INDUSTRIAL TRAINING AT THERMAL POWER PLANT,GANDHINAGAR

Aim of the trining and why we select this company:-

Generally the aim of the any industrial training is to get the practical knowledge about particular field and to take the industrial experience.

By the training one should know the real aspects of the technology and to know how the applications actually used in industry.

My aim for the training is to know about how technology is utilized and how it is become more useful to mankind.

Ans also to gain knowledge which we don’t get in our text books and lectures and to know about duties and engineering ethics.From the training I also got the industrial experience of working and the atmosphere of the industry.

I select this company because Gandhinagar thermal power station is one of the most leading power station in Gujarat.It has total generating capacity of 870 MW.The main vision of the company is to To become one of the most efficient power generating companies globally & being ethically & socially responsive.

And also the subject of power plant engineering we have studied in our fifth semester so after theoritical knowledge I also got the practical knowledge of thermal power station and the response of gandhinagar power station is very good as compared to other industries in which we applied.

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Company profile:-

Gandhinagar power station is one of the most leading power sectors in Gujarat the total generating capacity of this plant is 870 MW.

Sr no.

OUR MISSION:

To generate power by adopting best practices through :-

_ Professional Excellence

_ Transparency

_ Value Addition

_ Highest level of productivity

_ Nation Building

_ Safety, Self Discipline

CORE VALUES:

_ Customer Satisfaction

_ Participative Work Culture

_ Pride of belongingness

_ Excellence

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Date of starting

capacity

1 13 March , 1977 120 MW

2 10 April , 1977 120 MW

2 22 March , 1990 210 MW

4 2o July , 1991 210 MW

5 17 March , 1998 210 MW

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 either drives an electrical generator . After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a rankine cycle.

Power  is energy  per time . The power output or capacity of an electric plant can be expressed in units of megawatts electric (MW).

The electric efficiency of a conventional thermal power station, considered as saleable energy (in MW) produced at the plant busbars as a percent of the heating value of the fuel consumed, is typically 33% to 48% efficient. This efficiency is limited as all heat engines are governed by the laws of thermodynamics  .

The rest of the energy must leave the plant in the form of heat. This waste heat  can go through a condenser  and be disposed of with cooling water  or in cooling towers . If the waste heat is instead utilized for district heating , it is called cogeneration .

Since the efficiency of the plant is fundamentally limited by the ratio of the absolute temperatures of the steam at turbine input and output, efficiency improvements require use of higher temperature, and therefore higher pressure steam is used.

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General technical data of GTPS for 120 mw unit:-

1. Boiler

Type Tangentially fired, balanced draft, natural circulation, radiant reheat, dry bottom with direct fired pulverized coal with coal mill

Capacity 383 tons/hr. At 136 kg/cm 2 and 540 c

Coal mills 2×5 nos.

2. Turbine

Type Horizontal, impulse type,at 538 c and 136 kg/cm 2

Output 1200 mw

Speed 3000 rpm

3. Generator

Capacity 120 mw each

Voltage 13.80 k v

Current 5906 A

4. Transformer

Capacity 140 m v a

Voltage ratio 13.8/220

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5. Other

Chimney height 118.6 m each

Cooling tower height 92 m each

Daily coal consumption 3734 m t

Daily ash disposal 1448 m t

General technical data of GTPS for 210 mw unit:-

6. Boiler

Type Tangentially fired, balanced draft, natural circulation, radiant reheat, dry bottom with direct fired pulverized coal with coal mill

Capacity 690 tons/hr. At 155 kg/cm2 and 540 c

Coal mills 2×6 nos.

7. Turbine

Type Horizontal, impulse type,at 538 c and 147.1 kg/cm2

Output 120 mw

Speed 3000 rpm

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8. Generator

Capacity 120 mw each

Voltage 15.75 kv

Current 9050 A

9. Transformer

Capacity 250 mva

Voltage ratio 15.75/220

10. Other

Chimney height 121 m each

Cooling tower height 120 m each

Daily coal consumption 6534 m t

Daily ash disposal 2530 mt

Line diagram of a thermal power plant:-

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The different components of a thermal power plant are as below:-

1. Drum2. Superheater3. Reheater4. Economiser5. Air-preheater6. Furnace7. Condenser8. Cooling tower9. F.d/I.d fan

10. Steam generator & steam turbine

General description of a line diagaram:-

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The boiler is designed to meet the nominal requirement of 120mw turbo generator set. the unit is designed for maximum continuous rating of 383 ton/hr. Of steam flow at pressure of 135 kg/ cm2 (abs.) and steam temperature of 540.c.

The unit is natural circulation type with complete water cooled furnace, tangentially fired, balanced draught, radiant reheat type, dry bottom with direct fired pulverised coal with bowl mills.

In natural circulation boiler the water flow from drum to down corner and from water wall to drum is established by a force created by difference in specific weight of cold and hot water.

The furnace is arranged for dry ash discharge and is fitted with 20 nos. Of coal burners located at different elevation at each four corners.

The 16 nos. Of oil burners with capacity to maintain mcr (maximum continuous rating) of boiler are also located at different elevation at each four corners sandwich between coal nozzles.

The unit is provided with 5 nos. Of coal mills, four of which are capable to take load upto mcr.

Two nos. Of f.d. (force draught) fans are provided per boiler to provide sufficient air required for proper combustion at mcr.

Two nos. Of i.d. (induced draught) fans are provided for each boiler to maintain the furnace draft at mcr.

R ankine cycle:-

Process 1-2: Water from the condenser at low pressure is pumped into the boiler athigh pressure. This process is reversible adiabatic.

Process 2-3: Water is converted into steam at constant pressure by the addition of heatin the boiler.

Process 3-4: Reversible adiabatic expansion of steam in the steam turbine.

Process 4-1: Constant pressure heat rejection in the condenser to convert condensation water. The steam leaving the boiler may be dry and saturated, wet or superheated. The corresponding T-s diagrams are 1-2-3-4-1; 1-2-3’-4’-1 or 1-2-3”-4”-1.

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Site selection:-

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A few important factors to be considered for the selection of the site for thermal power plants are:-

1. Availability of Coal : The major source of energy which is available in India for thermal power plant is coal. The huge quantity of coal is required for large thermal power stations. A thermal power plant of 400 MW capacity requires 12000 to 13000 tons of coal per day. Therefore, it is necessary to install power station near the coal mines.

2. Ash Disposal Facilities: The ash removal problem has become more serious particularly in India because the coal used for power generation contains large % of ash. The ash handling problem is more serious than coal handling because it comes out in hot condition and it is highly corrosive. Its effects on atmospheric pollution are more serious as the human health is concerned. Therefore, there must be sufficient space to dispose off large quantities of ash.

3. Nature of Land: The selection site for the power plant should have good bearing capacity as it has to withstand the dead load of plant and force transmitted to the foundation due to the machine operation.

4. Availability of Water: The large quantity of water is required for condenser, for disposal of ash and as feed water to the boiler and drinking water for the working staff.

5. Transportation Facility: It is always necessary to have a railway line available near power station for bringing the heavy machinery for installation and for bringing the coal.

6. Public Problems: The proposed site should be far away from the town to avoid the nuisance from smoke, fly-ash and heat discharged from the power plan.

Different parts of boiler with diagram:-

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The main parts of the boiler are:- Boiler drum Furnace Economiser Superheater Air preheater Reheater

Details of different parts:-

Drum:- The boiler drum is made of alloy steel plate.the drum dished ends are provided with

manholes and covers.welded studs are provided for all connections including large bore down corners.

The drum internal consists of an internal feed distribution system.the water in the furnace side walls and the extended side walls absorbs heat.the resulting mixture of water and steam is collected in the outlet headers and discharged into the steam drum through a series of riser tubes.

Steam generated in the front and rear wall is supplied directly to the steam drum where seperation of water and steam take place.

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The boiler water mixes with the incoming feed water.the saturated steam is led to the superheater via the superheater connecting tubes.

Moreover,level controller,level indicator and gauge glasses are fitted with drum.level should be maintained to normal.if level rises,the carry over to turbine increases.if level goes too low,the water walls starve and fail due to overheating.

Two nos. Of safety valves are provided on the drum,one on left hand side and the other on right hand side.the set values of these safety valves are 158 kg/cm2 and 162 kg/cm2.the safety valve when opens can handle full steaming capacity of boiler.

Superheater:-

Superheater Type H.s. In m 2

Stage-1 Low temp. S.h 3220

Stage-2 Platen s.h. 545

Stage-3 Final s.h. 875

Superheater in which no. of tubes are placed inside the shell to super heat the steam and to increase the quality of the steam.

By super heat the steam the efficiency of our plant is incrased because the steam coming out of the superheater is completely dry.

The superheater is composed of four stages or sections a platen section, a pendant section, a rear horizontal section and the steam cooled wall and roof section.

The platen section is located directly above the furnace in front of the furnace arch.it is located in back of the screen wall tubes.

The horizontal section of the superheater is located in the rear vertical gas pass above the economiser.

The steam cooled wall sections form the side, front and rear walls and roof of the vertical gas pass.

Reheater:- Type-pendant Total h.s. In m2- 1925 Control- burner tilt

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The reheater is composed of two stages or sections, the front pendant section the rear pendant section.the front pendant section is located between the rear water wall hanger tubes and superheater platen section.

The rear pendant section is located above the furnace arch between the water cooled screen wall tubes and the rear water wall hanger tubes.

Economiser:- Type- bare tube Total h.s. In m2-2500 No. Of stages – one The purpose of economiser is to preheat the boiler feed water before it is introduced

into the steam drum andd to recover some of the heat from flue gases living the boiler. The economiser is locatd in the boiler rear gas pass below the rear horizontal super heater.

Feed water is supplied to the economiser inlet header via the feed stop and check valves.the feed water flow is upward through the economiser that is in counter flow to the hot flue gases.

Most efficient heat transfer is here accomplished.any difficulty with steam generation within the economiser is eliminated by the upward water flow.

From the outlet header the feed water is led to the drum via the economiser outlet links.it increases efficiency by 1% per 25.c in the temperature.

Air – preheater:- Type-tubular Heating surface-25700 sq.mt No. Of blocks-12

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The tubular air heater is arranged in two seperate stage below the economiser, bottom block and top block.

The air heater is designed such that the flue gases pass through the tubes in the vertical direction, while the air to be heated flows outside the tubes in a direction perpendicular to the direction of the flue gases.

The air used in the pulverisers for transporting the coal and drying it is known as primary air.the air supplied to wind box for burning of the fuel is known as secondary air.

Furnace:- The furnace of boiler is completely water cooled. The furnace is enclosed in a skin

casing which is placed directly behind the furnace tubes. Skin casing is provided with suitable insulation and exterior of furnace is finished off

with casing of ripped Aluminum sheets. The front and rear water walls of the furnaces are tapered at the bottom to form a hopper with suitable manhole door.

The construction of the furnace bottom depends on fuel and ash conditions. Bottom designs most commonly used for coal fired units are of the open hooper type.

Often referred as the dry bottom type. For gaseous and oil fuels, closed bottoms are generally utilized.

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In the bottom type construction two furnace water walls, slope down towards the centre of the furnace of from the inclined sides of the bottom.

Ash and/ or slag from the furnace is discharged through the bottom opening into the ash hopper directly below it.

Depending on the height of the furnace six to fourteen inches clearance between the furnace and ash hopper is allowed for downward expansion of the furnace walls.

Leakage of air at this point is prevented by either a water seal arrangement or a mechanical seal (expansion joint).

The primary air from the discharge of f.d. Fan passes through air preheater and hot air for combustion from air preheater is led to common wind box located on the side of the furnace.

2 nos. Of steam coal air preheater are (scaph) are provided on discharge side of f.d. Fans before enters to a.p.h.

In order to ensure reliable and continuous operation ample soot blowing equipments are provided.

Condenser:-

Working principal:-

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.

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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 °c where the vapour pressure  of water is much less than atmospheric pressure, the condenser generally works under vacuum . Thus leaks of non -condensable air into the closed loop must be 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.

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Deaerator:- Diagram of boiler feed water deaerator (with vertical, domed aeration

section and horizontal water storage section is shown below.

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 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.

There are many different designs for a deaerator and the designs will vary from one manufacturer to another.

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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).

Cooling tower:- Cooling tower provides cold water in order to condense the steam.the cold water

which exchanges the heat from steam becomes hot.

Now a days hyperbolic cooling towers are widely used due to its efficiency, simple operation, no requirement of i.d. Fans & robust construction.

The hot water is then carried from the condenser to the cooling tower at a certain rate in order to cool it.

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From that height it is allowed to fall down against the direction of the cold air draft.this draft may induce naturally by pressure difference principle and it can be produced artistically by using the i.d. Fan.

As there is no requirement of any fan in hyperboplic cooling tower the operation cost is low & operation is very simple.

The tower is shown in figure which is used.

Steam turbine:-

The schematic diagram of a turbine is shown in figure.

There are three stages in the turbine operation which are-

1. High pressure stage2. Intermediate pressure stage3. Low pressure stage

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The steam turbine-driven generators  have auxiliary systems enabling them to work satisfactorily and safely. The steam turbine generator being rotating equipment generally has a heavy, large diameter shaft. The shaft therefore requires not only supports but also has to be kept in position while running.

In other words turbine is the steady flow machine in which steam enters in the high pressure turbine through fixed blades.

They are one types of nozzle with very high pressure of 139 kg/cm2 and temperature of 540 .c.

The steam passing through the i.p. Turine blades.as a result of its pressure and temperarure drops so before admitting the same steam to i.p. Turbine.

It is again heated to the required temperature by passing it through the reheater, now the steam have temperarure of 540 .c and pressure of 32.1 kg/cm2 is fed to i.p. Turbine.

Then the steam is directly fed to the l.p turbine where steam has temperarure of 218.c.then the steam is led to the condenser.

To minimise the frictional resistance to the rotation, the shaft has a number of bearings . The bearing shells, in which the shaft rotates, are lined with a low friction material like babitt metal .

Oil lubrication is provided to further reduce the friction between shaft and bearing surface and to limit the heat generated.

The drop in pressure across the turbine blade is converted into mechanical work, thereby which the rotor of turbine rotates at a speed of 3000 rpm continuously.

To achieve the maximum efficiency the pressure of the steam at the outlet of the turbine shoud be much as possible.

Generator:- Generator is the electricity generating unit in power plants.it is two poles cylindrical rotor

type, which is driven by directly coupled to steam turbine. In generator three phase a.c. Voltage is generated at standard frequency of 50 hz. The stator core consists of high quality silicon iron laminations each comprising a

number of punched segments which fit between accurately spaced key bars inside the yoke.

The individual segment is insulated from one another to prevent the circulation of eddy current.

It has two windings.one is the stator winding is of the volute type comprising short pitched half coils arranged in two layers and brazed together.

The another one is the rotor winding which consists of straps of high conductivity silver bearing copper each slotted at intervals and grooved along and across one face in the end winding parts.

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Cooling is done by generally hydrogen gas which enters each ends of the rotor through opening in the end discs,passes into peripheral, axial and redial ventilation ducts and is discharged through the generator and coolers.

It has the capacity of generating 110 mw power at a voltage of 1 kv.it rotates at a speed of 3000 rpm.the excitation voltage varies from 300 to 490 v dc according to load.this is done by auto voltage regulator.

Principal and operation:- The basic principle used here is to convert the chemical energy of the coal into the

electrical energy of the generator.these can be shown in the block diagram below.

By this turns rotor of the generator rotates.thus magnetic flux lines of the generator are cut down and emf is produced.

This means conversion of chemical energy of coal to form steam, kinetic energy of steam to run shaft, mechanical energy of steam to drive turbine and finally to get conversion to electrical energy of generator takes place.

Energy conversation diagram:-

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COAL

PULVERISER

BOILER

TURBINE

GENERATOR

Chemical energy of coal

Kinetic energy of steam

Mechanical energy of turbine

Electrical energy of generator

The differene cycles takes place in this operation are:- Coal cycle Air and flue gas cycle Steam cycle Condensation cycle Feed water cycle Ash cycle

Coal cycle:-

The coal from the coal yard is crushed sent by conveyer belts to coal bunkers and then pulveriser.

Primary air picks this coal and takes it to the furnace where it is combusted. This coal with help of the secondary air burns completely. For effective burning the coal is crushed to increase its surface area By increasing

surface area of coal we can get more efficient combustion which is help us to increase efficiency.

For pulverising of coal bowl mills are used which is shown below.

Unloading and processing of coal:-

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Coal is primarily used as a solid fuel  to produce electricity and heat through combustion. World coal consumption was about 6,743,786,000 short tons  in 2006[10]  and is expected to increase 48% to 9.98 billion short tons by 2030.[11]  china  produced 2.38 billion tons in 2006. India  produced about 447.3 million tons in 2006. 68.7%  of china's electricity comes from coal. The usa consumes about 14% of the world total, using 90% of it for generation of electricity.

When coal is used for electricity generation , it is usually pulverized and then combusted (burned) in a furnace  with a boiler .

The furnace heat converts boiler water to steam , which is then used to spin turbines  which turn generators  and create electricity. The thermodynamic efficiency  of this process has been improved over time. "standard" steam turbines have topped out with some of the most advanced reaching about 35% thermodynamic efficiency for the entire process, although newer combined cycle plants can reach efficiencies as high as 58%. Increasing the combustion temperature can boost this efficiency even further. 

The emergence of the supercritical turbine  concept envisions running a boiler at extremely high temperatures and pressures with projected efficiencies of 46%, with further theorized increases in temperature and pressure perhaps resulting in even higher efficiencies.

Other efficient ways to use coal are combined cycle power plants , combined heat and power cogeneration , and an mhd topping cycle .

Approximately 40% of the world electricity production uses coal. The total known deposits recoverable by current technologies, including highly polluting, low energy content types of coal (i.e., lignite, bituminous), is sufficient for many years. However, consumption is increasing and maximal production could be reached  within decades (see world coal reserves , below).

A more energy-efficient way of using coal for electricity production would be via solid-oxide fuel cells  or molten-carbonate fuel cells  (or any oxygen ion transport based fuel cells that do not discriminate between fuels, as long as they consume oxygen), which would be able to get 60%–85% combined efficiency (direct electricity + waste heat steam turbine).[citation needed ]currently these fuel cell technologies can only process gaseous fuels, and they are also sensitive to sulfur poisoning, issues which would first have to be worked out before large scale commercial success is possible with coal.

As far as gaseous fuels go, one idea is pulverized coal  in a gas carrier, such as nitrogen. Another option is coal gasification  with water, which may lower fuel

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cell voltage by introducing oxygen to the fuel side of the electrolyte, but may also greatly simplify carbon sequestration .

However, this technology has been criticised as being inefficient, slow, risky and costly, while doing nothing about total emissions from mining, processing and combustion.

 Another efficient and clean way of coal combustion in a form of coal-water slurry fuel  (cws) was well developed in russia (since the soviet union  time). Cws  significantly reduces emissions saving the heating value of co.

Wagon tippler:-

The wagon tippler is used for unloading the coal from the wagon.there are total 4 wagon tippkers in this plant.

In this system a single bogie is brought on its special platform where this bogie is clapped by hydraulic clampers.Then according to the signal given by the operator to the bogie it is rotated at an angle of 165.

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After this the coal from the bogie is dumped on to the conveyor belt through a mechanical gate.

The time taken for unloading one bogie is about 5 minutes.and thus it follows that an entire rack is emptied in about 5 hours .thus this is an ideal mechanism for unloading the coal from the wagons.

The company “Elecon” has manufactured these wagon tipplers.

Processing and feeders of coal:-

The coal which falls on conveyor belt from wagon tippler is taken over to crusher house.this coal before entering house is passed through a metal detector and a magnet.

By this all its metallic impurities are removed & then it is taken to crusher house where it is crushed to fixed dimension of around 3mm diameter.

The crushed coal from the crusher is now taken on to the bunkers with the help of conveyor belts.bunkers are basically storage device for coal whose shape is like bif hopper.

There are total 6 bunkers in each unit.each bunker has the capacity to store 500 tons of coal.then it is further passed through coal feeders.coal feeders feed coal to the bowl mill where it is pulverised.

Feed rate of the coal is measured by using the device which is known as gravimetric analysis.To stop the entry of coal from bunker to the feeder, damper are provided in all six of them.

There are total six mills for each plant and total four output lines are taken out from each mill which goes to all four corners of the boiler furnace where it is tangentially fired.

The diagram is shown below

Coal firing and pulverising:-

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WAGON TIPPLER

CRUSHER HOUSE

BOWL MILL

COAL FEEDER

BOILER FURNACE

The function of this mill is to pulverise the coal mainly for its effective burning.these mills are named from a to f.

To avoid communication problem and confusion they use the following terms for each mill.

A – Ahmedabad B – Bombay C – Calcutta D – Delhi E – England F – Faridabad Tangential firing of coal-

Tangential firing is a method of firing a fuel to heat air in thermal power stations . The flame envelope rotates ensuring thorough mixing within the furnace, providing complete combustion and uniform heat distribution.

The most effective method for producing intense turbulence is by the impingement of one flame on another. This action is secured through the use of burners located in each of the four corners of the furnace, close to the floor or the water-screen.

The burner nozzles are so directed that the streams of coal an air are projected along a line tangent to a small circle, lying in a horizontal plane, at the center of the furnace.

Intensive mixing occurs where these streams meet. A scrubbing action is present which assures contact between the combustible and oxygen, thus promoting rapid combustion and reducing carbon loss.

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A rotative motion, similar to that of a cyclone, is imparted to the flame body, which spreads out and fills the furnace area. The ignition at each burner is aided by the flame from the preceding one.

With tangential firing the furnace is essentially the burner, consequently air and coal quantities need not be accurately proportional to the individual fuel nozzle assemblies.

Turbulence produced in the furnace cavity is sufficient to combine all the fuel and air. This continuously insures uniform and complete combustion so that test performance can be maintained throughout daily operation.

With other types of firing the fuel and air must be accurately proportioned to individual burners making it difficult to always equal test results.

With this type of firing, combustion is extremely rapid, and short flame length results.

The mixing is so intense that combustion rates exceeding 35,000 btu per cu ft per hr are practical under certain conditions.

However, since there is considerable impingement of flame over the furnace walls it is absolutely necessary that they be fully water-cooled. This sweeping of the water-cooled surfaces, in the furnace, by the gas increases the evaporation rate.

Thus, in addition to absorption by radiation from the flame envelope, there is transfer by convection, and the resulting furnace temperatures are lower than with other types of burners, even though the heat liberation rates may be somewhat higher.

Tangentially-fired furnaces are usually clean in the upper zone and, as a result, both the furnace and the boiler are comparatively free from objectionable slag deposits.

Coal cycle:-

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The coal from the coal yard is crushed sent by conveyer belts to coal bunkers and then pulveriser.

Primary air picks this coal and takes it to the furnace where it is combusted. This coal with help of the secondary air burns completely. For effective burning the coal is crushed to increase its surface area By

increasing surface area of coal we can get more efficient combustion which is help us to increase efficiency.

For pulverising of coal bowl mills are used which is shown below.

The bowl mill:- It consists of two rotating bowls and a mesh type system below it. When the coal coming from yhe hopper is fed to the mill is crushed between two

bowls and collected at boul having mesh of 20 mm. So, the coal pulverised and it is send to the boiler furnace for combustion.

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Air & flue gas cycle:-

Secondary air:- For burning anything we need air.in the boiler we required air to burn oil and coal to

heat up water for steam to runturbine. For fresh air we normally have two f.d. Fans to fulfil our requirement.these fans are

sucking air from the atmosphere. These air is passed through the steam coil air pre heater for primary heating and

then it is passed through air pre heater.

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Here the air is heated up with the help of the flue gases temperatute after the air being heated at air preheater it comes towind beg and there after goes to boiler for burning of the fuel.

Primary air:-

This air is also sucked from the atmosphere by primary air fans.these fans may be two in numbers or individually one for each coal mill.

The air sucked is about 66% portion of the air preheaters.after being heated up it goes to boiler furnace.

This way the primary air has the two functions.

1. Being used as carrier of coal from coal mill upto boiler and2. After reaching to boiler furnace it takes part in combustion

In this power station number of fans are used in each units are as follows-1. Induced draft fan – 32. Forced draft fan – 23. Primary air fan – 6

Draft system- Draft may be defined as the pressure difference for producing air flow.the function of

draft is to force the furnace and carry away the product of combustion. Draft is most essential to provide oxygen in sufficient quantity to complete the

combustion satisfactorily. Types of draft:-

Natural draft:-

It is a draft produced by chimney alone.the basic principle being the difference in weight between the column of hot gases in the chimney and a column of a col air outside the same height and cross section causes the chimney gases to rise and the heavy cool air flows through the ashpit for combustion.

Artificial draft:-

As the name itself suggests , the mechanical meshes such as by steam jet or fans produce it artificially.

In large industrial plant draft of 6 to 8 in. Is obvious essential requirement for overcoming the resistance offered by the boiler, economiser, as well as preheater.

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It is not build stack high enough to produce draft of desired magnitude. By forced or induced draft this pressure requirement can be satisfied.

Effect of draft:- The combustion flue gases inside the flue gas stacks are much hotter than the

ambient outside air and therefore less dense  than the ambient air. That causes the bottom of the vertical column of hot flue gas to have a

lower pressure  than the pressure at the bottom of a corresponding column of outside air.

That higher pressure outside the chimney is the driving force that moves the required combustion air into the combustion zone and also moves the flue gas up and out of the chimney. That movement or flow of combustion air and flue gas is called "natural draft (or draught)","natural ventilation" , "chimney effect", or "stack effect ". The taller the stack, the more draft (or draught) is created

Steam cycle:-

Steam cycle is not complicated as other cycles but it is simply denoted the flow of the steam within the plant.it is explained as below.

First of all water inside the drum is heated due to the burning of coal in the furnace.Thus steam is produced from the boiler.

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SUPER HEATER

FINAL SUPERHEATER

TURBINE

DESUPERHEATER

BOILER DRUM

CONDENSER

This steam is then passes through the superheater where its temperature is increased.then its passes through the desuperheater where water is sprayed to control its tmperature.

Then it is passes through the final superheater where temperature of 540 c is achieved.

Now steam enters the turbine where the shaft is rotated at the speed of 3000 rpm.this shaft is coupled with generator to produce electricity.

This used steam is not expelled in the atmosphere but is again reused.this steam after passing through hpt, lpt, ipt respectively andthen goes to condenser.

In the condenser steam is condensed to water.this water is again introduced to boiler drum and again the cycle is repeated.

Thus, steam flows in the plant in this ways and it is repeated continuously and energy is produced

Condensation cycle:-

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Figure showing the schematic diagram of the condensation cycle:-

As shown in the figure the condensate is divided into 2 parts. The steam coming out from the lpt is coming to this condenser where this steam passes through number of tubes bunched together.

The flow of cold raw water is kept sorroundings this tubes.this condensed steam sets colleccted in to a tank like steucture which is known as hot-well.

Hot well collects this water and this water is given a special nane demineralized water.this dm water is then extracted from hot well using condensate extraction pump.

This condensate then passes through drain cooler for achieving more and more condensate as possible.

The temperature of this dm water is then increased with the help of the heat energy of the heaters.heaters are placed in series to achieved our desired temperature.

The water contains many gases too among this oxygen is most dangerous because it causes corrosion and many problems.

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So it is necessary to remove this gases with the help of deaerator before it enters in the boiler feed pump.

So, this process of removal of gases from the water with the help of deaerator is known as deaeration.this is stored in deaerator tank.

Feed water cycle:-

The water required for boiler feed purposes i.e for steam generation should be of very high quality and thus requires a lot of treatment. Untreated waters, containing impurities may lead to the following problems in boilers:

1. Scale and sludge formation

2. Boiler corrosion

3. Caustic embrittlement

4. Priming and foaming

The feedwater has to be specially conditioned to avoid problems in the boiler and downstream components:

Corrosion  - corrosive components, especially o2  and co2  have to be removed, usually by use of a deaerator . Remnants can be removed chemically, by use of oxygen scavenger . Furthermore feedwater has to be alkalized to a ph  of 9 or higher, to reduce oxidation and to support the forming of a stable layer of magnetite  on the water-side surface of the boiler, protecting the material underneath from further corrosion.

This is usually done by dosing alkalic agents into the feedwater, like sodium hydroxide  (caustic soda ) or volatile ammonia .

Deposits  / sediments  / fouling  - deposits reduce the heat transfer in the boiler, reduce the flow rate and eventually block boiler tubes.

Any non-volatile  salts and minerals that would remain in soluted form when the feedwater is evaporated  have to be removed, because these would be concentrated in the liquid phase and require excessive "blow-down" (draining) to avoid that the liquid eventually becomes saturated and solid crystals fall out.

The diagram of feed water cycle is shown below-

For generating power about 660 mw we need a lot of water and the same is arranged from sabarmati river from three french well.

At the sump primary alum chlorine treatment is given to the water and the water taken to d.m. Plant for purification.

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The dm water is then coming to condensate storage tanks situated very near to boiler.

When dm water leaves deaerator storage tank its temperature is around 160.c and pressure is about 6-8 kg/cm2 this is then passed through booster pump where its pressure is increased about 15 kg/cm2.

When the pressure of water is sufficient and also deaerator level is maintained, this water is enters boiler feed pump where pumping of water is done.

There are total 3 nos. Of bfp out of which 2 are working and 1 is remain stand by.this bfp is used to increase pressure of water about 175 kg/cm2 so that it can reach up to the height of 62 m where boiler drum is located.

Before entering the drum the final heat to the water is provided by economiser. The temperarure is increased about 330 c and pressure is about 175 kg/cm2.

Then the water enters the boiler drum which is filled less than 50% of its capacity and this cycle is continuously repeated.

Ash cycle:-

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This cycle mainly consist two systems.

Esp(electro static precipitator)

Bottom ash handling & flue gases

Bottom ash:-

Bottom ash refers to the non-combustible  constituents of coal  with traces of combustibles embedded in forming clinkers and sticking to hot side walls of a coal-burning furnace during its operation.

The portion of the ash that escapes up the chimney or stack is, however, referred to as fly ash . The clinkers  fall by themselves into the water or sometimes by poking manually, and get cooled.

The clinker lumps get crushed to small sizes by clinker grinders mounted under water and fall down into a trough from where a water ejector  takes them out to a sump.

From there it is pumped out by suitable rotary pumps to dumping yard far away. In another arrangement a continuous link chain scrapes out the clinkers from under water and feeds them to clinker grinders outside the bottom ash hopper.

An alternative bottom ash handling system is the mac (magaldi ash cooler) system; the mac dry bottom ash system is a unique system for dry extraction, cooling and handling of bottom ash from pulverized coal-fired boilers.

It eliminates water usage in the cooling and conveying of bottom ash. This system cools ash using only a small controlled amount of ambient air.

Bottom ash may be used as an aggregate in road construction and concrete, where it is known as furnace bottom ash (fba), to distinguish it from incinerator bottom ash  (iba), the non-combustible elements remaining after incineration .

Theory of esp and its working principle:-

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An electrostatic precipitator (esp), or electrostatic air cleaner is a particulate  collection 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 that minimally impede the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream.

In contrast to wet scrubbers which apply energy directly to the flowing fluid medium, an esp applies energy only to the particulate matter being collected and therefore is very efficient in its consumption of energy (in the form of electricity).

The sectional view is shown in figure.

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Normally two types of ash are there

1. Heavy ash

2. Fly ash

If we consider ratio wise then out of 750 tons of total ash, 150 tones is heavy ash and 600 tones is fly ash.the heavy ash is normally collected at bottom of the furnace and is taken away with the help of water filled pipe line.

The fly ash which got esp is taken over to silo system via various operations, this fly ash from e.s.p. Is taken to the furnace, which contains a ring of total 56 separators.

It has fly ash sticks.the entire chamber is vaccum tight and exhaust of air is taken out as shown in figure.

When this chamber gets filled this ash transfer to the next chamber finally into a big vessel called silo.

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The silo has the capacity to store 500 mt of ash.the entire operation of air jet, opening and closing of various chambers and silo is done on computer.

This ash is used in manufacturing of cement & hence is purchased by various cement manufacturing companies.

In this way best is achieved from the waste.

Thus in this way ash is disposed and it concludes the operation of the ash plant.

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conclusion :-

After the successive completion of my training I got the practical knowledge of

power plant and make my knowledge better than before.

I hope this training will help me for my career and to enrich my knowledge to

become a good engineer.

I am very thankful to everyone who helped me directly or indirectly during my

training.

It was a memorable experience for me to take training.

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