Intrinsic Kinetics Study On Methane Steam Reforming

Hydrogen is currently the most attractive clean and efficient energy source,which has been widely used in the fuel cell,petrochemical,automotive energy,aerospace technology,and other fields.Hydrogen production from methane steam reforming is a widely used hydrogen production method.In order to better understand the methane steam reforming reaction mechanism and improve the methane conversion rate and hydrogen production rate,the intrinsic kinetics experiments of methane steam reforming were firstly carried out based on the micro-fluidized bed reaction system with the commercial nickel-based catalyst.Based on the differences of the intrinsic kinetic equations of different reaction mechanisms,the intrinsic kinetic equations that better describe the methane steam reforming process are determined.Then,the effects of different water-carbon ratio?1.5-4.5?,pressure?0 MPa-1.0 MPa?,inlet velocity?0.1m/s-0.2 m/s?,and preheating temperature?400 K-600 K?on methane conversion rate,hydrogen production rate,CO selectivity,and reactor pressure drop in different reaction temperature from 500? to 700? were investigated on FLUENT 14.0 simulation software.Based on the parallel and serial reaction mechanism of methane steam reforming,two possible intrinsic kinetic models were established.By comparing and screening,this paper finally selected the parallel reaction mechanism,and an intrinsic kinetic model based on the parallel reaction mechanism was obtained.The activation energies of CO and CO₂ formation rates were 81.69 kJ/mol and 59.38 kJ/mol,respectively,and the pre-exponential factors were 316.6 mol/(g·h·kPa^0.85)and 0.00263 mol/(g·h·kPa^3.1),respectively.As the reaction temperature increases,the rate of CO formation increases gradually,while the rate of CO₂ formation decreases gradually.When the reaction temperature is raised from 500? to 800?,the methane conversion rate,hydrogen production rate and CO selectivity are gradually increased from 31.84%,1.05,0.45 to 92.28%,3.34,0.99.When the temperature is 800?,almost all of CH₄ is converted to CO and H₂.The hydrogen production rate is more than 3.0 due to the methane cracking at the high temperature.With the increase of the steam-to-carbon ratio and pressure,the methane conversion rate and hydrogen production rate increase gradually,while the CO selectivity decreases gradually.The higher the temperature,the weaker the promoting effect of the steam-to-carbon ratio and pressure on methane conversion.When the temperature reaches 700?,the steam-to-carbon ratio and pressure have little effect on the methane conversion rate.The H₂ and CO mole fractions gradually increase along the length of the reactor,while the CO₂ mole fraction gradually stabilizes along the length of the reactor.The change of inlet speed has a great influence on the formation of CO.As the preheating temperature increases,the methane conversion rate,hydrogen production rate,and CO selectivity gradually increase.At different reaction temperatures,the pressure drop of the reactor showed different trends with the change of the steam-to-carbon ratio.When the reaction temperature is lower than 600?,the pressure drop of the reactor increases first and then decreases with the increase of the steam-to-carbon ratio.As the temperature increases,the corresponding steam-to-carbon ratio becomes smaller when the pressure drop of the reactor appears.When the reaction temperature exceeds 600?,the pressure drop of the reactor gradually decreases as the steam-to-carbon ratio increases.As the pressure and inlet velocity increase,the pressure drop of the reactor increases approximately linearly.At different reaction temperatures,the reactor pressure drop doubled as the inlet velocity increased from 0.1 m/s to 0.2 m/s.As the preheating temperature increases,the reactor pressure drop gradually decreases.