BIOMASS

What is biomass?

Biomass is living matter. In terms of domestic renewable energy it is recently living matter which we can easily burn such as wood or other plant material either in its raw state, after very little processing, (e.g. logs) or after more advanced processing (e.g. wood chips or pellets).
Biomass requires sunlight for energy in which to grow, and so can be thought of as another form of indirect solar renewable energy, which has the advantage of convenient storage.

Biomass should be considered as a ?nearly? carbon neutral energy resource. Burning biomass releases no more carbon dioxide than was removed from the atmosphere when it was growing, but there are some emissions from transporting and processing this resource, highlighting the necessity of sourcing biomass fuel from local and sustainable sources.

Typically wood is burnt to release heat for space heating and hot water purposes in the home. To ensure that biomass used in this way is done so sustainably, it is important not to waste energy in order to prevent biomass from being consumed more quickly than it is replenished.

Types of biomass technology
Biomass heating systems can be described by the type of feedstock it needs:
•Feedstock:
 oLogs require very little processing other than being sawn to the correct dimensions and being kept dry, or ?seasoned?. Seasoning reduces the moisture content of the wood to about 20% by mass and can take up to three years. These are used in log stoves and boilers
 oWood chips are typically derived from waste wood products, and due to the nature of delivering the feedstock to the fire chamber of the boiler, they are better suited to larger applications
 oWood pellets undergo the greatest amount of processing of all the biomass products. Because of this pellets boast the advantage of having a very high and consistent energy content whilst having a low moisture content, as well as being more convenient to store, transport and burn

Types of heating system available include:
•Log stoves/boilers which burn logs directly
•Wood chip boilers which burn wood chips
•Pellet stoves/boilers burn wood pellets
•Multifuel stoves can burn a range of solid fuel types
•Ceramic stoves burn wood products and store heat in thermally massive ceramic tiles for release throughout the day

Other biomass technologies include gasification and pyrolysis, but these will not be presented here.

Fig 7. Wood pellet stove

How do biomass systems work?
Biomass systems operate quite simply, with the burning of biomass material to provide space heating and/or domestic hot water. Fuel is loaded into a hopper, or by hand for some log systems and released in a controlled manner into a fire chamber. Heat output is regulated via a fan, allowing more air to be available to the combusting material for a higher temperature and quicker burning flame when needed.

The main waste products from burning biomass are CO2 gas, and ash. All biomass heating systems require periodic de-ashing, the interval of which depends on the system being used.

Heat output can take the form of either hot air blown into the room (and radiating from the device), or via a conventional central heating system. In this case, and for domestic hot water, a back boiler will be a necessary addition to stoves to store the heat from the burning wood.

Many biomass systems work best when burning constantly for a number of hours and storing the heat produced in a thermal store for use throughout the day.

What components comprise biomass heating?
1.Place to burn biomass: stove/ boiler; and store for fuel
2.Back boiler (optional for stoves)
3.Thermal store (optional)
4.Central heating system (optional)

How much energy can I expect a biomass heating system to produce?
Space heating and domestic hot water requirements may represent as much as 70-80% of the annual energy consumption of your home. Therefore a well designed and installed system could be capable of providing this proportion of your households energy needs.

What are the benefits of biomass?
•Make use of an abundant local supply of energy
•Create many local jobs and businesses
•Wide range of systems available
•Energy available on demand
•Cheaper than or competitive with traditional (fossil) energy sources

Suitability
Biomass heating systems are usually easily incorporated into existing heating systems. Your HETAS registered installer should be able to discuss with you the most suitable system to meet your requirements.

Maintenance
Biomass systems require regular fuelling and periodic de-ashing. A system inspection should also be carried out every year or several years as required by the equipment installed

© 2008 West Wales ECO Centre