Steam Cycle Chemistry in Air-Cooled Condensers. NV Energy ACC User s Group * November 12-13, 2009 Andrew Howell * Xcel Energy

Transcription

1 Steam Cycle Chemistry in Air-Cooled Condensers NV Energy ACC User s Group * November 12-13, 2009 Andrew Howell * Xcel Energy

2 Steam Cycle Chemistry Goal for ACC: minimize corrosion of carbon steel Resulting in: minimal particulate transport (iron oxide) minimal through-wall leaks

3 Consequences of particulate transport

4 Consequences of particulate transport steam generating tube chemical cleans steam generating tube failures frequent filter element replacement (if condensate filter) resin contamination / difficult regeneration (if condensate polisher)

5 Rapid loading of condensate filters

6 Rapid loading of condensate polishers

7 Consequences of through-wall leaks Air inleakage: potential vacuum deterioration (air binding) increased steam cycle contamination with oxygen and carbon dioxide rapid loading of anion resin (if polisher)

8 Iron Corrosion: contributing issues early condensate steam / condensate velocity vacuum conditions

9 Early Condensate Environment (steam cycle ph ~9) NH 3 Vacuum Vacuum CO 2 NH 3 NH 3 CO 2 NH3 NH 3 NH 3 NH 3 NH 3 NH 3 CO 2 CO 2 NH 3 Condensate: ph ~8 Condensate: ph ~9

10 Steam / Condensate Velocity: laminar flow in pipe (velocity vectors)

11 Steam / Condensate Velocity: turbulent flow (velocity vectors)

12 Flow

13 Flow

14 Mechanism of metal loss: 2-phase flow-accelerated corrosion (???)

15 Chemistry optimization: Elevate ph in early condensate.

16 Early Condensate Environment: increased ammonia feed (ph ~10) NH 3 Vacuum NH 3 Vacuum NH 3 NH CO 2 3 NH 3 NH 3 NH 3 NH 3 CO 2 NH 3 NH 3 NH3 NH 3 NH 3 NH 3 NH 3 Condensate: ph ~9 NH 3 NH 3 NH 3 NH 3 NH NH 3 3 NH NH NH CO 2 CO NH 2 NH 3 NH 3 3 Condensate: ph ~10 NH 3 NH 3

17 -- or feed alternative less-volatile chemical (e.g. amine) [ decomposition byproducts may generate concerns in some systems ]

18 Other resolution options for iron corrosion: alternative material to carbon steel low-alloy or stainless steel inserts / coatings depends on mechanism confirmation design to minimize overall velocity and turbulence

19 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

20 Combined Cycle Power Plant condenser turbine-generator steam drums heat recovery steam generator combustion chamber combustion turbinegenerator blowdown

21 Combined Cycle Power Plants steam drums / blowdown for some contaminant removal frequent operation in cycling mode no polisher or filter typically included

22 Supercritical Once-through Power Plant crossover HP turbine IP turbine LP turbine steam SH condenser boiler econ RH steam attemperation hotwell condensate pump HP heaters boiler feed pump DA LP heaters polisher

23 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

24 ACC Design & Construction: Chemistry Impacts weld debris and fluoride contamination

25 Weld flux debris

26 ACC Design & Construction: Chemistry Impacts weld debris and fluoride contamination iron oxides / miscellaneous crud

27 Iron oxides / miscellaneous construction crud

28 ACC Design & Construction: Chemistry Impacts weld debris and fluoride contamination iron oxides / miscellaneous crud improper galvanic tube coating

29 Improper Galvanic Tube Coating

30 ACC Design & Construction: Chemistry Impacts weld debris and fluoride contamination iron oxides / miscellaneous crud improper galvanic tube coating cleanup for initial unit startup

31 Initial Operation: System Cleanup

32 Initial Operation: System Cleanup

33 Initial Operation: System Cleanup

34 Initial Operation: System Cleanup

35 Initial Operation: System Cleanup

36 Initial Operation: System Cleanup

37 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

38 Ideal Upper Duct Access

39 Non-Ideal Upper Duct Access

40 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

41 Condensate Deaerator

42 Condensate Deaerator

43 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

44 Upper Duct Isolation

45 Upper Duct Isolation

46 Guidelines for Off-Line Inspection of Air Cooled Condensers - document through the PowerPlant & Environmental Chemistry research subcommittee of ASME Air-Cooled Condenser Interest Group - communications & discussions

47 Conclusions Steam Cycle Chemistry is an important factor to be considered in the design and operation of power plants with air-cooled condensers.