The water quality characteristics of a coal slurry were found to vary widely, depending upon the coal used and the use of a corrosion inhibitor. The coal-water interactions were evaluated in a pilot-plant closed-loop coal slurry pipeline. Pulverized coal from eastern Kentucky and tap water were slurred and pumped through a 40 foot (12.2 m) pipe loop for ten days. Slurry samples were collected at 3 hours, 7 hours, 1 day, 2 days, 4 days, 7 days and 10 days from the start of a run. The samples were filtered and analyzed for 29 water quality parameters, including 15 metals. Two runs were performed without adding a corrosion inhibitor and two runs were performed with the addition of a corrosion inhibitor. The coal slurry filtrate contained high levels of sulfates, total dissolved solids, conductivity, acidity, iron, magnesium, manganese, lead and aluminum. The pH dropped initially, depending upon the percent sulfur in the dry coal and the alkalinity in the slurry, but returned to 6-7 after 10 days in the pipeline. Metal concentrations were a function of the pH, which affected solubility. Organics in the filtrate were at low levels. The addition of a corrosion inhibitor increased the concentrations of most parameters.

A complete wastewater characterization study was performed on an eastern Kentucky coal slurry after a 10-day circulation period in a 40 foot (12.2 m) pilot-scale pipeline. The resulting wastewater was settled and decanted for additional lime and alum treatability studies. Easter coal slurries were characterized by high TDS, conductivity, sulfates and iron. Significant concentrations of a number of trace metals were also found; however, organics were very low. Wastewater quality varied considerably among several experiments and was presumed to be influenced by different properties of the coal and the addition of a corrosion inhibitor. The major treatment concern was removal of high concentrations of iron, manganese, and trace metals if wastewaters were to be discharged. Lime treatment was found to effectively remove iron, magnesium, manganese and many other trace metals from coal slurry wastewaters. Alum treatment methods were considerably less effective for metals removal; however, alum was more effective in removing organics, color and turbidity. The addition of a corrosion inhibitor was found to reduce treatment removals for both lime and alum treatment. Several alternative uses were proposed for slurry wastewaters based on predicted water quality and volumes.

One of the important factors in developing an emission control strategy for a coal fired steam generator is the characterization of the insitu variability of the coal being used in the furnace. Development of a model to correctly capture the insitu variability of the coal is thus fundamental to the analyses of emission control strategies. A simulation model of a portion of the Upper Freeport coal seam in Western Pennsylvania was developed using the recently developed technique called conditional simulation. This model was constructed so that it has the same mean, variance, and distribution of values as the real deposit, and most importantly, has the same spatial correlations as the real deposit. Validation of the model confirmed that the statistical characteristics of the model closely matched the characteristics of the real deposit. A second validation of the model showed that when the model is "mined" according to an actual daily mining sequence, the resulting daily variability corresponded extremely well to what was observed during the actual mining. This second verification served not only to validate the model but also served as a practical demonstration that the model can be successfully used to predict day by day variation in the quality of run of mine coal. One potential use of conditional simulation to "test" how well a mine plan works in actual mining was illustrated by an example where four mine plans were tested on their ability to correctly estimate coal production and sulfur content on a yearly basis. In each case, the simulated deposit was mined out according to the mine plan. The resulting comparison of "actual" production and estimated production clearly shows the adequacy or inadequacy of each one.

Thesis submitted in fulfilment of requirements for the degree Magister Technologiae: Chemical Engineering In the FACULTY OF ENGINEERING At the CAPE PENINSULA UNIVERSITY OF TECHNOLOGY, 2012 / The generation of electricity from coal in South Africa results in millions of tons of fly ash being produced each year. Less than 10 % of the fly ash generated is being used constructively and the remaining unused ash is currently inducing disposal and environmental problems. Intensive research on the utilisation of fly ash has been conducted either to reduce the cost of disposal or to minimise its impact on the environment. It has been shown that South African fly ash can be used as a feedstock for zeolite synthesis due to its compositional dominance of aluminosilicate and silicate phases. Most of the studies conducted on zeolite synthesis using South African fly ash are performed on small laboratory scale. Therefore, production of zeolites on an industrial/pilot plant scale would, in addition to producing a valuable product, help abate the pollution caused by the disposal of fly ash in the country. This research focuses on the investigation of the scale-up opportunity of zeolite synthesis from South African fly ashes with the view of understanding the effects of some reactor and operational parameters on the quality of the zeolite produced. Two types of zeolites (zeolite Na-P1 and zeolite A) were synthesised via two different routes in this study: (1) a two stage hydrothermal synthesis method (zeolite Na-P1) and (2) alkaline fusion prior to hydrothermal synthesis (zeolite A). The synthesis variables evaluated in this study were; the effect of impeller design and agitation rates during the aging step (zeolite Na-P1) using three different impellers (anchor, 4-flat-blade and Archimedes screw impeller) at three agitation speeds (150, 200 and 300 rpm), the effect of fly ash composition and solvents (water sources) on the phase purity of both zeolite Na-P1 and zeolite A, and the effect of the hydrothermal reaction time during the synthesis of zeolite Na-P1 using low amorphous phase fly ash i.e. aging time (12-48 hours) and hydrothermal treatment time (12-48 hours). The raw materials (fly ashes from Arnot, Hendrina, Tutuka, Lethabo and Matla power stations) and the synthesised zeolite product were characterised chemically, mineralogically and morphologically by X-ray fluorescence spectrometry, X-ray powder diffraction and scanning electron microscopy. Other characterisation techniques used in the study were 1) Fourier transform infrared spectroscopy to provide structural information and also monitor the evolution of the zeolite crystals during synthesis and 2) inductively coupled plasma atomic emission (ICP-AES) and mass spectrometry for multi-elemental analysis of the synthesis solution and the solvents used in this study. The experimental results demonstrated that the phase purity of zeolite Na-P1 was strongly affected by agitation and the type of impeller used during the aging step of the synthesis process. A high crystalline zeolite Na-P1 was obtained with a 4-flat-blade impeller at a low agitation rate of 200 rpm. Although a pure phase of zeolite Na-P1 was obtained at low agitation rates, the variation in the mineralogy of the fly ash was found to affect the quality of the zeolite produced significantly. The results suggested that each batch of fly ash would require a separate optimisation process of the synthesis conditions. Therefore, there is a need to develop a database of the synthesis conditions for zeolite Na-P1 based on the fly ash composition. As a consequence, the scale-up synthesis of zeolite Na-P1 would require step-by-step optimisation of the synthesis conditions, since this zeolite was sensitive to the SiO2/Al2O3 ratio, agitation and the mineralogy of the fly ash. On the other hand, zeolite A synthesis had several advantages over zeolite Na-P1. The results suggested that a pure phase of zeolite A can be produced at very low reaction temperature (i.e. below 100 °C, compared to 140 °C for zeolite Na-P1), shorter reaction times (i.e. less than 8 hours compared to 4 days for zeolite Na-P1), with complete dissolution of fly ash phases and more importantly less sensitive to the SiO2/Al2O3 ratio of the raw materials. The zeolite A synthesis process was found to be more robust and as a result, it would be less rigorous to scale-up despite the energy requirements for fusion. This study showed for the first time that different impeller designs and agitation during the aging step can have a profound impact on the quality of the zeolite produced. Therefore, it is not only the hydrothermal synthesis conditions and the molar regime but also the dissolution kinetics of the feedstock that influence the outcome of the zeolite synthesis process. This study has also shown for the first time that a pure phase of zeolite A can be synthesised from various sources of South African fly ash containing different mineralogical and chemical compositions via the alkali fusion method under the same synthesis conditions. Therefore, the effective zeolitisation of fly ash on a large scale would assist to mitigate the depletion of resources and environmental problems caused by the disposal of fly ash.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg 2016 / Stringent worldwide emissions legislation, the drive to lower carbon emissions, together with the ever increasing demand to preserve the environment has led to a considerable demand for cleaner and more efficient coal combustion technologies. A primary technology for the reduction of emissions of oxides of nitrogen (NOx) is the installation of low NOx coal combustion burners. Extensive research into various burner characteristics and, in particular, the aerodynamic characteristics required to improve combustion performance of low NOx coal burners has been extensively undertaken and is ongoing. In this work the aerodynamic behaviour of a full-scale, aerodynamically staged, single low-NOx coal burner was numerically investigated. The objective of the study was to develop a single low NOx burner CFD model in Ansys Fluent, to better characterize and understand the flame shape in terms of the temperature profile achieved. CFD serve as an additional tool to assist with plant optimization, design proposals and occurrence investigations. To have confidence in the single burner coal combustion CFD model, the results of the model were compared to data obtained from an existing operational low NOx burner on site during a pre-defined load condition. To further improve on the theoretical CFD combustion model, drop tube furnace (DTF) experiments have been done to calculate the single rate Arrhenius kinetic parameters (pre-exponential factor and activation energy) for coal devolatilization and char combustion of the specific South African coal used. The combustion CFD simulations showed with a lower than design air flow through the burner, a reduced amount of swirl was achieved. This reduced amount of swirl produces a jet like flame and influences the way in which the combustion species are brought together. Under these operating conditions the flame distance from the burner mouth was predicted to be 1.2 (m). A very promising result was obtained through CFD and compared well with the in-flame temperature measurement obtained through the burner centre-line of approximately 1.4 (m). In an attempt to improve the aerodynamic profile of the burner under the same operating conditions the swirl angle on the tertiary air (TA) inlet was increased. The increased swirl on the TA inlet of the burner showed an improvement on the aerodynamic profile and had a significant impact on the temperature distribution within the flame. The increased swirl resulted in an improved flame distance of approximately 0.5 (m) from the burner mouth. The effect of increased swirl on the temperature profile of the flame displayed the aerodynamic dependence of the low NOx burner on combustion performance. / MT2017

MSc (Botany) / Department of Botany