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JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITYHYDERABAD

STEAM TURBINES OPERATION, PERFORMANCE AND ITS TROUBLE

SHOOTINGSubmitted to

Jawaharlal Nehru Technological University, Hyderabad in partial fulfillmentOf Bachelor Of Technology in Mechanical Engineering.

Submitted By

N. SHRAVAN KUMAR (09D41A0374)

B. VIKRAM SENA YADAV (09D41A0375)

I. RAJASEKHAR (09D41A03B1)

Under the Guidance of

Mr. M SRINIVAS RAO

HOD

DEPARTMENT OF MECHANICAL ENGINEERING


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SRI INDU COLLEGE OF ENGINEERING AND TECHNOLOGY,

IBRAHIMPATNAM, RR DIST

DEPARTMENT OF MECHANICAL ENGINEERING

CERTIFICATE

Certified that the project work entitled STEAM TURBINES OPERATION,

PERFORMANCE AND ITS TROUBLE SHOOTING which is a bonafide work

carried out by Mr. N SHRAVAN KUMAR, Mr. B VIKRAM SENA YADAV,

Mr. I RAJA SEKHAR, bearing register Nos.09D41A0374, 09D41A0375

09D41A03B1, in partial fulfillment for the award of the degree of Bachelor of

Technology in MECHANICAL ENGINEERING of Jawaharlal Nehru Technological

University, Hyderabad during the year 2012-2013. It is certified that all

corrections/suggestions indicated for internal assessment have been incorporated in

the report. The project report has been approved as it satisfies the academic

requirements in respect of project work prescribed for the said degree.

Guide Head of the Department

Principal

Examiner 1 Examiner 2


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ANDHRA PRADESH POWER GENERATIONCORPORATION LIMITED

Dr. NARLA TATA RAO THRMAL POWER STATION

CERTIFICATE

This is to certify that the project work entitled STEAM

TURBINES OPERATION, PERFORMANCE AND ITS TROUBLE

SHOOTING is the bonafied project work carried out by these students

of SRI INDU COLLEGE OF ENGINEERING AND

TECHNOLOGY, IBRAHIMPATNAM submitted in partial

fulfillment of the requirements for the award of the degree of Bachelor

of Technology in Mechanical Engineering during the year 2012-2013.

This is a record of the student own work carried out by them under our

supervision and my guidance from 20.02.2013 to 19.03.2013. During the

above period they attended plant regularly.

List of students:




ASST. DIVISIONAL ENGINEER

TURBINE MAINTENANCE

STAGE-II/ Dr.NTTPS.

IBRAHIMPATNAM.


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DECLARATION

We the members of the project SteamTurbine Operation, Performance

and its Trouble Shooting , hereby declare that the matter embodied in this project

is the genuine work done by us and not been submitted either to this university or to

any other university/institute for the fulfillment of the requirement of any course of

study.





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ACKNOWLEDGEMENT

Fruitful thoughts from the delightful hearts to thank all the ingenious pillars behind

us.

We would like to express our sincere thanks to external project guide

Mr.M.RAGHUNATH, A.D.E/T.M/STAGE-II, Dr. NTTPS, for his magnificent

guidance which enlighten us the thing achievable from inconceivable.

We would like to acknowledge the perfectionist, R V RAO, Director ofSRI

INDU COLLEGE OF ENGINEERING AND TECHNOLOGY, HYDERABAD .

We are indebted to our beloved Principal , Mr. P MALLESHAM, for his

kind consent in doing the course, project and incitement towards us.

We found immense pleasure in expressing our gratitude to M. SRINIVAS

RAO, HEAD OF THE DEPARTMENT, department of mechanical engineering, for

his timely help through out the project schedule and the course of study.

We would like to express our sincere thanks to project guide

Mr.M.RAGHUNATH, for sparing his valuable time in coordinating the project and

taking active interest at each step.

We feel extremely proud to thank all the staff members for their stunning

support during the course of our dissertation work.

Finally we thank one and all who directly and indirectly helped us to

complete our project successfully.


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ABSTRACT

To meet the variation of fluctuating demands of different consumers from

time to time, the power plants has to optimize their efficiency of its components like

boiler, turbine etc. The study of turbine operation and performance plays a vital role

for different working conditions of power plant.

The project deals with the operation and evaluating the performance of steam

turbines and find out some of the troubles and suggesting suitable remedies in steam

turbines and highlighting the modifications for optimum performance taking Dr.

Narla Tatarao Thermal Power Station station (Dr.NTTPS) as our work place.

An ideal steam turbine is considered to be an isentropic process in which

entropy of the steam entering is equal to entropy of steam leaving. Because of its

greater thermal efficiency and higher-power to weight ratio, steam turbines are

almost replaced reciprocating steam engine.

The main focus of this project is on the calculation of turbine efficiency and

comparing it with design efficiency by taking into consideration of steam pressure

values for HP and IP turbines at outlets and inlets. We also concentrate on operating

conditions and some of the trouble shooting factors that affects the steam turbine.


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CONTENTS

Chapter No. Description Page No.

1 INTRODUCTION TO

THERMAL POWER PLANTS

1.1 GEOGRAPHYCAL LOCATION & DETAILS1

OF INSTALATION

1.2 SPECIAL DESIGN FEATURES OF Dr.NTTPS 2

1.3 ENERGY CYCLE 2

1.4 GENERATION FLAME 3

1.5 GENERATION OF STEAM 4

1.6 GENERATION OF POWER 4

1.7 POWER PLANT CYCLE 5

2 PLANT LAYOUT

2.1 PLANT LAYOUT OF Dr.NTTPS 6

2.2 SPECIFICATIONS OF TURBINE 13

3 BASIC CYCLES IN POWER PLANTS

3.1 RANKINE CYCLE 14

3.2 REGENERATIVE CYCLE 18

3.3 REHEAT CYCLE 20

4 BOILER FEED PUMPS

4.1 INTRODUCTION

4.2 PRINCIPLE OF CENTRIFUGAL PUMPS

4.3 HIGH PRESSURE FEED PUMP

4.4 ROTOR

4.5 INSIDE STATOR


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4.6 MECHANICAL SEAL

4.7 BALANCING DEVICE

4.8 CAVITATION

4.9 SUCTION HEAD

4.10 WORKING PRINCIPLE OF BOILER FEED PUMP

4.11 TYPICAL SPECIFICATIONS OF BFP

4.12 RECIRCULATION SYSTEM

4.13 BOOSTER PUMP

4.14 TYPICAL SPECIFICATIONS OF BOOSTER PUMP

4.15 BFP DRIVE

4.16 HYDRAULIC COUPLING

4.17 LUBRICATING SYSTEM

4.18 OPERATIONAL CHECKS

11 CONCLUSION 83

BIBILOGRAPHY 84


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LIST OF FIGURES

S. No. Description Page No.

2.1 PLANT LAYOUT OF Dr.NTTPS 6

2.2 DEAERATOR 11

2.3 CROSS-SECTIONAL VIEW OF TURBINE 12

3.1 RANKINE CUCLE 14

3.2 RANKINE CYCLE ON P-V CHART 16

3.3 RANKINE CYCLE ONT-S AND H-S CHARTS 17

3.4 REGENERATIVE CYCLE AND ITS T-S CHART 19

3.5 REHEATING CYCLE ON T-S AND H-S CHART S 21

LIST OF TABLES


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Chapter 1

Introduction to

Thermal PowerPlant


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1.1 GEOGRAPHICAL LOCATION AND DETAILS OF

INSTALLATION:

Dr. Narla Tatarao Thermal Power Station is located on the left side bank of

the river KRISHNA within a distance of 2KM and is located in between

Ibrahimpatnam and Kondapalli villages and 16KM of the north side of Vijayawada.

The site lies at an elevation of about 26.5 mtrs above the mean sea level. Dr. Narla

Tatarao Thermal Power Station complex consists of four stages. First three stages

consists of two units each, which are of 210 MW and Fourth stage consists of one

unit of 500 MW. The total capacity of the station is 1760MW. Units 1 to 7 are

commissioned as detailed below.

Stage no Unit Capacity Date of

commissioning

1 1 210MW 01/11/1979

2 210MW 10/10/1980

2 3 210MW 05/10/19894 210MW 23/08/1990

3 5 210MW 31/03/1994

6 210MW 24/02/1995

4 7 500 MW 06/04/2009

Table 1.1: UNIT CAPACITIES

Dr. Narla Tatarao Thermal Power Station is unique in its layout and

famous for easy operation and maintenance. The large reservoir created by Prakasam

barrage provides an efficient direct circulation of cooling water system and meets

other requirements for the plant.

Originally the Dr. Narla Tatarao Thermal Power Station is linked to

Singareni Collieries Company Limited (S.C.C.L) for supply of coal. The average

distance of S.C.C.L Coalfields by train is about 250KM.


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Dr.NTTPS, stage 2&3 are linked to Talcher coalfields in Orissa to meet

the increased demand. The average distances of Talcher coalfield by train 950KM.

1.2 SPECIAL DESIGN FEATURES OF Dr.NTTPS:

STAGE-1:

The coal bunkers and mills are located in between boiler house and

electrostatic precipitators unlike usual arrangement elsewhere in the country of

placing the bunkers and mills between the turbine house and boiler. Thus the turbine

house is completely isolated from mills so as to ensure dust free atmosphere in the

turbine house and also to ensure easy accessibility of the mills for the maintenance.

Multiple flue chimneys are also a new feature at this power station.

STAGE-2&3:

The second and third stages consist of boilers, turbines and generators.

These are completely of new design. Tower type boilers of single pass design are

manufactured by M/s B.H.E.L. Ltd; under collaboration with M/s stein industries.

KWU turbines and generators of West Germany design are installed in the 2 &3

stages.

1.3 ENERGY CYCLE:

In this process of power generation which involves various

transformations of energy is discussed in brief.

Chemical energy in the form of coal is converted in to heat energy by

burning it in the boiler furnace, which release high temperature gas. These gases

exchanges heat to water which converts it into steam and this steam is further super

heated and passed through the steam turbine. The turbine shaft rotates; the


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mechanical energy thus produced is converted into electrical energy by means of a

generator. In this way electrical energy is produced from the chemical energy of coal.

1.4 GENERATION OF FLAME:

The coal from the mines is brought to the plant through the conveyor belt and is

sent to Ball mills. Here the coal is pulverized to fine powder with the coal powder

now called pulverized fuel is filtered by using very fine filters up to size of around 70

microns. Primary air is blown into the mills with the help of primary air fans. This

will preheat the pulverized fuel in the mills and bring to the furnace here the

pulverized fuel (PF) is injected in to the boiler from the burners arranged at the four

corners at six elevations of the boiler. This type of firing is called tangential firing

and this will create a swirling effect and give increased turbulence for the complete

combustion of the PF. In between coal guns there are oil and secondary air guns

alternatively.

Many coal fired power stations use oil for light up purpose and for low load

operations. The preheated secondary air supplied by forced draft fans is utilized for

the proper combustion of fuel.

1.5 GENERATION OF STEAM:


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To avoid corrosion in the pipes dematerialized water is used in the whole

process. This water is taken in the water drum at the top of the boiler and is

circulated continuously through the water walls of the boiler as a result the water

in the pipes is heated by radiation process and becomes the steam being less dense

flows up and assumes upper position. The drum equipped with mechanical turbo

separators to alienate saturated steam from water. The saturated steam thus produced

is again superheated in the super heater of the boiler. This will eliminate the

moisture contents present in the saturated steam thus obtained is called main steam

and which has a temperature of 5400C and a pressure of 150 Kg/sq cm.

1.6 GENERATION OF POWER:

The main steam from super heater pipes of the boiler is passed through

high pressure turbine (HPT). This steam moves through number of sets of fixed and

moving blades of the HPT and rotates the shaft. As a result the main steam loses its

temperature to 3400 C and pressure to 35 Kg/sq cm. as the steam at the end of the

HPT is colder than the main steam. It is called Cold Re Heat (CRH) steam and this

doesnt posses enough energy to drive intermediate pressure turbine (IPT). Hence

this CRH is reheated to 5400C while maintaining the same pressure. Now the

obtained steam, called Hot Re Heat (HRH) steam is sent to IPT. The steam that

comes out of IPT has a temperature of 3300C and a pressure of 7 Kg/sq cm. This

steam is directly sent through the low pressure turbine (LPT) and finally to

condenser for recirculation.

The shaft passes through all the three turbines and is also connected to

generator and exciter by means of rigid couplings. Because of the rotation of shaft,


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the flux developed by exciter in the rotor is cut by the armature conductors fixed in

the casing of generator. Then the generated power is taped and is synchronized to

the grid.

1.7 POWER PLANT CYCLE:

A working fluid goes through a respective cyclic change and this cyclic

change involving heat and work is known as thermodynamic cycle.

Thus a thermodynamic cycle is a series of operations, involving a heat receiver, a

machine or utilizes between the source and the receiver and a working substance.

In steam power station, heat is released by burning fuel; this heat is taken

up by water which works as the working fuel. Water is converted into steam as it

receives heat in a boiler. The steam then expands in a turbine producing mechanical

work which is then converted into electrical energy through a generator. The exhaust

steam from the turbine is then condensed in a condenser and condensate thereafter

pumped to the boiler where it again receives heat and the cycle is repeated.


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Chapter 2

Plant Layout of

Dr.NTTPS


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2.1 PLANT LAYOUT OF Dr.NTTPS

FIG 2.1: PLANT LAYOUT OF Dr.NTTPS


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BOILER:

Water is evaporated into steam inside the boiler necessary heat is obtained by

burning coal in boiler furnace to save time and economize fuel consumption feed

water is preheated in economizer. Flue gases from the boiler provide heat to feed

water. They are also used to preheat air before they flow to chimney. A modern

boiler produces steam at the rate of 300 to 400 tons per hour at 130 to 140 bar

absolute pressure and 5400C by burning the coal at the rate of 200 tons per hour.

STEAM TURBINE:

This is a prime mover and the main power unit of the plant. Steam from

super heater is admitted into the turbine through nozzle. It expands over the blades of

turbine rotor pressure falls and thus heat in steam drops. This drop in enthalpy (heat

energy) is converted in to mechanical energy. As a results turbine shaft rotates at

high rotational speeds and this shaft connected to generator.

CONDENSER:

Condenser is placed at the exhaust end of turbine so that the exhaust steam

from turbine is discharged into it. Condenser condenses the steam making use of

certain cooling medium such as water. Condensed steam is called condensate this is

recirculated to boiler as feed water.

BOILER FEED PUMP:

The main aim of feed pump is to send condensate from hot well to boiler and

also increase the pressure of the condensate.


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FURNACE:

A boiler furnace is that space under or adjacent to a boiler in which fuel is burned

and from which the combustion products pass into the boiler properly. It provides a

chamber in which the combustion reaction can be isolated and confined so that the

reaction remains a controlled force.

DRUM:

The drum is a pressure vessel. The boiler drum forms a part of the circulation

system of the boiler. The drum serves two functions:

a. It separates steam from the mixture of water and steam.

b. The drum houses all equipment used for purification of steam after being

separated from water. This purification equipment is commonly referred to as

the drum internals. The boiler drum is made of carbon steel plates.

SUPER HEATER:

Super heaters are usually classified according to the shape of the tube banks

and position of the header, also according to whether they receive heat by radiation

or convection, although in some instance it may be a combined of both methods. The

super heaters increase the heat energy in the steam supplied to steam turbines and to

ensure that the dry steam supplied until it reaches the last stage of LPT .

REHEATER:

Increased capacity of generators necessitates increased capacity units. The

steam entering high pressure turbine does some work due to steam expanding

through various stages. The steam exhaust in high pressure turbine is again admitted

in the reheater circuit to reheat the steam at constant pressure to raise its temperature

to almost equal to super heated steam. The heat energy in the steam is increased in


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the reheater and this reheated steam is admitted into IPT and steam is expanded

doing some additional work before exhausting into condenser from LPT.

RAW COAL MILLS:

The most efficient way of utilizing coal for steam generation is to burn it is in

pulverized form. In pulverized fuel firing method the coal pulverized to a fineness of

70% to 80% by hot primary air through pipes directly to burners.

The motives behind the development of pulverized fuel firing systems are:

a. Efficient utilization of cheaper and low grade coals.

b. Flexibility in firing with ability to meet fluctuating loads.

c. The ability to use higher combustion air temperature there by increasing the

overall efficiency of the steam operator.

AIR HEATERS:

Air heater is a heat transfer surface in which air temperature is raised by

transferring heat from other media such as flue gas. Since air heater can be

successfully employed for reclaim heat from flue gas at low temperature levels than

is possible with economizer. The heat rejected to chimney can be reduced to higher

extent thus increasing the efficiency of the boiler. For every 20 0C drop in flue gas

temp, the boiler efficiency increased by about 1%.

FANS:

The purpose of the fan is to move air/gas continuously against moderate

pressure. Fans are used in boiler for different applications such as supplying air

for combustion, removal of combustion products, and air for cooling of

equipment working in hot zone set. Fans are designed according to the fans they

do in the boiler, e.g. Induced draft fan, forced draft fan, primary air fan etc.


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Primary Air fan [PA fan]:

The primary air has two functions, drying the coal and transportation

into the furnace. Boiler provided with two nos of primary air fans. Each PA fan

is provided with blade pitch control for controlling the loading on fans. Outlet

damper for isolation to facilitate start up or maintenance of fan.

Forced Draft fan: [FD fan]

The function of FD fan is to supply excess air required for complete

combustion. Boiler is provided with two no. of forced draft fans. Each FD fan is

provided with blade pitch control for controlling the loading on fans. Outlet

damper for isolation to facilitate start up/maintenance of fan.

Induced Draft fan [ID fan]:

The function of induced draft fan is to suck the gases out of furnaces

and throw them into stack. Boiler is provided with two no. of induced draft fans.

Each ID fan is provided with regulating damper control and scoop control for

controlling the load on fans, inlet/outlet gates for isolation to facilitate start

up/maintenance of fan. Flue gas inter connection with damper is provided before

ESP in order to maintain balanced flow through both the APH second pass when

only one ID fan is running.

DEAERATOR:

The function of the deaerator is to remove dissolved non condensate

gases and to heat boiler feed water. It consists of a pressure vessel in which water

and steam are mixed in a controlled manner. When this occurs, water temperature

rises


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FIG 2.2: DEAERATOR

and all non condensable dissolved gases are liberated and removed the efficient

water may be considered corrosion free from an oxygen or carbon dioxide stand

point. Free air or other non condensable gases should be rented prior permitting

the fluid to enter the deaerator.

A deaerator protects the feed pumps, piping, boiler and any other

piece of equipment that is in the boiler feed and return cycle from the effects of

corrosive gases, i.e. oxygen and carbon dioxide to a level where they are no

longer a corrosive factor.

CONDENSATE EXTRACTION PUMPS:

The function of these pumps is to pump the condensate to the deaerator

through ejectors, gland steam cooler, drain cooler and LP heaters. In a 210MW

unit 3pumps are installed, having a pumping capacity of 50% each. Two pumps

are for normal operation and one is stand by. Since the suction is at a negative

pressure, the special arrangements have been made for providing sealing to

glands.


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EJECTORS:

Ejectors are used to extract non condensing gases from condenser and

heat exchangers of turbine. The pressure and discharge of non condensing gases

depend upon the conditions of working of condensers and ejectors.

ECONOMISER:

An economizer is device in which the waste heat of the flue gases is utilized

for heating the feed water.

GENERATOR:

Generator is used to convert the mechanical energy into electrical

energy.

FIG 2.3: CROSS-SECTIONAL VIEW OF TURBINE


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Chapter 3

Basic Cycles inPower Plants


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3.1 Rankine Cycle:

The Rankine cycle is a steam cycle for a steam plant operating under the best

theoretical conditions for most efficient operation. This is an ideal imaginary cycle

against which all other real steam working cycles can be compared.

The theoretic cycle can be considered with reference to the figure

below. There will no losses of energy by radiation, leakage of steam, or frictional

losses in the mechanical components. The condenser cooling will condense the

steam to water with only sensible heat (saturated water). The feed pump will add no

energy to the water. The chimney gases would be at the same pressure as the

atmosphere.

FIG 3.1: RANKINE CYCLE


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Within the turbine the work done would be equal to the energy entering the

turbine as steam (h1) minus the energy leaving the turbine as steam after perfect

expansion (h2) this being isentropic (reversible adiabatic) i.e. (h1- h2). The energy

supplied by the steam by heat transfer from the combustion and flue gases in the

furnace to the water and steam in the boiler will be the difference in the enthalpy of

the steam leaving the boiler and the water entering the boiler = (h1 - h3).

Basic Rankine Cycle

The ratio output work / Input by heat transfer is the thermal efficiency of the Rankine

cycle and is expressed as

Although the theoretical best efficiency for any cycle is the Carnot Cycle the Rankine

cycle provides a more practical ideal cycle for the comparison of steam power cycles

(and similar cycles). The efficiencies of working steam plant are determined by use

of the Rankine cycle by use of the relative efficiency or efficiency ratio as below:


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A steam turbine is a prime mover that derives its energy of rotation due to

conversion of the heat energy of steam into kinetic energy as it expands through a

series of nozzles mounted on the casing or the fixed blades.

Water is converted to steam by application of heat in the boiler, which makes the

steam at specified pressure and temperature. To convert the steams energy into

work, it must go through a thermodynamic cycle that combines expansion

compression, heat input, and heat rejection. The most efficient thermodynamic cycle

for an ideal fluid is Carnot cycle. It consists of an isothermal heat input, isentropic

expansion, isothermal heat rejection, and an isentropic compression. Regardless of

the combination, the efficiency of the cycle, assuming constant mass flow is based on

the difference in the enthalpy and between the beginning and end of the cycle.

FIG 3.2: RANKINE CYCLE ON P-V CHART

1 to 2: Isentropic expansion

2 to 3: Isothermal heat rejection

3 to 4: Isentropic compression

4 to 1: Isothermal heat supply

Steam can be used as the working fluid in the Carnot Cycle. But its properties

adversely impact its usefulness. In this case the steam expansion process takes place


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completely in the moisture region. This requires compression of a vapour/moisture

mixture to return to the cycles starting point. Moisture is an expansion process

imposes large mechanical efficiency losses. Also, vapour compression is inefficient

and consumes relatively large amounts of power.

To avoid a two-phase vapour compression process, turbines are based on the

Rankine cycle. It is similar to the Carnot Cycle, except that the initial pressure of the

steam is raised and the condensation process that accompanies heat rejection

continues until the liquid saturation point is reached. At the end of the cycle, then,

condensate is simply pumped back to the boiler to begin the cycle. The role of the

steam turbine is to expand the steam from high pressure and temperature to lower

pressure and temperature.

Rankine cycle is a heat engine with vapor power cycle. The common working

fluid is water. The cycle consists of four processes

FIG

3.3:

RANKINE CYCLE ON T-S AND H-S CHARTS

1 to 2: Isentropic expansion

(Steam turbine)

2 to 3: Isobaric heat rejection

(Condenser)

3 to 4: Isentropiccompression (Pump)


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4 to 1: Isobaric heat supply

(Boiler)

Several things can be done to steam to improve the Rankine Cycle

efficiency. Raise initial steam condition and reduce the amount of moisture near the

end of expansion stage. The first is accomplished by superheating the steam before it

does any work. The second involves reheating steam to near initial-conditions after

it is partially expanded by directing it back to the heat source, then completing the

expansion. In converting the thermal energy of steam into mechanical energy

turbines takes advantage of these facts- as it expands or drops in pressure, through a

small nozzle or opening, it accelerates and forms a high-speed jet. Directing this

momentum in a rotating blade provides mechanical energy.

3.2 REGENERATIVE CYCLE:

In the Rankine cycle it is observed that the condensate which is fairly at low

temperature has an irreversible mixing with hot boiler water and this result in

decreases of cycle efficiency. Methods are therefore, adopted to heat feed water from

the hot well of condenser irreversibly by interchange of heat within the system and

thus improving the cycle efficiency. This heating method is called regenerative feed

heat and cycle is called regenerative cycle.

The principle f steam generation can be practically utilized by extracting steam

from the turbine at several locations and supplying it to the regenerative heaters. The

resulting cycle known as regenerative or bleeding cycle. The heating arrangement

comprises of: (1) For medium capacity turbines not more than 3 heaters ;(2) For

high pressure high capacity turbinesnot more than 5 to 7 heaters ;and (3) For

turbines of super critical parameters 8 to 9 heaters. The most advantageous


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condensate heating temperature is selected depending on the turbine throttle

conditions and this determines the number of heaters to be used. The final condensate

heating temperature is kept 50 to 60degreeC below the boiler saturated steam

temperature so as to prevent evaporation of water in the feed mains following a drop

in the boiler drum pressure. The conditions of steam bled for each heater are so

selected that the temperature of saturated steam will be 4 to 40 degree C higher than

the final condensate temperature.

FIG 3.4: REGENERATIVE CYCLE AND ITS T-S CHART


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Shown in a diagrammatic layout of a condensing steam power plant in which

a surface condenser is used to condense all the steam that is not extracted for feed

water heating. The turbine is double extracting and the boiler is equipped with a

super heater. The cycle diagram (T-s) would appear as shown in figure. This

arrangement constitutes a regenerative cycle.

3.3 REHEAT CYCLE:

For attaching greater thermal efficiencies when the initial pressure of steam

was raised beyond 42 bars it was found that resulting condition of steam after,

expansion was increasingly wetter and exceeded in the safe limit of 2 percent

condensation. It therefore, became necessary to reheat the steam after part of

expansion was over so that the resulting condition after complete expansion fell

within the region of permissible wetness.

The reheating or re superheating of steam is now universally used when high

pressure and temperature steam conditions such as 100 to 250bar and 500 degree C

to 600 degree C are employed for throttle. For plants of still higher pressure and

temperature, a double reheating may be used.

In actual practice reheat improves the cycle efficiency by about 5% for an

85/bar cycle. A second reheat will give a much less gain while the initial cost

involved would be so high as to prohibit use of two stage reheat except in case of

very high initial throttle conditions. The cost of reheat equipped consisting of

boiler ,piping and controls may be 5%to 10% more than that of the conventional

boilers and this additional expenditure s justified only of gain in thermal efficiency is


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sufficient to promise a return of this investment. Usually a plant with a base load

capacity of 50000kW and initial steam pressure of 42bar would economically justify

the extra cost of reheating.

The improvement in thermal efficiency due to reheat is greatly dependent

upon the reheat pressure with respect to the original pressure of steam.

Schematic diagrams of a theoretical single-stage reheat cycle. The

corresponding representation of ideal reheating process on T-s and h-s chart is shown

in figure.

FIG 3.5: REHEATING CYCLE ON T-S AND H-S CHART

5-1 shows the formation of steam in the boiler. The steam as at state point 1

(i.e., pressure P1 and temperature T1) enter as the turbine and expands isentropically

to a certain pressure P2 and temperature T2. From this state point 2 the whole of

steam is drawn out of the turbine and is reheated in a reheater to a temperature T3.

(Although there is an optimum pressure at which the steam should be removed for


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reheating, if the highest return is to be obtained, yet, for simplicity, the whole steam

is removed from the high pressure exhaust, where the pressure is about one-fifth of

boiler pressure, and after undergoing a 10% pressure drop, in circulating through the

heater, it is then readmitted to the turbine where it is expanded to condenser pressure

isentropically.

BOILER FEED PUMP

1. INTRODUCTION:

Boiler Feed pump (BFP) is a multistage pump provided for

pumping feed water to economizer

Generally three pumps each of 50% of total capacity are provided. For

rated capacity two pumps will be working in parallel and the third will be in

service.

The high pressure BFP is a very expensive machine, which can comply with

the stated requirements. The safety in operation and efficiency of the feed pump

does not only depend on the correct design and careful manufacturing in the works,

but also reliable operation and maintenance, so the operation and maintenancestaff should be well acquainted with the instructions and procedures laid down by

supplier.

1. PRINCIPLE OF CENTRIFUGAL PUMP:

A Centrifugal pump is defined as a machine, which increases the pressure

energy of a fluid with the help of centrifugal action. Whirling motion is imparted

to the fluid by means of blades mounted on the disc known as impeller. It

consists mainly of one or more impellers equipped with vanes, mounted on a

rotating shaft and enclosed by a casing. Fluid enters into the impeller axially near

the shaft and has energy both kinetic and potential, imparted to it by the

vanes. As the fluid leaves the impeller at a relatively high velocity, it is collected in

a volute or series of diffusing passages which transforms the kinetic energy into

pressure. This is of course, accompanied by a decrease in the veloci ty.

After the convers ion is accomplished, the fluid is discharged from the machine.

1. HIGH PRESSURE FEED PUMP:

The high pressure feed pump KHI of barrel type satisfy in all respects the

latest developments achieved for the design and operation of the feed pumps. It

consists of the pump barrel into which is mounted the inside stator together with therotor. The hydraulic part is closed by the HP cover along with the balancing device.


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The LP covers along with the stuffing box casings close the suction side of the

barrel and the space in the HP cover behind the balancing device. The bracket of

the radial bearing of the suction side and the bracket of the radial thrust bearing

of the discharge side are fixed to the LP covers. The entire pump is mounted on a

foundation frame. The Hydraulic coupling and two claw couplings with

coupling guards are also provided. The water-cooling and oil lubricatingconnections are provided with their accessories. All the instruments necessary

for observing a perfect run of the feed pump are mounted on the pump and on the

piping.

Feed pumps consist of the following major parts.

1. Rotor2. Inside Stator3. Mechanical seal4. Balancing device

I. ROTOR:

The rotor of the BFP consists of the shaft, impellers, distance bushes, throttle

bush, balancing disc, supporting rings, stuffing box bushes, nuts for holding the

stuffing box bushes, the disc of the axial thrust bearing, with the lock nut, nuts for

screwing the claw coupling, shaft keys and lubricating rings. For obtaining the

shrink fitting of the impellers on to the shaft, the impellers are first heated and then

assembled on to the shaft. The balancing disc (which is keyed to the shaft) takes

up the axial thrust of the rotor, which is limited to the extent of dilation gap that

exists between the throttle bush and the supporting ring. The dilation gap should be

within the limit of 0.2 to 0.3mm. The Maximum run out of the assembled rotor, at thesealing impeller diameters, the throttle bush and stuffing box bushings is up to

0.06mm. The impeller (statically balanced) and the rotor as a whole is dynamically

balanced with in the permissible inbalance according to the standard of the works.

Prior to the dynamic balancing of the rotor, the deflection of the rotor due to its self-

weight is also measured. The deflection of the rotor due to self weight moves in the

limits of 0.01 to 0.12mm.

I. INSIDE STATOR:

The inside stator consists stage bodies and diffuses (consists diffusingvanes and guide vanes), which are assembled together. Diffuses are centrally

mounted in the stage bodies. They are secured against motion by locating pins.

Stage bodies are fitted with wearing rings at the place where it is likely to come into

contact with the wearing rings of impeller and the wearing rings are secured to the

stage bodies with the help of screws. The entire inside stator is connected together by

four connecting bolts. Another four connecting bolts are screwed on to the

suction side of the barrel and they connect the inside stator to the barrel. The nuts at

the ends of these bolts are tightened in order to pre-stress the bolts to suit the working

pressure and they are screwed with the help of locking washers.

The centering of the inside stator is carried out by aligning the inlet stage tothe suction side of the barrel and by aligning the HP cover to the end diffuses while


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the pump is in operation the inside stator will get heated earlier than the pump

barrel together with the HP cover. This means that the expansion of the inside

stator owing to the temperature will be more than the expansion of the barrel and of

the HP cover. A dilation gap of 6mm is therefore maintained between the end

diffuses and the HP cover.

I. MECHANICAL SEAL: The advantages are:

a) The Mechanical seal eliminates the losses of feed water in stuffing box.

b) Working ability of the feed pump increases.C) With the mechanical seal, cooling of stuffing box space should be perfect.

d) Cooling is carried out by the circulation of water by means of a pumping ringthrough a cooler.

e) Cooling of the stuffing box space is different from the seal cooler.f) Even after stopping of the pump stuffing box space temperature below 80C.g) Pump need not be removed from base frame, to'replace mechanical seals.

IV. BALANCING DEVICE:

Balancing system of the pump takes up the entire axinl thrust of the rotor, by

means of the balancing disc. Balancing device is an important aspect ofthe pump as far as the design and material selection is concerned.Balancing device consists of balancing disc, secured to the shafts !Deal ingring fitted to the HP cover by means of the tightening flange and bolts withnuts, which are locked by washers. Axial sealing gap is formed betweenthe bearing ring and the balancing disc. Contact surfaces of bearing ringand balancing disc are mutually lapped against each other. Full

pressure developed by the last impeller is not carried on to the balancingdevice but throttled by means of the taper bush mounted on the shaftbefore the balancing disc. The feed water passes through the taperbush, through the axial sealing gap. The axial sealing gap isapproximately 0.1mm.

3.1 CAVITATION:

If the pressure at any point inside a pump drops below the vapour pressure

corresponding to the temperature of the liquid, the liquid will vapourise and form

cavities of vapour. The vapour bubbles are carried along with the stream until

a region of higher pressure is reached, where they collapse or implode

with a tremendous shock on the adjacent walls. This phenomenon is calledcavitation.

3.2 SUCTION HEAD OR NPSH (Net Positive Suction Head):Since cavitation occurs when the absolute pressure on the liquid reaches its vapour

pressure, it is obvious that the phenomena is closely related to the pump suction

head, The suction head has the equivalent total head at the center line.

3.3 WORKING PRINCIPLE OF BOILER FEED PUMP:

The water with the given operating temperature should flow to the pump

under a certain minimum pressure (NPSH); water passes through thesuction branch into the intake spiral and from here is directed to the


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first impeller. After leaving through the impeller it passes through thedistributing passages of the diffuser where it get certain pressure riseand flows over to guide vanes to the inlet of the next impeller.

This process repeats from one stage to the other till it passes through the last

impeller and the end diffusers. Thus the feed water arriving into thedischarge space develops the necessary operating pressure. A small part of feed

water i.e. about 10% is taken off from the space behind the last impeller for the

operation of the automatic balancing device to balance the hydraulic axial

thrust of the pump rotor.

3.4 TYPICAL SPECIFICATIONS OF BOILER FEED PUMP (200 KHI TYPE):

1) No. of stages 6

2) Suction pressure 12.3 atm

3) Quantity of water for 100 Tons/hr.4) Discharge capacity/ head 430'T/hr./1830 MWC5) Quantity of water for warming up 8 Tons/hr.

6) Feed water temperature 164.2 C.

7) Consumption of cooling water 280 PM.8) Speed 4320 'rpm.9) Lubrication Forced10) Stuffing box Mech. seal

11) Net weight of pump 5850 Kg.12) Axial Thrust of Designed Speed. 34 Tonnes.

13) MOTOR Output 4000 KW14) Rated Voltage 6.6 KV15) Current 421 Amps16) Speed 1483 rpm17) Frequency, Power factor 50 c/s, 0.914

3.5 RECIRCULATION SYSTEM:

To maintain a reasonable efficiency in the pump, running clearances

between stationary and rotating part must be fairly narrow. Liquid flow

through these clearances acts as a lubricant to prevent seizure. The power

input to the pump is partly converted into hydraulic energy due to the increase inpressure of the liquid. The remaining energy is wasted in the form of friction,

eddies and mechanical losses. This power loss causes slight increase in the liquid

temperature while the liquid passes from suction to discharge. This temperature

rise to maximum at zero discharge and the water soon flashes into steam.

Flashing breaks down the thin film of lubricating water between the parts and

this usually causes seizure. The trouble occurs so quickly that stationary

parts cannot expand as rapidly as the rotating parts, because they will be heated

more slowly, being of greater mass and also exposed to atmosphere.

Greater expansion of rotating parts will reduce the normal running clearance and

aggravate the conditions. It is therefore, imperative that sufficient water mustbe kept moving through the pump to prevent its temperature from reaching the


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flash point in the pump when the regulator closes the main discharge line due to

low load or less water requirements in the drum or when the pump is just started.

To ensure this an automatic leak off system is provided between the pump

discharge and the deaerator to establish a minimum flow through the pump. A

solenoid operated diaphragm valve or a motorised valve is installed in the leak

off line which opens when the pump runs at a lower capacity.

The recirculation valve opens when the flow at pump suction is below

100T/hr. and closes when it increases to 220 T/hr. The flow through

recirculation line is 125 T/hr.

WARMING UP:

Centrifugal pumps handling hot water should always be maintained nearly at

operating temperature when idle, if suddenly hot water is admitted into the pump, the

relative expansion of the casing barrel and of the inner elements goes through two

separate phases. The inner elements expand faster than the barrel resulting in

distortion of the pump. To avoid this, a small quantity of the medium is always

passed through the steam pump for warm up. Various methods are used for this

purpose. In some, the flow is from the suction, through the pump and out through the

balancing chamber to the flash tank. In others, a by pass across the main discharge

non-return valve is provided with a pressure reducing orifice, The flow is from the

discharge and through the pump and back to the deaerator.


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Chapter 11

Conclusion


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CONCLUSION

Since the power output of the power plant is to be maintained at a constant

frequency with very less tolerance, steam turbine plays very important role in

achieving the above task. Out of various turbines that are used in power plants,

reaction turbine is proved to be the most efficient one because with the development

of steam power plants, large flow rates of steam have to be operated which may not

be possible by conventional turbines.

The performance of steam turbine can be further improved by reducing the

prior mentioned losses. The efficiencies of the turbines are calculated and are found

to be nearer to the design values thus concluding that the recorded values are correct.

By our experimental study the efficiency of H.P. Turbine is found to be

74.35% and the design efficiency value is 87.973% and in the same way the

efficiency of I.P. Turbine is found to be 89.6% which is nearer to the design value of

90.78%. The over all plant efficiency is found to be 40.7% which is nearer to the

design value of 42.97%. This can be improved further by taking some factors into

consideration and recovering the waste heat that is lost to a maximum extent.

In this project we also studied the Constructional features, Operation of steam

turbines and also some common Trouble Shootings in power plants.

We have also executed the efficiency of H.P. Cylinder at different values of

pressures and temperatures by using C program and finally we conclude that the

actual efficiency of the turbine is nearly equal to designed efficiency.


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Bibilography


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1. A Course in Power Plant Engineering:

-S.C.Arora, S.Domkundwar Dhanapat Rai & Co.2001

2. Thermal Engineering:

-R.S.Khurmi, S.Chand Publisher

3. Thermal Engineering:

-R.K.Rajput, Laxmi Publishers, 2000

4. Power plant Engineering:

-G.Nagpal

5. Steam Turbine Operation & Maintenance

-B.H.E.L.Hardwar

6. Modern Power Station Practice 3rd Edition, Volume C

-British Electricity International, London

7. Blade Plane LPT

-Drawing No: 9-10304-01000C, Dr.NTTPS Drawing Manual

8. www.Matweb.com


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