Laser-initiated combustion of single coal particles in quiesent oxygen environments

Tidona, R.J.

doi:10.1016/0010-2180(80)90064-4

Cited by 15 publications

(4 citation statements)

References 3 publications

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“…With the same partial pressure of oxygen, however, the maximum oxidation rate significantly decreased as the total pressure was increased from 100 to 1000 kPa. Similar results were also reported in other work , at pressures below atmospheric. These combined results thusly indicate dependence of reaction rate on oxygen concentration (mole fraction), but not (or not significantly) on pressure.…”

Section: Introductionsupporting

confidence: 92%

Large Char Particle High-Pressure Oxidation Rates and Mechanisms

et al. 2003

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The main objective of this study was to investigate the high-pressure oxidation rates of large (6-9 mm diameter) char particles for a wide range of five experimental conditions, with particular focus on the role of the ratio of the carbon-oxide combustion products at the reaction surface and on its analytical consequences on the Stefan flow (BLD) behavior. The char particles were obtained by pyrolytic heating of a Pittsburgh HV bituminous coal in nitrogen. The experimental conditions and ranges were gas temperature (825-1200 K), gas (oxidizer) velocity (0.08-1.28 m/s), particle mass (0.056-0.16 g), oxygen mole fraction (0.04-0.21), and total pressure (1-5 atm). This allowed for a suite of 13 different permutations of operating conditions, with each repeated five times for a total of 65 experiments, generating about 1000 experimental data points. The experiments were conducted in a high-pressure, controlled-profile (HPCP) laboratory reactor with a cantilever balance attachment. The particles were suspended from the balance attachment in a wire basket for continuous weighing to obtain the oxidation rates. The reaction was found to be mostly governed (controlled or dominated) by boundary layer diffusion (BLD), as broadly expected and predicted for particles of this size from the Stefan flow BLD analysis, but results also showed numerical variabilities in the carbon oxides ratio (CO/CO 2 ) that are believed to be original in this work. In sum, reaction rate increased with increasing temperature, oxygen concentration, and ambient velocity, in agreement with past work. Burn-out time was found to be independent of total pressure, in agreement with prediction where the reaction rate is controlled or dominated by boundary layer oxidizer diffusion. The particles burned in two stages: stage I extended through 85% to 90% of the char mass loss at which point there was a temperature drop or (nominal) "extinction" accompanied by slower reaction in the subsequent stage II. The primary focus in this study was on the stage I where comparison with rigorous theory established that the reaction was diffusion-controlled for nine of the 13 sets of experimental conditions. In the remaining four sets (high velocity, low pressure, and low oxygen concentration), there was a measurable chemical reaction resistance; however, diffusion, though not controlling, was still dominant. For eight of the 13 sets of test conditions, analysis indicated full conversion of CO to CO 2 at the particle surface. For the other five sets of test conditions (low oxygen, low temperature, and low velocity), however, CO accounted for 14% to 79% of the product gas leaving the surface, with the balance being CO 2 . The effects of the test variables were quantitatively accounted for by incorporating Stefan flow behavior in a rigorous theory of particle burning. IntroductionIn this paper, we report results of experimental and analytical studies on high-pressure oxidation rates of large char particles, obtained from a bituminous coal,

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Section: Introductionsupporting

confidence: 92%

Large Char Particle High-Pressure Oxidation Rates and Mechanisms

et al. 2003

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“…Studies using individual single particles, of whatever shape, can be made using supported particles ignited either by a flame or laser, e.g. see ref . The results quoted here are based on single suspended particles of a wood, willow, which are easily suspended in a gas flame.…”

Section: Experiments With Single Particlesmentioning

confidence: 99%

Combustion of a Single Particle of Biomass

et al. 2007

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Biomass is one of the important renewable energy sources. Biomass fuels exhibit a range of chemical and physical properties, particularly size and shape. Investigations of the behavior of a single biomass particle are fundamental to all practical applications, including both packed and fluidized-bed combustion, as well as suspended and pulverized fuel (pf) combustion. In this paper, both experimental and mathematical modeling approaches are employed to study the combustion characteristics of a single biomass particle ranging in size from 10 µm to 20 mm. Different subprocesses such as moisture evaporation, devolatilization, tar cracking, gas-phase reactions, and char gasification are examined. The sensitivity to the variation in model parameters, especially the particle size and heating rates, is investigated. The results obtained from this study are useful in assessing different combustion systems using biomass as a fuel. It helps to clarify the situations where the thermally thin and thermally thick cases interface. It is clear that simple models of particle combustion assuming constant particle temperature are sometimes inadequate and that for large particles a more detailed mathematical representation should be applied.

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“…Coal or char combustion under elevated pressure behaves differently than combustion in atmosphere conditions. [2][3][4][5][6][7][8][9][10] The rate of combustion was found to increase with pressure in the chemical-reaction control regime, but is less affected by pressure in the pore diffusion influence and is invariant with pressure in gas-film diffusion control regimes. The mechanism underlying the relationship between pressure and NO x emission during coal or char combustion is not yet understood.…”

Section: Introductionmentioning

confidence: 99%

Effect of Pressure on NO_x Emission from Char Particle Combustion

2002

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The effect of pressure on NO x emission during char particle combustion was examined in chemical-reaction control and diffusion control regimes. A fixed bed was used for batch testing under 0.1−1.6 MPa. It was found that with increasing pressure, NO x emission decreased extremely, when char combustion rate was controlled by reactant gas diffusion into the char particle at high temperature. The extent to which NO x was reduced in char particles strongly influenced the NO x emission from char pressurized combustion. Pressure increased residence time for diffusion of NO x throughout the char particle and consequently further increased the reduction of NO x in the char particle. Both pressure and temperature strongly influenced the conversion of fuel-N in char to NO x . When pressure was raised from 0.1 to 1.1 MPa, the conversion of fuel-N to NO x fell from 0.18 to 0.06 at 973 K, and from 0.68 to 0.13 at 1173 K. NO x emissions were lower when large char particles were combusted than when small ones were combusted. It was also observed that practically no N2O was formed in to any extent in the char particle.

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Laser-initiated combustion of single coal particles in quiesent oxygen environments

Cited by 15 publications

References 3 publications

Large Char Particle High-Pressure Oxidation Rates and Mechanisms

Large Char Particle High-Pressure Oxidation Rates and Mechanisms

Combustion of a Single Particle of Biomass

Effect of Pressure on NO_x Emission from Char Particle Combustion

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Laser-initiated combustion of single coal particles in quiesent oxygen environments

Cited by 15 publications

References 3 publications

Large Char Particle High-Pressure Oxidation Rates and Mechanisms

Large Char Particle High-Pressure Oxidation Rates and Mechanisms

Combustion of a Single Particle of Biomass

Effect of Pressure on NOx Emission from Char Particle Combustion

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Product

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Effect of Pressure on NO_x Emission from Char Particle Combustion