The Rankine cycle is a power cycle which operates with steam. It is currently used in the generation of electricity thermoelectric plants. Water is used as working fluid passing through different equipment and producing a mechanical work through its expansion in the inside of a steam turbine, a generator connected to the mechanical shaft of the turbine produces the electrical output stream.
The performance of the Rankine cycle is determined by dividing the remainder of the work produced by the turbine and that consumed by the pump, divided by the heat of the steam transferred from the steam generator.
Numerous improvements have been introduced in Rankine cycle over the years with the aim of increasing the efficiency of the cycle, and thereby improve the efficiency of the power plant. In addition to increasing the performance of the equipment that take part in the process (pump, turbine, boiler…), it has become necessary to alter the layout of the plant. The main improvements to increase performance of the Rankine cycle are the following:
- Superheating of steam at the beginning of expansion (Hirn cycle).
- Modifications of the operating conditions at the beginning and the end of expansion, increase of the initial pressure of expansion, decresase of pressure at the end of expansion, supercritical conditions.
- Reheating (working with higher pressures, avoiding the formation of moisture at the end of the expansion).
- Regeneration (the feed water is preheated before it reaches the boiler using open or closed heaters with the steam of the extractions of steam turbine).
- Binary cycle (two circuits in serial, one high temperature working and the other one a low temperature).
- Decreasing the pressure of the expansion term. This is limited by the temperature of the coolant (water or air mainly) in the condenser.