Page 196 - Separation process engineering

relative volatility (which can be estimated for hydrocarbons from the DePriester charts).
A8. What happens if we try to step off stages from the top down and E is given? Determine how to
MV
do this calculation.
A9. When would it be safe to ignore subcooling of the reflux liquid and treat the reflux as a saturated

liquid? Do a few numerical calculations for either methanol and water or ethanol and water to
illustrate.
A10. Eqs. (4-53) and (4-54) are mass balances on particular phases. When will these equations be
valid?

A11. When might you use an intermediate condenser on a column? What are the possible advantages?
A12. When would just a stripping column be used?

A13. We have a binary distillation column. The feed flow rate, F, the mole fraction MVC in the feed, z,
and the initial feed temperature are constant. The column pressure, p, and the distillate and
bottoms mole fractions, x and x , are constant. The reflux is a saturated liquid, and the reflux
D B
ratio is L/D = 1.20 × (L/D) min . A heat exchanger uses waste heat, Q , to heat the feed.
w
As Q increases, does,
w

Think your way through this problem using the tools developed in this course (definition of q and
feed line, mass and energy balances, and McCabe-Thiele diagrams) as reasoning tools.

Hint: The parts of this problem are listed in a logical order of solution.
A14. Explain with a McCabe-Thiele diagram how changing feed temperature (or equivalently, q) may
help an existing column achieve the desired product specifications.

A15. Develop a key relations chart for binary McCabe-Thiele distillation. That is, on one sheet of
paper summarize everything you need to know about binary distillation. You will probably want
to include information about operating lines, feed lines, efficiencies, subcooled reflux, and so
forth.

B. Generation of Alternatives

B1. Invent your own problem that is distinctly different from those discussed in this chapter. Show
how to solve this problem.
B2. Several ways of adapting existing columns to new uses were listed. Generate new methods that
might allow existing systems to meet product specifications that could not be met without

modification. Note that you can postulate a complex existing column such as one with an
intermediate reboiler.

C. Derivations

C1. For Example 4-4 (open steam), show that the x intercept (y = 0) is at x = x .
B