Organic Rankine cycle

In the ideal cycle described by the engine's theoretical model, the expansion is isentropic and the evaporation and condensation processes are isobaric.

Those irreversibilities mainly occur:[6] The organic Rankine cycle technology has many possible applications, and counts more than 2.7 GW of installed capacity and 698 identified power plants worldwide.

It can be applied to heat and power plants (for example a small scale cogeneration plant on a domestic water heater), or to industrial and farming processes such as organic products fermentation, hot exhausts from ovens or furnaces (e.g. lime and cement kilns), flue-gas condensation, exhaust gases from vehicles, intercooling of a compressor, condenser of a power cycle, etc.

The problem of high specific investment costs for machinery, such as steam boilers, are overcome due to the low working pressures in ORC power plants.

Another advantage is the long operational life of the machine due to the characteristics of the working fluid, that unlike steam is non eroding and non corroding for valve seats tubing and turbine blades.

Optimal characteristics of the working fluid: Since the purpose of the ORC focuses on the recovery of low grade heat power, a superheated approach like the traditional Rankine cycle is not appropriate.

Therefore, a small superheating at the exhaust of the evaporator will always be preferred, which disadvantages "wet" fluids (that are in two-phase state at the end of the expansion).

Unlike water, organic fluids usually suffer chemical deteriorations and decomposition at high temperatures.

A fluid with a high latent heat and density will absorb more energy from the source in the evaporator and thus reduce the required flow rate, the size of the facility, and the pump consumption.

Simulating ORC cycles requires a numerical solver in which the equations of mass and energy balance, heat transfer, pressure drops, mechanical losses, leakages, etc.