Biomass feedstocks, conversion

Table 11. Biomass Feedstock Characteristics that Affect Suitability of Conversion Process...

Particle Size Reduction. Changes in the physical characteristics of a biomass feedstock often are requited before it can be used as a fuel. Particle size reduction (qv) is performed to prepare the material for direct fuel use, for fabrication into fuel pellets, or for a conversion process. Particle size of the biomass also is reduced to reduce its storage volume, to transport the material as a slurry or pneumatically, or to faciHtate separation of the components. 

A potential source of particulates is char formed when the biomass feedstock is incompletely gasified. These particles undergo devolatilization and subsequent reactions at gasification temperatures that leave them less reactive than fresh biomass feedstock. They can pass through the gasifier before they are completely gasified, particularly in those configurations with turbulent beds. Char entrained in the product gas also represents unconverted biomass that contributes to lower conversion efficiencies. 

Many available biomass feedstocks have a high moisture content, which lowers their heat value. Preprocessing can help, but adds to the cost. There are also some biomass conversion technologies that are only marginally beneficial and this keeps them from being cost-competitive. 

Second-generation biofuel technologies make use of a much wider range of biomass feedstock (e.g., forest residues, biomass waste, wood, woodchips, grasses and short rotation crops, etc.) for the production of ethanol biofuels based on the fermentation of lignocellulosic material, while other routes include thermo-chemical processes such as biomass gasification followed by a transformation from gas to liquid (e.g., synthesis) to obtain synthetic fuels similar to diesel. The conversion processes for these routes have been available for decades, but none of them have yet reached a high scale commercial level. 

Conversion of such biomass into chemicals may be expected to have a much longer future perspective. Most chapters in this book are committed to the catalysis of biomass feedstock to bulk or fine chemicals. Here one notes the need to define platform molecules and their conversion technologies as well as the need for more insights in the fundamental catalysis of these processes. 

A biorefinery is a facility that integrates biomass conversion processes and eqtrip-ment to produce fuels, power, and value-added chemicals from biomass. Biorefinery is the co-production of a spectram of bio-based products and energy from biomass. The biorefinery concept is analogous to today s crude oil refinery. Biorefinery is a relatively new term referring to the conversion of biomass feedstock into a host of valuable chemicals and energy with minimal waste and emissions. 

A core aspect of the model is the determination of the chemical conversion of gasifier SG to hydrogen by the RP. For conditions where steam availability is not limiting, the chemical conversion relates to the difference between the initial and final combustion/fuel ratio of the fuel gas. The initial CP/SG ratio is determined by the gasifier and the biomass feedstock. The final CP/SG ratio is determined by the thermochemical properties of the metal oxide material. Ideally the difference between the initial (CP/SG),and final (CP/SG)j , ratios should be as large as possible. In reality the availability of steam for the re-oxidation of the metal oxide is limiting for conditions where the difference in the CP/SG ratios are large. 

The attractiveness of production of liquid fuels from biomass lies in the renewable characteristics of biomass. As a consequence, the costs of an industry based on biomass conversion would be more or less predictable by inflation forecasting, and essentially independent of external political factors. With the incorporation of municipal solid waste as a biomass feedstock, such an industry also presents the opportunity of developing improved methods of recycling and waste disposal. 

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... 

Industrialbiobased products have enormous potential in the chemical and material industries. The diversity of biomass feedstocks (sugars, oils, protein, lignocellulosics), combined with the numerous biochemical and thermochemical conversion technologies, can provide a wealth of products that can be used in many applications. Targeted markets include the polymer, lubricant, solvent, adhesive, herbicide, and pharmaceutical markets. Industrial bioproducts have already penetrated some of these markets, but improved technologies promise new products that can compete with fossil-based products in both cost and performance. 

As illustrated in Fig. 33.14, biomass feedstocks can vary widely in the number of constituents and the concentration of each constituent. In biomass conversion processes, up to 20 constituents may need to be monitored to characterize the conversion of feedstock into a desired product or products. Standard wet chemical methods for the chemical characterization of biomass feedstocks and biomass-derived materials have been validated through the International Energy Agency and are available from the American Society for Testing and... 

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