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Powering Up in Cross, S.C.
Santee Cooper is Building Two Additional
Units at Cross Generating Station
By Carter Langston
Current population projections estimate that a million more
people will move to South Carolina over the next 20 years,
and one electric utility is investing in needed infrastructure
improvements to meet ever-increasing power demands.
And it's doing it in the Lowcountry, where the water table
is shallow and hurricanes and earthquakes are possible.
South Carolina Public Service Authority/Santee Cooper Power
of Moncks Corner, S.C., is building two coal-fired generating
stations in Cross, S.C., at a total cost of $1.4 billion.
"At the moment, we have more contract workers onsite
than Santee Cooper employees," said Laura Varn, vice
president of corporate communication and media relations for
Santee Cooper Power. The utility operates fossil-fueled, nuclear
and hydroelectric generators and produces energy for all 46
counties of South Carolina.
Varn estimated that the utility serves 48 percent of the people
in the state. It directly powers about 150,000 homes and businesses
and also generates power for 20 electric cooperatives in the
state, which means the utility ultimately powers roughly 800,000
to 900,000 households.
The company employs 1,740 people. And there are 1,800 contract
workers onsite building the Cross Generating Station 3 and
Cross Generating Station 4. Both new generating units are
located along a linear configuration with two older generating
units on a 3,000-acre site between lakes Marion and Moultrie
in Berkeley County.
Currently, the Cross Generating Station produces 1,160 megawatts
of electricity per hour. The additional capacity that units
3 and 4 will produce when they are commissioned will bring
this station's total output to 2,360 megawatts per hour.
While Santee Cooper is the general contractor, the projects
employ 20 different contractors on a multiprime concept, including
WorleyParsons of Reading, Pa., as the engineer and managing
contractor, said Jack Holden, Santee Cooper's manager of station
construction. There are about 50 subcontractors also onsite,
he said.
"We coordinate all the collateral work internally and
manage about 140 specific contracts," Holden added.
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Project Details
Both of the new units, like their two older counterparts at
the Cross Generating Station, are pulverized coal-fired plants
and are designed to meet Title I air quality compliance requirements.
Unit 4, though it adds the same 600 megawatts of generating
capacity as Unit 3, represents the greater cost of the expansion.
Unit 4 is estimated to cost about $755 million and is scheduled
to begin producing electricity in January 2009.
Construction on Unit 3 will cost about $675 million and is scheduled
for completion in January. Holder attributes the $80 million
additional cost for Unit 4 to the time costs associated with
increased equipment and labor costs.
Construction started on Unit 3 on Feb. 23, 2004. Unit 4 was
approved for construction on Feb. 24, 2004, and has been generally
built in tandem with its linear counterpart.
Varn said construction is on budget, but there have been some
challenges.
New generating facilities must meet strict air quality standards.
The water table is about 4 ft. below surface here, hurricanes
tend to visit with some frequency and the Cross Generating Station
sits atop a fault line that nearly leveled Charleston in 1886.
To meet the exacting requirements of Title I air quality standards,
Santee Cooper is installing state-of-the-art scrubber units
and pollution control equipment to reduce nitrogen oxide and
sulfur dioxide. Company officials said other generating stations
throughout the state will be retrofitted with similar equipment.
and by 2009, Santee Cooper anticipates the controls will reduce
the pounds per unit of electricity generated for NOX by 70 percent
and reduce SO2 by 50 percent.
Because the Cross Generating Station's four generating units
sit within the possible strike zone of hurricanes and earthquakes,
current building codes require heavy steel and prestressed concrete
piles that are driven to the limestone layer. The foundations
of the 20 new structures for units 3 and 4, which spread across
roughly 12 acres on the Cross Generating Station's 3,000-acre
site, comprise 20,000 prestressed concrete piles.
The 20 buildings include two turbine buildings, which are constructed
lengthwise and tie in to the existing turbine building, connecting
each of the four generating units along a .25-mi. stretch. There
also are two coal silos and bay areas; two boiler buildings;
two selective catalytic reduction structures; two electrostatic
precipitators; two flue gas desulphurization buildings; one
chimney with two flues that serves both units 3 and 4; reagent
preparation structure; limestone handling structure; two fly
ash silos; gypsum processing building; and two cooling towers.
Each structure is built to sustain extreme conditions.
"According to the building codes, units 3 and 4 are constructed
to withstand up to 120 mph sustained winds and can endure seismic
movement," Holden said. "You can physically see the
difference between the new units and the older two units (built
according to different code requirements)."
In the chimney, for example, there are about 660 tons of reinforcing
steel and about 5,000 cu. yds. of concrete in the 464-ft. structure.
The chimney that supports units 1 and 2 stands about 625 ft.
and was built according to earlier building codes, Holder said.
He said the biggest difference in the building codes is the
foundation construction. The first two units, built in 1983
and 1995, are built on a socketed caisson foundation system
drilled into the limestone layer and filled with concrete. Current
codes require the prestressed concrete pilings. |
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