Slagging FoulingCo-firing Biomass Fluidized bed a b s t r a c tOver 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 K 2 SO 4 in the deposits confirmed the higher tendency for fouling of fruit biomass tested rather than wood pellets. ª

a b s t r a c tThree species of biomass origin (straw pellets, olive cake and wood pellets) and two coals from different countries (Coal Polish and Coal Colombian) have been studied to understand the fate of their ash forming matter during the combustion process and to investigate the influence of co-firing biomass with coal. Three different approaches to investigate the ash behaviour were employed: (1) chemical fractionation analysis to evaluate the association/reactivity of ash forming elements in the fuels as a prediction tool, (2) establishment of elements partitioning in ash streams produced in the combustion and co-combustion trials, and (3) evaluation of enrichment factors of elements in the ash streams. The chemical fractionation analysis was applied to all fuels used to evaluate how the association/reactivity of elements making up ash may influence their behaviour during combustion. Combustion tests were carried out on a pilot scale fluidized bed combustor (FBC). Four ash streams were obtained at different locations. The uncertainty of measurements was estimated allowing a critical evaluation of mass balances over the combustion system and the partitioning of elements in the ash streams. The enrichment factors of elements in the several ash streams were estimated, incorporating uncertainties associated with analytical measurements. Results obtained showed that for FBC the relation between the chemical fractionation and the experimental partitioning is strongly affected by elutriation of particles. The element enrichment factor estimated for each ash stream, using Al as a reference element, revealed better correlations with the elements reactivity obtained by chemical fractionation because it overcomes particles elutriation effects. Nevertheless, it was observed that the reactivity estimated by chemical fractionation could not be solely interpreted as tendency of the elements to volatilize on FBC system, as reaction in bed zone of boiler may also occur retaining reactive elements.

In this work, an enhancement of Ni0 particle dispersion over zeolite-supported catalysts was intended by tuning the impregnation solvent. For this purpose, a series of 15 wt % Ni catalysts supported over a Cs-USY zeolite were prepared by incipient wetness impregnation using water, ethanol, methanol, 2-propanol, acetone, or ethylene glycol as solvents. Samples were characterized by TGA, N2 adsorption, XRD, DRS UV–Vis, H2-TPR, CO2-TPD, and TEM and catalytically tested at atmospheric pressure under CO2 methanation conditions (86,100 mL gcat –1 h–1, P CO2 = 0.16 bar, H2/CO2 = 4:1). The use of organic solvents rather than water increased the number of weak and medium basic sites, while 2-propanol and ethylene glycol promoted metal–support interactions. The average Ni0 particle sizes after reduction at 470 °C were significantly different for all the studied solvents, ranging from 13 to 34 nm. Despite the beneficial properties exhibited by the catalyst prepared using ethylene glycol concerning metal particle dimensions and the number of weak and medium basic sites, 2-propanol allowed the highest CO2 conversion and CH4 selectivity (64 and 95%, respectively, at 350 °C), probably because of the partial damage of the zeolite structure observed when ethylene glycol was used. Materials prepared within this work were finally compared with other Ni-based catalysts from the literature, assessing the corresponding catalytic activity from CH4 production rates. Their performances were shown to be similar to or higher than those of the literature materials, thus confirming the relevance of these Ni/zeolite catalytic systems and motivating further developments towards this reaction.

A 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.

This work presents a study of the influence of sol−gel synthesis conditions on the reactivity and stability of synthetic sol−gel CaO sorbents for Ca-looping CO 2 capture. The temperature of the synthesis calcination and the amount of granular activated carbon introduced during sol−gel synthesis play key roles in the performance of sol−gel sorbents along the Ca-looping cycles. A higher initial CO 2 uptake was achieved for the sol−gel sorbents calcined at 750 °C. For the sol−gel sorbents calcined at 850 °C, both the reactivity and stability strongly depend on the amount of activated carbon incorporated during the sol−gel synthesis. By the combination of an adequate synthesis calcination temperature with the addition of an adequate amount of granular activated carbon during the sol−gel synthesis of CaO sorbents, it is possible to design and optimize synthetic sol−gel sorbents, tailoring their performance with regard to a desired high CO 2 capture capacity, an excellent stability, or both.