Effect of Mixing Ratio on Performance of Mixture of Palm Kernel Shell and Lignite Co-Torrefied by Mild Pressurization Technique

In the present study, the mixtures of palm kernel shell (PKS) and lignite was co-torrefied using a new technique, that was called as mild pressurization technique. If compared to the conventional technique, the present technique has an advantage in terms of elimination of using costly inert gas. The co-torrefaction process was carried out at a fixed temperature of 300 °C for duration of 30 min, with weight percentage of lignite in the mixing ratios ranging from 0% to 30%. The absolute pressure of 0.0230 MPa was applied during co-torrefaction. The results indicate that there was no significant difference in the gross calorific value (GCV) for various mixing ratios. However, the energy density and ash content of the biofuel increased with the proportion of lignite. Based on the overall results, particularly regarding energy yield and proximate analysis, it can be concluded that mixtures with a higher proportion of lignite perform better. However, since the use of considerable amount of PKS is also prioritized, mixture of PKS and lignite with mixing ratio of 70:30 co-torrefied at 300 °C for 30 min is considered as the best in terms of combustion properties, with GCV of 22.35 MJ/kg, an energy yield of 0.874, a moisture content of 1.33%, and an ash content of 12.63%. The torrefied mixture meets all international standards except for ash content, but it remains competitive compared to commercial coal based on Van Krevelen diagram. Additionally, the mild pressurization technique shows competitive results compared to conventional methods.