1Bharat Heavy Electricals Limited

WORKSHOP ON CRITICAL PIPING & ASSOCIATED SYSTEMS

(7–8TH AUGUST’ 2002, AT TS-HQ, KRIBHCO BHAWAN, NOIDA)

PRESENTATION

ON

CRITICAL PIPING DRAINAGE SYSTEM

BY

VIPIN GUPTA, DGM, PEM

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ANY PIPE CONNECTION TO THE TURBINE IS A POTENTIAL SOURCE OF WATER EITHER BY INDUCTION FROM EXTERNAL EQUIPMENT OR BY ACCUMULATION OF CONDENSED STEAM

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DESIGN BASIS

• ASME TDP – 1

• RECORD NOTES OF DISCUSSION HELD AT TS-HQ, N.DELHI ON 12.09.91 REGARDING DRAINS SYSTEM

• SPECIFIC CUSTOMER REQUIREMENTS

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DESIGN CRITERIA

• DETECTION OF THE PRESENCE OF WATER

• ISOLATION OF THE WATER BY MANUAL OR PREFERABLY AUTOMATIC MEANS • DISPOSAL OF THE WATER BY MANUAL OR PREFERABLY AUTOMATIC MEANS  • NO SINGLE FAILURE OF EQUIPMENT SHOULD RESULT IN WATER ENTERING THE TURBINE

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MAIN STEAM PIPING

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MAIN STEAM PIPING

• MS PIPING DRAINS UPTO TURBINE VALVES ARE LED TO ATMOSPHERE

• DRAINS DOWNSTREAM OF TURBINE STOP VALVES ARE LED TO CONDENSER  • START-UP DRAIN IS PROVIDED AT THE UPSTREAM OF BOILER STOP VALVE  • MS STRAINER IS THE LOWEST POINT AND FORMS THE DRAIN POINT • BEFORE SEAT DRAIN IS CASCADED BACK TO THE MAIN STEAM LINE  • DURING START-UP MS STRAINER / LINE DRAINS ARE OPEN TO ATMOSPHERE  CONTD.

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MAIN STEAM PIPING

 • AUTOMATIC CLOSURE OF MS STRAINER & LINE DRAINS  • SEPARATE ATMOSPHERIC FLASH TANK (UFT) IS PROVIDED IN TG AREA TO RECEIVE MS DRAINS / HP BYPASS DRAINS TO MINIMIZE ROUTING PROBLEM • DRAINAGE SYSTEM AS DESCRIBED HAS BEEN ADOPTED IN VARIOUS 210 MW / 250 MW / 500 MW PROJECTS LIKE DADRI, UNCHAHAR, BAKRESWAR, DAHANU, SURATGARH, KOTHAGUDEM, SIMHADRI ETC.

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START-UP DRAIN UPSTREAM OF BOILER STOP VALVE

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MAIN STEAM LINE DRAINS(TYPICAL FOR ONE LEG)

HPT

FLASH BOX(MAL SYSTEM)(AFTER SEAT DRAIN)

(L.O.)(MS STRAINER DRAIN)

TO UNIT FLASH TANK

MAIN STEAM

TO TURBINEDRAIN)

SEAT(BEFORE

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MAIN STEAM STRAINER DRAIN

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HOT REHEAT PIPING

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HOT REHEAT PIPING

• DRAINAGE SYSTEM IS SIMILAR TO THAT OF MAIN STEAM EXCEPT THAT PRIOR TO STARTING THE TURBINE THE HOT REHEAT PIPING WILL BE AT CONDENSER PRESSURE, HENCE HOT REHEAT PIPING DRAINS ARE TO BE LED TO CONDENSER

• HRH DRAIN VALVES ARE OPEN BEFORE START OF VACUUM PULLING

• AUTOMATIC CLOSURE OF HRH STRAINER & LINE DRAINS

• ADDITIONALLY MANUAL DRAIN IS PROVIDED AT THE UPSTREAM OF RH ISOLATING DEVICE TO FACILITATE DRAINING OF PIPING AFTER HYDRO TEST OF RH

SECTIONS

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HRH RH ISOLATING DEVICE

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HRH LINE DRAINS (TYPICAL FOR ONE LEG )

IPT

TO TURBINEFLASH BOX

(MAL SYSTEM)

(AFTER SEAT DRAIN)

(L.O.)(HRH STRAINER DRAIN)

TO CONDENSERFLASH TANK

HOT REHEAT

DRAIN)SEAT

(BEFORE

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HRH DRAIN BETWEEN IPT & VALVE

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HRH STRAINER DRAIN

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COLD REHEAT PIPING

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COLD REHEAT PIPING

• THE POTENTIAL SOURCE OF WATER INGRESS INTO CRH PIPE ARE: REHEATER SPRAY HP BYPASS SPRAY TOP HEATER EXTRACTION PIPING FROM HP EXHAUST

• DESIGN OF DRAINAGE SYSTEM TO REMOVE THE ENTIRE WATER THAT CAN ENTER INTO CRH LINE IS IMPRACTICAL

• SYSTEM IS DESIGNED TO PROVIDE SIGNAL TO ENABLE OPERATOR TO TAKE CORRECTIVE ACTION TO PREVENT WATER INFLOW

• CRH PIPING DRAINS ARE LED TO CONDENSER AS IT COMES UNDER VACUUM DURING START-UP

CONTD.

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COLD REHEAT PIPING

• PIPING DOWNSTREAM OF CRH NRV FORMS LOWEST POINT IN THE CRH LINE

• ADDITIONALLY DRAIN IS PROVIDED BETWEEN HP TURBINE EXHAUST & CRH NRV

• A MANUAL DRAIN IS ALSO PROVIDED AT THE DOWNSTREAM OF RH ISOLATING DEVICE TO FACILITATE DRAINING OF PIPING AFTER HYDRO TEST OF RH SECTIONS

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CRH RH ISOLATING DEVICE

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COLD REHEAT LINE DRAINS

FLASH TANKTO CONDENSER

(L.O.)

AHH

LSH A

DRAIN POT

LS(L.O.)

HPT

TO TURBINE

(MAL SYSTEM)FLASH BOX

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CRH PIPING DRAIN BETWEEN HPT EXHAUST & NRV

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CRH PIPING DRAINS

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CRH PIPING DRAIN POT

• DRAIN POT OF 6 INCH DIA IS PROVIDED IN 210 MW / 250 MW & 12 INCH DIA IN 500 MW AT THE EACH LOW POINT

• TWO LEVEL SWITCHES ARE INSTALLED ON THE DRAIN POT FOR SENSING OF PRESENCE OF CONDENSATE IN THE DRAIN POT AND EFFICIENT EVACUATION OF THE SAME

• LEVEL SWITCH AT HIGH LEVEL SHALL INITIATE FULL OPENING OF THE DRAIN VALVE AS WELL AS PROVIDE AN ALARM IN CONTROL ROOM

• LEVEL SWITCH AT HIGH HIGH LEVEL SHALL INITIATE AN ALARM AND REPEAT COMMAND FOR OPENING DRAIN VALVE

CONTD.

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CRH PIPING DRAIN POT

• HIGH HIGH LEVEL IS A WARNING TO THE OPERATOR TO INVESTIGATE & ISOLATE THE SOURCE OF WATER INGRESS

• BEFORE START OF VACUUM PULLING CRH DRAINS ARE OPEN TO CONDENSER AND OPERATOR TO ENSURE NO ALARM CONDITION ( CW PUMP & CEP ARE RUNNING)

• SPRAY IS ENVISAGED IN FLASH TANK TO COOL DRAINS

• CLOSING OF CRH DRAIN VALVE IS REMOTE MANUAL

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CRH DRAIN POT ARRANGEMENT

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HP BYPASS PIPING

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HP BYPASS PIPING

• HP BYPASS WARM-UP & DRAIN ARRANGEMENT HAS BEEN ADOPTED IN LINE WITH DELIBERATIONS DTD. 20-21ST FEB. ‘ 1998 AT TRICHY

• HP BYPASS PIPING LAYOUT IS SUCH THAT ENTIRE PIPING IS SELF DRAINABLE TOWARDS MAIN STEAM / COLD REHEAT PIPING

• WARM-UP TAPPING IS PROVIDED CLOSE TO THE BYPASS VALVE FROM BOTTOM OF THE PIPING

• WARMING-UP LINE IS CONNECTED TO CRH LINE MINIMUM 5M AWAY FROM TEMPERATURE TAPPING POINTS

• START-UP DRAIN IS PROVIDED ON THE WARM-UP LINE AND IS LED TO ATMOSPHERE CONTD.

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HP BYPASS PIPING

• START-UP DRAIN OPENS PRIOR TO STARTING THE UNIT AND CLOSES WHEN HP BYPASS VALVE IS TAKEN INTO SERVICE

• TEMPERATURE MEASUREMENT SHALL BE PROVIDED AT HP BYPASS VALVE INLET

• HP BYPASS VALVE TO BE LOCATED ABOVE THE MAIN STEAM & CRH PIPING

• WARMING-UP LINE TO DOWNSTREAM OF MS STRAINER IS NOT PREFERRED AT IT WOULD LEAD TO UNSTRAINED STEAM TO TURBINE

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HP BYPASS WARMING-UP SCHEME

MAIN STEAM LINE

TE

COLD REHEAT LINE

250 mm

TO UFT

HP BYPASS

TE

TE

(LO)

START-UP DRAIN

WARM-UP LINE

VALVE

5 M (min)

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HP BYPASS WARM-UP PIPING

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LP BYPASS PIPING

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LP BYPASS WARM-UP PIPING

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LP BYPASS WARM UP PIPING

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LP BYPASS PIPING

• IN EARLIER 210MW SETS AN ISOLATING VALVE WAS ENVISAGED IN LP BYPASS WARM-UP SCHEME

• THE PURPOSE OF ISOLATING VALVE IS TO ISOLATE WARM-UP LINE DURING INITIAL COLD START-UP

• THIS VALVE HAS TO BE KEPT OPEN IN ALL OTHER MODES OF OPERATION

• BASED ON THE SITE FEEDBACK AN ANALYSIS WAS DONE & IT WAS OBSERVED THAT OPERATION OF ISOLATING VALVE WAS NOT PROPER AND WAS USUALLY LEFT CLOSED WHICH LEAD TO PROBLEMS WITH LP BYPASS SYSTEM

• FROM DADRI 210MW TPS ONWARDS THIS ISOLATING VALVE HAS BEEN DISPENSED WITH CONTD.

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LP BYPASS PIPING

• IN 500MW PROJECTS ALSO THERE IS NO ISOLATING VALVE IN THE WARM-UP LINE

• THIS HAS ENHANCED THE SYSTEM RELIABILITY AND EASE IN OPERATION

• LP BYPASS LOOP PIPING DRAINS CAN BE CASCADED BACK TO HRH PIPING (BETWEEN TURBINE & STRAINER) AT AN LOWER ELEVATION OTHERWISE DRAIN CAN BE LED TO CONDENSER

• DRAIN ON WARMUP LINE IS PROVIDED CLOSE TO VALVE TO ENSURE WARMING UP

CONTD.

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LP BYPASS PIPING

• BEFORE PULLING VACUUM IN THE CONDENSER OPEN ABOVE DRAINS TO CONDENSER

• ONCE LP BYPASS VALVE IS TAKEN INTO OPERATION THESE DRAIN VALVES CAN BE CLOSED

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LP BYPASS WARMING UP SCHEME FOR 210 MW UNITS

WARM-UP STEAM FLOW DURING NORMAL RUNNING OF TURBINE

WARM-UP STEAM FLOW IN COLD CONDITION

MAIN LINELP BY PASS

TO TURBINE

HRHSTRAINER

Nb 50

HRH LINE

TO CONDENSER

STOP VALVE

CONTROL VALVE

WARM-UP LINE

LP BY PASS

Nb 450

VIA FLASH TANKTO CONDENSER

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LP BYPASS WARMING UP SCHEME FOR 500 MW UNITS

WARM-UP STEAM FLOW DURING NORMAL RUNNING OF TURBINE

WARM-UP STEAM FLOW IN COLD CONDITION

MAIN LINELP BY PASS

TO TURBINE

HRHSTRAINER

CONTROL VALVE

Nb 50

HRH LINE

CONDENSER

STOP VALVE

WARM-UP LINE

LP BY PASS

Nb 650

TO VIA FLASH TANKTO CONDENSER

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OPERATING MODES

• COLD START-UP

DRAINS SHALL BE OPERATED AS DESCRIBED EARLIER

• HOT START-UP

DURING TURBINE TRIPPED / BOILER TRIPPED CONDITION, OPEN AND CLOSE DRAINS AS IN COLD START-UP. MS

STRAINER DRAINS ARE TO BE CLOSED AS SOON AS 50°COF SUPERHEAT IS ACHIEVED AND BYPASS IS ESTABLISHED.

DURING TURBINE TRIPPED / BOILER IN SERVICE WITH HP/LP BYPASS CONDITION NO DRAINS TO BE OPENED

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NTPC SPECIFIC REQUIREMENTS

FOLLOWING ARE ADDITIONAL FEATURES PROVIDED IN NTPC PROJECTS AS PER THE CONTRACTUAL REQUIREMENT:

• ANGLE VALVES INSTEAD OF GLOBE VALVES IN DRAIN LINES

• NTPC SPECN. CALLS FOR TWO DRAINS FOR EACH DRAIN POINT I.E. ONE AS NORMAL DRAIN TO DRAIN FLASH TANK AND THE OTHER AS ALTERNATE DRAIN TO ATMOSPHERIC FLASH TANK. AFTER DELIBERATIONS ALTERNATE PATH ARE PROVIDED FOR MAIN STEAM DRAINS & HOT REHEAT DRAINS ONLY

• CLEAN OUT VALVES FOR DRIP POTS

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ANGLE VALVE DRAIN ARRANGEMENT

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FLASH TANKS SPRAY SYSTEM

FOR COOLING OF INCOMING HOT DRAINS FOLLOWING SPRAYS ARE ENVISAGED IN THE FLASH TANKS:

• CONDENSATE SPRAY FROM CEP DISCHARGE TO CONDENSER FLASH TANK THROUGH TEMPERATURE REGULATED ON / OFF TYPE CONTROL VALVE

• CONTINUOUS SPRAY THROUGH A MANUAL REGULATING VALVE & RESTRICTION ORIFICE FROM SERVICE WATER SYSTEM TO UNIT FLASH TANK

• CONTINUOUS SPRAY THROUGH A RESTRICTION ORIFICE FROM CEP DISCHARGE VALVE GLAND SEALING HEADER TO HP DRAIN FLASH TANK

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UNIT FLASH TANK ARRANGEMENT (TYP)

HPBP WARM-UPLINE DRAINS (TYP)

( LO ) ( LO )

3 M

TANKFLASHUNIT

DRAINS (TYP)MS STRAINER

TRENCH

WATER SYSTEM

TO DRAIN

FROM SERVICESPRAY WATER

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GENERAL RECOMMENDATIONS

• DESIGN , CONTROL AND OPERATION OF ALL SYSTEM THAT HAVE A POTENTIAL FOR ALLOWING WATER TO THE TURBINE SHALL PREVENT ANY UNUSUAL ACCUMULATION

• DRAINS SHALL BE INSTALLED AT EVERY LOW POINT WITH ADEQUATE MEANS (MANUAL / AUTOMATIC) TO DISPOSE OFF THE CONDENSATE COLLECTED

• DRAIN LINE SIZE SHALL BE SUFFICIENT TO PREVENT RISK OF PLUGGING BY FOREIGN MATERIAL. NORMALLY DRAIN LINE SIZE IS 2 INCH

• ALL DRAIN LINES SHALL PREFERABLY BE RUN INDIVIDUALLY AND HAVE CONTINUOUS SLOPE TOWARDS THE DISPOSAL POINT

CONTD.

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GENERAL RECOMMENDATIONS

• HIGH PRESSURE DRAINS SHALL BE PROVIDED WITH TWO VALVES IN SERIES , UPSTREAM LOCKED OPEN VALVE & DOWNSTREAM MOTORIZED VALVE. LOW PRESSURE DRAINS SHALL BE PROVIDED WITH MOTORIZED VALVE

• ALL MOTORIZED DRAINS SHALL HAVE FACILITY TO OPERATE FROM UNIT CONTROL ROOM WITH OPEN / CLOSE POSITION INDICATION

• OPERATOR TO ENSURE THAT ALL THE MOTORISED DRAIN VALVES SHALL BE CLOSED IMMEDIATELY ON ATTAINMENT OF 10% BLOCK LOAD ON TURBINE

• INSTALLATION LEVELS OF MS STRAINER. HRH STRAINER , CRH NRV ETC SHALL BE SUCH THAT DRAIN CAN BE LED WITH CONTINUOUS PROPER SLOPE TO THE TERMINAL POINT

CONTD.

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GENERAL RECOMMENDATIONS

• ALTERNATE PATH SHOULD BE AVOIDED AS IT BECOMES SOURCE OF AIR INGRESS. ALSO AT SOME SITES ITS MAL-OPERATION RESULTED SUCKING OF WATER FROM ATMOSPHERIC TANK INTO THE MAIN PIPING LEADING TO SEVERE PROBLEMS

• DRAINS TO MANIFOLD SHALL BE GROUPED IN APPROXIMATELY SAME PRESSURE RANGES OTHERWISE DRAINS SHALL BE ARRANGED IN A DECREASING ORDER OF THE PRESSURE

• DRAIN LINES TO THE MANIFOLD SHALL BE MOUNTED AT 450 TO THE MANIFOLD AXIAL CENTRE LINE WITH THE DRAIN LINE DISCHARGE POINTING TOWARDS THE DISPOSAL POINT

CONTD.

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GENERAL RECOMMENDATIONS

• DRAIN SHALL BE PREFERABLY TAPPED THROUGH A DRIP POT

• LOOPS REQUIRED FOR FLEXIBILITY SHALL BE IN THE PLANE OF THE SLOPE

• LOOP DRAINS CAN BE CASCADED BACK TO THE MAIN PIPING BY GRAVITY AT A LOWER ELEVATION

• OPERATION OF DRAIN VALVE, PLUGGING OF DRAIN LINES AND HEALTHINESS OF INSTRUMENTS SHALL BE PERIODICALLY CHECKED

• LEVEL ACTUATED MECHANISM SHALL BE TESTED AT INTERVALS TO ENSURE THEIR PROPER FUNCTIONING

• DRIP POTS, TRAPS & ORIFICES FOR ALL DRAIN LINES SHALL BE REGULARLY CLEANED

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