Mechanical Arrangements of Steam Turbines • Solutions to Turbo-machinery Issues. • Tandem Reheat Steam Turbine • Cross Compound Steam Turbine
Parson’s concept of multi-stage had produced an additional but marginal thermodynamic advantage.
Enthalpy Entropy Diagram for Multistage Turbine Turbine Inlet Stage 1 h Stage 2 Stage 3 Stage 4 Stage 5 Turbine Exit s
Internal Reheating due to Irreversibilities 4Ia 4Is 4IIa 4IIs 4IIIa 4IIIs 4IVa 4IVs 4Va 4Vs 4VIa 4VIs 3 T 4s s
3 4Ia 4Is 4IIa 4IIs 4IIIa 4IIIs 4IVa 4IVs 4Va 4Vs 4VIa 4VIs 4s Steam Flow Path in a Multi Stage Impulse Turbine • Global available enthalpy for Power: • Internally available enthalpy for Power: 4IIss 4IIIss 4IVss • Total actual stage work output per unit mass: 4Vss
Define Stage Efficiency: Global internal efficiency of turbine:
qi is always positive. Therefore, • Multistage turbines will increase the possibility of recovering lost availability! • The larger the number of stages, the greater is the heat recovery. • The difference is called heat recovery factor, • General value of is 0.04 to 0.06.
Compounding of impulse turbine • Compounding is done to reduce the rotational speed of the impulse turbine to practical limits. • Compounding is achieved by using more than one set of nozzles, blades, rotors, in a series, keyed to a common shaft; so that either the steam pressure or the jet velocity is absorbed by the turbine in stages. • Three main types of compounded impulse turbines are: • a) Pressure compounded Steam Turbine : The Rateau Design • b) velocity compounded Steam Turbine : The Curtis Design • c) pressure and velocity compounded Impulse turbines : The Rateau-curtis Design.