Packed Bed Filtration: Experimental Investigation and Conceptual Analysis of a Filter Ripening Model

摘要

A theory for filter ripening (Ali, 1977) is subjected to experimental and conceptual analysis in order to test its applicability under conditions much different than those for which it was calibrated and verified. The filtration theory incorporates physical and chemical characteristics of the entire filtration system in predicting the removal of suspended solids and the development of head loss throughout a filter run. Filtration performance is a function of filter variables (bed depth, porosity, filtration velocity, media size and type) and suspension variables (solids concentration, temperature, particle size and type). The chemistry of the system (ionic strength, polymer type and dose) also controls filter performance and is included in the theory. Experiments are conducted by filtering suspensions of Min-U-Sil particles at two different size ranges at two concentrations and flow rates through pilot filters. Four identical filter columns, each containing different sized media, are used in each experiment. Solids removal efficiency is evaluated by measuring the light scattering of influent and effluent samples. Head loss is determined from open manometers connected to the filter columns. The experimental results are compared to predictions obtained from the theory for filter ripening. In general, the effects of variations in collector size, suspended solids concentration, flow rate and particle size on filter performance are modeled correctly, but exact fits using consistent values for model coefficients are not obtained. Removal efficiency is modeled well but head loss predictions are not generally in agreement with the experimental results. Conceptual considerations yield possible explanations for these discrepancies.