Page 174 - Separation process engineering

Intersection: y = x = z = 0.4
2

Top Operating Line: We can derive the top operating equation:

This is the usual top operating line. With saturated liquid reflux the slope is,

Intersection: y = x = x = 0.72
D
Bottom Operating Line: We can derive the bottom operating equation:

This is the usual bottom operating line. Then, slope = / is unknown.

y = x intersection is at y = x = x = 0.02. One other point is the intersection of the F feed line and the
1
B
middle operating line, if we can find the middle operating line. Middle Operating Line: To derive an
operating equation for the middle section, we can write a mass balance around the top or the bottom
of the column. The resulting equations will look different, but they are equivalent. We arbitrarily use
the mass balance envelope around the top of the column as shown in Figure 4-18. These mass
balances are
F + V′ = L′ + D
2
F z + V′ y = L′ x + Dx (MVC)
2 2
D
Solve this equation for y to develop the middle operating equation,

(4-44)

One known point is the intersection of the F feed line and the top operating line. A second point is
2
needed. We can try y intercept =

but this is unknown.

The intersection of the middle operating line with the y = x line is found by setting y = x in Eq. (4-44)
and solving,

From the overall balance equation,

V′ − L′ = D − F 2

Thus,