Optimization of slow pyrolysis process parameters using a fixed bed reactor for biochar yield from rice husk

Abstract

A fixed bed reactor has been used to assess the influence of slow pyrolysis process parameters on biochar yield from rice husk. Taguchi's method (L9) was used for such a purpose, which four parameters varied according to three different levels: heating rate (β) of 5, 10 and 20 °C/min; temperature (T) of 300, 400, and 500 °C; residence time (t) of 3600, 5400 and 7200 s; rice husk mass (m) of 125, 250, and 500 g. ANOVA were utilized to verify the statistical significance of process parameters. Different physical-chemistry techniques have been performed to assess the energy potential of processing rice husk through thermochemical processes. The results showed that the highest biochar yield (37.71 %wt) was achieved through the following experimental conditions: 500 g of biomass, β = 20 °C/min, T = 300 °C, and t = 5400 s. However, the highest heating value (HHV = 23.41 MJ/kg) was obtained by using 125 g of biomass, β = 10 °C/min, T = 500 °C, and t = 5400 s. However, optimal conditions for higher fixed carbon content (60.10 %wt) were 500 g of biomass, β = 5 °C/min, T = 500 °C, and t = 7200 s. It was 49.05% higher than HHV found for raw rice husk. ANOVA results have revealed that temperature is the most significant parameter for the slow pyrolysis process. Furthermore, Taguchi's method was applied to define the levels of experimental conditions and optimize the process. Energy ratio assessment yielded values ranging between 0.38 and 1.77, which indicates that it is technically feasible to obtain energy gains through the slow pyrolysis of rice husk.