A supercritical water gasification hydrogen production system and method suitable for high concentration lignocellulosic biomass

Abstract

The present application belongs to the technical field of hydrogen production method, and particularly relates to a supercritical water gasification hydrogen production system and method suitable for high-concentration lignocellulose biomass, which realizes preparation and pumping of high-concentration cellulose biomass slurry, does not cause a substantial breakage of chemical bonds of material molecular structure in the slurry preparation process, only generates a small amount of gas, and has excellent slurry uniformity, stability and flowability; by using the physicochemical properties of supercritical water, a two-step gasification method is adopted, a primary reactor is based on the supercritical water liquefaction principle, realizes alkali salt recovery and macromolecular depolymerization, and a causticizing device is used to increase the reusability of alkali salt, improve the economy of the pulping process, and realize low-cost slurry preparation; based on the simplification of material molecular structure in the primary reactor, the occurrence of carbon deposition and reactor corrosion in a secondary reactor is substantially reduced, high-efficiency gasification of lignocellulose biomass is realized, and the efficiency of the system gasification efficiency is ensured.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrogen production methods, and particularly relates to a supercritical water gasification hydrogen production system and method suitable for high-concentration lignocellulosic biomass. BACKGROUND

[0002] Lignocellulosic biomass has a huge output, various types and rich resources. For example, the world produces 4 billion cubic meters of tree bark every year, and the output of straw in China has reached 800 million tons every year. Reasonable resource utilization is in line with the needs of future social development, but traditional gasification, incineration, cracking, fermentation and other treatment processes have the disadvantages of low efficiency, poor economy, high pollution and the like.

[0003] The supercritical water gasification technology (critical temperature 374 DEG C, critical pressure 22.1 MPa) can convert various organic matters into clean energy such as hydrogen-rich gas, and has the advantages of mild reaction conditions, no NO X , SO X generation, and system energy potential matching, and is a technology process that can reasonably realize the resource utilization of waste.

[0004] The lignocellulosic biomass is composed of macromolecular structures (cellulose, hemicellulose and lignin), has strong water absorption and swelling properties, and cannot be prepared into high-concentration slurry, and the slurry concentration is not more than 16%, and the system cannot realize self-heating.

[0005] Tar and coke are generated in the gasification process, and the gasification efficiency is low. Even if a catalyst is added, the catalyst and the material are in a dispersed phase, the fusion effect is poor, and the catalytic effect is limited.

[0006] The traditional regenerator layout design cannot realize reasonable heat recovery for the gasification system.

[0007] The traditional lignocellulosic biomass supercritical water gasification hydrogen production system has the following disadvantages: 1) high-concentration lignocellulosic biomass slurry preparation cannot be realized, and the feeding pipe is often blocked; 2) coking and carbon deposition are serious; 3) the conditions for realizing complete gasification are harsh; 4) the catalytic effect is poor, and the input cost is high; 5) the energy recovery design is unreasonable, and the system economy is poor. SUMMARY

[0008] The purpose of the present application is to overcome the above-mentioned deficiencies, provide a supercritical water gasification hydrogen production system and method suitable for high-concentration lignocellulosic biomass, realize low-cost high-concentration slurry preparation and pumping feeding, improve the gasification efficiency and reduce the generation of tar and coke, and at the same time, propose a heat recovery distribution scheme for the endothermic zone and the hydrogen-oxygen exothermic zone of the supercritical water gasification, to ensure the efficiency and economy of the system operation.

[0009] In order to achieve the above-mentioned purpose, a supercritical water gasification hydrogen production system suitable for high-concentration lignocellulosic biomass, comprising a pulping device, the pulping device is connected with a first reactor, the first reactor is connected with a second reactor, the second reactor is connected with an oxidation device, the oxidation device is connected with the tube side of a heat exchanger group, the tube side of the heat exchanger group is connected with a gas-liquid separator, the gas-liquid separator is connected with a water tank and a hydrogen separator, the pulping device is connected with a storage device, and the oxidation device is connected with an oxygen production device.

[0010] The inorganic salt outlet of the first reactor is connected with a caustic mixing device, and the caustic mixing device is connected with the pulping device.

[0011] The heat exchanger group sends liquid of different temperatures in the shell side into corresponding caustic mixing devices, first reactors and second reactors.

[0012] The water tank is connected with the inlets of the pulping device, the first reactor and the second reactor.

[0013] The pulping device is connected with an air pump.

[0014] A first pressurizing device is arranged between the storage device and the pulping device.

[0015] A second pressurizing device is arranged between the pulping device and the first reactor.

[0016] A third pressurizing device is arranged between the first reactor and the second reactor.

[0017] The heat exchanger group comprises a high-temperature heat exchanger, a medium-temperature heat exchanger and a low-temperature heat exchanger connected in sequence in the tube side, the tube side inlet of the high-temperature heat exchanger is connected with the oxidation device, the tube side outlet of the low-temperature heat exchanger is connected with the gas-liquid separator, the water tank is connected with the shell side inlets of the high-temperature heat exchanger, the medium-temperature heat exchanger and the low-temperature heat exchanger, and the shell side outlets of the high-temperature heat exchanger, the medium-temperature heat exchanger and the low-temperature heat exchanger are connected with the second reactor, the first reactor and the caustic mixing device respectively.

[0018] A circulating water pump is arranged between the water tank and the heat exchanger group.

[0019] A working method of a supercritical water gasification hydrogen production system suitable for high-concentration lignocellulosic biomass, comprising the following steps:

[0020] The water tank is opened, and the water flows into the first reactor and the second reactor through the heat exchanger group of the backwater path;

[0021] The outer wall of the first reactor and the second reactor is opened and heated to a reaction temperature, the preheated water in the first reactor and the second reactor is heated to a supercritical temperature, and the internal pressure of the first reactor and the second reactor is controlled and reaches a supercritical pressure;

[0022] The alkaline substance required for pulping is mixed with the material in the storage device, pressurized and then sent into the pulping device through the first pressurizing device.

[0023] The air pump provides initial pressure required for the pulping device, ensuring that the water in the pulping device exists in liquid state;

[0024] The outer wall of the pulping device is heated, and the alkaline substance causes the hydrolysis of the macromolecular structure in the pulping device and forms high-concentration slurry after being combined with water, and a small amount of carbon dioxide generated forms inorganic salt dissolved in the slurry;

[0025] The high-concentration slurry and the generated gas flow out of the pulping device through the outlet of the pulping device, and are pressurized by the second pressurizing device and then enter the primary reactor;

[0026] The speed of the high-concentration slurry and the gas flowing into the primary reactor is controlled, and the reaction time of the high-concentration slurry in the primary reactor is adjusted;

[0027] The inorganic salt in the high-concentration slurry is in the form of salt solution from the outlet of the primary reactor to the causticizing mixing device under the working condition of trans-critical or low-temperature supercritical;

[0028] The calcium hydroxide in the causticizing mixing device reacts with the low-temperature salt solution to generate calcium carbonate precipitate and alkali solution, which is sent to the pulping device to realize the recycling use of the alkaline substance;

[0029] The slurry after reaction in the primary reactor is pressurized by the third pressurizing device and then enters the secondary reactor to start gasification;

[0030] The residual liquid after reaction in the secondary reactor and the generated gas flow into the oxidation device, and the oxygen device injects oxygen into the oxidation device;

[0031] The residual gas after reaction and the residual liquid are sent to the heat exchanger group, and the water in the water tank is sent to the heat exchanger group by the circulating water pump and is subjected to heat exchange in the heat exchanger group;

[0032] The heat exchanger group sends the shell-side liquid at different temperatures to the corresponding causticizing mixing device, primary reactor and secondary reactor;

[0033] The liquid in the heat exchanger group is sent to the gas-liquid separator, the liquid phase in the gas-liquid separator flows into the water tank, and the gas phase passes through the hydrogen separator to realize the separation of hydrogen and carbon dioxide.

[0034] The alkaline substance is soda ash or strong alkali weak acid salt, and the addition amount of the alkaline substance accounts for 10%–40% of the slurry in the primary reactor.

[0035] The residual gas after reaction and the residual liquid flow out of the oxidation device and then enter the high-temperature heat exchanger to form a water inlet path, and the first backwater path from the water tank is subjected to heat exchange in the shell side of the high-temperature heat exchanger to form preheated water at 550℃–650℃, which is sent to the secondary reactor;

[0036] The water inlet path after once heat exchange is sent into the medium-temperature heat exchanger, continues heat exchange with the second section water return path from the water tank in the shell side of the medium-temperature heat exchanger, and forms 300-400 DEG C preheated water and is sent into the first reactor;

[0037] The water inlet path after twice heat exchange is sent into the low-temperature heat exchanger, continues heat exchange with the third section water return path from the water tank in the shell side of the low-temperature heat exchanger, and forms 100-200 DEG C preheated water and is sent into the causticizing mixing device.

[0038] Compared with the prior art, the present application realizes preparation and pumping of high-concentration cellulose biomass slurry, does not make the chemical bonds of material molecular structure break greatly in the slurry preparation process, only a small amount of gas is generated, and meanwhile the slurry uniformity, stability and flowability are excellent; the two-step gasification is adopted by using the physical and chemical properties of supercritical water, the alkali salt recovery and macromolecule depolymerization are realized based on the supercritical water liquefaction principle in the first reactor, the alkali salt reusability is increased by using the causticizing device, the economic efficiency of the pulping process is improved, and the low-cost slurry preparation is realized; based on the material molecular structure simplification in the first reactor, the carbon deposition and reactor corrosion in the second reactor are greatly reduced, the efficient gasification of lignocellulosic biomass is realized, and the high efficiency of the system gasification efficiency is ensured. The supercritical water gasification system gasification efficiency of lignocellulosic biomass is greatly improved by adopting high-concentration slurry preparation, multi-stage gasification and multi-stage heat recovery in the present application, the efficient resource utilization of waste is realized, the operation cost and investment cost are reduced, meanwhile, the heat recovery distribution scheme of the supercritical water gasification endothermic zone and the hydrogen-oxygen exothermic zone is proposed, and the high efficiency and economy of the system operation are ensured.

[0039] Further, the heat exchanger group of the present application includes a high-temperature heat exchanger, a medium-temperature heat exchanger and a low-temperature heat exchanger, can adopt multi-group heat exchangers for different equipment for staged heat exchange, and makes the heat recovery maximally rationalized. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The system diagram of the present application;

[0041] Among them, 1, gas pump; 2, storage device; 3, first pressurizing device; 4, pulping device; 5, second pressurizing device; 6, first reactor; 7, third pressurizing device; 8, second reactor; 9, oxygen making device; 10, oxidation device; 11, causticizing mixing device; 12, high-temperature heat exchanger; 13, medium-temperature heat exchanger; 14, low-temperature heat exchanger; 15, gas-liquid separator; 16, water tank; 17, circulating water pump; 18, hydrogen separator. DETAILED DESCRIPTION

[0042] The present application will be further described below in combination with the drawings.

[0043] Referring toFigure 1 A supercritical water gasification hydrogen production system suitable for high concentration lignocellulosic biomass, comprising a pulping device 4, the pulping device 4 being connected to a first reactor 6 and a gas pump 1, the first reactor 6 being connected to a second reactor 8, the second reactor 8 being connected to an oxidation device 10, the oxidation device 10 being connected to the tube side of a heat exchanger group, the tube side of the heat exchanger group being connected to a gas-liquid separator 15, the gas-liquid separator 15 being connected to a water tank 16 and a hydrogen separator 18, the pulping device 4 being connected to a storage device 2, and the oxidation device 10 being connected to an oxygen production device 9; the water tank 16 being connected to the inlet of the pulping device 4 and the shell side of a high-temperature heat exchanger 12, a medium-temperature heat exchanger 13 and a low-temperature heat exchanger 14. The inorganic salt outlet of the first reactor 6 is connected to a causticizing mixing device 11, and the causticizing mixing device 11 is connected to the pulping device 4; a first pressurizing device 3 is arranged between the storage device 2 and the pulping device 4. A second pressurizing device 5 is arranged between the pulping device 4 and the first reactor 6. A third pressurizing device 7 is arranged between the first reactor 6 and the second reactor 8. A circulating water pump 17 is arranged between the water tank 16 and the heat exchanger group.

[0044] The heat exchanger group sends liquid of different temperatures in the shell side to corresponding causticizing mixing devices 11, first reactors 6 and second reactors 8; the heat exchanger group comprises a high-temperature heat exchanger 12, a medium-temperature heat exchanger 13 and a low-temperature heat exchanger 14 connected in sequence in the tube side, the tube side inlet of the high-temperature heat exchanger 12 being connected to the oxidation device 10, the tube side outlet of the low-temperature heat exchanger 14 being connected to the gas-liquid separator 15, the water tank 16 being connected to the shell side inlets of the high-temperature heat exchanger 12, the medium-temperature heat exchanger 13 and the low-temperature heat exchanger 14, and the shell side outlets of the high-temperature heat exchanger 12, the medium-temperature heat exchanger 13 and the low-temperature heat exchanger 14 being connected to the second reactor 8, the first reactor 6 and the causticizing mixing device 11 respectively.

[0045] The pulping device 4 is provided with temperature and pressure sensors, the operating temperature is 150-200℃, and the pulping concentration is 30%-50%. The low-temperature salt discharge outlet of the first reactor 6 is connected to the circulating backwater outlet of the low-temperature heat exchanger 14 and is in communication with the causticizing mixing device 11, and the causticizing mixing device 11 is provided with calcium hydroxide. The temperature of the first reactor 6 is 300-400℃, the pressure is 22-23 MPa, and the outer wall is provided with a heat preservation device. The temperature of the second reactor 8 is 550-650℃, the pressure is 23-24 MPa, and the outer wall is provided with a heat preservation device.

[0046] The outer wall of the pulping device 4, the first reactor 6 and the second reactor 8 is provided with a heater. The inlet of the first reactor 6 and the second reactor 8 is provided with a flow controller, and the outlet is provided with a back pressure controller. The oxidation device 10 is provided with a combustion chamber, and the combustion temperature is 800-900℃. The oxidation device 10 is provided with a sensor, which can separate the hydrogen required for self-heating and enter the combustion chamber with the remaining generated combustible gas. The circulating water inlet is connected with the high-temperature heat exchanger 12, the medium-temperature heat exchanger 13 and the low-temperature heat exchanger 14 in sequence. The water path of the gas-liquid separator 15 is connected with the water tank 16, and the water tank 16 is connected with the circulating water pump 17. The circulating water return path is divided into three sections, which are connected with the high-temperature heat exchanger 12, the medium-temperature heat exchanger 13 and the low-temperature heat exchanger 14 respectively. The outlet of the circulating water return path of the high-temperature heat exchanger 12, the medium-temperature heat exchanger 13 and the low-temperature heat exchanger 14 is provided with a temperature sensor, and the high-temperature heat exchanger 12, the medium-temperature heat exchanger 13 and the low-temperature heat exchanger 14 all use a double-pipe structure. The water tank 16 is connected with the pulping device 4 after passing through the circulating water pump 17.

[0047] A working method of a supercritical water gasification hydrogen production system suitable for high-concentration lignocellulosic biomass, comprising the following steps:

[0048] S1, open the water tank 16 and the circulating water pump 17, so that the water flows into the first reactor 6 and the second reactor 8 through the heat exchanger group of the water return path;

[0049] S2, open the outer wall heating of the first reactor 6 and the second reactor 8, and heat and raise the temperature to the reaction temperature, so that the preheated water of the first reactor 6 and the second reactor 8 is heated to the supercritical temperature, and the internal pressure of the first reactor 6 and the second reactor 8 is controlled to reach the supercritical pressure through the back pressure controller at the outlet;

[0050] S3, mix the alkaline substance required for pulping with the material in the storage device 2, and then send it into the pulping device 4;

[0051] S4, the water in the water tank 16 enters the pulping device 4 through the circulating water pump 17.

[0052] S5, the air pump 1 provides the initial pressure required for pulping to the pulping device 4, so that the water in the pulping device 4 exists in a liquid state;

[0053] S6, open the outer wall heating of the pulping device 4, the alkaline substance makes the hydrolysis of the macromolecular structure in the pulping device 4 and the fusion with water to form a high-concentration slurry, at the same time, a small amount of carbon dioxide generated forms an inorganic salt dissolved in the slurry, and the metal ions in the alkaline substance are loaded to the surface of the small molecular structure of the biomass;

[0054] S7, the high-concentration slurry and the generated gas flow out of the outlet of the pulping device 4, are pressurized by the second pressurizing device 5, and then enter the first reactor 6;

[0055] S8, control the speed of the high-concentration slurry and gas flowing into the first reactor 6, adjust the reaction time of the high-concentration slurry in the first reactor 6;

[0056] S9, use the unique physical and chemical properties of supercritical water to further simplify the molecules in the slurry at 300-400°C, facilitate complete gasification, and inhibit the production of coke. Inorganic salts in the high-concentration slurry are in the form of salt solution from the outlet of the first reactor 6 to the caustic mixing device 11 under trans-critical or low-temperature supercritical working conditions; wherein the basic substance is soda ash or strong base weak acid salt, and the addition amount of the basic substance accounts for 10-40% of the slurry in the first reactor 6.

[0057] S10, the calcium hydroxide in the caustic mixing device 11 reacts with the low-temperature salt solution to generate calcium carbonate precipitate and alkali solution, which is sent to the pulping device 4 to realize the recycling use of the basic substance;

[0058] S11, the slurry after reaction in the first reactor 6 is pressurized by the third pressurizing device 7 and then enters the second reactor 8 to start gasification;

[0059] S12, the liquid after reaction in the second reactor 8 and the generated gas flow into the oxidation device 10, the oxygen injection device 9 injects oxygen into the oxidation device 10, and part of the hydrogen and other hydrocarbon gases in the sensor of the oxidation device are used for combustion and heat release.

[0060] S13, the oxidation device 10 sends the remaining gas and residual liquid after reaction into the high-temperature heat exchanger 12 to form a water inlet path, which exchanges heat with the first section of the backwater path from the water tank 16 to form preheated water at 550-650°C, which is sent into the second reactor 8;

[0061] S14, the water inlet path after the first heat exchange is sent into the medium-temperature reactor 13, which exchanges heat with the second section of the backwater path from the water tank in the shell side of the medium-temperature heat exchanger to form preheated water at 300-400°C, which is sent into the first reactor 6;

[0062] S15, the water inlet path after the second heat exchange is sent into the low-temperature heat exchanger 14, which continues to exchange heat with the third section of the backwater path from the water tank in the shell side of the low-temperature heat exchanger to form preheated water at 100-200°C, which is sent into the caustic mixing device 11.

[0063] S16, the liquid in the heat exchanger group is sent into the gas-liquid separator 15, the liquid phase in the gas-liquid separator 15 flows into the water tank 16, and the gas phase realizes the separation of hydrogen and carbon dioxide through the hydrogen separator 18.

[0064] The material of the application has wide applicability, and any biomass mainly composed of lignocellulose can be used, and excrement or municipal sludge can also be directly used as the material, realizing harmless treatment and resource utilization of waste biomass. The pulping temperature, the amount of added alkaline substances and the pulping time are all low, and the original components of the material are complete. The preparation of high-concentration uniform slurry is realized, and the material surface is also loaded with metal ions, improving the catalytic effect.

[0065] The application realizes the recycling of alkali salt based on a pulping device and a causticizing device, greatly improves the economy of the pulping process, uses the physicochemical properties of supercritical water to realize two-step gasification, realizes alkali salt recovery and macromolecular depolymerization in a first reactor based on the supercritical water liquefaction principle, realizes efficient gasification of lignocellulosic biomass in a second reactor, and ensures the efficiency of the system gasification. The application adopts multiple heat exchangers for staged heat exchange for different equipment, so that the heat recovery is maximized and rationalized. The application realizes efficient resource utilization of waste through high-concentration slurry preparation, alkali salt recovery, multi-stage gasification and multi-stage heat recovery, greatly improves the gasification efficiency of the supercritical water gasification system of lignocellulosic biomass, reduces the operation cost and investment cost, and makes the gasification system more reasonable and economical.

[0066] The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A supercritical water gasification system for hydrogen production suitable for high concentration lignocellulosic biomass, characterized in that, The system comprises a pulping device (4), the pulping device (4) is connected with a first reactor (6), the first reactor (6) is connected with a second reactor (8), the second reactor (8) is connected with an oxidation device (10), the oxidation device (10) is connected with a tube pass of a heat exchanger group, the tube pass of the heat exchanger group is connected with a gas-liquid separator (15), the gas-liquid separator (15) is connected with a water tank (16) and a hydrogen separator (18), the pulping device (4) is connected with a storage device (2), and the oxidation device (10) is connected with an oxygen production device (9); The inorganic salt outlet of the first reactor (6) is connected with a caustic mixing device (11), and the caustic mixing device (11) is connected with the pulping device (4); The heat exchanger group sends liquid with different temperatures in the shell pass into corresponding caustic mixing devices (11), first reactors (6) and second reactors (8); The water tank (16) is connected with the inlets of the pulping device (4), the first reactor (6) and the second reactor (8); The first pressurizing device (3) is arranged between the storage device (2) and the pulping device (4), the second pressurizing device (5) is arranged between the pulping device (4) and the first reactor (6), the third pressurizing device (7) is arranged between the first reactor (6) and the second reactor (8), and the outer walls of the pulping device (4), the first reactor (6) and the second reactor (8) are provided with heaters.

2. The system for hydrogen production by supercritical water gasification of high concentration lignocellulosic biomass according to claim 1, wherein, The pulping device (4) is connected with a gas pump (1).

3. The system for hydrogen production by supercritical water gasification of high concentration lignocellulosic biomass according to claim 1, wherein, The heat exchanger group comprises a high-temperature heat exchanger (12), a medium-temperature heat exchanger (13) and a low-temperature heat exchanger (14) connected in sequence in the tube pass, the tube pass inlet of the high-temperature heat exchanger (12) is connected with the oxidation device (10), the tube pass outlet of the low-temperature heat exchanger (14) is connected with the gas-liquid separator (15), the water tank (16) is connected with the shell pass inlets of the high-temperature heat exchanger (12), the medium-temperature heat exchanger (13) and the low-temperature heat exchanger (14), and the shell pass outlets of the high-temperature heat exchanger (12), the medium-temperature heat exchanger (13) and the low-temperature heat exchanger (14) are connected with the second reactor (8), the first reactor (6) and the caustic mixing device (11) respectively.

4. The system for hydrogen production by supercritical water gasification of high concentration lignocellulosic biomass according to claim 1 or 3, characterized in that, The circulating water pump (17) is arranged between the water tank (16) and the heat exchanger group.

5. A method of operating a system for hydrogen production by supercritical water gasification of high concentration lignocellulosic biomass according to claim 1, characterized in that, The method comprises the following steps: The water tank (16) is opened, and water flows into the first reactor (6) and the second reactor (8) through the heat exchanger group of the backwater path; The first reactor (6) and the second reactor (8) are heated to a reaction temperature, the preheated water of the first reactor (6) and the second reactor (8) is heated to a supercritical temperature, and the internal pressure of the first reactor (6) and the second reactor (8) is controlled to reach a supercritical pressure; The alkaline substance required for pulping is mixed with the material in the storage device (2), is pressurized and then is sent into the pulping device (4) through the first pressurizing device (3); The gas pump (1) provides an initial pressure required for pulping to the pulping device (4), so that the water in the pulping device (4) exists in a liquid state; The outer wall of the pulping device (4) is heated, the alkaline substance realizes hydrolysis of a macromolecular structure in the pulping device (4) and is fused with water to form a high-concentration slurry, at the same time, inorganic salts generated by the alkaline substance and carbon dioxide are dissolved in the slurry, and metal ions in the alkaline substance are loaded on the surface of a small-molecule structure of biomass. The high-concentration slurry and the generated gas flow out of the outlet of the slurry preparation device (4), and are pressurized by the second pressurizing device (5) and then enter the first reactor (6); The speed of the high-concentration slurry and the gas flowing into the first reactor (6) is controlled, and the reaction time of the high-concentration slurry in the first reactor (6) is adjusted; The inorganic salt in the high-concentration slurry is in the form of a high-concentration salt solution from the outlet of the first reactor (6) to the causticizing mixing device (11) under the trans-critical or low-temperature supercritical working condition; The calcium hydroxide in the causticizing mixing device (11) reacts with the low-temperature salt solution to generate calcium carbonate precipitate and alkali solution, which is sent to the slurry preparation device (4) to realize the recycling use of the alkaline substance; The slurry after the reaction in the first reactor (6) is pressurized by the third pressurizing device (7) and then enters the second reactor (8) to start gasification; The liquid and the generated gas after the reaction in the second reactor (8) flow into the oxidation device (10), and the oxygen preparation device (9) injects oxygen into the oxidation device (10); The remaining gas and the residual liquid after the reaction in the oxidation device (10) are sent to the heat exchanger group, and the water in the water tank (16) is sent to the heat exchanger group to perform heat exchange in the heat exchanger group; The liquid at different temperatures in the heat exchanger group is sent to the corresponding causticizing mixing device (11), the first reactor (6), and the second reactor (8); The liquid in the heat exchanger group is sent to the gas-liquid separator (15), the liquid phase in the gas-liquid separator (15) flows into the water tank (16), and the gas phase passes through the hydrogen separator (18) to realize the separation of hydrogen and carbon dioxide.

6. The method of claim 5, wherein the supercritical water gasification system for hydrogen production from high concentration lignocellulosic biomass is characterized in that, The alkaline substance is soda ash or a strong alkali weak acid salt, and the addition amount of the alkaline substance accounts for 10%–40% of the slurry in the first reactor (6).

7. The method of claim 5, wherein the supercritical water gasification system for hydrogen production from high concentration lignocellulosic biomass is characterized in that, The remaining gas and the residual liquid after the reaction in the oxidation device (10) flow out and are sent to the high-temperature heat exchanger (12) to form a water inlet path, and perform heat exchange with the first section of the backwater path from the water tank (16) to form preheated water at 550°C–650°C, which is sent to the second reactor (8); The water inlet path after the first heat exchange is sent to the medium-temperature reactor (13) to continue heat exchange with the second section of the backwater path from the water tank (16) to form preheated water at 300°C–400°C, which is sent to the first reactor (6); The water inlet path after the second heat exchange is sent to the low-temperature heat exchanger (14) to continue heat exchange with the third section of the backwater path from the water tank (16) to form preheated water at 100°C–200°C, which is sent to the causticizing mixing device (11).

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