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Jun Shen - One of the best experts on this subject based on the ideXlab platform.
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theoretical study on the specific role of superfine Char Surface oxygen no consumption mechanism
Powder Technology, 2013Co-Authors: Hai Zhang, Xiumin Jiang, Jiaxun Liu, Jun ShenAbstract:Abstract Mechanochemistry plays a crucial role in Characterizing the superfine Char Surface chemistry properties. Conventional Char with carbonyl oxygen(> C O) bonded to its Surface is applied to represent the superfine Char model for the first time. Comparisons of two Char models are performed and the results reveal that Surface oxygen is responsible for high reactivity of CO desorption. Comprehensive density functional theory (DFT) calculations at B3LYP/6–31 G(d) level are performed to determine the NO consumption mechanism in the presence of oxygen. The results show that a certain amount of NO is trapped in the carbonaceous matrix in the form of Char(N), leading to a satisfactory agreement with previous experimental observations. CO desorption, NO fixation, CO vertical chemisorption, oxygen migration and CO 2 desorption take place to yield Char(N). The order of the calculated energetic penalty is NO fixation (7.23 kJ/mol) 2 desorption (68.26 kJ/mol)
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Theoretical study on the specific role of superfine Char Surface oxygen—NO consumption mechanism
Powder Technology, 2013Co-Authors: Hai Zhang, Xiumin Jiang, Jiaxun Liu, Jun ShenAbstract:Abstract Mechanochemistry plays a crucial role in Characterizing the superfine Char Surface chemistry properties. Conventional Char with carbonyl oxygen(> C O) bonded to its Surface is applied to represent the superfine Char model for the first time. Comparisons of two Char models are performed and the results reveal that Surface oxygen is responsible for high reactivity of CO desorption. Comprehensive density functional theory (DFT) calculations at B3LYP/6–31 G(d) level are performed to determine the NO consumption mechanism in the presence of oxygen. The results show that a certain amount of NO is trapped in the carbonaceous matrix in the form of Char(N), leading to a satisfactory agreement with previous experimental observations. CO desorption, NO fixation, CO vertical chemisorption, oxygen migration and CO 2 desorption take place to yield Char(N). The order of the calculated energetic penalty is NO fixation (7.23 kJ/mol) 2 desorption (68.26 kJ/mol)
Adel F Sarofim - One of the best experts on this subject based on the ideXlab platform.
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combustion behavior of single particles from three different coal ranks and from sugar cane bagasse in o2 n2 and o2 co2 atmospheres
Combustion and Flame, 2012Co-Authors: Reza Khatami, Christopher William Stivers, Kulbhushan Joshi, Yiannis A. Levendis, Adel F SarofimAbstract:The combustion behavior of single fuel particles was assessed in O2/N2 and O2/CO2 background gases, with oxygen mole fractions in the range of 20–100%. Fuels included four pulverized coals from different ranks (a high-volatile bituminous, a sub-bituminous and two lignites) as well as pulverized sugarcane-bagasse, a biomass residue. Particles of 75–90 lm were injected under laminar flow in a bench-scale, transparent drop-tube furnace (DTF), electrically-heated to 1400 K where, upon experiencing high heating rates, they ignited and burned. The combustion of individual particles was observed with three-color optical pyrometry and high-speed high-resolution cinematography to obtain temperature and burnout time histories. Based on combined observations from these techniques, a comprehensive understanding of the behaviors of these fuels was developed under a variety of conditions, including simulated oxy-fuel combustion. The fuels exhibited distinct combustion behaviors. In air, the bituminous coal particles burned in two distinctive modes; the volatiles burned in bright envelope flames surrounding the devolatilizing Char particles followed by heterogeneous Char combustion. The volatile matter of sub-bituminous coal particles burned either in subdued envelope flames, surrounding devolatilizing and occasionally fragmenting Chars, or heterogeneously at the Char Surface. Lignite particles typically burned with extensive fragmentation, and their volatiles burned simultaneously with the Char fragments. The volatiles of bagasse particles burned in spherical and transparent envelope flames. Increasing the oxygen mole fraction in N2, increased flame and Char Surface temperatures, and decreased burnout times; particles of all fuels burned more intensely with an increasing tendency of the volatiles to burn closer to the Char Surface. When the background gas N2 was substituted with CO2, the combustion of all fuels was distinctly less intense; at moderate O2 mole fractions (<30%) most particles did not ignite under active flow conditions in the furnace (they did ignite under quiescent gas flow conditions in the DTF). Increasing the oxygen mole fraction in CO2 increased the likelihood of combustion and its intensity. Combustion of volatiles in envelope flames was suppressed in the presence of CO2, particularly under active gas flow in the DTF.
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Combustion behavior of single particles from three different coal ranks and from sugar cane bagasse in O2/N2 and O2/CO2 atmospheres
Combustion and Flame, 2012Co-Authors: Reza Khatami, Christopher William Stivers, Kulbhushan Joshi, Yiannis A. Levendis, Adel F SarofimAbstract:The combustion behavior of single fuel particles was assessed in O2/N2 and O2/CO2 background gases, with oxygen mole fractions in the range of 20–100%. Fuels included four pulverized coals from different ranks (a high-volatile bituminous, a sub-bituminous and two lignites) as well as pulverized sugarcane-bagasse, a biomass residue. Particles of 75–90 lm were injected under laminar flow in a bench-scale, transparent drop-tube furnace (DTF), electrically-heated to 1400 K where, upon experiencing high heating rates, they ignited and burned. The combustion of individual particles was observed with three-color optical pyrometry and high-speed high-resolution cinematography to obtain temperature and burnout time histories. Based on combined observations from these techniques, a comprehensive understanding of the behaviors of these fuels was developed under a variety of conditions, including simulated oxy-fuel combustion. The fuels exhibited distinct combustion behaviors. In air, the bituminous coal particles burned in two distinctive modes; the volatiles burned in bright envelope flames surrounding the devolatilizing Char particles followed by heterogeneous Char combustion. The volatile matter of sub-bituminous coal particles burned either in subdued envelope flames, surrounding devolatilizing and occasionally fragmenting Chars, or heterogeneously at the Char Surface. Lignite particles typically burned with extensive fragmentation, and their volatiles burned simultaneously with the Char fragments. The volatiles of bagasse particles burned in spherical and transparent envelope flames. Increasing the oxygen mole fraction in N2, increased flame and Char Surface temperatures, and decreased burnout times; particles of all fuels burned more intensely with an increasing tendency of the volatiles to burn closer to the Char Surface. When the background gas N2 was substituted with CO2, the combustion of all fuels was distinctly less intense; at moderate O2 mole fractions (
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REDUCTION OF NITRIC OXIDE ON THE Char Surface AT PULVERIZED COMBUSTION CONDITIONS
Proceedings of the Combustion Institute, 2002Co-Authors: Alejandro Molina, Eric G. Eddings, David W. Pershing, Adel F SarofimAbstract:This study presents an experimental evaluation of the rate of nitric oxide reduction on the Char Surface. It addresses the claim that the rate for the destruction of nitric oxide on the Char Surface has been underpredicted due to Char deactivation in the process of Char formation. Experiments conducted with Chars produced in situ, Char previously produced at pulverized combustion conditions, and Char produced with an activated carbon showed the existence of three phenomena during the reduction of nitric oxide: (1) the homogeneous reaction of the volatiles that evolved after the injection of the solid into the reaction with nitric oxide; (2) the accumulation of nitrogen on the Char Surface, probably through the formation of C(N) complexes, and (3) the heterogeneous reaction of nitric oxide with Char. The nitric oxide reaction with Char was found to be dominant at pulverized combustion conditions (T 1500 K) with a rate within 1 order of magnitude of that predicted by an expression recommended in previous studies. At fluidized-bed conditions (T 1300 K), the second phenomenon may be important and traditional rate expressions may underpredict the nitric oxide conversion to N2 when used at combustion conditions when the nitric oxide–Char reactions begin immediately after Char formation and before a pseudo-steady state is reached. For the solid used in this study, the increase in nitric oxide reduction due to formation of C(N) sites was a factor of 2–3.
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Char nitrogen conversion: implications to emissions from coal-fired utility boilers
Progress in Energy and Combustion Science, 2000Co-Authors: Alejandro Molina, Eric G. Eddings, David W. Pershing, Adel F SarofimAbstract:Abstract The contribution of nitrogen present in the Char on the production of nitrogen oxides during Char combustion was analyzed. A literature review summarizes the current understanding of the mechanisms that account for the formation of NO and N2O from the nitrogen present in Char. The review focused on: (1) the functionalities in which nitrogen is present in the coal and how they evolve during coal devolatilization; (2) the mechanism of nitrogen release from the Char to the homogeneous phase and its further oxidation to NO; and (3) the reduction of NO on the Surface of the Char. The critical analysis of these three issues allowed identification of uncertainties and well-founded conclusions observed in the literature for this system. The existing models for the production of nitrogen oxides from Char-N were also reviewed. A critical analysis of the assumptions made in these models and how they affect the final predictions is presented. Finally, a simplified version of these models was used to perform a parametric analysis evaluating the impact of several parameters on the total conversion of Char-N to NO. These parameters include: (1) the rate of NO reduction on the Char Surface; (2) the rate of carbon oxidation; and (3) early vs. late nitrogen release during the Char oxidation process. The results underscore the importance of the reaction of NO reduction on the Char Surface to the final conversion of Char-N to NO.
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the products of the high temperature oxidation of a single Char particle in an electrodynamic balance
Symposium (International) on Combustion, 1991Co-Authors: Leonardo Tognotti, John P. Longwell, Adel F SarofimAbstract:The ratio CO2/CO from oxidation of Spherocarb Char has been measured over a wide temperature range making use of the electrodynamic balance where single particles are heated by laser irradiation but are immersed in room temperature gas. This has allowed measurement of the CO2/CO ratio formed by the heterogeneous reaction on the Char Surface for temperatures up to 1670 K. For these conditions, an exponential decrease with a temperature coefficient of 3100/K is found. The CO2/CO ratio is proportional to the oxygen partial pressure raised to a power of 0.21. These results are in substantial agreement with work reported at lower temperatures. At normal combustion temperature the CO2/CO ratio from heterogeneous reaction is less than 0.1. Gas phase oxidation of CO to CO2 near the Char Surface, however, can become important at high Char temperatures, even in a gas maintained at room temperature, and can have an important impact on Surface temperature. The temperature at which gas phase reactions begin to contribute to CO2 formation and Surface temperature was found to be reduced by the presence of water vapor.
Thomas Aicher - One of the best experts on this subject based on the ideXlab platform.
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Catalytic decomposition of biomass tars: The impact of wood Char Surface Characteristics on the catalytic performance for naphthalene removal
Fuel Processing Technology, 2016Co-Authors: F. Nestler, Luisa Burhenne, Meike Juliane Amtenbrink, Thomas AicherAbstract:Abstract Catalytic decomposition of naphthalene over four different wood Chars has been investigated. The effect of the pyrolysis temperature and activation with CO 2 on the Char structure and catalytic activity of the wood Char has been studied in order to elucidate the tar decomposition rate and Char stability towards deactivation. The wood Char catalysts were produced by pyrolyzing spruce wood chips in a tubular batch reactor at 500 and 800 °C. Part of both Char samples was further activated by purging CO 2 through a bed of the pyrolysis Char at 800 °C. The wood Char reactivity for naphthalene cracking was investigated using a fixed bed quartz reactor in a heated furnace with a constant inlet gas flow of naphthalene. Thermal decomposition was evaluated at temperatures between 700 and 1050 °C and taken into account when assessing the catalytic activity of each wood Char at 850 and 1050 °C. The structural features of the Char catalyst were examined before and after the tar cracking experiment by CO 2 and N 2 adsorption technique as well as scanning electron microscopy (SEM). Catalytic deactivation was studied by analyzing the Surface structure of the Char samples over exposure time to naphthalene. The self produced wood Char samples were compared to a commercial activated carbon to classify their structural and catalytic properties. Catalytic tar cracking tests with all wood Char catalysts confirmed that the activated Char samples showed a high catalytic activity for naphthalene decomposition into carbon and hydrogen, whereas the non-activated Char samples did not enhance the tar cracking reaction at 850 °C significantly. N 2 adsorption revealed that deactivation of the Char catalyst happens mainly due to coke deposition blocking the Char active sites. The time evolution of the wood Char's tar cracking activity was found to be proportional to the amount of micropores with a pore diameter smaller than 0.7 nm. SEM measurements visualized structural changes on the macroscopic Char Surface caused by naphthalene decomposition under an inert nitrogen atmosphere.
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benzene removal over a fixed bed of wood Char the effect of pyrolysis temperature and activation with co2 on the Char reactivity
Fuel Processing Technology, 2014Co-Authors: Luisa Burhenne, Thomas AicherAbstract:Abstract Benzene removal using spruce wood Char as catalyst was investigated. The influence of pyrolysis temperature and activation with CO 2 on the Char structure and reactivity for benzene adsorption and cracking was analyzed. The structural features of the Char were examined by the CO 2 adsorption technique and Fourier transform infrared spectroscopy (FTIR). The reactivity for benzene removal was investigated using a fixed bed quartz reactor. Surface analysis showed that the microporous Char Surface area was influenced by the pyrolysis temperature and was almost doubled by activation with CO 2 . The benzene adsorption capacity of the Char decreased with increasing pyrolysis temperature. Activation with CO 2 however, increased the fraction of adsorbed benzene by a factor of two and 10 for Char produced at 500 and 800 °C, respectively. The total microporous Surface above 700 m 2 /g was found to be a good indicator for the reactive Char Surface for benzene cracking at high temperatures. At 1050 °C the main mode of benzene conversion was homogeneous thermal decomposition. We confirmed that wood Char has the potential to serve as an effective catalyst for benzene removal. However, benzene decomposed over the Charcoal by carbon deposition which led to a fast deactivation of the wood Char catalyst.
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effect of feedstock water content and pyrolysis temperature on the structure and reactivity of spruce wood Char produced in fixed bed pyrolysis
Fuel, 2013Co-Authors: Luisa Burhenne, Marco Damiani, Thomas AicherAbstract:Abstract The influence of initial water content and temperature on the pyrolysis product distribution as well as on the structure and reactivity of the pyrolysis Char was investigated. Spruce wood chips with 2.4%, 16.4%, and 55.4% initial water content were pyrolyzed in a tubular batch reactor at 500 and 800 °C with a heating rate between 4 and 12.6 °C/min. The structural features of the Char samples were examined with scanning electron microscopy, Brunauer–Emmett–Teller (BET) method, and mercury porosimetry. The reactivity in CO 2 was investigated using thermo-gravimetric analysis and a fixed bed quartz reactor. It could be seen that higher water content led to a higher yield of condensable products and a lower amount of Char. At a pyrolysis temperature of 500 °C the CO-content of the product gas did increase significantly with increasing water content. Moreover, initial water content had no significant effect on the microscopic structure of wood Chars. The specific Char Surface area did increase with increasing initial water content up to the fiber saturation point. It was also observed that the specific Char Surface area was strongly influenced by the pyrolysis temperature. When the pyrolysis temperature increased from 500 to 800 °C, the BET Surface area became at least 200 times smaller and the average size of micropores became about 10 times smaller. Most likely, pyrolysis at 800 °C induced more secondary reactions that were responsible for the occlusion of the micropores within the Char [1] . Finally, it was found that reactivity in CO 2 significantly decreased with increasing pyrolysis temperature. However, initial wood water content did not have a significant effect on Char reactivity in CO 2 .
Hai Zhang - One of the best experts on this subject based on the ideXlab platform.
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theoretical study on the specific role of superfine Char Surface oxygen no consumption mechanism
Powder Technology, 2013Co-Authors: Hai Zhang, Xiumin Jiang, Jiaxun Liu, Jun ShenAbstract:Abstract Mechanochemistry plays a crucial role in Characterizing the superfine Char Surface chemistry properties. Conventional Char with carbonyl oxygen(> C O) bonded to its Surface is applied to represent the superfine Char model for the first time. Comparisons of two Char models are performed and the results reveal that Surface oxygen is responsible for high reactivity of CO desorption. Comprehensive density functional theory (DFT) calculations at B3LYP/6–31 G(d) level are performed to determine the NO consumption mechanism in the presence of oxygen. The results show that a certain amount of NO is trapped in the carbonaceous matrix in the form of Char(N), leading to a satisfactory agreement with previous experimental observations. CO desorption, NO fixation, CO vertical chemisorption, oxygen migration and CO 2 desorption take place to yield Char(N). The order of the calculated energetic penalty is NO fixation (7.23 kJ/mol) 2 desorption (68.26 kJ/mol)
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Theoretical study on the specific role of superfine Char Surface oxygen—NO consumption mechanism
Powder Technology, 2013Co-Authors: Hai Zhang, Xiumin Jiang, Jiaxun Liu, Jun ShenAbstract:Abstract Mechanochemistry plays a crucial role in Characterizing the superfine Char Surface chemistry properties. Conventional Char with carbonyl oxygen(> C O) bonded to its Surface is applied to represent the superfine Char model for the first time. Comparisons of two Char models are performed and the results reveal that Surface oxygen is responsible for high reactivity of CO desorption. Comprehensive density functional theory (DFT) calculations at B3LYP/6–31 G(d) level are performed to determine the NO consumption mechanism in the presence of oxygen. The results show that a certain amount of NO is trapped in the carbonaceous matrix in the form of Char(N), leading to a satisfactory agreement with previous experimental observations. CO desorption, NO fixation, CO vertical chemisorption, oxygen migration and CO 2 desorption take place to yield Char(N). The order of the calculated energetic penalty is NO fixation (7.23 kJ/mol) 2 desorption (68.26 kJ/mol)
Xiumin Jiang - One of the best experts on this subject based on the ideXlab platform.
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theoretical study on the specific role of superfine Char Surface oxygen no consumption mechanism
Powder Technology, 2013Co-Authors: Hai Zhang, Xiumin Jiang, Jiaxun Liu, Jun ShenAbstract:Abstract Mechanochemistry plays a crucial role in Characterizing the superfine Char Surface chemistry properties. Conventional Char with carbonyl oxygen(> C O) bonded to its Surface is applied to represent the superfine Char model for the first time. Comparisons of two Char models are performed and the results reveal that Surface oxygen is responsible for high reactivity of CO desorption. Comprehensive density functional theory (DFT) calculations at B3LYP/6–31 G(d) level are performed to determine the NO consumption mechanism in the presence of oxygen. The results show that a certain amount of NO is trapped in the carbonaceous matrix in the form of Char(N), leading to a satisfactory agreement with previous experimental observations. CO desorption, NO fixation, CO vertical chemisorption, oxygen migration and CO 2 desorption take place to yield Char(N). The order of the calculated energetic penalty is NO fixation (7.23 kJ/mol) 2 desorption (68.26 kJ/mol)
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Theoretical study on the specific role of superfine Char Surface oxygen—NO consumption mechanism
Powder Technology, 2013Co-Authors: Hai Zhang, Xiumin Jiang, Jiaxun Liu, Jun ShenAbstract:Abstract Mechanochemistry plays a crucial role in Characterizing the superfine Char Surface chemistry properties. Conventional Char with carbonyl oxygen(> C O) bonded to its Surface is applied to represent the superfine Char model for the first time. Comparisons of two Char models are performed and the results reveal that Surface oxygen is responsible for high reactivity of CO desorption. Comprehensive density functional theory (DFT) calculations at B3LYP/6–31 G(d) level are performed to determine the NO consumption mechanism in the presence of oxygen. The results show that a certain amount of NO is trapped in the carbonaceous matrix in the form of Char(N), leading to a satisfactory agreement with previous experimental observations. CO desorption, NO fixation, CO vertical chemisorption, oxygen migration and CO 2 desorption take place to yield Char(N). The order of the calculated energetic penalty is NO fixation (7.23 kJ/mol) 2 desorption (68.26 kJ/mol)