Control of a Fixed-Bed Chemical Reactor

Abstract

Disturbances in a fixed-bed reactor are controlled by exploiting the interaction between the traveling waves of temperature and concentration within the bed. A secondary reactant stream, injected at an intermediate point along the bed and modulated in accordance with temperature measurements only, provides a localized and traveling corrective action that annihilates a disturbance by the time it reaches the reactor effluent. Calculations for a first-order, homogeneous, exothermic reaction show that a temperature upset is the most difficult disturbance to control. Further, because of the dominance of the slower thermal wave in these reactors, the task of composition control is similar to that of temperature control. An approximation technique, developed to match both the short-and long-time behavior of the reactor and its controllers, simplified the study of the dynamics of the reactor under control.

Feedback control of hyperbolic PDE systems

“…Chemical engineering processes are inherently nonlinear and very frequently involve state variables that change in both time and space. Representative examples of processes with significant spatial variations include plug-flow reactors (Ray, 19811, countercurrent absorbers-reactors (Rhee et al, 1986), fixed-and fluidized-bed reactors (Stangeland and Foss, 1970;Ray, 1981;Georgakis et al, 1977). The mathematical models of these processes are typically derived from the dynamic conservation equations and consist of nonlinear partial differential equations (PDEs).…”

The Representation and Approximation of the Dynamics of a Class of High Order Distributed Parameter Processes

“…Figure 5 shows the response in concentration at the reactor outlet to an impulse change in inlet temperature computed in this way. The conditions and exact response are from Stangeland & Foss (1970). The five term approximation of the Riemann matrix does an acceptable job of approximating the response for this problem.…”

The parameter domain of convective instability of the adiabatic packed‐bed reactor

“…Because of the hazards of unstable operation, system stability is a central issue in process control . It is recognized that the differences in propagation speeds of concentration and temperature disturbances in PBR with exothermic reactions can pose challenging control problems, for example due to wrong‐way behaviour, or more generally, reactor “inverse response.” It is also recognized that reactors with large steady‐state gain (or PS) are more likely to exhibit instability in the presence of thermal feedback (e.g. feed‐effluent heat exchange) and are more difficult to control .…”