Purge Stream in a System with Recycle: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • Solving material balances on a system with recycle and purge usually requires an iterative solution.
  • When a feed with an impurity is fed to a system with recycle, a purge is usually necessary to obtain steady-state operation (unless the impurity is removed in a separator).
  • The compositions of the two streams after a splitting point are identical.
From studying this module, you should now be able to:
  • Explain why a purge stream is needed in a system with recycle.
  • Write down material balances for a system with recycle and purge.
  • Calculate molar flow rates in a system with reaction, recycle, and a purge stream.
A related topic is bypass:

This screencast describes a bypass stream in a process and provides an example.

Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder