43(Lecture - Instrumentation for P&ID's - Cookbook)

INSTRUMENTATION FOR

P&ID’s

But first.... Design pressures...

It’s best to group equipment and give it all the same maximum op. pressure

What groups would you create? What would the max op. pressure be?

Ground rules for additional equipment Send non-useful gases (Gas_purge 200 kg/hr,

Lights 51 kg/hr) for combustion in the syngas htr (it’s a fired heater)

Send Fusil_oil (19 kg/hr) to waste treatment plant or to the syngas htr (need tank & pump) - implications?

Ground rules for additional equipmentStorage Tanks Provide an ‘off spec’ tank for the Product sized for 12

hours of hold-up at normal rates In addition, provide at least 2 tanks for the Product Provide an 8 hour storage tank for the Recovr_water Storage Tanks can have L/D = 1 (or less)

Show product storage tanks sending material to “existing truck and railcar loading”

Show Recovr_water storage tank sending water to “waste treatment” plant - recycle issues?

Ground rules for additional equipmentPumps Put a pump on the “acetone column” bottoms

product so we can run it at as low a pressure as possible (at simulation stated pressures) to ensure we remove all lights etc.

don’t put a pump on “degasser” bottoms (let’s increase the pressure accordingly) what are the trade-off’s?

Provide a pump on the “off spec” storage tank to recirc material back to the Acetone column feed. This will help us during start-up or upsets

Ground rules for additional equipment

8 hrs

12hrs

?hrs

?hrs

Now Back to our regularly scheduled show...

Instrumentation Cookbook

Instrumentation Why Are We Doing This

ESTIMATOR - To Size The Pumps We Need To Include “Inline” Instrumentation

Provide A Basic Understanding Of Controls Nomenclature and Their Application

PIFE


Instrumentation Objective:

To Produce A Viable Control Scheme in a way that uses and improves our understanding of the simulation and gives us essential information to size the pumps

To have some examples of controls that could be applied to our process

To understand why these control schemes were selected so that you can form your own judgement


Control Loop A Simple Feedback Control Loop

Set Point

MeasuredVariable (temp, pressure, flow...)

ControllerManipulatedVariable

Often not shown

FICFITFV

FE

Instrumentation Naming Instrument 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


P&ID’s - Symbology Equipment Symbology Instrumentation Symbology

See the document “P&ID Symbols and Photos.DOC”


P&ID’s - Symbology

LICLocated in DCS(process control

computer)

LTPhysically

located‘in field’

Physical wire “hardwired”

Software Signal


The “Control Valve”

Elec SignalTo valve(4-20 mADC signal)

Actuator - driven by Compressed Air

Valve


Typical Controls Level Flow Pressure Temperature Composition

Instrumentation Cookbook Level Control Purpose

Prevent the tank from overfilling / running dry

LT

LV

LIC


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

Control SystemsAside - Speed Measured Variable can be slow to

measure (I.e. the composition using an analyser) or fast (pressure)

The Manipulated Variable can be slow too (I.e. adjusting the hot water tap in your shower)

The level in a tank can take hours to change (slow)

Control SystemsAside - Speed Slow Things

Say > few seconds Reducing Pressure

by Opening a valve on a large gas filled tank

Measure Composition (analysers)

Change Level In Large Tank

Fast Things Less than a

second Measure Pressure Measure Flow (Diff

Press) Measure Temp (?)

But…. It’s all RELATIVE !!

Instrumentation CookbookFlow Control Purpose: Ensure steady material flow rate

Smooth feed to columns Set Production rate

Fast to Measure Flow Changes usually require a control valve to

change it’s 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/density effects

Instrumentation Cookbook- Ratio Flow Control

FV

FT

FIC

FE

FV

FT

FE

FIC

FRIC SP

SP

SP

Set one flow rate

Other 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 fluids Hard to say for compressible fluids,

depends on system volume but probably slow

Instrumentation CookbookPressure Control

Control Upstream | Control Downstream

PIC

PT

PV

PIC

PT

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?


Liquid Pressure Control

PIC

PT

PV

Control pump discharge pressure - not very useful


Liquid Pressure Control

PIC

PT

PV

Control pump discharge pressure - ensure constant feed pressure to FV

FV

FT

FIC

FE

Instrumentation CookbookTemperature Control Normally control the ‘flow’ of one fluid

to change the temperature of another In Reality it’s an LMTD change that

affects the exchanger duty

Q = U A Tln

Instrumentation CookbookTemperature Control Liquid / Liquid - control on cooling

media

C/w

Instrumentation CookbookTemperature Control Liquid / Liquid - control on process

C/w

Instrumentation CookbookTemperature Control Steam Pressure Control

T Increase StmPressure

Instrumentation CookbookTemperature Control Condensate Level Control

Reduce floodedArea


Cascade Control Example - Driving to Montreal

You’re driving / steering the car Someone else is telling you which

roads to drive on and when to turn

Instrumentation Cookbook Cascade Control One Control Loop Determines Setpoint

of a Second Loop

M

I

FT

SIC

Variable Speed Drive

FEFIC

SP

SP

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

Flow

P

High Speed

Low Speed

Instrumentation Cookbook Cascade Control

Common Around Distillation Columns Where There Are Slow Loops

PT

FV

FT

FE

FICPIC


Controller Interaction Many Controllers Interact but some

configurations Interfere with each other I.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)


Controller Interaction Duelling Control ?

LT

LV

LIC

FTFIC

FE



LT

LV

LIC

FTFIC

FE



PIC

PT

PV

PIC

PT

PV

100 psigCompressedAir

SP= 75 psig SP= 35 psig

User 2

User 3User 1 User 2

User 3User 1

P&ID Cookbook-By Equipment

P&ID Cookbook- Pumps

PRV

MIHS

HS

PIPI

Pump - Min Flow Bypass

MIHS

HS

PI

PI

LV

LICLT

RO

Reflux Tanks

NLL = 3’-6”LLL = 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 Condenser

Set@

Compressors - Centrifugal For our purposes treat controls as a black box But... Provide an input control signal (cascade) Remember cooling water req’d (lube system...)

MBy VendorBy Owner

CWRCWS

SICControlFrom ?

Columns

Put 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

Columns -Bottoms

LICLAHL

LIT

TE

TIC

T

5 barStm

LowP Cond

LLLL

LLL

NLL

HLL

HHLL

Put level control on bottoms outflow when

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

boilup rate > 10 x outflow rate otherwise either scheme okay

FT

FIC

Columns - Overhead

NLL = 3’-6”LLL = 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 TIC

FICPV

PT PIC

CWS

CWR

Instrumentation CookbookColumn Control If a flow rate dominates use it to control

the level

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

Manipulate Distillate draw rate to control Reflux level

Manipulate reflux rate to control Column Composition

Instrumentation CookbookColumn Control Column Overhead Control - Scheme 2

when the reflux rate is 10 x > draw rate

Manipulate Distillate draw rate to Manipulate Column Composition

Manipulate reflux rate to control control Reflux Drum level

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?

Workshop Draw the level control that should go on a

storage tank Provide a different control scheme for the

reactor / condenser / flasher P&ID draw it explain how your scheme works and responds to

upsets explain the pros/cons of your scheme

using a BFD, including the syngas process, show how pressure control can be done

Hand this in at the end of class...

END

Instrumentation CookbookTanks - Process Surge

PSV

LV

LT LIC

Consider Pressure Control

Heat Exchangers - Condenser

Vent to Safe Locn

TV

TV on condenser outlet to prevent c/w flashing inside condenser during turndown

TIC

TAHL

TE

CWS

Documents

43(Lecture - Instrumentation for P&ID's - Cookbook)