New Fuels. Zn And Pm Pollution From Waste Tire Combustion

The economic and environmental problems associated with waste tire generation produce a growing concern due to the non-biodegradability of this residue. Currently, the global production of this waste is around 6 million tones per year.Waste tires are mainly constituted by natural rubber, synthetic rubber, mainly styrene-butadiene (SBR) and poly-butadiene (PB) as well as carbon black. Certain inorganic components are added as fillers, like SiO2, or catalysts for the vulcanization process, like ZnO. Trace elements can be also found in rubber tire composition as a result of the manufacturing process or because of their external incorporation during the tire life.One of the main advantages, when comparing the nature of tires with other traditional fossil fuels like coal, is related to the high calorific value of tires (28-37 MJ/kg), higher than most of the coals. This fact joined to the lower moisture and ash content present in tire makes rubber tire a potential non-fossil fuel that would allow reducing inorganic emissions and solid scoria or bottom ash in comparison to the ones from coal. In this way, waste tires seem to be a promising fuel to produce cheap energy not only from an economic point of view but also from residues generation. Nevertheless, little is known about the pollution originated by its combustion.In this paper, the introduction of new fuels, "waste tire", in the power generation processes is studied from an environmental point of view taking into account the pollution produced by Zn and particulate matter (PM), fly ashes collected in cyclones and bottom ashes. The mineral matter transformations are studied by using X-ray diffraction and atomic absorption spectroscopy observing that the original zincite present in the rubber tire reacts with the silicate phases and it is transformed into willemite and hardystonite. However, this process is not instantaneous and requires long combustion times.