steam cycle chemistry in air-cooled condensers · steam cycle chemistry in air-cooled condensers...
TRANSCRIPT
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Steam Cycle Chemistryin Air-Cooled Condensers
NV Energy ACC User’s Group * November 12-13, 2009 Andrew Howell * Xcel Energy
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Steam Cycle Chemistry Goal for ACC:minimize corrosion of carbon steel
Resulting in:
• minimal particulate transport (iron oxide)• minimal through-wall leaks
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Consequences of particulate transport
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• steam generating tube chemical cleans• steam generating tube failures• frequent filter element replacement
(if condensate filter)• resin contamination / difficult regeneration
(if condensate polisher)
Consequences of particulate transport
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Rapid loading of condensate filters
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Rapid loading of condensate polishers
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Air inleakage:
• potential vacuum deterioration (air binding)
• increased steam cycle contamination with oxygen and carbon dioxide
• rapid loading of anion resin (if polisher)
Consequences of through-wall leaks
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• early condensate• steam / condensate velocity• vacuum conditions
Iron Corrosion: contributing issues
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Early Condensate Environment(steam cycle pH ~9)
NH3
NH3
NH3
NH3
NH3
CO2
CO2
Condensate: pH ~8
Vacuum
NH3
NH3
NH3NH3 NH3
CO2CO2
Condensate: pH ~9
Vacuum
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Steam / Condensate Velocity:laminar flow in pipe (velocity vectors)
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Steam / Condensate Velocity:turbulent flow (velocity vectors)
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Flow
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Flow
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Mechanism of metal loss:2-phase flow-accelerated corrosion
(???)
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Chemistry optimization:Elevate pH in early condensate.
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Early Condensate Environment:increased ammonia feed (pH ~10)
NH3
NH3
NH3
NH3
NH3
CO2
CO2
Condensate: pH ~9
Vacuum
NH3
NH3
NH3NH3 NH3
CO2CO2
Condensate: pH ~10
Vacuum
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3
NH3 NH3
NH3 NH3
NH3
NH3
NH3
NH3
NH3
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-- or feed alternative less-volatile chemical (e.g. amine)
[ decomposition byproducts may generate concerns in some systems ]
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• alternative material to carbon steel– low-alloy or stainless steel– inserts / coatings– depends on mechanism confirmation
• design to minimize overall velocity and turbulence
Other resolution options for iron corrosion:
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ACC impact depends on unit type & design:
• combined cycle– more tolerant of particles and air ingress– high pH operation typically simple
• once-through supercritical– low tolerance for particles– impact of leaks on polisher– impact of high pH operation on polisher
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combustion turbine-
generator
combustion chamber
heat recovery steam generator
turbine-generator
steam
condenser
Combined Cycle Power Plant
drums
blowdown
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Combined Cycle Power Plants
• steam drums / blowdown for some contaminant removal
• frequent operation in cycling mode• no polisher or filter typically included
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condenser
hotwell
boiler
HPturbine
IPturbine
LP turbine
DA LP heatersHP heaters
econ
SH
RH
crossover
condensatepump
boilerfeed pump
attemperationsteam
steam
Supercritical Once-through Power Plant
polisher
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Supercritical Once-through Power Plants
• superior water quality required (polisher and condensate filter)
• high pH and air inleakage impacts polisher performance and costs
• normally in baseload operation mode
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ACC Design & Construction: Chemistry Impacts
• weld debris and fluoride contamination
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Weld flux debris
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ACC Design & Construction: Chemistry Impacts
• weld debris and fluoride contamination• iron oxides / miscellaneous crud
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Iron oxides / miscellaneous construction crud
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ACC Design & Construction: Chemistry Impacts
• weld debris and fluoride contamination• iron oxides / miscellaneous crud• improper galvanic tube coating
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Improper Galvanic Tube Coating
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ACC Design & Construction: Chemistry Impacts
• weld debris and fluoride contamination• iron oxides / miscellaneous crud• improper galvanic tube coating• cleanup for initial unit startup
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Initial Operation: System Cleanup
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Initial Operation: System Cleanup
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Initial Operation: System Cleanup
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Initial Operation: System Cleanup
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Initial Operation: System Cleanup
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Initial Operation: System Cleanup
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ACC Design & Construction: Chemistry Impacts
• weld debris and fluoride contamination• iron oxides / miscellaneous crud• improper galvanic tube coating• cleanup for initial unit startup• upper duct access for future inspections
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Ideal Upper Duct Access
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Non-Ideal Upper Duct Access
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ACC Design & Construction: Chemistry Impacts
• weld debris and fluoride contamination• iron oxides / miscellaneous crud• improper galvanic tube coating• cleanup for initial unit startup• upper duct access for future inspections• condensate deaerator
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Condensate Deaerator
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Condensate Deaerator
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ACC Design & Construction: Chemistry Impacts
• weld debris and fluoride contamination• iron oxides / miscellaneous crud• improper galvanic tube coating• cleanup for initial unit startup• upper duct access for future inspections• condensate deaerator• upper duct isolation
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Upper Duct Isolation
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Upper Duct Isolation
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Guidelines for Off-Line Inspection of Air Cooled Condensers
- document through the PowerPlant & Environmental Chemistry
research subcommittee of ASME
Air-Cooled Condenser Interest Group- email communications & discussions
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Conclusions
Steam Cycle Chemistry is an important factor to be considered in the design and operation of power plants with air-cooled condensers.