Thursday, November 12, 2015: 3:15 PM
254C (Salt Palace Convention Center)
Christos Altantzis1, Addison K. Stark2, Richard B. Bates1, Whitney S. Jablonski3, Daniel Carpenter3, Akhilesh Bakshi1, Rajesh Sridhar4, Aaron Garg5, John L. Barton5, Ran Chen5 and Ahmed F. Ghoniem1, (1)Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, (2)Advanced Research Projects Agency - Energy, Washington, DC, (3)National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, (4)Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, (5)Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA
Numerical simulation of biomass gasification is a steam-blown
bubbling fluidized bed: A validation study
Christos
Altantzis1, Addison K. Stark2, Richard B. Bates1,
Whitney Jablonski3, Danny Carpenter3,
Akhilesh
Bakshi1, Rajesh Sridhar1, Aaron Garg4, John L.
Barton4, Ran Chen4, Ahmed F. Ghoniem1
1Department
of Mechanical Engineering, Massachusetts Institute of Technology
77 Massachusetts Avenue, Cambridge, MA
02139-4307, USA
2Advanced
Research Projects Agency-Energy (ARPA-E), US Department of Energy
1000 Independence Avenue, SW Washington, DC
20585
3National
Bioenergy Center, National Renewable Energy Laboratory
Golden, Colorado 80401
4Department
of Chemical Engineering, Massachusetts Institute of Technology
77 Massachusetts Avenue, Cambridge, MA
02139-4307, USA
Biomass is a renewable energy resource
with increasing potential because it is abundant and widely distributed. Energy
crops, agricultural byproducts or forest residues can be utilized in
gasification processes to produce syngas, which can be further processed to
liquid fuels. Owing to the favorable heat and mass transfer rates obtained in
fluidized bed reactors, they are the most widely used type of gasifier for
biomass feedstocks. On the other hand, the differences in size and density of
biomass and inert particles can lead to a non-uniform distribution across the
bed under certain conditions, resulting in a segregated solids mixture with
unfavorable temperature distribution and deteriorating reactivity causing lower
product yields and increased tar production, thus reducing gasification
efficiency. The investigation of the reacting hydrodynamics of the multiphase
flow system via numerical modeling complements the knowledge acquired by
experimental measurements overcoming their limitations and contributes to the
optimization of the reactor operation.
In the current work, an Eulerian multiphase approach, where
both the gas and the solid phases are described as interpenetrating continua,
is employed for modeling the gasification of biomass in a lab-scale reactor.
The kinetic theory of granular flows is used for the evaluation of the solid
phase properties of the ternary mixture consisting of biomass particles, char
and sand. The bed is fluidized with steam at different temperatures and it is
externally heated. The hydrodynamic model is coupled with a chemical mechanism
for the description of the gasification process consisting of heterogeneous
biomass devolatilization and char gasification reactions and homogeneous
gas-phase reactions (tar cracking and water-gas shift reactions). The computational results are validated
against experimental measurements conducted in a steam-blown bubbling fluidized
bed at the National Renewable Energy Laboratory (NREL). The influence of the
operating temperature is investigated together with the effect of the thermal
boundary condition. The numerical tool
used to solve the governing equations is the Multiphase Flow with Interphase eXchanges (MFIX) code developed by the U.S. Department of
Energy (DOE) National Energy Technology Laboratory (NETL).
Extended Abstract: File Not Uploaded
