Predicting the pressure drop of a biofilter and the specific surface area of the packing material
Résumé
An analytical pore-scale model is proposed for predicting the pressure drop of a biofilter by taking the effect ofbiofilm development into account. Besides the average particle radius and fluid parameters, the pressure dropis expressed in terms of the initial bed porosity, the biofilm affected porosity, particle sphericity, surface roughnesscoefficient, coordination number and biofilm thickness. The coordination number represents the numberof particles in contact with a single one in the bed. The biofilm affected porosity is based on the assumption ofbiofilm overlap and particle contact. The sphericity for a cluster of particles in contact and biofilm overlap is quantifiedin terms of the biofilm thickness and coordination number and its effect on the pressure drop investigated.Themodel predictions are verified against experimental pressure drop data obtained froma biofilter in operationfor 107 days. Expanded schist was used as packingmaterial. The proposedmodel is also compared to amodifiedErgun equation from the literature of which the empirical coefficients and porosity exponents were adjusted tobe applicable to a biofilter. The model proposed in this study contains no empirical coefficients. An equation isalso presented for predicting the biofilm affected specific surface area which requires the measured pressuredrop and superficial velocity values as input parameters. The effect of the biofilm affected porosity on the pressuredrop is also investigated in the case of no biofilm overlap and no particle contact. Lastly a sensitivity analysisis performed on the initial bed porosity and coordination number.