13.11. Relationship between McCabe-Thiele and Triangular Diagrams for Partially Miscible Systems

Stepping off a lot of stages on a triangular diagram can be difficult and inaccurate. More accurate calculations can be done with a McCabe-Thiele diagram. Since total flow rates are not constant, the triangular diagram and the Δ point are used to plot a curved operating line on the McCabe-Thiele diagram. This construction is illustrated in Figure 13-26 for a single point. For any arbitrary operating line (which must go through Δ), the values of the extract and raffinate concentrations of passing streams (y_A,op, x_A,op) are easily determined. These concentrations must represent a point on the operating line in the McCabe-Thiele diagram. Thus, the values of y_A,op and x_A,op are transferred to the diagram. Since the raffinate value is an x, the y = x line is used to find x. A very similar procedure was used in Figure 2-6B to relate McCabe-Thiele to enthalpy-composition diagrams.

Figure 13-26. Use of triangular diagram to plot operating line on McCabe-Thiele diagram