COMBUSTION TURBINE OPERATIONS TECHNICAL FORUM

THE CTOTF USER GROUP TACKLES THE CHANGING GRID, DIGITIZATION AND POLYALKYLENE GLYCOL OILS (PAGS) VERSUS MINERAL OILS

By Drew Robb

Our annual visit to the Combustion Turbine Operations Technical Forum (CTOTF) conference provided plenty to think about. While the topic of digitization has been largely a matter for boardroom discussion up until now, its coverage at CTOTF indicates that it is filtering down to the user level. Featured speakers from GE Power, Siemens and Emerson Power & Water laid out how their various organizations are bringing digitization products to market. They addressed user concerns about cybersecurity, data ownership and management of risk.

The show featured an update from the North American Electric Reliability Corp. (NERC), a rundown on the basics of PAGS versus mineral oils, and the item most users come for — turbine-specific tracks where they can share their experiences, problems and solutions. This included sessions devoted to GE F Class, GE B&E Class, Siemens aeroderivatives (legacy Rolls-Royce), PWPS, Siemens 501, MHPS and GE GT11/GT24 (legacy Alstom).

CTOTF began in 1975 when a small group of gas turbine (GT) operators gathered to discuss how to get the best out of their machines. It has evolved over the years to become a thriving user community anchored around two annual shows. The east coast Spring conference and the west coast Fall conference. This year, over 100 users and almost as many vendors gathered in Orlando, Florida. Jack Borsch, CTOTF Chairman and Director of Operations at IHI Power Services, welcomed the gathering. Users develop the programs, decide on outside speakers and topics presented, and determine the structure and flexibility of the organization, he said. “CTOTF is a working user organization for serious professionals interesting in learning and sharing experience-based knowledge with their peers.”

Rapid grid changes

James Merlo, Vice President, Reliability and Risk Management, NERC, delivered the keynote, addressing the massive changes assailing the U.S. electric grid. There is so much change, he said, that regulations can barely keep up. A recent incident involved the sudden disappearance of 1,200 MW from the grid. The common denominator was solar. Yet it involved 26 solar farms going offline immediately for more complex reasons than the appearance of cloud cover. NERC is investigating the actual causes.

Unchecked, such events could become commonplace when you consider that California is adding 6,000 solar cells to roofs each month. This is spurring interest in the California Duck Curve (Figures 1), a graph of the California Independent System Operator’s (CAISO) typical daily load curve that resembles the side view of a duck.

Figure 1: Total grid demand (actual demand) and net demand (supplied by non-renewable sources, in green). In the morning, solar and wind add significant amounts of power to the grid. By afternoon, they are supplying more than half the total demand. But output from solar and wind can vary by 10% or more on an hourly basis

Traditional electrical load is highest in the late afternoon and through the early morning. But as the sun rises, load falls off rapidly. Solar generation largely takes over until late afternoon where a sudden ramp up of traditional generation sources is required as people come home from work and the sun sets. Current projects show this condition steadily worsening each year as more solar is added.

“We hit instantaneous highs of 57% renewables in California in March — something that wasn’t projected to happen until 2020,” said Merlo. “Profound changes are occurring on the power system, and these system behaviors and characteristics require new measurements for reliability. These emerging reliability issues bring technical and political challenges.”

NERC, as the Electric Reliability Organization, is the international regulatory authority whose mission is to assure the reliability and security of the bulk power system in North America. NERC does this through developing and enforcing reliability standards; assessing reliability; monitoring system awareness; and educating, training and certifying industry personnel. NERC’s area of responsibility spans the continental United States, Canada and the northern portion of Baja California, Mexico.

NERC has realized it cannot regulate fast enough to effectively regulate during these rapid transformations. To keep up with ongoing changes, it needs to move to more of a risk-based approach, which focuses resources on risks with the most potential to impact reliability. As such, NERC aims to continue a collaborative partnership with power producers to encourage dialogue to jointly resolve issues. Human error also plays a part.

“Human capital is the most important factor on the grid regardless of the energy source,” said Merlo. “People sometimes drift downwards in their performance over time but are unaware of it, so you sometimes experience unexpected emergencies.”

But some errors being attributed to people, he added, may be more systemic in origin. For example, when something goes wrong, people running the equipment may have no idea what is happening as they lose situation awareness. Examples of this can be found in a few recent airline incidents.

Another problem might be signage or documents that are open to interpretation. A switching incident, for example, involved two switches beside each other. One was labeled “…1A” and the other “…7A.” Add in factors, such as the work being done at high distances above the ground, the close proximity of a bee’s nest, a worker allergic to bees, fatigue and poor signage, and you have elements that can add up to potential reliability risks.

“Error precursors include task demands, work environment, individual capabilities and human nature,” said Merlo. “There is also the impact of poor signage and procedures written by people who may not be as knowledgeable of the work being completed in the field.”

Digitization

There is no escaping digitization these days (Turbomachinery International Jan/Feb and Mar/Apr 2017). Even traditionally conservative niches, such as gas turbine user groups are now hearing the chorus. CTOTF invited speakers from GE, Siemens and Emerson to educate users on this hot topic. David Jacobs, Product Owner for Operations Optimization at GE Power, showcased how digitization can harness existing assets to improve revenues. “Digitization is all about how you can use the terabytes of data that currently exists inside your business to give you the right insight,” he said.

He offered an example of a plant that experienced an emissions excursions when it turned its turbines down below 60% load. This led to a directive to never run GTs below 60% load. Yet operators could realize major fuel savings if they operated at 55% load. Data provided from GE’s modeling software revealed that a 55% load was sustainable without incurring the risk of component failure or unscheduled maintenance. This data validated the opinion of plant personnel, and convinced management to act. “If you can save $1 million on fuel in one plant using the digital twin, that data can be relayed up to the C-suite to be implemented across the entire fleet,” said Jacobs. A major barrier to achieving that, though, is disparate data. Each plant has lots of systems that do not talk to each other. Jacobs faced such issues as a plant manager: Each system in the plant had its data in a separate silo. The ability to link them together was almost nonexistent. The idea behind digitization, then, is to get these systems interacting to improve operations and increase revenue.

“If you can save $1 million on fuel in one plant using the digital twin, that data can be relayed up to the C-suite to be implemented across the entire fleet,” said Jacobs. A major barrier to achieving that, though, is disparate data. Each plant has lots of systems that do not talk to each other. Jacobs faced such issues as a plant manager: Each system in the plant had its data in a separate silo. The ability to link them together was almost nonexistent. The idea behind digitization, then, is to get these systems interacting to improve operations and increase revenue.

“The key is to connect all assets on a common network” said Jacobs. GE Predix GE’s Predix is one such platform. The company is developing various software applications running on Predix to improve plant efficiency and profitability. Jacobs focused upon GE Operations Optimization, which deals with operational outcomes using plant data, thermal outcomes and digital twin capability. It is supported by other tools. Advisor, for example, offers suggestions on possible areas of improvement. Sensor Health isolates those sensors which are suspect.

“There are 47 components in the plant where we recommend you use Sensor Health,” said Jacobs. He ended with examples of users taking advantage of Operations Optimization. PSEG improved heat rate, reduced production costs, minimized fuel start costs, and improved reliability by 1%. This added up to $2 million in savings. TransCanada’s Mackay River facility realized a 10% boost in output capacity and a 2% gain in fuel efficiency. And its Ravenswood plant boosted output by 5% and fuel efficiency by 1%. Digital hype Karen Ratcliff, Head of Business Model Development at Siemens Power Services, said it was important to sift through the digital hype to isolate the signal

“If you can save $1 million on fuel in one plant using the digital twin, that data can be relayed up to the C-suite to be implemented across the entire fleet,” said Jacobs.

A major barrier to achieving that, though, is disparate data. Each plant has lots of systems that do not talk to each other. Jacobs faced such issues as a plant manager: Each system in the plant had its data in a separate silo. The ability to link them together was almost nonexistent. The idea behind digitization, then, is to get these systems interacting to improve operations and increase revenue. “The key is to connect all assets on a common network” said Jacobs.

GE Predix

GE’s Predix is one such platform. The company is developing various software applications running on Predix to improve plant efficiency and profitability. Jacobs focused upon GE Operations Optimization, which deals with operational outcomes using plant data, thermal outcomes and digital twin capability. It is supported by other tools. Advisor, for example, offers suggestions on possible areas of improvement. Sensor Health isolates those sensors which are suspect.

“There are 47 components in the plant where we recommend you use Sensor Health,” said Jacobs.

He ended with examples of users taking advantage of Operations Optimization. PSEG improved heat rate, reduced production costs, minimized fuel start costs, and improved reliability by 1%. This added up to $2 million in savings. TransCanada’s Mackay River facility realized a 10% boost in output capacity and a 2% gain in fuel efficiency. And its Ravenswood plant boosted output by 5% and fuel efficiency by 1%.

Digital hype

Karen Ratcliff, Head of Business Model Development at Siemens Power Services, said it was important to sift through the digital hype to isolate the signal within the noise. She advised users to focus on how digitization could be used to achieve things faster, more flexibly, with better quality and more efficiently. Siemens is releasing applications for industrial equipment, like those available in the consumer sector, such as Uber, AirBnB and Apple Pay.

Running on the Siemens MindSphere operating system, they focus on availability, performance, risk management & compliance, and mobile enablement of data. They include Remote Outage Services, Virtual Guidance, Health Advisor, Power Diagnostics Center, Combustion Optimization, StartUp Advisor, Performance Advisor, Cyber Security Services, and Emissions Optimization. Auto-Tuner, another data-driven service, conducts automated tuning of major plant components to minimize post-outage or seasonal engine tuning. This encompasses the tuning of emissions and engine combustion dynamics with the help of self-learning algorithms using vast amount of operations data. It is currently installed on a number of Siemens 5000F, 6000G and 8000H turbines.

Siemens monitors its large GTs from Orlando, Florida and Muelheim, Germany. They detect deviations from normal operations down to the component level. In addition, users of these services can view a comparison of a specific GT unit against the performance of the entire fleet.

“We are able to identify statistically significant anomalies,” said Ratcliff.

For its large GT fleet, Siemens monitors 530 GTs and 130 steam turbines (STs). This amounts to 230,000 sensors being monitored, and over 9 TB of data processed per day.

Rick Kephart, Director of Research and Technology for Emerson Automation Solutions’ Power and Water business, discussed the Emerson Ovation platform for digitization. He began by confessing that he once believed controls and automation were the answer to top-notch turbine and plant operations.

But he has since concluded that the human operator is just as crucial. “We have to learn how to build control systems that make the human being more effective,” said Kephart. As plants and GTs become more complex, process applications require far more automation, he said. But the more advanced the automated system, the more critical becomes the contribution of the human operator. When you factor in the large number of pending retirements in the power sector, hard-won know-how is disappearing daily. “New personnel coming

“New personnel coming in to the industry are tech savvy and bring new skills,” said Kephart. “But they are missing knowledge of plant operations and lack experience.”

Emerson is working to create GT and plant controls that capture experience and Situation Awareness, while comprehending their meaning and perception.

Simulation technology

Simulation technology was another topic covered. Older generation simulation, said Kephart, was done offline. Training aids are a good example. The latest wave of simulation technology is carried out online. This means that they operate while the plant and its turbomachinery are running. These types of simulations provide control systems with predictions of future consequences and offer the ability to run scenarios.

“If you want to make a change in controls, you can first run it on a simulator and see what would happen,” said Kephart.

Emerson has added Embedded Simulation into Ovation, enabling faster startup and unit load changes. For example, it can be used to evaluate alarm management strategies using simulated malfunctions. Additionally, after a controls outage, a simulated startup should be performed to ensure everything is set up correctly. And after any software patches or system upgrades, simulations should be done. This approach is also helpful in postmortem analysis after a failure.

The Ovation Virtual Power Plant has the goal of bringing simulation and control onto the same platform. “Within a decade, most operations and maintenance work will be performed on a replica of the plant,” said Kephart.

Unplanned events

Tom Christiansen, Senior Vice President of Strategic Power Systems (SPS), discussed equipment susceptibility to high-impact unplanned events as an aid in contingency planning and the use of data in risk mitigation at power plants.

This was based on a study led by Rick Tomlinson at Chevron using SPS Operational Reliability Analysis Program (ORAP) data gathered from a group of peer plants, numbering 640 GTs, primarily GE B & E class turbines. The study looked for commonalities among forced and unscheduled outage events — high-impact events of two weeks’ duration considered over a period of 15 years. A categorization of outage reasons was compiled.

A review by Subject Matter Experts (SMEs) at Chevron, supported by ORAP, determined there were 137 high impact events in the group, spanning 18 areas. These events required an average downtime of 73 days and had an occurrence rate of 8.6 events per million fired hours (Figure 2).

Figure 2: One of the 18 areas of interest for high impact events was the gas turbine starting system, which was an unexpected result and not something that would have been a focal point without the use of data Courtesy of Chevron/SPS

Three contingency playbooks were developed by Chevron on how to deal with various types of event. These were separated into the GT core systems, the generator and accessory systems. Each playbook had chapters to address the 18 areas and outlined a plan of action to be taken. Site-specific logistical challenges, scopes of work, environmental, safety and quality control considerations were highlighted to reduce downtime.

Christiansen ended with another example of ORAP data in action. This time it involved a company that decided to cut costs by saving 10% on circuit breakers. Over the next year, ORAP numbers identified those circuit breakers as the leading cause of problems.

“By reverting to the previous circuit breakers at a cost of $100s, it saved $10,000 or more per trip,” said Christiansen. “The lesson here is you have to have an organized system of data to understand and corroborate the correct decision, and then measure the impact of that decision on your business.”

PAGs vs. mineral oils

Varnish has been an ongoing problem in GTs for over ten years. The CTOTF crowd learned more about the subject from Jim Kovanda, Vice President at American Chemical Technologies (ACT). Polyalkylene Glycols (PAGs) are synthetic oils formulated for demanding applications. Specific to power generation, they have provided a way to reduce varnish problems and extend the life of turbine lubricants.

Current petroleum-based turbine oil formulations have had more propensity to produce varnish and less solvency to hold varnish in solution. Failed starts and trips can occur. PAGs are valued for their low volatility in high-temperature applications, and for resistance to formation of residue and deposits. They hold varnish in solution, have superior air release and do not spark.

“Using PAGs, there are no varnish issues despite temperature excursions,” said Kovanda. “Further, moisture contamination does not affect PAGs.”

Earlier petroleum-based oils did not create much varnish, he said. But hydrotreating carried out to eliminate carcinogens in crude oil changed the chemistry, and varnish began to show up. He said PAGs have a 12-year track record and 50,000 hours of success in the field. The chemistry has been in use in over 100,000 installations.

ACT has developed a PAG called EcoSafe turbine fluid, which has been successfully used in over 80 turbines. The OG&E Redbud plant in Luther, OK, for example, has used it since 2012 in four 7F GTs and four Alstom STs (total capacity 1,380 MW). It was spending $60,000 on Moog servo valves and associated labor per year. These servo failures almost always created a trip event. Varnish was the primary culprit. When PAG turbine fluid was put into the turbines, annual spend on servo valves dropped to $2,500.

Another example: The AEP NE 1&2 facility at Oolagah, OK, has two 7Fs. In 2007, the plant experienced about 50 trips and 18 servo valve failures. The plant changed from mineral oil to PAG that year. Since then, it has had no servo valve failures or trips due to varnish. If a site does not have an upcoming outage scheduled, or is not budgeted for an oil change, but is threatened or plagued with varnish, ACT offers EcoSafe Revive. Adding a small amount of it to lube oil heavy with varnish, solubilizes the varnish, and extends the life of the oil.

Kovanda said that adding 10% of EcoSafe Revive to existing oil will dissolve the varnish and hold it in suspension. This provides an alternative to scheduling an outage, draining the oil and subjecting the machine to a chemical clean. Users experiencing varnish sometimes deploy a mechanical varnish filter skid.

“Varnish removal skids deplete critical antioxidants regardless of claims to the contrary,” said Kovanda. “Varnish is a chemical problem, not an OEM problem and PAGs provide a chemical solution.”

Breakouts

Turbine-specific breakouts are highly valued elements of CTOTF. The combined cycle track featured a talk on how to reduce compressor corrosion via filtration; and how arrestance, the ability of an air filtration device to remove synthetic dust from the air, is being employed to prevent corrosion and keep compressors clean.

The GE B&E class roundtable marched through a wide variety of topics. This included clashing within the compressor, blade upgrade materials, non-destructive testing techniques, aging equipment strategies and auxiliary components.

EthosEnergy presented OEM alternatives for extending 7EA rotor life. The 7E rotor has a 17-stage compressor and a three-stage turbine section. The compressor is built from wheels, a speed ring, a forward stub shaft, blades and tie bolts. Each wheel has broached slots around the periphery in which the blades are installed. The turbine portion of the rotor assembly consists of turbine wheel shafts, and stages 1 to 3 wheel assemblies with spaces and buckets. Broached slots are also used for bucket installation. To extend the life of aging 7EA GTs, an engineering assessment must be done of the existing operation stresses and temperatures. An understanding of material failure modes and NDE inspection play an important part. EthosEnergy favors a “Zero-Hour” rotor approach for the 7EA. This involves a replacement compressor and turbine wheels, recently done for a U.S. customer.

A track on environmental systems explained the basics of measuring stack emissions. Emissions from GTs are high in flow but low in concentration compared to those coming from boilers and other emission sources. These low concentrations can be difficult to measure accurately. The session outlined how to correctly measure particulate matter, VOCs and NH3 emissions.

The environmental track zeroed in on the impact of a higher volume of renewables on compliance for existing combustion turbines. As GTs quickly ramp up to offset sudden declines in output from renewable sources, those with older air permits can lack the permit flexibility to adjust to these changing market dynamics. The session offered strategies for obtaining permit modifications and how to avoid a lengthy permitting process or possible rejection.

The CTOTF conference takes place twice a year. The Fall 2017 conference will be held in San Antonio, Texas from September 17th through 21st. For more information, visit www.CTOTF.org