Optimization of combustion parameters of carbonized rice husk briquettes in a fixed bed using RSM technique

Abstract

This study investigates the combustion of carbonized rice husk briquettes in a fixed bed to establish the optimum briquetting and combustion conditions. The combustion properties, namely, the average flame propagation speed, the average burning rates, the reaction zone thickness, maximum flame temperature and the ignition time, were optimized with respect to air-flow rate, binder ratio and particle size using response surface methodology (RSM). Seventeen experiments with different combinations of air-flow rate, binder ratio, and particle sizes, each at three levels set according to Box-Behnken Design (BBD), an RSM technique, were performed. Mathematical models for predicting the responses were developed by fitting experimental data. It was established that the binder and air-mass flux predominantly affected all fuel samples during processing and combustion. Optimal values of the ignition time and reaction zone thickness were established to be 249.08 s and 102.43 mm when air-mass flux, binder ratio and particle size were 0.31 kg/m2.s, 25% and 2.6 mm, respectively. On the other hand, the optimal peak bed temperature was 1226.25 °C when air-mass flux, binder ratio and particle size were 0.31 kg/m2.s, 25% and 0.3 mm, respectively.