Introductory guide to biomass boiler systems and biomass fuel
People have been producing energy from biomass for centuries, and in many parts of the world it is still the principle source of heat. However modern technologies are now far more efficient and cleaner than the old open fire and there are an increasing number of fuels that are being used, including logs, chips, pellets and briquettes.
Energy from biomass refers to energy that is produced from organic matter of recent origin. This excludes fossil fuels, which have taken millions of years to evolve. Biomass is often termed as 'bioenergy' or 'biofuels'. Any solid, liquid or gaseous fuel produced from organic materials either directly from plants or indirectly from industrial, commercial, domestic or agricultural wastes can be considered a biomass fuel.
Producing energy from wood brings environmental and economic advantages both nationally and locally and has considerable potential within the UK.
Biomass heating systems, unlike other renewables, do emit carbon dioxide. However, the carbon dioxide (CO2) released when the wood is burnt is taken from the atmosphere and used by trees to grow during photosynthesis, this closed cycle is why wood heating is considered a renewable energy source and is classed as carbon neutral.
The carbon neutral wood heating cycle
For sustainably managed woodland, or energy crops, the process is similar. On balance, wood is never removed faster than it is added by new growth. Therefore, the CO2 released when the wood fuel is burned is never more than the CO2 absorbed by new tree growth.
However, for biomass there are small net emissions of CO2 to the atmosphere through such operations as harvesting, transport, processing and the construction and commissioning of the energy plant. Wood fuel emits 25 grams of carbon per kilowatt-hour (g/kWh); wind energy emits 8g/kWh; gas emits 194g/kWh; oil emits 265g/kWh and coal emits 291g/kWh1.
Types of biomass fuel
Biomass used for fuel falls into two main categories:
Woody biomass, including:
- Forest residues – from woodland thinnings, and "lop and top" after felling, arboricultural trimmings
- Untreated wood waste – e.g. from sawmills, furniture factories
- Crop residues – e.g. straw
- Short Rotation Coppice (SRC) – e.g. willow, miscanthus (elephant grass)
Non-woody biomass, including:
- Animal wastes – e.g. slurry from cows and pigs, chicken litter
- Industrial and municipal wastes including food processing wastes
- High energy crops – e.g. rape, sugar cane, maize
Currently the most conveniently available wood fuels are logs, pellets and wood chips.
Biomass fuel - benefits
Benefits include:
- Woodlands, forestry and agriculture are generally perceived to be an environmentally and socially attractive amenity by the UK population, providing opportunities for recreation and leisure activities.
- Biomass fuels generate significantly lower levels of atmospheric pollutants than fossil fuels. Pollutants such as sulphur dioxide, a major cause of 'acid rain'.
- Modern biomass combustion systems are highly sophisticated, offering combustion efficiencies comparable with the best fossil fuel boilers.
- Using arboricultural residues, forestry arisings, sawmill co-products and waste as fuel diverts materials that would otherwise be consigned to landfill. This eliminates costs for disposal, and reduces the burden on limited landfill resources.
- Utilising biomass as fuel encourages more woodlands to be sustainably managed, thus benefiting biodiversity.
Legal and planning constraints
There are several things you must check with your local planning department depending on your situation.
If you live in an urban area you should check if it is in a smoke control zone (see UK smoke control areas), if this is the case the biomass boiler you install must be an exempted appliance. See UK smoke control areas or ask your installer.
Outside smoke control areas there is no legislation other than a general prohibition on not creating a nuisance, and a requirement not to emit "dark smoke". Burning dry wood on well designed appliances should give no cause for concern. Chimneys should be designed in accordance with Building Regulations Document J.
Visual impact - If you live in a listed building, conservation area, AONB, National Park or other designated area then you will need to consult your local planning authority about the installation and construction of a chimney flue, fuel storage silo or boiler house.
Fuel deliveries - For larger installations the number of vehicle movements may be a planning issue, as might the size and type of delivery trucks.