Comparison of Efficiencies of Microwave and Conventional Electric Ovens in the Drying of Slime-Coal Agglomerates

Abstract

Currently nearly 6 million tonnes of bituminous coal are produced in Turkey and more than 0.3 million tonnes of slime coal are discarded from the coal-washing plants. Slime coal is a low-calorie fuel containing clay and other minerals and high levels of moisture. The filter cake sample used for the study was obtained from a hydrocyclone overflow. The moisture content of the disc-filtered bituminous coal was 26% and its average particle size was similar to 30 microns. The slime-coal filter cake sample was agglomerated in 2 cm diameter material before the drying experiments. The agglomerates were dried separately in both microwave and conventional ovens. After the drying process, the efficiency of each oven was determined. The surface temperatures and compressive strengths of the agglomerates dried in both types of oven were compared. In the microwave oven, micro- and macrocracks appeared on the agglomerates causing them to dry faster. In that manner, the drying efficiency of the microwave was found to be higher. As the microwave energy heated the agglomerate selectively, the surface temperature was found to be lower. However, the quick-drying process caused a decrease in the strength of agglomerates.