Energy Balance in Steady-State PFR: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • In general, the mass and energy balances for a non-isothermal PFR should be solved numerically because the rate constant depends exponentially on temperature.
  • For exothermic reactions in a PFR, small changes in feed temperature (or parameters used in the model such as heat of reaction or activation energy) can result in large changes in reactor temperature, and can result in thermal runaway.
  • For a reversible exothermic reaction in an adiabatic PFR, as the feed temperature increases, the equilibrium conversion decreases. For an endothermic reaction, as the feed temperature increases, the equilibrium conversion increases.
  • Exothermic reactions in a PFR with heat exchange can exhibit a temperature maximum because the rate of reaction slows as the reactant concentration decreases, and the rate of heat removal increases as the reactor temperature increases.
From studying this module, you should now be able to:
  • Be able to solve mass and energy balances simultaneously for a steady-state PFR.
  • Be aware that PFR with exothermic reactions can exhibit sensitivity to feed conditions and model parameters.
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder