Page 175 - Separation process engineering

(4-45)

This point is not known, but it can be calculated once D is known.

Slope = L′/V′ is unknown, but it can be calculated from the feed-stage calculation. From the definition
of q ,
2

(4-46)

where L = (L/D)D. Once D is determined, L and then L′ can be calculated. Then the mass balance
gives
V′ = L′ + D − F 2

and the slope L′/V′ can be calculated.

The conclusion from these calculations is, we have to calculate D. To do this we need external mass
balances:

(4-47a)

(4-47b)

These two equations have two unknowns, D and B, and we can solve for them. Rearranging the first,
we have B = F + F − D. Then, we substitute this into the more volatile component (MVC) mass
2
1
balance,
F z + F z = Dx + (F + F )x −Dx B
1
2
B
D
1 1
2 2
and we solve for D:

(4-48)

D. Do It. The two feed lines and the top operating line can immediately be plotted on a y-x diagram.
This is shown in Figure 4-19. Before plotting the middle operating line we must find D from Eq.
(4-48).

Figure 4-19. Solution for Example 4-5