Thesis (Ph. D. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 128-133).

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 79-84).

Please read the abstract in the section 00front of this document / Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2007. / Mechanical and Aeronautical Engineering / unrestricted

The high temperature interactions of alkali metal compounds with solids present in coal conversion processes are investigated. A temperature and concentration programmed reaction method is used to investigate the mechanism by which organically bound alkali is released from carbonaceous substrates. Vaporization of the alkali is preceded by reduction of oxygen-bearing groups during which CO is generated. A residual amount of alkali remains after complete reduction. This residual level is greater for potassium, indicating that potassium has stronger interactions with graphitic substrates than sodium. Other mineral substrates were exposed to high temperature alkali chloride vapors under both nitrogen and simulated flue gas atmospheres to investigate their potential application as sorbents for the removal of alkali from coal conversion flue gases. The compounds containing alumina and silica are found to readily adsorb alkali vapors and the minerals kaolinite, bauxite and emathlite are identified as promising alkali sorbents. The fundamentals of alkali adsorption on kaolinite, bauxite and emathlite are compared and analyzed both experimentally and through theoretical modeling. The experiments were performed in a microgravimetric reactor system; the sorbents were characterized before and after alkali adsorption using scanning Auger microscopy, X-ray diffraction analysis, mercury porosimetry and atomic emission spectrophotometry. The results show that the process is not a simple physical condensation, but a complex combination of several diffusion steps and reactions. There are some common features among these sorbents in their interactions with alkali vapors: In all cases the process is diffusion influenced, the rate of adsorption decreases with time and there is a final saturation limit. However, there are differences in reaction mechanisms leading to potentially different applications for each sorbent. Bauxite and kaolinite react with NaCl and water vapor to form nephelite and carnegieite and release HCl to the gas phase. However, emathlite reacts to form albite and HCl vapor. Albite has a melting point significantly lower than nephelite and carnegieite; therefore, emathlite is more suitable for lower temperature sorption systems downstream of the combustors/gasifiers, while kaolinite and bauxite are suitable as in-situ additives.

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.

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M.Ing. / The dissertation is an investigation on the implementation of new technologies (five off) in a coal pulverising with main aim to optimise mill maintenance interventions. The technologies in question are: • Stationary air throat replaced with a rotating throat assembly. • Hydro-pneumatic mill loading cylinders replaced with airbags. • Classifier cone modification. • Introduction of triton material for the mill spider guide plates. • High chrome mill grinding balls. Every maintenance intervention, even if planned, negatively affects a plant’s availability and reliability. A Babcock and Wilcox (B&W) at Kriel power station (ESKOM) was used for the testing of the mentioned technologies. The mill model/size is a B&W 10.8E mill. The aim of the introduction of new technology on a mill is to optimise the period between required maintenance activities. A higher availability will assist in achieving good plant maintenance performance indicators. It needs to be noted that the dissertation focussed on the financial and technical parameters of a specific modification. This in an effort to increase uptime and reduce costs as part of a business drive for bigger profit margins. The new technologies tested were thus evaluated from a technical and financial point of view. Each technology was implemented at different time periods and nowhere was any tests performed in parallel on a single mill. To get approval from an investment committee for release of money for tests/modifications, technical and financial assumptions need to be made regarding the performance parameters of the modification/change. Once a modification is being tested, actual plant data can be used as inputs into the execution phase of the modification as assumptions can be replaced with test data. A financial model was developed to “test” the financial feasibility of the proposed changes/modifications. With new technology successful implemented in the plant the current maintenance strategies for maintenance interventions can be re-evaluated as the proposed modifications removed historic barriers that determined the current used based maintenance intervals. An example is where a mill is taken from service to replace or repair the stationary air throat (typically every 5 000 operating hours). With the newly applied technology (rotating throat assemblies), there is no need for maintenance interventions every 5 000hrs as a rotating throat assembly can run without major interventions for 60 000hrs.

A study has been made of the enhancement of the mechanical strength of bricks fabricated from five Sri Lankan Quaternary and post-Quaternary brick clays with the objective of identifying and optimising those factors which control the quality and performance characteristics of fired clay products of this type. Mineralogical investigations have shown that the clays are predominantly kaolinitic. Of the accessory minerals, feldspars and gibbsite are the chief constituents. The experimental programme involved the development of feasible processing techniques for clay bodies, the establishment of optimum heat treatments for their firing, and the testing and evaluation of material properties of the fired products. The microstructures of fired materials have been characterized using optical and electron microscopical techniques, as well as X-ray diffraction, electron probe microanalysis and chemical analysis. A limited study was also made of the durability of laboratory fired specimens. Methods of strength enhancement included use of the reactions of phosphates with natural clays, use of mineralizers to induce mullitization and surface coating by an efflorescence process. A kinetic analysis based on the first order kinetics is proposed for the estimation of optimum firing conditions for kaolinitic clays. The study has shown that surface coating of bricks increases the load at the elastic limit by up to 30% and the ultimate failing load by 19% in the clays examined. The measured increases in modulus of rupture and modulus of elasticity are over 33% and 40% respectively. A fabrication technique which requires the incorporation of phosphates has been developed. This provides the possibility of lowering the peak temperature of firing to 500°C. Flexural strength increase of up to 60% over the normally fired unbonded specimens can be achieved using this technique. Relevant compatibility relations in the ternary system Si02- P205-AI203 at 500'C are proposed. The presence of an optimum amount of mineralizer in a clay body may alter its sintering characteristics resulting in an increase in modulus of rupture up to 55%. However, uncontrolled additions exceeding 4 wt% cause deleterious effects. Microstructural analysis provides evidence that liquid phase sintering, development of mullite, development of pores and bloating are the dominant strength determining features in these clays. An empirical equation correlating the functional relation between modulus of rupture, mullite content and porosity is proposed. Mechanisms of strength development are discussed in the light of these findings.

A gradual increase in the price of oil, a decline in the supply of gas, and a lag in nuclear construction leaves coal (a potential major resource for the future energy needs) as a fuel in ample supply. The major portion of the United States' electricity is generated by steam-driven generators where steam is produced by fossil fuel-fired boilers. In 1978, 47 percent of the total electricity generation was fueled by coal, up from 43 percent in 1975. Use of coal in generation of electricity has spawned numerous research projects concerning the economics of the coal-fired electric power industry. The majority of the empirical works employed estimates of cost or production functions derived from the traditional strong separable functions (i.e., Cobb-Douglas or Constant Elasticity Substitution models). In the case of multiple-output, multiple-input models, constancy of elasticity of substitution proves to be highly restrictive. Limitations of conventional models have motivated the use of more general models, specifically the transcendental logarithmic function which imposes no separability restriction a priori. Absence of new empirical studies for the industry, provides sufficient justification for the empirical study of the economic relationship between inputs and outputs in the coal-fired electric power industry. Also absent in previous works is the element of machine mix and air pollution control factors. The analysis of substitution possibilities between inputs and the existence of a technological change from the objectives of the present study. Substitution and price demand elasticities are estimated which provide guidelines and useful information for planning and design of optimally more efficient coal-fired power plants. These estimated elasticities can be used to analyze the impacts of some selected government or industry policies, or they can provide guidance in further policy development and research. A transcendental logarithmic multiple-input, multiple-output cost function is adapted to the cross-section data of the coal-fired electric power industry for 1973 at the plant level. The maximum-likelihood ratio test is used to empirically test the validity of various restrictions on the productive structure. The model used in this study provides for a share-specific elasticity to be computed for each price and share observation. Results drawn from this study suggest that models with constant elasticity of substitution (i.e., Cobb-Douglas, and the Constant Elasticity Substitution and Separable models) do not appropriately represent the structure of the United States' coal-fired electric power industry. Although the empirical findings at the industry level provide substitution possibilities can be found for several vintages. Scale economies are present; and contrary to the findings for the power industry, it was found that the coal-fired power plants do not operate on the flat portion of the average cost curve.