Page 318 - Design of Simple and Robust Process Plants

304 Chapter 8 Instrumentation, Automation of Operation and Control
Similar dynamic simulations and optimizations can be performed for other irreversi-
ble reactor systems with defined objective functions. As example is the hydro-dealky-
lation (HDA) process where toluene is converted to benzene in a reactor system with
a large hydrogen recycle (Figure 8.9). Benzene is the product, and diphenyl the by-
product, this being a non-catalytic exothermal gas-phase reaction performed with
excess hydrogen, and the kinetics and rate equations being well-known. A problem-
free start-up, first-pass prime production of such a reactor system can be designed
through dynamic simulations. There should be no reason why catalytic fixed-bed
reactors (eventually cooled) or CSTRs could not be analyzed in a similar manner.
This technique proves that first-pass prime operation is achievable for irreversible
plug flow reactor systems when a recycle is available to condition the system before-
hand. A precondition for development of the operational strategy is that the main
reaction kinetics and rate functions are known, although these need not be highly
detailed for operational studies. However, the overall conversion rate must be de-
scribed accurately.

Products
Recycle mono
di

tri
Reaction Separation Separation Separation
IR R R R R R R
IR
Reactants
Fig. 8.8. Hydration process with irreversible reactor and
reversible separations.

H recycle
2
Compressor CH purge
4
R R Steam
Boiler water
Quench Benzene
H
2
Reactor H 2 B/T
system separation separation
IR
Toluene IR R R R R
T/DP
separation
Toluene recycle
R R
Diphenyl
Fig. 8.9. Hydro de-alkylation process with irreversible reactor,
reversible separation and compressor units.