Effect of pre-washing and torrefaction processes on the physical and thermal properties of bio-briquettes produced from king grass (Pennisetum Purpuroides).

The Indonesian government is encouraging a co-firing system by adding biomass fuel for steam power plants. This strategy is motivated by coal supplies which continue to decrease over the time. This situation is encountered by utilization of biomass energy to produce solid fuels such as briquettes or pellets with energy equivalent to coal. Another main consideration is that the source of biomass should be sustainable without any conflict with food security. One of sources of accessible, sustainable, and non-edible biomass is the king grass plant. This plant can grow in marginal areas with a relatively short growth period. The main challenge in using this biomass lies in its low energy density. Therefore, it is necessary to develop technology to improve the properties of the solid fuel produced from king grass biomass. In the last few decades, torrefaction at low temperatures has been widely used since this technology effectively improves the biomass properties. The main objective of the torrefaction process is to increase the calorific value and reduce the water content. Prior to torrefaction process, the feedstock was washed and soaked with tap water for 20 h to reduce the ash content. During torrefaction process, biomass was heated in a non-oxidative environment at temperatures below 300°C. Resulting biochar was then ground, sieved and mixed with starch binder at 5 wt% and 10 wt%. Briquette characterization were performed under several techniques including bomb calorimetry, proximate, density, dropped-test and relaxation analyses. The results showed that the highest calorific value was 4648 kcal/kg obtained from TKG60m5b sample. Proximate test results showed that the ash content decreased by up to 11% after the washing process. Overall, the washing and torrefaction processes applied to the king grass biomass caused significant improvement in term of caloric value, ash content, friability and density. [ABSTRACT FROM AUTHOR]