The influence of particle packing density on wood combustion in a fixed bed under oxy-fuel conditions

Presented in this paper is a study of the influence of particle packing density on fixed bed combustion of wood in an oxy-fuel burning environment. The packing density, which determines the region porosity, is influenced by fuels' geometry. Size and shape were determined directly from fuel particles and used to evaluate the particle sphericity which is an input in the computational model. Euler-Lagrange method was used to model conversion of wood in a fixed bed. The computational model was validated by performing experiments in a fixed bed using wood of different shapes and sizes which formed a wide range of bed porosity. It was established that the packing density affects combustion process by changing the burning conditions and flammability limits. The combustion condition is shifted from fuel-rich to fuel-lean side as bed porosity is increased. Consequently, the flame front propagation speed and conversion rates increase while the ignition time reduces. The operational range with respect to porosity was decreased in an oxy-fuel burning condition due to higher quenching effects of CO2. Furthermore, the study revealed that there is an optimum packing density, chi = 0.71, beyond which the efficiency falls due to the onset of quenching in the spaces. (C) 2019 Elsevier Ltd. All rights reserved.