Preparation system and method for synthesizing green LNG (Liquefied Natural Gas) based on double-bed chemical looping gasification of biomass

Abstract

The invention provides a preparation system and method for synthesizing green LNG based on double-bed chemical looping gasification of biomass, according to the preparation system, a pressurized gasification furnace is combined with the catalytic action of an oxygen carrier to carry out gasification catalytic oxidation treatment on the biomass to produce synthesis gas, the gasification reaction temperature can be uniform and stable, gas components are stable, the biomass conversion rate is increased, and the production cost is reduced. The gas production rate is high, and the effective gas content is higher, so that the gasification efficiency can be improved, the biomass consumption is reduced, and the production cost is reduced; and a filter element dust removal unit, a waste heat recovery unit, a water washing unit, a desulfurization and decarbonization unit, a synthesis gas compression unit, a methane synthesis unit, a compression drying unit and a natural gas liquefaction unit are combined, so that green LNG can be efficiently prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquefied natural gas preparation, and in particular relates to a preparation system and method for synthesizing green LNG based on double-bed chemical chain gasification of biomass. Background Art

[0002] LNG is the abbreviation of liquefied natural gas (Liquefied Natural Gas), which is an important chemical raw material and fuel, widely used in chemical industry, transportation and energy. LNG mainly comes from natural gas in gas fields and partly from coal chemical industry. However, these fossil fuel resources are limited and have serious impacts on the environment. Biomass gasification synthesis of LNG is an alternative method of sustainable development. Renewable biomass resources, such as wood, crop straw, food waste and animal manure, are converted into synthesis gas through gasification reaction, and then natural gas is synthesized. This process not only reduces carbon dioxide emissions, but also reduces dependence on fossil energy, which helps to achieve the goal. At the same time, this technology realizes the clean and comprehensive recycling of biomass resources, greatly improves resource utilization efficiency and promotes sustainable development.

[0003] However, in the current process of preparing natural gas from biomass, the synthesis gas obtained by biomass gasification is not stable enough and has a low gas production rate, resulting in low efficiency in preparing LNG. Summary of the invention

[0004] The present invention provides a system and method for preparing green LNG based on dual-bed chemical chain gasification of biomass, which is used to solve the problems in the prior art that the synthesis gas obtained by biomass gasification is not stable enough, the gas production rate and biomass conversion rate are low, and the efficiency of preparing LNG is low.

[0005] In the first aspect, the present invention provides a preparation system for synthesizing green LNG from biomass based on double-bed chemical chain gasification, characterized in that it includes: a crushing and molding unit, a pressurized conveying unit, a biomass gasification unit, a filter element dust removal unit, a waste heat recovery unit, a water washing unit, a desulfurization and decarbonization unit, a synthesis gas compression unit, a methane synthesis unit, a compression and drying unit, and a natural gas liquefaction unit; The biomass gasification unit includes an air reactor and a gasifier; the oxygen carrier outlet of the gasifier is connected to the oxygen carrier inlet of the air reactor, and the oxygen carrier outlet of the air reactor is connected to the oxygen carrier inlet of the gasifier; The biomass is communicated with the inlet of the pulverizing and molding unit, the outlet of the pulverizing and molding unit is communicated with the inlet of the pressurized conveying unit, the outlet of the pressurized conveying unit is communicated with the material inlet of the gasifier, the material outlet of the gasifier is communicated with the inlet of the filter element dust removal unit, the material outlet of the filter element dust removal is communicated with the inlet of the waste heat recovery unit, the outlet of the waste heat recovery unit is communicated with the inlet of the water washing unit, the outlet of the water washing unit is communicated with the inlet of the desulfurization and decarbonization unit, the material outlet of the desulfurization and decarbonization unit is communicated with the inlet of the synthesis gas compression unit, the outlet of the synthesis gas compression unit is communicated with the inlet of the methane synthesis unit, the outlet of the methane synthesis unit is communicated with the inlet of the compression and drying unit, the outlet of the compression and drying unit is communicated with the inlet of the natural gas liquefaction unit, and the outlet of the natural gas liquefaction unit is used to output LNG; The atmosphere of the air reactor is air atmosphere, and the atmosphere of the gasifier is nitrogen atmosphere; the pressure of the gasifier is 1.0~4.0MPa.

[0006] Compared with the prior art, the beneficial effects of the present invention are as follows: the use of a pressurized gasifier combined with the catalytic action of an oxygen carrier to gasify and catalytically oxidize biomass to produce synthesis gas can make the gasification reaction temperature uniform and stable, the gas components stable, the biomass conversion rate is improved, the gas production rate is high, and the effective gas content is higher, thereby improving the gasification efficiency, reducing biomass consumption, and reducing production costs; combined with a filter element dust removal unit, a waste heat recovery unit, a water washing unit, a desulfurization and decarbonization unit, a synthesis gas compression unit, a methane synthesis unit, a compression and drying unit, and a natural gas liquefaction unit, green LNG can be efficiently produced.

[0007] Further, the pressure of the air reactor is 1.0-4.0 MPa; and / or, The temperature of the air reactor is 800-870°C, and the temperature of the gasifier is 850-900°C.

[0008] Furthermore, the oxygen concentration of the gasifier is not higher than 0.2%.

[0009] Furthermore, the hydrogen-to-carbon atomic ratio in the methane synthesis unit is 2.9-3.0, the pressure is 3.8-4.5 MPa, and the reaction temperature is 580-650°C.

[0010] Furthermore, the composite oxygen carrier component includes at least one of Fe, Ca, Ni or Cu, and the added amount is 20-60% of the total mass of the composite oxygen carrier.

[0011] Further, the pressurized delivery unit includes a normal pressure storage tank, a pressurized tank, a feed tank and a carbon dioxide compression unit; The outlet of the crushing and molding unit is connected to the inlet of the atmospheric pressure storage tank, the outlet of the atmospheric pressure storage tank is connected to the inlet of the pressure tank, the outlet of the pressure tank is connected to the inlet of the feed tank, and the outlet of the feed tank is connected to the inlet of the gasifier; The carbon dioxide outlet of the gasifier is communicated with the inlet of the carbon dioxide compression unit, and the outlet of the carbon dioxide compression unit is communicated with the pressurization port of the pressurization tank.

[0012] Further, it also includes a KCl extraction unit and a compound fertilizer synthesis unit; The ash outlet of the gasifier is connected to the inlet of the KCl extraction unit, the fly ash outlet of the filter element dust removal unit and the outlet of the KCl extraction unit are respectively connected to the inlet of the compound fertilizer synthesis unit, and the outlet of the compound fertilizer synthesis unit is used to output compound fertilizer.

[0013] Furthermore, it also includes a sulfur recovery unit, the hydrogen sulfide outlet of the desulfurization and decarbonization unit is connected to the inlet of the sulfur recovery unit, and the outlet of the sulfur recovery unit is used to output sulfur products; The carbon dioxide outlet of the sulfur recovery unit is used to export the carbon dioxide product.

[0014] Furthermore, it also includes a water electrolysis hydrogen production device, which includes a wind and solar power generation unit, an electric energy storage device, an electrolyzer, a hydrogen compressor and a hydrogen storage tank; The wind and solar power generation units are connected to the electric energy storage device and the electrolyzer respectively. The hydrogen outlet of the electrolyzer is connected to the inlet of the hydrogen compressor, the outlet of the hydrogen compressor is connected to the inlet of the hydrogen storage tank, and the outlet of the hydrogen storage tank is connected to the inlet of the synthesis gas compression unit.

[0015] In a second aspect, the present invention provides a method for preparing green LNG based on dual-bed chemical chaining gasification of biomass, which is performed by the preparation system for preparing green LNG based on dual-bed chemical chaining gasification of biomass described in the first aspect, and is characterized in that it comprises the following steps: (1) crushing and shaping the biomass to obtain crushed biomass; (2) Pressurizing the crushed biomass and subjecting it to catalytic oxidation and gasification treatment to obtain a crude synthesis gas; (3) The raw synthesis gas is subjected to filter element dust removal treatment, waste heat recovery treatment, water washing treatment and desulfurization and decarbonization treatment in sequence to obtain synthesis gas; (4) compressing the synthesis gas and then subjecting it to methane synthesis treatment to obtain natural gas; (5) The natural gas is compressed, dried and liquefied in sequence to obtain LNG. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of a preparation system for synthesizing green LNG from biomass based on dual-bed chemical chaining gasification in one embodiment of the present invention.

[0017] Description of reference numerals: 01. Crushing and molding unit; 02. Pressurized conveying unit; 031. Gasification furnace; 032. Air reactor; 04. Filter element dust removal unit; 05. Waste heat recovery unit; 06. Water washing unit; 07. Desulfurization and decarbonization unit; 08. Synthesis gas compression unit; 09. Methane synthesis unit; 10. Compression and drying unit; 11. Natural gas liquefaction unit; 12. KCl extraction unit; 13. Compound fertilizer synthesis unit; 14. Sulfur recovery unit; 15. Wind and solar power generation unit; 16. Electric energy storage equipment; 17. Electrolyzer; 18. Hydrogen compressor; 19. Hydrogen storage tank. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] First, see Figure 1 The present invention provides a preparation system for synthesizing green LNG from biomass based on double-bed chemical chain gasification, comprising: a crushing and molding unit 01, a pressurized conveying unit 02, a biomass gasification unit, a filter element dust removal unit 04, a waste heat recovery unit 05, a water washing unit 06, a desulfurization and decarbonization unit 07, a synthesis gas compression unit 08, a methane synthesis unit 09, a compression and drying unit 10 and a natural gas liquefaction unit 11; The biomass gasification unit includes an air reactor 032 and a gasifier 031; the oxygen carrier outlet of the gasifier 031 is connected to the oxygen carrier inlet of the air reactor 032, and the oxygen carrier outlet of the air reactor 032 is connected to the oxygen carrier inlet of the gasifier 031; The biomass is connected to the inlet of the crushing and molding unit 01, the outlet of the crushing and molding unit 01 is connected to the inlet of the pressurized conveying unit 02, the outlet of the pressurized conveying unit 02 is connected to the material inlet of the gasifier 031, the material outlet of the gasifier 031 is connected to the inlet of the filter element dust removal unit 04, the material outlet of the filter element dust removal is connected to the inlet of the waste heat recovery unit 05, the outlet of the waste heat recovery unit 05 is connected to the inlet of the water washing unit 06, the outlet of the water washing unit 06 is connected to the inlet of the desulfurization and decarbonization unit 07, and the material outlet of the desulfurization and decarbonization unit 07 is connected to the synthesis gas compression unit The inlet of the synthesis gas compression unit 08 is connected, the outlet of the synthesis gas compression unit 08 is connected to the inlet of the methane synthesis unit 09, the outlet of the methane synthesis unit 09 is connected to the inlet of the compression and drying unit 10, the outlet of the compression and drying unit 10 is connected to the inlet of the natural gas liquefaction unit 11, and the outlet of the natural gas liquefaction unit 11 is used to output LNG; the atmosphere of the air reactor 032 is air atmosphere, and the atmosphere of the gasifier 031 is nitrogen replacement before feeding. During the gasification reaction, the oxygen carrier releases oxygen and biomass to carry out gasification reaction; the pressure of the gasifier 031 is 1.0~4.0MPa.

[0020] Specifically, the biomass raw material enters the crushing and molding unit 01 through the inlet of the crushing and molding unit 01 for crushing and molding treatment to obtain crushed biomass. After leaving the crushing and molding unit 01, the crushed biomass enters the pressurizing and conveying unit 02 through the inlet of the pressurizing and conveying unit 02 for pressurization, and then enters the gasifier 031 in the biomass gasification unit for catalytic oxidation gasification treatment to obtain crude synthesis gas. The raw synthesis gas leaves the biomass gasification unit through the material outlet of the gasifier 031, and then enters the filter element dust removal unit 04 through the inlet for filter element dust removal treatment. After dust removal, the material leaves the filter element dust removal unit 04 through the material outlet, and then enters the waste heat recovery unit 05 through the inlet for preheating recovery treatment to recover high-temperature sensible heat and produce saturated steam as a by-product. Then, the material leaves the waste heat recovery unit 05 through the outlet, and then enters the water washing unit 06 through the inlet for water washing treatment. After further purification, the material leaves the water washing unit 06 through the outlet and enters the desulfurization and decarbonization unit 07 through the inlet for desulfurization and decarbonization treatment to remove carbon dioxide and acid gas. The synthesis gas obtained after desulfurization and decarbonization treatment leaves the desulfurization and decarbonization unit 07 through the material outlet, and is sent to the synthesis gas compression unit 08 as a raw material for synthesizing methane. The compressed synthesis gas enters the methane synthesis unit 09 through the inlet thereof for methane synthesis treatment to obtain natural gas, which then enters the compression and drying unit 10 and the natural gas liquefaction unit 11 in sequence for compression and drying treatment and liquefaction treatment to obtain green LNG.

[0021] Among them, the pressure of the gasifier 031 is 1.0~4.0MPa, which can improve the gasification reaction speed and gasification efficiency.

[0022] The present invention provides a preparation system for synthesizing green LNG based on dual-bed chemical chain gasification of biomass, which adopts a pressurized gasifier 031 combined with the catalytic action of an oxygen carrier to gasify and catalytically oxidize biomass to produce synthesis gas, and then combines a filter element dust removal unit 04, a waste heat recovery unit 05, a water washing unit 06, a desulfurization and decarbonization unit 07, a synthesis gas compression unit 08, a methane synthesis unit 09, a compression and drying unit 10 and a natural gas liquefaction unit 11, so that the gasification reaction temperature can be uniform and stable, the gas composition can be stable, the biomass conversion rate can be improved, the gas production rate can be high, and the effective gas content can be higher, thereby improving the gasification efficiency, reducing biomass consumption, reducing production costs, and being able to efficiently produce green LNG.

[0023] Furthermore, the pressure of the air reactor 032 is 1.0-4.0 MPa; the temperature of the biomass gasification unit is 800-900° C.; further, the temperature of the air reactor 032 is 800-870° C., and the temperature of the gasifier 031 is 850-900° C. By further limiting the temperature and pressure of the air reactor 032 and the gasifier 031, the oxygen carrier can be further loaded with oxygen in the air reactor 032, and the oxygen carrier releases oxygen in the gasifier 031 to catalyze the gasification and oxidation reaction of the biomass, which can further reduce the biomass gasification temperature, increase the biomass gasification reaction rate and carbon conversion rate, and have a high gas production rate, further improving the efficiency of synthetic LNG.

[0024] Furthermore, the air reactor 032 is an air atmosphere, and the gasifier 031 is replaced with nitrogen before feeding, and the oxygen content is less than 0.2%. The oxygen carrier can be further loaded with oxygen in the air reactor 032, and the oxygen is released in the gasifier 031 to catalyze the biomass to undergo gasification and oxidation reaction, which can further reduce the biomass gasification temperature, increase the biomass gasification reaction rate and carbon conversion rate, and have a high gas production rate, further improving the efficiency of synthetic LNG.

[0025] In a specific embodiment, the hydrogen-to-carbon atomic ratio in the methane synthesis unit 09 is 2.9-3.0, the pressure is 3.8-4.5 MPa, and the reaction temperature is 580-650° C. Specifically, the hydrogen-to-carbon ratio can be adjusted by introducing hydrogen into the methane synthesis unit 09. The inventors have found that under the above-mentioned specific execution parameters, the efficiency of synthesizing LNG can be further improved.

[0026] Furthermore, the composite oxygen carrier component includes at least one of Fe, Ca, Ni or Cu, and the content of Fe, Ca, Ni or Cu in the composite oxygen carrier is 20-60%. It can be understood that the composite oxygen carrier also includes a binder, auxiliary material components for strengthening hardness and strength, etc. The oxygen released by the composite oxygen carrier enters the gasifier 031 and undergoes a catalytic oxidation reaction with the biomass, which can achieve low-temperature and efficient gasification of the biomass, and achieve efficient and directional conversion of semi-coke, tar and methane, further reducing the consumption of synthetic natural gas; and there is no need to design air separation, reduce equipment investment, reduce the amount and cost of gasification agents, and do not produce black gasification wastewater.

[0027] Optionally, the pressurized conveying unit 02 includes a normal pressure storage tank, a pressurized tank, a feeding tank and a carbon dioxide compression unit; the outlet of the crushing and molding unit 01 is connected to the inlet of the normal pressure storage tank, the outlet of the normal pressure storage tank is connected to the inlet of the pressurized tank, the outlet of the pressurized tank is connected to the inlet of the feeding tank, and the outlet of the feeding tank is connected to the inlet of the gasifier 031; the carbon dioxide outlet of the gasifier 031 is connected to the inlet of the carbon dioxide compression unit, and the outlet of the carbon dioxide compression unit is connected to the pressurization port of the pressurized tank.

[0028] Optionally, the operating pressure of the feed tank is 1.0~4.8MPa, and the biomass in the feed tank is pressurized by CO2 and transported to the gasifier 031. When in use, the biomass is first stored in the atmospheric pressure storage tank. When the lower high-pressure feed tank needs to be refilled, the biomass in the atmospheric pressure tank flows into the biomass pressure tank by gravity. After the material level of the pressure tank reaches the requirement, it is isolated from all atmospheric pressure equipment, and then pressurized by high-pressure CO2 until the pressure is the same as that of the feed tank. At this time, the pressure tank is connected to the high-pressure feed tank, and the biomass flows from the pressure tank to the feed tank by gravity. After all the biomass in the pressure tank enters the high-pressure feed tank, the two tanks are isolated, and then the pressure of the pressure tank is relieved, and the above process is repeated.

[0029] In a specific embodiment, it also includes a KCl extraction unit 12 and a compound fertilizer synthesis unit 13; the ash outlet of the gasifier 031 is connected to the inlet of the KCl extraction unit 12, the fly ash outlet of the filter element dust removal unit 04 and the outlet of the KCl extraction unit 12 are respectively connected to the inlet of the compound fertilizer synthesis unit 13, and the outlet of the compound fertilizer synthesis unit 13 is used to output compound fertilizer.

[0030] Biomass is rich in K element, which is one of the main components required for crop growth. Fly ash is an excellent soil conditioner. KCl is extracted from the ash of the biomass gasification unit and fed into the compound fertilizer synthesis unit 13 together with the fly ash of the filter dust removal unit 04 to produce compound fertilizer, which further improves the utilization efficiency and economy of the effective components of biomass and reduces waste treatment costs and environmental pollution.

[0031] In another specific embodiment, a sulfur recovery unit 14 is further included, and the hydrogen sulfide outlet of the desulfurization and decarbonization unit 07 is connected to the inlet of the sulfur recovery unit 14. The outlet of the sulfur recovery unit 14 is used to output sulfur products; the carbon dioxide outlet of the sulfur recovery unit 14 is used to output carbon dioxide products.

[0032] The synthesis gas is further desulfurized and decarbonized in the desulfurization and decarbonization unit 07 to remove CO2 and H2S. The removed CO2 can be sold, and the removed acid gas rich in H2S enters the sulfur recovery unit 14 to generate sulfur products, further reducing production costs.

[0033] In another specific embodiment, it also includes a water electrolysis hydrogen production device, which includes a wind-solar power generation unit 15, an electric energy storage device 16, an electrolyzer 17, a hydrogen compressor 18 and a hydrogen storage tank 19; the wind-solar power generation unit 15 is connected to the electric energy storage device 16 and the electrolyzer 17 respectively, the hydrogen outlet of the electrolyzer 17 is connected to the inlet of the hydrogen compressor 18, the outlet of the hydrogen compressor 18 is connected to the inlet of the hydrogen storage tank 19, and the outlet of the hydrogen storage tank 19 is connected to the inlet of the synthesis gas compression unit 08.

[0034] The wind and solar power generation unit 15 is connected to the electric energy storage device 16. Part of the electricity is used to supply power to the electrolyzer 17 of the water electrolysis hydrogen production device, and part of the electricity is connected to the power grid as plant power. The hydrogen and synthesis gas produced by the water electrolysis hydrogen production device participate in the methane synthesis process together, which further reduces the production cost, realizes the clean and comprehensive recycling of biomass resources, greatly improves the resource utilization efficiency, and promotes sustainable development.

[0035] In a second aspect, the present invention provides a method for preparing green LNG based on dual-bed chemical chaining gasification of biomass, which is performed using the preparation system for preparing green LNG based on dual-bed chemical chaining gasification of biomass according to the first aspect, and comprises the following steps: (1) crushing and shaping the biomass to obtain crushed biomass; (2) Pressurizing the crushed biomass and subjecting it to catalytic oxidation and gasification treatment to obtain a crude synthesis gas; (3) The raw synthesis gas is subjected to filter element dust removal treatment, waste heat recovery treatment, water washing treatment and desulfurization and decarbonization treatment in sequence to obtain synthesis gas; (4) compressing the synthesis gas and then subjecting it to methane synthesis treatment to obtain natural gas; (5) The natural gas is compressed, dried and liquefied in sequence to obtain LNG.

[0036] The technical effect of the method for preparing green LNG based on dual-bed chemical chaining gasification of biomass provided by the present invention is similar to that of the system for preparing green LNG based on dual-bed chemical chaining gasification of biomass in the first aspect, which will not be repeated here.

[0037] The following is a detailed introduction to the system and method for preparing green LNG based on dual-bed chemical chaining gasification of biomass provided by the present invention through specific embodiments. Example

[0038] Use Figure 1 The preparation system shown is carried out, comprising the following steps: (1) The collected biomass enters the crushing and molding unit 01 for crushing and molding to obtain crushed biomass; (2) The crushed biomass is pressurized in the pressurized conveying unit 02, and then introduced into the gasifier 031 in the biomass gasification unit to be catalytically oxidized and gasified together with the oxygen carrier from the air reactor 032 to obtain a crude synthesis gas; Among them, the pressure of the gasifier 031 is 2.5MPa and the temperature is 870℃, and the pressure of the air reactor 032 is 2.5MPa and the temperature is 850℃; (3) The raw synthesis gas is sequentially fed into the filter element dust removal unit 04, the waste heat recovery unit 05, the water washing unit 06, and the desulfurization and decarbonization unit 07, and is subjected to filter element dust removal treatment, waste heat recovery treatment, water washing treatment, and desulfurization and decarbonization treatment to obtain synthesis gas; (4) The synthesis gas is sent to the synthesis gas compression unit 08 for compression, and then sent to the methane synthesis unit 09 for methane synthesis treatment to obtain natural gas; Among them, the hydrogen-carbon atomic ratio in the methane synthesis unit 09 is 3.0, the pressure is 4 MPa, and the reaction temperature is 600°C; (5) The natural gas is sequentially introduced into the compression and drying unit 10 and the natural gas liquefaction unit 11 for compression, drying and liquefaction treatment to obtain LNG.

[0039] In the above method, the carbon conversion rate is 98%; the effective gas concentration is 89%, and the hydrogen-carbon atomic ratio of H2 to CO is 0.9:1.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein by equivalents. If these modifications and variations fall within the scope of the claims of the present invention and their equivalent technologies, they should be considered to be within the protection scope of the present invention.

Claims

1. A preparation system for synthesizing green LNG from biomass using dual-bed chemical chaining gasification, characterized in that: include: Crushing and molding unit, pressurized conveying unit, biomass gasification unit, filter element dust removal unit, waste heat recovery unit, water washing unit, desulfurization and decarbonization unit, synthesis gas compression unit, methane synthesis unit, compression and drying unit and natural gas liquefaction unit; The biomass gasification unit includes an air reactor and a gasifier; the oxygen carrier outlet of the gasifier is connected to the oxygen carrier inlet of the air reactor, and the oxygen carrier outlet of the air reactor is connected to the oxygen carrier inlet of the gasifier; The biomass is communicated with the inlet of the pulverizing and molding unit, the outlet of the pulverizing and molding unit is communicated with the inlet of the pressurized conveying unit, the outlet of the pressurized conveying unit is communicated with the material inlet of the gasifier, the material outlet of the gasifier is communicated with the inlet of the filter element dust removal unit, the material outlet of the filter element dust removal is communicated with the inlet of the waste heat recovery unit, the outlet of the waste heat recovery unit is communicated with the inlet of the water washing unit, the outlet of the water washing unit is communicated with the inlet of the desulfurization and decarbonization unit, the material outlet of the desulfurization and decarbonization unit is communicated with the inlet of the synthesis gas compression unit, the outlet of the synthesis gas compression unit is communicated with the inlet of the methane synthesis unit, the outlet of the methane synthesis unit is communicated with the inlet of the compression and drying unit, the outlet of the compression and drying unit is communicated with the inlet of the natural gas liquefaction unit, and the outlet of the natural gas liquefaction unit is used to output LNG; The atmosphere of the air reactor is air atmosphere, and the atmosphere of the gasifier is nitrogen atmosphere; the pressure of the gasifier is 1.0~4.0MPa.

2. The preparation system for synthesizing green LNG based on dual-bed chemical chaining gasification of biomass according to claim 1 is characterized in that: The pressure of the air reactor is 1.0 to 4.0 MPa; and / or, The temperature of the air reactor is 800-870°C, and the temperature of the gasifier is 850-900°C.

3. The preparation system for synthesizing green LNG based on dual-bed chemical chaining gasification of biomass according to claim 2 is characterized in that: The oxygen concentration in the gasifier is not higher than 0.2%.

4. The preparation system for synthesizing green LNG based on dual-bed chemical chaining gasification of biomass according to claim 3 is characterized in that: The hydrogen-carbon atomic ratio in the methane synthesis unit is 2.9~3.0, the pressure is 3.8~4.5MPa, and the reaction temperature is 580~650℃.

5. The preparation system for synthesizing green LNG based on dual-bed chemical chaining gasification of biomass according to claim 4 is characterized in that: The composite oxygen carrier component includes at least one of Fe, Ca, Ni or Cu, and the content of Fe, Ca, Ni or Cu in the composite oxygen carrier is 20-60%.

6. The preparation system for synthesizing green LNG based on dual-bed chemical chaining gasification of biomass according to claim 5 is characterized in that: The pressurized delivery unit includes a normal pressure storage tank, a pressurized tank, a feed tank and a carbon dioxide compression unit; The outlet of the crushing and molding unit is connected to the inlet of the atmospheric pressure storage tank, the outlet of the atmospheric pressure storage tank is connected to the inlet of the pressure tank, the outlet of the pressure tank is connected to the inlet of the feed tank, and the outlet of the feed tank is connected to the inlet of the gasifier; The carbon dioxide outlet of the gasifier is communicated with the inlet of the carbon dioxide compression unit, and the outlet of the carbon dioxide compression unit is communicated with the pressurization port of the pressurization tank.

7. The preparation system for synthesizing green LNG from biomass based on dual-bed chemical chaining gasification according to any one of claims 1 to 6, characterized in that: It also includes a KCl extraction unit and a compound fertilizer synthesis unit; The ash outlet of the gasifier is connected to the inlet of the KCl extraction unit, the fly ash outlet of the filter element dust removal unit and the outlet of the KCl extraction unit are respectively connected to the inlet of the compound fertilizer synthesis unit, and the outlet of the compound fertilizer synthesis unit is used to output compound fertilizer.

8. The preparation system for synthesizing green LNG from biomass based on dual-bed chemical chaining gasification according to any one of claims 1 to 6, characterized in that: It also includes a sulfur recovery unit, the hydrogen sulfide outlet of the desulfurization and decarbonization unit is connected to the inlet of the sulfur recovery unit, and the outlet of the sulfur recovery unit is used to output sulfur products; The carbon dioxide outlet of the sulfur recovery unit is used to export the carbon dioxide product.

9. The preparation system for synthesizing green LNG from biomass based on dual-bed chemical chaining gasification according to any one of claims 1 to 6, characterized in that: It also includes a water electrolysis hydrogen production device, which includes a wind and solar power generation unit, an electric energy storage device, an electrolyzer, a hydrogen compressor and a hydrogen storage tank; The wind and solar power generation units are connected to the electric energy storage device and the electrolyzer respectively. The hydrogen outlet of the electrolyzer is connected to the inlet of the hydrogen compressor, the outlet of the hydrogen compressor is connected to the inlet of the hydrogen storage tank, and the outlet of the hydrogen storage tank is connected to the inlet of the synthesis gas compression unit.

10. A method for preparing green LNG based on dual-bed chemical chaining gasification of biomass, which is performed by using the preparation system for preparing green LNG based on dual-bed chemical chaining gasification of biomass according to any one of claims 1 to 9, characterized in that: The following steps are involved: (1) crushing and shaping the biomass to obtain crushed biomass; (2) Pressurizing the crushed biomass and subjecting it to catalytic oxidation and gasification treatment to obtain a crude synthesis gas; (3) The raw synthesis gas is subjected to filter element dust removal treatment, waste heat recovery treatment, water washing treatment and desulfurization and decarbonization treatment in sequence to obtain synthesis gas; (4) compressing the synthesis gas and then subjecting it to methane synthesis treatment to obtain natural gas; (5) The natural gas is compressed, dried and liquefied in sequence to obtain LNG.

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