(137f) Investigation of Particle Characteristics Influence of Crumbler® Rotary Shear Comminuted Granular Biomass on the Performance of Screw Feeding: Modeling and Experiment

Advances in bioenergy research will allow this energy source to play a vital role in shaping the clean energy portfolio to meet increasing global energy demands while satisfying the proposed measures to mitigate climate changes. Promoting fundamental understanding of the impact of the critical material attributes on the biomass feedstocks response can guide the selection of the critical processing parameters. For lignocellulosic biomass feedstocks, feeding and handling represent a substantial challenge in the supply system, due to the unfavorable properties of the raw biomass materials, e.g., low bulk density, high cohesiveness, variability, and characteristic flow behavior that involves complex localized elastic and plastic deformation patterns with strong dependency on the stress history. This poor flowability usually cause interruptions in the feeding systems and process upsets (such as jamming and clogging), which results in operation under an average feeding rate much lower than the design capacity and increased downtime. This, in turn, eventually leads to missed business opportunities and higher operation cost. Thus, identifying the underlying mechanisms controlling the mechanical behavior of this biomass feedstocks and determining critical parameters is crucial for the optimization of preprocessing unit operation and engineering favorable flowability of biomass in feeding and handling. This progress will render bioenergy technologies economically competitive and enable their deployment at commercial scale. Motivated by the quality-by-design approach, the current work investigates the effect of particle characteristics of rotary sheared pine particles on the performance of a screw feeding system using computational and experimental approaches. The system consists of a hopper, an agitator, and a screw conveyor, with materials fed at constant rpm. Using a Forest Concepts Crumbler^® rotary shear system, two different particle sizes (2 mm and 6 mm) with different size distributions were produced from “matched” bulk feedstock samples from conifer veneer. Those produced Crumbles have a cubic shape. The specific energy consumption for the comminution of these Crumbles and moisture content for different particle sizes were also measured. This data can be used to inform a prospective technoeconomic analysis. To experimentally characterize the impact of particle size on the flowability of this biomass feedstock, several samples were prepared by blending the original two Crumbles sizes at different fractions and fed into the screw feeding system. The influence of particle size on the typical design parameters, i.e., the driving torque, mass flow, and energy consumption, were analyzed for different rotational velocities. Furthermore, numerical experiments were utilized to simulate the conducted experiment and elucidate the underlying mechanisms. For this purpose, discrete element method (DEM) was employed using similar feeding system and clumped-sphere model. The DEM simulation results aided in gaining valuable insights by assessing the effect of additional factors on the flowability of the Crumbles, e.g., surface roughness, cohesion model, and rolling resistance. Our experimental results showed that while smaller particle size (2 mm) of pine particles achieves better flowability (with a smaller driving torque), the energy cost of comminution is significantly higher, and the bulk density is almost the same as the 6-mm pine particles. Furthermore, the DEM results identified the mechanical interlocking between contacting particles as the dominant mechanism in determining the driving torque. Alternating flow patterns were observed in the hopper, which led to remarkable variation in the mass flow rate over the course of simulation. Simulation and experimental results were found in a good agreement. It is worth mentioning that using simple particle shapes (e.g., mono-sphere) in conjunction with an elaborate contact model to capture the plastic deformation behavior (along with rolling resistance) did not achieve the same level of agreement that was accomplished by invoking clumped-sphere particle model with a layout mimicking the shape of the corresponding Crumble, which evidences the importance of capturing the particle shape and surface roughness to reliably simulate biomass granular flow.