Low-temperature low-sulfur low-carbon methanol washing technology matched with coal water slurry gasification device

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to a low-temperature low-sulfur low-carbon methanol washing method and a low-temperature low-sulfur low-carbon methanol washing device matched with a coal water slurry gasification device.According to the method, the H2S absorption process is optimally set, low-sulfur carbon-rich methanol and low-H2S methanol are used for washing synthesis gas, and the use amount of CO2-rich methanol is reduced; a medium-pressure flash evaporation process is optimally arranged, so that the CO2 content is increased while the H2S content in the second stream of low-carbon methanol is slightly increased, and the ratio of the CO2 gas polluted by the H2S gas in the whole system is reduced; according to the low-temperature methanol washing device, the reabsorption process is optimized, low-H2S methanol is generated, meanwhile, the low-H2S methanol is prevented from being deeply polluted, and the low-temperature methanol washing device has the advantage of being low in comprehensive energy consumption.

Description

Technical Field

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

[0002] In the syngas produced by 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 and ammonia after adjusting the hydrogen-carbon ratio through the conversion unit. The acidic 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, and utilizes the characteristic that low-temperature methanol has a great solubility for acidic gases to remove H 2 S and CO 2 and other acidic gases 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 CO 2 -rich methanol through pressure reduction and flashing. The typical process flow mainly includes the lean liquid-semi-lean liquid process, but there are technical bottlenecks in further optimizing and innovating the lean liquid-semi-lean liquid process. Therefore, it is necessary to adjust the technical innovation 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 pressure reduction and flashing, 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, how to enhance the use efficiency of the H 2 S-rich methanol is the key factor in technological innovation. Specifically, it is necessary to achieve that before the thermal regeneration of the H 2 S-rich methanol, its absorption of H 2 S gas in the syngas reaches the upper limit, so as to reduce the production amount of the H 2 S-rich methanol and the subsequent thermal regeneration amount.

[0005] CN201110260570.0 discloses a low-temperature methanol washing process. First, in this low-temperature methanol washing process, the CO 2 -rich methanol is used to wash the syngas in the entire H 2 S absorption tower.2 Rich CO₂ methanol in the S absorption tower 2 Large consumption of methanol, rich in H₂S 2 Rich H₂S methanol needs thermal regeneration to be recycled, with high energy consumption; second, in the CO₂ flash section of the reabsorption tower, rich CO₂ 2 methanol, in the flash section, rich CO₂ 2 methanol is used to wash rich H₂S 2 methanol in the flash gas of rich H₂S methanol and is directly mixed with rich H₂S 2 methanol, and itself is contaminated by rich H₂S 2 methanol, and the resulting low-concentration H₂S 2 methanol is not fully utilized either. Generally, it is not conducive to reducing the comprehensive energy consumption of the cold methanol washing unit; third, the CO₂ gas flashed from the upper tower of the medium-pressure flash tower is contaminated while being washed by rich H₂S 2 methanol, with high energy consumption; fourth, the semi-lean methanol has a relatively high CO₂ 2 content, and the circulating absorption capacity is limited, which is not conducive to reducing the comprehensive energy consumption of the cold methanol washing unit. 2 Summary of the Invention

[0006] The object of the present invention is to overcome the above technical problems and provide a low-temperature, low-sulfur, and low-carbon methanol washing method for a coal water slurry gasification unit and a low-temperature, low-sulfur, and low-carbon methanol washing device for a coal water slurry gasification unit. By optimizing the H₂S absorption process, using low-sulfur and carbon-rich methanol and low-H₂S methanol to wash the syngas, the usage amount of rich CO₂ 2 methanol is reduced; by optimizing the medium-pressure flash process, while slightly increasing the H₂S content in the second stream of low-carbon methanol, the CO₂ content is increased, and the proportion of CO₂ gas contaminated by H₂S gas in the whole system is reduced; by optimizing the reabsorption process, low-H₂S methanol is generated, and at the same time, the deep contamination of low-H₂S methanol is avoided, making the cold methanol washing unit have the characteristics of low comprehensive energy consumption. 2 methanol is reduced; by optimizing the medium-pressure flash process, while slightly increasing the H₂S content in the second stream of low-carbon methanol, the CO₂ content is increased, and the proportion of CO₂ gas contaminated by H₂S gas in the whole system is reduced; by optimizing the reabsorption process, low-H₂S methanol is generated, and at the same time, the deep contamination of low-H₂S methanol is avoided, making the cold methanol washing unit have the characteristics of low comprehensive energy consumption. 2 methanol is reduced; by optimizing the medium-pressure flash process, while slightly increasing the H₂S content in the second stream of low-carbon methanol, the CO₂ content is increased, and the proportion of CO₂ gas contaminated by H₂S gas in the whole system is reduced; by optimizing the reabsorption process, low-H₂S methanol is generated, and at the same time, the deep contamination of low-H₂S methanol is avoided, making the cold methanol washing unit have the characteristics of low comprehensive energy consumption. 2 content, while reducing the proportion of CO₂ gas contaminated by H₂S gas in the whole system; by optimizing the reabsorption process, low-H₂S methanol is generated, and at the same time, the deep contamination of low-H₂S methanol is avoided, making the cold methanol washing unit have the characteristics of low comprehensive energy consumption. 2 content, while reducing the proportion of CO₂ gas contaminated by H₂S gas in the whole system; by optimizing the reabsorption process, low-H₂S methanol is generated, and at the same time, the deep contamination of low-H₂S methanol is avoided, making the cold methanol washing unit have the characteristics of low comprehensive energy consumption. 2 gas contaminated by H₂S 2 gas; by optimizing the reabsorption process, low-H₂S methanol is generated, and at the same time, the deep contamination of low-H₂S methanol is avoided, making the cold methanol washing unit have the characteristics of low comprehensive energy consumption. 2 methanol, while avoiding the deep contamination of low-H₂S 2 methanol, making the cold methanol washing unit have the characteristics of low comprehensive energy consumption.

[0007] To achieve the above object, the first aspect of the present invention provides a low-temperature, low-sulfur, and low-carbon methanol washing method for a coal water slurry gasification unit, and the method includes:

[0008] Performing H₂S absorption on the syngas to obtain two streams of first rich H₂S 2 methanol, and performing CO₂ 2 absorption on the obtained desulfurized gas to obtain two streams of first rich CO₂ 2 methanol, and performing CO₂ 2 absorption on the second stream of rich CO₂ 2 methanol​​​​​​​​2 Flash evaporation is carried out to obtain rich CO after flash evaporation 2 The methanol is divided into two streams. After the first cooling and the second cooling respectively, the first flash evaporation and the second flash evaporation are carried out respectively to obtain semi-lean methanol and flash liquid; the second stream of rich H 2 After heat exchange, the S methanol is subjected to H 2 S flash evaporation is carried out to obtain rich H after flash evaporation 2 The S methanol is subjected to the third flash evaporation, and the sulfur-containing gas phase obtained and the flash liquid are subjected to the first washing to obtain low-H 2 S methanol;

[0009] Among them, the semi-lean methanol is divided into two streams. The first stream of semi-lean methanol is subjected to stripping after the heat exchange, and the obtained low-carbon methanol is divided into two streams. The first stream of low-carbon methanol returns and is subjected to the CO 2 absorption, and the second stream of low-carbon methanol is successively combined with the CO 2 flash evaporation and H 2 The flash gas of the S flash evaporation is subjected to the second washing to obtain low-sulfur rich-carbon methanol;

[0010] Among them, the first stream of rich H 2 S methanol, the first stream of rich CO 2 methanol, low-H 2 S methanol and low-sulfur rich-carbon methanol independently return and are subjected to the H 2 S absorption.

[0011] The second aspect of the present invention provides a low-temperature, low-sulfur and low-carbon methanol washing device for supporting a water coal slurry gasification device. The device includes: H 2 S absorption tower, CO 2 absorption tower, CO 2 medium-pressure flash evaporation tower, H 2 S medium-pressure flash evaporation tower, reabsorption tower and stripping tower;

[0012] The H 2 S absorption tower is used for H 2 S absorption of the synthesis gas to obtain the first rich H 2 S methanol in two streams, and desulfurized gas; the CO 2 absorption tower is used for CO 2 absorption of the desulfurized gas to obtain the first rich CO 2 methanol in two streams, and purified gas;

[0013] The lower part of the CO 2 medium-pressure flash evaporation tower is used for CO 2 flash evaporation of the second stream of rich CO 2 methanol to obtain rich CO after flash evaporation 2 methanol in two streams; among them, the first stream of rich CO after flash evaporation 2 methanol and the second stream of rich CO after flash evaporation2 After methanol passes through the first cooler and the second cooler respectively, it enters the upper part and the middle part of the reabsorption tower respectively, and undergoes the first flash evaporation and the second flash evaporation respectively to obtain semi-lean methanol and flash liquid respectively;

[0014] H 2 The lower part of the medium-pressure flash tower for the second rich H 2 After the S methanol passes through the heat exchanger, it undergoes H 2 S flash evaporation, and the rich H 2 S methanol after flash evaporation enters the lower part of the reabsorption tower for the third flash evaporation, and the sulfur-containing gas phase and the flash liquid come into contact and undergo the first washing to obtain low-H 2 S methanol;

[0015] The stripping tower is used to strip the first semi-lean methanol after passing through the heat exchanger to obtain low-carbon methanol in two streams. The first stream of low-carbon methanol is recycled to the CO 2 absorption tower, and the second stream of low-carbon methanol sequentially enters the CO 2 medium-pressure flash tower and H 2 The upper part of the S medium-pressure flash tower undergoes the second washing to obtain low-sulfur carbon-rich methanol;

[0016] Among them, the first rich H 2 S methanol, the first rich CO 2 methanol, low-H 2 S methanol and low-sulfur carbon-rich methanol are each independently recycled to the H 2 S absorption tower.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) In the method provided by the present invention, by optimizing the medium-pressure flash evaporation process flow, using the second stream of low-carbon methanol to wash the CO 2 flash vapor, compared with the prior art, while reducing the CO 2 component in the CO 2 flash vapor, it is not polluted by the rich H 2 S methanol; using the carbon-rich methanol that absorbs the CO 2 flash vapor to wash the H 2 S flash vapor, compared with the prior art, while absorbing the CO 2 component in the H 2 S flash vapor, it is not polluted by the rich H 2 S methanol after flash evaporation; realizing the separate flash evaporation and separate washing of the second rich CO 2 methanol and the second rich H 2 S methanol, avoiding the transfer of the CO 2 gas in the rich CO 2 methanol after flash evaporation to the rich H 2Technical problems in methanol, and at the same time, the secondary utilization of low-sulfur and carbon-rich methanol after washing is beneficial to reducing the energy consumption of the device;

[0019] (2) The method provided by the present invention realizes the absorption of sulfur components in the product gas by the flash liquid for the flash-rich H 2 S methanol flash by optimizing the reabsorption process, but does not mix with the third flash-rich H 2 S methanol after flashing. Therefore, after the flash liquid absorbs the flashed H 2 S gas, compared with the prior art, the H 2 S content in the solution is lower, which is called low-H 2 S methanol, creating conditions for the reuse of this low-H 2 S methanol; 2 S methanol;

[0020] (3) The method provided by the present invention optimizes the H 2 S absorption process. By introducing low-H 2 S methanol and low-sulfur and carbon-rich methanol to jointly absorb H 2 S and CO 2 gas in the syngas, the recycling of low-H 2 S methanol and low-sulfur and carbon-rich methanol is realized, reducing the usage amount of the first rich-CO 2 methanol in the H 2 S absorption, which is equivalent to reducing the second rich-H 2 S methanol that needs to be thermally regenerated; at the same time, by pre-absorbing CO 2 gas with low-H 2 S methanol and low-sulfur and carbon-rich methanol, the working load of the subsequent CO 2 absorption tower is correspondingly reduced, and the usage amounts of lean methanol and semi-lean liquid methanol in the CO 2 absorption are also reduced;

[0021] (4) In order to further reduce the CO 2 content in the semi-lean liquid methanol and maximize the CO 2 absorption capacity of the semi-lean liquid methanol, the optimized reabsorption process performs nitrogen stripping on the semi-lean liquid methanol again, so that the CO 2 content in the semi-lean liquid methanol is further reduced to 5-7%, 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 circulation amount of lean methanol in the CO 2 absorption tower also decreases, and the reduction of the lean methanol flow rate will be transmitted to the rich-H 2S methanol, rich in H that requires thermal regeneration 2 The flow rate of S methanol will also decrease, and the energy consumption of the corresponding thermal regeneration system will also decrease accordingly. Description of the Drawings

[0022] Figure 1 It is a schematic structural diagram of a low-temperature, low-sulfur, and low-carbon methanol washing device provided by the present invention for supporting a water coal slurry gasification device.

[0023] Description of the Reference Numerals

[0024] T-1, H 2 S absorption tower; T-2, CO 2 Absorption tower; T-3, CO 2 Medium-pressure flash tower; T-4, H 2 S medium-pressure flash tower; T-5, reabsorption tower; T-6, stripping tower; Q, heat exchanger; E-1, first cooler; E-2, second cooler; E-3, third cooler; E-4, fourth cooler; E-5, fifth cooler; E-6, sixth cooler;

[0025] 1, syngas; 2, low H 2 S methanol; 3, second rich H 2 S methanol; 4, first 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 S methanol; 5-i, first stream of rich H 2 S methanol; 5-ii, second stream of rich H 2 S methanol; 6, desulfurized gas; 7, second rich CO 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, purified gas; 11, low-sulfur, carbon-rich methanol; 12, low-carbon methanol; 12-i, first stream of low-carbon methanol; 12-ii, second stream of low-carbon methanol; 13, rich CO 2 Methanol after flashing; 13-i, first stream of rich CO 2 Methanol after flashing; 13-ii, second stream of rich CO 2 Methanol; 14, carbon-containing methanol; 15, flash gas; 15-i, first flash gas; 15-ii, second flash gas; 16, rich H 2 S methanol after flashing; 17, CO 2 Product gas; 18, third rich H 2 S methanol; 19, tail gas; 20, nitrogen; 21, rich H 2 S methanol after heat exchange; 22, semi-lean methanol after heat exchange. Detailed Embodiments

[0026] The endpoints and any values disclosed in this text for ranges are not limited to the exact ranges or values. 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 in this text.

[0027] In the present invention, without special circumstances, "first", "second", "third", "fourth", "fifth" and "sixth" neither represent the order nor play a limiting role on each material or step, and are only used to distinguish that these are not the same material or step. For example. "First rich H 2 S methanol", "second rich H 2 S methanol" and "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.

[0028] 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.

[0029] The first aspect of the present invention provides a low-temperature, low-sulfur and low-carbon methanol washing method for supporting a water coal slurry gasification device, and the method includes:

[0030] Subject the syngas to H 2 S absorption, divide the obtained first rich H 2 S methanol into two streams, and subject the obtained desulfurized gas to CO 2 absorption, divide the obtained first rich CO 2 methanol into two streams, subject the second stream of rich CO 2 methanol to CO 2 flash evaporation, divide the obtained flash-evaporated rich CO 2 methanol into two streams, after the first cooling and the second cooling respectively, perform the first flash evaporation and the second flash evaporation respectively to obtain semi-lean liquid methanol and flash liquid respectively; subject the second stream of rich H 2 S methanol to heat exchange, then perform H 2 S flash evaporation, subject the obtained flash-evaporated rich H 2 S methanol to the third flash evaporation, perform the first washing on the obtained sulfur-containing gas phase and the flash liquid to obtain low-H 2 S methanol;

[0031] Among them, the semi-lean liquid methanol is divided into two streams. After the first stream of semi-lean liquid methanol is heat-exchanged, it is stripped to obtain low-carbon methanol, which is divided into two streams. The first stream of low-carbon methanol returns and undergoes the CO 2 absorption, and the second stream of low-carbon methanol is successively in contact with the CO 2 flash vapor and the flash vapor of H 2 S flash vapor for the second washing to obtain low-sulfur rich-carbon methanol; among them, the first stream of H 2 S-rich methanol, the first stream of CO 2 -rich methanol, low-H 2 S methanol, and low-sulfur rich-carbon methanol each independently return and undergo the H 2 S absorption.

[0032] In some embodiments of the present invention, preferably, the H 2 S absorption includes the first H 2 S absorption and the second H 2 S absorption. Among them, the first stream of H 2 S-rich methanol returns and undergoes the first H 2 S absorption, and the first stream of CO 2 -rich methanol, low-H 2 S methanol, and low-sulfur rich-carbon methanol each independently return and undergo the second H 2 S absorption.

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

[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 CO 2The molar content 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 source of the synthesis gas has a relatively wide selection range, as long as the synthesis gas meets the above limitations. Preferably, the synthesis gas is selected from the upstream synthesis gas cooling process.

[0035] In some embodiments of the present invention, preferably, the molar flow ratio of the synthesis gas to the first stream of H 2 S methanol is 70-80:1.

[0036] In the present invention, the primary H 2 S absorption is intended to remove impurities such as HCN and NH 3 in the synthesis gas, as well as a small amount of H 2 S, CO 2 . Preferably, the molar content of H 2 S in the second rich H 2 S methanol is 2-3%, and the molar content of CO 2 is 70-75%.

[0037] In some embodiments of the present invention, preferably, the molar flow ratio of the synthesis gas to the low H 2 S methanol is 5-6:1; the molar flow ratio of the synthesis gas to the low-sulfur rich-carbon methanol is 22-25:1; the molar flow ratio of the synthesis gas to the first stream of rich CO 2 methanol is 2-3:1.

[0038] In the present invention, the secondary H 2 S absorption is intended to further remove H 2 S in the synthesis gas, as well as a small amount of CO 2 . Preferably, the molar content of CO 2 in the first rich H 2 S methanol is 35-40%, and the molar content of H 2 S is 1.3-1.6%; the temperature is -10 to -5 °C, and the pressure is 5.3-5.5 MPa(G).

[0039] In the present invention, the first rich H 2 S methanol is divided into two streams. The first stream returns and undergoes the first H 2 S absorption, and the second stream undergoes the H 2 S flash. Preferably, the first rich H 2 S methanol is divided into the first stream of rich H 2 S methanol and the second stream of rich H 2 S methanol with a molar flow ratio of 1:50-60.

[0040] 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 35 - 40%; the temperature is -20 to -10 °C; the pressure is 5.3 - 5.4 MPa(G).

[0041] In some embodiments of the present invention, more preferably, after the low-H 2 S methanol is pressurized to 5.8 - 6 MPa(G) for the first time, it is returned and the second H 2 S absorption is carried out.

[0042] In some embodiments of the present invention, preferably, the CO 2 absorption includes: the first CO 2 absorption and the second CO 2 absorption, wherein the first stream of low-carbon methanol is returned and the second CO 2 absorption is carried out.

[0043] In some embodiments of the present invention, preferably, the process of the first CO 2 absorption includes: contacting the desulfurized gas with the second rich CO 2 methanol and carrying out the first CO 2 absorption to obtain a pre-purified gas and the first rich CO 2 methanol; the process of the second CO 2 absorption includes: sequentially contacting the pre-purified gas with the first stream of low-carbon methanol and lean methanol and carrying out the second CO 2 absorption to obtain a purified gas and the second rich CO 2 methanol.

[0044] In some embodiments of the present invention, preferably, the molar flow ratio of the desulfurized gas to the second rich CO 2 methanol is 1:1 - 1.2.

[0045] In some embodiments of the present invention, preferably, the molar content of CO 2 in the first rich CO 2 methanol is 30 - 34%, and the molar content of H 2 S is 0.1 - 0.5 ppm; the temperature is -10 to -5 °C, and the pressure is 5.2 - 5.4 MPa(G).

[0046] In the present invention, the first rich CO 2 methanol is divided into two streams. The first stream is returned and the second H 2 S absorption is carried out, and the second stream is subjected to CO 2 flash evaporation. Preferably, the first rich CO 2The methanol is divided into the first rich CO methanol and the second rich CO methanol with a molar flow ratio of 1:1.5 - 2. 2 methanol and the second rich CO 2 methanol.

[0047] In some embodiments of the present invention, preferably, in the direction of the material flow, the first rich CO methanol is first pressurized to 5.8 - 6 MPa(G) and then cooled to -35 to -25 °C, and then returned to carry out the second H 2 S absorption. 2 S absorption.

[0048] In some embodiments of the present invention, preferably, the molar flow ratio of the purified gas to the first lean methanol is 2 - 3:1; the molar flow ratio of the purified gas to the lean methanol is 1:0.95 - 1.15.

[0049] In some embodiments of the present invention, preferably, the molar content of H 2 S in the purified gas < 0.1 ppm, and the molar content of CO 2 is < 20 ppm; the temperature is -55 to -50 °C, and the pressure is 5.2 - 5.3 MPa(G).

[0050] In some embodiments of the present invention, further preferably, the second rich CO methanol is cooled to -36 to -34 °C and then returned to carry out the first CO 2 absorption. 2 absorption.

[0051] In some embodiments of the present invention, preferably, the process of CO 2 flashing includes: flashing the second rich CO methanol to obtain CO 2 flashed gas and the rich CO 2 methanol after flashing; further preferably, the pressure of the CO 2 flashing is 1.6 - 2 MPa(G). 2 methanol after flashing; further preferably, the pressure of the CO 2 flashing is 1.6 - 2 MPa(G).

[0052] In some embodiments of the present invention, further preferably, the second rich CO methanol is cooled to -36 to -34 °C and returned to carry out the CO 2 flashing. In the present invention, the fifth cooling reduces the temperature of the second rich CO methanol, aiming to reduce the total amount of medium-pressure flashed gas and lay a foundation for obtaining low temperature (high-quality cold energy) for the reabsorption tower. 2 flashing. In the present invention, the fifth cooling reduces the temperature of the second rich CO methanol, aiming to reduce the total amount of medium-pressure flashed gas and lay a foundation for obtaining low temperature (high-quality cold energy) for the reabsorption tower. 2 methanol, aiming to reduce the total amount of medium-pressure flashed gas and lay a foundation for obtaining low temperature (high-quality cold energy) for the reabsorption tower.

[0053] In some embodiments of the present invention, preferably, the H 2 in the rich CO methanol after flashing2 The molar content of S is 0.1 - 0.5 ppm, and the molar content of CO 2 is 29.5 - 33.5%; the temperature is -36.5 to -34.5 °C; further preferably, the CO-rich methanol after flashing is divided into a first stream of CO-rich methanol and a second stream of CO-rich methanol with a molar flow ratio of 2 - 3:1. 2 methanol. 2 methanol and a second stream of CO-rich methanol after flashing. 2 methanol.

[0054] In some embodiments of the present invention, preferably, the temperature of the first cooled material is -42 to -38 °C, and the temperature of the second cooled material is -52 to -48 °C.

[0055] In some embodiments of the present invention, preferably, the heat exchange process includes: exchanging heat between the second stream of H 2 S-rich methanol and the first stream of semi-lean methanol to obtain heat-exchanged H 2 S-rich methanol transformed from the second stream of H 2 S-rich methanol, and heat-exchanged semi-lean methanol transformed from the first stream of semi-lean methanol; further preferably, the temperature of the heat-exchanged H 2 S-rich methanol is -24 to -22 °C; the temperature of the heat-exchanged semi-lean methanol is -55 to -50 °C.

[0056] In some embodiments of the present invention, preferably, the H 2 S flashing process includes: flashing the heat-exchanged H 2 S-rich methanol to obtain H 2 S flash gas and flash gas after flashing. 2 S-rich methanol and flash gas after flashing. 2 S-rich methanol.

[0057] In some embodiments of the present invention, further preferably, after the heat-exchanged H 2 S-rich methanol is cooled to -33 to -30 °C by the sixth cooler, the H 2 S flashing is carried out.

[0058] In some embodiments of the present invention, preferably, the molar content of H 2 in the flash gas after flashing. 2 S is 1.3 - 1.6%, and the molar content of CO 2 is 34.5 - 39.5%; the temperature is -33.5 to -30.5 °C.

[0059] In some embodiments of the present invention, preferably, the first flashing process includes: flashing the first cooled material to obtain the semi-lean methanol and the first CO 2Product gas; the process of the second flash includes: subjecting the second cooled material to the second flash to obtain the flash liquid and second CO 2 Product gas; the process of the third flash includes: subjecting the H 2 S-rich methanol after flashing to the third flash to obtain the sulfur-containing gas phase and third H 2 S-rich methanol.

[0060] In some embodiments of the present invention, further preferably, the pressure of the first flash is 0.05 - 0.08 MPa(G); the pressure of the second flash is 0.06 - 0.09 MPa(G); the pressure of the third flash is 0.12 - 0.16 MPa(G).

[0061] In some embodiments of the present invention, preferably, the molar content of CO 2 in the semi-lean methanol is 22 - 24%, and the molar content of H 2 S is ≤ 0.5 ppm; the temperature is -66 to -62 °C; the pressure is 0.05 - 0.08 MPa(G). Further preferably, the semi-lean methanol is divided into a first stream of semi-lean methanol and a second stream of semi-lean methanol with a molar flow ratio of 1.5 - 2.5:1.

[0062] In the present invention, the semi-lean methanol is divided into two streams, the first stream returns and undergoes the stripping, and the second stream is sent to subsequent processes for treatment.

[0063] In some embodiments of the present invention, preferably, the molar content of H 2 S in the third H 2 S-rich methanol is 1.4 - 1.6%, and the molar content of CO 2 is 24 - 28%; the temperature is -68 to -64 °C; the pressure is 0.13 - 0.17 MPa(G).

[0064] In some embodiments of the present invention, preferably, the process of the first washing includes: bringing the flash liquid into contact with the sulfur-containing gas phase and performing the first washing to obtain the third CO 2 product gas and low-H 2 S methanol.

[0065] In the present invention, the first CO 2 product gas, second CO 2 product gas and third CO 2 product gas are mixed to obtain a CO 2 product gas in which the molar content of H 2 S < 1 ppm and CO 2The molar content is 99.5 - 99.7%; the temperature is -65°C to -60°C, and the pressure is 0.05 - 0.08 MPa(G).

[0066] In some embodiments of the present invention, preferably, the low-H 2 S in methanol has an H 2 S molar content of 0.5 - 1%, and a CO 2 molar content of 22 - 26%; the temperature is -62 to -58°C, and the pressure is 0.12 - 0.16 MPa(G).

[0067] In some embodiments of the present invention, preferably, the stripping process includes: bringing the semi-lean methanol after heat exchange into contact with nitrogen and performing the stripping to obtain the low-carbon methanol and the tail gas.

[0068] In some embodiments of the present invention, preferably, the low-carbon methanol has an H 2 S molar content of ≤0.5 ppm and a CO 2 molar content of 5 - 7%; the temperature is -69 to -65°C; the pressure is 0.15 - 0.25 MPa(G); further preferably, the low-carbon methanol is divided into a first stream of low-carbon methanol and a second stream of low-carbon methanol with a molar flow ratio of 6 - 7:1.

[0069] In some embodiments of the present invention, more preferably, the low-carbon methanol is pressurized to 5.8 - 6 MPa(G) by a third stage and then divided into two streams, and then returned respectively and subjected to a second CO 2 absorption and a second washing.

[0070] In the present invention, the tail gas has an H 2 S molar content of ≤0.5 ppm and a CO 2 molar content of 80 - 84%; the temperature is -57 to -51°C; the pressure is 0.15 - 0.25 MPa(G).

[0071] In some embodiments of the present invention, preferably, the second washing process includes: bringing the second stream of low-carbon methanol into contact with CO 2 flash gas and performing washing to obtain a first flash gas and carbon-containing methanol; bringing the carbon-containing methanol into contact with H 2 S flash gas and performing washing to obtain a second flash gas and low-sulfur carbon-rich methanol.

[0072] In some embodiments of the present invention, preferably, the carbon-containing methanol has an H 2 S molar content of 0.1 - 0.5 ppm and a CO 2 molar content of 12 - 16%; the temperature is -50 to -40°C.

[0073] In the present invention, the temperature of the first flash vapor is -65°C to -60°C, and the pressure is 1.6 - 2 MPa(G); the temperature of the second flash vapor is -48°C to -42°C, and the pressure is 1.6 - 2 MPa(G). The above-mentioned first flash vapor and second flash vapor are respectively sent to the process for treatment.

[0074] In some embodiments of the present invention, preferably, the molar content of H 2 S in the low-sulfur and carbon-rich methanol is <0.1%, and the molar content of CO 2 is 16 - 20%; the temperature is -35 to -30°C.

[0075] In some embodiments of the present invention, preferably, after the low-sulfur and carbon-rich methanol is pressurized to 5.8 - 6 MPa(G) for the fourth time, it is returned and subjected to H 2 S absorption.

[0076] The second aspect of the present invention provides a structural schematic diagram of a low-temperature, low-sulfur, and low-carbon methanol washing device for a coal water slurry gasification device as shown in Figure 1 and it can be seen that the device includes: H Figure 1 S absorption tower T-1, CO 2 absorption tower T-2, CO 2 medium-pressure flash tower T-3, H 2 S medium-pressure flash tower T-4, reabsorption tower T-5, and stripping tower T-6; 2

[0077] H 2 S absorption tower T-1 is used to perform H 2 S absorption on the syngas 1 to obtain the first H 2 S-rich methanol 5 divided into two streams, and desulfurized gas 6; CO 2 absorption tower T-2 is used to perform CO 2 absorption on the desulfurized gas 6 to obtain the first CO 2 rich methanol 4 divided into two streams, and purified gas 10;

[0078] CO 2 The lower part of the medium-pressure flash tower T-3 is used to perform CO 2 flash on the second stream of CO 2 rich methanol 4-ii to obtain the flash-vaporized CO 2 rich methanol 13 divided into two streams; among them, the first stream of flash-vaporized CO 2 rich methanol 13-i and the second stream of flash-vaporized CO 2 rich methanol 13-ii are respectively passed through the first cooler E-1 and the second cooler E-2, and then enter the upper and middle parts of the reabsorption tower T-5 respectively to perform the first flash and the second flash, and respectively obtain semi-lean liquid methanol 8 and flash liquid;​

[0079] H 2 The lower part of the medium-pressure flash column T-4 for S is used to subject the second rich H 2 S methanol 5-ii, after passing through the heat exchanger Q, undergoes H 2 S flash evaporation to obtain the flashed rich H 2 S methanol 16 enters the lower part of the reabsorption column T-5 for the third flash evaporation. The sulfur-containing gas phase and the flashed liquid obtained come into contact and undergo the first washing to obtain low H 2 S methanol 2;

[0080] The stripping column T-6 is used to subject the first semi-lean methanol 8-i to stripping after passing through the heat exchanger Q. The obtained low-carbon methanol 12 is divided into two streams. The first stream of low-carbon methanol 12-i is recycled to the CO 2 absorption column T-2, and the second stream of low-carbon methanol 12-ii successively enters the CO 2 medium-pressure flash column T-3 and H 2 the upper part of the medium-pressure flash column T-4 for S for the second washing to obtain low-sulfur rich-carbon methanol 11;

[0081] Among them, the first rich H 2 S methanol 5-i, the first rich CO 2 methanol 4-i, low H 2 S methanol 2 and low-sulfur rich-carbon methanol 11 are each independently recycled to H 2 S absorption column T-1.

[0082] In the present invention, as Figure 1 shown, H 2 S absorption column T-1 is divided into a first H 2 S absorption section and a second H 2 S absorption section from bottom to top. The first H 2 S absorption section and the second H 2 S absorption section are connected through lifting holes. That is, the pre-desulfurized gas from the first H 2 S absorption section enters the second H 2 S absorption section through the lifting holes.

[0083] In the present invention, as Figure 1 shown, the H 2 S absorption column T-1 is divided into a first H 2 S absorption section and a second H 2 S absorption section from bottom to top; among them, the first H 2 S absorption section is used to bring the syngas 1 into contact with the first rich H 2 S methanol 5-i and perform the first H 2 S absorption to obtain pre-desulfurized gas and the second rich H 2 S methanol 3; the second H 2The S absorption section is used to successively contact the pre-desulfurized gas with the low-H 2 S methanol 2, low-sulfur carbon-rich methanol 11, and the first stream of CO-rich 2 methanol 4-i and carry out the second H 2 S absorption to obtain the first H-rich 2 S methanol 5 and desulfurized gas 6.

[0084] In the present invention, as Figure 1 shown, the CO 2 absorption tower T-2 is divided into a first CO 2 absorption section and a second CO 2 absorption section from bottom to top. The first CO 2 absorption section and the second CO 2 absorption section are connected by lifting holes, that is, the pre-purified gas from the first CO 2 absorption section enters the second CO 2 absorption section through the lifting holes.

[0085] In the present invention, as Figure 1 shown, the CO 2 absorption tower T-2 is divided into a first CO 2 absorption section and a second CO 2 absorption section from bottom to top; wherein, the first CO 2 absorption section is used to contact the desulfurized gas 6 and the second CO-rich 2 methanol 7 and carry out the first CO 2 absorption to obtain pre-purified gas and the first CO-rich 2 methanol 4; the second CO 2 absorption section is used to successively contact the pre-purified gas with the first stream of low-carbon methanol 12-i and lean methanol 9 and carry out the second CO 2 absorption to obtain purified gas 10 and the second CO-rich 2 methanol 7.

[0086] In the present invention, the medium-pressure flash tower T-3 of CO 2 is divided into an upper part and a lower part, and the upper part and the lower part are connected by lifting holes, that is, the CO 2 flash gas from the lower part enters the upper part through the lifting holes for washing.

[0087] In the present invention, as Figure 1 shown, the lower part of the medium-pressure flash tower T-3 of CO 2 is used to carry out CO 2 flash on the second stream of CO-rich 2 methanol 4-ii to obtain CO 2 flash gas and flash-post CO-rich 2 methanol 13; CO 2The upper part of the medium-pressure flash column T-3 is used to wash the CO 2 flash gas and the second stream of low-carbon methanol 12-ii to obtain the first flash gas 15-i and carbon-containing methanol 14.

[0088] In the present invention, as Figure 1 shown, the heat exchanger Q is used to exchange heat between the second stream of H 2 S-rich methanol 5-ii and the first stream of semi-lean methanol 8-i to obtain the heat-exchanged H 2 S-rich methanol 21 transformed from the second stream of H 2 S-rich methanol and the heat-exchanged semi-lean methanol 22 transformed from the first stream of semi-lean methanol 8-i.

[0089] In the present invention, the H 2 S medium-pressure flash column T-4 is divided into an upper part and a lower part, and the upper part and the lower part are connected by lifting holes. That is, the H 2 S flash gas from the lower part enters the upper part through the lifting holes for washing.

[0090] In the present invention, as Figure 1 shown, the lower part of the H 2 S medium-pressure flash column T-4 is used to subject the second stream of H 2 S-rich methanol 5-ii to H 2 S flash evaporation after passing through the heat exchanger Q to obtain H 2 S flash gas and flash-evaporated H 2 S-rich methanol 16; the upper part of the H 2 S medium-pressure flash column T-4 is used to wash the H 2 S flash gas and the carbon-containing methanol 14 to obtain the second flash gas 15-ii and low-sulfur carbon-rich methanol 11.

[0091] In the present invention, as Figure 1 shown, the upper part and the middle part of the reabsorption column T-5 are connected by lifting holes, and the middle part and the lower part are also connected by lifting holes. Among them, the upper part is used to subject the first stream of flash-evaporated CO 2 -rich methanol 13-i to the first cooling and then to the first flash evaporation to obtain semi-lean methanol 8 and the first CO 2 product gas; the middle part is used to subject the second stream of flash-evaporated CO 2 -rich methanol 13-ii to the second cooling and then to the second flash evaporation to obtain the flash liquid and the second CO 2 product gas; the lower part is used to subject the flash-evaporated H 2 S-rich methanol 16 to the third flash evaporation to obtain the sulfur-containing gas phase and the third H 2 S-rich methanol 18; among them, the flash liquid and the sulfur-containing gas phase are subjected to the first washing to obtain low-H 2 S methanol 2 and the third CO 2 product gas, and the first CO2 Product gas, second CO 2 Product gas and third CO 2 The product gas is mixed to obtain CO 2 Product gas 17.

[0092] In the present invention, as Figure 1 shown, the stripping column T-6 is used to bring the semi-lean methanol 22 after heat exchange into contact with nitrogen 20 and perform stripping to obtain low-carbon methanol 12 and tail gas 19.

[0093] In the present invention, as Figure 1 shown, a first pump P-1 is provided on the pipeline connecting the low-H 2 S methanol outlet of the reabsorption column T-5 and the second H 2 S absorption section, and is used to return the low-H 2 S methanol 2 after being pressurized for the first time and perform the second H 2 S absorption.

[0094] In the present invention, as Figure 1 shown, in the direction of material flow, a second pump P-2 and a third cooler E-3 are successively provided on the pipeline connecting the first rich CO 2 methanol outlet of the CO 2 absorption column T-2 and the second H 2 S absorption section, and are used to return the first stream of rich CO 2 methanol 4-i after being pressurized for the second time and cooled for the third time and perform the second H 2 S absorption.

[0095] In the present invention, as Figure 1 shown, in the direction of material flow, a fourth cooler E-4 is provided on the pipeline connecting the bottom of the second CO 2 absorption section and the upper part of the first CO 2 absorption section, and is used to cool the second rich CO 2 methanol 7 and perform the first CO 2 absorption.

[0096] In the present invention, as Figure 1 shown, a fifth cooler E-5 is provided on the pipeline connecting the first rich CO 2 methanol outlet of the CO 2 absorption column T-2 and the lower part of the CO 2 medium-pressure flash column T-3, and is used to cool the second stream of rich CO 2 methanol 4-ii and perform the CO 2 flash.

[0097] In the present invention, as Figure 1As shown, connect the heat exchangers Q and H 2 A sixth cooler E-6 is provided on the pipeline at the lower part of the medium-pressure flash tower T-4 in S, for cooling the rich H after heat exchange 2 After the methanol 21 in S is cooled by the sixth cooler, the H 2 S flash distillation is carried out.

[0098] In the present invention, as Figure 1 shown, connect the low-carbon methanol outlet of the stripping tower T-6, the second CO 2 absorption section and CO 2 A third pump P-3 is provided on the pipeline at the upper part of the medium-pressure flash tower T-3 in S, for dividing the low-carbon methanol 12 after being pressurized by the third pump into a first stream of low-carbon methanol 12-i and a second stream of low-carbon methanol 12-ii, and respectively returning them to carry out the second CO 2 absorption and the second washing.

[0099] In the present invention, as Figure 1 shown, connect the H 2 low-sulfur rich-carbon methanol outlet of the medium-pressure flash tower T-4 in S and the second H 2 A fourth pump P-4 is provided on the pipeline of the S absorption section, for returning the low-sulfur rich-carbon methanol 11 after being pressurized by the fourth pump to carry out the second H 2 S absorption.

[0100] The present invention will be described in detail below through embodiments.

[0101] Embodiment 1

[0102] The device is as Figure 1 shown, and the device includes: H 2 S absorption tower T-1, CO 2 absorption tower T-2, CO 2 medium-pressure flash tower T-3, H 2 S medium-pressure flash tower T-4, reabsorption tower T-5 and stripping tower T-6, heat exchanger Q, first cooler E-1, second cooler E-2, third cooler E-3, fourth cooler E-4, fifth cooler E-5 and sixth cooler E-6, and first pump P-1, second pump P-2, third pump P-3 and fourth pump P-4;

[0103] H 2 The S absorption tower T-1 is divided into a first H 2 S absorption section and a second H 2 S absorption section from bottom to top; CO 2 The absorption tower T-2 is divided into a first CO 2 absorption section and a second CO 2 absorption section from bottom to top; CO 2 The medium-pressure flash tower T-3 is divided into an upper part and a lower part; H2 The medium-pressure flash column T-4 in S is divided into an upper part and a lower part.

[0104] The method is carried out in the above-mentioned device, and the method includes:

[0105] The syngas (H 2 The molar content of S is 0.9 - 1.2%, and the molar content of CO 2 is 40 - 50%; the temperature is -15 to -5 °C, the pressure is 5.2 - 5.7 MPa(G)), and the first rich H 2 S methanol contacts countercurrently at a molar flow rate ratio of 70 - 80:1 and undergoes the first H 2 absorption to obtain the second rich H 2 S methanol (H 2 The molar content of S is 2 - 3%, and the molar content of CO 2 is 70 - 75%) and the pre-desulfurized gas; the above-mentioned pre-desulfurized gas is successively contacted countercurrently with low H 2 S methanol (pressurized to 5.8 - 6 MPa(G) for the first time), low-sulfur rich-carbon methanol (pressurized to 5.8 - 6 MPa(G) for the fourth time), and the first rich CO 2 methanol (pressurized to 5.8 - 6 MPa(G) for the second time, cooled to -35 to -25 °C for the third time) and undergoes the second H 2 S absorption to obtain the desulfurized gas (H 2 The molar content of S is 0.5 - 1 ppm, and the molar content of CO 2 is 35 - 40%; the temperature is -20 to -10 °C; the pressure is 5.3 - 5.4 MPa(G)) and the first rich H 2 S methanol (H 2 The molar content of S is 1.3 - 1.6%, and the molar content of CO 2 is 35 - 40%; the temperature is -10 to -5 °C, the pressure is 5.3 - 5.5 MPa(G)); among them, the molar flow rate ratio of low H 2 S methanol to syngas is 1:5 - 6; the molar flow rate ratio of syngas to low-sulfur rich-carbon methanol is 22 - 25:1; the molar flow rate ratio of the first rich CO 2 methanol to syngas is 1:2 - 3;

[0106] The above-mentioned first rich H 2 S methanol is divided into the first rich H 2 S methanol and the second rich H 2 S methanol with a molar flow rate ratio of 1:50 - 60;

[0107] The above-mentioned desulfurized gas and the second rich CO 2 methanol from the upper section (cooled to -36 to -34 °C for the fourth time) contact countercurrently at a molar flow rate ratio of 1:1 - 1.2 and undergo the first CO2 Absorption is carried out to obtain the first CO-rich 2 methanol (the molar content of CO 2 is 30 - 34%, and the molar content of H 2 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. The first CO-rich 2 methanol is divided into the first stream of CO-rich 2 methanol and the second stream of CO-rich 2 methanol with a molar flow rate ratio of 1:1.5 - 2; the pre-purified gas, the first stream of low-carbon methanol, and the lean methanol are contacted and the second CO 2 absorption is carried out to obtain the purified gas (the molar content of H 2 S < 0.1 ppm, and the molar content of CO 2 < 20 ppm; the temperature is -55 to -50 °C, and the pressure is 5.2 - 5.3 MPa (G)) and the second CO-rich 2 methanol; the molar flow rate ratio of the purified gas to the first stream of low-carbon methanol is 2 - 3:1; the molar flow rate ratio of the purified gas to the lean methanol is 1:0.95 - 1.15;

[0108] The second stream of CO-rich 2 methanol is cooled to -36 to -34 °C by the fifth cooler and then undergoes CO 2 flashing (the pressure is 1.6 - 2 MPa (G)) to obtain the CO 2 flashed gas and the CO-rich 2 methanol after flashing (the molar content of H 2 S is 0.1 - 0.5 ppm, and the molar content of CO 2 is 29.5 - 33.5%; the temperature is -36.5 to -34.5 °C). The CO-rich 2 methanol after flashing is divided into the first stream of CO-rich 2 methanol after flashing and the second stream of CO-rich 2 methanol after flashing with a molar flow rate ratio of 2 - 3:1, and then the first cooling and the second cooling are carried out respectively;

[0109] The second stream of H 2 S-rich methanol and the first stream of semi-lean liquid methanol are heat-exchanged to obtain the heat-exchanged H 2 S-rich methanol at -24 to -20 °C, and the heat-exchanged semi-lean liquid methanol at -55 to -50 °C;

[0110] The heat-exchanged H 2 S-rich methanol is cooled to -33 to -30 °C by the sixth cooler and then undergoes H 2 S flashing to obtain the H 2 S flashed gas and the H 2 S-rich methanol after flashing (the molar content of H 2The molar content of S is 1.3 - 1.6%, and the molar content of CO 2 is 34.5 - 39.5%; the temperature is -33.5 to -30.5 °C);

[0111] The first cooled material (temperature: -42 to -38 °C) is subjected to the first flash (pressure: 0.05 - 0.08 MPa(G)) to obtain the semi-lean methanol (CO 2 with a molar content of 22 - 24%, and H 2 with a molar content of S ≤ 0.5 ppm; the temperature is -66 to -62 °C; the pressure is 0.05 - 0.08 MPa(G)) and the first CO 2 product gas; the second cooled material (temperature: -52 to -48 °C) is subjected to the second flash (pressure: 0.06 - 0.09 MPa(G)) to obtain the flash liquid and the second CO 2 product gas; the flashed H 2 -rich methanol is subjected to the third flash (pressure: 0.12 - 0.16 MPa(G)) to obtain the sulfur-containing gas phase and the third H 2 -rich methanol (H 2 with a molar content of S of 1.4 - 1.6%, and CO 2 with a molar content of 24 - 28%; the temperature is -68 to -64 °C; the pressure is 0.13 - 0.17 MPa(G)); wherein, the above-mentioned flash liquid and the sulfur-containing gas phase are contacted and subjected to the first washing to obtain the third CO 2 product gas and low-H 2 -S methanol (H 2 with a molar content of S of 0.5 - 1%, and CO 2 with a molar content of 22 - 26%; the temperature is -62 to -58 °C, and the pressure is 0.12 - 0.16 MPa(G));

[0112] Among them, the above-mentioned first CO 2 product gas, the second CO 2 product gas and the third CO 2 product gas are mixed to obtain the CO 2 product gas with an H 2 molar content of S < 1 ppm and a CO 2 molar content of 99.5 - 99.7%; the temperature is -65 °C to -60 °C, and the pressure is 0.05 - 0.08 MPa(G);

[0113] The above-mentioned semi-lean methanol is divided into a first semi-lean methanol and a second semi-lean methanol with a molar flow ratio of 1.5 - 2.5:1; the heat-exchanged semi-lean methanol is contacted with nitrogen and subjected to stripping to obtain low-carbon methanol (H 2 with a molar content of S ≤ 0.5 ppm, and CO2 The molar content is 5 - 7%; the temperature is -69 to -65 °C; the pressure is 0.15 - 0.25 MPa(G)) and the tail gas (H 2 The molar content of S is ≤0.5 ppm, CO 2 The molar content is 80 - 84%; the temperature is -57 to -51 °C; the pressure is 0.15 - 0.25 MPa(G));

[0114] After pressurizing the above - mentioned low - carbon methanol to 5.8 - 6 MPa(G) for the third time, it is divided into the first low - carbon methanol and the second low - carbon methanol with a molar flow ratio of 6 - 7:1; among them, the above - mentioned second low - carbon methanol is contacted with the CO 2 flash gas and washed to obtain the first flash gas (temperature is -65 °C to -60 °C, pressure is 1.6 - 2 MPa(G)) and carbon - containing methanol (H 2 The molar content of S is 0.1 - 0.5 ppm, CO 2 The molar content is 12 - 16%; the temperature is -50 to -40 °C); and the carbon - containing methanol is contacted with the H 2 S flash gas and washed to obtain the second flash gas (temperature is -48 °C to -42 °C, pressure is 1.6 - 2 MPa(G)) and low - sulfur carbon - rich methanol (H 2 The molar content of S is <0.1%, CO 2 The molar content is 16 - 20%; the temperature is -35 to -30 °C).

[0115] Comparative Example 1

[0116] Taking the 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 are compared with those of the lean liquid - semi - lean liquid process (i.e., a low - temperature methanol washing process disclosed in CN201110260570.0) in Table 1.

[0117] Table 1

[0118]

[0119] It can be seen from the results in Table 1 that taking the hydrogen - production device based on coal - water slurry gasification for gas production as an example, for the syngas purification process of the supporting coal - water slurry gasification device provided in Example 1, the lean methanol circulation volume is 90.4% of the lean methanol circulation volume in Comparative Example 1 (lean liquid - semi - lean liquid process), the semi - lean liquid methanol circulation volume is 66.7% of the semi - lean methanol circulation volume in Comparative Example 1 (lean liquid - semi - lean liquid process), and the amount of rich CO 2 methanol used in the H 2 S absorption tower is the amount of rich CO2 83.2% of the methanol usage, with the cumulative reduction of external cooling consumption by 700 KW / h, showing significant overall energy-saving effect.

[0120] 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 the combination of each technical feature in any other suitable manner. 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. A low-temperature, low-sulfur, low-carbon methanol washing method for a water-coal slurry gasification device, characterized in that: The method comprises: The synthesis gas is subjected to H2S absorption, and the obtained first H2S-rich methanol is divided into two streams, and the obtained desulfurized gas is subjected to CO2 absorption, and the obtained first CO2-rich methanol is divided into two streams, and the second stream of CO2-rich methanol is subjected to CO2 flash evaporation, and the obtained flashed CO2-rich methanol is divided into two streams, and after a first cooling and a second cooling, a first flash evaporation and a second flash evaporation are respectively performed to obtain semi-lean liquid methanol and a flashed liquid, respectively; the second stream of H2S-rich methanol is subjected to H2S flash evaporation after heat exchange, and the obtained flashed H2S-rich methanol is subjected to a third flash evaporation, and the obtained sulfur-containing gas phase and the flashed liquid are subjected to a first washing to obtain low-H2S methanol; The semi-lean liquid methanol is divided into two streams, the first stream of the semi-lean liquid methanol is stripped after the heat exchange, and the obtained low-carbon methanol is divided into two streams, the first stream of the low-carbon methanol is returned and subjected to the CO2 absorption, and the second stream of the low-carbon methanol is sequentially subjected to a second washing with the flash gas of the CO2 flash and the H2S flash to obtain low-sulfur carbon-rich methanol; The first stream of H2S-rich methanol, the first stream of CO2-rich methanol, the low H2S methanol and the low-sulfur carbon-rich methanol are each independently returned and subjected to the H2S absorption.

2. The method according to claim 1, wherein: The H2S absorption includes a first H2S absorption and a second H2S absorption, wherein the first stream of H2S-rich methanol is returned and subjected to the first H2S absorption, and the first stream of CO2-rich methanol, low H2S methanol and low-sulfur carbon-rich methanol are each independently returned and subjected to the second H2S absorption; Preferably, the first H2S absorption process comprises: contacting the synthesis gas with a first stream of H2S-rich methanol and performing the first H2S absorption to obtain pre-desulfurized gas and a second H2S-rich methanol; the second H2S absorption process comprises: contacting the pre-desulfurized gas with the low H2S methanol, the low-sulfur carbon-rich methanol and the first stream of CO2-rich methanol in sequence and performing the second H2S absorption to obtain the first H2S-rich methanol and desulfurized gas; and / or, the molar content of CO2 in the first H2S-rich methanol is 35-40%, the molar content of H2S is 1.3-1.6%; the temperature is -10 to -5°C, and the pressure is 5.3-5.5MPa(G); and / or, dividing the first H2S-rich methanol into the first stream of H2S-rich methanol and the second stream of H2S-rich methanol at a molar flow ratio of 1:50-60; and / or, the molar content of H2S in the desulfurized gas is 0.5-1ppm, the molar content of CO2 is 35-40%; the temperature is -20 to -10°C; the pressure is 5.3-5.4MPa(G); Preferably, the low H2S methanol is first pressurized to 5.8-6 MPa(G) and then returned to undergo the second H2S absorption.

3. The method according to claim 1 or 2, wherein: The CO2 absorption includes: a first CO2 absorption and a second CO2 absorption, wherein the first stream of low-carbon methanol is returned and the second CO2 absorption is performed; Preferably, the first CO2 absorption process comprises: contacting the desulfurized gas with the second CO2-rich methanol and performing the first CO2 absorption to obtain pre-purified gas and the first CO2-rich methanol; the second CO2 absorption process comprises: contacting the pre-purified gas with the first stream of low-carbon methanol and lean methanol in sequence and performing the second CO2 absorption to obtain purified gas and the second CO2-rich methanol; and / or, the molar content of CO2 in the first CO2-rich methanol is 30-34%, 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 first CO2-rich methanol into the first CO2-rich methanol and the second CO2-rich methanol at a molar flow ratio of 1:1.5-2; and / or, according to the flow direction of the logistics, the first stream of CO2-rich methanol is successively pressurized to 5.8-6 MPa (G) and cooled to -35 to -25°C, and then returned to the second H2S absorption; Preferably, the second CO2-rich methanol is cooled to -36 to -34°C for the fourth time and then returned to the first CO2 absorption.

4. The method according to any one of claims 1 to 3, wherein: The CO2 flashing process comprises: subjecting the second stream of CO2-rich methanol to the CO2 flashing to obtain CO2 flash gas and the flashed CO2-rich methanol; And / or, the pressure of the CO2 flash evaporation is 1.6-2MPa(G); and / or, cooling the second stream of CO2-rich methanol to -36 to -34°C through a fifth step, returning the second stream of CO2-rich methanol to undergo the CO2 flash evaporation; and / or, the molar content of H2S in the CO2-rich methanol after the flash is 0.1-0.5 ppm, the molar content of CO2 is 29.5-33.5%; the temperature is -36.5 to -34.5°C; and / or, dividing the flashed CO2-rich methanol into a first stream of flashed CO2-rich methanol and a second stream of flashed CO2-rich methanol at a molar flow ratio of 2-3:1; And / or, the temperature of the first cooled material is -42 to -38°C; And / or, the temperature of the second cooled material is -52 to -48°C.

5. The method according to any one of claims 1 to 4, wherein: The heat exchange process comprises: performing heat exchange on the second stream of H2S-rich methanol and the first stream of semi-lean methanol to obtain heat-exchanged H2S-rich methanol converted from the second stream of H2S-rich methanol and heat-exchanged semi-lean methanol converted from the first stream of semi-lean methanol; Preferably, the temperature of the H2S-rich methanol after the heat exchange is -24 to -22°C; the temperature of the semi-lean methanol after the heat exchange is -55 to -50°C; And / or, the H2S flash evaporation process comprises: subjecting the H2S-rich methanol after heat exchange to the H2S flash evaporation to obtain H2S flash gas and H2S-rich methanol after flash evaporation; Preferably, the H2S-rich methanol after the heat exchange is cooled to -33 to -30°C for the sixth time, and then the H2S flash is performed; And / or, the molar content of H2S in the H2S-rich methanol after the flash evaporation is 1.3-1.6%, the molar content of CO2 is 34.5-39.5%; the temperature is -33.5 to -30.5°C.

6. The method according to any one of claims 1 to 5, wherein: The first flash evaporation process includes: subjecting the first cooled material to the first flash evaporation to obtain the semi-lean liquid methanol and the first CO2 product gas; the second flash evaporation process includes: subjecting the second cooled material to the second flash evaporation to obtain the flashed liquid and the second CO2 product gas; the third flash evaporation process includes: subjecting the flashed H2S-rich methanol to the third flash evaporation to obtain the sulfur-containing gas phase and the third H2S-rich methanol; 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 22-24%, the molar content of H2S is ≤0.5ppm; the temperature is -66 to -62°C; the pressure is 0.05-0.08MPa(G); and / or, dividing the semi-lean methanol into a first stream of semi-lean methanol and a second stream of semi-lean methanol at a molar flow ratio of 1.5-2.5:1; And / or, the first washing process includes: contacting the flash liquid with the sulfur-containing gas and performing the first washing to obtain a third CO2 product gas and low-H2S methanol; And / or, the molar content of H2S in the low H2S methanol is 0.5-1%, the molar content of CO2 is 22-26%; the temperature is -62 to -58°C, and the pressure is 0.12-0.16 MPa(G).

7. The method according to any one of claims 1 to 6, wherein: The stripping process comprises: contacting the semi-lean liquid methanol after 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 5-7%; the temperature is -69 to -65°C; the pressure is 0.15-0.25MPa(G); and / or, dividing the low-carbon methanol into the first stream of low-carbon methanol and the second stream of low-carbon methanol at a molar flow ratio of 6-7:1; and / or, the low-carbon methanol is pressurized to 5.8-6 MPa(G) for a third time and then divided into two streams; And / or, the second washing process includes: contacting and washing the second stream of low-carbon methanol with CO2 flash gas to obtain first flash gas and carbon-containing methanol; contacting and washing the carbon-containing methanol with H2S flash gas to obtain second flash gas and low-sulfur carbon-rich methanol; and / or, the molar content of H2S in the low-sulfur, carbon-rich methanol is <0.1%, the molar content of CO2 is 16-20%; the temperature is -35 to -30°C; And / or, the low-sulfur, carbon-rich methanol is pressurized to 5.8-6 MPa(G) for the fourth time and then returned to perform the H2S absorption.

8. A low-temperature, low-sulfur, low-carbon 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 CO2 medium-pressure flash tower, an H2S medium-pressure flash tower, a reabsorption tower and a stripping tower; The H2S absorption tower is used to absorb H2S from the synthesis gas to obtain the first H2S-rich methanol in two streams and desulfurized gas; the CO2 absorption tower is used to absorb CO2 from the desulfurized gas to obtain the first CO2-rich methanol in two streams and purified gas; The lower part of the CO2 medium-pressure flash tower is used to perform CO2 flashing on the second stream of CO2-rich methanol, and the flashed CO2-rich methanol obtained is divided into two streams; wherein, the first stream of flashed CO2-rich methanol and the second stream of flashed CO2-rich methanol are respectively passed through the first cooler and the second cooler, and then enter the upper part and the middle part of the reabsorption tower respectively, and perform the first flash evaporation and the second flash evaporation respectively, to obtain semi-lean liquid methanol and flash liquid respectively; The lower part of the H2S medium-pressure flash tower is used to flash the second stream of H2S-rich methanol through a heat exchanger. The flashed H2S-rich methanol enters the lower part of the reabsorption tower for the third flash. The sulfur-containing gas phase is contacted with the flash liquid and washed for the first time to obtain low-H2S methanol. The stripping tower is used to strip the first stream of semi-lean liquid methanol after passing through the heat exchanger, and the obtained low-carbon methanol is divided into two streams. The first stream of low-carbon methanol is recycled to the CO2 absorption tower, and the second stream of low-carbon methanol enters the upper part of the CO2 medium-pressure flash tower and the H2S medium-pressure flash tower in turn for the second washing to obtain low-sulfur carbon-rich methanol; Among them, the first stream of H2S-rich methanol, the first stream of CO2-rich methanol, the low H2S methanol and the low-sulfur carbon-rich methanol are independently recycled to the H2S absorption tower.

9. The device according to claim 8, wherein: The H2S absorption tower is divided into a first H2S absorption section and a second H2S absorption section from bottom to top; The first H2S absorption section is used to contact the synthesis gas with the first stream of H2S-rich methanol and perform the first H2S absorption to obtain pre-desulfurized gas and second H2S-rich methanol; the second H2S absorption section is used to contact the pre-desulfurized gas with the low-H2S methanol, the low-sulfur carbon-rich methanol and the first stream of CO2-rich methanol in sequence and perform the second H2S absorption to obtain the first H2S-rich methanol and desulfurized gas; And / or, the CO2 absorption tower is divided into a first CO2 absorption section and a second CO2 absorption section from bottom to top; Among them, the first CO2 absorption section is used to contact the desulfurized gas with the second CO2-rich methanol and perform the first CO2 absorption to obtain pre-purified gas and the first CO2-rich methanol; the second CO2 absorption section is used to contact the pre-purified gas with the first low-carbon methanol and lean methanol in sequence and perform the second CO2 absorption to obtain purified gas and the second CO2-rich methanol.

10. The device according to claim 9, wherein: A first pump is provided on the pipeline connecting the low H2S methanol outlet of the reabsorption tower and the second H2S absorption section, for returning the low H2S methanol after the first pressurization and performing the second H2S absorption; And / or, according to the material flow direction, a second pump and a third cooler are sequentially arranged on the pipeline connecting the first CO2-rich methanol outlet and the second H2S absorption section of the CO2 absorption tower, so as to return the first stream of CO2-rich methanol to the second H2S absorption after the second pressurization and the third cooling; and / or, in accordance with the material flow direction, a fourth cooler is provided on the pipeline connecting the bottom of the second CO2 absorption section and the upper part of the first CO2 absorption section, for subjecting the second CO2-rich methanol to the fourth cooling before subjecting it to the first CO2 absorption; And / or, a fifth cooler is provided on the pipeline connecting the first CO2-rich methanol outlet of the CO2 absorption tower and the lower part of the CO2 medium-pressure flash tower, for flashing the CO2 after cooling the second stream of CO2-rich methanol through the fifth cooler; And / or, a sixth cooler is provided on the pipeline connecting the heat exchanger and the lower part of the H2S medium-pressure flash tower, for flashing the H2S after the heat exchange with the H2S-rich methanol after the sixth cooling; And / or, a third pump is provided on the pipeline connecting the low-carbon methanol outlet of the stripping tower, the second CO2 absorption section and the upper part of the CO2 medium-pressure flash tower, for separating the low-carbon methanol into a first stream of low-carbon methanol and a second stream of low-carbon methanol after the third pressurization, and returning them to perform the second CO2 absorption and the second washing respectively; And / or, a fourth pump is provided on the pipeline connecting the low-sulfur and carbon-rich methanol outlet of the H2S medium-pressure flash tower and the second H2S absorption section, for returning the low-sulfur and carbon-rich methanol after the fourth pressurization and performing the second H2S absorption.

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