Photographs of a rich flame (1:2 O2/CH4) in the annular burner at low (upper) and high (lower) steam-to-carbon ratios at 300 psi. Note the distinct orange incandescence from the soot being formed in the upper photo.

Autothermal reforming is an effective and energy-efficient way to produce hydrogen or synthesis gas for ammonia production and gas-to-liquids processes. However, soot formation at elevated pressures is a drawback. Sandia is investigating the formation of soot in a fuel-rich burner at high pressure and high temperature designed to mimic the conditions in the inlet burner of an autothermal reformer.

The experimental apparatus uses an annular co-flow burner configuration at pressures ranging from 250–1000 psi at various oxidation stoichiometries and steam-to-carbon ratios. A unique high-pressure optical cell is used to identify soot formation by measuring the attenuation of transmitted light.

Using pure methane as the feed fuel, recent results have revealed carbon dioxide content does not affect the soot formation process as much as originally presumed. The primary controlling factors are oxidation stoichiometry and fuel-steam ratio independent of total carbon. At these elevated pressures, the effect of additional CO₂ in the system is small with respect to soot formation.