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Industrial Training Project Report
“Thermal Power Plants”
National Thermal Power Corporation,
(Submitted on completion of vocational training at NTPC,
Submitted To: Submitted By:
Mr. Amiya Kumar Sahu Devanshu Yadav,
Training & Placement In-charge Enrl.No-111628
Mechanical Engineering Deptt. B.Tech (Mechanical)
4th year(7th semester)
I hereby declare that this project is being submitted in fulfillment of the INDUSTRIAL
TRAINING PROGRAMME in NTPC Vindhyanagar , and is the result of self done work
carried out by me under the guidance of various Engineers and other officers.
I further declare that to my knowledge, the structure and content of this project are original
and have not been submitted before for any purpose.
This is to certify that Mr. Devanshu Yadav of Jaypee University OF
Engineering & Technology, Guna has undergone Vocational Training for a period
of 45 days from 01.07.2014 to 14.08.2014 at Vindhyanagar Super Thermal
Power Project, in the Boiler Maintenance Department, and has made the project report
under my guidance.
Mr Shaji john , AGM(BMD)
Boiler Maintenance Department(BMD)
Mechanical Erection Department (ME)
I am truly thankful to all the guides who imparted the lectures on various
subjects topics and took me to the plant in a guided study visit along detailed
explaining about the plant and machinery.
I would give thanks to Mr. Utkarsh Kumar & HR Dept. of NTPC Ltd,Vindhyanagar
as they have given me the chance of having this wonderful learning experience.
I am also indebted to respected Officers and Engineers
1) Mr. Azad Kumar
2) Mr. Shaji John
3) Mr. Utkarsh Kumar
they went out of their way to provide me with as much information as they could, in spite of
the fact that they were laden with their own work. I can’t really express my feeling of gratitude
Topic Page no.
2-About NTPC vindhyanchal 13
3-Basic power plant cycles 16
4-Boiler maintenance department (BMD) 24
5-Associated Systems in power plants 35
6-Turbine & its uses 42
7-How to increase the thermal efficiency of power plants 44
8-Losses during operation & maintenance of plant 47
LIST OF FIGURES
Serial no. Description Page No.
Strategies of NTPC
View of NTPC vindhyanchal stage 4 foundation
Modified rankine cycle for processes in power plant
Arrangement of furnaces
Typical non regenerative cycle followed by subcritical plant
Typical non regenerative cycle followed by supercritical plant
Types of waterwall arrangement
Compnents of deaerator
Boiler depicting the flow of fuel & gases along the arrows
Electrostatic precipitator (ESP)
Components of mill
Diagram of steam , impulse & reaction turbine
Effect of lowering of condenser pressure on efficiency
Effect of superheating the steam to high temperature
Effect of increasing the boiler pressure to efficiency
NTPC Limited (formerly known as National Thermal Power Corporation
Limited) is a Central Public Sector Undertaking (CPSU) under the Ministry of Power,
Government of India, engaged in the business of generation of electricity and allied
activities. It is a company incorporated under the Companies Act 1956 and a "Government
Company" within the meaning of the act. The headquarters of the company is situated at
New Delhi. NTPC's core business is generation and sale of electricity to state-owned
power distribution companies and State Electricity Boards in India. The company also
undertakes consultancy and turnkey project contracts that comprise of engineering,
project management, construction management and operation and management of power
plants. The company has also ventured into oil and gas exploration and coal mining
activities. It is the largest power company in India with an electric power generating
capacity of 42,964 MW.Although the company has approx. 18% of the total national
capacity it contributes to over 27% of total power generation due to its focus on operating
its power plants at higher efficiency levels (approx. 83% against the national rate of 78%).
The company was founded in November 1975 as "National Thermal Power Corporation
Private Limited". It started work on its first thermal power project in 1976 at singrauli in
Uttar Pradesh. In the same year, its name was changed to "National Thermal Power
Corporation Limited". In 1983, NTPC began commercial operations (of selling power)
and earned profits of INR 4.5 crores in FY 1982-83. By the end of 1985, it had achieved
power generation capacity of 2000 MW.
In 1986, it completed synchronization of its first 500 MW unit at Singrauli. In 1988, it
commissioned two 500 MW units, one each in Rihand and Ramagundam. In 1989, it
started a consultancy division. In 1992, it acquired Feroze Gandhi Unchahar Thermal
Power Station (with 2 units of 210MW capacity each) from Uttar Pradesh Rajya Vidyut
Utpadan Nigam of Uttar Pradesh.
By the end of 1994, its installed capacity crossed
Strategies of NTPC
Fig.1.1 Strategies of NTPC
o Introduction of steam generators (boilers) of the size of 800 MW.
o Integrated Gasification Combined Cycle (IGCC) Technology.
o Launch of Energy Technology Centre -A new initiative for development
of technologies with focus on fundamental R&D.
o The company sets aside up to 0.5% of the profits for R&D.
o Roadmap developed for adopting µClean Development.
o Mechanism to help get earn µCertified Emission Reduction.
Corporate Social Responsibility
o As a responsible corporate citizen NTPC has taken up number of CSR initiatives.
o NTPC Foundation formed to address Social issues at national level
o NTPC has framed Corporate Social Responsibility Guidelines committing up to
0.5% of net profit annually for Community Welfare.
o The welfare of project affected persons and the local population around
NTPC projects are taken care of through well drawn Rehabilitation and
o Thecompanyhasalsotakenupdistributedgeneration forremoterural areas.
Partnering government in various initiatives
o Disseminate technologies to other players in the sector.
o Consultant role ³Partnership in Excellence´ Programme for improvement of
PLF of 15 Power Stations of SEBs.
o Rural Electrification work under Rajiv Gandhi Garmin Vidyutikaran.
o Allstationsof NTPCareISO14001certified.
o Centre for Power Efficiency & Environment Protection.
o NTPC is the second largest owner of trees in the country after the forest
"To be the world‟s largest and best power producer, powering India‟s growth."
"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."
Core Values - BE COMMITTED
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
NTPC environment issues in singrauli:
Singrauli region has been identified as a critically polluted area (CPA) by the Union
Ministry of Environment and Forests (MoEF). Incremental coal mining activities in the region
and the rapid development of coal-based thermal power plants has resulted in acute air and
water pollution, leading to serious health problems among the residents of the locality, which
With the coming up of many more power companies the problem is
expected to increase. Power plants in the area are poisoning the air and water in the district
with mercury, a neurotoxin. Mercury is one of the natural, and perhaps the most harmful,
components of coal. During combustion at temperature above 1,100°C, it vapourises. Given
the large quantity of coal burned in thermal plants, considerable amount of mercury is released
into the atmosphere. Some of it cools down and condenses while passing through the plant’s
boiler and air pollution control system and enters the environment through soil and water. It
also enters the environment through run-off from coal mines. In humans, mercury can cause
several chronic diseases and death. In 1998, the Indian Institute of Toxicology Research (IITR),
a premier publicly funded scientific agency based in Lucknow, tested over 1,200 people from
the Singrauli region for mercury poisoning. It found high levels of mercury in humans and in
The Central Pollution Control Board analysed 11 coal samples from
Singrauli and found mercury concentration in coal ranging between 0.09 parts per million
(ppm) and 0.487 ppm
Harmony between man and environment is the essence of healthy life and growth.
Therefore, maintenance of ecological balance and a pristine environment has been of
utmost importance to the Union Ministry of Power (MoP). NTPC being the leading
organization under the ministry in the areas of power generation, has been taking various
measures discussed below for mitigation of environment pollution due to power generation.
Environment Policy & Environment Management System:
Driven by its commitment for sustainable growth of power, NTPC has evolved a well
defined environment management policy and sound environment practices for minimising
environmental impact arising out of setting up of power plants and preserving the
National Environment Policy:
At the national level, the Ministry of Environment and Forests had prepared a draft
Environment Policy (NEP) and the Ministry of Power along with NTPC actively participated
in the deliberations of the draft NEP. The NEP 2006 has since been approved by the Union
Cabinet in May 2006.
NTPC Environment Policy:
As early as in November 1995, NTPC brought out a comprehensive document entitled
"NTPC Environment Policy and Environment Management System". Amongst the guiding
principles adopted in the document are company's proactive approach to environment,
optimum utilisation of equipment, adoption of latest technologies and continual environment
improvement. The policy also envisages efficient utilisation of resources, thereby minimising
waste, maximising ash utilisation and providing green belt all around the plant for
maintaining ecological balance.
ABOUT NTPC VINDHYANCHAL
It is one of the most prestigious flagships of NTPC striving ahead to bridge the country
generation gapespecially in the western region. It was incorporated in the October 1987.
TheStation is located in Singrauli district in MP in the North-Western side of thecountry. It has
secured ISO 14001 and ISO 9002 certificate in the field of environment and power generation
but also in various other fields. On September 2002 it made glorious achievement by ensuring
production up to 2260 MW.
In2011 total production of Vindhyachal becomes 4260MW by adding 2 units of each
500MW. And now new 1 units of 500 MW are in under process for the fourthunit of station
and are likely to be completed till 2014-15. Now Vindhyachalbecomes largest power plant of
And the team of NTPC’s efficient and experienced engineers and associate is carrying
out the final testing, calibration,commissioning and synchronizations of various instrument and
systems. It has wonnumber of awards from Government of India for proper utilization and
consumptionand has bagged the safety awards presented by U.S.A. and British safety council.
Fig.2.1 View of NTPC vindhyanchal stage 4 foundation
The coal source of NTPC VINDHYACHAL is from Northerncoalfields limited (NCL)
mines at Dudhichua (7Km) and Nigahi (10Km) andJayant (5Km). These coal mines are located
in Singrauli district in MP.
2.FUEL OIL SOURCE
Indian Oil Corporation (IOC), COLD (Customer Operated Lubricantand Oil Deposit) at
Discharge canal of Singrauli Super Thermal Power Station (SSTPS).
Madhya Pradesh, Chattisgarh, Maharastra, Gujarat, Goa, Daman & Diuand Dadar &
Nagerhaveli.7.Vindhyachal Station belongs to the western region and feeds power to statesand
union territories of: Madhya Pradesh (24.4%), Chhattisgarh (4.7%),Maharashtra (32.3%),
Gujarat (20.8%), Goa, Daman & Diu (2.4%), Dadar&nagerhaveli (0.4%), Unallocated (15
%).The power flows out from Vindhyachal through 400KV power transmission system.
NTPC acquired 50% equity of the SAIL Power Supply CorporationLtd. (SPSCL). This
JV Company operates the captive power plants of Durgapur (120 MW), Rourkela (120 MW)
and Bhilai (74 MW). NTPC also has 28.33% stakein Ratnagiri Gas & Power Private Limited
(RGPPL) a joint venture company between NTPC, GAIL, Indian Financial Institutions and
Maharashtra SEB Co Ltd. NTPC's coal based power stations are at: Singrauli (Uttar Pradesh),
Korba(Chattisgarh), Ramagundam (Andhra Pradesh), Farakka (West Bengal),Vindhyachal
(Madhya Pradesh), Rihand (Uttar Pradesh), Kahalgaon (Bihar), NTCPP (Uttar Pradesh),
Talcher (Orissa), Unchahar (Uttar Pradesh), Simhadri(Andhra Pradesh), Tanda (Uttar Pradesh),
Badarpur (Delhi), and Sipat(Chattisgarh). NTPC's Gas/Liquid based power stations are located
at: Anta(Rajasthan), Auraiya (Uttar Pradesh), Kawas (Gujarat), Dadri (Uttar Pradesh),
2Jhanor-Gandhar (Gujarat), Rajiv Gandhi CCPP Kayamkulam (Kerala), andFaridabad
(Haryana). NTPC's Power Plants with Joint Ventures are located atDurgapur (West Bengal),
Rourkela (Orissa), Bhilai (Chhattisgarh), and RGPPL(Maharashtra).3.NTPC has emerged as a
diversified power major with presence in the entirevalue chain of the power generation
business. Apart from power generation, whichis the mainstay of the company, NTPC has
already ventured into consultancy, power trading, ash utilization and coal mining. NTPC is the
4th largest power generating company in Asia in terms of million units of power sold. It has
beenranked 411th in the year 2007 and ranked 317th in the year 2009, in the ForbesGlobal
2000 ranking of the World’s biggest companies. Its size is matched by its profitability. In a
recent study, leading industry analysts have placed NTPC amongthe five 'Top Buys' in Asia in
the utility segment covering power generation, power equipment and gas.4.NTPC has been
operating its plants at high efficiency levels. Although thecompany has 18.79% of the total
national capacity it contributes 28.60% of total power generation due to its focus on high
BASIC POWER PLANT CYCLE
The Rankine cycle is a cycle that converts heat into work. The heat is supplied
externally to a closed loop, which usually uses water. This cycle generates about 80% of all
electric power used throughout the world, including virtually all solar thermal, biomass, coal
and nuclear power plants. It is named after William John Macquorn Rankine, a Scottish
polymath. The Rankine cycle is the fundamental thermodynamic underpinning of the steam
Overview of NTPC Vindhyanagar Super Thermal Power Project:-
A thermal power station consists of all the equipments and a subsystem required to
produce electricity by using a steam generating boiler fired with fossil fuels or biofuels to drive
an electric generator. Some prefer to use the term ENERGY CENTER because such facilities
convert form of energy like nuclear energy, gravitational potential energy or heat energy
(derived from the combustion of fuel) into electrical energy.
The description of some of the components of the thermal power plant is as follows:
1. Cooling towers:
Cooling towers are eveporative coolers used for cooling water. Cooling tower uses
the concept of evaporation of water to reject heat from processes such by cooling the
circulaing water used in oil refineries, chemical plants, power plants, etc. Smaller towers
are normally factory built while larger ones are constructed on site. The primary use of
large, industrial cooling tower system is to remove the heat by circulating the hot water
used by the plants.The absorbed heat is rejected to the atmosphere by the evaporation of
some of the cooling water in mechanical forced – draft or induced draft towers or in natural
draft hyperbolic shaped cooling towers as seen at most nuclear power plants.
2. Three phase transmission line& step- up transformer:
Three phase electric power is a common method of electric power transmission. It is a
type of polyphase system mainly used for power motors and many other devices. In a three
phase system, three circuits reach their instantaneous peak values at different times. Taking
one conductor as reference, the other two conductors are delayed in time by one-third and
two-third of cycle of the electrical current. This delay between phases has the effect of giving
constant power over each cycle of the current and also makes it impossible 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 currents 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 at the power station. Transformers
step-up this voltage for suitable transmission after numerous further conversions in the
transmission and distribution network, the power is finally transformed to standard mains
voltage i.e. the household voltage. This voltage transmitted may be in three phase or in one
phase only where we have the corresponding step-down transformer at the receiving stage.
The output of the transformer is usually star connected with the standard mains voltage being
the phase neutral voltage.
3. Electrical generator:
An electrical generator is a device that coverts mechanical energy to electrical energy,
using electromagnetic induction whereas electrical energy is converted to mechanical energy
with the help of electric motor. The source of mechanical energy may be a rotating shaft of
steam turbine engine. Turbines are made in variety of sizes ranging from small 1 hp(0.75 kW)
used as mechanical drives for pumps, compressors and other shaft driven equipment to
2,000,000 hp(1,500,000 kW) turbines used to generate electricity.
4. Steam turbine:
A steam turbine is a mechanical device that extracts thermal energy from pressurized
steam, and converts it into rotary motion. Its modern manifestation was invented by Sir
Charles Parsons in 1884. It has almost completely replaced the reciprocating piston steam
engine primarily because of its greater thermal efficiency and higher power-to-weight ratio.
Because the turbine generates rotary motion, it is particularly suited to be used to drive an
electrical generator – about 80% of all electricity generation in the world is by use of steam
turbines. The steam turbine is a form of heat engine that derives much of its improvement in
thermodynamic efficiency through the use of multiple stages in the expansion of the steam,
which results in a closer approach to the ideal reversible process.
4. Steam Condenser:
The condenser condenses the steam from the exhaust of the turbine into liquid
to allow it to be pumped. If the condenser can be made cooler, the pressure of the
exhaust steam is reduced and efficiency of the cycle increases. The surface condenser
is a shell and tube heat exchanger in which cooling water is circulated through the
exhaust steam from the low pressure turbine enters the shell where it is cooled
andconverted to condensate (water) by flowing over the tubes as shown in the adjacent
diagram. Such condensers use steam ejectors or rotary motor-driven exhausters for
continuous removal of air and gases from the steam side to maintain vacuum.
5. Boiler Feed Pump:
A Boiler Feed Pump is a specific type of pump used to pump water into steam
boiler. The water may be freshly supplied or retuning condensation of steam produced
by the boiler. These pumps are normally high pressure units that use suction from a
condensate return system and can be of centrifugal pump type or positive displacement
type. Construction and Operation feed water pumps range from sizes upto many
horsepower and the electric motor is usually separated from the pump body by some
form of mechanical coupling. Large industrial condensate pumps may also serve as the
feed water pump. In either case, to force water into the boiler, the pump must generate
sufficient pressure to overcome the steam pressure developed by the boiler. This is
usually accomplished through the use of centrifugal pump. Feed water pumps usually
run intermittently and are controlled by a float switch or other similar level-sensing
device energizing the pump when it detects a lowered liquid level in the boiler
substantially increased. 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.
6. Control valve:
Control Valves are the 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.
A De-aerator is a boiler feed device for air removal and used to remove dissolved
gases from water to make it non-corrosive. A de-aerator typically includes a vertical
domed de-aeration section as the de-aeration 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 (due to cavitations). The solids will deposit on
heating surfaces giving rise to localized heating and tube ruptures due to overheating. De-
aerator level and pressure must be controlled by adjusting control valves-the level by
regulating condensate flow and pressure by regulating steam flow. Most de-aerators
guarantee that if operated properly, oxygen in de-aerated water will not exceed 7ppb by
8. Feed Water Heater:
A feed water heater is a power plant component used to pre heat water delivered to a
steam generating boiler. Feed water heater improves the efficiency of the system. This reduces
plant operating costs and also helps to avoid thermal shock to boiler metal when the feed water
is introduced back into the steam cycle. Feed water heaters allow the feed water to be brought
upto the saturation temperature very gradually. This minimizes the inevitable irreversibility
associated with heat transfer to the working fluid(water). A belt conveyer consists of two
pulleys, with a continuous loop of material- the conveyer belt that rotates around them. The
pulleys are powered, moving the belt and the material on the belt forward. Conveyer belts are
extensively used to transport industrial and agricultural material, such as grain, coal, ores, etc.
A pulverizer is a device for grinding coal for combustion in a furnace, in a coal
based fuel power plant.
10. Boiler Steam Drum:
Steam Drums are a regular feature of water tube boilers. It is reservoir of water/steam
at the top end of the water tubes in the water-tube boiler. They store the steam generated in
the water tubes and act as a phase separator for the steam/water mixture. The difference in
densities between hot and cold water helps in the accumulation of the “hotter”-water/and
saturated –steam into steam drum. Made from high-grade steel (probably stainless) and its
working involves temperatures 411’C and pressure well above 350psi (2.4MPa). The
separated steam is drawn out from the top section of the drum. Saturated steam is drawn off
the top of the drum. The steam will re-enter the furnace in through a super heater, while the
saturated water at the bottom of steam drum flows down to the mud- drum /feed water drum
by down comer tubes accessories include a safety valve, water level indicator and fuse plug.
A steam drum is used in 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 higher tendency at
11. 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 and decreasing the likelihood that it will
condense inside the engine. Super heaters increase the efficiency of the steam engine, and
were widely adopted. Steam which has been superheated is logically known as superheated
steam; non-superheated steam is called saturated steam or wet steam; Super heaters were
applied to steam locomotives in quantity from the early 20th century, to most steam
vehicles, and so stationary steam engines including power stations.
Economiser is mechanical devices intended to reduce energy consumption, or to
perform another useful function like preheating a fluid. The term economizer is used for other
purposes as well, e.g. air conditioning. Boiler heating in power plants. In boilers, economizer
are heat exchange devices that heat fluids , usually water, up to but not normally beyond the
boiling point of the fluid. Economizers are so named because they can make use of the
enthalpy and improving the boiler’s efficiency. They are a device fitted to a boiler which saves
energy by using the exhaust gases from the boiler to preheat the cold water used for feed into
the boiler (the feed water). Modern day boilers, such as those in coal fired power stations, are
still fitted with economizer which is decedents of Green’s original design. In this context they
are turbines before it is pumped to the boilers. A common application of economizer is steam
power plants is to capture the waste hit 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 lowers stack temperatures which may
cause condensation of combustion gases (which are acidic in nature) and may cause serious
equipment corrosion damage if care is not taken in their design and material selection.
13. Air Preheater:
Air preheater is a general term to describe any device designed to heat air before
another process (for example, combustion in a boiler). The purpose of the air preheater is to
recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler
by reducing the useful heat lost by the flue gases. 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 (chimney).
14 Electrostatic Precipitator:
An Electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate device
that removes particles from a flowing gas (such As air) using the force of an induced
electrostatic charge. Electrostatic precipitators are highly efficient filtration devices, and can
easily remove fine particulate matter such as dust and smoke from the air steam. ESP’s
continue to be excellent devices for control of many industrial particulate emissions,
including smoke from electricity-generating utilities (coal and oil fired), salt cake collection
from black liquor boilers in pump mills, and catalyst collection from fluidized bed catalytic
crackers from several hundred thousand ACFM in the largest coal-fired boiler application.
The original parallel plate-Weighted wire design (described above) has evolved as more
efficient ( and robust) discharge electrode designs were developed, today focusing on rigid
discharge electrodes to which many sharpened spikes are attached , maximizing corona
production. Transformer –rectifier systems apply voltages of 50-100 Kilovolts at relatively
high current densities. Modern controls minimize sparking and prevent arcing, avoiding
damage to the components. Automatic rapping systems and hopper evacuation systems
remove the collected particulate matter while on line allowing ESP’s to stay in operation for
years at a time.
15. Fuel gas stack:
A Fuel gas stack is a type of chimney, a vertical pipe, channel or similar structure
through which combustion product gases called fuel gases are exhausted to the outside air.
Fuel gases are produced when coal, oil, natural gas, wood or any other large combustion
device. Fuel gas is usually composed of carbon dioxide (CO2) and water vapor 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
sulfur 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 aria and thereby reduce the concentration
of the pollutants to the levels required by governmental environmental policies and
BOILER MAINTENANCE DEPARTMENT (BMD)
MAKE : Doosan Heavy Industries & Construction Co LTD, Korea.
DESIGNATION : Once-Thru in super Super-critical and Two-pass, balanced draft,
Outdoor, Radiant Reheat, Top support in sub-critical.
VOLUME : 21,462 m³
TYPE OF BOTTOM : Coutant
WIDTH : 18,816 mm
DEPTH : 18,144 mm
Spiral Wall Tubes
Material : SA213T22
NO : 440
OD : 38.0 mm
A boiler is the central or an important component of the thermal power plant which
focuses on producing superheated steams that is used for running of the turbines which in turn
is used for the generation of electricity. A boiler is a closed vessel in which the heat produced
by the combustion of fuel is transferred to water for its conversation into steam of the
desired temperature & pressure.
The heat-generating unit includes a furnace in which the fuel is burned. With the
advantage of water-cooled furnace walls, super heaters, air heaters and economizers, the
term steam generator was evolved as a better description of the apparatus.
Boilers may be classified on the basis of any of the following characteristics:
Tube Shape and position
Use: The characteristics of the boiler vary according to the nature of service
performed.Customarily boiler is called either stationary or mobile. Large units used primarily
for electric power generation are known as control station steam generator or utility
To provide safety control over construction features, all boilers must be
constructed in accordance with the Boiler codes, which differentiates boiler as per their
Selection of construction materials is controlled by boiler code material
specifications. Power boilers are usually constructed of special steels.
Rating code for boiler standardize the size and ratings of boilers based on
heating surfaces. The same is verified by performance tests.
In addition to ordinary shell type of boiler, there are two general steel boiler
classifications, the fire tube and water tube boilers. Fire tube boiler is boilers with
straight tubes that are surrounded by water and through which the products of
combustion pass. Water tube boilers are those, in which the tubes themselves contain
steam or water, the heat being applied to the outside surface.
The boiler may be a fired or unfired pressure vessel. In fired boilers, the heat
applied is a product of fuel combustion. A non-fired boiler has a heat source other than
The heat may be derived from (1) the combustion of fuel (2) the hot
gasses of other chemical reactions (3) the utilization of nuclear energy.
Boilers are often designated with respect to the fuel burned.
Fluid: The general concept of a boiler is that of a vessel to generate steam. A
few utilities plants have installed mercury boilers.
The majority of boilers operate with natural circulation. Some utilize positive
circulation in which the operative fluid may be forced 'once through' or controlled with
The boiler is an external combustion device in which the combustion takes
place outside the region of boiling water. The relative location of the furnace to the
boiler is indicated by the description of the furnace as being internally or externally
fired.The furnace is internally fired if the furnace region is completely surrounded by
water cooled surfaces. The furnace is externally fired if the furnace is auxiliary to the
Furnace type: The boiler may be described in terms of the furnace type.
General Shape: During the evaluation of the boiler as a heat producer, many
new shapes and designs have appeared and these are widely recognized in the trade.
Trade Name: Many manufacturers coin their own name for each boiler and these
names come into common usage as being descriptive of the boiler.
Special features: some times the type of boiler like differential firing and
Tangential firing are described.
Categorisation of Boilers:
Fire tube Boilers
Water tube Boilers
Horizontal straight type Boilers
The boiler is generally used for power production are two types:-
2-Front fire boiler
The boiler mainly has natural circulation of gases, steam and other things. They contain
vertical membrane water. The pulverized fuel which is being used in the furnace is
fixed tangentially. They consume approximately 700 ton.hr of coal of about
1370kgcm2 of pressure having temperature of 540оC.
The first pass of the boiler has a combustion chamber enclosed with water walls of fusion
welded construction on all four sides. In addition there are four water platens to increase the
radiant heating surface.Beside this platen super heater reheater sections are also suspended in
the furnace combustion chamber. the first pass is a high heat zone since the fuel is burn
in this pass. the second pass is surrounded by steam cooled walls on all four sides as well as
roof of the boiler. A horizontal super heater, an economizer & two air heaters are located in
the second pass.
The main components of a boiler and their functions are given below:
It is a type of storage tank much higher placed than the level at which the boiler is
placed, and it is also a place where water and steam are separated. First the drum is filled
with water coming from the economizer, from where it is brought down with the help of
down-comers, entering the bottom ring headers. From there they enter the riser, which
are nothing but tubes that carries the water (which now is a liquid-vapor mixture), back to
the drum. Now, the steam is sent to the super heaters while the saturated liquid water is again
circulated through the down-comers and then subsequently through the risers till all the
water in the drum turns into steam and passes to the next stage of heating that is
Fig.4.2 Typical non regenerative rankine cycle followed by sub critical plant.
Fig.4.2 Typical non regenerative rankine cycle followed by supercritical plant
b) SUPER HEATERS:
The steam from the boiler drum is then sent for superheating. This takes place in
three stages. In the first stage, the steam is sent to a simple super heater, known as the low
temperature super heaters (LTSH), after which the second stage consists of several divisional
panels super heaters (DPSH). The final stage involves further heating in the Platen super
heaters (PLSH), after which the steam is sent through the Main Steam (MS) piping for
driving the turbine.
Superheating is done to increase the dryness fraction of the exiting steam. this is
because if the dryness fraction is low, as is the case with saturated steam, the presence of
moisture can cause corrosion of the blades of the turbine. Super heated steam also has several
merits such as increased working capacity, ability to increase the plant efficiency, lesser
erosion and so on. It is also of interest to know that while the super heater increases the
temperature of the steam, it does not change the pressure. There are different stages of super
heaters besides the sidewalls and extended sidewalls. The first stage consists of LTSH (low
temperature super heater), which is conventional mixed type with upper & lower banks
above the economizer assembly in rear pass. The other is Divisional Panel Super heater
which is hanging above in the first pass of the boiler above the furnace. The third stage is the
Platen Super heater from where the steam goes into the HP turbine through the main steam
line. The outlet temperature & pressure of the steam coming out from the super heater is 540
degrees Celsius & 157kg/cm
After the HP turbine part is crossed the steam is taken out through an outlet as
CRH(Cold Re-heat steam) to be re-heated again as HRH(Hot Re-heat steam) and then is fed
to the IPT(Intermediate pressure turbine) which goes directly to the LPT(Low pressure
turbine) through the IP-LP cross-over.
c) WATER WALLS:
The water from the bottom ring header is then transferred to the water walls, where
the first step in the formation of steam occurs by absorbing heat from the hot interior of the
boiler where the coal is burned continuously. This saturated water steam mixture then
enters the boiler drum.
In a 500 MW unit, the water walls are of vertical type, and have rifled tubing whereas
in a 660 MW unit, the water walls are of spiral type till an intermediate ring header from where
it again goes up as vertical type water walls. The advantage of the spiral wall tubes ensures
an even distribution of heat, and avoids higher thermal stresses in the water walls by
reducing thefluid temperature differences in the adjacent tubes and thus minimizes the sagging
produced in the tubes.
Figure depicting the difference between the vertical water wall and the spiral water wall
type of tubing where the vertical water walls have the rifle type of tubes to increase the
surface area unlike the spiral ones that have plain, smooth surfaces.
The economizer is a tube-shaped structure which contains water from the boiler
feed pump. This water is heated up by the hot flue gases which pass through the
economizer layout, which then enters the drum. The economizer is usually placed below
the second pass of the boiler, below the Low Temperature Super heater. As the flue gases
are being constantly produced due to the combustion of coal, the water in the economizer
is being continuously being heated up, resulting in the formation of steam to a partial
extent. Economizer tubes are supported in such a way that sagging, deflection &
expansion will not occur at any condition of operation.
A deaerator is a device that is widely used for the removal of air and other
dissolved gases from the feedwater to steam-generating boilers. In particular, dissolved
oxygen in boiler feedwaters will cause serious corrosion damage in steam systems by
attaching to the walls of metal piping and other metallic equipment and forming oxides (rust).
Water also combines with any dissolved carbon dioxide to form carbonic acid that causes
further corrosion. Most deaerators are designed to remove oxygen down to levels of 7 ppb
by weight (0.005 cm³/L) or less.
In addition to these there are several other smaller components attached to a boiler,
including several safety valves, which have their own special significance.
So briefly, the boiler functions this way. The water enters the boiler through the
economizer. From there it passes to the drum. Once the water enters the drum it comes
down the down comers to the lower inlet water wall headers. From the headers the water
rises through the water walls and is eventually turned into steam due to the continuous
heat being generated by the burners. As the steam is formed it enters the steam drum.
Here the steam and water is separated. The separators and dryers remove the droplets of
water and the cycle through the water walls is repeated. This cycle is known as natural
circulation cycle. In the forced circulation of water pumps are used to maintain the flow
ASSOCIATED SYSTEMS IN A POWER PLANT
There are several systems in a power plant which assist the main units to
carry out their functions properly:
a) PA FANS:
The primary air fans are used to carry the pulverized coal particles from the
mills to the boiler. They are also used to maintain the coal-air temperature. The
specifications of the PA fan used at the plant under investigation are: axial flow,
double stage, reaction fan.
The PA fan circuit consists of:
Primary air fan through cold duct.
Hot air duct
The model no. of the PA fan used at NTPC Vindhyanagar is AP2 20/12, where
A refers to the fact that it is an axial flow fan, P refers to the fan being progressive,
2 refers to the fan involving two stages, and the numbers 20 and 12 refer to the
distances in decimeters from the centre of the shaft to the tip of the impeller and the
base of the impeller, respectively. A PA fan uses 0.72% of plant load for a 500 MW
b) FD FANS: The forced draft fans, also known as the secondary air fans are used
to provide the secondary air required for combustion, and to maintain the wind box
differential pressure. Specifications of the FD fans are: axial flow, single stage,
The fd fan consists of :
Secondary air path through cold air duct
Hot air duct
The model no. of the FD fan used at NTPC Vindhyanagar is AP1 26/16, where
the nomenclature has been described above. FD fans use 0.36% of plant load for a
500 MW plant.
c) ID FAN: An induced fan circuit consists of
Flue gases through waterwalls
Low temperature superheater
The main purpose of an ID fan is to suck the flue gas through all the above
mentioned equipments and to maintain the furnace pressure. ID fans use 1.41% of plant
load for a 500 MW plant.
d) AIR PRE-HEATERS:
Air pre-heaters are used to take heat from the flue gases and transfer it to the incoming
air. They are of two types:
The APH used at NTPC Vindhyanagar is a Ljungstrom regenerative type
APH. A regenerative type air pre-heater absorbs waste heat from flue gas and transfers
this heat to the incoming cold air by means of continuously rotating heat transfer
elements of specially formed metal sheets. A bi-sector APH preheats the combustion air.
Thousands of these high efficiency elements are spaced and compactly arranged within
sector shaped compartments of a radially divided cylindrical shell called the rotor. The
housing surrounding the rotor is provided with duct connections at both ends.
ESPs continue to be excellent devices for control of many industrial particulate
emissions, including smoke from electricity-generating utilities (coal and oil fired), salt
cake collection from black liquor boilers in pulp mills, and catalyst collection from
fluidized bed catalytic cracker units in oil refineries to name a few. These devices treat gas
volumes from several hundred thousand ACFM to 2.5 million ACFM (1,180 m³/s) in the
largest coal-fired boiler applications. For a coal-fired boiler the collection is usually
performed downstream of the air preheater at about 160 °C (320 °F) which provides
optimal resistivity of the coal-ash particles. For some difficult applications with low-sulfur
fuel hot-end units have been built operating above 370 °C (698 °F).
As the name suggests the coal particles are grinded into finer sized granules. The
coal which is stored in the bunker is sent into the mill, through the conveyor belt which
primarily controls the amount of coal required to be sent to the furnace. It on reaching a
rotating bowl in the bottom encounters three grinding rolls which grinds it into fine
powder form of approx. 200 meshes per square inch. the fine coal powder along with the
heated air from the FD and PA fan is carried into the burner as pulverized coal while the
trash particles are rejected through a reject system.
g) SEAL AIR FAN: The seal air fan is used near the mill to prevent the loss of any
heat from the coal which is in a pulverized state and to protect the bearings from coal particle
h) WIND BOX: these acts as distributing media for supplying secondary/excess air to
the furnace for combustion. These are generally located on the left and and right sides of
the furnace while facing the chimney.
j) IGNITER FAN: Igniter fans which are 2 per boiler are used to supply air for cooling
Igniters & combustion of igniter air fuel mixture.
k) CHIMNEY: These are tall RCC structures with single & multiple flues. Here, for I & II
we have 1 chimney, for unit III there is 1 chimney & for units IV & V there is 1 chimney.
So number of chimneys is 5 and the height of each is 250 metres.
l) COAL HANDLING PLANT:
This part of the thermal power plant handles all the requirements of coal that needs to
be supplied to the plant for the continuous generation of electricity. Coal is generally
transported from coal mines ( mostly located in peninsular regions of India ) to Thermal
power plant with the help of rail wagons. A Single rail wagon can handle upto 80 tons of
coal( gross weight) . When these rail wagons reach the thermal plant the coal is unloaded with
the help of wagon tipplers. A wagon tippler is actually a huge J shaped Link pinned at its
top. Powerful motors are used to pull the ropes attached to an end which lets the wagon to
rotate at an angle of 135 degree. The coal falls down due to action of gravity into the coal
bunkers. Vibration motors then are used to induce the movement the coal through its way. as
the coal reaches the hopper section of the bunker , it is taken away by conveyer belts to
either the storage yard or to the assembly points where the coal gets distributed on
different conveyers. Initially, the size of coal is taken as 250mm in size. The macro coal has
to be converted into micro ( 25mm ) size coal for the actual combustion. This is attained by
using high pressure crushers located at the coal handling plants. Here various metal are
separated by various mechanisms. There are various paths through which a coal can go to
boiler section. These paths are alternative such as A and B and only one is used at a time
letting the other standby.
The conveyor belts are monitored with various mechanisms such as:
Coal on the conveyer belts moves into raw coal bunkers known as RC bunkers.
There are six raw coal bunkers for each unit of the plant. The coal from six RC bunkers falls
onto six RC feeders and moves to six Ball mills.
m) COAL BUNKER:
These are in process storage used for storing crushed coal from the coal handling
system. Generally, these are made up of welded steel plates. Normally, these are located on
top of mills to aid in gravity feeding of coal. There are 10 such bunkers corresponding to
n) ASH HANDLING PLANT:
The ash produced in boiler is transported to ash dump area by means of sluice type
hydraulic ash handling system, which consists of:
Bottom Ash System: In the Bottom Ash system the ash slag discharged from
the furnace bottom is collected in two water impounded scraper troughs installed
below bottom ash hoppers. The ash is continuously, transported by means of the
scraper chain conveyor, on to the respective clinker grinders which reduce the lump
sizes to the required fineness.
Fly Ash System: In this system, Fly ash gets collected in these hoppers drop
continuously to flushing apparatus where 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.
Ash Water System: High pressure water required for B.A hopper quenching
nozzles, B.A hopper`s window spraying, clinker grinder sealing scraper bars,
cleaning nozzles B.A hopper seal through flushing, Economizer Hoppers` flushing
nozzles and sluicing trench jetting nozzles is tapped from the high pressure water
ring main provided in the plant area.
Ash Slurry System: Bottom Ash and Fly Ash slurry of the system is sluiced up to
ash slurry pump along the channel with the aid of high pressure water jets located
at suitable intervals along the channel. Slurry pump section line consisting of
reducing elbow with drain valve, reducer and butterfly valve and portion of
slurry pump delivery line consisting of butterfly valve, Pipe and fitting has also been
The function of reheater is to reheat the steam coming out from the high pressure
turbine to a temperature of 540 degrees Celsius. It is composed of two sections: the rear
pendant section is located above the furnace arc & the front pendant section is located
between the rear water hanger tubes & the Platen superheater section.
There are total 20 pulverised coal burners for the boiler present here, & 10 of the
burners provided in each side at every elevation named as A,B,C,D,E,F,G,H,J,K. There are
oil burners present in every elevation to fire the fuel oil (LDO & HFO) during lightup.
Apart from these units and systems, piping is another important system which is
essential for the proper transfer of fluids of different types from one unit to another. In a
power plant, pipes are used to transfer steam, water, oil, air etc. from one unit to the other.
Some criteria for the selection of the pipes are given below:
o The piping should be of necessary size to carry the required flow of fluids.
o Pipes should be able to withstand the high temperatures and expansions
due to changes in temperatures.
o Piping system should withstand the high pressures to which it may be
For smooth and safe operation of the power plant it is desirable to use minimum length of
pipes, and they should be as direct and straight as possible.
TURBINE & ITS USE
A mechanical device is amechnical device that extracts thermal energy from
pressurized steam and convert in to useful mechanical work.
Three turbines, HP turbine, IP turbine and LP turbine, are synchronized together with
a common shaft connected to the generator. HP and IP turbines have single flow unit while
LP turbine has double flow unit so as to accommodate the increase in volume of steam due
to the drop in pressure.
High pressure steam enters the HP turbine at 170 Kg/cm2 and 540o C temperature.
The steam leaves the HP turbine at a pressure of 30 Kg/cm2 and is carried to re-heaters
which heats it up to a temperature of 540o C while maintaining its pressure at 30 Kg/cm2.
This steam is carried to IP turbine after which it is directly send to LP turbin. The steam
reaches to LP turbine at a pressure of 1.5 Kg/cm2.
The steam is also carried from turbines to LP heaters and HP heaters to heat the water
entering the boiler. After loosing its pressure and temperature steam is taken to the condenser.
The regenerative heaters are used to heat the Condensate from the condenser to
the boiler inlet.
This makes the mean temperature of heat addition in boiler high resulting in
The heating is done by steam bled from different stages of HP, IP and LP turbines.
The heaters are non mixing type.
The drip formed is cascaded to lower heaters in the line and finally to deaerator( for
HP heaters) and condenser ( for LP heaters)
Fig.6.1 diagram of steam ,impulse & reaction turbine
How increase the thermal efficiency of power plants
The basic idea behind all the modifications to increase the thermal efficiency of
a power cycle is the same: Increase the average temperature at which heat is transferred
to the working fluid in the boiler, or decrease the average temperature at which heat is
rejected from the working fluid in the condenser. That is, the average fluid temperature
should be as high as possible during heat addition and as low as possible during heat rejection.
Lowering the Condenser Pressure (Lowers Tlow,avg):
Steam exists as a saturated mixture in the condenser at the saturation temperature
corresponding to the pressure inside the condenser. Therefore, lowering the operating pressure
of the condenser automatically lowers the temperature of the steam, and thus the temperature
at which heat is rejected. The effect of lowering the condenser pressure on the Rankine cycle
efficiency is illustrated on a T-s diagram in Fig.1. For comparison purposes, the turbine inlet
state is maintained the same. The colored area on this diagram represents the increase in net
work output as a result of lowering the condenser pressure from P4 to P4’. The heat input
requirements also increase (represented by the area under curve2_-2), but this increase is very
small. Thus the overall effect of lowering the condenser pressure is an increase in the thermal
efficiency of the cycle.
Superheating the Steam to High Temperatures (Increases Thigh,avg):
The average temperature at which heat is transferred to steam can be increased
without increasing the boiler pressure by superheating the steam to high temperatures. The
effect of superheating on the performance of vapor power cycles is illustrated on a T-s
diagram in Fig.2. The colored area on this diagram represents the increase in the net work.
The total area under the process curve 3-3_ represents the increase in the heat input. Thus
both the net work and heat input increase as a result of superheating the steam to a higher
temperature. The overall effect is an increase in thermal efficiency,however, since the
average temperature at which heat is added increases.
Increasing the Boiler Pressure (Increases Thigh,avg):
Another way of increasing the average temperature during the heat-addition
process is to increase the operating pressure of the boiler, which automatically raises
the temperature at which boiling takes place. This, in turn, raises the average
temperature at which heat is transferred to the steam and thus raises the thermal
efficiency of the cycle. The effect of increasing the boiler pressure on the performance
of vapor power cycles is illustrated on a T-s diagram in Fig.3. Notice that for a
fixedturbine inlet temperature, the cycle shifts to the left and the moisture content of
steam at the turbine exit increases. This undesirable side effect can be corrected,
however, by reheating the steam, as discussed in the next section.
LOSSES DURING OPERATION & MAINTAINANCE
It increases friction & resistance. It can be due to Chemical deposits, Solid
particle damage, Corrosion Pitting & Water erosion. As a thumb rule, surface
roughness of about 0.05 mm can lead to a decrease in efficiency of 4%.
Turbine end Gland Leakages
About 2 - 7.5 kW is lost per stage if clearances are increased by
0.025 mm depending upon LP or HP stage.
3) WETNESS LOSS:
Due to difference in the velocities of the steam & waterparticles,water
particles lag behind & can even take different trajectory leading to
Sudden condensation can create shock disturbances & hence losses.
About 1% wetness leads to 1% loss in stage efficiency.
4) OFF DESIGN LOSSES:
o Losses resulting due to turbine not operating with design terminal conditions.
o Change in Main Steam pressure & temperature.
o Change in HRH pressure & temperature.
o Condenser Back Pressure
o Convergent-Divergent nozzles are more prone to Off Design losses then
Convergent nozzles as shock formation is not there in convergent nozzles.
5) PARTIAL ADMISSION LOSSES:
o In Impulse turbines, the controlling stage is fed with means of nozzle boxes,
the control valves of which open or close sequentially.
o At some partial load some nozzle boxes can be partially open
o Shock formation takes place as rotor blades at some time are full of steam
& at some other moment, devoid of steam leading to considerable losses.
6) LOSS DUE TO EROSION OF LP LAST STAGE BLADES:
o Erosion of the last stage blades leads to considerable loss of energy. Also,It
is the least efficient stage.
o Erosion in the 10% length of the blade leads to decrease in 0.1% of efficiency.
Industrial training being an integral part of engineering curriculum provides not only
easier understanding but also helps acquaint an individual with technologies. It exposes an
individual to practical aspect of all things which differ considerably from theoretical models.
During my training, I gained a lot of practical knowledge which otherwise could have been
exclusive to me. the practical exposure required here will pay rich dividends to me when I will
set my foot as an Engineer.
The training at NTPC Vindhyachal was altogether an exotic experience, since work,
culture and mutual cooperation was excellent here. Moreover fruitful result of adherence to
quality control awareness of safety and employees were fare which is much evident here.
All the minor & major sections in the thermal project had been visited & also understood
to the best of my knowledge. I believe that this training has made me well versed with the various
processes in the power plant. As far as I think there is a long way to go till we use our newest of
ever improving technologies to increase the efficiency because the stocks of coal are dwindling
and they are not going to last forever. Its imperative that we start shouldering the burden together
to see a shining and sustainable future INDIA.
o ANNUAL REPORTS OF NTPC
o IN HOUSE MAGAZINES OF NTPC
o WEBSITES VISITED :
NTPC/ VSTPP (Intranet)