The shortest distance between two points is a straight line. A single-shaft configuration means that both the gas turbine and steam turbine are arranged on one shaft and drive the same generator. Courtesy: Siemens
The benefits of using a single-shaft design for combined cycle operation have been on display at various sites globally, including
the recent Panda Liberty site (Figure 2) in Bradford County, Pennsylvania, and Panda Patriot site in Lycoming County, Pennsylvania.
Both were commissioned in 2016 and designed to utilize Marcellus shale gas to power their communities in the most-efficient manner. The plants each feature two single-shaft power blocks with Siemens H-class gas turbines.
Liberty for all. The 829-MW Panda Liberty Power Project’s single-shaft power plant blocks include two SGT6-8000H gas turbines, two SST6-5000 steam turbines, two hydrogen-cooled SGen6-2000H generators, and two heat recovery steam generators, along with the control system SPPA-T3000. Courtesy: Siemens
Siemens is continuing to expand the boundaries of output and efficiency with the latest SCC-9000HL single-shaft combined cycle design. Building off of proven H-class technology, the 9000HL-class provides an efficiency of up to 63% in combined cycle operation and 25% higher power output. The SCC-9000HL utilizes trusted and validated design concepts allowing for combined cycle operation in both single- or multi-shaft configurations.
Weighing the Options
With extensive experience designing and constructing combined cycle power plants across the globe, Siemens can offer several objective cases for both single-shaft and multi-shaft configurations, as well as innovative approaches to maximize the benefits of both. While single-shaft designs provide benefits with regard to footprint, availability, and efficiency, the decision is not a simple “one-design-fits-all” matter, as multi-shaft configurations offer distinct benefits as well, particularly on projects where layout flexibility and phased construction are required. Ultimately, the configuration that delivers the most value over the life of the power plant will be dictated by operator and load requirements, and site-specific variables.