Dust Filtration

1
Dust Filtration
Corus Consulting Limited, Teesside Technology
Centre, P.O. Box 11, Grangetown,
Middlesbrough, Teesside TS6 6UB U.K. Telephone
44 (0)1642 467144 Fax [phone]
460321 E-mail paul.marsden_at_corusgroup.com
The most effective and economic equipment for
filtering particulate material from gas streams
is the bag filter. These devices employ an array
of fabric sleeves through which dirty gas is
passed, to emerge to atmosphere with very low
levels of dust remaining - typically a few mg/m3.
This often represents a filtration efficiency of
99.9. Whilst bag filters offer the best
performance for filtering many of the gas streams
encountered in iron and steel production, they
have limitations with respect to temperature,
fire resistance, and their ability to handle
abrasive, moist, or sticky dust. These are
attributable to the properties of the fabrics
available at reasonable cost. A novel device,
the KN-Filter, employing metallic mesh screens,
offers the possibility of providing bag filter
performance levels on some of the gas streams
which presently require the use of other, less
effective dust removal techniques. The ability to
filter at high temperature (up to 600oC or more)
also gives the attractive possibility of heat
recovery from filtered gases. The Environmental
Science Department is currently testing this
technology at pilot scale.
The principle of operation is based on the belief
that in conventional fabric filters the bag
performs some filtration but the layer, or cake,
of filtered material adhering to the fabric acts
as the major filtration medium. Extending this
principle, it has been demonstrated that by
passing the gas stream through a relatively
coarse metallic mesh (typically 60 to 300 mesh),
which has gaps many times the size of the
particles, a cake can be built which acts as an
effective filter. The KN-Filter uses this
property. One chamber of mesh modules undergoes a
cake building process whilst one or more chambers
which already have an established cake perform
the filtration. When the minimum necessary layer
has been established in the off-line chamber,
this can be brought on-line and one of the others
can be isolated and pulse-cleaned, prior to
re-establishing a cake. Initial tests on the
off-gas from an Electric Arc Furnace have shown
that the test unit (see below) can give outlet
dust loadings well within those required by the
permitting authorities, and at levels very
similar to those from fabric filters on similar
applications.
TEST FILTER Testing on an ironworks application
is now proceeding.
GENERAL ARRANGEMENT
72