This is the link of an online application for finding out the theoretical number of plates for distillation column:
enggaze.com/applications/mccabethielecalculator/
Steps to find out the number of plates:
enggaze.com/applications/mccabethielecalculator/
Steps to find out the number of plates:

In the first step, the application asks
you to define a Data Source. There are three options available viz.:
Available Systems, Relative volatitliy and raw VLE data.

Available System: These are a few
commonly used systems which are already present there in the
application. You just have to select the appropriate System.

Relative Volatiltiy: Enter a value for
the relative volatility. The application will use this value to form the
VLE curve.

Raw VLE data: If you have VLE data
points of the system which you wish to use. Just enter the Points in the
specified format. You can control the number of data points you have to
enter. The application will fit the data for you after clicking on the
"Fit Data" button. Choose the appropriate polynomial degree for a good
data fit. Remember that the polynomial degree should be less than the
number of data points you have entered.

In the second and the final step, the
application will ask you various parameters required to draw the Mccabe
Thiele Diagram.

After pressing the finish button, the
application will give you the result in form of a Mccabe Thiele Diagram
which can be saved as an image to your system. The application will give
you the number of Theoretical Trays and the Feed Tray.