Biomass feedstocks, conversion processes

The data required for operation of the model consist of the resource availabilities of the various types of biomass feedstocks, the process economics of biomass conversion options, a framework of energy demands and market prices, and a set of three parameters that are used to describe the interaction of the biomass-derived products with the markets in which they compete. 

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

The need to meet environmental regulations can affect processing costs. Undesirable air emissions may have to be eliminated and Hquid effluents and soHd residues treated and disposed of by incineration or/and landfilling. It is possible for biomass conversion processes that utilize waste feedstocks to combine waste disposal and treatment with energy and/or biofuel production so that credits can be taken for negative feedstock costs and tipping or receiving fees. 

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. 

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. 

Figure 2.13 did not include all the biomass conversion processes discussed above. It only considered those that produce transportation fuels. The processes that convert bio-feedstock into biocrude or electricity could not be included because their products have a different value than the transportation fuels. Such a comparison can be attempted by displaying the total manufacturing cost of biobased products in a graph that shows typical relationships between the price of crude and that its derivatives, i.e., of fuel oil, transportation fuel and electricity. This has been done in Fig. 2.14 for the lignocellulose conversion processes. 

Biomass conversion processes are still expensive today, being competitive at crude oil prices between 50 and 100 bbl-1. Lignocellulose might be a fairly cheap feedstock, cheaper than crude oil. However, its conversion requires large... 

Ensuring a constant feed supply is very important, because most of the biomass is only available on a seasonal basis. In such cases continuous operation of the conversion facility will require either extensive long-term storage of the feedstock or a feed reactor that is flexible enough to accommodate multiple feedstocks. Most thermal conversion processes demand a finely divided, substantially dry feed and therefore some pre-treatment is required to match the feedstock to the process. The main pre-treatment operations are [19] ... 

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. 

The Fischer-Tropsch (FT) catalytic conversion process can be used to synthesize diesel fuels from a variety of feedstocks, including coal, natural gas and biomass. Synthetic diesel fuels can have excellent autoigitition characteristics. The Fischer-Tropsch diesel is composed of only straight-chain hydrocarbons and has no aromatics or sulfur. The synthetic Fischer-Tropsch diesel fuel can provide benefits in terms of both PM and NO, emissions. 

Hydrogen can be produced from biorenewable feedstocks via thermochemical conversion processes such as pyrolysis, gasification, steam gasification, steam reforming of bio-oils, and supercritical water gasification (SWG) of biomass. 

Although technologies have been developed over past 50 years to process petroleum-based feedstock efficiently to generate hydrogen, its production from rene v-able biomass-derived resources remains a major challenge, because conversion processes often suffer from low hydrogen production rates and/or complex processing requirements [24, 25]. 

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... 

The fossil load factor is an important issue and its origin so evident and often unavoidable that we asked ourselves the question what the consequences are when this factor is reduced to zero. Whenever, in a biomass conversion process, a fossil fuel contribution was spotted, we replaced this contribution by one from biomass origin. For example, the process may require electricity, which is supplied by a nearby coal-fed power station. Then this amount of electricity was thought to be generated by a power station fed by biomass. Or the process may require heat or chemicals and again biomass is the raw material from which these requirements were met. Dr. Feng Wei made such an analysis for a process where a diesel-type product was obtained from wood chips as a feedstock. His work has been discussed as an example at the end of Chapter 13. 

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