Efficient, reliable wood chip and pellet boilers
are readily available. They provide heat for a very wide range of
uses, from homes to commercial and industrial applications.
Important: before purchasing any equipment,
read Managing a successful wood fuel
installation and get expert advice.
Most systems are 'wet', i.e. they deliver hot water and central
heating via radiators, but warm air systems (suitable for heating
large spaces, like factories) are also available.
Wood fuel boilers typically work best under a relatively
constant load. So, to maximise efficiency, it may be worth fitting
a wood fuel boiler that provides, say, 80% of the annual energy,
with a back-up boiler (either another wood fuel boiler or small
gas/oil boiler) to kick-in when the heat load peaks. Accumulator tanks can also help with
fluctuating loads.
Wood fuel boilers use different types of technology, usually
classified by the type of grate used. The main types of automated
boiler use either a moving grate, a plane grate or a stoker-burner,
the
Carbon Trust's biomass heating guide (pages 38-41) details the
advantages and disadvantages of each type of boiler.
Automated systems
Wood chip and pellet boilers systems can be as automated as oil
or gas boilers. A wide range of systems are commercially available
but all share the same basic features of a boiler, storage and a feed mechanism.
Wood chip boiler or wood pellet boiler?
The choice of whether to install a wood pellet or wood chip
boiler will largely depend on circumstances e.g. heat load and
availability of different fuel types. For most projects either
solution will offer advantages and disadvantages, some of which are
outlined below:
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Wood chip systems
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Wood pellet systems
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Fuel availability
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Can be readily produced locally
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Production is more centralised, but can readily be delivered
over longer distances.
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Fuel quality
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Range of standards - must ensure boiler demands match
local supply
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Very standardised
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Fuel storage
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Bulky fuel
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Compact fuel
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Capital costs
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High installation costs compared to fossil fuel alternatives
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High installation costs compared to fossil fuel alternatives,
though can be cheaper than wood chip systems, particularly for
storage
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Running (fuel) costs
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Very competitive compared to both gas and oil -
for cost comparisons see the Biomass Energy Centre website
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Very competitive compared to oil and LPG, becoming more
competitive with natural gas -
for cost comparisons see the Biomass Energy Centre website
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Energy used to produce woodfuel (embodied energy)
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Very low <5%
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Low 5-10%
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Some boilers designed for wood chips can also burn pellets,
however boilers designed specifically for pellets cannot generally
use wood chips.
Maintenance
Biomass boilers have greater maintenance requirements than
fossil fuelled boilers.
The boiler manufacturer's representative or boiler installer
will usually carry out an annual maintenance, including a full
internal and external inspection of the boiler, replacement of worn
components (particularly grate components on moving grate boilers),
lubrication and cleaning.
The main maintenance tasks that the user needs to do at regular
intervals are: a weekly visual inspection, emptying of the ash bin,
greasing of induced draught fan bearings and manual brushing of the
flueways. If automatic flue cleaning is installed a significant
reduction in boiler downtime and maintenance time is possible,
reducing manual flue cleaning from a weekly to a 6-monthly
exercise.
Publications to download
The Biomass Energy Centre have produced useful guides to small
and medium wood fuel systems: