Study of a new macro-particle model for the low-temperature pyrolysis of dried wood chips |
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Authors: | L M L Helsen E V M Van den Bulck |
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Institution: | (1) Department of Mechanical Engineering Katholieke Universiteit Leuven Celestijnenlaan 300A B-3001, Heverlee e-mail: lieve.helsen@mech.kuleuven.ac.be, |
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Abstract: | This paper presents a transient one-dimensional mathematical model which simulates the pyrolysis of a single dried wood particle.
The porous wood particle is considered as a two-phase system: the solid phase consisting of wood and char and the gas phase
consisting of volatiles and tar. Conservation equations for mass, momentum and energy are developed for each phase. Chemical
processes are described through an existing one-stage three-reactions scheme, leading separately to char, tar and volatiles
evolution dynamics. The variation of transport and physical properties with temperature and with composition is presented
by algebraic equations. The model presented in this paper is more advanced than the current models found in literature, since
it contains physical effects not included in past models, such as cross diffusion, differing solid and gas phase temperatures
and a transient gas phase momentum equation incorporating the wall friction experienced by a fluid flowing through a porous
medium. Furthermore, an adequate reference system for enthalpy, based on temperature dependent reaction heats, is used. The
mathematical equations with initial and boundary conditions are solved numerically by means of a commercial CFD code (PHOENICS).
The validity of the pyrolysis kinetics scheme is examined through comparison with experimental data. Furthermore, the macro-particle
model is validated by (1) examining the limitations and importance of the newly-modelled effects (different solid phase and
gas phase temperature, cross diffusion and wall friction) and (2) making a comparison between predicted and experimental results
for large particles.
Received on 18 December 2000 |
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