Where does it come from?
Perhaps the first thing to establish when buying biomass fuel is the origin of the fuel. Although wood and other biomass fuels can be transported considerable distances and still offer potential carbon savings, to maximise benefits the fuel should come from local, sustainably managed woodland. Slab wood, pellets or chip produced by local sawmills may also be available – ideally the wood used by the mill should be sourced locally. For most applications wood that has been treated with preservatives, paint or varnish should be avoided – using this material can produce harmful emissions unless specific combustion conditions can be achieved and the appropriate abatement equipment installed. Using treated wood can shorten the life of the boiler unless it has been specifically designed for this type of fuel.
Does the fuel conform to existing standards?
Fuel standards are very important. Like filling a diesel car with petrol, using the wrong type of fuel in a boiler can result in damaged equipment, poor performance and a hefty bill. A range of standards covering all forms of solid biomass fuels is currently under development in Europe. Many countries have representatives on the technical committee responsible for these standards. Once in use, the standards, collectively known as CEN/TC 335, will help ensure that all relevant properties of a particular type of fuel (including logs, pellets, woodchips, briquettes and saw dust) are explained in a consistent manner between producers, suppliers and countries within Europe. At the moment fuel suppliers should be aware of these standards even if they continue to use other classification types such as the Austrian Onorm standards. It is vital that the standard of fuel specified by the manufacturer of the boiler you intend to use can be met by your chosen fuel supplier. Even owners of simple log stoves can benefit by ensuring that they buy only good quality fuel, this note describes what to look for.
Is the moisture content and particle size suitable for my boiler?
These two variables are most important when buying wood fuel. Again, reference should be made to the specifications supplied by the boiler manufacturer but in general, most boilers in the 50kW – 250kW class will require fuel with a moisture content of 30%. Larger woodchip boilers or boilers with a stepped grate may be able to use fuel with a wider range of moisture contents, perhaps as high as 50%. The particle size should be uniform and compatible with the mechanism (typically a screw auger) used to move fuel from the store to the boiler. Long shards or slivers of wood may bridge over the auger and prevent fuel reaching the boiler. Fuel with high quantities for very small particle and dust can also present fuel feed and combustion problems.
Storing fuel
Once you have gone to the trouble of procuring fuel from a sustainable source which also meets the technical requirements of the boiler, care must taken to ensure that the fuel does not become damaged or contaminated whilst in the store. In particular, stores for wood chips and wood pellets should be water tight to prevent rain damaging the fuel. When designing a fuel store it is important to consider how fuel will be delivered to the site. Make sure site access meets the requirements of the delivery vehicle whether it is a tipping trailer, pneumatic delivery lorry or a containerised deliver system. It is also important to make sure the fuel store is of an adequate size to minimise the number of fuel deliveries required during the heating season.
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