The moisture content of coal has become more important in the product analysis. The high content surface area and corresponding high moisture of fine coal can contribute to most of the overall product moisture. As the preparation engineer exhausts his talents and capital budget to bring product moisture into compliance, alternate methods of fine coal dewatering must be considered. One such method is the chemical dewatering aid.
Filtration tests were carried out with the standard laboratory test filter. Each evaluation was performed with a 30% solids, 28×0 mesh coal slurry. Test series included several dewatering aid concentrations and a blank to assure reproducibility of the method.
The results of tests in which the Dewatering Aid candidate actually increases the filter cake weight while sulfosuccinate was detrimental to filter productivity. In numerous tests on different types of coal, the dewatering aid showed either no change or very significant increases in filter cake weight.
Tests were performed to simulate the foamability of the reagents in high shear machinery, such as pumps. Laboratory apparatus consisted of a food blender, stopwatch, thermometer, and a five hundred milliliter graduated cylinder. A 0.25% solution of reagent was mixed at low speed for one minute and poured into the graduated cylinder.
Total adsorption of a dewatering aid on the coal surface would be a bonus for two reasons: 1) this would eliminate buildup of the reagent in recirculating water, and 2) would indicate a conditioning of the coal surface.
Centrifugal dryers are typically treated by spraying a dilute solution of Dewatering Aid on the coal feed. The dilution rate is critical as only a small volume of Dewatering Aid will be sprayed on a large surface area. The amount of dilution water required is determined by spraying water on the dryer feed at various rates, monitoring dryer product moisture, and choosing the largest spray rate that doesn’t increase product moisture.
