1. Study of Multi Stage Steam Turbines
P M V Subbarao
Professor
Mechanical Engineering Department
Techno-economical Viable Solution forLow Capacity Mechanical Power ……

2. Blade Power at Maximum Efficiency COnditions
Ideal Impulse Stage :
Ideal Parson Stage :

3. Moderate Capacity of Parson : Same Blade Velocity
At optimum U/Va1, an impulse stage produces TWICE the power of a 50% reaction stage for same blade speed!
This means that an impulse turbine requires only half the number of stages as a 50% reaction turbine for a given application!
This fact has a major impact on the construction of the turbine
It is also responsible for some of the greatest miss understandings, since people assume that this means that impulse blading is cheaper overall - this is NOT true!
Impulse turbines have fewer stages, but they must use a different form of construction which is expensive

4. Capacity of Parson : Same Inlet Steam Velocity
So at optimum U/Va1, a 50% reaction stage produces TWICE the power of an impulse stage for same value of Highest Steam jet velocity.
This means that a 50% reaction turbine requires only half the number of stages as an impulse turbine for a given application!
This fact has a major impact on achieving lower fluid dynamic losses with improved capital cost.
Reaction turbines with fewer stages and less expensive cost are highly preferred in large power plants.

5. Mechanical Arrangements of Steam Turbines
Solutions to Turbo-machinery Issues.
Tandem Reheat Steam Turbine
Cross Compound Steam Turbine

6. Tandem Reheat Steam Turbine

7. Cross Compound Reheat Steam Turbine

8. Tandem-compound four-flow steam turbine

9. Large-Capacity Steam Turbines for Fossil Thermal Power Plant

10. Parson’s concept of multi-stage had produced an additional but marginal thermodynamic advantage.

11. Enthalpy Entropy Diagram for Multistage Turbine
Turbine Inlet
Stage 1 h
Stage 2
Stage 3
Stage 4
Stage 5
Turbine Exit s

12. Internal Reheating due to Irreversibilities3
4Is
4Ia
4IIs
4IIa
4IIIs
4IIIa
4Vs
4IVs
4IVa
4Va
4VIs
4VIa T 4s s

13. Behavior of Superheated Steam

14. Well Behavior of Superheated Steam

15. Steam Flow Path in a Multi Stage Impulse Turbine
Global available enthalpy for Power: 3 4s
4IIs
4IIIs
4Is
4Vs
4IVs
4Ia
4IIa
4IIIa
4IVa
4Va
4VIs
4VIa
Internally available enthalpy for Power:
4IIss
4IIIss
4IVss
Total actual stage work output per unit mass:
4Vss

16. Define Stage Efficiency:
Global internal efficiency of turbine:

17. 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, a.
General value of a is 0.04 to 0.06.

18. 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.

19. Pressure compounded impulse turbine