1.3 Analyse the Operation of Magnetically Coupled Circuits (1)
1.3 Plant Operation System
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Transcript of 1.3 Plant Operation System
7/25/2019 1.3 Plant Operation System
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Plant OperationSystems
DR. AA
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Typical Objectives of Plant Operation
1. Protect people
2. Protect Environment
3. Protect Equipment
4. Maintain Smooth operation5. Achieve Product rates and quality
6. Profit = optimising first five
7. Monitoring & diagnosis
These are Achieved Through Process Control…
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Distributed Control System (DCS)
DCS (Distributed Control System) is a computerized control system
used to control the production line in the industry
DCS was introduced in 1975 by Honeywell (TDC2000) and Yokogawa
(CENTUM)
Other vendors: ABB (Bailey etc), Foxboro, Emerson (Fischer,
Rosemount etc)
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DCS Architecture
Process Transmitters and Actuators
Data Highway
(Shared Communication Facilities)
......
DataStorage UnitHostComputer SystemConsoles PLC
4-20 mA
Local
Console
Local
Control
Unit
4-20 mA
Local
Control
Unit
Local
Console
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Fieldbus Technology
Introduced 1988 but underwent many
development
Standard IEC61158 introduced in
1999
Based upon smart devices installed
in the field.
Uses data highway to replace wires
for signal transfer.
Can mix sensors, transmitters, and
control valves from different vendors
CEAG
I/O
P5001 0... 150 bar
•Foundation Fieldbus (FF)
•Profibus (Process Field Bus)
•Others: ControlNet, P-Net, SwiftNet ,
WorldFIP, Interbus, EtherCAT, SERCODS etc
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Fieldbus Architecture
Plant Optimization
.................
Smart
Sensors
Smart Control
Valves and
Controllers
Local
Area
Network
Smart
Sensors
Smart Control
Valves and
Controllers
Local
Area
Network
H1 Fieldbus Networ k H1 Fieldbus Network
H1 Fieldbus H1 Fieldbus
Data Storage
PLCs
High Speed Ethernet
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PLC Architecture
Processor PowerSupply
Data Highway
PLC Cabinet
Programming
Interface
I/O Modules
Input
Devices
Output
Devices
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We desire independent protection layers, without common-cause failures - Separate systems
sensors
SIS system
i/o i/o………….
sensors
Digital control system
i/o i/o………….
DCS handles controls
and alarms functions.PLC handles SIS and
Alarms associated with SIS
Redundancy
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Control Diagram of a Typical Control Loop
Controller
F 1
T 1
T
F
F 2
T 2
TC
Actuator System
TT
Sensor
System
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Sensor System
Sensors– Temperature, Flow, Liquid Level, Pressure, pH,
Transmitter
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Temperature Measurement
Expansion Thermometer
– Liquid in Glass
– Mercury in Steel
– Bimetallic Elements
Thermoelectric Thermometers (Thermocouple)
– Type J, K, T, R, S, ...
Resistance Thermometers
– Thermister
– Resistance Thermal Detector (RTD), e.g. Pt100
Radiation Thermometers (Optical Pyrometers)
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Pressure Measurement
Direct pressure Measurement
– manometer
Indirect Pressure Measurement
– Bourdon Tubes, Bellows, Diaphragms
Electrical Pressure Transducers– Capacitive, Resistive, Inductive
Other Pressure Transducers
–
Force Balance, DP Cell, Piezoelectric Transducer
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Flow Measurement
Point Velocity Measurement
– Pitot Tube, Hot Wire Anemometer, Transit TimeVelocimeters
Gross Volume Flow Measurement
– Venturi Tube, Orifice Plate, Nozzle, Dall Tube,
Rotameter, Turbine Meter, Positive DisplacementMeters (piston, gear etc)
Gross Mass Flow measurement
– Direct Method - Momentum Type, Thermal Type
– Indirect Method - calculate density & pressure etc.
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Liquid Level
Dipstick, Sight glass, Float
Diaphragm
Load Cell
Manometer, Direct Pressure, Differential
Pressure
Capacitive Probe
Ultrasonic
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Chemical Composition
Refractive Index
Spectroscopy
– IR/UV/Visible Spectrophotometer, Mass
Spectrophotometer, Atomic Absorption
Spectrophotometer Chromatography
– Gas Chromatography, Liquid Chromatography
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Actuators System
On/Off
– On-Off Valves
– Pumps (motor)
Variable position
– Control Valves– Variable speed pump
• DC motor
• 3-phase motor
• Turbine drive
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Control valve
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Butterfly valve
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Actuator
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Valve with actuator
& positioner
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Wh l F il O d Whil
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Why are some valves Fail-Opened, While
Others Fail-Closed
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Typical response of Control Valves
A. Quick-Opening
B. Linear
C. Square-root
D. Equal Percentage
Percentage of
Maximum f low
Percentage of Stem Travel
A
B
D
C
Why do we need different shapes of plugs in the
control valves ?
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Motor Speed Control
DC Motor Speed Control
– Adjust the power of motor by varying current or
voltage
AC Motor Speed Control (3 Phase Motor)
–
Adjust the power of motor by varying the frequency ofthe AC cycles
Steam Driven Turbine
– Adjust the turbine speed to adjust the pumping rates
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Safety Features
Alarms & Enunciators
Interlocks
– To isolate the impact of process failures from one
section from another
Rupture Disks, Pressure Relieve Valves, etc
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Controller System
Stand Alone Controller
Supervisory Control
DCS
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How Reliable are Those Instruments?
Reliability can be estimated using the
following equation
t e R
Here R is reliability, is the annual failurefrequency (failure/year) and t is time (year)
t e R p
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The failure probability can then be estimated:
Here p is the annual probability of failure
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Safety Integrity Level (SIL)
A SIL is a measure of safety system performance, in
terms of probability of failure on demand (PFD). The
higher the SIL is, the more reliable or effective the
system is.
Every Safety Instrumented Function (SIF) has a SIL
classification guided by the IEC 61508 standard
ANSI/ISA S84.01 and IEC 61508 require that companies
assign a target SIL for any new or retrofitted SIS.
Three sector specific standards have been released
using the IEC 61508 framework, IEC 61511 (process),
IEC 61513 (nuclear) and IEC 62061 (manufacturing).
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SIL and PFD
Safety IntegrityLevel (SIL)
PFD(Low Demand Mode)
PFD(High Demand Mode)
1 > 10-2 to < 10-1 > 10-6 to < 10-5
2 > 10-3 to < 10-2 > 10-7 to < 10-6
3 > 10-4 to < 10-3 > 10-8 to < 10-7
4 > 10-5 to < 10-4 > 10-9 to < 10-8
PFD - Probability of Failure on Demand per year
• Low Demand Mode – intermittent operation (less than once a
year)
• High Demand Mode – Continuous operation or systems that
operates more than once a year
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Examples
Component Failure Rate
(faults/year)
ReliabilityR=e(- t)
FailureProbability
P=1-R
DP Cell 1.41 0.24 0.76
Control Valve 0.6 0.55 0.45
Standalone
Controller
0.29 0.75 0.25
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How to Assign SIL Level?
PFD requirement typically determine by thePHA Team. Based on this, required SIL is
identified.
There are various methodology available e.g.
HSE Research report no 216 as well as others
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Typical Product SIL (General Motors)
Product SIL Suitability
Level
FL4000 Flame Detector (Multi-
Spectral IR)
3
FL3111 Flame Detector (UV) 2
S100C Combustible gas detector 3Field Mounted Display 2
TA102A Controller 2
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End of Topic 1.3