Page 104 - Separation process engineering

respectively.
d. K = x/y, where x and y are mole fractions of the component in the liquid and vapor phases,
respectively.

A12. In a sequential solution procedure for flash distillation,

a. the mass balances, equilibrium relationships, and energy balances are solved simultaneously.
b. the mass balances and equilibrium relationships are solved first, and then the energy balance is
solved.

c. the energy balance is solved first, and then the mass balances and equilibrium relationship are
solved.
A13. Calculations are simpler for multicomponent flash distillation if the feed flow rate and mole
fractions of the feed are specified plus

a. the drum pressure and feed temperature.
b. the drum temperature and feed temperature.

c. the drum temperature and the drum pressure.
d. the feed temperature and feed pressure.

e. all of the above; they are all equally difficult.
A14. The Rachford-Rice equation,

a. has excellent convergence properties for flash distillation.

b. was derived from the mass balances, equilibrium relationships, and energy balances.
c. is only useful for binary flash distillation.
d. all of the above.

e. none of the above.

A15. Use the DePriester chart:
a. What is the K value of propane at 240 kPa and 25°C?

b. What is the normal boiling point of n-pentane?
A16. Flash distillation is usually operated adiabatically. Where does the energy to vaporize part of the
feed come from?

B. Generation of Alternatives

B1. Think of all the ways a binary flash distillation problem can be specified. For example, we have
usually specified F, z, T drum , p drum . What other combinations of variables can be used? (I have

over 20.) Then consider how you would solve the resulting problems.
B2. An existing flash drum is available. The vertical drum has a demister and is 4 ft in diameter and
12 ft tall. The feed is 30 mol% methanol and 70 mol% water. A vapor product that is 58 mol%
methanol is desired. We have a feed rate of 25,000 lbmol/h. Operation is at 1 atm pressure. Since
this feed rate is too high for the existing drum, what can be done to produce a vapor of the desired
composition? Design the new equipment for your new scheme. You should devise at least three
alternatives. Data are given in Problem 2.D1.

B3. In principle, measuring VLE data is straightforward. In practice, actual measurement may be very
difficult. Think of how you might do this. How would you take samples without perturbing the
system? How would you analyze for the concentrations? What could go wrong? Look in your
thermodynamics textbook for ideas.