Crude-Oil Foaming Problems at the Sullom Voe Terminal
- Ian C. Callaghan (BP Research Centre) | Clive M. Gould (BP Research Centre) | Alan J. Reid (BP Petroleum Development (U.K.) Ltd.) | Dennis H. Seaton (BP Petroleum Development (U.K.) Ltd.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- December 1985
- Document Type
- Journal Paper
- 2,211 - 2,218
- 1985. Society of Petroleum Engineers
- 4.1.6 Compressors, Engines and Turbines, 5.2.1 Phase Behavior and PVT Measurements, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.1.4 Gas Processing, 6.1.5 Human Resources, Competence and Training, 4.6 Natural Gas, 4.3.4 Scale, 1.6 Drilling Operations, 4.2 Pipelines, Flowlines and Risers, 4.1.3 Dehydration, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating
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Early in the program of commissioning the Ninian stabilization trains at Sullom Voe terminal, problems of severe foaming in the first- and second-stage separators occurred. This resulted in massive carry-over of crude into the gas lines. Injection of a conventional anti-foam compound into the crude alleviated the problem somewhat. At higher gas/oil ratios (GOR's), however, conventional anti-foam agents did not control the foaming, adequately. BP Research Centre at Sunbury investigated the foaming characteristics of the crude and developed, with others, a novel foam inhibitor that effectively prevented foam generation in the separators. Also, gamma ray monitoring equipment with alarms and emergency trips was installed on the separators to protect the downstream gas-compression trains. protect the downstream gas-compression trains. Brent crude had similar, but less severe, foaming characteristics. These problems were solved in the same way as those with the Ninian crude.
The Sullom Voe terminal in Shetland processes and exports oil and gas from offshore fields in the East Shetland basin, about 100 miles 1161 km) northeast of the island. The fields are divided into two groups-the Ninian Pipeline Group and the Brent Pipeline Group. Unstabilized crude from each group flows through a 36-in. 191 -cm] -diameter pipeline to the terminal. The Ninian pipeline crude comes from two fields, while the Brent pipeline crude is from five fields. The properties of the crudes from each field are different, properties of the crudes from each field are different, particularly the foaming characteristics. particularly the foaming characteristics. Parallel stabilization trains-two for the Ninian crude and three for the Brent crude-are located at the terminal. The two crudes have different gas and water contents and different pressures. Their processing facilities and operating conditions are similar but not identical. One Ninian stabilization train was commissioned to prove the plant and to provide gas for power and steam prove the plant and to provide gas for power and steam generation. Very early in the commissioning operation, however, severe foaming occurred in the second-stage (low-pressure [LP]) gas/oil separator, which operated at 0. 7 bar gauge [10 lbf/sq in.], when the temperature of the initial dead-crude feed was raised to 914 deg.F [490 deg.C]. As a result, large quantities of crude were carried into the flare relief system.
BP Sunbury Research Centre confirmed the severe foaming tendency and recommended a suitable anti-foam agent. Adjusting the operating conditions had little effect on the foam level, but injecting the anti-foam agent and installing adequate foam detection and trip systems brought it under control. At a later stage in the commissioning process, a very stable foam persisted in the first-stage (high-pressure [HP]) gas/oil separator, which operated at a pressure of 1.7 bar gauge [24.7 lbf/sq in.], despite the injection of conventional anti-foam agent. Further laboratory and plant trials resulted in the development of an improved antifoam agent that destabilized this foam. As gas rates were increased to facilitate the commissioning of downstream equipment, a degree of unpredictability in separator performance became evident owing to the varying quality of performance became evident owing to the varying quality of crude. Adequate techniques to control foam level finally were developed. They called for appropriate rates of antifoam addition supported by trip systems. This technique prevented significant carry-over of crude into downstream prevented significant carry-over of crude into downstream compressor suction drums. Later, when the Brent stabilization trains were commissioned, a similar. less severe foaming tendency was observed. The phased commissioning program allowed installation and assessment of the performance of parallel plates (Dixon plates) in the separators as a method of plates (Dixon plates) in the separators as a method of breaking down foam.
Description of the Crude Stabilization Processes
Crude from the Ninian and Brent pipelines enters the process plant where it is dehydrated and stabilized. The process plant where it is dehydrated and stabilized. The Ninian and Brent pipelines operate at pressures of 26 and 9 bar gauge 1377 and 130 lbf/sq in. 1, respectively. The crude streams are processed separately in that each pipeline feeds a number of parallel dehydration/stabilization trains-two for the Ninian and three for the Brent. Each train is designed to produce 330,000 B/D 152 466 m 3 /d] of stabilized crude. One Ninian and two Brent trains are currently operating, and the remaining Brent and Ninian trains will be commissioned shortly. Figs. 1 and 2 are simplified block diagrams of the Ninian and the Brent dehydration/stabilization processes.
Ninian Stabilization. Cold Ninian unstabilized crude at 26 bar gauge [377 lbf/sq in.) is heated in three stages: first. by exchange of heat with hot stabilized crude; second, with steam condensate; and third, with medium- pressure steam. pressure steam. JPT
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