<P> In particular the efficiency of the steam turbine will be limited by water droplet formation . As the water condenses, water droplets hit the turbine blades at high speed causing pitting and erosion, gradually decreasing the life of turbine blades and efficiency of the turbine . The easiest way to overcome this problem is by superheating the steam . On the Ts diagram above, state 3 is at a border of the two phase region of steam and water so after expansion the steam will be very wet . By superheating, state 3 will move to the right (and up) in the diagram and hence produce a drier steam after expansion . </P> <P> The overall thermodynamic efficiency can be increased by raising the average heat input temperature (T _̄ i n = ∫ 2 3 T d Q Q i n) (\ displaystyle \ left ((\ bar (T)) _ (\ mathit (in)) = (\ frac (\ int _ (2) ^ (3) T \, dQ) (Q_ (\ mathit (in)))) \ right)) of that cycle . Increasing the temperature of the steam into the superheat region is a simple way of doing this . There are also variations of the basic Rankine cycle which are designed to raise the thermal efficiency of the cycle in this way; two of these are described below . </P> <P> The purpose of a reheating cycle is to remove the moisture carried by the steam at the final stages of the expansion process . In this variation, two turbines work in series . The first accepts vapor from the boiler at high pressure . After the vapor has passed through the first turbine, it re-enters the boiler and is reheated before passing through a second, lower - pressure, turbine . The reheat temperatures are very close or equal to the inlet temperatures, whereas the optimum reheat pressure needed is only one fourth of the original boiler pressure . Among other advantages, this prevents the vapor from condensing during its expansion and thereby damaging the turbine blades, and improves the efficiency of the cycle, because more of the heat flow into the cycle occurs at higher temperature . The reheat cycle was first introduced in the 1920s, but was not operational for long due to technical difficulties . In the 1940s, it was reintroduced with the increasing manufacture of high - pressure boilers, and eventually double reheating was introduced in the 1950s . The idea behind double reheating is to increase the average temperature . It was observed that more than two stages of reheating are unnecessary, since the next stage increases the cycle efficiency only half as much as the preceding stage . Today, double reheating is commonly used in power plants that operate under supercritical pressure . </P> <P> The regenerative Rankine cycle is so named because after emerging from the condenser (possibly as a subcooled liquid) the working fluid is heated by steam tapped from the hot portion of the cycle . On the diagram shown, the fluid at 2 is mixed with the fluid at 4 (both at the same pressure) to end up with the saturated liquid at 7 . This is called "direct contact heating". The Regenerative Rankine cycle (with minor variants) is commonly used in real power station . </P>

Advantage of using reheat cycle in steam power plant