McCabe-Thiele Diagrams: Screencasts

Demonstrates conceptually how to step off stages on a McCabe-Thiele diagram.

We suggest that after watching this screencast, you list the important points as a way to increase retention.

Uses an interactive simulation to describe the impact of the state of the feed to a distillation column on the liquid and vapor flow rates in the column.

We suggest that after watching this screencast, you list the important points as a way to increase retention.

Uses mass balances to derive the equation for the q-line used in the McCabe-Thiele method, which is used to analyze a distillation column for a binary mixture.

We suggest that after watching this screencast, you list the important points as a way to increase retention.

Important Equations:

Operating line (rectifying line):

$y = \frac{L}{V} x + \frac{D}{V} x_D$

where $$L$$ is the total liquid flow rate, $$V$$ i the total vapor flow rate, $$D$$ is the total distillate flow rate, $$x$$ is the liquid mole fraction of the more volatile component at a specified point, $$x_D$$ is the mole fraction of the more volatile component in the distillate, and $$y$$ is the vapor mole fraction of the more volatile component at a specified point.

$R = \frac{L}{D}$

where $$R$$ is the reflux ratio.

Operating line in terms of reflux ratio:

$y= \left( \frac{R}{R + 1} \right) x +\left( \frac{1}{R + 1} \right) x_D$

Boil-up ratio definition:

$V_B = \frac{\overline V}{B}$

where $$V_B$$ is the boil-up ratio, $$\overline V$$ is the molar flow rate of vapor in stripping section, and $$B$$ is the total bottoms flow rate.

Definition of $$\overline L$$ over $$\overline V$$ in terms of $$V_B$$:

$\frac{V_B + 1}{V_B} = \frac{\overline L}{\overline V}$

$$\overline L$$ is the total molar flow rate of liquid in stripping section (not the same as $$L$$)

Operating line of stripping section:

$y = \frac{\overline L}{\overline V} x – \frac{B}{\overline V} x_B$

where $$x_B$$ is the mole fraction of the more volatile component in the bottoms.

Definition of $$q$$ (from mole balance around feed stage):

$q = \frac{\overline L – L}{F}$

$1 – q = \frac{V – \overline V}{F}$

where $$q$$ is the feed quality, and $$F$$ is the total molar flow rate of the feed stream.

$$q$$-line equation:

$y = \frac{q}{q – 1} x – \frac{z_F}{q -1}$

where $$z_F$$ is the mole fraction of the more volatile component in the feed.