Conversion of the feedstock into its final form is usually a long process composed of many steps that starts with the harvesting and continues with various purification and transformation steps, in order to make the primary feedstock utilizable in order to perform its final work.
Harvesting
Due to the possibility of using unconventional feedstocks for the production of bioenergy, some products need to use innovative harvesting equipments. This can be a challenge in certain areas, because the harvesting techniques often need to be similar to the way people would harvest other crops. A good example of this is the development of new machinery to harvest wood biomass in the field of agroforestry.
Extraction
In some cases, it is possible to produce energy directly from the primary feedstock. However, in most cases, certain compounds need to be extracted before they can be utilized. Microbial populations often need an extraction step (either to extracts microbes from their medium or to extract the released products) in order to produce bioenergy. Producing algal biodiesel first requires an energy-intensive lipid extraction process that requires dewatering or the use of hydrophilic enzymes. Most of the lipid extraction methods are either mechanical or thermal, but enzymes can also be used to degrade cell walls and extract the necessary compounds.
Transformation
Other transformation processes often have to be completed before the final step of utilization. These processes are either thermal, chemical, mechanical or biological. Here are some examples of each of these types of processes. Anil Patel
Thermal transformation process
The first application of thermal transformations is to decrease the moisture content of various materials. In the case of wood pellets, drying the materials is one way to efficiently ensure the feedstock will release more energy upon its direct combustion in the final step.
Chemical transformation process
In order to produce a quality biodiesel, the viscosity of vegetable oils needs to be reduced. Most of the chemical bonds that cause an increased viscosity are triglycerides. In order to break these bonds, it is possible to make a catalyzed chemical reaction between alcohols (methyl or ethyl alcohols) and vegetable oils in order to separate glycerin molecules from the vegetable oil. This chemical reaction creates methyl or ethyl esters (biodiesel) floating on top of a glycerin solution that can be recovered for other purposes.
Mechanical transformation process
The transformation of herbaceous crops or wood biomass to pellets requires 4 critical steps: the drying of the feedstock, a size reduction phase, followed by a densification phase and the cooling of the final product. The size reduction phase usually implies the use of a mill that will grind the primary feedstock to finer chips.
The densification process, however, uses high-pressure or rotary engines in order to bond fine materials into small wooden pellets in order to create an efficient fuel with sufficiently constant properties. Densification also makes the processed material easier to handle and is also used in the food industry in order to make cattle feed.
Mechanically, biological materials are hard to process, because they are very often inelastic materials and are treated into grinders made of ductile, elastic metals. Thus, most of the models used for such applications are man-scale prototypes of machines.
Biological transformation process
What is usually referred to as second-generation ethanol concerns the use of cellulose-based feedstocks in order to generate ethyl alcohol and to make a fuel that can be used in a combustion engine. First-generation ethanol refers to the degradation of complex sugars in order to generate ethanol. One of the suggested ways to produce an economic cellulose-based ethanol is to break lignin bonds in wood biomass and to use fungi (such as Trichoderma reesei) that would transform cellulose and hemicellulose into complex fungal sugars. These sugars could then be transformed into ethanol by using fermentation yeasts.