Riken Keiki Co’s OHC-800 (photo), a relatively new type of calorimeter, uses optical and sonic sensors to provide real-time monitoring with high accuracy. The instrument’s use in optimizing turbine and boiler air/fuel ratios make it of interest to O&M personnel at gas-turbine-based simple- and combined-cycle plants.
Recall that competitor gas chromatographs provide highly accurate analyses of fuel-gas composition, but do not offer real-time monitoring. And combustion-type calorimeters can offer real-time monitoring, but they generally are not accurate enough for process control.
The OHC-800’s sonic sensor measures the sound velocity of the gas, the optical sensor the refractive index of the gas. Stated advantage of the optical interferometric sensor is that because no chemical reaction is used—unlike methods relying on catalytic combustion and thermal decomposition—components do not wear out or deteriorate.
There also is no reported effect from the change in light-source intensity over time. While the sensitivity of an infrared sensor can deteriorate because of lamp ageing or cell contamination, the “light-wave interference” principle employed by the OHC-800 relies on a mirrored image unaffected by changes in light intensity.
Advantages of the OHC-800 touted by Riken Keiki in the 12-min recorded webinar produced by the manufacturer are highlighted below.
- High accuracy. Comparison of calorific measurements of fuel gas containing nitrogen shows the OHC-800 and gas chromatographs have comparable high accuracies, but the former’s advantage is the ability to measure calorific value continuously.
- Real-time monitoring with high response speed. Data can be updated every 0.25 seconds. The instrument’s robust design is said to accommodate all measurement environments, eliminating the risk of “measurement outages.” Response time to changes in calorific value is less than five seconds.
- Minimum effects of N2, O2, CO2, etc. Use of both optical and sonic sensors eliminates the possibility of interference from gases that do not have heat content.
- Essentially maintenance-free because the physical-based optical and sonic sensors do not require periodic calibration.
- Easy parts replacement. The OHC-800 has only four parts—sonic sensor, optical sensor, main controller, and power supply.
- Installation flexibility. Explosion proof, operating-temperature profile extends from -4F to 140F.
- No carrier gas is required; instrument air or nitrogen is used as the reference gas.
If your interest is piqued by the webinar, a field-test demo is available.
The 501F Users Group returns to in-person conferencing in 2022 with a year of experience in the virtual meeting world under its belt. The organization’s 22nd annual conference convenes in New Orleans at the Hyatt Regency on Sunday, February 20, and runs through noon on the 24th (Thursday).
Sunday is reserved for socializing. There’s a golf tournament at TPC Louisiana starting at noon and a welcome reception from 7 to 9 in the evening.
Work begins in earnest Monday morning at 8:25 with the group’s interactive safety roundtable—following breakfast, welcome, and introductions. Chairman Russ Snyder will be missing from the podium for the first time in 11 years, replaced by Ivan Kush, Cogentrix Energy Power Management. Snyder retired from his day job as VP generation operations at Cleco Power LLC at the end of 2021. No longer employed by a 501F owner or operator, he had to resign his volunteer position at that time as well.
February 20 – 24
New Orleans, La
Officers and Board of Directors
Ivan Kush, principal CT and controls engineer, Cogentrix Energy Power Management
Carey Frost, program manager, Duke Energy
Secretary and Board Member
Brian Berkstresser, plant manager, Liberty Utilities
Blaine Gartner, principal engineer, Xcel Energy
John Burke, O&M manager, Cottage Grove Power Plant, NAES Corp
Dave Gundry, senior engineer, Xcel Energy
Greg Dolezal, managing director, Klamath Energy LLC (Avangrid Renewables)
Jaime Oliveira, O&M senior manager, Norte Fluminense, EdF
Vendorama begins after morning refreshments and runs until 3 p.m. with a break for lunch. It comprises 20 half-hour technical presentations by third-party services providers, selected by the steering committee (Sidebar 1) to bring attendees up-to-date on equipment and services of primary interest to the 501F community. The Vendorama program is arranged in four tracks, each having five concurrent presentations. The vendor fair from 4 to 7:30 features exhibits from about 70 manufacturers and service firms (Sidebar 2).
Tuesday’s first hour is reserved for a user’s closed session, followed by a generator roundtable. Siemens’ presentations to users starts after the morning break and runs until lunch at noon. PSM presentations begin after lunch and go until 5 p.m. A three-hour evening event, hosted by PSM, starts at 6:00.
The group gathers again Wednesday at 8 a.m. Hour-long roundtables on inlet/exhaust and compressor are followed by rotor and HGP roundtables—also an hour each—completing the morning program. Owner/operators of advanced F frames have a breakout option in place of the first two roundtables. Mitsubishi Power owns the afternoon, presenting from 1 to 5.
Three roundtables Thursday morning—combustor, auxiliaries, and outage—budgeted for 60 minutes each, complete the 2022 program by noon.
Several vendors committed to assuring attendees wouldn’t go hungry by sponsoring meals Tuesday and Wednesday. They are LPG Industries and AGT Services (breakfast) and ARNOLD Group and Mitsubishi Power (luncheons).
2021 conference review
The 501F Users Group’s first virtual conference was conducted over seven 6-hr days, Feb 15-18 and 23-25, 2021. Owner/operators of 501G engines, and Siemens H and V frames, were invited to participate in selected sessions as well.
Day One featured the annual safety roundtable and 30-min Vendorama presentations by ARNOLD Group, Allied Power Group, Dürr Universal, AGT Services, and National Electric Coil. A big benefit of the virtual meeting is that it enables all attendees access to all presentations. Recall that at 501F in-person conferences the Vendorama program is comprised of several tracks, each with several presentations conducted in parallel.
Day Two began with a generator roundtable; presentations by Braden Filtration, Donaldson Company, Frenzelit, Parker Hannifin, and C C Jensen followed.
A 90-min vendor fair was conducted at the end of both the Day One and Day Two programs, with only the Vendorama presenters for each of those days participating.
Day Three started with an inlet and exhaust roundtable; 501G and advanced-frame owner/operators had the option of participating in concurrent breakouts for those machines. Next, National Electric Coil conducted a 60-min training session, Generator Rotor 101, with non-generator SMEs (subject matter experts) in mind. A two-and-a-half hour PSM super session for F users closed out the day.
Day Four was much the same as Day Three except that the 501F compressor was the subject of the opening roundtable and NEC’s training session focused on the generator stator. Mitsubishi Power’s super session followed.
The programs for Days Five and Six (Week Two) were arranged like those on the first two days but with rotor and combustion roundtables the opening sessions on these agendas. Vendorama presentations by Voith Turbo, ORR Protection Systems, SVI Dynamics, Shell, Reliability 360, and Nord-Lock (four-way joint) were featured on Day Five; Nord-Lock (coupling bolts), EMW filtertechnik, ARNOLD Group, Doosan Turbomachinery Services, and GE presentations were conducted on Day Six. Both days ended with vendor fairs featuring the Vendorama presenters.
Day Seven, the final day of the 2021 conference, with no pressures imposed by hotel checkouts, traffic, airline schedules, etc, began with two roundtables (HGP and auxiliaries) and concluded with Siemens’ super session.
Another benefit of virtual conferences is the ability to record their proceedings. PowerPoint slide decks and recordings of all the presentations and roundtables from the 2021 meeting are accessible to registered 501F users at https://forum.501fusers.org/ (search the user-only forums for “2021 Conference Materials”). That is, all presentations except for those made by Siemens, which are available only through the company’s Customer Extranet Portal.
The next section of this report provides precises or thumbnails of all vendor presentations, enabling you to see what you might have missed—or don’t remember—and might want to follow up via a simple search on the user group’s website.
Finally, the last portion of the report features best practices submitted by 501F users for CCJ’s 2021 awards program. The successful plants: CPV Valley Energy Center, South Point Energy Center, Klamath Energy LLC, and Rolling Hills Generating LLC.
Two dozen of the leading third-party suppliers of products and services for the 501F fleet made nominal half-hour presentations at the user group’s 2021 virtual conference. They are available for viewing by owner/operators of 501F engines who are registered on the organization’s website at https://forum.501fusers.com. To access the presentations, look through the user-only forums for “2021 Conference Materials.” Precises of selected presentations follow.
Advanced steam-turbine warming systems to increase startup flexibility
Pierre Ansmann opened his presentation on “the most advanced turbine insulation combined with a high-performance heating system to improve startup flexibility,” by summarizing its value proposition thusly:
- Increased in-market availability.
- Lower startup costs.
- Reduced thermal fatigue and longer mean time to repair for critical components.
- Increased operating flexibility.
He reviewed alternative warming-system arrangements, rejecting those integrating the heating circuits in insulation blankets, installing the heater on a thin mattress below the blanket, and using glass-fiber-insulated heating cable. The optimal system for the upper casing, they said, is heater on metal mesh baffle, for the lower casing, permanent mounting of heating cable below the split line.
The ARNOLD system features interlocking high-performance blankets which conform perfectly to the turbine surface. High-quality materials and manufacturing, and long-term high-temperature resistance, allow the company to guarantee reuse of its insulation system for 15 outages without a decrease in efficiency.
Dozens of thermocouples, strategically located on the turbine, ensure proper heating. Each of the 18 or so heating zones has t/cs installed on the heating wires to double check if the zone is responding correctly and at the specified temperature. Below every heating zone, multiple t/cs are mounted on the casing to confirm even heating of the turbine.
Ansmann said a properly maintained ARNOLD insulation system can maintain your turbine in a hot-start condition for at least four or five days after shutdown. No preheating of the turbine is required prior to a start within this time period, reducing startup fuel consumption and auxiliary power.
Combining high-quality insulation and warming systems enables tight control of casing-to-casing and rotor-to-casing expansion during shutdowns. A goal for operations personnel to aim for, Ansmann said, is a homogeneous cooldown to maintain the temperature difference between the upper and lower casings to less than about 100 deg F.
A case study presented attested to the value of a warming system for a 4.5-day shutdown. Major concerns with the turbine analyzed were the following: casing-to-casing and rotor-to-casing expansion issues during startup; rotor fatigue attributed to differential-expansion control mechanisms; and valve thermal fatigue caused by the turbine startup procedure to deal with thermal expansion.
The solution described in a series of charts included preventing casings and valves from going into cold conditions, plus reducing heat loss to maintain casing and rotor elongation.
Generator high-voltage connection, bushing box, and bushing inspections
Jamie Clark’s well illustrated presentation focused on these three areas:
- High-voltage connection inspections, answering the questions most often asked by users: How/why do HV connections overheat? He covered flexible connections, the importance of tight surface contact, hardware (bolt/nut, washers, etc) selection, and connection restoration.
- HV bushings for pressurized gas-cooled generators: What to look for in bushing inspections and how to locate gas leaks.
- Main-bushing construction methods—addressing porcelain insulators, flange designs, and conductor designs.
Asked what type of bolts AGT Services uses on HV bushing mounting flanges, Clark responded thusly: Typically carbon steel, but sometimes duronze. Stainless-steel bolts are avoided because they tend to gall on aluminum or stainless terminal plates or nuts/hardware.
He went on to say that tight connections are critical for keeping HV bushings cool, recommending the blue-checking of electrical connections at disassembly and reassembly and verifying proper alignment.
When bushings must be replaced, Clark said pre-planning is key to a successful project. For example, be sure to arrange for access to both the inside and outside of the bushing box and be familiar with plant auxiliary equipment removal and lockout/tagout requirements, scaffolding needs, foreign material exclusion, etc.
Outage results, experience with first 501F FlameTOP7, hydrogen, future developments
PSM’s session, at two and a half hours, was about the same length as the other major players on the 2021 program: Siemens, Mitsubishi, and GE. President Alex Hoffs led off with an overview of the company’s activities and safety program.
Chris Johnston, director of product execution, followed with a review of PSM’s outage experiences in the US, Asia, and Mexico—positive outcomes despite Covid-19 challenges. Field service hours worked in 2020 established a new record for the firm. One of Johnston’s brief case histories involved emergency support to deal with a generator exciter failure.
Brian Micklos, senior manager, project management, directed the longest presentation on the program—an in-depth review of the first 501F FlameTOP7 installation, at SRP’s Desert Basin Generating Station, a 2 × 1 501FD2-powered combined cycle. It should be of interest to most, if not all, 501F owner/operators given the detailed comments on the project by SRP’s Jess Bills and Moh Saleh, both long-term participants in the industry’s leading users groups.
Recall that FlameTOP7 essentially integrates the gas-turbine optimization aspects of GTOP7 with the output and efficiency improvements from the FlameSheet combustion system, with AutoTune thrown in for good measure. GTOP and FlameSheet are hardware upgrades, while AutoTune embodies advanced controls.
Highlights of the project provided by Bills and Saleh include the following:
- Combustion conversion to FlameSheet™.
- Hot-gas-path upgrade to GTOP7—exchange of all capital components.
- Installation of an upgraded exhaust system—cylinder and manifold.
- Installation of an inlet bleed heat system.
- Controls logic upgrade to include AutoTune and Part Load Performance features.
- ARNOLD insulation upgrade for the gas turbine.
Detailed planning of the project work scope, critical for others considering a FlameTOP7 upgrade, was part of the presentation. Project results and recommissioning highlights closed out this portion of the PSM session.
The company’s experience in the combustion of hydrogen and mixtures of it and natural gas followed. A look ahead at developments being pursued by the company’s engineers closed out the PSM program.
Remote monitoring of lube oil and diesel conditioning
Oil conditioners/kidney-loop filters are known for their ability to keep oil, and the machines relying on it, clean and healthy. In his presentation, Axel Wegner shows you how to keep lube, diesel, and transformer insulating oils in top condition; plus, how to receive alerts as soon as anything oil-related drifts out of spec—such as cooling-water temperature, excessive wear of machine parts, ISO particle count, etc.
Wegner’s message is clear: The optimal condition-monitoring and filtration system for any machine and oil type allows you to identify problems remotely and to take action before they get out of control. This presentation is one you might want to consider sharing with your plant’s O&M staff during a lunch-and-learn session.
Technology solutions providing more power to you
The Donaldson presentation opened with an overview of the company’s capabilities and moved quickly to a review of its “Three Pillars of Filtration” methodology for rating gas-turbine inlet air filters. HEPA filtration and efficiency testing was next, followed by a look at the company’s quick-lock yoke technology which helps enable rapid filter changeout and its secure installation. A brief summary of Donaldson’s connected solutions to help users better manage their filtration and reduce operating costs closed out the program.
First, a refresher on “Three Pillars.” Given the existence of several standards for the classification of gas-turbine inlet filters, which can cause confusion in the minds of at least some owner/operators, Donaldson has developed a user-friendly filter rating system with the goal of building a consensus to support adoption of its three-part rating system industry-wide.
The three performance factors most important to selection of the proper filter for your plant are efficiency, water-tightness, and, in pulse-cleanable applications, pulse recovery rate. Think of them as the key filtration “pillars” that support optimal gas-turbine operation. In most cases, all three performance factors are important, but their ranking may vary depending on the local environment and operating conditions.
The “Three Pillars” are described as follows:
Efficiency. The proportion of particulates entrained in the inlet air and captured by the filter is the most widely recognized performance metric. Because higher-efficiency filters have associated costs, operators need to determine an efficiency rating that delivers the best return on investment (ROI).
Water-tightness. In humid or ocean-front locations, resistance to moisture becomes a high priority. Salts and other dissolved solids carried by water can be highly corrosive and oftentimes more detrimental than airborne contaminants.
Pulse recovery rate. How readily filters regain peak performance after pulsing is a third key concern. High pulse recovery rises to top priority in desert or arctic environments, where there is either continual exposure to dust, snow, and ice buildup, or potentially sudden episodes of heavy loading.
Careful and objective evaluation is necessary on a case-by-case basis to determine the ranking of these factors for a local situation and operating budget. Identifying priorities enables the most appropriate inlet design and filter combination to be incorporated into your gas turbine system.
Next topic was the success the company has had with its TurbO-Tek™ H2O+ HEPA grade filters which feature very high capture efficiency, water tightness, high dust holding capacity, durability, and insensitivity to humidity/moisture plus coastal and offshore environments. A couple of dozen slides attest to the high performance of this filter in several areas of the country as well as in Asia. The filter is suitable for use in pulse systems.
Generator 101 rotor and stator
W Howard Moudy, director of operations at National Electric Coil (NEC) presented two tutorials of lasting value at the 2021 501F conference, one on the basics of generator rotors and the other on stators. Plant managers, O&M managers, and other responsible parties might consider these presentations among their assets for training staff.
The rotor tutorial first. Moudy began at the beginning—in this case with William Sturgeon’s finding in 1823 that current running through copper wire wound around a piece of iron produces a magnetic field. He reviewed the basic components of rotors and their purposes. For example, the shaft, retaining rings, and wedges are of forged steel, the winding of copper. Then there’s the insulation.
The photo nearby shows the slots machined in the rotor forging to hold the winding’s copper turns. Wedge grooves, “fir tree-” or “T-” shaped allow wedges to hold copper turns in place during rotation. He went on to describe the various types/designs of retaining rings and the material preferred for them for holding the windings in place.
Cooling was Moudy’s next topic. He covered conventional indirect cooled, inner-cooled conductors, inner-cooled coils and insulation, and GE’s diagonal cooled windings. Details on coil-to-coil and pole-to-pole connectors for a variety of machines (Aeropac, Westac, Siemens TLRI, Alstom) followed.
Remaining segments of the presentation included end-turn blocking, rotor slot wedges, slip rings/collector rings, radial and axial connections, J-strap leads, rotor journals and bearings, and rotor fans/blowers.
The stator tutorial resembled a medical text showing all the body parts. The illustrations will benefit greatly O&M personnel who have never seen the machine apart. The stator, Moudy said, consists of the frame, core iron, and coils, the first “holding everything together.” The core iron provides a magnetic path for the flux, while the coils carry the current generated by the induced voltage.
Illustrations of proper core clamping and the types of core laminations (GE’s key-bar slot and the Westinghouse building-bolt design) followed.
Spark erosion then was explained and described with photos showing the progression of a failure. Side ripple filler was touted as a cure for SE and that fact was verified at two plants.
Final topics in this portion of the program: stator slot wedges, stator coil bracing, coil design, endwinding stability, phase leads and phase rings, main/neutral lead transitions, and bushings.
Business and technical updates
Mitsubishi’s primary goal was to showcase its technologies critical to solving known fleet issues with turbine parts, exhaust section, compressor diaphragms, and the rotor torque tube. The company believes it offers the market’s lowest lifecycle cost for these items based on its successes in both the M501F and W501F fleets.
The first two segments of the Mitsubishi program provided overviews of business and outage-execution improvements, and field-service performance—including metrics, dealing with Covid-19 challenges, outage-improvement initiatives, and safety. Even if these areas are not a top priority for you, the slides are worth perusing, if only for the responsibilities and photos of key personnel that plant staff wouldn’t ordinarily see during an outage. Given the travel restrictions of the last two years, this material helps keep you “connected.”
Subject matter of greatest importance to attendees with feet on the deck plates began with Matt McGough’s rotor presentation. The product line manager reviewed the following:
- Comprehensive rotor inspection, recommended at 100,000 hours of operation or 12 years, whichever comes first—what’s involved and the importance of a pre-CRI assessment.
- Rotor service options, including value/benefits and schedule impacts.
- Historical rotor findings: dirt and erosion in cooling passages, blade groove wear from turning-gear operation, cracking of spindle bolt threads, corrosion, etc.
- Upgrades for the torque tube and air separator.
Travis Pigon followed McGough with presentations on gas-turbine parts and exhaust-manifold and exhaust-cylinder improvements. The former reviewed the company’s design and development cycle and how improvements now allow service runs of 32,000 hours/1200 starts for first-stage blades and vanes. Photos show these parts in excellent condition even beyond the recommended intervals. Combustor durability improvements were included in this portion of the program as well.
Pigon said that Mitsubishi’s solutions for the W501F exhaust cylinder and manifold address recurring durability issues—such as cracking of the diffuser and strut shields. Improvements have been adopted from the successful exhaust systems on the company’s advanced turbines which operate at higher temperatures than F engines.
Recall that the Mitsubishi Power two-piece exhaust cylinder is a drop-in replacement for the W501F; no changes to auxiliary piping and foundation are necessary. Experience shared by two customers pointed to no indications or abnormalities for this design in 83,000 equivalent operating hours in one case and 68,000 hours in the other.
Andrew Ogden then discussed performance upgrades and offered two case studies that quantified output and heat-rate improvements made possible by the upgrades.
The Turbine and Generator Repairs Organization closed out the technical portion of Mitsubishi’s two-and-a-half-hour program with a 40-slide presentation on generators, including:
- Stator diagnostics.
- High-voltage bushing refurbishment or replacement.
- Collector-ring inspection, machining, and replacement.
- Reverse engineering of a generator rotor.
- Air-cooled stator rewinds.
- Stator rewinds.
- Ansaldo stator design issues and solutions.
Planning HGP exhaust component upgrades
Scott Schreeg’s presentation on gas-turbine exhaust systems, an afterthought in maintenance planning at some plants, is practical and easy to follow. A quick review of his dozen slides might help keep you out of unnecessary trouble. Visual (unit offline) and thermographic (unit in operation) inspections are important, Schreeg said, and can alert you to impending problems. He suggested an annual interval for this activity.
Expect your exhaust system to last between about 10 and 20 years, depending on the quality of design and construction, capacity factor, and level of maintenance since commissioning. OEM design issues—aerodynamic, thermal, acoustic, and structural—often are associated with problems encountered. Aerodynamics is a big deal, he said, but CFD modeling can point to issues associated with ductwork, silencers, gas recirculation, flow concentrations, pressure drop, etc. Oftentimes, corrections are relatively easy to implement at manageable cost.
Original equipment workmanship is another reason some systems do not last as long as expected. Inspections sometimes reveal use of the wrong weld wire, lack of weld penetration, use of dissimilar metals in construction, etc.
Whether you repair or replace/upgrade depends to a large degree on the extent of degradation found during the all-important inspection. Schreeg stressed the need to consider lifecycle costs when you’re spending money. Justifying a bigger spend now could save later, he said.
Different GT filters, different compressor efficiency results
Florian Winkler’s presentation provides users a methodology for selecting the optimal filter for their gas turbines. It does this by way of a series of performance charts that are easy to understand.
He begins by answering the question: Who is EMW filtertechnik? Then briefly describes his company’s products and identifies some of its customers—a few likely more familiar to you by name than EMW.
One reason filter selection can be challenging is because five filter test standards may be involved—EN779, ISO 16890, Ashrae 52.2. EN 1822, and ISO 26463—and there are many filter classes (different ones for each standard as the handy table included in the presentation attests).
Add to this the product names used by the more than a dozen filter manufacturers serving gas-turbine owner/operators, and you can understand why plant personnel are often left scratching their heads when it comes to choosing the “best” inlet filters for their machines. After all, this is not their only responsibility and decisions on filter purchases typically are years apart.
For those not quite sure how much difference there is between one filter rating and another, there’s a slide with comparison photos of compressor airfoils “protected” by F8, F9, E10, E11, and E12 final filters after 5000 hours of operation in a Siemens H-class gas turbine. It’s an eye-opener. A bar chart confirms the differences.
A series of slides comparing the impact on performance of E10, E11, and E12 final filters installed in a Siemens SGT6-5000F are worth serious review. Winkler’s conclusion from the data plots: E10 filters designed to the EN 1822 standard should not be considered as the final filter for a high-performance gas turbine. Better filtration pays for itself, he said, adding that in the near and long term an E12’s efficiency is what users demanding maximum performance from their engines should select.
Other presentations of interest
APG, Extending the life and capability of a M501F3 R1 turbine blade through repair modifications. Reviews field experience of R1 turbine blades from several suppliers, design/repair related issues, repair process, coatings.
Dürr Universal, Field evaluation of combustion turbine exhaust and inlet systems. Inspection basics supported by excellent photos of key components and their associated issues.
National Electric Coil, Key generator considerations for 501F applications. The five key considerations addressed in the presentation: spark erosion, speed cycling (starts/stops), endwinding support system, partial discharge, and global VPI.
Braden Filtration, To pulse or not to pulse. “Functionalization of cartridge filter technologies.” Asks: How do you judge performance? What are you trying to address—pressure drop, turbine protection, filter life? Explains how pulse filters work and what makes a good pulse filter. Identifies new surface treatments and composites. Highly informative, fast-moving presentation.
Frenzelit, Expansion joint upgrade for legacy 501FD units. Photos describe the steps in removing the existing exhaust manifold, surface preparation of mating surfaces, welding of a new scalloped TEM flange, installation of insulation and new expansion joint.
Parker Hannifin, Challenges and solutions for gas-turbine fluid systems. Covers the development of custom gas-turbine check and ball valves used to control fuel, water, and purge air in challenging turbine-compartment environments.
Voith Turbo, Options for legacy 501F starting systems. Reliability improvement is the focus of the presentation.
ORR Protection, Improving the life safety of CO2 fire extinguishing system water mist technology. Checklist of CO2 system safety features and introduction to water mist systems—including the hybrid water mist system which uses nitrogen to atomize the water to a sub-10-micron level.
Shell, Interpreting oil analysis. Thumbnail descriptions of laboratory tests—including color/clarity, viscosity, trace metals, water content, total acid number, infrared analysis, and particle count.
Reliability 360, Oil condition monitoring digital solution. Fluid (lube oil, diesel oil, and other liquid fuels) condition monitoring using optical technology focuses on reducing downtime and operating expenses of critical equipment.
Nord-Lock Group, 501F 4-way joint solution. Describes the company’s Boltight™ and Superbolt technologies for mitigating leakage at the four-way joint—typically in three shifts during an HGP or major inspection.
Solutions for turbine coupling bolt issues. Discusses through- and fitted-bolt issues and how the company’s EzFit expansion bolts can eliminate them.
Doosan Turbomachinery Services, Turbine blade-ring assembly fundamentals.
Blade-ring disassembly and inspection details covers special fixturing and procedures believed necessary to assure proper repairs. A checklist of things to be aware of during shop work is included.
Advanced Turbine Support
AGT Services Inc
Allied Power Group
Alta Solutions Inc
American Thermal Solutions
BBM-CPG Technology Inc
Braden Filtration LLC
Brüel & Kjær Vibro
C C Jensen, Oil Maintenance
Catalytic Combustion Corp
Crossby Systems Inc
Doosan Turbomachinery Services Inc
Dürr Universal Inc
EMW filtertechnik GmbH
Environment One Corp
Falcon Crest Aviation Supply Inc
Groome Industrial Service Group
Hilco Filtration Systems
Industrial Air Flow Dynamics Inc
Koenig Engineering Inc
LPG Industries Inc
Mee Industries Inc
National Electric Coil
NRG Energy Services
ORR Protection Systems Inc
Parker Hannifin Corp
PowerFlow Engineering Inc
Precision Iceblast Corp
Rochem Technical Services
ROMCO Manufacturing Inc
Sensatek Propulsion Technology Inc
Shell Oil Products
Sulzer Turbo Services Houston Inc
SVI Industrial (SVI Dynamics/Bremco)
Tetra Engineering Group Inc
TOPS Field Services
Trinity Turbine Technology
TRS Services LLC
Umicore Catalyst USA LLC
Veracity Technology Solutions
Viking Turbine Services Inc
New purge procedure allows faster start of gas-line maintenance
Challenge. CPV Valley Energy Center’s procedure for depressurization and purge of its fuel-gas system for inspection and maintenance required multiple movements of equipment (nitrogen trailers and hook-ups). Plant’s goal was having a procedure that didn’t require the movement of equipment and one conducive to faster purging.
Solution involved adding new valves to permit isolation of each section of the gas train (Fig 1) and a detailed procedure for depressurization and purge that stressed safety. The gas-line regulator manufacturer provided comprehensive instructions (more than a hundred steps) to achieve the plant’s goals.
The added isolation valves allowed depressurization and purging of sections of the gas line versus purging the entire line to both generating units each time repairs were needed. The regulator manufacturer provided instructions for staff to hold open the regulator, allowing the nitrogen purge to flow through the regulator at low pressure.
The procedure developed allowed one location for the nitrogen trailer to accommodate either a sectional or complete purge.
Results. The improvements made allow staff to depressurize and then purge the gas line in sections, or end-to-end, without moving equipment. Other benefits:
- Reduced the time needed to achieve safe working conditions for gas-line work.
- Reduced the amount of fuel vented when working on isolated parts of the line.
- Ability to isolate one gas turbine at a time, potentially allowing the other unit to remain in service.
John Anderson, operations technician
Ed Peters, maintenance manager
Dave Engelman, operations manager
Josh Zimmer, plant engineer
Ben Stanley, plant manager
How Valley reduced the costs of plant makeup, discharges
Challenge. While air-cooled condensers (ACC) contribute to a significant reduction in overall water use at combined-cycle facilities, CPV Valley was struggling with high usage and discharge rates. This created issues with overall water-management expenses—including higher gray-water intake and discharge costs, higher chemical usage, heat losses in the HRSGs (contributing to higher heat rates), and the need for increased operator involvement in maintaining plant chemistry and tank levels.
Solution. Through a collaborative effort, the CPV Valley team developed the following key action items:
- Conduct a comprehensive review of chemistry logs with third-party consultant HDR Engineering. Outcome: The cycle-chemistry control strategy (intermittent and continuous blowdown rates) was adjusted to optimize system performance while dramatically reducing blowdown and quench-water costs.
- Initiate monthly chemistry review meetings with the O&M staff and HDR Engineering.
- Update the plant’s Cycle Chemistry Manual; train the O&M team on the changes.
- Conduct a plant-wide thermographic survey to find leaking drain valves. Outcome: More than 100 valves in the steam cycle damaged or worn out during commissioning required replacement or repair.
- Review and optimize water-treatment-system self-cleaning and backwash rates to reduce waste.
- Update operator process screens to show daily intake and discharge rates to raise awareness of their impacts on the plant budget (Fig 2).
- Perform a recapture pilot to collect valuable process and chemistry data for possible capital system upgrades in the future.
Key results of implementing the solutions above included the following:
- Reductions of from 30% to 50% in monthly water use, discharge rates, and chemical use.
- Overall net heat-rate improvement.
- Reduced wear and tear on water-treatment-system components (less operation, cleanings, and filter replacements).
Dave Engelman, operations manager
Ed Peters, maintenance manager
Josh Zimmer, plant engineer
Ben Stanley, plant manager
Donald G Atwood, asset manager
Dan Sampson, principal technical consultant, HDR Engineering
Safely managing, preventing gearbox failures
Challenge. CPV Valley’s “In-Air” air-cooled condensers (ACC) are US serial numbers 1 and 2 (Fig 3). Though there are many benefits to the induced-draft design, there also are many maintenance challenges.
Example: Traditional ACCs are designed for ease of maintenance, typically having an access platform/rail trolley system which allows equipment to be rigged and lowered out the bottom of a cell. Design of the In-Air system allowed for maintenance by use of a davit assembly in each cell—roughly 35 ft in the air above the cell platform. There are several factors to consider when using this method for maintenance—including safety, manpower, downtime, accessibility, and logistics.
While the system as designed is feasible, it presents many challenges. Among them: Setting up of scaffolding in the fan cell, erecting a davit (with multiple pieces) on the fan deck, and disassembling the fan one blade at a time and lowering down the components before the equipment requiring maintenance can be accessed. The fan hub, blades, and gearbox must be manipulated to fit through the ACC floor, requiring adjustment of the suspended load. This process creates significant safety risk, is labor intensive, and requires significant downtime. Plus, it is logistically difficult.
The rigging challenge became obvious when several gearboxes experienced output-shaft seal leaks. To replace a seal with OEM parts requires full disassembly as described above.
Solution. Plant personnel recognized the challenges and took a comprehensive approach towards maintenance activities and scenarios. Solutions for each problem are presented below.
Output-shaft seal failures. Knowing the challenges and time associated with disassembly and reassembly of the fan blades and hub assembly to change out a seal, the maintenance department pursued development of a seal design that would require minimal disassembly. The team worked to understand the failure mechanism and engaged Corrosion Products & Equipment to collaborate on a solution. A flange-mounted split seal design was chosen. The Inpro/Seal solution continues to be leak-free and reliable after more than a year’s operation (Fig 4).
Major equipment changeout service. Staff recognized quickly that a plan was needed to change out a fan motor and/or gearbox. Several scenarios were evaluated and the pros/cons weighed for feasibility. The team worked with IPE Rigging Corp to develop an engineered plan and offer solutions to the problem.
The first solution proposed was to use a “davit arm” concept (Fig 5), which involved rigging equipment up to the fan deck. This would allow the fan to be jacked up and locked in place above the gearbox. The gearbox then could be lifted, slid out on a rail and beam-trolley system attached to the fan jacks, and then lowered to the ground.
During the design phase of the davit/jacking system, one of the ACC gearboxes failed. This created an opportunity for the team to prove that concept. However, it quickly became evident that the approach was logistically infeasible, created numerous safety issues, and would have taken seven full days to complete. Working from the top seemed to be the better approach.
The affected gearbox happened to be in the second row from the outside, which made it easily accessible by crane. A 175-ton crane with a jib could access the fan at a radius of 105 ft, approximately 95 ft above ground level. The process involved removing the entire 36-ft-diam fan-blade assembly from the gearbox, placing it on the ground, and then removing the gearbox (Fig 6).
The first gearbox change was completed successfully—including setup, demob, and final alignments—in four days. With many lessons learned, the team was confident that if it planned properly, the work could be done safely in three days.
A design review found a crane could reach all 36 fans on the ACC. There are many details and obstacles that still must be reviewed—including terrain, setup area, underground utilities, crane size, and cost—before this can be confirmed. But this approach would give CPV Valley a viable solution for having any fan up and running in a three-day window, as opposed to seven days or longer using the davit assembly.
- A safer approach to equipment maintenance on the ACC.
- The split seal bearing design played a key role in equipment reliability and reduced downtime.
- A comprehensive study and plan involving major equipment removal and maintenance was developed for the site.
Tom Viertel, lead maintenance mechanic
Charlie McDonough, maintenance mechanic
Corrosion Products & Equipment
IPE Rigging Corp
Benefits of an equipment maintenance review process
Challenge. Establishing a comprehensive maintenance program takes critical focus by the O&M staff on a continual basis. When getting the initial work-management process set up, not all items for each piece of equipment, skid assembly, or system always are captured.
Solution. Team Valley developed and refined an Equipment Maintenance Review Process that takes a comprehensive approach to equipment maintenance. Key elements of the program:
- System/equipment identification. The original list of systems/equipment from the EPC contractor was reviewed and updated to ensure accuracy.
- System review checklist. A standard list was developed to assure questions are asked about each system and piece of equipment—including inventory, critical spares, lubrication, calibration requirements, etc. All information was reviewed and updated in the CMMS (computerized maintenance management system).
- Periodic meetings are conducted with key O&M stakeholders to review the checklist, O&M manuals, service bulletins, etc.
- Operator rounds and surveillance checks are reviewed and updated based on any findings from the review.
- Engineering and EHS personnel review any potential regulatory or compliance requirements.
- Team members are assigned action items for completion and follow up prior to the next meeting. Examples of action items: Creation of PMs, modification of existing PMs, obtaining quotes, and submission of new inventory forms.
- CMMS is updated with any new items related to preventive maintenance, spare parts, and inventory.
- Status of the program/action items is distributed weekly and posted in common areas so all can see and monitor program process.
- Developed a more comprehensive preventive-maintenance and work-management program for plant systems and equipment.
- O&M team members increased their knowledge of systems and equipment through the more-focused reviews of individual components.
- Less corrective/reactive maintenance is required.
Ed Peters, maintenance manager
Ben Stanley, plant manager
A collaborative, comprehensive approach to safety
Challenge. Sustaining a best-in-class approach to safety requires continuous effort by plant employees. The best way to maintain the program is to make sure that safety issues are addressed in a timely manner and results are reported back to all hands so they know action will be taken when they bring up safety issues.
Solution. There are several key elements to a plant safety program—such as proper training, proactive safety discussions during daily meetings, employee-led safety committees, safety recognition, job hazard analysis, near-miss reporting, lessons learned, etc. This entry focuses on a few key safety program elements at CPV Valley Energy Center, as described below:
Safety work management. While there still is a use for the dusty safety suggestion box, a better way to track safety concerns is through the plant’s work management system. Team Valley implemented the following features in their CMMS:
- Safety work orders are classified as “Safety” (immediate concern) or “Safety suggestion” (a safety improvement).
- If a Safety work order is submitted, an email to the entire plant staff is generated making all personnel aware of the issue.
- Plant management reviews the Safety work order immediately and ensures that preliminary mitigation measures have been taken.
- If the issue can be resolved quickly, it is addressed and the work order closed. If a long-term fix is required then mitigation measures are put in place. The work-order status is changed to “Safety Mitigated” until it can be addressed permanently through proper planning and budgeting.
- When the work order is closed out, another email informs all employees that the issue was resolved.
- The entire list of safety work orders, safety suggestions, and safety mitigation work orders is reviewed during the plant’s periodic work-management meetings and by the plant employee-led safety committee. Some of the best items/actions may be selected for recognition, with contributing staff members receiving a recognition notice along with a gift card thanking them for their attention to safety.
Housekeeping is an important safety program item. CPV Valley staff took an area ownership approach. Teams were developed (based on shifts) and physical areas designated on a facility map. Cleaning stations were set up for easy access to cleaning equipment and trash cans. Periodically, site management chooses a new area to inspect to ensure the crews are keeping their areas clean and have the resources to do so. Management also has an assigned area and meets periodically to roll up their sleeves and maintain their areas of responsibility.
Visitor management and orientation—pandemic and beyond. With the onset of the pandemic, the tracking and admitting of visitors without exposing anyone became more of a challenge. Several key processes were developed, including these:
- Contractor orientation. Contractors are contacted before they arrive at the site to review the plant’s orientation video online. They still are required to complete the exams associated with the video and report back to the site’s EHS coordinator, who validates attendance and ensures all site documentation requirements are met.
- Job hazard analysis. Blank forms are sent to contractors for completion ahead of time; the contractor returns the forms prior to arriving at the plant. This gives the sponsor the opportunity to review and make changes, if necessary. The JHA still is reviewed and signed in person, but the initial time taken to complete the forms is done remotely, minimizing exposure time between employees and contractors.
- Sign-in/sign-out process. Site personnel came up with a better way to track visitors and contractors onsite using LobbyTrack, software that allows for contactless registration through use of a Quick Response code that can be scanned by any smartphone. The visitor enters his or her contact information into the system and is automatically registered in the plant’s visitor log.
- The system also has features such as host notification, whereby the host can pre-register visitors and will be notified when the check-in process is completed. The system can be used to notify visitors and contractors via text message when evacuation orders are initiated. Lastly, the visitor log can be viewed from anywhere using a computer, smartphone, or tablet.
- A safety program that values employee input.
- Quick resolution of safety issues.
- Clear communication on safety items and progress.
- Constant input and improvement to safety programs.
- Streamlined contractor orientation and check-in along with minimal social interaction and touchless registration options.
CPV Valley O&M team
Ed Peters, maintenance manager
Dave Engelman, operations manager
James Longhenry, EHS coordinator
Elizabeth Judge, plant administrative assistant
John Anderson, operations tech and chairman of the Safety Committee
CPV Valley Energy Center
Owned by CPV/Diamond Generating Corp
Managed by Competitive Power Ventures
Operated by DGC Operations LLC
680 MW, gas-fired 2 × 1 SGT6-5000-powered combined cycle located in Middletown, NY
Plant manager: Ben Stanley
Electronic log enables tighter control of boiler chemistry
Challenge. The need for proper control of boiler chemistry is well known. An important part of any operator’s shift involves monitoring of boiler chemistry parameters and taking action to ensure they are maintained within posted specifications. The actions in real time help assure long-term integrity of boiler systems and, by extension, plant reliability.
There are time limits on how long chemistry parameters can be out of spec. For example, EPRI’s “Action Levels” establishes the time limits based on the severity of the out-of-spec parameter.
When logs were maintained on paper, tracking the time boilers operated in these levels was cumbersome—if done at all. The challenge to South Point staff: Find a more efficient way to track chemistry action levels to allow better decisions on boiler chemistry control.
Solution. Chemistry logs at South Point now are maintained in an electronic software format. The logs include the date and time of the analysis and the readings for the chemistry parameter.
If an out-of-spec reading is found while taking chemistry readings, the operations team responds immediately, taking appropriate steps to return chemistry to the proper control band.
The application used allows downloading of the data to an Excel format. The spreadsheet has the capability to flag when parameters are out of spec. The date and time stamp allows calculation of how long the out-of-spec condition lasted. Then the out-of-spec time periods can be added to determine the time in each action level. Posting the results on a monthly basis gives staff and management insight into the efficacy of the chemistry control plan.
Results. By monitoring the plant’s adherence to chemistry action levels, the efficacy of the plant’s chemistry control plan can be measured and acted upon. Tracking magnitude and time of out-of-spec chemistry parameters can offer insight into potential future maintenance issues.
Sharing of this information with the operations staff can foster ownership of the chemistry control program. Trending improvements attributed to the chemistry control program over time could become part of an incentive plan.
Kurt Fetters, plant manager
Darren Otero, operations manager
Stan Avallone, Calpine chemistry program manager
Vincent Powers, plant engineer
South Point Energy Center
580-MW, gas-fired, 2 × 1 combined cycle powered by 501FD2 gas turbines, located in Mohave Valley, Ariz
Plant manager: Kurt Fetters
Permanent monitoring system cuts time, cost of vibration analysis
Background. Klamath Energy’s mechanical-draft counterflow cooling tower was built by Balcke-Dürr in 2000 without vibration probes installed on its gearboxes. The CT is of fiberglass-reinforced polyester (FRP) construction with eight cells, each 48 ft wide × 48 ft long. The tower’s fans are driven by 200-hp, two-speed motors. The single-piece, full-floating composite horizontal drive shaft transmits drive-motor torque to Flender right-angle gearboxes.
Challenge. Direct vibration readings of the gearboxes were cumbersome at best, a process involving the following steps:
- Operations to approve the cell being removed from service. Decision-making required consideration of generation load and weather conditions.
- A LOTO and confined-space permit were required for cell entry.
- Remove the fan cowling access panel.
- Install scaffolding and/or personnel safety systems for cells with no provision for gearbox access.
- Enter cell and install two vibration probes—one on the input shaft, one on the output shaft.
- Route wires from the probes to the cell exterior by zip-typing the wires to supports/piping/railing, and attach the wires to the monitoring device.
- Reinstall the cell cowling.
- Remove the LOTO to make the cell available for testing.
- Start and monitor the motor and gearbox vibrations at both high and low speeds.
- 10. Secure the cell from vibration analysis.
- Reapply the LOTO.
- Remove the fan cowling access panel.
- Enter the cell and remove the vibration probes, wiring, and zip ties.
- Remove scaffolding and/or personnel safety systems.
- Reinstall the cell cowling.
- Remove the LOTO and make the cell available for normal operation.
Bear in mind that staff had to repeat the process seven more times to analyze vibrations in all cells. This typically took three days (approximately three hours per cell) and involved two mechanics. Total cost of the analyses: $4200.
Mechanics also attempted to get reliable indications of gearbox vibrations by recording readings from the motor mount and support tube to the gearbox. But analysis of vibrations analysis using this method was unreliable.
Solution. Install a permanent vibration monitoring system. All components were installed, wired-up, and commissioned with a crew of three in two days during the spring outage (photos). Hardware and installation costs totaled $12,000 ($8500 for parts, $3500 for labor). Vibration analyses are conducted semiannually, so payback was approximately a year and a half.
Results. Today, the checking of gearbox vibrations is a simple one-person task done this way:
- Operations confirms that a cell can be manipulated from high- to low-speed and then returned to normal service.
- Analysis of vibrations is next, a process that takes about 25 minutes per cell.
The positive effects of permanent probe installations for analysis of vibrations are the following:
- Only one person is required for data acquisition.
- No LOTO and/or confined-space permits are required.
- An analysis easily can be repeated at any time if further investigation is required.
- The cost today for analyzing vibrations in all cells is only $300.
Doug Hudson, maintenance supervisor
Klamath Energy LLC
536-MW, gas-fired, 2 × 1 combined-cycle cogeneration plant powered by 501FD3/6 gas turbines, located in Klamath Falls, Ore
Plant manager: Greg Dolezal
Single-permissive remote start, automated fuel equalizing
Challenge. Rolling Hills recently updated its run profile from a 30-min start window to five minutes. Like many other plants with a 5-min window, a remote start program was implemented.
The challenge that Rolling Hills faced was to simplify the old startup sequence so an operator could bring units online successfully while working remotely from a secure device, and then drive to the plant.
Before project implementation, the starting procedure required the operator to open the main fuel-gas valve, start the demineralized-water pump, start the fuel-gas heater, and put the unit on turning gear. The first three already were integrated into the control system, but the turning gear was not. It was controlled by a hand switch located in the electrical package for each unit.
Lastly, Rolling Hills faced the challenge of fuel surging and popping relief valves from opening the main fuel-gas valve without first equalizing the plant pressure. This was done via a hand-operated valve, also opened by the operator before each start.
Solution. Logic changes were required to implement a simple remote start/stop routine. The plan: Create a single remote-start page that had only five buttons, one for each of the plant’s five gas turbines. With the main fuel-gas valve, fuel-gas heater, and demin-water pump already integrated into the DCS, focus of the plan was to electrically control the turning gear and the fuel-gas equalizing valve.
The turning-gear hand switch was located inside each units’ electrical package, where the PLC also was housed. A wire was run from an output card directly to the “auto” side of the hand switch, then mapped to the DCS for programming.
The last piece of the puzzle was how to ensure the pressure differential between the plant side and supply side of the fuel-gas system would not be so great as to impede safe operation. Bear in mind that the main fuel-gas valve is an instantaneous open/close valve to protect the plant in case of an emergency. Opening this valve when there is a high pressure differential would open relief valves throughout the plant, causing a high pressure drop.
Thus, the replacement for the hand valve had to be one that could be controlled by a 4-20-mA signal to regulate the equalization pressure. Plant employees installed the valve (Fig 2), ran the power and control wires, and mapped the valve back to the DCS for programming.
Lastly, the logic was created to automatically equalize Rolling Hills’ fuel-gas pressure, open the main fuel-gas valve, start the fuel-gas heater, reset any trips on the unit, place the turbine on turning gear, and then, after a set time, start the unit. Staff mapped the new logic to pictograms and placed it all on a special, designated remote-start page, reducing the start and stop sequences to a single-button permissive per unit (Fig 1).
Result. All employees were trained on the new start procedure. The simplified process helps prevent operators from missing any steps and has allowed them to start units remotely with ease. Success: Every technician has started units remotely and Rolling Hills has not missed a dispatch within the 5-min window.
Logic was reversed to make the unit stop sequence as easy as the start. By simply sending an “off” permissive using the same single remote-start button, the unit virtually runs the logic backwards and shuts down everything automatically—all while remaining smart enough to know when another unit is running and not to stop the fuel and water system. Plus, also placing itself back on turning gear for unit cooldown.
All Rolling Hills OMTs
Covid-19 initiatives protect plant, contractor personnel
Challenge. The questions Covid-19 presented to Rolling Hills and other plants included the following:
- How do we keep our employees safe?
- How do we keep up ongoing maintenance with reduced staffing?
- How do we keep our contractors and employees working safely during scheduled outages?
At plants with a relatively small workforce, like Rolling Hills, outage work had to be broken down methodically into step-by-step procedures to analyze the potential contamination of tools, equipment, and staff. Industry standard procedures were rewritten to adapt to the “new normal.” With only a handful of employees at this simple-cycle facility, the need to limit staff exposure to sickness was particularly important. One of the first things that had to be addressed was the need to get contractors into the plant and ready for work while limiting staff exposure.
Solution. First step was to improve the plant’s safety orientation plan. Contractor orientation and visitor registration procedures were rewritten, paying close attention to detail to limit Covid exposure from outside sources.
Prior to being admitted onsite, contractors were emailed an information packet that included instructions on where to park and report to for a wellness screening conducted by contracted health professionals (Fig 3). Good health verified, contractors were directed to the plant warehouse, which was converted to a breakroom for safety orientation—complete with DVD player, procedures, and required paperwork.
Rolling Hills staff was on hand (at a safe distance) to answer any questions contractor personnel might have had during their self-guided orientation using strategically placed plant radios.
Rolling Hills Generating LLC
Owned by Eastern Generation LLC
Operated by Consolidated Asset Management Services LLC
850-MW, gas-fired, simple-cycle generating facility powered by five 501F engines, located in Wilkesville, Ohio
Plant manager: Corey Lyons
An owner/operator presenting on aqueous-ammonia (NH3) storage tank inspections at the CCUG2020 Week Four session said that according to the governing standard, API510, a “fitness for service” assessment should be conducted every 10 years (or half the remaining life calculated during the last inspection) for pressure tanks. The method results in a calculated remaining life, and typically the work is performed by a specialist contractor squad including an API specialist, NDE technicians (usually two), a confined-space entry team, standby rescue team, environmental contractor, scaffolders, and the ammonia supplier.
Plant management should assign a point person to the project who coordinates with the contractors, prepares the tank documentation, gathers previous inspection reports, etc.
Since tank wash-down water must be disposed of as hazardous waste, an accurate estimate of residual NH3 is necessary ahead of the work. You can expect between about 2000 and 3000 gallons of RCRA-type waste which will have to be disposed of or stored onsite in a tanker. Plant should allow a full day for tank cleaning.
Once cleaned, the actual tank inspection is “pretty straightforward.” The NDE inspectors divide the tank surface into a grid and record thicknesses from ultrasonic transmitter (UT) readings at each location. Allow a second day for the inspection work. Plant staff should take the opportunity to service pressure relief valves, vacuum breakers, and other components, and to leak-check the manway ports (easier for vertical tanks). Make sure to have on hand sufficient calibrated air monitors and extra ammonia sensors.
In response to questions, the presenter said that (1) they had not considered neutralizing aqueous NH3 prior to opening the tank, (2) the dump valve should be inspected and/or replaced at each inspection, and (3) the tanks are carbon steel, piping is stainless, and that iron can mix with the NH3.
EPRI Technical Executive Sam Korellis opened the CCUG2020 Week Four agenda with a review of EPRI’s cooling-tower (CT) fan-motor-drive and gearbox field evaluation program and its implications for CTs serving more than 800 units at about 300 powerplants.
Many CTs are equipped with multiple fans which start and stop depending on load and ambient temperature. With many plants cycling more and more, these fans cycle on and off more as well. Since each draws auxiliary power, excess fans in operation penalize heat rate.
Korellis noted that the criterion to start or stop a fan is simple: If it allows an increase in net power. Starting a fan improves CT thermal performance and unit efficiency but draws additional power. Stopping a fan has the opposite effect.
Starting and stopping fans frequently leads to gearbox failures. Gearboxes suffer failures at a 10% to 20% annual rate industry-wide, said Korellis, and they are costly. A new one runs about $30,000, plus about $5k in labor. They also require replacement power while out of service. Failures can damage fan blades and other components, and can contribute to oil contamination of the tower water.
Objective of the drive optimization project was to evaluate the start/speed regime under unit cycling. Operating wet-bulb temperatures ranged from 35F to 85F and steam-turbine load from 200 to 900 MW during the test program.
Three starting/speed regimes were tested: one-speed (on/off), a soft start (two-speed), and a variable frequency drive (VFD) capability. Under a variety of operating conditions (load, cold-water temperature, ambient temperature, fan speeds, number of fans in operation, etc), the VFD option offered the greatest net benefit in optimizing performance, and was similar in cost to the two-speed option, even if the latter is of a simpler design.
For the gearbox evaluation, the project team purchased several new right-angle gearboxes, and installed and operated them in one CT, with additional monitoring capability, where they would be subject to identical operating conditions. Objective was an attempt to determine causes of frequent failures, effect of repeated start/stop cycles on gearbox reliability, and the relative reliabilities of gearboxes paired with the three start/speed regimes.
During the evaluation, four gearbox failures were experienced in one year. Elevated lube-oil failures also were noted. There were signs of low oil level, moisture contamination of oil, and high oil-pressure levels which caused vaporization and loss of oil. Oil temperatures greater than 200F were observed in the winter, and as high as 300F in the summer.
Near-term modifications suggested by the results include the following:
- Upgrade to synthetic oil or higher-grade mineral oil.
- Check oil level and condition during warm operating months.
- Develop oil sampling and analysis to detect early degradation.
- Impose quality threshold levels for oil rejection and replacement.
- Continuously monitor gearbox temperature.
- Deploy real-time vibration monitoring sensors.
- Reduce dead air space around gearbox to promote better cooling.
Longer term and more involved/costly solutions include an automated lube-oil refill system and lube-oil sampling; addition of an external lube-oil filter and cooling system; or convert to a direct-drive system and eliminate the gearbox.
One attendee asked how to feed this knowledge into a design spec and Korellis said to add fins and/or a diverter to improve gearbox cooling, and add instrumentation to monitor temperature inside the gearbox. Another asked whether there was any difference in the performance of the soft-start versus VFD and the answer was “no.” A third asked about the oil sampling and the suggestion was to sample and analyze weekly, but cautioned that sampling apparatus could contaminate the CT water if the sampling tube leaks. Best to locate the sampling apparatus outside of the CT internals, he added.
The main messages from the presentation on fire suppression systems during Week Four of the CCUG2020 meeting, by ORR Protection’s Chuck Hatfield, are that NFPA Code requirements include the life (human) safety and reliability of suppression equipment, whether low- or high-pressure type; and that the industry is “moving away from CO2-based suppression to water-mist systems.”
One reason for the shift is that life safety risk is higher with CO2. Another is the psychological effects—there has been a higher level of deaths in confined spaces protected by CO2 in recent years. A third is that water presents an effectively “unlimited” supply of suppressant compared to CO2.
The presenter distinguished among three types of areas with respect to fire: those requiring lock out/tag out for entry; normally occupied areas, those not governed by LOTO; and normally unoccupied areas, those which cannot be occupied by a person. NFPA has new requirements for equipment to enhance life safety in normally occupied areas. Visit www.nfpa.org for details. An odorizer is an option and is very expensive, according to the presenter. Lockout valves must be monitored.
NFPA 750 and FM 5560 apply to water-mist systems. Fundamentally, all convert water mist into steam which acts like an inert gas, and promote three extinguishing mechanisms—inerting, cooling, and fuel wetting. System varieties include self-contained cylinder units, or diesel engine, gas engine, or electric power drives.
Attributes include the following: They incorporate smoke scrubbing devices, consume a relatively small amount of water, one pump/system can serve multiple generating units (for example, three gas-turbine units), and can be equipped with plug-and-play releasing panels.
The presenter responded to questions on the following topics:
- Sources of water: Fire-water main loop if potable water, cooling water, or demineralizer water (provided the tank is large enough).
- Spent water collection. Generally not required; some fire-prone skids like lube oil have a containment wall around them.
- Testing spray heads for atomization: Test on system commissioning, then blow air to make sure nozzles are free-flowing. NFPA requires blowout with air annually, annual water bottle inspection, and backup-battery tests every six months.
Steve Shulder, EPRI’s subject matter expert on water and steam chemistry addressed chemistry-related damage from flexible operations during Week Four of the CCUG2020 program. Thorough to a fault, most of Shulder’s slides are laden with bullet points, likely summarizing chapters of EPRI reports on the subject. It’s almost impossible to condense the 45-slide deck into useful highlights, so users should both review it and watch the recording on the Power Users website. The presentation is packed with good material for whoever is responsible for plant chemistry.
Two areas worth reviewing here, however, are (1) maintaining sampling and online analyzer systems and (2) plant layup and storage. Keeping the former in top working order is critical because, during operation, “you can’t control what you can’t see,” stressed Shulder.
Of course, online analyzer systems are also impacted by cycling operations and improper layup. Debris in the water/steam circuits can plug sample lines. Sample lines should be equipped with blowdown lines; lines and analyzers should have de-ionized water flowing through them so they don’t dry out. Other checklist items are shown in Table 1.
The table on best available techniques for layup and protection (Table 2) is a convenient guide organized by plant subsystems and components. Of note as well is a recently developed dehumidified-air system (figure), proven at several combined-cycle plants in the south, which protects the turbine steam path from moisture condensation when offline for long periods. “Deposits cannot lead to pitting without moisture,” Shulder reminded the audience.