Steady-State Operating Policies for Plants with Multiple Reactions of Equal Overall Order

Abstract

A simple methodology for determining optimal steady-state operating policies for plants with recycle has been developed by Ward et al. (Ward, J. D.; Mellichamp, D. A.; Doherty, M. F. Ind. Eng. Chem. Res. 2004, 43, 3957). Heuristics were developed to classify irreversible process chemistries into two groups, bounded and nonbounded. This classification has important implications for how to design a control system and operate a chemical plant that contains excess equipment capacity. In this paper, formal rules are developed and presented for classifying a common special case of process chemistries that have multiple undesired irreversible reactions with equal overall reaction order. This new classification procedure is essential for determining the optimal steady-state operating policy for process chemistries of multiple parallel or series/parallel reactions.

Selectivity versus conversion and optimal operating policies for plants with recycle

“…As discussed by Ward et al13 and Griffin et al,14 optimal operating policies can be classified based on the kinetics of the process chemistry. All reactions are assumed homogenous and to have elementary kinetic rate expressions (the latter assumption is easy to relax).…”

“…To classify the overall process chemistry, each reactant species must also be classified as bounded or nonbounded. Definitions of bounded and nonbounded reactant species and chemistries and the corresponding rules on how to classify them have been presented by Griffin et al14 and are summarized in this section. The numbering and order of the following rules and definitions have been retained from the original article for consistency of presentation.…”

“…The current methodology distinguishes between process chemistries of parallel, series, or series/parallel reactions that can have equal or unequal overall reaction order. The case of all parallel reactions of equal overall order is a special case that is discussed in the Parallel Reactions of Equal Overall Order section and is covered by Rule 1 taken from Griffin et al14…”

“…The heuristics developed by Ward et al13 are valid for irreversible process chemistries that have a single undesired reaction, and they are exact when the side reaction has the same overall forward reaction order as the main reaction. This work was recently extended by Griffin et al14 to include irreversible process chemistries with multiple undesired reactions, all of equal overall order.…”

Analysis of Dynamic Behavior of a Thermally Coupled Distillation Column Implemented on a Process with Recycles

“…This phenomenon is a steady state characteristic, but it depends on the control structure. Ward et al (2004) and Griffin et al (2006) analyzed the effect of different kinetics on the snowball effect existence, Zeyer et al (2003) studied the nonlinearity introduced by the separator model solution. According to Larsson et al (2003), the control structure selection has to take into account the economic performance of the process; depending on the economical and operational goals (minimize energy consumption or maximize production), the better option may not include the control of a recycle flowrate.…”