Faculty of Engineering, Built Environment and Information Technology
School of Engineering
Department of Chemical Engineering
Selected Highlights from Research Findings
Control of batch processes in the absence of in-line measurements is a real engineering challenge. A new controller for batch pulp digesters was developed in the Department of Chemical Engineering. Using available process information and reliable process modelling techniques, Monte Carlo modelling was used to obtain theoretical values for variance to be used as a benchmark for performance comparison between the existing control system and the new controller. Once a basis for comparison had been established, in-situ testing showed that the new controller had 43% less variance and reduced the average error by 90% compared to the old controller. Additional benefits of the new controller include easy inclusion of new measurements and clear relations between the tuning parameters used and the conditions in the digester. Applying modern technology and engineering insight in this manner provides a new lease of life to existing processing plants.
Contact person: Prof PL de Vaal.
A novel approach to wetting efficiency in trickle bed systems was developed by using the saturation fraction of the residual holdup. This method helps to quantify the difference between operating on a pre-flooded or dry bed. It was further proven that holdup hysteresis couldn't be solely attributed to the increase in residual holdup at higher liquid flowrates. Furthermore the commonly accepted relationship between static liquid holdup and residual holdup was disproved by using Residence Time Distribution (RTD) analyses for increasing liquid flowrates, starting with a dry bed. This research aims to provide a better understanding of the behaviour of complex systems by taking an innovative approach to understanding 'old' concepts.
Contact person: Dr W Nicol.
The rate inhibiting effect of water in the reaction system where mesityl oxide (MSO) and water are formed from acetone over a commercial cation exchange resin catalyst was modelled with a Freundlich adsorption isotherm to describe site deactivation. Application of our developed model to published reaction rate data for other similar reaction systems shows that this approach may be generally applicable. The experimental work further showed a pseudo-equilibrium (other than the thermodynamically predicted equilibrium) for the MSO system, which may be explained by the reversible site deactivation due to the presence of water. Where the MSO reaction is the first step in the formation of methyl isobutyl ketone (MIBK) over a multifunctional palladium impregnated cation exchange resin, this inhibiting effect also becomes significant when the optimum trickle bed reactor operating regime is determined. The important factors influencing this optimum were determined and quantified.
Contact person: Dr W Nicol.
The search for bio-degradable plastic bags led to the discovery of such a material by Prof Walter Focke, director of the Institute of Applied Materials, and his team. The action of the product depends on photo-oxidation. It was licensed to Evergreen (Pty) Ltd.
Die soektog na biologies afboubare plastieksakke het gelei tot die ontdekking van sodanige materiaal deur Prof Walter Focke, direkteur van die Instituut vir Toegepaste Materiale, en sy mede-werkers. Die werking van die produk berus op foto-oksidasie en is onder lisensie by Evergreen (Pty) Ltd.
Contact person: Prof WW Focke.
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