This article presents an overview of GE’s HA gas turbines that represent the most reliable and efficient machines in the world for converting natural gas into electricity. In a combined cycle arrangement, these turbines provide cost-effective and clean generation that offers reliable electricity to an expanding, global population. The 7/9HA turbine is based upon the original H-class 4-stage gas turbine with exception of simplification by eliminating steam cooling. Metals chosen for the 7/9HA are proven alloys with over 50 million hours of operation on F- and H-class gas turbines. The first 9HA.01 entered commercial operation on June 17, 2016 at the Électricité de France Bouchain plant, located in the Nord Pas-de-Calais region of France. GE followed the Guinness Book of World Records’ definition for a consistent and traceable operating condition for establishing efficiency in world records. Under the oversight of Guinness World Records staff, GE set the record for the world’s most efficient combined-cycle power plant with an efficiency of 62.22% while producing more than 605 MW of electricity.
Whenever you turn on a light-switch in your home, there is a strong likelihood that those electrons were generated by a gas turbine combined cycle (GTCC) power plant. These jet-engines-on-the-ground represent the most efficient conversion of natural gas into electricity. In April 2016, under the auspices of the Guinness Book of World Records, a 9HA.01 GTCC set a world record for combined cycle efficiency of 62.22%. Achieving this new record, and setting new ones in the years to come, involves the science and inventions of hundreds of engineers.
H-Class Gas Turbine Heritage And Evolution Of 7/9HA Gas Turbines
Gas turbine technology level is commonly identified by letter designation, with higher letters representing increased combustion temperatures and higher efficiencies. Development of H-class technology began in the early 1990’s leading to the first commercial operation (COD) in 2003. This original H-class gas turbine pioneered many technologies, including the 4-stage, steam-cooled turbine section and 4 stages of variable guide vanes at the compressor inlet.
Experience and knowledge gained from operation and maintenance of the original GE H-machines paved the way for a new set of H-class products, designated the 7HA and 9HA. The 7/9HA gas turbine hot gas path is entirely air-cooled, facilitated by technological advances in turbine cooling, sealing, materials, and coatings. The “H” signifies H-class firing temperature with the addition of “A” denoting air-cooling.
The 7HA and 9HA are speed and geometric scales with factors of 0.83 (versus 9HA) and 1.2 (versus 7HA), respectively. The 7HA serves the 60 Hz market while the 9HA serves the 50 Hz market. Scaling based upon this approach has been routinely applied for industrial gas turbines, including the 7/9E’s and 6 / 7/9F’s offered by GE Power.
The 7/9HA family of gas turbines offers two output sizes for both 7HA and 9HA. The “.02’s” are flow scales of the “.01’s”. The process of flow scaling can be summarized by increasing compressor inlet and turbine exit annulus areas to accommodate higher air flow with resultant increase in power output. Pressure ratio is increased to maintain aerodynamic flow function in the mid-to-later compressor and first and second turbine stages. Overall length increases by about one meter for both the 7HA.02 and 9HA.02. Fuel supply capability and fuel nozzle sizing are increased to maintain constant firing temperature.
Table 1 provides today’s output and efficiency for simplecycle and combined-cycle configurations of the HA products. These performance values are shown on a net basis at ISO with boundary conditions per the Gas Turbine World (2017) standard. SS is an abbreviation for 1x1, single-shaft configuration.
The 7/9HA compressor is a direct evolution from the 7F.05 gas turbine. The 7F.05 compressor has a 14-stage architecture with inlet guide vanes followed by three stages of variable guide vanes. There are two extraction points for supply of cooling air to the hot gas path. This compressor incorporates the latest aerodynamic and durability enhancements. Features include 3D aerodynamics, field replaceable blades and application of ‘super-finishing’ or coating of blades. These elements combine to provide high efficiency, wide operability, minimal degradation, optimal reliability and maintainability. The 9HA.01 compressor is shown by Figure 1.
The 7/9HA gas turbines operate with lower than 25/15 ppm NOx/CO from 30 to 100 percent load. Even lower emissions can be guaranteed for both 7HA and 9HA via reduction in firing temperature or inclusion of exhaust Selective Catalytic Reduction (SCR). The 9HA.01 gas turbine was introduced with DLN 2.6+ combustion technology. This system employs multiple fuel circuits supplying 6 fuel nozzles with five arranged circumferentially around a center nozzle. The operational strategy uses fuel staging to achieve low emissions with robust maneuverability.
The 7HA.01 and 7HA.02 gas turbines incorporate combustion improvements enabling further reduction in emissions levels and improved turndown capability. “Axial Fuel Staging” (AFS) system enables lower NOx emissions with improved turndown. It also reduces thermal loading that combines with advanced materials and coatings to deliver state-of-the-art durability. The 7HA combustor is shown in Figure 2 along with a photograph of the flame from full-scale laboratory testing.
9HA.01 and 9HA.02 gas turbines with shipment dates from 2018 and onward can incorporate an evolutionary improvement to the premixing fuel nozzles, in addition to AFS. The 5 around 1 fuel nozzles can be replaced by an equivalent number of arrays with smaller, tubular premixers., shown by Figure 3.
The 7/9HA turbine is based upon the original H-class 4-stage gas turbine with exception of simplification by eliminating steam cooling. Metals chosen for the 7/9HA are proven alloys with over 50 million hours of operation on F and H-class gas turbines. Turbine cooling was enhanced based upon combination of this experience coupled with use of state-of-the-art computational and experimental methods. Development benefited from use of Computational Fluid Dynamics (CFD), and component testing, aided by partnerships with multiple Universities and National Laboratories. The turbine section and corresponding velocity field as generated by CFD are shown in Figure 4. Engineers and researchers advanced the understanding of near-wall flow physics to allow optimization of the turbine aerodynamic and cooling architectures. The inner and outer turbine shell applies passive measures for optimization of clearances. Abradable and honeycomb shrouds and shorter shank buckets were carried forward from the original H-class gas turbine, while near-flowpath seals were leveraged from GE’s Aviation products.
4. Full-Speed, Full-Load Validation
In 2008, GE developed the world’s largest and most comprehensive full-speed, full-load (FSFL) gas turbine test facility in Greenville, South Carolina, USA. This off-grid, worldclass facility provides full-scale, full load validation of 50 and 60 hertz gas turbine systems. The first usage of this facility was for the 7F.05 compressor in 2011 followed by the 7F.05 gas turbine in 2012. The facility was subsequently used for v a lidation of the 9HA.01, 7HA.01 and 7HA.02 gas turbines.
The FSFL facility enables operation independent of the grid. Key elements of the FSFL train are the gas turbine, a load compressor, and starting means. The facility was developed to allow for the load compressor to utilize a production version of the gas turbine compressor. The load compressor can be operated at different points on the map versus the actual gas turbine compressor. Instrumentation of the load compressor also enables doubling the amount of compressor validation data. Nearly 6,000 sensors and instruments collect data on all aspects of operation and components of the gas turbine during validation. Gas turbine performance is mapped over a broader operating envelope: isolation from the grid facilitates off-speed (90%-110% speed) operation over a range of loaded conditions. Variable speed also enables testing at ambient t e mperature equivalent over a range from -37°C to 50°C.
Compressor aeromechanics are validated through use of strain-gauges and light probes applied along the flow-path. Loaded speed sweeps greater than +/-10% provide parametric sensitivities to frequency and operating condition variation. Surge margin is quantified by intentionally maneuvering the load compressor into a surge condition and monitoring the response. Multiple surge events are performed for each platform. Gas turbine transient events including grid disturbances, fuel transfers, and load rejections are performed under highly monitored conditions.
The standard FSFL validation test plan is portioned into three sections: validation, demonstration, and growth. Validation includes extensive testing to provide measurements to support comparison with analytical predictions to validate the methods. The demonstration phase leverages off-grid capabilities to exercise operational capability. Significant testing is dedicated to exploring the growth capability of the HA gas turbine technology for future upgrades. Aeromechanic, combustor and aerothermal data are collected for operations up to 115 percent of rated output.
9HA.01 World Record At EDF Bouchain
The first 9HA.01 entered commercial operation on June 17, 2016 at the Électricité de France (EDF) Bouchain plant, located in the Nord Pas-de-Calais region of France. GE followed the Guinness Book of World Records’ definition for a consistent and traceable operating condition for establishing efficiency world records. Under the oversight of Guinness World Records staff, GE set the record for the world’s most efficient combined-cycle power plant with an efficiency of 62.22% while producing more than 605 MW of electricity.
GE’s HA gas turbines represent the most reliable, and efficient machines in the world for converting natural gas into electricity. In a combined cycle arrangement, these turbines provide cost-effective and clean generation that offers reliable electricity to an expanding, global population.
Innovations from aerodynamics, to combustion, to heat transfer, to materials, and many other areas, representing the work of hundreds of dedicated engineers, made this worldrecord machine possible. And those same engineers are busy at work preparing to set a new world record…stay tuned!