Steam turbines, first introduced in the late 19th century, have been greatly in demand ever since for electricity generation, marine propulsion and in industry. They are responsible for producing some 80% of the world’s electricity, from fossil and nuclear fuels as well as from certain renewable sources, and are likely to continue generating most of it in the foreseeable future.
Steam turbines, which use heat derived from burning fossil fuels (coal or oil), from nuclear reactors and from biomass and other renewable sources to drive generators, were first introduced in the 1890s.
Developed from an initial 1884 design by British engineer Charles Parsons, steam (and hydraulic) turbines rapidly became the main source of electricity generation. Steam turbine generator technology has evolved considerably over the years and the flexibility of steam turbines enables them to be used for a wide range of applications, operating in combination with different energy sources and other systems to improve their overall efficiency.
Flexible / multiple applications
Most of the electricity produced in the world today is generated by steam turbines. Their capacity can range from 50 kW to several hundreds of MWs for large power plants. Unlike gas turbines, in which heat is a by-product of power generation, steam turbines generate electricity from a derivative of heat (steam).
This enables them to operate with a wide range of fuels including fossil fuels, biomass and nuclear energy, and in a variety of installations not necessarily primarily designed for electricity generation. These may include CHP (combined heat power) systems, in which steam is extracted from the turbine and is used for heating entire districts or is converted to other forms of thermal energy including hot or chilled water, as well as in industrial installations like refineries, chemical plants or pulp and paper mills. In the last category, inexpensive fuels such as residual refinery oils, wood chips, hog fuel (a mix of coarse chips of bark and wood fibre) and other by-product fuels are burnt to power steam turbines, maximizing energy use and reducing the quantity of waste products.
International Standards matter
Steam turbines have been installed for over a century, the technology is mature and International Standards prepared by TC (Technical Committee) 5: Steam turbines, have contributed to the expansion of the sector.
These Standards concern specifications, as well as acceptance tests related to the accuracy of various types and sizes of turbines and of speed control systems. Standards for thermal verification tests of retrofitted steam turbines are also important since “today the market in retrofitting older existing machines or components is comparable to that of the new machines of any size”, according to TC 5 data.
TC 5 has also published a Technical Specification for steam purity, a highly important factor in minimizing the risk of turbine failure due to corrosion or loss of efficiency or output. However, this specification does not apply to “geothermal plants in which the turbine is fed direct from the geothermal sources”, as steam from these sources may contain naturally occurring solid particles and corrosive chemicals.
Manufacturers have highlighted the importance of IEC International Standards for steam turbines in their documents, stressing in particular that their test results “met or exceeded requirements set by IEC Standards”.
Written by Morand Fachot for our e-tech Magazine. To find out more check out our e-tech article.