The control of a tubular fixed-bed catalytic reactor (TFBCR) system has been studied both experimentally and by simulation. A description is given of the modifications made to a tubular reactor pilot-plant (designed originally for steady-state operation) in order to facilitate full computer control under both steady-state and dynamic experimental conditions. Details are presented of self-tuning control algorithms that were employed to adjust the principal process variables. The reactor involved oxidises sulphur dioxide over a vanadium pentoxide catalyst at temperatures in excess of 673K. For dynamic work, good control of the process variables (viz. air and sulphur dioxide mass flowrates and the gas temperature at the reactor inlet) is required. As the oxidation reaction is exothermic, an additional control problem arises whereby the maximum temperature within the reactor must be limited such that catalyst deactivation or 'reactor runaway' do not take place. Changes made to the pilot-plant included improvements in the control microcomputer, the interfacing with the plant and the installation of mass flow controllers to adjust reliably both air and sulphur dioxide flowrates. A fast acting heater was added to allow rapid changes to be made in the temperature of the reactor inlet gases. Desired experimental conditions could be achieved using the process computer, which also had the capability to carry out full data logging, reactor start-up, shut-down and emergency shut-down. The control study involved two single-input single-output loops i.e. that controlling reactor gas inlet temperature and that controlling the maximum temperature within the reactor and the multi-variable control of the 'hot-spot' temperature and position using both inlet gas temperature and flowrate. Control difficulties were encountered since all loops exhibited considerable time delays coupled with large time-constants; additionally there appeared to be no linear relationships between controlling and controlled variables over the range of reactor operating conditions. The performances of a number of different feedback and feedforward/feedback self-tuning algorithms were assessed with respect to the process variables and comparisons were made with the standard proportional-integral-derivative (PID) controller and its variants. It has been demonstrated that the applications of self-tuning generalised predictive control (GPC) algorithms can provide robust control, with better performance than both self-tuning generalised minimum variance and (both self-tuning and fixed parameter) PID techniques, over a wide range of process operating conditions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:638173 |
| Date | January 1991 |
| Creators | Mehta, A. H. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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