Energy-saving low-temperature low-sulfur 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 an energy-saving low-temperature low-sulfur methanol washing method and device matched with a coal water slurry gasification device.According to the method, by optimally configuring a medium-pressure flash evaporation process, the method has the advantages that only CO2-rich methanol is subjected to flash evaporation in first-stage flash evaporation, flash steam does not need to be washed, and the pressure of the flash steam is high; the secondary CO2 flash evaporation and the H2S flash evaporation respectively use semi-barren liquor methanol for independent washing, so that the method has the advantages that the content of H2S in secondary flash steam is low, the secondary flash steam can be directly connected into a gas pipe network, the use efficiency of low H2S methanol is high, and the comprehensive energy consumption of a low-temperature methanol washing device is low.

Description

Technical Field

[0001] The present invention relates to the technical field of low-temperature methanol washing, and specifically relates to an energy-saving low-temperature and low-sulfur methanol washing method for a coal water slurry gasification device and an energy-saving low-temperature and low-sulfur 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 shift 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 pressure-reduced flash evaporation of the CO 2 -rich methanol. The typical process flow mainly has 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 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 pressure-reduced flash evaporation, but the H 2 S-rich methanol must be recycled through rectification regeneration, which is the main energy-consuming source of the low-temperature methanol washing. Therefore, how to enhance the utilization efficiency of the H 2 S-rich methanol is the direction and key factor of technical innovation. Specifically, it is necessary to achieve that before the rectification 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 rectified and regenerated.

[0005] CN201110260570.0 discloses a low-temperature methanol washing process. First, in this low-temperature methanol washing process, all the H 2 S absorption tower uses CO 2Methanol is used to wash the syngas, and the low-H₂S methanol solution existing in the system is not studied and used, allowing it to undertake part of the potential of absorbing H₂S gas in the syngas. Because the CO-rich methanol that has absorbed H₂S gas becomes H₂S-rich methanol, it needs to be regenerated by consuming steam in the rectification system and cooled by cooling water before it can be recycled. Therefore, in the H₂S absorption tower for removing H₂S gas, the CO-rich methanol has a large consumption and high energy consumption; second, in the CO flash evaporation section of the reabsorption tower, the CO-rich methanol directly mixes with the H₂S-rich methanol while washing the H₂S-rich methanol flash gas, and itself is contaminated by the H₂S-rich methanol, which is generally not conducive to reducing the comprehensive energy consumption of the low-temperature methanol washing unit; third, the medium-pressure flash evaporation process has a simple setting, only using one-stage flash evaporation, the flash gas pressure is relatively low, and a large compression power consumption is required to recover the flash gas. 2 The potential of absorbing H₂S gas in the syngas is not utilized by studying and using the low-H₂S methanol solution existing in the system. 2 Since the H₂S gas is absorbed, the CO-rich methanol becomes H₂S-rich methanol, which needs to be regenerated by consuming steam in the rectification system and cooled by cooling water before it can be recycled. 2 CO-rich 2 H₂S-rich 2 methanol, and it can only be recycled after being regenerated by consuming steam in the rectification system and cooled by cooling water. Therefore, in the H₂S absorption tower for removing H₂S gas, the CO-rich methanol has a large consumption and high energy consumption; second, in the CO flash evaporation section of the reabsorption tower, the CO-rich methanol directly mixes with the H₂S-rich methanol while washing the H₂S-rich methanol flash gas, and itself is contaminated by the H₂S-rich methanol, which is generally not conducive to reducing the comprehensive energy consumption of the low-temperature methanol washing unit; third, the medium-pressure flash evaporation process has a simple setting, only using one-stage flash evaporation, the flash gas pressure is relatively low, and a large compression power consumption is required to recover the flash gas. 2 The H₂S absorption tower is used to remove H₂S gas. 2 CO-rich 2 methanol has a large consumption and high energy consumption; second, in the CO flash evaporation section of the reabsorption tower, the CO-rich methanol directly mixes with the H₂S-rich methanol while washing the H₂S-rich methanol flash gas, and itself is contaminated by the H₂S-rich methanol, which is generally not conducive to reducing the comprehensive energy consumption of the low-temperature methanol washing unit; third, the medium-pressure flash evaporation process has a simple setting, only using one-stage flash evaporation, the flash gas pressure is relatively low, and a large compression power consumption is required to recover the flash gas. 2 In the flash evaporation section of the reabsorption tower, the CO-rich 2 methanol washes the H₂S-rich methanol flash gas and directly mixes with the H₂S-rich methanol while washing the H₂S-rich methanol flash gas, and itself is contaminated by the H₂S-rich methanol, which is generally not conducive to reducing the comprehensive energy consumption of the low-temperature methanol washing unit; third, the medium-pressure flash evaporation process has a simple setting, only using one-stage flash evaporation, the flash gas pressure is relatively low, and a large compression power consumption is required to recover the flash gas. 2 The CO-rich methanol directly mixes with the H₂S-rich methanol while washing the H₂S-rich methanol flash gas. 2 The CO-rich methanol is contaminated by the H₂S-rich methanol, which is generally not conducive to reducing the comprehensive energy consumption of the low-temperature methanol washing unit; third, the medium-pressure flash evaporation process has a simple setting, only using one-stage flash evaporation, the flash gas pressure is relatively low, and a large compression power consumption is required to recover the flash gas. 2 methanol, which is generally not conducive to reducing the comprehensive energy consumption of the low-temperature methanol washing unit; third, the medium-pressure flash evaporation process has a simple setting, only using one-stage flash evaporation, the flash gas pressure is relatively low, and a large compression power consumption is required to recover the flash gas. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above technical problems and provide an energy-saving low-temperature and low-sulfur methanol washing method for a supporting water coal slurry gasification device and an energy-saving low-temperature and low-sulfur methanol washing device for a supporting water coal slurry gasification device. By optimizing the configuration of the medium-pressure flash evaporation process, this method has the advantages of only flashing CO-rich methanol in the first-stage flash evaporation, the flash gas does not need to be washed, and the flash gas pressure is high. The second-stage CO flash evaporation and H₂S flash evaporation are separately washed with semi-lean methanol, and have the advantages that the H₂S content in the second-stage flash gas is low and can be directly connected to the gas pipeline network, the utilization efficiency of low-H₂S methanol is high, and the comprehensive energy consumption of the low-temperature methanol washing unit is low. 2 methanol, the flash gas does not need to be washed, and the flash gas pressure is high. The second-stage CO 2 flash evaporation and H₂S 2 flash evaporation are separately washed with semi-lean methanol, and have the advantages that the H₂S content in the second-stage flash gas is low and can be directly connected to the gas pipeline network, the utilization efficiency of low-H₂S methanol is high, and the comprehensive energy consumption of the low-temperature methanol washing unit is low. 2 The H₂S content in the second-stage flash gas is low and can be directly connected to the gas pipeline network, the utilization efficiency of low-H₂S methanol is high, and the comprehensive energy consumption of the low-temperature methanol washing unit is low. 2 The utilization efficiency of low-H₂S methanol is high, and the comprehensive energy consumption of the low-temperature methanol washing unit is low.

[0007] The first aspect of the present invention provides an energy-saving low-temperature and low-sulfur methanol washing method for a supporting water coal slurry gasification device, and the method includes:

[0008] Performing H₂S absorption on the syngas to obtain desulfurized gas and first H₂S-rich methanol; performing CO absorption on the desulfurized gas, and after the obtained CO-rich methanol is cooled for the first time, it is divided into two streams. The second stream of CO-rich methanol undergoes first-stage CO flash evaporation to obtain the first-stage CO 2 The syngas is subjected to H₂S absorption to obtain desulfurized gas and first H₂S-rich methanol. 2 The desulfurized gas is subjected to CO absorption, and after the obtained CO-rich methanol is cooled for the first time, it is divided into two streams. 2 CO-rich 2 methanol, and after the second stream of CO-rich methanol is cooled for the first time, it is divided into two streams. 2 The second stream of CO-rich methanol undergoes first-stage CO flash evaporation. 2 flash evaporation to obtain the first-stage CO2 The flash liquid undergoes secondary CO 2 flash evaporation to obtain CO 2 The flash gas undergoes first washing to obtain the first washing liquid and secondary CO 2 The flash liquid is mixed to obtain a mixed CO-rich 2 The methanol is divided into two streams; the first H-rich 2 S methanol is divided into two streams, and the second H-rich 2 S methanol undergoes H 2 flash evaporation after the third cooling to obtain H 2 The flash gas of S undergoes second washing to obtain the second washing liquid and H 2 The flash liquid of S undergoes third flash evaporation to obtain a sulfur-containing gas phase;

[0009] Among them, the first stream of the mixed CO-rich 2 methanol undergoes first flash evaporation, and the obtained semi-lean liquid methanol is divided into two streams; the second stream of the mixed CO-rich 2 methanol undergoes second flash evaporation after the second cooling, and the obtained flash liquid and the sulfur-containing gas phase undergo third washing to obtain low-H 2 S methanol;

[0010] Among them, the first stream of the semi-lean liquid methanol is divided into three streams, which are respectively returned and undergo the above-mentioned CO 2 absorption, first washing, and second washing; the first stream of CO-rich 2 methanol, the first stream of H-rich 2 S methanol, and the low-H 2 S methanol are respectively returned and undergo the above-mentioned H 2 S absorption.

[0011] The second aspect of the present invention provides an energy-saving low-temperature and low-sulfur methanol washing device for a coal water slurry gasification device, and the device includes: a connected shift gas absorption tower, a CO 2 flash tower, a medium-pressure flash tower, and a reabsorption tower; among them, the shift gas absorption tower is divided into an H 2 S absorption section and a CO 2 absorption section from bottom to top; the H 2 S absorption section is used for H 2 S absorption of the synthesis gas to obtain the first H-rich 2 S methanol divided into two streams and desulfurized gas; the CO 2 absorption section is used for CO 2 absorption of the desulfurized gas to obtain the obtained CO-rich 2 methanol divided into two streams after the first cooler; the CO 2 flash tower is used for primary CO 2 flash evaporation of the second stream of CO-rich 2 methanol to obtain primary CO 2 flash liquid;

[0012] The medium-pressure flash tower is divided into an H 2 S flash section and a CO 2 flash section from bottom to top. The CO 2 flash section is used to perform a secondary CO 2 flash on the primary CO 2 flash liquid, and the resulting CO 2 flash gas is subjected to a first washing, and the resulting first washing liquid is mixed with the secondary CO 2 flash liquid to obtain a mixed rich CO 2 methanol in two streams; The H 2 S flash section is divided into a flash part and a washing part from bottom to top. The flash part is used to subject the second stream of rich H 2 S methanol to H 2 flash after passing through the third cooler, obtaining H 2 S flash gas and H 2 S flash liquid, and the washing part is used to perform a second washing on the H 2 S flash gas to obtain a second washing liquid;

[0013] The first stream of mixed rich CO 2 methanol enters the upper part of the reabsorption tower for a first flash, obtaining semi-lean liquid methanol in two streams; The second stream of mixed rich CO 2 methanol, after passing through the second cooler, enters the middle part of the reabsorption tower independently of the second washing liquid for a second flash, obtaining flash liquid; The H 2 S flash liquid enters the lower part of the reabsorption tower for a third flash, and the resulting sulfur-containing gas phase and flash liquid are subjected to a third washing to obtain low-H 2 S methanol; Among them, the first stream of semi-lean liquid methanol is divided into three streams and recycled to the CO 2 absorption section, the CO 2 flash section and the washing part respectively; The first stream of rich CO 2 methanol, the first stream of rich H 2 S methanol and low-H 2 S methanol are recycled to the H 2 S absorption section independently.

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

[0015] (1) In the method provided by the present invention, a two-stage medium-pressure flash technology is adopted. In the first stage, only the second stream of rich CO 2 methanol is flashed, and the flash pressure is relatively high. The effective gas flashed out is directly sent to the compression process without washing, which can reduce the power consumption of the compressor; In the second stage, the primary CO 2 flash liquid and the second stream of rich H 2 S methanol are separately treated. The flash pressure is relatively low, ensuring that the second stream of rich CO 2 methanol and the second stream of rich H2 The effective gas in methanol flashes out completely and is sent to the fuel gas pipeline network for use as fuel gas;

[0016] (2) The method provided by the present invention also optimizes the secondary medium-pressure flashing process, and uses semi-lean methanol (for example, B-share semi-lean methanol and C-share semi-lean methanol) to respectively conduct the first washing and the second washing on the secondary CO 2 flash gas and H 2 S flash gas. After the obtained first washing gas and second washing gas are mixed, secondary flash gas is obtained; compared with the prior art, while reducing the CO 2 component in the secondary CO 2 flash gas, it is not contaminated by rich H 2 S methanol. While reducing the CO 2 component in the H 2 S flash gas, it is not contaminated by rich H 2 S methanol. The separate flashing and separate washing of the primary CO 2 flash liquid and the second rich H 2 S methanol are realized, avoiding the technical problem that the CO 2 gas in the rich CO 2 methanol after secondary flashing is transferred to the rich H 2 S methanol after secondary flashing. At the same time, the secondary utilization of the second washing liquid is beneficial to reducing the energy consumption of the device;

[0017] (3) The method provided by the present invention optimizes the reabsorption process, and realizes the absorption of the sulfur component in the CO 2 product gas generated by the flash liquid of the second mixed rich CO 2 methanol and the second washing liquid for the H 2 S flash liquid, obtaining low H 2 S methanol with a lower H 2 S content, but without mixing with the third rich H 2 S methanol after flashing;

[0018] (4) The method provided by the present invention optimizes the H 2 S absorption process. By introducing low H 2 S methanol and the first rich H 2 S methanol to jointly absorb H 2 S and CO 2 gas in the synthesis gas, the recycling of low H 2 S methanol and the first rich H 2 S methanol is realized, reducing the usage amount of the first rich CO 2 methanol, which is equivalent to reducing the second rich H 2 S methanol that needs to be thermally regenerated; at the same time, using low H 2 S methanol and the first rich H2 Pre-absorption of CO by methanol, correspondingly reducing the working load of the subsequent CO 2 absorption tower, and also reducing the consumption of lean methanol and semi-lean methanol in the CO 2 absorption process. 2 Description of the Drawings

[0019] Figure 1 The present invention provides an energy-saving low-temperature and low-sulfur methanol washing device for supporting a water coal gasification device.

[0020] Description of the Reference Numerals in the Drawings

[0021] T-1, shift gas absorption tower; T-2, CO 2 flash tower; T-3, medium-pressure flash tower; T-4, re-absorption tower; E-1, first cooler; E-2, second cooler; E-3, third cooler; E-4, fourth cooler; E-5, fifth cooler; P-1, first pump; P-2, second pump

[0022] 1, synthesis gas; 2, low-H 2 S methanol; 3, second rich-H 2 S methanol

[0023] 4, purified gas; 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, rich-CO 2 methanol

[0024] 6-i, first stream of rich-CO 2 methanol; 6-ii, second stream of rich-CO 2 methanol; 7, CO-containing 2 methanol

[0025] 8, semi-lean methanol; 8-i, first stream of semi-lean methanol; 8-ii, second stream of semi-lean methanol; 8-i-A, A-stream of semi-lean methanol; 8-i-B, B-stream of semi-lean methanol; 8-i-C, C-stream of semi-lean methanol; 9, lean methanol; 11, primary CO 2 flash liquid; 12, primary flash gas; 13, mixed rich-CO 2 methanol; 13-i, first stream of mixed rich-CO 2 methanol

[0026] 13-ii, second stream of mixed rich-CO 2 methanol; 14-i, first washing gas; 14-ii, second washing gas; 14, secondary flash gas; 15, second washing liquid; 17, H 2 S flash liquid; 18, CO 2 product gas; 19, third rich-H2 S methanol Detailed implementation manners

[0027] The endpoints and any values within the ranges disclosed herein 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 herein.

[0028] In the present invention, without special circumstances, "first", "second", "third", "fourth", and "fifth" neither represent the order of sequence 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. "The first H-rich 2 S methanol", "the second H-rich 2 S methanol", and "the third H-rich 2 S methanol" where "first", "second", and "third" are only used to indicate that these are not the same H-rich 2 S methanol.

[0029] 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.

[0030] The first aspect of the present invention provides an energy-saving low-temperature and low-sulfur methanol washing method for a supporting coal water slurry gasification device, and the method includes:

[0031] Subject the syngas to H 2 S absorption to obtain desulfurized gas and the first H-rich 2 S methanol; subject the desulfurized gas to CO 2 absorption, and the obtained CO-rich 2 methanol is divided into two streams after the first cooling. The second stream of CO-rich 2 methanol undergoes primary CO 2 flashing, and the obtained primary CO 2 flash liquid undergoes secondary CO 2 flashing, and the obtained CO 2 flash gas undergoes the first washing to obtain a first washing liquid which is mixed with the secondary CO 2 flash liquid to obtain a mixed CO-rich 2 methanol divided into two streams; the first H-rich 2The methanol is divided into two streams, and the second stream is rich in H 2 The methanol is cooled for the third time and then undergoes H 2 flash evaporation to obtain the H 2 flash evaporation gas, which is subjected to the second washing to obtain the second washing liquid, and the H 2 The flash evaporation liquid is subjected to the third flash evaporation to obtain a sulfur-containing gas phase;

[0032] Among them, the first mixed rich CO 2 methanol undergoes the first flash evaporation to obtain semi-lean methanol that is divided into two streams; the second mixed rich CO 2 methanol, after being cooled for the second time, independently undergoes the second flash evaporation with the second washing liquid to obtain the flash evaporation liquid, which is subjected to the third washing with the sulfur-containing gas phase to obtain low-H 2 S methanol;

[0033] Among them, the first stream of semi-lean methanol is divided into three streams, which are respectively returned and subjected to the CO 2 absorption, the first washing, and the second washing; the first stream of rich CO 2 methanol, the first stream of rich H 2 S methanol, and the low-H 2 S methanol independently return and undergo the H 2 S absorption.

[0034] 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 syngas and the first stream of rich H 2 S methanol are contacted and subjected to the first H 2 S absorption to obtain pre-desulfurized gas and the second rich H 2 S methanol; the pre-desulfurized gas, the low-H 2 S methanol, and the first stream of rich CO 2 methanol are contacted and subjected to the second H 2 S absorption to obtain the first rich H 2 S methanol and desulfurized gas.

[0035] In the present invention, 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, there is a relatively wide selection range for the source of the syngas, as long as the syngas meets the above limitations. Preferably, the syngas is selected from the upstream syngas cooling process.

[0036] In some embodiments of the present invention, preferably, the syngas and the first stream of rich H 2The molar flow rate ratio of S methanol is 70 - 80:1.

[0037] In the present invention, the primary H 2 S absorption aims to remove impurities such as HCN and NH in the syngas, 3 as well as a small amount of H 2 S and CO 2 . Preferably, the molar content of H 2 S in the second H-rich 2 S methanol is 2 - 3%, and the molar content of CO 2 is 70 - 76%. In the present invention, the temperature of the second H-rich 2 S methanol is -15 to -5 °C, and the pressure is 5.2 - 5.6 MPa(G).

[0038] In some embodiments of the present invention, preferably, the molar flow rate ratio of the low H 2 S methanol to the syngas is 1:4 - 4.5; the molar flow rate ratio of the first CO-rich 2 methanol to the syngas is 1:2 - 2.5.

[0039] In some embodiments of the present invention, preferably, the low H 2 S methanol is pressurized to 5.8 - 6 MPa(G) for the first time, returned, and subjected to the second H 2 S absorption.

[0040] In the present invention, the secondary H 2 S absorption aims to further remove H 2 S in the syngas, as well as a small amount of CO 2 . Preferably, the molar content of H 2 S in the first H-rich 2 S methanol is 1.2 - 1.6%, and the molar content of CO 2 is 36 - 42%.

[0041] In the present invention, the first H-rich 2 S methanol is divided into two streams. The first stream is returned and subjected to the first H 2 S absorption, and the second stream is subjected to H 2 S flash evaporation. Preferably, the first H-rich 2 S methanol is divided into a first H-rich 2 S methanol and a second H-rich 2 S methanol with a molar flow rate ratio of 1:55 - 65.

[0042] In some embodiments of the present invention, preferably, the CO 2 absorption includes a first CO 2 absorption and a second CO 2Absorption; wherein, the desulfurized gas and the CO-containing 2 methanol are contacted and subjected to a first CO 2 absorption to obtain a pre-purified gas and a CO-rich 2 methanol; the pre-purified gas, the A-type semi-lean methanol and the lean methanol are contacted and subjected to a second CO 2 absorption to obtain a purified gas and a CO-containing 2 methanol.

[0043] In some embodiments of the present invention, preferably, the molar flow rate ratio of the desulfurized gas to the CO-containing 2 methanol is 1:1.2 - 1.4.

[0044] In some embodiments of the present invention, preferably, after the CO-containing 2 methanol is cooled to -36 to -34 °C by the fourth cooler, the first CO 2 absorption is carried out.

[0045] In some embodiments of the present invention, preferably, the molar content of CO in the CO-rich 2 methanol is 28 - 34%, and the molar content of H 2 S is 0.1 - 0.5 ppm; the pressure is 5.2 - 5.4 MPa(G). 2 In the present invention, the CO-rich

[0046] methanol is divided into two streams. The first stream is returned and subjected to a second H 2 S absorption, and the second stream is subjected to a first-stage CO 2 flash evaporation. 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 1:1.5 - 2.5. 2 methanol.

[0047] In some embodiments of the present invention, further preferably, the CO-rich 2 methanol is cooled to -36 to -33 °C by the first cooler and then divided into two streams.

[0048] In some embodiments of the present invention, preferably, the molar flow rate ratio of the purified gas to the A-type semi-lean methanol is 1.4 - 1.6:1; the molar flow rate ratio of the purified gas to the lean methanol is 1:1.1 - 1.3.

[0049] In some embodiments of the present invention, preferably, the molar content of H 2 S in the CO-containing 2 methanol is 0.1 - 0.5 ppm, and the molar content of CO 2 is 17 - 22%.

[0050] In some embodiments of the present invention, preferably, the molar content of H2S in the purified gas < 0.1 ppm, and the molar content of CO < 20 ppm; the temperature is -55 to -50 °C, and the pressure is 5.2 - 5.3 MPa(G). 2 S molar content < 0.1 ppm, CO 2 molar content < 20 ppm; the temperature is -55 to -50 °C, and the pressure is 5.2 - 5.3 MPa(G).

[0051] In the present invention, the first cooling is achieved by reducing the temperature of the rich CO methanol, on the one hand, to increase the CO solubility in the first stream of rich CO methanol, on the other hand, to reduce the total amount of medium-pressure flash gas, and at the same time, to lay a foundation for obtaining low temperature (high-quality cold energy) for the reabsorption tower. 2 In the present invention, the first cooling is achieved by reducing the temperature of the rich CO methanol, on the one hand, to increase the CO solubility in the first stream of rich CO methanol, on the other hand, to reduce the total amount of medium-pressure flash gas, and at the same time, to lay a foundation for obtaining low temperature (high-quality cold energy) for the reabsorption tower. 2 methanol's CO 2 solubility, on the other hand, to reduce the total amount of medium-pressure flash gas, and at the same time, to lay a foundation for obtaining low temperature (high-quality cold energy) for the reabsorption tower.

[0052] In the present invention, the process of the first-stage CO flash evaporation includes: subjecting the first stream of rich CO methanol to first-stage CO flash evaporation to obtain first-stage CO flash gas and first-stage CO flash liquid. Preferably, the pressure of the first-stage CO flash evaporation is 3.5 - 3.7 MPa(G). 2 In the present invention, the process of the first-stage CO flash evaporation includes: subjecting the first stream of rich CO methanol to first-stage CO flash evaporation to obtain first-stage CO flash gas and first-stage CO flash liquid. Preferably, the pressure of the first-stage CO flash evaporation is 3.5 - 3.7 MPa(G). 2 methanol to first-stage CO 2 flash evaporation to obtain first-stage CO 2 flash gas and first-stage CO 2 flash liquid. Preferably, the pressure of the first-stage CO 2 flash evaporation is 3.5 - 3.7 MPa(G).

[0053] In some embodiments of the present invention, preferably, the molar content of H2S in the first-stage CO flash liquid is 0.1 - 0.5 ppm, and the molar content of CO is 27.5 - 33.5%; the temperature is -36.5 to -33.5 °C. 2 In some embodiments of the present invention, preferably, the molar content of H2S in the first-stage CO flash liquid is 0.1 - 0.5 ppm, and the molar content of CO is 27.5 - 33.5%; the temperature is -36.5 to -33.5 °C. 2 S in the first-stage CO flash liquid is 0.1 - 0.5 ppm, CO 2 molar content is 27.5 - 33.5%; the temperature is -36.5 to -33.5 °C.

[0054] In some embodiments of the present invention, preferably, the molar content of H2 in the first-stage CO flash gas obtained from the first-stage CO flash evaporation is 71 - 76%, and the molar content of CO is 23 - 27%; the molar content of CO is 0.7 - 0.75%, and the temperature is -36.5 to -33.5 °C. 2 In some embodiments of the present invention, preferably, the molar content of H2 in the first-stage CO flash gas obtained from the first-stage CO flash evaporation is 71 - 76%, and the molar content of CO is 23 - 27%; the molar content of CO is 0.7 - 0.75%, and the temperature is -36.5 to -33.5 °C. 2 in the first-stage CO flash gas obtained from the first-stage CO flash evaporation is 71 - 76%, CO 2 molar content is 23 - 27%; CO molar content is 0.7 - 0.75%, and the temperature is -36.5 to -33.5 °C.

[0055] In the present invention, the process of the second-stage CO flash evaporation includes: subjecting the first-stage CO flash liquid to second-stage CO flash evaporation to obtain second-stage CO flash gas and second-stage CO flash liquid; the process of the H2S flash evaporation includes: subjecting the second stream of rich H2S methanol to H2S flash evaporation after the third cooling to obtain H2S flash gas. 2 In the present invention, the process of the second-stage CO flash evaporation includes: subjecting the first-stage CO flash liquid to second-stage CO flash evaporation to obtain second-stage CO flash gas and second-stage CO flash liquid; the process of the H2S flash evaporation includes: subjecting the second stream of rich H2S methanol to H2S flash evaporation after the third cooling to obtain H2S flash gas. 2 flash liquid to second-stage CO 2 flash evaporation to obtain second-stage CO 2 flash gas and second-stage CO 2 flash liquid; the H 2 S flash evaporation process includes: subjecting the second stream of rich H 2 S methanol to H 2 S flash evaporation after the third cooling to obtain H2 S flash vapor and H 2 S flash liquid. Preferably, the secondary CO 2 flash and H 2 The pressures of S flash are each independently 1.6 - 2 MPa(G).

[0056] In the present invention, the process of the first washing includes: washing the secondary CO 2 flash vapor and B - share semi - lean methanol to obtain a first washing gas and a first washing liquid; the process of the second washing includes: washing the H 2 S flash vapor and C - share semi - lean methanol to obtain a second washing gas and a second washing liquid.

[0057] In the present invention, mixing the secondary CO 2 flash liquid and the first washing liquid to obtain a mixed rich CO 2 methanol, that is to say, the mixed rich CO 2 methanol includes not only the flash liquid but also the first washing liquid. Preferably, the molar content of H 2 S in the mixed rich CO 2 methanol is 0.1 - 0.5 ppm, and the molar content of CO 2 is 19 - 23%; the temperature is - 37 to - 33 °C.

[0058] In the present invention, dividing the mixed rich CO 2 methanol into two streams, the first stream directly undergoes the first flash, and the second stream undergoes the second flash after the second cooling. Preferably, the mixed rich CO 2 methanol is divided into a first - stream mixed rich CO 2 methanol and a second - stream mixed rich CO 2 methanol with a molar flow rate ratio of 3.5 - 4.5:1.

[0059] In the present invention, the third cooling reduces the temperature of the second - stream rich H 2 S methanol, reduces the total amount of medium - pressure flash gas, and at the same time lays a foundation for obtaining low temperature (high - quality cold energy) for the re - absorption tower. Preferably, the temperature of the material after the third cooling is - 33 to - 30 °C.

[0060] In some embodiments of the present invention, preferably, the molar content of H 2 S in the H 2 S flash liquid is 1.4 - 1.5%, and the molar content of CO 2 is 35 - 40%; the temperature is - 33.5 to - 30.5 °C.

[0061] In some embodiments of the present invention, preferably, the molar content of H 2The molar content of S is < 0.1%, and the molar content of CO 2 is 22 - 25%; the temperature is -50 to -48 °C.

[0062] In some embodiments of the present invention, preferably, the first washing gas obtained from the first washing and the second washing gas obtained from the second washing are mixed, and the temperature of the secondary flash gas is -63 °C to -60 °C, and the pressure is 1.6 - 2 MPa(G).

[0063] In some embodiments of the present invention, preferably, the pressure of the first flash < the pressure of the second flash < the pressure of the third flash; 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).

[0064] In some embodiments of the present invention, preferably, the first mixed rich CO 2 methanol is subjected to the first flash to obtain the semi-lean liquid methanol and the first CO 2 product gas; the second mixed rich CO 2 methanol is cooled by the second cooler and then independently subjected to the second flash with the second washing liquid to obtain the flash liquid and the second CO 2 product gas; the H 2 S flash liquid is subjected to the third flash to obtain the sulfur-containing gas phase and the third H 2 S-rich methanol; wherein, the flash liquid and the sulfur-containing gas phase are subjected to the third washing to obtain the low H 2 S methanol and the third CO 2 product gas.

[0065] In the present invention, the first CO 2 product gas, the second CO 2 product gas and the third CO 2 product gas are mixed, and the molar content of H 2 S in the obtained CO 2 product gas is < 1 ppm, and the molar content of CO 2 is 99.4 - 99.7%; the temperature is -65 to -60 °C, and the pressure is 0.05 - 0.08 MPa(G).

[0066] In some embodiments of the present invention, preferably, the molar content of CO 2 in the semi-lean liquid methanol is 18 - 22%, and the molar content of H 2 S is ≤ 0.5 ppm; the temperature is -63 to -61 °C; the pressure is 0.05 - 0.08 MPa(G).

[0067] In the present invention, the semi-lean methanol is divided into two streams. The first stream is recycled, and the second stream is sent to subsequent processes for treatment. Preferably, the semi-lean methanol is divided into the first semi-lean methanol stream and the second semi-lean methanol stream with a molar flow rate ratio of 1.5 - 2.5:1.

[0068] In the present invention, the first semi-lean methanol stream is divided into three streams. Stream A is returned and subjected to CO 2 absorption, preferably the second CO 2 absorption; Stream B is returned and subjected to the first washing; Stream C is returned and subjected to the second washing. Preferably, the first semi-lean methanol stream is divided into Stream A semi-lean methanol, Stream B semi-lean methanol, and Stream C semi-lean methanol with a molar flow rate ratio of 13 - 15:1:1.5 - 2.5.

[0069] In some embodiments of the present invention, more preferably, the first semi-lean methanol stream is pressurized to 5.6 - 5.8 MPa(G) by a second pressurization and then divided into three streams.

[0070] In the present invention, the second cooling is achieved by reducing the temperature of the second mixed rich CO 2 methanol. The purpose is to generate low temperature through pressure reduction and flashing, and improve the absorption capacity of the rich CO 2 methanol for H 2 S gas after flashing, which is beneficial to washing H 2 S gas in the CO 2 product gas after flashing. Preferably, the temperature of the material after the second cooling is -55 to -50 °C.

[0071] In some embodiments of the present invention, more preferably, the second washing liquid is cooled to -36 to -34 °C by a fifth cooling, returned, and subjected to the second flashing. The purpose is to improve the absorption capacity of the second washing liquid for H 2 S gas after flashing by reducing the temperature of the second washing liquid, which is beneficial to washing H 2 S gas in the CO 2 product gas after flashing.

[0072] In some embodiments of the present invention, preferably, the molar content of H 2 S in the low-H 2 S methanol is 0.5 - 1%, and the molar content of CO 2 is 22 - 27%; the temperature is -62 to -58 °C, and the pressure is 0.12 - 0.16 MPa(G).

[0073] In some embodiments of the present invention, preferably, the molar content of H 2 S in the third rich-H 2 S methanol is 1.4 - 1.7%, and CO2 The molar content is 25 - 30%; the temperature is -68 to -64 °C; the pressure is 0.13 - 0.17 MPa(G).

[0074] The second aspect of the present invention provides a schematic structural diagram of an energy-saving low-temperature and low-sulfur methanol washing device for a coal water slurry gasification device as Figure 1 shown, from Figure 1 it can be seen that the device includes: a connected shift gas absorption tower T-1, CO 2 flash tower T-2, medium-pressure flash tower T-3 and reabsorption tower T-4;

[0075] Among them, the shift gas absorption tower T-1 is divided into an H 2 S absorption section and a CO 2 absorption section from bottom to top; the H 2 S absorption section is used to carry out H 2 S absorption on the syngas 1 to obtain the first rich H 2 S methanol 5 divided into two streams, and desulfurized gas; the CO 2 absorption section is used to carry out CO 2 absorption on the desulfurized gas to obtain the rich CO 2 methanol 6 which is divided into two streams after passing through the first cooler E-1; the CO 2 flash tower T-2 is used to carry out primary CO 2 flash on the second stream of rich CO 2 methanol 6-ii to obtain the primary CO 2 flash liquid 11;

[0076] The medium-pressure flash tower T-3 is divided into an H 2 S flash section and a CO 2 flash section from bottom to top. The CO 2 flash section is used to carry out secondary CO 2 flash on the primary CO 2 flash liquid 11 to obtain the CO 2 flash gas which is subjected to the first washing to obtain the first washing liquid and the secondary CO 2 flash liquid are mixed to obtain the mixed rich CO 2 methanol 13 divided into two streams; the H 2 S flash section is divided into a flash part and a washing part from bottom to top. The flash part is used to carry out H 2 S flash on the second stream of rich H 2 S methanol 5-ii after passing through the third cooler E-3 to obtain the H 2 S flash gas and the H 2 S flash liquid 17, and the washing part is used to carry out the second washing on the H 2 S flash gas to obtain the second washing liquid 15;

[0077] The first stream of mixed rich CO2 Methanol 13-i enters the upper part of the reabsorption tower T-4 for the first flash evaporation, and the semi-lean methanol 8 is divided into two streams; the second stream is mixed with rich CO 2 After passing through the second cooler E-2, methanol 13-ii and the second washing liquid 15 independently enter the middle part of the reabsorption tower T-4 for the second flash evaporation to obtain a flash evaporation liquid; H 2 The H2S flash evaporation liquid 17 enters the lower part of the reabsorption tower T-4 for the third flash evaporation, and the sulfur-containing gas phase and the flash evaporation liquid obtained are subjected to the third washing to obtain low-H 2 S methanol 2;

[0078] Among them, the first stream of semi-lean methanol 8-i is divided into three streams and recycled to CO 2 absorption section, CO 2 flash evaporation section and washing section respectively; the first stream of rich CO 2 methanol 6-i, the first stream of rich H 2 S methanol 5-i and low-H 2 S methanol 2 are independently recycled to the H 2 S absorption section.

[0079] In the present invention, as Figure 1 shown, the shift gas absorption tower T-1 is divided into an H 2 S absorption section and a CO 2 absorption section from bottom to top, and the H 2 S absorption section and the CO 2 absorption section are connected through lifting holes, that is, the desulfurized gas from the H 2 S absorption section enters the CO 2 absorption section through the lifting holes.

[0080] In the present invention, as Figure 1 shown, the H 2 S absorption section includes: a first H 2 S absorption part arranged at the lower part and a second H 2 S absorption part arranged at the upper part; among them, the first H 2 S absorption part is used to contact the synthesis gas 1 and the first stream of 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 2 S absorption part is used to contact the pre-desulfurized gas, low-H 2 S methanol 2 and the first stream of rich CO 2 methanol 6-i and perform the second H 2 S absorption to obtain the first rich H 2 S methanol 5 and desulfurized gas.

[0081] In the present invention, H2 The S absorption section includes: a first H disposed below 2 S absorption part and a second H disposed above 2 S absorption part, the first H 2 S absorption part and the second H 2 S absorption parts are connected through upflow holes.

[0082] In the present invention, as Figure 1 shown, the CO 2 absorption section includes: a first CO disposed below 2 absorption part and a second CO disposed above 2 absorption part; wherein, the first CO 2 absorption part is used to bring the desulfurized gas into contact with methanol containing CO 2 7 and perform first CO 2 absorption to obtain a pre-purified gas and rich CO 2 methanol 6; the second CO 2 absorption part is used to bring the pre-purified gas, A-share semi-lean methanol 8-i-A and lean methanol 9 into contact and perform second CO 2 absorption to obtain a purified gas 4 and methanol containing CO 2 7.

[0083] In the present invention, the CO 2 absorption section includes: a first CO disposed below 2 absorption part and a second CO disposed above 2 absorption part, the first CO 2 absorption part and the second CO 2 absorption parts are connected through upflow holes.

[0084] 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 lower part of the second CO 2 absorption part and the upper part of the first CO 2 absorption part, and is used to cool the methanol containing CO 2 7 through the fourth cooler and then perform the first CO 2 absorption.

[0085] In the present invention, as Figure 1 shown, the medium-pressure flash tower T-3 is divided into an H 2 S flash section and a CO 2 flash section from bottom to top, the H 2 S flash section is divided into a flash part and a washing part from bottom to top, and the flash part and the washing part are connected through upflow holes.

[0086] In the present invention, as Figure 1As shown, the upper and middle parts of the reabsorption tower T-4 are connected by lifting holes, and the middle and lower parts are also connected by lifting holes. Among them, the upper part is used to perform the first flash evaporation on the first mixed rich CO 2 methanol 13-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 mixed rich CO 2 methanol 13-ii independently after the second cooling and the second washing liquid 15 respectively 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 H 2 S flash liquid 17 to obtain the sulfur-containing gas phase and the third rich H 2 S methanol 19; among them, the flash liquid and the sulfur-containing gas phase are subjected to the third washing to obtain low H 2 S methanol 2 and the third CO 2 product gas, and the 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 18.

[0087] In the present invention, as Figure 1 shown, a fifth cooler E-5 is provided on the pipeline connecting the washing section and the middle part of the reabsorption tower T-4, and is used to perform the second flash evaporation on the second washing liquid 15 after the fifth cooling.

[0088] 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 tower T-4 and the second H 2 S absorption section, and is used to return the low H 2 S methanol 2 after the first pressurization and perform the second H 2 S absorption.

[0089] In the present invention, as Figure 1 shown, a second pump P-2 is provided on the pipeline connecting the semi-lean methanol outlet of the reabsorption tower T-4, the second CO 2 absorption section, the CO 2 flash section and the washing section, and is used to divide the first semi-lean methanol 8-i into three strands after the second pressurization, and return them respectively to perform the second CO 2 absorption, the first washing and the second washing.

[0090] The present invention will be described in detail below through embodiments.

[0091] Example 1

[0092] DeviceAs Figure 1 shown, the device includes: a connected shift gas absorption tower T-1, a CO 2 flash tower T-2, a medium-pressure flash tower T-3, and a reabsorption tower T-4, a first cooler E-1, a second cooler E-2, a third cooler E-3, a fourth cooler E-4, and a fifth cooler E-5, as well as a first pump P-1 and a second pump P-2;

[0093] Among them, the shift gas absorption tower T-1 is divided into an H 2 S absorption section and a CO 2 absorption section from bottom to top; the H 2 S absorption section is divided into a first H 2 S absorption part and a second H 2 S absorption part from bottom to top; the CO 2 absorption section is divided into a first CO 2 absorption part and a second CO 2 absorption part from bottom to top; the medium-pressure flash tower T-3 is divided into an H 2 S flash section and a CO 2 flash section from bottom to top, and the H 2 S flash section is divided into a flash part and a washing part from bottom to top.

[0094] The method is carried out in the above device, and the method includes:

[0095] Mixing syngas (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 rich H 2 S methanol in a molar flow ratio of 70 - 80:1 for countercurrent contact and carry out the first H 2 S absorption to obtain the second rich H 2 S methanol (the molar content of H 2 S is 2 - 3%, the molar content of CO 2 is 70 - 76%) and pre-desulfurized gas; successively contacting the above pre-desulfurized gas with low H 2 S methanol (pressurized to 5.8 - 6 MPa(G) for the first time), the first rich CO 2 methanol for countercurrent contact and carry out the second H 2 S absorption to obtain desulfurized gas and the first rich H 2 S methanol (the molar content of H 2 S is 1.2 - 1.6%, the molar content of CO 2 is 36 - 42%); among them, the molar flow ratio of low H 2 S methanol and syngas is 1:4 - 4.5; the first rich CO 2The molar flow rate ratio of methanol to syngas is 1:2 - 2.5; the above-mentioned first rich H 2 S methanol is divided into a first rich H 2 S methanol and a second rich H 2 S methanol with a molar flow rate ratio of 1:55 - 65;

[0096] The above-mentioned desulfurized gas and the CO-containing 2 methanol (cooled to -36 to -34 °C in the fourth stage) are in countercurrent contact at a molar flow rate ratio of 1:1.2 - 1.4 and undergo the first CO 2 absorption to obtain rich CO 2 methanol (the molar content of CO 2 is 28 - 34%, the molar content of H 2 S is 0.1 - 0.5 ppm; the pressure is 5.2 - 5.4 MPa(G)) and pre-purified gas. Among them, after the rich CO 2 methanol is cooled to -36 to -33 °C in the first stage, it is divided into a first rich CO 2 methanol and a second rich CO 2 methanol with a molar flow rate ratio of 1:1.5 - 2.5; the pre-purified gas, A-type semi-lean methanol, and lean methanol are in contact and undergo the second CO 2 absorption to obtain purified gas (the molar content of H 2 S < 0.1 ppm, the molar content of CO 2 < 20 ppm; the temperature is -55 to -50 °C, the pressure is 5.2 - 5.3 MPa(G)) and CO-containing 2 methanol (the molar content of H 2 S is 0.1 - 0.5 ppm, the molar content of CO 2 is 17 - 22%); the molar flow rate ratio of the above-mentioned A-type semi-lean methanol to the purified gas is 1:1.4 - 1.6; the molar flow rate ratio of lean methanol to the purified gas is 1.1 - 1.3:1;

[0097] The second rich CO 2 methanol undergoes primary CO 2 flashing (the pressure is 3.5 - 3.7 MPa(G)) to obtain primary flash gas (the molar content of H 2 is 71 - 76%, the molar content of CO 2 is 23 - 27%; the CO molar content is 0.7 - 0.75%; the temperature is -36.5 to -33.5 °C) and primary CO 2 flash liquid (the molar content of H 2 S is 0.1 - 0.5 ppm, the molar content of CO 2 is 27.5 - 33.5%; the temperature is -36.5 to -33.5 °C); the above-mentioned primary CO 2The flash liquid undergoes secondary CO 2 flash (at a pressure of 1.6 - 2 MPa(G)) to obtain secondary CO 2 flash gas and secondary CO 2 flash liquid, and the secondary CO 2 flash gas and B - stream semi - lean methanol are subjected to the first washing to obtain the first washing gas and the first washing liquid, and the secondary CO 2 flash liquid and the first washing liquid are mixed to obtain the mixed rich CO 2 methanol (the molar content of H 2 S is 0.1 - 0.5 ppm, and the molar content of CO 2 is 19 - 23%; the temperature is - 37 to - 33 °C) is divided into two streams;

[0098] The second stream of rich H 2 S methanol is cooled to - 33 to - 30 °C by the third cooler and then undergoes H 2 S flash (at a pressure of 1.6 - 2 MPa(G)) to obtain H 2 S flash gas and H 2 S flash liquid (the molar content of H 2 S is 1.4 - 1.5%, and the molar content of CO 2 is 35 - 40%; the temperature is - 33.5 to - 30.5 °C). The H 2 S flash gas and C - stream semi - lean methanol are subjected to the second washing to obtain the second washing gas and the second washing liquid (the molar content of H 2 S is < 0.1%, and the molar content of CO 2 is 22 - 25%; the temperature is - 50 to - 48 °C);

[0099] The above - mentioned first washing gas and second washing gas are mixed to obtain the secondary flash gas with a temperature of - 63 °C to - 60 °C and a pressure of 1.6 - 2 MPa(G);

[0100] The first stream of mixed rich CO 2 methanol undergoes the first flash (at a pressure of 0.05 - 0.08 MPa(G)) to obtain semi - lean methanol (the molar content of CO 2 is 18 - 22%, and the molar content of H 2 S is ≤ 0.5 ppm; the temperature is - 63 to - 61 °C; the pressure is 0.05 - 0.08 MPa(G)) and the first CO 2 product gas; The second stream of mixed rich CO 2 methanol is cooled to - 55 to - 50 °C by the second cooler and then, together with the second washing liquid cooled to - 36 to - 34 °C by the fifth cooler, independently undergoes the second flash (at a pressure of 0.06 - 0.09 MPa(G)) to obtain the flash liquid and the second CO 2 product gas; The H2 The S flash liquid undergoes a third flash (at a pressure of 0.12 - 0.16 MPa(G)) to obtain a sulfur-containing gas phase and a third H-rich 2 S methanol (H 2 The molar content of S is 1.4 - 1.7%, and the molar content of CO 2 is 25 - 30%; the temperature is -68 to -64 °C; the pressure is 0.13 - 0.17 MPa(G)); the above flash liquid and the sulfur-containing gas phase are subjected to a third wash to obtain a low-H 2 S methanol (H 2 The molar content of S is 0.5 - 1%, and the molar content of CO 2 is 22 - 27%; the temperature is -62 to -58 °C, and the pressure is 0.12 - 0.16 MPa(G)) and a third CO 2 product gas;

[0101] Mix the first CO 2 product gas, the second CO 2 product gas and the third CO 2 product gas to obtain a CO 2 In the product gas obtained, the molar content of H 2 S < 1 ppm, and the molar content of CO 2 is 99.4 - 99.7%; the temperature is -65 to -60 °C, and the pressure is 0.05 - 0.08 MPa(G);

[0102] Divide the above semi-lean methanol into a first stream of semi-lean methanol and a second stream of semi-lean methanol with a molar flow rate ratio of 1.5 - 2.5:1. After the first stream of semi-lean methanol is secondarily pressurized to 5.6 - 5.8 MPa(G), it is divided into an A-stream of semi-lean methanol, a B-stream of semi-lean methanol, and a C-stream of semi-lean methanol with a molar flow rate ratio of 13 - 15:1:1.5 - 2.5.

[0103] Comparative Example 1

[0104] Taking a hydrogen production plant using coal water slurry gasification for gas production as an example, the effective gas (H 2 +CO) entering the low-temperature methanol washing unit is 230000 Nm 3 / h. Based on this benchmark, a comparison of the main technical parameters with the lean liquid - semi-lean liquid process (i.e., a low-temperature methanol washing process disclosed in CN201110260570.0) is shown in Table 1.

[0105] Table 1

[0106]

[0107] 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 93.3% 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 rich CO 2 in Comparative Example 1 (lean liquid - semi-lean liquid process). The cumulative reduction in external cooling consumption is 600 KW / h, and the overall energy-saving effect is remarkable.

[0108] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope 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 and low-sulfur methanol washing method for a water-coal slurry gasification device, characterized in that: The method comprises: The synthesis gas is subjected to H2S absorption to obtain a desulfurized gas and a first H2S-rich methanol; the desulfurized gas is subjected to CO2 absorption, the obtained CO2-rich methanol is divided into two streams after a first cooling, the second stream of CO2-rich methanol is subjected to a first CO2 flash, the obtained first CO2 flash liquid is subjected to a second CO2 flash, the obtained CO2 flash gas is subjected to a first washing, the first washing liquid is mixed with the second CO2 flash liquid, and the mixed CO2-rich methanol is divided into two streams; the first H2S-rich methanol is divided into two streams, the second stream of H2S-rich methanol is subjected to H2S flash after a third cooling, the obtained H2S flash gas is subjected to a second washing to obtain a second washing liquid, and the H2S flash liquid is subjected to a third flash to obtain a sulfur-containing gas phase; The first stream of mixed CO2-rich methanol is subjected to a first flash evaporation, and the obtained semi-lean liquid methanol is divided into two streams; the second stream of mixed CO2-rich methanol is subjected to a second cooling, and then independently subjected to a second flash evaporation with the second washing liquid, and the obtained flashed liquid is subjected to a third washing with the sulfur-containing gas phase to obtain low-H2S methanol; The first stream of semi-lean methanol is divided into three streams, which are returned to perform the CO2 absorption, the first washing and the second washing respectively; the first stream of CO2-rich methanol, the first stream of H2S-rich methanol and the low H2S methanol are returned independently to perform the H2S absorption.

2. The method according to claim 1, wherein: The H2S absorption includes a first H2S absorption and a second H2S absorption; The synthesis gas is contacted with the first stream of H2S-rich methanol and subjected to a first H2S absorption to obtain pre-desulfurized gas and a second H2S-rich methanol; the pre-desulfurized gas, low H2S methanol and the first stream of CO2-rich methanol are contacted and subjected to a second H2S absorption to obtain the first H2S-rich methanol and desulfurized gas; 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); Preferably, the low H2S methanol is first pressurized to 5.8-6 MPa(G), returned and subjected to the second H2S absorption; and / or, the molar content of H2S in the first H2S-rich methanol is 1.2-1.6%, and the molar content of CO2 is 36-42%; And / or, the first H2S-rich methanol is divided into a first stream of H2S-rich methanol and a second stream of H2S-rich methanol with a molar flow ratio of 1:55-65.

3. The method according to claim 1 or 2, wherein: The CO2 absorption includes a first CO2 absorption and a second CO2 absorption; The desulfurized gas is contacted with CO2-containing methanol and subjected to a first CO2 absorption to obtain pre-purified gas and CO2-rich methanol; the pre-purified gas, A-share semi-lean liquid methanol and lean methanol are contacted and subjected to a second CO2 absorption to obtain purified gas and CO2-containing methanol; Preferably, the CO2-containing methanol is subjected to a fourth cooling to -36 to -34°C before the first CO2 absorption is performed; And / or, the molar content of CO2 in the CO2-rich methanol is 28-34%, the molar content of H2S is 0.1-0.5 ppm; 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 1:1.5-2.5; And / or, the CO2-rich methanol is first cooled to -36 to -33°C and divided into two streams.

4. The method according to any one of claims 1 to 3, wherein: The pressure of the first-stage CO2 flash evaporation is 3.5-3.7MPa(G); and / or, the molar content of H2S in the primary CO2 flash liquid is 0.1-0.5 ppm, the molar content of CO2 is 27.5-33.5%; the temperature is -36.5 to -33.5°C; And / or, the first-stage flash gas obtained by the first-stage CO2 flash evaporation has a molar content of H2 of 71-76%, a molar content of CO2 of 23-27%, a molar content of CO of 0.7-0.75%, and a temperature of -36.5 to -33.5°C.

5. The method according to any one of claims 1 to 4, wherein: The pressures of the secondary CO2 flash and H2S flash are independently 1.6-2MPa(G); and / or, the molar content of H2S in the mixed CO2-rich methanol is 0.1-0.5 ppm, the molar content of CO2 is 19-23%; the temperature is -37 to -33°C; and / or, dividing the mixed CO2-rich methanol into a first stream of mixed CO2-rich methanol and a second stream of mixed CO2-rich methanol at a molar flow ratio of 3.5-4.5:1; And / or, the temperature of the material after the third cooling is -33 to -30°C; and / or, the molar content of H2S in the H2S flash liquid is 1.4-1.5%, the molar content of CO2 is 35-40%; the temperature is -33.5 to -30.5°C; and / or, the molar content of H2S in the second scrubbing liquid is <0.1%, the molar content of CO2 is 22-25%; the temperature is -50 to -48°C; And / or, the first scrubbing gas obtained by the first scrubbing and the second scrubbing gas obtained by the second scrubbing are mixed to obtain secondary flash gas having a temperature of -63°C to -60°C and a pressure of 1.6-2 MPa(G).

6. The method according to any one of claims 1 to 5, wherein: The pressure of the first flash vaporization is less than the pressure of the second flash vaporization and less than the pressure of the third flash vaporization; 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, subjecting the first stream of mixed CO2-rich methanol to the first flash evaporation to obtain the semi-lean methanol and the first CO2 product gas; subjecting the second stream of mixed CO2-rich methanol to the second flash evaporation independently with the second washing liquid after the second cooling to obtain the flash liquid and the second CO2 product gas; subjecting the H2S flash liquid to the third flash evaporation to obtain the sulfur-containing gas phase and the third H2S-rich methanol; subjecting the flash liquid and the sulfur-containing gas phase to the third washing to obtain the low-H2S methanol and the third CO2 product gas; and / or, the molar content of CO2 in the semi-lean methanol is 18-22%, the molar content of H2S is ≤0.5ppm; the temperature is -63 to -61°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 1.5-2.5:1; and / or, dividing the first stream of semi-lean methanol into stream A, stream B and stream C of semi-lean methanol at a molar flow ratio of 13-15:1:1.5-2.5; and / or, the first stream of semi-lean methanol is pressurized to 5.6-5.8 MPa(G) for a second time and then divided into three streams; And / or, the temperature of the second cooled material is -55 to -50°C; and / or, cooling the second washing liquid to -36 to -34°C for the fifth time, returning the second washing liquid for the second flash evaporation; And / or, the molar content of H2S in the low H2S methanol is 0.5-1%, the molar content of CO2 is 22-27%; the temperature is -62 to -58°C, and the pressure is 0.12-0.16 MPa(G).

7. An energy-saving low-temperature and low-sulfur methanol washing device supporting a water-coal slurry gasification device, characterized in that: The device comprises: a shift gas absorption tower, a CO2 flash tower, a medium-pressure flash tower and a reabsorption tower connected to each other; wherein the shift gas absorption tower is divided into an H2S absorption section and a CO2 absorption section from bottom to top; the H2S absorption section is used to absorb H2S on the synthesis gas to obtain a first H2S-rich methanol divided into two streams, and desulfurized gas; the CO2 absorption section is used to absorb CO2 on the desulfurized gas, and the obtained CO2-rich methanol is divided into two streams after passing through a first cooler; the CO2 flash tower is used to perform a first-level CO2 flash on the second stream of CO2-rich methanol to obtain a first-level CO2 flash liquid; The medium-pressure flash tower is divided into an H2S flash section and a CO2 flash section from bottom to top. The CO2 flash section is used to perform a secondary CO2 flash on the primary CO2 flash liquid, and the obtained CO2 flash gas is subjected to a first washing. The obtained first washing liquid is mixed with the secondary CO2 flash liquid to obtain mixed CO2-rich methanol in two streams; the H2S flash section is divided into a flash section and a washing section from bottom to top. The flash section is used to perform H2S flash on the second stream of H2S-rich methanol after passing through the third cooler to obtain H2S flash gas and H2S flash liquid, and the washing section is used to perform a second washing on the H2S flash gas to obtain a second washing liquid; The first stream of mixed CO2-rich methanol enters the upper part of the reabsorption tower for the first flash evaporation to obtain semi-lean liquid methanol which is divided into two streams; the second stream of mixed CO2-rich methanol passes through the second cooler and then independently enters the middle part of the reabsorption tower with the second washing liquid for the second flash evaporation to obtain flash liquid; the H2S flash liquid enters the lower part of the reabsorption tower for the third flash evaporation, and the obtained sulfur-containing gas phase and flash liquid are subjected to the third washing to obtain low H2S methanol; wherein the first stream of semi-lean liquid methanol is divided into three streams and respectively reused in the CO2 absorption section, the CO2 flash evaporation section and the washing section; the first stream of CO2-rich methanol, the first stream of H2S-rich methanol and the low H2S methanol are independently reused in the H2S absorption section.

8. The device according to claim 7, wherein: The H2S absorption section comprises: a first H2S absorption part arranged at the bottom and a second H2S absorption part arranged at the 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, low H2S methanol and the first stream of CO2-rich methanol and perform the second H2S absorption to obtain the first H2S-rich methanol and desulfurized gas; And / or, the CO2 absorption section comprises: a first CO2 absorption section arranged at the bottom and a second CO2 absorption section arranged at the top; Among them, the first CO2 absorption section is used to contact the desulfurized gas and CO2-containing methanol and perform the first CO2 absorption to obtain pre-purified gas and CO2-rich methanol; the second CO2 absorption section is used to contact the pre-purified gas, A-share semi-lean liquid methanol and lean methanol and perform the second CO2 absorption to obtain purified gas and CO2-containing methanol.

9. The device according to claim 8, wherein: A fourth cooler is provided on the pipeline connecting the lower part of the second CO2 absorption part and the upper part of the first CO2 absorption part according to the material flow direction, and is used to perform the first CO2 absorption after the CO2-containing methanol is subjected to the fourth cooling; And / or, a fifth cooler is provided on the pipeline connecting the washing part and the middle part of the reabsorption tower, for performing the second flash evaporation on the second washing liquid after the fifth cooling.

10. The device according to claim 8 or 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 part, for returning the low H2S methanol after the first pressurization and performing the second H2S absorption; And / or, a second pump is provided on the pipeline connecting the semi-lean liquid methanol outlet of the reabsorption tower, the second CO2 absorption section, the CO2 flash section and the washing section, for dividing the first stream of semi-lean liquid methanol into three streams after the second pressurization, and returning them respectively for the second CO2 absorption, the first washing and the second washing.

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