Method and apparatus for producing a co2 product gas

Abstract

The present application relates to the technical field of CO2 preparation, in particular to a method for preparing CO2 product gas and a device for preparing CO2 product gas. The method comprises the following steps: flashing carbon-rich methanol to obtain carbon-rich methanol flash liquid, sequentially performing first pressurization and first heat exchange on the carbon-rich methanol flash liquid to obtain heat-exchanged flash liquid, performing first separation on the heat-exchanged flash liquid to obtain first-stage CO2 gas and semi-lean methanol; sequentially performing first cooling and second separation on the first-stage CO2 gas to obtain second-stage CO2 gas, sequentially performing water washing, second cooling and third separation on the second-stage CO2 gas to obtain third-stage CO2 gas as CO2 product gas; the pressure of the CO2 product gas is 3-5 MPa. The method fully utilizes the difference in solubility of methanol solution for CO2 at different pressures and different temperatures, pressurizes the carbon-rich methanol first and then heats it, and combines three-stage separation to obtain high-purity CO2 product gas; meanwhile, the method also has low energy consumption and low investment.

Description

Technical Field

[0001] This invention relates to the field of CO2 preparation technology, specifically to a method for preparing CO2 product gas and an apparatus for preparing CO2 product gas. Background Technology

[0002] With increasing restrictions on greenhouse gas emissions, more and more coal chemical enterprises are focusing on the capture and comprehensive utilization of CO2 gas. Currently, in most coal chemical plants, the crude syngas produced by coal gasification is processed using a low-temperature methanol washing process. This process is a physical absorption method that uses low-temperature methanol as the absorbent. It utilizes the excellent solubility properties of low-temperature methanol for gases such as H2S and CO2 to desulfurize and decarbonize them. The absorption of H2S and CO2 is carried out under high pressure, and the absorption pressure depends on the upstream gasification operation pressure. The methanol rich in H2S and CO2 after absorption is regenerated into lean methanol through depressurization, stripping, and heating, thus realizing the recycling of methanol. Conventional low-temperature methanol washing processes can obtain CO2 with a concentration of over 98% by depressurizing and flashing carbon-rich methanol. This CO2 gas has a high concentration, is sulfur-free, and has a large volume, but the pressure is relatively low, generally around 0.15 MPaG. To meet the comprehensive utilization needs of downstream CO2 enterprises, CO2 compressors are commonly used to pressurize it to 3-5 MPaG (generally using three-stage compression). At the same time, methanol entrained in the CO2 gas is removed by water washing before it is sent out. The high compression ratio during CO2 boosting results in high energy consumption and cooling water consumption for the CO2 compressor.

[0003] The conventional low-temperature methanol washing process described above produces CO2 gas that is pressurized from 0.15 MPaG to 3-5 MPaG. During the pressurization process, the compression ratio is large, the compressor energy consumption is high, and the investment in CO2 compressors is high and the footprint is large.

[0004] To address the problems of high energy consumption, high investment, and large land occupation associated with the production of CO2 by-products in existing technologies, this invention provides an energy-saving method and apparatus for preparing CO2 product gas, eliminating the need for a gas compressor and reducing power consumption and equipment investment. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical problems and provide a method and apparatus for preparing CO2 product gas. This method makes full use of the difference in CO2 solubility of methanol solution under different pressures and temperatures, pressurizes and then heats carbon-rich methanol, and combines three-stage separation to obtain high-purity CO2 product gas. At the same time, this method also has low energy consumption and low investment.

[0006] To achieve the above objectives, a first aspect of the present invention provides a method for preparing CO2 product gas, the method comprising:

[0007] Carbon-rich methanol is flash-evaporized to obtain carbon-rich methanol flash liquid. After passing through the first pressurization and the first heat exchange, the flash liquid after heat exchange is subjected to the first separation to obtain primary CO2 gas and semi-lean methanol.

[0008] The primary CO2 gas is subjected to a first cooling and a second separation in sequence to obtain a secondary CO2 gas. This secondary CO2 gas is then subjected to water washing, a second cooling, and a third separation in sequence to obtain a tertiary CO2 gas as the CO2 product gas. The pressure of the CO2 product gas is 3-5 MPa.

[0009] The second aspect of the present invention provides an apparatus for preparing CO2 product gas, wherein the method provided in the first aspect is carried out in the apparatus, the apparatus comprising a medium-pressure flash distillation tower, a first pump, a first heat exchanger, a CO2 separator tank 1, a water cooler, a CO2 separator tank 2, a CO2 scrubbing tower, a propylene cooler, and a CO2 separator tank 3 connected in sequence.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] (1) The method provided by the present invention makes full use of the difference in CO2 solubility of methanol solution under different pressures and temperatures. The carbon-rich methanol is first pressurized and then heated, and then separated in three stages to obtain high-purity CO2 product gas. At the same time, the method also eliminates conventional gas compression, reducing energy consumption and investment.

[0012] (2) The method provided by the present invention makes full use of the system’s own cooling and heating capacity. While producing CO2 product gas, it obtains semi-lean methanol which can be used as washing methanol and makes full use of it to minimize system energy consumption.

[0013] (3) The CO2 product gas produced by the method provided by the present invention has the characteristics of high concentration, few impurities, and excellent environmental protection effect. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the apparatus for preparing CO2 product gas provided by the present invention;

[0015] Figure 2 This is a schematic diagram of the apparatus for preparing CO2 product gas provided in Example 1.

[0016] Explanation of reference numerals in the attached figures

[0017] 01. Raw material gas; 02. Lean methanol; 03. Washed methanol; 04. Purified gas; 05. Carbon-rich methanol; 06. Carbon-rich methanol flash liquid; 07. Flash vapor; 08. Pressurized flash liquid; 09. Heat-exchanged flash liquid; 010. Circulating gas; 011. Semi-lean methanol; 012. Primary CO2 gas; 012'. Primary CO2 gas-liquid mixture; 013. Primary liquid phase; 014. Secondary CO2 gas; 015. Water; 016. Methanol solution; 017. Washed CO2 gas; 017'. Secondary CO2 gas-liquid mixture; 018. Secondary liquid phase; 019. Tertiary CO2 gas; 020. CO2 product gas.

[0018] 1. Raw material gas cooler; 2. Methanol scrubbing tower; 3. Medium-pressure flash distillation tower; 4. First pump; 5. First heat exchanger; 6. No. 1 CO2 separator; 7. Second pump; 8. Second heat exchanger; 9. Water cooler; 10. No. 2 CO2 separator; 11. CO2 scrubbing tower; 12. Propylene cooler; 13. No. 3 CO2 separator; 14. Third pump. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] In this invention, unless otherwise specified, "first," "second," and "third" do not indicate a sequence or limit the specific materials or steps; they are merely used to distinguish or indicate that these are not the same material or step. For example, "first," "second," and "third" in "first separation," "second separation," and "third separation" are only used to indicate that these are not the same separation.

[0021] In this invention, the “top” of the container refers to 0-10% of the container from top to bottom; the “upper part” of the container refers to 10-40% of the container from top to bottom; the “middle part” of the container refers to 40-60% of the container from top to bottom; the “lower part” of the container refers to 60-90% of the container from top to bottom; and the “bottom” of the container refers to 90-100% of the container from top to bottom.

[0022] The first aspect of this invention provides a method for preparing CO2 product gas, the method comprising:

[0023] Carbon-rich methanol is flash-evaporized to obtain carbon-rich methanol flash liquid. After passing through the first pressurization and the first heat exchange, the flash liquid after heat exchange is subjected to the first separation to obtain primary CO2 gas and semi-lean methanol.

[0024] The primary CO2 gas is subjected to a first cooling and a second separation in sequence to obtain a secondary CO2 gas. This secondary CO2 gas is then subjected to water washing, a second cooling, and a third separation in sequence to obtain a tertiary CO2 gas as the CO2 product gas. The pressure of the CO2 product gas is 3-5 MPa.

[0025] In this invention, unless otherwise specified, lean methanol has a CO2 content of 0 mol% and an H2S content of 0 mol%; carbon-rich methanol refers to a methanol solution that absorbs only CO2; semi-lean methanol refers to a methanol solution with a CO2 content of 10-18 mol% after flash evaporation and separation of CO2 from carbon-rich methanol.

[0026] In this invention, preferably, the CO2 content in the carbon-rich methanol is 20-40 mol%, the H2S content is ≤0.3 ppm, and the temperature is -40 to -10℃.

[0027] In this invention, all pressure parameters are gauge pressures.

[0028] In this invention, the flash evaporation is intended to remove the effective gases (H2 and CO) from carbon-rich methanol. Preferably, the flash evaporation pressure is 0.1-1.5 MPa, for example, 0.1 MPa, 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 0.9 MPa, 1 MPa, 1.2 MPa, 1.5 MPa, and any value within any range of two such values, preferably 0.6-1 MPa.

[0029] In this invention, preferably, the CO2 content in the carbon-rich methanol flash liquid is 18-38 mol%, for example, 18 mol%, 20 mol%, 25 mol%, 30 mol%, 35 mol%, 38 mol%, or any value within any range of any two values; the temperature is -40 to -15℃, for example, -40℃, -30℃, -25℃, -20℃, -17℃, -15℃, or any value within any range of any two values.

[0030] In this invention, preferably, after the carbon-rich methanol flash liquid is pressurized, a pressurized flash liquid with a pressure of 3.1-5.1 MPa is obtained, for example, 3.1 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, 5.1 MPa, or any value within the range of any two values.

[0031] In this invention, the first heat exchange aims to increase the temperature of the pressurized flash liquid. Preferably, the pressurized flash liquid undergoes the first heat exchange to obtain a flash liquid with a temperature of 85-95°C.

[0032] In one specific embodiment of the present invention, the pressurized flash liquid is subjected to heat exchange with high-temperature lean methanol at a temperature of 95-100°C to obtain a heat-exchanged flash liquid at a temperature of 85-95°C after the pressurized flash liquid is transformed, and a lean methanol at a temperature of -60 to -50°C is obtained after the high-temperature lean methanol is transformed.

[0033] In this invention, the carbon-rich methanol is subjected to a first pressurization and a first heat exchange in sequence, making full use of the difference in CO2 solubility of methanol solution under different pressures and temperatures, so that CO2 is desorbed from the carbon-rich methanol, and a flash liquid after heat exchange is obtained. A three-stage separation is then used to obtain CO2 product gas at 3-5 MPa.

[0034] In this invention, the first separation aims to perform gas-liquid separation on the flash liquid after heat exchange to obtain primary CO2 gas and semi-lean methanol. Preferably, the primary CO2 gas has a CO2 content of 85-90 mol%.

[0035] In this invention, the semi-lean methanol is subjected to a second pressurization and a second heat exchange sequentially to obtain washed methanol. Preferably, the semi-lean methanol is subjected to a second pressurization to obtain a pressurized semi-lean methanol with a pressure of 4-7.5 MPa, and then subjected to a second heat exchange to obtain the washed methanol with a temperature of -30 to -20°C.

[0036] In this invention, the first cooling reduces the temperature of the primary CO2 gas, thereby removing residual methanol and improving CO2 purity. Preferably, the primary CO2 gas, after the first cooling, yields a primary CO2 gas-liquid mixture at a temperature of 37-43°C.

[0037] In this invention, the second cooling process includes: cooling the primary CO2 gas and circulating water to obtain the primary CO2 gas-liquid mixture.

[0038] In this invention, the second separation aims to separate the primary CO2 gas-liquid mixture to obtain a secondary CO2 gas and a primary liquid phase. Preferably, the secondary CO2 gas has a CO2 content of 91-98 mol%.

[0039] In this invention, preferably, the water washing process includes: contacting the secondary CO2 gas with water and washing it to obtain a methanol solution and washed CO2 gas. In this invention, the water washing is intended to further remove residual methanol.

[0040] In this invention, the second cooling and the third separation are intended to further separate water from the washed CO2 gas after deep cooling. Preferably, after the washed CO2 gas undergoes the second cooling, a secondary CO2 gas-liquid mixture is obtained at a temperature of 5-15°C.

[0041] In this invention, preferably, the CO2 content in the three-stage CO2 gas is ≥98.5 mol%, and more preferably 98.5-99.9 mol%.

[0042] In this invention, the source of the carbon-rich methanol is selected from a wide range, as long as the above limitations are met. Preferably, the carbon-rich methanol is obtained by decarbonizing pre-cooled feed gas and lean methanol.

[0043] In this invention, the third heat exchange aims to exchange heat between the raw material gas and the tertiary CO2 gas, resulting in a pre-cooled raw material gas transformed from the raw material gas, and a CO2 product gas transformed from the tertiary CO2 gas. More preferably, the third heat exchange between the raw material gas and the tertiary CO2 gas yields the pre-cooled raw material gas at a temperature of -20 to -5°C and the CO2 product gas at a temperature of 20-40°C.

[0044] In this invention, the decarbonization process includes: contacting the pre-cooled raw gas, lean methanol and washing methanol and performing decarbonization treatment to obtain purified gas and carbon-rich methanol that adsorbs CO2.

[0045] In this invention, the raw material gas refers to a raw material gas containing CO2. Preferably, the CO2 content in the raw material gas is 30-60 mol%, for example, 30 mol%, 40 mol%, 50 mol%, 55 mol%, 60 mol%, or any value within any range of two such values.

[0046] In this invention, the raw gas contains CO and H2 in addition to CO2. More preferably, the raw gas contains 0.5-50 mol% CO and 5-50 mol% H2.

[0047] In this invention, unless otherwise specified, the CO2 content parameter, CO content parameter, H2 content parameter and H2S content parameter are all measured by gas chromatography.

[0048] In this invention, preferably, the temperature of the raw material gas is 25-50°C, for example, 25°C, 30°C, 40°C, 50°C, or any value within the range of any two values; the pressure is 2-6 MPa, for example, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, or any value within the range of any two values.

[0049] In this invention, the source of the feed gas has a wide range of selection, as long as the above-mentioned limitations are met. Preferably, the feed gas is selected from the crude syngas from the upstream coal gasification process.

[0050] In some embodiments of the present invention, the raw material gas contains 30-60 mol% CO2, 0.5-50 mol% CO, and 5-50 mol% H2.

[0051] In this invention, preferably, the method further includes: returning the flash vapor obtained from the flash evaporation and mixing it into the feed gas; more preferably, the flash vapor is pressurized to 3-6 MPa in a third pressurization process before being returned and mixed into the feed gas. The method provided by this invention, which recycles the flash vapor, primarily reduces the loss of CO and H2 in the system.

[0052] In this invention, preferably, the method further includes: returning the primary liquid phase obtained from the second separation to perform the first separation. This arrangement involves reflux of the separated liquid phase methanol.

[0053] In this invention, preferably, the method further includes: returning the secondary liquid phase obtained from the third separation to perform the second separation. This arrangement involves reflux of the separated liquid phase, methanol.

[0054] In this invention, the primary and secondary liquid phases are recycled to reduce the loss of methanol in the system.

[0055] The method provided by this invention not only yields high-purity CO2 product gas, but also reduces methanol loss in the system, offering advantages of low energy consumption and low cost.

[0056] In this invention, preferably, the CO2 content in the CO2 product gas is ≥98.5 mol%, and more preferably 98.5-99.9 mol%.

[0057] The second aspect of the present invention provides a schematic diagram of an apparatus for preparing CO2 product gas, as shown below. Figure 1 As shown, the device includes a medium-pressure flash evaporator 3, a first pump 4, a first heat exchanger 5, a CO2 separator 6, a water cooler 9, a CO2 separator 10, a CO2 scrubbing tower 11, a propylene cooler 12, and a CO2 separator 13 connected in sequence.

[0058] In this invention, preferably, as follows: Figure 2 As shown, according to the material flow direction, the device further includes: a raw material gas cooler 1 and a methanol washing tower 2 connected in sequence before the medium-pressure flash tower 3.

[0059] In this invention, preferably, as follows: Figure 2 As shown, the bottom of the #1 CO2 separator 6 is connected to the methanol washing tower 2 according to the material flow direction.

[0060] In this invention, preferably, as follows: Figure 2As shown, the top of the No. 3 CO2 separator 13 is connected to the raw material gas cooler 1 according to the material flow direction.

[0061] In this invention, such as Figure 2 As shown, the raw material gas cooler 1 is used to perform a third heat exchange between the raw material gas 01 and the third-stage CO2 gas 019 to obtain pre-cooled raw material gas and CO2 product gas 020; the methanol washing tower 2 is used to contact the pre-cooled raw material gas, lean methanol 02, and washing methanol 03 for decarbonization treatment to obtain purified gas 04 and carbon-rich methanol 05; the medium-pressure flash distillation tower 3 is used to flash distill the carbon-rich methanol 05, obtaining carbon-rich methanol flash liquid 06 at the bottom and flash vapor 07 at the top; the first pump 4 is used to pressurize the carbon-rich methanol flash liquid 06 to obtain pressurized flash liquid 08, which is then sent to the first heat exchanger 5 for the first heat exchange to obtain heat-exchanged flash liquid 09; the #1 CO2 separator 6 is used to perform the first separation of the heat-exchanged flash liquid 09, obtaining first-stage CO2 gas 012 at the top and semi-lean methanol 011 at the bottom; water Cooler 9 is used to first cool the primary CO2 gas 012 to obtain a primary CO2 gas-liquid mixture 012'; CO2 separator 10 is used to second separate the primary CO2 gas-liquid mixture 012', obtaining secondary CO2 gas 014 at the top of the column and primary liquid phase 013 at the bottom of the column; water washing column 11 is used to contact and wash the secondary CO2 gas 014 with water 015, obtaining washed CO2 gas 017 at the top of the column and methanol solution 016 at the bottom of the column; propylene cooler 12 is used to second cool the washed CO2 gas 017 to obtain a secondary CO2 gas-liquid mixture 017'; CO2 separator 13 is used to third separate the secondary CO2 gas-liquid mixture 017', obtaining tertiary CO2 gas 019 at the top of the column and secondary liquid phase 018 at the bottom of the column.

[0062] According to the present invention, preferably, such as Figure 2 As shown, according to the material flow direction, the device further includes: a second pump 7 and a second heat exchanger 8 are sequentially installed on the pipeline connecting the bottom of the No. 1 CO2 separator 6 and the methanol washing tower 2, for sequentially pressurizing and heat-exchanging the semi-lean methanol 011 to obtain washed methanol 03.

[0063] According to the present invention, preferably, such as Figure 2 As shown, according to the material flow direction, the device further includes: a third pump 14 is installed on the pipeline connecting the top of the medium-pressure flash tower 3 and the raw material gas cooler 1, which is used to return the flash vapor 07 after third pressurization and mix it with the raw material gas 01 for the first cooling.

[0064] According to the present invention, preferably, such as Figure 2As shown, the bottom of the #2 CO2 separator 10 is connected to the #1 CO2 separator 6, which is used to return the primary liquid phase 013 and perform the first separation.

[0065] According to the present invention, preferably, such as Figure 2 As shown, the bottom of the CO2 separator 13 is connected to the CO2 washing tower 11, which is used to return the secondary liquid phase 018 and perform the water washing.

[0066] According to a particularly preferred embodiment of the present invention, a method for preparing CO2 product gas includes:

[0067] Carbon-rich methanol is flash-evaporized to obtain carbon-rich methanol flash liquid. After passing through the first pressurization and the first heat exchange, the flash liquid after heat exchange is subjected to the first separation to obtain primary CO2 gas and semi-lean methanol.

[0068] The primary CO2 gas is subjected to a first cooling and a second separation process to obtain a secondary CO2 gas. This secondary CO2 gas is then subjected to water washing, a second cooling, and a third separation process to obtain a tertiary CO2 gas as the CO2 product gas. The pressure of the CO2 product gas is 3-5 MPa.

[0069] The carbon-rich methanol contains 20-40 mol% CO2 and ≤0.3 ppm H2S at a temperature of -40 to -10°C; the CO2 product gas contains 98.5-99.9 mol% CO2.

[0070] The present invention will be described in detail below through embodiments.

[0071] Raw material gas Q1: crude syngas from the upstream coal gasification process (pressure 5.6 MPa, temperature 40℃, CO2 content 30 mol%, CO content 20 mol%, H2 content 45 mol%);

[0072] Raw material gas Q2: crude syngas from the upstream coal gasification process (pressure 3MPa, temperature 40℃, CO2 content 46mol%, CO content 1mol%, H2 content 48mol%).

[0073] Example 1

[0074] Devices such as Figure 2 As shown, it includes a raw material gas cooler 1, a methanol washing tower 2, a medium-pressure flash evaporator 3, a first pump 4, a first heat exchanger 5, a CO2 separator 1# 6, a water cooler 9, a CO2 separator 2# 10, a CO2 washing tower 11, a propylene cooler 12, and a CO2 separator 3# 13 connected in sequence.

[0075] The bottom of CO2 separator 6 is connected to methanol washing tower 2; the top of CO2 separator 13 is connected to the raw material gas cooler 1; according to the material flow direction, a second pump 7 and a second heat exchanger 8 are sequentially installed on the pipeline connecting the top of CO2 separator 6 and methanol washing tower 2; a third pump 14 is installed on the pipeline connecting medium-pressure flash evaporator 3 and raw material gas cooler 1; the bottom of CO2 separator 10 is connected to CO2 separator 6; the bottom of CO2 separator 13 is connected to CO2 washing tower 11.

[0076] The method is carried out in the above-described apparatus and includes:

[0077] After passing through the third heat exchanger, the raw gas Q1 is pre-cooled to -18℃. It then comes into contact with lean methanol 02 and washing methanol 03 at -60℃ and undergoes decarbonization treatment to obtain carbon-rich methanol 05 (temperature -20℃; pressure 5.6MPa; CO2 content 30mol%, H2S content 0.1ppm) and purified gas.

[0078] The carbon-rich methanol 05 was flash-evaporized (pressure 0.6 MPa). The flash vapor 07 obtained at the top of the column was returned by the third pressurized circulating gas at 5.6 MPa and mixed into the feed gas Q1. The carbon-rich methanol flash liquid 06 (CO2 content 25 mol%) obtained at the bottom of the column was successively pressurized to 3.1 MPa and heat-exchanged to 90°C to obtain the heat-exchanged flash liquid 09. The flash liquid 09 was then subjected to the first separation. The first-stage CO2 gas 012 (CO2 content 89 mol%) was obtained at the top of the column, and the semi-lean methanol 011 (CO2 content 13 mol%) was obtained at the bottom of the column. The semi-lean methanol 011 was successively pressurized to 7.0 MPa and heat-exchanged to -30°C to obtain the washed methanol 03.

[0079] The first-stage CO2 gas 012 is cooled first to obtain a first-stage CO2 gas-liquid mixture 012' at a temperature of 40°C. This mixture is then subjected to a second separation, resulting in a second-stage CO2 gas 014 (CO2 content of 98.4 mol%) at the top of the column. The first-stage liquid phase 013 is obtained at the bottom of the column and returned to undergo the first separation process.

[0080] The above-mentioned secondary CO2 gas 014 is washed with high-pressure boiler water at 40°C, and washed CO2 gas 017 is obtained at the top of the column, and methanol solution 016 is obtained at the bottom of the column. The washed CO2 gas 017 is cooled a second time to obtain a secondary CO2 gas-liquid mixture 017' at 10°C. This mixture is then subjected to a third separation, and tertiary CO2 gas 019 (CO2 content of 99 mol%) is obtained at the top of the column. The secondary liquid phase 018 is obtained at the bottom of the column and is returned to be washed with water as described above.

[0081] Specifically, the three-stage CO2 gas 019 is returned and subjected to the third heat exchange to obtain CO2 product gas S1 (temperature 30℃, CO2 content 99mol%).

[0082] Example 2

[0083] The apparatus according to Example 1;

[0084] The method provided in Example 1 is different,

[0085] After passing through the third heat exchanger, the feed gas Q2 is pre-cooled to -18℃. It then comes into contact with lean methanol O2 and washing methanol O3 at -50℃ and undergoes decarbonization treatment to obtain carbon-rich methanol (temperature -20℃; pressure 3.1MPa; CO2 content 25mol%, H2S content 0.1ppm) and purified gas.

[0086] The carbon-rich methanol 05 was flash-evaporized (at a pressure of 1.4 MPa). The flash vapor 07 obtained at the top of the column was returned by the third pressurized circulating gas at 3.4 MPa and mixed into the feed gas Q2. The carbon-rich methanol flash liquid 06 (CO2 content of 26 mol%) obtained at the bottom of the column was successively pressurized to 4.1 MPa and heat-exchanged to 90°C to obtain the heat-exchanged flash liquid 09. The flash liquid 09 was then subjected to the first separation. The first-stage CO2 gas 012 (CO2 content of 90 mol%) was obtained at the top of the column, and the semi-lean methanol 011 (CO2 content of 15 mol%) was obtained at the bottom of the column. The semi-lean methanol 011 was successively pressurized to 4.0 MPa and heat-exchanged to -30°C to obtain the washed methanol 03.

[0087] The first-stage CO2 gas 012 is cooled a second time to obtain a first-stage CO2 gas-liquid mixture 012' at a temperature of 40°C. This mixture is then subjected to a second separation, resulting in a second-stage CO2 gas 014 (CO2 content of 98 mol%) at the top of the column. The first-stage liquid phase 013 is obtained at the bottom of the column and returned to undergo the first separation process described above.

[0088] The above-mentioned secondary CO2 gas 014 is washed with high-pressure boiler water at 40°C, and washed CO2 gas 017 is obtained at the top of the column, and methanol solution 016 is obtained at the bottom of the column. The washed CO2 gas 017 is cooled in the third stage to obtain a secondary CO2 gas-liquid mixture 017' at 10°C. This mixture is then subjected to a third separation, and tertiary CO2 gas 019 (CO2 content of 99.5 mol%) is obtained at the top of the column. The secondary liquid phase 018 is obtained at the bottom of the column and is returned to be washed with water as described above.

[0089] The three-stage CO2 gas is returned and subjected to the third heat exchange to obtain CO2 product gas S2 (temperature 30℃, CO2 content 99mol%).

[0090] Comparative Example 1

[0091] Taking a methanol plant producing 900,000 tons / year using 65 kg coal-water slurry gasification as an example, the purification unit adopts a low-temperature methanol washing process, producing byproducts of 3.5 MPa and 10,000 Nm³ / h. 3 Based on the CO2 product gas DS1 per hour, a comparison is made between conventional gas compression processes and energy-saving CO2 product gas preparation methods, as shown in Table 1.

[0092] Table 1

[0093] project Comparative Example 1 Example 1 <![CDATA[CO₂ product gas volume, Nm 3 / h]]> 10000 10000 <![CDATA[CO₂ concentration, wt%]]> ≥98.5，98 ≥99，99 <![CDATA[CO2 pressure, MPa]]> 3.5 3.5 <![CDATA[Shaft power of CO₂ compressor, kW]]> 1060 none Shaft power of carbon-rich methanol booster pump, kW none 91 Circulating water, t / h 150 90 Equipment investment, 10,000 yuan 800 300

[0094] As can be seen from the results in Table 1, compared with the conventional gas compression process used in Comparative Example 1, the method provided by this invention in Example 1 reduced power consumption by 91.4%, circulating water consumption by 40%, and equipment investment by 62.5%.

[0095] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing CO2 product gas, characterized in that, The method includes: Carbon-rich methanol (05) is flashed to obtain carbon-rich methanol flash liquid (06). After passing through the first pressurization and the first heat exchange, the flash liquid (09) after heat exchange is obtained. After the first separation, primary CO2 gas (012) and semi-lean methanol (011) are obtained. The primary CO2 gas (012) is subjected to a first cooling and a second separation to obtain a secondary CO2 gas (014). The secondary CO2 gas (014) is then subjected to water washing, a second cooling, and a third separation to obtain a tertiary CO2 gas (019) as the CO2 product gas (020). The pressure of the CO2 product gas (020) is 3-5 MPa.

2. The method according to claim 1, wherein, The carbon-rich methanol (05) has a CO2 content of 20-40 mol%, an H2S content of ≤0.3 ppm, and a temperature of -40 to -10℃. And / or, the flash evaporation pressure is 0.1-1.5 MPa, preferably 0.6-1 MPa; And / or, the CO2 content in the carbon-rich methanol flash liquid (06) is 18-38 mol%; the temperature is -40 to -15°C; And / or, the carbon-rich methanol flash liquid (06) is pressurized to obtain a pressurized flash liquid (08) with a pressure of 3.1-5.1 MPa after the first pressurization; And / or, the pressurized flash liquid (08) is subjected to the first heat exchange to obtain a heat-exchanged flash liquid (09) at a temperature of 85-95°C.

3. The method according to claim 1 or 2, wherein, The CO2 content in the primary CO2 gas (O12) is 85-90 mol%. And / or, the semi-lean methanol (011) is subjected to a second pressurization to obtain pressurized semi-lean methanol with a pressure of 4-7.5 MPa, which is then subjected to a second heat exchange to obtain washed methanol (03) with a temperature of -30 to -20°C. And / or, the primary CO2 gas (012) is subjected to the first cooling to obtain a primary CO2 gas-liquid mixture (012') at a temperature of 37-43°C; And / or, the CO2 content in the secondary CO2 gas (014) is 91-98 mol%.

4. The method according to any one of claims 1-3, wherein, The water washing process includes: contacting the secondary CO2 gas (014) and water (015) and washing them with water to obtain a methanol solution (016) and washed CO2 gas (017); And / or, the washed CO2 gas (017) is subjected to the second cooling to obtain a secondary CO2 gas-liquid mixture (017') at a temperature of 5-15°C; And / or, in the third-stage CO2 gas (019), the CO2 content is ≥98.5 mol%, preferably 98.5-99.9 mol%.

5. The method according to any one of claims 1-4, wherein, The carbon-rich methanol (05) is obtained by decarbonization treatment of pre-cooled feed gas and lean methanol (02); Preferably, the raw material gas (01) and the third-stage CO2 gas (019) are subjected to a third heat exchange to obtain the pre-cooled raw material gas at a temperature of -20 to -5°C and the CO2 product gas (020) at a temperature of 20-40°C. Preferably, the CO2 content in the raw gas (01) is 30-60 mol%; the temperature is 25-50℃; and the pressure is 2-6 MPa.

6. The method according to claim 5, wherein, The method further includes: returning the flash vapor (07) obtained by flash evaporation and mixing it into the raw material gas (01); Preferably, the flash vapor (07) is pressurized to 3-6 MPa in a third pressurization process and then returned and mixed into the raw material gas (01); And / or, the preparation method further includes: returning the primary liquid phase (013) obtained from the second separation and performing the first separation; And / or, the preparation method further includes: returning the secondary liquid phase (018) obtained by the third separation to perform the second separation.

7. The method according to any one of claims 1-6, wherein, The CO2 product gas (O2O) has a CO2 content of ≥98.5 mol%, preferably 98.5-99.9 mol%.

8. An apparatus for preparing CO2 product gas, characterized in that, The method described in any one of claims 1-7 is carried out in the apparatus, which comprises a medium-pressure flash evaporator (3), a first pump (4), a first heat exchanger (5), a CO2 separator (6) 1#, a water cooler (9), a CO2 separator (10) 2#, a CO2 scrubbing tower (11), a propylene cooler (12) and a CO2 separator (13) connected in sequence.

9. The apparatus according to claim 8, wherein, According to the material flow direction, the device also includes: a raw material gas cooler (1) and a methanol washing tower (2) connected in sequence before the medium-pressure flash tower (3); Preferably, the bottom of the No. 1 CO2 separator (6) is connected to the methanol washing tower (2) according to the material flow direction; Preferably, the top of the #3 CO2 separator (13) is connected to the raw material gas cooler (1) according to the material flow direction.

10. The apparatus according to claim 9, wherein, According to the material flow direction, the device also includes: a second pump (7) and a second heat exchanger (8) are sequentially installed on the pipeline connecting the bottom of the No. 1 CO2 separator (6) and the methanol washing tower (2); And / or, according to the material flow direction, the device further includes: a third pump (14) installed on the pipeline connecting the top of the medium-pressure flash tower (3) and the raw material gas cooler (1); And / or, the bottom of the 2#CO2 separator (10) is connected to the 1#CO2 separator (6); And / or, the bottom of the 3#CO2 separator (13) is connected to the CO2 scrubbing tower (11).

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