SGT5-4000F Gas Turbine and Combined Cycle Power Plant Evolution reflecting the changing Market Requirements

Transcription

1 SGT5-4000F Gas Turbine and Combined Cycle Power Plant Evolution reflecting the changing Market Requirements Eberhard Deuker Siemens AG, Energy Sector, Germany Mike H. Koenig Siemens Energy Inc, U.S.A. Michael Moeller Siemens AG, Energy Sector, Germany Jan Slad Siemens AG, Energy Sector, Germany Holger Streb Siemens AG, Energy Sector, Germany

2 Abstract Since the introduction of the SGT5-4000F gas turbine the performance has been increased significantly. In parallel, the emission requirements have become more restrictive and the operational flexibility (load gradients, fuel flexibility, turndown capability) has gained more attention in the market. This caused the need for continuing evolutionary design improvements of both the gas turbine, especially of the combustion system, and the overall combined cycle plant design. Several design modifications allowed an increase of the TiT design level, which improves power output and efficiency Fuel preheating improves efficiency and NOx emissions. Several measures for reduction of the CO emissions have been established. The capability for fast cycling and grid support has been extended and successfully demonstrated on several engines. The SGT5-4000F is capable to fulfill the national british grid code. The engines can be operated over a large Wobbe range without restrictions regarding performance or emissions. A new combustion controller system has been developed that analyzes the frequency spectrum excited by the combustion. This system is used for optimization of stability and NOx emission. Most of the design features are available as upgrade packages for retrofit. The new generation of Reference Power Plants SCC5-4000F was optimized for the latest version of SGT5-4000F. The modularized design is sized to cover a wide range of potential projects. Equipped with a Benson type HRSG and the Fast Cycling concept and other improvements the power plant is designed for intermediate load operation according to European market requirements. All the development steps have been successfully tested and introduced to the fleet. The SGT5-4000F is a well established engine with proven technology, high performance, very good reliability and availability, and best in class regarding life time cost.

3 1 Introduction Major Upgrade Steps Improvements of Water-Steam Cycle and the Entire Plant Gas Turbine Development Evolutionary Development of the Combustion System Fundamental Steps in Development of the Combustion System Cooling Air Saving Measures at the Annular Combustion Chamber Evolution of the HR3 Hybrid Burner Engine Experience and Validation Emissions in Fuel Gas Operation NOx CO Emissions in Fuel Oil Operation Operational Flexibility Wobbe Range Increase due to Improved Burner Design New Combustion Controller Concept Advanced Stability Margin Controller Fast Cycling and Grid Support Summary and Outlook Literature Nomenclature: asmc CAR CHS CBO DLN EOH FACY FSNL HBR advanced Stability Margin Controller Cooling Air Reduced Combustion Chamber Ceramic Heat Shield Cylindric Burner Outlet Dry Low Nox Equivalent Operating Hours FAst CYcling Full Speed No Load Hybrid Burner Ring

4 HR3 HCO I&C IGV MHS P PMP R&D Tgas TiT TT2 Hybrid Burner Hydraulic Clearance Optimization Instrumentation and Control Inlet Guide Vanes of the compressor Metallic Heat Shield Power Output, Load Premixed Pilot Burner Research & Development Fuel Gas Temperature Turbine Inlet Temperature Temperature at Turbine Outlet (Exhaust Gas Temperature) 1 Introduction The demand for electricity is constantly growing due to increasing global population and industrialization, combined with a general rise in prosperity in many countries. At the same time there is a trend towards environmentally friendly power generation solutions. Despite the forecast increase in the prices of oil, gas, and coal over the longer term, fossil energy sources will continue to play a significant role in ensuring a reliable supply and network stability. With respect to fossil energy sources, the weight is shifting in favor of natural gas: since stable gas prices are be expected for the foreseeable future and a satisfactory CO 2 balance can be achieved through the relatively lower CO 2 emissions compared to coal fired power plants. Despite the rapid increase in demand for wind and solar power plants as well as nuclear power plants, fossil fuels will maintain their dominance in the worldwide power generating mix over the next two to three decades. As a result, efforts to meet future expectations for environmentally compatible fossil-fueled power generation are especially important. The reduction of greenhouse gases and harmful emissions is a key factor in fossil-fueled power plants.[1] The steadily growing share of renewable power generation sources and the ongoing shift toward competitive electricity and gas markets demands flexibility features not only for new, but also for existing gas fired power plants. With the growing renewable power generation (wind, solar) portfolio, the requirement for reserve capacity that can be provided on demand is also increasing. In Germany, for example, wind generation accounts for more than 26 GW of installed capacity with significant additional growth coming from new offshore wind parks. Wind generation in Germany typically accounts for between five and ten percent of annual energy generation, with generation duration of approximately 18 percent on an annual hourly basis. [2] The Siemens gas turbine SGT5-4000F, which was introduced in 1996, has been continuously improved to respond to the changing market needs. In addition to the retrofitable upgrades for performance increases, also many developments were made to address the need for even better operational flexibility without deteriorating the excellent serviceability of the gas turbine. 2 Major Upgrade Steps Gas turbine design and manufacturing technologies have advanced significantly in the years since the first gas turbine VM1 was designed in More than 14 different gas turbine types have been developed by Siemens since then, reflecting the evolution of the electricity

5 market, changing environmental requirements, including stewardship of available fuel resources, and the globalization of the energy market. Based on the 60 Hz Model V84.3A gas turbine, which achieved a new efficiency record at the time, Siemens introduced the 50 Hz gas turbine variant V94.3A (now called SGT5-4000F) in Didcot, UK in Since then, the SGT5-4000F has been continuously improved to meet today s challenges and future requirements. Figure 1 depicts the main four upgrade steps of the SGT5-4000F up to All upgrade steps have been made using an evolutionary design principle, which requires, among others, a full retrofit possibility to the existing fleet. This evolutionary upgrade strategy reduces risks, as the change scope is based on proven designs and pretested in test rigs and in the field. Changes to the geometry of components as well as changes of material have been limited by this principle, further limiting the risks. Figure 1: Development roadmap of SGT5-4000F gas turbine performance 2000 and 2004 Upgrade The 2000 upgrade for example, consists of an improved compressor within the existing flow path with the key benefit of increasing the power of the gas turbine by 10%. The power and the efficiency level of the 2004 upgrade on the other hand was achieved mainly by Hydraulic Clearance Optimization in addition to another compressor upgrade of the front stages. Also in 2004, the cooling air of the combustor was reduced. The benefits of fuel gas preheating, also introduced in 2004, increased not only the efficiency, but also added the flexibility to burn a wider range of different fuels with low NOx emissions Upgrade The main development targets of the 2008 upgrade step were to the increase of power and efficiency, as well as an increase of the lifetime of the components. Again, as per the evolutionary design principle, this upgrade was fully retrofitable into the existing fleet of older variants. Consequently, the geometries of the components were unchanged and the design changes

6 were within the field of experience. Furthermore, the experience of the ten years of operations of the first SGT5-4000F could be used to identify possible improvement measures. The main lever for the increased performance was the reduction of cooling and leakage air in the hot gas path. This saving allowed an increase of the turbine inlet temperature (TiT) without a significant increase of the flame temperature in the combustion chamber. Higher TiT increased the gas turbine performance but also the Combined Cycle performance due to the higher turbine exit temperature. To enable this upgrade, the latest technology of high performance coating was applied, which had already been used in other Siemens gas turbines. The power and efficiency improvement measures as well as the component behavior were tested in November 2007 as part of a comprehensive test phase. In addition, the components were inspected after 2000, 4000, 8000, and Equivalent Operating Hours (EOH) to validate their long term durability. Improvement Step 2010 The positive experience with the 2008 upgrade and the application of different design improvements, already proven in the other Siemens gas turbine frames, enabled further performance increases with a high confidence level. Beside the compressor pressure ratio increase by a restaggered first turbine vane, the secondary air system was optimized and the turbine inlet temperature was again slightly increased. Meanwhile several R&D projects have been started to further enhance the combustion systems capabilities and to evaluate further potential upgrade steps. 3 Improvements of Water-Steam Cycle and the Entire Plant In order to fully utilize the potential of the improvements to the gas turbine in a combined cycle plant, the reference plant layout required re-optimization. In the latest upgrade, special attention was paid to the changing market requirements. The efficiency, the operating flexibility and start up time, as well as the service concept were targeted for optimization. With the evolution of the reference power plant, the process parameters were raised. The original process based on conventional steam temperatures of 540 C for live steam and reheat steam. In the current version of the power plant the temperatures were increased to 565 C. The live steam pressure was increased from 110 to 130 bar to optimize the cycle efficiency. Besides the optimization of the process parameters, the heat exchanger surfaces were enlarged. The new heat exchanger design results in reduction of the pinch point which leads to a better utilization of the exhaust gas energy. The utilization of steam for fuel preheating represents a further optimization of the efficiency. Considering all the improvements the combined cycle power plant efficiency was improved by about 3% points and the power output by about 70 MW in comparison with the first plant based on the SGT5-4000F gas turbine. 4 Gas Turbine Development 4.1 Evolutionary Development of the Combustion System The major design change for the SGT5-4000F from the previous Siemens gas turbines was the switch from two silo combustors to one annular combustor. This change was motivated by

7 generating a more homogeneous temperature distribution in front of the turbine, minimizing the cooling air amount of the combustor and increasing the firing temperature while keeping NOx emissions on a low level. The SGT5-4000F is equipped with 24 state-of-the-art dry low NOx (DLN) HR3 hybrid burners in an annular combustion chamber, the so called hybrid burner ring HBR [5], [6]. The fundamental design of this configuration is shown in Figure 2 and has not changed since the introduction. Figure 2: SGT5-4000F annular combustor with HBR (hybrid burner ring) The main design features of the well known HR3 hybrid burner of the silo engine were adapted to the annular combustor and optimized for the fuels natural gas and fuel oil combining the advantages of diffusion and premix combustion. The HR3 hybrid burner is depicted schematically in Figure 3 showing the three discrete modular components: the burner carrier with the natural gas pilot burner (green), the main stage premix burner with natural gas and oil nozzles (yellow) and the fuel oil burner with the pilot oil. All components can be replaced independently, thereby ensuring a high level of service-ability [3]. Figure 3: HR3 Burner for dual fuel operation

8 4.2 Fundamental Steps in Development of the Combustion System As part of the evolution of the SGT5-4000F engine, the combustion system has been upgraded in several steps over the years to improve the operation, emissions and robustness. Figure 4 shows the pathway of the combustion development program over the last 16 years by showing the trend of NOx emissions relative to flame temperature. Figure 4: Implemented NOx reduction features By reducing the amount of cooling air in the turbine and combustion chamber the lower flame temperature leads to lower NOx emissions (step 1). The change from a diffusion pilot to a well mixed premixed pilot burner leads to lower NOx emissions at the same flame temperature (step 2) and the optimization of the main swirler mixing field finally lowers NOx emissions and increases the combustion stability targeting for higher power output (step 3). 4.3 Cooling Air Saving Measures at the Annular Combustion Chamber In 2000 the original combustor metallic heat shields (MHS) were replaced by ceramic heat shields (CHS) to reduce the required cooling air for the combustor by approximately 30 % (step 1). Accordingly, the burners were adapted to the changed acoustical feedback loop (time lag distribution) by the introduction of the Cylindrical Burner Outlet extension (CBO) as described in [3], [4], [7]. Additional cooling air reduction features were implemented in The Cooling-Air Reduced Combustion Chamber (CAR) was developed by changing the cooling design strategy. The ceramic heat shields (CHS) do not require any cooling but the metallic tile holders do. Instead of purging the gaps and grooves between the CHS to avoid hot gas penetration, only the metallic tile holders are now cooled via impingement cooling. This keeps the tile holders cool enough to avoid any overheating and corrosion. An additional advantage of this strategy is the reduction of thermal stresses for the CHS because the surface temperature is nearly con-

9 stant. The change of the design strategy cool where needed compared to purge sufficiently resulted in a cooling air reduction of the annular combustor approx. by 25 % and lower exchange rates of the CHS at the service interval. In a third step (2007) the cooling air of the turbine inlet bowls and vane 1 was reduced by optimizing the design. The interface between combustor and turbine is equipped with metallic heat shields which are impingement cooled from the backside. The outlet of the cooling air of the inlet bowls directly cools the front of the vane 1 of the turbine reducing the overall consumption of the cooling air by approx. 5 %. All this cooling air savings in the combustor and additional cooling air savings in the turbine led to a reduction of the flame temperature and lower NOx emissions. Nevertheless, over this time frame of more than 16 years the compressor and turbine upgrades allowed for an increase in power output and efficiency of the gas turbine by increasing the turbine inlet temperature. 4.4 Evolution of the HR3 Hybrid Burner At the introduction of the annular combustor the engine could be operated in diffusion and premixed mode for natural gas and fuel oil. Nevertheless the more complex thermo-acoustic behavior in the annular combustor required the implementation of the Cylindrical Burner Outlet (CBO). In the beginning the engines were started in diffusion mode and switched over to premix mode piloted by a diffusion pilot burner. The high NOx emissions in part load were eliminated by developing a new start up procedure: the diffusion stage was skipped and the engine was operated from full speed no load (FSNL) to base load in premixed gas operation supported by the pilot burner. Lower NOx emission demands were the driver to develop and introduce the next evolution of the SGT5-4000F annular combustion system configuration in As shown in Figure 3 the HR3 burner featured a central pilot swirler with a diffusive gas pilot burner. The diffusive pilot burner creates a strong and locally very hot pilot flame and thus a considerable portion of the NOx emissions. The development of the premixed pilot burner leveraged the experience of the premixed stage. The gas nozzles were integrated into the vanes of the axial swirler to generate a homogeneous mixing of pilot gas and axial swirler air. Following the product development process the new pilot burner was tested under high pressure conditions before implementing into an engine. The premixed pilot burner is completely retrofitable to the diffusive pilot burner (Figure 3, green). The engines tests with the premixed pilot burner system showed lower NOx emissions from FSNL to base load. At base load a NOx reduction of approximately 50% was demonstrated at the constant firing temperature. The turn down range was unchanged and the combustion stability was improved. During fuel gas operation all stages are in operation, therefore a purge system is not necessary. For dual fuel engines a purge system is available. All the improvements at the combustion chamber and the hybrid burner were combined in the latest SGT5-4000F upgrade step in Small adaption on the CBO and the mixing field were necessary to minimize the changes on mass flow, heat release and time lag distribution. This led to a higher firing temperature of the engine due to the improved thermo acoustic stability margin.

10 4.5 Engine Experience and Validation All evolutionary design steps of the combustion system (see Figure 5) described in the previous sub-chapters were extensively tested under high pressure conditions in combustion test rigs and successfully validated in different fleet engines. The Cooling Air Reduced Combustor (CAR) has been implemented in 170 engines with about 2,000,000 cumulative operating hours. The premixed pilot burner (PMP) in combination with the CAR-optimized main burner is implemented in about 80 engines with almost 750,000 cumulative operating hours. Finally, the latest development step, the optimized main burner, has been implemented in eight gas turbines and with more than 50,000 cumlative operating hours. Figure 5: Introduction of SGT5-4000F combustion system design evolution steps 5 Emissions in Fuel Gas Operation 5.1 NOx As described in chapter 4, the NOx emissions depend mainly on the flame temperature and the quality of the mixing of fuel and air in the burners. Progress was made in both areas. The fuel-air mixture quality, and therefore, the NOx emissions are strongly affected by fuel gas temperature and the Wobbe index of the fuel, since both parameters affect the velocity at the fuel nozzles and hence the penetration depth and the mixing process of fuel and air. Higher fuel temperature improves NOx but reduces the margin for combustion stability. The same effect is reached by reducing the Wobbe number, see Figure 6 for illustration.

11 The current burner design is optimized for highest load and efficiency (high turbine inlet temperature, high fuel preheating) operation with high calorific natural gas (H-gas) with NOx emissions below 20 ppm. The engine can also be operated at 15 ppm with only a slight reduction in power and efficiency. NOx high combustion dynamics Penetration depth Fuel preheating Wobbe Index Figure 6: Impact of Penetration Depth on NOx In the part load range NOx is significantly lower than at baseload, especially for preheated fuel (Figure 7). The contractually guaranteed NOx level is usually determined by the baseload point under worst case ambient conditions. Hence, the daily or yearly average NOx emissions can be far below the guarantee level, especially for engines that are frequently operated in part load conditions.

12 Figure 7: NOx emissions at partload (preheated fuel) 5.2 CO While CO emissions are usually negligible at baseload, they increase exponentially with decreasing load. Main driver for the CO increase is the decreasing flame temperature. Therefore, flame temperature should be as high as possible. Constant load but higher flame temperature can only be achieved by reducing the air mass flow to the burners. Hence, every measure that reduces the air mass flow to the burners while keeping the load constant will increase flame temperature and, as a consequence, result in a reduction of CO. Figure 8 shows the main development steps which improved the CO emissions of the SGT5-4000F: Step 1: Further development of the compressor allowed a decrease of the minimum air mass flow at the compressor inlet. Step 2: The introduction of a modified burner design enabled an increase in the exhaust gas temperature in the load range of IGV operation to the baseload level (part load TT2 = baseload TT2). Step3: With the current combustion system a further increase of the partload TT2 has been successfully tested, resulting in an additional CO reduction and an increase of part load efficiency.

13 Figure 8: Improvement of CO emissions over several development steps

14 Available options for further CO reduction are the use of the anti-icing bypass (reduces the air flow to the burners), the use of the secondary air control system to maximize turbine cooling air flow at partload (reduces the air flow to the burners) and the use of a compressor inlet air preheater (reduces the compressor mass flow and improves efficiency). With the measures of step 1-3 it was possible to increase the CO compliant load range by nearly 10% points. The further options have a potential of up to 6 % points load range extension (depending on individual site conditions). 6 Emissions in Fuel Oil Operation The SGT5-4000F can also be operated on fuel oil. For low NOx and CO emission the fuel oil is added to the combustion air via premix oil nozzles in the diagonal swirler hub of the HR3 burner (Figure 3). A diffusive pilot oil burner in the center of the HR3 burner increases the operation range. In dry operation the SGT5-4000F achieves a NOx emissions level below 58 ppm. To reduce NOx during operation in fuel oil premix mode, water can be admixed to the fuel oil. This water reduces flame temperature peaks and, as a consequence, forms less NOx. The fuel oil-water emulsion is injected directly via the fuel oil nozzles and reduces the NOx emissions to less than of 42 ppm (Figure 9). Figure 9: NOx emissions in dry and emulsion fuel oil operation 7 Operational Flexibility 7.1 Wobbe Range Increase due to Improved Burner Design The burners of the SGT5-4000F are designed in a way, that the effect of increasing the Wobbe index can be compensated by an increase of the fuel temperature and vice versa (see

15 Figure 6). For decreasing Wobbe index, the NOx emissions will improve but the engine gets closer to the thermoacoustic stability limit. This tendency can be compensated by decreasing the fuel gas temperature. Figure 10 illustrates this behavior for a given NOx and TiT target (at baseload under ISO ambient conditions). The lowest possible Wobbe index is achieved with cold fuel gas. The highest possible Wobbe index is defined by reaching the NOx target with the highest fuel gas temperature. With the latest combustion system design operation in a Wobbe range of 40 to 51 MJ/m³ is possible for the reference TiT and NOx level. There are even two options for a further increase of the Wobbe range: If higher NOx values are allowed, the maximum possible Wobbe index increases further. If a lower TiT level is possible, the possible Wobbe range is increased on both sides. (this is of particular interest for upgrade projects where TiT is limited by boiler restrictions) Figure 10: Possible Wobbe range for a selected NOx and TiT target 7.2 New Combustion Controller Concept Advanced Stability Margin Controller Combustion instability (combustion dynamics) is a well known phenomenon in premix combustion. Under certain abnormal operational conditions the pressure oscillations in the combustion chamber can be amplified (in some cases very suddenly) and might cause strong periodic accelerations. A reliable protection system is installed on the engines which measures pressure amplitudes as well as the acceleration of the outer shell of the combustion chamber. If the accelerations exceed a certain threshold, a load shed is initiated. This prevents the engine damage, but the load shed is still a disturbance of the normal operation that should be avoided whenever possible. Therefore, the basic operation curve of the gas turbine must be set up in a way that areas

16 with combustion dynamics are avoided. Figure 11 shows a typical stability map in a qualitative way. Load 100% Baseload IGV range IGV closed Operation curve Area of combustion dynamics (not suitable for operation) Position and shape can vary with changing ambient and operational conditions TT2 Figure 11: Areas of combustion dynamics The areas of dynamics can move slightly, or can change their shape, depending on the ambient conditions. They can also be influenced by tuning parameters like pilot gas fraction or fuel gas temperature. A good setup for the tuning parameters must be found that makes sure that for any ambient condition an appropriate operation curve is installed. Additionally, there are further impact parameters which cannot be measured during operation, such as fouling or degradation. The basic control setup must provide sufficient margin to the areas of high dynamics to cover these effects. Additional margin is necessary to cover effects like measurement uncertainty, uncertainty resulting from hardware tolerances etc. If the sum of all margins becomes large enough, the engine operation can be impacted, causing higher emissions or a reduction in power output or efficiency. A new feature for closed loop dynamics control has been developed to minimize these effects: The Advanced Stability Margin Controller (asmc) analyzes the actual frequency spectrum in the combustion chamber (pressure and acceleration amplitudes) and utilizes advanced algorithms to determine the stability margin of the combustion system. If operation too close to an area of high dynamics is detected, the asmc adjusts the combustor tuning parameters to ensure sufficient margin for the actual conditions. The algorithms used in the asmc are able to identify different patterns of frequency spectra. These patterns indicate the margin from a stability limit, with each pattern requiring different tuning actions to add margin:

17 Example 1: Depending on the ambient conditions, two different patterns can occur in the lower load range. Pattern 1 can be damped by increasing pilot gas, while pattern 2 requires less pilot gas. If accelerations increase, the asmc detects which of the patterns is present and readjusts the pilot gas accordingly. Example 2: Another pattern occurs occasionally in load range of IGV operation especially during transient conditions. More pilot gas dampens this pattern but increases NOx. With the asmc the basic setup can be modified in a way that NOx is reduced to a lower level. In some rare instances the asmc generates a pilot gas peak for less than 1 minute during transient operation to ensure stable operation. This is illustrated in Figure 12: The two panels show the same engine on two days at the same load level. On the left side operation without asmc is shown. At a certain point accelerations increase slightly, but the basic setup provides enough pilot gas (red curve) to keep accelerations (blue curve) on an acceptable level. On the right panel the pilot gas in the basic setup is reduced, and the asmc is activated. The NOx level is approximately 2 ppm lower. During a deload step the accelerations increase suddenly. The asmc increases immediately the pilot gas flow, which dampens the accelerations. The pilot gas peak and the corresponding NOx peak take only 50 seconds. Figure 12: asmc action (pilot gas peak) during transient operation Example 3: A special pattern can occur if the engine is overfired. Figure 13 shows a situation at baseload conditions (no asmc was available at that time). During a special test situation the TiT was continuously increased, thereby exceeding the limits that were released for commercial operation. Accelerations keep on a very low level until the combustion stability limit is reached. At this point, accelerations increase rapidly, causing an immediate trip of the engine. Although the acceleration level does not initially increase, the shape of the frequency spectrum changes. The asmc calculates a special stability parameter (yellow curve) from the shape of the frequency spectrum which represents the margin to the area of high dynamics. If this parameter drops below a certain limit, the asmc prevents further TiT increases or even reduces the TiT slightly if necessary.

18 Figure 13: Overfiring: spontaneous increase of accelerations With the asmc the baseload performance can be improved by minimizing the amount of stability margin required in the baseload setpoint while ensuring stable engine operation. Figure 14 shows an engine that was initially operated with only low fuel gas preheating for several Figure 14: Performance improvement (increase of fuel preheating) enabled by asmc

19 months (data is filtered for baseload operation). asmc was activated but did not modify the control parameters. Analysis of the stability parameter revealed that there was more margin than necessary, enabling an increase in the fuel preheating during an outage. The asmc subsequently modified the control parameters several times, mainly at the beginning of a baseload period, when the engine was not completely warmed up, and usually only for a few minutes. 7.3 Fast Cycling and Grid Support Since the end of nineties the power market has increasingly demanded quicker and more frequent startups. This trend resulted in the launch of a development project (FACY FAst CYcling) which combined a set of engineering ideas into a single integrated plant concept. The aim of the R&D program was to design a plant for an increased number of starts and to reduce startup times. If possible, no limits were to be placed on the gas turbine by other power plant components, such as the heat recovery steam generator or steam turbine, during a hot and warm start. In the course of the project, potential areas came to light in which further optimization could be achieved, which enabled a second development generation to be implemented. The major improvement offered by this second generation involved the startup procedure. Hold points at which a plant waits until certain steam parameters have been reached were eliminated as part of the shortened "Start on the Fly" startup procedure. The steam turbine is now started up parallel to the gas turbine using the first steam which becomes available after a hot start. Whereas the first FACY generation reduced startup times for a hot start from 100 to 55 minutes, the second generation succeeded in pushing startup times down below the 30-minute mark. Shortening startup times and improving the starting reliability while increasing the number of starts was only one of many requirements regarding plant flexibility. The requirements with respect to grid support, which are usually defined in a grid code, have recently become more rigorous due to the continuously increasing percentage of renewable resources on the grid. Some of the most stringent requirements are to be found in the UK grid code. The topics Load stabilization at low frequencies Primary and secondary frequency response Island operation capability represent a special challenge for combined cycle power plants. Siemens recently demonstrated that the FACY targets could be reached with the commissioning of a 840 MW Multi- Shaft F-class power plant in which all of the required technical features were implemented and the plant concept was optimized without compromising maximum efficiency. A decisive success factor in the development of FACY was the integrated approach, which combined the potential of several systems and components in a single solution. The challenges were met based on the use of gas turbine compressor and firing reserves and fast wet compression combined with an optimized I&C / closed-loop control concept.

20 8 Summary and Outlook In 1996 Siemens introduced a new gas turbine frame with an annular combustion system. Over the last 16 years the SGT5-4000F was further developed to meet increasing market requirements. All components of the gas turbine have been redesigned in order to increase the power output and efficiency. The annular combustion system took several steps of evolution to improve the operational behavior and robustness of the engine while keeping the NOx emissions on a low level. Cooling air savings in the combustion chamber and further developments on the HR3 hybrid burner guaranteed a flexible operation for different natural gas compositions and fuel oil. In turn down operation and at base load, CO and NOx emissions were minimized. The life time of the combustor parts, such as metallic and ceramic heat shields, were improved due to advanced cooling concepts and material developments. The starting reliability and availability of the engine fleet is quite high. Several maintenance concepts and easy accessibility to the combustion chamber made inspection of the hot gas parts possible over the weekend and reduced the outage time. All developed parts are retrofitable and are offered by Siemens Energy Service to upgrade earlier designs. Further developments of the gas turbine controller have enabled higher operational flexibility regarding gas composition and ambient conditions while ensuring stable operation. With the asmc an additional feature for optimizing the operation curve at actual ambient conditions is available. The fleet of more than 300 engines has accumulated more than 7,000,000 operating hours. The Cooling Air Reduced Combustor (CAR) in combination with the HR3 optimized main burner and premixed pilot burner (PMP) has been implemented in about 80 engines with a cumulative operating experience of almost 750,000 hours. All development steps have been successfully tested and introduced into the fleet. The SGT5-4000F is a well established engine with proven technology, high performance, very good reliability and availability, and best in class regarding life time cost. Because of the continuously ongoing evolutionary upgrading efforts of the SGT5-4000F gas turbine frame several R&D projects have been started to further enhance the combustion systems capabilities in all major categories of requirements, especially fuel flexibility, emissions, stability, reliability and life cycle cost. The retrofitability of these new designs enables upgrades of older engines in the operating fleet to state-of.the-art standards. In addition to the enhancements of the combustion system which mainly address flexibility features, Siemens is also evaluating further potential upgrade steps of other components to increase the overall gas turbine performance 9 Literature [1] Siemens AG, Energy Sector Message, March [2] Michalke, Schmuck, Siemens AG, Powerful Products for the Enhanced Flexibility of Gas Turbines, [3] Krebs, W., Flohr, P., Prade, B., and Hoffmann, S., 2002, Thermoacoustic stability chart for high-intensity gas turbine combustion systems, Combustion Science and Technology, Vol. 174, no. 7, pp

21 [4] Streb, H., Prade, B., Hahner, T., and Hoffmann, S., 2001, Advanced burner development for the Vx4.3A gas turbines, ASME Paper No GT [5] Becker, B., Schulenberg, T., and Termuehlen, H., 1995, The 3A-series gas turbines with HBRTM combustors, ASME Paper No. 95-GT-458. [6] Prade, B., Streb, H., Berenbrink, P., Schetter, B., and Pyka, G., 1996, Development of an improved hybrid burner initial operating experience in a gas turbine, ASME Paper No. 96-GT-45. [7] Hermsmeyer, H., Prade, B., Gruschka, U., Schmitz, U., Hoffmann, S., and Krebs, W., 2002, V64.3A gas turbine natural gas burner development, ASME Paper No. GT Permission for use The content of this paper is copyrighted by Siemens and is licensed to PennWell for publication and distribution only. Any inquiries regarding permission to use the content of this paper, in whole or in part, for any purpose must be addressed to Siemens directly. Disclaimer These documents contain forward-looking statements and information that is, statements related to future, not past, events. These statements may be identified either orally or in writing by words as expects, anticipates, intends, plans, believes, seeks, estimates, will or words of similar meaning. Such statements are based on our current expectations and certain assumptions, and are, therefore, subject to certain risks and uncertainties. A variety of factors, many of which are beyond Siemens control, affect its operations, performance, business strategy and results and could cause the actual results, performance or achievements of Siemens worldwide to be materially different from any future results, performance or achievements that may be expressed or implied by such forward-looking statements. For us, particular uncertainties arise, among others, from changes in general economic and business conditions, changes in currency exchange rates and interest rates, introduction of competing products or technologies by other companies, lack of acceptance of new products or services by customers targeted by Siemens worldwide, changes in business strategy and various other factors. More detailed information about certain of these factors is contained in Siemens filings with the SEC, which are available on the Siemens website, and on the SEC s website, Should one or more of these risks or uncertainties materialize, or should underlying assumptions prove incorrect, actual results may vary materially from those described in the relevant forward-looking statement as anticipated, believed, estimated, expected, intended, planned or projected. Siemens does not intend or assume any obligation to update or revise these forward-looking statements in light of developments which differ from those anticipated. Trademarks mentioned in these documents are the property of Siemens AG, its affiliates or their respective owners.