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

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

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Process Equipment and Plant Design
In the design of a shell and tube heat exchanger, the corrosion allowance

For internal cover and tube sheet is provided on both the sides
For carbon steel and cast iron pressure parts is 1.5 mm (except for tubes) and for severe conditions it is 3 mm
All of these
Need not be provided for non-pressure parts like tie rods, spacers, baffles, supports etc

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