Pretreatment of Pittsburg seam B coals to decrease its ash content and increase its solvent extractable material was investigated by anodically electrolysing acidified coal-water slurries at potentials around 1.0V SCE. The effects of the pretreatment were examined as functions of coal particle size, acid strength of the slurry, time of electrolysis and applied potential. The coal electrolysis was found to be most efficient at low acid strengths and short electrolysis times. The morphology of the coal surface changed with the conditions of the electrolysis and related to the percentage ash removal and the amount of solvent extractable material present in the coal. The anodic oxidation of the coal is suspected to occur via an electrocatalytic(EC) mechanism, whereby ferrous ions in the coal are first oxidised at the anode to the ferric state. The ferric ions migrate into the coal and accept electrons from accessible bonds in the coal micelle thereby reducing themselves back to ferrous ions and return to the anode for re-oxidation to the ferric state. The acceptance of electrons from certain bonds in the coal micelle results in the break-up of the micelle in to simpler compounds. Accordingly, the solubility of the coal in an organic solvent should increase and this was found to be so when ferrous ions were externally added to the electrolyte. The electrolytic process was also found to transfer metallic ions present in the coal into solution in the electrolyte. / Master of Science

A flotation column has been developed Incorporating the use of fine air bubbles (less than 100 microns) to remove ash-forming minerals from micronized coal. The microbubble generator used In this work has been characterized and found to yield a very narrow size distribution. Microbubble column flotation tests have been conducted to study a series of operating variables such as time, bubble size, feed rate, feed point, feed percent solids, column height, bubble number concentration, make-up water addition and countercurrent wash water addition. The results show that i) fine air bubbles are Inherently better suited for floating small particles; ii) both ash and recovery rates Increase with Increasing feed rate, distance of the feed point from the tailings port, feed percent solids and bubble number concentration; iii) taller columns result In Improved recovery and ash rejection; and iv) the countercurrent wash water addition minimizes the entrainment of mineral matter to the froth product. Proper control of these parameters makes It possible to produce super clean coal (< 2% ash). / M.S.

In order to produce coal containing less than 2% ash using a physical cleaning process, the coal must initially be ground to liberate the mineral matter. The result is a micronized feed material that cannot be efficiently treated using the commercial methods currently available. Therefore, an advanced physical cleaning technique for ultrafine coal, called"selective-shear coagulation", is presently being investigated. The process utilizes high shear conditions to overcome the strong electrostatic repulsive force between particles. The attractive hydrophobic interaction and van der Waals forces control the coagulation of the coal particles. The effects of various chemical parameters, such as pH and ion concentration, were studied. An optimum pH range was established for tap water and distilled water media. The presence of multivalent cations in the system increased coal recovery, but decreased selectivity. Physical parameters of the selective coagulation process, such as particle size, percent solids, and specific energy input, were studied. It was found that separation efficiency improved with decreasing particle size. An optimum feed percent solids was found by maximizing separation efficiency. In the case of distilled water, test results revealed that additional specific energy provided by mechanical agitation was required to induce coagulation after grinding. However, additional mixing was found unnecessary in the case of tap water. A continuous selective-shear coagulation process using an elutriation column as the separator was designed and characterized. A steady-state population balance model of the elutriation column was developed. The predictions were found to be in good agreement with experimental results. / Master of Science

In recent years, a great deal of interest has been shown in developing methods for preparing super—clean coal containing less than 2% ash and 0.5% sulfur. New techniques for recovering fine coal, such as micro—bubble flotation, can achieve the desired result provided mineral matter is sufficiently liberated. To achieve sufficient liberation, however, it is often necessary to grind to a mean particle size finer than 10 microns. Since conventional ball mills are highly inefficient in this fine size range, the stirred ball mill has been proposed as a more suitable means for ultrafine grinding. / Master of Science

The objective of this study was to evaluate various multi-stage circuit arrangements that may be used to improve the column flotation of micronized coal. Laboratory flotation tests were performed with two different samples of Pittsburgh No. 8 seam coal. The first coal, Coal A, was ground to two different particle sizes and subjected to both column and conventional flotation. These tests were performed to obtain an initial understanding of the operational behavior of the column process and to compare the results with those of conventional flotation. The second coal, Coal B, was used in the actual testing of three different column circuit arrangements. The experimental test results were compared to simulated results obtained using a rate-based flotation model constructed in the present work. Several hypothetical flotation circuits were also examined using the simulation model and experimental flotation rate data. The circuit test results showed that each of the different circuit configurations possessed specific advantages in terms of throughput capacity, combustible recovery, ash rejection and sulfur rejection. However, the overall performance curves for each circuit were all found to fall on or just below the maximum separation curve predicted using the release analysis technique. Also, the simulated results in almost all cases predicted better results than what was actually obtained. This discrepancy was attributed to the inability of the rate-based model to adequately describe restrictions associated with the carrying capacity of the column froth. / Master of Science

In order to demonstrate the ability of microbubble flotation to superclean coal to ash levels of less than 2%, several Eastern U. S. coals have been tested. The results show that the process is capable of producing superclean coal with improved recovery as compared to the conventional flotation process.To further improve and understand the microbubble flotation process, electrokinetic studies of the hydrocarbon oils used in flotation as collectors have been conducted. Also, the effect of oil emulsifiers on the zeta potential of oil droplets has been studied. In general, oil droplets are negatively charged and negative zeta potential is reduced with the addition of nonionic and cationic surfactants. On the other hand, the negative charge is increased with the addition of an anionic reagent. It has also been shown that the negative zeta potential of oil droplets increases with increasing hydrocarbon chain length.The effects of different collectors on induction time and flotation have been determined by conducting microflotation and induction time experiments using an Elkhorn seam coal sample. The results show that industrial oils combined with the coal have the shortest induction times and, therefore, the highest flotation yields as compared to pure hydrocarbon oils. It has also been shown that oil emulsifiers tend to increase flotation yield and reduce particle/bubble induction time. / Master of Science

The Chemical and Electrochemical Coal Cleaning (CECC) process, designed to remove mineral matter from coal, has been investigated by treating coal samples in acidified slurries. Various coals, characterized by different maceral structures and mineral matter contents, were subjected to several experimental procedures under mild conditions. Substantial amounts of mineral matter (up to 70%) could be extracted from coals which were resistant to physical cleaning, while 22% of sulfur could be removed from pyritic coals. The operating conditions of the CECC were studied in order to determine their influence on the process efficiency. Analyses conducted on solids and leachates resulting from the tests demonstrated that different mechanisms were achieving demineralization by the CECC. Between 50% and 95% of the feed mineral matter was removed by dissolution, whereas the balance could be ascribed to liberation. The CECC process is suitable for cleaning middlings, as well as for further extracting mineral matter from physically clean coals, especially from pyritic vitrinite and fusinite type coals. / Master of Science

M.S.

A new method for demineralizing coal has been developed which is based on the osmotic pressures that occur when electrical double layers overlap. In this technique, coal is exposed to ferric ions in an acidic medium which causes the coal to lose electrons and become positively charged, thereby establishing ionic double layers in the vicinity of its surface. Inside the pores and crevices in which mineral matter is entrapped, the ionic double layers overlap and reduce the chemical potential of water, creating an osmotic pressure. The build-up of such pressure pushes the mineral matter out of the crevices, resulting in mineral liberation. Since the process, which is termed electro catalytically induced liberation (EIL), relies on surface-chemical reactions, the energy consumption is substantially lower than in conventional liberation processes based on comminution. Tests on several different seams of coal from varying geological locations have indicated that the process may be used to remove over 70% of the mineral matter present in coal. Mass balance studies conducted on a Wyodak coal indicate that approximately 90% of the ash removed is by the EIL mechanism, while the balance may be attributed to acid dissolution and the loss of material during handling. Scanning electron micrographs of the coal samples taken before and after treatment show morphological changes consistent with the proposed EIL mechanism. The technique has been used successfully to clean bituminous coals, low-rank coals and preparation plant refuse, and to further reduce the ash content of coals pre-cleaned by other means. A theoretical model has been developed to calculate the osmotic pressure that occurs inside a typical coal crevice during the EIL treatment. The changes in the aqueous chemical potential are calculated using semi-empirical equations derived from solution theory, while partial molar volume changes are accounted for in the final calculation of the osmotic pressure. The model indicates that pressures on the order of 4-7 atmospheres can develop inside crevices with walls 100-1000Å apart. These values are numerically consistent with those predicted by other models developed using different approaches. / Ph. D.

In recent years the Central Appalachian coal industry has suffered from a number of changes in the structure of the coal market. Foremost among these changes have been the collapse of the domestic steel industry and the passage of the Staggers Act. In the past high quality central Appalachian coal was sold mainly as premium coking coal. This market failed, and continues to shrink. Regional coal producers are now looking to the rising demand for steam coal in a nation which is turning away from oil and nuclear power generation. With the possible passage of the Clean Air Act, low sulfur central Appalachian coal may have a promising future, but only if its production can reach this new market. Prior to 1980, regulated rail tariffs gave coal producers access to most consumers, while independent railroads competed for freight. Railroad deregulation greatly improved the position of the railroads, but weakened that of regional coal producers. Central Appalachia and the southern coastal states were left with only two railroads, CSX and NS. These railroads now set their own rates and secretly negotiate contracts with shippers. Due to the configuration of ownership of these tracks, the vast majority of mines and utility plants were left with access to only one carrier. In this situation rail transportation has become the primary concern. Mines unable to originate shipments on the same railroad which is serving the utility plant find themselves locked out of that market unless their mine price is sufficiently low enough to compensate for the increased rail rate. Most of the coal burning plants in Virginia are located on CSX, while the vast majority of southwest Virginia's coal production is served by NS. With a higher mining cost than in eastern Kentucky and southern West Virginia, Virginia producers are having great difficulty in competing in the state's steam coal market. This dissertation is the first effort to quantitatively specify the regional steam coal market. This is done by identifying sources of data which are subsequently used to generate short term forecasts of mine price. These forecasts are used in the cost vector of a Virginia coal Purchasing model which is solved to determine the optimal pattern of coal purchases for Virginia utilities. The structure of the model is based on a detailed market analysis which accounts for the influence of rail rates. / Ph. D.