Hydrothermal treatment (HTT) improves the combustion properties of regional biomass waste to face the increasing sustainable energy demand in Africa

Abstract

The increasing worldwide energy demand in parallel to the increasing climate change effects require the utilization of sustainable energy sources. Biomass residues are a feasible energy source, but their chemical composition often compromises their utilization due to slag formation or high emissions. It is investigated in this study whether hydrothermal treatment (HTT) can improve the combustion properties of biomass residues from Ghana. Six biomass residues (Prekese pods, ground nut husks, coconut husks, cassava peels, shea cake, deoiled shea cake) treated at three temperatures (150 °C, 170 °C, 185 °C) were analyzed for combustion properties and emission precursors according to European Standards. The results were evaluated considering consistencies of combustion related properties and especially of ash element reduction behavior. There was a clear trend to increasing mass loss and increasing heating value with increasing treatment temperature that was reflected in the carbon, hydrogen and oxygen amounts, while the ash content and its composition varied. Consistencies in the ash element behavior were highlighted and discussed in order to identify chemical key parameters that led to or inhibited specific ash element reductions. HTT was identified as a feasible biomass upgrade method with advantages over water leaching at room temperature and high temperature hydrothermal carbonization in case of the availability of off-heat from e.g. biomass electricity production.