Theory And System Study Of Mid-temperature Solar Methane Reforming For Hydrogen Production

Global climate change is a severe challenge,and the task of reducing carbon dioxide emissions is imminent.It is an effective way to reduce carbon dioxide emissions by replacing fossil energy combustion with renewable energy.In the past decade,renewable energy technologies such as solar energy and wind energy have developed rapidly.However,due to its intermittent nature,renewable energy cannot replace fossil energy in a short time.Solar thermochemical technology for hydrogen production could be a promising solution.Hydrogen energy is a high-density energy carrier with zero carbon emissions,and the development of efficient,clean,economical,and sustainable solar thermochemical technology is of great significance for mitigating global climate change and accelerating the transformation of energy structure.Supported by the projects of National Natural Science Foundation of China and the National Key Research and Development Program,this thesis proposes a method of mid-temperature solar methane reforming for hydrogen production,and explores the thermodynamics of solar thermochemical hydrogen production with product separation.An experimental platform for solar methane hydrogen production is developed.This thesis also proposes a distributed hydrogen supply system by solar methane reforming.The main content and conclusions of this thesis are as follows:1.Based on the energy cascade utilization and reaction equilibrium thermodynamic theory,the energy level improvement mechanism of the solar methane hydrogen production process is analyzed.The theoretical advantages of multi-product separation are demonstrated.It is found that the theoretical separation work required for 99%methane conversion is lower than that of single product separation by 40%.Leverage effect of product separation on the improvement of solar thermal energy level is deduced.The relationship between "quality" and "quantity" in the solar energy conversion process is clarified by EUD analysis method,and the improvement of solar thermal exergy by product separation is quantitatively revealed.2.Experimental research on hydrogen production from solar methane reforming with multi-product separation is carried out.By sequential separation of two(or multiple)products,we can achieve close-to-100%conversion of methane to targeted products of H2 and CO2 in their pure form in a mild temperature range around 400?.which is much lower than the reaction temperature of conventional steam methane reforming.The optimal catalyst type and reaction operating parameters are obtained.Stable and fast production of H2 and CO2 was demonstrated over 6000 cycles.,which proves the repeatability of the experimental method and the durability of the material.A prototype solar methane reforming reactor is built,which achieved>90%methane conversion rate and hydrogen recovery rate.Solar-to-H2 efficiency of 3.4%was achieved with direct solar illumination,while efficiencies close to 43%can be practically achievable.This experiment realizes solar methane reforming at 400? for the first time,confirming the feasibility of hydrogen production from mid-temperature solar methane with product separation.3.A novel concept of hydrogen production by solar thermo-electrochemical looping SMR is designed.The solar thermal-driven SMR reactor is electrochemically pumped by a PCEC for H2 separation and an MCEC for CO2 separation.Based on the concept,a distributed energy system for producing high-purity H2 supplying heat and power,and supplying high-purity CO2 for electrochemical conversion to feedstocks can be envisaged.Technical and economic analysis shows that the solar land demand of this system is only 12%-21%of the photovoltaic water electrolysis system,and the levelized hydrogen supply cost is about 35.5-38.9 yuan/kg.The complementary utilization of fossil energy and solar energy,combined with electrochemical product separation to reduce the reaction temperature,promotes the miniaturization,low temperature and low carbonization of the solar methane reforming hydrogen production system,which further promotes the smooth transition of fossil energy to renewable energy.4.A hybrid solar energy conversion and storage system integrating CdTe solar PV and methanol thermochemistry with a spectral filter is proposed,based on the concept of energy cascade utilization of solar spectrum.A thermodynamic model and an optical model of the system are established to study the photovoltaic and thermal performance of this system with different mirror field designs.The spectral filter's optical property calibrated by a real filter's measured data.The spectral filtering,as well as the "double-heat-source" design effectively improve the system performance.The results show that the system features high net solar power generation efficiency(up to 39%),and the temperature resistance requirement of photovoltaic is reduced to below 80?.The economic assessment indicates that the levelized cost of electricity is as low as$0.20/kWh.