A Practile Training Report (2)

8/4/2019 A Practile Training Report (2)

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A PRACTICAL TRANING REPORT

ON

NTPC POWER STATION, BADARPUR

(III YEAR)

SUBMITTED IN PRACTICAL FULFILLMENT OF THE REQUIREMENT

BACHELORS OF TECHNOLOGY. FOR THE AWARD OF

IN

MECHANICAL ENGINEERING

PROJECT BY

NISHU GUPTA (09-ME-1238)

DEPARTMENT OF MECHANICAL

Echelon Institute of TechnologyKabulpur,

Jasana-Manjawali Road,

12 k.m. from badkal chowk,

Faridabad - 121101

Haryana

JULY 2011


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ACKNOWLEDGEMENT

With profound respect and gratitude, I take the opportunity to convey my thanks to

complete the training here.

I do extend my heartfelt thanks to Ms. Rachna singh Bahel for providing me this

opportunity to be a part of this esteemed organization.

I am extremely grateful to all the technical staff of BTPS / NTPC 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.

I would also like to thank the training incharge of Echelon Institute of Technology,

Faridabad and all the faculty members of Mechanical Engineering Department for their effort of

constant co- operation, which have been a significant factor in the accomplishment of my

industrial training.

NISHU GUPTA

EIT, FARIDABAD


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CERTIFICATE

This is to certify that student of Batch Mechanical Branch IIird Year; EchelonInstitute of Technology Faridabad has successfully completed his industrial training at Badarpur

Thermal power station New Delhi for 27days from 4th July to 30th July 2011.

He has completed the whole training as per the training report submitted by him.

Training Incharge

BTPS/NTPC

NEW DELHI


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Training at BTPS

I was appointed to do eight-week training at this esteemed organization from 18th June

to 11th august 2007. In these eight weeks I was assigned to visit various division of the

plant which were

1. Boiler Maintenance Department(BMD I/II/III)2. Plant Auxiliary Maintenance(PAM)3. Turbine Maintenance Department(TMD)

This 27 days training was a very educational adventure for me. It was really amazing to

see the plant by your self and learn how electricity, which is one of our daily

requirements of life, is produced.

This report has been made by self-experience at BTPS. The material in this report has

been gathered from my textbooks, senior student report, and trainer manual provided

by training department. The specification & principles are at learned by me from the

employee of each division of BTPS.

NISHU GUPTA


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INDEX

1. Introduction NTPC

Badarpur Thermal Power Station

2. Basic steps of Electricity generation COAL TO STEAM

STEAM TO MECHANICAL POWER

COAL CYCLE

ELECTRICITY FROM COAL

3. RANKINE CYCLE PROCESS OF RANKINE CYCLE

RANKINE CYCLE WITH REHEAT

4. Boiler Maintenance Department

BMD I

BMD II

BMD III

5. Plant Auxiliary Maintenance

6. Turbine Maintenance Department


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ABOUT NTPC

NTPC Limited is the largest thermal power generating company of India. A 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 FIIs, Domestic Banks, Public and others hold the balance

10.5%. 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.

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, 10000MW 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 set new benchmarks for the power industry both in the area of power plant construction

andoperations. Its providing power at the cheapest average tariff in the country..

NTPC is committed to theenvironment, generating power at minimal environmental cost and

preserving the ecology in the vicinity of the plants. NTPC has undertaken massive a forestation in

the vicinity of its plants. Plantations have increased forest area and reduced barren land. Themassive a forestation by NTPC in and around its Ramagundam Power station (2600 MW) have

contributed reducing the temperature in the areas by about 3c. NTPC has also taken proactive

steps forash utilization. In 1991, it set up Ash Utilization Division

A "Centre for Power Efficiency and Environment Protection(CENPEEP)"has been established in

NTPC with the assistance of United States Agency for International Development. (USAID).

Cenpeep is efficiency oriented, eco-friendly and eco-nurturing initiative - a symbol of NTPC's

concern towards environmental protection and continued commitment to sustainable power

development in India.

As a responsible corporate citizen, NTPC is making constant efforts to improve the socio-economic

status of the people affected by its projects. Through itsRehabilitation and Resettlement

programmes, the company endeavours to improve the overall socio economic status Project

Affected Persons.

NTPC was among the first Public Sector Enterprises to enter into a Memorandum of

Understanding (MOU) with the Government in 1987-88. NTPC has been placed under the

'Excellent category' (the best category) every year since the MOU system became operative.
http://www.ntpc.co.in/operations/operations.shtmlhttp://www.ntpc.co.in/operations/operations.shtmlhttp://www.ntpc.co.in/operations/operations.shtmlhttp://www.ntpc.co.in/infocus/environment.shtmlhttp://www.ntpc.co.in/infocus/environment.shtmlhttp://www.ntpc.co.in/infocus/environment.shtmlhttp://www.ntpc.co.in/infocus/ashutilisation.shtmlhttp://www.ntpc.co.in/infocus/ashutilisation.shtmlhttp://www.ntpc.co.in/infocus/ashutilisation.shtmlhttp://www.ntpc.co.in/otherlinks/cenpeep.shtmlhttp://www.ntpc.co.in/otherlinks/cenpeep.shtmlhttp://www.ntpc.co.in/otherlinks/cenpeep.shtmlhttp://www.ntpc.co.in/infocus/socialcomm.shtmlhttp://www.ntpc.co.in/infocus/socialcomm.shtmlhttp://www.ntpc.co.in/infocus/socialcomm.shtmlhttp://www.ntpc.co.in/infocus/socialcomm.shtmlhttp://www.ntpc.co.in/otherlinks/cenpeep.shtmlhttp://www.ntpc.co.in/infocus/ashutilisation.shtmlhttp://www.ntpc.co.in/infocus/environment.shtmlhttp://www.ntpc.co.in/operations/operations.shtml


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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

NTPC. It has been taking various measures discussed below for mitigation of environment

pollution due to power generation.

Environment Policy & Environment Management SystemDriven by its commitment for sustainable growth of power, NTPC has evolved a well defined

environment management policy and sound environment practices for minimizing environmental

impact arising out of setting up of power plants and preserving the natural ecology.

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 utilization

of equipment, adoption of latest technologies and continual environment improvement. The

policy also envisages efficient utilization of resources, thereby minimizing waste, maximizing ash

utilization and providing green belt all around the plant for maintaining ecological balance.

Environment Management, Occupational Health and Safety Systems:

NTPC has actively gone for adoption of best international practices on environment, occupational

health and safety areas. The organization has pursued the Environmental Management System(EMS) ISO 14001 and the Occupational Health and Safety Assessment System OHSAS 18001 at its


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different establishments. As a result of pursuing these practices, all NTPC power stations have

been certified for ISO 14001 & OHSAS 18001 by reputed national and international Certifying

Agencies.

Pollution Control systems:

While deciding the appropriate technology for its projects, NTPC integrates many environmental

provisions into the plant design. In order to ensure that NTPC comply with all the stipulated

environment norms, various state-of-the-art pollution control systems / devices as discussed

below have been installed to control air and water pollution.

JOURNEY OF NTPC

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

.

In 1997, Government of India granted NTPC status of Navratnabeing one of the nine

Jewels of India, enhancing the powers to the Board of Directors

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

NTPC became third largest market capitalization of listed by companies.

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.

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

Forbes Global 2000 for 2008 ranked it 411th in the world.

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

Forbes Global 2000 for 2008 ranked it317th in the world.

National Thermal Power Corporation has also set up to a plan to achieve a target of

50,000MW generation capacity.

1975

1997

2004

2005

2008

2009

2012


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.

National Thermal Power Corporation has embarked on plans to became a

75,000MW Company by 2017.

ABOUT BTPS

Badarpur thermal power station started working in 1973 with a single 95 mw unit. There were 2more units (95 MW each) installed in next 2 consecutive years. Now it has total five units with

total capacity of 720 MW. Ownership of BTPS was transferred to NTPC with effect from 01.06.2006

through GOIs Gazette Notification.

Given below are the details of unit with the year they are installed.

Address: Badarpur, New Delhi -110044

Telephone: (STD-011)-26949523

Fax: 26949532

Installed Capacity 720 MW

Derated capacity 705 MW

Location New Delhi

Coal source Jharia coal fields

Water source Agra canal

Beneficary states Delhi

Unit sizes 3x95 MW

2X210 MWUnits Commissioned Unit I- 95 MW - July 1973

Unit II- 95 MW August 1974

Unit III- 95 MW March 1975

Unit IV - 210 MW December 1978

Unit V - 210 MW - December 1981

Transfer of BTPS to NTPC Ownership of BTPS was transferred to

NTPC with effect from 01.06.2006

through GOIs Gazette Notification

2017


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BASIC STEPS OF ELECTRICITY GENERATION

The basic steps in the generation of electricity from coal involves following steps:

Coal to steamSteam to mechanical power

Mechanical power to electrical power

COAL TO ELECTRICITY: BASICS

\


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Coal to Steam

Coal from the coal wagons is unloaded in the coal handling plant. This Coal is

transported up to the raw coal bunkers with the help of belt conveyors. Coal is

transported to Bowl mills by Coal Feeders. The coal is pulverized in the Bowl Mill,where it is ground to powder form. The mill consists of a round metallic table on which

coal particles fall. This table is rotated with the help of a motor. There are three large

steel rollers, which are spaced 120 apart.

When there is no coal, these rollers do not rotate but when the coal is fed to the table it

packs up between roller and the table 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 the 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 to10 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 theturbine, where it passes through a ring of stationary blades fixed to the cylinder wall.


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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 that of the

turbine, also rotates. It results in rotation of the coil of the generator, which causes

induced electricity to be produced.

(COAL CYCLE)

From Jharia mines

Railway wagon

BTPS wagon tripper


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Magnetic separator

Crusher house

Coal stock yard

RC bunker

RC feeder

Bowl mill Furnace

ELECTRICITY FROM COAL

Coal from the coal wagons is unloaded with the help of wagon tipplers in the C.H.P. this

coal is taken to the raw coal bunkers with the help of conveyor belts. Coal is then

transported to bowl mills by coal feeders where it is pulverized and ground in thepowered form.


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This crushed coal is taken away to the furnace through coal pipes with the help of hot

and cold mixture P.A fan. This fan takes atmospheric air, a part of which is sent to pre

heaters while a part goes to the mill for temperature control. Atmospheric air from F.D

fan in the air heaters and sent to the furnace as combustion air.

Water from boiler feed pump passes through economizer and reaches the boiler drum .

Water from the drum passes through the 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 density difference the water rises up in the water wall tubes. This

steam and water mixture is again taken to the boiler drum where the steam is sent to

super heaters for super heating. The super heaters are located inside the furnace and

the steam is super heated (540 degree Celsius) and finally it goes to the turbine.

Fuel gases from the furnace are extracted from the induced draft fan, which maintains

balance draft in the furnace with F.D fan. These fuel gases heat energy to the various

super heaters and finally through air pre heaters and goes to electrostatic precipitatorswhere the ash particles are extracted. This ash is mixed with the water to from slurry is

pumped to ash period.

The steam from boiler is conveyed to turbine through the steam pipes and through stop

valve and control valve that automatically regulate the supply of steam to the turbine.

Stop valves and controls valves are located in steam chest and governor driven from

main turbine shaft operates the control valves the amount used.

Steam from controlled valves enter high pressure cylinder of turbines, where it passes

through the ring of blades fixed to the cylinder wall. These act as nozzles and direct the

steam into a second ring of moving blades mounted on the disc secured in the turbine

shaft. The second ring turns the shaft as a result of force of steam. The stationary and

moving blades together.

MAIN GENERATOR

Maximum continuous KVA rating 24700KVA

Maximum continuous KW 210000KW

Rated terminal voltage 15750VRated Stator current 9050 A

Rated Power Factor 0.85 lag

Excitation current at MCR Condition 2600 A

Slip-ring Voltage at MCR Condition 310 V

Rated Speed 3000 rpm

Rated Frequency 50 Hz

Short circuit ratio 0.49

Efficiency at MCR Condition 98.4%

Direction of rotation viewed Anti Clockwise

Phase Connection Double Star

Number of terminals brought out 9( 6 neutral and 3 phase)


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MAIN TURBINE DATA

BASIC POWER PLANT CYCLE

The thermal (steam) power plant uses a dual (vapour+ liquid) phase cycle. It is a closecycle 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 appreciablyincreased. 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.

Rated output of Turbine 210 MWRated speed of turbine 3000 rpm

Rated pressure of steam before emergency 130 kg/cm^2

Stop valve rated live steam temperature 535 degree Celsius

Rated steam temperature after reheat at inlet to receptor valve 535 degree Celsius

Steam flow at valve wide open condition 670 tons/hour

Rated quantity of circulating water through condenser 27000 cm/hour

1. For cooling water temperature (degree Celsius) 24,27,30,33

1.Reheated steam pressure at inlet of interceptor valve in

kg/cm^2 ABS23,99,24,21,24,49,24.82

2.Steam flow required for 210 MW in ton/hour 68,645,652,662

3.Rated pressure at exhaust of LP turbine in mm of Hg 19.9,55.5,65.4,67.7


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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.

Regenerative feed water heating.


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RANKINECYCLE

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. This cycle

generates about 80% of all electric power used throughout the world, including virtually allsolar thermal, biomass, coal and nuclear power plants. It is named after William John

Macquorn Rankine, a Scottish polymath..

The Rankine cycle is sometimes referred to as a practical Carnot cycle because, when an

efficient turbine is used, the TS diagram begins to resemble the Carnot cycle. The main

difference is that heat addition (in the boiler) and rejection (in the condenser) are isobaric in the

Rankine cycle and isothermal in the theoretical Carnot cycle. A pump is used to pressurize the

working fluid received from the condenser as a liquid instead of as a gas. All of the energy in

pumping the working fluid through the complete cycle is lost, as is most of the energy of

vaporization of the working fluid in the boiler. This energy is lost to the cycle because the

condensation that can take place in the turbine is limited to about 10% in order to minimize

blade erosion; the vaporization energy is rejected from the cycle through the condenser.

But pumping the working fluid through the cycle as a liquid requires a very small fraction ofthe energy needed to transport it as compared to compressing the working fluid as a gas in a

compressor (as in the Carnot cycle).

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

reaching super critical levels for the working fluid, the temperature range the cycle can operate

over is quite small: turbine entry temperatures are typically 565C (the creep limit of stainless

steel) and condenser temperatures are around 30C. This gives a theoretical Carnot efficiency of

about 63% compared with an actual efficiency of 42% for a modern coal-fired power station.

This low turbine entry temperature (compared with a gas turbine) is why the Rankine cycle is

often used as a bottoming cycle in combined-cycle gas turbine power stations.
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Description

A Rankine cycle describes a model of the operation of steam heat engines most commonly found

in power generation plants. Common heat sources for power plants using the Rankine cycle are

coal, natural gas, oil, and nuclear. The Rankine cycle is sometimes referred to as a practical

Carnot cycle as, when an efficient turbine is used, the TS diagram will 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 the Carnot

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

the pressure going super critical the temperature range the cycle can operate over is quite small,

turbine entry temperatures are typically 565C (the creep limit of stainless steel) and condenser

temperatures are around 30C. This gives a theoretical Carnot efficiency of around63%

compared with an actual efficiency of 42% for a modern coal-fired power station. This low

turbine entry temperature (compared with a gas turbine) is why the Rankine cycle is often used

as a bottoming cycle in combined cycle gas turbine power stations.The working fluid in a Rankine cycle follows a closed loop and is re-used constantly. The

water vapor and entrained droplets often seen billowing from power stations is generated by the

cooling systems (not from the closed loop Rankine power cycle) and represents the waste heat

that could not be converted to useful work. Note that cooling towers operate using the latent

heat of vaporizationof the cooling fluid.

The white billowing clouds that form in cooling tower operation are the result of water droplets

which are entrained in the cooling tower 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 its thermodynamic properties. One of the principal advantages it holds over other cycles

is that during the compressions tage 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, thework required by the pump will only consume approximately 1% to 3% of the turbine power
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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

i.Process 1-2 : The working fluid is pumped from low to high pressure, as the fluid is a liquid at

this stage the pump requires little input energy.

ii.Process 2-3 : The high pressure liquid enters a boiler where it is heated at constant pressure

by an external heat source to become a dry saturated vapour.iii.Process 3-4 : The dry saturated vapour expands through a turbine, generating power.This

decreases the temperature and pressure of the vapour, and some condensation may occur.

iv.Process 4-1 : The wet vapor then enters a condenser where it is condensed at a constant

pressure and temperature to become a saturated liquid. The pressure and temperature of the

condenser is fixed by the temperature of the cooling coils as the fluid is undergoing a phase-

change. In an ideal Rankine cycle the pump and turbine would be isentropic ,i.e., the pump and

turbine would generate no entropy and hence maximize the net work output. Processes 1-2and

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 vapour ending up in the superheat

region after the expansion in the turbine, which reduces the energy removed by the condensers.
http://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Surface_condenserhttp://en.wikipedia.org/wiki/Boiling_pointhttp://en.wikipedia.org/wiki/Phase_Transitionhttp://en.wikipedia.org/wiki/Phase_Transitionhttp://en.wikipedia.org/wiki/Isentropichttp://en.wikipedia.org/wiki/Isentropichttp://en.wikipedia.org/wiki/Phase_Transitionhttp://en.wikipedia.org/wiki/Phase_Transitionhttp://en.wikipedia.org/wiki/Boiling_pointhttp://en.wikipedia.org/wiki/Surface_condenserhttp://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Gas_turbine


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

In a real Rankine cycle, the compression by the pump and the expansion in the turbine are not

isentropic. In other words, these processes are non-reversible and entropy is increased during

the two processes. This somewhat increases the power required 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.
http://en.wikipedia.org/wiki/Pumphttp://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Entropyhttp://en.wikipedia.org/wiki/Power_%28physics%29http://en.wikipedia.org/wiki/Power_%28physics%29http://en.wikipedia.org/wiki/Entropyhttp://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Pump


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Rankine cycle with reheat

In this variation, two turbines work in series. The first accepts vapour from the boiler at high

pressure. After the vapour 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 vapour 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 a sub cooled liquid) the working fluid is heated by steam tapped 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

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

'bleed steam' from between turbine stages is sent to feed water heaters to preheat the water on

its way from the condenser to the boiler.
http://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Vaporizationhttp://en.wikipedia.org/wiki/Boilerhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Subcooled_liquidhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Feedwater_heaterhttp://en.wikipedia.org/wiki/Feedwater_heaterhttp://en.wikipedia.org/wiki/Feedwater_heaterhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Subcooled_liquidhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Boilerhttp://en.wikipedia.org/wiki/Vaporizationhttp://en.wikipedia.org/wiki/Turbine


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BOILER MAINTENANCE DEPARTMENT

Boiler and its description

A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized

fluid exits the boiler for use in various processes or heating applications Construction of

boilers is mainly ofsteel, stainless steel, and wrought iron. In live steam models,

copper or brass is often used. Historically copper was often used for fireboxes(particularly

for steam locomotives), because of its better thermal conductivity. The price of copper

now makes this impractical.

Cast iron is used for domestic water heaters. Although these are usually termed "boilers",

their purpose is to produce hot water, not steam, and so they run at low pressure and try

to avoid actual boiling. The brittleness of cast iron makes it impractical for steam pressure

vessels. 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 hottestpart of the combustion gases as they exit the furnace. Here the steam is superheated to

1,000 F (540C) to prepare it for the turbine. The steam generating boiler has to produce

steam at the high purity, pressure and temperature required for the steam turbine that

drives the electrical generator. The generator includes the economizer, the steam drum,

the chemical dosing equipment, and the furnace with its steam generating tubes and the

superheated coils. Necessary safety valves are located at suitable points to avoid

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

fan, air preheated (APH), boiler furnace, induced draft (ID) fan, fly ash collectors

(electrostatic precipitator or bag house) and the flue gas stack.

For units over about 210 MW capacity, redundancy of key components is provided byinstalling 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.
http://en.wikipedia.org/wiki/Pressure_vesselhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Mild_steelhttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Wrought_ironhttp://en.wikipedia.org/wiki/Live_steamhttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Brasshttp://en.wikipedia.org/wiki/Fireboxhttp://en.wikipedia.org/wiki/Steam_locomotivehttp://en.wikipedia.org/wiki/Cast_ironhttp://en.wikipedia.org/wiki/Cast_ironhttp://en.wikipedia.org/wiki/Steam_locomotivehttp://en.wikipedia.org/wiki/Fireboxhttp://en.wikipedia.org/wiki/Brasshttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Live_steamhttp://en.wikipedia.org/wiki/Wrought_ironhttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Mild_steelhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Pressure_vessel


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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 boiler

includes the economizer, the steam drum, the chemical dosing equipment, and

The furnace with its steam generating tubes and the super heater coils. Necessary safety

valves are located at suitable points to avoid excessive boiler pressure. The air and flue

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 .
http://en.wikipedia.org/wiki/Furnacehttp://en.wikipedia.org/wiki/Centrifugal_fanhttp://en.wikipedia.org/wiki/Air_preheaterhttp://en.wikipedia.org/wiki/Electrostatic_precipitatorhttp://en.wikipedia.org/wiki/Dust_collector#Fabric_filtershttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Dust_collector#Fabric_filtershttp://en.wikipedia.org/wiki/Electrostatic_precipitatorhttp://en.wikipedia.org/wiki/Air_preheaterhttp://en.wikipedia.org/wiki/Centrifugal_fanhttp://en.wikipedia.org/wiki/Furnace


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Schematic diagram of typical coal-fired power plant steam generator highlighting the air

preheater (APH) location

SPECIFICATION:.

MAIN BOILER AT 100% LOAD

Evaporation 700t/hr

Feed water temperature 247C

Feed water leaving economizer 276C

STEAM TEMPERATURE:

:

Drum 341C

Super heater outlet 540C

Reheat inlet 332C

Reheat outlet 540C


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STEAM PRESSURE:

Drum design 158.20 kg/cm2

Drum operating 149.70 kg/cm2

Super heater outlet 137.00 kg/cm2

Reheat inlet 26.35 kg/cm2

Reheat outlet 24.50 kg/cm2

FUEL SPECIFICATION

:COAL DESIGN WORST

Fixed carbon 38% 25%

Volatile matter 26% 25%

Moisture 8% 9%

Grind ability 50% hard grove 45% hard grove

OIL:

Calorific value of fuel oil 10,000 kcal/kg

Sulphur content 4.5% W/W

Moisture content 1.1% W/WFlash point 66C

HEAT BALANCE

Dry gas loss 4.63%

Carbon loss 2%

Radiation loss 0.26%

Unaccounted loss 1.5%

Hydrogen in air and water in fuel 4.9%Total loss 13.3%

Efficiency 86.7%

AUXILIARIES OF BOILER

1. FURNACEFurnace is primary part of boiler where the chemical energy of fuel is converted

to thermal energy by combustion. Furnace is designed for efficient and completecombustion. Major factors that assist for efficient combustion area mount of fuel


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inside the furnace and turbulence, which causes rapid mixing between fuel and air.

In modern boilers, water-cooled furnaces are used.

2. BOILER DRUMDrum is of fusion-welded design with welded hemi-spherical 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 opposed 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 runsdown 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 separation.

3. Classifier

It is an equipment which serves separation of fine pulverized coal particles medium from

coarse medium. The pulverized coal along with the carrying medium strikes the impactplate through the lower part. Large particles are then transferred to the ball mill.


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4. Worm Conveyor

It is equipment used to distribute the pulverized coal from bunker of one system to

bunker of other system. It can be operated in both directions.

5. WATER WALLS:

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

the two side water walls constitute the main evaporation surface absorbing the bulk

of radiant heat of the fuel burnt in the chamber. The front and rear walls are bent at the

lower ends to form a water-cooled slag hopper. The upper part of the chamber is

narrowed to achieve perfect mixing of combustion gases. The water walls tubes are

connected to headers at the top and bottom. The rear water walls tubes at the top are

grounded in four rows at a wider pitch forming the grid tubes.

6. REHEATER

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

extracted in high- pressure turbine. This is another method of increasing the cycle

efficiency. Reheating requires additional equipment I.e. Heating surface connecting boiler

and turbine pipe safety equipment like safety valve, non-return valve, isolating valves,

high pressure feed pump, etc. Reheater is composed to two sections namely front and

rear pendant section which is located above the furnace arch between water-cooled

screen wall tubes and rear wall hanger tubes.


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7. Super heaters

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.

Fig. A water tube boiler with a super heater

If accurate control of the degree of superheat is required, as would be the case if the

steam is to be used to drive turbines, then an attemperator (desuperheater) is fitted. This

is a device installed after the superheater, which injects water into the superheated steam

to reduce its temperature.


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8. ECONOMISER

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

gases and add as a sensible heat to the feed water before the water enters the

evaporation circuit of the boiler.

Earlier economizer were introduced mainly to recover the heat available in the flue gases

that leaves the boiler and provision of this addition heating surface increases the

efficiency of steam generators. In the modern boilers used for power generation feed

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

water temperature.

Use ofeconomizer 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 andair heaters. In low capacity, air heaters may alone be selected.

. An economizer

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.


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9. 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.

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 blowers to

clean normal devices and washing devices to clean the element when soot blowing alone

cannot keep the element clean.

An air preheater

10. 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.


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A Pulverize

Types of Pulverize.

i. Ball and Tube millsA ball mill is a pulverizer that consists of a horizontal cylinder, up to three diameter sin

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.

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

Bowl Mill: - One of the most advanced designs of coal pulverizes presently manufactured.

Motor specificationsquirrel cage induction motor

Rating-340 KW

Voltage-6600KV

Curreen-41.7A

Speed-980 rpm

Frequency-50 HzNo-load current-15-16 A


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An external view of a Coal Pulverizer

Advantages of Pulverized Coal

Pulverized coal is used for large capacity plants.

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.

The combustion process is almost free from clinker and slag formation.

The boiler can be easily started from cold condition in case of emergency.Practically no ash handling problem.

The furnace volume required is less as the turbulence caused aids in complete

combustion of the coal with minimum travel of the particles.

11. CYCLONE SEPARATOR

Cyclonic separation is a method of removing particulates from an air, gas or liquid stream,

without the use offilters, through vortex separation. Rotational effects and gravity are

fine droplets of liquid from a gaseous stream.
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A high speed rotating (air)flow is established within a cylindrical or conical container

called a cyclone. Air flows in a spiral pattern, beginning at the top (wide end) of the

cyclone and ending at the bottom (narrow) end before exiting the cyclone in a straight

stream through the center of the cyclone and out the top. Larger (denser) particles in the

rotating stream have too much inertia to follow the tight curve of the stream, and strike

the outside wall, then falling to the bottom of the cyclone where they can be removed. In

a conical system, as the rotating flow moves towards the narrow end of the cyclone, the

rotational radius of the stream is reduced, thus separating smaller and smaller particles.

The cyclone geometry, together with flow rate, defines the cut point of the cyclone. This is

the size of particle that will be removed from the stream with a 50% efficiency. Particles

larger than the cut point will be removed with a greater efficiency, and smaller particles

with a lower efficiency.
http://en.wikipedia.org/wiki/Flow_ratehttp://en.wikipedia.org/wiki/Flow_rate


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PLANT AUXILIARY MAINTENANCE

1. 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 absorption surface is called circulation ratio.

Types of Boiler Circulating System

i.Natural circulation system

ii.Controlled circulation system

iii.Combined circulation system

i. Natural circulation SystemWater 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 super heater 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 densitybetween 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/ cm.

ii. Controlled circulation SystemBeyond 80 kg/ cm 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/ cm).


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1. ASH HANDLING PLANTThe widely used ash handling systems are:

i. Mechanical Handling System

ii. Hydraulic System.

iii. Pneumatic System.

iv. Steam jet System.

Ash Handling System at Badarpur Thermal Power Station, New Delhi

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

Hydraulic Ash Handling System

The hydraulic system carried the ash with the flow of water with high velocity througha 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.


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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 belowthe precipitators or bag filters. Generally, the fly ash is pneumatically transported to

storage silos for subsequent transport by trucks or railroad cars.

Bottom Ash Collection and Disposal

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

ash from the bottom of the furnace. This hopper is always filled with water to quench

the ash and clinkers falling down from the furnace. Some arrangement is included to

crush the clinker sand for conveying the crushed clinkers and bottom ash to a storagesite.

1. WATER TREATMENT PLANTAs 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 demineralised

water. No doubt, this plant has to be engineered very carefully keeping in view the typeof raw water to the thermal plant, its treatment costs and overall economics.


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A water treatment plant

The type of demineralization process chosen for a power station depends on three main

factors.i. The quality of raw material.ii. The degree of de-ionization i.e. treated water quality.iii. Selectivity of resins.

Water treatment process is generally made up of two sections:

Pre-treatment section.

Demineralization section

Pre-treatment Section

Pre-treatment 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 settling able. Long term ability to remain suspended in water is basically afunction of both size and specific gravity.

Demineralization

This filter water is now used for demineralising 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 toaction resin and must be eliminated before its entry to this bed.


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A demineralization tank

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 whichis 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 salt sin 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., theVacuum 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 itself.


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WTP-II Flash mixture (Cl2 +Pac (Poly aluminium chorine) )

Clarifier tank Storage tank Clarifier pump(A or B)

+Cation anion Active carbon filter Pressure filter (A, B, C, D)

Degasser tank (Co2 removed)

Degasser pump -Anion (NaoH used)

Strong base anion Mixed bed(6.57 ph)

DM Storage tank

Systematic arrangement of water treatment II

1.DRAUGHT SYSTEM

There are four types of draught system:

i.Natural Draught

ii.Induced Draught

iii.Forced Draught

iv.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, airis admitted into the furnace


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A natural draught system

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.

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.

Balanced Draught SystemHere 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.

1. INDUSTRIAL FANSID 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


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Inlet Vane Control

Impeller

Outlet Guide Vane Assembly

ID Fans: - Located between electrostatic precipitator and chimney.

Type-radical

Speed-1490 rpm

Rating-300 KW

Voltage-6.6 KV

Lubrication-by oil

An ID fan

FD FanThe fan, normally of the same type as ID Fan, consists of the following components:

Silencer

Inlet Bend

Fan Housing

Impeller with blades and setting mechanism

FD Fans: - Designed to handle secondary air for boiler. 2 in number and provide

ignition of coal.

Type-axial

Speed-990 rpm

Rating-440 KW

Voltage-6.6 KV


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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 duringoperation. 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.

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 Fans: - Designed for handling the atmospheric air up to 50 degrees Celsius,

2 in number

And they transfer the powered coal to burners to firing.

Type-Double suction radial

Rating-300 KW

Voltage-6.6 KV

Lubrication-by oil

Type of operation-continuous


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Primary air fan

1. COMPRESSOR HOUSEInstrument 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.

A compressor house

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.

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


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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, while 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 Air from L.P. cylinder enters at one end of the intercooler and goes to

the opposite end where from it is discharged to the high-pressure cylinder; cooling

water flows through the nest of the tubes and cools the air. A safety valve is set at rated

pressure. Two selectors switch one with positions auto load/unload and another with

positions auto start/stop, non-stop have been provided on the control panel of the

compressor. In auto start-stop position, the compressor will start.


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TURBINE MAINTENANCE DEPARTMENT

TURBINE CLASSIFICATION:

1. Impulse turbine:

In impulse turbine steam expands in fixed nozzles. The high velocity steam from nozzles

does work on moving blades, which causes the shaft to rotate. The essential features of

impulse turbine are that all pressure drops occur at nozzles and not on blades.

2. Reaction turbine:

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

moving blades act like nozzles. Work done by the impulse effect of steam due to reverse

the direction of high velocity steam. The expansion of steam takes place on moving

blades.

A 95 MW Generator at BTPS, New Delhi

COMPOUNDING:

Several problems occur if energy of steam is converted in single step and so compoundingis done. Following are the type of compounded turbine:


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i. 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.

ii. Pressure Compound 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 take 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 givenpressure 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. 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 rotor

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 ofthe machine and has not as in the reciprocating engine to be transmitted through a


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system of connecting links, which are necessary to transform are reciprocating motion

into rotary motion. Hence since the steam turbine possesses for its moving parts rotating

elements only if the manufacture is good and the machine is correctly designed, it ought

to be free from out of balance forces. If the load on a turbine is kept constant the torque

developed at the coupling is also constant. A generator at a steady load offers a constant

torque.

Therefore, a turbine is suitable for driving a generator, particularly as they are both high-

speed machines. A further advantage of the turbine is the absence of internal lubrication.

This means that the exhaust steam is not contaminated with oil vapour and can be

condensed and fed back to the boilers without passing through the filters. It also means

that turbine is considerable saving in lubricating oil when compared with 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 centre line. 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 strikes the next row of moving

blades. As the steam flows through the turbine, its pressure and temperature decreaseswhile 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.


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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 is 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 thrustbearing. The main superheated steam branches off into two streams from the boiler and

passes through the emergency stop valve and control valve before entering the governing

wheel chamber of the H.P. turbine.

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

reheating. The reheated steam for the boiler enters the I.P> turbine via the interceptor

valves and control valves and after expanding enters the L.P. turbine stage via 2 nos of

cross-over pipes. In the L.P. stage the steam expands in axially opposite direction to

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


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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 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 thegland sealing. Steam for this purpose is obtained from deaerator through a collection


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where pressure of steam is regulated. From the condenser, condensate is pumped with

the help of 3*50% capacity condensate pumps to deaerator through the low-pressure

regenerative equipments. Feed water is pumped from deaerator to the boiler through the

H.P. heaters by means of 3*50% capacity feed pumps connected before the H.P. heaters

The turbine cycle

SPECIFICATIONS OF THE TURBINE

Type: Tandem compound 3 cylinder reheated type.

Rated power: 210 MW.

Number of stages: 12 in H.P., 11 in I.P. and 4*2 in L.P. cylinder.

Rated steam pressure: 130 kg /sq. cm before entering the stop valve.

Rated steam temperature: 535C after reheating at inlet.Steam flow: 670T / hr.

H.P. turbine exhaust pressure: 27 kg /sq. cm., 327C

Condenser back pressure: 0.09 kg /sq. cm.

Type of governing: nozzle governing.

Number of bearing; 5 excluding generator and exciter.

Lubrication Oil: turbine oil 14 of IOC.

Gland steam pressure: 1.03 to 1.05 kg /sq. cm (Abs)

Critical speed: 1585, 1881, 2017.

Ejector steam parameter: 4.5 kg /sq. cm.

Condenser cooling water pressure: 1.0 to 1.1 kg /sq. cm.

Condenser cooling water temperature: 27000 cu. M /hr.Number of extraction lines for regenerative heating of feed water: seven


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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 start-up 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.

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.

ROTORSHP Rotor:

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

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

them, which results in reduction of axial thrust.

First stage has integral shrouds while other rows have shrouding, riveted to the blades are

periphery.


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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 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:

Aerofoil: working part.

Root.

Shrouds.

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

VACUUM SYSTEM

This comprises of:

Condenser: 2 for 200 MW units at the exhaust of LP turbine.

Ejectors:

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

C.W. Pumps: Normally two per unit of 50% capacity.

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.


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Typical water cooler condenser

EJECTORS

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

evacuate air and other non-condensation gases from the condensers and thus maintain the

vacuum in the condensers. The ejector has three compartments. Steam is supplied generally at a

pressure of 4.5 to 5kg /cm 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 followingi. Condensate Pumps: 3 per u

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