1.3 Plant Operation System

7/25/2019 1.3 Plant Operation System

http://slidepdf.com/reader/full/13-plant-operation-system 1/32

Plant OperationSystems

DR. AA

1



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…

2



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)

3



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

4



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

5



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

6



PLC Architecture

Processor PowerSupply

Data Highway

PLC Cabinet

Programming

Interface

I/O Modules

Input

Devices

Output

Devices

7



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

8



Control Diagram of a Typical Control Loop

Controller

F 1

T 1

T

F

F 2

T 2

TC

Actuator System

TT

Sensor

System

9



Sensor System

Sensors– Temperature, Flow, Liquid Level, Pressure, pH,

Transmitter

10



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)

11



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

12



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.

13



Liquid Level

Dipstick, Sight glass, Float

Diaphragm

Load Cell

Manometer, Direct Pressure, Differential

Pressure

Capacitive Probe

Ultrasonic

14



Chemical Composition

Refractive Index

Spectroscopy

– IR/UV/Visible Spectrophotometer, Mass

Spectrophotometer, Atomic Absorption

Spectrophotometer Chromatography

– Gas Chromatography, Liquid Chromatography

15



Actuators System

On/Off

– On-Off Valves

– Pumps (motor)

Variable position

– Control Valves– Variable speed pump

• DC motor

• 3-phase motor

• Turbine drive

16



Control valve

17



Butterfly valve

18



Actuator

19



Valve with actuator

& positioner

20

Wh l F il O d Whil



Why are some valves Fail-Opened, While

Others Fail-Closed

21



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 ?

22



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

23



Safety Features

Alarms & Enunciators

Interlocks

– To isolate the impact of process failures from one

section from another

Rupture Disks, Pressure Relieve Valves, etc

24



Controller System

Stand Alone Controller

Supervisory Control

DCS

25



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

11

The failure probability can then be estimated:

Here p is the annual probability of failure

26



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).

27



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

28



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

29



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

30



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

31



End of Topic 1.3

Date post:	13-Apr-2018
Category:	Documents
Upload:	arunkumar23101
View:	222 times
Download:	0 times

1.3 Plant Operation System

Documents