Algonquin Power Plant in Windsor Locks, Conn. Courtesy Cianbro Corporation.

Algonquin Power Plant



Thornton Tomasetti provided structural engineering for the erection of a massive CHP (combined heat and power) boiler on a narrow, inaccessible site. The electricity and steam it generates operates an onsite mill which manufactures nonwoven and specialty papers. The challenging project required the installation of a Solar Titan 130 Series natural-gas-fired combustion turbine generator with an IST once-through steam generator.

Developing Solutions

The main project challenges were related to the massive size of the boiler, the constrained access/egress, and the lack of physical space inside the existing facility. Normally, a boiler of this size is built prior to erecting the building enclosure or brought in through the roof of an existing building. It was not feasible, however, to remove the plant’s 70-foot-high roof, which is supported by a massive truss, due to access issues. The contractor developed an alternative scheme of erecting the boiler on a 600-ton crane in a narrow space outside the building and transporting it into the building on heavy-lift rails, using a strand-jacking process. The boiler consisted of four modules, stacked and welded onsite. The finished unit was and placed on rollers so that it could be pulled into the building through a space created by removing an entire wall.

Rising to the Challenge

To facilitate this installation, Thornton Tomasetti engineers developed crucial analyses and designs that facilitated raising a utility bridge six feet to allow the crane to pass beneath it, established the feasibility of removing the bracing bay from the existing building, and secured the foundations and access platforms for the massive units during erection and final installation.

Our engineers used micropiles were used to isolate the turbine to avoid damaging a 24-inch-diameter cooling pipe underneath it. Heavy machines of this type can produce eccentric loading patterns that cause excess vibrations and compromise nearby structures. Foundation construction, with proximity to “live” systems, included slab removal; excavation; and installation of formwork, reinforcing, anchor bolts, and conduits. The piping from the mass foundation was isolated using temporary cardboard forms.

Project Successes

The installation of the boiler, which converted the facility to cogeneration, increased the plant’s energy efficiency and cost effectiveness and reduced its emissions below Department of Environmental Protection requirements. Power that is not needed by the client will be sold back to the grid.

The project, which took months of planning, was accomplished with only a three-day shutdown of the plant. It was completed under budget and ahead of schedule, with no lost time incidents or regulatory NOVs (notices of violations).

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