Basics of bag filter based de-dusting system.

2.  Air pollution is the introduction into the
atmosphere of chemicals, particulates, or
biological matters that cause discomfort,
disease, or death to humans, damage other
living organisms such as food crops, or
damage the natural environment or built
environment.

3. Basic Concept

6.  Dust laden air enters through the
hopper by suction or positive
pressure
 The heavier dust particles fall
immediately into the hopper,
while the lighter ones deposit on
the outer surface of filter bags
 Dust deposited on bag surface is
dislodged & bag is cleaned by
pulse of high pressure
compressed air.

7. Penthouse
with hoist
Dust particles Insulation to
are avoid
retained on the undershooting
surface of the of dew point
filter (hot gas
medium and version
the
cleaned air Top-Down flow
passes in filter housing
through the
filter Dust collection
medium and hopper or tray
flows with material
into the clean discharge
gas screw or
chamber or scraper chain
duct. conveyor

8. Bagfilters : Classification based on how the
fabric is cleaned
1. Shaking 2. Compressed Air 3. Reverse Air
Reverse Air

9. Types of Cleaning

10. Bag Filter - Basics
 In an industrial system of gas cleaning, the fabric is media made into
either an envelope or a tube. These envelopes or tubes are called
the bags and a housing of these is called Bag Filter or Bag House.

11. FACTORS GOVERNING SELECTION
OF TYPE OF APC EQUIPMENT - 1
• Inlet dust load in gm/
Nm3
• Gas volume in Nm3/
hr
• Gas temperature
• Nature of pollutant : Gaseous /Particulate
• Properties of dust : Physical (density /size
fraction /
temperature /‘wettability’)
• Properties of gas : Physical /Chemical (nature:
acidic /
alkaline, moisture content critical)

12. FACTORS GOVERNING SELECTION
OF TYPE OF APC EQUIPMENT - 2
• Nuisance value /Recovery value of both dust
and gas
• Outlet emission requirements /Efficiency
required
• Space availability
• Economics /Budget /Fund availability
/Return on Investment

13. Air-to Cloth Ratio =
Total volume of gas (or air) handled by the Bag filter [m3/min] /
Total filtration area provided in the Bag Filter [m2]
= [ m3/min-m2 = m/min, => velocity unit; hence also called filtration
velocity, and is actually the velocity at which the dust laden gases travel
across the filter element ]
The more critical the dust { fine, light, sticky, non-agglomerating, abrasive, etc}
or higher the dust loading, the larger is the filtration area provided, i.e. lower is
the air-to-cloth ratio maintained.

14. Can Velocity =
Velocity at which the gas travels upwards across the cross
section of the Bag filter =
Total volume of gas (or air) handled by the Bag filter [m3/min] /
Cross sectional area of Bag Filter casing [m2]
This is an important aspect and has to be restricted especially for fine, light,
and non-agglomerating dust (lime, carbon black are typical examples) as
otherwise the dust may remain in a fluidised state in the bag filter and not get
discharged from the unit at all.

16. Filter Fabric selection

17. Online type :-
Cleaning is done on line ( chamber in operation)
Off Line type :-
Cleaning is done in the off line mode. i.e cleaning
of the chamber after isolating the flue gas
entry .
 This avoids re entrainment of dislodged dust
 Used in case of fine dust

18. Bag Filter – Type-Online
Single module-hopper Entry

19. Bag Filter – Type-Offline
How it works – Normal Gas Flow

20. Bag Filter – Type-Offline
How it works – Reverse Gas Flow

21. Bag Filter – Type-Offline
 In offline Pulse Jet Bag Filter which is a
compartmentalized Bag Filter, one
compartment is sequentially taken out
for cleaning purpose. Rest all the
compartments are under filtration
process. Typically offline cleaning is
employed for finer dust particle sizes
which does not settle easily.
 In Modular construction Pulse Jet Bag
Filter which is Online in cleaning
operation, one compartment can be
taken out doe maintenance purpose if
required.
• The cleaning in this type of filter is online i.e. filtration and cleaning simultaneously occurs
in a compartment. These type of filters are usually designed for Process application which
handle large gas volumes.
• In both the above types of Bag Filters outlet type poppet dampers pneumatically operated
are required for isolation of compartments.
PJBF-Offline

22.  Constant emission air pollution control (APC) equipment.
 Suspended particulate emission control using positive filtration.
 Possible to achieve lower outlet emission.
 Suitable upto gas temp. of 260 deg C.
 Can handle various types dust viz. explosive/non-explosive, abrasive,
hygroscopic, sticky, coarse/fine.
 Low initial set-up cost.

23. Pulse Jet:
 Pulse Valve

24.  Pulse Jet Components - Diaphragm Valve

25. Pulse Jet Component – Air Manifold Tank

26. Pulse Jet Components – Tubesheet (Cell Plate)

27. Pulse Jet Components - Venturis

28. Pulse Jet Components - Bags

29. Pulse Jet Components –
Bags

30. Pulse Jet Components - Cages

31. Pulse Jet Components – Cleaning system

32. Pulse Jet Components – Cleaning system

33. Pulse Jet Components – Timer or DP Based Control

34. Pulse Jet Cleaning Operation through Timer

35. 6 Ways Dust Gets to Clean Air Plenum
 Hole in Bag
 Snapband/Flange Top
 Welding Cracks
 Clean too soon (Over Cleaning)
 Not Cleaning (Under Cleaning)
 Air Leaks at Door Seal

36. Pulse Jet Component – Blowpipe
Normal Holes
Enlarged Holes

37. Pulse Jet– Blowpipe Misalignment Problem
of Cage
of Blowpipe
Less than 1/4 inch
(6.35 mm)

44. PROBLEM POSSIBLE SOLUTION
CAUSE
High DP Bad Gauge Check gauge by blowing into it. If
needle does not move replace
gauge
Leaking gauge Repair leaking gauge pipe
pipe
Choked gauge Clean / replace gauge pipe
pipe
Low header Minimum required pressure is
pressure 6.3kg/cm2g (90psi). Check
supply pipe, drain valve for
leaks. Check Diaphragm &
solenoid operation

45. PROBLEM POSSIBLE SOLUTION
CAUSE
High DP Static Charge Static Electricity will interfere with the
on Filter cleaning operation. Ground the filter
Water in Air Remove water & clean the system.
Line Check regularly the manual/Auto drain
valve of Air Filter. Replace the
defective one.
Bag Blinding High moisture & condensation will
or chocking cause dust cakes, which are difficult to
remove & it blinds/chokes bags.
1)Preheat Bag Filter on start-up & use
space heater ON for long shutdown.
2)Wash bags & use after drying.
3) Membrane bags – Permanent soln.

46. PROBLEM POSSIBLE SOLUTION
CAUSE
High DP Wet Humid compressed Air allows dust
Compressed cake to stick to the bags. Ensure,
Air clean & dry compressed air
Too high Check for airflow figure. If it is very
System Air high the A/C Ratio will also be very
Flow high causing high DP as well as Re-
entrainment
Dust Particles Ask customer for actual particle size
– Too fine analysis & compare with figures given
in the order – Excessive fines will
simply choke the pores on bag surface
Pulse pipe The pulse pipe nozzle should be
mis alignment concentric with the bag centre

47. PROBLEM POSSIBLE SOLUTION
CAUSE
High DP Bag-Cage For normal felt bags the bag –cage
Pinch – not pinch should be within 6mm ~ 12mm.
Okay Replace ‘Too tight’ bags, as well as
‘Too loose’ bags
Long Pulse Adjust OFF Time by observing Bag
Frequency Filter DP and set. Reduce OFF Time
by 5seconds interval and watch till DP
stabilize
Pulse ON Pulse ON time should Typically in the
Time range of 80~100ms. Some Fine dust
application, it may require higher ON
time, but that should be verified first

48. PROBLE POSSIBLE SOLUTION
M
CAUSE
High DP Sequential Any malfunction can cause irregular
Controller pulsing, causing raise in DP across
Problem BF. Repair/replace card(s)
RAV Leakage
High Dust If actual value is higher than design,
Load check everything and then increase
pulse frequency till 10sec interval time.
Else, advice customer to go for pre-
filter
Failure of
solenoid valve
diaphragm

49. PROBLEM POSSIBLE SOLUTION
CAUSE
Low DP Bad Gauge Check gauge by blowing into it. If
needle does not move replace gauge
Leaking / Repair leaking gauge pipe
choked
gauge pipe
Holes in Bags Replace worn bags
Low System Check duct systems for deposits &
air volume closed dampers – It causes work area
problem for dedusting system
Wrong Bag Look for dust on clean air plenum &
installation blank /dummy the defective bags

50. PROBLEM POSSIBLE SOLUTION
CAUSE
Emission Holes in Replace damaged bags
bags, cut in
snapbands
Precoating / Carryout proper precoat/ seeding. If
seeding not not possible, wait for sometime till the
done for new process stabilizes after start-up
bags
Wrongly Check all dummies and ensure tight fit,
installed else replace them
dummies
Chemical Check whether bags are being torn
attack just by hand pressure. If so, chemical
attack is confirmed

51. PROBLEM POSSIBLE SOLUTION
CAUSE
Poor Bag Overcleaning Increase pulse frequency or OFF time
Life duration
Abrasion Poor inlet design causing high inlet
velocity and elbows at inlet can cause
accelerated abrasion of bags –
Bent / Replace bent / corroded cages
corroded
Cages
High Air High A/C ratio shortens bag life.
Volumes

52. PROBLEM POSSIBLE SOLUTION
CAUSE
Poor Bag Moisture in Moisture in compressed air might cause
Life Comp air acid mist in some application and
weaken bags. Moisture also shrink some
fabric materials. Take corrective action to
control moisture
Thermal Some Fabrics like PPS (Ryton) is having
Shrinkage thermal shrinkage. Over exposure of
high temperature might cause such
shrinkage. Setting of temperature alarm
is important

53. PROBLEM POSSIBLE SOLUTION
CAUSE
Hopper Cleaning Check pulsing system as a whole and
Plugging malfunction take corrective action
Dust disposal Inform customer about mal functioning
system – about RAV/Screw Conveyors/ chain
malfunction conveyors
Wrong design Establish thru’ data collection
of Dust
disposal
system