Study of Multi Stage Steam Turbines
P M V SubbaraoProfessor
Mechanical Engineering Department
Techno-economical Viable Solution forLow Capacity Mechanical Power ……
Blade Power at Maximum Efficiency COnditions
Ideal Impulse Stage : UVUmP aBladeimpulse 11 cos2
Ideal Parson Stage : UVUmP aParson 11 cos2
2
cos 1
1
aV
U 22 UmP Bladeimpulse
2
cos 122
1 aBladeimpulse
VmP
11
cosaV
U 2UmPParson
122
1 cos aParson VmP
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
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.
Mechanical Arrangements of Steam Turbines
• Solutions to Turbo-machinery Issues.
• Tandem Reheat Steam Turbine
• Cross Compound Steam Turbine
Tandem Reheat Steam Turbine
Cross Compound Reheat Steam Turbine
Tandem-compound four-flow steam turbine
Large-Capacity Steam Turbines for Fossil Thermal Power Plant
Parson’s concept of multi-stage had produced an additional but marginal thermodynamic advantage.
Enthalpy Entropy Diagram for Multistage Turbine
h
s
Turbine Inlet
Turbine Exit
Stage 1
Stage 2
Stage 3
Stage 4
Stage 5
Internal Reheating due to Irreversibilities
3
4s
4IIs
4IIIs
4Is
4Ia
4IIa
4IIIa
4Vs
4IVs
4IVa
4Va
4VIs
4VIa
T
s
Behavior of Superheated Steam
h
T
Well Behavior of Superheated Steam
T
pT
h
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
savg hhh 43,
• Internally available enthalpy for Power:
n
is
ia
Is
avstageav
hhhh
hh
24
1443
,int,
• Total actual stage work output per unit mass:
n
ia
ia
Iaact hhhhw
24
1443
4IIss
4IIIss
4IVss
4Vss
Define Stage Efficiency:
Is
Iast
stage hh
hh
43
431
is
ia
ia
iaith
hh
hhstage
41
4
41
4
n
is
ia
ithstage
Is
ststageact hhhhw
24
1443
1
Global internal efficiency of turbine:
s
actturbine hh
w
43
s
nis
ia
ithstage
Is
ststage
turbine hh
hhhh
43
24
1443
1
s
n
iiss
iss
ithstage
Is
ststage
turbine hh
qhhhh
43
24
1443
1
qi is always positive.
Therefore, istageturbine
•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.
Pressure compounded impulse turbine