| With the rapid development of economy,the number of vehicles has increased dramatically in China.Research shows that the automobile energy in the form of waste heat accounts for 55%-80% of the total fuel energy,so the automobile exhaust wastes a lot of energy,waste heat recovery for the improvement of fuel efficiency and the reduction of environmental pollution is very important.At the same time,with the increasing depletion of fossil fuels and its environmental pollution,the search for new alternative clean energy has attracted worldwide attention.Hydrogen has many excellent properties,its combustion product is water and has no pollution to the environment,so it is one of the outstanding alternatives.In a variety of hydrogen production technologies,because of the mild reaction,high hydrogen production,the methanol steam reforming for hydrogen production attracts the industry attention.The reaction is an endothermic process,using the automotive exhaust to heat the reaction not only can recycle the energy and improve the fuel utilization,but also can generate hydrogen,then hydrogen can be fed into internal combustion engine,its efficiency can be improved and pollutant emissions can be reduced.In view of this,this paper designed automobile exhaust heating methanol steam reforming for hydrogen production experimental system,the heater and plate micro-reactor were combined,methanol water vapor mixture was passed to the reforming side,the automobile exhaust was simulated by hot air which heated by the hot air gun,the hot air passed through the heating side to heat the reactor.The reformer temperature rising characteristics,heater performance and methanol steam reforming characteristics were studied with the inlet temperature of hot air increasing from 574 K to 884 K.The experimental results show that with the increasing of the exhaust gas inlet temperature,methanol conversion and hydrogen production rate increase firstly and then remain unchanged.Experimental results show that the heat transfer of the separated plate reactor and heater system is not good,heat loss of this system is large.Therefore,the fin reactor with integrated heating and reaction was designed.Accuracy of the simulation model was verified by experiments,and then the numerical analysis of the same volume of the fin reactor and plate reactor was carried out under the same conditions.The results show that the outlet temperature difference between reaction side and hot air side of the fin reactor is lower than that of the plate reactor,the methanol conversion and thermal efficiency are higher than that of the plate reactor,so the fin reactor is superior in heat transfer in methanol steam reforming.Based on the above research,the influence of different materials and structural parameters on the heat transfer and methanol steam reforming performance for hydrogen production in the fin reactor was further analyzed.Results show that using stainless steel as the reactor material,with the radius of 35 mm,the middle partition is located at a distance of 26 mm from the axis and a single reaction unit angle of 10 degrees are the optimized reactor material and size condition.Then,the effects of operating parameters,such as the hot air inlet velocity and inlet temperature,the reactants inlet velocity and inlet temperature,ratio of water to methanol,cocurrent and countercurrent flow type on the performance of methanol steam reforming were investigated.Results show that at countercurrent flow,water methanol ratio of 1.3,hot air inlet velocity of 1.1m/s and inlet temperature of 773 K conditions,reactants inlet velocity of 0.1m/s and inlet temperature of 493 K are the best parameters of the reaction,methanol conversion reaches 99.4%,thermal efficiency reaches 28%,volume fraction of hydrogen reaches 69.6%.The above results can be used as reference for the comprehensive utilization of automobile exhaust waste heat including engine exhaust reforming for hydrogen production. |
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