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How do I select the optimal location for an impeller inside a tank?
Q: I am new to tank mixing and I have a question about selecting the optimal location (and orientation) for an impeller inside a tank. I am dealing with a tank that contains very light materials (0.7 and 0.8 SG). The contents have been sitting in the tank and are stratified. Please let me know if there is some sort of general process for selecting the proper impeller position.
The tank is 120 ft. in diameter, 45 ft. high. It is allowed to only have one mixer. The first layer of material has a specific gravity of 0.75 is 32 ft. high. The second layer of the tank has a specific gravity of 0.67 and is 10 ft. high; making the total contents of the tank 42 ft. high. The purpose of the mixer is to have complete mixing within 6 hours.
A:
Based on the tank dimensions and liquid densities, this is a storage tank for hydrocarbon liquids. Therefore, the logical mixer is a side-entering mixer, which is usually sized based on horsepower, with a practical gear reduction and impeller speed. The impeller and corresponding pumping capacity is sized to utilize the available motor power. For content uniformity, between 3 and 10 tank turnovers are typical for side-entering mixers. This application would require a 30 hp to 50 hp side-entering mixer.
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