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

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Process Equipment and Plant Design
Ponchon Savarit method is based on the use of enthalpy concentration diagram, which contains the bubble point curve (saturated liquid curve), dew point curve (saturated vapour curve) and equilibrium tie lines. As compared to McCabe-Thiele's method, this method

Facilitates direct calculation of heat load on reboiler & condenser from, the diagram used in this method
Is more accurate in finding the number of equilibrium stages
All of these
Accounts for the enthalpy changes in the process

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