CN111547678A - Method and system for preparing methanol by thermal catalysis of all components of biogas - Google Patents

Abstract

The invention provides a method for preparing methanol by full-component thermal catalysis of methane, which comprises the following steps: providing dried and desulfurized biogas, mixing the biogas with steam to obtain mixed gas, carrying out dry-wet double reforming in the presence of a catalyst, reacting to obtain synthesis gas, and preparing to obtain methanol. The invention provides a novel method for deep utilization of biogas, which utilizes the reaction of methane, carbon dioxide and water vapor in the biogas to produce biological methanol. The invention directly prepares the environment-friendly chemical product methanol by using renewable biogas as a raw material, and the components such as methane, carbon dioxide and the like in the biogas participate in the reaction, thereby having obvious carbon emission reduction effect; the energy utilization efficiency is high; the steam is introduced to react with the methane, so that the incomplete methane reaction can be avoided, the environment is polluted, the energy utilization rate is reduced, and the generation of carbon deposition in the reaction can be inhibited; the method avoids the environmental pollution caused by reaction wastes while obtaining the methanol with high energy efficiency.

Description

Method and system for preparing methanol by thermal catalysis of all components of biogas

technical field

The present invention relates to the technical field of methanol preparation, in particular to a method and a system for preparing methanol through thermal catalysis of all components of biogas.

Background technique

The energy supply in today's world is mainly based on three non-renewable fossil resources: coal, oil and natural gas. The pace of globalization is now entering the new century. The rapid increase in the population and the rapid growth of the total economic volume have led to the indiscriminate use of the earth's resources. Although there are still deep-sea oil and gas, combustible ice, coalbed methane and shale gas and other resources For development and utilization, human beings have also begun to pay attention to the potential shortage of non-renewable fossil fuels. Before 2050, non-renewable natural resources such as oil and natural gas will be exhausted. This view has been unanimously recognized by the whole society. At the same time, the unbalanced problem of energy distribution has also led to and aggravated the real social chain contradictions such as the oil crisis. As the foundation of the survival and development of human civilization, energy is also an important indicator used to measure the comprehensive national strength and restrict the national economy, so it plays a key role in national security. my country's oil reserves and production are seriously deficient, and the current oil consumption activities mainly rely on imports, which are heavily dependent on foreign supplies, causing my country to face a great threat to energy security. Therefore, oil resources and national security have become inseparable and become the core content of my country's energy security strategy. CO ₂ is the main component of greenhouse gases, and more than 90% of anthropogenic CO ₂ emissions are considered to be generated when fossil energy is used. A large number of greenhouse gas emissions increase the concentration of greenhouse gases in the atmosphere and enhance the greenhouse effect, thereby leading to global climate change. warming, rising sea levels and many other issues. Extensive use of fossil energy is also an important reason for the current air pollution problem in my country. Therefore, the development of clean energy alternatives to fossil energy is of great significance to my country's national security and economic development. When human beings face the realistic threat of decreasing fossil energy reserves year by year, with the reduction of methanol cost and price, the use of methanol as a new source of petrochemical raw materials has developed into a trend.

Syngas refers to a mixture of carbon monoxide and hydrogen. The ratio of CO and H ₂ in the syngas varies with the raw materials and production methods, and the molar ratio is 1/2 to 3/1. Syngas is one of the raw materials for organic synthesis and a source of hydrogen and carbon monoxide, and plays an important role in the chemical industry. The raw materials for preparing syngas are various, and many carbon-containing resources such as coal, natural gas, petroleum or residual oil can be used to manufacture syngas. Syngas can be converted into liquid and gaseous fuels, bulk chemicals and high value-added fine organic chemicals. In the prior art, the source of synthesis gas mainly comes from fossil fuels, which is not conducive to the promotion of the sustainable development green road policy, and the production of methanol from the step-separated synthesis gas is severely limited by time and space. The technology of full-component conversion achieves the characteristics of instant production and use, which is free from the constraints of time and space, and greatly exerts the characteristics of production flexibility. Therefore, using renewable biogas as a raw material to develop a method for directly producing syngas to methanol from biogas has far-reaching significance for my country's current national conditions.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the defects and deficiencies of the existing biogas, such as the need to separate carbon dioxide in advance, and provide a method for preparing methanol by thermal catalysis of all components of biogas, without pre-separation of carbon dioxide and other components, so that all components in the biogas are All points participate in the reaction, effectively improve the conversion rate of methane and carbon dioxide, and efficiently produce methanol.

Another object of the present invention is to provide a system for preparing methanol by thermal catalysis of full biogas components.

The above-mentioned purpose of the present invention is achieved by the following technical solutions:

A method for preparing methanol by thermal catalysis of full biogas components, comprising the following steps:

The biogas after drying and desulfurization treatment is provided, and the biogas is mixed with water vapor to obtain a mixed gas, and in the presence of a catalyst, dry and wet double rectification is carried out to react to obtain synthesis gas, and then methanol is prepared.

The invention introduces the reaction of water vapor and biogas, which can avoid the incomplete methane reaction to pollute the environment and reduce the energy utilization rate, and at the same time can suppress the generation of carbon deposits in the reaction. At the same time, the dry and wet double reforming method adopted is the combined double reforming method of carbon dioxide-methane and water-methane dry reforming and wet reforming, which not only improves the utilization rate of carbon dioxide in the biogas, but also adjusts the reaction process. The medium hydrogen to carbon ratio is beneficial to the later stage of the synthesis gas-to-methanol reaction; in the reforming process, about 1/3 of the methane participates in the carbon dioxide-methane dry reforming, and 2/3 of the methane participates in the water-methane wet reforming , the hydrogen-to-carbon ratio of the obtained synthesis gas is about 2.2:1, which meets the requirements of synthesis gas to methanol and unconverted gas recovery.

Preferably, the volume ratio of the methane in the biogas to the water vapor is 3:1.5˜2.2 (preferably 3:2). The amount of water vapor is determined according to the methane content in the biogas, and the purpose is to make the methane in the biogas react completely.

Preferably, the volume content of H ₂ S in the biogas after the desulfurization treatment is less than 1.0 ppm.

Specifically, the content of CH ₄ in the biogas is 50% to 70% by volume, and the content of CO ₂ is 30% to 50% by volume.

Preferably, when the volume ratio of CO ₂ to CH ₄ in the biogas is less than 1/3, add CO ₂ to the mixed gas until the volume ratio of CO ₂ to CH ₄ is ≥ 1/3, preferably, CO ₂ The volume ratio to _CH4 is 0.43-1.0.

Preferably, when the volume ratio of CO ₂ to CH ₄ in the biogas is ≥1/3, the CO ₂ contained in the biogas can already make CH ₄ react completely, and it is not necessary to supplement CO ₂ into the mixed gas.

Preferably, the catalyst is selected from at least one of Ni-based catalysts, copper-based catalysts, and copper-zinc catalysts.

Preferably, when preparing the synthesis gas, the reaction temperature is 750°C to 850°C.

Preferably, methanol is prepared by heating the synthesis gas to 100-300° C. under the action of a catalyst.

Preferably, the synthesis gas to methanol catalyst is a copper-zinc catalyst, and a mature catalyst can be selected.

The present invention also claims to protect a system for realizing the thermal catalytic conversion of all components of biogas, including a biogas tank 1, a biogas preheating furnace 2, a wet and dry double reforming reactor 3, and a waste heat recovery heat exchanger 4. , the first water cooling heat exchanger 5, the first gas-liquid separation device 6, the first gas booster 7, the carbon dioxide separation device 8, the second gas booster 9; the synthesis gas preheating furnace 10, the methanol synthesis reactor 11. Heat recovery heat exchanger 12, second water cooling heat exchanger 13, second gas-liquid separation device 14; biogas in biogas tank 1 enters biogas preheating furnace 2, preheating biogas to the required temperature; preheating The resulting biogas enters the wet and dry double reforming reactor 3 to produce synthesis gas, which enters the waste heat recovery heat exchanger 4, which is connected to the first water cooling heat exchanger 5, which is cooled by the first water. The gas passage of the heat exchanger 5 is connected to the first gas-liquid separation device 6, the separated gas enters the first gas booster 7, the pressurized gas enters the carbon dioxide separation device 8, and the synthesis gas after carbon dioxide separation enters the second gas booster. Pressurizing device 9, the pressurized syngas enters the syngas preheating furnace 10, and after preheating, enters the methanol synthesis reactor 11, where the syngas reacts to synthesize methanol, and the obtained methanol-containing mixed gas enters the heat conversion furnace The heat exchanger 12 realizes heat recovery, and the gas flowing out of the heat exchanger 12 enters the second water cooling heat exchanger 13, and then enters the second gas-liquid separation device 14, and the separated liquid is methanol.

Preferably, the second gas-liquid separation device 14 is connected with a pipeline for conveying gas, the pipeline is connected to the second gas booster device 9, and the unreacted CO and _H2 separated in the second gas-liquid separation device 14 are sent to The second gas booster 9 re-enters the subsequent synthesis gas preheating furnace 10, and then enters the methanol synthesis reaction furnace 11 to participate in the reaction again to synthesize methanol.

Preferably, there is a certain amount of untreated synthesis gas in the gas channel of the first water cooling heat exchanger 5, and the gas outlet of the first water cooling heat exchanger 5 is connected to the methanol synthesis reactor, so that the synthesis gas participates in the reaction, Synthesis of methanol.

Preferably, the liquid outlet of the first gas-liquid separation device 6 is connected to the second gas-liquid separation device 14, so that the water separated by the first gas-liquid separation device 6 can enter the second gas-liquid separation device 14 and be separated again. .

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

The present invention provides a new method for deep utilization of biogas, which mainly comprises the following steps: using the biogas to directly produce synthetic gas to produce methanol, and using the methane in the biogas to react with carbon dioxide and water vapor to produce biomethanol. The method utilizes the renewable biogas as raw material to directly prepare the environment-friendly chemical product methanol, and components such as methane, carbon dioxide, water and the like in the biogas all participate in the reaction. Compared with the biogas combustion power generation and utilization technology, the present invention has significant carbon emission reduction effect; compared with the biogas fuel cell technology, the present invention has high energy utilization efficiency; the introduction of water vapor to react with the biogas can avoid the incomplete methane reaction to pollute the environment The utilization rate of energy is reduced, and the generation of carbon deposits in the reaction can be suppressed at the same time; the methanol with high energy efficiency can be obtained, and the environmental pollution of the reaction waste can be avoided. At the same time, a system to realize the thermal catalysis of all components of biogas to prepare methanol is proposed. Under the premise of maximizing the conversion rate of biogas, the exhaust gas and other substances can be recycled to avoid the emission of harmful substances and maximize the utilization of resources.

Description of drawings

FIG. 1 shows a schematic diagram of a process flow of an embodiment of the present invention.

Numeral description: 1- biogas digester; 2- biogas preheating furnace; 3- wet and dry double reactor; 4- waste heat recovery heat exchanger; 5- first water cooling heat exchanger; 6- first gas-liquid separation device ; 7- first gas booster device; 8- carbon dioxide separation device; 9- second gas booster device; 10- syngas preheating furnace; 11- methanol synthesis reactor; 12- heat recovery heat exchanger; 13- The second water cooling heat exchanger; 14- the second gas-liquid separation device.

Detailed ways

The present invention is further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field.

Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

The method provided by the embodiment of the present invention is as follows:

The biogas is first processed by the raw gas purification and raw water metering and conveying modules, and the desulfurization index reaches <1.0ppm, and the treated purified biogas enters the next reaction stage, that is, the purification gas dry-wet dual-integration module, and the reaction process of the purified gas dry-wet dual-integration module. It is a dry and wet double reforming operation for purified gas, and a combined double reforming method of dry reforming and wet reforming of carbon dioxide-methane and water-methane. The reacted syngas enters the syngas-to-methanol operation module, and the syngas preheating system preheats the reaction gas to the reaction temperature. After preheating, the syngas enters the syngas-to-methanol reactor for reaction to obtain methanol, which is then taken out through an aqueous solution and enters The collection device obtains biomethanol.

The main reaction equation is as follows:

3CH ₄ +2H ₂ O+CO ₂ →4CO+8H ₂

CO+2H ₂ →CH ₃ OH

As shown in Figure 1, the embodiment of the present invention uses regenerable biogas as a raw material to directly produce chemical intermediate synthesis gas and then produce liquid fuel methanol, which specifically includes the following steps:

_Biogas from livestock and poultry manure, forestry waste and municipal sludge is first processed by the raw material gas purification and raw water metering and conveying modules _{. 2} content 40% by volume) is pumped to the gas purification operation module through the power equipment (induced fan), and the gas pumped through the power equipment enters the gas drying and desulfurization tower for drying and desulfurization of the gas, and the desulfurization index reaches <1.0ppm. The treated purified biogas enters the next reaction stage, that is, the double dry and wet integrated module of the purified gas. The combined double reforming method of dry reforming and wet reforming of methane not only improves the utilization rate of carbon dioxide in the biogas, but also adjusts the hydrogen-carbon ratio in the reaction process, which is beneficial to the synthesis gas to methanol in the later stage. conduct. The reacted synthesis gas enters the synthesis gas to methanol operation module. Specifically, the synthesis gas preheating system preheats the reaction gas to the reaction temperature, and after preheating, the synthesis gas enters the synthesis gas to methanol reactor for reaction to obtain methanol, and then The aqueous solution is carried out into a collection device to obtain biomethanol. The auxiliary work required for the whole process is completed by auxiliary utility operation modules, namely: pure water preparation module, cooling water reserve and cooling water module, power equipment module, heating and combustion boiler module, and necessary power supply module.

In the gas purification operation module, the purified biogas after dehydration and desulfurization (CH ₄ content 60 vol %, CO ₂ content 40 vol %) is divided into two parts, one part (about 50 vol % of the total gas) enters as fuel The heating and combustion boiler module provides heat for the reaction; the other part (about 50% by volume of the total gas volume) enters the power equipment operation module (secondary compressor) as a dry and wet double-rectified reaction gas for pressurization (after pressurization) The pressure is controlled at about 0.8MPa), and the pressurized gas enters the wet and dry dual operation module after passing through the buffer system, flow control and metering system. In the reaction process, in order to adjust the hydrogen-carbon ratio, the module is equipped with a module operation for measuring and transporting pure water, so as to complete the transport and measurement of the pure water required for the reaction and the pure water required for cooling. This not only realizes the function of conveying the reaction raw materials, but also realizes the heat recovery function of waste heat recovery. In the dry and wet double reforming module of purified gas, the heat required for the dry and wet double reforming reaction of biogas is provided by the combustion of the biogas. During this reforming process, about 1/3 of the volume of methane participates in the dry reforming of carbon dioxide-methane. 2/3 volume of methane participates in the wet reforming of water-methane, and the hydrogen-to-carbon ratio of the obtained syngas is about 2.2:1 (that is, the molar ratio of H to _CO in the syngas is about 2.2:1), which is in line with the syngas Demand for methanol production and unconverted gas recovery. In the synthesis gas-to-methanol operation module, the product undergoes two-stage condensation heat exchange and then gas-liquid separation. The functions of the two-stage condensation heat exchange are: the first stage condensation heat exchange The purpose of heat is the deep cooling of the product, thereby realizing the recovery of methanol and water and the separation of unreacted gas. After separation, methanol and water are automatically discharged as products; after separation, the unreacted gas enters the syngas pressurized operating system for reuse. In the auxiliary utility operation module, the pure water preparation operation module only provides a sufficient amount of pure water for the reaction process, including the pure water preparation system and the pure water storage system. The cooling water reserve and cooling water operation module is mainly to provide the cooling water necessary for cryogenic cooling and the heat exchange of the water after heat exchange for the whole system to ensure the cooling effect. The power equipment operation module mainly includes power pump, multi-stage supercharger system, etc., which provide transmission power for the material transportation of the equipment. The heating and combustion boiler operation module mainly provides the necessary heat for equipment operation. The power supply operation module of the necessary equipment mainly provides the necessary power for the control system and power equipment of the equipment.

The working process of the system shown in Figure 1 is as follows: the biogas in the biogas digester 1 enters the biogas preheating furnace 2, and the biogas is preheated to the required temperature (usually 750-850°C), and the biogas preheating furnace 2 is connected with a water supply for supplementary water. steam pipes.

The preheated biogas enters the dry and wet double reforming reactor 3 to obtain synthesis gas, which enters the waste heat recovery heat exchanger 4, and the waste heat recovery heat exchanger 4 is connected to the first water cooling heat exchanger 5, and the first The gas channel of the water cooling heat exchanger 5 is connected to the first gas-liquid separation device 6, the separated gas enters the first gas pressurizing device 7, the pressurized gas enters the carbon dioxide separation device 8, and the synthesis gas after carbon dioxide separation enters the second gas Gas pressurizing device 9, the pressurized syngas enters the syngas preheating furnace 10, and after preheating, enters the methanol synthesis reactor 11, where the syngas reacts in the reactor to synthesize methanol, and the obtained mixed gas containing methanol enters the The heat exchanger 12 realizes heat recovery. The gas flowing out of the heat exchanger 12 enters the second water cooling heat exchanger 13, and then enters the second gas-liquid separation device 14. The separated liquid is methanol, which can be collected and stored by the collection device. .

The second gas-liquid separation device 14 is connected with a pipeline for conveying gas, and the pipeline is connected to the second gas booster device 9. The gas separated by the second gas-liquid separation device 14 contains H ₂ , CO, etc., and the gas enters through the pipeline. The second gas pressurizing device 9 re-enters the subsequent synthesis gas preheating furnace 10, and then enters the methanol synthesis reaction furnace 11 to participate in the reaction again to synthesize methanol, so as to realize the effective recovery of the tail gas, and it will not be discharged into the atmosphere, and thus will not be discharged into the atmosphere. polluted environment.

Regarding the fresh water replenishment system, the following system can be adopted specifically. The pipeline for replenishing fresh water is connected to the first water cooling heat exchanger 5, and the waste heat of the gas flowing out of the heat exchanger 4 is used for the waste heat recovery to heat the fresh water for the first time. The water outlet of a water cooling heat exchanger 5 is connected to the water inlet channel of the waste heat recovery heat exchanger 4, so that the new water is reheated in the waste heat recovery heat exchanger 4, and the water outlet of the waste heat recovery heat exchanger 4 is connected through a pipeline to the biogas preheating furnace 2, so that the new water heated in the waste heat recovery heat exchanger 4 enters the biogas preheating furnace 2 through the pipeline. After preheating, steam is formed and enters the wet and dry double reforming reactor 3 to participate in the reaction.

There will be a certain amount of untreated synthesis gas in the gas channel of the first water cooling heat exchanger 5, and the gas outlet of the first water cooling heat exchanger 5 is connected to the methanol synthesis reactor, so that the synthesis gas participates in the reaction to synthesize methanol.

The liquid outlet of the first gas-liquid separation device 6 is connected to the second gas-liquid separation device 14 , so that the water separated by the first gas-liquid separation device 6 can enter the second gas-liquid separation device 14 and be separated again.

Each heat exchanger allows the heat in the system to be fully recovered, and about 60% of the released heat can be recovered.

Example 1

After the biogas is desulfurized by the gas purification operation module, under the treatment of the raw water metering and conveying module, methane and water vapor are mixed in a volume ratio of 3:2. In an environment of 800 ℃, using a nickel-based catalyst, the reaction is carried out with a methane conversion rate of about 100% and The conversion rate of carbon dioxide is more than 50% to generate synthesis gas (CO and H ₂ ), and then the synthesis gas (CO and H ₂ ) is processed in the synthesis gas to methanol operation module at 300 ° C, and the reaction reaches a methanol of about 192.5 mol/h. yield, the product is passed into the aqueous solution collection device, that is, methanol is obtained, and the tail gas enters the synthesis device again for cyclic reaction.

Example 2

After the biogas is desulfurized by the gas purification operation module, under the treatment of the raw water metering and conveying module, methane and water vapor are mixed according to the volume ratio of 3:2. In the environment of 850 ℃, using a nickel-based catalyst, the conversion rate of methane is about 100% and carbon dioxide is about 100%. The conversion rate is over 60% to generate synthesis gas (CO and H ₂ ), and then the synthesis gas (CO and H ₂ ) is processed in the synthesis gas to methanol operation module at a temperature of 300 ° C, and the reaction reaches a methanol yield of about 211.4 mol/h , the product is passed into the aqueous solution collection device, that is, methanol is obtained, and the tail gas enters the synthesis device again for cyclic reaction.

Example 3

After the biogas is desulfurized by the gas purification operation module, under the treatment of the raw water metering and conveying module, the methane and water vapor are mixed according to the volume ratio of 3:2. The conversion rate is more than 40% to generate synthesis gas (CO and H ₂ ), and then the synthesis gas (CO and H ₂ ) is processed in the synthesis gas to methanol operation module at 300 ° C, and the reaction reaches a methanol output of about 153.7 mol/h , the product is passed into the aqueous solution collection device to obtain methanol, and the tail gas enters the synthesis device again for cyclic reaction.

Example 4

After the biogas is desulfurized by the gas purification operation module, under the treatment of the raw water metering and conveying module, methane and water vapor are mixed in a volume ratio of 3:2. In an environment of 800 ℃, using a nickel-based catalyst, the reaction is carried out with a methane conversion rate of about 100% and The conversion rate of carbon dioxide is more than 50% to generate synthesis gas (CO and H ₂ ), and then the synthesis gas (CO and H ₂ ) is processed in the synthesis gas-to-methanol operation module at 100 ° C, and the reaction reaches about 148.2 mol/h of methanol. yield, the product is passed into the aqueous solution collection device, that is, methanol is obtained, and the tail gas enters the synthesis device again for cyclic reaction.

Example 5

After the biogas is desulfurized by the gas purification operation module, under the treatment of the raw water metering and conveying module, methane and water vapor are mixed in a volume ratio of 3:2. In an environment of 800 ℃, using a nickel-based catalyst, the reaction is carried out with a methane conversion rate of about 100% and The conversion rate of carbon dioxide is more than 50% to generate synthesis gas (CO and H ₂ ), and then the synthesis gas (CO and H ₂ ) is processed at 200 ° C under the synthesis gas to methanol operation module, and the reaction reaches a methanol output of about 159.7 mol/h , the product is passed into the aqueous solution collection device, that is, methanol is obtained, and the tail gas enters the synthesis device again for cyclic reaction.

To sum up, the embodiment of the present invention provides a new method for deep utilization of biogas, which mainly uses biogas to directly produce synthesis gas to methanol, and uses methane, carbon dioxide and water vapor in biogas to purify raw gas and raw water. Metering and conveying module, purified gas dry-wet dual integrated module, synthesis gas-to-methanol module and auxiliary utility operation modules, namely: pure water preparation module, cooling water reserve and cooling water module, power equipment module, heating and combustion boiler module, necessary 4 main operation modules, including the power supply module, produce bio-methanol. The method utilizes the renewable biogas as raw material to directly prepare the environment-friendly chemical product methanol. Compared with the biogas combustion power generation and utilization technology, the present invention has significant carbon emission reduction effect; compared with the biogas fuel cell technology, the present invention has high energy utilization efficiency; the introduction of water vapor to react with the biogas can avoid the incomplete methane reaction to pollute the environment The utilization rate of energy is reduced, and the generation of carbon deposits in the reaction can be suppressed at the same time; the methanol with high energy efficiency can be obtained, and the environmental pollution of the reaction waste can be avoided.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, The simplification should be equivalent replacement manners, which are all included in the protection scope of the present invention.

Claims (10)

1. A method for preparing methanol by full-component thermal catalysis of marsh gas is characterized by comprising the following steps: providing dried and desulfurized biogas, mixing the biogas with steam to obtain mixed gas, carrying out dry-wet double reforming in the presence of a catalyst, reacting to obtain synthesis gas, and preparing to obtain methanol.

2. The method of claim 1, wherein the volume ratio of methane to the water vapor in the biogas is 3: 2.

3. the method of claim 1, wherein the desulfurized biogas is H-enriched₂The volume content of S is less than 1.0 ppm.

4. Method according to claim 1, characterized in that CH is present in the biogas₄50-70% of CO₂The content is 30-50%.

5. The method of claim 1, wherein the CO is present in the biogas₂And CH₄When the volume ratio of (3) is less than 1/3, adding CO into the mixed gas₂To CO₂And CH₄The volume ratio of (A) is more than or equal to 1/3.

6. The method of claim 1, wherein the catalyst is selected from at least one of Ni-based catalysts, copper-based catalysts, and copper-zinc catalysts.

7. The method of claim 1, wherein the synthesis gas is prepared at a reaction temperature of 750 ℃ to 850 ℃.

8. The method of claim 1, wherein the synthesis gas is heated to 100 to 300 ℃ to produce methanol.

9. A system for preparing methanol by converting full-component methane through thermal catalysis and thermal catalysis into synthesis gas is characterized by comprising a methane tank (1), a methane preheating furnace (2), a dry-wet double reforming reactor (3), a waste heat recovery heat exchanger (4), a first water cooling heat exchanger (5), a first gas-liquid separation device (6), a first gas pressurization device (7), a carbon dioxide separation device (8) and a second gas pressurization device (9); a synthesis gas preheating furnace (10), a methanol synthesis reaction furnace (11), a heat recovery heat converter (12), a second water cooling heat exchanger (13) and a second gas-liquid separation device (14); the biogas in the biogas digester (1) enters a biogas preheating furnace (2) and is preheated to the required temperature; the preheated methane enters a dry-wet double reforming reactor (3) to prepare synthesis gas, the synthesis gas enters a waste heat recovery heat exchanger (4), the waste heat recovery heat exchanger (4) is communicated with a first water cooling heat exchanger (5), a gas channel of the first water cooling heat exchanger (5) is communicated with a first gas-liquid separation device (6), the separated gas enters a first gas pressure boosting device (7), the pressurized gas enters a carbon dioxide separation device (8), the synthesis gas after carbon dioxide separation enters a second gas pressure boosting device (9), the pressurized synthesis gas enters a synthesis gas preheating furnace (10), the synthesis gas enters a methanol synthesis reaction furnace (11) after preheating, the synthesis gas reacts in the reaction furnace to synthesize methanol, the obtained mixed gas containing the methanol enters a heat converter (12) to realize heat recovery, the gas flowing out of the heat converter (12) enters a second water cooling heat exchanger (13), then enters a second gas-liquid separation device (14) to obtain liquid, namely methanol.

10. A system according to claim 9, characterized in that the second gas-liquid separation device (14) is connected to a gas supply line which is connected to the second gas pressurisation device (9) and which connects the second gas-liquid separation device (14) to itSeparated unreacted CO and H₂And the gas is conveyed to a second gas supercharging device (9) and enters a subsequent synthesis gas preheating furnace (10) again, and then enters a methanol synthesis reaction furnace (11) to participate in the reaction again to synthesize the methanol.

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