Study of a Fixed-Bed Biomass Combustor: Influential Parameters on Ignition Front Propagation Using Parametric Analysis

This paper presents a study of the parameters influencing the combustion behavior of an experimental counter-current fixed-bed combustor. An innovative parametric analysis has been conducted to examine a wide range of parameters from very different biomasses. This analysis based on the parametrization of front propagation velocity versus the airflow rate curve not only allows fuel properties to be compared in terms of maximum or minimum values of ignition or air flux but also enables the shape of their performance curve to be examined. The study of the data has identified the moisture content and particle size as the most influential parameters. These factors strongly determine the operational range of the fuel in terms of air mass flux and ignition front propagation velocity. Furthermore, a new parameter called char stoichiometry is defined to examine fuel combustion regimes. This factor represents the stoichiometric ratio of the air and char fraction (assuming the fuel is pure carbon). The results obtained show that the transition from an oxygen-limited regime to a reaction-limited phase takes place when the air mass flow rate reaches char stoichiometry values. This may suggest that the first phase of combustion is determined mainly by the behavior of the char matter in the fuel. On the other hand, certain parameters, such as porosity of the bed or particle shape, did not show identifiable effects in our tests, suggesting that their influence in the process seems to be less decisive than that of the other parameters previously mentioned.