Effects of intraparticle heat and mass transfer on biomass devolatilization: Experimental results and model predictions. Bharadwaj, A., Baxter, L., L., & Robinson, A., L. Energy Fuels, 18:1021-1031, 2004.
abstract   bibtex   
This paper examines the effects of intraparticle heat and mass transfer on the devolatilization of millimeter-sized biomass particles under conditions similar to those found in commercial coal-fired boilers. A computational model is presented that accounts for intraparticle heat and mass transfer by diffusion and advection during particle heating, drying, and devolatilization. To evaluate the model, devolatilization experiments under high-temperature and high-heating rate conditions were conducted using the Multifuel Combustor at Sandia National Laboratories. Measurements of mass-loss and changes in particle size for millimeter-sized alfalfa and wood particles are presented as a function of reactor residence time. For millimeter-sized particles, both fuels completely devolatilized in approximately 1 s with rapid initial mass loss. The total volatile yield of the wood was 92% on a dry, ash-free basis, significantly higher than that reported by a standard ASTM test, indicating dependence of the ultimate yield on local conditions. Particles for both fuels shrink significantly and become less dense during devolatilization. The comprehensive model accurately predicts the devolatilization behavior of millimeter-sized biomass particles; these measurements could not be reproduced with a simple lumped model that ignores intraparticle transport effects. The comprehensive model is used to examine the effects of particle size and moisture content on devolatilization under conditions representative of those found in coal boilers. Biomass particles of radii up to 2 mm and moisture content up to 50% are considered. As expected, intraparticle heat and mass effects are more significant for larger particles. These effects can significantly delay particle heating and devolatilization; for example, intraparticle effects delay the heating and devolatilization of millimeter-size particles by as much as several seconds for a particle with a 1.5-mm radius compared to predictions of a lumped model. This delay is significant considering the short residence times of commercial boilers and should be accounted for in computational models used to evaluate the effects of biomass-coal cofiring on boiler performance. C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA. Carnegie Mellon Univ, Ctr Energy & Environm Studies, Pittsburgh, PA 15213 USA. Brigham Young Univ, Dept Chem Engn, Provo, UT 84602 USA.
@article{
 title = {Effects of intraparticle heat and mass transfer on biomass devolatilization: Experimental results and model predictions},
 type = {article},
 year = {2004},
 pages = {1021-1031},
 volume = {18},
 id = {c38711e6-5d08-3962-a40b-daf798660863},
 created = {2014-10-08T16:28:18.000Z},
 file_attached = {false},
 profile_id = {363623ef-1990-38f1-b354-f5cdaa6548b2},
 group_id = {02267cec-5558-3876-9cfc-78d056bad5b9},
 last_modified = {2017-03-14T17:32:24.802Z},
 read = {false},
 starred = {false},
 authored = {false},
 confirmed = {true},
 hidden = {false},
 citation_key = {Bharadwaj:EF:2004a},
 source_type = {article},
 private_publication = {false},
 abstract = {This paper examines the effects of intraparticle heat
and mass transfer on the devolatilization of millimeter-sized
biomass particles under conditions similar to those found in
commercial coal-fired boilers. A computational model is presented
that accounts for intraparticle heat and mass transfer by diffusion
and advection during particle heating, drying, and
devolatilization. To evaluate the model, devolatilization
experiments under high-temperature and high-heating rate conditions
were conducted using the Multifuel Combustor at Sandia National
Laboratories. Measurements of mass-loss and changes in particle
size for millimeter-sized alfalfa and wood particles are presented
as a function of reactor residence time. For millimeter-sized
particles, both fuels completely devolatilized in approximately 1 s
with rapid initial mass loss. The total volatile yield of the wood
was 92% on a dry, ash-free basis, significantly higher than that
reported by a standard ASTM test, indicating dependence of the
ultimate yield on local conditions. Particles for both fuels shrink
significantly and become less dense during devolatilization. The
comprehensive model accurately predicts the devolatilization
behavior of millimeter-sized biomass particles; these measurements
could not be reproduced with a simple lumped model that ignores
intraparticle transport effects. The comprehensive model is used to
examine the effects of particle size and moisture content on
devolatilization under conditions representative of those found in
coal boilers. Biomass particles of radii up to 2 mm and moisture
content up to 50% are considered. As expected, intraparticle heat
and mass effects are more significant for larger particles. These
effects can significantly delay particle heating and
devolatilization; for example, intraparticle effects delay the
heating and devolatilization of millimeter-size particles by as
much as several seconds for a particle with a 1.5-mm radius
compared to predictions of a lumped model. This delay is
significant considering the short residence times of commercial
boilers and should be accounted for in computational models used to
evaluate the effects of biomass-coal cofiring on boiler
performance.
C1 Carnegie Mellon Univ, Dept Mech Engn, Pittsburgh, PA 15213 USA.
Carnegie Mellon Univ, Ctr Energy & Environm Studies, Pittsburgh,
PA 15213 USA. Brigham Young Univ, Dept Chem Engn, Provo, UT 84602
USA.},
 bibtype = {article},
 author = {Bharadwaj, A and Baxter, L L and Robinson, A L},
 journal = {Energy Fuels}
}

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