The production of synthetic fuels (synfuels) in coal–to–liquids (CTL) facilities has contributed to global warming due to the huge CO2 emissions of the process. This corresponds to inefficient carbon conversion, a problem growing in importance particularly given the limited lifespan of coal reserves. These simultaneous challenges of environmental sustainability and energy security associated with CTL facilities have been defined in earlier studies. To reduce the environmental impact and improve the carbon conversion of existing CTL facilities, this paper proposes the concept of a nuclear–assisted CTL plant where a hybrid sulphur (HyS) plant powered by 10 modules of the high temperature nuclear reactor (HTR) splits water to produce hydrogen (nuclear hydrogen) and oxygen, which are in turn utilised in the CTL plant. A synthesis gas (syngas) plant mass–analysis model described in this paper demonstrates that the water–gas shift (WGS) and combustion reactions occurring in hypothetical gasifiers contribute 67% and 33% to the CO2 emissions, respectively. The nuclear–assisted CTL plant concept that we have developed is entirely based on the elimination of the WGS reaction, and the consequent benefits are investigated. In this kind of plant, the nuclear hydrogen is mixed with the outlet stream of the Rectisol unit and the oxygen forms part of the feed to the gasifier. The significant potential benefits include a 75% reduction in CO2 emissions, a 40% reduction in the coal requirement for the gasification plant and a 50% reduction in installed syngas plant costs, all to achieve the same syngas output. In addition, we have developed a financial model for use as a strategic decision analysis (SDA) tool that compares the relative syngas manufacturing costs for conventional and nuclear–assisted syngas plants. Our model predicts that syngas manufactured in the nuclear–assisted CTL plant would cost 21% more than that produced in the conventional CTL plant when the average cost of producing nuclear hydrogen is US$3/kg H2. The model also evaluates the cost of CO2 avoided as $58/t CO2. Sensitivity analyses performed on the costing model reveal, however, that the cost of CO2 avoided is zero at a hydrogen production cost of US$2/kg H2 or at a delivered coal cost of US$128/t coal. The economic advantages of the nuclear–assisted plant are lost above the threshold cost of $100/t CO2. However, the cost of CO2 avoided in our model works out to below this threshold for the range of critical assumptions considered in the sensitivity analyses. Consequently, this paper demonstrates the practicality, feasibility and economic attractiveness of the nuclear–assisted CTL plant. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.

Fossil fuels continue to deplete with use as they are irreplaceable. In addition, the environmental impact with the continuous use of these conventional fuels has generated global concern due to the production of harmful emission gases. An alternative source of energy has become inevitable. Technological advancements in the area of biomass use for both aviation and power generation are at different levels of development. There is however the need for an integrated approach to assess gas turbine engine behaviour in terms of performance, emission and economics when they are running on biofuels. The current research work is concerned with finding alternative fuel resources for use on stationary gas turbine engines for power generation with the necessary identification of suitable biofuels using a multidisciplinary approach. A techno-economic, environmental and risk assessment (TERA) model comprising the performance, emissions, economics and risk modules has been developed. There had been several simulations of two gas turbine engines (GTEs) to ascertain the effects of both ambient and operating conditions and the effect of fuel types on the engines. These simulations were done with the use of an in-house code-the Turbomatch and a code developed for the steam cycle which is employed for the combined cycle simulation. Cont/d.

The main aim of this work was to investigate the propensity of bed materials to retain ash-forming elements from biomass under conditions relevant to dual fluidized bed gasification (DFBG). The investigation was carried out in a laboratory-scale bubbling fluidized bed reactor in which biomass was gasified with steam and the unconverted char was combusted in the temperature range 800–900 ° C. Three bed materials (sand, olivine and bauxite) and two biomass fuels (forestry residue and wheat straw) were studied. From the results obtained and literature on the ash transformation chemistry during thermal conversion of biomass, it was found that the extent to which ash-forming elements from biomass are retained on bed materials depend among other factors on (1) the abundance of ash-forming elements in the fuel, (2) the ability of the bed material to react and form compounds with ash-forming elements and (3) the atmosphere surrounding the fuel in the reactor. For example, Ca, P and K (which were among the most abundant ash-forming elements in the forestry residues) were also the main ashforming elements retained on sand, olivine and bauxite during thermal conversion of the forestry residues. However, the retention of these elements differed on the three bed materials. With respect to reactor atmosphere, Ca and P were retained on olivine primarily during char combustion while the retention of K on olivine was somewhat similar during gasification and char combustion. In addition to the experimental results, the effect of the retention of ash-forming elements on bed agglomeration tendency and the composition of the product gas is discussed as well as the relevance of the obtained results for the DFBG process.

Lignin, a byproduct of the chemical pulping can be gasified to produce fuel gas and value-added products. Two lignins, MeadWestvaco (MWV) lignin and Sigma Aldrich (SA) lignin, were studied using two different reactors. A laminar entrained flow reactor (LEFR) was used initially to determine the effect of lignin type, temperature and residence time on char yield and fixed carbon conversion during pyrolysis and gasification. During both pyrolysis and gasification, the maximum decrease in char yield took place in the initial stage of the reaction and there was little change at longer residence times. There was not much difference between pyrolysis and gasification in the residence times obtained in the LEFR. Furthermore, a thermogravimetric analyzer (TGA) was used to study the effect of lignin type on pyrolysis and gasification. The reaction rates and char yields were affected by the lignin composition. Lignin pyrolysis showed similar behavior until 600°C but only the high-ash SA lignin showed secondary pyrolysis reactions above 600°C. Carbon gasification reactions were delayed in SA lignin. Na2CO3 addition made the primary pyrolysis reaction occur at a lower rate and enhanced the rate for secondary pyrolysis reactions. Fourier Transform Infrared (FTIR) Spectroscopy results showed that the significant loss of spectral detail started at different temperatures for MWV lignin and SA lignin. Kinetic parameters obtained using differential and Coats - Redfern integral method were comparable at lower temperatures but varied at high temperatures. Na2CO3 addition decreased the activation energy of primary pyrolysis.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 322-338).

Thesis (PhD.(Metallurgy)--University of Pretoria, 2008. / Includes bibliographical references.

Thesis (M.S.) -- Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M. Sc.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 79-83).

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.