A purification method for removing carbon dioxide

Abstract

The present invention provides a purification method for removing carbon dioxide, comprising the following steps: making a raw gas contact with a sulfur-containing semi-lean liquid and at least a part of a sulfur-free rich liquid in reverse order to carry out a desulfurization treatment to obtain a desulfurized raw gas and a sulfur-containing rich liquid; making the desulfurized raw gas carry out a first condensation-gas-liquid separation treatment to obtain a first raw gas and a first condensate; making the first raw gas carry out a second condensation-gas-liquid separation treatment to obtain a second raw gas and a second condensate; making the second raw gas contact with a sulfur-free semi-lean liquid and a lean liquid in reverse order to carry out a decarbonization treatment to obtain a purified gas and a sulfur-free rich liquid; making the first condensate and the second condensate carry out a carbon dioxide distillation treatment to obtain light component impurities and liquid carbon dioxide; making the liquid carbon dioxide provide cooling capacity for the second condensation-gas-liquid separation treatment to obtain a carbon dioxide product; high-purity carbon dioxide can be separated from the raw gas obtained from coal gasification, and the consumption of methanol and the energy consumption of the system are reduced.

Description

Technical Field

[0001] The invention belongs to the field of coal chemical production equipment and energy-saving technology, and specifically relates to a purification method for removing carbon dioxide. Background Art

[0002] In the coal chemical production process, the raw gas after coal gasification contains acidic gases such as carbon dioxide and sulfide. In the process of using the raw gas to process and produce chemical products, the gas needs to be purified first. At present, the low-temperature methanol washing process is generally used to purify the raw gas. Low-temperature methanol has good adsorption selectivity and can selectively remove carbon dioxide and hydrogen sulfide. The gas purification degree is high, and the total sulfur in the purified gas can be less than 0.1ppm, ensuring the purity of the product.

[0003] However, since the raw gas obtained from coal gasification has a high carbon dioxide content and a low content of other acidic gases such as sulfides, in order to remove a large amount of carbon dioxide, it is necessary to maintain a large amount of low-temperature methanol circulation, which makes the device huge in size, and to maintain the low temperature, a high-power ice machine needs to be installed, which increases the manufacturing, construction and operating costs of the device.

[0004] Therefore, if the characteristic of carbon dioxide being easy to liquefy under high pressure and low temperature can be utilized, and part of the carbon dioxide can be liquefied and separated by cooling the raw gas, the demand for low-temperature methanol for absorbing carbon dioxide can be reduced accordingly. However, in the existing technology, most of the carbon dioxide in the raw gas is liquefied by using a high-grade cold source with a temperature below -55°C, and a separate ice machine with high power consumption is required for this purpose, which is very expensive in terms of equipment investment and energy consumption.

[0005] Therefore, there is an urgent need for a purification method that has low methanol consumption, low operating costs, and can efficiently remove carbon dioxide. Summary of the invention

[0006] The invention provides a purification method for removing carbon dioxide, which is used to solve the problems of large methanol consumption and high system energy consumption in the purification of raw gas obtained from coal gasification in the prior art.

[0007] The present invention provides a purification method for removing carbon dioxide, comprising the following steps:

[0008] The raw gas is brought into reverse contact with the sulfur-containing semi-lean liquid and at least part of the sulfur-free rich liquid to perform a desulfurization treatment to obtain a desulfurized raw gas and a sulfur-containing rich liquid;

[0009] Subjecting the desulfurized raw gas to a first condensation-gas-liquid separation process to obtain a first raw gas and a first condensate;

[0010] subjecting the first raw gas to a second condensation-gas-liquid separation process to obtain a second raw gas and a second condensate;

[0011] The second raw gas is brought into reverse contact with the sulfur-free semi-lean liquid and the lean liquid to perform a decarbonization treatment to obtain a purified gas and the sulfur-free rich liquid;

[0012] subjecting the first condensate and the second condensate to carbon dioxide rectification to obtain light component impurities and liquid carbon dioxide;

[0013] The liquid carbon dioxide is used to provide cold energy for the second condensation-gas-liquid separation process, and then a carbon dioxide product is obtained.

[0014] Furthermore, before the first condensate and the second condensate are subjected to the carbon dioxide distillation treatment, a first decompression treatment is performed to obtain a decompression condensate; the pressure of the decompression condensate is 0.81-2.51 MPa; and / or,

[0015] Before the liquid carbon dioxide provides cooling capacity for the second condensation-gas-liquid separation process, a second decompression process is performed to obtain decompressed liquid carbon dioxide; the pressure of the decompressed liquid carbon dioxide is 0.45-1.30 MPa.

[0016] Furthermore, a hydrogen sulfide concentration unit is used, which is internally divided into an upper section, a middle section and a lower section from top to bottom, comprising the following steps:

[0017] Allow the remaining sulfur-free rich liquid to enter the upper part of the upper section for a first desorption treatment to obtain an intermediate sulfur-free semi-lean liquid and a first exhaust gas; allow at least a portion of the intermediate sulfur-free semi-lean liquid to enter the upper part of the middle section;

[0018] The remaining intermediate sulfur-free semi-lean liquid is allowed to leave the hydrogen sulfide concentration unit, and is contacted with nitrogen in reverse direction to undergo sulfur-free gas stripping treatment to obtain the sulfur-free semi-lean liquid and the second exhaust gas;

[0019] The sulfur-rich liquid is allowed to enter the middle of the middle section for a second desorption treatment to obtain an intermediate sulfur-containing semi-lean liquid and a third exhaust gas; the third exhaust gas is reversely contacted with the intermediate sulfur-free semi-lean liquid entering the middle section for an absorption treatment to obtain a desulfurized exhaust gas and the intermediate sulfur-containing semi-lean liquid; the desulfurized exhaust gas ascends to enter the upper section and merges with the first exhaust gas; at least a portion of the intermediate sulfur-containing semi-lean liquid is allowed to enter the upper part of the lower section;

[0020] The remaining intermediate sulfur-containing semi-lean liquid is allowed to leave the hydrogen sulfide concentration unit, and is contacted with the nitrogen in reverse direction to undergo sulfur-containing gas stripping treatment to obtain the sulfur-containing semi-lean liquid and a fourth exhaust gas;

[0021] allowing the fourth exhaust gas to enter the hydrogen sulfide concentration unit to participate in the absorption process;

[0022] The intermediate sulfur-containing semi-lean liquid entering the upper part of the lower section is brought into countercurrent contact with the nitrogen gas to perform a first gas stripping treatment to obtain the fifth exhaust gas and methanol liquid; the fifth exhaust gas ascends to participate in the absorption treatment.

[0023] Further, the first exhaust gas and the second exhaust gas are subjected to exhaust gas condensation treatment to obtain exhaust gas and a first recovery liquid;

[0024] The first recovery liquid is contacted with the nitrogen gas in reverse order to participate in the sulfur-containing gas stripping treatment;

[0025] The sulfur-containing semi-lean liquid provides cooling capacity for the exhaust gas condensation process before the desulfurization process.

[0026] Furthermore, before the remaining sulfur-free rich liquid enters the upper part of the upper section for the first desorption treatment, the first heat exchange treatment and the sulfur-free flash treatment are sequentially performed to obtain the first recycled gas and the intermediate sulfur-free rich liquid; the intermediate sulfur-free rich liquid is then made to enter the upper part of the upper section as the sulfur-free rich liquid for the first desorption treatment; the first recycled gas is combined with the feed gas to participate in the desulfurization treatment; and / or,

[0027] Before the sulfur-containing rich liquid enters the middle part of the middle section for the second desorption treatment, the first heat exchange treatment and the sulfur-containing flash treatment are carried out in sequence to obtain the second recovered gas and the intermediate sulfur-containing rich liquid; the intermediate sulfur-containing rich liquid is then made to enter the middle part of the middle section as the sulfur-containing rich liquid for the second desorption treatment; the second recovered gas is combined with the feed gas to participate in the desulfurization treatment.

[0028] Further, the methanol liquid is subjected to a second heat exchange treatment and a first distillation treatment in sequence to obtain a first intermediate lean liquid and sulfuric acid-containing gas; wherein the methanol liquid provides cooling capacity for the first heat exchange treatment;

[0029] The first intermediate lean liquid is subjected to the second heat exchange treatment to obtain a second intermediate lean liquid.

[0030] Furthermore, at least a portion of the second intermediate lean liquid is subjected to a second distillation treatment to obtain water and methanol vapor; and the methanol vapor is brought into countercurrent contact with the methanol liquid to participate in the first distillation treatment.

[0031] Furthermore, after the liquid carbon dioxide provides cooling capacity for the second condensation-gas-liquid separation process, a methanol recovery process is performed to obtain the carbon dioxide product and a second recovered liquid; and the second recovered liquid is allowed to participate in the second distillation process.

[0032] Further, the remaining second intermediate lean liquid is subjected to a third heat exchange treatment to obtain the lean liquid; wherein, before at least part of the intermediate sulfur-containing semi-lean liquid enters the upper part of the lower section, the intermediate sulfur-containing semi-lean liquid is caused to leave the hydrogen sulfide concentration unit to provide cooling capacity for the third heat exchange treatment and the first heat exchange treatment in sequence; and / or,

[0033] Before the raw gas is subjected to desulfurization treatment, a cooling-gas-liquid separation treatment is performed to obtain a cooled raw gas and a third recovered liquid; the cooled raw gas is used as the raw gas for the desulfurization treatment; the third recovered liquid is allowed to participate in the second distillation treatment; the purified gas, the exhaust gas, the light component impurities and the carbon dioxide product provide cooling capacity for the cooling-gas-liquid separation treatment.

[0034] Furthermore, the desulfurization treatment is carried out at a pressure of 2.02 to 8.05 MPa and a temperature of -30.5 to -5.2°C; and / or

[0035] The decarburization treatment is performed at a pressure of 1.97 to 8.00 MPa and a temperature of -66.8 to -45.9°C; and / or

[0036] The temperature of the first raw gas is not higher than -12°C; and / or,

[0037] The temperature of the second raw gas is not higher than -20°C; and / or,

[0038] The operating pressure of the carbon dioxide distillation treatment is 0.80-2.51Mpa and the temperature is -40 to -22°C; and / or,

[0039] The upper section of the hydrogen sulfide concentration unit has a pressure of 0.15-0.20 MPa and a temperature of -70.2-50.1°C, the middle section has a pressure of 0.17-0.22 MPa and a temperature of -51.2-70.1°C, and the lower section has a pressure of 0.19-0.24 MPa and a temperature of -38.6-58.2°C; and / or,

[0040] The sulfur-free gas stripping treatment has a pressure of 0.15 to 0.20 MPa and a temperature of -89.8 to -72.1°C; and / or,

[0041] The sulfur-containing gas stripping treatment has a pressure of 0.17 to 0.22 MPa and a temperature of -89.1 to -71.3°C; and / or,

[0042] The temperature of the exhaust gas is not higher than -67°C; and / or,

[0043] The sulfur-free flash treatment has a pressure of 0.6 to 2.1 MPa and a temperature of -22.1 to -38.3°C; and / or,

[0044] The temperature of the intermediate sulfur-free rich liquid is not higher than -72.1°C; and / or,

[0045] The sulfur-containing flash treatment has a pressure of 0.6 to 2.1 MPa and a temperature of -22.3 to -38.5°C; and / or,

[0046] The temperature of the intermediate sulfur-rich liquid is not higher than -71.3°C; and / or,

[0047] The first distillation treatment has a pressure of 0.25-0.42 MPa and a temperature of 38-118° C.; and / or,

[0048] The temperature of the second intermediate lean liquid is not higher than -33.5°C; and / or,

[0049] The second distillation treatment has a pressure of 0.27-0.44 MPa and a temperature of 95-146° C.; and / or,

[0050] The pressure of the methanol recovery treatment is 0.55 to 1.30 MPa and the temperature is -30.5 to -55.4°C; and / or,

[0051] The temperature of the lean liquid is not higher than -46.2°C; and / or,

[0052] The temperature of the cooled raw gas is not higher than -5°C.

[0053] The present invention provides a purification method for removing carbon dioxide, which can separate high-purity carbon dioxide from raw gas obtained by coal gasification, and reduces the consumption of methanol and the energy consumption of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 is a schematic diagram of a purification system in one embodiment of the present invention;

[0055] Figure 2 Schematic diagram of a purification system in another embodiment of the present invention.

[0056] Description of reference numerals:

[0057] 1: cooling-gas-liquid separation unit; 3: first condensation-gas-liquid separation unit; 5: second condensation-gas-liquid separation unit; 7: carbon dioxide distillation unit; 8: second pressure reducing unit; 10: methanol recovery unit; 12: desulfurization unit; 13: first heat exchange unit; 14: first pressure reducing valve; 15: sulfur-free flash unit; 16: second pressure reducing valve; 17: sulfur-containing flash unit; 18: compressor; 19: hydrogen sulfide concentration unit; 21: fourth booster pump; 22: sulfur-free gas stripping unit; 23: first booster pump; 24: sulfur-containing gas stripping unit; 25: second booster pump; 26: thermal regeneration unit; 27: second heat exchange unit; 28: third booster pump; 29: third heat exchange unit; 30: methanol-water separation unit; 31: exhaust gas condensation unit; 32: sulfur-free methanol pressure reducing valve; 33: sulfur-containing methanol pressure reducing valve; 34: first pressure reducing unit; 35: raw gas pipeline; 41: nitrogen pipeline; 45: decarbonization unit. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0059] The present invention provides a purification method for removing carbon dioxide, comprising the following steps:

[0060] The raw gas is brought into reverse contact with the sulfur-containing semi-lean liquid and at least part of the sulfur-free rich liquid to perform a desulfurization treatment to obtain a desulfurized raw gas and a sulfur-containing rich liquid;

[0061] Subjecting the desulfurized raw gas to a first condensation-gas-liquid separation process to obtain a first raw gas and a first condensate;

[0062] subjecting the first raw gas to a second condensation-gas-liquid separation process to obtain a second raw gas and a second condensate;

[0063] The second raw gas is brought into reverse contact with the sulfur-free semi-lean liquid and the lean liquid to perform a decarbonization treatment to obtain a purified gas and a sulfur-free rich liquid;

[0064] Subjecting the first condensate and the second condensate to carbon dioxide rectification treatment to obtain light component impurities and liquid carbon dioxide;

[0065] The liquid carbon dioxide provides cold energy for the second condensation-gas-liquid separation process, and then obtains the carbon dioxide product.

[0066] Among them, the raw gas is the raw gas obtained from coal gasification, and its main components include hydrogen, carbon monoxide, carbon dioxide, sulfur-containing compounds, and the rest are other inert gases such as nitrogen; the above-mentioned lean liquid, semi-lean liquid and rich liquid are all methanol liquids, lean liquid refers to methanol liquid that does not contain carbon dioxide and sulfide, semi-lean liquid refers to methanol liquid from which part of the adsorbed carbon dioxide and sulfide have been removed and still has a certain adsorption capacity for carbon dioxide and sulfide, and rich liquid refers to methanol liquid that has adsorbed saturated amounts of carbon dioxide and sulfide.

[0067] The present invention does not limit the specific configuration of the purification system used. Figure 1 Taking the purification system shown in the figure as an example, the raw gas enters the lower part of the desulfurization unit 12 through the raw gas inlet via the raw gas pipeline 35, the sulfur-containing semi-lean liquid enters the middle part of the desulfurization unit 12 through the sulfur-containing semi-lean liquid inlet, and at least part of the sulfur-free rich liquid enters the upper part of the desulfurization unit 12 through the sulfur-free rich liquid inlet. Under the action of gravity, the raw gas goes up and contacts with the sulfur-containing semi-lean liquid and the sulfur-free rich liquid in reverse direction to perform desulfurization treatment to absorb all sulfur-containing compounds and part of carbon dioxide in the raw gas, thereby obtaining a desulfurized raw gas and a sulfur-containing rich liquid that absorbs a large amount of sulfides and part of carbon dioxide; the desulfurized raw gas continues to go up and leaves the desulfurization unit 12 through the raw gas outlet of the desulfurization unit 12, and the sulfur-containing rich liquid continues to go down and leaves the desulfurization unit 12 through the sulfur-containing rich liquid outlet;

[0068] The desulfurized raw gas enters the first condensation-gas-liquid separation unit 3 through the material inlet of the first condensation-gas-liquid separation unit 3, and the first condensation-gas-liquid separation treatment is carried out therein to obtain the first raw gas and the first condensate whose main component is liquid carbon dioxide; the first condensate leaves through the liquid phase outlet of the first condensation-gas-liquid separation unit 3, and is subjected to gas-liquid separation from the raw gas; the first raw gas leaves the first condensation-gas-liquid separation unit 3 through the gas phase outlet of the first condensation-gas-liquid separation unit 3, and enters the second condensation-gas-liquid separation unit 5 through the material inlet of the second condensation-gas-liquid separation unit 5, and is subjected to the second condensation-gas-liquid separation treatment, and the second raw gas and the second condensate whose main component is liquid carbon dioxide are obtained; the second condensate also leaves through the liquid phase outlet of the second condensation-gas-liquid separation unit 5, and is further subjected to gas-liquid separation from the raw gas;

[0069] The second raw gas leaves the second condensation-gas-liquid separation unit 5 through the gas phase outlet of the second condensation-gas-liquid separation unit 5, and enters the lower part of the decarbonization unit 45 through the raw gas inlet of the decarbonization unit 45, the sulfur-free semi-lean liquid enters the middle part of the decarbonization unit 45 through the sulfur-free semi-lean liquid inlet, and the lean liquid enters the upper part of the decarbonization unit 45 through the lean liquid inlet. Under the action of gravity, the raw gas goes up and contacts the sulfur-free semi-lean liquid and the lean liquid in reverse direction to perform decarbonization treatment to absorb all or most of the carbon dioxide in the raw gas, and obtains the purified gas after decarbonization and the sulfur-free rich liquid that absorbs a large amount of carbon dioxide. The purified gas continues to go up and leaves the decarbonization unit 45 through the purified gas outlet, and the sulfur-free rich liquid continues to go down and leaves the decarbonization unit 45 through the sulfur-free rich liquid outlet;

[0070] The first condensate and the second condensate, whose main component is liquid carbon dioxide, are combined and enter the carbon dioxide distillation unit 7 through the middle inlet of the carbon dioxide distillation unit 7 to undergo carbon dioxide distillation treatment to obtain light impurities, a very small amount of sulfide gas and high-purity liquid carbon dioxide; the light impurities and a very small amount of sulfide gas ascend and leave through the top outlet of the carbon dioxide distillation unit 7, and the light impurities are output; the liquid carbon dioxide descends and leaves through the bottom outlet of the carbon dioxide distillation unit 7, and enters the second condensation-gas-liquid separation unit 5 through the cold medium inlet of the second condensation-gas-liquid separation unit 5, where the liquid carbon dioxide is gasified and absorbs a large amount of heat during the gasification process, providing cold capacity for the second condensation-gas-liquid separation treatment, thereby realizing the condensation of a large amount of carbon dioxide gas in the raw gas into liquid, reducing the energy consumption of the system, and the gasified carbon dioxide leaves through the cold medium outlet of the second condensation-gas-liquid separation unit 5, and the carbon dioxide product is output.

[0071] The present invention provides a purification method for removing carbon dioxide, wherein a raw gas is brought into reverse contact with a sulfur-containing semi-lean liquid and at least a part of a sulfur-free rich liquid to perform a desulfurization treatment, thereby removing all sulfides in the raw gas; then, the raw gas is cooled in multiple stages through a first condensation-gas-liquid separation treatment and a second condensation-gas-liquid separation treatment, thereby realizing a step-by-step reduction in the temperature of the raw gas and pre-condensation of carbon dioxide, thereby reducing the demand for methanol liquid; a second raw gas is brought into reverse contact with a sulfur-free semi-lean liquid and a lean liquid to perform a decarbonization treatment, thereby removing all carbon dioxide and a very small amount of sulfides in the raw gas, thereby realizing purification of the raw gas; a high-purity carbon dioxide product is obtained through a carbon dioxide distillation treatment; liquid carbon dioxide is used to provide cooling capacity for the second condensation-gas-liquid separation treatment, thereby realizing recovery of the cooling capacity of the system itself, reducing the demand for external cooling capacity, and saving energy consumption of the system.

[0072] In a specific embodiment, before the first condensate and the second condensate are subjected to carbon dioxide distillation treatment, a first decompression treatment is performed to obtain a decompression condensate; the pressure of the decompression condensate is 0.81-2.51 MPa;

[0073] In another specific embodiment, before the liquid carbon dioxide provides cooling capacity for the second condensation-gas-liquid separation process, a second decompression process is performed to obtain decompressed liquid carbon dioxide; the pressure of the decompressed liquid carbon dioxide is 0.45-1.30 MPa.

[0074] Figure 2 This is a schematic diagram of a purification system in another embodiment of the present invention. Figure 2 Taking the purification system shown as an example, the first condensate and the second condensate leave through the liquid phase outlet of the first condensation-gas-liquid separation unit 3 and the liquid phase outlet of the second condensation-gas-liquid separation unit 5 respectively, and enter the first decompression unit 34 after merging, in which the first decompression treatment is carried out to obtain a decompression condensate whose main component is liquid carbon dioxide. The inventors found that when the pressure of the decompression condensate is 0.81-2.51Mpa, the decompression condensate enters the carbon dioxide distillation unit 7 through the middle inlet of the carbon dioxide distillation unit 7, which is conducive to the carbon dioxide distillation treatment, and is conducive to further separation of light component impurities and sulfide gas from carbon dioxide liquid, and further improves the purity of the carbon dioxide product;

[0075] The liquid carbon dioxide obtained by distillation in the carbon dioxide distillation unit 7 flows downward through the bottom outlet of the carbon dioxide distillation unit 7 and leaves, and enters the second decompression unit 8, in which a second decompression treatment is performed to obtain decompressed liquid carbon dioxide. The inventors have found that when the pressure of the decompressed liquid carbon dioxide is 0.45-1.30 MPa, its bubble point temperature can be reduced to -60°C, and then enters the second condensation-gas-liquid separation unit 5 through the cold medium inlet of the second condensation-gas-liquid separation unit 5, providing cold capacity for the second condensation-gas-liquid separation treatment, which is beneficial to the large amount of heat absorption in its gasification process, thereby further condensing a large amount of carbon dioxide in the raw gas into liquid phase.

[0076] Through the first decompression treatment, the condensate is used to gasify and separate the light components in the carbon dioxide distillation treatment in the form of decompression flash evaporation, thereby realizing the rational use of energy and being able to achieve the purpose of independently purifying liquid carbon dioxide; through the second decompression treatment, the bubble point temperature of the liquid carbon dioxide obtained by the carbon dioxide distillation treatment is further reduced, and the heat absorption of its gasification process is increased, providing cold capacity for the second condensation-gas-liquid separation treatment, so as to achieve the purpose of liquefying and separating a large amount of carbon dioxide in the raw gas, thereby saving refrigeration energy consumption.

[0077] Preferably, a hydrogen sulfide concentration unit is used, which is internally divided into an upper section, a middle section and a lower section from top to bottom, comprising the following steps:

[0078] The remaining sulfur-free rich liquid is allowed to enter the upper part of the upper section for a first desorption treatment to obtain an intermediate sulfur-free semi-lean liquid and a first exhaust gas; at least a portion of the intermediate sulfur-free semi-lean liquid is allowed to enter the upper part of the middle section;

[0079] The remaining intermediate sulfur-free semi-lean liquid is allowed to leave the hydrogen sulfide concentration unit, contacted with nitrogen in reverse, and subjected to sulfur-free gas stripping treatment to obtain sulfur-free semi-lean liquid and second exhaust gas;

[0080] The sulfur-rich liquid is allowed to enter the middle of the middle section for a second desorption treatment to obtain an intermediate sulfur-containing semi-lean liquid and a third exhaust gas; the third exhaust gas is reversely contacted with the intermediate sulfur-free semi-lean liquid entering the middle section for an absorption treatment to obtain a desulfurized exhaust gas and an intermediate sulfur-containing semi-lean liquid; the desulfurized exhaust gas ascends to the upper section to merge with the first exhaust gas; at least part of the intermediate sulfur-containing semi-lean liquid enters the upper section;

[0081] The remaining intermediate sulfur-containing semi-lean liquid leaves the hydrogen sulfide concentration unit, contacts with nitrogen in reverse, and undergoes sulfur-containing gas stripping treatment to obtain sulfur-containing semi-lean liquid and fourth discharge gas;

[0082] Allowing the fourth exhaust gas to enter the hydrogen sulfide concentration unit to participate in absorption treatment;

[0083] The intermediate sulfur-containing semi-lean liquid entering the upper part of the lower section is brought into countercurrent contact with nitrogen to perform the first gas stripping treatment to obtain the fifth exhaust gas and methanol liquid; the fifth exhaust gas goes upward to participate in the absorption treatment.

[0084] The present invention does not limit the specific arrangement of the hydrogen sulfide concentration unit. For example, the hydrogen sulfide concentration unit has a tower body with a cavity, a first chimney plate and a second chimney plate; the plate surfaces of the first chimney plate and the second chimney plate are both arranged in the horizontal direction, dividing the interior from top to bottom into an upper section, a middle section and a lower section, and the first chimney plate and the second chimney plate are both provided with a channel that allows gas to pass from bottom to top.

[0085] Specifically, a part of the sulfur-free rich liquid obtained by the decarbonization treatment enters the upper part of the desulfurization unit 12 through the sulfur-free rich liquid inlet, and the remaining sulfur-free rich liquid enters the hydrogen sulfide concentration unit 19 through the lower inlet of the upper section for a first desorption treatment. At this time, the sulfur-free rich liquid desorbs carbon dioxide and its own temperature is reduced to obtain an intermediate sulfur-free semi-lean liquid and a first exhaust gas rich in desorbed carbon dioxide gas; the first exhaust gas ascends and leaves through the top outlet of the upper section for outputting the exhaust gas; the intermediate sulfur-free semi-lean liquid descends to the lower outlet of the upper section and leaves the hydrogen sulfide concentration unit 19, a part of it enters the sulfur-free gas stripping unit 22 through the upper inlet of the sulfur-free gas stripping unit 22, and the other part enters the upper middle section of the hydrogen sulfide concentration unit 19 again through the upper inlet of the middle section;

[0086] The remaining intermediate sulfur-free semi-lean liquid entering the sulfur-free stripping unit 22 is reversely contacted with nitrogen here to perform sulfur-free stripping treatment, wherein the carbon dioxide therein is further desorbed, and its own temperature is further reduced, thereby obtaining a second exhaust gas rich in carbon dioxide and a sulfur-free semi-lean liquid with a stronger carbon dioxide absorption capacity and a lower temperature; the sulfur-free semi-lean liquid leaves the sulfur-free stripping unit 22 through the bottom outlet of the sulfur-free stripping unit 22, enters the decarbonization unit 45 through the sulfur-free semi-lean liquid inlet after being pressurized by the first pressure pump 23, and participates in the decarbonization treatment; the second exhaust gas stripped by the gas leaves the sulfur-free stripping unit 22 through the top outlet of the sulfur-free stripping unit 22, and merges with the first exhaust gas, and is used to output the exhaust gas;

[0087] After the sulfur-containing rich liquid obtained by the desulfurization treatment leaves the desulfurization unit 12 through the sulfur-containing rich liquid outlet, it enters the hydrogen sulfide concentration unit 19 through the middle inlet of the middle section, and the sulfur-containing rich liquid flows from the middle of the middle section from top to bottom for a second desorption treatment, wherein carbon dioxide is desorbed and its own temperature is reduced, thereby obtaining an intermediate sulfur-containing semi-lean liquid and a third emission gas containing carbon dioxide and a small amount of sulfide; the third emission gas ascends, and the intermediate sulfur-free semi-lean liquid entering the middle section flows from top to bottom by gravity, and contacts the third emission gas in reverse direction for absorption treatment, absorbing the sulfur-containing components therein, thereby obtaining a desulfurized emission gas and an intermediate sulfur-containing semi-lean liquid; the desulfurized emission gas ascends through the chimney plate and merges with the first emission gas of the upper section; the intermediate sulfur-containing semi-lean liquid descends to the lower outlet of the middle section and leaves the hydrogen sulfide concentration unit 19, a part of which enters the sulfur-containing stripping unit 24 through the upper inlet of the sulfur-containing stripping unit 24, and the other part enters the lower section upper part of the hydrogen sulfide concentration unit 19 again through the upper inlet of the lower section;

[0088] The remaining intermediate sulfur-containing semi-lean liquid entering the sulfur-containing stripping unit 24 is again contacted with nitrogen in reverse direction to undergo sulfur-containing stripping treatment, thereby obtaining a fourth emission gas rich in carbon dioxide and a small amount of sulfide and a sulfur-containing semi-lean liquid having a stronger absorption capacity for carbon dioxide and sulfide and a lower temperature; the sulfur-containing semi-lean liquid leaves the sulfur-containing stripping unit 24 through the bottom outlet of the sulfur-containing stripping unit 24, and enters the desulfurization unit 12 through the sulfur-containing semi-lean liquid inlet after being pressurized by the second pressure pump 25; the fourth emission gas leaves the sulfur-containing stripping unit 24 through the top outlet of the sulfur-containing stripping unit 24, and enters the hydrogen sulfide concentration unit 19 through the upper inlet of the lower section, participates in the absorption treatment, and further removes the sulfur-containing components therein;

[0089] In the lower section of the hydrogen sulfide concentration unit 19, nitrogen enters the hydrogen sulfide concentration unit 19 through the lower inlet of the lower section via the nitrogen pipeline 41, and contacts the intermediate sulfur-containing semi-lean liquid entering the lower section in reverse, and performs the first gas stripping treatment, and gas strips out carbon dioxide and a small amount of sulfur-containing gas in the intermediate sulfur-containing semi-lean liquid to obtain the fifth exhaust gas and methanol liquid containing carbon dioxide and a small amount of sulfur-containing gas; the fifth exhaust gas goes up through the chimney plate and enters the middle section to participate in the absorption treatment, and further removes the sulfur-containing components therein, and further reduces the sulfur content in the exhaust gas to meet the standard.

[0090] By adopting a hydrogen sulfide concentration unit which is divided into an upper section, a middle section and a lower section from top to bottom to carry out the first desorption treatment and the second desorption treatment, the sulfur-free rich liquid and the sulfur-containing rich liquid can achieve the desorption of carbon dioxide and self-cooling, and obtain an intermediate sulfur-free semi-lean liquid and an intermediate sulfur-containing semi-lean liquid, thereby realizing the preliminary regeneration of methanol liquid; then, through sulfur-free gas stripping treatment and sulfur-containing gas stripping treatment, the intermediate sulfur-free semi-lean liquid and the intermediate sulfur-containing semi-lean liquid are stripped with nitrogen to further release the carbon dioxide dissolved in the intermediate semi-lean liquid, thereby obtaining a sulfur-free semi-lean liquid and a sulfur-containing semi-lean liquid with a lower temperature and a lower carbon dioxide concentration, thereby further enhancing the removal function of the sulfur-free semi-lean liquid and the sulfur-containing semi-lean liquid for sulfide and carbon dioxide, and reducing the demand for methanol lean liquid at the same time.

[0091] Further, the first exhaust gas and the second exhaust gas are subjected to exhaust gas condensation treatment to obtain exhaust gas and a first recovery liquid;

[0092] The first recovery liquid is contacted with nitrogen in reverse direction to participate in the sulfur-containing gas stripping treatment;

[0093] The sulfur-containing semi-lean liquid provides cooling capacity for the exhaust gas condensation process before desulfurization.

[0094] Specifically, after the first exhaust gas obtained by the first desorption treatment is merged with the second exhaust gas obtained by the sulfur-free gas stripping treatment, it enters the exhaust gas condensation unit 31 through the material inlet of the exhaust gas condensation unit 31, where the exhaust gas condensation treatment is performed, and the methanol therein is condensed into a liquid phase, thereby obtaining an exhaust gas with a lower temperature and a lower methanol content and a first recovered liquid whose main component is methanol;

[0095] The first recovered liquid leaves the exhaust gas condensation unit 31 through the liquid phase logistics outlet of the exhaust gas condensation unit 31, and enters the sulfur-containing gas stripping unit 24 through the upper inlet of the sulfur-containing gas stripping unit 24, participates in the sulfur-containing gas stripping treatment, and further recovers the methanol solution; the exhaust gas leaves the exhaust gas condensation unit 31 through the gas phase material outlet of the exhaust gas condensation unit 31;

[0096] The sulfur-containing semi-lean liquid obtained by the sulfur-containing gas stripping treatment is the lowest temperature point in the purification method provided by the present invention. It provides cooling capacity for the exhaust gas condensation treatment, thereby achieving further cooling and condensation of the exhaust gas and further reducing the methanol content in the exhaust gas. The sulfur-containing semi-lean liquid obtained by the sulfur-containing gas stripping treatment provides cooling capacity for the exhaust gas condensation treatment before the desulfurization treatment, thereby achieving further cooling and condensation of the exhaust gas, realizing the step-by-step utilization of energy, and reducing the refrigeration energy consumption.

[0097] The exhaust gas condensation treatment and the sulfur-containing semi-lean liquid obtained by the sulfur-containing gas stripping treatment provide cooling capacity for the exhaust gas condensation treatment before the desulfurization treatment, so that the exhaust gas can be further condensed, thereby condensing and recovering the methanol component therein, reducing the loss of methanol and saving refrigeration costs.

[0098] In a specific embodiment, before the remaining sulfur-free rich liquid enters the upper part of the upper section for the first desorption treatment, the first heat exchange treatment and the sulfur-free flash treatment are sequentially performed to obtain the first recycled gas and the intermediate sulfur-free rich liquid; the intermediate sulfur-free rich liquid is then allowed to enter the upper part of the upper section as the sulfur-free rich liquid for the first desorption treatment; the first recycled gas is combined with the raw gas to participate in the desulfurization treatment;

[0099] In another specific embodiment, before the sulfur-containing rich liquid enters the middle part of the middle section for the second desorption treatment, the first heat exchange treatment and the sulfur-containing flash treatment are sequentially performed to obtain the second recovered gas and the intermediate sulfur-containing rich liquid; the intermediate sulfur-containing rich liquid is then allowed to enter the middle part of the middle section as the sulfur-containing rich liquid for the second desorption treatment; the second recovered gas is combined with the raw gas to participate in the desulfurization treatment.

[0100] After the sulfur-free rich liquid leaves the decarbonization unit 45 through the sulfur-free rich liquid outlet, a part of the sulfur-free rich liquid first passes through the first heat exchange unit 13 for the first heat exchange treatment to reduce the temperature before entering the upper part of the upper section for the first desorption treatment; preferably, after the pressure reduction treatment through the first pressure reducing valve 14, it enters the sulfur-free flash unit 15 through the upper inlet of the sulfur-free flash unit 15, and performs sulfur-free flash treatment under medium pressure and low temperature environment to desorb as little carbon dioxide as possible and as much effective gas (hydrogen and carbon dioxide) as possible, to obtain the first recycled gas rich in hydrogen and carbon dioxide and the intermediate sulfur-free rich liquid; the desorbed first recycled gas goes up through the top outlet of the sulfur-free flash unit 15 to leave the sulfur-free flash unit 15, is compressed by the compressor 18, is connected to the raw gas pipeline 35, merges with the raw gas to participate in the desulfurization treatment, and recovers the effective gas; then the intermediate sulfur-free rich liquid is allowed to enter the upper part of the upper section as the sulfur-free rich liquid for the first desorption treatment;

[0101] After the sulfur-containing rich liquid leaves the desulfurization unit 12 through the sulfur-containing rich liquid outlet, it first passes through the first heat exchange unit 13 for the first heat exchange treatment to reduce the temperature before entering the middle part of the middle section for the second desorption treatment; preferably, after the pressure reduction treatment through the second pressure reducing valve 16, it enters the sulfur-containing flash unit 17 through the upper inlet of the sulfur-containing flash unit 17, and performs sulfur-containing flash treatment under medium pressure and low temperature environment to desorb as little carbon dioxide and as much effective gas as possible to obtain a second recovered gas rich in hydrogen and carbon dioxide and an intermediate sulfur-containing rich liquid; the desorbed second recovered gas goes up through the top outlet of the sulfur-containing flash unit 17 to leave the sulfur-containing flash unit 17, is compressed by the compressor 18, is connected to the raw gas pipeline 35, merges with the raw gas and the first recovered gas, participates in the desulfurization treatment, and further recovers the effective gas.

[0102] Through the first heat exchange treatment, the sulfur-free rich liquid and the sulfur-containing rich liquid are cooled. After cooling, the sulfur-free flash evaporation treatment and the sulfur-containing flash evaporation treatment are performed to desorb as little carbon dioxide as possible and as much effective gas as possible, further recovering the effective gas and improving the purification efficiency.

[0103] Preferably, the methanol liquid is subjected to a second heat exchange treatment and a first distillation treatment in sequence to obtain a first intermediate lean liquid and sulfuric acid-containing gas; wherein the methanol liquid provides cooling capacity for the first heat exchange treatment;

[0104] The first intermediate lean liquid is subjected to a second heat exchange treatment to obtain a second intermediate lean liquid.

[0105] It can be understood that the methanol liquid obtained by the first gas stripping treatment leaves the lower section of the hydrogen sulfide concentration unit 19 through the bottom outlet of the lower section, enters the second heat exchange unit 27 through the cold medium inlet of the second heat exchange unit 27 for the second heat exchange treatment, and provides a cold source for the second heat exchange unit 27. After the heat exchange treatment, its own temperature rises, and leaves the second heat exchange unit 27 through the cold medium outlet of the second heat exchange unit 27, and then enters the heat regeneration unit 26 through the middle and upper inlet of the heat regeneration unit 26, where the first distillation treatment is carried out, and the methanol liquid is subjected to heating distillation to separate all sulfuric acid-containing gas from the methanol solution, so as to obtain a completely regenerated first intermediate lean liquid and sulfuric acid-containing gas; wherein, the sulfuric acid-containing gas ascends through the top outlet of the heat regeneration unit 26 and leaves the heat regeneration unit 26;

[0106] The first intermediate lean liquid flows downward through the bottom outlet of the heat regeneration unit 26, leaves the heat regeneration unit 26, and enters the second heat exchange unit 27 through the material inlet of the second heat exchange unit 27, where it undergoes a second heat exchange treatment with the methanol liquid to lower its own temperature to obtain a second intermediate lean liquid; the second intermediate lean liquid leaves the second heat exchange unit 27 through the material outlet of the second heat exchange unit 27, and enters the decarbonization unit 45 to participate in the decarbonization treatment.

[0107] Through the first distillation treatment, the methanol liquid can be completely regenerated from a semi-lean liquid to a lean liquid, all the acidic gases in the methanol liquid can be removed, and the purification capacity of the methanol liquid for the raw gas can be further improved; through the second heat exchange treatment, the cold energy in the system can be recovered; through the second heat exchange unit 27, the methanol liquid and the first intermediate lean liquid are subjected to heat exchange treatment, thereby realizing the step-by-step utilization of energy.

[0108] Furthermore, at least a portion of the second intermediate lean liquid is subjected to a second distillation treatment to obtain water and methanol vapor; and the methanol vapor is brought into countercurrent contact with the methanol liquid to participate in the first distillation treatment.

[0109] Preferably, at least part of the second intermediate lean liquid is pressurized by the third pressure pump 28 and enters the methanol-water separation unit 30 through the upper inlet of the methanol-water separation unit 30, where a second distillation treatment is performed to separate methanol and water, and the methanol liquid is dehydrated to obtain methanol vapor and water; the water flows downward and leaves the methanol-water separation unit 30 through the water outlet, and the methanol vapor flows upward and leaves the methanol-water separation unit 30 through the top outlet of the methanol-water separation unit 30, and enters the heat regeneration unit 26 through the lower inlet of the heat regeneration unit 26, contacts with the methanol liquid in reverse, participates in the first distillation treatment, and recovers the methanol liquid therein.

[0110] The second distillation treatment is beneficial for further recovering methanol and reducing the methanol consumption of the system.

[0111] Furthermore, after the liquid carbon dioxide provides cooling capacity for the second condensation-gas-liquid separation process, methanol recovery treatment is carried out to obtain a carbon dioxide product and a second recovered liquid; and the second recovered liquid is allowed to participate in the second distillation process.

[0112] The liquid carbon dioxide is vaporized and absorbs a large amount of heat in the second condensation-gas-liquid separation treatment. After its own temperature rises, it enters the methanol recovery unit 10 through the inlet of the methanol recovery unit 10, where a methanol recovery treatment is carried out, and the methanol therein is recovered by gas-liquid separation to obtain a carbon dioxide product and a second recovery liquid whose main component is methanol. The second recovery liquid leaves the methanol recovery unit 10 through the liquid phase outlet of the methanol recovery unit 10, and enters the methanol-water separation unit 30 through the upper inlet of the methanol-water separation unit 30, participates in the second distillation treatment, and further refines and recovers the methanol therein; and the carbon dioxide product leaves the methanol recovery unit 10 through the gas phase outlet of the methanol recovery unit 10.

[0113] By utilizing methanol recovery processing, methanol in the carbon dioxide product can be recovered, further reducing the consumption of methanol and further improving the purity of the carbon dioxide product.

[0114] Preferably, the remaining second intermediate lean liquid is subjected to a third heat exchange treatment to obtain lean liquid; wherein, before at least part of the intermediate sulfur-containing semi-lean liquid enters the upper part of the lower section, the intermediate sulfur-containing semi-lean liquid is caused to leave the hydrogen sulfide concentration unit to provide cooling for the third heat exchange treatment and the first heat exchange treatment in turn;

[0115] Before the raw gas is subjected to desulfurization treatment, a cooling-gas-liquid separation treatment is performed to obtain a cooled raw gas and a third recovered liquid; the cooled raw gas is used as the raw gas for desulfurization treatment; the third recovered liquid is used for the second distillation treatment; and the purified gas, exhaust gas, light component impurities and carbon dioxide products provide cooling capacity for the cooling-gas-liquid separation treatment.

[0116] Among them, after the second intermediate lean liquid obtained by cooling in the second heat exchange treatment is pressurized by the third pressure pump 28, a part of it enters the third heat exchange unit 29 again through the material inlet of the third heat exchange unit 29, and performs the third heat exchange treatment here to obtain lean liquid with a further reduced temperature; the lean liquid leaves the third heat exchange unit 29 through the material outlet of the third heat exchange unit 29, and then enters the decarbonization unit 45 to participate in the decarbonization treatment;

[0117] Before at least part of the intermediate sulfur-containing semi-lean liquid enters the upper part of the lower section, the intermediate sulfur-containing semi-lean liquid from the lower outlet of the middle section is pressurized by the fourth pressure pump 21, enters the third heat exchange unit 29 through the cold medium inlet of the third heat exchange unit 29, provides cold for the third heat exchange treatment, leaves the third heat exchange unit 29 through the cold medium outlet, and then enters the first heat exchange unit 13 through the cold medium inlet of the first heat exchange unit 13, further provides cold for the first heat exchange treatment. After the two heat exchange treatments, the intermediate sulfur-containing semi-lean liquid itself has a higher temperature and partially undergoes a phase change, and then enters the hydrogen sulfide concentration unit 19 through the upper inlet of the lower section, where gas-liquid separation is first performed, and the gas phase therein ascends through the chimney plate into the middle section, and the liquid phase therein descends and contacts with the nitrogen from the bottom in reverse to perform the first gas stripping treatment.

[0118] In order to prevent the moisture in the raw gas from affecting the purification effect, methanol solution can be sprayed into the raw gas in advance to prevent the moisture in the raw gas from freezing when it is cooled to below zero degrees, and it is beneficial to separate the moisture from the raw gas; the raw gas sprayed with methanol solution enters the cooling-gas-liquid separation unit 1 through the material inlet of the cooling-gas-liquid separation unit 1 before undergoing desulfurization treatment, and performs cooling-gas-liquid separation treatment therein to obtain the third recovered liquid and the cooled and partially condensed cooled raw gas; the cooled raw gas leaves the cooling-gas-liquid separation unit 1 through the gas phase outlet of the cooling-gas-liquid separation unit 1, and enters the desulfurization unit 12 to participate in the desulfurization treatment; the third recovered liquid leaves the cooling-gas-liquid separation unit 1 through the liquid phase outlet of the cooling-gas-liquid separation unit 1, and enters the methanol-water separation unit 30 through the middle inlet of the methanol-water separation unit 30, where it participates in the second distillation treatment to further refine and recover methanol, thereby reducing the consumption of methanol;

[0119] The purified gas, exhaust gas, light component impurities and carbon dioxide product are respectively passed through the cooling-gas-liquid separation unit 1, in which cooling capacity is provided for the cooling-gas-liquid separation process to realize the cooling-gas-liquid separation process of the raw gas, and the cooling capacity of the system itself is recovered, thereby realizing the step-by-step utilization of energy and reducing the operating cost of the system.

[0120] Through the first heat exchange treatment and the third heat exchange treatment, the cold recovery of the sulfur-containing semi-lean liquid from the middle section of the hydrogen sulfide recovery unit is achieved, further reducing the energy consumption of the system; by utilizing the cooling-gas-liquid separation treatment, the raw gas is pre-cooled and partially condensed, the moisture in the raw gas is removed, and the methanol solution therein is recovered, further reducing the consumption of methanol, and the cold capacity of the system is recovered through the cooling-gas-liquid separation treatment.

[0121] In one embodiment, the desulfurization treatment pressure is 2.02 to 8.05 MPa and the temperature is -30.5 to -5.2°C; and / or,

[0122] The decarburization treatment pressure is 1.97 to 8.00 MPa and the temperature is -66.8 to -45.9°C; and / or,

[0123] The temperature of the first raw gas is not higher than -12°C; and / or,

[0124] The temperature of the second raw gas is not higher than -20°C; and / or,

[0125] The operating pressure of carbon dioxide distillation treatment is 0.80-2.51Mpa and the temperature is -40 to -22°C; and / or,

[0126] The pressure of the upper section of the hydrogen sulfide concentration unit is 0.15-0.20Mpa and the temperature is -70.2--50.1°C, the pressure of the middle section is 0.17-0.22Mpa and the temperature is -51.2--70.1°C, and the pressure of the lower section is 0.19-0.24Mpa and the temperature is -38.6--58.2°C; and / or,

[0127] The pressure of the sulfur-free gas stripping treatment is 0.15 to 0.20 MPa and the temperature is -89.8 to -72.1°C; and / or,

[0128] The pressure of sulfur-containing gas stripping treatment is 0.17 to 0.22 MPa and the temperature is -89.1 to -71.3°C; and / or,

[0129] The exhaust gas temperature is not higher than -67°C; and / or,

[0130] The sulfur-free flash treatment has a pressure of 0.6 to 2.1 MPa and a temperature of -22.1 to -38.3°C; and / or,

[0131] The temperature of the intermediate sulfur-free rich liquid is not higher than -72.1°C; and / or,

[0132] The pressure of sulfur flash treatment is 0.6~2.1Mpa and the temperature is -22.3~-38.5℃; and / or,

[0133] The temperature of the intermediate sulfur-rich liquid is not higher than -71.3°C; and / or,

[0134] The first distillation treatment has a pressure of 0.25-0.42 MPa and a temperature of 38-118° C.; and / or,

[0135] The temperature of the second intermediate lean liquid is not higher than -33.5°C; and / or,

[0136] The second distillation treatment has a pressure of 0.27-0.44 MPa and a temperature of 95-146° C.; and / or,

[0137] The pressure of methanol recovery treatment is 0.55~1.30Mpa and the temperature is -30.5~-55.4℃; and / or,

[0138] The temperature of the lean liquid is not higher than -46.2°C; and / or,

[0139] The temperature of the cooled raw gas is not higher than -5°C.

[0140] It can be understood that by further limiting the execution parameters of each part of the purification method, the purification effect can be further optimized and the purification efficiency can be improved; a method for independently purifying liquid carbon dioxide can be obtained; the various materials obtained in the purification method can achieve step-by-step energy utilization and efficiently recover their own cooling capacity; methanol can be efficiently recovered to further reduce the methanol content in the exhaust gas, thereby reducing the demand for methanol liquid in the methanol washing process, reducing refrigeration energy consumption, and saving costs.

[0141] In a specific embodiment, the cooling capacity of the first condensation-gas-liquid separation process and the carbon dioxide distillation process is provided by an external refrigerant commonly used in conventional low-temperature methanol washing; the temperature of the refrigerant is preferably -45 to -30°C; in the first distillation process and the second distillation process, a steam heat source is required because heating distillation is required, and the temperature of the steam heat source is preferably 140 to 155°C;

[0142] The purification method provided by the present invention can separate high-purity carbon dioxide from the raw gas obtained by coal gasification, and reduces the consumption of methanol and the energy consumption of the system.

[0143] Hereinafter, a purification method for removing carbon dioxide according to the present invention is described in detail through specific examples.

[0144] Example 1

[0145] The raw gas volume composition used in this embodiment is: 53.78% hydrogen, 0.49% carbon monoxide, 45.03% carbon dioxide, 0.17% sulfur compounds, and the rest is nitrogen and other inert gases; the initial pressure of the raw gas is 5.2MPa, the temperature is 40°C, and the flow rate is 256000Nm 3 / h. A purification method for removing carbon dioxide, comprising the following steps:

[0146] 1) subjecting the raw gas to cooling-gas-liquid separation treatment to obtain cooled raw gas and third recovered liquid; subjecting the third recovered liquid to the second distillation treatment; and subjecting the purified gas, exhaust gas, light component impurities and carbon dioxide product to provide cooling capacity for the cooling-gas-liquid separation treatment.

[0147] 2) The cooled raw gas is brought into reverse contact with a sulfur-containing semi-lean liquid and a part of a sulfur-free rich liquid to perform a desulfurization treatment to obtain a desulfurized raw gas and a sulfur-containing rich liquid; the desulfurized raw gas is subjected to a first condensation-gas-liquid separation treatment to obtain a first raw gas and a first condensate; the first raw gas is subjected to a second condensation-gas-liquid separation treatment to obtain a second raw gas and a second condensate; the second raw gas is brought into reverse contact with a sulfur-free semi-lean liquid and a lean liquid to perform a decarbonization treatment to obtain a purified gas and a sulfur-free rich liquid;

[0148] The first condensate and the second condensate are subjected to carbon dioxide rectification treatment to obtain light component impurities and liquid carbon dioxide; the liquid carbon dioxide provides cooling capacity for the second condensation-gas-liquid separation treatment, and then a carbon dioxide product is obtained;

[0149] 3) before the first condensate and the second condensate are subjected to carbon dioxide distillation treatment, a first decompression treatment is performed to obtain a decompression condensate; the pressure of the decompression condensate is 1.6 MPa;

[0150] 4) The remaining sulfur-free rich liquid is sequentially subjected to the first heat exchange treatment and the sulfur-free flash treatment to obtain the first recycled gas and the intermediate sulfur-free rich liquid; the sulfur-containing rich liquid is sequentially subjected to the first heat exchange treatment and the sulfur-containing flash treatment to obtain the second recycled gas and the intermediate sulfur-containing rich liquid; the first recycled gas, the second recycled gas and the raw gas are combined to participate in the desulfurization treatment;

[0151] 5) A hydrogen sulfide concentration tower is used, which is internally divided into an upper section, a middle section and a lower section from top to bottom, so that the intermediate sulfur-free rich liquid enters the upper part of the upper section for a first desorption treatment to obtain an intermediate sulfur-free semi-lean liquid and a first emission gas; the intermediate sulfur-free semi-lean liquid with a volume fraction of 58% enters the upper part of the middle section; the remaining intermediate sulfur-free semi-lean liquid leaves the hydrogen sulfide concentration unit, contacts with nitrogen in reverse, and performs a sulfur-free gas stripping treatment to obtain a sulfur-free semi-lean liquid and a second emission gas;

[0152] The intermediate sulfur-rich liquid enters the middle part of the middle section for the second desorption treatment to obtain the intermediate sulfur-containing semi-lean liquid and the third exhaust gas; the intermediate sulfur-containing semi-lean liquid with a volume fraction of 65% leaves the hydrogen sulfide concentration unit, provides cooling for the third heat exchange treatment and the first heat exchange treatment in turn, and then enters the upper part of the lower section; the third exhaust gas is reversely contacted with the intermediate sulfur-free semi-lean liquid entering the middle section, and is subjected to absorption treatment to obtain the desulfurized exhaust gas and the intermediate sulfur-containing semi-lean liquid; the desulfurized exhaust gas goes up into the upper section and merges with the first exhaust gas;

[0153] The remaining intermediate sulfur-containing semi-lean liquid is allowed to leave the hydrogen sulfide concentration unit, and is contacted with nitrogen in reverse, and is subjected to sulfur-containing gas stripping treatment, so as to obtain sulfur-containing semi-lean liquid and the fourth emission gas; the fourth emission gas is allowed to enter the hydrogen sulfide concentration unit to participate in the absorption treatment; the intermediate sulfur-containing semi-lean liquid entering the upper part of the lower section is allowed to contact with nitrogen in reverse, and is subjected to the first gas stripping treatment, so as to obtain the fifth emission gas and methanol liquid; the fifth emission gas is allowed to ascend to participate in the absorption treatment;

[0154] 6) subjecting the first exhaust gas and the second exhaust gas to exhaust gas condensation treatment to obtain exhaust gas and a first recovered liquid; subjecting the first recovered liquid to reverse contact with nitrogen to participate in the sulfur-containing gas stripping treatment; allowing the sulfur-containing semi-lean liquid to provide cooling capacity for the exhaust gas condensation treatment before the desulfurization treatment;

[0155] 7) subjecting the methanol liquid to a second heat exchange treatment and a first distillation treatment in sequence to obtain a first intermediate lean liquid and sulfuric acid-containing gas; wherein the methanol liquid provides cooling capacity for the first heat exchange treatment; and subjecting the first intermediate lean liquid to a second heat exchange treatment to obtain a second intermediate lean liquid;

[0156] 8) subjecting the second intermediate lean liquid with a volume fraction of 15% to a second distillation treatment to obtain water and methanol vapor; subjecting the remaining second intermediate lean liquid to a third heat exchange treatment to obtain lean liquid; and subjecting the methanol vapor to reverse contact with the methanol liquid to participate in the first distillation treatment;

[0157] 9) After the liquid carbon dioxide provides cooling capacity for the second condensation-gas-liquid separation process, a methanol recovery process is performed to obtain a carbon dioxide product and a second recovered liquid; and the second recovered liquid is allowed to participate in a second distillation process.

[0158] Among them, the pressure of cooling-gas-liquid separation treatment is 5.12MPa and the temperature is -37.8℃; the temperature of cooling raw gas is -12.3℃;

[0159] The pressure of desulfurization treatment is 5.1MPa and the temperature is -12.3℃; the temperature of the sulfur-containing semi-lean liquid participating in the desulfurization treatment is -72.3℃ and the pressure is 5.2MPa, and the temperature of the sulfur-free rich liquid is -12.8℃ and the pressure is 5.12MPa;

[0160] The pressure of the first condensation-gas-liquid separation process is 5.14MPa and the temperature is -18.6°C; the pressure of the second condensation-gas-liquid separation process is 5.12MPa and the temperature is -37.8°C;

[0161] The temperature of the external refrigerant is -45°C; the temperature of the first raw gas is -18.6°C; the temperature of the second raw gas is -37.8°C;

[0162] The pressure of decarbonization treatment is 5.05MPa and the temperature is 65.2℃; the temperature of sulfur-free semi-lean liquid participating in decarbonization treatment is -74.3℃ and the pressure is 5.2MPa, and the temperature of lean liquid is -65.3℃ and the pressure is 5.2MPa;

[0163] The sulfur-free rich liquid with a volume fraction of 42.8% obtained from the decarburization treatment participates in the desulfurization treatment;

[0164] The operating pressure of carbon dioxide distillation treatment is 1.6MPa, the top temperature is -40.5℃, the bottom temperature is -38.4℃; the temperature of liquid carbon dioxide is -38.4℃;

[0165] The pressure of the upper section of the hydrogen sulfide concentration unit is 0.18Mpa and the temperature is -62.4°C, the pressure of the middle section is 0.20Mpa and the temperature is -68.3°C, and the pressure of the lower section is 0.22Mpa and the temperature is -44.8°C;

[0166] The pressure of sulfur-free gas stripping treatment is 0.18Mpa and the temperature is -74.3℃;

[0167] The pressure of sulfur-containing gas stripping treatment is 0.20Mpa and the temperature is -72.3℃;

[0168] The pressure of the exhaust gas condensation treatment is 0.18MPa and the temperature is -71.0℃; the temperature of the exhaust gas is -71.0℃;

[0169] The pressure of sulfur-free flash treatment is 1.4MPa and the temperature is -34.2℃; the pressure of the intermediate sulfur-free rich liquid is 1.4MPa and the temperature is -34.2℃;

[0170] The pressure of sulfur-containing flash treatment is 1.4MPa and the temperature is -34.3℃; the pressure of the intermediate sulfur-containing rich liquid is 1.4MPa and the temperature is -34.3℃;

[0171] The pressure of the first distillation treatment is 0.32MPa and the temperature is 114°C;

[0172] The temperature of the second intermediate lean liquid is -39.8°C;

[0173] The second distillation treatment has a pressure of 0.34 MPa and a temperature of 144°C;

[0174] The pressure of methanol recovery treatment is 0.8MPa and the temperature is -37.8℃.

[0175] Example 2

[0176] The difference between this embodiment and embodiment 1 is that:

[0177] Before the first condensate and the second condensate are subjected to carbon dioxide distillation treatment, a first decompression treatment is performed to obtain a decompression condensate; the pressure of the decompression condensate is 1.7 MPa;

[0178] Before the liquid carbon dioxide provides cooling capacity for the second condensation-gas-liquid separation process, a second decompression process is performed to obtain decompressed liquid carbon dioxide; the pressure of the decompressed liquid carbon dioxide is 0.81 MPa.

[0179] Example 3

[0180] The difference between this embodiment and embodiment 1 is that the raw gas volume composition used in this embodiment is: 54.26% hydrogen, 1.73% carbon monoxide, 42.83% carbon dioxide, 0.23% sulfur-containing compounds, and the rest is other inert gases such as nitrogen; the initial pressure of the raw gas is 5.5MPa, the temperature is 40°C, and the flow rate is 256000Nm 3 / h;

[0181] The temperature of the first raw gas is -20°C; the temperature of the second raw gas is -41°C;

[0182] The pressure of the vacuum condensate is 1.7MPa, the operating pressure of the carbon dioxide distillation treatment is 1.7MPa, the tower top temperature is -38.7℃, the tower bottom temperature is -35.4℃; the pressure of the vacuum liquid phase carbon dioxide is 0.60MPa;

[0183] The temperature of the sulfur-free gas stripping treatment is -73.1°C; the temperature of the sulfur-containing gas stripping treatment is -72.5°C;

[0184] The exhaust gas temperature is -75.2°C.

[0185] Example 4

[0186] The difference between this embodiment and embodiment 1 is that the raw gas volume composition used in this embodiment is: 47.70% hydrogen, 13.87% carbon monoxide, 37.13% carbon dioxide, 0.72% sulfur compounds, and the rest is other inert gases such as nitrogen; the initial pressure of the raw gas is 3.8MPa, the temperature is 40°C, and the flow rate is 586480Nm 3 / h;

[0187] The temperature of the first raw gas is -32°C; the temperature of the second raw gas is -50°C;

[0188] The pressure of the vacuum condensate is 1.7MPa, the operating pressure of the carbon dioxide distillation treatment is 1.7MPa, the tower top temperature is -38.7℃, the tower bottom temperature is -35.4℃; the pressure of the vacuum liquid phase carbon dioxide is 0.54MPa;

[0189] The temperature of the sulfur-free gas stripping treatment is -72.7℃; the temperature of the sulfur-containing gas stripping treatment is -71.8℃;

[0190] The exhaust gas temperature is -70.0°C.

[0191] Example 5

[0192] The difference between this embodiment and embodiment 1 is that the raw gas volume composition used in this embodiment is: 53.42% hydrogen, 1.02% carbon monoxide, 44.28% carbon dioxide, 0.35% sulfur-containing compounds, and the rest is other inert gases such as nitrogen; the initial pressure of the raw gas is 3.6MPa, the temperature is 40°C, and the flow rate is 574950Nm 3 / h;

[0193] The temperature of the first raw gas is -27°C; the temperature of the second raw gas is -48°C;

[0194] The pressure of the vacuum condensate is 1.6MPa, the operating pressure of the carbon dioxide distillation treatment is 1.6MPa, the tower top temperature is -40.5℃, the tower bottom temperature is -38.4℃; the pressure of the vacuum liquid phase carbon dioxide is 0.57MPa;

[0195] The temperature of the sulfur-free gas stripping treatment is -74.5℃; the temperature of the sulfur-containing gas stripping treatment is -73.6℃;

[0196] The exhaust gas temperature is -73.1°C.

[0197] Comparative Example 1

[0198] The present embodiment differs from the first embodiment in that the first condensation-gas-liquid separation treatment, the second condensation-gas-liquid separation treatment and the carbon dioxide distillation treatment are not performed.

[0199] Comparative Example 2

[0200] The difference between this embodiment and embodiment 1 is that the cooling capacity of the second condensation-gas-liquid separation process is provided by a refrigerant, and the product is liquid carbon dioxide.

[0201] Test example

[0202] The chemical purity and recovery rate of the carbon dioxide product obtained by the methods in the above embodiments and comparative examples, the refrigeration energy consumption required for preparing the refrigerant, the steam consumption required to provide a heat source for the first distillation treatment and the second distillation treatment, and the methanol loss were tested. The results are shown in Table 1.

[0203] Table 1

[0204]

[0205] As can be seen from Table 1, the purification method provided by the present invention can reduce cold consumption, lower refrigeration consumption, and can achieve independent purification of liquid carbon dioxide to produce carbon dioxide product gas with a purity of not less than 99%, effectively reducing the loss of methanol.

[0206] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A purification method for removing carbon dioxide, characterized in that: The following steps are involved: The raw gas is brought into reverse contact with the sulfur-containing semi-lean liquid and at least part of the sulfur-free rich liquid to perform a desulfurization treatment to obtain a desulfurized raw gas and a sulfur-containing rich liquid; Subjecting the desulfurized raw gas to a first condensation-gas-liquid separation process to obtain a first raw gas and a first condensate; subjecting the first raw gas to a second condensation-gas-liquid separation process to obtain a second raw gas and a second condensate; The second raw gas is brought into reverse contact with the sulfur-free semi-lean liquid and the lean liquid to perform a decarbonization treatment to obtain a purified gas and the sulfur-free rich liquid; subjecting the first condensate and the second condensate to carbon dioxide rectification to obtain light component impurities and liquid carbon dioxide; The liquid carbon dioxide provides cold energy for the second condensation-gas-liquid separation process, and then obtains a carbon dioxide product; A hydrogen sulfide concentration unit is used, which is divided into an upper section, a middle section and a lower section from top to bottom, and includes the following steps: Allow the remaining sulfur-free rich liquid to enter the upper part of the upper section for a first desorption treatment to obtain an intermediate sulfur-free semi-lean liquid and a first exhaust gas; allow at least a portion of the intermediate sulfur-free semi-lean liquid to enter the upper part of the middle section; The remaining intermediate sulfur-free semi-lean liquid is allowed to leave the hydrogen sulfide concentration unit, and is contacted with nitrogen in reverse direction to undergo sulfur-free gas stripping treatment to obtain the sulfur-free semi-lean liquid and the second exhaust gas; The sulfur-rich liquid is allowed to enter the middle of the middle section for a second desorption treatment to obtain an intermediate sulfur-containing semi-lean liquid and a third exhaust gas; the third exhaust gas is reversely contacted with the intermediate sulfur-free semi-lean liquid entering the middle section for an absorption treatment to obtain a desulfurized exhaust gas and the intermediate sulfur-containing semi-lean liquid; the desulfurized exhaust gas ascends to enter the upper section and merges with the first exhaust gas; at least a portion of the intermediate sulfur-containing semi-lean liquid is allowed to enter the upper part of the lower section; The remaining intermediate sulfur-containing semi-lean liquid is allowed to leave the hydrogen sulfide concentration unit, and is contacted with the nitrogen in reverse direction to undergo sulfur-containing gas stripping treatment to obtain the sulfur-containing semi-lean liquid and a fourth exhaust gas; allowing the fourth exhaust gas to enter the hydrogen sulfide concentration unit to participate in the absorption process; The intermediate sulfur-containing semi-lean liquid entering the upper part of the lower section is brought into countercurrent contact with the nitrogen gas to perform a first gas stripping treatment to obtain a fifth exhaust gas and methanol liquid; the fifth exhaust gas ascends to participate in the absorption treatment; Before the first condensate and the second condensate are subjected to the carbon dioxide distillation treatment, a first decompression treatment is performed to obtain a decompression condensate; the pressure of the decompression condensate is 0.81-2.51 MPa; and / or, Before the liquid carbon dioxide provides cooling capacity for the second condensation-gas-liquid separation process, a second decompression process is performed to obtain decompressed liquid carbon dioxide; the pressure of the decompressed liquid carbon dioxide is 0.45-1.30 MPa.

2. The purification method according to claim 1, characterized in that: subjecting the first exhaust gas and the second exhaust gas to exhaust gas condensation treatment to obtain exhaust gas and a first recovery liquid; The first recovery liquid is contacted with the nitrogen gas in reverse order to participate in the sulfur-containing gas stripping treatment; The sulfur-containing semi-lean liquid provides cooling capacity for the exhaust gas condensation process before the desulfurization process.

3. The purification method according to claim 2, characterized in that: Before the remaining sulfur-free rich liquid enters the upper part of the upper section for the first desorption treatment, the first heat exchange treatment and the sulfur-free flash treatment are sequentially performed to obtain the first recycled gas and the intermediate sulfur-free rich liquid; the intermediate sulfur-free rich liquid is then made to enter the upper part of the upper section as the sulfur-free rich liquid for the first desorption treatment; the first recycled gas is combined with the feed gas to participate in the desulfurization treatment; and / or, Before the sulfur-containing rich liquid enters the middle part of the middle section for the second desorption treatment, the first heat exchange treatment and the sulfur-containing flash treatment are carried out in sequence to obtain the second recovered gas and the intermediate sulfur-containing rich liquid; the intermediate sulfur-containing rich liquid is then made to enter the middle part of the middle section as the sulfur-containing rich liquid for the second desorption treatment; the second recovered gas is combined with the feed gas to participate in the desulfurization treatment.

4. The purification method according to claim 3, characterized in that: The methanol liquid is subjected to a second heat exchange treatment and a first distillation treatment in sequence to obtain a first intermediate lean liquid and sulfuric acid-containing gas; wherein the methanol liquid provides cooling capacity for the first heat exchange treatment; The first intermediate lean liquid is subjected to the second heat exchange treatment to obtain a second intermediate lean liquid.

5. The purification method according to claim 4, characterized in that: At least a portion of the second intermediate lean liquid is subjected to a second distillation treatment to obtain water and methanol vapor; the methanol vapor is brought into countercurrent contact with the methanol liquid to participate in the first distillation treatment.

6. The purification method according to claim 5, characterized in that: After the liquid carbon dioxide provides cooling capacity for the second condensation-gas-liquid separation process, methanol recovery treatment is performed to obtain the carbon dioxide product and the second recovered liquid; and the second recovered liquid is allowed to participate in the second distillation process.

7. The purification method according to claim 6, characterized in that: subjecting the remaining second intermediate lean liquid to a third heat exchange treatment to obtain the lean liquid; wherein, before at least part of the intermediate sulfur-containing semi-lean liquid enters the upper portion of the lower section, the intermediate sulfur-containing semi-lean liquid is allowed to leave the hydrogen sulfide concentration unit to sequentially provide cooling capacity for the third heat exchange treatment and the first heat exchange treatment; and / or, Before the raw gas is subjected to desulfurization treatment, a cooling-gas-liquid separation treatment is performed to obtain a cooled raw gas and a third recovered liquid; the cooled raw gas is used as the raw gas for the desulfurization treatment; the third recovered liquid is allowed to participate in the second distillation treatment; the purified gas, the exhaust gas, the light component impurities and the carbon dioxide product provide cooling capacity for the cooling-gas-liquid separation treatment.

8. The purification method according to claim 7, characterized in that: The desulfurization treatment has a pressure of 2.02-8.05 MPa and a temperature of -30.5--5.2°C; and / or, The decarburization treatment is performed at a pressure of 1.97 to 8.00 MPa and a temperature of -66.8 to -45.9°C; and / or The temperature of the first raw gas is not higher than -12°C; and / or, The temperature of the second raw gas is not higher than -20°C; and / or, The operating pressure of the carbon dioxide distillation treatment is 0.80-2.51 MPa and the temperature is -40~-22°C; and / or, The pressure of the upper section of the hydrogen sulfide concentration unit is 0.15~0.20MPa and the temperature is -70.2~-50.1°C, the pressure of the middle section is 0.17~0.22MPa and the temperature is -51.2~-70.1°C, and the pressure of the lower section is 0.19~0.24MPa and the temperature is -38.6~-58.2°C; and / or, The sulfur-free gas stripping treatment has a pressure of 0.15-0.20 MPa and a temperature of -89.8--72.1°C; and / or, The pressure of the sulfur-containing gas stripping treatment is 0.17~0.22MPa and the temperature is -89.1~-71.3℃; and / or, The temperature of the exhaust gas is not higher than -67°C; and / or, The sulfur-free flash treatment has a pressure of 0.6 to 2.1 MPa and a temperature of -22.1 to -38.3°C; and / or, The temperature of the intermediate sulfur-free rich liquid is not higher than -72.1°C; and / or, The sulfur-containing flash treatment has a pressure of 0.6 to 2.1 MPa and a temperature of -22.3 to -38.5°C; and / or, The temperature of the intermediate sulfur-rich liquid is not higher than -71.3°C; and / or, The first distillation treatment has a pressure of 0.25-0.42 MPa and a temperature of 38-118° C.; and / or, The temperature of the second intermediate lean liquid is not higher than -33.5°C; and / or, The second distillation treatment has a pressure of 0.27-0.44 MPa and a temperature of 95-146° C.; and / or, The pressure of the methanol recovery treatment is 0.55~1.30MPa and the temperature is -30.5~-55.4℃; and / or, The temperature of the lean liquid is not higher than -46.2°C; and / or, The temperature of the cooled raw gas is not higher than -5°C.

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