Weathering and moisture effects on switchgrass size reduction in a hammermill

Authors: PORDESIMO, LESTER - Archer Daniels Midland; Holt, Gregory; IGATHINATHANE, CANNAYEN - North Dakota State University

Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: 8/10/2010
Publication Date: 8/16/2010
Citation: Pordesimo, L., Holt, G.A., Igathinathane, C. 2010. Weathering and moisture effects on switchgrass size reduction in a hammermill [abstract]. Proceedings of the American Society of Agricultural and Biological Engineers (ASABE) International Meeting, June 20-23, 2010, Pittsburgh, Pennsylvania. Paper No. 1008999.

Interpretive Summary: Exposure of baled grasses to weathering causes deterioration of the material. Much of the existing research addressing the effects of storage conditions on baled grasses has focused on their effects on the animal nutritional quality as forage for domesticated ruminant animals. Considering there is an increased focus on grasses as a bioenergy feedstock and that grasses collected in the form of bales will have to undergo some form of size reduction for biorefinery utilization, information pertaining to the quality of stockpiled biomasses is needed. 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 unreplicated study was undertaken using switchgrass bales available in Starkville, Mississippi, in an effort to obtain preliminary data on the consequences of weathering of a biomass material prior to processing. Switchgrass from round bales produced in November of 2006 at Mississippi State University left exposed in the field and square bales produced in November 2007 kept under roof were subjected to test grinding in a hammermill using different screen sizes. Findings of the study indicate that in the case of weathered material, it appears that a larger screen size or even no screen at all would produce an optimally small particle size. This is contrary to the general perception that a smaller screen size results in smaller particles for all input materials into a hammermill. Throughput through the hammermill increased linearly with increasing screen size opening for both the weathered and unweathered switchgrass. Although limited, the data provides an insight into the processing characteristics of weathered baled grasses, provides a reference for estimating the length of exposed storage before desired size reduction characteristics are compromised, and gives an insight into what size reduction operational adjustments can be made to account for the structural deterioration of the feedstock.

Technical Abstract: Exposure of baled grasses to weathering causes deterioration in chemical composition and physical integrity. Much of the existing research addressing the effects of storage conditions on baled grasses have focused on their effects on the animal nutritional quality subset of chemical composition because of the historical principal use of the grasses as forage for domesticated ruminant animals. Considering that grasses, and herbaceous biomass in general, are now targeted as a bioenergy feedstock, there is a reduced concern for nutritional composition and a greater consideration for physical characteristics. The fact that grasses collected in the form of bales will have to undergo some form of size reduction to be handled in a mass flow manner and be in a convenient form for biorefinery utilization causes this shift in information need. 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 unreplicated study was undertaken using switchgrass bales available in Starkville, Mississippi, in an effort to obtain preliminary data on the consequences of weathering of a biomass material prior to processing. Switchgrass from round bales produced in November of 2006 at Mississippi State University left exposed in the field and square bales produced in November 2007 kept under roof were subjected to test grinding in a hammermill using different screen sizes. Grinding weathered switchgrass in a 18.6-kW hammermill using screen sizes 9.72 mm to no screen (infinite screen size opening) produced particles with geometric mean length ranging from 0.053 0.059 mm as measured through machine vision. The grinds of unweathered switchgrass produced particles ranging in geometric length from 0.056-0.064 mm. The particle size measures calculated from the particle size distribution analysis indicated that to produce smaller particles from unweathered switchgrass a smaller screen size should be used. In the case of weathered material, it appears that a larger screen sizes or even no screen at all would produce an optimally small particle size. This is contrary to the general perception that a smaller screen size results in smaller particles for all input materials into a hammermill. Throughput through the hammermill increased linearly with increasing screen size opening for both the weathered and unweathered switchgrass. Although limited, the data provides an insight into the processing characteristics of weathered baled grasses, provides a reference for estimating the length of exposed storage before desired size reduction characteristics are compromised, and gives an insight into what size reduction operational adjustments can be made to account for the structural deterioration of the feedstock.