Flow Field Optimization Of Hydrogen Production Mixer For Diesel Autothermal Reforming

Autothermal reformering can produce hydrogen from diesel fuel to power for the fuel cell.It can be used as an auxiliary power unit when the large transport equipment is unloaded.The design of the mixer plays an important role in the long-term stable operation of the ATR system.When the heterogeneous mixture enters the downstrean catalytic reforming region,it is easy to form hot spots and carbon deposition due to the heterogeneous exothermic reactions.The coking can block the pipe in the worst,which leading to the system failure.In addition,the reactants will inevitably occur the low temperature oxidation reaction during the mixing,and it will produce ethylene,a well-known deposit precursor.Excessive ethylene(>0.1 mol%)will form carbon deposits in downstream catalytic reforming region.The paper is to optimize the mixer of autothermal reforming system.To ensure a homogeneous sygnas at the outlet of the mixer and reduce the gas-phase reactions in the mixing region,the CFD numerical simulation method is used to study the flow field characteristics of the reactants in the mixer and optimize the configuration of the mixer.The paper study the flow field distribution of the reactants in the mixer under different angle of the venturi nozzle.The results show that the sufficient mixing can be achieved when the nozzle contraction angle and diffusion angle are both 90°.Considering the structural characteristics of the mixer,the structure size of the mixer is reduced to make the system more compact.The mixing effect of the miniaturized mixer is still good.Compared with the direct injection of air from the throat in the traditional mixer,the reactant cannot be rapidly mixed at the mixer outlet due to the large gas velocity,which is harmful to the long stable operation of the system.In this paper,the mixing effect will be improved by a swirl inlet.The results show that it can realize a sufficient mixing between the reactants by injecting the air into the mixer as a swirl way.Considering the low temperature oxidation reaction of fuel with superheated oxygen in the mixer,the influence of temperature and reactant ratio on the gas-phase reaction was studied.The results show that the ethylene in the system increases with the increase of temperature.And it will reduce the residence time of the reactants by increasing the proportion of oxygen so that reducing the production of ethylene.In addition,the increase in water vapor will promotes mixing,but the sufficient mixing will lead to reacting sufficiently and produce excessive ethylene.