POWER April 2012 - 59

PLANT COOLING
Noncoastal regions appear to be more
concerned with reducing the thermal load
placed on a river (million Btu/hr) and
the temperature of the cooling water discharge.
A good example of a plant that
has made a conversion is PPL's Brunner
Island plant, located in York County, Penn.
The owners of the three-unit, 1,546-MW
plant invested approximately $100 million
to install perhaps the largest forced-draft
cooling towers in the world to reduce the
thermal loading and discharge temperature
to the Susquehanna River. The new cooling
towers began operation in April 2010
(Figure 2).
Before You Make the Switch
A feasibility study for a potential oncethrough
cooling system conversion to a
closed system in order to reduce cooling
water discharge temperature and thermal
load begins with asking questions designed
to help develop an understanding
of the actual condenser heat exchange requirements
and the current state of repair
of plant equipment. It makes no sense to
add new equipment until all the possible
plant performance has been extracted from
existing equipment.
Other questions will help determine
if the existing cooling water system performance
is marginal or if it has any surplus
capacity. If a cooling water system
has been the victim of inadequate maintenance,
then a renovation may be costeffective
because a smaller cooling tower
or a less-complicated solution may be all
that is needed. What about the condition
of the steam turbine? A steam turbine upgrade
or overhaul may reduce the thermal
duty on the cooling water system, improve
steam turbine reliability, and produce a net
increase in plant efficiency, avoiding additional
major plant cooling water system
modifications.
Many other questions must be answered
before the true condition of a plant's cooling
water system can be determined and repairs
or upgrades can be recommended. Other areas
of the existing plant must be explored for
degradation of the existing cooling water system
caused by:
■ Intake system fouling (intake screens, intake
area silt deposition, and mechanical
equipment degradation).
■ Fouling and pluggage of cooling water
system pipelines.
■ Cooling water pump performance degradation.
■
Condenser tube fouling, failure, and
pluggage.
2. Cooling tower retrofit completed. PPL's Brunner Island power plant added forceddraft
cooling towers to reduce the thermal loading and discharge temperature of the cooling
water discharge to the Susquehanna River. The 34-cell cooling tower requires four 3,500-hp
pumps to deliver about half a million gallons every minute. The cooling towers are used during
the nine warmest months of the year, from March through November. Courtesy: PPL
■ Chemical treatment regimens that are
limited due to direct discharge to a body
of water.
■ Steam turbine blade erosion or copper
plating of blades (resulting in higher cooling
system heat load).
■ Impact on the cost of operations and
maintenance.
Some facilities that already have a closed
cooling water system are also being asked
to reduce thermal loading and cooling water
discharge temperatures. If your plant falls
into that category, then you must also explore
other potential sources of system degradation
and repairs required before identifying new
system upgrades. Sources of degradation of
existing cooling towers include:
■ Cooling tower fill fouling (including biofouling,
scaling, improper spray patterns,
trash, or silt pluggage).
■ Regular tower structural or piping-related
failures due to age, biological, and chemical
attack on members.
■ Operation at high cycles of concentration
resulting in material failures, large mineral
deposits, and the like.
■ Legacy issues such as cooling towers
that never met original performance
guarantees.
■ Lack of discipline in circulating water
chemistry treatment or insufficient makeup
water pretreatment.
■ Repeating failures of unreliable components.
Finally, in addition to the previously mentioned
issues, the engineering analysis must
consider several additional factors, such as:
■ Several (10 or more) years of historic
weather datasets for the site to allow projection
of cooling tower performance. This
may be provided from site records or from
nearby data collection sites.
■ Historic station data on cooling system
performance and/or performance tests of
towers, circulating water pumps, condensers,
and steam turbine(s).
■ Recent evaluations of current cooling system
performance.
■ Plant operability limitations (such as turbine
backpressure limits, vacuum system
capability, and water usage restrictions).
■ Project financial inputs (including required
return on investment and financing
interest rates).
■ Value of electrical power, preferably on a
monthly basis.
Over the years, we have seen utilities proceed
directly with a new cooling tower project
without a thorough analysis that considered
April 2012 | POWER
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POWER April 2012

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