The energy balance in modeling gas-phase chemical reactor dynamics

✍ Scribed by Pertti M. Makila; Kurt V. Waller

• Publisher: Elsevier Science
• Year: 1981
• Tongue: English
• Weight: 762 KB
• Volume: 36
• Category: Article
• ISSN: 0009-2509
• DOI: 10.1016/0009-2509(81)85080-4

✦ Synopsis

Enthalpy cannot be stored. In spite of this fact it is frequently assumed in analysis of chemical reactor dynamics that the energy balance can be replaced by an "enthalpy balance", which actually implies that enthalpy would be stored. No investigation of the errors introduced by this assumption has been found in the literature.

In this paper the errors obtained when using an "enthalpy balance" in modeling gas-phase reactor dynamics are studied. After formulating the general energy balance as well as its linearized version for gas phase CSTRreactors, a computation of the local stability of two simple exothermic reaction systems quantitatively illustrates the inaccuracy of the "entha!py balance" formulation.

In the examples treated, the use of an "enthalpy balance" results in nonconservative design for stability. Further, it gives results which numerically are considerably in error and it predicts another type of behavior than the energy balance does (nonoscillatory compared to oscillatory behavior).

Since there are no methods available to estimate the size of the errors, and since the energy balance is not more difficult to use than the "enthalpy balance" is, the latter concept could without loss be buried once and for all.