Page 189 - Separation process engineering

Now, L/V cannot be directly calculated from the external reflux ratio L /D, since L and V change on the
0
top stage.

Balances on vapor and liquid streams give

(4-61)

(4-62)

An energy balance using the balance envelope in Figure 4-29 is

(4-63)

With CMO, H ~ H . Then Eq. (4-63) becomes
1
2
(V − V )H ~ L h − L h
2 1 1 1 0 reflux
Using Eqs. (4-61) and (4-62), this becomes

cH ~ (L + c)h − L h
0 reflux
1
0
Solving for amount condensed, c, we obtain

(4-64a)

which can also be written as

(4-64b)

or

(4-64c)

where f is the fraction condensed per mole of reflux. We can now calculate the internal reflux ratio, L/V
c
= L /V . To do this, we start with the ratio we desire and use Eqs. (4-61), (4-62), (4-64), and (4-65).
1 2