A realistic computational fluid dynamics (CFD) simulation of a field three-phase separator has been developed. This realistic CFD simulation provides an understanding of both the microscopic and macroscopic features of the three-phase separation phenomenon. For simulation purposes, an efficient combination of two multiphase models of the commercial CFD software, Fluent 6.3.26 (ANSYS 2006a), was implemented. The flow-distributing baffles and wire mesh demister were also modeled using the porous media model. Furthermore, a useful approach to estimating the particle size distribution in oilfield separators was developed. The simulated fluid-flow profiles are realistic and the predicted separation efficiencies are consistent with oilfield experience.
Once a crude oil has reached the surface, it must be processed so that it can be sent either to storage or to a refinery for further processing. In fact, the main purpose of the surface facilities is to separate the produced multiphase stream into its vapor and liquid fractions. On production platforms, a multiphase separator is usually the first equipment through which the well fluid flows, followed by other equipment such as heaters, exchangers, and distillation columns. Consequently, a properly sized primary multiphase separator can increase the capacity of the entire facility.
CFD simulation is routinely used to modify the design and to improve the operation of most types of chemical process equipment, combustion systems, flow measurement and control systems, material handling equipment, and pollution control systems (Shelley 2007). There are two approaches to developing CFD models of a multiphase flow: the Euler-Lagrange approach and the Euler-Euler approach. In the Euler-Lagrange approach, the continuous fluid phase is modeled by solving the time-averaged Navier-Stokes equations, and the dispersed phase is simulated by tracking a large number of droplets through the flow field based on Newton’s second law. The Euler-Euler approach, on the other hand, deals with the multiple phases as continuous phases that interact with each other. Because the volume of a phase cannot be occupied by the other phases, phase-volume fractions are assumed to be continuous functions of space and time, and their sum is equal to 1.