NAME -- DIPANJAN BARMAN

INSTITUTION -- JADAVPUR UNIVERSITY

YEAR -- 3RD (6TH SEMESTER)

DEPARTMENT – MECHANICAL ENGINEERING

TITAGARH GENERATING STATION REPORT OF VOCATIONAL TRAINING

INDEX

CESC

TGS

Thermal Power Plant

Thermodynamic cycle

Four basic cycles on which power generation plant operates

Fuel handling Plant

Water Treatment Plant

Generation of steam- Boiler & Accessories

Turbine

Feed Water Cycle

Alternator

Ash Handling Plant

Cooling Tower

Distributed Control System

Conclusion

References

ACKNOWLEDGEMENT

In the end of such compassionately grueling but informative training I felt myself much more confident and competitive. The entire credit goes to excellent and competent personnel of your esteemed company. Your training and guidance showered on me by Mr. M. Choudhury (HRD), Mr. S. Chaterjee (Planning manager), Mr. A. Dey (WTP), Mr. M. Sarkar (Safety Officer), Mr. A. Patra (FHP), Mr.T.Choudhury, put me in solid rock to garner courage and expertise in facing any challenges in the years to come.

I am thankful rather grateful for such whole hearted cooperation of not only them but also all members of TGS who helped me with their patient & friendly behaviour throughout the training tenure to demonstrate & illustrate the plant & helping us in every single step & to bring up this report.

CESC (CALCUTTA ELECTRIC SUPPLY COPORATION)

Kolkata has come a long way on the wings of power. Through rapid growth and change during the world’s most eventful decades. CESC, a power utility in India was set up in 1899. It was first Thermal Power Generation Co. in India. In 1989 CESC became a part of RPG group which has a strong presence in the fields of power generation, and supplies power to the city Kolkata, serving 2.4 million populations across its area of 567 sq. km. It has an initial licensed area of 14.44 sq. km. CESC brought electricity to Kolkata 10 years after it came in London. The peak load so far handled more than 1300 MW and it’s no of employees are 10460 (2009-10)

From its first DC station at Emambaugh Lane operating from April of 1899 units of CESC now became an ISO 9001: 2000 & 14001:2004 Co. & established its latest station at Budge Budge (1997) with a capacity of 500 MW which is one of the largest ever private industrial investments in West Bengal.

CESC have now four generating station.

Generating Station Year of starting

Installed capacity Feature of boiler

New Cossipore (NCGS) 1949 100 MW Stoker Fired

Titagarh (TGS) 1983 (60 x 4) MW Pulverized fuel

Southern 1991 (67.5 x 2) MW Pulverized fuel

Budge Budge 1997 (250 x 2)+(1 x 250) MW Pulverized fuel

CESC is not only a generating station but also a power distribution company. Its substation capacity is 7258 MVA. It’s no of receiving stations are 6. The no of 132 KV substations is 7. It’s no distribution station is around 94. The no of transformers is above 6304. Power is distributed in industrial, domestic and commercial purposes. It has suitable voltage levels of 220 KV, 132 KV, 33 KV, 11 KV, 6.6 KV, 400 V, 230V. We all know that pollution is main obstacle in way of power generation. CESC is so much concerned about the environment that it is the India’s best environment friendly generation station and received Silver National Award for Environmental Management in Thermal Power Station for 2008-09.

TITAGARH GENERATING STATION

TGS is one of the oldest generating stations & is the first pulverized fuel thermal station of CESC situated on B.T. road, Titagarh. It has total installed capacity of 240 MW comprising four units each rated 60 MW. Its generating voltage is 10.5 KV. The plant started commercial generation since 1983, when the first unit started operating. Subsequently the other three units started in the years 1983, 1984 & 1985. Plant Load Factor (P.L.F) of this plant is generally high 95.4%. TGS is committed to ensure required power supply to the CESC’s distribution network in line with the varying level of electricity demand. In TGS the generating voltage 10.5 KV is stepped up by generating transformer to 33KV. This 33 KV supply is again stepped up to 132KV in the receiving station & is sent to distribution station & stepped down to 11KV. Thereafter it is again stepped down to 6 KV, 415 V for distributing to consumers. The steam raising unit comprises of a single radiant furnace boiler with auxiliary equipment designed to generate 272 tons of steam/hr. at 91.4 kg/cm2 pressure and at a temperature of 515oc. The plant is designed is to operate at an altitude of 457m above the sea level. The ambient temperature is 40oc with humidity of 70%.Operation & maintenance of the plant is part of the business activity of TGS. CESC central Turbine Maintenance department (CTM) is responsible for Turbo-Alternator sets while, testing & calibration of protection metering equipment are done by company’s test department. In 2006-2007 TGS captured the 5th position all over India due to its great performance..

THERMAL POWER PLANT

In a thermal power plant mainly coal is burnt to convert chemical energy to heat and then using turbine the energy is transformed into mechanical energy and by alternator finally electrical energy is achieved.

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.

HistoryReciprocating 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.

BOILER

CHEMICAL ENERGY

THERMALENERGY

MECHANICAL ENERGY

ELECTRICALENERGY

ALTERNATORTURBINE

EfficiencyThe energy efficiency of a conventional thermal power station, considered as salable energy produced at the plant as a percentage of the heating value of the fuel consumed, is typically 33% to 48% efficient, limited as all heat engines are by the laws of thermodynamics. The rest of the energy must leave the plant in the form of heat. This waste heat can be disposed of with cooling water or in cooling towers. If the waste heat is instead utilized for e.g. district heating, it is called cogeneration. An important class of thermal power station is associated with desalination facilities; these are typically found in desert countries with large supplies of natural gas and in these plants, freshwater production and electricity are equally important co-products.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. Historically, other working fluids such as mercury have been experimentally used in a mercury vapour turbine power plant, since these can attain higher temperatures than water at lower working pressures. However, the obvious hazards of toxicity, and poor heat transfer properties, have ruled out mercury as a working fluid.

A   Rankine cycle   with a two-stage   steam turbine   and a single feed water heater.

THERMODYNAMIC CYCLERANKINE CYCLE

The Rankine cycle is a thermodynamic cycle which converts heat into work. The heat is supplied externally to a closed loop, which usually uses water as the working fluid. This cycle generates about 80% of all electric power used in America and throughout the world including virtually all solar thermal, biomass, coal and nuclear power plants. It is named after William John Macquorn Rankine, a Scottish polymath.

Description

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

A Rankine cycle describes a model of the operation of steam heat engines most commonly found in power generation plants. Common heat sources for power plants using the Rankine cycle are coal, natural gas, oil, and nuclear.

The Rankine cycle is sometimes referred to as a practical Carnot cycle as, when an efficient turbine is used, the TS diagram will begin to resemble the Carnot cycle. The main difference is that a pump is used to pressurize liquid instead of gas. This requires about 100 times less energy than that compressing a gas in a compressor (as in the Carnot cycle).

The efficiency of a Rankine cycle is usually limited by the working fluid. Without the pressure going super critical the temperature range the cycle can operate over is quite small, turbine entry temperatures are typically 565°C (the creep limit of stainless steel) and condenser temperatures are around 30°C. This gives a theoretical Carnot efficiency of around 63% compared with an actual efficiency of 42% for a modern coal-fired power station. This low turbine entry temperature (compared with a gas turbine) is why the Rankine cycle is often used as a bottoming cycle in combined cycle gas turbine power stations.

The working fluid in a Rankine cycle follows a closed loop and is re-used constantly. The water vapor often seen billowing from power stations is generated by the cooling systems (not from the closed loop Rankine power cycle) and represents the waste heat that could not be converted to useful work. Note that steam is invisible until it comes in contact with cool, saturated air, at which point it condenses and forms the white billowy clouds seen leaving cooling towers. While many substances could be used in the Rankine cycle, water is usually the fluid of choice due to its favorable properties, such as nontoxic and unreactive chemistry, abundance, and low cost, as well as its thermodynamic properties.

One of the principal advantages it holds over other cycles is that during the compression stage relatively little work is required to drive the pump, due to the working fluid being in its liquid phase at this point. By condensing the fluid to liquid, the work required by the pump will only consume approximately 1% to 3% of the turbine power and so give a much higher efficiency for a real cycle. The benefit of this is lost somewhat due to the lower heat addition temperature. Gas turbines, for instance, have turbine entry temperatures approaching 1500°C. Nonetheless, the efficiencies of steam cycles and gas turbines are fairly well matched.

Process of the Rankine cycle

There are four processes in the Rankine cycle, each changing the state of the working fluid. These states are identified by number in the diagram to the right.

Process 1-2: The working fluid is pumped from low to high pressure, as the fluid is a liquid at this stage the pump requires little input energy.

Process 2-3: The high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturated vapor.

Process 3-4: The dry saturated vapor expands through a turbine, generating power. This decreases the temperature and pressure of the vapor, and some condensation may occur.

Process 4-1: The wet vapor then enters a condenser where it is cooled at a constant pressure and temperature to become a saturated liquid. The pressure and temperature of the condenser is fixed by the temperature of the cooling coils as the fluid is undergoing a phase-change.

In an ideal Rankine cycle the pump and turbine would be isentropic, i.e., the pump and turbine would generate no entropy and hence maximize the net work output. Processes 1-2 and 3-4 would be represented by vertical lines on the T-s diagram and more closely resemble that of the Carnot cycle. The Rankine cycle shown here prevents the vapor ending up in the superheat region after the expansion in the turbine, which reduces the energy removed by the condensers.

T-s diagram   of a typical Rankine cycle operating between pressures of 0.06bar and 50bar

Real Rankin cycle (non-ideal)

In a real Rankine cycle, the compression by the pump and the expansion in the turbine are not isentropic. In other words, these processes are non-reversible and entropy is increased during the two processes. This somewhat increases the power required by the pump and decreases the power generated by the turbine.

In particular the efficiency of the steam turbine will be limited by water droplet formation. As the water condenses, water droplets hit the turbine blades at high speed causing pitting and erosion, gradually decreasing the efficiency of the turbine. The easiest way to overcome this problem is by superheating the steam. On the T-s diagram above, state 3 is above a two phase region of steam and water so after expansion the steam will be very wet. By superheating, state 3 will move to the right of the diagram and hence produce a dryer steam after expansion.

Variations of the real Rankine cycle

The overall thermodynamic efficiency (of almost any cycle) can be increased by raising the average heat input temperature of that cycle. Increasing the temperature of the steam into the superheat region is a simple way of doing this. There are also variations of the basic Rankine cycle which are designed to raise the thermal efficiency of the cycle in this way; two of these are described below.

Regenerative Rankine cycle

The regenerative Rankine cycle is so named because after emerging from the condenser (possibly as a sub-cooled liquid) the working fluid is heated by steam tapped from the hot portion of the cycle. On the diagram shown, the fluid at 2 is mixed with the fluid at 4 (both at the same pressure) to end up with the saturated liquid at 7. The Regenerative Rankine cycle (with minor variants) is commonly used in real power stations.

Another variation is where 'bleed steam' from between turbine stages is sent to feedwater heaters to preheat the water on its way from the condenser to the boiler.

Rankine cycle with superheat Regenerative Rankine cy

FOUR BASIC CYCLES ON WHICH A POWER GENERATING PLANT OPERATES

Any COAL FIRED Power Generating Plant operates on the following four basic cycles:

1. Coal & Ash cycle

2. Air & Flue Gas cycle

3. Water & Steam cycle

4. Cooling Water cycle

NOTE:

Of all the above four mentioned cycles, the first two i.e. COAL & ASH CYCLE & AIR & FLUE GAS CYCLE are called OPEN CYCLES.

The next i.e. WATER & STEAM CYCLE is a CLOSED CYCLE.

The fourth and the last mentioned cycle i.e. the COOLING WATER CYCLE occurs in the condenser

Coal & Ash cycle

Raw coal is fed into the Coal Handling Plant (CHP) after which it is sent to the coal bunker. Then through the coal feeder the coal is fed into the pulverizer/ crusher where the coal (50mm dia.) is pulverized. After that the pulverized coal is fed through the 24(6x4) coal burners by primary air fans into the boiler furnace.

After proper combustion (determined by the 3-Ts : Temperature, Time and Turbulence) ash is formed. This ash is of two types. The heavier variety is called the Bottom Ash while the lighter variety passes out as flue gas into the Economizer. From the Economizer also bottom ash is obtained. The bottom ash is obtained as clinkers which are crushed into powder form by the scrapper-clinker grinder conveyer. Then the bottom ash thus obtained is converted to slurry by water through the ash water pumps.

The flue gas from the furnace is fed to the economizer and the Air Preheaters (APH).Then from the Electrostatic Precipitator (ESP) the flue gas is vent out into the atmosphere by ID fans through the chimney.

The ESP collects all the suspended ash particles by high voltage discharge. The ash thus obtained is the second variety of ash and is called Fly Ash. This fly ash, as the bottom ash, is converted into slurry. The slurry (of bottom ash + fly ash) is collected in the Ash Slurry Sump. The slurry from the sump by a set of three ash slurry pumps is sent to the Ash Pond.

This ash is used in several applications like cement industry, manufacture of bricks, etc.

Air Flue Gas cycle

Air cycle

The air requirement of the boiler is met by two forced draft fans (FD FANS). The forced draft fans supply the necessary primary and secondary air. About 80% of the total air which is the secondary air goes directly to the furnace wind box and 20% of the air goes to the mill via primary air fans. This air is known as the primary air. The air before it goes into the furnace or to the mill it is pre heated in the air pre heaters. The air pre heater installed is a tubular type heat exchanger in which the heat exchanger takes place between flue gas and air. The flue gas flows through the tubes and air flows over the tubes. The air heater serves to recovers the useful heat in the outgoing flue gas (after recovery in the economizer) and thus improves the efficiency of the boiler. At the air heater cold end the outgoing flue gas contains constituents like sulpher dioxide. If the operating temperature goes below the dew point of the vapours then the vapours get condensed and react with sulpher dioxide and sulphuric acid is former

which is corrosive in nature. The possibility of cold and corrosion is more during lighting up of the boiler and at low load. To avoid this corrosion problem the flue gas bearing the air is to be maintained at a higher temperature. This is accomplished by passing the Air Pre-heater during lighting up and low load condition when flue gas temperature is low.

The primary air is supplied to the five mills by the five primary air fans. The primary air is used in the mill to dry the pulverized coal and to carry it into the furnace. To ensure drying of coal a portion primary air is taken after passing through the air pre-heater. A cold air line is also connected to the hot primary air line before it enters into the mills. The temperature of the coal air mixture at the mill outlet is controlled by admitting the cold and hot primary air proportionately.

Flue Gas cycle

The flue gases move upward in the furnace and through the rear gas pass in a downward direction to the air pre-heaters. The flue gas leaving the air pre-heater pass through the electrostatic precipitators and then the induced draft fan (ID FAN) sucks and forces the flue gas through the stack. The flue gas, while leaving the boiler furnace, carries with it particles like ash, unburnt carbon etc. The quantity of these matters is small when oil is fired but it becomes quite considerable when coal is fired, particularly when high ash content coal is fired. The ESP helps in minimizing the dust concentration of flue gas thus reducing the erosion of ID FAN impellers, ducting and the atmospheric pollution.

Water & Steam cycle

Feed water is supplied to the boiler drum from economiser outlet header through economiser links and these two links at the point of entering the drum have been divided into 4 branch pipes. Altogether there are 8 downcomers from boiler drum, out of which two downcomer pipes termed as ‘short loop’ (water platen) divided into 4 branches before entering the boiler and ultimately water flows to the drum through these 4 water platen outlet headers.The front & the rear wall inlet headers feed the front and rear furnace wall tubes. The furnace side walls are fed by two side wall inlet headers. The water in the furnace side wall, water wall platen and the extended side wall absorb heat from the furnace. The resultant 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 the rear walls is supplied directly into the drum. In the drum separation of water and steam takes place. The boiler water mixes with the incoming water. The saturated steam is led to the roof radiant inlet header and from there to the final SH outlet header via LTSH and platen superheater stages. The steam is superheated to the designed temperature and from the superheater outlet header the steam is led to the turbine via the main steam line.

Cooling Water cycle

There are NINE cooling tower fans each of voltage rating: 415 V. They are of ID fan type. All of them are controlled by MCC blocks.

FUEL HANDLING PLANT

The working substance of the energy conversion device viz., prime-mover (which converts the natural resources of energy into power or electricity) is called fuel. The most common fuel is fossil fuel viz., coal and diesel in the case of steam power plants.

Combustion of fuel is must in any energy conversion device. It is defined as rapidly proceeding chemical reaction with liberation of heat and light.

This phenomenon incurved in the case of thermal power plants especially in IC engines and gas turbines.

Coal Handling Plant

Coal is the primary fuel. Source of coal varies from thermal power plants of CESC as per design parameters of individual boiler.

Coal is used as fuel because of several reasons – Abundantly available in India Low cost Technology for power generation well developed Easy to handle transport & store

A good coal handling plant must perform two duties as unloading the coal from railway wagons as fast as possible and then transferring the unloaded coal either to coal bunkers or in the stock piles for storage and then feeding the coal from the stock piles to the bunkers when railway wagons are not available.

Requirement of coal at TGS is about 3000 tons per day.

There are some properties of coals which are used in TGS ---

SWELLING INDEX: Some types of coal during and after release of volatile matter become soft and pasty and form agglomerates called caking coals.

GRINDABILITY: This property is measured by grindability index.

WEATHERABILITY: It is a measure of how coal can be stockpiled for long periods of time without crumbling to pieces.

SULPHER CONTENT: Sulpher content in coal is combustible but the product after combustion i.e.SO2 is a major source of atmospheric pollution. The amount of sulpher content in the coal used in TGS is very low. So the amount of so 2

produced is not a matter of concern.

HEATING VALUE: The coal used in TGS has 4000-5000 kcal/kg of heating value.

Transmission of Coal

1. Coal is brought by rail wagons, which the Indian Railways deliver till the coal yard of TGS. From there, six to eight wagons are separated and are pulled by locomotive engines to the wagon tippler where they are unloaded one by one.

2. Wagon tippler is a device by which the wagon is tippled to unload the coal to the bunker. There are two wagon tipplers. The wagon tippler consists of a moveable platform, which also acts as a Computerized Weight Bridge. A single wagon is first brought to the platform. Then by a pulley and weight arrangement, powered by an electric motor, the platform is tilted towards the bunker by 140 degree while a support from the top catches the wagon and tilts it which causes the coal to fall down to the hopper. While the unloading is done, water is sprayed through water pipes on the coal to avoid spreading of coal dust.

Picture of a wagon while tippling

3. Coal from wagon is dropped to vibrating feeder through a 300 mm square mesh. Any large coal chunk is broken manually. The first conveyer belt starts below the ground and with an angle of 20o with the ground and then after certain distance it makes an angle of 45o with the ground. It moves through underground and discharges the coal to another conveyer belt. There are two parallel belts, the left one is denoted by A and the right one is denoted by B. There are provisions for transferring the coal to field to stock it. Three different types of coal is stocked at three different places from there they are fed by bulldozers through reclaiming hoppers

4. There are total 18 conveyor belts from wagon tipplers to bunker and total 19 flap gates are here. Average speed of belt conveyors varies from 200-300 rpm. Here RH1 (reclaim hopper 1) is for ECL, RH3 for ICML & RH2 for both ECL & ICML. 5-6 minutes are required to carry the coal from wagon tippler to bunker.

5. Coal conveyor system is consisting of a metal frame with rollers at either end of a flat metal bed. The belt is looped around each of the rollers and when one of the rollers is powered (by an electrical motor) the belting slides across the solid metal frame bed, moving the product. In heavy use applications the beds which the belting is pulled over are replaced with rollers. The rollers allow weight to be conveyed as they reduce the amount of friction generated from the heavier loading on the belting. There are three rollers among which the two side rollers are at angle of 18o with the horizon.

Conveyor belts are made of high tension fibers sandwiched between several rubber layers.

6. The types of coal conveyed to the Reclaim Hopper are as follows-

RH1 - ECL (Eastern Coal Ltd., from Ranigaunge )RH2 - ICML & ECLRH3 - ICML (Integrated Coal Mining Ltd., from Sorsetholi ) Sometimes BCCL (Bharat Coaking Coal )

Conveyor capacity - 55 tons/hr.

7. The coal is transferred to crusher. But before the crusher, impurities like iron parts, which get carried so far, are separated by a magnetic separator which is oriented in cross way. Sufficient air flow is provided underground through where coal is carried out.

8. In the crusher, solid metallic, non-ferrous crushing wheels are used to crush the coals into small pieces of sizes not exceeding 20 mm in diameter.From there by conveyor belt, the coal is taken through the chute and sent to the top of the main building.

Type - Ring hammer coal crusher No. of crushers - 2Make - Tata-Robinson-Fraser Ltd.Shaft/crusher - 4Hammers/shaft - 18Hammer - steel alloyCrusher motor type - Squirrel cage induction motorCrusher motor - 6.6 KVSpecification - 500 HP (capacity)

750 rpm

Ring hammer coal crusher

9. The coal is then dumped into an area from where it is fed into by conveyor belts to the tripper trolley which gathers the coal, decides which bunker requires coal, then it rolls over to the of that bunker and pours the required amount of coal in it.

Bunkers/unit - 5Bunker capacity - 5 wagon coalBunker depth - 60 ft.Time taken to fill up a bunker - 10-15 min.C bunker - ECLD bunker - ECL or ICMLRemaining’s - ICMLOne full bunker can run for 10-14 hrs. approximately.ECL coal (good quality) is fed to the lower part of furnace for better ignition and to reduce the oil consumption. ICML (medium quality) is fed to the upper part of the furnace.

Tripper Trolley

TP1

TP2

TP7

TP3

TP4

TP5

TP6

CH

RH1

RH2

RH3

PH

TC-1 TC-2

LAY OUT OF CHP, TGS(60MWX4)

WT - 1

WT - 2C – 1B

C – 1A

C – 2B C – 2A

C – 10

C – 9

C – 3A

C – 3B

C – 3A

C – 3B

C – 11

C – 7

C – 4B C – 4A

C – 12

C – 8

C – 5B

C – 5A

C – 6AC – 6B

BUNKERS

TP – Transfer Point

RH – Reclaim Hopper

TC – Telescopic Chute

C - Conveyor

10. From the bunker, the coal comes down through the hopper to the Besta Feeder. There is a gate between the hopper and the Besta feeder which is used manually to control the coal feeding rate.

11. The Besta Feeder controls the rate of the amount of coal to be fed tot the pulverizer.Besta Feeder is a device consisting of a conveyor belt, which transfers the coal from the hopper to the mouth of the pulverizer. The transfer rate of coal is controlled from the controlled room by monitoring the speed of the Besta feeder. This is because as the coal is grounded in the pulverizer, it becomes explosive in nature and cannot be stored.

12. The coal is sent to the pulverizer to get crushed into the size of 200 micron in diameter. The pulverizing process is composed of several stages.

The first is the feeding system, which must automatically control the fuel-feed rate according to the boiler demand and the air rates for drying and transporting fuel to the burner (primary air).

The next stage is drying. Part of the air from the stem-generator air preheater, the primary air is forced into the pulverizer at 650o F or more by primary air fan (PA Fan). There it is mixed with the coal as it is being circulated and ground.

The heart of the equipment is pulveriser, also called grinding mill. Grinding is accomplished impact, attrition, crushing or combination of these.

They operate on the principles of crushing and attrition. Pulverization takes place between two surfaces, one rolling on top of the other. The rolling may be balls or ring shaped rolls. Primary air causes coal feed to circulate between the grinding elements and when it becomes fine enough; it becomes suspended in the air and carried to the classifier.

The coal bunker, coal feeder and coal mill are located in a vertical line. After completion of the pulverization, the exhaust coal is taken out from the mill through pipe lines. One coal pipe is divided into three pipes, which are connected to three burners and enters the furnace. In TGS there are five coal burners group vertically stacked in each other. They are named as A, B, C, D and E. The complete combustion of the pulverized coal in the furnace results the generation of heat to produce the steam.

This procedure is taken to achieve complete combustion of coal as the surface area of coal particles increases, better control of furnace temperature and increasing the efficiency of the boiler.

No. of pulverizer/unit - 5Type - Ball & RaceCapacity - 15 tons/hr. (single pulverizer)Speed - 49 rpmPower - 100 KW

13. Generally the necessary air for the combustion of the coal is taken by the PA fan and the FD fan. The PA fan supplies 20% of the required air which will be mixed the coal powder and FD fan supplies the 80% air for the complete combustion of the pulverized coal.

Specification of Crushing Motor:

Manufactured by: Crompton & GreavesPower rating: 373 KWVoltage rating: 66 KVRated speed: 740 rpmCurrent rating: 44 amp

Model of pulverizing mill

Pulverizing MillTop- Opened for repairBottom- An active mill

Flow Chart of Path of coal traveling in a Power Plant

Flow chart of Coal Handling Plant

RAW COAL

WAGON TIPPLER GRIDE

CRUSHER

MILL

FURNACE

300 mm (12”)

20 mm (3/ 4”)

75 micron (0.075 mm)

WAGON

W/ TIPPLER

CONVEYORS

CRUSHER

CONVEYORS

T/ TROLLEY

BUNKERS

COAL MILL

BOILER FURNACE

STOCK

LDO Unloading & Transfer

LDO (Light Diesel Oil) is used invariable proportion in furnace to help the initiation when the coals are wet or in other circumstances. It increases the burning capacity of the pulverized coal. It is stored in two big tanks and by pipeline it foes to two smaller tanks situated Boiler-front.There are pump systems to drive the fuel oil. There is a lever just before entering the burner and by this lever the oil feed can be manually controlled.

No. of pumps - 4Pressure of pump - 7.5 kg/cm2

Tank CapacityHFO 1 750 m3

HFO 2 750 m3

LDO tank 200 m3

LDO new storage tank 57119 lit.

WATER TREATMENT PLANT

In TGS total water source of the plant is the Ganges. There are 5 pumps on the river side to supply the water through huge underground tunnel. This water is for boiler system, cooling system, plant requirement etc.

But the river water contains suspended matter in the form of colloid and some of organic and inorganic impurities which make it necessary for chemical and mechanical treatment in water treatment plant before being used as clarified and filtered water. These impurities are of two kinds, volatile & non-volatile.

Impurities in raw water input to the plant generally consist of Ca and Mg salts which impart hardness to the water. Hardness in the make up to the boiler will form deposits which will lead to overheating and failure of the tubes.

Demineralized Water Treatment Plant

1. Water directly coming from the river is first dozed with alum. The alum (K2SO4.Al2(SO4)3.24H2O) is mixed with water in a separate place by a stirrer. River water is dozed with alum mixture and moves in a small tank, where air is blowed to mix the water and alum very well. The water is stirred vigorously in a flash mixer to assure quick, uniform dispersion of the alum. Provisions are here for Cl2 dozing if necessary.Alum is also used in purification of water. The alum reacts rapidly with compounds in the water that contain carbonates, bicarbonates and hydroxides to produce a jelly-like substance that absorbs impurities. At the same time, alum, with a positive charge, neutralizes the negative charge common to natural particles, which draws them together. Small particles called microfloc are formed and stick together and get heavy (flocculate). The following equation shows the reaction of alum with alkalinity:

Al2(SO4)3 .14H2O + 3Ca(HCO3) 2Al(OH)3 + 3CaSO4 + 6CO2 + 14H2O Aluminum Sulfate Calcium Bicarbonate Aluminum Hydroxide Calcium Sulfate Carbon Dioxide Water

2. The water moves from the flash mixer to the inner cylinder of the clariflocculator, which contain mechanical stirrer. The gate mixers provide a gentle, constant mixing of the microfloc formed during coagulation. This stirring promotes formation of larger and heavier floc. After 20 to 30 minutes, the floc particles are usually visible and will look like tiny tufts of cotton or wool, separated by clear water. Once the flow is of sufficient size and density to be settled, the water moves into the sedimentation i.e. outer zone of the clariflocculator. Sedimentation is the removal of solids from water by gravity settling. This part is designed to hold large volumes of water for several hours and to give a smooth, even flow. This design allows the velocity and turbulence of the water to be decreased to the point that the water will no longer transport the flocculated solids and they will settle to the bottom, and this sediment is collected by scrappers and drained through pipe line at bottom. There is a bridge over the clariflocculator with three motors which rotates the gate mixers and rotate itself gently

to scrap the sediment from all over the bottom surface. There are 2 gate mixers at 180o

apart. The diameter of clariflocculator is about 200m.

3. The clarified water is reserved in a big reservoir. The reservoir has a partition. One reservoir is used for clarified water and another is used for service water storage.

4. Clarified water is pumped into PSF through clarified pump.

No. of pumps - 4 (1 working)Speed - 2920 rpmVolt - 415 VCurrent - 31 amp

5. In PSF (Pressurized Sand Filter) there are layers of several sized sand. In the upper layer coarse sand filters the coarse insoluble impurities. Size of the sand particles decreases downwards. Smaller sand filters small impurities.

No. of PSF tank - 4 (2 working)Pressure - 6.5 kg/cm2 & 5.8 kg/cm2

Diameter - 2600 mm

6. From PSF the water goes to ACF (Activated Carbon Filter). Activated carbon absorbs the chlorine and some of other impurities.

No. of filters - 3 Pressure - 5.8 kg/cm2

Diameter - 2000 mm

7. Water afterwards moves to SAC (Strong Acidic Cation), where resin is used to remove the cationic parts from water.

RH + CaSO4 RCa + H2SO4

No. of filters - 3Pressure - 5.8 kg/cm2

Diameter - 1800 mmCapacity - 800 m3

8. Water goes to degasser from SAC. In degasser air is passed through water by blower. Here atmospheric degasser is used. In water there are plastic disks which act as baffles. Water hits the baffles and because of the stirring mixed air in water moves out. CO2 mixed in water in the form of carbonic acid is mainly removed here in degasser.

No. of degasser tank - 2Diameter of tank - 3400 mmNo. of degasser tower - 2Diameter of tower - 1200 mmDegasser fan - 2 + 2

9. Water from degasser tank goes to WBA by DEG W pumps.

No. of pumps - 4Pressure - 6 kg/cm2

10. In WBA (Weak Base Anion), resin is used to remove anionic parts from the water.

R’OH + H2SO4 R’SO4 + H2O

No. of filters - 3Pressure - 5.8 kg/cm2

Diameter - 1200 mmCapacity - 755 m3

11. From WBA water moves to SBA (Strong Base Anion). SBA is specially used to remove the silica content in water. Because silica vapourises with water and goes to turbine, which causes severe damage in turbine blades.

12. After SBA water passes through MB (Mixed Bed). In mixed bed both the cationic resin and anionic resin is used. It is kept for safety if any of the SAC, WBA & SBA fails then MB will check.

No. of filters - 2Pressure - 6 kg/cm2

13. From MB water is transferred to DM tank by DM transfer pump.

No. of pumps - 3 (2 running)Speed - 2900 rpmVolts - 415 VCurrent - 20 APressure - 8 kg/cm2

14. From DM tank water goes to CST (Condensate Storage Tank) and is stored there. From which it goes to the RFW (Reserve Feed Water tank) by which the level of hot well is maintained. The water from CST also goes for deaerator cold filling, boiler cold filling & condensate emergency filling. Thus we can explain the full water treatment cycle in a power plant.

REGENERATION

While supply of exchangeable ions with the resin is exhausted, the quality of treated water from the resin deteriorates & the resin requires regeneration. SAC is regenerated with acid.HCl is stored in BAT (Bulk Acid Tank). WBA & SBA is regenerated with NaOH, which is stored in BCT (Bulk Caustic Tank). There are 2 BAT & 2 BCT in TGS.

SAC: RNa + HCl RH + NaCl

WBA: R’Cl + NaOH R’OH + NaCl

SBA: R’Cl + NaOH R’OH + NaCl

SERVICE WATER

Water from the other part of the reservoir is used for make-up water in cooling system. Now from this reservoir the water is pumped out by service water pump, and is used as heat absorber in case of ID fan, FD fan, PAF, generator, air compressor etc. & this water is cooled at cooling tower and is used again and excess water is pumped back to the reservoir.The water from service water pump is also used as heat exchanger for ash water system bearing & rotary un-loader bearing.

No. of service water pump - 3Speed - 2920 rpm

Now the water from drinking water pump goes to bathroom etc.

No. of pumps - 2 (not in use)Speed - 2940 rpmPower - 18.5 hp

EFFLUENT TREATMENT PLANT

In this plant all kinds of used water is recycled and purified for using repeatedly. Here water from bathrooms, toilets, wasted water from ash handling plant is recycled. All the drains are connected to ETP1. The water then passes through ETP2, ETP3 & ETP4 & then it goes to the circular reservoir after passing through the oil schemer. At ETP3 PAC (Poly Aluminum Chloride) is dozed in water. When the water flooded in ETP then to extract this extra flooded water a tapping is there which is connected directly to the ganga & when it returns to its normal condition then again it get back to the tapping line of cooling water. Again from the pump where water comes by tapping raw Ganga water; the water goes to the ash water pump & by creating a slurry the ashes goes to the drain & then to the EADA (ash pond) from which the water goes to the ETP1 & ETP2. Water from ETP4 is passed through PSF and ACF, if necessary chlorine is dozed in water and finally stored in the reservoir.

AIR FLOW PATH

Forced Draught FanExternal fans are provided to give sufficient air for combustion. The forced draft fan takes air from atmosphere and, warming it in the air preheater for better combustion, injects it via the air nozzles on the furnace wall. It can either be sized to overcome all the boiler losses (pressurized system) or just put the air in furnace (balanced draft units).

Number of fan per boiler 2Rating (KW/HP) 270/362Rated voltage 6.6 KVP.F. at full load 0.85Rated speed 985 RPM

Induced Draft Fan The induced draft fan assists the FD fan by drawing out combustible gasses from the furnace and send it to stack, maintaining a slightly negative pressure to avoid backfiring through any opening.

Number of fan per boiler 2Rating (KW/HP) 450/603Rated voltage 6.6 KVP.F. at full load 0.85Rated speed 740 RPM

Primary Air FanPrimary air fan is used for pulverizing system. Primary air transfers coal to the furnace and helps in burning. Number of fan per boiler 5Motor type 3 phase AC 50Hz IMRating (KW/HP) 235/315Rated voltage 6.6 KVP.F. at full load 0.87Rated speed 1490 RPM

GENERATION OF STEAM

BOILER

Boiler is a steam raising unit of single radiant furnace type with auxiliaries, designated to generate steam 272 kg/hr. at 91.4 kg/cm2 pressure. The unit burns pulverized low grade bituminous coal and is equipped with oil burners. This plant is designed to operate at a 475m. above sea level the ambient temperature is 40oC with a humidity of 70%.Furnace consists of walls, tangent bare water tubes. Rear water tubes from a cavity for the pendant super-heater.There are many advantages of using water tube boiler: Water tube boilers are small in size, the volume of the boiler is comparatively small in comparison to the same size fire tube boiler, better circulation of water in the boiler is possible.

Manufacturer ACC BABCOCK LTD.

Steam pressure 91.4kg/cm2

Steam temperature 515oC

Furnace volume 1558m3

Drum Length 12.97m

Pressure 102.7kg/cm2

Temperature 312oC

STEAM DRUM

The steam drum is made up of high carbon as its thermal stress is very high. There is a safety valve in the drum, which may explode if the temperature and the pressure of the steam are beyond a set value.

A safety is a valve mechanism for the automatic release of a gas from a boiler, pressure vessel or other system when the pressure or temperature exceeds preset limits. It is a part of a bigger set named Pressure Safety Valve (PSV) or Pressure Relief Valve (PRV). The other parts of the set are named relief valves.

The boiler drum has the following purpose:1. It stores and supplies water to the furnace wall headers and the generating tubes.2. It acts as the collecting space for the steam produced.3. The separation of water and steam tube place here.4. Any necessary blow down for reduction of boiler water concentration is done from

the drum.

RISER AND DOWN COMERS

Boiler is a closed vessel in which water is converted into the steam by the application of the thermal energy. Several tubes coming out from the boiler drum surrounding the furnace.

Outside the water wall there is a thermal insulation such that the heat is not lost in the surroundings. Some of the tubes of the water wall known as the down comer, which carries the cold water to the furnace and some of other known as the riser comer, which take the steam in the upward direction. At the different load riser and the down comers may change their property. There is a natural circulation of water in the riser and the down comers due to different densities of the water and the steam water mixture. As the heat is supplied, the steam is generated in the risers. Lower density of the steam water mixture in the riser than water in the down comer causes natural circulation of water. Down comer connected to the mud drum, which accumulates the mud and the water. When the plant takes shut down the mud drum is allowed to clean manually.

BURNERS

15 Y jet sprayers are provided for lighting up and PF flame stabilization of 15 numbers burners. There are 3 burners in each tier and thus having 5 vertically placed tier. Lower tiers are provided with high grade coal (ECL), where upper tier burners are provide with low grade coal (ICML). There is a provision for firing both the heavy fuel oil and light diesel oil. The oil firing is done initially during the starting up and when the coal used in TGS is of poor quality, then the plant is allowed to run on oil support. In TGS light diesel oil (LDO) is used for the initiation for ignition of the pulverized coal. The LDO charged into the furnace through the oil burners. It increases the burning capacity of the pulverized coal.Heavy fuel oil passes through the pumping and heating unit to reduce the viscosity as required for firing. For LDO no heating is required. Separate oil pumps are provided for LDO. The burner has a capacity of 3.6 T/hr/burner.

For both the type of oil, the oil pump discharge a pressure is 14 kg \ cm². Constant steam pressure 10.5 kg \ cm² is maintained for oil atomization and oil heating. P 34 gas igniters are provided for ignition.

Furnace

Width - 9.144 mDepth - 7.969 mHeight - 23.164 mVolume - 1558 m3

Furnace temperature - 800oCLiberation of energy - 205440KCAL/hr/m2

SUPER HEATER

The super heater rises the temperature of the steam above its saturation point and there are two reasons for doing this:FIRST- There is a thermodynamic gain in the efficiency.SECOND- The super-heated steam has fewer tendencies to condense in the last stages of the turbine.

It is composed of four sections, a platen section, pendant section, rear horizontal section and steam cooled wall and roof radiant section. The platen section is located directly above the furnace in front of the furnace arch. It is composed of 29 assemblies spaced at 457.2mm centers from across the width of the furnace. The pendant section is located in the back of the screen wall tubes. It is composed of 119 assemblies at 1114mm centers across the furnace width. The horizontal section of the superheater is located in the rear vertical gas pass above the economizer. It is composed of 134 assemblies spaced at 102 mm centers across furnace width. The steam cooled wall section from the side front and rear walls and the roof of the vertical gas pass.No reheater is used here.

SPRAY ATTEMPERATOR

In order to deliver a constant steam temperature over a range of load, a steam generating unit (Boiler) may incorporate a spray attemperator. It reduces the steam temperature by spraying controlled amount of water into the super-heated steam. The steam is cooled by evaporating and super heating the spray water. The spray nozzle is situated at the entrance to a restricted venture sections and introduces water into the steam. A thermal sleeve linear protects the steam line from sudden temperature shock due to impingement of the spray droplets on the pipe walls. The spray attemperator is located in between the primary super heater outlet and the secondary super heater inlet.

Except on recommendation of the boiler manufacturer the spray water flow rate must never exceed the flow specified for maximum designed boiler rating. Excessive attemperation may cause over heating of the super heater tubes preceding the attemperator, since the steam generated by evaporation of spray water and it does not pass through the tubes. Care must also be taken not to introduce so much that the unevaporated water enters the secondary stage of the super heaters.

STEAM FLOW PATH

Steam goes again in superheater after attemperator and then goes to HP & LP turbine subsequently. Form HP turbine some amount of steam is collected to heat the feed water and it goes to HP 5, and then to HP 4. From HP 4 steam goes to deaerator. By the same way from LP turbine some amount of steam is collected to heat the feed water while passing through LP 2 and LP 1 subsequently. From LP 1 steam goes to condenser and mixes with feed water.

AIR PRE-HEATER

The air heater is placed after the economizer in the path of the boiler flue gases and preheats the air for combustion and further economy. There are 3 types of air pre heaters: Tubular type, rotary type and plate type. Tubular type of air heater is used in TGS. Hot air makes the combustion process more efficient making it more stable and reducing the energy loss due to incomplete combustion and unburnt carbon. The air is sent by FD fan heated by the flue gas leaving the economizer. The preheated air is sent to coal mill as primary air where coal is pulverized. The air sucked is heated to a temperature of 240-280oC. The primary air transports the pulverized coal through three burners at TGS after drying in the mill.

ECONOMIZER

The heat of the flue gas is utilized to heat the boiler feed water. During the start up when no feed water goes inside the boiler water could stagnate and over heat in the economizer. To avoid this, economizer re circulation is provided from the boiler drum to the economizer inlet. The feed water coming out from deaerator passes through to special shape of pipes inside the economizer. The special shapes of tubes provide increase the contact surface area between the flue gas and the feed water, so that maximum heat exchanging can take place.

ELECTROSTATIC PRECIPITATOR

It is a device that separates fly ash from outgoing flue gas before it discharged to the stack. There are four steps in precipitation.

1. Ionization of gases and charging of dust particles.2. Migration of particle to the collector.3. Deposition of charged particles on collecting surface.4. Dislodging of particles from the collecting surface.

By the electrostatic discharge the ash particles are charged due to high voltage (56KV) between two electrodes. Generally maximum amount of ash particles are collected in the form of dry ash, stored inside the SILO. Rest amount of ash (minimum) are collected in the form of bottom ash and stored under the water inside HYDROBIN.

TURBINE

Turbine is a rotating device which converts heat energy of steam into mechanical energy. It is a two cylinder machine of impulse reaction type comprising a single flow high pressure turbine and a double flow low pressure turbine. The H.P. turbine shaft and the generator are all rigidly coupled together, the assembly being located axially by a thrust bearing at the inlet end of H.P. turbine.The turbine receives high pressure steam from the boiler via two steam chests. The H.P. turbine cylinder has its steam inlets at the end adjacent to the no. one bearing block, the steam flow towards the generator. Exhaust steam passes through twin over-head pipes to the L.P. turbine inlet belt where the steam flows in both directions through the L.P. turbine where it

exhausts into under slung condenser. Steam is extracted from both the H.P. & L.P. turbine at various expansion stages & fed into four feedwater heaters.Here spherically seated Journal Bearing is used.

Economical and max continuous rating 60MWSteam pressure at emergency stop valve

89kg/cm2

Steam temperature at emergency stop valve

510oC

Absolute pressure at exhaust 0.088kg/cm2

1st critical speed 1520 rpm2nd critical speed 2433 rpmRotational speed 3000rpmTripping speed 3375rpm

TURBINE SHAFT GLAND

The purpose of the gland steam system is to reduce steam leakage to a minimum. Steam leakage leads to the requirement for increased make up; this increases the load on the feed and boiler water treatment chemicals and to a deterioration of the working environment surrounding the power plant. The system consists of a set of glands fitted to the turbine, and a steam supply and exhaust system to service them. The two means of controlling the gland receiver pressure; the first is by having a dump in split range with the make-up valve, the

second is the use of a pressure regulating valve which dumps excess pressure to the exhaust line.

FEED WATER CYCLE

CONDENSER

It has several functions. To condensate the steam exhausted from the L.P. turbine. To accept & condense the steam

from turbine & vents of heaters through flash box.

To maintain the vacuum. To accommodate the air and

non-condensable gases in the coolest zone of the condenser.

To receive make up water for the system & de-aerate the same.

To act as reservoir for the extraction pump.

The steam coming out of the turbine no longer remains superheated, so this warm steam is allowed to condense for recycling inside the condenser. Pressure inside the condenser is very low. So when water enters in the condenser water splashes. To prevent this, a flash box is used where splashing of water takes place. The condensate is extracted from the condenser extraction pump. This extraction should be kept free from the air & air rejecter. Pipes serve this purpose. Then water from CEP enters the drain cooler through AEJ (Air Ejector) and GSC (Gland Steam Condenser) and warm water is cooled there and increases boiler efficiency. In the drain cooler it gets the temperature of 47oC & enters the L.P. heater 1, where water temperature increases to 70oC and then it enters the L.P. heater 2 n the temperature becomes 102oC.

Diagram of a typical water-cooled surface condenser

AIR EJECTOR

Air ejectors are used to eject the air and create vacuum in the condenser. There are 3 AEJ - 1 Hawking ejector and 2 Service ejectors. Hawking ejector is used at the beginning of the cycle as the load is high but it is not used in running condition of plant as its power consumption and losses both are high. While the plant is in running condition service ejectors are used.

GLAND STEAM CONDENSOR

The gland steam condenser is cooled by the condensate extracted from the main condenser and so acting as a feed heater. The gland steam often shares its condenser with the air ejector reducing the cost of having two units.

DE-AERATOR

It helps to separate the corrosive gasses (oxygen) from the feed water. In this process feed water is sprayed in the upward direction through spray pipes and the waterfalls in the form of uniform showers over the heating trays and the air separating trays and finally it is collected in the strong space.

Deaerator

LP & HP HEATERS

These are used to heat the feedwater supplying it to the boiler.The steaming capacity of boiler is increased by preheating. It also removes the dissolved gasses. In TGS there are two types of heaters (L.P. & H.P.). Further L.P. heater is divided into L.P. 1 & L.P. 2. The warm water from the drain cooler enters the L.P. heater 1, where the temperature of water is increased by feedback portion of the steam an there after it enters the L.P. heater 2, where the water temperature rises up to 102oC. After that this feed water is heated in the H.P. heater 4, where the temperature is increased to 175oC. Then it shifted to the H.P. heater 5 where temperature increases to 210oC.

FEEDWATER HEATER

There are some functions of feed water heaters in a power station.

1. The heaters are provided on the condensate and feed cycle to improve cycle efficiency. The cycle is inefficient because of latent heat in the exhaust steam is absorbed by condenser circulating water and so lost. If a portion of steam is allowed to expand to a certain extent in the turbine and perform useful work before it is allowed to transfer its remaining heat to feed water, thus the cycle efficiency is improved.

2. If the water entering the boiler is at condensate temperature 30oC to 40oC. This reduces economizer tube metal temperature.

Combined feed water condensate

ALTERNATOR

Alternator generates electricity. In general the electrical and magnetic circuits of the generator are of conventional design.

The generator stator casing contains the core and windings which are enclosed at the ends with inner and outer and covers. At both sides of casing, air coolers are mounted on the generator soleplate and connect to a re-circulatory air ventilation system. The covers over the coolers direct air to and from the generator casing via the air coolers.

Two axial flow fans, one at each end of the rotor circulate the cooling air through the generator and air coolers.

The generator rotor, when excited, provides the magnetic field for the generator. The shaft is hollow bored at the exciter end and machined to carry the rotor winding. The rotor is threaded through the bore of the generator stator and is supported at each end by a white metal bearing. The alternator and main exciter are of the brushless type and copper links, connect the rotor winding to a rotating rectifier on the main exciter shaft.

The excitation for the generator rotor is obtained from a shaft driven permanent magnet single phase pilot exciter which supplies the static field winding of the main exciter through a

rectifier in the automatic voltage regulator cubicle. The alternating current output from the armature of the main exciter is connected onto the input side of a rotating rectifier and the rectified output is connected to the generator rotor field winding.

Maximum continuous rating 60 MW outputMaximum continuous rating 70.59 MVA o/pRated power factor 0.85 laggingRated terminal voltage 10500 voltsRated phase current 3881 ampsRated speed 3000 rpmFrequency 50HzNumber of phases 3Number of poles 2Short circuit ratio 0.6Anti-condensation heater rating 6off-1KW,415V,3ph,4wires 50Hz

EXCITATION SYSTEM

MAIN EXCITER:

Maximum continuous rating 207KWRated terminal volt at rectifier DC term

225V

Rated current at rectifier 920AFrequency 150HzRated speed 3300 rpmNumber of poles 6

PILOT EXCITER:

Number of phase 1Rated peak voltage 130V ( rms)Power factor peak 0.9 Y - ConnectionNumber of poles 8

Alternator

Exciter

ASH HANDLING PLANT

BOTTOM ASH REMOVAL SYSTEM

Here for removal bottom ash “Zero Discharge System” is used. In this system overflow transfer tank, overflow transfer pump, two numbers of hydro bin, one number of settling tank, one number of surge tank, three HP pumps, two LP pumps, ejector and three number of surge recirculation pumps are present.

The bottom ash hopper filled with the water. When the bottom ash come into the contact of water it forms clinker then the ash passes through flap gate and goes to the clinker grinder to reduce the size of the clinker formed ash. After clinker grinder it goes to the ejector where power water create the jet velocity to convey the bottom ash to the hydro bin.

Hydro bin is a conical shaped tank which can separate the ash and the water. Here two numbers of hydro bins are used. When one hydro bin is filled with the ash other comes into the service. Each hydro bin can store four days ash. In the hydro bin a horizontal plate is present that is baffle plate upon which the mouth of the slurry pipes are opened. There is a little gap between the plate and the mouth of the pipe. When the slurry water comes out from the pipe and falls on the plate the turbidity is reduced. It helps the slurry water to settle down the ash at the bottom. The ash settle down in the bottom and the water (not pure) comes out from the vertical cylindrical centerised strainer. The water from the upper most portion of the hydro bin means overflow water comes out and goes to the settling tank for more settlement of ash. In the bottom portion there is a flap gate for ash extraction through this gate the ash is collected in the truck to dispatch.

The settling tank is a conical shaped tank. Here the slurry water from hydro bin over flow comes and settle the ash. Here ash is settling down by gravity separation like hydro bin but here no baffle plate and strainer are present. Overflow of the settling tank goes to the surge tank for getting more clear water. In the bottom of the settling tank one SRP (Surge Recirculation Pump) is present to convey the settle down slurry of the settling tank to the hydro bin. The diameter of the pipe which goes to settling tank to hydro bin is small than the main ash slurry conveying pipe.

In the surge tank more ash is separated and this bottom ash is conveyed to the hydro bin through another SRP. There is no overflow facility of the surge tank. The clear water from surge tank through three number of HP pumps goes to the ejector as power water to convey the bottom ash. Similarly, two LP pumps also connected with the surge tank. It conveys the water to the bottom ash hopper for sealing purpose. The overflow water of the bottom ash hopper goes to the hydro bin through overflow transfer tank and overflow transfer pump. Here no water comes out from the system. For this reason this system is called “Zero Discharge System”.

ELECTROSTATIC PRECIPITATOR

ENVIRONMENTAL PROTECTION

To prevent the atmosphere from different poisonous gas & coal dust E.S.P is used here. There are 2 E.S.P in TGS for 2 separate boilers.

The equipment consists of different electronic & electrical circuits some of which are mounted on PCBS. The input supply of 415V, 50Hz, single phase A.C regulator is formed by connecting two thyrister. A.C regulator is fed to the primary of the high voltage transformer with the linear reactor connected in series. The secondary voltage of high voltage transformer is rectified & brought out by a high voltage brushing choke.

CONTROL CIRCUIT

To control the operation & protection of the control circuit is provided which comprises the following modules:

1. Ramp setting2. Power supply3. Power amplifier4. Synchronizing & firing module5. Flashing over sensing6. Under alarm & voltage annunciator

OPERATION OF ESP

1. Steady state load operation:

During steady state resistance load it is a DC power supply with a constant current, constant voltage characteristics where the limiting parameter can be set under manual mode of operation. The limiting action of parameters is achieved by controlling the triggering angle of the thyrister of AC regulator.

2. Operation Under Flash Over Condition:

When the spark occurs it is sensed & a common signal is given to the reference by a set amount which in turn reduces the output voltage proportionally. Dust of fly ash gets deposited in the plates which have to be regularly removed by doing raping. Seven raping system is continuously operating through the microprocessor.

FLY ASH REMOVAL SYSTEM

For fly ash removal Macawaber system is used. It consists of dome valve, solenoid valve, air seal, Macawaber compressor, some presser switches, ash vessel, ash hopper, silo etc.At first, suppose there is no ash in the ash vessel, seal air presser is proper then dome valve is in closed condition.

After that ash is in hopper seal air is drained to the atmosphere through pneumatic switch and quick exhaust valve so that dome valve can easily open without friction.

Then the five-port solenoid valve is opened &instrument air helps to open the dome valve.

Then ash fall on the ash vessel and dome valve is closed .the pneumatic switch closes which makes the seal air to the seal of the dome valve .a pressure switch is used to maintain the pressure sure of the seal.5kg \cm2. Then pressure switch gives a signal that the seal air pressure is ok.

Then solenoid valve opens &the blow valve opens through which Mac air enters for conveying the ash to the silo .the conveying pressure 1.5 kg/cm2. There are two pressure switches near blow valve. One set at a pressure of 4.5 kg/cm2, another switch at 0.39 kg/cm2. It means that suppose there is a chock age in the dry ash line, then the pressure will increase. If it is more than 4.5kg/cm2 then blow valve will close the line to be free from choc age.

Compressed air from macawaber compressor enters into the air receiver from which air enters into the piston of the 5 port solenoid valve at a pressure of 6kg /cm2 .the blow valve and its corresponding solenoid valve is present only for one row of hoppers not for every hopper. Ash conveyed to the silo when pressure in the line falls below 0.35kg/cm2 then another pressure switch operates the blow valve to close down.

The cycle then again starts after 30 sec, known as cycle gap time .the main conveying time , suppose if the ash content in the receiver is small ,then the line pressure which fall very quickly which will quickly close the blow valve , without cleaning the ash vessel .so a min time of 30 sec is given for small ash conveying to the silo.

COOLING TOWER

Cooling tower is newly placed in TGS. Cooling tower is used to cool water but not the condenser water; rather it is used to cool service water after use.

Water is required to cool several machines like generators, boiler feed pump, motors, compressors, all kinds of bearings and etc. This service water comes from Ganga and after using it is transferred to the top of cooling tower by several pipes. There are 2 cooling tower each having 3 big ID fans placed at the top. Water comes down through holes at the top of the tower and passes through metal plates. These big fans suck air. Air comes through the gaps of the metal plates and while in contact with the water it absorbs heat from the water. Thus the water is cooled and is ready to use again. Excess cooled water goes back to service water reservoir. This cooling tower works on the principle of cross flow heat exchanger.

Cooling water tower with ID fans

DISTRIBUTED CONTROL SYSTEM

Titagarh Generating Station currently runs on Distributed Control System (DCS).A distributed control system (DCS) refers to a control system usually of a manufacturing system, process or any kind of dynamic system, in which the controller elements are not central in location (like the brain) but are distributed throughout the system with each component sub-system controlled by one or more controllers. The entire system of controllers is connected by networks for communication and monitoring.A DCS typically uses custom designed processors as controllers and uses both proprietary interconnections and communications protocol for communication. Input and output modules form component parts of the DCS. The processor receives information from input modules and sends information to output modules. The input modules receive information from input instruments in the process (a.k.a. field) and transmit instructions to the output instruments in the field. Computer buses or electrical buses connect the processor and modules through multiplexer or demultiplexers. Buses also connect the distributed controllers with the central controller and finally to the Human-Machine Interface (HMI) or control consoles. See Process Automation System.Elements of a distributed control system may directly connect to physical equipment such as switches, pumps and valves or may work through an intermediate system such as a SCADA system.DCSs are connected to sensors and actuators and use set point control to control the flow of material through the plant. The most common example is a set point control loop consisting of a pressure sensor, controller, and control valve. Pressure or flow measurements are transmitted to the controller, usually through the aid of a signal conditioning Input/output (I/O) device. When the measured variable reaches a certain point, the controller instructs a valve or actuation device to open or close until the fluidic flow process reaches the desired set point. Large oil refineries have many thousands of I/O points and employ very large DCSs. Processes are not limited to fluidic flow through pipes, however, and can also include things like paper machines and their associated variable speed drives and motor control centers, cement kilns, mining operations, ore processing facilities, and many others.A typical DCS consists of functionally and/or geographically distributed digital controllers capable of executing from 1 to 256 or more regulatory control loops in one control box. The input/output devices (I/O) can be integral with the controller or located remotely via a field network. Today’s controllers have extensive computational capabilities and, in addition to proportional, integral, and derivative (PID) control, can generally perform logic and sequential control.DCSs may employ one or several workstations and can be configured at the workstation or by an off-line personal computer. Local communication is handled by a control network with transmission over twisted pair, coaxial, or fiber optic cable. A server and/or applications processor may be included in the system for extra computational, data collection, and reporting capability.

CONCLUSION

CESC’s environmental management system focuses on continuous improvement and up-gradation, with state-of-the-art principles and equipment, setting high targets and reviewing its performances. CESC recognizes its responsibility towards protecting the ecology, health and safety of the employees and consumers.

The vocational training has been organized by the CESC limited and has been undertaken at the Titagarh Generating Station. The purpose of the vocational training is to get an industrial exposure in our engineering career.

Students can learn a lot from different books about various subjects such as operations of a plant, various constituents of a plant, power production, power distribution etc. but a practical experience helps in better understanding and enhancement of knowledge in various subjects. I am grateful to CESC limited for organizing this vocational training.

REFERENCES

TGS manual Power Plant Engineering by P.K Nag Power Plant Engineering by A.K. Raja, Amit Prakash Srivastava www.cescltd.com www.wbpower.nic.in/cesc.htm www.wikipedia.org An analysis of a thermal power plant working on a Rankine Cycle by R.K. Kapooria,

S. Kumar, K.S. Kasana