(341g) Control Strategies for the Spinning Disk Reactor

Boodhoo, K., Newcastle University
Tham, M., Newcastle University

Spinning Disk Reactors (SDRs) are particularly suited to carrying out reactions with inherently fast kinetics. Although abundant experimental work is available in the literature on intensification aspects of SDRs, in terms of enhancement of reaction rates and improvements in yield and product selectivity, very little has been done on devising appropriate control strategies for the unit. Effective control of SDRs may be challenging due to their fast dynamics and short residence times, for example because the conventional sensors and actuators may be too slow. However, some key features of SDRs may prove to be advantageous from a control point of view. For example, the rotational speed of the disc offers an extra degree of freedom in control system design, since the residence time and mixing intensity, thus conversion, may be controlled by adjusting the rotational velocity, instead of more commonly used methods of varying reactant flow rates. Further, in conventional reactors, mixing limitations may introduce large lags in implementation of the controller’s command. On the other hand, the enhanced mixing achieved in a SDR may ensure that the controller’s corrective action brings the controlled variable back to the set-point value with practically no delays.

In the present work two test processes, namely neutralization of HCl and NaOH, and precipitation of barium sulphate are chosen to investigate the control aspects of SDRs experimentally. The most commonly used controllers based on PI/PID algorithms implemented in LabVIEW, coupled with commercially available instrumentation, are employed to achieve the control objectives. Set-point tracking performance data show that the pH control of the neutralization process can be successfully achieved using a PID controller which manipulates the flow rate of the base stream to the SDR. Addition of a disturbance observer scheme results in further enhancement of the control performance by suppressing the undesired effects of pH system nonlinearity. The conductivity control of the precipitation process is also successfully achieved by manipulating the disc rotational speed, which presents a vastly appealing potential for adopting an innovative approach to process control for SDRs.

Overall, our study indicates that, in order to achieve a given control task in SDRs, it is essential to first develop a comprehensive understanding of the relationship between the manipulated variable and the controlled parameter. It is also required to account for the interaction of different operating parameters which define the hydrodynamics of the thin films. Depending on the complexity of the system it may be unavoidable to resort to more advanced control schemes to achieve a satisfactory performance.