Torrefaction of Palm Kernel Shell and Petcoke Blends for Various Mixing Ratios and Temperatures

In the present study, torrefaction of palm kernel shell (PKS) and petcoke blends was performed for the production of solid biofuels with high energy density. The torrefaction process was performed for mixtures with various mixing ratios (by weight) from 90:10 to 60:40 (PKS:petcoke). For torrefaction under various temperatures of 250℃ to 300℃, the mixing ratio of 60:40 was used. Meanwhile, residence time and nitrogen flow rate were fixed at 30 minutes and 1 l/min, respectively. In general, the fixed carbon and ash contents increased, while the moisture and volatile matter contents decreased after torrefaction. It has been elucidated that mass yield is a dominant factor that affects the energy yield of torrefied mixtures rather than the higher heating value (HHV) ratio. Based on the energy yield and ultimate analysis, it was found that a higher amount of petcoke and higher temperature give better performance, thus causing the torrefied mixture to become very close to coals region in Van Krevelen diagram. In this case, the mixture with a mixing ratio of 60:40 torrefied under the temperature of 300℃ gives the best performance. It was also found that this mixture is thermally stable than the mixture torrefied at 250℃.