Adiabatic Plug Flow Reactor with Recycle

A first-order reaction is carried out in an adiabatic plug flow reactor (PFR) with recycle. The fresh feed concentration is known. Select the fresh feed temperature and the recycle ratio with sliders. The correct exit temperature is obtained iteratively: the PFR feed temperature is guessed with the slider (and the feed concentration to the PFR calculated using the adiabatic relation between temperature and concentration), the PFR mass and energy balances are solved to determine and , and an energy balance around the mixing point before the PFR is then solved to determine the calculated . Next, guess until the calculated (black arrow on the left) equals the value (the center of the green circle). The graph shows the temperature in the PFR as a function of distance using the guessed value for . Multiple solutions are obtained under some conditions, and the solution observed depends on how the reactor is started up. High recycle ratios approach continuous stirred-tank reactor (CSTR) behavior.
  • Contributed by: Rachael L. Baumann
  • Additional contributions by: John L. Falconer and Nick Bongiardina
  • (University of Colorado Boulder, Department of Chemical and Biological Engineering)

SNAPSHOTS

  • [Snapshot]
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DETAILS

Mass and energy balance:
,
,
,
,
,
where is temperature (K), is length down the reactor (m), is the velocity of the stream exiting the reactor (m/s), is concentration of entering the reactor (), is heat capacity (), is heat of reaction (J/mol), is the rate constant (1/s), is concentration of reactant (), is a pre-exponential factor (1/s), and are the temperatures of the stream entering and exiting the reactor (K), is the fresh feed temperature (K), is activation energy (J/mol), is the ideal gas constant (J/[mol K]), is the recycle ratio, and is the velocity of the fresh feed (m/s).
The screencast video at [1] shows how to use this Demonstration.
Reference
[1] Adiabatic Plug Flow Reactor with Recycle. www.colorado.edu/learncheme/kinetics/AdiabaticPFRRecycle.html.
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