The Phenomenon of Flame Jump in Counter–current Flame Propagation in Biomass Packed Beds–Experiments and Theory

In this paper the phenomenon of flame jump vis-a-vis steady propagation in biomass packed beds in counter-current mode is discussed. By analyzing the fuel flux and propagation rate data from experiments with a range of oxidizers, namely, air, O2-N2, O2-CO2, and O2-steam mixtures, parameter regimes of steady propagation, and flame jump are identified. A theoretical basis for this classification is developed by analyzing the thermo-chemical conversion of single particles subject to flow and thermal conditions in a packed bed. The ratio of the ignition ((Formula presented.)) to devolatilization ((Formula presented.)) times is shown to emerge as the controlling parameter in determining the flame propagation regimes. It is found from the theoretical analysis that steady propagation occurs for (Formula presented.) < 2 and transition to flame jump occurs if (Formula presented.) 2. Operational zones of a packed bed biomass system is mapped using the predicted ratio of (Formula presented.) as a function of volatiles-based equivalence ratio ((Formula presented.)). Implications of these results to practical ligno-cellulosic biomass combustion and gasification systems, especially using oxygen-steam mixtures for hydrogen generation, are brought out.