View
117
Download
11
Category
Tags:
Preview:
DESCRIPTION
(Lecture - Instrumentation for P&ID's - Cookbook)
Citation preview
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 Cookbook
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
Instrumentation Cookbook
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
Instrumentation Cookbook
P&ID’s - Symbology Equipment Symbology Instrumentation Symbology
See the document “P&ID Symbols and Photos.DOC”
Instrumentation Cookbook
P&ID’s - Symbology
LICLocated in DCS(process control
computer)
LTPhysically
located‘in field’
Physical wire “hardwired”
Software Signal
Instrumentation Cookbook
The “Control Valve”
Elec SignalTo valve(4-20 mADC signal)
Actuator - driven by Compressed Air
Valve
Instrumentation Cookbook
Typical Controls Level Flow Pressure Temperature Composition
Instrumentation Cookbook Level Control Purpose
Prevent the tank from overfilling / running dry
LT
LV
LIC
Instrumentation Cookbook Level Control Purpose
Hold a liquid “Seal”
LT
LV
LIC
No Gas!
Instrumentation Cookbook Level Control Purpose
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
Instrumentation CookbookPressure Control
Condensable Gas
PIC
PT
PV
Need to control vessel pressure
Fast or slow?
Instrumentation CookbookPressure Control
Liquid Pressure Control
PIC
PT
PV
Control pump discharge pressure - not very useful
Instrumentation CookbookPressure Control
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
Instrumentation Cookbook
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
Instrumentation Cookbook
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)
Instrumentation Cookbook
Controller Interaction Duelling Control ?
LT
LV
LIC
FTFIC
FE
Instrumentation Cookbook
Controller Interaction Duelling Control ?
LT
LV
LIC
FTFIC
FE
Instrumentation Cookbook
Controller Interaction Duelling Control ?
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
Recommended