Process Equipment and Plant Design
Smoker's equation for the calculation of number of equilibrium stages in a continuous binary distillation column is used, when the

Feed is not at its bubble point
Relative volatility is close to one (e.g., separation of close boiling isomers)
Number of equilibrium stages in only stripping section is to be calculated
Number of equilibrium stages required is likely to be very small

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

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
Using split flow, radial flow or cascade flow for column diameter large than 4 ft
Providing a higher skirt clearance or a higher weir
All of these

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