flashing, second flashing and third flashing, respectively, to obtain three streams of semi-lean liquid methanol, two streams of low-sulfur methanol and first H2S-rich methanol; the first stream of low-sulfur methanol, the first H2S-rich methanol and the second H2S-rich methanol are each independently contacted with nitrogen and subjected to gas stripping, the obtained gas stripping gas is subjected to third washing with the first stream of semi-lean liquid methanol to obtain the second H2S-rich methanol;

[0040] The first stream of non-shift H2S-rich methanol, the second stream of non-shift H2S-rich methanol and the third stream of non-shift H2S-rich methanol are subjected to the primary H2S absorption, primary purification and first washing, respectively; the first stream of non-shift CO2-rich methanol and the second stream of non-shift CO2-rich methanol are subjected to the secondary H2S absorption and secondary purification, respectively; the first stream of primary CO2-rich methanol and the second stream of low-sulfur methanol are subjected to the secondary H2S absorption, respectively; the second stream of semi-lean liquid methanol and the third stream of semi-lean liquid methanol are subjected to the secondary CO2 absorption and second washing, respectively.

[0041] In the present application, the non-shifted gas and the synthesis gas are both derived from a pulverized coal gasification device, wherein the synthesis gas is prepared from the non-shifted gas by a shift process, unless otherwise specified.

[0042] In the present application, the primary purification is aimed at removing HCN, NH3 and other impurities in the non-shifted gas as well as a small amount of H2S and CO2. Preferably, the non-shifted gas is contacted with a second stream of non-shifted H2S-rich methanol and the primary purification is performed to obtain the pre-purified non-shifted H2S-rich methanol and pre-desulfurized non-shifted gas.

[0043] In some embodiments of the present application, preferably, the molar content of H2S in the non-shifted gas is 0.4-0.6%, the molar content of CO2 is 5-10%, the temperature is -35 to -25°C, and the pressure is 3.5-3.6 MPa (G).

[0044] In the present application, further preferably, the molar flow ratio of the non-shifted gas to the second stream of non-shifted H2S-rich methanol is 52-62:1.

[0045] In some embodiments of the present application, preferably, the molar content of H2S in the pre-purified non-shifted H2S-rich methanol is 0.8-1.2%, the molar content of CO2 is 3-6%, and the temperature is -35 to -25°C. In the present application, the pre-purified non-shifted H2S-rich methanol is sent to subsequent processes.

[0046] In the present application, the secondary purification is aimed at further removing H2S in the non-shifted gas. Preferably, the pre-desulfurized non-shifted gas is contacted with a second stream of non-shifted CO2-rich methanol and the secondary purification is performed to obtain the non-shifted H2S-rich methanol and desulfurized non-shifted gas.

[0047] In the present application, further preferably, the molar flow ratio of the second stream of non-shifted CO2-rich methanol to the non-shifted gas is 1:1-2.

[0048] In some embodiments of the present application, preferably, the molar content of H2S in the non-shifted H2S-rich methanol is 0.5-0.8%, the molar content of CO2 is 3-7%, and the temperature is -33 to -28°C.

[0049] In some embodiments of the present application, preferably, the molar flow ratio of the first stream of non-shifted H2S-rich methanol, the second stream of non-shifted H2S-rich methanol, and the third stream of non-shifted H2S-rich methanol is 8-10:1:28-32.

[0050] In the present application, the tertiary purification refers to further purifying the desulfurized non-shifted gas obtained from the secondary purification to obtain purified non-shifted gas, unless otherwise specified.

[0051] In the present application, the third purification is aimed at further removing CO2 in the non-shifted gas. Preferably, the desulfurized non-shifted gas is contacted with the first lean methanol and the third purification is carried out to obtain the non-shifted CO2-rich methanol and the purified non-shifted gas.

[0052] In the present application, further preferably, the molar flow ratio of the first lean methanol to the non-shifted gas is 1.5-2.5:1-2.

[0053] In some embodiments of the present application, preferably, the lean methanol has a molar content of H2S of 0% and a molar content of CO2 of 0%. In the present application, the lean methanol is selected from subsequent processes. In the present application, without special circumstances, the lean methanol is divided into the first lean methanol and the second lean methanol; the present application does not limit the molar flow ratio of the first lean methanol to the second lean methanol.

[0054] In some embodiments of the present application, preferably, the non-shifted CO2-rich methanol has a molar content of H2S of 0.5-1 ppm and a molar content of CO2 of 3-8%; the temperature is -40 to -33℃; further preferably, the molar flow ratio of the first non-shifted CO2-rich methanol to the second non-shifted CO2-rich methanol is 1:1-1.1.

[0055] In some embodiments of the present application, the purified non-shifted gas has a molar content of H2S of ≤0.1 ppm, a molar content of CO2 of ≤20 ppm, a temperature of -55 to -45℃, and a pressure of 3.4-3.5 MPa(G).

[0056] In the present application, the primary H2S absorption is aimed at removing impurities such as HCN, NH3, etc. and a small amount of H2S and CO2 in the synthesis gas. Preferably, the synthesis gas is contacted with the first non-shifted H2S-rich methanol and the primary H2S absorption is carried out to obtain the pre-desulfurized gas and the primary H2S-rich methanol.

[0057] In some embodiments of the present application, preferably, the synthesis gas has a molar content of H2S of 0.3-0.35% and a molar content of CO2 of 40-50%; the temperature is -25 to -15℃, and the pressure is 3.12-3.15 MPa(G).

[0058] In the present application, further preferably, the molar flow ratio of the synthesis gas to the first non-shifted H2S-rich methanol is 25-35:1.

[0059] In some embodiments of the present application, preferably, the primary H2S-rich methanol has a molar content of H2S of 0.6-0.8% and a molar content of CO2 of 30-36%; the temperature is -25 to -15℃.

[0060] In the present application, the secondary H2S absorption is aimed at further removing H2S and CO2 in the synthesis gas. Preferably, the pre-desulfurized gas, the second low-sulfur methanol, the first non-shift CO2-rich methanol and the first primary CO2-rich methanol are contacted and subjected to the secondary H2S absorption to obtain the desulfurized gas and the secondary H2S-rich methanol.

[0061] In the present application, further preferably, the molar flow ratio of the second low-sulfur methanol to the synthesis gas is 6-9:1; the molar flow ratio of the first non-shift CO2-rich methanol to the synthesis gas is 6-7:1; and the molar flow ratio of the first primary CO2-rich methanol to the synthesis gas is 6-7:2-3.

[0062] In some embodiments of the present application, preferably, the molar content of H2S in the secondary H2S-rich methanol is 0.4-0.6%, the molar content of CO2 is 24-30%, and the temperature is -20 to -14°C.

[0063] In some embodiments of the present application, preferably, the first primary CO2-rich methanol is sequentially subjected to the first pressurization to 3.6-4 MPa (G), the first cooling to -46 to -43°C, and the secondary H2S absorption in the order of material flow direction.

[0064] In some embodiments of the present application, preferably, the molar content of H2S in the desulfurized gas is 0.5-1 ppm, the molar content of CO2 is 34-38%, the temperature is -25 to -20°C, and the pressure is 3.05-3.1 MPa (G).

[0065] In the present application, both the primary CO2 absorption and the secondary CO2 absorption are aimed at further removing CO2 in the desulfurized gas. Preferably, the desulfurized gas and the secondary CO2-rich methanol are contacted and subjected to the primary CO2 absorption to obtain the primary CO2-rich methanol and the pre-purified gas; and the pre-purified gas, the second semi-lean liquid methanol and the second lean methanol are contacted and subjected to the secondary CO2 absorption to obtain the secondary CO2-rich methanol and the purified gas.

[0066] In the present application, further preferably, the molar flow ratio of the desulfurized gas to the secondary CO2-rich methanol is 1:1.5-2.5.

[0067] In some embodiments of the present application, preferably, the molar content of H2S in the primary CO2-rich methanol is 0.1-0.5 ppm, the molar content of CO2 is 18-23%, the temperature is -22 to -18°C, and the pressure is 3.05-3.09 MPa (G).

[0068] In the present application, the primary CO2-rich methanol is divided into two streams. Preferably, the molar flow ratio of the first stream of primary CO2-rich methanol and the second stream of primary CO2-rich methanol is 1:3-5.

[0069] In the present application, further preferably, the molar flow ratio of the second stream of semi-lean methanol and the purified gas is 1.1-1.3:1; the molar flow ratio of the second stream of lean methanol and the purified gas is 1.5-1.7:1.

[0070] In some embodiments of the present application, preferably, after the secondary CO2-rich methanol is cooled to -36 to -33℃ by the second cooling, the primary CO2 absorption is performed.

[0071] In some embodiments of the present application, preferably, the H2S molar content in the purified gas is ≤0.1 ppm, the CO2 molar content is ≤20 ppm; the temperature is -55 to -50℃, and the pressure is 3-3.05 MPa(G).

[0072] In the present application, the H2S flashing is intended to remove the H2S flashing gas from the secondary H2S-rich methanol. Preferably, the pressure of the H2S flashing is 0.8-1 MPa(G).

[0073] In some embodiments of the present application, preferably, the H2S molar content in the H2S flashing liquid is 0.35-0.55%, the CO2 molar content is 22.5-28.5%; the temperature is -22 to -16℃.

[0074] In the present application, the first washing is intended to further reduce the CO2 in the H2S flashing gas. Preferably, the process of the first washing comprises: contacting the H2S flashing gas and the third stream of non-shift H2S-rich methanol and performing the first washing to obtain the washed H2S flashing gas, and mixing the obtained first washing liquid into the H2S flashing liquid.

[0075] In the present application, further preferably, the H2 molar content in the washed H2S flashing gas is 34-39%, the CO molar content is 32-37%, the CO2 molar content is 25-29%; the temperature is -30 to -20℃, and the pressure is 0.8-1 MPa(G).

[0076] In the present application, the CO2 flashing is intended to remove the CO2 flashing gas from the second stream of primary CO2-rich methanol. Preferably, the pressure of the CO2 flashing is 0.8-1 MPa(G).

[0077] In some embodiments of the present application, preferably, the H2S molar content in the CO2 flashing liquid is 0.1-0.5 ppm, the CO2 molar content is 17.5-22.5%; the temperature is -25 to -20℃.

[0078] In the present application, the CO2 flash liquid is divided into two streams. Preferably, the molar flow ratio of the first stream of CO2 flash liquid and the second stream of CO2 flash liquid is 4-6:1.

[0079] In the present application, the second washing aims to reduce the CO2 concentration in the CO2 flash gas. Preferably, the process of the second washing comprises: contacting the CO2 flash gas and the third stream of semi-lean liquid methanol and performing the second washing to obtain a washed CO2 flash gas, and mixing the obtained second washing liquid into the CO2 flash liquid.

[0080] In the present application, further preferably, the molar content of H2 in the washed CO2 flash gas is 42-47%, the molar content of CO is 38-43%, and the molar content of CO2 is 48-53%; the temperature is -40 to -30℃, and the pressure is 0.8-1 MPa(G).

[0081] In some embodiments of the present application, preferably, the first stream of CO2 flash liquid is subjected to the first flashing to obtain the semi-lean liquid methanol and a first CO2 product gas; the second stream of CO2 flash liquid is subjected to the second flashing to obtain a flash liquid and a second CO2 product gas; the H2S flash liquid is subjected to the third flashing to obtain a first H2S-rich methanol and a sulfur-containing gas; wherein the flash liquid and the sulfur-containing gas are subjected to the fourth washing to obtain a low-sulfur methanol, and the third CO2 product gas obtained is mixed with the first CO2 product gas and the second CO2 product gas to obtain a CO2 product gas.

[0082] In some embodiments of the present application, preferably, the pressure of the first flashing is 0.05-0.08 MPa(G); the pressure of the second flashing is 0.06-0.09 MPa(G); and the pressure of the third flashing is 0.12-0.16 MPa(G).

[0083] In the present application, further preferably, after the H2S flash liquid is cooled to -36 to -30℃ by the third cooling, the third flashing is performed.

[0084] In the present application, further preferably, after the CO2 flash liquid is cooled to -36 to -30℃ by the fourth cooling, the CO2 flash liquid is divided into two streams, wherein the first stream of CO2 flash liquid is subjected to the first flashing, and the second stream of CO2 flash liquid is subjected to the second flashing after being cooled to -52 to -48℃ by the fifth cooling.

[0085] In some embodiments of 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 10-14%, the temperature is -58 to -52℃; and the pressure is 0.05-0.08 MPa (G).

[0086] In the present application, the semi-lean liquid methanol is divided into three streams. Preferably, the molar flow ratio of the first stream of semi-lean liquid methanol, the second stream of semi-lean liquid methanol and the third stream of semi-lean liquid methanol is 6-8:10-12:1.

[0087] In some embodiments of the present application, preferably, after the second stream of semi-lean liquid methanol and the third stream of semi-lean liquid methanol are respectively pressurized to 3.6-4 MPa (G), the secondary CO2 absorption and the second washing are respectively carried out.

[0088] In some embodiments of the present application, preferably, the molar content of H2S in the low-sulfur methanol is 0.2-0.3%, the molar content of CO2 is 16-20%; the temperature is -58 to -54℃, and the pressure is 0.12-0.16 MPa (G).

[0089] In some embodiments of the present application, further preferably, the molar flow ratio of the first stream of low-sulfur methanol and the second stream of low-sulfur methanol is 1-1.1:1.

[0090] In some embodiments of the present application, further preferably, after the low-sulfur methanol is pressurized to 3.6-4 MPa (G), it is divided into the first stream of low-sulfur methanol and the second stream of low-sulfur methanol.

[0091] In some embodiments of the present application, preferably, the molar content of H2S in the first H2S-rich methanol is 0.3-0.5%, the molar content of CO2 is 13-17%; the temperature is -65 to -55℃, and the pressure is 0.13-0.17 MPa (G).

[0092] In some embodiments of the present application, preferably, after the first H2S-rich methanol is sequentially pressurized to 0.5-1 MPa (G) and the first heat exchange is -40 to -36℃, the gas stripping is carried out.

[0093] In some embodiments of the present application, preferably, the gas stripping also obtains the first H2S-rich methanol after gas stripping, in which the molar content of H2S is 0.2-0.5%, the molar content of CO2 is 1-4%; the temperature is -52 to -48℃, and it is sent to the subsequent process.

[0094] In some embodiments of the present application, preferably, the process of the third washing comprises: contacting the gas stripping gas and the first stream of semi-lean liquid methanol and carrying out the third washing to obtain tail gas and the second H2S-rich methanol.

[0095] In some embodiments of the present invention, further preferably, after the first semi-lean methanol is pressurized to 0.5-1 MPa(G) by the fifth compressor, the third washing is carried out.

[0096] In some embodiments of the present invention, preferably, the molar content of H2S in the second H2S-rich methanol is 0.1-0.3%, and the molar content of CO2 is 8-13%; the temperature is -58 to -53 °C.

[0097] In some embodiments of the present invention, preferably, after the second H2S-rich methanol is heat-exchanged to -40 to -36 °C by the second heat exchanger, the stripping is carried out.

[0098] In some embodiments of the present invention, preferably, the molar content of H2S in the tail gas is ≤1 ppm, and the molar content of CO2 is 70-76%; the temperature is -62 to -55 °C, and it is sent to the subsequent process.

[0099] The second aspect of the present invention provides a structural schematic diagram of a low-temperature methanol washing device supporting a pulverized coal gasification device as Figure 1 shown. It can be seen from Figure 1 that the device includes: a connected non-shift gas washing tower T-1, H2S absorption tower T-2, CO2 absorption tower T-3, H2S medium-pressure flash tower T-4, CO2 medium-pressure flash tower T-5, reabsorption tower T-6, and H2S concentration tower T-7;

[0100] Among them, the non-shift gas washing tower T-1 is divided into a first-stage purification section, a second-stage purification section, and a third-stage purification section from bottom to top; among them, the first-stage purification section is used to perform first-stage purification on the non-shift gas 1 to obtain pre-purified non-shift H2S-rich methanol 4, and the pre-desulfurized non-shift gas enters the second-stage purification section through the up-hole for second-stage purification to obtain three streams of non-shift H2S-rich methanol 2, and the desulfurized non-shift gas enters the third-stage purification section through the up-hole for third-stage purification to obtain two streams of non-shift CO2-rich methanol 8 and purified non-shift gas 5;

[0101] Among them, the H2S absorption tower T-2 is used to perform first-stage H2S absorption and second-stage H2S absorption on the syngas 6 in sequence to obtain first-stage H2S-rich methanol 7, second-stage H2S-rich methanol 10, and desulfurized gas 11; the CO2 absorption tower T-3 is used to perform first-stage CO2 absorption and second-stage CO2 absorption on the desulfurized gas 11 to obtain two streams of first-stage CO2-rich methanol 9, second-stage CO2-rich methanol 12, and purified gas 14;

[0102] The H2S medium-pressure flash distillation tower T-4 is used to flash distill the secondary H2S-rich methanol 10 to obtain H2S flash liquid 19, and H2S flash vapor is used for the first washing; the CO2 medium-pressure flash distillation tower T-5 is used to flash distill the second primary CO2-rich methanol 9-ii to obtain CO2 flash liquid 24 divided into two streams, and CO2 flash vapor is used for the second washing.

[0103] The reabsorption tower T-6 is divided into a first flash section, a second flash section and a third flash section from top to bottom. These sections are used to perform the first flash evaporation, the second flash evaporation, and the third flash evaporation on the first CO2 flash liquid 24-i, the second CO2 flash liquid 24-ii and the H2S flash liquid 19, respectively, to obtain three streams of semi-lean methanol 13, two streams of low-sulfur methanol 21 and the first H2S-rich methanol 20.

[0104] The H2S concentration tower T-7 is divided into a stripping section and a washing section from bottom to top. The stripping section is used to independently contact the first stream of low-sulfur methanol 21-i, the first stream of H2S-rich methanol 20, and the second stream of H2S-rich methanol 16 with nitrogen 25 for stripping. The stripped gas is then introduced into the washing section through the gas riser, where it is contacted with the first stream of semi-lean methanol 13-i for a third washing to obtain the second stream of H2S-rich methanol 16.

[0105] Specifically, the first non-conversion H2S-rich methanol 2-i, the second non-conversion H2S-rich methanol 2-ii, and the third non-conversion H2S-rich methanol 2-iii are returned to the H2S absorption tower T-2, the primary purification section, and the H2S medium-pressure flash tower T-4, respectively; the first non-conversion CO2-rich methanol 8-i and the second non-conversion CO2-rich methanol 8-ii are returned to the H2S absorption tower T-2 and the secondary purification section, respectively; the first primary CO2-rich methanol 9-i and the second low-sulfur methanol 21-ii are returned to the H2S absorption tower T-2, respectively; and the second semi-lean methanol 13-ii and the third semi-lean methanol 13-iii are returned to the CO2 absorption tower T-3 and the CO2 medium-pressure flash tower T-5, respectively.

[0106] According to the present invention, preferably, such as Figure 1 As shown, the H2S absorption tower T-2 is divided into a primary H2S absorption section and a secondary H2S absorption section from bottom to top. The primary H2S absorption section is used to contact the synthesis gas 6 and the first non-conversion H2S-rich methanol 2-i for primary H2S absorption to obtain primary H2S-rich methanol 7. The obtained pre-desulfurized gas enters the secondary H2S absorption section through the riser hole, and contacts the second low-sulfur methanol 21-ii, the first non-conversion CO2-rich methanol 8-i, and the first primary CO2-rich methanol 9-i for secondary H2S absorption to obtain desulfurized gas 11 and secondary H2S-rich methanol 10.

[0107] According to the present application, preferably, as shown in Figure 1 The CO2 absorption tower T-3 is divided into a primary CO2 absorption section and a secondary CO2 absorption section from bottom to top; wherein the desulfurized gas 11 and the secondary CO2-rich methanol 12 are contacted in the primary CO2 absorption section to carry out the primary CO2 absorption, to obtain the primary CO2-rich methanol 9, and the obtained pre-purified gas enters the secondary CO2 absorption section through the riser hole, and is contacted with the second semi-lean liquid methanol 13-ii and the second lean methanol 3-ii respectively to carry out the secondary CO2 absorption, to obtain the secondary CO2-rich methanol 12 and the purified gas 14.

[0108] According to the present application, preferably, as shown in Figure 1 According to the present application, preferably, as shown in

[0109] According to the present application, preferably, as shown in Figure 1 According to the present application, preferably, as shown in

[0110] In the present application, as shown in Figure 1 The H2S medium-pressure flash tower T-4 is used to carry out H2S flashing on the secondary H2S-rich methanol 10 to obtain H2S flashing liquid 19 and H2S flashing gas; the H2S flashing gas is washed with the third non-shift H2S-rich methanol 2-iii to obtain first washing liquid, which is mixed into the H2S flashing liquid 19, and the washed H2S flashing gas 18 is obtained.

[0111] In the present application, as shown in Figure 1 The CO2 medium-pressure flash tower T-5 is used to carry out CO2 flashing on the second primary CO2-rich methanol 9-ii to obtain CO2 flashing liquid 24 and CO2 flashing gas; the CO2 flashing gas is washed with the third semi-lean liquid methanol 13-iii to obtain second washing liquid, which is mixed into the CO2 flashing liquid 24, and the washed CO2 flashing gas 23 is obtained.

[0112] In the present application, as shown in Figure 1As shown, the reabsorption tower T-6 is divided into a first flash section, a second flash section and a third flash section from top to bottom, the first flash section is used for first flashing the first CO2 flash liquid 24-i to obtain semi-lean liquid methanol 13 and first CO2 product gas; the second flash section is used for second flashing the second CO2 flash liquid 24-ii to obtain flash liquid and second CO2 product gas; the third flash section is used for third flashing the H2S flash liquid 19 to obtain first H2S-rich methanol 20 and sulfur-containing gas, wherein the sulfur-containing gas and the flash liquid are contacted and third washed to obtain low-sulfur methanol 21 and third CO2 product gas; the CO2 product gas 22 includes the first CO2 product gas, the second CO2 product gas and the third CO2 product gas.

[0113] According to the present application, preferably, as shown in Figure 1 As shown, a third cooler E-3 is arranged on the pipeline connecting the H2S medium-pressure flash tower T-4 and the third flash section, which is used for third cooling the H2S flash liquid 19 before the third flashing.

[0114] According to the present application, preferably, as shown in Figure 1 As shown, a fourth cooler E-4 is arranged on the pipeline connecting the CO2 medium-pressure flash tower T-5, the first flash section and the second flash section, which is used for fourth cooling the CO2 flash liquid 24 into the first CO2 flash liquid 24-i and the second CO2 flash liquid 24-ii for the first flashing and the second flashing respectively; further preferably, a fifth cooler E-5 is arranged on the pipeline connecting the fourth cooler E-4 and the second flash section, which is used for sequentially fourth cooling and fifth cooling the second CO2 flash liquid 24-ii before the second flashing.

[0115] According to the present application, preferably, as shown in Figure 1 As shown, a third pump P-3 is arranged on the pipeline connecting the second flash section, the stripping section and the secondary H2S absorption section, which is used for third pressurizing the low-sulfur methanol 21 into the first low-sulfur methanol 21-i and the second low-sulfur methanol 21-ii for the stripping and the secondary H2S absorption respectively.

[0116] According to the present application, preferably, as shown in Figure 1 As shown, a fourth pump P-4 and a first heat exchanger Q-1 are arranged on the pipeline connecting the third flash section and the stripping section in sequence, which are used for sequentially fourth pressurizing and first heat exchanging the first H2S-rich methanol 20 before the stripping.

[0117] According to the present application, preferably, as shown in Figure 1As shown, a fifth pump P-5 is installed on the pipeline connecting the first flash evaporation section and the washing section, which is used to pressurize the first semi-lean methanol 13-i and then perform the third washing.

[0118] According to the present invention, preferably, such as Figure 1 As shown, a second heat exchanger Q-2 is installed on the pipeline connecting the washing section and the gas stripping section, which is used to perform gas stripping on the second H2S-rich methanol 16 after the second heat exchange.

[0119] The present invention will be described in detail below through embodiments.

[0120] In this invention, unless otherwise specified, both the non-shift gas and the syngas originate from the pulverized coal gasification unit.

[0121] Example 1

[0122] Devices such as Figure 1 As shown, the apparatus includes: a non-shift gas scrubbing tower T-1, an H2S absorption tower T-2, a CO2 absorption tower T-3, an H2S medium-pressure flash tower T-4, a CO2 medium-pressure flash tower T-5, a reabsorption tower T-6, and an H2S concentration tower T-7; a first cooler E-1, a second cooler E-2, a third cooler E-3, a fourth cooler E-4, and a fifth cooler E-5; a first pump P-1, a second pump P-2, a third pump P-3, a fourth pump P-4, and a fifth pump P-5; and a first heat exchanger Q-1 and a second heat exchanger Q-2.

[0123] Among them, the non-shift gas scrubbing tower T-1 is divided into a primary purification section, a secondary purification section, and a tertiary purification section connected by air risers from bottom to top; the H2S absorption tower T-2 is divided into a primary H2S absorption section and a secondary H2S absorption section connected by air risers from bottom to top; the CO2 absorption tower T-3 is divided into a primary CO2 absorption section and a secondary CO2 absorption section connected by air risers from bottom to top; the reabsorption tower T-6 is divided into a first flash section, a second flash section, and a third flash section connected by air risers from top to bottom; and the H2S concentration tower T-7 is divided into a gas stripping section and a scrubbing section connected by air risers from bottom to top.

[0124] The method is carried out in the above-described apparatus and includes:

[0125] The non-shifted gas 1 (molar content of H2S is 0.4-0.6%, molar content of CO2 is 5-10%; temperature is -35 to -25°C, pressure is 3.5-3.6 MPa(G)) and the second non-shifted H2S-rich methanol 2-ii are contacted at a molar flow ratio of 52-62:1 and subjected to primary purification, to obtain the pre-purified non-shifted H2S-rich methanol 4 (molar content of H2S is 0.8-1.2%, molar content of CO2 is 3-6%; temperature is -35 to -25°C) and the pre-desulfurized non-shifted gas; the above pre-desulfurized non-shifted gas and the second non-shifted CO2-rich methanol 8-ii are contacted and subjected to secondary purification, to obtain the non-shifted H2S-rich methanol 2 (molar content of H2S is 0.5-0.8%, molar content of CO2 is 3-7%; temperature is -33 to -28°C) and the desulfurized non-shifted gas; the above desulfurized non-shifted gas and the first methanol-lean 3-i are contacted and subjected to tertiary purification, to obtain the non-shifted CO2-rich methanol 8 (molar content of H2S is 0.5-1 ppm, molar content of CO2 is 3-8%; temperature is -40 to -33°C) and the purified non-shifted gas 5 (molar content of H2S is ≤0.1 ppm, molar content of CO2 is ≤20 ppm; temperature is -55 to -45°C, pressure is 3.4-3.5 MPa(G));

[0126] wherein the above non-shifted H2S-rich methanol 2 is divided into three streams, and the molar flow ratio of the first non-shifted H2S-rich methanol 2-i, the second non-shifted H2S-rich methanol 2-ii and the third non-shifted H2S-rich methanol 2-iii is 8-10:1:28-32;

[0127] wherein the above non-shifted CO2-rich methanol 8 is divided into two streams, and the molar flow ratio of the first non-shifted CO2-rich methanol 8-i and the second non-shifted CO2-rich methanol 8-ii is 1:1-1.1;

[0128] wherein the molar flow ratio of the above second non-shifted CO2-rich methanol 8-ii and the non-shifted gas 1 is 1:1-2; the molar flow ratio of the above first methanol-lean 3-i and the non-shifted gas 1 is 1.5-2.5:1-2;

[0129] The synthesis gas 6 (molar content of H2S is 0.3-0.35%, molar content of CO2 is 40-50%; temperature is -25 to -15°C, pressure is 3.12-3.15 MPa(G)) and the first non-shift H2S-rich methanol 2-i are contacted at a molar flow ratio of 25-35:1 and subjected to primary H2S absorption to obtain pre-desulfurization gas and primary H2S-rich methanol 7 (molar content of H2S is 0.6-0.8%, molar content of CO2 is 30-36%; temperature is -25 to -15°C); the above pre-desulfurization gas, the second low-sulfur methanol 21-ii, the first non-shift CO2-rich methanol 8-i and the first primary CO2-rich methanol 9-i (after first pressurization to 3.6-4 MPa(G) and first cooling to -46 to -43°C) are contacted and subjected to secondary H2S absorption to obtain the desulfurization gas 11 (molar content of H2S is 0.5-1 ppm, molar content of CO2 is 34-38%; temperature is -25 to -20°C; pressure is 3.05-3.1 MPa(G)) and the secondary H2S-rich methanol 10 (molar content of H2S is 0.4-0.6%, molar content of CO2 is 24-30%; temperature is -20 to -14°C);

[0130] wherein the molar flow ratio of the above second low-sulfur methanol 21-ii to the synthesis gas 6 is 1:6-9; the molar flow ratio of the above first primary CO2-rich methanol 9-i to the synthesis gas 6 is 2-3:6-7; the molar flow ratio of the above first non-shift CO2-rich methanol 8-i to the synthesis gas 6 is 1:6-7;

[0131] The above desulfurization gas 11 and the secondary CO2-rich methanol 12 (after second cooling to -36 to -33°C) are contacted at a molar flow ratio of 1:1.5-2.5 and subjected to primary CO2 absorption to obtain the primary CO2-rich methanol 9 (molar content of H2S is 0.1-0.5 ppm, molar content of CO2 is 18-23%, temperature is -22 to -18°C, pressure is 3.05-3.09 MPa(G)) and pre-purification gas; the above pre-purification gas, the second semi-lean liquid methanol 13-ii (after second pressurization to 3.6-4 MPa(G)) and the second lean methanol 3-ii are contacted and subjected to secondary CO2 absorption to obtain the secondary CO2-rich methanol 12 and the purified gas 14 (molar content of H2S is ≤0.1 ppm, molar content of CO2 is ≤20 ppm; temperature is -55 to -50°C, pressure is 3-3.05 MPa(G));

[0132] wherein the above first-stage CO2-rich methanol 9 is divided into a first stream of first-stage CO2-rich methanol 9-i and a second stream of first-stage CO2-rich methanol 9-ii, the molar flow ratio of the first stream of first-stage CO2-rich methanol 9-i to the second stream of first-stage CO2-rich methanol 9-ii being 1:3-5; the molar flow ratio of the above second stream of semi-lean liquid methanol 13-ii to purified gas 14 being 1.1-1.3:1; the molar flow ratio of the above second stream of lean methanol 3-ii to purified gas 14 being 1.5-1.7:1;

[0133] The above second-stage H2S-rich methanol 10 is subjected to H2S flashing (at a pressure of 0.8-1 MPa(G)) to obtain H2S flashed liquid 19 (having a molar content of H2S of 0.35-0.55%, a molar content of CO2 of 22.5-28.5%, and a temperature of -22 to -16°C) and H2S flashed gas, and the H2S flashed gas and the third stream of non-shift H2S-rich methanol 2-iii are subjected to first washing to obtain washed H2S flashed gas 18 (having a molar content of H2 of 34-39%, a molar content of CO of 32-37%, a molar content of CO2 of 25-29%, a temperature of -30 to -20°C, and a pressure of 0.8-1 MPa(G)), and the first washing liquid is mixed into the H2S flashed liquid 19;

[0134] The above second stream of first-stage CO2-rich methanol 9-ii is subjected to CO2 flashing (at a pressure of 0.8-1 MPa(G)) to obtain CO2 flashed liquid 24 (having a molar content of H2S of 0.1-0.5 ppm, a molar content of CO2 of 17.5-22.5%, and a temperature of -25 to -20°C) and CO2 flashed gas, and the CO2 flashed gas and the third stream of semi-lean liquid methanol 13-iii (which is second pressurized to 3.6-4 MPa(G)) are subjected to second washing to obtain washed CO2 flashed gas 23 (having a molar content of H2 of 42-47%, a molar content of CO of 38-43%, a molar content of CO2 of 48-53%, a temperature of -40 to -30°C, and a pressure of 0.8-1 MPa(G)), and the second washing liquid is mixed into the CO2 flashed liquid 24;

[0135] wherein the above CO2 flashed liquid 24 is divided into a first stream of CO2 flashed liquid 24-i and a second stream of CO2 flashed liquid 24-ii, the molar flow ratio of the first stream of CO2 flashed liquid 24-i to the second stream of CO2 flashed liquid 24-ii being 4-6:1;

[0136] The first CO2 flash liquid 24-i (cooled to -36 to -30°C by the fourth cooling) is subjected to a first flash (at a pressure of 0.05-0.08 MPa(G)) to obtain a semi-lean methanol 13 (having a molar content of H2S of 0.1-0.5 ppm and a molar content of CO2 of 10-14%, at a temperature of -58 to -52°C, and at a pressure of 0.05-0.08 MPa(G)) and a first CO2 product gas; the second CO2 flash liquid 24-ii (cooled to -36 to -30°C by the fourth cooling and then cooled to -52 to -48°C by the fifth cooling) is subjected to a second flash (at a pressure of 0.06-0.09 MPa(G)) to obtain a flash liquid and a second CO2 product gas; and the H2S flash liquid 19 (cooled to -36 to -30°C by the third cooling) is subjected to a third flash (at a pressure of 0.12-0.16 MPa(G)) to obtain a first H2S-rich methanol 20 (having a molar content of H2S of 0.3-0.5% and a molar content of CO2 of 13-17%, at a temperature of -65 to -55°C, and at a pressure of 0.13-0.17 MPa(G)) and a sulfur-containing gas;

[0137] The flash liquid and the sulfur-containing gas are subjected to a fourth washing to obtain a low-sulfur methanol 21 (having a molar content of H2S of 0.2-0.3% and a molar content of CO2 of 16-20%, at a temperature of -58 to -54°C), and a third CO2 product gas, which is mixed with the first CO2 product gas and the second CO2 product gas to obtain a CO2 product gas 22 (having a molar content of H2S of ≤1 ppm and a molar content of CO2 of 99.4-99.7%, at a temperature of -60 to -55°C, and at a pressure of 0.05-0.08 MPa(G));

[0138] The semi-lean methanol 13 is divided into three streams, a first semi-lean methanol 13-i, a second semi-lean methanol 13-ii, and a third semi-lean methanol 13-iii, at a molar flow ratio of 6-8:10-12:1;

[0139] The low-sulfur methanol 21 is divided into a first low-sulfur methanol 21-i and a second low-sulfur methanol 21-ii at a molar flow ratio of 1-1.1:1 after being pressurized to 3.6-4 MPa(G);

[0140] The first low-sulfur methanol 21-i, the first H2S-rich methanol 20 (sequentially pressurized to 0.5-1 MPa (G), first heat exchange to -40 to -36℃), and the second H2S-rich methanol 16 (second heat exchange to -40 to -36℃) are respectively contacted with nitrogen 25 and subjected to gas stripping to obtain a stripping gas and a H2S-rich methanol 17 after stripping (the molar content of H2S is 0.2-0.5%, the molar content of CO2 is 1-4%, and the temperature is -52 to -48℃); the first semi-lean liquid methanol 13-i and the stripping gas are subjected to third washing to obtain the second H2S-rich methanol 16 (the molar content of H2S is 0.1-0.3%, the molar content of CO2 is 8-13%, and the temperature is -58 to -53℃) and the tail gas 15 (the molar content of H2S is ≤1 ppm, the molar content of CO2 is 70-76%, and the temperature is -62 to -55℃).

[0141] Comparative Example 1

[0142] 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 Nm3 / h, and based on this benchmark, 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 in Table 1. 3

[0143] Table 1

[0144]

[0145]

[0146] 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 low-temperature methanol washing method provided in Example 1 for the supporting pulverized coal gasification device, the lean methanol circulation amount is 86.2% of the lean methanol circulation amount in Comparative Example 1 (lean liquid-semi-lean liquid process), the semi-lean methanol circulation amount is 81.7% of the semi-lean methanol circulation amount in Comparative Example 1 (lean liquid-semi-lean liquid process), the use amount of the first H2S absorption tower rich CO2 methanol is 75.7% of the use amount of the rich CO2 methanol in Comparative Example 1 (lean liquid-semi-lean liquid process), and the cumulative external cold consumption is reduced by 1000 KW / h, and the overall energy-saving effect is remarkable.

[0147] The preferred embodiments of the application are described in detail above, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the 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 application and fall within the protection scope of the application.​

Claims

1. A rectisol process for a coal gasification plant, characterized in that, The method comprises: carrying out primary purification on the non-reforming gas (1) to obtain pre-purified non-reforming H2S-rich methanol (4) and pre-desulfurized non-reforming gas, carrying out secondary purification on the pre-desulfurized non-reforming gas to obtain non-reforming H2S-rich methanol (2) in three streams and desulfurized non-reforming gas, and carrying out tertiary purification on the desulfurized non-reforming gas to obtain non-reforming CO2-rich methanol (8) in two streams and purified non-reforming gas (5); carrying out primary H2S absorption and secondary H2S absorption on the synthesis gas (6) in sequence to obtain primary H2S-rich methanol (7), secondary H2S-rich methanol (10) and desulfurized gas (11); carrying out primary CO2 absorption and secondary CO2 absorption on the desulfurized gas (11) to obtain primary CO2-rich methanol (9) in two streams, secondary CO2-rich methanol (12) and purified gas (14); carrying out H2S flashing on the secondary H2S-rich methanol (10) to obtain H2S flashing liquid (19) and H2S flashing gas for first washing; carrying out CO2 flashing on the second stream of primary CO2-rich methanol (9-ii) to obtain CO2 flashing liquid (24) in two streams and CO2 flashing gas for second washing; wherein the first stream of CO2 flashing liquid (24-i), the second stream of CO2 flashing liquid (24-ii) and the H2S flashing liquid (19) are subjected to first flashing, second flashing and third flashing respectively to obtain semi-lean liquid methanol (13) in three streams, low-sulfur methanol (21) in two streams and first H2S-rich methanol (20); the first stream of low-sulfur methanol (21-i), the first H2S-rich methanol (20) and the second H2S-rich methanol (16) are each independently contacted with nitrogen (25) and subjected to gas stripping, the gas stripping gas obtained is subjected to third washing with the first stream of semi-lean liquid methanol (13-i) to obtain the second H2S-rich methanol (16); wherein the first stream of non-reforming H2S-rich methanol (2-i), the second stream of non-reforming H2S-rich methanol (2-ii) and the third stream of non-reforming H2S-rich methanol (2-iii) are subjected to the primary H2S absorption, primary purification and first washing respectively; the first stream of non-reforming CO2-rich methanol (8-i) and the second stream of non-reforming CO2-rich methanol (8-ii) are subjected to the secondary H2S absorption and secondary purification respectively; the first stream of primary CO2-rich methanol (9-i) and the second stream of low-sulfur methanol (21-ii) are subjected to the secondary H2S absorption respectively; the second stream of semi-lean liquid methanol (13-ii) and the third stream of semi-lean liquid methanol (13-iii) are subjected to the secondary CO2 absorption and second washing respectively.

2. The method of claim 1, wherein, contacting the non-reforming gas (1) and the second stream of non-reforming H2S-rich methanol (2-ii) and carrying out the primary purification to obtain the pre-purified non-reforming H2S-rich methanol (4) and pre-desulfurized non-reforming gas; contacting the pre-desulfurized non-reforming gas and the second stream of non-reforming CO2-rich methanol (8-ii) and carrying out the secondary purification to obtain the non-reforming H2S-rich methanol (2) and desulfurized non-reforming gas; contacting the desulfurized non-reformed gas with a first stream of lean methanol (3-i) and performing the third stage purification to obtain the non-reformed CO2-rich methanol (8) and purified non-reformed gas (5); Preferably, the non-reformed gas (1) has a molar content of H2S of 0.4-0.6%, a molar content of CO2 of 5-10%, a temperature of -35 to -25℃, and a pressure of 3.5-3.6 MPa (G); Preferably, the non-reformed H2S-rich methanol (2) has a molar content of H2S of 0.5-0.8%, a molar content of CO2 of 3-7%, and a temperature of -33 to -28℃; Preferably, the non-reformed H2S-rich methanol (2) has a molar content of H2S of 0.5-0.8%, a molar content of CO2 of 3-7%, and a temperature of -33 to -28℃; Preferably, the first stream of non-reformed H2S-rich methanol (2-i), the second stream of non-reformed H2S-rich methanol (2-ii), and the third stream of non-reformed H2S-rich methanol (2-iii) have a molar flow ratio of 8-10:1:28-32; Preferably, the non-reformed CO2-rich methanol (8) has a molar content of H2S of 0.5-1 ppm, a molar content of CO2 of 3-8%, and a temperature of -40 to -33℃; Preferably, the first stream of non-reformed CO2-rich methanol (8-i) and the second stream of non-reformed CO2-rich methanol (8-ii) have a molar flow ratio of 1:1-1.

1.

3. The method of claim 1 or 2, wherein, contacting the desulfurized non-reformed gas with a first stream of lean methanol (3-i) and performing the third stage purification to obtain the non-reformed CO2-rich methanol (8) and purified non-reformed gas (5); contacting the desulfurized non-reformed gas with a first stream of lean methanol (3-i) and performing the third stage purification to obtain the non-reformed CO2-rich methanol (8) and purified non-reformed gas (5); Preferably, the non-reformed gas (1) has a molar content of H2S of 0.4-0.6%, a molar content of CO2 of 5-10%, a temperature of -35 to -25℃, and a pressure of 3.5-3.6 MPa (G); Preferably, the non-reformed H2S-rich methanol (2) has a molar content of H2S of 0.5-0.8%, a molar content of CO2 of 3-7%, and a temperature of -33 to -28℃; Preferably, the first stream of non-reformed H2S-rich methanol (2-i), the second stream of non-reformed H2S-rich methanol (2-ii), and the third stream of non-reformed H2S-rich methanol (2-iii) have a molar flow ratio of 8-10:1:28-32; Preferably, the non-reformed CO2-rich methanol (8) has a molar content of H2S of 0.5-1 ppm, a molar content of CO2 of 3-8%, and a temperature of -40 to -33℃; 4. The method of any of claims 1-3, wherein, Preferably, the first stream of non-reformed CO2-rich methanol (8-i) and the second stream of non-reformed CO2-rich methanol (8-ii) have a molar flow ratio of 1:1-1.

1. contacting the desulfurized non-reformed gas with a first stream of lean methanol (3-i) and performing the third stage purification to obtain the non-reformed CO2-rich methanol (8) and purified non-reformed gas (5); contacting the pre-purified gas, a second stream of semi-lean methanol (13-ii) and a second stream of lean methanol (3-ii) and performing the secondary CO2 absorption to obtain the secondary CO2-rich methanol (12) and the purified gas (14); Preferably, the molar content of H2S in the primary CO2-rich methanol (9) is 0.1-0.5 ppm, the molar content of CO2 is 18-23%, the temperature is -22 to -18℃, and the pressure is 3.05-3.09 MPa (G); Preferably, the molar flow ratio of the first stream of primary CO2-rich methanol (9-i) and the second stream of primary CO2-rich methanol (9-ii) is 1:3-5; Preferably, after the secondary CO2-rich methanol (12) is cooled to -36 to -33℃, the primary CO2 absorption is performed; Preferably, the molar content of H2S in the purified gas (14) is ≤0.1 ppm, the molar content of CO2 is ≤20 ppm; the temperature is -55 to -50℃, and the pressure is 3-3.05 MPa (G).

5. The method of any of claims 1-4, wherein, The molar content of H2S in the H2S flash liquid (19) is 0.35-0.55%, and the molar content of CO2 is 22.5-28.5%; the temperature is -22 to -16℃; Preferably, the pressure of the H2S flashing is 0.8-1 MPa (G); Preferably, the first washing process comprises: contacting the H2S flash gas and a third stream of non-shift H2S-rich methanol (2-iii) and performing the first washing to obtain the washed H2S flash gas (18), and the obtained first washing liquid is mixed into the H2S flash liquid (19); Further preferably, the molar content of H2 in the washed H2S flash gas (18) is 34-39%, the molar content of CO is 32-37%, and the molar content of CO2 is 25-29%; the temperature is -30 to -20℃, and the pressure is 0.8-1 MPa (G); Preferably, the molar content of H2S in the CO2 flash liquid (24) is 0.1-0.5 ppm, and the molar content of CO2 is 17.5-22.5%; the temperature is -25 to -20℃; Preferably, the molar flow ratio of the first stream of CO2 flash liquid (24-i) and the second stream of CO2 flash liquid (24-ii) is 4-6:1; Preferably, the pressure of the CO2 flashing is 0.8-1 MPa (G); Preferably, the second washing process comprises: contacting the CO2 flash gas and a third stream of semi-lean methanol (13-iii) and performing the second washing to obtain the washed CO2 flash gas (23), and the obtained second washing liquid is mixed into the CO2 flash liquid (24); Further preferably, the molar content of H2 in the washed CO2 flash gas (23) is 42-47%, the molar content of CO is 38-43%, and the molar content of CO2 is 48-53%; the temperature is -40 to -30℃, and the pressure is 0.8-1 MPa (G).

6. The method of any of claims 1-5, wherein, The first CO2 flash liquid (24-i) is subjected to the first flash to obtain the semi-lean liquid methanol (13) and a first CO2 product gas; the second CO2 flash liquid (24-ii) is subjected to the second flash to obtain a flash liquid and a second CO2 product gas; the H2S flash liquid (19) is subjected to the third flash to obtain a first H2S-rich methanol (20) and a sulfur-containing gas; wherein the flash liquid and the sulfur-containing gas are subjected to the fourth washing to obtain low-sulfur methanol (21), and the third CO2 product gas obtained is mixed with the first CO2 product gas and the second CO2 product gas to obtain a CO2 product gas (22); Preferably, the H2S flash liquid (19) is subjected to the third flash after being cooled to -36 to -30°C by the third cooling; Preferably, the CO2 flash liquid (24) is divided into two streams after being cooled to -36 to -30°C by the fourth cooling, wherein the first CO2 flash liquid (24-i) is subjected to the first flash, and the second CO2 flash liquid (24-ii) is subjected to the second flash after being cooled to -52 to -48°C by the fifth cooling; Preferably, the semi-lean liquid methanol (13) has a molar content of H2S of 0.1-0.5 ppm, a molar content of CO2 of 10-14%, a temperature of -58 to -52°C, and a pressure of 0.05-0.08 MPa (G); Preferably, the molar flow rate ratio of the first semi-lean liquid methanol (13-i), the second semi-lean liquid methanol (13-ii), and the third semi-lean liquid methanol (13-iii) is 6-8:10-12:1; Preferably, the second semi-lean liquid methanol (13-ii) and the third semi-lean liquid methanol (13-iii) are subjected to the secondary CO2 absorption and the second washing, respectively, after being pressurized to 3.6-4 MPa (G) by the second pressurization, respectively; Preferably, the low-sulfur methanol (21) has a molar content of H2S of 0.2-0.3%, a molar content of CO2 of 16-20%, a temperature of -58 to -54°C, and a pressure of 0.12-0.16 MPa (G); Preferably, the molar flow rate ratio of the first low-sulfur methanol (21-i) and the second low-sulfur methanol (21-ii) is 1-1.1:1; Further preferably, the low-sulfur methanol (21) is divided into the first low-sulfur methanol (21-i) and the second low-sulfur methanol (21-ii) after being pressurized to 3.6-4 MPa (G) by the third pressurization; Preferably, the first H2S-rich methanol (20) has a molar content of H2S of 0.3-0.5%, a molar content of CO2 of 13-17%, a temperature of -65 to -55°C, and a pressure of 0.13-0.17 MPa (G).

7. The method of any of claims 1-6, wherein, The first H2S-rich methanol (20) is subjected to the stripping after being pressurized to 0.5-1 MPa (G) by the fourth pressurization and being heat-exchanged to -40 to -36°C by the first heat exchange, respectively; Preferably, the stripping also obtains a stripped H2S-rich methanol (17) having a molar content of H2S of 0.2-0.5% and a molar content of CO2 of 1-4%; The temperature is -52 to -48℃; Preferably, the third washing process comprises: contacting the stripping gas and the first semi-lean liquid methanol (13-i) and performing the third washing to obtain tail gas (15) and the second H2S-rich methanol (16); Preferably, the mole content of H2S in the second H2S-rich methanol (16) is 0.1-0.3%, the mole content of CO2 is 8-13%, and the temperature is -58 to -53℃; Preferably, after the second H2S-rich methanol (16) is cooled to -40 to -36℃ by the second heat exchange, the stripping is performed; Preferably, after the first semi-lean liquid methanol (13-i) is pressurized to 0.5-1 MPa (G) by the fifth pressurization, the third washing is performed.

8. A rectisol unit of a coal gasification plant, characterized in that, The device comprises: connected non-shift gas washing tower (T-1), H2S absorption tower (T-2), CO2 absorption tower (T-3), H2S medium-pressure flash tower (T-4), CO2 medium-pressure flash tower (T-5), reabsorption tower (T-6) and H2S concentration tower (T-7); The non-shift gas washing tower (T-1) is divided into a primary purification section, a secondary purification section and a tertiary purification section from bottom to top; the primary purification section is used for primary purification of the non-shift gas (1) to obtain pre-purified non-shift H2S-rich methanol (4), and the obtained pre-desulfurization non-shift gas enters the secondary purification section through a riser hole for secondary purification to obtain three streams of non-shift H2S-rich methanol (2), and the obtained desulfurization non-shift gas enters the tertiary purification section through a riser hole for tertiary purification to obtain two streams of non-shift CO2-rich methanol (8) and purified non-shift gas (5); The H2S absorption tower (T-2) is used for sequentially performing primary H2S absorption and secondary H2S absorption on the synthesis gas (6) to obtain primary H2S-rich methanol (7), secondary H2S-rich methanol (10) and desulfurized gas (11); the CO2 absorption tower (T-3) is used for performing primary CO2 absorption and secondary CO2 absorption on the desulfurized gas (11) to obtain two streams of primary CO2-rich methanol (9), secondary CO2-rich methanol (12) and purified gas (14); The H2S medium-pressure flash tower (T-4) is used for H2S flashing of the secondary H2S-rich methanol (10) to obtain H2S flashing liquid (19), and the H2S flashing gas is subjected to first washing; the CO2 medium-pressure flash tower (T-5) is used for CO2 flashing of the second stream of primary CO2-rich methanol (9-ii) to obtain two streams of CO2 flashing liquid (24), and the CO2 flashing gas is subjected to second washing; The reabsorption tower (T-6) is divided into a first flash section, a second flash section and a third flash section from top to bottom, and is respectively used for first flashing, second flashing and third flashing of the first stream of CO2 flashing liquid (24-i), the second stream of CO2 flashing liquid (24-ii) and the H2S flashing liquid (19) to obtain three streams of semi-lean liquid methanol (13), two streams of low-sulfur methanol (21) and first H2S-rich methanol (20); The H2S concentration tower (T-7) is divided into a stripping section and a washing section from bottom to top; the stripping section is used for independently contacting the first low-sulfur methanol (21-i), the first H2S-rich methanol (20) and the second H2S-rich methanol (16) with nitrogen (25) respectively and performing stripping to obtain stripping gas which enters the washing section through a riser hole, contacts the first semi-lean liquid methanol (13-i) and performs third washing to obtain the second H2S-rich methanol (16); The first non-shift H2S-rich methanol (2-i), the second non-shift H2S-rich methanol (2-ii) and the third non-shift H2S-rich methanol (2-iii) are returned to the H2S absorption tower (T-2), the primary purification section and the H2S medium-pressure flash tower (T-4) respectively; the first non-shift CO2-rich methanol (8-i) and the second non-shift CO2-rich methanol (8-ii) are returned to the H2S absorption tower (T-2) and the secondary purification section respectively; the first primary CO2-rich methanol (9-i) and the second low-sulfur methanol (21-ii) are returned to the H2S absorption tower (T-2) respectively; the second semi-lean liquid methanol (13-ii) and the third semi-lean liquid methanol (13-iii) are returned to the CO2 absorption tower (T-3) and the CO2 medium-pressure flash tower (T-5) respectively.

9. The apparatus of claim 8, wherein, The H2S absorption tower (T-2) is divided into a primary H2S absorption section and a secondary H2S absorption section from bottom to top; the primary H2S absorption section is used for contacting the synthesis gas (6) and the first non-shift H2S-rich methanol (2-i) and performing the primary H2S absorption to obtain the primary H2S-rich methanol (7), and the obtained pre-desulfurization gas enters the secondary H2S absorption section through a riser hole, contacts the second low-sulfur methanol (21-ii), the first non-shift CO2-rich methanol (8-i) and the first primary CO2-rich methanol (9-i) respectively and performs the secondary H2S absorption to obtain the desulfurization gas (11) and the secondary H2S-rich methanol (10); The CO2 absorption tower (T-3) is divided into a primary CO2 absorption section and a secondary CO2 absorption section from bottom to top; the primary CO2 absorption section is used for contacting the desulfurization gas (11) and the secondary CO2-rich methanol (12) and performing the primary CO2 absorption to obtain the primary CO2-rich methanol (9), and the obtained pre-purification gas enters the secondary CO2 absorption section through a riser hole, contacts the second semi-lean liquid methanol (13-ii) and the second lean methanol (3-ii) respectively and performs the secondary CO2 absorption to obtain the secondary CO2-rich methanol (12) and the purified gas (14); Preferably, a first pump (P-1) and a first cooler (E-1) are arranged on a pipeline connecting the primary CO2 absorption section and the secondary H2S absorption section in sequence in the direction of material flow, which are used for performing the secondary H2S absorption after the first primary CO2-rich methanol (9-i) is sequentially subjected to first pressurization and first cooling. Preferably, a second cooler (E-2) is arranged on the pipeline connecting the bottom of the secondary CO2 absorption section and the upper part of the primary CO2 absorption section, for carrying out the primary CO2 absorption after the secondary CO2-rich methanol (12) is secondarily cooled.

10. The apparatus of claim 9, wherein, A third cooler (E-3) is arranged on the pipeline connecting the H2S medium-pressure flash tower (T-4) and the third flash section, for carrying out the third flash after the H2S flash liquid (19) is thirdly cooled. Preferably, a fourth cooler (E-4) is arranged on the pipeline connecting the CO2 medium-pressure flash tower (T-5), the first flash section and the second flash section, for dividing the CO2 flash liquid (24) into the first CO2 flash liquid (24-i) and the second CO2 flash liquid (24-ii) after the CO2 flash liquid (24) is fourthly cooled, and carrying out the first flash and the second flash respectively. Further preferably, a fifth cooler (E-5) is arranged on the pipeline connecting the fourth cooler (E-4) and the second flash section, for carrying out the second flash after the second CO2 flash liquid (24-ii) is sequentially fourthly cooled and fifthly cooled. Preferably, a third pump (P-3) is arranged on the pipeline connecting the second flash section, the stripping section and the secondary H2S absorption section, for dividing the low-sulfur methanol (21) into the first low-sulfur methanol (21-i) and the second low-sulfur methanol (21-ii) after the low-sulfur methanol (21) is thirdly pressurized, and carrying out the stripping and the secondary H2S absorption respectively. Preferably, a fourth pump (P-4) and a first heat exchanger (Q-1) are arranged on the pipeline connecting the third flash section and the stripping section in sequence, for carrying out the stripping after the first H2S-rich methanol (20) is sequentially fourthly pressurized and firstly heat-exchanged. Preferably, a fifth pump (P-5) is arranged on the pipeline connecting the first flash section and the washing section, for carrying out the third washing after the first semi-lean liquid methanol (13-i) is fifthly pressurized. Preferably, a second heat exchanger (Q-2) is arranged on the pipeline connecting the washing section and the stripping section, for carrying out the stripping after the second H2S-rich methanol (16) is secondly heat-exchanged.

Images