H.P.G.C.LINDUSTRIAL TRAINING

AT UNIT – 2PANIPAT THERMAL POWER STATION

PANIPAT (HARYANA)

INSTITUTE OF INSTRUMENTATION ENGINEERINGKURUKSHETRA UNIVERSITY

KURUKSHETRA

TRAINING REPORT ONCONTROL AND INSTRUMENTATION

FROM 19 JUNE TO 30 JULY 2009

THE AWARD OF THE DEGREE OFINSTRUMENTATION ENGINEERING OF 4TH SEM

SUBMITTED BY: SUBMITTED TO:SALMAN KHAN XENIIE, KUK MR. ASHWANI SHARMA

A.E.E MR. D. V. RAO

INDEXS. No. Title

1. Acknowledgement

2. Introduction

3. Functional description

4. Control systems

CERTIFICATE

This is to certify that the dissertation work is bonafide work done by Mr. Salman Khan in partial fulfilment of the requirement for the award of the B. Tech in instrumentation engineering at I.I.E, KUK has carried out six week training in P.T.P.S, Haryana under our supervision and guidance.

NAME - Salman Khan

Roll No. - 10

DIVISION - PTPS stage - 2

DATE OF COMMENCEMENT - 19-06-2009

DATE OF COMPLITION - 30-07-2009

Salman Khan has worked under my supervision during training period. I have read this report, it meets out exception and it accurately reflects work done by him.

XEN Mr. ASHWANI SHARMA A.E.E Mr. D. V. RAOC & I (II) C & I (II)

ACKNOWLEDGEMENT

This present report would not have been possible without the help, I have received from various quarters, and I should have failed in my duties if I did not acknowledge the help and guidance from these sources. I extend my special thanks to Mr. Ashok Saini /XEN J.E training division and Mr. R. S. Kataria for their guidance and special kind of operation throughout whole training period. I also convey my special thanks to all staff members for plant familiarization and understanding various plant processes.

SALMAN KHANB. TECH 3rd yearI.I.E, KUK

INTRODUCTION

Panipat Thermal Power Station is a project of Haryana Power Generation Company Limited (HPGCL) situated in Panipat Jind road at about 11 kms from Panipat Bus Stand.

Name and Address Stage Units Capacity Date of commissioning

Panipat Thermal Power Station,

Village Assan, Jind road,

Panipat.

Phone: 0180-2561573

Fax: 0180-2566806

Stage-I Unit-I 117.8 MW 01.11.1979Unit-II 110 MW 27.03.1980

Stage-II Unit-III 110 MW 01.11.1985Unit-IV 110 MW 11.01.1987

Stage-III Unit-V 210 MW 28.03.1989Stage-IV Unit-VI 210 MW 31.03.2001Stage-V Unit-VII 250 MW 28.09.2004Stage-VI Unit-VIII 250 MW

Panipat Thermal Power Station (PTPS) has a total installed generation capacity of 1367.8 MW comprising of four Units of 110 MW each( unit1 uprated to 117.8 MW ) , two Units of 210 MW each and two Units of 250 MW each. As all the balance of plant facilities viz. Coal Handling Plant, Ash Handling Plant, Cooling towers, C.W. System are separate for 4x110 MW Unit 1 to 4 and are completely independent from Units 5 to 8. Keeping this in view and in order to improve the performance of the Plant and to have a better control, a need was felt to bifurcate PTPS into two Thermal Power Station i.e. PTPS-1, comprising of 4x110MW Units 1 to 4 and PTPS-2 comprising of 210MW /250MW Units 5 to 8.

Coal is used as primary fuel for generation of electricity, however Light Diesel Oil (L.D.O) and Heavy Fuel Oil (H.F.O) are also used in power plant under emergency conditions as an additional support for coal flames.

Super heated system is used as an energy carrier medium and it carries heat energy from boiler to turbine obtained by burning of coal in boiler. Western Yamuna Canal (WYC) is the main source of water for this power station. Water is taken from main WYC to the mini branch canal and is kept reserved in a tank at raw water pump house. Later on, this raw water is treated in Classifiers and DM water plant (Demineralization) for removal of suspended and dissolved impurities and then it is used in boiler for generation of steam.

Water and coal are main raw materials used in generation of electricity. Coal is transported through wagons from M/s Coal India Limited and is kept reserved in a buffer stock in coal handling station. Recently imported coal is also being used after blending it with indigenous coal on experimental basis.

FUNCTIONAL DESCRIPTION OFTHERMAL POWER PLANT

Working of Thermal Power Plant can be explained with the help of a block diagram. The various equipments used in the working of thermal power plant are shown in fig. 1. The primary fuel, coal, is brought out by railway wagons to Coal Handling Station. These are unloaded with the help of Wagon Tipplers.

All the coal pieces are passed through a mesh to avoid entry of big sized coal pieces. The mesh allows the coal pieces of size 10’’ to 12’’ and bigger pieces are rejected by mesh. These big pieces are crushed to proper size. Then this coal is carried by conveyer belt up to crusher house where it is crushed to normal size of 1 mm cube to 1 cm cube as per the demand of coal in furnace in the powerhouse. This coal from the crusher is carried directly to coal bunkers attached directly above the coal mills.

If there is no demand in the furnace or the unit is not running, then this coal from crusher is carried up to coal storage through the conveyer belt where it is kept as reserve for emergency. Raw coal is sent from coal bunkers to coal mills through Raw Coal Feeders (RCF). Function of RCF is to regulate the quantity of the coal going to mills. The speed of RCF is lowered or increased as per requirement of coal in furnace.

Coal-fired thermal power station1. Cooling tower. 2. Cooling water pump. 3. Transmission line (3-phase). 4. Unit transformer (3-phase). 5. Electric generator (3-phase). 6. Low pressure turbine. 7. Condensate extraction pump. 8. Condenser. 9. Intermediate pressure turbine. 10. Steam governor valve. 11. High pressure turbine. 12. Deaerator. 13. Feed heater. 14. Coal conveyor. 15. Coal hopper. 16. Pulverised fuel mill. 17. Boiler drum. 18. Ash hopper. 19. Superheater. 20. Forced draught fan. 21. Reheater. 22. Air intake. 23. Economiser. 24. Air preheater. 25. Precipitator. 26. Induced draught fan. 27. Chimney Stack.

In coal mills, more rpm of RCF means more intakes of coal to coal mills. In coal mills, coal is converted into fine pulverized powder with the help of big rollers in unit-5 (Bowl and Roller Mill) and with the help of Balls in unit-6 (Ball and Tube Mill). Then this coal powder is taken into furnace with the help of Hot Primary Air. It is burnt with the help of Secondary Air in the furnace.

As can be noticed from the above Para – there are two kind of air which helps in transportation and combustion of coal: -

1. Primary Air2. Secondary Air

Primary Air serves as carrier for coal powder from coal mills to furnace. Secondary Air provides Oxygen required for the coal combustion in the furnace.

The regulation helps to maintain excess oxygen in the flue gas up to 3% maximum. It is regulated with the help of wind box damper provided at all corners of the boiler.

BOILER

Boiler is the equipment used to generate the steam. At PTPS, boilers with tangentially fired water tubes are used. The four walls of the boiler are constructed with water tubes and the heat produced due to combustion of coal in the furnace heats the water in the boiler. Boiler is hung with the help of girders and is free to expand downwards due to thermal expansion. It is called tangentially fired due to the reason

that direction of fuel entering the furnace remains tangential to the fireball. The colour of the flame is golden-yellow at its peak performance.

In case the coal flame is weak, oil is injected into the coal furnace to give support to weak flames. Oil support is needed particularly in rainy season when coal is wet or when requisite coal mills are not available. The biggest disadvantage of using oil support is that cost of electricity goes up enormously.

Low pressure turbine is cooled with the help of circulating water. The circulating water is fed in tubes in condenser, which are surrounded by the exhaust, which heats up the

water. This water is cooled at this thermal power plant by spraying it from certain height in the huge cooling towers built solely for this purpose called Natural Draft Cooling Towers. Thus the water cools due to evaporation and is collected in a tank to be used again for cooling. This forms a close cycle for reuse.

TURBO GENERATOR

There is a turbo generator, which generates electricity with the help of a 3-phase alternator of 210 MW capacity. The turbine here has three stages for rotating the rotor of the alternator. First stage of turbine is called High Pressure Turbine (HPT) in which steam entry pressure is 125 kg/cm2 to 135 kg/cm2. The steam used here loses pressure and temperature and the exhaust of HPT goes into Cold Reheat Line (CRH) which is taken to the Re-heater section in the boiler furnace. There the steam gains pressure and temperature through waste flue gases of furnace and is labelled as Hot Reheat Line (HRH). The HRH steam is brought to the second stage of turbine called Intermediate Pressure Turbine (IPT) at about 40 kg/cm2. The exhaust of second stage is passed on to the third stage called Low Pressure Turbine (LPT). The exhaust of third stage is collected below LPT and is condensed into water with the help of condenser. The water is collected in a Hot Well. The rotors of HPT, IPT, LPT and generator are coupled together.

ECONOMIZER

It consists of large number of closely spaced parallel tubes with thin walls and of diameter above 50 mm. The feed water is passed through the economizer before supplying it to the boiler. Here the heat of the flue gases is partially utilized by the economizer, which would otherwise be lost. Thus, temperature of feed water is raised leading to an increase in the efficiency of the boiler.

ROTARY AIR HEATER

For proper burning of the coal in the boiler, air drawn from the atmosphere by a Forced Draft Fan and Primary Air Fan is heated in Rotary Air Heaters by utilizing the waste heat of the flue gases and then sent to the boiler and coal mills resp., thus increasing the efficiency of the boiler.

CONDENSER

The function of the condenser is to condense the low-pressure steam coming out of LPT to water and to create suction at very low pressure at the exhaust of the turbine, thereby permitting expansion of the steam to a very low pressure and increasing efficiency of the Plant.

Unit-5 has coal mills with only one feeder whereas Unit-6 has two feeders in each coal mill to increase the capacity of the production.

CONTROL SYSTEMS

There are two types of control loops in use in PTPS Unit-6 loaded in the FCS: -

Open Closed

Following modes are available for control: Auto Manual Cascaded

The closed loops use PID controllers and open loops use AND, OR SR Flip-Flops etc. The closed loops use: -

Process Variable (PV) – the actual value of the parameter

Set Value (SV) – the desired value of the parameter Manipulated Value – the value used to send out control

signals Difference Value – it is the difference b/w PV and SV

Out of all ICS, HICS available, only HICS the capacity to alter any control logic loaded in the FCS in live as well as shutdown mode.

Various indicators are used in control system to indicate low, high, very low, very high values of parameters with different colours.

To understand the various modes and loops involved, three examples of real plant control system are explained in following pages.

EXAMPLE – 1

Statement: - The level of water in the boiler drum has to be maintained within specified levels to ensure that boiler water tubes do not starve due to lack of water or cause damage to the turbine due to the excess of water in drum overflowing into the turbine.

For the drum to be controlled, either – The speed of the motor should be increased or

decreased according to the requirement of water level, or

The interlock fixed before the drum be closed to decrease water flow or opened to increase water flow and drain is opened to let excess water flow out or closed to stop out-flow.

The designer of the control system has to decide which of the above mentioned strategies he will employ. Suppose he chooses the later one. Then,Process Variable = Level + Net Water Flow + Net Steam Flow

Units of variable in PV: - Level - mm Net Water Flow - tons/hr Net Steam Flow - tons/hr

The best way to make units of all the quantities involved is to convert them to their percentages: -

NAME RANGE PV PERCENTAGELevel -300 to 300 47.3 (47.3 + 300)/(600)Net Water Flow 0 to 900 30 30/900Net Steam Flow 0 to 750 636.4 636.4/750

PV = 57.88 + 3.33 + 84.85 = 146.06

The SV is fed to the PID controller built for the purpose.

EXAMPLE – 2

Statement: - The feeder speed has to be kept under control to maintain the level of coal in the mill. Excess of this quantity would lead to overloading of the coal mill and inadequate quantity would lead to underutilization of the resources.

As can be seen from the figure, there are three PIDs involved in the control system. The first one is the auto mode and the other two are in the cascaded mode. Cascaded mode is the

one in which the set value is decided by another stage and need not be decided by the user.

The transmitter in the field indicates the coal level in DP. Two readings are taken and the better of the two as decided by the FCS is taken as SV for the first PID.

The level of the differential pressure between the driving end of the mill and non-driving end of the mill is used as the set value for the first PID I auto mode. The user, therefore, decides this SV. The MV of this PID gives the SV for the other two PIDs used to control the feeder rate. Thus they are in cascaded mode.

EXAMPLE – 3

Statement: - Many types of equipments in the power plant need certain other equipments in the specified conditions to ensure their smooth running. This example covers Forced Draft Fan (FDF).

For running FDF, there are certain permissive and certain protections. The various permissive and protections from inputs for an AND gate as shown in figure. Thus it is an open loop control system.

Another way of classifying permissive and protections is to classify them into initial permissive denoted by FDIL and those leading to tripping of plant denoted by FDTT.

FDIL (permissive) comprises of: - Inlet damper should be closed. At least on ID fan should be running, otherwise the flue

gases would not escape. Temperature of the NDE and DE ends of fan should be

within limits.

FDTT (protections) comprises of: - Bridge temperature should not be very high. Lubricating oil pressure should not be very low.

CALIBERATION

If pressure (1 – 150 kg/cm2) has to be measured, then 4 mA stands for 1 kg/cm2 and 20 mA stands for 150 kg/cm2. The intermediate ones are measured accordingly, say 75 kg/cm2 for 12 mA.

For measuring differential pressure, the pressure on both sides of diaphragm causes spindle to move, giving output in current form (in ampere).

For measuring flow, square root is calculated in microprocessor card.

Earlier transmitters used to employ concept of change on capacitance due to movement of diaphragm to measure pressure.

One of the most appreciated aspects of this instrument is that calibration of these devices can be done from computer in remote control room by HART protocol or BRAIN protocol.

I/P CONVERTOR

If any control signal has to be sent to the field by the FCS and has implementations to be done by pressure, then this instrument requires I/P Converter whereby current is converted into pressure. In short, it is used for controlling pneumatic valves. Pneumatic valves are used to control

opening and closing valves partially, which is difficult to control through electric motors. The pressure exerts force on a diaphragm connected to the piston, which moves down closing the valve.

WORKING: - A constant supply of air of pressure of range 0-7 kg/cm2 is maintained at one terminal. The input signal is of range 4-20 mA. When signal of 4 mA is received, the lid shown in the figure moves far enough from the nozzle to let an output pressure of 0-20 kg/cm2 given out through the output pipe. When the signal of 20 mA is received, the lid moves near enough to the nozzle to let air pressure of 1 kg/cm2 flow through the outlet. For intermediate current values, pressure of range 0.2-1 kg/cm2 is given out for exerting pressure.

TEMPERATURE MEASURING DEVICES

Temperature measuring devices used in PTPS are RTD and thermocouple. They both are suitable for automatic temperature control. Interestingly, they both look alike. For better accuracy, RTD is used. These are the only instruments which have their readings reaching the system cabinet directly, not through marshalling cabinet.

THERMOCOUPLE

The principle used in thermocouple is that dissimilar metals have different energy levels and when connected together, EMF is produced. It has accuracy of 1 %. Most widely used thermocouple is Chromel-Almel type. Ceramic protection tubes for higher temperature and metal protection tubes for lower temperature protects the thermocouple assembly from, say, the high temperature of the furnace and gases like SO2.

Following are very interesting from practical point of view: -

Law of Homogeneous Metals: -Current cannot be sustained in a circuit of a single homogenous material however, varying in cross-section by application of heat alone.

Law of Intermediate Metals: -Algebraic sum of thermo-emf in a circuit composed of any number of dissimilar materials is zero if all of circuits are at a uniform temperature.

A third metal added to the thermocouple doesn’t affect emf.

Any junction whose temperature is uniform and makes a good electrical contact doesn’t affect emf.

If thermal emf of any two metals (A & B) w.r.t a reference metal (C) is known, emf of combination of the two metals is algebraic sum of their emf w.r.t Reference.

TRANSMITTER

This equipment is used to measure1. Pressure2. Differential pressure3. Flow

It can display output unit to be tons or kg/cm2 or mm. It has two terminals for applying input. If pressure is to be measured, medium enters through one terminal and leaves the other.

WORKING: - When pressure has to be measured, the medium passes through a diaphragm whose movement causes spindle to move in a magnetic field and EMF is generated. Thus, transmitter converts pressure into current. This current is converted into milli ampere by the microprocessor card.

Note: all the measurements has to be converted to 4 to 20 milli amperes as computers in control room can accept current of this range only. Normally all instruments have microprocessor card installed for this purpose.

OXYGEN ANALYZER

The steam water analysis station uses Oxygen Analyzer. It is designed to measure the net concentration of O2 in an industrial process i.e. the oxygen remaining after all fuel has been oxidized. This equipment is permanently positioned within the exhaust duct. No sampling is required.

It measures O2 by reading the voltage developed across a heated electro-chemical cell consisting of small Ythria-stabilized, zirconia disc. Both sided of disc coated with porous metal electrodes. It must be operated at a requisite temperature which is supplied by a battery. EMF generated is given by –

EMF = KT log10 (P1/P2) + C

WhereP2 is the partial pressure of oxygen in the

measured gas on one side of cellP1 is the partial pressure of oxygen in

reference gas on the other sideC is cell constantK is arithmetic constant

The method used for measurement is that when the cell is at operating temperature and there are unequal oxygen concentrations across the cell, oxygen ions will travel from high partial pressure of oxygen to low partial pressure side of the cell.