Preparation method of synthesis gas for synthesizing methane

Abstract

The invention relates to a preparation method of synthesis gas for synthesizing methane, and belongs to the technical field of natural gas chemical industry. The method comprises the following steps: electrolyzing and decomposing water to obtain hydrogen and oxygen; the method comprises the following steps: pyrolyzing a biomass raw material to obtain biomass charcoal, biomass gas and biomass oil; gasifying the biomass charcoal to obtain carbon monoxide; mixing the hydrogen and the carbon monoxide to obtain synthesis gas; heating the synthesis gas to obtain reaction gas; the reaction gas is used for a methane synthesis process; and capturing the carbon dioxide generated by the pyrolysis and the gasification for cyclic utilization. By adopting biomass as a raw material, green electricity as an energy medium, trapping and recycling carbon dioxide and other technical means, the carbon emission in the methane synthesis process is remarkably reduced. Compared with coal-based natural gas, the biomass-based natural gas has an obvious low-carbon emission level, and even can realize zero-carbon or negative-carbon emission.

Description

Technical Field

[0001] The present application relates to the field of natural gas chemical technology, and in particular to a method for preparing synthesis gas for synthesizing methane. Background Art

[0002] Natural gas (methane) is a major energy source and a key raw material worldwide, playing a crucial role in national economic development and energy security. In recent years, China has increased investment in natural gas exploration, but its dependence on foreign sources remains around 40%. Faced with this natural gas supply shortage, domestic coal-to-gas conversion has become an important alternative.

[0003] The coal-to-natural gas process mainly includes the following steps: gasification, shift conversion, purification, and methanation. However, due to the low hydrogen-carbon ratio in coal, in order to meet the hydrogen-carbon ratio required for methanation (H2 / CO=3:1), part of the CO needs to be converted into H2 in the shift conversion section, while a large amount of CO2 is produced as a by-product. In other words, the coal-to-natural gas process has a large carbon emission (about 4.8tCO2 / kNm 3 The development of natural gas (methane) synthesis technology urgently requires cleaner synthesis gas sources to gradually reduce carbon dioxide emissions. Summary of the Invention

[0004] The present application provides a method for preparing synthesis gas for synthesizing methane to solve the following technical problem: how to reduce carbon emissions from a methane synthesis process.

[0005] The present invention provides a method for preparing synthesis gas for synthesizing methane, the method comprising:

[0006] Electrolyze water to produce hydrogen and oxygen;

[0007] Pyrolyzing the biomass raw materials to obtain biochar, biogas and biooil;

[0008] gasifying the biochar to obtain carbon monoxide;

[0009] mixing the hydrogen and the carbon monoxide to obtain synthesis gas;

[0010] heating the synthesis gas to obtain reaction gas;

[0011] Using the reaction gas in a methane synthesis process;

[0012] The carbon dioxide generated by the pyrolysis and gasification is captured for recycling.

[0013] Optionally, the pyrolysis method is slow pyrolysis, the pyrolysis temperature is 400° C. to 500° C., and the heating medium of the pyrolysis is the biomass gas.

[0014] Optionally, the heating medium for gasification is the biomass gas, biomass oil and / or green electricity.

[0015] Optionally, the gasification agent for the gasification is carbon dioxide and / or oxygen, and the carbon dioxide is carbon dioxide captured from the tail gas of the pyrolysis and gasification.

[0016] Optionally, the gasification temperature is 850° C. to 950° C., and the catalytic component of the gasification is one or more of K metal oxide, Na metal oxide, Ca metal oxide and Mg metal oxide.

[0017] Optionally, the electrolysis adopts alkaline water electrolysis technology, the oxygen is used in the pyrolysis and gasification processes, and the electrolyzed water is the water removed from the tail gas of the pyrolysis, gasification and methane synthesis processes.

[0018] Optionally, the heating method is high-temperature plasma heating, the temperature of the heated gas is 450° C. to 650° C., and the heating energy medium is green electricity.

[0019] Optionally, in the reaction gas, the sum of the volume fractions of hydrogen and carbon monoxide is greater than 95%.

[0020] Optionally, the capture method is an alcoholamine solution chemical absorption method.

[0021] Optionally, the energy used for the pyrolysis and the gasification comes from the combustion of the biomass gas and the biomass oil.

[0022] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0023] The embodiment of the present application provides a method for preparing synthesis gas for synthesizing methane, the method comprising: electrolyzing water to decompose and obtain hydrogen and oxygen; pyrolyzing biomass raw materials to obtain biochar, biogas and biooil; gasifying the biochar to obtain carbon monoxide; mixing the hydrogen and carbon monoxide to obtain synthesis gas; heating the synthesis gas to obtain reaction gas; using the reaction gas for a methane synthesis process; and capturing the carbon dioxide generated by the pyrolysis and gasification for recycling. By adopting biomass as raw material, green electricity as energy medium, and the capture and recycling of carbon dioxide, the carbon emissions of the methane synthesis process are significantly reduced. Compared with coal-to-natural gas, biomass-to-natural gas has a significantly low carbon emission level, and can even achieve zero or negative carbon emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0026] Figure 1 A schematic flow chart of a method for preparing synthesis gas for synthesizing methane provided in an embodiment of the present application;

[0027] 1-pyrolysis unit; 2-gasification unit; 3-gas heating unit; 4-synthetic methane unit; 5-hydrogen production unit; 6-dehydration unit; 7-carbon dioxide capture unit; F1-CO2 gas source; F2-biomass; F3-green electricity; F4-pure water; P1-biochar; P2-carbon monoxide; P3-reaction gas; P4-methane; P5-H2; P6-O2; P7-biomass gas; P8-biomass oil; P9-combustion exhaust gas. DETAILED DESCRIPTION

[0028] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0029] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range; for example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range; in addition, whenever a numerical range is indicated in this document, it is meant to include any cited number (fractional or integer) within the indicated range.

[0030] As used herein, the terms "including," "comprising," and the like mean "including but not limited to." Relational terms such as "first" and "second" are used solely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. "And / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, "A and / or B" can mean: A exists alone, A and B exist at the same time, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, "plurality" means two or more; "at least one," "at least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items; for example, "at least one of a, b, or c" or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or plural. "Parts" notation, such as parts by weight or parts by mass, indicates the proportional relationship between components. In this article, the parameters described by ratio should be understood as the first term of the proportional formula, in the order in which they are described, and the proportional figures should be understood as the second term. For example, if the mass ratio of substances A, B, and C is 1:2:3, then substances A, B, and C should correspond to the proportional figures in the proportional formula, in the order in which they are described: that is, the mass of substance A:the mass of substance B:the mass of substance C = 1:2:3.

[0031] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this article can be purchased from the market or prepared by existing methods.

[0032] An embodiment of the present application provides a method for preparing synthesis gas for synthesizing methane. The method integrates technologies such as biomass pyrolysis, biomass char gasification, water electrolysis to produce hydrogen, gas heating, methane synthesis, and carbon dioxide capture and utilization, thereby reducing carbon emissions from the methane synthesis process and achieving green methane production.

[0033] Specific process flow such as Figure 1As shown: Green electricity F3 is used in hydrogen production unit 5, and pure water F4 is electrolyzed to produce H2 (i.e., P5) and O2 (i.e., P6); biomass F2 is pyrolyzed by pyrolysis unit 1 to produce biochar P1, biogas P7, and biooil P8; biochar P1 is gasified in gasification unit 2 by CO2 gas source F1 or O2 gas source P6 to produce CO (i.e., P2); the gasification product CO and H2 gas source P5 are mixed and enter the gas heating unit 3 for heating to produce high-temperature reaction gas (CO+H2) P3, which is used for methane synthesis unit 4. In addition, biogas P7, biooil P8, and O2 gas source P6 are used for heating in pyrolysis unit 1 and gasification unit 2; product methane P4 passes through dehydration unit 6, and combustion tail gas P9 passes through dehydration unit 6 and carbon capture unit 7 in sequence. The water obtained is further used in hydrogen production unit 5, and the captured CO2 is further used in gasification unit 2, and recycled for methane synthesis.

[0034] The present invention provides a method for preparing synthesis gas for synthesizing methane, including:

[0035] Electrolyze water to produce hydrogen and oxygen;

[0036] Pyrolyzing the biomass raw materials to obtain biochar, biogas and biooil;

[0037] gasifying the biochar to obtain carbon monoxide;

[0038] mixing the hydrogen and the carbon monoxide to obtain synthesis gas;

[0039] heating the synthesis gas to obtain reaction gas;

[0040] Using the reaction gas in a methane synthesis process;

[0041] The carbon dioxide generated by the pyrolysis and gasification is captured for recycling.

[0042] In some embodiments, the electrolysis adopts alkaline water electrolysis technology, the oxygen is used in the pyrolysis and gasification processes, and the electrolyzed water is the water removed from the tail gas of the pyrolysis, gasification and methane synthesis processes.

[0043] In the embodiment of the present application, the electrolysis process adopts alkaline electrolysis water technology. Alkaline electrolysis water technology uses KOH and NaOH aqueous solutions as electrolytes. Through the action of direct current, water molecules are electrolyzed into hydrogen and oxygen. This technology is not only efficient, but also the oxygen produced can be directly used in subsequent pyrolysis and gasification processes as combustion-supporting gas or gasifying agent, thereby achieving effective utilization of resources. At the same time, the embodiment of the present application also focuses on the recycling of water. In pyrolysis, gasification and synthetic methane processes, a certain amount of tail gas will be produced. These tail gases contain recyclable water. These tail gases are processed by a special dehydration unit, and the water therein can be removed and recycled. The recycled water is then used as the raw material for electrolysis, thereby achieving the recycling of water. This recycling method not only saves water resources, but also reduces the discharge of wastewater, reflecting the concept of environmental protection and sustainable development.

[0044] In some embodiments, the pyrolysis method is slow pyrolysis, the pyrolysis temperature is 400° C. to 500° C., and the heating medium of the pyrolysis is the biomass gas.

[0045] Slow pyrolysis is a pyrolysis process that occurs at lower temperatures and longer reaction times. This helps biomass feedstock decompose more fully, producing high-value products such as biochar, biogas, and biooil. Within this temperature range (400°C to 500°C), product formation is optimized while avoiding excessive temperatures that could lead to product decomposition or excessive carbonization.

[0046] Using biomass gas as a heating medium is an efficient and environmentally friendly practice. Biomass gas, produced during the pyrolysis process, primarily consists of combustible gases such as hydrogen, carbon monoxide, and methane. These gases serve as a heat source to provide the energy required for the pyrolysis process. Recycling biomass gas not only reduces external energy consumption but also lowers production costs and carbon emissions, aligning with the principles of green and sustainable development.

[0047] In some embodiments, the heating medium for gasification is the biomass gas, biomass oil and / or green electricity.

[0048] In the embodiments of the present application, the heating medium of the gasification process has a variety of options, including biomass gas, biomass oil and / or green electricity. This flexible and diverse selection of heating media not only makes full use of the by-products produced during the pyrolysis of biomass, but also introduces clean energy green electricity, thereby achieving efficient energy utilization and low carbon emissions to the environment. Specifically, biomass gas and biomass oil, as by-products of the pyrolysis process, are rich in energy and easy to burn, and can be directly used as heating media for the gasification process. This utilization method not only saves additional energy input, but also achieves effective conversion and utilization of by-products. At the same time, the introduction of green electricity as a clean energy provides a more environmentally friendly heating method for the gasification process. Green electricity usually comes from renewable energy sources, such as solar energy, wind energy, etc., and has the characteristics of zero emissions and sustainability. Using green electricity for heating in the gasification process can not only reduce the use of fossil energy and carbon emissions, but also conform to the concept of sustainable development.

[0049] In some embodiments, the gasification agent of the gasification is carbon dioxide and / or oxygen, and the carbon dioxide is carbon dioxide captured from the tail gas of the pyrolysis and gasification.

[0050] In the present application embodiment, the gasifying agent of gasification process has innovative selection, i.e. adopts carbon dioxide and / or oxygen. In particular, described carbon dioxide is not supplied from outside, but comes from the tail gas in pyrolysis and gasification process, is recycled and reused by special capture technology. Specifically, in pyrolysis and gasification process, a certain amount of tail gas will be produced, wherein comprises the components such as carbon dioxide, by adopting the capture technology such as advanced alcohol amine solution chemical absorption method, these carbon dioxide can be effectively separated from tail gas, and purified, the carbon dioxide after treatment can be used as the gasifying agent of gasification process, gasification reaction occurs with biochar, generates gaseous products such as carbon monoxide, this mode of using carbon dioxide as gasifying agent, not only realizes the resource utilization of carbon dioxide, also reduces the emission of greenhouse gases, has significant environmental benefits. At the same time, because carbon dioxide comes from the tail gas of pyrolysis and gasification process, therefore also reduces the raw material cost of gasification process, in addition, oxygen can also be used as the gasifying agent of gasification process, is used together with carbon dioxide or is used alone. The introduction of oxygen can accelerate the gasification reaction and improve the gasification efficiency. Moreover, oxygen can also be captured and recovered through the tail gas in the pyrolysis and gasification process for recycling.

[0051] In some embodiments, the gasification temperature is 850° C. to 950° C., and the catalytic component of the gasification is one or more of K metal oxide, Na metal oxide, Ca metal oxide, and Mg metal oxide.

[0052] In the embodiment of the present application, the temperature of the gasification process is limited to the range of 850°C to 950°C. This temperature range is intended to ensure that the gasification reaction can proceed efficiently and stably. Within this temperature range, biochar can fully react with the gasification agent (such as carbon dioxide, oxygen, etc.) to generate high-quality gas products such as carbon monoxide.

[0053] In order to further improve the gasification efficiency and product quality, the embodiments of the present application also introduce specific catalytic components. These catalytic components include one or more of metal oxides of K, Na, Ca, and Mg. These metal oxides can play a significant catalytic role in the gasification process, reduce the activation energy of the reaction, and thus accelerate the progress of the gasification reaction. Specifically, the addition of catalytic components can promote a more complete and uniform reaction between the biochar and the gasifying agent, reduce the generation of by-products during the reaction, and increase the yield and selectivity of target products such as carbon monoxide. At the same time, the catalytic components can also stabilize the reaction conditions in the gasification process, reduce energy consumption, and improve the overall gasification efficiency.

[0054] In some embodiments, the energy used for the pyrolysis and the gasification is derived from the combustion of the biomass gas and the biomass oil.

[0055] In the embodiment of the present application, the energy used in the pyrolysis and gasification processes mainly comes from the combustion of biomass gas and biomass oil. This design makes full use of the by-products produced in the biomass pyrolysis process, and realizes self-sufficiency and efficient utilization of energy. During the pyrolysis process, the biomass raw material is heated and decomposed under anoxic or micro-oxygen conditions to produce biochar, biomass gas and biomass oil. Among them, biomass gas and biomass oil are rich in energy and can be directly used as fuel for the heating of pyrolysis and gasification processes. By burning these by-products, it is not only possible to provide the required heat energy for pyrolysis and gasification reactions, but also to reduce dependence on external energy sources and reduce production costs. In addition, the heat energy generated by the combustion of biomass gas and biomass oil also has the characteristics of cleanliness and high efficiency. Compared with fossil fuels, the carbon dioxide emissions generated by the combustion of biomass fuels are relatively low, and the carbon dioxide absorbed by biomass during growth is basically equivalent to the carbon dioxide emitted by its combustion, so it can be regarded as a carbon-neutral energy source.

[0056] In some embodiments, the heating method is high-temperature plasma heating, the temperature of the heated gas is 450° C. to 650° C., and the heating energy medium is green electricity.

[0057] In the embodiments of the present application, the heating of the synthesis gas adopts advanced high-temperature plasma heating technology. This heating method is characterized by high efficiency, rapidity and uniformity, and can quickly heat the synthesis gas to the required reaction temperature, thereby improving the efficiency of the subsequent methanation reaction. Specifically, the high-temperature plasma heating technology transfers heat energy directly to the synthesis gas by generating high-temperature, high-energy and highly reactive plasma. During the heating process, the temperature of the synthesis gas is precisely controlled within the range of 450°C to 650°C. This temperature range is the optimal condition for the methanation reaction, which can ensure the efficient progress of the reaction and the high-quality generation of the product. In addition, the heating energy medium in the embodiments of the present application is green electricity, which is usually derived from renewable energy sources such as solar energy, wind energy, etc., and is clean, environmentally friendly and renewable. Using green electricity as a heating energy source not only reduces the use of fossil energy and carbon emissions, but also conforms to the concept of sustainable development.

[0058] In some embodiments, the sum of the volume fractions of hydrogen and carbon monoxide in the reaction gas is greater than 95%.

[0059] In the examples of this application, strict requirements are imposed on the volume fractions of hydrogen and carbon monoxide in the reaction gas: the sum of their volume fractions must be greater than 95%. Hydrogen and carbon monoxide are the primary feedstock gases for methane synthesis, and their concentrations and ratios directly impact the efficiency of the methanation reaction and the purity of the product. When the sum of the volume fractions of hydrogen and carbon monoxide exceeds 95%, the impurity content in the reaction gas is extremely low, which helps reduce the occurrence of side reactions and improves the selectivity and yield of the methanation reaction.

[0060] In some embodiments, the capture method is an alcoholamine solution chemical absorption method.

[0061] In the present application embodiment, for the carbon dioxide produced in pyrolysis and gasification process, alcohol amine solution chemical absorption method is adopted to capture.Alcohol amine solution chemical absorption method is a kind of mature and efficient carbon dioxide capture technology, is widely used in gas purification field, the basic principle of the method is to utilize alcohol amine solution (such as ethanolamine, diethanolamine etc.) as absorbent, in absorption tower, fully contact with the gas containing carbon dioxide, because alcohol amine solution has alkalescence, can chemically react with carbon dioxide, generate stable compound, so that carbon dioxide is separated from gas, subsequently, in desorption tower, by heating or decompression mode, these compounds can have reverse reaction, release carbon dioxide, realize the regeneration of alcohol amine solution simultaneously, so that recycle.Alcohol amine solution chemical absorption method has multiple advantages, first, the method has higher absorption efficiency and selectivity, can efficiently capture the carbon dioxide in gas, even for low concentration of carbon dioxide also can reach good capture effect, secondly, the technical process of alcohol amine solution chemical absorption method is mature, stable and reliable operation, and absorbent regeneration is easy, can long-term stable operation, in addition, the method can also adapt to different working conditions, flexibly adjust operating parameters, to meet the carbon dioxide capture demand under different scenes. In the embodiments of the present application, by using the chemical absorption method of alcohol amine solution to capture the carbon dioxide generated during the pyrolysis and gasification process, not only the effective recovery and recycling of carbon dioxide is achieved, but it also helps to reduce greenhouse gas emissions and improve the environmental performance of the entire methane synthesis process. At the same time, the captured carbon dioxide can also be used as a gasification agent in the gasification process, further realizing the comprehensive utilization of resources and the recycling of carbon.

[0062] The present application is further described below with reference to specific examples. Experimental methods in the following examples where specific conditions are not specified are generally measured in accordance with national / industry standards. If there are no corresponding national / industry standards, the methods are carried out in accordance with commonly used international standards, conventional conditions, or conditions recommended by the manufacturer.

[0063] Comparative Example

[0064] The coal-to-natural gas process mainly includes coal gasification, carbon monoxide shift, synthesis gas purification, methanation and other steps. Taking the production of 1,000 cubic meters of natural gas as an example, material balance shows that the production of 1,000 cubic meters of natural gas requires about 2.14 tons of coal, and the energy medium consumption (electricity and steam, etc.) is equivalent to 2,620 kWh. The carbon emissions of the entire coal-to-natural gas process are calculated to be 4.794 t / kNm 3 Natural gas, as shown in Table 1. Due to the high carbon content in coal, the CO content in the gasification product gas is high, so the synthesis gas needs to undergo a shift reaction to adjust the volume ratio of H2 and CO to 3:1. This process produces a large amount of CO2 emissions. Production practice shows that the process carbon emissions reach 2.7t / kNm 3 natural gas.

[0065] Example

[0066] Biomass energy has zero carbon properties. Biomass pyrolysis is used to produce biochar, with biogas and biooil as by-products. The biochar is then gasified with carbon dioxide to produce carbon monoxide (containing some hydrogen). Hydrogen is replenished through water electrolysis, adjusting the volume ratio of H2 to CO to 3:1. Then, a methanation reaction is used to produce green, low-carbon natural gas.

[0067] The analysis results of a biomass industry are: fixed carbon 16.4%, volatile matter 72.7%, ash 5.1%, moisture 5.8%, calorific value 16.9MJ / kg. Slow pyrolysis of 1 ton of biomass at 450℃ produces about 265m3 of biomass gas. 3 (calorific value is about 15.2MJ / m 3 ), biochar about 286kg (fixed carbon 57.3%, volatile matter 24.9%, ash 17.8%, calorific value about 23.6MJ / kg), biooil 395kg (containing water, calorific value about 15.5MJ / kg).

[0068] The efficiency of carbon dioxide gasification of biochar is 95%, and the conversion rate of CO used for methanation is 97.1%. According to material balance, the production of 1,000 cubic meters of natural gas requires about 1.34 tons of biomass and about 2750m3 of hydrogen. 3 , can absorb and utilize about 510m 3 , the energy medium consumption (electricity and steam, etc.) is equivalent to 2200kWh. If the combustion thermal efficiency of biomass gas and biomass tar produced as by-products of biomass pyrolysis required for the production of 1,000 cubic meters of natural gas is 60%, the total energy produced is equivalent to 2267kWh. Therefore, the energy medium consumption of biomass-to-natural gas can be provided by the direct combustion of its process by-products, without the need for additional input, and the carbon emissions of this part are 0. If green hydrogen is supplied in the form of hydrogen produced by photovoltaic power generation and water electrolysis, the carbon emissions of the entire process of biomass-to-natural gas production are calculated to be -0.390t / kNm 3 Natural gas, as shown in Table 1.

[0069] Table 1 Material balance and carbon emission calculation of biomass pyrolysis gasification and coal-based natural gas (calculated on a thousand cubic meter basis)

[0070]

[0071] It can be seen from Table 1 that the same production of 1kNm 3 Natural gas, coal-to-gas routes have carbon emissions of 4.794 tons, while biomass-to-gas routes have carbon emissions of -0.390 tons. This shows that compared to coal-to-gas, biomass-to-gas has significantly lower carbon emissions. Using biomass and green electricity to produce natural gas can achieve zero or even negative carbon emissions.

[0072] One or more technical solutions in the embodiments of the present invention may have at least the following technical effects or advantages:

[0073] The preparation method provided by the embodiment of the present invention reduces greenhouse gas emissions by capturing and recycling carbon dioxide.

[0074] The preparation method provided by the embodiments of the present invention converts biomass resources into high-value syngas, which in turn produces natural gas, achieving efficient resource utilization and circular economy goals. Furthermore, through the recycling of water resources and the closed-loop utilization of carbon dioxide, the resource utilization efficiency of the entire system is further improved.

[0075] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but rather is intended to conform to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing synthesis gas for synthesizing methane, the method comprising: Electrolyze water to produce hydrogen and oxygen; Pyrolyzing the biomass raw materials to obtain biochar, biogas and biooil; gasifying the biochar to obtain carbon monoxide; mixing the hydrogen and the carbon monoxide to obtain synthesis gas; heating the synthesis gas to obtain reaction gas; Using the reaction gas in a methane synthesis process; The carbon dioxide generated by the pyrolysis and gasification is captured for recycling.

2. The method according to claim 1, characterized in that The pyrolysis method is slow pyrolysis, the pyrolysis temperature is 400° C. to 500° C., and the heating medium of the pyrolysis is the biomass gas.

3. The method according to claim 1, characterized in that The heating medium for gasification is the biomass gas, biomass oil and / or green electricity.

4. The method according to claim 1, wherein The gasification agent for the gasification is carbon dioxide and / or oxygen, and the carbon dioxide is carbon dioxide captured from the tail gas of the pyrolysis and gasification.

5. The method according to claim 1, characterized in that The gasification temperature is 850° C. to 950° C., and the gasification catalytic component is one or more of K metal oxide, Na metal oxide, Ca metal oxide and Mg metal oxide.

6. The method according to claim 1, characterized in that The electrolysis adopts alkaline water electrolysis technology, the oxygen is used in the pyrolysis and gasification processes, and the electrolyzed water is the water removed from the tail gas of the pyrolysis, gasification and methane synthesis processes.

7. The method according to claim 1, characterized in that The heating method is high-temperature plasma heating, the temperature of the heated gas is 450° C. to 650° C., and the heating energy medium is green electricity.

8. The method according to claim 1, characterized in that In the reaction gas, the sum of the volume fractions of hydrogen and carbon monoxide is greater than 95%.

9. The method according to claim 1, characterized in that The capture method is an alcohol amine solution chemical absorption method.

10. The method according to claim 1, characterized in that The energy used for the pyrolysis and the gasification comes from the combustion of the biomass gas and the biomass oil.

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