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How Micro-Tunneling Made Way For N.Y. City Hall's Fuel Cell

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Photo by ENR/Tom Sawyer
The City Hall renovation in New York City includes a fuel cell near the building that will be generating most of the its daily load of electricity. Tricky tunneling work paved the way for the box, which has also attracted controversy.
Photo by Tom Sawyer/ENR
A trench helps bring in upgraded ConEd electrical feeds before it turns about 30 for a 200-ft run to City Hall, which was part of construction management firm Hill International's plan to build new power lines while working around the archaeological hotspots in lower Manhattan.
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New York City's seat of government is about to pull back from its main electricity source and start running base-load operations from a "Bloom box," a fuel cell that sits next to City Hall and generates electricity from its own natural-gas feed.

When the installation of the specially equipped fuel cell, supplied by Bloom Energy from their San Jose, Calif., facilities, is complete this month, the 201-year-old City Hall building will have a new source of just under 100 kilowatts of electricity from the box, according to city and project officials. Electrical utility ConEd is still supplying peak loads, however. The Bloom box is part of Mayor Mike Bloomberg's (R) green initiative as well as efforts to harden City Hall infrastructure in the aftermath of Superstorm Sandy.

Although the distributed generation (DG) Bloom-box project is just one facet of the city's multi-phase, $148-million renovation plan, it is certainly not the first DG project in New York City. But it may be more controversial than other forms of distributed generation that ConEd says are in use across New York City.

As ENR has reported, the Bloom Energy boxes use solid-oxide fuel cells, which, unlike many others, run off natural gas instead of pure hydrogen. The boxes have generated controversy as well as electricity, primarily over whether it is fair to call them "green" or just cleaner than other forms of generation that use fossil fuels.

Despite the questions about the Bloom boxes, and whether they are cheaper and cleaner technology, the work preparing the natural gas feed and other upgrades for the city hall campus represent a capstone of achievements underground in the City Hall Park area rimmed by Broadway, Chambers Street and Park Row in lower Manhattan. The job could have been equally controversial. It included tricky planning to hook City Hall into a natural-gas feed that runs near the Nos. 4, 5 and 6 subway lines and around archaeologically sensitive areas such as the nearby African Burial Ground.

"The logistics were the killer," says Michael J. Brothers, a vice president with construction manager Hill International and project manager for the 4.5-year-long renovation.

Many Permission Slips

Although the work of running a 300-ft pipe from a ConEd feeder station to City Hall was relatively simple, it needed approval and coordination by many city agencies: the Dept. of Transportation, to help manage traffic during the dig; easements from the Metropolitan Transit Authority, in order to build new pipes near the subway lines under City Hall Park; and coordination with the buildings, fire, police, parks and administrative services departments, to name a few.

"The main gas line running close to the site was underneath the approach to the Brooklyn Bridge, and it had to run underneath City Hall Plaza," Brothers explains. But the desired route was above the No. 6 subway tunnel, which didn't provide a lot of headroom. However, another line on Chambers Street didn't extend far enough and was too close to the African Burial Ground, he says.

Margarett Jolly, a DG specialist with the engineering and planning department of ConEd, says the line runs along Frankfort Street fairly straight to the middle of City Hall's south wall and under Park Row, then east up to the east corner of City Hall.

"City Hall still has its existing ConEd supply of electricity, but what they're doing is backing down their load with the Bloom-box production," Jolly says. The gas feed is using older gas lines; crews had to install boosters to bring up the pressure in the line to work with the design of the Bloom boxes. (See ENR's recent story on a Bloom Energy manufacturing project in Delaware for more on the design, which has been the subject of a lawsuit over its costs to Delaware ratepayers.)

"The line is metered just for City Hall, but other buildings are expected to start tapping into a new source of natural gas coming into the city," she says. Spectra Energy, which is building new natural-gas supplies to Manhattan, says the line should be functional by November.

Little Bores for Big Problems

Planning for the natural-gas line could not start until crews met another challenge some two years before: finding a way to bring 14 new feeder lines from a ConEd substation to City Hall—a signicant amount of power needed to bring the City Hall complex up to code—while avoiding the area's archaeological hot spots. "We found significant architectural findings that were bypassed or never uncovered," Brothers says of the work preparing for the dig.

"The plan got difficult. We had a vault [at City Hall] at 25-plus feet below grade and a ConEd box on Broadway at 14 feet below grade to feed the vault," he says. Crews were looking at hand-digging the tunnel to avoid sensitive areas, which would have added three to four years and more costs to the job.

Brothers consulted with tunneling teams working on New York City's No. 7 subway line extension and located a contractor that could do micro-tunneling, taking a 30° turn to avoid the problem areas and connect to the ConEd source.

The micro-tunneling auger bored the 32-in.-dia hole for the City Hall vault, and it was lined with a ¾-in.-thick steel-tube pipe liner jacked in behind it as it advanced. The auger ran 200 ft to another turning vault, where the trajectory was turned for another 200-ft run to the 25-ft-deep, 23-ft x 42-ft terminal vault between the Tweed Courthouse and City Hall.

The work took about three months, saved the project almost $3 million and upgraded City Hall's power supplies. By improving its electrical infrastructure, crews paved the way for the new fuel cell to come into the government campus this month, Brothers says. He should know: Just to make sure all was well and to inspect the welds and integrity of work, he crawled through the 32-in.-dia tunnel before crews filled it with conduit.


This story is an extended version of the one that ran in the July 15, 2013 print edition of ENR.


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