A preliminary environmental analysis for a sustainable pyrolysis process of Acacia tortilis encroacher bush.

Abstract A shortcut method of environmental assessment was applied procedurally to an Acacia Tortillis pyrolysis project which is in early stages of process development. The method uses mass balance data from the process simulation, which is done in ChemCAD. The ChemCAD model was developed using characterization data for raw biomass and the product bio-oil and data from literature. The shortcut assessment method started off by scoring the impact of inputs and outputs as high (A=1), medium (B= 0.3) and very low (C= 0) under impact categories such as raw material availability, use of critical materials, chronic toxicity, global warming potential, odour and eutrophication potential. An aggregated metric called the general effect index (GEI) was then calculated using this data and mass indices derived from mass balance. The GEI was calculated for inputs, outputs and the overall process. It fell within the scale of 0-1, with values below 0.5 indicating a low environmental impact, while those above that threshold indicated high impact. A GEI of 0 for the inputs reflected on the renewability of biomass and neutral impact of nitrogen and air. A GEI of 0.370 for the outputs showed they do have a significant effect on the environment and organisms, though overall, the process is relatively benign. The impact could be further reduced by utilizing the fuel gas waste stream which has a high methane content. The results obtained generally tally with other literary findings on biomass pyrolysis.