Coal, Gas

Successful Gas Turbine O&M

Issue 9 and Volume 116.

GE's Generation IQ Monitoring and Diagnostic Center in Atlanta, Ga. enables GE to proactively monitor equipment and alert its customers to potential issues that could cause damage to the plant. Photos courtesy GE Energy.
GE’s Generation IQ Monitoring and Diagnostic Center in Atlanta, Ga. enables GE to proactively monitor equipment and alert its customers to potential issues that could cause damage to the plant. Photos courtesy GE Energy.

By Lindsay Morris, Associate Editor

With an increasing number of combined-cycle natural gas and simple-cycle natural gas plants commencing operations due to astonishingly low natural gas prices, a full-life operations and maintenance (O&M) plan for the gas turbine must be established. Additionally, as many natural gas plants begin to operate at higher efficiencies than they have in the past, O&M procedures may need to be reviewed on a more regular basis.

GE Energy provides O&M services to more than 50 power plants worldwide through a total life-cycle approach to gas facilities, said Terry Schoenborn, operations leader for total plant optimization. GE’s customers are concerned not only about costs associated with the gas turbine, but also how to effectively manage the life-cycle costs of their entire power plant, he said.

“During a turbine’s construction phase, there may be a less expensive piece of equipment that can be installed. However, over the life-cycle of the plant, the customer might save money by benefitting from increased reliability with a more expensive one. These are the types of long-term decisions we help our customers make,” he said.

The proper selection of a modern large-frame gas turbine should include several considerations, such as engine efficiency and emissions reduction, said Chirag Rathi, senior consultant for Frost & Sullivan. “It’s all about pushing for the extra 1 percent of efficiency.”

In this drive for maximum efficiency, much research is being conducted on constructing turbines out of innovative materials that can handle higher temperatures, including ceramics. In an effort to cut emissions, gas turbines are now being tested and operated to run at ultra-cool temperatures, Rathi said. “From a pollution control point of view, the lower the temperature that you can obtain combustion, the better it is for your gas turbine.”

These aspects of the designs of modern large-frame gas turbines must be taken into consideration throughout the installation and ongoing maintenance of the turbine. A number of gas turbine design options are available, which were discussed in detail in the story “Building Better Gas Turbines” in the June issue of Power Engineering. This article will focus mainly on the O&M requirements for large-frame gas turbines.

Installation Considerations

The installation of a new gas plant can take anywhere from 12 to 24 months, Schoenborn said, with simple cycles typically taking about 12 months and combined cycle plants closer to 24 months. GE works closely with engineering, procurement and construction (EPC) firms during the planning and construction phases. At the same time the gas turbine is being prepared for installation, GE also provides equipment accessories such as skids, piping, controls and other electrical systems that integrate with the balance of plant equipment. After initial installation of various pieces of equipment such as the lube oil accessory module, generator and control system, each is tested to ensure proper material integrity and operation.

During the final plant commissioning, GE conducts a performance test to ensure that the turbine meets output, heat rate and emissions specifications. Once the plant is in service, it’s time for the real O&M to begin.

Methods for Successful O&M

Technology is playing an increasingly large role in gas turbine O&M. Through GE’s Generation IQ Monitoring and Diagnostic Center, which has been operating in Atlanta, Ga. since the mid-1990s, the majority of plants that use GE’s O&M services are monitored remotely. This enables GE to proactively monitor equipment and alert its customers to potential issues that could cause damage to the plant, Schoenborn said. This proactive monitoring can also help prevent potential financial strain related to unplanned maintenance and downtime.

GE's frame 7FA gas turbine is one of many products on the market that needs a successful O&M strategy in order to get the most operating efficiency.
GE’s frame 7FA gas turbine is one of many products on the market that needs a successful O&M strategy in order to get the most operating efficiency.

Through plant data monitoring and anomaly detection, GE is even able to predict subtle changes in equipment operations that may cause a potential failure. This could include unusual vibrations, exhaust temperature spreads, abnormal emissions and combustion dynamics.

“Technology is playing a big role in developing increasingly robust analytics to manage O&M operations with less downtime,” Schoenborn said.

Since most new GE gas turbines are equipped with dry low NOx combustion systems, proper O&M should be performed to tune for the optimization of acoustic dynamics (pressure oscillations), emissions and performance. Therefore, GE offers auto-tuning technology that improves turbine performance within changing environmental conditions such as temperature, pressure and humidity. This process can be performed while the plant remains online.

Another key to the ongoing maintenance of a large-frame gas turbine is keeping the compressor clean,” Schoenborn said. Various airborne contaminants can be ingested into the turbine compressor, causing fouling which could lead to pitting and blade corrosion damage. Two options for keeping the compressor clean are an on-line water wash and an off-line water wash. During an online water wash, the unit does not have to be shut down. However, washing the unit while it’s still on-line is “not as effective” as an off-line water wash, Schoenborn said, because only the first few compressor stages are cleaned. .

Obviously, the unit is taken offline during an off-line water wash. Water and detergent are then injected into the compressor to remove contaminants. After employing an offline water wash, the turbine can regain anywhere from 2 to 5 MW, or more, depending on the degree of fouling.

“If we’re losing megawatts and efficiency, we need to do a wash and gain those megawatts and performance back,” Schoenborn said.

Another turbine maintenance recommendation by GE is a borescope inspection. This process involves using a tiny camera to inspect internal gas turbine components. “We recommend it annually for gas fueled units,” Schoenborn said. “It gives us a good gage on what the parts’ conditions are, and if there is any rubbing, cracking or other concerns.”

An effective O&M strategy is an integral part of a high-performing gas power plant. Enacting a successful strategy can lead to reduced maintenance costs and increased revenues, Schoenborn said.

Turbines will naturally degrade in performance over time, but an effective O&M regimen can translate to a remarkable increase in production. “Performance is typically measured in reliability and output. If we took a gas turbine that had 35,000 fired hours on it, with the proper maintenance, a customer can reduce output degradation by 2.6 percent, and increase plant output by 0.5 to 1 percent,” Schoenborn said. This performance retention can translate to significant bottom line growth.

Successful O&M results in shorter and fewer outages, which ultimately means increased reliability and better positioning for plants to meet their market needs.