Steam turbine: the story on HearLore

Steam turbine

In the first century, a Greek engineer named Hero of Alexandria built a spinning sphere that used steam to rotate, creating what is now known as the Aeolipile. This device was little more than a toy, yet it contained the fundamental principle that would eventually power the modern world. For over a thousand years, the concept remained a curiosity, appearing in the writings of Taqi al-Din in Ottoman Egypt in 1551, who described a steam turbine with the practical application of rotating a spit, and later by Giovanni Branca in 1629 and John Wilkins in 1648. These early devices, known today as steam jacks, were simple and lacked the power to drive industry, but they laid the groundwork for a revolution that was centuries in the making. The true transformation began not in a factory, but in a laboratory where a man named Charles Parsons sought to turn a toy into a machine that could generate electricity and propel ships. In 1884, Parsons invented the modern steam turbine, a reaction type that was so effective it made cheap and plentiful electricity possible. His invention revolutionized marine transport and naval warfare, changing the course of history within a single lifetime. The size of generators increased from his first setup to units of capacity that were 10,000 times larger, and the total output from turbo-generators constructed by his firm and their licensees for land purposes alone exceeded thirty million horse-power. This was not merely an improvement on existing technology; it was a complete reimagining of how thermal energy could be converted into mechanical work.

The Race For Speed And Scale

The early years of steam turbine development were defined by a desperate race to reconcile the high rotational speeds of the turbine with the slow turning requirements of ship propellers. In 1894, the Turbinia, the first steam turbine-powered ship, demonstrated that the technology could work, but it required direct drive to each propeller shaft, meaning the turbine had to spin at thousands of revolutions per minute to move the ship. This was a massive engineering challenge because efficient reduction gears were not yet available for the high powers required by ships. The Turbinia likely totaled around 200 turbine stages operating in series to reduce the efficient speed of the turbine after initial trials. The United States Navy faced a similar dilemma, launching the first US turbine-powered destroyer in 1909, which had direct drive turbines and whose three shafts turned at 724 rpm. The quest for economy was even more important when cruising speeds were considered, as cruising speed is roughly 50% of a warship's maximum speed and 20 to 25% of its maximum power level. Early turbine ships had poor cruising ranges because turbine efficiency was greatly reduced at these lower speeds. A solution that proved useful through most of the steam turbine propulsion era was the cruising turbine, an extra turbine to add even more stages, attached directly to one or more shafts, exhausting to a stage partway along the high-pressure turbine, and not used at high speeds. The United States Navy reverted to reciprocating machinery on the s of 1912, then went back to turbines on Nevada in 1914, highlighting the lingering fondness for reciprocating machinery due to the need for fuel economy. The US Navy had the greatest need of any nation for fuel economy, especially as the prospect of war with Japan arose following World War I. This need was compounded by the US not launching any cruisers from 1908 to 1920, so destroyers were required to perform long-range missions usually assigned to cruisers. Once fully geared turbines proved economical in initial cost and fuel, they were rapidly adopted, with cruising turbines also included on most ships. Beginning in 1915 all new Royal Navy destroyers had fully geared turbines, and the United States followed in 1917.

Who invented the modern steam turbine and when was it invented?

Charles Parsons invented the modern steam turbine in 1884. This reaction type invention made cheap and plentiful electricity possible and revolutionized marine transport and naval warfare.

What is the largest steam turbine ever built and where will it be installed?

The largest steam turbine ever built is the 1,770 MW Arabelle steam turbine. Two units of this turbine will be installed at Hinkley Point C Nuclear Power Station in England.

How much electricity generation in the United States used steam turbines in 2022?

About 42% of all electricity generation in the United States in 2022 was by the use of steam turbines. Electrical power stations use large steam turbines to produce most of the world's electricity, which is about 80% of the total.

When did the Royal Navy decommission its last conventional steam-powered surface warship class?

The Royal Navy decommissioned its last conventional steam-powered surface warship class, the Type 45 destroyer, in 2002. The Italian Navy followed in 2006 by decommissioning its last conventional steam-powered surface warships, the Maestrale class.

What are the common rotational speeds for steam turbines used in electric power generation?

The most common speeds for steam turbines used in electric power generation are 3,000 rpm for 50 Hz systems and 3,600 rpm for 60 Hz systems. Nuclear reactor turbine generator sets may operate at half these speeds to reduce erosion of turbine blades.

The Engineering Of Steel And Steam

The interior of a steam turbine comprises several sets of blades or buckets, arranged to intermesh with certain minimum clearances to efficiently exploit the expansion of steam at each stage. A major challenge facing turbine design was reducing the creep experienced by the blades, as the high temperatures and high stresses of operation cause steam turbine materials to become damaged through these mechanisms. To limit creep, thermal coatings and superalloys with solid-solution strengthening and grain boundary strengthening are used in blade designs. Protective coatings are often stabilized zirconium dioxide-based ceramics, which limit the temperature exposure of the nickel superalloy and reduce the creep mechanisms experienced in the blade. The nickel-based blades are alloyed with aluminum and titanium to improve strength and creep resistance, and the microstructure of these alloys is composed of different regions of composition. A uniform dispersion of the gamma-prime phase, a combination of nickel, aluminum, and titanium, promotes the strength and creep resistance of the blade due to the microstructure. Refractory elements such as rhenium and ruthenium can be added to the alloy to improve creep strength, reducing the diffusion of the gamma prime phase and preserving the fatigue resistance, strength, and creep resistance. The manufacturing of a modern steam turbine involves advanced metalwork to form high-grade steel alloys into precision parts using technologies that first became available in the 20th century. The largest steam turbine ever built is the 1,770 MW Arabelle steam turbine built by Arabelle Solutions, two units of which will be installed at Hinkley Point C Nuclear Power Station in England. Continued advances in durability and efficiency of steam turbines remain central to the energy economics of the 21st century. Technical challenges include rotor imbalance, vibration, bearing wear, and uneven expansion, various forms of thermal shock. When warming up a set for use, the main steam stop valves have a bypass line to allow superheated steam to slowly bypass the valve and proceed to heat up the lines in the system along with the steam turbine. In addition, when there is no steam, a turning gear is engaged to slowly rotate the turbine to ensure even heating and prevent uneven expansion. The warm-up procedure for large steam turbines may exceed ten hours.

The Silent Power Of The Grid

Electrical power stations use large steam turbines driving electric generators to produce most of the world's electricity, about 80% of the total. The advent of large steam turbines made central-station electricity generation practical, since reciprocating steam engines of large rating became very bulky and operated at slow speeds. Most central stations are fossil fuel power plants and nuclear power plants, and some installations use geothermal steam or use concentrated solar power to create the steam. Steam turbines can also be used directly to drive large centrifugal pumps, such as feedwater pumps at a thermal power plant. The turbines used for electric power generation are most often directly coupled to their generators, and as the generators must rotate at constant synchronous speeds according to the frequency of the electric power system, the most common speeds are 3,000 rpm for 50 Hz systems and 3,600 rpm for 60 Hz systems. Since nuclear reactors have lower temperature limits than fossil-fired plants, with lower steam quality, the turbine generator sets may be arranged to operate at half these speeds, but with four-pole generators, to reduce erosion of turbine blades. About 42% of all electricity generation in the United States in 2022 was by the use of steam turbines. The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency from the use of multiple stages in the expansion of the steam, which results in a closer approach to the ideal reversible expansion process. Because the turbine generates rotary motion, it can be coupled to a generator to harness its motion into electricity. Such turbogenerators are the core of thermal power stations which can be fueled by fossil fuels, nuclear fuels, geothermal, or solar energy. Maintenance requirements of modern steam turbines are simple and incur low costs, typically around 0.005 dollars per kilowatt-hour, and their operational life often exceeds 50 years.

The Battle For Efficiency And Control

The control of a turbine with a governor is essential, as turbines need to be run up slowly to prevent damage and some applications, such as the generation of alternating current electricity, require precise speed control. Uncontrolled acceleration of the turbine rotor can lead to an overspeed trip, which causes the governor and throttle valves that control the flow of steam to the turbine to close. If these valves fail, the turbine may continue accelerating until it breaks apart, often catastrophically. Turbines are expensive to make, requiring precision manufacture and special quality materials. During normal operation in synchronization with the electricity network, power plants are governed with a five percent droop speed control, meaning the full load speed is 100% and the no-load speed is 105%. This is required for the stable operation of the network without hunting and drop-outs of power plants. Normally the changes in speed are minor, and adjustments in power output are made by slowly raising the droop curve by increasing the spring pressure on a centrifugal governor. The steam turbine operates on basic principles of thermodynamics using the part 3-4 of the Rankine cycle shown in the adjoining diagram. Superheated steam or dry saturated steam, depending on application, leaves the boiler at high temperature and high pressure. At entry to the turbine, the steam gains kinetic energy by passing through a nozzle, a fixed nozzle in an impulse type turbine or the fixed blades in a reaction type turbine. When the steam leaves the nozzle it is moving at high velocity towards the blades of the turbine rotor. A force is created on the blades due to the pressure of the vapor on the blades causing them to move. A generator or other such device can be placed on the shaft, and the energy that was in the steam can now be stored and used. The steam leaves the turbine as a saturated vapor or liquid-vapor mix depending on application at a lower temperature and pressure than it entered with and is sent to the condenser to be cooled. The first law enables us to find a formula for the rate at which work is developed per unit mass. Assuming there is no heat transfer to the surrounding environment and that the changes in kinetic and potential energy are negligible compared to the change in specific enthalpy, we arrive at the following equation.

The End Of The Steam Age

Since the 1980s, steam turbines have been replaced by gas turbines on fast ships and by diesel engines on other ships, with exceptions being nuclear-powered ships and submarines and LNG carriers. Some auxiliary ships continue to use steam propulsion, and in the U.S. Navy, the conventionally powered steam turbine is still in use on all but one of the Wasp-class amphibious assault ships. The Royal Navy decommissioned its last conventional steam-powered surface warship class, the Type 45 destroyer, in 2002, with the Italian Navy following in 2006 by decommissioning its last conventional steam-powered surface warships, the Maestrale class. In 2013, the French Navy ended its steam era with the decommissioning of its last Mistral class amphibious assault ship. Amongst the other blue-water navies, the Russian Navy currently operates steam-powered Kirov-class battlecruisers and Slava-class cruisers. The Indian Navy currently operates INS Vikramaditya, a modified Kiev-class aircraft carrier, and also operates three Talwar-class frigates commissioned in the early 2000s. The Chinese Navy currently operates steam-powered Type 051 destroyers, Type 052 destroyers, along with Type 055 destroyers and the lone Type 051B destroyer. Most other naval forces have either retired or re-engined their steam-powered warships. As of 2020, the Mexican Navy operates four steam-powered former U.S. Knox-class frigates. The Egyptian Navy and the Republic of China Navy respectively operate two and six former U.S. Knox-class frigates. The Ecuadorian Navy currently operates two steam-powered Almirante Latorre-class destroyers. Today, propulsion steam turbine cycle efficiencies have yet to break 50%, yet diesel engines routinely exceed 50%, especially in marine applications. Diesel power plants also have lower operating costs since fewer operators are required. Thus, conventional steam power is used in very few new ships. An exception is LNG carriers which often find it more economical to use boil-off gas with a steam turbine than to re-liquify it. Nuclear-powered ships and submarines use a nuclear reactor to create steam for turbines. Currently, the main propulsion steam turbines for United States Navy nuclear-powered Nimitz and Ford class aircraft carriers are manufactured by Curtiss-Wright, while the steam turbines for Virginia and Columbia class submarines are manufactured by Northrop Grumman. Nuclear power is often chosen where diesel power would be impractical, as in submarine applications, or the logistics of refueling pose significant problems, for example, icebreakers. It has been estimated that the reactor fuel for the Royal Navy's HMS Dreadnought is sufficient to last 40 circumnavigations of the globe, potentially sufficient for the vessel's entire service life. Nuclear propulsion has only been applied to a very few commercial vessels due to the expense of maintenance and the regulatory controls required on nuclear systems and fuel cycles.