Air pollution is one of many issues that have a direct impact upon the economy and the well-being of society in South Africa. Domestic coal combustion contributes significantly to the air pollution problem in the country. Both qualitative and quantitative methods of data collection have been employed in this study. A questionnaire survey was conducted in 100 households in Doornkop (Soweto) and 100 households in KwaGuqa (Witbank). The observations were carried out simultaneously while the questionnaire surveys were being administered in both study areas. Interviews were also held with Eskom (the Electricity Supply Commission of South Africa) officials. Finally, the indoor concentrations and elemental composition of respirable particulate matter (PM7) were measured in three different types of households: electrified without coal burning, electrified with coal burning, and un-electrified with coal burning. The results show that township households, whether electrified or not, continue to burn coal. In both study areas, 80 % of electrified households burn coal for space heating and cooking. Although the major obstacles preventing people from discontinuing domestic coal combustion are poverty and the ready availability and social acceptability of coal, the social value of a fire inside township households cannot be underrated. Previously developed coal-supply networks still exist in the townships and makes coal utilisation very convenient. The findings also point to use of multiple fuels in the communities studied. The key fuels used for domestic energy supply are coal, electricity and paraffin. Emergent patterns of domestic coal combustion, driven in part by various societal dimensions, are also observed. Further, despite the previously observed increase in respiratory ailments in winter, township residents do not think that such increases are linked to domestic coal combustion. The study, as shown here, is in line with theories of the energy ladder which posits that as people’s financial situations improve, their energy-use patterns change. Indoor aerosol concentrations followed the same trends in all selected households with morning and evening peaks. These peaks are directly related to the making of coal fires. The highest aerosol levels, reaching a maximum of 2344.89 μg.m-3, are recorded in the un-electrified coal-burning household. Aerosol concentrations are slightly lower, averaging 1854.07 μg.m-3, in the electrified coal-burning household, implying a slight decrease in the amount of coal burnt. The lowest aerosol concentrations, averaging 478.74 μg.m-3, are recorded in the electrified household with no coal-burning. Elemental analysis reveals that the biggest contributor to respirable particles in KwaGuqa is soil dust followed by coal smoke, and then emissions from neighbouring steel smelters, whilst traffic emissions are the lowest contributor. Most importantly, it is people’s activities that determine the type and levels of respirable aerosols that they are exposed to as compared to the fuel-use patterns and types of fuels used in their household. In conclusion, electrification might phase out domestic coal combustion in the long term but only if the economic status of coal users improves. Alternatively, there is an opportunity to reduce emissions by introducing a low-smoke solid fuel, however, households will only use it if it is priced competitively and its heating and ignition properties are similar to, or better than, those of coal.

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Commercial ceramic candle filters were exposed to harsh environments to determine the effects of alkali and steam on their long-term durability. Ceramic candle filters are composed of relatively coarse aggregates fixed by a ceramic bond. The filters studied include a clay-bonded, granular aluminosilicate candle and three types of clay-bonded, granular SiC candles. The alkali, steam, and steam-alkali corrosion of these commercial ceramic candle filters was examined at temperatures ranging from 450 to 1225°C and pressures up to 1000 psi. Results indicate that the aluminosilicate candle filters perform better than filters made from granular SiC. The SiC filters show binder degradation in steam as well as in alkali-containing environments at temperatures as low as 700°C, with oxidation of the SiC occurring in the steam environments at higher temperatures. Sodium and potassium contaminants in the steam atmospheres accelerate the degradation of both types of filter material. / Master of Science

Traditionally, coal combustion residuals (CCRs) were disposed of with little engineering consideration. Initially, common practice was to use a wet-scrubbing system to cut down on emissions of fly ash from the combustion facilities, where the ash materials were sluiced to the disposal facility and allowed to sediment out, forming deep deposits of meta-stable ash. As the life of the disposal facility progressed, new phases of the impoundment were constructed, often using the upstream method. One such facility experienced a massive slope stability failure on December 22, 2008 in Kingston, Tennessee, releasing millions of cubic yards of impounded ash material into the Watts Bar reservoir and damaging surrounding property. This failure led to the call for new federal regulations on CCR disposal areas and led coal burning facilities to seek out geotechnical consultants to review and help in the future design of their disposal facilities. CCRs are not a natural soil, nor a material that many geotechnical engineers deal with on a regular basis, so this thesis focuses on compiling engineering characteristics of CCRs determined by different researchers, while also reviewing current engineering practice when dealing with CCR disposal facilities. Since the majority of coal-burning facilities used the sluicing method to dispose of CCRs at one point, many times it is desirable to construct new "dry-disposal" phases above the retired ash impoundments; since in-situ sampling of CCRs is difficult and likely produces highly disturbed samples, a sample reconstitution technique is also presented for use in triaxial testing of surface impounded CCRs. / Master of Science

Experiments were performed to determine a suitable binder material for silicon carbide-based ceramic filter. These experiments included exposure of 42% and 60% alumina, aluminosilicates to potassium and sodium containing environments for the purpose of determining the phases that would form and to determine concentration profiles. In addition, thermodynamic calculations were performed to predict the phases that would form when the alkali reacted with the aluminosilicate. The results of the thermodynamic calculations indicated that the alkali compounds will react at temperatures as low as 800°C. The exposure experiments verified this result. The phases that formed during the sodium vapor exposures and confirmed the thermodynamic calculations and were as follows: 1. sodium metasilicate and a solid solution of sodium aluminum silicates and carnegieite and for potassium vapor exposure. 2. potassium disilicate, kaliophilite-nepheline, potassium aluminate, and 5K₂O-5Al₂O₃-8SiO₂. Experiments also revealed that penetration depth by alkali compounds was restricted to a region near the surface of the material when the combination of temperature and sodium concentration alowed a melt to form. The results also indicated that the 42% alumina, aluminosilicate had superior resistance to alkali attack than the 60% alumina, aluminosilicate at temperatures below 1225°C. / Master of Science

In recent decades, advances in low NOₓ coal combustion and increasingly strict CO₂ reduction mandates have changed power plant boiler operations quite significantly. As a result of these necessary efforts, the characteristics of fly ash generated at many power plants have also changed. In particular, increases in unburned carbon content have been observed with detrimental implications on the utility of these fly ashes in concrete applications. Over the same time period, the combustion of biomass for energy generation has received increased attention due to the potential benefits of reducing CO₂ emissions and improved sustainability when compared to fossil fuel combustion. Biomass is directly burned, gasified, or co-fired with coal to achieve this goal. Currently, close to 120 million metric tons of coal combustion by products are produced in the U.S. annually. As with coal combustion, production of energy from biomass combustion/gasification results in significant by-product generation that must either be productively reused or geologically disposed. While much research effort has been devoted to understanding the properties and potential productive reuse alternatives for coal combustion residuals, relatively little work has been done on the by-products of biomass combustion. This study investigated the properties and engineering behavior of sixteen ash samples that were produced in eleven different power plants. Specifically, three high carbon content Class F fly ashes, eight coal and biomass co-fired ashes, three pure biomass ash samples, and two high quality, low carbon content ash samples, one of which is commercially marketed (for reference) were chosen. The various ash samples were characterized by means of: electron microscopy; laser diffraction and dry sieve particle size analysis; loss on ignition and total organic carbon analysis; specific surface area analysis; as well as x-ray fluorescence and x-ray diffraction. The ash samples were also investigated for their potential engineering application in the fired clay brick industry, as low-cost adsorptive agents, and in alkali activated geopolymer synthesis for geotechnical and geoenvironmental applications. Results from physical and chemical characterization of the ash samples show no significant differences between pure coal ash and coal co-fired with biomass ash samples from the same power plant. However, there are significant morphological, chemical, and mineralogical differences between coal ash and pure biomass ash. Unlike pure coal ash, biomass ash is not composed primarily of aluminosilicate glass cenospheres but rather consists mainly of charred, fibrous woody remnants with elevated calcite content as compared to coal ash. Bench scale fired bricks produced by partial replacement of clay material with high carbon coal ash, co-fired ash, and pure biomass ash, respectively, was successful. Physical properties of a number of the mix designs exceeded the highest ASTM weathering grade requirements. As sorptive agents, high carbon concentrates from coal and co-fired ash samples, along with all the biomass ash samples, showed significant uptake of lead. The unaltered as- received ash samples (i.e. no acid or steam activation) showed only moderate arsenic (V) and selenium (VI) sorption capacity. Finally, solidification/stabilization by geopolymerization of high carbon content, co-fired ash with as little as 3 molar NaOH in the activator solution was successful, possibly paving the way for various geotechnical and geoenvironmental applications in ground improvement and soil/ash-pond stabilization.

Nearly half of the electrical power produced in the United States is generated with coal. Coal power is inexpensive and reliable, but coal combustion releases harmful pollutants including NOx and SOx into the atmosphere if not controlled. CO2, a greenhouse gas, is also released during coal combustion and may contribute to global warming. A promising technology enabling carbon capture is oxy-coal combustion. During oxy-combustion, coal is burned in an atmosphere of O2 and recycled flue gas to eliminate nitrogen which makes up the majority of air-combustion flue gas. Oxy-combustion flue gas is mainly composed of CO2 and H2O. H2O can be condensed out of the gas, and the CO2 can then be captured and permanently stored relatively easily. The composition of the gas inside an oxy-fired boiler will be different due to the absence of nitrogen and the recycling of flue gas. Corrosive sulfur and chlorine gas species concentrations will be higher, and CO and NOx concentrations will be effected. An understanding of the differences in gas concentrations is critical to oxy-combustion boiler design. Four different pulverized coals were combusted in a reactor under staged and unstaged oxy-combustion conditions with warm recycled flue gas (420°F) to simulate conditions in an oxy-fired coal boiler. The gas composition was measured in the reducing and oxidizing zones for staged combustion, and in the same locations, 57 cm and 216 cm from the burner, for unstaged combustion. The results were compared to the results from similar staged air-combustion experiments using the same coals and burner. CO concentrations were higher for staged oxy-combustion compared to air-combustion, and the increase was more substantial for lower rank coals. H2S concentrations in the reducing regions were also higher, and the fraction of gas phase sulfur measured as H2S was higher for oxy-combustion. SO2 concentrations were 2.9 to 3.8 times as high as air-combustion concentrations. The measured conversion of coal sulfur to SO3 was lower for oxy-combustion, and ranged from 0.61% to 0.98%. The average fraction of coal sulfur measured in the gas phase was 84%, 80%, and 85% for staged oxy-combustion, unstaged oxy-combustion, and staged air-combustion respectively. HCl concentrations were 2.8 to 3.1 times higher in the staged oxy-combustion oxidizing zone, and a smaller fraction of coal chlorine was measured in the reducing zone. On average 70.8%, 79.5%, and 71.1% of the coal chlorine was measured as HCl for staged oxy-combustion, unstaged oxy-combustion, and staged air-combustion respectively. The fractions of coal chlorine and sulfur measured in the gas phase for staged combustion were not significantly affected by combustion media. Some staged oxy-combustion NO concentrations were lower than air-combustion concentrations while others were slightly higher, and NO emission rates were much lower due to recycling NO through the burner.

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

A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfillnent of the requirements for the degree of Doctor of Philosophy, 1992 / The self-heating of coal is a problem which concerns the mining industry not only in South Africa, but also in many other countries. This thesis deals with the contouring of spontaneous combustion liabilities (WITS-ERAC index values) of different seams at the Durban Navigation Colliery and the relationship between the WITS-EHAC index values and the properties of the coal samples. In the determination of the spontaneous combustion liabilities 58 different coal samples were tested with an ignition-temperature test apparatus, crossing-point temperature tests and differential thermal analysis were conducted simultaneously. [Abbreviated abstract. Open document to view full version] / MT2017