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Yiannis A Levendis - One of the best experts on this subject based on the ideXlab platform.
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soot loading temperature and size of Single Coal particle envelope flames in conventional and oxy combustion conditions o2 n2 and o2 co2
Combustion and Flame, 2015Co-Authors: Reza Khatami, Yiannis A Levendis, Michael A DelichatsiosAbstract:Abstract A fundamental laboratory study on the volatile-phase combustion of pulverized Coal was conducted at the particle level. A primary goal has been to simultaneously assess soot volume fraction, fv, and soot temperature, T, in the diffusion flame (soot mantle) forming around a Single burning bituminous Coal particle, upon ignition of its volatile matter. This assessment was conducted with emission-based pyrometric methods. A secondary goal of this study has been to compare these radiative parameters, fv and T, in conventional air- and in simulated dry oxy-fuel combustion. Both fv, and T measurements were spatially averaged in the flame but temporally resolved throughout the combustion history of Single particles. In addition, the size of the volatile envelope flames was assessed both pyrometrically and cinematographically. Combustion of three different bituminous Coals took place with various oxygen partial pressures in nitrogen and in carbon dioxide background gases. Single particles, 75–90 μm, were injected and burned in a transparent drop-tube furnace (DTF) at laminar-flow atmospheric-pressure and a wall temperature of 1400 K. The free-falling bituminous Coal particles heated up and devolatilized, their volatile matter ignited and formed bright envelope flames, often with distinctive soot contrails in the wakes of the flames. The radiative parameters fv, T and flame size, of these luminous envelope flames were assessed using different emission-based models for the analysis of the three-color pyrometric intensities. The particle envelope flames of all three Coals were found to contain comparable to each other soot volume fractions, in the range of 20–90 ppm. At identical furnace gas temperatures and identical O2 mole fractions, when the background N2 gas was replaced with CO2, the particle envelope flames of the bituminous Coals were characterized by lower soot volume fractions, lower temperatures and bigger sizes. As the O2 mole fraction increased in either N2 or CO2 background gases, soot volume fractions increased to a maximum and then decreased, temperatures increased monotonically and flame sizes decreased. In CO2-based combustion, an oxygen mole fraction in the neighborhood of 35% was necessary to elevate the measured flame temperature to match that of conventional air-based combustion; however, the soot volume fraction was lower than that in air-based combustion regardless of the oxygen mole fraction.
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experimental and modeling study of Single Coal particle combustion in o2 n2 and oxy fuel o2 co2 atmospheres
Combustion and Flame, 2013Co-Authors: Tiziano Maffei, Reza Khatami, Sauro Pierucci, Tiziano Faravelli, E Ranzi, Yiannis A LevendisAbstract:Abstract Coal particle combustion experiments were performed in a drop tube furnace (DTF) with oxygen concentration from 21% to 100%, in N 2 and CO 2 mixtures, under quiescent flow conditions. Small particles (75–90 μm) of a high-volatile bituminous Coal (PSOC-1451) and a lignite Coal (DECS-11) are analyzed with particular attention to the particle burnout times and the particle surface temperatures. These experimental measurements are compared with the predictions of a comprehensive model of Coal combustion. Combustion of Coal particles is a multi-scale process where both chemical and physical phenomena are involved, thus it requires a coupled and accurate description of the kinetics as well as of the heat and mass transport phenomena. Important features of the model are a multistep kinetic scheme of Coal volatilization and detailed kinetics of the successive gas-phase reactions and of the heterogeneous reactions of both char oxidation and gasification. The achieved overall agreement between the experimental data and the numerical predictions, in terms of particle temperature and burnout times, highlights the capability of the model to simulate the effect of different operating conditions in the Coal combustion processes.
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Experimental and modeling study of Single Coal particle combustion in O2/N2 and Oxy-fuel (O2/CO2) atmospheres
'Elsevier BV', 2013Co-Authors: Tiziano Maffei, Reza Khatami, Sauro Pierucci, Tiziano Faravelli, E Ranzi, Yiannis A LevendisAbstract:Coal particle combustion experiments were performed in a drop tube furnace (DTF) with oxygen concentration from 21% to 100%, in N2 and CO2 mixtures, under quiescent flow conditions. Small particles (75–90 micron) of a high-volatile bituminous Coal (PSOC-1451) and a lignite Coal (DECS-11) are analyzed with particular attention to the particle burnout times and the particle surface temperatures. These experimental measurements are compared with the predictions of a comprehensive model of Coal combustion. Combustion of Coal particles is a multi-scale process where both chemical and physical phenomena are involved, thus it requires a coupled and accurate description of the kinetics as well as of the heat and mass transport phenomena. Important features of the model are a multistep kinetic scheme of Coal volatilization and detailed kinetics of the successive gas-phase reactions and of the heterogeneous reactions of both char oxidation and gasification. The achieved overall agreement between the experimental data and the numerical predictions, in terms of particle temperature and burnout times, highlights the capability of the model to simulate the effect of different operating conditions in the Coal combustion processes
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ignition characteristics of Single Coal particles from three different ranks in o2 n2 and o2 co2 atmospheres
Combustion and Flame, 2012Co-Authors: Reza Khatami, Christopher William Stivers, Yiannis A LevendisAbstract:Abstract This work assessed the ignition behavior of Single-Coal and Single-char particles in O2/N2 and O2/CO2 atmospheres, with oxygen mole fractions in the range of 20–100%. Fuels included four pulverized Coals from three different ranks (one high-volatile bituminous, one sub-bituminous and two lignites) as well as chars prepared from two of the Coals. Particles of 75–90 μm were injected in a bench-scale, transparent drop-tube furnace (DTF), electrically-heated to 1400 K. Optical access of the furnace allowed the ignition of individual particles to be observed with high-speed cinematography. A particle’s ignition delay was defined as the time lapsed from the instant when the particle exited the injector to the onset of its luminous combustion in the furnace. The experiments were conducted at two different gas conditions inside the furnace: (a) quiescent gas condition (i.e., no flow or inactive flow) and, (b) an active gas flow condition in both the injector and the furnace. In the former case, the axial gas temperatures in the DTF were found to be similar in the N2 and CO2 background cases and, consequently, small differences were observed in the ignition delay and in the ignition behavior of Coal particles in O2/CO2 and O2/N2 atmospheres. These small differences were easily accounted for by disparities in the physical properties of the background gases. Increasing the oxygen mole fraction in either N2 or CO2 reduced the ignition delay mildly. To the contrary, in the latter case, i.e., under the active gas flow condition the axial gas temperatures in the DTF were found to be disparate in the N2 and CO2 background cases. The ignition delay of Coal particles was drastically prolonged in the slow-heating O2/CO2 atmospheres, relative to the faster-heating O2/N2 atmospheres, particularly at high-diluent mole fractions. Photographic evidence showed that under active gas flow, which is relevant to practical applications in utility furnaces, ignition of volatiles in envelope flames was suppressed in the presence of CO2. As a result, whereas in the quiescent gas condition, bituminous and sub-bituminous Coal particles experienced homogeneous ignition in both O2/N2 and O2/CO2 atmospheres, in the active gas flow condition heterogeneous ignition was evident in O2/CO2. Lignite Coal particles often fragmented before ignition; this increased the likelihood of heterogeneous ignition in both O2/N2 and O2/CO2, in either active or inactive gas flows.
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On the deduction of Single Coal particle combustion temperature from three-color optical pyrometry
Combustion and Flame, 2011Co-Authors: Reza Khatami, Yiannis A LevendisAbstract:Abstract Temperature–time histories of burning Single Coal particles can be obtained with multi-color (multi-wavelength) optical pyrometry. With this method, a number of different temperatures can be deduced from the resulting number of two-color ratios. However, these two-color temperatures do not always agree, causing considerable uncertainty in the temperature measurement. This work used a three-color pyrometer and focused on identifying and minimizing the causes of disparity among the three deduced temperatures. Components of the pyrometer (such as dichroic filters, interference filters and photo-detectors) were modeled mathematically, taking into account their wavelength-dependent properties. The pyrometer was calibrated with both a high-temperature pre-calibrated tungsten lamp, and a moderately-high temperature blackbody cavity, to span the temperature range of interest in pulverized Coal combustion. Temperatures were deduced based not only on a suitably-modified pyrometric signal ratio method but also, on a similarly modified pyrometric signal non-linear least-square method, to provide comparison. Results are exemplified by presenting radiation-signal-time and temperature–time profiles of Single particles burning in air. The variation of the projected luminous area of burning particles was also computed using both methods, and area–time profiles are presented herein. The char particle emissivity was either treated as a quantity independent of the wavelength (i.e., assuming gray-body behavior), or as a quantity assumed to depend linearly on the wavelength and using pertinent published emissivity data. Finally, a sensitivity analysis was performed to investigate individual effects of parameters, such as the calibration method, the wavelength dependencies of filter transmissivities, and the photo-detector responsivities on the pyrometric signal ratio method temperature consistency.
Reza Khatami - One of the best experts on this subject based on the ideXlab platform.
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soot loading temperature and size of Single Coal particle envelope flames in conventional and oxy combustion conditions o2 n2 and o2 co2
Combustion and Flame, 2015Co-Authors: Reza Khatami, Yiannis A Levendis, Michael A DelichatsiosAbstract:Abstract A fundamental laboratory study on the volatile-phase combustion of pulverized Coal was conducted at the particle level. A primary goal has been to simultaneously assess soot volume fraction, fv, and soot temperature, T, in the diffusion flame (soot mantle) forming around a Single burning bituminous Coal particle, upon ignition of its volatile matter. This assessment was conducted with emission-based pyrometric methods. A secondary goal of this study has been to compare these radiative parameters, fv and T, in conventional air- and in simulated dry oxy-fuel combustion. Both fv, and T measurements were spatially averaged in the flame but temporally resolved throughout the combustion history of Single particles. In addition, the size of the volatile envelope flames was assessed both pyrometrically and cinematographically. Combustion of three different bituminous Coals took place with various oxygen partial pressures in nitrogen and in carbon dioxide background gases. Single particles, 75–90 μm, were injected and burned in a transparent drop-tube furnace (DTF) at laminar-flow atmospheric-pressure and a wall temperature of 1400 K. The free-falling bituminous Coal particles heated up and devolatilized, their volatile matter ignited and formed bright envelope flames, often with distinctive soot contrails in the wakes of the flames. The radiative parameters fv, T and flame size, of these luminous envelope flames were assessed using different emission-based models for the analysis of the three-color pyrometric intensities. The particle envelope flames of all three Coals were found to contain comparable to each other soot volume fractions, in the range of 20–90 ppm. At identical furnace gas temperatures and identical O2 mole fractions, when the background N2 gas was replaced with CO2, the particle envelope flames of the bituminous Coals were characterized by lower soot volume fractions, lower temperatures and bigger sizes. As the O2 mole fraction increased in either N2 or CO2 background gases, soot volume fractions increased to a maximum and then decreased, temperatures increased monotonically and flame sizes decreased. In CO2-based combustion, an oxygen mole fraction in the neighborhood of 35% was necessary to elevate the measured flame temperature to match that of conventional air-based combustion; however, the soot volume fraction was lower than that in air-based combustion regardless of the oxygen mole fraction.
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experimental and modeling study of Single Coal particle combustion in o2 n2 and oxy fuel o2 co2 atmospheres
Combustion and Flame, 2013Co-Authors: Tiziano Maffei, Reza Khatami, Sauro Pierucci, Tiziano Faravelli, E Ranzi, Yiannis A LevendisAbstract:Abstract Coal particle combustion experiments were performed in a drop tube furnace (DTF) with oxygen concentration from 21% to 100%, in N 2 and CO 2 mixtures, under quiescent flow conditions. Small particles (75–90 μm) of a high-volatile bituminous Coal (PSOC-1451) and a lignite Coal (DECS-11) are analyzed with particular attention to the particle burnout times and the particle surface temperatures. These experimental measurements are compared with the predictions of a comprehensive model of Coal combustion. Combustion of Coal particles is a multi-scale process where both chemical and physical phenomena are involved, thus it requires a coupled and accurate description of the kinetics as well as of the heat and mass transport phenomena. Important features of the model are a multistep kinetic scheme of Coal volatilization and detailed kinetics of the successive gas-phase reactions and of the heterogeneous reactions of both char oxidation and gasification. The achieved overall agreement between the experimental data and the numerical predictions, in terms of particle temperature and burnout times, highlights the capability of the model to simulate the effect of different operating conditions in the Coal combustion processes.
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Experimental and modeling study of Single Coal particle combustion in O2/N2 and Oxy-fuel (O2/CO2) atmospheres
'Elsevier BV', 2013Co-Authors: Tiziano Maffei, Reza Khatami, Sauro Pierucci, Tiziano Faravelli, E Ranzi, Yiannis A LevendisAbstract:Coal particle combustion experiments were performed in a drop tube furnace (DTF) with oxygen concentration from 21% to 100%, in N2 and CO2 mixtures, under quiescent flow conditions. Small particles (75–90 micron) of a high-volatile bituminous Coal (PSOC-1451) and a lignite Coal (DECS-11) are analyzed with particular attention to the particle burnout times and the particle surface temperatures. These experimental measurements are compared with the predictions of a comprehensive model of Coal combustion. Combustion of Coal particles is a multi-scale process where both chemical and physical phenomena are involved, thus it requires a coupled and accurate description of the kinetics as well as of the heat and mass transport phenomena. Important features of the model are a multistep kinetic scheme of Coal volatilization and detailed kinetics of the successive gas-phase reactions and of the heterogeneous reactions of both char oxidation and gasification. The achieved overall agreement between the experimental data and the numerical predictions, in terms of particle temperature and burnout times, highlights the capability of the model to simulate the effect of different operating conditions in the Coal combustion processes
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ignition characteristics of Single Coal particles from three different ranks in o2 n2 and o2 co2 atmospheres
Combustion and Flame, 2012Co-Authors: Reza Khatami, Christopher William Stivers, Yiannis A LevendisAbstract:Abstract This work assessed the ignition behavior of Single-Coal and Single-char particles in O2/N2 and O2/CO2 atmospheres, with oxygen mole fractions in the range of 20–100%. Fuels included four pulverized Coals from three different ranks (one high-volatile bituminous, one sub-bituminous and two lignites) as well as chars prepared from two of the Coals. Particles of 75–90 μm were injected in a bench-scale, transparent drop-tube furnace (DTF), electrically-heated to 1400 K. Optical access of the furnace allowed the ignition of individual particles to be observed with high-speed cinematography. A particle’s ignition delay was defined as the time lapsed from the instant when the particle exited the injector to the onset of its luminous combustion in the furnace. The experiments were conducted at two different gas conditions inside the furnace: (a) quiescent gas condition (i.e., no flow or inactive flow) and, (b) an active gas flow condition in both the injector and the furnace. In the former case, the axial gas temperatures in the DTF were found to be similar in the N2 and CO2 background cases and, consequently, small differences were observed in the ignition delay and in the ignition behavior of Coal particles in O2/CO2 and O2/N2 atmospheres. These small differences were easily accounted for by disparities in the physical properties of the background gases. Increasing the oxygen mole fraction in either N2 or CO2 reduced the ignition delay mildly. To the contrary, in the latter case, i.e., under the active gas flow condition the axial gas temperatures in the DTF were found to be disparate in the N2 and CO2 background cases. The ignition delay of Coal particles was drastically prolonged in the slow-heating O2/CO2 atmospheres, relative to the faster-heating O2/N2 atmospheres, particularly at high-diluent mole fractions. Photographic evidence showed that under active gas flow, which is relevant to practical applications in utility furnaces, ignition of volatiles in envelope flames was suppressed in the presence of CO2. As a result, whereas in the quiescent gas condition, bituminous and sub-bituminous Coal particles experienced homogeneous ignition in both O2/N2 and O2/CO2 atmospheres, in the active gas flow condition heterogeneous ignition was evident in O2/CO2. Lignite Coal particles often fragmented before ignition; this increased the likelihood of heterogeneous ignition in both O2/N2 and O2/CO2, in either active or inactive gas flows.
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On the deduction of Single Coal particle combustion temperature from three-color optical pyrometry
Combustion and Flame, 2011Co-Authors: Reza Khatami, Yiannis A LevendisAbstract:Abstract Temperature–time histories of burning Single Coal particles can be obtained with multi-color (multi-wavelength) optical pyrometry. With this method, a number of different temperatures can be deduced from the resulting number of two-color ratios. However, these two-color temperatures do not always agree, causing considerable uncertainty in the temperature measurement. This work used a three-color pyrometer and focused on identifying and minimizing the causes of disparity among the three deduced temperatures. Components of the pyrometer (such as dichroic filters, interference filters and photo-detectors) were modeled mathematically, taking into account their wavelength-dependent properties. The pyrometer was calibrated with both a high-temperature pre-calibrated tungsten lamp, and a moderately-high temperature blackbody cavity, to span the temperature range of interest in pulverized Coal combustion. Temperatures were deduced based not only on a suitably-modified pyrometric signal ratio method but also, on a similarly modified pyrometric signal non-linear least-square method, to provide comparison. Results are exemplified by presenting radiation-signal-time and temperature–time profiles of Single particles burning in air. The variation of the projected luminous area of burning particles was also computed using both methods, and area–time profiles are presented herein. The char particle emissivity was either treated as a quantity independent of the wavelength (i.e., assuming gray-body behavior), or as a quantity assumed to depend linearly on the wavelength and using pertinent published emissivity data. Finally, a sensitivity analysis was performed to investigate individual effects of parameters, such as the calibration method, the wavelength dependencies of filter transmissivities, and the photo-detector responsivities on the pyrometric signal ratio method temperature consistency.
Guangsuo Yu - One of the best experts on this subject based on the ideXlab platform.
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conversion characteristics of a Single Coal char particle with high porosity moving in a hot o2 co2 atmosphere
Fuel, 2019Co-Authors: Yan Gong, Guangsuo Yu, Yifei WangAbstract:Abstract The conversion characteristics of a Single particle with high porosity moving in a high temperature O2/CO2 atmosphere were simulated to complement the particle conversion sub-model. Considering the significant changes in the pore structure of high porosity particles, the effects of the high porosity (0.5–0.9) on conversion process were investigated. According to the experimental studies, two different types of char structures were considered for the particles with different porosity to establish the particle structure model, which include large pore structure and cenosphere structure. The reaction model contains water-gas-shift reaction, CO oxidation reaction and four heterogeneous reactions. The results show that the diffusion of the species is less limited inside the particle when the particle porosity is higher than 0.8. With the increase of particle size, the surface temperature and temperature gradient decrease. With the increase of the particle porosity, the surface temperature decreases and the temperature gradient increases. In addition, the specific carbon consumption rates decrease along with the increase of the particle size. When the particle porosity increases, the specific carbon consumption rates decrease firstly then significantly increase.
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numerical study of a reacting Single Coal char particle with different pore structures moving in a hot o2 co2 atmosphere
Fuel, 2017Co-Authors: Yan Gong, Jianliang Xu, Guangsuo YuAbstract:Abstract Based on pseudo-steady-state approach, the effect of particle size and porosity on conversion characteristics of Single Coal char particle moving in high temperature O2/CO2 atmosphere was studied to analyze the particle conversion mechanism. The particle size and porosity were variable in the range of 0.1–1.0 mm and 0–0.4 respectively. The particle structure model is developed referring to experimental Coal char particle pore structure. The Navier-Stokes equations were coupled with energy and species conservation equations to solve the problem. Stefan flow, Maxwell-Stefan equation and Soret effect were considered for mass transport. Water-gas-shift reaction, CO oxidation reaction and four heterogeneous reactions were taken into account. The reacting particles moving in different oxygen concentration were modeled for validation against experimental results of literatures. The results show that with the decrease of particle size, the reactive zone expands relative to the particle but shrinks relative to the space and attaches to the particle surface because of the low Reynolds number and the small pore size. The particle with high porosity is more sensitive to the change of the ambient oxygen concentration due to the large contact surface with gas flow. Additionally, the detaching of the flame sheet and the endothermic Boudouard reaction are two significant factors affecting the surface temperature. The insufficient supply of oxidant causes the decrease of the specific carbon consumption rate along with the enhancing of the particle size and porosity.
Martin Schiemann - One of the best experts on this subject based on the ideXlab platform.
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investigations on the emissivity of burning Coal char particles influence of particle temperature and composition of reaction atmosphere
Fuel, 2020Co-Authors: Philipp Graeser, Martin SchiemannAbstract:Abstract Radiative properties of burning char particles are one of the key parameters for heat transfer in pulverized fuel boilers. Among the parameters which are suspected to change emissivity of burning char surfaces, particle temperature and the reaction atmosphere (air-fired vs. oxy-fuel) are two factors needing investigation. An experimental campaign is presented which studies the effect of both factors in the spectral range from 1.25 µm to 5.5 µm. An in-flight spectrometer test rig measuring thermal radiation emitted by Single Coal particles was employed. Particle temperature was adjusted by varying the oxygen content in the oxy-fuel atmosphere between 15 and 40%. Average char particle temperatures increase from 1952 to 2582 K with increasing oxygen content. The emissivity drops from e = 0.6 to e = 0.26 (λ = 2.4–5.5 µm) and e = 0.33 to e = 0.24 (λ = 1.25–2.25 µm) with increasing temperature. The influence of the reaction atmosphere was investigated by performing experiments in a N2/O2 atmosphere and comparing to the results to data from an oxy-fuel atmosphere, both containing 20% of oxygen. The difference e oxy-fuel - e N 2 / O 2 is in the range of 0.1 and 0.2 for λ = 1.25–2.25 µm and λ = 2.4–5.5 µm. Effects of burnout and char structure are discussed to evaluate the results.
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multi parameter diagnostics for high resolution in situ measurements of Single Coal particle combustion
Proceedings of the Combustion Institute, 2019Co-Authors: J. Köser, Martin Schiemann, A. Dreizler, Nikita Vorobiev, B. BöhmAbstract:Abstract To study volatile combustion processes of Single Coal particles non-intrusive simultaneous multi-parameter measurements were performed. The experiment was carried out in a fully premixed flat flame burner with well-defined boundary conditions. For flame visualization high-speed luminescence imaging was combined with high-resolution high-speed OH-PLIF. To address particle size and shape a stereoscopic high-resolution backlight-illumination system was set up. Due to simultaneous recording of individual particle events the volatile combustion duration related to particle size, shape and velocity was measured. A comparison of luminescence imaging and OH-PLIF for flame visualization was investigated to define their application areas in Coal combustion. The stereoscopic backlight-illumination setup was benchmarked to a well characterized bituminous Coal. With a pixel resolution of ∼2.5 µm fine particle contours were resolved. The particle diameter and eccentricity were evaluated by an ellipse approximation. The experimental setup can be used to investigate different Coal ranks and biomass in N2/O2 and CO2/O2 atmospheres in future.
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emissivity of burning bituminous Coal char particles burnout effects
Fuel, 2017Co-Authors: Philipp Graeser, Martin SchiemannAbstract:Abstract The investigation of burnout effects on the char particle emissivity in the spectral range from 1.25 to 5.5 µm is presented. Single Coal particles of a bituminous Coal were combusted in a flat flame burner under oxy-fuel conditions (20.1 mol%). The emissivity was determined using a test-rig, which also measures particle temperature and diameter, both being necessary input parameters for Single particle emissivity, in the visual spectral range. The infrared radiation was measured spectrally resolved with a fiber spectrometer (1.25–2.25 µm) and integrated with an InSb detector (2.4–5.5 µm). The emissivity decreases clearly with progressing burnout: E.g. at 1255 nm the emissivity decreases from 0.49 to 0.38. The effect is larger in the spectral range from 1.25 to 2.25 µm, but still visible in the longer wave length range.
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devolatilization and volatiles reaction of individual Coal particles in the context of fgm tabulated chemistry
Combustion and Flame, 2016Co-Authors: R Knappstein, Martin Schiemann, G Kuenne, J. Köser, L. G. Becker, A. Dreizler, Anja Ketelheun, S Heuer, Viktor Scherer, A SadikiAbstract:Abstract The method of Flamelet Generated Manifolds (FGM) is coupled with a Coal devolatilization model to perform transient simulations of a well-defined Single Coal particle combustion experiment for the first time. The gas phase chemistry is mapped onto a three-dimensional manifold controlled by the mixture fraction, a reaction progress variable and the enthalpy. A simulation of an electrically heated inert pyrolysis reactor is performed in order to evaluate transferability and applicability of experimentally obtained devolatilization kinetic parameters to Large Eddy Simulation (LES) codes for combustion configurations. Finally, the FGM modeling approach is applied to a premixed flat flame configuration, in which the Coal particles cross a laminar flame front and are exposed to the hot gases. Numerical results regarding the volatiles reaction are compared to experimental findings. Particle and gas phase states are studied. Overall, good agreement between numerical results and experimental findings regarding the volatiles ignition range could be observed.
Fabrizio Scala - One of the best experts on this subject based on the ideXlab platform.
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Fluidized-Bed Combustion of Single Coal Char Particles: An Analysis of the Burning Rate and of the Primary CO/CO2 Ratio
Energy & Fuels, 2011Co-Authors: Fabrizio ScalaAbstract:The fluidized-bed combustion of large Coal char particles was studied with a focus on the burning rate and the primary CO/CO2 ratio at the particle surface. To this end, Single particle laboratory-...
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Fluidized bed combustion of Single Coal char particles at high CO2 concentration
Chemical Engineering Journal, 2010Co-Authors: Fabrizio Scala, Riccardo ChironeAbstract:Combustion of Single Coal char particles was studied at 850 ◦ C in a lab-scale fluidized bed at high CO2 concentration, typical of oxyfiring conditions. The burning rate of the particles was followed as a function of time by continuously measuring the outlet CO and O2 concentrations. Some preliminary evaluations on the significance of homogeneous CO oxidation in the reactor and of carbon gasification by CO2 in the char were also carried out. Results showed that the carbon burning rate increases with oxygen concentration and char particle size. The particle temperature is approximately equal to that of the bed up to an oxygen concentration of 2%, but it is considerably higher for larger oxygen concentrations. Both CO2 gasification of char and homogeneous CO oxidation are not negligible. The gasification reaction rate is slow and it is likely to be controlled by intrinsic kinetics. During purely gasification conditions the extent of carbon loss due to particle attrition by abrasion (estimated from the carbon mass balance) appears to be much more important than under combustion conditions. © 2010 Elsevier B.V. All rights reserved.