| Maximizing the recovery of combustible values from mined coal is essential for increasing energy availability, improving coal mining profitability and reducing environmental impacts of coal mining. Hence, very efficient heavy medium separation technologies are utilized in coal preparation to treat the +1 mm size fractions. Research over the past two decades has focused on improving the efficiency of cleaning the -1 mm size fraction. For treating the 1 mm x 149 mum size fraction, spirals have become commonplace with a host of other enhanced gravity technologies available for use. Recovery of the ultra-fine 149 mum x 0 size fraction still remains a challenge. Development of column flotation in the 1980s provided major advantages over the conventional flotation cells. Despite the improvement, the application of column flotation in coal preparation has been limited due to lack of efficient dewatering technologies that can dewater the flotation product to acceptably low moisture contents such that the product can be blended with coarse clean coal without impacting the overall product quality. Hence, even where column flotation has been used, it has been applied for cleaning primarily the 149 x 44 mum size fraction with the -44 mum size fraction still being discarded in refuse ponds which are a significant environmental liability.; Through this research on existing commercial technologies, the author has developed, demonstrated and presented a comprehensive technology here that can maximize the recovery of combustible values in the ultra-fines. For the application of this comprehensive technology, a methodology is devised and demonstrated which not only overcomes the limitations related to dewatering on the product quality but in fact enables the new technology to enhance the overall product quality while still maximizing the energy recovery. This dissertation compiles the author's work in the areas of developing mathematical models to improve the predictability of flotation column carrying capacities, ultra-fines dewatering, circuit optimization, coal quality enhancement through the application of fine coal cleaning, and development of innovative coarse coal circuits for improving efficiency. The original dissertation work has led to the evolution of a technology and an approach which can maximize the energy recovery from mined coal and make ultra-fines recovery a universally applicable technology. In the marketplace of the future with increasing emphasis on reducing the environmental footprint of coal mining, ultra-fines recovery will further enable improved product qualities - higher heating value and lower pollutants (sulfur, mercury and other trace elements) without impacting recovery or economics. |
