Heat And Mass Transfer Analysis And Structure Optimization In Microreactor For Hydrogen Production From Reforming

With the increasingly serious energy crisis and global warming,hydrogen energy as a clean energy with high energy density has gradually come into people’s sight.Although hydrogen shows great potential as an alternative energy source,its storage and transportation needs are considered major limitations to its large-scale utilization.Methanol reforming hydrogen production technology has the advantages of low reaction temperature,low CO concentration in the product and high hydrogen selectivity.After purification,the generated gas can provide high quality hydrogen for application in fuel cell system,so it develops rapidly and provides strong technical support for large-scale application of fuel cell power generation system.Microreactor can not only provide a higher surface to volume ratio,but also increase the residence time of reaction gas in the catalytic surface layer.How to achieve the balance of heat and mass transfer in the microreactor is a complex problem,so it is very necessary to study the heat and mass transfer analysis and structure optimization in the microreactor for hydrogen production by methanol reforming.This paper adopts the method of theoretical analysis,numerical simulation and experiment.Based on the porous medium model and laminar finite rate model,a three-dimensional numerical model was established for hydrogen production from methanol reforming,and the heat and mass transfer process in the combustion channel and reforming channel was studied in the reactor.The influence of atmospheric pressure,water alcohol ratio and inlet flow rate on the heat and mass transfer performance of the microreactor was simulated by numerical calculation software,and the structure of the reforming channel was optimized.The influence of different atmospheric pressure on catalytic combustion and reforming reaction in microchannel reactor was analyzed.The simulation results show that the catalytic combustion reaction is mainly concentrated in the front of the channel,and the heat generated is transferred to the reforming channel through the reactor wall.Adding grooves to the reforming channel can interfere with local flows near the channel wall,leading to the formation of recirculation zones that increase the contact time with the catalyst,thereby increasing heat and mass transfer and maximizing the use of heat generated by the combustion channel.The geometrical parameters of the groove also affect the methanol conversion and hydrogen yield of reforming channel.When the width of the groove is constant,the methanol conversion rate of reforming channel increases with the increase of the groove depth.When the groove is located in the front part of the channel entrance,the hydrogen yield rate is larger.The overall performance of the microreactor is greatly changed by atmospheric pressure.The reaction rates of combustion reaction and reforming reaction speed up with the increase of atmospheric pressure,but the acceleration gradually slows down,and the peak position of the reaction rate moves backward with the increase of atmospheric pressure.Under atmospheric pressure,low flow rate has little influence on reforming reaction,but under four atmospheric pressure,each flow rate has great influence on reforming channel methanol conversion.In order to maintain high evaluation factor values,different atmospheric pressures correspond to the optimal inlet velocity.By building the experimental platform of methanol steam reforming reactor,the effects of temperature,space velocity,water to alcohol ratio and atmospheric pressure on hydrogen yield and methanol conversion in reforming reaction were studied by orthogonal experiment and gas chromatography were used for analysis.The exhaust gas was detected and quantitatively analyzed by gas chromatograph,and the effects of different factors on reactor performance were obtained.The experimental results show that the selectivity of hydrogen is the highest at533 K.Increasing the ratio of water to alcohol can promote the positive transformation of methanol reforming reaction and increase the methanol conversion and hydrogen yield.When the ratio of water to alcohol is 1.6,it has the greatest influence on hydrogen yield.In reforming reaction,methanol conversion decreases and hydrogen selectivity increases with increasing space speed.The reforming reaction rate increases with the increase of reaction pressure.The results of simulation and experiment show that the microreactor has higher methanol conversion and hydrogen yield under normal pressure and low flow rate.The best performance of the reactor can be achieved only at different inlet velocities corresponding to different pressures.The reaction channel temperature should be strictly controlled to reduce the occurrence of more CO in reforming channel under high temperature.