Steady-state and dynamic modeling of indirect partial oxidation of methane in a wall-coated microchannel

Steady and dynamic characteristics of catalytic indirect partial oxidation (combined total oxidation and steam reforming) of methane to hydrogen in a wall-coated microchannel are investigated using computational techniques. Steady-state behavior is initially modeled using a two-dimensional axisymmetrical wall-coated reactor model. Considering the small channel diameter, adiabatic operation and negligible transport resistances, response of the microchannel is also investigated using a one-dimensional pseudohomogeneous tubular reactor model. Simulations of the microchannel are carried out using both models for different feed conditions ranging between 1.89 and 2.24 for CH4/O2 and 1.17–2.34 for H2O/CH4. Outcomes from both models are found to be close, allowing the use of the low-cost one-dimensional model in dynamic simulations. Analysis of transients during the system start-up indicate that steady state is reached between 100 and 120 s depending on the feed composition. Product temperature and flow rates obtained from steady-state and dynamic simulations are found to be close with some differences arising from the finite difference-based numerical method used to solve partial differential equations of the dynamic model. Dynamic responses of the microchannel to several disturbances in the feed are analyzed. The response to a step increase in the inlet oxygen flow rate (decrease of CH4/O2 from 2.24 to 1.89) is the elevation of temperature by ca. 100 K, which in turn leads to ca. 33% in hydrogen yield, and the time to reach the new steady state is around 90 s. If the disturbance involves an increase in inlet steam flow, temperature and hydrogen yield decrease in time to a local minimum within 10 s and then gradually increase to the subsequent steady state within 50 s ending up with net reductions of ca. 1.6% and 9%, respectively.