How is biomass processed in EU-28?
Today, the European bioenergy sector utilises a wide variety of processes to upgrade or convert the energetic potential of biomass feedstocks. In fact, most modern bioenergy installations require more advanced fuels to work at their maximum capacities. On the other hand, biomass processing industries are increasingly developing different fuels and/or bio-based materials out of the same initial feedstock. Thanks to these technologies, today bioenergy is one of the most reliable sources of clean energy adopted by companies, municipalities and households all across Europe. This section offers a brief overview of these specific processes and technologies.
Solid Biomass Conversion Processes
Most solid biomass is used in thermal applications. If you have ever tried to make a fire using green-coloured wood, you already know that combustion performs better when moisture is limited. This is why most technologies developed by the solid biomass processing sector in the past decades focused on reducing the presence of water in the final fuel, either through using traditional drying methods or more advanced ways. Not only is limited moisture content essential for combustion, but having a very dry fuel increases the energy potential for the same volume of fuel, improving its storage and its transportation.
- Logging, grinding, screening and/or drying operations are mechanical processes carried out to enhance solid biomass fuels. These operations help transform the biomass into a more homogeneous fuel that is easier to handle and has a higher energy recovery (eg. wood chips, wood logs, agrofuel). In general, moisture content in wood chips used for energy generation in municipal or industrial plants ranges from 20-30%.
- Densification is another popular way to transform woody material into an advanced fuel with a high calorific value. This process involves compressing biomass and lowering moisture levels between 8-10%, allowing for a more homogenous fuel–either in the form of pellets or briquettes. The heat during compression fuses the lignin in the biomass, naturally binding the biomass together in its new, enhanced shape. Thanks to densification, the homogenous biomass fuel is easier to transport and can be used in automated biomass installations, such as pellet stoves and boilers.
- Thermo-chemical conversions are now used to produce fuel with an even higher calorific value such as torrefaction or steam explosion technologies. During the torrefaction process, wood is subjected to 230 to 300ºC at atmospheric pressure in the absence of oxygen. Comparable to coffee torrefaction, this method allows the creation of a fuel with very interesting characteristics. Compared with conventional wood, torrefied wood has a very low (>5%) moisture content, is easily grindable and is relatively hydrophobic.
- Thanks to advanced technologies, woody biomass can also produce liquid or gaseous fuels. Pyrolysis, for instance, is a thermal-chemical conversion that requires a high temperature (>400 °C) and limited oxygen to convert the biomass into other forms including gas, liquid fuels (pyrolysis oil), and biochar. Gasification is another thermo-chemical conversion that takes place at high temperatures (>800 °C), with limited oxygen and/or steam, converting solid biomass into synthesis gas, or syngas, which contains carbon and hydrogen and can be used to produce liquid fuels such as biodiesel.
Wet Biomass Conversion Processes
Wet biomass is also present in high volumes across Europe (manure, agricultural waste or by products). As wet biomass has too high of moisture content to be turned efficiently into energy via a direct combustion process, other conversion pathways and energy outputs have been developed, especially by the biogas (anaerobic digestion) and biofuel sector (fermentation). Anaerobic digestion and fermentation are the two main conversion pathways used to turn wet biomass feedstocks into advanced fuels.
- Anaerobic digestion is the microbiological process of the decomposition of organic matter, in the absence of oxygen, which is common to many natural environments and largely applied today to produce biogas in airproof reactor tanks known as digesters. A wide range of micro-organisms are involved in the anaerobic process which has two main end-products: biogas and digestate. Biogas is a combustible gas consisting of methane, carbon dioxide and small amounts of other gases and trace elements. Digestate is the decomposed substrate, rich in macro- and micro-nutrients and therefore suitable to be used as plant fertiliser. Biogas can be used for direct combustion to produce heat but also power if converted in a cogeneration plant or directly in adapted gas motors. Biogas can also be “upgraded” through purification processes to obtain biomethane that can be injected into existing natural gas networks, used as a chemical products or as vehicle fuel.
- Fermentation is a biochemical conversion whereby microorganisms including yeast and bacteria convert bioenergy into products such as ethanol and liquid transport fuels (biodiesel). This process is done through several stages. First, sugary and starchy feedstocks such as corn must be crushed and combined with water, allowing the enzymes to convert these starches into sugar. This then ferments along with the addition of yeast, and is distilled into bioethanol. Bioethanol can also be produced from cellulosic biomass such as grass, wood, and stalks, via fermentation; however, this process is more complex and involves a mechanical pre-treatment and the addition of enzymes or breakdown of the lignocellulose into sugar through hydrolysis, before following the same procedure.