Investigating the co-processing of municipal solid waste as an alternative fuel in cement production

Master of Science in Environmental Sciences ,North-West University, Vanderbijlpark Campus

Pillar 1 of the National Waste Management Strategy, which focuses on waste minimisation, has a focus area aimed at “Advancing Waste as a Resource” that, amongst others, aims to expand the use of refuse-derived fuel (RDF) in South Africa. This research aims to investigate the co-processing of municipal solid waste (MSW) as an alternative fuel in cement production in South Africa. Unlike the conventional method in cement rotary kilns, that primarily depends on coal as a fuel source, RDF from MSW can facilitate the transition toward a circular economy. The transition from a primarily coal-based energy source to RDF has the advantage of diverting MSW from landfill and reducing carbon dioxide emissions. The experimental design was modelled from a combination of mechanical treatment and bio-drying of waste. To develop a coal substitute in the form of RDF, a mechanical treatment process involved a series of downsizing the waste by way of shredding and granulating, while magnetic separation was done to eliminate ferrous metals. Furthermore, three sets of waste samples were tested. The samples had biogenic MSW, which comprises paper and synthetic carbon MSW which comprises plastic. The samples were dried and sampled in a controlled laboratory to examine the physio-chemical properties of RDF, utilising the proximate analysis of the ASTM D7582 standard. The results proved that at 28.15 MJ/kg, a 50% biogenic to 50% synthetic carbon source ratio will meet and exceed the operational efficiency requirements of heating the pre-calciner at 14 MJ/kg. Furthermore, the ratio meets the technical efficiency criteria with less than 0.3% chlorine, and less than 3% moisture. The sample emits a CO2 factor of 72 CO2 tonnes/TJ compared to 94.1 CO2 tonnes/TJ emitted by coal. Although RDF was considered a suitable alternative fuel for cement production, based on technical and efficiency aspects, challenges may exist in terms of operational/practical implementation. The research, thus, explored the perceptions of 22 specialists involved in the cement manufacturing process to determine potential opportunities and challenges. Perceived opportunities included increased kiln efficiency, improved innovation, reduced cost of cement production, reduced cost of waste management, reduced greenhouse gas emissions, promotion of landfill diversion, promotion of environmental sustainability, reduced fossil fuel (coal) dependency, pollution prevention, and bringing about positive changes in the public perception of waste. On the other hand, perceived challenges included concerns around incompatibility of cement kilns, cost of infrastructure, cost of waste (once it has value), emissions from burning of MSW, as well as difficulties in licensing.

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