Reforming Of Methane For Hydrogen Production Via Non-equilibrium Plasma

Hydrogen is considered to be an ideal source of energy that could play a key role in fuel cells, combustion engines or gas turbines. Currently, the technology of hydrogen storage and transportation is not yet mature. Consequently, the design and operation of compact and distributed hydrogen production devices has attracted considerable interest for combining plasma-chemical activation of reactants with heterogeneous catalysis in hydrogen production. Compared with traditional chemical processes, plasma technology has the potential to allow design of smaller hydrogen production units with the capability of rapid response to load variations, and to offer a unique way to induce gas phase reactions. Non-equilibrium plasmas have been considered very promising for fuel gas treatment because of their non-equilibrium properties, low power requirement and capacity to induce reactions at relatively low temperatures. Non-equilibrium plasmas that have been applied to hydrogen production include non-thermal arc, spark discharge, corona discharge, microwave discharge and dielectric barrier discharge (DBD).Base the technology of non-equilibrium plasma, dielectric barrier discharge and non-thermal arc discharge combined with catalyst were used to conversion methane for hydrogen production, respectively. We designed packed-bed dielectric barrier discharge reactor, porous ceramic dielectric barrier discharge reactor, non-thermal arc reactor and supporting experimental system. Discharge experiments, hydrogen production experiments, numerical simulation and reactor structural optimization were conducted. The main research contents and results are as follows:Larger discharge gap and volume may be important issues to develop a compact DBD reactor as an in situ hydrogen production device. A novel corona inducing dielectric barrier discharge (CIDBD) reactor with discharge gap10mm, with nickel powder uniformly distributed in the discharge zone, was developed to reduce the applied voltage and improve plasma uniformity. This corona inducing technique allows dielectric barrier discharge to occur uniformly in a large gap at relatively low applied voltage. Hydrogen production by reforming methane with steam and air was investigated with the hybrid reactor under atmospheric pressure and temperatures below600℃. The effects of input power, O2/C molar ratio and preheat temperature on methane conversion and hydrogen selectivity were investigated experimentally. It was found that higher methane conversions were obtained at higher discharge power, and methane conversion increased significantly with input power less than50W; the optimized molar ratio of O2/C was0.6to obtain the highest hydrogen selectivity (112%); under the synergy of dielectric barrier discharge and catalyst, methane conversion was close to the thermodynamic equilibrium conversion rate.Porous ceramics are sintered from alumina (wt94%), silica (wt3.5%) and MgO (wt2.5%), and the thickness range of the ceramics is4.0mm to10.7mm, the pore size of the ceramics is100μm, and the porosities of the ceramics are35%,39%and45%, respectively. We investigate the physical characteristics of discharge in porous ceramics by photographic visualization and electrical measurements. The microdischarges generated inside porous ceramics by AC high voltage represent a novel way to create stable atmospheric pressure plasmas. The physical characteristics of discharge in porous ceramics are investigated by photographic visualization and electrical measurements. Experimental results show that the surface discharge do not transit into pore microdischarges, and the onset voltage of pore microdischarges increases with thickness of ceramics, while significantly decreases with increasing porosity of ceramics.In order to improve the efficiency of arc discharge energy, we increase non-equilibrium degree of non-thermal arc plasma combined with catalyst. Discharge characteristics and ignition performance of the non-thermal arc reactor were studied. When first rotating gas flow rate greater than80sL/min the non-thermal arc was produced uninterruptedly. The methane conversion rate was higher than80%when the molar ratio of oxygen to carbon greater than0.8. Hydrogen selectivity was higher than70%within large range of variation of the molar ratio of oxygen to carbon. Maximum hydrogen yield of the non-thermal arc reactor is1.07kgH2/h. The specific power consumption of non-thermal arc reactor is0.47MJ/kgH2. The non-thermal arc reactor has fast start-up performance, it can start to produce hydrogen within30seconds at pre-heating condition and reach steady state within3minutes. At non-preheating condition, it can be started to produce hydrogen within10minutes.