The Organic Rankine Cycle (ORC) is a Clausius–Rankine Cycle in
which an organic working fluid is used instead of water–steam. In
the last years it became quite popular in energy production processes,
due to the fact that it gives the possibility to use exhaust
heat of low energy and temperature level. Fig. 1 shows the main
components of the ORC process. The organic working fluid is compressed
with a pump, which forces the fluid through a regenerator.
The regenerator allows the preheating of the liquid working fluid
by desuperheating the expanded vapour. The preheated working
fluid is then evaporated, superheated and expanded in a turbine,
which drives a generator. The desuperheated vapour is condensed
in a condenser. If the temperature level of the condensation is high
enough, as for example in the case of biomass combustion, the
waste heat can be used in a district heating net. If low temperature
heat is used for driving the ORC, like geothermal or waste heat, the
condenser is cooled back by means of cooling water.
Most of the efforts in the literature include ways of maximizing
the efficiency of the thermodynamic cycle for best waste heat
recovery [1].
The use of ORC process for waste heat recovery has been applied
for many years. An overview of manufacturers together with
the appropriate temperature range of the applications is presented
in Table 1. In this table, also the expansion machine which is used
for the superheated organic fluid vapour is presented.