A Techno-economic evaluation of integrating first and second generation bioethanol production from sugarcane in Sub-Saharan Africa

Van Der Westhuizen, Willem Andries (2013-12)

Thesis (MScEng)-- Stellenbosch University, 2013.

Thesis

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.

AFRIKAANSE OPSOMMING: Klimaatsverandering wat veroorsaak word deur kweekhuisgasse wat vrygestel word deur die verbranding van fossielbrandstowwe en die stygenede olieprys het belangstelling in hernubare biobrandstowwe laat opvlam. Die produksie van biobrandstowwe hou ook potensiële sosioekonomiese voordele in. Daar is twee tegnologieë vir bioetanol produksie: · Eerste generasie bioetanol word vanaf voedsel bronne soos suikersap geproduseer. · Tweede generasie bioetanol word van nie-voedsel bronne (lignosellulose materiaal) geproduseer. Hierdie projek handel oor 1ste en 2de generasie bioetanol produksie van suikersap en suikerriet bagasse en die integrasie van hierdie tegnologieë. Hierdie projek bestaan uit ‘n kombinasie van eksperimentele- en prosesmodellering werk om die energiedoeltreffendheid en ekonomise vatbaarheid van geïntegreerde en alleenstaande prosesse in die sub-Sahara konteks te ondersoek. Eerste generasie fermentasie eksperimente is uitgevoer en hoë etanol konsentrasies van tot 113.7 g/L is gekry. Dit was bepaal dat ‘n rekombinante gisras ‘n natuurilke heksose fermenterende gisras kan vervang vir 1ste generasie fermentasies om kostes te bespaar. 2de generasie fermentasie eksperimente is gedoen en etanol konsentrasies van amper 40 g/L is behaal. Kombinasies van 1ste en 2de generasie fermentasie-eksperimente was uitgevoer om die 2de generasie fermentasie te verbeter. In een van die eksperimente is dit bepaal dat die kombinasie van 1ste en 2de generasie fermentasie die 2de generasie fermentasie beduidend verbeter het met ‘n etanol konsentrasie van 57.6 g/L en dít in ‘n korter tyd as vir die suiwer 2de generasie eksperimente. Dit was bepaal vanuit pers- en was eksperimente dat om die pre-hidrolisaat vloeistof uit die stoombehandelde bagasse te pers, die vlak van inhibitore in ‘n 2de generasie fermentasie voldoende verlaag vir die gebruik van ‘n verharde gis. Van die data van die 1ste generasie eksperimente was saam met literatuurdata gebruik om ‘n 1ste generasie proses in Aspen Plus® te modelleer wat 493 ton suikerriet per uur prosesseer (tc/hr). Pinch hitte integrasie was gebruik om die dienste vereistes te verminder. In die proses word die bagasse gebruik om stoom en elektrisiteit te genereer. In een geval was die oortillge bagasse bepaal as 57.5%. Hierdie bagasse was verkoop aan ‘n alleenstaande 2de generasie aanleg. Die eerste generasie proses het 85.5 liter etanol per ton suikerriet geproduseer (L/tc), die geïntegreerde proses het 128 L/tc geproduseer terwyl die 2de generasie proses 185 liter etanol etanol per ton bagasse (50% vog) of 25.5 L/tc geproduseer het. Die hoeveelhede oortillige elektrisiteit wat geproduseer is wissel van 14.3 tot 70.2 kWh/tc. Ekonomiese analieses is gedoen met Suid-Afrikaanse ekonomiese parameters om die sub-Sahara Afrika-konteks uit te beeld. Data van die 1ste generasie prosesmodel en literatuurdata van geïntegreerde 1ste en 2de generasie en alleenstaande 2de generasie prosesse was vir die analieses gebruik. Dit is bepaal dat die geïntegreerde model die mees ekonomies vatbare model is (IRR = 11.66%) terwyl die 1ste generasie proses basies gelyk gebreek het (IRR = 1.62%) en die 2de generasie proses is ekonomies onvatbaar. Hierdie bevindinge is as gevolg van hoë suikerrietpryse en te min aansporings vir 2de generasie etanol.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/85611
This item appears in the following collections: