CHAPTER 1 1.1 INTRODUCTION Guru Nanak Dev Thermal Power Plant is a coal-based plant. The requirement of coal for four units based on specific fuel consumption of 0.60 kg / kWh. The conveying and crushing system will have the same capacity as that of the unloading system. The coal comes in as large pieces. This coal is fed to primary crushers, which reduce the size of coal pieces from 400mm to 150mm. Then the coal is sent to secondary crusher through forward conveyors where it is crushed from 150mm to 200mm as required at the mills. Then the coal is sent to boilers with the help of primary fans. The coal is burnt in the boiler. Boiler includes the pipes carrying water through them; heat produced from the combustion of coal is used to convert water in pipes into steam. This steam generated is used to run the turbine. When turbine rotates, the shaft of generator, which is mechanically coupled to the shaft of turbine, gets rotated so, three phase electric supply is produced. The basic requirements are:- Fuel (coal) ♣ Boiler ♣ Steam turbine ♣ Generator ♣ MANPREET KAUR [21302101] Page 1
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CHAPTER 1
1.1 INTRODUCTION
Guru Nanak Dev Thermal Power Plant is a coal-based plant. The requirement of coal
for four units based on specific fuel consumption of 0.60 kg / kWh. The conveying and
crushing system will have the same capacity as that of the unloading system. The coal
comes in as large pieces. This coal is fed to primary crushers, which reduce the size of
coal pieces from 400mm to 150mm. Then the coal is sent to secondary crusher through
forward conveyors where it is crushed from 150mm to 200mm as required at the mills.
Then the coal is sent to boilers with the help of primary fans. The coal is burnt in the
boiler. Boiler includes the pipes carrying water through them; heat produced from the
combustion of coal is used to convert water in pipes into steam. This steam generated is
used to run the turbine. When turbine rotates, the shaft of generator, which is
mechanically coupled to the shaft of turbine, gets rotated so, three phase electric supply is
produced.
The basic requirements are:-
♣ Fuel (coal)
♣ Boiler
♣ Steam turbine
♣ Generator
♣ Ash handling system
♣ Unit auxiliaries
MANPREET KAUR [21302101] Page 1
CHAPTER 2
2.1WORKING OF THERMAL PLANT
Coal received from collieries in the rail wagon is mechanically unloaded by Wagon
Tippler and carried by belt Conveyor System Boiler Raw Coal Bunkers after crushing in
the coal crusher. The crushed coal when not required for Raw Coal Bunker is carried to
the coal storage area through belt conveyor. The raw coal feeder regulates the quantity of
coal from coal bunker to the coal mill, where the coal is pulverized to a fine powder. The
pulverized coal is then sucked by the vapour fan and finally stored in pulverized coal
bunkers.
The pulverized coal is then pushed to boiler furnace with the help of hot air steam
supplied by primary air fan. The coal being in pulverized state gets burnt immediately in
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the boiler furnace, which is comprised of water tube wall all around through which water
circulates. The water gets converted into steam by heat released by the combustion of
fuel in the furnace. The air required for the combustion if coal is supplied by forced
draught fan. This air is however heated by the outgoing flue gases in the air heaters
before entering the furnace.
.The steam after doing the useful work in turbine is condensed to water in the
condenser for recycling in the boiler. The water is pumped to deaerator from the
condenser by the condensate extraction pumps after being heated in the low pressure
heater (L.P.H) from the deaerator, a hot water storage tank. The boiler feed pump
discharge feed water to boiler at the economizer by the hot flue gases leaving the boiler,
before entering the boiler drum to which the water walls and super heater of boiler are
connected.
2.1.1 COAL MILLING PLANT
Since G.N.D.T.P. units are primarily coal fired units so each boiler is provided with
closed milling circuits to pulverize the raw coal which is received from coal conveying
system after coal crushes before it is fired in the furnace. The necessity of pulverizing the
coal is to be ensuring its maximum possible combustion in the furnace. The coal data for
units are: -
COAL DATA UNITS 1 & 2 UNITS 3 & 4
Type of Coal
Net Calorific Value
Moisture
Ash Content
Bituminous
4300 Kcal/kg
10 %
30 %
Bituminous
4727 Kcal/Kg
7.5 %
32 %
2.2 SWITCHGEAR
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2.2.1 INTRODUCTION
The apparatus including its associated auxiliaries employed for switching, controlling and
protecting the electrical circuits and equipments is known as switchgear.
A tumbler switch, which is an ordinary fuse, is the simplest form of switchgear and is
generally used to control and protect the domestic and commercial appliances and
equipments. For high rating circuits, a high rupturing capacity (H.R.C.) fuse in
conduction with switch may serve the purpose. However, such switchgear cannot be
applied on power system operating at high voltages, i.e. more than 11 KV because of the
following reasons: -
1. When fuse blows, it takes some time to replace it and consequently there is
interruption of power supply.
2. On high voltage system, a fuse cannot successfully interrupt large fault currents.
3. When fault occurs, fault takes some time to blow. During this time the costly
equipments e.g. generators, transformers etc. may be damaged.
Therefore in order to protect lines, generators, transformers and other electrical
equipments from damage, an automatic protective device or switchgear are required.
Automatic protective switchgear mainly consists of the relays and circuit breakers. A
circuit breaker is switchgear, which can be open or close the circuit after an operation.
Therefore, a circuit breaker is rather preferred even in the instance when a fuse is
adequate
Switch: -
It makes and breaks the circuit under full load or no load condition but cannot be
operated under fault conditions. It is generally operated manually.
.
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2.2.2 Isolator: -
It is only operated under no load conditions. Its main purpose is to isolate a portion of
the circuit from the other. Isolators are generally place on the both sides of a circuit
breaker from the other in order to make repairs and maintenance on the circuit breaker
without any danger. There are two types of isolators: -
TYPES OF ISOLATER:-
Single pole Isolator
Double pole Isolator
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CHAPTER 33.1 D.C. SUPPLY SYSTEM
D.C Supply is the brain of the plant. Each unit has its own 220volts D.C system located
in the electrical bay. 48 battery of requisite rating are also being provided. Each D.C
system comprises of the following:-
1. Storage battery
2 Battery Charges
3. Distribution & sub-distribution boards
The batteries are of lead acid type. Battery cells have high discharge performance cell
types each of 2volts. Battery charge are static type & capable of trickle charging & boost
charging. Adequate standby provision is also made for the outage of the charger in the
form of installation of standby charges.
The D.C distribution & sub-station boards are compartmentalized; draw out type,
construction, housing switches & fuses for various feeders are as per the requirements for
the plant.
The battery rooms are well ventilated & well lighted & there is adequate provision for
expelling acid fumes & fumes h2 gas out from the battery room.
1. Dry cell batteries
2. Lead acid batteries
3. Alkaline cell batteries.
Lead acid cells are of further two types:-
1) Automobile battery
2) Stationary lead acid battery.
POWER REQUIREMENT
A DC source capable of delivering current as specified. The voltage required will be two
times the No. of cells in battery. The initial charging of the battery will takes approximate
55 to 90 hours.
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CHAPTER 4
4.1 BOILER SECTION
The steam generating unit is designed to meet the nominal requirements of 110MW turbo
generator set. The unit is designed for a maximum continuous rating of 375 tones/hr. at a
pressure of 139kg/cm2 and a steam temperature of 5400C. the reheated steam flows at
MCR 32H tones/hr. at the feed water temp at MCR is 2400C. The unit is a balance
draught dry bottom; single drum natural circulation, vertical water tube type, construction
with skin casing and a single reheat system. The furnace is arranged for dry ash discharge
and is fitted with burners located at the four corners. Each corner burner comprises coal,
vapour oil and secondary air compartments. The unit is provided with three ball mills and
arranged to operate with intermediate cool powder bunker. The steam super heater
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consists of 4 stages Viz. Ceiling, convection, platen and final superheated. The ceiling
super heated forms the roof of the furnace and horizontal pass and finishes as the rear
wall of the second pass. The convection super heated is made up of horizontal banks
located in the second pass. While the platens are located at the furnace exit, the portion
above the furnace nose encloses the final superheated reheated are in two stages, first
stage is the trifle heat exchangers located in the second pass, which absorbs heat from
superheated steam as well as from the flue gases. The second stage is exit reheated
located in the horizontal pass as pendant tubular loops.
(a) The flue gas for drying the cool in the mills is tapped off after the trifle heat
exchangers. The damper located in the hot flue gases pipe leading to mill controls the
quantity. Control the circulating vapour of the mill entry effect temperature control.
Immediately after the trifle heat exchanger, the air heaters and economizers are located.
The air heater is in 2 stages.
(b) The hot air for combustion from air heater stage 2 is led into the common wind box
located on the sided of the furnace. 4 cool air mixed pipes from pulverized coal bounders
are connected to 4 cool burners’ nozzle at the corners. There will be totally 16 coal
nozzles. 4 located in each corner. Oil guns will be located in the secondary air nozzle for
coal burning. The turn down ratio of the guns will be so selected that it will be possible to
use them also for pulverized fuels flame stabilization while operating under load below
the control point.
(c) Take into consideration the high % age of ash and the relatively poor quality of coal
due regards has been paid to wide pitching the tubes and to the gas velocity across the
heating surface areas. In order to insure reliable and continuous operation sample sot
blowing equipment is provided. There are short retractable steam root blowers provide at
the top of furnace fully retractable rotary type blowers are located for cleaning of the
secondary super heater and final heater partly retractable steam blowers are arranged for
the horizontal reheated and super heaters in the second pass. The steam root blowers are
electrically operated.
(d) Root blowing nozzles using blow down from boilers drum are provide for the
cleaning of areas around the burners nozzles zone for dislodging of slag boulder if any in
the bottom ash hopper in the furnace.
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(e) Two FD fans are provided per boiler. The FD fans are of the axial type driven by
constant speed motor. The regulation of quantity and pressure is done by inlet vane
control. The flue gases are sucked through the mechanical and electrostatic precipitators
by I.D. fans and delivered into the chimney. Two I.D. fans are provided for each boiler
and they are of the axial type driven by constant speed motors. Inlet vane control effects
the capacity change with reference to load. Both the I.D. and FD fans have been
dimensioned taking into account the minimum margins of 15% on volume and 32% on
pressure.
Specification
Manufacturer B.H.E.L
Maximum continuous rating 375tones/hr.
Super heater outlet pressure 139kg /cm2
Reheated outlet pressure 33.8 kg/cm2
Final super heater temperature 540 dig’s
Feed water temperature 240deg.c
Efficiency 86% (stage-1)
87% (stage-2)
Coal consumption per day 1500 tones
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CHAPTER 5
5.1TURBINE SECTION
The turbine is the prime mover for the generator in the power plant Different types of
steam turbines used in thermal power plants, but the ones. Which are used at G.N.D.T. P.
are categorized as follows
S.No. Type of Turbine Turbine at G.N.D.T.P.
1. Horizontal/vertical Horizontal
2. Single/multi cylinder Multi cylinder
3. Condensing/non condensing condensing
4. Reheat/ non-reheat Reheat
5. Regenerative/non regenerative Regenerative
6. With by pas/without bypass with by pass (stage-1)
Without bypass (stage-2)
5.2 BASIC WORKING OF TURBINE
First of all the turbine is run on gear motor with the help of exciter. At that time steam is
kept on recalculating with the help of bypass valve. When the pressure of steam is
increased to an optimum level and turbine acquires a particular rpm then steam is
introduced in the H.P. (high-pressure) cylinder first. The temperature of steam at entrance
is 540C and pressure is about 139 Kg/cm2. After doing its work on the H.P. Turbine, the
steam is taken out for reheating rated temperature of steam at reheated inlet is 360C. The
temperature of steam is increased upto 535C in the boiler shell and steam is again
introduced in M.P (Medium pressure) turbine. After M.P.turbine, the steam is passed on
to L.P. (Low-pressure) turbine. This process helps the turbine to reach the speed of 3000
rpm. After L.P. turbine, the steam is condensed in condenser, build below the turbine
unit. The condenser contains a number of brass tubes through which cooling out from
L.P. turbine it comes in contact with colder brass tubes then steam get transformed into
water. This water get collected in HOT WELL just below the condenser. From here the
hot water is again pumped with the help of condensate pumps. The cooling water is used
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to condense steam gets heated up and is cooled by falling from cooling tower. This
completes the processing of steam through turbine and condenser.
5.3 ROTOR OF TURBINE
All the rotors are manually by means of rigid coupling, including the rotors of the
generator. The speed of whole system of rotor lies in the following ranges of the speed at
the operating conditions: -
1900 to 2000 rpm Best noticed on the M.P. and L.P. rotors and generators.
2350 rpm Best noticed on H.P. rotor.
1. BEARING OF ROTORS
The axial load of the entire system of rotors is taken up by a double-sided axial bearing
located in the bearing stand between the H.P. and M.P casing. These are two protections
mounted near the axial bearing one hydro chemical and one electromagnetic, which fouls
the turboset during the non-permissible movement of the rotor.
The rotors are placed on radial bearing which are machined to elliptical shape. Further
scrapping operations or change top and side clearances and change in temperature of oil,
influence the oil wedge and the position of the journal bearing to maintain the same
condition as existed during the initial assembly.In the lower half of bearing a hollow
groove is provided in the babbit metal through which oil the supplied through a drilled
hole through H.P. jacking oil pumps.
The high-pressure oil rotors are lifted in the bearing so that any scrapping of the bearing
is prevented.
2. TURBINE CASING
The high-pressure part of turbine is consisted of two-concentric horizontal casing. Inner
casing is connected in such a way to the other casing that it enables to expand in all
direction. The nozzles are attached to the inner casing. The steam pipe is connected to the
condensers and the condensers are supported by springs. The casings are inter connected
by the system of guide keys through bearing pedestals in such a way that thermal
expansion of casing does not destroy the various parts of turbine.
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The displacement-bearing pedestal between M.P. and H.P parts is measured by the
electromagnetic pick up. This valve is about of 15 mm to prevent deformation at the
casing. It is very important that sliding part clean lubricated and free from hazard for
connecting parts bolts elements. The heating of bolts before tightening up and before the
locking presents. The flanges of M.P. and H.P. casings are designed to heat up by steam
during the starting up of turbo boost by which the difference in temperature between the
cylindrical position of the casing flanges and connected bolts is reduced to limited
deformation. The thermo couples are used for measuring temperatures. The thermo
couple is partially connected to the indicated apparatus. Cooling fluid is generally used
for reducing the temperature of various parts.
3. REGULATION AND SAFETY EQUIPMENT FOR TURBINE GOVERNING
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The quality of steam entering in the turbine is regulated by the four governing valves on
the inlet to the M.P. part. The amount of opening at any instant of these valves is
controlled by the pressure of secondary oil, which is indirectly depending on the primary
oil pressure and directly depending upon the spring force in the transformer during the
stand still and during starting of the turbo set. The pressure of primary oil is directly
depending on the speed of the set through the speed-sensing element. Operating the speed
changer or the normal speed changer can vary the tension in the spring in the transformer.
Thus make it possible to vary the speed before synchronizing. In case break down of any
equipment of the block the quick closing devices are provided in the regulation system of