Air Preheater in Thermal Power Plant Problem n Sol

8/13/2019 Air Preheater in Thermal Power Plant Problem n Sol

1/25

PROBLEMS FACED & ACTION TAKEN

E R O S I O NProblem :

High pressure air mixes with ash and leaks to low pressure sideleads to erosion of static seals, radial seals etc.

Action Taken :

Reverse rotation of APH ( Gas to SA to PA )

Additional layer of by-pass seal near sector plate.

Kao-wool packing carried out at the inboard sector plates,static seals and ASP TO SP seal.

Seal thickness increased (1.6 mm to 2.5 mm)

Seal tabs introduced in Axial & Radial seals.


2/25


Problem :

High Leakage of Air to Gas path

Action Taken :

1. Double sealing arrangement introduced in Khaperkheda,Simhadri & Talcher projects etc.

2. PG tests conducted in various R&M projects and resultsfound

encouraging.2. Before PG tests, APHs are attended for seal adjustments,

issued Technical Directive regarding Leakage & necessaryoperations.


3/25


F I R EDuring start up with oil firing, impropercombustion may result in the accumulation ofcondensed oil vapours and un burnt carbon onAir preheater surfaces by carry over from

furnace.PREVENTIVE

Soot blower should be in operation.

Fire sensing device ( Thermocouples ) to be

commissioned.Oil carry over detector to be commissioned andmonitored during oil firing.

Heat rate of firing should be controlled.


4/25


BEARING FAILURESOil contamination

Starvation of oil

Mis-alignment

Lack of maintenanceHigher operating oil

temperature

Foreign materials in

bearing

Action Taken:

Technical directive

issued.


5/25


PROBLEMS IN DRIVE UNIT ASSY ;

Over running clutch failure:Over heating

Sealed bearings

No oil circulation

Action Taken:

New design evolved eliminating

Overrunning clutches in main

and stand by electric drives.

Vibration of drive unit:Misalignment.

Failure of bearings in motor,

gear box etc


6/25


CLEANING DEVICE ASSY :

Drive unit failure

Chandrapur unit-7 SAPH failed due to closure of

soot blower drain valve.

- The drain valve to be kept crack open

- Technical directive issued.Nozzle erosion

- Parking position to be at inboard end.


7/25


FIRE SENSING DEVICE ASSY :

Failure of Thermocouples:

Design changed to individual thermocouples.

Failure of scanners:

Local Temperature scanners eliminated anddirectly connected to DDCMIS for betteroperation from Khaperkheda project onwards.


8/25

OPERATION PROBLEMS

HIGHER PRESSURE DROP ACROSS APH

1. Choking of heating elements

2. Higher flows

3. Eroded/damaged heating elements -obstructs flow path.

4. Improper steam parameters and

eroded nozzles and steam pipes.

5. Low cold end average temperature.


9/25

OPERATION PROBLEMS

HIGH GAS LEAVING TEMPERATURES

1. More gas flow with high inlet temperature

temp.2. Less air flow and high inlet temp.

3. Choking of SCAPH less air flow

4. Choking of heating elements

5. Erosion & corrosion of heating elements


10/25

OPERATION PROBLEMS

CHOKING OF HEATING ELEMENTS :1. Improper evacuation of economiser hopper.

2. Corrosion of heating elements

3. Boiler slagging

4. Improper drying of heating elements after waterwashing.

5. Excess air operation.

6. Leak in SCAPH and water washing & deluge line,soot blower passing etc.

7. Frequent water washing of heating elements andimproper drying.

8. Proper exit gas temperature with respect to % ofsulphur in fuel.


11/25


12/25

TROUBLE SHOOTING


13/25

Sl. FAULT PROBABLE CAUSES REMEDY

01 Excessive leak

between gas and air

side

Damaged / worn out

seals.

- Due to high gas

inlet temp. Less air

flow.

Inspect all seals and

adjust or replace if

necessary.

02. Excessive noise

from rotor

Warped rotor due to

excessive

expansion.

Foreign object in

rotor.

Bad bearings

Reduce boiler load

or admit more cold

air.

Stop rotor and

visually inspect it

Replace Bearings.


14/25

03. Rotor does not turn Defective drive unit

Foreign object in

rotor

Ensure power is

available to drive

unit

Check pinion gear

and pin rack.

Inspect rotor and

remove any foreign

object.

04 Drive unit

overheats

Inadequate

lubrication in drive

unit.

Pinion gear and pin

rack meshing too

hard due to

expansion

Hard rubbing seals

Bad bearings in gear

reducer.

Lubricate drive unit

components

Adjust drive unit to

proper clearances.

Adjust seals *

Change the

bearings.

* Slight overheating due to hard rubbing seals may be relieved when the Air preheater

reaches normal running temperature or after the seals have worn in properly.


15/25

05 Noisy Bearings Inadequate

lubrication

Check that oil is

flowing through

Flow indicator and

check oil line, if

necessary

06 Oil temperature too

high

Insufficient cooling

Improper oil

viscosity being used.

Absorption of

radiation heat due to

improper insulation.

Check that

adequate water flow

is going into oil

cooler

Replace oil with

proper type of oil.

Insulate properly.

07. Circulating oil

foamy

Air leak into the oil

system

Check for an air leak

on the suction side

of the oil system.


16/25

08. Low oil level Leak in oil system Locate and arrest the leak.

09. Soot blower

not

functioning

Power failure

Swivel header travel

incorrect.

Incorrect steampressure

Check electrical connection.

Check the speed reducermoveable parts for binding.

Adjust travel of nozzle pipe.

Ensure adequate steam

supply is available.

Check DA head valve.

10. Excessive

pressure

drop through

gas & air

sides

Badly fouled heating

elements.

- due to improper

combustion.

Excessive plugging.

Thinned down and

damaged elements

Operate soot blower and

check soot blower steam for

proper pr. and temperature.

Investigate & remeditate the

cause. If soot blower is noteffective, heater can be

isolated and water washed

off load (in worst case),

remove the basket and clean

them outside. Rectify and

replace the element baskets.


17/25

11. Variation

(periodic

kick) in the

main driveammeter

current

Excessive rubbing

of some seals.

Faulty bearings

Locate faulty seals and

replace.

Rectify or replace thebearings.

12. Abnormalincrease in

the

temperature

Starting up of fireinside the Air

preheater

Immediately isolate airheater and check for fire

and admit large quantity

of water. CO2 foam,

steam should not be

used.


18/25

13. Increase in

gas outlet

temp. and

steady fall

of air outlet

temp.

Air preheater

stalled.

Heating elements

plugged

Isolate Air pre heater

and check for troubles

in the drive system.

Clean heating

elements.

14. Excessive

pressure

build up by

Lub oilpump.

Oil filter chocked Clean or replace the

cartridge.


19/25

IMPROVEMENTS REQUIRED - INSTALLATION

1. Storage of APH components.

2. Maintenance of stored components.

3. Support bearing - oil contamination.

4. Improper locking of shim type sector plate adjusters.

5. Welding of drive panel before final alignment

6. Insulation of primary centre section sector plate adjusters.

7. Ensure free movement of hot end sector plates after staticseal welding to avoid guide bearing failures.

8. Check the main drive motor alignment with gear box andcorrect if necessary before trial operation.


20/25

IMPROVEMENTS REQUIRED - COMMISSIONING

Before light up: Commission Cleaning device assy, oil carryover probe, fire sensing device, RSA & wash pipe assy.

Maintain gas outlet tempr is same in both APHs (with in 10 C )

If one APH is used out of two, the other APH should be kept inrotation or should be blanked properly to avoid fire.

Ash accumulation over guide bearing assy, soot blower assy &

LOPs must be avoided.

Ensure clean dry air to Air motor without moisture. Keep the airmotor in working condition by operating 5 minutes in a day.


21/25

IMPROVEMENTS REQUIRED - COMMISSIONING

1. Lub oil pumps should not be started when the lub oiltemperature is less than 40 c to avoid pump oil sealfailure.

1. Water washing is to be done during shutdown when the gasinlet temperature is 100 c. Do not water wash APH justbefore light up since proper drying is not possible which maylead to more unburnt deposition which in turn cause APHfire.


22/25


23/25

IMPORTANT INSTRUCTIONS - DO'S

1. Plan in advance the sequence of erection.

2. Keep the necessary tools and tackles ready before start of erection.3. Contact the Airpreheater engineering / BAP / Ranipet if any deviation

or rectification is to be made.

4. Apply rust preventive oil to protect components from rusting due to

long storage and bad weather.

5. Store the heating elements covered with tarpaulin and ensure cover

sheets even after installation into the rotor.6. Maintain the required accuracy in erection, which leads for a

satisfactory operation.

7. Tighten bolts to the required torque.

8. Fill the bearings with specified oil or equivalent even during erection.

9. Rotate the Airpreheater in the correct direction of rotation.

10. Keep a record of the readings in the check sheets which shall be

despatched for the reference of Airpreheater Engineering / BAP /

Ranipet.

11. Seal weld outside and inside for rotor housing panels, connecting

plates (hot and cold) to housing panels, connecting plates (hot and

cold) to air and gas ducts.


24/25

IMPORTANT INSTRUCTIONS - DON'TS

1. Do not mix up items belonging to different Airpreheaters.2. Do not use shop lugs for lifting components / assemblies.

3. Do not support rotor on hot end connecting plate while lifting.

4. Do not carry out the bearing assemblies in open, dusty

atmosphere.

5. Do not spoil the seal leaf by standing on them, by any otherexternal load or interference with foreign material or by wrong

direction of rotation.

6. Do not allow any foreign particle such as electrode bits, slag

wool etc enter into heat transfer elements during erection.

7. Do not carry out final welds before final alignments, checks etc.8. Do not spoil the seal straight edge during trail run.

9. Do not start Airpreheater without filling with specified lubricants

during erection check up.

10. Do not operate air motor without filter lubricator during trial run.


25/25

DAILY CHECK

Oil levels in :

Support bearing, Guide bearing, Main drive gear reducer &

Air line lubricator

For any unusual noise in:

Rotor , Rotor main drive bearings, Drive motor, Main gear reducer,

Cleaning device during operation & Oil circulation systems

For cleanliness near:Rotor drive unit, Rotor main bearings,

Cleaning device & Oil circulation system

Instruments for proper working:

Bearing lube oil thermometers, Bearing lube oil pressure gauges ,

Thermocouples if provided in bearings for alarm or remote

indication. Air inlet and outlet, gas inlet and outlet temperature

measuring instruments. Manometers for measuring pressure drop

across air preheater for gas and air flows.

The condition of cold end elements

Documents

Air Preheater in Thermal Power Plant Problem n Sol