Short Rotation Coppice
Courtesy of IACR-Rothamsted
Biomass is a collective term for all plant and animal material. A number of different forms of biomass can be burned or digested to produce energy. Examples include wood, straw, poultry litter and energy crops such as willow and poplar grown on short rotation coppice and miscanthus. Biomass is a very versatile material and can be used to produce heat (for space and water heating), electricity and a combination of heat and power (electricity). The UK has some of the largest examples of the use of Biomass to generate electricity in Europe.
Energy from Wood
In order not to increase the amount of carbon dioxide in the atmosphere it is important that the wood burned as a fuel comes from sustainable sources. This means that as trees are felled to be use as a fuel, more trees should be planted. That way, the carbon released during the combustion of the wood is reabsorded by the new trees growing and the process is carbon neutral. Other examples of sustainable sources of wood include forest residues (what is left over after timber has been extracted), tree surgery waste and other wood residue.
Wood can then be used as logs, wood chip and wood pellets in wood/pellet burning stoves or wood chip/pellet boilers for space and water heating.
On a larger scale wood can also be used for the production of electricity. The main method of producing electricity from wood is a combustion plant (where the material is burned to produce steam), although there are two other possibilities, namely, gasification (where the material is heated in such a way that gases are given off) and pyrolysis (where the wood is heated in the absence of oxygen to produce a bio-oil liquid with some charcoal and gas).
For more information and lists of suppliers, please visit the Log Pile website at www.logpile.co.uk
Today fast growing trees like willow and poplar are being grown on a Short Rotation Coppice (SRC) system because they are fast growing they can be coppiced every 3-4 years.
The perennial grasses Miscanthus and Switch-grass are other examples of energy crops as they produce high yield of dry matter.
Some agricultural crops are grown specifically with energy use in mind. Crops such as wheat and oil seed rape are being processed to produce liquid transport fuels such as ethanol and biodiesel.
Biodiesel can fuel most cars without any modification to the engine. Most car manufacturers are happy for a blend of 5% Biodiesel and 95% fossil diesel to be used and this is what is typically sold in some petrol stations. Biodiesel can also be made from used vegetable oils (from restaurants etc.). The production costs are higher than for fossil diesel however due to the introduction of a tax break and the current high price of fossil diesel it is currently cheaper to purchase.
Clean vegetable oil can also be used as an effective fuel for diesel engines. As opposed to biodiesel, where the oil is modified, some modifications to the engine are required. There are modification kits available and the changes to the engine still allow the car to run on fossil diesel if needed.
For more information, please visit the following websites:
British Association for Bio Fuels and Oils (BABFO) – the trade body for producers: www.biodiesel.co.uk
Veg Oil Motoring: www.vegoilmotoring.com
Where to buy Biodiesel: www.biodieselfillingstations.co.uk
Suppliers of Biodiesel: www.rixbiodiesel.co.uk or www.broadlandfuels.co.uk
Where to go for training on how to make your own: www.lowimpact.org
Other forms of biomass produced by farmers are by-products of conventional agricultural activity. They include 'dry' agricultural wastes such as straw that can be combusted (burned) to produce energy.
'Wet' wastes such as green matter or slurry can be 'digested' to produce methane in a process known as anaerobic digestion. This can then be used to fuel a gas engine to produce electricity and heat.
There are already examples of chicken litter combustion, animal slurry digestion and straw combined heat and power projects working well in this country. In many cases however, these projects are only economically viable if an outlet can be found for the heat produced (such as nearby factories) and the by products (fertilisers for farms).
Municipal and Industrial Waste
Municipal waste products need to be minimised or recycled wherever possible. However there will always be some requirement for disposal. Some forms of municipal and industrial waste can be described as biomass - such as waste food and waste wood (from the construction industry, for example). Whether the burning of other types of municipal waste to produce energy can be described as renewable is a matter of some debate. There can be environmental benefits if these wastes are used to generate electricity and/or heat such as the reduction of the demand for landfill space. However care has to be taken with emissions and residues as they can cause environmental problems.