Instrumentation Scheme of Thermal Power Plant

ToMr. Ram Murat Singh

By:Shilpa MishraME(Regular), I&C 122509

There are basically three main units of a thermal power plant:

1. Steam Generator or Boiler

2. Steam Turbine

3. Electric Generator

Electricity From Coal

Basic Principle

Objectives of Instrumentation & Control

Efficient Operation of the plant.

Economic Operation of the plant.

Safe operation of the plant.

Pollution control

This entire task is often taken up by control & instrumentation or simply instrumentation system which has following functions:-

a) Measurementb) Controlc) Operationd) Monitoringe) Protection

Quantities To Be Measured:

For a Plant Measurement system needs to be:

Very accurate Reliable Delays should be as small as possible Should be switched on manually when a overall control

system fails.

Pressure Temperature Flow Level Expansion/ Contraction Analysis of (1) Water (2) Steam (3) Flue Gases And Others

Measurement Points & Variables

Variables/ Measuring Points Types Of Sensors/ Approx. number Parameters Instruments in the plant

(1) Pressure (a) Boiler Bourdon Tube, (b) Turbine Diaphragm, (c) Turbine Throttle Bellows 375-400 (d) Furnace Bell Gauges

(2)Tempera (a Steam at superheater Thermocouple ture inlet & outlet (b Feed Water at economiser inlet (c Water at condenser RTD 700-750 inlet (d Air Preheater (e Flue Gases Thermocouple

(e Bearing of turbine & Thermocouple generator (f feed pump, condensate RTD pump (3) Flow (a High Pressure Steam Orifice, Venturi, 75-100 (b Feed water inlet Flow Nozzle,etc. (c Condensate

(4) Level (a Boiler Drum (b condensate tank Differential 75-100 (c Water line pressure methods

(5) Expansion (a Turbine Shaft Relative 6-8 (b Turbine casing Displacement

(6) Vibration (a turbine & generator Mass spring with shafts & bearing shells Potentiometric Capacitive, eddy 30-50 current, piezo electric & optical types are used

(7) Analysis(i) WATER (a feed water at econ- -omiser inlet (b Boiler inlet Conductive cell 8-12 (c Condenser with meter (d Condensate pump discharge(ii) STEAM (a Saturated steam Conductive cell 4-6 (b Main line steam with meter (c Super heater inlet Na Analyser 1-2(iii) FLUE

GASES (a O2 – Economiser to air Zirconia cell 2-4 heater (b CO2 – Air heater inlet CO2 analyser 2-4 & outlet (c CO – stack CO analyser 2-4 (d SO2 - Stack SO2 analyser 1-2

(e Nitrogen Oxide- stack N- Oxide Analysesr 1-2

(f Dust concn.- stack Optical method 2-3

Measurement of PressurePressure measuring devices are divided into two groups: Liquid Columns Expansion ElementsLiquid columns: . Low range pressure measurement May be of U-Tube type or well-Type.

Unknown Pressure

These are not favoured in modern power plant but are still used in older power plants.

Expansion Elements: Used in modern power plants. Usually metallic & its movement indicates the pressure. Either directly coupled with mechanical linkages or indirectly by an

electrical transducer connected to a read out device . Main Expansion Elements are:

Diaphragms.

Bellows

Bourden tube

Diaphragms

Commonly corrugated diaphragms are used because large deflection can be produced without nonlinearity compared with flat type.

In order to increase the deflection capabilities two or more corrugated diaphragms are welded at the circumferences--- Capsule element.

Bellows:

Manufactured from Brass, Brass alloys,

Stainless steel.

Used for low pressure measurement.

For high pressure measurement bellows

are connected with spring.

Bourden Tube

C shaped and made into an

arc of about 2700

Material from which it made depends upon the pressure range of the device Bourdon tubes are also used in forms other than C type:- Spiral element: large movement than C tube.Helical element: produce more or less circular movement which is useful for driving a recorder pen directly.

Measurement of Temperature

Temperature can be measured only by using indirect methods.

The most important parameter in thermal power plant is temperature and its measurement plays a vital role in safe operation of the plant.

Rise of temperature in a substance is due to the resultant increase in molecular activity of the substance on application of heat; which increases the internal energy of the material .

The efficiency of generation also depend on the temperature measurement

T2 = Tempreture inside the condenser.

T1= Superheater temperature.

1T

2T1

Measurement of Temperature

Expansion Thermometer In this type of measurement two dissimilar metal tube having different

expansion coefficient are attached end to end. For same temperature change difference in the lengths are compared and

calibrated for unknown temperature measurement. Variation in length is slight and has to be magnified for detection.

THERMOELECTRIC THERMOMETRY

This device is based on SEEBACK and PELTIER effect. It comprises of two junctions at different temperature. Then the emf is induced in the circuit due to the flow of electrons. This is an important part in the plant.

The actual value depend upon the material used and on temperature difference between the junctions.

RESISTANCE THERMOMETRY

Suggested by Siemens in 1871- but not satisfactory used for high temperature .

Today RTD is given by H.L.Calender in 1891 PROPERTY-The resistance of the conductor changes when its temperature

is changed. Copper is occasionally used. Platinum, nickel or nickel alloys are commonly used . Tungsten is used for high temperature applications

METAL MIN. TEMP. MAX.TEMP. MELTING POINT

PLATINUM -2600C 110

0C 1773

0C

COPPER 00C 180

0C 1083

0C

NICKEL -2200C 300

0C 1435

0C

TUNGSTEN -2000C 1000

0C 3370

0C

RTDs

ULTRA VIOLET SENSOR

This device is used in furnace and it measures the intensity of ultra violet rays there and according to the wave generated which directly indicates the temperature in the furnace.

Measurement of Flow

A universal flow meter for all applications in power station is not available.

Infect there are more ways of measuring flow than measuring pressure & temperature.

Dual function meters usually measure flow rate with linear output & minimum error.

Vortex & Ultrasonic meters have become available in recent years (1986) & their full potential is not still fully developed.

Two principle measurements are made by flow meters viz. quantity of flow and rate of flow.

'Quantity of flow' is the quantity of fluid passing a given point in a given time, i.e. gallons or pounds.

‘Rate of flow' is the speed of a fluid passing a given point at a given instant and is proportional to quantity passing at a given instant, i.e. gallons per minute or pounds per hour.

There are two groups of measuring devices:-

1. POSITIVE, OR VOLUMETRIC, which measure flow by transferring a measured quantity of fluid from the inlet to the outlet.

2. INFERENTIAL, which measures the velocity of the flow and the volume passed is inferred, it being equal to the velocity times the cross sectional area of the flow. The inferential type is the most widely used.

Analysis

pH, DO,TURBIDITY & HYDRAZINE:

Need to be checked for acidity (pH), Dissolved oxygen(DO) Turbidity arising out of contamination by suspended

particles . Hydrazine which is added from outside to the feed water

but the excess should be monitored. Oxygen reacts with thallium to form thallium oxide which in

aqueous solution show good conductivity.

C&I DEPARTMENT OF THERMAL PLANT

Functions

Control and instrumentation in any process industry, can be compared to the nerve system in the human being.

The way the nerve system controls the operation of various limbs of human beings, C&I in the same way controls and operates various motors, pumps, etc and thus helps us to achieve our targets.

C&I, as the name indicates, is a branch in engineering which deals with various measurement, indication, transmission and control in different technical field.

The main work of C&I department is to observe, control and manipulate electrical as well as non-electrical quantities like temperature, pressure, vibrations.

C&I department governs the whole functioning and operation of

power plant through the Central Control System (DDC-MIS) “Distributed Digital Control Monitoring and Information System”.

Labs in Control and Instrumentation Department of Thermal Plant

Control and Instrumentation Department has following labs:

1. Manometry Lab

2. Protection and Interlocks Lab

3. Automation Lab

4. Electronics Lab

5. Water Treatment Plant

6. Furnaces Safety Supervisory System Lab

Manometry Lab

1. TRANSMITTERSIt is used for pressure measurements of gases and liquids, its working

principle is that the input pressure is converted into electrostatic capacitance and from there it is conditioned and amplified. It gives an

output of 4-20 ma DC. It can be mounted on a pipe or a wall. For liquid or steam measurement transmitters is mounted below main process piping

and for gas measurement transmitter is placed above pipe.

2. MANOMETERIt’s a tube which is bent, in U shape. It is filled with a liquid. This device

corresponds to a difference in pressure across the two limbs.

3. BOURDEN PRESSURE GAUGEIt’s an oval section tube. Its one end is fixed. It is provided with a pointer

to indicate the pressure on a calibrated scale. It is of 2 types:(a) Spiral type: for Low pressure measurement.(b) Helical Type: for High pressure measurement.

Protection and Interlocking Lab

INTERLOCKING

It is basically interconnecting two or more equipments so that if one equipments fails other one can perform the tasks. This type of

interdependence is also created so that equipments connected together are started and shut down in the specific sequence to avoid damage.

For protection of equipments tripping are provided for all the equipments. Tripping can be considered as the series of instructions connected through OR Gates.

When a fault occurs and any one of the tripping is satisfied a signal is sent to the relay, which trips the circuit. The main equipments of this lab are relay and circuit breakers

Some of instrument used for protection are:

1. RELAY It is a protective device. It can detect wrong condition in electrical circuits by constantly measuring the electrical quantities flowing under normal and faulty conditions. Some of the electrical quantities are voltage, current, phase angle and velocity.

2. FUSES It is a short piece of metal inserted in the circuit, which melts when heavy current flows through it and thus breaks the circuit. Usually

silver is used as a fuse material .

3. MINIATURE CIRCUIT BREAKER They are used with combination of the control circuits to-

a) Enable the staring of plant and distributors. b) Protect the circuit in case of a fault.

In consists of current carrying contacts, one movable and other fixed. When a fault occurs the contacts separate and are is stuck between

them.

Automation Lab

This lab deals in automating the existing equipment and feeding routes.

Earlier, the old technology dealt with only (DAS) Data Acquisition System known as primary systems.

The modern technology or the secondary systems are coupled with (MIS) Management Information System.

All the control instruments are excited by 24V supply (4-20mA) because voltage can be mathematically handled with ease therefore all control systems use voltage system for computation.

FURNACE SAFETY AND SUPERVISORY SYSTEM LAB

This lab has the responsibility of starting fire in the furnace to enable the burning of coal..

Unburnt coal is removed using forced draft or induced draft fan. The temperature inside the boiler is 1100 degree Celsius and its height

is 18 to 40 m. It is made up of mild steel. An ultra violet sensor is employed in furnace to measure the intensity

of ultra violet rays inside the furnace and according to it a signal in the same order of same mV is generated which directly indicates the temperature of the furnace.

For firing the furnace a 10 KV spark plug is operated for ten seconds over a spray of diesel fuel and pre-heater air along each of the feeder-mills.

Electronics Lab

This lab undertakes the calibration and testing of various cards. It houses various types of analytical instruments like oscilloscopes, integrated circuits, cards auto analyzers etc.Various processes undertaken in this lab are:1. Transmitter converts mV to mA.2. Auto analyzer purifies the sample before it is sent to electrodes

Operation and Maintenance Lab

Electrical Maintenance Division:

It is responsible for maintenance of:

1. Boiler side motors2. Turbine side motors3. Outside motors4. Switchgear

Protection By switch gear It makes or breaks an electrical circuit.

Pollution Control systems: In order to ensure that NTPC comply with all the stipulated environment

norms, various pollution control systems / devices as discussed below have been installed to control air and water pollution.

1. Electrostatic Precipitators: The ash left behind after combustion of coal is arrested in high efficiency

Electrostatic Precipitators (ESP’s) and particulate emission is controlled well within the stipulated norms. The ash collected in the ESP’s is disposed to Ash Ponds in slurry form.

2. Flue Gas Stacks: Tall Flue Gas Stacks have been provided for wide dispersion of the gaseous

emissions (SOX, NOX etc) into the atmosphere.

3. Neutralisation Pits: Neutralisation pits have been provided in the Water Treatment Plant (WTP) for pH correction of the effluents nbefore discharge into Effluent Treatment Plant (ETP) for further treatment and use.

5. Cooling Towers Cooling Towers have been provided for cooling the hot Condenser cooling

water in closed cycle Condenser Cooling Water (CCW) Systems. This helps in reduction in thermal pollution and conservation of fresh water.

6. Ash Water Recycling System: In the AWRS, the effluent from ash pond is circulated back to the station for further ash sluicing to the ash pond. This helps in savings of fresh water requirements for transportation of ash from the plant.

Liquid Waste Water/Effluents Treatment Plants & Management System:

1. The objective of industrial liquid effluent treatment plant (ETP) is to discharge lesser and cleaner effluent from the power plants to meet environmental regulations.

2. After primary treatment at the source of their generation, the effluents are sent to the ETP for further treatment.

3. The scheme involves collection of various effluents and their appropriate treatment centrally and re-circulation of the treated effluent for various plant uses.

THANKS FOR THE

ATTENTION