Simulation of catalytic oxidation of lean hydrogen–methane mixtures

The combustion of preheated lean homogeneous mixtures of hydrogen with methane in air in a catalytic packed-bed reactor was modeled at atmospheric pressure. The non-equilibrium, one-dimensional model developed employs multi-step surface and gas-phase reactions and accounts for the three modes of heat transfer within the bed as well as for heat loss from the bed. The catalyst considered was platinum. It was demonstrated that the model could predict the effects of changes in operational conditions such as inlet mixture temperature, fuel composition and mixture equivalence ratio on the methane and hydrogen conversions, as well as species concentrations and gas temperature profiles along the bed. It was shown that the hydrogen is consumed completely within the early part of the reactor length in all the cases considered for simulations. It was also shown that the improving effect of hydrogen on methane conversion is particularly evident at relatively low inlet temperatures and for very lean mixtures. However, this effect diminishes significantly with increasing inlet temperature and equivalence ratio. It was also shown that the positive effect of hydrogen addition which is more pronounced at its low concentrations in the fuel mixture, decreases somewhat with a further increase of the hydrogen content. The displayed trends were in good agreement with the corresponding experimentally observed.