p1. INTRODUCTION

The word power is attractive to any one in this world of today. Everybody is

after power where it is Money power, Electrical power and Political power. Out

of these we can electric power is the power, which affects the masses not

individual alone. Today the standard of life and industrial development so largely

on the use of power that the amount of use power per capita in any country is an

index of the material and industrial development in that country and the standard

of civilization that has been attained in it.

In olden days man had to rely for power on his own physical strength and those

of his tamed cattle and animals. Today man has discovered and development

many sources of electric power for his industrial and cultural development. The

sources of power can be divided into two major groups:

Conventional Methods

Non Conventional Methods

The major share of electric power generation is through Conventional Method as

for.

CONVENTIONAL METHOD: -

1. Coal based thermal power project

2. Hydro power project

3. Nuclear power project

4. Gas turbine based power project

5. Oil based power project

In India out of 84500 M.W. of installed power generation units 50000M.W. is

through coal based thermal power plants. 31220 M.W. is from Hydro power

plants. 2005 M.W. from Nuclear and 1280 M.W. is from Gas based power plants.

NON CONVENTIONAL METHODS: -

1. Wind generator

2. Solar power

3. Sea bed

1

The major source of power generation in India as well as abroad is coal based

thermal projects. Despite immense electric installation of recent years, thermal

power still today play a vital role and occupies a position of prime importance.

There are thermal projects of different ratings that are from 30 M.W. to 500

M.W. In this also 200/210 M.W. units i.e. 119 such have been commissioned in

India contribute a major share of thermal generation.

Even in the near future, traveling in the planets with the help of rockets propelled

by thermal power is not at all a dream or fantasy.

GURU NANAK DEV THERMAL PLANT is situated in Bathinda (Punjab)

on Bathinda-Malout Road. The foundation stone of this prestigious Thermal

Plant, comprising of four units of 110 MW each was laid on 19th November,

1969, the quincentenary year of the birth of the great Guru Nanak Dev Ji from

whom it gets its present name. This project was completed in two phases at a

total cost of about Rs 115 crore. The first unit was commissioned in September,

1974 and the others were subsequently commissioned in September, 1975,

March, 1978 and last one in January, 1979. The commissioning of these units not

only helped bridge the gap between supply and demand in Punjab but also solved

the chronic problem of low voltage prevailing in the Malwa region. Each unit of

GNDTP, Bathinda, when operated at full capacity is capable of generating 26.4

lac units of electricity a day. The coal consumption is about 1500 to 1600 MT per

unit depending upon the quality of coal. The total daily coal requirement is about

6500 M.T.( about two rakes of 58 wagons each) when all the four units are in

operation. The coal supplies are being received from Jharkhand /Madhya Pradesh

which are more than 1500 KMs from this Power Station.This power plant has

been performing exceeding well over the years. The actual Plant Load Factor

during 2004-05 on three unit basis (unit-2 is under R&M) is

about 70% which is among the highest achieved in the country for 110 MW

units. Conservation of fuel oil in the context of power generation has become a

way of working at this power station. As in the previous years, GNDTP has

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further brought economy in fuel oil consumption during the year 2004-05 in

which fuel oil consumption is as low as 1.46 ml/kwh. This consumption level is

lowest in the country amongst power stations having similar capacity units. Due

to better performance the plant has won a number of National Awards from Govt.

of India.It is a matter of pride that all the four units have successfully completed

Silver Jubilee (25 Years) of their operation. At the same time all the units have

outlived their designed life. Hence, ’Residual Life Assessment’ study of the units

have been got carried out through M/S CPRI, Bangalore. All these units have

clocked more than 1, 65,000 running hours against designed life of 1, 00,000

hours. Accordingly, extensive ‘Renovation & Modernization’ based on Residual

Life Assessment (RLA) study of all the four units

has been planned to be executed in a phased manner to restore rated capacity of

110 MW in respect of unit-1&2 and enhanced capacity of 120 MW for unit-3&4 ,

increase efficiency, reduce auxiliary consumption and extend useful life of the

plant by another 15-20 years. Work Orders amounting to Rs. 183 crores for major

R&M of Boiler furnaces, rotating machinery, H.P. turbine, Instrumentation &

Control systems, D.M. Plant, ash handling plant etc. have been placed on M/s

NASL, New Delhi for units I & II. The total cost of this project is Rs. 229

crores . Loan for this R&M work has been arranged from M/S PFC, New Delhi.

The work also includes updating of Electrostatic Precipitators to bring down

SPM (Suspended particulate matter) level below 90 mg/NM3 to reduce pollution

in the area. However to bring down the pollution level till R&M is completed,

‘Ammonia flue gas conditioning system’ has been installed and SPM level as

prescribed by the ‘Pollution Control Board’ has been achieved on these units.

Generating capacity of unit-III & IV is proposed to be enhanced to 120 MW from

existing 110 MW after replacement of all the three turbine rotors. The Plant Load

Factor of each unit and station as a whole will improve to more than 80% on

completion of R & M works of the units.

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The basic requirements are:-

♣ Fuel (coal)

♣ Boiler

♣ Steam turbine

♣ Generator

♣ Ash handling system

♣ Unit auxiliaries

1.1 MAIN FEATURES  

The main features of the Thermal Plant are as given below.

1) Location Bathinda (Punjab)

2)

Main Features Highest Generation achievement in 2000-01

(2793.67MU)

Highest PLF in March 1987 (88.14%)

Lowest Ever yearly aux. consumption 2002-03

(9.32% without T&E Losses)

Lowest DM Water make up in 2004-05 (2.02%)

Lowest Oil Consumption in 2002-03

(1.35ml/Kwh)

3)No. of Power

HouseONE

4) No. of Unit FOUR

5)Total generating

capacity4 x 110 MW = 440 MW

6)Source of water

supplyCanal water

7) Fuel Used Primary Fuel: Bituminous coal with calorific

4

value 3500-4500 kcal/kg

Secondary Fuel: Fuel oil/L.D.O.HPS/FO with

calorific value of 9000 to 10,000 K.Cal / liter.

8) Turbine Three casing type impulse turbines 110 MW

capacity with 3000 rpm, 29 stages with exhaust

pressure 0.08 kg/sq. cm

9) Generator BHEL make three phase synchronous type  110

MW,11000 V with H2 cooling and DC/Static

exciter ( 2 units with Static Exciter & 2 units with

separate DC exciter)

10) Commissioning U-1 = 22.9.74   U-2 = 19.9.75

U-3 = 29.3.78   U-4 = 31.1.79

Date of commissioning after R&M :

U-1 = 01.01.2006 U-2 = 15.04.2007

11) Cost of Project115 crores(Original),R&M Cost for U#1 &

U#2=229 Crore

12) Cost per unit Rs.2.20 (2006-07)

13)

Total energy

contribution

annually

2359.18 MUs  (2005-06) ,2221.12 MUs (2006-07)

(Table 1.1)

1.2 SITE SELECTION

5

The selection of site for Thermal Power Plant is more difficult compared to

Hydro Power Plant, as it involves number of factors to be considered for its

economic justification. The following consideration should be examined in detail

before selection of the site for the Plant. The location for plant should be made

with full consideration not only of the trends in the development and location but

also the availability and location of the cheapest source of primary energy:-

Availability of fuel

Ash disposal facilities

Space requirement

Nature of land

Availability of labor

Transport facilities

Public society problems

Development of Backward Area

1.3 LANDMARK ACHIEVED

G.N.D.T.P. won an award of Rs. 3.16 crores from Govt. of India for better

performance in 1983-84. It achieved a rare distinction of scoring hart Rick by

winning meritorious productivity awards of Govt. of India, Ministry of Energy

for year 1987, 1988 and 1989 due to its better performance. It again won

meritorious productivity awards during the year 1992-1993 and 1993-94 and

has become entitled for the year 1996-1997 for better performance. It also won

awards for reduction in fuel oil consumption under Govt. of India incentive

scheme years from 1992-1993 (awards money for 1992, 1993 and 1994 already

released for 1995, 1996 and 1997 under the consideration of Govt. of India).

G.N.D.T.P. had achieved a generation of 2724240 LU’s (at a PLf of 70%) and

registering an oil consumption as low as 1.76ml/kwh during the year 1993-94 has

broken all previous records of performance since the inception of plant.

1.4 CONTRIBUTION OF THE PLANT6

Guru Nanak Dev Thermal Plant, Bathinda, in addition to indirect contribution in

various facts of state economy, is also responsible for:-

Narrowing the gap between power demand and power availability of the

state.

Providing employment potentials to thousands of workers.

Covering the backward surrounding area into fully developed Industrial

Township.

Providing additional relief to agricultural pumping sets to meet the

irrigation needs for enhancing the agriculture production.

Reliability and improvement in continuity of supply and system voltage.

Achieving cent percent rural electrification of the state.

1.5 HISTORY OF THERMAL POWER PRODUCTION

Although electric power generation in India on a commercial basis is almost a

century old, substantial power development efforts began only after

independence. At the launch of the First Five-Year plan in 1951, power

generation was recognized as a major input for the country's economic

development and was accorded high priority. Power sector outlays have been

among the highest in successive five-Year Plans ever since. The first two Plans

focused on hydro power (as component of multi-purpose projects). Subsequent

plans emphasized on rapid installations of thermal power stations. As a result of

Plan efforts, India's installed power generation capacity grew to 16,664 MW in

1974. However, assessment of the planned growth since 1951 indicated that with

the uneven distribution of resources, power development with only States as

spatial units, would result in large inter-state imbalances. This, and the need for

quicker and greater capacity addition, led the Government of India to assume a

leading role in large scale power generation as a matter of policy and, through an

amendment of the Electricity (Supply) Act, National Thermal Power Corporation

Ltd. (NTPC) and National Hydroelectric Power Corporation Ltd. (NHPC) were

set up in the central sector to supplement the efforts of the States. Consequently,

total installed capacity of power utilities has increased 7

from 1,362 MW in 1947 to 104918 MW in March, 2002. Electricity generation,

which was only about 4.1 billion units in 1947, has risen to 515 billion units in

2001-02.

1.6 WORKING OF THERMAL PLANT

The various organs combine together and made a human body. Every organ of

human being has a defined role to play e.g. eye to see, hand to work, mind to

process etc. these activity of the body similarly all major and auxiliary systems of

a thermal power plant which function together and produce electricity.

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

vapors 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 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 products of combustion

in the furnace are the flue gases and the ash. About 20% of the ash falls in the

bottom ash hopper of the boiler and is periodically removed mechanically. The

remaining ash carried by the flue gases, is separated in the electrostatic

precipitators and further disposed off in the ash damping area. The cleaner flue

gases are let off to atmosphere through the chimney by induced draught fan. The

chemically treated water running through the water walls of boiler furnace gets

evaporated at high temperature into steam by absorption of furnace heat. The

steam is further heated in the super heater. The dry steam at high temperature is 8

then led to the turbine comprising of three cylinders. The thermal energy of this

steam is utilized in turbine for rotating its shaft at high speed. The steam

discharged from high

(Fig 1.a)

pressure (H.P.) turbine is returned to boiler reheated for heating it once again

before passing it into the medium pressure (M.P.) turbine. The steam is then let to

the coupled to turbine shaft is the rotor of the generator, which produces

electricity. The power from the generator is pumped into power grid system

through the generator transformer by stepping up the voltage. The steam after

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doing the useful work in turbine is condensed to water in the condenser for

recycling in the boiler. The water is pumped to desecrator from the condenser by

the condensate extraction pumps after being heated in the low pressure heater

(L.P.H) from the desecrator, 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. The condenser is having a large number of brass tubes

through which the cold water is circulated continuously for condensing the steam

passing out sides the surface of the brass tubes, which has discharged down by

circulating it through the cooling tower shell. The natural draught of cold air is

created in the cooling tower, cools the water fall in the sump and is then

recirculated by circulating water pumps to the condenser.

1.7 AIR COMPRESSOR

A machine providing air at high pressure is known as air compressor. The air

compressor is driven by some prime mover. The object of all the compressors is

to raise the pressure of the air with the expenditure of energy. Air is taken into

the compressor from the atmosphere through an air cleaner. The air is

compressed and delivered to the storage tank. The compressed air from the

storage tank may be taken by means of pipes to any point where so ever the

supply of the compressed air is required.

(Fig 1.b)

GENERAL ARRANGEMENT OF COMPRESSOR

PRIME MOVER COMPRESSOR

HEAT SINK

HEAT SOURCE

HEAT LOSES TO COOLANT

ATMOSPHERIC AIR

COMPRESSED AIR

10

The compressor receives energy from the prime mover. The compressor for its

operation absorbs some part of this energy. Out of the remaining, some part is

lost to the coolant and rest is maintained within the compressed air.

USES OF COMPRESSED AIR: -

The compressed air may be used in the different fields, which are given below: -

1. It is used for operate the opening valves and closing of feed gates of

chutes.

2. It is used in mines to operate pneumatic appliances such as drills, motor

generators, pumps etc.

3. It is used to operate pneumatic lifts and elevators.

4. It is used in foundry for sand blasting.

5. It is used for operate the tools used for chipping and riveting etc.

6. It is used to produce air blast.

7. It is used to atomize the perfumes etc. by means of sprayers.

8. It is used in painting spray guns.

9. It is used in spray gun for killing insects etc.

10.It is used in air breaks.

1.7.1 CLASSIFICATION OF COMPRESSORS: -

The compressor may be grouped into two categories- Reciprocating and Rotary.

Besides this the compressors may be classified as follow: -

1. ACCORDING TO THE OPERATION

a) Single acting

b) Double acting

2. ACCORDING TO DESIGN

a) Reciprocating

b) Rotary

3. ACCORDING TO NO. OF CYLINDERS

a) Single cylinder

11

b) Multi cylinder

4. ACCORDING TO NO. STAGES

a) Single stage

b) Double stage

c) Multi stage

5. ACCORDING TO PRESSURE LIMIT

a) Low pressure

b) Medium pressure

c) High pressure

6. ACCORDING TO THE METHOD OF COOLING

a) Air cooled

b) Water cooled

7. ACCORDING TO INSTALLATION

a) Portable

b) Fixed

RECIPROCATING AIR COMPRESSOR: -

The reciprocating air compressor essentially consists of a piston and cylinder a

simple type of positive displacement compressor from which the delivery is

intermittent. The piston reciprocates in the cylinder. The cranck shaft through the

connecting rod drives it. There are two valves mounted on the head of cylinder.

These valves are inlet and delivery valves. Both the valves usually operate as a

result of pressure difference across them.

OPERATION: -

During the downward movement of the piston the residual compressed air is

clearance volume will expend. When the pressure inside the cylinder falls below

the outside pressure, the inlet valve will lift off from its seat. Air from the out

side is admitted into the cylinder through the inlet valve, during the downward

movement of piston. This is known as induction stroke of the piston. During this

stroke the delivery remains closed. After the completion of induction stroke the

12

piston starts moving in the upward direction. The inlet valve will be closed as the

pressure inside the cylinder increases with the upward movement of the piston

now both the valves are closed so the air entrapped in the cylinder is compressed

to high pressure .the delivery valve is lifted up as soon as inside the air pressure

in the delivery chamber. The compressed air is now delivered during the

remaining upward movement of the piston this stroke of piston is known as

compression stroke. At the end of this stroke, the piston again starts moving in

the downward direction, for its induction stroke. The delivery valve closes and

the inlet valve opens. Thus the cycle is repeated. The compressed air is stored in

a storage tank from which it may be taken out according to requirement.

PRINCIPLE AND WORKING OF DOUBLE STAGE DOUBLE ACTING

COMPRESSOR: -

In double stage double acting compressor two cylinders are positioned on either

side of crank case facing each other being driven by same crank shaft with the

two cranks at 180 degree, the reciprocating mechanism in the two cylinders will

always have movements exactly opposed to each other thus imparting perfect

dynamic balance into the system. The balanced opposed piston compressors are

either single stage design where input pressure for both the cylinders are same P1

and so also the output pressure P2 or two stage design where the output of low

pressure cylinder will be the input for high pressure cylinder. The output pressure

of two-stage compressor P3 will be higher than that of a corresponding single

stage compressor. The compressor crankshaft can be made to drive a number of

pairs of such cylinders to give a multi bank compressor for higher output usually

low pressure compressors are belt driven or directly coupled type. Sometimes it

may not be possible to get a very high pressure of air in a single cylinder, and

then double stage compressor is employed.

COMPRESSED AIR DELIVERY

ATMOSPHERIC AIR

WATER

13

(Fig 1.c)

DOUBLE STAGE COMPRESSOR

The atmospheric air is first compressed in a cylinder. During compression air

become hot to some extent It is cooled down to its initial temperature by passing

it through the heat exchanger which is known as inter cooler. The cooled air from

the intercooler is supplied to the second cylinder where it further compressed to

desired pressure. The first cylinder is known as low-pressure cylinder and it is

first stage of compression. The second stage receive the compressed air through

the intercooler is known as high-pressure cylinder and it is second stage of

compression. The dimensions of the H.P. cylinder is smaller than that of L.P.

cylinder because the volume of air is decreased when it is compressed. The

intercooler saves some amount of work required during the second stage of

compression. The L.P. and H.P. cylinders are coupled and are driven by same

prime mover. After H.P. it goes into heaters where it dries silica gel is used in

heaters.

L.P.CYLINDER

H.P.CYLINDER

INTER COOLER

RECEIVER

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1.8 COAL HANDLING PLANT

(Fig 1.d)

In G.N.D.T.P, the main fuel is COAL. It is burnt to get the thermal energy, which

is used to convert water into steam. This energy is released by the combustion of

certain chemicals (e.g. carbon, hydrogen etc.) present in coal with oxygen.

The various types of fuels in steam thermal plants used are: solid fuels (coal,

coke), liquid fuel (petrol, diesel), gas fuel (natural gas, biogas). In steam thermal

plants, the selection of a particular type of fuel is a problem of economics.

However in G.N.D.T.P, coal is used.

In coal handling plant, the coal is transferred from the coal storage site to the

bunkers (capacity of bunker is 500MT) through conveyors belt connected from

one place to other place. Firstly, the coal from the wagon is unloaded through

wagon tippler and then the coal is transferred to the crusher house and finally the

crushed coal is stored at the coal storage site.

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1.8.1 COAL AND ITS SELECTION

Coal is a general term that encompasses large organic minerals with widely

differing compositions and properties, although all are essentially rich in

amorphous elemental carbon. The main types of coal are:

1. Peat

2. Lignite

3. Sub-bituminous

4. Bituminous

5. Semi- bituminous

6. Anthracite

7. Super-anthracite.

The primary fuels, which are burned to release heat and generate steam in boilers,

are the fossil fuels in the form of coal, oil and natural gas. Coal is the principal

energy source because of its large deposits and availability. Coal originated from

vegetable matter, which grew millions of year ago.

Peat contains up to 90% moisture and is not attractive as a utility fuel. Rank is a

measure of carbon content in coal. Lignite is considered to be low rank and

anthracite to highest rank.

The coal is transported in the rail wagons from collieries to the plant site. A rake

of train means to 58 wagon. And capacity of each wagon is 60MT.At the plant

site, the coal is unloaded mechanically by means of wagon tipplers. Tippling it in

the coal hopper form where the coal is carried by belt conveyor to the crusher

house empties the loaded wagon. The coal is sent by one or more of these

companies by railway transportation. In plant, the properties of coal are examined

by chemical methods. Main methods are:

1. Proximate analysis

2. Ultimate analysis.

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Proximate analysis gives the principal characteristics of the coal, whereas

ultimate analysis gives its chemical composition. On the basis of the properties of

coal studied, coal is ranked as per standards maintained.

Then payment of coal is done on the basis of rank observed by the Punjab State

Electricity Board to the concerned companies.

The coal should have the following properties:

1. LOW MOISTURE CONTENT

2. LOW ASH CONTENT

3. LOW VOLATILE MATTER

4. LOW SULPHUR CONTENT

5. LOW HYDROGEN

6. HIGH CARBON CONTENT.

1.8.2 COAL SAMPLING

The coal testing starts from coal sampling. In coal sampling a standard

technique to take samples of coal suggested by P.S.E.B. is followed. In this

technique, there is a set of 75 lists of 15 wagon numbers chosen randomly. A list

is taken. Then in those wagon nos. the coal sample of weighing about 1 kg is

taken. This amount is taken from 1meter depth of wagon. Thus we collect 15 kg

of coal.

Then this coal is mixed well.

Now the coal is divided into four parts.

Two parts are randomly rejected

The other two parts are mixed and again divided in four parts. From which

two are rejected.

This procedure continues till we get 2 kg of coal.

Then it is crushed and is sent to coal testing room.

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1.8.3 COAL TESTING AND GRADING

Here the properties of coal are examined by applying the chemical tests.

The following tests are done on coal sample.

1. Proximate analysis

2. Ultimate analysis.

Proximate analysis gives the principal characteristics of the coal, whereas

ultimate analysis gives its chemical composition. On the basis of the properties of

coal studied, coal is ranked as per standards maintained.

From Proximate analysis, we get the following data:

PERCENTAGE OF MOISTURE CONTENT

PERCENTAGE OF ASH CONTENT

PERCENTAGE OF VOLATILE MATTER

PERCENTAGE OF CARBON CONTENT.

From the Ultimate analysis, we get the following data:

percentage of sulphur content

percentage of hydrogen content

Percentage of ash content.

After getting the above information, the grading of coal is done. It is done by

studying the features like

ash content

sulhur content

Calorific value.

On the basis of grade of coal, the payment is done to the relative Coal Company

by P.S.E.B.

1.8.4 COAL HANDLING 18

(Fig 1.e)

Coal handling is done mechanically instead of manually, due to following

reasons:

1. Large quantity of Coal has to be handled everyday,

2. Reliability of mechanical devices,

3. Mechanical handling is cheaper one,

4. Unloading of Coal from rail wagons is difficult and time consuming by

manual handling,

MAJOR PARTS

The main parts are divided into two parts:

1.General Working Parts,

2.Emergency Working Parts.

General Working Parts are:19

1. Wagon Tippler

2. Junction Tower

3. Primary crusher

4. Secondary crusher

5. Bunkers

6. Conveyer System

Emergency Working Parts are:

1. Stacker cum Reclaimer

2. Manual Handling Hopper

3. Emergency Reclaimer Hopper

Also there are spare General Working Parts i.e. each General Working Part has

duplicate of its own. If one part is under breakdown, the other can be used at

that time.

1.8.5 PLANT ORGANISATION STRUCTURE

Coal Handling Plant has been divided into two departments:

1. Mechanical Department

a. Operation Department

b. Control Department

c. Maintenance Department

2. Electrical Department

a. Wiring and Lighting Maintenance Department

b. Electrical Equipment Maintenance Department

20

PARTS DESCRIPTION

WAGON TIPPLER

(Fig 1.f)

It is an Unloading Device used in plant to unload COAL from rail wagons. There

are two no of WT. One is kept under maintenance and other is working.

The effective unloading output is designed for:

Useful load 55 tons

Wagon tare weight 25 to 30 tons

Total weight 80 to 90 tons.

(Table 1.2)

21

TYPES OF WAGONS TO BE HANDLED

TYPE MAXIMUM DIMENSIONS GROSS

WEIGHT

O 14428*2955*2836 33

OZ 14740*3166*3040 40

BOX 13730*3075*3160 82

BOZ 13192*2950*3150 80

(Table 1.3)

TECHANICAL DATA OF WAGON TIPPLER

The tippler drive unit consists of:

the electric motor

the connection coupling with brake arranged between motor and gearbox

the spur wheel gearbox

the coupling shaft with 480 dia. Pinions

Toothed rims diameter 8470mm connected to the end shields by screws.

Base frame

Flexible couplings

The main function of tippler drive unit is to tilt the end Frame

The tippler platform is rated for 120-ton weight maximum.

Total weight to be unloaded 105 tons

Maximum tilting angle 155 deg.

Tipping cycle time 175 sec(app)

Tipping cycle/hour max 20

Tipping cycle/hour guaranteed 16

Circumferential speed 0.27m/s

Gearbox ratio 1:140

(Table 1.5)

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The main components are:

1 end shield with gear teeth

2 Counterweights

3 Main Hydraulic Cylinder

4 Main Bearing and main Shaft

5 Drive pinion

6 Line Shaft

7 Upper Holding Beam

8 Cross arm Cylinder

9 Side Arm

10 Wagon Fixture

11 Tippler Platform

12 Side Arm Charger

13 Chock Beam

14 Hopper

15 Drive

16 Operator Cabin

Main parts are described below:-

Tippler drive Unit:

The drive unit consists of the following components:

a. Base Frame

b. Eddy Current Brake

c. Slip ring motor

d. Spur Gear Unit

e. Flexible Couplings

f. Drum Brake

g. Drive pinions for Rotating End Shields

h. Line Shaft and set of Bearings and Bearing Housings

23

End Shield: The 8520mm-dia.end shield is in a sector form weighs about 9 tons

and (without counterweights) is fabricated out of plate works. This is roughly of

semicircular shape and rotates on main Pedestal bearing supported on the R.C.C.

Pedestals. End Shield is having tooth rim on its periphery; these teeth are driven

through a pinion mounted on the line shaft. When End shield gets its motion

through pinion it moves the table and the wagon placed on it along it. The end

Shield is having Counter Weight, which designed to balance part of the Wagon

and the platform.

Platform: Platform approx. 19.7m long is a plate fabricated structure weighing

about 10 tons, a bridge shaped structure carrying a section of the rail track,

bearing eye centering device and the rollers. It has sufficient length to

accommodate all types of wagons listed above, including “O” and ”OZ” in pairs.

The platform rests on civil foundation via a centering device.

Upper Holding Beam: This is a18.2m long, 7.5 ton structural work made out

of heavy plate work, and connected at the Side Arms which are supported on the

main bearings. The Upper Holding Beam gets its forward motion through a pair

of main Hydraulic Cylinder and gets clamped with the Wagon fixtures (PAWS).

This also supports the weight of the Wagon during tipping and prevents from

falling from the platform.

Chock Beam: Chock beam is fabricated out of plate work and weighs about

13.5 tons. At the start of tipping operation when the table along with wagon tilts

about the cantilever arm pin. The wagon rests on its side on the chock beam. To

avoid damage to wagon the chock beam is lined with thick rubber, which absorbs

any impact due to wagon resting.

Side Arm Charger (S.A.C.): The Side Arm Charger moves the selected

portion of the train rake to a position of readiness. Further it moves the Wagon to

be unloaded on the Tippler table. After the Wagon has been unloaded S.A.C.

helps in ejecting the empty Wagon from the Tippler table.

24

TECHANICAL DATA:

No of Wagons that can be pulled 24

Weight of loaded Wagon 90

Travel Speed forward 0.5 m/sec

Backward 1.0 m/sec

Max. Pulling force 200kN

Required pulling force 170kN

Pinion diameter of planetary gearbox 280mm

Speed of hydra. Motor 1600/3200 rpm

Speed of planetary gearbox forward 34,104 rpm

Backward 62,208 rpm

(Table 1.6)

MAJOR PARTS: The travel drive is achieved Electro-hydraulically via pinion

and toothed rack.

The travel drive consists of 2 complete drive units to be vertically arranged on

the drive frame, their pinion mesh with the toothed rack fixed at the sub-

structure. Each drive unit is combined with a hydraulic motor, planetary gearbox

and toothed pinion, whereas one drive unit is equipped with a brake.

Lifting and lowering of the holding arm as well as hydraulic cylinders achieve

coupling and uncoupling of the wagons at its beam end.

Hydraulic buffers to be arranged with in the area of the holding beam of he

wagons as is compensate shocks, which occur with the shifting of the wagons

due to acceleration or deceleration.

The total length of travel of the S.A.C. is controlled by a set of Magnetic

Switches.

An over travel limit Switch is set by he back-up Heavy duty Mechanical

Switches.

The moving parts are provided with grease Lubrication system.

25

JUNCTION TOWER: It is a structure used to divert the conveyor system at 90

deg. There are junction towers installed in coal plant. The main parts of a

junction tower are:

Motor drive

Sector gates

Chute

Dust suction system

The main purposes of Junction Tower are:

To divert the conveyor system at 90 deg

To make the connections between two conveyors

With the help of Junction Tower, we have many optional ways of carrying

coal.

PULVERIZED COAL: The coal available is not in suitable form it is present in

pieces of average size 50 to 100 mm. These pieces cannot be used in Furnace

directly. The reason is that its surface area is not so enough to combust it fully

and properly. As surface area of coal increases, it catches fire very easily and

soon.

The main advantages of using pulverized are given below:

Surface area is increased, hence combustion is completed.

Coal is dried effectively

No/reduced clinkers formed

Efficiency increases as complete combustion.

Easy transportation of coal into furnace.

26

Hence we have to convert the pieces of coal into pulverized coal to take the

advantages of it.Two types of crushers has been used to convert the bigger coal

pieces into smaller ones. Then these pieces are converted into pulverized

(powder) form with the help of mills (known as PULVERIZER). These crushers

and mills are:

1 PRIMARY CRUSHER

2 SECONDARY CRUSHER

3 BOWL MILLS.

Name of equipment Type No.

Primary Crusher Rotary crusher 2

Secondary Crusher Ring granulator 2

Pulverizer Bowl mill 6 (for each unit)

(Table 1.7)

PRIMARY CRUSHER: It is a type of crusher used to break the bigger pieces

into smaller ones. There are TWO Primary Crushers PC A and PC B. The

purpose of having two is to have uninterrupted crushing of coal. Suppose one

P.C. breaks down during crushing, then at the same time the other is started.

Meanwhile the first one is undergone repair and maintenance, thus making it

ready for further operation.

When one is working the other is kept always ready for meeting emergencies.

These are used shift by shift. One is working in day sift and remains at

maintenance and is ready for working in next shift.

27

Main parts of it are:

1. CASING

2. PERFORATED CYLINDER

3. LIFTER SHELVES

4. MOTOR DRIVE SYSTEM

PURPOSE OF PC: The main purposes are:

To break the bigger pieces into smaller ones

To reject the foreign particles and the coal pieces which do not break in PC.

WORKING OF PRIMARY CRUSHER: This crusher s composed of a large

cylinder. It consists of a large no of holes on its surface area. The diameter of

these holes has been varied along the periphery. Some initial rows have the holes

of dia 25cm, next ones have the hole dia of 20 mm, and others have hole dia

15mm. On the inner periphery of cylinder lifting shelves are attached. The

cylinder rotates at a small speed of 20rev per min. The cylinder receives the coal

feed at motor drive side. The smaller pieces (Dai <25mm) directly falls from

holes. The lifting shelves lift the bigger ones. When shelves go on top, the coal

pieces falls down and break and pass through the holes. This procedure continues

until the pieces are broken down. Although there are some pieces, those do not

break, are lifted by shelves ad are thrown in rejection duct.

SECONDARY CRUSHER: In this crusher, the coal pieces coming from P.C.

are further crushed. The size of coal pieces is reduced from 25mm to 10-15mm.

Like P.C., there are two no of S.C. SC A and SC B. The type of S.C. is RING

GRANULATOR. The purpose of having two is to have uninterrupted crushing of

coal. Suppose one S.C. breaks down during crushing, then at the same time the

28

other is started. Meanwhile the first one is undergone repair and maintenance,

thus making it ready for further operation.

When one is working the other is kept always ready for meeting emergencies.

These are used shift by shift. One is working in day sift and remains at

maintenance and is ready for working in next shift.

Main parts of it are:

1. HAMMERS (LOOSE RINGS )

2. VIBERATING SCREEN

3. SCREEN BAR( PERFORATED PLATES )

4. MOTOR DRIVE SYSTEM

5. SHAFT

6. PRESSURE PLATES

WORKING OF SC: The coal coming from Primary Crusher is fed in

VIBERATING SCREEN. The Vibrating Screen separates the fine coal dust

particles from the coal pieces. The coal dust falls down. The coal pieces are

allowed to fall in casing of SC. Here the main Shaft is rotated at a normal speed

of 100-130 rpm. On this shaft, hammers are mounted. These are the loose rings

made of cast iron. Here are five sets of loose ring rod. On each rod there are 15

loose rings. As shaft rotates, the hammers, due to Centrifugal forces, tend to

come outside. The coal pieces now come between two surfaces. One is of

hammers and other is of pressure plate. As there is very small gap (of 10mm)

between two surfaces, the coal is broken. Now this crushed coal is fallen down

on the conveyors and is sent further.

29

STACKER CUM RECLAIMER: It is a huge structure used to store the coal

when not needed and reclaim it when required. Sometimes there is no need of

coal in bunkers. But the is a rake of coal. To avoid railways penalty and to have a

stock of coal in emergencies (like no coal is coming), the coal is stored with the

help of STACKER. When there is need of coal in bunkers and no fresh coal is

coming, the stored coal is conveyed to the bunkers with the same structure. That

is why it is called STACKER CUM RECLAIMER. The purpose of having two is

to have uninterrupted crushing of coal. Suppose one S.C. breaks down during

crushing, then at the same time the other is started. Meanwhile the first one is

undergone repair and maintenance, thus making it ready for further operation.

When one is working the other is kept always ready for meeting emergencies.

These are used shift by shift.

1.8.6 EMERGENCY OPERATION SYSTEMS

The emergency means that at any time any part can be stop working and system

can be come to at halt. Any type of breakdown may occur which can stop the

work along with huge damage.

In order to avoid interrpution in work operation, the emergency operation

systems are provided.

The main emergency operation systems are:

MANUAL HANDLING HOPPER

EMERGENCY RECLAIMER HOPPER

CONVEYOR SYSTEM HAS BEEN DOUBLED.

EVERY PART HAS BEEN DOUBLED.

1.9 WATER TREATMENT PLANT30

The water is required for two purposes at GURU NANAK DEV THERMAL

POWER PLANT:-

1) For Boiler feed makeup taken from D.M. plant

2) A. Cooling tower makeup

B. Portable water

C. Service water and other requirement

D. For fire protections

Total hourly requirement of 1 unit of 110MW is nearly 1200 m³/hr.

1.9.1 SOURCE OF RAW WATER:- The source of raw water for the plant is

Sirhind canal or river water. It contains impurities like Calcium, Magnesium

salts, Silica suspended solids and minerals to a 300-500 ppm during monsoon

period and a normal supply has 200-300 ppm.

Hardness of water indicates calcium and magnesium salts present in water.

Bicarbonates and carbonates of these salts constitute temporary hardness

sulphates, nitrates chlorides etc. constitute permanent hardness. These cause scale

formation in boiler.

To avoid the deposition of scale on metal surfaces, corrosion of boiler

tube metal etc. difficulties, water treatment process is used. This knows the

impurities of water as

External water treatment

Internal water treatment

1.9.2 External Water Treatment comprises of: -

31

a) Chlorination.

b) Sedimentation & Clarification.

c) Filtration.

d) Demineralization.

a) Chlorination.

Bacteria and other living organisms results in the formation of algae on the

surface of tanks, pipes and other equipments. Addition of oxidizing agents such

as chlorine & bleaching powder destroy the bacteria or any other micro

organisms. At present, chlorine dosing is done at Intake. Pump House and at both

CW Pump House with Gas Chlorinator of vacuum type at the rate of 10 Kg/Hr.

b) Sedimentation & Clarification

The suspended impurities in water are removed by sedimentation and

clarification. When the river or cannel water is allowed to stand for sometime in a

big tank or reservoir most of the suspended material settles down. The process of

clarification is done in clarifier and is accelerated by adding coagulant such as

alum (aluminium and ferrous sulphate) or Sodium Aluminate. These results in

the formation of precipitate of aluminium hydroxide, which tends to agglomerate

colloidal,Organic and suspended impurities in water. The precipitates so formed

settles at the bottom of clarifier. These are removed by operating desludging

valve.

Al2(SO4)3 + 3Ca(HCO3)2 3CaSO4 + 2Al(OH)3 +CO2.

Impurities not removed in this process are removed by filteration. At present, we

have 4 clarifiers with a clarifying capacity of 1200 MT/Hr each to reduce

turbidity upto 20ppm.

c) Filtration

It is the process of passing of liquid containing suspended matter through a

suitable porous material (Filtering Medium) to effectively remove the suspended

matter in the liquid. For the process of filtration there are 3 pressure filters in

32

each D.M.Plant having a capacity of 27 M3/Hr each. Turbidity of filtered water

from pressure filters is not greater than 2 ppm. Filter media commonly employed

are graded and washed sand of effective size of 0.35 mm to 0.5 mm resting on

supporting under bed of crushed gravel and pebbles of four varying size with

coarsest size at the bottom of the bed.

d) Demineralization (Removal of dissolved impurities)

The development of modern high-pressure boilers has been accompanied by

serious problems connected with the formation of scale, corrosion etc.The

principle scale forming and hardness producing substances found in natural water

are the soluble salts of calcium and magnesium. The most common are bi-

carbonates Ca(HCO3)2, Mg(HCO3)2.The sulphate CaSO4,MgSO4. The chlorides

CaCl2, Mg/Cl2 and sometimes nitrates are also present. The processes which are

used for water softening are:

1. Boiling (For removing temporary hardness only).

2. Lime Soda Treatment.

3. Base Exchanger Zeolite process.

4. Ion Exchange.

ION EXCHANGE

The demineralization of water at GNDTP, BATHINDA is done by ion exchange

process. There are two D.M. Plants each having capacity 900 MT/day design for

5% station make up. The ion exchange process is used in removing all the above

scale forming constituents. This is the most modern and latest method. The ion

exchange is the process in which there are irreversible interchanges of ions of

like sign between a solution and an insoluble solid. In this process the cations in

water are exchanged with H+ ions of cations resins and anions are exchanged

with OHions of anion resins.

RESIN

33

Resin consists of a giant organic molecule arranged in the form of porus

framework, having replaceable H+ions attached to it in case of cations resin and

replaceable OH-ions in case of anion resins. The demineralization process

consists of 3 units in series, one is called “Cation Exchange Unit” and the other is

called “Anion Exchange Unit”. Mixed bed unit follows this.

1. Cation Exchange Unit

This exchanger removes all the cations such as Sodium (Na+), Potassium (K+),

Calcium (Ca++), Magnesium(Mg++)etc. When the water passes through cations

resin the functional hydrogen ion are replaced by the cations with the formation

of respective acid. The equation is represented as:

(a) R'H+ + Ca (HCO3)2 R'Ca+ + H2CO3

(b) R'H+ + CaSO 4 R'Ca+ + H2SO4

(c) R'H+ + NaCl R'Na + HCl

When the resin gets exhausted, it needs regeneration (i.e. reconversion of resin

into the operating form) for cation exchange units mineral acid such as

hydrochloric acid is used for regeneration

e) RCa + 2HCl 2RH+ + CaCl2

2. Degasser Unit

The treatment water is passed through degasser unit, since it has large amount of

CO2 and here the CO2 is removed. This reduces load on the anion exchanger. The

treatment water from cation exchanger is sprayed from the top of the degasser

tower. The degasser tower is packed with rasching, rings and air flowing

arrangement is provided from bottom to top with air outlet at the top. Air which

is being pushed from the bottom comes in contact with water droplets & finally,

CO2 is removed in sufficient amount & is ejected out by air draft.

a) H2CO3 H2O + CO2

3. Anion Exchanger Units

34

This unit removes all the anions such as Sulphates, Chlorides, Nitrates, SiO2 and

residual CO2from degasser. When the water passes through anion exchange resin,

all the anions are exchanged with functional OH- group of the resin.

1) R+OH' + HCl RCl + H2O

2) R+OH' + H2SIO4 RSiO3 + H2O

After sometimes when it gets exhausted, it needs regeneration. It is regenerated

with 5% NaOH

3) R+Cl' + NaOH ROH + NaCl

(Exhausted Resin) (Regenerated to Drain Resin)

4. Mixed Bed

Mixed bed contains both the cations and anion resins. Any cation or anion which

has slipped from the cation exchanger and anion exchanger are removed here in

the mix bed unit. After mixes bed treated water is quit suitable for use in boiler.

PH = 6.8 to 7.2

Conductivity = 1.0 micromhos/cm

SiO2 = < 0.02 ppm.

Others = NIL

1.9.3 Internal Water Treatment

When after standard treatment it is necessary to further condition the boiler feed

water because D.M. Water dissolves CO2 andO2 in the storage tanks and

becomes slightly acidic and corrosive in character. This is treatment at various

stages of feed water is called internal water treatment. Internal Water Treatment

is required by chemical dosing to combat the following:

(a) Corrosion.

(b)Scaling

(c) Pitting

(d)Foaming

(e) Caustic Embrittlement. 35

(a) Corrosion

Corrosion is the gradual destruction of metal by chemical or electro chemical

reaction of metal with the surrounding medium. Corrosion begins at the surface

and gradually penetrates into the metal. It also changes the mechanical and

physical properties of material.

(b) Scaling

Once in boiler the water is heated to saturation. The temperature thus evaporates

at the point of contact with heated tube surface. The impurities are left in boiler

water whose concentration thereby increases. The impurities to deposit on the

tube surface a scale. Scaling may take place in boiler drum, water walls heater

and feed water piping. It reduces the flow requiring an increase in pressure to

maintain water delivery and more fuel consumption. Then this condition occurs

tube failure due to overheating, blistering and rupturing may be expected.

(c) Pitting

When minute holes are created on metal surface by oxidation it is know as

pitting. This type of corrosion is caused by dissolved oxygen in water. The

residual oxygen is removed by treatment with hydrazine.

(d) Foaming

Foaming priming and carry over are closely associated terms production of stable

foam over the surface of water is called foaming. Too high concentration of

dissolved salts is the cause of foaming.

(e) Caustic Embrittlement

The tendency of caustic (Sodium Hydroxide) to concentrate in drum seals, under

rivets or at rolled tube joints injuring the metal is called caustic embrittlement.

Foaming, priming, carryover, caustic embrittlement can be controlled by

maintain proper alkalinity, operating blow down and maintaining proper drum

level i.e. 30 to – 60 mm.

CHEMICAL DOZING FOR INTERNAL TREATMENT OF WATER

36

To take care of scaling and corrosion following chemical dosing is done to

neutralize effect of CO2, O2 Calcium Magnesium, Salts and silica etc.

(1)Morrholine dozing.

(2)Hydrazine dozing.

(3)Phosphate dozing.

(1) Morrholine dozing

This dozing is done to increase the pH of the feed water and remove any in the

system

2C4H9ON + 2CO2 2C4H9CO3 + N2

The pH of the feed and steam cycle is maintained between 8.4 to 8.8 to minimize

corrosion, it is dozed at the discharge of condensate extraction pump.

(2) Hydrazine dozing

It is a powerful reducing agent which reacts with dissolved oxygen under boiler

water condition to produce water and nitrogen only as follows.

N2H4 + O2 2H2O2 + N2

Hydrazine also reduces non-protective iron oxide to protective magnetite.

(3) Phosphate dozing

It is done with two aims:

a. Any hardness (salts of Ca and Mg) entering the boiler is likely to form

scale in boiler. The addition of phosphate prevents this. The phosphate

reacts with calcium and magnesium to form sludge, which can be removed

by blow down. In this way, Ca and Mg scales are completely removed

from the boiler drum.

b. T.S.P. maintains proper pH of the boiler water. T.S.P. on hydrolysis with

boiler water liberates NaOH with the reaction.

Na3PO4 + H2O Na2HPO4 + NaOH

37

1.9.4 RAW WATER AND CIRCULATING WATER SYSTEM:-

RAW WATER:- The total water requirements for running of the units are

supplied by the intake pump house in the raw water form. The raw water is taken

from Sirhind canal near the plant area and stored in the storage ponds. There are

separate ponds for units. The ponds act as a water reservoirs since the canal runs

dry once in a month for 7 days. Normal season has a normal supply of water. In

order to destroy algae and bacteria in water chlorination is done intermittently at

the suction of intake pumps. In the intake pump house which is common for

stage-1,2 there are six number of pumps, one pump for each unit and two acts as

standby.

Particulars of pumps:-

Capacity of each pump 1200 m3/hr.

Total head 8 MWC

Suction pressure 0.3-0.46 kg/cm2

Motor 415 Volts, 45 kW

(Table 1.8)

These pumps take suction and pump the raw water to the clarifier.

CLARIFIER:-

The basic purpose of clarifier is to remove or to precipitate out the

undissolved impurities present in raw water which coagulates by putting alum

and settles down at the bottom in the form of sludge which is further removed

with the help of valves provided for this purpose. The quantity of alum is

regulated depending upon the raw water. There are four clarifiers for four units.

The raw water from intake pump house comes into the clarifiers. Each clarifier is

capable of clarifying raw water at the rate of 1200 m3/hr. The size of clarifier is

34.74 meters in diameter and 3.7 meters in depth. It has a floculator of 12 meters

diameter. The water in floculator is stirred by a motor operated stirrer. The water

38

from clarifier is transferred to the clear well of 1200 m3. The clarifier water from

the clear water well is utilized for the different purposes as:-

For D.M. plant i.e. D.M. water is to be used in the boiler or for boiler

make up in the hot well through D.M. transfer pumps.

For fire fighting.

For servicing in the plant.

For drinking/portable purposes.

For makeup of the circulating water in the circulating water sump.

CIRCULATING WATER:-

There are two C.W. pump houses, one for unit-1,2 (stage-1) and other for

unit-3,4 (stage-2). In each C.W. pump house there are five number of pumps for

circulating water, two pumps for each unit having 50% capacity and pump is

stand by for both units. The particulars of C.W. pumps for unit 1,2 are:-

Manufacturer : M/s Johnson Pumps Ltd. Calcutta

Type of pump : Wet pit, mixed flow, vertical directly coupled

with an electrical motor drive.

Pump Bearing lubrication : Forced fresh water from external source.

Design capacity : 8600 m3/hr.

Motor : 800 kW, 6.6 kV, 50Hz, AC Induction

motor of BHEL, Haridwar.

The required cooling and sealing for the circulating pump is done with the

help of water pump. which circulates the water through bearing and periphery for

sealing of circulating water pump. the details are:-

39

PUMP

(Table 1.9)

MOTOR

Make Kirloskar

Power 12.5 HP

Voltage 440 Volts

(Table 1.10)

PARTICULARS OF C.W. PUMPS UNIT 3 AND 4:-

Manufacturers : Flow more Pvt. Ltd., New Delhi

Type : Mixed flow, vertical

Capacity : 8600 m3/hr.

Lubrication : Forced external water lubrication

Discharge pressure : 2 kg/cm2 (approx.)

Motor : 1000 HP, 6kV, BHEL

(Table 1.11)

The pumps are of vertical type and suction from the C.W. pump and the

discharge of each pump is connected to a common discharge header from where

the water enters in a cold water tunnel which is further distributed for various

40

Make Bestand

Company

Speed 2900 rpm

No. of stages 2

No. of pumps 3 for each

purposes mainly in the condenser. This water in the condenser tubes takes the

heat of the steam and gets heated up. The outlet of the condenser is sent to the

cooling tower through another hot water tunnel. Where the hot circulating water

is cooled down by 10C by the natural draught of air, capacity of each cooling

tower is 18000 m3/hr. The water falling at the height of about 10.5 meters from

the cooling tower is collected in the sump, which further overflows, to the CW

sump. The make of the CW is added to the sump as required.

There are three numbers of seal water pumps for sealing of the glands of

the CW pumps for stage C. The suction of these pumps are taken from the

concerned sumps. One direct seal water line is taken from the overhead service

tank which serves in case of failure.

1.9.5 COOLING WATER SYSTEM:-

1) For Condensers:- Approximately 15000 m3/hr. of CW water is required for

condensing steam at fuel load per unit. The water is tapped from cold water

tunnel and after condensing steam in the condensers, hot water enters the hot

water tunnel and then leads to cooling tower.

2) For Hydrogen Coolers:- The water for the hydrogen cooler is taken from the

cold water tunnel, there are two hydrogen cooler booster pumps for each unit.

One works at a time and second remains standby. The discharge of H2 coolers

is mainly connected to the hot water tunnel but during startup it can be sent to

blow down sump for ash disposal.

3) Turbine Lubrication Oil Coolers:- There are six number of turbine lubrication

oil coolers for each unit, the cooling water tunnel is taken for inlet and outlet

is connected to hot water tunnel.

4) Bearing Cooling Water System:- There are three number of BCW pumps for

each unit which supplies cooling water to various boilers and turbine

auxiliaries of the unit at the required pressure. The pumps take suction from

the line taken from the cold water tunnels and outlet goes to the blow down

sump of ash disposal.

41

1.10 BOILER

A boiler is a combination of systems and equipment in which the chemical

energy of fossil fuels is converted into thermal energy, which is then

transferred to a working fluid (water) so as to convert it into steam at high

pressure and temperature. This high pressure and temperature steam is then

used for the development of power in a turbine.

(Fig 1.g)

It is the main portion part of STEAM GENERATOR. It is an assembly of a large

no. Of vertical riser tubes embedded in refractory walls. There are two boilers

one for each unit. The type of the boiler is NATURAL CIRCULATION,

RADIENT SINGLE REHEAT boiler. The four refractory walls make a closed

box called FURNACE. The walls are given special names. These are:

1. RIGHT WALL consisting 130 TUBES.

2. LEFT WALL consisting 130 TUBES.

3. FRONT WALL consisting 181 TUBES.

4. REAR WALL consisting 181 TUBES.

On the right and left wall, the WIND BOXES are installed.

At the joint of two walls a FURNACE CORNER is installed. Thus there are Four

Furnace Corners.

42

The water tubes cool the walls by absorbing the heat and transferring it to the

water running in them. The tubes are embedded in refractory walls very close

(the gap between two tubes is 10mm). The inner diameter of the tube is 63.5mm.

JUSTIFICATION OF THE BOILER TYPE:The type of the boiler is WATER

TUBE, NATURAL CIRCULATION, RADIENT SINGLE REHEAT boiler. The

meaning of each word has been explained below:

WATER TUBE: It means the water runs in the tubes and the fire is outside the

tubes.

NATURAL CIRCULATION: The CIRCULATION word means how the water

is risen in the walls. We know that to rise the water upwards we have to supply

some external power e.g. some pump system. But here a law does this work

naturally. The saturated water collected at the bottom known as RING HEADER.

The water rises from it in riser pipes naturally. There is a TWO PHASE

MIXTURE of WATER and STEAM in risers. There is a DIFFERENCE

BETWEEN the DENSITIES of the MIXTURE and SATURATED WATER in

Ring Header. Also there is a STATIC HEAD. Due to the result of both factors

there is NATURAL CIRCULATION operates in boiler.

RADIENT TYPE:As the name implies, the heat is transferred from combustion

gas to the water walls by RADIATION. The heat is then CODUCTED to water

tubes and through the thickness of tubes. Then is CONVECTED to the TWO

PHASED MIXTURE.

SINGLE REHEAT : It implies that the steam is reheated only once. When

the steam goes to HP Turbine, its temperature decreases from 540 deg to 343

deg. It is then send to reheater to increase the temp to again 540 deg.

43

1.10.1 ESSENTIALS OF A GOOD BOILER

1. It should be absolutely reliable and capable of raising maximum amount of

steam for minimum fuel consumption, attention, initial cost and maintenance

charges.

2. It should be light in weight and should occupy small space.

3. It should be capable of quick starting and meeting rapidly large variation of

load demands.

4. The water surface and the tube should be so arranged so as to avoid priming.

5. The tubes should not accumulate soot or water deposits.

6.The refractory material should be as little as possible, but sufficient to secure

easy ignition and smokeless combustion of the fuel on reduced load.

The boiler site comprises with the following auxiliaries required to run the

boiler:

COAL BUNKERS

The coalbunker is a large hopper containing crushed coal coming from the coal

storage plant. Its capacity is 1000MT i.e. it can store the coal of 1000MT. There

are six coalbunkers out of which one remains stand by according to the schedule

of working of the machine. There is a level indicator for knowing the amount of

coal in the bunker. From the bunker, the coal comes into the coal mill through the

RC feeder. The RC feeder gives an indication of how much coal is in the coal

mill. It has a belt that is being rotated with a motor at a constant known speed.

Coal/Bowl Mills

There are six coal mills out of which one acts as stand by as according to the

schedule of operating a machine. The coal mill is also called the bowl mill,

because it contains the bowl. The bowl is rotated with a shaft connecting with an

asynchronous 3-phase motor through gearbox. The function of gearbox is to

reduce the speed of the motor, because the speed of the motor is 930rpm and it is

required to rotate the mill at 500RPM. From the coal mill, the four pipes going

44

outward to the each corners of the boiler. There are total 6*4=24 pipes and each

corner of the boiler gets six pipes of coal. The function of coal mill is to grind the

coal in the pulverized form. The air pressure from the P.A. fan is taken to blow

the pulverized coal in the boiler at its combustion chamber.

P.A. Fan

P.A.Fan

Machine

3-Phase Induction

motor

Output 1250KW

Voltage 6.6KV

Current 131.A

Speed 1493RPM

Power

factor 88.00%

(Table 1.12)

The full form of P.A. fan is primary air fan. It sucks the air from the

atmosphere. And force it towards coal mills. The P.A fan produces cold air. This

air is passed through air preheated. Here it converts into hot air, called primary

air. This air dries the pulverized coal and removes the moisture contents as well.

There are two P.A. fans per unit.

F.D.Fan

Machine

3-Phase Induction

motor

Output 750KW

Voltage 6.6KV

45

Current 66A

Speed 1490RPM

F.D. Fan:

(Table 1.13)

The F.D. fan sucks air from the atmosphere and force it to the boiler. The air

firstly passes through the air preheater From here it converts into the secondary

air. At the starting of the boiler, F.D fan is on firstly for 10minutes. After this I.D

fan and then P.A. fan are on.

There are two F.D. fans per unit.

I.D. Fan:

I.D.Fan

Machine

3-Phase Induction

motor

Output 1300KW

Voltage 6.6KV

Current 131.A

Speed 993RPM

(Table 1.14)

46

To recover the heat of combustion gases, the flue gas is forced to flow through

economizer,superheated,reheater, air preheater etc, This is done by I.D.fan.

I.D.fan is on after the F.D. fan for maintaining the pressure below a critical

value in the boiler. If I.D. fan is not on, then the air pressure in the boiler may

exceed the limit, result in the damage of boiler walls. I.D. Fan extracts the flue

gases from the boiler in such a way that flue gases come in contact with

superheated, reheater, air preheater and economizer etc, From boiler to chimney,

there are hoppers and ESP’s to remove the fly ash. There are three I.D. fans, out

of which one serves as stand by.

1.10.2 TECHNICAL DESCRIPTION OF BOILER

The boiler is a single drum unit with natural circulation, with dry bottom furnace,

outdoor type. The boiler is designed to supply steam to the turbo set of 210-mw

rating.

SUPPORTING STRUTURE, GALLERIES & STAIRCASE

The supporting structure serves for arranging and suspending the water wall

system, steam super heater, reheater, economizer, air heater, galleries, brickwork

and sheet steel casing. The entire steel structure is so designed to permit

undisturbed expansion of individual boiler parts and also to avoid any damage to

the boiler or brickwork setting due to thermal influences. The supporting

structure is designed strong enough with reference to the outdoor design of the

boilers.

Boilers comprises of following things:

Boiler Drum

It is made of alloy steel plate of 97mmnominal thickness and has an outside

diameter of 1800mm.The boiler drum level is 60mm.

Economizer

An economizer is a heat exchanger, which raises the temperature of the feed

water leaving the H.P. Heaters to about the saturation temperature corresponding

to the boiler pressure. The hot flue gases exiting the super-heater at a temperature 47

varying from 370 to 540 degree centigrade do this. The economizer with a

heating surface of 4930M2 is made of seamless steel tubular loops.

Air preheater

The use of air preheater is more economical with pluralized fuel boilers because

of temperature of flue gases going out is sufficiently large and high air

temperature is always desirable for better combustion. The tubular air heaters

having a total heating surface of 21690M2 are made of tubular tubes of outside

diameter 40mm.

Super-heater

The super-heater is a heat exanchanger in which heat is transferred to the

saturated steam to increase its temperature. It raises overall cycle efficiency. The

steam superheated has a total heating surface of 3782M2.

Reheater

The use of reheater is same as that of super-heater. The steam reheater having a

total heating surface of 3366M2 are made of pendant and horizontal tubular

loops.

Pulverized coal burner

Tilting type pulverized coal burners are arranged in the four corners of the

combustion chamber. In each corners there are six blowing pulverized coal

primary air mixture into the furnace. The pulverized coal is supplied to the

burners through pipes.

Auxiliaries for running the boiler:

Soot blowers

During boiler operation, the heating surfaces become coated with products of

combustion i.e. dusts, soot, cinder and fly ash. This phenomenon is especially

present in the coal fired water tubes boiler. The effect of these deposits is to

reduce the heat transfer. Therefore, for the efficient working of the boiler the

regular cleaning of these deposits is very essential. This is achieved by means of

soot blower, which use super-heated steam for blowing of the deposits from the

external heating surface of boiler, superheated, economizer and air preheater.

48

Fire Guns

There are total twelve fire guns. Each corner of the boiler gets one fire gun. There

are three floors at which the coal, air and oil are introduced in the combustion

chamber of the boiler.The fire gun is also called the oil gun. At AB stage the oil

gun has LOP with air and HOP with steam guns. The remaining guns at CD and

EF are only LOP with air gun. The function of the oil gun is to ignite the furnace

in starting of the boiler.

Deaerator

The function of the deaerating header is to remove dissolved non-

condensable gases and to heat boiler feed water. A deaerating header consists of

a pressure vessel in which water and steam are mixed in a controlled manner.

When this occurs water temperature rise, and all non-condensable dissolved

gases are liberated.

A deaerator header is the watch dog of a boiler as it protects the feed pump

piping boilers and any other piece of equipment that is in the boiler feed and

return cycle from the effect of corrosive gases that is oxygen and CO2 to a level

where are no longer a corrosion factors.

1.10.3 FURNACE

Furnace is the primary part of boiler where the chemical energy

available in the fuel is converted to thermal energy by combustion. Furnace is

designed for efficient and complete combustion. Major factors inside the furnace,

temperature inside the furnace, and turbulence, which causes rapid mixing

between fuel and air.

Bharat Heavy Electricals limited has developed the modern water-cooled

furnace. At the present time water cooled furnaces are supplied on every type and

size of boiler. Water cooled furnace has the following advantages:

a) In furnace not only combustion but also heat transfer is taking place

simultaneously.

49

b) The maintenance work involved in replacing the fire bricks (which is

otherwise necessary) is practically eliminated.

c) Due to heat transfer in the furnace the fuel gas leaving the furnace is

reduced to the acceptable level to the superheating surface.

d) Higher heat lading in the furnace is possible as heat transfer is

simultaneously removing heat. And have total economy in surfacing.

The furnace hopper outlet section is provided with an opening

of approx 1100 mm depth, for the fuel width of the furnace. On each side wall, in

the furnace hopper area, one water cooled access door (oval in shape of size

406*457 mm is provided. These openings are provided for taking maintenance of

the furnace.

1.11 ELECTROSTATIC PRECIPITATOR

(Fig 1.h)

Dust extractions from industrial gases become a necessity for environmental

reasons. Most of the plants in India use coal as fuel for generating steam. The

exhaust gases contain large amount of smoke and dust, which are being emitted

into atmosphere. This poses a real threat to the mankind as a health hazards.

Hence it has become necessary to free the exhaust gases from smoke and dust.

50

1.11.1 Need of New Electrostatic Precipitator

The electrostatic precipitators installed at GNDTP units are designed to give an

emission level of 789 mg/NM3 for a coal having an ash content of not more than

30%. However on actual testing it has been found that emission level from ESP’s

was about 3.0 mg/M3. The high level of emission is due to the fact that coals

burnt in the boiler have much higher ash content than what boilers are designed

for. The pollution control board of Punjab Govt. has specified an emission level

of 380 mg/M3 from chimney. In order to achieve this new emission level

additional ESP’s have been installed at GNDTP Bathinda.

1.11.2 Working Principle

The Electrostatic precipitator utilizes electrostatic forces to separate the dust

particle form the gas to be cleaned. The gas is conducted to a chamber containing

“Curtains” of vertical steel plates. These curtains divide the chamber into a

number of parallel gas passages. The frames are linked to each other to form a

rigid framework. The entire framework is held in place by four supports

insulators, which insulates it electrically from all parts, which are grounded. A

high voltage DC is applied between the framework and the ground thereby

creating a strong electrical field between the wires in the framework and the steel

curtains. The electrical field becomes strongest near the surface of the wire, so

strong that an electrical discharges. “The Corona” discharge is developed along

the wires. The gas is ionized in the corona discharge and large quantities of

positive and negative ions are formed. The positive wires are immediately

attracted towards the negative wires by strength of the field induced. The

negative ions however have to travel the entire space between the electrodes to

reach the positive curtains. On routes towards the steel curtains the ions collide

with each other and get charged and also this charge is transferred to the particles

in the gas. The particles thereby become electrically charged and also begin to

travel in the same direction as the ions towards the steel curtains. The electrical

force on each particle becomes much greater than gravitational force. The speed

51

of migration towards the steel curtains is therefore much greater than the speed of

sedimentation in free fall.

(Fig 1.i)

General Description

There various parts of the precipitators are divided into two groups: -

1. Mechanical system comprising of casing, hoppers, gas distribution

system, collecting and emitting systems, rapping mechanism, stairway and

galleries.

2. Electrical system comprising of transformer rectifier units with Electronic

Controller, Auxiliary Control Panels, Safety Interlocks and Field

Equipment Devices.

52

Precipitator Casing

The precipitator casing is an all welded pre-fabricated wall and roof panels. The

casing is provided with inspection doors for entry into the chamber at each field.

The doors are of heavy construction with machined surface to ensure a gas tight

seal.

(Fig 1.j)

The roof carries the precipitator’s internals, insulator housings, transformers etc.

The casing rests on roller a support which allows for free thermal expansion of

the casing during operating conditions. Galleries and stairway are provided on

the sides of the casing in easy access to rapping motors, inspection doors,

transformers etc. walkways are provided inside EP between fields for inspection

and maintenance. The dust is collected in large quantities on the curtains, the

collected electrodes. Due to periodic rapping, the dust falls into the hopper.

53

1) Hoppers

The hoppers are sized to hold the ash for 8 hrs. collection. Buffer plates are

provided in each hopper to avoid gas leakage. Inspection door is provided on the

one side of hoper wall. Thermostatically controlled heating elements are arranged

at the bottom portion of the hopper to ensure free flow of ash.

(Fig 1.k)

2) Gas Distribution System

The good performance of the precipitators depends on the event distribution of

gas over the entire cross-section of the field. As the gas expands ten-fold while

entering the precipitator, guide vanes, splitters and screens are provided in the

inlet funnel to distribute the flue gas evenly over the entire cross section of the

EP.

3) Collecting Electrode system

The collecting plates are made of 1.6 mm cold rolled mild steel plate and

shaped in piece by roll forming. The collecting plates and shaped in one piece

by roll forming. The collecting electrode has unique profile with a special

configuration on its longitudinal edges. This profile is designed to give rigidity

and to contain the dust in quiescent zone free from re-entertainment; collecting

plates are provided with hooks at their top edge for suspension. The hooks

engage in slot of the supporting angle. All the collecting plates in arrow are

held in position by a shock bar at the bottom. The shock bars are spaced by

guides.

54

4) Emitting Electrode system

The most essential part of precipitators is emitting electrode system. Four

insulators support this, the frames for holding the emitting electrodes are

located centrally between collecting electrodes curtains. The entire discharge

frames are welded to form a rigid box like structure. The emitting electrodes are

kept between the frames.

5) Rapping System

Rapping mechanism is provided for collecting and emitting electrodes. Geared

motors drive the rapping mechanism. The rapping system employs tumbling

hammers, which are mounted on a horizontal shaft. As the shaft rotates slowly

the hammers tumble on the shock bar/shock, which transmits blow to the

electrodes. One complete revolution of the rapping shaft will clean the entire

field. The rapper programmer decided the frequency of rapping. The tumbling

hammers disposition and the periodicity of the rapping are selected in such a

way that less than 2% of the collecting area is rapped one time. This avoids re-

entertainment of dust and puffing at the stock outlet.

(Fig 1.L)

The rapping shaft of emitting electrodes system is electrical isolated from the

geared motor driven by a shaft insulator. The space around the shaft insulator is

continuously heated to avoid condensation.

55

(Fig 1.m)

Following are the Modules for the Outgoing Feeders

1. Hopper heater for each field

2. Support insulator heaters.

3. Shaft insulator heaters.

4. Collecting electrode-rapping motor for each field.

5. Emitting electrode rapping motor for each filed.

1.11.3 ELECTRICAL SYSTEM

High Voltage Transformer Rectifier (HVR) with Electronic Controlled (EC)

The rectifier supplies the power for as particle charging and collection. The basic

function of the EC is to feed the precipitator with maximum power input under

constant current regulation should there be any flash between collecting and

emitting electrodes, the EC will sense the flash and quickly react by bringing the

input period voltage to zero and blocking it for a specific period. After the

ionized gases are cleaned and the dielectric strength restored, the control will

quickly bring back the power to a present value and raise it to the original non-

sparking level. Thus the EC ensure the electrical disturbance within precipitator.

Regulated AC power from EC is fed to the primary of the transformer, which is

stepped up and rectified to give a full wave power output. The transformer is

mounted on roof of the precipitator while the EC is located in an air conditional

room.

56

Auxiliary Control Panel (ACP)

The ACP houses the power and circuits required for energizing rapping motor

and heating elements of the precipitator. ACP controls each gas path. The

complete ACP is of modular type with individual module for each feeder. Each

module houses the power and control circuit with meters. Push buttons, witches

and indicating lamps are mounted on the door of the compartments.

Flue Gas Velocity (Flow)

If the flue gas velocity is more than desired, the treatment time in the fields will

reduce. It will cause poor performance of EP’s. Percentage oxygen on higher side

is an indication of excess flow of the flue gases. Efforts should be made to bring

percentage oxygen near to 6% at boiler outlet. Proper flue gas flow can be

achieved by plugging air leakages into the boiler. The ducts and the EP’s and also

by regulating primary air and secondary air required for proper combustion in the

furnace.

Maximizing the Performance OF ESP

The performance of the ESP is influenced by a number of factors many of which

may be controllable. It should be the aim of every operator to maximize the

performance by judiciously adjusting the controllable variables.

Cleaning Of Electrodes

The performance of the ESP depends on the amount of electrical power absorbed

by the system. The highest collection efficiency is achieved when maximum

possible electric power for a given set of operating conditions is utilized on the

fields. Too thick a dust layer on the collecting plates will lead to drop in the

effective voltage, which consequently reduces the collection efficiency. It also

leads to unstable to unstable operating conditions. Therefore the rapping system

of collecting and emitting electrodes should be kept in perfectly working

condition. All the rapping motors have been programmed to achieve the optimum

efficiency.57

Spark Rate

The operating voltage and current keep changing with operating conditions. The

secondary current of HVR’s have been set just below the spark level, so that only

few sparks occur during an hour. Spark rate between 5 to 10 sparks per minute is

the most favorable limit, as per the practical experience. Too high flash over will

not only result in reduction in useful power and interruption of precipitation

process but will cause snapping of emitting electrodes due to electrical erosion.

How to Control the Spark Rate ?

One number s-pot and one number t-pot have been provided on the front of each

electronic controller. The s-pot controls the drop rate of rise of field current after

the spark is over. The operator can control the rate of spark by adjusting these

two pots manually. Both the pots if turned anticlockwise will cause increase in

spark rate.

Ash Hopper Evacuation

Improper/incomplete hopper evacuation is a major cause for the precipitator

malfunction. If the hoppers are not emptied regularly, the dust will build up to the

high tension emitting system causing shot circuiting. Also the dust can push the

internals up causing misalignment of the electrodes. Though the hoppers have

been designed for a storage capacity of 8 hours, under MCR conditions, this

provision should be used in case of emergency. Normally, the hopper should not

be regarded as storage as storage as storage space for the collected ash.

Oil combustion

The combustion of oil used during start up or for stabilization of the flames can

have an important impact on precipitator operation. Un burnt oil, if passed into

ESP can deposit on the emitting and collecting electrodes and deteriorates the

electrical condition i.e. reduce the precipitators operating voltage due to high

electrical resistivity and consequently the ESP’s performance is affected 58

adversely. The precipitator performance remains poor until the oil vaporizes and

the ash layer gets rapped off, which usually takes along time.

Air Conditioning of the ESP’s Control Room

The ESP’s control room houses sophisticated electronic controller. The

operation of these controllers directly reflects on precipitator performance. In

order to ensure that the controllers are in proper working conditions, it is

essential to maintain a dust free atmosphere with controlled ambient conditions.

Therefore, the air conditioners should be kept in proper working conditions.

GENERAL DISCRIPTION OF ELECTRONIC CONTROLLER

The EC-HVR is the High voltage DC power supply equipment for the

electrostatic precipitator used for extracting fly ash from the exhaust gases. The

equipment is supplied in two parts: -

1. The High Voltage Transformer Rectifier (HVR).

2. The Electronic Controller (EC).

The transformer rectifier unit (HVR) consists of an oil immersed step up

transformer ac reactor, high voltage, high frequency choke, measuring and

protection components. The electronic controller (EC) contains the anti parallel-

connected thyristors pair for controlling the input voltage to the transformer

rectifier unit & necessary control circuit. The complete equipment is designed to

provide a continuously adjustable dc output voltage up to 70 KV peak across the

precipitator electrode. The controls are arranged i.e. the unit operate as constant

current source adjustable up to an average current of 800 mA max. Occurrence of

spark at the electrodes is sensed & made to block the output voltage for a specific

period & the voltage is built up again in a specified manner to provide optimum

operational efficiency of the precipitator.

Principle of Operation

Controlling the voltage on the primary of the transformer controls the output

voltage & current at high voltage DC terminals. The voltage control is achieved

by two thyristors connected in anti-parallel configuration. In normal operation,

the output of the thyristors is controlled by the gate pulse circuit, which in turn 59

gets its control signal from the current regular output. The output of current

regulator adjusts itself i.e. the actual current is maintained equal to set reference

value. In case of a spark detection unit detects the same. Wide ranges of

adjustment are provided for selecting blocking period & range of ‘S’ & ‘T’

control to make equipment suitable to different operating conditions. Persistent

low voltage at the primary of transformer or the persistent excess current on

primary side that may occur to short-circuiting initiates tripping of equipment.

TECHNICAL DATA OF ELECTROSTATIC PRECIPITATOR

60

Design Conditions Unit-1,3,4

1. Gas flow rate

2. Temperature

3. Dust concentration

4. Number of precipitator

5. Number of gas path per

boiler

6. No. of fields in series in each

gas pass

200m3/sec

1450 C

38.9

gms/Nm3

One

2

5

(Table 1.15)

COLLECTING ELECTRODE

1. Total No. of collecting plates

2. Nominal height of collecting plate

3. Nominal Length of collecting

plate

2480

12.5 m

400

mm

(Table 1.16)

EMITTING ELECTRODES

1. Type

2. Size

3. No. of electrodes in each field

4. Plate/Wire spacing.

Spiral

2.7mm

1440

150

mm

(Table 1.17)

RAPPERS FOR COLLECTING ELECTRODES

1. No. & type of One drop hammer per row of collecting

61

rapper

2. Frequency of

Rap

3. Drive

4. Location

electrodes surface area 90 m2

Varying from 12 raps/hr at the inlet field to 1

rap/hr at exist.

Geared electric motor controlled by synch.

Programmer.

At the bottom of collecting system.

(Table 1.18)

RAPPERS FOR EMMITING ELECTRODES

1.No. and type of rappers

2. Frequency of Rap

3. Driver

Approx. one drop hammers/two rows of

electrodes.

10 raps/hour.

Geared Electric Motor controlled by

Synch. Programmer.

On the side of emitting frame

(Table 1.19)

HOPPERS

1. Type

2 .No of Hoppers

3. Capacity

Pyramidal

20

8 hour storage

62

(Table 1.20)

MOTORS

RAPPING OF EMMITING ELECTODE

1. Quantity

2. Rating

3. Location

10 Nos.

Geared Motor 0.33hp/2.5

rpm at 3-phase 415 V, 50 Hz

On the top EP

(Table 1.21)

RAPPING OF COLLECTING ELECTODE

1. Quantity

2. Rating

3. Location

10 Nos.

Geared Motor, 33hp/2.5 rpm

at

3- Phase 415 V 50 Hz.

63

On the top EP

(Table 1.22)

ELECTRICAL ITEM

RECTIFIERS

1. Rectifier Rating

2. Number/Boiler

3. Type

4. Location

70 KV (peak),800 MA (Mean)

10

Silicon Diode Full Wave, Bridge

connection

Mounted on the top of

precipitator

(Table 1.23)

RECTIFIER CONTROL PANEL

64

1. Type of Control

2. Location

Thyristor

In the Control Room

(Table 1.24)

1.12 ASH HANDLING SYSTEM

Operation & maintenance features of ash handling system, for the said power

station, is being executed by M/S.DC industrial plant services Ltd., (DCIPS),

Calcutta. The ash handling system is furnished with necessary in- built facilities

and devices for removal of ash. Generated in boiler furnace on combustion of

coal, to a distant location.

Bottom ash formed in lumps falls down into a water impounded furnace hopper,

namely “Bottom ash hopper”, directly beneath the furnace. The ash is cooled and

stored therein and is hydraulically removed in slurry state from the hopper into an

in-plant slurry sump followed by further transportation to a remote ash pond. Fly

ash which is extremely fine in nature and shares the major amount of the total

generation is also carried by the flue gas and is collected, in steps, in economizer

hopper, Air heater hoppers, ESP Hoppers and Stack hopper on the flue gas path.

Out of the total quantity of fly ash, the major amount is separated from the flue

gas in ESP and is collected in corresponding ESP hoppers. The fly ash thus

collected in various hoppers is disposed in dry state to silo. The dry disposal is

achieved by collecting the ash in dry form in station silos and further unloading it

on road trucks for conveying it away for necessary commercial utilization.

In the case of wet disposal how ever, the fly ash in the form of slurry is received

into the in-plant slurry sump followed by final disposal to remote ash pond.

Necessary slurry pumping facilities are in that system for disposal of bottom ash,

and fly ash slurry under wet state disposal i.e. slurry disposal from silos) from the

65

in plant slurry sump to remote ash pond. Necessary water supply arrangements

through pumps are also induced in the system to cater to water requirement at

various consumption points during system operation.

(Fig 1.n)

1.12.1 BOTTOM ASH HANDLING SYSTEM

Bottom ash, generated in lumps in the boiler furnace for each unit, falls down

into respective water impounded and self supported bottom ash hopper installed

directly beneath the furnace. The bottom ash hopper so of adequate capacity to

provide, effective storage if ash and is continuously supplied with make up water

to cool the ash from furnace temperature down to a substantially lower

temperature permissible inside the hopper.

The bottom ash hopper belongs to a w-type configuration with a common

rectangular section at the upper part and two integral V-Section at the lower part

of the hopper.

Each V-Sections is furnished with two (2) sets of ash discharge equipment

consisting of feed –gate, double roll clinker grinder, feed sump and jet pump

installed one after another in above sequence. Out of two gats of ash discharge

equipment for each v Section, one is normally utilized for cleaning of ash and

the other stand by. During ash cleaning operation, the bottom ash mixed with

water, is allowed to get discharge from the hopper by opening the feed gate. The

mixer is further diluted by high-pressure spray water from dilution water by and

66

thick bottom ash slurry in turn is fed directly into the crusher located below the

feed gate. Big clinkers of bottom ash are fragmented in the crusher into smaller

sizes convenient for pipeline Transportation and are fed into the jet pump. The jet

pump is hydraulically operated by means of High pressure water supply and

conveys the input ash in the form of slurry to the in plant ash slurry sump.

Bottom ash cleaning operation for each unit is carried out at least once in every

shift from respective local panel, designated as “Bottom Ash System Panel “.

1.12.2 FLY ASH SYSTEM

Fly ash system utilizes pressure-conveying principal for onward transportation of

fly ash from fly ash hopper to station silos. There are two type of ash disposal.

1. Dry Ash Disposal

2. Wet Ash Disposal

In Dry Ash Disposal, some of Fly Ash is sent to the cement factory and

remaining fly ash is disposed in Wet Ash Disposal way.

In Wet Ash Disposal, Fly Ash is mixed with high-pressure water and produce ash

slurry is discharge to ash slurry sump and from there to ash pond for disposal.

Ash pond has length of 1.5 K.M, Breadth of 500 M and depth of 10M.

NEED OF WET ASH DISPOSAL

Since, the hopper capacity is 500 T, and the rate of Fly Ash is 100 T /H .It is

difficult to store dry ash because of short capacity of silo.

1.13 TURBO-GENERATOR (T.G.)

The generator is directly coupled to the turbine shaft, converts mechanical energy

of turbine shaft into electrical energy. It consists of two electrical windings. One

is mounted on the turbine shaft, rotating with it, and is called the rotor. The other

is arranged as a shroud around the rotor, fixed to the floor, and is called stator.

67

The relative motion of rotor and stator generates the electricity. The generator,

which is hydrogen, cooled produces electricity at 15,750Volt.

The T-G is two pole type with cylindrical rotor (Non -Salient Pole type) using

direct water cooling of stator winding, including phases connecting bus bar,

terminal bushing and direct hydrogen cooling of rotor winding. The stator frame

is of pressure –resistant and gas tight construction with 4 horizontal coolers in the

frame itself forming part of ventilation and closed cooling circuit.

GENERATOR CAPABILITY

The generator is capable of delivering 247MVA continuously at 15.75KV

terminal voltage, 9050 Amps stator current and 3.5Kg/Cm2 hydrogen pressure

with cold gas temperature not exceeding 44degrree Celsius and distillate

temperature at inlet of stator winding not exceeding 45 degree celicsus. Output of

the generator at the various lagging and leading power factors at rated hydrogen

pressure are as per the generator capability curve given. Characteristics (O.C.C,

S.C.C) and v-curves of the generator are shown on the diagrams.

HYDROGEN COOLER:

The turbo-generator has been provided with four Nos. gas coolers mounted

longitudinally in side stator body for cooling of hot gas, thus taking away the heat

looses generated by rotor winding, stator core and wind age losses. The gas

cooler is a shell and tube heat exchanger consisting of cooling tubes with coiled

copper wire around them to increase the surface area of cooling. Cooling water

flows through the tubes while hydrogen flowing across coolers comes into

contact with external surface of cooling tubes. Heat removed from hydrogen is

dissipated through cooling water.

AUXILIARIES

SEAL OIL SUPPLY SYSTEM

The shaft seals are supplied with seal oil from a separate circuit, which consists

to the following principal component Vacuum Tank, AC seal oil pumps 1&2, DC

seal oil pump, Vacuum pump, oil coolers, and Seal oil filters, Intermediate oil

tank.68

A vacuum tank pump keeps the seal oil in the vacuum tank under vacuum and

largely extracts the gas absorbed by the oil while passing through the hydrogen

and air atmospheres. The seal oil is drawn from the vacuum tank and delivered to

the shaft seals via a cooler and filter. In the event of a failure of seal oil pump1.

Seal oil pump 2. Automatically takes over the seal oil supply. Upon failure of

seal oil pump2, the standby DC seal oil pump is automatically takes over the oil

supply to the shaft seals.

GAS SUPPLY SYSTEM

The gas system has the following functions:

To provide means for safely putting H2 into or taking it out of the machine.

To maintain gas pressure in the machine at the desired value.

To indicate to the operator at all tomes the condition of gas in the machine, its

pressure and purity.

To dry the gas in the machine and remove any water vapour which may get into

it from the seal oil.

The gas system essentially comprises the following equipments

H2 and CO2 cylinders

Pressure reducers

CO2 vaporizer

Gas drier

Humidity Monitors

Purity measuring instruments.

Hydrogen is admitted to the generator through a perforated pipe header extending

along the length of the casing at the top.

To prevent formation of an explosive mixture in the generator casing during

filling and removing the hydrogen. The air or hydrogen in the casing is first

removed with carbon dioxide respectively. The latter is introduced through CO2

feed pipe, and the air or hydrogen in the casing is discharged to atmosphere

69

through the hydrogen feed line. The hydrogen driers, services to dry the gas

inside the generator.

1.13.1 STATOR WATER COOLING SYSTEM

The water for cooling the stator winding, phase connection and bushing is

circulated in a closed circuit. To ensure uninterrupted generator operation 100%

capacity pumps sets are provided. In the event of a failure of one pump the

standby pump is immediately cut in by automatic starting equipment.

The stator water supply system essentially comprise the following components:

Expansion Tank

Stator Water Pump A&B

Stator Water Cooler A&B

Stator Water Filter A&B

The operating pump draws the water from the expansion tank. The water after

passing through water coolers, filters enter the winding and returns back to the

expansion tank.

1.13.2 START UP OF GENERATOR

Prior to start up, it should be ascertained that the following auxiliaries are in

operation and will continue to remain in service.

Seal oil system

Gas System

Stator water system

Secondary cooling water system

Prior to startup, all the connections should be rechecked. This applies to the

piping as well as to cabling. When checking the cabling, special attention should

be paid to testing the metering and signal cables. All alarm systems should be

checked. All temperature measuring points should also be checked . This applies

to the local as well as remote reading thermometers.

70

1.13.3 SHUT DOWN OF GENERATOR

When shutting down the generator all excitation should be removed by the time

speed reaches to 2000rpm. If this is not done the field winding temperature will

rise to lack ventilation since rate of gas circulation is proportional to speed.

1.14 TURBINE

FUNCTION OF TURBINE

The steam turbine is a prime mover that converts the stored mechanical energy in

steam into the rotational mechanical energy. The thermal energy of the steam

delivered to the turbine is converted into the kinetic energy of the steam flow

through steam nozzles. The function of a steam nozzle is to convert the heat

energy of the steam into the kinetic energy. Its chief use is to produce a high

velocity jet of steam, which is used to drive a steam turbine. This is achieved by

allowing the steam to expand from a region of high pressure at the inlet to a

region of low pressure at the outlet. The jets of high velocity steam are then

directed on to a ring of blades, which are free to rotate. These moving blades are

fixed to the rim of a revolving wheel. Between each row of moving blades, there

is a ring of fixed blades. These stationary blades are fixed to the turbine casing

and they face the opposite direction to the moving blades. The function of fixed

blades is only to receive the steam jet coming out of the moving blade ring and to

divert it on to the next ring of moving blades by changing its direction.

GENERAL DESCRIPTION:

There are two live steam lines connecting the boiler to the turbine. There are to

cold reheat and two hot reheat lines connecting the repeater and the turbine. In

each of the two live steam lines, one electrically operated isolating valve, one 71

water separator and one quick closing stop valve are mounted. In each of the cold

reheat lines a non-return flap valve, controlled by quick closing oil is provided.

Both the hot reheat lines are provided with water separators just before the

interceptor valves.

1.14.1 CONSTRUCTION

The turbine is a tandem compound machine with HP, IP and LP parts. The HP

part is a single-flow cylinder and the IP and LP parts are double flow cylinder.

Rigid coupling connects the individual turbine rotors and the generator rotor.

Hp Turbine, Barrel Type Casing

The outer casing of the HP turbine is of the barrel type and has neither an axial

nor a radial flange. The barrel type casing permits flexibility of operation in the

form of short start-up times and a high rate of change of load even at high initial

steam conditions.

IP Turbine

The IP parts are of double flow construction. Attached in the axially split outer

casing is an inner casing supported cinematically and taking the guide blades.

The arrangement of an inner casing confines the high steam inlet conditions to

the admission branch of the casing, while the joint of the outer casing is only

subjected tom the lower pressure and lower temperature at the exhaust of the

inner casing.

LP Turbine

The casing of the double-flow LP cylinders is of three-shell design. The shells

are axially split and of rigid welded construction. The inner shell taking the first

rows of guide blades is attached cinematically in the middle shell.

BALDING

The entire turbine is provided with reaction balding. The moving blades of the

HP and IP parts and the front row of the LP part with T-roots and shrouding are

72

milled from the solid. The last stages of the LP part consist of twisted, drop

forged moving blades.

CONSTRUCTION

Three Cylinders reheat condensing turbine

1. Single flow HP turbine wit 25 reaction stages

2. Double flow IP turbines with 20 reaction stages per flow

3. Double flow LP turbines with 8 reaction stages per flow

TURBINE SITE CONTAINS THE FOLLOWING MAIN MACHINES:

1. Boiler feed Pump

BFP

Machine

3-Phase Induction

motor

Output 4000KW

Voltage 6.6KV

Current 410A

Speed 1493RPM

Power factor 89.00%

Connection Star

Rotor type SQ. Cage

Efficiency 96%

Weight 19700Kg

73

(Table 1.25)

The 210MW turbo set is provided with the three boilers feed pumps, each

for 100% of the total quantity. This pump feeds feed water to the boiler. This is

the largest auxiliary of the unit with 100% capacity which takes suction of feed

water from the deaerator and supplies to the boiler drum after preheating the

same in the H.P. heaters 1&2 and economizer. The delivery capacity of B.F.P is

445T/Hr.to meet the boiler requirement corresponding t the various load. The

following table gives the rating of the motor connecting in the pump.

2. Condensate Extraction Pump

CEP

Machine 3-Phase Induction motor

Output 600KW

Voltage 6.6KV

Current 63.5A

Speed 1484RPM

Power factor 88.00%

Connection Star

Rotor type SQ. Cage

Efficiency 94%

Weight 5880Kg

74

(Table 1.26)

The steam after working in three casing of turbine is condensed in

the two surface condenser in each unit installed just below the L.P.exhaust.

The condensate is collected in the bottom portion of each condenser so to call

hot well pumps from where it is pumped up to the deaerator by the condensate

extraction pumps through the L.P. heaters. There are two CEP, out of which

one remains as stand by.

1.15 SWITCH GEAR

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 sometime 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 sometime 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

75

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.

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 Isolators

Single pole Isolator

Double pole Isolator

Fuses

A fuse is short piece of metal, insert in series with the circuit, which melt

excessive current flows through it and thus breaks the circuit. The material used

for the fuse element should possess the following properties: -

Low melting point.

High conductivity.

Free from oxidation.

The common materials used for the fuse element are copper, tin-lead alloy (tin

63% and lead 37%, silver, aluminum etc.)A fuse is connected in series with the

circuit to be protected and carries the load current without overheating under

normal conditions. However when an abnormal condition occurs, excessive

current flows through it. This raises the temperature, which melt the fuse element

and open the circuit. This protects the machine or apparatus from the damage,

which can be used by excessive currents.

Circuit Breakers

76

Circuit breaker is on/off switch operating in an electric circuit in normal as well

as abnormal operating conditions. While making or breaking contact there is a

transition stage of arcing between contacts which is governed by electric

discharge between the contacts at instant of separation, thus current continuous in

the circuit till discharge appears. The study of this phenomenon is very important

for design and operational characteristics of C.B.

1.15.1 Functions of Switchgear

Under different conditions CB is subjected to varying stresses as current varies

from few amp due to no load current of T/F up to many K amp heaviest short

circuit current and varying circuit impedance. CB not only interrupts, but also

closes the circuit. If breaker closes during short circuit it causes some trouble

because then the voltage break down that bridges the contact gap produces high

current arc which melt the contact before closer such situations is not desirable as

breaker may not reopen. Often automatic re-closing is required because usually

fault is of temporary nature. About 20% of the short circuit current persists

however immediately after re-closing the breaker has to re-interrupt the short

circuit current. This is main function specially if there are extremely high

currents, which would result in the contact wear and tear.

The main function, which CB has in addition to satisfy the rated breaking

capacity and rated making and breaking times are: -

Short Circuit interruption.

Interruption of small induction currents.

Capacitor Switching.

Asynchronous Switching.

Interruption of Shot Line Faults.

Operating Principle of Circuit Breaker

A circuit breaker is a device which: -

77

Makes or Breaks a circuit either manually or by remote contact under

normal (full load) conditions.

Breaks a circuit manually or by remote control under abnormal

conditions.

Breaks a circuit automatically under abnormal conditions i.e. fault

conditions.

Thus circuit breaker is just a switch, which can be operated under normal

and abnormal conditions both manually and automatically.

To perform the above operation a circuit breaker essentially consists of fixed and

moving contacts, called electrodes. When fault occurs on the power system, the

trip coil of the circuit breaker is energized, which pulls apart the moving contacts

from the fixed contacts as shown in fig thus opens the circuit. When the moving

contacts are separated from the fixed contacts, an arc is struck between them. The

production of arc not only delays the current interruption process but also

generates enormous heat which may cause damage to the equipments of the

power system or the breaker itself. Therefore every effort is made to extinguish

the arc produced in the circuit breaker as quickly as possible.

RELAYS

Relay is a device that detects the fault mostly in the high voltage circuits and

initiates the operation of the circuit breaker to isolate the defective section from

the rest of the circuit. Whenever fault occurs on the power system, the relay

detects that fault and closes the trip coil circuit. This results in the opening of the

circuit breaker, which disconnects the faulty circuit. Thus the relay ensures the

safety of the circuit equipment from damage, which the fault may cause.

Switch Gear supplied to G.N.D.T.P. BATHINDA

In 6.6/0.415 KV switchgear we have two unit transformer and one station T/f that

after stepping down the voltage, fed it to two 6.6 KV unit buses and to station

bus. Various feeders are connected to 6.6 KV buses and in order to avoid 78

complete shutdown, supply is maintained by drawing supply from station bus, to

3B & 4B bus. Supply from 3A bus is stepped down to 415 V by 1000 KVA

SWGR T/F – 1 & fed to 415 V bus. As same in 4B bus. In case of tripping

standby bus used. Various feeders are connected to these buses. We generate

electricity at 11 KV & step-down to 7 KV by UAT. Rating of UAT T/F is 15

MVA & station T/f is 225 MVA, 11/7 KV.

CIRCUIT BREAKER USED IN INDOOR SWITCHGEAR

Mainly two types of CB’s are used in switchgear according to the requirement

1. 6.6KV MOCB’s

2. 415 V ACB’s

Minimum Oil CB (6.6 KV)

It is provided for each motor feeder of rating 6.6 KV and as incoming breaker for

6.6 KV bus. In these CB’s arc is quenched in arcing chamber with minimum

quantity of oil.

SPECIFICATIONS OF MOCB OF MOTOR FEEDER

Rated Voltage 6.6 KV, 50 Hz, 3-pole

Rated current 1250 Amperes

Breaking Current 34.7 KA (Sym)-378 (Asym)

Breaking Capacity 395 MVA

Making Capacity 88 Peaks KA

Short Time Current Capacity 34.7 KA for 1 Sec

MOCB uses solid material for insulating purposes and use just minimum oil for

arc quenching. The arc-interruption device is enclosed in a tank of insulating

material, which is a line voltage in normal operation. Thus are also known as live

tank breathers.

Various protections relay are used in conjunction with MOCB’s according to

requirement of connected equipment are

Over current relay

79

Instantaneous relay

Locked rotor relay

Unbalanced protection relay

Earth fault protection relay

Under voltage relay

415V ACB’s

In these CB’s air at atmospheric pressure is used for quenching the arc.

Specifications of ACB’s

Rated Voltage 660 V (AC)

Rated Current 1600 Amperes

Rated Making Capacity 95 KA (PEAK)

Rated Breaking Capacity 45 KA (rms)

Max. Switching Frequency/hour 15 make/break open

Opening Time 20msec

Total Opening Time Included

Arcing Time 30.35 msec

Closing Time 500 msec

This CB is provided with Three Main Protection Trips

1. Thermal Delayed Over Current Trip

This consists of three bimetal strips, each headed by a current T/F, which is slid

on to the appropriate phase conductor. Tuning the calibrated knob vary the

setting. A temp, compensating strip is also used which makes the tripping time

largely independent of ambient temperature.

2. Instantaneous Over Current Trip

This is fitted in contact assemblies. The U shaped magnet cores with associated

armature are mounted on the conductor and energized by breaker current.

3. Under Voltage Trip

It open the breaker instantly if the auxiliary as main voltage drop to 50% of the

rated coil voltage.

80

VARIOUS REQUIREMENTS OF CB USED IN S/G

a. All the CB should be three-pole and there should be suitable for

remote/local electrical operation and manual operation also.

b. The CB should be suitable for the operation on 220 V dc auxiliary control

supply.

c. The CB is required to drive motors and also be suitable for incoming from

LT T/F.

d. The closing Of CB should be direct motor drive type as stored energy type.

e. The CB should be provided with manual closing and tripping device also.

f. The CB should also be provided with shunt tripping coil suitable for 220

V.

g. CB should have mechanical indication for ON/OFF position.

h. CB should be provided with the device, which does not allow closed

breaker reached in as reached out

i. The CB’s should be suitable for locking, test & service position & it

should also be suitable for electrical/mechanical operation in both testing

service position.

Bus Bars (6.6 KV/415 V)

This term is used for main bar on conductor carrying electric current through

which many connections are made for connecting switches and the equipments

like bus bar made of Aluminum because it has higher conductivity, corrosion

resistant and lower cost as compared to copper

Switch Gear 6.6 KV

Circuit Breakers Minimum Oil Type

Rupturing Capacity 350 MVA

Current Rating 1250 Amperes

Switch Gear 415 V

Circuit Breakers Air Type

Current Rating 0.8Amperes

81

1.16 SWITCH YARD

The electricity generated at 11KV by the turbo-generation sets is stepped up by

power transformers to132 KV in case of stage-1 and to 220 KV in case of stage-2

for further transmission through 7, 220 KV and 15, 132 KV air blast circuit

breakers along with their associated protective systems.

The major equipments installed at G.N.D.T.P. sub-stations are: -

Transformers

Circuit Breakers

Isolators

Bus-Bars

Lightening Arrestors

Current Transformers

Indicating Lamps

1.16.1 CLASSIFICATION

According to design Sub-Stations are classified as: -

Indoor Sub-Station

It is installed with in the building of the sub-station and hence the named Indoor

Sub-Stations. Such s/s are usually designed for 11 KV but can be constructed for

33 KV or 66 KV, if the surrounding atmosphere is containing impurities such as

snow, heavy rainfall, dense fog, dust etc, which may damage the equipments.

Outdoor Sub-station

In this type the apparatus of the s/s is installed in the open and hence the name

outdoor s/s. such s/s can be designed to handle low, high, extra high voltage. The

outdoor s/s may be further classified as: -

Pole Mounted S/S

Foundation Mounted S/S.

Sub-Station Equipments

Following are the important equipments/apparatus employed at sub-stations:

Transformers82

It is static device or machine, which is isolated, input voltage from the output

voltage at the same frequency. It is used to step up or step down the voltage.

Power Transformers

These are provided for stepping up the generation voltage. For units 1 & 2 the

power transformer step up the voltage from 11 KV to 132 KV and for units 3 & 4

the power transformers step up the voltage from 11 KV to 220 KV. All the four

transformers have a rated capacity of 125 MVA each.

(Fig 1.o)

Auto Transformer

The auto transformers are used to balance the load between the 132 KV bus bars

and the 220 KV bus bars. The auto transformers have a capacity of 100 MVA

each.

(Fig 1.p)

Unit Auxiliary Transformer

83

There is one unit of auxiliary transformer provided on each unit to step down the

voltage from 11 KV to 6.6 KV which is require for major plant auxiliaries. These

transformers have a capacity of 15 MVA each.

(Fig 1.q)

Station Transformers

Two No’s station transformers one for each unit are provided to step down the

voltage from 132 KV to 6.6 KV. These transformers have capacity of 22.5 MVA.

They serve as the standby source of supply to auxiliaries.

(Fig 1.r)

84

Circuit Breakers

It is device, which makes and breaks the circuit under no load, full load or fault

conditions. It can be operated manually under normal conditions and

automatically under abnormal conditions with the help of relays. These are

installed to perform the following duties: -

To carry full load current continuously.

To open and close the circuit on no load.

To make and break the normal operating current.

To make and break the short circuit current.

At G.N.D.T.P. switch yard air blast circuit breakers are employed instead of oil

circuit breakers due to following reasons: -

There is no risk of fire hazard and explosion.

Due to less arc energy in it as compared to that in oil circuit breakers burning

contact is less.

Axial-Blast Air Circuit Breakers

A schematic arrangement of an axial-blast air circuit breaker is as shown in

figure. The arcing potions of the fixed and moving contacts are coated with silver

tungsten alloy. The moving contacts are coated to a piston and shaft of the

contact is guided by guide spring.

Opening the lower air valve closes the circuit breaker and under normal

conditions the valve remains open. Whenever a fault occurs, the upper valve is

opened and the lower valve is closed by the mechanism not shown in figure. Air

enters the upper vessel at a high pressure, which separates the moving contacts

from the fixed. An arc is struck between the contacts, which is extinguished by

the axial blast of cold air and current is interrupted. Once the arc is extinguished,

the upper valve is closed and the lower valve is opened to close the circuit.

SF6 Circuit Breakers: - Sulpher hexafluoride CB is shown in fig. In this the

movable cylinder is coupled with the moving contacts, whereas the piston is

fixed. When fault occurs the moving contacts is separated from the fixed contact.

Since the movable cylinder is attached with the moving contacts, it moves against 85

the fixed piston. Thus the gas filled in the cylinder is compressed and released

through the nozzle as shown in fig.

The gas moves along the arc and reduces its diameter by axial convection and

radial

(Fig 1.s)

dissipation. At zero current, the diameter becomes too small and the arc gets

extinguished. The gas is not exhausted to the atmosphere; it is rather again used

for arc extinction.

Advantages

They are smaller in size because of high dielectric strength of SF6 gas.

No danger of or explosion.

They require minimum maintenance.

Since same gas is recycled, a small quantity of SF6 gas is required for long

run.

They give silent operation; they do not make any sound like A.C.B. during

operation.

It requires less maintenance.

Isolators

86

One of the cardinal measures for ensuring full safety in carrying out work on

piece of equipment in electrical installation is to disconnect reliably the unit or

section on which the work is to be performed from all other live parts of the

installation. To guard against mistake it is necessary that an apparatus, which

make visible break in the circuit, should do this. Such an apparatus is the isolator.

Isolators do not have the arc control devices and therefore cannot be used to

interrupt current at which an arc will be drawn across the contacts. The open arc

that would be drawn in such a case is very dangerous in that it will not only

damage or destroy the isolator and the equipments surrounding it, but will also as

a rule will cause Flash Over between phases, in other words results is short

circuit in the installation. This is why isolators are used only for disconnecting

and connecting parts or units after de-energizing them by opening their circuit

with respective circuit breakers. It is operated only at no load. These are

generally placed on the both the sides of a circuit breaker in order to make repair

and maintenance on the circuit breaker without any danger.

(Fig 1.t)

Bus Bars

87

Bus bar is the term used for the main bar of the conductor carrying an electric

current to which many connecting switches and other equipments in various

arrangements. At G.N.D.T.P. there are 2 No’s of 132 KV bus bars and 220 KV

bus bars. These bus bars are made up of aluminum. Two number bus couplers

connect the 132 KV bus bars and 220 KV bus bars with each other.

Lightening Arrestors

These are the arc apparatus devices designed to protect insulators of power lines

and electrical installations from lightening surges by diverting surge to earth and

instantly restoring the circuit insulation to its normal strength with respect to

earth. These are connected between earth and line.

(Fig 1.u)

Current Transformer

These are the instrument transformers. The secondary winding of the C.T. is

connected to the instruments placed on the panel boards. The secondary winding

is also connected to various relays for their operations.

88

(Fig 1.v)

Insulators

Generally suspension and strain insulators are employed at the sub-station. They

provide insulation between the conductors and the earth sheet towers.

Wave Traps

These are used in carrier communication circuits and are mounted on the lines.

(Fig 1.w)

EARTHING

Earthing

Process of connecting metallic bodies of all the electrical apparatus and

equipment to the huge mass of the earth by a wire of negligible resistance is

called earthing.When a body is earthed, it is basically connected to the huge mass

89

INDUSTRIAL PROJECTSINDUSTRIES, HOUSEHOLD COMMERCIAL SUPPLIES

MAJOR PROJECTS MINOR PROJECTS

GENERATION BASED

Designing The Drum Level Controller SoftwareStudy Of The Plant Working (UCBS / Cells)

ENVIRONMENTAL STUDY

MANAGEMENT

Auto ESP Design For The Air Pollution ControlRain Water Harvesting

of earth by a wire having negligible resistance. Thus, the body attains zero

potential i.e., potential of earth. This ensures that whenever a live conductor

comes in contact with the outer body, the charge is released to the earth

immediately. The meaning of the term ‘Earthing’ or ‘Grounding’ is to connect

the electrical equipment to earth i.e., to connect the apparatus with a water pipe

or to an artificial earth electrode through a conductor having negligible

resistance. When a body is earthed, it is said to have zero potential and thus will

avoid shock to the operator. According to “Indian Electricity Rules”, the means

connection with general mass of earth in such a manner so as to ensure at all

times an immediate discharge of energy without danger.

Chapter No.2

2.Introduction To project

Touring and Study of the various plant cells and their respective working (Fig. 2.a)

90

(fig 2.a)

2.1 GENERATION/ PRODUCTION BASED PROJECT

Project Objective:

Touring various plant cells

To study the various plant sectors and understanding the working of the

plant

Dm plant and cooling towers

Coal plant

Boiler and furnace section

ESP units

Turbine / Generation sector

Power distribution sector

2.1.1 Designing the Drum Level Control

To always maintain an optimum water level in the drum (refers to the BOILER

DRUM which is used for the generation of high pressure steam in the boiler

plant) for the efficient working of the boiler and the turbine section, this in turn

results in the effective generation of electricity. The project aims at providing a

security cover to the drum if accidentally the critical conditions are met. The

project aims at developing: 91

CONTROLLER

FURNACE ZONE

DRUM SECTION

BOILING WATER

COILED WATER PIPES

O-LEVEL

MAIN STEAM SUPERHEATERS HIGH PRESSURE TURBINE

REHEATERS

MEDIUM PRESSURE TURBINE

REHEATERS

LOW PRESSURE TURBINE

CONDENSER

BOILER FEED PUMP

CONDENSER EXTRACTION PUMP

DEAERATOR

FEED FLOW

Flow control diagrams

Designing the control structure for the drum

Visiting the site (installation plans)

Identifying design parameters and the ambient conditions

Drum Level Controller

(Fig 2.b)

Color Coding

1. RED Control Inputs & Outputs

2. GREEN Steam Flow Path

3. BLUE Water Flow

4. ORANGE Furnace/ Coal Firing Zone92

5. GREY Turbine Shaft Coupling

(Table 2.1)

2.2 ENVIRONMENTAL STUDY BASED PROJECTS

2.2.1 Project Objective:

Environmental studies aims at infusing a strong feeling of Love & Concern

towards the nature. It teaches the trainee the importance of protecting the

environment and urges to implement the eco- friendly methods for the power

industry.

1. Coal Waste Management

i. Highlighting the problem

ii. Working for the Remedial solution

2. Rain Water Harvesting

i. Concept

ii. Design issues

iii. Finding out the potential site for the project

implementation.

2.2.2 Waste Management

Since the Thermal Plant works on the Coal Consumption for the generation of

power electricity, thus the burning of coal leads to the emission of many harmful

gases such as carbon dioxide, carbon monoxide, sulphur dioxide and nitrous

compounds. The emission of such gases in the atmosphere leads to the air

pollution of the adjoining city and the localities. The smoke from the chimney is

often accompanied by the fly ash content which is not only harmful for the living

beings but is also a poison for the agricultural land nearby.

This waste from the coal burning has always been the major issue for the

organization. The plant earlier dumped the fly ash and the slurry (coal ash +

water) in the adjoining barren land which resulted in the pollution of the

underground water. The land became totally useless and the slurry after drying 93

Boiler And Furnace ZoneDry Ash And Slurry

Waste

Electrostatic Precipitator

Flue Gases

High voltage Supply

Ammonia DosingExhaust Free from Fly Ash

was carried away by the blowing winds in the nearby surroundings thus polluting

both the atmosphere and hampering the agricultural production.

ESP DESIGN ISSUES

(fig 2.c)

2.2.3 Rain Water Harvesting

General Introduction:

Rain water harvesting is one of the methods of water conservation. The rain

water is collected in small pits which are in turn connected with a big water

reservoir. So the rain water keeps on accumulating in the reservoir which can be

harnessed for any suitable purpose at any instant of time.

Since this belt of Punjab receives very scanty rainfall. Still when it showers, it

becomes a major drainage problem. Effort has been taken to club the drainage

pipes from the roof-tops to a common collector zone. Thus the rain water is

progressively collected in the reservoir for the future use.

94

2.3 RESOURCE MANAGEMENT BASED PROJECT

2.3.1 Project Objective:

Resource management always plays an important role in the effective working of

any organization. This project aims at making the trainee aware of the following:

Human resource management

Employee demands

Plant employee relationship

Resources management (Coal /Fuel management)

Safety issues

Coal Management deals with the concept of effective usage of coal. Coal being

one of the valuable non- renewable resources must be efficiently used. Now a

day coal is not a cheaper commodity, due to limited stock available within the

country domain. The coal reservoirs are depleting at a much faster pace due to

rapid usage and dependency.

For the efficient use of the coal, the coal is used with the at most care and

management. This flow chart depicts the coal chain in the plant. Some of the key

factors leading the coal management are stated as:

Key Factors:

Certain minimum stock should always be available for efficient working of

the plant.

Since quality and quantity are closely related, so the amount of the coal

required highly depends upon the quality of the coal in use.

Low ash content coal is the major demand of any coal based industry.

95

Start

Coal is mechanically unloaded from the rail wagons using tipplers

Monitor the status of the coal

Is coal Fine grated? Coal is shifter to the crusher house on magnetic conveyor beltNo

Fine grated coal is stored in boiler raw coal bunkersGrated coal heap

Yes

Coal storage

Surplus

Raw coal chain feeder feeds the coal mill

Powdered coal is finally stored in the pulverized bunkers

At last the powdered coal is carried with a stream of hot air to the furnace for ignition

Stop

FLOW CHART ON COAL PROCESSING

(Fig 2.d)

96

Abstract

Fossil fuel such as coal are concentrated form of energy and produce cheap

thermal energy. India being rich in Coal reserves which are predicted to last for

200 years has set up Thermal Plant in most of states. The capital investment and

gestation period are less in conducting thermal pants. However the major

drawbacks is that these Power Plant generates environmental pollution like Air,

Water, Noise and Solid waste but by taking suitable corrective measures the

Thermal Plants can be made eco-friendly and efficient. Secondly, it is being

noted that all the units are being working automatically by the Engineers through

the Control Room Unit that is UCBS. In order to operate the plant one should

have the proper knowledge of each unit thoroughly.

97