The Curtis Turbine & The Parson Turbine
P M V SubbaraoProfessor
Mechanical Engineering Department
Options for Economically Viable Speeds……
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.
Multistage Impulse Turbine : GE Product
Pressure compounded impulse turbine
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 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
1
coscos
cos,1
,2,,1,1,
i
iibiiaib kUVUmP
Total enthalpy drop available for mechanical power
n
iitotal hh
1ioia hVV 2,1
1
coscos
cos2,1
,2,,1,
i
iibiiiid k
total
n
i i
iibiii
d h
k
1 ,1
,2,,1 1
coscos
cos2
d
Stages Stage 1 Stage Z
Diameter
Variation of Diameter along a stages
The Curtis Design
A System of Velocity Triangles for Curtis Turbine
U
1Vr11Va1
1Vr2
1Va2
11 2
U
3Vr13Va13Vr23Va2
112 2
U
2Vr12Va1
2Vr2
2Va2
112 2
The Curtis Impulse Turbine
1
coscos
cos,1
,2,,1,1,
i
iibiiaib kUVUmP
Total enthalpy drop available for mechanical power
totaloa hVV 21,1
1
coscos
cos2,1
,2,,1,
i
iibiiiid k
total
n
i i
iibiii
d h
k
1 ,1
,2,,1 1
coscos
cos2
11,2,1 iVV iaia
Curtis Turbine With 2 Rotors
1
coscos
cos1,1
1,21,1,11,11,
bab kUVUmP
1
coscos
cos2,1
2,22,2,12,12,
bab kUVUmP
U
1Vr1
1Va11Vr2
1Va211
2
Total power with similar blading
UVUVkUmP aabtb
2,12,11,11,1
1
21,, coscos1
coscos
1cossin
coscos
1,2
2
1
1,11,12,1
UV
V aa
Efficiency of two rotor Curtis Turbine
2
coscos1coscos
21,
2,12,11,11,11
21,
a
aab
curtis Vm
UVUVkUm
1,2,1
1,1
2,1
1,1,1
1
21,
1,
coscos1coscos2
aia
a
aib
aicurtis V
UVV
VUk
VU
1
cossin
cos
cos
1,2
2
1
1,11,1
1,1
2,1
a
a
a VU
VV
Efficiency of two rotor Curtis 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
Efficiency of Multi Rotor Curtis Turbine
2,13,1
2,1
3,1
1,12,1
1,1
2,1
1,1,1
1
21,
1,
coscoscos1coscos2
aa
a
aa
a
aib
aicurtis V
UVV
VU
VV
VUk
VU
For a three rotor Curtis Turbine:
1
cossin
cos
cos
2,2
2
1
2,12,1
2,1
3,1
a
a
a VU
VV
For a n-rotor Curtis Turbine:
1
1 ,11,1
,1
1,1
1,1,1
1
21,
1,
coscos1coscos2
n
i iai
ia
ia
aib
aicurtis V
UVV
VUk
VU
1cos
sincos
cos
1,2
2
1
1,12,1
,1
1,1
i
ia
ia
ia VU
VV
The Curtis-Rateau Design
Compound Impulse-Reaction turbine
• The shape of the blade improves considerably.• The blade sizes varyies at a uniform rate, thus
contributing to more economic designs.• As a result of enthalpy drop occurring in the moving
blades, there is a considerable amount of pressure is exerted on the rotor.
• This is transmitted to thrust bearing.• To void large axial thrust it is usual to allow:• Low degree of reaction in high pressure stages.• In large steam turbines (>300 MW), it is now usual to
allow 60 – 70% of degree of reaction in low pressure stages.
Customization of DoR Irreversible Flow Through A Stage
SteamThermalPower
SteamkineticPower
BladekineticPower
Nozzle Losses
Moving Blade Losses
Stage Losses
Isentropic efficiency ofNozzle
Blade Friction Factor
Losses in Nozzles
• Losses of kinetic energy of steam while flowing through nozzles or guide blade passages are caused because of – Energy losses of steam before entering the nozzles, – Frictional resistance of the nozzles walls, – Viscous friction between steam molecules, – Deflection of the flow, – Growth of boundary layer, – Turbulence in the Wake and – Losses at the roof and floor of the nozzles.
• These losses are accounted by the velocity coefficient, .
Losses in Moving Blades• Losses in moving blades are caused due to various factors.• The total losses in moving blades are accounted for by the
load coefficient, ψ.• These total losses are comprised of the following:• Losses due to trailing edge wake.• Impingement losses.• Losses due to leakage of steam through the annular space
between stator and the shrouding.• Friction losses.• Losses due to the turning of the steam jet in the blades• Losses due to shrouding.
Stage with General Value of Degree of Reaction
stageper enthalpy in total drop Theblades moving in the dropenthalpy static The
First law for fixed blades:
2
20
21
10aa VVhh
First law for relative flow through moving blades:
2
21
22
21rr VVhh
22
21
22
20
21
20rraa VVVVhh
22
21
22
20
21
20rraa VVVVhh
2222
22
20
21
22
20
21
2000aarraa VVVVVVhh
22
22
2
20
02000aa VhVhhh
22
21
22
22
21
2000rraa VVVVhh
True Available Enthalpy
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