Process Equipment and Plant Design
Overall distillation column efficiency for most of the refinery columns can be given by (for μ = 0.07 - 1.4 cp and relative volatility < 4) (where η = overall column efficiency, % μ = molal average viscosity of feed at average column temperature and pressure, cp Δp = pressure drop per tray, psi)

Η = 17 - 61.1 log μ
Η = 1.66 - 0.25 log μ
Η = 0.25 log μ - 1.67
Η = 24.6 (Δp/μ)

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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 required is likely to be very small
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)

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