ecust proii advanced training
DESCRIPTION
PROII Advanced TrainingTRANSCRIPT
ECUSTECUSTPRO/II PRO/II
Advanced Advanced TrainingTraining
PRO/II Training
Copyright © 2004 SIMSCI-ESSCOR™ All Rights Reserved
PRO/II Training
2
focused on simulation
trusted resultsWho we are– Provider of software and services to the
Hydrocarbon and Power industries that allow for efficient:
design operate
optimize
plants and processes –steady state & dynamic
simulation
(PRO/II, HEXTRAN, VISUAL FLOW,INPLANT
PIPEPHASE, DYNSIM, TACITE,
iFEED Suite/COMOS)
plant start-up, operation and training of operators with modeling, dynamic simulation & control emulation
(PRO/II, DATACON, OTS, DYNSIM, FSIM)
advisory and closed loop of their processes
(ROMeo, ARPM, Connoisseur, PRO/II, NETOPT)
increased profitability
What is the Power of Simulation3?
PRO/II Training
3
Be the leading provider of software and solutions for– Simulation & Modeling– Performance Monitoring– Optimization– Operator Training– Integrated Process Engineering
Use the Best-in Class Technology & Expertise– Thermodynamics– Separations– Heat Exchange– Fluid Flow– Optimization
− Data Reconciliation− Collaborative Engineering− Control Checkout− Reactors− Intuitive Engineering GUI
Deliver Improved Asset Performance for our CustomersApplied Simulation on Every Engineer’s Desktop
SimSci-Esscor’s Vision
PRO/II Training
4
sim4me
design
prod
uct
s
optimizeoperate
Plant Lifecycle Management
sam
ple
appl
icat
ion
sMRA &ROMeo
PowRx
Ethylene
CrudeFCCU
Gas LiftOptimization
ProcessDesign
Flare SystemDesign
Well Design/Nodal Analysis
Oil/GasCrudeFCCU
Ethylene
High FidelityOTS
DecisionSupport
EngineeringStudies
Debottlenecking
Oil/GasCrudeFCCU
HydrocarbonPower
Pulp & Papervert
ical
s
PRO/IIHEXTRANVISUAL FLOWPIPEPHASENETOPT
ROMeoARPMMRA
Connoisseur
DYNSIMOTSFSIM
TACITE
ATI/Hyprotech CANNOT do this easily with their
current architecture!
SIM4ME - Delivering on our Vision
PRO/II Training
5
Concept
Basic DesignDetailed Design
PlantDesign
Construction
Controls
OperationCommissioning
Revamp
Steady State Engineering Dbs Dynamic Simulation
Control System
Operator Training
Simulation & Planning
Advanced Control
Online Optimization
SIM4MEApplication During Plant Lifecycle
PRO/II Training
6
PRO/II® Process Flowsheet Simulator for Design, Operational Analysis, and Optimization
HEXTRAN® Heat Exchanger Network Simulator for Design, Operational Analysis, and Optimization
DATACON™ Data Reconciliation Program for Heat/Mass/Composition balance on plant data
INPLANT™ Plant Piping and Utility Systems Flow Simulator
VISUAL FLOW™ Flare Network and Regulatory Compliance Simulator
Process Engineering Suite
PRO/II Training
7
PLANT PLANT LIFE LIFE
CYCLECYCLE
Basic DesignDetailed Design
PlantDesign
Construction
Controls
Basic DesignDetailed Design
Commissioning
Concept
Operation &Troubleshooting
Revamp
PES Features
Enhances productivity in the plant life cycle
PRO/II Training
8The Plant
Visual Flow
CompleteCould be done
Datacon Inplant
MS Office
PRO/II
Hextran
Integration within PES
PRO/II Training
9
History of PRO/IIFirst Generation: 1974– SSI/100 Simulation Program
Second Generation: 1979– Process Simulation Program
Third Generation: 1988– PRO/II Simulation Program– Version 3.30 - Spring of 1993
Forth Generation: 1995– PRO/II with Provision 4.x
Fifth Generation: 1997– PRO/II with Provision 5.x– version 5.61 – March of 2002
Sixth Generation: 2003– Over 40 new features
Seven Generation: 2004– Just released in August 2004
Introduction
PRO/II Training
10
PES Solution Client BenefitsReduced process engineering time & costReduced plant capital costReduced plant lifecycle costs Increased plant operating profits– higher product rates– improved product quality– lower operating costs– more feed flexibility
A valuable tool for experienced process manager and engineers
PRO/II Training
11
Flowsheets FeaturesPRO/II is much better for larger flowsheets– No over-specify flowsheet– Recycles estimates not required– Recycle block not required– More option to define sequence– Easier diagnosis of problems since each specification in
linked to a particular unit operation and color indicates status.
PRO/II Training
12
Distillation FeaturesMultiple column algorithms to model complex columns– IO, Sure, Chemdist, Liquid-Liquid, Electrolytes, Enhanced IO
Multiple methods for generating initial estimated values– Simple, Conventional, Refinery, Chemdist, Electrolytes
Reactive distillation– robust algorithm– derivative data not required
Tray Hydraulic for rating and design– Volve, Sieve, and Cap structured tray– Sulzer structured packing– Norton random packing
PRO/II Training
13
First Createa Library of
Reaction Data
Then SelectReactions
for Each Unit
Reaction OptionEnter reactions in the reaction data sectionIn Reactor units, select which reactions to use
PRO/II Training
14
Reactor TypesGeneral: (no reactor geometry required)– CONVERSION REACTOR (multiple reactions)– EQUILIBRIUM REACTOR (multiple reactions)
Kinetic: (reactor geometry required)– PLUG FLOW REACTOR (PFR)– CONTINUOUS STIRRED TANK REACTOR (CSTR)
GIBBS: (stoichiometry optional)– Free energy minimization– Kinetics not considered
PRO/II Training
15
Optimizer FeaturesOptimize based on an objective functionUtilizing tag data valuesNo needs to have a dynamic calculationAutomatic identification of the best design or operating conditions from a collection of alternativesFrees user from evaluating all possible cases
PRO/II Training
16
User-Added Program FeaturesUAS/PDTS enhancements– additional function calls– additional subroutines– additional simulation database access– full documentation– supported in PROVISION
PRO/II Training
17
Tag Data FeaturesDirectly access plant historical dataRead tag data from a fileRead tag data from server– PI– ODBC– @aGlance/IT– AIM
Write tag data back to a file
PRO/II Training
18
OLE FeaturesOLE/COM Automation Layer– documented access to simulation database for most
data– two way link
simulation data out, design/plant data in
– any OLE compliant applicatione.g. MS Office can use VB or VBA
– used for Zyqad or Icarus interface– examples available at www.simsci.com
PRO/II Training
19
Spreadsheet Tools
PRO/II Training
20
OLE Automation
PRO/II Training
21
D1
V1
X1
1
2
3
4
5
6
7
8
9
10T1
E1
E2
C1
3
4
5
6
7
8
9
100
2
10
3X
11
TURBOEXPANDER PLANT
Feed 100 Range Products 9 11Flowrate 1016700.0000 FT3/HR Flowrate 483.7454 2195.4231 LB-MOL/HRPressure 587.0000 PSIG Pressure 125.0000 161.2292 PSIGTemperature 120.0000 F Temperature 24.0874 157.5738 FComposition Composition
N2 7.9100 N2 0.0000 0.0965C1 73.0500 C1 0.0086 0.8896C2 7.6800 C2 0.3633 0.0137C3 5.6900 C3 0.3141 0.0002IC4 0.9900 IC4 0.0548 0.0000NC4 2.4400 NC4 0.1351 0.0000IC5 0.6900 IC5 0.0382 0.0000NC5 0.8200 NC5 0.0454 0.0000NC6 0.4200 NC6 0.0233 0.0000NC7 0.3100 NC7 0.0172 0.0000
UnitsX1 adiabatic efficiency 80.0000 % 0-100 UnitsX1 outlet pressure 125.0000 PSIG Reboiler duty 2.2889 MM BTU/HRC1 adiabatic efficiency 75.0000 % 0-100 E1 duty 5.2814 MM BTU/HRC1 work from X1 0.9000 0-1 E2 duty 4.9133 MM BTU/HRT1 top pressure 125.0000 PSIG X1 actual work 392.2247 HPT1 C1:C2 ratio bottom 0.0150 0-1 C1 actual work 353.0023 HPE1 HICO 10.0000 FStream 3 temperature -83.9990 F Run Simulation
Operator Interface
PRO/II Training
22
1Build
Flowsheet
2 Check Units
of Measur
e
Simulation in Seven StepsIntroduction
Define Compone
nts
3
4Select Therm
oSuppl
y Strea
m Data
5
Provide Process
Conditions
6
Run & View
Results
7
PRO/II Training
Defining the Defining the ComponentsComponents
PRO/II Training
24
Component Types
Library componentPetroleum componentUser-defined componentSolid componentPolymer componentIonic component
Defining the Components
PRO/II Training
25
Component SelectionDefining the Components
PRO/II Training
26
PRO/II Component LibraryComposite of several databanksDatabank search order– PROCESS (default)– SIMSCI (default)– DIPPR or OLI available as an optional PRO/II add-on
Component selection by list or access namePure component data– Fixed properties– Temperature-dependent properties
Defining the Components
PRO/II Training
27
Adding Library ComponentsDefining the Components
PRO/II Training
28
Component Data PrintoutComponent nameComponent type
PROJECT TRAINING PRO/II INPUTPROBLEM COMPONENTS COMPONENT DATA============================================================================
NO. COMPONENT NAME COMP. TYPE PHASE MOL. WEIGHT SPGR --- -------------- ----------- ----------- ----------- ---------- 1 N2 LIBRARY VAP/LIQ 28.013 0.80811 2 C1 LIBRARY VAP/LIQ 16.043 0.30000 3 C2 LIBRARY VAP/LIQ 30.070 0.35640 4 C3 LIBRARY VAP/LIQ 44.097 0.50770
NO. COMPONENT NAME NBP CRIT. TEMP. CRIT. PRES. CRIT. VOLM. F F PSIG GAL/LB-MOL --- -------------- ----------- ----------- ----------- ----------- 1 N2 -320.440 -232.420 477.619 10.7963 2 C1 -258.682 -116.680 652.499 11.8628 3 C2 -127.534 90.140 693.648 17.7343 4 C3 -43.726 206.006 601.652 24.3247
NO. COMPONENT NAME ACEN. FACT. HEAT FORM. G FORM. BTU/LB-MOL BTU/LB-MOL --- -------------- ----------- ----------- ----------- 1 N2 0.04500 0.00 0.00 2 C1 0.01040 -32066.21 -21726.14 3 C2 0.09860 -36120.21 -13810.45 4 C3 0.15290 -44650.04 -10139.64
Defining the Components
Phase typeNine fixed properties
PRO/II Training
29
Using DATAPREPMenu-driven DOS interfaceTotal access to PRO/II component databaseAdditional information:– Fixed properties– Data source – Data accuracy– Plots and tables
Defining the Components
PRO/II Training
30
Enthalpy Curve for Water from DATAPREP
-500 -250 0 250 500 750-80
0
80
160
240
320(10E+ 2)
Temperature F
ENTH
ALPY
BTU
/lbm
ol Heat of Vaporizat ion at NBP
Sat urat ed Vapor Curve
Ideal Gas Curve
Crit ical Point
Sat urat ed Liquid Curve
Solid CurveHeat of Fusion
at NMP
Defining the Components
PRO/II Training
31
Petroleum ComponentsNormal Boiling PointGravity Molecular Weight
At least two of three required
Defining the Components
PRO/II Training
32
User-defined ComponentsComponent NameComponent Properties
Defining the Components
PRO/II Training
33
Component PropertiesFixed propertiesTemperature-dependent propertiesUser Defined and Refinery Inspection propertiesSolid propertiesPolymer propertiesStructure data
Defining the Components
PRO/II Training
34
Component Property Window Defining the Components
Selecting the Selecting the ThermodynamicsThermodynamics
PRO/II Training
PRO/II Training
36
Example: Propane-Propylene SplitterChoice of Thermo strongly effects results!
ThermodynamicSystem
CondenserDuty
Reflux/FeedRatio
Peng-Robinson -59.6 13.1
Grayson-Streed -37.3 8.2
Selecting the Thermodynamics
PRO/II Training
37
Thermodynamic DataRequired for all flowsheetsThermodynamic Property MethodsTransport Property Methods– Required for certain units:
Column DissolverRigorous heat exchanger Depressuring unitPipe Output tables
Selecting the Thermodynamics
PRO/II Training
38
Thermodynamic PropertiesK-Values(Mass Balances)
Enthalpies(Heat Balances)
EntropiesDensities
Selecting the Thermodynamics
PRO/II Training
39
K-Value Calculation MethodsIdealEquation of StateLiquid ActivityGeneralized CorrelationsSpecial PackagesElectrolytesPolymers
Selecting the Thermodynamics
PRO/II Training
40
Selecting the Thermodynamic MethodSelecting the Thermodynamics
PRO/II Training
41
Enabling VLLE Calculations
Default
Selecting the Thermodynamics
PRO/II Training
42
ModificationsVery important to choose the correct thermodynamic methodEven more important to insure that binary interaction parameters are available
Selecting the Thermodynamics
PRO/II Training
43
Modifications (Cont.)Advanced Equations of State– Model hydrocarbon behavior– Advanced Alpha forms– Advanced mixing rules– Databank of regressed binary interaction
coefficient
Selecting the Thermodynamics
PRO/II Training
44
Modifications (Cont.)Liquid Activity Coefficient methods– Model non-ideal behavior– Databank of regressed binaries– Databank of azeotropes– Fill options for binaries
Selecting the Thermodynamics
PRO/II Training
45
Modifications (Cont.)Generalized Correlation– Typically designed for a specific application– Do a good job for heavier hydrocarbons
Selecting the Thermodynamics
PRO/II Training
46
Modifications (Cont.)Enthalpy, Entropy and Density– Library correlation for enthalpy– No Library correlation for entropy– Library correlation for density– Rackett parameters in Library
Selecting the Thermodynamics
PRO/II Training
47
Transport PropertiesViscositiesThermal conductivitiesSurface tensionLiquid diffusivity
4 methods: Pure, Petroleum, Trapp, User-defined
Selecting the Thermodynamics
PRO/II Training
48
Calculation with Two Liquid PhasesWater decant option Rigorous VLLE
calculations
Selecting the Thermodynamics
V
L = HC + W
W = pure water
V
L1 = HC + W
L2 = W + HC
PRO/II Training
49
Water Decant Option
Vapor
Pure WaterLiquid
Water VaporPressureVLE K-values
Water Solubility
Selecting the Thermodynamics
PRO/II Training
50
Rigorous VLLE Calculations
Vapor
Liquid 2Liquid 1
VLE K-valuesVLE K-values
LLE K-values
Must enable two-liquid phase calculations.
Selecting the Thermodynamics
PRO/II Training
51
Hydrocarbon SystemsRefining Processes:– Grayson-Streed: Hydrogen rich systems, Crude tower,
Vacuum unit, Coker fractionator, FCC main fractionator
– SRK and PR: Light ends columns, Splitters, Gas recovery plants, Hydrogen rich systems (SRKM)
– SOUR, GPSWATER: Sour water systems
– SRKK, SRKM, SRKS, IGS: Use if H/C solubility in liquid water (VLLE) is important.
Selecting the Thermodynamics
PRO/II Training
52
Hydrocarbon SystemsGas Processing:– SRK and PR: All types of processing plants, cryogenic
systems– SRKM, PRM, and SRKS: Systems with water,
methanol, and other polar components– GLYCOL: Dehydration with TEG. Improved for
aromatic emissions. Based on SRKM.– AMINE: Natural gas sweetening.– SRKK, IGS, SRKM, SRKS: Use if light gas solubility in
water (VLLE) is important.
Selecting the Thermodynamics
PRO/II Training
53
Online Thermodynamic HelpReference Manual– Detailed technical reference
Application Guidelines– When to use each method
Selecting the Thermodynamics
PRO/II Training
54
Chemical Systems: Activity coefficient methods
Non-ideal componentsLow to medium pressuresRely on binary interaction parameters (if missing will be close to Ideal!)Missing parameters estimated from structures, azeotrope composition, mutual solubilities etc.Used with Henry’s Law for non-condensiblesVLLE with some methods
Selecting the Thermodynamics
PRO/II Training
55
Chemical Systems: Activity coefficient methods
Two Binary parameters Liquids? in databank?
NRTL Yes Yes
UNIQUAC Yes Yes
WILSON No No
UNIFAC Yes Estimates non-ideality from structure
Other methods - see Reference Manual
Selecting the Thermodynamics
PRO/II Training
56
Chemical Systems: Equations of StateSRK-SIMSCI, SRKM, and PRM for polar mixturesSRK-Hexamer for mixtures involving HFCan model high-pressuresAlso rely on binary interaction parametersSome binary parameters in databanks for above methods
Selecting the Thermodynamics
PRO/II Training
57
MulticomponentDistillation
MulticomponentMulticomponentDistillationDistillation
PRO/II Training
58
Tray Model
Subscript denotestray number
Tj Pj
Qj
LDj
VDj
Vj yj_
Lj-1 xj-1_
Lj xj_
Vj+1 yj+1_
Fj XF
_
Overbar denotes component vectors: e.g., x = (x1, x2, ...xNC)
_
_
Lj , Vj
Fj
Qj
xj , yj
XF
hj , Hj
Tj , Pj
LDj
VDj
Liquid, vapor flowrate
Feed flowrate
Heater/cooler duty
Liquid, vapor mole frac
Feed mole fractions
Liquid, vapor enthalpies
Temperature, pressure
Liquid Draw rate
Vapor Draw rate
__
Multicomponent Distillation
PRO/II Training
59
Tray NumberingNormally use Theoretical Trays (Stages)Numbered from top downCondenser is Stage 1– Even for subcooled condenser
Reboiler is last stage – Thermosiphon adds 2 stages
Convert packing to stages– Rule of Thumb: 2 to 3 feet of packing per stage
Multicomponent Distillation
PRO/II Training
60
Tray Efficiency
xA
75% efficient:step 3/4 to
equilibrium curve
yA
xA
100% efficient:step to
equilibrium curve
Murphree Efficiency = 75%
Multicomponent Distillation
PRO/II Training
61
Other Tray Efficiency ModelsVaporization yi = ciKixi
Equilibrium K’s adjusted towards 1.0Vapor leaving stage not at dew pointCan lead to Mixed Phase Condenser productBetter to use Overall Efficiencies– Theoretical / Actual trays to carry out separation– Use different values in different column zones– Tune from experimental data if possible
Multicomponent Distillation
PRO/II Training
62
Overall EfficienciesEfficiency increases as components decreaseEfficiency increases as reflux increasesResults can be very sensitive to number of trays
Number of Stages
Low reflux:number of stagesis less important
High reflux: number ofstages stronglyaffects results
Ref
lux
Multicomponent Distillation
PRO/II Training
63
Typical Overall Tray EfficienciesSERVICE PERCENT
Simple Absorbers/StrippersReboiled Absorbers/StrippersDeethanizersDepropanizersDebutanizersDeisobutanizers (Refluxed)
20-3040-5060-6565-7580-9085-95
SplittersC2, C2-C3, C3-C4抯 or C5抯
85-9595-10090-100
Notes:1) Assume 65-75% for most columns with reboilers and condensers.2) At low reflux, split insensitive to number of trays in the model.3) Pumparounds usually modeled as 2 stages.
Multicomponent Distillation
PRO/II Training
64
All Column Algorithms are IterativeWant to solve f(x) = 0Generate a sequence of estimates of solution:
x0, x1, x2, ... xN
Equations are satisfied when x stops changing:| xN - xN-1 | < 0.00001
xN is regarded as the solution
Multicomponent Distillation
PRO/II Training
65
Convergence of Newton’s method ...
x x fx
f xn n
x
n
n
+
−
= −⎡
⎣⎢
⎤
⎦⎥
11
∂∂
( )
Solution
f(X)
0
Xx1 x2 x*
Good initial guessleads to solution
x0
Multicomponent Distillation
PRO/II Training
66
Convergence is not guaranteed!
f(x)
x* X
0
Multicomponent Distillation
PRO/II Training
67
Convergence is not guaranteed!
f(x)
x* X
0
Periodic
Multicomponent Distillation
PRO/II Training
68
Convergence is not guaranteed!
X
Bad guessconverges...
But betterguess fails!
f(x)
x*
0
Multicomponent Distillation
PRO/II Training
69
Available Distillation Algorithms in PRO/II
Multicomponent Distillation
Inside Out (I/O)
Chemdist
Sure
Liquid-liquid
Enhanced I/O
PRO/II Training
70
Inside Out (I/O) Algorithm– Relatively ideal thermodynamics including hydrocarbon
with water decant– Incorporates sidestrippers into column -- No recycle!– Thermosiphon reboilers– Flash zone model– Very forgiving of bad initial estimates– Fast!– No VLLE
Multicomponent Distillation
PRO/II Training
71
I/O ColumnFeatures
2 phasecondenser +water decant
N-1
21
Side Columns
Side Streams
Heater/Cooler
Heat Source/Sink
Multiple Feeds
Kettle andThermosiphon
Reboilers
Pumparounds
N
Multicomponent Distillation
PRO/II Training
72
I/O Algorithm Uses Nested LoopsInner Loop– Simple thermo model (Fast)– Approximate Matrix Inversion (Fast)– Converge enthalpy balance and performance specs
Outer Loop– Updates, checks thermo using rigorous model (Slow)– Checks Bubble Point Criteria– If thermo changing or not bubble point, goto Inner Loop
Multicomponent Distillation
PRO/II Training
73
I/O Algorithm
x, T, L, V, Q ...
1) Calculate rigorous K(x,T,P), H(x,T,P).2) If K and H differ significantly from
previous iterate, repeat from beginning.Done, solution is: x, T, L, V,
Q ...
Inner Loop
Out
er L
oop
Approx. Thermo.Model
ConvergenceCheck
Iteratively solve the column equations using approximate thermo, K*(T,P) and H*(T,P).
Prepare approximate thermo models for K*(K) and H*L(HL), and H*V(HV).
Multicomponent Distillation
PRO/II Training
74
Initial Estimate Generator (IEG)Generates “good” initial estimates for all column variables
P1 P2PN LN x* y* T*
P V* L*
Q*R Q*
C
x0 y0 T0
P V0 L0
Q0R Q0
C
IEG Solver
You supply columnspecs and guessesfor a few variables...
IEG calculatesinitial estimates for
all column variables...
Solver (I/O, Chemdist)converges on solution
ColumnSpec’s
Multicomponent Distillation
PRO/II Training
75
Four Types of IEGSIMPLE (default): Simple columns– Only choice for liquid-liquid extraction
CONVENTIONAL: Works well with most columns– Based on shortcut methods– Strongly dependent on your product rate estimates
REFINING: Complex refinery columns (e.g., Crude, Vacuum, FCC main fractionator, Coker)
CHEMICAL: Nonideal thermodynamics (e.g., azeotropicand extractive distillation). Can be slow.
Multicomponent Distillation
PRO/II Training
76
Specifications and VariablesSpecifications are constraints to be met by the column
Variables are calculated to meet specifications.
Column always balances equations and unknowns
To impose a specification, you must add a variable, otherwise equations and unknowns don’t balance.
Example: Impose two product specifications by declaring reboiler & condenser duties as variables.
Multicomponent Distillation
PRO/II Training
77
Column Status at InitializationFixed quantities remain at their current values unless you declare them as variables.
If no specs/variables provided, default status used:
Multicomponent Distillation
QUANTITY STATUS
Overhead and Bottoms RatesSide Draw RatesDutiesFeed RatesTray TemperaturesTray PressuresVapor and Liquid RatesProduct Properties (e.g. Viscosity)Tray Vapor or Liquid Properties
CalculatedFixedFixedFixed
CalculatedFixed
CalculatedCalculatedCalculated
PRO/II Training
78
Improper Specifications 0% methane in crude column bottoms– Infinitely many solutions
300 lb-mole/hr propylene in overhead– No solutions if column feed only 250 mol/hr propylene
98% ethanol product– No solutions if Water-Ethanol Azeotrope present
Multicomponent Distillation
PRO/II Training
79
What is alpha (α)?Length of correction: Xn+1 = Xn + αn δn 0< |α| < 1
Decrease α if full step increases error
Unknown 2
Unknown 1
X1
X3
X2
Solution
δ3
α1 = .7
α2 = 1
Reject: full stepincreases error
Multicomponent Distillation
PRO/II Training
80
You Can Help I/O by Using DampingDamping reduces iteration step and suppresses oscillationConventional columns: DAMP = 1.0 (default)Columns with steam: DAMP = 0.6 - 0.8– Crude, Vacuum, FCC Main Fractionator
Less-ideal: DAMP = 0.2 - 0.6– Increase number of allowed iterations– If oscillations persist, use Chemdist
Multicomponent Distillation
PRO/II Training
81
Reboiler ModelsMost reboilers can be simulated as:– Kettle– Thermosiphon with Baffles– Thermosiphon without Baffles
Multicomponent Distillation
PRO/II Training
82
N-1Bottom Tray
NReboilerBTMS Q
VN-1 LN-2
VN LN-1
BTMS
LN-1
VN
Kettle Reboilers
Vapor in Equilibriumwith Bottoms
Multicomponent Distillation
PRO/II Training
83
BTMS
LN-1
VN
BottomSump Reboiler
Sump
Baffle
LN-1
VN
BTMS
Bottom Sump
Single Pass (Once Through) Thermosiphon
Equivalent to a Kettle Reboiler because Bottoms is in Equilibrium with VN
Multicomponent Distillation
PRO/II Training
84
N-2Bottom Tray
N-1Combined Sump
NReboiler
BTMS
Q
VN-1 LN-2
RL RF
R V
LN-2
VN-1R V
RL
RFBTMS
Combined Sump
Circulating Thermosiphon Adds 2 Stages
Simulate as TS without Baffles
Multicomponent Distillation
PRO/II Training
85
BTMS
VN-1
BottomSump
RF
RV
RL
LN-2
ReboilerSump
N-2Bottom Tray
N-1Reboiler Sump
NReboiler
BTMS
Q
VN-1 LN-2
RL RF
R V
Circulating Thermosiphonä Simulate as TS without baffle
Multicomponent Distillation
PRO/II Training
86
BTMS RL
RF
Lo
RV
N-2Bottom Tray
N-1Reboiler Sump
NReboiler
BottomSump
Q
VN-1 LN-2
BTMS
LN-2
VN-1
BottomSump Reboiler
Sump
RF
RV
RL
LO
Preferential Thermosiphonä Simulate as TS with baffle
Multicomponent Distillation
PRO/II Training
87
Tips...Start simple– Converge water decant thermo before trying VLLE– Converge side draws before trying sidestrippers– Test pumparound duties with side coolers– Remove coolers from pumparounds so all cooling is
taken at condenser. Then add duties to pumparound.
Recovery usually safer than composition specsSpec reflux ratio and product rateSpec reflux rate and component recovery
Multicomponent Distillation
PRO/II Training
88
Tips...If Water condenses in column:– Increase temperature estimates to keep water in vapor – Reduce steam flow:
0.1 lb/Gallon bottoms in main column0.1--0.2 lb/Gallon sidestripper product
Pumparounds solve best when you:– Fix rate and duty, calculate return temperature
Multicomponent Distillation
PRO/II Training
89
Tips...
FZ
Multicomponent Distillation
Excess cooling cause drying above PA return– Remedy: Specify liquid
flow above return tray and calculate pumparound duty
Eliminate loops whenever possible– Break thermal recycles
with reference stream– Simulate furnace as
column tray heater
Specify TrayLiquid rate
Declare Dutyas a Variable
PRO/II Training
90
Tips...Don’t believe your answers until you:– Verify thermodynamic method with expert– Rerun with tighter column and loop tolerances– Rerun with more pseudocomponents– Rerun with different assay characterization method– Check sensitivity to estimated parameters, i.e.,
number of traysExample: Add a stage to column. If results change drastically, then model is very sensitive to this parameter.Assess if this is physical reality or model defect.
Multicomponent Distillation
PRO/II Training
91
Distillation Algorithm Selection
• Generality: complex column and thermo
• Total pumparounds• VLWE on any tray• Water draw any tray
• Slow• Sensitive to initial guesses
• Free water or water draw on trays other than condenser
• Total pumparounds or vapor bypass
Inside/Out (I/O) CHEMDIST
• Very fast• Insensitive to initial estimates
• Thermo non-ideality • NO VLLE capability (VLWE at condenser)
• Hydrocarbons• EOS & slightly non-ideal LACT thermo
• Interlinked columns
• Side and main columns solved simultaneously
• Reactive distillation• VLLE on any tray
• Highly non-idealsystems
• No pumparounds• Side columns solved as recycles
• Non-ideal systems• Mechanically simple columns
• VLLE within column
Unique Features
Strengths
Limitations
Applicability
SURE
Multicomponent Distillation
PRO/II Training
92
Distillation Algorithm SelectionLiquid-Liquid Enhanced I/O
• Thermo must be a liquid activity method
• LLE on each stage • Total draws and waterdecants off trays
• Converges when zero flowrates on trays
• IEG does not work for all cases
• Same as I/O
Unique Features
Strengths
Limitations
Applicability
• Perform liquid-liquid extraction
• Liquid-liquid extraction columns
Multicomponent Distillation
PRO/II Training
93
FlowsheetFlowsheetOptimizationOptimization
PRO/II Training
94
Optimization allows...Automatic identification of the best design or operating conditions from a collection of alternativesFrees you from evaluating all possible cases
Flowsheet Optimization
PRO/II Training
95
Setting Up the OptimizerObjective function– A result calculated in PRO/II (duty, product recovery,...)– Usually evaluated with a calculator unit operation– Minimize or maximize this value (i.e., maximize profit)– Include all relevant costs
Optimization variables– A fixed input parameter with defined MIN, MAX values
Flowsheet Optimization
PRO/II Training
96
Setting Up the OptimizerProcess constraints (inequality)– Limits on flowsheet values which cannot be violated– Physical limitations on equipment
Constrain compressor operation to prevent surgingConstrain column tray flows to prevent flooding
Process specifications (equality)– Additional criteria imposed on optimum solution
Total cooling water flowrate = 100Kerosene product rate = 10000
Flowsheet Optimization
PRO/II Training
97
One Variable OptimizationValue of OVHD [$/lb-mole] is proportional to the square of its mole fraction C1 and C2What temperature maximizes profit from OVHD?Objective: maximize [ OVHD (YC1 + YC2)2 ]
H2O; C1-C6-60ºF900 psia
T=?30 psia
OVHD
Flowsheet Optimization
PRO/II Training
98
One Variable Optimization
0
200
400
600
800
1000
-150 -110 -50 10 70
Flash TemperatureOptimization Variable
Flowrate of C1 and C2 times Purity of C1 and C2
OptimalTemperature
ObjectiveFunction
110
Flowsheet Optimization
PRO/II Training
99
Multivariable OptimizationWhat temperature and pressure maximize profit from OVHD?Objective: maximize [ OVHD (YC1 + YC2)2 ]
H2O; C1-C6-60ºF900 psia
T=?P=?
OVHD
Flowsheet Optimization
PRO/II Training
100
Multivariable Optimization
-150
-110
-70
-30 10
50 90
5
15
25
35
0
200
400
600
800
1000
1200
1400
Temperature
ObjectiveFunction
Maximum
Pressure
Flowsheet Optimization
PRO/II Training
101
Optimization with ConstraintsVary temperature and pressure to maximize flowrate of C1 and C2 in OVHD The OVHD purity must be at least 90%
H2O; C1-C6-60ºF900 psia
T=?P=?
OVHD YC1 + YC2 > 0.9
Flowsheet Optimization
PRO/II Training
102
Optimization with Constraints
Flash Pressure
OptimizationVariable
Flash TemperatureOptimization Variable
-150 -110 -70 -30 10 50 905
15
25
35
Constraint
Optimum(1411)
0
360
650
860
1147
Flowsheet Optimization
PRO/II Training
103
Analyzing your Results: Shadow Prices
Flowsheet Optimization
Indicates the potential benefit of relaxing a limit, specification, or constraint– Positive: Increasing the value increases the
objective function
– Negative: Increasing the value decreases the objective function
– Zero: Constraints and/or limits on optimization variables (MINI, MAXI) are not active
PRO/II Training
104
Reading the Optimizer SummaryBest results– Objective Function– Values of Variables
Optimizer history at each cycle– Values for objective function and variables– Derivatives (Objective Function/Variable)– Shadow Prices
Convergence plots in output report
Flowsheet Optimization
PRO/II Training
105
- SHADOW PRICES ----CYCLE 1 5 BEST - 6 7 8---------- ----------- ----------- ----------- ----------- -----------VARY 1 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00VARY 2 0.0000E+00 -3.1750E+01 -3.1430E+01 -3.1428E+01 -3.1116E+01CNSTR 1 -2.4824E+03 -1.4458E+03 -1.4146E+03 -1.4149E+03 -1.4338E+03
** BEST OBJECTIVE FUNCTION = 1.41158E+03 AT CYCLE NUMBER 6
VARY --------- VARIABLE ----------INDEX INITIAL VALUE OPTIMUM VALUE----- ------------- ------------- 1 1.00000E+01 -4.12426E+01 2 3.00000E+01 5.00000E+00
---- VALUES ----CYCLE 1 5 BEST - 6 7 8---------- ----------- ----------- ----------- ----------- -----------VARY 1 1.0000E+01 -3.9238E+01 -4.1243E+01 -4.1439E+01 -4.1454E+01VARY 2 3.0000E+01 5.0000E+00 5.0000E+00 5.0000E+00 5.0000E+00CNSTR 1 9.2355E-01 8.9303E-01 8.9935E-01 8.9995E-01 9.0000E-01
REL ERR 0.00E+00 -7.74E-03 0.00E+00 0.00E+00 0.00E+00SUM SQ ERR 0.0000E+00 5.9977E-05 0.0000E+00 0.0000E+00 0.0000E+00OBJECTIVE 9.5967E+02 1.4210E+03 1.4116E+03 1.4106E+03 1.4106E+03
Optimizer OutputFlowsheet Optimization
PRO/II Training
106
Shadow Price Examples1) Where should you send any extra steam?
ProcessStm1
Stm2
Stm3Profit
2) Which heat exchanger should you clean first?
1 2 3 4GasT=200ºF
GasT=10ºF
Flowsheet Optimization
PRO/II Training
107
Solution Technique: Successive Quadratic
Programming (SQP)Initialization
Second order method(with derivatives) to
determine search direction
First order method(no derivatives) to check
progress towards the solution
Convergence
QuadraticProgrammingSub problem
Line Search
Flowsheet Optimization
PRO/II Training
108
ConvergenceConverging loops requires more interventionDerivative step sizes are very importantTolerances of units in loops should be lowered
Flowsheet Optimization
PRO/II Training
109
ConvergenceSpecifications and constraints are satisfied and– Scaled error below tolerance (10-7) or– Variables stop changing (tol=0.1%) or– Objective function stops changing (tol=0.5%)
Warning: Optimum is T=100, but any guess between 50 and 150 satisfies objective test
150
1000
1005
50 T (ºC)
Objective Function
995
Tn
100
Flowsheet Optimization
PRO/II Training
110
Convergence: Relative TolerancesExample: want L = 0.99 FWhich specification should you use?– Form 1: L/F = 0.99– Form 2: V/F = 0.01
PRO/II converges this to a relative tolerance εForm 1:– Converges when: | (L/F - 0.99) / 0.99 | < ε– so L = 0.99F ± 0.99F ε
LF
V
Flowsheet Optimization
PRO/II Training
111
Convergence: Relative TolerancesForm 2:– Converges when: | (V/F - 0.01) / 0.01 | < ε– But, V=F-L : | (1-L/F - 0.01) / 0.01 | < ε– so L = 0.99F ± 0.01F ε
If ε=0.01 (the default) and F=1000– Form 1: L=990 ± 9.9– Form 2: L=990 ± 0.1
Form 2 is much more accurate!To use Form 2, tighten relative tolerance
Flowsheet Optimization
PRO/II Training
112
Convergence: Compounding of ErrorsExample: specify each flash as Ln = 1/2 Ln-1
Exact solution: LN = (1/2)N L0
If each flash specification relative tolerance = εThen worst case LN relative error ~ NεExample: N=5, ε=1%, then L5 = L0/32 ± 5%
1 L1 2 L2 3 L3 N LNLN-1L0
Flowsheet Optimization
PRO/II Training
113
Flowsheet TolerancesOptimization requires flowsheets to be solved more accurately than for simulation– Tighten tolerances (columns, recycle loops, controllers)– Choose appropriate finite difference steps– Tighter tolerances allow smaller finite difference
steps to be used which is more efficientInaccurate flowsheet information may cause optimizer to fail or converge prematurely
Flowsheet Optimization
PRO/II Training
114
Finite Difference DerivativedF(xn)/dx = [F(xn +Δx) - F(xn)] / Δx
xn+Δx
F(x) Largest slope
Smallest slope
Error Bar
xn
Flowsheet Optimization
PRO/II Training
115
Finite Difference DerivativeSmaller step size can worsen derivatives
xn+Δx
F(x)
Calculated slopecan be negative!
xn
Flowsheet Optimization
PRO/II Training
116
Finite Difference Derivative
xn+Δx
F(x)
xn
Smaller error bars improve derivative calculations
Flowsheet Optimization
PRO/II Training
117
RecommendationsSolve base case separately - Check resultsTighten flowsheet tolerances for improved accuracyCarefully select bounds and constraints to ensure physically well-defined flowsheetSelect appropriate convergence criteria
Flowsheet Optimization
PRO/II Training
QuestionsQuestionsQuestions
Getting Started