Methanol synthesis system and method

Abstract

The invention relates to a methanol synthesis system and method. The system comprises a gasification unit, a carbon dioxide separation unit, a carbon dioxide boosting unit, a methanol synthesis unit and a water electrolysis unit. According to the method, hydrogen / oxygen production through water electrolysis, biomass gasification and methanol synthesis are coupled, so that the problems of high carbon dioxide hydrogen consumption, low equilibrium conversion rate, high energy consumption and the like in traditional methanol production through biomass gasification are solved, the production cost of green methanol is remarkably reduced, and the method has remarkable economic and social benefits.

Description

Technical Field

[0001] The present disclosure relates to a methanol synthesis system and method. Background Art

[0002] Methanol is an important industrial chemical raw material and intermediate, widely used in organic synthesis, pharmaceuticals, pesticides, coatings, and dyes. It is also a clean fuel used in the production of methanol fuel and methanol gasoline.

[0003] The main technical routes for producing methanol are: 1) Natural gas to methanol: Using natural gas as the raw material, methanol is produced through catalytic conversion. This route has the advantages of abundant raw materials, mature processes, and high product quality, but it is relatively costly, and the extraction and use of natural gas are also subject to environmental and energy security restrictions. 2) Coal to methanol: Using coal as the raw material, methanol is produced through gasification, purification, and synthesis processes. Although this route is relatively low-cost, it is subject to environmental pollution and energy consumption issues. 3) Biomass to methanol: Using biomass (such as wood and crop waste) as the raw material, methanol is produced through gasification and fermentation processes. The produced methanol is called green methanol. This route has the advantages of being environmentally friendly and renewable, but it also faces challenges in terms of raw material sourcing and production costs. 4) Carbon dioxide to methanol: Using carbon dioxide and hydrogen as raw materials, methanol is synthesized in the presence of a catalyst. This route can reduce and utilize carbon dioxide emissions, offering environmental and sustainable advantages. However, the production cost of this technology is currently high and requires further research and optimization.

[0004] With global climate change and environmental issues becoming increasingly serious, reducing carbon emissions and achieving carbon neutrality have become a global consensus. Demand for green methanol has surged due to its low-carbon and environmentally friendly advantages. However, existing technologies for producing green methanol face limitations, including high investment, costs, lengthy processes, extensive equipment, and high energy consumption. Summary of the Invention

[0005] The purpose of the present disclosure is to provide a methanol synthesis system and method to solve the shortcomings of the prior art such as high cost, high hydrogen consumption, and high energy consumption.

[0006] In order to achieve the above-mentioned object, the present disclosure provides a methanol synthesis system in a first aspect, the system comprising: a gasification unit, a carbon dioxide separation unit, a carbon dioxide boosting unit, a methanol synthesis unit and a water electrolysis unit;

[0007] The gasification unit has a biomass feedstock inlet, a gasification agent inlet and a gasification product outlet; the carbon dioxide separation unit has a gasification product inlet, a carbon dioxide-lean gasification product outlet and a carbon dioxide outlet; the carbon dioxide boosting unit has a carbon dioxide inlet and a circulating carbon dioxide outlet; the methanol synthesis unit has a carbon dioxide-lean gasification product inlet, an electrolyzed water hydrogen inlet and a methanol product outlet; the water electrolysis unit has a supplementary water inlet, an electrolyzed water hydrogen outlet and an electrolyzed water oxygen outlet;

[0008] The gasification product outlet is connected to the gasification product inlet, the carbon dioxide-lean gasification product outlet is connected to the carbon dioxide-lean gasification product inlet, the carbon dioxide outlet is connected to the carbon dioxide inlet, the electrolyzed water hydrogen outlet is connected to the electrolyzed water hydrogen inlet, and the circulating carbon dioxide outlet and the electrolyzed water oxygen outlet are respectively connected to the gasifying agent inlet.

[0009] Optionally, the carbon dioxide separation unit includes at least one of low-temperature methanol washing equipment, membrane separation equipment, pressure swing adsorption equipment, temperature swing adsorption equipment and cryogenic separation equipment.

[0010] Optionally, the methanol synthesis unit further has a steam outlet and a water outlet, the steam outlet is connected to the gasifying agent inlet, and the water outlet is connected to the supplementary water inlet through a water purification device.

[0011] Optionally, the gasification unit includes at least one of a fixed bed reaction device, a fluidized bed reaction device, an entrained bed reaction device and a rotating bed reaction device.

[0012] Optionally, the carbon dioxide boosting unit includes at least one of a reciprocating compressor, a centrifugal compressor and a screw compressor.

[0013] Optionally, the water electrolysis unit includes at least one of an alkaline water electrolysis device, a proton exchange membrane electrolysis device, an anion exchange membrane electrolysis device, and a solid oxide electrolysis device;

[0014] Preferably, the power supply of the water electrolysis unit is selected from at least one of grid power, photovoltaic power generation, wind power generation, tidal power generation and nuclear power.

[0015] In a second aspect of the present disclosure, a method for synthesizing methanol using the system described in the first aspect of the present disclosure is provided, the method comprising:

[0016] Feeding the supplementary water into the water electrolysis unit to perform a water electrolysis reaction to obtain electrolytic water hydrogen and electrolytic water oxygen;

[0017] The biomass raw material is fed into the gasification unit and brought into contact with the gasification agent to undergo a gasification reaction to obtain a gasification product;

[0018] sending the gasification product into the carbon dioxide separation unit for carbon dioxide separation to obtain carbon dioxide and a carbon dioxide-lean gasification product;

[0019] sending the carbon dioxide into the carbon dioxide boosting unit to obtain circulating carbon dioxide;

[0020] feeding at least part of the recycled carbon dioxide and at least part of the electrolyzed water oxygen as the gasifying agent into the gasification unit;

[0021] The carbon dioxide-poor gasification product and the electrolyzed water hydrogen are fed into the methanol synthesis unit as methanol synthesis raw materials to carry out a methanol synthesis reaction to obtain a methanol product.

[0022] Optionally, the make-up water is selected from at least one of deoxygenated water, desalted water, fresh water and recycled water.

[0023] Optionally, the biomass raw material is selected from at least one of agricultural waste, forestry waste, urban and industrial solid waste, aquatic plants, energy crops and animal manure.

[0024] Optionally, the gasifying agent includes at least one of oxygen, water vapor, carbon dioxide, air and oxygen-rich gas.

[0025] Optionally, the carbon dioxide content of the carbon dioxide-lean gasification product is 0 to 3.5% by volume.

[0026] Optionally, the conditions for the water electrolysis reaction include: the pressure of the oxygen gas generated by the water electrolysis is 0.01 to 4.5 MPaG, and the pressure of the hydrogen gas generated by the water electrolysis is 0.01 to 4.5 MPaG.

[0027] Optionally, the conditions for the gasification reaction include: a temperature of 650 to 1650° C. and a pressure of 0.01 to 6.5 MPaG.

[0028] Optionally, the pressure of the circulating carbon dioxide is 0.01 to 6.5 MPaG.

[0029] Optionally, the conditions for the methanol synthesis reaction include: a temperature of 155 to 350°C and a pressure of 0.5 to 8.5 MPaG; in the methanol synthesis raw material, the ratio of the volume of hydrogen to the total volume of carbon monoxide and carbon dioxide is (1.95 to 2.5):1, and the carbon dioxide content of the methanol synthesis raw material is 0 to 3.0 volume %.

[0030] And / or, the method further comprises:

[0031] collecting water and / or water vapor obtained from the methanol synthesis unit;

[0032] At least a portion of the water is purified and then fed into the water electrolysis unit as the supplementary water; and / or at least a portion of the water vapor is fed into the gasification unit as the gasification agent.

[0033] Compared with the prior art, the advantages of the present invention include:

[0034] 1. In the present disclosure, the gasification product produced by the gasification unit is sent to a carbon dioxide separation unit to separate part or all of the carbon dioxide. After being pressurized, the gasification product is returned to the gasification unit as a gasifying agent. This ensures that the carbon dioxide-depleted gasification product sent to the methanol synthesis unit contains no or only a small amount of carbon dioxide, thereby reducing the hydrogen consumption of the methanol synthesis unit.

[0035] 2. Since the hydrogen consumption entering the methanol synthesis unit is reduced, the scale of hydrogen production in the water electrolysis unit can be reduced, which can further reduce the scale of upstream electricity consumption, minimize the number of equipment, land occupation and investment on the upstream hydrogen production side, and enhance the technical competitiveness of green methanol synthesis.

[0036] 3. The gasification agent uses oxygen generated by the water electrolysis unit and recycled carbon dioxide. By adjusting the amount of recycled carbon dioxide, the operating load of the gasification unit can be adjusted, which is beneficial to further improve the operating stability and reliability of the gasification unit.

[0037] 4. Biomass is used as the raw material for the gasification reaction. The oxygen used in the gasification reaction and the hydrogen used in the methanol synthesis reaction both come from the water electrolysis unit. The green methanol product produced by the system and method disclosed in this disclosure can be used as an alternative energy source, reducing dependence on fossil energy such as oil and improving energy security.

[0038] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following detailed description, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0040] Figure 1 A schematic diagram of a methanol synthesis system and process according to a specific embodiment of the present disclosure is shown.

[0041] Figure 2 A schematic diagram of the process flow of traditional methanol synthesis method is shown.

[0042] Figure 3 A schematic diagram of a methanol synthesis system and process according to a second specific embodiment of the present disclosure is shown.

[0043] Figure 4A schematic diagram of a methanol synthesis system and process according to a third specific embodiment of the present disclosure is shown.

[0044] Description of Reference Numerals

[0045] 101 - Gasification Unit, 102 - Carbon Dioxide Separation Unit, 103 - Carbon Dioxide Pressurization Unit, 104 - Methanol Synthesis Unit, 105 - Water Electrolysis Unit,

[0046] S1—biomass raw material, S2—oxygen generated by electrolysis of water, S3—hydrogen generated by electrolysis of water, S4—gasification product, S5—carbon dioxide-lean gasification product, S6—methanol product, S7—carbon dioxide, S8—circulating carbon dioxide, S9—supplemental oxygen, S10—water vapor, S11—supplemental water, S12—water generated by methanol synthesis reaction, S13—supplemental oxygen, S14—supplemental hydrogen, S20—electrolysis power supply. DETAILED DESCRIPTION

[0047] The following describes the specific embodiments of the present disclosure in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0048] In the present disclosure, unless otherwise specified, directional words such as "upper" and "lower" generally refer to the upper and lower parts of the device in normal use, and "inside" and "outside" refer to the outline of the device. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present disclosure, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0049] In a first aspect, the present disclosure provides a methanol synthesis system, Figure 1 As shown, the system includes: a gasification unit 101, a carbon dioxide separation unit 102, a carbon dioxide pressurizing unit 103, a methanol synthesis unit 104 and a water electrolysis unit 105.

[0050] The gasification unit 101 is used to contact the biomass feedstock with the gasifying agent to undergo a gasification reaction to obtain a gasified product. The gasification unit 101 has a biomass feedstock inlet, a gasifying agent inlet, and a gasified product outlet. The gasified product outlet is connected to the carbon dioxide separation unit 102.

[0051] Furthermore, the gasification unit 101 may include common equipment for implementing the gasification reaction. Specifically, the gasification unit 101 may include at least one of a fixed bed reaction device, a fluidized bed reaction device, an entrained bed reaction device, and a rotating bed reaction device, such as a fixed bed gasifier, a fluidized bed gasifier, an entrained bed gasifier, a rotating bed gasifier, etc. In the present disclosure, the gasification unit 101 preferably includes a fluidized bed reaction device.

[0052] The carbon dioxide separation unit 102 is used to separate the carbon dioxide from the gasification product to produce a carbon dioxide-depleted gasification product and carbon dioxide. The carbon dioxide-depleted gasification product refers to a gasification product with a low carbon dioxide content obtained after separation. Separating the gasification product using the carbon dioxide separation unit 102 helps reduce equipment investment, floor space, and hydrogen consumption in the methanol synthesis system.

[0053] The carbon dioxide separation unit 102 has a gasification product inlet, a carbon dioxide-lean gasification product outlet, and a carbon dioxide outlet. The gasification product inlet is connected to the gasification product outlet of the gasification unit 101, the carbon dioxide outlet is connected to the carbon dioxide boosting unit 103, and the carbon dioxide-lean gasification product outlet is connected to the methanol synthesis unit 104.

[0054] In a preferred embodiment, the carbon dioxide separation unit 102 includes at least one of a low-temperature methanol washing device, a membrane separation device, a pressure swing adsorption (PSA) device, a temperature swing adsorption (TSA) device and a cryogenic separation device, and the above-mentioned equipment is conducive to achieving efficient separation of carbon dioxide in the gasification product. The specific device composition and separation principle of the low-temperature methanol washing device, membrane separation device, pressure swing adsorption device, temperature swing adsorption device and cryogenic separation device are well known to those skilled in the art, and the present disclosure has no special restrictions. Further preferably, the carbon dioxide separation unit 102 includes a low-temperature methanol washing device, specifically, the low-temperature methanol washing device may include a medium-pressure flash tower, a thermal regeneration tower, a nitrogen stripping tower, a lean methanol cooler and an H2S gas-liquid separation device.

[0055] The carbon dioxide boosting unit 103 is used to boost the pressure of the carbon dioxide from the carbon dioxide separation unit 102. The pressurized carbon dioxide can be circulated as a gasifying agent in the gasification reaction. The carbon dioxide boosting unit 103 has a carbon dioxide inlet and a circulating carbon dioxide outlet. The carbon dioxide inlet is connected to the carbon dioxide outlet of the carbon dioxide separation unit 102, and the circulating carbon dioxide outlet is connected to the gasifying agent inlet of the gasification unit 101. Specifically, the gasifying agent inlet may include a circulating carbon dioxide inlet, and the circulating carbon dioxide outlet is connected to the circulating carbon dioxide inlet.

[0056] Furthermore, the carbon dioxide boosting unit 103 may include common equipment for boosting the pressure of gaseous materials by compressing gas. Specifically, the carbon dioxide boosting unit 103 may include at least one of a reciprocating compressor, a centrifugal compressor, and a screw compressor, preferably a reciprocating compressor. The number of compressor stages may be determined based on the operating pressure of the gasification unit 101 and the operating pressure of the carbon dioxide separation unit 102. Reciprocating compressors are well known in the art and will not be further described in detail in this disclosure.

[0057] The methanol synthesis unit 104 is used to supply methanol synthesis raw materials such as hydrogen, carbon monoxide, and carbon dioxide for a methanol synthesis reaction to obtain a methanol product. The methanol synthesis unit 104 has a carbon dioxide-lean gasification product inlet, an electrolytic water hydrogen inlet, and a methanol product outlet. The carbon dioxide-lean gasification product inlet is connected to the carbon dioxide-lean gasification product outlet of the carbon dioxide separation unit 102, and the electrolytic water hydrogen inlet is connected to the water electrolysis unit 105. The methanol product is obtained from the methanol product outlet.

[0058] In a preferred embodiment, to maximize water resource utilization and reduce make-up water or wastewater discharge, the methanol synthesis reaction water separated by the methanol synthesis unit 104 can be purified and used as make-up water for the water electrolysis unit 105. Furthermore, as a highly exothermic reaction, the methanol synthesis reaction releases heat that can generate water vapor, which serves as a gasifying agent for the gasification unit 101. Specifically, the methanol synthesis unit 104 further comprises a water vapor outlet and a water outlet. The water vapor outlet is connected to the gasifying agent inlet, and the water outlet is connected to the make-up water inlet via a water purification device. Specifically, the gasifying agent inlet can include a water vapor inlet, which is connected to the water vapor inlet.

[0059] Furthermore, the methanol synthesis unit 104 may include common equipment for realizing the methanol synthesis reaction. Specifically, the methanol synthesis unit 104 may include a methanol synthesis tower, a raw gas compressor, a methanol separator, a stabilization tower, a washing tower, a crude methanol water cooler and a crude methanol air cooler.

[0060] The water electrolysis unit 105 is used to perform a water electrolysis reaction to obtain high-purity electrolytic water oxygen and electrolytic water hydrogen. The electrolytic water oxygen can be provided to the gasification unit 101 as a gasifying agent, and the electrolytic water hydrogen can be provided to the methanol synthesis unit 104 as a methanol synthesis raw material. The water electrolysis unit 105 has a supplementary water inlet, an electrolytic water hydrogen outlet, and an electrolytic water oxygen outlet. The supplementary water inlet is used to introduce supplementary water for electrolysis, the electrolytic water hydrogen outlet is connected to the electrolytic water hydrogen inlet of the methanol synthesis unit 104, and the electrolytic water oxygen outlet is connected to the gasifying agent inlet of the gasification unit 101. Specifically, the gasifying agent inlet may include an electrolytic water oxygen inlet, and the electrolytic water oxygen outlet is connected to the electrolytic water oxygen inlet. In addition, the gasification unit 101 can also replenish the required gasified oxygen from the outside.

[0061] The water electrolysis unit 105 may include common equipment for achieving the water electrolysis reaction. Preferably, the water electrolysis unit 105 may include at least one of an alkaline water electrolysis device, a proton exchange membrane (PEM) electrolysis device, an anion exchange membrane (AEM) electrolysis device, and a solid oxide electrolysis device. The above electrolysis devices are conducive to achieving the production of green and low-carbon methanol. The specific device composition of the alkaline water electrolysis device, PEM electrolysis device, anion exchange membrane electrolysis device, and solid oxide electrolysis device can adopt conventional selections in the field and are not particularly limited in this disclosure.

[0062] In a preferred embodiment, in order to improve the technical and economic efficiency of the water electrolysis unit 105, the water electrolysis unit 105 includes a combination of PEM electrolysis equipment and alkaline water electrolysis equipment. The hydrogen and oxygen products obtained in this way have high purity, low electricity consumption per unit hydrogen / oxygen, and fast response to hydrogen and oxygen production. It is also beneficial to solve the impact of upstream fluctuating power sources such as wind power and photovoltaics on the electrolyzer, and can realize the rapid start and stop function of the electrolyzer, providing a relatively stable gas source supply for downstream hydrogen and oxygen users, further improving the operational flexibility of green electricity hydrogen production and reducing production costs.

[0063] Furthermore, the number of electrolytic cells in the water electrolysis unit 105 can be adjusted according to the amount of hydrogen required by the methanol synthesis unit 104 and / or the amount of oxygen required by the gasification unit 101. Specifically, the number of electrolytic cells can be 1 to 1024, preferably 2. n In order to achieve stable operation of the water electrolysis unit 105, the electrolysis cells are preferably arranged symmetrically to reduce the problem of biased flow caused by the gas-liquid two-phase flow.

[0064] Furthermore, the power supply of the water electrolysis unit 105 can be selected from at least one of grid electricity, photovoltaic power generation, wind power generation, tidal power generation and nuclear power, and more preferably selected from photovoltaic power generation and / or wind power generation, thereby further reducing the production cost of hydrogen / oxygen production, significantly reducing the emission of carbon dioxide greenhouse gas, and helping to alleviate the problem of global climate change.

[0065] In a second aspect of the present disclosure, a method for synthesizing methanol using the system described in the first aspect of the present disclosure is provided, referring to Figure 1 , the method comprising:

[0066] The supplementary water S11 is fed into the water electrolysis unit 105 to undergo water electrolysis reaction to obtain electrolytic water hydrogen S3 and electrolytic water oxygen S2;

[0067] The biomass raw material S1 is fed into the gasification unit 101 and is contacted with a gasifying agent to undergo a gasification reaction to obtain a gasification product S4;

[0068] The gasification product S4 is sent to the carbon dioxide separation unit 102 for carbon dioxide separation to obtain carbon dioxide S7 and a carbon dioxide-lean gasification product S5;

[0069] The carbon dioxide S7 is fed into the carbon dioxide boosting unit 103 to obtain circulating carbon dioxide S8;

[0070] Sending at least part of the recycled carbon dioxide S8 and at least part of the electrolyzed water oxygen S2 as the gasifying agent into the gasification unit 101;

[0071] The carbon dioxide-poor gasification product S5 and the electrolyzed water hydrogen S3 are fed into the methanol synthesis unit 104 as methanol synthesis raw materials to carry out a methanol synthesis reaction to obtain a methanol product S6.

[0072] Figure 2 The figure shows a schematic diagram of a conventional biomass gasification process for producing methanol. In this method, biomass feedstock S1 and supplemental oxygen S13 undergo a gasification reaction in gasification unit 101. The gasification product S4 and supplemental hydrogen S14 enter methanol synthesis unit 104 for a methanol synthesis reaction, producing methanol product S6. Compared to this method, the present disclosure provides hydrogen through a water electrolysis unit 105. The carbon dioxide produced in gasification unit 101 is separated by a carbon dioxide separation unit 102, pressurized by a carbon dioxide booster unit 103, and then recycled back to gasification unit 104. Under conditions of equivalent methanol production scale, hydrogen usage can be reduced by 5-55%, significantly reducing the production cost of methanol synthesis.

[0073] In the water electrolysis unit 105, the make-up water can be selected from at least one of deoxygenated water, demineralized water, fresh water, and recycled water. To extend the operating cycle of the water electrolysis unit 105 and maintain stable operation, the present disclosure prefers deoxygenated water or demineralized water as the make-up water for the water electrolysis unit 105. The conductivity of the make-up water can be adjusted within a certain range, specifically 0 to 10 μS / cm.

[0074] To match the operating pressures of the gasification unit 101 and the methanol synthesis unit 104, the conditions for the water electrolysis reaction may include: a pressure of the electrolyzed oxygen gas of 0.01 to 4.5 MPaG, preferably 0.01 to 3.0 MPaG; and a pressure of the electrolyzed hydrogen gas of 0.01 to 4.5 MPaG, preferably 0.01 to 3.0 MPaG. When the pressures of the electrolyzed oxygen gas and / or the electrolyzed hydrogen gas do not match (for example, the pressure on the gas-consuming side is higher than the pressure on the gas-source side), a compressor may be provided to boost pressure to meet the operating pressure requirements. The types of boosters are well known in the art and are not described in detail herein.

[0075] The electrolytic water oxygen S2 obtained by the water electrolysis unit 105 can be sent to the gasification unit 101 alone or sent to a downstream unit, and the electrolytic water hydrogen S3 can be sent to the methanol synthesis unit 104 alone or sent to a downstream unit.

[0076] In the gasification unit 101, the biomass feedstock can be selected from at least one of agricultural waste, forestry waste, municipal and industrial solid waste, aquatic plants, energy crops, and animal manure. Specifically, agricultural waste includes crop straw, rice husks, peanut shells, and sugarcane bagasse; forestry waste includes sawdust, prunings, and bark; municipal and industrial solid waste includes waste plastics, used tires, waste paper, and wastewater sludge; aquatic plants include reeds and algae; and energy crops include oilseed plants.

[0077] The gasifying agent may include at least one of oxygen, water vapor, carbon dioxide, air, and oxygen-rich gas, preferably at least one of oxygen, water vapor, and carbon dioxide. The oxygen is preferably generated by the water electrolysis unit 105, and the remaining oxygen may be generated from an external source, such as an air separation unit. The carbon dioxide is preferably generated from the recycled carbon dioxide obtained by the carbon dioxide boosting unit 103. The ratio of the gasifying agent to the biomass feedstock can be adjusted within a certain range. Specifically, the weight ratio of the biomass feedstock involved in the gasification reaction to the recycled carbon dioxide and the water electrolysis oxygen can be 1:(0.015-5):(0.01-10), preferably 1:(0.1-4.85):(0.01-8.5).

[0078] To maximize biomass conversion, the gasification reaction conditions include: a temperature of 650-1650°C, preferably 850-1350°C; a pressure of 0.01-6.5 MPaG, preferably 0.01-4.5 MPaG. The gasification products include CO, CH4, H2, H2O, CO2, etc.

[0079] In the carbon dioxide separation unit 102, the circulation volume (referring to the processing volume of the gasification product) can be 2.5 to 63.5% by volume, and the operating conditions may include: temperature of 25 to 150°C and pressure of 0.005 to 2.8 MPaG; the carbon dioxide content of the carbon dioxide-lean gasification product can be 0 to 3.5% by volume, preferably 0 to 1.5% by volume.

[0080] In the carbon dioxide pressurizing unit 103 , the pressure of the circulating carbon dioxide can be 0.01-6.5 MPaG.

[0081] In the methanol synthesis unit 104, the methanol synthesis reaction conditions may include: a temperature of 155 to 350°C, preferably 205 to 300°C; and a pressure of 0.5 to 8.5 MPaG, preferably 4.5 to 8.0 MPaG. Furthermore, in the methanol synthesis feedstock, the ratio of the volume of hydrogen to the total volume of carbon monoxide and carbon dioxide may be (1.95 to 2.5):1, preferably (1.95 to 2.25):1; and the carbon dioxide content in the methanol synthesis feedstock may be 0 to 3.0% by volume, preferably 0 to 2.95% by volume.

[0082] In a preferred embodiment, the method further comprises:

[0083] Collecting water S12 and / or water vapor S10 generated by the methanol synthesis reaction obtained by the methanol synthesis unit 104;

[0084] At least a portion of the methanol synthesis reaction generated water S12 is purified and then fed into the water electrolysis unit 105 as the make-up water S11; and / or at least a portion of the water vapor S10 is fed into the gasification unit 101 as the gasifying agent.

[0085] In this embodiment, the pressure of the water vapor may be 0.05 to 4.5 MPaG; and the weight ratio of the biomass raw material participating in the gasification reaction to the water vapor may be 1:(0.1 to 5).

[0086] The present invention utilizes water electrolysis to obtain high-purity hydrogen and oxygen, wherein high-purity oxygen is used as a biomass gasification agent to obtain a gasification product. The carbon dioxide-rich gasification product passes through a carbon dioxide separation unit and a carbon dioxide boosting unit, and the separated carbon dioxide is circulated back to the gasification unit as a supplementary gasification agent. The carbon dioxide-poor gasification product is mixed with the high-purity hydrogen obtained by water electrolysis and then sent to a methanol synthesis unit, where a methanol product is synthesized. The present invention avoids the problems of high carbon dioxide and hydrogen consumption, low equilibrium conversion rate, and high energy consumption in traditional biomass gasification to produce methanol by coupling water electrolysis to produce hydrogen / oxygen, biomass gasification, and methanol synthesis. By using green electricity to produce hydrogen / oxygen and gasifying biomass to produce green methanol, the carbon dioxide produced by gasification can be returned to the gasification unit, significantly reducing the production cost of green methanol and having significant economic and social benefits.

[0087] The present disclosure will be further described below through embodiments with reference to the accompanying drawings, but the present disclosure is not limited thereto.

[0088] In the following examples and comparative examples, energy consumption, biomass conversion rate and production cost were calculated according to the following formulas:

[0089] Energy consumption = total electricity consumption (EC) + circulating water consumption (XC) + demineralized water consumption (DC) + deoxygenated water consumption (DAC) + steam consumption (SC) + nitrogen consumption (NC) + fuel gas consumption (FC). Energy consumption is calculated according to the method specified in GB / T2589 "General Rules for Calculation of Comprehensive Energy Consumption", unit: kgce / t methanol.

[0090] Biomass conversion rate = mass of biomass converted to gasification products / total biomass mass (dry basis) × 100%;

[0091] Production cost = cost of raw materials (biomass, desalted water) + cost of utilities (circulating water, electricity, instrument air, nitrogen, etc.) + depreciation cost of equipment (gasification, CO2 separation, pressurization and methanol synthesis unit equipment) + labor cost + other expenses, unit: Yuan / ton methanol.

[0092] Comparative Example 1

[0093] The methanol synthesis system and process flow diagram of this comparative example are shown in FIG. Figure 2 The system includes a gasification unit 101 and a methanol synthesis unit 104 .

[0094] The biomass raw material S1 and the supplementary oxygen S13 are subjected to a gasification reaction in the gasification unit 101, and the gasification product S4 and the supplementary hydrogen S14 enter the methanol synthesis unit 104 for a methanol synthesis reaction to obtain a methanol product S6.

[0095] The amount of hydrogen added in this comparative example is 50000Nm3 / h, the amount of supplementary oxygen is 20000Nm 3 / h, the biomass raw material S1 used by the gasification unit 101 is straw, the operating temperature of the gasification reaction is 1050℃, the pressure is 0.05MPaG, and the weight ratio of the biomass raw material S1 to the supplementary oxygen S13 is 1:1.35; the operating pressure of the methanol synthesis unit 104 is 7.5MPaG and the temperature is 280℃.

[0096] The energy consumption of this comparative example is 1702 kgce / t methanol, the biomass conversion rate is 93%, and the production cost is 3800 yuan / t methanol.

[0097] Example 1

[0098] The methanol synthesis system and flow diagram of this embodiment are shown in Figure 1 The system includes a gasification unit 101 , a carbon dioxide separation unit 102 , a carbon dioxide pressurization unit 103 , a methanol synthesis unit 104 and a water electrolysis unit 105 .

[0099] Make-up water S11 is fed into the water electrolysis unit 105 for water electrolysis reaction to obtain electrolytic water hydrogen S3 and electrolytic water oxygen S2; the biomass raw material S1 is fed into the gasification unit 101 and contacts with the gasifying agent for gasification reaction to obtain gasification product S4; the gasification product S4 is fed into the carbon dioxide separation unit 102 for carbon dioxide separation to obtain carbon dioxide S7 and a carbon dioxide-lean gasification product S5; the carbon dioxide S7 is fed into the carbon dioxide boosting unit 103 to obtain circulating carbon dioxide S8; the circulating carbon dioxide S8 and the electrolytic water oxygen S2 are fed into the gasification unit 101 as the gasifying agent; the carbon dioxide-lean gasification product S5 and the electrolytic water hydrogen S3 are fed into the methanol synthesis unit 104 as methanol synthesis raw materials to carry out methanol synthesis reaction to obtain methanol product S6.

[0100] The amount of hydrogen added in this embodiment (the amount of hydrogen required by the methanol synthesis unit minus the amount of hydrogen contained in the carbon dioxide-depleted gasification product S5) is 12000 Nm 3 / h, the oxygen consumption of the gasification unit is 8000Nm 3 / h, the water electrolysis unit 105 scale is calculated to be max (12000, 2×8000=16000), that is, the water electrolysis unit 105 uses 16 1000Nm 3 / h hydrogen production, 500Nm 3 / h oxygen production is achieved using an alkaline water electrolyzer. The make-up water used is demineralized water with a conductivity of 0.05 μS / cm and a consumption rate of 13,500 kg / h. The electrolysis power supply S20 is powered by a combination of wind and photovoltaic power generation. The water electrolysis reaction conditions are: electrolyzer temperature 90°C, oxygen side pressure 1.6 MPaG, hydrogen side pressure 1.6 MPaG. The electrolyzed hydrogen S3 is boosted to 8.0 MPaG via a two-stage reciprocating compressor and fed into the methanol synthesis unit 104.

[0101] The biomass feedstock S1 used in gasification unit 101 consists of agricultural waste such as crop straw and rice husks. After being formed, it is fed into the fluidized bed gasifier in unit 101. The gasification reaction operates at a temperature of 1200-1350°C and a pressure of 0.05-0.1 MPaG. The weight ratio of biomass feedstock S1, recycled carbon dioxide S8, and electrolyzed water oxygen S2 involved in the gasification reaction is 1:0.35:1.5. The composition of the gasification product S1 (crude syngas) produced by gasification unit 101 is shown in Table 1.

[0102] The carbon dioxide separation unit 102 uses low-temperature methanol washing equipment, including a medium-pressure flash tower, a thermal regeneration tower, a nitrogen stripping tower, a lean methanol cooler and an H2S gas-liquid separation device. The circulation volume is 10.4% by volume. The operating conditions include: temperature of 55°C and pressure of 0.03 MPaG. The carbon dioxide content of the separated carbon dioxide-lean gasification product S5 is 0.02% by volume.

[0103] The carbon dioxide pressurizing unit 103 uses a reciprocating compressor to obtain a circulating carbon dioxide pressure of 0.2 MPaG.

[0104] The methanol synthesis unit 104 uses a methanol synthesis tower, a raw gas compressor, a methanol separator, a stabilizer, a scrubber, a crude methanol water cooler, a crude methanol air cooler and other equipment. The operating pressure is 8.0 MPaG and the temperature is 295°C. The H2 / (CO+CO2) volume ratio is 2.05 and the carbon dioxide content is 1.0 volume%. The composition of the methanol synthesis raw material (synthesis gas) is shown in Table 2.

[0105] The energy consumption of this embodiment is 1692 kgce / t methanol, the biomass conversion rate is 98%, and the production cost is 3350 yuan / ton methanol.

[0106] Compared with Comparative Example 1, the hydrogen consumption of this embodiment can be reduced by 32%, while significantly reducing the investment and land occupation of the upstream hydrogen production unit and ancillary facilities, thereby reducing the production cost and energy consumption of green methanol and effectively improving the biomass conversion rate.

[0107] Table 1

[0108] composition content CO, volume % 22.34 <![CDATA[H2, volume %]]> 25.01 <![CDATA[CH4, volume %]]> 2.95 <![CDATA[N2, volume %]]> 0.25 <![CDATA[H2S, volume %]]> 0.05 <![CDATA[H2O, volume %]]> 30.53 <![CDATA[CO2, volume %]]> 18.62 <![CDATA[NH3, volume %]]> 0.21 Ar, volume % 0.04 <![CDATA[O2, volume %]]> 0 Total, volume % 100.00

[0109] Table 2

[0110] composition content CO, volume % 30.89 <![CDATA[H2, volume %]]> 65.38 <![CDATA[CH4, % by volume]]> 2.31 <![CDATA[N2, volume %]]> 0.36 <![CDATA[CO2, volume %]]> 1.00 Ar, volume % 0.06 total 100.00

[0111] Example 2

[0112] The methanol synthesis system and flow diagram of this embodiment are shown in Figure 3 , which differs from Example 1 in that:

[0113] 1) The circulation volume of the carbon dioxide separation unit 102 is 18.6% by volume, and the operating conditions include: a temperature of 50° C. and a pressure of 0.05 MPaG, so that the carbon dioxide content in the outlet carbon dioxide-depleted gasification product S5 is 0.005% by volume;

[0114] 2) The gasification unit 101 is supplemented with a stream of supplementary oxygen S9 sent from the air separation unit;

[0115] 3) The water electrolysis unit 105 uses wind power as the electrolysis power source and is equipped with two PEM electrolyzers (500Nm 3 / h hydrogen production, 250Nm 3 / h oxygen production) and 15 alkaline water electrolyzers (1000Nm 3 / h hydrogen production, 500Nm 3 / h oxygen production), keeping the overall scale of hydrogen / oxygen production unchanged.

[0116] The energy consumption of this embodiment is 1659 kgce / t methanol, the biomass conversion rate is 98%, and the production cost is 3205 yuan / ton methanol.

[0117] This embodiment can further reduce the hydrogen consumption of the methanol synthesis system, which can be sold by about 1280Nm 3 / h of hydrogen, under the same scale, compared with Example 1 (using 16 1000Nm 3 / h hydrogen production, 500Nm 3 / h oxygen production alkaline water electrolyzer), hydrogen consumption can be reduced by about 40%.

[0118] Example 3

[0119] The methanol synthesis system and flow diagram of this embodiment are shown in Figure 4 , which differs from Example 2 in that:

[0120] 1) The water vapor S10 generated by the methanol synthesis unit 103 is added to the gasification unit 101 as a gasifying agent. The pressure of the water vapor S10 is 2.45 MPaG, and the weight ratio of the biomass raw material S1 participating in the gasification reaction to the water vapor S10 is 1:0.65;

[0121] 2) The water S12 generated by the methanol synthesis reaction is purified and used as the make-up water S11 of the water electrolysis unit 105, with an external water make-up rate of 3500 kg / h.

[0122] The energy consumption of this embodiment is 1695 kgce / t methanol, the biomass conversion rate is 98%, and the production cost is 3223 yuan / ton methanol.

[0123] This embodiment helps reduce the amount of external water supply to the water electrolysis unit 105. In addition, the use of water vapor produced by the methanol synthesis unit 104 as a supplementary gasification agent improves the energy efficiency and operational stability of the device and reduces dependence on external utilities.

[0124] The preferred embodiments of the present disclosure are described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details of the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the scope of protection of the present disclosure.

[0125] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0126] In addition, the various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A methanol synthesis system, characterized in that: The system includes: a gasification unit, a carbon dioxide separation unit, a carbon dioxide boosting unit, a methanol synthesis unit and a water electrolysis unit; The gasification unit has a biomass feedstock inlet, a gasification agent inlet and a gasification product outlet; the carbon dioxide separation unit has a gasification product inlet, a carbon dioxide-lean gasification product outlet and a carbon dioxide outlet; the carbon dioxide boosting unit has a carbon dioxide inlet and a circulating carbon dioxide outlet; the methanol synthesis unit has a carbon dioxide-lean gasification product inlet, an electrolyzed water hydrogen inlet and a methanol product outlet; the water electrolysis unit has a supplementary water inlet, an electrolyzed water hydrogen outlet and an electrolyzed water oxygen outlet; The gasification product outlet is connected to the gasification product inlet, the carbon dioxide-lean gasification product outlet is connected to the carbon dioxide-lean gasification product inlet, the carbon dioxide outlet is connected to the carbon dioxide inlet, the electrolyzed water hydrogen outlet is connected to the electrolyzed water hydrogen inlet, and the circulating carbon dioxide outlet and the electrolyzed water oxygen outlet are respectively connected to the gasifying agent inlet.

2. The system according to claim 1, wherein: The carbon dioxide separation unit includes at least one of a low-temperature methanol washing device, a membrane separation device, a pressure swing adsorption device, a temperature swing adsorption device and a cryogenic separation device.

3. The system according to claim 1, wherein: The methanol synthesis unit further comprises a steam outlet and a water outlet, wherein the steam outlet is connected to the gasifying agent inlet, and the water outlet is connected to the supplementary water inlet via a water purification device.

4. The system according to claim 1, wherein: The gasification unit includes at least one of a fixed bed reaction device, a fluidized bed reaction device, an entrained bed reaction device and a rotating bed reaction device.

5. The system according to claim 1, wherein The carbon dioxide boosting unit includes at least one of a reciprocating compressor, a centrifugal compressor and a screw compressor.

6. The system according to claim 1, wherein: The water electrolysis unit includes at least one of an alkaline water electrolysis device, a proton exchange membrane electrolysis device, an anion exchange membrane electrolysis device, and a solid oxide electrolysis device; Preferably, the power supply of the water electrolysis unit is selected from at least one of grid power, photovoltaic power generation, wind power generation, tidal power generation and nuclear power.

7. A method for synthesizing methanol using the system according to any one of claims 1 to 6, characterized in that: The method includes: Feeding the supplementary water into the water electrolysis unit to perform a water electrolysis reaction to obtain electrolytic water hydrogen and electrolytic water oxygen; The biomass raw material is fed into the gasification unit and brought into contact with the gasification agent to undergo a gasification reaction to obtain a gasification product; sending the gasification product into the carbon dioxide separation unit for carbon dioxide separation to obtain carbon dioxide and a carbon dioxide-lean gasification product; sending the carbon dioxide into the carbon dioxide boosting unit to obtain circulating carbon dioxide; feeding at least part of the recycled carbon dioxide and at least part of the electrolyzed water oxygen as the gasifying agent into the gasification unit; The carbon dioxide-poor gasification product and the electrolyzed water hydrogen are fed into the methanol synthesis unit as methanol synthesis raw materials to carry out a methanol synthesis reaction to obtain a methanol product.

8. The method according to claim 7, wherein: The supplementary water is selected from at least one of deoxygenated water, desalted water, fresh water and recycled water; and / or, the biomass raw material is selected from at least one of agricultural waste, forestry waste, urban and industrial solid waste, aquatic plants, energy crops and animal manure; and / or, the gasifying agent comprises at least one of oxygen, water vapor, carbon dioxide, air and oxygen-enriched gas; And / or, the carbon dioxide content of the carbon dioxide-lean gasification product is 0 to 3.5% by volume.

9. The method according to claim 7, wherein: The conditions of the water electrolysis reaction include: the pressure of the oxygen gas in the electrolysis water is 0.01 to 4.5 MPaG, and the pressure of the hydrogen gas in the electrolysis water is 0.01 to 4.5 MPaG; And / or, the gasification reaction conditions include: temperature of 650-1650° C. and pressure of 0.01-6.5 MPaG; and / or, the pressure of the circulating carbon dioxide is 0.01 to 6.5 MPaG; And / or, the conditions of the methanol synthesis reaction include: a temperature of 155 to 350° C. and a pressure of 0.5 to 8.5 MPaG; in the methanol synthesis raw material, the ratio of the volume of hydrogen to the total volume of carbon monoxide and carbon dioxide is (1.95 to 2.5):1, and the carbon dioxide content of the methanol synthesis raw material is 0 to 3.0 volume%.

10. The method according to claim 7, wherein: The method further includes: collecting water and / or water vapor obtained from the methanol synthesis unit; At least a portion of the water is purified and then fed into the water electrolysis unit as the supplementary water; and / or at least a portion of the water vapor is fed into the gasification unit as the gasification agent.

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