Improving Boiler Availability by Better Steam Temperature Control

by | Sep 20, 2013 | Industrial Energy & Onsite Utilities, Industry, Power Generation | 0 comments

Tightening up boiler control strategies and improving the sensing and final control elements not only improves energy efficiency and reduces variability, it can improve overall availability of the boiler as Emerson’s Douglas Morris of the Power and Mining industries explains.

Emerson's Douglas MorrisTube leaks are something that every utility deals with on a regular basis.

As a matter of fact, when you look at NERC’s [North America Electric Reliability Corporation] Generating Availability Data System (GADS), you’ll find out that boiler tube leaks are the leading cause of forced outages for both coal-fired and combined-cycle plants.

Chart based on NERC GADS data for a nominal 500MW coal-fired boiler

Chart based on NERC GADS data for a nominal 500MW coal-fired boiler

This makes tube leaks the single biggest cause for plant unavailability. To mitigate tube leaks, there are some strategies that can be deployed that address root causes; reheat and superheat temperature variability. These temperature excursions place undue stress on the tubes which can lead to metal fatigue. Simply put, if the boiler is operated with more stable steam temperatures, tube leaks will be fewer, as will the number of forced outages.

To accomplish better temperature control, a boiler gets a solution that is unique to that unit and provides closed loop control recommendations that reduce temperature variability. A side benefit to this solution is that boiler response and ramp rates are often improved, and in the world of renewable power with its variable supply, better fossil unit flexibility and faster ramp rates are always welcomed.

Examples of installed solutions:

  • 550MW plant: steam temperature swings taken from +/- 40F to +/- 5F with subsequent reduction in tube leaks and a step change improvement in availability
  • 450MW plant: reduced average occurrence of exceeding reheat temperatures by 85%
  • 250MW plant: improved ramp rate by 70%

For utilities looking for a cost effective way to improve availability and unit control, perhaps better steam temperature control is a place to start. In fact, the costs associated in this strategy are minimal when compared to the costs associated with a single forced outage for many plants.

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The opinions expressed here are the personal opinions of the authors. Content published here is not read or approved by Emerson before it is posted and does not necessarily represent the views and opinions of Emerson.

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