FROM THE EDITOR: ‘As for my HRSGs, I wish I didn’t know now what I didn’t know then’

A maintenance manager from an F-class plant sharing his challenges with the editors at the Combined Cycle Users Group 2017 meeting at the end of August borrowed that thought from Bob Seger’s “Against the Wind” to illustrate the unappreciated changing behavior of his plant following a gas-turbine upgrade.

The “behavioral changes” he mentioned included high gas temperatures deep into the boiler, deteriorating catalyst performance, and duct burners not operating the way they used to. This did not come as a surprise to the editors, who attend about a dozen user-group meetings in a given year. Speakers—users and vendors alike—with cycle expertise have urged attendees for the last two or three years to evaluate the impacts of increasing GT exhaust flow and temperature on downstream components before making changes. Many users listened to the message, but only some heard it.

The editors’ perspective is that because most attendees at user-group meetings have responsibilities associated with gas turbines they pay little attention to much else—except safety. That’s not a criticism: GT upgrades can deliver faster starts, more power, increased turndown, and other favorable outcomes. They’re all good ideas, as long as you don’t compromise the operation of the heat-recovery steam generator and other downstream components.

Might plant reliability and performance be affected adversely by engine upgrades that have failed to consider cycle impacts? An immediate answer of “yes” came from the chairman of the HRSG Forum with Bob Anderson, who has decades of related experience from his time as both a plant manager and corporate subject matter expert (SME) for Progress Energy, and from recent consulting assignments—including O&M assessments of more than four dozen HRSGs worldwide.

Anderson told the editors that the impacts of GT upgrades on HRSG reliability and performance is a cornerstone of the technical program for the 2018 HRSG Forum, March 5 – 7 at the Hyatt Regency Houston, adding that he recently attended the European HRSG Forum (EHF) where a boiler expert addressed that very topic. Anderson regularly participates in/helps organize HRSG meetings worldwide to keep current on global technology developments and to engage the leading SMEs for input to the annual forum here bearing his name.

If low-load turndown is your goal, the EHF speaker began, be aware that the resulting reduction in exhaust-gas mass flow and increase in exhaust-gas temperature may impact attemperator capability, superheat temperature, temperature differential between tube bundles, and cold-end issues such as flow instability and steaming economizer. He went on to discuss the effects on the HRSG of increasing GT output and of enlarging the engine’s operating envelope to increase plant flexibility. Get all the facts at the Houston meeting.

Presentations scheduled for the 2018 HRSG Forum include the following:

  • Update on the evolving issues with creep-strength-enhanced steels.

  • 3D printing of custom parts and scaled mockups of HRSG components for planning repair activities.

  • Latest developments in drum-level instrumentation and code requirements.

  • F-class plant experience in replacing high-pressure- and reheat-steam attemperators.

  • Update on the use of film-forming products in HRSG cycle chemistry.

  • Managing combined-cycle and HRSG chemistry fleet-wide.

  • Why FAC continues to be the No. 1 problem in HRSGs.

The last is particularly important given its possible personnel safety implications. Most puzzling is that there’s no reason for flow-accelerated corrosion to exist in any plant today; the solutions for both single- and two-phase FAC are well known and relatively easy to implement and maintain. Listen to Dr R Barry Dooley on the short podcast giving the three actions to avoid FAC and the repair costs and downtime associated with it. Simply click this link and listen for five minutes. . .then register for the HRSG Forum.