Impact of carbonization on the combustion and gasification reactivities of olive wastes

Abstract

As an alternative to biomass, biochar is known as a promising candidate to replace or co-process with coal as solid fuel. In this study, biochars were obtained from pyrolysis of olive tree pruning (OP) at different temperatures and duration in order to investigate their possible use in combustion and gasification processes alone or with lignite. Steam gasification experiments of raw biomass, biochars and their blends with lignite were conducted in two-stage reactor at 850 °C to produce hydrogen-rich gas. The combustion behavior of fuels was investigated using thermogravimetric analyzer. The temperature was more effective than duration on the yield and properties of biochar. Biochars obtained above 350 °C had more aromatic structure with higher fixed carbon content. Gasification of biochar was more efficient than that of biomass, due to its high carbon content, homogeneous properties, and minimized tar formation. Hydrogen yield increased with the increase in the potassium and fixed carbon contents of biochars. Slagging and fouling indices of biochars indicated the tendency of slagging and fouling during their combustion alone. For the blends containing OP and biochars produced at low temperatures, antisynergistic effect was observed, lowering the combustion reactivity. In contrast, no interaction was found for the blend containing high-temperature biochar.