2. Baghouse
Fabric filters collect particles with sizes ranging from submicron to several hundred
microns in diameter at efficiencies generally in excess of 99 or 99.9 percent.
The layer of dust, or dust cake, collected on the fabric is primarily responsible for such high
efficiency. APC - Pratibha Gautam
5. Cleaning Mechanism
• Shaking
For small, single-compartment baghouses, usually operated
intermittently, a lever attached to the shaker mechanism may be
operated manually at appropriate intervals, typically at the end of a
shift. In multi-compartment baghouses, usually operated
continuously, a timer or a pressure sensor responding to system
pressure drop initiates bag shaking automatically.
• Reverse Air
Reverse-air cleaning was developed as a less intensive way to impart
energy to the bags. In reverse-air cleaning, gas flow to the bags is
stopped in the compartment being cleaned and reverse (outside-in)
air flow is directed through the bags.
• Pulse Jet
This form of cleaning uses compressed air to force a burst of air down
through the bag and expand it violently. As with shaker baghouses,
the fabric reaches its extension limit and the dust separates from
the bag. Air escaping through the bag carries the separated dust
away from the fabric surface.
APC - Pratibha Gautam
6. Properties of some fibre material
Fibre Relative
strength
Max. usable
Temp. (°C)
Relative resistance to attack by Other Properties
Acid Base Organic
solvent
Cotton Strong 80 Poor Medium Good Low Cost
Wool Medium 95 Medium Poor Good Fair resistance to
abrasion
Polyamide Strong 100 Medium Good Good Easy to clean,
Fair resistance to
abrasion
Polyester Strong 135 Good Medium Good Easy to clean
Teflon Medium 260 Good Good Good Expensive
Glass Strong 280 Medium Medium Good Poor resistance
to abrasion
“Nomex”
nylon
Strong 230 Good Medium Good Poor resistance
to abrasion
APC - Pratibha Gautam
7. Numerical
• A fabric filter is to be constructed using bags
that are 0.3m in dia and 6.0 m long. The
baghouse is to receive 10m3/s of air, and the
appropriate filtering velocity has been
determine to be 2m/min. Determine the
number of bags required for a continuously
cleaned operation.
APC - Pratibha Gautam
8. Solution…
• Area required= Q/Vi
= 10/ (2/60)= (10*60)/2
= 300 m2.
Now area of one bag= πdh= 3.14*0.3*6
= 5.65 m2
Now, total no. of bags= Total area/ area of one bag
=300/5.65
= 53.05 = 54 bags.
APC - Pratibha Gautam
9. Wet Scrubber
• Work on Wet precipitation mechanism
• Basic function: Provide contact b/w scrubbing
liquid(water) and the particulate to be collected.
• Collection mechanisms are same as in filters
(Inertial impaction, Direct interception and
diffusion)
• Major types are:
o Spray tower
o Centrifugal Scrubbers
o Packed bed towers
o Venturi scrubbers
APC - Pratibha Gautam
10. Spray tower
Clean gas out
APC - Pratibha Gautam
Water is introduced from the top
with the help of spray nozzles.
Polluted gas flows upward and the
particle collection results because of
inertial impaction and interception.
Efficiency of spray tower depends
upon droplet size.
11. Centrifugal Scrubber
• It can be constructed by
inserting banks of nozzle
inside a conventional cyclone
separator.
• The spray acts on the
particles in the outer vortex.
• In absence of spray, the
efficiency of a centrifugal
scrubber will be same as dry
cyclone separator.
APC - Pratibha Gautam
12. Packed bed towers
APC - Pratibha Gautam
Packed towers are special kind of Spray towers,
in which packing/trays are used to provide
better contact of water and fine particles.
Packed towers are generally chosen for
scrubbing particles that are soluble in the
scrubbing liquid; otherwise, the packing will
encounter plugging problems.
13. Venturi Scrubber
APC - Pratibha Gautam
Venturi Scrubbers offers high
performance for fine particles, usually
smaller than 2 to 3μ in dia.
Gas streams are acclerated to very high
velocities (60-120 m/s).
Water is introduced in a uniform fashion
across the throat through several spray
nozzles.
The droplets accelerate in the throat section and due to the velocity difference b/w the
particle and droplets the particles are impacted against the slow-moving droplets.
This acceleration of particles is not likely to be completed at the end of the throat, so that
paticle collection continues to some extent into diverging section of the venturi.
The gas-liquid mixture is then directed to a separation device such as cyclone separator
where droplets carrying the PM are separated from the gas stream.
