A method and system for producing green methanol by CO2 hydrogenation

Abstract

This invention belongs to the field of green methanol preparation technology, and specifically relates to a method and system for preparing green methanol by CO2 hydrogenation. The method includes the following steps: 1) crushing and granulating biomass raw materials to generate flue gas and steam in a biomass boiler, and obtaining CO2 by carbon capture of the flue gas; 2) producing H2 by water electrolysis; 3) using the CO2 obtained in step 1) and the H2 obtained in step 2) as fresh gas to carry out a methanol synthesis reaction under the action of a catalyst to obtain methanol synthesis reaction gas, which is then subjected to heat exchange, water cooling, and separation to obtain first crude methanol and recycle gas; the first crude methanol is flash-distilled to obtain second crude methanol and flash vapor; wherein at least a portion of the recycle gas is recycled for the methanol synthesis reaction; 4) distilling the second crude methanol obtained in step 3) to obtain refined methanol. This invention achieves high-value and clean utilization of agricultural and forestry waste biomass raw materials while producing green methanol that meets the carbon neutrality target.

Description

Technical Field

[0001] This invention belongs to the field of green methanol preparation technology, and in particular relates to a method and system for preparing green methanol by CO2 hydrogenation. Background Technology

[0002] Methanol, as a major raw material and an important form of clean energy in modern chemical industry, has been deeply embedded in multiple core industrial chains, from basic chemical synthesis and pharmaceutical production to high-end materials manufacturing and clean fuel supply. However, for a long time, methanol production has mainly relied on fossil energy conversion pathways such as coal-based and natural gas reforming, making it one of the typical carbon-intensive representatives in the chemical industry. Under the national "dual carbon" policy, it faces severe transformation pressure.

[0003] Meanwhile, agricultural and forestry waste biomass, represented by straw, is rich in natural carbon structure and convertible energy, making it a widely distributed, renewable green carbon source with inherent advantages such as carbon neutrality, resource recycling, and low environmental impact. Traditional disposal methods such as incineration or landfill not only lead to the disorderly emission of pollutants but also cause the systematic loss of carbon resources. If targeted conversion technology can efficiently convert biomass carbon sources such as straw into methanol, it will not only open up a new path for the high-value and clean utilization of agricultural and forestry waste but also produce truly carbon-neutral green methanol, thus providing the chemical and energy industries with renewable and green raw material and fuel alternatives. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method and system for producing green methanol by CO2 hydrogenation, which enables the high-value and clean utilization of agricultural and forestry waste biomass raw materials while producing green methanol that meets the carbon neutrality target. This solves the problems in the prior art.

[0005] The technical solution of this invention is:

[0006] This invention provides a method for preparing green methanol by CO2 hydrogenation, the method comprising the following steps:

[0007] 1) Crush and granulate biomass raw materials to generate flue gas and steam in a biomass boiler, and obtain CO2 by carbon capture of the flue gas;

[0008] 2) Producing H2 through water electrolysis;

[0009] 3) The CO2 obtained in step 1) and the H2 obtained in step 2) are used as fresh gas. The fresh gas and the recycled gas are subjected to methanol synthesis reaction under the action of a catalyst to obtain methanol synthesis reaction gas. The methanol synthesis reaction gas is subjected to heat exchange, water cooling and separation in sequence to obtain first crude methanol and recycled gas. The first crude methanol is flashed to obtain second crude methanol and flash vapor. At least part of the recycled gas is recycled for methanol synthesis reaction.

[0010] 4) The second crude methanol obtained in step 3) is distilled to obtain methanol.

[0011] A second aspect of the present invention provides a system for producing green methanol by CO2 hydrogenation, the system comprising a biomass boiler, a carbon capture device, a methanol synthesis device, a methanol intermediate tank, and a methanol distillation device connected in sequence; and further comprising a water electrolysis device connected to the methanol synthesis device.

[0012] By adopting the aforementioned technical solution, the beneficial effects of the present invention are:

[0013] This invention uses biomass such as straw as raw materials and couples a biomass boiler with a methanol synthesis unit. This provides both the steam required for the process unit and the green carbon source CO2 required for methanol synthesis, avoiding the disorderly emission of pollutants and the systematic loss of carbon resources caused by traditional incineration or landfill disposal methods.

[0014] Due to the fluctuations in wind and solar power, the hydrogen supply capacity of the water electrolysis hydrogen production unit also fluctuates. The methanol synthesis unit uses hydrogen balloon tanks at the front end to balance the impact of upstream fluctuations on the methanol synthesis unit, and uses intermediate methanol tanks at the downstream end to balance the impact of upstream fluctuations on the methanol distillation unit, thus achieving stable operation of the methanol distillation unit. Attached Figure Description

[0015] Figure 1 This diagram shows a system for producing green methanol by CO2 hydrogenation.

[0016] Component labels in the diagram

[0017] 1-Biomass boiler; 11-Biomass feedstock inlet; 12-Flue gas outlet; 13-Steam outlet; 14-Fuel gas inlet;

[0018] 2-Carbon capture device; 21-Induced draft fan; 211-Flue gas inlet; 22-Carbon dioxide trap; 221-First steam inlet; 23-Carbon dioxide compressor; 231-Flash steam inlet; 24-Desulfurization tower;

[0019] 3-Methanol synthesis unit; 31-Circulating gas compressor, 311-Carbon dioxide inlet, 312-H2 circulating gas compressor inlet, 313-Circulating gas inlet, 314-Synthesis gas outlet; 32-Gas-to-gas heat exchanger, 321-Mixed gas inlet, 322-Heated synthesis gas outlet, 323-Methanol synthesis reaction gas inlet, 324-Cooled methanol synthesis reaction gas outlet; 33-Methanol synthesis reactor, 331-Heated mixed gas inlet, 332-Methanol synthesis reaction gas outlet; 34-Water cooler; 35-Methanol separator, 351-Purge gas outlet; 36-Methanol flash evaporator, 361-Second crude methanol outlet, 362-Flash vapor outlet;

[0020] 4-Methanol distillation unit; 41-Pre-distillation column; 42-Pressurized column; 43-Ambient pressure column;

[0021] 5-Water electrolysis device, 51-Water inlet, 52-First hydrogen outlet;

[0022] 6-Hydrogen balloon tank, 61-First hydrogen inlet, 62-Second hydrogen outlet;

[0023] 7- Hydrogen compressor, 71- Second hydrogen inlet, 72- Third hydrogen outlet;

[0024] 8-Methanol intermediate tank;

[0025] 9-Finished product can. Detailed Implementation

[0026] The following describes in detail the implementation of the method and system for preparing green methanol by CO2 hydrogenation provided by the present invention.

[0027] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0028] [Methods for preparing green methanol by CO2 hydrogenation]

[0029] This invention provides a method for producing green methanol by CO2 hydrogenation, specifically a process route that couples a biomass boiler 1 for heating and provides CO2, the green carbon source required for methanol synthesis. The method includes the following steps:

[0030] 1) The biomass raw material is crushed and granulated to generate flue gas and steam in biomass boiler 1, and CO2 is obtained by carbon capture of the flue gas.

[0031] 2) Producing H2 through water electrolysis;

[0032] 3) The CO2 obtained in step 1) and the H2 obtained in step 2) are used as fresh gas. The fresh gas and the recycled gas are subjected to methanol synthesis reaction under the action of a catalyst to obtain methanol synthesis reaction gas. The methanol synthesis reaction gas is subjected to heat exchange, water cooling and separation in sequence to obtain first crude methanol and recycled gas. The first crude methanol is flashed to obtain second crude methanol and flash vapor. At least part of the recycled gas is recycled for methanol synthesis reaction.

[0033] 4) The second crude methanol obtained in step 3) is distilled to obtain refined methanol.

[0034] In the preparation method provided by this invention, step 1) involves crushing and granulating the biomass raw material, generating flue gas and steam in a biomass boiler 1, and then capturing carbon in the flue gas to obtain CO2. Specifically:

[0035] In step 1) of this invention, the biomass raw material typically includes one or more of the following: corn stalks, cotton stalks, wheat stalks, peanut shells, rice husks, sawdust, and sugarcane bagasse. The particle size of the pulverized and granulated biomass raw material is ≤25mm, or the pulverized biomass raw material has the following dimensions: length ≤80mm, thickness ≤10mm.

[0036] In step 1) of this invention, the temperature of the biomass boiler 1 is 400℃~450℃ and any value between them or any two values, which can be selected as 400℃~420℃ or 420℃~450℃. The pressure is 3.82~4.2MPa(G) and any value between them or any two values, which can be selected as 3.82~4.0MPa(G) or 4.0~4.2MPa(G).

[0037] In step 1) of this invention, the generated steam can be used as a byproduct as a heat source for the reboiler at the bottom of the column during carbon capture in step 1) and distillation in step 4).

[0038] In step 1) of this invention, the CO2 obtained from carbon capture is high-purity CO2, with a purity of, for example, ≥92% mol. It can be used as a raw material for subsequent methanol synthesis.

[0039] In the preparation method provided by this invention, step 2) involves producing H2 through electrolysis of water. Specifically:

[0040] In step 2) of this invention, the green electricity required for the H2 production process via water electrolysis is generated by wind / solar power generation. Due to the inherent fluctuations in wind / solar power, the hydrogen supply capacity of the water electrolysis device 5 used for hydrogen production also fluctuates. Therefore, the green hydrogen obtained by the water electrolysis device 5 is first sent to the hydrogen balloon tank 6 to balance the impact of upstream fluctuations on the methanol synthesis device 3. When the amount of H2 produced by water electrolysis is greater than the amount of hydrogen needed for methanol synthesis, the excess hydrogen is temporarily stored in the hydrogen balloon tank 6; when the amount of H2 produced by water electrolysis is less than the amount of hydrogen needed for methanol synthesis, hydrogen needs to be released from the hydrogen balloon tank 6 for use in methanol synthesis. Excess green electricity from the wind / solar power generation system can be temporarily stored through energy storage devices.

[0041] In step 2) of the present invention, the operating pressure for the electrolysis of water to produce hydrogen is 0.01~3.5MPa(G), which can be selected as 0.01~1.6 MPa(G) or 1.6~3.5MPa(G), and the operating temperature is 65~90℃ or any value between them or any two values, which can be selected as 65~80℃, 80~85℃ or 85~90℃.

[0042] In the preparation method provided by this invention, step 3) involves using the CO2 obtained in step 1) and the H2 obtained in step 2) as fresh gases to carry out a methanol synthesis reaction under the action of a catalyst to obtain methanol synthesis reaction gas. The methanol synthesis reaction gas is then subjected to heat exchange, water cooling, and separation to obtain first crude methanol and purge gas. The first crude methanol is flash-distilled to obtain second crude methanol and flash vapor. At least a portion of the recycled gas is reused in the methanol synthesis reaction. The fresh gas and recycled gas involved in this invention are all under stable operating conditions. In this invention, "at least a portion" means all or a part.

[0043] Specifically:

[0044] In step 3) of the present invention, the molar ratio of H2 to CO2 in the fresh gas is 2~5:1, which can be selected as 2~3:1 or 3~5:1.

[0045] In step 3) of this invention, the molar ratio of recirculated gas to fresh gas is 3~15:1, which can be 3~10:1 or 10~15:1. Further, the molar ratio of H2 to CO2 in the recirculated gas is 3~10:1, which can be 3~5:1 or 5~10:1.

[0046] In step 3) of this invention, the catalyst is a Cu-based catalyst.

[0047] In step 3) of the present invention, the reaction temperature is 200~270℃ and any value between them or any two values, which can be selected as 200~250℃ or 250~270℃, and the reaction pressure is 4.5~5.0 MPa(G) and any value between them or any two values, which can be selected as 4.5~4.8 MPa(G) or 4.8~5.0 MPa(G).

[0048] In step 3) of this invention, 0-1 wt% of the recycle gas is recycled as fuel gas for biomass boiler 1 (specifically, 0-1 wt% of the recycle gas is incorporated into the fuel gas pipeline as purge gas and then recycled as fuel gas for biomass boiler 1). The purge gas can be selected as 0-0.01 wt%, 0.01-1 wt%, 0.01-0.1 wt%, 0.1-0.5 wt%, 0.5-1 wt%, 0.1-0.3 wt%, 0.3-0.5 wt%, 0.5-0.8 wt%, or 0.8-1 wt% as fuel gas for biomass boiler 1; the remaining recycle gas is recycled for methanol synthesis reaction.

[0049] In step 3) of this invention, the water is cooled to 35~45℃, which can be selected as 35~40℃ or 40~45℃.

[0050] In step 3) of this invention, flash vapor is recycled for carbon capture.

[0051] In step 3) of the present invention, the pressure reduction of flash evaporation is 0.05~0.6MPa(G) and any value between them or any two values, and can be selected as 0.05~0.3MPa(G) or 0.3~0.6MPa(G).

[0052] In one specific embodiment, during the stable operation phase, H2 from the water electrolysis unit 5 and CO2 from the carbon capture unit 2 are used as fresh gas and mixed with recirculated gas at the outlet of the recirculated gas compressor 31. The mixed synthesis gas is heated to a certain temperature by the methanol reactor outlet gas in the gas-to-gas heat exchanger 32 and then sent to the methanol synthesis reactor 33, where a methanol synthesis reaction occurs under the action of a catalyst. The methanol synthesis reaction gas flows sequentially through the gas-to-gas heat exchanger 32 and the water cooler 34, and after being cooled to 40°C, it enters the methanol separator 35. In the methanol separator 35, the first crude methanol is separated from the recirculated gas (i.e., unreacted gas). To control the system inert gas content, a small portion of the recirculated gas is used as purge gas and recycled as fuel gas for the biomass boiler 1, while most of the recirculated gas is pressurized by the recirculated gas compressor 31 and re-enters the methanol synthesis loop as recirculated gas. The second crude methanol from the methanol separator 35 is depressurized in the methanol flash tank, releasing most of the gas dissolved in the second crude methanol (flash vapor). The second crude methanol flowing out of the methanol flash tank is sent to the distillation unit, and the flash vapor is sent to the inlet of the carbon dioxide compressor 23 in the carbon capture unit 2.

[0053] In the preparation method provided by this invention, step 4) involves distilling the second crude methanol obtained in step 3) to obtain methanol. Specifically:

[0054] In step 4) of the present invention, the second crude methanol first enters the methanol intermediate tank 8 and then undergoes distillation.

[0055] In step 4) of this invention, the distillation is carried out sequentially in a pre-distillation column 41, a pressurized column 42, and an atmospheric column 43. The pressure in the pre-distillation column 41 is 0.05~0.1 MPa(G), and the temperature is 80~120℃. The pressure in the pressurized column 42 is 0.6~1.0 MPa(G), and the temperature is 120~160℃. The pressure in the atmospheric column 43 is 0.01~0.1 MPa(G), and the temperature is 50~120℃.

[0056] In step 4) of this invention, the purity of methanol is ≥99.85 wt%.

[0057] In one specific embodiment, the feed of the methanol distillation unit 4 comes from the methanol intermediate tank 8. The methanol intermediate tank 8 eliminates the influence of upstream system fluctuations on the methanol distillation unit 4. The methanol distillation unit 4 is equipped with a pre-distillation tower 41, a pressurized tower 42 and an atmospheric tower 43. The second crude methanol is distilled through the three towers to obtain high-purity refined methanol, which is then sent to the finished product tank area 9.

[0058] A system for producing green methanol via CO2 hydrogenation.

[0059] This invention provides a system for producing green methanol by CO2 hydrogenation. The system includes a biomass boiler 1, a carbon capture device 2, a methanol synthesis device 3, a methanol intermediate tank 8, and a methanol distillation device 4 connected in sequence; it also includes a water electrolysis device 5, which is connected to the methanol synthesis device 3.

[0060] In the system provided by the present invention, the biomass boiler 1 includes a biomass raw material inlet 11, a flue gas outlet 12, a steam outlet 13, and a fuel gas inlet 14, wherein the flue gas outlet 12 is connected to the carbon capture device 2.

[0061] In the system provided by this invention, the carbon capture device 2 includes an induced draft fan 21, a carbon dioxide trap 22, a carbon dioxide compressor 23, and a desulfurization tower 24 connected in sequence. The induced draft fan 21 includes a flue gas inlet 221, and the desulfurization tower 24 includes a carbon dioxide outlet 241. The flue gas inlet 221 is connected to the flue gas outlet 12, and the carbon dioxide outlet 241 is connected to the methanol synthesis unit 3. A first steam inlet 221 is provided on the reboiler at the bottom of the carbon dioxide trap 22, and the first steam inlet 221 is connected to the inlet of the reboiler at the bottom of the carbon dioxide trap 22. Further, the induced draft fan 21 also includes an induced draft fan outlet, which is connected to the inlet of the carbon dioxide trap 22, the outlet of the carbon dioxide trap 22 is connected to the inlet of the carbon dioxide compressor 23, and the outlet of the carbon dioxide compressor 23 is connected to the inlet of the desulfurization tower 24.

[0062] The carbon dioxide trap 22 typically includes a cooling and dust removal tower, an absorption tower, and a regeneration tower connected in sequence. The cooling and dust removal tower is connected to the induced draft fan 21, and the regeneration tower is connected to the carbon dioxide compressor 23. The reboiler at the bottom of the carbon dioxide trap 22 is located at the bottom of the regeneration tower.

[0063] In the system provided by the present invention, a hydrogen balloon tank 6 and a hydrogen compressor 7 are sequentially provided on the connecting pipeline between the water electrolysis device 5 and the methanol synthesis device 3. The hydrogen balloon tank 6 is connected to the water electrolysis device 5, and the hydrogen compressor 7 is connected to the methanol synthesis device 3.

[0064] Furthermore, the water electrolysis device 5 includes a water inlet 51 and a first hydrogen outlet 52, the hydrogen balloon tank 6 includes a first hydrogen inlet 61 and a second hydrogen outlet 62, and the hydrogen compressor 7 includes a second hydrogen inlet 71 and a third hydrogen outlet 72. The first hydrogen outlet 52 and the first hydrogen inlet 61 are connected, the second hydrogen outlet 62 and the second hydrogen inlet 71 are connected, and the third hydrogen outlet 72 is connected to the circulating gas compressor 31.

[0065] The green electricity needed to produce hydrogen through water electrolysis comes from upstream wind / solar power generation.

[0066] In the system provided by this invention, the methanol synthesis unit 3 includes a circulating gas compressor 31, a gas-to-gas heat exchanger 32, and a methanol synthesis reactor 33. It also includes a water cooler 34, a methanol separator 35, and a methanol flash tank 36 connected in sequence. The methanol flash tank 36 is connected to the methanol distillation unit 4. The methanol flash tank 36 includes a second crude methanol outlet 361 and a flash vapor outlet 362. The second crude methanol outlet 361 is connected to a methanol intermediate tank 8. The flash vapor outlet 362 is connected to a carbon capture device 2; specifically, it is connected to a carbon dioxide compressor 23, and more specifically, it is connected to a flash vapor inlet 231.

[0067] The circulating gas compressor 31 includes a carbon dioxide inlet 311, an H2 circulating gas compressor inlet 312, a circulating gas inlet 313, and a syngas outlet 314.

[0068] The gas-to-gas heat exchanger 32 includes a mixed gas inlet 321, a heated synthesis gas outlet 322, a methanol synthesis reaction gas inlet 323, and a cooled methanol synthesis reaction gas outlet 324.

[0069] The methanol synthesis reactor 33 includes a heating mixed gas inlet 331 and a methanol synthesis reaction gas outlet 332.

[0070] The carbon dioxide inlet 311 is connected to the carbon capture device 2, specifically, the carbon dioxide inlet 311 is connected to the carbon dioxide outlet.

[0071] The H2 circulating gas compressor inlet 312 is connected to the water electrolysis device 5. More preferably, the H2 circulating gas compressor inlet 312 is connected to the third hydrogen outlet 72 of the hydrogen compressor 7.

[0072] The syngas outlet 314 is connected to the mixed gas inlet 321, the heated syngas outlet 322 is connected to the heated mixed gas inlet 331, the methanol synthesis reaction gas outlet 332 is connected to the methanol synthesis reaction gas inlet 323, and the cooled methanol synthesis reaction gas outlet 324 is connected to the water cooler 34.

[0073] The methanol separator 35 includes a circulating gas outlet 351, which is connected to the circulating gas inlet 313 and the fuel gas inlet 14.

[0074] In the system provided by this invention, the inlet of the methanol intermediate tank 8 is connected to the second crude methanol outlet 361 of the methanol flash tank 36. The outlet of the methanol intermediate tank 8 is connected to the methanol distillation unit 4, and the presence of the methanol intermediate tank 8 eliminates the influence of upstream system fluctuations on the methanol distillation unit 4.

[0075] In the system provided by this invention, the distillation apparatus includes a pre-distillation column 41, a pressurized column 42, and an atmospheric column 43 connected in sequence. The pre-distillation column 41 is connected to the methanol intermediate tank 8. Specifically, the outlet of the methanol intermediate tank 8 is connected to the inlet of the pre-distillation column 41. The atmospheric column 43 is connected to the finished product tank 9.

[0076] In summary, this invention uses biomass such as straw as raw materials and couples the biomass boiler 1 with the methanol synthesis unit, providing both the steam required for the process and the green carbon source CO2 needed for methanol synthesis. This avoids the disorderly emission of pollutants and the systematic loss of carbon resources caused by traditional incineration or landfill disposal methods. Simultaneously, by setting up a hydrogen balloon tank 6 and a methanol intermediate tank 8, the impact of upstream fluctuations on the downstream system is balanced, achieving stable operation of the methanol synthesis unit.

[0077] The working process of the device of the present invention:

[0078] Biomass raw materials are crushed and granulated to generate flue gas and steam in biomass boiler 1. The flue gas is then passed sequentially through induced draft fan 21, carbon dioxide collector 22, carbon dioxide compressor 23 and desulfurization tower 24 for carbon capture to obtain CO2.

[0079] Hydrogen gas is produced by water electrolysis device 5 and stored in hydrogen balloon tank 6.

[0080] During stable operation, hydrogen enters the recycle gas compressor 31 through the hydrogen compressor 7, and CO2 also enters the recycle gas compressor 31, where it is mixed with the hydrogen as fresh gas at the synthesis gas outlet 314 of the recycle gas compressor 31. The mixed synthesis gas is heated to a certain temperature by the methanol reactor outlet gas in the gas-to-gas heat exchanger 32 and then sent to the methanol synthesis reactor 33, where a methanol synthesis reaction occurs under the action of a catalyst. The methanol synthesis reaction gas flows sequentially through the gas-to-gas heat exchanger 32 and the water cooler 34, and after being cooled to 40°C, it enters the methanol separator 35. In the methanol separator 35, the first crude methanol is separated from the recycle gas (i.e., unreacted gas). To control the system's inert gas content, a small portion of the recycle gas is used as purge gas and recycled as fuel gas for the biomass boiler 1, while most of the recycle gas is pressurized by the recycle gas compressor 31 and re-enters the methanol synthesis loop. The second crude methanol from the methanol separator 35 is depressurized in the methanol flash tank, releasing most of the gas dissolved in the second crude methanol (flash vapor). The second crude methanol flowing out of the methanol flash tank is sent to the methanol intermediate tank 8, and the flash vapor is sent to the inlet of the carbon dioxide compressor 23 in the carbon capture device 2.

[0081] The methanol distillation unit 4 is fed from the methanol intermediate tank 8. The methanol intermediate tank 8 eliminates the impact of upstream system fluctuations on the methanol distillation unit 4. The methanol distillation unit 4 is equipped with a pre-distillation column 41, a pressurized column 42 and an atmospheric column 43. The second crude methanol is distilled through the three columns to obtain high-purity refined methanol, which is then sent to the finished product tank area 9.

[0082] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0083] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Unless otherwise specified, specific experimental or operational conditions in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0084] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0085] In the following embodiments, unless otherwise specified, all the raw materials of the present invention are commercially available or prepared according to conventional methods in the art.

[0086] Example 1

[0087] S1: 15t / h biomass feedstock is crushed and granulated. The dimensions of the crushed biomass feedstock are: length ≤ 80mm, thickness ≤ 10mm. 80,000 Nm³ / h is generated in biomass boiler 1 at 400℃ and 4.0MPa pressure. 3 The flue gas is fed by 65t / h of steam. The flue gas is passed sequentially through an induced draft fan 21 (at atmospheric pressure), a carbon dioxide trap 22 (15kPa(G)), a carbon dioxide compressor 23, and a desulfurization tower 24 (40℃, 1.4~1.8MPa(G)) to capture carbon and obtain CO2 with a purity of 92mol%.

[0088] S2: 26000 Nm³ of water was prepared using water electrolysis device 5 (pressure 1.6 MPa(G), operating temperature 85 °C). 3 Hydrogen gas is produced at a rate of / h, and water is electrolyzed under conditions of 1.6 MPa (G). Excess hydrogen gas is stored in hydrogen balloon tank 6.

[0089] S3: Under stable operating conditions, fresh hydrogen enters the recirculating gas compressor 31 via the hydrogen compressor 7, at a speed of 9400 Nm. 3 / hCO2 enters the recirculating gas compressor 31, with 26000Nm 3 / h of hydrogen, along with fresh gas, at 283200 Nm 3 The circulating gas (mainly 12 mol% CO2 and 86 mol% H2, with 2% other inert gases) is mixed at the synthesis gas outlet 314 of the circulating gas compressor 31. The mixed synthesis gas is heated to 200-230°C in the gas-to-gas heat exchanger 32 by the gas from the methanol synthesis reaction gas outlet 332, and then sent to the methanol synthesis reactor 33. Methanol synthesis occurs under Cu-based catalyst conditions at 250°C and 5 MPa(G). The methanol synthesis reaction gas flows sequentially through the gas-to-gas heat exchanger 32 and the water cooler 34, cooling to 40°C before entering the methanol separator 35. In the methanol separator 35, the first crude methanol is separated from the circulating gas. To control the system inert gas content, 0.1 wt% of the circulating gas is recycled as fuel gas to the biomass boiler 1, while the remaining circulating gas is pressurized by the circulating gas compressor 31 and re-enters the methanol synthesis loop. The second crude methanol from methanol separator 35 is depressurized to 0.5 MPa (G) in a methanol flash tank at 4.8 MPa (G), releasing 200 Nm³ of methanol dissolved in the second crude methanol. 3 / h of flash vapor. The second crude methanol flowing out of the methanol flash tank 36 is sent to the methanol intermediate tank 8, and the flash vapor from the flash vapor outlet 362 is sent to the flash vapor inlet 231 of the carbon dioxide compressor 23 in the carbon capture unit 2 for reuse.

[0090] The methanol distillation unit 4 is fed from the methanol intermediate tank 8. The methanol distillation unit 4 is equipped with a pre-distillation column 41 (temperature 90℃, pressure 0.08MPa(G)), a pressurized column 42 (temperature 130℃, pressure 0.8MPa(G)) and an atmospheric column 43 (temperature 80℃, pressure 0.02MPa(G)). The second crude methanol is distilled through the three columns to obtain refined methanol with a purity of 99.85%wt, which is then sent to the finished product tank area 9.

[0091] Example 2

[0092] S1: Crush and granulate 7.5 t / h biomass feedstock. The dimensions of the crushed biomass feedstock are: length ≤ 80 mm, thickness ≤ 10 mm. Generate 40,000 Nm³ / h of feedstock in biomass boiler 1 at 400℃ and 4.0 MPa pressure. 3The flue gas is fed by 35t / h of steam. The flue gas is passed sequentially through an induced draft fan 21 (at atmospheric pressure), a carbon dioxide trap 22 (20KPa(G)), a carbon dioxide compressor 23, and a desulfurization tower 24 (40℃, 3.0~3.4MPa(G)) to capture carbon and obtain CO2 with a purity of 93mol%.

[0093] S2: 8000 Nm³ of water was prepared using water electrolysis device 5 (pressure 3.2 MPa(G), operating temperature 65 °C). 3 / h of hydrogen. Store excess hydrogen in hydrogen balloon tank 6.

[0094] S3: Under stable operating conditions, fresh hydrogen enters the recirculating gas compressor 31 through the hydrogen compressor 7, at a speed of 2900 Nm. 3 / hCO2 enters the recirculating gas compressor 31, with 8000Nm 3 / h of hydrogen gas, along with 90000Nm³, is used as fresh gas. 3 The circulating gas (mainly 3 mol% CO2 and 95 mol% H2, with 2% other inert gases) is mixed at the synthesis gas outlet 314 of the circulating gas compressor 31. The mixed synthesis gas is heated to 200-230°C in the gas-to-gas heat exchanger 32 by the gas from the methanol synthesis reaction gas outlet 332, and then sent to the methanol synthesis reactor 33. Methanol synthesis occurs under Cu-based catalyst conditions at 255°C and 4.9 MPa(G). The methanol synthesis reaction gas flows sequentially through the gas-to-gas heat exchanger 32 and the water cooler 34, cooling to 42°C before entering the methanol separator 35. In the methanol separator 35, the first crude methanol is separated from the circulating gas. To control the system inert gas content, 0.03 wt% of the circulating gas is recycled as fuel gas to the biomass boiler 1, while the remaining circulating gas is pressurized by the circulating gas compressor 31 and re-enters the methanol synthesis loop. The second crude methanol from methanol separator 35 is depressurized to 0.1 MPa (G) in a methanol flash tank at 4.7 MPa (G), releasing 9 Nm³ of methanol dissolved in the second crude methanol. 3 / h of flash vapor. The second crude methanol flowing out of the methanol flash tank 36 is sent to the methanol intermediate tank 8, and the flash vapor from the flash vapor outlet 362 is sent to the flash vapor inlet 231 of the carbon dioxide compressor 23 in the carbon capture unit 2 for reuse.

[0095] The methanol distillation unit 4 is fed from the methanol intermediate tank 8. The methanol distillation unit 4 is equipped with a pre-distillation column 41 (temperature 81℃, pressure 0.064MPa(G)), a pressurized column 42 (temperature 144℃, pressure 0.84MPa(G)) and an atmospheric column 43 (temperature 114℃, pressure 0.07MPa(G)). The second crude methanol is distilled through the three columns to obtain refined methanol with a purity of 99.91%wt, which is then sent to the finished product tank area 9.

[0096] Example 3

[0097] S1: Crush and granulate 11t / h biomass feedstock. The dimensions of the crushed biomass feedstock are: length ≤ 80mm, thickness ≤ 10mm. Generate 56000 Nm of power in biomass boiler 1 at 400℃ and 4.0MPa pressure. 3 The flue gas has a capacity of 46t / h and steam. The flue gas is sequentially passed through an induced draft fan 21 (at atmospheric pressure), a carbon dioxide trap 22 (15kPa(G)), a carbon dioxide compressor 23, and a desulfurization tower 24 (40℃, 1.4~1.8MPa(G)) to capture carbon and obtain CO2 with a purity of 94mol%.

[0098] S2: 19000 Nm³ was prepared by electrolysis of water device 5 (pressure 1.6 MPa(G), operating temperature 85 °C). 3 / h of hydrogen. Store excess hydrogen in hydrogen balloon tank 6.

[0099] S3: Under stable operating conditions, fresh hydrogen enters the recirculating gas compressor 31 via hydrogen compressor 7, at a speed of 6700 Nm. 3 / hCO2 enters the recirculating gas compressor 31, with 19000Nm 3 / h of hydrogen gas, along with 140000 Nm³, is used as fresh gas. 3 The circulating gas (mainly 7 mol% CO2 and 90 mol% H2, with 3% other inert gases) is mixed at the synthesis gas outlet 314 of the circulating gas compressor 31. The mixed synthesis gas is heated to 220°C in the gas-to-gas heat exchanger 32 by the gas from the methanol synthesis reaction gas outlet 332, and then sent to the methanol synthesis reactor 33. Methanol synthesis occurs under Cu-based catalyst conditions at 220°C and 4.78 MPa(G). The methanol synthesis reaction gas flows sequentially through the gas-to-gas heat exchanger 32 and the water cooler 34, cooling to 35°C before entering the methanol separator 35. In the methanol separator 35, the first crude methanol is separated from the circulating gas. To control the system inert gas content, 0.01 wt% of the circulating gas is recycled as fuel gas to the biomass boiler 1, while the remaining circulating gas is pressurized by the circulating gas compressor 31 and re-enters the methanol synthesis loop. The second crude methanol from methanol separator 35 is depressurized to 0.1 MPa (G) in a methanol flash tank at 4.68 MPa (G), releasing 70 Nm³ of methanol dissolved in the second crude methanol. 3 / h of flash vapor. The second crude methanol flowing out of the methanol flash tank 36 is sent to the methanol intermediate tank 8, and the flash vapor from the flash vapor outlet 362 is sent to the flash vapor inlet 231 of the carbon dioxide compressor 23 in the carbon capture unit 2 for reuse.

[0100] The methanol distillation unit 4 is fed from the methanol intermediate tank 8. The methanol distillation unit 4 is equipped with a pre-distillation column 41 (temperature 90℃, pressure 0.08MPa(G)), a pressurized column 42 (temperature 130℃, pressure 0.8MPa(G)) and an atmospheric column 43 (temperature 80℃, pressure 0.02MPa(G)). The second crude methanol is distilled through the three columns to obtain refined methanol with a purity of 99.9%wt, which is then sent to the finished product tank area 9.

[0101] In summary, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0102] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing green methanol by CO2 hydrogenation, characterized in that, The method includes the following steps: 1) Crush and granulate biomass raw materials to generate flue gas and steam in a biomass boiler, and obtain CO2 by carbon capture of the flue gas; 2) Producing H2 through water electrolysis; 3) The CO2 obtained in step 1) and the H2 obtained in step 2) are used as fresh gas. The fresh gas and the recycled gas are subjected to methanol synthesis reaction under the action of a catalyst to obtain methanol synthesis reaction gas. The methanol synthesis reaction gas is subjected to heat exchange, water cooling and separation in sequence to obtain first crude methanol and recycled gas. The first crude methanol is flashed to obtain second crude methanol and flash vapor. At least part of the recycled gas is recycled for methanol synthesis reaction. 4) The second crude methanol obtained in step 3) is distilled to obtain methanol.

2. The method for preparing green methanol by CO2 hydrogenation according to claim 1, characterized in that, Step 1) also includes one or more of the following conditions: A1) The particle size of the biomass raw material after crushing and granulation is ≤25mm, or the size of the biomass raw material after crushing is: length ≤80mm, thickness ≤10mm; A2) The biomass raw materials include one or more of the following: corn stalks, cotton stalks, wheat stalks, peanut shells, rice husks, sawdust, and sugarcane bagasse; A3) The temperature of the biomass boiler is 400℃~450℃, and the pressure is 3.82~4.2MPa (G). A4) The steam is used as a heat source for the reboiler at the bottom of the column during carbon capture in step 1) and distillation in step 4).

3. The method for preparing green methanol by CO2 hydrogenation according to claim 1, characterized in that, Step 2) also includes one or more of the following conditions: B1) In step 2), the green electricity required for the electrolysis of water to produce H2 is generated by wind / solar power generation; B2) In step 2), the operating conditions for hydrogen production by water electrolysis are: operating pressure 0.01-3.5 MPa(G) and operating temperature 65-90℃. In step 2) of B3, the H2 is first sent to the hydrogen balloon tank. When the amount of H2 produced by water electrolysis is greater than the amount of hydrogen used for methanol synthesis, the excess hydrogen is sent to the hydrogen balloon tank for temporary storage. When the amount of H2 produced by water electrolysis is less than the amount of hydrogen used for methanol synthesis, hydrogen needs to be released from the hydrogen balloon tank for use in methanol synthesis.

4. The method for preparing green methanol by CO2 hydrogenation according to claim 1, characterized in that, Step 3) also includes one or more of the following conditions: In step 3) of C1), the molar ratio of H2 to CO2 in the fresh gas is 2~5:1; In step 3) of C2), the molar ratio of recirculated gas to fresh gas is 3~15:1; In step 3) of C3), the catalyst is a Cu-based catalyst; In step 3) of C4, the reaction temperature is 200~270℃ and the reaction pressure is 4.5~5.0 MPa(G); In step 3) of C5, 0-1 wt% of the recycle gas is recycled as fuel gas for the biomass boiler; the remaining recycle gas is recycled for the methanol synthesis reaction. C6) In step 3), water cool to 35~45℃; In step 3) of C7), the flash vapor is recycled for carbon capture; In step 3) of C8, the pressure reduction for flash evaporation is 0.05~0.6 MPa(G).

5. The method for preparing green methanol by CO2 hydrogenation according to claim 1, characterized in that, Step 4) also includes one or more of the following conditions: In step 4) of D1), the second crude methanol first enters the methanol intermediate tank and then undergoes distillation; In step 4) of D2, the distillation is carried out sequentially in a pre-distillation column, a pressurized column, and an atmospheric column. The pressure of the pre-distillation column is 0.05~0.1 MPa(G), and the temperature is 80~120℃; the pressure of the pressurized column is 0.6~1.0 MPa(G), and the temperature is 120~160℃; and the pressure of the atmospheric column is 0.01~0.1 MPa(G), and the temperature is 50~120℃. In step 4) of D3, the purity of the methanol is ≥99.85wt%.

6. A system for producing green methanol by CO2 hydrogenation, characterized in that, The system includes a biomass boiler (1), a carbon capture device (2), a methanol synthesis device (3), a methanol intermediate tank (8), and a methanol distillation device (4) connected in sequence; it also includes a water electrolysis device (5), which is connected to the methanol synthesis device (3).

7. The system for producing green methanol by CO2 hydrogenation according to claim 6, characterized in that, The biomass boiler (1) includes a biomass raw material inlet (11), a flue gas outlet (12), a steam outlet (13), and a fuel gas inlet (14). The flue gas outlet (12) is connected to the carbon capture device (2).

8. The system for producing green methanol by CO2 hydrogenation according to claim 7, characterized in that, The carbon capture device (2) includes an induced draft fan (21), a carbon dioxide capture device (22), a carbon dioxide compressor (23), and a desulfurization tower (24) connected in sequence. The induced draft fan (21) includes a flue gas inlet (211), and the desulfurization tower (24) includes a carbon dioxide outlet (241). The flue gas inlet (211) is connected to the flue gas outlet (12), and the carbon dioxide outlet (241) is connected to the methanol synthesis device (3). The bottom reboiler of the carbon dioxide capture device (22) is provided with a first steam inlet (221), and the first steam inlet (221) is connected to the steam outlet (13).

9. The system for producing green methanol by CO2 hydrogenation according to claim 6, characterized in that, The methanol synthesis unit (3) includes a circulating gas compressor (31), a gas-to-gas heat exchanger (32), a methanol synthesis reactor (33), and a water cooler (34), a methanol separator (35), and a methanol flash tank (36) connected in sequence. The methanol flash tank (36) includes a second crude methanol outlet (361) and a flash vapor outlet (362). The second crude methanol outlet (361) is connected to a methanol intermediate tank (8), and the methanol intermediate tank (8) is connected to a methanol distillation unit (4). Preferably, the circulating gas compressor (31) includes a carbon dioxide inlet (311), an H2 circulating gas compressor inlet (312), a circulating gas inlet (313), and a syngas outlet (314); the gas-gas heat exchanger (32) includes a mixed gas inlet (321), a heated syngas outlet (322), a methanol synthesis reaction gas inlet (323), and a cooled methanol synthesis reaction gas outlet (324); the methanol synthesis reactor (33) includes a heated mixed gas inlet (331) and a methanol synthesis reaction gas outlet (332); the carbon dioxide inlet (311) is connected to the carbon capture device (2); and the H2 circulating gas compressor inlet (312) is connected to the carbon capture device (2). 312) is connected to the water electrolysis device (5), the synthesis gas outlet (314) is connected to the mixed gas inlet (321), the heated synthesis gas outlet (322) is connected to the heated mixed gas inlet (331), the methanol synthesis reaction gas outlet (332) is connected to the methanol synthesis reaction gas inlet (323), the cooled methanol synthesis reaction gas outlet (324) is connected to the water cooler (34); the methanol separator (35) includes a purge gas outlet (351), the purge gas outlet (351) is connected to the circulating gas inlet (313), and the flash vapor outlet (362) is connected to the carbon capture device (2).

10. The system for producing green methanol by CO2 hydrogenation according to claim 6, characterized in that, It also includes one or more of the following conditions: E1) A hydrogen balloon tank (6) and a hydrogen compressor (7) are sequentially installed on the connecting pipeline of the water electrolysis device (5) and the methanol synthesis device (3). The hydrogen balloon tank (6) is connected to the water electrolysis device (5), and the hydrogen compressor (7) is connected to the methanol synthesis device (3). E2) The distillation apparatus includes a pre-distillation column (41), a pressurized column (42) and an atmospheric column (43) connected in sequence. The pre-distillation column (41) is connected to the methanol intermediate tank (8). The apparatus also includes a finished product tank (9). The atmospheric column (43) is connected to the finished product tank (9).

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