Steam turbine generator system or in thermodynamics is known as the simplest Rankine cycle that consists of four components as follow (see Figure 1):
|Figure 1: Rankine Cycle of Steam Turbine Generator|
Steam boiler serves to heat water until it is converted to superheated steam phase. Superheated steam is then flowed into steam turbine generator to rotate turbine blades so as to rotate generator that is coupled to steam turbine.
The pressure and temperature of output steam from steam turbine generator has been decreased and then output steam is distributed directly into condenser for cooling steam so that the fluid will changes into liquid phase. Then fluid is forwarded into pump to increase its pressure to match with steam boiler's pressure.
|Figure 2: T-S Diagram of Steam turbine Generator|
In accordance with Figure 1 and Figure 2, Rankine cycle above can be described as follow:
Stage 1-2 : The process of isentropic pumping in the pump.
Stage 2-3: The process of heat inclusion or heating at constant pressure in the steam boiler.
Stage 3-4 : isentropic expansion process in the steam turbine generator.
Stage 4-1 : The process of spending heat or condensation at constant pressure in the condenser.
From the figure Rankine cycle and T-S diagram above, it will take assumption that the cycle in steady state, potential energy and kinetic energy is ignored, so the equation can be obtained as follow:
(qin - qout) + (win - wout) = he - hi
There is not work in steam boiler and condenser, while at the pump and steam turbine generator isentropic process is assumed to occur. By using the conservation law of energy, equation of each section can be obtained as follow:
- Pump (q = 0) → Wpump, in = h2 - h1 = v(P2 - P1)
- Steam Boiler (w = 0) → qin = h3 - h2
- Steam Turbine Generator (q = 0) → Wturb, out = h3 - h4
- Condenser (w = 0) → qout = h4 - h1
Thermal efficiency of Rankine cycle is