Final Report: DOE/ID/14215 Page: 2 of 45
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Lignin content variability between anatomical fractions can approach 6%. The NREL
studies showed that total structural sugar content can vary between 45-88% as a
function of variety and environment. Of further interest, the glucan and lignin content was
least sensitive to these genetic and environmental factors; as such, the compositional
variability of these constituents between anatomical fractions appears to be significant
and have some degree of stable predictability that could be exploited to improve
feedstock structural carbohydrate content. Since ethanol yield is a function of feedstock
structural carbohydrate content, biomass anatomical fractions of higher product yield can
have a significant beneficial impact on minimum ethanol selling price. However, tests
conducted by INL showed that by using baffles and other machine adjustment
measures, the best achievable anatomical fractionation of cereal straw stems was
between 70-80% straw stem purity. This separation process also resulted in significant
losses of the desirable stem material, and represented only a 2.2% increase in glucan
content. However, based on analytical analysis of the discreet cereal straw anatomical
fractions, a 6% glucan content increase is potentially achievable if a high-fidelity
separation in excess of 80% stem purity can be achieved. Additionally, improvements in
separations are needed to prevent yield losses of desirable biomass components
resulting from simply losing the material during the harvest/collection. The purpose of
these advanced biomass separation computation engineering models is to more
effectively and efficiently engineer high-fidelity and high throughput separation systems
for biomass components.
Early in the project, INL and Iowa State University (ISU) developed a computational
modeling strategy for simulating multi-phase flow with an integrated solver using various
computational fluid dynamics (CFD) codes. INL and ISU then began simulating the multi-
phase flow with an integrated solver using various CFD codes: MFIX (Multiphase Flow
with Interphase eXchanges), ANSYS CFX, and ANSYS Fluent 6. ISU set up a classic
multi-phase test problem to be solved by the various CFD codes. The benchmark case
was based on experimental data for bubble gas holdup and bed expansion for a
gas/solid fluidized bed. Preliminary fluidization experiments identified some unexpected
fluidization behavior, where rather than the bed uniformly fluidizing, a "blow out" would
occur where a hole would open up in the bed through which the air would preferentially
flow, resulting in erratic fluidization.
To improve understanding of this phenomena and aid in building a design tool, improved
computational tools were developed. MFIX-DEM (discrete element model) functionality
was improved in terms of computational efficiency and numerical accuracy. Specifically,
the following tasks were completed:
" A pressure correction numerical method for the Semi-Implicit Method for
Pressure Linked Equations (SIMPLE) algorithm was developed and implemented
in MFIX. This numerical method improved the coupling between the particle
phase and the gas phase decreased the computational time by about four folds.
" A method of calculating drag force based on individual particle velocity was
implemented into MFIX. This method differentiated the drag force between
particles in the same computational cell while the original method assigned the
same drag force. This method gave a more physically realistic description of the
drag forces on particles.
" A method of estimating particle mean field using Monaghan's kernel function was
implemented into MFIX. A fixed bandwidth, which is wider than the Eulerian grid
spacing for the gas phase, was used for the kernel function. Therefore, the
method eliminated the increase of statistical error with refining the Eulerian grid.2
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Bryden, Kenneth; Hess, J. Richard; Ulrich, Thomas & Zemetra, Robert. Final Report: DOE/ID/14215, report, August 18, 2008; United States. (https://digital.library.unt.edu/ark:/67531/metadc893859/m1/2/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.