This site is best viewed with Internet Explorer 10, Firefox or Google Chrome. Please consider upgrading.×
• VIDEO
• WEBCASTS
• SUPPLIERS DIRECTORY
• EVENTS
• MAGAZINE
•HOME
•BOILERS
•COAL
•GAS
•RENEWABLES
•NUCLEAR
•ONSITE POWER
•O&M
•EMISSIONS
•BUSINESS
•WATER TREATMENT
•NEW PROJECTS
◦ ABOUT US
◦ ADVERTISE
◦ BLOGS
◦ CLASSIFIED ADS
◦ CONTACT US
◦ CURRENT ISSUE
◦ EVENTS
◦ MAGAZINE
◦ MOBILE
◦ NEWSLETTERS
◦ PAST ISSUES
◦ POWER GENERATION COMPANY NEWS
◦ PRODUCT SHOWCASE
◦ SPONSOR VIDEO CHANNEL
◦ SUBMIT AN ARTICLE
◦ SUBSCRIBE
◦ SUPPLIER SHOWCASE
◦ SUPPLIERS DIRECTORY
◦ TOPIC INDEX
◦ WEBCASTS
◦ WHITE PAPERS
◦ BOILER CONTROL SYSTEMS
◦ BURNER & COMBUSTION SYSTEMS
◦ GAS
◦ POLICY & REGULATION
◦ STEAM
◦ UPGRADES
◦ COAL RETROFITS & UPGRADES
◦ COAL NEW PROJECTS
◦ COAL O&M
◦ COAL EMISSIONS CONTROL
◦ COAL EQUIPMENT
◦ CLEAN COAL TECHNOLOGIES
◦ GAS RETROFITS & UPGRADES
◦ GAS NEW PROJECTS
◦ COMBINED CYCLE
◦ GAS O&M
◦ GAS EMISSIONS CONTROL
◦ GAS EQUIPMENT
◦ WIND
◦ SOLAR
◦ HYDROELECTRIC
◦ BIOMASS
◦ GEOTHERMAL
◦ MARINE
◦ REACTORS
◦ RETROFITS & UPGRADES
◦ WASTE MGMT. & DECOMMISSIONING
◦ NUCLEAR O&M
◦ NUCLEAR EQUIPMENT
◦ NPI LATEST ISSUE
◦ DIESEL & GAS ENGINES
◦ SOLAR
◦ COGENERATION
◦ WIND
◦ POLICY & REGULATION
◦ PLANT AUTOMATION
◦ PLANT OPTIMIZATION
◦ SAFETY & PROTECTION
◦ INSTRUMENTATION & CONTROLS
◦ TESTING
◦ PUMPS & VALVES
◦ O&M RETROFITS & UPGRADES
◦ AIR POLLUTION CONTROL EQUIP. & SERVICES
◦ DIAGNOSTICS & TESTING
◦ WATER TREATMENT EQUIPMENT & SERVICES
◦ ENERGY EFFICIENCIES
◦ EMISSIONS REGULATION
◦ FINANCIAL
◦ ENVIRONMENTAL
◦ BUSINESS POLICY
◦ M&A
◦ CONTRACTS & PROJECTS
◦ PERSONNEL-STAFFING
◦ PROJECT MANAGEMENT
◦ BUSINESS REGULATION
◦ COOLING WATER TECHNOLOGIES
◦ POLICY & REGULATION
◦ WATER TREATMENT
◦ WATER USAGE
◦ COAL
◦ GAS
◦ RENEWABLES
◦ NUCLEAR
◦ EMISSIONS
◦ BUSINESS
POWER ENGINEERING
Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control
08/01/2012
By Brad Buecker, Contributing Editor, and Dan Dixon, Project Engineer, Lincoln Electric System
Damage that can occur in steam generators due to in-leakage of contaminants during normal
operation is a subject of much discussion. However, very serious damage is possible in systems that
cycle on and off but are not shut down, laid-up or started up properly. Combined-cycle plants are
particularly susceptible to these problems because of typical numerous startups and shutdowns.
This article examines the most important issues with regard to off-line chemistry.
Oxygen is the Darth Vader of Poor Layups
Home More Coal Industry News Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control
Page 1 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power Engin...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
Both conventional and heat recovery steam generators (HRSG) are a complex maze of waterwall
piping, superheater and reheater tubing, boiler drums, and other equipment. When a unit is taken
off-line due to reduced load requirements or other issues, the water inside the circuits contracts in
volume. This volume reduction induces a slight vacuum within the system, which in turn draws in
outside air. Now, a stagnant condition with oxygen saturation, at least at water-air interfaces, has
been established.
Oxygen attack can be extremely serious for several reasons. The corrosion mechanism itself can
induce severe metal loss in those areas of high oxygen concentration.
The attack often takes the form of pitting, where the concentrated corrosion can cause through-wall
penetration and equipment failure in a short period of time. Also of major importance is that off-line
oxygen attack will generate corrosion products that then carry over to the steam generator during
startups. Deposition of iron oxides in the waterwall tubes leads to loss of thermal efficiency and,
most importantly, establishes sites for under-deposit corrosion. These mechanisms may include the
very insidious hydrogen damage, [1] acid phosphate corrosion in improperly treated units, and
caustic gouging.
Oxygen corrosion in a steam generator tube.
Source: www.power-eng.com.
Page 2 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power Engin...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
Another method by which oxygen can infiltrate steam generators is at startup when stored
condensate or fresh demineralized water is needed for filling or boiler top-off. Quite often, high-
purity water is stored in atmospherically-vented storage tanks. The water absorbs oxygen and
carbon dioxide, and may even become saturated with these chemicals. When the makeup is injected
into a cold steam generator, additional attack will occur.
Nitrogen Blanketing at Terry Bundy
At the Lincoln Electric System (LES) Terry Bundy combined-cycle plant, utility personnel have
implemented several of the most effective techniques to prevent oxygen ingress and corrosion. We
will examine these techniques plus some alternatives that can also be effective.
First and foremost is nitrogen blanketing during the last stages of shutdown and subsequent short-
term layups. Experience has shown that introduction of nitrogen to key points in the system before
the pressure has totally decayed will minimize ingress of air. Then, as the system continues to cool,
only nitrogen enters, not oxygen-laden air. Key points for nitrogen protection in HRSGs include the
evaporator, economizer, and feedwater circuits.
At Terry Bundy, primary power is produced by two GE LM 6000 combustion turbines and two Nooter-
Eriksen dual pressure HRSGs (no reheat) feeding a 26 MW steam turbine. Feedwater conditioning is
all-volatile treatment oxidizing [AVT(O)], with ammonium hydroxide injection to maintain feedwater
pH within a range of 9.6 to 10. High-pressure evaporator chemistry is based on EPRI’s phosphate
continuum guidelines, with tri-sodium phosphate as the only phosphate species and control within
a 1 to 3 parts-per-million (ppm) range. The HP evaporator pH control range is 9.5 to 10. Free caustic
concentrations are maintained at or below 1 ppm to minimize the risk of caustic gouging.
Following early operation of the combined-cycle units, plant personnel discovered oxygen pitting in
one of the high-pressure evaporators. The first step to mitigate this issue was installation of a
nitrogen blanketing system in 2005. One question that often arises is how best to store or generate
nitrogen. Certainly it can be provided from nitrogen bottles provided by local gas-supply or welding
firms, and liquid nitrogen is another possibility. LES personnel selected a different method, nitrogen
generation via a pressure-swing adsorption (PSA) system.
The process utilizes a carbon molecular sieve (CMS), which, when compressed air is introduced at
high pressure, adsorbs oxygen, carbon dioxide, and water vapor, but allows nitrogen to pass
through. Obviously, the nitrogen can then be collected in receivers for use as needed. At a pre-
selected interval, pressure is released from the unit allowing O2, CO2, and H2O to desorb from the
material, at which time these gases are vented off to the atmosphere. The table below outlines
nitrogen purity from this system as a function of production rate.
Page 3 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power Engin...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
The Terry Bundy N2-generator applies nitrogen, at a pressure of 5 psig, to the LP and HP drums
during wet layups, and the nitrogen is utilized to “push” water from an HRSG during dry layup
draining. A nitrogen pressure of 5 psig is maintained during the dry layup, provided no major tube
work is required. An obvious major concern with nitrogen blanketing, and the reasoning behind its
rejection at some plants, involves safety. Of course, elemental nitrogen is not poisonous, as it
constitutes 78 percent by volume of our atmosphere. However, an individual who enters a confined
space where nitrogen has not been purged may pass out nearly instantaneously due to lack of
oxygen. Death can occur within minutes.
An alternative to pressure swing adsorption is gas separation by membrane technology. In these
systems, compressed air flows along specialty hollow fiber membranes. The material allows oxygen
and water to pass through each membrane, but N2 does not penetrate and can be collected at an
outlet port. The literature indicates that this process can produce 99.5 percent pure nitrogen.
Another important point with regard to wet layup chemistry is periodic water circulation. This
minimizes stagnant conditions that can concentrate oxygen in localized areas to cause pitting.
Both Terry Bundy HRSGs have circulating systems installed on the high-pressure and low-pressure
circuits for use during wet layups. Each circuit utilizes one of two redundant pre-heater recirculation
pumps, which normally are in service during HRSG operation to mitigate acid dew point corrosion of
external circuits. Each pump provides approximately 100 gpm of flow per circuit. Valves and piping
have been added to provide to allow for seamless transition from layup circulation to normal
operation. Sample/injection systems are available to allow operators to test the layup chemistry for
pH and dissolved oxygen (using colorimetric ampules), and to inject ammonium hydroxide if the pH
needs to be raised. Also, modifications made in each boiler drum allow the layup water to bypass
the drum baffle, promoting circulation and minimizing short-circuiting via the downcomers. The
pumps are typically started once drum pressure is less than 50 psig, and remain in service for the
duration of the layup.
Page 4 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power Engin...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
A PSA nitrogen generator.
Source: www.balstonfilters.com
Dissolved Oxygen Removal from Condensate and Makeup Water
Very often, demineralized water is stored in atmospherically-vented storage tanks. Thus, oxygen-
laden water enters the steam generator during normal operation and even more critically during
boiler filling operation. In the latter case, the influx of cold, oxygen-saturated water can cause
severe difficulties. A possible method to minimize this problem is to limit oxygen ingress to storage
tanks, but this is typically a difficult proposition. Terry Bundy personnel selected another gas
transfer membrane technology to treat condensate return and makeup water.
The process is similar to the gas-gas transfer membrane process outlined above, but in this case the
carrier is water. As the liquid flows along the hollow fiber membranes in the vessel, gases pass
through the membrane walls but the water is rejected. The technology is capable of reducing
dissolved oxygen concentrations to less than 10 parts-per-billion (ppb). Most importantly, the
system eliminates introduction of air-saturated makeup (where the oxygen concentration may be
7.5 ppm, which is 75 times the recommended limit) during boiler fills.
Don’t Forget the Steam Turbine
Page 5 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power Engin...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
During my (author Buecker) 30-plus years in or affiliated with the power industry, I have seen many
instances where the condenser hotwell was allowed to remain moist, or even contain standing
water, during outages where the condenser vacuum was broken and air entered the condenser and
LP turbine. The combination of a moist-laden atmosphere and the salt deposits that collect on LP
turbine blades during routine operation can be quite damaging. Pitting and stress corrosion
cracking (SCC), two very harmful mechanisms, are two of the potential outcomes.
A very practical method to combat this corrosion, and one that has been adopted at Terry Bundy, is
desiccated air injection to the condenser during all but short-term layups (<72 hours).
This system is capable of providing 700 standard cubic feet per minute (SCFM) of 100oF air at 10
percent humidity to the condenser and low-pressure turbine. This flow can lower the relative
humidity from nearly 100 percent to less than 30 percent in just a few hours.
Results
In 2005, drum inspections showed significant pitting. It was after this inspection that the changes
outlined above were implemented. A repeat inspection in 2008 showed no new pitting.
Iron level monitoring, via particulate collection on 0.45-micron filters showed a significant decrease
in samples from the condensate pump discharge (CPD) and both LP and HP drums. Quicker startups
are now commonplace. Main steam cation conductivity drops to within the recommended guideline
(0.2 µS/cm) up to 1.5 hours sooner, and CPD cation conductivity consistently remains below 0.1
µS/cm, whereas in the past it might climb as high as 0.45 µS/cm. Of significant importance is that
the units can be left in wet layup for extended periods, which saves the plant six hours (over dry
layup) to reach full load per a dispatchers request.
References
1. Cycle Chemistry Guidelines for Shutdown, Layup and Startup of Combined Cycle Units with Heat
Recovery Steam Generators, EPRI, Palo Alto, CA: 2006, 1010437.
Page 6 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power Engin...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
Fuel Tech receives air pollution control contracts worth $3.6Mn
Fuel Tech Inc. has received multiple air pollution control (APC) contracts, worth approximately $3.6 million, from customers in China, Europe and the U.S.
Duke Energy completes ash excavation at W.S. Lee Steam Station
Duke Energy (NYSE: DUK)has submitted filings, to state regulators, outlining additional ash excavation plans for its W.S. Lee Steam Stationin Belton, South Carolina.
Missouri nuclear power plant expected to reopen soon
Ameren Corp.'s nuclear power plant in mid-Missouri is expected to reopen later Friday, a day ...
VIDEO: SCE&G places CA01 module at Summer nuclear plant
South Carolina Electric & Gas Co. (SCE&G) and its project partners placed a 2.4-milli...
Latest News
Dynamic Fluoride Ion Cleaning of IGT Parts
Everyone Friends
Products Showcase
RELATED ARTICLES
Recent user activity on Power Engineering:
Richard Goodwin shared:
Iran lawmakers said to need at least 60 days for nuke
deal :"ran's par…
Sat Jul 25 2015
arthur zhuo commented on:
Selecting the Right Pumps and Valves for Flue Gas
Desulfurization :"L…
Wed Jul 22 2015
Hoppy Hotchkiss commented on:
FPL plans to add new 1,600-MW combined-c
power plant :"NextEr…
Sat Jul 18 2015
Page 7 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power Engin...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
Court upholds commission's OK of plan to use trash for power
A state appellate court has upheld the Arizona Corporation Commission's approval of an electr...
Massachusetts Senate passes bill to prep for climate change
The Massachusetts Senate has approved a bill supporters say will help the state better adapt ...
Commission expects no major Michigan power shortfall in 2016
The Michigan Public Service Commission says it's unlikely there will be a significant power s...
Colorado officials ready for new carbon emission air rules
Colorado officials say they're ready for an expected EPA rule by next month that would requir...
Mississippi delegation attacks carbon dioxide limits
All members of Mississippi's congressional delegation say new federal carbon dioxide reductio...
The Dynamic Fluoride Ion Cleaning (DFIC) Process from Hi-Tech Furnace Systems is able to clean deep, narrow cracks of oxides by cycling between negative, atmospheric, and positive pressure.
ARCHIVED ARTICLES
2000 | 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 | 2008 | 2009 | 2010 | 2011 | 2012 | 2013
TOP BLOG POSTS
CSAPR the unfriendly EPA rule
Control Solutions
CNG is key for Oklahoma's Energy Future
Seizing the Opportunity
EPRI discusses implications of 316(b)
Obama pushes for Smart Grid
Power Engineering Look Inside >
Cover
Page 8 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power Engin...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
Weekly Coal Production Report
The Weekly Coal Production Report has been updated for the week ended July 18, 2015.
MORE POWER GENERATION NEWS
POWER ENGINEERING CURRENT ISSUE
V I E W T H I S I S S U E
V I E W A R C H I V E S
Navigating the Stormy Seas of Today's Power Grid
Power Gen Emergency Response Solutions
ASME and EuroNorm Compared for HRSG Design
Study and Design Considerations of HRSG Evaporators in Fast Start Combined Cycle Plants
Cycling Tolerance - Natural Circulation Vertical HRSGs
Application of CFD Modeling in HRSG Evase Design
Current Digital Issue
Featured Whitepaper
03/01/2014 Volume 118, Issue 3
Page 9 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power Engin...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
Return on Investment Analysis: The Economics of Regular Condenser Maintenance
Innovations in Cleaning Technology for Condensers: Case Studies
MORE WHITEPAPERS
BUYERS GUIDE CATEGORIES
Equipment rental
Heaters
clothing
repair
Prev 1 2 3 4 5 6 7 8 9 10 Next
BUYERS GUIDE PRODUCT LISTINGS
Predictive MaintenanceIPS field service technicians use state-of-the-...
Mitsubishi Gas Turbines
GenerationHub Quarterly Market Update: August 2015
( 08/26/2015 / 11:00 AM
Speakers Gary D. MooneyMichael J. Roush II, P.E.Richard MunsonTony HabibTyler Littler
Coal Ash Management & Storage
Speakers Kent Knutson
TransmissionHub Quarterly Market Update: June 2015
Webcasts
Page 10 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power En...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
MORE BUYERS GUIDE PRODUCT LISTINGS
Mitsubishi's advanced turbine technology includ...
Condition MonitoringTIGER® Monitoring System automates the knowledg...
Turbine Services LimitedTurbine Services Limited, a wholly owned subsid...
BUYERS GUIDE COMPANY LISTINGS
Caterpillar Power Plants
TEi Construction Services
Inc
Tech Development
Tower Performance Inc
Prev 1 2 3 4 5 6 7 8 9 10 Next
European Energy Transition – Embracing the Opportunity of Change
Speakers Kent KnutsonWayne BarberBarry Cassell
Power Generation Quarterly Market Update-Presented by GenerationHub
Speakers Gary E. FischerAnthony LaPorte
The Total Condenser Performance Workshop™: Leak Detection
Speakers Sue Briggum
Navigating the EPA’s New Coal Combustion Regulations
Speakers Connie SeniorRob Broglio
Emissions Control: Understanding your Options
MORE WEBCASTS
Power Industry Wire News
Page 11 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power En...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
Magnum Hunter Resources Announces Dismissal of Last Remaining Stockholder Lawsuit
Magnum Hunter Resources Announces Dismissal of Last Remaining Stockholder Lawsuit
FLIR Systems Announces Second Quarter 2015 Financial Results
FLIR Systems Announces Second Quarter 2015 Financial Results
SEACOR Holdings Announces Results for Its Second Quarter Ended June 30, 2015
SEACOR Holdings Announces Results for Its Second Quarter Ended June 30, 2015
Northwest Pipe Company's Water Transmission Group Awarded Section 15-2 of the Integrated Pipeline Project
Northwest Pipe Company's Water Transmission Group Awarded Section 15-2 of the Integrate...
California ISO Hosts Global Forum in Support of Clean Energy Vision
California ISO Hosts Global Forum in Support of Clean Energy Vision
MORE WIRENEWS
Court upholds commission's OK of plan to use trash for power
Commission expects no major Michigan power shortfall in 2016
Environmental groups ask judge to dismiss part of Duke suit
United States could slip from top tier of nuclear leaders, speakers warn conference
EDITORS PICKS
People who read this article also read the following:2D high-harmonic spectroscopy sees multiple molecular orbitalsFiber versus CO2 laser cutting
Page 12 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power En...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
Remineralization confusion... runs rampant in my mind. Where do I begin?The dental assistant’s guide to dental equipment maintenanceFive keys to successful PoE deployment
POWER ENGINEERING
TOPIC INDEX
View Power Engineering articles by topic, A-Z
Article Archives for Power Engineering Magazine
BUYERS GUIDE
• Categories• Companies• Products• Applications• Complete plant supply• Boilers• Valves• Finance and investment• Instruments, measuring• Component supply and manufacture• Air pollution control services• Monitoring equipment
MORE BUYERS GUIDE LISTINGS >>
CONTINUING EDUCATION
Professional Development Hours
To access a course listing associated to a specific topic listed below, click on the topic of choice from the list below.
• View All
Page 13 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power En...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
� � � �
Contact Us
Advertising
UTILITY
Current Issue
Online Archives
Register
Login
RESOURCES
Copyright © 2007-2014. PennWell Corporation, Tulsa, OK. All Rights Reserved. PRIVACY POLICY | TERMS AND CONDITIONS
• Balance of Plant• Coal-Fired Generation• Emissions Control• Gas-fired Generation• Hydro• Nuclear• Renewables• Rotating Machinery• Steam Generation
LATEST ENERGY JOBS
Power Generation Technician – Terror
Lake Hydroelectric FacilityKodiak Electric Association, Inc.
Country: United States
POSITION DUTIESKodiak Electric Association
(KEA) is seeking to fill the position of Power
Generation Technician at the Terror Lake
Hydroelectric Facility on Kodiak Island. This full-time position is responsible for servicing,
repairing, maintaining, and operating remote
generators and equipment at a...
View more Job Listings >>
Page 14 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power En...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...
Subscribe
About Us
PennWell EventsPennWell Websites
RSS Feeds
Buyer's Guide
Videos
Forgot Password
Site Map
Boilers
Coal
Gas
Renewables
Nuclear
Onsite Power
O&M
Emissions
Business
Water Treatment
New Projects
Topic Index
TOPICS
HydroWorld
Renewable Energy World
COSPP
TransmissionHUB
GenerationHUB
PennEnergy
Nuclear Power International
Power Engineering
Power Engineering International
PENNWELL POWER SITES
Page 15 of 15Combined-Cycle HRSG Shutdown, Layup, and Startup Chemistry Control - Power En...
7/26/2015http://www.power-eng.com/articles/print/volume-116/issue-8/features/combined-cycle-hrs...