The mining of coal in arid regions has led to calls for research in to the field of dry beneficiation, / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

Graduation date: 1995

No description available.

Fluidized-bed combustion residue (FBCR) results from mixing coal with limestone during the combustion process. This by-product may be used as a liming agent. A grazing trial was conducted on an acidic mine soil to compare FBCR to dolomitic limestone and no amendment (control). Six steers per treatment were grazed rotationally on three replications (rep) of three .8 ha pastures. Both materials increased soil pH similarly, and reduced plant uptake of Fe, Zn, Mn, and Ni similarly. Calcium concentration increased in forages by both amendments, Mg increased with limestone and S with FBCR application. Cell wall components decreased, while ash and lignin increased with both amendments. Serum mineral levels of cattle were normal except Cu was low. Animal tissues reflected differences in mineral concentration observed in forages. Hay harvested from one rep was used in a mineral balance trial with 18 wethers. Apparent digestibility of dry matter, crude protein and fiber components, and N retention were not affected by treatment. Control animals were in negative Ca balance. Apparent absorption of Mg was higher (P < .01) for limestone treatment animals; S absorption was higher for the FBCR group; and, Zn absorption was higher for controls. Serum mineral levels of sheep were normal except Cu was low. No appreciable accumulation of heavy metals occurred in forage or animal tissues. Low Cu levels observed for all treatment groups indicate a problem inherent of the study site. FBCR appears to be a safe and efficient soil pH amendment. / Master of Science

The effect of the solid-circulation rate and pattern as well as the air-gap size on heat-transfer coefficients between a horizontal, cylindrical heater and vibrated beds of Master Beads (spherical alumina) and glass spheres was studied. Solid piles were observed to form at specific bed locations. Solid-circulation paths were directed from the shallowest toward the deepest region of the vibrated bed. For beds in which the solid pile formed above the heating surface, local solid-circulation loops were observed above and below the heater. Air gaps developed at the top and bottom of the cylindrical heater. Heat-transfer coefficients of 140-350 W/m²K in beds of glass spheres and 180-480 W/m²K in beds of Master Beads were determined for a temperature difference of 30°C between the heater and vibrated bed. The trends in the behavior of the heat-transfer coefficient could be explained in terms of a model that accounted for the air-gap size and particle renewal in the layer closest to the heater. Increased solid-circulation rates improved the heat-transfer performance until larger air-gap sizes eventually compromised any increase in solid circulation. The expansion of the interlayer spacing of H-Magadiite (a layered silicic acid) by the introduction of pillars containing silicon atoms was investigated. A trisiloxane and two trichloroorganosilane compounds were used as the pillaring agents. The interlayer space of H-Magadiite was successfully expanded by pillaring with trichloroorganosilanes. The minimum dimensions of the pores that access the interlayer space of the pillared compounds were determined as being 6.2 Å and 9.5 Å (dimensions at perpendicular directions). Pillaring of H-Magadiite at low pH and temperatures close to 0 °C yielded the highest surface areas, e.g., increasing the surface area from 35 to 130-200 m²/g. The pillared compounds were found to be thermally stable up to temperatures of 650°C. / Ph. D.

Ceramic candle filters were subjected to 500 hour high temperature/ high pressure (HTHP) exposure tests to examine their extended durability in simulated coal pressurized-fluidized bed combustion (PFBC) environments. The candle filter materials analyzed included two SiC filters, one with clay binder and one with a minimal amount of clay binder, a cordierite filter, a mullite candle filter and an aluminosilicate refractory concrete filter. Exposure testing conditions included a range of temperature from 700-850°C and a pressure ranging from 1.7-1.8 MPa. The HTHP tests included exposing the ceramic filter materials to steam and steam-alkali environments. The presence of alkali significantly accelerated the deterioration of the filters. The results of the analysis show that significant crushing strength losses were exhibited by the SiC filters after exposure to HTHP alkali-steam conditions at temperatures as low as 700°C. The expansive and destructive cristobalite phase developed in the SiC filters after most of the treatments. The cordierite candle filter showed a decrease in crushing strength associated with grain growth after each high temperature exposure but few other signs of deterioration were detected. The mullite candle filter and the refractory concrete candle filter showed the least amount of change in crushing strength and overall the most candle stability. / Master of Science

Particulate beds which are mobilized and expanded by the application of mechanical vibrations are called vibrated beds. These beds are generally defined as shallow, if the depth-to-width ratio is less than unity. The dynamics of shallow vibrated beds and the heat transfer from immersed tubes to such beds are investigated using a vibrational frequency of 25 Hz. The vibration equipment is designed to minimize distortions in the applied displacement waveform. Transducers used are of a sufficiently high frequency response to accurately follow the variation of bed properties over a vibrational cycle. An electronic circuit is designed to exactly phase-match data collected by a transducer with the vibrational displacement. The circuit may also be used to trigger a strobe lamp at any phase angle, thus permitting an accurate examination of the evolution of bed characteristics over a cycle. Measurements of floor pressures beneath the bed, indicate cyclic characteristics, caused by the bed motion. Horizontal floor-pressure gradients cause the bed to pile up or bunker within the vessel. In bunkered beds, particle motion is determined by horizontal gas flows, and a compaction wave which propagates diagonally through the bed during the bed-vessel collision. In non-bunkered beds, particle motion is driven largely by wall friction. The observed instant of bed-vessel separation lags the theoretical prediction by several degrees, most likely because of bed expansion associated with the bed lift-off. Different "states" of shallow vibrated beds are identified, each with a unique set of characteristics. One state which exists in ultra-shallow beds of depths between 6 and 15 particle diameters is characterized by a high porosity and good gas-solid interaction, making it potentially useful for studies of reaction kinetics. Surface-to-bed heat-transfer coefficients are measured for Master Beads and glass beads, and found to vary with particle size and vibrational intensity. Heat-transfer coefficients as high as 484 W/m²-K are obtained. Heat transfer depends on particle circulation and the formation of air gaps which periodically surround the heater surface. A simplified theoretical formulation for the heat-transfer coefficient appears to qualitatively predict observed trends in heat transfer. / Ph. D.

In Victoria, Australia, brown coal is utilised as a major source of energy for the power generation industry. Victorian and South Australian brown coals have a very high moisture content and therefore, the efficiencies of power generation in traditional pulverised fuel fired furnaces are low. Fluidised beds offer a number of advantages over conventional furnaces, leading to improvements in efficiency and environmental impact. A disadvantage with implementing fluidised bed technology is the issue of scale-up. Fluidised bed behaviour can alter significantly with changes in scale, because of their strong dependence on the bed hydrodynamics. Hence, there is a need to accurately model bed behaviour to ensure that the effect of changes in scale are well understood and will not become costly and time consuming. Computational Fluid Dynamics (CFD) techniques can be applied to fluidised bed systems to gain a better understanding of the hydrodynamic behaviour involved. In the past, numerical models have considered only single particle sizes due to the added complexity of interaction between particles of differing sizes and densities. Industrial fluidised beds typically contain more than one particle size and density, therefore there is a need to develop a numerical model which takes this into account. The aim of this thesis is to develop and validate CFD techniques for modelling the behavior of a gas-solid fluidised bed containing more than one particle size and density. To provide validation data for the numerical model, physical experiments are undertaken on a small two-dimensional bubbling gas-solid fluidised bed. Mixing and segregation behaviour of different materials are investigated. The experiments demonstrate that whilst only a small proportion of the bed consists of different size/density particles, significant changes in bed behaviour are apparent. Changes in bubble rise velocity, bubble size and bubble shape are observed. A number of constitutive equations must be included in the numerical model, including relationships for the momentum transfer between various phases and solids pressure. Different combinations of these constitutive equations are investigated. A new equation for particle-particle interactions is derived and included in a CFD model. The CFD model is validated against both data in the literature and physical experiments. From the validation studies, an optimum equation set is identified. This optimum equation set produces numerical results that closely resemble experimental bed behaviour, thus bringing the goal of solving scale-up problems one step closer. The use of this type of CFD model will ultimately result in timely and cost effective solutions for both the power generation and chemical processing industries.

Fly ashes generated from fluidized bed combustion of low calorific value, high ash content Turkish lignites are characterized by high content of acidic oxides, such as SiO2, Al2O3 and Fe2O3, varying in the range 50-70%. However, there exists no study for the investigation of the possibility of using these ashes as concrete admixture. Therefore, in this study, characterization of fly ashes from fluidized bed combustion of a Turkish lignite and evaluation of these fly ashes as a substitute for Portland cement in production of pastes and mortars were carried out. The samples were subjected to chemical, physical, mineralogical and morphological analyses. Results of chemical and physical analyses of three fly ash samples show that they satisfy the requirements of EN 197-1, EN 450 and ASTM C 618, except for CaO and SO3, owing to high content of acidic oxides of these ashes contrary to majority of FBC fly ashes reported in the literature. In addition to characterization studies, water requirement, compressive strength, setting time and soundness tests were also performed for 10%, 20% and 30% fly ash-cement blends and the reference cement. Results of these tests reveal that the blends meet compressive strength, setting time and soundness requirements of ASTM C 595 without any pre-hydration treatment, and that fly ashes from fluidized bed combustion of Turkish lignites have significant potential for utilization as an admixture in manufacture of blended cements.

Fluidized bed combustion (FBC) ashes containing significant amount of free CaO and CaSO4 in addition to valuable inorganic acidic oxide ingredients such as SiO2, Fe2O3 and Al2O3 can be utilized as potential raw materials in the production of nonexpansive belite-rich calcium sulfoaluminate cement which is one of the special cement type of sulfoaluminate-belite cements having performance characteristics similar to those of ordinary portland cement besides lower energy requirements and CO2 emissions during manufacturing. Therefore, in this thesis study, possibility of producing non-expansive belite-rich calcium sulfoaluminate cement by adding FBC ashes in various proportions to the raw meal was investigated. For this purpose, a raw meal composed a mixture of limestone, bauxite, gypsum together with 10 wt % bottom ash and 15 wt % baghouse filter ash was prepared. It was sintered in a laboratory scale muffle furnace at temperatures of 1200, 1250 and 1300 &deg / C for various holding times. The results of chemical and mineralogical analysis as well as microscopic examination reveal that FBC ashes have the potential to be used in the raw meal due to the presence of characteristic mineral phases of this type of cements, i.e. yeelimite, larnite, ferrite and anhydrite, in the sample obtained at optimum sintering temperature of 1250 &deg / C for 60 min.