Effects of Pretreatment Outside of Torrefaction Range on Combustion Characteristics of Chars from Lignocellulosic Biomass

Lignocellulosic woody biomasses such as rhododendron (RD), ash tree (AT), and hybrid poplar (HP) were heated under N2 at 200 °C and 400 °C, which are regarded as outside the range of efficient torrefaction temperatures. Also, several Turkish brown coals were carbonized at 750°C for comparison. The obtained biochars/chars were characterized by scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), and thermal analysis. Combustion reactivity of the raw samples and the chars was estimated using the burning profiles. Burning kinetics was established by the Borchardt and Daniels (B&D) kinetic analysis method that was based on the evaluation of the differential scanning calorimetry (DSC) data. Ignition index (Ci), burnout index (Cb), comprehensive combustibility index (S), and burning stability index (DW) were considered to evaluate the combustion performance. It was concluded that although treatment at 200 °C did not lead to considerable changes on the biomass structure, the combustion performance of the treated biomass became highly improved in comparison with the raw biomass. However, treatment at 400 °C led to serious variations in the biomass structure mainly due to reduction in O content and volatiles so that the fuel properties and the burning characteristics were affected, and the combustion performance was negatively influenced.