Increased Uptime In New Siemens Gas TurbineNew 35.9 MW gas turbine for power generation and oil and gas applications
by bo svensson
Siemens has introduced a new industrial gas turbine, the SGT-750, with an output of 35.9 MW and 38.7% efficiency in power generation. The Siemens industrial gas turbine range has covered eight models with capacities from 4 to 47 MW. The newly introduced gas turbine will fill the gap between the Siemens SGT-700 and SGT-800 gas turbines. The delivery of the first unit is expected in 2012. “Initially, we are looking for power generation applications to get a chance to test the new unit on full power under long periods,” said Anders Hellberg, SGT-750 product manager, Siemens. “However, primarily we see the SGT-750 as a fit for the future mechanical drive market, where the demand for increased turbine output seems to be growing into the range of our new gas turbine. For mechanical drive, the SGT-750 offers a shaft output of 37.1 MW at an efficiency of 40%.
“The unit’s high efficiency and rapid start capability, in addition to its being designed to meet the stringent requirements of the oil and gas industry, will also make it a very competi-tive machine for the power generation market,” he added. Siemens did its homework regarding the market’s requirements and spent time on designing a robust industrial gas turbine with a unique uptime capability. “Our primary aim has been serviceability and robustness. We schedule as little as 17 days’ maintenance time over a 17-year service period,” said Mikael Nilsson, SGT-750 program manager, Siemens. “The first stop for a more extensive check is programmed after four years of operation. The complete gas generator can be replaced in 24 hours, which is key to the high uptime capability.”
The estimated maintenance schedule proposed for the SGT-750 indicates that the first action is a remote, online check of the complete engine. This is performed once a year at Siemens in Finspong, Sweden. The first maintenance level is a borescope inspection of the gas turbine every second year. Openings for the borescope allow for a thorough inspection of all important sections throughout the machine. The time required is one day per inspection. The second level of maintenance, after four years of operation, is an exchange of the gas generator and an inspection of the two-stage power turbine. The time required for this is estimated to be two days. If the gas generator is disassembled at site instead of being replaced and maintained off-site, the required standstill is estimated to be 12 days.
The third level of maintenance comes after eight years and comprises an exchange of the core engine and an inspection of the power turbine, plus inspections and maintenance of the whole package. The time required for this procedure is five days, or 16 days if conducted on-site. In order to ensure that required maintenance checks and actions would be both possible and feasible, an advanced 3-D visualization program was developed during the design period. This made it possible to check that the design allowed full serviceability of important components and areas without major disassembly of the unit. Full-scale plastic models of combustor parts and the intermediate casing have also been built and tested for the same reason. The SGT-750 has eight combustor cans, which the company said makes control and service of the combustor system easier than with an annular combustor system.
Nilsson said, “We have tested the burners extensively in atmospheric conditions as well as under medium and fully pressurized conditions. The aerodynamically optimized radial swirl brings the air into the burner and controls the flame stability and the general performance of the system. The SGT-750 is designed for single-digit emissions and our testing on gaseous fuel so far indicates NOx emissions ≤ 15 ppmV (with DLE, corrected to 15% O2). We also run the gas turbine down to 50% load with maintained flame stability.” The SGT-750 can operate on dual fuel with on-load switchover between fuels.
The SGT-750 features a 13-stage axial compressor driven by a twostage high-pressure turbine providing a pressure ratio of 24:1. For power generation applications, the free, twostage power turbine runs at a speed of 6100 r/min. For mechanical drive applications the shaft speed is 3050 to 6405 r/min. The compressor turbine stages are cooled, while the power turbine is not cooled.
The lubrication pumps are electric, but a mechanically driven pump is available as an option. The footprint of the SGT-750 gas turbine package is similar in dimensions and layout to that of the smaller SGT-700. “With its high exhaust energy, the SGT-750 is a nice fit for efficient power generation and cogeneration. It only takes 10 minutes from start to full load,” said Hellberg. “The turbine inlet temperature is 1144°C, which is on a par with the SGT-700.” The entire design of the SGT-750 has been targeted to meet the requirements of the oil and gas industry.
The core engine is suitable for operation in extreme climates, from arctic to desert environments, from -60° to 55°C. Harco_Mar08_WW.qxp 9/30/08 2:26 Additionally, the gas turbine meets the pitch-and-roll requirements for installations on FPSO and marine applications in accordance with the DNV rules and regulations. The design of the compressor and turbines has been benchmarked against the modern aero industry and found to be competitive, said the company.