MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...
MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ... MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...
2) The effectiveness factor approach developed in this study overcomes the theoretical and practical difficulties encountered when using the “second effectiveness factor” approach proposed by Essenhigh (1988). 3) The “Extended Resistance Equation” (ERE), developed to avoid iteration (Essenhigh, 1988), was shown in this study to work only for a few special cases. The iterative approach used in this study solves this problem with minimal computational efforts. 4) The correction function developed in this study reduces the error of the general asymptotic solution of the effectiveness factor from up to 17% to less than 2%. 128
9. Recommendations The predictive capability of a model is believed to rely on the fundamental understandings of the physical and chemical processes in char oxidation. The following ideas are recommended for future work in improving the char oxidation model: • Only a limited number of high-pressure char oxidation data are available. Additional data sets would be very valuable in order to explore the applicability of this model. • More theoretical and experimental studies should be conducted to better understand the mechanism of the carbon-oxygen reaction. Other Langmuir- Hinshelwood rate expressions may better describe the kinetics of char oxidation and therefore should be explored. However, care should be taken to minimize the number of unknown rate coefficients. • The accurate modeling of the effective diffusivity is important in order to predict char oxidation rates. More studies are recommended for pore structure and its evolution with burnout. Pore structure models based on measurable properties (N 2 and/or CO 2 surface areas, porosity, etc.) are recommended. • Work should be conducted to establish correlations between kinetic parameters (E 1p, A 1p, E 0, A 0) to measurable properties (coal rank, H and O content of coal and char, CaO surface area, etc.). 129
- Page 98 and 99: HP-CBK Model Development The HP-CBK
- 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
- Page 117 and 118: Reactor Head Flow Straightener Reac
- Page 119 and 120: the large size of the particle, and
- Page 121 and 122: taking into account convection, rad
- Page 123 and 124: 2.5x10 -4 2 /sec) 2.0 1.5 Rate (g/c
- Page 125 and 126: Table 7.5. The Experimental Conditi
- Page 127 and 128: The burnout and particle velocity d
- Page 129 and 130: The HP-CBK was used to predict the
- Page 131 and 132: TGA and FFB Data-This Study The rea
- 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
- Page 139 and 140: Currently the correlations between
- 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
- Page 147: II, in agreement with many observat
- 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
- Page 161 and 162: Introduction Appendix A: Experiment
- 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
- Page 175 and 176: temperature profile of the post-fla
- Page 177 and 178: Apparent densities 1.00 0.75 0.50 0
- Page 179 and 180: This observation is somewhat surpri
- Page 181 and 182: It is interesting to compare Figure
- Page 183 and 184: The N 2 BET surfacea areas and H/C
- Page 185 and 186: collected in the #4 reactor conditi
- Page 187 and 188: Rate (gC /g C remaining /sec) 1.6x1
- Page 189 and 190: close to zero, the accumulated erro
- Page 191: Appendix B: Errors and Standard Dev
9. Recommendations<br />
The predictive capability of a model is believed to rely on the fundamental<br />
understandings of the physical and chemical processes in char oxidation. The following<br />
ideas are recommended for future work in improving the char oxidation model:<br />
• Only a limited number of high-pressure char oxidation data are available.<br />
Additional data sets would be very valuable in order to explore the applicability of<br />
this model.<br />
• More theoretical and experimental studies should be conducted to better<br />
understand the mechanism of the carbon-oxygen reaction. Other Langmuir-<br />
Hinshelwood rate expressions may better describe the kinetics of char oxidation<br />
and therefore should be explored. However, care should be taken to minimize the<br />
number of unknown rate coefficients.<br />
• The accurate modeling of the effective diffusivity is important in order to predict<br />
char oxidation rates. More studies are recommended for pore structure and its<br />
evolution with burnout. Pore structure models based on measurable properties (N 2<br />
and/or CO 2 surface areas, porosity, etc.) are recommended.<br />
• Work should be conducted to establish correlations between kinetic parameters<br />
(E 1p, A 1p, E 0, A 0) to measurable properties (coal rank, H and O content of coal and<br />
char, CaO surface area, etc.).<br />
129
Change language