ccgt process control dec 2010.359152853

8/12/2019 CCGT Process Control Dec 2010.359152853

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CCGT Operations Principles

Process Control


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Process ControlLesson Objectives

> Understand some of the parameters which need to be measured

in the power station environment

> Describe methods of measuring pressure, temperature, level and

flow

> Explain methods of transmitting information to the control system

> Describe the principle of a control system

> Examine examples of control configurations

> Explain the configurations of hardware used to implement control

systems


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HistoricalInstrumentation and Control


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A Boiler Operator!Photo Circa 1960s


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Carrington Boiler Control PanelCirca 1956


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Battersea Power StationEngineer

Synchronising for the morning peak!


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Agecroft P.S. Unit Control RoomDesign Circa -1960s (photo probably 1980s)


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Drax Power Station CCR-1970s and 80s


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The Computer Age and DCS


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DCSST Overview (Early Pembroke)

Note: simulated screen


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DCS ST Vibrations(EarlyPembroke)


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Field Instruments

> Pressure Measurement

> Level Measurement

> Flow Measurement

> Temperature Measurement


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Pressure Measurement - Definitions

Gauge

Absolute

Absolute

Gauge

Vacuum

Absolute Zero

Atmospheric Pressure

( Variable )

Differential

Pressure


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Manometers


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Pressure due to a head of water =

DENSITY x GRAVITY x HEIGHT

= Kg/m x m/sec x M = N/M

Manometer Principle


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Bourdon Gauge

Bourdon Tube

Cross-Section

Pressure

Applied

No PressureApplied

"C" Shaped

Bourdon Tube

Threaded Pressure

Connection

Applied Pressure

Sealed End

MovementOfTube When

Pressure Applied

" C" Shaped

Bourd on Tube


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Bourdon Gauge - Movement

Applied Pressure

Bourdon Tube

End Piece

Adjusting Screw

( Angularity Adjustment)

Adjusting Screw

( Span Adjustment )

Block

Gauge Pointer

Pinion And

Pointer Shaft

Hair Spring

( Reduces Backlash )

( Zero Adjustment )

Quadrant ( Meshes With Pinion )

Pivot Pin

Threaded

PressureConnection

This measure principle can be adapted for remote reading

by connecting the measuring element to a transducer such

as an LVDTLinear Variable Differential Transformer


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Electronic Pressure Transmitters


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Differential Pressure Transmitter and

Transducer


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Capacitance Transducer


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Level Measurement


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Level MeasurementSight Glass

Scale

Drain Valve

DrainValve

Isolators for easy removal of

gauge or to shut off if

glass breaks


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Level MeasurementDifferential Pressure

Open Tank

Datum

D.P. Cell

+_

VentedS.G. 1.0

Maximum

Level

3 Metres

Liquid

70 mm


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Level MeasurementDifferential Pressure -

Closed Tank

D.P. Cell

+_

Datum

Liquid

DrainValve


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Closed Tank Measurement with Constant Head

Chambere.g. condenser or boiler drum

ConstantHead

D.P. Cell

+_

70mm

3 Metres

Datum

Vapour

Liquid


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Boiler Drum MeasurementConstant Head

HL

Constant

HeadSteam

0 mm

Water


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Drum Level Measurement

> Accuracy due to density of fluid in wet legs (reference leg and

measured leg)

Caused by effects of drum pressure at different loads

Caused by difference in temperature between measuring device

and fluids in drum


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Drum Density Compensation - Graph

PRESSURE IN BARS

0

0.2

0.4

0.6

0.8

1

1.2

000

1

000000

R

E

L

A

T

I

V

E

D

E

N

S

I

T

Y

WATER

STEAM

RELATIVE DENSITY GRAPH

0 20 40 60 80 100 120 140 160 180 200 220


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Drum Density Compensation Traditional UK

methodPressure Transmitter

Force on measuring

element is equal to height

difference

Drum Pressure

TransmitterConstant Head

Chamber

Reference

Leg

Drum centre

line 0 mm

Drum level

Transmitter

Density is inferred from

pressure measurement and is

used to electronically correct

the level signal

Corrected signalis used in three

element control

scheme


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Drum Density Compensation - Development -

Devices such as the IMV 31

shown here can process the

information from thermocouplesinstalled on the legs and

compensate for density

differences with on-board

processor


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Hydrastep - Components

DETEC

TOR

AND

LOG

IC

UNIT

DISPLAY

UNIT

Electrodes

Drum Steam

Connection

Drum Water

Connection

Hydrastep Vessel ElectrodeTip

CeramicInsulator

Electricalconnection to

Detector

Hydrastep Vessel

Electrode


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Hydrastep - Installation

Boiler Drum

X

Y

X

Y

A B

Steam

Water

DetectorUnit

B

DetectorUnit

A

Odds

EvensOddsEvens

Hi/Lo Alarms

Logic

Unit

PowerUnit A

PowerUnit B

Drum LevelControl Room Level

Odd Even Odd Even

PowerSupplySource

PowerSupplySource

RedLights

GreenLights

Pressure Vessel A Pressure Vessel B


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Level MeasurementUltra sound

1234

A

B

CLiquid

Transceiver

LevelDisplay

Transducer

Path of SoundPulses

(Ultrasonic Wave)


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Flow Measurement


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Quantity Measurement

> There are two different types of quantity meter, inferential and

positive displacement meters

The principle of operation of a positive displacement quantity

meter is that a known volume is passed from the inlet to the

outlet of the meter

The principle of operation of an inferential quantity meter is that

the quantity is inferred by measuring the velocity


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Venturi Principles

> The principle of operation of an inferential quantity meter (1)is thatthe quantity is inferred by measuring the velocity

> Therefore by measuring the difference in pressure across the

orifice plate, the rate of flow can be calculated

> Rate of flow is proportional to the square root of the differential

pressure (head)


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Venturi Principle


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Flow MeasurementPitot Tube

Fig.26 Pitot Tube Principle of Operation

P1

P2

Differential Pressure

Flow Indicator


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Flow Measurement - Electromagnetic

Principle of Operation

The operation of a magnetic flowmeteror mag meter is based upon Faraday's Law,

which states that the voltage induced across

any conductor as it moves at right angles

through a magnetic field is proportional

to the velocity of that conductor.

Faraday's Formula:E is proportional to V x B x D where:

E = The voltage generated in a conductor

V = The velocity of the conductor

B = The magnetic field strength

D = The length of the conductor


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Ultrasonic Flow Metering

Insertion

Technology

Clamp On

Technology


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Vortex Shedding Flow Metering (Water)


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Temperature Measurement


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Temperature MeasurementLiquid Methods

Melting Point

Boiling Point

0 Deg. C 32 Deg. F

of Water100 Deg.C 212 Deg.F

of Ice

Range

100 Deg.C

Range

180 Deg.F

Over Temperature

Bulb

Glass Stem

Cavity


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Temperature measurements based on the use of a

thermocouple rely on the basic principle that:

If two dissimilar metals are connected at one end to form a

measuring (hot) junction and are connected to a temperature

indicator at the other end to form a reference (cold) junction, a

voltage is produced at the measuring instrument which is

determined by the temperature difference between the two

junctions. (Thermoelectric effect)

Thermocouples


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Temperatutre Measurement - Thermocouples

Measuring ( Hot )Junction

Reference ( Cold )

Junction

o

o

o

o

.

...

A

B

A

B

Junction

ConnectionHead

0 Deg C Fridge or Oven

at Typically 50 Deg C

Compensating Cable

Copper Cable

Temperature

Indicator

Reference or Cold Junction

0 100

0 100Deg C

Deg C

50

50

..

..+

_

+

_

+

_

+

_

"X"

"Y"

Measuringor Hot

Reference or

Cold Junction

Extension or


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The resistance of a metallic conductor will

increase with increase in temperature

This principle is utilised in resistancethermometer detectors (RTD's).

Platinum is used for its resistance to corrosion

and its stability.

An accurately known value of platinum

resistance wire is wound on a suitable former to

make the RTD

Resistance ThermometerDetectors (RTDs)


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The basic construction of an RTD consists of:

Platinum wire wound in a helix and encased in a ceramic insulator

Sealed with high temperature glass forming an impervious coating and

sealed in a metal sheath similar to a thermocouple.

Construction of RTDs


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DCS


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DCS

DATA STORAGE

PRINTERCONTROL ROOM

COMPUTEROPERATOR

STATION

DATA HIGHWAY "A"

DATA HIGHWAY "B"

PLANT MOUNTED CONTROLLERS / COMPUTERS

TX TX TX TX TX

ONTROL

VALVE

CONTROL

VALVEPOWER

CYLINDER


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DCS

DATA STORAGE

PRINTERCONTROL ROOM

COMPUTEROPERATOR

STATION

DATA HIGHWAY "A"

DATA HIGHWAY "B"

TX TX TX TX TX

ONTROL

VALVE

CONTROL

VALVEPOWER

CYLINDER

GT

Controller

ST

Controller

HRSG

Controller

BOP

Controller


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DCS System (Part)Plant Controllers

HMI

Turbine Process Station

Input/OutputModule

GT Controller ST ControllerOpen Loop Control

Sequence Programmer

Closed Loop Control

Protection

Digital Inputs

Digital outputs

Analogue Inputs

Analogue Outputs

Human Machine

Interface

Data Highway


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HMIHuman Machine Interface


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DCS System (Part)Plant Controllers

HMI


Input/OutputModule


Sequence Programmer

Closed Loop Control

Protection

Digital Inputs

Digital outputs

Analogue Inputs

Analogue Outputs

Human Machine

Interface

Data Highway


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DCS System (Part)Plant Controller

Systems

HMI


Input/OutputModule


Sequence Programmer

Closed Loop Control

Protection

Digital Inputs

Digital outputs

Analogue Inputs

Analogue Outputs

Human Machine

Interface

Data Highway

Egatrol and GT

Control System


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Egatrol and GT Control System


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Systems

HMI


Input/OutputModule


Sequence Programmer

Closed Loop Control

Protection

Digital Inputs

Digital outputs

Analogue Inputs

Analogue Outputs

Human Machine

Interface

Data Highway

Egatrol and GT

Control System


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What are Open Loop Control Functions

> Used for final control elements such as pumps, valves and

breakers and for drive groups of relevant process areas

> Includes logic for manual and automatic commands, supervision of

protection signals and interlocks

> Not to be confused with the definition of open loop control within

modulating or auto control circles!


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Starting Lubricating Oil System - Generic

1

2

Lub Oil Tank Level? Consider: Interlocks, Releases, Permissives

Tank Lub Oil Temperature? Open Loop Control starts each item of sequence!


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Systems

HMI


Input/OutputModule


Sequence Programmer

Closed Loop Control

Protection

Digital Inputs

Digital outputs

Analogue Inputs

Analogue Outputs

Human Machine

Interface

Data Highway

Egatrol and GT

Control System


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Sequence Programmer

> Interfaces with other relevant systems to complete specific tasks

e.g. start oil systems, place GT on turning gear

> Capable of starting open and closed loop items to ensure

satisfactory progress

> High level Automation Function sequencer capable of complete

plant start up

> Example of GT Start Up Sequence for Staythorpe


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Systems

HMI


Input/OutputModule


Sequence Programmer

Closed Loop Control

Protection

Digital Inputs

Digital outputs

Analogue Inputs

Analogue Outputs

Human Machine

Interface

Data Highway

Egatrol GT

Control System


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Closed Loop Control Functions

> Closed loop control is used for final control elements such as

control valves, guide vanes and for level, temperature, pressure,

flow control of the process together with the necessary interlocks

and protections


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Closed Loop Control System


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Protection Functions

> Three Channelseach channel connected to triple redundant,dual redundant or single measuring loops

> evaluated in 2 o o 3 logic, 1o o 2 logic and 1 o o 1 logic accordingto the redundancy of measuring loops

> The measurement redundancy minimises the number of spurioustrips

> Protection channels fed via redundant power supply modules

> Supervision of the three channels monitors discrepancies between

sensors and/or sensor disturbances

> Trip circuit is failsafede-energised to trip

T i l R d d t M t


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Triple Redundant Measurements

1oo2

1oo2

1oo2

1oo1

1oo1

1oo1

&

&

&

CHANNEL 1

CHANNEL 2

CHANNEL 3

Outputs to2 o o 3

Tripping

Device

High Speed

Link HSL

SENSOR 1

SENSOR 2

SENSOR 3

DE-ENERGISED TO TRIP DE-ENERGISED TO TRIP

LIMIT VALUE

CONNECTION TO OTHER

1oo2 & 1oo1 voting

2 o o 3

2 o o 3

2 o o 3

E l f 2 3 T i i Phil h


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Example of 2 o o 3 Tripping Philosophy

DCS S t (P t) Pl t C t ll


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Systems

HMI


Input/Output

Module


Sequence Programmer

Closed Loop Control

Protection

Digital Inputs

Digital outputs

Analogue Inputs

Analogue Outputs

Human Machine

Interface

Data Highway

Egatrol GT

Control System

A l d Di it l Si l ?


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Analogue and Digital Signals?

T i l S f A l d Di it l I f ti


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Typical Sources of Analogue and Digital Information

S M Ph t h !


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Some More Photographs!

St th B P l


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Staythorpe B Panel

M l S h St th C i 2010


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Manual Synch Staythorpe C circa 2010

Manual SynchBatterseacirca 1952


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And One Who Failed His Desk Authorisation!


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And One Who Failed His Desk Authorisation!

End of Session


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End of Session

ccgt process control dec 2010.359152853

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