Mechanical Technology — February 2014
5
⎪
On the cover
⎪
Left:
For an air volume of 6,0 m
3
/s, for example, or 360 m
3
/min, a traditional Downflo design limits the air filtration speed to 0,5 m/s and therefore
requires more filter area (720 m
2
). Because the heavy dust is being dropped out when using the plenum design, the filtering speed can be
increased to 1,0 m/min, hence only 360 m
2
of filter area is needed.
Right:
PowerCore, mostly because of the new cartridge design, has a 50%
smaller footprint than the traditional baghouse and cartridge collectors.
Donaldson’s Downflo DFT dust collectors with proprietary Ultra-Web
®
filter media in use at a seed
corn plant.
the filter media. By removing the ‘heav-
ies’ before the filter cartridges, this filter
rate can be doubled, ie, increased to
1,0 m/min, which allows the total
filter area when using a plenum-based
designed to be halved,” he points out.
For an air volume of 6,0 m
3
/s, for
example, or 360 m
3
/min, using the
maximum industry standard speed
for filtering heavy dust, the air volume
needs to be divided by the filtering area
to give the filtration velocity or air to
media ratio. “For a traditional Downflo
design, therefore, 720 m
2
of filter area
will be needed,” Knight calculates, “and
since each cartridge provides 21 m
2
of
filter media, the system requires 34
cartridges for effective filtration.”
Comparing traditional and plenum-
based designs, Knight points out
that, because the heavy dust is being
dropped out, the filtering speed can
be increased to 1,0 m
2
/min, hence
only 360 m
2
of filter area is needed,
ie, 17 cartridges. “So, by using ple-
num technology, instead of needing a
4DF32 – four rows of filters and 32
Downflo cartridges – one can now use
a 4DF16, with only 16 cartridges,” he
explains. Working back to calculate the
filter speed for this solution, Knight says
that 16 cartridges of 21 m
2
each gives
a total filter area of 336 m
2
, with an
airflow of 360 m
3
/min through the filter,
divided by 336 m
2
of filter area results
in a 1,07 m/min air speed through the
media – “perfectly safe for Downflo
Ultraweb filter cartridges extracting
lighter dusts,” he says pointing towards
an illustration comparing traditional and
plenum technologies.
“Also, on traditional designs, heavier
dust loading on the media results in
higher pressure drops (
∆
P), so you need
a more powerful fan, making the system
less energy efficient,” Knight adds.
Mobile labs
Key historical successes for Donaldson
are the Torit filtration systems used for
mobile sampling laboratories. “We have
installed numerous mobile lab systems
over the years through-out Africa. These
labs are built into standard 6-ft contain-
ers, which are fitted with all of the test-
ing equipment needed by the inspection
specialist, such as SGS.
For most ore sampling laboratories, dust
is extracted and passed through a Donald-
son Torit Downflo (DFT) dust collector.
