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Contours of liquid volume
fraction inside of a crude
vacuum distillation tower
 
Eulerian multi-phase model

Mixing in an Oil Storage Tank



Mixing of Crude Oil Fractions in a Storage Tank

(click on the pictures to start the animation)

The following animation shows mixing in an Oil Storage Tank over 40 hours. Tank parameters are as noted on the simulation. The objective was to obtain adequate mixing within 20 hours. To this end a Fluent scheme function was written to dynamically display fraction of each crude at selected locations. When the fractions equal each other then mixing is essentially complete. The objective was to achieve good mixing of the two phases, Brent Light Crude (API 37.5) and Heavy Crude (API 15) within 20 hours. There is a small amount of water present in the tank bottom which was not desired to be mixed.

 

Original Impellor Design


Storage Tank Mixing, Original Impellor Design



As you can see adequate mixing was not achieved within the target time frame and in fact required about 36 hours for good mixing.

Modified-1 Impellors


Storage Tank Mixing, Modified Impellor Location

The impellor design was not changed, however the locations of the impellors were. As you can see the mixing, requiring the same hp, proceeded more quickly and adequate mixing was achieved in 26 hours.

Run 3, 3-Phase Eulerian Simulation

Storage Tank Crude Mixing, modeling the water fraction

Here we tried to run a 3-phase Eulerian simulation. The object was to track the small water fraction and verify that although the light and heavy crudes are well mixed, the heavier water fraction did not become mixed in. As you can see, although the problem can be set up and run in Ansys Fluent 14.0, convergence was difficult. This necessitated small time steps with the result that the requisite 20 hours of real time would be very lengthy to run. After ~8,000 timesteps we got through 0.14 seconds of elapsed time.