Techno-economic and environmental analysis of bio-oil production from forest residues via non-catalytic and catalytic pyrolysis processes

Van Schalkwyk, Dominique Lisa (2019-12)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Bosbou residu is ʼn hoë brandrisiko en word dikwels weggemaak deur verbranding of te verkoop as vuurmaakhout; al twee dra by tot lugbesoedeling, en die laasgenoemde het lae ekonomiese waarde. Die 1.5 miljoen droë metrieke ton bosbou residu beskikbaar in Suid-Afrika elke jaar kan eerder omgeskakel word in vloeistof bio-olie en vastestof bioverkoolsel deur intermediêre pirolise. Bio-olie is egter suurvormend en het ʼn lae energiewaarde as gevolg van sy hoë suurstofinhoud. Bio-olie kan opgegradeer word om sy suurstofinhoud te verbeter deur ʼn CaO-katalisator in situ in die pirolise proses bekend te stel. Opgegradeerde bio-olie kan dan gekoprosesseer word in ʼn ru-olieraffinadery om bio-afgeleide brandstowwe te produseer. Daarom is die doel van hierdie projek om vas te stel of die produksie van ru- en opgegradeerde bio-olies via nie-katalitiese en katalitiese pirolise van bosbou residu vir koprosessering in ʼn olieraffinadery uitvoerbaar is vir die ekonomie en omgewing, of nie. Prosessimulasies is ontwikkel in Aspen PlusTM gebaseer op loodsaanlegdata vir nie-katalitiese en katalitiese pirolise prosesse. Al die nie-kondenseerbare gasse en 21.5 wt. % van die verkoolsel (slegs vir nie-katalitiese pirolise bioraffindery scenario’s) is verbrand om aan die energievereistes van die bioraffinadery scenario’s te voldoen. Die netto waarde van nie-katalitiese piroliese produkte uit Eucalyptus grandis bosbou residu (8.28 wt. % vog) was 22.6 wt. % bioverkoolsel en 19.8 wt. % ru bio-olie, terwyl die netto opbrengs van katalitiese piroliese produkte 16.5 wt. % bioverkoolsel en 18.4 wt. % opgegradeerde bio-olie was. Daar was ʼn duidelike ekonomie-van-skaal-voordeel vir nie-katalitiese en katalitiese pirolise bioraffinadery scenario’s soos wat die afstand van die biomassa versameling vergroot het van 100 tot 300 km radius van die bioraffinadery. Die Minimum Verkoopsprys (MSP) van opgegradeerde olie ($1.35/L) was beduidend hoër as die MSP van ru bio-olie ($0.75/L) vir ʼn verlangde 22% Interne Opbrengskoers (IRR) by ʼn 300 km radius van die bioraffinadery. Die kwaliteit van opgegradeerde bio-olie was egter superieur teenoor ru bio-olie vir koprosessering in ʼn olieraffinadery. Koprosessering van ru bio-olie sal waarskynlik bio-afgeleide brandstowwe met ʼn beduidende laer hernubare koolstofinhoud en hoër opbrengs van ongewensde CO, CO2 en H2O produseer. Die prys premie vir ru en opgegradeerde bio-olies is bevestig deur beduidende omgewingsvoordeel. ʼn Lewensiklusimpakassessering is gedoen deur die CML-IA basislyn metode in SimaProTM te gebruik om die omgewingsimpak van die produsering van 1 MJ van ru of opgegradeerde bio-olie, in plaas van ru-olie of diesel, te assesseer. Die netto Globale Verwarmingspotensiaal vir ru bio-olie, opgegradeerde bio-olie, ru-olie en diesel was -0.30, -0.14, 0.0052 en 0.013 kg CO2 eq/MJ van brandstof, onderskeidelik. Toepassing van bioverkoolsel op grond het ʼn substansiële invloed op die Globale Verwarmingspotensiaal van bio-olie produksie deur verwante koolstof sekwestrasie. Koprosessering van ru en opgegradeerde bio-olies op loodsskaal is aanbeveel om die verhouding tussen vermengverhouding, distribusie van olieraffinadery produkte en omvang van reaksies van deoksigenering te evalueer. Verder moet die omvang van hierdie projek verbreed word om ʼn tegno-ekonomiese analise vir koprosessering van ru en opgegradeerde bio-olies in te sluit om die ekonomiese uitvoerbaarheid van ru en opgegradeerde bio-olie produksie te evalueer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107238
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