Low-temperature methanol washing flash evaporation and reabsorption technology matched with pulverized coal gasification device

Abstract

The invention relates to the technical field of low-temperature methanol washing, in particular to a low-temperature methanol washing flash evaporation and reabsorption method matched with a pulverized coal gasification device and a low-temperature methanol washing flash evaporation and reabsorption device matched with the pulverized coal gasification device. According to the method, the technical problem that CO2 flash steam is polluted by H2S flash steam in the medium-pressure flash process is solved by optimally setting the medium-pressure flash process and adopting classified flash and classified washing technologies; the flow of the re-absorption tower is optimized, so that low-sulfur methanol is generated, and meanwhile, the low-sulfur methanol is reutilized; the gas stripping process is optimized, H2S-rich gas stripping gas generated by gas stripping is subjected to multi-stage series absorption, and the method has the characteristic of low comprehensive energy consumption.

Description

TECHNICAL FIELD

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

[0002] H2 and CO in the synthesis gas produced by the pulverized coal gasification technology are called effective gas, and the synthesis gas also contains a large amount of CO2 and a small amount of H2S, COS, NH3, HCN and other components. H2 and CO after the hydrogen-carbon ratio adjustment in the conversion unit are raw gas for synthesizing chemical products such as methanol and ammonia. Acid gases CO2 and H2S are generally poisons of synthesis catalysts, so they must be removed before the synthesis process.

[0003] The low-temperature methanol washing technology is to absorb and remove H2S and CO2 and other acid gases in the synthesis gas with low-temperature methanol as the absorption solvent, and to remove HCN, NH3 and other trace components. In the poly-generation low-temperature methanol washing process, a small amount of H2 and CO gas is dissolved in the CO2-rich methanol and H2S-rich methanol which have absorbed acid gas, H2 and CO are effective gas and need to be recovered by medium-pressure flash evaporation. At the same time, in order to produce CO2 gas to meet the demand of coal conveying in the pulverized coal gasification unit and the subsequent unit, and to improve the H2S gas concentration of the H2S-rich methanol, a resorption tower needs to be set. When designing the poly-generation low-temperature methanol washing process, optimizing the resorption tower process setting is the key to reducing the total amount of H2S-rich methanol and reducing the energy consumption of the device.

[0004] CN201110260570.0 discloses a low-temperature methanol washing process. First, the CO2 gas flashed out of the upper tower of the medium-pressure flash evaporation tower is sent to the lower tower and washed and absorbed by the H2S-rich methanol, causing the CO2 gas to be transferred to the H2S-rich methanol and the CO2 gas to be contaminated. Second, in the CO2 flash evaporation section of the resorption tower, the CO2-rich methanol is directly mixed with the H2S-rich methanol while washing the H2S-rich methanol flash gas, and the CO2-rich methanol is contaminated by the H2S-rich methanol, and the low-concentration H2S methanol produced is not fully used, resulting in high energy consumption. Third, the tail gas washing setting is not reasonable, and different H2S content methanol is not selectively set for washing according to the H2S content in the tail gas, so as to reduce the heat regeneration energy consumption of the entire low-temperature methanol washing. SUMMARY

[0005] The present application aims to overcome the problems of unreasonable process settings of the existing rectisol technology, such as the intermediate pressure flash tower and the reabsorption tower, and provides a rectisol flash and reabsorption method matched with a pulverized coal gasification device and a rectisol flash and reabsorption device matched with a pulverized coal gasification device. The method solves the technical problem of CO2 flash gas being polluted by H2S flash gas in the intermediate pressure flash process by optimizing the intermediate pressure flash process and adopting classified flash and classified washing technology. The low-sulfur methanol is generated by optimizing the reabsorption tower process, and the low-sulfur methanol is used twice. The rich H2S stripping gas generated by the gas stripping process is absorbed by multiple stages in series, and the method has the characteristics of low comprehensive energy consumption.

[0006] The first aspect of the present application provides a rectisol flash and reabsorption method matched with a pulverized coal gasification device, which comprises the following steps:

[0007] The synthesis gas from the pulverized coal gasification device is subjected to H2S absorption to obtain first H2S-rich methanol, and the obtained desulfurized gas is subjected to CO2 absorption to obtain first CO2-rich methanol;

[0008] The first H2S-rich methanol is subjected to H2S flash to obtain H2S flash liquid and H2S flash gas, and the first CO2-rich methanol is subjected to CO2 flash to obtain CO2 flash liquid in three streams and CO2 flash gas;

[0009] The first stream of CO2 flash liquid, the second stream of CO2 flash liquid and the H2S flash liquid are subjected to first flash, second flash and third flash, respectively, to obtain semi-lean liquid methanol in two streams, low-sulfur methanol in two streams, second H2S-rich methanol and first CO2 product gas; the third stream of CO2 flash liquid is subjected to fourth flash to obtain second CO2-rich methanol and second CO2 product gas;

[0010] The H2S flash gas and non-shift H2S-rich methanol from a non-shift gas purification process are subjected to first washing; and the CO2 flash gas and the first stream of semi-lean liquid methanol are subjected to second washing;

[0011] The first stream of low-sulfur methanol, the second H2S-rich methanol, the third H2S-rich methanol and nitrogen are contacted and subjected to gas stripping to obtain stripping gas; the third H2S-rich methanol is obtained by third washing of the second CO2-rich methanol and the stripping gas; the second stream of low-sulfur methanol is returned to the H2S absorption, and the second stream of semi-lean liquid methanol is returned to the CO2 absorption.

[0012] The second aspect of the present application provides a rectisol flash and reabsorption device matched with a pulverized coal gasification device, and the method provided in the first aspect is carried out in the device. The device comprises an H2S intermediate pressure flash tower, a CO2 intermediate pressure flash tower, a reabsorption tower and a low pressure flash tower.

[0013] Wherein, the H2S medium pressure flash tower is divided into H2S flash section and H2S washing section from bottom to top, the CO2 medium pressure flash tower is divided into CO2 flash section and CO2 washing section from bottom to top; the reabsorption tower is divided into upper tower and lower tower, the upper tower is divided into first flash section, second flash section and third flash section connected by riser from top to bottom, the lower tower is divided into stripping section and washing section connected by riser from bottom to top;

[0014] Wherein, the H2S flash section and third flash section are connected by pipeline; the CO2 flash section is connected by pipeline with first flash section, second flash section and low pressure flash tower respectively; the first flash section is connected by pipeline with CO2 washing section; the second flash section and third flash section are connected by pipeline with stripping section respectively; the low pressure flash tower is connected by pipeline with washing section; the washing section is connected by pipeline with stripping section.

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

[0016] (1) The present application adopts three-stage tail gas washing technology, selectively sets second CO2-rich methanol, first H2S-rich methanol and first low-sulfur methanol according to different H2S content in tail gas, and the three different H2S content methanol is washed from high to low in turn, so as to ensure that the tail gas emission meets the standard and the second CO2-rich methanol is used as little as possible, thereby reducing the heat regeneration energy consumption of the whole low-temperature methanol washing.

[0017] (2) The method provided by the present application optimizes the medium pressure flash process, introduces non-shift H2S-rich methanol to wash H2S flash gas, and introduces semi-lean liquid methanol to wash CO2 flash gas, compared with prior art, realizes separate flashing and separate washing of first CO2-rich methanol and first H2S-rich methanol, avoids the technical difficulty of transferring CO2 flash gas to H2S-rich methanol, and is conducive to reducing the energy consumption of the device;

[0018] (3) The method provided by the present application optimizes the reabsorption process, realizes the absorption of sulfur-containing gas phase (for example, H2S) generated by the third flash of H2S flash liquid, the H2S content in the solution is lower, which is called low-sulfur methanol, which creates conditions for the reuse of the low-sulfur methanol, and this setting also avoids the mixing of second H2S-rich methanol. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a structure schematic view of a low-temperature methanol washing flash and reabsorption device matched with a pulverized coal gasification device provided by the present application.

[0020] REFERENCE SIGNS

[0021] T-1, H2S medium-pressure flash distillation tower; T-2, CO2 medium-pressure flash distillation tower; T-3, reabsorption tower; T-4, low-pressure flash distillation tower;

[0022] E-1, First cooler; E-2, Second cooler; E-3, Third cooler; E-4, Fourth cooler; Q-1, First heat exchanger; Q-2, Second heat exchanger; P, Pump;

[0023] 1. First H2S-rich methanol; 2. H2S flash liquid; 3. Non-conversion H2S-rich methanol; 4. Washed H2S flash vapor; 5. First CO2-rich methanol; 6. CO2 flash liquid; 6-i. First CO2 flash liquid; 6-ii. Second CO2 flash liquid; 6-iii. Third CO2 flash liquid; 7. Semi-lean methanol; 7-i. First semi-lean methanol; 7-ii. Second semi-lean methanol; 8. Second H2S-rich methanol; 9. Low-sulfur methanol; 9-i. First low-sulfur methanol; 9-ii. Second low-sulfur methanol; 10. First CO2 product gas; 11. Third H2S-rich methanol; 12. Nitrogen; 13. H2S-rich methanol after stripping; 14. Second CO2 product gas; 15. Second CO2-rich methanol; 16. Tail gas; 17. Washed CO2 flash vapor. Detailed Implementation

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] In this invention, unless otherwise specified, the terms "first," "second," "third," and "fourth" do not indicate a sequential order, nor do they limit the specific materials or steps; they are merely used to distinguish that these are not the same material or step. For example, in "first cooling," "second cooling," "third cooling," and "fourth cooling," the terms "first," "second," "third," and "fourth" are used only to indicate that these are not the same cooling process.

[0026] In this invention, unless otherwise specified, the “top” of the container refers to 0-10% of the container’s height from top to bottom; the “upper part” of the container refers to 10-40% of the container’s height from top to bottom; the “middle part” of the container refers to 40-60% of the container’s height from top to bottom; the “lower part” of the container refers to 60-90% of the container’s height from top to bottom; and the “bottom” of the container refers to 90-100% of the container’s height from top to bottom.

[0027] The first aspect of the present application provides a low-temperature methanol washing flash and resorption method for a complete pulverized coal gasification device, the method comprising:

[0028] H2S absorption of synthesis gas from the pulverized coal gasification device to obtain first H2S-rich methanol, and CO2 absorption of the obtained desulfurized gas to obtain first CO2-rich methanol;

[0029] H2S flash of the first H2S-rich methanol to obtain H2S flash liquid and H2S flash gas; CO2 flash of the first CO2-rich methanol to obtain CO2 flash liquid in three streams and CO2 flash gas;

[0030] First flash, second flash and third flash of the first stream of CO2 flash liquid, the second stream of CO2 flash liquid and the H2S flash liquid to obtain semi-lean methanol in two streams, low-sulfur methanol in two streams, second H2S-rich methanol and first CO2 product gas; fourth flash of the third stream of CO2 flash liquid to obtain second CO2-rich methanol and second CO2 product gas;

[0031] The H2S flash gas and non-shift H2S-rich methanol from a non-shift gas purification process are subjected to first washing; the CO2 flash gas and the first stream of semi-lean methanol are subjected to second washing;

[0032] The first stream of low-sulfur methanol, the second H2S-rich methanol, the third H2S-rich methanol and nitrogen are contacted and subjected to gas stripping to obtain gas stripping gas; the third H2S-rich methanol is obtained by third washing of the second CO2-rich methanol and the gas stripping gas; the second stream of low-sulfur methanol is returned to the H2S absorption, and the second stream of semi-lean methanol is returned to the CO2 absorption.

[0033] In the present application, without special circumstances, H2S absorption refers to H2S absorption of synthesis gas from the pulverized coal gasification device to obtain desulfurized gas and first H2S-rich methanol; CO2 absorption refers to CO2 absorption of the desulfurized gas from the H2S absorption to obtain purified gas and first CO2-rich methanol.

[0034] In some embodiments of the present application, preferably, the molar content of H2S in the first H2S-rich methanol is 0.4-0.6%, the molar content of CO2 is 24-29%, the temperature is -20 to -14℃, and the pressure is 3.05-3.1 MPa(G).

[0035] In some embodiments of the present application, preferably, the molar content of H2S in the synthesis gas is 0.3-0.35%, the molar content of CO2 is 40-50%, the temperature is -25 to -15℃, and the pressure is 3.12-3.15 MPa(G).

[0036] In some embodiments of the present application, preferably, the molar content of H2S in the desulfurized gas is 0.5-1 ppm, the molar content of CO2 is 34-38%, the temperature is -25 to -20°C, and the pressure is 3.05-3.1 MPa (G).

[0037] In some embodiments of the present application, preferably, the molar content of H2S in the first CO2-rich methanol is 0.1-0.5 ppm, the molar content of CO2 is 18-23%, the temperature is -22 to -18°C, and the pressure is 3.05-3.09 MPa (G).

[0038] In the present application, unless otherwise specified, the non-shift gas purification process refers to purifying the non-shift gas from a pulverized coal gasification device to obtain non-shift H2S-rich methanol and purified non-shift gas. Preferably, the molar content of H2S in the non-shift H2S-rich methanol (3) is 0.5-0.9%, the molar content of CO2 is 3-7%, the temperature is -32 to -28°C, and the pressure is 3.5-3.55 MPa (G).

[0039] In the present application, the H2S flashing is intended to reduce the concentrations of H2S and CO2 in the first H2S-rich methanol. Preferably, the molar content of H2S in the H2S flashing liquid is 0.35-0.55%, the molar content of CO2 is 23.5-28.5%, and the temperature is -16 to -22°C. In the present application, the pressure of the H2S flashing is 0.8-1 MPa (G).

[0040] In some embodiments of the present application, preferably, the H2S flashing gas and the non-shift H2S-rich methanol are subjected to the first washing to obtain a washed H2S flashing gas and the first washing liquid obtained is mixed into the H2S flashing liquid.

[0041] In some embodiments of the present application, further preferably, the molar content of H2S in the washed H2S flashing gas is 0.6-0.8%, the molar content of CO2 is 25-30%, the temperature is -30 to -20°C, and the pressure is 0.8-1 MPa (G).

[0042] In the present application, the CO2 flashing is intended to reduce the concentration of CO2 in the first CO2-rich methanol. Preferably, the molar content of H2S in the CO2 flashing liquid is 0.1-0.5 ppm, the molar content of CO2 is 17.5-22.5%, and the temperature is -25 to -20°C. In the present application, the pressure of the CO2 flashing is 0.8-1 MPa (G).

[0043] In the present application, the CO2 flash liquid is divided into three streams. Preferably, the molar flow ratio of the first stream of CO2 flash liquid, the second stream of CO2 flash liquid and the third stream of CO2 flash liquid is 2-4:1:1-2.

[0044] In some embodiments of the present application, preferably, the second washing is performed on the CO2 flash gas and the first stream of semi-lean liquid methanol, to obtain washed CO2 flash gas and a second washing liquid, and the obtained second washing liquid is mixed into the CO2 flash liquid; further preferably, the molar content of H2S in the washed CO2 flash gas is 0.1-0.5 ppm, the molar content of CO2 is 48-52%, the temperature is -36 to -30℃, and the pressure is 0.8-1 MPa(G).

[0045] In some embodiments of the present application, preferably, the first flash is performed on the first stream of CO2 flash liquid, to obtain a first stream of CO2 product gas and semi-lean liquid methanol; the second flash is performed on the second stream of CO2 flash liquid, to obtain a second stream of CO2 product gas and flash liquid; the third flash is performed on the H2S flash liquid, to obtain a sulfur-containing gas phase and a second H2S-rich methanol; wherein the fourth washing is performed on the flash liquid and the sulfur-containing gas phase, to obtain the low-sulfur methanol and a third stream of CO2 product gas, and the third stream of CO2 product gas, the first stream of CO2 product gas and the second stream of CO2 product gas are mixed to obtain the first CO2 product gas; wherein the pressure of the first flash is < the pressure of the second flash < the pressure of the third flash.

[0046] In some embodiments of the present application, 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); and the pressure of the third flash is 0.12-0.16 MPa(G).

[0047] In some embodiments of the present application, preferably, the first stream of CO2 flash liquid is cooled to -36 to -30℃ by a first cooling device before the first flash; preferably, the second stream of CO2 flash liquid is cooled to -52 to -50℃ by a second cooling device before the second flash; and preferably, the H2S flash liquid is cooled to -36 to -30℃ by a third cooling device before the third flash.

[0048] In some embodiments of the present application, preferably, the molar content of H2S in the semi-lean liquid methanol is 0.1-0.5 ppm, the molar content of CO2 is 10-14%, and the temperature is -58.5 to -52.5℃.

[0049] In the present application, the semi-lean liquid methanol is divided into two streams, the first stream is subjected to the second washing, and the second stream is subjected to the CO2 absorption. Further preferably, the molar flow ratio of the first stream of semi-lean liquid methanol and the second stream of semi-lean liquid methanol is 1:10-12.

[0050] In the present application, more preferably, the semi-lean liquid methanol is pressurized to 1-1.2 MPa (G) and then divided into the first stream of semi-lean liquid methanol and the second stream of semi-lean liquid methanol.

[0051] In some embodiments of the present application, preferably, the molar content of H2S in the low-sulfur methanol is 0.2-0.3%, the molar content of CO2 is 9-14%, and the temperature is -58 to -54℃.

[0052] In the present application, the low-sulfur methanol is divided into two streams, the first stream is subjected to stripping, and the second stream is subjected to the H2S absorption. Further preferably, the molar flow ratio of the first stream of low-sulfur methanol and the second stream of low-sulfur methanol is 1-1.05:1.

[0053] In some embodiments of the present application, preferably, the molar content of H2S in the second H2S-rich methanol is 0.4-0.6%, the molar content of CO2 is 12-16%, and the temperature is -65 to -55℃.

[0054] In some embodiments of the present application, preferably, the molar content of H2S in the first CO2 product gas is ≤1 ppm, the molar content of CO2 is 99.4-99.7%, and the temperature is -65 to -55℃.

[0055] In some embodiments of the present application, preferably, the process of stripping comprises: each of the first stream of low-sulfur methanol, the second H2S-rich methanol, and the third H2S-rich methanol is independently contacted with nitrogen and subjected to the stripping to obtain the stripping gas and the post-stripping H2S-rich methanol.

[0056] In some embodiments of the present application, preferably, the third H2S-rich methanol is subjected to the first heat exchange to -40 to -36℃ and then subjected to the stripping.

[0057] In some embodiments of the present application, preferably, the second H2S-rich methanol is subjected to the second heat exchange to -36 to -30℃ and then subjected to the stripping.

[0058] In some embodiments of the present application, preferably, the molar content of H2S in the post-stripping H2S-rich methanol is 0.2-0.5%, the molar content of CO2 is 1-5%, and the temperature is -52 to -48℃.

[0059] In some embodiments of the present application, preferably, the second CO2-rich methanol has a molar content of H2S of 0.1-0.5 ppm, a molar content of CO2 of 13-18%, and a temperature of -35 to -30°C.

[0060] In some embodiments of the present application, preferably, the fourth flash has a pressure of 0.45-0.55 MPa (G).

[0061] In some embodiments of the present application, preferably, the second CO2 product gas has a molar content of H2S of ≤1 ppm, a molar content of CO2 of 99-99.5%, and a temperature of -34 to -30°C.

[0062] In some embodiments of the present application, preferably, the second CO2-rich methanol is cooled to -50 to -47°C, and the third washing is performed with the stripping gas to obtain tail gas and third H2S-rich methanol.

[0063] In the present application, further preferably, the tail gas has a molar content of H2S of ≤1 ppm, a molar content of CO2 of 70-74%, and a temperature of -62 to -58°C; further preferably, the third H2S-rich methanol has a molar content of H2S of 0.1-0.3%, a molar content of CO2 of 10-13%, and a temperature of -58 to -55°C.

[0064] The second aspect of the present application provides a structure diagram of a low-temperature methanol washing flash and reabsorption device matched with a pulverized coal gasification device, as shown in the figure. Figure 1 The method provided by the first aspect is performed in the device, as shown in the figure. Figure 1 As can be seen, the device comprises an H2S medium-pressure flash tower T-1, a CO2 medium-pressure flash tower T-2, a reabsorption tower T-3, and a low-pressure flash tower T-4.

[0065] The H2S medium-pressure flash tower T-1 is divided into an H2S flash section and an H2S washing section from bottom to top, and the CO2 medium-pressure flash tower T-2 is divided into a CO2 flash section and a CO2 washing section from bottom to top; the reabsorption tower T-3 is divided into an upper tower and a lower tower, the upper tower is divided into a first flash section, a second flash section, and a third flash section connected by riser holes from top to bottom, and the lower tower is divided into a stripping section and a washing section connected by riser holes from bottom to top.

[0066] The H2S flash section and the third flash section are connected by a pipeline; the CO2 flash section, the first flash section, the second flash section, and the low-pressure flash tower T-4 are respectively connected by a pipeline; the first flash section and the CO2 washing section are connected by a pipeline; the second flash section and the third flash section are respectively connected by a pipeline to the stripping section; the low-pressure flash tower T-4 and the washing section are connected by a pipeline; and the washing section and the stripping section are connected by a pipeline.

[0067] In the present application, as shown in Figure 1 H2S medium pressure flash tower T-1 is divided into H2S flash section and H2S washing section from bottom to top; wherein, H2S flash section is used for H2S flashing of first H2S-rich methanol 1, to obtain H2S flash gas and H2S flash liquid 2; H2S washing section is used for first washing of H2S flash gas and non-shift H2S-rich methanol 3, to obtain washed H2S flash gas 4, and the obtained first washing liquid is mixed into H2S flash liquid 2.

[0068] In the present application, as shown in Figure 1 CO2 medium pressure flash tower T-2 is divided into CO2 flash section and CO2 washing section from bottom to top; wherein, CO2 flash section is used for CO2 flashing of first CO2-rich methanol 5, to obtain CO2 flash gas and CO2 flash liquid 6; CO2 washing section is used for second washing of first semi-lean liquid methanol 7-i and CO2 flash gas, to obtain washed CO2 flash gas 17, and the obtained second washing liquid is mixed into CO2 flash liquid 6.

[0069] According to the present application, preferably, as shown in Figure 1 In the reabsorption tower T-3, the upper tower is divided into first flash section, second flash section and third flash section connected by gas lift holes; wherein, the first flash section is used for first flashing of the first CO2 flash liquid 6-i, to obtain the first CO2 product gas and semi-lean liquid methanol 7; the second flash section is used for second flashing of the second CO2 flash liquid 6-ii, to obtain the second CO2 product gas and flash liquid; the third flash section is used for third flashing of H2S flash liquid 2, to obtain sulfur-containing gas phase and second H2S-rich methanol 8; wherein, the flash liquid and sulfur-containing gas phase are subjected to fourth washing, to obtain the low-sulfur methanol 9, and the third CO2 product gas is mixed with the first CO2 product gas and the second CO2 product gas, to obtain the first CO2 product gas 10.

[0070] According to the present application, preferably, as shown in Figure 1 In the reabsorption tower T-3, the lower tower is divided into stripping section and washing section from bottom to top, connected by gas lift holes; wherein, the stripping section is used for contacting and stripping of the second H2S-rich methanol 8, the first low-sulfur methanol 9-i and the third H2S-rich methanol 11 with nitrogen 12 respectively, to obtain stripping gas and stripped H2S-rich methanol 13; the washing section is used for third washing of the stripping gas with second CO2-rich methanol 15, to obtain tail gas 16 and the third H2S-rich methanol 11.

[0071] According to the present application, preferably, as shown in Figure 1As shown, the low-pressure flash tower T-4 is used to perform the fourth flash of the third CO2 flash liquid 6-iii, to obtain the second CO2 product gas 14 and the second CO2-rich methanol 15.

[0072] According to the present application, preferably, as shown in Fig. 1, the pipeline connecting the CO2 flash section and the first flash section is provided with a first cooler E-1, which is used to perform the first flash of the first CO2 flash liquid 6-i after the first cooling. Figure 1

[0073] According to the present application, preferably, as shown in Fig. 1, the pipeline connecting the CO2 flash section and the second flash section is provided with a second cooler E-2, which is used to perform the second flash of the second CO2 flash liquid 6-ii after the second cooling. Figure 1

[0074] According to the present application, preferably, as shown in Fig. 1, the pipeline connecting the H2S flash section and the third flash section is provided with a third cooler E-3, which is used to perform the third flash of the H2S flash liquid 2 after the third cooling. Figure 1

[0075] According to the present application, preferably, as shown in Fig. 1, the pipeline connecting the low-pressure flash tower T-4 and the washing section is provided with a fourth cooler E-4, which is used to perform the third washing of the second CO2-rich methanol 15 after the fourth cooling. Figure 1

[0076] According to the present application, preferably, as shown in Fig. 1, the pipeline connecting the washing section and the stripping section is provided with a first heat exchanger Q-1, which is used to perform the stripping of the third H2S-rich methanol 11 after the first heat exchange. Figure 1

[0077] According to the present application, preferably, as shown in Fig. 1, the pipeline connecting the third flash section and the stripping section is provided with a second heat exchanger Q-2, which is used to perform the stripping of the second H2S-rich methanol 8 after the second heat exchange. Figure 1

[0078] According to the present application, preferably, as shown in Fig. 1, the pipeline connecting the first flash section and the CO2 washing section is provided with a pump P, which is used to perform the pressurization of the semi-lean liquid methanol 7, to divide the semi-lean liquid methanol 7 into the first semi-lean liquid methanol 7-i and the second semi-lean liquid methanol 7-ii. Figure 1

[0079] The present application will be described in detail below through examples.

[0080] ​​​​​​​The first H2S-rich methanol is obtained by H2S absorption from the synthesis gas from the pulverized coal gasification device, the first CO2-rich methanol is obtained by H2S absorption and CO2 absorption from the synthesis gas from the pulverized coal gasification device in sequence, and the non-shift H2S-rich methanol is obtained by the non-shift gas purification process from the non-shift gas from the pulverized coal gasification device.

[0081] Embodiment 1

[0082] The H2S medium-pressure flash tower T-1 is divided into an H2S flash section and an H2S washing section from bottom to top, the H2S flash section is used for H2S flashing (pressure: 0.8-1 MPa(G)) of the first H2S-rich methanol 1 (molar content of H2S: 0.4-0.6%, molar content of CO2: 24-29%, temperature: -20 to -14℃, pressure: 3.05-3.1 MPa(G)), to obtain H2S flash gas and H2S flash liquid 2 (molar content of H2S: 0.35-0.55%, molar content of CO2: 23.5-28.5%, temperature: -16 to -22℃); the H2S washing section is used for first washing of the H2S flash gas and the non-shift H2S-rich methanol 3, to obtain washed H2S flash gas 4 (molar content of H2S: 0.6-0.8%, molar content of CO2: 25-30%, temperature: -30 to -20℃, pressure: 0.8-1 MPa(G)), and the first washing liquid obtained is mixed into the H2S flash liquid 2;

[0083] The CO2 medium-pressure flash tower T-2 is divided into a CO2 flash section and a CO2 washing section from bottom to top; wherein, the CO2 flash section is used for CO2 flashing (pressure: 0.8-1 MPa(G)) of the first CO2-rich methanol 5 (molar content of H2S: 0.1-0.5ppm, molar content of CO2: 18-23%, temperature: -22 to -18℃, pressure: 3.05-3.09 MPa(G)), to obtain CO2 flash gas and CO2 flash liquid 6; the CO2 washing section is used for second washing of the first semi-lean liquid methanol 7-i and the CO2 flash gas, to obtain washed CO2 flash gas 17 (molar content of H2S: 0.1-0.5ppm, molar content of CO2: 48-52%, temperature: -36 to -30℃, pressure: 0.8-1 MPa(G)), and the second washing liquid obtained is mixed into the CO2 flash liquid 6;

[0084] The CO2 flash liquid 6 is divided into the first CO2 flash liquid 6-i, the second CO2 flash liquid 6-ii and the third CO2 flash liquid 6-iii with a molar flow ratio of 2-4:1:1-2;

[0085] The reabsorption tower T-3 is divided into an upper tower and a lower tower, the upper tower is divided into a first flash evaporation section, a second flash evaporation section and a third flash evaporation section which are connected by riser holes, and the lower tower is divided into a stripping section and a washing section from bottom to top which are connected by riser holes;

[0086] The first flash evaporation section is used for flash evaporation of the first CO2 flash liquid 6-i after being cooled to -36 to -30°C to obtain a first CO2 product gas and a semi-lean liquid methanol 7 (the molar content of H2S is 0.1-0.5 ppm, the molar content of CO2 is 10-14%, and the temperature is -58.5 to -52.5°C); the second flash evaporation section is used for flash evaporation of the second CO2 flash liquid 6-ii after being cooled to -52 to -50°C to obtain a second CO2 product gas and a flash liquid; the third flash evaporation section is used for flash evaporation of the H2S flash liquid 2 after being cooled to -36 to -30°C to obtain a sulfur-containing gas phase and a second H2S-rich methanol 8 (the molar content of H2S is 0.4-0.6%, the molar content of CO2 is 12-16%, and the temperature is -65 to -55°C); the flash liquid and the sulfur-containing gas phase are subjected to a fourth washing to obtain a low-sulfur methanol 9 (the molar content of H2S is 0.2-0.3%, the molar content of CO2 is 9-14%, and the temperature is -58 to -54°C), and the third CO2 product gas is mixed with the first CO2 product gas and the second CO2 product gas to obtain a first CO2 product gas 10 (the molar content of H2S is ≤1 ppm, the molar content of CO2 is 99.4-99.7%, and the temperature is -65 to -55°C);

[0087] The semi-lean liquid methanol 7 is pressurized to 1-1.2 MPa(G) and divided into a first semi-lean liquid methanol 7-i and a second semi-lean liquid methanol 7-ii with a molar flow ratio of 1:10-12; the low-sulfur methanol 9 is divided into a first low-sulfur methanol 9-i and a second low-sulfur methanol 9-ii with a molar flow ratio of 1-1.05:1;

[0088] The stripping section is used for contacting and stripping each of the second H2S-rich methanol 8 (second heat exchange is -36 to -30°C), the first low-sulfur methanol 9-i and the third H2S-rich methanol 11 (first heat exchange is -40 to -36°C) with nitrogen 12, to obtain stripping gas and H2S-rich methanol 13 after stripping (molar content of H2S is 0.2-0.5%, molar content of CO2 is 1-5%; temperature is -52 to -48°C); the washing section is used for third washing of the above stripping gas with the second CO2-rich methanol 15 (after fourth cooling, -50 to -47°C), to obtain tail gas 16 (molar content of H2S is ≤1ppm, molar content of CO2 is 70-74%; temperature is -62 to -58°C) and the third H2S-rich methanol 11 (molar content of H2S is 0.1-0.3%, molar content of CO2 is 10-13%; temperature is -58 to -55°C);

[0089] The low-pressure flash tower T-4 is used for fourth flashing of the third CO2 flash liquid 6-iii (pressure is 0.5MPa(G)), to obtain the second CO2 product gas 14 (molar content of H2S is ≤1ppm, molar content of CO2 is 99-99.5%; temperature is -34 to -30°C) and the second CO2-rich methanol 15 (molar content of H2S is 0.1-0.5ppm, molar content of CO2 is 13-18%, temperature is -35 to -30°C).

[0090] Comparative Example 1

[0091] Taking a hydrogen production device using a pulverized coal gasification gasification as an example, the effective gas (H2+CO) entering the low-temperature methanol washing device is 161000Nm 3 / h, and the main parameters of the technology of the lean-lean process (i.e., CN201110260570.0 discloses a low-temperature methanol washing process) are compared with the above baseline, as shown in Table 1.

[0092] Table 1

[0093]

[0094] As can be seen from the results in Table 1, taking a hydrogen production device based on a pulverized coal gasification gasification as an example, the low-temperature methanol washing flash and reabsorption technology of the pulverized coal gasification device provided in Example 1 uses the medium-pressure flash classification washing technology, the CO2 flash liquid substock subpressure flash technology and the multi-stage tail gas washing technology, and the cumulative external cold consumption is reduced by 500KW / h, and the overall energy saving effect is remarkable.

[0095] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that each technical feature is combined in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method for low-temperature methanol washing flash evaporation and reabsorption in conjunction with a pulverized coal gasification unit, characterized in that, The method includes: The syngas from the pulverized coal gasification unit is subjected to H2S absorption to obtain the first H2S-rich methanol (1), and the obtained desulfurized gas is subjected to CO2 absorption to obtain the first CO2-rich methanol (5). The first H2S-rich methanol (1) was subjected to H2S flash evaporation to obtain H2S flash liquid (2) and H2S flash vapor; the first CO2-rich methanol (5) was subjected to CO2 flash evaporation to obtain CO2 flash liquid (6) which was divided into three streams and CO2 flash vapor. The first CO2 flash liquid (6-i), the second CO2 flash liquid (6-ii), and the H2S flash liquid (2) are subjected to first flash evaporation, second flash evaporation, and third flash evaporation, respectively, to obtain semi-lean methanol (7) split into two streams, low-sulfur methanol (9) split into two streams, second H2S-rich methanol (8), and first CO2 product gas (10); the third CO2 flash liquid (6-iii) is subjected to fourth flash evaporation to obtain second CO2-rich methanol (15) and second CO2 product gas (14); The H2S flash vapor and the non-shift H2S-rich methanol (3) from the non-shift gas purification process are subjected to a first wash; the CO2 flash vapor and the first semi-lean methanol (7-i) are subjected to a second wash. In this process, the first low-sulfur methanol (9-i), the second H2S-rich methanol (8), the third H2S-rich methanol (11), and nitrogen (12) are contacted and stripped to obtain stripped gas; the third H2S-rich methanol (11) is obtained by the second CO2-rich methanol (15) and the stripped gas through a third washing process; the second low-sulfur methanol (9-ii) is returned to the H2S absorption, and the second semi-lean methanol (7-ii) is returned to the CO2 absorption.

2. The method according to claim 1, wherein, The first H2S-rich methanol (1) has a molar content of 0.4-0.6% for H2S, a molar content of 24-29% for CO2, a temperature of -20 to -14℃, and a pressure of 3.05-3.1 MPa (G). Preferably, the syngas contains 0.3-0.35% H2S and 40-50% CO2; the temperature is -25 to -15°C; and the pressure is 3.12-3.15 MPa(G). Preferably, the desulfurization gas has a molar content of H2S of 0.5-1 ppm and a molar content of CO2 of 34-38%; a temperature of -25 to -20°C; and a pressure of 3.05-3.1 MPa(G). Preferably, the molar content of H2S in the first CO2-rich methanol (5) is 0.1-0.5 ppm, the molar content of CO2 is 18-23%, the temperature is -22 to -18°C, and the pressure is 3.05-3.09 MPa(G); Preferably, the non-conversion H2S-rich methanol (3) has a molar content of 0.5-0.9% for H2S and a molar content of 3-7% for CO2; a temperature of -32 to -28°C; and a pressure of 3.5-3.55 MPa (G).

3. The method according to claim 1 or 2, wherein, The H2S flash liquid (2) contains 0.35-0.55% H2S and 23.5-28.5% CO2; the temperature is -16 to -22℃. Preferably, the pressure of H2S flash evaporation is 0.8-1 MPa(G); Preferably, the H2S flash vapor and non-conversion H2S-rich methanol (3) are subjected to the first washing to obtain washed H2S flash vapor (4), and the obtained first washing liquid is mixed into the H2S flash liquid (2); More preferably, the molar content of H2S in the washed H2S flash vapor (4) is 0.6-0.8%, the molar content of CO2 is 25-30%, the temperature is -30 to -20°C, and the pressure is 0.8-1 MPa (G).

4. The method according to any one of claims 1-3, wherein, The CO2 flash liquid (6) contains 0.1-0.5 ppm H2S and 17.5-22.5% CO2; the temperature is -25 to -20℃. Preferably, the molar flow ratio of the first CO2 flash liquid (6-i), the second CO2 flash liquid (6-ii), and the third CO2 flash liquid (6-iii) is 2-4:1:1-2; Preferably, the pressure of the CO2 flash evaporation is 0.8-1 MPa(G); Preferably, the CO2 flash vapor and the first semi-lean methanol (7-i) are subjected to the second washing to obtain washed CO2 flash vapor (17), and the obtained second washing liquid is mixed into the CO2 flash liquid (6); More preferably, the molar content of H2S in the washed CO2 flash vapor (17) is 0.1-0.5 ppm, the molar content of CO2 is 48-52%, the temperature is -36 to -30°C, and the pressure is 0.8-1 MPa (G).

5. The method according to any one of claims 1-4, wherein, The first CO2 flash liquid (6-i) is subjected to the first flash evaporation to obtain the first CO2 product gas and semi-lean methanol (7); the second CO2 flash liquid (6-ii) is subjected to the second flash evaporation to obtain the second CO2 product gas and flash liquid; the H2S flash liquid (2) is subjected to the third flash evaporation to obtain the sulfur-containing gas phase and the second H2S-rich methanol (8); wherein, the flash liquid and the sulfur-containing gas phase are subjected to the fourth washing to obtain the low-sulfur methanol (9) and the third CO2 product gas, and the third CO2 product gas, the first CO2 product gas and the second CO2 product gas are mixed to obtain the first CO2 product gas (10); Wherein, the pressure of the first flash evaporation is less than the pressure of the second flash evaporation and the pressure of the third flash evaporation; Preferably, 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); and the pressure of the third flash evaporation is 0.12-0.16 MPa(G). Preferably, the first CO2 flash liquid (6-i) is cooled to -36 to -30°C before the first flash evaporation is performed; Preferably, the second CO2 flash liquid (6-ii) is subjected to a second cooling to -52 to -50°C before the second flash evaporation is performed; Preferably, the H2S flash liquid (2) is subjected to a third cooling to -36 to -30°C before the third flash evaporation is performed; Preferably, the molar content of H2S in the semi-lean methanol (7) is 0.1-0.5 ppm, and the molar content of CO2 is 10-14%; the temperature is -58.5 to -52.5℃; more preferably, the molar flow ratio of the first semi-lean methanol (7-i) and the second semi-lean methanol (7-ii) is 1:10-12; More preferably, the semi-lean methanol (7) is pressurized to 1-1.2 MPa (G) and then divided into a first semi-lean methanol stream (7-i) and a second semi-lean methanol stream (7-ii); Preferably, the molar content of H2S in the low-sulfur methanol (9) is 0.2-0.3%, and the molar content of CO2 is 9-14%; the temperature is -58 to -54°C; more preferably, the molar flow ratio of the first stream of low-sulfur methanol (9-i) and the second stream of low-sulfur methanol (9-ii) is 1-1.05:1; Preferably, the molar content of H2S in the second H2S-rich methanol (8) is 0.4-0.6%, the molar content of CO2 is 12-16%, and the temperature is -65 to -55°C. Preferably, the molar content of H2S in the first CO2 product gas (10) is ≤1ppm, the molar content of CO2 is 99.4-99.7%, and the temperature is -65 to -55℃.

6. The method according to any one of claims 1-5, wherein, The gas stripping process includes: independently contacting the first low-sulfur methanol (9-i), the second H2S-rich methanol (8), and the third H2S-rich methanol (11) with nitrogen (12) and performing the gas stripping to obtain the stripped gas and the stripped H2S-rich methanol (13). Preferably, the third H2S-rich methanol (11) is subjected to a first heat exchange to a temperature of -40 to -36°C before the gas stripping is performed; Preferably, the second H2S-rich methanol (8) is subjected to a second heat exchange to a temperature of -36 to -30°C before the gas stripping is performed; Preferably, the molar content of H2S in the stripped H2S-rich methanol (13) is 0.2-0.5%, the molar content of CO2 is 1-5%, and the temperature is -52 to -48°C.

7. The method according to any one of claims 1-6, wherein, The second CO2-rich methanol (15) has a molar content of H2S of 0.1-0.5 ppm, a molar content of CO2 of 13-18%, and a temperature of -35 to -30°C. Preferably, the pressure of the fourth flash evaporation is 0.45-0.55 MPa(G); Preferably, the molar content of H2S in the second CO2 product gas (14) is ≤1ppm, and the molar content of CO2 is 99-99.5%; the temperature is -34 to -30℃.

8. The method according to any one of claims 1-7, wherein, The second CO2-rich methanol (15) is cooled to -50 to -47°C in the fourth step and then washed with the stripping gas in the third step to obtain tail gas (16) and third H2S-rich methanol (11). Preferably, the molar content of H2S in the exhaust gas (16) is ≤1ppm, the molar content of CO2 is 70-74%, and the temperature is -62 to -58℃; Preferably, the molar content of H2S in the third H2S-rich methanol (11) is 0.1-0.3%, the molar content of CO2 is 10-13%, and the temperature is -58 to -55°C.

9. A low-temperature methanol washing flash evaporation and reabsorption device for a pulverized coal gasification unit, characterized in that, The method described in any one of claims 1-8 is carried out in the apparatus, which comprises: a medium-pressure flash evaporator for H2S (T-1), a medium-pressure flash evaporator for CO2 (T-2), a reabsorption tower (T-3), and a low-pressure flash evaporator (T-4); The H2S medium-pressure flash evaporator (T-1) is divided into an H2S flash section and an H2S washing section from bottom to top; the CO2 medium-pressure flash evaporator (T-2) is divided into a CO2 flash section and a CO2 washing section from bottom to top; the reabsorption tower (T-3) is divided into an upper tower and a lower tower. The upper tower is divided into a first flash section, a second flash section, and a third flash section connected by air risers from top to bottom; the lower tower is divided into a stripping section and a washing section connected by air risers from bottom to top. The H2S flash section and the third flash section are connected by pipelines; the CO2 flash section is connected by pipelines to the first flash section, the second flash section, and the low-pressure flash tower (T-4); the first flash section and the CO2 washing section are connected by pipelines; the second flash section and the third flash section are connected by pipelines to the stripping section; the low-pressure flash tower (T-4) and the washing section are connected by pipelines; and the washing section and the stripping section are connected by pipelines.

10. The apparatus according to claim 9, wherein, A first cooler (E-1) is installed on the pipe connecting the CO2 flash section and the first flash section; Preferably, a second cooler (E-2) is provided on the pipe connecting the CO2 flash section and the second flash section; Preferably, a third cooler (E-3) is provided on the pipe connecting the H2S flash section and the third flash section; Preferably, a fourth cooler (E-4) is installed on the pipe connecting the low-pressure flash evaporator (T-4) and the washing section; Preferably, a first heat exchanger (Q-1) is installed on the pipeline connecting the washing section and the air-lift section; Preferably, a second heat exchanger (Q-2) is installed on the pipeline connecting the third flash section and the stripping section; Preferably, a pump (P) is installed on the pipeline connecting the first flash section and the CO2 washing section.

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