POWER September 2015 - 40

TOP PLANTS
POWER POINTS
Winning Attributes
Innovative cold-weather
reclaimed-water cooling system
also cuts wastewater discharges
into local river
Largest gas-fired plant in gas-rich
Alberta but also one of the most
efficient fossil-fueled plants in
Western Canada
Designed to ensure reliable
operation across a wide range of
temperature extremes
budget with zero lost-time accidents. Craft
labor peaked at 950, of which 90% were
based in Alberta.
The Shepard Energy Centre is an 800MW,
two-unit combined cycle plant, making
it the largest gas-fired power plant in Alberta-large
enough to supply more than half
the electricity used in Calgary. Two 240-MW
MHPS 501G gas turbines feed two duct-fired
Vogt Power International triple-pressure
heat-recovery steam generators, which feed
a single 320-MW MHPS reheat steam turbine,
all of these provided as part of MHPS's
Power Island.
Cooling is provided by a Thermal Engineering
International wet surface condenser
and a cooling tower supplied by International
Cooling Tower. Selective catalytic reduction,
also supplied by Vogt, is used to keep NOx
emissions at 3 ppm. The plant manages an
impressive 6,221 kJ/kWh net heat rate.
A video about the plant is available at
https://youtu.be/Tk5U3MEhoI0.
Challenges
Several key goals had to be met in building
the plant.
The southern Alberta grid requires that
power plants in the Calgary area be designed
in a manner such that no single failure mode
causes an instantaneous loss of more than one
generator to ensure grid stability. Because of
this, additional control system redundancy
was built in to ensure the entire facility will
not go offline at once.
The next constraint was the extreme ambient
weather conditions. Weather in the
Calgary area is notoriously unpredictable,
often experiencing 20F- to 30F-degree temperature
swings in a few hours, as a result of
the region's Chinook winds. Temperatures
in the summer can exceed 90F while falling
well below 0F in the winter. The area is also
subject to violent summer thunderstorms,
often accompanied by hail, and heavy snow
in the winter.
As a result, the plant had to be engineered
to withstand prolonged freezing temperatures
in the winter while still operating efficiently
in hot weather. The plant's design basis is
-40C. Underground ducting and piping had
1. Deep freeze. The Shepard Energy Centre gets its cooling and process water from a local
waste treatment plant via a 14-kilometer reclaimed water pipeline. To prevent frost upheaval during
winter, the pipeline had to be buried well below the frost zone. Courtesy: ENMAX
to be buried at least 2.7 meters below the
surface to prevent frost upheaval. Where this
was not possible, piping was protected with
thermal board. All outdoor equipment, such
as condensers, transformers, and air intakes,
had to be designed for reliable operation in
sub-zero weather.
Weather concerns affected another key
constraint, which was minimizing the environmental
impact. Rather than draw on area
freshwater resources, ENMAX decided to
use reclaimed water for process and cooling
needs. The plant takes up to 14 million liters
per day of tertiary output from Calgary's Bonnybrook
Wastewater Treatment Plant through
a 14-kilometer underground pipeline (Figure
1). Once at the site, it's purified further before
use. This makes Shepard the first power
plant in Alberta to use reclaimed water.
The water sensitivity doesn't end with the
intake. Rather than being discharged into the
area watershed, site runoff is directed into
a detention pond using a bioswale process,
whereby the water naturally percolates back
into the ground. In addition to avoiding added
stress on freshwater supplies, this approach
also reduced wastewater discharge into the
Bow River, which is a key local water resource.
Again because of the winter weather,
the reclaimed water pipeline had to be buried
below the frost zone.
The final constraint was the location of the
site, which is in a new mixed-use industrial
park within city limits. That meant extra efforts
were necessary to reduce plant noise as
well as the visual impact of the facility.
Looking Ahead
The Shepard Energy Centre is ahead of the
curve on future demand, but that won't last
forever. It's currently supplying about 7%
of demand on the area grid, but with much
of the province's 3,600 MW of coal-fired
power slated for retirement, more will have
to be done. Through another joint venture,
ENMAX and Capital Power are currently developing
an even larger gas-fired plant near
Edmonton: the proposed 1,060-MW Genesee
4 and 5 project.
" With the increasing demand for electricity
in Alberta, ENMAX set a course to meet
that need by providing cleaner, more efficient
electricity generation to Albertans. The natural
gas-fuelled Shepard Energy Centre adds
800 MW to the Alberta grid and reduces
Alberta's reliance on coal-fired generation, "
Dave Rehn, ENMAX's executive vice president,
generation, told POWER. " We continue
to develop plans to invest in natural gas and
renewable generation to support Alberta's
transition to cleaner electricity sources. " ■
-Thomas W. Overton, JD is a POWER
associate editor.
40
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POWER | September 2015

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POWER September 2015

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