Fluidized Bed Studies of Carbon Particle Oxidation: Gas Phase Surface Products and Surface Area Evolution

N. R. Purzer, Richard A. Yetter, F. L. Dryer, R. J. Lawson

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The oxidation of Spherocarb carbon particles is studied in a research-scale fluidized bed reactor (FBR) over the temperature range of 630K-1300K at atmospheric pressure. The reactor uses nitrogen carrier gas to which various amounts of oxidizer (from 6%-30% by volume) are added. Carbon loading (spherical 60/80 mesh spherocarb particles) is kept low so that the reactor remains nearly isothermal overall. A procedure for a non-intrusive approximation of average particle temperature rise was developed and indicated that particle temperatures do not rise more than 20 K above the bed temperature. Oxidation rates are determined by measuring the bed temperature and the time dependent formation of gas-phase carbon oxides. Assuming a first order dependence on oxidizer concentration, overall rates of oxidation for various pure oxidizers in nitrogen are determined. The overall activation energy for O2 (37 ± 2 kcal/mole) corresponds well with previously published values. Overall activation energies for CO2 (61 ± 9 kcal/mole), and H2O (82 ± 8 kcal/mole) are considerably larger than those for oxygen, and overall rates were found to be the same order of magnitude as those for oxygen at 1500 K and 1380 K, respectively. The overall activation energy for N2O (33 ± 3 kcal/mole) is similar to that for oxygen with a rate about 75% slower. The surface reaction product distribution generated by surface reactions with oxygen was determined as a function of temperature below about 960 K (above which temperature the gas phase oxidation of CO to CO2 becomes significant). As temperatures decrease from 960K-760K, the fraction of carbon oxides produced as CO2 increases exponentially, in agreement with the literature. However, the CO2/CO ratio reaches a maximum at about 760 K and then decreases significantly with further decreases in temperature. The active particle surface area evolved as a function of the extent of burnout in oxygen was found to increase initially, reaching a maximum (75% greater than the initial area) at about 25% conversion. With the exception of the decreasing CO2/CO ratio at low surface temperatures, FBR results are quantitatively consistent with published data obtained from oxidation studies on individual, levitated Spherocarb particles. The FBR technique described here is therefore an accurate means of determining an “average” burning behavior of individual particles of varying size and morphological properties.

Original languageEnglish (US)
Pages (from-to)147-167
Number of pages21
JournalCombustion science and technology
Issue number1
StatePublished - Jan 1 1995

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • General Chemical Engineering
  • Fuel Technology
  • Energy Engineering and Power Technology
  • General Physics and Astronomy


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