Design and application of an experiment platform for hydrogen production by low-temperature plasma-enhanced ammonia decomposition
[Objective]Ammonia emerges as a pivotal,carbon-free fuel for future maritime transportation.However,its adoption faces challenges owing to ammonia's high ignition temperature and low flame diffusion rate.These characteristics complicate the ignition and combustion processes in ammonia-fueled engines,typically necessitating the introduction of reactive fuels like hydrogen to facilitate engine ignition.[Methods]To address these challenges,this study introduces an innovative experimental platform for NH3 decomposition.This platform combines catalysis with low-temperature plasma technologies.Specifically,our paper investigates the effects of different packing materials and variations in discharge power on the NH3 decomposition within a packed-bed dielectric barrier discharge(DBD)plasma reactor operating at ambient conditions.[Results]As the discharge power increases,we observe a corresponding rise in the reactor's effective capacitance value,from 72.4 pF to 97.2 pF.This facilitates the generation of additional discharge channels and free electrons within the packed-bed DBD plasma reactor.Electron collision with NH3 molecules enhances the production of reactive species in the reactor.These atoms and molecules are more susceptible to dissociation owing to their excited state.In addition,the high discharge powers lead to a high"electrical heat"in the rector,which further activates the packing materials.The integration of plasma technology and packing materials strengthens the discharge characteristics of the packed-bed DBD plasma reactor,thereby boosting NH3 decomposition performance.When comparing non-packed reactors with those packed with ZSM-5,ZSM-35,and ZSM-23 materials,the NH3 decomposition performance increases from 59.2%to 71.7%,73.2%,and 77.3%,respectively,at a discharge power of 16 W.Moreover,energy efficiency increases from 208.1 mmol/kWh in the non-packed reactor to 1359.3 mmol/kWh using ZSM-23 packing material,marking an improvement of approximately 653.2%.The active sites on the surface and within the pores of the packing materials provide a larger number of reaction sites for gas-phase molecules.The special pore structure of ZSM-23 materials facilitates the diffusion of gas-phase molecules,promoting a higher frequency of multiphase reactions per unit time.In addition,this study investigates the effect of various process parameters on the NH3 decomposition performance using the packed-bed DBD plasma reactor at a discharge power of 16 W.The NH3 decomposition performance starts to decrease as the gas flow rate increases,with the lowest NH3 efficiency of 47.9%recorded at a gas flow rate of 300 mL/min.When the NH3 concentration is 0.4%,0.7%and 1.0%,the NH3 decomposition performance is 73.4%,59.2%and 51.2%,respectively.This variation in performance can be attributed to the number of gas particles in the discharge region.Specifically,an increase in the number of NH3 molecules flowing through the discharge region per unit time elevates the frequency of collisions between electrons and NH3 molecules,which in turn enhances the dissociation of these molecules.[Conclusions]The platform is designed to utilize ammonia as a reactant,facilitating teaching and exploratory experiments on NH3 decomposition and hydrogen production under different working conditions.Simultaneously,the teaching component covers fundamental disciplines such as ship main propulsion power plants,physical chemistry,and plasma science.This integrated approach aims to foster students'interdisciplinary knowledge,deepening their understanding of cutting-edge technologies for energy conservation and carbon reduction in marine diesel engines.
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