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Prof. Mário Costa
Instituto Superior Técnico, University of Lisbon, 1000-001 Lisbon, Portugal

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0 Gas Turbines
0 New Concepts
0 heterogeneous processes
0 Conventional and alternative fuels
0 Particulate and aerosol formation and abatement

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Gas Turbines
Small- and large-scale stationary combustion and power generation

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Review article
Published: 08 March 2021 in Journal of Cleaner Production
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Ammonia and hydrogen carry great potential as carbon-free fuels with promising applications in energy systems. Hydrogen, in particular, has been generating massive expectations as a carbon-free economy enabler, but issues related to storage, distribution, and infrastructure deployment are delaying its full implementation. Ammonia, on the other hand, stands as a highly efficient energy vector delivering high energy density and an established and flexible infrastructure capable of mitigating hydrogen’s key drawbacks. This mature infrastructure together with the possibility of producing ammonia through renewable energy sources triggered an exploring route to the transition of ammonia as the next sustainable fuel solution for power generation. In this regard, the transportation sector as one of the main culprits for carbon emissions can benefit from ammonia-powered internal combustion engines. However, the use of pure ammonia as fuel still presents important constraints leading researchers to develop strategies such as dual-fuel concepts or novel combustion approaches. Therefore, this review covers these issues by delving into the underpinning mechanisms required for developing pure ammonia combustion in internal combustion engines. To do so, fundamentals, technical, environmental, and economic aspects associated with the use of ammonia as a transportation fuel are broadly addressed. While the emphasis is given to pure ammonia and ammonia fuel blends operation, NOx emissions control, current challenges related to the detailed and accurate understanding of the ammonia chemistry, and the lack of high-fidelity numerical models are also deeply discussed on their role into aiding the commercial deployment of this technology.

ACS Style

João Sousa Cardoso; Valter Silva; Rodolfo C. Rocha; Matthew J. Hall; Mário Costa; Daniela Eusébio. Ammonia as an energy vector: Current and future prospects for low-carbon fuel applications in internal combustion engines. Journal of Cleaner Production 2021, 296, 126562 .

AMA Style

João Sousa Cardoso, Valter Silva, Rodolfo C. Rocha, Matthew J. Hall, Mário Costa, Daniela Eusébio. Ammonia as an energy vector: Current and future prospects for low-carbon fuel applications in internal combustion engines. Journal of Cleaner Production. 2021; 296 ():126562.

Chicago/Turabian Style

João Sousa Cardoso; Valter Silva; Rodolfo C. Rocha; Matthew J. Hall; Mário Costa; Daniela Eusébio. 2021. "Ammonia as an energy vector: Current and future prospects for low-carbon fuel applications in internal combustion engines." Journal of Cleaner Production 296, no. : 126562.

Review
Published: 28 February 2021 in Energy & Fuels
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ACS Style

A. Valera-Medina; F. Amer-Hatem; A. K. Azad; I. C. Dedoussi; M. de Joannon; R. X. Fernandes; P. Glarborg; H. Hashemi; X. He; S. Mashruk; J. McGowan; C. Mounaim-Rouselle; A. Ortiz-Prado; A. Ortiz-Valera; I. Rossetti; B. Shu; M. Yehia; H. Xiao; M. Costa. Review on Ammonia as a Potential Fuel: From Synthesis to Economics. Energy & Fuels 2021, 35, 6964 -7029.

AMA Style

A. Valera-Medina, F. Amer-Hatem, A. K. Azad, I. C. Dedoussi, M. de Joannon, R. X. Fernandes, P. Glarborg, H. Hashemi, X. He, S. Mashruk, J. McGowan, C. Mounaim-Rouselle, A. Ortiz-Prado, A. Ortiz-Valera, I. Rossetti, B. Shu, M. Yehia, H. Xiao, M. Costa. Review on Ammonia as a Potential Fuel: From Synthesis to Economics. Energy & Fuels. 2021; 35 (9):6964-7029.

Chicago/Turabian Style

A. Valera-Medina; F. Amer-Hatem; A. K. Azad; I. C. Dedoussi; M. de Joannon; R. X. Fernandes; P. Glarborg; H. Hashemi; X. He; S. Mashruk; J. McGowan; C. Mounaim-Rouselle; A. Ortiz-Prado; A. Ortiz-Valera; I. Rossetti; B. Shu; M. Yehia; H. Xiao; M. Costa. 2021. "Review on Ammonia as a Potential Fuel: From Synthesis to Economics." Energy & Fuels 35, no. 9: 6964-7029.

Research article
Published: 25 January 2021 in Energy & Fuels
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The environmental impact and the dependence upon fossil fuels in the aeronautical sector have promoted the demand for alternative and greener fuels. The implementation of alternative fuels is one of the main challenges for this sector in the near future. A possible short-term solution might be the blending of biofuels with jet fuel, which would allow for the use of greener fuels and a reduction in the greenhouse gases and pollutant emissions without significant changes in the existing fleets of the companies, with the purpose to develop a “drop-in” fuel. In this context, this work examines the combustion characteristics of single droplets of Jet A-1 (JF), hydroprocessed vegetable oil (NExBTL), and their mixtures in a drop-tube furnace (DTF). The objective of this work is to evaluate the influence of the mixture composition on the fuel characteristics. Droplets with diameters of 155 ± 5 μm, produced by a commercial droplet generator, were injected into the DTF, whose wall temperature and oxygen concentration were controlled. Experiments were conducted for three temperatures (900, 1000, and 1100 °C). The combustion of droplets was evaluated through the images obtained with a high-speed camera coupled with a high magnification lens and an edge detection algorithm. From the images allowed for the analysis of droplet combustion, data are reported for the temporal evolution of droplet sizes and burning rates. The results revealed that the mixtures followed the D2 law, except the mixture with 75% JF for a DTF wall temperature of 1100 °C. The 75% JF mixture did not follow the D2 law as a result of the occurrence of puffing and microexplosions, which enhanced the burning rates. Additionally, it was observed that the mixtures with a higher content of JF present brighter flames and higher burning rates.

ACS Style

Gonçalo Pacheco; André Silva; Mário Costa. Single-Droplet Combustion of Jet A-1, Hydroprocessed Vegetable Oil, and Their Blends in a Drop-Tube Furnace. Energy & Fuels 2021, 35, 7232 -7241.

AMA Style

Gonçalo Pacheco, André Silva, Mário Costa. Single-Droplet Combustion of Jet A-1, Hydroprocessed Vegetable Oil, and Their Blends in a Drop-Tube Furnace. Energy & Fuels. 2021; 35 (9):7232-7241.

Chicago/Turabian Style

Gonçalo Pacheco; André Silva; Mário Costa. 2021. "Single-Droplet Combustion of Jet A-1, Hydroprocessed Vegetable Oil, and Their Blends in a Drop-Tube Furnace." Energy & Fuels 35, no. 9: 7232-7241.

Research article
Published: 22 January 2021 in Energy & Fuels
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This paper presents a joint experimental and numerical study on premixed laminar ammonia/methane/air flames, aiming to characterize the flame structures and NO formation and determine the laminar flame speed under different pressure, equivalence ratio, and ammonia fraction in the fuel. The experiments were carried out in a lab-scale pressurized vessel with a Bunsen burner installed with a concentric co-flow of air. Measurements of NH and NO distributions in the flames were made using planar laser-induced fluorescence. A novel method was presented for determination of the laminar flame speed from Bunsen-burner flame measurements, which takes into account the non-uniform flow in the unburned mixture and local flame stretch. NH profiles were chosen as flame front markers. Direct numerical simulation of the flames and one-dimensional chemical kinetic modeling were performed to enhance the understanding of flame structures and evaluate three chemical kinetic mechanisms recently reported in the literature. The stoichiometric and fuel-rich flames exhibit a dual-flame structure, with an inner premixed flame and an outer diffusion flame. The two flames interact, which affects the NO emissions. The impact of the diffusion flame on the laminar flame speed of the inner premixed flame is however minor. At elevated pressures or higher ammonia/methane ratios, the emission of NO is suppressed as a result of the reduced radical mass fraction and promoted NO reduction reactions. It is found that the laminar flame speed measured in the present experiments can be captured by the investigated mechanisms, but quantitative predictions of the NO distribution require further model development.

ACS Style

Rodolfo C. Rocha; Shenghui Zhong; Leilei Xu; Xue-Song Bai; Mário Costa; Xiao Cai; Haisol Kim; Christian Brackmann; Zhongshan Li; Marcus Aldén. Structure and Laminar Flame Speed of an Ammonia/Methane/Air Premixed Flame under Varying Pressure and Equivalence Ratio. Energy & Fuels 2021, 35, 7179 -7192.

AMA Style

Rodolfo C. Rocha, Shenghui Zhong, Leilei Xu, Xue-Song Bai, Mário Costa, Xiao Cai, Haisol Kim, Christian Brackmann, Zhongshan Li, Marcus Aldén. Structure and Laminar Flame Speed of an Ammonia/Methane/Air Premixed Flame under Varying Pressure and Equivalence Ratio. Energy & Fuels. 2021; 35 (9):7179-7192.

Chicago/Turabian Style

Rodolfo C. Rocha; Shenghui Zhong; Leilei Xu; Xue-Song Bai; Mário Costa; Xiao Cai; Haisol Kim; Christian Brackmann; Zhongshan Li; Marcus Aldén. 2021. "Structure and Laminar Flame Speed of an Ammonia/Methane/Air Premixed Flame under Varying Pressure and Equivalence Ratio." Energy & Fuels 35, no. 9: 7179-7192.

Journal article
Published: 12 January 2021 in Energies
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The main purpose of the present work was to evaluate the efficiency of the gasification process of three different types of agro-forest biomass residue (rapeseed, softwood, and sunflower husks) along with the characterization of size-segregated particulates’ emissions. The experiments were carried out in a drop tube furnace (DTF), using two different gasifying agents (O2/N2 and O2/N2/CO2) at atmospheric pressure and a constant temperature of 1000 °C. In focus was the effect of biomass and the gasifying agent on syngas composition (CO, H2, CH4, and CO2), cold gas and carbon conversion efficiency, and on the emissions of by-products, such as particulate matter (PM), known for having negative environmental and health impacts. The collected particulates were characterized by SEM/EDS and XPS analysis. The results reveal that: (i) the introduction of CO2 increased the production of CO and CH4 and syngas’ lower heating value (LHV), thus leading to higher cold gas and carbon conversion efficiency; (ii) CO2 decreased the production of H2, leading to lower H2/CO ratio (between 0.25 and 0.9). Therefore, the generated syngas is suitable for the synthesis of higher hydrocarbons, (iii) CO2 lowered the emissions of char (cyclone) particles but increased the overall PM10–0.3. Submicron size PM was the dominant fraction (PM1–0.3) in O2/N2 and (PM1.6–0.3) in O2/N2/CO2. Unimodal PM size distribution was observed, except for sunflower husks gasification in O2/N2/CO2; (iv) the SEM/EDS and XPS analysis confirmed that submicron-sized PM1–0.3 contain above 80% of carbon associated to soot, due to incomplete oxidation, whereas in cyclone (char) particles, carbon decreased to about 50%. The SEM/EDS results showed that K and Cl are typical constituents of the submicron size PM, whereas the alkaline earth metals were detected mainly in fine and coarse particulates. Detailed analysis of the XPS (C1s) spectra showed that the most common oxygen-containing groups on the PM1 surface were carbonyl and carboxyl.

ACS Style

Ricardo Ferreira; Tsvetelina Petrova; Ana F. Ferreira; Mário Costa; Iliyana Inaydenova; Stela Atanasova-Vladimirova; Bogdan Ranguelov. Size-Segregated Particulate Matter from Gasification of Bulgarian Agro-Forest Biomass Residue. Energies 2021, 14, 385 .

AMA Style

Ricardo Ferreira, Tsvetelina Petrova, Ana F. Ferreira, Mário Costa, Iliyana Inaydenova, Stela Atanasova-Vladimirova, Bogdan Ranguelov. Size-Segregated Particulate Matter from Gasification of Bulgarian Agro-Forest Biomass Residue. Energies. 2021; 14 (2):385.

Chicago/Turabian Style

Ricardo Ferreira; Tsvetelina Petrova; Ana F. Ferreira; Mário Costa; Iliyana Inaydenova; Stela Atanasova-Vladimirova; Bogdan Ranguelov. 2021. "Size-Segregated Particulate Matter from Gasification of Bulgarian Agro-Forest Biomass Residue." Energies 14, no. 2: 385.

Conference paper
Published: 07 October 2020 in Proceedings of the Combustion Institute
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This study reports the effects of gas preheat temperature on soot formation in a series of methane (CH4), ethylene (C2H4) and nitrogen-diluted C2H4 co-flow diffusion flames with a constant mass flow rate of carbon element. The flames were established in a Santoro-type burner and the temperatures of co-flow air and fuel were varied simultaneously from 293 K to 723 K. Planar distributions of soot volume fraction and soot temperature were measured using laser-induced incandescence and two-color pyrometry based on incandescence, respectively. The results show that the preheat temperature of gases has no significant effect on the shape of the CH4 and nitrogen-diluted C2H4 flames, but significantly influences that of the C2H4 flames with high soot loadings. With an increase in gas preheat temperature, both soot formation and oxidation are enhanced and soot loading increases for all flames. The magnitude of enhancement correlates with the soot loading, while the effect is more significant in the flames with lower soot loading. Soot temperature in the CH4 and nitrogen-diluted C2H4 flames also increases but is not as much as the change in the gas preheat temperature. However, for the C2H4 flames, an inverse tend is found in the central region of the flames, i.e., that lower soot temperatures are found in the flame with the higher gas preheat temperature.

ACS Style

Sheng Qi; Zhiwei Sun; Zhihua Wang; YingZu Liu; Yong He; Siyu Liu; Kaidi Wan; Graham J. Nathan; Mário Costa. Effects of gas preheat temperature on soot formation in co-flow methane and ethylene diffusion flames. Proceedings of the Combustion Institute 2020, 38, 1225 -1232.

AMA Style

Sheng Qi, Zhiwei Sun, Zhihua Wang, YingZu Liu, Yong He, Siyu Liu, Kaidi Wan, Graham J. Nathan, Mário Costa. Effects of gas preheat temperature on soot formation in co-flow methane and ethylene diffusion flames. Proceedings of the Combustion Institute. 2020; 38 (1):1225-1232.

Chicago/Turabian Style

Sheng Qi; Zhiwei Sun; Zhihua Wang; YingZu Liu; Yong He; Siyu Liu; Kaidi Wan; Graham J. Nathan; Mário Costa. 2020. "Effects of gas preheat temperature on soot formation in co-flow methane and ethylene diffusion flames." Proceedings of the Combustion Institute 38, no. 1: 1225-1232.

Conference paper
Published: 26 September 2020 in Proceedings of the Combustion Institute
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This work investigated the combustion characteristics of single pulverized biomass-derived char particles. The char particles, in the size range 224–250 µm, were prepared in a drop tube furnace at pyrolysis temperatures of 1273 or 1473 K from four types of biomass particles – wheat straw, grape pomace, kiwi branches and rice husk. Subsequently, the char particles were injected upward into a confined region of hot combustion products produced by flat flames stabilized on a McKenna burner, with mean temperatures of 1460, 1580 and 1670 K and mean O2 concentrations of 4.5, 6.5 and 8.5 vol%. The data reported include particle temperature, obtained using a two-color pyrometry technique, and potassium release rate, measured using a laser-induced photofragmentation fluorescence imaging technique. In addition, particle ignition delay time and burning time, obtained from the temporal evolution of the thermal radiation intensity of the burning char particles, are also reported. The results indicated that ignition of the char particles occurs simultaneously with the starting of the potassium release, then the particle burning intensity increases rapidly until it reaches a maximum, after which both the particle temperature and the potassium release rate remain approximately constant until the end of the char oxidation process. The char ignition process is temperature controlled, and the char oxidation process is oxygen diffusion controlled, with the total potassium release being independent of the oxygen concentration and the temperature of the combustion products. The combustion behavior of the chars studied is more affected by the char type than by the conditions used to prepare them.

ACS Style

Wubin Weng; Shen Li; Mário Costa; Zhongshan Li. Particle temperature and potassium release during combustion of single pulverized biomass char particles. Proceedings of the Combustion Institute 2020, 38, 3949 -3958.

AMA Style

Wubin Weng, Shen Li, Mário Costa, Zhongshan Li. Particle temperature and potassium release during combustion of single pulverized biomass char particles. Proceedings of the Combustion Institute. 2020; 38 (3):3949-3958.

Chicago/Turabian Style

Wubin Weng; Shen Li; Mário Costa; Zhongshan Li. 2020. "Particle temperature and potassium release during combustion of single pulverized biomass char particles." Proceedings of the Combustion Institute 38, no. 3: 3949-3958.

Conference paper
Published: 10 September 2020 in Proceedings of the Combustion Institute
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Ammonia (NH3) is considered as a promising carbon free energy carrier for energy and transportation systems. However, its low flammability and high NOx emission potential inhibit the implementation of pure NH3 in these systems. On the other hand, methane is a favorable low emission fuel that can be used as a co-firing fuel in ammonia combustion to promote the reactivity and control the emission levels. However, knowledge of the ignition properties of NH3/CH4 mixtures at intermediate temperatures and elevated pressures is still scarce. This study reports ignition delay times of NH3/CH4/O2 mixtures diluted in Ar or Ar/N2 over a temperature range of 900–1100 K, pressures of 20 and 40 bar, and equivalence ratios of 0.5, 1.0, and 2.0. The results demonstrate that a higher CH4 mole fraction in the fuel mixture increases its reactivity, and that the reactivity decreases with increasing the fuel-oxygen equivalence ratio. The most recent mechanisms of Glarborg et al. (2018) and Li et al. (2019) were compared against the experimental data for validation purposes. Both mechanisms can predict the measurements fairly well, and key elementary reactions applied in both mechanisms were compared. A modified mechanism is provided, which can reproduce the measurements with smaller discrepancies in most cases. Detailed modeling for emissions indicated that adding CH4 to the fuel mixture increases the emission of NOx.

ACS Style

B. Shu; X. He; C.F. Ramos; R.X. Fernandes; M. Costa. Experimental and modeling study on the auto-ignition properties of ammonia/methane mixtures at elevated pressures. Proceedings of the Combustion Institute 2020, 38, 261 -268.

AMA Style

B. Shu, X. He, C.F. Ramos, R.X. Fernandes, M. Costa. Experimental and modeling study on the auto-ignition properties of ammonia/methane mixtures at elevated pressures. Proceedings of the Combustion Institute. 2020; 38 (1):261-268.

Chicago/Turabian Style

B. Shu; X. He; C.F. Ramos; R.X. Fernandes; M. Costa. 2020. "Experimental and modeling study on the auto-ignition properties of ammonia/methane mixtures at elevated pressures." Proceedings of the Combustion Institute 38, no. 1: 261-268.

Conference paper
Published: 20 August 2020 in Proceedings of the Combustion Institute
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Combustion of ammonia (NH3) presents a number of challenges due to its low reactivity, poor flame stability, very low flame speed and high NOx emissions in a range of burning conditions. Therefore, its application in combustion systems requires device modifications, either by adapting existing systems or developing new ones. In this work, a novel combustor fired by a swirl and bluff-body stabilized burner was designed and tested. Initially, flame stability diagrams were established for NH3/H2 fuel mixtures. Then, emissions of NOx and unburnt NH3 were measured for a range of equivalence ratios and NH3 mole fractions in the fuel mixture. In addition, in-flame data for O2 and NOx concentrations and gas temperature were measured for five combustor operating conditions. A parallel mathematical modelling exercise was performed to obtain a qualitative knowledge of the burner aerodynamics and assist the interpretation of the experimental results. The predicted aerodynamic pattern suggests the establishment of an extended central recirculation zone that allows long residence times in the near burner region (NBR) that are critical to ensure stable combustion of the NH3/H2/air mixtures. The measurements revealed that the burner presents a wide range of stable flames for xNH3 between 0.6 and 0.8, showing the positive effects of adding relatively small amounts of H2 to the fuel mixture. The in-flame data show that the flame initiates close to the burner inlet and presents two main reaction zones. NOx is formed in the NBR and is consumed afterwards, through selective non-catalytic reduction reactions. Overall, the present laboratory combustor performs well in terms of flame stability and both NOx and NH3 emissions, and it is foreseen that industrial combustors based on the present design would be able to ensure flame stability and NOx and NH3 emissions control with simple complementary systems.

ACS Style

Miguel C. Franco; Rodolfo C. Rocha; Mário Costa; Mohamed Yehia. Characteristics of NH3/H2/air flames in a combustor fired by a swirl and bluff-body stabilized burner. Proceedings of the Combustion Institute 2020, 38, 5129 -5138.

AMA Style

Miguel C. Franco, Rodolfo C. Rocha, Mário Costa, Mohamed Yehia. Characteristics of NH3/H2/air flames in a combustor fired by a swirl and bluff-body stabilized burner. Proceedings of the Combustion Institute. 2020; 38 (4):5129-5138.

Chicago/Turabian Style

Miguel C. Franco; Rodolfo C. Rocha; Mário Costa; Mohamed Yehia. 2020. "Characteristics of NH3/H2/air flames in a combustor fired by a swirl and bluff-body stabilized burner." Proceedings of the Combustion Institute 38, no. 4: 5129-5138.

Conference paper
Published: 31 July 2020 in Proceedings of the Combustion Institute
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In this paper, the interaction between different organic and inorganic K/S/Cl compounds in the solid structure of biomass is studied and a model is presented to predict the temporal release of Kg, HCl, CH3Cl, KCl, KOH, K2SO4 and SO2 from biomass devolatilization. Four types of pulverized biomass are chosen from literature, two of which have no chlorine content and two with chlorine content in lower stoichiometry to potassium. The results of the model are compared with the experimental measurements. In the presence of chlorine, KCl, HCl and Kg were found to be the dominant chlorine and potassium species. In the absence of chlorine, Kg dominates the release of potassium. KOH and K2SO4 release into the gas phase towards the end of devolatilization due to the overlapping with char combustion. SO2 is the main sulfur species released into the gas phase. The model is coupled with a CFD solver where the gas phase chemistry of the K/S/Cl system can be studied using available chemical mechanisms for these species.

ACS Style

Hesameddin Fatehi; Mário Costa; Xue-Song Bai. Numerical study on K/S/Cl release during devolatilization of pulverized biomass at high temperature. Proceedings of the Combustion Institute 2020, 38, 3909 -3917.

AMA Style

Hesameddin Fatehi, Mário Costa, Xue-Song Bai. Numerical study on K/S/Cl release during devolatilization of pulverized biomass at high temperature. Proceedings of the Combustion Institute. 2020; 38 (3):3909-3917.

Chicago/Turabian Style

Hesameddin Fatehi; Mário Costa; Xue-Song Bai. 2020. "Numerical study on K/S/Cl release during devolatilization of pulverized biomass at high temperature." Proceedings of the Combustion Institute 38, no. 3: 3909-3917.

Journal article
Published: 24 July 2020 in Fuel
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Biomass gasification offers a significant potential to close the loop of agriculture and many other activities that produce biomass residues. Pig manure, a residue produced in farms, has a huge pollutant potential due to its high production and chemical characteristics. It is necessary to take some control measures to decrease it, being pig manure gasification an interesting option. The present work studies the impact of the gasification temperature and atmosphere on the syngas composition (CO, H2, CH4 and CO2) and formation of soot and char in the gasification of pig manure in a drop tube furnace. The temperature varied between 900 and 1200 °C, and the gasification atmospheres included mixtures of O2/N2, O2/CO2/N2 and O2/H2O/N2. The results revealed that i) the syngas H2/CO ratio and its low heating value increase as the gasification temperature increases regardless of the gasification atmosphere; ii) the addition of H2O to the O2/N2 gasification atmosphere augments significantly the syngas H2/CO ratio, but does not enhance its low heating value, while the addition of CO2 increases slightly the H2/CO ratio, but significantly the heating value, iii) for the present reactor, the optimum operating conditions for the gasification of the pig manure in terms of syngas heating value and yield are a gasification temperature of 1200 °C and a gasification atmosphere composed of a mixture of O2/CO2/N2; and iv) soot yields increase as the temperature increases when gasification occurs in the O2/N2 and O2/CO2/N2 environments, remaining almost constant in the O2/H2O/N2 environment.

ACS Style

I. Adánez-Rubio; R. Ferreira; T. Rio; M.U. Alzueta; M. Costa. Soot and char formation in the gasification of pig manure in a drop tube reactor. Fuel 2020, 281, 118738 .

AMA Style

I. Adánez-Rubio, R. Ferreira, T. Rio, M.U. Alzueta, M. Costa. Soot and char formation in the gasification of pig manure in a drop tube reactor. Fuel. 2020; 281 ():118738.

Chicago/Turabian Style

I. Adánez-Rubio; R. Ferreira; T. Rio; M.U. Alzueta; M. Costa. 2020. "Soot and char formation in the gasification of pig manure in a drop tube reactor." Fuel 281, no. : 118738.

Journal article
Published: 16 June 2020 in Journal of Analytical and Applied Pyrolysis
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The present work studies the effects of the crystallinity level of cellulose on the primary reactions during the slow and fast pyrolysis conducted in a wire-mesh reactor at 40 °C/min and 6000 °C/min, respectively. The sugars present in the water-soluble intermediates were analysed in a chromatogram equipped with a Q-exactive high-resolution mass spectrometer. The products in the washed primary tars were quantified through GC/MS. Slow pyrolysis experiments were also performed in a thermogravimetric analyser at four different heating rates (5, 10, 20 and 40 °C/min). All experimental data was used to develop a modified kinetic model that considers the effects of crystallinity on cellulose pyrolysis, which is based on the cellulose sub-mechanism of the Bio-PoliMi kinetic model. The kinetic parameters of each reaction in the modified model were calibrated using a two-step fitting procedure. The experimental results show that low crystallinity promotes the dehydration reactions in the cellulose solid base and the formation of oligosaccharides in the water-soluble reaction intermediates, increasing the formation of furans and decreasing that of levoglucosan in the final primary tar. The effect of crystallinity on the pyrolysis characteristics of cellulose is weaker during fast pyrolysis than during slow pyrolysis. The isoconversional kinetic approach of cellulose pyrolysis presents a low initial activation energy of the pyrolysis of amorphous cellulose, which is close to the activation energy of cellulose hydrolysis. Assuming that the amorphous region of cellulose decomposition path prefers depolymerization through hydrolysis accompanied by the dehydration of nearby hydroxyl group, the modified kinetic model succeeds to predict the effect of crystallinity on the thermal stability and the yields of char, levoglucosan and furans during cellulose pyrolysis.

ACS Style

E. Leng; Ana Isabel Ferreiro; T. Liu; X. Gong; M. Costa; X. Li; M. Xu. Experimental and kinetic modelling investigation on the effects of crystallinity on cellulose pyrolysis. Journal of Analytical and Applied Pyrolysis 2020, 152, 104863 .

AMA Style

E. Leng, Ana Isabel Ferreiro, T. Liu, X. Gong, M. Costa, X. Li, M. Xu. Experimental and kinetic modelling investigation on the effects of crystallinity on cellulose pyrolysis. Journal of Analytical and Applied Pyrolysis. 2020; 152 ():104863.

Chicago/Turabian Style

E. Leng; Ana Isabel Ferreiro; T. Liu; X. Gong; M. Costa; X. Li; M. Xu. 2020. "Experimental and kinetic modelling investigation on the effects of crystallinity on cellulose pyrolysis." Journal of Analytical and Applied Pyrolysis 152, no. : 104863.

Research article
Published: 26 May 2020 in Energy & Fuels
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Fast pyrolysis of two biomass materials (mallee wood and pine wood) at 1300 °C was conducted in a novel drop-tube furnace (DTF) with a double-tube configuration, which enables the direct determination of char yields. Three particle sizes (90-106 µm, 150-250 µm, 250-355 µm) were considered for investigating the effect of particle size on char yield, retention of alkali and alkaline earth metallic (AAEM) species and shape of derived char particles from pyrolysis at such a high temperature. The experimental results show that the char yield increases with the biomass particle size, and that the use of the ash tracer method with total ash, Mg and Ca as tracer can substantially overestimate the char yield by as high as 4.0% (absolute error) at actual char yields of merely ~1.0-3.4%. Additionally, a decrease in particle size significantly enhances the release of AAEM species during biomass pyrolysis. Such observations can be at least attributed to the considerably-higher heating rate experienced by small particles during rapid pyrolysis, which is estimated to be 5.4 times of that experienced by large particles. For mallee wood, rapid pyrolysis of small biomass particles (90-106 µm) forms near-spherical char particles while that of large biomass particles (250-355 µm) tend to retain their elongated shape. This is due to extensive melting of small particles during rapid pyrolysis at 1300 °C, while large biomass particles only experience partial melting. For pine wood, particle size has no obvious effect on particle shape of pine chars that are mainly cenospheres with smooth surfaces, demonstrating severe melting of the cell structure.

ACS Style

Qiqing Shen; Sui Boon Liaw; Mário Costa; Hongwei Wu. Rapid Pyrolysis of Pulverized Biomass at a High Temperature: The Effect of Particle Size on Char Yield, Retentions of Alkali and Alkaline Earth Metallic Species, and Char Particle Shape. Energy & Fuels 2020, 34, 7140 -7148.

AMA Style

Qiqing Shen, Sui Boon Liaw, Mário Costa, Hongwei Wu. Rapid Pyrolysis of Pulverized Biomass at a High Temperature: The Effect of Particle Size on Char Yield, Retentions of Alkali and Alkaline Earth Metallic Species, and Char Particle Shape. Energy & Fuels. 2020; 34 (6):7140-7148.

Chicago/Turabian Style

Qiqing Shen; Sui Boon Liaw; Mário Costa; Hongwei Wu. 2020. "Rapid Pyrolysis of Pulverized Biomass at a High Temperature: The Effect of Particle Size on Char Yield, Retentions of Alkali and Alkaline Earth Metallic Species, and Char Particle Shape." Energy & Fuels 34, no. 6: 7140-7148.

Articles
Published: 12 April 2020 in Combustion Science and Technology
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Ammonia (NH3) is considered a promising alternative fuel, capable of producing energy with zero CO2 emissions. Its combustion, however, poses a series of challenges due to the low reactivity of NH3 and the formation of very high quantities of NOx. This work numerically investigates the combustion and emission characteristics of ammonia in three modern stationary gas turbine concepts, namely (a) lean-burn dry-low emissions (DLE); (b) rich-burn, quick-quench and lean-burn (RQL); and (c) moderate or intense low oxygen dilution (MILD), under operating conditions typical of commercial gas turbines (inlet temperatures of 500 K and pressure of 20 bar). Numerical simulations employing detailed chemical kinetic mechanisms are carried out to study the propagation speed of ammonia, the combustor temperatures, and the emissions of NOx and NH3. The simulations are first validated against literature NOx data and then the most accurate mechanism is selected. The performance of the different gas turbine engine concepts is subsequently compared based on the results from the selected mechanism. The results show that the lowest emissions are achieved with the RQL and MILD combustion concepts, while the DLE combustion concept only presents acceptable emission values under conditions deemed unstable, where the laminar flame speeds are below 3 cm/s.

ACS Style

Rodolfo C. Rocha; Mário Costa; Xue-Song Bai. Combustion and Emission Characteristics of Ammonia under Conditions Relevant to Modern Gas Turbines. Combustion Science and Technology 2020, 1 -20.

AMA Style

Rodolfo C. Rocha, Mário Costa, Xue-Song Bai. Combustion and Emission Characteristics of Ammonia under Conditions Relevant to Modern Gas Turbines. Combustion Science and Technology. 2020; ():1-20.

Chicago/Turabian Style

Rodolfo C. Rocha; Mário Costa; Xue-Song Bai. 2020. "Combustion and Emission Characteristics of Ammonia under Conditions Relevant to Modern Gas Turbines." Combustion Science and Technology , no. : 1-20.

Journal article
Published: 14 March 2020 in Fuel
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A study on the coal particle history during combustion in a large-scale furnace using large eddy simulation is presented. The massively parallel execution produces a high-resolution representation of the fluid mixing and particle dispersion throughout the whole computational domain. The coal combustion is modelled using well-established, cost-effective combustion models. A specific feature of the devolatilization model is the optimisation of the kinetic constants for the furnace operating condition, which were obtained through an iterative procedure between particle heating rates from full large eddy simulation runs and the advanced model Chemical Percolation Devolatilization. In a previous work, we showed that the classical coal combustion models, when used in a high-resolution massively parallel large eddy simulation, lead to satisfactory predictions of the in-flame gas properties, namely gas temperature and gas species concentrations. In this work, we went beyond the comparisons between gas phase measurements and predictions. Single particles were tracked over time and instantaneous ensambles were collected to obtain a better understanding of the conditions that coal particles are subjected to in the investigated test case. The particles trajectory, combustion history and instantaneous state distribution were analysed. The volatile flame features were related with the characteristic trajectory of different sized particles. The combustion history revealed that particles are subjected to large variations of heating rates, including very short sequential periods alternating between heating and cooling during the early stages of combustion, due to the high turbulence intensity in the near burner region. Finally, the state distribution of the ensamble provided a global picture of the instantaneous coal combustion process.

ACS Style

Miriam Rabaçal; Mário Costa; Martin Rieth; Andreas M Kempf. Particle history from massively parallel large eddy simulations of pulverised coal combustion in a large-scale laboratory furnace. Fuel 2020, 271, 117587 .

AMA Style

Miriam Rabaçal, Mário Costa, Martin Rieth, Andreas M Kempf. Particle history from massively parallel large eddy simulations of pulverised coal combustion in a large-scale laboratory furnace. Fuel. 2020; 271 ():117587.

Chicago/Turabian Style

Miriam Rabaçal; Mário Costa; Martin Rieth; Andreas M Kempf. 2020. "Particle history from massively parallel large eddy simulations of pulverised coal combustion in a large-scale laboratory furnace." Fuel 271, no. : 117587.

Journal article
Published: 09 March 2020 in Energy
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The integration of renewable energy sources (RES) in islands is crucial to improve their economy allowing them to be energy independent. However, the intermittency of some RES originates grid stability problems and the mismatch between demand and supply. These issues must be carefully addressed according to each island’s peculiarities. The connection between isolated power systems can decrease the RES variability and, thereby, minimize the problems associated with their intermittency. Furthermore, linking all fossil fuel consuming sectors can help to shift demand and supply according to the system’s requirements, following a smart energy system approach. This approach is rarely considered in studies on 100% RES in islands, as most of them only consider the power sector. The scientific contribution of this study is the assessment of the impact of the interconnection of two small islands in the path to 100% RES of the whole energy system. The EnergyPLAN model is used, and the Islands of Pico and Faial, in Azores, are the case studies considered. Although these islands can increase significantly their RES penetration with lower costs, only their interconnection allows for a complete elimination of fossil fuels’ use in both islands.

ACS Style

M. Alves; R. Segurado; Mario Costa. On the road to 100% renewable energy systems in isolated islands. Energy 2020, 198, 117321 .

AMA Style

M. Alves, R. Segurado, Mario Costa. On the road to 100% renewable energy systems in isolated islands. Energy. 2020; 198 ():117321.

Chicago/Turabian Style

M. Alves; R. Segurado; Mario Costa. 2020. "On the road to 100% renewable energy systems in isolated islands." Energy 198, no. : 117321.

Journal article
Published: 12 January 2020 in Energies
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The supercritical CO2 power cycle (s-CO2) is receiving much interest in the utilization of waste heat sources in the medium-to-high temperature range. The low compression work and highly regenerative layout result in high thermal efficiencies, even at moderate turbine inlet temperatures. The capability of heat extraction from the waste heat source is, however, limited because the heat input takes place over a limited temperature range close to the maximum cycle temperature. Accordingly, novel s-CO2 layouts have been recently proposed, aimed at increasing the heat extraction from the heat source while preserving as much as possible the inherently high thermal efficiency. Among these, the most promising ones feature dual expansion, dual recuperation, and partial heating. This work concentrates on the conceptual design of these novel s-CO2 layouts using a systematic approach based on the superimposition of elementary thermodynamic cycles. The overall structure of the single flow split with dual expansion (also called cascade), partial heating, and dual recuperated cycles is decomposed into elementary Brayton cycles to identify the building blocks for the achievement of a high performance in the utilization of waste heat sources. A thermodynamic optimization is set up to compare the performance of the three novel layouts for utilization of high temperature waste heat at 600 °C. The results show that the single flow split with a dual expansion cycle provides 3% and 15% more power compared to the partial heating and dual recuperated cycles, respectively, and 40% more power compared to the traditional single recuperated cycle used as the baseline. The separate evaluation of thermal efficiency and heat recovery effectiveness shows the main reasons behind the achievement of the highest performance, which are peculiar to each novel layout.

ACS Style

Giovanni Manente; Mário Costa. On the Conceptual Design of Novel Supercritical CO2 Power Cycles for Waste Heat Recovery. Energies 2020, 13, 370 .

AMA Style

Giovanni Manente, Mário Costa. On the Conceptual Design of Novel Supercritical CO2 Power Cycles for Waste Heat Recovery. Energies. 2020; 13 (2):370.

Chicago/Turabian Style

Giovanni Manente; Mário Costa. 2020. "On the Conceptual Design of Novel Supercritical CO2 Power Cycles for Waste Heat Recovery." Energies 13, no. 2: 370.

Journal article
Published: 20 December 2019 in Fuel
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The release of potassium from single burning pulverized wheat straw char particles was quantitatively measured using laser-induced photofragmentation fluorescence (LIPF). The char particles were prepared in a drop tube furnace at 1000 °C from wheat straw particles with sizes in the range 224–250 µm. Subsequently, the char particles were injected upward into a hot flue gas flow produced by a premixed CH4/air flame anchored on a McKenna burner. The flue gas had a mean temperature of 1580 K and a mean O2 concentration of 6.5 vol%. The 193 nm laser beam from an ArF Excimer laser was formed into a collimated laser sheet to photodissociate potassium hydroxide (KOH) and potassium chloride (KCl) around the burning char particles, and the signal of the produced fluorescence was captured by a camera. The measurements were conducted for char particles during residence times in the flue gas between 10 and 70 ms. Quantitative data was obtained from a direct calibration of the LIPF signal in hot gas products doped with known amounts of KOH and KCl. The maximum potassium concentration measured surrounding the burning char particles was over 40 ppm. During the oxidation period until 70 ms, the measured potassium release rate remained almost constant at around 0.5 µg/s, with more than 60% of the potassium being released in the form of KOH. The results indicate that the LIPF imaging method can be used to study the potassium release from burning biomass fuels.

ACS Style

Wubin Weng; Shen Li; Mário Costa; Zhongshan Li. Quantitative imaging of potassium release from single burning pulverized biomass char particles. Fuel 2019, 264, 116866 .

AMA Style

Wubin Weng, Shen Li, Mário Costa, Zhongshan Li. Quantitative imaging of potassium release from single burning pulverized biomass char particles. Fuel. 2019; 264 ():116866.

Chicago/Turabian Style

Wubin Weng; Shen Li; Mário Costa; Zhongshan Li. 2019. "Quantitative imaging of potassium release from single burning pulverized biomass char particles." Fuel 264, no. : 116866.

Journal article
Published: 07 December 2019 in Energies
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With a severe seasonal concentration of precipitation and unevenly distributed water resources, the water supply in Portugal is under stress, and the problem is expected to increase with climate change. Water desalination is increasingly becoming the preferred solution to fight water scarcity, but, because it is energy-intensive, the underlying costs and sustainability concerns over the power sources chosen remain a challenge to its implementation. This study aims to assess if the introduction of renewable energy sources (RES) powered desalination in mainland Portugal is viable and can contribute to guarantee water security. The Portuguese Algarve region is a viable case study to be considered because it is particularly water stressed and subject to highly varying demographics depending on the season. Taking the region’s freshwater demand, hourly RES production and power demand, a cost analysis was performed in order to obtain the levelized cost of water (LCOW) for two different strategies (centralized and decentralized). Two models were developed to estimate the LCOW: a simplified model and a subsequent optimization model, minimizing electricity costs. The resulting LCOW of 72.66 c€/m3, obtained for the decentralized solution, fits within the industry standard rate despite being 61.3% higher than the estimated conventional water supply production cost.

ACS Style

Gil Azinheira; Raquel Segurado; Mário Costa. Is Renewable Energy-Powered Desalination a Viable Solution for Water Stressed Regions? A Case Study in Algarve, Portugal. Energies 2019, 12, 4651 .

AMA Style

Gil Azinheira, Raquel Segurado, Mário Costa. Is Renewable Energy-Powered Desalination a Viable Solution for Water Stressed Regions? A Case Study in Algarve, Portugal. Energies. 2019; 12 (24):4651.

Chicago/Turabian Style

Gil Azinheira; Raquel Segurado; Mário Costa. 2019. "Is Renewable Energy-Powered Desalination a Viable Solution for Water Stressed Regions? A Case Study in Algarve, Portugal." Energies 12, no. 24: 4651.

Research article
Published: 10 November 2019 in Energy & Fuels
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Ammonia (NH3) is currently in the spotlight because of its potential in serving as an energy resource devoid of carbon. Combustion of NH3, however, presents several drawbacks, such as high ignition temperature, low flame speed and high NOx emissions. Furthermore, although dual-fuel approaches may provide a solution for some of these problems, scarcity of information on the resulting emissions inhibits a large-scale adoption. Therefore, the present work is focused on studying gaseous pollutants, namely NOx, CO and unburned NH3, emitted from premixed flames of mixtures of NH3 and either CH4 or H2 as combustion enhancers in a porous media burner. An inert alumina-zirconia porous media-based burner fuelled with NH3/CH4/air and NH3/H2/air mixtures was employed. Temperatures and concentrations of NOx, CO and NH3 were measured as a function of the NH3 molar fraction in the fuel mixture for both type of mixtures. The experimental data were compared with results from simulations performed with recently developed chemical kinetic mechanisms, updated with the latest nitrogen chemistry sub-mechanisms. The experimental results for NH3/CH4 mixtures showed that the NOx emissions peak at a NH3 molar fraction in the fuel mixture of around 0.5, while for NH3/H2 mixtures, the NOx emissions present maxima at NH3 molar fractions in the fuel mixture of 0.5 and 0.8. The CO emission data indicated complete combustion of CH4, but the presence of unburnt NH3 in the flue-gas reveals its incomplete oxidation for the studied conditions. The kinetic simulations showed similar NOx emission patterns, but over-predicted significantly the experimental data in most cases.

ACS Style

Rodolfo C. Rocha; C. Filipe Ramos; Mario Costa; Xue-Song Bai. Combustion of NH3/CH4/Air and NH3/H2/Air Mixtures in a Porous Burner: Experiments and Kinetic Modeling. Energy & Fuels 2019, 33, 12767 -12780.

AMA Style

Rodolfo C. Rocha, C. Filipe Ramos, Mario Costa, Xue-Song Bai. Combustion of NH3/CH4/Air and NH3/H2/Air Mixtures in a Porous Burner: Experiments and Kinetic Modeling. Energy & Fuels. 2019; 33 (12):12767-12780.

Chicago/Turabian Style

Rodolfo C. Rocha; C. Filipe Ramos; Mario Costa; Xue-Song Bai. 2019. "Combustion of NH3/CH4/Air and NH3/H2/Air Mixtures in a Porous Burner: Experiments and Kinetic Modeling." Energy & Fuels 33, no. 12: 12767-12780.