A system and method for separating CO2 from methanol-rich liquid in a low-temperature methanol washing system

Abstract

The present invention provides a system and method for separating CO2 from methanol-rich liquid in a low-temperature methanol washing system, and belongs to the technical field of gas purification of coal chemical plants. The separation system of the present invention can separate and recover high-purity and high-yield CO2 by connecting a first CO2 desorption tower, a second CO2 desorption tower and a hydrogen sulfide concentration tower in series, and adding a flash section to the gas stripping tower, which is beneficial to the reuse of CO2 and can reduce the nitrogen consumption of the hydrogen sulfide concentration tower by about 15-20%. In addition, the system of the present invention does not require a large amount of tail gas post-processing equipment, is economical and environmentally friendly, has low operating costs, is easy to operate, and is safe and feasible.

Description

Technical Field

[0001] The invention belongs to the technical field of gas purification in coal chemical plants, and in particular relates to a system and method for separating CO2 from methanol-rich liquid in a low-temperature methanol washing system. Background Art

[0002] In the low-temperature methanol washing device, the raw gas is washed with low-temperature methanol to obtain purified gas, and the CO2 and H2S in the raw gas are dissolved in methanol to obtain methanol-rich liquid. The methanol-rich liquid is depressurized and CO2 is desorbed in the CO2 desorption tower. The purity of the analyzed CO2 is above 98.5%, which is used to meet the demand for CO2 in coal transportation, synthetic urea or soda ash production. Due to the limitation of CO2 dissolved in the rich liquid, the output of high-concentration CO2 product gas obtained by decompression and heat exchange and temperature rise is certain, accounting for only about 50% of the CO2 in the raw gas. Some CO2 dissolved in methanol is desorbed by nitrogen stripping in the hydrogen sulfide concentration tower and the normal temperature stripping tower. This part of the desorbed CO2 has a low concentration due to mixing with N2, and is difficult to use, so it can only be discharged as tail gas.

[0003] The tail gas discharged from low-temperature methanol washing mainly consists of CO2 and N2, both of which are inert gases with similar chemical and physical properties. They can be separated in a liquefied state by different boiling points; small amounts of methanol, hydrogen sulfide, water and other components contained in the tail gas can be effectively removed by adsorption drying. Therefore, the most common method for recovering CO2 in the tail gas of low-temperature methanol washing is adsorption distillation. For example, Chinese patent document CN 111977654A discloses a device and process for recovering CO2 in a low-temperature methanol washing section. The device includes a pretreatment unit, a distillation unit and a propylene refrigeration unit. Through the coordinated cooperation of each unit, industrial-grade CO2 and food-grade CO2 can be co-produced. However, the above method requires additional large amounts of machinery and equipment and sites, which is time-consuming and labor-intensive, and reduces the economic benefits of the enterprise. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a system and method for separating CO2 from methanol-rich liquid in a low-temperature methanol washing system. Through the separation system of the present invention, high-purity and high-yield CO2 can be separated and recovered, which is conducive to the reuse of CO2 and can reduce the nitrogen consumption of the hydrogen sulfide concentration tower by about 15-20%. In addition, the system of the present invention does not require a large amount of tail gas post-processing equipment, which is economical and environmentally friendly.

[0005] One object of the present invention is to provide a system for separating CO2 from methanol-rich liquid in a low-temperature methanol washing system, the separation system comprising:

[0006] The first CO2 desorption tower includes a D desorption section, a C desorption section, a B desorption section and an A desorption section which are arranged from top to bottom and are gas-connected, so that the desorption gas from the lower desorption section rises and enters the upper desorption section for washing and impurity removal; wherein,

[0007] The A desorption section is configured to decompress and desorb CO2 in the desorption liquid output from the H desorption section of the hydrogen sulfide concentration tower to obtain the A section desorption liquid;

[0008] The B desorption section is configured to decompress and desorb the CO2 in the A-section desorption liquid to obtain the B-section desorption liquid;

[0009] The C desorption section is configured to decompress and desorb CO2 in the sulfur-rich methanol, and introduce sulfur-free rich methanol for washing the CO2 desorption gas in the desorption section C at its upper part to obtain a C section desorption liquid;

[0010] The D desorption section is configured to decompress and desorb CO2 in the sulfur-free rich methanol to obtain a D section desorption liquid and a first CO2 desorption gas discharged from the top;

[0011] The second CO2 desorption tower includes a F desorption section and an E desorption section which are arranged from top to bottom and are gas-phase connected, so that the desorption gas from the lower desorption section rises and enters the upper desorption section for washing and impurity removal; wherein,

[0012] The E desorption stage is configured to decompress and desorb the CO2 in the B stage desorption liquid to obtain the E stage desorption liquid;

[0013] The F desorption section is configured to decompress and desorb the CO2 in the C section desorption liquid to obtain the F section desorption liquid and the second CO2 desorption gas discharged from the top, and wash the second CO2 desorption gas before or after it is discharged to remove sulfur element therein;

[0014] A hydrogen sulfide concentration tower, comprising an I desorption section, an H desorption section and a G stripping section arranged from top to bottom, wherein the H desorption section and the G stripping section are gas-connected to each other, so that the stripping gas from the lower stripping section rises and enters the upper desorption section for washing and impurity removal;

[0015] The I desorption stage is configured to desorb CO2 in the D stage desorption liquid by reducing pressure to obtain the I stage desorption liquid as semi-lean methanol discharged from the bottom and the third CO2 desorption gas discharged from the top;

[0016] The G stripping section is configured to further strip the CO2 in the E-stage desorption liquid by using nitrogen and the first stripping gas while decompressing and desorbing the CO2 in the E-stage desorption liquid to obtain the G-stage stripping liquid and the second stripping gas;

[0017] The H desorption section is configured to desorb CO2 in the F desorption liquid under reduced pressure, and introduce part of the I desorption liquid for washing the gas phase in the H desorption section into the upper part thereof to obtain the H desorption liquid and the third stripping gas discharged from the top;

[0018] A stripping tower, comprising a K stripping section and a J stripping section arranged from top to bottom; wherein the K stripping section is configured to decompress and desorb CO2 in the G stripping liquid to obtain the K stripping liquid and send the obtained stripping gas to the first CO2 stripping tower for washing to remove the sulfur element therein; the J stripping section is configured to strip the K stripping liquid with nitrogen to discharge the J stripping liquid as sulfur-rich methanol and the first stripping gas sent to the G stripping section.

[0019] In some embodiments, a D-stage desorption liquid feed pipe is further provided at the upper portion of the F desorption stage, which is used to introduce part of the D-stage desorption liquid to wash the second CO2 desorption gas to be discharged to remove the sulfur element therein, that is, to wash the second CO2 desorption gas before it is discharged to remove the sulfur element therein;

[0020] The desorbed gas from the K desorption section is sent to the B desorption section via a pipeline.

[0021] In some embodiments, the system further includes a first booster pump and a first heat exchanger; wherein the first booster pump is used to boost the first mixed gas of the second CO2 desorption gas and the third CO2 desorption gas that has been heated by heat exchange in the first heat exchanger to obtain the first pressurized mixed gas; the first heat exchanger is used to heat exchange and cool the second mixed gas obtained by mixing the pressurized first mixed gas and the K-stage desorption gas with the first mixed gas before pressurization, and send the cooled second mixed gas to the C desorption stage to wash and remove the sulfur element therein, that is, wash the second CO2 desorption gas after it is discharged to remove the sulfur element therein.

[0022] In some embodiments, the pipeline for delivering the H-section desorption liquid into the A-section desorption liquid is further provided with a third booster pump and a third heat exchanger for heating the conveyed material; the pipeline for delivering the A-section desorption liquid into the B-section desorption liquid is further provided with a fourth booster pump and a fourth heat exchanger for heating the conveyed material; the pipeline for delivering the G-section stripping liquid into the K-section desorption liquid is further provided with a fifth booster pump and a fifth heat exchanger for heating the conveyed material; the pipeline for delivering the E-section desorption liquid into the G-stripping liquid is further provided with a sixth booster pump; the pipeline for delivering the F-section desorption liquid into the H-desorption liquid is further provided with a seventh booster pump; the pipeline for delivering the J-section stripping liquid to the outside of the system is further provided with an eighth booster pump.

[0023] In some embodiments, on the side wall of the C desorption section, a pipeline for inputting sulfur-free rich methanol, a pipeline for inputting sulfur-containing rich methanol, a pipeline for inputting the second mixed gas, and a pipeline for outputting the C section desorption liquid are arranged in sequence from top to bottom.

[0024] In some embodiments, on the side wall of the G stripping section, the pipeline for inputting the first stripping gas is located above the pipeline for inputting nitrogen.

[0025] In some embodiments, the system further includes a second booster pump and a second heat exchanger, wherein the second heat exchanger is used to exchange heat and cool the conversion gas as the raw gas to be entered into the low-temperature methanol washing system to remove sulfur and CO2 with the materials transported by the first gas pipeline, the second gas pipeline and the third gas pipeline, wherein the first gas pipeline is used to heat the first CO2 desorbed gas from the D desorption section through the second heat exchanger to recover cold and then send it out as a high-pressure CO2 product gas, the second gas pipeline is used to heat the third stripping gas and the second stripping gas from the H desorption section through the second heat exchanger to recover cold and then send it out as tail gas, and the third gas pipeline is used to heat the second CO2 desorbed gas from the F desorption section and the third CO2 desorbed gas from the I desorption section through the second heat exchanger to recover cold and then send them out as a low-pressure CO2 product gas; the second booster pump is used to pressurize the low-pressure CO2 product gas after heat exchange to obtain a high-pressure CO2 product gas.

[0026] In some embodiments, the system also includes a second heat exchanger, which is used to exchange heat and cool the conversion gas as the raw gas to be entered into the low-temperature methanol washing system to remove sulfur and CO2 with the materials transported by the first gas pipe and the second gas pipe, wherein the first gas pipe is used to heat the first CO2 desorption gas and the second mixed gas from the D desorption section through the second heat exchanger to recover the cold and then send it out as a high-pressure CO2 product gas, and the second gas pipe is used to heat the third stripping gas and the second stripping gas from the H desorption section through the second heat exchanger to recover the cold and then send it out as exhaust gas.

[0027] Another object of the present invention is to provide a method for separating and recovering CO2 in methanol-rich liquid in a low-temperature methanol washing system using any of the separation systems described above.

[0028] In some embodiments, the operating pressure of the D desorption section is 0.27-0.29 MPa(A), the operating pressure of the F desorption section is 0.17-0.19 MPa(A), and the operating pressure of the I desorption section is 0.17-0.19 MPa(A).

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The system of the present invention can separate and recover high-purity (more than 98.5%) and high-yield CO2 (more than 50%) by arranging a first CO2 desorption tower, a second CO2 desorption tower and a hydrogen sulfide concentration tower in series, and adding a flash evaporation section to the gas stripping tower, which is beneficial to the reuse of CO2 and can reduce the amount of gas stripping nitrogen used in the hydrogen sulfide concentration tower by about 15-20%. In addition, the system of the present invention does not require a large amount of tail gas post-processing equipment, is economical and environmentally friendly, has low operating costs, is easy to operate, and is safe and feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the structure of a system for separating CO2 from methanol-rich liquid in a low-temperature methanol washing system in one embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the structure of a system for separating CO2 from methanol-rich liquid in a low-temperature methanol washing system in another embodiment of the present invention;

[0033] Figure 3 It is a schematic diagram of the structure of the separation system of CO2 in the methanol-rich liquid in the low-temperature methanol washing system in the comparative example of the present invention;

[0034] The reference numerals in the figure are as follows: 1: first CO2 desorption tower; 2: second CO2 desorption tower; 3: hydrogen sulfide concentration tower; 4: stripping tower; 5: first booster pump; 6: first heat exchanger; 7: third booster pump; 8: third heat exchanger; 9: fourth booster pump; 10: fourth heat exchanger; 11: fifth booster pump; 12: fifth heat exchanger; 13: sixth booster pump; 14: seventh booster pump; 15: eighth Booster pump; 16: second booster pump; 17: second heat exchanger; 18: first gas pipeline; 19: second gas pipeline; 20: third gas pipeline; 21: A desorption section; 22: B desorption section; 23: C desorption section; 24: D desorption section; 25: E desorption section; 26: F desorption section; 27: G stripping section; 28: H desorption section; 29: I desorption section; 30: J stripping section; 31: K desorption section. DETAILED DESCRIPTION

[0035] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0036] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", "bottom", "top" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", "fourth" and the like are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0037] Unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] In one embodiment, the separation system of CO2 in the methanol rich liquid in the low temperature methanol washing system is described in detail. Figure 1 ,include:

[0039] The first CO2 desorption tower 1 includes a D desorption section 24, a C desorption section 23, a B desorption section 22 and an A desorption section 21 which are arranged from top to bottom and are gas-phase connected, so that the desorption gas in the lower desorption section rises and enters the upper desorption section for washing and impurity removal; wherein,

[0040] The A desorption section 21 is configured to decompress and desorb CO2 in the desorption liquid output from the H desorption section 28 of the hydrogen sulfide concentration tower 3 to obtain the A section desorption liquid;

[0041] The B desorption section 22 is configured to decompress and desorb the CO2 in the A section desorption liquid to obtain the B section desorption liquid;

[0042] The C desorption section 23 is configured to desorb CO2 in the sulfur-rich methanol under reduced pressure, and

[0043] Introducing sulfur-free and rich methanol for washing CO2 desorption gas in C desorption section 23 at its upper part to obtain C desorption liquid;

[0044] The D desorption section 24 is configured to desorb CO2 in the sulfur-free rich methanol under reduced pressure to obtain a D section desorption liquid and a first CO2 desorption gas discharged from the top;

[0045] The second CO2 desorption tower 2 includes an F desorption section 26 and an E desorption section 25 which are arranged from top to bottom and are gas-phase connected, so that the desorption gas from the lower desorption section rises and enters the upper desorption section for washing and impurity removal; wherein,

[0046] The E desorption section 25 is configured to decompress and desorb the CO2 in the B-section desorption liquid to obtain the E-section desorption liquid;

[0047] The F desorption section is configured to decompress and desorb the CO2 in the C section desorption liquid to obtain the F section desorption liquid and the second CO2 desorption gas discharged from the top, and wash the second CO2 desorption gas before or after it is discharged to remove sulfur element therein;

[0048] The hydrogen sulfide concentration tower 3 comprises an I desorption section 29, an H desorption section 28 and a G stripping section 27 arranged from top to bottom, wherein the H desorption section 28 is gas-connected with the G stripping section 27 so that the stripping gas from the lower stripping section rises and enters the upper desorption section for washing and impurity removal;

[0049] The I desorption stage 29 is configured to desorb CO2 in the D stage desorption liquid under reduced pressure to obtain the I stage desorption liquid as semi-lean methanol discharged from the bottom and the third CO2 desorption gas discharged from the top;

[0050] The G stripping section 27 is configured to further strip the CO2 in the E-stage desorption liquid by using nitrogen and the first stripping gas while decompressing and desorbing the CO2 in the E-stage desorption liquid to obtain the G-stage stripping liquid and the second stripping gas;

[0051] The H desorption section 28 is configured to decompress and desorb the CO2 in the F desorption liquid, and

[0052] Introducing part of the I-stage desorption liquid used for washing the gas phase in the H-stage desorption stage at the upper part thereof to obtain the H-stage desorption liquid and the third stripping gas discharged from the top;

[0053] The stripping tower 4 includes a K desorption section 31 and a J stripping section 30 arranged from top to bottom; wherein the K desorption 31 is configured to decompress and desorb the CO2 in the G-section stripping liquid to obtain the K-section stripping liquid and send the obtained stripping gas to the first CO2 desorption tower 1 for washing to remove the sulfur element therein; the J stripping section 30 is configured to strip the K-section desorption liquid with nitrogen to discharge the J-section stripping liquid as sulfur-containing and methanol-rich and the first stripping gas sent to the G stripping section 27.

[0054] Furthermore, a D-stage desorption liquid feed pipe is provided at the upper portion of the F desorption section 26, for introducing part of the D-stage desorption liquid to wash the second CO2 desorption gas to be discharged to remove the sulfur element therein, that is, to wash the second CO2 desorption gas before it is discharged to remove the sulfur element therein; the desorption gas of the K desorption section 31 is fed into the B desorption section 22 via a pipeline.

[0055] Furthermore, a third booster pump 7 and a third heat exchanger 8 for heating the conveyed material are provided on the pipeline for conveying the desorption liquid of section H into the desorption liquid of section A 21; a fourth booster pump 9 and a fourth heat exchanger 10 for heating the conveyed material are provided on the pipeline for conveying the desorption liquid of section A into the desorption liquid of section B 22; a fifth booster pump 11 and a fifth heat exchanger 12 for heating the conveyed material are provided on the pipeline for conveying the stripping liquid of section G into the desorption liquid of section K 31; a sixth booster pump 13 is provided on the pipeline for conveying the desorption liquid of section E into the stripping liquid of section G 27; a seventh booster pump 14 is provided on the pipeline for conveying the desorption liquid of section F into the desorption liquid of section H 28; an eighth booster pump 15 is provided on the pipeline for conveying the stripping liquid of section J to the outside of the system.

[0056] Furthermore, on the side wall of the G stripping section 27, a pipeline for inputting the first stripping gas is located above a pipeline for inputting nitrogen.

[0057] Furthermore, the system also includes a second booster pump 16 and a second heat exchanger 17, wherein the second heat exchanger 17 is used to exchange heat and cool the converted gas as the raw gas to be introduced into the low-temperature methanol washing system to remove sulfur and CO2 with the materials transported by the first gas pipeline 18, the second gas pipeline 19 and the third gas pipeline 20, wherein the first gas pipeline 18 is used to heat the first CO2 desorbed gas from the D desorption section 24 through the second heat exchanger 17 to recover the cold and then send it out as a high-pressure CO2 product gas, The second gas pipeline 19 is used to transfer the third stripping gas and the second stripping gas from the H desorption section 28 through the second heat exchanger 17 to recover the cold and then send them out as exhaust gas; the third gas pipeline 20 is used to transfer the second CO2 desorption gas from the F desorption section 26 and the third CO2 desorption gas from the I desorption section 29 through the second heat exchanger 17 to recover the cold and then send them out as low-pressure CO2 product gas; the second booster pump 16 is used to pressurize the low-pressure CO2 product gas after heat exchange to obtain high-pressure CO2 product gas.

[0058] When the system is in operation, the method for separating and recovering CO2 in the methanol-rich liquid in the low-temperature methanol washing system comprises the following steps:

[0059] 1) The desorption liquid output from the H desorption section 28 of the hydrogen sulfide concentration tower 3 is fed into the A desorption section 21, and the CO2 in the desorption liquid is desorbed under reduced pressure to obtain the A section desorption liquid; the A section desorption liquid is fed into the B desorption section 22, and the CO2 in the A section desorption liquid is desorbed under reduced pressure to obtain the B section desorption liquid; the sulfur-containing rich methanol is fed into the C desorption section 23, and the CO2 in the sulfur-containing rich methanol is desorbed under reduced pressure, and sulfur-free rich methanol for washing the CO2 desorption gas in the C desorption section 23 is introduced into the upper part of the C desorption section 23 to obtain the C section desorption liquid; at the same time, the sulfur-free rich methanol is fed into the D desorption section 24, and the CO2 in the sulfur-free rich methanol is desorbed under reduced pressure to obtain the D section desorption liquid and the first CO2 desorption gas discharged from the top;

[0060] 2) The B-stage desorption liquid is sent to the E-stage desorption stage 25, and the CO2 in the B-stage desorption liquid is desorbed under reduced pressure to obtain the E-stage desorption liquid; the C-stage desorption liquid is sent to the F-stage desorption stage 26, and the CO2 in the C-stage desorption liquid is desorbed under reduced pressure to obtain the F-stage desorption liquid and the second CO2 desorption gas discharged from the top, and the second CO2 desorption gas is washed before or after it is discharged to remove sulfur element therein;

[0061] 3) The D-stage desorption liquid is fed into the I-desorption section 29, and the CO2 in the D-stage desorption liquid is desorbed under reduced pressure to obtain the I-stage desorption liquid as semi-lean methanol discharged from the bottom and the third CO2 desorption gas discharged from the top; the E-stage desorption liquid is fed into the G-stripping section 27, and while the CO2 in the E-stage desorption liquid is desorbed under reduced pressure, the CO2 in the E-stage desorption liquid is further stripped using nitrogen and the first stripping gas to obtain the G-stage stripping liquid and the second stripping gas; at the same time, the F-stage desorption liquid is fed into the H-desorption section 28, and the CO2 in the F-stage desorption liquid is desorbed under reduced pressure, and part of the I-stage desorption liquid used to wash the gas phase in the H-desorption section 28 is introduced into the upper part thereof to obtain the H-stage desorption liquid and the third stripping gas discharged from the top;

[0062] 4) The G-section stripping liquid is fed into the K desorption section 31, and the CO2 in the G-section stripping liquid is decompressed and desorbed to obtain the K-section stripping liquid and the obtained desorption gas is fed into the first CO2 desorption tower 1 for washing to remove the sulfur element therein; the K-section stripping liquid and nitrogen are fed into the J stripping section 30, and the K-section stripping liquid is stripped to discharge the J-section stripping liquid as sulfur-rich methanol and the first stripping gas to be fed to the G stripping section 27.

[0063] Among them, the operating pressure of the D desorption section 24 is 0.27-0.29 MPa(A), the operating pressure of the F desorption section 26 is 0.17-0.19 MPa(A), and the operating pressure of the I desorption section 29 is 0.17-0.19 MPa(A).

[0064] In another embodiment, the separation system of CO2 in the methanol rich liquid in the low temperature methanol washing system is as follows: Figure 2 ,include:

[0065] The first CO2 desorption tower 1 includes a D desorption section 24, a C desorption section 23, a B desorption section 22 and an A desorption section 21 which are arranged from top to bottom and are gas-phase connected, so that the desorption gas in the lower desorption section rises and enters the upper desorption section for washing and impurity removal; wherein,

[0066] The A desorption section 21 is configured to decompress and desorb CO2 in the desorption liquid output from the H desorption section 28 of the hydrogen sulfide concentration tower 3 to obtain the A section desorption liquid;

[0067] The B desorption section 22 is configured to decompress and desorb the CO2 in the A section desorption liquid to obtain the B section desorption liquid;

[0068] The C desorption section 23 is configured to desorb CO2 in the sulfur-rich methanol under reduced pressure, and

[0069] Introducing sulfur-free and rich methanol for washing CO2 desorption gas in C desorption section 23 at its upper part to obtain C desorption liquid;

[0070] The D desorption section 24 is configured to desorb CO2 in the sulfur-free rich methanol under reduced pressure to obtain a D section desorption liquid and a first CO2 desorption gas discharged from the top;

[0071] The second CO2 desorption tower 2 includes an F desorption section 26 and an E desorption section 25 which are arranged from top to bottom and are gas-phase connected, so that the desorption gas from the lower desorption section rises and enters the upper desorption section for washing and impurity removal; wherein,

[0072] The E desorption section 25 is configured to decompress and desorb the CO2 in the B-section desorption liquid to obtain the E-section desorption liquid;

[0073] The F desorption section 26 is configured to decompress and desorb the CO2 in the C-stage desorption liquid to obtain the F-stage desorption liquid and the second CO2 desorption gas discharged from the top, and wash the second CO2 desorption gas before or after it is discharged to remove sulfur elements therein;

[0074] The hydrogen sulfide concentration tower 3 comprises an I desorption section 29, an H desorption section 28 and a G stripping section 27 arranged from top to bottom, wherein the H desorption section 28 is gas-connected with the G stripping section 27 so that the stripping gas from the lower stripping section rises and enters the upper desorption section for washing and impurity removal;

[0075] The I desorption stage 29 is configured to desorb CO2 in the D stage desorption liquid under reduced pressure to obtain the I stage desorption liquid as semi-lean methanol discharged from the bottom and the third CO2 desorption gas discharged from the top;

[0076] The G stripping section 27 is configured to further strip the CO2 in the E-stage desorption liquid by using nitrogen and the first stripping gas while decompressing and desorbing the CO2 in the E-stage desorption liquid to obtain the G-stage stripping liquid and the second stripping gas;

[0077] The H desorption section 28 is configured to decompress and desorb the CO2 in the F desorption liquid, and

[0078] Introducing part of the I-stage desorption liquid used for washing the gas phase in the H-stage desorption stage at the upper part thereof to obtain the H-stage desorption liquid and the third stripping gas discharged from the top;

[0079] The stripping tower 4 comprises a K desorption section 31 and a J stripping section 30 arranged from top to bottom; wherein the K desorption section 31 is configured to decompress and desorb the CO2 in the G-section stripping liquid to obtain the K-section desorption liquid and send the obtained desorption gas to the first CO2 desorption tower 1 for washing to remove the sulfur element therein; the J stripping section 30 is configured to strip the K-section desorption liquid with nitrogen to discharge the J-section stripping liquid as sulfur-containing and methanol-rich and the first stripping gas sent to the G stripping section 27.

[0080] Furthermore, the system also includes a first booster pump 5 and a first heat exchanger 6; wherein the first booster pump 5 is used to boost the first mixed gas of the second CO2 desorbed gas and the third CO2 desorbed gas that has been heated by heat exchange in the first heat exchanger 6 to obtain a first mixed gas after boosting; the first heat exchanger 6 is used to heat exchange and cool the second mixed gas obtained by mixing the boosted first mixed gas with the K-stage desorbed gas with the first mixed gas before boosting, and send the cooled second mixed gas to the C desorption stage 23 to wash and remove the sulfur element therein, that is, wash the second CO2 desorbed gas after it is discharged to remove the sulfur element therein.

[0081] Furthermore, a third booster pump 7 and a third heat exchanger 8 for heating the conveyed material are provided on the pipeline for conveying the desorption liquid of section H into the desorption liquid of section A 21; a fourth booster pump 9 and a fourth heat exchanger 10 for heating the conveyed material are provided on the pipeline for conveying the desorption liquid of section A into the desorption liquid of section B 22; a fifth booster pump 11 and a fifth heat exchanger 12 for heating the conveyed material are provided on the pipeline for conveying the stripping liquid of section G into the desorption liquid of section K 31; a sixth booster pump 13 is provided on the pipeline for conveying the desorption liquid of section E into the stripping liquid of section G 27; a seventh booster pump 14 is provided on the pipeline for conveying the desorption liquid of section F into the desorption liquid of section H 28; an eighth booster pump 15 is provided on the pipeline for conveying the stripping liquid of section J to the outside of the system.

[0082] Furthermore, on the side wall of the C desorption section 23, a pipeline for inputting sulfur-free rich methanol, a pipeline for inputting sulfur-containing rich methanol, a pipeline for inputting the second mixed gas and a pipeline for outputting the C section desorption liquid are arranged in sequence from top to bottom.

[0083] Furthermore, on the side wall of the G stripping section 27, a pipeline for inputting the first stripping gas is located above a pipeline for inputting nitrogen.

[0084] Furthermore, the system also includes a second heat exchanger 17, which is used to exchange heat and cool the conversion gas as the raw gas to be entered into the low-temperature methanol washing system to remove sulfur and CO2 with the materials transported by the first gas pipe 18 and the second gas pipe 19, wherein the first gas pipe 18 is used to heat the first CO2 desorption gas and the second mixed gas from the D desorption section 24 through the second heat exchanger 17 to recover the cold and then send it out as a high-pressure CO2 product gas, and the second gas pipe 19 is used to heat the third stripping gas and the second stripping gas from the H desorption section 28 through the second heat exchanger 17 to recover the cold and then send it out as exhaust gas.

[0085] When the system is in operation, the method for separating and recovering CO2 in the methanol-rich liquid in the low-temperature methanol washing system comprises the following steps:

[0086] 1) The desorption liquid output from the H desorption section 28 of the hydrogen sulfide concentration tower 3 is fed into the A desorption section 21, and the CO2 in the desorption liquid is desorbed under reduced pressure to obtain the A section desorption liquid; the A section desorption liquid is fed into the B desorption section 22, and the CO2 in the A section desorption liquid is desorbed under reduced pressure to obtain the B section desorption liquid; the sulfur-containing rich methanol is fed into the C desorption section 23, and the CO2 in the sulfur-containing rich methanol is desorbed under reduced pressure, and sulfur-free rich methanol for washing the CO2 desorption gas in the C desorption section 23 is introduced into the upper part of the C desorption section 23 to obtain the C section desorption liquid; at the same time, the sulfur-free rich methanol is fed into the D desorption section 24, and the CO2 in the sulfur-free rich methanol is desorbed under reduced pressure to obtain the D section desorption liquid and the first CO2 desorption gas discharged from the top;

[0087] 2) The B-stage desorption liquid is sent to the E-stage desorption stage 25, and the CO2 in the B-stage desorption liquid is desorbed under reduced pressure to obtain the E-stage desorption liquid; the C-stage desorption liquid is sent to the F-stage desorption stage 26, and the CO2 in the C-stage desorption liquid is desorbed under reduced pressure to obtain the F-stage desorption liquid and the second CO2 desorption gas discharged from the top, and the second CO2 desorption gas is washed before or after it is discharged to remove sulfur element therein;

[0088] 3) The D-stage desorption liquid is fed into the I-desorption section 29, and the CO2 in the D-stage desorption liquid is desorbed under reduced pressure to obtain the I-stage desorption liquid as semi-lean methanol discharged from the bottom and the third CO2 desorption gas discharged from the top; the E-stage desorption liquid is fed into the G-stripping section 27, and while the CO2 in the E-stage desorption liquid is desorbed under reduced pressure, the CO2 in the E-stage desorption liquid is further stripped using nitrogen and the first stripping gas to obtain the G-stage stripping liquid and the second stripping gas; at the same time, the F-stage desorption liquid is fed into the H-desorption section 28, and the CO2 in the F-stage desorption liquid is desorbed under reduced pressure, and part of the I-stage desorption liquid used to wash the gas phase in the H-desorption section 28 is introduced into the upper part thereof to obtain the H-stage desorption liquid and the third stripping gas discharged from the top;

[0089] 4) The G-section stripping liquid is fed into the K desorption section 31, and the CO2 in the G-section stripping liquid is decompressed and desorbed to obtain the K-section stripping liquid and the obtained desorption gas is fed into the first CO2 desorption tower 1 for washing to remove the sulfur element therein; the K-section stripping liquid and nitrogen are fed into the J stripping section 30, and the K-section stripping liquid is stripped to discharge the J-section stripping liquid as sulfur-rich methanol and the first stripping gas to be fed to the G stripping section 27.

[0090] Among them, the operating pressure of the D desorption section 24 is 0.27-0.29 MPa(A), the operating pressure of the F desorption section 26 is 0.17-0.19 MPa(A), and the operating pressure of the I desorption section 29 is 0.17-0.19 MPa(A).

[0091] The separation system and method of the present invention are further described below through specific examples.

[0092] Example 1

[0093] For the large-scale low-temperature methanol washing system supporting pulverized coal gasification, the raw gas is divided into conversion gas (flow rate 712560Nm 3 / h, CO2 content 42.31% mol) and unconverted gas (flow rate 209940Nm 3 / h, CO2 content 7.96% mol), the sulfur-free rich methanol and sulfur-containing rich methanol produced in the purification process of the raw gas are Figure 1 The separation system shown is used to recover CO2. The CO2 production (in terms of pure CO2) in the first CO2 desorption tower 1 and the hydrogen sulfide concentration tower 3 is 163950 Nm 3 / h, accounting for 51.52% of the CO2 content in the raw gas; the low-pressure CO2 product gas (in terms of pure CO2) obtained in the second CO2 desorption tower 2 is 63650Nm 3 / h, accounting for 20.00% of the CO2 in the raw gas; the CO2 gas obtained in the stripping tower 4 is 3560Nm 3 / h, accounting for 1.12% of the CO2 in the raw gas. The overall CO2 recovery rate reached 72.65%, and the output of high-concentration CO2 products increased significantly. At the same time, the amount of nitrogen stripping in the H2S concentration tower was reduced by about 15%.

[0094] Example 2

[0095] For the large-scale low-temperature methanol washing system supporting pulverized coal gasification, the raw gas is divided into conversion gas (flow rate 712560Nm 3 / h, CO2 content 42.31% mol) and unconverted gas (flow rate 209940Nm 3 / h, CO2 content 7.96% mol), the sulfur-free rich methanol and sulfur-containing rich methanol produced in the purification process of the raw gas are Figure 2 The separation system shown is used to recover CO2. The CO2 production (in terms of pure CO2) in the first CO2 desorption tower 1 and the hydrogen sulfide concentration tower 3 is 163950 Nm 3 / h, accounting for 51.52% of the CO2 content in the raw gas; the high-pressure CO2 product gas (in terms of pure CO2) obtained in the second CO2 desorption tower 2 is 67210Nm 3 / h, accounting for 21.12% of the CO2 in the raw gas; 3560Nm of CO2 gas is obtained in the stripping tower 4 3 / h, accounting for 1.12% of the CO2 in the raw gas. The overall CO2 recovery rate reached 73.76%, and the output of high-concentration CO2 products increased significantly. At the same time, the amount of nitrogen in the H2S concentration tower was reduced by about 20%.

[0096] Comparative Example

[0097] For the large-scale low-temperature methanol washing system supporting pulverized coal gasification, the raw gas is divided into conversion gas (flow rate 712560Nm 3 / h, CO2 content 42.31% mol) and unconverted gas (flow rate 209940Nm 3 / h, CO2 content 7.96% mol), the sulfur-free rich methanol and sulfur-containing rich methanol produced in the purification process of the raw gas are Figure 3The separation system shown is used to recover CO2, wherein the low-temperature methanol washing and absorbing rich liquid is subjected to medium-pressure flash evaporation to recover effective gas, and then enters the first CO2 desorption tower 1 for desorption and recovery of CO2 gas. A portion of the sulfur-free rich methanol enters the D desorption section 24 of the first CO2 desorption tower 1 for decompression desorption, and the sulfur-containing rich methanol enters the lower part of the C desorption section 23 of the first CO2 desorption tower 1 for decompression desorption, and another portion of the sulfur-free rich methanol enters the upper part of the C desorption section 23 of the first CO2 desorption tower 1, desorbing CO2 while washing the sulfide in the sulfur-containing desorption gas to ensure that the sulfur content in the CO2 product gas meets the requirements. The top operating pressure of the first CO2 desorption tower 1 is 0.27-0.29 MPa (A), and the desorbed D section desorption liquid is sent to the upper part of the hydrogen sulfide concentration tower 3 through the pressure difference, and the top operating pressure of the hydrogen sulfide concentration tower 3 is 0.17-0.19 MPa (A). The D-segment desorption liquid in the D-segment desorption section 24 of the first CO2 desorption tower 1 enters the I-segment desorption section 29 of the hydrogen sulfide concentration tower 3, the pressure is reduced, and part of the CO2 gas is desorbed. This CO2 gas is mixed with the gas in the H-segment desorption section of the hydrogen sulfide concentration tower 3 and then goes to the second heat exchanger 17 for heat exchange and is sent out as tail gas. The I-segment desorption liquid in the I-segment desorption section 29 of the hydrogen sulfide concentration tower 3 can be partially returned to the washing tower as semi-lean methanol, and partially to the upper part of the H-segment desorption section 28 of the hydrogen sulfide concentration tower 3 to wash the sulfide in the gas in the tower. The C-segment desorption liquid in the C-segment desorption section 23 of the first CO2 desorption tower 1 enters the lower part of the H-segment desorption section 28 of the hydrogen sulfide concentration tower 3, and the desorption effect is further increased under the action of nitrogen while desorbing under reduced pressure. CO2 is desorbed from the H-segment desorption liquid, and after being washed by the I-segment desorption liquid from the I-segment desorption section 29 of the hydrogen sulfide concentration tower 3, it is sent out as tail gas. The H-segment desorption liquid obtained in the H-stripping section 28 of the hydrogen sulfide concentration tower 3 is sent to the A-stripping section 21 of the first CO2 desorption tower 1 after heat exchange in the third heat exchanger 8, and part of the CO2 is desorbed by heating. The A-segment desorption liquid in the A-stripping section 21 of the first CO2 desorption tower 1 is returned to the B-stripping section 22 of the first CO2 desorption tower 1 after heat exchange in the fourth heat exchanger 10, and continues to desorb CO2 gas. The B-segment desorption liquid in the B-stripping section 22 of the first CO2 desorption tower 1 is sent to the G-stripping section 27 of the hydrogen sulfide concentration tower 3, where nitrogen is used for stripping. The G-stripping liquid in the G-stripping section of the hydrogen sulfide concentration tower 3 is heat exchanged to about 30°C and sent to the normal temperature stripping tower 4, where nitrogen is continued to be stripped at a higher temperature. The stripping liquid with a low CO2 content obtained at the bottom of the stripping tower 4 is sent to the heat regeneration system.

[0098] The CO2 product gas after heat exchange in the second heat exchanger 17 has a pressure of 0.23-0.24 MPaA and is sent out of the system.

[0099] The CO2 production (in pure CO2) in the first CO2 desorption tower 1 and the hydrogen sulfide concentration tower 3 is 163950Nm 3 / h, accounting for 51.52% of the CO2 in the raw gas. The overall CO2 recovery rate reached 51.52%. At the same time, the nitrogen stripping capacity of the H2S concentration tower was about 41000Nm 3 / h.

[0100] The above embodiments are only specific implementation methods of the present invention, which are used to illustrate the technical solutions of the present invention rather than to limit them. The protection scope of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the aforementioned embodiments, ordinary technicians in the field should understand that any technician familiar with the technical field can still modify the technical solutions recorded in the aforementioned embodiments within the technical scope disclosed by the present invention, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the protection scope of the present invention.

Claims

1. A system for separating CO2 from methanol-rich liquid in a low-temperature methanol washing system, characterized in that: The separation system comprises: The first CO2 desorption tower includes a D desorption section, a C desorption section, a B desorption section and an A desorption section which are arranged from top to bottom and are gas-connected, so that the desorption gas from the lower desorption section rises and enters the upper desorption section for washing and impurity removal; wherein, The A desorption section is configured to decompress and desorb CO2 in the desorption liquid output from the H desorption section of the hydrogen sulfide concentration tower to obtain the A section desorption liquid; The B desorption section is configured to decompress and desorb the CO2 in the A-section desorption liquid to obtain the B-section desorption liquid; The C desorption section is configured to decompress and desorb CO2 in the sulfur-rich methanol, and introduce sulfur-free rich methanol for washing the CO2 desorption gas in the desorption section C at its upper part to obtain a C section desorption liquid; and at the same time, the sulfur-free rich methanol is sent to the D desorption section; The D desorption section is configured to decompress and desorb the CO2 in the sulfur-free rich methanol to obtain a D section desorption liquid and a first CO2 desorption gas discharged from the top; The second CO2 desorption tower includes a F desorption section and an E desorption section which are arranged from top to bottom and are gas-phase connected, so that the desorption gas from the lower desorption section rises and enters the upper desorption section for washing and impurity removal; wherein, The E desorption stage is configured to decompress and desorb the CO2 in the B stage desorption liquid to obtain the E stage desorption liquid; The F desorption section is configured to decompress and desorb the CO2 in the C section desorption liquid to obtain the F section desorption liquid and the second CO2 desorption gas discharged from the top, and wash the second CO2 desorption gas before it is discharged to remove sulfur element therein; A hydrogen sulfide concentration tower, comprising an I desorption section, an H desorption section and a G stripping section arranged from top to bottom, wherein the H desorption section and the G stripping section are gas-connected to each other, so that the stripping gas from the lower stripping section rises and enters the upper desorption section for washing and impurity removal; The I desorption stage is configured to desorb CO2 in the D stage desorption liquid by reducing pressure to obtain the I stage desorption liquid as semi-lean methanol discharged from the bottom and the third CO2 desorption gas discharged from the top; The G stripping section is configured to further strip the CO2 in the E-stage desorption liquid by using nitrogen and the first stripping gas while decompressing and desorbing the CO2 in the E-stage desorption liquid to obtain the G-stage stripping liquid and the second stripping gas; The H desorption section is configured to desorb CO2 in the F desorption liquid under reduced pressure, and introduce part of the I desorption liquid for washing the gas phase in the H desorption section into the upper part thereof to obtain the H desorption liquid and the third stripping gas discharged from the top; A stripping tower, comprising a K stripping section and a J stripping section arranged from top to bottom; wherein the K stripping section is configured to decompress and desorb CO2 in the G stripping liquid to obtain the K stripping liquid and send the obtained stripping gas to the first CO2 stripping tower for washing to remove sulfur elements therein; the J stripping section is configured to strip the K stripping liquid with nitrogen to discharge the J stripping liquid as sulfur-rich methanol and the first stripping gas sent to the G stripping section; The upper part of the F desorption section is also provided with a D-section desorption liquid feed pipe for introducing part of the D-section desorption liquid to wash the second CO2 desorption gas to be discharged to remove sulfur elements therein; The desorbed gas from the K desorption section is sent to the B desorption section via a pipeline; The system also includes a second booster pump and a second heat exchanger, wherein the second heat exchanger is used to exchange heat and cool the conversion gas as the raw gas to be entered into the low-temperature methanol washing system to remove sulfur and CO2 with the materials transported by the first gas pipeline, the second gas pipeline and the third gas pipeline, wherein the first gas pipeline is used to heat the first CO2 desorbed gas from the D desorption section through the second heat exchanger to recover the cold and then send it out as a high-pressure CO2 product gas, the second gas pipeline is used to heat the third stripping gas and the second stripping gas from the H desorption section through the second heat exchanger to recover the cold and then send it out as tail gas, and the third gas pipeline is used to heat the second CO2 desorbed gas from the F desorption section and the third CO2 desorbed gas from the I desorption section through the second heat exchanger to recover the cold and then send them out as a low-pressure CO2 product gas; the second booster pump is used to pressurize the low-pressure CO2 product gas after heat exchange to obtain a high-pressure CO2 product gas.

2. The system for separating CO2 from methanol-rich liquid in a low-temperature methanol washing system according to claim 1, characterized in that: The pipeline for delivering the desorption liquid of section H to the desorption section A is also provided with a third booster pump and a third heat exchanger for heating the conveyed material; the pipeline for delivering the desorption liquid of section A to the desorption section B is also provided with a fourth booster pump and a fourth heat exchanger for heating the conveyed material; the pipeline for delivering the stripping liquid of section G to the desorption section K is also provided with a fifth booster pump and a fifth heat exchanger for heating the conveyed material; the pipeline for delivering the desorption liquid of section E to the stripping section G is also provided with a sixth booster pump; the pipeline for delivering the desorption liquid of section F to the desorption section H is also provided with a seventh booster pump; the pipeline for delivering the stripping liquid of section J to the outside of the system is also provided with an eighth booster pump.

3. The system for separating CO2 from methanol-rich liquid in a low-temperature methanol washing system according to claim 1, characterized in that: On the side wall of the G stripping section, a pipeline for inputting the first stripping gas is located above a pipeline for inputting nitrogen.

4. A method for separating and recovering CO2 from methanol-rich liquid in a low-temperature methanol washing system using the separation system according to any one of claims 1 to 3; wherein: 1) The desorption liquid output from the H desorption section of the hydrogen sulfide concentration tower is sent to the A desorption section, and the CO2 in the desorption liquid is desorbed under reduced pressure to obtain the A desorption liquid; the A desorption liquid is sent to the B desorption section, and the CO2 in the A desorption liquid is desorbed under reduced pressure to obtain the B desorption liquid; the sulfur-containing rich methanol is sent to the C desorption section, and the CO2 in the sulfur-containing rich methanol is desorbed under reduced pressure, and sulfur-free rich methanol for washing the CO2 desorption gas in the C desorption section is introduced into the upper part of the C desorption section to obtain the C desorption liquid; at the same time, the sulfur-free rich methanol is sent to the D desorption section, and the CO2 in the sulfur-free rich methanol is desorbed under reduced pressure to obtain the D desorption liquid and the first CO2 desorption gas discharged from the top; 2) The B-stage desorption liquid is sent to the E-stage desorption liquid, and the CO2 in the B-stage desorption liquid is depressurized and desorbed to obtain the E-stage desorption liquid; the C-stage desorption liquid is sent to the F-stage desorption liquid, and the CO2 in the C-stage desorption liquid is depressurized and desorbed to obtain the F-stage desorption liquid and the second CO2 desorption gas discharged from the top, and the second CO2 desorption gas is washed before it is discharged to remove the sulfur element therein; 3) The D-stage desorption liquid is fed into the I-stage desorption stage, and the CO2 in the D-stage desorption liquid is desorbed under reduced pressure to obtain the I-stage desorption liquid as semi-lean methanol discharged from the bottom and the third CO2 desorption gas discharged from the top; the E-stage desorption liquid is fed into the G-stripping stage, and while the CO2 in the E-stage desorption liquid is desorbed under reduced pressure, the CO2 in the E-stage desorption liquid is further stripped using nitrogen and the first stripping gas to obtain the G-stage stripping liquid and the second stripping gas; at the same time, the F-stage desorption liquid is fed into the H-stage desorption stage, and the CO2 in the F-stage desorption liquid is desorbed under reduced pressure, and part of the I-stage desorption liquid used for washing the gas phase in the H-stage desorption stage is introduced into the upper part thereof to obtain the H-stage desorption liquid and the third stripping gas discharged from the top; 4) sending the G-stage stripping liquid to the K-stage desorption stage, and decompressing and desorbing the CO2 in the G-stage stripping liquid to obtain the K-stage desorption liquid, and sending the obtained desorption gas to the first CO2 desorption tower for washing to remove the sulfur element therein; The K-stage desorption liquid and nitrogen are sent to the J-stage stripping stage, and the K-stage desorption liquid is stripped to discharge the J-stage stripping liquid as sulfur-containing and methanol-rich and the first stripping gas sent to the G-stage stripping stage.

5. The method according to claim 4, characterized in that The operating pressure of the D desorption section is 0.27-0.29 MPa, the operating pressure of the F desorption section is 0.17-0.19 MPa, and the operating pressure of the I desorption section is 0.17-0.19 MPa.

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