Mitsubishi Heavy Industries Technical Review Vol. 60 No. 3 (September 2023)
1Achievement of World's Highest Thermal Efficiency andHigh Flexibility Joetsu Thermal Power Station Unit No. 1,Tohoku Electric Power Co., Inc.

MASAKAZU INOUE*1

TAKAHIRO HARADA*2

NAOYA TATSUMI*3

TAKASHI NISHIUMI*3

TAKUYA UWAMI*4

KENTO TANAKA*5

The Joetsu Thermal Power Station Unit No. 1 of Tohoku Electric Power Co., Inc., whichstarted operation in December 2022, employs a 1,650°C class JAC gas turbine from Mitsubishi
Heavy Industries, Ltd. (MHI) and has achieved the world's highest plant thermal efficiency of
63.62%. Even with regard to the operability, which generally has a trade-off relationship with thethermal efficiency, this plant attained about 25% shorter start-up time and about 3 times higher
power output change rate (ramp rate) compared to conventional gas turbine combined cycle
plants, and has a minimum output as low as 25% of the rated output. Thus, it is also expected topromote the introduction and expansion of renewable energy sources with large fluctuations. This
report describes the features of the plant, which we believe will contribute to the development of
the electric power industry toward further environmental load reduction and carbon neutrality due
to its high efficiency and high operability.

|1. Introduction
In recent years, as seen from the spread of the SDGs(Note 1), people have become moreenvironmentally conscious, and thermal power plants are expected to reduce the environmental
burden by reducing carbon dioxide emissions and to have the ability to adjust the power supply inresponse to the introduction of renewable energy, which fluctuates widely. MHI delivered the latest
JAC-type gas turbine, heat recovery steam boiler, steam turbine, and other major auxiliaries for
Joetsu Thermal Power Station Unit No. 1 of Tohoku Electric Power Co., Inc. (Joetsu Unit No. 1),
realizing the world’s most thermally efficient gas turbine combined cycle (GTCC) plant. In
addition, the plant has both high thermal efficiency and high operability, which generally have a
trade-off relationship, and has received high evaluations from external parties, including Tohoku
Electric Power Co., Inc.
Note 1: SDGs: Sustainable Development Goals|2. Overview of plant planning
2.1

Plant overview and main features(1)

Main equipment specifications
Table 1 shows the main plant equipment specifications and the schedule outline for theJoetsu Unit No. 1.

*1Senior Engineer, Power Systems Project Engineering Department, GTCC Business Division, Energy System, Mitsubishi*2

Takasago Plant Engineering Department, GTCC Business Division, Energy System, Mitsubishi heavy Industries, Ltd.

*3

Gas Turbine Engineering Department, GTCC Business Division, Energy System, Mitsubishi heavy Industries, Ltd.

*4

Chief Staff Engineer, Steam Turbine Engineering Department, GTCC Business Division, Energy System, Mitsubishi heavy*5Engineering Department, Steam Power Maintenance Innovation Business Division, Energy System, Mitsubishi heavy

heavy Industries, Ltd.

Industries, Ltd.
Industries, Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 60 No. 3 (September 2023)
2Table 1

Power generation equipment specifications and schedule outline

Plant generalGas turbine

Steam turbine

Heat recovery steam
boiler

Generator end output

572,000 kW

Unit configuration

572,000 kW x 1 (new)Model

M701JAC

Turbine inlet temperature

1,650°C

Pressure ratio

25ModelTC2F-40.5 Side exhaust

Steam conditionsHigh pressure : 16.4 MPaG x 600°C
Reheat: 3.35 MPaG x 600°C
Low pressure : 0.41 MPaG x 325°C
Horizontal reheat triple-pressure naturalcirculation typeHigh pressure: 403 t/hMedium pressure : 62 t/h
Low pressure: 49 t/hHorizontal-shaft cylindrical rotary-fieldmagnetic synchronous generator
Indirect hydrogen cooling

TypeMaximum evaporation

Generator

TypeCooling method

Schedule(2)Contract signed
January 2018
Installation of main system
May 2021
BurningMarch 2022
Connection to grid
March 2022
December 2022 Commencement of commercial operation (scheduled for June 2023 atthe time the contract was signed)

Main system configuration
The Joetsu Unit No. 1 employed a single-shaft CGS arrangement(Note 3) reheat
combined-cycle power generation system in which MHI's latest large-capacity, high-efficiency
1,650°C class gas turbine (M701JAC), generator, and steam turbine (TC2F-40.5) were arrangedon the same axis and an SSS clutch(Note 2) was installed between the generator and steamturbine. The CGS layout and the side-exhaust steam turbine instead of the conventional
downward exhaust steam turbine minimized the amount of excavation needed and lowered theheight of the power plant building, thereby reducing construction costs (Figure 1).
Note 2 : SSS clutch: Synchro self-shifting clutch
Note 3 : CGS arrangement: Axial configuration arranged in sequence of gas turbine (combustionturbine), generator, and steam turbine

Figure 1

2.2(1)

Appearance of turbine floor

Plant performance and environmental performance

Plant performance
The M701JAC gas turbine used in the Joetsu Unit No. 1 is based on a J-type gas turbine(turbine inlet temperature: 1,600°C class), which is highly regarded for its high thermal
efficiency and has been operated in many countries, and has achieved even higher efficiency byincreasing the turbine inlet temperature to the 1,650°C class through the use of a forced
air-cooling system and other measures.
As a result, the plant achieved a thermal efficiency of 63.62% (based on the lower
heating value), and was certified by Guinness World RecordsTM as the "Most efficient
combined cycle power plant in the world" (January 24, 2023).
(2) Environmental performance
The forced air-cooling system can suppress the generation of nitrogen oxides because
there is little introduction of cooling air into the combustion gas and the combustion

Mitsubishi Heavy Industries Technical Review Vol. 60 No. 3 (September 2023)
3temperature and turbine inlet temperature can be kept at the same level. Table 2 shows theenvironmental performance of the Joetsu Unit No. 1.
In addition, carbon dioxide emissions can be greatly reduced due to the reduction in fuelconsumption that accompanies the improved thermal efficiency.
Table 2 Joetsu Unit No. 1 environmental performance
Joetsu Unit No. 1 environmental performance (actual achievement)
Nitrogen oxide
Sulfur oxide
Dust

Emission concentration

3 ppm

Emission amount

12 m3N/hEmission concentration- (Note 4)

Emission amount- (Note 4)

Concentration- (Note 4)

Emission amount- (Note 4)

Note 4: Below measurable lower limit

2.3

Operability

The JAC-type gas turbine does not require the combustor cooling steam system used in theJ-type. Furthermore, the application of gas turbine clearance control and improvements in the shapeof the steam turbine rotor have resulted in a higher operability, such as shorter plant start-up time,higher power output change rate (Ramp rate), and lower minimum power output, compared toconventional combined cycle power generation plants. Table 3 shows the operational performanceof the Joetsu Unit No. 1.
Table 3
Joetsu Unit No. 1
achievements

Joetsu Unit No. 1 operability

Targets for GTCC set byworking group of
Ministry of Economy,
Trade and Industry (Note 5)

Current situation
researched by working
group of Ministry ofEconomy, Trade andIndustry (Note 5)

Current situation of
once-through coal-fired
thermal power generation
researched by working groupof Ministry of Economy,
Trade and Industry (Note 5)
4 hours

Start-up time
41 minutes
30 minutes
60 minutes
Power output
change rate
15%/min14%/min
1-5%/min
1-3%/min(Ramp rate)
Minimum
25%
25%
About 50%30%
power output
Note 5: Grid Working Group of Electricity and Gas Basic Policy Subcommittee, Electricity and Gas Business Sectional
Meeting, New Energy Subcommittee, Energy Conservation and New Energy Sectional Meeting, #32 Advisory
Committee on Natural Resources and Energy|3. Features of main equipment
3.1Gas turbine

The M701JAC gas turbine is a state-of-the-art gas turbine that incorporates advanced
technology into the proven J-type gas turbine to achieve a high turbine inlet gas temperature of
1,650°C in order to increase the plant efficiency.
Specific technologies incorporated therein are introduced below (Figure 2).
(1) Forced air-cooled combustor system
The forced air-cooled combustor system, jointly developed by Tohoku Electric Power
Co., Inc. and MHI, increases the turbine inlet gas temperature from 1,600 to 1,650°C, compared
to conventional steam-cooled combustors, and reduces the overall plant start-up time byeliminating the need for external steam for cooling during start-up.
(2) Thicker-film TBC(Note 6)
By applying ultra-thick-film TBC with even better heat shielding performance than
before based on the technology obtained through the national project and joint research withTohoku Electric Power Co., Inc., the reliability of the combustor and turbine blades is ensured
while increasing the gas temperature.
Note 6: TBC: Thermal-Barrier-Coating

Mitsubishi Heavy Industries Technical Review Vol. 60 No. 3 (September 2023)
4(3)Turbine clearance control
In general, due to the difference in thermal expansion between the turbine rotor andstator, the turbine clearance tends to narrow during power plant start-up and power output
changes, and widen during rated power operation. By supplying the appropriate amount offorced cooling air, which cools the combustor, to the turbine blade rings located on theperiphery of the turbine rotor blades according to the output, the clearance is expanded toincrease the power output change rate during start-up and power output change, and is reduced
during constant power operation to improve efficiency, thereby ensuring both high efficiency
and high operability.
(4) High-pressure ratio compressor
While also taking into account the achievements of the MHI M501H type, the use of ahigh-pressure ratio compressor with a pressure ratio of 25 suppresses the rise in exhaust gas
temperature and reduces the thermal effects on the exhaust heat recovery steam boiler andsteam turbine.
In order to confirm the performance and reliability of these technologies, we conducted
more than 1,500 large-scale special measurements at the Joetsu Thermal Power Plant andobtained detailed operational data of the aerodynamic stability of the compressor, metal
temperature of the combustor/turbine blades, and chip clearance of the compressor/turbine fromstart-up to rated output over a period of about 4 months. By sharing the problems identified in
the obtained data with Tohoku Electric Power Co., Inc. as needed, we were able to improve
both performance and operability while ensuring reliability.

Figure 2

3.2

Features of JAC-type gas turbine

Steam turbine

The steam turbine adopted is a proven two-casing turbine suitable for the flow rate of steam
generated by the heat recovery steam boiler and achieved high efficiency by adopting
high-efficiency reaction blades designed by the latest three-dimensional flow analysis and a
40.5-inch ISB(Note 7) end-blade group.
Note 7: Integral shroud blade

Furthermore, the building height was reduced by adopting a side-exhaust low-pressureMitsubishi Heavy Industries Technical Review Vol. 60 No. 3 (September 2023)
5turbine with reduced exhaust loss, which was developed as next-generation equipment, and acompact layout was achieved by adopting a main valve unit that integrates a stop valve and acontrol valve. Also, the latest MHI technologies, such as a high contact pressure-type bearing thatcan withstand higher bearing contact pressure than conventional bearings and a new seal structure,were adopted. All these technologies have a high reliability tested and verified at MHI's
demonstration test facilities, resulting in further improvement of the efficiency.
Figure 3 is a cross-sectional view of the steam turbine, and Figure 4 shows the features ofthe side-exhaust steam turbine.

Figure 3 Cross-sectional view of steam turbine

Figure 43.3

Features of side-exhaust steam turbineHeat recovery steam boiler

The heat recovery steam boiler adopted for Joetsu Unit No. 1 is a horizontal reheat
triple-pressure natural circulation type. The high-temperature steam conditions of 600°C for
high-pressure main steam and 600°C for reheat steam (at the steam turbine inlet) due to the higher
exhaust gas temperature resulting from the adoption of a high-temperature gas turbine improves thethermal efficiency. The adoption of a triple-pressure reheat method, which consists ofhigh-pressure, reheat, medium-pressure, and low-pressure systems, allows for an efficientheat-absorbing tube arrangement for the exhaust heat from the gas turbine in consideration of thefluid temperature characteristics (Figure 5).

Figure 5

Heat recovery steam boiler

To further improve the thermal efficiency, a TCA cooler(Note 8) and FGH(Note 9) areincorporated into the boiler feed water system to minimize the heat loss due to heat discharge from

Mitsubishi Heavy Industries Technical Review Vol. 60 No. 3 (September 2023)
6

the plant cycle. Exchanging heat between the gas turbine cooling air and boiler feed water in theTCA cooler contributes to steam generation in the heat recovery steam boiler. In addition, theboiler feed water heated by the heat recovery steam boiler is used to heat the fuel gas in the FGH inorder to increase the fuel gas temperature at the inlet of the gas turbine. This contributes to theimprovement of the gas turbine thermal efficiency.
As an environmental measure, the denitration device installed inside the heat recovery steam
boiler decomposes nitrogen oxides (NOx) contained in the exhaust gas into nitrogen and water
through a reduction reaction. This device employs technology MHI has cultivated over the years toreduce nitrogen oxides in the exhaust gas released into the atmosphere, resulting in a highdenitration rate.
Note 8: Turbine cooling air cooler
Note 9: Fuel gas heater|4. Conclusion
The Joetsu Thermal Power Station Unit No. 1 of Tohoku Electric Power Co., Inc., which is agas turbine combined cycle plant with the latest technology, achieved the world's highest thermal
efficiency and has demonstrated high economic efficiency and reduction of environmental impact,
thereby contributing to the local electric power supply. We believe that with its high operability
achieved at the same time, this plant will not only stabilize the power grid, but also contribute to
the development of the electric power industry and even industrial development, which are on theway to achieving carbon neutrality, by further reducing environmental impact through thepromotion of the introduction and expansion of renewable energy and by reducing operating costs
by lowering the supply-demand imbalance.
In recognition of these achievements, Joetsu Unit 1 has received the following awards fromexternal parties.
- Minister of Economy, Trade and Industry Award, Excellent Energy-saving Equipment andSystem Award, FY 2008 (JAC-type gas turbine)- Certified by Guinness World Records as the world record for highest power generation
efficiency ("Most efficient combined cycle power plant in the world", January 24, 2023)(Joetsu Unit No. 1)- Special prize of judging committee, 52nd Japan Industrial Technology Awards, 2023
(Joetsu Unit No. 1)