Modeling of the Propagation of a Reaction Front in Fixed Bed Combustion of Wood Particles

Abstract

The goal of the combustion research is to achieve optimum combustion mode. Reaction Front velocity is one of the most important parameter that is studied in this field. Most biomass consumed at the present time is burned in fixed or moving beds. Fixed-bed combustion systems are characterized by the slow combustion of large particles subjected to an oxidizing ambient. In this paper a model for propagation of a reaction front of wood particles in a fixed Bed is presented. Once the bed is ignited, an apparent flame zone is formed at the bed's top surface and the flame front moves downwards into the bed of fuel at a speed depending on fuel type and operating parameters. Effect of different parameters such as air flow rate through the bed, primary air temperature, moisture content, particle size and number density of fuel particles on the reaction front velocity has been studied. In order to compare the results of this model with the associated experimental data three species of wood fuels are studied and the agreement is found to be satisfactory.

Biomass Fuel and Combustion Conditions Selection in a Fixed Bed Combustor

“…However, the os moisture content has no effect on the maximum temperature. Although the effect of the moisture content has been sufficiently verified [24,29,42], the results warn against the generalization of such an effect on low moisture content fuels. Along the same line, several studies [43,44] have found that an increase in the moisture content decreases the ignition front propagation speed due to the energy that is consumed by the evaporation process, although no drastic changes in the reached temperature were observed up to a moisture content of greater than 20%.…”

“…The highest calorific value of the fuel determines the ignition front speed (the ignition mass flow) [12]. However, high bed temperatures could lead to ash fusion, which, in turn, reduces the energy that is released in the bed [29].…”

The influence of parameters variability on biomass selection for energy use

“…The fixed-bed combustion process is influenced by characteristic fuel-dependent parameters. The most important are as follows [11,[27][28][29]:…”

“…Thus, most papers published on this issue are based on statistical techniques such as multivariate data analysis [10] or mathematical models of dependence [11][12][13]. These multi-criteria decision analysis methods are used as tools for the classification and selection of the best alternative amongst a set of options.…”