Evaluating Lab-, Pilot-, and Bench-scale Pressure Filtration Systems for Dewatering of Coal Refuse Slurry

Pressure filtration testing was carried out to dewater coal refuse slurry obtained from the thickener underflow stream of an operating coal preparation facility in Pennsylvania. Pressure filtration offers an opportunity to dewater refuse solids so that they can be stacked for long-term storage, while increasing the quantity of water available for recycling. Lab-, pilot- and bench-scale pressure filters were tested. Results from the lab-scale plate filter indicated a steep decrease in cake moisture for the first 120 seconds of the filtration cycle, beyond which further decrease in cake moisture was achieved only by initiation of air-blow. Similar trends were observed with the pilot-scale plate filter, with a 1.5% cake moisture reduction for every minute of air-blow after the initial sharp decrease. Cake moistures of about 30% were achieved for both units, though cake thickness can influence cake moisture. Filtrate flux values were also similar for the lab- and pilot-scale plate filters, indicating a linear scale-up with respect to the filter area. Analysis of the filtrate flux for various thicknesses in the lab-scale plate filter indicated that filtrate flux, for a given filter area, increased with increase in cake thickness. Upon normalization of filtrate flux based on cake thickness, the thinnest cake was shown to have the highest filtrate flux per unit thickness. Bench-scale pressure filtration results gave similar trends on filtrate flux and cake moisture, indicating that testing at this level can be used as a screening tool prior to scale-up testing.