MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...

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experiments (and reported by many researchers as true activation energies) are actually still coupled with mass diffusion effects in the micropores. TGA Reactivities: Effects of Coal Types Chars were prepared from all six parent coals (Koonfontain, Middleburg, Cerrejon, Yang Quan, Pittsburgh, and Han Cheng coals) under CH 4 fuel-lean condition at 1” sampling height. The TGA reactivities of these chars were measured at 550 °C in 10 mole- % O 2 and plotted in Figure A.8. 2.4x10 -3 Rate (g C /g C remaining /sec) 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 Cerrejon 20 Middleburg 40 162 Yang Quan %Burnout Pittsburgh 60 Koonfontain Han Cheng Figure A.8. TGA reactivities of all chars (prepared under CH 4 fuel-lean condition, collected at 1” sampling height) measured at 550 C in 10 mole-% oxygen. 80 100
The N 2 BET surfacea areas and H/C ratios of these chars are plotted in Figure A.9. The chars are in the order of decreasing TGA reactivity from left to right in Figure A.9. It can be seen that the N 2 surface areas and H/C ratios tend to decrease from left to right with a few exceptions. This means TGA reactivities are correlated with N 2 surface areas and H/C ratios even for chars of different parent coals. N 2 surface area and 1000*H/C ratio 160 140 120 100 80 60 40 20 0 Yang Quan Pittsburgh Middleburg Cerrejon Koonfontain Han Cheng N2 surface area 1000x H/C Figure A.9. N 2 surface areas and H/C ratios of six chars (at condition #2 and 1” sampling height) High Temperature Reactivity The percent of the daf mass remaining (m/m 0) of Koonfontain chars #2 and #4 from high temperature FFB experiments are plotted as functions of residence time in Figure A.10. The reactivities based on (a) the amount of carbon available in the particles, and (b) the external surface area of a representative particle (which has an average particle size), are shown in Figures A.11 and A.12. From Figures A.11 and A.12 it can be seen that the average (i.e., last set of bars) high temperature reactivity of char #4 is about twice 163
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MODELING CHAR OXIDATION AS A FUNCTI
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BRIGHAM YOUNG UNIVERSITY As chair o
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CBK model uses: 1) an intrinsic Lan
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Table of Contents List of Figures..
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Appendices.........................
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Figure A.2. Mass releases of the Ko
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Table 7.6. Parameters Used in Model
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Ed activation energy of desorption,
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vc the volume of combustible materi
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Background 1. Introduction The rate
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the CBK model developed at Brown Un
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Zone III rate ∝ C og E obs → 0
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coal-general kinetic rate constants
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Boundary Layer Diffusion The molar
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= q obs q max The factor can be use
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where k 1 and K are two kinetic par
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particle can therefore be convenien
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This is the first time that the gen
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Data of Mathias Mathias (1996) perf
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urn with shrinking diameters, and t
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3. Objectives and Approach The obje
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Introduction 4. Analytical Solution
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Task and Methodology Task One of th
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2 [ (i +1) − (i − 1)] i b = −
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Table 4.1. The Relative Error * (%)
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The resulting observations regardin
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correction. The values of functions
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Table 4.6. The Relative Error* (%)
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Table 4.8. The Relative Error* (%)
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general asymptotic solution. An arc
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5. Theoretical Developments The int
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order of a reaction is usually dete
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nobs = 1 (KCs ) 2 2 1 [KCs − ln(1
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The observed reaction order in Zone
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Bulk Diffusion vs. Knudsen Diffusio
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where D K is in cm 2 /sec, r p is t
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where T p is in K, P is in atm. The
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Both of these assumptions are argua
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2 r obs ′ − [kD Pog + k d + kD
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oxygen partial pressure (Suuberg et
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Farrauto and Batholomew (1997) prop
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assumes a homogeneous, non-interact
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Single-Film Char Oxidation Submodel
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where and An energy balance is used
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where is the empirical burning mode
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calculation uses a 7 × 7 × 7 matr
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HP-CBK Model Development The HP-CBK
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Effective Diffusivity The major obs
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where r p1 and r p2 are the average
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where r p1 is the macro-pore radius
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7. Model Evaluation and Discussion
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experiments are non-porous, the rat
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and 2850 K). For consistency with t
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The value of the roughness factor w
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= S int S ext D e r p a 2 2M C M O2
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Reactor Head Flow Straightener Reac
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the large size of the particle, and
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taking into account convection, rad
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2.5x10 -4 2 /sec) 2.0 1.5 Rate (g/c
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Table 7.5. The Experimental Conditi
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The burnout and particle velocity d
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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 and 148: II, in agreement with many observat
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
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: It is interesting to compare Figure
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
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MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...

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