Abstract
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.
Highlights
In order to limit the global average temperature increase to below 2 ◦C above pre-industrial levels as stated in the Paris agreement, green house gas emissions need to be reduced to zero in less than twenty years [1]
This study presents an investigation of the interaction between ilmenite and two different waste fuels at two commercial circulating fluidized bed (CFB) units employing oxygen carrier aided combustion, or Oxygen Carrier Aided Combustion (OCAC)
This study focuses on ilmenite, which is a benchmark oxygen carrier, and as it contains Fe, the results should be highly applicable for other types of Fe-based oxygen carriers [63]
Summary
In order to limit the global average temperature increase to below 2 ◦C above pre-industrial levels as stated in the Paris agreement, green house gas emissions need to be reduced to zero in less than twenty years [1]. This is a difficult task unless active removal of carbon dioxide (CO2) from the atmosphere is enforced. The Nordic countries are world leading with respect to heat and power generation from sustainable biofuels. It is likely that the transition to renewable energy will result in an expansion of biomass resources [3,4]. This expansion leads to larger variation in both ash content and composition [5]
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