CESC PROJECT

CALCUTTA ELECTRICITY SUPPLY CORPORATION LIMITED (CESC LTD.)

BUDGE BUDGE GENERATING STATION

NAME: AYAN MONDAL

ADDRESS: NORTH-EAST-NOAPARA, RABINDRA ROAD,

P.O. - NOAPARA, P.S-BARASAT, NORTH 24

PARGANAS, KOL-700125

COLLEGE: TECHNO INDIA COLLEGE OF TECHNOLOGY

NEWTOWN, MEGACITY

STREAM: APPLIED ELECTRONICS AND INSTRUMENTATION

ENGINEERING (AEIE)

YEAR: 2ND (4TH SEMESTER)

DURATION: FROM 30TH JUNE 2014 TO 12TH JULY 2014

I am extremely greatful to MR. A.SAHA (GENERAL MANAGER, BBGS),

MR. D.MAITRA (GENERAL MANAGER, HR), MR. S.ROY (DEPUTY

GENERAL MANAGER, BBGS), MR. P.DUTTA (SR.MANAGER, BBGS)

For giving the Opportunity to do the training.

I am also highly indebted to the following people under whose guidance I Successfully completed my training in various departments of BBGS:

Mr. ARIJIT GHOSH (MANAGER, PLG)

Mr. SAMIR BANDOPADHYAY (MANAGER, MMD)

Mr. KAUSHIK CHAUDHURI (MANAGER, OPS)

Mr. SUSOVAN NARAYAN CHOUDHURY (MANAGER, E & I)

Mr. SUBRATA MONDAL (MANAGER, F & A)

Mr. MONOTOSH CHOUDHURY (ASST. MANAGER, HRD)

Last but not the least, I would like to show my gratitude to all the labours, workers& various other employees of BBGS who have cordially helped me to understand the various technical aspects of the power-plant at different instants throughout the training period

Dept:- OPSName:- Signature:-

Dept:- F& AName:- Signature:-

Dept:- MMDName:- Signature:-

Dept:- E & IName:- Signature:-

Dept:- PLGName:- Signature:-

Marks Obtained In Written Test:- Attendance:-

Dept:- PTCName:- Signature:-

ABOUT CESC

PROJECT PROFILE

ABOUT BBGS

OPERATIONS

PLANNING

FUEL AND ASH

MECHANICAL MAINTENANCE

ELECTRICAL AND INSTRUMENTATION

CONCLUSION

The Calcutta Electric Supply Corporation or CESC is an Indian electricity generating company serving the area administered by the kolkata municipal corporation in addition to the city of Kolkata.it also serves parts of the Howrah,Hoogly,24 parganas(North),24 parganas(South) districts of West Bengal.

On 7 January 1897 Kilburn & Co. secured the Calcutta (Now Kolkata) electric lighting license as agents of The Indian Electric Company Limited. The company soon changed its name to the Calcutta Electric Supply Corporation Limited. The first power generating station was begun on April 17, 1899 near The Princep Ghat.The Calcutta Trumways Company switched to electricity from horse drawn carriages in 1902. Three new power generating stations were started by 1906. The company was shifted to the Victoria House in Dharmatala in 1933, and still operates from this address.

Load-shedding (interruption of power supply due to shortage of electricity) wascommon in Kolkata during 1970s and 1980s. In 1978 the company was christened asThe Calcutta Electric Supply Corporation (India) Limited. Thewas associatedwith The Calcutta Electric Supply Corporation (India) Limited from 1989, and the name was changed from The Calcutta Electric Supply Corporation (India) Limited to CESC Limited.

Recently the Calcutta power grid has seen progressively better performance and fewer outages. In the power sector, CESC, currently having a generating capacity of 1225 MW, has major plans to expand generating capacity to 7000 MW over the next five or six years. The new power generating projects -thermal, hydal and solar –wil linvolve investments of more than ` 30,000 crore. Presently CESC Ltd is the flagship company of RP-SANJIV GOENKA GROUP .

Generation and Distribution of Electricity since 1897 First Thermal Power Generation Company in India Brought Electricity to Kolkata 10 years after it came to London Tunnel under Ganga for power transmission In 1989, CESC became a part of RPG Group In 2011, CESC became a part of RP-Sanjiv Goenka Group

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SALIENT FEATURES:

No. of Consumers: 2.5 million No. of Employees: 10000 Generation Capacity: 1225 MW Substation Capacity: 7483 MVA Transmission and Distribution Network: 18449 ckt. KM Power Generation in the year 2010-11: 8756 MU Power export in the year 2010-11: 146 MU Power Import in the year 2010-11: 1523 MU Total Revenue in the year 2010-11: 4092 crores Profit after tax in the year 2010-11: 488 crores

GENERATING STATION FEATURES:

New Cossipore(NCGS): Commissioned: 1949 Capacity: 100 MW (derated) Feature of boiler: Stoker fired

Titagarh(TGS): Commissioned: 1983 Capacity: 240 MW Feature of boiler: P.F.

Southern(SGS): Commissioned: 1991 Capacity: 135 MW Feature of boiler: P.F.

Budge Budge(BBGS): Commissioned: 1997 Capacity: 750 MW Feature of boiler: P.F.

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Capacity 750 MW (3 x 250 MW)

Location PUJALI, BUDGE BUDGE, 24 PGS(S), WESTBENGAL

COMMERCIAL GENERATION

Unit # 1 07.10.97

Unit # 2 01.07.99

Unit # 2 28.01.10

Fuel source ECL, BCCL, ICML & ImportedCoals

Fuel requirement 2.45 million tons of coal per annum

Mode of transportation Rail

Water source River Hooghly

Land area 225 acres

Ash dumping area 91 acre

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No of units 3

Capacity 250 MW Unit # 1

Trial Synchronization 16.9.97

Commercial generation 07.10.97

Full Load Generation 26.02.98

Unit # 2




Unit # 3




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RANKINE 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. 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 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 quitesmall,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 around63% compared with an actual efficiency of 42% for a modern coal-fired PowerStation. This low turbine entry temperature (compared with a gas turbine) is why theRankine cycle is often used as a bottoming cycle in combined cycle gas turbine powerstationsOne 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 thesis 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. There are four processes in the Rankine cycle. These states are identified by numbers (in brown) in the above Ts diagram. Process 1-2: The working fluid is pumped from low to high pressure. As the fluid is 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 enter a condenser where it is condensed at a constant temperature to becomes a saturated liquid In an ideal Rankine cycle the pump and turbine would be isoentropic i.e., the pump and turbine would generate no entropy and hence maximize the net work output. Processes1-2 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

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This department deals with the controlling the plant generation according to the load demand.

BOILER

Manufacturer: Unit# 1 & 2 : M/S ABB ABL Limited, Durgapur, W.B. Unit# 3 : M/S BHEL

Type : Unit# 1 & 2 : Natural Circulation, Balanced Draft, Two Pass, Vertical Down-Shot Fired, Water Wall Tube, Two-Pass, Horizontal Single Drum, Single Re- heat Drum Type Boiler Unit# 3 : Natural Circulation, Balanced Draft, Two pass, Corner Fired, Water Wall Tube, Two-Pass, Horizontal Single Drum, Single Re-heat Drum Type Boiler.

Furnace : Unit# 1 & 2 Unit# 3 Width : 17940 mm 14326 mm Depth : 17173 mm 11506 mm

Super Heater : Primary/LTSH, Platen, Final.

Air Heater : Unit# 1 & 2 – 3 nos. Unit# 3 – 2 nos.

No. of FD Fan/unit : Unit# (1, 2 & 3) – 2

No. of ID Fan/unit : Unit# (1 & 2) – 3, Unit# 3 – 2

No. of PA Fan/unit : Unit# 1, 2 & 3 – 2 No. of Coal Mills/unit :

Unit# 1 & 2 – 6,

Unit# 3 – 5

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Different equipment present in the BOILER

LRSB (soot blower) : In boiler steam is used to remove soot. These soot blowers are present at the top of the boiler because large amount of soot is stored at the top level of the boiler compared to lower levels. So here to remove these soot these soot blowers are used.

These soot blowers are operated once in a day. There are 20 LRSB in this boiler.

Wall Blower: Comparatively less soot sublimes at the lower levels. So relatively smaller soot blower, known as Wall Blower, is used. Wall Blowers also uses steam for clearing soot.

There are total 56 wall blowers present. Poppet Valve is present in each Wall Blower.

Flame Scanner, Oil gun, Oil igniter: The flame scanner, oil gun and the igniter are placed at the same place combined. They are placed between two levels e.g. A-B, B-C, C-D, D-E.

The flame scanner air fan is supplied by an ac or dc source. Ac source is normally connected but when Ac is not available then dc is used. Oil igniter is HEA type (high energy arc). There are total 12 set of Flame Scanner, Oil Gun and Oil Igniter present in the boiler for Unit# 3.

Sampling Valve For Steam: There are valves present outside the boiler from where the quality of steam produced in the boiler can be collected for testing and analysis.

Main Steam Stop Valve: This valve is present at the top of the boiler. By operating this valve we can stop the main stream.

Down-comer: This is the pipe through which water from the boiler drum circulates downwards. Secondary Air Damper Controller: Depending on the amount of coal send to the boiler requirement of secondary air also changes. This valve is used to control the secondary air. C.B.D. (Continuous Blow Down): It is a pipe through which silica, if present in the water, will drain down continuously. Superheater: It consists of three stages – Primary, Platen & Final

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TURBINE

No. Of Cylinders: HP – 1 Single Flow, IP – 1 Single Flow, LP - 1 Double Flow

SV Pressure & Temp. : 146.0 Kg/cm2 Abs & 537 ˚C

Reheat Pressure & Temp. : 35.7 Kg/cm2 Abs & 535 ˚C

Speed: 3000 Rev/min

Number of Blading Stages: Unit# 1 & 2 Unit# 3

HP: 1 no – Impulse & 18 nos. – 50& Reaction 25 nos. Reaction

IP: 16 – 50 % Reaction 17 - Reaction

LP: 4 – 50 % Reaction per Flow, 3 Variable Reaction 8 – Reaction per Flow

Steaming Conditions at 100% ECR load

HP Turbine: Unit# 1 & 2 Unit# 3

Inlet Pressure: 146.0 Kg/cm2 Abs 146.0 Kg/cm2 Abs

Outlet Pressure: 41.53 Kg/cm2 Abs 39.56 Kg/cm2 Abs IP Turbine: Unit# 1 & 2 Unit# 3

Inlet Pressure: 37.35 Kg/cm2 Abs 35.62 Kg/cm2 Abs

Outlet Pressure: 4.93 Kg/cm2 Abs 6.72 Kg/cm2 Abs

LP Turbine: Unit# 1 & 2 Unit# 3

Inlet Pressure: 4.71 Kg/cm2 Abs 6.72 Kg/cm2 Abs Outlet Pressure: 76 mm Hg Abs 76 mm Hg Abs

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CONDENSOR

Condenser is a device used for converting a gas or vapour to liquid. Condensers are employed in power plants to condense exhaust steam from turbines. In doing so, the latent heat is given up by the substance and it will be transferred to the condensercoolant.A surface condenser is a shell and tube heat exchanger installed at the outlet of every steam turbine in thermal power stations. The cooling water flows through the tube side and the steam enters the shell side where the condensation occurs on the outside of the heat transfer tubes. The condensate drips down and collects at the bottom, in a pan called hot well. Initial air extraction from the condenser and steady vacuum inside the condenser is achieved by two nos. motor driven, water sealed, air extraction pumps commonly called NASH pump. During normal operation of the plant, vacuum is maintained by the circulating water flowing inside the condenser and the non-condensable gases are extracted by one of the NASH pumps. 2 nos. separate condensate storage tanks, interconnected to each other.

DEAERATOR

Deaerator is a device widely used for the removal of oxygen and other dissolved gasses from thefeedwater. It mostly uses low pressure steam obtained from an extraction point in their steam turbine system. They use steam to heat the water to the full saturation temperature corresponding to the steam pressure in the deaerator and to scrub out and carry away dissolved gases. Steam flow may be parallel, cross, or counter to the water flow. The deaerator consists ofa deaeration section, a storage tank, and a vent. In the deaeration section, steam bubbles through the water, both heating and agitating it. Steam is cooled by incoming water and condensed at the vent condenser. No condensable gases and some steam are released through the vent. Steam provided to the deaerator provides physical stripping action and heats the mixture of returned condensate and boiler feed water makeup to saturation temperature. Most of the steam will condense, but a small fraction must be vented to accommodate the stripping requirements. Normal design practice is to calculate the steam required for heating and then make sure that the flow is sufficient for stripping as well.

REHEATER: After passing through HP Turbine pressure and temperature of steam drops. This steam is then passed through Re-heater where the pressure and temperature of steam is again increased to the previous level. Then this steam is passed through IP Turbine and LP Turbine. There are two types of re-heater: horizontal and vertical.

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ECONOMIZER: Feed water is taken from the De-aerator, a feed water storage tank, by motor driven feed water pumps, and discharged through two stages of high pressure regenerative feed water heaters and the flue gas heated Economizer into the boiler drum.

HP BYPASS SYSTEM

The HP Bypass system comprises of an HP Bypass valve Steam control valve with integral Spray water injection, an HP Spray water control valve and HP Spray water pressure reducing / isolating valve. All valves are complete with Electro-hydraulic actuators, which are powered by oil supplied from a central hydraulic supply unit (HSU) shared with LP Bypass system. A quick opening device is provided to facilitate rapid opening of HP Bypass Steam control valve whenever any of the following conditions occur:

1. Turbine is tripped from a load > 20%

2. Turbine acceleration > 9% per second ( i.e. Load rejection)

3. Deviation of actual pressure from pressure set point high i.e.

(Inhibited for loads < 20%)

LP BYPASS SYSTEM

The LP bypass system passes Steam from upstream of the Reheat Stop Valves directly into the condenser thus bypassing the IP & LP turbines. Specific volume of the Steam handled by LP Bypass valves being much higher than HP Bypass system, a parallel path twin-line system is employed, each path comprising an LP Bypass Steam control valve, a ‘compact cooler’ desuperheater mounted directly on the condenser neck and a steam distributor within the condenser. All valves are complete with Electro-hydraulic actuators, which are powered by oil supplied from the central oil supply unit (shared with HP Bypass).

COMPRESSORS

Plant Air Compressor: The air required in different parts of plant is provided by these compressors.

Instruments Air Compressor: Air required in different instruments is provided by these compressors. There are a number of instruments which are

pneumatically operated. So this compressed air is required. The plant air compressor and instrument air compressors are situated in a single compressor house. Both of the above compressors are reciprocator type compressors.

Ash Plant Air Compressor: These compressors mainly fall under the fuel and ash department. These compressors are centrifugal type and are situated in a separate house. Centrifugal compressors are used here because centrifugal compressors has a large amount of discharge but it has a less pressure head.

CONDENSATE EXTRACTION PUMP

The pumps are vertical multi-stage bowl diffuser type, arranged inside a suction barrel. The condensate pump is normally located adjacent to the main condenserhotwell often directly below it. The condensate water is drawn from the condenser by the extraction pumps and sent to the low pressure feed heaters.

BOILER FEED PUMP A boiler feed water pump is a specific type of pump used to pump feed water into a stream boiler. The water may be freshly supplied or condensate produced as a result of the condensation of the steam produced by the boiler. It consists of two parts, first the booster pump then the main pump. I t i s achieved by increasing the speed to about 5700 r.p.m. If the amount of oil is decreased in between the fluid coupling then the speed will decrease. Thus a gear box is not required, instead a device called scoop is required that removes the oil and control the speed of rotation. It consumes the highest amount of power about 8.8 MW.

COOLING TOWERSThe cooling towers acts as a heat exchanger. There are fans placed at the top of the cooling towers. These fans force the air to pass from the bottom of the cooling tower to the top. Pipes from the condenser (carrying condensate) are connected to the top of the cooling towers. So the water (condensate) falls from the top and the air extracts the heat from the condensate. There are DG (diesel generators) for each unit. These generators are used to supply whenever load shedding occurs. These generators are also used to supply few large machines which require large power supply.

WATER HANDLING

Water is drawn from the River Ganges by means of Intake Water Pump. It is then sent to Flash Mixture tank, where mud floculates by means of alum and polyelectrolyte dosing.

Next, it goes to the Floculation tank, where suitable chemicals are added to remove the additional mud present in the water. The sludge passes to the sludge inspection pit.

Then, it passes to Inclined Settling Surface (ISS), where the plates are inclined at an angle of 45 degree to remove dirt present in the water (which adhere to the plates). Hypo is also added here to kill any living bacteria present in the water.

From ISS, the water goes to the Filtered Water Reservoir (FWR)via Gravity Sand Filter. A part of the filtered water is used for service, while the rest goes to the De-Mineralizing (DM) Water Plant.

DM WATER PLANT

Filtered water from the FWR is pumped to Activated Carbon Filter tank by means of DM Supply Pump. There, the remaining impurities are removed. Then, it is passed successively through Strong Acid Cation tank and De-gasser , whereby the strong cations are exchanged and weak acids formed like carbonic acid etc are dissociated to form CO2 and water by rotating the pump at high speed. The CO2 is eventually vented to the atmosphere.

Next, it is passed successively through the Weak Base Anion tank (to remove weak base anions), Strong Base Anion tank (to remove the strong base anions) and finally through Mixed Bed to remove any more cations/anions still remaining in the water.

Next, it is sent to DM storage tank, and from here it is pumped to Condensate Storage Tank (CST) by means of DM Transfer pumps.

A part of the water from the CST goes to the boiler, while the rest goes to the cooling tower

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PURPOSE

To laydown procedure for planning and maintenance related activities with a view to reduce down time of equipments to a minimum condition monitoring of plants and equipments to predict any failure, efficient management of environment, improvement in safety standards,Meeting statutory requirements related to safety and environment, generation of MIS as per business requirements and providing service to other departments.

SCOPE

This procedure is applicable for all planning activities pertaining to operations and maintenance of plants/equipments, condition monitoring of equipments, maintaining the environmental condition of the whole plant with in statutory limits, and ensuring safe and healthy working conditions for one and all of BBGS

RESPONSIBILITY AND ACCOUNTABILITY

The manager (P&E) is responsible for overall process and its instrumentation. Responsibility is delegated for the sub processes have been defined in the subsequent sections. He is also accountable to the top management for deviations from the targets set in the annual plan.

PROCESS DETAIL

In order to plan operation and maintenance related activities, monitor condition of equipments, efficiently manage environmental aspects etc. planning department has adopted the following process; a. Preparation of MIS reports.

b. Software development and Improvement of safety standards.

d. Efficient management of environment.

e. Complying with statutory requirements.

f. Condition monitoring of critical equipments.

g. Maintenance planning.

h. Collection/preparation of samples.

MEASURES AND/OR MONITORINGRelated to quantity measurement system and environment management system.

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This department deals with the handling of fuel (i.e., coal, water and air) , as well as ash which is produced as a waste in the boiler.

COAL HANDLING PLANT

Capacity: Design: 960T/Hr Rated: 800T/Hr No. of wagon tippler: 2 Track(s): 1

Primary Crusher:

Quantity: 2 Types: Rotary Breaker

Secondary Crusher:

Quantity: 2 Types: Ring Granulator

Stacker-cum-Reclaimer

Type: Slewing & luffing Boom Stacker with Bucket Wheel Reclaimer, Rail Mounted, suitable for reversible yard conveyor.

Nos.: 2 Height of pile(m): 10.5 Total travel(m): 308 Material: semi-crushed coal Lump size: (-)100 mm

ASH HANDLING PLANT

Fly Ash Handling System

Fly Ash Evacuation Rate 80 Mt/Hr

Capacities of Tank / Vessel

Air Heater 57 Liters ESP 1 & 2 485 Liters ESP 3 145 Liters ESP 4 To 7 85 Liters

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Bottom Ash System

Bottom Ash Cleaning Rate 60 MT/Hr Bottom Ash Hopper 150 MT (Approx) De Watering Bin 432 MT (Approx) Settling Tank 1240 CUM (Approx) Surge Tank 1670 CUM (Approx) Overflow Transfer Tank 21 CUM (Approx) Decant Water Transfer Tank 35 CUM (Approx)

COAL HANDLING

The primary fuel for BBGS is bituminous coal, which is mainly sourced from ECL (Eastern Coal-fields Limited), BCCL (rat Coking Coal Limited), ICML (Integrated Coal Mines Limited) and imported coals from Indonesia. Around 2.45 million tons of coal are required per annum, and the coal handling plant has been designed for 960MTH coal of (-) 300mm size, which is generally received at the site from the coal mines. Coal is unloaded in the yard either by Rota side wagon tipplers or in the track hopper through bottom discharge wagons. Normally, coal comes in rakes having 59-60 wagons each.

WAGON TIPPLER

The wagon tippler takes 7-8 hours for unloading. Each boggy is disengaged and tippled by the wagon tippler, which turns by an angle of 135 degrees, thus emptying the coal into the wagon tippler hopper. The coal is conveyed to belts 1C and 1D by means of six Vibratory Feeders-three for each belt. From each of 1C and 1D,it is made to fall into 1A or 1B by controlling the respective Flap Gates.

TRACK HOPPERThe BOBR(Bottom opening bottom release) type wagons take around 2.5 hours for unloading. The track hopper can handle 18 wagons at a go. The coal falls into the track hopper, from where it is conveyed to belts 101A and 101B by means of four Paddle

Feeders.

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From each of 101A and 101B,the coal is sent to either of belts 1A and 1B by operating the respective Flap Gate.

From flap gate coal is passed through few electro-magnets so that metallic impurity present in the coal is separated.

Then coal is transferred to PRIMARY CRUSHER HOUSE (PCH) through TP#101 where the coal is crushed to a size less than 100 mm by using a ROTARY BREAKER.

Then from primary crusher house coal is transferred either to STOCKYARD (COAL STOCK)for storage or to the SECONDARY CRUSHER HOUSE (SCH).

At the SCH coal pieces having size greater than 20mm is passed to SCREEN CRUSHER and pieces having size less than 20mm is bypassed to TP#2 through belts 4A and 4B.

Then crushed coal is transferred to TP#2 from where it is either transferred to the BUNKER of unit# 1 or towards TP#3.

From TP#3 coal is directed towards BUNKER of unit# 2 or towards TP#3/1. From TP#3/1 coal is transferred to BUNKER of unit# 3. From Bunker of each unit coal is fed to the FEEDER. This feeder controls the

amount of coal that is to be supplied to the COAL MILL. (For Unit# 1 & 2 there are 6 feeders and 6 coal mills).

From coal mill after crushing the coal to a size small than 75μm coal is fired to the BOILER furnace from particular heights.

ASH HANDLING

In the Ash Circuit there are mainly three parts. A. Fly Ash Conveying System

B. High Concentration Slurry System

C. Bottom Ash Conveying System

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FLY ASH CONVEYING SYSTEM:

Fly ash collected in the hoppers located below the Air Pre-heaters and E.S.P.

E.S.P.(Electrostatic Precipitator) : There are 2 passes in the E.S.P. : A pass and B pass. The ash which results after the hammering of the e.s.p. plates is stored in the hoppers below the e.s.p. This is the fly ash present in the flue gas (removal of bottom ash is described in the boiler section). After ash is stored in the lower part of the e.s.p. there are valves which open for a time of 25-26 seconds. After the closure of this valve the ash is blown by air to the ash handling plant.

HIGH CONCENTRATION SLURRY SYSTEM:

In B.B.G.S. this special system is used for fly ash disposal. Fly-ash from SILO is mixed with water to form homogeneous SLURRY using the mixer. Then this high-concentration slurry is directed to disposal area situated at a distance of 3.5 kms from the main plant. An emergency pump is kept so that in case of any blockage in the disposal line high pressure air from this pump is used to clear the blockage.

BOTTOM ASH CONVEYING SYSTEM:

Bottom ash collected from the hoppers below the boiler is mixed with water and passed to the ECCENTRIC CRUSHER. Then mixture of ash and water is transferred to DEWATERING BIN. Water overflows from the top of the dewatering bin and this water is transferred to the SETTLING TANK. The ash is collected at the bottom. This ash is then loaded in truck. Water from the ash is collected through the strainers and this water is transferred to the DECANT WATER TRANSFER TANK. Then water from this tank is transferred to the SETTLING TANK. Then water is transferred to the SURGE TANK. This water is then re-circulated. Surge collected from the bottom of the settling tank and the surge tank is transferred to the dewatering bin.

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There are 3 main type of maintenance: -

1. Preventive Type

2. Predictive Type

3. Breakdown Type

PREVANTIVE TYPE

This type of maintenance is preventive type. This maintenance is done mainly to prevent any type of occurrence of breakdown or other faults of particular equipment. Preventive type maintenance is done as per schedule provided by the manufacturing company.

PREDICTIVE TYPE

This type of maintenance is done at regular interval. Various parameters (e.g. temperature, vibration etc.) are measured using different equipments of a power plant. From the corresponding values of the parameters any chance of occurrence of fault is predicted and required steps are taken.

BREAKDOWN TYPE

This type of maintenance is done when breakdown of particular equipment occurs. This maintenance is done only when a breakdown or fault occurs. This maintenance is done as soon as possible so that fault is cleared and generation is resumed.

The major divisions in this department include: Maintenance of Boiler & its auxiliaries

Boiler,ID Fan,FD Fan,P A Fan, Coal Mill , Various Pumps, etc. Maintenance of Turbine & its auxiliaries

:Turbine,CEP,BFP,NASH Pump,HP-LP Bypass, System, Condensate Transfer Pump, Circulating Cooling Water (CW) Pumps, Service Cooling Water Pumps, etc.

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Maintenance of Fuel and Ash

Conveyor System, Rotary Breakers, Crusher, Wagon Tipplers, Track Hoppers, Bottom & Fly Ash

Main equipments and systems which fall under the MMD department are briefly described below: -

PULVARIZED COAL MILL

The mill is a large ball slow speed, E-type machine with horizontally disposed grinding rings. The ring elements consist of top and bottom grinding rings having machine tracks in which run 10 Alloy Steel Hollow cast balls each of 830 mm. After certain running hours when the balls come down to a dia 760 mm a fill in ball (11th ball) of that dia is inserted in the grinding track. No further action will be then be necessary until all the 11 balls reach the dia of 720 mm. Then they require replacing. The bottom ring is mounted on the yoke, which sits on the gearbox output shaft flange, and this rotates at 33.41 rpm. The top ring is prevented from rotating by a spider, which is keyed to it. The spider has four hard steel guide carried on a large diameter pins and these blocks are controlled to move in a vertical direction only by guides attached to the mill housing and fitted with hard steel wear plates.A static type classifier is situated on the top of the mill housing and a centrally disposed coal chute ensured that raw coal is fit to the centre of the grinding elements. Centrifugal action forces the coal outwards between the balls and the grinding rings where it is pulverized.Two PA Fans supply the required primary air for 6 nos. mills (normally 4 nos. running). Hot PA bus and old PA bus runs over the 6-nos. mills. Mill outlet temperature and PF flow are properly maintained by HAD and CAD operation of individual mill. It then passes through throat ring gap and air grid plates window. The resulting increase in velocity prevents particles of coal from falling past the ring. The air string passed towards the classifier picks up finer particles. Larger particles separate out and fall back on to the grinding zone. The mixture of coal and air then passes through classifier where over size particles are returned further grinding and the fine product passes to the coal pipes and the burners. Rejects falling through the throat gap are carried around and fall into reject chamber, which is scraped out by scrapper plough and controlled through reject gate. When reject gate is being open then pyrite gate is closed. There is one Relief gate. The relief gate is protected from metal plate called metal apron plate against any damage by scrape iron or large stone piece. There is one scrapper plough under the bottom yoke, which scrap the reject and drops the materials into pyrite chamber.

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The classifier is mounted on the top of the mill and is fitted with individually adjustable for fineness control. At the bottom of the classifier a ring of hanging plates (skirt plate) is arranged so that over size coal can pass back into the grinding elements but primary air

is prevented from short-circuiting the classifier vanes..Turing the vanes towards their radial position will decreases the fineness of the PF and turning them towards the

closed position will increase fineness. There is a provision for sampling the P. F. from vertical portion of the coal pipe at the Burner Front.

MILL GEAR BOX LUBRICATION SYSTEM

The oil lubrication system is designed to lubricate the 10.9E Mill gearbox unit. The complete system is mounted as a substantial steel solo plate on a concrete foundation. It consists of pump motor, fillers, cooler etc. The oil is drawn from the reservoir of the sump of the gearbox by the motor drives gear pump & is fed to the dual filter. The oil is then passed through a water tube cooler & hence via the flow indicator to the gearbox. The interconnecting piping take the oil to the gear unit internal lubrication system. Four spring loaded relief valves are incorporated in the system.

First two are after the pumps & act as a Safety valve for the pump increase of filter blockage.

Third one acts as a cooler by pass & operated when the oil is cold at the time of starting.

The forth one act as a pressure regulator is adjusted to maintain specific working pressure at the gear unit.

The system has one main pump & one stand by pump, duplex filter, one main cooler & one stand by cooler. So that in case of failure of any one of them, the stand by equipment can take over.

SEAL AIR SYSTEM

The mill operates under pressure. It is therefore necessary to prevent the escape of coal dust laden air where the mill main shaft penetrates the mill housing. Using a gland supplied with clean seal air at higher pressure then that inside

the mill effects this. This air is supplied by seal air fan & fed by seal air pipe onto the seal air ring (Al cast ring) is piped to the mill shaft seals and prevents the leakage of P.F. into adjacent bearing or out to atmosphere.

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This department basically deals with the electrical and instrumentation aspects of BBGS.

GENERATOR

Unit#1&2 Unit#3 Maximum continuous rating 250MW 250 MW Maximum continuous rating 294MVA 294 MVA Rated power factor 0.85 0.85 Rated terminal voltage 16500V 16500 V Rated current 10291A 10291 A Frequency 50 Hz 50 Hz No. of phases 3 3

GENERATOR TRANSFORMER

Make Phase, Freq

No. of unit /generators

Rated voltage(kV)

Rated current(A)

UNIT#1&2 TELK1PH,50 HZ

3 nos.,1Ph 138/√3 ,16.5 LV

1318 HV,6364 LV

UNIT#3 BHEL3PH,50 HZ

1 nos.,,3 Ph

235 HV,16.5 LV

773.9 HV,11022.14 LV

STATION TRANSFORMER

Make Phase, Freq

No. of unit /generators

Rated voltage(kV)

Rated current(A)

UNIT#1&2CGL 3 Ph,50

HZ3 Ph 132 HV,6.9

LV 262.4 HV

UNIT#3 BHEL 3 Ph,50HZ 3 Ph 235 HV

UNIT TRANSFORMER

Make Phase, Freq No. of unit /generators

Rated voltage(kV)

Rated current(A)

UNIT#1&2 HHE3Ph,50Hz 1 nos.,3Ph 16.5 HV,6.9

LV1,6.9LV2 1410.3 HV,2094.3 LV1,1256.6 LV2

UNIT#3 BHEL3Ph,50Hz 1 nos.,3Ph 16.5 HV,6.9

LV1,6.9LV2

ELECTRICAL NETWORK IN BBGS

There are 2 switchyards in B.B.G.S., a 132 kV switchyard for Unit# 1 & 2 and a 220 kV switchyard for Unit# 3. There are 2 ICTs(Interconnecting Transformers) for connecting (electrically) two switchyards. In each section there are 2 main buses M1 and M2. There is another bus named Transfer Bus which is used during the change in load of M1 and M2 or during maintenance, for uninterrupted power supply. For the 132 kV switchyard M1 is fed from one GT (Generating Transformer) and M2 from the GT of other unit. There is MBC (Main Bus Coupler) in both the switchyards for coupling M1 and M2. From M1 and M2 of each switchyard power is supplied to the Feeder# 1, 2, 3, 4 (132 kV switchyard) and Feeder# 5 & 6 (220 kV switchyard).

Output of the generator (16.5 kV) is fed to the primary of the GT which steps up the voltage to 132 kV (Unit#1 & 2) or 220 kV (Unit# 3). Output of the generator is also fed to the primary of the UT (Unit Transformer) which steps down it to 6.6 kV which is used to supply different parts of a unit. ST (Station Transformer) is fed from the 132 kV and the 220 kV bus and ST steps down it to 6.6 kV. This ST is used to supply common parts of different units of the Generating Station, e.g. lighting etc.

In case if due to any fault any of the two switchyard supplies is disconnected from the GT then that switchyard is supplied by the other one through ICT. There are both Isolators and Circuit Breakers in the switchyard. Circuit Breakers are operated in on-load condition where as isolators are operated in off load condition. So, during the connection of any bus the sequence of operation is- firstly, isolator is closed, then the corresponding CB (circuit breaker) is closed. Reverse sequence is followed during the opening of a certain bus.

MAJOR COMPONENTS OF SWITCHYARD

Circuit Breaker. Bus Isolators with & without Earth switch. Line Isolators with Earth switch. CT. PT with PT Isolator & Earth switch. Main Bus. Transfer Bus. Jack Bus. Aluminum Bus Pipe.

Total No of Bays: 8

1 No. Generator Transformer Bay. (GT 3). 1 No. Station Transformer Bay. (ST 3). 2 Nos. Interconnecting Transformer Bays. (ICT1, ICT2). 2 No. Line Feeder Bays. (Line 5, Line 6). 1 No. Bus Coupler Bay. (MBC). 1 No. Bus Transfer Bay. (TBC).

A Bay Consists of:

Circuit Breaker (52X). M1 Bus Isolator (29A) with Earth Switch (29AE). M2 Bus Isolator (29B). Line Isolator (29L) with Earth Switch (29LE). PT with PT Isolator (29PT) & E/S (29PTE). CT.

ISOLATOR

Two types of Isolators used:

1) Horizontal double end break, center post rotating, motorized, mechanically ganged type with one earth switch: 29 Nos. 2) Pantograph type, motorized without earth switch: 7 Nos.

Rated current: 1600 Amp. 245 KV rated, 3 phase.

Suitable to connect with ACSR Moose conductor & Al bus pipe.

DBR Isolator: M1 Bus isolator (29A), Line Isolator (29L), Transfer Bus Isolator (29T), PT Isolator (29 PT) in all bays and M2 Bus Isolator (29B) for MBC Bay only (All with E/S). Pantograph Isolator: M2 Bus Isolator (29B) for 7 Bays except MBC bay. Isolators are 3 pole disconnecting switch. They should carry the rated current continuously & short circuit current for a specified time.

UPS SYSTEM

A power station is meant for supply power to the user. Normally the power flows from the generating station to the load end. But in an adverse situation when any unit or the power station is dead suddenly it requires adequate planning to restore from the adverse situation keeping the process parameters & the equipments safe. For running the vital equipments the following stable powers are used here as described below –

220V DC :- The principal duty of this system is to provide secure DC supply for the following loads :

Emergency lighting Providing power to the emergency motors (Turbine DC EOP, DC JOP, DC Seal

oil of Generator etc). Providing control power to trip/close the breakers (here 6.6KV) as needed for

during normal/emergency. Providing power to trip the fuel systems (both oil & coal) Emergency valve operation (TLR, extraction valves) Running dc scanner fan when ac power is not available.

UPS (Uninterruptable Power Supply), 230V AC :- this is considered the second stable source. The main functions of UPS are

To provide power in uninterrupted manner to the load. The power should be pure. Output Power should be stable irrespective of input voltage or frequency

variations. Frequency Variation

MODES OF OPERATION

NORMAL MODE: When the utility is normal, the UPS powers the load through the rectifier and inverter and charges the batteries at the same time.

BATTERY MODE: When the utility fails, the battery will power the load through the inverter. When utility becomes normal, it automatically returns to the normal mode. BYPASS MODE :

In the event of inverter overload which lasts longer than the typical time, an output short-circuit or fault of an inverter, UPS transfers the load to bypass. Two types of bypass modes are present. In the first kind, UPS can set to return to normal automatically when the fault is cleared. In the second kind, Ups is set to return to normal only by manual transfer. When main UPS circuit fails, the battery is depleted or a severe fault occurs, inverter will be shut down and system remains in bypass mode. System can return only with a manual reset after fault is cleared.

MAINTENANCE MODE : When UPS has to be repaired or has to undergo routine maintenance, UPS can be set to maintenance mode by switching on maintenance bypass circuit breaker. The load will be powered from maintenance bypass supply without interruption. 24V DC: - The principal duty of this system is to provide secure DC for the following loads

Process control panels Annunciation panels Display of vital parameters Providing power to some vital remote panels which require 24V power, like LP

bypass, AVR etc

DCS & PLC SYSTEM

There are two basic types of controls-open loop and closed loop control. In open loop control, the input is directly fed to the system via a controller to get the output, and the input does not depend on the output. In closed loop control, the error signal derived by comparing the input with the output is fed to the system via a controller. Normally, in a plant, most control systems are open loop controls, where the error signal derived by comparing the measured input with a desired set point to get the output, and the output is not fed back to the input.

The physical quantity to be controlled is measured by means of a transducer, which converts a mechanical variable (usually pressure) to an electrical signal, i.e., current within a range of 4-20 mA .The value of 4mA corresponds to the lowest value of the quantity, while 20mA corresponds to the highest value of the quantity. The current

signal is fed to the CPU, which consists of many cards, which converts the analog signal into an equivalent ASCII or hex code. The signal is then controlled by a PID controller present in the CPU; this ASCII code is reconverted to a current signal in the range of 4-20 mA by means of another set of cards. These cards are of various types like analog input analog output (AIAO) etc. The current signal is converted to pressure signal by means of an I-to-P converter (i.e., an actuator). This pressure signal is compared with another pressure signal calibrated in the range of 0.2-1 Kg/Cm2 to produce a positioner signal, which causes movement of the corresponding valve to bring the input value nearer to the setpoint, thus producing the desired output. The parameter values are controlled from the Control rooms, while the logic may be changed from the Engineer’s room. Normally, each major equipment of the plant like boiler, turbine, generator etc.is controlled by a separate CPU which consists of various cards for each controllable parameter of the equipment; for example, the parameters for the boiler are boiler temperature, drum level etc. Each parameter consists of two cards (A & B), one for operation and the other for standby, so that complete shutdown of the control system does not occur. The various cards within a particular CPU communicate with each other by means of a switch. Again, a parameter of particular equipment (e.g. boiler) may require a signal from a parameter of another equipment (e.g. turbine). Thus, interconnection among the various CPUs is necessary, and this is achieved by a core switch. All the CPUs are also connected to form a network by means of another switch. This network is known as DCS (Distributed Control System), and there is one DCS system for each of the three units of BBGS. Units 1 & 2 employ Foxboro DCS form Invensys, while Unit 3 employs Max DCS from Metso. In some DCS systems, TM R (Triple Modular Redundancy) system is employed, where the error signal is obtained by comparing three signals, thus decreasing chances of a shutdown. Sometimes, four redundancy is also employed. For oil related controls, Invensys –make Triconex DCS is used. Each stand-alone unit is a PLC( Programmable Logic Controller), and all the PLCs are interconnected to form a DCS.

Input Devices: -

Inputs are defined as real-world signals giving the DCS a real time status of process variables. The signals can be of analog or digital, maintained or momentary, low or high voltage/current signals. Common type signals are any switch /relay changeover contact, push button, limit switch, lockout switch any protection device switching etc. Analog types are resistance, current or voltage input.

Output Devices: -

The outputs are also mainly of two types digital or analog. The digitals again can be subdivided into low current type (<500mA) or high current type (normally known as relay output type) (< 3A). Practical digital outputs are indication lamps, solenoid valves, and annunciation windows, command to MCC/breaker to drive a load.

CPU :-

The CPU (central processing unit) performs the tasks necessary to fulfil the DCS function. It reads the program as stored in its memory block, checks the input status & gives command to output devices as per program. It also checks the health of the total devices connected to it. Normally to do the job of scanning.

Programmer: - The programmer unit provides an interface between the DCS and the user program during program development, start-up, & on-line troubleshooting.

From all the study it can be concluded that the Budge Budge generating station of 250X3 unit is a fairly organized generation station with the latest machinery available. The turbine is a very sophisticated assembly of machinery which requires specific conditions of steam temperature and pressure to work efficiently. Any alteration of the specific requirements may prove to be hazardous. Another interesting yet worrying fact is the quantity of coal consumed which approximately10, 800 tonne per day. The level of pollution is always controlled according the established norms, but still I consider it to be quite enough. Well, efforts are always underway in reducing the pollution and improving the efficiency of the plant. All in all, a thermal power plant is a very large establishment with many components and it awesome to see how all the components work in a synchronized manner.

CESC PROJECT

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