MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...

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To Air Water Bath Water Traps Flowmeters Vacuum Pumps F Soot-Leg Filter F Cooling Water Char-Leg Filter Flat- Flame Burner 144 Coal Particles from the Feeder Cyclone/ Char Collector Virtual Impactor Suction Probe Quartz Tower Cooling Water Quench Nitrogen Char Stream Soot Cloud Oxidizer Figure A.1. Schematic of the flat-flame burner and the particle collection and separation system. Fuel
To study the effects of steam, CO was used in the place of methane, while again maintaining the total flow rate and temperature profile in the first inch after the injection. Typical methane flames produce 16-25 mole-% steam in the post-flame gases. CO is an ideal alternative fuel to reduce steam in the post-flame gases, but as mentioned above, some hydrogen is necessary to stabilize the CO flame. Therefore, a total absence of steam in the post-flame gases was not possible. However, by using CO as the fuel, the steam concentration was reduced from about 17 mole-% to less than 1 mole-%. The four different char preparation conditions are described in Table A.1, and the measured temperature profiles for these conditions are given in Table A.2. Table A.1. Reactor Conditions Used Condition number #1 #2 #3* #4 Condition name CH4 fuel-rich CH4 fuel-lean CO fuel-rich CO fuel-lean CH4 (slpm) 4.84 1.52 0 0 CO (slpm) 0 0 16.9 6.41 H2 (slpm) 2.79 4.63 0.37 2 N2 (slpm) 5.41 0 6.46 0 Air (slpm) 38.6 43.7 21.0 40.7 Total flow rate (slpm) 51.6 49.9 44.8 49.1 Quench nitrogen (slpm) 65 65 65 65 Carrier nitrogen (slpm) 0.037 0.037 0.037 0.037 Equivalence ratio 1.37 0.58 1.96 0.49 Post-flame H2O (mole-%) 17.1 16.1 0.69 4.45 Post-flame O2 (mole-%) † 0 8.0 0 9.6 * Flow rates in condition #3 were measured with rotameters while those in other conditions were measured with mass flow meters. † Post-flame H 2O and O 2 mole fractions were calculated using EDWRDS code at 1600 K. 145
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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
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 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: detaching the flame from the burner
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
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MODELING CHAR OXIDATION AS A FUNCTION OF PRESSURE ...

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