The Combustion Turbine Operations Technical Forum (CTOTF) recently announced the winners of the 2nd annual CTOTF/POWER Innovation Excellence awards, which recognize outstanding performance in various categories. Exelon Generation, Oglethorpe Power Corp., NV Energy, and IHI Power Services Corp. were all recognized for notable projects.
The Combustion Turbine Operations Technical Forum (CTOTF) is a membership organization of combustion turbine owners and operators. CTOTF’s user-defined mission is to be the premier forum for the exchange of information and experiences related to the design, operation, and maintenance of combustion turbine and combined cycle power plants, and to provide a collective voice for its members to express issues and concerns.
The group, in association with POWER, recently announced the winners of its annual Innovation Excellence awards program. Selections were made in five categories: operational, technical, maintenance, environmental stewardship, and safety process areas.
In the operations category, Exelon’s Mystic Generating Station in Charlestown, Massachusetts, was recognized for successful windscreen projects completed on its Units 8 and 9 air-cooled condensers (ACCs). According to Plant Manager Brian Pettenati, the projects were necessary to ensure the units could reliably operate at maximum capacity during the summer.
“On hot, windy days, we had to de-rate the units due to a reduction in ACC efficiency,” Pettenati explained. “We needed something that would stop hot air from recirculating from the top of the ACC back to the suction of the fans, and we wanted to eliminate the wind-tunnel effect under the ACC, which tended to stall the natural air flow to the fans.”
Pettenati asked Mike Brown, Exelon’s technical manager for the Northeast region, to find a solution. Brown tasked Ying Ng, senior site engineer, with managing the project. Ng did some digging and identified a windscreen solution offered by UK-based Galebreaker Industrial. So, Galebreaker and its subcontractor, Ergon Research, were brought in to study the Mystic site.
The team analyzed the topography and building layout, then used computational fluid dynamic models to determine how different wind conditions and other characteristics affected ACC performance. Once the problem was completely understood, Galebreaker proposed the installation of polyvinyl chloride (PVC) windscreens, which are 75% solid and 25% permeable.
Ng sat down with the structural engineer and studied the design to determine the load the ACC structure would need to support with new windscreens installed. Some structures would require enhancements to handle the burden. “We had to strike the right balance between maximizing the effectiveness of the screens while minimizing requirements to add new support structures to manage installation costs,” Ng said.
1. Windscreens were installed under the Mystic 8 and 9 air-cooled condensers to minimize de-rates on hot, windy summer days. Courtesy: Exelon Generation
The most-effective layout was found to be a cruciform pattern of windscreens installed under the fans (Figure 1). Ultimately, material was fitted around the perimeter of the ACC along the top of the understructure.
“The windscreens work,” Pettenati said. “Last summer, when weather conditions would have predicted a problem for us in the past, our ACCs continued to perform well.”
And the improvement is paying dividends. Pettenati said there were 368 hours with wind speeds greater than 10 mph and temperatures greater than 85F in 2018, and 217 hours exceeding those thresholds in 2019. Based on the average power price and previous de-rates during such conditions, the project is expected to pay for itself within about two and a half years.
A generator cooling gas change from hydrogen to helium won CTOTF’s Innovation Excellence award in the technical category. The project was completed at Oglethorpe Power Corp.’s (OPC’s) Doyle Energy Facility in Walton County, Georgia.
As most power plant personnel know, hydrogen is regularly used as the cooling medium in large electric generators because it is better than air at transferring heat. In fact, it is seven times more effective, and it has one-fourteenth the density of air, which means there are less friction losses in the generator when hydrogen cooling is employed.
Doyle Unit 1 is a GE Frame 7B gas turbine with a 64-MVA/14.4-kV, 30 psi hydrogen-cooled generator, which was manufactured in Lynn, Massachusetts, in 1968. In 2017, OPC engineers conducted a thorough assessment of the generator. The inspection and testing indicated that the stator asphalt insulation had deteriorated. Evaluators estimated the unit had less than two years of remaining life. Additionally, several operational performance and equipment condition gaps were found on the unit’s hydrogen cooling system.
The cost of getting the hydrogen cooling system up to industry standards was not insignificant. The estimated investment required to upgrade the hydrogen control panel, add auto-purging logic, install hydrogen hazardous gas detectors, make general system repairs, and refurbish the seal oil system regulator and float trap was approximately $400,000 to $500,000. The combination of issues and the short expected remaining life led OPC’s team to look for alternatives to hydrogen cooling in order to continue operating the unit as long as possible without investing a great deal of additional capital.
Air was considered as a cooling medium alternative, but it would have resulted in greater than a 50% de-rate of the machine. So, with support from industry subject matter experts, OPC personnel researched using helium instead. Compared to hydrogen, helium has very similar thermal conductivity properties, but it is about twice as dense. This could be compensated for by operating the helium pressure at half of the hydrogen design pressure.
There are several additional benefits of using helium. They include lower gas consumption because it would leak less easily; it’s an inert/non-flammable gas; it doesn’t react with oxygen, making the purity very stable; and it doesn’t require scavenging to maintain purity throughout operations. One potential disadvantage was the cost of helium, which was about three times that of hydrogen at the time of testing in 2018. Still, the team decided it would be worthwhile to test the helium cooling option given the short remaining life expectancy of the generator.
Testing was completed in April 2018 with successful results. The unit operated across its full range of loads with minimal impact on generator operating temperature. Generator gas and stator temperatures were only elevated by 20F to 25F at 175F.
During the 2018 peak summer season, Doyle Unit 1 was dispatched 12 times for peaking purposes, operating 57.2 hours. As predicted, a generator fault caused by age and insulation deterioration did occur as the summer was winding down; however, an inspection found no connection between helium cooling and the failure.
In summary, the helium cooling alternative eliminated highly flammable hydrogen gas from the unit, and the helium usage rate proved to be meaningfully less than hydrogen, which meant the cost differential between the two gases was insignificant. This operational testing of helium cooling verified the viability of the gas as a cooling alternative for power generators—knowledge that could be useful in the future.
CTOTF recognized Exelon Generation with its Innovation Excellence award in the maintenance category. The award-winning project came about because Exelon’s Renewables division was finding high gas content in some of its pad-mounted transformers (PMTs). Engineers determined that frequent changes in power levels, caused by wind turbines ramping up and down regularly with changing wind speeds, were inducing immense stress on PMTs, resulting in gases being produced in the transformer oil.
2. The DGA LT1 is a dissolved gas analyzer designed as a wireless sensor to measure dissolved hydrogen in transformer oil as well as transformer oil temperature and moisture concentration. It collects data without the need for additional power or communications infrastructure. Courtesy: Qualitrol
Hydrogen in transformer oil, above all other gases, is a key indicator of potential problems. Therefore, Exelon’s engineers decided part of the solution would be to install new monitoring systems to better track hydrogen levels. They identified Fairport, New York-based Qualitrol Co. as a supplier that could help. Qualitrol’s DGA LT1 (Figure 2) is a wireless, self-powered dissolved gas analyzer that monitors hydrogen, as well as moisture concentrations and temperature in the dielectric insulating oil.
In the past, it’s been impractical to install dissolved gas analyzers on smaller electrical assets due to high capital costs, and even higher installation costs when power sources and communications networks are not readily available. With Qualitrol’s wireless, self-powered equipment, however, the installation could be accomplished at a much lower cost, and it could be done in a fraction of the time.
With the use of this new solution, Exelon can now trend hydrogen levels in real time to aid engineers in understanding how the PMTs operate under these unique conditions. It also enables closer monitoring of PMTs with extremely high hydrogen, so operations can be managed to prevent transformers from reaching catastrophic failure thresholds. Although this particular installation pertained specifically to wind turbines, it is a shared application that can be used at CT sites as well.
Environmental Stewardship Excellence
Las Vegas, Nevada-based NV Energy won CTOTF’s environmental stewardship award for its power plant air permitting approach. Historically, the company’s generating station air permits did not allow excursions beyond normal emission limits, and the Clark County Department of Air Quality (DAQ) would not issue variances. Therefore, when an operational problem resulted in high emissions, the typical response was to shut the unit down to avoid exceeding a permit limit. Workers would fix the problem while offline and then restart the plant, but the cycling was hard on units, and in many cases, was not really necessary.
Although the process successfully complied with air permit requirements, it often resulted in increased total emissions due to time spent operating in startup and shutdown modes, as well as under less-efficient, low-load conditions. For example, most of NV Energy’s CTs employ selective catalytic reduction and oxidation catalyst in addition to low-NOx burners. Most catalyst-based systems aren’t fully functional during startup, and low-NOx burners are similarly not optimized, this results in higher emissions per MWh than a unit typically produces during normal full-load operation, when systems perform at peak efficiency.
Furthermore, testing or tuning after outages or following new equipment installation was very constrained, due to the inability to obtain a variance from the DAQ. In fact, there had been times when NV Energy was forced to decline requests to perform Western Electricity Coordinating Council and North American Electric Reliability Corp. regulatory testing because it was incompatible with air permit emissions limits.
To solve the problem, NV Energy’s team of experts developed a case for permitting a very limited set of circumstances during which higher emissions would be allowed. It drew on the U.S. Environmental Protection Agency’s rule addressing emissions during startup, shutdown, and malfunction to provide guidance for both numeric and non-numeric emission limitations for periods of non-normal operation outside of startup and shutdown. NV Energy’s Environmental Services Manager Kim Williams said the team met with the permitting agency multiple times during the process to explain its proposed new approach and gain concurrence from the agency.
In the end, the team submitted carefully crafted permit applications requesting alternate operating scenarios for limited periods during unplanned operating events and for testing or tuning, that is, planned operation outside of normal limits for the purposes of data collection, diagnostics, or operational adjustment. The permit modification process required scouring historical emissions monitoring data for every CT and reviewing scenarios to ensure no unintended consequences would result. Training on the new scenarios was also required.
“The operators themselves were indispensable in the development of the training,” Williams said.
Through January 2020, the team successfully permitted new alternate operating scenarios at one generating station, with four others pending and more in the queue. As expected, the alternate operating scenarios benefit not only the plant, but also the environment, through the avoidance of unnecessary shutdown-startup cycles.
“Under the new alternate operating scenarios, when the facility encounters an unplanned operating event on any combustion turbine, the plant operations may resolve the issue promptly—within the permitted duration and frequency limits—and thereby eliminate the need for a shutdown-startup cycle,” said Williams. “Therefore, the total mass emissions from the turbines may be reduced—and the emissions per megawatt-hour would most likely be reduced—when operated under the conditions of the new alternate operating scenario.”
Additionally, adoption of the new approach gives NV Energy the ability to operate in testing or tuning modes when required. This will allow the company to participate in testing protocols that have previously gone unperformed and will allow NV Energy to ensure combustion dynamics are optimized following repairs and overhauls.
In the safety category, CTOTF recognized IHI Power Service Corp. for implementing a new crisis management platform throughout its fleet. The system—developed in partnership with Everbridge Inc., a global software company that provides enterprise applications to automate and accelerate responses to critical events—allows plant and corporate sites to notify employees and senior leadership of emergency situations at any level.
3. An effective critical event management program and strategy is an integrated, end-to-end process that enables organizations to significantly speed up responses to critical events and improve outcomes. Smart phones can play a key role in crisis management platforms. Courtesy: IHI Power Services Corp.
The crisis management protocol can be triggered by a number of events including a fatality, workplace violence incident, fire with significant damage, major environmental release, terrorist threat, natural disaster, and more. A threshold event can be activated using a standard control room desktop computer or by utilizing the Everbridge application (Figure 3).
There are also a number of ways for employees to receive notifications when a threshold event occurs, including via email or text on work or personal cell phones and computers. When employees receive an incident notification, they are asked to respond.
“This feature is very useful when senior leadership members responsible for certain facilities are not available,” explained Mike Garrett, director of Health and Safety for IHI Power Services Corp. “This allows the rest of the senior leadership team to coordinate available resources based on the nature of the incident.”
The system streamlines communication between plants and senior leadership, allowing technicians to focus on managing the situation rather than answering calls from multiple people looking for status updates. IHI Power Services Corp. is also utilizing the platform for corporate-wide emergency drills and for facility-specific drills.
“Since implementation, we have had seven threshold events that triggered the crisis management response system utilizing the Everbridge platform,” Garrett said. “In all seven events, the incident command was set-up and the senior leadership member was able to coordinate with the facility and provide resources, as needed.” ■
—Aaron Larson is POWER’s executive editor.