Steam Methane Reforming(SMR)for Hydrogen Production By Gliding Arc Plasma Catalysis

Hydrogen is a clean and efficient energy.In order to reduce the dependence on fossil fuel,it is imperative to develop hydrogen energy.Since Germany introduced the policy of suspending the sale of fuel vehicles by 2030,the Ministry of Industry and Information Technology of China is also considering the timetable for this policy.Fuel cell vehicles have entered the market and are still limited by hydrogen architecture networks.At present,hydrogen is mainly derived from fossil fuel,that is,steam or partial oxidation methane reforming and coal gasification for hydrogen production（referred as traditional hydrogen supply）.Traditional hydrogen supply is large-scale centralized hydrogen supply.From a social and economic point of view,it is necessary to pay sufficient attention to the safety issues of hydrogen（preparation,storage,transportation,use）.In order to build hydrogen architecture network,decentralized hydrogenation stations are constructed and used around the world.Traditional（thermal）catalytic steam methane reforming for hydrogen production is more suitable for large-scale continuous industrial production due to its slow start-stop rate and low specific yield（large reactor volume）.Nevertheless,thermal catalytic reforming of methane（or lower alcohol）for distributed hydrogen production is also researching hotpot.The gliding arc plasma technology has the characteristics of rapid start-stop,high energy efficiency and compact structure.The combination of gliding arc plasma and catalyst has the advantages of two processes,and is applied to steam methane reforming,which provides an effective way for distributed hydrogen production technology.This thesis intends to address the above-mentioned issues of traditional hydrogen supply and the needs of hydrogen refueling stations,and proposes the following solutions for distributed hydrogen production.In this thesis,steam methane reforming by gliding arc warm plasma is investigated for distributed hydrogen production.Thermodynamic equilibrium calculation of steam methane reforming reaction;research on steam methane reforming in gliding arc plasma alone and gliding arc plasma catalytic steam methane reforming.The main results are as follows:（1）In the thermodynamic equilibrium calculation of steam methane reforming reaction（SMR）,two parameters of reaction temperature(T_SMR,600¹000 ^oC)and H₂O/CH₄ ratio（S/C,1.5⁴）were investigated.The reaction is a strong endothermic reaction,and the increase of the reaction temperature and the feed ratio are both favorable to increase the thermodynamic equilibrium conversion of CH₄.The critical conditions(S/C and T_SMR)are 1.5,865 ^oC（or 4,740 ^oC）when CH₄ is completely converted.Furthermore,in order to obtain hydrogen-rich gas having CO dry basis concentration≤1%to meet actual needs,water gas shift（WGS,exothermic reaction）is followed the above SMR reaction.When the reaction temperature(T_SMR)is greater than 600°C,S/C ratio must be not less than 2 in order to obtain hydrogen-rich gas that meets the requirements.Under the conditions of T_SMR=600°C and S/C ratio=1.5,hydrogen-rich gas can also be obtained,however the former energy cost is significantly less than the latter（including the full range of S/C）.（2）In gliding arc plasma alone process,methane conversion increases with specific energy input（SEI）,H₂O/CH₄ ratio and inlet flow rate（F_t）.In parallel,the selectivity of C₂H_x reduces and hence the selectivity of CO and CO₂ increases with SEI and S/C,while with F_t the selectivity is approximately constant.Hence the reaction pathway can be influenced by SEI and S/C rather F_t.To utilize the heat with the reaction in plasma zone,Ni/CeO₂/Al₂O₃ catalyst bed is coupled with warm plasma in a heat-insulated reactor without external heating.For the coupled process,the methane and water conversion remarkably increases to 90%and 42%that approaches equilibrium state values,with the complete selectivity of CO and CO₂ and the favorable disappearance of C₂H_x selectivity under optimal conditions with gas hourly space velocity of 18000 ml·g^-1·h^-1.Compared to 59%and 2.3 kWh/Nm³ of plasma alone process,such a coupled process achieves the energy efficiency（of methane to hydrogen）of 75%and the low energy cost of 1.5 kWh/Nm³ at total hydrogen of 2.7 SLM.