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Junichi Sato - One of the best experts on this subject based on the ideXlab platform.
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Numerical Investigations of CO/CO2 Ratio in Char Combustion
Combustion Science and Technology, 2011Co-Authors: Takamasa Ito, Toshiyuki Suda, Junichi SatoAbstract:The CO/CO2 ratio of reactions during Char Combustion was investigated numerically. The simulations used the pore model with fractal properties, a gas diffusion model suitable for fractal pores, and a carbon-oxygen reaction model to describe the Char oxidation. The CO/CO2 ratio in the primary reactions was derived assuming Gaussian distributions of the activation energies and Maxwell distribution of the oxygen molecular velocity. The numerical simulations of the Char Combustion for various particle sizes, pore structures, and temperatures revealed that the effects of the secondary reactions and the pore structure on the CO/CO2 ratio are the main reasons why different researchers obtain different experimental results for of the CO/CO2 ratio.
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NUMERICAL SIMULATIONS OF GAS DIFFUSION AND REACTION IN FRACTAL PORES DURING Char Combustion
Combustion Science and Technology, 2007Co-Authors: Qun Chen, Zhanggang Liang, Junichi SatoAbstract:Classic molecular gas dynamics and fractal pore models are used to simulate gas diffusion and reaction within Char pores in Combustion. Through numerical simulations it is found that the Char Combustion model based on Thiele modulus can be well used in regular pores, but is not well used in real Char particles that have fractal pore structures. When oxygen concentrations are the same in different Char pores, which is often happened in initial stage of Combustion, fractal dimensions of pores will affect Char Combustion rates in exponential form. These numerical simulations can partly explain the previous experimental results.
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effects of particle sizes on transport phenomena in single Char Combustion
International Journal of Heat and Mass Transfer, 2003Co-Authors: Rong He, Toshiro Fujimori, Toshiyuki Suda, Junichi SatoAbstract:A one-dimensional Char Combustion model including pore structure effects is used to numerically investigate single Char particle Combustion for several different types of Char samples. Previously, it is expected that small Char particles have less Combustion time. However, the present work shows that this is true only if the Combustion time is defined as that needed for a Char particle diameter diminished below a certain value. If the Combustion time is defined as time needed for the carbon conversion ratio higher than a certain value, there are optimal particle sizes in a limited Combustion period. Just reducing the Char particle sizes may not get high carbon conversion ratios. It has also been found that, in general, the larger particles have higher temperatures at the exterior surfaces.
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Modeling Char Combustion with fractal pore effects
Combustion Science and Technology, 2002Co-Authors: Junichi Sato, Changhe ChenAbstract:The effects of Char pores on Char Combustion has been studied with fractal theory. The fractal properties of different Char samples were derived from mercury porosimetry measurements. Gas diffusion in pores affects Combustion in Char pores and this diffusion is affected by the geometrical complexity of pores. To explore gas diffusion and Combustion in fractal pores, a fractal geometrical factor β is defined with pore fractal dimensions and other fractal geometrical factors. It has been found that both apparent activation energy and pre-exponential factor have linear relations with the factors β and the Char Combustion can be modeled with the fractal geometrical factor.
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Thermogravimetric analysis of Char Combustion
Combustion Science and Technology, 2002Co-Authors: Junichi Sato, Qun Chen, Changhe ChenAbstract:Nine different Char samples were tested in thermogravimetric analyzers with continuously rising temperatures and a global one-step kinetic reaction model was used to describe the Char Combustion. A mathematical method has been presented to deduce the activation energy and pre-exponential factor. The results show that this method has good convergence and is relatively easy for applications. The deduced apparent activation energies and pre-exponential factors will be used for analyzing diffusion effects within Char pores in He, Sato, and Chen (2002).
Qinggang Lu - One of the best experts on this subject based on the ideXlab platform.
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tg ms study on coal Char Combustion by equivalent Characteristic spectrum analysis
International Symposium on Coal Combustion, 2015Co-Authors: Zhiqiang Gong, Qinggang LuAbstract:Combustion of Shenmu coal and Shenmu Char was comprehensively studied with online thermogravimetry–mass spectrum (TG-MS) system by equivalent Characteristic spectrum analysis (ECSA). This method makes continuous and online measurement of coal/Char Combustion, a continuous and rapid thermal process, possible and quantified. The evolved gases were quantified by ECSA, and the mass flow rate of evolved gas agreed well with the mass loss data of DTG for both Shenmu coal and Shenmu Char. NH3 and HCN are detected out as the major precursors of NO x while the volumetric of HCN is larger than that of NH3 for both Shenmu coal and Shenmu Char. NO and NO2 emissions are lower for Shenmu Char than those of Shenmu coal. H2S and COS are detected out as the major precursors of SO2 in Combustion of Shenmu coal. COS and SO2 are not detected out during Combustion of Shenmu Char.
Christopher R. Shaddix - One of the best experts on this subject based on the ideXlab platform.
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the effect of bulk gas diffusivity on apparent pulverized coal Char Combustion kinetics
Proceedings of the Combustion Institute, 2019Co-Authors: Christopher R. Shaddix, Cristina Gonzalotirado, Ethan S Hecht, Brian S HaynesAbstract:Abstract Apparent Char kinetic rates are commonly used to predict pulverized coal Char burning rates. These kinetic rates quantify the Char burning rate based on the temperature of the particle and the oxygen concentration at the external particle surface, inherently neglecting the impact of variations in the internal diffusion rate and penetration of oxygen. To investigate the impact of bulk gas diffusivity on these phenomena during Zone II burning conditions, experimental measurements were performed of Char particle Combustion temperature and burnout for a subbituminous coal burning in an optical entrained flow reactor with helium and nitrogen diluents. The combination of much higher thermal conductivity and mass diffusivity in the helium environments resulted in cooler Char Combustion temperatures than in equivalent N2 environments. Measured Char burnout was similar in the two environments for a given bulk oxygen concentration but was approximately 60% higher in helium environments for a given Char Combustion temperature. To augment the experimental measurements, detailed particle simulations of the experimental conditions were conducted with the SKIPPY code. These simulations also showed a 60% higher burning rate in the helium environments for a given Char particle Combustion temperature. To differentiate the effect of enhanced diffusion through the external boundary layer from the effect of enhanced diffusion through the particle, additional SKIPPY simulations were conducted under selected conditions in N2 and He environments for which the temperature and concentrations of reactants (oxygen and steam) were identical on the external Char surface. Under these conditions, which yield matching apparent Char burning rates, the computed Char burning rate for He was 50% larger, demonstrating the potential for significant errors with the apparent kinetics approach. However, for specific application to oxy-fuel Combustion in CO2 environments, these results suggest the error to be as low as 3% when applying apparent Char burning rates from nitrogen environments.
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kinetic modeling of the formation and growth of inorganic nano particles during pulverized coal Char Combustion in o2 n2 and o2 co2 atmospheres
Combustion and Flame, 2016Co-Authors: Yanqing Niu, Christopher R. Shaddix, Shuai Wang, Shien HuiAbstract:Abstract In the formation of nano-particles during coal Char Combustion, the vaporization of inorganic components in Char and the subsequent homogeneous particle nucleation, heterogeneous condensation, coagulation, and coalescence play decisive roles. However, conventional measurements cannot provide detailed information on the dynamics of nano-particle formation and evolution. In this work, a sophisticated intrinsic Char kinetics model that considers ash effects (including ash film formation, ash dilution, and ash vaporization acting in tandem), both oxidation and gasification by CO 2 and H 2 O, homogeneous particle nucleation, heterogeneous vapor condensation, coagulation, and coalescence mechanisms is developed and used to compare the temporal evolution of the number and size of nano-particles during coal Char particle Combustion as a function of Char particle size, ash content, and oxygen content in O 2 /N 2 and O 2 /CO 2 atmospheres. Based on comparisons with measurements of Char particle temperature, carbon conversion, mineral vaporization, and mean size of nano-particles at various residence times, the model can accurately predict the transient Combustion of pulverized coal Char particles and nano-particle formation and growth. Model results show that in either O 2 /N 2 or O 2 /CO 2 atmospheres, the Char Combustion temperature has a dominant effect on the formation and growth of nano-particles. High Char burning temperatures result in a high mineral vaporization rate within the Char particle, and subsequent high nucleation and condensation rate, and consequently more and larger nano-particles. As a result, high oxygen content, low ash content, and small sized Char particles, all of which promotes high local Char burning temperatures, yield more nano-particles and shift the nano-particle size distribution to larger sizes. In comparison to Combustion in O 2 /N 2 , both the number density and size of the nano-particles formed in O 2 /CO 2 are lower. Unlike condensation, which contributes to particle growth until the vapor molecules are fully consumed, nucleation ceases during the last stage of Char Combustion.
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Ignition, flame stability, and Char Combustion in oxy-fuel Combustion
Oxy-Fuel Combustion for Power Generation and Carbon Dioxide (CO2) Capture, 2014Co-Authors: Christopher R. Shaddix, Alejandro MolinaAbstract:Abstract: This chapter discusses the influence of oxy-fuel Combustion conditions on coal ignition, flame stability, Char Combustion, and carbon burnout. Both experimental results and theoretical analysis are employed to illustrate the predominant influences of elevated concentrations of O2, CO2, and H2O on these important aspects of the Combustion process. In some instances substantial differences in the Combustion behavior are apparent relative to traditional air-fired Combustion practices, whereas in other cases the influence is relatively minor. Both an understanding of the governing physics of the processes and detailed simulations lead to an understanding of which aspects of gas transport properties or reactions involving CO2 and H2O are likely to be responsible for the observed trends.
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Analysis of the errors associated with typical pulverized coal Char Combustion modeling assumptions for oxy-fuel Combustion
Combustion and Flame, 2013Co-Authors: Ethan S Hecht, Christopher R. Shaddix, Joann S. LightyAbstract:Abstract In CFD models of pulverized coal Combustion, which often have complex, turbulent flows with millions of coal particles reacting, the Char Combustion sub-model needs to be computationally efficient. There are several common assumptions that are made in Char Combustion models that allow for a compact, computationally efficient model. In this work, oft used single- and double-film simplified models are described, and the temperature and carbon Combustion rates predicted from these models are compared against a more accurate continuous-film model. Both the single- and double-film models include a description of the heterogeneous reactions of carbon with O 2 , CO 2 , and H 2 O, along with a Thiele based description of reactant penetration. As compared to the continuous-film model, the double-film model predicts higher temperatures and carbon consumption rates, while the single-film model gives more accurate results. A single-film model is therefore preferred to a double-film model for a simplified, yet fairly accurate description of Char Combustion. For particles from 65 to 135 μm, in O 2 concentrations ranging from 12 to 60 vol.%, with either CO 2 or N 2 as a diluent, particle temperatures from the single-film model are expected to be accurate within 270 K, and carbon consumption rate predictions should be within 16%, with greater accuracies for a CO 2 diluent and at lower bulk oxygen concentrations. A single-film model that accounts for reactant penetration and both oxidation and gasification reactions is suggested as a computationally efficient sub-model for coal Char Combustion that is reasonably accurate over a wide range of gas environments.
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Oxy-Combustion of pulverized coal : modeling of Char-Combustion kinetics.
2010Co-Authors: Christopher R. Shaddix, Brian S Haynes, Manfred GeierAbstract:In this study, Char Combustion of pulverized coal under oxy-fuel Combustion conditions was investigated on the basis of experimentally observed temperature-size Characteristics and corresponding predictions of numerical simulations. Using a Combustion-driven entrained flow reactor equipped with an optical particle-sizing pyrometer, Combustion Characteristics (particle temperatures and apparent size) of pulverized coal Char particles was determined for Combustion in both reduced oxygen and oxygen-enriched atmospheres with either a N{sub 2} or CO{sub 2} bath gas. The two coals investigated were a low-sulfur, high-volatile bituminous coal (Utah Skyline) and a low-sulfur subbituminous coal (North Antelope), both size-classified to 75-106 {micro}m. A particular focus of this study lies in the analysis of the predictive modeling capabilities of simplified models that capture Char Combustion Characteristics but exhibit the lowest possible complexity and thus facilitate incorporation in existing computational fluid dynamics (CFD) simulation codes. For this purpose, Char consumption Characteristics were calculated for Char particles in the size range 10-200 {micro}m using (1) single-film, apparent kinetic models with a chemically 'frozen' boundary layer, and (2) a reacting porous particle model with detailed gas-phase kinetics and three separate heterogeneous reaction mechanisms of Char-oxidation and gasification. A comparison of model results with experimental data suggests that single-film modelsmore » with reaction orders between 0.5 and 1 with respect to the surface oxygen partial pressure may be capable of adequately predicting the temperature-size Characteristics of Char consumption, provided heterogeneous (steam and CO{sub 2}) gasification reactions are accounted for.« less
Zhiqiang Gong - One of the best experts on this subject based on the ideXlab platform.
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TG-MS Study on Coal/Char Combustion by Equivalent Characteristic Spectrum Analysis
Clean Coal Technology and Sustainable Development, 2016Co-Authors: Zhiqiang Gong, Hongde Xia, Zhi-cheng LiuAbstract:Combustion of Shenmu coal and Shenmu Char was comprehensively studied with online thermogravimetry–mass spectrum (TG-MS) system by equivalent Characteristic spectrum analysis (ECSA). This method makes continuous and online measurement of coal/Char Combustion, a continuous and rapid thermal process, possible and quantified. The evolved gases were quantified by ECSA, and the mass flow rate of evolved gas agreed well with the mass loss data of DTG for both Shenmu coal and Shenmu Char. NH3 and HCN are detected out as the major precursors of NO x while the volumetric of HCN is larger than that of NH3 for both Shenmu coal and Shenmu Char. NO and NO2 emissions are lower for Shenmu Char than those of Shenmu coal. H2S and COS are detected out as the major precursors of SO2 in Combustion of Shenmu coal. COS and SO2 are not detected out during Combustion of Shenmu Char.
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tg ms study on coal Char Combustion by equivalent Characteristic spectrum analysis
International Symposium on Coal Combustion, 2015Co-Authors: Zhiqiang Gong, Qinggang LuAbstract:Combustion of Shenmu coal and Shenmu Char was comprehensively studied with online thermogravimetry–mass spectrum (TG-MS) system by equivalent Characteristic spectrum analysis (ECSA). This method makes continuous and online measurement of coal/Char Combustion, a continuous and rapid thermal process, possible and quantified. The evolved gases were quantified by ECSA, and the mass flow rate of evolved gas agreed well with the mass loss data of DTG for both Shenmu coal and Shenmu Char. NH3 and HCN are detected out as the major precursors of NO x while the volumetric of HCN is larger than that of NH3 for both Shenmu coal and Shenmu Char. NO and NO2 emissions are lower for Shenmu Char than those of Shenmu coal. H2S and COS are detected out as the major precursors of SO2 in Combustion of Shenmu coal. COS and SO2 are not detected out during Combustion of Shenmu Char.
Ranajit Saha - One of the best experts on this subject based on the ideXlab platform.
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modeling and experimental studies on single particle coal devolatilization and residual Char Combustion in fluidized bed
Fuel, 2011Co-Authors: Anup Kumar Sadhukhan, Parthapratim Gupta, Ranajit SahaAbstract:Single particle devolatilization followed by Combustion of the residual coal Char particle has been analyzed in a batch-fluidized bed. The kinetic scheme with distributed activation energy is used for coal devolatilization while multiple chemical reactions with volume reaction mechanism are considered for residual Char Combustion. Both the models couple kinetics with heat transfer. Finite Volume Method (FVM) is employed to solve fully transient partial differential equations coupled with reaction kinetics. The devolatilization model is used to predict the devolatilization time along with residual mass and particle temperature, while the combined devolatilization and Char Combustion model is used to predict the overall mass loss and temperature profile of coal. The computed results are compared with the experimental results of the present authors for Combustion of Indian sub-bituminous coal (15% ash) in a fluidized bed combustor as well as with published experimental results for coal with low ash high volatile matter. The effects of various operating parameters like bed temperature, oxygen mole fraction in bulk phase on devolatilization time and burn-out time of coal particle in bubbling fluidized bed have been examined through simulation.