Biomass, types processing

It is sometimes desirable to physically separate potential biomass feedstocks into two or more components for different applications. The subject is quite broad in scope because of the wide range of biomass types processed and the variety of separation methods that are used. Even the harvesting of virgin biomass involves physical separation technologies. Examples are the separation of agricultural biomass into foodstuffs and residues that may serve as fuel or as a raw material for synfuel manufacture, the separation of forest biomass... 

Liquefaction. Siace the 1970s attempts have been made to commercialize biomass pyrolysis for combiaed waste disposal—Hquid fuels production. None of these plants were ia use ia 1992 because of operating difficulties and economic factors only one type of biomass Hquefaction process, alcohohc fermentation for ethanol, is used commercially for the production of Hquid fuels. 

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. 

Knowledge of the effects of various independent parameters such as biomass feedstock type and composition, reaction temperature and pressure, residence time, and catalysts on reaction rates, product selectivities, and product yields has led to development of advanced biomass pyrolysis processes. The accumulation of considerable experimental data on these parameters has resulted in advanced pyrolysis methods for the direct thermal conversion of biomass to liquid fuels and various chemicals in higher yields than those obtained by the traditional long-residence-time pyrolysis methods. Thermal conversion processes have also been developed for producing high yields of charcoals from biomass. 

Examples of the various types of biomass gasification processes are reviewed in the next few sections before commercial and near-commercial processes are described. 

The process sub-models contain a sufficient level of resolution to allow all of the above areas to be examined. All parameters not referred to above are held constant throughout the study. A single "generic biomass type is considered, the data actually ctHTesponding to chipped short rotation poplar wood. 

Effective utilization of biomass for value-added chemical product synthesis will require development of new applications of important unit operations. Carbohydrate recovery from the biomass is the key near-term application for production of commodity chemicals. Protein recovery will continue to have an important niche market in tlie purified form as food and a larger low-value market in the crude form as animal feed. Important processing information for carbohydrate depolymerization can be found in the literature from biochemical conversion of biomass. New process applications of separation technologies are just now being developed and refined for use with biomass-derived carbohydrate and protein streams. The use of an aqueous processing environment for carbohydrates will require careful consideration of the differences that type of environment entails, such as the effect on catalyst formulations. 

Next, methane and carbon monoxide can be further converted into hydrogen by means of steam reforming or the water-gas shift reaction. The most important pyrolysis reactor types are ablative, fluidized bed, circulating fluidized bed and entrained flow reactors. Hydrogen yields can vary substantially with biomass type, facility size and process conditions... 

Liquid fuels equivalent to existing commerical products (kerosine, diesel, jet fuel, high octane gasoline) can be produced using biomass type feedstocks. A summary of potential products and operating conditions is shown in Figure XII and Table XVI. The present status of the project is indicated in Table XVII. Liquid hydrocarbon yields of 50-100 gal/ton of feedstock (dry, ash free) are to be expected. The process is characterized by ... 

The biomass conversion processes are not new and they are basically composed by pyrolysis processes and heat treatments, which depend on the type of organic load, conditions of preparation, reaction, etc. 

For the most part, the antibiotic industry uses batch-type processes. The reason for this stems from the fact that most efficient antibiotic-producing organisms are highly mutated and are readily replaced by fastgrowing, less efficient antibiotic producers in a continuous culture. In order to avoid substrate repression or inhibition, some batch processes are continuously fed concentrated substrate on demand during the course of the batch cycle. This is referred to as a batch-fed fermentation. The production of bakers yeast is an example of a batch-fed process. In some highly mycelial antibiotic fermentation, 20 to 40 percent draw-off followed by fresh media makeup is practiced. In the trade, this is referred to as a repeated draw-off process. Strict continuous processes are practiced only in processes for the production of biomass for feed or food and the treatment of wastes. 

Although the preceding study artificially amended hydrolysates with known toxins, actual concentrations of these fermentation inhibitors in the final steam-exploded and acid-catalyzed hydrolysates depend on the severity of pretreatment eonditions and the type of biomass being processed. Generally, removal or conversion of these inhibitory compounds is the most efficient pretreatment procedure for subsequent fermentation and bioconversion of the hydrolysate. There are a variety of physical, chemical, and biological detoxification procedures (Mussatto and Roberto, 2004b) that effectively reduce the concentration of toxic compounds or convert these substances to nontoxic derivatives. 

The primary types of conversion processes for biomass can be divided into four groups, ie, physical, biological—biochemical, thermal, and chemical. 

Steam also is blended with air in some gasification units to promote the overall process via the endothermic steam—carbon reaction to form carbon monoxide and hydrogen. This was common practice at the turn of the nineteenth century, when so-called producer gasifiers were employed to manufacture LHV gas from different types of biomass and wastes. The producer gas from biomass and wastes had heating values around 5.9 MJ /mr at... 

Lujuefaction. Eigure 21 outlines most of the biomass Hquefaction methods under development. There are essentially three basic types of biomass Hquefaction technologies, ie, fermentation, natural, and thermochemical processes. 

The nonvisual or subtle effects of air pollutants involve reduced plant growth and alteration of physiological and biochemical processes, as well as changes in the reproductive cycle. Reduction in crop yield can occur without the presence of visible symptoms. This type of injury is often related to low-level, long-term chronic exposure to air pollution. Studies have shown that field plantings exposed to filtered and unfiltered ambient air have produced different yields when no visible symptoms were present (5). Reduction in total biomass can lead to economic loss for forage crops or hay. 

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