training report ntpc muzaffarpur bihar

“NATIONAL THERMAL POWER CORPORATION LTD.” An

Industrial Training Report

On

“GENERATION SYSTEM”

Submitted

In partial fulfillment

For the award of the Degree of

Bachelor of Technology

In

Department of Electrical Engineering

Submitted to: Submitted By: Mr. Piyush Sharma SS COLLEGE OF ENGINEERING EE/EEE/EC (HOD)

Dilip Kumar 12ECOEE005

B-Tech Final Year

Department of Electrical Engineering

SS College of Engineering, Udaipur, Rajasthan

Rajasthan Technical University, Kota, Rajasthan

Candidate Declaration:

SS College of Engineering, Udaipur, Rajasthan Technical University is a record of my own in-

vestigations carried under the Guidance of Mr. PIYUSH SHARMA, H.O.D Department of Electrical

Engineering ,” in Department of Electrical Engineering and submitted to the Department of Electrical

Engineering, SS College Of Engineering, Udaipur.

I have not submitted the matter presented SS College of Engineering I hereby declare that the

work, which is being presented in the Industrial Training Seminar Report, entitled in partial fulfilment

for the award of Degree of “Bachelor of Technology in this report anywhere for the award of any other

Degree.

Submitted to:

Submitted By: Mr. Piyush Sharma (HOD) SS COLLEGE OF ENGINEERING UDAIPUR (RAJASTHAN)

Dilip Kumar 12ECOEE005

B-TECH FINAL YEAR

ABSTRACT

Any thermal power plant is converting the chemical energy of fossil fuel (coal) into electrical energy. The process involved for this conversion is based upon the Modified Rankin Cycle. The major components that are used to accomplish the modified Rankin cycle are

• Boiler feed pump • The steam generator water walls (evaporator) • Steam generator super heaters • Steam turbine • Re heater • Condenser • Regenerative feed heaters All components of a power generating cycle are vital and critical in operation. In Modified Rankin

Cycle, the two most important aspects that is added are reheating & regenerative heating. By reheating we used to send the steam coming from exhaust of the turbines back to the re heater of the boiler so that its enthalpy increases and more work can be done by this steam the other purpose is to make steam dry so that no harm will be done to the blades of the turbine. In NTPC, Kanti, we have three turbines in Tandem coupling namely one H.P Turbine, one I.P Turbine & one L.P Turbine coupled with the generator to which is synchronized with the grid to produce electricity at 50Hz. In all my modesty, I wish to record here that a sincere attempt has been made for the presentation of this project report. I also trust that this study will not only prove to be of academic interest but also will be able to provide an insight into the area of technical management.

Contents

CHAPTER No.

TOPIC Pg. No.

1 Introduction To NTPC 1 1.1 Growth of NTPC Installed Capacity & Generation 1 1.2 Introduction To KBUNL 1 1.3 Basic Theory of Thermal Power Generation 2 1.4 Line Diagram of Power Plant 3 1.5 Over View Of Thermal Power Plant 4 1.6 General Layout of Thermal Power Plant 6 1.7 MTPC Plants Introduction 6 1.8 Light Up Process 9 1.9 Milling System 9 1.9.1 Coal Bunker 9 1.9.2 Coal Feeder 9 1.9.3 Pulverize Mill 10 2 2.1 Main Boiler Components 10 2.1.1 Furnace 11 2.1.2 Economizer 11 2.1.3 Boiler Drum 11 2.1.4 Drum Internals 11 2.1.5 Down comers 12 2.1.6 Water Walls 12 2.1.7 Riser Tube 12 2.1.8 Super Heater 12 2.2 Repeater 13 2.3.1 Desupperheaters 13 2.3.2 SuperheaterDesuperheater 13 2.3.3 Reheater Desuperheater 13 2.3 Electrostatic Precipitator 14 3 3.1 Types of Fan 15 3.1.1 P A Fan 15 3.1.2 FD Fan 15 3.1.3 ID Fan 15 4 4.1 Types of Pumps 16 4.1.1 Condensate Extraction Pump 16 4.1.2 Air extraction Pump 16 4.1.3 Boiler Feed Pump 16 4.2 Types of Cycle 17 4.2.1 Steam cycle 17 4.2.2 Water cycle 18 4.2.3 Flue Gas Cycle 18 5 5.1 Type of Heater 18 5.1.1 Higher Pressure Heater 18 5.1.2 Low Pressure Heater 18 5.1.3 Types of Turbine 18

6 6.1 Types of Turbine 19 6.1.1 HP Turbine 19 6.1.2 IP Turbine 19 6.1.3 LP Turbine 19 7 7.1 Assembly of Turbine Generator 20 8 8.1 Exciter & baring Gear 20 9 9.1 Flame Scanner 21 9.1.1 Important Control Loop In a Thermal Power Plant 21 9.1.2 Set Point 21 9.1.3 Measurement 21 9.1.4 Comparator 21 9.1.5 Controller 21 9.1.6 Final Control 21 9.2 Drum Level Control 22 9.3 DP Cross Feed Control Station 23 9.4 Combustion Control 24 10 10.1 Re-heater Steam 25 10.2 BFP Minimum Flow 25 10.3 Hot Well Level control 25 10.4 Desecrator High & Low Level Control 25 11 11.1 Unit Control Desk & Panels 26 12 12.1 220KV/132KV Substation 27 13 13.1 Power Supply For Plant Auxiliary 27 13.2 AC Power Distribution 27 13.2.1 Main Plant 27 13.2.2 Station Service Switch Gear(415V) 27 13.2.3 Unit Service Switch gear(415V) 28 14 14.1 Coal Handling Plant 28 14.1.1 Coal Handling Plant of MTPC 29

1 Introduction to NTPC NTPC is India’s largest energy conglomerate with roots planted way back in 1975 to accelerate

power development in India. Since then it has established itself as the dominant power major with presence in the entire value chain of the power generation business. From fossil fuels it has forayed into generating electricity via hydro, nuclear and renewable energy sources. This foray will play a major role in lowering its carbon footprint by reducing green house gas emissions. To strengthen its core business, the corporation has diversified into the fields of consultancy, power trading, training of power professionals, rural electrification, ash utilization and coal mining as well.

NTPC became a Maharatna Company in May 2010, one of the only four companies to be awarded this status. NTPC was ranked 431st in the 2015, Forbes Global 2000’ ranking of the World’s biggest companies.

1.1 Growth of NTPC installed capacity and generation

The total installed capacity of the company is 45,048 MW (including JVs) with 18 coal based and 7 gas based stations. 7 Joint Venture stations are coal based and 8 renewable energy projects. The company has set a target to have an installed power generating capacity of 1,28,000 MW by the year 2032. The capacity will have a diversified fuel mix comprising 56% coal, 16% Gas, 11% Nuclear and 17% Renewable Energy Sources including hydro. By 2032, non fossil fuel based generation capacity shall make up nearly 28% of NTPC’s portfolio. NTPC has been operating its plants at high efficiency levels. Although the company has 17.73% of the total national capacity, it contributes 25.91% of total power generation due to its focus on high efficiency.

In October 2004, NTPC launched its Initial Public Offering (IPO) consisting of 5.25% as fresh issue and 5.25% as offer for sale by the Government of India. NTPC thus became a listed company in November 2004 with the Government holding 89.5% of the equity share capital. In February 2010, the Shareholding of Government of India was reduced from 89.5% to 84.5% through a further public offer. Government of India has further divested 9.5% shares through OFS route in February 2013. With this, GOI's holding in NTPC has reduced from 84.5% to 75%. The rest is held by Institutional Investors, banks and Public actor; it is also among the great places to work.

1.2 Introduction to Kanti Bijlee Utpadan Nigam Ltd. (KBUNL)

Muzaffarpur Thermal Power Station (MTPS) (2x110 MW) belonged to Bihar State Electricity Board (BSEB). Both the units of the station were shut down due to high cost of generation in Oct, 2003. Govt. of Bihar and BSEB wanted to revive the station. Govt. of Bihar decided to hand over the station to a joint venture company formed by NTPC and BSEB, with NTPC having a majority stake in the JV. Accordingly, a Memorandum of Agreement (MOA) was signed between Govt. of Bihar, BSEB and NTPC on 26/12/2005, for further reviving the station, operation and maintenance of the establishment and takeover of MTPS by the proposed Joint Venture Company of NTPC & BSEB. As per MOA, NTPC would have 51% of the equity in the JV Company and BSEB 49%. However present equity holding stands as 64.57 % by NTPC & 35.43 % by BSEB.

JV Company named as Vaishali Power Generating Company Limited” was incorporated on 06.09.2006. However JV name changed to “Kanti Bijlee Utpadan Nigam Limited” on 10.04.2008.

R&M of 110 MW Unit-1 & 2 was completed by KBUNL in are under running condition. LocationLinkage & Quantity : At present bore well water is being used fowater from river Budhi Gandak will be used (15 Cusec for Stage

Coal source and quantityQuantity required: 1.3 MTA for both the units (at 80% PLF).Bihar

KBUNL Stage-II :- 2 x 195 MW Coal Fired units are also being erected by KBUNL, power of which shall go the Bihar and other eas2015. Erection of Unit-4 and Balance of the plant(BOP) is under process.

was completed by KBUNL in Nov. 2013&Nov. Location: Village: Kanti, District: Muzaffarpur, State : Bihar

At present bore well water is being used for running the plant. After R&M,water from river Budhi Gandak will be used (15 Cusec for Stage -I).

Coal source and quantity: ECL mines. Chitra/ Jamtara, Mugma, Salanpur & Raniganj mines. Quantity required: 1.3 MTA for both the units (at 80% PLF).Allocation of Stage

Figure:-1.1 NTPC Unit 1

2 x 195 MW Coal Fired units are also being erected by KBUNL, power of which shall go the Bihar and other eastern states. 195 MW Unit-3 was test synchronized on 31

4 and Balance of the plant(BOP) is under process.

Figure:-1. 2 NTPC Unit 2

Nov. 2014 and both the units : Kanti, District: Muzaffarpur, State : Bihar Water

r running the plant. After R&M,

Salanpur & Raniganj mines. Allocation of Stage-1 Power :100% to

2 x 195 MW Coal Fired units are also being erected by KBUNL, power of 3 was test synchronized on 31st March

1.3 Basic Theory of Thermal Power Generation

Thermal power generation plant or thermal power stations the most conventional source of

electric power. Thermal power plants also referred as coal thermal power planted steam turbine power

plant. Before going into detail of this topic, we will try to understand the line diagram of electric power

generation plant.. A power generation plant mainly consists of alternator which runs with help of steam

turbine. The steam is obtained from high pressure boilers. Generally in India, bituminous coal, brown

coal and peat are used as fuel of boiler. The bituminous coal is used as boiler fuel has volatile matter

from 8 to 33 % and ash content 5 to 16 %. To increase the thermal efficiency, the coal is used in the

boiler in powder form.

In coal fired thermal power plant, the steam is produced in high pressure in the steam boiler due

to burning of fuel (pulverized coal) in boiler furnaces. This steam is further supper heated in a super

heater. This supper heated steam then enters into the turbine and rotates the turbine blades. The turbine

is mechanically so coupled with alternator that its rotor will rotate with the rotation of turbine blades.

After entering in turbine the steam pressure suddenly falls and corresponding volume of the steam

increases. After imparting energy to the turbine rotor the steam passes out of the turbine blades into the

condenser. In the condenser the cold water is circulated with the help of pump which condenses the low

pressure wet steam. This condensed water is further supplied to low pressure water heater where the

low pressure steam increases the temperature of this feed water, it is again heated in high pressure.

For better understanding we furnish every step of function of a thermal power station as follows,

1) First the pulverized coal is burnt into the furnace of steam boiler.

2) High pressure steam is produced in the boiler.

3) This steam is then passed through the super heater, where it further heated up.

4) This supper heated steam is then entered into a turbine at high speed.

5) In turbine this steam force rotates the turbine blades that means here in the turbine the stored

potential energy of the high pressured steam is converted into mechanical energy.

1.4 Line Diagram of Power Plant

Figure:

6) After rotating the turbine blades, the steam has lost its high pressure, passes out of turbine blades

and enters into a condenser.

7) In the condenser the cold water is circulated with help of pump which condenses the low pressure

wet steam.

8) This condensed water is then further supplied to low pressure water heater where the low pressure

steam increases the temperature of this feed water, it is then again heat

where the high pressure of steam is used for heating.

9) The turbine in thermal power station acts as a prime mover of the

Line Diagram of Power Plant

Figure:-1.3 Line Diagram of Power plant

After rotating the turbine blades, the steam has lost its high pressure, passes out of turbine blades

water is circulated with help of pump which condenses the low pressure


steam increases the temperature of this feed water, it is then again heated in a high pressure heater

where the high pressure of steam is used for heating.

9) The turbine in thermal power station acts as a prime mover of the alternator

After rotating the turbine blades, the steam has lost its high pressure, passes out of turbine blades

water is circulated with help of pump which condenses the low pressure


ed in a high pressure heater

alternator.

1.5 Overview of ThermalA typical Thermal Power Station Operates on a Cycle which is shown below.

The working fluid is water and steam. This is called feed water and steam cycle. The ideal

Thermodynamic Cycle to which the operation of a Thermal P

RANKINE CYCLE.

In steam boiler the water is heated up by burning the fuel in air in the furnace & the function of

the boiler is to give dry super heated steam at required temperature.

The steam so produced is used in driving the steam Turbines. This turbine is coupled to

generator (usually three phase synchronous alternator), which generates electrical energy.

The exhaust steam from the turbine is allowed to condense into water in

which creates suction at very low pressure and allows the expansion of the steam in the turbine to a

very low pressure. The principle advantages of condensing operation are the increased amount of

energy extracted per kg of steam and thereby increasing efficiency and

the boiler again reduces the amount of fresh feed water.

The condensate along with some fresh make up feed water is again fed into the boiler by pump (called

the boiler feed pump).

In condenser the steam is condensed by coo

tower. This constitutes cooling water circuit.

The ambient air is allowed to enter in the boiler after dust filtration. Also the flue gas comes out of the

boiler and exhausted into atmosphere through stacks. These constitute air and flue gas circuit. The flow

of air and also the static pressure inside

called Forced Draught (FD) fan and

power station along with different circuits is illustrated below.

Overview of Thermal Power Plant A typical Thermal Power Station Operates on a Cycle which is shown below.


Thermodynamic Cycle to which the operation of a Thermal Power Station closely resembles is the

the water is heated up by burning the fuel in air in the furnace & the function of

is to give dry super heated steam at required temperature.

The steam so produced is used in driving the steam Turbines. This turbine is coupled to

y three phase synchronous alternator), which generates electrical energy.

The exhaust steam from the turbine is allowed to condense into water in steam condenser of turbine

s suction at very low pressure and allows the expansion of the steam in the turbine to a


energy extracted per kg of steam and thereby increasing efficiency and the condensate which is fed into

the boiler again reduces the amount of fresh feed water.


In condenser the steam is condensed by cooling water. Cooling water recycles through cooling

tower. This constitutes cooling water circuit.



of air and also the static pressure inside the steam boiler (called draught) is maintained by two fans

fan and Induced Draught (ID) fan.The total scheme of a typical thermal

r station along with different circuits is illustrated below.

A typical Thermal Power Station Operates on a Cycle which is shown below.


ower Station closely resembles is the

the water is heated up by burning the fuel in air in the furnace & the function of

The steam so produced is used in driving the steam Turbines. This turbine is coupled to synchronous

y three phase synchronous alternator), which generates electrical energy.

steam condenser of turbine,

s suction at very low pressure and allows the expansion of the steam in the turbine to a


the condensate which is fed into


ling water. Cooling water recycles through cooling



(called draught) is maintained by two fans

The total scheme of a typical thermal

Figure:

Inside the boiler there are various heat exchangers, viz.’

in the fig above, it is basically the water tubes, i.e.

(sometimes ‘Reheated’, ‘air preheated

In Economizer the feed water is heated to considerable amount by the remaining heat of flue gas.

The Boiler Drum actually maintains a head for natural circulation

through the water tubes.There is also Super Heater which also takes heat from flue gas and raises the

temperature of steam as per requirement.

1.5.1 Efficiency of Thermal Power Station or Plant

The overall efficiency of a thermal power

plant capacity. Installed plant capacity Average overall thermal efficiency

upto 1MW 4%

1MW to 10MW 12%

10MW to 50MW 16%

50MW to 100MW 24%

above 100MW 27%

Figure:-1.4 Block Diagram Of NTPC

Inside the boiler there are various heat exchangers, viz.’ Economizer’, ‘

in the fig above, it is basically the water tubes, i.e. down comer riser circuit), ‘

preheated’ are also present).

the feed water is heated to considerable amount by the remaining heat of flue gas.

The Boiler Drum actually maintains a head for natural circulation of two phase mixture (steam + water)


temperature of steam as per requirement.

Efficiency of Thermal Power Station or Plant

thermal power station or plant varies from 20%to

Average overall thermal efficiency

’, ‘ Evaporator’ (not shown

riser circuit), ‘Super Heater’

the feed water is heated to considerable amount by the remaining heat of flue gas.

of two phase mixture (steam + water)


to 27%and it depends upon

1.6 General layout of thermal power plants

Figure:

1.7 MTPS PLANT INTRODUCTION Salient Features of Boiler PlantGeneral a) Type of boiler

Reheat type.

a) Type of fuel used Heavy oil & L.D.O. (for light up &flame stabilization) b) No. of Mills c) Type of Mills d) Furnace e) P.A. Fans f) F.D. Fans

layout of thermal power plants

igure:-1.5 Layout of Thermal Power Plant

PLANT INTRODUCTION

f Boiler Plant

Single drum tangential firing &

Type of fuel used Pulverized coal (Main Fuel)Heavy oil & L.D.O. (for light up

6

Pressurized type Bowl Mill

Balanced draught

2 nos. (each 60% capacity)


Single drum tangential firing &

Pulverized coal (Main Fuel)

ressurized type Bowl Mill

Balanced draught



g) I.D. Fans 3 nos. (one standby) (Each 60% capacity) h) Air Heater 2 nos. i) Type of Air Heater Trisect or Regenerative j) Electrostatic Precipitator 1 nos.

2. M.C.R. Parameter M.C.R. Value a) S.H. Outlet Steam Flow 375 T/Hr b) R.H. Steam Flow 331 T/Hr c) Pressure at S.H. Outlet 141.5 Ata d) Temp. at S.H. Outlet 540oC e) Pressure at R.H. Inlet 37 ata f) Pressure at R.H. Outlet 32.9 ata g) Temp. at R.H. Inlet 369oC h) Temp. at R.H. Outlet 540oC i) Pressure in Drum 148.69 ata j) Design Pressure 158.0 kg/cm2 k) Flue Gas temp. leaving Economizer 350oC l) Flue Gas temp. leaving Air Heater 142oC m) Feed Water Temp. before Economizer 235oC

� Salient Feature Of Turbine

1. General

a) Type Of Turbine Reheat

b) No. Of Cylinders 3 (HP,IP & LP) c) No. Of LP Heater 5 d) No. Of HP Heater 2 e) Desecrator 1 (Variable pressure type) f) No. Of Extraction pump 3 (one standby) g) No. Of BFP 2 (one standby) 2. M.C.R. Parameter M.C.R. Value a) Rated output 110 MW b) M.S. Pressure at H.P. turbine inlet 130 ata c) M.S. temp. at H.P. turbine inlet 535oC d) H.R.H. Temp. at I.P. turbine inlet 535oC e) Turbine speed 3000 rpm f) Condenser Vacuum 0.1 kg/cm2 (abs) g) No. of Extraction 7 h) Quantity of cooling water 15,400 m3/hr � Salient Feature Of Generator a) Rating Continuous b) Active Output 110 MW c) Rated Voltage 11000 +/- 5% V d) Rated Current 7220 A e) Power Factor 0.8 Lagging f) Frequency 50 Hz g) Excitation System Static type

h) Field Current at rated output 1335 A i) Type of Cooling System Hydrogen Cooled j) Hydrogen Pressure 2 ata k) No. of H2 Cooled elements 6 l) Cooling Medium for H2 Soft water

1.8 LIGHT UP PROCESS MTPC Kanti has direct firing system. In this system, a controlled quantity of crushed coal is fed to each bowl mill (pulveriser) by its respective feeders and primary air is supplied from the primary air fans which dries the coal as it is being pulverized and transports the pulverized coal through the coal piping system to the coal burners. There are six pulverizes out of which four are used and two remains in standby. The raw coal feeders supply 74 TPH of coal to each mill. The pulverized coal and air discharged from the coal burners is directed towards the center of the furnace to form firing circle. There are 24 tilting, tangentially fired coal burners fitted at the four corners of the boiler at six elevations. The secondary air heating system supplies secondary air for combustion in the furnace around the pulverized coal burners and through auxiliary air compartments directly

1.9 MILLING SYSTEM 1.9.1 COAL BUNKER: - These are in-process storage silos used for storing crushed coal coming from the coal handling plant through conveyor belts. There are six coalbunkers supplying coal to each mill and are located at top of the mills to aid in gravity feeding of the coal. Each bunker can store coal, which can be used for 12hrs. 1.9.2 COAL FEEDER: - The purpose of coal feeder is to transfer coal at a pre- determined rate, from coalbunker to the mill. The coal feeder comprises two continuous chains with L sections flight bars mounted between the chains at every fifth link .The chains runs on sprockets mounted at each end of the feeder to given an upper strand movement towards the driven ends and a lower strand movement in the opposite direction. The drive shaft is supported on two self aligning bearing mounted in the Plummer block on support out side the feeder casing, shaft sealing is achieved by the lip seals in the sealing housing and mounted in board of the bearing to abut the feeder casing.

The tail sprocket shaft is mounted in adjustable bearing blocks adjacent to the feeder casing with positioned which allow the feeder chain to be tensioned. Both upper and lower strands run over full width carrying plates with the lower strands located by angle section guides mounted on the feeder wall. The upper and lower carrying plates and the inside wall are protected from wear by replaceable stainless steel panels, chains are kept clean by rubber wiper.

Feeder input is achieved by roller chain drive to the conveyor via a fixed speed electric motor driving a variable speed gear box, torque limiter and fixed out put gear box The electric motor is flanged mounted to variable speed gear box, coupled to the fixed output gear box by a flexible coupling and torque limiter.

The principle of operation of coal feeder is that coal flows from the bunker into the chain feeder via feed hopper and is conveyed to the mill, when the feeder is in the operation, the conveyor chain drag a fixed head of coal towards the driven ends of the feeder. At the end of the carrying plates the coal falls through the conveyor onto the bottom plate, where it is picked up by the returning flight bars and dragged back along the feeder to fall into the mill.

1.9.3 PULVERISER MILL:-

There are six mills located adjacent to the furnace at 0 m level .These mills pulverize coal to desired fineness to be fed to the furnace for combustion . The main structure of the pulverisering mill is fabricated from mild steel in three cylindrical sections, the bottom section (the mill housing support )which support the entire unit and en-closes the mill drive gear unit, a center section (the mill housing)that contains the rotary grinding element and upper section (the classifier housing )comprising an accommodate the gas loading cylinders of the mill loading gear .A platform around the upper section provide an access to an inspection door and to the top of the mill routine maintenance and is served by detachable ladder .The grinding element comprises of 3 rotatory rollers. The raw coal enter the mill through inlet and fall into the grinding zones ,where rotating bot-tom grinding and transport coal through the grinding element into the primary air stream. The primary air enters through the inlet duct in the mill while goes to the furnace from four outlet ducts at the top of the mill.The ground fuel particle are picked up by the primary air stream after it is passed through the throat plates and carried upwards towards the classifier The larger particle are initially carried upwards by the air stream and circulate over the upper grinding ring before falling back into the grinding zone by virtue of their weight .The coal air mixture then passes into the classifier ,where any remaining oversize particle are separated out and fall down to the return skirt until their commutative weight is sufficient to deflect the flaps and return them into the grinding zone . The setting of the classifier vane control the fineness of the ground product . Heavy material such as pyrites and tramp iron which has passed through grinding zone with-out being pulverized is carried around throat plate and discharged through a counter balance relief gate into the space below the yoke . 2.1 Main Boiler Components The major accessories of a steam-generating unit are listed as below:

� Furnace. � Economizer. � Boiler drum. � Down comers. � Water walls. � Riser tubes. � Super heaters. � Repeaters. � Desupeheaters.

2.1.1 Furnace

A boiler furnace is the first pass of the boiler in which fuel is burned and from which the combustion products pass to the super heater and second pass of boiler. The combustion process is a continuous process, which takes place in first pass of the boiler and controlled by fuel input through coal feeders. It is a radiant type and water-cooled furnace and enclosure is made up of water wall. The furnace is open at the bottom to allow ash/clinkers to fall freely into the furnace bottom ash hopper (through a ‘furnace throat’), and at the top of its rear wall, above the arch, to allow hot gases to enter the rear gas pass. The basic requirements that a furnace must satisfy are:

1. Proper installation, operation and maintenance of fuel burning equipment. 2. Sufficient volume for combustion requirements. 3. Adequate refractoriness and insulation.

2.1.2 Economizer

The function of an economizer in a steam-generating unit is to absorb heat from the flue gases and add this as sensible heat to the feed water before the feed water enters the evaporative circuit of the boiler. This additional heating surface in the path of the feed water increases the efficiency of the steam generating cycle, saving in fuel consumption, thus this additional surface was named as ‘economizer’. The economizer is placed in the path of the flue gases leaving the boiler, in the boiler rear gas pass below the rear super heater. The economizer is continuous ‘unlined loop type’ and water flows in upward direction and gas flows in the downward direction. Since water flow is from bottom to top so if any steam is formed during the heat transfer it also moves along with water and prevent the lock up steam which will cause overheating and failure of economizer tube. A recalculation line with a stop valve and non return valve is incorporated to keep circulation in economizer into boiler drum when there is fire in furnace but it prevents the feed water flow into the boiler drum.

2.1.3 Boiler drum The boiler drum is a cylindrical pressure vessel with hemispherical ends. It contains two rows of cyclone separators, four rows of drier boxes, a perforated feed water distribution pipe, and a chemical dosing pipe. The boiler drum is located on the upper front of the boiler. It is suspended from roof steel-work by two u-shaped slings. It forms a part of the water circulation system of the boiler. The drum serves mainly two functions:

I. The first and primary one is that it separates steam from the mixture of water and steam discharged into it and to reduce the dissolved solid contents of the steam to below the prescribed limit of 1 ppm.

II. Secondly, the drum houses all equipments used for purification of steam after being separated from water. These equipments are knownas ‘drum internals’.

2.1.4 Drum internals These are the equipments, which are used to separate water from steam and to direct the flow of water and steam to obtain an optimum distribution of drum metal temperature in boiler operation. The drum internals consists of baffle arrangements, devices which change the di-rection of flow of steam and water mixture, separators employing spinning action for remov-ing water from steam or steam purifiers as washers and screen dryers.

2.1.5 Down comers Down comers provide a passage for water from the boiler drum to bottom ring header. From bottom ring header the water goes to water walls for heat absorp-tion and conversion into steam heating .To achieve the circulation of water into water wall Boiler circulation pumps are provided in down comers.

2.1.6 Water walls Water walls are the necessary elements of the boiler. They serve as the means of heating and evaporating the feed water supplied to the boiler from the economizers via boiler drum and down comers. In large boilers, water walls completely cover the interior surfaces of the furnace providing practically complete elimination of exposed refractory surface. They usually consist of ver-tical tubes membrane and are connected at the top and at the bottom to headers. These tubes receive water from the boiler drum by means of down comers connected between drum and water walls lower header. Water walls absorb 50 percent of the heat released by the combustion of fuel in the furnace, which is utilized for evaporation of feed water. The mixture of water and steam is discharged from the top of the water walls into the upper wall header and then passes through riser tubes to the steam drum. The design and construction of the water walls depends upon the combustion and steam con-ditions and the size of the boiler. 2.1.7 Riser tubes A riser is a tube through which the mixture of water and steam pass from an upper water wall header to the steam drum. 2.1.8 Super heater The steam generated by the boiler is usually wet or at the most dry saturated because it is in direct contact with water. So, in order to get superheated steam, a device known as superhea-ter has to be incorporated in the boiler. The function of the super heater system, is to accept dry saturated steam from the steam drum and to supply superheated steam at the specified final temperature of 540oC, by means of a series of heat transfer surfaces arranged within the boiler gas passes. A superheated is a surface type heat exchanger generally located in the passage of hot flue gases. The dry saturated steam from the boiler drum flows inside the super heater tubes and the hot flue gases flows over the tubes and in this way its temperature is increased at the same pressure. The super heater consists of three sections classified as primary super heater, secondary super heater and final super heater. In Kanti, there are 14 super heater coils which are divided into above different sections where temperature is increased from approx. 340oC to 540oC. Dry saturated steam from the drum passes through the three sections of super heater, increas-ing the temperature to approx. 540oC as it travels through each section.

2.2 Repeater A repeater is a device that is incorporated in the upper arch of the boiler near the gooseneck in the path of the outgoing flue gases. As the name indicates, it reheats the. Outlet steam from the HP turbine and thus increasing its temperature up to the desired value. The repeater accept cold reheat steam from the HP turbine exhaust and supply hot reheat steam at the specified outlet steam temperature of 540oC by means of heat transfer surfaces arranged within the boiler gas passes. The repeater consists of 2 heating coils which finally raise the temperature of the steam to the required level. Steam from the HP turbine exhaust enters the reheater system through two parallel mounted spray water desuperheaters liners located in the cold reheat pipe work, then passes through reheated, increasing the temperature as it travels through it. Reheated outlet temperature is controlled by raising or lowering the angle of burner tilt. When this reheated steam enters the IP turbine, the net efficiency of the cycle is increased. 2.3 Desuperheaters 22..33..11 SSuuppeerr HHeeaatteerr DDeessuuppeerrhheeaatteerr TThhee ssuuppeerr hheeaatteerr ddeessuuppeerrhheeaatteerr iiss ff ii tttteedd aaff tteerr 1100tthh ccooii ll ttoo ccoonnttrrooll tthhee ssuuppeerrhheeaatteedd sstteeaamm aatt tthhee ssppeeccii ff iieedd tteerrmmiinnaall tteemmppeerraattuurree ooff 554400ooCC.. TThhee mmaaxxiimmuumm ddeessiiggnn tteemmppeerraattuurree rreedduuccttiioonn aatt tthhee ssuuppeerr hheeaatteerr ddeessuuppeerrhheeaatteerr iiss ff rroomm 444466 ooCC ttoo 338888 ooCC.. TThhee ddeessuuppeerrhheeaatteerr ccoommpprriisseess aa sspprraayy nnoozzzzllee sshheell ll aanndd aassssoocciiaatteedd sspprraayy aasssseemmbbllyy pprroojjeeccttiinngg iinnttoo aa sseeccttiioonn ooff tthhee ssuuppeerr hheeaatteerr sstteeaamm ll iinnee.. TThhiiss sseeccttiioonn ooff tthhee sstteeaamm ll iinnee ffoorrmmss tthhee ddeessuuppeerr--hheeaatteerr sshheell ll .. SStteeaamm aassssiisstteedd sspprraayy nnoozzzzllee aasssseemmbbllyy pprroovviiddeess aa ff iinnee sspprraayy ooff wwaatteerr wwhhiicchh aatt--tteemmppeerraatteess tthhee sstteeaamm ppaassssiinngg tthhrroouugghh tthhee ddeessuuppeerrhheeaatteerr.. Spray water for desuperheater is taken from the boiler feed water pump discharge. In addi-tion, spray water regulating stations are provided further downstream in each line. 2.3.2 Reheater Desuperheater The reheater desuperheater is only brought into use when the reheater outlet temperature ris-es above the normal temperature. The reheater desuperheater comprises of a spray nozzle shell and associated spray nozzle as-sembly projecting into a section of the steam line between the HP turbine outlet and the re-peater inlet headers. This section of the steam line forms the desuperheater shell. Water is fed into the shell from the discharge side of the boiler feed pumps via a repeater desuperheater spray water regulating station When the reheated desuperheater is called into service water is fed via the water tube and through the desuperheater and thus decreasing the quantity of water in the boiler. Drum is relatively small compared to the total steam output. So, the drum size is determined by the space required to accommodate the steam separating and purifying equipments.

2.3 Electrostatic precipitator The ash content in the Indian coal is of the order of 30% to 40%. When coal is fired in the boiler, ashes are liberated and about 80% of ash is carried along with the flue gases. If this ash is allowed to atmosphere, it is hazardous to health. So, it became necessary to incorporate an electrostatic pre-cipitator in the path of the flue gases going in the atmosphere. The electrostatic pre-cipitators are preferred to mechanical precipitators because they are capable of pre-cipitating particles from sub micron to large sizes of particles. The efficiency of the modern ESP’s is of the order of 99.9%.The electrostatic precipitator consists of a large chamber, which comprises of parallel rows of sheet type collecting electrodes suspended from the precipitator casing with wire type discharge electrodes arranged mid-way between them. At the inlet of the chamber, gas distributor screens for uni-form distribution of the gases in the chamber, are provided. The collectors are connected to earth at positive polarity while the discharge elec-trodes are connected to a high voltage dc supply at negative polarity. When dust-laden gas flows between the electrodes, the corona discharge causes the dust par-ticles to become charged, the particles then being attracted towards and, eventually, deposited on the collector electrodes. This dust falls as the collecting electrodes are continuously rapped through a rapping system and is collected into the pyramid type hoppers, located beneath each collecting electrodes, from where it is removed by the ash handling system Air heaters Air heater is a heat transferring device in which air temperature is raised by transferring heat from flue gases. Air heaters are capable of reclaiming heat from the flue gases at low temperature levels and thus reducing the amount of heat rejected to chimney. This results in increasing the boiler efficiency. For every 20 0C drop in flue gas exit temperature, the boiler efficiency increases by about 1%. In MTPC Kanti, regenerative type of air heaters is mainly used. In regenerative air heaters, the heating medium i.e. flue gases flows through a closely packed matrix structure and then air is passed through the matrix to pickup the heat. There are two regenerative type of main air heaters for heating up the air from fans.

3.1 TYPES OF FAN A fan is a device by which the air is made to flow at required velocity and pressure in a defined path imparting K.E of its impellers to air/flue gases . This pressure boost is used to create a draught in the air and flue gas system. Fans mainly performs two functions:

i. They supply air required for combustion in the furnace with required pressure & flow.

ii. They evacuate the product of combustion i.e. flue gases into the atmosphere via chimney.

3.1.1 P.A. FAN

The primary air fan supplies heated air to the coal mills known as primary air, to give dry and pulverized coal to the furnace for efficient combustion. There are two P.A fans per boiler. The fan impeller is a double inlet, centrifugal wheel with backward curved plate blades. Ambient air is drawn into the P.A duct by two 50% duty, motor driven centrifugal fans. The air from each fan discharges into a hot air crossover duct via a steam air heater. This duct extends around to each side of the boiler to supply the hot air to mills duct, both of which are branched to supply hot air to four coal mills. 3.1.2 F.D. FAN

The forced draught fan system is provided to supply secondary air required for pulverized coal combustion in the furnace, air for fuel oil combustion and over fire air to minimize No production. The F.D fan system comprises of two single stage axial flow, constant speed, and auto variable pitch fans per boiler. These fans provide pressurized atmospheric air to the boiler for combustion. Ambient air is drawn into the secondary air system by two 50% duty, motor driven, axial flow forced draught fans with variable pitch control. The air from each fan discharges into a hot air crossover duct via a main air heater. This duct extends around to each side of the boiler furnace to form two secondary air to burners ducts. At the sides of the furnace, each duct split to supply air to two corners. 3.1.3 I.D. FAN The induced draught fan system comprises of three centrifugal double inlet fans per boiler, two operating and one standby. Each fan unit consists of a backward curved plate bladed impeller, which is driven by an electric motor through a variable speed hydraulic coupling. The I.D fan serves the purpose of evacuating the products of combustion or the flue gases in the atmosphere via chimney. The flue gases after being cleaned in the precipitators is directed towards the atmosphere through the chimney.

4.1 TYPES OF PUMP 4.1.1Condensate Extraction Pump (CEP)

The function of Condensate extraction pumps is to pump out the condensate to the desecrator through, LP heaters. The steam from the LP cylinders exhausts into the con-denser shells where it is constrained to flow across the water tubes, through which cool-ing water is circulated. The steam condensed on the tubes drain to the bottom of the shell and is collected in a hot well .The condensate is retained in the hot well by means of the condenser level control valve. The water in a condenser provides a head of water for the condensate extraction pump to suppress cavitations in its suction impellers.There are two 100% duty extraction pumps, one remains in duty and one remains stand by. With all the necessary instruments such as suction and discharge valve isolating and dump valves to insure efficient operation.

The thrust bearings in the driving motors have temperatures sensor, which can trip the motors automatically. The pump discharge the condensate to the LP heater system with a pressure increased to approx. 18 kg/sq. cm from 70-75 mm of Hg.

4.1.2 Air Extraction Pump (AEP) The function of the air extraction pump is to raise and maintain the vacuum condi-

tions in the turbine main condensers, and to remove air and other non-condensable gases vented to the condenser from various parts of the turbine and feed water heating system.

4.1.3 Boiler Feed Pump (BFP) Boiler feed pump is the most critical component of a power plant. It is a rotary

machine, which is coupled to a motor through variable speed coupling or turbo coupling.

Feed water is supplied to the boiler of each turbo-generator se ler feed water pump sets. Under normal conditions two 50% boiler feed water pump sets are run in parallel to undertake the complete load of feeding the boiler, while the third 50% pump set is on standby duty.

BFP

Figure:-1.6 Boiler Feed Pump

Booster Pump

Motor

Hydraulic Coupling

Desecrator

4.2 TYPES OF CYCLE

4.2.1 Steam Cycle Drum S. H. H. P. T. R. H. I. P. T.

Condenser I. P. T A thermal power plant is based upon the principle of conversion of heat energy

(steam energy) into mechanical energy. For this conversion of energy a power plant requires a turbo machine.A turbo machine is a power producing thermodynamic ma-chine. It requires a suitable working fluid, a source of high-grade energy and a sink for low-grade energy. In a thermal power plant water is used as a working fluid and it is converted into steam.The steam turbine is a device that converts heat energy of the steam coming from the boiler into the mechanical energy (kinetic energy) with the help of which we rotate our shaft.

Steam is formed in the rising tubes of water walls and is collected in the upper portion of the drum which is separated by the water in the drum by the drum internals. This steam contains some water droplets which is to be removed before reaching tur-bines. This steam is heated in superheater (primary superheater, secondary superheater & final superheater) which makes this steam free from water droplets. Main steam is then 1st applied to high pressure turbine (HPT) at temp. approx. 540oC & pressure 138kg/cm2. The steam coming out from HPT has low temp. & pressure and required to raise this temp. & pressure before applying to next turbine. Hence, it is passed through reheater due to which its temp. & pressure is raised enough and is then applied to intermediate pressure turbine(IPT) and steam coming out of this turbine is directly used to rotate the final low pressure turbine(LPT). Steam from this turbine has very low pressure & temp. and can’t be further used to rotate the turbine. So, it is condensed and converted to water before sending to the drum for reuse. 4.2.2 Water Cycle

Hotwell C. E. P. L. P. H. Deaerator

Drum Economizer H. P. H. B. F. P. Water cycle starts from the condenser and ends to the drum.

Steam from the LPT is condensed in the condenser while condensed steam known as condensate is collected in a hotwell having temp. about 40oC & pressure 70-75 mm of Hg. The pressure of this condensate is increased to approx. 18 kg/cm2 by using CEP while the temp. is increased to approx. 80oC by using low pressure heater(LPH). To re-move the dissolved oxygen from condensate, deaerator is used and then it is passed through BFP to raise its pressure approx. to the drum water. To further increase its temp. upto 130oC, it is passed through high pressure heater (HPH). Then finally before sending it to drum its temp. is raised to approx. 250oC by passing it through economizer. Hence, the extra steam is condensed and reused.

4.2.3 Flue Gas Cycle Furnace S. H. R. H. Economizer Chimney E. S. P. A. P. H The fuel such as coal when heated in the furnace produces smoke and ash. This smoke produced is known as FLUE GAS whose temperature is very high and so used to heat few systems such as superheater & reheater. The flue gas is produced in the furnace. It then heats superheater & reheater after which it heats economizer and air preheater (APH). Since now also its temperature is quite high and also contains some dust hence, it is precipitated in electrostatic precipitator (ESP) before leaving chimney. 5.1 TYPES OF HEATER 5.1.1 High Pressure Heater (HPH) In the water cycle, temperature of feed water from BFP is increased to approx. 130oC by heating it in HP heater. As the heating of the feed water in HP heater is done by the extra steam coming out of the High Pressure Tur-bine(HPT) hence, it is named as High Pressure Heater(HPH). 5.1.2 Low Pressure Heater (LPH) In the water cycle, temperature of condensate from CEP is raised to approx. 80oC by heating it in LP heater. As the heating of the con-densate in LP heater is done by the extra steam coming out of the Low Pressure Tur-bine(LPT) hence, it is named as Low Pressure Heater(LPH).

6.1 TYPES OF TURBINE

6.1.1 HP Turbine HP turbine is a single flow design with eight stages of balding .Each stage comprises

stationary and moving blades which are positioned into the rotor mounted on the diaphragms, directs steam into the rotor mounted on the moving blades. H.P. turbine is double shell construction comprising inner and outer casing. H.P steam enters the H.P. turbine inner casing through vertical inlet connection are mounted on the top and bottom outer casing .The steam directed through the diaphragm expands through the rotor blades and diaphragm towards the fronts of the cylinder. The steam exhausts through the two branches in the bottom half casing and returns to the boiler to be reheated to increase the temperature of the steam to 538oC so that the efficiency of Rankin Cycle increases. 6.1.2 I.P. Turbine:-

Intermediate pressure turbine is a double flow design with seven stage of balding on either side of central steam inlet. Each stage comprises stationary and moving blades which are positioned so that the stationary blades mounted on diaphragm, directs the steam into the rotor mounted moving blades. Turbine is double shell construction inner casing , two diaphragm carries the ring , and outer casing .The first 4 stage of each flow are located within the inner casing and re-maining stage within the diaphragm carries the ring .The inner casing, diaphragm carrier ring and outer casing are made in halves bolted together in the horizontal centre. 6.1.3 L.P. Turbine:-

LP turbine is of double flow design incorporating six stages in each of its front and rear flow paths. Each stage consists of number of stationary blades incorporating in the diaphragm located in the casing and a set of rotating blades mounted on a rotor disc. A spray water system design to operate automatically ,ensure that excessive temperature are not produced in the exhaust flow during prolonged operation at low turbine load /low condenser vacuum.

7.1 ASSEMBLY OF TURBINE GENERAT OR & EXCITER AND BARRING GEAR

DB IPTLPT 1 ) HPT Exciter

CA Electrical Barring Gear Generator (15.7 KV, 3000 rpm) Steam Condenser (3 phase, 50 Hz) CRH

C & D:-STOP VALVES A & B:-GOVERNING VALVE

Figure:-1.7 Assembly Of turbine & Generator

8.1 FLAME SCANNERS In a flame there are three zones. 1. Visible zone 2. UV zone 3. Infrared zone The flame scanner consists of UV light sensi-tive tube and UV light sensitive element filled inside the tube on which 700 DC Volt is supplied. Initially there is no contact between the two Electrode on which 700 DC volt is supplied. As there is UV light sensitive element present inside the tube, it scans the UV zone of the flame. When it scans the UV zone, the UV element present inside the tube conducts and the two Electrodes are in contact. Now, the supplied voltage is reduced to zero. Hence, whenever it scans the UV zone, the supplied voltage becomes 0V otherwise it is 700V. Therefore, on an average the scanner shows 400V – 450V which confirms the presence of flame inside the furnace. As there are two types of fuel which are the main source of burning. Hence, basically there are two types of flame scanners depending upon the fuel used. So, to sense the flame due to oil used in the furnace there are oil flame scanners and to sense the flame due to coal used are known as coal flame scanners

9.1 IMPORTANT CONTROL LOOPS IN A THERMAL POWER PLANT

� Basic Block Diagram Of Any Closed Control Loop

Set Point Error

Figure:-1.8 control Loop Process: The equipment whose present level, pressure and other values is to be meas-ured is known as process. 9.1.1 Set Point: The required value of parameter is set by the manual which is to be maintained in order to protect the process from damage. 9.1.2 Measurement: The present value of parameter in process is measured here. Generally, capacitance type of measurement is used. Two tapping from the process, one at high pressure & other at low pressure, is taken and transmitted through isolating diaphragm and silicon oil fill fluid to a sensing diaphragm in the centre of the differential pressure cell. The sensing diaphragm deflects in response to differential pressure. The position of the sensing diaphragm is deflected by capacitor plates on both sides of the sensing diaphragm. The differential capacitor between the sensing diaphragm and the capacitor plate is converted electronically to a 4-20 mA signal and transmitted to comparator. This measurement sometimes also known as transmitter 9.1.3 Comparator: It compares the signal between set point and measured value. If the two values differ from one another, an error signal is generated and sent to the con-troller. 9.1.4 Controller: It is an electronic card which, according to the error signal sent by comparator, gives a current signal between 4-20 m A to final control element. 9.1.5 Final Control Element: It is that portion of the loop which directly changes the value of the manipulated process variable and finally do some work to maintain the set point of the process.

+

Controller Final Control Element

Process

Measurement

9.2 Drum Level Control

Set Point Error

Figure:-1.9 Drum Level Control

The required drum level is set at the set point. The present drum level is then measured which is done by capacitor type transmitter. Two tapping, one at the bottom in water while other at the top in steam, is made and allowed to flow to the transmitter. Since, the two elements are in different states, steam is condensed and collected in a constant head unit (CHU) before going to the transmitter where the present drum level is measured and converted to current signal between 4-20 mA. This set value and measured value are then compared in a comparator and an error signal, if any, is generated and sent to con-troller which finally directs the final control element to control the drum level. Here, the final control element is a control valve through which a fluid passes that adjusts the size of the flow passage as directed by a signal from controller to modify the rate of flow of the fluid. Hence, the drum level is controlled.

+

Controller Feed Water Control Valve

Process

Measurement/FB

9.3 D.P. Across Feed Control Station

Set Point Error

Figure:-2.1 Feed Control In order to maintain the linear characteristics of the feed regulating valves under dif-ferent loads, the differential pressure(D.P.) control loops maintains a fixed differential across the regulating valves and BFP discharge pressure is varied by changing BFP motor speed through hydraulic scoop tube device which is the final control element here. The D.P. across feed station (comparator) is sensed and is fed to the controller. The controller are automatically adjusted as function of steam flow to achieve stable condition. The re-serve Boiler Feed pump scoop tube automatically follows the running pump scoop tube and the changeover to the reserve BFP takes place with the scoop tube in the same posi-tion of the scoop tube. 9.4 Combustion Control The combustion control proposed for this boiler comprises of the following loops: a. Master pressure control b. Pulverized coal flow control c. Combustion air flow control d. Oxygen trim control e. Mill temperature and air flow control

9.4.1 Master Pressure Control The turbine throttle pressure which is a measure of turbine and boiler mismatch, is maintained by proper fuel and air flow control to the burners. Actual steam pressure at turbine inlet is measured and error against a set value is fed to the individual pulverize control loop through controller.

+

Controller BFP Scoop Process

Measurement

9.4.2 Flow Control In order to maintain an air rich furnace, air flow demand signal is superimposed over total fuel flow signal through a high limiter unit. This way when master demand sig-nal increases and if air flow is low, fuel flow is not straightaway increased. Instead, main demand signal first increases the air flow and only when demand signal is low as com-pared to air flow, tie selector unit in the fuel control loop increases the fuel flow. When the master demand calls for a reduction of combustion, fuel flow and air flow are reduced simultaneously with fuel flow leading air flow, thus ensuring always an air rich furnace.

9.4.3 Combustion Air Flow Control Total air flow signal is fed to control and this controller output adjusts the FD fan vanes. Provision also exists to ensure a minimum air flow (30% of maximum) through a high signal selector. 9.4.4Oxygen Trim Control

To ensure some percentage of excess air for optimum combustion, Oxygen trim control is employed. Oxygen contain in flue gas before air preheater is measured and er-ror is fed to controller. A maximum/minimum limiter is introduced so that should the oxygen supply fall, a minimum disturbance is introduced in the flue/air control loop. 9.4.5 Mill Temperature and Flow Control This control loop is envisaged to maintain constant air flow to the mills and also to maintain constant mill outlet temperature. Primary air flow and mill outlet temperature signals are measured and fed to the controller respectively. Output of the controllers are connected to each of the two error modules, the output of which are going to coal and hot air dampers through respective auto manual stations. The provision of variable air flow supply exists in the hardware supplied and shall be adopted on site, if required. 9.4.6Furnace Draft Control The furnace draft is maintained by modulating the I D fan Hydraulic coupling (3 nos.). Furnace draft at combustion chamber outlet is measured and the error is fed to the controller. Output of this controller accordingly positions the vanes to maintain constant furnace pressure to improve the system dynamic response. An anticipator total air flow signal is also added in the loop. 9.4.7 Primary Air Header Pressure Control A control loop always ensure sufficient PA to the pulveriser hot air duct at the set pressure and achieves the same by modulating the PA fan vanes (2 nos.). 9.4.8 Superheat Steam Temperature Control The super heater steam temperature control system makes use of three parameters, secondary super heater outlet temperature, total steam flow and superheater inlet tem-perature. The final super heaters temperature error is fed to controllers which positin spray control valves left & right sides to maintain constant superheater outlet tempera-ture.

10.1 Reheat Steam Temperature Control Reheat outlet steam temperature is maintained by tilting the burner to in-crease/decrease heat absorption in the reheat section of the boiler. Additional emergency reheat spray is used to maintain temp. When burner tilts are unable to reduce the temp. Sufficiently. Left and right reheated temp. Signals are averaged and fed to controller. Controller output is indexed with total steam flow signal and through an auto-manual sta-tion drives nozzle tilt drive. In case of differential reheated temp. difference above allow-able limits, respective spray control valve left or right are used to bring balance in left and right side R.H. steam temperatures. 10.2 BFP Minimum Flow Recirculation Control In order to ensure safety of the pump against overheating, the minimum flow is to be maintained when the pump flow reduces below a preset limit. This is achieved by a reliable pneumatically operated minimum flow recirculation control valve with built-in pressure breakdown device. The control envisaged is an on-off control, the operation of which is initiated by a low range DP switch sensing the boiler feed pump flow. Whenever the flow falls below 100 T/hr., the minimum circulation valve is opened and when the flow increases above 200 T/hr., this valve is kept closed. Indication is provided on the UCB to indicate the operator the status of this valve by open-close position indication lamp. 10.3 Hot well Level Control Hot well level is maintained by recirculation of the condensate after steam jet air ejector through a level controller and split-range control valves. Any excess condensate is, therefore, fed to the desecrator. 10.4 Desecrator High & Low Level Control The generator low level control acts on the condenser make-up control valve to add DM wa-ter in the hot well and the high level control acts on the excess condensate to Unit condensate floating tank. Two separate control loops have been provided for the above.

11.1 UNIT CONTROL DESK & PANELS The operation of each unit is envisaged from the central unit control room. It is located in the control bay at 9.0m TG floor. It is adequately illuminated and is centrally air conditioned. For opertional convenience, the control room front wall has complete two double doors for entry from TG hall.

The control board has a special profile with three sloping surfaces for mounting a large facias, instruments and controls. The automatic control station and drive contrl switcated on the first sloping surface. The process indicators/recorders and ammeters are mounted on the second sloping surface and the alarm annunciation window facias are mounted on the top i.e. third sloping surface. The unit control board are arranged in logical operating sequence from the left to right starting with (i.)Air & Flue Gas, (ii.)Fuel oil, (iii)Bowl Mills, (iv)Steam & Feed

Figure:

UNIT CONTROL DESK & PANELS operation of each unit is envisaged from the central unit control room. It is located in the

control bay at 9.0m TG floor. It is adequately illuminated and is centrally air conditioned. For opertional convenience, the control room front wall has complete glass paneling for TG hall view and the two double doors for entry from TG hall.

The control board has a special profile with three sloping surfaces for mounting a large facias, instruments and controls. The automatic control station and drive contrl switches & Indications are lcated on the first sloping surface. The process indicators/recorders and ammeters are mounted on the second sloping surface and the alarm annunciation window facias are mounted on the top i.e. third

l board are arranged in logical operating sequence from the left to right starting with (i.)Air & Flue Gas, (ii.)Fuel oil, (iii)Bowl Mills, (iv)Steam & Feed

Figure:-2.2 Unit Control Desk 7 Panel

operation of each unit is envisaged from the central unit control room. It is located in the control bay at 9.0m TG floor. It is adequately illuminated and is centrally air conditioned. For opera-

glass paneling for TG hall view and the

The control board has a special profile with three sloping surfaces for mounting a large facias, ches & Indications are lo-

cated on the first sloping surface. The process indicators/recorders and ammeters are mounted on the second sloping surface and the alarm annunciation window facias are mounted on the top i.e. third

l board are arranged in logical operating sequence from the left to right starting with (i.)Air & Flue Gas, (ii.)Fuel oil, (iii)Bowl Mills, (iv)Steam & Feed water, (v)Regenerative

12.1 220KV/132 KV SUBSTATION: MTPS Substation Consists of 220KV & 132KV Switchyard, with associated Control & Protection System and Power Transformers. 220KV and 132KV Switchyard are Double Main & Transfer Bus Scheme. Both Switchyards are interconnected through three 100MVA, 220KV/132KV, Inter Bus Transformers (IBT). Power generated from the 2 x 110MW Stage-1 Units are fed to the 220KV MTPS Switchyard through 140MVA, 11KV/230KV Generator Transformers(GT-1&2). Power Evacuation from the switchyard is done through 220 KV Lines of Darbhanga, Gopalganj, Begusarai, Kaffen and 132KV Lines of Motihari, Muzaffarpur, Samastipur, SKMCH. MTPS switchyard is the main sub-station centre for catering the load of total North Bihar.

13.1 POWER SUPPLY FOR PLANT AUXILIARIES:

Auxiliary Power for Plant Auxiliaries are taken from 220KV Switchyard through Two Nos. 31.5MVA, 220KV/7KV Station Transformers (ST-1 & 2). Power Supply to Unit Auxiliaries are also taken from 20MVA, 11KV/7KV, Unit Auxiliary Transformers(UAT-1 & 2) when unit is in service. Both Station Transformers and UATs feed to 6.6KV Switchboards as shown in Single Line Diagram. 6.6KV SWITCHGEAR : 6.6KV Switchgears supply the unit & common drives of 200KW or more and 6.6KV/415V Distribution Transformers. It consists of following switchboards : 1. Two Unit Switchboards(1BA & 1BB) for Unit-1 Auxiliaries fed from UAT-1. 2. Two Unit Switchboards (2BA & 2BB) for Unit-2 Auxiliaries fed from UAT-2. 3. Two Station Switchboards(9BA & 9BB) for Unit-1 and Common Auxiliaries fed from Station Transformer-1 4. Two Station Switchboards(9BC & 9BD) for Unit-2 and Common Auxiliaries fed from Station Transformer-2 5. Two Coal Handling Plant Switchboard(9KA & 9KB) for Coal Crushers, CHP Auxiliaries and Colony Transormer-1/2 fed from Board-9BB & 9BD respectively. Unit Switchboards are interconnected to Station Switchboards (1BA-9BA, 1BB-9BB, 2BA-9BC & 2BB-9BD) through tie breakers as shown in Single Line Diagram to cater its auxiliaries in case of non-availability of power from connected UAT. Station Switchboards are also interconnected (9BA-9BC, 13.2 AC POWER DISTRIBUTION :

9BB-9BD) to cater its auxiliaries in case of non-availability of power from connected Station Transformer. Both the CHP Switchboards are interconnected by Bus-Coupler. All 6.6KV Feeders are switched from 6.6KV Vacuum Circuit Breakers and are protected by numerical relays. Auxiliaries of 140KW or less are fed from 415V Switchgear. 415V Switchgear consists of following : 13.2.1 Main plant

There are two types of LT supply system. One is station service which is common for both the unit and other is for respective units service. 13.2.2 Station Service switchgear(415V) It has two section with bus coupler, charged through station service transformer having LT breakers in each section. Important feeders are:

1. ACW pump-1 and 2

2. Outgoing feeder to compressor MCC

3. Outgoing feeder to station emergency board

4. Station lighting

13.2.3 Unit service switch gear(415V) It has two section with bus coupler, charged through unit service transformer having LT breaker. Important feeders are :

1. Outgoing feeder to Boiler MCC Section-A & B

2. Outgoing feeder to Turbine MCC section-A&B

3. Unit lighting

4.

13.2.3.1 Boiler MCC

It has two section A and B with bus coupler mainly it provides power control to all the LT drive in boiler area. Important drives are: 1. Mill Seal Air Fan A and B

2. Air preheater lub oil P/P-A and B

3. Hydrazine dosing pump A and B

4. Ammonia dosing pump A and B

5. Phosphate dosing pump A and B

13.2.3.2. Turbine MCC It has two section with bus coupler, mainly it provides power to turbine aux. Important drives

are: 1. BCW pump –A,B,C

2. Starting oil pump A and B

3. Drip pump A and B

4. Oil centrifuge

5. Chimney exhaust fan-A and B

13.2.3.3 Station emergency board It has two sections A and B having bus coupler. One section charged from Stn. Service PCC and

other from Station DG set. Normally the board is charged through Stn. Service PCC I/C. In case of power failure in station, DG set is started and the board is charged through DG I/C breaker. Important feeders are:

1. Outgoing feeder to respective unit emergency board

2. Station Battery charger

3. Inst. Air Compressor-4

13.2.3.4 Unit emergency board

It has two I/C one from Unit PCC and other from Stn. Emergency board. Initially it is charged through Unit PCC. In case of power failure automatically it changes over to emergency supply system. Important drives are:

1. AC seal oil pump

2. AC EOP

3. AC JOP

4. Turbine barring gear

5. AC scanner fan

6. Unit emergency lighting

13.2.3.5 Turbine V/V and damper MCC It has two source one from Turbine MCC and other from Unit Emergency board having auto change over circuit. It mainly supplies power to all The valve in turbine areas. Boiler v/v and damper MCC It has two source one from Boiler MCC and other from Unit Emergency board having auto change over ckt. Mainly supply power to all the valve and dampers in boiler areas. 13.2.3.6OFF-SITE LT SWITCHGEAR:

Like main plant, in all the offsite area there are LT Switchgear .They are charged through their respective

transformer to provide power to electric drives of that area.

Offsite areas are:

1. DM PLANT

2. RAW WATER

3. COOLING TOWER

4. ASH HANDLING PLANT

5. FUEL OIL PUMP HOUSE

6. COMPRESSOR

7. COAL HANDLING PLANT

13.2.3.7 DC SYSTEM DC supply in plant is used at three levels :

1. 220V DC :

a. As control power supply of HT/LT Switchgear/Switchyard &

b. For Emergency DC Drives e.g. DC Seal Oil P/P, DC Jacking Oil P/P, DC Scanner Fan.

c. For Plant Emergency Lighting

2. 24V DC : Used in C&I Control of DDCIMS etc.

3. 48V DC : For PLCC Communication of Overhead Lines (Under control of BSEB)

13.4 220V STATION DC SYSTEMThere are common DCDB of 220V DC system connected with two set of 1000AH Station Batteries and two main chargers and one standby charger, supplying to DC Drives, DC Control Power to Plant & CHP and Emergency lighting etc.

Fig

As control power supply of HT/LT Switchgear/Switchyard & Protection System etc.

For Emergency DC Drives e.g. DC Seal Oil P/P, DC Jacking Oil P/P, DC Scanner Fan.

For Plant Emergency Lighting

24V DC : Used in C&I Control of DDCIMS etc.

48V DC : For PLCC Communication of Overhead Lines (Under control of BSEB)

220V STATION DC SYSTEM There are common DCDB of 220V DC system connected with two set of 1000AH Station Batteries and two main chargers and one standby charger, supplying to DC Drives, DC Control Power to Plant & CHP and Emergency lighting etc.

Figure:-2.3 220V Station DC System

Protection System etc.

For Emergency DC Drives e.g. DC Seal Oil P/P, DC Jacking Oil P/P, DC Scanner Fan.

48V DC : For PLCC Communication of Overhead Lines (Under control of BSEB)

There are common DCDB of 220V DC system connected with two set of 1000AH Station Batteries and two main chargers and one standby charger, supplying to DC Drives, DC Control Power to Plant &

14.1 Coal Handling PlantIn a coal based thermal power plant

Handling”. The huge amount of coalinto the power station and the coal is deliof delivery by means of wagon tippler

site to dead storage by belt conveyors

Figure:

14.1.1 Coal handling Plant of MTPS Stagetended to receive coal in railway wagons and deliver it after crushing either to Stack Coal Bunkers on top of the Unit-1/2 Boiler House through Coal Conveyor Belts. The system consists of following:

1. Wagon Tippler-1/2 : For Railway Wagon tippling to hopper.

2. 550 T/H Conveyor Belts-1A/1B(1400 mm width), 2A/2B(1200 mm width), 5A/5B, 6, 7, 8A/8B and 9A/9B(All 1000mm width) : For raw/crushed coal transportation to Unit Coal Bunkers or Coal Stack yard.

3. Coal Crusher-A/B (375KW) : For crushing raw coal to crushed coal of size < 20 mm.

4. Vibrating Feeder with variable sptrolled quantity of coal from coal hopper to conveyor belt and thus prevent overloading of conveyor.

5. Vibrating Screen(VS)-1/2 : For screening raw coal of size > 20mm which is discharged to Coal Crusher-A/B. Raw coal of size <20 is passed through bypass gate to Conveyor

Coal Handling Plant thermal power plant, the initial process in the power generation is “Coal

coal is usually supplied through railways. A railway siding line is taken into the power station and the coal is delivered in the storage yard. The coal is unloaded from the point

wagon tippler. It is rack and pinion type. The coal is taken from the unloading belt conveyors. The belt deliver the coal to 0m level to the

further moves to transfer points.

Figure:-2.4 Coal Handling Plant

Coal handling Plant of MTPS Stage-1 : As shown in layout above the system is itended to receive coal in railway wagons and deliver it after crushing either to Stack

1/2 Boiler House through Coal Conveyor Belts. The system consists

1/2 : For Railway Wagon tippling to hopper.

1A/1B(1400 mm width), 2A/2B(1200 mm width), 5A/5B, 6, 7, 8A/8B and 9A/9B(All 1000mm width) : For raw/crushed coal transportation to Unit Coal

A/B (375KW) : For crushing raw coal to crushed coal of size < 20 mm.

Vibrating Feeder with variable speed drive VF-1,2,3,4,5,6,7,8,9,10,11,12 : For feeding cotrolled quantity of coal from coal hopper to conveyor belt and thus prevent overloading of conveyor.

1/2 : For screening raw coal of size > 20mm which is discharged to Coal A/B. Raw coal of size <20 is passed through bypass gate to Conveyor

, the initial process in the power generation is “Coal is usually supplied through railways. A railway siding line is taken

vered in the storage yard. The coal is unloaded from the point . It is rack and pinion type. The coal is taken from the unloading

. The belt deliver the coal to 0m level to the pent house an

As shown in layout above the system is in-tended to receive coal in railway wagons and deliver it after crushing either to Stack yard or to Unit

1/2 Boiler House through Coal Conveyor Belts. The system consists

1A/1B(1400 mm width), 2A/2B(1200 mm width), 3A/3B, 4A/4B, 5A/5B, 6, 7, 8A/8B and 9A/9B(All 1000mm width) : For raw/crushed coal transportation to Unit Coal

A/B (375KW) : For crushing raw coal to crushed coal of size < 20 mm.

1,2,3,4,5,6,7,8,9,10,11,12 : For feeding con-trolled quantity of coal from coal hopper to conveyor belt and thus prevent overloading of conveyor.

1/2 : For screening raw coal of size > 20mm which is discharged to Coal A/B. Raw coal of size <20 is passed through bypass gate to Conveyor-3A/3B.

6. Suspended Magnet(SM)-2A/2B, 4A/4B : These high power electro-magnets are installed over Conveyor-2A/2B, 4A/4B respectively and remove tramp iron from the coal fed through respective con-veyor. Iron piece attracted and attached at the bottom of Magnet is removed time to time stopping the belt, when its amount becomes high.

7. Over Band Magnetic Separator(OBMS)-1/2 : These high power electro-magnets fitted with cross belt from the direction of coal feed are installed over Conveyor-2A/2B discharge point respec-tively and remove tramp iron from the raw coal fed through respective conveyor without stopping of conveyor.

8. Inline Magnetic Separators(ILMS)-4A/4B : These high power electro-magnets fitted with run-ning belt in direction of coal feed are installed over Conveyor-4A/4B discharge point respectively and remove tramp iron from the crushed coal fed through respective conveyor without stopping of conveyor.

9. Metal Detector (MD)-3A/3B, 4A/4B : These MDs with sandbag marker are installed over Con-veyor-3A/3B, 4A/4B respectively and detect ferrous/non-ferrous metals of size 25 cubic feet or greater passing in crushed coal. Respective conveyor belt is tripped if metal particles are detected by MD. Metals are removed by operator, MD is reset and conveyor is re-started.

10. Stacker : For stacking of crushed coal to stack yard when its feeding is not required in coal bunker. It consists of Conveyor-6 and Boom Conveyor-7.

11. Mobile Tripper(MT)-1/2/3/4 : Coal received through Conveyor-5A/5B is delivered through ho-rizontally moving motor operated tripper on rail to Unit-1/2 coal bunkers. These trippers can travel in forward & reverse direction independent of conveyor movement thus filling bunker evenly.

12. Rack & Pinion Gate(RPG)/Flap Gate : For opening of coal discharge from hopper to selected conveyor belt.

13. Pull Cord Switches(PCS) : These are installed along the conveyor belt for stopping the con-veyor by operator in emergency or as per requirement.

14. Belt Sway Switches(BSS) : These are installed on both side of conveyor belts and stop the con-veyor belt if it sways beyond the limit.

15. Zero Speed Switches (ZSS) : These are installed at trailing end of conveyor belt and stop the

conveyor if drive motor is running but conveyor is not moving(due to snapping of belt etc.).

16. Belt weightier : It is used to keep an account of the tension on the belt carrying coal and is moves accor-

dingly to release tension on the belt.

15.1 References � In house magazines of NTPC

� MTPS Technical Diary

� Websites used

� www.kbunl.co.in

� www.electricals4you.com

� www.ntpc.co.in