HP & LP Bypass Operation and Protection

HP & LP Bypass Operation and Protection

Purpose

• Boiler operation independent of the turbine
• Minimum steam flow through SH & RH tubes during start-ups, low load operation & sudden unloading of unit
• Utilized or building up of steam parameters
• Avoiding the boiler trip on Reheat protection
• No steam flow through Boiler steam tubes will lead to starvation & thereby overheating and lead to premature failure of tubes 
• The capacity of HPLP bypass is 60% of full load turbine steam flow 

Reheat Protection:

RH protection (delay=10 sec) will act if

1. TURBINE HP V/V & HPBP CLOSED [ either turbine HP stop v/v or HP CV in both HP line closed ] & [ both HP BP <2%]             OR
2. TURBINE IP V/V & LP BP closed [ Either IP stop v/v or IP CV v/v in both IP line closed ] & [ Either LP BP stop v/v or LP BP C/V in both LP line is closed] OR  
3. Generator ckt bkr open & [both HP BP closed OR both LP BP closed

HPBP Oil Supply Unit Interlocks:

• Pump Auto off Oil Press high >160ksc
• Pump Auto on Oil Press Low <120ksc
• Pump Auto off Oil Temp high >70 DegC
• Pump Auto off Oil Level low <18 Lit
• Alarm Oil Press too high >170ksc
• Alarm Oil Press too Low <90ksc

Pressure Mode:

Stg-2 Mode of Operation 

• Initial Pressure Mode  -
  Importance to the load 
• Fixed Pressure Mode -
  Importance to the Health of turbine.

HP BP Protection:

BP Valve Priority Close Conditions:

• Condenser Vacuum Low (<-0.6 ksc)
• Bypass Downstream Temp very high (>380 degC) 

                    Under these conditions 

• Steam Press Controller Switches to Manual from Auto 
• spray water valve will close
• This protection will override the Fast opening signal & open push button operation

HP Bypass Fast Opening Conditions 

• Generator Circuit Breaker Opening & Boiler on & no priority close
• Turbine Trip & Boiler on & no priority close
• Turbine Load Shedding Relay Operation
• HP BP Pressure Controller Deviation > 8 ksc
• Pressing the Fast Opening Button

BP Valve Auto Blocking Conditions  

• Bypass valve priority close command
• BP position transmitter failed 
• OSU-1 &  2 Oil Pressure <90 ksc
• Main steam Pressure transmitter failed

HP BP Interlocks:

BPE Valve Conditions  

• Steam Bypass Valves BP1 or BP2<2 % Auto Close Command to ensure positive shut off
• Steam Bypass Valves BP1 or BP2<2 % Spray Water Pressure Control Valve (BD Valve) close
• Steam Bypass Valves BP1 or BP2>2 % Spray Water System (BPE1, BPE2, BD Valve) will switch over to Auto

BPE Valve Auto Blocking Conditions  

• Bypass Downstream Temp very high (>380 degC)
• BP auto command blocking
• BPE valve position transmitter failed 
• BPE Temp transmitter deviation high 
• Therefore, it is necessary to make proper set values for Spray Water Header Pressure & HP BP downstream temperature before operating the Steam Bypass Valves

LP Bypass:

Functions of LP Bypass System are:

• Maintaining minimum Steam Flow through Re-heater
• Maintaining desired Steam Pressure in the Re-heater
• Providing an alternative path for dumping the steam (not accepted by the IP & LP Turbines) into the condenser

LP BP System comprises of : 

• Steam Pressure Control Loop
• Valve Position Control Loop
• Automatic Control Interface (ACI)
• Condenser Temperature Protection
• Tracking Unit

LPBP Protections:

Close LP Bypass under following conditions:

1. Condenser Vacuum Low (<-0.6 ksc)
2. Spray Water Pressure Low (<8 ksc)
3. Condenser Wall Temperature High ( > 90 DegC)
4. LPBP Down Steam Pressure High (>19 ksc)
5. Spray Water valve open command at Steam pressure before bypass valve >6.8 ksc 

Boiler Start-Up After BTL

Boiler Start-Up After BTL

• Boiler is out for 1-2 days due to BTL. HP Casing Temp in b/w 300-400 Deg
• One HFO i/s. HFO charged with >110 Deg upto Boiler Front
• Start ID and FD fan. Purge Boiler (5 min cycle)
• Check SH/RH vents Open. APH Soot Blowing lined up.Charge Oil Carry over Probe.
• Turbine on Barring. Start AB all 4 guns(Atom Steam Pr in b/w 6-7 ksc)
• Take Another gun CD(all 4). HFO Prssure~8-10 ksc. Drum Metal Temp Rise~2 Deg/min
• APH Soot Blowing(10-12 ksc Pr) to be done non-stop.
• Drum  Pr~2 ksc. Close SH/RH Vents. Open HPBP Warm-Up valves. Open BSV bypass valves.
• Drum Pr~5 ksc. Open BSVs. Open HPBP~10%. Close HPBP Warm up Valves. 
• Close SH/RH Header drains at ~ 14 ksc(Drum Pr). Put HPBP spray on Auto.
• FG path of PA fan through. Start one PA Fan and one Seal Air Fan
• MS Pr~80 ksc & MS Temp~365 Deg. HRH Pr~12 ksc & HRH Temp~325 Deg. Maintain using HPBP and LPBP valves.
• Float A mill(charge air). Cut in A mill ~ min flow 17 TPH.
• No SH/RH spray till now. Secondary Air Temp~175 Deg. 1st Mill Before synchronization.
• Reduce firing accordingly to control Temp Rise
• Turbine Running ~ 3000 rpm. Synchronise Machine. Take ~50 MW Block Load. 
• Ensure Closing of HPBP and LPBP valves with spray on Auto. Increase HPBP set point. 
• Float 2nd Mill(B). Charge all ESP Fields. Increase Mill-A firing.
• Firing to maintained ~1.5 T/min upto 250 MW to limit any abrupt Temp Rise for that spray is required.
• Load~60 MW. MS~60 ksc. Load Controller in action. Charge LPH-2 & 3 with Level controller in Auto. 
• Charge Deaerator Pegging by CRH Ext. Cut in all Auto controllers. Cut in 2nd Mill.
• Load ~110 MW. MS~80 ksc. Charge PRDS from CRH. Cut HP Heaters and Level controller in auto. Cut in 3rd Mill.
• Load~150 MW. MS (100 ksc/435 Deg). Start 2nd PA fan(FG & Air Path available)
• Control MS & RH Temp by spray if Required. Cut in 4th Mill. Check Scanners,'
• Load~250 MW. MS~125 ksc/450 Deg.  Cut in 5th Mill. Roll 1st TDBFP & Put on Load.
• Cut-off Oil Support Completely. Cut in 6th Mill if required. 
• Change MDBFP with TDBFPs. And stop MDBFP.
• Load~350MW. MS~140ksc/480 Deg. Increase Set point of SH/RH Spray to achieve rated SH and RH Temp
• Load~500 MW and Scan all Parameters/ Loops/ Controllers.

Safe Shut Down Procedure-StageII 500 MW Rihand

1	MDBFP – Available & Standby
2	Oil gun: HFO Pr/Temp=16 ksc/>110 Deg , Atom Steam: 6.5ksc/>220 Deg (Open steam drains @AB elevation)
3	Turbine on LP mode, Boiler Master in Manual(Manual Mode)
4	Isolate PRDS from CRH for this unit, Increase the set point to other units @ 13.5 ksc/ Temperature >280 deg
5	Open GS supply line drain to atmosphere
6	Charge APH soot blowing line from PRDS
7	Load-500 MW with 6 Mills(Roughly @ 55 tph each)
8	Cut feeding in top mill & Stop mill, other 5 mills >=40 tph/ load ~325 MW,In b/w reduce ThrotPr- 170 to 150 ksc
9	Take AB & CD elevation gun/ Start APH Soot blowing
10	Start MDBFP in Manual(cold) & Load/ unload anyone TDBFP(<=3500 rpm), MDBFP-auto & FW master-Auto
11	Switch off ESP fields as guns been taken & proved
12	Cut feeding in Bottom Mill & stop it/ Now 4 mills/ Ms Pr ~130 ksc/ load <=300 MW (Reduce feed in top mill too)
13
14	Load~225 MW with 3 Mills+ 2 elev oil guns/ Unload TDBFP, keep load on MDBFP(Off CRH block v/v of TDBFP)
15	Trip the other TDBFP/ Reduce feed in bottom mill/Load~175 MW/ Unload one PA fan/ Reduce MsPr~90-100 ksc
16	Changeover UT to ST / Trip 2nd TDBFP
17	Trip bottom mill/ Load 140 MW/ 2 Mills +AB1324 CD13 or CD24 guns / only MDBFP in service
18	Bring load ~80 MW by cutting upper mill & opening HPBP further
19	Maintain drum at least +50mm to +100mm before hand tripping turbine(to avoid boiler trip on drum level Lo-Lo)
20	Hand Trip Turbine/ Turbine tripped (1 mill +6 guns i/s + MDBFP i/s)
21	Maintain TG lube oil temp>50 deg/MAL drain open/AOP starts @2850rpm/close all S/ RH spray v/vs
22	Stop mill, Stop guns/ boiler will Trip on Loss of all fuel/ All PA, HOTV/LOTV
23	Depressurise boiler to 45-50 ksc before closing boiler stop valve thru HP/LP bypass
24	Close Boiler stop valve/ De pressurise MS/HRH line thru HP/Lp BP/ after that close HPLP bypass/ Close manual of HPBP spray v/v
25	Purge boiler for 10 min(2 cycles)
26	Stop one set of ID and Fd fans after purging
27	cool boiler furnace Pr(= -10 to -20 mm)/ Monitor rate of ccoling by following BCW suction manifold temp<87 deg/hr
28	Drum level to be maintained as such till drum metal temp reaches 100 deg

PA Fan : Stg-II : Operation & Important

PA Fan : Stg-II : Operation & Important

Important Information :

• Capacity: 700 TPH
• Total Head Devleoped: 1200 mm WC
• Speed: 1480 rpm
• Rating: 2.775 MW and 11 KV
• Full Load current: 169 Amp
• Overload alarm: 180 Amp (TD 20 sec)
• Overload Trip: 192 Amp
• Normal Header Pressure: 820 mm WC
• Current: 90 Amp
• Blade-Pitch: 60 %
• Blade Pitch Locking: 85 %
• Trip : Low =650 mmWC(TD-5 sec) | Low-Low=550 mmWC(Instant)

Prestart checks & Loading:

• Check air path is available .  At least one PAPH is ON and air path of the APH available (APH air I/L & O/L dampers are open), for second PA fan both PAPH must be on 
• Remote / local selector switch of blade pitch mounted on the actuator is selected in remote and the blade pitch is in minimum position. 
• Check that the outlet (discharge) damper is in closed position and in remote 
• Check the PA fan discharge duct drain valve is in closed position .After shut down with
  air preheater water washing this duct drain should be opened first to check any water
  accumulation inside fan casing, before taking PA fan into service.
• Keep cold air gate damper of at least two mills open so that minimum air flow is assured 
•  Start the fan with blade pitch minimum position and ensure opening of discharge damper fully. Then gradually increase the blade pitch position to load the fan.  

STARING OF SECOND PA FAN:-  

• Both PAPH must be ON and its inlet and outlet damper open 
• At least three mills be in service 
• Put blade pitch of 1st PA fan in CAS and PA header pr. In auto with set point 850 mmwcl – 900mmwcl. 
• Start 2nd PA fan and put blade pitch of 2nd PA fan a command of 10-15% as the discharge damper starts opening and close feed back disappears. 

Trip:   

• PA Header Pr Low =650 mmWC(TD-5 sec) | Low-Low=550 mmWC(Instant)
• Vibration: 20 mm/sec for 120 sec OR 28 mm/sec for 5 sec

PTW Preparing steps

PTW Preparing steps

• Use T-code WCLE
• Enter Planning Plant-1005
• Set filter- Operational WCDs
• Select Prepared  WCDs
• Enter- Valide From and TO Date
• Select " Reference Object" tab
• Type " cr2" in train blank place
• click " Execute" button (clock button)
• Select  PTWs to be prepared(Using Checks)
• Click " Hierarchy" Button
• Click "Switching Screen" (gear shape)
• Click " Select all Button"
• Click " tag" button
• Click " continue" button
• Click " Edit/ Print/ Operational List/ tagging List
• Click "Print Preview" button
• Click back button
• Click " tagged" button
• Click back button
• Click " Operational WCD/ function/Print
• Check Information below.

PTW Closing steps

PTW Closing steps

• Use T-code WCLE
• Enter Planning Plant-1005
• Set filter- Operational WCDs
• Select CLOSED (green) WCDs
• Enter- Valide From and TO Date
• Select " Reference Object" tab
• Type " cr2" in train blank place
• click " Execute" button (clock button)
• Select  PTWs to be closed(Using Checks)
• Click " Hierarchy" Button
• Click "Switching Screen" (gear shape)
• Click " Select all Button"
• Click " Untag" button
• Click " continue" button
• Click " Edit/ Print/ Operational List/ Untagging List
• Click "Print Preview" button
• Click back button
• Click " Untagged" button
• Click back button
• Click " Operational WCD/ function/Close
• Check Information below.

Boiler Hydro Checklist

Equipment availability:

• CW duct charged
• ACW pump available,ACW strainer boxed up
• ECW pump available
• ECW tank filled.
• DM/CST pump available.
• Boiler fill pump available.
• Wet Lay up pump, NH3, N2H4 pump available.
• Condenser Hotwell normal level.
• CEP available, DA level C/V, Isol. Valve operation OK
• CPU one stream available.
• Deaerator boxed up, level normal.
• MD BFP’C’ available, lined up.
• Feed line vented upto FRS.
• FRS LOW range C/V, Isol. Valve opn OK OK
• LPH, HPHs bypass valve available & lined up.
• Eco inlet valve E2 open (Operation) OK
• Eco R/C valve E18, E20 Opn OK.
• Boiler drum clearance.
• Low point drains header valve clearance.
• SH header valves clearance.
• SH spray valve clearance & all valve closed.
• All CC pumps cavity filled.
• Boiler stop valve (L&R) opn checked, Integral bypass opn OK
• EBD, CBD, IBD valve cleared, opn checked.
• SH drain valve before Blr. Stop valve opn OK.
• SH air/startup vents opn OK.
• Drum vents Opn OK.
• Soot blowing steam Isol. (Manual) valve closed.
• RH spray main block valve close.
• Main steam strainer drain & MS line drain open.
• CRH line drain open.
• HP bypass spray line manual valve close.

SAFETY PRECAUTIONS:

• Lighting on all boiler elevations are available.
• All scrap materials/Insulation materials removed & areas cleaned.
• All permits on required equipment/valve cleared & clearance given.
• The fire water pump is running.
• The healthiness of all supports & hangers are checked.
• Hydrostatic test plugs/gags were fitted on all the boiler safety valve.

Following systems Readiness/Trial was taken:

• DM Tank/CST tank flushed, water quality ensured.
• DM plant informed for Hyd. Test.
• Hotwell flushing done on______ & filled to normal level.
• ECW tank flushing done on______& filled upto normal level.
• D/A flushing done on_______& filled upto high level.
• D/A level, level switches alarm OK.
• CW ducts are charged by opening ICV on__________
• ACW trial taken on_________ kept I/s.
• DMCW pump trial taken on_________kept I/s.
• CEP Protection/Interlock checked, Trial taken on_________.
• MD BFP’C’ protection & interlocks checked & trial taken on________
• Boiler drum level Tx, hydrastep, PG/ pr.Tr for drum & MS line before ESV charged & made available.
• CC pump filling completed on  

Drum Filling Procedure

• Blr. Filling clearance from O/H group on -----.
• Blr. Stop valve, Int. bypass valve fully closed.
• Startup vents, SH vents, Drum vents are fully open.
• SH header drain individual valves open & master drain closed.
• Boiler water sample line is closed.
• Low paint drain header lined up through Bottom ring header.
• CBD, EBD, IBD valve, SH header drain valve before ESV closed.
• FRS low range is lined up, Eco inlet valve open.
• PO4 dosing line valve, SB manual valve closed.
• All SH/RH spray valve closed.
• MS strainer & MS line drain, CRH line drain valve open.
• Boiler fill pump started & kept on R/C.
• NH3, N2H4 dosing soln. ready & lined up for BFP.
• Start wet lay Pump.
• Start filling the Boiler through SH filling line for back flushing.
• MD BFP’C’ is started & in R/C.
• Maintain water quality by running NH3 & N2H4 pump, Wet lay p/p.
• Start taking water through BFP’C’/TDBFP.
• When drum level becomes normal, isolate filling line & stop BFP.
• When water starts coming out through Drum vents SH vents, closed all vents at 2KSC drum pr.
• Close SH start up vents after closing all air vents.
• Drum level high, high high alarm checked.

BOILER PRESSURISATION:

• Boiler is pressurized slowly upto desired pr. (as per requirement of Blr. Inspector or maintenance).
• Drum Pr. high, high high alarm appeared.
• Pr. maintained for 10 mts. at required pr.
• Boiler pr. reduced to 120 KSC.
• Inspection of boiler pr. parts, Drums, CC pumps carried out.
• Leakages observed.
• Rate of pr. drop observed.
• Boiler depressurized & drum/SH vents opened at 2KSC,
• SH,W/W,Economizer drained.
• Drum level low/low low alarm appeared.
• Remark:

BOILER HYDRO TEST CHECKLIST1. WORK IN BOILER STEAM & WATER CIRCUIT COMPLETED.
2. BOILER DRUM BOXED UP.
3. RING HDR MANHOLES BOXED UP.
4. DRUM VENTS,SH VENTS/START UP VENTS AVAILABLE
5. SH DRAIN(18 NO) + MASTER DRAIN BOXED UP.
6. SH FILLING LINE CONNECTION TO SH DRAIN HEADER COMPLETED
7. ALL V/V’S IN LOW POINT DRAIN HDR ALONG WITH MASTER DRAIN
BOXED UP.
8. CBD/EBD/IBD ISOLATING V/V’S AT DRUM LEVEL CLOSE
9. SOOT BLOWER STEAM LINE Ist ISOLATING V/V TOWARDS BOILER
CLOSE
10. PHOSPHATE DOSING ISOLATING V/V CLOSE,
11. CC P/PFILL&PURGE COMPLETED/ANY ONE CC P/P DISCH V/V OPEN
12. BOILER DRUM & SH SAMPLING LINE ISOLATING V/V CLOSED
13. MDBFP AVAILABLE.
14. D/A & FST AVAILABLE FILLED UPTO NORMAL LEVEL.
15. BOILER FILL P/P’S AVAILABLE
16. ALL BFP’S SH & RH SPRAY LINE ISOLATING V/V’S CLOSE.
17. BD V/V’S MANUAL ISOLATING CLOSED
18. MS 1,2,3,4,5&6 CLOSED TIGHTLY & SUPPLY ISOLATED.
19. MS 9 & 10 CLOSED( SUPPLY ISOLATED). THEIR MANUAL ISOLATING
V/V CLOSED.
20. E2 & E2A AVAILABLE –OPEN
21. E20 ( ECO RECIRCULATION )AVAILABLE.
22. ALL TURBINE SIDE (MS/HRH/CRH) LINE ATMOSPHERIC DRAINS FULL
OPEN.
23. MS/HRH STRAINER DRAIN TO IBD TANK OPEN.
24. HP/IP STOP V/V’S GAGGED IN CLOSE POSITION.
25. HYDRASTEP & DRUM PR. TRANSMITTERS AVAILABLE.
26. MS PR. GAUGE( BEFORE STOP STOP V/V’S) AT DRUM LEVEL AVL.
27. HP HEATERS FW CIRCUITS & FRS V/V’S AVAILABLE.
28. MS PRDS MANUAL V/V AT PRDS TIGHTLY CLOSD.
29. ECW/DMCW SYSTEM AVAILABLE WITH ATLEAST ONE DMCW P/P I/S
FOR MDBFP COOLING WATER.
30. ATLEAST ONE CLCW P/P I/S(OPTIONAL)
31. ATLEAST ONE PHE CHARGED FROM DMCW/CLCW SIDE.
32. WETLAY P/P AVAILABLE(LINED UP TO LOW POINT DRAIN HDR.
33. CHEMICAL SOLUTION AT DOSING TANKS( HYDRAZINE/AMMONIA)
AVL.
34. CC P/P CAVITIES FILLED/ FILL PURGE COMPLETED.
35. ERV(MS LINE) MANUAL V/V CLOSED.

500 MW BOILERS

CHECKLIST FOR HYDRO – TEST

UNIT:                                                                                                                                 DATE:
S.N. DESCRIPTION RESP. STATUS REMARKS

01. CC Pumps cavity filled. Opn.
02. MS stop valves & equalisers closed. Opn.
03. MS ERVs isolating valves closed. Opn.
04. Soot blowing station isolated. Opn.
05. CBD root valve closed. Opn.
06. SH attemperation valves from all BFPs Opn.
Closed.
07. RH attemperation valves from all BFPs Opn.
Closed.
08. SH / RH attemperation station cleared. PP
09. HP Bypass spray valves & manual Opn.
Valve closed.
10. PRDS spray, manual valves closed. Opn.
11. Condensate system cleared & charged. TM/Opn.
12. Feed water system cleared & charged. TM/Opn.
13. CEP, MDBFP P&I checks completed, C&I/Opn.
Pumps started & kept in service.
14. HP Bypass valves & main turbine TM/Opn.
Stop valves are closed.
15. MS line drains are kept open. Opn.
S.N. DESCRIPTION RESP. STATUS REMARKS
16. MS and Drum safety valves are gagged PP
(for pressures above 180 KSC).
17. Necessary C&I indicators and recorders C&I
are available.
18. Men & material removed from Boiler PP
first and second pass.
19. Men & material removed from bottom AHM
ash hopper and economiser hoppers.
20. Clearance for boiler filling obtained, PP
from Pressure Parts.CLEARANCESS.N. DEPARTMENT SIGNATURE REMARKS
01. Pressure Parts (PP)
02. Turbine Maintenance (TM)
03. C&I Maintenance (C&I)
04. Ash Handling Maint. (AHM)
05. Opn. / Recommissioning
HYDRO-TEST DETAILSINTERNAL:Date / Time :
Pressure (KSC) :
Leakages, if any :
Result :EXTERNAL:Date / Time :
Pressure (KSC) :
Leakages, if any :
Result :Signatures:Pressure Parts Opn./ Recommissioning