TRANSLAM INSTITUTE OF TECHNOLOGY &

MANAGEMENT, MEERUT (U.P)

SUMMER TRAINING PROJECT REPORT

On

POWER GENERATION OF COAL BASED THERMAL POWER

PLANT

At

NATIONAL THERMAL POWER CORPORATION

LIMITED

Session: 2014-2015

Submitted by:

ISHANT GAUTAM (1232140025)

B.Tech, 4th yr., Mechanical Engineering

10 July 2015 – 06 August 2015

ACKNOWLEDGEMENT

The successful completion of project work requires efforts of several

intellectual minds. Working with NTPC DADRI has been a great learning

experience for which I would like to thank everybody who has been instrumental in

the completion of my project work.

I wish to express my deep sense of gratitude to my Guide, Mr. Rampal

Singh (DGM-BMD), for his able guidance and useful suggestions, which helped

me in completing the project work, in time.

I would like to give a special thanks to Mr. Ashish Kumar (DGM) and

Mr. Bhaskar Singh Palia for providing me the opportunity to do summer training

at NTPC DADRI.

Thanking You,

ISHANT

GAUTAM

COMPANY PROFILE

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 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 45,548 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 on 13 May 2015 (after divestment of its stake in 2004, 2010, 2013,

and 2015). In May 2010, NTPC was conferred Maharatna status by the Union

Government of India. It is ranked 431st in in the Forbes Global 2000 for 2015.

NTPC Installed Capacity

Present installed capacity of NTPC is 45,548 MW (including 6,196 MW

through JVs) comprising of 41 NTPC Stations (18 Coal based stations, 7 combined

cycle gas/liquid fuel based stations, 1 Hydro based station), 7 Joint Venture stations

(6 coal based and one gas based) and 8 renewable energy projects.

S.No. NO. OF PLANTS CAPACITY (MW)

NTPC Owned

Coal 18 34,425

Gas/Liquid Fuel 7 4,017

Hydro 1 800

Renewable energy projects 8 110

Total 34 39,352

Owned By JVs

Coal & Gas 7 6,196

Total 41 45,548

NTPC Dadri Plant

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 plant totaling 2642 MW.

1. Coal based

The coal for the power plant is sourced from Piparwar Mines, Jharkhand.

Source of water for the power plant is Upper Ganga Canal.

Stage

Unit

Number

Installed Capacity

(MW)

Date of Commissioning

1st

1

210

1991 October

2

210

1992 December

3

210

1993 March

4

210

1994 March

2nd

5

490

2010 January

6

490

2010 July

Total

Six

1820

2. Gas based

The gas for the power plant is sourced from GAIL HBJ Pipeline, it also supports

HSD as alternate fuel. Source of water for the power plant is Upper Ganga Canal.

Stage

Unit

Number

Installed Capacity

(MW)

Date of

Commissioning

GT / ST

1st

1

130.19

1992 March

GT

2

130.19

1992 May

GT

3

130.19

1992 June

GT

4

130.19

1992 November

GT

5

154.51

1993 February

ST

6

154.51

1993 March

ST

Total

Six

829.78

3. Solar plant

The total project capital cost is put at Rs. 48.59 crore. Wipro limited has designed

the project over 27 acres of land within the premises of existing NTPC Dadri plant.

GRAND TOTAL CAPACITY OF NTPC DADRI = 2642 MW

Vision:

COMPANY’S VISION AND MISSION

To be the world’s largest and best power producer, powering India’s growth.

Mission:

Develop and provide reliable power, related products and services at competitive

prices, integrating multiple energy sources with innovative and ecofriendly

technologies and contribute to society.

Core Values – BE COMMITTED

• B- Business Ethics

• E- Environmentally & Economically Sustainable

• C- Customer Focus

• O- Organisational & Professional Pride

• M- Mutual Respect & Trust

• M- Motivating Self & others

• I- Innovation & Speed

• T- Total Quality for Excellence

• T- Transparent & Respected Organisation

• E- Enterprising

• D- Devoted

LAYOUT OF A TYPICAL COAL FIRED THERMAL POWER

STATION

Following are the basic components of a coal fired thermal power station :-

1. Coal stockpile

2. Coal conveyer

3. Work shop

4. Coal hopper

5. Pulverized fuel mill

6. Boiler

7. Flue gas cleaning

8. Stack

9. Steam turbine

10. Generator

11. Transformer

12. Steam condenser

13. Cooling unit

14. Electrical grid

BASIC WORKING OF A THERMAL POWER PLANT

Fig. Coal fired thermal power plant

Firstly, water is taken into the boiler from a water source. The boiler is

heated with the help of coal. The increase in temperature helps in the transformation

of water into steam. The steam generated in the boiler is sent through a steam turbine.

The turbine has blades that rotate when high velocity steam flows across them. This

rotation of turbine blades is used to generate electricity. A generator is connected to

the steam turbine. When the turbine turns, electricity is generated and given as output

by the generator, which is then supplied to the consumers through high-voltage

power lines.

The coal is brought and crushed to powder. This is feed to boiler for producing

heat .

In Boiler the water is converted to steam.

In Superheater the moisture content is removed from the steam and that

steam is called super heated steam.

The superheated steam rotates the shaft of the High Pressure(HP) turbine.

The exhausted steam is sent to Reheater and the steam then rotates the

Intermediate Pressure (IP) turbine.

The steam from the IP Turbine is then feed to Low Pressure(LP) turbine.

The turbine shaft is connected to the Generator, which produces electric

power.

The steam expanded in turbine is condensed in a Condenser to be feed into

the boiler again.

BASIC POWER PLANT CYCLE

The basic principle of the working of a thermal power plant is quite simple.

The fuel used in the plant is burned in the boiler, and the heat thus generated is used

to boil water which is circulated through several tubes, and the steam that is

generated is then used to drive a turbine, which in turn is coupled with a generator,

which then produces electricity.

The working of the coal based plant is based upon a modified Rankine

cycle. The Rankine cycle is represented most commonly on a temperature-entropy

diagram. The topmost point is known as Critical point.

MAJOR SUB-SYSTEMS OF A POWER PLANT

1. COAL HANDLING PLANT (C.H.P.) :-

Coal Handling Plant is the place where processing of raw coal occurs

before it is transferred to the bunkers. CHP enhances the calorific value of coal and

makes its transportation cost lower and easier. The coal is provided by the Deepika

mines under the S.E.C.L, with the help of a dedicated merry-go-round (MGR).When

the coal is supplied at the CHP, the coal is moved along the track hopper towards

the crusher, where the lumps of coal are crushed into 20 mm sized particles, from

where they may be stored in the stack-yard, or sent to the bunkers before being fed

into the boilers.

Salient Features of CHP Stage-I :

• Conveyor Capacity – 2000/2600MTPH

• Conveyor Width – 1600 mm

• Paddle Feeder cap- 1500MTPH

• Crusher Capacity- 1250MTPH

• SR Capacity-2000mtph

• Inter Connection Between ST-1&ST-2

PLC Based Operation

Salient Features of CHP Stage-II :

• Conveyor Capacity – 2600 MTPH

• Conveyor Width - 1800 mm

• Conveyor Speed – 3.2 m/sec

• Paddle Feeder capacity- 1950 MTPH

• VGF Capacity – 1625 MTPH

• Crusher Capacity – 1625 MTPH

• STACKER /RECLAIMER Capacity- 2600MTPH

• CCTV compatible to integrated FIRE ALARM SYSTEM

• PLC Based Operation

• Lifts at Crusher House & TP19

• Inter Connection between ST-1&ST-2

MILL:-

The coal particles are ground into finer sized granules. The coal which is

stored in the bunker is sent into the mill, which is primarily a ball type, in which a

drum contains a ball, and when the drum rotates the ball also does, and this causes

the coal particles caught in between to be ground.

After grinding, the coal is then passed through a desired size of mesh, so that

any coal particle not properly ground is not allowed through. Then the coal is forced

by a blast of air coming from the primary air fans to enter the boiler. Coal is fed to

the mills from the bunkers via the raw coal feeders.

Another type of mill is the ball and race mill, in which the coal passes between

the rotating elements again and again until it has been pulverized to the desired

degree of fineness. However, there is greater wear in this mill as compared to other

pulverizers. There are 10 mills located adjacent to the furnace. These mills pulverise

coal to the desired fineness to be fed to the furnace for combustion. Capacity of 1

mill is 62.9 tonnes/hr.

Factors affecting bowl mill performance:-

• Size of raw coal

• Raw coal grindability

• Raw coal moisture content

• Pulverized fuel fineness

• Mill internals wear and poor quality of raw coals.

Mill drive system mainly consists of three components namely mill motor,

mill coupling and mill gear box. Mill coupling comprises of Bibby coupling (present

on the motor side) and gear coupling (present on the gear box side). In a bowl mill,

the major grinding element grinding roll is conical in shape and is three in number

per mill.

INTERIOR OF BOWL MILL

2. WATER TREATMENT PLANT:

Since water is the basic requirement for the production of the working

substance, it is necessary to have an arrangement to provide water which is not

contaminated by unwanted materials. For this a water treatment unit is provided

which receives water from a source, then demineralizes it and finally after further

treatment, is fed into a boiler feed pump. This is a unit which consumes relatively

low power compared to other units in a power plant. Some of the systems involved

in the treatment of water are de-mineralization plant, raw water pump house,

clarification plant and many others. The type of water used is different for different

purposes.

The process of cooling requires raw water, whereas steam formation, and

many other major processes require de-mineralized water. De-mineralization plants

consist of cation, anion and mixed bed exchangers. The final water from this stage

consists of hydrogen ions and hydroxyl ions which is the chemical composition of

pure water.

3.BOILER:

A boiler is the central component of a power plant, and it is the unit where the steam required for driving the turbine is generated. The heat absorbing parts subject to internal pressure in a boiler are called as pressure parts. The main pressure parts in a boiler are Drums, Water walls, Super heaters, Re heaters, Economisers and valves & fittings. The Drum, Down comers, water wall headers and water walls forms the circulation system and cover the furnace zone. The components of Boiler and their functions are as follows :-

a) Boiler Drum : The drum provides the necessary space for locating the steam

separating equipment for separation of steam from mixture of steam and water. It

also serves as a reservoir for the supply of water to circulation system to avoid

possible starvation during operation. The drum is filled with water coming from the

economizer, from where it is brought down with the help of down-comer tubes,

entering the bottom ring headers. From there they enter the riser, which carries the

water (which now is a liquid-vapor mixture), back to the drum. Now, the steam is

sent to be superheated.

For a 660 MW plant, the boiler does not employ any drum; instead the water and

steam go directly into the super heater.

Drum is located at 78 m elevation in the boiler front. Water enters the drum from the

bottom via three ECO links. Drum has connections for Chemical dozing, Emergency

drain, Continuous blow down & sample cooler tapping. Total 5 no. of vents and 6

no of safety valves, 3 on each side are provided on the drum. Total 18 MTM

thermocouples, 6 no of level transmitters, 3 pressure transmitters and 3 pressure

indicators are provided on the drum. There are 2 no of Electronic Water Level

Indicators (EWLI) and 1 no of Direct Water Level Gauge (DWLG) provided on each

side of the drum.

b) Economiser : The economizer is a tube-shaped structure which contains water

from the boiler

feed pump. This water is heated up by the hot flue gases which pass through the

economizer layout, which then enters the drum. The economizer is usually placed

below the second pass of the boiler. As the flue gases are being constantly produced

due to the combustion of coal, the water in the economizer is being continuously

being heated up, resulting in the formation of steam to a partial extent. Feedwater

(FW) from Feed Regulating Station (FRS) with parameters P=200.2 ksc, T=255.2 C

travels to Economiser inlet header located at Elevation 44.2m through ECO feed

line. ECO feed line connects to the ECO inlet header at the right side of boiler

backpass. One NRV and motorised ECO stop valve is provided in the ECO feed line

just before it connects to the ECO inlet header. One no of drain is also provided in

the ECO feed line just after the ECO stop valve. The drain is connected to the water

wall (WW) drain header located at „0‟ meter. One no of ECO recirculation line is

provided after the ECO stop valve which connects to the rear ring header.

ECO inlet header:- It is arranged parallel to the drum at the bottom of backpass

middle at the elevation 44.2m. One no of drain is provided in the header. The drain

is connected to the WW drain header.192 x 3 loose tubes connect the ECO inlet

header to the ECO lower assembly.

ECO outlet header:- Located at the Elevation 57.5m, it is arranged parallel to the

drum in backpass. Two links from ECO outlet header project out from back pass

side walls and join again at the boiler front at 66.5m elevation. From this junction

three pipes carry feed water to the drum.

c) CC Pumps:- Six no. of Downcomers carry feedwater(FW) from drum to suction manifold of

CC Pumps located at 29.5m elevation. 3 no. of suction spool pieces carry FW from suction manifold to the 3 no. of CC Pumps located at 23.3m elevation. The pumps are of double discharge type. Parameters at the pump: P=197.4 ksc, 359.1 C and flow/pump= 3135 cu.m/hr. Connections to the pump include HP fill and purge lines, LP coolant lines. Inter tie line connecting discharges of all pumps. One equalising line from the center pump suction connects to the intertie line. Two no of coolers are also provided: HP Fill and Purge Cooler and LP Cooler for

motor.

Source of HP fill & Purge is from 1. Feed line (for periodic use) 2. From

Condensate system (low pressure fill source).

Source of LP coolant supply: 1. Normal supply 2. From Emergency tank

d) Bottom Ring Header:- The 6 no. of CC pump discharge lines carry FW to the bottom ring

header located at 10.6m. Ring header is provided with one no of blow off line from front ring header which is connected to the IBD Tank. One no of drain is also provided from the rear ring header which is connected to the WW drain header. ECO recirculation line also connects to the rear ring header.

e) Water walls:- 331 tubes each from front & rear ring headers form the front, rear and corner

water walls. There are 25 tubes in each corner wall & 281 tubes in front and rear water walls each. Front water wall is integral with the corners 1 & 4 and rear wall is integral with the corners 2 & 3. Each side water wall (Left & Right) has 224 tubes. All water wall tubes are rifled from inside except the „S‟ panel tubes. Total no of tubes originating from Bottom ring header = 331x2 + 224x2 = 1110.

In a 500 MW unit, the water walls are of the vertical type, and have rifled tubing

while in 600 MW, the water walls are spiral type and have smooth tubing.

f) De-aerator: A de-aerator is a device that is widely used for the removal of air

and other dissolved gases from the feedwater to steam-generating boilers.

There are two basic types of deaerators, the tray-type and the spray-type

g) Super-Heaters: Super-heaters are used to raise the steam temperature above

the saturation temperature by absorbing heat from flue gas to increase the cycle

efficiency.

Super heating takes place in three stages. In the first stage, the steam is

sent to a simple super heater, known as the low temperature super heater, after which

the second stage consists of several divisional panels. The final stage involves

further heating in a Platen super heater, after which the steam is released for driving

the turbine. After the HP stage of the turbine the steam is re-heated and then again

released.

Superheating is done to increase the dryness fraction of the exiting steam.

This is because if the dryness fraction is low, as is the case with saturated steam, the

presence of moisture can cause corrosion of the blades of the turbine. Super heated

steam also has several merits such as increased working capacity, ability to increase

the plant efficiency, lesser erosion and so on. It is also of interest to know that while

the super heater increases the temperature of the steam, it does not change the

pressure. There are different stages of superheaters besides the sidewalls and

extended sidewalls. The first stage consists of LTSH(low temperature superheater),

which is conventional mixed type with upper & lower banks above the economiser

assembly in rear pass. The other is Divisional Panel Superheater which is hanging

above in the first pass of the boiler above the furnace. The third stage is the Platen

Superheater from where the steam goes into the HP turbine through the main steam

line. The outlet temperature & pressure of the steam coming out from the superheater

is 540 degrees Celsius & 157 kg/cm2.

4. TURBINES :

The turbine employed in a thermal power plant is a steam turbine. The initial

steam is admitted ahead of the blading via two main stop and control valve

combinations. The turbine unit of any thermal power plant is not a single stage

operation, rather it consists of three stages:

High Pressure Turbine Stage (HPT Stage): This stage takes place immediately

after the Platen super heater stage. This is the first stage of the turbine operation. Its

outer casing is of a barrel type and has neither a radial nor an axial flange. The inner

casing is axially split and supported so as to be free to move in response to thermal

expansion.

Intermediate Pressure Turbine Stage (IPT Stage): After the HPT stage, the steam

gets saturated and, consequently, gets cooled. It is, therefore, first sent back to the

boiler unit to be reheated, after which it is sent to the IPT stage. Its section is of

double flow construction with horizontally split casings.

Low Pressure Turbine Stage (LPT Stage): After the IPT, the steam gets cooled to

an intermediate extent, thus directly entering the LPT, where it gets saturated. Its

casing is of the three-shell design. After this stage the water enters the condenser,

which is connected to a condensate extraction pump.

A turbine assembly consists of a rotor assembly on whose circumference is attached

a series of vanes, a bearing assembly to support the shaft, a metallic casing

surrounding the blades, nozzle, rotor etc, a governor to control the speed and a

lubrication system.

The shaft of the turbine is connected to the generator. The purpose of the generator

is to convert the mechanical shaft energy it receives from the turbine into electrical

energy. Steam turbine driven AC synchronous generators (alternators) are of two or

four pole designs. These are three phase machines offering economic advantages in

generation and transmission. Large generators have cylindrical rotors with minimum

heat dissipation surface and so they have forced ventilation to remove the heat. Such

generators generally use an enclosed system with air or hydrogen coolant. The gas

picks up the heat from the generator and gives it up to the circulating water in the

heat exchanger.

Every turbine, except the LPT, has a stop valve and a regulating valve attached to it.

The stop valve is used to stop the flow of steam, whenever required, whereas the

regulating valve is also a kind of a flow controlling device. Each turbine also has an

inlet and an outlet pipe for the steam to enter and exit, respectively. Between the

HPT-IPT combine and the IPT-LPT combine is attached a bearing assembly. It is

constructed using a cross around pipe.

After the steam leaves the turbine, it enters the condenser . The condenser is meant

to receive the steam from the turbine, condense it and to maintain a pressure at the

exhaust lower than the atmospheric pressure. The condenser is an important unit and

some of the auxiliaries required for it to function properly are the cooling water

supply pump, the condensate extraction pump, feed water pump and the air removal

pump.

Fig. Schematic diagram of turbine

5. ASH HANDLING & DISPOSAL:

There are two types of ash handling methods: dry ash handling and wet ash handling.

Dry ash handling is carried out by storing the ash deposited in large pits, whereas in

the wet ash handling method, the ash is deposited into large reservoirs or ponds.

1.Wet mode:--Ash evacuated from ESP hoppers through vacuum pumps & fed to wetting head (vacuum system) and collector tank units where ash is mixed with water & resultant slurry is discharged to slurry trenches. 2.Dry mode:--Ash evacuated from ESP hoppers through vacuum pumps & collected in Buffer hoppers & Air lock tank, is transported to storage silo by compressed air (pressure conveying system) through pressure conveying pipe lines.

Components of wet fly ash system

1. ESP hopper

2. Plate valve for isolation . 3. Material Handling Valve (MHV)

4. Piping up to wetting head

5. Wetting head

6. Air washer 7. Vacuum pump

Auxiliaries in a power plant

1) PA FANS: The primary air fans are used to carry the pulverized coal particles from the mills to the boiler. They are also used to maintain the coal-air temperature. The specifications of the PA fan used at the plant under investigation are: axial flow, double stage, reaction fan.

The PA fan circuit consists of:

a) Primary air path through cold air duct b) Air pre-heater c) Hot air duct d) Mills

The model no. of the PA fan used at NTPC Sipat is AP2 20/12, where A refers

to the fact that it is an axial flow fan, P refers to the fan being progressive, 2 refers

to the fan involving two stages, and the numbers 20 and 12 refer to the distances in

decimeters from the centre of the shaft to the tip of the impeller and the base of the

impeller, respectively. A PA fan uses 0.72% of plant load for a 500 MW plant.

2) FD FANS: The forced draft fans, also known as the secondary air fans are used to provide the secondary air required for combustion, and to maintain the wind box differential pressure. Specifications of the FD fans are: axial flow, single stage, impulse fan.

The FD fan circuit consists of:

a) Secondary air path through cold air duct b) Air pre-heater c) Hot air duct d) Wind box

The model no. of the FD fan used at NTPC Sipat is AP1 26/16, where the

nomenclature has been described above. FD fans use 0.36% of plant load for a 500

MW plant.

3) ID FANS: An induced fan circuit consists of a) Flue gas through water walls b) Super heater c) Re-heater d) Platen super heater e) Low temperature super heater f) Air pre-heater g) Electrostatic precipitator

The main purpose of an ID fan is to suck the flue gas through all the above mentioned

equipments and to maintain the furnace pressure. ID fans use 1.41% of plant load

for a 500 MW plant.

4) SCANNER AIR FAN: Scanner air fan is used to provide air to the scanner. For a tangentially fired boiler, the vital thing is to maintain a stable ball of flame at the centre. A scanner is used to detect the flame, to see whether it is proper and stable. The fan is used to provide air to the scanner, and it is a crucial component which prevents the boiler from tripping

5) SEAL AIR FAN: The seal air fan is used near the mill to prevent the loss of any heat from the coal which is in a pulverized state and to protect the bearings from coal particle deposition.

6) AIR PRE-HEATERS: Air pre-heaters are used to take heat from the flue gases and transfer it to the incoming air. They are of two types: a) Regenerative b) Recuperative

The APH used at NTPC DADRI is a Ljungstrom regenerative type APH. A

regenerative type air preheater absorbs waste heat from flue gas and transfers this

heat to the incoming cold air by means of continuously rotating heat transfer

elements of specially formed metal sheets. A bi-sector APH preheats the combustion

air. Thousands of these high efficiency elements are spaced and compactly arranged

within sector shaped compartments of a radially divided cylindrical shell called the

rotor. The housing surrounding the rotor is provided with duct connections at both

ends, and is adequately sealed by radial and axial sealing members forming an air

passage through one half of the APH and a gas passage through the other.

As the rotor slowly revolves the elements alternately pass through the air and gas

passages; heat is absorbed by the element surfaces passing through the hot gas

stream, then as the same surfaces pass through the air stream, they release the heat

to increase the temperature of the combustion of process air.

A single APH is divided into 4 parts: 2 PAPHs and 2 SAPHs. The P and S refer to

primary and secondary respectively. Each part is divided into two slots, one slot

carrying the primary/secondary air, and the other slot carrying the hot flue gases

coming from the 2nd pass of the boiler. The PAPH is connected to the mills, whereas

the SAPH is connected to a wind box.

7) ELECTROSTATIC PRECIPITATORS: They are used to separate the ash

particles from the flue gases. In this the flue gas is allowed into the ESP, where there

are several metallic plates

placed at a certain distance

from each other. When

these gases enter, a very

high potential difference is

applied, which causes the

gas particles to ionize and

stick to the plates, whereas

the ash particles fall down

and are collected in a

hopper attached to the

bottom of the ESP. The flue

gas is allowed to cool down and is then released to the ID fan to be sent to the

chimney. Indian coal contains about 30% of ash. The hourly consumption of coal of

a 200 MW unit is about 110 tons. With this, the hourly production of ash will be 33

tons. If such large amount of ash is discharge in atmosphere, it will create heavy air

pollution thereby resulting health hazards. Hence it is necessary to precipitate dust

and ash of the flue gases. Precipitation of ash has another advantage too. It protects

the wear and erosion of ID fan. To achieve the above objectives, Electrostatic

Precipitator (ESP) is used. As they are efficient in precipitating particle form

submicron to large size they are preferred to mechanical precipitation.

Construction

An ESP has series of collecting and emitting electrons in a chamber collecting electrodes are steel plates while emitting electrodes are thin wire of 2.5mm diameter and helical form. Entire ESP is a hanging structure hence the electrodes are hung on shock bars in an alternative manner. It has a series of rapping hammer mounted on a single shaft device by a motor with the help of a gear box at a speed of 1.2 rpm. At the inlet of the chamber there are distributor screens that

distributes the gas uniformly throughout the chamber. There are transformer and rectifiers located at the roof of chamber. Hopper and flushing system form the base of chamber.

Working

Flue gases enter the chamber through distributor screen and get uniformly distributed. High voltage of about 40 to 70 KV form the transformer is fed to rectifier. Here ac is converted to dc. The negative polarity of this dc is applied across the emitting electrode while the positive polarity is applied across the collecting electrodes. This high voltage produces corona effect negative (–ve) ions from emitting electrode move to collecting electrode. During their motion, they collide with ash particles and transfer their charge. On gaining this charge, ash particles too move to collecting electrode and stock to them. Similar is the case with positive (+ve) ions that moves in opposite direction. The rapping hammers hit the shock bars periodically and dislodge the collected dust from it. This dust fall into hopper and passes to flushing system. Here it is mixed with water to form slurry which is passed to AHP.

Efficiency of ESP is approximately 99.8%.

Theory of Precipitation

Electrostatic precipitation removes particles from the exhaust gas stream of

Boiler combustion process. Six activities typically take place:

Ionization - Charging of particles

Migration - Transporting the charged particles to the collecting surfaces

Collection - Precipitation of the charged particles onto the collecting

surfaces

Charge Dissipation - Neutralizing the charged particles on the collecting

surfaces

Particle Dislodging - Removing the particles from the collecting surface

to the hopper

Particle Removal - Conveying the particles from the hopper to a

disposal point

The ash produced on the combustion of coal is collected by ESP. This ash is

now required to be disposed off. This purpose of ash disposal is solved by Ash

Handling Plant (AHP).

8) CONDENSATE EXTRACTION PUMP: The condensate extraction pump (CEP) is a centrifugal, vertical pump, consisting of the pump body, the can, the distributor housing and the driver lantern. A rising main of length depending upon NPSH available, is also provided. The pump body is arranged vertically in the can and is attached to the distributor body with the rising main. The rotor is guided in bearings lubricated by the fluid pumped, is suspended from the support bearing, which is located in the bearing pedestal in the driver lantern. The shaft exit in the driver lantern is sealed off by one packed stuffing box.

Casing

It is split on right to the shaft and consists of suction rings and 4 no. of guide vane housing. Casing components are bolted together and sealed off from one another by 'O' rings. For internal sealing of individual stages, the casing components are provided with exchangeable casing wear rings in the arc of impeller necks. In each guide vane casing, a bearing bush is installed to guide the shaft of pump.

Rotor

The pump impellers are radially fixed on the shaft by keys. The impellers are fixed in position axially by the bearing sleeves and are attached to the shaft by means of impeller nut. Impellers are single entry type, semi-axial and hydraulically balanced by means of balance holes in the shroud and throttle sections at suction and discharge side. A thrust bearing located in the motor stool absorbs residual axial thrusts.

Bearings

In each guide vane housing the shaft is guided by a plain bearing. These bearings do not absorb any axial forces. Pump bearings consist of bearing sleeve, rotating with the shaft and bearing bush, mounted in guide vane housing. The intermediate shaft is guided in bearing spider and shaft sleeve. The arrangement of bearing corresponds to the bearings of pump shaft. They are lubricated by condensate itself. A combined thrust and radial bearing is installed as support bearing to absorb residual thrust. Axial load is transmitted to the distributor casing via the thrust bearing plate, the thrust bearing and bearing housing. A radial bearing attached to the bearing is installed in an enclosed housing and is splash lubricated by oil filled in the enclosure. Built-in cooling coils in the bath and cooling water control oil temperature.

9) BOILER FEED PUMP: The auxiliary component which consumes the maximum amount of power earmarked for such purposes is the boiler feed pump. At NTPC Sipat, the auxiliaries consume about 7% of the plant load. The boiler feed pump is used to feed water to the boiler, as the name suggests, through the

economizer. The BFP is fed from the CEP and the water source. The BFP is of two types

a) TDBFP: turbo-driven boiler feed pump. b) MDBFP: motor driven boiler feed pump.

The boiler feed pump is fed water from the condensate extraction pump. The

condensate extraction pump collects the condensate from the condenser. Then the

condensate is further cooled by being sent into the gland steam coolers, after which

it is sent into the BFP.

10) COOLING TOWERS: Cooling towers are used to remove the heat from the condensers. In this cooling water is discharged to the condenser with the help of a cooling water pump (CW pump). This water enters the condenser through several tubes. Steam entering the condenser from the turbine after expansion further loses heat and condenses, while the water circulating inside the tube gains heat and goes back to the cooling tower. Inside the tower is a cooling fan which takes the heat from this batch of water, which is then sent back again for the cycle to be repeated. It is hence known as a regenerating cycle.

Cooling towers are eveporative coolers used for cooling water. Cooling

tower uses the concept of evaporation of water to reject heat from processes such

by cooling the circulaing water used in oil refineries, chemical plants, power

plants, etc. Smaller towers are normally factory built while larger ones are

constructed on site. The primary use of large, industrial cooling tower system is to

remove the heat by circulating the hot water used by the plants

The absorbed heat is rejected to the atmosphere by the evaporation of

some of the cooling water in mechanical forced – draft or induced draft towers or

in natural draft hyperbolic shaped cooling towers as seen at most nuclear power

plants.

4 Nos Induced draft cooling towers with 10 fans each tower are installed at

NTPC Dadri for the above said pupose.

11) WIND BOX: These act as distributing media for supplying secondary/excess air to the furnace for combustion. These are generally located on the left and and right sides of the furnace while facing the chimney.

12) IGNITER FAN: Igniter fans which are 2 per boiler are used to supply air for

cooling Igniters & combustion of igniter air fuel mixture. 13) CHIMNEY: These are tall RCC structures with single & multiple flues. Here,

for I & II we have 1 chimney, for unit III there is 1 chimney & for units IV & V there is 1 chimney. So number of chimneys is 5 and the height of each is 275 metres.

14) COAL BUNKER: These are in process storage used for storing crushed coal

from the coal handling system. Generally, these are made up of welded steel plates. Normally, these are located on top of mills to aid in gravity feeding of coal. There are 10 such bunkers corresponding to each mill.

15) REHEATER: The function of reheater is to reheat the steam coming out from the high pressure turbine to a temperature of 540 degrees Celsius. It is composed of two sections: the rear pendant section is located above the furnace arc & the front pendant section is located between the rear water hanger tubes & the Platen superheater section.

16) BURNERS: There are total 20 pulverised coal burners for the boiler present here, & 10 of the burners provided in each side at every elevation named as A,B,C,D,E,F,G,H,J,K. There are oil burners present in every elevation to fire the

fuel oil (LDO & HFO) during light up.

REFERENCE

1. www.ntpc.co.in/index.php?option=com_content&id=312&Itemid.

2. en.wikipedia.org/wiki/NTPC_Dadri

3. wikimapia.org › India › Uttar Pradesh › Dadri

4. articles.economictimes.indiatimes.com › Collections › Solar Plant

5. www.ndtv.com › Topic

6. www.business-standard.com/.../no-shortage-of-coal-supply-to-ntpc-sdad.

7. globalenergyobservatory.org/geoid/4562

8. ntpc.co.in/index.php?option=com_content&id=28&Itemid=41