Assessing the Potential of Torrefaction for Locally Available Biomass in Mauritius

Abstract

Mauritius is highly dependent on fossil fuel imports for its own energy provision with only a minor contribution of renewable energy sources. Mauritius has however got potentials to increase its renewable energy share through increased biomass use. Conversely, there are several problems associated with biomass which reduces its appeal as a fuel compared to conventional fossil fuels. Pre-treatment technologies can nevertheless help valorise biomass. Torrefaction is known to be a mild pyrolysis process during which the lignocellulosic material in the biomass is decomposed and moisture and volatiles are eliminated. In this paper, the effect of torrefaction on the energy content and the chemical composition of four different locally available biomass feedstocks in Mauritius namely: Elephant grass (Napier grass), cane tops and leaves, wood wastes and palm trunks have been investigated. Samples of the biomass were treated at varying temperatures in the range of 200–300 °C in an inert atmosphere with a residence time of 1–3 h. The optimum residence time and temperature for each of the different biomass feedstock were determined. Enhancement ratios in the energy content of the torrefied biomass varied from 1.01 to 1.42. It was found that 1 kg of torrefied biomass could displace 0.776–0.855 kg of coal and reduce emissions of greenhouse gases from 2.01 to 2.34 kg. It was evaluated that savings of Rs. 3.19, Rs. 3.34, Rs. 3.52 and Rs. 3.29 per kg of torrefied sawdust, elephant grass, and CTL and palm wastes could also be made.