POWER July 2013 - 33

WATER MANAGEMENT
to be cooled below the ambient wet-bulb
temperature (the current limit of cooling
temperature), or even to the dew point temperature
of the incoming air, with substantially
lower water and energy consumption
requirements.
To achieve this low cooling temperature,
an airflow/tower fill arrangement
is proposed. Incoming airflow is drawn
through dry passages arranged in the fill
to be indirectly precooled by evaporating
water. The GTI team says this process differs
from conventional cooling tower fills,
which have wet evaporation channels only.
The advanced cooling tower fills have dry
channels between the evaporation channels
to allow incoming ambient air to be precooled
by evaporation to about dew point
temperature before the air turns into adjacent
wet channels to remove heat from the
water. The precooled air enables evaporation
at a much lower temperature, resulting
in cooled water temperature close to dew
point temperature and below the ambient
air wet-bulb temperature.
The lower temperatures and decreased
evaporative losses compared to conventional
cooling towers result in 15% to 20%
less cooling water and makeup water usage,
according to the GTI.
Based on modeling results, EPRI said
it expects to initiate engineering, fabrication,
and proof-of-concept evaluation of an
experimental section of cooling tower fill
this year, in collaboration with the GTI and
a commercial manufacturer. Parallel engineering
and economic modeling will be
done to compare cost and performance for
the advanced fill system and a conventional
cooling tower in both retrofit and new construction
applications at 500-MW plants.
This will include assessing possible heat
rate improvements associated with operation
at lower turbine back-pressure. Results
from these activities are expected to support
the launch of field demonstration projects
by the end of 2014.
Global Water Initiatives
Efforts are also under way outside of North
America to address water consumption issues.
NETL said that countries aggressively
implementing dry cooling technology include
China, South Africa, and Australia.
China has adopted dry cooling for many
new plants. The Huaneng Qinling Power
Plant provides an example of how dry
cooling is being used in China. In Shanxi
Province, water shortages are hindering
development of the central Shaanxi plain,
consequently, the 1,300-MW Huaneng
Qinling Power Plant uses an indirect dry
cooling system. The technology relies on a
traditional steam surface or jet condenser
and a circulating water system to transfer
waste heat to the natural draft concrete
cooling towers using air-cooled heat exchanger
bundles. The system also uses a
3. Air-cooled in South Africa. Eskom's six-unit, 3,600-MW Matimba Station uses direct
closed-circuit cooling technology, which enables it to use 0.1 liters of water per kWh produced.
Courtesy: Eskom
two-level cooling arrangement designed to
increase cooling efficiency. This two-level
arrangement was also used at the 1,320MW
Huaneng Shanxi ZuoQuan Power
Plant. The cost of the cooling system is
estimated at $33 million.
South Africa's state-owned electric utility,
Eskom, has implemented dry cooling
technology on power stations, where feasible,
despite the loss of efficiency, which
may be on the order of 1% to 1.5%, as at
the 750-MW Kogan Station in Australia,
which also uses dry cooling. Eskom operates
one of the world's largest indirect
dry-cooled power plants (the 4,116-MW
Kendal plant) and one of the largest direct
dry-cooled plants (the six-unit, 3,600-MW
Matimba Plant, see Figure 3).
The Kendal Power Station uses an indirect
dry cooling system. In this system,
water from a standard condenser is circulated
to the tower, where it enters a series
of heat-exchange elements at the base. Air
enters the bottom periphery of the tower,
passing over the heat-exchange elements.
Inside the tower, the heated air rises, pulling
in more cooled air. Fans are not required.
Water consumption at the Kendal
Plant is about 0.08 liters per kWh.
The Matimba Power Plant uses a direct
closed-circuit cooling technology. Water
consumption is about 0.1 liters per kWh.
That compares with about 1.9 liters on average
for wet-cooled stations. The choice
of dry-cooled technology for Matimba was
largely influenced by a scarcity of water
in the area.
In Australia, dry cooling is used in two
Queensland power stations (Millmerran
and Kogan Creek). The 850-MW supercritical
Millmerran plant opened in 2003
and is one of the most energy-efficient
plants in Australia. It uses air cooling to
condense steam from the turbine exhaust
and consumes 90% less water than conventional
coal-fired power projects. Recycled
wastewater from a nearby sewage
treatment plant is treated on site and used
as makeup water. All runoff water is contained
on site and reused. The 750-MW
supercritical Kogan Creek power plant in
Queensland began operations in 2007. It
has an air-cooled condenser that uses up to
90% less water than conventional plants.
Drought conditions are only one factor
driving worldwide interest in reducing
water consumption for electric power generation.
Competing uses make it almost
imperative for the sector to rethink how it
uses water and to take steps to reduce its
use as much as possible. ■
-David Wagman is executive editor
of POWER.
July 2013 | POWER
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