The Impact of Pre-Turbine Catalyst Placement on Methane Oxidation in Lean-Burn Gas Engines: An Experimental and Numerical Study

The effect of increased pressure relevant to pre-turbine catalyst positioning on catalytic oxidation of methane over a commercial Pd-Pt model catalyst under lean conditions is investigated both experimentally and numerically. The possible gas phase reactions due to high temperature and pressure were tested with an inert monolith. Catalyst activity tests were conducted for both wet and dry gas mixtures and the effect of pressure was investigated at 1, 2 and 4 bar. Aside from the water in the inlet stream, the water produced by oxidation of methane in dry feed inhibited the activity of the catalyst as well. Experiments were carried out to check the effect of added water in the concentration range of water produced by methane oxidation on the catalyst activity. Based on the experimental results, a global oxidation rate equation is proposed. The reaction rate expression is first order with respect to methane and -1.15 with respect to water. Although higher pressure leads to longer residence time, the higher pressure also increases the water concentration on the catalyst surface. Thus, the beneficial effect of pressure is affected by the inhibitory effect of water on the catalyst activity, particularly at lower temperatures.