Numerical modeling of self-heating and self-ignition in a packed-bed of biomass using XDEM

Abstract

In a packed bed of biomass, spontaneous ignition might occur due to oxidation of volatiles and causes a serious and unforeseen risk. On the other hand self-ignition may be useful in gasifiers and combustors if it occurs at the expected location and time. Therefore self-ignition can be categorized as a favorable or an unfavorable process, which can be controlled by managing some parameters such as gas velocity and temperature. However, spontaneous ignition originates from a complex combination of physiochemical processes such as gas flow through the void space of the bed, heat and mass transfer between two phases, drying, devolatilization, gas phase reaction and char combustion and gasification. The main aim of this work is to investigate the characteristics of self-heating and self-ignition in a packed bed using XDEM as an Euler–Lagrange model. The influence of different parameters such as gas velocity, gas temperature, particle size and moisture content will be studied and discussed in details. The numerical model is validated with experimental data. Good agreements were achieved between predicted results and measurements. The results show that ignition delay increases with fuel properties such as moisture content and particle size, while it decreases with process conditions such as gas velocity and temperature. However ignition height shows an increase with gas velocity and a decrease with gas temperature and moisture content.