F-class Gas Turbine Research Articles

Technological solutions for an advanced IGCC plant

The paper studies the basic methods offered by different sources for raising the efficiency of the air-blown integrated gasification combined cycle (IGCC). The technological solutions that can minimise the efficiency gap between IGCC and natural gas combined cycle (NGCC) were selected. The flow diagram for an air-blown IGCC is proposed which ensures cycle efficiency and exceeds that of O2-blown IGCC owing to a decreased need for fuel gas. The proposed scheme would enable the approximation of the cycle efficiency to NGCC. The role of integration linkages in raising the efficiency of IGCC was also assessed. Thermodynamic models for the basic elements of IGCC were developed. We calculated the efficiency of steam-air blast and cycle air heating during cold fuel syngas clean-up using IGCC with an M 701F4 gas turbine that runs on syngas processed from Kuznetsk bituminous coal as a model. We also established that steam-air blast heating increases the heat value of fuel gas by 10%, conversion efficiency by 84.2%, and gross/net efficiency of IGCC by 0.44/0.53%. Steam-air blast and cycle air heating decreased coal consumption for gasification by 44% and led to an additional increase in gross/net efficiency by 0.77/1.06%. The solutions proposed in the paper enable the creation of a flowchart for IGCC with F-class gas turbine and one gasifier with a capacity of 2000 t/d for coal and gross/net efficiency of 52.47/50.64%.

Performance maximization of IGCC plant considering operating limitations of a gas turbine and ambient temperature

We predicted the available maximum power output of Integrated gasification combined cycle (IGCC) plants under the operating limitations of a gas turbine. The power block of the IGCC using an F-class gas turbine was modeled, and its interactions of mass and energy with other components such as a gasifier and an air separation unit were considered. Variation in the gas turbine power output with nitrogen dilution was simulated, and the operating conditions under which the power should be limited below an allowable maximum were determined. The maximum net power output of the IGCC plant under the restrictions of syngas turbine power (232 MW) and blade temperature were estimated in a wide range in terms of ambient temperature and integration degree, and the optimal integration degree for each ambient temperature is suggested. At relatively high temperatures over 19°C, zero integration degree (air for the air separation unit is supplied solely from the ambient) provides the highest net power output and efficiency. As ambient temperature decreases, a higher integration degree provides higher net power. The optimal net IGCC power output varies from 260 MW to 347 MW (33%) in the ambient temperature range of 40°C to -10°C, while the optimal net efficiency varies by about one percentage point.

GE Power Services Ships First F-class Extended-Life Rotors

This article presents an overview of technical aspects of the first F-class gas turbine life-extended rotors. Power Services, a GE Power Business, has shipped from the Greenville, S.C., facility its two F-class extended-life rotors, building upon a foundation of experience gained by executing more than 20 E-class rotor life extensions (RLEs). Experience has shown that additional features that require inspection, including rabbet fillets on wheels other than on stage one, cannot be inspected without a complete rotor disassembly. Each rotor is uniquely characterised by the combination of its particular configuration and operational history. Expanding the value of an RLE upgrade also requires that it be executed at the right point in the rotor’s life. For the two rotors evaluated to date, there have been no unexpected issues uncovered from the part inspections as compared to analytical predictions.

Low NOx Lean Premix Reheat Combustion in Alstom GT24 Gas Turbines

Reducing gas turbine emissions and increasing their operational flexibility are key targets in today's gas turbine market. In order to further reduce emissions and increase the operational flexibility of its GT24 (60 Hz) and GT26 (50 Hz), Alstom has introduced an improved sequential environmental (SEV) burner and fuel lance into its GT24 and GT26 upgrades 2011 sequential reheat combustion system. Sequential combustion is a key differentiator of Alstom GT24/GT26 engines in the F-class gas turbine market. The inlet temperature for the SEV combustor is around 1000 °C and reaction of the fuel/oxidant mixture is initiated through auto-ignition. The recent development of the Alstom sequential combustion system is a perfect example of evolutionary design optimizations and technology transfer between Alstom GT24 and GT26 engines. Better overall performance is achieved through improved SEV burner aerodynamics and fuel injection, while keeping the main features of the sequential burner technology. The improved SEV burner/lance concept has been optimized toward rapid fuel/oxidant mixing for low emissions, improved fuel flexibility with regard to highly reactive fuels (higher C2+ and hydrogen content), and to sustain a wide operation window. The burner front panel features an improved cooling concept based on near-wall cooling as well as integrated acoustics damping devices designed to reduce combustion pulsations, thus extending the SEV combustor's operation window even further. After having been validated extensively in Alstom's high pressure (HP) sector rig test facility, the improved GT24 SEV burner has been retrofitted into a commercial GT24 field engine for full engine validation during long-term operation. This paper presents the obtained HP sector rig and engine validation results for the GT24 (2011) SEV burner/lance hardware with a focus on reduced NOx and CO emissions and improved operational behavior of the SEV combustor. The HP tests demonstrated robust SEV burner/lance operation with up to 50% lower NOx formation and a more than 70 K higher SEV burner inlet temperature compared to the GT24 (2006) hardware. For the GT24 engine with retrofitted upgrade 2011 SEV burner/lance, all validation targets were achieved including an extremely robust operation behavior, up to 40% lower GT NOx emissions, significantly lower CO emissions at partload and baseload, a very broad operation window (up to 100 K width in SEV combustor inlet temperature), and all measured SEV burner/lance temperatures in the expected range. Sector rig and engine validation results have confirmed the expected SEV burner fuel flexibility (up to 18 vol. % C2+ and up to 5 vol. % hydrogen as standard).

Using Hydrogen as Gas Turbine Fuel: Premixed Versus Diffusive Flame Combustors

This work aims at estimating the efficiency gain resulting from using lean premixed combustors in hydrogen-fired combined cycles with respect to diffusive flame combustors with significant inert dilution to limit NOx emissions. The analysis is carried out by considering a hydrogen-fired, specifically tailored gas turbine whose features are representative of a state-of-the-art natural gas–fired F-class gas turbine. The comparison between diffusion flame and lean premixed combustion is carried out considering nitrogen and steam as diluents, as well as different stoichiometric flame temperatures and pressure drops. Results show that the adoption of lean premixed combustors allows us to significantly reduce the efficiency decay resulting from inert dilution. Combined cycle efficiency slightly reduces from 58.5%–57.9% when combustor pressure drops vary in the range 3%–10%. Such efficiency values are comparatively higher than those achieved by diffusive flame combustor with inert dilution. Finally, the study investigated the effects of decreasing the maximum operating blade temperature so as to cope with possible degradation mechanisms induced by hydrogen combustion.

Risk-Based Assessment of Unplanned Outage Events and Costs for Combined-Cycle Plants

Unexpected outages and maintenance costs reduce plant availability and can consume significant resources to restore the unit to service. This paper describes a survey and analysis of unplanned outage events for 388 combined-cycle plants, based on 164 D/E-Class and 224 F-Class gas turbines. The 15-year timeframe included over 3000 unit-years of data. The causes and durations of forced outages and unscheduled maintenance were identified, and overall reliability and availability were established for each class of plant. Costs to restore the unit to service for each main outage cause were estimated, as were net revenues lost due to unplanned outages. A statistical approach to estimated costs and lost revenues provides a risk-based means to quantify the impact of unplanned events on plant cash flow as a function of class of gas turbine and plant subsystem. The risk-based assessment defines the range of probable costs of unplanned outage events.

냉각공기의 예냉각이 가스터빈 복합발전 성능에 미치는 영향

고온부에 해당하는 터빈 노즐과 로터의 냉각은 가스터빈의 성능에 큰 영향을 미친다. 본 연구에서는 냉각공기의 예냉각이 가스터빈과 복합화력 발전 성능에 미치는 영향을 알아보았다. 계산에 사용된 모델은 F-Class 가스 터빈이며 냉각을 고려한 터빈의 구성요소를 사용해 냉각공기의 변화에 대해 보다 정확한 모사를 구사하였다. 냉각공기의 예냉각에 따른 가스터빈의 성능변화를 나타내기 위해 탈설계 해석이 수행되었다. 노즐 및 로터의 냉각에 따른 성능 변화를 보다 정확하게 나타내기 위해 열역학적 냉각모델과 속도삼각형을 고려한 모델이 고려되었다. 또한 복합발전의 경우 냉각공기에서 추출된 열을 하부사이클에서 회수하여 스팀터빈을 구동하는데 추가적인 열을 공급하는 시스템이 구성되었다. 복합발전 시스템의 모든 냉각공기의 온도를 200K 예냉각하는 경우에 주유동가스의 유량증가로 인해 약 1.78%의 출력 증가를 나타내었으며 동일한 터빈 입구온도 유지를 위한 연료소모의 증가로 효율은 0.70% 포인트 감소하였다.

Keeping it Cool

This article provides details of various aspects of air cooling technologies that can give gas turbines a boost. Air inlet cooling raises gas turbine efficiency, which is proportional to the mass flow of air fed into the turbine. The higher the mass flow, the greater the amount of electricity produced from the gas burned. Researchers at Mee Industries conduct laser scattering studies of their company’s fogging nozzles to determine if the nozzles project properly sized droplets for cooling. The goal for turbine air cooling systems is to reduce the temperature of inlet air from the dry bulb temperature, the ambient temperature, to the wet bulb temperature. The Turbidek evaporative cooling system designed by Munters Corp. of Fort Myers, Florida, is often retrofit to turbines, typically installed in front of pre-filters that remove particulates from inlet air. Turbine Air Systems designs standard chillers to improve the performance of the General Electric LM6000 and F-class gas turbines during the hottest weather.