A model for predicting solid particle behavior in petroleum sludge during centrifugation

An efficient model is proposed for predicting the behavior of solid particles in petroleum sludge during centrifugation, from the particle size distribution and petroleum viscosity. Petroleum sewage sludge (PSS) and oil-tank bottom sludge (OBS), respectively collected from a sewage reservoir containing petroleum waste water and a petroleum oil storage tank, were studied. The solid particle removal and oil recovery rates were measured to assess the efficiency of the model. The model predicted that solid particles could be separated into three groups during centrifugation, with critical separation sizes of 69.2 and 80.3 mu m for the PSS and 91.2 and 110.3 mu m for the OBS, and that particles larger than the smaller critical separation size could be removed from each sludge efficiently at room temperature without pretreatment. The predicted cumulative particle removal rates using a three-stage centrifugation process were 50%, 61%, and 70%, for the three PSS-particle size ranges (in ascending order), which agreed well with experimental measurements (54%, 65%, and 75%, respectively). The experimental water/oil emulsion recovery rates were 86%, 81%, and 75%, respectively. Preheating enhanced the solid particle removal rate by 29% for PSS whose viscosity decreasing quickly with increasing temperature. Adding a solvent increased the solid particle removal rates to 90% for the PSS and 82% for the OBS, but caused the water/oil emulsion recovery rates to decrease to 69% for the PSS and 67% for the OBS. The model and experimental results suggest that the optimum centrifugation time should be determined after assessing the petroleum viscosity and the solid particle size distribution. (C) 2013 Elsevier Ltd. All rights reserved.