Process Equipment and Plant Design
Liquid gradient over a tray can be minimised by

Providing a higher skirt clearance or a higher weir
Decreasing the number of rows of caps through which the liquid flows or by decreasing the velocity of liquid flow past the caps or by reducing the distance along the tray through which the liquid must
All of these
Using split flow, radial flow or cascade flow for column diameter large than 4 ft

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Process Equipment and Plant Design
A forced circulation long tube vertical evaporator as compared to the natural circulation evaporator

Employs high velocity, high heat transfer rate and less heating surface requirement
Both B & C
Is economical in operation
Employs a centrifugal pump placed between external downtake from vapor drum and inlet to tube bundle

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