I. INTRODUCTION

As discussed in previous chapters, there are numerous aquatic and terrestrial virgin biomass species and many types of waste biomass that are potential fuels or feedstocks. With the exception of microalgae and some high-moisture — content biomass, essentially all are solid materials. They contain organic com­pounds, minerals, and moisture. Some of the compositional differences are large. The aquatics, municipal biosolids, and animal manures are high in moisture content; the terrestrial species contain relatively small amounts of moisture. The ash contents of woody biomass species are small; some aquatics and agricultural crops contain large amounts of ash. On a moisture- and ash­free basis, the heating value of most biomass is in the same range, but on a dry basis, these materials can exhibit wide variations.

Because of these broad differences, many of the possible feedstock-process — energy product combinations are not feasible. For example, untreated mu­nicipal biosolids contain very large amounts of moisture and are normally unsuitable for thermochemical conversion. Such feedstocks do not support self-sustained combustion under conventional conditions unless the moisture is reduced by a considerable amount, a high-cost process in wastewater treat­ment plants. Biosolids are more suited for microbial conversion in aqueous systems where a liquid water medium is essential. In contrast, woody biomass is often suitable for direct use as a solid fuel or as a feedstock for thermochemical conversion. Predrying to remove some of the moisture, if needed, is readily accomplished at low cost.

Chapters 6 to 12 address specific groups of processes and methods employed for converting biomass to energy and fuels. In this chapter, the physical pro­cesses employed to prepare biomass for use as fuel or as a feedstock for a conversion process are discussed. The processes examined are dewatering and drying, size reduction, densification, and separation. The physical process, a few specific examples of the process, and its relationship to the thermochemical or microbial process that may be used for subsequent conversion are described.