Many processes can be used to produce energy or gaseous, liquid, and solid fuels from virgin and waste biomass. In addition, chemicals can be produced from biomass by a wide range of processes. It is evident from the data and information presented in this chapter, however, that the characteristics of potential feedstocks, particularly their moisture and energy contents, can have profound effects on the utility of specific biomass species and waste biomass. Table 3.10 is a summary of the principal feedstock, process, and product types that are considered in developing a synfuel-from-biomass process. There are many interacting parameters and possible feedstock—process—product combi­nations, but not all are feasible from a practical standpoint. For example, the separation of small amounts of metals present in biomass and the direct

TABLE 3.10 Summary of Feedstock, Conversion Process, and Primary Energy Product Types

Feedstock Conversion process Primary energy product

combustion of high-moisture-content algae are technically possible, but ener­getically unfavorable.

Moisture content of the biomass chosen is especially important in the selection of suitable conversion processes. The giant brown kelp, Macrocystis pyrifera, contains as much as 97 wt % intracellular water, so thermal gasification techniques such as pyrolysis and hydrogasification cannot be used directly without first drying the algae. Anaerobic fermentation is preferred because the water does not need to be removed. Wood, on the other hand, can often be processed by several different thermal conversion techniques without drying. Figure 3.7 illustrates the effects of thermal drying on biomass used for produc­tion of synthetic natural gas (SNG). A large portion of the feed’s equivalent energy content can be expended for drying, so the properties of a potential feedstock must be considered carefully in relation to the conversion process.

Table 3.11 lists the important feedstock characteristics to be examined when developing a conversion process for a specific virgin or waste biomass feedstock. A particular process also may have specific requirements within a given process type. For example, biological gasification and alcoholic fermenta-

Feed moisture content, %

tion are both microbiological conversion processes, but animal manure, which has a relatively high biodegradability, is not equally applicable as a feedstock for both processes.

In summary, it is not a simple matter to select the proper conversion process for a given biomass feedstock. Both biomass properties and process

Process type

requirements must be examined together and in depth to develop a technically and economically feasible system for producing the desired synfuels and energy products. These subjects will be examined in some detail in subsequent chapters.