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Bioenergy
Bioenergy is energy derived from biomass. In essence bioenergy is the utilisation of solar energy that has been bound up in biomass during the process of photosynthesis. The photosynthesis process uses solar energy to combine carbon dioxide from the atmosphere with water and various nutrients from the soil to produce plant matter - biomass. Bioenergy is therefore a renewable energy resource.
What is biomass?
Biomass is organic material, either raw or processed, with an intrinsic chemical energy content that allows conversion into electricity or heat. It can be divided into “bioheat” the thermal energy and “bioelectricity” the electrical energy from biomass.
Biofuels are fuels generated from biomass, including solid (logs, pellets and chips), liquid (bioethanol, biodiesel, bio-oils), and gaseous (biogas, hydrogen and other gases).
Biomass is a widespread resource and can be derived from waste streams and purpose grown material as follows:
- Waste streams including residues from forestry and related industries, recycled wood, agricultural residues and agri-food effluents, manures, the organic fraction of municipal solid waste, separated household waste and sewage sludge.
- Purpose grown energy crops including short rotation forestry, miscanthus grass, etc.
The EU Directive on Sustainable Electricity from RES defines biomass as including the biodegradable fraction of products, wastes and residues from agriculture (including vegetable and animal substances), forestry and related industries, as well as the biodegradable fraction of industrial and municipal waste.
Uses of bioenergy
Bioenergy can be exploited primarily through:
- Combustion - Biomass (e.g. wood chips) can be burned to provide process and/or space heating. The combustion of biomass can also be used to raise steam to drive engines/turbines which are coupled to generators producing electricity.
- Anaerobic digestion - Biomass (e.g. animal manure) can be transformed to biogas by anaerobic digestion and the biogas can be used to fuel a gas engine or gas turbine, or burned in a boiler to provide heat or to raise steam.
Other technologies for the exploitation of bioenergy include gasification and pyrolysis but these are not as commercially developed as combustion and anaerobic digestion.
Heat Production
The majority of current biomass-derived energy comes from wood combustion to produce heat. Direct combustion processes for heat production and driving a steam cycle are already commercial, with a constant drive for the improvement of their efficiency and reduction of their pollutant emissions. There are two different systems of creating heat: small scale heating and district heating systems. The first ones uses logwood, pellets, woodchips, etc., the other, typically based on either fluidised bed boilers, can burn wood chips, peat, refuse-derived fuel, waste wood, sawdust and straw.
Co-generation of heat and power
Combined heat and power (CHP), the simultaneous production of heat and power, is suitable for small scale applications. It can be used to provide space heating and domestic hot water to individual houses or a group of buildings. Excess electricity generated may often be exported to the grid. This relatively new technology has reached the commercialisation stage also for small scale applications (50-500 kW).
Content courtesy of Sustainable Energy Ireland