#### 9.5.1 Constant Reflux Ratio

The most common operating method is to use a constant reflux ratio and allow x_{D} to vary. This procedure corresponds to a simple batch operation where x_{D} also varies. The relationship between x_{D} and x_{W} can now be found from a stage-by-stage calculation using a McCabe-Thiele analysis. Operating Eq. (9-26) is plotted on a McCabe-Thiele diagram for a series of x_{D} values. Then we step off the specified number of equilibrium contacts on each operating line starting at x_{D} to find the x_{W} value corresponding to that x_{D}. This procedure is shown in Figure 9-5 and Example 9-2.

**Figure 9-5. McCabe-Thiele diagram for multistage batch distillation with constant L/D, Example 9-2**

The McCabe-Thiele analysis gives x_{W} values for a series ...