Impact of Torrefaction on Vine Pruning’s Fuel Characteristics

Abstract

Agricultural and waste-derived solid biomass fuels are available in vast amounts for the generation of sustainable energy. Since these fuels usually have rather low heating values, low bulk densities and are disadvantageous concerning their storage behavior, the torrefaction of such materials (low-temperature pyrolysis between 200°C and 320°C) represents an interesting procedure to improve their fuel properties. After the torrefaction of vine prunings for 30 min at 200°C and 220°C was performed in a pilot hearthtype reactor located in Ptolemais-Greece, the lower heating value (LHV) was increased by 3.7% and 10.5%, respectively, leading to important cost reductions during transport and storage. A comparative analysis of chemical properties between raw material and torrefied material is presented followed by calculating fuel-specific indices concerning corrosion risk, aerosol formation, and slagging tendency. Based on the NOx emission index, a lower conversion was predicted for the torrefied fuel than for the untreated fuel. High aerosol emissions are expected for raw fuel, even higher aerosol emissions for the torrefied fuel. According to the measured ash melting temperatures and calculation of the Rs index, raw fuel and torrefied fuel at 200°C present medium trend for deposit formulation, whereas there is a high trend for deposit formulation in the case of torrefied fuel at 220°C.