**4. Conclusions**

In contrast, a close coupling between instrumented lab and pilot scale tests and multiscale modeling may be able to elucidate the appropriate constitutive relations that are needed to augment the Cauchy equations of force and momentum conservation for successful continuum modeling. The powerful outcome of empirically-based numerical simulations is that the results would be scalable within any reasonable equipment size and the impact of specific material properties, such as those described above, could be determined to understand the operational envelope of specific processes. The multiscale models would operate as a direct transfer function to translate microscopic and macroscopic material properties that can be measured in the laboratory to material flow performance in biomass feeding and handling systems. The flow simulations could be used to identify cost effective approaches to modify the biomass materials and/or the transportation and handling equipment to reduce supply chain costs and also to minimize the equipment down-time due to material feeding problems. Continuum models may also be augmented by discrete element method (DEM) modeling that can simulate the motion and even the deformation of each particle in a flow field. **Figure 9** show an example of DEM model of a material that consists of particles with different shapes flowing in a wedge-shaped hopper. Simulating each individual particle in the flow offers the possibility of realistically capturing particle size and shape effects that cannot be directly incorporated into continuum models; however, such models have very high computational costs, so they are typically limited to simulations that involve not more than a few million

A final need that should be addressed is real-time, inline feeding and handling quality assurance (QA) and quality control (QC). Even with near perfect understanding of how material

**Figure 9.** DEM model of flow in a wedge-shaped hopper. The material consists of particles with different shapes as

indicated by particle color. Image courtesy of Hai Huang and Yidong Xia at Idaho National Laboratory.

particles with relatively simple shapes.

132 Advances in Biofuels and Bioenergy

Feeding and handling of biomass has been a primary factor causing pioneer industrial biorefineries to struggle to achieve production targets. The primary biomass properties that impact feeding behavior include bulk density, moisture content, compressibility, elasticity or spring back, particle size and shape distributions, cohesive strength, unconfined yield strength, internal friction angle, and wall friction angle (a property shared with the container surface). The primary issues in the design of hoppers and chutes are: (1) solid flow pattern, (2) slope angle of discharge, and (3) size of the discharge opening. Comprehensive methodologies have been developed to test material properties and design equipment systems for wellbehaved particulate materials, such as the Jenike method and tester. However, these methods are not always reliable for compressible, elastic, and anisotropic materials, such as biomass. Solving biomass feeding and handling challenges will require a combination of techniques and capabilities including numerical simulation, comprehensive material characterization, and mechanical tests. Numerical simulations to date have not had great impact in evaluating the flowability of biomass in handling equipment because of the extreme complexity of the flow problem. However, a close coupling between instrumented lab tests and multiscale modeling may be able to elucidate the appropriate constitutive relations that are needed for successful continuum modeling. These models could operate as a transfer function to translate microscopic and macroscopic material properties that can be measured in the laboratory to material flow performance in biomass feeding and handling systems at lab, pilot, and industry scale to understand the impact of variation in key flow properties on process reliability. This combination of experiments and flow simulations could be used to identify cost effective approaches to modify the biomass materials and/or the transportation and handling equipment to reduce supply chain costs and also to minimize equipment down-time due to material feeding problems.

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