Adiabatic Plug Flow Reactor with Recycle
An adiabatic plug flow reactor (PFR) with recycle is used to carry out a first-order reaction. The fresh feed inlet temperature Ti and concentration are known, but the inlet temperature T0 and the inlet concentration to the PFR are not. Since T0 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 T0 can be calculated only when the differential equations are solved for Tfinal. Thus, the value of T0 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 Tfinal from the PFR is then obtained from the solution of the differential equations. The estimated value of T0 is adjusted until the calculated value of Ti (arrow in figure on left) equals the known Ti (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 Ti and the recycle ratio can be varied.

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