| dc.description.abstract | Dewatering coal, and especially fine coal (-600μm), is a significant problem in the preparation of coal. The final moisture level of fine coal can be anything up to 30% by weight, depending on the type of dewatering equipment used. Moisture in coal can cause many problems, for example by increasing the transportation costs, as well as decreasing the calorific value of the coal. In industry today there is a need for a dewatering technique that will produce a drier final product. It was found that an interruption in the application of vacuum during a single dewatering cycle yielded a filter cake with a lower final moisture content. It was also demonstrated that the rate at which the coal is being dewatered is much higher than during continuous vacuum application. A further study of this phenomenon showed a twofold time dependency involving both the duration of the vacuum break, and the instant it is introduced in the dewatering cycle. An optimum was found at about 29s time duration and an introduction time of 30s, after the start of the cycle. The possibilities of diffusion and cake structural changes were investigated. For the diffusion tests, repeated interruptions of the vacuum were performed during a single dewatering cycle. Although the kinetics agreed with what was expected, the final moisture content was not as low as that found for the optimum single break test. The compressibility of a coal filter cake was one of the structural changes investigated, the other being an increase in area and, thus, airflow through the cake. Coal filter cakes were shown to be largely incompressible. It was, however, shown that an increase in area, and thus an increase in the airflow through the cake, gave excellent results. An increased area resulted in a much lower final moisture content as well as an increase in the dewatering rate. The addition of a cake surface cutter to a standard vacuum belt filter will make the application of these finfings relatively easy to industry. | |
