Study On SnO₂/Sn/CH₄ Solar Thermochemical Cycle Energy Storage Characteristics

With the rapid development of economy and society,the overall energy consumption of our country is also increasing rapidly.While coal,petroleum and other fossil fuels meet the huge energy demand of our country,they also bring a series of serious environmental pollution problems.As an inexhaustible and inexhaustible clean and renewable energy,solar energy is an important energy source that can effectively replace traditional fossil energy.However,due to large fluctuations and other reasons,it needs to be combined with heat storage systems to achieve sustainable and stable applications.In this paper,SnO₂/Sn/CH₄was used as the reaction material to carry out a metal oxide methane thermochemical cycle,and the feasibility of the solar thermochemical cycle for heat storage was analyzed.For the SnO₂/Sn/CH₄solar thermochemical cycle system,systematic research on mechanism,oxidation-reduction kinetics,two-step decomposition,cycle characteristics and other aspects are carried out.Firstly,using the first-principles calculation method of density functional theory,using the DMol³module and the CASTEP module in Materials Studio 8.0 software,the unit cell model of the SnO₂/CH₄reduction reaction is constructed and the first-principles calculation of the system-related energy is used to construct SnO₂with the molecular crystal structure of CH₄,the microscopic reaction path is studied.For each possible reaction path,the path reaction energy and energy barrier are calculated,and the hydrogen atom reaction path in CH₄is first to reduce SnO₂,and then carbon to reduce SnO₂.Then,the reaction of methane molecule tin dioxide crystal is analyzed,and the energy barrier and reaction energy required for four dissociation of hydrogen and the generation of H₂and CO are obtained by simulation calculation.In each dissociation step,methane dissociates H energy for the second time.The barrier is 52.868 kcal/mol,which is the reaction rate limiting step,that is,the speed step.In order to verify the feasibility of the SnO₂/Sn/CH₄solar thermal chemical cycle reaction,a corresponding experimental platform was built,the experimental content and scheme were designed,and the reduction reaction of the thermal storage cycle was experimentally studied,and the reaction temperature and gas concentration were obtained.The influence law of reaction products:as the temperature rises,the obtained H₂concentration and CO concentration become larger and larger;as the proportion of methane in the gas increases,the H₂concentration and CO concentration produced by the reaction increase.The working conditions are CH₄0.2 L/min and N₂0.8 L/min,The maximum H₂concentration reaches 2338 ppm at a temperature of 700℃,and the maximum reaches 23543 ppm at a temperature of 850℃;the maximum CO concentration reaches 85 ppm at a temperature of700℃,The maximum temperature is 556 ppm at 850℃.Finally,using HSC Chemistry6.0 software to simulate the thermochemical cycle reaction system of SnO₂/Sn/CH₄at different temperatures,pressures,and material ratios,the thermodynamic balance and cycle efficiency calculations were performed.The effects of oxidation-reduction temperature,reactant ratio,gas pressure in the reduction reactor on the balance of material components,energy upgrade factor U,and solar fuel conversion efficiency are obtained.When R=2,X=2,T_red=1260℃,T_oxi=25℃,the maximum solar fuel conversion efficiency of 0.5 can be obtained.The above research provides a theoretical basis for the application of SnO₂/Sn/CH₄solar thermal chemical energy storage cycle system.