In a steam turbine, heat energy contained in high-pressure and high-temperature steam – independently from the heat source – is converted into mechanical energy. This energy is then converted into electricity through a generator.
The main components of a steam turbine are:
- Rotor, where the energy from the steam is extracted by an impeller with mounted blades and transferred to the shaft
- Turbine blades, which may be stationary blades with increasing size connected to the rotor shaft or moving blades connected to the casing. The blades are turned by the steam passing through them, driving a generator to produce electrical energy
- Casing, whose function is to dissipate the steam and ensure proper sealing
Different heat sources may be used, many of them of renewable origin, such as solar or geothermal energy. Similarly, biomass or waste may also be used as fuel to generate steam, which can then be utilised to drive a steam turbine – without any emissions connected to the turbine technology.
Depending on site conditions, power range and heat parameters, different cycles may be considered to achieve maximum performance. Turbine manufacturers continuously work on developing the use of new working fluids to extend the technology’s operation range and maximise the use of heat to produce power:
- Rankine cycles use water steam as working fluid. This approach describes the traditional process of a steam turbine-based system, with temperatures typically above 300°C
- Organic Rankine Cycles (ORC) use an organic liquid as working fluid, which has a lower boiling point. This approach allows the use of low-temperature heat (down to 150°C) – such as industrial waste heat or geothermal heat
- Supercritical CO2 cycles use CO2 in a supercritical state (i.e. in fluid form). This approach has a similar temperature range as steam (225°C to 650°C) but provides higher performance and allows a better use of high-temperature heat – such as industrial waste heat or concentrated solar heat
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