Rankine cycle is the theoretical cycle which includes basic working principle of steam power plant. Rankine cycle is different from air cycle in term of working fluid that had changed its phase during cycle especially at evaporation and condensation time. Therefore, the fluids that work in Rankine cycle are water and steam.
Rankine cycle ideally does not involve some internal irreversibility problems. Irreversibility is resulting from friction fluid, throttling, and mixing. Irreversibility can also occur in steam turbine generator and pump and will lead to heat loss and pressure loss in heat exchanger equipment, pipes, bends, and valves.
|Figure: Simple Diagram of Rankine Cycle|
|Figure 2: Simple TS Diagram of Rankine Cycle|
In the figure 1: Simple diagram of rankine cycle above, feedwater to be supplied into steam boiler is heated either with feedwater heater or deaerator. At condition 2, water is compressed by boiler feed pump into steam drum or boiler. In the boiler, water is converted into steam at condition 3. Steam is heated again until to be superheated steam which has available temperature and pressure for steam turbine generator. Superheated steam at condition 3 is distributed and expanded isentropic to turbine generator and perform rotation shaft which is connected to electric generator.
During on the turbine generator process, temperature and pressure of steam will decrease and reach point 4 where steam is distributed to condenser. Steam which enter the condenser is saturated steam and has high quality. Condenser is one of heat exchanger equipment where steam is condensed there and its temperature is decreased by cooling medium in the condenser.