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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