Browsing by Author "Van Schalkwyk, Dominique Lisa"
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- ItemTechno-economic and environmental analysis of bio-oil production from forest residues via non-catalytic and catalytic pyrolysis processes(Stellenbosch : Stellenbosch University, 2019-12) Van Schalkwyk, Dominique Lisa; Gorgens, Johann F.; Mandegari, Mohsen A.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: Forest residues are a high fire risk and often disposed of by burning or sold as firewood; both contribute to air pollution, and the latter has low economic value. The 1.5 million dry metric tonnes of forest residues available in South Africa every year can instead be converted into liquid bio-oil and solid biochar through intermediate pyrolysis. However, bio-oil is acidic and has a low energy value as a result of its high oxygen content. Bio-oil can be upgraded to improve its oxygen content by introducing a CaO catalyst in situ to the pyrolysis process. Upgraded bio-oil can then be co-processed in a crude-oil refinery to produce bio-derived fuels. Therefore, the aim of this project was to determine whether or not the production of crude and upgraded bio-oils via non-catalytic and catalytic pyrolysis of forest residues for co-processing in an oil refinery is economically and environmentally feasible. Process simulations were developed in Aspen PlusTM based on pilot plant data for non-catalytic and catalytic pyrolysis processes. All of the non-condensable gas and 21.5 wt. % of the char (for non-catalytic pyrolysis biorefinery scenarios only) were combusted to meet the energy demands of the biorefinery scenarios. The net yield of non-catalytic pyrolysis products from Eucalyptus grandis forest residues (8.28 wt. % moisture) was 22.6 wt. % biochar and 19.8 wt. % crude bio-oil, while the net yield of catalytic pyrolysis products was 16.5 wt. % biochar and 18.4 wt. % upgraded bio-oil. There was a clear economy-of-scale benefit for non-catalytic and catalytic pyrolysis biorefinery scenarios as the biomass collection distance increased from a 100 to 300 km radius of the biorefinery. The Minimum Selling Price (MSP) of upgraded bio-oil ($1.35/L) was significantly higher than the MSP of crude bio-oil ($0.75/L) for a desired 22 % Internal Rate of Return (IRR) at a 300 km radius of the biorefinery. However, the quality of upgraded bio-oil was superior to crude bio-oil for co-processing in an oil refinery. Co-processing crude bio-oil will likely produce bio-derived fuels with a significantly lower renewable carbon content and higher yield of undesirable CO, CO2 and H2O gases. The price premium for crude and upgraded bio-oils was substantiated by a significant environmental benefit. A Life Cycle Impact Assessment (LCIA) was conducted using the CML-IA baseline method in SimaProTM to assess the environmental impact of producing 1 MJ of crude or upgraded bio-oil, instead of crude-oil or diesel. The net Global Warming Potentials (GWPs) for crude bio-oil, upgraded bio-oil, crude-oil and diesel were -0.30, -0.14, 0.0052 and 0.013 kg CO2 eq/MJ of fuel, respectively. Biochar application to soils had a substantial influence on the GWP of bio-oil production through associated carbon sequestration. Co-processing crude and upgraded bio-oils at pilot-scale was recommended to evaluate the relationship between blending ratio, distribution of oil refinery products and extent of deoxygenation reactions. Furthermore, the scope of this project should be expanded to include a techno-economic analysis for co-processing crude and upgraded bio-oils to further evaluate the economic feasibility of crude and upgraded bio-oil production.