Gas Operations recently worked through a series of obstacles and challenges to complete a 2.2-mile-long pipeline to supply natural gas to fire combustion turbines at Black Dog Generating Station in Burnsville, Minnesota.
The 16-inch-diameter pipeline originally had been planned to run under a nearby lake and a set of railroad tracks on its final approach to the power plant on the banks of the Minnesota River, said David Butler, project manager.
The project fought challenge after challenge as it progressed from Northern Natural Gas Co.’s Cedar Station to the power plant. The crossing of Black Dog Lake was the final challenge that forced the team to regroup and work on an alternative route to the plant.
A hiatus then began in October 2017 as Gas Operations set about producing a matrix of possible alternatives. An open cut through the lake was considered, as were open-cut excavation routes on either the north or side of the plant.
Those options were then considered and discussed with other company engineers and contractors to compare costs and potential issues, he said. In the end, the south option was chosen, which would require coming under the railroad tracks and around the south side of Lake Black Dog, across a bridge on plant property and finally to the plant itself.
The auger bore under the railroad tracks was simple and short, Butler said, but hanging the pipeline from the bridge proved a bit more difficult. The main issue now, however, involved doing all this work in the middle of a Minnesota winter in far-from-ideal working conditions.
A new deadline of May 1, 2018, had been set in order for Black Dog to be available for summer demand. That meant proceeding with the alternative route throughout the winter and spring.
“It was a challenge in many ways,” he said. “The project faced so many issues from start to finish involving the weather, permitting issues, soil conditions and other discoveries onsite.
On top of all that, the Minnesota River decided to flood at times during the project, adding to concerns and worries.
“The negatives could have easily affected the team,” Butler said. “But we continued to work together, stayed positive and always found a way to keep moving forward.”
Energy Supply competitively bid the project and Xcel Energy Gas was selected as the winner. This project addressed the need for a new natural gas supply to the Black Dog in order to complete the conversion of the facility from coal-fired generators to a gas-fired facility.
The pipeline was required to allow for increased pressure and gas supply for a new unit at the plant, as well as increased control of overall system operations.
In order to minimize impacts to people and the environment, the pipeline followed existing transportation or electric transmission line corridors, and was primarily located within road right-of-way, on land owned by the City of Burnsville and land owned by Xcel Energy.
Finally, on April 24, natural gas began flowing through the newly installed Black Dog pipeline, bringing the project to a close in a welcomed victory.
“Between Gas Operations, Energy Supply, Engineering, Environmental Services, Community Relations, Siting and Land Rights and Corporate Communications, I regularly witnessed the partnerships that were critical to overcoming the significant challenges along the way,” Butler said. “Even when we were discouraged because of the various issues, internally we knew we could handle anything that arose.”
Black Dog, originally built as a coal plant, is the latest company power plant to be converted to a natural gas-fired plant. It followed the path of High Bridge, Cherokee and Riverside – power plants that went before Black Dog in the transition from coal to natural gas.
The first two original coal-powered units were replaced from 1999 to 2002 with a natural gas, combined-cycle facility. Then three years ago, Black Dog saw its two remaining coal units retired.
A new gas-fired combustion turbine now sits in the place of once coal-fired Unit Four, after its removal to make room for the larger, more powerful combustion turbine, now named Unit Six. Black Dog now has a total production of roughly 500 megawatts from three generating units.
“I’ve never been on a project that came across so many issues and challenges,” Butler said in summing up the pipeline-installation effort. “But we finished it well, and had it completed a few days ahead of the revamped schedule. People didn’t give up and fought through it until it was done.”
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