Browsing by Author "Petersen, Abdul Muhaymin"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Comparisons of the technical, financial risk and life cycle assessments of various processing options of sugercane bagasse to biofuels in South Africa
    (Stellenbosch : Stellenbosch University, 2012-03) Petersen, Abdul Muhaymin; Gorgens, Johann F.; Knoetze, J. H.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering
    ENGLISH ABSTRACT: Through many years of research, a number of production schemes have been developed for converting lignocellulosic biomass into transport fuels. These technologies have been assessed through a number of techno-economic studies for application in a particular context in terms of the technical and economic feasibility. However, previous studies using these methods have tended to lack vigour in various aspects. Either the energy efficiency of the processes were not maximised through adequate heat integration, or a competing technology which existed was not considered. From an economic perspective, the financial models would often lack the vigour to account for the risk and uncertainty that is inherent in the market prices of the commodities. This phenomenon is especially relevant for the biofuel industry that faces the full fledge of uncertainties experienced by the agricultural sector and the energy sector. Furthermore, from an environmental perspective, the techno-economic studies had often ignored the environmental impacts that are associated with biofuel production. Thus, a comparative study could have favoured an option due to its economic feasibility, while it could have had serious environmental consequences. The aim of this study was to address these issues in a South African context, where biofuels could be produced from sugarcane bagasse. The first step would be to modify an existing simulation model for a bioethanol scenario that operates with a Separate Hydrolysis and Fermentation (SHF process) configuration into a second processing scenario that operates with a Simultaneous Saccharification and Fermentation (SSF process) configuration using reliable experimental data. The second step was to ensure that the maximum energy efficiency of each scenario was realised by carrying out pinch point analysis as a heat integration step. In contrast to these biological models is the thermochemical model that converts bagasse to gasoline and diesel via gasification, Fischer-Tropsch synthesis and refining (GFT process). While there were no significant advances in technology concerning this type of process, the energy efficiency was to be maximised with pinch point analysis. The GFT process obtained the highest energy efficiency of 50.6%. Without the affects of pinch point technology, the efficiency dropped to 46%, which thus emphasises the importance of heat integration. The SSF had an efficiency of 42.8%, which was superior to that of the SHF at 39.3%. This resulted from a higher conversion of biomass to ethanol in the SSF scenario. Comparing the SHF model to an identical model found in literature that did not have pinch point retrofits, this study showed lower efficiency. This arose because the previous study did not account for the energy demands of the cold utility systems such as the cooling tower operation, which has been shown in this study to account for 40% of the electrical energy needs. The economic viability of all three processes was assessed with Monte Carlo Simulations to account for the risks that the fluctuations in commodity prices and financial indices pose. This was accomplished by projecting the fluctuations of these parameters from samples of a historical database that has been transformed into a probability distribution function. The consequences were measured in terms of the Net Present Value (NPV) and Internal Rate of Return (IRR) for a large number of simulations. The results of these variables were aggregated and were then assessed by testing the probability that the NPV<0, and that the IRR recedes below the interest rate of 12.64%. The investment was thus deemed unfeasible if these probabilities were greater than 20%. Both biological models were deemed profitable in terms of this standard. The probabilities were 13% for the SSF and 14% for the SHF. The GFT process however was deemed completely unfeasible because the probability that the NPV<0 was 78%. Given that the GFT process had the highest energy efficiency, this result arises mainly because the capital investment of 140,000USD/MWHHV of biomass energy input is to enormous for any payback to be expected. The environmental footprint of each process was measured using Life Cycle Assessments (LCAs). LCAs are a scientifically intricate way of quantifying and qualifying the effects of a product or process within a specified boundary. The impacts are assessed on a range of environmental issues, such as Global Warming, Acidification, Eutrophication and Human toxicity. Furthermore, if the project under concern has multiple output products, then the impacts are distributed between the output products in proportion to the revenue that each generates. The impacts were either relative to the flow of feedstock, which was 600MW of bagasse, or to the functional unit, which was the amount of fuel required to power a standard vehicle for a distance of 1 kilometre. In either case, the GFT scenario was the least burdening on the environmental. This was expected because the GFT process had the highest energy efficiency and the process itself lacked the use of processing chemicals. Relative to the feedstock flow, the SSF was the most environmentally burdening scenario due to the intensive use of processing chemicals. Relative to the functional unit, the SHF was the most severe due to its low energy efficiency. Thus, the following conclusions were drawn from the study:  The GFT is the most energy and environmentally efficient process, but it showed no sign of economic feasibility. iv  There is no significant difference in the economic and environmental evaluation of the SSF and SHF process, even though the SSF is considered to be a newer and more efficient process. The major cause of this is because the setup of the SSF model was not optimised.
  • Thumbnail Image
    Item
    Integration of second generation biofuel production into existing industrial processes for short term commercial implementation
    (Stellenbosch : Stellenbosch University, 2015-12) Petersen, Abdul Muhaymin; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Since the production of second-generation biofuel (SGB) from lignocellulosic plant biomass is only economically attractive if driven by government incentives, stakeholders are reluctant to commercialise the product despite its potential to mitigate global warming and socio-economic conditions. Integrating SGB processes with the facilities of biomass-based industries could reduce the production costs of SGB through pre-existing services and infrastructure. Integrating SGB, however, is technically viable only if available biomass residues are used effectively to co-produce fuel while maintaining the overall energy balance, financially viable only if it attracts private investment without governmental assistance and environmentally viable only if it reduces the carbon imprint of a fossil-intensive host industry. In this dissertation, novel scenarios for integrating SGB with the South African raw sugar and the pulp and paper industries (RSI and P&PI, respectively) were explored. Focus was on ethanol production based on fermenting hemicellulose substrates, potentially available in both industries, and on SGB production through gasification-synthesis processes in the contextual representatives of these industries. This was accomplished through flow-sheet analysis in Aspen Plus® using process simulations constructed from protocols in published literature and experimental data. In respect of RSI, integrating bioethanol production with electricity from sugarcane bagasse and harvesting residues were deemed both technically and economically viable and competitive against the exclusive generation of electricity. The necessity of Pinch Point Analysis was established through flow-sheet analysis, which had also shown the synergistic interaction of technologies in various processing stages, such as the variants in ethanol distillation technologies and heat and power production technologies. In respect of P&PI, represented by sulphite mills, ethanol production from spent sulphite liquor (SSL) pulping residue was deemed economically viable if the SSL fermentation substrate was concentrated. To attain net reduction of greenhouse gas emissions for the integrated ethanol-sulphite facility, it was essential to provide all process energy requirements from supplementary biomass sources rather than coal. In respect of RSI, integrating methanol or Fischer-Tropsch syncrude via gasification synthesis was deemed not feasible at the current state of efficiency with which sugar mills are operating. In respect of P&PI, combining synthetic fuel production with bioethanol production at a sulphite mill improved economic potential, since disposal costs were negated through the use of waste biomass for synthesis processes and the yield of valuable products was enhanced on a small scale. In respect of both RSI and P&PI, however, integrating gasification-synthesis processes required the statistical optimisations of flow sheets to arrive at the optimum operating parameters for competing technologies for syngas production. In these contexts, syngas production based on optimised allothermal gasification had lower costs than optimised autothermal gasification. To validate the process concepts developed in this thesis, it is firstly recommended that robust and recombinant microbial strains be readily available to ferment pentose-rich substrates, such as SSL and hemicellulose hydrolysates. Secondly, the effect of the chemical alteration of SSL on the recovery performance of process chemicals at sulphite mills should be examined and, thirdly, the catalytic gasification of biomass should be developed and demonstrated on pilot and pre-commercial scales.