SUMMER Training report AT NTPC FOR INSTRUMENTATION (kbunl)
VOCATIONAL TRAINING AT
Kanti Bijlee Utpadan Nigam Limited .
(A Joint Venture Of NTPC Ltd. & BSEB)
Kanti , Muzaffarpur.
FROM 13/04/2013 TO 12/05/2013
Submitted By ,
ELECTRONICS & INST. ENGG.
GURU NANAK INSTITUTE OF TECH.
WEST BENGAL UNIVERSITY OF TECHNOLOGY
I am highly indebted to HOD of C& I Department, all faculty members of
department for providing me an opportunity to have practical exposure at
KBUNL/MTPS Kanti (Joint venture of NTPC Ltd & BSEB)
I express my sincere thanks to Sh. S Mundle (AGM, C&I) for giving me an
opportunity to take such valuable vacational training in his department.
I also pay my sincere gratitude to Sh.J P Kushwaha (Dy. MGR,C&I) , Sh.
Anjani Kr Verma (Asst. MGR,C&I), Sh. R N Verma (Asst. MGR,C&I),
Vikas Kumravat(Asst. MGR,C&I) & Vikas Koshta(Asst. MGR,C&I) for
their continuous assistance, guidence and valuable suggestions .
Last but not the least I am also thankful to Sh. Arun Kr Singh for his
My special thanks to HR deptt for faciliating me to impart training at this
B.TECH(Electronics & Instru. Engg.)
‘VI’ th Semester
Roll No. - 14300510053
Guru Nanak Institute of Tech.
West Bengal University of tech. (Kolkata)
Any thermal power plant is converting the chemical energy of fossil
fuel (coal) into electrical energy. The process involved for this
conversion is based upon the Modified Rankine Cycle. The major
components that are used to accomplish the modified rankine cycle
Boiler feed pump,
The steam generator water walls (evaporator),
Steam generator super heaters,
Regenerative feed heaters etc.
All components of a power generating cycle are vital and critical in
operation. In Modified Rankin Cycle, the two most important aspects
that is added are reheating & regenerative heating. By reheating we used
to send the steam coming from exhaust of the turbines back to the
reheater of the boiler so that its enthalpy increases and more work can
be done by this steam the other purpose is to make steam dry so that no
harm will be done to the blades of the turbine.
In MTPS Kanti, we have three turbines in Tandem coupling namely
one H.P Turbine, one I.P Turbine & one L.P Turbine coupled with
the generator to which is synchronized with the grid to produce
electricity at 50Hz.
In all my modesty, I wish to record here that a sincere attempt has
been made for the presentation of this project report. I also trust that
this study will not only prove to be of academic interest but also will
be able to provide an insight into the area of technical management.
Sl No. Description Page-No
01 An Over View -6-
02 Process of Generation of Electricity -9-
03 Light Up Process -11-
04 Milling System -11-
05 Main Boiler Components -13-
06 Electrostatic Precipitator -17-
07 Air Heaters -17-
08 Types of Fan -18-
09 Types of Pump -19-
10 Types of Cycle -20-
11 Types of Heater -22-
12 Types of Turbine -23-
13 Flame Scanner -24-
Important Control Loops in a Thermal
15 Unit Control Desk and Panels -30-
16 References -31-
NTPC was set up in 7th
November 1975, the MAHARATNA power giant today generates
more than one fourth of the total power in the country, Ranked 5th
generating utility in the world, NTPC is the second most efficient in capacity utilization
among the top ten thermal generating companies according to a survey conducted by
Data Monitor, United kingdom. In a short span of two decades, NTPC has earned its
prime status by setting up a total generating capacity of 22,249 MW. With 19.14% of
India’s operating capacity, the company generates 26.7% of country electricity through
its 13 coal and 7 gas based power plants spread all over the country.
Today, the country needs a 10 percent sustained growth in power generation to ensure the
momentum for a 7 percent overall growth in the economy. Recognizing this, NTPC has
committed itself to achieving the status of a 30,000MW plus company by the year 2007
and 40,000MW plus company by the year 2012 and power generating capacity addition
programme of 51,000 MW (Including nuclear energy and non-conventional sources of
energy) for the tenth plan.
Super critical technology at NTPC Sipat project (3X600MW) to increase the
efficiency of the cycle and to decrease the green house gas emission.
Closed cycle seawater cooling at Simhadri project for first time in India.
Introduction of IGCC (Integrated gasified combined cycle) for clean and efficient
utilization of coal.
Liquid water treatment plants at Farakka and Kahalgaon.
Ash water recycling system at Kahalgaon and Korba to reduce water requirement for
ash disposal at these station
Salient Features Of Boiler Plant
a) Type of boiler Single drum tangential firing &
b) Type of fuel used Pulverized coal (Main Fuel)
Heavy oil & L.D.O. (for light up
& flame stabilization)
c) No. of Mills 6
d) Type of Mills Pressurized type Bowl Mill
e) Furnace Balanced draught
f) P.A. Fans 2 nos. (each 60% capacity)
g) F.D. Fans 2 nos. (each 60% capacity)
h) I.D. Fans 3 nos. (one standby)
(each 60% capacity)
i) Air Heater 2 nos.
j) Type of Air Heater Trisector regenerative
k) Electrostatic Precipitator 1 nos.
2. M.C.R. Parameter M.C.R. Value
a) S.H. Outlet Steam Flow 375 T/Hr
b) R.H. Steam Flow 331 T/Hr
c) Pressure at S.H. Outlet 141.5 Ata
d) Temp. at S.H. Outlet 540o
e) Pressure at R.H. Inlet 37 ata
f) Pressure at R.H. Outlet 32.9 ata
g) Temp. at R.H. Inlet 369o
h) Temp. at R.H. Outlet 540o
i) Pressure in Drum 148.69 ata
j) Design Pressure 158.0 kg/cm2
k) Flue Gas temp. leaving
l) Flue Gas temp. leaving
Air Heater 142o
m) Feed Water Temp. before
Salient Feature Of Turbine
a) Type Of Turbine Reheat
b) No. Of Cylinders 3 (HP,IP & LP)
c) No. Of LP Heater 5
d) No. Of HP Heater 2
e) Deaerator 1 (Variable pressure type)
f) No. Of Extraction pump 3 (one standby)
g) No. Of BFP 2 (one standby)
2. M.C.R. Parameter M.C.R. Value
a) Rated output 110 MW
b) M.S. Pressure at H.P. turbine inlet 130 ata
c) M.S. temp. at H.P. turbine inlet 535o
d) H.R.H. temp. at I.P. turbine inlet 535o
e) Turbine speed 3000 rpm
f) Condenser Vacuum 0.1 kg/cm2
g) No. of Extraction 7
h) Quantity of cooling water 15,400 m3
Salient Feature Of Generator
a) Rating Continuous
b) Active Output 110 MW
c) Rated Voltage 11000 +/- 5% V
d) Rated Current 7220 A
e) Power Factor 0.8 Lagging
f) Frequency 50 Hz
g) Excitation System Static type
h) Field Current at rated output 1335 A
i) Type of Cooling System Hydrogen Cooled
j) Hydrogen Pressure 2 ata
k) No. of H2 Cooled elements 6
l) Cooling Medium for H2 Soft water
PROCESS OF GENERATION OF ELECTRICITY
MTPS Kanti is a Thermal Power Plant. The functioning of every thermal power plant is based
on the following processes: -
1. Coal To Steam.
2. Steam To Mechanical Power
3. Power Generation, Transmission & Distribution.
Coal To Steam
Coal and Water are primary inputs to a thermal power plant.
This process of conversion of water to steam by using the heat energy
Produced by burning coal for producing heat takes place in the boiler
and its auxiliaries. Coal burns in a furnace located at the bottom
part of the boiler. Feed water is supplied to the boiler drum by boiler
feed pumps, where water is heated and converted into saturated steam
This is further superheated in the super heaters.
Steam to Mechanical Power.
This is the most important process of a power plant. The superheated
Steam produced in the boiler at high pressure and temperature is feed
to the turbine. The steam expands in the turbine giving up heat energy, which is
transformed into mechanical energy on turbine shaft. Thus,
Mechanical power is obtained from the turbine shaft.
Power Generation, transmission &
Mechanical power produced at the shaft of the turbine is used to
rotate the rotor of an electrical generator that produces electric
power. The electric power produced by the generator is boosted to a
higher voltage by a generator transformer to reduce the transmission
This power at EHV i.e. 400 kV is transmitted and distributed by EHV transmission
A generator consists of rotor which consists of carbon brushes. The rotor rotates at 3000rpm
in case of any fault if production of plants stops then we have bearing motor which rotates
shaft of turbine continuously and rotor at 65rpm. This is because if shaft doesn’t rotates then
due to load it may bend.
As generator produces 110MW or generates 11kv output. The output of generator is step up
to 220kv by using step up transformer or generating transformer. Three phase is fed to station
transformer. There are two station transformer1 and 2 which is step down transformer. Here
220kv is step down to 6.6kv for internal purpose. This 6.6kv is step down to 415v for low
rating motors. At generating transformer we are using lighting arrestor which protects G.T
from lighting. This 220kv is given to grid substation. In grid substation we are using some
protective system before distribution we have Bus isolator, SF6 breaker, Line isolator, CT,
lightning arrestor. Similarly we have two unit auxiliary transformer UAT-1 and UAT-2,
which will step down voltage from 11kv to 6.6kv and it will supply to unit auxiliary board
Similarly station transformer will supply to station board 9BA, 9BB. One unit is tie with
other unit because during the failure of any one of the unit other unit will able to supply.
LIGHT UP PROCESS
MTPS Kanti has direct firing system. In this system, a controlled quantity of crushed
coal is fed to each bowl mill (pulveriser) by its respective feeders and primary air is
supplied from the primary air fans which dries the coal as it is being pulverized and
transports the pulverized coal through the coal piping system to the coal burners.
There are six pulverisers out of which four are used and two remains in standby. The
raw coal feeders supply 74 TPH of coal to each mill.
The pulverized coal and air discharged from the coal burners is directed towards the
center of the furnace to form firing ball.There are 24 tilting, tangentially fired coal
burners fitted at the four corners of the boiler at six elevations.
The secondary air heating system supplies secondary air for combustion in the furnace
around the pulverized coal burners and through auxiliary air compartments directly
adjacent to the coal burner compartments. There are 12 air-atomizing ignitors per
boiler, which initially ignite the coal and air mixture.
Above a predictable minimum loading condition, the ignition becomes self-sustaining.
Combustion is completed as the gases spiral up in the furnace.
1. COAL BUNKER: -
These are in-process storage silos used for storing crushed coal coming from the coal
handling plant through conveyor belts.
There are six coalbunkers supplying coal to each mill and are located at top of the mills to aid
in gravity feeding of the coal. Each bunker can store coal, which can be used for 12hrs.
2. COAL FEEDER: -
The purpose of coal feeder is to transfer coal at a pre- determined rate, from coalbunker to
The coal feeder comprises two continuous chains with L sections flight bars mounted
between the chains at every fifth link .The chains runs on sprockets mounted at each end of
the feeder to given an upper strand movement towards the driven ends and a lower strand
movement in the opposite direction. The drive shaft is supported on two self aligning bearing
mounted in the Plummer block on support out side the feeder casing, shaft sealing is
achieved by the lip seals in the sealing housing and mounted in board of the bearing to abut
the feeder casing.
The tail sprocket shaft is mounted in adjustable bearing blocks adjacent to the feeder casing
with positioned which allow the feeder chain to be tensioned.
Both upper and lower strands run over full width carrying plates with the lower strands
located by angle section guides mounted on the feeder wall. The upper and lower carrying
plates and the inside wall are protected from wear by replaceable stainless steel panels,
chains are kept clean by rubber wiper.
Feeder input is achieved by roller chain drive to the conveyor via a fixed speed electric motor
driving a variable speed gear box, torque limiter and fixed out put gear box The electric
motor is flanged mounted to variable speed gear box, coupled to the fixed output gear box by
a flexible coupling and torque limiter.
The principle of operation of coal feeder is that coal flows from the bunker into the chain
feeder via feed hopper and is conveyed to the mill, when the feeder is in the operation, the
conveyor chain drag a fixed head of coal towards the driven ends of the feeder. At the end of
the carrying plates the coal falls through the conveyor onto the bottom plate, where it is
picked up by the returning flight bars and dragged back along the feeder to fall into the mill.
3. PULVERISER MILL :-
There are six mills located adjacent to the furnace at 0 m level .These mills pulverize coal to
desired fineness to be fed to the furnace for combustion .
The main structure of the pulverisering mill is fabricated from mild steel in three cylindrical
sections, the bottom section (the mill housing support )which support the entire unit and
encloses the mill drive gear unit, a center section (the mill housing)that contains the rotary
grinding element and upper section (the classifier housing )comprising an accommodate the
gas loading cylinders of the mill loading gear .A platform around the upper section provide
an access to an inspection door and to the top of the mill routine maintenance and is served
by detachable ladder .
The grinding element comprises of 3 rotatory rollers.
The raw coal enter the mill through inlet and fall into the grinding zones ,where rotating
bottom grinding and transport coal through the grinding element into the primary air stream
.The primary air enters through the inlet duct in the mill while goes to the furnace from four
outlet ducts at the top of the mill.
The ground fuel particle are picked up by the primary air stream after it is passed through the
throat plates and carried upwards towards the classifier .The larger particle are initially
carried upwards by the air stream and circulate over the upper grinding ring before falling
back into the grinding zone by virtue of their weight .The coal /air mixture then passes into
the classifier ,where any remaining oversize particle are separated out and fall down to the
return skirt until their commutative weight is sufficient to deflect the flaps and return them
into the grinding zone .
The setting of the classifier vane control the fineness of the ground product .
Heavy material such as pyrites and tramp iron which has passed through grinding zone
without being pulverized is carried around throat plate and discharged through a counter
balance relief gate into the space below the yoke .
. Main Boiler Components
The major accessories of a steam-generating unit are listed as below:
A boiler furnace is the first pass of the boiler in which fuel is burned and from which the
combustion products pass to the super heater and second pass of boiler.
The combustion process is a continuous process, which takes place in first pass of the boiler
and controlled by fuel input through coal feeders. It is a radiant type and water-cooled
furnace and enclosure is made up of water wall.
The furnace is open at the bottom to allow ash/clinkers to fall freely into the furnace bottom
ash hopper (through a ‘furnace throat’), and at the top of its rear wall, above the arch, to
allow hot gases to enter the rear gas pass.
The basic requirements that a furnace must satisfy are:
1. Proper installation, operation and maintenance of fuel burning equipment.
2. Sufficient volume for combustion requirements.
3. Adequate refractories and insulation.
The function of an economizer in a steam-generating unit is to absorb heat from the flue
gases and add this as sensible heat to the feed water before the feed water enters the
evaporative circuit of the boiler. This additional heating surface in the path of the feed water
increases the efficiency of the steam generating cycle, saving in fuel consumption, thus this
additional surface was named as ‘economizer’.
The economizer is placed in the path of the flue gases leaving the boiler, in the boiler rear
gas pass below the rear super heater.
The economizer is continuous ‘unfinned loop type’ and water flows in upward direction and
gas flows in the downward direction. Since water flow is from bottom to top so if any steam
is formed during the heat transfer it also moves along with water and prevent the lock up
steam which will cause overheating and failure of economizer tube.
A recalculation line with a stop valve and non return valve is incorporated to keep
circulation in economizer into boiler drum when there is fire in furnace but it prevents the
feed water flow into the boiler drum.
3. Boiler drum
The boiler drum is a cylindrical pressure vessel with hemispherical ends. It contains two
rows of cyclone separators, four rows of drier boxes, a perforated feed water distribution
pipe, and a chemical dosing pipe.
The boiler drum is located on the upper front of the boiler. It is suspended from roof
steelwork by two u-shaped slings.
It forms a part of the water circulation system of the boiler. The drum serves mainly two
The first and primary one is that it separates steam from the mixture of water and
steam discharged into it and to reduce the dissolved solid contents of the steam to
below the prescribed limit of 1 ppm.
Secondly, the drum houses all equipments used for purification of steam after being
separated from water. These equipments are known as ‘drum internals’.
These are the equipments, which are used to separate water from steam and to direct the flow
of water and steam to obtain an optimum distribution of drum metal temperature in boiler
operation. The drum internals consists of baffle arrangements, devices which change the
direction of flow of steam and water mixture, separators employing spinning action for
removing water from steam or steam purifiers as washers and screen dryers.
Steam output. So, the drum size is determined by the space required to accommodate the
steam separating and purifying equipments. The level of water in the stream is monitored by
control and interlock equipment.
Drum level is monitored by four level transmitters which are connected across individual
drum mounted, short-range constant head chambers.
Water level gauge is mounted on each end of the steam drum. If water level goes outside of
the prescribed operating limit then the boiler is tripped.
Transformer:- A transformer is an electrical device which works on the principle of
mutual induction. The autotransformer used in power station. It has three windings primary,
secondary and tertiary. The 220kv voltage is fed as input to primary by step down 132kv fed
MTPS as input
Down comers provide a passage for water from the boiler drum to bottom ring header. From
bottom ring header the water goes to water walls for heat absorption and conversion into
steam heating .To achieve the circulation of water into water wall Boiler circulation pumps
are provided in down comers.
Water walls are the necessary elements of the boiler. They serve as the means of heating and
evaporating the feed water supplied to the boiler from the economizers via boiler drum and
In large boilers, water walls completely cover the interior surfaces of the furnace providing
practically complete elimination of exposed refractory surface. They usually consist of
vertical tubes membrane and are connected at the top and at the bottom to headers. These
tubes receive water from the boiler drum by means of down comers connected between drum
and water walls lower header.
Water walls absorb 50 percent of the heat released by the combustion of fuel in the furnace,
which is utilized for evaporation of feed water. The mixture of water and steam is discharged
from the top of the water walls into the upper wall header and then passes through riser tubes
to the steam drum.
The design and construction of the water walls depends upon the combustion and steam
conditions and the size of the boiler.
6. Riser tubes
A riser is a tube through which the mixture of water and steam pass from an upper water wall
header to the steam drum.
The steam generated by the boiler is usually wet or at the most dry saturated because it is in
direct contact with water. So, in order to get superheated steam, a device known as
superheater has to be incorporated in the boiler.
The function of the superheater system, is to accept dry saturated steam from the steam drum
and to supply superheated steam at the specified final temperature of 540o
C, by means of a
series of heat transfer surfaces arranged within the boiler gas passes.
A superheater is a surface type heat exchanger generally located in the passage of hot flue
gases. The dry saturated steam from the boiler drum flows inside the superheater tubes and
the hot flue gases flows over the tubes and in this way its temperature is increased at the
The super heater consists of three sections classified as primary super heater, secondary super
heater and final super heater. In Kanti, there are 14 super heater coils which are divided into
above different sections where temperature is increased from approx. 340o
C to 540o
Dry saturated steam from the drum passes through the three sections of super heater,
increasing the temperature to approx. 540o
C as it travels through each section.
A reheater is a device that is incorporated in the upper arch of the boiler near the gooseneck
in the path of the outgoing flue gases. As the name indicates, it reheats the
outlet steam from the HP turbine and thus increasing its temperature up to the desired value.
The reheater accept cold reheat steam from the HP turbine exhaust and supply hot reheat
steam at the specified outlet steam temperature of 540o
C by means of heat transfer surfaces
arranged within the boiler gas passes.
The reheater consists of 2 heating coils which finally raise the temperature of the steam to the
Steam from the HP turbine exhaust enters the reheater system through two parallel mounted
spray water desuperheaters liners located in the cold reheat pipe work, then passes through
reheater, increasing the temperature as it travels through it. Reheater
outlet temperature is controlled by raising or lowering the angle of burner tilt.
When this reheated steam enters the IP turbine, the net efficiency of the cycle is increased.
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Spray water for desuperheater is taken from the boiler feed water pump discharge. In
addition, spray water regulating stations are provided further downstream in each line.
B. Reheater Desuperheater
The reheater desuperheater is only brought into use when the reheater outlet
temperature rises above the normal temperature.
The reheater desuperheater comprises of a spray nozzle shell and associated spray
nozzle assembly projecting into a section of the steam line between the HP turbine
outlet and the reheater inlet headers. This section of the steam line forms the
desuperheater shell. Water is fed into the shell from the discharge side of the boiler feed
pumps via a reheater desuperheater spray water regulating station.
When the reheater desuperheater is called into service water is fed via the water tube and
passes through the spray nozzle thereby forming a spray which attemprates the steam
passing through the desuperheater and thus decreasing the quantity of water in the boiler.
Drum is relatively small compared to the total steam output. So, the drum size is
determined by the space required to accommodate the steam separating and purifying
The ash content in the Indian coal is of the order of 30% to 40%. When coal is fired
in the boiler, ashes are liberated and about 80% of ash is carried along with the flue
gases. If this ash is allowed to atmosphere, it is hazardous to health. So, it became
necessary to incorporate an electrostatic precipitator in the path of the flue gases
going in the atmosphere. The electrostatic precipitators are preferred to mechanical
precipitators because they are capable of precipitating particles from sub micron to
large sizes of particles. The efficiency of the modern ESP’s is of the order of
The electrostatic precipitator consists of a large chamber, which comprises of
parallel rows of sheet type collecting electrodes suspended from the precipitator
casing with wire type discharge electrodes arranged mid-way between them. At the
inlet of the chamber, gas distributor screens for uniform distribution of the gases in
the chamber, are provided.
The collectors are connected to earth at positive polarity while the discharge
electrodes are connected to a high voltage dc supply at negative polarity. When
dust-laden gas flows between the electrodes, the corona discharge causes the dust
particles to become charged, the particles then being attracted towards and,
eventually, deposited on the collector electrodes.
This dust falls as the collecting electrodes are continuously rapped through a
rapping system and is collected into the pyramid type hoppers, located beneath
each collecting electrodes, from where it is removed by the ash handling system
Air heater is a heat transferring device in which air temperature is raised by
transferring heat from flue gases. Air heaters are capable of reclaiming heat from
the flue gases at low temperature levels and thus reducing the amount of heat
rejected to chimney. This results in increasing the boiler efficiency. For every 20 0
drop in flue gas exit temperature, the boiler efficiency increases by about 1%. In
MTPS Kanti, regenerative type of air heaters is mainly used. In regenerative air
heaters, the heating medium i.e. flue gases flows through a closely packed matrix
structure and then air is passed through the matrix to pickup the heat. There are two
regenerative type of main air heaters for heating up the air from fans.
TYPES OF FAN
A fan is a device by which the air is made to flow at required velocity and pressure in a
defined path imparting K.E of its impellers to air/flue gases . This pressure boost is used
to create a draught in the air and flue gas system. Fans mainly performs two functions:
i. They supply air required for combustion in the furnace with required pressure &
ii. They evacuate the product of combustion i.e. flue gases into the atmosphere via
1. P. A. FAN
The primary air fan supplies heated air to the coal mills known as primary air, to give dry
and pulverized coal to the furnace for efficient combustion. There are two P.A fans per
boiler. The fan impeller is a double inlet, centrifugal wheel with backward curved plate
Ambient air is drawn into the P.A duct by two 50% duty, motor driven centrifugal fans.
The air from each fan discharges into a hot air crossover duct via a steam air heater. This
duct extends around to each side of the boiler to supply the hot air to mills duct, both of
which are branched to supply hot air to four coal mills.
2. F.D. FAN
The forced draught fan system is provided to supply secondary air required for pulverized
coal combustion in the furnace, air for fuel oil combustion and over fire air to minimize
The F.D fan system comprises of two single stage axial flow, constant speed, and auto
variable pitch fans per boiler. These fans provide pressurized atmospheric air to the boiler
Ambient air is drawn into the secondary air system by two 50% duty, motor driven, axial
flow forced draught fans with variable pitch control. The air from each fan discharges
into a hot air crossover duct via a main air heater.
This duct extends around to each side of the boiler furnace to form two secondary air to
burners ducts. At the sides of the furnace, each duct split to supply air to two corners.
3. I.D. FAN
The induced draught fan system comprises of three centrifugal double inlet fans per
boiler, two operating and one standby. Each fan unit consists of a backward curved plate
bladed impeller, which is driven by an electric motor through a variable speed hydraulic
coupling. The I.D fan serves the purpose of evacuating the products of combustion or the
flue gases in the atmosphere via chimney. The flue gases after being cleaned in the
precipitators is directed towards the atmosphere through the chimney.
TYPES OF PUMP
1. Condensate Extraction Pump (CEP)
The function of Condensate extraction pumps is to pump out the condensate to the
deaerator through, LP heaters. The steam from the LP cylinders exhausts into the
condenser shells where it is constrained to flow across the water tubes, through which
cooling water is circulated.
The steam condensed on the tubes drain to the bottom of the shell and is collected in a
hotwell .The condensate is retained in the hotwell by means of the condenser level
control valve. The water in a condenser provides a head of water for the condensate
extraction pump to suppress cavitations in its suction impellers.
There are two 100% duty extraction pumps, one remains in duty and one remains stand
by. With all the necessary instruments such as suction and discharge valve isolating and
dump valves to insure efficient operation.
The thrust bearings in the driving motors have temperatures sensor, which can trip the
The pump discharge the condensate to the LP heater system with a pressure increased to
approx. 18 kg/sq. cm from 70-75 mm of Hg.
2. Air Extraction Pump (AEP)
The function of the air extraction pump is to raise and maintain the vacuum conditions in
the turbine main condensers, and to remove air and other non-condensable gases vented
to the condenser from various parts of the turbine and feedwater heating system.
3. Boiler Feed Pump (BFP)
Boiler feed pump is the most critical component of a power plant. It is a rotary machine,
which is coupled to a motor through variable speed coupling or turbo coupling.
Feed water is supplied to the boiler of each turbo-generator set by three 50% tandem
boiler feed water pump sets. Under normal conditions two 50% boiler feed water pump
sets are run in parallel to undertake the complete load of feeding the boiler, while the
third 50% pump set is on standby duty.
Feed water suppied to the boiler drum should have high pressure which is achieved when
passed through boiler feed pump. Whenever the pressure of water is to be raised, BFP is
The discharge pressure of a boiler feed pump is approx. 150 kg/sq. cm.
TYPES OF CYCLE
1. Steam Cycle
Drum S. H. H. P. T. R. H. I. P. T.
Condenser L. P. T.
A thermal power plant is based upon the principle of conversion of heat energy (steam
energy) into mechanical energy. For this conversion of energy a power plant requires a
A turbo machine is a power producing thermodynamic machine. It requires a suitable
working fluid, a source of high-grade energy and a sink for low-grade energy. In a
thermal power plant water is used as a working fluid and it is converted into steam.
The steam turbine is a device that converts heat energy of the steam coming from the
boiler into the mechanical energy (kinetic energy) with the help of which we rotate our
Steam is formed in the rising tubes of water walls and is collected in the upper portion of
the drum which is separated by the water in the drum by the drum internals. This steam
contains some water droplets which is to be removed before reaching turbines. This
steam is heated in superheater (primary superheater, secondary superheater & final
superheater) which makes this steam free from water droplets.
Main steam is then 1st
applied to high pressure turbine (HPT) at temp. approx. 540o
. The steam coming out from HPT has low temp. & pressure and
required to raise this temp. & pressure before applying to next turbine. Hence, it is passed
through reheater due to which its temp. & pressure is raised enough and is then applied to
intermediate pressure turbine(IPT) and steam coming out of this turbine is directly used
to rotate the final low pressure turbine(LPT).
Steam from this turbine has very low pressure & temp. and can’t be further used to rotate
the turbine. So, it is condensed and converted to water before sending to the drum for
2. Water Cycle
Hotwell C. E. P. L. P. H. Deaerator
Drum Economizer H. P. H. B. F. P.
Water cycle starts from the condenser and ends to the drum.
Steam from the LPT is condensed in the condenser while condensed steam known as
condensate is collected in a hotwell having temp. about 40o
C & pressure 70-75 mm of
Hg. The pressure of this condensate is increased to approx. 18 kg/cm2
by using CEP
while the temp. is increased to approx. 80o
C by using low pressure heater(LPH). To
remove the dissolved oxygen from condensate, deaerator is used and then it is passed
through BFP to raise its pressure approx. to the drum water. To further increase its temp.
C, it is passed through high pressure heater (HPH). Then finally before sending
it to drum its temp. is raised to approx. 250o
C by passing it through economizer. Hence,
the extra steam is condensed and reused.
3. Flue Gas Cycle
Furnace S. H. R. H. Economizer
Chimney E. S. P. A. P. H
The fuel such as coal when heated in the furnace produces smoke and ash. This smoke
produced is known as FLUE GAS whose temperature is very high and so used to heat
few systems such as superheater & reheater.
The flue gas is produced in the furnace. It then heats superheater & reheater after which it
heats economizer and air preheater (APH). Since now also its temperature is quite high
and also contains some dust hence, it is precipitated in electrostatic precipitator (ESP)
before leaving chimney.
TYPES OF HEATER
1. High Pressure Heater (HPH)
In the water cycle, temperature of feed water from BFP is increased to approx. 130oC by
heating it in HP heater. As the heating of the feed water in HP heater is done by the extra
steam coming out of the High Pressure Turbine(HPT) hence, it is named as High Pressure
2. Low Pressure Heater (LPH)
In the water cycle, temperature of condensate from CEP is raised to approx. 80oC by
heating it in LP heater. As the heating of the condensate in LP heater is done by the extra
steam coming out of the Low Pressure Turbine(LPT) hence, it is named as Low Pressure
TYPES OF TURBINE
1. HP Turbine
HP turbine is a single flow design with eight stages of blading .Each stage comprises
stationary and moving blades which are positioned into the rotor mounted on the
diaphragms, directs steam into the rotor mounted on the moving blades. H.P. turbine is
double shell construction comprising inner and outer casing. H.P steam enters the H.P.
turbine inner casing through vertical inlet connection are mounted on the top and bottom
outer casing .The steam directed through the diaphragm expands through the rotor blades
and diaphragm towards the fronts of the cylinder. The steam exhausts through the two
branches in the bottom half casing and returns to the boiler to be reheated to increase the
temperature of the steam to 538oC so that the efficiency of Rankine Cycle increases.
2. I.P. Turbine:-
Intermediate pressure turbine is a double flow design with seven stage of blading on
either side of central steam inlet. Each stage comprises stationary and moving blades
which are positioned so that the stationary blades mounted on diaphragm, directs the
steam into the rotor mounted moving blades .
Turbine is double shell construction inner casing , two diaphragm carries the ring , and
outer casing .The first 4 stage of each flow are located within the inner casing and
remaining stage within the diaphragm carries the ring .The inner casing, diaphragm
carrier ring and outer casing are made in halves bolted together in the horizontal centre.
3. L.P. Turbine:-
LP turbine is of double flow design incorporating six stages in each of its front and rear
flow paths. Each stage consist of number of stationary blades incorporating in the
diaphragm located in the casing and a set of rotating blades mounted on a rotor disc .
A spray water system design to operate automatically ,ensure that excessive temperature
are not produced in the exhaust flow during prolonged operation at low turbine load /low
ASSEMBLY OF TURBINE GENERATOR
EXCITER AND BARRING GEAR
IPT LPT 1
C A Electrical Barring Gear
Generator (15.7 KV, 3000 rpm)
Steam Condenser (3 phase, 50 Hz)
C & D :- STOP VALVES
A & B :- GOVERNING VALVE
In a flame there are three zones.
2. UV zone
The flame scanner consists of UV light sensitive tube and UV light sensitive element
filled inside the tube on which 700 DC volt is supplied.
Initially there is no contact between the two electrode on which 700 DC volt is supplied.
As there is UV light sensitive element present inside the tube, it sacns the UV zone of the
flame. When it scans the UV zone, the UV element present inside the tube conducts and
the two electrode are in contact. Now, the supplied voltage is reduced to zero. Hence,
whenever it scans the UV zone, the supplied voltage becomes 0V otherwise it is 700V.
Therefore, on an average the scanner shows 400V – 450V which confirms the presence
of flame inside the furnace.
As there are two types of fuel which are the main source of burning. Hence, basically
there are two types of flame scanners depending upon the fuel used. So, to sense the
flame due to oil used in the furnace there are oil flame scanners and to sense the flame
due to coal used are known as coal flame scanners.
There are 12 oil guns present in the four corners of the furnace in the elevations AB, CD
& EF known as oil elevations. Hence, there are 12 oil flame scanners present
corresponding to each oil guns. There are 16 coal flame scanners present inside the
furnace, four on each corners between AB, BC, DE & EF where A,B,C,D,E & F are the
coal ducts. Coal flame scanners are also known as fireball scanners.
IMPORTANT CONTROL LOOPS IN A THERMAL
Basic Block Diagram Of Any Closed Control Loop
Set Point Error
Process: The equipment whose present level, pressure and other values is to be
measured is known as process.
Set Point: The required value of parameter is set by the manual which is to be
maintained in order to protect the process from damage.
Measurement: The present value of parameter in process is measured here. Generally,
capacitance type of measurement is used.
Two tapping from the process, one at high pressure & other at low pressure, is taken and
transmitted through isolating diaphragm and silicon oil fill fluid to a sensing diaphragm
in the centre of the differential pressure cell. The sensing diaphragm deflects in response
to differential pressure. The position of the sensing diaphragm is deflected by capacitor
plates on both sides of the sensing diaphragm. The differential capacitor between the
sensing diaphragm and the capacitor plate is converted electronically to a 4-20 mA signal
and transmitted to comparator. This measurement sometimes also known as transmitter.
Comparator: It compares the signal between set point and measured value. If the two
values differ from one another, an error signal is generated and sent to the controller.
+ Controller Final Control
Controller: It is an electronic card which, according to the error signal sent by
comparator, gives a current signal between 4-20 mA to final control element.
Final Control Element: It is that portion of the loop which directly changes the
value of the manipulated process variable and finally do some work to maintain the set
point of the process.
1. Drum Level Control
Set Point Error
The required drum level is set at the set point. The present drum level is then measured
which is done by capacitor type transmitter. Two tapping, one at the bottom in water
while other at the top in steam, is made and allowed to flow to the transmitter. Since, the
two elements are in different states, steam is condensed and collected in a constant head
unit (CHU) before going to the transmitter where the present drum level is measured and
converted to current signal between 4-20 mA. This set value and measured value are
then compared in a comparator and an error signal, if any, is generated and sent to
controller which finally directs the final control element to control the drum level. Here,
the final control element is a control valve through which a fluid passes that adjusts the
size of the flow passage as directed by a signal from controller to modify the rate of flow
of the fluid. Hence, the drum level is controlled.
+ Controller Feed Water
2. D.P. Across Feed Control Station
Set Point Error
In order to maintain the linear characteristics of the feed regulating valves under different
loads, the differential pressure(D.P.) control loops maintains a fixed differential across
the regulating valves and BFP discharge pressure is varied by changing BFP motor speed
through hydraulic scoop tube device which is the final control element here. The D.P.
across feed station (comparator) is sensed and is fed to the controller. The controller are
automatically adjusted as function of steam flow to achieve stable condition. The reserve
Boiler Feed pump scoop tube automatically follows the running pump scoop tube and the
changeover to the reserve BFP takes place with the scoop tube in the same position of the
3. Combustion Control
The combustion control proposed for this boiler comprises of the following loops:
a. Master pressure control
b. Pulverized coal flow control
c. Combustion air flow control
d. Oxygen trim control
e. Mill temperature and air flow control
a. Master Pressure Control
The turbine throttle pressure which is a measure of turbine and boiler mismatch, is
maintained by proper fuel and air flow control to the burners. Actual steam pressure
at turbine inlet is measured and error against a set value is fed to the individual
pulveriser control loop through controller.
+ Controller BFP Scoop Process
b. Flue Flow Control
In order to maintain an air rich furnace, air flow demand signal is superimposed over
total fuel flow signal through a high limiter unit. This way when master demand
signal increases and if air flow is low, fuel flow is not straightaway increased.
Instead, main demand signal first increases the air flow and only when demand signal
is low as compared to air flow, tie selector unit in the fuel control loop increases the
fuel flow. When the master demand calls for a reduction of combustion, fuel flow and
air flow are reduced simultaneously with fuel flow leading air flow, thus ensuring
always an air rich furnace.
c. Combustion Air Flow Control
Total air flow signal is fed to control and this controller output adjusts the FD fan
vanes. Provision also exists to ensure a minimum air flow (30% of maximum)
through a high signal selector.
d. Oxygen Trim Control
To ensure some percentage of excess air for optimum combustion, Oxygen trim
control is employed. Oxygen contain in flue gas before air preheater is measured and
error is fed to controller. A maximum/minimum limiter is introduced so that should
the oxygen supply fall, a minimum disturbance is introduced in the flue/air control
e. Mill Temperature And Flow Control
This control loop is envisaged to maintain constant air flow to the mills and also to
maintain constant mill outlet temperature. Primary air flow and mill outlet
temperature signals are measured and fed to the controller respectively. Output of the
controllers are connected to each of the two error modules, the output of which are
going to coal and hot air dampers through respective auto manual stations. The
provision of variable air flow supply exists in the hardware supplied and shall be
adopted on site, if required.
4. Furnace Draft Control
The furnace draft is maintained by modulating the I D fan Hydraulic coupling (3
nos.). Furnace draft at combustion chamber outlet is measured and the error is fed to
the controller. Output of this controller accordingly positions the vanes to maintain
constant furnace pressure to improve the system dynamic response. An anticipator
total air flow signal is alsoadded in the loop.
5. Primary Air Header Pressure Control
A control loop always ensure sufficient PA to the pulveriser hot air duct at the set
pressure and achieves the same by modulating the PA fan vanes (2 nos.).
6. Superheat Steam Temperature Control
The superheater steam temperature control system makes use of three parameters,
secondary superheater outlet temperature, total steam flow and superheater inlet
temperature. The final superheaters temperature error is fed to controllers which
positin spray control valves left & right sides to maintain constant superheater outlet
7. Reheat Steam Temperature Control
Reheat outlet steam temperature is maintained by tilting the burner to
increase/decrease heat absorption in the reheat section of the boiler. Additional
emergency reheat spray is used to maintain temp. when burner tilts are unable to
reduce the temp. sufficiently.
Left and right reheater temp. signals are averaged and fed to controller. Controller
output is indexed with total steam flow signal and through an auto-manual station
drives nozzle tilt drive. In case of differential reheater temp. difference above
allowable limits, respective spray control valve left or right are used to bring balance
in left and right side R.H. steam temperatures.
8. BFP Minimum Flow Recirculation Control
In order to ensure safety of the pump against overheating, the minimum flow is to be
maintained when the pump flow reduces below a preset limit. This is achieved by a
reliable pneumatically operated minimum flow recirculation control valve with
built-in pressure breakdown device. The control envisaged is an on-off control, the
operation of which is initiated by a low range DP switch sensing the boiler feed pump
flow. Whenever the flow falls below 100 T/hr., the minimum circulation valve is
opened and when the flow increases above 200 T/hr., this valve is kept closed.
Indication is provided on the UCB to indicate the operator the status of this valve by
open-close position indication lamp.
9. Hotwell Level Control
Hotwell level is maintained by recirculation of the condensate after steam jet air ejector
through a level controller and split-range control valves. Any excess condensate is,
therefore, fed to the deaerator.
10. Deaerator High & Low Level Control
The deaerator low level control acts on the condenser make-up control valve to add DM
water in the hotwell and the high level control acts on the excess condensate to Unit
condensate floating tank. Two separate control loops have been provided for the above.
11. Secondary Air Damper Controls
The function of a secondary air damper control system is to distribute the secondary air
from the windbox requirements. Electronic analog control system is used for this
application. Duplicate transmitters of 4-20 mA dc output for Heavy oil and furnace/wind
box differential pressure are used to improve system availability. The 4-20 mA dc
output from the control system is converted into pneumatic signal using E/P signal
converter to position power cylinder operated dampers at all the elevations on four
corners. Electric to pneumatic (E/P) signal converters are field mounted type.
UNIT CONTROL DESK & PANELS
The operation of each unit is envisaged from the central unit control room. It is located in
the control bay at 9.0m TG floor. It is adequately illuminated and is centrally air
conditioned. For operational convenience, the control room front wall has complete glass
paneling for TG hall view and the two double doors for entry from TG hall.
The control board has a special profile with three sloping surfaces for mounting a large
facias, instruments and controls. The automatic control station and drive contrl switches
& Indications are located on the first sloping surface. The process indicators/recorders
and ammeters are mounted on the second sloping surface and the alarm annunciation
window facias are mounted on the top i.e. third sloping surface. The unit control board
are arranged in logical operating sequence from the left to right starting with (i.)Air &
Flue Gas, (ii.)Fuel oil, (iii)Bowl Mills, (iv)Steam & Feed water, (v)Regenerative System,
(vi)Turbine and (vii) Generator.
‘Modern power station practice-Volume-B.
‘ Power plant Engg.’ By P.K.NAG
Control & Instrumentation-Volumel
Operation & Maintenance Manual (MTPS)-Volume H