Influence of pressure on the combustion rate of carbon

doi:10.1016/S0082-0784(96)80152-4

Symposium (International) on Combustion

Volume 26, Issue 2, 1996, Pages 3085-3094

https://doi.org/10.1016/S0082-0784(96)80152-4 Get rights and content

The influence of pressure on the combustion rates of carbon (or coal) particles is shown, by comparison of prediction with experiment, to be zero to minor in the temperature range studied. This result is contrary to the empirical (nth order) assumption widely adopted in much of the literature that predicts a substantial pressure dependence at all temperatures. Two models were used in the comparison, and the results were compared with three independent experimental sets of data. These experiments were measurements of burning times of single coal particles by Tidona [19] at 1, 1.5, and 2 atm; reaction rates of char particles by Monson et al. [15] at 1, 5, 10, and 15 atm; and (noncritical) ignition temperatures of coal particles in the pressure range 0.4–1.7 atm [20]. The first model was based on the fundamental Langmuir-Nusselt-Thiele suite of theoretical equations in the form of the extended resistance equation (ERE) [35]. The second model combined the Nusselt BLD analysis with the empirical nth order assumption that the reaction rate at all temperatures is proportional to the nth power of the partial pressure of the oxygen concentration (p_oxⁿ) [2,3]. The ERE model was able to predict the structural form of the experimental results with adequate prediction of numerical values, particularly of the reaction rates measured by Monson et al. In particular, the ERE predictions and experiments jointly showed small to no dependency of the rates on pressure, contrary to the predictions of the empirical model. We conclude that the empirical model has no experimental support for the assumptions made and that fundamentally based equations can be developed or already exist that can be used to predict carbon combustion reaction rates at elevated or reduced pressure with acceptable confidence.

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Pressurized oxy-coal combustion has been regarded as a promising carbon capture and storage (CCS) technology, and the combustion characteristics of char particles under pressurized oxy-fuel combustion conditions have been extensively investigated. However, most previous studies used the char samples prepared under the atmospheric N₂ condition rather than under the pressurized CO₂ condition, which may lead to the misunderstanding of the combustion characteristics. In this study, the effects of devolatilization atmosphere and pressure on the physical structure of char particles were experimentally investigated. The char particles produced under different devolatilization conditions were then used for the oxy-char combustion experiments conducted in a fluidized bed with the operating pressure between 0.1 and 0.5 MPa. In view of the limitations of the experiment, an experimental verified particle-scale char combustion model was further used for predicting the char particle’s combustion reactivity and temperature, and the influence of physical structure on the combustion characteristics was analyzed. The results obtained from the experiments demonstrated that higher devolatilization pressure led to larger mean pore sizes and specific surface areas of char particles. The char particles obtained with CO₂ atmosphere had larger specific surface areas but smaller mean pore sizes than those obtained with N₂ atmosphere. Besides, increasing devolatilization pressure resulted in shorter burnout times of char particles. The simulation results showed that using the char samples prepared under the atmospheric N₂ condition for the pressurized oxy-fuel combustion experiments led to the underestimations of char combustion reactivity and peak temperature.
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Influence of pressure on the combustion rate of carbon

Carbon

Quarterly Reports of the Sandia National Laboratories Combustion Research Facility

Sandia Report SAND92-8208-UC-361

Fuel Proces.. Technol.

Combust. Flame

J. Electrochem. Soc.

Combust. Flame

V.D.I.

Fundamentals of Coal Combustion

J. Chem. Soc.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

Ind. Eng. Chem. Res.

AIChE J.

Combust. Sci. Technol.

Combust. Sci. Technol.