P&ID

1INSTRUMENTATION FOR

P&IDs

http://www.chemeng.queensu.ca/undergraduate/evaluations/2006-2007/CHEE470/peer/

Peer EvaluationPhase 1 (not confidential to your peers) ends Nov 13 5pm

You provide the feedbackDistribute 100 marks among your group based on how you feel their contribution to the project has been (see instructions on website). Provide any additional comments

I will send comments to any people with low peer assessments to warn them of impending doom

Phase 2 (confidential) opens Dec 1, closes Dec 7You provide the feedback (same as above)The peer assessment is worth approx 10%Very low peer assessments will result in an exam being written

Failure to provide a peer assessment (both Phases) will result in you receiving 0 of 10% for that part of the course.

2Learning ObjectivesBe Able to Interpret Controls SymbologyKnow what the physical manifestation of the symbology isKnow the parts of a control loopKnow what a Control Valve looks like and how it worksBe able to look at a control scheme and understand how it worksBe able to design some basic control schemes

Instrumentation Cookbook Instrumentation

Why Are We Doing This For this ProjectChemEcon Includes Controls in factorsChemEcon To Size The Pumps We Need To Include Inline Instrumentation

Anything that generates pressure drop

PIFE

3Instrumentation Cookbook Control Loop

A Simple Feedback Control Loop

Set Point

MeasuredVariable (temp, pressure, flow...)

ControllerManipulatedVariable

Often not shown

FICFITFV

FE

Instrumentation NamingInstrument Society Of America (ISA)

Initiating or Measured Variable

First Letter Recording Indicating blind

Self Actuated Control Valves Recording Indicating High Low Comb Recording Indicating Blind

Analysis A ARC AIC AC AR AI ASH ASL ASHL ART AIT ATBurner, Combustion B BRC BIC BC BR BI BSH BSL BSHL BRT BIT BTUsers Choice CUsers Choice DVoltage E ERC EIC EC ER EI ESH ESL ESHL ERT EIT ETFlow Rate F FRC FIC FC FCV FICV FR FI FSH FSL FSHL FRT FIT FTFlow Quantity FQ FQRC FQIC FQR FQI FQSH FQSL FQIT FQTFlow Ratio FF FFRC FFIC FFC FFR FFI FFSH FFSLUsers Choice GHand H HIC HC HR HI HS HRT HIT HTCurrent (Electrical) I IRC IIC IR II ISH ISL ISHL IRT IIT ITPower J JRC JIC JR JI JSH JSL JSHL JRT JIT JTTime K KRC KIC KC KCV KR KI KSH KSL KSHL KRT KIT KTLevel L LRC LIC LC LCV LR LI LSH LSL LSHL LRT LIT LTUsers Choice M

Controllers Readout Devices Switches and Alarm Devices Transmitters

ISA Typical Letter Combinations.xls

Initiating or Measured Variable

First Letter

Solenoids, Relays, Computing Devices

Primary Element Test Point

Well Of Probe

Viewing Device, Glass

Safety Device

Final Element

Analysis A AY AE AP AW AVBurner, Combustion B BY BE BW BG BVUsers Choice CUsers Choice DVoltage E EY EE EZFlow Rate F FY FE FP FG FVFlow Quantity FQ FQY FQE FQVFlow Ratio FF FE FFVUsers Choice GHand H HY HVCurrent (Electrical) I IY IE IZPower J JY JE JVTime K KY KE KV

4Instrumentation Cookbook P&IDs - Symbology

Equipment SymbologyInstrumentation Symbology

See the document P&ID Symbols and Photos.DOC

Instrumentation Cookbook The Control Valve Elec Signal

To valve(4-20 mADC signal)

Actuator -driven by Compressed Air

Valve

5Instrumentation Cookbook P&IDs - Symbology

LICLocated in DCS(process control

computer)

LTPhysically

locatedin field

Physical wire hardwired

Software Signal

LIC

6LIC DCS cabinet

PIT

FIT

7PCPI

HS

8JULIAN

MI

PowerMultivariableLevelIndicatingAnalysingUser

MI SIC

9Instrumentation Cookbook The Control Valve

Control Valve SizingCV vs % Opening Characteristic

CV Volumetric_Flow Spec_GravityPressure_Differential

Volumetric_Flow galmin

Pressure_Differential psi

PressureDrop

Flow Rate

Instrumentation Cookbook The Control Valve

CV vs % Opening Characteristic

% open

Cv

10

Instrumentation Cookbook Typical Controls

LevelFlow PressureTemperatureComposition

Instrumentation CookbookLevel ControlPurpose

Prevent the tank from overfilling / running dry

LT

LV

LIC

11


Hold a liquid Seal

LT

LV

LIC

No Gas!


Prevent pump from running dry and thus being destroyed

LT

LV

LIC

Note: - valve always on disch to prevent flashing on pump suction- pump may also require a minimum flow bypass

RO

12

Control SystemsAside - Speed

Measured Variable can be slow to measure (i.e. the composition using an analyser) or, fast (i.e. pressure)The Manipulated Variable can be slow too

i.e. adjusting the hot water tap in your showerThe level in a tank can take hours to change (slow)

Control SystemsAside - Speed

Slow ThingsSay > few secondsReducing Pressure by Opening a valve on a large gas filled tankMeasure Composition (analysers)Change Level In Large Tank

Fast ThingsLess than a secondMeasure PressureMeasure Flow (Diff Press)Measure Temp (?)

But. Its all RELATIVE !!

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Instrumentation CookbookFlow Control

Purpose: Ensure steady material flow rate Smooth feed to columnsSet Production rate

Fast to MeasureFlow Changes usually require a control valve to change its position which can take seconds.Vapour systems have a capacitance that need to be overcome before the flow changes are experienced everywhere in the system

Instrumentation CookbookFlow Control

FV

FT

FIC

M

I

FT

SIC

FIC

Variable Speed DriveFE

FE

Mount FE upstream in vapour systems to minimize pressure/densityeffects

14

Instrumentation Cookbook- Ratio Flow Control

FV

FT

FIC

FE

FV

FT

FE

FIC

FRIC SP

SP

SP

Set one flow rateOther flow is proportionally controlled to first flow

Ensure correct mixture / recipes

Instrumentation CookbookPressure Control

Similar to Level (control of material inventory)Very fast for incompressible fluidsHard to say for compressible fluids, depends on system volume but probably slow

15


Control Upstream | Control Downstream

PICPT

PV

PICPT

PV

Need to control vessel pressure Need to downstream (header or process) pressure


Condensable Gas

PIC

PT

PV

Need to control vessel pressure

Fast or slow?

16


Liquid Pressure Control

PICPT

PV

Control pump discharge pressure - not very useful


Liquid Pressure Control

PICPT

PV

Control pump discharge pressure - ensure constant feed pressure to FV

FV

FT

FIC

FE

17

Instrumentation CookbookTemperature Control

Normally control the flow of one fluid to change the temperature of anotherIn Reality its an LMTD change that affects the exchanger duty

Q = U A DTln


Liquid / Liquid - control on cooling media

C/w

18


Liquid / Liquid - control on process

C/w


Steam Pressure Control

T Increase StmPressure

19


Condensate Level Control

Reduce floodedArea

Rookie Mistake- Temperature Control

Controlling an outlet temperature on a 2 phase exchanger

T

TE

TIC

Horiz Reboiler

20

Instrumentation Cookbook Cascade Control

Example - Driving to MontrealYoure driving / steering the carSomeone else is telling you which roads to drive on and when to turn


One Control Loop Determines Setpoint of a Second Loop

M

I

FT

SICVariable Speed Drive

FE FIC SP

SP

-Using the flow through the pump to control the rotational speed of the pump

Flow

DP

High Speed

Low Speed

21


Common Around Distillation Columns Where There Are Slow Loops

PT

FV

FT

FE

FICPIC

Instrumentation Cookbook Controller Interaction

Many Controllers Interact but some configurations Interfere with each otherI.e.

the control of reflux flow interacts with the column bottom level control but two flow controllers on the same pipe will interfere with each other (they duel for control of the flow)

22


Duelling Control ?

LT

LV

LIC

FTFIC

FE


Duelling Control ?

LT

LV

LIC

FTFIC

FE

23


Duelling Control ?

PICPT

PV

PICPT

PV

100 psigCompressedAir

SP= 75 psig SP= 35 psig

User 2User 3

User 1 User 2User 3

User 1

P&ID Cookbook-By Equipment

24

P&ID Cookbook- Pumps

PRV

MIHS

HS

PIPI

Pump - Min Flow Bypass

MIHS

HS

PI

PI

LV

LICLT

RO

25

Reflux Tanks

NLL = 3-6LLL = 2-0

HLL = 4-6

LLLL = 2-0

LIT

LSLL

I PumpS/D

LICTI

PI

To Pump

From Pump

TO LV

Vent to Safe Locn

LAHL

LALL

From CondenserSet@

Compressors - CentrifugalFor our purposes treat controls as a black boxBut... Provide an input control signal (cascade)Remember cooling water reqd (lube system...)

MBy VendorBy Owner

CWRCWS

SICControlFrom ?

26

Requirements for Column ControlFeed rate control, as best as possibleLevel control for reboiler and condensate receiverColumn pressure controlTwo controllers, corresponding to the two degrees of freedom, to deal with the specifications in PRO/IIThis is a very complex topic and can only be dealt with superficially in this course

Columns

Provide a control scheme to ensureFeed rate is constant or is slowly changing

Pressure control Level control

Level control

Composition control

Composition control

Treat thetop and bottom independently of each other

27

Columns -Bottoms

LICLAHL

LIT

TE

TIC

T

5 barStm

LowP Cond

LLLL

LLLNLLHLL

HHLL

Put level control on bottoms outflow when

outflow rate > 10 x boil up ratePut level control on Steam control

boilup rate > 10 x outflow rateotherwise either scheme okay

FT

FIC

Columns - Overhead

NLL = 3-6LLL = 2-0

HLL = 4-6

LLLL = 2-0

LIT

LSLL

I PumpS/D

LICTI

PI

LAHL

LALL

Set@

MIHS

HS

PI

PI

LV

RO

FV

FT

TE XIC

FIC PV

PT PIC

CWS

CWR

28

Instrumentation CookbookColumn ControlHow to Choose the Stream that will control

Level in the reflux tank

Column Overhead Control - Scheme 1when the draw rate is 10 x > reflux rate

Manipulate Distillate draw rate to control Reflux levelManipulate reflux rate to control Column Composition

Instrumentation CookbookColumn Control

Column Overhead Control - Scheme 2when the reflux rate is 10 x > draw rate

Manipulate Distillate draw rate to Manipulate Column CompositionManipulate reflux rate to control control Reflux Drum level

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Instrumentation CookbookTanks - Storage

LIT

LSHH

PRV

M

LI LSLL

I

LAHL

I

s

LY TI LSHH

LAHH

LV

Temperature Control May Be Required-does material freeze / boil?

WorkshopAdd the composition control to the overhead

Hint: use the pressure and temperature

33,316 kg/hr, 113 C

420 kg/hr, 113 C

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END

Documents

P&ID