Effect of secondary waste fuels on atmospheric trace pollutants emissions from clinker production facilities

The utilization of secondary fuels derived from urban and industrial wastes is a well-established opportunity for containing the climate change impacts associated with conventional fossil fuels consumption in the cement industry. Large substitution of heat input required by clinker production with several different types of these fuels is extensively adopted, with air emissions inventories demonstrating significant greenhouse gases reductions arising from fossil fuels savings. However, the stack release of some trace pollutants of toxic concern, mainly heavy metals and dioxins, is not equally well documented, due to the more extensive ensemble of factors that, merely beyond fuel type and characteristics, might affect their air emissions. Present paper reports the main results of a study addressed to the analysis and comparative evaluation of real world emissions of toxic trace compounds arising from non conventional fuels utilisation in several full-scale cement plants operated in Italy. Data considered cover a relatively wide range of fuel types and substitution rates in different technological configurations of the clinker furnace and of the emissions control system, including most recent designs considered as BAT references in the cement sector. Main results demonstrate any appreciable variation in the stack emissions of trace metals and dioxins (PCDD/F) during coincineration of secondary fuels with respect to full conventional fossil fuels utilization, either for all the various types of alternative fuels burned than within the different clinker plant designs. For dioxins and furans, the results further indicate in dry kilns with cyclonic preheater and precalciner the most affordable designs for utilizing high levels of fuel cocombustion ratios without any risk of increasing stack emissions assets.