POWER April 2012 - 58

PLANT COOLING
Clever " Helper " Tower Solves
Cooling Water Dilemma
Gone are the days when ocean or river water for once-through cooling of
a new power plant was assumed to be available. Today, more than 500
fossil-fueled and 38 nuclear plants use once-through cooling. However,
regulators in several states are aggressively pushing what is essentially
a ban on the use of once-through water cooling, forcing a conversion to
closed-cycle cooling.
By Jeffrey S. Mallory PE, Sargent & Lundy
T
he availability of open-cycle cooling
water was usually the determining
factor when siting a new power plant
in years past. Along the coasts, seawater
was available; river water was favored elsewhere.
If a suitable river wasn't available,
then a cooling lake was created. Technical
advances in cooling technology, often driven
by emerging regulatory requirements,
soon made historic cooling water sources
more problematic.
By the 1970s, new plants used large-scale
cooling towers for cooling a plant's condenser.
Today, plants that still rely on opencycle
cooling are exploring how to make the
transition to closed cooling systems because
of tightening regulatory requirements with
respect to protecting aquatic life, reducing
the thermal discharge into the water, and concerns
about protecting water supplies.
This article focuses on evaluating power
plant thermal discharges. A previous article
presented many of the aquatic protection technologies
available to plant owners to comply
with National Pollutant Discharge Elimination
System (NPDES) permit requirements
(see " CWA 316(b) Update: Fish Guidance
and Protection " in the October 2011 issue or
in the archives at www.powermag.com).
Cooling Water Trends
The responsibility for meeting Clean Water
Act (CWA) section 316(b) requirements to
protect aquatic life and manage thermal discharges
through technology-based solutions
is delegated to the states. The states manage
individual water discharges through the issuance
of NPDES permits.
The current trend concerning revisions in
NPDES permits requires reducing the amount
of thermal energy rejected or reducing the
cooling water outlet temperature, or both.
Short of reducing plant load, reducing the
thermal energy discharge is a euphemism for
converting all or part of the cooling water heat
58
rejection process from once-through cooling
to one of the many closed-cooling options.
The only other option is plant closure.
The challenge for designers asked to make
an assessment of the feasibility and economics
of a conversion from open to closed
cooling is that there is no one-size-fits-all solution.
Each plant presents a unique design
challenge. In fact, many plant owners have
received poor advice about cooling system
conversions, resulting in inaccurate cost estimates,
overly aggressive construction schedules,
and unrealistic operational expectations.
Additionally, plant owners often fail to consider
their plant's unique design and operations
features and are unaware of the many
new technology solutions now available.
Why Are Cooling Towers Added
or Replaced?
New cooling towers are added and existing
ones are replaced if the current cooling syswww.powermag.com
tem
heat rejection capability is inadequate or
emerging regulatory requirements make the
conversion a requirement.
In California, for example, the State Water
Resources Control Board (SWRCB) adopted
" Water Quality Control Policy on the Use
of Coastal and Estuarine Waters for Power
Plant Cooling, " which became effective Oct.
1, 2010. The policy effectively requires all
19 of the state's coastal plants (including two
nuclear plants) to transition to closed cooling
to meet the state's best technology available
requirement under CWA section 316(b).
Implementation plans prepared by fossil
plant owners were submitted to the SWRCB
on April 1, 2011, and implementation dates
are under negotiation. A " Scope of Work Report "
outlining consultant qualifications and
study requirements for the two nuclear plants
was completed on Nov. 7, 2011. Selection of
the consulting engineering companies to perform
the studies is pending (Figure 1).
POWER | April 2012
1. Cooling system conversions. California's San Onofre (pictured) and Diablo Canyon
nuclear power plants have been tasked with evaluating technologies and strategies to comply
with Clean Water Act section 316(b) best technology available requirements, including the option
of switching from an open cooling system to a closed or dry cooling system, among many
other requirements. Source: Southern California Edison/Nuclear Regulatory Commission

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POWER April 2012

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