ANTON VERISSIMO | Instituto Superior Técnico (original) (raw)
Papers by ANTON VERISSIMO
Anais do IX Congresso Nacional de Engenharia Mecânica, 2016
Combustion Science and Technology, 2016
ABSTRACT Steam gasification of crude glycerin was carried out in a laboratory packed bed reactor ... more ABSTRACT Steam gasification of crude glycerin was carried out in a laboratory packed bed reactor and the effects of the bed temperature and flow rate of glycerin on the yields and characteristics of the syngas produced were examined. The tests were performed at bed temperatures of 700°C, 800°C, and 900°C over a wide range of water to glycerin ratios (W/G) using aluminum oxide as a packing material. Subsequently, the influence of the glycerin flow rate was studied at a fixed bed temperature of 800°C and a W/G of 4. The main conclusions are: (1) as the bed temperature increases, the hydrogen and carbon dioxide contents increase, the carbon monoxide and methane contents decrease, the heating value of the syngas produced slightly reduces, and the syngas production augments; (2) the glycerin flow rate does not influence the syngas production nor its heating value up to a certain value beyond which the production drops and the heating value increases a little; and (3) the minimum water content required for steam gasification to take place without reactor blocking decreases as the bed temperature increases, and increasing the glycerin flow rate increases the risk of bed deposition for the same W/G ratio.
This article examines the flow, combustion and emission characteristics of a laboratory combustor... more This article examines the flow, combustion and emission characteristics of a laboratory combustor as a function of the inlet air velocity (V air). Variations in V air were accomplished by changing the air nozzle diameter while maintaining constant all remaining input parameters. Initially, laser-Doppler anemometry was employed to evaluate the combustor flow aerodynamics under non-reacting conditions. Subsequently, flue-gas composition data and hydroxyl radical chemiluminescence (OH*) imaging were obtained as a function of V air. For two of these combustor operating conditions, spatial distributions of temperature, recorded with fine wire thermocouples, and of O 2 , CO 2 , unburned hydrocarbons, CO and NO x concentrations, measured with the aid of a sampling probe, were also obtained. The OH* images showed that as V air increases at a constant excess air coefficient (λ) of 1.3, the main reaction zone, typical of flameless combustion condition, remains approximately in the same region of the combustor, because of the flow aerodynamics similarity, but the OH* intensities decrease, which indicates higher entrainment ratios of the fuel and burned gases by the central air jet. For λ greater than 1.7, however, flameless oxidation could not be established regardless of the air jet momentum. This suggests that the establishment of the flameless combustion condition in future gas turbines through the dilution of the reactants with a substantial amount of flue gases in configurations where the combustion air is provided by a central highmomentum air jet that is surrounded by a number of low-momentum fuel jets may be problematic.
Journal of Physics: Conference Series, 2012
This work reports numerical simulations of a small-scale cylindrical combustor operating in the m... more This work reports numerical simulations of a small-scale cylindrical combustor operating in the mild combustion regime. Preheated air is supplied by a central nozzle, while the fuel (methane) is injected through 16 holes placed equidistantly in a concentric circumference. The calculations were carried out using the commercial code Ansys-Fluent-v13. Turbulence was modelled using the realizable k-ε model. Three different combustion models were employed, namely the finite rate/eddy dissipation, the eddy dissipation concept and the joint composition probability density function transport model. A detailed chemical mechanism, SK-17 was used. Subsequently, the pre-heated air temperature influence is studied and compared with experimental measurements. The combustion models with the detailed mechanism are able to accurately predict the temperature and the O 2 and CO 2 molar fractions over most of the combustor. Regarding the pre-heated combustion air temperature influence, there is a decrease in the recirculation rate when that temperature is lower. When the air nozzle diameter decreases, the reaction occurs closer to the burner.
Fuel Processing Technology, 2013
ABSTRACT The reaction zone of a small-scale laboratory combustor operating under flameless oxidat... more ABSTRACT The reaction zone of a small-scale laboratory combustor operating under flameless oxidation conditions is examined with the aid of hydroxyl radical chemiluminescence (OH*) imaging and measurements of local mean gas temperatures and local mean major gas species (O2, CO2, CO, unburnt hydrocarbons and NOx) concentrations along the combustor axis, as a function of the fuel (methane) thermal input, which was varied between 7 and 13 kW. As the fuel thermal input increases, the reaction zone, as typified by the OH* distribution, enlarges and, simultaneously, moves progressively closer to the combustor exit (exhaust) due to the increase in the central jet momentum, while maintaining constant the excess air level. The excess air values used in the present study were low enough to preserve the flameless combustion regime regardless of the fuel thermal input, with the combustor yielding very low NOx (< 6 ppm@15% O2) and CO emissions (< 14 ppm@15% O2) regardless of the fuel thermal input. The low NOx emissions, almost independent of the fuel thermal input, are attributed to the suppression of the thermal mechanism promoted by the flameless oxidation regime. Despite being always low, the CO emissions increase with the fuel thermal input presumably because of the lower residence times associated with the higher burner thermal loads.
Experimental Thermal and Fluid Science, 2013
This article examines the importance of the inlet air velocity (V air) on the establishment of fl... more This article examines the importance of the inlet air velocity (V air) on the establishment of flameless combustion in a 10 kW laboratory scale combustor. Variations in V air were accomplished by changing the air nozzle diameter while maintaining constant all remaining input parameters. Initially, laser-Doppler anemometry was employed to evaluate the combustor flow aerodynamics under non-reacting conditions. Subsequently, flue-gas composition data and hydroxyl radical chemiluminescence (OH Ã) imaging were obtained as a function of V air. For two of these combustor operating conditions, spatial distributions of temperature, recorded with fine wire thermocouples, and of O 2 , CO 2 , unburned hydrocarbons, CO and NO x concentrations, measured with the aid of a sampling probe, were also obtained. The OH Ã images showed that as V air increases at a constant excess air coefficient (k) of 1.3, the main reaction zone, typical of flameless combustion condition, remains approximately in the same region of the combustor, because of the flow aerodynamics similarity, but the OH Ã intensities decrease, which indicates higher entrainment ratios of the fuel and burned gases by the central air jet. For k greater than 1.7, however, flameless oxidation could not be established regardless of the air jet momentum. This suggests that the establishment of the flameless combustion condition in future gas turbines through the dilution of the reactants with a substantial amount of flue gases in configurations where the combustion air is provided by a central highmomentum air jet that is surrounded by a number of low-momentum fuel jets may be problematic.
Energy & Fuels, 2011
ABSTRACT This article examines the operational, combustion, and emission characteristics of a sma... more ABSTRACT This article examines the operational, combustion, and emission characteristics of a small-scale combustor. Flue-gas composition data and hydroxyl radical chemiluminescence (OH*) imaging are reported as a function of the excess air coefficient (λ), which in the present configuration implies also changes in the inlet air velocity. For two of these combustor operating conditions, spatial distributions of temperature and of O2, CO2, unburned hydrocarbons, CO, and NOx concentrations are also reported. The OH* images showed that as λ increases the main reaction zone moves progressively closer to the burner presumably due to the increase in the central jet momentum, which leads to a faster entrainment of fuel and burnt gases, and due to the increase in the oxygen concentration in the recirculated flue-gas. The OH* images also reveal that the structure of the main reaction zone and the combustion regime change with λ. For low values of λ the reaction zone is uniformly distributed over a relatively large volume of the combustor (flameless combustion, also known as MILD combustion, HiTAC, or colorless distributed combustion), whereas for high values of λ, the OH* images suggest and still photographs confirm the presence of a flame front located at the strong shear region between the central jet and the external recirculation zone (conventional lean combustion). The present combustor yields very low NOx (< 10 ppm @ 15% O2) and CO emissions (< 12 ppm @ 15% O2) for all conditions studied, which is attributed to the suppression of the thermal mechanism brought about by the flameless oxidation and conventional lean combustion modes. Finally, the detailed measurements made inside the combustor for the two operating conditions, a flameless oxidation condition and a conventional lean combustion condition, confirmed the observations based on the OH* images.
Combustion Science and Technology, 2012
This article examines the combustion regimes occurring in a small-scale laboratory cylindrical co... more This article examines the combustion regimes occurring in a small-scale laboratory cylindrical combustor, in which the burner and the exhaust port are mounted at the top end of the combustion chamber. Flue-gas composition data and hydroxyl radical chemiluminescence (OH*) imaging are presented as a function of the air inlet preheat temperature and excess air coefficient, which in the present configuration implies also changes in the air inlet velocity. For three of these combustor operating conditions, detailed in-combustor measurements of temperature and of O2, CO2, CO, unburned hydrocarbons, and NOx concentrations are also reported. The flue-gas data reveal that, for a given air inlet preheat temperature, the air inlet velocity has an important impact on the NOx emissions, which decrease as the air inlet velocity increases. Furthermore, as the air inlet temperature increases, the burner is able to operate with higher excess air coefficients. For a given air inlet temperature, the combustion regime in the present combustor develops from conventional lean combustion at lower air inlet velocities (or lower excess air coefficients) to flameless combustion at higher air inlet velocities (or higher excess air coefficients). The OH* images and both the temperature and the chemistry fields indicate that the reaction zone for the conventional lean combustion regime is well defined and established near the burner with relatively high gradients along the combustion chamber length. In contrast, the flameless combustion regime, which occurs for higher reactants jet momenta, is characterized by a more distributed reaction zone, located far from the burner, as revealed by the chemiluminescence images that show relatively small gradients disperse over a large volume of the combustion chamber. In line with this, the spatial temperature and gas species concentration gradients are much lower in this case than in the case of the conventional lean combustion regime.
Anais do IX Congresso Nacional de Engenharia Mecânica, 2016
Using non-intrusive techniques to study physical and chemical properties of flames take to more r... more Using non-intrusive techniques to study physical and chemical properties of flames take to more realistic results. The tomographic backprojection algorithm together with the Algebraic Reconstruction Technique (ART), can reconstruct an object internal structure or properties of a restrict region of the space from their projection data. This work presents a few data tomography technique using the emission of light by a Bunsen burner laminar flame . The chemicals radicals in a flame emit light in a series of characteristics wavelength. With some CCD cameras and light filters one can mount a simple tomograph to obtain the bidimensional radicals distribution in a flame cross section through computerized tomography techniques (CT).
The combustion and pollutant characteristics of a small-scale laboratory combustor operating unde... more The combustion and pollutant characteristics of a small-scale laboratory combustor operating under flameless oxidation conditions are examined with the aid of OH* chemiluminescence images and measurements of local mean gas temperatures and local mean major gas species (O2, CO2, CO, unburnt hydrocarbons and NOx) concentrations along the combustor axis, as a function of the fuel (methane) thermal input, which was varied between 7 and 13 kW. The results show that the combustor, operating under flameless conditions, yields very low NOx (< 6 ppm@15% O2) and CO emissions (< 14 ppm@15% O2) regardless of the fuel thermal input. As the fuel thermal input increases, the main reaction zone, as typified by the OH* chemiluminescence intensities, enlarges and, simultaneously, moves progressively closer to the combustor exit mainly due to the increase in the central air jet momentum. Moreover, as the fuel thermal input increases the OH* intensity gradients within the increasingly larger reac...
Neste trabalho é apresentado um estudo sobre modelos matemáticos empregados na reconstrução bi-di... more Neste trabalho é apresentado um estudo sobre modelos matemáticos empregados na reconstrução bi-dimensional de propriedades físicas utilizando poucos ângulos de projeção. Para reconstruir tais propriedades utilizou-se os algoritmos de reconstrução tomográfica ART e SIRT que dependendo da modelagem empregada para descrever a área intersecção entre um raio e a região de reconstrução pode gerar resultados que não condizem com a realidade. Foram estudadas algumas decisões para a matriz que descreve a intersecção utilizando modelos matemáticos para testar a fidelidade de tais algoritmos. Estes modelos matemáticos utilizados na reconstrução também são chamados de fantasmas.
Anais do IX Congresso Nacional de Engenharia Mecânica, 2016
Combustion Science and Technology, 2016
ABSTRACT Steam gasification of crude glycerin was carried out in a laboratory packed bed reactor ... more ABSTRACT Steam gasification of crude glycerin was carried out in a laboratory packed bed reactor and the effects of the bed temperature and flow rate of glycerin on the yields and characteristics of the syngas produced were examined. The tests were performed at bed temperatures of 700°C, 800°C, and 900°C over a wide range of water to glycerin ratios (W/G) using aluminum oxide as a packing material. Subsequently, the influence of the glycerin flow rate was studied at a fixed bed temperature of 800°C and a W/G of 4. The main conclusions are: (1) as the bed temperature increases, the hydrogen and carbon dioxide contents increase, the carbon monoxide and methane contents decrease, the heating value of the syngas produced slightly reduces, and the syngas production augments; (2) the glycerin flow rate does not influence the syngas production nor its heating value up to a certain value beyond which the production drops and the heating value increases a little; and (3) the minimum water content required for steam gasification to take place without reactor blocking decreases as the bed temperature increases, and increasing the glycerin flow rate increases the risk of bed deposition for the same W/G ratio.
This article examines the flow, combustion and emission characteristics of a laboratory combustor... more This article examines the flow, combustion and emission characteristics of a laboratory combustor as a function of the inlet air velocity (V air). Variations in V air were accomplished by changing the air nozzle diameter while maintaining constant all remaining input parameters. Initially, laser-Doppler anemometry was employed to evaluate the combustor flow aerodynamics under non-reacting conditions. Subsequently, flue-gas composition data and hydroxyl radical chemiluminescence (OH*) imaging were obtained as a function of V air. For two of these combustor operating conditions, spatial distributions of temperature, recorded with fine wire thermocouples, and of O 2 , CO 2 , unburned hydrocarbons, CO and NO x concentrations, measured with the aid of a sampling probe, were also obtained. The OH* images showed that as V air increases at a constant excess air coefficient (λ) of 1.3, the main reaction zone, typical of flameless combustion condition, remains approximately in the same region of the combustor, because of the flow aerodynamics similarity, but the OH* intensities decrease, which indicates higher entrainment ratios of the fuel and burned gases by the central air jet. For λ greater than 1.7, however, flameless oxidation could not be established regardless of the air jet momentum. This suggests that the establishment of the flameless combustion condition in future gas turbines through the dilution of the reactants with a substantial amount of flue gases in configurations where the combustion air is provided by a central highmomentum air jet that is surrounded by a number of low-momentum fuel jets may be problematic.
Journal of Physics: Conference Series, 2012
This work reports numerical simulations of a small-scale cylindrical combustor operating in the m... more This work reports numerical simulations of a small-scale cylindrical combustor operating in the mild combustion regime. Preheated air is supplied by a central nozzle, while the fuel (methane) is injected through 16 holes placed equidistantly in a concentric circumference. The calculations were carried out using the commercial code Ansys-Fluent-v13. Turbulence was modelled using the realizable k-ε model. Three different combustion models were employed, namely the finite rate/eddy dissipation, the eddy dissipation concept and the joint composition probability density function transport model. A detailed chemical mechanism, SK-17 was used. Subsequently, the pre-heated air temperature influence is studied and compared with experimental measurements. The combustion models with the detailed mechanism are able to accurately predict the temperature and the O 2 and CO 2 molar fractions over most of the combustor. Regarding the pre-heated combustion air temperature influence, there is a decrease in the recirculation rate when that temperature is lower. When the air nozzle diameter decreases, the reaction occurs closer to the burner.
Fuel Processing Technology, 2013
ABSTRACT The reaction zone of a small-scale laboratory combustor operating under flameless oxidat... more ABSTRACT The reaction zone of a small-scale laboratory combustor operating under flameless oxidation conditions is examined with the aid of hydroxyl radical chemiluminescence (OH*) imaging and measurements of local mean gas temperatures and local mean major gas species (O2, CO2, CO, unburnt hydrocarbons and NOx) concentrations along the combustor axis, as a function of the fuel (methane) thermal input, which was varied between 7 and 13 kW. As the fuel thermal input increases, the reaction zone, as typified by the OH* distribution, enlarges and, simultaneously, moves progressively closer to the combustor exit (exhaust) due to the increase in the central jet momentum, while maintaining constant the excess air level. The excess air values used in the present study were low enough to preserve the flameless combustion regime regardless of the fuel thermal input, with the combustor yielding very low NOx (< 6 ppm@15% O2) and CO emissions (< 14 ppm@15% O2) regardless of the fuel thermal input. The low NOx emissions, almost independent of the fuel thermal input, are attributed to the suppression of the thermal mechanism promoted by the flameless oxidation regime. Despite being always low, the CO emissions increase with the fuel thermal input presumably because of the lower residence times associated with the higher burner thermal loads.
Experimental Thermal and Fluid Science, 2013
This article examines the importance of the inlet air velocity (V air) on the establishment of fl... more This article examines the importance of the inlet air velocity (V air) on the establishment of flameless combustion in a 10 kW laboratory scale combustor. Variations in V air were accomplished by changing the air nozzle diameter while maintaining constant all remaining input parameters. Initially, laser-Doppler anemometry was employed to evaluate the combustor flow aerodynamics under non-reacting conditions. Subsequently, flue-gas composition data and hydroxyl radical chemiluminescence (OH Ã) imaging were obtained as a function of V air. For two of these combustor operating conditions, spatial distributions of temperature, recorded with fine wire thermocouples, and of O 2 , CO 2 , unburned hydrocarbons, CO and NO x concentrations, measured with the aid of a sampling probe, were also obtained. The OH Ã images showed that as V air increases at a constant excess air coefficient (k) of 1.3, the main reaction zone, typical of flameless combustion condition, remains approximately in the same region of the combustor, because of the flow aerodynamics similarity, but the OH Ã intensities decrease, which indicates higher entrainment ratios of the fuel and burned gases by the central air jet. For k greater than 1.7, however, flameless oxidation could not be established regardless of the air jet momentum. This suggests that the establishment of the flameless combustion condition in future gas turbines through the dilution of the reactants with a substantial amount of flue gases in configurations where the combustion air is provided by a central highmomentum air jet that is surrounded by a number of low-momentum fuel jets may be problematic.
Energy & Fuels, 2011
ABSTRACT This article examines the operational, combustion, and emission characteristics of a sma... more ABSTRACT This article examines the operational, combustion, and emission characteristics of a small-scale combustor. Flue-gas composition data and hydroxyl radical chemiluminescence (OH*) imaging are reported as a function of the excess air coefficient (λ), which in the present configuration implies also changes in the inlet air velocity. For two of these combustor operating conditions, spatial distributions of temperature and of O2, CO2, unburned hydrocarbons, CO, and NOx concentrations are also reported. The OH* images showed that as λ increases the main reaction zone moves progressively closer to the burner presumably due to the increase in the central jet momentum, which leads to a faster entrainment of fuel and burnt gases, and due to the increase in the oxygen concentration in the recirculated flue-gas. The OH* images also reveal that the structure of the main reaction zone and the combustion regime change with λ. For low values of λ the reaction zone is uniformly distributed over a relatively large volume of the combustor (flameless combustion, also known as MILD combustion, HiTAC, or colorless distributed combustion), whereas for high values of λ, the OH* images suggest and still photographs confirm the presence of a flame front located at the strong shear region between the central jet and the external recirculation zone (conventional lean combustion). The present combustor yields very low NOx (< 10 ppm @ 15% O2) and CO emissions (< 12 ppm @ 15% O2) for all conditions studied, which is attributed to the suppression of the thermal mechanism brought about by the flameless oxidation and conventional lean combustion modes. Finally, the detailed measurements made inside the combustor for the two operating conditions, a flameless oxidation condition and a conventional lean combustion condition, confirmed the observations based on the OH* images.
Combustion Science and Technology, 2012
This article examines the combustion regimes occurring in a small-scale laboratory cylindrical co... more This article examines the combustion regimes occurring in a small-scale laboratory cylindrical combustor, in which the burner and the exhaust port are mounted at the top end of the combustion chamber. Flue-gas composition data and hydroxyl radical chemiluminescence (OH*) imaging are presented as a function of the air inlet preheat temperature and excess air coefficient, which in the present configuration implies also changes in the air inlet velocity. For three of these combustor operating conditions, detailed in-combustor measurements of temperature and of O2, CO2, CO, unburned hydrocarbons, and NOx concentrations are also reported. The flue-gas data reveal that, for a given air inlet preheat temperature, the air inlet velocity has an important impact on the NOx emissions, which decrease as the air inlet velocity increases. Furthermore, as the air inlet temperature increases, the burner is able to operate with higher excess air coefficients. For a given air inlet temperature, the combustion regime in the present combustor develops from conventional lean combustion at lower air inlet velocities (or lower excess air coefficients) to flameless combustion at higher air inlet velocities (or higher excess air coefficients). The OH* images and both the temperature and the chemistry fields indicate that the reaction zone for the conventional lean combustion regime is well defined and established near the burner with relatively high gradients along the combustion chamber length. In contrast, the flameless combustion regime, which occurs for higher reactants jet momenta, is characterized by a more distributed reaction zone, located far from the burner, as revealed by the chemiluminescence images that show relatively small gradients disperse over a large volume of the combustion chamber. In line with this, the spatial temperature and gas species concentration gradients are much lower in this case than in the case of the conventional lean combustion regime.
Anais do IX Congresso Nacional de Engenharia Mecânica, 2016
Using non-intrusive techniques to study physical and chemical properties of flames take to more r... more Using non-intrusive techniques to study physical and chemical properties of flames take to more realistic results. The tomographic backprojection algorithm together with the Algebraic Reconstruction Technique (ART), can reconstruct an object internal structure or properties of a restrict region of the space from their projection data. This work presents a few data tomography technique using the emission of light by a Bunsen burner laminar flame . The chemicals radicals in a flame emit light in a series of characteristics wavelength. With some CCD cameras and light filters one can mount a simple tomograph to obtain the bidimensional radicals distribution in a flame cross section through computerized tomography techniques (CT).
The combustion and pollutant characteristics of a small-scale laboratory combustor operating unde... more The combustion and pollutant characteristics of a small-scale laboratory combustor operating under flameless oxidation conditions are examined with the aid of OH* chemiluminescence images and measurements of local mean gas temperatures and local mean major gas species (O2, CO2, CO, unburnt hydrocarbons and NOx) concentrations along the combustor axis, as a function of the fuel (methane) thermal input, which was varied between 7 and 13 kW. The results show that the combustor, operating under flameless conditions, yields very low NOx (< 6 ppm@15% O2) and CO emissions (< 14 ppm@15% O2) regardless of the fuel thermal input. As the fuel thermal input increases, the main reaction zone, as typified by the OH* chemiluminescence intensities, enlarges and, simultaneously, moves progressively closer to the combustor exit mainly due to the increase in the central air jet momentum. Moreover, as the fuel thermal input increases the OH* intensity gradients within the increasingly larger reac...
Neste trabalho é apresentado um estudo sobre modelos matemáticos empregados na reconstrução bi-di... more Neste trabalho é apresentado um estudo sobre modelos matemáticos empregados na reconstrução bi-dimensional de propriedades físicas utilizando poucos ângulos de projeção. Para reconstruir tais propriedades utilizou-se os algoritmos de reconstrução tomográfica ART e SIRT que dependendo da modelagem empregada para descrever a área intersecção entre um raio e a região de reconstrução pode gerar resultados que não condizem com a realidade. Foram estudadas algumas decisões para a matriz que descreve a intersecção utilizando modelos matemáticos para testar a fidelidade de tais algoritmos. Estes modelos matemáticos utilizados na reconstrução também são chamados de fantasmas.