Industrial Training Report on NTPC, Dadri Page 2
CONTENT
1. Acknowledgement
2. Declaration
3. Brief Introduction to project
4. NTPC- Introduction
5. Working(Coal To Electricity)
6. Thermal Power Plant
7. Main Components of plant
8. Uses of Coal Ash
9. Advantages of Ash Mound
10. Features of Ash Mound
11. Measurement of Parameters
12. Control Valves
13. Conclusion
14. References
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ACKNOWLEDGEMENT
I take this opportunity to thank Mr. Kailash Chandra (Supritendent C&I) for his valuable
guidance and support during complete internship period.
I sincerely thank to complete NTPC staff for extending all the help and cooperation during the
visit in plant.
ADITI JAIN
(8503897)
(ECE- A7)
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DECLARATION
I Aditi Jain hereby state that this final evaluation report has been submitted to Jaypee
Institute of Information Technology in partial fulfillment of the requirements of Summer
Internship Program in B. Tech program of class 2008.
The empirical information of this report is based on my experience in student internship
program. Any part of this project has not been reported or copied from any report of the
university and others.
ADITI JAIN
(8503897)
(ECE- A7)
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BRIEF INTRODUCTION TO THE PROJECT
Our Project has following objectives:-
1. To know the working of DADRI thermal plant (Stage I and Stage II).
2. To know the specifications of main components in plant.
3. To understand the control unit of plant which is based on DDCMIS (discrete digital
control monitoring and information system), under the department of computerized data
acquisition system (DAS).
4. To know the methods of measurements in control units.
NTPC:- A Brief Introduction
NTPC is one of the India's leading power generating
corporations. Established on 7th
November 1975.
NTPC is the 6th
largest in terms of thermal generation
and second most efficient in terms of capacity utilization
amongst top 10 utilities in the world.
NTPC contributes one-fourth of India's total power generation with less than one-fifth
capacity.
Its current capacity is 24249 MW. It has 13 coal based, 7 gas based and 3 joint venture
projects.
The National Capital Power Station [NCPS], DADRI, has the distinction of being the
country's only three in one project ; consisting of 840 MW of coal based units , 829 MW
gas based modules , and a 1,500 MW H.V.D.C. converter station {under the operational
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control of P.G.C.I.L. since October '93}. Besides the station has the largest switchyard in
the country with a power handling capacity of 4,500 MW.
NTPC – WORKING (COAL TO ELECTRICITY)
STEP1: COAL TO STEAM:-
Coal from the coal wagons is unloaded in the Coal Handling Plant.
This coal is transported to the coal bunkers with the help of conveyors belts. Coal is
then transported to the bowl mills by coal feeders. This coal is pulverized in the bowl
mill where it is grounded to a powder form.
The crushed coal is taken away to the furnace through coal pipes with the help of hot
and cold air mixture from PA fan (primary air fan).
Atmospheric airs, from FD fan (force draft fan) is heated in the air heaters and send to
furnace as combustion air.
Water from the boiler feed pump passes through economizer and reaches the boiler
drum.
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Due to heat and density difference the water rises up in the water wall tubes. Water is
partly converted into steam as it rises up in the furnace. This steam and water mixture
is again taken to the boiler drum where the steam is separated from water. Water
follows the same path while the steam is send to super heater for super heating.
Flue gases from the furnace are extracted by induced draft fan.
STEP2: STEAM TO MECHANICAL POWER:-
A steam pipe from the boiler conveys steam to turbine through a stop valve and
control valve.
Steam from the control valves enter the high pressure cylinder of the turbine (HPT)
where it passes through a ring of stationary blades fixed to the cylinder wall.
The steam leaving the high pressure cylinder goes back to the boiler for reheating and
returns by a further pipe to the intermediate pressure cylinder (IPT).
Finally the steam is taken to the low pressure cylinders (LPT) as the steam gives up
its heat energy to drive the turbine its temperature and pressure fall and it expands.
The turbine shaft usually rotates at 3000 revolution per minute (rpm) this speed is
determined by the frequency of the electrical system used in this country and is the
speed at which a two pole generator must be driven to generate alternating current at
a frequency of 50 cycles per seconds.
When maximum energy has been extracted from the steam it is exhausted directly to
the condenser.
From the condenser the condensate is pumped through low pressure heaters by the
extraction pump, after which its pressure is raised to boiler pressure by boiler feed
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pump. It is passing through further feed heather to the economizer and the boiler for
re-conversion to steam.
STEP3: MECHANICAL TO ELECTRICAL POWER:-
The turbine is coupled to 2-pole generator, which produce the electrical power (210
MW-typical) at a frequency of 50Hz and voltage 16.5kv (typical).
STEP4: TRANSMISSION AND DISTRIBUTION:-
Electricity is usually produced in the stator winding of large generators at about 16.5
to 25kv and is fed to terminal connection to one side of generator transformer that
steps up the voltage to 132kv, 220kv or 400kv.
From here conductors carry it to a series of three switches comprising an isolator, a
circuit breaker and another isolator.
Thermal Power Plant
Stage I of Thermal plant has 4 units each of capacity 210 MW while StageII has 2 units
of 490 MW each.
The two basic neccesities are Coal and Water. Supply of coal is from North Karanpura
Bihar (1150km from plant). Water is taken from Dehra feeder, Upper Ganga Canal.
The Water used in plant is in Demineralised Form for which separate DM plant is
established.
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Main Components of Plant
1) Boiler
2) Turbine
3) Generator
The C&I department handles the Boiler and Turbine .
Figure 2. Plant Layout
Real Time Data : Steam : 683 t/h F. Water : 668 t/h
Coal : 185.4 t/h Oil : .00 t/h
Air : 781 t/h
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BOILER
The stage I of plant has 4 units. Each unit has its own Boiler, Turbine Generator, fans etc.
arrangement. Each unit has two ID Fans, two FD Fans, two PA Fans, 6 Coal mills (4- full
load + 2- stand by), 6 Coal Feeders (4- full load + 2- stand by), 4 oil guns etc.
The height of boiler is 56m.
Figure 3. Arrangement of main Boiler
Boiler Drum: The Function of steam drum is to separate the water from the steam
generated in the furnace wall and to reduce the dissolved solid contents of he steam to
below the prescribed limit of 1 ppm. The drum is located on the upper front of boiler.
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Economiser: the purpose of economiser is to preheat the boiler feed water before it is
introduced into the steam drum by recovering heat from the flue gases leaving the boiler.
The economiser is located in the boiler rear gas pass below the rear horizontal
superheater. The economiser is continuous unfinned loop type and water flows in upward
direction and gas in the downward direction.
Super Heater: There are three stages of superheater besides the side walls and extended
sidewalls. The first stage consists of horizontal superheater of convection mixed flow
type with upper and lower banks located above economiser assembly in the rear pass.
The upper bank terminates into hanger tubes, which are connected to outlet header of the
first stage superheater. The second stage superheater consists of pendant platen which is
of radiant parallel flow type. The third stage superheater pendant spaced is of convection
parallel flow type.
The outlet temperature and pressure of the steam coming out from superheater is 540° C
and 157 Kg/Cm2 respectively for H.P. units.
Reheater : The function of reheater is to reheat the steam coming out from high pressure
turbine to a temperature of 540° C. The reheater is composed of two sections. The front
pendant section and rear pendant section.
Burners: there are total 24 pulverised coal burners for corner fired C.E. type boilers and
12 oil burners provided each in between two pulverized fuel burner.
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The pulverized coal burners are arranged in such a way that six mills supply the coal the
burners at 4 corners, of the furnace. All the nozzles of the burners are inter linked and can
be tilted as a single unit from 30° to -30°.
The oil burners are fed with heavy fuel oil till boiler load reaches to about 25%.
Igniters: There are 12 side eddy plate oil/H.E.A. igniters per boiler. The atomizing air for
ignitor is taken from plant air compressors at 7 Kg/cm2.
Boiler has 4 corners. The powdered coal is blowed from the four corners into the
chamber.
Water circulation system
Water must flow through the heat absorption surface of the boiler in order that it be
evaporated into steam. In drum type units ( natural and controlled circulation) the water is
circulated from the drum through the generating circuits and back to the drum where
steam is separated and directed to the superheater. The water leaves the drum through the
downcomers at a temperature slightly below saturation temperature. The flow through the
furnace wall is at saturation temperature. Heat absorbed in water wall is latent heat of
vaporization creating a mixture of steam and water. The ratio of the weight of water to
the weight of steam in the mixture leaving the heat absorption surfaces is called
Circulation Ratio.
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Various auxiliary equipments are shown in the figure 4.
Figure 4. Arrangement of boiler auxiliaries.
Mills: Pulverised fuel firing is a method whereby the crushed coal, generally reduces to a
fineness such that 70-80% passes through a 200 mesh sieve, is carried forward by air through
pipes directly to burners or storage bins from where it is passed to burners. When discharged into
combustion chamber, the mixture of air and coal ignites and burns in suspension.
Burner arrangement: There are twenty four pulverized coal burners arranged on the corners at
a height of 18 to 25 meters and twelve oil burners provided each in between two pulverized fuel
burners. The pulverized coal burners are arranged in such a way that six mills supply the coal to
burners at 4 corners, of the furnace, all the nozzle of the burners are inter linked and can be tilted
as a single unit from +30 deg. to -30 deg.
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The oil burners are fed with heavy fuel oil till boiler load reaches to about 25%. There are four
wind boxes fixed at 4 corners of the furnace. There are 13 nozzle in each wind box 6 for coal and
7 for air.
Turbines
The 210 MW turbine installed in our power stations is predominantly of condensing tandom
compound, three cylinder, horizontal, disc and disphragm, reheat type with nozzle governingand
regenerative system of feed water heating and is coupled directly with A.C. Generator.
Figure5: Turbine and its auxiliaries
The superheated steam from boiler is led towards H.P.T (High Pressure Turbine) which is rotates
it and cools down. This steam is reheated and passed to I.P.T (Intermediate Pressure Turbine)
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from where the left out steam goes to L.P.T (Low Pressure Turbine). The steam left from LPT
goes to condenser from where it is sent to LP Heater and then to Deaerator from where it is
again sent to Boiler.
FUELS: The Fuels required in the power plant are Coal and Oil. Oil used is of two types : LDO
(Light Diesel Oil) and HFO (High Fuel Oil). Normally, HFO is fired first in the furnace due to its
High viscosity it is not suitable in winters. So LDO is fired first in winters however LDO is
costlier than HFO.
USES OF COAL ASH:
DADRI ash has been successfully used in the following applications:
LAND FILLS
ROAD EMBANKMENTS
ROAD CONSTRUCTION
PORTLAND POZZOLONA CEMENT
BUILDING PRODUCTS
CONCRETE
Use of Dadri ash in above applications have resulted in saving in terms of m o n ey ,
co ns e r va t io n o f n a tu r a l r e so u r ce s v i z m ot he r e a r t h , l i me s to n e , coal, sand,
energy, land and water apart from reduction in CO2 emission and thus environment.
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PRESENT SENARIO IN INDIA :
65% of the total installed power generation is coalbased.
230 - 250 million MT coal is being used every year.
High ash contents vrying from 30 to 50%.
95 million MT ash generated every year.
Ash generation likely to reach 170 million MT by 2010.
Presently 65000 Acres of Land occupied by AshPonds.
The NCPS Dadri project has the unique distinction of having Asia's first 100 percent dry ash
extraction with transit ash storage silos and final storage place converted to an green ash mound
Ash can be collected in following categories:
DRY FLY ASH:-
Dry ash is collected from different rows of electrostatic precipitators. It is available in
two different grades of fineness in silos for use as resource material by different users.
BOTTOM ASH:-
Bottom ash collected from bottom of boiler and transported to hydro bins and then ash mound
for use in Road Embankment.
CONDITIONED FLY ASH: -
Conditioned fly ash is also available in Ash mound for use in Landfills and Ash Building prod
NTPC -A trend setter in the country has set up 100 % dry ash extraction cum disposal in the
form of Ash Mound at NTPC Dadri.
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Ash mound has come out as the most viable alternative for ash disposal in an economic friendly
way by minimum use of land and water.
ADVANTAGES OF ASH MOUND :
Less requirement of land only 1/3rd land requirement compared to wet disposal system.
375 acres of land is required as compared to 1000acres for installed capacity of 840 MW
at Dadri.
Only 1/50th water required in comparison to wetsystem
Eliminates leaching effect.
Separate storage of fly ash (PFA) and furnace bottomash(FBA).
Facilitates large scale utilization at later stage.
The green ash mound can be used as a useful piece of land.
FEATURES OF ASH MOUND:
Ash mound covers area of 375 acres.
Ultimate height 55 meters.
Side slope 1:4 with haulage road at 15 m interval.
Top most flat area 140 acres.
Capacity of ash storage 53 million cum.
Sufficient for running 840 MW for 40 years.
Side slopes covered with green grass and plantation of trees .
Beautiful green spot in the vicinity of power house.
Some differences in specification of Stage II compared to Stage I :
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Instead of 6 mills, we have 9 mills in stage II ( 6- full load, 3- stand by).
Five Oil Elevations in stage II compared to four in Stage I.
In Stage II pressure is 190 KSC while in Stage I it is 170 KSC.
Excitation system in Stage II is AVR (Automatic Voltage Regulator) system.
There are 10 scanners in stage II.
Control system is MAX DNA which works on commands only.
In stage I all 3 BFPs (Boiler Feed Pump) are motor driven while in stage II two are
Turbine driven (TDBFP) and one is motor driven.
Before TDBFP, Booster pump are used to increase suction pressure.
In stage I, reheated steam has temp. 540 deg C while in stage II it is 568 deg C.
In stage II circulation is done by CCP (Controlled Circulation Pump).
MEASUREMENT of PARAMETERS:
1) Temperature: Temperature can be measured by a
diverse array of sensors. All of them infer temperature by
sensing some change in a physical characteristic. The most
popular types are: thermocouples, resistive temperature detectors (RTD's)
Thermocouples
Thermocouples consist of two electrical conductors made of different metals that are joined at
one end. Changes in temperature at the measurement junction induce a change in electromotive
force (emf) between the other ends. Refer to the International Temperature Scale of 1990 (ITS-
90) for standardized tables of temperature vs thermocouple emf valves. ISA and ASTM have
designated letters for particular types of thermocouples. There are two groups, the base metal
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thermocouples J, K, T, E and N and the precious metal thermocouples R, S and B. Each type has
a characteristic emf vs temperature curve and application range. The EMF curve is very
dependant on the composition of each conductor. Type J and K are the most widley used in
industrial applications. Type J (iron vs copper-nickel(Constantan)) is versatile in that it can be
used in both oxidizing and reducing atmospheres up to 1,400°F. Iron rusts at low temperatures
where condensation can form. Type K (nickel-chromium(Chromel) vs nickelaluminum(
Alumel)) can be used up to 2,300°F in an oxidizing or inert atmosphere.
Type K thermocouples exhibit a number of instabilities and inaccuracies, particularly at higher
temperatures, changing their emf/temperature characteristics. In reducing atmospheres (lack of
oxygen) at temperatures of 1,500 to 1,750°F the positive thermoelement forms a greenish
chromic oxide, commonly known as "green rot". This causes a decrease in the electromotive
force of the thermocouple. Type K is also subject to aging when exposed to 800 to 1,200°F for a
few hours. Temperature cycling above 1,400°F and then below 700°F causes a random error due
to changes in the composition (inter-granular structure) of the conductors.
Resistive Temperature Detectors (RTD's)
RTD's contain a sensing element whose resistance changes with temperature. The sensors are
usually packaged so they can be placed into a position in the process where it can reach the same
temperature. Platinum wire or film RTD's are the most common type in use today. Platinum
RTD's are used to measure temperatures from -450 °F to 1200 °F.
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The signal transmission system can have a negative effect on the accuracy and reliability of the
temperature signal. This is true for thermocouples and RTD’s. Thermocouple signals must be
transmitted via thermocouple extension wire made from the same material as the thermocouple
elements. Use of wire materials other than the thermocouple materials will result in errors where
the ambient temperature changes. Voltage drops could also develop which would cause
additional errors.
RTD extension wire can cause an error because the resistance of the wire is added to the sensor
resistance. 3 and 4 wire RTD’s have compensating leads that can be used to eliminate the wire
resistance.
2) Pressure :
Pressure Sensors:
Figure 6: Different pressure sensors
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3) Flow : Some typical head meters are described briefly in the following:
a) Orifice: An orifice plate is a restriction with an opening smaller than the pipe
diameter which is inserted in the pipe; the typical orifice plate has a concentric, sharp
edged opening, as shown in Figure 1. Because of the smaller area the fluid velocity
increases, causing a corresponding decrease in pressure. The flow rate can be
calculated from the measured pressure drop across the orifice plate, P1-P3. The
orifice plate is the most commonly used flow sensor, but it creates a rather large non-
recoverable pressure due to the turbulence around the plate, leading to high energy
consumption (Foust, 1981).
b) Venturi Tube: The venturi tube shown in Figure 2 is similar to an orifice meter, but
it is designed to nearly eliminate boundary layer separation, and thus form drag. The
change in cross-sectional area in the venturi tube causes a pressure change between
the convergent section and the throat, and the flow rate can be determined from this
pressure drop. Although more expensive that an orifice plate; the venturi tube
introduces substantially lower non-recoverable pressure drops (Foust, 1981).
Figure 7. Venturi flow meter
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c) Flow Nozzle: A flow nozzle consists of a restriction with an elliptical contour
approach section that terminates in a cylindrical throat section. Pressure drop between
the locations one pipe diameter upstream and one-half pipe diameter downstream is
measured. Flow nozzles provide an intermediate pressure drop between orifice plates
and venturi tubes; also, they are applicable to some slurry systems.
d) Elbow meter: A differential pressure exists when a flowing fluid changes direction
due to a pipe turn or elbow, as shown in Figure 3 below. The pressure difference
results from the centrifugal force. Since pipe elbows exist in plants, the cost for these
meters is very low. However, the accuracy is very poor; there are only applied when
reproducibility is sufficient and other flow measurements would be very costly.
Figure 8. Elbow flow meter.
CONTROL VALVES
A valve is a device that regulates the flow of substances (either gases, fluidized solids, slurries or
liquids) by opening, closing , or partially obstructing various passageways.
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There are three types of valves that are used in power industries besides the handle valves. They
are:
Pneumatic Valves – they are air or gas controlled which is compressed to turn or move
them.
Hydraulic valves – they utilize oil in place of Air as oil has better compression.
Motorized valves– these valves are controlled by electric motor.
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CONCLUSION
As I have been undergoing training, I was able to know the practical application of theory what I
used to study from books. With trainings help understood that studies helps us to know things
but practical helps to apply theories for betterment of Human kind. I would like to give special
thanks to the NTPC DADRI staff for their cordial support for making the training a success.
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REFERENCES
1) www.ntpc.co.in
2) http://www.wxboiler.com/english/cpjs_1.htm
3) “Power Plant Familiarization” by Power Management Institute, Noida
4) http://www.temperatures.com`
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