A large number of 7F gas turbines were installed during the boom years of 1999 to 2004. Now, nominally 25 years later, the industry is facing a “7F rotor wave” with many turbine rotors nearing “end-of-life” (EOL, 5000 factored fired starts or 144,000 factored fired hours) and coming due for an exchange, replacement, or lifetime extension. Because maintaining rotor inventory on a user’s balance sheet gets expensive quickly, most owners do not have enough spare rotors to cover their total installed base.

PSM’s Katie Koch, global product manager, and Brian Loucks engineering manager for rotors and casings, told the editors that the Hanwha company has developed an exchange program to help customers better manage their assets by providing fully vetted rotors for up to two major intervals—including any new replacement components—in exchange for EOL assets. Rotor installation can be accomplished during a major inspection. The bottom line: Customers avoid unnecessary downtime and can continue to operate with a reliable asset.

However, the large number of rotors needed is pressing against supply-chain constraints. Simply put: The OEM can’t meet the industry’s needs alone. And other vendors are challenged as well. Development of forgings, especially ones of the nickel alloys required in the 7F turbine section, can take considerable time. Be mindful that rotor demand must be addressed now to ensure power production is not compromised in the future.

PSM’s lifetime extension program can help in this regard, say Koch and Loucks. In their presentation at the upcoming 7F Users Group conference (May 15-19, Atlanta) the duo will explain how PSM can help you manage the rotor wave with its improved nickel turbine wheels, robust back-end conversions, and other offerings.

With relevant design and operational expertise, and applied data science, digital twins can be harnessed for areas such as fleet comparisons, plant-specific KPIs, and forward-looking predictions.

However, the twins are only as good as the domain expertise and data tools implemented to provide the analytics. PSM’s Greg Vogel, senior engineering manager for technology programs, will update attendees at the upcoming 7F Users Group conference (May 15-19, Atlanta) about how his company’s gas-turbine GT domain expertise has grown over the last 20 years.

Today, PSM’s design and validation methods and data sets, says Vogel, provide extensive learning opportunities for assessing data trends. By integrating this capability into a fleet of monitored GT assets, the company can tune its models both on a fleet and individual-unit basis.

Tuned digital twins allow operators to understand how a unit (or fleet) should be performing and highlight areas of lost potential as seen in the operational data.  The web-based solution PSM is currently validating provides visualizations that start at a high-level health score and allow subsequent drill-down through analytical layers all the way to the individual twins.

Essential Power Newington

Owned by Essential Power Investments
Operated by Cogentrix Energy Power Management
565-MW, dual-fuel 2 × 1 combined cycle located in Newington, NH. Plant operated baseload from COD in 2002 until it began cycling in 2008
Plant manager: Tom Fallon

Electronic safety orientation program for contractors

Challenge. Essential Power Newington annually processes hundreds of contractors through its site-specific safety orientation program, consisting of an instructional safety-related video and certificate of completion. The rate of certifications increases significantly during outage periods.

The challenge of completing site safety and compliance training efficiently and effectively without impact to outage work schedules can be demanding. Beginning in early 2020, and continuing through 2021, Covid-19 concerns limited personal interaction and congregation in an effort to minimize risk of transmission. With contractors arriving from all areas of the country, the site explored digital and remote avenues which had not been invested in previously.

Solution. Staff explored various electronic resources to deliver its safety orientation video, facility EH&S rules (Fig 1), and NERC CIP compliance protocols to personnel arriving onsite. Critical quality features included the following: (1) ease of use for the end user and administrator, (2) ability to edit content as needed going forward, (3) compatibility with mobile phone use, and (4) ability to electronically verify completion.

Microsoft Office 365’s Forms program was the solution selected. It has the ability to e-mail contractors/vendors a message with an optional QR code and/or forms.office.com hyperlink.

Use of a mobile device and QR code allows quick navigation and orientation, and completion of required tasks. A hyperlink also is provided for PC use. Once the user receives the e-mail and accesses the form using either the QR code or link, he or she is able to review a customizable and site-specific embedded SharePoint link to the site’s 7-min orientation video (Fig 2).

There also are several easily navigable electronic forms to review and verify completion.

Once the video has been watched and the form completed, the user initials the electronic form and submits it to the site’s EH&S manager. From there, data are compiled in a user-friendly electronic database for staff to review and to track the completion status of contractors. Electronic timing of form completion identifies potential attempts at subversion of the orientation process.

Results. The Office 365 Forms program has been tested by several employees and found effective and easy to use. Having the ability to watch the video and review and submit the electronic form from a mobile device provides contractors a user-friendly method for completing site orientation from outside the plant prior to arriving for the Newington outage.

Plus, electronic submission frees up significant paper resources and filing requirements.

Also, headcounts onsite in contractor orientation workspaces are reduced to those infrequent occurrences where electronic submission was not feasible ahead of time. When prequalified contractor personnel arrive onsite, they immediately report to the specified Point of Contact (POC) and receive their orientation-completion hardhat stickers.

The POC is able to quickly review orientation completion status in the electronic repository and directly answer any questions relevant to the training in the context of the contractor’s work scope.

In sum, investment in electronically facilitated site orientation saves resources and time and the efficiency of contractor safety- and compliance-training certification.

Project participant:

John Pierce

Upgrade to boiler-water sample panel helps ensure proper chemistry

Challenge. EPC engineers integrated a firetube boiler into the design Essential Power Newington for use during cold-plant startups to provide steam for turbine seals and HRSG sparging. The auxiliary steam system includes a deaerator supplied with cold demineralized-water makeup. Aux boiler use for HRSG sparging has increased as the plant moved from its original baseload operating profile to more of a seasonal peaking operation.

Sparging can be necessary for days at a time, or longer, depending on market dynamics and ambient temperature. Treatment chemicals are added via small electronic metering pumps. Chemical-pump stroke rates are adjusted manually based on grab-sample analysis in the water lab by an auxiliary plant operator. The original construction did not include any continuous analyzers to ensure proper control of boiler-water chemistry.

Solution. Site personnel reviewed water-chemistry key parameters for the low-pressure firetube boiler, selecting these three characteristics for continuous measurement: blowdown pH and conductivity, and feedwater dissolved oxygen. Staff then worked with a vendor to design a sample panel to measure the three variables using sampling equipment currently used onsite in the HRSG sampling system (Fig 3).

The final challenge for design of the sample panel was to find a location in the aux-boiler building where the panel would be close to the sample sources while also allowing O&M personnel proper access to other equipment. This involved minimizing the wall panel’s depth to maximize aisle space.

Results. Personnel completed installation of the sample panel during a recent plant outage. Analyzer outputs were wired to the DCS, where screen graphics were added and alarm triggers set. The analyzer outputs also were added to the PI historian for long-term trending and alerts.

While several additional continuous analyzers would be necessary to automatically control boiler chemistry, these three continuously measured characteristics help ensure proper chemistry maintenance between grab-sample analyses.

Project participants:

Kyle Malenfant, I&E technician
Michael Dill, I&E technician
Eric Pigman

Automating chemical injection key to tighter control of cooling-tower operation

Challenge. Because Newington was designed to operate baseload, it did not have an automatic scale-inhibitor injection system for the 1.5-million-gal saltwater cooling tower, which operates at 2.0 cycles of concentration and has a 150,000-gpm recirculation rate. A single salinity meter was installed on the circulating-water-pump discharge but there was no means for measuring makeup-water salinity continuously to accurately monitor for tower cycles.

The chemical treatment program for scale and dispersant control is an HEDP/polymer combination, which is injected into the tower basin. River-water makeup quality, 2.0 cycles of concentration, high surface temperatures in the condenser, and desired operating pH range were used to arrive at the optimal concentrations of treatment chemicals. A buffer is included to allow for routine fluctuations in makeup-water quality or upsets.

Given water-sample testing interferences with tower salinity, injection feed rates were based on blowdown flow rates, adjusted manually. This led to many occurrences of over- and under-injection because blowdown rates can fluctuate daily and seasonally.

Solution. Two new chemical-injection metering pumps were installed with microprocessor controls. The scale-inhibitor pump injection controls now run in automatic via a 4-20-amp control signal based on tower blowdown flow rate. In addition, a salinity meter was installed at the river makeup source to accurately monitor for tower cycles for tighter control.

These changes are conducive to a better tower chemistry program, one with both consistent scale protection and chemical control ranges. The makeup-water salinity instrument ensures consistent as-designed tower cycles, which, in effect, increases the concentration in the tower, and by automating the scale-inhibitor pumps, reduces chemical consumption. In sum, these changes reduce chemical costs and maintain a tighter tower-chemistry control program.

Results. With additional training on blowdown control rates and chemical injection operations, the control for combatting scale in the surface condenser is much tighter. Having accurate tower cycles, because of the added makeup salinity meter, allows staff to better regulate tower blowdown and injection feed rates to accurately manage the system during all operational profiles—while still offering opportunities for reductions in chemical consumption.

The scale-inhibitor automation improvement allows for less manual intervention when tower blowdown rates are fluctuating frequently based on plant operating profiles.

Project participants:

Joshua Leighton, Eric Pigman, and Scott Courtois

Warning lights for overhead doors make plant safer for staff, visitors

Challenge. Large overhead roll-up doors are a concern in industrial workplaces—a recognized hazard that could cause serious physical injury or equipment damage if not acknowledged and controlled. Reasons include these: They are heavy, may fall closed while traveling if the head works fails, and may not be equipped to auto-reverse when they come in contact with an object or person.

Solution. Staff analyzed options for improving the safety and communications protocols for traversing through the plant’s large 20 × 20-ft turbine-hall overhead doors (Fig 4), commonly used by a large number of people. Visual indicators were deployed to provide additional warning and to remind personnel and visitors about overhead-door safety and site expectations.

Industrial LED light strips were a practical solution. The power and controls for them are incorporated easily into the operation of the door opener while providing warning lights by flashing RED when the door is in motion. Once the door reaches its fully open limit switch, the light strips turn solid GREEN (Fig 5). When the door moves closed, the LED strips again flash RED until the door fully closes against the pressure limit switch; the lights shut off after 30 seconds. The warning-light system is installed on both sides of the door frame, and both inside and outside.

In addition, large floor markings were developed to remind walking personnel to use the adjacent walk-through door for exiting and entering the turbine hall rather than an overhead door.

In conjunction with installation of the light strips on the door frame and conspicuous floor markings (Fig 6), the site instituted a standing directive that the doors not be driven or walked through while in motion. They can be traversed only when in the fully open position and the lights are solid GREEN.

Results. Use of visual stimuli to let staff and contractor personnel know a door is in motion, and communicating that you must not drive/walk through an overhead door in motion, has helped to prevent equipment damage and other safety events. While nothing is fail-safe, the addition of warning lights and floor markings remind about site protocols and the need to wait for the fully open status before moving through.

Project participants:

Mike Dill, I&E technician
Kyle Malenfant, I&E technician

Central Eléctrica Pesquería (CEP)

Owned and operated by Techgen
900-MW, 7FA.05-powered 3 × 1 combined cycle located in Pesquería, Nuevo León, Méxicó
Plant manager: Mario Alberto Ontiveros de la Torre

‘Improved’ brush holder offers safety benefits

Background. CEP’s four generators are equipped with the OEM’s EX2100e excitation system to control ac voltage at the generator terminals and/or reactive volt-amperes (VAr). Plant’s excitation system has a collector on the free side of the generator, where carbon brushes transfer the excitation current to the rotating slip rings and produce an electromagnetic field in the generator.

Incident. During normal monthly preventive maintenance, the following occurred when changing a brush on the negative pole: Technician inserted the brush holder, using its insulated handle (Fig 1), unaware that the carbon brush had slid out and been pushed to the middle space between the collector rings. The resulting electric arc damaged the rings and generator rotor.

Solution. After the event, the maintenance and technical control team conducted a root cause analysis (RCA) and investigated collector-brush-system replacement options. GE’s “improved” brush holder (Fig 2) was selected for the following reasons: (1) Reduced the possibility of contact with live brushes, a significant safety benefit; (2) Provided higher reliability by eliminating incomplete insertions; and (3) Assured higher availability by reducing the risk of collector discharges.

Plus, brush wear can be seen easily through the inspection window, or by inspecting the wear indicator on the brush pigtail.

Results:

• Separation from energized components makes for a safer system, especially when changing out brushes with the turbine/generator in operation.
• Reduced risk of brush hang-ups.
• Tool-less maintenance given the permanently attached handle, which also reduces the time required for brush change-out.
• Reduced risk of collector flashovers.
• Increased brush size/life.
• Lightweight aluminum construction with a durable and anodized surface coating.
• Less susceptibility to brush-current selectivity (uneven current distribution between brushes).
• Direct replacement of single-wide holders without modification to the brush rigging.

Project participants:

Arturo González, technical control chief
Odon Acosta, maintenance chief
Arturo Macías, electrical coordinator

Copper braids outperform carbon brushes for shaft grounding

Challenge. Eliminate an unsafe condition present in the grounding-brush systems for CEP’s gas turbine/generators and implement an operating practice to enhance personnel safety and reduce the risk of equipment damage during routine maintenance.

The original grounding-brush system has a spring-type lock (Fig 3 left) that must be pulled and removed to release the brush for replacement or to perform maintenance, which sometimes must be done with the generator in operation (Fig 3 right).

These factors are conducive to an unsafe condition because of the close distance between the operator and the working generator—a noisy environment with strong air currents.

Solution. After an exhaustive analysis by technical staff, an alternative grounding system was identified—one similar to that used in the steam turbine/generator. It uses copper braids that are extracted easily by pulling the fixing lever (Fig 4 left) and removing the braid to the side (Fig 4 right).

The new grounding system reduces the time required for maintenance: It is of simpler design than its predecessor and maintenance consists only of cleaning with dielectric solvent and verifying that the braid is not too worn (or replacing it if it is).

For insertion, the braid is placed on one side and pressed with the locking lever and it is ready for operation.

Results. The increased accessibility afforded by the new grounding system allows handling the components at a safer distance than previously—further away from the rotating machinery. Plus, the maintenance interval has been extended from one month to two, making the grounding system safer and easier to maintain.

Project participants:

Odon Acosta, maintenance chief
Arturo Macías, electrical coordinator
Plus, Isaí Real, Jorge González, and Jorge Rosalio

Replacement valve actuators provide ergonomic benefits, speed maintenance

Background. CEP has a ZLD (zero liquid discharge) gray-water treatment plant incorporating softening, ultrafiltration, reverse osmosis, and electrodeionization.

Throughput extends to nearly 6200 gpm.

Challenge 1. Reduce or eliminate failures of actuators for valves serving CEP’s five ultrafiltration modules. The original actuators were of a very robust design, each weighing about 200 lb. Thus, their removal for maintenance required cranes and the intervention of specialist personnel from different areas of the plant’s O&M team (Fig 5).

Regular actuator maintenance, typically required every six months because of wear and tear experienced by positioners, instruments, and other components primarily attributed to high vibrations, took about 16 hours. Actuator location complicated maintenance because of ergonomic concerns.

Solution 1 involved replacement of the original actuators with smaller, lighter ones (about 50 lb), thereby improving maintenance access to mitigate ergonomic concerns. Remote positioners were another improvement. Maintenance on the new actuators can be performed in-situ, eliminating the need for cranes and specialist personnel.

Results 1:

• Improved system availability.
• Time required for maintenance cut in half.
• Increased efficiency of maintenance personnel.
• Reduced costs of maintenance and spare parts.
• Less noise.
• Fewer module ruptures attributed to vibration.
• Ergonomic benefits included fewer accidents and fewer injuries to maintenance personnel.

Challenge 2. Increase the availability of the ZLD, which requires a heat exchanger to increase water temperature before it enters the crystallizer. This heat exchanger must be cleaned of scale deposits every two weeks using EDTA and nitric acid to maintain the level of performance required. Cleaning takes from 18 to 24 hours.

Solution 2. A second heat exchanger, independent of the original with all instrumentation required, was installed for use during cleaning turns and as a backup for the original.

Results 2. ZLD system availability and efficiency are assured.

Challenge 3. Eliminate or reduce recurring problems in the sludge-dewatering portion of the gray-water treatment plant. The two dewatered-product transfer pumps in the line to the cold-lime softening system suffered continual impeller damage and mechanical-seal wear, which caused pipes to plug and contributed to excessive maintenance.

Solution 3. The original multistage centrifugal pumps were replaced by single-stage units equipped with mechanical seals lubricated by service water to flush the seal cavity continuously, mitigating wear.

Results 3.

• Improved system reliability and availability.
• Eliminated corrective maintenance; only preventive maintenance is required today.
• Reduced the cost of maintenance and spare parts.
• No lubrication problems were associated with the seal flush system.
• Reduced the cost of system cleaning.

Project participants:

Odon Acosta, maintenance chief
Plus, Moises Arroyo, Daniel Mendoza, Rolando Goytortua, Alma Rivera, Jonathan Herrera, Marco Lopez, Alejandro Domínguez, Juan Carlos Facio, and Luis Melgarejo

Planning to attend the 7F Users Group meeting at the Renaissance Atlanta Waverly, May 15-19? Registered? If not, sign up now and book your room.

That done, flag 11 a.m. Tuesday (May 16) in your electronic planner/reminder, when four platinum sponsors will begin their one-hour presentations on topics of importance to owner/operators.

If your work-related responsibilities focus on getting more from your gas turbines—more power, more operational flexibility, more time between overhauls, etc—consider attending the PSM session, “7F combustion and full engine solutions for a variety of energy-market applications.”

Greg Vogel, senior engineering manager for technology programs, and Bryan Kalb, combustion engineering manager, will cover two main topics:

• Combustion upgrades with FlameSheet™.
• GTOP development and performance upgrades.

If you have attended a gas-turbine meeting or read CCJ in the recent past, you probably have heard about FlameSheet™ and might think you can skip the PSM presentation. Not true. This preso is not a rehash of marketing materials. Rather, it focuses on the operational and fuel flexibility experiences achieved globally, up to the minute, by the innovative radially staged “combustor-within-a-combustor” (Sidebar) now installed or under contract in 27 units (mostly 7F), also including 501F, 7EA, and Fr5/1PA.

Design updates that further enhance the operational window of FlameSheet™ will be presented in detail, along with a road map covering the near- and long-term outlook of the 7F engine.

How FlameSheet™ works

PSM’s novel FlameSheet™ combustor relies on a simple, two-stage radially inflow “combustor-within-a-combustor” design concept that enables staged operation of each at various load conditions. Leveraging trapped vortex stabilization aerodynamics, the outer combustor operates with excellent stability, designers say.

This allows an increased operational zone, because the combustor can operate at much lower loads while maintaining stability and low CO, which generally restrict operation at low loads.

FlameSheet™ also is designed to handle a variety of fuels and fuel blends while keeping NOx and CO emissions low, without need for diluents or an SCR. This flexibility enables the combustor to satisfy industry needs with respect to the rapid onboarding of renewables as well as achieving decarbonization goals by mixing hydrogen with traditional fuels.

Fuel flexibility. Here are some of the highlights regarding fuel flexibility that will be covered:

• Current experience burning hydrogen blends and details of two major projects happening this spring.
• Details of E- and F-class combustion retrofit projects operating on hydrogen blends with PSM technology since 2018.
• Operational update on the first tri-fuel FlameSheet (natural gas, hydrogen-rich refinery off-gas, and back-up liquid fuel).
• Adaptation and installation of our FlameSheet™ platform to the Frame 7EA, including co-firing with hydrogen.

The operational flexibility portion of the presentation looks at the challenges posed by onboarding of renewables and shut down of traditional base load coal-fired assets. The speakers will explain how PSM can achieve turndown limits, within emissions compliance, under 30% in a 7F gas turbine with its latest generation of FlameSheet™ combustors.

Addition of the company’s GTOP package to FlameSheet™, 7F top-end performance can increase while remaining at low emissions limits for optimal peak performance. Actual installations and results will be presented.

PSM’s 7F upgrade packages, which provide users the flexibility to optimize performance and maintenance schedules to their individual requirements, are covered in the second part of the session presented by Greg Vogel, senior engineering manager for technology programs, and Bryan Kalb, combustion engineering manager. Part one, outlined here, focuses on the company’s increasingly popular FlameSheet™ combustion system.

GTOP (Gas Turbine Optimization Package) supports three modes of operation—maintenance performance, and peak—and allows users to toggle among the three for optimal performance, depending on operational and business needs. Targeted hot-gas-path and compressor-part upgrades ensure a cost-efficient, reliable upgrade compatible with existing OEM 7F hardware. Remember, too, GTOP is compatible with multiple combustion systems—including FlameSheet™—to maximize the performance improvement.

Recall that GTOP 3.1 and 4.1 upgrades incorporate aerodynamically redesigned compressor parts—R0, S0, and S1—for increased compressor inlet flow and enhanced mechanical integrity. Recent installations and results will be reviewed by the speakers. Plus, the latest GTOP upgrades compatible with both 7F.03 and 7F.04 machines will be described.

New technology will be introduced as part of PSM’s GTOP4 program, which leverages the company’s experience gained in expanding its performance offerings to the 501F engine, promotes more cooling in the first stages of the turbine section. This suggests maintenance and life cycle costs with the PSM improvement may be more favorable compared to those experienced by users with the OEM’s AGP design.

PSM reminds readers of the typical performance improvements (below) recorded by installation of GTOP 3/3.1 on standard 7F.03 engines:

Simple-cycle power

• Maintenance mode (32k), up to 6%
• Performance mode (24k), up to 8.8%
• Peak mode, up to 11.7%

Performance improvements possible with GTOP 4/4.1 will be presented at the 7F Users Group meeting—another reason to attend.