Solar-driven energy storage-hydrogen production system and operation method thereof

Abstract

The invention discloses a solar-driven energy storage-hydrogen production system and an operation method thereof.The system selects CaO / CaCO3 as an energy storage medium of a thermochemical energy storage system, and storage and release of solar energy are achieved through the reversible reaction of CaCO3 and CaO; the heat required by the methane steam reforming reaction is provided by a thermochemical energy storage system, and meanwhile, the heat of a hydrogen production product is recycled by a supercritical carbon dioxide Brayton cycle. According to the system, in the heat storage stage, CaCO3 is calcined and decomposed into CaO and CO2 through a solar calcination reactor, CaO is stored at high temperature, and CO2 supplies heat to methane steam reforming reaction. In the heat release stage, CaO and CO2 react to release heat, and the heat is absorbed by excessive CO2 to supply heat to the methane steam reforming reaction. The temperature of a methane steam reforming product is high, and the methane steam reforming product is used for heating supercritical carbon dioxide to expand and do work. When solar energy is sufficient, the energy storage process and the energy release process work simultaneously, when solar energy is insufficient, only the energy release process works, and continuous and stable operation of the system is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar thermochemical hydrogen production, and in particular relates to a solar-driven energy storage-hydrogen production system and an operation method thereof. Background Art

[0002] Hydrogen energy is a secondary energy source with abundant sources, zero carbon and great potential. It is of great significance to build a clean, low-carbon, safe and efficient energy system. According to the different levels of carbon emissions in the hydrogen production process, hydrogen can be divided into green hydrogen, blue hydrogen and gray hydrogen. Among them, the cost of green hydrogen and blue hydrogen is relatively high, and the current hydrogen energy supply is still dominated by gray hydrogen. Gray hydrogen is produced from fossil energy such as coal and natural gas. The cost of hydrogen production is low, but it will emit a large amount of carbon dioxide. Among various fossil energy hydrogen production technologies, the methane hydrogen production technology route is mature and natural gas reserves are abundant. The methane hydrogen production process can be mainly divided into methane steam reforming, methane dry reforming, methane cracking and methane partial oxidation. Among them, methane steam reforming technology is relatively mature and widely used in commercial applications.

[0003] Methane steam reforming is a strong endothermic reaction, and a large amount of heat is consumed in the hydrogen production process. Traditional methane steam reforming reactions mainly rely on fossil energy combustion for heat supply, but this will further increase carbon emissions in the hydrogen production process. Solar energy is a clean, zero-carbon energy source. Using solar energy instead of fossil energy combustion to heat the methane steam reforming reaction can effectively reduce carbon emissions in the hydrogen production process. However, due to factors such as the environment and weather, solar energy also has prominent shortcomings. When solar energy is sufficient, it cannot be effectively and fully utilized; and when energy is needed, solar energy input cannot meet the requirements, and the imbalance between energy supply and demand is extremely serious. Coupling energy storage technology can effectively improve this problem. Therefore, in order to ensure the safe and stable operation of the hydrogen production system and improve its continuous hydrogen production and supply capabilities, it is urgent to transform and upgrade the methane steam reforming hydrogen production system. Summary of the invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a solar-driven energy storage-hydrogen production system and its operation method. The system selects the CaO / CaCO3 material system as the energy storage medium of the thermochemical energy storage system, and uses the reversible thermochemical reaction of CaCO3 and CaO to realize the storage and release of solar energy; the heat required for the methane steam reforming reaction is provided by the thermochemical energy storage system, and the supercritical carbon dioxide Brayton cycle is coupled to recycle the heat of the hydrogen production product. In the heat storage stage, the system first uses a solar calcination reactor to calcine and decompose CaCO3 to generate CaO and CO2, and the generated CaO is stored in a calcium oxide storage tank, and the generated CO2 is used to heat the methane hydrogen reforming reaction. In the heat release stage of the system, the stored CaO and CO2 react in the carbonation reactor to release heat, and this part of the heat is absorbed by the excess CO2 to heat the methane steam reforming reaction. The product temperature of methane steam reforming is relatively high, and it is used to heat the supercritical carbon dioxide to expand and do work, thereby improving the energy utilization efficiency of the system. When there is sufficient solar energy, the energy storage and release processes work simultaneously. When there is no solar energy, only the release process works, ensuring the continuous and stable operation of the system.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A solar-driven energy storage-hydrogen production system, comprising a methane steam reforming system and a CaO / CaCO3 thermochemical energy storage system and a supercritical carbon dioxide Brayton cycle system coupled thereto;

[0007] The methane steam reforming system comprises a methane storage tank 12, a methane booster pump 13, a methane heater 14, a water storage tank 16, a water pump 17, a steam generator 18, a mixer 15, a methane steam reforming reactor 19, a carbon dioxide heater 20, a product cooler 21, a steam-water separator 22, a gas product storage tank 23 and a liquid product storage tank 24; the outlet of the methane storage tank 12 is connected to the inlet of the methane heater 14 via the methane booster pump 13, the outlet of the water storage tank 16 is connected to the inlet of the steam generator 18 via the water pump 17; the outlet of the methane heater 14 is connected to the inlet of the methane heater 14 ...; the outlet of the methane product storage tank 12 is connected The outlet of the steam generator 18 is connected to the inlet of the mixer 15 respectively, and the outlet of the mixer 15 is connected to the reactant inlet of the methane steam reforming reactor 19; the product outlet of the methane steam reforming reactor 19 is connected to the hot side inlet of the carbon dioxide heater 20, and the hot side outlet of the carbon dioxide heater 20 is connected to the product cooler 21; the outlet of the product cooler 21 is connected to the inlet of the steam-water separator 22, and the outlet fluid of the steam-water separator 22 is divided into two streams, one of which is connected to the gas product storage tank 23, and the other is connected to the liquid product storage tank 24;

[0008] The CaO / CaCO3 thermochemical energy storage system is composed of a heat storage circuit and a heat release circuit; the heat storage circuit includes a heliostat 2, a solar calcination reactor 1, a calcium oxide storage tank 3, a carbon dioxide gas bag 10, a high-pressure cooler 9, a compressor 8 and a low-pressure cooler 7; the heat release circuit includes a carbonation reactor 4, a calcium carbonate-carbon dioxide heat exchanger 5, a calcium carbonate storage tank 6, a carbon dioxide control valve 11, a carbon dioxide gas bag 10, a high-pressure cooler 9, a compressor 8 and a low-pressure cooler 7; during heat storage, solar energy is collected by the heliostat 2 and received by the solar calcination reactor 1; the outlet of the calcium carbonate storage tank 6 is connected to the reactant inlet of the solar calcination reactor 1, and the product outlet of the solar calcination reactor 1 is divided into two paths, one of which is connected to the inlet of the calcium oxide storage tank 3, and the other is connected to the carbon dioxide inlet of the methane steam reforming reactor 19, and the carbon dioxide outlet of the methane steam reforming reactor 19 is connected to the reactant inlet of the solar calcination reactor 1. The low-pressure cooler 7 is connected to the inlet of the compressor 8, and the outlet of the compressor 8 is connected to the inlet of the carbon dioxide air bag 10 via the high-pressure cooler 9; when releasing heat, the outlet of the calcium oxide storage tank 3 is connected to the calcium oxide inlet of the carbonation reactor 4, the outlet carbon dioxide control valve 11 of the carbon dioxide air bag 10 is connected to the carbon dioxide working medium inlet of the calcium carbonate-carbon dioxide heat exchanger 5, and the carbon dioxide working medium outlet of the calcium carbonate-carbon dioxide heat exchanger 5 is connected to the carbon dioxide working medium inlet of the carbonation reactor 4; the outlet of the carbonation reactor 4 is divided into two routes, one route is connected to the calcium carbonate storage tank 6 after passing through the calcium carbonate-carbon dioxide heat exchanger 5, and the other route is connected to the carbon dioxide inlet of the methane steam reforming reactor 19, the carbon dioxide outlet of the methane steam reforming reactor 19 is connected to the inlet of the compressor 8 via the low-pressure cooler 7, and the outlet of the compressor 8 is connected to the inlet of the carbon dioxide air bag 10 via the high-pressure cooler 9;

[0009] The supercritical carbon dioxide Brayton cycle system includes a carbon dioxide heater 20, a carbon dioxide turbine 25, a generator 31, a high-temperature regenerator 26, a low-temperature regenerator 27, a precooler 28, a main compressor 29 and a recompressor 30; the outlet of the carbon dioxide turbine 25 is connected to the hot side inlet of the low-temperature regenerator 27 through the high-temperature regenerator 26, and the hot side outlet of the low-temperature regenerator 27 is divided into two paths, one of which is connected to the inlet of the main compressor 29 after passing through the precooler 28, and the other is connected to the inlet of the recompressor 30; the outlet of the main compressor 29 is connected to the cold side inlet of the low-temperature regenerator 27, and the cold side outlet of the low-temperature regenerator 27 is connected to the cold side inlet of the high-temperature regenerator 26 after merging with the outlet of the recompressor 30; the cold side outlet of the high-temperature regenerator 26 is connected to the carbon dioxide working medium inlet of the carbon dioxide heater 20, and the carbon dioxide working medium outlet of the carbon dioxide heater 20 is connected to the carbon dioxide turbine 25, driving the generator 31 to output power to the outside.

[0010] Furthermore, the operating temperature range of the CaO / CaCO3 thermochemical energy storage system is 800-1000°C, and the operating temperature of the methane steam reforming system is 800-900°C.

[0011] Furthermore, the carbon dioxide heater 20, the high temperature regenerator 26, and the low temperature regenerator 27 are all gas-gas heat exchangers; and the calcium carbonate-carbon dioxide heat exchanger 5 is a gas-solid heat exchanger.

[0012] Furthermore, the carbon dioxide gas bag 10 is made of elastic material, and its volume can change with the pressure, and the carbon dioxide is stored at room temperature and low pressure.

[0013] Furthermore, the heat required by the methane steam reforming reactor 19 is provided by a CaO / CaCO3 thermochemical energy storage system. When storing heat, it is provided by high-temperature carbon dioxide generated by calcining calcium carbonate; when releasing heat, it is provided by the heat released by the reaction of calcium oxide and carbon dioxide, and this part of the heat is carried by excess carbon dioxide.

[0014] Furthermore, in order to promote the reaction of calcium oxide and carbon dioxide and improve the energy storage efficiency of the CaO / CaCO3 thermochemical energy storage system, the calcium oxide storage tank 3 is a high-temperature, insulated storage tank, and the storage temperature of calcium oxide is the reaction temperature of the solar calciner, and it is not cooled; at the same time, carbon dioxide needs to be preheated by the calcium carbonate-carbon dioxide heat exchanger 5.

[0015] Furthermore, in order to improve the energy utilization efficiency of the system, the hot side fluid of the carbon dioxide heater 20 is the high-temperature product of the methane steam reforming reaction, and the cold side fluid is supercritical carbon dioxide. The supercritical carbon dioxide Brayton cycle adopts a two-stage regenerative heater and a recompression cycle.

[0016] An operation method of a solar-driven energy storage-hydrogen production system is as follows:

[0017] 1) When there is sufficient solar energy during the day, the CaO / CaCO3 thermochemical energy storage system stores and releases heat at the same time; the solar calcination reactor 1 of the heat storage loop receives solar energy to calcine calcium carbonate, and the generated high-temperature carbon dioxide provides heat for the methane steam reforming reaction; part of the generated calcium oxide is stored in the calcium oxide storage tank 3, and the other part enters the carbonation reactor 4 of the heat release loop; at the same time, the carbon dioxide control valve 11 of the heat release loop is opened, and the carbon dioxide in the carbon dioxide gas bag 10 also enters the carbonation reactor 4 after being heated by the calcium carbonate-carbon dioxide heat exchanger 5, and reacts with the calcium oxide to release heat; this part of the heat is carried by the excess carbon dioxide to provide heat for the methane steam reforming reaction; at this time, the methane steam reforming system is heated by the heat storage loop and the heat release loop at the same time, and the supercritical carbon dioxide is heated by the methane steam reforming reaction product through the carbon dioxide heater 20, and the system produces hydrogen energy and electricity at the same time;

[0018] 2) When there is no solar energy at night or on cloudy days, the energy storage circuit of the CaO / CaCO3 thermochemical energy storage system stops working and only the heat release circuit operates; the carbon dioxide control valve 11 of the heat release circuit is opened, and the carbon dioxide in the carbon dioxide gas bag 10 is heated by the calcium carbonate-carbon dioxide heat exchanger 5 and reacts with the calcium oxide stored in the calcium oxide storage tank 3 in the carbonation reactor 4 to release heat; this part of the heat is carried by the excess carbon dioxide to provide heat for the methane steam reforming reaction; at this time, the methane steam reforming system is only heated by the heat release circuit, and the supercritical carbon dioxide is heated by the methane steam reforming reaction product through the carbon dioxide heater 20, and the system produces hydrogen energy and electrical energy at the same time.

[0019] Furthermore, it is assumed that there are 8 hours of sufficient solar energy in 24 hours a day; therefore, the operating time of the heat storage circuit is only 8 hours a day, while the heat release circuit can operate for 24 hours a day; in order to ensure the stable operation of the system, it is necessary to calculate the mass conservation of calcium carbonate and calcium oxide; according to the operating time of the heat storage circuit and the heat release circuit, it can be calculated that the mass flow rate of calcium oxide at the inlet of the calcium oxide storage tank 3 is 3 times the mass flow rate of calcium oxide at the outlet, and the mass flow rate of calcium carbonate at the outlet of the calcium carbonate storage tank 6 is 3 times the mass flow rate of calcium carbonate at the inlet.

[0020] Compared with the prior art, the advantages of the present invention are as follows:

[0021] (1) The present invention couples a methane steam reforming hydrogen production system with a thermochemical energy storage system based on a calcium oxide-calcium carbonate cycle, uses solar energy as a heat source to calcine calcium carbonate, and converts low-density, unstable solar energy into high-density, stable chemical energy stored in calcium oxide. The methane steam reforming hydrogen production system is heated by the thermochemical energy storage system, which effectively copes with the fluctuation of solar energy and ensures the stable and continuous operation of the hydrogen production system;

[0022] (2) The present invention utilizes the high-temperature product of methane steam reforming to heat supercritical carbon dioxide, which then expands in a turbine to perform work. At the same time, a two-stage heat recovery heater is used to recycle the heat of the low-pressure supercritical carbon dioxide at the turbine outlet, thereby realizing the cascade utilization of energy and improving the energy utilization efficiency.

[0023] (3) The present invention enables the methane steam reforming system to operate continuously for 24 hours by coupling the thermochemical energy storage system, and can ensure the production of hydrogen even at night or on cloudy days. The present invention transforms the methane steam reforming hydrogen production system in a modular form, involving only the heat source part of the methane steam reforming reactor, and can be used in both new systems and existing systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the system of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0026] like Figure 1 As shown, a solar-driven energy storage-hydrogen production system includes a methane steam reforming system and a CaO / CaCO3 thermochemical energy storage system and a supercritical carbon dioxide Brayton cycle system coupled thereto.

[0027] The methane steam reforming system includes a methane storage tank 12, a methane booster pump 13, a methane heater 14, a water storage tank 16, a water pump 17, a steam generator 18, a mixer 15, a methane steam reforming reactor 19, a carbon dioxide heater 20, a product cooler 21, a steam-water separator 22, a gas product storage tank 23 and a liquid product storage tank 24. The outlet of the methane storage tank 12 is connected to the inlet of the methane heater 14 via the methane booster pump 13, and the outlet of the water storage tank 16 is connected to the inlet of the steam generator 18 via the water pump 17. The outlet of the methane heater 14 and the outlet of the steam generator 18 are respectively connected to the inlet of the mixer 15, and the outlet of the mixer 15 is connected to the reactant inlet of the methane steam reforming reactor 19. The product outlet of the methane steam reforming reactor 19 is connected to the hot side inlet of the carbon dioxide heater 20, and the hot side outlet of the carbon dioxide heater 20 is connected to the product cooler 21. The outlet of the product cooler 21 is connected to the inlet of the steam-water separator 22 . The outlet fluid of the steam-water separator 22 is divided into two streams, one of which is connected to the gas product storage tank 23 , and the other is connected to the liquid product storage tank 24 .

[0028] The CaO / CaCO3 thermochemical energy storage system is composed of a heat storage circuit and a heat release circuit. The heat storage circuit includes a heliostat 2, a solar calcination reactor 1, a calcium oxide storage tank 3, a carbon dioxide gas bag 10, a high-pressure cooler 9, a compressor 8 and a low-pressure cooler 7. The heat release circuit includes a carbonation reactor 4, a calcium carbonate-carbon dioxide heat exchanger 5, a calcium carbonate storage tank 6, a carbon dioxide control valve 11, a carbon dioxide gas bag 10, a high-pressure cooler 9, a compressor 8 and a low-pressure cooler 7. During heat storage, solar energy is collected by the heliostat 2 and received by the solar calcination reactor 1. The outlet of the calcium carbonate storage tank 6 is connected to the reactant inlet of the solar calcination reactor 1, and the product outlet of the solar calcination reactor 1 is divided into two paths, one of which is connected to the inlet of the calcium oxide storage tank 3, and the other is connected to the carbon dioxide inlet of the methane steam reforming reactor 19. The carbon dioxide outlet of the methane steam reforming reactor 19 is connected to the inlet of the compressor 8 through the low-pressure cooler 7, and the outlet of the compressor 8 is connected to the inlet of the carbon dioxide gas bag 10 through the high-pressure cooler 9. When releasing heat, the outlet of the calcium oxide storage tank 3 is connected to the calcium oxide inlet of the carbonation reactor 4, the outlet carbon dioxide control valve 11 of the carbon dioxide air bag 10 is connected to the carbon dioxide working medium inlet of the calcium carbonate-carbon dioxide heat exchanger 5, and the carbon dioxide working medium outlet of the calcium carbonate-carbon dioxide heat exchanger 5 is connected to the carbon dioxide working medium inlet of the carbonation reactor 4. The outlet of the carbonation reactor 4 is divided into two routes, one of which is connected to the calcium carbonate storage tank 6 after passing through the calcium carbonate-carbon dioxide heat exchanger 5, and the other is connected to the carbon dioxide inlet of the methane steam reforming reactor 19. The carbon dioxide outlet of the methane steam reforming reactor 19 is connected to the inlet of the compressor 8 through the low-pressure cooler 7, and the outlet of the compressor 8 is connected to the inlet of the carbon dioxide air bag 10 through the high-pressure cooler 9.

[0029] The supercritical carbon dioxide Brayton cycle system includes a carbon dioxide heater 20, a carbon dioxide turbine 25, a generator 31, a high temperature regenerator 26, a low temperature regenerator 27, a precooler 28, a main compressor 29 and a recompressor 30. The outlet of the carbon dioxide turbine 25 is connected to the hot side inlet of the low temperature regenerator 27 through the high temperature regenerator 26, and the hot side outlet of the low temperature regenerator 27 is divided into two paths, one of which is connected to the inlet of the main compressor 29 after passing through the precooler 28, and the other is connected to the inlet of the recompressor 30. The outlet of the main compressor 29 is connected to the cold side inlet of the low temperature regenerator 27, and the cold side outlet of the low temperature regenerator 27 is connected to the cold side inlet of the high temperature regenerator 26 after merging with the outlet of the recompressor 30. The cold side outlet of the high temperature regenerator 26 is connected to the carbon dioxide working medium inlet of the carbon dioxide heater 20, and the carbon dioxide working medium outlet of the carbon dioxide heater 20 is connected to the carbon dioxide turbine 25, driving the generator 31 to output power to the outside.

[0030] As a preferred embodiment of the present invention, the operating temperature range of the CaO / CaCO3 thermochemical energy storage system is 800-1000°C, and the operating temperature of the methane steam reforming system is 800-900°C. The operating temperature zones of the thermochemical energy storage system and the methane steam reforming system are well matched, which reduces the irreversible loss of the system and improves the energy utilization efficiency of the system.

[0031] As a preferred embodiment of the present invention, the carbon dioxide heater 20, the high-temperature regenerator 26, and the low-temperature regenerator 27 are all gas-to-gas heat exchangers, which recycle and utilize the heat of the low-pressure supercritical carbon dioxide, thereby improving the system's cycle power generation efficiency; the calcium carbonate-carbon dioxide heat exchanger 5 is a gas-solid heat exchanger, which uses calcium carbonate to preheat carbon dioxide, promotes the reaction of carbon dioxide and calcium oxide, and improves the efficiency of the energy storage system.

[0032] As a preferred embodiment of the present invention, the carbon dioxide bag 10 is made of elastic material, and its volume can change with the pressure, thereby ensuring the constant pressure of carbon dioxide in the bag; carbon dioxide is stored at room temperature and low pressure.

[0033] As a preferred embodiment of the present invention, the heat required by the methane steam reforming reactor (19) is provided by a thermochemical energy storage system. When storing heat, it is provided by high-temperature carbon dioxide generated by calcining calcium carbonate; when releasing heat, it is provided by the heat released by the reaction of calcium oxide and carbon dioxide, and this part of the heat is carried by excess carbon dioxide. Selecting carbon dioxide as a heat transfer medium can not only promote the conversion of calcium oxide, but also does not require additional gas separation, thereby reducing the energy consumption of the system.

[0034] As a preferred embodiment of the present invention, in order to promote the reaction of calcium oxide and carbon dioxide and improve the energy storage efficiency of the energy storage system, the calcium oxide storage tank 3 is a high-temperature, insulated storage tank, and the storage temperature of calcium oxide is the reaction temperature of the solar calciner, and it is not cooled; at the same time, carbon dioxide needs to be preheated by the calcium carbonate-carbon dioxide heat exchanger 5.

[0035] As a preferred embodiment of the present invention, in order to improve the energy utilization efficiency of the system, the hot side fluid of the carbon dioxide heater 20 is the high-temperature product of the methane steam reforming reaction, and the cold side fluid is supercritical carbon dioxide. The supercritical carbon dioxide Brayton cycle adopts a two-stage regenerative heater and a recompression cycle, which can effectively avoid the "pinch point" problem of the heat exchanger and improve the cycle power generation efficiency of the system.

[0036] like Figure 1 As shown, an operation method of a solar-driven energy storage-hydrogen production system is as follows:

[0037] 1) When there is sufficient solar energy during the day, the thermochemical energy storage system stores and releases heat at the same time. The solar calcination reactor 1 of the heat storage loop receives solar energy to calcine calcium carbonate, and the generated high-temperature carbon dioxide provides heat for the methane steam reforming reaction. Part of the generated calcium oxide is stored in the calcium oxide storage tank 3, and the other part enters the carbonation reactor 4 of the heat release loop; at the same time, the carbon dioxide control valve 11 of the heat release loop is opened, and the carbon dioxide in the carbon dioxide gas bag 10 also enters the carbonation reactor 4 after being heated by the calcium carbonate-carbon dioxide heat exchanger 5, and reacts with calcium oxide to release heat. This part of the heat is carried by excess carbon dioxide to provide heat for the methane steam reforming reaction. At this time, the methane steam reforming system is heated by the heat storage loop and the heat release loop at the same time, and the supercritical carbon dioxide is heated by the methane steam reforming reaction product through the carbon dioxide heater 20, and the system produces hydrogen energy and electrical energy at the same time.

[0038] 2) When there is no solar energy at night or on cloudy days, the energy storage circuit of the energy storage system stops working and only the heat release circuit operates. The carbon dioxide control valve 11 of the heat release circuit is opened, and the carbon dioxide in the carbon dioxide gas bag 10 is heated by the calcium carbonate-carbon dioxide heat exchanger 5 and reacts with the calcium oxide stored in the calcium oxide storage tank 3 in the carbonation reactor 4 to release heat. This part of heat is carried by excess carbon dioxide to provide heat for the methane steam reforming reaction. At this time, the methane steam reforming system is only heated by the heat release circuit, and the supercritical carbon dioxide is heated by the methane steam reforming reaction product through the carbon dioxide heater 20, and the system produces hydrogen energy and electrical energy at the same time.

[0039] Further, it is assumed that there are 8 hours of sufficient solar energy in 24 hours a day. Therefore, the operation time of the heat storage circuit in a day is only 8 hours, while the heat release circuit can run 24 hours a day. In order to ensure the stable operation of the system, it is necessary to calculate the mass conservation of calcium carbonate and calcium oxide. According to the operation time of the heat storage circuit and the heat release circuit, it can be calculated that the calcium oxide mass flow rate at the inlet of the calcium oxide storage tank 3 is 3 times the mass flow rate of the calcium oxide at the outlet, and the calcium carbonate mass flow rate at the outlet of the calcium carbonate storage tank 6 is 3 times the mass flow rate of the calcium carbonate at the inlet.

[0040] The present invention provides a solar-driven energy storage-hydrogen production system, which selects the CaO / CaCO3 material system as the energy storage medium of the thermochemical energy storage system, and uses the reversible thermochemical reaction of CaCO3 and CaO to realize the storage and release of solar energy; the heat required for the methane steam reforming reaction is provided by the thermochemical energy storage system, and the heat of the hydrogen production product is recycled by the supercritical carbon dioxide Brayton cycle. In the heat storage stage, the system first uses a solar calcination reactor to calcine and decompose CaCO3 to generate CaO and CO2, and the generated CaO is stored in a solid storage tank, and the generated CO2 is used to heat the methane hydrogen reforming reaction. In the heat release stage, the stored CaO and CO2 react in the carbonation reactor to release heat, and this part of the heat is absorbed by excess CO2 to heat the methane steam reforming reaction. The product temperature of methane steam reforming is relatively high, and it is used to heat the supercritical carbon dioxide to expand and do work, thereby improving the energy utilization efficiency of the system. When there is sufficient solar energy, the energy storage and energy release processes work simultaneously. When there is no solar energy, only the energy release process works, ensuring the continuous and stable operation of the system.

Claims

1. A solar-driven energy storage-hydrogen production system, characterized in that: The invention comprises a methane steam reforming system and a CaO / CaCO3 thermochemical energy storage system and a supercritical carbon dioxide Brayton cycle system coupled thereto; the methane steam reforming system comprises a methane storage tank (12), a methane booster pump (13), a methane heater (14), a water storage tank (16), a water pump (17), a steam generator (18), a mixer (15), a methane steam reforming reactor (19), a carbon dioxide heater (20), a product cooler (21), a steam-water separator (22), a gas product storage tank (23) and a liquid product storage tank (24); the outlet of the methane storage tank (12) is connected to the inlet of the methane heater (14) via the methane booster pump (13), and the outlet of the water storage tank (16) is connected to the inlet of the methane heater (14) via the water pump. (17) and the inlet of the steam generator (18); the outlet of the methane heater (14) and the outlet of the steam generator (18) are respectively connected to the inlet of the mixer (15), and the outlet of the mixer (15) is connected to the reactant inlet of the methane steam reforming reactor (19); the product outlet of the methane steam reforming reactor (19) is connected to the hot side inlet of the carbon dioxide heater (20), and the hot side outlet of the carbon dioxide heater (20) is connected to the product cooler (21); the outlet of the product cooler (21) is connected to the inlet of the steam-water separator (22), and the outlet fluid of the steam-water separator (22) is divided into two streams, one of which is connected to the gas product storage tank (23) and the other is connected to the liquid product storage tank (24); The CaO / CaCO3 thermochemical energy storage system is composed of a heat storage circuit and a heat release circuit; the heat storage circuit comprises a heliostat (2), a solar calcination reactor (1), a calcium oxide storage tank (3), a carbon dioxide gas bag (10), a high-pressure cooler (9), a compressor (8) and a low-pressure cooler (7); the heat release circuit comprises a carbonation reactor (4), a calcium carbonate-carbon dioxide heat exchanger (5), a calcium carbonate storage tank (6), a carbon dioxide control valve (11), a carbon dioxide gas bag (10), a high-pressure cooler (9), a compressor (8) and a low-pressure cooler (7); during heat storage, solar energy is collected by the heliostat (2) and received by the solar calcination reactor (1); the outlet of the calcium carbonate storage tank (6) is connected to the reactant inlet of the solar calcination reactor (1), and the product outlet of the solar calcination reactor (1) is divided into two paths, one of which is connected to the inlet of the calcium oxide storage tank (3) and the other is connected to the carbon dioxide inlet of the methane steam reforming reactor (19). The carbon dioxide outlet of the methane steam reforming reactor (19) is connected to the reactant inlet of the solar calcination reactor (1). The inlet of the compressor (8) is connected to the low-pressure cooler (7), and the outlet of the compressor (8) is connected to the inlet of the carbon dioxide bag (10) via the high-pressure cooler (9); when releasing heat, the outlet of the calcium oxide storage tank (3) is connected to the calcium oxide inlet of the carbonation reactor (4), the outlet carbon dioxide control valve (11) of the carbon dioxide bag (10) is connected to the carbon dioxide working medium inlet of the calcium carbonate-carbon dioxide heat exchanger (5), and the carbon dioxide working medium outlet of the calcium carbonate-carbon dioxide heat exchanger (5) is connected to the carbon dioxide working medium inlet of the carbonation reactor (4); the outlet of the carbonation reactor (4) is divided into two paths, one path is connected to the calcium carbonate storage tank (6) after passing through the calcium carbonate-carbon dioxide heat exchanger (5), and the other path is connected to the carbon dioxide inlet of the methane steam reforming reactor (19), the carbon dioxide outlet of the methane steam reforming reactor (19) is connected to the inlet of the compressor (8) via the low-pressure cooler (7), and the outlet of the compressor (8) is connected to the inlet of the carbon dioxide bag (10) via the high-pressure cooler (9); The supercritical carbon dioxide Brayton cycle system comprises a carbon dioxide heater (20), a carbon dioxide turbine (25), a generator (31), a high-temperature regenerator (26), a low-temperature regenerator (27), a precooler (28), a main compressor (29) and a recompressor (30); the outlet of the carbon dioxide turbine (25) is connected to the hot side inlet of the low-temperature regenerator (27) via the high-temperature regenerator (26); the hot side outlet of the low-temperature regenerator (27) is divided into two paths, one of which is connected to the inlet of the main compressor (29) after passing through the precooler (28), and the other is connected to the hot side outlet of the low-temperature regenerator (27). One path is connected to the inlet of the recompressor (30); the outlet of the main compressor (29) is connected to the cold side inlet of the low-temperature regenerator (27); the cold side outlet of the low-temperature regenerator (27) and the outlet of the recompressor (30) are combined and then connected to the cold side inlet of the high-temperature regenerator (26); the cold side outlet of the high-temperature regenerator (26) is connected to the carbon dioxide working fluid inlet of the carbon dioxide heater (20); the carbon dioxide working fluid outlet of the carbon dioxide heater (20) is connected to the carbon dioxide turbine (25), driving the generator (31) to output power to the outside.

2. A solar-driven energy storage-hydrogen production system according to claim 1, characterized in that: The operating temperature range of the CaO / CaCO3 thermochemical energy storage system is 800-1000°C, and the operating temperature of the methane steam reforming system is 800-900°C.

3. A solar-driven energy storage-hydrogen production system according to claim 1, characterized in that: The carbon dioxide heater (20), the high-temperature regenerator (26), and the low-temperature regenerator (27) are all gas-to-gas heat exchangers; and the calcium carbonate-carbon dioxide heat exchanger (5) is a gas-to-solid heat exchanger.

4. A solar-driven energy storage-hydrogen production system according to claim 1, characterized in that: The carbon dioxide gas bag (10) is made of elastic material, and its volume can change with pressure. The carbon dioxide is stored at room temperature and low pressure.

5. A solar-driven energy storage-hydrogen production system according to claim 1, characterized in that: The heat required by the methane steam reforming reactor (19) is provided by the CaO / CaCO3 thermochemical energy storage system. When storing heat, it is provided by the high-temperature carbon dioxide generated by the calcination of calcium carbonate; when releasing heat, it is provided by the heat released by the reaction of calcium oxide and carbon dioxide, and this part of the heat is carried by excess carbon dioxide.

6. A solar-driven energy storage-hydrogen production system according to claim 1, characterized in that: In order to promote the reaction of calcium oxide and carbon dioxide and improve the energy storage efficiency of the CaO / CaCO3 thermochemical energy storage system, the calcium oxide storage tank (3) is a high-temperature, insulated storage tank, and the storage temperature of calcium oxide is the reaction temperature of the solar calciner, and it is not cooled; at the same time, carbon dioxide needs to be preheated by a calcium carbonate-carbon dioxide heat exchanger (5).

7. A solar-driven energy storage-hydrogen production system according to claim 1, characterized in that: In order to improve the energy utilization efficiency of the system, the hot side fluid of the carbon dioxide heater (20) is the high-temperature product of the methane steam reforming reaction, and the cold side fluid is supercritical carbon dioxide.

8. A solar-driven energy storage-hydrogen production system according to claim 1, characterized in that: The supercritical carbon dioxide Brayton cycle adopts a two-stage regenerative heater and a recompression cycle.

9. The method for operating a solar-driven energy storage-hydrogen production system according to any one of claims 1 to 8, characterized in that: 1) When there is sufficient solar energy during the day, the CaO / CaCO3 thermochemical energy storage system stores and releases heat at the same time; the solar calcination reactor (1) of the heat storage loop receives solar energy to calcine calcium carbonate, and the generated high-temperature carbon dioxide provides heat for the methane steam reforming reaction; part of the generated calcium oxide is stored in the calcium oxide storage tank (3), and the other part enters the carbonation reactor (4) of the heat release loop; at the same time, the carbon dioxide control valve (11) of the heat release loop is opened, and the carbon dioxide in the carbon dioxide gas bag (10) is heated by the calcium carbonate-carbon dioxide heat exchanger (5) and also enters the carbonation reactor (4), reacting with the calcium oxide to release heat; this part of the heat is carried by the excess carbon dioxide to provide heat for the methane steam reforming reaction; at this time, the methane steam reforming system is heated by the heat storage loop and the heat release loop at the same time, and the supercritical carbon dioxide is heated by the methane steam reforming reaction product through the carbon dioxide heater (20), and the system produces hydrogen energy and electrical energy at the same time; 2) When there is no solar energy at night or on cloudy days, the energy storage circuit of the CaO / CaCO3 thermochemical energy storage system stops working and only the heat release circuit operates; the carbon dioxide control valve (11) of the heat release circuit is opened, and the carbon dioxide in the carbon dioxide gas bag (10) is heated by the calcium carbonate-carbon dioxide heat exchanger (5) and reacts with the calcium oxide stored in the calcium oxide storage tank (3) in the carbonation reactor (4) to release heat; this part of the heat is carried by the excess carbon dioxide to provide heat for the methane steam reforming reaction; at this time, the methane steam reforming system is only heated by the heat release circuit, and the supercritical carbon dioxide is heated by the methane steam reforming reaction product through the carbon dioxide heater (20), and the system produces hydrogen energy and electrical energy at the same time.

10. The method for operating a solar-driven energy storage-hydrogen production system according to claim 9, characterized in that: It is assumed that there are 8 hours of sufficient solar energy in a 24-hour day; therefore, the operation time of the heat storage circuit is only 8 hours in a day, while the heat release circuit operates for 24 hours in a day; in order to ensure the stable operation of the system, it is necessary to calculate the mass conservation of calcium carbonate and calcium oxide; according to the operation time of the heat storage circuit and the heat release circuit, it can be calculated that the mass flow rate of calcium oxide at the inlet of the calcium oxide storage tank (3) is 3 times the mass flow rate of calcium oxide at the outlet, and the mass flow rate of calcium carbonate at the outlet of the calcium carbonate storage tank (6) is 3 times the mass flow rate of calcium carbonate at the inlet.

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