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- Toxicity of Ashes Produced During the Combustion and Co-combustion of Coal and Meat and Bone Meal in a Fluidized- Bed ReactorPublication . Barbosa, Rui; Lapa, Nuno; Lopes, Helena; Gulyurtlu, Ibrahim; Mendes, BenildeThe replacement of fossil fuels by renewable fuels can contribute to improve the environmental performance of the power production and to move forward in the sustainability way. The experience has shown that the availability of alternative fuels can be an obstacle for its extensive use for energy production, since biomass is not always available. The use of non-hazardous wastes may be a good alternative to biomass, mainly if they are economically unattractive for recycling or if they present a high cost for land-filling. The co-firing of non-hazardous wastes with coal is, therefore, a subject of great interest for the sustainability of energy production and the reduction of the emissions of fossil greenhouse gases. The use of these wastes for energy is promising if they combine well with other fuels during the conversion process for energy production and have no negative effect on the combustion system, on the ash quality and on the gaseous emissions.
- 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.