Page 111 - Separation process engineering

and L A,new as products. Calculate these new flow rates when L with mole fraction 0.2 is
B
recycled.

E. More Complex Problems.

E1. A vertical flash drum will be used to separate 1000 kmol/h of a feed that is 10 mol% isopropanol
and 90 mol% water. The feed is at 9 bar and 75°C. V/F drum = 0.5 and p drum = 1.0 bar.
a. Find L, V, x, y, T drum , the heat duty in kW, and the drum diameter.
i
i
b. Unfortunately, the drum available is 1.0 m in diameter, which is too small. Your boss suggests
raising the drum pressure to use the existing drum with V/F = 0.5. The maximum pressure for the
drum is 9.0 bar. Will the current drum work at a pressure < 9.0 bar?

c. If yes, what is the lowest drum pressure that works (that is, for what pressure does D drum = 1.0
m)? Find L, V, x, y, T drum , and the heat duty in kW.
i
i
E2. A flash drum is to flash 10,000 lbmol/h of a feed that is 65 mol% n-hexane and 35 mol% n-octane
at 1 atm pressure. V/F = 0.4.

a. Find T drum , liquid mole fraction, vapor mole fraction.

b. Find the size required for a vertical flash drum.
Note, y, x, T equilibrium data can be determined from the DePriester charts. Other required
physical property data are given in Example 2-4.

F. Problems Requiring Other Resources

F1.* Benzene-toluene equilibrium is often approximated as α = 2.5. Generate the y-x diagram for
BT
this relative volatility. Compare your results with data in the literature (see references in Table 2-
2). Also, generate the equilibrium data using Raoult’s law, and compare your results to these.
F2. Ethylene glycol and water are flash distilled in a cascade of three stills connected as shown in the
figure. All stills operate at 228 mm Hg. Feed is 40 mol% water. One-third of the feed is
vaporized in the first still, two-thirds of the feed to the second still is vaporized, and one-half the
feed to the third still is vaporized. What are the compositions of streams L and V ? Note that
3
3
water is the more volatile component.