1
Effect of O2 and CO2 content on particle surface temperature
and size of coal char during combustion
Milena Rodriguez and Risto Raiko
Tampere University of Technology
Department of Energy and Process Engineering
FINNISH-SWEDISH FLAME DAYS
Naantali Finland, 28 - 29 January 2009
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Effect of O2 and CO2 content on particle surface
temperature and size of coal char during combustion
Presentation Outline:
• Introduction
• Char Combustion Model
• Experiments
• Equipment
• Conditions
• Results
• Conclusions
• Future Plan
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Introduction
The Project:
Oxy-concepts and Flue gases recirculation (FGR)
Main Goals:
• To produce information for CFD modelling on coal char burning and for
theoretical combustion model
• Pyrolysis and Combustion mass loss
• Particle surface temperature
• Particle velocity and diameter
• Developing a method for measurements
• Developing equipment for measurements
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Char Combustion Model
Regimes of Char combustion
Char combustion controlled by Diffusion
R"
Ni "
; N " MolarFlow
i
i
Number of Moles, Stoichiometric Coef .
N " kd C
Sh
Cs
kd d p
2 0.6 Re p
Sh
Di
1
2
Sc
1
3
From Poltto ja palaminen
Energy Balance
Char combustion controlled by Kinectic
R" kc C sO2
kc
Ae
E
mol
q conv
m2s
RT
Ts4 Tw4
hc Ts Te
q rad
hc Ts Te
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
Hm
W / m2
Ts4 Tw4
A: Pre-exponential factor, for first order [1/s]
E: Activation Energy [kJ/mol]
kc: Reaction rate constant
R"
W / m2
C O2
C
1
O2
2
CO2
CO
Hm
Hm
393.55kJ / mol
110.54kJ / mol
4.2.2009
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Experiments
Measurement Devices
Conditions needed for
measurements
• Stable temperature profile
• Different atmospheres
• Visualization
Drop-Tube Reactors
•
•
•
•
Pyrolysis and combustion reactor, 60
cm, after modification 15 cm
Measuring windows
Pyrometer
High-speed Camera
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Experiments
Specifications of the Drop-Tube Reactor
•
•
•
•
Height: 1.3 m, Heating length: 60 cm
Inside diameter: 26.3 mm
Material: Stainless Steel, Austenitic
Cr-Ni Heat resisting. 253 MA ASTM
A-312
Temperature resistance: Up to 1373 K
Parameters
•
•
•
•
•
•
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Fuel: USA Coal Char
Particle size: 100 – 200 m
Temperature: 973, 1123 and 1273 K
Volume flow: 1.4, 1.6 and 1.8 l/min
O2 content: 3, 6, 12 , 25, 35 and 50 (vol-% in N2)
O2 content: 3, 6, 12 , 25, 35 and 50 (vol-% in CO2)
Combustion lenght: 15 cm
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Experiments
Measurement Devices
Two-Colour Pyrometer
• Temperature (above detection limit)
• Diameter and velocity (used as reference values to back up the camera)
• Emissivity of the particles has to be evaluated
• At the end of combustion the pyrometer detects only the ”super particles”
High Speed Camera
• Accurate velocity and diameter
• Particle flame disturbes the analysis
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Experiment
Fuel analysis: High volatile bitiminous
Analysis
Proximate
Moisture (as received)
Volatile (TG)
Fixed C (TG)
Ash (815 C)
Ash (TG)
CO2 (TG)
C (TG)
Ultimate
C
H
N
S
Cl
O (Calculated)
Department of Energy and Process Engineering
Unit
wt-%
wt-% dry
wt-% dry
wt-% dry
wt-% dry
wt-% dry
wt-% dry
Coal
USA
2.1
30.8
50.2
8.1
7.3
5.9
1.6
wt-% dry
wt-% dry
wt-% dry
wt-% dry
wt-% dry
wt-% dry
66.6
4.2
1.05
0.52
0.0013
19.5
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Experiment
Temperature profile along length of reactor
Temperature profiles 700°C
Temperature [°C]
1000
800
600
Average Temp Wall
400
Temp.gas
200
0
0
10
20
30
40
50
60
Reactor length [cm]
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
10
Results
RESULTS
• Pyrolysis
• Mass loss in function of temperature and size
• Char combustion
• Temperature in function of oxygen concentration
• Temperature in function of the gas temperature
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
11
Results
Pyrolysis: Mass loss in function of temperature and size
USA COAL
Reactor length 15 cm
60%
100-125 m
40%
180-200 m
20%
0%
700°C
850°C
Vo latile M at ter
(w t% m f)
Vo latile M atter
(w t% m f)
USA COAL
Reactor length 60 cm
60%
40%
100-125 m
20%
180-200 m
0%
1000°C
700°C
Tem perature (°C)
1000°C
Temperature (°C)
Volatile matter of USA coal
as a function of gas temperature and particle size
Department of Energy and Process Engineering
850°C
Volatile matter of USA coal
as a function of gas temperature and particle size
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Results
Char combustion: Particle surface temperature and diameter in
function of oxygen concentration
USA coal char, Tg: 850°C, 100-125 m
Department of Energy and Process Engineering
USA coal char, Tg: 850°C, 100-125 m
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Results
USA Coal
100-125 µm
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Results
Char USA coal
100-125 µm
850 ° C
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Results
Char combustion: Particle temperature and diameter of
individual coal char at different oxygen concentration.
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Results
Velocity distribution of coal char by two colour pyrometer an CCD.
(Dp = 100-125 m, Tp = 1123 K and O2 = 3 vol-% in CO2)
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Results
Char combustion: Particle surface temperature in function of
oxygen concentration in nitrogen and carbon dioxide
Gas Temperature: 1273K and particle size: 180-200 m
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Results
Char Combustion: Particle surface temperature in function of
time
P arti cle Tempera ture
2600
3 vol% O2/N2 Measured
2400
12 vol% O2/N2 Measured
Tp [K]
2200
30 vol% O2/N2 Measured
2000
30 vol% O2/CO2 Measured
1800
3 vol% O2/N2
12 vol% O2/N2
1600
30 vol% O2/N2
1400
30 vol% O2/CO2
1200
1000
0
0,1
0,2
0,3
0,4
0,5
0,6
time [s]
Char USA Coal , 100-125 µm, Tg: 850°C
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Results
Char Combustion: Mass loss in function of time
Mass Loss
100
90
Mass Loss [%]
80
70
3 vol-% O2 in N2
60
12 vol-% O2 in N2
50
30 vol-% O2 in N2
40
30 vol-% O2 in CO2
3 vol-% O2 in N2 Measured
30
12 vol-% O2 in N2 Measured
20
30 vol-% O2 in N2 Measured
10
30 vol-% O2 in CO2 Measured
0
0
0,2
0,4
0,6
0,8
1
1,2
tim e [s]
USA Coal Char , 100-125 µm, Tg: 850°C
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Conclusion
Device
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Experimental equipment is now working
Experiments
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The oxygen concentration has more effect on
the particle surface temperature and diameter
that the gas temperature.
The Carbon dioxide has a cooling effect on the
burning particle.
Char combustion model (data)
• Particle sphericity
• Measurements errors
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
21
Future plans
• Coal combustion mass loss
• Moving to smaller particle size
(chemical kinetics)
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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Acknowledgements
TEKES, VTT, Metso Power Oy, Fortum Oy, PVO Oy and Foster Wheeler
Energy Oy.
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009
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THANK YOU FOR YOUR ATTENTION!!!
QUESTIONS?
Department of Energy and Process Engineering
Milena Rodriguez – Combustion at Different Oxygen Content
4.2.2009