Combustion turbine operations technical forum report

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 polyalkylene glycol (PAG) oils 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).

 Digitization

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 digitization to 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 had once experienced a serious incident when it turned its turbines down below 60% load. This led to a rule 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 digital twin simulation revealed that 55% load was sustainable without incurring the risk of component failure or unscheduled maintenance. This data validated the opinion of plant floor 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. “The key is to connect all assets on a common network” said Jacobs.

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 a digital twin.

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%. 

PAGs v mineral oils

Varnish has been an ongoing problem in gas turbines over the past ten years. The CTOTF crowd learned more about the subject from Jim Kovanda, Vice President at American Chemical Technologies (ACT).

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 a propensity to produce varnish and lack the 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 are said to hold varnish in solution, have superior air release and not to 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.  

ACT has developed a PAG called EcoSafe, which has been successfully used in over 80 turbines. The OG&E Redbud plant in Luther, OK, for example, had four 7F GTs and four Alstom STs (total capacity 1380 MW).

It was spending $60,000 on Moog servo valves and associated labor per year. These servo failures were almost always due to 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. 

If there is some reason that mineral oil cannot be changed, or funds do not immediately exist to change to PAG, ACT offers EcoSafe Revive. Adding a small amount of EcoSafe to lube oil heavy with varnish, shifts the polarity, extending its life.

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.”

You can read the full text of this article in the May/June 2017 issue of Turbomachinery International.