steam prime movers

STEAM PRIME MOVERSA device which convert any source of energy

into Mechanical work is defined prime movers.

Steam Engine.

Steam turbine.

1A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR

Nozzle is duct of smoothly varying cross-sectional area in which a steadily flowing fluid can be made to accelerate by a pressure drop along the duct.

Applications:

steam and gas turbinesJet engines Rocket motorsFlow measurement


When a fluid is decelerated in a duct causing a rise in pressure along the stream, then the duct is called a diffuser.

Two applications in practice in which a diffuser is used are :

The centrifugal compressor Ramjet

Diffuser


Steam Nozzle

Steam nozzle is an insulated passage of varying cross-sectional area through which heat energy (Enthalpy), pressure of steam is converted into kinetic energy.


Functions of Nozzle :-

1) The main function of the steam nozzle is to convert heat energy to kinetic energy.2) To direct the steam at high velocity into blades of turbine at required angle.

Applications :-

1) Steam & gas turbines are used to produces a high velocity jet.2) Jet engines and rockets to produce thrust (propulsive force)


Types of nozzles :-

1) Convergent nozzle

2) divergent nozzle

3) convergent - divergent nozzle


1) Convergent nozzle :-

It is a nozzle with large entrance and tapers gradually to a smallest section at exit. It has no diverging portion.

2) Divergent nozzle :-

It is a nozzle with small entrance and tapers gradually to a large section at exit. It has no converging portion at entry.

3) convergent - divergent nozzle :-

convergent - divergent nozzle is widely used in steam turbines. The nozzle converges first to the smallest section and then diverges up to exit. The smallest section of the nozzle is called throat. The divergent portion of nozzle allows higher expansion ratio i.e., increases pressure drop. The taper of diverging sides of the nozzle ranges from 60 to 150 . If the taper is above 150 turbulent is increased. However if it is less than 60, the length of the nozzle will increases.


Nozzle ShapeApplying Steady flow energy equation:

…………………………….. (1)


If the area at section X - X is A, and the specific volume is v, then , using equation:

Substituting the valve of C in above equation,

Area per unit mass flow


STEAM TURBINES


“Steam Turbine is a prime-mover in which Pressure energy of steam is transformed into Kinetic energy, and later in its turn is transformed into the mechanical energy of rotation of turbine shaft”

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A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR

WORK IN A TURBINE VISUALIZEDWORK IN A TURBINE VISUALIZED


CLASSIFICATION OF STEAM TURBINE

Classification of steam turbines may be done as following:1.According to action of steam (a) Impulse turbine (b) Reaction turbine (c) Combination of both

A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR 13

2. According to direction of flow:(a)Axial flow turbine(b)Radial flow turbine3. According to number of stages(a)Single stage turbine(b)Multi stage turbine(4). According to number of cylinders(a)Single cylinder turbine(b)Double cylinder turbine(c)Three cylinder turbine


(5)According to steam pressure at inlet of Turbine:

(a) Low pressure turbine(b) Medium pressure turbine.(c) High pressure turbine(d) Super critical pressure turbine.

(6)According to method of governing:(a) Throttle governing turbine.(b) Nozzle governing turbine.(c) By pass governing turbine.


(7) According to usage in industry: (a) Stationary turbine with constant speed. (b) Stationary turbine with variable speed. (c) Non stationary turbines.


Classification based on Principle of Action1.Impulse Turbine Pressure energy of Steam is converted into Kinetic

Energy. Impulse action of high velocity jet of steam, due to

change in its direction is used to rotate the turbine shaft.

2.Reaction Turbine Reaction force due to expansion of high pressure steam

when it passes through a set of moving and fixed blades is used to rotate the turbine shaft.

Due to expansion of steam, pressure drop occurs continuously over both fixed and moving blades.

This pressure difference exerts a thrust on the blades. The resulting reaction force imparts rotary motion.

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Impulse Turbine1. Casing2. Nozzle – Pressure energy

of Steam is converted into Kinetic Energy

3. Turbine Blade – Convert kinetic energy into mechanical work.

4. Rotor5. Shaft



NOZZLE

STEAMCHEST

ROTOR

Impulse turbine - WorkingHigh pressure steam from boiler is supplied to

fixed nozzles.Nozzle – Pressure falls from boiler pressure to

condenser pressureReduction in pressure increases velocity.High velocity steam impinges on moving curved

vanesCauses change in momentum Impulsive force

on blades.Pressure remains constant when steam flows

through blades.Eg: De Lavel Turbine


Impulse Turbine


Disadvantages of Impulse Turbine

The velocity of Rotor is too high for practical purpose

The velocity of steam leaving the turbine considerably high and hence there is a loss Kinetic Energy

These problems can be overcome by expanding the steam in different stages.

This is known as Compounding.

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Reaction Turbine1. Casing2. Fixed Blades• Performs the function

of Nozzle in Impulse turbine.

• It directs steam to adjacent moving blade.

3. Moving Blades4. Shaft5. Rotor


A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR 24STEAM CHEST

ROTOR

WorkingHigh pressure steam directly supplied to turbine

blades with out nozzles.Steam expands(diameter increases) as it flows

through fixed and moving blades Continuous drop of pressure.

Produces reaction on bladesReaction causes rotor to rotate.Propulsive force causing rotation of turbine is

the reaction force. Hence called reaction turbine.Eg: Parson’s Turbine


Reaction Turbine


IMPULSE TURBINE IMPULSE TURBINE BLADEBLADE

REACTION TURBINE BLADEREACTION TURBINE BLADE28A.N.KHUDAIWALA (L.M.E) G.P.PORBANDAR

Problems in steam turbine:Stress corrosion carkingCorrosion fatiguePittingOil lubricationimbalance of the rotor can lead to vibration misalignmentThermal fatigue


Compounding of Impulse Turbine

The extreme high speed of Impulse Turbine of the order of 30,000rpm, cannot be directly used for practical purpose. To reduce the speed more than one set of blades are used. This is called compounding.

There are three types of compoundingVelocity CompoundingPressure CompoundingPressure – Velocity Compounding

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Velocity Compounding .. 1

1. Nozzle2. Moving Blades3. Fixed Blades4. Rotor5. Shaft



• Velocity of steam absorbed in stages

• Moving and fixed blades placed alternatively.

• Entire pressure drop takes place in nozzle.

• Kinetic energy of steam converted into mechanical work in 2 stages in figure


Velocity Compounding ..

• Velocity reduced to intermediate velocity in the 1st row of moving blades

• Fixed blade direct steam to 2nd set of moving blades.

• Velocity further reduced in 2nd set of moving blades

• Eg: Curtis Turbine


Pressure Compounding ..1

1. Nozzle 2. Moving Blades3. Casing4. Rotor5. Shaft



• Pressure energy of steam absorbed in stages.

• Expansion of steam takes place in more than one set of nozzles

• Nozzles followed by set of moving blades

• Pressure energy of steam converted into kinetic energy in nozzles



• Kinetic energy transformed to mechanical work in moving blades.

• No change in pressure in blades.


Pressure Velocity Compounding..1

Combination of pressure compounding and velocity compounding.

In a 2 stage pressure velocity compounded turbine – total drop in steam pressure carried out in 2 stages.

Velocity obtained in each stage is compounded.

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1st stage and 2nd stage taken separately are identical to velocity compounded turbine.

Combines advantages of pressure and velocity compounding.

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Section 3.2 – Steam Turbine Design

Materials

• Blades•Stainless Steel – 403 & 422 (+Cr)•17-4 PH steel (+ Ti)•Super Alloys

• Rotor•High “Chrome – Moley” Steel – Cr-

Mo-V•Low “Ni Chrome Steel – Ni-Cr-Mo-V

steam prime movers

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