Page 161 - Separation process engineering

Calculate the feed line slope for the following cases.
a. A two-phase feed where 80% of the feed is vaporized under column conditions.

Solution. The slope is q/(q − 1), where q = (L below feed − L above feed )/F (other expressions could also

be used). With a two-phase feed we have the situation shown.

= L + L . Since 80% of the feed is vapor, 20% is liquid and L = 0.2F.
F
F
Then

This agrees with Figure 4-10.

b. A superheated vapor feed where 1 mole of liquid will vaporize on the feed stage for each 9 moles
of feed input.
Solution. Now the situation is shown in the following figure.

When the feed enters, some liquid must be boiled to cool the feed. Thus,

(4-40)
and the amount vaporized is v = (1/9) F.

Thus,

which agrees with Figure 4-10.

c. A liquid feed subcooled by 35°F. Average liquid heat capacity is 30 Btu/lbmol°F and λ = 15,000
Btu/lbmol.

Solution.