A SUMMER INTERSHIP PROJECT REPORT

ON

STUDY OF TURBINES & ITS MAINTANENCES

IN

POWER PLANT
Submitted by
K.SHIVA KUMAR (16UC5A0308)

B.SHIVA PRASAD (16UC5A0303)

D.SAI KRISHNA (16UC5A0305)

R.ANUSHA (16UC5A0313)

K.VENKATESH (15UC1A0303)

R.VINAY KUMAR (15UC1A0305)

In partial fulfillment of summer internship for the award of degree

of

BACHELOR OF TECHNOLOGY

IN

MECHANICAL ENGINEERING

TALLA PADMAVATHI COLLEGE OF ENGINEERING

Somidi-506003, Kazipet, Telangana

1
TALLA PADMAVATHI COLLEGE OF ENGINEERING
Somidi-506003, Kazipet, Telangana

CERTIFICATE

This is to certify that the project report entitled

STUDY OF TURBINES & ITS MAINTANENCES

Is the bonafide work done by

K.SHIVA KUMAR (16UC5A0308)

B.SHIVA PRASAD (16UC5A0303)

D.SAI KRISHNA (16UC5A0305)

R.ANUSHA (16UC5A0313)

K.VENKATESH (15UC1A0303)

R.VINAY KUMAR (15UC1A0305)

Department Of Mechanical Engineering

TALLA PADMAVATHI COLLEGE OF ENGINEERING

Somidi-506003, Kazipet, Telangana

a partial fulfillment of the requirements for the award of B.tech degree in

MECHANICAL ENGINEERING

2
 TELANGANA STATE POWER GENERATION CORPORATION LIMITED

KAKATIYA THERMAL POWER PROJECT ,1X600MW

CHELPUR,JAYASHANKAR DIST-506170

CERTIFICATE

This is to certify that the project entitled “STUDY OF TURBINES & ITS
MAINTANENCES ” is a bonafide report of strenuous work carried out
by
K.SHIVA KUMAR (16UC5A0308)

B.SHIVA PRASAD (16UC5A0303)

D.SAI KRISHNA (16UC5A0305)

R.ANUSHA (16UC5A0313)

K.VENKATESH (15UC1A0303)

R.VINAY KUMAR (15UC1A0305)

Under the guidance of SRI.AMARNATH, ADE/TM KTPP during the period of

06-06-2018 to 20-06-2018. In partial fulfillment of the requirement according to the
university curriculum after completion of their second semester of third year B.tech in the
discipline, Mechanical Engineering, TALLA PADMAVTHI COLLEGE OF
ENGINEERING, SOMIDI,KAZIPET,TELANGANA

(AMARNATH) (L.THIRUPATHI)

3
 ACKNOWLEDGEMENT
We wish to avail this opportunity to express our gratitude to
Mr.L.THIRUPATHI, Divisional Engineer/ Turbine Maintenance,
TGENCO, Kakatiya Thermal Power Project, Chelpur For permitting us,
providing all the facilities in the site and for supporting us throughout the
project period.

We express our special thanks to MR. AMARNATH, Assistant

Engineer/turbine Maintenance, TGENCO,Kakatiya Thermal Power
Project, Chelpur for providing us extensive support in our project.

4
 CONTENTS
Abstract
CHAPTER-1
INTRODUCTION TO KAKATIYA THERMAL POWER PROJECT
1.1 Objectives

CHAPTER-2
TYPICAL COAL FIRED POWER PLANT CYCLE
2.1 Simple Rankine Cycle
2.2 Rankine cycle with reheat
2.3 Regenerative Rankine cycle
2.4 Power Plant Scheme with Reheat and Regeneration

CHAPTER-3
INTRODUCTION TO STEAM TURBINES
3.1 STEAM TURBINE

3.2 CLASSIFICATION OF STEAM TURBINE

CHAPTER-4
MAIN TURBINE AT KTPP, 1 X 600MW

4.1 CONSTRUCTION AND STEAM FLOW

4.2 EXISTING TURBINES

4.2.1 HP TURBINE

4.2.2 IP TURBINE

4.2.3 LP TURBINE

CHAPTER-5
TURBINE AUXILLIARIES
5.1 CONDENSER

5.2 CONDENSOR TUBE CLEANING SYSTEM

5
5.3 VACUUM PUMP

5.4 COOLING TOWER

5.5 HOT WELL

5.6 CONDENSATE EXTRACTION PUMPS

5.6.1 SPECIFICATIONS

5.6.2 DESCRIPTION

5.6.3 ASSOCIATED EQUIPMENT

5.6.3.1 Canister and Foundation Ring

5.6.3.2 Discharge Head piece

56.3.3 Motor Stool

5.6.4 Stuffing Box Assembly

5.6.4.1 Mechanical Seal

5.6.4.2 Combined Thrust and Journal Bearing Assembly

5.6.5 Couplings

5.7 GLAND STEAM CONDENSER (GSC)

5.8 CONDENSATE POLISHING UNIT

5.8.1 INTRODUCTION

5.8.2 CONDENSATE POLISHING UNIT

5.9 CONDENSATE CONTROL STATION

5.10 DRAIN COOLER

5.11 LOW PRESSURE HEATERS

5.12 DEAERATOR

5.12.1 INTRODUCTION

5.12.2 FUNCTION

5.12.3 PRINCIPLES OF DEAERATION

5.12.4 OPERATION

5.12.5 ELEVATION OF DEAERATING HEATER

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 5.12.6 WATER PRESSURE

5.12.7 STEAM REQUIREMENTS

5.12.8 FEED STORAGE TANK

5.13 BOOSTER PUMP

5.13.1 INTRODUCTION

5.13.2 Pump Casing

5.13.3 Rotating Assembly

5.13.4 Journal and Thrust Bearings

5.13.5 Bearing Housings

5.13.6 Mechanical Seals

5.14 Turbine Driven Boiler Feed Pump

5.15 BOILER FEED PUMPS

5.15.1 INTRODCTION

5.15.2 DESCRIPTION

5.15.2.1 Pump Casing

5.15.2.2 Discharge Cover

5.15.2.3 Suction Guide

5.15.2.4 Ring Sections

5.15.2.5 Rotating Assembly

5.15.3 MECHANICAL SEAL

5.15.3.1 Journal and Thrust Bearings

5.15.3.2 Bearing Housings

5.15.3.3 Hydraulic Balance

5.15.3.4 HYDRAULIC COUPLING

5.16 HIGH PRESSURE HEATERS

5.16.1 FEED WATER HEATER

5.17 ECONOMIZER

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CHAPTER-6
TURBINE LUBE OIL SYSTEM

6.1 LUBRICATING SYSTEM

6.2 MAIN COMPONENTS

6.2.1 Main Oil Pump

6.2.2 Auxiliary Oil Pump

6.2.3 Emergency Oil Pump

6.2.4 Jacking Oil Pump

CHAPTER-7

TURBINE LOSSES IN THERMAL POWER PLANT

7.1 Internal losses

7.1.1 Loss of Nozzle Friction

7.1.2 Loss of Blade Friction

7.1.3 Diaphragm Gland and Tip leakage Losses

7.1.4 Losses due to wetness of steam

7.1.5 Exhaust losses

7.2 External losses

7.2.1 Shaft gland leakage

7.2.2 Journal and thrust bearings7.2.2 Journal and thrust bearings

7.2.3 Governor and oil pump

7.2.4 Losses due to radiation

CONCLUSION

8
 ABSTRACT

A steam turbine is a rotary type of steam engine, having a rotating

wheel to which is secured a series of blades or vanes, uniformly spaced on
its periphery. Steam from nozzles or guide blade is directed continuously
against these blades, thus causing their rotation. Expansion of steam in the
nozzles converts its heat energy into energy of motion and gives it a high
velocity which is expended on the moving blades. The difference in the
various types of steam turbines is due to different methods of using the
steam depending upon the construction and arrangement of the nozzles,
steam passages and blades.

The steam turbine is essentially a high speed machine. It is used to

advantage with direct connection to electric generators, centrifugal pumps
and compressors and with geared connections to rolling mills, fans and other
machinery which are run at low speed.

The advantage of steam turbines are comparatively low intial cost,

low expense for maintenance, small floor space, large overload capacity,
exhaust steam is free of oil contamination as no internal lubrication is
needed and high efficiency over a wide range of load conditions. The steam
turbine can be built in a unit of much greater capacity than is practical with
the reciprocating steam engines.

In this project we have mainly presented the construction of steam

turbine At kakatiya thermal power project. In power generation mostly
steam turbine is used because of its greater thermal efficiency and higher
power-to-weight ratio. Because the turbine generates rotary motion, it is
particularly suited to be used to drive an electrical generator about 80% of
all electricity generation in the world is by use of steam turbines.

9
 CHAPTER-1

INTRODUCTION TO KAKATIYA THERMAL POWER PROJECT

The Kakatiya Thermal Power Project of Telangana Power Generation

Corporation Limited is situated at Chelpur village of Ghanpur mandal in the
Jayashankar Bhuapalpally district. It is connected to Warangal by road at a distance of
60 kms and 220 kms from Hyderabad. Kakatiya Thermal Power Project consists of
1X500MW Stage-I and 1X600MW-Stage-II. Stage-I commissioned and COD
declared on 14.09.2010. Stage-II is constructed with 1X600MW load. The fuel (Coal)
is supplying by SCCL from the Mines of Bhupalpally and Godavarikhani. Water is
lifting from the river Godavari by underground pipe line from Kaleswaram which is
60 kms. Kakatiya Thermal Power Project is a green filled project and is a pit head
station. The first stage was synchronized with grid first time on 31.03.2010. The
Power Generated from Kakatiya Thermal Power Project is evacuated by 2X400KV
lines and connected to Power Grid Corporation of India Ltd substation at Oglapur.

Next to Chelpur 132KV sub-station of TS TRANSCO was selected for

sitting the proposed project.

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 Chelpur (V), Ghanpur (M), Jayashankar Bhupalpally (Dist.),
Location
Telangana.

Latitude 180 26’ 54” N

Longitude 790 45’ 32” E

Nearest Highway NH-363 Connecting Parkal with Sironcha.

Rice during rainy season, cash crops such as maize, groundnut,

Major Crops
cotton etc. in other seasons.

Nearest City Warangal (60 km) SW

Uppal Railway Station of South Central Railway Located at

Nearest Railway Station
about 40 km from plant site.

Nearest Air Port Hyderabad, 220 km

1.1 Objectives:
One of the important objectives of K.T.P.P. is to generate thermal power
efficiently and economically. It is also fulfilling the role of social responsibility
objective by encouraging local small-scale industries, providing employment to the
people of the backward and tribal areas.

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 CHAPTER-2
TYPICAL COAL FIRED POWER PLANT CYCLE

2.1 Simple Rankine Cycle

Fig 2.1 Ts diagram of a typical Rankine cycle

operating between pressures of 0.06bar and 50bar
There are four processes in the Rankine cycle. These states are identified by numbers
(in brown) in the above Ts diagram.

 Process 1-2: The working fluid is pumped from low to high pressure. As the fluid
is a liquid at this stage, the pump requires little input energy.
 Process 2-3: The high pressure liquid enters a boiler where it is heated at constant
pressure by an external heat source to become a dry saturated vapour. The input
energy required can be easily calculated using moiler diagram or h-s
chartor enthalpy-entropy chart also known as steam tables.
 Process 3-4: The dry saturated vapour expands through a turbine, generating
power. This decreases the temperature and pressure of the vapour, and some
condensation may occur. The output in this process can be easily calculated using
the Enthalpy-entropy chart or the steam tables.
 Process 4-1: The wet vapour then enters a condenser where it is condensed at a
constant pressure to become a saturated liquid

2.2 Rankine cycle with reheat

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 Fig: 2.2 Rankine cycle with reheat T-S diagram

The purpose of a reheating cycle is to remove the moisture carried by the steam at
the final stages of the expansion process. In this variation, two turbines work in series.
The first accepts vapour from the boiler at high pressure. After the vapour has passed
through the first turbine, it re-enters the boiler and is reheated before passing through a
second, lower-pressure, turbine. The reheat temperatures are very close or equal to the
inlet temperatures, whereas the optimum reheat pressure needed is only one fourth of the
original boiler pressure. Among other advantages, this prevents the vapour
from condensing during its expansion and thereby damaging the turbine blades, and
improves the efficiency of the cycle, given that more of the heat flow into the cycle
occurs at higher temperature. The reheat cycle was first introduced in the 1920s, but was
not operational for long due to technical difficulties. In the 1940s, it was reintroduced
with the increasing manufacture of high-pressure boilers, and eventually double reheating
was introduced in the 1950s. The idea behind double reheating is to increase the average
temperature. It was observed that more than two stages of reheating are unnecessary,
since the next stage increases the cycle efficiency only half as much as the preceding
stage. Today, double reheating is commonly used in power plants that operate under
supercritical pressure.

2.3 Regenerative Rankine cycle

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 Fig:2.3 Regenerative Rankine cycle T-s diagram

The regenerative Rankine cycle is so named because after emerging from the
condenser (possibly as a sub cooled liquid) the working fluid is heated by steam tapped
from the hot portion of the cycle. On the diagram shown, the fluid at 2 is mixed with the
fluid at 4 (both at the same pressure) to end up with the saturated liquid at 7. This is
called "direct contact heating". The Regenerative Rankine cycle (with minor variants) is
commonly used in real power stations.
Another variation is where bleed steam from between turbine stages is sent to feed water
heaters to preheat the water on its way from the condenser to the boiler. These heaters do
not mix the input steam and condensate, function as an ordinary tubular heat exchanger,
and are named "closed feed water heaters".
The regenerative features here effectively raise the nominal cycle heat input temperature,
by reducing the addition of heat from the boiler/fuel source at the relatively low feed
water temperatures that would exist without regenerative feed water heating. This
improves the efficiency of the cycle, as more of the heat flow into the cycle occurs at
higher temperature. This process ensures cycle economy.

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Fig: 2.4 Power Plant Scheme with Reheat and Regeneration

CHAPTER-3

15
 INTRODUCTION TO STEAM TURBINES

The thermal power plant uses a dual (vapour liquid) phase cycle. It's a closed
cycle to enable the working fluid (water) to be used again and again. The cycle used is
'Rankine Cycle' modified to include superheating of steam, regenerative feed water
heating and reheating of the steam.

3.1 STEAM TURBINE

Steam turbine is a machine for generating mechanical power in rotary motion from the
energy of steam at temperature and pressure above that of an available sink. By far the
most widely used and most powerful turbines are those driven by steam. Until the 1960s
essentially all steam used in turbine cycles was raised in boilers burning fossil fuels (coal,
oil, and gas) or in minor quantities, certain waste products. However, modern turbine
technology includes nuclear steam plants as well as production of steam supplies from
other sources.

3.2 CLASSIFICATION OF STEAM TURBINE

Steam turbine may be classified as follows: -

(A) On the Basis of Principle of Operation:

(i) Impulse turbine

(a) Simple

(b) Velocity stage

(c) Pressure stage

(d) Combination of (b) and (c).

(ii) Impulse-reaction turbine

(a) 50% (Parson’s) reaction

(b) Combination of impulse and reaction.

(i) Impulse Turbine: If the flow of steam through the nozzles and moving blades of
a turbine takes place in such a manner that the steam is expanded only in nozzles and
pressure at the outlet sides of the blades is equal to that at inlet side; such a turbine is
termed as impulse turbine because it works on the principle of impulse. In other
words, in impulse turbine, the drop in pressure of steam takes place only in nozzles

16
and not in moving blades. This is obtained by making the blade passage of constant
cross- section area. As a general statement it may be stated that energy
transformation takes place only in nozzles and moving blades (rotor) only cause
energy transfer. Since the rotor blade passages do not cause any acceleration of fluid,
hence chances of flow separation are greater which results in lower stage efficiency.

(ii) Impulse-Reaction Turbine: In this turbine, the drop in pressure of steam takes
place in fixed (nozzles) as well as moving blades. The pressure drop suffered by
steam while passing through the moving blades causes a further generation of kinetic
energy within the moving blades, giving rise to reaction and adds to the propelling
force which is applied through the rotor to the turbine shaft. Since this turbine works
on the principle of impulse and reaction both, so it is called impulse-reaction turbine.

This is achieved by making the blade passage of varying cross-sectional area

(converging type).In general, it may be stated that energy transformation occurs in
both fixed and moving blades.

The rotor blades cause both energy transfer and transformation. Since there is an
acceleration of flow in moving blade passage hence chances of separation of flow is
less which results in higher stage efficiency.

(B) On the basis of “Direction of Flow’’:

(i) Axial flow turbine,

(ii) Radial flow turbine,

(iii) Tangential flow turbine.

(i) Axial Flow Turbine: In axial flow turbine, the steam flows along the axis of the
shaft. It is the most suitable turbine for large turbo-generators and that is why it is
used in all modem steam power plants.

(ii) Radial Flow Turbine: In this turbine, the steam flows in the radial direction. It
incorporates two shafts end to end, each driving a separate generator. A disc is fixed
to each shaft. Rings of 50% reaction radial-flow bladings are fixed to each disk. The
two sets of bladings rotate counter to each other. In this way, a relative speed of
twice the running speed is achieved and every blade row is made to work. The final
stages may be of axial flow design in order to achieve a larger area of flow. Since this
type of turbine can be warmed and started quickly, so it is very suitable for use at
times of peak load.

Though this type of turbine is very successful in the smaller sizes but formidable
design difficulties have hindered the development of large turbines of this type. In
Sweden, however, composite radial/axial flow turbines have been built of outputs up
to 275 MW. Sometimes, this type of turbine is also known as Liungstrom turbine
after the name of its inventor B and F. Liungstrom of Sweden (Fig. 2.3).

17
 Fig 3.3 Radial flow turbine

(iii) Tangential Flow Turbine: In this type, the steam flows in the tangential
direction. This turbine is very robust but not particularly efficient machine, sometimes
used for driving power station auxiliaries. In this turbine, nozzle directs steam
tangentially into buckets milled in the periphery of a single wheel, and on exit the
steam turns through a reversing chamber, reentering bucket further round the
periphery. This process is repeated several times, the steam flowing a helical path.
Several nozzles with reversing chambers may be used around the wheel periphery.

(C) On the Basis of Means of Heat Supply:

(i) Single pressure turbine,

(ii) Mixed or dual pressure turbine

(iii) Reheated turbine.

(a) Single

(b) Double

(i) Single Pressure Turbine: In this type of turbine, there is single source of steam
supply.

(ii) Mixed or Dual Pressure Turbine: This type of turbines, use two sources of
steam, at different pressures. The dual pressure turbine is found in nuclear power
stations where it uses both sources continuously. The mixed pressure turbine is found
in industrial plants (e.g., rolling mill, colliery, etc.) where there are two supplies of
steam and use of one supply is more economical than the other; for example, the
economical steam may be the exhaust steam from engine which can be utilized in the
L. P. stages of steam turbine. Dual pressure system is also used in combined cycle.

(iii) Reheated Turbine: During its passage through the turbine steam may be taken
out to be reheated in a reheater incorporated in the boiler and returned at higher

18
temperature to be expanded in boiler. This is done to avoid erosion and corrosion
problems in the bladings and to improve the power output and efficiency. The
reheating may be single or double or triple.

(D) On the Basis of Means of Heat Rejection:

(i) Pass-out or extraction turbine,

(ii) Regenerative turbine,

(iii) Condensing turbine,

(iv) Non-condensing turbine,

(v) Back pressure or topping turbine.

(i) Pass-out Turbine: In this turbine, (Fig. 2.4), a considerable proportion of the
steam is extracted from some suitable point in the turbine where the pressure is
sufficient for use in process heating; the remainder continuing through the turbine.
The latter is controlled by separate valve-gear to meet the difference between the
pass-out steam and electrical load requirements. This type of turbine is suitable where
there is dual demand of steam-one for power and the other for industrial heating, for
example sugar industries. Double pass-out turbines are sometimes used.

Fig 3.4 Pass out turbine

(ii) Regenerative Turbine: This turbine incorporates a number of extraction

branches; through which small proportions of the steam are continuously extracted for
the purpose of heating the boiler feed water in a feed heater in order to increase the
thermal efficiency of the plant. Now a day, all steam power plants are equipped with
reheating and regenerative arrangement.

(iii) Condensing Turbine: In this turbine, the exhaust steam is condensed in a

condenser and the condensate is used as feed water in the boiler. By this way the
condensing turbine allows the steam to expand to the lowest possible pressure before
being condensed. All steam power plants use this type of turbine.

19
(iv) Non-Condensing Turbine: When the exhaust steam coming out from the turbine
is not condensed but exhausted in the atmosphere is called non-condensing turbine.
The exhaust steam is not recovered for feed water in the boiler.

(v) Back Pressure or Topping Turbine: This type of turbine rejects the steam after
expansion to the lowest suitable possible pressure at which it is used for heating
purpose. Thus back pressure turbine supplies power as well as heat energy. The back
pressure turbine generally used in sugar industries provides low pressure steam for
heating apparatus, where as a topping turbine exhausts into a turbine designed for
lower steam conditions.

(E) On the Basis of Number of Cylinders Turbine may be classified

as:
(i) Single cylinder and

(ii) Multi-cylinder.

(i) Single Cylinder: When all stages of turbine are housed in one casing, then it is
called single cylinder. Such a single cylinder turbine uses one shaft.

(ii) Multi-Cylinder: In large output turbine, the number of the stages needed
becomes so high that additional bearings are required to support the shaft. Under
these circumstances, multi-cylinders are used.

(F) On the Basis of Arrangement of Cylinder Based on General Flow

of Steam:
(i) Single flow,

(ii) Double flow, and

(iii) Reversed flow

(i) Single Flow: in a single flow turbine, the steam enters at one end, flows once
through the bladings in a direction approximately parallel to this axis, emerges at the
other end. High pressure cylinder uses single flow. This is also common in small
turbines.

(ii) Double Flow: In this type of turbines, the steam enters at the centre and divides,
the two portions passing axially away from other through separate sets of blading on
the same rotor Fig. 2.5(b). The low pressure cylinder normally uses double flow).
This type of unit is completely balanced against the end thrust and gives large area of
flow through two sets of bladings. This also helps in reducing the blade height as
mass flow rate becomes half as compared to single flow for the same conditions.

(iii) Reversed Flow: Reversed flow arrangement is sometimes used in h.p, cylinder
where higher temperature steam is used on the larger sets in order to minimise

20
 differential expansion i.e. unequal expansion of rotor and casing. The use of single,
double and reversed flow is shown in the layout Fig. 2.5(c).

Fig 3.5 General flow of steam

(G) On the Basis of Number of Shafts:

(i) Tandem compound,

(ii) Cross compound

(i)Tandem Compound: Most multi-cylinder turbines drive a single shaft and single
generator. Such turbines are termed as tandem compound turbines.

(ii) Cross Compound: In this type, two shafts are used driving separate generator.
The may be one of turbine house arrangement, limited generator size, or a desire to
run shafting at half speed. The latter choice is sometimes preferred so that for the
same centrifugal stress, longer blades may be used, giving a larger leaving area, a
smaller velocity and hence a small leaving loss.

(H) On the Basis of Rotational Speed:

(i) Constant speed turbines

(ii) Variable speed turbines

(i) Constant Speed Turbines: Requirements of rotational speed are extremely rigid
in turbines which are directly connected to electric generators as these must be a-c
unit except in the smallest sizes and must therefore run at speeds corresponding to the
standard number of cycles per second and governed by the following equation :

N = 120 × Number of cycles per second = 120 f/p

Number of poles

The minimum number of poles, in a generator is two and correspondingly the

maximum possible speed for 60 cycle is 3,600 rpm; for 50 c/s of frequency, the
speeds would be 3,000, 1500 and 750 rpm for 2, 4 and 8 poles machines respectively.

21
(ii) Variable Speed Turbines: These turbines have geared units and may have
practically any speed ratio between the turbine and the driven machine so that the
turbine may be designed for its own most efficient speed. Such turbines are used to
drive ships, compressors, blowers and variable frequency generators.

Fig 3.6 internals of impulse and reaction turbine

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 CHAPTER-4

MAIN TURBINE AT KTPP, 1 X 600MW

23
4.1 CONSTRUCTION AND STEAM FLOW:

The turbine is a reaction, condensing type tandem compound with throttle

governing and regenerative system of feed water heating .It is coupled directly to the
generator.

The turbine has one single flow HP one double flow IP and one double flow LP
cylinders. The HP, IP & LP rotors are connected by rigid couplings .The critical speeds
of HP and IP rotors are well above the operating speed while that of LP rotor is below
operating speed.

Steam is admitted to the HP turbine through two nos. combined main steam stop
and control valves. The lines leading from two HP exhaust branches to the re-heater are
provided with check valves, which prevent flow of hot steam from the re-heater back to
the HP turbine. The steam coming from the re-heater goes to the IP turbine through two
combined stop and control valves and the exhaust from the IP turbine is taken to the LP
turbine by two cross around pipes one either side of the turbine at the operating floor
level. This reduces the requirements on the overall height of the turbine bay.

4.2 EXISTING TURBINES:

The Tandem compound turbines are:

1. HP TURBINE

2. IP TURBINE

3. LP TURBINE

24
4.2.1 HP TURBINE:

The outer casing of the HP turbine is of barrel type construction. This avoids mass
accumulation due to absence of flanges. As a result of the almost Complete rotation
symmetry the wall thickness is kept moderate and of nearly equal strength at all
section .The inner casing carries the guide blades and is axially split and Cinematically
supported. The space between the inner and outer shells is sealed from the neighbouring
spaces by sealing rings .As the inner casing is not subjected to large pressure drops the
joint flange and bolts are designed for less stringent conditions. The inner casing is fixed
in the horizontal and vertical planes in the outer casing so that it can freely expand
radially in all direction and axially from a fixed point when heating up while maintaining
eccentrically.

The barrel construction permits rapid start up and higher rates of load changes due
to absence of high thermal stresses. Barrel type casing are also easy to cast which means
the castings can be of exceptionally good quality. The connections of the main steam
piping with the HP turbine are by means of sleeve joint having buttress threads. These
threads are located in the outer casing and connection with the piping is made through
breech nuts. This arrangement provides ease of opening the joint during maintenance.

4.2.2 IP TURBINE:

The IP casing is split horizontally and is of double shell and double flow
construction, with the inner casing carrying the guide blades and kinematically supported
within the outer casing. The construction provides flexibility for choosing the locations of
bleed steam point to suit the best thermal efficiency. The reheated steam enters the inner
casing through the top & bottom.

25
 Fig 4.2.2 IP TURBINE

The arrangement confines the high steam temperature to the admission branch of the
casing while the joint of the outer casing is only subjected to lower pressure and
temperature at the exhaust of the inner casing. Although the casings are of split design yet
these do not impose restriction in startup timings and rapid load changes due to the
provision of suitable stress relieving grooves built in the inner casing. The hydraulic
turning gear blades are located on the coupling of the IP rotor.

4.2.3 LP TURBINE:

The LP casing is of triple shell fabricated construction. The outer casing consists
of the front & rear end walls; two side members called longitudinal girders and top cover.

26
 Fig. 4.2.3 LP TURBINE

The shell inner casing is supported kinematically at each end by two support arms
resting on the side members of the outer casing. The inner shell of the inner casing
carriers the guide blade carrier of the first idle blade carriers, which constitute the
remaining stages of the turbine, are bolted to the middle inner outer casing.

27
Technical Data:

Rated load 500MW

Rated speed 50.0 c/s

Single flow HP Turbine with 17 reaction stages

Double flow IP Turbine with 12 reaction stages per flow

Double flow LP Turbine with 6 reaction stages per flow

HP casing 2 Main Stop and Control valves mounted

STEAM-PRESSURE :

Initial Steam 166.7 bar

Before 1 HP drum stage 154.4 bar

HP cylinder exhaust 44.03 bar

IP cylinder stop valve inlet 39.63 bar

Extraction6 44.03 bar

Extraction 5 17.02 bar

Extraction 4 6.9 bar

Extraction 3 2.75 bar

Extraction 2 1.47 bar

Extraction 1 0.339 bar

LP cylinder exhaust 0.0953 bar

*All pressures are absolute pressures

28
STEAM TEMPERATURE:

HP turbine inlet 535 °C

HP turbine exhaust 338.9 °C

Extraction 6 338.9 °C

Extraction 5 414.8 °C

Extraction 4 290.9 °C

Extraction 3 191.4 °C

Extraction 2 133.4 °C

Extraction 1 70.9 °C

LP turbine exhaust 44.9 °C

CHAPTER-5
29
TURBINE AUXILLIARIES

30
HPT – High Pressure Turbine IPH – Intermediate Pressure Turbine

LPH – Low Pressure Turbine CEP – Condensated Extraction Pump

GSC – Gland Steam Condenser CPU – Condensate Polishing Unit

DC – Drain Cooler LPH – Low Pressure Heater

HPH – High Pressure Heater DA – Deaerator

FST – Feed Storage Tank BP – Booster Pump

TDBFP – Turbine Driven Boiler Feed Pump

MDBFP – Motor Driven Boiler Feed Pump

HPH – High Pressure Heater

5.1 CONDENSER

Condenser is a shell and tube heat exchanger that condenses hot steam into water.
Steam after rotating all turbines and outlets of several heat exchangers using steam as hot
fluid in a plant enter into condenser shell side. Cool water is supplied from cooling tower.
Cool water flows in condenser through tubes, are previously vacant by vacuum pumps.
Hot water after condensation sent back to the cooling tower to cool.

Fig. 5.1 CONDENSER

31
 Condensers are classified as jet condensers and surface condensers. In jet condensers
the steam to be condensed mixes with the cooling water and the condensate can't be
recovered for use as feed water to the boiler. In this plant surface condensers are using. In
surface condensers there is no direct contact between the steam to be condensed and the
circulating cooling water. There is a wall interposed between them through heat must be
connectively transferred. The temperature condensate may be higher than the temperature
of the cooling water at outlet and the condensate is recovered as feed water to the boiler.
Both the cooling water and the condensate are separately with drawn. Separated
condensate can be reused as feed water. This condensate maintains approx.45.60C,-
0.9Kg/cm2 temperature and pressure respectively.

The purpose of condenser to condense steam to obtain maximum efficiency and

also to get the condensed steam in the form of pure water, otherwise known as
condensate, sent back to boiler as boiler feed water. However, in this thermal power plant
the LP Turbine steam extraction can be given to the condenser shell side to exchange the
heat with cooling water (flow in tubes) from cooling tower to use as feed water again.
After condensation, still some non-condensable gases / leakage air may be there in
condenser. These gases and air will create back pressure in the condenser. These are to be
removed.

Type of condenser Surface type

1 Number of surface condensers per No. One

STG unit

2 Number of passes No. Two

3 Steam from turbine exhaust at turbine

VWO condition at design cooling
water temperature and 0% make-up

a) quantity T/h 1004.877

b) pressure Kg/cm2 (a) 0.107

c) temperature 0
C 46.7

d) enthalpy Kcal/kg 566.2

4 Cooling water design parameters

a) Quality Raw water

b) Flow quantity m3/h 54300

c) density Kg/m3 1000

5 Oxygen content in condensate at cc/lit 0.03

32
 condenser hot well outlet with 3%
make-up to hot well from 30% TG
MCR to TGVWO

5.2 CONDENSOR TUBE CLEANING SYSTEM

Tube cleaning system of the Condensers by using Sponge Rubber Balls has been
in use all over the world for more than four decades now. This system is found to be an
effective solution for maintaining the cleanliness factor at the optimum level.

Sponge rubber balls with a special composition and size 1 to 3mm greater than the
inner diameter of the Condenser Tubes are injected into the Cooling Water stream at the
inlet. These balls which have specific gravity close to that of the cooling water are
carried into the Condenser by the velocity of the inlet water. Cleaning balls are then
pushed through the tubes by the differential pressure against the walls of the tube
removing all deposits on the inner surface of the tubes. A specially designed screen
arrangement called the Ball Separator separates the balls from the main Cooling Water
system and the balls collected in the Ball Vessel. The balls are injected into the Cooling
Water through the Ball Recirculating Pump. The Ball Separator is specially designed to
facilitate the smooth passage of the Cleaning Balls to the extraction point. The unique
design of the Ball Separator ensures that the Cleaning Balls will have to move through
only a small angle, since lager angles may result in the balls sticking to the screen in case
of adverse conditions.

The main advantages of a Tube Cleaning System are:

* Increase in the Heat Transfer Rate

* Optimum Turbine Back Pressure

* Increased Generation Efficiency

* Avoidance of corrosion in Tubes

* Avoidance of Shutdown for Manual Cleaning

* Reduction of Chemical costs for Water Treatment

* Reduction in fuel costs.

33
5.3 VACUUM PUMP

The vacuum pump is a two-stage liquid ring type pump. Rotor revolves without
metal contact in a circular body that contains a liquid compressant. The rotor is
eccentrically fitted into the circular body. So during each revolution liquid compressant
will be compressed (discharge of air) to atmosphere and expanded (suction of air from the
system). Evacuated air discharge by the first stage of vacuum pump finds way to second
stage manifold.

Fig. 5.3 VACUUM PUMP

During normal vacuum operation, a check valve in the 2nd stage discharge
manifold allows the incoming air & compressant from 1st stage directly to outside
separator bypassing the second stage. During low vacuum operation, a check valve closes
allowing the 1st stage discharge into 2nd stage suction, the air and compressant from 2nd
stage is discharged to the separator. Circulating water pump sucks seal water from the
separator tank. The tank level is maintained automatically by an external DM water
source through a float operated make-up valve. The discharge of the pump passes through
a strainer and water to water cooler and is fed to vacuum pump for liquid ring formation
and stuffing box sealing and lubrication.

34
5.4 COOLING TOWER:

Fig.5.4 Natural Draft Hyperbolic Cooling Tower

35
 Cooling tower is building like structure constructed in thermal power
plants to cool the hot water. The cool water passes through condenser tubes become hot
by absorbing heat from hot steam. this hot water circulate to the cooling tower through
header and lifts to certain level of cooling tower by using own head absorbed previously
means no pumping action is required to lift the water.

Hot water reached cooling tower sprays into cool air. Nozzles are used for
spraying of water, thereby we can increase the Surface area exposed to atmosphere and
cooling action occurs very fast. The shape of the tower governs the air to escape easily by
the phenomenon called “Natural draft”. Means air flows through tower due to pressure
difference at different height. The cooled water is drained at the bottom to recalculate. To
the condenser circulation of water can be done using cooling water pumps. Here in this
plant four pumps are running to feed the cooling water to condenser. There are three
auxiliary pumps running to supply cooling water to cool the hot DM water in plant.

Here, in this plant we encountered the evaporative type natural draft cooling tower.

5.5 HOT WELL:

Semi cylindrical tank like structure, Below the condenser, is present

that is known as Hot well, the purpose of this hot well is to collect condensed saturated
steam from the condenser shell side discharge. A particular level is maintained in the hot
well by the help of control valve. This water (condensed steam) can be pumped by CEPs
(Condensate Extraction Pumps) (here 3 pumps) to the LP heaters. The discharge of CEPs
Pass to the Gland Steam Condenser.

5.6 CONDENSATE EXTRACTION PUMPS

The function of these pumps is to pump the condensate to the deaerator through
gland steam condenser, drain cooler and LP heaters. In KTPP, 1x500MW unit, 3pumps
are installed, having a pumping capacity of 50%each. Two pumps are for normal
operation and one is standby. Since the suction is at a negative pressure, the special
arrangements have been made for providing sealing to glands.

5.6.1 SPECIFICATIONS

CONDENSATE EXTRACTION PUMPS

1 Number of pumps per STG unit No. 3X50%(2 working, 1 stdby)

2 Type of pump Vertical, canister type

3 Design capacity per pump m3/h 775

4 Run-out flower per pump m3/h 830

5 Minimum flow per pump m3/h 200

36
6 Total head at design capacity mlc 265

7 Pump efficiency at design point % 81

8 Drive motor rating KW 900

5.6.2 DESCRIPTION

The condensate extraction pumps are of the vertical centrifugal canister type with
the driving motor supported on a fabricated motor stool. The motor is supported on a
fabricated head piece which is secured to a fabricated canister. The canister is secured to
a foundation ring which is held to the floor with nuts on foundation bolts.

The pump stage casings from an interconnected assembly which is attached to the
underside of the head piece and is suspended within the canister. The head piece is
provided with a stuffing box which contains a mechanical seal to prevent pump leakage.
Small bore pipe work, for sealing purpose, is connected to the stuffing box. The head
piece also supports the water cooled oil lubricated thrust and journal bearing.

The pump discharge branch and vent pipe are integral with the head piece and the
pump suction branch is integral with the canister. The motor stool, secured to the top of
the head piece, supports the driving motor. Cooling water pipe work along with the oil
filling/vent pipe and gauge glass extension pipe are attached to the motor stool.

Apertures formed on the motor stood and head piece provide access to the coupling thrust
bearing and mechanical seal.

The motor shaft is connected to a top shaft via a flexible spacer coupling and the
top shaft connects to connect to the intermediate shaft via a solid muff coupling. The
intermediate shaft in turn is connected to a bottom shaft through muff coupling. The top
shaft passes through the combined thrust and journal bearing and stuffing box, and also
carries the fourth to sixth stage rotating assemblies. The intermediate shaft carries second
and third stage rotating assemblies. The bottom shaft carries the first stage rotating
assembly. The shafts are supported by two cut less rubber bearings at the first stage and
by a single cut less rubber bearing at the second to sixth stages. The thrust bearing
absorbs the downward axial thrust from the pump rotating assembly, and the white metal
lined journal bearing with in the thrust bearing assembly supports the shafts along with
the cut less rubber journal bearing within each intermediate stage assembly and element
assembly.

A snubber secured into the bottom of the canister engages the suction bell mouth fitted to
the first stage casing. This arrangement provides support to the bottom end of the pump.

37
 5.6.3 ASSOCIATED EQUIPMENT

5.6.3.1 Canister and Foundation Ring

The canister is fabricated tubular chamber formed with a dished bottom end which
is closed by a snubber which is located and secured to the bottom of the canister by
screws, tab-washers and dowels. Leakage between the canister and snubber is prevented
by a joint, and a cylindrical extension of the snubber provides rigid support to the first
stage pump casing assembly.

A suction branch integral with the canister is positioned above floor level and a
flange provided below the suction branch accommodates screws for securing the canister
to the foundation ring. The canister top flange supports the discharge head piece. The
foundation ring is provided with holes for foundation bolts and tapped holes for canister
securing screws. The foundation bolts and foundation ring are grouted to the floor.

5.6.3.2 Discharge Head piece

The fabricated head piece, secured to the pump canister with screws, incorporates
the discharge branch and supports the thrust bearing housing and motor stool. The head
piece is sealed where the shaft passes through by a stuffing box which incorporates a
mechanical seal.

Small bore pipe work connects to the stuffing box, for inlet and outlet sealing
water. The outlet pipe work, which returns the sealing water to the pump suction, is
provided with two orifice plates. A vent pipe provided with a spigot flange is
incorporated within the structure of the head piece for connecting to condenser. A Valve
is provided for installing between the vent pipe and condenser.

Tapped holes on the inner flange situated on the underside of the head piece
provide location for the top rising main screws and holes drilled through the outlet of the
outer flange provide location for screws which secure the head piece to the canister
flange. Tapped holes provided on the inner flange situated on the topside of the head
piece, provide location for the stuffing box securing screws. Tapped holes on the topside
outer flange provide location for the motor stool securing bolts. Apertures formed on the
head piece provide access to the stuffing box and are closed by wire mesh guards. Lugs
are situated at the top of the head piece for lifting purposes.

5.5.3.3 Motor Stool

The fabricated motor is dowelled to the head piece and secured by bolts. A recess
formed on the top flange of the motor stool locates the driving motor, which secured with
screws to the motor stool.

Small bore pipe work is provided within the motor stool for thrust bearing inlet
and outlet oil cooling water. A combined oil filler and vent pipe extends through the side
of the motor stool. The thrust bearing oil level gauge glass is secured to a pipe which also

38
extends through the side of the motor stool. Apertures formed on the motor stool provide
access to the flexible spacer coupling and thrust bearing, and are closed by wire mesh
guards.

5.6.4 Stuffing Box Assembly

5.6.4.1 Mechanical Seal

The stuffing box is secured to the head piece with screws, leakages being
prevented by a joint.

The entry of pumped condensate at the underside of the stuffing box is restricted
by a gap between a restriction bush, secured with screws to the stuffing box and a sleeve
secured to the shaft with "Loctite".

The stationary seal face of the mechanical seal is retained by an "O" ring in the
seal plate, and the rotating components of the mechanical seal are retained on a sleeve
held by a retaining collar. The retain collar is secure to the sleeve with grub screws and
secure to the shaft with grub screws.

The sleeve is of 'cartridge' type and seal setting is done by seal manufacturer at
their works itself.

The seal plate is spigot located and secured to the stuffing box with screws,
leakage being prevented by an "O" ring. Tapped holes are provided on the seal plate for
jacking screws, to assist with dismantling. Small bore pipe work connects to the seal plate
to sealing water purposes.

Two additional orifice plates are supplied for each pump to be installed in client's
small bore pipe work which connects to the common discharge. This feature enables an
adequate flow of flushing water to the maintained at the stuffing box, during the time the
pump is on standby.

5.6.4.2 Combined Thrust and Journal Bearing Assembly

The combined thrust and journal, water cooled bearing assembly is mounted on
the head piece and absorbs the pump hydraulic downward thrust, and takes the weight of
the pump rotating assembly.

The casing base plate is spigot-located on to an adapter plate which also locates
by a spigot to the head piece. The casing base plate and adapter plate are secured together
with nuts on studs, and the adapter plate is secured to the head piece with screws.

The thrust collar which is a tight fit and keyed on the shaft is retained against a
shoulder on a shaft by the thrust collar nut. Tapped holes are provided on the collar for
fitting and removal purposes. The thrust is absorbed by the white metal faced thrust pads

39
fitted to the base plate, under the collar. White metal lined journal pads are fitted in the
casing and locate the collar radially.

The casing top is closed by a split cover secured to the casing with bolts, the
halves of the split cover being secured together with nuts on fitted studs and nuts on bolts.
Tapped holes on the split covers facilitate eye-bolts for lifting and removal purposes.
Provisions is also available for a temperature probe. Leakage between the split cover and
casing is prevented by a joint. Leakage between the sleeve and the underside of the base
plate is prevented by a joint. The bearing casing is supplied with inlet and outlet cooling
water connections, an oil level gauge, a combined air vent and oil filler and an oil drain
plug on the base plate. Tapped holes in the casing facilitate jacking screws for
dismantling purposes.

Leakage between the casing and baseplate is prevented by an "O" ring fitted in a
groove machined in the baseplate.

5.6.5 Couplings

The drive from the motor to the top shaft is transmitted via a spacer type flexible
coupling. Each half coupling is a tight fit and keyed to its respective shafts, the halves
being connected by means of a spacer which interconnects via flexible membranes at
each end.

The coupling is designed to accommodate a certain amount of both offset and

angular misalignment and also any free end float or vertical movement of the shafts.

The top shaft half coupling abuts the thrust collar nut, and a recess machined in
the bore of the top shaft half coupling accommodates thrust plate which corresponds with
the LFF button.

5.7 GLAND STEAM CONDENSER (GSC)

Gland steam condenser is a shell & tube type heat exchanger having water boxes on
both side and stainless tubes for heat exchanger surface. Gland steam leak from the
turbines is provided to the GSC shell side to exchange the heat with condensate (water)
flowing through the tubes of GSC for the criteria of efficiency of the boiler. Here
condensate gains the temperature of 47.60C.

5.8 CONDENSATE POLISHING UNIT

5.8.1 INTRODUCTION

The condensate from the GSC Pass to CPU (Condensate Polishing Unit),
here is no heat exchange occurs but polishing of condensate can be done by some
chemicals like resins in the CPU. After polishing the condensate move to Condensate
Control Station, from here condensate proceed to LP heaters as per the requirement.

40
TECHNICAL DATA

1 Capacity of service vessels 2 x 50%

2 Resin transfer pumps 2 x 50%

3 Resin operation time Days 15

4 Mode of CCP operation Cycle H2 / (H2 & NH3)

5 Total solids in the effluents ppb 20

6 Silica concentration in effluent ppb 5

7 Effluent conductivity after removal of

ammonia & amines
µ-mho/cm ≤ 0.1 at 25 0C

5.8.2 CONDENSATE POLISHING UNIT

The condensate polishing plant consists of one set of two units per set, each unit
capable of 50% flow of 656m^3/hour. The temperature of the condensate will
50Deg.C(Max).The maximum pressure drop under dirty conditions through the unit will
be 3.5Kg/cm2

The pressure drop through the clean bed including effluent resin trap will be
2.1Kg/cm2. The average velocity of condenser through the unit will not exceeded 2
m/minute at design flow rate.

The condensate polishing units are arranged with an emergency automatic by pass
so that in the event of the pressure differential being exceeded through the units. The
control valve will automatically open until the differential is reduced to the normal limit.
This will be also used for part are full bypass of service vessel.

The design pressure of the polishing units is 41 Kg/cm2.

The resign being used in the polishing units are:-

Cation resin HCL (4-8%)

Anion resin NAOH (4-10%)

These resins are selected for their physical strength when used with condensate
for their resilience considering that they need to be removed from the service unit to be
regenerated, as well as their performance qualities.

The function of resin is :

41
 a. To behave as a filter and remove all suspended solids from the condensate.

b. To preserve the quality of the condensate by removal of the dissolved solids.

The resin will be operated through from the hydrogen form into ammoniated form.

The plant is designed to operate for 50 hours based on additional influent

Load/corresponding to 2000ppb(TDS) on the top of the normal analysis loading.
During this period the sodium content will be limited to 20ppb.

The resin beds in the polishing plant are supported on a flat nozzle plant into
which are fitted stainless steel nozzles. The incoming water is distributed over the
resin bed by distributor inlets, and after passage through the resin bed is collected by
the nozzle collecting systems before being passed through the outlet.

Between the inlet and outlet of the resin trap is located a pressure differential
indicator fitted with an alarm so that indication is given of the possibility of resin
blockage indicating that investigation is necessary.

Indication that regeneration of resins is necessary is given by an increase in

differential pressure across the headers are a resin in conductivity(alarm) when this
occurs the resins need then to be transferred to the regeneration plant to be regenerated.

The valves used on this section of the plant for everyday operation will be either
butterfly valves pneumatically actuated or ball valves pneumatically operated
dependent upon the size.

5.9 CONDENSATE CONTROL STATION:

It is a set of pneumatic ,electrical and hand operated valves. The pneumatic

control valves controls the condensate flow to the deaerator as per the load,deaerator level
etc., at that time.

5.10 DRAIN COOLER:

It is a shell-full vacuum tube heat exchanger. Condensate flow in tubes and steam
flows in shell side to exchange heat, the steam extraction given from the LP H1’s drip.
After this steam moves to condenser through flash tanks.

TYPE UNIT VALUE

Number of Tubes -- 666

Pressure of Drain Ata 0.34

Pressure of Condensate Ata 21.99

Condensate outlet Deg.C 45.8

42
temperature

Condensate outlet Deg.C 48.6

temperature

Number of shell zones -- 1

Number of tube side passes -- 1

5.11 LOW PRESSURE HEATERS

These are shell & tube heat exchangers. Steam flows in shell side and condensate
flows in tubes. In this heat exchanger cold condensate gains heat from hot steam. Here,
there are 3 LP Heaters connected one after the other. These LP Heaters are designated as
LP Heater1, LPHeater2 and LPHeater3. These are same in construction (design) but
differ in heat source.

Fig 5.11 L.P HEATER

Condensate from drain cooler enters into LPHeater1. It gains heat from
steam, which is extracted from LP Turbine 5 th stage. The temperature of condensate will
be rose up to 200C, so condensate at the outlet of the heater will be at 65 0C .From this
condensate will move to LPHeater2.

43
 Condensate flowing in tube side of LPHeater2 will get heat from the shell side steam.
This steam is extracted from LP Turbine 3rd stage. By this it’s temperature will rise up to
400C.Feed water at a temperature of 1050C will enter into LPHeater3.

This steam extracted from LP Turbine 2rd stage flowing in shell side of LP Heater3
will lost its energy to the condensate. In LP Heater3, the condensate will be heated up to
1250C. From here the condensate will move into Deaerator.

Thesteam, bleed from the turbine, after condensation is termed as drip/ drain. the drip in
the LP heaters will not loose its total energy and the same may be utilised to Down
stream condensate flow in the LP heaters. The drip formed in LP heater-3 will flow into
LP heater-2 and then pass to LP heater-1, the drip in the LP heater-1 pass to the Drain
cooler, which do not have its own Extraction, so the heating source is drip only, finally
the drip loosing its heat content in the drain cooler goes to the condenser through the LP
flash tank

5.12 DEAERATOR

5.12.1 INTRODUCTION

The principles of deaeration of water are outlined in these instructions and

physical equipment which accomplishes this deaeration are basically described. It is the
intent of these instructions to present these principles in broad terms only and to allow
this manual to recover any possible vibrations of equipment or operational conditions.

Deaerating heaters are flexible and will meet the guarenties of deaeration
and accordance with these instructions provided that operating conditions and load
fluctuations are within the design limits and operating personnel understand the principles
of deaeration and the equipment.

5.12.2 FUNCTION

The function of the deaerating heater is to remove dissolve non-

condensable gases and to heat boiler feed water. A deaerating heater consists of a
pressure vessel in which water and steam are mixed in a controlled manner. When this
occurs, water temperature rises, and all non-condensable dissolved gases are liberated
and removed and the effluent water may be considered corrosion free from an oxygen or
carbondioxide stand point. Free air or other non-condensable gases should be vented prior
permitting the fluid to enter the deaerator.

A deaerating heater is the watched dog of a boiler plant as it protects the

feed pumps,piping boilers, and any other piece of equipment that is in the boiler feed and
return cycle from the effects of corrective gases, i.e, oxygen and carbondioxide, to a
level where they are no longer a corrosion factor.

44
5.12.3 PRINCIPLES OF DEAERATION

There is physical law which states that solubility of any gas in a liquid is
directly proportional to the partial pressure of the gas above the liquid surface. Another
law states that the solubility of a gas in a liquid decreases with an increase in temperature
of the liquid. Experience has shown that more rapid and more complete removal of non-
condensable gases from a liquid is obtained when the liquid is vigorously boiled or
scrubbed by condensable or carrier gas bubbles. Therefore essentially the deaerating
heater must first heat the feed water to as high temperature as possible i.e, to the
temperature corresponding to the steam pressure. It must vigorously boil and scrub the
heater water with fresh steam, which can carry to the liquid surface any traces of oxygen
and carbondioxide. The partial pressure of the oxygen and carbondioxide in the steam
atmosphere must be maintained as low as possible, particularly at the point where the
deaerated water seperates from the steam. Non-condensable gases must be continually
withdrawn from the heater at the rate at which they are being liberated.

5.12.4 OPERATION

A deaearating heater utilizes steam by spraying the incoming water into an

atmosphere of steam in the preheater section(1st stage). It then mixes with water with
fresh incoming steam in the deaearator section(2nd stage).

In the first stage the water is heated to within 2 degrees of steam

saturation temperature and virtually all of the oxygen and free carbondioxide are
removed. This is accomplished by spraying the water through self-adjusting spray valves
which are designed to produce a uniform spray film under all conditions of load and
consequently a constant temperature and uniform gas removal is obtained at this point.

From the first stage the preheated water, containing minute traces of
dissolved gases flows into the second stage. This section consists of either a distributer or
a several assemblies of trays. Here the water is in intimate contact with an excess of fresh
gas-free steam. This steam passes into this stage and it is mixed with preheated water.
Deaeration is accomplished at all rates of flow if conditions are maintained in accordance
with design criteria. Very little steam is condensed here as the incoming water has a high
temperature caused the preheating. The steam then rises to the first stage and carries the
small traces of residual gases. In the first stage most of the steam is condensed and the
remaining gas pass to the vent where the non-condensable gases flow to the atmosphere a
very small amount of steam is also discharged to the atmosphere which assures that the
deaearating heater is adequately vented at all times.

The water which leaves the second stage falls to the storage tanks where it
is stored for use. At this time the water is completely deaerated and is seated to the steam
saturation temperature corresponding to the pressure within the vessel.

45
5.12.5 ELEVATION OF DEAERATING HEATER

Any deaerating heater must be elevated above the the boiler feed pump to insure
sufficient net positive suction at the inlet side of the boiler feed pump. The minimum heat
required on the suction of the pump should be carefully checked with the pump
manufacturer, emphasizing the fact that the pump is handling water at a temperature
corresponding to the saturated temperature of the steam supplied to the deaerating heater.
Flashing and consequent "steam blinding" of the pump may occur if the boiler feed pump
is operated with a low or negative suction head. The suction head is considered that
distance from the low water line in the deaerating heater or bottom of storage tank to the
centerline of the feed pump.

5.12.6 WATER PRESSURE

Sufficient water pressure must be supplied at the inlet of the deaearating heater for
all entering water supplied, this pressure must be high enough to overcome any loss of
heat caused by pipe friction, control valves, and spray valves. It must also overcome
internal steam pressure. Normally, minimum pressure for condensate not flowing through
controllers, etc, must be equal to the steam pressure in the vessel plus approximately 3 psi
at the heater connection where spray valves are used and approximately 7.9 psi is
required where spray pipes are used.

Inlet control valves have been selected to operate within the range or pressures. If
the pressure is too low, sufficient water will not enter the heater. If water pressure is too
high, difficulty may be experienced with the control valve. A high pressure valve across
control vavle could cause valve clatter, “hunting” of the unit, and reduce the efficiency of
the plant. In such cases, it is necessary to install a water pressure deducting valve and
regulator.

5.12.7 STEAM REQUIREMENTS

Steam is required to heat and deaearate the water in a deaearating heater. The
amount of steam required does not depend upon the design of deaearating heater. By only
upon thermodynamic loss to determine accurately the amount of steams required, it is
necessary to perform heat balance.

The amount of steam consumed by any deaearating heater is that amount

determined by the heat balance required to heat all of the incoming water to the saturated
steam temperature within the heater, plus a minute that is vented with the gases loss any
flashed steam from hot condensate or trap returns. This calculation should be made with
the incoming water at its lowest temperature. If there is sufficient exhaust or bleed steam,
then make-up or auxillary steam should be supplied at the required pressure.

46
5.12.8 FEED STORAGE TANK

It is placed below the deaerator & it stores the feed-water, which comes from the
deaerator after removing dissolved gases and It acts as the suction source for the Booster
pumps and helps in maintaining minimum suction pressure at inlet.

5.13 BOOSTER PUMP

5.13.1 INTRODUCTION

Each boiler feed pump is provided with a booster pump in its suction line which is
driven by the main motor of the boiler feed pump. One of the major damages which may
occur to a B.F. pump is from cavitation or vapor bounding at the pump suction due to
suction failure. Cavitation will occur when the suction pressure of the pump at the pump
at the pump suction is equal or very near to the vapor pressure of the liquid to be pumped
at a particular feed water temperature. By the use of a booster pump in the main pump
suction line, always there will be positive suction pressure which will remove the
possibility of Cavitation Therefore all the feed pumps are provided with a main shaft
driven booster pump in its suction line for obtaining a definite positive suction pressure

Performance particulars of BP Main BP

1 a) Design temperature of feed water 0

C 162.7

b) rated capacity m3/hr 990

c) inlet flow m3/hr 990

d) minimum flow through the pump m3/hr 400

e) runout flow (one pump at design m3/hr 1100

speed)

f) total dynamic head at rated speed

and capacity
mlc

g) Maximum shut off head mlc 266

h) efficiency % 81.5

2 Impeller arrangement Horizontal

3 No. of stages 1

47
 4 Thrust Bearing Type Tilting pad

Three Booster Pumps are Existing in KTPP, 1x500 MW Unit. Each consists of
FA1B75 type Booster Stage Pump. Two are driven by turbine through gear box and one
is Motor Driven.

The FA1B75 type Booster stage pump is a single stage, horizontal, axial split
casing type, having the suction and discharge branches on the casing bottom half thus
allowing the pump internals to be removed without disturbing the suction and discharge
pipe work or the alignment between the pump and driving motor.

The pump shaft is sealed at the drive and non-drive end by mechanical seals
which are flushed by boiler feed water pumped round a closed circuit. The rotating
assembly is supported by plain white metal lined journal bearing sand axially located by a
double thrust bearing. The bearings in the pump are lubricated by forced oil lubrication
system.

5.13.2 Pump Casing

The cast steel pump casing is of the double volute type, split on the horizontal
center line. The top and bottom half casing are located to each other by dowel pins and
secured by the studs and nuts, sealing at the axial split being effected by a two-ply brown
paper joint.

The bottom half pump casing has the suction and discharge branches and support
feet, cast integrally. The pump casing is machined internally to accept the casing rings
and stuffing boxes are also formed at each end of the casing to accommodate the water
jackets and the mechanical seals, thus preventing leakage along the pump shaft. The
interface of the casing and base plate supports is near the shaft axial. Dowels and a guide
key are arranged to maintain longitudinal and transverse alignments whilst
accommodating thermal expansion. A tapped air vent connection is provided on the top
half casing. Connections are also provided on the suction and discharge branches for
pressure gauges and a drain.

5.13.3 Rotating Assembly

The rotating assembly consists of the shafts, impellers, nuts, keys, seal sleeves,
thrust collar, the rotating parts of the mechanical seals and pump half coupling. The
double entry impeller is keyed to the shaft and is located axially by an impeller nut on
each side of the impeller hub. The impeller is fitted with a wear ring on each shroud, the
rings being retained by grub screws.

The seal sleeves are keyed to the shaft and are located and secured by grub
screws. Leakage between the shaft and sleeve is prevented by an 'O' ring fitted in a
groove machined in the bore of the sleeve. The thrust collar is keyed to the shaft and is
secured against a shoulder on the shaft by the thrust collar nut. The pump half coupling is
keyed to tapered end of the shaft and is secured by a coupling nut, locked by a screw.

48
5.13.4 Journal and Thrust Bearings

The rotating assembly is supported at each end of the shaft by a white metal lined
journal bearing and the residual axial thrust is taken up by a tilting pad double thrust
bearing mounted at the non-drive end of the pump. The journal bearing shells are of mild
steel, white metal lined, thick wall type, and are split on the horizontal plane through the
shaft axis. Each bearing is prevented from rotating by dowel pin located in a recess in the
top half bearing housing.

The thrust bearing is fitted at the non-drive end of the pump and has eight titling
pads in a split carrier ring on each slide of a thrust collar, which is keyed to the pump
shaft and secured by a nut and lock-washer. The carrier rings are held in non-drive end
bearing housing and are prevented from turning with the thrust collar by dowels locating
in slots in the top half of the housing. The thrust pads are retained on the carrier rings by
special pads stops screwed into the rings. Machined spacers are fitted behind each carrier
ring during manufacturer to effect the axial running position of the rotating assembly. The
thrust bearing is provided with for resistance temperature detectors.

A split floating oil seal is fitted in a groove in the housing to maintain a level of
lubricating oil with in the housing, around the thrust bearing, when the pump is stopped.
The floating seal is prevented from turning by an anti-rotation pin fitted in a slot in the
bottom half of the housing. An orifice plug fitted at the thrust bearing lubricating oil
outlet ensures a flooded bearing housing when the pump is stationary. The bearings are
supplied with lubricating oil from the forced lubricating oil system.

5.13.5 Bearing Housings:

The bearing housings are in the form of cylindrical castings, split horizontally.
Secured to each bracket by set screws and dowels located. Each housing is provided with
lubricating oil inlet and outlet connections, vent connections are instrument entry points.

The top and bottom halves of the drive end bearing housings are secured together
by studs and nuts, and the housing is closed the drive end by a cover plate. An oil
retaining shield at each end of the housing prevents oil leakage from the housing when
the pump is running. The top and bottom halves of the non-drive end bearing housing are
secured together by studs and nuts and located by dowel pins. Leakage of lubricating oil
from the non-drive end bearing housing is prevented by an oil retaining shield in board
side of the housing and by a bearing housing end cover and joint secured to the out board
side of housing by hexagon head screws.

5.13.6 Mechanical Seals

The drive and non-drive end seal cooling jackets are fitted with mechanical seals
mounted on the seal sleeves and located within seal cooling jackets. The cooling jacket,
which provides a heat soak barrier between the pump casing and the mechanical seal, is
continuously flushed with cooling water from an external source.

49
 A pumping ring incorporated in the mechanical seal pumps a supply of boiler feed
water through a heat exchanger in a closed circuit, thus keeping the seal circuit
temperature at approximately 60 C Driver / Pump Coupling The drive from the driver to
the pump shaft is transmitted through a spacer flexible coupling.

5.14 Turbine Driven Boiler Feed Pump

The single cylinder turbine is of the axial flow type. The live steam(which is
Extracted from IP Exhaust steam/CRH steam /PRDS steam) flows through the emergency
stop valve and then through the main Control Valves. These valves regulate the steam
supply through the turbine in accordance with load requirements. The control valves are
actuated by a lift bar which is raised or lowered via a lever system by the relay cylinder
mounted on the turbine casing.

The journal bearings supporting the turbine shaft are arranged in the two bearing
blocks. The front end-bearing block also houses the thrust bearing, which locates the
turbine shaft and takes up "the axial forces. There are 21 stages of reaction blading. The
balancing piston is provided at the. Steam admission side to compensate the axial thrust
to the maximum extent. Since the axial thrust varies with the load, the residual thrust is
taken up by the thrust bearing. The turbine is provided with hydraulic and electro-
hydraulic governing system. The steam exhaust from the BFP- Turbine is connected to
the main condenser and the turbine glands are sealed by gland steam.

5.15 BOILER FEED PUMPS

5.15.1 INTRODCTION

Boiler feed pump(BFP) plays an important role in the supply of feed water to the
boiler through the HP heaters at requisite pressure. FK4E36 type Boiler Feed Pump is a
four stage horizontal centrifugal pumps of barrel design casing. The pump internals are
designed as a cartridge which can be easily removed for maintenance without disturbing
the suction and discharge pipe work, or the alignment of the pump and the turbo
coupling.

The pump shaft is sealed at the drive end and non-drive end by Mechanical seals.
The rotating assembly is supported by plain white metal lined journal bearings and
axially located by a double titling pad thrust bearing.

TECHNICAL DATA

Design temperature of feed water 162.9Deg.C

Power input to pump set at rated flow and head 6898KW

Number of stages for Main Pump 4

50
Number of stages for Booster Pump 1

Journal bearing Thick Wall Babit

Lined

Oil Tank Storage Capacity 2500 Liters

Pump efficiency 80%

5.15.2 DESCRIPTION:

5.15.2.1 Pump Casing

The pump casing consists of a forged steel barrel with welded suction, discharge
branches, inter stage tapping and mounting feet. The drive end of the casing is closed by a
suction guide which is entered from the non-drive end of the casing and is located by a
spigot against the outer face of the casing.

A metaflex joint is located between the suction guide spigot and the casing outer
face to prevent leakage between the barrel casing and suction guide. A split pull up ring is
secured to the pump casing and suction guide by a ring of screws. Leakage between the
suction annulus and the discharge annulus of the pump casing is provided by copper
coated mild steel joint located between the inner face of the casing and the first stage ring
section spigot. The non-drive end of the casing is closed by a discharge cover
secured to the casing by a ring of studs, washers and nuts, sealing being effected by a
metaflex joint located in a machined recess in the pump casing. On each side of casing,
on its horizontal center line, are two support feet which are secured to the base plate
pedestals by spacer pieces, washers and holding down bolts, thus allowing for expansion.
Transverse keys in the drive end pump feet and longitudinal keys under the casing
transfer moments and thrust to the base plate, while allowing the casing, freedom to
expand.

Provision is made on the pump casing for a drain connection and temperature probes.

5.15.2.2 Discharge Cover

The discharge cover closes the non-drive end of the pump casing and also forms
the balance chamber which, in turn, is closed by the gland housing. The discharge cover
is a close fit in the casing bore and is held in place by a ring of studs and nuts. A spring
disc is located between the last stage diffuser and outlet guide to provide the force
required to hold the ring section assembly in place against the drive end of the barrel
before start-up. Once running the discharge presence assists the spring disc in holding the
ring sections in place. The last stage diffuser is free to slide over the outlet guide.

Two holes are drilled radially through the periphery of the discharge cover to
provide outlet connections through which the liquid from the balance chamber is returned

51
to the pump suction piping and two similarly drilled holes are also provided in the
discharge cover for the welded connections of the kicker stage deliveries. The non-drive
end bearing housing is attached to the gland housing secured to the outer face of the
discharge cover by socket head screws and dowel pins.

To assist in removing the cover, two tapped holes are provided on the flange for
the use of starting screws and a tapped hole is provided on the top of the cover for an eye-
bolt.

5.15.2.3 Suction Guide

The suction guide closes the drive end of the pump carrying and forms the suction
annulus. As a suction of the pump cartridge, the suction guide is not secured to the pump
casing but is held against an internal shoulder in the casing by the pull up ring.

The drive end bearing housing is secured to the outer face of the suction guide by
cap screws and dowel pins..

5.15.2.4 Ring Sections

The ring section assembly consist of ring sections which locate one to another by
radial dowel pins are secured to each other by socket head screws in counter bored holes,
sealing being effected by metal-to-metal joint faces. Diffusers are dowel and spigot
located to the ring sections and secured to the ring section with socket head screws. The
outlet guide for the kicker stage impeller is secured to the discharge cover by means of
cap screws which are locked in position with plugs. Packing rings are shrunk into the
bores of the ring sections and diffusers and are secured by grub screws, the purpose of the
packing rings being to restrict the recirculation of the pumped liquid between the stages.

The ring sections and diffusers form the transfer passages from the impeller outlet
of one stage of the pump to the impeller inlet of the next stage of the diffusers are
designed to convert some of the kinetic energy of the product into pressure energy.

The first stage ring section is spigot located to the suction guide and to radially
located by means of a slot in the ring section and a cast key block in the suction guide. At
the non-drive end a dowel pin fitted to the outlet guide is located in a hole in the last stage
diffuser thus the ring section assembly is kept in the correct position relative to the
casing. A circular spring disc is located in the last stage diffuser and over the inner
end of the outlet guide. A shoulder on the outlet guide bears against the spring disc and
clamps the ring section assembly to suction guide in position.

5.15.2.5 Rotating Assembly

The dynamically balanced rotating assembly consists of the shaft assembly,

abutment rings, keys, shaft nuts, balance drum, thrust collar and the pump half coupling.
The shaft is chromium plated at each end where it is supported by the journal bearings,

52
and its diameter increases in increments from the non-drive end towards the drive end to
facilitate and removal of the impellers.

The impellers are of the single entry shrouded inlet type and are keyed and shrunk
onto the shaft, the keys, one per impeller, being alternately fitted on diametrically
opposite sides of the shaft to maintain rotational balance. The hub of each impeller butts
against a split shear ring fitted in a groove in the shaft. The shear ring is retained by an
extension of the impeller hub.

The balance drum is keyed and shrunk on the shaft and held in place against the
shaft locating shoulder by the balance drum nut and lock-washer. The inner end of the
balance drum is recessed and the bore of the recess is a close to over the kicker stage
impeller hub. The face of the balance drum incorporates tapped holes for withdrawal
purposes. The rotating parts of the seals are fitted to the shafts where it passes through the
seal housings. The seal sleeves are keyed to the shaft and are clamped in position by shaft
nut and shaft lock-nuts.

The thrust collar which is keyed to the non-drive end of the shaft , has the thrust
collar probe indicator fastened and doweled to its hub and is located against a shoulder on
the shaft by the thrust collar nut, locked by a lock washer.

The pump half coupling is located on the tapered end of the shaft by keys and it is
secured by a coupling nut locked by a grub screw.

5.15.3 MECHANICAL SEAL

The drive and non-drive end stuffing boxes are fitted with mechanical seals
mounted on seal sleeves and located within seal cooling jackets to prevent feed water
escaping along the shaft. tapped holes are provided on each seal plate and cooling jacket
for clarified cooling water inlet and outlet connections.

5.15.3.1 Journal and Thrust Bearings

The rotating assembly is supported at each end of the shaft by a white metal lined
journal bearing and the residual thrust is taken up by a tilting pad double thrust bearing
mounted at the non-drive end of the pump. The journal bearing shells are of mild steel,
white metal lined, thick wall type, and are split on the horizontal plane through the shaft
axis. Each bearing is secured in a bearing and prevented from rotating by a dowel pin
located in the bearing keep.

The thrust bearing has eight white metal lined titling pads held in a split carrier
ring positioned on each side of the thrust collar. The carrier rings are prevented from
rotating with shaft by dowel pins in each ring which engages in slots in the bearing
housing top half. The thrust pads are retained on the carrier rings by a special pad stops

53
into the rings. The split floating oil sealing ring is located in a groove in the thrust bearing
housing to restrict the escape of the lubricating oil from the thrust bearing chamber. To
ensure that the thrust bearing remains flooded, an orifice is fitted at the oil outlet.

Machined spaces are fitted behind the carrier rings to effect the axial position
setting of the rotating assembly on the original build. The bearings are supplied with
lubricating oil from the forced lubrication oil system.

5.15.3.2 Bearing Housings

The bearing housings are in the form of cylindrical castings split on the horizontal
shaft axis. The top and bottom halves, of each bearing housing, are located by fitted bolts
and secured together by cap screws. The journal bearing in each housing is located by a
dowel pin in the bearing keep and the bearing keep is dowel located to the bottom half
housing and secured by cap screws. On the top half housing there is provision for an air
vent, vibration probes and a temperature check point. On the bottom half housing there is
provision for oil inlet and oil outlet, R.T.D probe and a temperature gauge.

The drive end bearing housing is secured to the suction by the screws and is
radially located by dowel pins fitted in the flange of the suction guide. Oil guards fitted in
a groove at each end of the bearing housing are dowel located and serve to prevent oil
escaping from the housing. As air breather is screwed into a tapped hole in the top half
bearing housing and a tapped hole is provided for a temperature gauge. Connections for
an oil inlet and outlet are provided in the bottom half bearing housing.

The non-drive end bearing housing, which contains both the journal and thrust
bearings, is located by taper dowel pins and secured to the gland housing by cap screws.
In addition to the features common to both bearing housing the follow features are
included. On the top half housing there are connections for reverse running indicators, an
accelerometer and a thrust bearing temperature check point. On the bottom half bearing
housing the additional provision is for thrust bearing temperature gauges. Leakage of
lubricating oil from the non-drive end bearing housing is prevented by an oil guard in the
inboard side of the housing.

5.15.3.3 Hydraulic Balance

The rotating assembly is subjected to varying forces due to differential pressure

forces acting on the impellers. The pump has therefore been designed so that the shaft is
kept in tension by the location of balance drum at the non-drive end, and is hydraulically
balanced so that only a small residual thrust remains which is carried by the thrust
bearing. The main components of the hydraulic balancing arrangement are the balance
chamber machined in the discharge cover the balance drum which is secured to the shaft
and the balance drum bush fitted in the bore of the discharge cover. The thrust caused by
the discharge pressure acting on the area outside each impeller wear ring on the inlet side
of the impeller wear ring balanced by the same pressure acting on an equal area on the
outlet side of each impeller. The thrust caused by the suction pressure acting on the area

54
inside the wear ring on the inlet side of each impeller is overcome by the much greater
thrust caused by the discharge pressure acting on the equivalent area on the outlet side of
each impeller. The resultant thrust force, due to the different pressures acting on these
equal areas, tends to move the rotary assembly towards the driven end of the pump.

The thrust force will vary with the load on the pump but the hydraulic balance
arrangement will reduce its effect, enabling the residual thrust to be taken by the titling
pad thrust bearing. This bearing has a double face so that the surges in opposite directions
which occur during the start-up period and during transient conditions will be
accommodated.

The hydraulic balance arrangement operates as follows

The pump product passes from the kicker stage of the pump between the balance
drum and the bush, and enters the balance chamber at a pressure approximately equal to
the suction pressure. Two ports in the discharge cover allow the product to be piped back
to the pump suction side. The pressure differential across the balance drum is therefore
equal to the across the impellers. The cross-section area of the balance drum is sized to
give a small residual thrust towards the drive end of the pump.

5.15.3.4 HYDRAULIC COUPLING

The geared variable speed turbo coupling is used for speed control of BFP. The
variable speed turbo coupling and step up gear are incorporated in a common housing,
while the lower section of the housing serves as an oil tank. Flexible connecting coupling
are applied for power transmission from the motor to the geared variable speed turbo
coupling and from there to BFP. The speed is increased between input and primary shaft
by means of a gear stage. Torque is transmitted from the primary wheel to the secondary
wheel by the working oil.

Fig 5.15.3.4 Hydraulic coupling

55
 A filling pump in the coupling housing supplies the variable speed hydraulic
coupling with oil. The primary shaft of variable speed hydraulic coupling drives this
pump via a gear stage. The scoop tube supplies the working oil out from the hydraulic
coupling back into the oil tank .This scoop tube determines that oil filling in the variable
speed hydraulic coupling and thus the output speed. An actuator is installed on the
coupling house controlling the scoop tube.

The drive machine torque accelerates the operating oil in the couplings primary
wheel(pump impeller).The oil is then decelerated by the secondary wheel(turbine) and
thus transmits the torque to the secondary shaft. oil pump circulates if there is a pressure
difference between the primary and secondary wheel that means slip is required for
power transmission.

The coupling is sized so that full power can be transmitted at 2-3% slip. The
output speed can be smoothly varied by changing the slip which is achieved by increasing
or decreasing the amount of oil in the working chamber between the primary and
secondary wheel that means By positioning the scoop tube to match the output speed.

5.16 HIGH PRESSURE HEATERS

Fig. 5.16 HP HEATERS

5.16.1 FEED WATER HEATER

A feed water heater is a special form of a shell and tube heat exchanger designed for the
unique application of recovering the heat from the turbine extraction steam by preheating
the boiler feed water. Its principal parts are a channel and tube sheet, tubes , and a shell.
The tubes may be either bent tubes or straight tubes feed water heaters are defined as high
pressure heaters when they are located in the feed water circuit upstream from the high

56
pressure feed water pump low pressure the discharge pressure from these pumps differs
greatly, the physical and thermal characteristics of high and low pressure feed water
heaters are vastly different. Typically low pressure feed-water heaters are designed for
feed-water pressure between 27 Kg/cm2 and 56 Kg/cm2, high pressure feed-water heaters
range from 112 Kg/cm2 for nuclear heat sources to 335 Kg/cm2 .for super critical
boilers. Regardless of the actual design pressure, the classification depends upon the
cycle location relative to the feed water pumps. The design pressure is specified
sufficiently high so as to not over-pressure the channel side of the heaters under any of
the various operating conditions, particularly cat pump shut-off.

Each feed-water heater bundle will contain from 1 to 3 separate heat transfer area
or zones these are condensing, desuperheating and sub cooling zones. Economics of
design will determine what combination of the three is provided in each heater.

A condensing zone is present in all feed-water heaters. Large volumes of steam

are condensed in these zone and most of the heat is transferred here.

The desuperheating zone is a separate heat exchanger contained within the heater
shell. This zones purpose is to remove superheat present in the steam because of the high
steam velocities employed, condensation within the desuperheating zone is undesirable.

The sub cooling zone like the desuperheating zone is another separate counter
flow heat exchanger whose purpose is to sub cool income drain and steam
condensate.

The discharge of boiler feed pumps passes through the HP heaters into 2 parallel
streams. HP Heaters are shell and tube heat exchangers, where steam flows in shell
side and feed water flows in tubes. HP Heater5A & HP Heater5B get heat extraction
from IPT 7th stage, while HP Heater6A & HP Heater6B get heat extraction from
CRH tapping. feed water in the tubes exchanges heat with shell side steam. At the
end of HP Heaters feed water temperature will reach nearly 165 0C to 2550C. The
stream in which HP heater 5A and 6A are in series is parallel with the other stream
in which HP heater 5B and 6B are in series. The common discharge after HP heaters
leads to Economizer through feed control station.
The drip formed in the HP heater 6A passes to 5A and the cumulative drip from
the HP heater 5A goes to Deaerator. The drip flow is also same in the other Stream
i.e. drip from HP heater 6B to 5B, then goes to Deaerator.

5.17 ECONOMIZER

The economizer preheats the boiler feed water before it enters the boiler drum by
recovering heat from the flue gases. In economiser, water is heated to about 30 to 40oC
below saturation temperature. The name economiser means it recovers the heat from the
flue gases leaving the boiler and provision of this additional heating surface increased the
efficiency of steam generation, saving in fuel consumption.

57
 CHAPTER-6
TURBINE LUBE OIL SYSTEM

6.1 LUBRICATING SYSTEM

Good lubrication is one of the most important factors effecting the safety and
availability of generating plant and considerable damage can occur if the correct care and
attention is not paid to the lubricating systems. Because of high capital cost of plant,
heavy losses are incurred if efficient plant is kept out of service for lengthy repairs.

During start-up & shut-down, aux oil pump supplies the control oil.

Once the turbine speed is more than 2850 rpm, the main oil pump (M.O.P) takes over. It
draws oil from main tank .The lubricating oil passes through oil cooler, before can be
supplied to the bearing (Under emergency, lube oil can be supplied by a DC oil
pump).Before the turbine is turned or barred, Jacking oil pump (2 nos.) supplies high
pressure oil to the jack up the TG shaft to prevent boundary lubrication and also supplies
high pressure oil to drive the hydraulic motor(turning gear).

6.2 MAIN COMPONENTS

1) Main Oil Pump

2)Auxiliary Oil Pump
3) Emergency Oil Pump
4) Jacking Oil Pump

6.2.1 Main Oil Pump

 This pump is located at the front bearing pedestal of the HP turbine.
 It is coupled to the turbine rotor through a gear coupling.
 When the turbine is running at a normal speed of 3000rpm, the lubrication
systems is supplied by this pump.
6.2.2 Auxiliary Oil Pump
 Auxiliary Oil Pump can meet the requirements of lubrication system under low
speed conditions i.e. during the start up operation.
 One stage vertical centrifugal pump driven by an A.C. Electric motor.
 It has radial impeller and volute casing.

58
  The pump automatically takes over under interlock action whenever the oil
pressure in the lubrication system fails below certain desired level.
6.2.3 Emergency Oil Pump
 Emergency oil pump has been foreseen by as a back-up protection to AC driven
standby oil pump.
 This is a centrifugal pump, driven by DC electric motor.
 This automatically cuts in whenever there is a failure of AC supply at power
station
6.2.4 Jacking Oil Pump
 Before the turbine is turned or barred, Jacking oil pump supplies high pressure oil
to the jack up the TG shaft to prevent boundary lubrication and AOP supplies high
pressure oil to drive the hydraulic motor(turning gear) to avoid the bearing
damages and shaft distortions when turbine trips.
 JOP ensures that there is no metal contact between a journal and the bearing.
 Positive displacement pumps that provide high pressure supply of oil under
strategic journals of the turbo generator and oil lifts the shaft slightly.
 This greatly reduces the static friction and bearing wear.
 The JOP can be stopped after the lubricating oil film is established between the
shaft and bearings.

59
 CHAPTER-7

TURBINE LOSSES IN THERMAL POWER PLANT

Steam turbine being work producing device running at quite high speed has
number of losses occurring in it. These losses when put together result into substantial
loss of energy. Therefore, while selecting a turbine due attention should be paid to the
losses in turbine. Some of the losses occur within turbine stages while some are external
to stage. These losses are described ahead.

7.1 Internal losses:

a. Nozzle friction

b. Blade friction

c. Disc friction

d. Diaphragm gland and blade tip leakage

e. Losses due to wetness of steam

f. Exhaust velocity losses

7.2 External losses:

a. Shaft gland leakage

b. Journal and thrust bearings

c. Governor and oil pump

7.1 INTERNAL LOSSES

7.1.1 Loss of Nozzle Friction:

Steam turbine nozzle is designed for isentropic expansion so as to result in

increase in velocity from inlet to exit. Practically in a nozzle the steam leaving nozzle
may not have velocity equal to the designed velocity value. This deviation in operating
state of nozzle may occur because of non-isentropic expansion. The reasons for non-
isentropic expansion may be friction losses between the steam and nozzle wall, viscous
friction resistance to flow in the steam particles, boundary layer formation and separation,
heat loss during flow etc. Mathematically, this shift from isentropic expansion to non-
isentropic expansion is quantified using the parameter called ‘nozzle efficiency’. Nozzle
efficiency as described earlier is defined by the ratio of ‘actual enthalpy drop’ to the
‘isentropic enthalpy drop' between inlet and exit of nozzle. The effect of nozzle friction is
to reduce the effective heat drop of steam as it passes over the nozzle. The velocity of
steam is reduced as it subsequently strikes the moving blades. Because of reduction of

60
velocity there will be some shock as steam strikes the blades because blade profile is
designed so that steam glides over it(for a particular steam velocity).

7.1.2 Loss of Blade Friction:

In steam turbine stage steam is supposed to glide smoothly over the moving
blades after leaving nozzles or fixed blades. In actual turbine stage during flow of steam
over moving blade, there may be number of factors causing loss of energy as given under:

i. Blade friction may incur frictional loss which is taken into account by the blade friction
factor. This friction factor largely depends on the Reynolds number, although it is defined
as the ratio of relative velocity leaving blades to the relative velocity of steam entering
blades.

ii.“Boundary layer separation” may occur due to sharp deflection of fluid within the blade
passage. Deflection results in centrifugal force which causes compression near concave
surface and the rarefaction near the convex surface of blade, thus resulting in separation
of boundary layer.

iii. Loss of energy may be due to turbulence at outlet of preceding row of nozzles due to
finite thickness of nozzle exit edge. There is mixing of steam jet leaving nozzles and
entering moving blade. Due to this transition of flow from nozzle passage to blade
passage there is formation of eddies and turbulence gets set in. This turbulence is
generally in the form of trailing vortices which keep on disappearing at high velocities.
These causes the reductions of kinetic energy delivered to blades and are called “wake
losses”. Wake losses are visible at the trailing edge of fixed blades too due to thickness of
trailing edge.

iv. Loss of energy is also there due to breakage of flow which occurs upon the
impingement of steam upon the leading edge of moving blade.

v. Loss of energy also occurs during passage of steam from one stage to other. And this
effect is same as nozzle friction. Without friction the outlet relative velocity of steam
would be same as inlet because friction cannot be avoided velocities are reduced to 90%.
As friction increases, steam expansion tends to be more irreversible.

Stage efficiency =Actual Heat Drop/Isentropic Heat Drop

7.1.3 Diaphragm Gland and Tip leakage Losses:

Steam leakage may occur across the turbine shaft and between stages. Leakage of
steam may result in availability of less work from stage as steam is not fully utilized for
producing work. Leakage occurs during flow from one stage to other stage through the
clearance space between diaphragm and shaft. Leakage also occurs across the blade tip.
Leakage across tip is not prominent in case of impulse turbine as the pressure difference
is very small. Tip leakage is prominent in reaction turbine stages.

61
 Due to this diaphragm and tip leakage effective mass flow rate for doing work
gets reduced and is consequently a loss of energy. Leakage loss can be minimized by
reducing the clearances as much as possible after providing for expansion of turbine parts
so that the metal-to-metal rubbing is avoided. Also in order to reduce leakage loss the
drum type construction is preferred to diaphragm and wheel type construction in reaction
turbines.

There are balancing holes on the discs through which steam can leak and cause
disturbances when it joins the steam coming from the nozzle. It is extremely important
therefore to maintain eccentricity to minimum during start-up and loading. On impulse
reaction machine, there is a pressure drop across each stage or blade; thus there is steam
flow around tips of all fixed and moving blades. Seals at the tips in radial and axial
directions are provided. Because of wear and tear of these seals leakage loss can amount
to about 0.55% to 1%

7.1.4 Losses due to wetness of steam:

The wetness of machine goes on increasing towards last stages of a turbine, a

given set of parameter. Condensation of steam causes wetness or formation of water
droplets on blades, which loss some mechanical work in throwing off the drops. Apart
from that severe erosion is also caused to blade tips of last stages. Generally 1% increases
in wetness causes 1% loss in efficiency.

7.1.5 Exhaust losses:

The kinetic energy of steam as it leaves the LP stage cannot be gainful employed
to do useful work, hence it is a loss.

Leaving loss = mv2/2

Where

m = mass steam flow

v = absolute velocity of steam at outlet of last rows of blades.

The loss varies as the square of velocity and velocity varies as back pressure varies.

H. Losses due to moisture:

The steam passing through the last stage of turbine has high velocity and large

moisture content. The liquid particles have lesser velocity than that of vapor particles and
hence the liquid particles obstruct the flow of vapor particles in the last stage of turbine
and therefore, a part of kinetic energy of steam is lost. If the dryness fraction of steam
falls below 0.88, the erosion and corrosion of blades can also take place.

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 7.2 External losses

7.2.1 Shaft gland leakage:

Steam leaves the Boiler and reaches the Condenser after passing through the main
valve,regulating valves, nozzles, clearance spaces between nozzles and moving blades,
diaphragm and rotating shaft etc. Further there is large pressure difference between inside
of steam turbine and the ambient and also from one location to another location across
these devices.

 Therefore steam leakage takes place through

 Main valve and regulating valve

 Seals and glands

 Spaces between nozzles and moving blades

 Spaces between diaphragm and shaft of turbine

 Space between moving blade rings and turbine casing

Leakage of steam through these is a direct loss of energy.

7.2.2 Journal and thrust bearings:

Turbine bearings are critical parts to support high speed rotation of shaft.
Generally, a loss to the tune of 1% of turbine output occurs in bearings. Although this
loss depends upon bearing load, oil viscosity, speed of shaft, bearing surface area and
film thickness etc.

7.2.3 Governor and oil pump:

Operation at reduced power but at constant speed is also permitted by the speed
governor, which throttles the steam to the nozzles as the power is reduced. Efficiency
may be improved by equipping the turbine with auxiliary steam valves that are closed for
reduced power operation. Closing these valves reduces the available nozzle area and
reduces the pressure drop across the governor valve. An auxiliary oil system pump is
used to supply oil at the start-up of the steam turbine generator. It supplies the hydraulic

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oil system required for steam turbine's main inlet steam stop valve, the governing control
valves, the bearing and seal oil systems, the relevant hydraulic relays and other
mechanisms. At a preset speed of the turbine during start-ups, a pump driven by the
turbine main shaft takes over the functions of the auxiliary system.

7.2.4 Losses due to radiation:

Radiation losses also occur in steam turbines, although they are very small
compared to other losses and may be neglected. In case of steam turbines the high
temperature steam is limited to small part of casing so losses are small. But the radiation
losses are quite significant in gas turbines. In order to prevent radiation losses the pipings,
turbine casing etc. carrying hot fluid should be well insulated.

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 CONCLUSION

The steam turbine itself is a device to convert the heat in steam to mechanical
power. The difference between the heat of steam per unit mass at the inlet to the turbine
and heat of steam per unit mass at the outlet to the turbine represents the heat which is
converted to mechanical power. Therefore, the more the conversion of heat per pound or
kilogram of steam to mechanical power gives more efficiency. Hence the steam turbine
places a vital role in the thermal power plant in achieving a greater efficiency. Steam
turbines generally operate very reliably and for lengthy periods between shutdowns for
major maintenance. During these periods however there may be slow degradation of
performance due to wear, erosion or fouling of critical components. This has a slight
detrimental effect on the overall plant efficiency but this translates in a very significant
increase in a fuel costs due to the high rate of energy conversion in a modern plant. To
optimize plant efficiency, the losses in performance need to be categorized and monitored
with a view to correcting deviations where possible.

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