Looking at times like a gargantuan, orange praying mantis, a 600-ton, 350-foot tall crane landed on Lake Avenue this week to place a new stainless steel liner into a flue in the campus power plant’s exhaust stack.
The liner is needed to activate a flue that will handle exhaust from the jet turbine system now being installed to expand the plant’s generating capacity to accommodate the Albert Sherman Center.
"We’re expanding the plant because the campus is expanding," said Joseph Collins, director of energy resources. "We currently use two flues in the stack, but when it was built, a third flue was included in case the school ever wanted to install an incinerator, which was never done, or to accommodate the very kind of expansion happening now. It’s an example of good planning by past leadership which has saved significant costs today."
Until the beginning of the plant expansion project, the spare flue was fitted with a ladder used to access the top of the stack for inspections and to maintain the warning lights that illuminate the stack so that it is visible to Life Flight and other aircraft. When the new gas turbine is fired up later this year, however, that spare flue needs to be put to use, Collins said.
To prepare for the new flue liner, the internal ladder and electrical lines were removed, and a new ladder, catwalk and electrical conduit were installed on the outside of the stack. This week a crew from Boston Chimney and Tower Company, supported by a crane from the Hallmore Corp., installed the 200-foot stainless steel liner in the third flue. The liner was fabricated in 50-foot sections, five feet in diameter, each section weighing seven tons.
Using a special transport cage, a team of chimney workers was hoisted to the top of the plant’s stack, carrying the heavy tools they would use to install the liner. Then, the crane operator lifted the first liner section high above the stack, and the workers helped guide it down into the flue, until it was nearly all inside the stack.
The exposed end of the liner section carried a flange fitting with 64 holes. A second section of liner (also with a flange fitting) was hoisted above it, and the chimney crew fitted the two sections together, tightening 64 bolts into place with a pneumatic wrench. Once joined together, the liner sections were lowered again, so the end of the second section was exposed, and the joining process repeated until all four sections were connected and fixed in place inside the flue. "The project went along very smoothly," Collins said.
The flue work is part of a $47 million expansion of the power plant to accommodate a new 7.5 megawatt, gas-fired combustion turbine and associated equipment that will boost the plant’s capacity to generate steam, electricity and chilled water.
When the new gas turbine is operating, one of the plant’s original gas and oil-fired steam boilers will be taken off line and kept in reserve as an emergency back-up. Since natural gas burns cleaner than oil, and the new jet turbine is highly efficient, the expanded power plant will actually have lower greenhouse gas emissions, despite its added energy capacity. Additionally, the new turbine will incorporate a catalytic reduction system to remove pollutants before the exhaust gasses are discharged through the existing stack.
Skanska USA is the general contractor for the plant expansion, which also includes construction of a new control room for the entire plant. The existing plant produces all the steam and chilled water currently needed on campus, and about half of the electricity used. The expanded plant will be able to meet nearly all of the campus’s electrical demand, even after the opening of the Sherman Center, but the school will maintain a connection to the external utility grid to handle peak demand and as a back-up resource.