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

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

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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
Number of equilibrium stages in only stripping section is to be calculated
Relative volatility is close to one (e.g., separation of close boiling isomers)
Number of equilibrium stages required is likely to be very small

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