54 ◾  Distillation Control, Optimization, and Tuning
6.2 With process water fed to the top of a stripping column
at its boiling point and stripped with a ratio of 0.02 kg
steam/kg water to remove 1,000 ppb of perchloroethylene down to 2 ppb, how many theoretical stages will
be required if the relative volatility of perchloroethylene
to water is 39,000?
6.3 With process water fed to the top of a stripping column
at its boiling point and stripped with a ratio of 0.02 kg
steam/kg water to remove, 1,000 ppb of perchloroethylene down to 2 ppb, how many liquid mass transfer
units will be required if the relative volatility of perchloroethylene to water is 39,000?
6.4 A vent gas stream of air contains 200 ppm hydrochloric
acid and is to be fed to an absorber to be cleaned to
0.1 ppm acid. A high molar flow rate of water is used
with caustic that is 10 times the amount of acid present
so the equilibrium concentration of HCL in the vapor
is zero. How many gas mass transfer units will be
required?
6.5 A computer simulation for the distillation of ethanol
and water shows that the second theoretical stage from
the bottom would operate with a stripping factor of 3.0.
How many liquid phase mass transfer units are equivalent to that theoretical stage?
6.6 The water vapor from an evaporator contains 0.5%
diethylene glycol, and this vapor is fed to an absorption column that runs with a reflux ratio of 0.1. How
many gas phase mass transfer units will be required
to reduce the concentration of glycol to 1 ppm in the
water if the equilibrium concentration of diethylene
glycol in liquid water is 350 times higher than the
vapor phase?