Abstract
D.Ing. (Engineering Management)
This research focused on identifying ways of contributing towards green manufacturing by improving environmental sustainability in the Zimbabwean steel industry. The research was carried out through literature search, industrial surveys that included interviews of key personnel and the use of a questionnaire, and experiments to verify a hypothesis that was formulated. The industrial survey utilised the Delphi approach in order to explore the strategies, tactics and practices that the companies in the steel industry are currently implementing, and other improvements needed in order to ensure economic, social and environmental sustainability. It also identified current processes and any mitigation methods in place to mitigate emissions of toxic gases and allowed for interviews of key personnel from which a questionnaire was then formulated. The main concern for all the companies represented was that policies need to be investor friendly as that would lead to economic sustainability which in turn would lead to improved social and environmental sustainability. The results of the survey were distributed to all participants for further implementation of possible environmentally friendly practices.
From the survey a hypothesis was formulated that cupola furnace slag may be used as a lubricant in the cutting of steel. Two samples of the cupola furnace slag were collected from two different companies and ground into powders. Experiments were set up using soluble oil as the control experiment and the powders were used as dry lubricants and Vaseline was added to produce a paste. The results showed that cupola furnace slag may be used as a lubricant in the cutting of steel as it outperformed oil-based cutting fluids. It has lubricating properties and is capable of inhibiting heat diffusion.
Another industrial process investigated was calcination for a new start-up company. Calcination is an endothermic reaction that converts limestone into lime. Making the calcination process greener was studied and ways of achieving this were identified as: addition of chimneys to the kilns to increase draught column and allow preheating of limestone, addition of exhaust allowing the flue gases to pass through an amine system as a means to strip the flue gas of CO2, and use of insulating material such as vermiculite between the inner brick skin and outer brick layer to optimise energy utilisation.
The main contribution to knowledge was that a new solution to the utilisation of cupola furnace slag was established. This will economically assist the companies by cutting out the purchases of soluble oil and commercializing the use of cupola furnace slag in cutting. Reduction of cupola furnace slag in landfills is a great contribution towards sustaining the environment and greener manufacturing. The selection of slag that has a high aluminium and silicon content will help in its use as a solid lubricant in dry drilling. It is also noted that both aluminium and silicon are key constituents of coatings for cutting tools. Promoting dry drilling will also advance sustainability by reducing the use of oil-based cutting fluids thus cutting costs and eliminating the environmental burden of oil usage.
The Industrial Impact was that companies that took part in the study are very happy with the results of the dry drilling. They now have a low-cost consumable for machining for their in-house operations or for commercialisation. Wider sustainability factors for Zimbabwe steel industry were also covered. The study has developed and documented the industry preferred solutions for promoting the revival of the Zimbabwe steel industry. The three main contributions to knowledge made by this research are solutions for the revival of the Zimbabwe steel industry, a new method for deriving value from slag waste and firm proposals for reducing emissions in the calcination plant.