# Formulation and validation of a computational model for a dilute biomass slurry undergoing rotational mixing

## Abstract

In this paper we develop a computational model for the mixing and transport of a dilute biomass slurry. The objective was to create a sufficiently simple and efficient model for biomass transport that can be coupled with reaction models for the study of conversion of cellulosic biomass into fermentable sugars. Our target system is 5%-by-mass ..alpha..-cellulose, which is our proxy for more complex lignocellulosic biomass. In the authors' previous work, an experimental investigation with ..alpha..-cellulose under two vane-mixer configurations showed a bifurcation between a settling regime, for which settling effects dominate, and a suspended regime, for which solids are mostly suspended. Here, a mixed-fluid model was chosen, for which the model for the mixture-velocity field is the incompressible Navier-Stokes equations under the Boussinesq approximation for buoyancy. Solids transport includes solids motion due to diffusion, settling, advection, and shear. Comparison of simulated and experimental results show good agreement in the suspended regime, and in capturing the bifurcation rate. While the model captured well the distribution of solids in the settling regime, the model was incapable of capturing the high torque values seen in experiments with vanishing mixer rotation rate.

- Authors:

- National Renewable Energy Lab. (NREL), Golden, CO (United States)

- Publication Date:

- Research Org.:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)

- Sponsoring Org.:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Bioenergy Technologies Office (EE-3B)

- OSTI Identifier:
- 1427349

- Alternate Identifier(s):
- OSTI ID: 1548687

- Report Number(s):
- NREL/JA-5000-70621

Journal ID: ISSN 0009-2509; TRN: US1802584

- Grant/Contract Number:
- AC36-08GO28308; AC36-08-GO28308

- Resource Type:
- Accepted Manuscript

- Journal Name:
- Chemical Engineering Science

- Additional Journal Information:
- Journal Volume: 182; Journal Issue: C; Journal ID: ISSN 0009-2509

- Publisher:
- Elsevier

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 09 BIOMASS FUELS; multi-phase flow; sedimentation; spectral finite elements; high-order methods

### Citation Formats

```
Sprague, Michael A., Stickel, Jonathan J., Sitaraman, Hariswaran, and Crawford, Nathan. Formulation and validation of a computational model for a dilute biomass slurry undergoing rotational mixing. United States: N. p., 2018.
Web. doi:10.1016/j.ces.2018.02.030.
```

```
Sprague, Michael A., Stickel, Jonathan J., Sitaraman, Hariswaran, & Crawford, Nathan. Formulation and validation of a computational model for a dilute biomass slurry undergoing rotational mixing. United States. doi:10.1016/j.ces.2018.02.030.
```

```
Sprague, Michael A., Stickel, Jonathan J., Sitaraman, Hariswaran, and Crawford, Nathan. Sat .
"Formulation and validation of a computational model for a dilute biomass slurry undergoing rotational mixing". United States. doi:10.1016/j.ces.2018.02.030. https://www.osti.gov/servlets/purl/1427349.
```

```
@article{osti_1427349,
```

title = {Formulation and validation of a computational model for a dilute biomass slurry undergoing rotational mixing},

author = {Sprague, Michael A. and Stickel, Jonathan J. and Sitaraman, Hariswaran and Crawford, Nathan},

abstractNote = {In this paper we develop a computational model for the mixing and transport of a dilute biomass slurry. The objective was to create a sufficiently simple and efficient model for biomass transport that can be coupled with reaction models for the study of conversion of cellulosic biomass into fermentable sugars. Our target system is 5%-by-mass ..alpha..-cellulose, which is our proxy for more complex lignocellulosic biomass. In the authors' previous work, an experimental investigation with ..alpha..-cellulose under two vane-mixer configurations showed a bifurcation between a settling regime, for which settling effects dominate, and a suspended regime, for which solids are mostly suspended. Here, a mixed-fluid model was chosen, for which the model for the mixture-velocity field is the incompressible Navier-Stokes equations under the Boussinesq approximation for buoyancy. Solids transport includes solids motion due to diffusion, settling, advection, and shear. Comparison of simulated and experimental results show good agreement in the suspended regime, and in capturing the bifurcation rate. While the model captured well the distribution of solids in the settling regime, the model was incapable of capturing the high torque values seen in experiments with vanishing mixer rotation rate.},

doi = {10.1016/j.ces.2018.02.030},

journal = {Chemical Engineering Science},

number = C,

volume = 182,

place = {United States},

year = {2018},

month = {2}

}

#### Figures / Tables:

Figures / Tables found in this record:

*Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.*