SafetyinDesignandInstalla0onofHeatRecoverySteamGenerator

CEPSI2016byJohnnyKwong

24Oct2016

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Content

●  Introduc9on●  HRSGsinLammaPowerSta9on●  CommonRisksandFailuresofHRSG●  SafetyforDesign●  SafetyforInstalla9on●  Conclusion

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Introduc0on

Stage I L1-3 : 250 MW x 3 (1982-84) Stage II L4-6 : 350 MW x 3 (1987-92) Stage III L7-8 : 350 MW x 2 (1995-97)

8 Coal-Fired Units 2,500 MW

GT1 : 55 MW (1978) GT2,3,4,6 : 125 MW x 4 (1989-90)

5 Oil-Fired Open Cycle GT Units 555 MW

2 Gas/Oil Dual-Fired CCGT Units

GT57CC : 345 MW (2002) L9 : 335 MW (2006) 335 MW

345 MW

~3,737 MW (Incl. Renewable)

Total Installed Capacity :

800kW

1MW

●  Lamma Power Station and Extension

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Introduc0on

●  Heat Recovery Steam Generators (HRSG) have been adopted widely due to growth in CCGT plants

●  HRSG is essentially a Boiler but without firing; it captures residual heat of high temperature flue gas (typically 540-650oC) and generate steam for power generation and/or district heating;

●  Heat present in flue gas falls typically within 40-70% of initial fuel energy of a F-class CCGT

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HRSGsinLammaPowerSta0onCCGT Unit GT 5&7 L9 L10 (future)

Flue Gas Flow Vertical Vertical Horizontal

Pressure Stages HP, LP HP, IP, LP; With Reheat

HP, IP, LP; With Reheat

Drum Type ü  ü  ü  SCR/CO Catalyst X X SCR catalyst

Supplementary Firing X X X

Casing design Cold/Hot casing Cold Cold

Steam Output 195.15 t/hr 512 oC

73.5 kg/cm2g

279.7 t/hr 539.9 oC

109.4 kg/cm2g

294.7 t/hr 582 oC

139.4 kg/cm2g

1 Preheater 2 LP evaporator 3 LP superheater 4 HP economizer 5 Catalyst 6 HP evaporator 7 NH3 injection 8 HP superheater

Typical Vertical Design HP drum

LP drum Feedwater tank

1 2 3 4 5 6 7 8

Typical Horizontal Design Feedwater tank LP drum HP drum

8 7 6 5 4 3 2 1

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CommonRisksandFailuresofHRSG●  Corrosion

Ø  General Corrosion Ø  Stress Corrosion Cracking Ø  Flow Accelerated Corrosion

●  Low Cycle Fatigue ●  Water/Steam Cycle Chemistry

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SafetyforDesignofHRSG

●  General Corrosion – Rate of corrosion

Relative Corrosion Rate of Fe and Cu

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SafetyforDesignofHRSG

●  Prevention Measures Ø  Materials Selection + Water Chemistry (pH, conductivity..)

SA 299

/Deaerator

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Flow Mal-distribution

• Mechanical configuration

• Un-even heat absorption during transient/load change

• High duct firing • Poor venting/drainage

Off-design Water

Chemistry

• Poor control of water quality (global FAC effects)

Poor Materials Selection

for vulnerable

section

• Low grade CS vs Higher Cr alloy steel (e.g. Grade 11 or above)

SafetyforDesignofHRSG

●  Flow Accelerated Corrosion

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SafetyforDesignofHRSG

●  Wear Rate of Carbon Steel and Various Alloy Steels

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SafetyforDesignofHRSG

●  Wear Rate of Carbon Steel and Various Alloy Steels

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SafetyforDesignofHRSG

●  Fatigue (Low Cycle Fatigue)

Two-shift Cycling

• Fast Start up/Shut down would increase thermal stress

Presence of condensate

• High difference in tube-to-tube temperature

•  Inadequate drains/vents

Unresolved thermal

expansion at harps

• Configuration that inhibit expansion, thus induces stress

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SafetyforDesignofHRSG●  Fatigue (Low Cycle Fatigue)

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SafetyforDesignofHRSG

●  Stress Corrosion Cracking

Corrosive Environment

Tensile Stress

Susceptible

Material

SCC

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SafetyforDesignofHRSG●  Water Cycle Chemistry

Failure Mechanisms

Affected by Water Cycle Chemistry

CF

FAC SCC

Hydrogen Damage Pitting

Deposit Related – Overheating or

Caustic Gouging

Controlled parameters: Oxygen, pH, Conductivity Insoluble, Carryover, TDS

Independent of Cycle Chemistry

LCF/HCF, Weld Failure,

Thermal Fatigue, Creep,

Cold end tube corrosion

With established Action Plan, such as blow down, chemical dosing, etc. in case of deviation

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SafetyforDesignofHRSG●  All Volatile Treatment (Oxidizing) – AVT(O) ●  Reddish color is the Hematite (Fe2O3) formed on the wall

while the black color is mainly the Magnetite (Fe3O4). AVT(R) AVT(O

)

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SafetyforDesignofHRSG

●  HRSG Dry Lay-up Arrangement (Preservation) Ø  Dry Lay-up

Dehumidifier

FWP

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SafetyforInstalla0onofHRSG

●  WelderQualifica0onTest

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SafetyforInstalla0onofHRSG

●  Pre-WeldingInspec0on

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SafetyforInstalla0onofHRSG●  HRSGModuleMovingInandLiMing(HorizontalHRSG)

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Conclusion

●  Safety in design and installation is a must in securing the performance of HRSG within its design life (~30 years).

●  Design-code compliance is the minimum requirement only;

More attention to be paid on the HRSG failure mechanisms and the prevention measures in design stage.

●  Live monitoring of water chemistry & metal temperature with good maintenance /lay-up practice are required to ensure the operation is within design boundaries.

KopKhunKrap!ThankYou!