Hammer milling switchgrass from weathered bales

Authors: PORDESIMO, LESTER - US Department Of Agriculture (USDA); IGATHINATHANE, CANNAYEN - North Dakota State University; HOLT, GREG - US Department Of Agriculture (USDA)

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2023
Publication Date: 3/30/2023
Citation: Pordesimo, L., Igathinathane, C., Holt, G. 2023. Hammer milling switchgrass from weathered bales. Industrial Crops and Products. 197. Article 116647. https://doi.org/10.1016/j.indcrop.2023.116647.
DOI: https://doi.org/10.1016/j.indcrop.2023.116647

Interpretive Summary: Considering that grasses have been targeted as raw material for bioenergy and will have to be handled in mass flow manner to be efficient, there is need to understand how grasses can be ground into easily flowing particles. For a biorefinery, the biomass will inevitably have to be stored, more than likely in an environment exposed to the elements. Consequently, there is a a need to understand how the weathered material will interact with processing equipment like a hammermill. Grinding tests with switchgrass stored for a year in the open (weathered) and under cover (unweathered) were undertaken at the USDA-ARS-CSRL Cotton Production and Processing Research Unit facilities in Lubbock, Texas. Results from this preliminary evaluation show that both weathered and unweathered switchgrass had grinding rates similarly increasing as the size of the screen openings increased with the unweathered material having a slightly higher throughput. The results from this study serve as reference for those who process grass biomass for bioenergy or industrial use on setting hammer mill operating parameters (screen size, operating speed) when grinding fresh cut or weathered material in obtaining the desired particle size at a given production rate. A more thorough study is needed to validate the findings from this preliminary study.

Technical Abstract: Considering that the grasses, and herbaceous biomass in general, have been targeted as a bioenergy feedstock, there is a greater consideration for the physical characteristics of grasses related to mass flow mechanical handling in industrial applications. To sustain a biorefinery, the biomass will inevitably have to be stockpiled. In a worst-case scenario, the stockpiled biomass will be exposed to the elements. Consequently, there is a need to understand how the weathered material will interact with processing equipment such as a hammermill. This study on grinding switchgrass in an 18.64 kW hammer mill with screen openings 9.52 mm, 31.75 mm, and ' mm (no screen) was undertaken to obtain preliminary data on the consequences of weathering of a biomass material prior to processing. Both switchgrass stored as bales for a year in the open (weathered, WSG) and under cover (unweathered, USG) had grind rates increasing with the increase in installed screen size with the grind rates for the USG consistently higher. With no screen installed in the hammer mill, the grind rate for the WSG was 0.23 kg/s compared to the 0.27 kg/s for the USG. When analyzed as a volume distribution of ground particles in machine vision methodology, switchgrass condition did not affect the particle size distribution (PSD) parameters of the ground material. However, it is noteworthy that the geometric mean length for WSG increased from 6 mm to 37 mm with increasing screen size for WSG, whereas the geometric mean length for USG increased from 6 mm to 31 mm.