Northern States Power Saves Downtime and Expense through Refurbishment

In 1999, Northern States Power (Xcel Energy) found it imperative to replace the deteriorating rectangular exhaust stacks on each of the six GE Frame 7B gas turbines at their Inver Hills, MN, USA, primary generating facility. The wear and design of the old stacks caused pressure drop and skin temperatures of the system to be abnormally high. To minimize downtime and cost, Xcel searched for a single supplier to provide all necessary services to replace the stacks.

Universal Provided a Total System Solution

Xcel selected Universal as its refurbishment partner for the project through a competitive bidding process and rigorous technical evaluation. Universal implemented a total system solution by first conducting an extensive site evaluation, which included acoustic surveys, validation of noise levels and determining local noise requirements. Then, the real work began as Universal demolished the old stacks, then engineered, designed, manufactured and managed the installation of the new stacks.

Universal's Design Improved Turbine Performance

Universal's new exhaust stack design not only decreased the skin temperature of the system and improved the turbine performance by lowering the pressure drop, but also saved Xcel extensive downtime and replacement expense by a quickly implemented solution requiring less material through a new, more efficient design. This project was the first of many, and the start of a long-lasting partnership between Xcel and Universal.

Before: Double switchback design of the Inver Hills gas turbine exhaust stack, stripped of appearance siding, shows rust and deterioration

After: Below, the newly installed Universal exhaust stack.