Field Confirmation of CFD Design for FPSO-mounted Separator
Authors: Lee Chang-Ming , van Dijk Eric , Legg Mark , Byeseda John 
Published: October 2008

Two new Free Water Knockout (FWKO) vessels were installed on an FPSO facility operating offshore Cabinda, Angola. They were installed to accommodate larger slugs and to debottleneck downstream facilities to cope with increasing water production. The paper describes process design and CFD work for placement of internal baffles to mitigate fluid sloshing in the new separators. Three CFD simulations were performed. First we demonstrated that the separator would not operate properly without custom-designed internal baffles. The second simulation demonstrated that customized baffles in the new vessel could suppress sloshing and prevent water spill over into the oil discharge stream. The final simulation showed that the advanced baffle arrangement would control the problems due to sloshing when fluid flow was introduced into the simulation. Field data is presented to confirm the validity of the simulation work and successful operation of the separators. The work gives confidence in the use of CFD to design separators with minimum weight and size. We show that for critical applications, the CFD design should be applied to the particular case - baffle designs are not "one-size-fits-all".

Introduction

The purpose of this CFD (Computational Fluid Dynamics) study was to evaluate the design and performance of internals installed in a horizontal Free Water Knockout separator (FWKO), located on SBMâ??s Kuito Floating Production Storage and Offloading (FPSO) facility in Kuito Field Block 14, offshore Cabinda, Angola. The new FWKO design included both a proprietary cyclonic inlet device and perforated baffles for flow distribution. The new internals were installed to accommodate larger slugs and to debottleneck downstream facilities to cope with increasing water production. The internal baffles were evaluated for suppression of fluid sloshing inside the vessel when it is subjected to acceleration wave motion under different sea states. Cyclonic inlet devices are industry proven separation technology for reducing or eliminating foam in a separator and for improving the efficiency of separation. Since the primary goal of the simulation work was to design perforated baffles that would allow the separator to operate effectively at the maximum wave-induced motion on the FPSO, the cyclonic inlet device was modeled in the CFD simulation as a simplified block component. The continued rapid improvement in the speed of computer hardware and increased size of available memory have led to the emergence of CFD since the 1960's, and the inception of the commercial CFD software industry started in the early 1980's. CFD complements theoretical and experimental fluid dynamics by providing a flexible and cost-effective means of testing theoretical advances or simulating the performance of alternative configurations for conditions that are very difficult to physically test in a complex flow system on n experimental basisand processes. Use of CFD simulation can lead to shorter design cycles and further compress the time between the conceptual stage of a project and field implementation and troubleshooting of existing equipment, evaluating retrofit designs, and minimizing equipment down time.