(135a) Blending in Above Ground Storage Tanks with Side-Entering Propellers: Effects of Geometry and Fluid Physical Properties

The blending of fluids in large, above ground storage tanks is widely practiced in the petroleum industry yet there have been very few studies of this mixing operation. The most demanding application is found when the tank contents have been allowed to stratify creating a light and heavy layer. The blend time in this case is defined as the time taken for the density of the fluid to become axially homogeneous.

Wesselingh (1975) measured blend times using brine and water to produce the heavy and light layers and measured conductivity changes to assess the blending process. He only looked at one propeller geometry but did study the effects of several important geometrical system properties, such as scale, the ratio of propeller to vessel diameter and liquid depth to vessel diameter. He regressed his data to generate a correlation to be used in estimating the blend time, but he did express some reservations regarding its accuracy in scale-up.

Wesselingh (1975) only studied on propeller geometry, essentially a marine propeller. This study uses his technique but examines the blending performance of four styles of propeller commonly used in storage tanks. The test vessel was six feet in diameter and the propellers were all two inches. Grenville et al. (2018) showed that the Advanced Pitch propeller sold by Philadelphia Mixing Solutions Ltd. and Mixing Solutions Ltd. is the most efficient when compared based on energy usage. More recently Giacomelli et al. (2018) have reported on the effects that propeller diameter and the number of agitators installed in a vessel have on the blend time.

New data will be presented in which blend times have been measured in a vessel that is four feet in diameter and in which the viscosity of the heavy phase has been increased.

Guidelines regarding scale-up and estimation of blend time in full-scale tanks will be discussed.

REFERENCES

Wesselingh, J. A., Mixing of liquids in cylindrical storage tanks with side-entering propellers, Chem. Eng. Sci., 30, 973 – 981, 1975.

Grenville, R. K., J. J. Giacomelli, G. J. VanOmmeren, C. F Hastings & M. J. Walters, Blending in above ground storage tanks with side-entering agitators, ChERD, 137, 395 – 402, 2018.

Giacomelli, J. J., B. A. Boyer, S. J. Johnson & R. K. Grenville, Blending in oil storage tanks with side-entering agitators, in the 16^th Europ Conf on Mixing, Toulouse France, 9^th – 12^th September 2018.