1,720,996 research outputs found
Mechanism and prediction of bed agglomeration during fluidized bed combustion of a biomass fuel: Effect of the reactor scale
No full textFluidized bed combustion of a biomass fuel: Comparison between pilot scale experiments and model simulations
No full textInsights into high temperature sorbents for carbon dioxide
No full textThis article reports on an experimental research dealing with the use of solid sorbents for CO2uptake from gaseous stream at high temperature. Hydroxyl-apatite and strontium carbonate have been adopted as starting materials for preparing a regenerable sorbent, upon calcination. Both sorbents have been characterized in TG tests with an alternating atmosphere of CO2/Ar and Ar, accomplishing steps of carbonatation and calcination/regeneration at temperature over 900 °C. The apatite based sorbent maintained its capability of CO2absorption for several cycles, whilst the Sr based sorbent exhibited a quick decay of its capability due to changes of the micro-structure. The CO2carrying capacity after conditioning reached stable values of around 3% and 5% for apatite and strontium sorbents, respectively. TG curves were worked out in order to obtain kinetic data for both carbonatation and calcination, showing that apatite is slightly more reactive than strontium sorbent. The TG tests were also complemented by a fixed bed experiment aimed at demonstrating the feasibility of apatite regeneration with steam
On the relevance of axial and transversal fuel segregation during the FB combustion of a biomass
No full textPressurized steam torrefaction of wet agro-industrial residues
No full textThis paper aims at demonstrating the viability of pressurized steam torrefaction (PST) as an effective pretreatment of wet agro-industrial residues for a flexible generation of biochar, along with secondary liquid products as “green” feedstocks of interest in chemical and process industries. A comprehensive experimental investigation program is presently going on at a laboratory scale by testing two wet agro-industrial residues typical of Italian agro-food sector, i.e., tomato peels and olive husks, produced in the Campania region (Italy). As a complement to the batch pressurized treatment in presence of water, the addition of a simple and cheap catalytic material has been taken into consideration during the torrefaction stage, and before the subsequent stage of solvent extraction of chemicals from the non-volatile torrefied products. This article reports the work-in-progress results, which are in the direction of boosting and upgrading the produced liquid fraction
Pseudo-component thermal decomposition kinetics of tomato peels via isoconversional methods
Full text linkThe kinetics of the thermal decomposition of tomato peel residues under nitrogen atmosphere was studied by non-isothermal thermogravimetric analysis in the heating rate range 2–40 °C/min. Due to the complexity of the kinetic mechanism, which implies simultaneous multi-component decomposition reactions, an analytical approach involving the deconvolution of the overlapping decomposition steps from the overall differential thermogravimetric curves (DTG) and the subsequent application of model-free kinetic methods to the separated peaks was employed. Two freely available Matlab functions, which adopt a non-linear optimization algorithm to decompose a complex overlapping-peak signal into its component parts, were used. Different statistical functions (i.e., Gaussian, Voigt, Pearson, Lorentzian, equal-width Gaussian and equal-width Lorentzian) were tested for deconvolution and the best fits were obtained by using suitable combinations of Gaussian and Lorentzian functions. For the kinetic analysis of the deconvoluted DTG peaks, the Friedman's isoconversional method was adopted, which does not involve any mathematical approximation. The reliability of the derived kinetic parameters was proved by successfully reproducing two non-isothermal conversion curves, which were recorded at a heating rate of 60 °C/min and 80 °C/min and not included in data set used for the kinetic analysis. Seven pseudo-components were identified as a result of the deconvolution procedure and satisfactorily associated with the main constituents of the investigated tomato peels
Segregation and fluidization behavior of poly-disperse mixtures of biomass and inert particles
No full textThis paper reports on the results of an experimental study aimed at investigating the fluidization and segregation behavior of poly-disperse binary mixtures consisting of small and dense inert particles mixed with less dense and coarse pieces of biomass fuels. In more details, orange peels (OP), conditioned to a moisture content of about 6% wt. and cut in square pieces (0.5 cm x 0.5 cm), were used as biomass feedstock. Three different materials (i.e., Ticino sand, quartz sand, alumina powder and alumina spheres) were tested as inert bed component in order to determine the prevalence of the effect of either size or density on the fluidization and segregation behavior of the investigated binary systems. Fluidization experiments were performed at room temperature in order to prevent that the formation of endogenous bubbles from devolatilizing fuel particles could come into play, which also impacts mixing and segregation phenomena in real fluidized bed reactors. Tests with different biomass weight fraction in the bed (XB) were performed both to study the effect of the bed composition on the characteristic velocities of the investigated binary systems (i.e., minimum and complete fluidization velocities) and to determine their maximum batch loading, i.e. the critical value of XBbeyond which the fluidization quality deteriorate (e.g., channelling, irreversible segregation, slugging)
Torrefaction of Tomato Peel Residues in a Fluidized Bed of Inert Particles and a Fixed-Bed Reactor
No full textThe potential of torrefaction treatment for upgrading low-value tomato peel residues into high-quality solid energy carriers was investigated by using a new bench-scale batch experimental apparatus based on fluidized-bed technology. In particular, the influence of the main process variables (i.e., temperature and time) on both the key performance parameters (i.e., mass and energy yields) and the main properties of the solid product (i.e., elemental composition, ash content, calorific value and equilibrium moisture content) was studied. Fluidized bed experimental runs were performed at 200, 240, and 285 °C by keeping the torrefaction time at 5, 15, and 30 min. Results suggested tomato peels as a good candidate for the torrefaction treatment. In more detail, it was observed that higher temperatures and longer holding times (with a more marked effect of the torrefaction temperature) led to an increase in the calorific value of the torrefied tomato peels, with respect to the parent ones. More specifically, the calorific value increased by a factor of 1.2 for the biomass treated at 285 °C and 30 min. Under the same experimental conditions, a 40% reduction in the O/C elemental ratio and an improved hydrophobicity of the torrefied tomato peels were also observed. These positive effects of the torrefaction treatment occurred while maintaining the mass yield (approximately between ∼75% and ∼94%, daf) and energy yield (∼90% and ∼96%, daf) at satisfactory levels. Fluidized-bed torrefaction experiments were also complemented by TGA-MS investigations and comparative tests carried out in a bench-scale fixed-bed reactor. Outcomes showed that the fluidized-bed technology is more suitable than the fixed bed one to cope with the exothermicity associated with the thermal degradation of nonwoody biomass, which has a tendency to ignite or carbonize easily during torrefaction. Furthermore, the fluidized bed proved to be more effective in ensuring a uniform and consistent quality of the torrefied solids
Fluidized bed combustion of a lignin-based slurry
No full textUnconverted lignin is available as residual sludge with water content in the range of 40-60% by mass from 2nd generation bio-ethanol production process. Fluidized bed combustion was studied as a possible method to valorize such a biomass material, upon mixing and homogenizing with rapeseed oil for producing a fuel slurry. Combustion tests were carried out at steady state in a pilot unit with submerged feeding of the fuel slurry. The operation with the slurry resulted reliable, after the adoption of measures for improving the slurry homogeneity and flowability. To this aim, particular care was dedicated to the production and characterization of the slurry, whose rheological properties are typical of a non-Newtonian (pseudo-plastic) fluid. The combustion tests proved that C content in the ash samples at the cyclone was very low and the combustion efficiency was higher than 99.5%. A temperature increase was registered in the freeboard with respect to the bed as consequence of volatile matter combustion, typical of biomass fuels. The normalized NO emission was compliant with the Italian regulation for biogenic fuels. The bed material was enriched in K and Na from the ashes, although no bed agglomeration phenomena occurred
Fluidized Bed Combustion and Gasification of Fossil and Renewable Slurry Fuels
No full textThis article provides a comprehensive review of the state of the art and more recent developments of the thermochemical treatments of slurry fuels in fluidized beds (FB). The review focuses on FB combustion and gasification of slurry fuels based on coal, biomass, sludge, and wastes from industry, agriculture, and the civil sector. The investigations at research and industrial levels over the last decades are presented and discussed, highlighting the adopted technological solutions, the results in terms of feasibility and efficiency, and the perspectives of future development. The different behavior between bubbling and circulating beds was addressed, in particular the optimal choice depending on the process (combustion/gasification/pyrolysis) and fuel properties (e.g., water content). Fundamental studies on interactions between the slurry fuels and the hot bed materials are also reviewed. The cumulative trend of reviewed investigations over the last decades depicts the abandonment of coal-based mixtures used in large plants, and the growing interest in the use of biomass-based slurries for small size application. In this respect, the shift from coal to biomass opens new challenges because of the different properties of biomass (density, fibrous structure, spontaneous degradation, hydrophilic behavior, etc.). Biomass-based slurries circumvent problems posed by using solid dry biomass, particularly in handling, storing, and feeding. Although slurry fuels represent a narrow sector, the results of the research investigations and the experience gained with coal can be exploited to contribute to the achievement of a circular approach based on renewable resources in the near future
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