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

ABSTRACT

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 ($t_{ig}$) to devolatilization ($t_v$) 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 $t_v/t_{ig}$ < 2 and transition to flame jump occurs if $t_v/t_{ig}>$ 2. Operational zones of a packed bed biomass system is mapped using the predicted ratio of $t_v/t_{ig}$ as a function of volatiles-based equivalence ratio (${\varphi }_v$). Implications of these results to practical ligno-cellulosic biomass combustion and gasification systems, especially using oxygen-steam mixtures for hydrogen generation, are brought out.

KEYWORDS:

• Flame jump
• biomass
• packed bed
• flame propagation regimes

Additional information

Funding

The authors thank SERB, DST, India for financial support for this study [grant # ECR/2018/001013].