Assessment of olive wastes as energy source: pyrolysis, torrefaction and the key role of H loss in thermal breakdown

The present work describes the first stage of a multi-stage process seeking to develop a usable and cheap design for a downdraft gasifier fed with lingo-cellulosic olive waste. The thermochemical behaviour of two types of olive waste has been assessed during pyrolysis and torrefaction experiments. Olive tree trimmings and olive pulp were pyrolysed in a quartz reactor at peak temperatures between 400 °C and 650 °C, during slow heating experiments (50 °C/min) under a helium blanket. These samples were also torrefied under nitrogen to temperatures between 200 °C and 325 °C. At the peak temperature of 650 °C, mass losses of up to 74% were recorded. Elemental analyses of the chars showed a consistent linear increase of Carbon to values around 75% and a linear decrease of oxygen to values near 10%. By contrast, the H-content remained relatively constant up to about 300 °C and then decreased to as the peak temperature was raised further. The results suggest that the combination of mass loss and H-content may be used as indicators for linear char-GCV increases up to the torrefaction limit of around 300 °C.