CFD ANALYSIS OF INDUSTRIAL INERTIAL SEPARATORS Predictions of intermittent flow regimes in a vapor-liquid separator

Large scale vessels provided with suitable internals for the inertial separation of multiphase mixtures are widely adopted in the process industries. The working principle of the operation is based on the density difference of the mixture components, therefore either centrifugal forces or gravity forces are adopted for achieving the phase separation. Although the equipment functioning is very simple, the achievement of high separation efficiency is far from being straightforward. The separation efficiency of the apparatuses strongly depends on the fluid dynamic features, which in turn are affected from the vessel internals design and the working conditions. In addition, the geometrical and operation parameters must be selected taking into account the applications and the location of the separator (off-shore, on-shore, Floating Production Storage and Offloading, etc.). The numerical solution of appropriate multiphase flow formulation of the Navier-Stokes equations can provide detailed information on the equipment fluid dynamics in a fully predictive way. As a result, design methods based on CFD are expected to significantly improve the separator design with respect to traditional design rules, which are based on empirical correlations and might lead to oversize the apparatuses [1]. Due to the tremendous impact of the separation efficiency on the overall process performances, development and investigation in this field is very attractive from both the academic and the industrial perspective. A review on the design rules and on the CFD studies of multiphase separators has been presented by Pourahmadi Laleh et al. [2], who addressed the potential benefits of the CFD application in this field. Although multiphase models still require further improvements, the advantages of CFD methods made their application appropriate in different scenarios of the Oil & Gas industry [3], including oilfield separators [4]. Most of the CFD studies carried out so far were aimed at evaluating the effects of the design of the internals [5], while among the uncovered issues of multiphase separators by CFD simulations, the departure from steady state operations has never being reported in literature. In this work, a vapor-liquid separator treating a two phase flow consisting of liquid water and steam for is specifically investigated considering an intermittent flow regime in the inlet pipeline. The usefulness of the CFD analysis for the mitigation of the slug entrance effects by design modification is demonstrated.