Determination of Pyrolysis Temperature for Charring Materials.
Determination of Pyrolysis Temperature for Charring
Materials.
(821 K)
Park, W. C.; Atreya, A.; Baum, H. R.
NIST GCR 07-913; 28 p. December 2007.
Sponsor:
National Institute of Standards and Technology,
Gaithersburg, MD
Keywords:
charring; pyrolysis; temperature; wood; kinetics;
experiments; equations; geometry; heat flux; thermal
properties
Abstract:
An energy and mass balanced method of determining the
pyrolysis temperature is proposed. The concept
is to find the pyrolysis temperature that consumes the
same amount of energy to produce the same amount
of mass when using the pyrolysis front model as when
using the finite rate kinetics model for the entire
charring process. The resulting pyrolysis temperature
has the form of pyrolysis rate weighted average
temperature. Comparisons between finite rate kinetics
and pyrolysis front models for various boundary
conditions, geometries, heats of decomposition, kinetic
parameters and assumptions used in the literature
were made to assess the proposed method. Models using
energy and mass balanced pyrolysis temperature
show good agreement with finite rate models and the
experiments. Extensive numerical studies on various
factors influencing the chaning material pyrolysis show
that heat flux, sample size, heat of decomposition
and kinetic parameters are the most important factors
for determining an appropriate pyrolysis
temperature. Thermal conductivity, specific heat and
density have a lesser effect on the pyrolysis
temperature. For practical application, a
non-dimensional correlation is developed to determine
the
appropriate pyrolysis temperature without solving the
problem by using the finite rate model. Using this
conelation the energy and mass balanced pyrolysis
temperature can be determined within 7.6K. These
predictions are validated by comparison with
measurements of wood cylinder pyrolysis. A good
agreement suggests that simpler pyrolysis front models
yield practically useful and accurate results given
an appropriate pryolysis temperature.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899