MODELING DISSOLVED AIR FLOTATION

Previously the Rotation process was mainly characterized on an empiric al basis. A model for dissolved air flotation (DAF) is presented that quantitatively describes the correlations and parameters used in both the contact and separation zones. This model includes two parameters, the hubble-hoc attachment efficiency (alpha(pb)) and the air-to-solid volume ratio in the agglomerates (beta). The sensitivity of the model for assumptions on physico-chemical and operational parameters and on the two parameters alpha(pb) and beta is thereafter investigated. Expe rimental flotation efficiencies in a coaxial DAF column under varying operational conditions were in excess of 90% at surface loadings of 15 m/h and in excess of 95% at 10 m/h. The flotation model, combining bu bble-filter and separation efficiencies, was thereafter used to predic t the efficiencies, and the model parameters alpha(pb) and beta were d etermined by a best fit-approach between model and experiment. The mod el is not too sensitive to values of these parameters. The defined alp ha(pb) and beta values correspond with previous literature data althou gh the concept of the coaxial DAF improves the efficiencies compared w ith traditional rectangular DAF-columns. The model can be used to calc ulate the efficiency for various possible operating conditions using e ither parameter values selected within the range of this paper or para meter values determined by fitting a limited number of small-scale exp eriments.