Purpose: A flash drum is one of the coolest separation processes in my opinion. How it works is a liquid feed containing multiple different chemical species is heated and pressurized before being passed through a throttling valve to a vessel. Once the liquid feed hits the vessel, a drastic decrease in pressure is introduced which causes an immediate separation of the mixture. The more volatile components are collected at the top as vapor and the less volatile components are collected at the bottom as liquid. It’s easy to grasp conceptually, but to determine exactly how much of each species that is in vapor and liquid gets more and more difficult the farther away you get from binary mixtures. What starts off as a simple material balance and Raoult’s law quickly becomes a nasty nonlinear equation only solvable by the painfully iterative “guess-and-check”, or numerical methods. I used Python to create this handy tool with a neat GUI that uses the Newton-Raphson algorithm behind the scenes to calculate a flash drum containing up to 4 chemical species.

Analysis: Solving this problem requires deconstructing the Rachford-Rice equation which is derived below, as well as a screenshot of the GUI and a link to the code: