PPT ON UNIT SHUT DOWN PROCEDURE

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UNIT SHUT DOWN PROCEDURE  Presentation Transcript

1.UNIT SHUT DOWN PROCEDURE

2.Presentation outline
Planned Shut Down procedure
APH Washing
Hydrogen purging
ATT

3.UNIT SHUT DOWN
Planned shutdown- For overhauling
Emergency shut down- Boiler tube leakage, major problems in Turbine, Generator etc, Transmission constraints.
Reserve shut down –Low demand

4.Planned shutdown
Preparation for shut down.
Mobilization of resources for overhauling- Manpower , Spares, consumables
Identification all Jobs to be carried out.
Carry out performance testing and identify performance gaps, parameter deviations and action plan for rectification.
Necessary clearance from RLDC/bulk customers .   

5.Activities
All coal bunkers should be preferably made empty before long shut down. Stop/ regulate coal feeding to bunkers accordingly.
Charging of auxiliary steam from other unit.
Ensure availability of all oil guns.
Take trial run of all emergency equipments like Dc Scanner air fan, DC EOP,DC SOP, DG set etc.
Ensure SGC oil and SLC of oil system is ON

6.Reduce coal firing in mills and bring down the unit load to 160 MW
 Gradually reduce boiler steam parameters (steam pressure and temp.) for  force cooling. Rate of reduction to be controlled as per the permissible limits. Ensure that the TSE margins are OK.
Carryout boiler soot blowing and APH soot blowing.

7.Set turbine load gradient at 5 MW/min.
Bypass turbine steam temp. low protection.
Check HP/LP Bypass operation.
Charge D/A pegging steam from CRH.
Cut out the top mill .Make the  bunker/feeder belt empty before stopping the mill.

8.Cut out HP heaters 5&6
Reduce unit load to 120MW after taking oil support in AB elevation.
Carryout ATT.
Cut out one more mill and reduce unit load to 80 MW.
Ensure that turbine gland sealing steam temp. >250o C and change over from leak  steam control to seal steam controller.

9.Change over unit bus power supply from UATs to station Bus .
Monitor and record  all turbine supervisory parameters like turbine bearing and shaft vibrations, Diff expansion of HPT, IPT & LPT ,Axial shift , Over all expansion Turbine brg temp. at different loads.
Monitor boiler drum Top/Bottom differential temp. while reducing pressure and load.

10. One set of ID ,FD, PA fans and one BFP can be stopped.
Cut out one more mill and reduce load to 50 MW.
Reduce load to 30MW. Open HP bypass to maintain boiler pressure.
Cutout LP heaters.
Ensure change over of drum level control from high range to low range.

11.Trip the turbine through trip push button on desk and open the HP/LP bypass.
Control boiler drum level.
Ensure the following after turbine trip.
Generator  circuit breaker opened
Generator Field  breaker opened.
Turbine AOP has taken start at 2850 RPM and Lub. Oil pressure is normal.

12. Turbine ESVs and IVs closed.
HP ,IP control v/vs closed
CRH NRV and all extraction valves and NRVs closed
Monitor turbine speed, bearing  vibrations, brg temp. and turbine supervisory measurements during coasting down.
Monitor hotwell level, D/A level,Cond vacuum.

13.ENSURE opening of the following drains:
HP casing drain.
Drain after CRH NRV's
Drain before/after IV's. NRV's.
Drain before extraction NRV's
Seal steam header drain.
Drain before ESV's.

14.Stop the last mill after ensuring the feeder is  empty.
Stop the PA fans and trip the boiler. (Boiler can be tripped by checking any of the boiler protections.)
Ensure the closure of HOTV,LOTV
Close HP/LP bypass and close boiler stop valves

15. Purge the boiler for 5 minutes and scavenge all the oil guns which were in service
Isolate HFO ,LDO stations and all oil guns
Isolate SH/RH spray stations.
Fill boiler drum level upto max. level.
Stop ID /FD fans if boiler force cooling is not required (During  boiler cooling ensure that boiler TOP Bottom differential is <50oc

16.Ensure that scanner air fan emergency damper has opened after stopping both FD fans.
Switch of all ESP fields and rapping system.
Ensure turbine JOP has taken start at 510RPM and jacking oil pr is >110 KSC
Ensure  Gate gearing valve has opened at 210RPM
Ensure speed ref. zero
Ensure turbine has come on barring and speed >100 RPM

17.MOT level is normal and duplex filter not choked.
Open generator bkr isolators on 220 KV side.
Depressurize MS, HRH steam lines .open MS ,HRH strainer drains to IBD tank
Stop condenser vacuum pump and kill vacuum. Open vac. Bkr at 200 mm of Hg condenser vacuum

18.Isolate seal steam supply to turbine glands and stop GSE.
Isolate generator Hydrogen coolers Stator water and seal oil coolers.
Stop one CW pump.
Monitor LP turbine exhaust hood temp. and stop CEP after 4 hours
CW system can be stopped after 4 hours from unit shut down

19.Stop BFP and ECW pump after drum top up requirement is completed.
Isolate auxiliary steam header.
Isolate power supply to all HT drives and ESP.
Generator hydrogen can be purged after the turbine coming to barring gear.
At 2ksc drum pressure open boiler drum vents, SH vents and SH hdr  drains

20. Drain the boiler when the boiler water temp. is below 90oC.
Stop APH and scanner air when flue gas temp. below 100oC.
Isolate all steam supply to Deaerator and drain Deaerator after opening the  vents.
Monitor turbine expansions and casing temp. during cooling down.

21. Turbine barring gear can be stopped at HP shaft/casing temp. less than 130 oC.
TG oil system can be stopped at turbine casing temp. of 95oC  after ensuring that hydrogen is purged out from generator.
Seal oil system can be stopped after hydrogen purging and stopping of barring.
 
23.APH WASHING.
Purpose- for cleaning of baskets of air heater
High pressure water jet is used
Washing to be carried out when the air heater is in hot condition (Temp.about 200oC).immediately after boiler shut down
Open the r plugs of APH ash hopper
Open the duct drains of SA and PA ducts

24.Start the APH water washing pumps
Open the water washing lines of the air heater .
Keep the air heater rotating.
Continue the washing till the PH of inlet and outlet water is same.
Run the ID /FD fans to dry out the baskets

25.Hydrogen Purging.
Ensure that the generator is tripped condition
Reduce the Hydrogen pressure to 0.5 KSC by opening the purge valve.
Connect CO2 cylinders to the filling manifold.
Start filling CO2  through the CO2filling valve
Crack open the purge valve to maintain the casing pr. At 0.5 ksc
Continue filling CO2 till purity of 95% is achieved.

26.Purge out CO2 by opening the air filling valve and purge out valve.
Continue air filling till CO2  concentration is Nil.
Disconnect the air connection after purging.

27. Automatic Turbine Testing (ATT)
To check the healthiness of turbine protections during normal operation
Turbine protections can be periodically tested on load.
Provides full protection to the turbine during the testing.

28.SALIENT FEATURES
Individual testing of each protective device and stop/control valve assembly.
 Automatic functional protective substitute devices that protect turbine during ATT.
 Only its pretest is carried out without any faults i.e. if the substitute circuit is healthy, the main test begins.
.
29.The testing system or ATT is sub divided in two functional sub-groups.
1. ATT STOP AND CONTROL VALVES
2.ATT PROTECTIVE DEVICES

30.AUTOMATIC TESTING OF PROTECTIVE DEVICES
ATT sub group for protective devices covers the following devices.
1. Remote trip solenoid-1.
2. Remote trip solenoid-2.
3. Over speed trip device.
4. Hydraulic low vacuum trip device.
5. Thrust bearing trip device.

31.Turbine actual over speed testing.

32. SHUT DOWN TO HOTSTAND BY
When the unit is to be shut down for short duration the boiler can be kept in Hot stand by.
Shut down due to grid restriction
Shut down due to problems in electrical systems, Generator  , GT, UAT ,Turbine etc (problems which requires short duration to attend )

33.Boiler pressure and temp. are maintained substantially to facilitate quick start up.
Turbine metal temp. can be brought down to reduce start up time during re rolling.
Shut down procedure is similar to normal shut down except reduction in pressure and temp.
Reduce the load to 120 - 140MW at rated steam parameters

34.Subsequent load reduction along with pressure and temp. drops should be decided by the turbine limitations
Trip the boiler when the desired parameters  reached.
After tripping the boiler to be boxed up.
Close boiler stop valves

35.Close all boiler drains and vents (CBD, IBD, EBD)
Stop ID/FD fans after boiler purging.
Close all dampers and gates in flue gas path.
APH can be stopped after the flue gas at APH inlet is below 200oC

36.SWITCHYARD OPERATION
Co-ordination with RLDC  for unit synchronization, line charging etc.
Line up of electrical systems
Ensuring healthiness of switchyard equipments like transformers, breakers, isolators, CTs etc.  

37.SHUT DOWN OF TRANSMISSION LINE
Obtain written message code for shut down of the feeder from RLDC.
Intimate the other end station  before opening the breaker.
Open the Tie Bkr of that bay and then open the main bkr.
Ensure that the sequential isolator opened  on auto
Open the remaining isolators (Bus and line isolators) of the bay

38.Give message to the other end about opening of the isolators and confirm that the line is isolated at their end.
See the line voltmeter and ensure that the voltage has become zero
Ensure the earthing at both ends

39.Charging of transmission line
Ensure the PTW has been returned and inspect the bay physically
Ensure that no Discharge rod/earthing connected on that bay
Give message to the RLDC and other end station and obtain clearance for charging the line.
Ensure opening of both end earthing

40.After getting written confirmation from other end close all isolators of the line and check their alignment.
Synchronize the feeder through the main Bkr and then close the tie bkr.
Check the line power flow .