Stopping- Starting of 2nd PAPH

Stopping- Starting of 2nd PAPH

Each unit is provided with two bi-sector type regenerative primary air preheaters to recover the

heat from waste flue gas leaving from the furnace and utilised to preheat the primary air which inturn

used to dry the raw coal and transport pulverised coal powder from mill to the furnace through coal pipes.

Air pre-heater consists mainly rotor housing, cylindrical cellular rotor, guide and Support bearings, oil

systems for guide and support bearings, soot blower system, Stationary water washing devices & fire

fighting devices , auxiliary air motor drive with over-running clutch, oil carryover probe , inspection lights s

etc. The complete rotor is supported by a thrust bearing at the bottom and guided by the radial bearing at

the upper end. An air motor is provided to ensure the continued operation of the air pre-heater, even if

power to electric motor is interrupted. It may also be used to control speed of the rotor during water

washing of heating surfaces.

When ever one APH trips in a running Unit the run back operates & Unit load gets

reduced to 300 MW( 60 %) . Normally 4-5 Mill operation permissive is available with one APH out

of service .

PROCEDURE FOR STOPPING AND ISOLATION OF ANY SECOND PAPH: -

E-1 PRE CONDITION OF THE UNIT: -

1. Unit is running at full load (500MW) with 7 mills in operation.

2. Both TDBFPs are in service and Feed water control in auto.

3. MDBFP # C is available on auto (Rapid start up mode).

4. Unit control is in CMC mode.

5. Airflow control is in auto with both FD fans in service.

6. Both PA fans in operation in CAS mode with PA header pressure set at 820mmwc.

7. Both ID fans in service and furnace draft control in auto.

E-2 ENSURE THE FOLLOWING:

1. Running contact of other running PAPH.

2. Revise the station DC as per the planned shut down programme.

3. Availability of PAPH / SAPH soot blowers for operation.

4. Availability of auxiliary drive (air motor) of the PAPH (which is to be stopped).

5. All (4nos) economizer bypass dampers are closed.

6. Availability of atomizing steam and HFO at requisite pressure & temp (oil: 100ºC / 17-18 kg/cm², Steam:

200 – 210ºC / 6.5 kg/cm²).

7. Completion of WB/LRSB operation before starting the load reduction.

8. Best communication between control room and local.

9. Bypass TDBFP – A / B recirculation valve auto-closing protection.

10. Check for the healthiness of the mill outlet temperature low to feeder tripping protection for all running

mills, Normally it is set at 50 deg C.

PAPH STOPPING AND ISOLATION PROCEDURE: -

1. Take the unit control to manual from CMC mode. (Turbine on limit pressure control and Boiler master on

manual).

2. Take fuel master to manual and gradually reduce the load to 400MW by slowly unloading and removing

7th running mill. Check airflow according to the load (1650T/ hr corresponding to 400MW).

3. Take HFO support in one elevation corresponding to any running mill according to the mill combination

(At least 3 oil guns in one elevation).

4. Gradually reduce the load to 300MW by slowly unloading and removing 6th running mill. Check airflow

according to the load (1450T/ hr corresponding to 300MW).

5. Reduce MS pressure set point according to the load during the process of load reduction.

6. Check the loading and suction flow of TDBFP A / B. If suction flow is low corresponding to the speed,

Then keep open any one TDBFP- A / B recirculation valve.

7. Probably keep five consecutive mills in service to ensure stable combustion.

8. Observe and slowly reduce the PA header pressure set to 800mmwc from 850mmwc.

9. Adjust the burner tilt position to maintain MS & HRH temperature up to maximum possible (540C).

10. Gradually close the PAPH (which is to be stopped) air outlet damper from local & lock it mechanically

and simultaneously maintain the flue gas outlet temperature by closing the FG outlet damper of

corresponding PAPH. Adjust the other running PAPH & SAPH A/B FG outlet temperature from remote.

Then isolate the air outlet damper actuator power supply. This activity needs best communication

between control room and local.

11. Check the PA header pressure for any variation while closing air outlet damper and adjust it, if required.

12. Slowly close the air inlet damper from local and lock it mechanically. Isolate the power supply.

13. Observe the mill outlet temperature and accordingly adjust mill loading.

14. Close flue gas inlet damper from local and lock it mechanically. Isolate the power supply.

15. Close flue gas outlet damper from remote fully and lock it mechanically. It can be opened to 10% with the

help of C& I to create negative draft in side the APH if it is required by BMD.

16. Observe the mill outlet temperature and APH flue gas outlet temperatures accordingly adjust the running

PAPH & SAPH – A / B flue gas outlet dampers.

17. Start running PAPH and SAPH – A / B soot blowing. (This is to be done at least twice in a shift as long as

oil guns in service).

18. After stopping the PAPH, Gradually increase the load to approximately 330MW with 5 mills operation by

observing PA outlet temperature, mill outlet temperature and PA header pressure.

19. Remove oil support after stabilisation of load at approximately 330MW with 5 mills operation with safe

mill outlet temperature (Should be >60ºC).

20. Keep PRAPH in service for attending any work outside the APH like air outlet duct fabric compensator

repair work.

21. Stop the PAPH (which is to be stopped) after cooling (air outlet side manhole can be kept open for

cooling) to normal temperature so that maintenance can be done and isolate the power supply of PRAPH

drive motor.

22. Close both main and bypass airlines for air motor.

23. Press the local EPB of the PAPH (which is stopped).

24. Issue PFW after ensuring proper isolation according to PFW procedure.

E-4 PROCEDURE FOR NORMALISATION AND STARTING PRAPH: -

1. Revise the station DC as per the planned programme.

2. Ensure the cancellation of PTW and clearance from maintenance BMD/EMD/C&I, then normalise the

drive motor power supply.

3. Check the PAPH for proper boxup (check all manholes are closed).

4. Check the PAPH by running air motor for any abnormal rubbing.

5. Normalise the drive motor power supply.

6. Release the local EPB.

7. Stop PAPH air motor and start main electric motor.

8. Normalise the air outlet damper power supply. Remove the lock and slowly open the PAPH air outlet

damper from local.

9. Normalise the flue gas inlet damper power supply. Remove the lock and slowly open the PAPH flue gas

inlet damper from local.

10. Slowly Increase the PA header pressure set point to normal (820mmwc) and wait for stabilisation of the

header pressure.

11. Normalise the air inlet damper power supply. Remove the lock and slowly open the air inlet damper from

local. Simultaneously open flue gas outlet damper from remote and maintain the flue gas outlet

temperature and observe PA header pressure while opening air inlet damper.

12. Take 6th mill into service and gradually increase the load to 450MW.

13. Adjust the MS pressure set point according to the variation of load.

14. Close TDBFP-A / B recirculation valve (which was kept opened previously) after sufficient loading of both

TDBFPs.

15. Take 7th mill into service and increase the load to full (500MW).

16. Adjust the FG outlet damper positions of PAPH – A / B and SAPH – A / B after stabilization of load.

17. Adjust the burner tilt to maintain M S & HRH temperature up to maximum possible (540C).

18. Normalise the TDBFPs recirculation control valve auto close protection.

19. Put fuel master in auto.

20. Transfer the unit control from manual to CMC mode.