Flame Stability of Methane and Syngas Oxy-fuel Steam Flames

Oxy-fuel combustion has been used previously in a wide range of industrial applications. Oxy-combustion is carried out by burning a hydrocarbon fuel with oxygen instead of air. Flames burning in this configuration achieve higher flame temperatures, which present opportunities for significant efficiency improvements and direct capture of CO2 from the exhaust stream. In an effort to better understand and characterize the fundamental flame characteristics of oxy-fuel combustion, this research presents the experimental measurements of flame stability of CH4/O-2 and syngas (H-2-CO)/O-2 flames. Effects of the H-2 concentration, fuel composition, exhaust gas recirculation ratio, firing inputs, and burner diameters on the flame stability of these fuels are discussed. Effects of exhaust gas recirculation, i.e., CO2 and H2O (steam) acting as diluents on burner operability, are also presented. The roles of firing input on flame stability are then analyzed. For this study, it was observed that many oxy-flames did not stabilize without exhaust gas recirculation because of their higher burning velocities. In addition, the stability regime of all compositions was observed to decrease as the burner diameter increased. A flashback model is also presented, using the critical velocity gradient (g(F)) values for CH4-O-2-CO2 flames. The scaling relation [g(F) = cS(L)(2)/alpha)] for different burner diameters was obtained for various diameter burners. The paper shows that results correlated linearly with a scaling value of c = 0.0174.