Big doings near Big Dig

June 16, 2008 at 12:55 am | Posted in Power Plant | Leave a comment

Chicago-based Exelon Power has announced that Mystic Generating Station Unit 9 in Everett, Mass., began operation on June 10. Unit 8 began commercial operation on April 14. Both units use Mitsubishi Heavy Industries (MHI) M501G turbines nominally rated at 255 MW (Figure 1).


1. Powering Boston. Exelon Corp.’s Mystic Units 8 and 9 recently went into commercial service. Each unit consists of a 2 x 1 combined-cycle power block with a nominal output of 800 MW. Both use MHI M501G turbines and are the second and third projects using the technology to go into commercial service in the U.S.

Courtesy: Exelon Corp.

Each unit consists of one 2 x 1 combined-cycle power block with a heat rate of 6,139 Btu/kWh and a nominal output of 800 MW. For each block, Deltak supplied the duct-fired heat-recovery steam generators, MHI supplied a 310-MW steam turbine, and Hamon supplied a 36-cell, air-cooled condenser. The plant’s distributed control system comes from Foxboro. The plant’s emissions are a minuscule 2 ppm for both NOx and CO.

Together, the new plants supply 1,600 MW to the electricity grid in the greater Boston region. The Mystic units join Exelon’s Fore River station in Weymouth, Mass., as the first MHI M501G projects in the U.S.

The plant’s confined site—only 17 acres in the heart of Boston—made it necessary to deliver most major equipment by barge. Workers had to park elsewhere and be bused to the site.

Exelon spent more than $30 million on an environmental remediation of the site, on the Mystic River, before constructing the new power plants; it cleared away wastewater and groundwater and removed asbestos and an estimated 50,000 tons of dirty soil. Exelon Generation completed the acquisition of Sithe New England in late 2002.

Washington Group International, originally Raytheon Engineers and Constructors, provided the balance of plant design and specification, provided on-site field engineering, and was the project’s original EPC contractor. In 2001, Raytheon Engineers and Constructors was purchased by Morrison Knudsen and became Washington Group International (WGI). Bankruptcy and reorganization by WGI then brought the project to a standstill. But after Raytheon returned as the prime contractor and assumed its original commitments, the project was completed.

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