Study On Concentrated Solar-driven Thermochemical Fuel Production

Since the environment pollution(such as Green House effect,air pollution)and energy security issues are more and more serious,caused by the large-scale use of fossil energy.It is urgently needed for clean energy to replace fossil energy partially or completely.Solar energy is a kind of renewable energy,which is abundant and clean.However,solar energy utilization still faces the severe problems of low efficiency,high cost and instability.This is attributed to the intermittent and unstable characteristics of solar energy and the incompleteness of the thermodynamic theory on solar energy utilization.Supported by the key project of National Natural Science Foundation of China and National Key Research,this paper has explored the thermodynamic theory of high-and medium-temperature solar thermochemical system and analyzed the essential problem of improving solar-chemical efficiency in solar thermochemistry utilization.Then,based on the solar simulator,the methane reforming and H2O/CO2 splitting experimental studies are carried out using a laboratory-scale reactor.The main contents and conclusions of this paper are as follows:1.Based on the theory of energy level,the mechanism of energy conversion and loss in solar-chemical energy process is explored.The T-S analysis method is used to analyze the solar thermolysis of CO2 and H2O,and the influence of key parameters(such as concentration ratio,temperature,pressure and operation mode)on system efficiency in solar thermochemistry process are investigated.In order to reduce the irreversible loss and improve the solar-thermal energy level,several specific measures for improving solar-chemical efficiency are proposed which also can provide guidance for the design of reactor.2.Thermodynamic and experimental studies of solar methane reforming are carried out.Firstly,a new perovskite catalyst is prepared for accelerating reaction rate and reducing reaction temperature.Compared with temperature(e.g.,850?)of methane reforming using traditional catalyst,the temperature can be lowered to 750?.Secondly,based on multi-physics coupling and analysis method,a numerical reactor model has been established,and the methods for homogenizing reactor temperature distribution and improving solar energy utilization rate are proposed.The solar-chemical efficiency can reach 59.16%in theory with 90%heat recovery,which also provided useful information for the design of the reactor.Finally,a 2kW solar methane reforming reactor is built.The influences of key operating parameters on the system efficiency,such as catalyst type,temperature and water-carbon ratio have been analyzed,and the optimal catalyst type and reactor operating parameters are obtained.The experimental solar-chemical efficiency of 39.46%is obtained,which has reached the world's advanced level.3.In the theoretical study of solar thermolysis of CO2 and H2O,the oxygen removal method of chemical chain is studied for reducing the energy consumption.The oxygen removal efficiency of chemical chain method is 5.70%,which is about two orders of magnitude higher than that of traditional methods,and the solar thermolysis system can achieve?15%solar-chemical efficiency in theory with considering the actual heat loss and the properties of oxygen carrier(CeO2).In the experimental study of solar thermolysis of CO2 and H2O,a reticulated porous ceramic foam-type structure with made of ceria is firstly fabricated.Secondly,a multi-physics coupling model is established to optimize the internal geometry of the reactor.Finally,the reactor and platform of solar thermolysis of CO2 and H2O are built for experimental research.In the experimental study,the methods of improving the solar-chemical efficiency are explored by the microscopic design of the oxygen carrier and the optimization of the operating parameters.The experimental solar-chemical efficiency of 1.30%is obtained,which validates the feasibility of solar thermolysis fuel production at the reactor level.4.A 70-kW indoor solar simulator for concentrating and non-concentrating solar applications is designed and built.The solar simulator can produce concentrated high-flux,medium-flux and non-concentrated quasi-collimated light with continuously adj ustable power output.Within a 60 mm-diameter circular target on the focal plane,the measured peak and mean radiative fluxes are 9200 kW/m2 and 5100 kW/m2,respectively.For a 4m×3m rectangular area illuminated by quasi-collimated light,the measured radiative flux,half divergence angle,and uniformity of the light are 0.94 kW/m2,1.3°,and 92%,respectively.The key parameters of this solar simulator have reached the world's advanced level.The solar simulator also has the advantages of high stability and good repeatability,which can provide constant solar radiation and simulate the variation of outdoor solar radiation.It provides a universal research platform for a wide range of solar energy technologies,such as solar thermal,solar thermochemical,solar photovoltaics and photocatalysis(with a minor upgrade of the spectrum).Moreover,by adjusting the output power of the solar simulator,the experimental process can be accurately controlled to meet the experimental requirement of solar thermochemical reactors.