NTPC Report

SUBMITTED BY
Vishal Singh
Mechanical & Automation Department
GB Pant Engineering College
SUBMITTED TO
Mr. Man Mohan Singh
Sr. Manager
VOCATIONAL TRAINING
REPORT
N A T I O N A L T H E R M A L P O W E R C O R P O R A T I O N , B A D A R P U R

Contents
1 Introduction 1
1-1 About NTPC 2
1-2 Vision & Mission 3
1-3 Core Values 3
1-4 Strategies & Policies 3
1-5 Health & Safety 4
1-6 Environment Policy & Management 5
1-7 About BPTS 8
1-8 About Training 10
2 Power Plant 13
2-1 Introduction 14
2-2 Plant Cycle 14
3 Operation 29
3-1 Introduction 30
3-2 Energy Transfer 35
4 Boiler 39
4-1 Introduction 40
4-2 Types of Boiler 40
4-3 Combustion 44
4-4 Boiler component design 45
4-5 Boiler fittings and accessories 54

iv Contents
5 Plant Auxiliary Maintenance 57
5-1 Introduction 58
5-2 Importance 61
5-3 Types of Boiler Circulation System 61
5-4 Ash Handling Plants 63
5-5 Water Treatment Plant 64
6 Turbine 69
6-1 Operating System 70
6-2 Turbine Classification 71
6-3 Turbine Operation 75
6-4 Turbine Components 76
6-5 Turbine Auxiliaries 78
Appendix 83
A. References
B. List of Figures
C. List of Tables

Acknowledgement
With profound respect and gratitude, i take the opportunity to convey thanks to all
the people who had helped me to complete the training at NTPC Limited, Badarpur,
New Delhi. Further I want to express my gratitude to Mr. N.S. Bhatia, Dy. GM, CHP and
Mr. Manmohan Singh, Sr. Manager, EDC for providing this opportunity to be a part of
this esteemed organization.
I am extremely grateful to Mr. Brahm Prakash, BMD Dept., Mr. Gaurav Goyal, PAM
Dept. and Mr. S.K. Singh, TMD Dept. for their guidance during whole training period.
Also I am extremely grateful to all the technical staff of BTPS-NTPC for their co-
operation and guidance that helped me a lot during the course of training. I have learnt
a lot working under them and I will always be indebted of them for this value addition
in me.
Finally, i need to thank all my fellow trainings who have contributed directly and
indirectly to learn and support for the preparation of this report work and friendly stay
at Badarpur Thermal Power Station, Badarpur, New Delhi.
Vishal Singh

Training Report
To,
The Head, Dept. of Training & Placement,
G.B. Pant Engineering College,
Okhala Industrial Estate, Phase – III,
New Delhi – 110020
(To be completed by the Training/ Personnel Officer and Counter signed by Training/ Personnel
Officer / General Manager).
NAME OF THE TRAINING ORGANISATION: NTPC, Badarpur, New Delhi
NAME OF THE STUDENT: VISHAL SINGH
ROLL NO: 00320903613
BRANCH OF STUDENT: Mechanical & Automation
DATE OF COMPLETION OF TRAING: 23rd
July 2016
No. of days training taken: 41 days
Dept./ Sections where the student took training with approximate days spent in each dept.
Department Period Authorized Signatory
Boiler Maintenance
Department
13th June 2016 - 25th June
2016
Plant Auxiliary
Maintenance
27th June 2016 -
9th July 2016
Turbine Maintenance
Department
11th June 2016 - 23rd July
2016
Signature: _______________________
Name: ___________________________
Designation: _____________________
Official Seal: _____________________
Phone (Off): _____________________
Email: ___________________________

2 Vocational Training Report (VT 0909)
1-1 | About NTPC
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.
The total installed capacity of the company is 47,178 MW (including JVs/
Subsidiaries) comprising of 44 NTPC Stations (18 Coal based stations, 7 combined
cycle gas/liquid fuel based stations, 1 Hydro based station), 9 Joint Venture
stations (8 coal based and one gas based) and 9 renewable energy projects. The
company has set a target to have an installed power generating capacity of
1,28,000 MW by the year 2032.
Although the company has approx. 16% of the total national capacity it contributes
to over 25% of total power generation due to its focus on operating its power
plants at higher efficiency levels (approx. 80.2% against the national PLF rate of
64.5%).
Fig 1.1 Comparison of NTPC PLF to national PLF

Introduction 3
1-2 | Vision & Mission
Vision
“To be the world’s largest and best power producer, powering India’s growth
”
Mission
Develop and provide reliable power, related products and services at competitive prices,
integrating multiple energy sources with innovative and eco-friendly technologies and
contribute to society.
1-3 | Core Values
B Business Ethics
E Environmentally & Economically Sustainable
C Customer Focus
O Organizational & Professional Pride
M Mutual Respect & Trust
M Motivating Self & others
I Innovation & Speed
T Total Quality for Excellence
T Transparent & Respected Organization
E Enterprising
D Devoted
1-4 | Strategies & Policies
 To contribute to sustainable development by discharging corporate social
responsibilities.
 To lead the sector in the areas of resettlement & rehabilitation, environment
protection including effective ash utilization, peripheral development and energy
conservation practices.

 To lead development efforts in the Indian power sector through efforts at policy
advocacy, assisting customers in reforms, disseminating best practices in the
operation and management of power plants etc.
Policies
NTPC is committed to generating and providing reliable power at competitive
prices in a sustainable manner by optimising the use of multiple energy resource
with innovative eco-friendly technologies thereby contributing to the economic
development of the nation, social upliftment of the society and promoting a
healthy environment.
In this process, NTPC shall strive to:
 Contribute towards clean and sustainable environment with respect to
land, water and air
 Conserve resources by reduction, reuse and recycling
 Initiate and support measures to optimise the use of renewable energy,
increase energy efficiency and reduce Green House Gases emissions.
 Support the measures for biodiversity conservation by following the
practices of protecting, conserving and restoring ecosystems.
 Be transparent, ethical and fair to all stakeholders
 Be supportive in developing and enhancing people’s standard of living in
and around the plants.
 Generate awareness, share knowledge and support training programmes
on sustainable development among the employees, neighbouring
communities and public at large
1-5 | Health & Safety
The health and safety is NTPC’s top priority. The ultimate aim is to have no
incidents that harm its people, neighbours or put its plants at risk. To this end,
NTPC management gives utmost importance to providing a safe working
environment and creating safety awareness among its employees.
The steps taken by NTPC towards the goal of “Zero Accidents” include:
 Generation of ‘clean power’ and ‘accident free power’ by using state of
the art technology, cleaner fuel, world class operation & maintenance
practices and excellent housekeeping

Introduction 5
 Using systems approach by adopting and implementing ISO-14001, ISO 9001-
2000, OHSAS-18001, 5S, Six Sigma, Benchmarking as per International norms
by world class certification agencies
 Formal joint management – worker health and safety committees to help
monitor and advise on occupational health and safety programmes are in place
in all the plants
 Regular plant inspections and review with Head of projects are undertaken.
Internal safety audits by safety officers of NTPC as well as external audits by
reputed organizations are carried out annually at each plant.
 Adequate numbers of qualified safety officers are posted at all units as per
statutory rules and provisions
1-6 | Environment Policy & Management
NTPC Environment Policy
“Going Higher on Generation, lowering Green House Gas Intensity” is NTPC vision
statement on managing our environment. NTPC has brought out a comprehensive
document entitled ‘NTPC Environment Policy and Environment Management System’.
Amongst the guiding principles adopted in the document are the company's pro-active
approach to environment, optimum utilization of equipment, adoption of latest
technologies and continual environment improvement. The policy envisages new
technology initiatives and efficient utilization of resources, thereby minimizing waste,
maximizing ash utilization and ensuring a green belt all around the plant for maintaining
ecological balance.
Pollution Control Systems
In order to ensure that NTPC complies with all the stipulated environment norms,
following state-of-the-art pollution control systems / devices have been installed to
control air and water pollution:
 Electrostatic Precipitators
 Flue Gas Stacks
 Low-NOX Burners
 Neutralization Pits
 Coal Settling Pits / Oil Settling Pits
 Dust Extraction & Dust Suppression Systems
 Cooling Tower

 Ash Dykes & Ash Disposal Systems
 Ash Water Recycling System
 Dry Ash Extraction System
 Liquid Waste Treatment Plants & Management System
 Sewage Treatment Plants & Facilities
 Environmental Institutional Set-up
Following are the additional measures taken by NTPC in the area of Environment
Management:
 Environment Management During Operation Phase
 Monitoring of Environmental Parameters
 On-Line Data Base Management
 Environment Review
 Up-gradation &
Retrofitting of Pollution
Control Systems
 Resources Conservation
 Waste Management
 Municipal Waste
Management
 Hazardous Waste
Management
 Bio-Medical Waste
Management
 Land Use / Bio-diversity
 Reclamation of Abandoned Ash ponds
 Green Belts, Afforestation & Energy Plantations
Ash Utilization
Fly ash is a byproduct of power generation with coal. Sustainable ash utilization is one
of the key concerns at NTPC. The Ash Utilization Division (AUD), set up in 1991, strives
to derive maximum usage from the vast quantities of ash produced at its power stations.
The ash is now being looked at as a commodity that could generate wealth for the
company. The AUD proactively formulates policies, plans and programmes for ash
utilizations. It further monitors the progress in these activities and works for developing
new segments of ash usage.
The fly ash generated at NTPC stations is used for manufacture of cement, concrete,
concrete products, cellular concrete products, bricks/blocks/ tiles, road embankment,
mine filling, land development, micro and macro-nutrients in agriculture etc. To facilitate
easy availability of dry fly ash to end users, dry fly ash evacuation and safe storage
system have been set up at coal based stations.
Fig 1.2 Roadside board for
environment awareness

Introduction 7
CenPEEP
Centre for Power Efficiency
& Environmental Protection
was established to take
initiatives to address
climate change issues as
well as improving the
overall performance of
coal-fired power plants.
NTPC has adopted a win-
win strategy at CenPEEP by
achieving synergy between
environmental concerns and utility needs by balancing the dual objectives of reducing
carbon-di-oxide emissions that contribute to climate change and facilitating higher
efficiency of power generation.
Afforestation
NTPC’s commitment to the protection of the environment and maintaining the
ecological balance is foremost. One of the main thrust areas in this mission is
afforestation on a gigantic scale. NTPC undertakes massive afforestation programmes
covering vast tracts
of land in and
around its projects
in a concerted bid
to counter the
growing ecological
threat. The
company has
planted 20 million
trees till date in and
around its projects.
Each tree on an
average offsets 50
pounds of carbon dioxide per year.
NTPC has an independent Horticulture Department at its projects headed by
experienced horticulture officers / supervisors. Saving existing trees, planting right at
the beginning of construction phase, upkeep of the trees and advice from State Forest
Departments and agricultural universities are a few general guidelines followed by
NTPC.
Fig 1.3 CenPEEP Strategy
Fig 1.4 NTPC luscious campus

1-7 | About BPTS
Badarpur Thermal Power Station is located at Badarpur area in NCT Delhi. The
power plant is one of the coal based power plants 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 705
MW.
The power is supplied to a 220 KV network
that is a part of the northern grid. It was
originally conceived to provide power to
neighboring states of Haryana, Punjab,
Jammu and Kashmir, U.P., Rajasthan, and
Delhi. But since year 1987 Delhi has become
its sole beneficiary. It is situated in south
east corner of Delhi on Mathura Road near
Faridabad and it comprises of 430 hectares
(678 acres). The coal for the plant is derived
from the Jharia Coal Fields.
Technology
The 100 MW unit’s capacity have been reduced to 95 MW. These units have
indirectly fired boiler, while 210 MW units have directly fired boiler. All the turbines
are of Russian Design. Both turbine and boilers have been supplied by BHEL. The
boiler of Stage-I units are of Czech. design. The boilers of Unit 4 and 5 are designed
by combustion engineering (USA). The instrumentation of the stage I units and
unit 4 are of The Russian design. Instrumentation of unit 5 is provided by M/S
Instrumentation Ltd. Kota, is of Kent design.
Stage
Unit
No.
Installed
Capacity
Date of
Commissioning
Status
First
1 95 MW Jul, 1973 Stalled
2 95 MW Aug, 1974 Stalled
3 95 MW Mar, 1975 Stalled
Second
4 210 MW Dec, 1978 Stalled
5 210 MW Dec, 1981 Working
Fig 1.5 NTPC, Badarpur
Main Gate
Table 1.1 NTPC Power Generation Units
Fig 1.5 NTPC, Badarpur
Main Gate

Introduction 9
Performance
In the initial years, the performance of the plant increased significantly and steadily till
2007, after the management takeover from CEA. But now the plant is facing various
issues. Being an old plant, Badarpur Thermal Power Station (BTPS) has little
automation. Its performance is deteriorating due to various reasons, like aging, poor
quantity and quality of cooling water etc. It receives cooling water from Agra Canal,
which is an irrigation canal from Yamuna river. Due to rising water pollution, the water
of Yamuna is highly polluted. This polluted water when goes into condenser, adversely
affect life of condenser tubes, resulting in frequent tube leakages. This dirty water from
tube leakages, gets mixed into feed water cycle causes numerous problems, like
frequent boiler tube leakages, and silica deposition on turbine blades. the quantity of
water supply is also erratic due to lack of co-ordination between NTPC and UP
irrigation which manages Agra Canal.
The quality of the coal supplied has degraded considerably. At worst times, there were
many unit tripping owing to poor quality. The poor coal quality also put burdens on
equipment, like mills and their performance also goes down. The coal for the plant is
fetched from far away, that makes the total fuel cost double of coal cost at coalmine.
This factor, coupled with low efficiency due to aging and old design makes electricity
of the plant costlier. The cost of power from Badarpur is Rs 4.62/kWh making it one of
the costliest in India.
Fig 1.6 NTPC’s Turnaround Capability Over Years

1-8 | About Training
The six-week training period started from 13th
June 2016 to 23rd
July 2016. The
training schedule was divided into periods in which the trainees had attended
different departments of the plant according to their specialization. The various
departments are as following:
 EMD – 1
 Administration
 EMD – 2
 BMD
 PAM
 TMD
 CHP/ NCHP
 WTP
 BI
 C&I
 MPD
 HR
 Civil
 Finance
 IT
Being in Mechanical & Automation Department, the training commenced with
basic introduction to the plant operation and general safety precaution classes.
The training followed according to the schedule provided at the Employee
Development Centre (EDC).
Department Period Reporting officer
Boiler Maintenance
Department
13th
June 2016 -
25th
June 2016
Mr. Brahm Shankar
(DGM, BMD)
Plant Auxiliary
Maintenance
27th
June 2016 -
9th
July 2016
Mr. Gaurav Goyal
(Dy. Manager, PAM)
Turbine Maintenance
Department
11th
June 2016 -
23rd
July 2016
Mr. S.K. Singh
(DGM, TMD)
Fig 1.7 Employee Development Centre
Table 1.2 Training Schedule

Introduction 11
Do’s
 Always be cautious while entering or moving in the plant.
 Always try to be in a group while visiting plant.
 Utilize the safety equipment’s (shoes, helmets etc.) at work place effectively.
 Follow the safety rules implemented by the company. Do not flout or ignore
them.
 Keep away from electrical hazard area.
 Consult the supervisor/ Engineer in case of any difficulty.
 Always remember Emergency No. Ambulance: 2666-2777 and Fire: 2222-2333.
Don’t
 Do not enter hazardous place or places marked with caution without
permission.
 Do not wear loose clothing when in the plant.
 Do not stand in the area where material is being lifted by a winch or a crane.
 Do not move alone.
 Do not temper with any safety equipment
 Do not make short cuts.
 Do not tease or make horse play.
 Do not get panic in case of emergency.
Fig 1.8 Roadside Safety Precaution Reminders

2-1 | Introduction
A power plant is assembly of systems or subsystems to generate electricity, i.e.,
power with economy and requirements. The power plant itself must be useful
economically and environmental friendly to the society.
A power plant may be defined as a machine or assembly of equipment that
generates and delivers a flow of mechanical or electrical energy. The main
equipment for the generation of electric power is generator. When coupling it to
a prime mover runs the generator, the electricity is generated.
2-2 | Plant Cycle
In most of the turbine is steam driven. 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 and recycled to where it was
heated; this is known as a Rankine cycle.
Rankine Cycle
The Rankine cycle is a model that
is used to predict the
performance of steam turbine
systems. The Rankine cycle is an
idealized thermodynamic cycle
of a heat engine that converts
heat into mechanical work. The
heat is supplied externally to a
closed loop, which usually uses
water as the working fluid.
Processes
There are four processes in the Rankine cycle:
 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.
 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.
 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.
Fig 2.1 Rankine Cycle Schematic Diagram

Power Plant 15
 Process 4-1: The wet vapour then enters a condenser where it is condensed at
a constant pressure to become a saturated liquid.
The actual vapor power cycle differs from the ideal Rankine cycle because of
irreversibility’s in the inherent components caused by fluid friction and heat loss to the
surroundings; fluid friction causes pressure drops in the boiler, the condenser, and the
piping between the components, and as a result the steam leaves the boiler at a lower
pressure; heat loss reduces the net work output, thus heat addition to the steam in the
boiler is required to maintain the same level of net work output.
Rankine cycle with reheat
The purpose of a reheating cycle is
to remove the moisture carried by
the steam at the final stages of the
expansion process. In this variation,
two turbines work in series. The first
accepts vapor from the boiler at
high pressure. After the vapor has
passed through the first turbine, it
re-enters the boiler and is reheated
before passing through a second,
lower-pressure, turbine. The reheat
temperatures are very close or equal
to the inlet temperatures, whereas
the optimum reheat pressure
needed is only one fourth of the
original boiler pressure.
Fig 2.2 Rankine Cycle
Fig 2.3 Rankine Cycle with Reheat

Among other advantages, this prevents the vapor from condensing during its
expansion and thereby damaging the turbine blades, and improves the efficiency
of the cycle, because more of the heat flow into the cycle occurs at higher
temperature.
Regenerative Rankine cycle
The regenerative Rankine cycle is so named because after emerging from the
condenser the working fluid is heated by steam tapped from the hot portion of
the cycle. The fluid at 2 is mixed
with the fluid at 4 (both at the
same pressure) to end up with
the saturated liquid at 7.
Regeneration increases the
cycle heat input temperature
by eliminating the addition of
heat from the boiler/fuel
source at the relatively low feed
water temperatures that would
exist without regenerative feed
water heating. This improves
the efficiency of the cycle, as
more of the heat flow into the
cycle occurs at higher
temperature.
Reheat-Regenerative Cycle
In steam power plants using high
steam pressure reheat
regenerative cycle is used. The
thermal efficiency of this cycle is
higher than only reheat or
regenerative cycle. This cycle is
commonly used to produce high
pressure steam (90 kg/cm2
) to
increase the cycle efficiency.
Fig 2.4 Rankine Cycle with Regeneration
Fig 2.5 Rankine Reheat – Regenerative
Cycle Schematic Diagram

Power Plant 17
2-3 | Parts of Power Plant
(1) Cooling tower (10) Steam Control valve (19) Super heater
(2) Cooling water pump
(11) High pressure steam
turbine
(20) Forced draught (draft)
fan
(3) Transmission line
(3-phase)
(12) Deaerator (21) Reheater
(4) Step-up transformer
(3-phase)
(13) Feed water heater (22) Combustion air intake
(5) Electrical generator
(3-phase)
(14) Coal conveyor (23) Economiser
(6) Low pressure steam
turbine
(15) Coal hopper (24) Air preheater
(7) Condensate pump (16) Coal pulverizer (25) Precipitator
(8) Surface condenser (17) Boiler steam drum
(26) Induced draught
(draft) fan
(9) Intermediate pressure
steam turbine
(18) Bottom ash hopper 27) Flue-gas stack
Fig 2.6 Thermal Power Plant diagram

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 temperature.
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.
Cooling Water Pump
It is used to pumps the water from the cooling tower which goes to the
condenser.
Three phase transmission line
Three phase electric power is a common method of electric power transmission.
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.
Fig 2.7 Cooling Tower

Power Plant 19
Unit transformer
It is a device that transfers electric energy
from one alternating-current circuit to one
or more other circuits, either increasing or
reducing the voltage. Transformers act
through electromagnetic induction,
current in the primary coil induces current
in the secondary coil.
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).
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 maybe water falling through
the turbine or steam turning a turbine (as is the
case with thermal power plants).
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 hot well
placed in lower parts of turbine.
Fig 2.8 Unit Transformer
Fig 2.9 Electric Generator

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.
Feed water pumps range in size up to many horsepower and the electric motor
is usually separated from the pump body by some form of mechanical coupling.
Feed water pumps usually run intermittently and are controlled by a float switch
or other similar level-sensing device energizing the pump when it detects a
lowered liquid level in the boiler. Some pumps contain a two-stage switch. As
liquid lowers to the trigger point of the first stage, the pump is activated. If the
liquid continues to drop, (perhaps because the pump has failed, its supply has
been cut off or exhausted, or its discharge is blocked) the second stage will be
triggered. This stage may switch off the boiler equipment (preventing the boiler
from running dry and overheating), trigger an alarm, or both.
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.
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.
Fig 2.10 Surface Condenser

Power Plant 21
Intermediate Pressure Turbine
Intermediate Pressure Turbine (IPT) consists of 11 stages. When the steam has been
passed through HPT it enters into IPT. Steam enters through front end and leaves from
Rear end.
Steam Governor Valve
It is used to put the initial charge of water into the boiler (before steam power was
available to operate the steam-powered feed water 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. 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.
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.
Deaerator
A Deaerator is a device for
air removal and used to
remove dissolved gases
from boiler feed water to
make it non corrosive. 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.
Fig 2.11 Deaerator

Deaerator level and pressure must be controlled by adjusting control valves the
level by regulating condensate flow and the pressure by regulating steam flow.
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. The dissolved oxygen and
carbon dioxide which would otherwise
cause boiler corrosion are removed in
feed water heater. 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.
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.
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 two purposes:
Fig 2.12 Feed Water Heater
Fig 2.13 Coal Conveyor Schematic Diagram

Power Plant 23
1. If 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.
Pulverized Fuel Mill
A pulveriser is a device for grinding coal for combustion in a furnace in a fossil fuel
power plant.
Types
 Ball and Tube Mill -Ball mill is a pulverizer that consists of a horizontal
rotating cylinder, up to three diameters in length, containing a charge of
tumbling or cascading
steel balls, pebbles, or
rods. Tube mill is a
revolving cylinder of up
to five diameters in
length used for fine
pulverization of ore,
rock, and other such
materials; the material,
mixed with water, is fed
into the chamber from
one end, and passes out
the other end as slime.
Fig 2.14 Coal Hopper
Fig 2.15 Ball & Tube Mill

 Ring and Ball - This type consists of two rings separated by a series
of large balls. The lower ring rotates, while the upper ring presses
down on the balls via a set of spring and adjuster assemblies. Coal
is introduced into the centre or side of the pulverizer and is ground
as the lower ring rotates causing the balls to orbit between the
upper and lower rings. The coal is carried out of the mill by the flow
of air moving through it. The size of the coal particles released from
the grinding section of the mill is determined by a classifier
separator.
Boiler drum
Boiler is an enclosed vessel in which water is heated and circulated until the water
is turned in to steam at
the required pressure.
Coal is burned inside the
combustion chamber of
boiler. The products of
combustion are nothing
but gases. These gases
which are at high
temperature vaporize the
water inside the boiler to
steam. Sometimes this
steam is further heated in
a super heater as higher
the steam pressure and
temperature the greater
efficiency the engine will
have in converting the
heat in steam in to
mechanical work.
This steam at high pressure and temperature is used directly as a heating
medium, or as the working fluid in a prime mover to convert thermal energy to
mechanical work, which in turn may be converted to electrical energy. Although
other fluids are sometimes used for these purposes, water is by far the most
common because of its economy and suitable thermodynamic characteristics.
Fig 2.16 Steam Generator

Power Plant 25
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.
Force Draught Fan
The circulation of air is caused by a difference in pressure, known as Draft. Draft is a
differential pressure between atmosphere and inside the boiler. It is necessary to cause
the flow of gases through boiler setting.
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 preheater for better combustion,
injects it via the air nozzles on the furnace wall.
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, thus increasing
the efficiency of the steam engine. The super
heater may consist of one or more stages of
tube banks arranged to effectively transfer heat
from the products of combustion.
Reheater
Some of the heat of superheated steam is used to
rotate the turbine where it loses some of its
energy. Reheater is a heater which is used to raise
the temperature of steam which has fallen from
the intermediate pressure turbine. The steam
after reheating is used to rotate the second steam
turbine where the heat is converted to
mechanical energy.
Air Intake
Air is taken from the environment by an air intake tower which is fed to the fuel.
Fig 2.17 Superheater
Fig 2.18 Reheater

Economizers
Economizer are mechanical
devices intended to reduce
energy consumption, or to
perform another useful
function like preheating a
fluid. In boilers, economizer
are heat exchange devices that
heat fluids, usually water.
Economizers are so named
because they can make use of the
enthalpy and improving the boiler’s 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). They 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.
Air Preheater
It is a device designed to heat air before
another process. 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.
Fig 2.19 Economizer
Fig 2.20 Air Preheater

Power Plant 27
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. It
charges the particles inductively with an
electric field, then attracting them to
highly charged collector plates.
Electrostatic precipitators are highly
efficient filtration devices, and can easily
remove fine particulate matter such as dust and smoke from the air steam.
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 and this additionally minimizes erosion of the ID fan.
Flue gas stack
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 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.
Fig 2.21 Electrostatic Precipitator

3-1 | Introduction
In figure 2-6, Coal is conveyed (14) from an external stack and ground to a very
fine powder by large metal spheres in the pulverized fuel mill (16). There it is mixed
with preheated air (24) driven by the forced draught fan (20).
The hot air-fuel mixture is forced at high pressure into the boiler where it rapidly
ignites. Water of a high purity flows vertically up the tube-lined walls of the boiler,
where it turns into steam, and is passed to the boiler drum, where steam is
separated from any remaining water. The steam passes through a manifold in the
roof of the drum into the pendant superheater (19) where its temperature and
pressure increase rapidly to around 200 bar and 540°C, sufficient to make the tube
walls glow a dull red.
The steam is piped to the high pressure turbine (11), the first of a three-stage
turbine process. A steam governor valve (10) allows for both manual control of the
turbine and automatic set-point following. The steam is exhausted from the high
pressure turbine, and reduced in both pressure and temperature, is returned to the
boiler reheated (21). The reheated steam is then passed to the intermediate
pressure turbine (9), and from there passed directly to the low pressure turbine set
(6).
The exiting steam, now a little above its boiling point, is brought into thermal
contact with cold water (pumped in from the cooling tower) in the condenser (8),
where it condenses rapidly back into water, creating near vacuum-like conditions
inside the condenser chest. The condensed water is then passed by a feed pump
(7) through a deaerator (12), and pre-warmed, first in a feed heater (13) powered
by steam drawn from the high pressure set, and then in the economiser (23), before
being returned to the boiler drum. The cooling water from the condenser is
sprayed inside a cooling tower (1), creating a highly visible plume of water vapor,
before being pumped back to the condenser (8) in cooling water cycle.
The three turbine sets are sometimes coupled on the same shaft as the three-
phase electrical generator (5) which generates an intermediate level voltage
(typically 20-25 kV). This is stepped up by the unit transformer (4) to a voltage
more suitable for transmission (typically 250-500 kV) and is sent out onto the
three-phase transmission system (3).
Exhaust gas from the boiler is drawn by the induced draft fan (26) through an
electrostatic precipitator (25) and is then vented through the chimney stack (27).

Operation 31
Fig3.1SchematicdiagramofThermalPowerPlant

The flow sheet of a thermal power plant consists of the following four main circuits:
 Feed water and steam flow circuit
 Coal and ash circuit

Operation 33
 Air and gas circuit

 Cooling water circuit
 Electricity generation circuit

Operation 35
3-2 | Energy Transfer
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
Coal to Steam
Coal from the coal wagons is unloaded in the coal handling plant. This Coal is
transported up to the raw coal bunkers with the help of belt conveyors. Coal is
transported to Bowl mills by Coal Feeders. The coal is pulverized in the Bowl Mill, where
it is ground to powder form. The mill consists of a round metallic table on which coal
particles fall. This table is rotated with the help of a motor. There are three large steel
rollers, which are spaced 120 apart. When there is no coal, these rollers do not rotate
but when the coal is fed to the table it packs up between roller and the table forces the
rollers to rotate. Coal is crushed by the crushing action between the rollers and the
rotating table. This crushed coal is taken away to the furnace through coal pipes with
the help of hot and cold air mixture from P.A. Fan.
P.A. Fan takes atmospheric air, a part of which is sent to Air-Preheaters for heating while
a part goes directly to the mill for temperature control. Atmospheric air from F.D. Fan is
heated in the air heaters and sent to the furnace as combustion air.
Water from the boiler feed pump passes through economizer and reaches the boiler
drum. Water from the drum passes through down comers and goes to the bottom ring
header. Water from the bottom ring header is divided to all the four sides of the furnace.
Due to heat and density difference, the water rises up in the water wall tubes. Water is
partly converted to steam as it rises up in the furnace. This steam and water mixture is
again taken to the boiler drum where the steam is separated from water. Water follows
the same path while the steam is sent to superheater for superheating. The superheater
are located inside the furnace and the steam is superheated (540 o
C) and finally it goes
to the turbine.
Flue gases from the furnace are extracted by induced draft fan, which maintains balance
draft in the furnace (-5 to –10 mm of wcl) with forced draft fan. These flue gases emit
their heat energy to various super heaters in the pent house and finally pass through air
preheaters and goes to electrostatic precipitators where the ash particles are extracted.
Electrostatic Precipitator consists of metal plates, which are electrically charged. Ash
particles are attracted on to these plates, so that they do not pass through the chimney
to pollute the atmosphere.

Regular mechanical hammer blows cause the accumulation of ash to fall to the
bottom of the precipitator where they are collected in a hopper for disposal.
Steam to Mechanical Power
From the boiler, a steam pipe conveys steam to the turbine through a stop valve
(which can be used to shut-off the steam in case of emergency) and through
control valves that automatically regulate the supply of steam to the turbine. Stop
valve and control valves are located in a steam chest and a governor, driven from
the main turbine shaft, operates the control valves to regulate the amount of steam
used. (This depends upon the speed of the turbine and the amount of electricity
required from the generator).
Steam from the control valves enters the high pressure cylinder of the turbine,
where it passes through a ring of stationary blades fixed to the cylinder wall. These
act as nozzles and direct the steam into a second ring of moving blades mounted
on a disc secured to the turbine shaft. The second ring turns the shafts as a result
of the force of steam.
The stationary and moving blades together constitute ‘A stage’ of turbine and in
practice many stages are necessary, so that the cylinder contains a number of rings
of stationary blades with rings of moving blades arranged between them. The
steam passes through each stage in turn until it reaches the end of the high-
pressure cylinder and in its passage some of its heat energy is changed into
mechanical energy.
The steam leaving the high pressure cylinder goes back to the boiler for reheating
and returns by a further pipe to the intermediate pressure cylinder. Here it passes
through another series of stationary and moving blades.
Finally, the steam is taken to the low-pressure cylinders, each of which enters at
the centre flowing outwards in opposite directions through the rows of turbine
blades through an arrangement called the ’double flow’- to the extremities of the
cylinder. As the steam gives up its heat energy to drive the turbine, its temperature
and pressure fall and it expands. Because of this expansion the blades are much
larger and longer towards the low pressure ends of the turbine.

Operation 37
Mechanical Power to Electrical Power
As the blades of turbine rotate, the shaft of the generator, which is coupled to the
turbine, also rotates. It results in rotation of the coil of the generator, which causes
induced electricity to be produced. As it rotates the amount of magnetic flux linked with
a circuit changes, an EMF is produced in the circuit, thus electricity is produced. Then
the electricity generated at the plant is sent to consumers through high-voltage power
lines.

4-1 | Introduction
Boiler is an apparatus to produce steam. Thermal energy released by combustion
of fuel is transferred to water, which vaporizes and gets converted into steam at
the desired temperature and pressure.
The steam produced is used for producing mechanical work by expanding it in
steam engine or steam turbine.
A boiler should fulfil the following requirements -
 Safety. The boiler should be safe under operating conditions.
 Accessibility. The various parts of the boiler should be accessible for repair
and maintenance.
 Capacity. The boiler should be capable of supplying steam according to
the requirements.
 Efficiency. To permit efficient operation, the boiler should be able to
absorb a maximum amount of heat produced due to burning of fuel in
the furnace.
 It should be simple in construction and its maintenance cost should be
low.
 Its initial cost should be low.
 The boiler should have no joints exposed to flames.
 The boiler should be capable of quick starting and loading.
The performance of a boiler may be measured in terms of its evaporative capacity
also called power of a boiler. It is defined as the amount of water evaporated or
steam produced in kg per hour. It may also be expressed in kg per kg of fuel
burnt or kg/hr/m2
of heating surface.
4-2 | Types of Boiler
The boilers can be classified according to the following criteria.
According to flow of water and hot gases
1. Water tube
In water tube boilers, water circulates through the tubes and hot products of
combustion flow over these tubes. Water tube boilers require less weight of
metal for a given size, are less liable to explosion, produce higher pressure,
are accessible and can response quickly to change in steam demand. Tubes
and drums of water-tube boilers are smaller than that of fire-tube boilers and
due to smaller size of drum higher pressure can be used easily. Water-tube
boilers require lesser floor space. The efficiency of water-tube boilers is more.

Boiler 41
1. Horizontal straight tube boilers
(a) Longitudinal drum (b) Cross-drum.
2. Bent tube boilers
(a) Two drum (b) Three drum
(c) Low head three drum (d) Four drum.
3. Cyclone fired boilers
Advantages of water tube boilers are as follows:
 High pressure of the order of 140 kg/cm2
can be obtained.
 Heating surface is large. Therefore, steam can be generated easily.
 Large heating surface can be obtained by use of large number of tubes.
 Because of high movement of water in the tubes the rate of heat transfer
becomes large resulting into a greater efficiency.
2. Fire tube
In fire tube boiler the hot products of combustion pass through the tubes, which
are surrounded, by water. Fire tube boilers have low initial cost, and are more
compacts. But they are more likely to explosion, water volume is large and due to
poor circulation they cannot meet quickly the change in steam demand. For the
same output the outer shell of fire tube boilers is much larger than the
shell of water-tube boiler.
1. External furnace
(i) Horizontal return tubular
(ii) Short fire box
(iii) Compact.
2. Internal furnace
(i) Horizontal tubular
(a) Short firebox (b) Locomotive (c) Compact (d) Scotch.
(ii) Vertical tubular.
(a) Straight vertical shell, vertical tube
(b) Cochran (vertical shell) horizontal tube.
Various advantages of fire tube boilers are as follows:
 Low cost
 Fluctuations of steam demand can be met easily
 It is compact in size.

Fig 4.1 Wall Fired Boiler with divided Convection Pass

Boiler 43
Fig 4.2 Corner Fired Boiler with Convection Pass

According to position of furnace
 Internally fired
In internally fired boilers the grate combustion chamber is enclosed within
the boiler shell
 Externally fired
In case of extremely fired boilers and furnace and grate are separated from
the boiler shell.
According to the position of principle axis
 Vertical
 Horizontal
 Inclined.
According to application
 Stationary
 Mobile (Marine, Locomotive)
According to the circulating water
 Natural circulation
 Forced circulation.
According to steam pressure
 Low pressure
 Medium pressure
 Higher pressure.
4-3 | Combustion
The primary function of oil and coal burning systems the process of steam
generation is to provide controlled efficient conversation of the chemical energy
of the fuel into heat energy which is then transferred to the heat absorbing
surfaces of the steam generator. The combustion elements of a fuel consist of
carbon, hydrogen and usually a small amount of sulphur. When combustion is
properly completed the exhaust gases will contain, carbon dioxide, water vapor,
sulphur dioxide and a large volume of Nitrogen, Combustion is brought about
by combining carbon and hydrogen or hydrocarbons with the oxygen in air.
When carbon burns completely, it results in the formation of a gas known as
carbon dioxide. When carbon burns incompletely it forms carbon monoxide.

Boiler 45
Factors affecting combustion
 Time:
It will take a definite time to heat the fuel to its ignition temperature and having
ignited, it will also take time to bum. Consequently, sufficient time must be
allowed for complete combustion of the fuel to take place in the chamber.
 Temperature:
A fuel will not burn until it has reached its ignition temperature. The speed at
which this temperature will be reached is increased by preheating the
combustion air. The temperature of the flame of the burning fuel may vary with
the quantity of air used. Too much combustion air will lower the flame
temperature and may cause unstable ignition.
 Turbulence:
Turbulence is introduced to achieve a rapid relative motion between the air and
the fuel particles. It is found that this produces a quick propagation of the flame
and its rapid spread throughout the fuel/air mixture in the combustion
chamber.
Combustion efficiency
It varies with individual different grades of fuel within each boiler. The idea to be aimed
at is the correct quantity of air together with good mixing of fuel and air to obtain the
maximum heat release.
It depends upon:
 Design of the boiler.
 Fuel used.
 Skill in obtaining combustion with the minimum amount of excess air.
4-4 | Boiler component design
The principal boiler components design is described as following:
 Furnace
 Drum
 Boiler circulating pumps
 Convection pass
- Superheater
- Reheater
- Economizer
 Air heater

 Air preheat coils
 Soot blowers
 Coal feeders
 Pulverizers
 Coal piping
 Burners
 Igniters and warmup burners
 Ductwork
 Insulation and lagging
Furnace
The furnace serves as an enclosure for the
combustion process. The furnace walls are formed
by water-filled tubes or water walls that contain the
upward flow of water and steam.
The size of the furnace is determined by the
required steam capacity and the characteristics of
the fired fuel.
Drum
The dram encloses the steam-water interface
in a subcritical boiler, and provides a
convenient point for addition of chemicals and
removal of dissolved solids from the feedwater
steam system. The drum also contains
equipment for removal of liquid from the
steam as the steam leaves the drum and enters
the connecting links to the primary
superheater.
Boiler Circulating Pumps
Boilers can have natural circulation through the furnace waterwalls or forced
circulation with boiler circulating pumps.
The forced circulation design allows the use of smaller diameter tubing in the
furnace walls, since the higher pressure drop in the smaller tubing can be offset
through pump circulation. The smaller diameter also allows thinner tube walls.
Fig 4.3 Typical Furnace
Fig 4.4 Boiler Drum

Boiler 47
Superheater
The superheater heat transfer surface may be radiant surface in the furnace or
convective surface in the convection pass.
Reheater
Like the superheater, the reheater heat transfer surface maybe composed of either
radiant or convective surface. Radiant reheater surface can be either radiant wall heat
transfer surface or pendant heat transfer surface. A radiant wall reheater can be
mounted on the front and/or side walls of the upper furnace.
Economizer
The economizer is composed of low-temperature
convection pass surface. The economizer tubes have bare
tubes, because finned tubes plug with ash when firing
with all but the best coals.
The tubes are arranged in line rather than staggered to
allow passage of large ash chunks through the tube bank.
The minimum clear space between economizer tubes
ranges from 63.5 to 102 mm.
Air Heater
The air heater for utility installations typically consists of a rotary regenerative air
heater. Tubular, heat pipe, and plate and frame air heaters are used on small boilers.
However, the rotary regenerative air heater design using either rotating heat transfer
surface or rotating air distribution hoods are used predominantly. The air heater
arrangement may consist of one, two, three, or four air heaters, depending on the size
of the unit and the degree of fuel flexibility.
Air Preheat Coils
Air preheat coils are installed upstream from the regenerative air heater. Although their
use increases the boiler efficiency, their primary purpose is to prevent corrosion of the
regenerative air heater by increasing heat transfer surface temperatures. The increased
heat transfer surface temperatures are less likely to cause condensation of acids from
the flue gas stream.
Fig 4.5 Economizer

Soot Blowers
Soot blowers are used for removal of ash deposits from the fireside of heat
transfer surfaces. Several types of soot blowers are used in utility steam
generators.
Wall blowers are used for furnace walls. Wall blowers have a very short lance with
a nozzle on the tip. The lance rotates as it moves into the furnace, and the nozzle
directs the soot blowing medium onto a circular area of the furnace wall.
Retractable water lances are used in difficult applications for spot removal of
heavy slag. Water lances are typically located at the furnace knuckle or in the
furnace throat, where heavy slag may accumulate. They are also used for cleaning
of furnace pendant surface and convection pass tube banks.
Retractable may be fully retractable or partially retractable, depending on the
temperature zone. Retractable soot blowers have a nozzle at the end of a lance
that rotates as the lance travels along the tube surface, perpendicular to the glue
gas flow.
Coal Feeders
Coal feeders are located between each coal silo and its respective pulverizer. The
principal function of a coal feeder is to control the flow of coal to the pulverizer,
thus matching the fuel flow to the steam demand. The feeder design commonly
used for large-scale power plants is the horizontal belt type. Coal flows onto the
moving belt from a vertical feed pipe and is discharged from the end of the belt
into the vertical pulverizer feed pipe. The belt speed is varied to control the coal
flow. The feed pipe is typically constructed of 304 stainless steel to enhance coal
flow.
Two variations of the belt feeder are the
volumetric feeder and the gravimetric
feeder. Volumetric belt feeders typically
use a fixed position levelling bar in
combination with a variable speed belt
to control the coal flow. The gravimetric
feeder is equipped with a belt scale that
weighs the coal as it passes through the
feeder. The associated feeder control
system measures and records both instantaneous coal feed rate and the
cumulative weight of coal fed. The gravimetric feeder is preferred for utility
installations because of its ability to sense and respond to changes in coal
density.
Fig 4.6 Coal Hopper

Boiler 49
Pulverizers
Fig4.7GravimetricFeeder

Fig4.8BallMillCoalPulveriser

Boiler 51
Pulverizer
Three types of pulverizers have been used on coal-fuelled utility boilers: the ball tube
mill, vertical spindle mill, and attrition mil.
The low-speed ball tube mill is characterized by very low maintenance costs but high
power consumption. Wear part maintenance consists of replacing wear liners on a 10-
to 15-year frequency and replenishing the ball charge several times a year.
The medium-speed vertical spindle mill can be either a bowl-and-roller or ball-and-
race mill.
 The bowl-and-roller type is used
predominantly in power installations. The
bowl-and-roller pulverizer is characterized
by medium to high maintenance and low
power consumption. Pulverizer overhauls
for replacement or renewal of roller wear
surfaces are required on a 2- to 5-year
frequency, depending on the abrasion
characteristics of the coal.
 Ball-and-race pulverizers typically
have been used on small unit sizes,
although some large installations do have
ball-and-race mills. Ball-and-race
pulverizers typically have been used on
small unit sizes, although some large
installations do have ball-and-race mills.
The high-speed attrition mill typically has been used on small installations. It is
characterized by high power consumption and high maintenance, and mill overhauls
are required approximately every year.
Coal Piping and Burners
Coal piping conveys the pulverized coal-primary air mixture to the burners. The
pulverized coal piping is typically steel with 12.7 mm wall thickness. Ceramic linings
are used on coal pipe bends if the pulverized coal is particularly abrasive.
The burner pipe arrangement and accessories are determined by the burner
arrangement in the furnace and the type of pulverizer. Two types of burner
arrangements are used on large utility boilers: wall-fired and corner- or tangentially
fired.
Fig 4.9 Ball & Roller Pulverizer

The wall-fired furnaces may be front wall-fired, rear wall-fired, or the burners may
be front and rear-wall opposed. The typical wall-fired burner arrangement is
configured such that one pulverizer feeds all the burners on one level on one
wall. Pressurized pulverizers have outlets equal in number to the burners fed by
the pulverizer. Exhauster pulverizers have a single outlet stream from the
exhauster fan. The exhauster fan discharge is divided with coal pipe splitters to
obtain an individual coal pipe for each burner served by the pulverizer. Exhauster
pulverizers are typically used in conjunction with tangentially fired furnaces. The
exhauster mill and wall-fired furnace combination is unusual, but does exist on
some older boilers.
For tangentially fired furnaces, modem designs are arranged to fire from four
furnace corners. Older tangential furnace designs may be arranged with a divided
furnace with two fire balls, one in each furnace side. The divided furnace design
has been built both with and without a centre division wall. The divided furnace
has eight burners per burner elevation. One pulverizer feeds all eight burners on
one elevation of a divided furnace or all four burners per elevation of a "single
fire ball" tangential furnace.
Igniters and Warmup Burners
Ignitors and warmup burners are necessary for
flame initiation and low load stabilization. The main
difference between the various burners lies in the
rapidity of air-coal mixing i.e., turbulence. For
bituminous coals the turbulent type of burner is
used whereas for low volatile coals the burners with
long flame should be used. A pulverised coal burner
should satisfy the following requirements:
 It should mix the coal and primary air thoroughly and should bring this
mixture before it enters the furnace in contact with additional air known
as secondary air to create sufficient turbulence.
 It should deliver and air to the furnace in right proportions and should
maintain stable ignition of coal air mixture and control flame shape and
travel in the furnace. The flame shape is controlled by the secondary air
vanes and other control adjustments incorporated into the burner.
Secondary air if supplied in too much quantity may cool the mixture and
prevent its heating to ignition temperature.
Fig 4.10 Coal Burner

Boiler 53
Ductwork, Ash Hoppers, and Dampers
The steam generator includes both air and flue gas ductwork.
The following ductwork systems typically are included in the steam generator
specification:
 Air heater secondary air outlet to wind box,
 Primary air fan discharges to air heater,
 Air heater primary air outlet to pulverizers,
 Tempering air to pulverizers,
 Seal air ducts,
 Flame detector cooling air ducts,
 Ignitor air ducts,
 Steam generator flue gas outlet to air heater, and
 Air heater gas outlet to a specified terminal point.
Insulation and Lagging
Insulation both reduces the heat loss from the boiler and protects operations and
maintenance personnel from contact with high-temperature surfaces. Lagging or
jacketing protects the insulation from physical damage.
Insulation typically is specified for surfaces that operate at a temperature exceeding
130° F (54° C). Coal piping between the pulverizers and the burners exceeds that
temperature, but typically is not insulated. Insulation on coal piping would obscure the
source of pulverized coal leaks as the coal piping wears.
Insulation is typically specified to limit the
cold face temperature to 120° F (49° C)
maximum based on an ambient air
temperature of 80° F (27° C) with an air
velocity of 60 ft. (18.3 m) per minute. This
requirement is typically met with 4 to 6 in.
(102 to 152 mm) of insulation on boiler flat
surfaces. Steam generator surfaces, hot air,
and gas ducts are insulated with mineral
fibre block insulation. Rigid calcium silicate moulded insulation may be used on the
penthouse roof and on the top surface of ducts. The rigid material is expected to
withstand occasional foot traffic.
Lagging may be specified as either aluminium or steel, although aluminium is used
most often.
Fig 4.11 Boiler Insulation

4-5 | Boiler fittings and accessories
 Pressuretrols: control the steam pressure in the boiler. Boilers generally
have 2 or 3 pressuretrols: a manual-reset pressuretrol, which functions
as a safety by setting the upper limit of steam pressure, the operating
pressuretrol, which controls when the boiler fires to maintain pressure,
and for boilers equipped with a modulating burner, a modulating
pressuretrol which controls the amount of fire.
 Safety valve: It is used to relieve pressure and prevent possible explosion
of a boiler.
 Water level indicators: They show the operator the level of fluid in the
boiler, also known as a sight glass, water gauge or water column.
 Bottom blowdown valves: They provide a means for removing solid
particulates that condense and lie on the bottom of a boiler. As the name
implies, this valve is usually located directly on the bottom of the boiler,
and is occasionally opened to use the pressure in the boiler to push
these particulates out.
 Continuous blowdown valve: This allows a small quantity of water to
escape continuously. Its purpose is to prevent the water in the boiler
becoming saturated with dissolved salts. Saturation would lead to
foaming and cause water droplets to be carried over with the steam – a
condition known as priming. Blowdown is also often used to monitor the
chemistry of the boiler water.
 Tricock: It is a type of valve that is often use to manually check a liquid
level in a tank. Most commonly found on a water boiler.
 Flash tank: High-pressure blowdown enters this vessel where the steam
can 'flash' safely and be used in a low-pressure system or be vented to
atmosphere while the ambient pressure blowdown flows to drain.
 Automatic blowdown/continuous heat recovery system: This system
allows the boiler to blowdown only when makeup water is flowing to the
boiler, thereby transferring the maximum amount of heat possible from
the blowdown to the makeup water. No flash tank is generally needed
as the blowdown discharged is close to the temperature of the makeup
water.
 Hand holes: They are steel plates installed in openings in "header" to
allow for inspections & installation of tubes and inspection of internal
surfaces.
 Steam drum internals, a series of screen, scrubber & cans (cyclone
separators).
 Low-water cutoff: It is a mechanical means (usually a float switch) that is
used to turn off the burner or shut off fuel to the boiler to prevent it
from running once the water goes below a certain point. If a boiler is
"dry-fired" (burned without water in it) it can cause rupture or
catastrophic failure.

Boiler 55
 Surface blowdown line: It provides a means for removing foam or other
lightweight non-condensable substances that tend to float on top of the
water inside the boiler.
 Circulating pump: It is designed to circulate water back to the boiler after it
has expelled some of its heat.
 Feedwater check valve or clack valve: A non-return stop valve in the feedwater
line. This may be fitted to the side of the boiler, just below the water level, or
to the top of the boiler.
 Top feed: In this design for feedwater injection, the water is fed to the top of
the boiler. This can reduce boiler fatigue caused by thermal stress. By spraying
the feedwater over a series of trays the water is quickly heated and this can
reduce limescale.
 Desuperheater tubes or bundles: A series of tubes or bundles of tubes in the
water drum or the steam drum designed to cool superheated steam, in order
to supply auxiliary equipment that does not need, or may be damaged by, dry
steam.
 Chemical injection line: A connection to add chemicals for controlling
feedwater pH.
Steam accessories
 Main steam stop valve
 Steam traps
 Main steam stop/check valve: It is used on multiple boiler installations.
Combustion accessories
 Fuel oil system: fuel oil heaters
 Gas system
 Coal system
 Soot blower
Other essentials
 Pressure gauges
 Feed pumps
 Fusible plug
 Inspectors test pressure gauge attachment
 Name plate
 Registration plate
Gas safe check
 It is essential to carry out gas safe check each year.

Plant Auxiliary Maintenance 5
57

5-1 | Introduction
Plant Auxiliary Maintenance (PAM) is an integral department of plant and known
for many crucial and variety of jobs. It is not heart of plant but responsible for
working of plant heart systems like boiler and turbine by providing water for
steam generation.
Various departments that comes under the plant auxiliary maintenance are as
following:
 CSPH
 WTP
 Wet Ash Handling System
 Dry Ash Handling System
 Compressed Air Handling System
 Ash Dyke Area
 CRS
 Cooling Towers
CSPH
CSPH stands for control structure pump house. From CSPH there is overall control
of water system not only for steam generation but also for fire protection system,
service water for cleaning etc. CSPH is structured on inlet canal.
It has the following components:
 CRW Pump
Clarified water pump provides raw water to the geomiller for clarified and
DM water.
 HP Pump
- HP 1&2 – Water supply to Ash trench Flushing
- HP 3,5&6 – Water supply to Stage 1 ESP deashing
- HP4- Pressure boost up of U#4, LP header at ESP side.
 LP Pump
Supply water for ash slurry preparation
 TWS Pump
Travelling water pumps used for boosting pressure of DEDS pumps
discharge. Discharge water used for cleaning of TWS.

PAM 59
 FS Pump
Fire Screen Pumps used to supply water for firefighting system, as service water
in boiler area and for cleaning of vertical screens.
 TWS
Travelling screen used for removing unwanted material like polythene, pieces
of cloth, debris from water by filtration method.
 VWS
Vertical water screens used as 2nd
filtration system after travelling water screens.
 DEDS Pump
Dust Extraction and Dust Suspension System is clarified water after generator
gas cooling is supplied by 3 vertical pump and 1 centrifugal pump for spraying
water in coal yard form preventing auto ignition of coal and to TWS pumps for
TWS cleaning.
WTP
WTP stands for water treatment plant. Raw water supply comes from CSPH by CRW
pumps. It prepares different types of water using different technologies.
 Clarified Water
It is prepared from raw water by addition of Chlorine. Clarified water is used as
cooling agent for generator gas and for different parts.
 DM Water
DM stands for de-mineralize water and used for steam generation and for
cooling of stator of generator.
 RO Water
It is prepared to be used for drinking purpose.
Dry Ash Handling System
In coal based power plants two type of ash generated. Wet ash and Dry ash. Ratio of
wet ash to dry ash is 30:70. Wet ash is only money consuming by product of coal plant
because it requires a lot of money for handling of wet ash.
Although, dry ash is by product, unlike wet ash it is a money making by product and
utilized in many fields like in cement industries and for brick making.

Compressor House
Compressor house is source of compressed air for plant. Compressed air as name
implies having pressure above atmospheric pressure and used to operate many
crucial functions.
Compressed air in plant used in two form.
 Plant Air
It also known as service air and used as service air for cleaning air at
different locations.
 Instrument Air
It is used to operate pneumatic valve at different areas and source of
energy for air pre heater motor in all five units.
Different compressors used at Plant
 Station Air Compressor
- All three station air compressors are reciprocating type.
- Compressed air is used mainly in stage 1.
 Instrument Air Compressor
- There are two instrument air compressor B&C.
- Compressed air after compressor is goes through air drying Unit
A&B. Air Drying Unit Consist of heaters and Silica gel and perform
the function of air drying.
 Plant Air Compressor
- There are three plant air compressor A, B, C.
- Compressed air of plant air compressor is used mainly as service air
and used for cleaning purpose
 Dense Air Compressor
- There are four dense air compressor A, B, C& D.
- Denso air compressor air is used mainly in Bowl mills of Unit 4 & 5.
CRS
CRS stands for central repair shop. In Central Repair Shop repairing related job
performed. In CRS not only repairing jobs are done but also production jobs are
done according to contingency plans.
CRS is a wonderful tool for emergency and many times, during exigencies had
worked as only tool. Some of the machines available at CRS are as following
 Lathe Machines
 Shaper Machine

PAM 61
 Drilling Machine
 Milling Machine
 Shearing Machine
 Balancing Machine
 Hydraulic Press
 Sheet Rolling Machine
Cooling Towers
There are three cooling towers in BTPS.
 Cooling Towers Fulfill the scarcity of water and is that component which
transform open cycle power plant to closed cycle.
 Cooling Towers are nothing more than heat exchanger.
In cooling towers, heat exchange process take place where cooling medium is
environmental air and interaction of hot water with environmental air brings
down temperature of hot water to environmental temperature.
5-2 | Importance
Water must flow through the heat absorption surface of the boiler in order that it be
evaporated into steam. In drum type units (natural and controlled circulation) the water
is circulated from the drum through the generating circuits and then back to the drum
where the steam is separated and directed to the super heater. The water leaves the
drum through the down comers 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.
5-3 | Types of Boiler Circulation System
Natural circulation system
Water delivered to steam generator from feed heater is at a temperature well below
the saturation value corresponding to that pressure. Entering first the economizer it is
heated to about 30-40˚C below saturation temperature. From economizer the water
enters the drum and thus joins the circulation system. Water entering the drum flows
through the down comer 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 super heater for super heating
and then sent to the high pressure turbine. Remaining water mixes with the
incoming water from the economizer and the cycle is repeated. The circulation in
this case takes place on the thermo-siphon principle. The down comers contain
relatively cold water whereas the riser tubes contain a steam water mixture.
Circulation takes place at such a rate that the driving force and the frictional
resistance in water walls are balanced. 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.
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, orifice plates are used. This system is applicable in the high sub-critical
regions (200 kg/cm²).
Combined circulation system
Beyond the critical pressure,
phase transformation is absent,
and hence once through system
is adopted. However, it has been
found that even at super critical
pressure, it is advantageous to
recirculate the water through
the furnace tubes and simplifies
the startup procedure. A typical
operating pressure for such a
system is 260 kg/cm2
.
Fig 5.1 Water Circulation System

PAM 63
5-4 | Ash Handling Plants
The ash produced in the boiler is transported to ash dump area by means of sluicing
type hydraulic ash handling system, which consists of Bottom ash system, Ash water
system and Ash slurry system.
Bottom ash system
In the bottom ash system, the ash discharged from the furnace bottom is collected in
two water compounded scraper through installed below bottom ash hoppers. The ash
is continuously transported by means of the scraper chain conveyor onto the
respective clinker grinders which reduce the lump sizes to the required fineness. The
crushed ash from the bottom ash hopper from where the ash slurry is further
transported to operation, the bottom ash can be discharged directly into the sluice
channel through the bifurcating chute bypass the grinder. The position of the flap gate
in the bifurcating chute bypasses the grinder. The position of the flap gate in the
bifurcating chute is to be manually changed.
The flushing apparatus are provided under E.P. hoppers, economizer hoppers, air pre
heaters, and stack hoppers. The fly ash gets mixed with flushing water and the resulting
slurry drops into the ash sluice channel. Low pressure water is applied through the
nozzle directing tangentially to the section of pipe to create turbulence and proper
mixing of ash with water. For the maintenance of flushing apparatus plate valve is
provided between apparatus and connecting tube.
Ash water system
High pressure water required for bottom ash hopper quenching nozzles, bottom ash
hopper spraying, clinker grinder sealing scraper bars, cleaning nozzles, bottom ash
hopper seal through flushing, economizer hopper flushing nozzles and sluicing trench
jetting nozzles is tapped from the high pressure water ring mainly provided in the plant
area.
Low pressure water required for bottom ash hopper seal through make up, scraper
conveyor make up, flushing apparatus jetting nozzles for all fly ash hoppers excepting
economizer hoppers, is trapped from low pressure water rings mainly provided in the
plant area.

Ash slurry system
Bottom ash and fly ash slurry of the system is sluiced upto ash pump along the
channel with the acid of high pressure water jets located at suitable intervals
along the channel Slurry pump suction line consisting of reducing elbow with
drain valve reducer and butterfly valve and portion of slurry pump delivery line
consisting of butterfly valve, pipe & fitting has also been provided.
5-5 | Water Treatment 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 are designed to process the raw
water to water with very low in dissolved solids known as "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
Actually, the type of demineralization process chosen for a power station
depends on three main factors:
 The quality of the raw water.
 The degree of de-ionization i.e. treated water quality
 Selectivity of resins.
Water treatment process which is generally made up of two
sections:
 Pre-treatment section
 Demineralization section
Pre-treatment 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 of two types of suspended solids in water.
Fig 5.2 Ash Slurry System

PAM 65
Firstly, the separable solids and secondly the non-separable solids (colloids). The
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. The
settling rate of the colloidal and finely divided (approximately 001 to 1 micron)
suspended matter is so slow that removing them from water by plain sedimentation is
tank shaving ordinary dimensions is impossible.
Settling velocity of finely divided and collide particles under gravity also are so small
that ordinary sedimentation is not possible.
It is necessary, therefore, to use procedures which agglomerate the small particles into
larger aggregates, which have practical settling velocities. The term "Coagulation" and
"flocculation" have been used indiscriminately to describe process of turbidity removal.
"Coagulation" means to bring together the suspended particles. The process describes
the effect produced by the addition of a chemical to a colloidal dispersion resulting in
particle destabilization by a reduction of force tending to keep particles apart. Rapid
mixing is important at this stage to obtain. Uniform dispersion of the chemical and to
increase opportunity for particles to particle contact. This operation is done by flash
mixer in the ariflocculator.
Second stage of formation of settle able particles from destabilized colloidal sized
particles is termed a "flocculation". Here coagulated particles grow in size by attaching
to each other. In contrast to coagulation where the primary force is electrostatic or
intrinsic, "flocculation" occurs by chemical bridging. Flocculation is obtained by gentle
and prolonged mixing which converts the submicroscopic coagulated particle into
discrete, visible & suspended particles. At these stage particles are large enough to
settle rapidly under the influence of gravity anomaly be removed. If pretreatment of
the water is not done efficiently then consequences are as follows:
 Si02 may escape with water which will increase the anion loading.
 Organic matter may escape which may cause organic fouling in the anion
exchanger beds. In the 'pre-treatment plant chlorine addition provision
is normally made to combat organic contamination.
 Cation loading may unnecessary increase due to addition of Ca(OH)2 in
excess of calculated amount for raising the pH of the water for maximum
floe formation and also may precipitate out. If less than calculated
amount of Ca(OH)2 is added, proper pH flocculation will not be obtained
and silica escape to demineralization section will occur, thereby
increasing load on anion bed.

Demineralization
This filter water is now used for demineralizing purpose and is fed to cation
exchanger bed, but enroute being first dechlorinated, 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.
Normally, the typical scheme of demineralization up to the mark against an
average surface water, is three bed system with a provision of removing gaseous
carbon dioxide from water before feeding to Anion Exchanger.
Resins, which are built on synthetic matrix of a styrene divinely benzene
copolymer, are manufactured in such a way that these have the ability to,
exchange one ion for another, hold it temporarily in chemical combination and
give it to a strong electrolytic solution. Suitable treatment is also given to them
in such a way that a particular resin absorbs only a particular group of ions.
Resins, when absorbing and releasing cationic portion of dissolved salts, is called
cation, exchanger resin and when removing anionic portion is called anion
exchanger resin. Preset trend is of employing 'strongly acidic cation exchanger
resin and strongly basic anion exchanger resin in a DM Plant of modern thermal
power station. We may see that the chemically active group in a cationic resin is
SOx-H (normally represented by RH) and in an anionic resin the active group is
either tertiary amine or quaternary ammonium group (normally the resin is
represented by ROH) The water from the ex-cation contains carbonic acid also
sufficiently, which is very weak acid difficult to be removed by strongly basic
anion resin and causing hindrance to remove silicate ions from the bed. It is
therefore a usual practice to remove carbonic acid before it is led to anion
exchanger bed. The ex-cation water is trickled in fine streams from top of a tall
tower packed with, ranching rings, and compressed air is passed from the
bottom. Carbonic acid breaks into C03 and water mechanically (Henry's Law) with
the carbon dioxide escaping into the atmosphere. The water is accumulated in
suitable storage tank below the tower, called degassed water dump from where
the same is led to anion exchanger bed, using acid resistant pump.
The ex-anion water is fed to the mixed bed exchanger containing both cationic
resin and anionic resin. This bed not only takes care of sodium slip from cation
but also silica slip from anion exchanger very effectively. The final output from
the mixed bed is Extraordinarily pure water having less than 0.2/Mho conductivity
7.0 and silica content less than 0.02 pm. Any deviation from the above quality
means that the resins in mixed bed are exhausted and need regeneration,
regeneration of the mixed bed first calls for suitable, back washing and settling.

PAM 67
So that the two types of resins are separated from each other. Lighter anion resin rises
to the top and the heavier cation resin settles to the bottom. Both the resins are then
regenerated separately with alkali and acid, rinsed to the desired value and air mixed,
to mix the resin again thoroughly. It is then put to final rinsing till the desired quality
is obtained.
It may be mentioned here that there are two types of strongly basic anion exchanger.
Type II resins are slightly less basic than type I, but have higher regeneration efficiency
than type I.
Again as type II resins are unable to remove silica effectively, type I resins also have to
be used for the purpose. As such, the general condition so far prevailing in India, is to
employ type II resin in anion exchangers bed and type I resin in mixed bed (for the
anionic portion).
It is also a general convention to regenerate the above two resins under through fare
system i.e. the caustic soda entering into mixed bed for regeneration, of type I anion
resin, is utilized to regenerate type II resin in anion exchanger bed. The content of
utilizing the above resin and mode of regeneration is now days being switched over
from the economy to a higher cost so as to have more stringent quality control of the
final D.M. Water.
Internal Treatment
This final D.M effluent is then either led to hot well of the condenser directly as
make up to boilers, or being stored in D.M. Water storage tanks first and then
pumped for makeup purpose to boiler feed. As the D.M. Water has a good
affinity to absorb carbon dioxide and oxygen, and both are extremely harmful
to metal surfaces for their destruction like corrosion, these have to be removed
before it is fed to boiler. This is being done in desecrator. Still the residual
oxygen which is remaining in the water is neutralized by a suitable doze of
hydrazine, at the point after desecrator. To have further minimum corrosion, the
pH of feed water is to be maintained at around 9.0 for which purpose ammonia
in suitable doze is added to this make up water at a point along with hydrazine
as stated above.

6-1 | Operating Principles
The principle of operation of steam turbine is entirely different from the steam
engine. In reciprocating steam engine, the pressure energy of steam is used to
overcome external resistance and the dynamic action of steam is negligibly small.
But the steam turbine depends completely upon the dynamic action of the steam.
According to Newton’s Second Law of Motion, the force is proportional to the
rate of change of momentum (mass × velocity). If the rate of change of
momentum is caused in the steam by allowing a high velocity jet of steam to
pass over curved blade, the steam will impart a force to the blade. If the blade is
free, it will move off (rotate) in the direction of force. In other words, the motive
power in a steam turbine is obtained by the rate of change in moment of
momentum of a high velocity jet of steam impinging on a curved blade which is
free to rotate. The steam from the boiler is expanded in a passage or nozzle where
due to fall in pressure of steam, thermal energy of steam is converted into kinetic
energy of steam, resulting in the emission of a high velocity jet of steam which,
Principle of working impinges on the moving vanes or blades of turbine.
Attached on a rotor which is mounted on a shaft supported on bearings, and
here steam undergoes a change in direction of motion due to curvature of blades
which gives rise to a change in momentum and therefore a force. This constitutes
the driving force of the turbine. It should be realized that the blade obtains no
motive force from the static pressure of the steam or from any impact of the jet,
because the blade in designed such that the steam jet will glide on and off the
blade without any tendency to strike it.
When the blade is locked the jet enters and leaves with equal velocity, and thus
develops maximum force if we neglect friction in the blades. Since the blade
velocity is zero, no mechanical work is done. As the blade is allowed to speed up,
the leaving velocity of jet from the blade reduces, which reduces the force. Due
to blade velocity the work will be done and maximum work is done when the
blade speed is just half of the steam speed. In this case, the steam velocity from
the blade is near about zero i.e. it is trail of inert steam since all the kinetic energy
of steam is converted into work.
The force and work done become zero when the blade speed is equal to the
steam speed. It follows that a steam turbine should have a row of nozzles, a row
of moving blades fixed to the rotor, and the casing (cylinder). A row of nozzles
and a raw of moving blades constitutes a stage of turbine.

Turbine 71
6-2 | Turbine Classification
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. A simple impulse
turbine is not very efficient because it does
not fully use the velocity of the steam.
Many impulse turbines are velocity
compounded. This means they have two or
more sets of moving blades in each stage.
Reaction Turbine
In this type of turbine pressure is reduced at both fixed & moving blades. Both fixed
& moving blades act as nozzles. Work done by the impulse effect of steam due to
reversals of direction of high velocity steam. The expansion of steam takes place on
moving blades.
Compounding
Several problems occur if energy of steam is converted in single step & so
compounding is done. Following are the types of compounded turbine:
 Velocity Compounded Turbine
Like simple turbine it has only one set of nozzle & entire steam pressure drop
takes place there. The kinetic energy of steam fully on the nozzles is utilized in
moving blades. The role of fixed blades is to change the direction of steam jet &
to guide it.
 Pressure Compounded Turbine
This is basically a no. of single impulse turbines in series or on the same shaft.
The exhaust of first turbine enters the nozzle of the next turbine. Total pressure
drop of steam does not take on first nozzle ring but divided equally on all of
them.
Fig 6.1 Simple Impulse Turbine

 Pressure Velocity Compounded Turbine
It is just the combination of the two compounding has the advantages of
allowing bigger pressure drops in each stage & so fewer stages are
necessary. Here for given pressure drop the turbine will be shorter length
but diameter will be increased
Steam turbines may be classified into different categories depending on their
construction, the process by which heat drop is achieved, the initial and final
conditions of steam used and their industrial usage.
According to the direction of steam flow
 Axial turbines
 Radial turbines
According to the number of cylinder
 Single - cylinder turbines.
 Double- cylinder turbines.
 Three-Cylinder turbines.
 Four-Cylinder turbines.
 Multi - Cylinder turbines
According to the steam conditions at inlet to turbines
 Low-pressure turbines
 Medium -pressure turbines
 High-pressure
 Turbines of very high pressures
 Turbines of supercritical pressures
According to the means of Heat Supply
 Single pressure turbine,
 Mixed or dual pressure turbine
 Reheated turbine.
(a) Single (b) Double
According to the means of heat rejection
 Pass-out or extraction turbine,
 Regenerative turbine,
 Condensing turbine,
 Noncondensing turbine,
 Back pressure or topping turbine

Turbine 73
Fig 6.2 Types of Turbines

Fig6.3SteamTurbineArrangement(SideView)

Turbine 75
According to their usage in industry
 Turbines with constant speed of rotation primarily used for driving alternators.
 Steam turbines with variable speed meant for driving turbo blowers, air
circulators, pumps etc.
 Turbines with variable speed: Turbines of this type are usually employed in
steamers, ships and railway locomotives (turbo locomotives).
6-3 | Turbine Operation
The 210MW turbine is a tandem compounded type machine comprising of H.P. & I.P.
cylinders. The H.P. turbine comprises of 12 stages the I.P. turbine has 11 stages & the
L.P. has four stages of double flow. The H.P. & I.P. turbine rotor are rigidly compounded
& the I.P. & the I.P. rotor by lens type semi flexible coupling. All the three rotors are
aligned on five bearings of which the bearing no.2 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
the steam returned in the boiler for reheating.
Fig 6.4 Steam Turbine Arrangement

The reheated steam from the boiler enter I.P. turbine via interceptor valves and
control valves and after expanding enters the L.P. turbine stage via 2 numbers of
cross over pipes.
In the L.P. stage the steam expands in axially opposite direction to counteract the
trust and enters the condenser placed directly 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 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 closed cycle.
Turbine Cycle
Fresh steam from boiler is supplied to the turbine through the emergency stop
valve. From the stop valves steam is supplied to control valves situated on H.P.
cylinders on the front bearing end. After expansion through 12 stages at the H.P.
cylinder steam flows back to boiler for reheating and reheated steam from the
boiler cover to the intermediate pressure turbine trough two interceptor valves
and four control valves mounted on the I.P. turbine.
After flowing through I.P. turbine steam enters the middle part of the L.P. turbine
through cross over pipes. In L.P. turbine the exhaust steam condenses in the
surface condensers welded directly to the exhaust part of L.P. turbine. The
selection of extraction points and cold reheat pressure has been done with a view
to achieve the highest efficiency. These are two extractions from H.P. turbine, four
from I.P. turbine and one from L.P. turbine. Steam at 1.10 to 1.03 g/sq cm Abs is
supplied for the gland sealing. 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 capacity condensate
pumps to deaerator through the low pressure regenerative equipment’s.
Feed water is pumped from deaerator to the boiler through the H.P. heaters by
means of 3x50% capacity feed pumps connected before the H.P. heaters.
6-4 | Turbine Components
Emergency Stop Valve
Steam from the boiler is supplied to the turbine through two emergency stop
valves. The emergency stop valve operated by hydraulic servomotor shuts off
steam supply to the turbine when the turbo set is tripped. The emergency stop
valves connected to the four control valves through four flexible loop pipes of
Chromium-Molybdenum-Vanadium steel.

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