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Study on the valorization routes of ashes from thermoelectric power plants working under mono-and co-combustion regimes
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The main objective of this thesis was to study new valorization routes of ashes produced in combustion and co-combustion processes. Three main valorization pathways were analyzed: (i)production of cement mortars, (ii) production of concretes, and (iii) use as chemical agents to remove contaminants from wastewaters.
Firstly, the ashes produced during the mono-combustion of coal, co-combustion of coal and meat and bone meal (MBM), and mono-combustion of MBM were characterized. The aim of this study was to understand the ashes properties in extreme levels of substitution of coal by a residue with a high contamination of specific metals. The substitution of coal by MBM produced ashes with higher content of heavy metals.
Secondly, the ashes coming from an industrial power plant working under mono-combustion(coal) and co-combustion conditions (coal+sewage sludge+MBM) were studied. The use of cofuels did not promote significant changes in the chemical and ecotoxicological properties of ashes. Fly ashes were successfully stabilized/solidified in cement mortar, and bottom and circulating ashes were successfully used as raw materials in concrete.
The third step involved the characterization and valorization of biomass ashes resulting from the combustion of forestry residues. The highest concentrations of metals/metalloids were found in the lowest particle size fractions of ashes. Biomass ashes successfully substituted cement and
natural aggregates in concretes, without compromising their mechanical, chemical, and
ecotoxicological properties.
Finally, the biomass ashes were tested as chemical agents to remove contaminants from
wastewaters. The removal of P, mainly phosphates, and Pb from wastewaters was assayed.
Biomass ashes presented a high capacity to remove phosphates. As fly ashes were more
efficient in removing phosphates, they were further used to remove Pb from wastewaters.
Again, they presented a high efficiency in Pb removal.
New potential valorization routes for these ashes are now opened, contributing to improve their valorization rates.
Descrição
Thesis submitted to obtain the Doctoral degree in Energy and Bioenergy
Palavras-chave
Ashes Concrete Ecotoxicology Eluates Valorization Wastewater treatment