Mitsubishi Heavy Industries Technical Review Vol. 56 No. 3 (September 2019)
1

Application of World’s Longest 50/60-Inch Titanium
Blades for Large Fossil Power Plants

TAKESHI KUDO*1YUTAKA YAMASHITA*2

KOJI OATA*3

HIDEO YODA*2

As a role of energy equipment manufacturers in dealing with environmental problems, inaddition to energy resource issues and CO2 emissions control, there is increasing demand toreduce the environmental impact of products considering their lifecycle, namely cost reduction ofpower plant construction and operational cost. Mitsubishi Hitachi Power Systems, Ltd. (MHPS)
has developed 50-inch and 60-inch titanium alloy blades, the world's largest blade length for
full-speed (3,000 rpm and 3,600 rpm) steam turbines using the latest design and verification
technologies. The construction of large coal-fired power plants applying these turbine blades has
been completed in Poland and Korea. The commercial operation of these plants has commenced
and they continue to operate stably. This paper describes the contents of the development designand verification test of the long blade and the outline of the applied power plant, and introducessome of the technology of MHPS’s power plants.

|1. Introduction
The low pressure final stage of a steam turbine is one of the most important elements that
determine the performance, reliability and overall configuration of the turbine because of its highoutput load. Longer blades for the last stage can contribute to a reduction of building size due to adecrease in the number of turbine cabins, as well as a reduction in terms of construction cost
including equipment manufacturing expenses, in addition to improved efficiency by lowering
exhaust loss and increasing single turbine capacity. MHPS developed the world’s largest class of
50-inch and 60-inch titanium last stage blades (50/60 LSB)(1). These blades meet recent demand forCO2 emissions reduction and expectations for higher efficiency in large-capacity coal-fired power
plants of over 1000 MW. In this paper, various verification examples carried out in thedevelopment of the blades are introduced, and examples of application in actual machines aredescribed.

|2. Basic design
Table 1 lists the specifications of the developed blades. As the material of the developed
blade, Ti -6 Al -4 V, which has been used for long steam turbine blades for more than 30 years, wasadopted. The blade structure is an integral shroud structure in which adjacent blades are connectedin contact with each other at the tip and middle of the blade by means of torsion return bycentrifugal force. The straight axial entry type, which offers abundant application examples andhigh reliability, is applied to the blade root which fixes the blade to the rotor. The 50/60 LSB has
an identical design reflecting the difference in rotational speed.

*1Manager, Steam Turbine Engineering Department, Steam Turbine Technology & Production Integration Division, Mitsubishi*2

Chief Staff Manager, Steam Turbine Engineering Department, Steam Turbine Technology & Production Integration Division,*3

Steam Turbine Engineering Department, Steam Turbine Technology & Production Integration Division, Mitsubishi Hitachi Power

Hitachi Power Systems,Ltd.
Mitsubishi Hitachi Power Systems,Ltd.
Systems,Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 56 No. 3 (September 2019)2

Table 1 50/60-inch LSB basic specifications
50-inch
3,600

3,000

Blade height (mm)

1,250

1,500

Annulus Area (m2)

11.5

16.5

Blade material
Blade root form

(1)60-inchTurbine speed (rpm)Ti -6 Al -4 V alloy
Straight
axial entry

Performance
The tip peripheral velocity of the newly-developed blade exceeds 780 (m/s), so it isnecessary to design a turbine blade profile with reduced supersonic flow loss. On the other
hand, since the peripheral velocity of the blade root is relatively low, it is necessary to reduce
the loss as much as possible in the flow field with strong three-dimensional characteristics
affected by the difference in the peripheral velocity in the blade height direction and therotating flow accompanied by rotation. For these performance issues, meridional flow line
curvature control was implemented by means of a proprietary three-dimensional stage
turbulence analysis method to verify the calculation accuracy, and designs of the stationary
blade profile, peripheral wall shape in meridional and rotor blade profile were created (1).
Figure 1 shows an example of the calculation of the Mach number distribution between
stationary blades and rotating blades. The loss is reduced by optimizing the relative Mach
number of the stationary blade outflow and rotating blade inflow.

Figure 1 Three-dimensional flow analysis results (Mach number distribution on meridionalplane)(2)

Strength
Titanium alloy is used as the blade material to reduce centrifugal load. Therefore, a long
blade with the world's largest annulus area was realized, while the conventional material (3.5.
Ni-Cr-V Steel) was used for the rotor. Titanium alloys are not only lightweight, but are alsosuperior to steel in terms of corrosion fatigue and stress corrosion cracking, which are problemsof turbine blades used in wet areas such as low-pressure final stage blades.
To increase the rigidity and vibration damping of one assembly blade structure, a contact
connection structure was adopted for this airfoil. Since the contact force acts on the contact area
during turbine rotation, it is important to have sufficient resistance against fretting fatigue andwear of the contact surface. A test method that can simulate the dynamic characteristics of thecontact area was devised (2), and the optimum design of the contact area shape was made toensure sufficient strength and avoid excessive wear. Figure 2 illustrates the static stress
distribution during blade rotation. The strength integrity was confirmed without exceeding thedesign-allowable stress at all positions of the blade.

Mitsubishi Heavy Industries Technical Review Vol. 56 No. 3 (September 2019)
3Figure 2(3)Static stress distribution

Vibration
This blade structure has a structure in which the entire circumference forms one ring, andforms a vibration mode similar to that of a disk as shown in Figure 3. These vibration modes
resonate at an integer multiple of the rotational speed, but it is essential to avoid resonance in alow-order vibration mode in which the vibration stress is particularly large. It is also necessary
to suppress the occurrence of rotational asynchronous vibration, such as flutter or random
vibration, which is influenced by the state of steam flow. These vibration responses are
predicted and analyzed in advance using vibration analysis (3) reflecting the contact state of theblades, and then verified by verification tests.

Figure 3

Vibration mode diagram (Example of 3 nodal diameters)|3. Verification test
(1)

Actual load performance test
Figure 4 depicts the appearance of the test turbine installed in the test facility, andFigure 5 presents the layout of the test turbine. This test facility is equipped with a boiler, acondenser, a cooling tower, etc., and can simulate the operating conditions of an actual machineover a wide range. Figure 6 shows the test turbine for the demonstration. The turbine has fourstages is four including the low-pressure last stage blades. For the 50/60 LSB, conditions forwhich various operating conditions were simulated were set, and reliability verification throughvibration stress measurement of moving blades and performance verification through themeasurement of internal pressure and temperature were conducted. Figure 7 gives an exampleof the turbine performance characteristics. This figure presents the results of measuring theturbine efficiency characteristics with respect to the steam flow rate at the final stage outlet bychanging the steam flow rate and the degree of exhaust vacuum. It was confirmed that theturbine performance was in good agreement with the prediction in the applicable flow velocityrange.

Mitsubishi Heavy Industries Technical Review Vol. 56 No. 3 (September 2019)
4Figure 4

Steam turbine in the test facility

Figure 5

Layout of test turbine facility

Figure 7

Test results of turbine performance(2)

Figure 6

Test turbine

Verification of reliability of rotating blades
It was verified that rotational asynchronous vibration such as random vibration andflutter, which are influenced by steam flow during operation, does not pose a problem in termsof reliability in actual machines. A telemeter was installed on the actual rotor, andmeasurements were carried out using a measuring device mounted on the rotating blade for the
purpose of avoiding resonance during operation and confirming the asynchronous vibrationlevel. Figure 8 is an example of the measurement results of the asynchronous vibration stressof a blade during operation. It was confirmed that the asynchronous vibration was sufficiently
lower than the design-allowable stress (100% of the graph's vertical axis) in the operational
range from the plant partial output to the rated output.

Mitsubishi Heavy Industries Technical Review Vol. 56 No. 3 (September 2019)
5Figure 8

Asynchronous vibration stress|4. Examples of application in actual machines
The 3000 rpm 60-inch titanium blades have been put into practical use in the steam turbineof a 1075 MW coal-fired plant for the ENEA Wytwarzanie S.A. Kozienice power plant No. 11 unitin Poland. Figure 9 depicts the appearance of the steam turbine and Figure 10 illustrates itsstructure. The plant is a joint order with a consortium partner, Polimex-Mostostal S.A., and MHPS
supplied the boiler, the generator, the environmental equipment and the steam turbine. The contract
was signed in September 2012, and commercial operation started in December 2017 after trialoperation. The turbine type is a tandem compound TC4F type with single-shaft series structure, andthe steam condition is ultra-supercritical pressure in which the main steam pressure is 25 MPa, themain steam temperature is 600°C and the reheat steam temperature 620°C. The plant efficiency met
the planned value, and the resulting CO2 emissions could be reduced by 25% compared with many
subcritical coal-fired power plants in Poland. In addition, the Environmental Regulations for Air
Pollutants, Industrial Emissions Directive (IED) requirements, which will come into effect in 2021,
have been significantly exceeded. Furthermore, 60-inch titanium blades will be applied to a 660
MW supercritical coal-fired power plant in Greece.

Figure 9 Poland Kozienice power plant
No. 11 unit

Figure 10 Structure of 1075 MW steam turbinewith 60 inch Last Stage BladeOn the other hand, 3600 rpm 50-inch titanium blades were adopted in a 1050 MW
supercritical coal-fired power plant for Tai'an No. 9 unit and No. 10 unit of Korea Western Power
Co., Ltd., and commercial operations of the No. 9 unit in October 2016 and No. 10 unit in June2017 commenced after construction and trial operation. These plants have the largest capacity
among thermal power plants in South Korea and play a role in the stable supply of electricity to theKorean capital.
These plants are operating satisfactorily, contributing to the stable supply of electricity andCO2 emissions reduction in Poland and South Korea.

|5. Conclusion
Developed using the latest design technology and validation methods, the 50/60 LSB has
been applied to high-capacity coal-fired power plants in Poland and South Korea and iscontributing to the stable supply of electricity globally. Although the construction of coal-fired

Mitsubishi Heavy Industries Technical Review Vol. 56 No. 3 (September 2019)
6power generation plants is decreasing from the perspective of CO2 emissions, it is difficult to stably
supply electricity using only renewable energy to meet the electricity demand resulting from
economic development on a global scale. For this reason, technological development of CCUS
(Carbon dioxide capture, utilization and storage) that captures CO2 and actively uses it has seen
progress in recent years. Along with these new technologies that make effective use of CO2, thisblade is expected to be utilized in the future as a technology for high-capacity and high-efficiency
coal-fired power plants to play a role in energy mix optimization.

References
(1)
(2)

(3)

Shigeki Senoo, et al, “Development of Titanium 3600rpm-50inch and 3000rpm-60inch Last Stage Bladesfor Steam Turbines”, Proceedings of IGTC 2011, IGTC2011-0249, (2011), pp. 1-8.
Kunio Asai, et al, “Experimental Validation of Fretting Fatigue Strength and Fretting Wear Rate atContact Surface of Turbine-Blade-Shroud Cover”, Proceedings of ASME Turbo Expo 2012,
0GT2012-68576, (2012), pp.1-8.
Yutaka Yamashita, et al, “Vibration characteristics of a continuous cover blade structure with friction
contact surfaces of a steam turbine”, 10th International Conference on Vibrations in Rotating Machinery,(2012), pp.323-332.