Even though a packed tower has continuous instead of discontinuous contact of liquid and vapor, it can be analyzed like a staged tower. We assume that the packed portion of the column can be divided into a number of segments of equal height. Each segment acts as an equilibrium stage, and liquid and vapor leaving the segment are in equilibrium. It is important to note that this staged model is not an accurate picture of what is happening physically in the column, but the model can be used for design. The staged model for designing packed columns was first used by Peters (1922).
We calculate the number of stages from either a McCabe-Thiele or Lewis analysis and then calculate the height as
The HETP, ...