(189b) Catalytic Combustion of Hydrogen/Methane Fuel Blends

Burning natural gas in current stove technologies is harmful to the environment primarily because it emits greenhouse gases like carbon dioxide, contributing to climate change. A proposed alternative is using blends of natural gas and hydrogen to reduce the carbon emissions. However, hydrogen burns at a much higher temperature than natural gas, resulting in increased levels of nitrogen oxides (NO_x) during combustion. Catalytic combustion takes place at a temperature that is considerably lower than flame temperature of traditional combustion, thereby minimizing NO_x emissions. Previous studies in literature have looked at the catalytic combustion of CH₄ and H₂ separately but not together as a blend.

This study set out to explore the efficiency and stability of a Pd-Al₂O₃ catalyst for catalytic combustion of H₂/CH₄ fuel blends. The investigation included determining the optimal operating conditions needed for the scalability of Pd-Al₂O₃ for practical applications such as commercial cooking. Various H₂/CH₄ blends with 0-100% H₂ with different equivalence ratios between 0.5-1, a total flow rate of 0.7-2.1 L/min and different preheating conditions were tested. Real-time temperature measurements were recorded at different locations on the catalyst using thermocouples. The exhaust species were measured using gas analyzers to determine the fuel conversion and NO_x concentration.

The findings revealed that higher temperatures are achievable by increasing the concentration, equivalence ratio (from lean to stoichiometric) and total flow rate, without surpassing the contact time for the catalyst. Additionally, the study identified precise operational conditions under which auto-ignites, which triggers flashback in the reactor causing instability. Complete conversion of the fuel was achieved as well as very low NO_x concentrations in the exhaust. The study also showed that self-sustaining reactions can be achieved after preheating for only 1 min from the start of the reaction.