A method and system for producing methanol from carbon dioxide and hydrogen

Abstract

The application provides a method and system for producing methanol from carbon dioxide and hydrogen, comprising a carbon dioxide turbine compressor, a hydrogen turbine compressor, a preheater, a methanol reactor, a high-pressure rectifying column, a methanol recovery column and a pressurizing fan; the carbon dioxide turbine compressor is connected with a carbon dioxide source, the carbon dioxide turbine compressor outlet is connected with a cold side inlet of the preheater, the hydrogen turbine compressor is connected with a hydrogen source, the hydrogen turbine compressor outlet is connected with the cold side inlet of the preheater, and the cold side outlet of the preheater is connected with a top inlet of the methanol reactor; the bottom outlet of the methanol reactor is connected with a hot side inlet of the preheater, the hot side outlet of the preheater is connected with an inlet of the high-pressure rectifying column, the bottom outlet of the high-pressure rectifying column is connected with an inlet of the methanol recovery column, the top outlet of the high-pressure rectifying column is connected with an inlet of the pressurizing fan, and the outlet of the pressurizing fan is connected with the cold side inlet of the preheater. The application has the advantages of short process flow, reduced equipment investment, energy saving and consumption reduction and low operation cost.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide recycling, and more specifically to a method and system for producing methanol from carbon dioxide and hydrogen. Background Technology

[0002] As an important C1 resource, the resource utilization of carbon dioxide into carbon-based chemicals plays a crucial supporting role in reducing greenhouse gas emissions and alleviating energy shortages. Methanol, as a carbon-based chemical, is not only a highly efficient energy carrier but also a bulk chemical and alternative fuel. The synthesis of methanol from carbon dioxide aligns with the concept of a "methanol economy" and is an effective greenhouse gas emission reduction solution. Currently, there are two main categories of carbon dioxide hydrogenation to methanol synthesis processes: direct carbon dioxide hydrogenation to methanol and the reverse water-gas shift (RWGS) process. The direct carbon dioxide hydrogenation to methanol process uses carbon dioxide and hydrogen as sources, directly synthesizing methanol through a catalytic reaction; this technology is also known as the direct method or one-step process. The CAMERE process also uses carbon dioxide and hydrogen as sources, converting carbon dioxide into syngas through a reverse water-gas shift (RWGS) reaction, and then synthesizing methanol from the syngas; this technology is also known as the indirect method or two-step process.

[0003] Currently, the one-step carbon dioxide hydrogenation to methanol synthesis process, both domestically and internationally, is as follows: Carbon dioxide and hydrogen are first compressed to 5.0–10.0 MPa by a turbine compressor, then heated by a preheater. The heated material enters the methanol reactor, where the reaction temperature is 230–290℃. This is an exothermic reaction with a conversion rate of approximately 10–20%. The reaction products then enter the preheater as a heat source, and after heat exchange, they enter a cooler for cooling. Methanol and water condense and enter a high-pressure separator and a low-pressure separator for two flash condensation processes. The pressure after flash condensation is 0.05–1.0 MPa. Unreacted carbon dioxide and hydrogen are compressed to 5.0–10.0 MPa by the turbine compressor and returned to the preheater inlet. After preheating, they re-enter the methanol reactor to participate in the reaction. The methanol and aqueous solution produced after flash condensation enter a distillation system for distillation. A simplified flow chart is shown below. Figure 1 This process requires cooling the reaction products, followed by two flash evaporation depressurizations, and then pressurization. The process is lengthy, energy-intensive, and costly. Summary of the Invention

[0004] To address the problems of the prior art, this invention provides a method and system for producing methanol from carbon dioxide and hydrogen, which has the advantages of a short process flow, reduced equipment investment, energy saving and consumption reduction, and low operating costs.

[0005] This invention is achieved through the following technical solution:

[0006] A system for producing methanol from carbon dioxide and hydrogen includes: a carbon dioxide turbine compressor, a hydrogen turbine compressor, a preheater, a methanol reactor, a high-pressure distillation column, a methanol recovery column, and a pressurizing blower;

[0007] The inlet of the carbon dioxide turbine compressor is connected to a carbon dioxide source, and the outlet of the carbon dioxide turbine compressor is connected to the cold-side inlet of the preheater. The inlet of the hydrogen turbine compressor is connected to a hydrogen source, and the outlet of the hydrogen turbine compressor is connected to the cold-side inlet of the preheater. The cold-side outlet of the preheater is connected to the top inlet of the methanol reactor. The bottom outlet of the methanol reactor is connected to the hot-side inlet of the preheater, and the hot-side outlet of the preheater is connected to the inlet of the high-pressure distillation column. The bottom outlet of the high-pressure distillation column is connected to the inlet of the methanol recovery column, and the top outlet of the high-pressure distillation column is connected to the inlet of the pressurized blower. The outlet of the pressurized blower is connected to the cold-side inlet of the preheater.

[0008] Preferably, the liquid at the bottom outlet of the high-pressure distillation column provides heat to the reboiler of the methanol recovery column.

[0009] Preferably, the high-pressure distillation column and the methanol recovery column are coupled together in the form of a partitioned column.

[0010] Preferably, the preheater is a shell-and-tube heat exchanger or a finned heat exchanger.

[0011] Preferably, the high-pressure distillation column is a plate column or a packed column.

[0012] Preferably, the methanol recovery tower is a bubble cap tower, a valve tower, a sieve tower, or a tongue-shaped tray tower.

[0013] Preferably, the pressurizing fan is a compressor or a turbine blower.

[0014] Preferably, the pressurizing blower is provided with a vent outlet.

[0015] A method for producing methanol from carbon dioxide and hydrogen, comprising:

[0016] Carbon dioxide gas and hydrogen gas are compressed by carbon dioxide turbine compressor and hydrogen turbine compressor respectively, and then mixed and entered into preheater for preheating;

[0017] Preheated carbon dioxide and hydrogen gas enter the methanol reactor to react, and the reaction products enter the preheater as a heat source to preheat the carbon dioxide and hydrogen gas.

[0018] The reaction products, after being cooled by the preheater, enter a high-pressure distillation column for distillation.

[0019] The vapor phase after distillation in the high-pressure distillation column enters the pressurizing fan through the top of the column and is pressurized. Then it returns to the preheater for preheating and re-enters the methanol reactor to participate in the reaction.

[0020] The bottom liquid phase after distillation in the high-pressure distillation column enters the methanol recovery column for methanol distillation.

[0021] Preferably, the high-pressure distillation column has a distillation operating pressure of 3-8 MPa, a column top operating temperature of 15-35℃, and a column bottom operating temperature of 170-280℃.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] Compared to the original process system, this invention reduces the number of coolers, thus eliminating the cooling process of the reaction products. It also replaces the original high- and low-pressure flash separation tanks with a high-pressure distillation column, significantly shortening the process flow and reducing equipment investment. Instead of the original two-stage flash separation process of high-pressure and low-pressure separation, this invention employs a direct high-pressure distillation process for the product. The separated gas phase only loses pressure drop due to the high-pressure distillation column, essentially maintaining the original system pressure. This significantly reduces the power consumption of the pressurizing fan used for depressurization and repressurization, resulting in substantial energy savings. Through this shortened process and the use of a high-pressure distillation column, the methanol synthesis product does not need to be cooled, saving circulating cooling water. Simultaneously, the system maintains high-pressure operation without flash depressurization and repressurization, reducing the power consumption of the pressurizing fan and lowering the overall operating cost of the process system. Using a high-pressure distillation column to separate the synthesis products can maximize the separation of water and methanol from the products. Since the hydrogenation of carbon dioxide to methanol is a reversible reaction, reducing the amount of methanol and water in the circulating gas can improve the system conversion rate, save energy in the circulation volume, and further reduce energy consumption.

[0024] Furthermore, by thermally coupling the high-pressure distillation column and the methanol recovery column, the heat from the high-pressure distillation column bottoms can be fully utilized as the heat source for the reboiler of the methanol-water distillation column, which can further reduce system energy consumption. Alternatively, using a separate column to directly separate methanol, water, and other products can also achieve energy saving. Attached Figure Description

[0025] Figure 1 This is a flowchart of the original process.

[0026] Figure 2 This is a schematic diagram of the system for producing methanol from carbon dioxide and hydrogen according to the present invention.

[0027] In the diagram: 1-Carbon dioxide turbine compressor, 2-Hydrogen turbine compressor, 3-Preheater, 4-Methanol reactor, 5-Cooler, 6-High-pressure separator, 7-Low-pressure separator, 8-Turbine compressor, 9-High-pressure distillation column, 10-Methanol recovery column, 11-Pressure blower. Detailed Implementation

[0028] To further understand the present invention, the present invention will be described below with reference to embodiments. These descriptions are only for further explaining the features and advantages of the present invention and are not intended to limit the claims of the present invention.

[0029] See Figure 2 The system for producing methanol from carbon dioxide and hydrogen according to the present invention includes: a carbon dioxide turbine compressor 1, a hydrogen turbine compressor 2, a preheater 3, a methanol reactor 4, a high-pressure distillation column 9, a methanol recovery column 10, and a pressurizing blower 11.

[0030] The inlet of the carbon dioxide turbine compressor 1 is connected to a carbon dioxide source, and the outlet of the carbon dioxide turbine compressor 1 is connected to the cold-side inlet of the preheater 3. The inlet of the hydrogen turbine compressor 2 is connected to a hydrogen source, and the outlet of the hydrogen turbine compressor 2 is connected to the cold-side inlet of the preheater 3. The cold-side outlet of the preheater 3 is connected to the top inlet of the methanol reactor 4, and the bottom outlet of the methanol reactor 4 is connected to the hot-side inlet of the preheater 3. The hot-side outlet of the preheater 3 is connected to the inlet of the high-pressure distillation column 9, and the bottom outlet of the high-pressure distillation column 9 is connected to the inlet of the methanol recovery column 10. The top outlet of the high-pressure distillation column 9 is connected to the inlet of the pressurized blower 11, and the outlet of the pressurized blower 11 is connected to the cold-side inlet of the preheater 3. The pressurized blower 11 is provided with a venting gas outlet.

[0031] The methanol from the top outlet of the methanol recovery tower 10 enters the downstream refined methanol recovery system, and the liquid from the top outlet of the methanol recovery tower 10 enters the wastewater system.

[0032] In one specific embodiment of the present invention, the liquid at the bottom outlet of the high-pressure distillation column 9 provides heat to the reboiler of the methanol recovery column 10. In another specific embodiment of the present invention, the high-pressure distillation column 9 and the methanol recovery column 10 are coupled together in the form of partitioned columns.

[0033] In one specific embodiment of the present invention, the preheater may be in the form of a shell-and-tube type or a finned type.

[0034] In one specific embodiment of the present invention, the high-pressure distillation column 9 may be in the form of a plate column or a packed column.

[0035] In one specific embodiment of the present invention, the methanol recovery tower 10 may be in the form of a bubble cap tower, a valve tower, a sieve tower, a tongue-shaped tray, or a plate tower.

[0036] In one specific embodiment of the present invention, the pressurizing blower 11 may be a high-pressure blower such as a compressor or a turbine blower.

[0037] The method for producing methanol from carbon dioxide and hydrogen according to the present invention is as follows:

[0038] Step 1: Carbon dioxide gas and hydrogen gas are first compressed to 5.0-10.0 MPa by carbon dioxide turbine compressor 1 and hydrogen turbine compressor 2 respectively, and then mixed and fed into preheater 3 to heat the compressed gas. The heat source comes from the reaction products of methanol reactor 4.

[0039] Step 2: The preheated material enters methanol reactor 3 for reaction (the reaction is exothermic), the reaction temperature is 230-290℃, the conversion rate is about 10%-20%, and the reaction product enters preheater 3 as a heat source for heating and cooling.

[0040] Step 3: After the reaction product is cooled down, it enters the high-pressure distillation column 9 for distillation separation. Methanol and water are separated from the bottom of the column as heavy components. The distillation operating pressure of the high-pressure distillation column 9 is 3-8 MPa, the top operating temperature is 15-35℃, and the bottom operating temperature is 170-280℃. At this time, the gas phase in the high-pressure distillation column 9 only needs to overcome the internal resistance of the column, so the pressure drop is very small, about 0.001-0.1 MPa.

[0041] Step 4: Then the gas phase of the high-pressure distillation column 9 enters the pressurizing blower 11 through the top of the column and is pressurized to 5.0-10.0 MPa. Then it returns to the inlet of the preheater 3 for preheating and re-enters the methanol reactor 5 to participate in the reaction.

[0042] Step 5: The liquid phase at the bottom of the high-pressure distillation column 9 enters the methanol recovery column 10 for methanol distillation. The light components are recovered from the top of the methanol distillation column 6, and the wastewater is discharged from the bottom of the column.

[0043] Case 1:

[0044] The following is combined with Figure 2 The energy-saving process for one-step synthesis of methanol from carbon dioxide and hydrogen and separation of reaction products according to the present invention is described as follows:

[0045] At room temperature, carbon dioxide and hydrogen gases are first compressed to 5.0 MPa by turbine compressors 1 and 2 respectively, and then mixed and fed into preheater 3 to heat the compressed gases to 230°C. The heat source for this heating is the reaction products from methanol reactor 4. The preheated material then enters methanol reactor 3 for an exothermic reaction at 250°C. The single-pass conversion rate is approximately 14%, and the molar fractions of the products at the methanol reactor outlet are approximately: CO2: 18.7%, CO: 2.9%, H2: 67.7%, CH4O: 5.3%, H2O: 5.1%, CH4: 0.3%. The reaction products then enter the preheater... The heater serves as the heating source and cools the product to 30°C. After cooling, the product enters high-pressure distillation column 9 for distillation separation. The distillation operating pressure is 4.8 MPa, the top operating temperature is approximately 20°C, and the bottom operating temperature is 220°C. At this point, the gas phase in high-pressure distillation column 9 only needs to overcome the internal resistance, resulting in a very small pressure drop of approximately 0.01 MPa. After passing through the high-pressure column, the composition of the top product is: CO2: 20.7%, CO: 3.2%, H2: 75.3%, CH4O: 0.01%, H2O: <1 ppm, CH4: 0.4%. The bottom product is: CH4O: 49.2%, H2O: 50.8%. Then, the gas phase of the high-pressure distillation column 9 enters the pressurizing blower 11 through the top of the column and is pressurized to 6MPa. Then it returns to the inlet of the preheater 3 for preheating and re-enters the methanol reactor 5 to participate in the reaction. The liquid phase at the bottom of the high-pressure distillation column 9 enters the methanol recovery column 10 for methanol distillation. The light components are recovered from the top of the methanol recovery column 10, and the wastewater is discharged from the bottom of the column.

[0046] The present invention has the following advantages:

[0047] 1. Short process flow, reduced equipment investment

[0048] Compared to the original process, this invention reduces the cooling process of the reaction products and changes the original high and low pressure separation to high pressure separation, thus greatly shortening the process flow and reducing equipment investment.

[0049] 2. High-pressure gas-liquid separation reduces power consumption.

[0050] Because the direct carbon dioxide methanol production process has a low reaction conversion rate, the amount of gas recycled after separation is large. Compared with the original two-stage flash separation process of high-pressure separation and low-pressure separation, this invention adopts a direct high-pressure distillation process for the product. The separated gas phase only loses the pressure drop of the high-pressure distillation column and basically maintains the original system pressure. This can significantly reduce the power consumption of the circulating pressurizing fan for depressurization separation and repressurization, and greatly reduce power consumption.

[0051] 3. Energy saving and consumption reduction, lowering operating costs

[0052] By using the above-mentioned short process and high-pressure separation, there is no need to cool the synthesized methanol product, and the circulating cooling water is saved. At the same time, the system maintains high-pressure operation without flash evaporation to reduce pressure and then pressurize, which reduces the operating power of the pressurization equipment and lowers the operating cost of the entire process system.

[0053] 4. Using a high-pressure distillation column to separate the synthesis products can maximize the separation of water and methanol in the products. Since the hydrogenation of carbon dioxide to methanol is a reversible reaction, reducing the amount of methanol and water in the circulating gas can improve the system conversion rate, save energy in the circulation volume, and further reduce energy consumption.

[0054] 5. Further reducing system energy consumption can be achieved by thermally coupling the high-pressure distillation column and the methanol recovery column, fully utilizing the heat from the high-pressure distillation column bottom discharge as the heat source for the methanol recovery column reboiler. Alternatively, using a partitioned column to directly separate methanol, water, and other products can also achieve energy savings.

Claims

1. A system for producing methanol from carbon dioxide and hydrogen, characterized in that, include: Carbon dioxide turbine compressor (1), hydrogen turbine compressor (2), preheater (3), methanol reactor (4), high-pressure distillation column (9), methanol recovery column (10) and pressurizing blower (11); The inlet of the carbon dioxide turbine compressor (1) is connected to a carbon dioxide source, and the outlet of the carbon dioxide turbine compressor (1) is connected to the cold side inlet of the preheater (3). The inlet of the hydrogen turbine compressor (2) is connected to a hydrogen source, and the outlet of the hydrogen turbine compressor (2) is connected to the cold side inlet of the preheater (3). The cold side outlet of the preheater (3) is connected to the top inlet of the methanol reactor (4). The bottom outlet of the methanol reactor (4) is connected to the hot side inlet of the preheater (3). The hot side outlet of the preheater (3) is connected to the inlet of the high-pressure distillation column (9). The bottom outlet of the high-pressure distillation column (9) is connected to the inlet of the methanol recovery column (10). The top outlet of the high-pressure distillation column (9) is connected to the inlet of the pressurizing fan (11), and the outlet of the pressurizing fan (11) is connected to the cold side inlet of the preheater (3).

2. The system for producing methanol from carbon dioxide and hydrogen according to claim 1, characterized in that, The liquid at the bottom outlet of the high-pressure distillation column (9) provides heat to the reboiler of the methanol recovery column (10).

3. The system for producing methanol from carbon dioxide and hydrogen according to claim 1, characterized in that, The high-pressure distillation column (9) and the methanol recovery column (10) are coupled together in the form of a partitioned column.

4. The system for producing methanol from carbon dioxide and hydrogen according to claim 1, characterized in that, The preheater is a shell-and-tube heat exchanger or a finned heat exchanger.

5. The system for producing methanol from carbon dioxide and hydrogen according to claim 1, characterized in that, The high-pressure distillation column (9) is a plate column or a packed column.

6. The system for producing methanol from carbon dioxide and hydrogen according to claim 1, characterized in that, The methanol recovery tower (10) is a bubble cap tower, a floating valve tower, a sieve tower, or a tongue-shaped tower.

7. The system for producing methanol from carbon dioxide and hydrogen according to claim 1, characterized in that, The pressurizing blower (11) is a compressor or a turbine blower.

8. The system for producing methanol from carbon dioxide and hydrogen according to claim 1, characterized in that, The pressurizing blower (11) is provided with a vent outlet.

9. A method for producing methanol from carbon dioxide and hydrogen, characterized in that, The system based on any one of claims 1-8 comprises: Carbon dioxide gas and hydrogen gas are compressed by carbon dioxide turbine compressor (1) and hydrogen turbine compressor (2) respectively, and then mixed and entered into preheater (3) for preheating; The preheated carbon dioxide gas and hydrogen gas enter the methanol reactor (4) to react, and the reaction products enter the preheater (3) as a heat source to preheat the carbon dioxide gas and hydrogen gas. The reaction products, after being cooled by the preheater (3), enter the high-pressure distillation column (9) for distillation; After being distilled by the high-pressure distillation column (9), the gas phase enters the pressurizing blower (11) through the top of the column and is pressurized. Then it returns to the preheater (3) for preheating and re-enters the methanol reactor (4) to participate in the reaction. The bottom liquid phase after distillation in the high-pressure distillation column (9) enters the methanol recovery column (10) for methanol distillation.

10. The method for producing methanol from carbon dioxide and hydrogen according to claim 9, characterized in that, The distillation operating pressure of the high-pressure distillation column (9) is 3-8 MPa, the top operating temperature is 15-35℃, and the bottom operating temperature is 170-280℃.

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