Froth flotation is a widely used, cost effective particle separation process. However, its high performance is limited to a narrow particle size range, e.g., between 50 µm and 600 µm for coal and between 10 µm and 100 µm for minerals. Outside this range, the efficiency of froth flotation decreases significantly, especially for difficult-to-float particles of weak hydrophobicity (e.g., oxidized coal). Nanobubbles integrated into a specially designed column flotation expanded the particle size range for efficient froth flotation as a result of increased probabilities of particle- bubble collision and attachment and reduced probability of detachment. The major advantages of nanobubble enhanced flotation include lower collector and frother dosages since nanobubbles that are mostly smaller than 1 µm can be formed selectively on hydrophobic coal particles from dissolved air in coal slurry. Nanobubbles act as a secondary collector on particle surfaces, thereby resulting in considerably lower operating costs. A systematic parametric investigation of the proposed technology was performed to understand the effects of process variables on separation performance with a typical coal sample using a specially designed flotation column and three 10-liters conventional flotation cells. Results indicate that the combustible recovery of a -150 µm coal increased by 5-50% in the presence of nanobubbles, depending on process operating conditions. Nanobubbles also significantly improved process separation efficiency and increased the flotation rate constant by more than 40%. Theoretical evaluation of the innovative flotation technology was employed using specially designed apparatus to study the nanobubbles stability and the roles of nanobubbles on particle-bubble interactions, froth stability, and surface area flux. In addition, a detailed technical performance and economic evaluation was performed.

McDonalds Lime Ltd, situated in Otorohanga, New Zealand, operate two dry process rotary lime kilns producing burnt and hydrated lime for a range of industries including agriculture, roading, water treatment, gold mining and steel making. The following Technology in Industry Fellowship (TIF) funded Masters Project is structured around investigating the combustion characteristics of Kiln Two at McDonald’s Lime Ltd using Computational Fluid Dynamics (CFD). Numerical results obtained using the commercial CFD code FLUENT were first validated against experimental data from the International Flame Research Foundation’s (IFRF) Furnace No.1. The validation study focussed on comparing the finite rate and mixture fraction/PDF approaches to combustion chemistry, as well as different methods for defining coal particle size distributions. Numerical modelling of Kiln Two at McDonald’s Lime Ltd began with full three-dimensional simulations, however due to their complexity and large computational times, two-dimensional axisymmetric models were primarily used for investigations. Comparisons were made between the two approaches. Investigations into the original pulverised coal fired system focussed on how the kiln aerodynamics and heat transfer properties were affected by changes to the coal and air inlet properties. The performance of a recently installed waste oil firing system was also investigated, with results showing that firing the kiln with a 25% thermal substitution of oil is the most efficient mode of operation. As the investigations focussed on the combustion characteristics the effects of the reacting limestone bed were ignored in all simulations. CFD modelling of the combustion characteristics within a large scale rotary kiln proved to be an extremely complex task. The work presented in this thesis has however provided some promising results which will ultimately assist McDonalds Lime Ltd in reducing their operating costs and environmental impact. Futhermore, the project has laid the foundation for further investigations.

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Coal quality plays a crucial role both economically and environmentally in the operation of a coal-fired power plant. These plants are designed to operate most efficiently when coal of consistently good quality is used as the feed. For example, the ash content should be monitored to control slagging problems in the burners. For emission control purposes the sulfur content of the feed should be carefully scrutinized. This realization of the importance of coal quality to the end-user has made the prediction of coal quality an important concern. Computerized mine planning systems can be used to help suppliers predict the quality of future coal shipments. One such system was implemented at an underground coal mine to determine its performance in an operating environment. Following some extensive revisions to the system, the results of the implementation exercise showed the ability of this mine planning system to account for coal quality while producing a workable short-range plan. To be of direct use to the end-user, the mine planning results should be adjusted to account for mining dilution and subsequent beneficiation of the run-of-mine coal. To help power plant owners in predicting the quality of the power plant feed a computer program was developed to solve the blending problem faced by plants dependent on multiple sources of supply. This interactive program utilizes the predictions from the mine planning system to obtain a goal programming formulation of the blending problem. This type of problem formulation gives the program the flexibility needed to solve the blending problem in both long and short term time frames. Use of the program in both planning scenarios was illustrated by examples. The results showed the ability of the program to determine the best blend possible based on a set of user-specified objectives. Use of this interactive blending program in conjunction with the mine planning system provides the capability of computerized prediction of coal quality from mine mouth to blended plant feed. Implementation of these planning aids on a routine basis will assist the owners of coal-fired power plants in their attempts to maximize plant efficiency and maintain environmental standards.

The focal point of the quality of life associated with the United States is a strong economy. Growth in the economy means growth in employment. The establishment of stringent environmental legislation is now a reality. However, those responsible for enacting environmental laws, as well intentioned as they may be, must strive to assess the socio-economic consequences of their actions so that the true net benefit of the environmental legislation is established. The main effort in this research centers around the analysis of how a particular resource, energy (i.e., energy in the form of electric power derived from strip-mined coal) is embedded in the economic growth of the Southwest. The basic econometric tool that has been utilized is a regional input-output model which evolved from a California-Arizona linked input-output model developed by H. O. Carter and D. Ireri. The decision space developed, which effectively acted as a mechanism for restricting coal-fired power availability in future years, was based on a schedule of electric energy capacity additions as delineated by the U.S. Department of Interior's Southwest Energy Study. The regional economic analysis, described in Chapter 5 of this dissertation, suggests there is a definite relationship between coal-fired power availability and regional economic growth in the Southwest. Furthermore, the estimates of incremental decreases in regional economic activity associated with certain levels of decreased coal-fired power development are of such a magnitude that one could characterize the relationship as very significant.

Extensive research has been conducted in numerous coalbed methane (CBM) basins; however, the Williston Basin (WB) remains largely unexamined due to the absence of CBM production despite large coal reserves. CBM in WB coalbeds has been reported, but there has been no systematic study on gas origin and distribution, or hydrogeochemical controls on gas generation to date. This study aims to determine differences in chemistry between groundwaters with and without the presence of CH₄ to better understand factors affecting CBM generation. Results reveal that shallow gas accumulations in WB coalbeds are microbial in origin and formed via CO₂ reduction. CBM is associated with Na-HCO₃ type groundwater with SO₄ concentrations<1 mmole/L due to cation exchange and sulfate reduction, respectively. These groundwaters occur in deeper units of the Fort Union Formation, underlying multiple coalbeds, suggesting that CH₄ is present in waters that have reacted extensively with formations containing low-rank (lignite) coals.

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No description available.

The Fluidised Bed Combustion (FBC) technology has been widely used internationally for power generation. This technology has good fuel flexibility and reduced S02 emissions with dry sorbent (Limestone or Dolomite) addition. South Africa has large reserves of coals that are difficult to combust in conventional pulverised fuel fired boilers. These reserves could be potential feedstocks for new build FBC boilers. The chemical composition of these coals is site specific and could have an impact on the combustion performance of the fuel. This necessitates the need for FBC coal tests in the presence of a sorbent. The objectives of this study were to investigate the changes in the production NO" SO" and the combustion efficiency of the three test coals under conditions of fluidised bed combustion, with the same sorbent. Tests with no sorbent were performed to evaluate the coals inherent calcium capabilities of capturing sulphur. Tests with varying ratios of sorbent were performed to evaluate the sorbent's capabilities for further levels of in-bed desulphurisation. The experimental equipment used in this investigation was the Eskom Fluidised Bed Test Facility (FBTF). This facility is a bubbling fluidised bed combustorlgasifier. The investigated bed temperature range was between 800 to 900°C, in intervals of 20°C. The operating pressure was 50kPa (gauge). The three coals were compared at CalS molar ratio of 1. Carbon in ash has shown to decrease with an increase in bed temperature for Coal A, Band C. The best performing coal in terms of least quantity of remaining carbon in ash was Coal A. The NO emissions increased for an increase in bed temperature for Coal A, Band C. The greatest NO emissions were recorded during Coal B tests. The N 20 emissions decreased with an increase in bed temperature for Coal A and B tests. Higher N 20 emissions were observed for Coal B than Coal A tests. In terms of S02 retention Coal C performed the best. The optimal operating bed temperature for S02 retention observed for the three coals was in the region of 800-860°C. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

The use of black liquor gasification as an alternative to conventional chemical and energy recovery systems for spent liquors is an area of particular interest to the pulp and paper industry. The motivation to explore this technology is to improve the thermal efficiency of the recovery process by utilizing the energy content of the spent black liquor more effectively and provide chemical recovery for sodium and sulphur containing liquors for a local pulp and paper mill. A study of the available gasification technologies showed that the steam reforming process marketed by ThermoChem Recovery International is particularly suited to the mill in that it can handle a change to a sulphite pulping chemistry and also handle silica removal which is an inherent problem with the bagasse raw material that the mill uses. However the technology required further development and confirmation of process suitability before implementation at the mill. This aim of this project was to build and operate a gasifier based on the TRI concept to determine if this process is suitable for recovery of SASAQ black liquor from bagasse pulping. This included gaining an understanding of the process variables like the black liquor solids composition and the non-process element levels and required carrying out a mass balance on inorganic components across the reactor as well. The focus of this investigation was primarily on the front end of the project and entailed basic and detailed design of a pilot gasification unit. The pilot unit was subsequently constructed, commissioned and operated to prove the unit met the design intent. Preliminary results showing the conceptual proof of the technology are presented as well as performance tests showing the unit capability of gasifying a 3.1 1Ihr 60% solid content black liquor feed. Problematic areas that could influence the design of a scale-up unit were identified and highlighted for further development, with proposed solutions. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2005.