Biomass is a very versatile material and can be used to produce:
- Heat - for space and hot water.
- A combination of heat and power (electricity) in a Combined Heat and Power (CHP) plant.
- A liquid fuel (e.g. biodiesel and vegetable oil) used to power vehicles or produce heat.
The Renewable Transport Fuel Obligation (RTFO) requires fuel suppliers to add 5% biofuel to petrol or diesel by 2013/14 (or pay a penalty). Some diesel vehicles can use higher blends of biodiesel without engine modification. It's always worth checking with the vehicle manufacturer before doing so. Using vegetable oil to run a motor car can be done but always requires engine modification. Where to buy biodiesel.
Biomass is a renewable fuel as long as it comes from sustainable sources such as: forest residues, tree surgery waste, energy crops, agricultural waste and other wood residues (such as sawdust).
Types of biomass
Wood can be used in the form of logs, woodchip and wood pellets in wood/pellet burning stoves or woodchip/pellet boilers for space and water heating. Logs and pellets are generally suitable for use on a domestic scale. Woodchips are generally only used in larger boilers, such as those used in schools, community buildings and offices. On a larger scale, wood can also be used for the production of electricity. The main method of doing this is a combustion plant (where the material is burned to produce steam). However, there are two other possibilities:
- Gasification (where the material is heated in such a way that gases are given off).
- Pyrolysis (where the wood is heated in the absence of oxygen to produce a bio-oil liquid with some charcoal and gas).
Energy crops are grown specifically for the production of energy. Examples include:
- Willow and poplar grown on a Short Rotation Coppice (SRC) system. Using this system the trees can be cut down to ground level every 3-4 years. The wood produced can then be chipped for use in a woodchip boiler or a combined heat and power (CHP) plant.
- The perennial grasses, miscanthus and switchgrass. These grasses produce a high yield of dry matter and can be used to produce liquid fuels such as bioethanol. They can also be co-fired with coal for the production of electricity.
- Sugar beet, sugar cane, wheat and maize. These can be fermented to produced bioethanol.
- Oil seed rape. This can be used to make vegetable oil, for use in modified vehicles.
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 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). Many local authorities now operate a waste food collection service. The waste food is then recycled and used to produce compost - or used for the production of electricity in an anaerobic digestion plant. Waste vegetable oil can be used in the production of bio-diesel.
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.