The answer to this question comes with some serious misgivings.  The batch volume seems very large for the vessel diameter.  For a 1500 mm diameter vessel to hold 6660 liters, the straight-side (height) of the tank needs to be 4500 mm.  A 3:1 height to diameter is like trying to mix a vertical pipe.  An anchor operating at any speed would take a long time to obtain batch uniformity.
 
For the sake of answering the question, if the anchor impeller operates at 45 rpm, the motor would have to be 20 KW.  Because of the extreme height to diameter ratio for the vessel, a helical impeller is strongly recommended.  An anchor impeller does not to a good job of mixing when the liquid level is approximately equal to the tank diameter, because it creates very little top to bottom motion.  With this tall tank, a helical impeller might work.  A helical impeller would also require 20KW at 45 rpm, but provide much better mixing than the anchor

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