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History of steam turbine technology
The first device that can be classified as a reaction steam turbine is the aeolipile proposed by Hero of Alexandria, during the 1st century CE. In this device, steam was supplied through a hollow rotating shaft to a hollow rotating sphere. It then emerged through two opposing curved tubes, just as water issues from a rotating lawn sprinkler. The device was little more than a toy, since no useful work was produced.
Another steam-driven machine, described in 1629 in Italy, was designed in such a way that a jet of steam impinged on blades extending from a wheel and caused it to rotate by the impulse principle. Starting with a 1784 patent by James Watt, the developer of the steam engine, a number of reaction and impulse turbines were proposed, all adaptations of similar devices that operated with water. None were successful except for the units built by William Avery of the United States after 1837. In one such Avery turbine two hollow arms, about 75 centimetres long, were attached at right angles to a hollow shaft through which steam was supplied. Nozzles at the outer end of the arms allowed the steam to escape in a tangential direction, thus producing the reaction to turn the wheel. About 50 of these turbines were built for sawmills, cotton gins, and woodworking shops, and at least one was tried on a locomotive. While the efficiencies matched those of contemporary steam engines, high noise levels, difficult speed regulation, and frequent need for repairs led to their abandonment.
Development of modern steam turbines
No further developments occurred until the end of the 19th century when various inventors laid the groundwork for the modern steam turbine. In 1884 Sir Charles Algernon Parsons, a British engineer, recognized the advantage of employing a large number of stages in series, allowing extraction of the thermal energy in the steam in small steps. Parsons also developed the reaction-stage principle according to which a nearly equal pressure drop and energy release takes place in both the stationary and moving blade passages. In addition, he subsequently built the first practical large marine steam turbines. During the 1880s Carl G.P. de Laval of Sweden constructed small reaction turbines that turned at about 40,000 revolutions per minute to drive cream separators. Their high speed, however, made them unsuitable for other commercial applications. De Laval then turned his attention to single-stage impulse turbines that used convergent-divergent nozzles, such as the one shown in Figure 3. From 1889 to 1897 de Laval built many turbines with capacities from about 15 to several hundred horsepower. His 15-horsepower turbines were the first employed for marine propulsion (1892). C.E.A. Rateau of France first developed multistage impulse turbines during the 1890s. At about the same time, Charles G. Curtis of the United States developed the velocity-compounded impulse stage.
Condensing Steam Turbine
Condensing steam turbines are most commonly found in thermal power plants. In a condensing steam turbine, the maximum amount of energy is extracted from the steam, because there is very high enthalpy difference between the initial (e.g. 6MPa; 275°C; x = 1) and final (e.g. 0.008MPa; 41.5°C; x = 0.9) conditions of steam. This is achieved by passing the exhaust steam into a condenser (called a surface condenser), which condenses the exhaust steam from the low-pressure stages of the main turbine (decreases the temperature and pressure of exhausted steam). The exhausted steam is condensed by passing over tubes containing water from the cooling system.
Steam is here to stay. Demand grows for small and medium-sized steam turbines
Wherever heat is available and there is a demand for power, you are likely to find one of turbomachinery’s oldest and world-changing inventions – the industrial steam turbine (ST). The technology has come a long way since its first modern manifestation in 1884, persisting through every market boom and bust.
Until 2016, coal’s fall from grace and the growing share of renewables on the grid had caused the ST market to contract. But growth and stability have returned. Demand is returning for small- and mid-sized combined cycle power plants (CCPP), combined heat and power (CHP), petrochemicals, biomass and concentrated solar power (CSP) solutions. All include an ST element.
With sales recovering, globalization is another trend noted by ST OEMs. Most have established joint ventures with customers and suppliers across the world, which helps turbine companies boost market share, decrease costs, and gain access to new business.
Innovation in STs may not be fast paced when compared to the developmental progress made in the gas turbine field. Nevertheless, OEMs such as Mitsubishi Compressor, Doosan ?koda Power, Siemens Energy, Fincantieri, Triveni Turbine, Baker Hughes, Howden, Ansaldo Energia, Elliott, GE Steam Power and MAN Energy Solutions, among others, have made strides in performance optimization, reduction of carbon emissions, improved efficiency, start-up speed/flexibility and in raising steam parameters.
Turbomachinery International Magazine interviewed several of these OEMs to find out the latest trends dominating the steam turbine sector. They offer a diverse set of market insights.