Page 109 - Separation process engineering

operates p drum = 700 kPa and T drum = 30°C. Feed flow rate is 100,000 kg/h.

a. Find V/F, V, L, liquid mole fraction, vapor mole fraction.
b. Find the dimensions in metric units required for a vertical flash drum. Assume the vapor is an
ideal gas to calculate vapor densities. Use DePriester chart for VLE. Be careful of units.

Arbitrarily pick h total /D = 4.
MW ethane = 30.07, MW pentane = 72.15

Liquid densitites: ρ = 0.54 g/ml (estimated), ρ = 0.63 g/ml
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D22. A flash drum is separating a feed that is 50 wt % n-propanol and 50 wt % isopropanol with
F=100 kmol/h. T drum = 90°C and p drum = 101.3 kPa. Use the Rachford-Rice equation to find V/F.

Note: This does not have to be trial and error. Then find y and x. Determine K values from
Raoult’s law using Antoine equation for vapor pressure. Watch your units.
The Antoine constants are (Dean, 1985):

n-propanol: A = 7.84767, B = 1499.2, C = 204.64
isopropanol: A = 8.11778, B = 1580.9, C = 219.61

where the form of the Antoine equation is

D23. We wish to flash distill 1000 kmol/h of a feed that is 40 mol% methane, 5 mol% ethylene, 35%
mole ethane, and 20 mol% n-hexane. Drum pressure is 2500 kPa and drum temperature is 0°C.
Use the DePriester charts. Find V/F, x, y, V, F.
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D24. We plan to separate a mixture of propane and n-hexane at 300 kPa.
a. Using the data in the DePriester charts, plot y propane versus x propane for this mixture at this
pressure.

b. If the feed is 30 mol% propane, and 40 mol% of the feed is vaporized, what are the liquid and
vapor mole fractions, and what is the drum temperature? Solve graphically.
c. What is the drum temperature in part b?

d. If y = 0.8 and the feed is 0.6 (both mole fraction propane), what is the value of V/F?
e. Use the Rachford-Rice equation to check the answers obtained in parts b and c.

D25. We wish to flash distill a mixture of methane and n-butane in a flash drum operating at 50°C. The
feed is 20 mol% methane and 80 mol% n-butane. Feed rate is 100 kmol/h. Feed is at a pressure
and temperature such that in the drum V/F = 0.40. Use the DesPriester charts.

a. Find the drum pressure.
b. Find the methane mole fraction in the liquid and the vapor.

D26. We are feeding 100 kmol/h of a 45 mol% propane, 55 mol% n-pentane feed to a flash distillation
system. We measure the outlet vapor and liquid mole fractions leaving the flash drum, which is an
equilibrium stage, and obtain, y propane = 0.8, x propane = 0.2162.

Find: (a) L and V. (b) x pentane and y pentane . (c) T drum and p drum .
Use the DePriester charts. Note: This is not trial and error.

D27. For the Antoine equation in the form