Browsing by Author "Manhongo, Tariro Tecla"

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    A comparative investigation of the technoeconomic feasibility and sustainability of mango waste biorefineries in South Africa: a process modeling approach
    (Stellenbosch : Stellenbosch University,, 2023-03) Manhongo, Tariro Tecla; Chimphango, Annie Fabian Abel; Thornley, Patricia; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering.
    ENGLISH ABSTRACT: Fruit processing waste (FPW) is a suitable biorefinery feedstock for conversion into bioenergy, biofuels, and chemicals. However, information on which processing routes and product combinations are economically viable and sustainable is limited. Using South Africa as a base developing economy, the availability of FPW as biorefinery feedstocks, economic viability, and sustainability of FPW-based biorefinery systems were evaluated in this study using mango processing waste as a base feedstock. Six biorefinery scenarios were evaluated; (I) combined heat and power (CHP) generation, (II) co-production of pectin and CHP, (III) co-production of pectin, polyphenols and CHP, (IV) co-production of pectin, bioethanol, and CHP, (V) co-production of pectin, polyphenols, bioethanol, and CHP, and (VI) co-production of bioethanol and CHP. In scenarios II to VI, residues from pectin and/or polyphenols recovery and wastewater are anaerobically digested for biogas production and the biogas in all scenarios is co-combusted with mango seed for steam generation (for use within the biorefinery and export to the host dried mango chips facility) and power (for consumption within the biorefinery and export if excess is generated). Aspen Plus process simulation models were developed at a plant capacity of 1500 tonnes per day (1200 tonnes process wastewater + 133.33 tonnes peel + 166.67 tonnes seed), operating for 24 h/day, and 120 days/annum. A discounted cash flow analysis was employed in assessing the economic viability of the six biorefinery models using the mass and energy flows from the models and incorporated in SimaPro-based attributional life cycle analysis models to evaluate the environmental impacts of the biorefineries. Using systems thinking, results from the technoeconomic analysis were employed in estimating the socio-economic benefits of the biorefineries using input-output Jobs and Economic Development Impact assessment models adopted from the National Energy Renewable Laboratory. Indicators for economic, environmental, and socio-economic performances of the biorefineries were normalized, weighted, and aggregated in a multi-criterion decision analysis approach to compare sustainability performances of the biorefineries. Scenarios I and VI are economically unattractive with net present values (NPVs) of -$94.4 and -$120.9 million, respectively. NPVs of the biorefineries increase with the recovery of more products in the order Scenario IV