MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...
MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ... MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...
Predicted Burnouts (%) 100 80 60 40 20 0 0 1 atm 5 atm 10 atm 20 40 110 60 80 Measured Burnouts (%) 100 Figure 7.6. Comparison of HP-CBK predictions of carbon burnouts with pulverized coal char data (Monson, 1992) at total pressures of 1, 5, and 10 atm. Predicted Burnouts (%) 100 75 50 25 0 0 20 15 atm 40 60 80 Measured Burnouts (%) 100 Figure 7.7. Comparison of HP-CBK predictions of carbon burnouts with pulverized coal char data (Monson, 1992) at a total pressure of 15 atm.
TGA and FFB Data-This Study The reactivities of a south African coal char (Koonfontain) were studied in this project at atmospheric pressure using a thermogravimetric analyzer (TGA) and the flat- flame burner (FFB) at this laboratory as reported in the appendix. Koonfontain coal particles (with a mean diameter of 60 μm) were injected into the FFB from the bottom and devolatilized within the first inch in the burner. In the fuel-lean flames (methane fuel- lean, condition #2, and CO fuel-lean, condition #4), the resulted char continued to react with oxygen in the gas. The char particles were collected at 1, 2, 4, and 6” above the flame and the mass releases of these partially oxidized char particles were measured. The high temperature reactivities were calculated from these mass releases. The TGA reactivities were also measured for these partially oxidized chars at a gas temperature of 823 K (550 °C). The HP-CBK model was used to unify the low temperature TGA rate data and the high temperature FFB rate data. The TGA reactivities are a function of burnout. The effects of burnout on reactivities were not the main interest of this project and were not explored in detail. Therefore, average TGA reactivities were used in this comparison with the HP-CBK model. The centerline gas temperatures were not uniform in the FFB. However, between two adjacent collection points the gas temperatures vary in a narrow range and may be approximated by an average temperature. The high temperature reaction rates between 4 and 6” were (somewhat arbitrarily) selected to evaluate the HP-CBK model. The rate data and experimental conditions are listed in Table 7.7. 111
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- Page 90 and 91: Single-Film Char Oxidation Submodel
- Page 92 and 93: where and An energy balance is used
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- Page 96 and 97: calculation uses a 7 × 7 × 7 matr
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- Page 100 and 101: Effective Diffusivity The major obs
- Page 102 and 103: where r p1 and r p2 are the average
- Page 104 and 105: where r p1 is the macro-pore radius
- Page 107 and 108: 7. Model Evaluation and Discussion
- Page 109 and 110: experiments are non-porous, the rat
- Page 111 and 112: and 2850 K). For consistency with t
- Page 113 and 114: The value of the roughness factor w
- Page 115 and 116: = S int S ext D e r p a 2 2M C M O2
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- Page 125 and 126: Table 7.5. The Experimental Conditi
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- Page 129: The HP-CBK was used to predict the
- Page 133 and 134: This equation can be derived as fol
- Page 135 and 136: q = A 1p e − E 1 p / RT P os 1 +
- Page 137 and 138: m obs = 0 at high temperatures) and
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- Page 141 and 142: 8. Summary and Conclusions The obje
- Page 143 and 144: 0.5 due to the contribution from th
- Page 145 and 146: Langmuir rate equation, the reactio
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- Page 149 and 150: 9. Recommendations The predictive c
- Page 151 and 152: References Ahmed, S., M. H. Back an
- Page 153 and 154: Essenhigh, R. H., D. Fortsch and H.
- Page 155 and 156: Mehta, B. N. and R. Aris , “Commu
- Page 157 and 158: Szekely, J. and M. Propster, "A Str
- Page 159 and 160: Appendices 139
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- Page 163 and 164: detaching the flame from the burner
- Page 165 and 166: To study the effects of steam, CO w
- Page 167 and 168: times at heights of 1, 2, 4, and 6
- Page 169 and 170: analysis. The char reactivities (in
- Page 171 and 172: Table A.5. Moisture, Ash and ICP Ma
- Page 173 and 174: Table A.9. Elemental Analyses of Fo
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TGA and FFB Data-This Study<br />
The reactivities of a south African coal char (Koonfontain) were studied in this<br />
project at atmospheric pressure using a thermogravimetric analyzer (TGA) and the flat-<br />
flame burner (FFB) at this laboratory as reported in the appendix. Koonfontain coal<br />
particles (with a mean diameter of 60 μm) were injected into the FFB from the bottom<br />
and devolatilized within the first inch in the burner. In the fuel-lean flames (methane fuel-<br />
lean, condition #2, and CO fuel-lean, condition #4), the resulted char continued to react<br />
with oxygen in the gas. The char particles were collected at 1, 2, 4, and 6” above the<br />
flame and the mass releases of these partially oxidized char particles were measured. The<br />
high temperature reactivities were calculated from these mass releases. The TGA<br />
reactivities were also measured for these partially oxidized chars at a gas temperature of<br />
823 K (550 °C). The HP-CBK model was used to unify the low temperature TGA rate<br />
data and the high temperature FFB rate data.<br />
The TGA reactivities are a function of burnout. The effects of burnout on<br />
reactivities were not the main interest of this project and were not explored in detail.<br />
Therefore, average TGA reactivities were used in this comparison with the HP-CBK<br />
model. The centerline gas temperatures were not uniform in the FFB. However, between<br />
two adjacent collection points the gas temperatures vary in a narrow range and may be<br />
approximated by an average temperature.<br />
The high temperature reaction rates between 4 and 6” were (somewhat arbitrarily)<br />
selected to evaluate the HP-CBK model. The rate data and experimental conditions are<br />
listed in Table 7.7.<br />
111
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