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

cos

coscos

,1

,2,,1,1,

i

iibiiaib kUVUmP

Total enthalpy drop available for mechanical power

n

iitotal hh

1ioia hVV 2,1

1

cos

coscos2

,1

,2,,1,

i

iibiiiid k

total

n

i i

iibiii

d h

k

1 ,1

,2,,1 1

cos

coscos2

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

cos

coscos

,1

,2,,1,1,

i

iibiiaib kUVUmP

Total enthalpy drop available for mechanical power

totaloa hVV 21,1

1

cos

coscos2

,1

,2,,1,

i

iibiiiid k

total

n

i i

iibiii

d h

k

1 ,1

,2,,1 1

cos

coscos2

11,2,1 iVV iaia

Curtis Turbine With 2 Rotors

1

cos

coscos

1,1

1,21,1,11,11,

bab kUVUmP

1

cos

coscos

2,1

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

cos

cos

1cos

sin

cos

cos

1,2

2

1

1,11,12,1

UV

V aa

Efficiency of two rotor Curtis Turbine

2

coscos1cos

cos

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,

coscos1cos

cos2

aia

a

aib

aicurtis V

U

V

V

V

Uk

V

U

1

cos

sin

cos

cos

1,2

2

1

1,11,1

1,1

2,1

a

a

a VU

V

V

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,

coscoscos1cos

cos2

aa

a

aa

a

aib

aicurtis V

U

V

V

V

U

V

V

V

Uk

V

U

For a three rotor Curtis Turbine:

1

cos

sin

cos

cos

2,2

2

1

2,12,1

2,1

3,1

a

a

a VU

V

V

For a n-rotor Curtis Turbine:

1

1 ,11,1

,1

1,1

1,1,1

1

21,

1,

coscos1cos

cos2

n

i iai

ia

ia

aib

aicurtis V

U

V

V

V

Uk

V

U

1cos

sin

cos

cos

1,2

2

1

1,12,1

,1

1,1

i

ia

ia

ia VU

V

V

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 The

blades moving in the dropenthalpy static The

First law for fixed blades:

2

20

21

10aa VV

hh

First law for relative flow through moving blades:

2

21

22

21rr VV

hh

22

21

22

20

21

20rraa VVVV

hh

22

21

22

20

21

20rraa VVVV

hh

2222

22

20

21

22

20

21

2000aarraa VVVVVV

hh

22

22

2

20

02000aa V

hV

hhh

22

21

22

22

21

2000rraa VVVV

hh

True Available Enthalpy