Focus on O&M

This installment of the series continues our review of different conditioning-monitoring techniques commonly in use at power plants using any generation technology. In the May issue we began exploring specific PdM techniques with an examination of electrical surge comparison and motor-current signature analysis.

The North American Electric Reliability Corp. (NERC) Reliability Standards are under constant revision even while new requirements are under active development. Three important regulatory definitions are currently being contested.

Radial, axial, and circumferential metallic seals installed on rotary, regenerative air preheaters have evolved little from the original metal strip designs that date back to the original Ljungström preheaters developed nearly a century ago. Unfortunately, metallic strip seals degrade soon after installation, allowing excessive air-to-gas leakage, which translates into increased fuel consumption and fan power.

In November 2008, a central Texas utility commissioned HPI, a full-service turbomachinery design and construction firm based in Houston, to perform a major upgrade of its plant’s power distribution and turbine control systems.

Many large utility-scale units with copper alloy condensers and feedwater heaters lose generating capacity when copper and copper oxide deposits develop on high-pressure (HP) steam turbine blading. It is not unusual for a 400-MW unit to lose 10% of its generating capacity over a six-month period when water treatment processes aren’t properly tuned to prevent copper transport in the steam and condensate systems. In fact, one utility reported that it lost 20 MW of capacity in one month because of such deposits. The financial implications of such deposits, particularly in power markets where plants are pushed to their generating limits, are tremendous.

This series of articles focuses on the nuts and bolts of predictive maintenance (PdM), also known as condition-based maintenance. A well-defined and well-executed PdM program saves time and money by reducing unneeded time-based maintenance tasks and by identifying and fixing problems before they cause equipment failure or plant shutdown. In this article, we begin introducing condition-monitoring techniques commonly in use at power plants.

This year’s series will focus on predictive maintenance (PdM), also known as condition-based maintenance.

Imagine this scenario: Two separate power plants experience a bowing problem greater than 18 mils with a steam-turbine rotor. The turbines are from the same manufacturer and several repair options are reviewed. Management at both plants selects an innovative approach involving removal of a substantial amount of material, which is replaced with weld overlay and then machined to correct diameters and centerline of the balance piston area. One plant’s insurance company covers the repair, the other plant’s doesn’t. Why?

Thule (“Two Lee”) Air Base is a 254–square mile base located in a coastal valley in the northwestern corner of Greenland, within the Arctic Circle. The base, the U.S.’s northernmost military installation, is nestled between mountains and surrounded by icebergs and glaciers as far as the eye can see.

Beginning each spring and continuing through the fall, backpressure readings at Rosebud Operating Services Inc. indicated substantial drops in the condenser’s efficiency. Increased backpressure results in higher net plant heat rate and a corresponding measurable decrease in power generation.