Calculate the minimum reflux for a fractionation column that
is designed to produce a distillate composition of 91.5 percent when feed is 36
percent in more volatile component. The
feed quality is 1.04 and the equilibrium data can be estimated by a relative
volatility of 4.12.
Solution:
Equilibrium curve (y versus x) can be generated using the
relationship: y is equal to alpha x over (one plus (alpha minus one) times x).
Draw a diagonal line (45 degree slope). Draw feed line that passes through point (xF,
xF) and has an intercept of xF over q. On the y-x diagram, locate point 1 having
coordinates (xF/q, 0) and point 2 (xF, xF). Join these points and extend to the
equilibrium curve and locate point 3.
This point 3 lies on the rectification line. Locate point 4 having coordinates (xD,
xD). Draw a line joining
points 4 and 3 and extend to the y-axis and obtain point 5. This intercept has a value of xD
over (Rmin plus one).
Plugging in the values of xD, Rmin.
Draw feed line that passes through point (0.36, 0.36) and
has an intercept of 0.346.
Locate point 1 having coordinates (0.346, 0) and point 2
(0.36, 0.36).
Join these points and extend to the equilibrium curve and
locate point 3.
Locate point 4 having coordinates (0.915, 0.915).
Draw a line by joining points 4 and 3 and extend to the
y-axis and obtain point 5.
Read the intercept value, I, as 0.57.
Plugging in the values of xD, Rmin can
be calculated as 0.6.