Jul
19
Peaking Power, Chapter Seventeen: The Long Anticipated 7EA!
Most of the early Frame 7 problems were been “ironed out,” as the design has evolved from the first 7A unit installed at LILCO on Long Island, NY in 1970. The 7B & C proved to be popular for peaking and emergency applications delivering between 40 to 55 MW (depending upon model) through the seventies and early eighties. The 7E of the late 1980s was even better and more reliable at about 60 MW. With new technology (improved design, better metallurgy, ceramic coatings and air cooling of nozzles and buckets), the 7EA gas turbine soon became an industry darling.
Fig. 17-1- Isometric Colored Cross-sectional Rendering of MS7001EA
The 7EA changed the philosophy of the General Electric’s Package Power Plant (PPP). Many more auxiliaries were motor driven and installed on off-base skids: atomizing air, cooling water, water or steam injection, water washing, fire protection and, of course, liquid fuel forwarding. Part of the reason for off-base skids is the sizes of the auxiliary equipment. However, in most cases, it was deemed more efficient to drive auxiliaries with motors than with an accessory gear. Only those devices that were critical to turbine operation and protection were driven by the accessory gear. They include: main lube oil, liquid fuel pump and the hydraulic supply pump.
The two photos below depict outside installations for power plants owned and operated by Aquila (formerly Missouri Public Service). Aquila was recently purchased by Kansas City Power & Light. There are four gas turbine/generators at this site.
Fig. 17-2: Outdoor installation of MS7001C at Greenwood, MO (converted to dual fuel)
At the site below, also now owned by Kansas City Power & Light, one GE 7E gas turbine rated at about 60 megawatts provides power to a local township.
Fig. 17-3: Outdoor installation of MS7001E at Pleasant Hill, MO (peaking applications)
Below, in Fig. 17-4, a used 7EA gas turbine originally installed in California was later sold and installed at its current site in Kalamazoo, Michigan.
Fig. 17-4: Outdoor installation of 7EA gas turbine generator at Kalamazoo, MI (gas fuel only)
The next two photos in Fig. 17-5 and 17-6, a 7EA rotor, split between the turbine and compressor sections, is resting on rotor stands outside a power plant in New Jersey.
Fig. 17-5: MS7001EA turbine rotor on temporary stands (from #2 bearing end)
Fig. 17-6: MS7001EA compressor rotor on temporary stands (from inlet end)
The 7EA gas turbine has many internal design features that are different from earlier frame 7 models. Fig. 17-7 shows air-cooled, Z-lock 2nd-stage buckets (the GE name for turbine blades). The 1st stage buckets are also air-cooled, but without shroud tips adjacent to the casing shrouds.
Note: The photo below was taken as the turbine rotor was being lowered into the turbine shell, so the tip clearances are greater than normal.
Fig. 17-7: Turbine section of modern unit with air-cooled, Z-lock buckets
Fig. 17-8: First-stage turbine buckets (end view) showing internal cooling holes
The most obvious area where the 7EA gas turbine deviates from earlier models of Frame 7s is in the combustion zone. In the early designs, the introduction of steam into the flame zone of combustors was sufficient to reduce the emissions to acceptable levels. As the limits became more stringent, a new combustion design was required. The introduction of dry-low nitrous oxide (DLN) combustors was a significant design change for these turbines, brought on by the requirements of the Environmental Protection Agency (EPA) requirements to limit hazardous exhaust emissions like nitrous oxide and carbon monoxide.
Fig. 17-9: Combustion Section for 7EA Turbine, Gas fuel only
Fig. 17-10: End view of dual fuel combustion system with steam injection connection above
Although the MS7001EA gas turbine has been manufactured by General Electric Company for over two decades, it remains the favorite of many owners because of its simplicity and similarities to its original design back in 1970. Unlike the MS7001FA, to be addressed in a future blog chapter, the 7EA is a 3-bearing design with the generator on the “hot end” of the turbine. The 7FA, on the contrary, took a major departure from the 7EA with its “cold end” drive concept.
