Bioenergy is a form of renewable energy generated from biomass which is organic matter like plants and dead organisms. Examples of biomass used in bioenergy include agricultural waste from forests or plants, wood, food crops, and organic waste from homes and schools.
Bioenergy is a source of energy for producing electricity, heat, transportation fuels, etc. During the combustion of biomass, carbon dioxide (CO2) is released into the atmosphere and gets taken up by plants during photosynthesis. This means bioenergy produces close to zero-emission fuels due to this absorption of carbon dioxide (CO2).
It accounts for 55% of renewable energy sources, making it the world’s biggest source of renewable energy. Biofuels are used every day in cars and even planes, examples include ethanol and biodiesel.
Types of biomass energy sources used in bioenergy
The different types of biomass used in making biofuel include
- Wood and wood residue: Wood is the largest biomass in use today. They are obtained from tree parts collected from the forests. It can be used as a source of fuel either directly or after being processed into pellet fuels.
- Energy food crops: Crops such as corn, wheat, willow, silage, bamboo, miscanthus, switchgrass, and oilseed rape are good biomass sources for producing various fuels.
- Farm waste: Animal dung, straws and leftover food from production are used for creating biofuels.
- Organic waste: This includes used cooking oil, food waste, manufacturing waste and byproducts of wood.
- Others include microalgae, purpose-grown grasses and municipal solid waste
Types of biomass fuel (Biofuel)
Biofuels are solid, liquid or gaseous fuels that are produced from biomass through combustion (burning).
1. Liquid fuel:
Liquid fuels are the fuels produced for transportation. They are grouped into two according to their biomass sources namely first generation biofuel and second generation biofuel. First-generation biofuels are made from energy food crops while second-generation biofuels are made from organic materials.
2. Solid fuel
Solid biofuels are the most common products of biomass. Examples include wood chips and wood pellets which are produced by wood refineries from wood waste of wood industry operations.
Biogas is produced through anaerobic processes and can also be processed into biomethane. Both of these fuels can be used as bioenergy for transportation, electricity and heat.
Methods used in converting biomass to biofuels
1. Chemical conversion: This usually involves known coal-based processes like the Fischer-Tropsch synthesis. Using the same processes undergone by coal, biomass is converted into various chemical products for bioenergy.
2. Thermal conversion: From the word ‘thermal’, this method requires heat as its main mechanism for the conversion of biomass into biofuel used in day-to-day activities. Different thermal conversion processes can be used based on temperature and the presence or absence of oxygen.
3. Biochemical process: Biochemical conversion involves processes like fermentation, composting and anaerobic digestion where microorganisms are usually required to break down the molecules of the biomass sources for the biofuel to be obtained.
Applications of Bioenergy
Biofuels used for transportation
The first-generation biofuels for transportation are made from biomass of food sources such as maize, sweet sorghum and sugarcane. Bioethanol, a biofuel, is made from the fermentation of sugars obtained from these carbohydrate food sources and can be used for the production of electricity or as an additive to gasoline. Biodiesel is produced from food oils like sugar beets and rapeseed. Biodiesel and bioethanol are the most common types of biofuels in use today.
The second-generation biofuels are derived from biomass that isn’t food-based such as agricultural waste, industrial waste and household waste. Anaerobic digestion, direct combustion and gasification are processes used in the production of biogas and biofuel.
Bioenergy for heat and electricity
Biomass heating systems and technologies help to convert biomass fuels into heat and electricity to be used. Different processes can be used for the conversion of biomass to bioenergy such as gasification (conversion to a gas), direct combustion (burning), and aerobic or anaerobic digestion (bacteria decay).
The use of bioenergy for generating electricity reduces the need for carbon fuels thereby ensuring less gas emissions. It also ensures the reliability and flexibility of electricity production.