Experimental analysis of the ignition front propagation of several biomass fuels in a fixed-bed combustor

Fixed-bed combustion in a tube reactor is a useful procedure to exploit a large variety of biomasses obtaining accurate in-bed data. In this paper, the ignition front propagation velocity is experimentally studied in a counter-current process for eight different biomass fuels with a wide range of origins, compositions and packing properties. Air mass flow rate is the main operative parameter and clearly distinguishes three stages of combustion (oxygen-limited, fuel limited and cooling by convection). The impact of the excess air ratio is also analyzed. This parameter confirmed that the maximum front velocity is achieved under sub-stoichiometric conditions, where the cooling effects of excessive air are minimized. Other variables with a major influence on the ignition front velocity are moisture and ash content. Finally, an uncertainty analysis is included to determine the accuracy of the entire measurement process.