Numerical Simulation On Methane Reforming Heated By Solar Energy Coupling Exhaust Gas Heat For Hydrogen Production

Hydrogen combustion only produces water and does not produce sulfides and hydrocarbons,so hydrogen is called zero carbon fuel.Industrially,methane reforming,mainly including Steam Methane Reforming(SMR)and Auto-thermal Reforming of Methane(ATR),is a good way for producing hydrogen production.However,the reaction requires a large amount of heat input,so a clean energy supply is required.Solar energy is a kind of universal,harmless and energy-rich clean energy.It is very advantageous as a heat source for methane reforming.In addition,the heat from high-temperature flue gas in industry has not been effectively utilized,so that high-temperature flue gas coupled with solar energy can be used as a heat source for methane reforming for hydrogen production.In this paper,the system is designed,and the transmission characteristics and influencing factors in SMR reactor heated by high temperature flue gas are numerically analyzed.Furthermore,ATR reactor is optimized and the effects of operating parameters,material parameters and structural parameters on the reaction process and reactor performance are studied.The paper first designs a methane reforming for hydrogen production system heated by solar and flue gas.This system selects dish-shaped parabolic concentrating and heat accumulator/receiver tank to achieve heat storage and utilization.Based on the mass and heat balance,via the research on solar high-temperature heat utilization system,according to the reactor size,the type of phase change material and the required quality are determined;and then the size of the heat accumulator/receiver tank is obtained.Combining the physical model,the mathematical model and the detailed reaction kinetic model of the reactor in the system,the effect of reactant inlet parameters,the flue gas inlet parameters and the flow form on reaction characteristics,such as temperature distribution,hydrogen production rate,methane conversion rate,molar fraction of each component outlet,thermal efficiency and heat flux,are studied.The results show that increase of reactants inlet velocity is not conducive to the SMR reaction,which should not be greater than 1.0m/s.The increase of reactant inlet temperature promotes the reaction,but utilization of flue gas and thermal efficiency of the system is lowered.As water-to-carbon ratio of the reactant inlet increases,the thermal efficiency decreases because high water-to-carbon ratio promotes water vapor shift reaction.The flue gas inlet speed is optimally in the range of 0.3m/s to 1.0m/s,as the flue gas supply is sufficient and thermal efficiency is high.When the high temperature flue gas inlet temperature is 1500 K to 2000 K,the reactor thermal efficiency is high.The trends in counter-flow and current-flow are the same,but when flue gas inlet velocity is less than 0.3m/s,the hydrogen production rate in current-flow is greater than the countercurrent.When the flue gas inlet speed is greater than 0.3m/s,the performance of the countercurrent reactor is better.The SMR reaction requires a large amount of thermal energy.Therefore,ATR reaction is one of the development directions of the methane reforming in the future,but the heat balance in ATR reactor has always been a major limiting to its application.This paper optimizes ATR reactor structure,comparing the reaction and heat transfer performance in the straight channel reactor,the folded reactor and the heat pipe reactor.The effects of reactant inlet speed,inlet water to carbon ratio and oxygen to carbon ratio on different structural reactors are investigated.The results show that optimizing reactor structure can increase the hydrogen production rate and methane conversion rate,the folding reactor is better than the heat pipe reactor.For the heat pipe reactor,the longer length of the heat pipe,the more uniform of the temperature distribution inside the reactor,and the higher the hydrogen production rate and methane conversion rate.The heat pipe locates in the front is better than in the end of reactor.For the folded reactor,the enhancement of thickness and thermal conductivity of dummy plate are beneficial to reaction performance.