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NRF/DST Chair: Sustainable Process Engineering

Prof. Thokozani Majozi

Group leader: Professor Thokozani Majozi

Thokozani Majozi is a full professor in the School of Chemical and Metallurgical Engineering at Wits where he also holds the NRF/DST Chair in Sustainable Process Engineering. Prior to joining Wits he spent almost ten years at the University of Pretoria, initially as an associate professor and later as a full professor of chemical engineering. He was also an associate professor in computer science at the Universty of Pannonia in Hungary from 2005 to 2009. He completed his PhD in Process Integration at the University of Manchester Institute of Science and Technology.



For further information, kindly contact:

Avanthi Singh 
Personal Assistant to:
Professor Thokozani Majozi
School of Chemical and Metallurgical Engineering:
Sustainable Process Engineering, University of the Witwatersrand
4th Floor, Richard Ward Building Johannesburg, RSA 
+27 11 717 7567 

Joel Croft

Joel Croft

On Optimum Design of Multipurpose Batch Plants for Multiple Products with Common Recipes

Batch facilities are generally encountered in the production of low volume high value add products, particularly when most of these products are meant to share a common set of operating units or equipment. Consequently, it is very common in practice to dedicate a particular facility to a group of products that largely share commonalities in their recipe. However, most of these plants tend to be overdesigned or underdesigned due to lack of proper understanding of underlying performance. Very critical in the perfomance of these processes are the granurality of time, capacity (size) of various units, capability of various units to conduct several tasks, the flexibility of individual recipes and compatibility of various intermediates and final products. The latter is of utmost importance where product integrity should be observed, which generally is the case in batch plants. Ultimately, this research is aimed at developing a systematic framework for superstructure generation that could be used as the basis for a robust and rigorous mathematical model to yield an optimum flowsheet under these circumstances. It is envisioned that the model will be premised on a continuous time domain, which has proven to result in fewer binary variables. In general, the number of binary variables largely determines the compexity of the mathematical model.

Jude Bonsu

Jude Bonsu 

A Mathematical Synthesis Framework for Integrated Gasification Combine Cycle

The Integrated Gasification Combined Cycle (IGCC) is a promising technology in addressing the increasing global energy demand. The IGCC comprises the combined energy cycle (i.e. the Brayton thermal and the Hirn-Rankine cycle) with an integrated gasifier. Other units in an IGCC process include an Air Separation Unit (ASU), a Gas Cleaning Unit, and a Heat Recovery Steam Generation Unit. The competitive advantages of the IGCC over the conventional coal power plants include the ability to use multiple feed sources, high energy efficiency, significantly reduced water consumption and environmental friendliness, particularly when a coal fired gasifier is employed. Notwithstanding the aforementioned advantages, challenges facing the IGCC process include lower energy efficiency and high capital cost as compared to the Combined Cycle. This is due to the existence of both high auxiliary power consumption and low efficiency units. There is, however, no evidence in published literature justifying the necessity of such auxiliary power consumption units. There is also no evidence indicating that the present process routes are the most energy efficient. The operating conditions of the units in the IGCC have also not been proven to be the most efficient. This study is aimed at synthesizing an optimal IGCC flowsheet. This goal will be achieved by developing a superstructure IGCC framework encompassing all possible process routes through mathematical modelling. The developed mathematical model will be optimized to achieve the flowsheet with the optimal energy efficiency.

Maduvha Nemadandila

Maduvha Nemadandila

Systematic approach for synthesis, design and optimization of comprehensive utility systems in chemical processes

The consumption of water and energy in chemical industry is relatively high. Power generation plants typically use large quantities of water, particularly as cooling water and for steam production. In general, a power generation plant comprises the cooling tower to supply cooling water for turbine exhaust stream condenser and a boiler to supply superheated steam. Even though the two utility systems complement each other as found in real power generation plant, the published literature has treated them as separate entities. Such individual analysis creates a false dichotomy between the cooling water and steam systems. The two systems constitute a comprehensive utility system. This research is aimed at developing a methodology for the synthesis, design and optimization of a plant utility system that exploits the integrated nature of such systems.

Sharon Mabitla

Sharon Mabitla

A process integration technique for integrated water and membrane networks that are characterized by variable removal ratios

Due to strict environmental regulations and depleting supplies of freshwater, process integration is employed in industries for sustainable water management through minimization of both freshwater requirements and wastewater generation. Most publications in this field solved the water network design problem using graphical and mathematical techniques independently. The objective of this work is to develop a robust hybrid system of water-pinch analysis and mathematical modelling as there are irrefutable merits for designing a combined system. In this particular context, pinch analysis would provide the conceptual insights while mathematical modelling would offer the detailed and rigorous design of a regeneration unit for effluent treatment. The main envisioned contribution of this investigation is the development of a graphical technique for integrated water and membrane networks, where removal ratios of the identified regenerators are not specified a priori. Furthermore, the influence of this approach on wastewater minimization, regeneration cost and configuration of the water network will be evaluated.

Shaun Engelbrecht

Shaun Engelbrecht, MSc

Synthesis, Design and Optimization of Heat Integrated Multipurpose Batch Plants

This research is aimed at developing a mathematical model that can be readily implemented in the synthesis, design and optimization of batch processes that are characterized by combinatorially complex recipes. These are generally referred to as multipurpose batch facilities. The intended benefit of the investigation is to capture the heat integration opportunities during the conceptual and the grassroot design phase of processes, without compromising on optimum plant throughputs. Experience with mathematical models that are intended for this purpose has consistently demonstrated that these models are very difficult to solve at best and impossible to solve at worst, using state-of-the-art computational frameworks. Consequently, the investigation is focused on the development of a mathematical model with minimum number of binary variables in a continuous-time domain. The choice of the continuous time is premised on exact time and reduced number of time points that signify the occurrence of a task in a particular unit. The reduction in the number of time points has proven to be an ideal starting point in pursuit of minimum number of binary variables. It is worth mentioning that all this has to be achieved without loss of problem generality and accuracy.