Debottlenecking of FPSO Facilities by Compact Separators

Abstract

The Bonga FPSO was designed to process 280 MBLPD gross liquid, constrained by the three-phase low pressure (LP) separator capacity. The projected production forecast indicated that additional future volumes of produced fluids from the Bonga field could exceed the design capacity of the installation. FMC's Inline PhaseSplitter was identified as a solution for debottlenecking the three-phase LP separator liquid handling capacity. The PhaseSplitter is a compact pipe-based cyclonic separator that splits the feed flow into a gas stream with limited liquid carry-over and a liquid stream with limited gas carry-under. The performance objective for the PhaseSplitter is 70 % or more gas removal while keeping liquid carry-over in the gas outlet below 1 % volume fraction. In this paper, we report results of a technical qualification program (TQP) for the PhaseSplitter as a debottlenecking tool for the three-phase LP separator. We used a down-scaled 3 inch pipe of the PhaseSplitter as compared to a 24 inch full-scale field unit. A model fluid whose physical properties resemble the Bonga fluids was used, thereby giving credence to the test results. A test matrix covering a range of representative feed conditions was probed: gas volume fraction (GVF) 75 - 90%, water cuts 20 - 80% and inlet momentums 4500 - 11000 Pa. We measured the percentage of gas removed from the feed and the amount of liquid carry-over into the removed gas as function of the flow split to the gas outlet. The results show that for almost all test conditions, acceptance criteria that were set for the PhaseSplitter were met, i.e. 75 - 80% gas removal and liquid carry-over with the gas less than 1%. Gas-liquid separation performance gradually decreases with decreasing momentum and GVF in the feed. We observed no dependence of separation performance on the feed water cut. We plotted the results as function of the normalized flow split showing universal trends. These trends provide a means to control the separation performance by monitoring the pressure drop over both outlets. We conclude that the PhaseSplitter delivers a robust performance under steady-state conditions over a wide range of operating conditions.

An Empirical Correlation for Zero-Net Liquid Flow in Gas-Liquid Compact Separator

“…The liquid holdup that existed during the critical ZNLF is called critical ZNLF holdup. By grouping some of the critical ZNLF holdup, a trend was realised that agreed with existing data by Kouba et al, and Apardi et al, that is: the critical ZNLF holdup decrease with increasing separator inlet superficial gas velocity [4,6]. Additionally, it was found that the critical ZNLF holdup increases with increasing separator inlet superficial liquid velocity.…”

“…Liquid holdup under ZNLF for a stagnant liquid condition was measured using electrical resistance tomography. The trend of present data of ZNLF holdup under stagnant liquid condition agrees with that reported by Kouba et al, [4] and Apardi et al, [6]. However, quantitatively, their data are not comparable with the present data, as the effect of inlet liquid flow on ZNLF was not considered in their work.…”

“…The existing model for predicting ZNLF in gas-liquid cyclonic separator was developed based on a stagnant liquid experiment rather than an actual separation condition [6][7][8]. Therefore, an empirical correlation for critical liquid holdup under ZNLF during actual separation condition is proposed in this section.…”