Cycling Experience of Large Heat Recovery Steam Generators in the New England ISO Market

摘要

The New England area of the United States has been in a competitive generation market for almost 2 years. There are a number of larger modern combined cycle power plants in this market that are 5 to 7 years old and are now being used in extensive cycling operation. The most common pattern is "two-shift" cycling, where overnight shutdowns are taken from about 23:00 Hours till 05:30 the next day. In addition load swings for Automatic Generation Control (AGC) are also seen during the day. This new loading of about 150-200 shutdowns per year plus a similar number of load swings raises the potential for damage to HRSG components from thermal and pressure cycling. Given the higher efficiency of newer plants now coming on line, plus existing nuclear plants, it is likely that many of these units will continue to cycle in the upcoming years. The immediate impact on HRSG systems is tube and pipe failures from corrosion-fatigue and flow accelerated corrosion. Failures are begin on boiler trim (drains, vents) and progress to weak points in superheaters, evaporators and economizers. Boiler tube and pipe leak failure rates rise by a factor of 4-5 from baseload operation and could rise higher. Design for cycling service should be a major concern in all new HRSG's.