POWER October 2015 - 28

TOP PLANT
Ottumwa Generating Station,
Ottumwa, Iowa
Owner/operator: Interstate Power & Light Co. (a subsidiary of Alliant Energy) and MidAmerican Energy
Co. (a subsidiary of Berkshire Hathaway Energy) / Alliant Energy
Courtesy: BWM
Alliant Energy recently completed a major renovation of the Ottumwa Generating
Station to improve air quality, plant reliability, and efficiency. By doing so it also reduced
its carbon footprint by ~5.6%.
Dr. Robert Peltier, PE
O
n August 3, 2015, the U.S. Environmental
Protection Agency finalized its
proposed Carbon Pollution Standards
for Existing Power Plants (known as the Clean
Power Plan, CPP). The stated purpose of the
CPP is to reduce CO2 emissions in the power
sector by establishing unique state target emission
rates to be met by 2030. The targets are
based on the " best system of emission reduction, "
which uses three " building blocks " designed
to " cost effectively " and " efficiently "
reduce CO2 emissions.
The first CO2 reduction building block
is to make coal-fired power plants more efficient.
However, increasing plant efficiency
and output normally requires a New Source
Review in order to obtain a revised Prevention
of Significant Deterioration (PSD) permit,
which utilities have been reluctant to pursue.
Applying for a new PSD permit inevitably
meant regulators would require installation
of expensive best available control technologies,
such as flue gas desulfurization.
In 2010, Alliant Energy began the arduous
process of developing a new long-term energy
resource strategy that would rebalance its
power generation portfolio to ensure its ability
to provide reliable, cost-effective service
28
for the next 30 years. Alliant Energy's Iowa
utility announced in August 2012 its strategy,
which included, in part, retiring older,
less-efficient coal-fired generating stations;
burning more natural gas instead of coal; and
renovating strategically important coal-fired
stations to reduce emissions and increase
efficiency. A key milestone was reached on
January 12, 2012, when the Iowa Department
of Natural Resources issued the Ottumwa
Generating Station (OGS) a PSD Construction
Permit to allow construction of the air
quality control system (AQCS) and other efficiency
improvements.
An Optimized Project Plan
OGS is an important electricity resource for
Alliant Energy, and will remain one, well into
the future. Located about 100 miles southeast
of Des Moines, the unit was previously
rated at 675 MW nominal output and features
a single unit that burned Wyoming Powder
River Basin coal in a Combustion Engineering
(now Alstom Power) tangentially fired
boiler, installed in 1981. The boiler, operating
at 2,400 psig, 1,005F/1,005F superheat
and reheat steam temperatures, was equipped
with low-NOx burners and was originally inwww.powermag.com
stalled
with a hot-side electrostatic precipitator
(ESP) for particulate control. Seven mills
supply fuel to seven levels of burners in the
boiler. The boiler also features two levels of
separated overfire air to stage combustion to
reduce NOx. An Emerson Ovation distributed
control system handles the plant's automation
tasks, and a NeuCo neural net and historian
provide real-time combustion and boiler
cleaning optimization.
The OGS project is a model for simultaneous
emissions reduction, capacity increase,
and plant efficiency improvements.
The required upgrades at OGS were substantial.
First, the emissions reduction portion,
detailed below, was significant. Second,
Alliant's Comprehensive Asset Management
Program (CAMP) was created to improve
plant safety, optimize plant heat rate, and
improve plant reliability. A key portion of
the project was to modernize the existing
steam turbine, which included replacement
of all four of the turbine rotors and associated
steam path components. Alliant Energy
completed additional efficiency and reliability
improvements that were identified and
completed as part of CAMP.
Burns & McDonnell (B&M) was retained
POWER | October 2015

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POWER October 2015

Table of Contents for the Digital Edition of POWER October 2015