Comparison of Microwave Drying and Conventional Drying of Coal
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The moisture contents of the final coal products from processing plants are often too high and do not meet the requirements of the client. In many cases, drying becomes a necessary step to control the moisture content. Conventional thermal drying is inefficient and is not environmentally friendly. This study investigates the application of microwaves as an alternative heat source for drying coal. The rate of drying was determined by the thermogravimetric analysis (TGA) technique. Several variables that have significant effects on the drying kinetics were investigated, including incident microwave power, initial moisture content and the sample mass. Microwave drying tests were performed under various conditions and the mass change was monitored continuously. The percentage mass loss, moisture fraction and drying rate were obtained for each experimental condition. The final temperature was measured and drying efficiencies were calculated. For comparison purposes, some conventional thermal drying tests were also carried out at temperatures ranging from 130 to 220oC and with coal masses ranging from 10g to 100g. The TGA results show that microwave drying has distinct advantages over conventional drying such as reducing the overall required time and increasing the drying efficiency. A multiple-regression analytical method was used for both microwave and conventional drying to find the best fit model among eleven different types. Finally, the sample mass, which proved to be the most dominant factor in microwave drying, was incorporated into the equation of the best fit model.