CFD simulations using FLUENT were preformed to study the plume flow in the vicinity of a floating production, storage, and offloading (FPSO) vessel operated by Kerr-McGee North Sea (U.K.) Ltd. It was of particular interest to ensure that hot gases emitted from the turbine exhausts did not result in significant temperature increases in the vicinity of the helideck in tail wind conditions. Contact with exhaust plumes more than two degrees Celsius above ambient can impact the aerodynamic performance of rotorcraft, and U.K. regulations require special procedures in that case.
The figure shows the exhaust cloud (in green) within which there is a temperature rise more than two degrees above ambient. The results demonstrated that during normal weather conditions, the wind and thermal environment around the vicinity of the helideck is satisfactory for helicopter operations.
Iso-surface of air temperature 2C above ambient for tail wind conditions
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Pipelines often encounter multiphase flows. In some cases, pipes in refinery operations may be carrying a combination of liquid, gas, and/or solids. Even pipelines designed for gas flow alone may encounter multiphase flow due to condensation or leakage. In this example, FLUENT's Volume of Fluid (VOF) model is used to analyze the behavior of a liquid slug in a U-Bend when forced out by pressurized gas. CFD provides a detailed understanding of the flow behavior and properties throughout the bend that would be both difficult and expensive to attain by other means such as laboratory testing.
FLUENT's Volume of Fluid (VOF) model is used to analyze the behavior of a liquid slug in a U-Bend when forced out by pressurized gas
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Hazards abound in offshore platforms due to large amounts of combustible, toxic, and volatile chemicals being confined to a relatively small space. Hazardous gas dispersion assessments are one of the many areas where CFD can help.
In this example, BHP Billiton Petroleum Limited used FLUENT to look into hydrogen sulfide gas dispersion during unfavorable wind conditions at an offshore platform in the Lennox field off the coast of England. The figures show the plume (in which the concentrations were greater than 15 ppm) for southwest and west-southwest wind directions, respectively. Despite the plume trajectory over and through the platform, the maximum H2S concentration was found to be approximately 40 ppm at all the sampling points, well within the margin of safety.
Liquid phase volume fraction at 5, 10, 15, 20, and 60 seconds
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Liquid product concentration at 5, 10, 15, 20, and 60 seconds
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Fischer-Tropsch Synthesis in a Bubble Column
Fischer-Tropsch synthesis is used to convert gaseous carbon monoxide and hydrogen into a variety of hydrocarbons in liquid form, often called "syngas conversion". Both hydrodynamics and chemical reactions are important in determining the amount of syngas conversion that takes place in any given system; hence CFD is ideally suited to model this process and to optimize the equipment.
In the example shown here, FLUENT is used to model the formation of liquid phase products (water and a collection of hydrocarbons in the methylene group) from syngas. The gas is injected through a circular opening with a diameter slightly less than the column diameter. The reaction rate is dominated by mass transfer across the gas-liquid interface. The first figure shows the volume fraction of liquid after 5, 10, 15, 20 and 60 seconds of operation. Red corresponds to pure liquid, and blue corresponds to pure gas. Gas eventually displaces the liquid and causes the liquid level to rise. The second figure shows the mass fraction of hydrocarbons (one of the products in the liquid phase) at 5, 10, 15, 20 and 60 seconds. The increased amount of product near the bottom of the column is the result of recirculation currents that become established during operation, which can be easily identified and predicted with CFD.
Liquid phase volume fraction at 5, 10, 15, 20, and 60 seconds
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Liquid product concentration at 5, 10, 15, 20, and 60 seconds
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