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Browsing UB - Artigos em revistas internacionais by Author "Abelha, Pedro"
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- Effects of experimental conditions and of addition of natural minerals on syngas production from lignin by oxy-gasification: comparison of bench- and pilot scale gasificationPublication . Pinto, Filomena; Andre, Rui N.; Carolino, Carlos; Miranda, Miguel; Abelha, Pedro; Direito, Daniel; Dohrup, Jesper; Sorensen, Hanne Risbjerg; Gírio, FranciscoGasification of spent lignin pellets was used to obtain a gas suitable for energy production. Spent lignin was obtained from second-generation cellulosic ethanol demo plant using wheat straw as feedstock. Gasification of lignin did not give rise to any feeding problems, thus no significant changes were needed in the existing gasification installation. The rise of temperature and steam flow rate favoured the formation of H2, while hydrocarbons (CnHm) and tar contents decreased. The increase of equivalent ratio (ER) also decreased hydrocarbons and tar contents, but syngas higher heating value (HHV) was reduced. The use of natural minerals improved lignin gasification. The presence of dolomite led to the highest H2 and to the lowest CnHm and tar contents. Results obtained at bench-scale were confirmed at pilot-scale, as similar trends were obtained. However, as the residence time in pilot gasifier was higher, greater gas yields with higher H2 and CH4 concentrations were obtained, while tar contents decreased. After syngas hot cleaning and upgrading, the final syngas composition showed to be suitable for a wide range of applications (e.g. energy production and synthesis of chemicals), since it was substantially enriched in hydrogen, whereas tar and heavier gaseous hydrocarbons were completely destroyed.
- Evaluation of slagging and fouling tendency during biomass co-firing with coal in a fluidized bedPublication . Teixeira, P. Alexandra; Lopes, Helena; Gulyurtlu, Ibrahim; Lapa, Nuno; Abelha, PedroOver the last decades, several indices based on ash chemistry and ash fusibility have been used to predict the ash behaviour during coal combustion, namely, its tendency for slagging and fouling. However, due to the physicalechemical differences between coals and biomass, in this work only the applicability of an ash fusibility index (AFI) to the combustion and co-combustion of three types of biomass (straw pellets, olive cake and wood pellets) with coals was evaluated. The AFI values were compared with the behaviour of ash during combustion in a pilot fluidized bed and a close agreement was observed between them. For a better understanding of the mechanisms associated with bed ash sintering, they were evaluated by SEM/EDS and the elements present on the melted ash were identified. Evidences of different sintering mechanisms were found out for the fruit biomass and herbaceous biomass tested, depending on the relative proportions of problematic elements. The particles deposited on a fouling probe inserted in the FBC were analyzed by XRD and the differences between the compounds identified allowed concluding that the studied biomasses present different tendencies for fouling. Identification of KCl and K2SO4 in the deposits confirmed the higher tendency for fouling of fruit biomass tested rather than wood pellets.
- Gasification improvement of a poor quality solid recovered fuel (SRF): Effect of using natural minerals and biomass wastes blendsPublication . Pinto, Filomena; Andre, Rui N.; Carolino, Carlos; Miranda, Miguel; Abelha, Pedro; Direito, Daniel; Perdikaris, Nikos; Boukis, IoannisThe need to produce energy from poor quality carbonaceous materials has increased, in order to reduce European dependency on imported fuels, diversify the use of new and alternative fuels and to guarantee secure energy production routes. The valorisation of a poor quality solid residual fuel (SRF), with high content of ash and volatile matter, through its conversion into fuel gas was studied. The rise of gasification temperature and equivalent ratio (ER) led to higher gas yields and to lower undesirable gaseous components, though higher ER values led to a gas with lower energetic content. To reduce the negative effect of SRF unfavourable characteristics and to diversify the feedstocks used, SRF blended with three different types of biomass wastes: forestry pine, almond shells and olive bagasse was co-gasified. The use of biomass wastes tested was valuable for SRF gasification, as there was an increase in the overall reactivity and in H2 production and a reduction of about 55% in tar released, without great changes in gas yield and in its HHV. The use of natural minerals mixed with silica sand was also studied with the aim of improving SRF gasification performance and fuel gas quality. The best results were obtained in presence of dolomite, as the lowest tar and H2S contents were obtained, while an increase in gas yield was observed. Co-gasification of this poor quality SRF blended with biomass wastes in presence of dolomite increased gas yield by 25% while tar contents decreased by 55%.
- Slagging and fouling during coal and biomass cofiring: chemical equilibrium model applied to FBCPublication . Teixeira, P. Alexandra; Lopes, Helena; Gulyurtlu, Ibrahim; Lapa, Nuno; Abelha, PedroA thermodynamic model was applied to foresee the occurrence of fouling, slagging, and bed agglomeration phenomena during fluidized bed monocombustion of three different types of biomass, namely straw pellets, olive cake, and wood pellets. The cocombustion effect in reducing the occurrence of deposits and agglomerates of blends of 5, 15, and 25% (wt.) biomass with coal was also assessed. Chemical fractionation was applied to evaluate the reactive and nonreactive fraction of elements in the fuels, which was used to estimate their partition between the freeboard and bottom zone of the boiler. Qualitative and semiquantitative analytical techniques, namely, X-ray diffraction and scanning electronic microscopy – energy dispersive spectroscopy were used to compare the results from the simulation with the mineralogical and morphological composition of ash and deposits formed during combustion. The thermodynamic modeling revealed to be a powerful tool in foreseeing the formation of melt and liquids salts, depending on the temperature and chemical composition of fuels. The main discrepancies observed between the experimental and simulated data were due to particularities of the combustion process, which are not incorporated in the software, namely, kinetic limitations of the reactions, possible occurrence of secondary reactions in the ashes, and elutriation effects of ash and silica sand particles.