|
Facing up to biomass emissions
Particulate emissions from biomass boilers are coming under the
spotlight and installers need to be aware of the issues. Kevin Stones,
Engineering and Service Director with Hoval, considers the implications
Moves to improve air quality across Europe have the potential to impact on
the use of biomass boilers, so anyone involved in their specification or
installation could find themselves subject to questioning about this issue. This
is because the smaller particles (down to 2.5 microns diameter) that are not
filtered by traditional mechanisms such as multi-cyclones will soon fall within
the remit of new legislation.
EC Directive 2008/50/EC, Ambient Air Quality and Cleaner Air for Europe
came into force on 11 June 2008 and must be transposed into national
legislation no later than June 2010. Of particular significance in these
regulations is the size of particles that will be controlled. In the past, emphasis
has been on particles with a diameter of 10 microns or above (PM10).
However, the new Directive will seek to introduce a new control framework for
particles down to 2.5 microns in diameter (PM2.5).
Size matters
The majority of these particles in the UK come from vehicle emissions but all
biomass boilers also make a small contribution to particulate emissions. The
level of emissions will vary with the quality of the fuel and combustion
efficiency of the boiler, so using boilers that comply with EN 303-5 Class 3, in
conjunction with high quality fuel, is the first step in minimising particulate
emissions.
Of course, many biomass installations already use a cyclone or multi-cyclone
to remove particles from flue gases. However, cyclones are totally dependent
on the mass of the particles for removal, so while they will remove around
50% of the coarser particles they do not remove particles below PM10.
One alternative to cyclones and multi-cyclones is electrostatic precipitation,
which is very effective for smaller particles but electrostatic filters tend to be
very expensive and very large – often too large for typical UK plant rooms.
Another option is a ceramic filter that is already used widely in industry and
has now been optimised for biomass use without making the overall cost of a
biomass installation prohibitive.
Capable of removing up to 96% of PM2.5 and PM10 particles, ceramic filters
can be used with any type of biomass boiler and can be retrofitted to existing
installations, so they have the potential to address many of concerns (real or
perceived) about particulate emissions from biomass.
Ceramic filters are connected to the back of the boiler, in the same way as a
cyclone. Each unit contains a matrix of porous ceramic tubes which are
closed at the lower end. The number of tubes in each matrix is aligned with
flue gas volumes for each boiler.
As flue gases are drawn through the filter by an inline fan, the gases are able
to pass through the walls of the ceramic tubes, while particles are trapped. At
regular intervals (timed and/or in response to a pressure drop across the filter)
a pulse of air is used to dislodge the particles, which fall into a collection bin.
Consequently, ceramic filters have the potential to meet the challenge of
particulate emissions and ensure that biomass remains as a viable element in
the UK’s renewable heating strategy without compromising on air quality.
Ends
Issued on behalf of Hoval by Market Force
Press enquiries: Paul Haddlesey
Market Force
45 Oakroyd Avenue
Potters Bar
Herts EN6 2EN
Tel: 01707 665088
Fax: 08700 562476
E-mail: paul@market-force.co.uk
Web: www.market-force.co.uk
Reader enquiries: Ian Dagley
Hoval Ltd
Northgate
Newark
Notts
NG24 1JN
Tel: 01636 672711
Fax: 01636 673532
E-mail: hoval@hoval.co.uk
Web: www.hoval.co.uk |
