Numerical analysis of NOx production within a hydrogen catalytic combustor

Hydrogen combustion reactions produce nitrogen oxides as a byproduct. They can be reduced by exploiting the catalytic combustion of hydrogen in a monolith. However, some nitrogen oxides can still be produced in the gas-phase of the catalytic combustor. The present work numerically investigates the production of nitrogen oxides as a by-product of the combustion of a lean air-hydrogen mixture in a catalytic monolith with an equivalence ratio lower than 0.3. The analysis is carried out with a 2D dynamic numerical model implemented in MATLAB. The model solves mass and energy balances in a domain describing a single channel of the monolith. The model involves a detailed reaction mechanism for the gas-phase combustion, including the subsets that model the production of nitrogen oxides. As a result, the model indicates that the catalytic combustor does not produce nitrogen oxides with an inlet hydrogen fraction lower than 9%vol. Furthermore, the maximum value of nitrogen oxide at the outlet of the channel is lower than 0.4 ppm, obtained with the highest hydrogen fraction simulated in this work (12%vol inlet hydrogen fraction).