TABLE OF CONTENTS More shortcut design methods and rules of thumb have been developed for fractionation than probably any other unit operation. For example the paper1 reprinted in Appendix 5 on development of shortcut equipment design methods contains 18 references for fractionation shortcut methods out of 37 total. Both the process and mechanical aspects of fractionation design have useful rules of thumb. Many of the mechanical design rules of thumb become included in checklists of do's and don'ts.
For troubleshooting fractionators see the troubleshooting section in this book. For a general understanding of how trayed and packed fractionating columns work, illustrated by actual field causes, I recommend Lieberman's design book.2
1. Branan, C. R., Development of Short-cut Equipment Design Methods, ASEE Annual Conference Proceedings, Computer Aided Engineering, American Society for Engineering Education, 1985.
2. Lieberman, N. P., Process Design For Reliable Operations, 2nd Ed., Gulf Publishing Co., 1989.
For quick estimates, a relative volatility can be estimated as follows:
The equilibrium vaporization constant K is defined for a compound by
where
| Y i | = Mole fraction of component i in the vapor phase |
| X i | = Mole fraction of component i in the liquid phase |
To calculate a distillation, the relative volatility ? is needed, it is defined as
where i and j represent two components to be separated.
Raoult's Law for ideal systems is
where
| p i | = Partial pressure of i |
| P i | = Vapor pressure of pure component i |
By definition
where
