Multi-Staging in Impulse Turbines P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Improvement in Initial Design - Inspired by Parson….

Simple Impulse Turbine

Availability of Steam for Condenser Temperature of 450C Turbine Inlet : 3500 kJ/kg Turbine Exit Specific Available Jet Velocity Pressure Temp Enthalpy Work MPa C kJ/kg m/s 1 509.9 2464 1036 1439 2 5 528.4 2232 1268 1592 3 10 549.6 2135 1365 1652 4 15 569 2080 1420 1685 20 586.7 2041 1459 1708 6 25 602.9 2012 1488 1725 7 30 617.7 1989 1511 1738 8 35 631.3 1969 1531 1750

Multi Stage Impulse Turbine

The most powerful steam turbine-generator in the world at the time of it's construction:1903 Built in 1903, the 5,000-kilowatt Curtis steam turbine-generator was the most powerful in the world. It stood just 25 feet high, much shorter than the 60 feet reciprocating engine-generator of a similar capacity

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 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.

Multistage Impulse Turbine : GE Product

The Curtis Design

Pressure compounded impulse turbine : Rateau Design

Impulse Turbines with pressure stages Multistage turbines with pressure stages have found a wide field of usage in industry as prime movers (~ 10 MW). The number of pressure stages vary from 4 to 5. The distribution of enthalpy drop in a large number of pressure stages enables the attainment of lower velocities for the steam flowing through the system of moving blades. As a result more advantageous values of blade speed ratio and blade friction factor are obtained .

Selection of Number of Stages

Impulse Turbines with pressure stages Total enthalpy drop available for mechanical power U Vr1 Va1 Vr2 Va2 b1 a1 a2 b2

Variation of Diameter along a stages Stage Z

The Curtis Design

A System of Velocity Triangles for Curtis Turbine Vr1,1 Va1,1 Vr2,1 Va2,1 b1,1 a1,1 a2,1 b2,1 U Vr1,2 Va1,2 Vr2,2 Va2,2 B1,2 a1,2 a2,2 b2,2 U Vr1,3 Va1,3 Vr2,3 Va2,3 b1,3 a1,3 a2,3 b2,3

The Curtis Impulse Turbine Total enthalpy drop available for mechanical power

Curtis Turbine With 2 Rotors Total power with similar blading U Vr1,1 Va1,1 Vr2,1 Va2,1 b1,1 a1,1 a2,1 b2,1

ith Reversible Symmetric Stage U Vr1,j Va1,j Vr2,j Va2,j b1,j a1,j a2,j b2,j

Efficiency of Multi Rotor Curtis Turbine For a three rotor Curtis Turbine: For a n-rotor Curtis Turbine:

The Curtis-Rateau Design