CW PASS ISOLATION PROCEDURE:

CW PASS ISOLATION PROCEDURE:
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 / manual mode.
5 Both PA fans and FD fans are in service.
6Both condenser circulating water passes in service.
7 One condenser vacuum pump in service and other is available in standby.
8 Vacuum is maintaining normal i.e. - 0.90 kg/cm².
9 Both ID fans in service and furnace draft control in auto.
10 All four CW pumps (Two pumps per unit) are in service with both units interconnection valves are in open
condition. Discharge header pressure normal (approx: 1.4 kg/cm²).
ENSURE THE FOLLOWING :
Revise the station DC as per the planned shut down programme.
2 Availability of atomizing steam and HFO at requisite pressure & temp (oil: 100ºC / 17-18 kg/cm², Steam: 200 –
210ºC / 6.5 kg/cm²).
3 Completion of WB/LRSB operation before starting the load reduction.
4 Availability of PAPH / SAPH soot blowers for operation.
5 Availability of second (standby) condenser vacuum pump.
6 Stop corresponding CW pass OLTC after collection of balls before starting CW pass isolation process.
7 Take care of ACW pump suction header pressure very low and discharge header pressure very high protection of
the pumps in both corresponding units (ACW suction and discharge header pressure may vary by 0.2kg/cm²).
8 All CT fans (20 fans per each unit) are in service.
9 Check and record CW pump discharge header pressure (CW discharge header pressure may raise approximately
0.2 Kg/cm² after isolation of one pass).
10 Best communication system between local and control room.
11 Availability of condenser pit sump pumps and sump level is normal.
12 Take care of TDBFP – A / B recirculation valve auto-closing when starting the load reduction.
PROCEDURE FOR CW PASSES ISOLATION: -
1 Start standby vacuum pump and check vacuum.
2 Take the unit control to manual from CMC mode. (Turbine on limit pressure control and Boiler master on manual).
3 Take fuel master to manual and gradually reduce the load to 400MW by slowly unloading and removing 7th running
mill.
4 Take HFO support in one elevation corresponding to any running mill according to the mill combination (At least 3
oil guns in one elevation).
5 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).
6 Reduce MS pressure set point according to the load during the process of load reduction.
7 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.
8 Preferably kept five consecutive mills in service to ensure stable combustion.
9 Start PAPH – A / B and SAPH – A / B soot blowing. (This is to be done at least twice in a shift as long as oil guns in
service).
10 Isolate the vacuum line manual isolation valve provided corresponding to the CW pass which is to be isolated at
the condenser end (8.5m near LPBP).
11 Switch of the CW pass (which is to be isolated) inlet valve power supply, Then gradually close the inlet valve
manually from local and simultaneously observe the vacuum, CW discharge header pressure. After full closing,
Isolate the actuator power supply.
12 Switch of the CW pass (which is to be isolated) outlet valve power supply, Then gradually close the outlet valve
manually from local and simultaneously observe the vacuum, CW discharge header pressure. After full closing,
Isolate the actuator power supply.
13 Open the corresponding condenser water box vent valves (2nos) for depressurisation.
14 Open the drain valve provided in the corresponding water box for draining after depressurisation.
15 If draining of inlet water duct is started, then check sump level and put sump pumps in auto or start / stop
condenser pit sump pump for dewatering manually.
16 Further tighten inlet and outlet valves if there is any passing.
17 After isolation of CW pass, Gradually increase the load to approximately 350MW with 5 mills operation and
simultaneously monitor condenser vacuum.
18 Close TDBFP – A / B recirculation valve, which was kept opened previously after sufficient loading of both
TDBFPs.
19 Remove oil support after stabilisation of load at approximately 350MW with 5 mills operation.
20 Issue PFW after ensuring complete draining and proper isolation.
PROCEDURE FOR CW PASSES NORMALISATION: -
Revise the station DC as per the planned programme.
2 Ensure the cancellation of PFW and clearance from maintenance (TMD).
3 Ensure the complete box up of the CW pass.
4 Close the drain valve provided at the bottom of the corresponding water box.
5 Open the vent valves provided at the top of the corresponding water box.
6 Crack open the CW pass (which is isolated) inlet valve manually from local and observe the CW discharge header
pressure.
7 Ensure air is coming from the vent line and close it after ensuring complete venting.
8 Gradually full open the CW pass (which is isolated) inlet valve manually from local and observe the CW discharge
header pressure.
9 Gradually open the CW pass (which is isolated) outlet valve from local manually and observe the vacuum and CW
discharge header pressure.
10 Normalise the inlet and outlet valve actuator power supply
11 After full opening of CW pass inlet and outlet valves, Open the corresponding CW pass vacuum line manual
isolation valve at 8.5m near LPBP, which is isolated previously.
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 Take 7th mill into service and increase the load to full (500MW).
15 Adjust the burner tilt to maintain M S & HRH temperature up to maximum possible (540C).
16 Take care of TDBFP – A /B recirculation control valve auto close protection.
17 Take care of ACW pump suction header pressure very low and discharge header pressure very high protection in
both corresponding units.
18 Put fuel master in auto.
19 Take corresponding CW pass OLTC into service.
20 Stop second vacuum pump and check vacuum.
21 Take unit control in to CMC mode.