Thesis (M.S.)--Ohio University, June, 1995. / Title from PDF t.p.

Thesis (M.S.)--Youngstown State University, 2008. / Includes bibliographical references (leaves 39-42). Also available via the World Wide Web in PDF format.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 246-266).

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 188-192). Available also in a digital version from Dissertation Abstracts.

Submitted in fulfillment of the requirements for the degree of Doctor of Philosophy: Biotechnology, Durban University of Technology, Durban, South Africa, 2017. / Fossil carbon dioxide emissions can be biologically fixed which could lead to the development of technologies that are both economically and environmentally friendly. Carbon dioxide, which is the basis for the formation of complex sugars by green plants and microalgae through photosynthesis, has been shown to significantly increase the growth rates of certain microalgal species. Microalgae possess a greater capacity to fix CO2 compared to terrestrial plants. Selection of appropriate microalgal strains is based on the CO2 fixation and tolerance capability, both of which are a function of biomass productivity. Microalgal biomass could thus represent a natural sink for carbon. Furthermore, such systems could minimise capital and operating costs, complexity, and energy required to transport CO2 to other places. Prior to the development of an effective CO2 mitigation process, an essential step should be to identify the most CO2-tolerant indigenous strains. The first phase of this study therefore focused on the isolation, identification and screening of carboxyphilic microalgal strains (indigenous to the KwaZulu-Natal province in South Africa). In order to identify a high carbon-sequestering microalgal strain, the physiological effect of different concentrations of carbon sources on microalgae growth was investigated. Five indigenous strains (I-1, I-2, I-3, I-4 and I-5) and a reference strain (I-0: Coccolithus pelagicus 913/3) were subjected to CO2 concentrations of 0.03 - 15% and NaHCO3 of 0.05 - 2 g/1. The logistic model was applied for data fitting, as well as for estimation of the maximum growth rate (µmax) and the biomass carrying capacity (Bmax). Amongst the five indigenous strains, I-3 was similar to the reference strain with regards to biomass production values. The Bmax of I-3 significantly increased from 0.214 to 0.828 g/l when the CO2 concentration was increased from 0.03 to 15% (r = 0.955, p = 0.012). Additionally, the Bmax of I-3 increased with increasing NaHCO3 concentrations (r = 0.885, p = 0.046) and was recorded at 0.153 g/l (at 0.05 g/l) and 0.774 g/l (at 2 g/l). Relative electron transport rate (rETR) and maximum quantum yield (Fv/Fm) were also applied to assess the impact of elevated carbon sources on the microalgal cells at the physiological level. Isolate I-3 displayed the highest rETR confirming its tolerance to higher quantities of carbon. Additionally, the decline in Fv/Fm with increasing carbon was similar for strains I-3 and the reference strain (I-0). Based on partial 28S ribosomal DNA gene sequencing, strain I-3 was found to be homologous to the ribosomal genes of Chlorella sp. The influence of abiotic parameters (light intensity and light:dark cycles) and varying nutrient concentrations on the growth of the highly CO2 tolerant Chlorella sp. was thereafter investigated. It was found that an increase in light intensity from 40 to 175 umol m2 s-1 resulted in an enhancement of Bmax from 0.594 to 1.762 g/l, respectively (r = 0.9921, p = 0.0079). Furthermore, the highest Bmax of 2.514 g/l was detected at a light:dark cycle of 16:8. Media components were optimised using fractional factorial experiments which eventually culminated in a central composite optimisation experiment. An eight-factor resolution IV fractional factorial had a biomass production of 2.99 g/l. The largest positive responses (favourable effects on biomass production) were observed for individual factors X2 (NaNO3), X3 (NaH2PO4) and X6 (Fe-EDTA). Thereafter, a three-factor (NaNO3, NaH2PO4 and Fe-EDTA) central composite experimental design predicted a maximum biomass production of 3.051 g/l, which was 134.65% higher when compared to cultivation using the original ASW medium (1.290 g/l). A pilot scale flat panel photobioreactor was designed and constructed to demonstrate the process viability of utilising a synthetic flue gas mixture for the growth of microalgae. The novelty of this aspect of the study lies in the fact that a very high CO2 concentration (30%) formed part of the synthetic flue gas mixture. Overall, results demonstrated that the Chlorella sp. was able to grow well in a closed flat panel reactor under conditions of flue gas aeration. Biomass yield, however, was greatly dependent on culture conditions and the mode of flue gas supply. In comparison to the other batch runs, run B yielded the highest biomass value (3.415 g/l) and CO2 uptake rate (0.7971 g/day). During this run, not only was the Chlorella strain grown under optimised nutrient and environmental conditions, but the culture was also intermittently exposed to the flue gas mixture. Results from this study demonstrate that flue gas from industrial sources could be directly introduced to the indigenous Chlorella strain to potentially produce algal biomass while efficiently capturing and utilising CO2 from the flue gas. / D

A research report submitted in partial fulfilment requiremenrs of degree Master of Science tothe School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa, January 2018 / South Africa’s energy sector is vital to the development of its economy. Instability in the form of disruption in supply affects production costs, investments, and social and economic growth. Domestic sources are no longer able to meet the country’s demands. South Africa must find a local alternative fuel source in order to reclaim stability and encourage social and economic development. Biomass is one of the most abundant renewable energy sources, and has great potential as a fuel source. Currently biomass contributes 12% of the world’s energy supply, while in some developing countries it is responsible for up to 50% of the energy supply. South Africa is the highest maize producer on the African continent. Many studies carried out indicated that maize, and its residue contain valuable materials, and has the highest lower heating value in comparison to other agricultural crops. This indicates that maize can be a potential biomass for renewable energy generation in South Africa. A means for energy conversion for biomass, is the process of gasification. Gasification results in gaseous products H2, CO and CO2. Since the process of biomass gasification involves a series of complex chemical reactions involving a number of parameters, which include flow, heat transfer and mass transfer, it is very difficult to study the process of gasification by relying on experimentation only. Numerical simulation was used to provide further insight on this process, and accelerate development and application of maize gasification in a cost effective and efficient manner. The objective of this study was therefore, to verify and evaluate the feasibility of maize gasification and liquid fuels production in South Africa from an economic and energy perspective. The simulation model was developed in Aspen Plus® based on two thermodynamic models specified as Soave – Redlich – Kwong and the Peng Robinson equation of state. All binary parameters required for this simulation were available in Aspen Plus®. The gasification unit was modelled based on a modified Gibbs free energy minimization model. Gasification of maize and downstream processing in the form of Fischer-Tropsch (FT) synthesis and gas to liquids (GTL) processing for liquid fuels production was modelled in Aspen Plus®. Sensitivity analyses were carried out on the process variables: equivalence ratio (ER), steam to biomass ratio (SBR), temperature and pressure, to obtain the optimum gasification conditions. The optimum reactor conditions, which maximized syngas volume and quality was found to be an ER of 0.22 and SBR of 0.2 at a temperature of 611ºC. An increase in pressure was found to have a negative effect; therefore atmospheric conditions of 101.325 kPa were chosen, in order to maximize CO and H2 molar volumes. Based on these conditions the produced syngas consisted of 35% H2, 16% CO, 24% CO2 and 3%CH4. The results obtained from gasification, based on a modified Gibbs free energy model, show a closer agreement with experimental data, than other simulations based on the assumption that equilibrium is reached and no tar is formed. However, these results were still idealistic as it under predicted the formation of CO and CH4. Although tar was accounted for as 5.5% of the total product from the gasifier (Barman et al., 2012), it may have been an insufficient estimation resulting in the discrepancy in CO and CH4. The feasibility of maize as a feed for gasification was examined based on quality of syngas produced in relation to the requirements for FT synthesis. A H2/CO ratio of 2.20 was found, which is within range of 2.1 – 2.56 found to support greater conversions of CO with deactivation of the FT catalyst (Lillebo et al., 2017). The syngas produced from maize was found to have a higher H2/CO ratio than conventional fossil fuel feeds; implying that maize can result in a syngas feed which is both renewable and richer in CO and H2 molar volumes. Liquid fuels generation was modelled based on experimental production distributions obtained from literature for FT synthesis and hydrocracking. The liquid fuel production for 1000 kg/hr maize feed, was found to be 152 kg/hr LPG, 517 kg/hr petrol and 155 kg/hr diesel. The simulation of liquid fuels production via the Fischer-Tropsch synthesis and hydrocracking process showed fair agreement with literature. Where significant deviations were found, they could be reasonably explained and supported. This simulation was found to be a suitable means to predict liquid fuels production from maize gasification and downstream processing. The feasibility of liquid fuels production from maize in South Africa was examined based on the country’s resource capacity to support additional maize generation. It was found that based on 450 000 hectares of underutilized land found in the Homelands, an additional 1.216 billion litre/annum of synthetic fuels in the form of diesel and petrol could be produced. This has the potential to supplement South African liquid fuels demand by 6% using a renewable fuel source. This fuel generation from maize will not impact food security due to the use of underutilized arable land for maize cultivation, or impact water supply as maize does not require irrigation. In addition, fuel generation in this manner supports the Biofuels Industry Strategy (2007) by targeting the use of underutilized land, ensuring minimal impact on food security, and exceeds its primary objective of achieving a 2% blending rate from renewable sources. The economic feasibility of liquid fuels derived from maize was determined based on current economic conditions in 2016. Based on these conditions of 49 $/bbl Brent Crude, 40 $/MT coal and 6.5 $/mmBTU of natural gas at a R/$ exchange rate of R14.06 per U.S. dollar, it was found that coal, natural gas and oil processing are more economically viable feeds for fuel generation relative to maize. However, based on projected market conditions for South Africa, the R/$ exchange rate is expected to weaken further, the coal supply is expected to diminish and supply of natural gas is expected to be a continued issue for South Africa. Based on this, maize should be considered as a feed for fuel generation to reduce the dependency on non-renewable fossil fuel sources. The energy feasibility of liquid fuels produced from maize was only evaluated from a thermal energy perspective. It was found that maize gasification and FT processing requires 0.91 kg steam/kg feed. This 0.91kg of steam accounts for the raw material feed, distillation and heating required for every 1kg of maize processed. It was found that 2.56 kg steam/kg feed was generated from the reactor units. This was assumed to be in the form of 10 bar steam, as in this form it can be sent to steam turbines for electricity generation to assist with overall energy efficiency for this process. In addition, the amount of CO2 (kg/kg feed) produced, was examined for maize processing in comparison to fossil fuel feeds: natural gas and coal. The CO2 production from liquid fuels processing based on a maize feed, was found to be the highest at 0.66 kg/kg feed. However, a coal feed has higher ash and fix carbon content indicating greater solid waste generation in the gasifer. While dry reforming of natural gas is a net consumer of CO2, but had significantly higher steam requirements in order to achieve the same H2/CO ratio as maize. This indicates that although maize results in more CO2/kg feed, it is 88% more energy efficient than dry methane reforming. Additional experimental work on FT processing using syngas derived from maize is recommended. This will assist in further verification of liquid fuels quantity, quality and process energy requirements. / XL2018

No description available.

An experimental system was built to test the effect of various process parameters on the performance of the Modified Dry Limestone Process (MDLP) for flue gas desulfurization. Two types of limestone, one calcitic and one dolomitic, were used. These materials were characterized by ICP analysis, X-ray diffraction, optical microscopy, SEM, and electron microprobe before and after reaction. Performance was judged on the basis of the formation of a friable gypsum reaction product and the maintenance of a pH of about 4.84 or higher in water through which the exit gases were bubbled. Two primary and one secondary parameter were identified as the most important for optimum performance of the MDLP. The two primary parameters were temperature and water content. A temperature of 68°-70°C promoted reaction, while no reaction occurred at 31°C. The solubility of SO₂ in water was the controlling factor for water content. A maximum ratio of about 3.4 g SO₂/100 g water at 69°C was necessary. The secondary parameter was the type of limestone used. A dolomitic limestone with a reasonable amount of Fe performed better than either marble or a calcitic limestone, both low in Fe. A reasonable amount of Fe and an extensive pore structure seem to be the most important factors in limestone SO₂ absorption performance. / Master of Science

An instrument (differential flow water meter) to measure the water vapor concentration in stack gases was developed. This is intended for use as a standard reference as well as a practical method for the determination of the moisture content of stack gases from wood stoves. The accuracy of the instrument was tested by generating gas mixtures with known water vapor content and comparing the measured concentrations with the actual values. Several tests were made under actual operating conditions, i.e., testing the water vapor concentration of stack gases from a wood stove under different firing conditions. The accuracy of the results was further checked by weighing the condensed catch and comparing the measured and predicted values. For each of the tests a wet and dry bulb technique was also used to measure the stack gas moisture content. A comparison of the results obtained using these two methods and the WHA (Wood Heating Alliance) standard method was also done. The results show that the wet and dry bulb method overpredicts the moisture content as compared to the differential flow water meter. / M.S.

A dissertation submitted to the faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfillment of the requirements for the degree of Master of Science in Engineering. 21 November 2016 / In this work a comprehensive exergy analysis and heat integration study was carried out on a coal based oxy-combustion power plant simulated using ASPEN plus. This is an extension on the work of Fu and Gundersen (2013). Several of the assumptions made in their work have been relaxed here. Their impact was found to be negligible with the results here matching closely with those in the original work. The thermal efficiency penalty was found to be 9.24% whilst that in the original work was 9.4%. The theoretical minimum efficiency penalty was determined to be 3% whilst that in the original work was 3.4%. Integrating the compression processes and the steam cycle was determined to have the potential to increase net thermal efficiency by 0.679%. This was close to the 0.72% potential reported in the original work for the same action. / MT2017