These equations are similar to Eqs. (7-16) and (7-17), and the same considerations relative to the constancy of molal rates of vapor and overflow apply in this case.

3. General Case. The derivations given in the two previous sections were for the case with no side streams, but the general case is similar.

In the system shown in Fig. 7-15, the over-all and component material balances above plate a are

Oa+1 - overflow rate from plate a + 1 N = net mols leaving section — Va — Oa+l Va, xa+i = mol fractions

Nxn = total mols of component leaving section other than with Va and Oa+i The enthalpy balances are

where Ha = molal enthalpy of vapor entering plate a + 1

ha+i = molal enthalpy of liquid leaving plate a 4- 1

NM = net enthalpy removed from the column above plate a + 1 For Fig. 7-15,

N=Lx+L2 + D- F NKn = Li(hL)i + L2(hL)2 + DhD — FhF + Qc + losses

These equations can be combined to give

Fig. 7-15. Schematic diagram of fractionating system with side streams.

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