Flame Stability Limit and Exhaust Emissions of Low Calorific Fuel Combustion in Turbulent Diffusion Combustor for a Small-Scale Fuel Cell(<Special Issue>International Conferences on Power and Energy System)

This paper describes an investigation conducted on flame stability and exhaust emissions from a turbulent diffusion combustor, fueled with low-calorific gas, for a small-scale fuel cell. It is important to maintain flame stability in the combustor, even under lean fuel conditions, and to suppress CO emission in the exhaust gas. An imitation off-gas, in which hydrogen and methane were diluted by adding nitrogen, with Wobbe indices ranging from ca. 4400-8700, corresponding to the fuel utility ratio of 90%-60% in the fuel cell, was supplied to the combustor, and the blow-off limits, CO, and NO_x emissions were experimentally investigated. The results show that the blow-off excess air ratios increases with an increasing Wobbe index and with decreasing fuel input to the combustor, and that they are proportional to the hydrogen concentration in the fuel to the power of 0.5-1.0. In addition, it was found that the Damkohler numbers at blow-off limits decreased with decreasing fuel input and with increasing Wobbe indices, and that the product of (S_S/V_M)A[H_2][O_2]^<0.5> was constant at blow-off limits. Furthermore, NO_x emissions from the combustor were low, less than 20ppmV (O_2=0%), it was also found that the apparent activation energy of NO_x emission derived from Arrhenius plots was almost equal to that of prompt NO in the combustion of imitation off-gas.