Oxygen carrier aided combustion (OCAC) of two waste fuels - Experimental and theoretical study of the interaction between ilmenite and zinc, copper and lead

Zinc, copper and lead are amongst the more abundant trace metals in waste fuels such as municipal solid waste and recovered waste wood. The ashes from waste fuels could contain high contents of these metals, which could be valuable but also toxic in certain environments. Oxygen carrier aided combustion, OCAC, is a novel technology for combustion of biomass and waste. Utilizing oxygen carriers could affect the fate of these metals and have implications for stability and recycling. The aim of this work is to study the fate of zinc, copper and lead during oxygen carrier aided combustion of two waste fuels utilizing ilmenite as an oxygen carrier. In total, four samples have been obtained from two different industrial fluidized bed boilers using ilmenite as bed material. Due to low concentrations, bulk analysis methods are not suitable for speciation, i.e. SEM/EDX and XRD. Hence, this investigation utilizes high resolution x-ray photoelectron spectroscopy (XPS), coupled to detailed thermodynamic modelling, with the aim of understanding trace metal speciation, distribution and phase composition. Characterization of the four samples show that iron at the surface of ilmenite particles interact with both copper and zinc to form ferrites, CuFe2O4 and ZnFe2O4. Lead, on the other hand, is more prone to end up in the fly ash as condensed PbCl2, but the mixed oxide PbTiO3 could be identified at the oxygen carrier surface. Thermodynamic calculations were shown to be in line with the identified compounds.

Automated summary

This study investigates the fate of zinc, copper, and lead in waste fuels during combustion utilizing oxygen carrier aided combustion technology. It was found that iron on the surface of the oxygen carrier interacts with copper and zinc to form corresponding compounds, while lead is more likely to end up in the fly ash as PbCl2. Thermodynamic calculations were consistent with the identified compounds.