Summer training report on NTPC Badarpur ,DELHI
This Report includes the following department
1. Turbine Maintenance Department
2. Boiler Maintenance Department
3. Plant Auxiliary Maintenance
4. Coal Handling Department
1. 1
A
Summer Training Report
On
“National Thermal Power Corporation”
Submitted by
RANJEET KUMAR
Course: B.Tech ( Third Year)
Branch: Mechanical & Automation Engineering.
Roll No: 00518003613
DEPARTMENTOF MECHANICAL & AUTOMATION ENGINEERING
DELHI TECHNICAL CAMPUS
28/1 KNOWLEDGE PARK-III, GREATER NOIDA, U.P. 201306
2. 2
ACKNOWLEDGEMENT
With deep reverence and profound gratitude I express my sincere thanks to Mr.
A.K.Sharma, (BMD) for giving me an opportunity to do training at NTPC/BTPS. I also
would like to thank Mr.S.K.Gurg, (TMD) who has helped me at the working sites,
explaining and giving me all the information I needed to complete this report. I am also
very much thankful to Mr.Gaurav Goyal, (PAM), helping me throughout the training At
last I would like to convey my thanks to all the members of the staff of NTPC/BTPS who
have helped me at every stage of training.
Training Period: June 15, 2015 to July 11, 2015.
RANJEET KUMAR
ROLL No:-00518003613
B.TECH (THIRD YEAR)
MECHANICAL & AUTOMATION ENGINEERING.
DELHI TECHNICAL CAMPUS, GREATER NOIDA
3. 3
ABSTRACT
I was appointed to do 4 week training at this esteemed organization from 15th June 2015 to 11th
July, 2015. I was assigned to visit various division of plant, which were;
Boiler Maintenance Department (BMD)
Turbine Maintenance Department (TMD)
Plant Auxiliary Maintenance (PAM)
These 4 weeks training was a very educational adventure for me. It was really amazing to see
the plant by yourself and learn how electricity, which is one of our daily requirements of life,
is produced. This report has been made by my experience at BTPS. The material in this report
has been gathered from my textbook, senior student reports and trainers manuals and power
journals provided by training department. The specification and principles are as learned by me
from the employees of each division of BTPS.
4. 4
TABLE OF CONTENTS
Contents Page no.
Acknowledgement 2
Certificate 3
Abstract 4
List of figures 5
1. Introduction 6
1.1 Company overview 6
1.2 Training overview 9
2. Product/Process details 10
2.1 Operation of a power plant 10
2.2 Basic steps of electricity generation 10
2.3 Rankine cycle 18
3. Details of training 20
3.1 Department/Section Detail 20
3.1.1 Boiler Maintenance Department 20
3.1.2 Plant Auxiliary Maintenance 26
3.1.3 Turbine Maintenance Department 29
3.2 Coal Handling Department 37
5. 5
LIST OF FIGURES
Figure Page No
Figure 1.1 Growth of NTPC Installed Capacity & Generation Chart 6
Figure 1.2 Power Contribution chart of NTPC in INDIA 7
Figure 1.3 Strategies Chart of NTPC 7
Figure 2.1: Block Diagram Of NTPC Power Plant 11
Figure 2.2 the various parts of the coal thermal power plants 12
Figure 2.3 Operation of a Rankine cycle 18
Figure 2.4 T-S diagram of a typical Rankine cycle 19
Figure 2.5 Boiler Drum 21
Figure 3.1 Reheater 23
Figure 3.2 Economizer 24
Figure 3.3 Air pre-heater 25
Figure 3.4 Pulverizer 26
Figure 3.5 Ash handling system 27
Figure 3.6 Water treatment plant 28
Figure 3.7 Demineralization 29
Figure 3.8 Operating principle of steam turbine 30
Figure 3.9 steam cycle diagram 31
Figure 3.10 Turbine & Turbine cycle 32
Figure 3.11 A Typical water cooled condenser 33
Figure 3.12 A Deaerator 35
Figure 3.13 Coal cycle diagram 36
Figure 3.14 Coal handling system 37
Figure 3.15 Coal handling division at BTPS 38
Figure 3.16 A Idler 38
Figure 3.17 Coal Storage Area of the BTPS 40
6. 6
1. INTRODUCTION
1.1 Company Overview
NTPC is the largest thermal power generating company of India. India’s largest power company,
NTPC was set up in 1975 to accelerate power development in India. NTPC is emerging as a diversified
power major with presence in the entire value chain of the power generation business. Apart from
power generation, which is the mainstay of the company, NTPC has already ventured into consultancy,
power trading, ash utilization and coal mining. NTPC ranked 341st in the 2010, Forbes Global 2000‟
ranking of the World’s biggest companies. NTPC became Maharatna Company in May, 2010, one of
the only four companies to be awarded this status.
The total installed capacity of the company is 39,174 MW (including JVs) with 16 coal based and 7
gas based stations, located across the country. In addition under JVs, 7 stations are coal based &
another station uses naphtha/LNG as fuel. The company has set a target to have an installed power
generating capacity of 128000 MW by the year 2032. The capacity will have a diversified fuel mix
comprising 56% coal, 16% Gas, 11% Nuclear and 17% Renewable Energy Sources(RES) including
hydro. By 2032, non-fossil fuel based generation capacity shall make up nearly 28% of NTPC”s
portfolio.
NTPC has been operating its plants at high efficiency levels. Although the company has 17.75% of the
total national capacity, it contributes 27.40% of total power generation due to its focus on high
efficiency.
Figure 1.1 Growth of NTPC Installed Capacity & Generation Chart
7. 7
In October 2004, NTPC launched its Initial Public Offering (IPO) consisting of 5.25% as fresh
issue and 5.25% as offer for sale by Government of India. NTPC thus became a listed company
in November 2004 with the Government holding 89.5% of the equity share capital. In February
2010, the Shareholding of Government of India was reduced from 89.5% to 84.5% through
Further Public Offer. The rest is held by Institutional Investors and the Public.
Figure 1.2 Power Contributions chart of NTPC in INDIA
Figure 1.3 Strategies Chart of NTPC
9. 9
1.2 Training Overview
ABOUT BTP
“BADARPUR THERMAL POWER STATION” was established on 1973 and it was the part of
Central Government. On 01/04/1978 is given as No Loss No Profit Plant of NTPC. Since then
operating performance of NTPC has been considerably above the national average. The
availability factor for coal stations has increased from 85.03 % in 1997-98 to 90.09 % in 2006-
07, which compares favourably with international standards. The PLF has increased from 75.2%
in1997-98 to 89.4% during the year 2006-07 which is the highest since the inception of NTPC
Badarpur thermal power station started with a single 95 mw unit. There were 2 more units (95
MW each) installed in next 2 consecutive years. Now it has total five units with total capacity of
720 MW. Ownership of BTPS was transferred to NTPC with effect from 01.06.2006 through
GOIs Gazette Notification.
The power is supplied to a 220 KV network that is a part of the northern grid. The ten circuits
through which the power is evacuated from the plant are:
1. Mehrauli
2. Okhla
3. Ballabgarh
4. Indraprastha
5. UP (Noida)
6. Jaipur Given below is the details of unit with the year they’re installed.
Address: Badarpur, New Delhi-110044
Fax: 26949532
Telephone: (STD-011)-26949523
Install Capacity: 720 MW
Dreaded Capacity: 705 MW
Location: New Delhi
Coal Source: Jharia Coal Fields
Water Source: Agra Canal
Beneficiary State: Delhi
Unit Size: 3x95 MW, 2x210 MW
Unit Commissioned: Unit 1-95 MW-July 1973,
Unit 2-95 MW -August 1974,
Unit 3-95 MW-March 1975,
Unit 4-210 MW-December 1978,
Unit 5-210 MW-December 1981
10. 10
Transfer of BTPS to NTPC: Ownership of BTPS was
Transferred to NTPC with effect
From 01-06-2006 through GOI’s
Gazette Notification.
Station Location
Badarpur is situated only 20 km away from Delhi. The plant is located on the left side of the
National Highway (Delhi-Mathura Road) and it comprises of 430 hectares (678 acres) bordered
by the Agra Canal from East and by Mathura-Delhi Road from West. However, the area for ash
disposal is done in the Delhi Municipal limit and is maintained with the help of Delhi
Development Authority. The plant is also close to the project of 220kv Double Circuit
Transmission line between the I.P. station and Ballabgarh Cooling Water is obtained from Agra
Canal for the cooling system. Additional 60 cusecs channel has also been constructed parallel to
the Agra Canal so as to obtain uninterrupted water supply during the slit removing operation in
Agra Canal.
2. PRODUCT/PROCESS DETAILS
2.1 Operation of a power plant
Basic Principle:-
As per FARADAY’S Law-“Whenever the amount of magnetic flux linked with a circuit changes,
an EMF is produced in the circuit. Generator works on the principle of producing electricity. To
change the flux in the generator turbine is moved in a great speed with steam.” To produce steam,
water is heated in the boilers by burning the coal. In Badarpur Thermal PowerStation, steam is
produced and used to spin a turbine that operates a generator. Water is heated, turns into steam and
spins a steam turbine which drives an electrical generator. After it passes through the turbine, the
steam is condensed in a condenser; this is known as a Rankin cycle.
The electricity generated at the plant is sent to consumers through high-voltage power lines The
Badarpur Thermal Power Plant has Steam Turbine-Driven Generators which has a collective
capacity of 705MW. The fuel being used is Coal which is supplied from the Jharia Coal Field in
Jharkhand. Water supply is given from the Agra Canal.
2.2 Basic steps of electricity generation
The basic steps in the generation of electricity from coal involves following steps:
Coal to steam
Steam to mechanical power
Mechanical power to electrical power
12. 12
The various parts of the coal thermal power plants are
Figure 2.2 the various parts of the coal thermal power plants
1. Cooling Tower: Cooling towers are heat removal devices used to transfer process waste heat
to the atmosphere. Cooling towers may either use the evaporation of water to remove process
heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed
circuit dry cooling towers rely solely on air to cool the working fluid to near the dry-bulb air
13. 13
temperature. Common applications include cooling the circulating water used in oil refineries,
chemical plants, power stations and building cooling. The towers vary in size from small roof-
top units to very large hyperboloid structures that can be up to 200 meters tall and 100 meters in
diameter, or rectangular structures that can be over 40 meters tall and 80 meters long. Smaller
towers are normally factory-built, while larger ones are constructed on site. The absorbed heat is
rejected to the atmosphere by the evaporation of some of the cooling water in mechanical forced-
draft or induced Draft towers or in natural draft hyperbolic shaped cooling towers as seen at most
nuclear power plants.
2. Cooling Water Pump it pumps the water from the cooling tower which goes to the
condenser.
3. Three phase transmission line: Three phase electric power is a common method of electric
power transmission. It is a type of poly phase system mainly used to power motors and many
other devices. A three phase system uses less conductive material to transmit electric power than
equivalent single phase, two phase, or direct current system at the same voltage. In a three phase
system, three circuits reach their instantaneous peak values at different times. Taking current in
one conductor as the reference, the currents in the other two are delayed in time by one-third and
two-third of one cycle .This delay between “phases” has the effect of giving constant power
transfer over each cycle of the current and also makes it possible to produce a rotating magnetic
field in an electric motor. At the power station, an electric generator converts mechanical power
into a set of electric currents, one from each electromagnetic coil or winding of the generator.
The current are sinusoidal functions of time, all at the same frequency but offset in time to give
different phases. In a three phase system the phases are spaced equally, giving a phase separation
of one-third of one cycle. Generators output at a voltage that ranges from hundreds of volts to
30,000 volts.
4. Unit transformer (3-phase): At the power station transformers step-up this voltage to one
more suitable for transmission. After numerous further conversions in the transmission and
distribution network the power is finally transformed to the standard mains voltage (i.e. the
“household” voltage). The power may already have been split into single phase at this point or it
may still be three phase. Where the step-down is 3 phase, the output of this transformer is usually
star connected with the standard mains voltage being the phase- neutral voltage. Another system
commonly seen in North America is to have a delta connected secondary with a centre tap on
one of the windings supplying the ground and neutral. This allows for 240 V three phase as well
as three different single phase voltages( 120 V between two of the phases and neutral , 208 V
between the third phase ( or wild leg) and neutral and 240 V between any two phase) to be
available from the same supply.
5. Electrical generator: An Electrical generator is a device that converts kinetic energy to
electrical energy, generally using electromagnetic induction. The task of converting the electrical
energy into mechanical energy is accomplished by using a motor. The source of mechanical
energy may be water falling through the turbine or steam turning a turbine (as is the case with
14. 14
thermal power plants). There are several classifications for modern steam turbines. Steam
turbines are used in our entire major coal fired power stations to drive the generators or
alternators, which produce electricity. The turbines themselves are driven by steam generated in
"boilers “or "steam generators" as they are sometimes called. Electrical power stations use large
steam turbines driving electric generators to produce most (about 86%) of the world’s electricity.
These centralized stations are of two types: fossil fuel power plants and nuclear power plants.
The turbines used for electric power generation are most often directly coupled to their-
generators .As the generators must rotate at constant synchronous speeds according to the
frequency of the electric power system, the most common speeds are 3000 r/min for 50 Hz
systems, and 3600 r/min for 60 Hz systems. Most large nuclear sets rotate at half those speeds,
and have a 4-pole generator rather than the more common 2-pole one.
6. Low Pressure Turbine: Energy in the steam after it leaves the boiler is converted into
rotational energy as it passes through the turbine. The turbine normally consists of several stages
with each stages consisting of a stationary blade (or nozzle) and a rotating blade. Stationary
blades convert the potential energy of the steam into kinetic energy and direct the flow onto the
rotating blades. The rotating blades convert the kinetic energy into impulse and reaction forces,
caused by pressure drop, which results in the rotation of the turbine shaft. The turbine shaft is
connected to a generator, which produces the electrical energy. Low Pressure Turbine (LPT)
consists of 4x2 stages. After passing through Intermediate Pressure Turbine steam is passed
through LPT which is made up of two parts- LPC REAR & LPC FRONT. As water gets cooler
here it gathers into a HOTWELL placed in lower parts of turbine.
7. Condensation Extraction Pump: A Boiler feed water pump is a specific type of pump used
to pump water into a steam boiler. The water may be freshly supplied or returning condensation
of the steam produced by the boiler. These pumps are normally high pressure units that use
suction from a condensate return system and can be of the centrifugal pump type or positive
displacement type.
8. Condenser: The steam coming out from the Low Pressure Turbine (a little above its boiling
pump) is brought into thermal contact with cold water (pumped in from the cooling tower) in the
condenser, where it condenses rapidly back into water, creating near Vacuum-like conditions
inside the condenser chest.
9. Intermediate Pressure Turbine: Intermediate Pressure Turbine (IPT) consists of 11 stages.
When the steam has been passed through HPT it enters into IPT. IPT has two ends named as
FRONT & REAR. Steam enters through front end and leaves from Rear end.
10. Steam Governor Valve: Steam locomotives and the steam engines used on ships and
stationary applications such as power plants also required feed water pumps. In this situation,
though, the pump was often powered using a small steam engine that ran using the steam
produced by the boiler a means had to be provided, of course, to put the initial charge of water
into the boiler (before steam power was available to operate the steam-powered feed water
15. 15
pump).The pump was often a positive displacement pump that had steam valves and cylinders at
one end and feed water cylinders at the other end; no crankshaft was required. In thermal plants,
the primary purpose of surface condenser is to condense the exhaust steam from a steam turbine
to obtain maximum efficiency and also to convert the turbine exhaust steam into pure water so
that it may be reused in the steam generator or boiler as boiler feed water. By condensing the
exhaust steam of a turbine at a pressure below atmospheric pressure, the steam pressure drop
between the inlet and exhaust of the turbine is increased, which increases the amount heat
available for conversion to mechanical power. Most of the heat liberated due to condensation of
the exhaust steam is carried away by the cooling medium (water or air) used by the surface
condenser. Control valves are valves used within industrial plants and elsewhere to control
operating conditions such as temperature, pressure, flow and liquid level by fully or partially
opening or closing in response to signals received from controllers that compares a “set point” to
a “process variable” whose value is provided by sensors that monitor changes in such conditions.
The opening or closing of control valves is done by means of electrical, hydraulic or pneumatic
systems.
11. High Pressure Turbine: Steam coming from Boiler directly feeds into HPT at a temperature
of 540°C and at a pressure of 136 kg/cm². Here it passes through 12 different stages due to which
its temperature goes down to 329°C and pressure as 27 kg/cm².This line is also called as CRH –
COLD REHEAT LINE. It is now passed to a REHEATER where its temperature rises to 540°C
and called as HRH-HOT REHEATED LINE.
12. Deaerator: A Deaerator is a device for air removal and used to remove dissolved gases (an
alternate would be the use of water treatment chemicals) from boiler feed water to make it
noncorrosive. A deaerator typically includes a vertical domed deaeration section as the
deaeration boiler feed water tank. A Steam generating boiler requires that the circulating steam,
condensate, and feed water should be devoid of dissolved gases, particularly corrosive ones and
dissolved or suspended solids. The gases will give rise to corrosion of the metal. The solids will
deposit on the heating surfaces giving rise to localized heating and tube ruptures due to
overheating. Under some conditions it may give rise to stress corrosion cracking. Deaerator level
and pressure must be controlled by adjusting control valves the level by regulating condensate
flow and the pressure by regulating steam flow. If operated properly, most deaerator vendors will
guarantee that oxygen in the deaerated water will not exceed 7 ppb by weight (0.005 cm3/L)
13. Feed water heater: A Feed water heater is a power plant component used to pre-heat water
delivered to a steam generating boiler. Preheating the feed water reduces the irreversibility
involved in steam generation and therefore improves the thermodynamic efficiency of the
system. This reduces plant operating costs and also helps to avoid thermal shock to the boiler
metal when the feed water is introduced back into the steam cycle. In a steam power (usually
modeled as a modified Rankin cycle), feed water heaters allow the feed water to be brought up to
the saturation temperature very gradually. This minimizes the inevitable irreversibility associated
with heat transfer to the working fluid (water).
16. 16
14. Coal conveyor: Coal conveyors are belts which are used to transfer coal from its storage
place to Coal Hopper. A belt conveyor consists of two pulleys, with a continuous loop of
material- the conveyor Belt – that rotates about them. The pulleys are powered, moving the belt
and the material on the belt forward. Conveyor belts are extensively used to transport industrial
and agricultural material, such as grain, coal, ores etc.
15. Coal Hopper: Coal Hoppers are the places which are used to feed coal to Fuel Mill. It also
has the arrangement of entering Hot Air at 200°C inside it which solves our two purposes:- 1. If
our Coal has moisture content then it dries it so that a proper combustion takes place. 2. It raises
the temperature of coal so that its temperature is more near to its Ignite Temperature so that
combustion is easy.
16. Pulverized Fuel Mill: A pulveriser is a device for grinding coal for combustion in a furnace
in a fossil fuel power plant.
17. Boiler drums: Steam Drums are a regular feature of water tube boilers. It is reservoir of
water/steam at the top end of the water tubes in the water-tube boiler. They store the steam
generated in the water tubes and act as a phase separator for the steam/water mixture. The
difference in densities between hot and cold water helps in the accumulation of the “hotter”-
water/and saturated –steam into steam drum. Made from high-grade steel (probably stainless)
and its working involve temperature of 390°C and pressure well above 350psi (2.4MPa). The
separated steam is drawn out from the top section of the drum. Saturated steam is drawn off the
top of the drum. The steam will re-enter the furnace in through a super heater, while the saturated
water at the bottom of steam drum flows down to the mud-drum /feed water drum by down
comer tubes accessories include a safety valve, water level indicator and fuse plug.
18. Ash Hopper:A steam drum is used in the company of a mud-drum/feed water drum which is
located at a lower level. So that it acts as a sump for the sludge or sediments which have a
tendency to accumulate at the bottom.
19. Super Heater: A Super heater is a device in a steam engine that heats the steam generated
by the boiler again increasing its thermal energy. Super heaters increase the efficiency of the
steam engine, and were widely adopted. Steam which has been superheated is logically known as
superheated steam; non- superheated steam is called saturated steam or wet steam. Super heaters
were applied to steam locomotives in quantity from the early 20th century, to most steam
vehicles, and also stationary steam engines including power stations.
20. Force Draught Fan: External fans are provided to give sufficient air for combustion. The
forced draught fan takes air from the atmosphere and, warms it in the air preheated for better
combustion, injects it via the air nozzles on the furnace wall.
21. Reheater: Reheater is a heater which is used to raise the temperature of steam which has
fallen from the intermediate pressure turbine
17. 17
22. Air Intake:Air is taken from the environment by an air intake tower which is fed to the fuel.
23. Economizers: Economizer, or in the UK economizer, are mechanical devices intended to
reduce energy consumption, or to perform another useful function like preheating a fluid. The
term economizer is used for other purposes as well-Boiler, power plant, heating, ventilating and
air-conditioning. In boilers, economizer are heat exchange devices that heat fluids , usually
water, up to but not normally beyond the boiling point of the fluid. Economizers are so named
because they can make use of the enthalpy and improving the boilers efficiency. They are
devices fitted to a boiler which save energy by using the exhaust gases from the boiler to preheat
the cold water used to fill it (the feed water). Modern day boilers, such as those in cold fired
power stations, are still fitted with economizer which is decedents of Green’s original design. In
this context there are turbines before it is pumped to the boilers. A common application of
economizer in steam power plants is to capture the waste heat from boiler stack gases (flue gas)
and transfer thus it to the boiler feed water thus lowering the needed energy input , in turn
reducing the firing rates to accomplish the rated boiler output . Economizer lower stack
temperatures which may cause condensation of acidic combustion gases and serious equipment
corrosion damage if care is not taken in their design and material selection.
24. Air Preheater : Air preheated is a general term to describe any device designed to heat air
before another process (for example, combustion in a boiler). The purpose of the air preheater is
to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler
by reducing the useful heat lost in the flue gas. As a consequence, the flue gases are also sent to
the flue gas stack (or chimney) at a lower temperature allowing simplified design of the ducting
and the flue gas stack. It also allows control over the temperature of gases leaving the stack.
25. Precipitator: An Electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate
device that removes particles from a flowing gas (such as air) using the force of an induced
electrostatic charge. Electrostatic precipitators are highly efficient filtration devices, and can
easily remove fine particulate matter such as dust and smoke from the air steam. ESPs continue
to be excellent devices for control of many industrial particulate emissions, including smoke
from electricity-generating utilities (coal and oil fired), salt cake collection from black liquor
boilers in pump mills, and catalyst collection from fluidized bed catalytic crackers from several
hundred thousand ACFM in the largest coal-fired boiler applications. The original parallel plate-
Weighted wire design (described above) has evolved as more efficient (and robust) discharge
electrode designs, today focus is on rigid discharge electrodes to which many sharpened spikes
are attached , maximizing corona production. Transformer –rectifier systems apply voltages of
50-100 Kilovolts at relatively high current densities. Modern controls minimize sparking and
prevent arcing, avoiding damage to the components. Automatic rapping systems and hopper
evacuation systems remove the collected particulate matter while on line allowing ESPs to stay
in operation for years at a time.
18. 18
26. Induced Draught Fan:The induced draft fan assists the FD fan by drawing out combustible
gases from the furnace, maintaining a slightly negative pressure in the furnace to avoid
backfiring through any opening. At the furnace outlet and before the furnace gases are handled
by the ID fan, fine dust carried by the outlet gases is removed to avoid atmospheric pollution.
This is an environmental limitation prescribed by law, which additionally minimizes erosion of
the ID fan.
27. Flue gas stacks: A Flue gas stack is a type of chimney, a vertical pipe, channel or similar
structure through which combustion product gases called flue gases are exhausted to the outside
air. Flue gases are produced when coal, oil, natural gas, wood or any other large combustion
device. Flue gas is usually composed of carbon dioxide (CO2) and water vapour as well as
nitrogen and excess oxygen remaining from the intake combustion air. It also contains a small
percentage of pollutants such as particulates matter, carbon mono oxide, nitrogen oxides and
sulphur oxides. The flue gas stacks are often quite tall, up to 400 meters (1300 feet) or more, so
as to disperse the exhaust pollutants over a greater area and thereby reduce the concentration of
the pollutants to the levels required by government's environmental policies and regulations. The
flue gases are exhausted from stoves, ovens, fireplaces or other small sources within residential
abodes, restaurants, hotels through other stacks which are referred to as chimneys.
2.3 RANKINE CYCLE:-
The Rankine cycle is a thermodynamics cycle which converts heat into work. The heat is
supplied externally to a closed loop, which usually uses water as the working fluid. This
cycle generates about 80% of all electricity power used throughout the world, including
virtually all solar thermal, biomass, coal and nuclear power plants. It is named after
William John Macqueen Rankine, a Scottish polymath.
DESCRIPTION: A Rankine cycle describes a model of the operation of a steam heat
Figure 2.3 Operation of Rankine cycle
19. 19
that a pump is used to pressurize liquid instead of gas. This requires about 1/100th (1%) as much
energy Engines most commonly found in power generation plants. Common heat sources for
power plants using the Rankine cycle are coal, natural gas ,oil, and nuclear.
The Rankine cycle is sometimes referred to as a practical Carnot cycle as, when an efficient
turbine is used, the T-S diagram will begin to resemble the Carnot cycle. The main difference is
as that compressing a gas in a compressor (as in the Carnot cycle).
The efficiency of a Rankine cycle is usually limited by the working fluid. Without the pressure
going super critical the temperature range the cycle can operate over is quite small, turbine entry
temperature are around 30°C. This gives a theoretical Carnot efficiency of around63% compared
with an actual efficiency of 42% for a modern coal-fired power station. This low turbine entry
temperature (compared with a gas turbine) is why the Rankine cycle is often used as a bottoming
cycle in combined cycle gas turbine power stations. The working fluid in a Rankine cycle
follows a closed loop and is re-used constantly. The water vapour and entrained droplets often
seen billowing from power stations is generated by the cooling systems (not from the closed
loop Rankine power cycle) and represents the waste heat that could not be converted to useful
work. Note that cooling towers operate using the latent heat of vaporization of the cooling fluid.
The white billowing clouds that form in cooling tower operation are the result of water droplets
which are entrained in the cooling tower air flow; it is not, as commonly thought, steam. While
many substances could be used in the Rankine cycle, water is usually the fluid of choice due to
its favourable properties, such as nontoxic and uncreative chemistry, abundance, and low cost, as
well as its thermodynamic properties. One of the principal advantages it holds over other cycles
is that during the compression stage relatively little work is required to drive the pump, due to
the working fluid being in its liquid phase at this point. By condensing the fluid to liquid, the
work required by the pump will only consume approximately 1% to 3% of the turbine power and
so give a much higher efficiency for a real cycle.
The benefit of this is lost somewhat due to the lower heat addition temperature. Gas turbines, for
instance, have turbine entry temperatures approaching 1500°C.Nonetheless, the efficiencies of
steam cycles and gas turbines are fairly well matched.
Figure 2.4 T-S diagram of a typical Rankine cycle
20. 20
T-S diagram of a typical Rankine cycle operating between pressures of 0.06bar and 50bar .There
are four processes in the Rankine cycle, each changing the state of the working fluid. These
states are identified by number in the diagram to the right.
i. Process 1-2: The working fluid is pumped from low to high pressure, as the fluid is a
liquid at this stage the pump requires little input energy.
ii. Process 2-3: The high pressure liquid enters a boiler where it is heated at constant
pressure by an external heat source to become a dry saturated vapour.
iii. Process 3-4: The dry saturated vapour expands through a turbine, generating power.
This decreases the temperature and pressure of the vapour, and some condensation
may occur.
iv. Process 4-1: The wet vapour then enters a condenser where it is condensed at a
constant pressure and temperature to become saturated liquid. The pressure and
temperature of the condenser is fixed by the temperature of the cooling coils as the
fluid is undergoing a phase change.
In an ideal Rankine cycle the pump and turbine would be isentropic, i.e. the pump and turbine
would generate no entropy and hence maximize the net work output. Process 1-2 and 3-4 would
be represented by vertical lines on the T-S diagram and more closely resemble that of the Carnot
cycle.
The Rankine cycle shown here prevents the vapour ending up in the super heated region after the
expansion in the turbine, which reduces the energy removed by the condensers.
3. DETAILS OF TRAINING
3.1 Department/Section Detail
3.1.1 Boiler Maintenance Department (BMD)
Boiler and Its Description:
The boiler is a rectangular furnace about 50 ft (15 m) on a side and 130 ft (40 m) tall. Its walls
are made of a web of high pressure steel tubes about 2.3inches (60 mm) in diameter. Pulverized
coal is air-blown into the furnace from fuel nozzles at the four corners and it rapidly burns,
foaming a large fireball at the centre. The thermal radiation of the fireball heats the water that
circulates through the boiler tubes near the boiler perimeter. The water circulation rate in the
boiler is three to four times the throughput and is typically driven by pumps. As the water in the
boiler circulates it absorbs heat and changes into steam at700 °F (370 °C) and 3200psi
(22.1MPa). It is separated from the water inside a drum at the top of furnace.
The saturated steam is introduced into superheat pendant tubes that hang in the hottest part of the
combustion gases as they exit the furnace. Here the steam is superheated to 1,000 °F (540°C)to
prepare it for the turbine. The steam generating boiler has to produce steam at the high purity,
pressure and temperature required for the steam turbine that drives the electrical generator. The
generator includes the economizer, the steam drum, the chemical dosing equipment, and the
furnace with its steam generating tubes and the superheated coils. Necessary safety valves are
21. 21
located at suitable points to avoid excessive boiler pressure. The air and flue gas path equipment
include: forced draft (FD) fan, air preheated (APH), boiler furnace, induced draft (ID) fan, fly
ash collectors (electrostatic precipitator or bag house) and the flue gas stack. For units over about
210MW capacity, redundancy of key components is provided by installing duplicates of the FD
fan, APH, fly ash collectors and ID fan with isolating dampers. On some units of about 60MW,
two boilers per unit may instead be provided.
AUXILARYIES OF BOILER:
I. FURNACE
Furnace is primary part of boiler where the chemical energy of the fuel is
converted to thermal energy by combustion. Furnace is designed for efficient and
complete combustion. Major factors that assist for efficient combustion are
amount of fuel inside the furnace and turbulence, which causes rapid mixing
between fuel and air. In modern boilers, water furnaces are used.
II. BOILER DRUM
Figure 2.5 Boiler Drum
22. 22
Drum is of fusion-welded design with welded hemispherical dished ends. It is provided with
stubs for welding all the connecting tubes, i.e. down comer, risers, pipes, saturated steam outlet.
The function of steam drum internals is to separate the water from the steam generated in the
furnace walls and to reduce the dissolved solid contents of the steam below the prescribed limit
of 1ppm and also take care of the sudden change of steam demand for boiler.
The secondary stage of two opposite banks of closely spaced thin corrugated sheets,
which direct the steam and force the remaining entertained water against the corrugated
plates. Since the velocity is relatively low this water does not get picked up again but
runs down the plates and off the second stage of the two steam outlets.
From the secondary separators the steam flows upwards to the series of screen dryers,
extending in layers across the length of the drum. These screens perform the final stage
of the separation.
Once water inside the boiler or steam generator, the process of adding the latent heat of
vaporization or enthalpy is underway. The boiler transfers energy to the water by the
chemical reaction of burning some type of fuel.
The water enters the boiler through a section in the convection pass called the
economizer. From the economizer it passes to the steam drum. Once the water enters the
steam drum it goes down the down comers to the lower inlet water wall headers. From
the inlet headers the water rises through the water walls and is eventually turned into
steam due to the heat being generated by the burners located on the front and rear water
walls (typically). As the water is turned into steam/vapour in the water walls, the
steam/vapour once again enters the steam drum.
The steam/vapour is passed through a series of steam and water separators and then
dryers inside the steam drum. The steam separators and dryers remove the water droplets
from the steam and the cycle through the water walls is repeated. This process is known
as natural circulation.
The boiler furnace auxiliary equipment includes coal feed nozzles and igniter’s guns, so
out blowers, water lancing and observation ports (in the furnace walls) for observation
of the furnace interior. Furnace explosions due to any accumulation of combustible gases
after a trip out are avoided by flushing out such gases from the combustion zone before
igniting the coal.
The steam drum (as well as the super heater coils and headers) have air vents and drains
needed for initial start-up. The steam drum has an internal device that removes moisture
from the wet steam entering the drum from the steam generating tubes. The dry steam
then flows into the super heater coils. Geothermal plants need no boilers incest they use
naturally occurring steam sources.
Heat exchangers may be used where the geothermal steam is very corrosive or contains
excessive suspended solids. Nuclear plants also boil water to raise steam, either directly
passing the working steam through the reactor or else using an intermediate heat
exchanger.
23. 23
III. WATER WALLS:
Water flows to the water walls from the boiler drum by natural circulation. The front and the two
side water walls constitute the main evaporation surface, absorbing the bulk of radiant heat of the
fuel burnt in the chamber. The front and rear walls are bent at the lower ends to form a water-
cooled slag hopper. The upper part of the chamber is narrowed to achieve perfect mixing of
combustion gases. The water wall tubes are connected to headers at the top and bottom. The rear
water wall tubes at the top are grounded in four rows at wider pitch forming the grid tubes.
IV. REHEATER:
Reheater is used to raise the temperature of steam from which a part of energy has been
extracted in high-pressure turbine. This is another method of increasing the cycle
efficiency. Reheating requires additional equipment i.e. heating surface connecting boiler
and turbine pipe safety equipment like safety valve, non return valves, isolating valves,
high pressure feed pump, etc; Reheater is composed of two sections namely the front and
the rear pendant section, which is located above the furnace arc between water-cooled,
screen wall tubes and rear wall tubes.
Figure 3.1 Reheater
V. SUPERHEATER:
Whatever type of boiler is used, steam will leave the water at its surface and passing to
the steam space. Steam formed above the water surface in a shell boiler is always
saturated and become superheated in the boiler shell, as it is constantly. If superheated
steam is required, the saturated steam must pass through a super heater. This is simply
a heat exchanger where additional heat is added to the steam.
In water-tube boilers, the super heater may be an additional pendant suspended in the
furnace area where the hot gases will provide the degree of superheat required. In other
cases, for example in CHP schemes where the gas turbine exhaust gases are relatively
cool, a separately fired super heater may be needed to provide the additional heat.
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VI. ECONOMIZER:
The function of an economizer in a steam-generating unit is to absorb heat
from the flue gases and add as a sensible heat to the feed water before the
water enters the evaporation circuit of the boiler.
Earlier economizer were introduced mainly to recover the heat available in
the flue gases that leaves the boiler and provision of this addition heating
surface increases the efficiency of steam
Figure 3.2 Economizer
generators. In the modern boilers used for power generation feed water heaters were
used to increase the efficiency of turbine unit and feed water temperature.
Use of economizer or air heater or both is decided by the total economy that will result in
flexibility in operation, maintenance and selection of firing system and other related
equipment. Modern medium and high capacity boilers are used both as economizers and
air heaters. In low capacity, air heaters may alone be selected.
Stop valves and non-return valves may be incorporated to keep circulation in
economizer into steam drum when there is fire in the furnace but not feed flow. Tube
elements composing the unit are built up into banks and these are connected to inlet and
outlet heaters.
VII. AIR PREHEATER:
Air pre heater absorbs waste heat from the flue gases and transfers this heat to incoming
cold air, by means of continuously rotating heat transfer element of specially formed
metal plates. Thousands of these high efficiency elements are spaced and compactly
25. 25
arranged within 12 sections. Sloped compartments of radially divided cylindrical shell
called the rotor. The housing surrounding the rotor is provided with duct connecting both
the ends and is adequately scaled by radial and circumferential scaling.
Special sealing arrangements are provided in the air pre heater to prevent the leakage
between the air and gas sides. Adjustable plates are also used to help the sealing
arrangements and prevent the leakage as expansion occurs. The air preheater heating
surface elements are provided with two types of cleaning devices, soot blowers to normal
devices and washing devices to clean the element when soot blowing alone cannot keep
the element clean.
Figure 3.3 Air preheater
VIII. PULVERIZER: A pulverizer is a mechanical device for the grinding of many types of
materials. For example, they are used to pulverize coal for combustion in the steam-generating
furnaces of the fossil fuel power plants.
Figure 3.4 Pulverizer
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3.1.2 PLANT AUXILIARY MAINTENANCE
I. WATER CIRCULATION SYSTEM
Theory of Circulation:
Water must flow through the heat absorption surface of the boiler in order that it is evaporated
into steam. In drum type units (natural and controlled circulation), the water is circulated from
the drum through the generating circuits and then back to the drum where the steam is separated
and directed to the super heater. The water leaves the drum through the down corners at a
temperature slightly below the saturation temperature. The flow through the furnace wall is at
saturation temperature. Heat absorbed in water wall is latent heat of vaporization creating a
mixture of steam and water. The weight of the water to the weight of the steam in the mixture
leaving the heat absorption surface is called circulation ratio.
Types of Boiler Circulating System:
i. Natural circulation system
ii. Controlled circulation system
iii. Combined circulation system
I. Natural Circulation System:
Water delivered to steam generator from feed water is at a temperature well below the saturation
value corresponding to that pressure. Entering first the economizer, it is heated to about 30-40C
below saturation temperature. From economizer the water enters the drum and thus joins the
circulation system. Water entering the drum flows through the down corner and enters ring
heater at the bottom. In the water walls, a part of the water is converted to steam and the mixture
flows back to the drum. In the drum, the steam is separated, and sent to superheat for
superheating and then sent to the high-pressure turbine. Remaining water mixes with the
incoming water from the economizer and the cycle is repeated.
As the pressure increases, the difference in density between water and steam reduces. Thus the
hydrostatic head available will not be able to overcome the frictional resistance for a flow
corresponding to the minimum requirement of cooling of water wall tubes. Therefore natural
circulation is limited to the boiler with drum operating pressure around 175 kg/cm².
II. Controlled Circulation System:
Beyond 80 kg/cm² of pressure, circulation is to be assisted with mechanical pumps to overcome
the frictional losses. To regulate the flow through various tubes, or if ice plates are used. This
system is applicable in the high sub-critical regions (200 kg/cm²).
II. ASH HANDLING PLANT
The widely used ash handling systems are:
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i. Mechanical Handling System
ii. Hydraulic System
iii. Pneumatic System
iv. Steam Jet System
Figure 3.5 Ash handling system
Hydraulic Ash handling system is used at the Badarpur Thermal Power Station.
The hydraulic system carried the ash with the flow of water with high velocity through a channel
and finally dumps into a sump. The hydraulic system is divided into a low velocity and high
velocity system. In the low velocity system the ash from the boilers falls into a stream of water
flowing into the sump. The ash is carried along with the water and they are separated at the
sump. In the high velocity system a jet of water is sprayed to quench the hot ash. Two other jets
force the ash into a trough in which they are washed away by the water into the sump, where
they are separated. The molten slag formed in the pulverized fuel system can also be quenched
and washed by using the high velocity system. The advantage of this system are that its clean,
large ash handling capacity, considerable distance can be traversed, absence of working parts in
contact with ash.
Fly Ash Collection:
Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag
filters (or sometimes both) located at the outlet of the furnace and before the induced draft fan.
The fly ash is periodically removed from the collection hoppers below the precipitators or bag
filters. Generally, the fly ash is pneumatically transported to storage silos for subsequent
transport by trucks or railroad cars.
Bottom Ash Collection and Disposal:
At the bottom of every boiler, a hopper has been provided for collection of the bottom ash from
the bottom of the furnace. This hopper is always filled with water to quench the ash and clinkers
28. 28
falling down from the furnace. Some arrangement is included to crush the clinkers and for
conveying the crushed clinkers and bottom ash to a storage site.
III. WATER TEATEMENT PLANT:
As the types of boiler are not alike their working pressure and operating conditions vary and so
do the types and methods of water treatment. Water treatment plants used in thermal power
plants used in thermal power plants are designed to process the raw water to water with a very
low content of dissolved solids known as µ dematerialized water. No doubt, this plant has to be
engineered very carefully keeping in view the type of raw water to the thermal plant, its
treatment costs and overall economics.
Figure 3.6 Water treatment plant
The type of demineralization process chosen for a power station depends on three main factors:
i. The quality of the raw water.
ii. The degree of de-ionization i.e. treated water quality.
iii. Selectivity of resins.
Water treatment process is generally made up of two sections:
Pretreatment section
Demineralization section
PRETREATEMENT SECTION:
Pretreatment plant removes the suspended solids such as clay, silt, organic and inorganic matter,
plants and other microscopic organism. The turbidity may be taken as two types of suspended
solid in water; firstly, the separable solids and secondly the non-separable solids (colloids). The
29. 29
coarse components, such as sand, silt, etc; can be removed from the water by simple
sedimentation. Finer particles, however, will not settle in any reasonable time and must be
flocculated to produce the large particles, which are settle able. Long term ability to remain
suspended in water is basically a function of both size and specific gravity
.
DEMINERALIZATION:
This filter water is now used for dematerializing purpose and is fed to cation exchanger bed, but
enroots being first de chlorinated, which is either done by passing through activated carbon filter
or injecting along the flow of water, an equivalent amount of sodium sulphite through some
stroke pumps. The residual chlorine, which is maintained in clarification plant to remove organic
matter from raw water, is now detrimental to action resin and must be eliminated before its entry
to this bed.
Figure 3.7 Demineralization
3.1.3 TURBINE MAINTENANCE DEPARTMENT:
TURBINE CLASSIFICATION:
1. Impulse Turbine: In impulse turbine steam expands in fixed nozzles. The high velocity
steam from nozzles does work on moving blades, which causes the shaft to rotate. The
essential features of impulse turbine are that all pressure drops occur at nozzles and not
on blades.
2. Reaction turbine:
30. 30
In this type of turbine pressure is reduced at both fixed and moving blades. Both fixed and
moving blades act like nozzles. Work done by the impulse effect of steam due to reverse the
direction of high velocity steam. The expansion of steam takes place on moving blades.
Figure 3.8 A 95 MW GENERATOR AT BTPS, BADARPUR
MAIN TURBINE:
The 210MW turbine is a cylinder tandem compounded type machine comprising of H.P, I.P and
L.P cylinders. The H.P. turbine comprises of 12 stages the I.P turbine has 11 stages and the L.P
has four stages of double flow. The H.P and I.P. turbine rotor are rigidly compounded and the
I.P. and L.P rotor by lens type semi flexible coupling. All the 3 rotors are aligned on five
bearings of which the bearing number is combined with thrust bearing. The main superheated
steam branches off into two streams from the boiler and passes through the emergency stop valve
and control valve before entering the governing wheel chamber of the H.P. Turbine.After
expanding in the 12 stages in the H.P. turbine then steam is returned in the boiler for reheating.
The reheated steam from boiler enters I.P. turbine via the interceptor valves and control valves
and after expanding enters the L.P stage via 2 numbers of cross over pipes. In the L.P. stage the
steam expands in axially opposed direction to counteract the thrust and enters the condenser
placed directly below the L.P. turbine. The cooling water flowing through the condenser tubes
condenses the steam and the condensate the collected in the hot well of the condenser. The
31. 31
condensate collected the pumped by means of 3x50% duty condensate pumps through L.P
heaters to deaerator from where the boiler feed pump delivers the water to the boiler through
H.P. heaters thus forming a closed cycle.
STEAM TURBINE:
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam and
converts it into useful mechanical work. From a mechanical point of view, the turbine is ideal,
because the propelling force is applied directly to the rotating element of the machine and has not
as in the reciprocating engine to be transmitted through a system of connecting links, which are
necessary to transform a reciprocating motion into rotary motion. Hence since the steam turbine
possesses for its moving parts rotating elements only if the manufacture is good and the machine
is correctly designed, it ought to be free from out of balance forces. If the load on a turbine is
kept constant the torque developed at the coupling is also constant. A generator at a steady load
offers a constant torque. Therefore, a turbine is suitable for driving a generator, particularly as
they are both high-speed machines. A further advantage of the turbine is the absence of internal
lubrication. This means that the exhaust steam is not contaminated with oil vapour and can be
condensed and fed back to the boilers without passing through the filters. It also means that
turbine is considerable saving in lubricating oil when compared with reciprocating steam engine
of equal power. A final advantage of the steam turbine and a very important one is the fact that a
turbine can develop many time the power compared to a reciprocating engine whether steam or
oil.
STEAM CYCLE:
The thermal(steam) power plant uses a dual(vapor + liquid) phase steam, regenerative feed water
heating and re heating of steam cycle. It is a closed cycle to enable the working fluid (water) to
be used again and again. The cycle used is ‘Rankine cycle’ modified to include superheating of
Figure 3.9 Steam cycle diagram
32. 32
MAIN TURBINE:
The 210MW turbine is a tandem compounded type machine comprising of H.P and I.P cylinders.
The H.P turbines comprise of 12 stages, I.P turbine has 11 stages and the L.P turbine has 4 stages
of double flow.
The H.P and I.P turbine rotors are rigidly compounded and the L.P. motor by the lens type semi
flexible coupling. All the three rotors are aligned on five bearings of which the bearing no. 2 is
combined with the thrust bearing.
The main superheated steam branches off into two streams from the boiler and passes through
the emergency stop valve and control valve before entering the governing wheel chamber of
the H.P turbine. After expanding in the 12 stages in the H.P turbine the steam is returned
in boiler for reheating.
The reheated steam for the boiler enters the I.P turbine via the interceptor valves and control
valves and after expanding enters the L.P turbine stage via 2 nos of cross-over pipes. In the L.P.
stage the steam expands in axially opposite direction to counter act the trust and enters the
condensers placed below the L.P turbine. The cooling water flowing throughout the
condenser tubes condenses the steam and the condensate collected in the hot well of the
condenser. The condensate collected is pumped by means of 3*50% duty condensate pumps
through L.P heaters to deaerator from where the boiler feed pump delivers the water to boiler
through H.P heaters thus forming a close cycle.
33. 33
Figure 3.10 Turbine & Turbine Cycle
The selection of extraction points and cold reheat pressure has been done with a view to achieve
a high efficiency. These are two extractors from H.P turbine, four from I.P turbine and one from
L.P turbine. Steam at1.10 and 1.03 g/sq.cm .As is supplied for the gland scaling. Steam for this
purpose is obtained from deaerator through a collection where pressure of steam is regulated.
From the condenser, condensate is pumped with the help of 3*50% capacity condensate pumps
to deaerator through the low-pressure regenerative equipments. Feed water is pumped from
deaerator to the boiler through the H.P. heaters by means of 3*50% capacity feed pumps
connected before the H.P. heaters.
TURBINE COMPONENTS:
Casing.
Rotor
Blades
Sealing System
Stop & control valves
Coupling & Bearing
Barring Gear
TURBINE CASINGS:
HP Turbine Casing:
34. 34
Outer casing: a barrel-type without axial or radial flange.
Barrel-type casing suitable for quick startup and loading.
The inner casing- cylindrically, axially split.
The inner casing is attached in the horizontal and vertical planes in the barrel casing so
that it can freely expand radially in all the directions and axially from a fixed point(HP-
inlet side)
.
I.P Turbine Casing:
The casing of the IP turbine is split horizontally and is of double-shell construction.
Both are axially split and a double flow inner casing is supported in the outer casing and
carries the guide blades.
ROTORS:
HP Rotor:
The HP rotor is machined from single Cr-Mo-V steel forging with integral discs.
In all the moving wheels, balancing holes are machined to reduce the pressure difference
across them, which results in reduction of axial thrust.
First stage has integral shrouds while other rows have surroundings, riveted to the blades
are periphery.
I.P Rotor:
The IP rotor has seven discs integrally forged with rotor while last four discs are shunk
fit.
BLADES:
Most costly element of the turbine.
Blades fixed in stationary part are called guide blades/ nozzles and those fitted inmoving
part are called rotating/working blades.
Blades have three main part:
i. Aerofoil: working part.
ii. Root.
iii. Shrouds.
Shroud is used to prevent steam leakage and guide steam to next set of moving blades.
VACUUM SYSTEM:
This comprises of:
Condenser: 2 for 200MW unit at the exhaust of L.P turbine.
Ejectors: One starting and two main ejectors connected to the condenser located near the
turbine.
C.W Pumps: Normally two per unit of 50% capacity.
35. 35
CONDENSER:
There are two condensers entered to the two exhausters of the L.P.
turbine.These are surface-type condensers with two pass arrangement. Cooling water pumped
into each condenser by a vertical C.W. pump through the inlet pipe.
Figure 3.11 A Typical Water Cooled Condenser
Water enters the inlet chamber of the front water box, passes horizontally through brass tubes to
the water tubes to the water box at the other end, takes a turn, passes through the upper cluster
of tubes and reaches the outlet chamber in the front water box. From these, cooling water leaves
the condenser through the outlet pipe and discharge into the discharge duct. Steam exhausted
from the LP turbine washes the outside of the condenser tubes, losing its latent heat to the
cooling water and is connected with water in the steam side of the condenser. This condensate
collects in the hot well, welded to the bottom of the condensers.
EJECTORS:
There are two 100% capacity ejectors of the steam eject type. The purpose of the ejector is to
evacuate air and other non-condensation gases from the condensers and thus maintain the
vacuum in the condensers. The ejector has three compartments. Steam is supplied generally at a
pressure of 4.5 to 5 kg/cm² to the three nozzles in the three compartments. Steam expands in the
nozzle thus giving a high-velocity eject which creates a low-pressure zone in the throat of the
eject. Since the nozzle box of the ejector is connected to the air pipe from the condenser, the air
and pressure zone. The working steam which has expanded in volume comes into contact with
the cluster of tube bundles through which condensate is flowing and gets condensed thus after
36. 36
aiding the formation of vacuum. The non-condensing gases of air are further sucked with the
next stage of the ejector by the second nozzle. The process repeats itself in the third stage also
and finally the steam-air mixture is exhausted into the atmosphere through the outlet.
Deaerator :
The presence of certain gases, principally oxygen, carbon dioxide and ammonia, dissolved in
water is generally considered harmful because of their corrosive attack on metals, particularly at
elevated temperatures. One of the most important factors in the prevention of internal corrosion
in modern boilers and associated plant therefore, is that the boiler feed water should be free as far
as possible from all dissolved gases especially oxygen. This is achieved by embodying into the
boiler feed system a deaerating unit, whose function is to remove
Figure 3.12 a Deaerator
PRINCIPAL OF DEAERATION:
It is based on following two laws.
Henry’s Law
Solubility
The Deaerator comprises of two chambers:
Deaerating column
Feed storage tank
37. 37
Boiler FeedPump:
This pump is horizontal and of barrel design driven by an Electric motor through a hydraulic
coupling. All the bearings of pump and motor are forced lubricated by a suitable oil lubricating
system with adequate protection to trip the pump if the lubrication oil pressure falls below a
preset value.
3.2.2 COAL HANDLING DEPARTMENT:
As coal is the prime fuel for thermal power plant, adequate emphasis should be given
for its proper handling and storage. Also it is equally important to have a sustained flow of this
fuel to maintain uninterrupted power generation. Coal is used as the fuel because of the
following advantages
.
Advantages of coal as fuel:
Abundantly available in India
Low Cost
Technology for power generation well developed.
Easy to handle, transport, store and use.
COAL CYCLE:
Figure 3.13 Coal cycle Diagram
COAL HANDLING SYSTEM:
In the coal handling system of NTPC, three coal paths are normally available for the diret
conveying of coal. These are:
Path A: From track hopper to boiler bunker.
Path B: From track hopper to stock yard.
38. 38
Path C: From stock yard to boiler bunkers.
Figure 3.14 Coal handling system
The storage facilities at the stockyards have been provided only for crushed coal. The
coal handling system is designed to provide 100% standby for all equipments and conveyors.
The 200 mm coal as received at the track hopper is fed to the crusher house for crushing. Crusher
of 50% capacity is provided and these are preferred to two crushers of 100% capacity because
of increased reliability and possible higher availability. A series of parallel conveyors are
designed thereafter to carry crushed coal directly to the boiler bunkers or to divert it to the
stockyard.
Figure3.15 Coal handling division at NTPC, Badarpur
COAL HANDLING EQUIPMENTS
i. PULLEY :
39. 39
They are made of mild steel. Rubber lagging is provided to decrease the friction factor in
between the belt and pulley.
ii. SCRAPPER:
Conveyors are provided with scrappers at the discharge pulley in order to clean the
carrying side of the belt built up material on idler rolls. Care should be taken to ensure
that scrapper is held against the belt with the pressure sufficient to remove material
without causing damage to the belt due to excessive force exerted by the wiper. The
following categories of scrapper are common in use :
Steel blade scrapper
Rubber/fabric blade scrapper
Nylon brush scrapper
Compressed air blast scrapper.
iii. IDLERS:
These essentially consist of rolls made out of seamless steel tube enclosed fully at each
end and fitted with stationary shaft, anti-friction bearing and seals. They support the belt
and enable it to travel freely without much frictional losses and also keep the belt
properly trained.
Figure3.16 an Idler
iv. CONVEYOR BELT:
The conveyor belt consists of layers or piles of fabric duck, impregnated with rubber and
protected by a rubber cover on both sides and edges. The fabric duck supplies the strength to
with stand the tension created in carrying the load while the cover protects the fabric arecas.
40. 40
Heat resistant belting is always recommended for handling materials at a temperature over
66˚ C.
Figure 3.17 Coal Storage Area of the Badarpur Thermal Power Station,
v. VIBRATING SCREEN: The function of vibrating screen is to send the coal of having size
less than 20 mm to the crusher. The screen is operated by four v-belts connected to motor.
vi. CRUSHER: The role of crusher is to crush the coal from 200 mm to 20 mm size of coal
received from the vibrating screen. This is accomplished by means of granulators of ring
type. There are about 37 crushing elevations; each elevation has 4 granulators-2 of plain type
and 2 of tooth type, arranged alternately.The granulators are made of manganese steel
because of their work hardening property. The coal enters the top of the crusher and is
crushed between rotating granulators and fluid case path. The crushed coal through a chute
falls on belt feeder. Normally these crushers have a capacity round 600tonnes/hr.
vii. MAGNETIC SEPAROTERS: This is an electromagnet placed above the conveyor to
attract magnetic materials. Over this magnet
There is one conveyor to transfer these materials to chute provided for dumping at ground level.
Because of this, continuous removal is possible. It can remove any ferrous impurity from 10gms
to 50kg.
