Property enhancement of mustard stalk biomass by Torrefaction: Characterization and optimization of process parameters using response surface methodology

Abstract

Present work is devoted to the study of independent operating parameters namely torrefaction temperature (TT), residence (torrefaction) time (RT), and heating rate (HR) on the slow pyrolysis or torrefaction of an important agro residue namely mustard stalk (MS). Response surface methodology along with three-factor and three-level Box-Behnken design is applied to find the effect of above mentioned three parameters on the higher heating value, energy yield, and fixed carbon of the torrefied MS. Experimentation and modeling analysis reveal that the effect of these three factors' responses follows the sequence: (TT) > (RT) > (HR). Also, the experimental data were analyzed using analysis of variance and fitted to a second-order polynomial model applying multiple regression analysis. Predictive models were obtained which were able to satisfactorily fit the experimental data, with the coefficient of determination (R2) values higher than 0.95. Derringer’s desirability function methodology was used for the optimization study which showed that the HHV, EY, and FC at optimum condition TT 300 °C, RT 20 min, HR 5 °C/min were obtained as 21.26 MJ/kg, 81.26 %, and 35.38 wt%, respectively for MS. Torrefied MS, as compared to raw MS, showed better solid fuel properties for co-combustion with coal and gasification. The experimental values closely agree with the corresponding predicted values. The functional behavior of raw and torrefied MS was studied by Fourier Transform Infra-Red Spectrometry.