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Facing up to biomass emissions
As more attention is paid to particulate emissions from biomass boilers, forthcoming air quality legislation
is set to force a re-think on how we handle these emissions. Kevin Stones, Engineering and Service Director
with Hoval, considers the implications and describes a new ceramic filter for these applications.
The recent growth in the use of biomass boilers Firstly, it’s worth reviewing the background to this situation. Capable of removing up to 96% of PM
2.5
and PM
10

means that particulate emissions from biomass are Directive 2008/50/EC came into force on 11 June 2008 and particles, ceramic filters can be used with any
beginning to come under closer scrutiny. And while must be transposed into national legislation no later than type of biomass boiler and can be retrofitted to
biomass still accounts for a tiny proportion of the June 2010. Of particular significance in these regulations existing installations, so they have the potential to
UK’s particulate emissions, this contribution clearly is the size of particles that will be controlled. In the past, address many of concerns (real or perceived) about
has the potential to increase with the growing use of emphasis has been on particles with a diameter of 10 particulate emissions from biomass.
biomass. microns or above (PM
10
). However, the new Directive will
seek to introduce a new control framework for particles Ceramic filters are connected to the back of the boiler,
In parallel with these developments, EC Directive down to 2.5 microns in diameter (PM
2.5
). in the same way as a cyclone. Each unit contains a
2008/50/EC, Ambient Air Quality and Cleaner Air for matrix of porous ceramic tubes which are closed at
Europe, creates a requirement for tighter control of
Size matters
the lower end. The number of tubes in each matrix is
the smaller particles that are not filtered by traditional
Biomass boilers make a small contribution to particulate
aligned with flue gas volumes for each boiler.
mechanisms such as multi-cyclones. Consequently,
emissions, compared to traffic, and the level of emissions
we will soon be faced with a need for more efficient,
will vary with the quality of the fuel and combustion
retrofittable filtration of particulate emissions from
efficiency of the boiler. So using boilers that comply with
biomassbiomass boilers boilers. . HoHoval’al s new CF cs new CF ceerraamic filtmic filter, , capable capable
EN 303-5 Class 3,EN 303-5 Class 3, in conjunction with high qualittion with high y fuel, is
oof rf removinving up tg up to 96% of particles of 10 and 2.5
the first step in minimising parep in minimising particulate emissionse em .
micronsons in diamet in diameter, is discussed in moris discussed in moree detail belo detail below.
OOff c course, man many biomass installations alry biomass installations alreeady use a cyclone
or multi-cyclone to remove particlticles fre om flue gases.
However, cyclones are totally dependent on the otally depep
mmass of the parass of the particles for removal,al, so while they will
As flue gases are drawn through the filter by an inline
rreemomoveve ar around 50% of the cound 550 oarser
fan, the gases are able to pass through the walls
parparticles they do not rticles they d emove
of the ceramic tubes, while particles are trapped.
parparticles beloticles belol w PM
At regular intervals (timed and/or in response to a
10
. This is
why ty the new Dirhe newe ective and its
pressure drop across the filter) a pulse of air is used to
emphasis on PMemphasis o
dislodge the particles, which fall into a collection bin.
2.5
has such
sigsignificancnificca e for biomass
installationsinstalla .
Moving forward
There are already strong indications that the Directive
One altOne alternative to will be largely enforced through local authority
ccyyclones and multi-clonen planning permission and Defra has stated that “local
ccyyclones is elecclonen trostatic authorities are delivery partners in relation to air
prpreecipitation,cipi whereby quality management”.
parparticles articlc e charged
and rand rreemoved from Indeed, some local authorities have already
the flue gases in an the flu expressed concern about biomass in urban areas,
elecelecttrrroostatic field so there is a very real concern that failing to find
to a colleco tor. This is a suitable solution could severely curtail the
veverryy eff effeective for smaller potential for biomass in the UK. This, in turn, would
particlesticles but elec b trostatic have a significant impact on our ability to meeting
filters teend tn o be both very the country’s commitments to reducing carbon
eexpensivxpensiveve and very large – emissions. Hoval CF filters have the potential to meet
oofften tooo lar ge for typical the challenge of particulate emissions and ensure
UUK plant rK plant rooms. that biomass remains as a viable element in the UK’s
renewable heating strategy without compromising
UUntil rntil ecently on air quality.
thetherree has not been
aa financially viable financn For further information please call 01636 672711
alaltteernativrnata e but Hoval or vist www.hoval.co.uk
hhas noas nowow optimised a
ceraamic filtmici er for use in
bbiomass installations iomass
- wit- without makhoou ing the
overallall c cost of a biomass
CF Model Depth Height Width
iinstallation prnstallata ohibitive.
50 990mm 1510mm 1120mm
500 2260mm 1925mm 2080mm
Twin 1000 2915mm 1926mm 3520mm
www.cibsejournal.com February 2010 CIBSE Journal 27
Hoval amended.indd 1CIBSEfeb10_school_pp27.indd 27 19/1/10 15:20:4620/1/10 15:32:06
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