Modeling Cotton Module Builder and Loader to Enhance Biomass Testing
Authors: Womac Alvin. R , Byers Erin  E. , Thomas Kimberly  G. , Hillenbrand Boone   , Smith Andrew   , Bitra Venkata Sambasiva Prasad 
Published: October 2021

Highlights

Physical models of module builder and module loader were developed to enhance biomass testing with reduced mass and volume of biomass.

Models used dimensional analysis, Pi Terms, and engineering factors and emphasis on reduced module upsetting and disturbance.

Some engineering terms such as tamping face pressure and velocity, and particle size were not scaled to reduce biological-material distortions.

Switchgrass bulk density at 8% wet basis for prototype and model were 115 and 80 kg m-3, respectively.

Abstract. The objective was to design and implement separate models of a first-generation cotton module builder and a module loader that facilitated tamping quasi-confined biomass and the minimal disturbances of modules during emptying from the builder and during loader operations including unloading. The 122-cm long model, compared to 978-cm long prototype, reduced the mass of module contents required for testing from 6188 to 44 kg, or by a factor of 141:1. The tamping process was emphasized with constant tamper pressure of 76.6 kPa applied to module contents for prototype and model. Consistent properties such as SG characteristic length were also held constant among module sizes to reduce the complications of introducing un-anticipated biological-material distortions. Similarities in design aspects beyond dimensional analysis were emphasized to reduce inadvertent module upset and disturbance. Hydraulics ensured uniform tamping and lifting. An efficient module box for the model resembled the prototype-scale commercial unit with z-shaped ribs and upward-tapered module sides. Seed cotton [8% moisture wet basis (w.b.)] bulk densities for prototype and model were 166 and 107 kg m-3, respectively. Bulk densities for switchgrass (8% w.b.) prototype and model were 115 and 81 kg m-3, respectively. Reduced bulk density of models was attributed to essentially no external confinement stresses being applied to modules at rest resulting in only self-imposed confinement stresses due to module content over-burden. However, unconfined modules may have a role in handling biomass for reduced distances. Also related to minimizing module upsetting, module loading emphasized the counter-motions of advancing the loader versus the conveyor motion in the opposite direction, all driven with an electric motor. Module stability during loading was attributed to a self-imposed normal stress of module weight acting downward onto a horizontal plane of the module. The fixed loading angle of 15° and material bulk properties were held constant between prototype and model. Dependent variable for the module loader was normal stress for module stability. Normal stresses resulting from seed cotton at 8% moisture content (wet basis) were 4.754 and 0.637 kPa, respectively. Normal stresses for chopped SG at 8% moisture content (wet basis) were 3.302 and 0.484 kPa, respectively. Biomass modules would not be as stable as cotton modules based on normal stress, and due to lack of intermeshing cotton fibers. Results of loading and unloading a dozen SG model modules resulted in one module failure due to upset, and that was attributed to a 2-layer fill versus 3-layer fill for that one module. Keywords: