Browsing by Author "Tarelho, L."
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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.
- Improving bio-oil fractions through fractional condensation of pyrolysis vapors from Eucalyptus globulus biomass residues in a prototype auger reactorPublication . Vilas-Boas, A.C.M.; Tarelho, L.; Marques, C.C.; Moura, J.M.O.; Santos, M.C.; Paradela, Filipe; Nunes, M.I.; Silvestre, A.J.D.ABSTRACT: Bio-oil produced from the pyrolysis of lignocellulosic biomass has potential as a biofuel or chemical precursor. However, its valorization is hindered by its complex composition, high water concentration, and the presence of oxygenated compounds. Operational strategies are therefore required to improve its quality. This study evaluated the technical feasibility of fractional condensation as an alternative to conventional single-stage condensation of vapors produced from pyrolysis of residual Eucalyptus globulus biomass to collect bio-oil fractions with improved properties. The process was carried out using a prototype-scale auger reactor with continuous operation. The fractional condensation system comprised four sequential condensation stages operating at progressively lower temperatures: 140, 100, 80, and 0 degrees C. The collected bio-oil fractions were analyzed in terms of product yields, water separation efficiency, elemental composition, heating value, and the presence of volatile and semi-volatile compounds. The results demonstrated that fractional condensation achieved total bio-oil yields comparable to those obtained with the single-stage condensation system, while enabling the recovery of bio-oil fractions with lower water concentration, higher carbon concentration and increased heating value. Notably, the first condensation stage collected heavy fractions with water concentration between 3 % and 6 %wt., oxygen concentration between 17 % and 21 %wt., and carbon concentration between 69 % and 72 %wt., resulting in O/C molar ratios between 0.17 and 0.22, values close to those of biodiesel. These fractions exhibited lower heating values of up to 31 MJ/kg, surpassing those of conventional liquid biofuels such as biomethanol and bioethanol. These findings highlight the potential of fractional condensation of pyrolysis vapors from residual biomass from Eucalyptus globulus as an effective strategy to produce bio-oil with properties more suitable for direct energy use or as an intermediate feedstock for biofuels synthesis. Further research is recommended to optimize the condensation stages and assess the long-term stability of recovered fractions.