praveen ntpc

7/30/2019 praveen ntpc

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ACKNOWLEDGEMENT

With profound respect and gratitude, I take this opportunity to convey my thanks to everyone for helping me

in completing the training.

I am extremely grateful to all the technical staff especially Mr. Ritesh Khetan ofNTPC, Dadri for their co-

operation and guidance that has 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.

- Praveen Kumar Shrivastava


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TRAINING AT NTPC

I was appointed to do 4 week training at this esteemed organization from 25th June to 23rd July 2013. I was

assigned to visit various division of the plant, which were:

Boiler Maintenance Department (BMD I/II/III)

Plant Auxiliary Maintenance (PAM)

Turbine Maintenance Department (TMD)

These 4 weeks training was a very educational adventure for me. It was really amazing to see the plant by

yourself and learn how electricity, which is one of our daily requirements of life, is produced.

This report has been made by my experience at NTPC. The material in this report has been gathered from my

textbook, senior student reports and trainers manuals and power journals provided by training department. The

specification and principles are as learned by me from the employees of each division of BTPS.


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CONTENTS

1. Introduction About NTPC

2. Thermal Power Station

3. Coal To Electricity Generation

4. Rankine Cycle

5. Mechanical Departments

Boiler Maintenance Department Plant Auxiliary Maintenance Turbine Maintenance Department


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ABOUT NTPC

NTPC Limited is the largest thermal power generating company of India, Public Sector Company. It was

incorporated in the year 1975 to accelerate power development in the country as a wholly owned company of

the Government of India. At present, Government of India holds 89.5% of the total equity shares of the

company and the balance 10.5% is held by FIIs, Domestic Banks, Public and others. Within a span of 31

years, NTPC has emerged as a truly national power company, with power generating facilities in all the major

regions of the country.

NTPC's core business is engineering, construction and operation of power generating plants and providing

consultancy to power utilities in India and abroad.

The total installed capacity of the company is 31134 MW (including JVs) with 15 coal based and 7 gas based

stations, located across the country. In addition under JVs, 3 stations are coal based & another station uses

naphtha/LNG as fuel. By 2017, the power generation portfolio is expected to have a diversified fuel mix with

coal based capacity of around 53000 MW, 10000 MW through gas, 9000 MW through Hydro generation,

about 2000 MW from nuclear sources and around 1000 MW from Renewable Energy Sources (RES). NTPC

has adopted a multi-pronged growth strategy which includes capacity addition through green field projects,

expansion of existing stations, joint ventures, subsidiaries and takeover of stations.

NTPC has been operating its plants at high efficiency levels. Although the company has 18.79% of the total

national capacity it contributes 28.60% of total power generation due to its focus on high efficiency. NTPCs

share at 31 Mar 2001 of the total installed capacity of the country was 24.51% and it generated 29.68% of the

power of the country in 2008-09. Every fourth home in India is lit by NTPC. 170.88BU of electricity was

produced by its stations in the financial year 2005-2006. The Net Profit after Tax on March 31, 2006 was INR

58,202 million. Net Profit after Tax for the quarter ended June 30, 2006 was INR 15528 million, which is

18.65% more than for the same quarter in the previous financial year. 2005).


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TECHNOLOGICAL INITIATIVES

Introduction of steam generators (boilers) of the size of 800 MW.

Integrated Gasification Combined Cycle (IGCC) Technology.

Launch of Energy Technology Centre -A new initiative for development of technologies with focus on

fundamental R&D.

The company sets aside up to 0.5% of the profits for R&D.

Roadmap developed for adopting Clean Development.

CORPORATE SOCIAL RESPONSIBILITY

As a responsible corporate citizen NTPC has taken up number of CSR initiatives.

NTPC Foundation formed to address Social issues at national level

NTPC has framed Corporate Social Responsibility Guidelines committing up to 0.5% of net profit annually

for Community Welfare.

The welfare of project affected persons and the local population around NTPC projects are taken care of

through well drawn Rehabilitation and Resettlement policies.

The company has also taken up distributed generation for remote rural areas.

Consultant role to modernize and improvise several plants across the country.

Disseminate technologies to other players in the sector.

Consultant role "Partnership in Excellence" Programme for improvement of PLF of 15 Power Stations of

SEBs.

Rural Electrification work under Rajiv Gandhi Garmin Vidyutikaran.


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ENVIRONMENT MANAGEMENT

All stations of NTPC are ISO 14001 certified.

Various groups to care of environmental issues.

The Environment Management Group.

Ash Utilization Division.

Afforestation Group.

Centre for Power Efficiency & Environment Protection.

Group on Clean Development Mechanism.

NTPC is the second largest owner of trees in the country after the Forest department.

JOURNEY OF NTPC

1975

NTPC was set up in 1975 with 100% ownership by the Government of India. In the last 30 years, NTPC has

grown into the largest power utility in India.

1997

In 1997, Government of India granted NTPC status of "Navratna being one of the nine jewels of India,

enhancing the powers to the Board of Directors.


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2004

NTPC became a listed company with majority Government ownership of 89.5%.

NTPC becomes third largest by Market Capitalization of listed companies

2005

The company rechristened as NTPC Limited in line with its changing business portfolio and transforms itself

from a thermal power utility to an integrated power utility.

2008

National Thermal Power Corporation is the largest power generation company in India. Forbes Global 2000

for 2008 ranked it 411th in the world.

2009

National Thermal Power Corporation is the largest power generation company in India. Forbes Global 2000

for 2008 ranked it 317th in the world.

2012

NTPC has achieved a target of 50,000 MW generation capacity.

COAL TO ELECTRICITY: BASICS

The basic steps in the generation of coal to electricity are shown below:

Coal to Steam

Coal from the coal wagons is unloaded in the coal handling plant. This Coal is transported up to the raw coal


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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 and ths 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 thee

boiler drum where the steam is separated from water.

Water follows the same path while the steam is sent to superheaters for superheating. The superheaters are located

inside the furnace and the steam is superheated (540C) 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.


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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.

Mechanical Power to Electrical Power

As the blades of turbine rotate, the shaft of the generator, which is coupled to tha of the turbine, also rotates. It

results in rotation of the coil of the generator, which causes induced electricity to be produced.


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Basic Power Plant Cycle

A simplified diagram of a thermal power plant

The thermal (steam) power plant uses a dual (vapour+ liquid) phase cycle. It is a close cycle to enable the working

fluid (water) to be used again and again. The cycle used is Rankine Cycle modified to include superheating of

steam, regenerative feed water heating and reheating of steam.

On large turbines, it becomes economical to increase the cycle efficiency by using reheat, which is a way of

partially overcoming temperature limitations. By returning partially expanded steam, to a reheat, the average

temperature at which the heat is added, is increased and, by expanding this reheated steam to the remaining stages

of the turbine, the exhaust wetness is considerably less than it would otherwise be conversely, if the maximum

tolerable wetness is allowed, the initial pressure of the steam can be appreciably increased.

Bleed Steam Extraction: For regenerative system, nos. of non-regulated extractions is taken from HP, IP turbine.

Regenerative heating of the boiler feed water is widely used in modern power plants; the effect being to increase

the average temperature at which heat is added to the cycle, thus improving the cycle efficiency.

Factors Affecting Thermal Cycle Efficiency

Thermal cycle efficiency is affected by following:

Initial Steam Pressure.

Initial Steam Temperature.

Whether reheat is used or not, and if used reheat pressure and temperature.

Condenser pressure.


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RANKINE CYCLE

The Rankine cycle is a thermodynamic cycle which converts heat into work. The heat is supplied externally to a

closed loop, which usually uses water as the working fluid.

Physical layout of the four main devices used in the Rankine cycle

A Rankine cycle describes a model of the operation of steam

heat enginesmost commonly found inpower generation plants. Common heat sources for power plants using the

Rankine cycle arecoal,natural gas,oil, andnuclear.

The Rankine cycle is sometimes referred to as a practical

Carnot cycleas, when an efficient turbine is used, theTS diagramwill begin to resemble the Carnot cycle. The

main difference is that a pump is used to pressurize liquid instead of gas. This requires about 1/100th (1%) as much

energy as that compressing a gas in a compressor (as in theCarnot cycle).

The efficiency of a Rankine cycle is usually limited by the working fluid. Without the pressure going

super criticalthe temperature range the cycle can operate over is quite small, turbine entry temperatures are

typically 565C (thecreeplimit of stainless steel) and condenser temperatures are around 30C. This gives a

theoreticalCarnot efficiencyof around 63% compared with an actual efficiency of 42% for a modern coal-fired

power station. This low turbine entry temperature (compared with agas turbine) is why the Rankine cycle is often

used as a bottoming cycle incombined cycle gas turbinepower stations.

The working fluid in a Rankine cycle follows a closed loop and is re-used constantly. The water
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vaporand entrained droplets often seen billowing from power stations is generated by the cooling systems (not

from the closed loop Rankine power cycle) and represents the waste heat that could not be converted to useful

work.

Note that

cooling towersoperate using the latentheat of vaporizationof the cooling fluid. The white billowing clouds that

form incooling toweroperation are the result of water droplets which are entrained in the cooling tower airflow; it

is not, as commonly thought, steam. While many substances could be used in the Rankine cycle, water is usually

the fluid of choice due to its favorable properties, such as nontoxic and unreactive chemistry, abundance, and low

cost, as well as itsthermodynamic properties.

One of the principal advantages it holds over other cycles is that during the compression stage relatively little work

is required to drive the pump, due to the working fluid being in its liquid phase at this point. By condensing the

fluid to liquid, the work required by the pump will only consume approximately 1% to 3% of the turbine power

and so give a much higher efficiency for a real cycle.

The benefit of this is lost somewhat due to the lower heat addition temperature.

Gas turbines, for instance, have turbine entry temperatures approaching 1500C. Nonetheless, the efficiencies of

steam cycles and gas turbines are fairly well matched.

Processes of the Rankine cycle

Ts diagram of a typical Rankine cycle operating between pressures of 0.06bar and 50bar.

There are four processes in the Rankine cycle, each changing the state of the working fluid. These states are

identified by number in the diagram to the right

Process 1-2
http://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FVapor&sa=D&sntz=1&usg=AFQjCNHWab-gNrJk8mhPmDuJDee5IQryUQhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FVapor&sa=D&sntz=1&usg=AFQjCNHWab-gNrJk8mhPmDuJDee5IQryUQhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCooling_towers&sa=D&sntz=1&usg=AFQjCNG_yyWON8nFZ3OX57E0lwnyjiM6Eghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCooling_towers&sa=D&sntz=1&usg=AFQjCNG_yyWON8nFZ3OX57E0lwnyjiM6Eghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FHeat_of_vaporization&sa=D&sntz=1&usg=AFQjCNHdXLcxOZOiUvxRenvWxYGeomNTQghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FHeat_of_vaporization&sa=D&sntz=1&usg=AFQjCNHdXLcxOZOiUvxRenvWxYGeomNTQghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FHeat_of_vaporization&sa=D&sntz=1&usg=AFQjCNHdXLcxOZOiUvxRenvWxYGeomNTQghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCooling_tower&sa=D&sntz=1&usg=AFQjCNGfIY1lGg-yW0LJoqE8jUuvtVa_sAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCooling_tower&sa=D&sntz=1&usg=AFQjCNGfIY1lGg-yW0LJoqE8jUuvtVa_sAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCooling_tower&sa=D&sntz=1&usg=AFQjCNGfIY1lGg-yW0LJoqE8jUuvtVa_sAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FWater_%2528molecule%2529&sa=D&sntz=1&usg=AFQjCNE6qlo2Ncx7weo43dNOskBD2lcVrQhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FWater_%2528molecule%2529&sa=D&sntz=1&usg=AFQjCNE6qlo2Ncx7weo43dNOskBD2lcVrQhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FWater_%2528molecule%2529&sa=D&sntz=1&usg=AFQjCNE6qlo2Ncx7weo43dNOskBD2lcVrQhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FGas_turbine&sa=D&sntz=1&usg=AFQjCNFItPyynvoUL9Cx6tOke2hT6bExvwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FGas_turbine&sa=D&sntz=1&usg=AFQjCNFItPyynvoUL9Cx6tOke2hT6bExvwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FGas_turbine&sa=D&sntz=1&usg=AFQjCNFItPyynvoUL9Cx6tOke2hT6bExvwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FWater_%2528molecule%2529&sa=D&sntz=1&usg=AFQjCNE6qlo2Ncx7weo43dNOskBD2lcVrQhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCooling_tower&sa=D&sntz=1&usg=AFQjCNGfIY1lGg-yW0LJoqE8jUuvtVa_sAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FHeat_of_vaporization&sa=D&sntz=1&usg=AFQjCNHdXLcxOZOiUvxRenvWxYGeomNTQghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCooling_towers&sa=D&sntz=1&usg=AFQjCNG_yyWON8nFZ3OX57E0lwnyjiM6Eghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FVapor&sa=D&sntz=1&usg=AFQjCNHWab-gNrJk8mhPmDuJDee5IQryUQ


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: 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 vapor expands through a

turbine, generating power. This decreases the temperature and pressure of the vapor, and some condensation may

occur.

Process 4-1

: The wet vapor then enters a

condenserwhere it is condensed at a constant pressure and temperature to become asaturated liquid. The pressure

and temperature of the condenser is fixed by the temperature of the cooling coils as the fluid is undergoing

aphase-change.

In an ideal Rankine cycle the pump and turbine would be

isentropic, i.e., the pump and turbine would generate no entropy and hence maximize the net work output.

Processes 1-2 and 3-4 would be represented by vertical lines on the Ts diagram and more closely resemble that of

the Carnot cycle.

The Rankine cycle shown here prevents the vapor ending up in the superheat region after the expansion in the

turbine, which reduces the energy removed by the condensers.
http://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FTurbine&sa=D&sntz=1&usg=AFQjCNEsaAWdIThb2xnC8NxvJEKD78h0jwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FTurbine&sa=D&sntz=1&usg=AFQjCNEsaAWdIThb2xnC8NxvJEKD78h0jwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSurface_condenser&sa=D&sntz=1&usg=AFQjCNEyVG99Q-TmsZbyVO2A9bn0DNbamghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSurface_condenser&sa=D&sntz=1&usg=AFQjCNEyVG99Q-TmsZbyVO2A9bn0DNbamghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FBoiling_point&sa=D&sntz=1&usg=AFQjCNFiE7pYswo1FfbOkq8mr3i8SXJlyghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FBoiling_point&sa=D&sntz=1&usg=AFQjCNFiE7pYswo1FfbOkq8mr3i8SXJlyghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FBoiling_point&sa=D&sntz=1&usg=AFQjCNFiE7pYswo1FfbOkq8mr3i8SXJlyghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPhase_Transition&sa=D&sntz=1&usg=AFQjCNHtBUSHRnbWAPLg8gD9zU-wUu0FmQhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPhase_Transition&sa=D&sntz=1&usg=AFQjCNHtBUSHRnbWAPLg8gD9zU-wUu0FmQhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPhase_Transition&sa=D&sntz=1&usg=AFQjCNHtBUSHRnbWAPLg8gD9zU-wUu0FmQhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FIsentropic&sa=D&sntz=1&usg=AFQjCNFBxqDOCe7r3OAgPnawGIx-REGx8Ahttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FIsentropic&sa=D&sntz=1&usg=AFQjCNFBxqDOCe7r3OAgPnawGIx-REGx8Ahttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FIsentropic&sa=D&sntz=1&usg=AFQjCNFBxqDOCe7r3OAgPnawGIx-REGx8Ahttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPhase_Transition&sa=D&sntz=1&usg=AFQjCNHtBUSHRnbWAPLg8gD9zU-wUu0FmQhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FBoiling_point&sa=D&sntz=1&usg=AFQjCNFiE7pYswo1FfbOkq8mr3i8SXJlyghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSurface_condenser&sa=D&sntz=1&usg=AFQjCNEyVG99Q-TmsZbyVO2A9bn0DNbamghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FTurbine&sa=D&sntz=1&usg=AFQjCNEsaAWdIThb2xnC8NxvJEKD78h0jw


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Real Rankine cycle (non-ideal) : Rankine cycle with superheat

In a real Rankine cycle, the compression by the

pumpand the expansion in theturbineare not isentropic. In other words, these processes are non-reversible

andentropyis increased during the two processes. This somewhat increases the powerrequired by the pump and

decreases the power generated by the turbine.

In particular the efficiency of the steam turbine will be limited by water droplet formation. As the water condenses,

water droplets hit the turbine blades at high speed causing pitting and erosion, gradually decreasing the life of

turbine blades and efficiency of the turbine. The easiest way to overcome this problem is by superheating the

steam. On the Ts diagram above, state 3 is above a two phase region of steam and water so after expansion the

steam will be very wet. By superheating, state 3 will move to the right of the diagram and hence produce a dryer

steam after expansion.

Rankine cycle with reheat

In this variation, two

turbineswork in series. The first acceptsvaporfrom theboilerat 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.

Among other advantages, this prevents the vapor from condensing during its expansion which can seriously

damage the turbine blades, and improves the efficiency of the cycle.

Regenerative Rankine cycle

The regenerative Rankine cycle is so named because after emerging from the condenser (possibly as the working

fluid is heated bysteamtapped from the hot portion of the cycle. On the diagram shown, 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. The Regenerative Rankine
http://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPump&sa=D&sntz=1&usg=AFQjCNHqomZFV0KSQBbqrp1b6PaOBQHSjghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPump&sa=D&sntz=1&usg=AFQjCNHqomZFV0KSQBbqrp1b6PaOBQHSjghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FTurbine&sa=D&sntz=1&usg=AFQjCNEsaAWdIThb2xnC8NxvJEKD78h0jwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FTurbine&sa=D&sntz=1&usg=AFQjCNEsaAWdIThb2xnC8NxvJEKD78h0jwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FTurbine&sa=D&sntz=1&usg=AFQjCNEsaAWdIThb2xnC8NxvJEKD78h0jwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FEntropy&sa=D&sntz=1&usg=AFQjCNHtc9tWxz9hKGawRJKUaa6iedIpRwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FEntropy&sa=D&sntz=1&usg=AFQjCNHtc9tWxz9hKGawRJKUaa6iedIpRwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FEntropy&sa=D&sntz=1&usg=AFQjCNHtc9tWxz9hKGawRJKUaa6iedIpRwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPower_%2528physics%2529&sa=D&sntz=1&usg=AFQjCNEMv-FZhO6aDnLHcuDSt4yNlws9fAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPower_%2528physics%2529&sa=D&sntz=1&usg=AFQjCNEMv-FZhO6aDnLHcuDSt4yNlws9fAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPower_%2528physics%2529&sa=D&sntz=1&usg=AFQjCNEMv-FZhO6aDnLHcuDSt4yNlws9fAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FTurbine&sa=D&sntz=1&usg=AFQjCNEsaAWdIThb2xnC8NxvJEKD78h0jwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FTurbine&sa=D&sntz=1&usg=AFQjCNEsaAWdIThb2xnC8NxvJEKD78h0jwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FVaporization&sa=D&sntz=1&usg=AFQjCNGFRRsE5eoJxE9aeqB86sU2YB5GFAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FVaporization&sa=D&sntz=1&usg=AFQjCNGFRRsE5eoJxE9aeqB86sU2YB5GFAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FVaporization&sa=D&sntz=1&usg=AFQjCNGFRRsE5eoJxE9aeqB86sU2YB5GFAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FBoiler&sa=D&sntz=1&usg=AFQjCNHAP6oyJR8738YWMABgNhEiHDENhghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FBoiler&sa=D&sntz=1&usg=AFQjCNHAP6oyJR8738YWMABgNhEiHDENhghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FBoiler&sa=D&sntz=1&usg=AFQjCNHAP6oyJR8738YWMABgNhEiHDENhghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSteam&sa=D&sntz=1&usg=AFQjCNGWeJXP6k6YnwQzSvrwt4EWGQbRMAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSteam&sa=D&sntz=1&usg=AFQjCNGWeJXP6k6YnwQzSvrwt4EWGQbRMAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSteam&sa=D&sntz=1&usg=AFQjCNGWeJXP6k6YnwQzSvrwt4EWGQbRMAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSteam&sa=D&sntz=1&usg=AFQjCNGWeJXP6k6YnwQzSvrwt4EWGQbRMAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FBoiler&sa=D&sntz=1&usg=AFQjCNHAP6oyJR8738YWMABgNhEiHDENhghttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FVaporization&sa=D&sntz=1&usg=AFQjCNGFRRsE5eoJxE9aeqB86sU2YB5GFAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FTurbine&sa=D&sntz=1&usg=AFQjCNEsaAWdIThb2xnC8NxvJEKD78h0jwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPower_%2528physics%2529&sa=D&sntz=1&usg=AFQjCNEMv-FZhO6aDnLHcuDSt4yNlws9fAhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FEntropy&sa=D&sntz=1&usg=AFQjCNHtc9tWxz9hKGawRJKUaa6iedIpRwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FTurbine&sa=D&sntz=1&usg=AFQjCNEsaAWdIThb2xnC8NxvJEKD78h0jwhttp://www.google.com/url?q=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FPump&sa=D&sntz=1&usg=AFQjCNHqomZFV0KSQBbqrp1b6PaOBQHSjg


15/44

cycle (with minor variants) is commonly used in real power stations.

Another variation is where 'bleed steam' from between turbine stages is sent to to preheat the water on its way from

the condenser to the boiler.

BOILER MAINTENANCE DEPARTMENT

Boiler and Its Description

The boiler is a rectangular furnace about 50 ft (15 m) on a side and 130 ft (40 m) tall. Its walls are made of a web

of high pressure steel tubes about 2.3 inches (60 mm) in diameter. Pulverized coal is air-blown into the furnace

from fuel nozzles at the four corners and it rapidly burns, forming a large fireball at the centre. The thermal

radiation of the fireball heats the water that circulates through the boiler tubes near the boiler perimeter. The water

circulation rate in the boiler is three to four times the throughput and is typically driven by pumps. As the water in

the boiler circulates it absorbs heat and changes into steam at 700 F (370 C) and 3,200 psi (22.1MPa). It is

separated from the water inside a drum at the top of the furnace.

The saturated steam is introduced into superheat pendant tubes that hang in the hottest part of the combustion gases

as they exit the furnace. Here the steam is superheated to 1,000 F (540 C) to prepare it for the turbine. The steam

generating boiler has to produce steam at the high purity, pressure and temperature required for the steam turbine

that drives the electrical generator.

The generator includes the economizer, the steam drum, the chemical dosing equipment, and the furnace with its

steam generating tubes and the superheater coils. Necessary safety valves are located at suitable points to avoid

excessive boiler pressure. The air and flue gas path equipment include: forced draft (FD) fan, air preheater (APH),

boiler furnace, induced draft (ID) fan, fly ash collectors (electrostatic precipitator or baghouse) and the flue gas

stack.


16/44

For units over about 210 MW capacity, redundancy of key components is provided by installing duplicates of the

FD fan, APH, fly ash collectors and ID fan with isolating dampers. On some units of about 60 MW, two boilers per

unit may instead be provided.

AUXILIARIES OF THE BOILER

FURNACE

Furnace is primary part of boiler where the chemical energy of the fuel is converted to thermal energy by

combustion. Furnace is designed for efficient and complete combustion. Major factors that assist for efficient

combustion are amount of fuel inside the furnace and turbulence, which causes rapid mixing between fuel and air.

In modern boilers, water furnaces are used.

BOILER DRUM

Drum is of fusion-welded design with welded hemispherical dished ends. It is provided with stubs for welding all

the connecting tubes, i.e. downcomers, risers, pipes, saturated steam outlet. The function of steam drum internals is

to separate the water from the steam generated in the furnace walls and to reduce the dissolved solid contents of

the steam below the prescribed limit of 1 ppm and also take care of the sudden change of steam demand for boiler.

The secondary stage of two opposite banks of closely spaced thin corrugated sheets, which direct the steam and

force the remaining entertained water against the corrugated plates. Since the velocity is relatively low this water

does not get picked up again but runs down the plates and off the second stage of the two steam outlets.

From the secondary separators the steam flows upwards to the series of screen dryers, extending in layers across

the length of the drum. These screens perform the final stage of the separation.

Once water inside the boiler or steam generator, the process of adding the latent heat of vaporization or enthalpy is

underway. The boiler transfers energy to the water by the chemical reaction of burning some type of fuel.


17/44

The water enters the boiler through a section in the convection pass called the economizer. From the economizer it

passes to the steam drum. Once the water enters the steam drum it goes down the down comers to the lower inlet

water wall headers. From the inlet headers the water rises through the water walls and is eventually turned into

steam due to the heat being generated by the burners located on the front and rear water walls (typically). As the

water is turned into steam/vapour in the water walls, the steam/vapour once again enters the steam drum.

The steam/vapour is passed through a series of steam and water separators and then dryers inside the steam drum.

The steam separators and dryers remove the water droplets from the steam and the cycle through the water walls is

repeated. This process is known as natural circulation.

The boiler furnace auxiliary equipment includes coal feed nozzles and igniter guns, soot blowers, water lancing

and observation ports (in the furnace walls) for observation of the furnace interior. Furnace explosions due to any

accumulation of combustible gases after a tripout are avoided by flushing out such gases from the combustion zone

before igniting the coal.

The steam drum (as well as the superheater coils and headers) have air vents and drains needed for initial start-up.

The steam drum has an internal device that removes moisture from the wet steam entering the drum from the steam

generating tubes. The dry steam then flows into the superheater coils. Geothermal plants need no boiler since they

use naturally occurring steam sources.

Heat exchangers may be used where the geothermal steam is very corrosive or contains excessive suspended

solids. Nuclear plants also boil water to raise steam, either directly passing the working steam through the reactor

or else using an intermediate heat exchanger.

WATER WALLS

Water flows to the water walls from the boiler drum by natural circulation. The front and the two side water walls

constitute the main evaporation surface, absorbing the bulk of radiant heat of the fuel burnt in the chamber. The

front and rear walls are bent at the lower ends to form a water-cooled slag hopper. The upper part of the chamber is


18/44

narrowed to achieve perfect mixing of combustion gases. The water wall tubes are connected to headers at the top

and bottom. The rear water wall tubes at the top are grounded in four rows at a wider pitch forming g the grid

tubes.

REHEATER

Reheater is used to raise the temperature of steam from which a part of energy has been extracted in highpressure

turbine. This is another method of increasing the cycle efficiency. Reheating requires additional equipment i.e.

heating surface connecting boiler and turbine pipe safety equipment like safety valve, non return valves, isolating

valves, high pressure feed pump, etc: Reheater is composed of two sections namely the front and the rear pendant

section, which is located above the furnace arc between water-cooled, screen wall tubes and rear wall tubes.

Tubes of a reheater

SUPERHEATER

Whatever type of boiler is used, steam will leave the water at its surface and pass into the steam space. Steam

formed above the water surface in a shell boiler is always saturated and become superheated in the boiler shell, as

it is constantly. If superheated steam is required, the saturated steam must pass through a superheater. This is

simply a heat exchanger where additional heat is added to the steam.

In water-tube boilers, the superheater may be an additional pendant suspended in the furnace area where the hot

gases will provide the degree of superheat required. In other cases, for example in CHP schemes where the gas

turbine exhaust gases are relatively cool, a separately fired superheater may be needed to provide the additional

heat.

ECONOMIZER

The function of an economizer in a steam-generating unit is to absorb heat from the flue gases and add as a


19/44

sensible heat to the feed water before the water enters the evaporation circuit of the boiler.

Earlier economizer were introduced mainly to recover the heat available in the flue gases that leaves the boiler and

provision of this addition heating surface increases the efficiency of steam generators. In the modern boilers used

for power generation feed water heaters were used to increase the efficiency of turbine unit and feed water

temperature.

An economizer

Use of economizer or air heater or both is decided by the total economy that will result in flexibility in operation,

maintenance and selection of firing system and other related equipment. Modern medium and high capacity boilers

are used both as economizers and air heaters. In low capacity, air heaters may alone be selected.

Stop valves and non-return valves may be incorporated to keep circulation in economizer into steam drum when

there is fire in the furnace but not feed flow. Tube elements composing the unit are built up into banks and these

are connected to inlet and outlet headers.

AIR PREHEATER

Air preheater absorbs waste heat from the flue gases and transfers this heat to incoming cold air, by means of

continuously rotating heat transfer element of specially formed metal plates. Thousands of these high efficiency

elements are spaced and compactly arranged within 12 sections. Sloped compartments of a radially divided

cylindrical shell called the rotor. The housing surrounding the rotor is provided with duct connecting both the ends

and is adequately scaled by radial and circumferential scaling.

An air preheater

Special sealing arrangements are provided in the provided in the air preheater to prevent the leakage between the

air and gas sides. Adjustable plates are also used to help the sealing arrangements and prevent the leakage as

expansion occurs. The air preheater heating surface elements are provided with two types of cleaning devices, soot


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blowers to clean normal devices and washing devices to clean the element when soot blowing alone cannot keep

the element clean.

PULVERIZER

A pulverizer is a mechanical device for the grinding of many types of materials. For example, they are used to

pulverize coal for combustion in the steam-generating furnaces of the fossil fuel power plants.

A Pulverizer

Types of Pulverizer

Ball and Tube mills

A ball mill is a pulverizer that consists of a horizontal cylinder, up to three diameters in length, containing a charge

of tumbling or cascading steel balls, pebbles or steel rods.

A tube mill is a revolving cylinder of up to five diameters in length used for finer pulverization of ore, rock and

other such materials; the materials mixed with water is fed into the chamber from one end, and passes out the other

end as slime.

Bowl mill

It uses tires to crush coal. It is of two types; a deep bowl mill and the shallow bowl mill.

Advantages of Pulverized Coal

Pulverized coal is used for large capacity plants.


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It is easier to adapt to fluctuating load as there are no limitations on the combustion capacity.

Coal with higher ash percentage cannot be used without pulverizing because of the problem of large amount ash

deposition after combustion.

Increased thermal efficiency is obtained through pulverization.

The use of secondary air in the combustion chamber along with the powered coal helps in creating turbulence and

therefore uniform mixing of the coal and the air during combustion.

Greater surface area of coal per unit mass of coal allows faster combustion as more coal is exposed to heat and

combustion.

PLANT AUXILIARY MAINTENANCE

WATER CIRCULATION SYSTEM

Theory of Circulation

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 corners at a temperature slightly below the saturation temperature. The flow through the furnace

wall is at saturation temperature. Heat absorbed in water wall is latent heat of vaporization creating a mixture of

steam and water. The ratio of the weight of the water to the weight of the steam in the mixture leaving the heat


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absorption surface is called circulation ratio.

Types of Boiler Circulating System

Natural circulation system

Controlled circulation system

Combined circulation system

Natural Circulation System

Water delivered to steam generator from feed water is at a temperature well below the saturation value

corresponding to that pressure. Entering first the economizer, it is heated to about 30-40C below saturation

temperature. From economizer the water enters the drum and thus joins the circulation system. Water entering the

drum flows through the down corner and enters ring heater at the bottom. In the water walls, a part of the water is

converted to steam and the mixture flows back to the drum. In the drum, the steam is separated, and sent to

superheater for superheating and then sent to the high-pressure turbine. Remaining water mixes with the incoming

water from the economizer and the cycle is repeated.

As the pressure increases, the difference in density between water and steam reduces. Thus the hydrostatic head

available will not be able to overcome the frictional resistance for a flow corresponding to the minimum

requirement of cooling of water wall tubes. Therefore natural circulation is limited to the boiler with drum

operating pressure around 175 kg/ cm2.

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, orifices plates are used. This system is applicable in the high

sub-critical regions (200 kg/ cm2).


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ASH HANDLING PLANT

The widely used ash handling systems are:

Mechanical Handling System

Hydraulic System

Pneumatic System

Steam Jet System

The Hydraulic Ash handling system is used at the Dadri Thermal Power Station.

Hydraulic Ash Handling System

The hydraulic system carried the ash with the flow of water with high velocity through a channel and finally

dumps into a sump. The hydraulic system is divided into a low velocity and high velocity system. In the low

velocity system the ash from the boilers falls into a stream of water flowing into the sump. The ash is carried along

with the water and they are separated at the sump. In the high velocity system a jet of water is sprayed to quench

the hot ash. Two other jets force the ash into a trough in which they are washed away by the water into the sump,

where they are separated. The molten slag formed in the pulverized fuel system can also be quenched and washed

by using the high velocity system. The advantages of this system are that its clean, large ash handling capacity,

considerable distance can be traversed, absence of working parts in contact with ash.

Fly Ash Collection

Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag filters (or sometimes

both) located at the outlet of the furnace and before the induced draft fan. The fly ash is periodically removed from

the collection hoppers below the precipitators or bag filters. Generally, the fly ash is pneumatically transported to


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storage silos for subsequent transport by trucks or railroad cars.

Bottom Ash Collection and Disposal

At the bottom of every boiler, a hopper has been provided for collection of the bottom ash from the bottom of the

furnace. This hopper is always filled with water to quench the ash and clinkers falling down from the furnace.

Some arrangement is included to crush the clinkers and for conveying the crushed clinkers and bottom ash to a

storage site.

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 used in thermal power plants are

designed to process the raw water to water with a very low content of dissolved solids known as demineralized

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.

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 is generally made up of two sections:

Pretreatment section.

Demineralization section


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Pretreatment Section

Pretreatment plant removes the suspended solids such as clay, silt, organic and inorganic matter, plants and other

microscopic organism. The turbidity may be taken as two types of suspended solid in water; firstly, the separable

solids and secondly the non-separable solids (colloids). The coarse components, such as sand, silt, etc: can be

removed from the water by simple sedimentation. Finer particles, however, will not settle in any reasonable time

and must be flocculated to produce the large particles, which are settle able. Long term ability to remain suspended

in water is basically a function of both size and specific gravity.

Demineralization

This filter water is now used for 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.

A DM plant generally consists of cation, anion and mixed bed exchangers. The final water from this process

consists essentially of hydrogen ions and hydroxide ions which is the chemical composition of pure water. The

DM water, being very pure, becomes highly corrosive once it absorbs oxygen from the atmosphere because of its

very high affinity for oxygen absorption. The capacity of the DM plant is dictated by the type and quantity of salts

in the raw water input. However, some storage is essential as the DM plant may be down for maintenance. For this

purpose, a storage tank is installed from which DM water is continuously withdrawn for boiler make-up. The

storage tank for DM water is made from materials not affected by corrosive water, such as PVC. The piping and

valves are generally of stainless steel. Sometimes, a steam blanketing arrangement or stainless steel doughnut float

is provided on top of the water in the tank to avoid contact with atmospheric air. DM water make-up is generally

added at the steam space of the surface condenser (i.e., the vacuum side). This arrangement not only sprays the

water but also DM water gets deaerated, with the dissolved gases being removed by the ejector of the condenser


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itself.

DRAUGHT SYSTEM

There are four types of draught system:

Natural Draught

Induced Draught

Forced Draught

Balanced Draught

Natural Draught System

In natural draft units the pressure differentials are obtained have constructing tail chimneys so that vacuum is

created in the furnace. Due to small pressure difference, air is admitted into the furnace.

Induced Draft System

In this system, the air is admitted to natural pressure difference and the flue gases are taken out by means of

Induced Draught (I.D.) fans and the furnace is maintained under vacuum.

An induced draught system

Forced Draught System

A set of forced draught (F.D.) fans is made use of for supplying air to the furnace and so the furnace is pressurized.

The flue gases are taken out due to the pressure difference between the furnace and the atmosphere.

A forced draught system


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Balanced Draught System

Here a set of Induced and Forced Draft Fans are utilized in maintaining a vacuum in the furnace. Normally all the

power stations utilize this draft system.

INDUSTRIAL FANS

ID Fan

The induced Draft Fans are generally of Axial-Impulse Type. Impeller nominal diameter is of the order of 2500

mm. The fan consists of the following sub-assemblies:

Suction Chamber

Inlet Vane Control

Impeller

Outlet Guide Vane Assembly

An FD fan

The centrifugal and setting forces of the blades are taken up by the blade bearings. The blade shafts are placed in

combined radial and axial anti-friction bearings, which are sealed off to the outside. The angle of incidence of the

blades may be adjusted during operation. The characteristic pressure volume curves of the fan may be changed in a

large range without essentially modifying the efficiency. The fan can then be easily adapted to changing operating

conditions.

The rotor is accommodated in cylindrical roller bearings and an inclined ball bearing at the drive side absorbs the

axial thrust.


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Lubrication and cooling these bearings is assured by a combined oil level and circulating lubrication system.

Primary Air Fan

PA Fan if flange-mounted design, single stage suction, NDFV type, backward curved bladed radial fan operating

on the principle of energy transformation due to centrifugal forces. Some amount of the velocity energy is

converted to pressure energy in the spiral casing. The fan is driven at a constant speed and varying the angle of the

inlet vane control controls the flow. The special feature of the fan is that is provided with inlet guide vane control

with a positive and precise link mechanism.

It is robust in construction for higher peripheral speed so as to have unit sizes. Fan can develop high pressures at

low and medium volumes and can handle hot-air laden with dust particles.

Primary air fan

COMPRESSOR HOUSE

Instrument air is required for operating various dampers, burner tilting, devices, diaphragm valves, etc: in the 210

MW units. Station air meets the general requirement of the power station such as light oil atomizing air, for

cleaning filters and for various maintenance works. The control air compressors and station air compressors have

been housed separately with separate receivers and supply headers and their tapping.

Instrument Air System

Control air compressors have been installed for supplying moisture free dry air required for instrument used. The

output from the compressors is fed to air receivers via return valves. From the receiver air passed through the

dryers to the main instrument airline, which runs along with the boiler house and turbine house of 210 MW units.

Adequate numbers of tapping have been provided all over the area.


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Air-Drying Unit

Air contains moisture which tends to condense, and causes trouble in operation of various devices by compressed

air. Therefore drying of air is accepted widely in case of instrument air. Air drying unit consists of dual absorption

towers with embedded heaters for reactivation. The absorption towers are adequately filled with specially selected

silica gel and activated alumina while one tower is drying the air.

Service Air Compressor

The station air compressor is generally a slow speed horizontal double acting double stage type and is arranged for

belt drive. The cylinder heads and barrel are enclosed in a jacket, whih extends around the valve also. The

intercooler is provided between the low and high pressure cylinder which cools the air between tag and collects the

moisture that condenses.

TURBINE MAINTENANCE DEPARTMENT

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.

Reaction turbine:

In this type of turbine pressure is reduced at both fixed and moving blades. Both fixed and moving blades act like


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nozzles. Work done by the impulse effect of steam due to reverse the direction of high velocity steam. The

expansion of steam takes place on moving blades.

COMPOUNDING:

Several problems occur if energy of steam is converted in single step and so compounding is done. Following are

the type of compounded turbine:

Velocity Compounded Turbine:

Like simple turbine it has only one set of nozzles and 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 and too guide it.

Pressure Compounded Turbine:

This is basically a number of single impulse turbines in series or on the same shaft. The

exhaust of first turbine enters the nozzles of next turbine. The total pressure drop of steam

does not tae on first nozzle ring but divided equally on all of them.

iii. Pressure Velocity Compounded Turbine:

It is just the combination of the two compounding and has the advantages of allowing bigger pressure drops in

each stage and so fewer stages are necessary.

Here for given pressure drop the turbine will be shorter length but diameter will be increased.

??

MAIN TURBINE:

The 210MW turbine is a cylinder tandem compounded type machine comprising of H.P. and I.P and L.P cylinders.


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The H.P. turbine comprises of 12 stages the I.P turbine has 11 stages and the L.P has four stages of double flow.

The H.P and I.P. turbine rotor are rigidly compounded and the I.P. and L.P rotor by lens type semi flexible

coupling. All the 3 rotors are aligned on five bearings of which the bearing number is combined with thrust

bearing.

The main superheated steam branches off into two streams from the boiler and passes through the emergency stop

valve and control valve before entering the governing wheel chamber of the H.P. Turbine. After expanding in the

12 stages in the H.P. turbine then steam is returned in the boiler for reheating.

The reheated steam from boiler enters I.P. turbine via the interceptor valves and control valves and after expanding

enters the L.P stage via 2 numbers of cross over pipes.

In the L.P. stage the steam expands in axially opposed direction to counteract the thrust and enters the condenser

placed directly below the L.P. turbine. The cooling water flowing through the condenser tubes condenses the steam

and the condensate the collected in the hot well of the condenser.

The condensate collected the pumped by means of 3x50% duty condensate pumps through L.P heaters to deaerator

from where the boiler feed pump delivers the water to the boiler through H.P. heaters thus forming a closed cycle.

STEAM TURBINE

A steam turbine is a mechanical device that extracts thermal energy from pressurized steam and converts it into

useful mechanical work.

From a mechanical point of view, the turbine is ideal, because the propelling force is applied directly to the

rotating element of the machine and has not as in the reciprocating engine to be transmitted through a system of

connecting links, which are necessary to transform a reciprocating motion into rotary motion. Hence since the

steam turbine possesses for its moving parts rotating elements only if the manufacture is good and the machine is


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correctly designed, it ought to be free from out of balance forces.

If the load on a turbine is kept constant the torque developed at the coupling is also constant. A generator at a

steady load offers a constant torque. Therefore, a turbine is suitable for driving a generator, particularly as they are

both high-speed machines.

A further advantage of the turbine is the absence of internal lubrication. This means that the exhaust steam is not

contaminated with oil vapour and can be condensed and fed back to the boilers without passing through the filters.

It also means that turbine is considerable saving in lubricating oil when compared with a reciprocating steam

engine of equal power.

A final advantage of the steam turbine and a very important one is the fact that a turbine can develop many time

the power compared to a reciprocating engine whether steam or oil.

OPERATING PRINCIPLES

A steam turbines two main parts are the cylinder and the rotor. The cylinder (stator) is a steel or cast iron housing

usually divided at the horizontal centerline. Its halves are bolted together for easy access. The cylinder contains

fixed blades, vanes and nozzles that direct steam into the moving blades carried by the rotor. Each fixed blade set

is mounted in diaphragms located in front of each disc on the rotor, or directly in the casing. A disc and diaphragm

pair a turbine stage. Steam turbines can have many stages. A rotor is a rotating shaft that carries the moving blades

on the outer edges of either discs or drums. The blades rotate as the rotor revolves. The rotor of a large steam

turbine consists of large, intermediate and low-pressure sections.

In a multiple-stage turbine, steam at a high pressure and high temperature enters the first row of fixed blades or

nozzles through an inlet valve/valves. As the steam passes through the fixed blades or nozzles, it expands and its

velocity increases. The high velocity jet of stream strikes the first set of moving blades. The kinetic energy of the

steam changes into mechanical energy, causing the shaft to rotate. The steam that enters the next set of fixed blades


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strikes the next row of moving blades.

As the steam flows through the turbine, its pressure and temperature decreases while its volume increases. The

decrease in pressure and temperature occurs as the steam transmits energy to the shaft and performs work. After

passing through the last turbine stage, the steam exhausts into the condenser or process steam system.

The kinetic energy of the steam changes into mechanical energy through the impact (impulse) or reaction of the

steam against the blades. An impulse turbine uses the impact force of the steam jet on the blades to turn the shaft.

Steam expands as it passes through thee nozzles, where its pressure drops and its velocity increases. As the steam

flows through the moving blades, its pressure remains the same, but its velocity decreases. The steam does not

expand as it flows through the moving blades.

STEAM CYCLE

The thermal (steam) power plant uses a dual (vapor+liquid) phase cycle. It is a closed cycle to enable the working

fluid (water) to be used again and again. The cycle used i s Rankine cycle modified to include superheating of

steam, regenerative feed water heating and reheating of steam.

MAIN TURBINE

The 210 MW turbine is a tandem compounded type machine comprising of H.P. and I.P. cylinders. The H.P.

turbines comprise of 12 stages, I.P. turbine has 11 stages and the L.P. turbine has 4 stages of double flow.

The H.P. and I.P. turbine rotors are rigidly compounded and the L.P. motor by the lens type semi flexible coupling.

All the three rotors are aligned on five bearings of which the bearing no. 2 is combined with the thrust bearing

The main superheated steam branches off into two streams from the boiler and passes through the emergency stop

valve and control valve before entering the governing wheel chamber of the H.P. turbine. After expanding in the

12 stages in the H.P. turbine the steam is returned in boiler for reheating.


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The reheated steam for the boiler enters the I.P> turbine via the interceptor valves and control valves and after

expanding enters the L.P. turbine stage via 2 nos of cross-over pipes.

In the L.P. stage the steam expands in axially opposite direction to counteract the trust and enters the condensers

placed below the L.P. turbine. The cooling water flowing throughout the condenser tubes condenses the steam and

the condensate collected in the hot well of the condenser.

The condensate collected is pumped by means of 3*50% duty condensate pumps through L.P. heaters to deaerator

from where the boiler feed pump delivers the water to boiler through H.P. heaters thus forming a close cycle.

The Main Turbine

TURBINE CYCLE

Fresh steam from the boiler is supplied to the turbine through the emergency stop valve. From the stop valves

steam is supplied to control valves situated in H.P. cylinders on the front bearing end. After expansion through 12

stages at the H.P. cylinder, steam flows back to the boiler for reheating steam and reheated steam from the boiler

cover to the intermediate pressure turbine through two interceptor valves and four control valves mounted on 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 Turbine Cycle

The selection of extraction points and cold reheat pressure has been done with a view to achieve a high efficiency.

These are two extractors from H.P. turbine, four from I.P. turbine and one from L.P. turbine. Steam at 1.10 and

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.


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From the condenser, condensate is pumped with the help of 3*50% capacity condensate pumps to deaerator

through the low-pressure regenerative equipments.

Feed water is pumped from deaerator to the boiler through the H.P. heaters by means of 3*50% capacity feed

pumps connected before the H.P. heaters.

TURBINE COMPONENTS

Casing.Rotor.Blades.Sealing system.Stop & control valves.Couplings and bearings.Barring gear.

TURBINE CASINGS

HP Turbine Casings:

Outer casing: a barrel-type without axial or radial flange.

Barrel-type casing suitable for quick startup and loading.

The inner casing- cylindrically, axially split.

The inner casing is attached in the horizontal and vertical planes in the barrel casing so that it can freely expand

radially in all the directions and axially from a fixed point (HP- inlet side).

IP Turbine Casing:

The casing of the IP turbine is split horizontally and is of double-shell construction.

Both are axially split and a double flow inner casing is supported in the outer casing and carries the guide blades.

Provides opposed double flow in the two blade sections and compensates axial thrust.

Steam after reheating enters the inner casing from Top & Bottom.


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LP Turbine Casing:

The LP turbine casing consists of a double flow unit and has a triple shell welded casing.

The shells are axially split and of rigid welded construction.

The inner shell taking the first rows of guide blades is attached kinematically in the middle shell.

Independent of the outer shell, the middle shell, is supported at four points on longitudinal beams.

Steam admitted to the LP turbine from the IP turbine flows into the inner casing from both sides.

ROTORS

HP Rotor:

The HP rotor is machined from a single Cr-Mo-V steel forging with integral discs.

In all the moving wheels, balancing holes are machined to reduce the pressure difference across them, which

results in reduction of axial thrust.

First stage has integral shrouds while other rows have shroudings, riveted to the blades are periphery.

??

IP Rotor:

The IP rotor has seven discs integrally forged with rotor while last four discs are shrunk fit.

The shaft is made of high creep resisting Cr-Mo-V steel forging while the shrunk fit discs are machined from high

strength nickel steel forgings.

Except the last two wheels, all other wheels have shrouding riveted at the tip of the blades. To adjust the frequency


37/44

of thee moving blades, lashing wires have been provided in some stages.

LP Rotor:

The LP rotor consists of shrunk fit discs in a shaft.

The shaft is a forging of Cr-Mo-V steel while the discs are of high strength nickel steel forgings.

Blades are secured to the respective discs by riveted fork root fastening.

In all the stages lashing wires are provided to adjust the frequency of blades. In the last two rows, satellite strips

are provided at the leading edges of the blades to protect them against wet-steam erosion.

BLADES

Most costly element of the turbine.Blades fixed in stationary part are called guide blades/ nozzles and those fitted

in moving part are called rotating/working blades.

Blades have three main parts:

1.Aerofoil: working part.

2.Root.

3.Shrouds.

Shroud are used to prevent steam leakage and guide steam to next set of moving blades.

VACUUM SYSTEM


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This comprises of:

Condenser:

2 for 200 MW unit at the exhaust of LP turbine.

Ejectors:

One starting and two main ejectors connected to the condenser locared near the turbine.

C.W. Pumps:

Normally two per unit of 50% capacity.

CONDENSER

There are two condensers entered to the two exhausters of the L.P. turbine. These are surface-type condensers with

two pass arrangement. Cooling water pumped into each condenser by a vertical C.W. pump through the inlet pipe.

Water enters the inlet chamber of the front water box, passes horizontally through brass tubes to the water tubes to

the water box at the other end, takes a turn, passes through the upper cluster of tubes and reaches the outlet

chamber in the front water box. From these, cooling water leaves the condenser through the outlet pipe and

discharge into the discharge duct.

Steam exhausted from the LP turbine washes the outside of the condenser tubes, losing its latent heat to the cooling

water and is connected with water in the steam side of the condenser. This condensate collects in the hot well,

welded to the bottom of the condensers.

A typical water cooled condensor


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EJECTORS

There are two 100% capacity ejectors of the steam eject type. The purpose of the ejector is to evacuate air and

other non-condensating gases from the condensers and thus maintain the vacuum in the condensers.

The ejector has three compartments. Steam is supplied generally at a pressure of 4.5 to 5 kg /cm2 to the three

nozzles in the three compartments. Steam expands in the nozzle thus giving a high-velocity eject which creates a

low-pressure zone in the throat of the eject. Since the nozzle box of the ejector is connected to the air pipe from the

condenser, the air and pressure zone. The working steam which has expanded in volume comes into contact with

the cluster of tube bundles through which condensate is flowing and gets condensed thus after aiding the formation

of vacuum. The non-condensing gases of air are further sucked with the next stage of the ejector by the second

nozzle. The process repeats itself in the third stage also and finally the steam-air mixture is exhausted into the

atmosphere through the outlet.

CONDENSATE SYSTEM

This contains the following

Condensate Pumps:

3 per unit of 50% capacity each located near condenser hot well.

LP Heater:

Normally 4 in number with no.1 located at the upper part of the condenser and nos. 2,3 & 4 around

4m level.

Condensate Pumps


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The function of these pumps is to pump out the condensate to the desecrator through ejectors, gland steam cooler

and LP heaters. These pumps have four stages and since the suction is at a negative pressure, special arrangements

have been made for providing sealing. The pump is generally rated for 160 m3/ hr at a pressure of 13.2 kg/ cm2 .

L.P. Heaters

Turbine has been provided with non-controlled extractions, which are utilized for heating the condensate, from

turbine bleed steam. There are 410 W pressure heaters in which the last four extractions are used. L.P. Heater-1 has

two parts LPH-1A and LPH-1B located in the upper parts of the condenser A and condenser B, respectively. These

are of horizontal type with shell and tube construction. L.P.H. 2,3 and 4 are of similar construction and they are

mounted in a row of 5m level. They are of vertical construction with brass tubes the ends of which are expanded

into tube plate. The condensate flows in the U tubes in four passes and extraction steam washes the outside of the

tubes. Condensate passes through these four L.P. heaters in succession. These heaters are equipped with necessary

safety valves in the steam space level indicator for visual level indication of heating steam condensate pressure

vacuum gauges for measurement of steam pressure, etc:

Deaerator

The presence of certain gases, principally oxygen, carbon dioxide and ammonia, dissolved in water is generally

considered harmful because of their corrosive attack on metals, particularly at elevated temperatures. One of the

most important factors in the prevention of internal corrosion in modern boilers and associated plant therefore, is

that the boiler feed water should be free as far as possible from all dissolved gases especially oxygen. This is

achieved by embodying into the boiler feed system a deaerating unit, whose function is to remove the dissolved

gases from the feed water by mechanical means. Particularly the unit must reduce the oxygen content of the feed

water to a lower value as far as possible, depending upon the individual circumstances. Residual oxygen content in

condensate at the outlet of deaerating plant usually specified are 0.005/ litre or less.

A Deaerator


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PRINCIPAL OF DEAERATION

It is based on following two laws.

Henrys Law

Solubility

The Deaerator comprises of two chambers:

Deaerating column

Feed storage tank

Deaerating column

is a spray cum tray type cylindrical vessel of horizontal construction with dished ends welded to it. The tray stack

is designed to ensure maximum contact time as well as optimum scrubbing of condensate to achieve efficient

deaeration. The deaeration column is mounted on the feed storage tank, which in turn is supported on rollers at the

two ends and a fixed support at the centre. The feed storage tank is fabricated from boiler quality steel plates.

Manholes are provided on deaerating column as well as on feed storage tank for inspection and maintenance.

The condensate is admitted at the top of the deaerating column flows downwards through the spray valves and

trays. The trays are designed to expose to the maximum water surfaces for efficient scrubbing to affect the

liberation of the associated gases steam enters from the underneath of the trays and flows in counter direction of

condensate. While flowing upwards through the trays, scrubbing and heating is done. Thus the liberated gases

move upwards alongwith the steam. Steam gets condensed above the trays and in turn heats the condensate.

Liberated gases escapes to atmosphere from the orifice opening meant for it. This opening is provided with a

number of dlflectors to minimize the loss of steam.


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FEED WATER SYSTEM

The main equipments coming under this system are:

Boiler feed Pump:

Three per unit of 50% capacity each located in the 0 meter level in the T bay.

High Pressure Heaters:

Normally three in number and are situated in the TG bay.

Drip Pumps:

generally two in number of 100% capacity each situated beneath the LP heaters.

Turbine Lubricating Oil System:

This consists of the Main Oil Pump (MOP), Starting Oil Pump (SOP), AC standby oil pumps and

emergency DC Oil Pump and Jacking Oil Pump (JOP). (one each per unit)

Boiler Feed Pump

This pump is horizontal and of barrel design driven by an Electric Motor through a hydraulic coupling. All the

bearings of pump and motor are forced lubricated by a suitable oil lubricating system with adequate protection to

trip the pump if the lubrication oil pressure falls below a preset value.

The high pressure boiler feed pump is a very expensive machine which calls for a very careful operation and

skilled maintenance. Operating staff must be able to find out the causes of defect at the very beginning, which can

be easily removed without endangering the operator of the power plant and also without the expensive dismantling

of the high pressure feed pump.


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Function

The water with the given operating temperature should flow continuously to the pump under a certain minimum

pressure. It passes through the suction branch into the intake spiral and from there; it is directed to the first

impeller. After leaving the impeller it passes through the distributing passages of the diffuser and thereby gets a

certain pressure rise and at the same time it flows over to the guide vanes to the inlet of the next impeller. This will

repeat from one stage to the other till it passes through the last impeller and the end diffuser. Thus the feed water

reaching into the discharge space develops the necessary operating pressure.

Booster Pump

Each boiler feed pump is provided with a booster pump in its suction line which is driven by the main motor of the

boiler feed pump. One of the major damages which may occur to a boiler feed pump is from cavitation or vapor

bounding at the pump suction due to suction failure. Cavitation will occur when the suction pressure of the pump

at the pump section is equal or very near to the vapor pressure of the liquid to be pumped at a particular feed water

temperature. By the use of booster pump in the main pump suction line, always there will be positive suction

pressure which will remove the possibility of cavitation. Therefore all the feed pumps are provided with a main

shaft driven booster pump in its suction line for obtaining a definite positive suction pressure.

Lubricating Pressure

All the bearings of boiler feed pump, pump motor and hydraulic coupling are force lubricated. The feed pump

consists of two radial sleeve bearings and one thrust bearing. The thrust bearing is located at the free end of the

pump.

High Pressure Heaters

These are regenerative feed waters heaters operating at high pressure and located by the side of turbine. These are

generally vertical type and turbine based steam pipes are connected to them.


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HP heaters are connected in series on feed waterside and by such arrangement, the feed water, after feed pump

enters the HP heaters. The steam is supplied to these heaters to form the bleed point of the turbine through motor

operated valves. These heaters have a group bypass protection on the feed waterside.

In the event of tube rupture in any of the HPH and the level of condensate rising to dangerous level, the group

protection devices divert automatically the feed water directly to boiler, thus bypassing all the 3 H.P. heaters.

Turbine Oil Lubricating System

This consists of main oil pump, starting oil pump, emergency oil pump and each unit.

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