Hydrogen production from rich combustion in porous media

This paper examines rich combustion of methanol, methane, octane and automotive-grade petrol inside inert porous media in an effort to examine the suitability of the concept for hydrogen production. Species concentrations were measured and operating limits were tested of steady rich flames stabilized inside a two-layer alumina foam burner and a two-layer alumina bead burner. Using a conversion efficiency based on lower heating values, up to 56% of the methanol was converted to syngas (H₂, CO) inside the alumina foam burner and 66% inside the alumina bead burner. Using the same efficiency definition, 45% percent of the methane and 36% of the octane and petrol was converted to syngas with a significant portion of the energy remaining trapped in CH₄, C₂H₂ and C₂H₄. For methanol, the highest equivalence ratio observed for stable combustion was 6.1 inside the foam burner and 9.3 inside the bead burner which are higher than the conventional upper flammability limit (UFL) of 4.1. Methane's UFL was increased to 1.9 and, at a minimum, the conventional upper flammability limits of iso-octane and petrol were attained. A wide operating envelope was observed, which allowed for large turndown ratios up to 20:1. The composition of the products of the methanol flames examined here were close to equilibrium for relatively low equivalence ratios, while those of hydrocarbon flames differed significantly from equilibrium for all φ suggesting that finite rate kinetics are important. The high conversion efficiencies, quick startup times, compact size, and the absence of a catalyst make the present burner suitable for consideration as part of a reformer in a fuel cell powered automobile.