This tank needs baffles for the viscosity described.  The recommendation is 4 baffles, 12 inches wide, mounted vertically, at 90 deg locations, with a 1- to 2-inch offset from the tank wall.
 
The maximum operating speed for the mixer described is 90 rpm.  This limit is set by the 2-inch diameter shaft.  Higher speeds would require a larger shaft diameter.  At 90 rpm, the mixer requires a 15-hp motor, which means that the drive torque will be 10,500 in-lbs.
 
The mounting should be designed for 26,300 in-lbs torque and 23,300 in-lbs bending to provide sufficient rigidity.  The impeller blades and baffles must be of sufficient thickness to handle the torque.  If the mixer is operated while the tank is being filled or emptied, the recommended speed must be reduced to avoid damage to the shaft.
 
The mixer should provide more than sufficient mixing intensity with the speed range between 60 rpm and 90 rpm.  Even 60 rpm will provide moderately intense mixing for most batch operations.
 
At 120 rpm, the drive would need to have a 40 hp motor with a 21,000 in-lb capacity drive.  The shaft would have to be 3 inches in diameter.  The mixing intensity at these conditions would be extremely violent.

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