A guide to small-scale wood fuel heating systems
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 far more efficient and cleaner than the traditional open fire and there are an increasing number of fuels are being used namely logs, wood chips, wood pellets and wood briquettes.
Energy from biomass refers to energy produced from organic matter of recent origin. This excludes fossil fuels which have taken millions of years to evolve. Biomass is also referred to as bioenergy or biofuels (in terms of renewable energy). Biofuels have been defined by the Energy Technology Support Unit (ETSU,
1991) as:
any solid, liquid or gaseous fuels produced from organic materials either directly from plants or indirectly from industrial, commercial, domestic or agricultural wastes.
However, throughout this document we are concerned with woody biomass logs, wood chips, wood pellets and wood briquettes. 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 renewable energy sources, do emit carbon dioxide. However, it is the carbon dioxide (CO2) taken from the atmosphere by trees for photosynthesis that is released during burning. This closed CO2 cycle means that biomass heating is considered a renewable energy source.
For sustainably managed woodland, or energy crops, the process is similar. 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, biomass heating systems in reality create small net emissions of CO2 to the atmosphere through operations including harvesting, transport, processing and the construction and commissioning of the boiler. Wood fuel emits 25 grams of CO2 per kilowatt-hour (g/kWh); wind energy emits 8g/kWh; gas emits 194g/kWh; oil emits 265g/kWh and coal emits 291g/kWh .
The species and quality of trees used for wood fuel production, and in particular wood chips, primarily determines the overall quality of the fuel. In many instances, woodland and tree management determines which trees are to be removed and therefore directly affects quality. For instance forestry thinnings, arboricultural waste, sawmill co-products, tree stumps and forestresidues that include needles/leaves and bark will all be different.
It is vitally important for customer confidence to have fuel which is fit for purpose and delivered to a quality standard and specification. This has been demonstrated time and time again internationally. Even with a specific form of fuel, such as wood chips, there can be major differences in characteristics and properties between different batches chipped using different chippers.
