Operating line ii

In the previous entry we have discussed how to obtain the equation for the operating line of the rectifying section. Now we will derive the second operating line but for the bottom part of the column. This column's part is also known as stripping section.

Here is again a picture to ease the derivation:

For the stripping section, we have a new parameter called reboiler ratio. It is actually quite comparable to reflux ratio. In fact the definition is also similar.

Reboiler ratio w = gas goes back to the column / liquid which is taken out at the bottom column

or

w = G/B

Total mass (flow) balance:

What comes in = what goes out

hence:

G + B = L

Mass balance for one component (the more volatile one):

G*y + B*xb = L*x

Combining these three equations and with some re-arrangements we will obtain our goal which looks like below:

y = (w+1)/w *x - xb/w

This is again an equation for a straigh line with the slope w+1/w and has a y-intercept -1/w.