BY FRANCISCO DOVALI-SOLIS, SIEMENS POWER AND GAS
Historically, the introduction of new gas turbines to the market has resulted in unforeseen problems during early operation. The risks of these problems can exist irrespective of developmental know-how, especially when technologies are rolled out directly to customer sites. To combat this problem, the industry has now developed a much greater awareness of risks than it had in the 1990s.
To reduce onsite problems, Siemens performed full in-house validation on its SGT-8000H series turbines, applying a rigid “keep the risk inside” approach to the SGT6-8000H. In addition to test-bed testing, the SGT5-8000H was validated for simple- and combined-cycle functionality via real world operation.
The SGT5-8000H was the first and only gas turbine to exceed 60 percent net plant efficiency, demonstrating a still unmatched, independently-verified world record since 2011. Since this time, the SGT-8000H series has reached proven combined-cycle efficiency levels of nearly 61 percent in commercial applications all over the world.
The “infant mortality” issues of new turbine designs present a high risk to early adopters of these new technologies. Although in the long term, problems can always be solved, in the short term losses due to handover delays or unscheduled outages can have a negative impact on a plant’s bottom line.
Working from this knowledge, Siemens endeavored to design the SGT-8000H within the existing design experience range. This reduced owner risks by incorporating specific features to aid in the reduction of downtime. Siemens also conducted a rigid pre-validation of new features and completed full in-house validation tests on a complete engine. This ensured that the very first customer would get a mature product into which short-term improvements had already been incorporated.
The SGT-8000H tests confirmed the anticipated robustness of the turbine’s design. Still, in order to reduce the risk of an unplanned standstill before or after the commercial operation date, the SGT-8000H design incorporated several features to minimize downtimes.
The compressor’s rotating blades, as well as all turbine vanes, were engineered to be replaceable without a rotor-lift. A Hydraulic Clearance Optimization (HCO) system was also installed in order to avoid rubbing of the turbine blades. Furthermore, in an effort to concentrate on the highest risk areas in the hot gas path, stage-one and last-stage turbine blades were designed to be replaced without a cover lift.
Before building and testing the SGT5-8000H, Siemens performed a full-scale test of the compressor, including off-frequency testing, on a modified SGT-5000F gas turbine in its Berlin Test Center.
In order to draw on the knowledge gained from the 24 G-class units already in operation (which have a combined total of 1.2 million fired hours), Siemens decided to stay within the firing temperature of its G-class engines.
Because the SGT5-8000H was only offered after validation, guarantees for even the first customer were supported by real base-load engine data. Prior to operation at the first customer site, the SGT6-8000H was also thoroughly tested in the Siemens test facility.
REAL WORLD PERFORMANCE
There are now sixteen SGT5-8000H units in commercial operation, and every unit has met given guarantees as demonstrated by performance test results. The units not only satisfy new and clean performance tests, which are often used for evaluation, but also satisfy actual degraded real-time performance tests.
Additionally, Siemens recently commissioned a burner test center in Ludwigsfelde, Germany. Here the company independently conducts intensive research of burner technology using contaminated gases, low-calorific process gases, or liquid fuels such as crude-oil, naphtha, heavy fuel-oil, and other condensates.
Seven years after its first fire, and four years into commercial operation, the SGT-8000 fleet is growing fast.
To date, the SGT-8000H series is the only commercially proven air-cooled technology in its class, with over 100,000 hours of operation and high starting reliability and availability. In the United States, there are now six SGT6-8000H turbines in commercial operation, with another nine units under construction.