A new processing technique, known as hydrophobic displacement, was explored as a means of simultaneously removing both mineral matter and surface moisture from coal in a single process. Previous thermodynamic analysis suggests that coal moisture will be spontaneously displaced by any oil with a contact angle greater than ninety degrees in water. Based on these results, six methods of hydrophobic displacement were evaluated: hand shaking, screening, air classification, centrifugation, filtration, and displacement. In the first five methods hydrophobic displacement took place during the cleaning stage. A recyclable non-polar liquid (i.e. pentane) was used to agglomerate coal fines followed by a physical separation step to remove the coal agglomerates from the mineral-laden slurry. Bench-scale tests were performed to identify the conditions required to create stable agglomerates. Only the last method, displacement, did not utilized agglomeration and performed hydrophobic displacement during dewatering, not cleaning. A procedure was also developed for determining moisture content from evaporation curves so that the contents of water and pentane remaining in a sample could be accurately distinguished. Two primary coal samples were evaluated in the test program, i.e., dry pulverized 80 mesh x 0 clean coal and 100 mesh x 0 flotation feed. These samples were further screened or aged (oxidized) to provide additional test samples. The lowest moisture, 7.5%, was achieved with centrifugation of the pulverized 80 mesh x 0 clean coal sample. Centrifugation provided the most reliable separation method since it consistently produced low moisture, high combustible recoveries, and high ash rejections. Hand shaking produced the next lowest moisture at 16.2%; however, the low moistures were associated with a drop in combustible recovery. There was also a great deal of error in this process due to its arbitrary nature. Factors such as oxidation, size distribution, and contact angle hysteresis influenced the concentrate moistures, regardless of the method utilized. / Master of Science

A simple thermodynamic analysis suggests that oil can spontaneously displace water from coal's surface if the coal particle has a water contact angle greater than 90°. However, the clean coal products obtained from laboratory-scale dewatering-by-displacement (DbD) test work assayed moistures substantially higher than expected. These high moisture contents were attributed to the formation of water-in-oil emulsions stabilized by coal particles. Four different approaches were taken to overcome this problem and obtain low-moisture agglomeration products. These included separating the water droplets by screening, breaking emulsions with ultrasonic energy, breaking agglomerates with ultrasonic energy, and breaking agglomerates using vibrating mesh plates. On the basis of the laboratory test work, a semi-continuous test circuit was built and tested using an ultrasonic vibrator to break the water-in-oil emulsions. The most promising results were obtained agglomerates were broken using the ultrasonic probe and the vibrating mesh plates. Tests conducted on flotation feed from the Kingston coal preparation plant gave a clean coal product containing 1% by weigh of moisture with a 94% combustible recovery. The separation efficiency of 93% is substantially higher than results achievable using froth flotation. When agglomerates formed from thermal coal from the Bailey coal preparation plant were broken using either ultrasonic energy or vibrating mesh plates, the obtained results were very similar: clean coal products assayed less than 5% moisture with separation efficiencies of 86% in average. / Master of Science