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A research report submitted to the School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, 2016. / The self-heating of coals is a complex problem which has been occurring for centuries. This problem has been fatal to coal miners, an economical challenge to coal mines and a health risk in a release of greenhouse gases to the public in general. Therefore, everyone is affected by the self-heating of coal, which leads to spontaneous combustion when the ignition temperature is reached. There are many test methods that have been used to test spontaneous combustion in coal, but all have one common factor or disadvantage of requiring long periods of time before a conclusion can be deduced. This then creates a need for a rapid and reliable method to test the liability of coal to self-heat in the coal industry and thus the motivation for this project. The thermogravimetry analysis (TGA) method was selected to test the liability of coal to self-heat due to its short analytical duration. The Smith-Glasser oxidation test was selected to validate the TGA results obtained. The main aim of this project is to investigate the reliability of the TGA method to predict the propensity of coal to self-heat. 29 samples from different regions of South Africa were used, prepared to 250 μm for all the analyses and self-heating tests. All samples were analysed for proximate, calorific value, sulphur and petrographic properties before the spontaneous combustion liability tests began. The TGA method followed two tests: 1) the O2 adsorption and 2) the ignition test. Five different heating rates (3, 5, 7, 10, and 20) °C/min were run in order to obtain five derivative slopes which would be used to obtain the TGspc index. The oxygen adsorption test studies the mass increase at low temperature under exposure of air between the temperature ranges of 100 – 300°C. The Smith-Glasser oxidation test method studies the reaction of coal with O2 and calculates the O2 absorbed per amount of coal tested. The Smith-Glasser test results collaborated with most of the other analytical results, and with the TGA results to a certain extent. The TGA spontaneous combustion liability test requires additional analytical work to back up its results because the results do not appear as accurate as the Smith-Glasser oxidation test. It also requires repeatability tests to ensure the integrity of the results. / EM2017

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Bibliography: leaves 429-434. / by Richard John Quann. / Sc.D.

Coal continues to be burned by direct combustion in packed or moving bed in small size domestic furnaces, medium size industrial furnaces, as well as small power stations. Recent stringent restrictions on exhaust emissions call for a better understanding of the process of combustion of coal in beds. The present study is a prelude to developing methods of analysis to obtain this improved understanding. A one-dimensional steady-state computational model for combustion of a bed of solid fuel particles with a counterflowing oxidant gas has been developed. Air, with or without preheating, is supplied at the bottom of the bed. Spherical solid fuel particles (composed of carbon and ash) are supplied at the top of the bed. Upon sufficient heating in their downward descent, the carbon in particles reacts with oxygen of the flowing gas. The governing equations of conservation of mass, energy, and species are integrated numerically to obtain the solid supply rate whose carbon content can be completely consumed by a given gas supply rate. The distributions of solid and gas temperatures, of concentrations of various gas species, of carbon content in solid, and of velocity and density of gas mixture are also calculated along the bed length. The dependence of these distributions on the solid and gas supply rates, the air supply temperature, the size of solid fuel particle, and the initial carbon content in solid is also investigated. The calculated distributions are compared with the available measurements from literature to find reasonable agreement. More gas supply is needed for complete combustion at higher solid supply rate. At a given gas supply rate, more solid fuel particles can be consumed at higher gas supply temperature, for larger particle size, and for lower initial carbon content in solid. The temperature of the bed becomes higher for higher solid supply rate, higher gas supply temperature, larger solid particle diameter, or lower initial carbon content in solid. These reasonable results lead one to encourage extension of the model presented here to more complex problems involving combustion of coals in beds including the effects of drying and pyrolysis. / Graduation date: 1994

An extensive study of intrinsic and extrinsic factors on biomass pyrolysis reactions is needed if valuable hydrocarbon gases are to be produced from pyrolysis of biomass. In the first phase of this study a spent coffee waste material was pyrolysed in a stainless steel batch reactor at 500 to 900°C with both N₂ and H₂ carrier gases. The use of H₂ gas did not affect the product distribution. Yields of pyrolysis gas products reached 61 and 74 wt% of the feed at 900°C for N₂ and H₂ carrier gases. Corresponding mass balance closures were obtained at 86 and 98 wt% of the feed. Catalytic effect of the stainless steel wall was confirmed. Maximum conversion of CO was found at pyrolysis zone temperature of 700°C. Pyrolysis experiments with spent coffee performed in a quartz (inert) batch reactor proved that the carrier gas had negligible influence on the primary pyrolysis product distribution. Pyrolysis with K₂CO₃ at 650, 700, and 800°C, showed catalysis of cracking reactions of pyrolysis tars and the water-gas shift reaction. Copyrolysis of biomass materials and coals were performed in the quartz reactor with the objective of producing a higher hydrocarbon content gas product. Copyrolysis of spent coffee and lignite coal at 800°C in a hydrogen atmosphere resulted in gas production of more than 45 wt% of the feed, compared with only 27 wt% for pure coal sample. Increases in production of CH₄ and C₂H₄ were 15.9 wt% and 21.3 Wt%. For copyrolysis with sub-bituminous coal, these synergistic increases were 36.5 wt% and 23.9 wt%. In the final phase of this research, a fluidized bed reactor was used to study hydropyrolysis of cellulose, spent coffee, aspen-poplar, bagasse and lignite coal in presence of sand (inert medium), ã-alumina catalyst, Engelhard US-260 (a silica alumina catalyst), 10 wt% nickel-ã-alumina, 10 wt% cobalt-ã-alumina and a 40 wt% nickel-refractory support catalyst. Over the temperature range of 500 to 600°C, the 10 wt% nickel catalyst was most effective in conversion of biomass. Overall it was found that the combination of cellulose with 10 wt% Ni catalyst at 550°C was the optimum catalyst-feed system for conversion of carbon content of biomass to methane. In this case the yield of CH₄ was 46.7 wt% of cellulose. Rate constants for (primary) pyrolysis, (secondary) tar-cracking and (tertiary) hydrogenation reactions at 550°C were determined. Rate constants for the above mentioned reactions were estimated to be k₁=2.88 s^-1 (pyrolysis model), k₁=2.88 and k₂=1.31 s^-1 (pyrolysis-cracking model), and k₁=2.88, k₂=13.1 and k₃=12.96 s^-1 (pyrolysis-cracking-hydrogenation model).

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>Magister Scientiae - MSc / In South Africa coal combustion constitutes up to 90 % of the country’s energy need. This coal combustion activity is known to contribute to the amount of about 40 % of the total CO2 atmospheric emissions worldwide that are responsible for global warming effects. In addition burning of coal generates a large quantity of fly ash which creates environmental pollution since only a small portion of it is currently used in some applications. In order, on one hand to mitigate and sequester CO2 and on the other hand to reprocess fly ash and reuse it, this study focuses on developing new technologies with cost-effective and less energy consumption in the domain of CO2 capture and sequestration. CO2 has priority attention for being the largest contributor to global warming. Various techniques have been used for CO2 capture and sequestration, such as aqueous alkylamine absorption or adsorption onto a solid adsorbent such as zeolites. In this study NaA zeolite adsorbent was hydrothermally synthesised from South African fly ash. This fly ash based NaA zeolite was then used as starting material to prepare LiA, CaA, and MgA zeolite catalysts via ion-exchange for comparative CO2 adsorption capacity. A systematic design of the ion-exchange procedure was undertaken at either 30 °C or 60 °C for a contact time of 1 hr, 4 hrs, and 8 hrs with 1, 2 and 3 consecutive exchanges in each case in order to determine the optimum conditions for loading each cation exchanged. The adsorption of CO2 on the ion- exchanged fly ash based zeolite-A catalysts was carried out at 40 °C similar to the temperature of flue gas since the catalysts obtained in this study were also prepared with a view to their applications in flue gas system. The CO2 desorption temperature ranged between 40-700 °C. All materials used in this study, starting from fly ash feedstock, werecharacterized using various techniques to monitor the mineral and structural composition, the morphology, surface area and elemental composition and the adsorption capacity. The techniques included mainly Fourier transform infra-red, X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, Energy dispersive spectroscopy, X-ray fluorescence, Temperature programmed desorption.The results obtained from both Fourier transform infra-red and the X-raydiffraction spectroscopy for samples exchanged at either 30° C or 60 °C showedlower crystallinity in CaA and MgA zeolite samples. This decrease in crystallinitymainly affected the D4R (0-20° 2) and was demonstrated in the study to beinversely proportional to the increase of the atomic radius of cations (Li+ > Mg2+ >Ca2+). In the Fourier transform infra-red, the vibration band at 677 cm-1 attributedto the extra-framework cation, also proportionally increased with the decrease ofthe atomic radius or size of the cations, and was intense in LiA zeolite samples.

>Magister Scientiae - MSc / Coal-fired power stations produce large volumes of coal combustion residues (CCRs), which are disposed of in hold ponds or landfill sites. These ash storage facilities are limited in space and are approaching the end of their capacities, thus additional land is required for extensions. If new land is not sourced, power plants will be forced to cease operations, resulting in increased expenditure costs and environmental liability. A proposed disposal solution is to backfill opencast coal mines with CCR monoliths. However, there is limited knowledge on the hydraulic behaviour of CCRs in an opencast coal mine environment. This leads to an inability to assess this applications feasibility and determine whether this activity will have a positive, negligible or negative effect on groundwater quality. This study aims to address this gap in knowledge by assessing the flow and transport properties of CCRs under numerous theoretical backfilling conditions.

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