Biomass is a renewable energy source that comes from organic materials. However, not all biomass is the same. Depending on the form it takes and the use to which it is put, it can broadly be divided into two types:
Solid biomass
This is the best-known form of biomass. It can take the form of plant residues, wood, pellets, wood chips or arable waste. It is mainly used to generate heat in boilers and stoves, in homes and industrial facilities. It can also be burned in power stations or used in cogeneration systems. It has the advantage of using local resources and reducing fossil-fuel dependence.
Solid biomass is found in nature in the form of forestry waste, energy crops and by-products from the agri-food industry. Using it for energy production requires appropriate collection, pre-treatment (e.g. drying or compaction) and adapted technology for efficient use.
Unlike fossil fuels, the carbon dioxide released when biomass is used has previously been captured by the plants as they grow. This means that with sustainable management, it produces no net emissions.
Gaseous biomass
Gaseous biomass is obtained when organic matter is broken down in the absence of oxygen, in a process known as anaerobic digestion. The result is biogas, a combination of methane and carbon dioxide. Biogas can be purified to produce biomethane, a renewable gas with of a similar quality to natural gas, which can be injected into the gas network or used as fuel in vehicles. Biomass can also be used to obtain liquid biofuels such as biodiesel or bioethanol, which can be employed in transport.
To sum up: solid biomass is burned directly to produce heat and electricity, whereas gaseous biomass is transformed into gases and fuels, allowing for more versatile use, for example in transport and in the gas network.
Advanced processes: Biomass gasification and pyrolysis
Biomass gasification is a thermos-chemical process whereby organic materials (e.g. wood and arable and forestry waste) is converted into a combustible gas called syngas. Syngas is primarily composed of carbon monoxide (CO), hydrogen (H₂) and methane (CH₄), along with smaller quantities of other compounds. Gasification is performed at high temperatures (700-1,000 °C) under low-oxygen conditions to avoid complete combustion. Syngas can be used to generate electricity or heat or as a feedstock for producing synthetic fuels and even green hydrogen. This technology produces fewer emissions than direct combustion and makes use of waste that would otherwise be thrown away.
Biomass pyrolysis consists of heating organic matter in the absence of any oxygen at all, generally at between 300 °C and 700 °C. The process breaks the biomass down into three main products: biochar (a carbon-rich solid), bio-oil (a liquid that can be refined as biofuel) and syngas. Biochar can be utilised to improve soil fertility and sequester carbon, while bio-oil and gas are used to produce electricity or chemical compounds. Pyrolysis is seen as a sustainable option because it reduces emissions, facilitates waste management and contributes to the circular economy.
Both processes are of key importance in valorising biomass and moving towards cleaner and more efficient energy systems.
