Browsing by Author "Freire, M."
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- Biomass quality in a thermoelectric plant along one yearPublication . Silva, D.; Tarelho, L.; Silva, J. Figueiredo; Freire, M.; Lopes, HelenaABSTRACT: The biomass quality is an important issue for the operation of a thermoelectric plant. Independently of the combustion technology, the biomass fuels and its characteristics are responsible for some operating problems during the thermochemical conversion of the biomass in thermal energy. These operation problems are related to the boiler and heat exchangers, dedusting technologies (e.g., electrostatic precipitator). Some studies show the phenomena of corrosion and incrustation on the walls of the boiler (named as fouling phenomenon) and on the walls of superheater, economizer, and equipments for flue gas treatment (named as slag phenomenon). When the biomass presents high levels of alkaline metals, like herbaceous and agro-industrial residues, these problems will be intensified. For example, the potassium and sodium decrease the melting point of the ashes, causing the incrustations and slag formation. On the other hand, magnesium and calcium in the biomass lead to the increase of the melting point of the ashes. The influence of the biomass quality on the bottom and fly ashes properties is related with the quantity of inert material, unburned carbon content and chemical composition. Thus, the main goal of this research work is focused on the characteristics of the forest biomass residues used as fuel in a Portuguese thermoelectric plant equipped with grate furnace technology. The results obtained allow the evaluation of the influence of some physical-chemical characteristics of the biomass on the produced ashes, and in the overall power plant performance.
- Critical aspects of biomass ashes utilization in soils: composition, leachability, PAH and PCDD/FPublication . Freire, M.; Lopes, Helena; Tarelho, L.Bottom and fly ashes streams collected along a year in several biomass thermal plants were studied. The bulk composition of ashes and other chemical characteristics that may impact soil application showed a high variability depending on the ash stream, combustion technology and ash management practice at the power plants. The acid neutralization capacity (ANC) and metal’s availability for leaching at fixed pH 7 and 4 was performed according with EA NEN 7371, as a quick evaluation method to provide information on the long-term behavior of ashes, regarding heavy metals and also plant nutrients release. Also the pH dependence leachability study was performed according to CEN/TS 14429 for predicting the leaching behavior under different scenarios. Leachability profiles were established between pH 3 and 12, allowing to distinguish different solubility control phenomena of toxic heavy metals (Cu, Cr, Mn, Ni, Zn, Pb) as well as other salts (Ca, K, Mg, Na, Cl). The ANC of fly ashes at pH 4 (3.6–9.6 molH+/kg) were higher than that observed for the bottom ashes (1.2–2.1 molH+/kg). Ashes were also characterized for persistent organic pollutants (POP), such as polycyclic aromatic hydrocarbons (PAH) and paradibenzodioxines and furanes (PCDD/F). Contents were found to be much higher in fly ash than in bottom ash streams. None of the PAH levels did reach the current national limit value of sewage sludge application in soils or the guide value for ash in north European countries. However, PCDD/F contents, which are not regulated, varied from non-detectable levels to high amounts, regardless the level of loss on ignition (LOI) or unburned carbon content in fly ashes. Given the current ash management practices and possible use of blends of bottom and fly ash streams as soil conditioners resembles clear the urgent need to regulate ash utilization in soils, incorporating limit values both for heavy metals, PAH and PCDD/F.
- Environmental risks of biomass ashes application in soils [Resumo]Publication . Freire, M.; Lopes, Helena; Tarelho, L.This work presents the potential environmental risks of biomass ashes application in forest soils. The ashes were collected in five industrial biomass thermal plants using different technologies: bubbling fluidized bed combustor and grate furnace.
- Valorização energética da fracção combustível dos resíduos de fragmentação automóvel: Estudo de cinzasPublication . Freire, M.No presente trabalho é apresentada a caracterização físico-química de Resíduos de Fragmentação Automóvel bem como das cinzas obtidas através da sua combustão num sistema piloto de leito fluidizado. A composição e a lixiviação do combustível foram comparadas com as cinzas utilizando as três metodologias de lixiviação mais usadas: o método europeu EN 12457-2, o método americano US TCLP 1311 e o método de disponibilidade holandês EA NEN 7371. Os resultados obtidos revelaram que, além da lixiviação de matéria orgânica, sob condições ácidas a libertação de metais pesados da FCRFA pode constituir um sério problema pelo que a sua deposição em aterro deverá ser abandonada. As cinzas resultantes do processo de combustão de FCRFA apresentaram alguns níveis de lixiviação de metais, como por exemplo Cr, todavia a destruição do conteúdo orgânico, associada à diminuição das quantidades de resíduo a depositar em aterro, fazem do tratamento térmico uma opcção a considerar na gestão deste tipo de resíduos.