Chapter 6 - Physical Conversion Processes

Abstract

This chapter discusses the physical processes that are employed to prepare biomass for use as fuel or as a feedstock for a conversion process. The processes examined are dewatering and drying, size reduction, densification, and separation. The physical processes, along with a few specific examples, and their relationship to the thermochemical or microbial process that may be used for subsequent conversion are described. Dewatering refers to the removal of all or part of the contained moisture from biomass as a liquid. The equipment used for dewatering includes filters and screening devices of various types, centrifuges, hydrocyclones, extrusion and expression presses, water extractors, and thickening, clarifying, and flotation hardware. Drying is a similar process, except that the moisture is removed as vapor. In some cases where a waste or virgin biomass feedstock is thermally processed directly for energy recovery, it may be necessary to partially dry the raw feed before conversion. Reduction in physical size is often required before biomass is used as a fuel or feedstock. Size-reduction techniques are employed to prepare biomass for direct fuel use, fabrication into fuel pellets, cubes, and briquettes, or conversion. Dry shredders are commercially used for reducing the size of biomass.