Active clearance control meeting expectations in Siemens V engines

Readers of CCJ ONsite typically focus their attention on gas-turbine operations and maintenance, as well as on design mods and equipment alternatives to correct issues impacting reliability, availability, safety, etc. The most compelling information resources in these subject areas available to the editors are the exclusive presentations by owner/operators and vendors at user-group meetings. With so many conferences, there’s rarely time to go beyond this activity, but there’s certainly more to cover—particularly in GT research and design.

Editorial contributions by talented engineers capable of explaining theory and design concepts in simple terms are helping CCJ staff enrich subscriber knowledge on subjects heretofore not covered. For example, you may recall Lee Langston’s recent articles, CMCs debut this year in GE aero engines, 7F gas turbines next and Turbine blades: Good, better, best, plus  Brent Gregory’s Why the number of turbine stages, blades vary among GT models, OEMs.

By way of background, Langston, professor emeritus of mechanical engineering, University of Connecticut, joined Pratt & Whitney Aircraft as a research engineer after receiving his PhD from Stanford University in 1964. A Life Fellow of ASME, he has served the society as editor of its Journal of Engineering for Gas Turbines and Power and as a director of the ASME International Gas Turbine Institute (IGTI).

Brent Gregory, who leads the activities of Creative Power Solutions in the US, has a demonstrable track record of leadership in gas-turbine new product introduction, technology innovation, and design retrofit. His resume includes nearly 50 years of professional service with major gas-turbine OEMs—including Rolls-Royce, GE Aircraft Engines, GE Power Systems, Honeywell Engines, and Alstom. CPS focuses on diagnosing problems with rotating machines—steam and gas turbines, in particular—and offering design corrections.

Langston’s long association with ASME recently took him to Seoul, South Korea, for Turbo Expo, the IGTI’s annual gas turbine conference—generally considered the world’s leading meeting on GT research, development, and practice. The 2016 conference, the group’s 61st annual meeting, was held June 13-17 and hosted about 3000 attendees; it included over 1000 technical papers—roughly half from outside North America. The papers, expert tutorials, and panel sessions were arranged in more than 300 sessions on gas-turbine research, technology, and operations.

Langston reported that a panel of large-frame OEM executives presented on their companies’ latest developments. Of particular interest to owner/operators was GE’s announcement that it had attained a combined-cycle plant efficiency of 62.2% with the company’s H machine, breaking Siemens’ 2011 record of 60.75%. Next goal is 65%.

AnsaldoEnergia had a spot on the program to talk about its future plans. Recall that AE took over production of Alstom’s reheat GT 26 machine, as well as development of the GT 36 H-class turbine (no reheat), to satisfy regulators’ anti-competition concerns associated with GE’s buyout of Alstom. The company now also owns PSM.

Langston’s participation in Turbo Expo was enhanced by a side trip to Korea Midland Power Co’s (Komipo) 1450-MW Incheon Thermal Power Site for a first-hand look at the use of active clearance control to minimize tip-leakage losses in Siemens V engines. He introduced this subject in The ABCs of blade-tip clearances. The Hydraulic Clearance Optimization feature offered as an option (for new units and as a retrofit) on V gas-turbine models 84.3A and later, promises greater operational flexibility and increased power output and efficiency.

According to company literature, performance enhancement is achieved by shifting the rotor against flow direction to optimize turbine clearances during steady-state operation. The axial shift of the rotor is performed automatically by hydraulic pistons behind the compressor thrust bearing. The gain in power quoted is up to 2 MW on a simple-cycle SGT6-4000F; efficiency improvement is up to three-tenths of a percentage point on qualifying simple-cycle V units.

The power boost and increase in efficiency are made possible, it is said, because of the conical shape of the turbine sections on these machines. Performance gains in the turbine section attributed to repositioning of the rotor are greater than the losses incurred in the compressor section. The HCO feature is in full function when the differential thermal expansion of rotor and casing components has equalized—about an hour after the machine is started.

Performance improvements aside, the greatest value provided by HCO may be as a rubbing solution to keep clearances from closing up on shutdown, thereby eliminating the need for cooldown before restart in some situations. The product has been most popular in the 50-Hz V94.3A fleet with several score engines so equipped since 2003. At least eight 50-Hz machines have been retrofitted with the HCO worldwide. First use on V84.3As was in March 2009 on two engines serving one of two 2 × 1 combined cycles at Incheon. No retrofits have been sold to date in the US.

Unit 1, the combined cycle without HCO performance enhancement is rated 503.5 MW; Unit 2, equipped with HCO, generates 508.9 MW. To evaluate the differences between the two combined cycles, Prof Langston met with three Komipo senior staff members: Youn-Kwang Kim, VP engineering and operations; Jung Hwa Kim, assistant manager—gas turbines; and Gi Tae Kim, service manager—steam turbines.

No hard data were available so the three plant employees spoke in general terms. They said the HCO-equipped engines were more efficient than the gas turbines for Unit 1, and Unit 2 produced power at less cost than its sister combined cycle. Further, that the plant has not experienced any problems with the HCO upgrades since commissioning.

The HCOs operate automatically through the Siemens control system. Operators are alerted when HCO is in operation, but don’t have to take any action. The bottom line: A happy customer.

501F clearance control. HCO is not adaptable for use in the Siemens 501F fleet popular in the US. However, all of Siemens’ advanced F designs (F4 and later) are equipped with the OEM’s Direct Air Injection System (DAIS) for better control of clearances and to avoid rubbing. It relies on “cool” compressed air injected into the turbine section on shutdown to prevent lockup between the casing and rotating components. For earlier engines (up through FD3) Siemens has developed process changes to better accommodate spin cool and hot restart. DAIS also can be retrofitted to these earlier 501Fs.

Mark your calendar. US-based gas-turbine owner/operators might consider attendance at Turbo Expo ’17, June 26-30, in Charlotte, NC. Langston points out there are at least two IGTI committees devoted to users (Industrial and Cogeneration and Electric Power). Plus each meeting offers tutorial sessions on all aspects of gas turbines and numerous panel sessions to bring you up to date on the latest GT developments. Yes, like user-group meetings there is an equipment/services exposition.

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