Synthesis gas purification method matched with pulverized coal gasification device and purification device thereof

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to a synthesis gas purification method matched with a pulverized coal gasification device and a purification device thereof. According to the method provided by the invention, the synthesis gas is sequentially subjected to first H2S absorption and second H2S absorption, and a part of first H2S-rich methanol is returned and subjected to first H2S absorption, and low H2S methanol is returned and subjected to second H2S absorption, so that not only is the low H2S methanol recycled, but also the use amount of CO2-rich methanol and the thermal regeneration load of H2S-rich methanol are reduced; and meanwhile, the use amount of lean methanol and low-CO2 methanol in the CO2 absorption process is also reduced.

Description

Technical Field

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

[0002] In the production of syngas by using pulverized coal 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 raw material gases for synthesizing chemical products such as methanol and ammonia after adjusting the hydrogen-carbon ratio through a shift unit. Acid gases CO 2 and H 2 S are generally poisons for synthesis catalysts, so they must be removed before the synthesis process.

[0003] The low-temperature methanol washing technology uses low-temperature methanol as an absorption solvent, and utilizes the excellent property that low-temperature methanol has a great solubility for acid gases to physically absorb and remove H 2 S and CO 2 and other acid gases in the syngas, and at the same time removes trace components such as HCN and NH 3 . This process has the advantages of high gas purification degree, good selectivity, large methanol absorption capacity, etc. The regeneration of the methanol solvent after absorbing acid gases is achieved through staged pressure reduction flashing and thermal regeneration.

[0004] Currently, the innovative research on low-temperature methanol washing technology mainly focuses on the recycling of the pressure reduction flashing of rich CO 2 methanol. The typical process is the lean liquid - semi-lean liquid process, and this technology has played a positive role in reducing the comprehensive energy consumption of the low-temperature methanol washing process. In the low-temperature methanol washing process flow, rich CO 2 methanol can be recycled through flashing, but H 2 S-containing methanol must be recycled through thermal regeneration, which is the main energy-consuming source of low-temperature methanol washing. Therefore, improving the utilization efficiency of H 2 S-containing methanol is the direction and key factor of future technological innovation. Specifically, it is necessary to achieve that before the thermal regeneration of H 2 S-containing methanol, its absorption of H 2 S gas in the syngas reaches the upper limit, so as to reduce the amount of rich H 2 S-containing methanol that needs to be thermally regenerated.

[0005] CN201110260570.0 discloses a low-temperature methanol washing process. First, in this low-temperature methanol washing process, all of the H 2 S absorption tower uses rich CO2 Methanol is used to wash the syngas, and there is no research and recycling system for the low-H 2 S methanol solution in the system, allowing it to undertake part of the potential of absorbing H 2 S gas in the syngas. Because the rich CO 2 after absorbing H 2 S gas becomes rich-H 2 S methanol, which cannot be regenerated by simple pressure reduction flashing, but needs to consume steam in the thermal regeneration system for regeneration. The lean methanol after regeneration has a relatively high temperature and needs to consume cooling water and other low-temperature cooling capacities to be cooled down before it can be recycled. Therefore, in the H 2 S absorption tower, a large consumption of rich CO 2 methanol necessarily results in high energy consumption; secondly, in the CO 2 flashing section of the reabsorption tower, the rich CO 2 methanol directly mixes with the rich-H 2 S methanol flash gas while washing the rich-H 2 S methanol, and itself is deeply contaminated by the rich-H 2 S methanol. The low-concentration H 2 S methanol after mixing is not fully utilized either, but is sent to the thermal regeneration system for regeneration, resulting in high energy consumption; finally, the semi-lean liquid methanol for the CO 2 absorption tower has a relatively high CO 2 content, and its absorption capacity for CO 2 gas is limited, which is not conducive to reducing the overall energy consumption of the cold methanol washing unit. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above technical problems, and provide a syngas purification method for a supporting pulverized coal gasification device and a syngas purification device for a supporting pulverized coal gasification device. This purification method recycles and reuses low-H 2 S methanol and low-CO 2 methanol respectively for H 2 S absorption and CO 2 absorption, with the characteristics of high use efficiency and strong absorption capacity, and can also effectively reduce the overall energy consumption of the cold methanol washing unit.

[0007] The first aspect of the present invention provides a syngas purification method for a supporting pulverized coal gasification device, and the method includes:

[0008] Performing a first H 2 S absorption on the syngas, and performing a second H 2 S absorption on the pre-washed syngas obtained, to obtain desulfurized gas and a first rich-H 2 S methanol. The first stream of rich-H 2 S methanol returns and performs the above-mentioned first H 2 S absorption, and the second stream of rich-H2 The methanol is heat-exchanged and then undergoes H 2 flash evaporation, and the flashed H-rich 2 methanol undergoes a third flash evaporation to obtain a sulfur-containing gas phase;

[0009] The desulfurized gas is subjected to CO 2 absorption, and the CO-rich 2 methanol is divided into two streams. The first stream of CO-rich 2 methanol returns and undergoes the second H 2 S absorption, and the second stream of CO-rich 2 methanol is first cooled and then undergoes CO 2 flash evaporation, and the flashed CO-rich 2 methanol is second cooled and then undergoes a first flash evaporation. The semi-lean methanol is divided into three streams. The first stream of semi-lean methanol is subjected to stripping after the heat exchange, and the low-CO 2 methanol returns and undergoes the CO 2 absorption; the second stream of semi-lean methanol undergoes a second flash evaporation, and the flashed solution contacts the sulfur-containing gas phase and is washed to obtain low-H 2 S methanol returns and undergoes the second H 2 S absorption.

[0010] Preferably, the heat exchange process includes: exchanging heat between the second stream of H-rich 2 S methanol and the first stream of semi-lean methanol to obtain heat-exchanged H-rich 2 S methanol and heat-exchanged semi-lean methanol.

[0011] The second aspect of the present invention provides a syngas purification device for a coal powder gasification device. The device includes an H 2 S absorption tower, a CO 2 absorption tower, an H 2 S flash evaporation tower, a CO 2 flash evaporation tower, a reabsorption tower and a stripping tower, as well as a first cooler and a second cooler;

[0012] Among them, the H 2 S absorption tower is divided into a first H 2 S absorption section and a second H 2 S absorption section from bottom to top. The syngas sequentially enters the first H 2 S absorption section and the second H 2 S absorption section to obtain desulfurized gas and a first H-rich 2 S methanol. The desulfurized gas enters the CO 2 absorption tower, and the obtained CO-rich 2 methanol is divided into two streams. The first stream of CO-rich 2 methanol is recycled and used in the second H 2 S absorption section, and the second stream of CO-rich2 After methanol passes through the first cooler, it enters the CO 2 flash tower, and the flashed CO-rich 2 After methanol passes through the second cooler, it enters the upper part of the reabsorption tower, and the semi-lean methanol is obtained in three streams. The first stream of semi-lean methanol enters the stripping tower after heat exchange, and the low-CO 2 methanol is recycled to the CO 2 absorption tower; the second stream of semi-lean methanol returns to the middle of the reabsorption tower to obtain the flashed solution;

[0013] The first H-rich 2 S methanol is divided into two streams. The first stream of H-rich 2 S methanol is recycled to the first H 2 S absorption section. The second stream of H-rich 2 S methanol enters the H 2 S flash tower after heat exchange, and the flashed H-rich 2 S methanol enters the lower part of the reabsorption tower, and the sulfur-containing gas phase is washed with the flashed solution to obtain the low-H 2 S methanol is recycled to the second H 2 S absorption section.

[0014] Preferably, the device further includes: a heat exchanger connecting the second H 2 S absorption section, the reabsorption tower, the H 2 S flash tower and the stripping tower, which is used to heat-exchange the second stream of H-rich 2 S methanol and the first stream of semi-lean methanol to obtain heat-exchanged H-rich 2 S methanol and heat-exchanged semi-lean methanol.

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

[0016] (1) In the method provided by the present invention, the syngas is sequentially subjected to first H 2 S absorption, second H 2 S absorption, and in combination with part of the first H-rich 2 S methanol (i.e., the first stream of H-rich 2 S methanol) is returned and subjected to first H 2 S absorption, and the low-H 2 S methanol is returned and subjected to second H 2 S absorption, which not only realizes the recycling of low-H 2 S methanol, but also reduces the usage amount of CO-rich 2 methanol and the heat regeneration load of H-rich 2 S methanol; at the same time, it also reduces the usage amount of lean methanol and low-CO 2 methanol in the CO 2 absorption process;

[0017] (2) The method provided by the present invention divides the semi-lean methanol into three streams. The first stream of semi-lean methanol exchanges heat with the second stream of H 2 S methanol and then is stripped to obtain low-CO 2 methanol, in which the molar content of CO 2 is further reduced to 4-7%; the flash solution after the second flash of the second stream of semi-lean methanol is used as a washing solution to wash the sulfur-containing gas phase of the flash-rich H 2 S methanol to generate low-H 2 S methanol;

[0018] (3) The method provided by the present invention returns the low-CO 2 methanol and conducts CO 2 absorption. First, with the improvement of the absorption capacity of the low-CO 2 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%; second, the low-CO 2 methanol can replace part of the lean methanol, so that the circulation amount of the lean methanol in the CO 2 absorption tower also decreases. The reduction of the lean methanol flow rate will be transmitted to the rich H 2 S methanol, and then the flow rate of the rich H 2 S methanol that needs to be thermally regenerated is reduced, and the energy consumption of the corresponding thermal regeneration system also decreases accordingly. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIG. is a schematic structural diagram of a syngas purification device supporting a pulverized coal gasification device provided by the present invention.

[0020] DESCRIPTION OF THE REFERENCE NUMERALS

[0021] T-1, H 2 S absorption tower; T-2, CO 2 absorption tower; T-3, H 2 S flash tower; T-4, CO 2 flash tower; T-5, re-absorption tower; T-6, stripping tower; Q, heat exchanger; E-1, first cooler; E-2, second cooler; E-3, third cooler; E-4, fourth cooler; P-1, first pump; P-2, second pump; P-3, third pump;

[0022] 1, syngas; 2, low-H 2 S methanol; 3, second rich-H 2 S methanol; 4, rich-CO 2 methanol; 4-i, first stream of rich-CO 2 methanol; 4-ii, second stream of rich-CO 2 methanol; 5, first rich-H2 S methanol; 5-i, the first rich H 2 S methanol; 5-ii, the second rich H 2 S methanol; 6, desulfurized gas; 7, containing CO 2 Methanol; 8, semi-lean methanol; 8-i, the first semi-lean methanol; 8-ii, the second semi-lean methanol; 8-iii, the third semi-lean methanol; 9, lean methanol; 10, purified gas; 11, rich CO after flashing 2 Methanol; 12, CO 2 Flashing gas; 13, rich H after flashing 2 S methanol; 14, low-temperature rich H 2 S methanol; 15, flashing gas; 16, rich CO after cooling 2 Methanol; 17, CO 2 Product gas; 18, tail gas; 19, the third rich H 2 S methanol; 20, nitrogen; 21, low CO 2 Methanol; 22, rich H after heat exchange 2 S methanol; 23, semi-lean methanol after heat exchange. Detailed implementation manners

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

[0024] Without special circumstances, "first", "second", "third" and "fourth" 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. The "first", "second", "third" and "fourth" in "first cooling", "second cooling", "third cooling" and "fourth cooling" are only used to indicate that these are not the same cooling.

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

[0026] The first aspect of the present invention provides a syngas purification method for a supporting pulverized coal gasification device, and the method includes:

[0027] Subject the syngas to a first H 2 S absorption, and subject the pre-washed syngas obtained to a second H 2 S absorption to obtain desulfurized gas and a first rich H 2 S methanol. Return the first stream of rich H 2 S methanol and conduct the aforesaid first H 2 S absorption. The second stream of rich H 2 S methanol is subjected to heat exchange and then to H 2 S flash evaporation to obtain the rich H 2 S methanol after flash evaporation, and conduct a third flash evaporation on the rich H

[0028] S methanol after flash evaporation to obtain a sulfur-containing gas phase; 2 Subject the aforesaid desulfurized gas to CO 2 absorption to obtain rich CO 2 methanol, which is divided into two streams. The first stream of rich CO 2 methanol is returned and subjected to the aforesaid second H 2 S absorption. The second stream of rich CO 2 methanol is subjected to CO 2 flash evaporation after the first cooling to obtain the rich CO 2 methanol after flash evaporation. The semi-lean methanol is divided into three streams after the second cooling and the first flash evaporation. The first stream of semi-lean methanol is subjected to stripping after the aforesaid heat exchange to obtain low-CO 2 methanol, which is returned and subjected to the aforesaid CO 2 absorption; the second stream of semi-lean methanol is subjected to a second flash evaporation, and the solution after flash evaporation contacts the aforesaid sulfur-containing gas phase and is washed to obtain low-H 2 S methanol, which is returned and subjected to the aforesaid second H

[0029] In some embodiments of the present invention, preferably, the process of the heat exchange includes: subjecting the second stream of rich H 2 S methanol and the first stream of semi-lean methanol to the heat exchange to obtain the rich H 2 S methanol after heat exchange and the semi-lean methanol after heat exchange; more preferably, the temperature of the rich H 2 S methanol after heat exchange is -36 to -31 °C; the temperature of the semi-lean methanol after heat exchange is -48 to -43 °C.

[0030] In some embodiments of the present invention, preferably, divide the first rich H 2 S methanol into the first stream of rich H 2 S methanol and the second stream of rich H 2 S methanol with a molar flow rate ratio of 1:50 - 60.

[0031] In some embodiments of the present invention, preferably, the H 2 in the first rich H 2The molar content of S is 0.4 - 0.5%, and the molar content of CO 2 is 25 - 30%.

[0032] In some embodiments of the present invention, preferably, the first H 2 S absorption process includes: contacting the syngas with the first stream of H 2 S-rich methanol and performing the first H 2 S absorption to obtain pre-washed syngas and a second H 2 S-rich methanol.

[0033] In the present invention, the source of the syngas has a relatively wide selection range, as long as the syngas meets the above limitations. Preferably, the syngas is selected from the waste heat boiler process or the quench process of pulverized coal gasification. Preferably, the molar content of H 2 S in the syngas is 0.25 - 0.45%, and the molar content of CO 2 is 40 - 50%; the temperature is -25°C to -15°C, and the pressure is 3.12 - 3.15 MPa(G).

[0034] In some embodiments of the present invention, preferably, the molar flow ratio of the syngas to the first stream of H 2 S-rich methanol is 60 - 70:1, for example, 60:1, 65:1, 70:1, and any value within the range composed of any two values.

[0035] In the present invention, the first H 2 S absorption aims to remove impurities such as HCN and NH 3 in the syngas, 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 2 S-rich methanol is 0.6 - 0.8%, and the molar content of CO 2 is 30 - 36%. In the present invention, the temperature of the second H 2 S-rich methanol is -25 to -15°C, and the pressure is 3.12 - 3.15 MPa(G).

[0036] In some embodiments of the present invention, preferably, the second H 2 S absorption process includes: contacting the pre-washed syngas, low-H 2 S methanol, and the first stream of CO 2 -rich methanol and performing the second H 2 S absorption to obtain the first H 2 S-rich methanol and desulfurized gas.

[0037] In the present invention, the second H2 S absorption is intended to further remove H from the synthesis gas 2 S, and a small amount of CO 2 . Preferably, the first H-rich 2 S H in methanol 2 The molar content of S is 0.4-0.5%, CO 2 The molar content of is 25-30%. In the present invention, the first H-rich 2 The temperature of S methanol is -25 to -15℃ and the pressure is 3.12-3.15MPa(G).

[0038] In some embodiments of the present invention, preferably, the first H-rich 2 S methanol is divided into the first stream rich in H with a molar flow ratio of 1:50-60 2 S methanol and the second H-rich stream 2 S methanol.

[0039] In some embodiments of the present invention, preferably, the synthesis gas and low H 2 S methanol molar flow ratio is 3-5:1; the synthesis gas and the first stream of CO-rich 2 The molar flow ratio of methanol is 1.5-2.5:1.

[0040] In some embodiments of the present invention, preferably, the desulfurized gas contains H 2 The molar content of S is 0.5-1ppm, CO 2 The molar content of is 31-36%; the temperature is -28 to -22°C; the pressure is 3.05-3.1MPa(G).

[0041] In some embodiments of the present invention, preferably, the low H 2 After the first pressurization to 3.5-4MPa(G), S methanol is returned and subjected to the second H 2 S absorbs.

[0042] In some embodiments of the present invention, preferably, the first stream of CO-rich 2 Methanol is pressurized to 3.5-4MPa(G) and cooled to -49 to -43°C in the second step, and then returned to the second H 2 S absorbs.

[0043] In some embodiments of the present invention, preferably, the CO 2 The absorption process includes: mixing the desulfurized gas with CO 2 Methanol contact and first CO 2 Absorption, obtaining pre-purified gas and the CO-rich 2 Methanol; the pre-purified gas, low CO​​​​​2 Methanol and lean methanol come into contact and carry out a second CO 2 absorption to obtain the purified gas and CO-containing 2 methanol.

[0044] In the present invention, the first CO 2 absorption aims to further remove CO from the desulfurized gas 2 . Preferably, the molar content of CO in the CO-rich 2 methanol is 15-20%, and the molar content of H 2 S is 0.1-0.5 ppm; the temperature is -20 to -15 °C, and the pressure is 3.05-3.1 MPa(G). 2 In some embodiments of the present invention, preferably, the CO-rich

[0045] 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 1:2.5-3. 2 methanol.

[0046] In some embodiments of the present invention, preferably, the molar flow rate ratio of the desulfurized gas and the CO-containing 2 methanol is 1:1.5-2.5.

[0047] In some embodiments of the present invention, preferably, the molar flow rate ratio of the purified gas and the low-CO 2 methanol is 1:1.3-1.4.

[0048] In some embodiments of the present invention, preferably, the molar flow rate ratio of the purified gas and the lean methanol is 1:1.4-1.6.

[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 < 20 ppm; the temperature is -55 to -50 °C, and the pressure is 3-3.1 MPa(G).

[0050] In some embodiments of the present invention, more preferably, the CO-containing 2 methanol is cooled to -36 to -33 °C by the fourth cooler and returned to carry out the first CO 2 absorption.

[0051] In the present invention, without special instructions, the first stream of CO-rich 2 methanol returns to carry out the second H 2 S absorption, and the second stream of CO-rich 2 methanol undergoes the CO 2 flash evaporation after the first cooling.

[0052] In some embodiments of the present invention, preferably, the temperature of the first cooled material is -36 to -33 °C.

[0053] In the present invention, the CO 2 is flash-evaporated to remove CO from the first cooled material 2 flash vapor. Preferably, the CO 2 flash evaporation pressure is selected from 0.8 - 1 MPa(G).

[0054] In some embodiments of the present invention, preferably, the molar content of H 2 S in the CO-rich methanol after flash evaporation is 0.1 - 0.5 ppm, and the molar content of CO 2 is 14.5 - 19.5%; the temperature is -36.5 to -33.5 °C. 2

[0055] In the present invention, the second cooling is intended to further reduce the temperature of the CO-rich methanol after flash evaporation to obtain the cooled CO-rich 2 methanol. Preferably, the temperature of the cooled CO-rich 2 methanol is -45 to -40 °C. 2

[0056] In the present invention, the first flash evaporation is intended to flash evaporate the cooled CO-rich 2 methanol to obtain the first CO 2 product gas and semi-lean methanol. Preferably, the pressure of the first flash evaporation is 0.05 - 0.08 MPa(G).

[0057] In some embodiments of the present invention, preferably, the semi-lean methanol is divided into the first semi-lean methanol, the second semi-lean methanol, and the third semi-lean methanol with a molar flow ratio of 3.5 - 3.8:1.1 - 1.2:1. In the present invention, the first semi-lean methanol is stripped after heat exchange (i.e., the semi-lean methanol after heat exchange), the second semi-lean methanol is subjected to a second flash evaporation, and the third semi-lean methanol is sent to the subsequent process.

[0058] In some embodiments of the present invention, preferably, the molar content of H 2 S in the semi-lean methanol is ≤0.5 ppm, and the molar content of CO 2 is 10 - 14%; the temperature is -60 to -55 °C, and the pressure is 0.05 - 0.08 MPa(G).

[0059] In the present invention, the second flash evaporation is intended to flash evaporate the second semi-lean methanol to obtain the second CO 2Product gas and the solution after flash evaporation. Preferably, the pressure of the second flash evaporation is 0.06 - 0.09 MPa (G).

[0060] In the present invention, the third flash evaporation aims to subject the second stream of H 2 S - rich methanol after heat exchange (i.e., H 2 S - rich methanol after heat exchange) to flash evaporation to obtain sulfur - containing gas phase and the third H 2 S - rich methanol. Preferably, the pressure of the third flash evaporation is 0.12 - 0.16 MPa (G).

[0061] In some embodiments of the present invention, preferably, the molar content of H 2 in the third H 2 S - rich methanol is 0.4 - 0.6%, and the molar content of CO 2 is 13 - 17%; the temperature is - 60 to - 55 °C; the pressure is 0.13 - 0.17 MPa (G).

[0062] In some embodiments of the present invention, preferably, subject the H 2 S - rich methanol after heat exchange to the H 2 S flash evaporation.

[0063] In the present invention, the H 2 S flash evaporation aims to remove the H 2 S flash evaporation gas in the H 2 S - rich methanol after heat exchange. Preferably, the pressure of the H 2 S flash evaporation is 0.8 - 1 MPa (G).

[0064] In some embodiments of the present invention, preferably, the molar content of H 2 in the H 2 S - rich methanol after flash evaporation is 0.4 - 0.6%, and the molar content of CO 2 is 22 - 27%; the temperature is - 39 to - 34 °C.

[0065] In some embodiments of the present invention, preferably, mix the CO 2 flash evaporation gas obtained from the CO 2 flash evaporation and the H 2 S flash evaporation gas obtained from the H 2 S flash evaporation, contact with low - temperature H 2 S - rich methanol and wash to obtain flash evaporation gas. With such a setting, flash evaporation gas with a low CO 2 concentration is obtained.

[0066] In some embodiments of the present invention, preferably, the molar content of H 2 in the flash evaporation gas is 85 - 90%, and the molar content of CO 2The molar content is 4-8%, and the molar content of CO is 2-4%; the temperature is -58°C to -52°C, and the pressure is 0.8-1 MPa(G).

[0067] In some embodiments of the present invention, preferably, the low-H 2 In H of S methanol 2 The molar content of S is 0.2-0.3%, and CO 2 The molar content is 13-18%; the temperature is -55 to -50°C, and the pressure is 0.12-0.16 MPa(G).

[0068] In some embodiments of the present invention, preferably, the first CO 2 product gas obtained from the first flash, the second CO 2 product gas obtained from the second flash, and the third CO 2 product gas obtained by washing the sulfur-containing gas phase are mixed to obtain a CO 2 product gas; more preferably, the molar content of H 2 in the CO 2 product gas 17 is <1 ppm, and the molar content of CO 2 is 99.3-99.7%; the temperature is -55°C to -50°C, and the pressure is 0.05-0.08 MPa(G).

[0069] The inventors of the present invention have found through research that: the ability of semi-lean liquid methanol to absorb CO 2 mainly depends on its own gas-liquid equilibrium at a certain temperature and pressure. If the concentration of CO 2 dissolved in semi-lean liquid methanol is high, the absorption ability of CO 2 is weak, and vice versa. In the method provided by the present invention, in order to further reduce the CO 2 content in semi-lean liquid and maximize the CO 2 absorption ability of semi-lean liquid, the optimized reabsorption process performs nitrogen stripping on semi-lean liquid methanol again, so that the CO 2 content in semi-lean liquid methanol is further reduced to 4-7%, becoming low-CO 2 methanol. This can produce two positive effects: one is that with the improvement of the absorption ability of low-CO 2 methanol and the reduction of the circulation volume, the operating cost of the pump can be reduced by about 15%, and the cross-sectional area of the CO 2 absorption tower can be reduced by about 5%; the other is that low-CO 2 methanol can replace part of the lean methanol, so that the circulation amount of lean methanol in the CO 2 absorption tower also decreases. The reduction of the lean methanol flow rate will be transmitted to the rich H 2 S methanol, and the rich H 2The S methanol flow rate will also decrease, and the energy consumption of the corresponding heat regeneration system will also decrease.

[0070] In the present invention, the stripping is intended to further reduce the CO in the semi-lean methanol after heat exchange 2 Concentration, get low CO 2 Methanol. Preferably, the low CO 2 H in methanol 2 S molar content ≤ 0.5ppm, CO 2 The molar content of is 4-7%; the temperature is -55 to -50°C; the pressure is 0.15-0.25MPa(G).

[0071] In some embodiments of the present invention, preferably, the low CO 2 Methanol is pressurized to 3.5-4MPa(G) for the third time and then returned to the second CO 2 Absorb.

[0072] In some embodiments of the present invention, preferably, the molar flow ratio of the semi-lean liquid methanol and nitrogen after the heat exchange is 55-65:1.

[0073] In some embodiments of the present invention, preferably, the stripping pressure is 0.15-0.25 MPa(G).

[0074] In some embodiments of the present invention, preferably, the H 2 S molar content ≤ 0.5ppm, CO 2 The molar content of is 83-87%; the temperature is -50 to -45°C; the pressure is 0.15-0.25MPa(G).

[0075] The second aspect of the present invention provides a structural schematic diagram of a synthesis gas purification device supporting a pulverized coal gasification device as shown in Figure 1 , by Figure 1 It can be seen that the device includes H 2 S absorption tower T-1, CO 2 Absorption tower T-2, H 2 S flash tower T-3, CO 2 Flash tower T-4, reabsorption tower T-5 and stripping tower T-6, as well as the first cooler E-1 and the second cooler E-2;

[0076] Wherein, the H 2 S absorption tower T-1 is divided into the first H 2 S absorption section and second H 2 S absorption section, synthesis gas 1 enters the first H 2 S absorption section, second H 2 S absorption section, to obtain desulfurized gas 6 and the first H-rich2 S methanol 5, and the desulfurized gas 6 enters CO 2 absorption tower T-2, and the resulting CO-rich 2 methanol 4 is divided into two streams. The first CO-rich 2 methanol 4-i is recycled and used in the second H 2 S absorption section. The second CO-rich 2 methanol 4-ii, after passing through the first cooler E-1, enters the above-mentioned CO 2 flash tower T-4, and the resulting flash CO-rich 2 methanol 11, after passing through the second cooler E-2, enters the upper part of the reabsorption tower T-5. The resulting semi-lean methanol 8 is divided into three streams. The first semi-lean methanol 8-i, after heat exchange, enters the stripping tower T-6, and the resulting low-CO 2 methanol 21 is recycled and used in the above-mentioned CO 2 absorption tower T-2; the second semi-lean methanol 8-ii returns to the middle part of the reabsorption tower T-5 to obtain the flashed solution;

[0077] The first H-rich 2 S methanol 5 is divided into two streams. The first H-rich 2 S methanol 5-i is recycled and used in the first H 2 S absorption section. The second H-rich 2 S methanol 5-ii, after passing through the above-mentioned heat exchange, enters the above-mentioned H 2 S flash tower T-3, and the resulting flash H-rich 2 S methanol 13 enters the lower part of the reabsorption tower T-5. The resulting sulfur-containing gas phase is washed with the flashed solution, and the resulting low-H 2 S methanol 2 is recycled and used in the second H 2 S absorption section.

[0078] In the present invention, as Figure 1 shown, the H 2 S absorption tower T-1 includes a first H 2 S absorption section provided at the lower part and a second H 2 S absorption section provided at the upper part. Specifically, the first H 2 S absorption section pre-washes and absorbs H 2 S in the syngas 1 through a part of the first H-rich 2 S methanol (i.e., the first H-rich 2 S methanol 5-i), HCN, and NH 3 ; the second H 2 S absorption section absorbs H 2 S and CO 2 in the pre-washed syngas by introducing low-H 2 S methanol 2, thereby achieving the absorption of low-H 2Recycling of methanol 2 reduces the first rich CO 2 The consumption of methanol 4-i, which is equivalent to reducing the rich H that needs to be thermally regenerated 2 S methanol; in addition, such a setting correspondingly reduces the subsequent CO 2 The working load of the absorption tower and is of positive significance for reducing the lean methanol and low CO in the CO 2 Absorption tower 2 The consumption of methanol also has a positive meaning

[0079] In the present invention, as Figure 1 Shown, in the H 2 S absorption tower T-1, the first H 2 S absorption section and the second H 2 S absorption sections are connected by lifting holes; the first H 2 S absorption section is connected to the first rich H of the second H 2 S methanol outlet, used to contact the syngas 1 with the first rich H 2 S methanol 5-i and perform the first H 2 S absorption to obtain the second rich H 2 S methanol 3 and pre-washed syngas; the second H 2 S absorption section is connected to the low H of the reabsorption tower T-5 2 S methanol outlet and the rich CO of the CO 2 Absorption tower T-2 2 Methanol outlet, used to sequentially contact the pre-washed syngas with low H 2 S methanol 2, the first rich CO 2 Methanol 4-i and perform the second H 2 S absorption to obtain the desulfurized gas 6 and the first rich H 2 S methanol 5 2

[0080] In some embodiments of the present invention, preferably, in the H 2 S absorption tower T-1, the number of trays in the first H 2 S absorption section is 9-12, and the number of trays in the second H 2 S absorption section is 60-80

[0081] In the present invention, without special instructions, in the first H 2 S absorption section, the contact mode between the syngas and the first rich H 2 S methanol is preferably countercurrent contact between the syngas and the first rich H 2 S methanol, that is, the syngas enters from the bottom of the first H 2 S absorption section, and the first rich H 2 S methanol enters from the first H 2 ​Enter from the upper part of the S absorption section.

[0082] 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.

[0083] In the present invention, as Figure 1 shown, the CO 2 absorption tower T-2 includes a first CO 2 absorption section provided at the bottom and a second CO 2 absorption section provided at the top; the first CO 2 absorption section and the second CO 2 absorption section are connected by lifting holes, wherein the upper part of the first CO 2 absorption section is connected to the lower part of the second CO 2 absorption section, for contacting the desulfurized gas 6 with the CO 2 -containing methanol 7 and performing the first CO 2 absorption to obtain the CO 2 -rich methanol 4 and the pre-purified gas; the second CO 2 absorption section is connected to the low-CO 2 methanol outlet of the stripping tower T-6 and the lean methanol 9 from the subsequent process, for contacting the pre-purified gas with the low-CO 2 methanol 21 and the lean methanol 9 in sequence and performing the second CO 2 absorption to obtain the purified gas 10 and the CO 2 -containing methanol 7.

[0084] In some embodiments of the present invention, preferably, in the CO 2 absorption tower T-2, the number of trays in the first CO 2 absorption section is 12-18, and the number of trays in the second CO 2 absorption section is 60-80.

[0085] In the present invention, without special instructions, in the CO 2 absorption tower T-2, in the first CO 2 absorption section, the contact mode between the desulfurized gas 6 and the CO 2 -containing methanol 7 is selected from the countercurrent contact between the desulfurized gas 6 and the CO 2 -containing methanol 7; that is, the desulfurized gas 6 enters from the bottom of the first CO 2 absorption section, and the CO 2 -containing methanol 7 enters from the upper part of the first CO 2 absorption section.

[0086] In the present invention, asFigure 1 As shown, the top of the CO 2 flash tower T-4 is connected to the middle part of the H 2 S flash tower T-3, and is used to flash the CO 2 flashed from the CO 2 flash gas 12 and the H 2 flashed from the H 2 S are mixed, and then washed with the low-temperature H 2 S methanol 14 to obtain flash gas 15.

[0087] In the device provided by the present invention, the reabsorption tower T-5 is divided into an upper part, a middle part and a lower part from top to bottom. Through the optimization of the internal structure of the CO 2 reabsorption, the flashed solution obtained after the second flash of the second semi-lean methanol 8-ii is realized to absorb the sulfur-containing gas phase generated by the third flash of the flashed rich H 2 S methanol 13, but does not mix with the third rich H 2 S methanol 19, and low H 2 S methanol 2 is obtained, creating conditions for the reuse of the low H 2 S methanol 2 next.

[0088] In the present invention, as Figure 1 shown, the upper part and the middle part of the reabsorption tower T-4 are connected through lifting holes, and the middle part and the lower part are also connected through lifting holes. Specifically, the upper part is used to perform the first flash on the cooled rich CO 2 methanol 16 to obtain semi-lean methanol 8 and the first CO 2 product gas; the middle part is used to perform the second flash on the second semi-lean methanol 8-ii to obtain the flashed solution and the second CO 2 product gas; the lower part is used to perform the third flash on the flashed rich H 2 S methanol 13 to obtain the third rich H 2 S methanol 19 and the sulfur-containing gas phase; among them, the sulfur-containing gas phase and the flashed solution are washed to obtain low H 2 S methanol 2 and the third CO 2 product gas; the CO 2 product gas 17 includes the first CO 2 product gas, the second CO 2 product gas and the third CO 2 product gas.

[0089] In the present invention, as Figure 1 shown, the stripping tower T-6 is used to make the heat-exchanged semi-lean methanol 23 contact countercurrently with nitrogen 20 and perform stripping to obtain tail gas 18 and low CO 2 methanol 21.

[0090] In the present invention, as Figure 1 shown, the device further includes: a heat exchanger Q connecting the second H 2 S absorption section, the reabsorption tower T-5, the H 2 S flash tower T-3 and the stripping tower T-6, for heating the second rich H 2 S methanol 5-ii and the first semi-lean methanol 8-i, and obtaining heated rich H 2 S methanol 22 and heated semi-lean methanol 23 after the heat exchange.

[0091] In the present invention, as Figure 1 shown, a first pump P-1 is provided on the pipeline connecting the middle of the reabsorption tower T-5 and the second H 2 S absorption section, for circulating the low H 2 S methanol 2 back to the second H 2 S absorption section after the first pressurization.

[0092] 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 CO 2 absorption tower T-2 and the second H 2 S absorption section, for circulating the first rich CO 2 methanol 4-i back to the second H 2 S absorption section after the second pressurization and the third cooling.

[0093] In the present invention, as Figure 1 shown, a third pump P-3 is provided on the pipeline connecting the stripping tower T-6 and the second CO 2 absorption section, for circulating the low CO 2 methanol 21 back to the second CO 2 absorption section after the third pressurization.

[0094] 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 first CO 2 absorption section and the second CO 2 absorption section, for circulating the CO 2 -containing methanol 7 back to the first CO 2 absorption section after the fourth cooling.

[0095] The present invention will be described in detail below through embodiments.

[0096] The syngas purification device supporting the pulverized coal gasification device is as Figure 1 shown. As Figure 1 can be seen, the device includes: H2 H₂S Absorption Tower T-1, CO 2 Absorption Tower T-2, H 2 H₂S Flash Tower T-3, CO 2 Flash Tower T-4, Re - absorption 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, and First Pump P-1, Second Pump P-2 and Third Pump P-3;

[0097] H 2 H₂S Absorption Tower T-1 includes a first H 2 H₂S Absorption Section arranged at the lower part and a second H 2 H₂S Absorption Section arranged at the upper part; CO 2 Absorption Tower T-2 includes a first CO 2 Absorption Section arranged at the lower part and a second CO 2 Absorption Section arranged at the upper part;

[0098] Heat Exchanger Q is connected to the second H 2 H₂S Absorption Section, Re - absorption Tower T-5, H 2 H₂S Flash Tower T-3 and Stripping Tower T-6.

[0099] A syngas purification method for a coal powder gasification device, the method includes:

[0100] Making syngas 1 (H 2 The molar content of H₂S is 0.25 - 0.45%, CO 2 The molar content of is 40 - 50%; the temperature is - 25 to - 15 °C, and the pressure is 3.12 - 3.15 MPa (G)) and the first rich H 2 H₂S methanol 5 - i contact counter - currently with a molar flow ratio of 60 - 70:1 and carry out the first H 2 H₂S Absorption to obtain the second rich H 2 H₂S methanol 3 (H 2 The molar content of H₂S is 0.6 - 0.8%, CO 2 The molar content of is 30 - 36%) and pre - washed syngas;

[0101] Making the above - mentioned pre - washed syngas contact counter - currently with low H 2 H₂S methanol 2, the first rich CO 2 Methanol 4 - i and carry out the second H 2 H₂S Absorption to obtain desulfurized gas 6 (H 2 The molar content of H₂S is 0.5 - 1 ppm, CO 2 The molar content of is 31 - 36%; the temperature is - 28 to - 22 °C; the pressure is 3.05 - 3.1 MPa (G)) and the first rich H 2 H₂S methanol 5 (H 2The molar content of S is 0.4 - 0.5%, and the molar content of CO 2 is 25 - 30%);

[0102] Among them, after the low-H 2 S methanol 2 is first pressurized to 3.5 - 4 MPa (G), the second H 2 S absorption is carried out; the molar flow ratio of syngas 1 and low-H 2 S methanol 2 is 3 - 5:1; the molar flow ratio of syngas 1 and the first rich-CO 2 methanol 4-i is 1.5 - 2.5:1;

[0103] Among them, the first rich-H 2 S methanol 5 is divided into the first rich-H 2 S methanol 5-i and the second rich-H 2 S methanol 5-ii with a molar flow ratio of 1:50 - 60;

[0104] The above desulfurized gas 6 and the CO-containing 2 methanol 7 (cooled to -36 to -33 °C in the fourth stage) are in counter-current contact with a molar flow ratio of 1:1.5 - 2.5 and the first CO 2 absorption is carried out to obtain rich-CO 2 methanol 4 (the molar content of CO 2 is 15 - 20%, the molar content of H 2 S is 0.1 - 0.5 ppm; the temperature is -20 to -15 °C, and the pressure is 3.05 - 3.1 MPa (G)) and pre-purified gas. Among them, the rich-CO 2 methanol 4 is divided into the first rich-CO 2 methanol 4-i and the second rich-CO 2 methanol 4-ii with a molar flow ratio of 1:2.5 - 3; the first rich-CO 2 methanol 4-i is secondarily pressurized to 3.5 - 4 MPa (G), thirdly cooled to -49 to -43 °C, and sent to the second H 2 S absorption section;

[0105] The above pre-purified gas is successively in counter-current contact with low-CO 2 methanol 21 and lean methanol 9 (the molar content of CO 2 is 0%, the molar content of H 2 S is 0%) and the second CO 2 absorption is carried out to obtain purified gas 10 (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 3 - 3.1 MPa (G));

[0106] Among them, the molar flow rate ratio of the above purified gas 10 and low-CO 2 methanol 21 is 1:1.3 - 1.4; the molar flow rate ratio of the above purified gas 10 and lean methanol 9 is 1:1.4 - 1.6;

[0107] After the second rich CO 2 methanol 4-ii is cooled to -36 to -33 °C for the first time, CO 2 flash evaporation (pressure is 0.8 - 1 MPa(G)) is carried out to obtain the rich CO 2 methanol 11 after flash evaporation (H 2 the molar content of S is 0.1 - 0.5 ppm, and the molar content of CO 2 is 14.5 - 19.5%; the temperature is -36.5 to -33.5 °C) and CO 2 flash vapor 12; after the above rich CO 2 methanol 11 after flash evaporation is cooled to -45 to -40 °C for the second time, and the first flash evaporation (pressure is 0.05 - 0.08 MPa(G)) is carried out to obtain the first CO 2 product gas and semi-lean liquid methanol 8 (H 2 the molar content of S is ≤0.5 ppm, and the molar content of CO 2 is 10 - 14%; the temperature is -60 to -55 °C, and the pressure is 0.05 - 0.08 MPa(G)), among which, the above semi-lean liquid methanol 8 is divided into the first semi-lean liquid methanol 8-i, the second semi-lean liquid methanol 8-ii, and the third semi-lean liquid methanol 8-iii with a molar flow rate ratio of 3.5 - 3.8:1.1 - 1.2:1;

[0108] The first semi-lean liquid methanol 8-i and the second rich H 2 S methanol 5-ii are heat-exchanged to obtain the heat-exchanged rich H 2 S methanol 22 at a temperature of -36 to -31 °C and the heat-exchanged semi-lean liquid methanol 23 at a temperature of -48 to -43 °C;

[0109] The second semi-lean liquid methanol 8-ii is subjected to a second flash evaporation (pressure is 0.06 - 0.09 MPa(G)) to obtain the second CO 2 product gas and the solution after flash evaporation;

[0110] After the heat-exchanged rich H 2 S methanol 22 is subjected to H 2 S flash evaporation (pressure is 0.8 - 1 MPa(G)), the rich H 2 S methanol 13 after flash evaporation is subjected to a third flash evaporation (pressure is 0.12 - 0.16 MPa(G)) to obtain a sulfur-containing gas phase and the third rich H 2 S methanol 19 (H 2 the molar content of S is 0.4 - 0.6%, and CO2 The molar content is 13 - 17%; the temperature is -60 to -55 °C; the pressure is 0.13 - 0.17 MPa(G)); the above sulfur-containing gas phase and the flashed solution are washed to obtain low H 2 S methanol 2 (H 2 The molar content of S is 0.2 - 0.3%, and the molar content of CO 2 is 13 - 18%; the temperature is -55 to -50 °C, and the pressure is 0.12 - 0.16 MPa(G));

[0111] Among them, the above CO 2 The flashed CO 2 The flash gas 12 and H 2 The flashed H 2 from the S flash are mixed, and then contacted with the low-temperature H-rich 2 S methanol 14 and washed to obtain the flash gas 15 (H 2 with a molar content of 85 - 90%, a molar content of CO 2 of 4 - 8%, and a molar content of CO of 2 - 4%; the temperature is -58 °C to -52 °C, and the pressure is 0.8 - 1 MPa(G));

[0112] The above heat-exchanged semi-lean methanol 23 and nitrogen 20 are contacted at a molar flow ratio of 55 - 65:1 and stripped (pressure is 0.15 - 0.25 MPa(G)) to obtain low-CO 2 methanol 21 (H 2 with an S molar content ≤ 0.5 ppm and a CO 2 molar content of 4 - 7%; the temperature is -55 to -50 °C; the pressure is increased from 0.15 - 0.25 MPa(G) to 3.5 - 4 MPa(G) and returned for the above second CO 2 absorption, and the tail gas 18 (H 2 with an S molar content ≤ 0.5 ppm and a CO 2 molar content of 83 - 87%; the temperature is -50 to -45 °C; the pressure is 0.15 - 0.25 MPa(G)).

[0113] Among them, the first CO 2 product gas obtained from the first flash, the second CO 2 product gas obtained from the second flash, and the third CO 2 product gas obtained by washing the sulfur-containing gas phase are mixed to obtain CO 2 product gas 17 (H 2 with an S molar content < 1 ppm and a CO 2The molar content is 99.3 - 99.7%; the temperature is -55°C to -50°C, and the pressure is 0.05 - 0.08 MPa(G).

[0114] Comparative Example 1

[0115] Taking the hydrogen production unit using pulverized coal gasification as an example, the effective gas (H 2 +CO) entering the low-temperature methanol washing unit is 161,000 Nm 3 / h. Based on this benchmark, the main technical parameters of the lean-rich liquid process (i.e., CN201110260570.0 discloses a low-temperature methanol washing process and a syngas purification process for a supporting pulverized coal gasification unit) are compared in Table 1.

[0116] Table 1

[0117]

[0118]

[0119] From the results in Table 1, taking the hydrogen production unit based on pulverized coal gasification as an example, for the syngas purification method of the supporting pulverized coal gasification unit provided in Example 1, the lean methanol circulation rate is 90.0% of the lean methanol circulation rate in Comparative Example 1 (lean-rich liquid process), the low CO 2 methanol circulation rate is 78.3% of the semi-lean methanol circulation rate in Comparative Example 1 (lean-rich liquid process), the amount of rich CO 2 methanol used in the H 2 S absorption tower is 88.6% of the amount of rich CO 2 methanol used in Comparative Example 1 (lean-rich liquid process), the power consumption of the pumps is 88.6% of the amount used in Comparative Example 1 (lean-rich liquid process), and the cumulative reduction in external cold energy consumption is 1100 KW / h, with a significant overall energy-saving effect.

[0120] In addition, the diameter of the CO 2 absorption tower is 97.8% of the diameter of the CO 2 absorption tower in Comparative Example 1 (lean-rich liquid process), that is, compared with Comparative Example 1, the cross-sectional area of the CO 2 absorption tower is reduced by 4.84%.

[0121] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for purifying synthesis gas of a pulverized coal gasification device, characterized in that: The method comprises: The synthesis gas is subjected to a first H2S absorption, the obtained pre-washed synthesis gas is subjected to a second H2S absorption to obtain a desulfurized gas and a first H2S-rich methanol, the first stream of H2S-rich methanol is returned and subjected to the first H2S absorption, 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 to obtain a sulfur-containing gas phase; The desulfurized gas is subjected to CO2 absorption, and the obtained CO2-rich methanol is divided into two streams. The first stream of CO2-rich methanol is returned and subjected to the second H2S absorption. The second stream of CO2-rich methanol is subjected to CO2 flash distillation after a first cooling. The obtained flashed CO2-rich methanol is subjected to a first flash distillation after a second cooling. The obtained semi-lean liquid methanol is divided into three streams. The first stream of semi-lean liquid methanol is stripped after the heat exchange, and the obtained low-CO2 methanol is returned and subjected to the CO2 absorption. The second stream of semi-lean liquid methanol is subjected to a second flash distillation, and the obtained flashed solution contacts and washes with the sulfur-containing gas phase, and the obtained low-H2S methanol is returned and subjected to the second H2S absorption.

2. The method according to claim 1, wherein: The heat exchange process includes: 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 and heat-exchanged semi-lean methanol; Preferably, the temperature of the H2S-rich methanol after the heat exchange is -36 to -31°C; the temperature of the semi-lean methanol after the heat exchange is -48 to -43°C.

3. The method according to claim 1 or 2, wherein: 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 a pre-washed synthesis gas and a second H2S-rich methanol; and / or, the molar content of H2S in the synthesis gas is 0.25-0.45%, the molar content of CO2 is 40-50%; the temperature is -25°C to -15°C, and the pressure is 3.12-3.15MPa(G); And / or, the second H2S absorption process comprises: contacting the pre-washed synthesis gas, low H2S methanol and the first stream of CO2-rich methanol and performing the second H2S absorption to obtain the first H2S-rich methanol and desulfurized gas; 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 first H2S-rich methanol is 0.4-0.5%, and the molar content of CO2 is 25-30%; and / or, the molar content of H2S in the desulfurized gas is 0.5-1ppm, the molar content of CO2 is 31-36%; the temperature is -28 to -22°C; the pressure is 3.05-3.1MPa(G); and / or, the low H2S methanol is first pressurized to 3.5-4 MPa(G) and then returned to perform the second H2S absorption; And / or, the first stream of CO2-rich methanol is successively pressurized to 3.5-4 MPa (G) and cooled to -49 to -43°C for a third time, and then returned to perform the second H2S absorption.

4. The method according to any one of claims 1 to 3, wherein: The CO2 absorption process includes: contacting the desulfurized gas with CO2-containing methanol and performing a first CO2 absorption to obtain pre-purified gas and the CO2-rich methanol; contacting the pre-purified gas, low-CO2 methanol and lean methanol and performing a second CO2 absorption to obtain the purified gas and CO2-containing methanol; 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 1:2.5-3; and / or, the molar content of CO2 in the CO2-rich methanol is 15-20%, the molar content of H2S is 0.1-0.5 ppm; the temperature is -20 to -15°C, and the pressure is 3.05-3.1 MPa(G); And / or, the CO2-containing methanol is cooled to -36 to -33°C for the fourth time and returned to the first CO2 absorption.

5. The method according to any one of claims 1 to 4, wherein: The temperature of the material after the first cooling is -36 to -33°C; And / or, the pressure of the CO2 flash evaporation is 0.8-1MPa(G); and / or, the molar content of H2S in the CO2-rich methanol after the flash evaporation is 0.1-0.5 ppm, the molar content of CO2 is 14.5-19.5%; the temperature is -36.5 to -33.5°C; and / or, the temperature of the CO2-rich methanol after cooling is -45 to -40°C; And / or, the pressure of the first flash evaporation is 0.05-0.08 MPa(G); and / or, the semi-lean methanol is divided into the first stream of semi-lean methanol, the second stream of semi-lean methanol and the third stream of semi-lean methanol with a molar flow ratio of 3.5-3.8:1.1-1.2:1; and / or, the molar content of H2S in the semi-lean methanol is ≤0.5ppm, the molar content of CO2 is 10-14%; the temperature is -60 to -55°C, and the pressure is 0.05-0.08MPa(G); And / or, the pressure of the second flash evaporation is 0.06-0.09 MPa(G); And / or, the pressure of the third flash evaporation is 0.12-0.16 MPa(G).

6. The method according to any one of claims 2 to 5, wherein: flash evaporation of H2S on the H2S-rich methanol after heat exchange; And / or, the pressure of the H2S flash evaporation is 0.8-1 MPa(G); and / or, the molar content of H2S in the H2S-rich methanol after the flash evaporation is 0.4-0.6%, and the molar content of CO2 is 22-27%; the temperature is -39 to -34°C; and / or, mixing the CO2 flash gas obtained by the CO2 flash distillation and the H2S flash gas obtained by the H2S flash distillation, contacting with low-temperature H2S-rich methanol and washing to obtain flash gas; And / or, the molar content of H2 in the flash gas is 85-90%, the molar content of CO2 is 4-8%, and the molar content of CO is 2-4%; the temperature is -58°C to -52°C, and the pressure is 0.8-1MPa(G).

7. The method according to any one of claims 2 to 6, wherein: The molar content of H2S in the low H2S methanol is 0.2-0.3%, and the molar content of CO2 is 13-18%; the temperature is -55 to -50°C, and the pressure is 0.12-0.16MPa(G); And / or, the stripping process includes: contacting the semi-lean liquid methanol after heat exchange with nitrogen and performing stripping to obtain the low-CO2 methanol and tail gas; and / or, the molar content of H2S in the low CO2 methanol is ≤0.5ppm, the molar content of CO2 is 4-7%; the temperature is -55 to -50°C; the pressure is 0.15-0.25MPa(G); And / or, the low CO2 methanol is pressurized to 3.5-4 MPa(G) for the third time and then returned to perform the second CO2 absorption.

8. A synthesis gas purification device supporting a pulverized coal gasification device, characterized in that: The device comprises an H2S absorption tower, a CO2 absorption tower, an H2S flash tower, a CO2 flash tower, a reabsorption tower and a stripping tower, as well as a first cooler and a second cooler; The H2S absorption tower is divided into a first H2S absorption section and a second H2S absorption section from bottom to top. The synthesis gas enters the first H2S absorption section and the second H2S absorption section in sequence to obtain desulfurized gas and the first H2S-rich methanol. The desulfurized gas enters the CO2 absorption tower. The obtained CO2-rich methanol is divided into two streams. The first stream of CO2-rich methanol is recycled and used in the second H2S absorption section. The second stream of CO2-rich methanol enters the CO2 flash tower after passing through the first cooler. The obtained flashed CO2-rich methanol enters the upper part of the reabsorption tower after passing through the second cooler. The obtained semi-lean liquid methanol is divided into three streams. The first stream of semi-lean liquid methanol enters the stripping tower after heat exchange. The obtained low-CO2 methanol is recycled and used in the CO2 absorption tower; the second stream of semi-lean liquid methanol returns to the middle part of the reabsorption tower to obtain a flashed solution. The first H2S-rich methanol is divided into two streams, the first stream of H2S-rich methanol is recycled to the first H2S absorption section, and the second stream of H2S-rich methanol enters the H2S flash tower after the heat exchange, and the flashed H2S-rich methanol obtained enters the lower part of the reabsorption tower, the obtained sulfur-containing gas phase is washed with the flashed solution, and the obtained low-H2S methanol is recycled to the second H2S absorption section.

9. The device according to claim 8, wherein: The CO2 absorption tower is divided into a first CO2 absorption section and a second CO2 absorption section from bottom to top; And / or, the top of the CO2 flash tower is connected to the middle of the H2S flash tower, so as to mix the CO2 flash gas obtained by the CO2 flash distillation with the H2S flash gas obtained by the H2S flash distillation, and then wash them with low-temperature H2S-rich methanol to obtain the flash gas; And / or, the device further comprises: a heat exchanger connected to the second H2S absorption section, the reabsorption tower, the H2S flash tower and the stripping tower, for obtaining heat-exchanged H2S-rich methanol and heat-exchanged semi-lean methanol by subjecting the second H2S-rich methanol and the first semi-lean methanol to heat exchange.

10. The device according to claim 9, wherein: A first pump is provided on the pipeline connecting the middle part of the reabsorption tower and the second H2S absorption section; and / or, according to the material flow direction, a second pump and a third cooler are sequentially arranged on the pipeline connecting the CO2 absorption tower and the second H2S absorption section; and / or, a third pump is provided on the pipeline connecting the stripping tower and the second CO2 absorption section; And / or, according to the material flow direction, a fourth cooler is provided on the pipeline connecting the first CO2 absorption section and the second CO2 absorption section.

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