Browsing by Author "Padi, Richard Kingsley"

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    Potential and economic impact of renewable energy in improving african rural food processing
    (Stellenbosch : Stellenbosch University, 2016-03) Padi, Richard Kingsley; Chimphango, Annie F. A.; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Traditional food processing technologies in rural settings of Sub Saharan Africa are characterised by small production scales, labour intensive processes and uneconomical operations, which contribute to high food losses postharvest. Mechanisation addresses some of these limitations although a lack of access to modern energy stands as additional drawback. Hence in order for advancing mechanisation to be feasible, an alternative approach to integrating energy supply into food processing systems is required. Little is known on the cost implications of such mechanisation and alternative energy integration on the profitability of the food processes. The general objective of this study was to investigate the economic impacts of mechanisation and/or bioenergy integration in crude palm oil (CPO), cassava flour (CF) and maize flour (MF) processes. This objective was achieved by developing process models for traditional, semi-mechanised and mechanised processes, with increasing extent or level of mechanisation, in which in-house energy integration was applied. The process/economic models were developed using Microsoft Excel. For each of the referred processes, Base-cases (B/C) entailing conventional energy-mix and corresponding improved-cases (I/C) with potential energy from process residues (in-house energy) were considered. Models of advanced in-house energy schemes were developed in Aspen Plus®. Economics were based on 2014 economic conditions of Ghana. Two funding schemes were assessed: 1. Private investor financing [60% of investment financed by loan (at 24% nominal interest rate) and remaining 40% investment from equity (at 40% nominal interest rate), having weighted nominal (before inflation) discount rate of 30%]. 2. Combinations of grant (at 0% nominal discount rate) and equity (at 40% nominal discount rate) financing (i.e. part of the financing covered by grant and the remaining investment financed by equity from an investor). Feasible advanced energy schemes considered in the I/C scenarios were: electricity/thermal energies from solid biomass residues for the CPO mechanised process, electricity/dryer fuel from anaerobic digestion of cassava peels/cattle dung for the CF semi- and mechanised process and, cob-fired dryer for MF semi- and mechanised drying operations. In the CPO process, there was a decrease in energy demands for the mechanised process at the B/C and I/C levels when compared to the traditional (79.2 and 83.8%) and semi-mechanised (48 and 51%) respectively. Thus an increase in the level of mechanisation was not necessarily associated with an increase in energy savings. In addition, under the private investor financing (nominal discount rate of 30%), only the mechanised process was economically viable with an Internal Rate of Return (IRR) of 47.2% under the B/C scenarios, while the semi- and mechanised processes were the economically viable options for the I/C scenarios with IRRs of 143% and 40.6% respectively. The poor performances of the traditional- B/C and -I/C and semi-mechanised B/C were due to combinations of high capital investment ($0.019 – 0.053/kg) and high production cost ($0.431 – 1.187/kg), as they remained unviable under 100% grant funding. Thus mechanisation is beneficial to the economics at the highest mechanised process level, while in-house energy integration from residues is most promising at the semi- and mechanised process levels. In the CF Process, the energy demand for the traditional process was higher by 37.6, 44.5 and 52.6% (for B/C) and 46.0, 52.0 and 59.0% (for I/C) than the semi-mechanised, mechanised-grating and mechanised-chipping processes respectively. Thus, mechanisation has an energy saving impact on the process. Under the private investor funding (discount rate of 30%), the mechanised chipping process was the only economically viable option (IRR of 36.3%), while the traditional B/C, traditional I/C and mechanised-chipping B/C were promising with IRRs of 16.3, 24 and 24.8% respectively. Under grant-equity funding, semi-mechanised and mechanised-grating processes remained unviable, thus not being able to achieve sufficient cash flows to pay off debt co-financing of new installations. Under the grant-equity financing, the traditional B/C and I/C, and mechanised-chipping I/C processes achieved Net Present Values (NPV) of $22, $60 and $67180 at grant funding of 60%, 40% and 1% respectively (with the remaining funding contributions provided by equity), suggesting their potential viability under grant subsidy. Thus, economic impact of mechanisation and that of in-house energy generation from the residues were inconsistent. The energy demand of the mechanised MF process was higher by 87.3 and 48.0% (B/C) and 89.1 and 51.2% (I/C) than the traditional and semi-mechanised scenarios, respectively. Conclusively, an increase in mechanisation also increased the process energy demands. All B/C scenarios attained negative NPVs and were thus economically unviable. The I/C scenario for the traditional process remained unviable with NPV of -$1854, while semi- and mechanised processes attained IRRs of 18.8 and 132.8% respectively; hence, only mechanised I/C was viable considering the 30% minimum expected IRR. At semi-mechanised I/C, feedstock obtained from farm gates rather than licensed buying companies (LBCs) resulted in production cost savings of 46.2%, while integration of cobs as dryer fuel increased production cost by 25.5%. Sourcing feedstock from farm gates rather than LBCs and using cobs residues as dryer fuel (replacing diesel) in the mechanised I/C process, resulted in production cost savings of 73.2 and 1.7% respectively. The traditional, semi- and mechanised B/C processes remained unviable under 100% grant funding, while semi-mechanised I/C process attained NPV of $1422 at 40% grant and 60% equity financing. Therefore, mechanisation did not improve economic performance; rather feedstock supply chain was the determining factor for profitability of MF processing. Cobs-fuelling dryer was technically viable but most beneficial (economically) to the mechanised process.
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    Techno-economic and sustainability models for integration of cassava waste-based biorefineries into cassava starch processes based on process simulation and a systems modelling approach
    (Stellenbosch : Stellenbosch University, 2021-03) Padi, Richard Kingsley; Chimphango, Annie F. A.; Roskilly, Anthony Paul; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Cassava crop high starch yields, accompanied by its tolerance to drought/low soil nutrients, have increased research attention towards the crop’s adoption as a potential food security and economic empowerment crop for South Africa. Widely consumed as food and livestock feed, cassava starch also has potential industrial applications in pharmaceuticals, specialty chemicals (e.g. succinic acid), ethanol, adhesive, and food derivatives (e.g. glucose syrup). Commercialization of industrial cassava starch facilities (CSF) depends on profitability and sustainable energy supply for operations. Residues generated by CSFs [cassava starch wastewater (CWW), bagasse (CB)], and cassava stalks (CS) could generate the requisite energy for cassava starch industries (CSI), thus there is potential to integrate waste-based bioenergy developments with CSFs. Cassava waste biorefineries (CWBs) for co-producing energy and high-value bio-products have been proposed as potential solutions to energy and cost limitations in CSFs. Attributed to knowledge gaps on the techno-economic feasibility (TEF) and long-term sustainability (economic + environmental + social) of such CWBs, conventional waste management schemes involve the burning of CS and anaerobic digestion of CWW & CB to produce biogas for starch drying heat, with the digestate being disposed into watercourses. This research, through Aspen Plus® process/economic modelling and SimaPro simulation, investigated the TEF and sustainability of CWBs in the South African socio-economic context, with an overall objective of contributing to knowledge towards the commercialization of CWBs. The investigated CWB scenarios include: (i) enhanced waste resource recoveries (energy, biofertilizer, water) through integrating CS into CSF waste treatment, and (ii) advanced CWBs [(I) combined heat & power, with (II) hexose-bioethanol, (III) pentose & hexose-bioethanol, (IV) pentose-bioethanol + glucose syrup, and (V) pentose-bioethanol + succinic acid)]. The results showed that combined treatment of CS (14.32 t/h) with CSF wastes (7.29 t/h DM CB + 377.83 t/h CWW) could ensure further resource recoveries, including bioelectricity (up to 31.96 MW), liquid/solid biofertilizer, and usable water, with potential energy self-sufficiency and economic enhancements for CSIs. Co-conversion of 450.89 t/h CS and CSF waste could ensure sufficient energy supplies for both CWBs and CSFs, plus 300 MW electricity (I), or 287 MW + 1.48 t/h bioethanol (II), or 121 MW + 8.95 t/h bioethanol (III), or 164 MW + 5.72 t/h bioethanol + 9.29 t/h glucose syrup (IV), or 161 MW + 5.72 t/h bioethanol + 6.9 t/h succinic acid (V). However, only scenarios (I)-(II) demonstrated economic viability, while (III)-(V) favor environmental sustainability. Revitalizing the CSI’s via integrations with the resource recovery schemes, where the recoveries are re-used in the CSFs and crop cultivations, could ensure viable circular economy strategies that may enhance sustainable industrial developments. Hence, integrating CSFs with resource recoveries or CHP (I) or CHP + hexose-bioethanol (II) represent viable strategies for the synergetic advancement of food-energy security and low-carbon economies.