Badarpur Thermal Power Station INDUSTRIAL TRAINING REPORT

   SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF THE DEGREE

BACHELOR OF TECHNOLOGY (MECHANICAL ENGINEERING)

At

SAM HIGGINBOTTOM INSTITUTE

OF

AGRICULTURE, TECHNOLOGY & SCIENCE

SUBMITTED BY: AYUSH KHARE TRAINING INCHARGE:

G.D. SHARMA SNR. MANAGER NTPC, BADARPUR

DECLARATION

I, Mr. AYUSH KHARE ,hereby declare that this industrial training report is the record of authentic work carried out by me during the period from 02 june 2015 to 20 june 2015 in NTPC BADARPUR under the super vision of my training incharge Mr. G.D. SHARMA(SN. MANAGER , TRAINING CENTRE, NTPC BADARPUR).

NAME OF STUDENT: AYUSH KHARE

SIGNATURE:

TRAINING AT BTPS

I was appointed to do 6 week training at this esteemed organization from 02ndJune to 20th June, 2015. I was assigned to visit various division of the plant, which were:

Boiler Maintenance Department (BMD I/II/III)

Plant Auxiliary Maintenance (PAM)

These 3 weeks training was a very educational adventure for me. It was really amazing to see the plant by yourself and learn how electricity, which is one of our daily requirements of life, is produced.This report has been made by my experience at BTPS. The material in this report has been gathered from my textbook, senior student reports and trainers manuals and power journals provided by training department. The specification and principles are as learned by me from the employees of each division of BTPS.

AYUSH KHARE

ACKNOWLEDGEMENT

I would like to express my deepest appreciation to all those who provided me the possibility to complete my industrial training. A special gratitude I give to our Training incharge , Mr. G.D. SHARMA(SNR. HR MGR.), whose contribution in stimulating suggestions and encouragement, helped me to coordinate in my training period.Furthermore I would also like to acknowledge with much appreciation the crucial role of the employee of Other sections who gave the permission to use all required equipment and the necessary materials to complete the task . A special thanks goes to my team mate, who help me to assemble the parts and gave suggestion about the task . . I have to appreciate the guidance given by other supervisor as well as the panels especially in our training period that has improved our presentation skills and knowledge.

A special thanks to Mr. A.K. SHARMA ( DGM, BMD ) For his guidance and care in NTPC.

Last but not least, many thanks to NTPC , who give me opportunity to complete my industrial training in such wonderful working environment,in achieving my goal.

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 alot 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 SHIATS, Allahabad 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.

CONTENTS

ABOUT NTPC ABOUT BTPS INTRODUCTION TO THERMAL POWER PLANT ENVIRONMENT POLICY POLLUTION CONTROL SYSTEM BASIC STEPS OF ELECTRICITY GENERATION RANKINE CYCLE BOILER MAINTENANCE DEPARTMENT PLANT AUXILIARY MAINTENANCE

ABOUT NTPC

NTPC 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 Government of India. At presents, 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. With in 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 consultancy to power utilities in India or abroad.

The total installed capacity of the company is 31134MW (including JVs) with 16 coal based and 7 gas based stations, located across the country. In addition under JVs, 7 stations are coal based & another station uses naptha/LNG as fuel. The company has set a target to have an installed power generating capacity of 1,28,000 MW by the year 2032. The capacity will have a diversified fuel mix comprising 56% coal, 16% Gas, 11% Nuclear and 17% Renewable Energy Sources(RES) including hydro. By 2032, non-fossil fuel based generation capacity shall make up nearly 28% of NTPC‟s portfolio. NTPC has been operating its plants at high efficiency levels. Although the company has 17.75% of the total national capacity, it contributes 27.40% of total power generation due to its focus on high efficiency.

In October 2004, NTPC launched its Initial Public Offering (IPO) consisting of 5.25% as fresh issue and 5.25% as offer for sale by Government of India. NTPC thus became a listed company in November 2004 with the Government holding 89.5%

of the equity share capital. In February 2010, the Shareholding of Government of India was reduced from 89.5% to 84.5% through Further Public Offer. The rest is held by Institutional Investors and the Public.

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 µClean Development. Mechanism to help get / earn µCertified Emission Reduction.

Corporate Social Responsbilities

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 hasalso taken up distributed generation forremoterural areas.

Partnering government in various initiatives Consultantrole tomodernize andimprovise severalplantsacrossthe country. Disseminate technologies to other players in the sector. Consultant role ³Partnership in Excellence´ Programme for improvement of PLF

of 15 Power Stations of SEBs. Rural Electrification work under Rajiv Gandhi Garmin Vidyutikaran.

Environment management Allstations ofNTPCare ISO14001 certified. Various groupsto care of environmental issues. TheEnvironment Management Group. Ash tilizationDivision. AfforestationGroup. Centre for Power Efficiency & Environment Protection. Group onCleanDevelopmentMechanism. NTPC is the second largest owner of trees in the country after the Forest

department

Vision

“To be the world’s largest and best power producer, powering India’s growth.”

Mission

“Develop and provide reliable power, related products and services at competitive prices, integrating multiple energy sources with innovative and eco-friendly technologies and contribute to society.”

Core Values – BE COMMITTED

B Business Ethics

E Environmentally & Economically Sustainable

C Customer Focus

O Organizational & Professional Pride

M Mutual Respect & Trust

M Motivating Self & others

I Innovation & Speed

T Total Quality for Excellence

T Transparent & Respected Organization

E Enterprising

D Devoted

Journey Of NTPC

NTPC was set up in 1975 with 100% ownership by the Governmentof 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 Navratna being one of

the nine jewels of India, enhancing the powers to theBoard of Directors.

NTPC became a listed company with majority Government ownership of

89.5%.

NTPC becomes third largest by Market Capitalization of listed 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 it 317th in the world.

NTPC has also set up a plan to achieve a target of 50,000 MW generation

capacity.

NTPC has embarked on plans to become a 75,000 MW company by 2017.

ABOUT BTPS

BADARPUR THERMAL POWER STATION was established on 1973 and it was the part of Central Government. On 01/04/1978 is was given as No Loss No Profit Plant of NTPC. Since then operating performance of NTPC has been considerably above the national average. The availability factor for coal stations has increased from 85.03 % in 1997-98 to 90.09 % in 2006-07, which compares favorably with international standards. The PLF has increased from 75.2% in1997-98 to 89.4% during the year 2006-07 which is the highest since the inception of NTPC.

Badarpur thermal power station started with a single 95 mw unit. There were 2 more units(95MWeach) installedin next2 consecutiveyears.Nowit hastotalfiveunitswith total capacityof 720MW. Ownership of BTPS was transferred to NTPC with effect from 01.06.2006 through GOIs Gazette Notification .

The power is supplied to a 220 KV network that is a part of the northern grid. The ten circuits through which the power is evacuated from the plant are:

1. Mehrauli

2. Okhla

3. Ballabgarh

4. Indraprastha

5. UP (Noida)

6. Jaipur

Badarpur thermal power station started working in 1973 with a single 95 mw unit. Therewere 2 more units (95 MW each) installed in next 2 consecutive years. Now

it has total fiveunits with total capacity of 720 MW. Ownership of BTPS was transferred to NTPC witheffect from 01.06.2006 through GOIs Gazette Notification .Given below are the details of unit with the year they are installed.

It supplies power to Delhi city. It is one of the oldest plant in operation. Its 100 MW units capacity have been reduced to 95 MW. These units have indirectly fired boiler, while 210 MW units have directly fired boiler. All the turbines are of Russian Design. Both turbine and boilers have been supplied by BHEL. The boiler of Stage-I units are of Czech. design. The boilers of Unit 4 and 5 are designed by combustion engineering (USA). The instrumentation of the stage I units and unit 4 are of The Russian design. Instrumentation of unit5 is provided by M/S Instrumentation Ltd. Kota, is of Kent design.

In 1978 the management of the plant was transferred to NTPC, from CEA. The performance of the plant increased significantly, and steadily after take over by NTPC till 2006, but now the plant is facing various issues.

Being an old plant, Badarpur Thermal Power Station (BTPS) has little automation. Its performance is deteriorating due to various reasons, like aging, poor quantity and quality of cooling water etc. It receive cooling water from Agra Canal, which is an irrigation canal from Yamuna river. Due to rising water pollution, the water of Yamuna is highly polluted. This polluted water when goes into condenser, adversely affect life of condenser tubes, resulting in frequent tube leakages. This dirty water from tube leakages, gets mixed into feed water cycle causes numerous problems, like frequent boiler tube leakages, and silica deposition on turbine blades.

Apart from poor quality, the quantity of water supply is also erratic due to lack of co-ordination between NTPC and UP irrigation which manages Agra Canal.

The quality of the coal supplied has degraded considerably. At worst times, there were many unit tripping owing to poor quality. The poor coal quality also put burdens on equipment, like mills and their performance also goes down.The coal for the plant is fetched from far away, that makes the total fuel cost double of coal cost at coalmine. This factor, coupled with low efficiency due to aging and old design makes electricity of the plant costlier.

Address Badarpur, New Delhi – 110044 Telephone (STD – 011) - 26949523 Fax 26949532 Installed Capacity 720 MW Deeated Capacity 705 MW Location NEW DELHI Coal Source Jharia Coal Fields Water Source Agra Canal Benefeciary States Delhi Unit Sizes 395MW

2210MW

Units 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.

INTRODUTION TO THERMAL POWER PLANT

We are well aware that electricity is a form of energy. There are number of methods by which electricity can be produced, but most common method of production of electrical energy is to rotate a conductor in a magnetic field continuously cutting of magnetic lines will cause E.M.F. to be generated at the ends of conductor. If these terminals are connected through load then electricity will start flowing through that conductor.        Now let us see what we are doing in Thermal Power Station for the purpose of production of Electricity. Actually speaking we are doing conversion of energies from form to another form, and our ultimate aim is to get Electrical energy.

 For this purpose the rotation movement is required to rotate the magnetic

field so that it may cut the stationery conductors of the machine. To be more precise this rotational or mechanical energy is derived from a machine to which we call Turbine which is actually capable enough to convert heat energy to rotational energy.

 For obtaining heat energy we have to make use of the chemical energy, to which we call fossil fuel i.e. coal, oil, gas etc. This is achieved in a plant to which we call furnace or sometimes Boiler.

For transportation of heat energy from furnace to turbine inlet, we require a medium and we have chosen water as media. This water is converted into steam in furnace. Quality of steam is always monitored properly process of Electrical generation.

So we see that the rotational movement required to rotate the magnetic field of the electric generator is produced by the steam turbine. The power to the steam turbine is given by steam generator in the form of high pressure and high temperature steam.

The steam after doing work on the turbine shaft is condensed and condensate is pumped back into Boiler as high pressure and low temperature water, by means of Boiler feed pump.

PARTS OF A POWER PLANT

1. Cooling tower 2. Cooling water pump 3. Transmission line (3-phase) 4. Unit transformer (3-phase) 5. Electric generator (3-phase) 6. Low pressure turbine 7. Condensate extraction pump 8. Condenser 9. Intermediate pressure turbine 10. Steam governor valve 11. High pressure turbine12. Deaerator 13. Feed heater 14. Coal conveyor 15. Coal hopper 16. Pulverised fuel mill 17. Boiler drum 18. Ash hopper 19. Super heater 20. Forced draught fan 21. Reheater 22. Air intake 23. Economiser 24. Air preheater 25. Precipitator 26. Induced draught fan 27. Flue Gas

1. Cooling Tower

Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely solely on air to cool the working fluid to near the dry-bulb air temperature. Common applications include cooling the circulating water used in oil refineries, chemical plants, power stations and building cooling. The towers vary in size from small roof-top units to very large hyperboloid structures that can be up to 200 meters tall and 100 meters in diameter, or rectangular structures that can be over 40 meters tall and 80 meters long. Smaller towers are normally factory-built, while larger ones are constructed on site. The absorbed heat is rejected to the atmosphere by the evaporation of some of the cooling water in mechanical forced-draft or induced 22 Draft towers or in natural draft hyperbolic shaped cooling towers as seen at most nuclear power plants.

2. Cooling Water Pump

It pumps the water from the cooling tower which goes to the condenser.

3. Three phase transmission line

Three phase electric power is a common method of electric power transmission. It is a type of polyphase system mainly used to power motors and many other devices. A three phase system uses less conductive material to transmit electric power than equivalent single phase, two phase, or direct current system at the same voltage. In a three phase system, three circuits reach their instantaneous peak values at different times. Taking current in one conductor as the reference, the currents in the other two are delayed in time by one-third and two-third of one cycle .This delay between “phases” has the effect of giving constant power transfer over each cycle of the current and also makes it possible to produce a rotating magnetic field in an electric motor. At the power station, an electric generator converts mechanical power into a set of electric currents, one from each electromagnetic coil or winding of the generator. The current are sinusoidal functions of time, all at the same frequency but offset in time to give different phases. In a three phase system the phases are spaced equally, giving a phase

separation of one-third of one cycle. Generators output at a voltage that ranges from hundreds of volts to 30,000 volts.

4. Unit transformer (3-phase)

At the power station, transformers step-up this voltage to one more suitable for transmission. After numerous further conversions in the transmission and distribution network the power is finally transformed to the standard mains voltage (i.e. the “household” voltage). The power may already have been split into single phase at this point or it may still be three phase. Where the step-down is 3 phase, the output of this transformer is usually star connected with the standard mains voltage being the phase- 23 neutral voltage. Another system commonly seen in North America is to have a delta connected secondary with a center tap on one of the windings supplying the ground and neutral. This allows for 240 V three phase as well as three different single phase voltages( 120 V between two of the phases and neutral , 208 V between the third phase ( or wild leg) and neutral and 240 V between any two phase) to be available from the same supply.

5. Electrical generator

An Electrical generator is a device that converts kinetic energy to electrical energy, generally using electromagnetic induction. The task of converting the electrical energy into mechanical energy is accomplished by using a motor. The source of mechanical energy maybe water falling through the turbine or steam turning a turbine (as is the case with thermal power plants). There are several classifications for modern steam turbines. Steam turbines are used in our entire major coal fired power stations to drive the generators or alternators, which produce electricity. The turbines themselves are driven by steam generated in "boilers “or "steam generators" as they are sometimes called. Electrical power stations use large steam turbines driving electric generators to produce most (about 86%) of the world‟s electricity. These centralized stations are of two types: fossil fuel power plants and nuclear power plants. The turbines used for electric power generation are most often directly coupled to their-generators .As the generators must rotate at constant synchronous speeds according to the frequency of the electric power system, the most common speeds are 3000 r/min

for 50 Hz systems, and 3600 r/min for 60 Hz systems. Most large nuclear sets rotate at half those speeds, and have a 4-pole generator rather than the more common 2-pole one.

6. Low Pressure TurbineEnergy in the steam after it leaves the boiler is converted into rotational energy as it passes through the turbine. The turbine normally consists of several stages with each stages consisting of a stationary blade (or nozzle) and a rotating blade. Stationary blades convert the potential energy of the steam into kinetic energy and direct the flow onto the 24 rotating blades. The rotating blades convert the kinetic energy into impulse and reaction forces, caused by pressure drop, which results in the rotation of the turbine shaft. The turbine shaft is connected to a generator, which produces the electrical energy. Low Pressure Turbine (LPT) consists of 4x2 stages. After passing through Intermediate Pressure Turbine steam is passed through LPT which is made up of two parts- LPC REAR & LPC FRONT. As water gets cooler here it gathers into a HOTWELL placed in lower parts of turbine.

7. Condensation Extraction Pump A Boiler feed water pump is a specific type of pump used to pump water into a steam boiler. The water may be freshly supplied or returning condensation of the steam produced by the boiler. These pumps are normally high pressure units that use suction from a condensate return system and can be of the centrifugal pump type or positive displacement type. Construction and operation: Feed water pumps range in size up to many horsepower and the electric motor is usually separated from the pump body by some form of mechanical coupling. Large industrial condensate pumps may also serve as the feed water pump. In either case, to force the water into the boiler, the pump must generate sufficient pressure to overcome the steam pressure developed by the boiler. This is usually accomplished through the use of a centrifugal pump. Feed water pumps usually run intermittently and are controlled by a float switch or other similar level-sensing device energizing the pump when it detects a lowered liquid level in the boiler. Some pumps contain a two-stage switch. As liquid lowers to the trigger point of the first stage, the pump is activated. If the liquid continues to drop, (perhaps because the pump has failed, its supply has been cut off or exhausted, or its discharge is blocked) the second stage will be triggered. This stage may switch off the boiler equipment

(preventing the boiler from running dry and overheating), trigger an alarm, or both.

8. Condenser

The steam coming out from the Low Pressure Turbine (a little above its boiling pump) is brought into thermal contact with cold water (pumped in from the cooling tower) in the condenser, where it condenses rapidly back into water, creating near Vacuum-like conditions inside the condenser chest.

9. Intermediate Pressure Turbine

Intermediate Pressure Turbine (IPT) consists of 11 stages. When the steam has been passed through HPT it enters into IPT. IPT has two ends named as FRONT & REAR. Steam enters through front end and leaves from Rear end.

10.Steam Governor Valve

Steam locomotives and the steam engines used on ships and stationary applications such as power plants also required feed water pumps. In this situation, though, the pump was often powered using a small steam engine that ran using the steam produced by the boiler a means had to be provided, of course, to put the initial charge of water into the boiler (before steam power was available to operate the steam-powered feed water pump).The pump was often a positive displacement pump that had steam valves and cylinders at one end and feed water cylinders at the other end; no crankshaft was required. In thermal plants, the primary purpose of surface condenser is to condense the exhaust steam from a steam turbine to obtain maximum efficiency and also to convert the turbine exhaust steam into pure water so that it may be reused in the steam generator or boiler as boiler feed water. By condensing the exhaust steam of a turbine at a pressure below atmospheric pressure, the steam pressure drop between the inlet and exhaust of the turbine is increased, which increases the amount heat available for conversion to mechanical power. Most of the heat liberated due to condensation of the exhaust steam is carried away by the cooling medium (water or air) used by the surface condenser. Control valves are valves

used within industrial plants and elsewhere to control operating conditions such as temperature, pressure, flow and liquid level by fully or partially opening or closing in response to signals received from controllers that compares a “set point” to a 26 “process variable” whose value is provided by sensors that monitor changes in such conditions. The opening or closing of control valves is done by means of electrical, hydraulic or pneumatic systems.

11.High Pressure Turbine

Steam coming from Boiler directly feeds into HPT at a temperature of 540°C and at a pressure of 136 kg/cm2. Here it passes through 12 different stages due to which its temperature goes down to 329°C and pressure as 27 kg/cm2. This line is also called as CRH – COLD REHEAT LINE. It is now passed to a REHEATER where its temperature rises to 540°C and called as HRH-HOT REHEATED LINE.

11.Deaerator

A Deaerator is a device for air removal and used to remove dissolved gases (an alternate would be the use of water treatment chemicals) from boiler feed water to make it noncorrosive. A dearator typically includes a vertical domed deaeration section as the deaeration boiler feed water tank. A Steam generating boiler requires that the circulating steam, condensate, and feed water should be devoid of dissolved gases, particularly corrosive ones and dissolved or suspended solids. The gases will give rise to corrosion of the metal. The solids will deposit on the heating surfaces giving rise to localized heating and tube ruptures due to overheating. Under some conditions it may give rise to stress corrosion cracking. Deaerator level and pressure must be controlled by adjusting control valves the level by regulating condensate flow and the pressure by regulating steam flow. If operated properly, most deaerator vendors will guarantee that oxygen in the deaerated water will not exceed 7 ppb by weight (0.005 cm3/L).

12.Feed water heater

A Feed water heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feed water reduces the irreversibility involved in steam generation and therefore improves the thermodynamic efficiency of the system. This reduces plant operating costs and also helps to avoid thermal shock to the boiler 27 metal when the feed water is introduced back into the steam cycle. In a steam power (usually modelled as a modified Rankine cycle), feed water heaters allow the feed water to be brought up to the saturation temperature very gradually. This minimizes the inevitable irreversibility associated with heat transfer to the working fluid (water).

13.Coal conveyor

Coal conveyors are belts which are used to transfer coal from its storage place to Coal Hopper. A belt conveyor consists of two pulleys, with a continuous loop of material- the conveyor Belt – that rotates about them. The pulleys are powered, moving the belt and the material on the belt forward. Conveyor belts are extensively used to transport industrial and agricultural material, such as grain, coal, ores etc.

14.Coal Hopper

Coal Hoppers are the places which are used to feed coal to Fuel Mill. It also has the arrangement of entering Hot Air at 200°C inside it which solves our two purposes:-

1. If our Coal has moisture content then it dries it so that a proper combustion takes place.

2. It raises the temperature of coal so that its temperature is more near to its Ignite Temperature so that combustion is easy.

16. Pulverized Fuel Mill

A pulveriser is a device for grinding coal for combustion in a furnace in a fossil fuel power plant.

17. Boiler drum

Steam Drums are a regular feature of water tube boilers. It is reservoir of water/steam at the top end of the water tubes in the water-tube boiler. They store the steam generated in the water tubes and act as a phase separator for the steam/water mixture. The difference in densities between hot and cold water helps in the accumulation of the “hotter”- water/and saturated –steam into steam drum. Made from high-grade steel (probably 28 stainless) and its working involve temperature of 390°C and pressure well above 350psi (2.4MPa). The separated steam is drawn out from the top section of the drum. Saturated steam is drawn off the top of the drum. The steam will re-enter the furnace in through a super heater, while the saturated water at the bottom of steam drum flows down to the mud-drum /feed water drum by down comer tubes accessories include a safety valve, water level indicator and fuse plug.

18. Ash Hopper

A steam drum is used in the company of a mud-drum/feed water drum which is located at a lower level. So that it acts as a sump for the sludge or sediments which have a tendency to accumulate at the bottom.

19. Super Heater

A Super heater is a device in a steam engine that heats the steam generated by the boiler again increasing its thermal energy. Super heaters increase the efficiency of the steam engine, and were widely adopted. Steam which has been superheated is logically known as superheated steam; non- superheated steam is called saturated steam or wet steam. Super heaters were applied to steam locomotives in quantity from the early 20th century, to most steam vehicles, and also stationary steam engines including power stations.

20. Force Draught Fan

External fans are provided to give sufficient air for combustion. The forced draught fan takes air from the atmosphere and, warms it in the air preheater for better combustion, injects it via the air nozzles on the furnace wall.

21. Reheater

Reheater is a heater which is used to raise the temperature of steam which has fallen from the intermediate pressure turbine.

22. Air Intake

Air is taken from the environment by an air intake tower which is fed to the fuel.

23. Economizers

Economizer, or in the UK economizer, are mechanical devices intended to reduce energy consumption, or to perform another useful function like preheating a fluid. The term economizer is used for other purposes as well-Boiler, power plant, heating, ventilating and air-conditioning. In boilers, economizer are heat exchange devices that heat fluids , usually water, up to but not normally beyond the boiling

point of the fluid. Economizers are so named because they can make use of the enthalpy and improving the boiler‟s efficiency. They are devices fitted to a boiler which save energy by using the exhaust gases from the boiler to preheat the cold water used to fill it (the feed water). Modern day boilers, such as those in cold fired power stations, are still fitted with economizer which is decedents of Green‟s original design. In this context there are turbines before it is pumped to the boilers. A common application of economizer in steam power plants is to capture the waste heat from boiler stack gases (flue gas) and transfer thus it to the boiler feed water thus lowering the needed energy input , in turn reducing the firing rates to accomplish the rated boiler output . Economizer lower stack temperatures which may cause condensation of acidic combustion gases and serious equipment corrosion damage if care is not taken in their design and material selection.

24. Air Preheater

Air preheater is a general term to describe any device designed to heat air before another process (for example, combustion in a boiler). The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas. As a consequence, the flue gases are also sent to the flue gas stack (or chimney) at a lower temperature allowing simplified design of the ducting and the flue gas stack. It also allows control over the temperature of gases leaving the stack.

25. Precipitator

An Electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices, and can easily remove fine particulate matter such as dust and smoke from the air steam. ESPs continue to be excellent devices for control of many industrial particulate emissions, including smoke from electricity-generating utilities (coal and oil fired), salt cake collection from black liquor boilers in pump

mills, and catalyst collection from fluidized bed catalytic crackers from several hundred thousand ACFM in the largest coalfired boiler applications. The original parallel plate-Weighted wire design (described above) has evolved as more efficient (and robust) discharge electrode designs, today focus is on rigid discharge electrodes to which many sharpened spikes are attached , maximizing corona production. Transformer –rectifier systems apply voltages of 50-100 Kilovolts at relatively high current densities. Modern controls minimize sparking and prevent arcing, avoiding damage to the components. Automatic rapping systems and hopper evacuation systems remove the collected particulate matter while on line allowing ESPs to stay in operation for years at a time.

26. Induced Draught Fan

The induced draft fan assists the FD fan by drawing out combustible gases from the furnace, maintaining a slightly negative pressure in the furnace to avoid backfiring through any opening. At the furnace outlet and before the furnace gases are handled by the ID fan, fine dust carried by the outlet gases is removed to avoid atmospheric pollution. This is an environmental limitation prescribed by law, which additionally minimizes erosion of the ID fan.

27. Flue gas stack

A Flue gas stack is a type of chimney, a vertical pipe, channel or similar structure through which combustion product gases called flue gases are exhausted to the outside air. Flue gases are produced when coal, oil, natural gas, wood or any other large combustion 31 device. Flue gas is usually composed of carbon dioxide (CO2) and water vapour as well as nitrogen and excess oxygen remaining from the intake combustion air. It also contains a small percentage of pollutants such as particulates matter, carbon mono oxide, nitrogen oxides and sulphur oxides. The flue gas stacks are often quite tall, up to 400 meters (1300 feet) or more, so as to disperse the exhaust pollutants over a greater area and thereby reduce the concentration of the pollutants to the levels required by government's environmental policies and regulations. The flue gases are exhausted from stoves ovens, fireplaces or other small sources within residential abodes, restaurants, hotels through other stacks which are referred to as chimneys.

VARIOUS CYCLES AT POWER STATION PRIMARY AIR CYCLE

SECONDARY AIR CYCLE

COAL CYLCE

ELECTRICITY CYCLE

FLUE GAS CYCLE

CONDENSATE CYCLE

FEED WATER CYCLE

STEAM CYCLE

PRIMARY AIR CYCLE

P A FAN

COLD AIR DUCT APH

STEAL AIR F AN HOT AIR DUCT

PULVERISER

SECONDRY AIR CYCLE

FD FAN

SCAPH

APH

WIND BOX

BOILER

IGNITER FAN

SCANNER AIR FAN

W

I

N

D

B

O

X

SCANNER COOLING

ELCTRICITY CYCLE

CONDENSATE CYCLE

GENERATOR

UAT UAT

MAIN TRANSFORMER

SWITCH YARD

OUTGOING FEEDER

FEED WATER CYCLE

HOT WELL CONDENSATE PUMPS HEAT EJECTOR GLAND STEAME COOLER WITH EJECTOR LP HEATER 2 LP HEATER 3 LP HEATER 4 DEARETOR BOILER FEED PUMP

STEAM CYCLE

BOILER DRUM

COAL CYCLE

ENVIRONMENT POLICYWhile leading the nation’s power generation league, NTPC has remained

committed to the environment. It continues to take various pro-active measures for protection of the environment and ecology around its projects.

NTPC was the first among power utilities in India to startEnvironment Impact Assessment (EIA) studies and reinforced it with Periodic Environmental Audits.

Enviroment Policy & Management

For NTPC, the journey extends much beyond generating power. Right from its inception, the company had a well defined environment policy. More than just generating power, it is committed to sustainable growth of power.

NTPC has evolved sound environment practices.

National Environment Policy

The Ministry of Environment and Forests and the Ministry of Power and NTPC were involved in preparing the draft Environment Policy (NEP) which was later approved by the Union Cabinet in May 2006.

Since its inception NTPC has been at the forefront of Environment management. 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 the company's pro-active approach to environment, optimum utilisation of equipment, adoption of latest technologies and continual environment improvement. The policy also envisages efficient utilisation of resources, thereby minimising waste, maximising ash utilisation and ensuring a green belt all around the plant for maintaining ecological balance.

Environment Management, Occupational Health and Safety Systems

NTPC has actively gone for adoption of the best international practices on environment, occupational health and safety areas. The organisation has pursued the Environmental Management System (EMS) ISO 14001 and the Occupational Health and Safety Assessment System OHSAS 18001 at its 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 SystemsWhile deciding the appropriate technology for its projects, NTPC integrates many environmental provisions into the plant design. In order to ensure that NTPC complies with all the stipulated environment norms, following state-of-the-art pollution control systems / devices have been installed to control air and water pollution:

• Electrostatic Precipitators

• Flue Gas Stacks

• Low-NOX Burners

• Neutralisation Pits

• Coal Settling Pits / Oil Settling Pits

• DE & DS Systems Cooling Tower

• Ash Dykes & Ash Disposal Systems

• Ash Water Recycling System

• Dry Ash Extraction System (DAES)

• Liquid Waste Treatment Plants & Management System

• Sewage Treatment Plants & Facilities

• Environmental Institutional Set-up

Following are the additional measures taken by NTPC in the area of Environment Management:

• Environment Management During Operation Phase

• Monitoring of Environmental Parameters

• On-Line Data Base Management

• Environment Review

• Upgradation & Retrofitting of Pollution Control Systems

• Resources Conservation

• Waste Management

• Municipal Waste Management

• Hazardous Waste Management

• Bio-Medical Waste Management

• Land Use / Bio-diversity Reclamation of Abandoned Ash Green Belts, Afforestation & Energy Plantations.

BASIC STEPS OF ELECTRICITY GENERATION

The complete and complex process of electricity generation in TPS can be divided into four major cycles for the sake of simplicity. The main systems are discussed in these cycles in a step by step manner and some useful drawings are also enclosed. The four cycles are:

1. Coal Cycle

2. Oil Cycle

3. Air and Flue Gas Cycle

4. Steam Water Cycle

OR

1. Coal to steam.2. Steam to mechanical power.3. Mechanical power to electrical power.

COAL TO ELECTRICITY: BASICS

The simplest of the above four cycles is the coal cycle. In this cycle as explained

earlier crushed coal of about 20mm is transported by conveyor belts to the coal

mill bunkers. From here the coal goes to coal mills through raw coal feeders. In

the coal mills the coal is further pulverized (crushed) to powder form. The

temperature of the coal mills are maintained at 180-200 degree centigrade by a

suitable mixture of hot & cold air.

The air comes from Primary Air fans (P.A FANS) which are 2 in Nos. - A&B. The

outlet duct after combining gets divided into two. One duct goes to the Air

Heaters (A.H- A&B) where primary air is heated by the hot flue gases in a Heat

Exchanger. This duct provides hot air & the other one provides cold primary air. A

suitable mixture of this hot & cold air is fed to the coal mills to maintain their

temperature. This is done to remove moisture of coal. More over this primary air

is also used for transportation of powdered coal from coal mills to the four

corners of the boiler by a set of four pipes. There are six coal mills – A, B, C, D,

E&F and their outlets in the Boiler are at different elevations. The high

Temperature of the primary air does not allow the air coal mixture to choke the

duct from mill to boilers. A portion of the primary air is further pumped to high

pressure and is known as seal air. It is used to protect certain parts of mills like

bearings etc. where powered coal may pose certain problems in the functioning

of the mill. When the air coal mixture enters the boiler it catches fire in the firing

zone and some ash along with clinkers settles down. This is removed periodically

by mixing it with water to make slurry.

Oil Cycle

In the oil cycle the oil is pumped and enters the boiler from four corners at three elevations. Oil guns are used which sprays the oil in atomized form along with steam so that it catches fire instantly. At each elevation and each corner there are separate igniters which ignite the fuel oil. There are flame sensors which sense the flame and send the information to the control roam.

Air & Flue Gas Cycle

                 For the proper combustion to take place in the boiler right amount of Oxygen or air is needed in the boiler. The air is provided to the furnace in two ways - Primary Air & Secondary Air. Primary air is provided by P.A. fans and enters the boiler along with powdered coal from the mills. While the secondary air is pumped through Forced Draft fans better known as F.D Fans which are also two in numbers A&B. The outlet of F.D fans combine and are again divided into two which goes to Steam coiled Air pre heaters (S.C.A.P.H) A&B where its temperature is raised by utilizing the heat of waste steam. Then it goes to Air Pre heater-A&B where secondary air is heated further utilizing the heat of flue gases. The temperature of air is raised to improve the efficiency of the unit & for proper combustion in the furnace. Then this air is fed to the furnace.

From the combustion chamber the fuel gases travel to the upper portion of the boiler and give a portion of heat to the Platen Super Heater. Further up it comes in contact with the Reheater and heats the steam which is inside the tubes of reheater. Then it travels horizontally and comes in contact with Final Super Heater. After imparting the heat to the steam in super heater flue gases go downward to the Economizer to heat the cold water pumped by the Boiler Feed Pumps (B.F.P.) these all are enclosed in the furnace. After leaving the furnace the fuel gases go to the Air Heaters where more heat of the flue gases is extracted to heat primary and secondary air. Then it goes to the Electrostatic Precipitators (E.S.P.) Stage A&B where the suspended ash from the flue gases is removed by passing the fuel gas between charged plates. Then comes the induced draft fan (I.D Fan) which sucks air from E.S.P. and releases it to the atmosphere through chimney. The pressure inside the boiler is kept suitably below the atmospheric pressure with the help of 1.0. Fans so that the flame does not spread out of the openings of boiler and cause

explosion. Further very low pressure in the boiler is also not desirable because it will lead to the quenching of flame.

Steam Water Cycle

The most complex of all the cycles is the steam & water cycle. Steam is the working substance in the turbines in all the thermal and nuclear power plants. As there is very high temperature and pressure inside the boiler, initially water has to be pumped to a very high pressure. Water has also to be heated to a suitably high temperature before putting it inside the boiler so that cold water does not cause any problem. Initially cold water is slightly heated in low pressure heaters. Then it is pumped to a very high pressure of about 200 Kg/Cm2 by boiler feed pumps A & B. After this it is further heated in high pressure heaters by taking the heat from the high pressure steam coming from various auxiliaries and / or turbines. Then this water goes to the economizer where its temperature is further raised by the flue gases.        This hot water then goes to the boiler drum. In the boiler drum there is very high temperature and pressure. It contains a saturated mixture of boiling water and steam which are in equilibrium. The water level in the boiler         is maintained between certain limit. From here relatively cold water goes down to the water header situated at the bottom, due to difference in density. Then this cold water rises gradually in the tubes of the boiler on being heated. The tubes are in the form of water walls. These tubes combine at the top in the hot water header. From here the hot water and steam mixture comes back to the boiler drum completing the small loop.        From the boiler drum hot steam goes to platen super heater situated in the upper portion of the boiler. Here the temperature of the steam is increased.  Then it goes to final super heater. Here its temperature is further increased.

The turbine is a three cylinder machine with high pressure (H.P), intermediate pressure (I.P) & low pressure (L.P) casings taking efficiency into account the .The turbine speed is controlled by hydro dynamic governing system. The three turbines are on the same shaft which is coupled with generator. The generator is equipped with D.C excitation system. The steam from the final super heater comes by main steam line to the H.P turbine. After doing work in the H.P turbine its temperature is reduced. It is sent back to the boiler by cold reheat line to

the reheater. Here its temperature is increased and is sent to the I.P turbine through hot reheat line. After doing work in the I.P turbine steam directly enters L.P turbine.

The pressure of L.P turbine is maintained very low in order to reduce the condensation point of steam. The outlet of L.P turbine is connected with condenser. In the condenser, arrangement is made to cool the steam to water. This is done by using cold water which is made to flow in tubes. This secondary water which is not very pure gains heat from steam & becomes hot. This secondary water is sent to the cooling towers to cool it down so that it may be reused for cooling. The water thus formed in the condenser is sucked by condensate water pumps (C.W. PUMPS) and is sent to deaerator. A suitable water level is maintained in the hot well of condenser.

Water or steam leakages from the system are compensated by the make up water, line from storage tanks which are connected to the condenser. The pressure in side condenser is automatically maintained less then atmospheric pressure and large volume of steam condense here to form small volume of water. In the deaerator the water is sprayed to small droplets & the air dissolved in it is removed so that it may not cause trouble at high temperatures in the Boiler. Moreover, the water level which is maintained constant in the deaerator also acts as a constant water head for the boiler feed pumps. Water from deaerator goes to the Boiler feed pumps after the heated by L.P. Heaters. Thus the water cycle in the boiler is completed and water is ready for another new cycle. This is a continuous and repetitive process.

BASIC POWER PLANT CYCLE

RANKINE CYCLE

A Rankine cycle describes a model of the operation of steam heat engines most commonlyfound in power generation plants. Common heat sources for power plants using the Rankinecycle are coal, natural gas, oil, and nuclear.The Rankine cycle is sometimes referred to as a practical Carnot cycle as, when an efficientturbine is used, the TS diagram will begin to resemble the Carnot cycle. The main differenceis that a pump is used to pressurize liquid instead of gas. This requires about 1/100th (1%) asmuch 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 565°C (the creep limit of stainless steel) andcondenser 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. Thislow turbine entry temperature (compared with a gas turbine) is why the Rankine cycle isoften 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. Thewater vapor and entrained droplets often seen billowing from power stations is generated bythe cooling systems (not from the closed loop Rankine power cycle) and represents the wasteheat that could not be converted to useful work. Note that cooling towers operate using the latent heat of vaporization of the cooling fluid.The white billowing clouds that form in cooling tower operation are the result of water droplets which are entrained in the cooling tower airflow it is not,

as commonly thought,steam. While many substances could be used in the Rankine cycle, water is usually the fluidof 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 compressionstage relatively little work is required to drive the pump, due to the working fluid being in itsliquid phase at this point. By condensing the fluid to liquid, the work required by the pumpwill only consume approximately 1% to 3% of the turbine power and so give a much higher efficiency for a real cycle.The benefit of this is lost somewhat due to the lower heat addition temperature. Gas turbines,for instance, have turbine entry temperatures approaching 1500°C. Nonetheless, theefficiencies of steam cycles and gas turbines are fairly well matched.

The Rankine cycle is a heat engine with a vapour power cycle. The common working fluid is water. The cycle consists of four processes as shown in

1 to 2: Isentropic expansion (Steam turbine)1 An isentropic process, in which the entropy of working fluid remains constant.

2 to 3: Isobaric heat rejection (Condenser) An isobaric process, in which the pressure of working fluid remains constant.

3 to 4: Isentropic compression (Pump) During the isentropic compression process, external work is done on the working fluid by means of pumping operation.

4 to 1: Isobaric heat supply (Steam Generator or Boiler) During this process, the heat from the high temperature source is added to the working fluid to convert it into superheated steam.

According to the T-s diagram shown in Figure1(b), the work output W1 during isentropic expansion of steam in the turbine, and the work input W2 during isentropic compression of working fluid in the pump are:

W1 = m (h1 – h2) (1.1)and

W2 = m (h4 – h3) (1.2) Where m is the mass flow of the cycle and h1, h2, h3, h4 is enthalpy. Heat supplied to the cycle (steam generator or boiler) Q1, and heat rejected from the cycle (condenser) Q2, are:

Q1 = m (h1-h4) (1.3)and

Q2 = m (h2-h3) (1.4)The net work output of the cycle is:

W = W1 – W2 (1.5)The efficiency of the Rankine cycle is:

η = W/Q1 (1.6)

Q1 – Q2 – W = 0 (1.7)

And the thermal efficiency of the cycle will be:

η = W/Q1 = 1 – T2 / T1 (1.8)

Due to mechanical friction and other irreversibility’s, no cycle can achieve this efficiency. The gross work output of the cycle, i.e. the work done by the system is:

Wg = W4-1 + W1-2 (1.9)

T-S DIAGRAM OF RANKINE CYCLE

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.

Thermal power plant based on a Rankine cycle

In a simple Rankine cycle, steam is used as the working fluid, generated from saturated liquid water (feed-water). This saturated steam flows through the turbine, where its internal energy is converted into mechanical work to run an electricity generating system. All the energy from steam cannot be utilized for running the generating system because of losses due to friction, viscosity, bend-on-blade etc. Most of the heat energy is rejected in the steam condenser. The feed water brings the condensed water back to the boiler.

BOILER MANTENANCE DEPARTMENT

BOILER THEORY

Boiler systems are classified in a variety of ways. They can be classified according to the end use, such as foe heating, power generation or process requirements. Or they can be classified according to pressure, materials of construction, size tube contents (for example, waterside or fireside), firing, heat source or circulation. Boilers are also distinguished by their method of fabrication. Accordingly, a boiler can be pack aged or field erected. Sometimes boilers are classified by their heat source. For example, they are often referred to as oil-fired, gas-fired, coal-fired, or solid fuel –fired boilers.

TYPES OF BOILER

Fire tube boilers : Fire tube boilers consist of a series of straight tubes that are housed inside a water-filled outer shell. The tubes are arranged so that hot combustion gases flow through the tubes. As the hot gases flow through the tubes, they heat the water surrounding the tubes. The water is confined by the outer shell of boiler. To avoid the need for a thick outer shell fire tube boilers are used for lower pressure applications. Generally, the heat input capacities for fire tube boilers are limited to 50 mbtu per hour or less, but in recent years the size of firetube boilers has increased.

Most modern fire tube boilers have cylindrical outer shells with a small round combustion chamber located inside the bottom of the shell. Depending on the construction details, these boilers have tubes configured in either one, two, three, or four pass arrangements. Because the design of fire tube boilers is simple, they are easy to construct in a shop and can be shipped fully assembled as a package unit.

These boilers contain long steel tubes through which the hot gases from the furnace pass and around which the hot gases from the furnace pass and around which the water circulates. Fire tube boilers typically have a lower initial cost, are more fuel efficient and are easier to operate, but they are limited generally to capacities of 25 tonnes per hour and pressures of 17.5 kg per cm2.

Water tube boilers:

Water tube boilers are designed to circulate hot combustion gases around the outside of a large number of water filled tubes. The tubes extend between an upper header, called a steam drum, and one or more lower headers or drums. In the older designs, the tubes were either straight or bent into simple shapes. Newer boilers have tubes with complex and diverse bends. Because the pressure is confined inside the tubes, water tube boilers can be fabricated in larger sizes and used for higher-pressure applications.Small water tube boilers, which have one and sometimes two burners, are generally fabricated and supplied as packaged units. Because of their size and weight, large water tube boilers are often fabricated in pieces and assembled in the field.

In water tube or “water in tube” boilers, the conditions are reversed with the water passing through the tubes and the hot gases passing outside the tubes. These boilers can be of a single- or multiple-drum type. They can be built to any steam capacity and pressures, and have higher efficiencies than fire tube boilers.

Almost any solid, liquid or gaseous fuel can be burnt in a water tube boiler. The common fuels are coal, oil, natural gas, biomass and solid fuels such as municipal solid waste (MSW), tire-derived fuel (TDF) and RDF. Designs of water tube boilers that burn these fuels can be significantly different.

Coal-fired water tube boilers are classified into three major categories: stoker fired units, PC fired units and FBC boilers.

Package water tube boilers come in three basic designs: A, D and O type. The names are derived from the general shapes of the tube and drum arrangements. All have steam drums for the separation of the steam from the water, and one or more mud drums for the removal of sludge. Fuel oil-fired and natural gas-fired water tube package boilers are subdivided into three classes based on the geometry of the tubes.

The “A” design has two small lower drums and a larger upper drum for steam-water separation. In the “D” design, which is the most common, the unit has two drums and a large-volume combustion chamber. The orientation of the tubes in a

“D” boiler creates either a left or right-handed configuration. For the “O” design, the boiler tube configuration exposes the least amount of tube surface to radiant heat. Rental units are often “O” boilers because their symmetry is a benefit in transportation

“D” Type boilers:

“This design has the most flexible design. They have a single steam drum and a single mud drum, vertically aligned. The boiler tubes extend to one side of each drum. “D” type boilers generally have more tube surface exposed to the radiant heat than do other designs. “Package boilers” as opposed to “field-erected” units generally have significantly shorter fireboxes and frequently have very high heat transfer rates (250,000 btu per hour per sq foot). For this reason it is important to ensure high-quality boiler feedwater and to chemically treat the systems properly. Maintenance of burners and diffuser plates to minimize the potential for flame impingement is critical.

“A” type boilers:

This design is more susceptible to tube starvation if bottom blows are not performed properly because “A” type boilers have two mud drums symmetrically below the steam drum. Drums are each smaller than the single mud drums of the “D” or “O” type boilers. Bottom blows should not be undertaken at more than 80 per cent of the rated steam load in these boilers. Bottom blow refers to the required regular blow down from the boiler mud drums to remove sludge and suspended solids.

AUXILIARIES OF THE BOILER

FURNACE

Furnace is primary part of boiler where the chemical energy of the fuel is

converted tothermal energy by combustion. Furnace is designed for efficient and

completecombustion. Major factors that assist for efficient combustion are

amount of fuel inside the furnace and turbulence, which causes rapid mixing

between fuel and air. Inmodern 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 thewater from the steam generated in the furnace walls and to reduce the dissolved solidcontents of the steam below the prescribed limit of 1 ppm and also take care of thesudden 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 thecorrugated plates. Since the velocity is relatively low this water does not get pickedup 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 finalstage of the separation.

The water enters the boiler through a section in the convection pass called theeconomizer. From the economizer it passes to the steam drum. Once the water entersthe 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 turnedinto 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.

Once water inside the boiler or steam generator, the process of adding the latent heatof vaporization or enthalpy is underway. The boiler transfers energy to the water bythe chemical reaction of burning some type of fuel.

Air Preheater ( Tubular Type)

• Waste heat recovery device in which the air to on its way to the furnace is heated utilizing the heat of exhaust gases

• The function of air pre-heater is to increase the temperature of air before enters the furnace.

• It is generally placed after the economizer; so the flue gases passes through the economizer and then to the air preheater.

• An air-preheater consists of plates or tubes with hot gases on one side and air on the other.

• It preheats the to be supplied to the furnace. Preheated air accelerates the combustion and facilitates the burning of coal.

Degree of Preheating depends on:

(i) Type of fuel,

(ii) Type of fuel burning equipment, and

(iii) Rating at which the boiler and furnaces are operated.

There are three types of air preheaters :

1. Tubular type

2. Plate type

3. Storage type.

Economizer

Function:

It is a device in which the waste heat of the flue gases is utilsed for heating the feed water.

• To recover some of the heat being carried over by exhaust gases.This heat is used to raise the temperature of feed water supplied to the boiler.

Advantages :

i) The temperature range between various parts of the boiler is reduced which results in reduction of stresses due to unequal expansion.

ii) If the boiler is fed with cold water it may result in chilling the boiler metal.

iii) Evaporative capacity of the boiler is increased.

iv) Overall efficiency of the plant is increased.

Super heater

• The function of super heater is to increase the temperature of the steam above its saturation point.• To superheat the steam generated by boiler.• Super heaters are heat exchangers in which heat is transferred to the saturated steam to increase its temperature.• Superheated steam has the following

Advantages :i) Steam consumption of the engine or turbine is reduced.ii) Losses due to condensation in the cylinders and the steam pipes are reduced.iii)Erosion of turbine blade is eliminated.iv) Efficiency of steam plant is increased.

Feed Pump

• The feed pump is a pump which is used to deliver feed water to the boiler.

• Double feed pump is commonly employed for medium size boilers.

• The reciprocating pump are continuously run by steam from the same boiler to which water is to be fed.

• Rotary feed pumps are of centrifugal type and are commonly run either by a small steam turbine or by an electric motor.

AIR PREHEATER

An air preheater (APH) is a general term used to describe any device designed to heat air before another process (for example, combustion in a boiler) with the primary objective of increasing the thermal efficiency of the process.The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas. As a consequence, the flue gases are also conveyed to the flue gas stack (or chimney) at a lower temperature, allowing simplified design of the conveyance system and the flue gas stack. It also allows control over the temperature of gases leaving the stack (to meet emissions regulations).

PULVERISER

A pulverizer or grinder is a mechanical device for the grinding of many different types of materials. For example, a pulverizer mill is used to pulverize coal for combustion in the steam-generating furnaces of fossil fuel power plants.

PLANT AUXILIARY MAINTENANCE

WATER CIRCULATION SYSTEM

Water must flow through the heat absorption surface of the boiler in order that it beevaporated into steam. In drum type units (natural and controlled circulation), the water iscirculated from the drum through the generating circuits and then back to the drum where thesteam is separated and directed to the super heater. The water leaves the drum through thedown corners at a temperature slightly below the saturation temperature. The flow throughthe 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 theweight of the steam in the mixture leaving the heat absorption surface is called circulationration ratio.

TYPES OF BOILER CIRCULATING SYSTEM

Natural circulation system Controlled circulation system Combined circulation system

NATURAL CIRCULATING SYSTEM

Water delivered to steam generator from feed water is at a temperature well below thesaturation 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 andthus joins the circulation system. Water entering the drum flows through the down corner andenters ring heater at the bottom. In the water walls, a part of the water is converted to steamand the

mixture flows back to the drum. In the drum, the steam is separated, and sent tosuperheater 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. Thusthe hydrostatic head available will not be able to overcome the frictional resistance for a flow corresponding to minimum requirement of cooling of water wall tubes.

ASH HANDLING PLANT

HYDRAULIC ASH HANDLING SYSTEM

The hydraulic system carried the ash with the flow of water with high velocity velocity through a channel and finally dumps into 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 astream of water flowing into the sump. The ash is carried along with the water and they areseparated at the sump. In the high velocity system a jet of water is sprayed to quench the hotash. 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 fuelsystem can also be quenched and washed by using the high velocity system. The advantagesof this system are that its clean, large ash handling capacity, considerable distance can betraversed, 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 bagfilters (or sometimes both) located at the outlet of the furnace and before the induced draftfan. The fly ash is periodically removed from the collection hoppers below the precipitatorsor 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 ashfrom the bottom of the furnace. This hopper is always filled with water to quench the ash andclinkers falling down from the furnace. Some arrangement is included to crush the clinkersand for conveying the crushed clinkers and bottom ash to a storage site.

WATER PLANT TREATMENT

As the types of boiler are not alike their working pressure and operating conditions vary andso 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 µdemineralized 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.

REFERENCE

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