A process and device for producing methanol by catalytic hydrogenation of carbon dioxide

Abstract

The present invention relates to the technical field of producing methanol by hydrogenation of carbon dioxide, and specifically to a process and device for producing methanol by catalytic hydrogenation of carbon dioxide. The process comprises the following steps: a mixed raw gas of carbon dioxide and hydrogen is compressed and mixed with circulating gas, and the mixed gas enters a methanol synthesis tower for methanol synthesis after heat exchange and heating; the synthesized gas provides a heat source for the waste heat reboiler of the atmospheric tower; the cooled gas is sent to a separator for gas-liquid separation; the separated gas phase is returned to the methanol synthesis tower to continue methanol synthesis, and the liquid phase is flashed to separate the light components, and the crude alcohol enters a pre-distillation tower to separate dissolved carbon dioxide, hydrogen, methane, etc. The present invention solves the contradiction between the low synthesis heat release and the high energy consumption of distillation, separation and purification, which are unique to carbon dioxide hydrogenation methanol devices, and does not require external steam supply. It realizes multi-effect heat coupling of the pre-distillation tower, atmospheric distillation tower and vacuum distillation tower, and has low comprehensive energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing methanol by hydrogenating carbon dioxide, and in particular to a process and device for preparing methanol by catalytic hydrogenating carbon dioxide. Background Art

[0002] The raw materials for the carbon dioxide hydrogenation to methanol reaction are carbon dioxide and hydrogen. There is a reverse reaction of the shift reaction during the reaction process. The reaction formula is as follows:

[0003] CO2+H2→CO+H2O△H=-41.2kJ / mol

[0004] The final reaction is the process of CO and CO2 generating methanol under the action of catalyst. Its main reaction formula is as follows:

[0005] CO+2H2→CH3OH△H=90.73kJ / mol

[0006] CO2+3H2→CH3OH+H2O△H=48.02kJ / mol

[0007] The reverse reaction of the conversion reaction is an endothermic reaction, and high temperature is conducive to the reaction proceeding to the right. However, methanol synthesis is an exothermic reaction, and high temperature is not conducive to the reaction proceeding to the right. Therefore, methanol synthesis is generally carried out in the range of 200-260°C. At this time, the reverse reaction of the conversion reaction is not deep, and the main raw gas for methanol synthesis is carbon dioxide; when the temperature is raised to above 350°C, methanol synthesis basically does not occur, and part of the carbon dioxide is converted into carbon monoxide through reverse conversion.

[0008] The heat released by synthesizing methanol from the same mole of carbon monoxide and carbon dioxide differs by nearly double. When methanol is produced from coke oven gas or coal gasification, the carbon monoxide content in the synthesis gas is 10-25% by volume after adjusting the hydrogen-to-carbon ratio, resulting in a high heat release. When methanol is produced from carbon dioxide hydrogenation, if the temperature is between 200°C and 260°C, the carbon monoxide content after reverse conversion is low, with a carbon monoxide content of ≤3% by volume at the synthesis tower inlet, resulting in a low heat release.

[0009] The methanol content of crude methanol produced from coke oven gas, coal gasification, and other sources is ≥85% by weight, while that of crude methanol produced from carbon dioxide hydrogenation is ≥64% by weight. Due to the higher water content, the crude methanol mixture from carbon dioxide hydrogenation has a higher boiling point, resulting in higher energy consumption for methanol separation and purification under the same conditions.

[0010] The production of methanol from CO2 hydrogenation suffers from the paradox of low synthesis heat release and high energy consumption for distillation separation and purification. Therefore, effectively coupling the heat release from synthesis and distillation is the key to energy efficiency in CO2 hydrogenation.

[0011] Patent CN109438185A discloses a "vacuum heat-coupled methanol distillation method and apparatus," characterized by employing a triple-effect heat coupling system: atmospheric pressure, pressurization, and vacuum. The overhead steam from the pressurized distillation tower is connected to the reboiler of the atmospheric distillation tower, and the overhead steam from the atmospheric distillation tower is connected to the reboiler of the vacuum distillation tower. The pre-distillation tower kettle material is preheated and connected to the atmospheric distillation tower. The atmospheric distillation tower kettle material is connected to the pressurized distillation tower, and the pressurized distillation tower kettle material is connected to the vacuum distillation tower. The side-line material from the vacuum distillation tower is connected to a recovery tower. This process can significantly reduce energy consumption, but the pressurized tower requires steam as a heat source. For a carbon dioxide hydrogenation methanol plant, the steam required for the pressurized tower exceeds the byproduct, necessitating external steam supply. Furthermore, the heat generated by the synthetic byproducts, especially the low-grade heat, is not effectively utilized.

[0012] Patent CN110280034A discloses a system comprising a light-removal tower, a vacuum distillation tower, a pressurized distillation tower, an atmospheric distillation tower, and a recovery tower, further optimizing the traditional five-tower process. The pre-tower still utilizes external steam for heating, while the vacuum distillation tower's heat source is derived from the low-level heat of methanol synthesis gas. The pressurized tower, atmospheric distillation tower, and light-removal tower form a multi-effect system, saving steam. However, the heat source for the synthesis tower is based on the synthesis of methanol from carbon monoxide, and the heat released by the synthesis of methanol from carbon dioxide is low, failing to meet the heat load of the vacuum distillation tower.

[0013] Patent CN111116317A discloses a five-tower four-effect methanol distillation process and equipment, which mainly includes a pre-distillation tower, a first pressure tower, a second pressure tower, a third pressure tower, a steam vacuum flash tank, a kettle liquid buffer tank, a recovery tower, etc. By adding a kettle liquid buffer tank, the problems of kettle liquid level fluctuations in the three distillation towers and feed fluctuations in the recovery tower are solved, and the operating difficulty of the recovery tower is reduced.

[0014] Patent CN107032959A combines heat pump distillation and differential pressure thermal coupling to utilize the latent heat of the system, reducing energy consumption compared to conventional four-tower distillation. However, the process flow adds a compressor, which greatly increases equipment investment and maintenance difficulty. The operating cost is too high, making it difficult to adopt in actual devices.

[0015] Patent CN107551586A combines the pre-tower and atmospheric pressure tower in a conventional four-tower process into a baffled tower, while retaining the other two towers. This process reduces equipment investment, but the design prevents the light fractions at the top of the pre-tower from entering the scrubber to recover methanol, causing a large amount of methanol to enter the tail gas system, significantly reducing the methanol yield.

[0016] Patent CN109761751A proposes a sequential five-tower four-effect thermally coupled distillation method. The advantage of this method is that it can further reduce the energy consumption of methanol products, but the disadvantage is that it requires higher pressure steam and larger equipment investment. After the multi-effect distillation exceeds three effects, the energy saving effect is no longer obvious and it loses its economic viability.

[0017] Patent CN101570446A describes a five-tower, three-effect methanol distillation process. This process achieves the most economical and feasible energy conservation while also taking into account the system's waste heat utilization and wastewater reuse. However, its drawbacks include the lack of a gradient design for waste heat utilization, and the salt content of the recovered tower bottom wastewater, which is directly used as wash water in the scrubber, impacting the quality of the methanol product.

[0018] The above distillation processes are all aimed at the process of producing methanol by hydrogenation of carbon monoxide. When the water content in crude methanol is low, the temperature gradient between the top and bottom of the tower is small. Only a small pressure difference is required between the towers to form a temperature difference between the methanol vapor at the top of the previous tower and the methanol in the bottom of the next tower.

[0019] If the carbon dioxide hydrogenation to methanol unit adopts a similar distillation process as mentioned above, in order to ensure the temperature difference between the top steam of the previous tower and the bottom of the next tower, the pressure difference between the towers of each level will have to be increased, resulting in a significant increase in equipment investment and an increase in the steam grade and amount of the high-pressure tower bottom reboiler. The low-level heat of methanol synthesis cannot be effectively utilized, resulting in high steam consumption and high production and operation costs.

[0020] Some patents have made targeted reports on the distillation of carbon dioxide to methanol.

[0021] Patent CN217119361U discloses a "carbon dioxide to methanol distillation system," characterized by comprising a lightness removal tower system, a negative pressure distillation tower system, a pressurized distillation tower system, an atmospheric pressure distillation tower system, and a recovery tower system; wherein the lightness removal tower system is connected to the negative pressure distillation tower system, the negative pressure distillation tower system is connected to the pressurized distillation tower system, the pressurized distillation tower system is connected to the atmospheric pressure distillation tower system, and the atmospheric pressure distillation tower system is connected to the recovery tower system. This process couples the heat source for carbon dioxide to methanol distillation with the heat source generated by methanol synthesis. The carbon dioxide to methanol device does not require external heat supply and has low energy consumption. However, the overall equipment investment for the five-tower distillation and heat pump is high, and the control process is complex.

[0022] Chinese patent CN 115671774A discloses a "device and method for refining a product produced by hydrogenating carbon dioxide to produce methanol." The device comprises a pre-rectifier, a pressurized tower, and an atmospheric tower. The heat from the overhead discharge of the pressurized tower serves as a heat source for the atmospheric tower's reboiler, while the heat from the bottom discharge of the tower serves as a heat source for the pre-rectifier's reboiler. The atmospheric tower's bottom treatment is used to preheat the pre-rectifier's distillation. This process offers advantages such as good energy integration. However, due to the high operating pressure of the pressurized tower, 0.6 to 0.9 MPa, the steam heat required exceeds the byproducts of the carbon dioxide synthesis reaction, necessitating an external steam supply. Summary of the Invention

[0023] The present invention provides a process for producing methanol by catalytic hydrogenation of carbon dioxide, and an apparatus for producing methanol by catalytic hydrogenation of carbon dioxide used in the process. This process is a novel process designed to address the low heat release of the synthesis reaction and the high energy consumption of distillation separation in carbon dioxide hydrogenation-to-methanol plants.

[0024] In terms of the device, the present invention achieves multi-effect heat coupling through the use of a pre-rectifier, an atmospheric distillation tower, and a vacuum distillation tower. High-temperature synthesis gas from the outlet of the methanol synthesis tower is used as a heat source for the atmospheric distillation tower, achieving a balance in the heat system between methanol synthesis and distillation, and increasing low-level heat utilization by more than 50%. Low-temperature synthesis gas from the outlet of the methanol synthesis tower is used as a heat source to drive the lithium bromide unit to produce 7-degree water as a by-product. This 7-degree water is used to cool the tops of the pre-rectifier and vacuum distillation towers, reducing the methanol content in low-boiling impurities at the top of the pre-rectifier and increasing the methanol yield by more than 1%. The thermal coupling of synthesis and distillation solves the contradiction between low synthesis heat release and high energy consumption for distillation, separation, and purification, which is unique to carbon dioxide hydrogenation to methanol devices, without requiring external steam supply.

[0025] The purpose of the present invention is achieved through the following technical solutions:

[0026] A process for producing methanol by catalytic hydrogenation of carbon dioxide comprises the following steps:

[0027] The mixed raw gas of carbon dioxide and hydrogen is compressed and mixed with the circulating gas. The mixed gas is heated and sent to the methanol synthesis tower for methanol synthesis. The synthesized gas provides heat source for the waste heat reboiler of the atmospheric tower. The cooled gas goes to the separator for gas-liquid separation. The separated gas phase returns to the methanol synthesis tower to continue to participate in methanol synthesis. After the liquid phase is flashed to separate the light components, the crude alcohol enters the pre-distillation tower to separate the dissolved carbon dioxide, hydrogen and methane. The gas phase at the outlet of the isothermal section of the methanol synthesis tower enters its gas heat exchanger to preheat the raw gas and enters the bromination tower. The lithium unit produces 7-degree water as a by-product, which then enters the cooler for further cooling, and then enters the high-efficiency separator to separate the methanol and water produced by the reaction; the gas phase at the top of the separator returns to the inlet of the circulating compressor for pressurized circulation reaction, and the liquid phase at the bottom goes to the flash tank to be flashed together with the crude alcohol produced by the aforementioned separator; the crude alcohol in the bottom of the pre-distillation tower is sent to the atmospheric distillation tower, and the steam at the top of the atmospheric distillation tower is sent to the vacuum distillation tower to provide heat source and then part of the refined alcohol product is extracted, and the crude alcohol in the bottom of the atmospheric tower is sent to the vacuum distillation tower for further purification; the remaining refined alcohol is produced at the top of the vacuum distillation tower, and wastewater is produced in the bottom of the tower.

[0028] A device for catalytic hydrogenation of carbon dioxide to methanol, used in the aforementioned process, comprises a feed gas compressor, an air-to-air heat exchanger, an electric heater, a methanol synthesis tower, an atmospheric tower waste heat reboiler, a primary high-efficiency separator, a secondary high-efficiency separator, a lithium bromide unit, a cooler, a flash tank, a recycle gas compressor, and a pre-distillation tower. A feed gas mixture of carbon dioxide and hydrogen is compressed in the feed gas compressor and then mixed with the outlet gas of the recycle gas compressor. The outlet of the mixed gas is sequentially connected to the air-to-air heat exchanger, the electric heater, and the methanol synthesis tower. The outlet of the adiabatic section of the methanol synthesis tower is sequentially connected to the atmospheric tower waste heat reboiler and the primary high-efficiency separator. The gas phase of the primary high-efficiency separator is connected to the isothermal section of the methanol synthesis tower, and the liquid phase is connected to the flash tank. The outlet of the isothermal section of the methanol synthesis tower is then sequentially connected to the air-to-air heat exchanger, the lithium bromide unit, the cooler, and the secondary high-efficiency separator. The gas phase of the secondary high-efficiency separator is then connected to the inlet of the recycle gas compressor, and the liquid phase is connected to the flash tank. Finally, the liquid outlet of the flash tank is connected to the pre-distillation tower.

[0029] Furthermore, the device also includes an atmospheric distillation tower and a vacuum distillation tower; the outlet gas of the methanol synthesis tower is connected to the atmospheric distillation tower kettle, the pre-distillation tower is connected to the atmospheric distillation tower, and the atmospheric distillation tower is connected to the vacuum distillation tower.

[0030] Furthermore, the pre-distillation tower is adapted to be equipped with a pre-distillation tower cooler and a pre-distillation tower reboiler; and the liquid outlet of the pre-distillation tower kettle is connected to the atmospheric distillation tower.

[0031] Furthermore, the atmospheric distillation tower is adapted to be equipped with an atmospheric distillation tower reboiler, the atmospheric distillation tower top gas phase is connected to the vacuum distillation tower reboiler, and the atmospheric distillation tower bottom liquid outlet is connected to the vacuum distillation tower. The vacuum distillation tower is adapted to be equipped with a vacuum distillation tower cooler, a vacuum distillation tower reboiler, and a wastewater pump.

[0032] Furthermore, part of the heat source of the atmospheric distillation tower comes from the waste heat at the outlet of the adiabatic section of the methanol synthesis tower, and the rest comes from the by-product steam of the isothermal section of the methanol synthesis tower provided by the atmospheric distillation tower reboiler.

[0033] Furthermore, the heat source of the pre-distillation tower comes from the steam condensate of the reboiler of the atmospheric distillation tower.

[0034] Furthermore, the heat source of the vacuum distillation tower comes from the steam at the top of the atmospheric distillation tower.

[0035] Furthermore, the 7-degree water used as refrigerant at the top of the pre-distillation tower and vacuum distillation tower comes from the lithium bromide unit.

[0036] Preferably, the operating pressure of the pre-distillation tower is 0.03-0.30 MPaG (specifically 0.03 MPaG, 0.05 MPaG, 0.1 MPaG, 0.15 MPaG, 0.2 MPaG, 0.25 MPaG, 0.3 MPaG, etc.), the top operating temperature is 17-25°C (specifically 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, etc.), and the bottom operating temperature is 70-90°C (specifically 70°C, 75°C, 80°C, 85°C, 90°C, etc.).

[0037] Preferably, the operating pressure of the atmospheric distillation tower is 0-0.01 MPaG (specifically 0 MPaG, 0.01 MPaG, etc.), the top operating temperature is 60-85°C (specifically 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, etc.), and the bottom operating temperature is 75-100°C (specifically 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, etc.).

[0038] Preferably, the operating pressure of the vacuum distillation tower is -0.09 to -0.075 MPaG, the operating temperature of the top of the tower is 17 to 25°C (specifically 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, etc.), and the operating temperature of the bottom of the tower is 45 to 65°C (specifically 45°C, 50°C, 55°C, 60°C, 65°C, etc.).

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The high-temperature synthesis gas at the outlet of the methanol synthesis tower is used as a heat source for the atmospheric distillation tower, achieving a balance in the heat system between methanol synthesis and distillation, and increasing the low-level heat utilization rate by over 70%. The low-temperature synthesis gas at the outlet of the methanol synthesis tower is used as a heat source to drive the lithium bromide unit to produce 7-degree water as a by-product. This 7-degree water is then used to cool the tops of the pre-distillation tower and the vacuum distillation tower, reducing the methanol content in the low-boiling impurities at the top of the pre-distillation tower and increasing the methanol yield by over 1%. The thermal coupling of synthesis and distillation solves the contradiction between the low synthesis heat release and the high energy consumption of distillation, separation and purification, which is unique to carbon dioxide hydrogenation to methanol units, without the need for external steam supply.

[0041] (2) The present invention utilizes the high-temperature synthesis gas from the outlet of the methanol synthesis tower as the heat source for the atmospheric distillation tower, the atmospheric distillation tower steam as the heat source for the vacuum distillation tower, and the post-steam condensate as the heat source for the pre-distillation tower. This achieves multi-effect thermal coupling among the pre-distillation tower, atmospheric distillation tower, and vacuum distillation tower, resulting in low overall energy consumption.

[0042] (3) After the pressure of the distillation system is reduced, the condensation temperature at the top of the tower is reduced. The low-temperature synthesis gas is driven by methanol to produce 7-degree water as a by-product of the lithium bromide unit. The 7-degree water is used to cool the top of the pre-distillation tower and the vacuum distillation tower, reducing the methanol content in the low-boiling impurities at the top of the pre-distillation tower, further improving the methanol yield.

[0043] (4) The integrated arrangement of the adiabatic section and the isothermal section of the methanol synthesis tower not only increases the heat release of methanol synthesis, but also improves the heat utilization rate of high-level heat and low-level heat.

[0044] (5) The overall thermal coupling of carbon dioxide hydrogenation to methanol increases the low-level heat utilization rate by more than 50% and the methanol yield by more than 1%. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a schematic diagram of the connection relationship of the traditional three-tower process.

[0046] Figure 2 This is a schematic diagram of the connection relationship of a process for producing methanol by catalytic hydrogenation of carbon dioxide according to an embodiment of the present invention.

[0047] Reference numerals:

[0048] 1- Raw gas compressor, 2- Gas-to-gas heat exchanger, 3- Electric heater, 4- Methanol synthesis tower,

[0049] 5- atmospheric tower waste heat reboiler, 6-1- primary high efficiency separator, 6-2- secondary high efficiency separator,

[0050] 7-lithium bromide unit, 8-cooler, 9-flash tank, 10-circulating gas compressor,

[0051] 11- pre-distillation tower, 12- pre-distillation tower cooler, 13- pre-distillation tower reboiler,

[0052] 14- atmospheric distillation tower, 15- atmospheric distillation tower reboiler, 16- vacuum distillation tower,

[0053] 17-vacuum distillation tower cooler, 18-vacuum distillation tower reboiler, 19-wastewater pump. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. The orientation or position relationship indicated therein is based on the orientation or position relationship shown in the drawings, or is the orientation or position relationship in which the application product is usually placed when in use, or is the orientation or position relationship commonly understood by those skilled in the art. The terms "set", "open", "installed", "connected" and "connected" should be understood in a broad sense.

[0055] It should be noted that similar reference numerals and letters represent similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined or explained in subsequent figures. In addition, the embodiments and features in the embodiments of this application can be combined with each other unless there is a conflict.

[0056] See specifically the following examples:

[0057] The present invention provides a process for producing methanol by catalytic hydrogenation of carbon dioxide, which is further illustrated by the following examples.

[0058] Example 1:

[0059] A process for producing methanol by catalytic hydrogenation of carbon dioxide comprises the following steps: a mixed raw gas of carbon dioxide and hydrogen is compressed and then mixed with a circulating gas, the mixed gas is subjected to heat exchange and heating, and then enters a methanol synthesis tower for methanol synthesis; the synthesized gas provides a heat source for a waste heat reboiler in an atmospheric tower; the cooled gas is sent to a separator for gas-liquid separation; the separated gas phase is returned to the methanol synthesis tower to continue participating in methanol synthesis, the liquid phase is subjected to flash evaporation to separate light components, and the crude alcohol enters a pre-distillation tower to separate dissolved carbon dioxide, hydrogen, and methane; the gas phase at the isothermal section outlet of the methanol synthesis tower enters its gas heat exchanger After preheating the raw gas, it enters the lithium bromide unit to produce 7-degree water as a by-product, then enters the cooler for further cooling, and then enters the high-efficiency separator to separate the methanol and water produced by the reaction; the gas phase at the top of the separator returns to the inlet of the circulating compressor for pressurized circulation reaction, and the liquid phase at the bottom goes to the flash tank to be flashed together with the crude alcohol produced by the aforementioned separator; the crude alcohol in the bottom of the pre-distillation tower is sent to the atmospheric distillation tower, and the steam at the top of the atmospheric distillation tower is sent to the vacuum distillation tower to provide heat source and then part of the refined alcohol product is extracted, and the crude alcohol in the bottom of the atmospheric tower is sent to the vacuum distillation tower for further purification; the remaining refined alcohol is produced at the top of the vacuum distillation tower, and wastewater is produced in the bottom of the tower.

[0060] The process includes a compression unit (raw gas compressor 1, circulating gas compressor 10), a methanol synthesis tower unit (gas-to-gas heat exchanger 2, electric heater 3, methanol synthesis tower 4, atmospheric tower waste heat reboiler 5, first-stage high-efficiency separator 6-1, second-stage high-efficiency separator 6-2, lithium bromide unit 7, cooler 8, flash tank 9), a pre-distillation tower unit (pre-distillation tower 11, pre-distillation tower cooler 12, pre-distillation tower reboiler 13), an atmospheric distillation tower unit (atmospheric distillation tower 14, atmospheric distillation tower reboiler 15), and a vacuum distillation tower unit (vacuum distillation tower 16, vacuum distillation tower cooler 17, vacuum distillation tower reboiler 18, and wastewater pump 19).

[0061] Among them, the outlet gas of the methanol synthesis tower 4 is connected to the bottom of the atmospheric distillation tower 14, the pre-distillation tower unit is connected to the atmospheric distillation tower unit, and the atmospheric distillation tower unit is connected to the vacuum distillation tower unit.

[0062] Furthermore, the raw mixed gas of carbon dioxide and hydrogen is compressed by the raw gas compressor 1 and then mixed with the outlet gas of the recycle gas compressor 10. The outlet of the mixed gas is sequentially connected to the gas-to-gas heat exchanger 2, the electric heater 3, and the methanol synthesis tower 4. The outlet of the adiabatic section of the methanol synthesis tower 4 is sequentially connected to the atmospheric tower waste heat reboiler 5 and the first-stage high-efficiency separator 6-1. The gas phase of the first-stage high-efficiency separator 6-1 is connected to the isothermal section of the methanol synthesis tower 4, and the liquid phase is connected to the flash tank 9. The outlet of the isothermal section of the methanol synthesis tower 4 is then sequentially connected to the gas-to-gas heat exchanger 2, the lithium bromide unit 7, the cooler 8, and the second-stage high-efficiency separator 6-2. The gas phase of the second-stage high-efficiency separator 6-2 is then connected to the inlet of the recycle gas compressor 10, and the liquid phase is connected to the flash tank 9. Finally, the liquid outlet of the flash tank 9 is connected to the pre-distillation tower 11.

[0063] Furthermore, the pre-distillation tower 11 is adapted to be equipped with a pre-distillation tower cooler 12 and a pre-distillation tower reboiler 13. The bottom liquid outlet of the pre-distillation tower 11 is connected to an atmospheric distillation tower 14. The atmospheric distillation tower 14 is adapted to be equipped with an atmospheric distillation tower reboiler 15. The vacuum distillation tower 16 is adapted to be equipped with a vacuum distillation tower cooler 17, a vacuum distillation tower reboiler 18, and a wastewater pump 19. The top gas phase of the atmospheric distillation tower 14 is connected to the vacuum distillation tower reboiler 18, and the bottom liquid outlet of the atmospheric distillation tower is connected to the vacuum distillation tower 16.

[0064] Furthermore, the atmospheric distillation tower 14's heat source is partially derived from waste heat at the outlet of the adiabatic section of the methanol synthesis tower 4, with the remainder supplied by by-product steam from the isothermal section of the methanol synthesis tower 4 via the atmospheric distillation tower reboiler 15. The pre-distillation tower 11's heat source is derived from steam condensate from the atmospheric distillation tower reboiler 15. The vacuum distillation tower 16's heat source is derived from overhead steam from the atmospheric distillation tower 14.

[0065] Furthermore, the 7-degree water used as the refrigerant at the top of the pre-distillation tower 11 and the vacuum distillation tower 16 comes from the lithium bromide unit 7.

[0066] Example 2:

[0067] The device and process described in Example 1 were used for treatment. Taking a methanol production capacity of 100,000 tons / year as an example, the parameters were as follows:

[0068] 1) Carbon dioxide 18225.8 kg / h, temperature 40°C, pressure 1.2 MPa, mass composition: 99% carbon dioxide, 1% nitrogen; raw hydrogen 2679.9 kg / h, temperature 40°C, pressure 1.2 MPa, mass composition: 92.6% hydrogen, 7.4% methane.

[0069] 2) The final crude alcohol yield is 19992.3 kg / h, with a mass composition of 63% methanol, 36% water, and 1% impurities.

[0070] 3) The inlet of the adiabatic section of the methanol synthesis tower is 350°C, the outlet of the adiabatic section is 295°C, and the outlet of the atmospheric tower waste heat reboiler is 205°C.

[0071] 4) The operating parameters of the distillation tower are as follows:

[0072] parameter Pre-distillation tower Atmospheric distillation Vacuum distillation tower Tower top temperature ℃ 19 65 18 Tower bottom temperature ℃ 80 75 48 Operating pressure MPaG 0.03 0 -0.09

[0073] 5) The composition of the top material of the distillation tower is as follows:

[0074]

[0075] 6) The atmospheric distillation tower condenser can provide 10.4952Gcal of heat, and the vacuum distillation tower reboiler requires 10.4017Gcal of heat, which can form heat coupling.

[0076] 7) The high-temperature waste heat of the methanol synthesis tower is 4.9793 Gcal, and the by-product steam can provide 7.5304 Gcal of heat. The atmospheric distillation tower requires 10.2647 Gcal of heat, which can meet the required heat and have a surplus of 2.2450 Gcal.

[0077] Example 3:

[0078] The same operating parameters as in Example 2, based on the synthesis of methanol by hydrogenation of carbon dioxide, were used. Figure 1 The conventional three-tower process and the process for producing methanol by catalytic hydrogenation of carbon dioxide according to the present invention (the specific apparatus and process are the same as those in Example 1) are heat coupled. The heat comparison is shown in the following table:

[0079]

[0080] Compared with the traditional three-tower process, the present invention can recover more than 70% of waste heat. The low-level heat that cannot be recovered by the traditional three-tower process also requires a large amount of circulating water to reduce the temperature to below 60°C to meet the purpose of water separation and circulating gas.

[0081] Example 4:

[0082] Same parameters as in Example 2, respectively Figure 1 The conventional three-tower process and the process for producing methanol by catalytic hydrogenation of carbon dioxide according to the present invention (the specific apparatus and process are the same as those in Example 1) are compared to see the following table for details:

[0083]

[0084]

[0085] The molar flow rate of the top of the pre-distillation tower using the present invention is 6.2011 kmol, while the molar flow rate of the top of the pre-distillation tower using the traditional three-tower process is 10.9559 kmol. 152 kg / h of additional methanol can be recovered, and the methanol production capacity is increased by 1.2%.

[0086] Example 5:

[0087] The device and process described in Example 1 were used for treatment. Taking a methanol production capacity of 200,000 tons / year as an example, the parameters were as follows:

[0088] 1) Carbon dioxide 35357.1 kg / h, hydrogen 4821.4 kg / h, other parameters are the same as in Example 2.

[0089] 2) The final crude alcohol yield is 39370.1 kg / h, with a mass composition of 63.5% methanol, 35.5% water, and 1% impurities.

[0090] 3) The operating parameters of methanol synthesis temperature and pressure are the same as those in Example 2.

[0091] 4) Distillation operating parameters

[0092] parameter Pre-distillation tower Atmospheric distillation Vacuum distillation tower Tower top temperature ℃ 16.5 66 17 Tower bottom temperature ℃ 78 77.5 46 Operating pressure MPaG 0.025 0.05 -0.085

[0093] 5) The output of refined alcohol is 25250.1 kg / h, and the quality meets the superior quality standards in "Industrial Methanol" (GB338-2011), with a methanol content of 99.999%.

[0094] The above is only a preferred embodiment of the invention and does not impose any formal limitation on the invention. Based on the technical essence of the invention and within the spirit and principles of the invention, any simple modification, equivalent replacement and improvement of the above embodiment shall still fall within the scope of protection of the technical solution of the invention.

Claims

1. A process for preparing methanol by catalytic hydrogenation of carbon dioxide, characterized in that The process includes the following steps: the mixed raw gas of carbon dioxide and hydrogen is compressed and mixed with the circulating gas, and the mixed gas enters the methanol synthesis tower for methanol synthesis after heat exchange and heating; the synthesized gas provides a heat source for the waste heat reboiler of the atmospheric tower; the cooled gas goes to the separator for gas-liquid separation; the separated gas phase is returned to the methanol synthesis tower to continue methanol synthesis, the liquid phase is flashed to separate the light components, and the crude alcohol enters the pre-distillation tower to separate the dissolved carbon dioxide, hydrogen and methane; the gas phase at the outlet of the isothermal section of the methanol synthesis tower enters its gas heat exchanger to preheat the raw gas, The 7-degree water produced as a by-product of the lithium bromide unit enters the cooler for further cooling, and then enters the high-efficiency separator to separate the methanol and water produced by the reaction; the gas phase at the top of the separator returns to the inlet of the circulating compressor for pressurized circulation reaction, and the liquid phase at the bottom goes to the flash tank and flashes together with the crude alcohol produced by the aforementioned separator; the crude alcohol in the bottom of the pre-distillation tower is sent to the atmospheric distillation tower, and the steam at the top of the atmospheric distillation tower is sent to the vacuum distillation tower to provide heat source and then a part of the refined alcohol product is extracted. The crude alcohol in the bottom of the atmospheric tower is sent to the vacuum distillation tower for further purification; the remaining refined alcohol is produced at the top of the vacuum distillation tower, and wastewater is produced in the bottom of the tower; The pre-distillation tower is adapted to be equipped with a pre-distillation tower cooler and a pre-distillation tower reboiler, and the liquid outlet of the pre-distillation tower kettle is connected to the atmospheric distillation tower; the atmospheric distillation tower is adapted to be equipped with an atmospheric distillation tower reboiler; The heat source of the atmospheric distillation tower is partly from the waste heat at the outlet of the adiabatic section of the methanol synthesis tower, and the rest is from the by-product steam of the isothermal section of the methanol synthesis tower provided by the atmospheric distillation tower reboiler; The heat source of the pre-distillation tower comes from the steam condensate of the reboiler of the atmospheric distillation tower; the heat source of the vacuum distillation tower comes from the steam at the top of the atmospheric distillation tower; the 7-degree water used as the refrigerant at the top of the pre-distillation tower and the vacuum distillation tower comes from the lithium bromide unit.

2. A device for preparing methanol by catalytic hydrogenation of carbon dioxide, used in the process for preparing methanol by catalytic hydrogenation of carbon dioxide as claimed in claim 1, characterized in that: The device comprises a raw gas compressor (1), an air-to-air heat exchanger (2), an electric heater (3), a methanol synthesis tower (4), an atmospheric tower waste heat reboiler (5), a primary high-efficiency separator (6-1), a secondary high-efficiency separator (6-2), a lithium bromide unit (7), a cooler (8), a flash tank (9), a circulating gas compressor (10) and a pre-distillation tower (11); wherein the raw mixed gas of carbon dioxide and hydrogen is compressed by the raw gas compressor (1) and then mixed with the outlet gas of the circulating gas compressor (10); the outlet end of the mixed gas is connected to the air-to-air heat exchanger (2), the electric heater (3) and the methanol synthesis tower (4) in sequence; the methanol synthesis tower (4) is thermally insulated. The outlet of the section is connected to the atmospheric tower waste heat reboiler (5) and the first-stage high-efficiency separator (6-1) in sequence; the gas phase of the first-stage high-efficiency separator (6-1) is connected to the isothermal section of the methanol synthesis tower (4), and the liquid phase is connected to the flash tank (9); the outlet of the isothermal section of the methanol synthesis tower (4) is connected to the gas-gas heat exchanger (2), the lithium bromide unit (7), the cooler (8), and the second-stage high-efficiency separator (6-2) in sequence; the gas phase of the second-stage high-efficiency separator (6-2) is connected to the inlet of the circulating gas compressor (10), and the liquid phase is connected to the flash tank (9); finally, the liquid outlet of the flash tank (9) is connected to the pre-distillation tower (11); the device also includes an atmospheric distillation tower (14) and a vacuum distillation tower (15). distillation tower (16); the outlet gas of the methanol synthesis tower (4) is connected to the bottom of the atmospheric distillation tower (14); the pre-distillation tower (11) is connected to the atmospheric distillation tower (14); the atmospheric distillation tower (14) is connected to the vacuum distillation tower (16); the pre-distillation tower (11) is adapted to be equipped with a pre-distillation tower cooler (12) and a pre-distillation tower reboiler (13), and the bottom liquid outlet of the pre-distillation tower (11) is connected to the atmospheric distillation tower (14); the atmospheric distillation tower (14) is adapted to be equipped with an atmospheric distillation tower reboiler (15); the vacuum distillation tower (16) is adapted to be equipped with a vacuum distillation tower cooler (17), a vacuum distillation tower reboiler (18), and a wastewater pump (19); the atmospheric distillation tower The gas phase at the top of the tower (14) is connected to the reboiler (18) of the vacuum distillation tower, and the liquid outlet of the kettle of the atmospheric distillation tower is connected to the vacuum distillation tower (16); the heat source of the atmospheric distillation tower (14) is partly derived from the waste heat at the outlet of the adiabatic section of the methanol synthesis tower (4), and the rest is derived from the by-product steam of the isothermal section of the methanol synthesis tower (4) provided through the reboiler (15) of the atmospheric distillation tower; the heat source of the pre-distillation tower (11) is derived from the steam condensate of the reboiler (15) of the atmospheric distillation tower; the heat source of the vacuum distillation tower (16) is derived from the steam at the top of the atmospheric distillation tower (14); the 7-degree water used as the refrigerant at the top of the pre-distillation tower (11) and the vacuum distillation tower (16) is derived from the lithium bromide unit (7).

3. The device for preparing methanol by catalytic hydrogenation of carbon dioxide according to claim 2, characterized in that: The operating pressure of the pre-distillation tower (11) is 0.03-0.30 MPaG, the operating temperature of the tower top is 17-25°C, and the operating temperature of the tower bottom is 70-90°C.

4. The device for preparing methanol by catalytic hydrogenation of carbon dioxide according to claim 2, characterized in that: The atmospheric distillation tower (14) has an operating pressure of 0-0.01 MPaG, a tower top operating temperature of 60-85°C, and a tower bottom operating temperature of 75-100°C.

5. The device for preparing methanol by catalytic hydrogenation of carbon dioxide according to claim 2, characterized in that: The vacuum distillation tower (16) has an operating pressure of -0.09 to -0.075 MPaG, a tower top operating temperature of 17 to 25°C, and a tower bottom operating temperature of 45 to 65°C.

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