Bag filter optimization in Cement Industry

© Confederation of Indian Industry
Bag Filter Optimization

Concept of Dedusting
Dedusting plants may be divided into the
following components:-
 Equipment's to be dedusted
 Dedusting pipes and valves
 Filter
 Fan and motor
 Insulation

How to design?
 Identify the equipment to be dedusted
 Maximum 6 dedusting points should be
connected to one common filter.
 Calculate the dedusting airflow for each
dedusting point and duct
 Calculate the air flow for the complete
dedusting pipe system.
 Determine the pipe sizes from the air flows

How to design?
 Choose the auxiliary equipment-
throttle valves, ventilation flaps ,
filter, fan and insulation-,based on
the dedusting air volumes
 Also check the physical site process
parameters such as temperature, RH
and barometric pressure.

Design Guidelines
 Amount of dust source to vent:-Not more than 8
venting points to be connected to bag filter.
 Venting Air Volume:-The true required venting air
volume that the ventilation system has to handle
must be determined first.
 Venting velocity norms are dependent upon
following parameters:-
 Characteristic of material (Explosive or not
explosive dust)
 Equipment Type(Open or Closed)

Venting Velocity Norms-Not explosive dust

Venting Velocity Norms- explosive dust(coal meal)

Open Equipment's-Bag Filter design
 Apron conveyor or feeder
 bucket conveyor
 Crushers
 Weigh feeders
 Belt conveyors

Closed Equipment's-Bag Filter design
 Drag Chain
 Pneumatic transport system
 silos
 screw conveyor
 Air lift
 Bucket conveyor

Insulation:-Bag Filter design Criteria
 In cases where the relative humidity of the
dedusting air is so high that condensation
may arise as a result of heat emitted by the
dedusting pipe
 The filter bottom hopper should in rare
situations be equipped with heating elements.

Dust Concentration
 The type dust concentration in the dedusting air
from the transport equipment, silos, stores etc.
is between 20 and 50 g/ cubic meter of the
dedusting air.

Hood Design
Intake Velocity at Hoods is almost equals to1.4 m/s

Venting hood velocity norms

Venting Hood designs
Venting
hood
V=1.4 m/s
Duct velocity=16-18 m/s

Pipe design Norms
 The pipe design after filter, as well as, the
exhaust from the fan should be one size larger
than the pipe just before filter
 Clean air velocity range in the pipe
 16-18 m/s
 Velocity with dust laden air:
 9-12 m/s(non explosive)
20 m/s(explosive)

Discharge Chute Height-Design

Discharge Chute Height-design

Venting Flow Requirement-Conveyors

Venting Flow Requirement:-Bucket elevator

Venting Flow Requirement:-Elevators & Conveyors

Venting Flow Requirement-Crushers

Venting Flow Requirement:-Packers

How to calculate dedusting air requirement in CF
silo?
CF Silo
BF2
Silo extraction
BF1
Aeration Blowers-Q3
Q Silo Top
Q Silo bottom

Dedusting Calculations
Q silo Top-Dedusting air requirement for top part of CF silo
q2 = Displacement Air
Displacement air = F / 60 m3/min;
F is the feed to silo/tank(m3/hr)
q3 = Air For aeration for CF silo
q1 = Temperature adjusted amount of
air from transport equipment
eg:-Pneumatic conveying

Dedusting Calculations
Q silo bottom-Dedusting air requirement for
bottom part of CF silo

Air for Aeration of CF silo

Clinker Storage Silo
 The required dedusting air requirement for air
tight clinker silo:-
Q=DXDX0.055
D= Diameter of Silo in meter
The value of Q should satisfy the minimum venting
velocity norms as per discussed earlier(9-12 m/s)

Air Requirement-Crusher section
1
2 3
4
5
H
Belt Conveyors-3,4,5
1-Point for
Apron
2-Main
dedusting

Point 1:-Air requirement-
Connected to Apron Conveyor
= 47 m3/min per m apron belt width
(As per design guidelines)
Point 2 :- Main Branch
Point 3,4,5 :- Sub branches
Point 2 :- Air requirement as per main branch
rule by using the below formulae
Q crusher = 11 X cube root of (P X HXH)

Q crusher = 11 X cube root of (P X HXH)
P = capacity of crusher(t/h)
H = Distance between crusher shaft & belt
conveyor(m)
H approx. = 3.6 -4.0 m
Point 3,4,5 - Air requirement as per rubber belt
conveyor designs
Total = Q1+Q2+Q3+Q4+Q5

 Calculation of dust concentration before filter:-
S = Crusher Output(t/hr) X 10^6 X0.3 g/m3
Total dedusting air(m3/min) X 60X100
Depending upon dust load concentration the filter load
is to be decided.
Dust Concentration

Bag Filter Material selection Criteria
 Filter Type
 Moisture level
 Gas Temperature
 Composition & Chemical properties(gas dust
load)
 Physical characteristic(Abrasiveness)
 Allow dust load
 Emission level

Air to Cloth ratio
 The air-to-cloth ratio (A/C ratio) is simply a mathematical
expression used to measure the amount of filtering cloth
area available to filter a given volume of air at a given
flow rate.
 Significance:-Determine the operating limits of the
baghouse.

Characteristic of filter material
 High air permeability ( low pressure loss)
 Good mechanical strength
 Good thermal stability at operational
temperature
 Good dimensional stability at operational
temperature

Selection Criteria

Bag Filter purging sequence

Troubleshooting points
Operation Problems Possible Reason Countermeasures
High pressure drop
across filter
Ineffective Cleaning
cycle & malfunction
Modify cleaning
cycle(check overall
cycle time),check
compressed air
pressure, solenoid
valves working.
Wetting of bags
Due to gas dew point;
moisture in
compressed air
High air cloth ratio
High volume of
ventilated gas.

Operation Problems Possible Reason Countermeasures
Low pressure drop
across filter
Venting lines are
plugged or jammed
Avoid the venting line
jamming problem by
maintaining sufficient
venting velocity & gas
temp above dew for
avoiding moisture.
Ineffective Utilization of
capacity
Add more venting lines
to increase the dust
load on filter
Bag permeability
increase
Bag inspection
Over cleaning of bags Modify cycle time.
Troubleshooting points

Latest developments:
Star Bag Filter Technology

What is an extended surface filter?
 Round Extended Surface filter bag with more
than 2.0 x the surface area of a standard bag,
using standard non-woven filter media
Star bag Tm

Working Principle
 Extended surface filter technology (Star Bags) was
originally developed to provide an alternative to capital
equipment upgrades in dust collectors whose design
was insufficient to meet increasing capacity
requirements. It is designed to offer twice the filter
surface area of traditional cylindrical filter bags.
 Filter cake porosity increases and cake specific
resistance decreases with decreasing superficial face
velocity.

Working Principle
 A broader distribution of dust cake over a greater
filtration area provides dramatically reduced air
and dust velocity at the face of the filter, yielding
lower particulate emissions and a significant
reduction in pulse frequency.
 The lower face velocity also alters the
morphology of the filter cake, resulting in less
resistance to air flow and greatly improved dust
cake release

Filtration Principles
Initial filtration relies solely on filter media, however most
filtration is done by both the media and the filter cake.
 Pulse cleaning is triggered by a timer or differential
pressure
 Particulate emissions spike with each cleaning pulse
Blinding occurs when particles penetrate the filter
surface
Media strength loss occurs by flex fatigue around cage
wires

Filtration Principles

Comparison between extended surface filter
technologies
Pleated Cartridges
•Low Dust Loads
•Temperature Limitations
•Limited Length
•Difficult to clean
•Up to 600% filter area
increase.
•Integral Core
Star Bags
•High Dust Loads
•No Limitations of Temperature
•No Length Limitation
•Uniform Cake, easy to clean
•Up to 100% filter area increase
•Re-usable cage

Concept of Baghouse Design
Velocity of dust/gas greatly affects filtration efficiency
High velocity compacts filter cake, drives dust into
filter mA well designed baghouse balances capital cost
with adequate operation
For best operation…
−ATC ≤ 1.0 m3/m2/min (dust/fabric dependent)
−Differential Pressure 1.0 - 1.5 kPa
−Moisture should be minimized
−Then use “On-demand” pulse cleaning

Concept of Baghouse Design

Star bag filter -History
 The Star Bag, first developed by SOLAFT, has
delivered significant operational improvements
for our customers in cement worldwide with
greater surface area within the same footprint

Star bag Filter –Benefits & features
Benefits
 Lower emissions
 Reduced fan energy consumption
 Reduced Compressed Air usage
 Reduced mechanical failure
 Longer bag life
Features
 Pleated bag construction
 Upto 2 times filtration area
 Lowers differential pressure
 Reduce pulse frequency

CASE STUDIES-Star Bag Filter
Location USA
Application Cement mill
Fabric type Polyester
Star length 2.13
Standard bag
length
3.05
outcomes Reduced DP & Bag filter life increased
from 2 to 4 years

CASE STUDIES-Star Bag Filter
Location Mexico
Application Raw mill
Fabric type Polyester
Star length 1.83
Standard bag
length
3.05
outcomes Reduced DP from 9-14” to 4”
Flow increased from 33,00cfm to
40,970cfm Bag life increased from 12
months to 4 yrs.

Case Studies

Clinker Bag filter-DBC
-41mmwg
V1-18 m/s
Power-22 kW
B/F
DB1
DB2
Yard
-51mmwg
-48mmwg
-3mmwg
-61mmwg
-94mmwg
Damper-40%
-540mmwg
-3mmwg
V1-22 m/s
V2-22 m/s
Belt
Conveyor
Belt Conveyor

Clinker Bag filter -DBC
 Observations
 No of main branches - 3
 No of sub branches - 2
 Header Pressure = 4.8 kg/cm2
 Static Pressure Below RAL = -3 mmwg
 Pressure Drop Across Bag filter = 10 mmwg
 Fan Flow = 13702 m3/hr
 Velocity at main branches = 22m/sec
 Fan efficiency = 97%
 Pressure Drop Across Damper = 431 mmwg
 Fan Power = 22 kW

Present Challenges
 Dust emissions from belt
conveyor
 High power consumption of
Fan
 Uneven venting velocity
 Low DP across Bag
filter(10mmwg)
 Un-utilization bag Filter
Capacity

 Recommendation
 Dust emissions from belt conveyor
 Install additional venting line in tail ends of belt
conveyor .
 Recommended Ventilation Volume in tail end
 3000m3/hr in tail end
 Velocity in venting line-10m/sec
 High power consumption of Fan
 Remove damper & replace with VFD.
 Saving Potential :-18 kW

Benefits:-After implementation
 After adding additional venting lines the differential
pressure across bag filter has been increased from
10 mmwg to 80 mmwg.
 No dust emission because bag filter is effectively
utilized with full capacity.
 Beauty of the project-Nil investment(in house)
Annual Saving - Rs 6.02 Lakhs
Investment - Rs 1.50 Lakhs
Simple Pay back - 3 months

Bag filter :-Additive Feeding
B/F
-16mmwg
V2-12 m/s
Belt
Conveyor1
-34mmwg
-1mmwg
-68mmwg
-72mmwg
Damper-50%
-371mmwg
+4mmwg
V’-15 m/s
Power-8.2 kW
-33mmwg
BeltConveyor2
V1-13 m/s

Bag filter:-Additive Feeding
Observations
 No Of Sub branches-2
 No of Main branches-1
 Velocity at Sub branch1-13m/s
 Velocity at Sub branch2-12m/s
 Fan flow -6501m3/hr
 Fan Efficiency-90%
 Pressure drop across damper-299 mmwg
 Fan Power-8.2 kW

Bag filter:-Additive Feeding
 Present Challenges
 High power consumption of Fan
 Uneven venting velocity

Bag filter :-Additive Feeding
 Recommendation
 Optimize fan flow as per standard velocity
 Velocity in venting line-10m/sec
 High power consumption of Fan-Remove damper
and replace with VFD.
 Saving potential-6.54 kW

Bag filter :-Fly Ash Silo Bin
B/F
B/E discharge
-145mmwg
-31mmwg
-36 mmwg
-166mmwg
-161mmwg
Damper-NW
-460mmwg
+2mmwg
V’-4m/s
Power-7.6 kw
-145mmwg
weigh bin
Air Slide
Bin Airslide
-136mmwg -136mmwg

Bag filter /Fly Ash Silo Bin
 Observations
 No of main branches-1
 No of sub branches-4
 Header Pressure-3.8 kg/cm2
 Static Pressure Below RAL = -36 mmwg
 Pressure Drop Across Bag filter = 22 mmwg
 Fan Flow = 1716 m3/hr
 Velocity at Fan duct = 4m/s
 Fan efficiency = 31%
 Pressure Drop Across Damper = 299 mmwg
 Fan Power = 7.6 kW

Bag filter:-Fly Ash Silo Bin
 Clean air velocity in duct is very low (4 m/s)
which should be around 16-18 m/s.
 Fan flow is not adequate for de-dusting air
requirement.
 Pressure drop across damper is 299 mmwg
that led energy losses of 4.9 kW

Present Challenges
 Compressed air pressure is maintained 3.8
kg/cm2, which is less than recommended.
 Physically damper is not working at site.
 Pressure below rotary air lock is -36 mmwg,
which is greater than -6 mmwg that indicates
RAL is not working properly and possibility of
ingress air has been increased

Bag filter :-Fly Ash Silo Bin
 Recommendation
 Maintain the fan flow(8000m3/hr)
 As per recommended velocity(9-12m/s) in main branch
 Remove damper and replace with VFD if
pressure drop is still high by increasing flow.
 Saving potential : 4.9 kW
 Replace existing RAL with new one to reduce
false air tendency across filter

Benefits
 Annual Saving - Rs 1.59 Lakhs
 Investment - Rs 0.55 Lakhs
 Simple Pay back - 4 months

Bag Filter :-Cement mill
B/F
Belt Conveyor1
-1mmwg
-90mmwg
-100mmwg
Damper-50%
-220mmwg
+3mmwg
Power-25.2 kW
V2- 10.4m/s
V- 10.5m/s
-32mmwg
V- 20 m/s
V- 5.4m/s
-47mmwg
Belt Conveyor2
Belt Conveyor3
Belt Conveyor4
V2- 7.5m/s

Bag Filter – Cement Mill
 Observations
 No of main branches - 4
 No of sub branches - 3
 Header Pressure - 5.0 kg/cm2
 Static Pressure Below RAL = -1 mmwg
 Pressure Drop Across Bag filter = 53 mmwg
 Fan Flow = 28821 m3/hr
 Velocity at main branches = 8.50m/sec
 Fan efficiency = 73.30%
 Pressure Drop Across Damper = 120 mmwg
 Fan Power = 25.2 kW

Bag Filter:-Cement mill
 It found that venting velocity was uneven in main
branch it should be in the range of 9-12m/s in all
branches.
 Velocity in sub-branches are also uneven that may
affect the bag filter efficiency.
 Pressure drop across damper is 120 mmwg that led the
energy loss of 14.4 kW

Bag Filter :-Cement mill
 Recommendation
 Fan flow should be maintained by optimizing the
velocity at main branches .
 Maintain uniform velocity by checking all the ventilation
lines whether it is working or jammed.
 Remove damper and replace with VFD.
 Saving potential is 14.4 kW

Benefits
 Annual Saving - Rs 4.7 Lakhs
 Investment - Rs 1.50 Lakhs
 Simple Pay back - 4 months

Crusher Bag Filter
B/F
-23mmwg
-184mmwg
-188mmwg
Damper-100%
-191mmwg
-26mmwg
Power-15 kW
V2- 7.3m/s
V1- 9.6m/s
-10mmwg
V- 10.5m/s
-109mmwg
V3- 12.3m/s
-12mmwg
Crusher
discharge
Belt
conveyor
Belt
conveyor

Crusher Bag filter
 Observations
 No of main branches - 3
 No of sub branches - 2
 Static Pressure Below RAL = -1 mmwg
 Velocity at main branches = 8.50 m/sec
 Fan efficiency = 93.30%
 Fan Power = 15 kW

Crusher Bag Filter
 It found that crusher bag-filter was running almost
100 % flow to maintain the venting velocity at main
branch.
 Pressure drop across filter is 79 mmwg that shows
additional venting lines could be add in main
branches to improve nuisance condition there.
 Compressed air pressure is slightly higher side

Crusher Bag Filter
 Recommendation
 Add the additional venting lines to utilize the
capacity of bag-filter upto 100%.
 Slightly reduce the compressed air pressure
and maintain in the range of 5-5.5 kg/cm2 to
avoid the energy losses.

Roto Packer1-Bag filter
B/F
-57 mmwg
-171mmwg
-381 mmwg
Damper-50%
+2 mmwg
Power- 30 kW
Packer1
V-12 m/s

Roto Packer1:-Bag filter
 Observations
 No of branches - 1
 Velocity at main branch = 12 m/sec
 Pressure drop across damper = 210 mmwg at
50% damper.
 Fanfficiency = 50 %
 Fan Power = 30 kW

Roto Packer1
 Pressure drop across damper is higher side
 210 mmwg.
 Compressed air pressure is maintained 6.2
kg/cm2 that may result energy losses.

 Recommendation
 Header pressure should be maintained in the
range of 5-5.5 kg/cm2 to avoid energy losses.
 Remove damper and replace with VFD.
 Saving Potential- 16.45 kW

Cement Silo –Bag filter
-40 mmwg
B/F
-181 mmwg
-560 mmwg
-19 mmwg
Power-28.7 kW
Cement Silo4
Cement Silo3
Screw
Conveyor
Damper-60%
18 m/s

 Observations
 No of branches - 3
 Velocity at fan inlet = 18 m/sec
 Pressure drop across damper = 379 mmwg at
60% damper.
 Fan efficiency = 79 %
 Fan Power = 28.7 kW

 Pressure drop across damper is higher side:-
379 mmwg.
 Compressed air pressure is maintained 6.2
kg/cm2 that may result energy losses.

Cement Silo –Bag Filter
 Recommendation
 Header pressure should be maintained in
the range of 5-5.5 kg/cm2 to avoid energy
losses.
 Remove damper and replace with VFD.
 Saving Potential- 20 kW

Cement Silo –Bag Filter

Key Encon points
 Installation of additional venting lines to the
bag filters.
 Optimization of branch velocity in the range
of 9-12 m/s.
 Replacement of inefficient RAL with new one
to reduce false air across bag filter.
 Removal of damper and then replace with
VFD.

Key Encon points
 Maintain the compressed air pressure in the
range of 5-5.5 kg/cm2
 Install baffle plate at inside discharge chute to
increase the collection efficiency
 Install DP transmitter for bag filter and interlock
air-purging operation with the bag filter DP.
 Maintain bag filter DP in the range of 90 to 120
mmwg

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@CII_GBC cii--godrej-gbc
For further details Contact:-
Nitin Asnani
Associate Counsellor
nitin.asnani@cii.in/8963965157

Bag filter optimization in Cement Industry

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