Browsing by Author "Van der Westhuizen, Willem Andries"

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    A Techno-economic evaluation of integrating first and second generation bioethanol production from sugarcane in Sub-Saharan Africa
    (Stellenbosch : Stellenbosch University, 2013-12) Van der Westhuizen, Willem Andries; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Climate change that results from greenhouse gases (GHG’s) released from the burning of fossil fuels, together with the rising price of oil, have sparked interest in renewable biofuels. The production of biofuels also presents potential socio-economic benefits. There are two types of technologies for bioethanol production: · First generation bioethanol is produced from food feedstocks such as juice of sugarcane. · Second generation bioethanol is produced from non-food feedstocks (lignocellulosic materials). This project is concerned with 1st and 2nd generation bioethanol production from sugarcane juice and bagasse and the integration of these technologies. This project comprises a combination of experimental and process modelling work to assess energy efficiencies and the economic viability of integrated and stand-alone processes in the sub-Saharan African context. First generation fermentation experiments were conducted and high ethanol concentrations of up to 113.7 g/L were obtained. It was concluded that a recombinant yeast strain may be able to replace a natural hexose fermenting yeast for 1st generation fermentations to reduce costs. 2nd generation fermentation experiments were performed and ethanol concentrations of close to 40 g/L were obtained. Combinations of 1st and 2nd generation fermentation experiments were performed to improve the 2nd generation fermentation. In one of the experiments it was concluded that the combination of 1st and 2nd generation fermentations significantly improved the 2nd generation fermentation with an overall ethanol concentration of 57.6 g/L in a shorter time than for the pure 2nd generation experiments. It was determined from washing and pressing experiments that pressing the pre-hydrolysate liquor out of the pre-treated bagasse will sufficiently lower the levels of inhibitors in a 2nd generation fermentation when using a hardened yeast. Some of the data from the 1st generation experiments were used along with literature data to model a first generation process in Aspen Plus® which processes 493 tons of cane per hour (tc/hr). Pinch heat integration was used to reduce the utility requirements. The process used the bagasse that was generated to co-produce steam and electricity. The excess electricity was sold for additional revenue. In one scenario the excess bagasse was determined at 57.5%. This bagasse was sold to a stand-alone 2nd generation plant. The first generation process produced 85.5 litres of ethanol per ton of cane (L/tc), the integrated process produced 128 L/tc while the stand-alone 2nd generation process produced 185 litres of ethanol per ton of bagasse (50% moisture) or 25.5 L/tc. The amount of excess electricity that was produced ranged from 14.3 to 70.2 kWh/tc. Economic analyses were performed using South African economic parameters to resemble the sub- Saharan African context. Data from the 1st generation process model and literature data for integrated 1st and 2nd generation and stand-alone 2nd generation processes were used for the analyses. It was found that the integrated plant is the most economically viable (IRR = 11.66%) while the 1st generation process basically broke even (IRR = 1.62%) and the 2nd generation process is unviable. This was as a result of high sugarcane prices and too few incentives for 2nd generation ethanol.