Method and device for preparing methanol by purifying and coupling raw material gas containing acid gas

Abstract

The invention provides a method and device for preparing methanol by purifying and coupling raw material gas containing acid gas, and the method comprises the following steps: enabling the raw material gas containing the acid gas to enter an acid gas absorption unit to be in contact with absorption liquid, and carrying out acid gas absorption treatment to respectively obtain purified gas and post-absorption liquid containing the acid gas; carrying out carbon dioxide desorption treatment on at least part of the first absorbed liquid to respectively obtain a first liquid phase and a first gas phase containing carbon dioxide; enabling the second post-absorption liquid, the rest of the first post-absorption liquid and the first liquid phase to enter a gas stripping unit, and carrying out hydrogen gas stripping treatment to respectively obtain a second liquid phase containing hydrogen sulfide and a second gas phase containing carbon dioxide and hydrogen; enabling the first gas phase and the second gas phase to enter a reaction unit, and contacting with hydrogen for hydrogenation reaction to generate methanol. According to the method, carbon dioxide can be fully utilized, resource waste is avoided, and greenhouse gas emission is reduced.

Description

Technical Field

[0001] The invention belongs to the field of synthesis technology, and in particular relates to a method and a device for preparing methanol by purifying raw gas containing acidic gas and coupling it. Background Art

[0002] In the existing coal chemical production, the crude synthesis gas contains a large amount of acidic gases such as CO2, H2S, COS, etc. These gases are harmful to downstream processes, especially sulfides that can cause catalyst poisoning. Although traditional desulfurization and decarbonization technologies, such as physical absorption and chemical absorption, are widely used in industry, they still have many shortcomings, such as large solvent consumption, high energy consumption, and insufficient purification. Low-temperature methanol washing technology uses cold methanol as the absorption solvent and utilizes the high solubility of methanol in acidic gases at low temperatures to efficiently remove acidic gases from the raw gas. This technology has the advantages of no solvent foaming, good chemical and thermal stability, and high purified gas quality. Especially under low temperature conditions, methanol has a strong selective absorption capacity for H2S, COS and CO2, and can achieve high-purity gas purification.

[0003] In the traditional low-temperature methanol washing process, a large amount of CO2 absorbed by lean methanol is diluted by N2 and directly discharged into the atmosphere as exhaust gas, resulting in waste of resources and increased greenhouse gas emissions. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for preparing methanol by purifying raw gas containing acidic gas, which can make full use of carbon dioxide, avoid waste of resources and reduce greenhouse gas emissions.

[0005] The present invention also provides a device for preparing methanol by purifying raw gas containing acidic gas. The device can be used to prepare methanol, which can fully utilize carbon dioxide, avoid waste of resources, and reduce greenhouse gas emissions.

[0006] In a first aspect, the present invention provides a method for preparing methanol by purifying a raw gas containing acidic gas, comprising the following steps:

[0007] Allowing a raw gas containing acidic gas to enter an acidic gas absorption unit, contact the raw gas with an absorption liquid entering the acidic gas absorption unit, and perform an acidic gas absorption process to obtain a purified gas and an absorption liquid containing the acidic gas, respectively; wherein the absorption liquid includes methanol, the acidic gas includes carbon dioxide and hydrogen sulfide, and the absorption liquid includes a first absorption liquid containing carbon dioxide and methanol, and a second absorption liquid containing carbon dioxide, hydrogen sulfide and methanol;

[0008] Desorbing carbon dioxide from at least a portion of the first absorbed liquid to obtain a first liquid phase and a first gas phase containing the carbon dioxide;

[0009] The second absorbed liquid, the remaining part of the first absorbed liquid and the first liquid phase enter a gas stripping unit to perform hydrogen stripping treatment to obtain a second liquid phase containing hydrogen sulfide and a second gas phase containing carbon dioxide and hydrogen, respectively;

[0010] The first gas phase and the second gas phase enter a reaction unit, and are contacted with hydrogen entering the reaction unit to perform a hydrogenation reaction to generate methanol;

[0011] performing methanol regeneration treatment on the second liquid phase to obtain a third liquid phase containing the methanol and a third gas phase containing the hydrogen sulfide;

[0012] At least a portion of the third liquid phase is returned to the acid gas absorption unit to participate in the acid gas absorption process as the absorption liquid.

[0013] In the above-mentioned method for preparing methanol by purifying raw gas containing acidic gas and coupling it, the raw gas containing acidic gas includes synthesis gas containing the acidic gas.

[0014] The method for preparing methanol by purifying raw gas containing acidic gas as described above further includes: allowing at least part of the purified gas to enter the reaction unit to participate in the hydrogenation reaction; wherein, at least part of the hydrogen entering the reaction unit is derived from the purified gas entering the reaction unit.

[0015] The method for preparing methanol by purifying raw gas containing acid gas coupled with the above method, wherein the raw gas enters the acid gas absorption unit from the lower part of the acid gas absorption unit, and the absorption liquid enters the acid gas absorption unit from the upper part of the acid gas absorption unit;

[0016] The first absorbed liquid is output from the lower part of the acid gas absorption unit, and then subjected to the carbon dioxide desorption treatment and the hydrogen stripping treatment respectively;

[0017] The second absorbed liquid is output from the bottom of the acid gas absorption unit and then enters the gas stripping unit.

[0018] The method for preparing methanol by purifying raw gas containing acidic gas coupled with the above method, wherein the third liquid phase contains water;

[0019] The process of returning at least a portion of the third liquid phase to the acid gas absorption unit includes: returning a portion of the third liquid phase to the acid gas absorption unit;

[0020] The method for preparing methanol by purifying raw gas containing acidic gas and coupling it also includes:

[0021] allowing the remaining portion of the third liquid phase to enter the first separation unit to separate methanol and water, thereby obtaining water and second crude methanol respectively;

[0022] The second crude methanol is fed into a distillation unit for distillation treatment to obtain a methanol product.

[0023] In the above-mentioned method for preparing methanol by purifying raw gas containing acidic gas and coupling it, the conditions of the gas stripping treatment are: the gas stripping temperature is -70°C to -40°C and the pressure is 0.05MPa to 0.15MPa.

[0024] The above-mentioned method for preparing methanol by purifying raw gas containing acidic gas,

[0025] The conditions for the acid gas absorption treatment are: absorption temperature is -70°C to -20°C and pressure is 2MPa to 8MPa;

[0026] And / or, the conditions for the carbon dioxide desorption treatment are: the desorption pressure is 0.2MPa to 0.4MPa;

[0027] And / or, the conditions of the hydrogenation reaction are: the hydrogenation temperature is 220°C to 280°C and the pressure is 3MPa to 7MPa;

[0028] And / or, the conditions of the methanol regeneration treatment are: the regeneration temperature is 80° C. to 110° C. and the pressure is 0.2 MPa to 0.4 MPa.

[0029] In a second aspect, the present invention provides a device for purifying raw gas containing acidic gas and preparing methanol, comprising:

[0030] The acid gas absorption unit comprises a first absorbed liquid outlet, a second absorbed liquid outlet, and a third liquid phase inlet;

[0031] A carbon dioxide desorption unit comprises a first absorbed liquid inlet, a first liquid phase outlet, and a first gas phase outlet; the first absorbed liquid inlet is connected to the first absorbed liquid outlet of the acid gas absorption unit;

[0032] The gas stripping unit comprises a first liquid phase inlet, a second liquid phase outlet, and a second gas phase outlet; the first liquid phase inlet is respectively connected to the first liquid phase outlet of the carbon dioxide desorption unit, the second absorbed liquid outlet of the acid gas absorption unit, and the first absorbed liquid outlet of the acid gas absorption unit;

[0033] The reaction unit comprises a first gas phase inlet; the first gas phase inlet is respectively connected to the first gas phase outlet of the carbon dioxide desorption unit and the second gas phase outlet of the gas stripping unit;

[0034] The regeneration unit comprises a second liquid phase inlet and a third liquid phase outlet; the second liquid phase inlet is connected to the second liquid phase outlet of the stripping unit, and the third liquid phase outlet is connected to the third liquid phase inlet of the acid gas absorption unit.

[0035] The above-mentioned device for preparing methanol by purifying raw gas containing acidic gas coupled thereto also includes a first separation unit and a rectification unit;

[0036] The first separation unit comprises a fourth liquid phase inlet and a second crude methanol outlet, and the distillation unit comprises a crude methanol inlet;

[0037] The fourth liquid phase inlet is communicated with the third liquid phase outlet of the regeneration unit, and the second crude methanol outlet is communicated with the crude methanol inlet of the distillation unit.

[0038] The above-mentioned device for preparing methanol by purifying raw gas containing acidic gas coupled with methanol, wherein the regeneration unit further comprises a third gas phase outlet, and the device further comprises a recovery unit;

[0039] The recovery unit comprises a third gas phase inlet, and the third gas phase inlet is connected to the third gas phase outlet of the regeneration unit;

[0040] And / or, the acid gas absorption unit further comprises a purified gas outlet;

[0041] The purified gas outlet is communicated with the first gas phase inlet of the reaction unit.

[0042] The method for preparing methanol by purifying raw gas containing acidic gas provided by the present invention uses hydrogen as a stripping medium to perform hydrogen stripping treatment on the second absorbed liquid, part of the first absorbed liquid and the first liquid phase, which can fully utilize carbon dioxide, avoid waste of resources and reduce greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the following briefly introduces the drawings required for use in the embodiments of the present invention or related technologies. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0044] Figure 1 A schematic diagram of a device for purifying raw gas containing acidic gas and coupling it to prepare methanol provided by the present invention.

[0045] Description of reference numerals:

[0046] 1-acid gas absorption unit; 2-carbon dioxide desorption unit; 3-gas stripping unit; 4-reaction unit; 5-regeneration unit; 6-first separation unit; 7-distillation unit; 8-recovery unit; 9-water electrolysis unit; 10-hydrogen compression unit; 11-gas phase compression unit; 12-second separation unit. DETAILED DESCRIPTION

[0047] 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.

[0048] In a first aspect, the present invention provides a method for preparing methanol by purifying a raw gas containing acidic gas, comprising the following steps:

[0049] Allowing a raw gas containing acidic gas to enter an acidic gas absorption unit, contact the raw gas with an absorption liquid entering the acidic gas absorption unit, and perform an acidic gas absorption process to obtain a purified gas and an absorption liquid containing the acidic gas, respectively; wherein the absorption liquid includes methanol, the acidic gas includes carbon dioxide and hydrogen sulfide, and the absorption liquid includes a first absorption liquid containing carbon dioxide and methanol, and a second absorption liquid containing carbon dioxide, hydrogen sulfide and methanol;

[0050] Desorbing carbon dioxide from at least a portion of the first absorbed liquid to obtain a first liquid phase and a first gas phase containing the carbon dioxide;

[0051] The second absorbed liquid, the remaining part of the first absorbed liquid and the first liquid phase enter a gas stripping unit to perform hydrogen stripping treatment to obtain a second liquid phase containing hydrogen sulfide and a second gas phase containing carbon dioxide and hydrogen, respectively;

[0052] The first gas phase and the second gas phase enter a reaction unit, and are contacted with hydrogen entering the reaction unit to perform a hydrogenation reaction to generate methanol;

[0053] performing methanol regeneration treatment on the second liquid phase to obtain a third liquid phase containing the methanol and a third gas phase containing the hydrogen sulfide;

[0054] At least a portion of the third liquid phase is returned to the acid gas absorption unit to participate in the acid gas absorption process as the absorption liquid.

[0055] In the method for preparing methanol by purifying raw gas containing acidic gas coupled with the present invention, the raw gas containing acidic gas can be pre-cooled and then enter the acidic gas absorption unit, contact with the absorption liquid of the acidic gas absorption unit, and carry out acidic gas absorption treatment to obtain purified gas and absorbed liquid containing acidic gas. The acidic gas absorption unit can be an acidic gas absorption tower, which is divided into three parts: upper, middle and lower parts, the upper part is a fine washing section, the middle part is a main washing section, and the lower part is a hydrogen sulfide absorption section. Hydrogen sulfide in the raw gas is absorbed in the hydrogen sulfide absorption section at the lower part of the absorption tower, and carbon dioxide is absorbed and removed in the upper and middle parts of the absorption tower. Among them, the absorption liquid includes methanol, and the acidic gas includes carbon dioxide and hydrogen sulfide, and may also include carbonyl sulfide. The purified gas can be output from the top of the acidic gas absorption tower and enter the reaction unit to generate methanol. The absorbed liquid containing acidic gas includes a first absorbed liquid and a second absorbed liquid, wherein the first absorbed liquid includes carbon dioxide and methanol, and the second absorbed liquid includes carbon dioxide, hydrogen sulfide and methanol.

[0056] At least a portion of the first absorbed liquid is subjected to carbon dioxide desorption treatment to obtain a first gas phase and a first liquid phase including carbon dioxide, wherein the first liquid phase mainly includes methanol and a small amount of carbon dioxide that has not been desorbed. The first gas phase enters a reaction unit and undergoes a hydrogenation reaction with hydrogen to generate methanol. The hydrogen can be obtained by electrolyzing water.

[0057] The second absorbed liquid, the remaining first absorbed liquid and the first liquid phase enter the stripping unit, and hydrogen is used as the stripping medium to strip carbon dioxide. The addition of hydrogen reduces the partial pressure of carbon dioxide in methanol, destroys the gas-liquid equilibrium state, and due to the pressure difference between the gas and liquid phases of carbon dioxide, carbon dioxide diffuses from the methanol liquid to the gas phase, reaching a new gas-liquid equilibrium state, thereby realizing the stripping process of carbon dioxide, and obtaining a second liquid phase containing hydrogen sulfide, that is, the second liquid phase includes hydrogen sulfide and methanol, and a second gas phase containing carbon dioxide and hydrogen. Both carbon dioxide and hydrogen in the second gas phase can be used as raw materials for synthesizing methanol, and the second gas phase enters the reaction unit for hydrogenation reaction to generate methanol, which can make full use of carbon dioxide and hydrogen, reduce resource waste, and reduce greenhouse gas emissions.

[0058] Since the second liquid phase includes hydrogen sulfide and methanol, the second liquid phase can be subjected to methanol regeneration treatment. For example, the second liquid can be heated to volatilize hydrogen sulfide, thereby obtaining a third liquid phase containing methanol and a third gas phase containing hydrogen sulfide, i.e., Claus gas, which can be subjected to sulfur recovery treatment. Part of the third liquid phase can be returned to the acid gas absorption unit to participate in the acid gas absorption treatment as an absorption liquid, i.e., fully utilizing the methanol solution, reducing resource waste, and saving costs.

[0059] The method for preparing methanol by purifying raw gas containing acidic gas provided by the present invention uses hydrogen as a stripping medium to perform hydrogen stripping treatment on the second absorbed liquid, part of the first absorbed liquid and the first liquid phase, which can fully utilize carbon dioxide, avoid waste of resources and reduce greenhouse gas emissions.

[0060] In some embodiments of the present invention, the raw gas containing acid gas includes synthesis gas containing the acid gas.

[0061] The synthesis gas containing acidic gas in the present invention may be synthesis gas produced by coal production process, that is, in addition to acidic gases: carbon dioxide, hydrogen sulfide and carbonyl sulfide, it also includes carbon monoxide and hydrogen. Therefore, the purified gas includes carbon monoxide and hydrogen.

[0062] In some embodiments of the present invention, the method further includes: allowing at least a portion of the purified gas to enter the reaction unit to participate in the hydrogenation reaction; wherein the hydrogen entering the reaction unit is at least partially derived from the purified gas entering the reaction unit.

[0063] In the present invention, the purified gas can enter the reaction unit for hydrogenation reaction to generate methanol, or it can be used as purified product gas for other purposes. Since the purified gas includes hydrogen, the hydrogen for hydrogenation reaction in the reaction unit can come from the purified gas, so that the hydrogen can be fully utilized.

[0064] In some embodiments of the present invention, the feed gas enters the acid gas absorption unit from the lower part of the acid gas absorption unit, and the absorption liquid enters the acid gas absorption unit from the upper part of the acid gas absorption unit;

[0065] The first absorbed liquid is output from the lower part of the acid gas absorption unit, and then subjected to the carbon dioxide desorption treatment and the hydrogen stripping treatment respectively;

[0066] The second absorbed liquid is output from the bottom of the acid gas absorption unit and then enters the gas stripping unit.

[0067] In the present invention, the raw gas enters the acid gas absorption unit from the lower part of the acid gas absorption unit, and the absorption liquid enters the acid gas absorption unit from the upper part of the acid gas absorption unit, so that the raw gas and the absorption liquid can be contacted in reverse, so that the absorption liquid and the raw gas can be fully contacted, and the absorption effect of the absorption liquid on the acid gas in the raw gas is enhanced. The first absorbed liquid including carbon dioxide and methanol is output from the lower part of the acid gas absorption unit, and part of the first absorbed liquid is subjected to carbon dioxide desorption treatment after ammonia cooling and decompression, desorbed at low pressure, and carbon dioxide is flashed and precipitated; the second absorbed liquid including carbon dioxide, hydrogen sulfide and methanol is output from the bottom of the acid gas absorption unit, and enters the gas stripping unit together with the remaining part of the first absorbed liquid to participate in hydrogen gas stripping treatment, and obtains a second liquid phase containing hydrogen sulfide and a second gas phase containing carbon dioxide and hydrogen after pressure drop and hydrogen gas stripping.

[0068] In some embodiments of the present invention, the third liquid phase contains water;

[0069] The process of returning at least a portion of the third liquid phase to the acid gas absorption unit includes: returning a portion of the third liquid phase to the acid gas absorption unit;

[0070] The method for preparing methanol by purifying raw gas containing acidic gas and coupling it also includes:

[0071] allowing the remaining portion of the third liquid phase to enter the first separation unit to separate methanol and water, thereby obtaining water and second crude methanol respectively;

[0072] The second crude methanol is fed into a distillation unit for distillation treatment to obtain a methanol product.

[0073] The third liquid phase containing methanol of the present invention also contains water, wherein the water comes from the raw gas and / or methanol. Part of the third liquid phase is returned to the acid gas absorption unit as an absorption liquid to participate in the acid gas absorption treatment, and the third liquid phase is fully utilized. The remaining part of the third liquid phase enters the first separation unit to separate methanol and water to obtain water and second crude methanol. The second crude methanol can be used directly or enter the distillation unit for distillation treatment to remove impurities to obtain a methanol product with higher purity for downstream use.

[0074] In addition, in the reaction unit, methanol is generated through hydrogenation reaction to obtain first crude methanol; the first crude methanol can also enter the distillation unit for distillation treatment to obtain methanol product.

[0075] The distillation units may be the same or different. In order to save costs, it is preferred that the first crude methanol and the second crude methanol enter the same distillation unit.

[0076] In some embodiments of the present invention, the conditions of the gas stripping treatment are: the gas stripping temperature is -70°C to -40°C, and the pressure is 0.05MPa to 0.15MPa.

[0077] For example, the stripping temperature may be -70°C, -65°C, -60°C, -55°C, -50°C, -40°C, or any two thereof. The stripping pressure may be 0.05 MPa, 0.08 MPa, 0.1 MPa, 0.12 MPa, 0.15 MPa, or any two thereof.

[0078] In the present invention, the conditions of the gas stripping treatment are within the above range, which can achieve sufficient gas stripping of carbon dioxide by hydrogen to obtain a second gas phase containing carbon dioxide and hydrogen.

[0079] In some embodiments of the present invention,

[0080] The conditions for the acid gas absorption treatment are: absorption temperature of -70°C to -20°C and pressure of 2MPa to 8MPa.

[0081] In some embodiments, the carbon dioxide desorption treatment is performed under the following conditions: the desorption pressure is 0.2 MPa to 0.4 MPa.

[0082] In some embodiments, the conditions of the hydrogenation reaction are: hydrogenation temperature is 220°C to 280°C and pressure is 3MPa to 7MPa.

[0083] In some embodiments, the conditions of the methanol regeneration treatment are: regeneration temperature is 80°C to 110°C and pressure is 0.2MPa to 0.4MPa.

[0084] Exemplarily, the temperature of the acid gas absorption treatment may be -70°C, -60°C, -50°C, -40°C, -30°C, -20°C, or a range consisting of any two thereof. The pressure of the acid gas absorption treatment may be 2MPa, 3MPa, 4MPa, 5MPa, 6MPa, 7MPa, 8MPa, or a range consisting of any two thereof. The pressure of the carbon dioxide desorption treatment may be 0.2MPa, 0.25MPa, 0.3MPa, 0.35MPa, 0.4MPa, or a range consisting of any two thereof. The temperature of the hydrogenation reaction may be 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, or a range consisting of any two thereof. The pressure of the hydrogenation reaction may be 3MPa, 4MPa, 5MPa, 6MPa, 7MPa, or a range consisting of any two thereof. The temperature of the methanol regeneration treatment may be 80° C., 90° C., 95° C., 100° C., 110° C., or a range consisting of any two thereof. The pressure of the methanol regeneration treatment may be 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, or a range consisting of any two thereof.

[0085] The conditions for the acid gas absorption treatment in the present invention are within the above range, which can increase the solubility of the acid gas, making it easier for the acid gas to dissolve in the absorption liquid, thereby improving the absorption efficiency.

[0086] When the conditions of the carbon dioxide desorption treatment are within the above range, more carbon dioxide can be desorbed from the methanol solution, which is convenient for subsequent full utilization.

[0087] When the conditions of the hydrogenation reaction are within the above range, the hydrogenation reaction can be fully carried out to produce more crude methanol.

[0088] The methanol regeneration treatment conditions are within the above range, which can achieve sufficient separation of methanol and hydrogen sulfide gas, and facilitate subsequent separation and distillation of methanol to obtain methanol with higher purity.

[0089] In a second aspect, the present invention provides a device for purifying raw gas containing acidic gas and preparing methanol, such as Figure 1 As shown, including:

[0090] The acid gas absorption unit 1 comprises a first absorbed liquid outlet, a second absorbed liquid outlet, and a third liquid phase inlet;

[0091] The carbon dioxide desorption unit 2 comprises a first absorbed liquid inlet, a first liquid phase outlet, and a first gas phase outlet; the first absorbed liquid inlet is connected to the first absorbed liquid outlet of the acid gas absorption unit 1;

[0092] The gas stripping unit 3 comprises a first liquid phase inlet, a second liquid phase outlet, and a second gas phase outlet; the first liquid phase inlet is respectively connected to the first liquid phase outlet of the carbon dioxide desorption unit 2, the second absorbed liquid outlet of the acid gas absorption unit 1, and the first absorbed liquid outlet of the acid gas absorption unit 1;

[0093] The reaction unit 4 comprises a first gas phase inlet; the first gas phase inlet is connected to the first gas phase outlet of the carbon dioxide desorption unit 2 and the second gas phase outlet of the gas stripping unit 3 respectively;

[0094] The regeneration unit 5 comprises a second liquid phase inlet and a third liquid phase outlet; the second liquid phase inlet is connected to the second liquid phase outlet of the stripping unit 3 , and the third liquid phase outlet is connected to the third liquid phase inlet of the acid gas absorption unit 1 .

[0095] In the present invention, raw gas containing acid gas enters the acid gas absorption unit from the lower part of the acid gas absorption unit, contacts with absorption liquid methanol entering the acid gas absorption unit from the upper part of the acid gas absorption unit, and performs acid gas absorption treatment to obtain purified gas and absorbed liquid containing acid gas, wherein the absorbed liquid includes a first absorbed liquid containing carbon dioxide and methanol, and a second absorbed liquid containing carbon dioxide, hydrogen sulfide and methanol.

[0096] At least part of the first absorbed liquid is output from the first absorbed liquid outlet of the acid gas absorption unit, enters the carbon dioxide desorption unit through the first absorbed liquid inlet of the carbon dioxide desorption unit for carbon dioxide desorption treatment, and obtains a first liquid phase and a first gas phase containing carbon dioxide; the remaining part of the first absorbed liquid is output from the first absorbed liquid outlet of the acid gas absorption unit, enters the gas stripping unit through the first liquid phase inlet of the gas stripping unit. The first liquid phase is output from the first liquid phase outlet of the carbon dioxide desorption unit, enters the gas stripping unit through the first liquid phase inlet of the gas stripping unit, and the second absorbed liquid is output from the second absorbed liquid outlet of the acid gas absorption unit, enters the gas stripping unit through the first liquid phase inlet of the gas stripping unit, and jointly performs hydrogen stripping treatment, wherein hydrogen is used as the gas stripping medium to obtain a second liquid phase containing hydrogen sulfide and a second gas phase containing carbon dioxide and hydrogen. Among them, the first liquid phase inlet can be one or more, for example, three, so that the first liquid phase enters the gas stripping unit from the first first liquid phase inlet, the remaining part of the first absorbed liquid enters the gas stripping unit from the second first liquid phase inlet, and the second absorbed liquid enters the gas stripping unit from the third first liquid phase inlet.

[0097] The first gas phase containing carbon dioxide is output from the first gas phase outlet of the carbon dioxide desorption unit, and enters the reaction unit through the first gas phase inlet of the reaction unit. The second gas phase containing carbon dioxide and hydrogen is output from the second gas phase outlet of the gas stripping unit, and enters the reaction unit through the first gas phase inlet of the reaction unit. The two gas phases are contacted with the hydrogen entering the reaction unit to perform a hydrogenation reaction to generate methanol.

[0098] The second liquid phase containing hydrogen sulfide is output from the second liquid phase outlet of the stripping unit, enters the regeneration unit through the second liquid phase inlet of the regeneration unit for methanol regeneration treatment, and obtains a third liquid phase containing methanol and a third gas phase containing hydrogen sulfide. Among them, at least part of the third liquid phase containing methanol is output from the third liquid phase outlet of the regeneration unit, enters the acid gas absorption unit through the third liquid phase inlet of the acid gas absorption unit, and participates in the acid gas absorption treatment as an absorption liquid.

[0099] The present invention uses hydrogen as a stripping medium to perform hydrogen stripping treatment on the second absorbed liquid and the first liquid phase, thereby making full use of carbon dioxide, avoiding resource waste and reducing greenhouse gas emissions.

[0100] In some embodiments of the present invention, a first separation unit 6 and a distillation unit 7 are further included;

[0101] The first separation unit 6 comprises a fourth liquid phase inlet and a second crude methanol outlet, and the distillation unit 7 comprises a crude methanol inlet;

[0102] The fourth liquid phase inlet is communicated with the third liquid phase outlet of the regeneration unit 5 , and the second crude methanol outlet is communicated with the crude methanol inlet of the distillation unit 7 .

[0103] In the present invention, the remaining third liquid phase is output from the third liquid phase outlet of the regeneration unit, enters the first separation unit through the fourth liquid phase inlet of the first separation unit, and separates methanol and water to obtain water and second crude methanol. The second crude methanol is output from the second crude methanol outlet of the first separation unit, enters the rectification unit through the crude methanol inlet of the rectification unit, and undergoes rectification treatment to obtain a methanol product for downstream use.

[0104] In some embodiments of the present invention, the regeneration unit 5 further comprises a third gas phase outlet, and the device further comprises a recovery unit 8;

[0105] The recovery unit 8 comprises a third gas phase inlet, and the third gas phase inlet is connected to the third gas phase outlet of the regeneration unit 5;

[0106] In some embodiments, the acid gas absorption unit 1 further comprises a purified gas outlet;

[0107] The purified gas outlet is communicated with the first gas phase inlet of the reaction unit.

[0108] In the present invention, the third gas phase containing hydrogen sulfide is output from the third gas phase outlet of the regeneration unit and enters the recovery unit through the third gas phase inlet of the recovery unit for sulfur recovery treatment, thereby reducing waste of resources and avoiding environmental pollution.

[0109] The purified gas in the present invention can be used directly as the purified product gas, or it can be output from the purified gas outlet of the acid gas absorption unit and enter the reaction unit through the first gas phase inlet of the reaction unit for hydrogenation reaction to generate methanol, thereby achieving full utilization of the purified gas.

[0110] In the present invention, the first gas phase inlet can be one or more, for example, three, so that the first gas phase enters the reaction unit from the first first gas phase inlet, the second gas phase enters the reaction unit from the second first gas phase inlet, and the purified gas enters the reaction unit from the third first gas phase inlet.

[0111] In addition, the reaction unit 4 in the present invention may also include a first crude methanol outlet. The first crude methanol is output through the first crude methanol outlet of the reaction unit 4 and enters the distillation unit 7 through the crude methanol inlet of the distillation unit 7 for distillation to obtain a methanol product with higher purity for downstream use.

[0112] The device of the present invention further comprises a water electrolysis unit 9 and a hydrogen compression unit 10, the water electrolysis unit 9 comprises a fourth gas phase outlet, the hydrogen compression unit 10 comprises a fifth gas phase outlet and a fourth gas phase inlet, the fourth gas phase outlet is connected to the fourth gas phase inlet of the hydrogen compression unit 10. The fifth gas phase outlet is connected to the fifth gas phase inlet of the gas stripping unit 3 and the first gas phase inlet of the reaction unit 4, respectively.

[0113] Hydrogen is obtained by electrolyzing water through green electricity such as wind energy and solar energy. The hydrogen is output through the fourth gas phase outlet of the water electrolysis unit, enters the hydrogen compression unit through the fourth gas phase inlet of the hydrogen compression unit for compression, and the compressed hydrogen is output through the fifth gas phase outlet of the hydrogen compression unit. Part of the hydrogen enters the gas stripping unit through the fifth gas phase inlet of the gas stripping unit to carry out gas stripping treatment of carbon dioxide, and the remaining part is output through the fifth gas phase outlet of the hydrogen compression unit, enters the reaction unit through the first gas phase inlet of the reaction unit to participate in the hydrogenation reaction to generate methanol.

[0114] The device of the present invention further comprises a gas phase compression unit 11 and a second separation unit 12;

[0115] The fifth gas phase outlet of the hydrogen compression unit 10 is communicated with the first gas phase inlet of the reaction unit 4 through the gas phase compression unit 11, the first gas phase outlet of the carbon dioxide desorption unit 2 is communicated with the first gas phase inlet of the reaction unit 4 through the gas phase compression unit 11, the second gas phase outlet of the gas stripping unit 3 is communicated with the first gas phase inlet of the reaction unit 4 through the gas phase compression unit 11, and the purified gas outlet of the acid gas absorption unit 1 is communicated with the first gas phase inlet of the reaction unit 4 through the gas phase compression unit 11.

[0116] The first crude methanol outlet of the reaction unit 4 is connected to the crude methanol inlet of the distillation unit 7 through the second separation unit 12. The first crude methanol generated by the hydrogenation reaction of the reaction unit 4 is output through the first crude methanol outlet of the reaction unit 4, enters the second separation unit 12 through the first crude methanol inlet of the second separation unit 12 for second separation, and obtains hydrogen and crude methanol. The crude methanol is output from the crude methanol outlet of the second separation unit 12, enters the distillation unit 7 through the crude methanol inlet of the distillation unit 7 for distillation treatment, and obtains a methanol product. That is, the first crude methanol first undergoes the second separation treatment to obtain hydrogen and crude methanol, and the crude methanol can enter the distillation unit 7 for distillation treatment, and the hydrogen can return to the gas phase compression unit 11, and then enters the reaction unit 4 to participate in the hydrogenation reaction to generate methanol.

[0117] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0118] Example 1

[0119] The device used in this embodiment is Figure 1 The device for preparing methanol by purifying raw gas containing acidic gas and coupling it as shown includes an acidic gas absorption unit 1 (absorption tower); a carbon dioxide desorption unit 2 (desorption tower); a gas stripping unit 3 (gas stripping tower); a reaction unit 4 (reactor); a regeneration unit 5 (regeneration tower); a first separation unit 6 (first separation tower); a distillation unit 7 (distillation tower); a recovery unit 8 (recovery tower); a water electrolysis unit 9 (electrolyzer); a hydrogen compression unit 10 (hydrogen compressor); a gas phase compression unit 11 (gas phase compressor); and a second separation unit 12 (second separation tower).

[0120] The first absorbed liquid inlet of the carbon dioxide desorption unit 2 is connected to the first absorbed liquid outlet of the acid gas absorption unit 1, the first liquid phase inlet of the gas stripping unit 3 is respectively connected to the first liquid phase outlet of the carbon dioxide desorption unit 2, the first absorbed liquid outlet of the acid gas absorption unit 1, and the second absorbed liquid outlet of the acid gas absorption unit 1, the first gas phase inlet of the reaction unit 4 is respectively connected to the first gas phase outlet of the carbon dioxide desorption unit 2, the second gas phase outlet of the gas stripping unit 3, the purified gas outlet of the acid gas absorption unit 1, and the fifth gas phase outlet of the hydrogen compression unit 10 through the gas phase compression unit 11, and the second liquid phase inlet of the regeneration unit 5 is connected to the second gas phase outlet of the gas stripping unit 3. The liquid phase outlet is connected, the third liquid phase outlet of the regeneration unit 5 is connected to the third liquid phase inlet of the acid gas absorption unit 1, the fourth liquid phase inlet of the first separation unit 6 is connected to the third liquid phase outlet of the regeneration unit 5, the second crude methanol outlet of the first separation unit 6 is connected to the crude methanol inlet of the distillation unit 7, the third gas phase outlet of the regeneration unit 5 is connected to the third gas phase inlet of the recovery unit 8, the first crude methanol outlet of the reaction unit 4 is connected to the crude methanol inlet of the distillation unit 7 through the second separation unit 12, the fourth gas phase outlet of the water electrolysis unit 9 is connected to the fourth gas phase inlet of the hydrogen compression unit 10, and the fifth gas phase outlet of the hydrogen compression unit 10 is connected to the fifth gas phase inlet of the gas stripping unit 3.

[0121] Specifically, a raw gas containing acidic gas (including synthesis gas containing acidic gas) is allowed to enter the acidic gas absorption unit 1 from the lower part of the acidic gas absorption unit 1, and is contacted with an absorption liquid entering the acidic gas absorption unit 1 from the upper part of the acidic gas absorption unit 1, and an acidic gas absorption treatment is performed to obtain a purified gas and an absorbed liquid containing acidic gas, respectively; wherein the absorption liquid includes methanol, the acidic gas includes carbon dioxide and hydrogen sulfide, and the absorbed liquid includes a first absorbed liquid containing carbon dioxide and methanol, and a second absorbed liquid containing carbon dioxide, hydrogen sulfide and methanol; wherein the conditions for the acidic gas absorption treatment are: an absorption temperature of -50°C and a pressure of 5MPa.

[0122] Part of the first absorbed liquid is output from the first absorbed liquid outlet at the bottom of the acid gas absorption unit 1, and enters the carbon dioxide desorption unit 2 through the first absorbed liquid inlet for carbon dioxide desorption treatment, thereby obtaining a first liquid phase and a first gas phase containing carbon dioxide. The carbon dioxide desorption treatment is performed under the condition of a pressure of 0.23 MPa. The remaining part of the first absorbed liquid is output from the first absorbed liquid outlet at the bottom of the acid gas absorption unit 1, and enters the gas stripping unit 3 through the first liquid phase inlet.

[0123] The second absorbed liquid is output from the second absorbed liquid outlet at the bottom of the acid gas absorption unit 1, and enters the stripping unit 3 through the first liquid phase inlet of the stripping unit 3. The first liquid phase is output from the first liquid phase outlet of the carbon dioxide desorption unit 2, and enters the stripping unit 3 through the first liquid phase inlet of the stripping unit 3. Hydrogen stripping treatment is carried out in the presence of stripping medium hydrogen to obtain a second liquid phase containing hydrogen sulfide and a second gas phase containing carbon dioxide and the stripping medium, respectively. The conditions for the stripping treatment are: temperature of -68°C and pressure of 0.10MPa.

[0124] The first gas phase and the second gas phase are compressed and enter the reaction unit 4, and are contacted with the hydrogen entering the reaction unit 4 to undergo a hydrogenation reaction to generate methanol; wherein the conditions for the hydrogenation reaction are: a temperature of 230° C. and a pressure of 3 MPa.

[0125] The second liquid phase is subjected to methanol regeneration treatment to obtain a third liquid phase containing methanol and a third gas phase containing hydrogen sulfide, respectively, and the third liquid phase contains water; wherein the conditions for the methanol regeneration treatment are: temperature of 98° C. and pressure of 0.35 MPa.

[0126] A portion of the third liquid phase is returned to the acid gas absorption unit 1 to participate in the acid gas absorption treatment as an absorption liquid, and the remaining portion of the third liquid phase enters the first separation unit 6 to separate methanol and water to obtain water and second crude methanol respectively, and the second crude methanol enters the distillation unit 7 for distillation treatment to obtain a methanol product.

[0127] The third liquid phase enters the recovery unit 8 for sulfur recovery treatment.

[0128] At least part of the purified gas is compressed and enters the reaction unit 4 to participate in the hydrogenation reaction; wherein, at least part of the hydrogen entering the reaction unit 4 comes from the purified gas entering the reaction unit 4.

[0129] The hydrogen obtained by electrolysis of water is compressed by the hydrogen compression unit 10, and then partially compressed by the gas phase compression unit 11 and enters the reaction unit 4 to participate in the hydrogenation reaction; the remaining hydrogen enters the stripping unit 3 as a stripping medium to strip carbon dioxide.

[0130] The methanol generated in the reaction unit 4 is subjected to the second separation treatment to obtain hydrogen and crude methanol, and the crude methanol enters the distillation unit 7 for distillation treatment to obtain a methanol product. The hydrogen can be returned to the reaction unit 4 for hydrogenation reaction after being compressed by the gas phase compression unit 11.

[0131] Example 2

[0132] The method and apparatus for preparing methanol by purifying raw gas containing acidic gas coupled with Example 2 are basically the same as those in Example 1, except that the conditions for gas stripping treatment are changed to: temperature of -40°C and pressure of 0.15MPa.

[0133] Example 3

[0134] The method and apparatus for preparing methanol by purifying raw gas containing acidic gas coupled with Example 3 are basically the same as those in Example 1, except that the conditions for gas stripping treatment are changed to: temperature of -70°C and pressure of 0.05 MPa.

[0135] Comparative Example 1

[0136] The method and apparatus for preparing methanol by purifying raw gas containing acidic gas coupled with Example 1 are basically the same, except that the stripping medium used in the stripping treatment is nitrogen, and a second gas phase containing carbon dioxide and nitrogen is obtained, which is directly discharged into the atmosphere as exhaust gas.

[0137] In Example 1-3, hydrogen is used as a stripping medium to carry out hydrogen stripping treatment on the second absorbed liquid and the first liquid phase, and carbon dioxide is not discharged into the atmosphere, so carbon dioxide can be fully utilized, resource waste can be avoided, and greenhouse gas emissions can be reduced. At the same time, after using hydrogen as a stripping medium and mixing it with the separated carbon dioxide, after supplementing / adjusting the ratio of carbon dioxide to hydrogen to close to 3:1, methanol can be synthesized in the reaction unit to increase the added value of the product. Using hydrogen instead of nitrogen can also reduce the investment in air separation units and make full use of existing green hydrogen resources.

[0138] In Comparative Example 1, nitrogen is used as the stripping medium to perform hydrogen stripping treatment on the second absorbed liquid and the first liquid phase, and the second gas phase containing carbon dioxide and nitrogen is directly discharged into the atmosphere as tail gas, resulting in a waste of resources and an increase in greenhouse gas emissions.

[0139] The flow rate of the raw gas and the second gas phase outlet of the stripping unit 3 is measured by using a flow meter, and the flow rate of the raw gas is measured to be F1, in kg / h, and the flow rate measured in comparative example 1 is F2, in kg / h; the carbon dioxide concentration of the raw gas and the second gas phase outlet of the stripping unit 3 is measured by using a gas chromatograph, and the carbon dioxide concentration of the raw gas is W1, and the carbon dioxide concentration measured in comparative example 1 is W2, then the carbon dioxide emission reduction S per hour in Example 1-3 is S=F2*W2, in kg; the calculation method of the carbon dioxide utilization rate improvement value P in Example 1-3 is P=(F2*W2) / (F1*W1)*100, in %. The carbon dioxide utilization rate in Example 1-3 is 100%.

[0140] 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 method for preparing methanol by purifying raw gas containing acidic gas, characterized in that: The following steps are involved: Allowing a raw gas containing acidic gas to enter an acidic gas absorption unit, contact the raw gas with an absorption liquid entering the acidic gas absorption unit, and perform an acidic gas absorption process to obtain a purified gas and an absorption liquid containing the acidic gas, respectively; wherein the absorption liquid includes methanol, the acidic gas includes carbon dioxide and hydrogen sulfide, and the absorption liquid includes a first absorption liquid containing carbon dioxide and methanol, and a second absorption liquid containing carbon dioxide, hydrogen sulfide and methanol; Desorbing carbon dioxide from at least a portion of the first absorbed liquid to obtain a first liquid phase and a first gas phase containing the carbon dioxide; The second absorbed liquid, the remaining part of the first absorbed liquid and the first liquid phase enter a gas stripping unit to perform hydrogen stripping treatment to obtain a second liquid phase containing hydrogen sulfide and a second gas phase containing carbon dioxide and hydrogen, respectively; The first gas phase and the second gas phase enter a reaction unit, and are contacted with hydrogen entering the reaction unit to perform a hydrogenation reaction to generate methanol; performing methanol regeneration treatment on the second liquid phase to obtain a third liquid phase containing the methanol and a third gas phase containing the hydrogen sulfide; At least a portion of the third liquid phase is returned to the acid gas absorption unit to participate in the acid gas absorption process as the absorption liquid.

2. The method for preparing methanol by purifying raw gas containing acidic gas according to claim 1, characterized in that: The raw gas containing the acid gas includes a synthesis gas containing the acid gas.

3. The method for preparing methanol by purifying raw gas containing acidic gas according to claim 2, characterized in that: Also includes: At least a portion of the purified gas is allowed to enter the reaction unit to participate in the hydrogenation reaction; wherein, at least a portion of the hydrogen entering the reaction unit is derived from the purified gas entering the reaction unit.

4. The method for preparing methanol by purifying raw gas containing acidic gas according to claim 1, characterized in that: The feed gas enters the acid gas absorption unit from the lower part of the acid gas absorption unit, and the absorption liquid enters the acid gas absorption unit from the upper part of the acid gas absorption unit; The first absorbed liquid is output from the lower part of the acid gas absorption unit, and then subjected to the carbon dioxide desorption treatment and the hydrogen stripping treatment respectively; The second absorbed liquid is output from the bottom of the acid gas absorption unit and then enters the gas stripping unit.

5. The method for preparing methanol by purifying raw gas containing acidic gas according to claim 1, characterized in that: The third liquid phase contains water; The process of returning at least a portion of the third liquid phase to the acid gas absorption unit includes: returning a portion of the third liquid phase to the acid gas absorption unit; The method for preparing methanol by purifying raw gas containing acidic gas and coupling it also includes: allowing the remaining portion of the third liquid phase to enter the first separation unit to separate methanol and water, thereby obtaining water and second crude methanol respectively; The second crude methanol is fed into a distillation unit for distillation treatment to obtain a methanol product.

6. The method for preparing methanol by purifying raw gas containing acidic gas according to claim 1, characterized in that: The conditions of the gas stripping treatment are: the gas stripping temperature is -70°C to -40°C, and the pressure is 0.05MPa to 0.15MPa.

7. The method for preparing methanol by purifying raw gas containing acidic gas coupled with preparation of methanol according to any one of claims 1 to 6, characterized in that: The conditions for the acid gas absorption treatment are: absorption temperature is -70°C to -20°C and pressure is 2MPa to 8MPa; And / or, the conditions for the carbon dioxide desorption treatment are: the desorption pressure is 0.2MPa to 0.4MPa; And / or, the conditions of the hydrogenation reaction are: the hydrogenation temperature is 220°C to 280°C and the pressure is 3MPa to 7MPa; And / or, the conditions of the methanol regeneration treatment are: the regeneration temperature is 80° C. to 110° C. and the pressure is 0.2 MPa to 0.4 MPa.

8. A device for preparing methanol by purifying raw gas containing acidic gas, characterized in that: include: The acid gas absorption unit comprises a first absorbed liquid outlet, a second absorbed liquid outlet, and a third liquid phase inlet; A carbon dioxide desorption unit, comprising a first post-absorption liquid inlet, a first liquid phase outlet, and a first gas phase outlet; The first absorbed liquid inlet is communicated with the first absorbed liquid outlet of the acid gas absorption unit; The gas stripping unit comprises a first liquid phase inlet, a second liquid phase outlet, and a second gas phase outlet; the first liquid phase inlet is respectively connected to the first liquid phase outlet of the carbon dioxide desorption unit, the second absorbed liquid outlet of the acid gas absorption unit, and the first absorbed liquid outlet of the acid gas absorption unit; The reaction unit comprises a first gas phase inlet; the first gas phase inlet is respectively connected to the first gas phase outlet of the carbon dioxide desorption unit and the second gas phase outlet of the gas stripping unit; The regeneration unit comprises a second liquid phase inlet and a third liquid phase outlet; the second liquid phase inlet is connected to the second liquid phase outlet of the stripping unit, and the third liquid phase outlet is connected to the third liquid phase inlet of the acid gas absorption unit.

9. The device for preparing methanol by purifying raw gas containing acidic gas according to claim 8, characterized in that: Also includes a first separation unit and a distillation unit; The first separation unit comprises a fourth liquid phase inlet and a second crude methanol outlet, and the distillation unit comprises a crude methanol inlet; The fourth liquid phase inlet is communicated with the third liquid phase outlet of the regeneration unit, and the second crude methanol outlet is communicated with the crude methanol inlet of the distillation unit.

10. The device for preparing methanol by purifying raw gas containing acidic gas according to claim 8 or 9, characterized in that: The regeneration unit further comprises a third gas phase outlet, and the device further comprises a recovery unit; The recovery unit comprises a third gas phase inlet, and the third gas phase inlet is connected to the third gas phase outlet of the regeneration unit; And / or, the acid gas absorption unit further comprises a purified gas outlet; The purified gas outlet is communicated with the first gas phase inlet of the reaction unit.

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