Energy Conversion Principles And Experimental Validation For Solar Fuels

Constructing effective mode of using fossil fuels and developing solar energy and biomass energy are effective ways to achieve the sustainable development both of energy and environment and of China's economy.Supported by the National Key Project of China(No.:90210032),this paper focused on the promotion of efficient use of fossil fuels and the exploitation of solar energy.The major aims of this research are to propose the thermodynamic mechanisms of energy cascade utilization for fossil fuels and the principles of energy conversion for solar fuels on the bassis of thermodynamic methods for quantifying energy quality,and to validate and demonstrate the principles by computer simulations and experimental studies of methanol decomposition powered by solar energy.The main contents are as follows:First,a method of energy quality was proposed based on the energy quality factory.Taking direct and indirect combustions routes of methane and methanol as examples,the processes of fossil fuels releasing energy were studied.And the thermodynamic mechanisms of energy cascade utilization for fossil fuels and the principles of energy conversion for solar fuels were proposed. Based on the reference state of exergy,a calculation method of the standard enthalpy of pure species was established.And a thermodynamic analysis method of the energy quality,calledα-H-εdiagram,was then proposed.Applying to the method,taking the direct combustuion of methane, the indirect combustion of methane after steam refoming,and the indirect combustuion of methane after CO₂ reforming as examples,the process of releasing energy were studied.It was found that the working abilities of intermediate fuels produced by steam reforming and CO₂ reforming of methane increase 21%and 35%respectively,when compared with methane. The reducing values of the energy quality factors of the intermediate fuels in their combustuions are smaller than that of methane.The exergy losses are also smaller.The irreversibilities of producing intermediate fuels and of the total using energy processes are smiler.Producing intermediate fuels increases their working abilities.The low grad heat using in producing process can be from theirowns system or from others.When the heat is solar thermal energy, the intermediate fuels are called solar fuels.The thermodynamic principles of energy conversion for solar energy were clarified.The irreversibilities of producing solar fuels and of the total using energy process are smiler,and the working abilities of solar fuels are higher,compared with fossil fuels.Second,taking methanol decomposition driven by solar energy as an example,computer simulations and experiment studies in a non-isothermal reactor were carried out to validate the principle of solar fuels. A procedure for analyzing the performance of non-isothermal solar reactors for methanol decomposition was developed,based on a model of thermal loss from direct steam generation collectors and on a comprehensive kinetic model of methanol decomposition employing BASF K3-110 catalyst. The converbility tends to 100%at the appropriate quantities of feeds.The reactor can provide 385-875 K solar thermal energy.Directly feeding the methanol into the catalyst bed was propitious.The reaction temperature tends constant which depends on the characters of solar energy donation and heat acception.The system efficiency increases slightly with the increasing of radiation intensity.The efficiencies are from55%to 58%.An original 5 kW middle temperature solar receiver/reactor prototype positioned along the focal line of one-axis parabolic trough concentrator was manufactured.It supplied 353-573 K heat.Experimental tests were conducted under solar radiation intensity 280-750 W·m^-2,and methanol feeding rate 0.9-4.5 dm³Â·h^-1.The convertibility of methanol yielded 0.50-0.95.The efficiency of solar thermal energy conversion to chemical energy reached 30%-60%.The exergy regeneration ratio reached 7%-23%.In the end,a new biodiesel production process driven by solar utility was proposed based on the experiments of transesterification reaction and refining at vacuum.In the transesterification reaction,the feeds are crude rapeseed oil and crude methanol.The experiments were carried out at pressure higher than the atmospheric pressure.Two processes on an 8000 t·a^-1 scale powered by solar utility facilities and fuels utility facilities were separately simulated by using Aspen Plus.The fossil fuel consumption saved amounts to 798 tonnes of standard coal and reduced 2926 tonnes of CO₂ emission every year.The renewability index of the biodiesel production process with solar utility facilities is 99.9%.This work developed the thermodynamic evaluation method of energy quality,studied the mechanism of energy cascade utilization for fossil fuels, and validated the significance and the feasibility of solar fuels by taking methanol as an example.