Enhancing Biofuel Pellet Quality using Combined Torrefaction and Co-pelletization Processes of Palm Kernel Shell and Empty Fruit Bunch

Abstract

Palm kernel shell (PKS) and empty fruit bunch (EFB) are potential biomass resources for producing solid biofuel for energy applications. However, raw EFB and PKS are not uniform in size and pose rotting behavior. Torrefaction and co-pelletization are both effective methods to improve their combustion and mechanical characteristics. This study aims to investigate the effect of torrefaction temperature and the blending ratio of PKS and EFB on the mechanical and combustion characteristics of co-pellets. Initially, PKS and EFB underwent torrefaction process for 30 minutes at three different temperatures (210°C, 240°C, and 270°C). Then, both torrefied PKS and EFB were blended at five different ratios (0:100, 25:75, 50:50, 75:25, 100:0) with carboxymethyl cellulose as a binder (10% by weight). The results showed that a higher torrefaction temperature resulted in an increment of the higher heating value (HHV) but weaker mechanical strength. Pellets with a blending ratio of PKS to EFB (75:25) torrefied at 240°C showed the comparatively best pellet quality in terms of HHV (17.94 MJ/kg), high compressive strength (3.5 MPa), low ash content (3.97 wt%), and the lowest density changes (0.66%), which satisfy the requirements set in standard EN ISO 17255-6 for good quality pellets, indicating that a high quality biofuel pellet can be produced using the combined approach of torrefaction and co-pelletization.