Biomass, types characteristics

Of the many factors which influence product yields in a fluid catalytic cracker, the feed stock quality and the catalyst composition are of particular interest as they can be controlled only to a limited extent by the refiner. In the past decade there has been a trend towards using heavier feedstocks in the FCC-unit. This trend is expected to continue in the foreseeable future. It is therefore important to study how molecular types, characteristic not only of heavy petroleum oil but also of e.g. coal liquid, shale oil and biomass oil, respond to cracking over catalysts of different compositions. 

The chemical characteristics of biomass vary over a broad range because of the many different types of species. Table 8 compares the typical analyses and energy contents of land- and water-based biomass, ie, wood, grass, kelp, and water hyacinth, and waste biomass, ie, manure, urban refuse, and primary sewage sludge, with those of cellulose, peat, and bituminous coal. Pure cellulose, a representative primary photosynthetic product, has a carbon content of... 

The main characteristics of a biomass conversion process are illustrated in Figure 13.21. The biomass feedstock, together with added water, is pumped and heated to a temperature and pressure not too different from water s critical point. The conversion process taking place at these conditions results in a transport fuel-type product, that... 

Biomass differs from conventional fossil fuels in the variability of fuel characteristics, higher moisture contents, and low nitrogen and sulfur contents of biomass fuels. The moisture content of biomass has a large influence on the combustion process and on the resulting efficiencies due to the lower combustion temperatures. It has been estimated that the adiabatic flame temperature of green wood is approximately 1000°C, while it is 1350°C for dry wood [41]. The chemical exergies for wood depend heavily on the type of wood used, but certain estimates can be obtained in the literature [42]. The thermodynamic efficiency of wood combustors can then be computed using the methods described in Chapter 9. 

The equations that have been developed for design using these pseudo constants are based on steady-state mass balances of the biomass and the waste components around both the reactor of the system and the device used to separate and recycle microorganisms. Thus, the equations that can be derived will be dependent upon the characteristics of the reactor and the separator. It is impossible here to present equations for all the different types of systems. As an illustration, the equations for a common system (a complete mix - stirred tank reactor with recycle) are presented below. 

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 3.11 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-... 

There are basically two types of municipal waste that offer opportunities for combined waste disposal and energy recovery—municipal solid waste (MSW, urban refuse, garbage) and biosolids (sewage, sludge). Each has its own distinctive set of characteristics as a biomass energy resource. 

Another conceptual approach to fermentation methanol from biomass is to convert biomass to acetate with suitable acetogenic populations, followed by direct conversion of acetate to methanol. This type of process does not involve intermediate methane and might possibly improve the operational characteristics of the process. The process can be represented by... 

It was not possible to justify the manufacture of most commodity-type organic chemicals from biomass after World War II, even though technically, all of them can be manufactured from biomass feedstocks. But the chemical industry is expected to slowly revert to biomass as petroleum and natural gas costs increase. Biomass is also expected to continue to be the preferred feedstock where its structural characteristics either facilitate certain processes or are desired in the end product. Examples include some chemicals in which... 

It should be noted that the combustion tests were conducted with only primary air supply. Attempts were made to keep the feed rate and excess air as similar as possible between trial burns, however, the operation conditions were very hard to keep fixed, as the excess air was controlled manually and these biomass fuels do not have good flow characteristics due to their inconstant particle shape, uneven particle size distribution and high moisture content. Many studies related to incomplete combustion have focused on processes with two-stage air supply and have identified that excess air is a key factor influencing the formation of CO and CH (2, 4, 5. 13). It has also been shown that each wood furnace has a typical correlation between the CO-emissions and the excess air ratio regardless of fuel type (13). 

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