18-15: Techno-economic analysis of different process configurations for bioethanol production from pretreated olive pruning biomass

In Mediterranean countries, olive tree pruning provides a widely available renewable agricultural residue, which has not got any industrial application yet. A typical olive tree pruning lot includes 70% thin branches and 30% wood. Disposal of pruning residues is necessary to keep fields clean and to prevent propagation of vegetal diseases. Usually the residues are disposed of either by burning or by grinding and scattering on the field. These residues could serve as feedstock for bioethanol production.

Eight process configurations regarding pretreatment, hydrolysis and fermentation are compared in techno-economic aspects, i.e. overall process energy efficiency and ethanol production cost. The process model is built in Aspen Plus V7.3 and economic evaluation is aided by Aspen Process Economic Analyzer V7.3. Upstream process steps (up to fermentation) are modelled using experimental data. Downstream part of the process consists of distillation, dehydration, evaporation of the thin stillage and combined heat and power production, in which the evaporated thin stillage, the thick stillage (solid fraction) and the biogas produced in wastewater treatment are incinerated. Diluted acid and liquid hot water pretreatments are combined with separate hydrolysis and fermentation (SHF), simultaneous hydrolysis and fermentation (SSF) and prehydrolysis and simultaneous saccharification and fermentation, which result in six configurations. In additional two cases steam pretreatment is combined with SHF and SSF. In each configuration the effects of solid loading on process performance and economics are also studied.