Value added utilisation possibilities of coal combustion products in South Africa

Abstract

The disposal of coal combustion products (CCP's), which includes coal ash and the new combustion product Flue Gas Desulphurisation (FGD) gypsum, causes significant environmental and economic difficulties. Only a small fraction of the coal ash currently produced in South Africa is utilised, whilst the bulk of it is held in ash storage facilities. The maximum possible utilisation rate for Eskom was in the range of 18% or 5.8 Mt for the 2015/2016 financial year. To reduce the environmental and economic impacts of the disposal of the coal ash and future FGD gypsum, alternative utilisation of these products was investigated. The proposed quality of FGD gypsum that can be expected from different South African limestone sources were evaluated. A Polish limestone and corresponding FGD gypsum sample was used as a base case in creating synthetic gypsum samples from three South African limestone samples. The aim of this exercise was to create gypsum samples that will replicate actual FGD gypsum samples from the wet FGD process. It was found that the gypsum quality correlates well with the limestone purity with a deviation of around 1-2% in laboratory conditions. Kusile will produce 900 000 tonnes/annum FGD gypsum which covers the demand for all the gypsum used in the cement and agriculture industry. It is important to use limestone of a high and consistent purity to ensure FGD gypsum end product suitable to use in the wallboard industry. Samples of ash from both Poland and South Africa were studied and compared to the South African legislation parameters. This comparison gave way to knowledge portraying that the fly ash from Poland and South Africa show strong similarities in terms of elemental composition and heavy metals. A comparison was drawn between the legislation regulating CCP in both South Africa and the European Union. This indicated that South African waste classification practises are more stringent in the current time and perhaps in environmental legislation terms a few years behind. The classification of CCP's in South Africa hinders the development of products and the utilisation thereof. The classification of European Union CCP's as by products enables the utilisation of it in a bigger spectrum of applications. The way forward in terms of waste legislation barriers in South Africa has been discussed. Global utilisation strategies cannot be implemented locally without considering South African legislation, high transport costs and a lack of proper infrastructure, additional capital and operational expenditure and stakeholder engagement. The proposed recommendations include offset interventions where CCP's can be used as thermal panels in low cost housing units. Coal ash can be successfully utilised in mine backfilling, road construction and agriculture solutions pending a change in legislation with pilot studies and the development of Norms and Standards. The work performed in this study contributes to the advancement of the utilisation of FGD gypsum and fly ash.