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Why are identical product units drawing different electric current?

Q: We have two identical production units in our facility. In each production unit there is one agitator and two stage impellers - one impeller with parabolic blades and one impeller with flat blades. The vessel on which the agitator is mounted is a flash crystallizer. The agitator is used to maintain the solid in a suspended state. The flash vapor is removed from the top of the vessel. The dimensions of vessel in both units are identical.

The problem is, since commissioning the motor in one of the units it is drawing more electric current than the motor in other unit. Why?

Another question, what will be the effect of rotating an impeller with parabolic blades in the reverse direction?

A:

The obvious answer is that the two production units are NOT identical.  If they were identical, then the results would be the same.  I would first question the dimensions of the vessels.  Minor differences in impeller clearance, spacing, or location could account for differences in power requirements.  A difference in amperage could be associated with a difference in voltage going to the motors.  Differences in the motors, manufacturer, windings and even non-standard designs could account for electric current differences.  The description does not say that different amperages are causing operational or process problems, so who cares?
 
Rotating an impeller with parabolic blades in the opposite direction is not advisable as it will substantially change process performance.  It is possible that direction of rotation also would account for the power differences mentioned.

This problem would require a thorough, on-site review of both the process and equipment to make a determination of the cause of the amperage differences.

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