Page | 1 CHAPTER 1 INTRODUCTION 1.1About NTPC NTPC Limited(also known as National Thermal Power Corporation Limited) is anIndian Central Public Sector Undertaking (CPSU) under the Ministry of Power, Government of India, engaged in the business of generation of electricity and allied activities. It is a company incorporated under the Companies Act 1956 and a "Government Company" within the meaning of the act. T he headquarters of the company is situated at New Delhi. NTPC's core business is generation and sale of electricity to state-owned power distribution companies and State Electricity Boards in India. The company also undertakes consultancy and turnkey project contracts that involve engineering, project management, construction management and operation and management of power plants. The company has also ventured into oil and gas exploration and coal mining activities. It is the largest power company in India with an electric power generating capacity of 43,803 MW . Although the company has approx. 18% of the total national capacity it contributes to over 27% of total power generation due to its focus on operating its power plants at higher efficiency levels (approx. 83% against the nationalPLF rate of 78%). It was founded byGovernment of India in 1975, which now holds 70% of its equity shares on 13 May 2015. In May 2010, NTPC was conferredMaharatna status by the Union Government of India. It is ranked 424th in in theForbes Global 2000 for 2014 The company has set a target to have an installed power generating capacity of 1,28,00 0 MW by the year 2032. The capacity will have a diversified fuel mix comprising 56% coal, 16% Gas, 11% Nuclear and 17% Renewable Energy Sources(RES) including hydro. By 2032, non-fossil fuel based generation capacity shall make up nearly 28% of NTPC‟s portfolio.
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NTPC Limited (also known as National Thermal Power Corporation Limited) is
an Indian Central Public Sector Undertaking (CPSU) under the Ministry of Power, Government
of India, engaged in the business of generation of electricity and allied activities. It is a
company incorporated under the Companies Act 1956 and a "Government Company" within
the meaning of the act. The headquarters of the company is situated at New Delhi. NTPC's
core business is generation and sale of electricity to state-owned power distributioncompanies and State Electricity Boards in India. The company also undertakes consultancy
and turnkey project contracts that involve engineering, project management, construction
management and operation and management of power plants. The company has also
ventured into oil and gas exploration and coal mining activities. It is the largest power
company in India with an electric power generating capacity of 43,803 MW . Although the
company has approx. 18% of the total national capacity it contributes to over 27% of total
power generation due to its focus on operating its power plants at higher efficiency levels
(approx. 83% against the national PLF rate of 78%).
It was founded by Government of India in 1975, which now holds 70% of its equity shares on13 May 2015.
In May 2010, NTPC was conferred Maharatna status by the Union Government of India. It is
ranked 424th in in the Forbes Global 2000 for 2014
The company has set a target to have an installed power generating capacity of 1,28,000 MW
by the year 2032. The capacity will have a diversified fuel mix comprising 56% coal, 16% Gas,
11% Nuclear and 17% Renewable Energy Sources(RES) including hydro. By 2032, non-fossil
fuel based generation capacity shall make up nearly 28% of NTPC‟s portfolio.
A coal based powerplant basically works on Rankine Cycle. Steam is produced in boiler i
exported in prime mover and is condensed in condenser to be fed into the boiler again. In
practice of good number of modifications are affected so as to have heat economy and to
increase the thermal efficiency of plant.
Many of the impracticalities associated with the Carnot cycle can be eliminated bysuperheating the steam in the boiler and condensing it completely in the condenser. The
cycle that results is the Rankine cycle, which is the ideal cycle for vapor power plants. The
ideal Rankine cycle does not involve any internal irreversibility's .
1 – 2 BFP work
2 – 3 Heating of water to convert it finally to superheated steam in boiler
3 – 4 Expansion in HP turbine
4 – 5 Reheating
5 – 6 Expansion in IP and LP turbine6 – 1 Cooling in Condenser
National Capital Power Station (NCPS) Or NTPC Dadri, is the power project to meet the
power demand of National Capital Region (India). It has a huge coal-fired thermal power plant
and a gas-fired plant and has a small township located in Uttar Pradesh, India for its
employees.
NTPC Dadri is a unique power plant of NTPC group which has both coal based thermal plant
and gas based thermal plant of 1820 MW and 817 MW respectively and 5 MW solar planttotaling 2642 MW
1.8.1 Installed Capacity
Coal basedThe coal-based station mainly meets power requirements of the National Capital Region
[NCR] , and the northern grid . With the World Bank funding component , the capital cost of
the units is Rs. 16.69 billion . There are four 210 MW coal based units and two 490MW coal
based units. The units have a coal-fired boiler and a steam turbine each . The boiler design isalso suitable for 100% operations with heavy furnace oil firing . For this , three storage tanks ,
each of capacity 15,000 kL , enough for 10 days continuous oil firing requirements have been
It is located in Gautam Budh Nagar district of Uttar Pradesh about 25 km from Ghaziabad and
about 9 km fromDadri. It is nearly 48 km from New Delhi towards Hapur. The township has an
area of about 500 acres over all. NTPC Dadri is a branch of National Thermal Power
Corporation, which is a public sector now. It is about 20km from Ghaziabad via Badalpur,
Mahawar, Bamabawar, and Akilpur Jagir.
1.8.3 Coal Source
The coal is transported from the Piparwar block of mines of the North Karanpura Coalfields of
Jharkhand , over a distance of about 1,200 kms. , by the Indian Railways bottom discharge ,
and Box 'N' type of wagons . The coal requirement for the six units is about 25000M.T. each
day. The station has its' own 14 kms. Long rail track from the Dadri Railway Statio , to the site,
and a 6 km in-plant track, on electric traction.
1.8.4 Water Source
Upper Ganga Canal Dehra Headworks, During closure of UGC through network of tube wells.The consumption of cooling water is 50 cusecs (1415.85 litres/sec).
2.2.3 Paddle FeederThese are movable elliptical feeders with paddle like structures so as to move the coal from
the bottom of the track hoppers to the conveyer belts. There are 4 paddle feeders which canmove along the bottom of the track hopper at different positions.
2.2.4 Conveyer BeltsA belt conveyor consists of two pulleys, with a continuous loop of material- the conveyor Belt
– that rotates about them. The pulleys are powered, moving the belt and the material on the
belt forward.
Conveyer belts are used in the CHP to transfer coal from one place to other as required in a
convenient & safe way. All the belts are numbered accordingly so that their function can be
easily demarcated. These belts are made of rubber & move with a speed of 250-300 m/min.
2.2.5 Safety Switches in ConveyersThere are certain switches which are used for safe operation of th conveyers used throughou
the plant.
Belt Sway Switch
These are the switches which are operated when there is sway in the conveyer belt, i.e
the belt move in a particular direction outside its fixed path. These are located on both
the sides of the belt. In case there is a sway in the belt, the switch gets activated andstop the conveyer so as to avoid accidents
Pull Cord Switch
These are the switches which are installed at every 10m gap in a conveyer belt to
ensure the safety of motors running the conveyer belts. If at any time some accident
happens or the conveyer belt is needed to be stopped immediately, then the cord is
pulled which activates the switch and stops the conveyer.
It is used as a safety device for the motor i.e. when the belt is not moving but the pulley
is rotating. This switch checks the speed of the belt & switches off the motor when
speed of the belt is zero.
2.2.6 Crusher House
After the coal is unloaded in the wagon tipplers and track hopper (size of coal=-250mm), it isconveyed to the crusher house for reducing the size of the coal upto -20mm which is the
optimum size for transfer via conveyers.
Table 2.1 – Crusher House
No. and Make of Crusher 8, Pennsylvenia, USA
Type and Size Ring Granulators, TKKGN-48093
Main Crusher Capacity 875 tonnes/hr
Motor Rating 800hp (597KW)
Power Supply 6.6kv, 3Φ, 50Hz
RPM 743
Fig 2.4 – Coal Sizes
2.2.7 Stacker cum ReclaimerIt is used for stacking (storage) of the excess coal in the coal yards. When there is a
requirement of the stored coal, reclaiming process starts and the coal is sent to the coa
bunkers through conveyer belts.
There are 3 Stacker Reclaimers at NTPC Dadri with stacking capacity of 1400tph and
reclaiming capacity of 1400tph with boom conveyer speed of 3m/s
2.2.8 Coal YardWhenever the coal bunkers are filled and there is excess crushed coal in the plant, it is stored
in the coal yard.
Capacity - 45 days coal of stagel requirement, 500000m3 of coal approx.
No. of coal piles in stockyard – 6
Length/Height of each pile - 470/10m
Water is continuously sprayed on the coal piles so as to settle the coal dust. The water also
cools the coal so as to prevent the escape of the volatile material from the coalThe coal yards of both the stages are interconnected by conveyers so as to supply coal to the
one who is in deficiency of coal at a particular time
2.2.9 Coal BunkerAfter the coal is crushed in the crusher house, it is either sent to the coal yards or directly to
the coal bunkers. These are very large coal storage containers which are placed above the
coal mills (where the coal is ground finely).
These are cylindrical in shape with conical cum hyperbolic hopper at bottom and made up o
2.2.10 Coal FeederIt is situated just below the coal bunkers. It is used to send calculated amount of coal from the
coal bunkers to the coal mills as per the requirement of the furnace. The quantity of coal fed
is controlled by controlling the speed of the conveyer inside it. Maximum and minimum
capacity of the feeder is 60MT/hr and 6MT/hr respectively2.2.11 Coal MillThe coal mills are situated just below the raw coal feeders. It’s main function i s to
pulverize the coal from -25mm size to 200mesh size. In NTPC Dadri there is a bow
type coal mill in which there is a bowl and three rollers at 120° to each other. The
bowl rotates at 50rpm and the rollers rotate about their own axis. The rollers are
pressed against the bowl using springs so as to facilitate the grinding of coal.
The coal comes in the coal mill from the top from the coal feeder through a single
pipe. After the coal is pulverized it is carried by the primary air (which enters themill from bottom towards the top) to the furnace through 4 pipes. These four
pipes carry the coal to the 4 corners of the furnace.
2.2.12 FURNACEFurnace is primary part of the boiler where the chemical energy available in the fuel is
converted into thermal energy by combustion. Furnace is designed for efficient and complete
combustion. Major factors that assist for efficient combustion are the temperature inside the
furnace and turbulence, which causes rapid mixing of fuel and air. In modern boilers, watercooled furnaces are used. The boiler fuel firing system is tangentially firing system in which
the fuel is introduced from wind nozzle located in the four corners inside the boiler. The
crushed coal from the coal crusher is transferred into the unit coalbunkers where the coal is
stored for feeding into pulverizing mill through rotary feeder. The rotary feeders feed the coa
to pulverize mill at a definite rate. Then coal burners are employed to fire the pulverized coa
along with primary air into furnace. These burners are placed in the corners of the furnace
3.2.4 DeaeraterA Deaerator is a device for air removal and used to remove dissolved gases (mainly O2 and
CO2) from boiler feed water to make it noncorrosive. A Steam generating boiler requires that
the circulating steam, condensate, and feed water should be devoid of dissolved gasesparticularly corrosive ones and dissolved or suspended solids. The gases will give rise to
corrosion of the metal. The solids will deposit on the heating surfaces giving rise to localized
heating and tube ruptures due to overheating. Under some conditions it may give rise to
stress corrosion cracking
Deaerator is a type of open feed water heater in which feedwater comes in direct contact
with the steam extracted from CRH line and IPT exhaust.
These are of three types
Spray type Deaerator
Tray type Deaerator
Spray Cum Tray type Deaerator
In NTPC Dadri, a spray cum tray type Deaerator is used. In this feedwater is first sprayed and
then made to cascade down a series of trays and bled steam flows upwards. Due to this wate
gets heated and scrubbed to release the dissolved gases.
. If operated properly, the deaerator will guarantee that oxygen in the deaerated water wil
not exceed 7 ppb by weight (0.005 cm3/L)
3.2.5 Feed Storage TankAfter the water is deaerated it is stored in the feed storage tank just below the deaerater
Feed Storage tank acts as the inlet for the Boiler Feed Pump. So it is kept about 25m above
the BFP so as to maintain a net positive suction head for the BFP so as to avoid cavitation.
Fig 3.4 – Deaerator (upper cylinder) and Feed Storage Tank (lower cylinder)
3.3 Feed Water Cycle Different Components of Feed Water Cycle
Boiler Feed Pump
High Pressure Heater
Feed Regulating Station
Economiser
Boiler Drum
Boiler
3.3.1 Boiler Feed Pump A Boiler feed water pump is a specific type of pump used to pump water into a steam boiler
The water may be freshly supplied or returning condensation of the steam produced by the
boiler. These pumps are normally high pressure units that use suction from a condensate
return system and can be of the centrifugal pump type or positive displacement type.
Construction and operation: Feed water pumps range in size up to many horsepower and the
electric motor is usually separated from the pump body by some form of mechanica
coupling. Large industrial condensate pumps may also serve as the feed water pump. In eithe
case, to force the water into the boiler, the pump must generate sufficient pressure toovercome the steam pressure developed by the boiler. This is usually accomplished through
the use of a centrifugal pump. Feed water pumps usually run intermittently and are
controlled by a float switch or other similar level-sensing device energizing the pump when it
detects a lowered liquid level in the boiler. Some pumps contain a two-stage switch. As liquid
lowers to the trigger point of the first stage, the pump is activated. If the liquid continues to
drop, (perhaps because the pump has failed, its supply has been cut off or exhausted, or its
3.3.2 Feed Regulating StationIt is the station which is used to regulate the amount of feed water into the economiser. Here
there are two lines
30% Line for the starting load
100% Line for the full load
3.3.3 EconomiserEconomiser is a mechanical device intended to reduce energy consumption, or to perform
another useful function like preheating a fluid. They are devices fitted to a boiler which save
energy by using the exhaust gases from the boiler to preheat the cold water used to fill it (thefeed water). A common application of economizer in steam power plants is to capture the
waste heat from boiler stack gases (flue gas) and transfer thus it to the boiler feed water thus
lowering the needed energy input , in turn reducing the firing rates to accomplish the rated
3.3.4 Boiler DrumSteam Drums are a regular feature of water tube boilers. It is reservoir of water/steam at the
top end of the water tubes in the water-tube boiler. They store the steam generated in the
water tubes and act as a phase separator for the steam/water mixture. The difference in
densities between hot and cold water helps in the accumulation of the hotter water and
saturated steam in drum. The separated steam is drawn out from the top section of the drumThe steam will re-enter the furnace in through a super heater, while the saturated water a
the bottom of steam drum flows down through downcomers to the ring header from where
the water sent to the boilerTable 3.5 – Boiler Drum specifications
Construction Fusion welded
Material specification SA-299
Design pressure, kg/cm2 abs. 176.4
Max. operating pressure, kg/cm2 abs. 167.2
Design temperature, 0C 354.0
Overall length of drum mm 12200
O.D. of Drum, mm 2083
Internal dia. of Drum, mm 1778
No. of distribution headers 6
Normal water level in drum 250 mm below drum centreline.
3.4.2 ReheaterReheater is a heater which is used to raise the temperature of steam which has fallen after
the expansion in High Pressure Turbine. This is done so as to increase the efficiency of the
power plant and to maintain the dryness fraction of the steam within the desired limit.Table 3.8 – Reheater Specifications
Type Spaced, single stage Max. operating pressure,kg/cm2 42.08
Design pressure, kg/cm2 50.00
Total circumferential heating suface, m2 2858
Gas flow path area, m2 118
Space between two banks in direction of gas flow,
mm
900
Mean effective length per one tube, mm 20.000
Gross length per tube, mm 22,000
Total no. of tubes 354
Acutal tube thickness O.D., mm 47.63/54.00
Tube material SA 210 Gr A1, SA 213T11, T 22
Tube pitch
(a)
Parallel to gas flow, mm
(b)
Across gas flow, mm
101.6
228.6
Method of joining long tubes Butt welded
3.4.3 Steam Lines
Main Steam Line
It is the pipeline which carries the superheated steam from the final superheater to the
HPT
Cold Reheat Line
It is the pipeline which carries the outlet steam of the HPT to the reheaters in the boile
where the temp of the steam is again brought back to 540°C at the same pressure
Hot Reheat Line
It is the pipeline which carries the reheated steam from the reheaters to the IPT
3.4.4 Condenser
These condensers are heat exchangers which convert exhaust steam from its gaseous to itsliquid state at a pressure below atmospheric pressure. This is done because handling of the
steam is more difficult and requires more power as compared to that for condensed water.
The condenser used is a shell and tube type condenser in which steam is in the shell while
cooling water is in the tubes. After condensing the steam, the cooling water gets heated up
and is sent to the cooling towers to cool it and use it again
Specifications of the condenser used in NTPC Dadri is as follows
4.1 TurbineA turbine, is a rotary mechanical device that extracts energy from a fluid flow and converts it
into useful work. A turbine is a turbomachine with at least one moving part called a rotor
assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so
that they move and impart rotational energy to the rotor. The turbine normally consists of
several stages with each stages consisting of a stationary blade (or nozzle) and a rotating
blade. Stationary blades convert the potential energy of the steam into kinetic energy and
direct the flow onto the rotating blades. The rotating blades convert the kinetic energy into
impulse and reaction forces, caused by pressure drop, which results in the rotation of theturbine shaft. The turbine shaft is connected to a generator, which produces the electrical
energy.
Here in Thermal Power Plant Superheated Steam is used as the fluid to run the turbine
4.1.1 High pressure TurbineSteam coming from Boiler directly feeds into HPT at a temperature of 540°C and at a pressure
of 156 kg/cm2. This turbine is a single flow 25 stage reaction turbine. After expansion the
temperature goes down to 352°C and pressure as 40.4 kg/cm2. The outlet of the HPT is taken
back to the reheaters in the boiler through CRH lines where the steam is again heated to
4.3 GeneratorThe generator works on the principle of electromagnetic induction. There are two
components stator and rotor. The rotor is the moving part and the stator is the stationary
part. The rotor, which has a field winding, is given a excitation through a set of 3000rpm to
give the required frequency of HZ. The rotor is cooled by Hydrogen gas, which has high hea
carrying capacity of low density. If oxygen and hydrogen get mixed then they will form very
high explosive and to prevent their combining in any way there is seal oil system. The statocooling is done by de-mineralized (DM) water through hollow conductors. Water is fed by one
end by Teflon tube. A boiler and a turbine are coupled to electric generators. Steam from the
boiler is fed to the turbine through the connecting pipe. Steam drives the turbine rotor. The
turbine rotor drives the generator rotor which turns the electromagnet within the coil of wire
conductors.
Hydrogen gas is used to cool down the rotor.
Lube oil is used to cool the bearings.
DM water is used to cool the stator.
Seal oil is used to prevent hydrogen leakage
Seal oil coolers are present to cool the seal oil
Hydrogen dryer are used which removes the moisture from hydrogen gas and then is
supplied to the generator.
Clarified water in cooling tower is used to cool down the hydrogen gas.
Table 4.2 – Stage I (210MW) Generator specifications
Make BHEL
Type THW - 201-2 Two pole, cylindrical, steam turbine
driven
Cooling Stator winding Directly water cooled
Stator core and Rotor Directly hydrogen cooled
MW rating 210
Rated terminal voltage 16.5 kv Rated terminal current 8,645 A
Rated power factor 0.85 lag
Rated speed/frequency 3000 rpm/50 HZ
Efficiency at MC Condition 98.55%
Phase connection Double star
The 210 MW generates 16.5 KV three phase electricity. The voltage is stepped up to 220 KV
with the help of station transformer and is connected to the switch yard. This electricity i
further stepped up to 400KV and then supplied to the grid
Some of the electricity is stepped down to 6.6KV with the help of Unit Auxiliary Transformer
to drive the different auxiliaries in the plant.
4.4 TransformerIt is a static machine which increases or decreases the AC voltage without changing the
frequency of the supply. It is a device that:
Transfer electric power from one circuit to another.
It accomplishes this by electromagnetic induction.
In this the two electric circuits are in mutual inductive influence of each other.It works on Faraday’s Law of Electromagnetic Induction (self or mutual induction depending
on the type of transformer).
There are two types of transformers
Station Transformer
It is the transformer which steps up the 16.5KV electricity generated by the generator
to 220KV
Unit Auxiliary Transformer
It is the transformer which steps down some of the electricity to 6.6KV so as to run the
5.2.1 Primary Air Fan (PA Fan)It is the fan which is used to carry pulverized coal from the coal mills to the furnace. The PA
Fan takes suction from the FD fan outlet from where the air is sent to the air preheaters
From APH, the heated air is sent to the coal mills. Heating of primary air is done so as toremove the moisture content from the coal so as to facilitate the combustion process.
Table 5.1 – PA Fan specifications
Manufacturer BHEL
No. per boiler Two
Type NDZV 19 HERKALES Axial double suction
radial discharge simply supported
Medium handled Clean air from FD fan discharge
Location Ground mounted on concrete floor
Orientation Top e ivery wit 45 inc ine suctionchamber.
Capacity 77.4 cu.m/sec.
Total head developed 931 mmwc
Temp. of medium 53 c
Speed 1480 rpm
5.2.2 Forced Draft Fan (FD Fan)It is the external fan provided to give sufficient air for combustion. The forced draught fan
takes air from the atmosphere and, warms it in the air preheater for better combustion and
injects it via the air nozzles on the furnace wall. This air is called secondary air.
In NTPC Dadri, a regenerative air preheater is used. Every unit consists of two air preheaters
It is of two types
Bisector Air Preheater
Trisector Preheater
Here, a trisector type preheater is used. In this the whole circular area is divided into three
sectors of 180° (for flue gas), 120° (for secondary air) and 60° (for primary air)
Fig 5.4 – Air Preheater
5.3.2 Electrostatic PrecipitatorAn Electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate device that
removes particles from a flowing gas (such as air) using the force of an induced electrostaticcharge. Electrostatic precipitators are highly efficient filtration devices, and can easily remove
fine particulate matter such as dust and smoke from the air steam. Here ESP is used to
separate ash particles from the flue gases. A DC current of 75 KV is passed through the
electrodes which ionizes the ash particles. These particles then get deposited on the
collecting electrodes. Automatic rapping systems and hopper evacuation systems remove the
collected particulate matter while on line allowing ESPs to stay in operation for years at a
5.4 Ash Handling PlantAsh handling refers to the method of collection, conveying, interim storage and load out o
various types of ash residue left over from solid fuel combustion processes. The most
common types of ash include bottom ash, fly ash and ash clinkers resulting from the
combustion of coal. Ash handling systems may employ pneumatic ash conveying o
mechanical ash conveyors. A typical pneumatic ash handling system will employ vacuum
pneumatic ash collection and ash conveying from several ash pick up stations with delivery toan ash storage silo for interim holding prior to load out and transport. Pressurized pneumatic
ash conveying may also be employed. Coarse ash material such as bottom ash is most often
crushed in clinker grinders (crushers) prior to being transported in the ash conveyor system
Very finely sized fly ash often accounts for the major portion of the material conveyed in an
ash handling system. It is collected from baghouse type dust collectors, electrostatic
precipitators and other apparatus in the flue gas processing stream.
There are two types of ash in a Power Plant:
Bottom Ash.
It refers to part of the non-combustible residues of combustion. In an industriacontext, it usually refers to coal combustion and comprises traces of combustibles
embedded in forming clinkers and sticking to hot side walls of a coal-burning furnace
during its operation. The portion of the ash that escapes up the chimney or stack is
however, referred to as fly ash. The clinkers fall by themselves into the water or
sometimes by poking manually, and get cooled.
Fly Ash
It is one of the residues generated in combustion, and comprises the fine particles that
rise with the flue gases. In an industrial context, fly ash usually refers to ash produced
during combustion of coal. Fly ash is generally captured by electrostatic precipitators oother particle filtration equipments before the flue gases reach the chimneys of coal
fired power plants.
There are basically 2 types of ash handling processes undertaken by AHP:
Dry ash system
Ash slurry system
Dry Ash System
Dry ash is required in cement factories as it can be directly added to cement. Hence the dry
ash collected in the ESP hopper is directly disposed to silos using pressure pumps. The dry ash
from these silos is transported to the required destination.
Ash Slurry System
Ash from boiler is transported to ash dump areas by means of sluicing type hydraulic system