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On Thermal Properties of a Pyrolysing Wood Particle
Ville Hankalin, Tuukka Ahonen, and Risto Raiko
Tampere University of Technology
Department of Energy and Process Engineering
Finnish-Swedish Flame Days 2009
January 28-29, 2009
Naantali, Finland
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Content
• Introduction
• Thermal conductivity
• Wood
• Wood char
• Specific heat capacity
• Experiments on thermal conductivity at TUT
• Device and procedure
• Results
• Thermal conductivity of a pyrolysing wood particle
• Summary and following steps
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Introduction
• Pyrolysis
• Thermal decomposition of a solid fuel in an inert atmosphere
• Tarry liquid, char, non-condensable gases
• Temperature, pressure, heating rate
• Biomass pyrolysis -> bio oil (= the tarry liquid)
• high heating rate, ~500 oC, rapid cooling of gases and
aerosols
• Energy balance equation for a pyrolysing fuel particle
T
(
)
(
)
T
c
T
p
p
t
1
r2 r
p (T )r
2
T
r
''
hvol
vol
t
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
cvol (T ) m vol
T
r
4.2.2009
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Introduction
• Pyrolysis rate of a fuel particle is controlled by
• chemical kinetics
• external heat transfer
• internal heat transfer
• mass transfer
• Excluding very small particles pyrolysis of wood is usually
controlled by internal heat transfer
• Physical, chemical and structural properties of wood change
during pyrolysis
• Thermal conductivity and density cause the highest sensitivity of
pyrolysis model predictions (Di Blasi, 2008)
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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• Introduction
• Thermal conductivity
• Wood
• Wood char
• Specific heat capacity
• Experiments on thermal conductivity at TUT
• Device and procedure
• Results
• Thermal conductivity of a pyrolysing wood particle
• Summary and following steps
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Thermal Conductivity
• Wood
• Function of grain direction, temperature, density and moisture
• Parallel with the grains
– 0.156 – 0.419 W/mK
• Perpendicular to the grains
– 0.074 – 0.214 W/mK
• Only few correlations for thermal conductivity of wood was found
• Constant values are still widely used in pyrolysis models
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Thermal Conductivity
• Wood char
• cellular structure
• grain direction, density and temperature
• little information in the literature
• 0.071 – 0.1156 W/mK
• Elevated temperatures
• Hardly any information in the literature
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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• Introduction
• Thermal conductivity
• Wood
• Wood char
• Specific heat capacity
• Experiments on thermal conductivity at TUT
• Device and procedure
• Results
• Thermal conductivity of a pyrolysing wood particle
• Summary and following steps
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Specific Heat Capacity
• Literature
• Wood
0.67 – 2.5 kJ/kgK
• Wood char 0.67 – 1.35 kJ/kgK
Wood (~T)
Wood char (~T2)
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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• Introduction
• Thermal conductivity
• Wood
• Wood char
• Specific heat capacity
• Experiments on thermal conductivity at TUT
• Device and procedure
• Results
• Thermal conductivity of a pyrolysing wood particle
• Summary and following steps
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Device and procedure
Fitch-type device
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Device and procedure
Temperature range 36 – 97 oC
(Ahonen, 2008)
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Results
Wood (pine, measurements at 36 oC)
Wood char
• pine
char
increased by 10 % (36 – 97 oC)
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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• Introduction
• Thermal Properties of wood and wood char – A literature review
• Thermal conductivity
• Wood
• Wood char
• Specific heat capacity
• Experiments on thermal conductivity at TUT
• Device and procedure
• Results
• Thermal conductivity of a pyrolysing wood particle
• Summary and following steps
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Thermal Conductivity of a Pyrolysing Wood Particle
Thermal conductivity of
wood particles that are
pyrolysed at different
temperatures
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Thermal Conductivity of a Pyrolysing Wood Particle
- Average of longitudinal
and radial directions
= 450 kg/m3)
char is a linear function
of T as measured
between 36 – 97 oC
o
char(36 C) = 0.09 W/mK
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Thermal Conductivity of a Pyrolysing Wood Particle
• Effect of radiation on thermal conductivity of char?
• Measurements only at 36 - 97 oC
• Some correlations for radiation
• 0.02 W/mK at 650 oC
(Atkinson and Merrick, 1983)
• 0.07 W/mK at 650 oC
(Di Blasi, 1996)
• 0.11 W/mK at 650 oC
(Chang, 1985)
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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• Introduction
• Thermal Properties of wood and wood char – A literature review
• Thermal conductivity
• Wood
• Wood char
• Specific heat capacity
• Experiments on thermal conductivity at TUT
• Device and procedure
• Results
• Thermal conductivity of a pyrolysing wood particle
• Summary and following steps
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Summary and following steps
• Literature review on thermal properties of wood and wood char
• Specific heat capacity fairly well known
• No good information on thermal conductivity
• Measurements on thermal conductivity of wood and wood char
• A draft of thermal conductivity derived
• A 3-year project (part of Biorefine program of TEKES)
• Thermal properties of wood and wood char
• Drop-tube experiments
• Pyrolysis model
• The draft of thermal conductivity will be used
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009
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Acknowledgement
•
•
•
•
•
•
Finnish Funding Agency for Technology and Innovation (TEKES)
Fortum Power and Heat
Lassila&Tikanoja
Metso Power
UPM-Kymmene
Graduate School for Energy Science and Engineering (EST)
Thank you!
Ville Hankalin – On Thermal Properties of a Pyrolysing Wood Particle
4.2.2009