Author(s)

AMILA CHANDRA KAHAWALAGE, MORTEN C. MELAAEN, LARS-ANDRÉ TOKHEIM

Abstract

Cement manufacturing is an energy intensive process where coal is the main energy source. Replacement of coal with refuse derived fuels (RDF) will reduce costs and CO₂ emissions as RDF is partly carbon neutral. In modern cement kilns, most of the calcination (CaCO₃(s) → CaO(s) + CO₂) is carried out in the precalciner, and the process conditions there make it a good reactor for combustion of alternative fuels like RDF. However, most waste-derived fuels have a poorer quality than coal, and this could negatively affect the process. In this study, a model of the calcination and fuel combustion in the precalciner has been developed, and different fuel input cases have been simulated. The results indicate that it is feasible to use RDF to fully replace coal as an energy source in the precalciner. However, to obtain the same degree of calcination, the specific energy consumption will increase by 10% compared to coal if the RDF moisture content is 25% (a quite typical value). This is due to the fuel characteristics. As a result of the increased energy consumption, the exhaust gas flow rate also increases. Using RDF with 25% moisture content increases the exhaust gas volume flow rate from the kiln system by 11%. This is equivalent to a reduction in the production capacity. Considering that waste fuels like RDF are usually less expensive than coal, operating a precalciner with RDF as a coal replacement becomes a trade-off between lower fuel costs and lower production capacity.

Keywords

refuse derived fuels, cement kiln system, precalciner