Power surge

Two $100 million Lafayette, La., plants provide electricity boost

By Karla Wall

TIC of Steamboat Springs, Colo., recently completed construction on the five-acre Hargis-Hebert Power Generation Plant, located in south Lafayette. The plant began commercial operation in June, just in time for the peak energy-use season.

The project, the second phase of a two-phase expansion totaling about $100 million, added 100 MW of power to the south Lafayette area, said Randy David of Lafayette Utilities System.

The first phase, involving an 8-acre site north of Hargis-Hebert, added 100 MW of power as well.

Together, the projects have boosted the power output for the area from 500 to 700 MW, said project engineer Randy Stephenson with TIC.

The price tag for the north site was $51 million and cost of construction at the south site was $49 million. The project was undertaken to boost power to the rapidly growing area, David said.

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"R.W. Beck, an architectural firm, did a study for us a few years ago, which said that the city (of Lafayette) would reach maximum capacity by this year," David said. "We've had a lot of growth in the area and this project was taken on to deal with that problem."

The site was built up using roughly 6,000 cu. yds. of structural fill to enhance drainage and waste discharge, Stephenson said. Cecil Perry Construction of Lafayette handled the site development.

"About half the site was developed," Stephenson said. "The rest was left as is."

A 100- by 120-ft., 3-ft.-deep retention pond was also excavated. The pond will handle excess stormwater, Stephenson said. Excavation was accomplished with trackhoes, skid steer lever excavators and front-loaders. The pond has the >> capacity to store 40,000 cu. ft. of water.

Excess fill dirt from the foundations of the power units was taken off the site, David said.

"Most of it was given to local residents or dirt haulers," David said. "The contractor was responsible for disposing of all waste materials."

The central-cycle power generation plant consists of two GE LN 6,000 Brush generators, each of which produces 50 MW of power. It also includes a chilled water unit, a waste treatment plant and an electrical control room.

Two change orders were involved in the project, including the switch to Brush generators and the decision was made to install gas heaters.

The turbine generator units, roughly 25 ft. by 120 ft. and 40 ft. high, were pre-assembled in sections and trucked into the site, Stephenson said.

"That really speeds up construction," he said. "This was a pretty straightforward modular construction."

The generators are housed in 13-ft. 6-in. by 28-ft. metal enclosures with structural steel framing, David said. The metal siding is roughly .75 in. thick. The housing for the gas turbine units is 13 ft., 6 in. by 29 ft., with exhaust stack of 60 ft.

The modular units rest on 4- to 6-in. concrete slabs formed using 4,000 cu. yds. of 4,000 psi concrete, David said. The slab sits on 24 concrete pilings driven to a depth of 40 ft.

The preassembled units were trucked in and hoisted into place using 150-ton and 200-ton cranes, Stephenson said.

"The structures were bolted into place using standard structural high-tensile strength bolts," he added.

David said the turbine and generators arrived contained in the metal housings and were attached to a skid.

"The synchronous condensers were installed on the foundations, and the metal housing was attached and bolted to the turbine and generator enclosure," he added.

All metal housings were insulated, and sound-proofing was provided with the installation of 3-in.-thick closed cell polyeurethane foam surrounding the equipment, Stephenson said.

"It's in a semiresidential area so noise control was important," he added.

Compressed air hydraulic starters were installed for each generator.

The site also holds a chilled water unit that feeds into a cooling basin with a cooling tower.

The water treatment plant, housed in a prefabricated metal building measuring roughly 60 by 100 ft., takes in city water to the plant and treats it for use in the generators. The reverse osmosis plant also consists of a booster pump and a chemical injection system, Stephenson said.

Two compressed air hydraulic starters have also been installed in the system, Stephenson said.

"One of those is redundant," he said. Two black-start generators have also been installed. "If we're totally off-grid, we can use the generator to start the equipment. We can fire the turbines and power up the units."

The electrical control building is a 20- by 60-ft. prefabricated modular metal structure with structural steel framing. It was trucked in in two pieces and assembled onsite.

The building houses the electrical equipment and switch gears.

"It's the brains of the plant," Stephenson said.

The plant was designed and the site developed to handle the addition of one or two more units, David said.

"We can add one or two more units later if needed, but we don't expect to need additions for 20 years or so and by then the technology will probably be completely different," he added.

The project, as was the case with most construction projects in the area, was hampered in the wake of hurricanes Katrina and Rita.

"We experienced some delays, and some labor shortage," David said. "There was a lot of overtime pay and things of that nature. A lot of our skilled laborers went to work in hurricane-effected areas, leaving us with a shortage."