Self-Tuning and Adaptive Control of a Pilot Plant Fluidized Bed Reactor

Abstract

<p>A pilot plant fluidized bed reactor in which complex and highly exothermic catalytic hydrogenolysis reactions are taking place, is being used to investigate the computer control of temperature, conversion and selectivities in such reactors. The process is highly nonlinear, characterized by asymmetric dynamics and considerable change in catalyst activity. Moreover, a deadtime of 360 s is introduced by an on-line process gas chromatograph employed to obtain the composition measurements. As a result, the cascade control system comprising a proportional-integral controller for reaction temperature in the inner loop and a Dahlin controller for propane selectivity in the outer loop was reported in previous works to have performed well in certain regions of operation at a given time but revealed very oscillatory and nearly unstable performance in other regions or at different times.</p> <p>This nonlinear behaviour of the reactor is further investigated. It is found that by better matching the process response characteristics and by detuning the Dahlin controller, this unstable oscillatory behaviour of the cascade control system can be overcome and acceptable performance can be achieved over a wider range of operating conditions. Later, self-tuning adaptive controllers are tried in an attempt to better account for the changing gains and time constants of the nonlinear process, as well as for the time-varying catalyst activity. The cascade control scheme with Dahlin and Self-tuning regulator (STR) demonstrated excellent performance. Finally a double STR configuration for both the inner and outer loops in carried out. Problems associated with this implementation are discussed and possible improvements suggested.</p>