### 12.4 Analytical Solution for Dilute Systems: Kremser Equation

When the solution is quite dilute (say less than 1% solute in both gas and liquid), the total liquid and gas flow rates will not change significantly since little solute is transferred. The column was shown in Figure 12-1 and the operating equation was given in Eq. (12-6).

To use Eq. (12-6) in a McCabe-Thiele diagram, we assume the following:

**1.** L/V (total flows) is constant.

**2.** Isothermal system.

**3.** Isobaric system.

**4.** Negligible heat of absorption.

These are reasonable assumptions for dilute absorbers and strippers.

**Figure 12-6. McCabe-Thiele diagram for dilute absorber with parallel equilibrium and operating lines**

**Figure 12-7. McCabe-Thiele diagram for dilute absorber. (L/V) < ...**