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World's First Large-Capacity Ultra-Supercritical-Pressure Steam Turbine

This historically significant technology was featured in “A Century of Power Engineering” in Power Engineering International magazine.

World's First Large-Capacity Ultra-Supercritical-Pressure Steam Turbine

The May 2010 issue of Power Engineering International (PEi), an international news magazine devoted to electric power technology, carried a feature article on worldwide developments in this field over the preceding 100 years (1910 to 2010). Entitled “A Century of Power Engineering,” the article featured around 50 historically significant technologies and events in chronological form. Toshiba was honored with the inclusion of one of its projects: the world's first ultra-supercritical-pressure turbine, which had been developed in 1989. A photograph of the turbine was also shown.

An ultra-supercritical-pressure turbine operates at a main steam pressure of 31.1 MPa, significantly higher than the 22.1 MPa critical-point pressure of water vapor. Such turbines were so named to distinguish them from the existing supercritical-pressure turbines, which operated at a main steam pressure of 24.2 MPa. By 1989, the world had experienced two oil crises and demand for improved power generation efficiency was rapidly increasing. However, after a pilot system in the U.S. malfunctioned, there was some anxiety about whether the state of technology was sufficient to withstand the high temperatures and high pressures an ultra-supercritical thermal power plant would require for improved thermal efficiency. There had been few developments in high-temperature/pressure engineering for more than a decade, but Toshiba's turbine broke through this technological stagnation.

The first two units were 4-cylinder steam turbines built for Chubu Electric Power Company's LNG-fired Thermal Power Station in Kawagoe. They were rated at 700 MW at 60 Hz output, with double-reheat steam conditions of 31.1 MPa/566°C/566°C/566°C (TC4F-33.5 type). Under these steam conditions, thermal efficiency at the generating end of the turbine plant increased to 41.7% from 39.7% for an existing equivalent machine, showing a relative improvement of 5%.

Toshiba made use of the technology in existing intermediatepressure and low-pressure turbines, and focused development on high- and ultrahigh-pressure turbines. The first design change to come out of Toshiba's research and development was the adoption of new 12 Cr steel for all static and rotating parts, in order to reduce the thermal stresses that would accompany increased pressure. The second change was to use new testing equipment to determine the rotor system characteristics in advance, in order to prevent unstable rotor shaft vibration due to ultrahigh-pressure steam whirl phenomena. The final change was to confirm the reliability of the first-stage moving blade, which was exposed to the most severe conditions, by conducting thorough numerical analysis and rotation tests using actual equipment.

This steam turbine has, as expected, continued to operate smoothly for the past 20 years. Toshiba received high evaluations for this achievement, and also received a number of awards in 1991, including the Japan Society of Mechanical Engineers Award and the Institution of Mechanical Engineers (U.K.) Research Paper Award.

After the introduction of these ultra-supercritical-pressure turbines, more efficient combined-cycle systems came into use in LNG thermal power generation systems, and gas turbines began to take over from steam turbines. However, Toshiba's technology continues to be used in coal- and oilfired power plants, which still account for the majority of the world's electric power production, and it is contributing to energy saving and global-warming prevention in Japan, China, and many other countries worldwide.

Toshiba's steam turbine is internationally recognized as having played a significant role in the adoption of steam turbines in the modern world.

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