Energy valorisation of citrus peel waste by torrefaction treatment
Czech University of Life Sciences Prague, Faculty of Engineering, Department of Technological Equipment of Buildings, Kamycka 129, CZ165 21 Prague, Czech Republic
The article deals with the issue of processing and utilization of citrus peel, which often ends unused with other biodegradable waste. The research is concerned with the energy potential of this raw material and its torrefaction conversion. The tested materials were orange peel (Citrus sinensis Osbeck cv ‘Valencia’, Citrus sinensis Osbeck cv ‘Murcia’) and grapefruit peel (Citrus paradise ‘Ruby red’). Samples of dried materials underwent torrefaction treatment at 225 °C, 250 °C and 275 °C for 30 minutes. Samples before and after torrefaction were analysed for proximate and elemental composition and for calorific value. Consequently, stoichiometric combustion analyses were done. The torrefaction was performed in a LECO TGA 701 thermogravimetric analyzer under nitrogen atmosphere. The results of proximate and elemental analysis showed positive influence of torrefaction on the samples. The highest net calorific value for orange peel is 24.97 MJ kg-1 at the temperature of 275 °C. The greatest differences in net calorific values are between 225 °C and 250 °C where the increase is almost 3 MJ kg-1. Subsequently, the increase between the 250 °C and 275 °C torrefaction temperatures is 1 MJ kg-1. Weight loss at respective torrefaction temperatures showed similar time-dependent curves for all samples. Stoichiometric combustion analysis shows slight differences between original samples, but great differences after torrefaction processing. Stoichiometric combustion parameters also change proportionately with increasing temperature of torrefication. The resulting comnbustion balance figures show significantly lower need for mass of fuel in the case of the torrefied material for a given heat output thanks to the net calorific value being nearly doubled.