Energy Densification of Cocoa Pod Shell by Torrefaction Method

Abstract

Torrefied biomass is a green alternative to coal, and thus the interest in the torrefaction process is rising very fast. This work presents the optimal conditions of densification of cocoa pod shells' energy content under varying torrefaction conditions of temperature and residence time by converting the waste pod shell as a feedstock to produce energy-rich biochar via the torrefaction method. A laboratory-size torrefaction reactor was used for the torrefaction experiments by varying temperatures at 250, 275, and 300 ℃ and residence times of 50, 60, and 70 minutes. Nitrogen gas was injected continuously into the reactor at a 250 mL/min flow rate to expel oxygen and some volatiles in the reaction chamber to achieve the inert condition for the process. The work also involved the characterisation of the raw cocoa pods and the torrefied products. Design-Expert Software was employed to analyse the data obtained from the experiments. The results show that cocoa pod torrefaction is technically feasible to produce solid biofuel. Both temperature and residence time have significant effects on the properties of the torrefaction products. An optimum temperature of approximately 286 ℃ and residence time of 63 minutes improved the cocoa pods' fuel properties. The torrefied cocoa pod was brittle with an increased energy density of 20 per cent more than the raw sample. The fixed carbon content increased while the moisture absorption rate, volatile matter, oxygen-carbon ratio and hydrogen-carbon ratio of the product decreased. The model equations derived in this research are vital for predicting torrefaction conditions of cocoa pod without necessarily performing the torrefaction experiment.