An adiabatic plug flow reactor (PFR) with recycle is used to carry out a first-order reaction. The fresh feed inlet temperature
and concentration are known, but the inlet temperature
and the inlet concentration to the PFR are not. Since
and the inlet concentration are initial conditions needed to solve the differential equations for the mass and energy balances for the PFR, an iterative solution is needed. The value of
can be calculated only when the differential equations are solved for
. Thus, the value of
is guessed using the slider (and the feed concentration to the reactor calculated using the adiabatic relation between temperature and concentration), and the exit temperature
from the PFR is then obtained from the solution of the differential equations. The estimated value of
is adjusted until the calculated value of
(arrow in figure on left) equals the known
(the green circle); multiple solutions are possible under some conditions.
High recycle ratios approach continuous-stirred tank reactor (CSTR) behavior. A plot of temperature as a function of distance down the PFR is generated. The inlet temperature to the system
and the recycle ratio can be varied.