Energy-saving low-temperature methanol washing process matched with coal water slurry gasification device

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to an energy-saving low-temperature methanol washing method matched with a coal water slurry gasification device and a device of the energy-saving low-temperature methanol washing method.According to the method, the H2S absorption process is optimally set, low-sulfur carbon-rich methanol is used for washing synthesis gas, and the use amount of CO2-rich methanol is reduced; the medium-pressure flash evaporation process is optimally arranged, and flash steam generated by secondary flash evaporation is washed and absorbed by using low H2S methanol, so that the absorption of CO2 gas by the low H2S methanol in the H2S absorption process can be effectively inhibited; by optimizing the flow of the re-absorption tower, low H2S methanol is generated, and the low H2S methanol is prevented from being deeply polluted; by optimizing the steam stripping process, the CO2 content in the semi-barren solution methanol is further reduced, the CO2 absorption capacity of the semi-barren solution methanol is improved, the consumption of barren methanol in CO2 absorption is reduced, and the low-temperature methanol washing device has the characteristic of low comprehensive energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of low-temperature methanol washing, and particularly relates to an energy-saving low-temperature methanol washing method for a coal water slurry gasification device and an energy-saving low-temperature methanol washing device for a coal water slurry gasification device. Background Art

[0002] In the syngas produced by using the coal water slurry gasification technology, H 2 and CO are called effective gases. At the same time, the syngas also contains a large amount of CO 2 and trace amounts of H 2 S, COS, NH 3 , HCN and other components. Among them, H 2 and CO are the raw material gases for synthesizing chemical products such as methanol, ammonia, and ethylene glycol after adjusting the hydrogen-carbon ratio through the conversion unit. Acid gases CO 2 and H 2 S are generally poisons for synthesis catalysts, so they must be removed before the synthesis process.

[0003] The low-temperature methanol washing technology uses low-temperature methanol as the absorption solvent. Utilizing the excellent property that low-temperature methanol has a great solubility for acid gases, it uses physical absorption to remove acid gases such as H 2 S and CO 2 in the syngas, and at the same time removes trace components such as HCN and NH 3 . At present, the innovative research on the low-temperature methanol washing technology mainly focuses on the recycling of the pressure-reducing flash evaporation of the CO 2 -rich methanol. The typical process flow mainly includes the lean liquid-semi-lean liquid process, which has played a positive role in reducing the comprehensive energy consumption of the low-temperature methanol washing, but there are technical bottlenecks in further optimization and innovation. Therefore, it is necessary to adjust the technical innovation and optimization direction of the low-temperature methanol washing process.

[0004] In the low-temperature methanol washing process flow, the CO 2 -rich methanol can be recycled through flash evaporation, but the H 2 S-rich methanol must be recycled through thermal regeneration, which is the main energy-consuming source of the low-temperature methanol washing. Therefore, improving the utilization efficiency of the H 2 S-rich methanol is the direction and key factor of the next technological innovation. Specifically, it is necessary to achieve that before the thermal regeneration of the H 2 S-rich methanol, its absorption of the H 2 S gas in the syngas reaches the upper limit, so as to reduce the amount of the H 2 S-rich methanol that needs to be thermally regenerated.

[0005] In the low-temperature methanol washing process flow, the H 2 S-rich methanol mainly comes from three aspects. One is the CO 2Methanol in H 2 S is absorbed in the absorber to produce rich H 2 S methanol after absorbing S gas; second, part of the rich CO 2 Methanol is used to wash the rich H 2 S methanol in the reabsorber. The H 2 S gas in the flash gas of rich H 2 S methanol is also contaminated to form rich H 2 S methanol; third, in order to ensure that the H 2 S in the vent tail gas meets the standard, part of the semi-lean liquid methanol is needed to wash the tail gas, and this part of the semi-lean liquid is also contaminated by H 2 S gas and becomes rich H 2 S methanol. As long as any one of the three streams of rich H 2 S methanol can be reduced, the energy consumption of the cold methanol wash can be effectively reduced.

[0006] CN201110260570.0 discloses a cold methanol wash process. First, in this cold methanol wash process, all rich CO 2 Methanol is used to wash the syngas in the H 2 S absorber. In the H 2 S absorber, the consumption of rich CO 2 Methanol is large, and the rich H 2 S methanol needs thermal regeneration to be recycled, resulting in high energy consumption; second, in the CO 2 Flash section of the reabsorber, when the rich CO 2 Methanol washes the flash gas of rich H 2 S methanol, it directly mixes with the rich H 2 S methanol, and itself is deeply contaminated by the rich H 2 S methanol. The low-concentration H 2 S methanol after mixing is not fully utilized and is sent to the thermal regeneration system for regeneration; third, the semi-lean liquid methanol with a high CO 2 content in the carbon dioxide absorber used to absorb CO 2 gas has a weak absorption capacity for CO 2 gas, and the semi-lean liquid circulation volume is large, which is generally not conducive to reducing the overall energy consumption of the cold methanol wash unit. Summary of the Invention

[0007] The purpose of the present invention is to overcome the above technical problems and provide an energy-saving cold methanol washing method for a coal water slurry gasification device and an energy-saving cold methanol washing device for a coal water slurry gasification device. This method optimizes the H 2 S absorption process, uses low-sulfur and rich-carbon methanol to wash the syngas, and reduces the consumption of rich CO 2 Methanol; by optimizing the medium-pressure flash process, using low-H 2The S - methanol is used to wash and absorb the flash gas generated by the secondary flash evaporation, which can effectively inhibit the low H 2 The S - methanol is in H 2 The S - absorption process is for the absorption of CO 2 Gas; by optimizing the re - absorption tower process, low H 2 S - methanol is generated, and the low H 2 S - methanol is prevented from being deeply contaminated; by optimizing the stripping process, the CO content in the semi - lean methanol is further reduced, and the CO 2 absorption capacity of the semi - lean methanol is improved, and the amount of medium - poor methanol used in the CO 2 absorption is reduced. The low - temperature methanol washing device has the characteristics of low comprehensive energy consumption. 2

[0008] To achieve the above - mentioned purpose, the first aspect of the present invention provides an energy - saving low - temperature methanol washing method for a supporting water - coal slurry gasification device, and the method includes:

[0009] The syngas is subjected to H 2 S - absorption, and the desulfurized gas obtained is subjected to CO 2 absorption to obtain rich CO 2 The methanol is divided into two streams. The second stream of rich CO 2 methanol, after the first cooling, successively undergoes primary CO 2 flash evaporation and secondary CO 2 flash evaporation to obtain the rich CO 2 methanol after flash evaporation, which is divided into two streams. The first stream of rich CO 2 methanol after flash evaporation undergoes primary flash evaporation, and the obtained semi - lean methanol is divided into two streams. The first stream of semi - lean methanol and the second stream of rich CO 2 methanol after flash evaporation are heat - exchanged to obtain the heat - exchanged semi - lean methanol and the heat - exchanged rich CO 2 methanol, which respectively undergo stripping and secondary flash evaporation, and low - carbon methanol and flash liquid are respectively obtained; wherein, the low - carbon methanol is returned and subjected to the above - mentioned CO 2 absorption;

[0010] The first rich H 2 S - methanol obtained by the H 2 S - absorption, after the second cooling, successively undergoes primary H 2 S flash evaporation and secondary H 2 S flash evaporation to obtain the rich H 2 S - methanol after flash evaporation, which undergoes tertiary flash evaporation. The obtained sulfur - containing gas phase and the flash liquid are subjected to the first washing to obtain low H 2 S - methanol, which is subjected to the second washing with the flash gas of the secondary CO 2 flash evaporation and the secondary H 2 S flash evaporation to obtain low - sulfur rich - carbon methanol and the first stream of rich CO 2 methanol, which independently return and undergo the above - mentioned H​2 S absorption.

[0011] The second aspect of the present invention provides an energy-saving low-temperature methanol washing device for a coal water slurry gasification device, and the device includes: an H 2 S absorption tower, a CO 2 absorption tower, a first flash tower, a second flash tower, a reabsorption tower, and a stripping tower; the first flash tower is divided into a first-stage CO 2 flash section and a first-stage H 2 S flash section from top to bottom; the second flash tower is divided into a second-stage CO 2 flash section and a second-stage H 2 S flash section from top to bottom;

[0012] Synthesis gas enters the H 2 S absorption tower for H 2 S absorption to obtain desulfurized gas and first rich H 2 S methanol; the desulfurized gas enters the CO 2 absorption tower for CO 2 absorption to obtain rich CO 2 methanol is divided into two streams, and the second stream of rich CO 2 methanol, after passing through the first cooler, sequentially enters the first-stage CO 2 flash section and the second-stage CO 2 flash section to obtain the flashed rich CO 2 methanol is divided into two streams, the first stream of flashed rich CO 2 methanol enters the upper part of the reabsorption tower for the first flash to obtain semi-lean liquid methanol divided into two streams, and the second stream of flashed rich CO 2 methanol and the first stream of semi-lean liquid methanol enter the heat exchanger to obtain the heat-exchanged rich CO 2 methanol and the heat-exchanged semi-lean liquid methanol respectively enter the middle part of the reabsorption tower and the stripping tower for the second flash and stripping respectively to obtain the flashed liquid and low-carbon methanol, and the low-carbon methanol is recycled and reused in the CO 2 absorption tower;

[0013] The first rich H 2 S methanol, after passing through the second cooler, sequentially enters the first-stage H 2 S flash section and the second-stage H 2 S flash section to obtain the flashed rich H 2 S methanol enters the lower part of the reabsorption tower for the third flash, and the sulfur-containing gas phase obtained is subjected to the first washing with the flashed liquid to obtain the low H 2 S methanol enters the second-stage H 2 S flash section to perform the second washing with the flashed gas in the second-stage CO 2 flash section and the second-stage H 2 S flash section to obtain the low-sulfur rich-carbon methanol and the first stream of rich CO2 Methanol is independently recycled back to H 2 S absorption tower.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] (1) The method provided by the present invention optimizes the medium-pressure flashing process: adopting a two-stage flashing technology, the first-stage flashing (i.e., the first-stage CO 2 flashing and the first-stage H 2 S flashing) adopts a relatively high flashing pressure, and the first-stage flash gas can be directly sent to the compression process without washing, which can reduce the power consumption of the compressor; the second-stage flashing (i.e., the second-stage CO 2 flashing and the second-stage H 2 S flashing) adopts a relatively low flashing pressure to ensure that the effective gas in the rich CO 2 methanol after the first-stage flashing and the rich H 2 S methanol solution after the first-stage flashing is fully recovered, and at the same time, the intake air volume of the first-stage cylinder of the compressor in the compression process can be reduced, correspondingly reducing the power consumption of the compressor;

[0016] (2) The method provided by the present invention optimizes the reabsorption process, realizing that the flash liquid of the rich CO 2 methanol after heat exchange absorbs the sulfur components in the product gas generated by the flash of the rich H 2 S methanol after flashing, but does not mix with the third rich H 2 S methanol after flashing, making the H 2 S content in the solution lower and obtaining low-H 2 S methanol; 2 S methanol;

[0017] (3) In the second-stage H 2 S flashing of the method provided by the present invention, by introducing low-H 2 S methanol to absorb the flash gas, the CO 2 S concentration in the low-H 2 S methanol is slightly increased while the CO 2 gas content is increased, further reducing the absorption of CO 2 S methanol in the H 2 S absorption process for CO 2 gas, so that as much CO 2 gas as possible is absorbed in the CO 2 absorption process. Correspondingly, the total amount of gas flashed from the rich H 2 S methanol after flashing in the reabsorption process is reduced, then the amount of flash liquid used to wash the sulfur-containing gas phase is also correspondingly reduced, and the rich H 2 S methanol for heat regeneration is also reduced, thereby reducing the comprehensive energy consumption of the cold methanol washing device;

[0018] (4) In the method provided by the present invention, in order to further reduce the CO content in the semi-lean methanol and maximize the CO absorption capacity of the semi-lean liquid, the optimized re-absorption process performs nitrogen stripping on the semi-lean methanol after heat exchange again, so that the CO content in the semi-lean methanol is further reduced to 13-17%, becoming low-carbon methanol. This can produce two positive effects: one is that with the improvement of the absorption capacity of low-carbon methanol and the reduction of the circulation volume, the operating cost of the pump can be reduced by about 15%, and the diameter of the CO absorption tower can be reduced by about 5%; the other is that low-carbon methanol can replace part of the lean methanol, so that the circulation amount of lean methanol in the CO absorption tower also decreases, and the reduction of the lean methanol flow rate will be transmitted to the rich CO methanol, and the flow rate of the rich H2S methanol that needs to be thermally regenerated will also decrease, and the energy consumption of the corresponding thermal regeneration system will also decrease accordingly. 2 content, and maximize the CO 2 absorption capacity of the semi-lean liquid, the optimized re-absorption process performs nitrogen stripping on the semi-lean methanol after heat exchange again, so that the CO 2 content in the semi-lean methanol is further reduced to 13-17%, becoming low-carbon methanol. This can produce two positive effects: one is that with the improvement of the absorption capacity of low-carbon methanol and the reduction of the circulation volume, the operating cost of the pump can be reduced by about 15%, and the diameter of the CO 2 absorption tower can be reduced by about 5%; the other is that low-carbon methanol can replace part of the lean methanol, so that the CO 2 circulation amount of lean methanol in the absorption tower also decreases, and the reduction of the lean methanol flow rate will be transmitted to the rich CO 2 methanol, and the flow rate of the rich H 2 S methanol that needs to be thermally regenerated will also decrease, and the energy consumption of the corresponding thermal regeneration system will also decrease accordingly. Description of the Drawings

[0019] Figure 1 is a schematic structural diagram of an energy-saving low-temperature methanol washing device supporting a water coal slurry gasification device provided by the present invention.

[0020] Description of the Reference Numerals in the Drawings

[0021] T-1, H 2 S Absorption Tower; T-2, CO 2 Absorption Tower; T-3, First Flash Tower; T-4, Second Flash Tower; T-5, Re-absorption Tower; T-6, Stripping Tower; Q, Heat Exchanger; E-1, First Cooler; E-2, Second Cooler; E-3, Third Cooler; E-4, Fourth Cooler; P-1, First Pump; P-2, Second Pump; P-3, Third Pump; P-4, Fourth Pump;

[0022] 1, Syngas; 2, Low-sulfur Rich-carbon Methanol; 2-i, First Stream of Low-sulfur Rich-carbon Methanol; 2-ii, Second Stream of Low-sulfur Rich-carbon Methanol; 3, Second Rich H 2 2S Methanol; 4, Rich CO 2 Methanol; 4-i, First Stream of Rich CO 2 Methanol; 4-ii, Second Stream of Rich CO 2 Methanol; 5, First Rich H 2 2S Methanol; 6, Desulfurized Gas; 7, CO-containing 2 Methanol; 8, Semi-lean Methanol; 8-i, First Stream of Semi-lean Methanol; 8-ii, Second Stream of Semi-lean Methanol; 9, Lean Methanol; 10, Low-carbon Methanol; 11, First-stage Flash Gas; 11-i, First-stage CO 2 Flash Gas; 11-ii, First-stage H 2S flash vapor; 12, purified gas; 13, rich CO after the first flash 2 methanol; 14, rich H after the first flash 2 S methanol; 15, second-stage flash vapor; 16, rich H after flashing 2 S methanol; 17, second-stage CO 2 flash vapor; 18, rich CO after flashing 2 methanol; 18-i, the first rich CO after flashing 2 methanol; 18-ii, the second rich CO after flashing 2 methanol; 19, the third rich H 2 S methanol; 20, CO 2 product gas; 21, nitrogen; 22, tail gas; 23, low H 2 S methanol; 24, semi-lean liquid methanol after heat exchange; 25, rich CO after heat exchange 2 methanol. Detailed implementation mode

[0023] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0024] In the present invention, without special circumstances, "first", "second", "third" and "fourth" neither represent the order nor limit each material or step, but are only used to distinguish that these are not the same material or step. For example. "The first rich H 2 S methanol", "the second rich H 2 S methanol" and "the third rich H 2 S methanol" in which "first", "second" and "third" are only used to indicate that these are not the same rich H 2 S methanol.

[0025] In the present invention, without special circumstances, the "top" of the container refers to the 0-10% height of the container from top to bottom; the "upper part" of the container refers to the 10-40% height of the container from top to bottom; the "middle part" of the container refers to the 40-60% height of the container from top to bottom; the "lower part" of the container refers to the 60-90% height of the container from top to bottom; the "bottom" of the container refers to the 90-100% height of the container from top to bottom.

[0026] The first aspect of the present invention provides an energy-saving low-temperature methanol washing method for supporting a water coal slurry gasification device, and this method includes:

[0027] The syngas is subjected to H 2 S absorption, and the desulfurized gas obtained is subjected to CO 2 absorption to obtain rich CO 2 methanol is divided into two streams. The second stream of rich CO 2 methanol, after the first cooling, successively undergoes primary CO 2 flashing and secondary CO 2 flashing to obtain the rich CO 2 methanol after flashing, which is divided into two streams. The first stream of rich CO 2 methanol undergoes primary flashing, and the semi-lean liquid methanol obtained is divided into two streams. The first stream of semi-lean liquid methanol and the second stream of rich CO 2 methanol are heat-exchanged to obtain the heat-exchanged semi-lean liquid methanol and the heat-exchanged rich CO 2 methanol respectively undergo stripping and secondary flashing, and low-carbon methanol and flashing liquid are respectively obtained; wherein, the low-carbon methanol is returned and subjected to the above-mentioned CO 2 absorption;

[0028] The first rich H 2 S methanol obtained by H 2 S absorption, after the second cooling, successively undergoes primary H 2 S flashing and secondary H 2 S flashing to obtain the rich H 2 S methanol after flashing undergoes tertiary flashing, and the sulfur-containing gas phase obtained and the flashing liquid are subjected to the first washing to obtain the low H 2 S methanol, which is subjected to the second washing with the flash gas of the secondary CO 2 flashing and secondary H 2 S flashing to obtain the low-sulfur rich-carbon methanol and the first stream of rich CO 2 methanol respectively return independently and undergo the above-mentioned H 2 S absorption.

[0029] In the present invention, without special description, the rich CO 2 methanol is divided into two streams. The first stream returns and undergoes the above-mentioned H 2 S absorption, and the second stream, after the first cooling, undergoes primary CO 2 flashing; the rich CO 2 methanol after flashing is divided into two streams. The first stream directly undergoes primary flashing, and the second stream undergoes secondary flashing after heat exchange; the semi-lean liquid methanol is divided into two streams. The first stream undergoes stripping after heat exchange, and the second stream is sent to subsequent processes for treatment.

[0030] In some embodiments of the present invention, preferably, the low-sulfur rich-carbon methanol is first pressurized to 5.8 - 6 MPa(G), and then returns and undergoes the above-mentioned H 2 S absorption.

[0031] In some embodiments of the present invention, more preferably, the low-sulfur and carbon-rich methanol is divided into two streams and respectively returned for the H 2 S absorption; more preferably, the low-sulfur and carbon-rich methanol is divided into a first low-sulfur and carbon-rich methanol stream and a second low-sulfur and carbon-rich methanol stream with a molar flow rate ratio of 1:11-13, and they are respectively returned for the H 2 S absorption.

[0032] In some embodiments of the present invention, preferably, in the direction of material flow, the first CO-rich 2 methanol is first pressurized to 5.8-6 MPa(G) and then cooled to -35 to -25 °C, and then returned for the H 2 S absorption.

[0033] In some embodiments of the present invention, preferably, the process of the H 2 S absorption includes: contacting the syngas with the first low-sulfur and carbon-rich methanol stream to perform the first H 2 S absorption to obtain a pre-desulfurized gas and a second H-rich 2 S methanol, contacting the pre-desulfurized gas, the second low-sulfur and carbon-rich methanol stream and the first CO-rich 2 methanol to perform the second H 2 S absorption to obtain the desulfurized gas and the first H-rich 2 S methanol.

[0034] In some embodiments of the present invention, preferably, the molar content of H 2 S in the syngas is 0.9-1.2%, and the molar content of CO 2 is 40-50%; the temperature is -15 to -5 °C, and the pressure is 5.2-5.7 MPa(G). In the present invention, the syngas is from the upstream syngas cooling process.

[0035] In some embodiments of the present invention, preferably, the molar flow rate ratio of the syngas to the first low-sulfur and carbon-rich methanol stream is 70-80:1.

[0036] In the present invention, the first H 2 S absorption aims to remove impurities such as HCN and NH 3 in the syngas and a small amount of H 2 S and CO 2 to obtain a pre-desulfurized gas and a second H-rich 2 S methanol. Preferably, the molar content of H 2 S in the second H-rich 2 S methanol is 2.5-3%, and the molar content of CO 2 is 72-75%.

[0037] In some embodiments of the present invention, preferably, the molar flow rate ratio of the syngas to the second low-sulfur carbon-rich methanol is 5-7:1; the molar flow rate ratio of the syngas to the first CO-rich 2 methanol is 2-3:1.

[0038] In the present invention, the second H 2 S absorption is intended to further remove H 2 S, as well as a small amount of CO 2 . Preferably, the molar content of H 2 S in the first H 2 S-rich methanol is 1.5-1.8%, and the molar content of CO 2 is 38-42%.

[0039] In some embodiments of the present invention, preferably, the molar content of H 2 S in the desulfurized gas is 0.5-1 ppm, and the molar content of CO 2 is 38-40%; the temperature is -20 to -10 °C; the pressure is 5.3-5.4 MPa(G).

[0040] In some embodiments of the present invention, more preferably, after the low-carbon methanol is pressurized to 5.8-6 MPa(G) for the third time, it is returned and the CO 2 absorption is carried out.

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

[0042] In some embodiments of the present invention, preferably, the molar flow rate ratio of the desulfurized gas to the CO-containing 2 methanol is 1:1-1.2; more preferably, in the direction of the material flow, after the CO-containing 2 methanol is cooled to -36 to -33 °C for the fourth time, it is returned and the first CO 2 absorption is carried out.

[0043] In the present invention, the first CO 2 absorption is intended to further remove CO 2 from the desulfurized gas. Preferably, the CO 2 in the CO-rich 2The molar content of is 32 - 34%, H 2 The molar content of H₂S is 0.1 - 0.5 ppm; the temperature is -10 to -5 °C, and the pressure is 5.2 - 5.4 MPa(G).

[0044] In some embodiments of the present invention, preferably, the CO-rich 2 methanol is divided into a first stream of CO-rich 2 methanol and a second stream of CO-rich 2 methanol with a molar flow rate ratio of 1:1.8 - 2.2.

[0045] In some embodiments of the present invention, preferably, the molar flow rate ratio of the purified gas to the low-carbon methanol is 1.8 - 2:1; the molar flow rate ratio of the purified gas to the lean methanol is 1:1 - 1.2.

[0046] In some embodiments of the present invention, preferably, the H₂S molar content in the purified gas < 0.1 ppm, and the CO 2 molar content < 20 ppm; the temperature is -55 to -50 °C, and the pressure is 5.2 - 5.3 MPa(G). 2 In the present invention, the first cooling is achieved by reducing the temperature of the second stream of CO-rich

[0047] methanol, generating low temperature through pressure reduction flashing, and improving the absorption capacity of the CO-rich 2 methanol after flashing for H₂S gas in the sulfur-containing gas phase, which is beneficial to washing H₂S 2 gas in the CO 2 product gas after flashing. Preferably, the temperature of the material after the first cooling is -36 to -33 °C. 2 In some embodiments of the present invention, preferably, the material after the first cooling is subjected to the first-stage CO 2 flashing to obtain first-stage CO

[0048] flash gas and first-stage CO-rich 2 methanol after flashing, and the first-stage CO-rich 2 methanol after flashing is subjected to the second-stage CO 2 flashing to obtain second-stage CO 2 flash gas and CO-rich 2 methanol after flashing. 2 In the present invention, the first-stage CO 2 flashing adopts a relatively high pressure, aiming to flash out the effective gas CO

[0049] and H₂S in the material after the first cooling. Preferably, the pressure of the first-stage CO 2 flashing is 3.5 - 3.7 MPa(G). 2 and H 2 In the present invention, the first-stage CO 2 flashing adopts a relatively high pressure, aiming to flash out the effective gas CO

[0050] In some embodiments of the present invention, preferably, after the first flash evaporation, the rich CO 2 The molar content of H 2 S in methanol is 0.1 - 0.5 ppm, and the molar content of CO 2 is 31.5 - 33.5%; the temperature is -36.5 to -33.5 °C.

[0051] In the present invention, the second-stage CO 2 flash evaporation adopts a lower pressure, aiming to further flash out the effective gas CO 2 and H 2 S in the rich CO 2 methanol after the first flash evaporation. Preferably, the pressure of the second-stage CO 2 flash evaporation is 1.6 - 2 MPa(G).

[0052] In some embodiments of the present invention, preferably, after the flash evaporation, the rich CO 2 The molar content of H 2 S in methanol is 0.1 - 0.5 ppm, and the molar content of CO 2 is 31 - 33%; the temperature is -37 to -34 °C.

[0053] In some embodiments of the present invention, preferably, the rich CO 2 methanol after the flash evaporation is divided into the first rich CO 2 methanol after the flash evaporation and the second rich CO 2 methanol with a molar flow rate ratio of 3.3 - 3.5:1.

[0054] In the present invention, the second cooling reduces the temperature of the first rich H 2 S methanol, generates low temperature through pressure reduction flash evaporation, and at the same time lays a foundation for obtaining low temperature (high-quality cold energy) for the reabsorption tower. Preferably, the temperature of the material after the second cooling is -32 to -30 °C.

[0055] In some embodiments of the present invention, preferably, the material after the second cooling is subjected to the first-stage H 2 S flash evaporation to obtain first-stage H 2 S flash vapor and first-stage flash evaporation-rich H 2 S methanol, and the first-stage flash evaporation-rich H 2 S methanol is subjected to the second-stage H 2 S flash evaporation to obtain second-stage H 2 S flash vapor and flash evaporation-rich H 2 S methanol.

[0056] In the present invention, the first-stage H 2The S flashing uses a relatively high pressure to flash off the effective gases CO 2 and H 2 S in the second cooled material. Preferably, the pressure of the primary H 2 S flashing is 3.5 - 3.7 MPa(G).

[0057] In some embodiments of the present invention, preferably, the molar content of H 2 S in the rich H 2 S methanol after the primary flashing is 1.5 - 1.8%, and the molar content of CO 2 is 37.5 - 41.5%; the temperature is -32.5 to -30.5 °C;

[0058] In the present invention, the secondary H 2 S flashing uses a relatively low pressure to further flash off the effective gases CO 2 and H 2 S in the rich H 2 S methanol after the primary flashing. Preferably, the pressure of the secondary H 2 S flashing is 1.6 - 2 MPa(G).

[0059] In some embodiments of the present invention, preferably, the molar content of H 2 S in the rich H 2 S methanol after flashing is 1.5 - 1.8%, and the molar content of CO 2 is 37 - 41%; the temperature is -33 to -31 °C.

[0060] In some embodiments of the present invention, more preferably, the primary CO 2 flash gas and the primary H 2 S flash gas are mixed to obtain a primary flash gas with a temperature of -35 to -30 °C and a pressure of 3.5 - 3.7 MPa(G). In the present invention, the primary flash gas does not need to be washed and is directly sent to the compression process, which can reduce the power consumption of the compressor and avoid mutual contamination.

[0061] In some embodiments of the present invention, preferably, the molar content of H 2 in the primary flash gas is 82 - 87%, the molar content of CO 2 is 12 - 17%, and the molar content of CO is 0.31 - 0.36%.

[0062] In some embodiments of the present invention, preferably, the first rich CO 2 methanol after flashing is subjected to the primary flashing to obtain the semi-lean liquid methanol and the first CO 2 product gas; more preferably, the pressure of the first flashing is 0.05 - 0.08 MPa(G).

[0063] In some embodiments of the present invention, preferably, the CO in the semi-lean methanol is 2 The molar content of is 20-24%, H 2 The molar content of S is ≤0.5ppm; the temperature is -65 to -63℃; the pressure is 0.05-0.08MPa(G).

[0064] In the present invention, the semi-lean methanol is divided into two streams. Preferably, the semi-lean methanol is divided into the first stream of semi-lean methanol and the second stream of semi-lean methanol with a molar flow ratio of 1.3-1.6:1.

[0065] In the present invention, the heat exchange process includes: the first stream of semi-lean methanol and the second stream of CO2-rich after flash evaporation 2 Methanol is heat exchanged to obtain the semi-lean liquid methanol after heat exchange obtained by converting the first semi-lean liquid methanol, and the CO-rich methanol obtained by flash evaporation of the second stream 2 CO-rich after heat exchange from methanol conversion 2 Methanol. Preferably, the temperature of the semi-lean methanol after the heat exchange is -62 to -60°C; the CO-rich 2 The temperature of methanol is -54 to -50°C.

[0066] In some embodiments of the present invention, preferably, the CO-rich 2 Methanol is subjected to the second flash evaporation to obtain the flash liquid and the second CO 2 Product gas; further preferably, the pressure of the first flash evaporation is 0.06-0.09MPa(G).

[0067] In some embodiments of the present invention, preferably, the flash-evaporated H-rich 2 S methanol is subjected to a third flash distillation to obtain the sulfur-containing gas phase and the third H-rich 2 S methanol; further preferably, the pressure of the third flash distillation is 0.12-0.16MPa(G).

[0068] In some embodiments of the present invention, preferably, the third H-rich 2 S in methanol 2 The molar content of S is 1.6-1.8%, CO 2 The molar content of is 27-30%; the temperature is -70 to -65°C; the pressure is 0.13-0.17MPa(G).

[0069] In some embodiments of the present invention, preferably, the first washing process comprises: first washing the sulfur-containing gas phase and the flash liquid to obtain the low H 2 S methanol and third CO 2 ​​​​Product gas.

[0070] In some embodiments of the present invention, preferably, the low H 2 S H in methanol 2 The molar content of S is 0.9-1.1%, CO 2 The molar content of is 28-30%; the temperature is -65 to -60°C, and the pressure is 0.12-0.16MPa(G).

[0071] In some embodiments of the present invention, it is further preferred that the first CO 2 Product gas, second CO 2 Product gas and third CO 2 After mixing the product gases, the obtained CO 2 H in product gas 2 S molar content <1ppm, CO 2 The molar content of is 99.4-99.7%; the temperature is -66℃ to -63℃, and the pressure is 0.05-0.08MPa(G).

[0072] In some embodiments of the present invention, preferably, the semi-lean liquid methanol after heat exchange is contacted with nitrogen and stripped to obtain the low-carbon methanol and tail gas.

[0073] In some embodiments of the present invention, preferably, the H in the low-carbon methanol is 2 S molar content ≤ 0.5ppm, CO 2 The molar content of is 13-17%; the temperature is -75 to -70°C; the pressure is 0.15-0.25MPa(G).

[0074] In some embodiments of the present invention, preferably, the exhaust gas contains H 2 The molar content of S is ≤0.5ppm, CO 2 The molar content of is 88-92%; the temperature is -65 to -63°C; the pressure is 0.15-0.25MPa(G).

[0075] In some embodiments of the present invention, preferably, the second washing process comprises: the secondary CO 2 Secondary CO obtained by flash distillation 2 Flash gas and the secondary H 2 Secondary H obtained by S flash distillation 2 S flash gas is mixed with the low H 2 S methanol is contacted and the second washing is performed to obtain the low-sulfur and carbon-rich methanol and secondary flash gas.

[0076] In some embodiments of the present invention, preferably, the low-sulfur carbon-rich methanol contains H 2 ​​The molar content of S is 0.8 - 1%, and the molar content of CO 2 is 27 - 32%; the temperature is -65 to -60 °C.

[0077] In some embodiments of the present invention, preferably, the temperature of the secondary flash gas is -65 °C to -60 °C, and the pressure is 1.6 - 2 MPa(G). In the present invention, the secondary flash gas is sent to the subsequent process for treatment. Such a setting not only enables the effective gas to be fully recovered, but also reduces the intake of the first-stage cylinder of the compressor in the compression process, and correspondingly reduces the power consumption of the compressor.

[0078] In some embodiments of the present invention, preferably, the molar content of H 2 in the secondary flash gas is 80 - 85%, the molar content of CO 2 is 14 - 19%, and the molar content of CO is 0.32 - 0.37%.

[0079] In some embodiments of the present invention, preferably, the low-H 2 S methanol is pressurized to 2 - 2.4 MPa(G) by the fourth stage and then undergoes the second washing.

[0080] The second aspect of the present invention provides a structural schematic diagram of an energy-saving low-temperature methanol washing device for a coal water slurry gasification device as shown in Figure 1 and, as can be seen from Figure 1 , the device includes: an H 2 S absorption tower T-1, a CO 2 absorption tower T-2, a first-stage flash tower T-3, a second-stage flash tower T-4, a reabsorption tower T-5, and a stripping tower T-6; the first-stage flash tower T-3 is divided into a first-stage CO 2 flash section and a first-stage H 2 S flash section from top to bottom; the second-stage flash tower T-4 is divided into a second-stage CO 2 flash section and a second-stage H 2 S flash section from top to bottom;

[0081] The syngas 1 enters the H 2 S absorption tower T-1 for H 2 S absorption, obtaining desulfurized gas 6 and first rich H 2 S methanol 5; the desulfurized gas 6 enters the CO 2 absorption tower T-2 for CO 2 absorption, and the obtained rich CO 2 methanol 4 is divided into two streams. The second stream of rich CO 2 methanol 4-ii, after passing through the first cooler E-1, sequentially enters the first-stage CO 2 flash section and the second-stage CO 2 flash section, and the flash-rich CO 2The 18 parts of methanol are divided into two streams. The first stream is flash-vaporized to be rich in CO 2 The 18-i part of methanol enters the upper part of the reabsorption tower T-5 for the first flash vaporization. The obtained semi-lean methanol of 8 parts is divided into two streams. The second stream is flash-vaporized to be rich in CO 2 The 18-ii part of methanol and the first semi-lean methanol of 8-i enter the heat exchanger Q, and the obtained heat-exchanged methanol is rich in CO 2 25 parts of methanol and 24 parts of heat-exchanged semi-lean methanol enter the middle part of the reabsorption tower T-5 and the stripping tower T-6 respectively, and are respectively subjected to the second flash vaporization and stripping, and respectively obtain flash liquid and low-carbon methanol of 10 parts, and the low-carbon methanol of 10 parts is recycled and used for CO 2 Absorption tower T-2;

[0082] The first H-rich 2 The 5 parts of H₂S methanol enter the first-stage H₂S flash evaporation section and the second-stage H₂S flash evaporation section in sequence after passing through the second cooler E-2 2 S flash evaporation section and the second-stage H₂S 2 S flash evaporation section, and the obtained flash-vaporized H₂S-rich 2 The 16 parts of H₂S methanol enter the lower part of the reabsorption tower T-5 for the third flash vaporization. The obtained sulfur-containing gas phase is subjected to the first washing with the flash liquid, and the obtained low-H₂S 2 The 23 parts of H₂S methanol enter the second-stage H₂S 2 S flash evaporation section, and are subjected to the second washing with the flash gas of the second-stage CO 2 Flash evaporation section and the second-stage H₂S 2 S flash evaporation section, and the obtained low-sulfur carbon-rich methanol of 2 parts and the first CO-rich 2 The 4-i part of methanol are each independently recycled and used for H₂S 2 Absorption tower T-1.

[0083] In the present invention, as Figure 1 shown, preferably, the H₂S 2 Absorption tower T-1 is divided into a second H₂S 2 Absorption section and a first H₂S 2 Absorption section from top to bottom. Specifically, in the first H₂S 2 Absorption section, the first low-sulfur carbon-rich methanol of 2-i parts pre-washes and absorbs H₂S 2 , HCN, NH₃ 3 in the syngas 1; in the second H₂S 2 Absorption section, by introducing the second low-sulfur carbon-rich methanol of 2-ii parts to absorb H₂S 2 and CO₂ 2 in the pre-washed syngas, the recycling of the low-sulfur carbon-rich methanol is realized, and the usage amount of the first CO-rich 2 The 4-i part of methanol is reduced, which is equivalent to reducing the first H₂S-rich 2 The 5 parts of H₂S methanol that needs to be thermally regenerated; in addition, such a setting correspondingly reduces the working load of the subsequent CO₂ 2 Absorption tower, and reduces CO₂2 The usage amounts of lean methanol 9 and low-carbon methanol 10 in the absorption tower.

[0084] In the present invention, as Figure 1 shown, preferably, a pipeline connecting the low-sulfur rich-carbon methanol outlet of the secondary H 2 S flash section and the H 2 S absorption tower T-1 is provided with a first pump P-1 for recycling the low-sulfur rich-carbon methanol 2 back to the H 2 S absorption tower T-1 after the first pressurization.

[0085] In the present invention, as Figure 1 shown, preferably, the low-sulfur rich-carbon methanol 2 is divided into a first stream of low-sulfur rich-carbon methanol 2-i and a second stream of low-sulfur rich-carbon methanol 2-ii, which are respectively recycled back to the first H 2 S absorption section and the second H 2 S absorption section.

[0086] In the present invention, as Figure 1 shown, in the H 2 S absorption tower T-1, the first H 2 S absorption section and the second H 2 S absorption section are connected by a riser hole; the first H 2 S absorption section is connected to the low-sulfur rich-carbon methanol outlet of the secondary H 2 S flash section for contacting the syngas 1 with the first stream of low-sulfur rich-carbon methanol 2-i and performing the first H 2 S absorption to obtain the second rich-H 2 S methanol 3 and the pre-desulfurized gas; the second H 2 S absorption section is connected to the low-sulfur rich-carbon methanol outlet of the secondary H 2 S flash section and the rich-CO 2 methanol outlet of the CO 2 absorption tower T-2 for sequentially contacting the pre-desulfurized gas with the second stream of low-sulfur rich-carbon methanol 2-ii and the first stream of rich-CO 2 methanol 4-i and performing the second H 2 S absorption to obtain the desulfurized gas 6 and the first rich-H 2 S methanol 5.

[0087] In the present invention, without special instructions, in the first H 2 S absorption section, the contact mode between the syngas and the first stream of low-sulfur rich-carbon methanol 2-i is preferably countercurrent contact between the syngas 1 and the first stream of low-sulfur rich-carbon methanol 2-i, that is, the syngas 1 enters from the bottom of the first H 2 S absorption section, and the first stream of low-sulfur rich-carbon methanol 2-i enters from the top of the first H 2 S absorption section.

[0088] In the present invention, as Figure 1 shown, preferably, in the direction of material flow, a second pump P-2 and a third cooler E-3 are successively arranged on the pipeline connecting the rich CO 2 methanol outlet of the absorption tower T-2 and the 2 H 2 S absorption tower T-1, for recycling the first stream of rich CO 2 methanol 4-i to the H 2 S absorption tower T-1 after secondary pressurization and tertiary cooling in sequence.

[0089] In the present invention, as Figure 1 shown, preferably, the CO 2 absorption tower T-2 is divided into a second CO 2 absorption section and a first CO 2 absorption section from top to bottom, and the bottom of the second CO 2 absorption section is connected to the upper part of the first CO 2 absorption section.

[0090] In the present invention, as Figure 1 shown, in the CO 2 absorption tower T-2, the first CO 2 absorption section and the second CO 2 absorption section are connected through upflow holes. Among them, the upper part of the first CO 2 absorption section is connected to the lower part of the second CO 2 absorption section, for bringing the desulfurized gas 6 into contact with the CO 2 -containing methanol 7 and performing the first CO 2 absorption to obtain the rich CO 2 methanol 4 and the pre-purified gas; the second CO 2 absorption section is connected to the low-carbon methanol outlet of the stripping tower T-6 and the lean methanol 9 from the subsequent process, for bringing the pre-purified gas into contact with the low-carbon methanol 10 and the lean methanol 9 in sequence and performing the second CO 2 absorption to obtain the purified gas 12 and the CO 2 -containing methanol 7.

[0091] In the present invention, without special description, in the CO 2 absorption tower T-2, for the first CO 2 absorption section, the contact mode between the desulfurized gas 6 and the CO 2 -containing methanol 7 is preferably countercurrent contact between the desulfurized gas 6 and the CO 2 -containing methanol 7; that is, the desulfurized gas 6 enters from the bottom of the first CO 2 absorption section, and the CO 2 -containing methanol 7 enters from the upper part of the first CO 2 absorption section.

[0092] In the present invention, as Figure 1 shown, preferably, in the direction of material flow, connect the second CO 2 The bottom of the absorption section is connected to the first CO 2 A fourth cooler E-4 is provided on the pipeline at the upper part of the absorption section for cooling the CO 2 methanol 7. After being cooled by the fourth cooler, it is recycled to the first CO 2 absorption section.

[0093] In the present invention, as Figure 1 shown, in the primary flash tower T-3, the primary CO 2 flash section is used to flash the second rich CO 2 methanol 4-ii after the first cooling to perform primary CO 2 flash, obtaining primary CO 2 flash gas 11-i and rich CO 2 methanol 13 after primary flash; the primary H 2 S flash section is used to flash the first rich H 2 S methanol 5 after the second cooling to perform primary H 2 S flash, obtaining primary H 2 S flash gas 11-ii and rich H 2 S methanol 14 after primary flash; among them, the primary CO 2 flash gas 11-i and the primary H 2 S flash gas 11-ii are mixed to obtain the primary flash gas 11, which is sent to the subsequent process for treatment.

[0094] In the present invention, as Figure 1 shown, in the secondary flash tower T-4, the secondary CO 2 flash section is used to flash the rich CO 2 methanol 13 after primary flash to perform secondary CO 2 flash, obtaining secondary CO 2 flash gas 17 and rich CO 2 methanol 18 after flash; the secondary H 2 S flash section is used to flash the rich H 2 S methanol 14 after primary flash to perform secondary H 2 S flash, obtaining secondary H 2 S flash gas and rich H 2 S methanol 16 after flash; among them, the secondary CO 2 flash gas 17 and the secondary H 2 S flash gas are mixed and then contacted with the low H 2 S methanol 23 for the second washing, and the obtained secondary flash gas 15 is sent to the subsequent process for treatment.

[0095] In the present invention, as Figure 1 shown, the upper and middle parts of the reabsorption tower T-5 are connected through riser holes, and the middle and lower parts are also connected through riser holes. Specifically, the upper part is used to perform the first flash evaporation on the first stream of rich CO 2 methanol 18-i to obtain semi-lean methanol 8 and the first CO 2 product gas; the middle part is used to perform the second flash evaporation on the second stream of rich CO 2 methanol 18-ii after heat exchange to obtain the rich CO 2 methanol 25 after heat exchange and perform the second flash evaporation to obtain the flash liquid and the second CO 2 product gas; the lower part is used to perform the third flash evaporation on the rich H 2 S methanol 16 to obtain the third rich H 2 S methanol 19 and the sulfur-containing gas phase; among them, the sulfur-containing gas phase and the flash liquid are subjected to the first washing to obtain the low H 2 S methanol 23 and the third CO 2 product gas; the CO 2 product gas 20 includes the first CO 2 product gas, the second CO 2 product gas, and the third CO 2 product gas.

[0096] In the present invention, as Figure 1 shown, the stripping tower T-6 is used to bring the heat-exchanged semi-lean methanol 24 obtained by heat-exchanging the first stream of semi-lean methanol 8-i into contact with nitrogen 21 and perform stripping to obtain low-carbon methanol 10 and tail gas 22.

[0097] In the present invention, as Figure 1 shown, preferably, a third pump P-3 is provided on the pipeline connecting the low-carbon methanol outlet of the stripping tower T-6 and the second CO 2 absorption section, which is used to recycle the low-carbon methanol 10 after the third pressurization to the second CO 2 absorption section.

[0098] In the present invention, as Figure 1 shown, preferably, a fourth pump P-4 is provided on the pipeline connecting the low H 2 S methanol outlet of the reabsorption tower T-5 and the secondary H 2 S flash section, which is used to recycle the low H 2 S methanol 23 after the fourth pressurization to the secondary H 2 S flash section.

[0099] The present invention will be described in detail below through examples.

[0100] Example 1

[0101] Energy-saving low-temperature methanol washing device for supporting coal water slurry gasification device, as Figure 1 shown, the device includes: an H 2 S absorption tower T-1, a CO 2 absorption tower T-2, a first-stage flash tower T-3, a second-stage flash tower T-4, a reabsorption tower T-5 and a stripping tower T-6, as well as heat exchangers Q, coolers E-1 to E-4, and pumps P-1 to P-4;

[0102] Among them, the H 2 S absorption tower T-1 is divided into a second H 2 S absorption section and a first H 2 S absorption section from top to bottom; the CO 2 absorption tower T-2 is divided into a second CO 2 absorption section and a first CO 2 absorption section from top to bottom, and the bottom of the second CO 2 absorption section is connected to the upper part of the first CO 2 absorption section; the first-stage flash tower T-3 is divided into a first-stage CO 2 flash section and a first-stage H 2 S flash section from top to bottom; the second-stage flash tower T-4 is divided into a second-stage CO 2 flash section and a second-stage H 2 S flash section from top to bottom.

[0103] Energy-saving low-temperature methanol washing method for supporting coal water slurry gasification device, the method includes:

[0104] Mixing syngas 1 (the molar content of H 2 S is 0.9 - 1.2%, the molar content of CO 2 is 40 - 50%; the temperature is -15 to -5 °C, and the pressure is 5.2 - 5.7 MPa (G)) and the first low-sulfur rich-carbon methanol 2-i in a molar flow ratio of 70 - 80:1 for countercurrent contact and perform the first H 2 S absorption to obtain the second H 2 S-rich methanol 3 (the molar content of H 2 S is 2.5 - 3%, the molar content of CO 2 is 72 - 75%) and pre-desulfurized gas; successively contacting the above-mentioned pre-desulfurized gas with the second low-sulfur rich-carbon methanol 2-ii and the first CO 2 -rich methanol 4-i (pressurized to 5.8 - 6 MPa (G) for the second time and cooled to -35 to -25 °C for the third time) for countercurrent contact and perform the second H 2 S absorption to obtain desulfurized gas 6 (the molar content of H 2 S is 0.5 - 1 ppm, CO 2The molar content is 38 - 40%; the temperature is -20 to -10 °C; the pressure is 5.3 - 5.4 MPa(G)) and the first H-rich 2 S methanol 3 (H 2 The molar content of S is 1.5 - 1.8%, and the CO 2 molar content is 38 - 42%);

[0105] Among them, the molar flow rate ratio of syngas 1 and the second low-sulfur carbon-rich methanol 2-ii is 5 - 7:1; the molar flow rate ratio of syngas 1 and the first CO-rich 2 methanol 4-i is 2 - 3:1;

[0106] Among them, after the low-sulfur carbon-rich methanol 2 is first pressurized to 5.8 - 6 MPa(G), it is divided into a first low-sulfur carbon-rich methanol 2-i and a second low-sulfur carbon-rich methanol 2-ii with a molar flow rate ratio of 1:11 - 13;

[0107] The above desulfurized gas 6 and the CO-containing 2 methanol 7 (cooled to -36 to -33 °C in the fourth stage) are in countercurrent contact at a molar flow rate ratio of 1:1.1 - 1.2 and undergo the first CO 2 absorption to obtain CO-rich 2 methanol 4 (the CO 2 molar content is 32 - 34%, and the H 2 molar content of S is 0.1 - 0.5 ppm; the temperature is -10 to -5 °C, and the pressure is 5.2 - 5.4 MPa(G)) and the pre-purified gas. Among them, the CO-rich 2 methanol 4 is divided into a first CO-rich 2 methanol 4-i and a second CO-rich 2 methanol 4-ii; the above pre-purified gas is successively in countercurrent contact with low-carbon methanol 10 (pressurized to 5.8 - 6 MPa(G) in the third stage), lean methanol 9 (the CO 2 molar content is 0%, and the H 2 molar content of S is 0%) and undergoes the second CO 2 absorption to obtain the purified gas 12 (the H 2 molar content of S < 0.1 ppm, and the CO 2 molar content < 20 ppm; the temperature is -55 to -50 °C, and the pressure is 5.2 - 5.3 MPa(G));

[0108] Among them, the molar flow rate ratio of the above purified gas 12 and low-carbon methanol 10 is 1.8 - 2:1; the molar flow rate ratio of the above purified gas 12 and lean methanol 9 is 1:1 - 1.2;

[0109] The second CO-rich 2Methanol 4-ii is cooled to -36 to -33 °C for the first time, and then undergoes primary CO 2 flash evaporation (at a pressure of 3.5 - 3.7 MPa(G)) to obtain primary CO 2 flash vapor 11-i and primary flash evaporation enriched CO 2 methanol 13 (H 2 The molar content of S is 0.1 - 0.5 ppm, and the molar content of CO 2 is 31.5 - 33.5%; the temperature is -36.5 to -33.5 °C). After the above primary flash evaporation, the enriched CO 2 methanol 13 undergoes secondary CO 2 flash evaporation (at a pressure of 1.6 - 2 MPa(G)) to obtain secondary CO 2 flash vapor 17 and flash evaporation enriched CO 2 methanol 18 (H 2 The molar content of S is 0.1 - 0.5 ppm, and the molar content of CO 2 is 31 - 33%; the temperature is -37 to -34 °C);

[0110] The above first H 2 S-rich methanol 5 is cooled to -32 to -30 °C for the second time and undergoes primary H 2 S flash evaporation (at a pressure of 3.5 - 3.7 MPa(G)) to obtain primary H 2 S flash vapor 11-ii and primary flash evaporation enriched H 2 S methanol 14 (H 2 The molar content of S is 1.5 - 1.8%, and the molar content of CO 2 is 37.5 - 41.5%; the temperature is -32.5 to -30.5 °C). After the above primary flash evaporation, the enriched H 2 S methanol 14 undergoes secondary H 2 S flash evaporation (at a pressure of 1.6 - 2 MPa(G)) to obtain secondary H 2 S flash vapor and flash evaporation enriched H 2 S methanol 16 (H 2 The molar content of S is 1.5 - 1.8%, and the molar content of CO 2 is 37 - 41%; the temperature is -33 to -31 °C);

[0111] The above primary CO 2 flash vapor 11-i and primary H 2 S flash vapor 11-ii are mixed to obtain primary flash vapor 11 (H 2 The molar content of is 82 - 87%, and the molar content of CO 2 is 12 - 17%, and the molar content of CO is 0.31 - 0.36%; the temperature is -35 to -30 °C, and the pressure is 3.5 - 3.7 MPa(G));

[0112] After the above-mentioned flash evaporation, the CO-rich 2 methanol 18 is divided into a first CO-rich methanol 18-i and a second CO-rich methanol 18-ii with a molar flow rate ratio of 3.3 - 3.5:1 2 after flash evaporation; 2

[0113] The first CO-rich methanol 18-i after flash evaporation 2 is subjected to primary flash evaporation (pressure: 0.05 - 0.08 MPa(G)) to obtain semi-lean liquid methanol 8 (with a molar content of CO 2 of 20 - 24%, a molar content of H 2 S of ≤ 0.5 ppm; temperature: -65 to -63 °C; pressure: 0.05 - 0.08 MPa(G)) and first CO 2 product gas; the above-mentioned semi-lean liquid methanol 8 is divided into a first semi-lean liquid methanol 8-i and a second semi-lean liquid methanol 8-ii with a molar flow rate ratio of 1.3 - 1.6:1; the first semi-lean liquid methanol 8-i and the second CO-rich methanol 18-ii after flash evaporation 2 are heat-exchanged to obtain heat-exchanged semi-lean liquid methanol 24 with a temperature of -62 to -60 °C, and heat-exchanged CO-rich methanol 25 with a temperature of -54 to -50 °C; 2

[0114] The above-mentioned heat-exchanged CO-rich methanol 25 2 is subjected to secondary flash evaporation (pressure: 0.06 - 0.09 MPa(G)) to obtain flash liquid and second CO 2 product gas; the above-mentioned H 2 S-rich methanol 16 after flash evaporation is subjected to tertiary flash evaporation (pressure: 0.12 - 0.16 MPa(G)) to obtain sulfur-containing gas phase and third H 2 S-rich methanol 19 (with a molar content of H 2 S of 1.6 - 1.8%, a molar content of CO 2 of 27 - 30%; temperature: -70 to -65 °C; pressure: 0.13 - 0.17 MPa(G)); the above-mentioned sulfur-containing gas phase and flash liquid are subjected to first washing to obtain low-H 2 S methanol 23 (with a molar content of H 2 S of 0.9 - 1.1%, a molar content of CO 2 of 28 - 30%; temperature: -65 to -60 °C, pressure: 0.12 - 0.16 MPa(G)) and third CO 2 product gas; the above-mentioned first CO 2 product gas, second CO 2 product gas and third CO 2 product gas are mixed to obtain the resulting CO​​2 The molar content of H in product gas 20 2 S is < 1 ppm, and the molar content of CO 2 is 99.4 - 99.7%; the temperature is -66°C to -63°C, and the pressure is 0.05 - 0.08 MPa(G);

[0115] The above-mentioned semi-lean methanol 24 after heat exchange is contacted with nitrogen 21 and stripped to obtain low-carbon methanol 10 (H 2 The molar content of S is ≤ 0.5 ppm, and the molar content of CO 2 is 13 - 17%; the temperature is -75 to -70°C; the pressure is 0.15 - 0.25 MPa(G)) and tail gas 22 (H 2 The molar content of S is ≤ 0.5 ppm, and the molar content of CO 2 is 88 - 92%; the temperature is -65 to -63°C; the pressure is 0.15 - 0.25 MPa(G));

[0116] Among them, the above-mentioned secondary CO 2 flash gas 17 and secondary H 2 S flash gas are mixed and then contacted with low-H 2 S methanol 23 (pressurized to 2 - 2.4 MPa(G) for the fourth time) and subjected to the second washing to obtain low-sulfur carbon-rich methanol 2 (H 2 The molar content of S is 0.8 - 1%, and the molar content of CO 2 is 27 - 32%; the temperature is -65 to -60°C) and secondary flash gas 15 (H 2 The molar content of is 80 - 85%, and the molar content of CO 2 is 14 - 19%, and the molar content of CO is 0.32 - 0.37%; the temperature is -65°C to -60°C, and the pressure is 1.6 - 2 MPa(G)).

[0117] Comparative Example 1

[0118] Taking a hydrogen production device using coal water slurry gasification for gas production as an example, the effective gas (H 2 +CO) entering the low-temperature methanol washing device is 230000 Nm 3 / h. Based on this benchmark, the main technical parameters of the lean-semi-lean liquid process (i.e., CN201110260570.0 discloses a low-temperature methanol washing process) are compared in Table 1.

[0119] Table 1

[0120]

[0121]

[0122] As can be seen from the results in Table 1, taking the hydrogen production unit based on coal water slurry gasification as an example, for the syngas purification process of the supporting coal water slurry gasification unit provided in Example 1, the lean methanol circulation rate is 92.6% of that in Comparative Example 1 (lean liquid - semi-lean liquid process), and the semi-lean methanol circulation rate is 66.7% of that in Comparative Example 1 (lean liquid - semi-lean liquid process). The H 2 S absorption tower is rich in CO 2 The methanol consumption is 89.5% of that of the rich CO 2 methanol consumption in Comparative Example 1 (lean liquid - semi-lean liquid process), and the cumulative reduction of external cooling consumption is 800 KW / h, with a remarkable overall energy-saving effect.

[0123] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. An energy-saving low-temperature methanol washing method for a water-coal slurry gasification device, characterized in that: The method includes: The synthesis gas is subjected to H2S absorption, and the obtained desulfurized gas is subjected to CO2 absorption, and the obtained CO2-rich methanol is divided into two streams. After the second stream of CO2-rich methanol is subjected to a first cooling, a primary CO2 flash and a secondary CO2 flash are sequentially performed, and the obtained flashed CO2-rich methanol is divided into two streams. The first stream of flashed CO2-rich methanol is subjected to a primary flash, and the obtained semi-lean liquid methanol is divided into two streams. The first stream of semi-lean liquid methanol and the second stream of flashed CO2-rich methanol are subjected to heat exchange, and the obtained semi-lean liquid methanol after heat exchange and the obtained CO2-rich methanol after heat exchange are respectively subjected to stripping and a second flash, and low-carbon methanol and flash liquid are respectively obtained; wherein the low-carbon methanol is returned and subjected to the CO2 absorption; The first H2S-rich methanol obtained by the H2S absorption is subjected to a second cooling, and then subjected to a primary H2S flash evaporation and a secondary H2S flash evaporation in sequence. The flashed H2S-rich methanol obtained is subjected to a third flash evaporation, and the sulfur-containing gas phase and the flash liquid are subjected to a first washing. The obtained low H2S methanol is subjected to a second washing with the flash gas of the secondary CO2 flash evaporation and the secondary H2S flash evaporation. The obtained low-sulfur carbon-rich methanol and the first CO2-rich methanol are each independently returned and subjected to the H2S absorption.

2. The method according to claim 1, wherein: After the low-sulfur and carbon-rich methanol is first pressurized to 5.8-6 MPa(G), it is returned and subjected to the H2S absorption; and / or, dividing the low-sulfur carbon-rich methanol into two streams, returning them respectively and performing the H2S absorption, preferably dividing the low-sulfur carbon-rich methanol into a first stream of low-sulfur carbon-rich methanol and a second stream of low-sulfur carbon-rich methanol with a molar flow ratio of 1:11-13, returning them respectively and performing the H2S absorption; And / or, according to the material flow direction, the first stream of CO2-rich methanol is successively pressurized to 5.8-6 MPa (G) and cooled to -35 to -25°C in a second step, and then returned to perform the H2S absorption.

3. The method according to claim 2, wherein: The H2S absorption process comprises: contacting the synthesis gas with a first stream of low-sulfur carbon-rich methanol and performing a first H2S absorption to obtain a pre-desulfurized gas and a second H2S-rich methanol, contacting the pre-desulfurized gas, the second stream of low-sulfur carbon-rich methanol and the first stream of CO2-rich methanol and performing a second H2S absorption to obtain the desulfurized gas and the first H2S-rich methanol; and / or, the molar content of H2S in the synthesis gas is 0.9-1.2%, the molar content of CO2 is 40-50%; the temperature is -15 to -5°C, and the pressure is 5.2-5.7MPa(G); and / or, the molar flow ratio of the synthesis gas to the first stream of low-sulfur and carbon-rich methanol is 70-80:1; and / or, the molar content of H2S in the second H2S-rich methanol is 2.5-3%, and the molar content of CO2 is 72-75%; and / or, the molar flow ratio of the synthesis gas to the second stream of low-sulfur carbon-rich methanol is 5-7:1; the molar flow ratio of the synthesis gas to the first stream of CO2-rich methanol is 2-3:1; and / or, the molar content of H2S in the first H2S-rich methanol is 1.5-1.8%, and the molar content of CO2 is 38-42%; And / or, the molar content of H2S in the desulfurized gas is 0.5-1 ppm, the molar content of CO2 is 38-40%; the temperature is -20 to -10°C; and the pressure is 5.3-5.4 MPa(G).

4. The method according to any one of claims 1 to 3, wherein: After the low-carbon methanol is pressurized to 5.8-6 MPa (G) for the third time, it is returned to perform the CO2 absorption; And / or, the CO2 absorption process includes: contacting the desulfurized gas with CO2-containing methanol and performing a first CO2 absorption to obtain pre-purified gas and the CO2-rich methanol; contacting the pre-purified gas, low-carbon methanol and lean methanol and performing a second CO2 absorption to obtain purified gas and the CO2-containing methanol; Preferably, according to the material flow direction, the CO2-containing methanol is cooled to -36 to -33°C for the fourth time, and then returned to the first CO2 absorption; and / or, the molar content of CO2 in the CO2-rich methanol is 32-34%, the molar content of H2S is 0.1-0.5 ppm; the temperature is -10 to -5°C, and the pressure is 5.2-5.4 MPa(G); and / or, dividing the CO2-rich methanol into a first stream of CO2-rich methanol and a second stream of CO2-rich methanol at a molar flow ratio of 1:1.8-2.2; and / or, the molar flow ratio of the purified gas to the low-carbon methanol is 1.8-2:1; the molar flow ratio of the purified gas to the lean methanol is 1:1-1.2; And / or, the molar content of H2S in the purified gas is less than 0.1 ppm, and the molar content of CO2 is less than 20 ppm; the temperature is -55 to -50°C, and the pressure is 5.2-5.3 MPa(G).

5. The method according to any one of claims 1 to 4, wherein: The temperature of the material after the first cooling is -36 to -33°C; And / or, subjecting the first cooled material to the primary CO2 flash to obtain primary CO2 flash gas and primary flash CO2-rich methanol, and subjecting the primary flash CO2-rich methanol to the secondary CO2 flash to obtain secondary CO2 flash gas and flash CO2-rich methanol; And / or, the pressure of the first-stage CO2 flash evaporation is 3.5-3.7 MPa(G); and / or, the molar content of H2S in the CO2-rich methanol after the first-stage flash is 0.1-0.5 ppm, the molar content of CO2 is 31.5-33.5%; the temperature is -36.5 to -33.5°C; And / or, the pressure of the secondary CO2 flash evaporation is 1.6-2MPa(G); and / or, the molar content of H2S in the CO2-rich methanol after the flash evaporation is 0.1-0.5 ppm, the molar content of CO2 is 31-33%; the temperature is -37 to -34°C; And / or, the flashed CO2-rich methanol is divided into the first stream of flashed CO2-rich methanol and the second stream of flashed CO2-rich methanol with a molar flow ratio of 3.3-3.5:

1.

6. The method according to any one of claims 1 to 5, wherein: The temperature of the material after the second cooling is -32 to -30°C; and / or, subjecting the second cooled material to the first-stage H2S flash evaporation to obtain first-stage H2S flash gas and H2S-rich methanol after the first-stage flash evaporation, and subjecting the first-stage H2S-rich methanol after the first-stage flash evaporation to the second-stage H2S flash evaporation to obtain second-stage H2S flash gas and H2S-rich methanol after the flash evaporation; And / or, the pressure of the first-stage H2S flash evaporation is 3.5-3.7 MPa(G); and / or, the molar content of H2S in the H2S-rich methanol after the first-stage flash is 1.5-1.8%, and the molar content of CO2 is 37.5-41.5%; the temperature is -32.5 to -30.5°C; And / or, the pressure of the secondary H2S flash evaporation is 1.6-2MPa(G); and / or, the molar content of H2S in the H2S-rich methanol after the flash evaporation is 1.5-1.8%, and the molar content of CO2 is 37-41%; the temperature is -33 to -31°C; And / or, the primary CO2 flash gas and the primary H2S flash gas are mixed to obtain the primary flash gas having a temperature of -35 to -30°C and a pressure of 3.5-3.7 MPa(G).

7. The method according to any one of claims 1 to 6, wherein: The first stream of CO2-rich methanol after flashing is subjected to the first-stage flashing to obtain the semi-lean methanol and the first CO2 product gas; And / or, the pressure of the first flash evaporation is 0.05-0.08 MPa(G); the pressure of the second flash evaporation is 0.06-0.09 MPa(G); the pressure of the third flash evaporation is 0.12-0.16 MPa(G); and / or, the molar content of CO2 in the semi-lean methanol is 20-24%, the molar content of H2S is ≤0.5ppm; the temperature is -65 to -63°C; the pressure is 0.05-0.08MPa(G); and / or, dividing the semi-lean methanol into the first stream of semi-lean methanol and the second stream of semi-lean methanol at a molar flow ratio of 1.3-1.6:1; and / or, the temperature of the semi-lean methanol after the heat exchange is -62 to -60°C; the temperature of the CO2-rich methanol after the heat exchange is -54 to -50°C; and / or, subjecting the CO2-rich methanol after heat exchange to the second flash evaporation to obtain the flash liquid and the second CO2 product gas; and / or, subjecting the flashed H2S-rich methanol to a third flash to obtain the sulfur-containing gas phase and a third H2S-rich methanol; And / or, the first washing process includes: performing a first washing on the sulfur-containing gas phase and the flash liquid to obtain the low-H2S methanol and the third CO2 product gas; and / or, the molar content of H2S in the low H2S methanol is 0.9-1.1%, the molar content of CO2 is 28-30%; the temperature is -65 to -60°C, and the pressure is 0.12-0.16MPa(G); and / or, after mixing the first CO2 product gas, the second CO2 product gas and the third CO2 product gas, the molar content of H2S in the obtained CO2 product gas is less than 1ppm, and the molar content of CO2 is 99.4-99.7%; the temperature is -66°C to -63°C, and the pressure is 0.05-0.08MPa(G); and / or, contacting the semi-lean liquid methanol after the heat exchange with nitrogen and performing the stripping to obtain the low-carbon methanol and tail gas; And / or, the molar content of H2S in the low-carbon methanol is ≤0.5ppm, the molar content of CO2 is 13-17%; the temperature is -75 to -70°C; the pressure is 0.15-0.25MPa(G); And / or, the second washing process comprises: mixing the secondary CO2 flash gas obtained by the secondary CO2 flash evaporation and the secondary H2S flash gas obtained by the secondary H2S flash evaporation, contacting with the low H2S methanol and performing the second washing to obtain the low-sulfur carbon-rich methanol and the secondary flash gas; and / or, the molar content of H2S in the low-sulfur, carbon-rich methanol is 0.8-1%, the molar content of CO2 is 27-32%; the temperature is -65 to -60°C; and / or, the temperature of the secondary flash gas is -65°C to -60°C and the pressure is 1.6-2MPa(G); And / or, the low H2S methanol is pressurized to 2-2.4 MPa(G) for the fourth time and then subjected to the second washing.

8. An energy-saving low-temperature methanol washing device supporting a water-coal slurry gasification device, characterized in that: The device comprises: an H2S absorption tower, a CO2 absorption tower, a primary flash tower, a secondary flash tower, a reabsorption tower and a stripping tower connected in sequence; the primary flash tower is divided into a primary CO2 flash section and a primary H2S flash section from top to bottom; the secondary flash tower is divided into a secondary CO2 flash section and a secondary H2S flash section from top to bottom; The synthesis gas enters the H2S absorption tower for H2S absorption to obtain desulfurized gas and the first H2S-rich methanol; the desulfurized gas enters the CO2 absorption tower for CO2 absorption, and the obtained CO2-rich methanol is divided into two streams. The second stream of CO2-rich methanol passes through the first cooler and then enters the primary CO2 flash section and the secondary CO2 flash section in sequence. The obtained CO2-rich methanol after flashing is divided into two streams. The first stream of CO2-rich methanol after flashing enters the upper part of the reabsorption tower for the first flash. The obtained semi-lean liquid methanol is divided into two streams. The second stream of CO2-rich methanol after flashing and the first stream of semi-lean liquid methanol enter the heat exchanger. The obtained CO2-rich methanol after heat exchange and the semi-lean liquid methanol after heat exchange enter the middle part of the reabsorption tower and the stripping tower respectively, and undergo the second flash and stripping respectively to obtain the flash liquid and low-carbon methanol respectively, and the low-carbon methanol is recycled back to the CO2 absorption tower; After passing through the second cooler, the first H2S-rich methanol enters the primary H2S flash section and the secondary H2S flash section in sequence, and the flashed H2S-rich methanol obtained enters the lower part of the reabsorption tower for the third flash, and the sulfur-containing gas phase obtained is subjected to the first washing with the flash liquid, and the low H2S methanol obtained enters the secondary H2S flash section and is subjected to the second washing with the flash gas of the secondary CO2 flash section and the secondary H2S flash section, and the low-sulfur carbon-rich methanol and the first CO2-rich methanol are independently circulated back to the H2S absorption tower.

9. The device according to claim 8, wherein: The H2S absorption tower is divided into a second H2S absorption section and a first H2S absorption section from top to bottom; and / or, a first pump is provided in the pipeline connecting the low-sulfur and carbon-rich methanol outlet of the secondary H2S flash section and the H2S absorption tower; Preferably, the low-sulfur carbon-rich methanol is divided into a first stream of low-sulfur carbon-rich methanol and a second stream of low-sulfur carbon-rich methanol, which are recycled back to the first H2S absorption section and the second H2S absorption section respectively; And / or, according to the material flow direction, a second pump and a third cooler are sequentially arranged on the pipeline connecting the CO2-rich methanol outlet of the CO2 absorption tower and the H2S absorption tower; And / or, the CO2 absorption tower is divided into a second CO2 absorption section and a first CO2 absorption section from top to bottom, and the bottom of the second CO2 absorption section is connected to the upper part of the first CO2 absorption section; Preferably, according to the material flow direction, a fourth cooler is arranged on the pipeline connecting the bottom of the second CO2 absorption section and the upper part of the first CO2 absorption section.

10. The device according to claim 9, wherein a third pump is provided on the pipeline connecting the low-carbon methanol outlet of the stripping tower and the second CO2 absorption section; And / or, a fourth pump is provided on the pipeline connecting the low H2S methanol outlet of the reabsorption tower and the secondary H2S flash section.

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