FD FAN.pdf forced draft fan for boiler operation and run its very important for boiler

Presentation On FD Fan
1 X 180 TPH (Gross) Gas fired Boile
Meghna Sugar Refinery
( Bangladesh)

Sl. No Description
1 Definition of Draft & various Types of draft
2 Fan Using Purpose & Working Principle
3 Fan Technical Specification
4 Process & Instrumentation diagram
5 Various type of Dampers & reason of Uses
6 Components Name & its Utilization
7 Cone Gap & coupling Gap checks
8 Bearing Parts & its Fixing Steps
9 Bearing Checks & proper lubrication advantange
10 Alignment and misalignment Impact on Bearing
11 Fan Pre Commissioning & Commissioning Checks, Steps
12 Running and Shut Down Maintenance Method
13 Trouble shooting
14 Do’s and Don’ts
INDEX

The difference between atmospheric pressure and
the pressure existing in the furnace or flue gas
passage of a Boiler is termed as draft.
When flue gases in Boiler are maintained above
atmospheric pressure normally by the help of a
forced draft fan, is called forced draft.
When air or flue gases flow under the effect of a
gradually decreasing pressure below atmospheric
pressure by ID fan , is called negative draft.
When the static pressure is equal to the
atmospheric pressure, the system is referred to as
balanced draft system. Both fans are installed here.
DRAFT DEFINITION & TYPES

Fan is a Mechanical device which is used to produce flow of air / gas from one
point to another by virtue of raising the pressure fluid while passing through the
impeller.
Forced Draft Fan is a type of a fan supplying pressurized air to a system. ... And this
requirement is compensated by a Forced Draft Fan.
DEFINITION OF FAN

For combustion of fuel, air has to be
supplied into the furnace and the gas
generated in the furnace has to be purged
into stack continuously.
Air enters the Impeller of Centrifugal fan,
through inlet opening provided in the
casing, axially.
The Impeller is equipped with number of
backward inclined blades which
accelerates the air flow and therefore has
higher velocity energy. When it leaves the
Impeller, the air flow reaches the scroll with
parallel side plates.
Here the velocity energy is transformed to a
large part into pressure energy.
PURPOSE
WORKING PRINCIPLE

Sl. No. DESCRIPTION PARAMETERS
1 Application Forced Draft Fan
2 Tag nos. FD FAN1
3 No. of fans per boiler 2 x 50% MCR
4 Total No of fans Two nos.
5
Fan type / Model / Make
Horizontal, Radial, Backward curved , Single Suction , Simply
Supported
6 Medium to be handled Atmospheric air
7 Impeller type and
mounting
Centrifugal, Backward curved, Directly coupled
8
Type of control
Variable frequency drive control and Inlet guide vane with
pneumatically operated power cylinder with suitable links)
9 Type of drive Variable frequency drive electric motor
10 Fan speed 1480 rpm (50 Hz frequency)
11 Recommended motor
rating
315 KW
FAN SPECIFICATION

8
Centrifugal fans are generally designed to work in several points on the
pressure-flow rate characteristic in order to fit different requirements in
industrial processes: this fan regulation may be done by varying its speed or
changing the system resistance, e.g. installing a damper.
Inlet/outlet damper-
Inlet damper Controls are Used to Adjust Flow to meet Fluctuating load
demand. this involves using damper controls for throttling or restricting flow
at the fan inlet and outlet dampers.
Inlet damper Control Can be Categorized in to two types.
1) MLD/IBD-Multi-louver damper/Inlet box damper.
2) VIV -Inlet variable guide Vane (VIV) Control.
DAMPERS

Variable inlet vanes and Inlet Box Damper pictures
DAMPERS

10
Inlet box damper whirl (a) and inlet vanes whirl (b)
a) b)
DAMPERS

Fan regulation devices
DAMPERS

12
 Before take a fan Trial Run, Please recheck damper Open and close position and
ensure there is no metal to metal contact between VIV blades to VIV Body and fan
shaft to VIV center hub. Take a Special Care when fan is operate along with direct
drive motor.
MULTILOUVER VANE POSITION
CLOSED POSITION OPEN POSITION

FLAP DIRECTION OF OPENING WITH
FAN ROTATION

G
A
P
Maintain Gap Between Fan Casing Side Plate & Impeller Back Plate As Per Drawing
CONE GAP / BACK PLATE GAP

Assembly of Bearings with adapter
sleeve in split Plummer Blocks:
(Procedure to be followed in case
Bearings are supplied loose or
assembling spare Bearings during
maintenance) e.g.: Bearing 22216K and
Plummer Block SN516
Slide the inner leap seal onto the
shaft. It should slide freely.
Position the adapter sleeve on
the shaft with the threads pointing
outboard. If necessary, apply a light
oilor/ powder graphite for easier
mounting.
BEARING PARTS & ASSEMBLY

 Check the internal clearance of the bearing before
placing it onto the adapter sleeve by standing the
bearing on a table or bench so that the rollers are
located at the bottom of the bearing and the clearance is
at the top.
 Slide the bearing over the adapter sleeve. It only slides In
one direction. Place the locknut, with lubricated threads,
on the adapter with the chamfered face toward the
bearing. The surface that contacts the bearing also
should be lubricated.
BEARING PARTS & ASSEMBLY

 Try to avoid old sleeve and washer to
assemble. In case interference is there
sleeve will get lose after continuous running.
 Open the top cover of housing.
 Place your fingers softly by both side of the
rollers body .Applied minor forces with your
fingers to check the play or rollers . It rollers
are playing , THEN ITS OK.
 In between outrace in roller insert the filler
gauge between the rollers of both the sides
This is internal bearing clearance .
Allowable 0.04 to .1 mm as per bearing sizes.
BEARING CHECKS

Keep the bearings at rest on the
housing.
Place the dial gauge pointer on the
outrace of bearing at 90 degree at axial
direction .
Magnetic stand should be on shaft.
Move the shaft left hand and right
hand direction as much as possible by
keeping the pointer 0 at vertical
position .
 Now if the readings you will get
within range of 0.05mm then it is fine .
Else make it adjustment via housing .
This is bearing skewness.
Skew monitoring is important
for bearing design as it is an indirect
measure of bearing life.
BEARING SKEWNESS

FIXED & FREE BEARING LOCATION
Normally no locating ring fitted in Free Bearing (NDE) but some manufacturer
used one locating ring on inboard side of Free Bearing (NDE).
Expansion at NDE end depends on air temperature along with shaft length

EFFECT OF GREASE QUANTITY ON BEARING
OPERATING TEMPERATURE:
Continuous monitoring of bearing
temperatures helps finding out the cause of
improper lubrication.
A) CORRECT LUBRICATION:
It can be noted that there is a
temperature rise initially and it
stabilizes to a low level over a
period of time.
This characteristic is because of
the mechanism of grease
lubrication.
A certain temperature is
required for oil to bleed out from
the grease soap. Hence, initially,
there is a metal to metal contact
which leads to temperature rise.
This temperature helps the oil to
bleed and form the lubricating
film. Once the lubricating film is
formed, the metallic contacts are
separated and the bearing
temperature stabilizes to low level.
ADVANCE OF PROPER LUBRICATION

In this case, the major cause
of temperature rise is the
churning of the grease filled in
the Plummer Block.
The bearing temperature
stabilizes at a very high level.
This is a dangerous situation
as high bearing temperature is
normally considered to be an
indication of inadequate
quantity of grease and there is
a tendency to pump more
grease in the Plummer Block.
Hence, it is advisable to
remove grease from housing
when such temperature
characteristics are observed.
OVER LUBRICATION IMPACT

 Pour the grease by hand on the bearing rollers. If you push the new grease
from one end the old grease will come out from other side very easily. Once
grease lubrication will get over please pour some grease in side housing.
 Very Careful That There Should Not Be Any Excess Grease At Inside Housing.
Not Require To Pour Grease 100% Inside Housing. Only Please Take Care That
Rollers Are Full Of Grease.
 Place the top cover of housing without giving much effort. Top cover will
take its own place without any problem. Tighten the top cover of bolts
 Tighten the housing fixing bolts diagonally and before that check the
condition of bolts and washers. If you have found those are OK go ahead for
fixing that. Else change the washers
24
BEARING READINESS

What is Misalignment?
Misalignment occurs when the centre lines of rotation of two machinery shafts
are not in line with one another.
There are two types of misalignment: parallel and angular. In most cases,
machine misalignment is actually caused by a combination of these two types.
Misaligned shafts can cause:
Increased load on bearing.
Reduce bearing life.
Increase wear on seals.
Increased vibrations and noise.
MISALIGNMENT

26
Do the alignment then. Once you get 0.05 mm misalignment in both direction
of axial as well as radial direction withdraw all dial gauges. Before alignment
will get start please ensure that coupling gap is as per drawing.
ALIGNMENT

Reason
Shaft misalignment is responsible for up to 50% of breakdowns in rotating
machinery. Those breakdown cause increased machine downtime, which translates
directly into higher costs.
Additionally, incorrect alignment places a greater load on machine components,
resulting in increased wear and tear.
Impact
Misaligned shafts generate a moment, which creates a reaction force in the shaft
bearings of the driven and drive units.
 A 20 % increase in load caused by misalignment will reduce the calculated
bearing life by almost 50 %. Other serious effects can be wear and tear of the seals,
allowing contamination to enter the bearing and lubricant to leak.
Other bad effects of shaft misalignment are excessive vibration and noise as well
as increased energy consumption.
COUPLING MISALIGNMENT

1. Designed bearing life is achieved.
2. Minimum stress on coupling
which reduces the risk of
overheating and breakdowns.
3. Minimum wear on seals which
reduces risk of contamination and
lubricant leakage.
4. Minimum vibration and noise.
5. Increased uptime.
ADVANTAGE OF ALIGNMENT

1. Coupling alignment .
2. All foundation bolts and holding down bolts.
3. Fan Casing and connecting duct work are air tight.
4. Inspection doors are properly closed.
5. Direction of rotation of fan.
To determine direction of rotation, switch on the motor for a
moment. The correct direction of rotation can be checked against
the arrow provided on DE side of Casing plate.
6. Bearings are adequately lubricated.
7. No foreign/loose material is left inside fan Casing.
8. All protective guards are properly installed.
FAN COMMISSIONING CHECKS

1. Protect the motor and bearings from any
radiated heat .
2. The supply of cooling air to motor must not
be restricted.
3. Monitor the behavior of the bearing during
trial run.
4. Measure the power consumption. During
the start up phase it can be 6-8 times
higher than the rated current mentioned
on motor name plate. At rated fan speed
the figure must not exceed the rated
current. If overloading occurs, fan must be
throttled back, so that the power
consumption is about 5% below the rated
current.
FAN COMMISSIONING

CARE TO BE TAKEN DURING MAINTENANCE:
1. Observe accident prevention regulations.
2. Maintenance must be carried out by trained personnel.
3. Determine the scope of work to be done.
4. Fan must be switched off during shut down maintenance and possibility of
switching on the fan must be prevented.
5. Ensure that Impeller is at standstill before opening fan casing.
RUNNING MAINTENANCE
1. Carry out lubrication of bearings as prescribed with correct quality and
quantity of lubricant.
2. If continuous vibration monitoring system is not employed, check
periodically vibrations at bearing points.
3. If bearing temperature is not monitored continuously, periodically check the
temperature.
4. Check foundation bolts and other bolts for looseness or corrosion.
MAINTENANCE

33
CASING:
Casing to be checked for any cracks developed or corrosion on any section.
Especially check scroll cut off area for corrosion. Remove any corroded portion and
weld with proper plate.
Check Impeller to Inlet Cone radial clearance and overlap. Clean Casing with water.
The collected drain water after cleaning Casing/Impeller can drained through drain
plug/drain pipe provided in bottom of Casing.
IMPELLER:
During maintenance the Impeller it should be cleaned and checked for any cracks
developed during running. Impeller may be cleaned by washing or carefully
scrapping.
If erosion or any damage is found on Impeller, report to vendor/ expert
immediately for taking corrective measures.
MAINTENANCE OF MAJOR PARTS

SHAFT SEAL:
1. Generally there are two types of Shaft Seal supplied with our Fans.
Aluminum disc type and Gland packing type.
2. Check Aluminum disc for possible damage and replace with new
one if required. For Gland type seal, check the packing rope in the
groove and replace with new rope as required.
BEARINGS:
GREASE LUBRICATED:
Open the Plummer Block and clean the bearing assembly. Check
Bearing and accessories for any damage/scoring and replace if
necessary. Reassemble bearing and put correct quantity and quality
of grease as recommended.
MAINTENANCE OF MAJOR PARTS

S.N. DO'S DON'T
1
Check & clean fan casing & impeller
periodically
If one fan running keep standby fan damper close
to prevent reverse rotation
2
Lubricate with proper grade of
lubricants as per the lubrication
schedule
Do not run the fan if any defect is noticed
3
Maintain history card of the fan
running parameters
Never attempt to run the fan in over load
condition
4
Start fan with suction damper close
OR in VFD Operation at
Minimum Speed
Do not run fan without checking interlocks,
protection & safety
5
Check up for lubrication for inlet
guide vane (IGV) unit control
Do not operate fan with higher vibration &
bearing temperature
6
Move dampers from their set
position at least once a week
Do not open suction damper / increase speed
until motor current becomes steady
DO’S & DON’TS

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