large capacity power generation at highest …thgr/gasturbiner/material_for_generating... · 2....

World Energy Council 18th Congress, Buenos Aires, October 2001

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(a) Increasing of Turbine Inlet Temperature (b) Improvement of C/C Plants

LARGE CAPACITY POWER GENERATION AT HIGHEST EFFICIENCY SHOZO KANEKO, OSAMU WAKAZONO, TAKUJI FUJIKAWA MITSUBISHI HEAVY INDUSTRIES, LTD., JAPAN 1. Introduction A power generation plant, which is basic to any modern human society, is required to save energy resources and have excellent environmental capability as well as high reliability. In the region of the conventional steam power generation using coal fuel, the latest pulverized-coal fired supercritical pressure and 600 degree C class steam power plants realized the plant efficiency of 44% level on generator terminal HHV basis. These plants are contributing much for the saving of coal resource and the protection of the environment. Three units of 1000MW class large capacity plants with 600 degree C supercritical steam conditions started commercial operation one after another in 1997, 1998 and 2000 in Japan. The first unit is 1000MW Matsuura No.2 Unit for Electric Power Development Co., with main steam conditions of 24.1MPa and 593 degree C and a steam reheating temperature of 593 degree C. The second is 1000MW Misumi No.1 Unit for Chugoku Electric Power Co., with the steam condition of 24.5MPa and 600/600 degree C. The latest unit is 1050MW Tachibana-wan No.2 Unit for Electric Power Development Co., with main steam conditions of 25MPa and 600/610 degree C. Those plants efficiency are 44% level on generator terminal HHV basis (48% on LHV basis). All steam turbines were manufactured by MHI and every one of them recorded each time as the largest power plant with 1000MW and 600 degree C class supercritical steam condition in the world. On the other hand, a gas turbine combined cycle power plant using natural gas fuel can achieve higher efficiency than the conventional steam power plant by using gas turbine that operated at remarkably higher temperature more than 1100 degree C. The first large scale combined cycle power plants started commercial operation in Higashi Niigata No.3 Unit of Tohoku Electric Power Co., in 1984. The plant output is 1090MW with 6 sets of MW701D gas turbine and the plant efficiency attainted in excess of 44% level on generator terminal HHV basis (48% on LHV basis). After this event, the gas turbine combined cycle power plant using natural gas was recognized as one of the best thermal power plants for its high efficiency and cleanliness. The share of gas turbine combined cycle plants has tended to increase very rapidly in the world market of power generation. Recently, another major change in the market has happened such that the number of non-utility company, such as IPP was considerably increasing. The trend of deregulation in the world forced the market to become more competitive and the world market requests the higher efficiency, lower emissions and higher availability. Under these circumstances, MHI developed the 1400 degree C class M501F/M701F gas turbines. Their high efficiency and reliability for combined cycle applications have been proven in field operations. Based on the fact that the combined cycle efficiency is highly dependent on the gas firing temperature, MHI has developed the 1500 degree C class M501G/M701G, which is called G-series, gas turbines. Figure I shows a trend of combined cycle efficiency. The combined cycle efficiency has been improved by raising firing temperature and has reached 53% level on HHV basis (58% on LHV basis) for the latest ‘G’ class.


Table I Performance of M501G and M701G Gas Turbine M501G M501F M701G M701F

Speed(rpm) 3,600 3,600 3,000 3,000 G/T Output(MW) 254 185.4 334 270.3

G/T Thermal Efficiency(%-LHV) 38.7 37.0 39.5 38.2

Pressure Ratio 20 16 21 17

This paper mainly focuses on the activities in development and commercialization of this 1500 degree C class G-series gas turbine. 2. 1500 degree C class G-series Gas Turbine

Turbine À Gaz Série G Classe 1500°C 2.1 Development History Development of the G-series gas turbine was started in early 1990’s and the design was based on the following concepts, which give excellent performance and high reliability to the G-series engine. Firstly, proven features from the F-series are kept. Secondly, the most advanced technologies in aerodynamic design, heat transfer design and new materials for the G-series are introduced. Thirdly, our conventional design criteria in industrial gas turbines are applied. Fourthly, the turbine inlet temperature is increased to the extent where the NOx and the metal temperature can be maintained at the same level as the F-series. Finally, verification tests are carried out before production of the M501G gas turbine to secure their high reliability. Table I shows the main performance specification of the G-series engine, in comparison with the F-series. The G-series is a heavy-duty gas turbine designed to serve both 60Hz and 50Hz power generating utility. The output of the M501G and the M701G are 254MW and 334MW respectively at a turbine inlet temperature of 1500 degree C on natural gas fuel. 2.2 Overall Structure The cross section of the M501G is shown in Figure II. The G-series inherit the proven MHI technology of the F-series and employ the advanced technology described in section 2.3. The basic structure of the G-series gas turbine is designed the same as our F-series gas turbine with the following proven characteristics.

(1) The single shaft rotor is made of compressor and turbine disks that are bolted with spindle bolts and is supported by two bearings. (2) Coupling with the generator shaft consists of a compressor shaft-end (cold end) drive system (3) Axial exhaust flow design is applied with benefits for the layout of the combined cycle power station. (4) The compressor is an axial flow design with seventeen stages. A four-stage axial turbine is applied to maintain the optimum aerodynamic loading even at the increased firing temperature and pressure ratio. (5) All gas turbine casings can be horizontally split to facilitate maintenance without rotor removal. Eight radial struts support the front bearing housing and six tangential struts support the rear bearing housing. Airfoil-shaped covers protect the

Figure II M501G Cross Section


tangential struts from the blade path gas and support the inner and outer diffuser cones. (6) The individual inner turbine casings that are called blade rings are used for the stationary part of each turbine stage and can be easily removed and replaced without rotor removal. Another feature of these blade rings is that they have high thermal response being independent of the outer casing and can be aligned concentric to the rotor to minimize the blade tip clearances. (7) Cooling circuits for the turbine section consist of a rotor cooling circuit and four stationary vane cooling circuits. Rotor cooling air is provided from compressor discharge air extracted from the combustor shell. This air is supplied as the cooling and seal air of the turbine disks and rotating blades after being externally cooled and filtered. Direct compressor discharge air is used to cool the 1st stage vane while the compressor bleed air from intermediate stages is used as the cooling air for turbine blade ring cavities and 2nd, 3rd and 4th stage vanes.

2.3 Advanced Technology in G-series gas Turbine The advanced technologies applied to G-series gas turbine are shown in Figure III. Those technologies have been fostered through various component researches carried out by MHI themselves. (1) Dry Low NOx steam-cooled combustor The G-series combustor design is based on the successful can-annular & pre-mixed dry low NOx combustor developed for the F-series. This combustor operates at less than 25ppm NOx level at 1400 degree C class Turbine Inlet Temperature (TIT) defined as the averaged combustor outlet gas temperature. On the other hand, 15 years have passed since the first Pre-Mixed type combustor was introduced. To reduce the NOx, Lean Pre-Mixed combustion has almost become the standard of the gas turbine manufacturers. Since the NOx is mainly formed in the process of combustion by thermal effects, NOx formation is strongly affected by the flame temperature. In order to keep the same NOx level as the F-series at 1500 degree C TIT, the transition piece of G-series gas turbine is cooled the steam to save the cooling air, which is used to decrease the NOx emission. For this reason, pre-mixed combustor with closed circuit steam cooling system was applied for the G-series combustor. To optimize the swirl strength and the configuration of fuel ejection holes, a flow test was conducted. Also, atmospheric and high-pressurized combustion tests were conducted using a full-scale combustor and a fuel nozzle as shown in Figure IV. The test results showed 25ppm NOx level and satisfactory wall temperatures without cooling steam leakage.

Figure IV Combustor Component Tests


(2) High temperature turbine It is essential to keep the metal temperature below the allowable limit to secure the same level of reliability at 1500 degree C TIT with minimum cooling airflow. To achieve this, a lot of advanced technologies like Full Coverage Film Cooling (FCFC), Thermal Barrier Coating (TBC), new heat resistant material and Directionally Solidification (DS) casting technology are introduced. Several heat transfer tests like measurement of film cooling effectiveness around the airfoil; heat transfer characteristics of serpentine cooling passage with turbulence promoters under rotating conditions were conducted. Based on the results obtained from these fundamental tests, the advanced cooled turbine airfoils were designed. Figure V shows the 1st stage blade of the turbine. The actual turbine blades and vanes were first verified in the hot cascade test facility shown in Figure VI. In the facility, the test was conducted with the average inlet gas temperature up to 1,550C in order to check the margin. Gas temperature distribution at the cascade inlet is measured with total temperature probes and the metal temperature of the vane and the blade is measured with the embedded thermocouples. With the hot cascade tests, the airfoil metal temperature distribution was obtained and the cooling effectiveness was verified. These features and technologies were finally verified through a High Temperature Demonstration Unit (HTDU) by testing the turbine airfoils under actual operating conditions. The HTDU, shown in Figure VII, is a special core turbine with 0.6 scale turbine blades and vanes of the M501G for demonstrating the key technologies.

Figure III Advanced Technologies Applied to G-series engine


Turbine Row 1 Vane Test Section

Figure VI Hot Cascade Test Rig for Turbine Cooling Performance Verification
Figure V Turbine Row 1 Blade
Figure VII HTDU Facility


Figure XI Result of M501G

Compressor Model Test

(3) Materials The advanced gas turbine requires heat resistant materials as well as advanced cooling technologies. For this purpose, some advanced materials for turbine blades and vanes, and thermal barrier coatings are developed. For the rotating blade material, MGA1400 alloy was developed. MGA1400 is a Nickel-base super alloy and can be used for DS casting as well as for conventional casting. Compared with IN738LC conventionally cast blade, the creep strength of MGA1400DS blade is 50 degree C higher, and that of the conventionally cast MGA1400 is 30 degree C higher as shown in Figure VIII. Both DS and CC blades are applied in the G-series gas turbine. A typical DS blade is shown in Figure IX. For the stationary vane material, MGA2400 alloy was developed. MGA2400 is also a Nickel-base super alloy that has excellent resistance against thermal fatigue, oxidation and hot corrosion as well as high creep strength. It also has good weldability for settlement of accessory parts and repair. Table II summarizes the materials for turbine vanes and blades. TBC is also important and indispensable material for its heat shield effect to design high temperature gas turbine. Plasma spray is used to coat the ceramics material on the blade surface. The durability and the heat shield effect have been confirmed through many long-term field operational experiences of MF61, MF111, MF221, M701D, M501F, M701F, etc.

(4) Advanced compressor The compressor has highly efficient axial flow design. The G-series compressor requires a larger flow rate and higher efficiency than the F-series. The result is that this compressor has a higher Mach number. To meet this requirement, the M501G incorporates Multiple Circular Arc (MCA) airfoils in the forward 3 stages of the rotating blades. Also, Controlled Diffusion Airfoils (CDA) are applied for the rest of the stages of the rotating blades, namely from the fourth to the seventeenth stage, and all stages of the stationary vanes. The flow field of the

Figure X Advanced CFD Result of

Compressor Blade

Figure VIII Creep Rupture Strength ofTussssrbine Blade Material

Table II G-series and F-series Turbine Blade Material

Figure IX DS Blade Aube DS

World Energy Council 18th Congress, Buenos Aires, October 2001 compressor can be predicted precisely due to the amazing improvement of the high-speed computer. An advanced CFD can predict the end wall effect and even the transient flow condition in the compressor. The efficiency of the compressor can be improved when they are designed using an advanced three-dimensional design method. Figure X shows the advanced CFD Result of Compressor Blade, which is designed by the three-dimensional method. The aerodynamic performance is verified with both the cascade test and model compressor test. Model compressor test results show that primary parameters of mass flow and efficiency meet the design range as shown in Figure XI Also, aerodynamic performance is proven with MF221 gas turbine, which has a half scale compressor of the M501G. The compressor is also equipped with variable inlet guide vanes, which improve the compressor surge characteristics during start-up and are used in the combined cycle applications to improve part-load performance. 2.4 Long-Term Operating Experience G-series gas turbine have been proven in long term field operation as a combined cycle power plant in MHI’s Takasago Machinery Works and a combined power plant of Higashi Niigata No.4 Unit of Tohoku Electric Power Co. The performance and inspection results of both plants during long-term operation will be shown in the following. (1) Operating experience of M501G MHI constructed a verification test facility with the M501G as a complete combined cycle power plant in its Takasago Machinery Works. MHI started the trial operation of the M501G in January 1997 to verify the performance and reliability. During the trial operation, more than 1,800 instrumentation probes were installed in the gas turbine. Figure XII shows the special measurement items. The flow path characteristics, metal temperatures, pressures, strains, sound pressure levels, exhaust emissions, etc. were measured over the full range of operating conditions. All-important characteristics, including the cooling characteristics and components’ reliability were verified. As an example, measured vibratory stresses of the blades and vanes are shown in Figure XIII. They were measured for the 1st stage to the 4th stage blades, the 1st stage to the 8th stage and the 17th stage vanes of the compressor and the 1st stage to the 4th stage blades of the turbine during starting period, rated speed, and up

Figure XIV Plant Layout of M501G Combined Cycle Verification Plant of Takasago Machinery Works

Figure XII Special Measurement Items

World Energy Council 18th Congress, Buenos Aires, October 2001 to 110% of the rated speed. These items were measured by a non-contact method using optical fibers for compressor blades and by strain gauges for compressor vanes and turbine blades (with telemeter). The results show that the vibratory stresses are low enough compared with the allowable values. At the end of June 1997, the combined cycle verification plant passed the Ministry of International Trade and Industry (MITI)’s qualification test as an industrial power plant, which consists of one M501G gas turbine, one HRSG and one steam turbine and started commercial operation as the long-term verification test. The plant layout is shown in Figure XIV. The electricity is sent to the grid of a domestic utility company. As this plant operates on demand of the utility company, it has mainly been operated with Daily Start and Stop (DSS) mode. Accumulated total operating hours/start-and-stop cycles are 10,897 hours / 588 cycles at the end of Oct. 2000. It is still accumulating operating experience successfully. The following is the detailed explanation of each operation and inspection. The result shows the high reliability of the M501G.

Figure XIII Summary of VibratoryStress

World Energy Council 18th Congress, Buenos Aires, October 2001 June-October 1997 The M501G started its first verificational operation for summer peaking duty. In October, summer peaking duty was completed and the first inspection of the M501G started. The hot gas path components like steam cooled combustor, advanced cooled turbine vanes and blades were found to be sound except minor cracks of steam cooled combustor transition piece exhaust mouth corners. December 1997-March 1998 After the first inspection, the M501G was back in service in December 1997. The load demand in winter tends to be lower, but to confirm the soundness in preparation for the next summer peaking duty, the second inspection was conducted in March 1998. The inspection proved the hot gas path components to be sound. June 1998-November 1998 The M501G was back in service. The result of the inspection in November 1998 showed no severe problem and everything was in sound condition. Till the next operation started in July 1999, the operating test of M501H, which has steam cooled 1st and 2nd stage vanes and blades as well as the steam cooled combustor, was conducted and the results were successful. July 1999-March 2000 The M501G was in service again for summer peaking duty. Accumulated operating hours / start-and-stop cycles were 8,633 hours / 514 cycles. The result of the inspection in March 2000 was very good even though partial peeling of TBC at row 1 blade was observed. May 2000-Oct.2000 After the fourth inspection, the M501G has returned to service and is successfully accumulating operating experience. Accumulated operating hours / start-and-stop cycles are 10,897 hours /588cycles by the end of October 2000. The result of the inspection in October 2000 showed no major problem and everything was in sound condition as shown in Figure XV. Till the next operation which will be started in July 2001, the operating test of M501H have been conducted again. The availability of M501G defined as the actual power supply hours over the demanded power supply hours reaches 98.6%. This is summarized in Figure XVI.

Figure XV Inspection Results in October, 2000


(2) Operating experience of M701G MHI constructed an advanced combined cycle power plant using two sets of M701G, G-series gas turbines of 50Hz, as Unit No.4 in the Higashi Niigata Thermal Power Station of Tohoku Electric Co.,Inc., which have a total power output of 805MW as one train. The plant started a trial operation in October 1998. The commissioning operation was running smoothly in close cooperation between the customer and MHI. As the result, plant achieved a thermal efficiency of 50.6% (HHV basis), which is the worldly highest level and also the introductory level of G-series gas turbine. And the plant began commercial operation in July 1999 and has been successfully accumulating the operating hours and start-and-stop cycles of 13,348 hours / 72 times for the No.1 gas turbine and 12,813 hours / 65 times for the No. 2 gas turbine (As of March 2000). Since the gas turbine has never stopped except for the scheduled outage, availability defined as the actual power supply hours over the demanded power supply hours is 100%. Figure XVII shows the first inspection results. All components were in sound condition. Based on the verified results of long term operating experience of the M501G/M701G, MHI has already received the order of forty M501Gs and seven M701Gs by March 2001 and further potential orders are expected.

Figure XVII Inspection Results in October, 2000

Figure XVI The Combined Cycle Verification Plant Up-to-date Operating Status

World Energy Council 18th Congress, Buenos Aires, October 2001 3. Current Status of H-Series Gas Turbine Development Since the NOx is mainly formed in the process of combustion by thermal effect, NOx formation is strongly affected by the flame temperature. For this reason, the flame temperature should be controlled below 1500 degree C to achieve the minimum NOx level. This means the highest turbine inlet temperature for industrial gas turbine is limited to around 1500 degree C Therefore, the efforts to increase the efficiency of power generation do not tend to increase the firing temperature after G-series developed, but foster the introduction of steam-cooled vanes and blades, that is H-series gas turbine. MHI’s H-series gas turbine inherits the proven MHI’s technology of the F and G-series gas turbines and employs the following advanced technology.

(1) H-series turbine has a closed steam cooling system of 1st&2nd turbine blades and vanes with bottoming steam cycle to get higher the efficiency and power than the open air cooled gas turbine. (2) H series gas turbine also adopts the advanced aero-engine technology for its compressor to get high efficiency under high-pressure ratio 25:1 which in necessary for the adequate exhaust temperature.

Steam cooling and steam sealing technology that are also very important for H-type are successfully designed and verified in advance. Before trial operation, various elementary tests were performed to select the best design for new developed parts of H series gas turbine. These elementary tests covered the verification of the following technology; “steam sealing”, “steam cooling blades & vanes”, “ new compressor” and “ turbine rotor with steam passage”, At the Verification Plant of MHI Takasago Machinery Works, the second trial operation of H-type began in December 2000, and finished in February 2001 successfully achieving the load operation with good steam cooling characteristics and good efficiency for the first time in the world. The combined cycle efficiency with H-series gas turbine is expected to reach to the 54% level on HHV basis (60% on LHV basis). 4. Conclusion According to modern human society demand, Mitsubishi Heavy Industries (MHI) has been introducing various power generating plant. In the region of coal fuel, MHI introduced the most efficient conventional steam power plants with 1000MW and 600 degree C class supercritical steam condition. And in the region gas fuel, MHI introduced G-series gas turbine combined power plants with the highest efficiency in the world and with low environment. These plants have been successfully accumulating total 37,000 operating hour. The availability of M501G plant is kept 98.6% and the M701G plant is kept 100%. These actual operating results proved MHI’s G-series gas turbine to have higher reliability including a certainty of MHI’s advanced technologies like steam cooled combustor, new heat resistant material, DS casting technology and latest aerodynamic design. The H-series gas turbine combined power plant with excellent efficiency of 54% level on HHV basis (60% level on LHV basis) will be introduced into market soon from MHI on the basis of the successful load operation of H-series gas turbine. We believe that these large capacity power generation units and the applied technologies will make a great contribution to future large–scale and high-efficiency plants projects and to energy savings and good global environmental issues.

World Energy Council 18th Congress, Buenos Aires, October 2001 References

1. Fukue I., “A New Generation of Advanced Gas Turbine”, 95-YOKOHAMA-IGTC-146 2. Sato M., Kobayashi Y., et al., “Final Report of the Key Technology Development Program for a Next Generation High Temperature Gas Turbine”, ASME 95-GT-407 3. Fukue I., Aoki S., et al., “A New High-Efficiency Heavy-Duty Combustion Turbine 701F”, ASME 93-GT-146. 4. Aoki S., Tsukuda Y., et al., “Development and the Next Generation 1500 degree C Class Advanced Gas Turbine for 50Hz Utilities”, ASME 96-GT-314 5. Aoki. S, Tsukuda Y., et al., “Technical Features and Operating Experience of Mitsubishi Advanced M501G Gas Turbine”, POWER-GEN Conference 1998 6. Murase T., Tsukuda Y., et al., “ Current Operating Status of M501G Gas Turbine”, ECOS 2000 7. Akita E., Arimura H., et al., “Technical features and long-term operating experience of Mitsubishi Advanced M501G

Gas Turbine”, POWER-GEN Conference 2000 8. Uematsu K , Fujioka M, et al , “ Large Capacity Gas Turbine” , Gas Turbine Technology in Japan

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