Objective
Primary separators are currently horizontal to provide a large contact surface area to encourage separation of gas from liquid. This surface area also allows waves to build-up when the separator is in motion. A vertical separator has a much smaller contact area reducing waves and foam/emulsions from forming. However a better engineering of internals is required for it to perform efficiently. The OCS offers this possibility but needs to be demonstrated under sea-state motions.
The aim is to characterizea prototype OCS (developed for fixed platforms and installations) for a Floating Production Storage and Off-loading (FPSO) application. Its performance has to be demonstrated on a sea-state simulator (as it is the only means of demonstrating the separator on a range of extreme weather conditions). The viability of the OCS has already been shown for static conditions and the successful tests under dynamic conditions will lead to field trials.
The OCS design proved to be efficient without adaptation when OCS is subject to simulated sea motions :
- the model is a 600 OCS with a liquid capacity of around 1200 BPD processed in such a way to be the scaled representation of a 3100, 75000 BPD industrial OCS,
- the test bench simulated pitch, roll, surge and heave motions. Sway and yaw are not simulated, being considered as having little, if any, effect. Based on data collected from a marine specialist and on typical specifications encountered on calls for tenders, the simulated amplitude and period of these motions correspond to the worst conditions of the North Sea,
- On the other hand, the OCS proved to be highly efficient with regards to the water-oil separation. Treated water outputs were always with a very small oil content, content limit for the droplet size analysis. The outlet emulsion with a water droplet medium size with an order of magnitude estimated to around 400?m, representative value for a standard crude,
- the OCS water-oil separation high performances are not affected by the simulated motions, in the range of amplitude and period which can possibly be encountered on real operation on FPSO, and for pure or combined motions,
- for periods above range, light perturbations have been recorded, but with no resonance effect on liquid-liquid interface, the insides probably ensuring an absorption of motions,
- the gas-liquid separation is not concerned by swell effects. Only liquid-liquid separation performances have been tested within the frame of this project.
The OCS separation performances are globally in accordance with the results of numerical calculations.
The concept applied is that of a vertical three-phase vessel, featuring custom designed internals built to decrease fluid residence time and reduce the development of waves inside the separator under excessive pitch and roll on the FPS. An obvious advantage of a vertical separator over a horizontal design is the reduced area of these interfaces, thus reduced disturbance. Some motion must be expected however. So the gas-liquid and liquid-liquid interfaces will be observed and compared with theoretical approach of these disturbances.
Based on recent bids for a Call for Tenders, where conventional horizontal separator and OCS were both proposed, the OCS highlighted the following advantages :
- reduced the equipment volume of 56%
- reduced the empty equipment weight of 40%
- reduced the required deck area of 78%
With the ratio of 10 tonnes of topside per tonne of process equipment, the OCS allows the saving of 750 tonnes of structure (40%).
Moreover experience gained on industrial definition about sand and waxes removing system are not modified.
Topic(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
78373 Plaisir
France