Biomass is a broad term understood to mean organic matter derived from living or recently dead organisms. Biomass can include woody wastes such as sawdust, forest litters, diseased wood, or tree trimmings; agricultural wastes such as crop residues, manures, anaerobic digestate, or poultry litters; grass such as fescue, CRP grasses, or native grasses; and miscellaneous sources such as noxious weeds, coffee grounds, railroad ties, nut shells, wood pallets, food waste, or any other landfill bound organic material. Impending regulations are changing the way that waste biomass streams may be disposed of or used in many cases.
The pathways available for disposal of these biomass streams include: combusting the biomass for energy production, composting the biomass, land-applying the manure-based streams as a fertilizer source, or anaerobically digesting some of the streams. Each pathway available for disposal offers benefits over other pathways as well drawbacks. Anaerobically digesting waste streams not only produces biogas that may be captured or flared but also produces another biomass waste stream in the form of digestate from the reactor. Composting the biomass, especially poultry litters and animal manures, requires large amounts of space to accommodate the compost as well as produces GHGs during the process. Depending on the biomass stream, combusting the biomass can result in boiler inefficiency due to the heterogeneous nature and ash content of the biomass. Combusting biomass also becomes problematic as the result of low bulk density, high moisture contents, and low heating values. Land applying the manure-based streams as a fertilizer is an inexpensive source of PKN but high application rates and mobility of the PKN can result in levels of contamination in the form of field runoff. This runoff has the potential to pollute shared water sources surrounding agricultural districts. Most notably of these pollutants are nitrates. High levels of nitrates have been linked to increased instances of Blue Baby Syndrome as well as increased instances of certain cancers, respiratory illness and livestock illness. High levels of other nutrients as well as off gassing of ammonia can lead to eutrophication of waters and contamination. The Rotary Compression Unit (RCU) provides a novel method for thermally upgrading these streams of biomass waste into either a biochar for soil remediation, a fertilizer product, or a solid fuel for co-combustion with coal in production of energy. This method remedies many of the issues associated with upgrading biomass with a higher energy efficiency and cost efficiency than other methods.
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