Abstract

As the conversion of coal utility boilers to 100% biomass combustors gains traction, understanding the interconnected impacts of harvesting and storage methods, fuel preparation, and thermochemical ash behavior is critical. This study evaluates miscanthus, switchgrass, and corn stover, targeting a < 1000 µm particle size through minimal (shredders/hammer mills) and heavy (pelletizing) pre-treatment. While heavy pre-treatment failed in a coal mill, minimal pre-treatment succeeded. Miscanthus (forage-harvested/silage-bagged) proved optimal, exhibiting minimal exogenous mineral accumulation up to (1.26 w%) and the smoothest mechanical feeding (deviation < 9%) due to its low particle aspect ratio. Conversely, baled switchgrass and corn stover accumulated up to 9.23 w% mineral matter and exhibited severe feeding resistance (>17% deviation) driven by fibrous, high-aspect-ratio morphologies. During combustion, agricultural residues yield low ash fusion temperatures (AFTs), generating deposits two to three times stronger than coal. To mitigate this severe fouling, mineral additives (coal fly ash, lime, and cement kiln dust) were injected. These additives effectively raised bulk AFTs and reduced deposit tenacity by up to 73%. Specifically, 2 w% coal fly ash or lime reduced miscanthus deposit tenacity to levels comparable to baseline coal. Severe deposition is primarily driven by volatile potassium; thus, precise control over its phase partitioning is essential. This study demonstrates that targeted mineral additives systematically reduce deposit potassium concentrations via chemical fixation, competitive displacement, and dilution. Volatile potassium transitions from low-melting aerosols to highly stable, high-melting refractory compounds (e.g., sanidine and leucite), effectively bypassing heat transfer surfaces. Optimizing minimal pre-treatment processes and implementing mineral additive strategies surmount both mechanical and chemical barriers to 100% agricultural biomass combustion.

Degree

PhD

College and Department

Ira A. Fulton College of Engineering; Chemical Engineering

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2026-04-20

Document Type

Dissertation

Keywords

bioenergy, fouling, milling, sootblower, additives, ash deposition, potassium, FactSage

Language

english

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Engineering Commons

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