Francesco Miccio

Fluidized Bed Combustion of a Biomass Fuel: Comparison Between Pilot Scale Experiments and Model Simulations

In the present work the efficiency of the fluidized bed combustion (FBC) of high-volatile fuels and the extent of volatile matter post-combustion in the splashing zone and freeboard are investigated. A typical Mediterranean biomass (pine-seed shells) has been burned in a pilot-scale bubbling FB combustor (200 kWt) at different operating conditions. Both over-and under-bed fuel feeding options have been considered. A FBC model specifically developed for high-volatile fuels has been also applied to provide a comparison with bed carbon loading, in-bed heat release and splashing region temperature experimental data

Formation rates of characteristic carbon phases during fuel-water slurry injection in a hot fluidized bed

Abstract The interaction of fuel-water slurries (FWS) with a hot fluidized bed has been studied and the allocation of fixed carbon resulting after FWS dehydration and devolatilization has been investigated. An experimental technique has been purposely set up. A pneumatic injector has been used to disperse FWS into an atmospheric fluidized bed reactor, 140 mm ID. Silica sand has been used as bed material. The experiments have been carried out at typical temperatures of atmospheric fluidized bed combustion (AFBC), but under inert conditions to prevent combustion. Nitrogen as inert gas has been used for fluidization and for dispersion of FWS. Experiments provide results in terms of relative formation rates of carbon aggregates (A-phase), tiny carbon deposits on individual sand particles (S-phase) and carbon fines (F-phase). Relative formation rates are controlled by injection conditions, i.e. by the velocity of dispersing gas at the nozzle and the gas-to-slurry mass feed ration. A further operating parameter is the hydrodynamics of the bed. Finally, the nature of the parent fuel in FWS is also of great importance. The above findings are critically reviewed in the paper in order to determine the rates controlling the formation of carbon phases in an actual FWS-fired FBC unit.

Modeling percolative fragmentation during conversion of entrained char particles

A numerical model of carbonaceous particle conversion under chemical and external diffusion control is proposed. The model accounts for different classes of particles which undergo chemical conversion in parallel with percolative fragmentation. It applies to typical conditions of entrained flow reactors. The system of algebraic and differential equations has been numerically solved. Results include the total carbon conversion as well as the determination of particle properties along the reactor. The model correctly predicts the change of the conversion rate at varying temperature, initial oxidant concentration and excess oxidant ratio. The influence of percolation parameters is also relevant and claims further investigations for more accurate determination. A comparison with experimental data available in literature is also provided

Segregation and fluidization behavior of poly-disperse mixtures of biomass and inert particles

Segregation and Fluidization Behavior of Poly-disperse Mixtures of Biomass and Inert Particles Paola Brachi , Riccardo Chirone, Francesco Miccio b, Michele Miccio ,Giovanna Ruoppolo Institute for Research on Combustion, (IRC-CNR), P.le Tecchio 80, 80125 Napoli, Italy Institute of Science and Technology for Ceramics (ISTEC-CNR), via Granarolo 64, 48018 Faenza (RA), Italy Department of Industrial Engineering, University of Salerno, via Giovanni Paolo II 132, 84084 Fisciano (SA), Italy p.brachi@cnr.irc.it

FB Combustion of a Biomass Fuel: Comparison Between Pilot Scale Experiments and Model Simulations

In the present work the efficiency of the fluidized bed combustion of high-volatile fuels and the extent of volatile matter post-combustion in the splashing zone and freeboard are investigated. A typical Mediterranean biomass (pine-seed shells) has been burned in a pilot-scale bubbling FB combustor (200kWt) at different operating conditions. Both over- and under-bed fuel feeding options have been considered. A FBC model specifically developed for high-volatiles fuels has been also applied to provide a comparison with bed carbon loading, in-bed heat release and splashing region temperature experimental data. Experimental results showed that the biomass combustion efficiency is always very high as a consequence of the high reactivity of the fuel. Extensive volatiles post-combustion above the bed is observed, whose extent appears to be sensitive to the over/under bed feeding option and to the excess air. Approximately 80% of the total heat is released/recirculated in the bed, the remainder leading to appreciable overheating of the freeboard with respect to the nominal bed temperature. Very low bed carbon loadings have been found. Model results compare well with the experimental temperature, heat release and carbon loading trends. However, detailed prediction of the freeboard temperature profiles requires further improvements of the model.Copyright

An Investigation on Low-Temperature Fluidized Combustion of Liquid Fuels

Presently, the combustion at low temperature is receiving a great deal of interest because emissions of micro- and nano-pollutants are expected to be greatly reduced. Following previous studies on the low temperature combustion behavior, the authors report results and discussion of steady-state experiments on an atmospheric, pre-pilot scale, 140 mm ID, FB reactor, equipped with an under-bed, air-assisted, liquid-fuel injector. The experimental program was focused on the operation at temperatures lower than the classical value for FBC of solid fuels (i.e., 850°C). The data series taken into consideration are the concentrations of the main unburned species in the splash zone, those of oxygen measured in the bed and in the splash zone as well as the freeboard pressure. The interpretation of the results is mainly based on the statistical analysis in the time domain. The combustion pattern of bio-diesel is compared to that of the diesel fuel under varying operating conditions (e.g., bed temperature, dispersion air velocity at the fuel nozzle, injector height in the bed). Conclusions that were previously published on the base of lab-scale results are checked against new data obtained on the pilot scale. An innovative technique for the analysis of the micro-explosive regime is presented. It consists in the comparison of oxygen concentration measured by the zirconia-based probes at different heights in the bed and in the splash region, pressure signals measured in the freeboard and purposely filtered, and video-recordings of the bed surface phenomena.Copyright

Fluidized Bed Combustion of a Lignin-based Slurry

Fluidized Bed Combustion of a Lignin-based Slurry Francesco Miccio, Roberto Solimene, Massimo Urciuolo, Paola Brachi, Michele Miccio a Institute for Research on Combustion CNR, P.le Tecchio 80, 80125 Napoli, Italy b Institute of Science and Technology for Ceramics CNR, via Granarolo 64, 48018 Faenza (RA), Italy c Department of Industrial Engineering, University of Salerno, via Giovanni Paolo II 132, 84084 Fisciano (SA), Italy francesco.miccio@cnr.it

Modeling Homogeneous Combustion in Bubbling Beds Burning Liquid Fuels

This paper presents a first implementation of a model for the description of homogeneous combustion of different fuels in fluidized bed combustors (FBC) at temperatures lower than the classical value for solid fuels, i.e. 850°C. Model construction is based on a key feature of the bubbling fluidized bed: a fuel-rich (endogenous) bubble is generated at the fuel injection point, travels inside the bed at constant pressure and undergoes chemical conversion in presence of mass transfer with the emulsion phase and of coalescence with air (exogenous) bubbles formed at the distributor and, possibly, with other endogenous bubbles. The model couples a fluid-dynamic sub-model based on the two phases theory of fluidization with a sub-model of gas phase oxidation. To this end, model development takes full advantage of a detailed chemical kinetics scheme, which includes both the low and high temperature mechanisms of hydrocarbon oxidation and accounts for about 200 molecular and radical species involved in more than 5000 reactions. Simple hypotheses are made to set-up and close mass balances of the various species as well as enthalpy balances in the bed. First, conversion and oxidation of gaseous fuels (e.g. methane) have been calculated as a test case for the model; then, n-dodecane has been taken into consideration to simply represent a diesel fuel by means of a pure hydrocarbon. Model predictions qualitatively agree with some evidences coming from experimental data reported in the literature. The fate of hydrocarbon species is extremely sensitive to temperature changes and oxygen availability in the rising bubble. A preliminary model validation has been attempted against the results of experiments carried out on a pre-pilot, bubbling combustor fired with underbed injection of a diesel fuel. In particular, model results confirm the trends that the heat release either in the bed or in the freeboard experimentally shows as a function of bed temperature. At lower emulsion phase temperatures many combustible species leave unburned the bed, post-combustion occurs past the bed and freeboard temperature considerably increases; as it is well known, this is an undesirable feature from the viewpoints of practical application and emission control.Copyright