Reheat Rankine Cycle
Reheating allows one to increase the boiler pressure without increasing the moisture content in the vapor exiting from the turbine.
By reheating, the averaged temperature of the vapor entering the turbine is increased, thus, it increases the thermal efficiency of the cycle.
Multistage reheating is possible but not practical. One major reason is because the vapor exiting will be superheated vapor at higher temperature, thus, decrease the thermal efficiency. Why?
Energy analysis: Heat transfer and work output both change
qin = qprimary + qreheat = (h3-h2) + (h5-h4)
Wout = Wturbine1 + Wturbine2 = (h3-h4) + (h5-h6)