Interactive Self-Study Module: Flash Separations
Department of Chemical and Biological Engineering, University of Colorado Boulder 

This module uses screencasts and interactive simulations to explain what happens when a feed enters a flash drum and exits as two streams in vapor-liquid equilibrium. In this module, the outlet conditions are calculated, assuming the temperature and pressure are known, by using Raoult's law (ideal solution and ideal gas) and mass balances. Example problems are provided to allow the user to test themselves. We suggest using the learning resources in the following order: 

  1. Attempt to answer the multiple choice ConcepTests before watching the screencasts or working with the simulations.
  2. Watch the screencasts that describe flash separations/distillation and answer the questions within the screencasts.
  3. Use the two interactive simulations to further understand the flash separations.
  4. Use the quiz interactive simulation to test your understanding by constructing an x-y diagram for flash distillation.
  5. Try to solve the two example problems before watching the solutions in the screencasts.
  6. Answer the ConcepTests.

Mixtures are flashed to effect partial separations so that one or more components is enriched in the vapor phase (relative to the feed). This is referred to as flash distillation. Only binary mixtures are considered in this module to simplify the explanations, but multi-component mixtures are used in real systems. 

This module is intended for Material and Energy Balances, Thermodynamics, and Separations courses.

Before studying this module, you should:

After studying this module, you should be able to:
  1. Use mass balances and Raoult's law to determine outlet compositions and flow rates for a flash separation (flash drum) if the outlet temperature is known.
  2. Use mass balances, Raoult's law, and an energy balance to determine outlet compositions and flow rates for an adiabatic flash separation.