Unsteady PFRs

Solution The dynamic model governing the flow of an inert tracer through an unsteady PFR is Equation (14.13) with =0 ... 

Unsteady behavior in an isothermal perfect mixer is governed by a maximum of -I- 1 ordinary differential equations. Except for highly complicated reactions such as polymerizations (where N is theoretically infinite), solutions are usually straightforward. Numerical methods for unsteady CSTRs are similar to those used for steady-state PFRs, and analytical solutions are usually possible when the reaction is first order. 

The mass balance equation for the SBR with slow fill resembles that of unsteady-state CMFR with variable volume. As originally conceived, SBR operation includes a react period after fill. Thus, a slow fill system s represented by a CMFR followed by a PFR, die minimum volume configuration for an activated sludge system capable of achieving the desired overall treatment performance (Irvine and Ketchum, 1989). 

In the CD-ROM, the unsteady energy balance is derived for a PFR. Neglecting changes in total pressure and shaft work, the following equation is derived ... 

PFR and CSTR with and witliout a Heal E.schanger Multiple Steady States Unsteady-Si.ite Heat Effects (Ch. 9) Reactor Safely Catalysis (Ch, 10)... 

In a tubular reactor, the concentration and temperature may vary both in time and space. One speaks about a distributed system. The ideal plug flow reactor (PFR) model is the most used. Because of the flat velocity profile, the concentrations and temperature varies only along the length. Consider for simplification a homogeneous reaction. The unsteady state material balance of the reactive species leads to the following equation ... 

Let us begin here with the PFR and, once again, A B, first-order and irreversible (otherwise known as Academic Reaction 1). The unsteady-state form of equation (4-42) is... 

In STR of periodical action (the problem with initial conditions), the solution is always unique and the process is unsteady by definition, while in STR of continuous action (with a constant feed of reactants) there may exist a multiplicity of steady-state solutions and the effects described above for PFR. 

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