GURU NANAK DEV THERMAL PLANT BATHINDA

By

NAME – SANJU SINGH Regd.No – 008045300156 Branch – Mech.Engg.

Submitted To.The department of Mech.Engg.

Of

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GURU NANAK DEV THERMAL PLANT BATHINDA

Acknowledgement

We cannot achieve any thing worth while in the field of technical education until or unless the theoretical education acquired in the classroom is effectively wedded to its practical approach that is taking place in the modern industries and research institute. Although an engineer can only be successful through sheer hand work, but the contribution of his teachers and all those who have been helpful cannot be overlooked. I express my deep sense of gratitude to Er. T.N. Bansal, Sr.additional superintendent Engineer technical training cell. Guru Nanak Dev Thermal Plant, Bathinda for providing me requisite facilities and cordial atmosphere during my training period. I am also thankful to Er. Ravinder pal singh, J.E. T.T.cell for his kind co-operation.

I also express my sincere thanks to all the other engineers and staff members of the plant for their co-operation and valuable guidance for completion of the project.

I would also like to thank my training in charge Dr.S.C. Sharma, Head of training and placement department. Without whose guidance I would not be able to complete my training. I pay my due regards to all other teachers for their help.

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INTRODUCTION

A Thermal Power Station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine

which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser; this is known as a Rankine cycle. The

greatest variation in the design of thermal power stations is due to the different fuel sources. Some prefer to use the term energy center because

such facilities convert forms of heat energy into electrical energy. However, power plant is the most common term in the United States, while power station prevails in many Commonwealth countries and especially in the

United Kingdom.

Almost all coal, nuclear, geothermal, solar thermal electric, and waste incineration plants, as well as many natural gas power plants are thermal. Natural gas is frequently combusted in gas turbines as well as boilers. The waste heat from a gas turbine can be used to raise steam, in a combined

cycle plant that improves overall efficiency.

Such power stations are most usually constructed on a very large scale and designed for continuous operation.

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HISTORY

Reciprocating steam engines have been used for mechanical power sources since the 18th Century, with notable improvements being made by James Watt. The very first commercial

central electrical generating stations in New York and London, in 1882, also used reciprocating steam engines. As generator sizes increased, eventually turbines took over due

to higher efficiency and lower cost of construction. By the 1920s any central station larger than a few thousand kilowatts would use a turbine prime mover.

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WORKING OF THERMAL POWER PLANT

WORKING DISCRIPTION

1. Cooling tower 10. Steam governor valve 19. Superheater

2. Cooling water pump 11. High pressure turbine 20. Forced draught fan

3. Transmission line (3-phase) 12. Deaerator 21. Reheater

4. Unit transformer (3-phase) 13. Feed heater 22. Air intake

5. Electric generator (3-phase) 14. Coal conveyor 23. Economiser

6. Low pressure turbine 15. Coal hopper 24. Air preheater

7. Condensate extraction pump 16. Pulverised fuel mill 25. Precipitator

8. Condensor 17. Boiler drum 26. Induced draught fan

9. Intermediate pressure turbine 18. Ash hopper 27. Chimney Stack

Coal is conveyed (14) from an external stack and ground to a very fine powder by large metal spheres in the pulverised fuel mill (16). There it is mixed with preheated air (24) driven by the forced draught fan (20). The hot air-fuel mixture is forced at high pressure into the boiler where it rapidly ignites. Water of a high purity

flows vertically up the tube-lined walls of the boiler, where it turns into steam, and is passed to the boiler drum, where steam is separated from any remaining water. The steam passes through a manifold in the roof of the

drum into the pendant superheater (19) where its temperature and pressure increase rapidly to around 200 bar and 570°C, sufficient to make the tube walls glow a dull red. The steam is piped to the high pressure turbine

(11), the first of a three-stage turbine process.

A steam governor valve (10) allows for both manual control of the turbine and automatic set-point following. The steam is exhausted from the high pressure turbine, and reduced in both pressure and temperature, is

returned to the boiler reheater (21).

The reheated steam is then passed to the intermediate pressure turbine (9), and from there passed directly to the low pressure turbine set (6). The exiting steam, now a little above its boiling point, is brought into thermal

contact with cold water (pumped in from the cooling tower) in the condensor (8), where it condenses rapidly back into water, creating near vacuum-like conditions inside the condensor chest. The condensed water is then

passed by a feed pump (7) through a deaerator (12), and pre-warmed, first in a feed heater (13) powered by

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steam drawn from the high pressure set, and then in the economiser (23), before being returned to the boiler drum. The cooling water from the condensor is sprayed inside a cooling tower (1), creating a highly visible

plume of water vapor, before being pumped back to the condensor (8) in cooling water cycle.

The three turbine sets are sometimes coupled on the same shaft as the three-phase electrical generator (5) which generates an intermediate level voltage (typically 20-25 kV). This is stepped up by the unit transformer (4) to a voltage more suitable for transmission (typically 250-500 kV) and is sent out onto the three-phase transmission

system (3).

Exhaust gas from the boiler is drawn by the induced draft fan (26) through an electrostatic precipitator (25) and is then vented through the chimney stack (27).

BRIEF HISTORY OF THE PLANT

A PENOROMIC VEIW OF G.N.D.T.P.

The foundation stone of this prestigious Thermal Plant comprising four units of 110 MW capacities each was laid on 19th,Nov.,1969 the quincentenary year of the birth of the Great Guru Nanak Dev Ji from whom it gets its present name. the project was completed in two phases at a total cost of about Rs. 115 crores. The first

unit was commissioned in September 1975, March 1978 and in January 1979 respectively. The commissioning

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of these units not only bridged the gap between supply and demand of power in the State but also solved the chronic problem of the low voltage prevailing in the Malwa region.

Each unit of GNDTP Bathinda, when operated at full capacity is capable of generating 26.4 lac units of electricity a day. The coal consumption is about 1500 to 1600 MT per day per unit depending upon the quality of coal. The to all daily coal requirement is about 600 M.T. when all the four units are in operation. The coal is being received from jhrkhand/ chhattisgarh which are more than 1500 KMs away from this power station. The

project is providing direct employment to about 3000 persons (approximate).

The performance of this power plant has been improving year after year and in spite of ageing of the units it is being maintained at an appreciably higher level. G.N.D.T.P. has won laurels at National levels by winning a

number of awards. Further due to reduction in fuel consumption, the plant has been

continuously winning national awards each year since 1992 when the Govt. of India first introduced these awards.

It is a matter of pride that all the four units have successfully completed silver jubilee (25 years) of its operation. At the same time all the units have outlived their designed life. Various equipment of boilers, turbines and other areas have largely dereiorated restricting the load on the units to about 95 MWagain installed capacity of 110 MW. Hence residual life assessment study of the units have been got carried out

through M/s CPRL, Banglore.

Accordingly, Extensive renovation & modernization based on RLA study of all the four units have been planned to be executed in a phased manner to restore rate capacity of the plant, increase efficiency, reduce auxiliary

consumption and extend useful life of the plant by another 15-20 years. Each unit of G.N.D.T.P. Bathinda when operated at full capacity os capable of generating 26.5 lack unit of electricity a day. The coal consumption is

about 1500 to 1600 MT per day per unit depending upon the quality of coal. The total daily coal requirement is about 6500 M. two rakes of 58 wagons each when all the four units are in operation. The coal is being received from Jharkhand / Chattisgarh which are more than 1500 km away from this power station. The

project is providing direct employment to about 3000 persons.

The performance of this power plant has been improving year after and in spite of ageing of the units or is being maintained at an appreciably higher level. GNDTP has won laurels at National level by winning a number

of awards.

Under guidance of PAU Ludhiana, various plants have been grown in ash dyke area to avoid blowing of ash by wind. These shall also help to press ash into a compact layer. A bulldozer has also been pressed into service for

this purpose.

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STEAM GENERATOR

Schematic diagram of typical coal-fired power plant steam generator highlighting the air preheater (APH) location. (For simplicity, any radiant section tubing is not shown.)

The steam generating boiler has to produce steam at the high purity, pressure and temperature required for the steam turbine that drives the electrical generator. The generator includes the economizer, the steam drum, the

chemical dosing equipment, and the furnace with its steam generating tubes and the superheater coils. Necessary safety valves are located at suitable points to avoid excessive boiler pressure. The air and flue gas path equipment include: forced draft (FD) fan, air preheater (APH), boiler furnace, induced draft (ID) fan, fly

ash collectors (electrostatic precipitator or baghouse) and the flue gas stack.

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For units over about 200 MW capacity, redundancy of key components is provided by installing duplicates of the FD fan, APH, fly ash collectors and ID fan with isolating dampers. On some units of about 60 MW, two

boilers per unit may instead be provided.

BOILER FURNACE

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

The water enters the boiler through a section in the convection pass called the economizer. From the economizer it passes to the steam drum. Once the water enters the steam drum it goes down the downcomers to

the lower inlet waterwall headers. From the inlet headers the water rises through the waterwalls and is eventually turned into steam due to the heat being generated by the burners located on the front and rear

waterwalls (typically). As the water is turned into steam/vapor in the waterwalls, the steam/vapor once again enters the steam drum. The steam/vapor is passed through a series of steam and water separators and then dryers inside the steam drum. The steam separators and dryers remove the water droplets from the steam and the cycle

through the waterwalls is repeated. This process is known as natural circulation.

The boiler furnace auxiliary equipment includes coal feed nozzles and igniter guns, soot blowers, water lancing and observation ports (in the furnace walls) for observation of the furnace interior. Furnace explosions due to

any accumulation of combustible gases after a trip-out are avoided by flushing out such gases from the combustion zone before igniting the coal.

The steam drum (as well as the superheater coils and headers) have air vents and drains needed for initial startup. The steam drum has internal devices that removes moisture from the wet steam entering the drum from

the steam generating tubes. The dry steam then flows into the superheater coils.

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Geothermal plants need no boiler since they use naturally occurring steam sources. Heat exchangers may be used where the geothermal steam is very corrosive or contains excessive suspended solids. Nuclear plants also

boil water to raise steam, either directly passing the working steam through the reactor or else using an intermediate heat exchanger.

CONDENSER

The surface condenser is a shell and tube heat exchanger in which cooling water is circulated through the tubes. The exhaust steam from the low pressure turbine enters the shell where it is cooled and converted to condensate

(water) by flowing over the tubes as shown in the adjacent diagram. Such condensers use steam ejectors or rotary motor-driven exhausters for continuous removal of air and gases from the steam side to maintain

vacuum.

For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressure in the condensing steam. Since the condenser temperature can almost always be kept

significantly below 100 oC where the vapor pressure of water is much less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-condensible air into the closed loop must be

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prevented. Plants operating in hot climates may have to reduce output if their source of condenser cooling water becomes warmer; unfortunately this usually coincides with periods of high electrical demand for air

conditioning.

The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through water from a river, lake or ocean

DEAERATOR

A steam generating boiler requires that the boiler feed water should be devoid of air and other dissolved gases, particularly corrosive ones, in order to avoid corrosion of the metal.

Generally, power stations use a deaerator to provide for the removal of air and other dissolved gases from the boiler feedwater. A deaerator typically includes a vertical, domed deaeration section mounted on top of a

horizontal cylindrical vessel which serves as the deaerated boiler feedwater storage tank.

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There are many different designs for a deaerator and the designs will vary from one manufacturer to another. The adjacent diagram depicts a typical conventional trayed deaerator. If operated properly, most deaerator

manufacturers will guarantee that oxygen in the deaerated water will not exceed 7 ppb by weight (0.005 cm³/L).

TURBINE

HISTORY:- The first device that may be classified as a steam turbine was little more than a toy, the classic Aeolipile, described in the 1st century by Hero of Alexandria in Roman Egypt. A thousand years later, a steam

turbine with practical applications was invented in 1551 by Taqi al-Din in Ottoman Egypt, who described it as a prime mover for rotating a spit.Another steam turbine device was created by Italian Giovanni Branca in year

1629. The modern steam turbine was invented in 1884 by the Englishman Charles A. Parsons, whose first model was connected to a dynamo that generated 7.5 kW of electricity. His patent was licensed and the turbine

scaled-up shortly after by an American, George Westinghouse.

A number of other variations of turbines have been developed that work effectively with steam. The de Laval turbine (invented by Gustaf de Laval) accelerated the steam to full speed before running it against a turbine

blade. This was good, because the turbine is simpler, less expensive and does not need to be pressure-proof. It can operate with any pressure of steam. It is also, however, considerably less efficient. The Parson's turbine also

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turned out to be relatively easy to scale-up. Within Parson's lifetime the generating capacity of a unit was scaled-up by about 10,000 times.

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

It has almost completely replaced the reciprocating piston steam engine (invented by Thomas Newcomen and greatly improved by James Watt) primarily because of its greater thermal efficiency and higher power-to-weight ratio. Also, because the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator, about 80% of all electric generation in the world is by use of steam turbines. — it doesn't require a

linkage mechanism to convert reciprocating to rotary motion.

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The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency through the use of multiple stages in the expansion of the steam (as opposed to the one stage in the Watt

engine), which results in a closer approach to the ideal reversible process.

BOILER FEED WATER PUMP

A boiler feedwater pump is a specific type of pump used to pump feedwater into a steam boiler. The water may be freshly supplied or returning condensate produced as a result of the 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

Feedwater 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

feedwater 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.

Feedwater 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. The pump then runs until the

level of liquid in the boiler is substantially increased. Some pumps contain a two-stage switch. As liquid lowers to the trigger point of the first stage, the pump is activated. If the liquid continues to drop (perhaps because the pump has failed, its supply has been cut off or exhausted, or its discharge is blocked), the second stage will be

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triggered. This stage may switch off the boiler equipment (preventing the boiler from running dry and overheating), trigger an alarm, or both.

PULVERIZER

Types of Pulverizers

Ball and Tube Mills

A ball mill is a pulverizer that consists of a horizontal rotating cylinder, up to three diameters in length, containing a charge of tumbling or cascading steel balls, pebbles, or rods.

A tube mill is a revolving cylinder of up to five diameters in length used for fine pulverization of ore, rock, and other such materials; the material, mixed with water, is fed into the chamber from one end, and passes out the

other end as slime.

Ring and Ball Mill

This type of mill consists of two rings separated by a series of large balls. The lower ring rotates, while the upper ring presses down on the balls via a set of spring and adjuster assemblies. The material to be pulverized is

introduced into the center or side of the pulverizer (depending on the design) and is ground as the lower ring rotates causing the balls to orbit between the upper and lower rings. The pulverized material is carried out of the mill by the flow of air moving through it. The size of the pulverized particles released from the grinding section

of the mill is determined by a classifer separator.

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HORIZONTAL BALL DRUM MILL

MPS Mill

Similar to the Ring and Ball Mill, this mill uses large "tires" to crush the coal. These are usually found in utility plants.

Bowl Mill

Similar to the MPS mill, it also uses tires to crush coal. There are two types, a deep bowl mill, and a shallow bowl mill

CONVEYING SYSTEM

A belt conveyor consists of two or more pulleys, with a continuous loop of material - the conveyor belt - that rotates about them. One or both of the pulleys are powered, moving the belt and the material on the belt

forward. The powered pulley is called the drive pulley while the unpowered pulley is called the idler. There are two main industrial classes of belt conveyors; Those in general material handling such as those moving boxes

along inside a factory and bulk material handling such as those used to transport industrial and agricultural materials, such as grain, coal, ores, etc. generally in outdoor locations. Generally companies providing general

material handling type belt conveyors do not provide the conveyors for bulk material handling. In addition there are a number of commercial applications of belt conveyors such as those in grocery stores. The belt consists of one or more layers of material they can be made out of rubber. Many belts in general material handling have two layers. An under layer of material to provide linear strength and shape called a carcass and an over layer

called the cover. The carcass is often a cotton or plastic web or mesh. The cover is often various rubber or plastic compounds specified by use of the belt. Covers can be made from more exotic materials for unusual

applications such as silicone for heat or gum rubber when traction is essential.

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A BELT CONVEYING SYSTEM IN THERMAL POWER PLANT

Material flowing over the belt may be weighed in transit using a beltweigher. Belts with regularly spaced partitions, known as elevator belts, are used for transporting loose materials up steep inclines. Belt Conveyors

are used in self-unloading bulk freighters and in live bottom trucks. Conveyor technology is also used in conveyor transport such as moving sidewalks or escalators, as well as on many manufacturing assembly lines.

Stores often have conveyor belts at the check-out counter to move shopping items.

Ski areas also use conveyor belts to transport skiers up the hill. A wide variety of related conveying machines are available, different as regards principle of operation, means and direction of conveyance, including screw

conveyors, vibrating conveyors, pneumatic conveyors, the moving floor system, which uses reciprocating slats to move cargo, and roller conveyor system, which uses a series of powered rollers to convey boxes or pallets.

The longest belt [conveyor system] in the world is in Western Sahara. It is 100 km long, from the phosphate mines of Bu Craa to the coast south of El-Aaiun. The longest single belt conveyor runs from Meghalaya in India

to Sylhet in Bangladesh. It is 17 miles long and conveys limestone and shale. The Conveyor belt was manufactured in about 300 meter lengths and was joined together and installed on the conveyor at site. The job was carried out by NILOS India Pvt. Ltd. in Chennai India.The Idlers or Rollers for this very special Conveyor was produced and supplied by Kali BMH Systems (P) Ltd, Kumbakonam, India. The Idler Rollers were unique for the project that they were designed to accommodate both Horizontal and Vertial Curves along the terrain.

Conveyors are used as components in automated distribution and warehousing. In combination with computer controlled pallet handling equipment this allows for more efficient retail, wholesale, and manufacturing

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distribution. It is considered a labor saving system that allows large volumes to move rapidly through a process, allowing companies to ship or receive higher volumes with smaller storage space and with less labor expense.

CRUSHER HOUSE

Coal unloaded by the wagon tippler is carried to crusher house through conveyors for crushing. Two nos. hammer type coal crushers are provided which can crush coal to a size of 10 mm. The crushed coal is then supplied to boiler Raw Coal Bunkers. The surplus cursed coal is carried to coal storage area by series of

conveyors. Crushing of coal is an essential requirement for its optimum pulverizing and safe storage.

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CRUSHER HOUSE IN THEMAL POWER PLANT

The crusher house accommodates the discharge ends of the conveyor 4A, 4Breceiveng ends of conveyor 5A, 5B and conveyor 7A and 7B, two crushers. Vibrating feeders and necessary chute work. There are two crushers

each driven by 700H.P. electric motor, 3 phase, 50 cycles and 6.6kV supply. The maximum size of the crushed coal is 10mm.The capacity of each crusher is 500tones/hr. One crusher works at a time and the other is standby. From the crusher the coal can be fed either to the conveyors 5A, 5B or 7A, 7B by adjusting the flap provided for these purpose. There is built in arrangements of bypassing the crusher by which the coal can be fed directly to

the conveyors bypassing crusher

BOILER

It is single drum, balanced draught, natural circulation, reheat type, vertical combustion chamber boiler producing steam @375 tons/hr at 139 Kg/Cm2 pressure. The combustion chamber consists of seamless steel

tube on all its sides through which water circulates and is converted into steam with the combustion of fuel. The temperature inside the furnace where fuel is burnt is of the order of 15000 C. The entire boiler structure is of 42

meter height.

Power plant boilers termed as steam generating unit is a major equipment of any thermal Station. The type of boiler installed at G.N.D.T.P. Bathinda is as follows:-

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WATER TUBE BOILER IN THERMAL POWER PLANT

The water contained in the boiler drums flows through the down corners and through rises back to the drum. The heat energy supplied in the furnace is absorbed by the water walls and water in the circuit is heated up. Then steam due to natural circulation moves up & mixture of water vapour and water is separated by steam

separator and then steam is led to super heater for further heating.

STATION CAPACITY OF BOILER

Manufacturers B.H.E.L.

Maximum continuous rating 375 T/hr.

Super heater outlet pressure 139kg/cm2

Re heater outlet pressure 33.8 kg/cm2

Final water temperature 540oC

Feed water temperature 240oC

Efficiency 88%

Coal consumption per day per unit 1400tons(approximate)

Reheated steam quantity 324T/Hr.

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SR.NO. GENERAL TYPE OF BOILER TYPE OF BOILER AT G.N.D.T.P.

1 Outdoor/indoor boiler Outdoor boiler2 Water tube/fire tube boiler Water tube Boiler

3 Forced draught/balanced draught Balanced draught boiler4 Direct coal fired/indirect coal fired Indirect coal fired5 Dry bottom/wet bottom boiler Dry bottom boiler

6 Single drum boiler/multi drum boile Single drum boiler7 Natural circulation/forced circulatio Natural circulation

GURU NANAK DEV THERMAL PLANT BATHINDA

COOLING TOWERS

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 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 plants and

building cooling. The towers vary in size from small roof-top units to very large hyperboloid structures (as in Image 1) that can be up to 200 metres tall and 100 metres in diameter, or rectangular structures (as in Image 2) that can be over 40 metres tall and 80 metres long. Smaller towers are normally factory-built, while larger ones

are constructed on site.

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COOLING TOWERS

Cooling towers are structures for cooling water or other working medium to near-ambient temperature. With respect to the heat transfer mechanism employed the main types are:

Wet cooling towers operate on the principle of evaporation, (see swamp cooler)

Dry cooling towers operate by heat transmission through a surface that divides the working fluid from ambient air.

In a wet cooling tower the warm water can be cooled to a temperature lower than ambient, if the ambient air is relatively dry. (see dew point)

ith respect to drawing air through the tower are three types of cooling towers:

Natural draft, which utilizes a tall chimney,

Fan assisted natural draft, and

Mechanical draft (or forced draft) which uses power driven fan motors to force or draw air through the tower.

If ambient conditions are right plumes (fog) can be seen rising out of a wet cooling tower. Cooling towers can cause growth of legionella bacteria, and should therefore be regularly checked Diameter of the cooling tower in

Bathinda Thermal Power Plant is about 88 feet and 40 stories high.

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RELAYS

Relay is a device that detects the fault mostly in the high voltage circuits and initiates the operation of the circuit breaker to the high voltage circuits and initiates the operation of the circuit breaker to isolate the defective

section from the rest of the circuit.

Whenever fault occurs on the power system, the relay detects that fault and closes the trio coil circuit. This results in the opening of the circuit breaker, which disconnects the faulty circuit. Thus the relay ensures the

safety of the circuit equipment from damage, which the fault may cause.

Purpose of Protective Relay and Relaying:-

The capital involved in a power system for the generation, transmission and distribution of electrical power is so great that the proper precautions must be taken to ensure that the equipment not, only operates as nearly as

possible to peak efficiency, but also that it is protected from accidents. The normal path of the electric current is from the power source through copper conductors in the generators, transformers and transmission lines to the load and it is confined to this path by insulation. The insulation however may be broken down, either by the

effect of temperature and age or by a physical accident, so that the current then follows an abnormal path generally known as a short circuit or fault. Whenever then occurs the destructive capabilities of the enormous

energy the power system may cause expensive damage to the equipment, severe drop in the voltage and loss of revenue due to interruption of service. Such faults may be made in frequent by good design of the power

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apparatus and lines and the provision of protective devices. Such as surge diverters and

ground fault neutralizers, but a certain number will occur inevitably due to lightening and unforeseen accidental conditions.

The purpose of protective relays and relaying systems is to operate correct circuit breaker so as to disconnect only the equipment from the system as quickly as possible. Thus minimizing the trouble and damage caused by faults when they do occurs. It would be ideal it protection could anticipate and prevent fault but the is obviously

impossible except where the original cause of fault creates some effect category; thus the gas detector relay, used to protect transformers, which operates when the oil level in the conservator pipe of a transformer is

lowered by the accumulation caused by a poor connection or by an incipient breakdown of insulation. With all other equipment it is only possible to mitigate the effects of short circuit by destructive effects of the energy

into the fault may be minimized.

FLUE GAS CIRCUIT

Coal after burning in the boiler forms flue gas which also contain some quantity of ash with it, which is

called fly ash. So flue gases are first made to enter the precipitators for the removal of fly ash. After this flue

gases are led to atmosphere through boiler chimney. It is a tall force concrete structure standing as high as

historic Qutab Minar. These are four in nos. i.e. each unit has one Ferro-concrete against the hot flue gases. A

protective coating of acid resistant paint is supplied outside at 10 meters. As we know that if the temperature of

flue gases reaches 145C or below it the sulphur combines with moisture to form sulphuric acid, so top 10m is

provided with protective coating with protective coating of paint.

The draught used in G.N.D.T.P. is balanced draught. Balance draught means that we use forced draught,

induced draught fan and dr aught due to high height of chimney. There are two induced draught fans of axial

flow type. This fan is placed near chimney and is used to exhaust the flue gases with some ash from boiler

furnace to dust extraction equipment and to chimney. The fan is driven by electric motor through a flexible

coupling and is equipped with remote controlled regulating vanes to maintain it balanced draught condition in

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the furnace. The fan is designed to handle hot flue gases with a small percentage of abrasive particles in the

suspension

The flue gases are finally let off to chimney to atmosphere due to created by I.D. fan. The ash content

disposed off along with the flue gases is allowed with about 3-5%. About 20% of ash falls out in bottom ash

hopper of the boiler and is periodically removed, mechanically. The remainder of the ash is separated by from

flue gases in the mechanical and electrostatic precipitators and disposed as discussed above.

ELECTROSTATIC PRICIPITATOR

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ELECTROSTATIC PRECIPITATOR

Dust extractions from industrial gases become a necessity for environmental reasons. Most of the

plants in India use coal as fuel for generating steam. The exhaust gases contain large amount of

smoke and dust, which are being emitted into atmosphere. This poses a real threat to the mankind

as a dezarting health hazards. Hence it has become necessary to free the exhaust gases from

smoke and dust.

Need For Installation Of New Electrostatic Precipitator at GNDTP Units: -

The electrostatic precipitators installed at GNDTP units are designed to give an emission level of 789 mg/NM3

for a coal having an ash content of not more than 30%. However on actual testing it has been found that

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emission level from ESP’s was about 3.0 mg/M3. The high level of emission is due to the fact that coals burnt in

the boiler have much higher ash content than what boilers are designed for. The pollution control board of

Punjab Govt. has specified an emission level of 380 mg/M3 from chimney. In order to achieve this new

emission level additional ESP’s have been installed at GNDTP Bathinda.

Working Principle: -

The Electrostatic precipitator utilizes electrostatic forces to separate the dust particle form the gas to be

cleaned. The gas is conducted to a chamber containing “Curtains” of vertical steel plates. These curtains divide

the chamber into a number of parallel gas passages. The frames are linked to each other to form a rigid

framework.

The entire framework is held in place by four supports insulators, which insulates it electrically from all parts,

which are grounded.

A high voltage DC is applied between the framework and the ground thereby creating a strong electrical field

between the wires in the framework and the steel curtains. The electrical field becomes strongest near the

surface of the wire, so strong that an electrical discharges. “The Corona” discharge is developed along the

wires. The gas is ionized in the corona discharge and large quantities of positive and negative ions are formed.

The positive wires are immediately attracted towards the negative wires by strength of the field induced. The

negative ions however have to travel the entire space between the electrodes to reach the positive curtains.

On routes towards the steel curtains the ions collide with each other and get charged and also this charge is

transferred to the particles in the gas. The particles thereby become electrically charged and also begin to

travel in the same direction as the ions towards the steel curtains. The electrical force on each particle

becomes much greater than gravitational force. The speed of migration towards the steel curtains is therefore

much greater than the speed of sedimentation in free fall.

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General Description: -

There various parts of the precipitators are divided into two groups: -

Mechanical system comprising of casing, hoppers, gas distribution system, collecting and emitting systems,

rapping mechanism, stairway and galleries.

a. Electrical system comprising of transformer rectifier units with Electronic Controller, Auxiliary Control

Panels, Safety Interlocks and Field Equipment Devices.

1) Precipitator Casing: -

The precipitator casing is an all welded pre-fabricated wall and roof panels. The casing is provided with

inspection doors for entry into the chamber at each field. The doors are of heavy construction with machined

surface to ensure a gas tight seal.

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The roof carries the precipitator’s internals, insulator housings, transformers etc. The casing rests on roller

supports which allows for free thermal expansion of the casing during operating conditions. Galleries and

stairway are provided on the sides of the casing in easy access to rapping motors, inspection doors,

transformers etc. walkways are provided inside EP between fields for inspection and maintenance. The dust is

collected in large quantities on the curtains, the collected electrodes. Due to periodic rapping, the dust falls

into the hopper.

2) Hoppers: -

The hoppers are sized to hold the ash for 8 hrs. collection. Buffer plates provided in each hopper to avoid gas

leakage. Inspection door is provided on the one side of hoper wall. Thermostatically controlled heating

elements are arranged at the bottom portion of the hopper to ensure free flow of ash.

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3) Gas Distribution System: -

The good performance of the precipitators depends on the event distribution of gas over the entire cross-

section of the field. As the gas expands ten-fold while entering the precipitator, guide vanes, splitters and

screens are provided in the inlet funnel to distribute the flue gas evenly over the entire cross section of the EP.

4) Collecting Electrode system: -

The collecting plates are made of 1.6 mm cold rolled mild steel plate and shaped in piece by roll forming. The

collecting plates and shaped in one piece by roll forming. The collecting electrode has unique profile with a

special configuration on its longitudinal edges. This profile is designed to give rigidity and to contain the dust in

quiescent zone free from re-entertainment; collecting plates are provided with hooks at their top edge for

suspension. The hooks engage in slot of the supporting angle. All the collecting plates in arrow are held in

position by a shock bar at the bottom. The shock bars are spaced by guides.

5) Emitting Electrode system: -

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The most essential part of precipitators is emitting electrode system. Four insulators support this, the frames

for holding the emitting electrodes are located centrally between collecting electrodes curtains. The entire

discharge frames are welded to form a rigid box like structure. The emitting electrodes are kept between the

frames.

6) Rapping System: -

Rapping mechanism is provided for collecting and emitting electrodes. Geared motors drive the rapping

mechanism. The rapping system employs tumbling hammers, which are mounted on a horizontal shaft. As the

shaft rotates slowly the hammers which are mounted on a horizontal shaft. As the shaft rotates slowly the

hammers tumble on the shock bar/shock, which transmits blow to the electrodes. One complete revolution of

the rapping shaft will clean the entire field. The rapper programmer decided the frequency of rapping. The

tumbling hammers disposition and the periodicity of the rapping are selected in such a way that less than 2%

of the collecting area is rapped et one time. This avoids re-entertainment of dust and puffing at the stock

outlet.

The rapping shaft of emitting electrodes system is electrical isolated from the geared motor driven by a shaft

insulator. The space around the shaft insulator is continuously heated to avoid condensation.

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7) Insulator

Housing: -

The support

insulator, supporting

the emitting

electrodes system is

housed in insulator housing. The HVDC connection is taken through bushing insulator mounted on the housing

wall.In order to avoid the condensation on the support insulator each insulator is provided with one electrical

heating system elements of one pass are controlled by one thermostat.

Following Are The Modules For The Outgoing Feeders: -

Hopper heater for each field

Support insulator heaters.

Shaft insulator heaters.

Collecting electrode-rapping motor for each field.

Emitting electrode rapping motor for each filed.

The performance of the ESP is influenced by a number of factors many of which may be controllable. It should

be the aim of every operator to maximize the performance by judiciously adjusting the controllable variables.

Cleaning Of Electrodes: -

The performance of the ESP depends on the amount of electrical power absorbed by the system. The highest

collection efficiency is achieved when maximum possible electric power for a given set of operating conditions

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is utilized on the fields. Too thick a dust layer on the collecting plates will lead to drop in the effective voltage,

which consequently reduces the collection efficiency. It also leads to unstable to unstable operating

conditions. Therefore the rapping system of collecting and emitting electrodes should be kept in perfectly

working condition. All the rapping motors have been programmed to achieve the optimum efficiency.

Spark Rate: -

The operating voltage and current keep changing with operating conditions. The secondary current of HVR’s

have been set just below the spark level, so that only few sparks occur during an hour. Spark rate between 5

to 10 sparks per minute is the most favorable limit, as per the practical experience. Too high flash over will not

only result in reduction in useful power and interruption of precipitation process but will cause snapping of

emitting electrodes due to electrical erosion.

How To Control The Spark Rate: -

One number s-pot and one number t-pot have been provided on the front of each electronic controller. The s-

pot controls the drop rate of rise of field current after the spark is over. The operator can control the rate of

spark by adjusting these two pots manually. Both the pots if turned anticlockwise will cause increase in spark

rate.

Ash Hopper Evacuation: -

Improper/incomplete hopper evacuation is a major cause for the precipitator malfunction. If the hopper are

not emptied regularly, the dust will build up to the high tension emitting system causing shot circuiting. Also

the dust can push the internals up causing misalignment of the electrodes. Though the hoppers have been

designed for a storage capacity of 8 hours, under MCR conditions, this provision should be used in case of

emergency. Normally, the hopper should not be regarded as storage as storage as storage space for the

collected ash.

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Oil combustion: -

The combustion of oil used during start up or for stabilization of the flames can have an important impact on

precipitator operation. Un burnt oil, if passed into ESP can deposit on the emitting and collecting electrodes

and deteriorates the electrical condition i.e. reduce the precipitators operating voltage due to high electrical

resistivity and consequently the ESP’s performance is affected adversely. The precipitator performance

remains poor until the oil vaporizes and the ash layer gets rapped off, which usually takes along time.

Air Conditioning Of The ESP’s Control Room: -

The ESP’s control room houses sophisticated electronic controller. The operation of these controllers directly

reflects on precipitator performance. In order to ensure that the controllers are in proper working conditions,

it is essential to maintain a dust free atmosphere with controlled ambient conditions. Therefore, the air

conditioners should be kept in proper working conditions.

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FLUID COUPLING

FLUID COUPLING USED TO CONNECT THE MOTOR AND BELTS :-

1. INTRODUCTION

The PEMBRIL fluid coupling is a simple power transmission unit to couple an electric motor (or

engine) to a machine. It consists of two rotating assemblies only, contained in a casing- one is driven by the

motor and the other is on the driven machine side. The casing is filled with light oil and it is this oil that

transmits the power from the lotor to the machine it is driving.

The fluid coupling greatly improves the performance of squirrel-cage motors. Full load is carried with

an insignificant loss in speed and no loss in torque.

DESCRIPTION

Construction

The construction of the fluid coupling is shown in typical illustration on coming pages.

The main components are:-

INPUT side : impeller and casing

OUTPUT side : runner and shaft

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The impeller, runner and casing are high tensile aluminium alloy casings, and the impeller and the runner

both have a large number of straight radial vanes. The runner shaft is carried in ball and roller bearings in the

casing and impeller. There is no mechanical connection between the impeller and runner.

The amount of oil in the coupling may be varied over a wide range, to give adjustment of acceleration and

overload torques.

A gland seal is fitted between the casing and runner shaft.

2.2 How the fluid coupling works

The impeller, driven by the motor (or engine), and runner, coupled to the driven machine, both have a large

number of straight radial vanes. The impeller behaves like a centrifugal pump, creating an outwardly flowing

stream of oil, which crosses the gap to the runner, which acts as a turbine. The oil stream gives up power as it

flows inwards between the vanes of the runner and, as it returns to the impeller again, the cycle is repeated.

2.3 Characteristics

Typical characteristics of the fluid coupling when used with a direct-on-line started squirrel-cage motor :-

Starting

At the motor switch-on, the fluid coupling has no torque capacity. As the motor accelerates, the coupling torque

remains low. The motor thus starts under light load and runs up to speed quickly, while the torque of the fluid

coupling increases smoothly to start the machine.

Running

Typical coupling torque/output speed characteristics available for bringing the machine up to speed smoothly

and rapidly are shown in figure 2

Note high torques available for starting and accelerating machine, also how accelerating torque and

stalling value can be adjusted simply by varying coupling oil fillings.

2.4 Mounting

This standard arrangement has a resilient driving disc and a multidisc semi-flexible coupling on the output

shaft. The weight of the fluid coupling unit is shared between the shaft of the motor (or engine) and driven

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machine. The resilience of the mounting at each end caters for a certain degrees of misalignment between the

motor and driven shaft.

Note, however, that it is necessary for the lining-up of the motor to the driven machine to be carried out with

care during installation, as, if the machines are appreciably out-of-line, the load on all bearings will be

increased, and the useful life of the whole installation will tend to be shortened.

For the same reason, it is important that any bedplate that is used to support the machines is of sufficiently stiff

construction, to ensure that it will not be distorted excessively if it is pulled down on to as uneven foundation.

2.5 Shaft location

It is recommended that the shaft of the driven machine is provided with end location. Make sure that the

distance between the resilient driving disc and the half-coupling on the shaft of the driven machine is set

accurately during installation to avoid undue bending of the driving disc.

In no case, driving boss face should rest on the shoulder of motor shaft. Ensure gap of minimum 5mm.

2.6 Screw threads

Bolt threads and sizes of hexagon are METRIC to Indian Standard IS: IS1364/IS1367.

3. INSTALLATION

3.1 Mounting of driving boss and output half-coupling

In many cases the driving boss is sent separately to the motor manufacturer for fitting to the motor shaft, and the

output half-coupling is sometimes sent to the makers of the driven machine.

Where a brake is required on the output shaft the brake drum, forming also an output half-coupling, may be part of the

driven machine. In this case the brake must be sent to our factory for jig drilling.

The half-couplings are machined to be a light interference fit on their shafts. Fit rectangular parallel keys, fitting well at

the sides and with a small clearance on the top. The half-couplings should be drawn on to the shafts- on to account

hammered on- and heating in oil first to expand them will help. After fitting the half-couplings, check with a clock gauge

that:

The register in the driving boss for the center spigot of the fluid coupling runs true.

The flange of the half-coupling on the driven machine runs true and that its face is square with the shaft.

In each case total variation in clock gauge readings must not be more than 0.002 in. (0.05 mm). If the

eccentricity is greater than this, the cause must be found and put right- on no account machine the half-coupling

to correct any faults.

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3.2 Fitting of engine crankshaft adapter (engine drives)

Detach the driving disc 18 from the input side of the fluid coupling and bolt it, with the adapter, to the engine crankshaft

flange. After fitting, check with a clock gauge that the register in the adapter for the center spigot of the fluid coupling

runs true.

The total variation in clock gauge readings must not be more than 0.002 in. (0.05 mm). If the eccentricity is greater than

this, the cause must be found and put right- on no account machine the adapter to correct any faults.

3.3 Erection

Detach the driving disc 18 from the input side coupling, and bolt it to the driving boss on the motor shaft, using bolts 20

and self-locking nuts 70.

It is now necessary to put the motor (engine) approximately in line with the input shaft of the driven machine, leaving

the right space for the fluid coupling and multidisc plate assembly in between, as shown by distance ‘X’ in figure.

If the motor shaft is not located endways by own bearings, set it at its magnetic center, as shown by the marking on the

shaft.

Distance ‘X’ for various sizes of fluid couplings is shown in the table (next page). Before going further, first measure the

thickness of the multidisc plate assembly to see that this is the same as the figure given in the table. Sometimes oversize

half-couplings are fitted, where the diameter of the driven machine shaft so demands, and this may mean that the plate

assembly is thicker than that given in the table. If so, add on the difference in thickness to the distance ‘X’ when setting

the position of the motor. Distance ‘X’ should be set to the actual length shown or greater up to 0.020 in.(0.5 mm) in

case of 8 to 11.5 FCU and 0.030 in. (0.8 mm) in case of 12.75 to 20 FCU- never less or it will be difficult to assemble the

multi-disc plate assembly in position later.

Remove protective coating from central spigot and bore of spigot register-petrol is the most suitable solvent.

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Smear the center spigot of the fluid coupling with grease. Lower the fluid coupling between the motor and the driven

machine and enter the center spigot in the register in the driving in the driving boss on the motor shaft. Support the

weight of the fluid coupling temporarily.

Slide the multidisc plate 25 between the two half-couplings, and bolt up, making sure to put in the spherical collars 77

which are fitted under the bolt heads and which are housed in the large holes in the two half-couplings.

Remove the temporary support or slings. Bolt the driving plate to the fluid coupling.

3.4 How to align the drive

1. The fluid coupling itself is a rigid unit, the shaft being fully supported in the ball and roller bearings.

2. The fluid couplings is therefore provided with flexible mountings at input and output ends, so that it can act

the shaft it is driving.

3. In setting up the drive, the shafts of the motor, fluid couplings and driven machine must be brought into one

line.

Normally the driven machine, such as a gearbox, is assumed to be fixed in position and lining up the drive

becomes a matter of bringing the motor shaft into line with the input shaft, using the fluid coupling in between as an

“erection shaft”.

This operation is most easily done in two stages, as follows:

(a) By moving the motor up-and-down and sideways, bring the shaft of the fluid couplings into line with the input shaft of

the driven machine (fig.).Misalignment will be shown by variation in the gap between the two half-couplings when

measured at top, bottom and both sides. Continue moving the motor until variation in the gap at four points comes with

in total tolerance given in following table:

Size Total Tolerance8 to 20 0.004 in (0.10 mm)

23 to 32 0.006 in. (0.15 mm)

36 to 41 0.008 in. (0.20 mm)

(b) The shaft of the fluid coupling now being in line with the shaft of the driven machine, with in the Rquired

limits, the position of the free end of the motor must now be adjusted to bring the deflection of the resilient driving disc

to an acceptable working value. To measure the deflection of the disc, clamp a bar to the driving boss and attach a clock

gauge to the bar with its spindle bearing on the driving bolts. (fig.)

Turn the fluid coupling by hand and note the clock gauge readings. Move the free end of the motor until the

variation in the reading, taken over a complete revolution, is within the total tolerance given in the following table,

showing that the motor shaft is now in line with the fluid coupling shaft.

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The last operation may have disturbed the alignment of the fluid coupling shaft to the driven machine shaft by a

small amount. Therefore check the gap between the two half-couplings again, and make any adjustment necessary by

moving the motor body.

Approved Oils

The following is a list of oils approved by PEMBRIL ENGINEERING PVT. LTD.

Oil Company Grade of Oil

Indian Oil Company Servo system 46

Hindustan Petroleum Enklo 46

Bharat Petroleum Tellus 46

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