Optimization of combustion characteristics of carbonized rice husk briquettes in fixed bed reactor under oxy-fuel environment

The aim of this study was to optimize the combustion properties of carbonized rice husk briquettes in fixed bed combustion under an oxy-fuel environment. Average flame propagation speed, average burning rates, average reaction zone thickness, peak flame temperature, and ignition time were optimized with respect to oxy-fuel mass flux, binder ratio, and oxy-fuel ratio (O₂/CO₂) using response surface methodology (RSM). Seventeen different tests were conducted using combinations of oxy-fuel mass flow rate, binder ratio, and oxy-fuel ratio, each set at three levels determined by the Box–Behnken Design method, a response surface methodology (RSM) tool. The developed models matched the test results to precisely forecast the results beforehand. Oxy-fuel ratio and mass flow rate had the most significant impact on the combustion properties across all fuel samples. The optimal values of ignition time were determined to be 120 s, with a reaction zone thickness averaging 355.73 mm and a peak optimal flame temperature reaching 1332 °C under conditions of oxy-fuel mass flux of 0.15 kg/m².s, binder ratio of 6.6 wt.%, and an oxy-fuel ratio of 40% O₂/60% CO₂. The maximum flame propagation speed and burning rate were 0.529 mm/s and 0.038 kg/m².s, respectively. These were accomplished using an optimal binder ratio of 6.6 wt.% molasses and an optimal oxy-fuel ratio of 40%, coupled with a mass flux of 0.15 kg/m².s.