ECUST PROII Advanced Training

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(1)PRO/II Training. ECUST PRO/II Advanced Training Copyright © 2004 SIMSCI-ESSCOR™ All Rights Reserved.

(2) PRO/II Training. What is the Power of Simulation3? ¾Who we are –. trusted results. Provider of software and services to the Hydrocarbon and Power industries that allow for plant start-up, operation and efficient: training of operators with. plants and processes – steady state & dynamic simulation (PRO/II, HEXTRAN, VISUAL FLOW,INPLANT PIPEPHASE, DYNSIM, TACITE, iFEED Suite/COMOS). modeling, dynamic simulation & control emulation. design. operate increased profitability. optimize. (PRO/II, DATACON, OTS, DYNSIM, FSIM). advisory and closed loop of their processes (ROMeo, ARPM, Connoisseur, PRO/II, NETOPT). focused on simulation 2.

(3) PRO/II Training. SimSci-Esscor’s Vision ¾ Be the leading provider of software and solutions for. – – – – –. Simulation & Modeling Performance Monitoring Optimization Operator Training − Data Reconciliation Integrated Process Engineering − Collaborative Engineering ¾ Use the Best-in Class Technology & Expertise − Control Checkout − Reactors – Thermodynamics − Intuitive Engineering GUI – Separations – Heat Exchange Applied Simulation Every Engineer’s Desktop Deliver Performance for our Customers – Improved Fluid Flow Asseton – Optimization 3.

(4) PRO/II Training. products. sample applications verticals. sim4me SIM4ME - Delivering on our Vision Hydrocarbon Power Pulp & Paper. Process Design. High Fidelity OTS. MRA & ROMeo. Flare System Design. Decision Support. PowRx. Well Design/ Nodal Analysis. Engineering Studies. Oil/Gas Crude FCCU Ethylene. Debottlenecking. PRO/II HEXTRAN. Oil/Gas Crude FCCU. PIPEPHASE NETOPT. DYNSIM OTS FSIM TACITE. design. operate. VISUAL FLOW. Plant. Lifecycle. ATI/Hyprotech CANNOT do this easily with their current architecture!. Ethylene Crude FCCU Gas Lift Optimization. ROMeo ARPM MRA Connoisseur. optimize Management. 4.

(5) PRO/II Training. Application During Plant Lifecycle SIM4ME. Basic Design Concept. Revamp. tate S y d Stea. Engin eering Dbs D. On line Op tim Ad iz a van tio ced n S im C on u la tro tio n& l Pla. nn ing. Detailed Design yn am. ic. Plant Design. Si m ul. at io n. ol r t n Co. m ste y S. Controls. Operator Training. Operation Commissioning. Construction 5.

(6) PRO/II Training. Process Engineering Suite 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 6.

(7) PRO/II Training. PES Features. ¾ Enhances productivity in the plant life cycle Basic Design Concept. Revamp. PLANT LIFE CYCLE. Detailed Design Plant Design. Controls Operation & Troubleshooting. Commissioning. Construction 7.

(8) PRO/II Training. Integration within PES Hextran MS Office. Datacon. PRO/II. Inplant. Complete Could be done The Plant. Visual Flow 8.

(9) PRO/II Training. Introduction. History of PRO/II ¾. First Generation: 1974. – ¾. Second Generation: 1979. – ¾. PRO/II with Provision 4.x PRO/II with Provision 5.x version 5.61 – March of 2002. Sixth Generation: 2003. – ¾. Version 3.30 - Spring of 1993. Fifth Generation: 1997. – – ¾. PRO/II Simulation Program. Forth Generation: 1995. – ¾. Process Simulation Program. Third Generation: 1988. – – ¾. SSI/100 Simulation Program. Over 40 new features. Seven Generation: 2004. –. Just released in August 2004. 9.

(10) PRO/II Training. PES Solution Client Benefits ¾ ¾ ¾ ¾. Reduced process engineering time & cost Reduced plant capital cost Reduced plant lifecycle costs Increased plant operating profits. – – – –. higher product rates improved product quality lower operating costs more feed flexibility. ¾ A valuable tool for experienced process manager and engineers 10.

(11) PRO/II Training. Flowsheets Features ¾ PRO/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.. 11.

(12) PRO/II Training. Distillation Features ¾ Multiple column algorithms to model complex columns – IO, Sure, Chemdist, Liquid-Liquid, Electrolytes, Enhanced IO ¾ Multiple methods for generating initial estimated values – Simple, Conventional, Refinery, Chemdist, Electrolytes ¾ Reactive distillation – robust algorithm – derivative data not required ¾ Tray Hydraulic for rating and design – Volve, Sieve, and Cap structured tray – Sulzer structured packing – Norton random packing 12.

(13) PRO/II Training. Reaction Option ¾ Enter reactions in the reaction data section ¾ In Reactor units, select which reactions to use First Create a Library of Reaction Data. Then Select Reactions for Each Unit. 13.

(14) PRO/II Training. Reactor Types ¾ General: (no reactor geometry required) – CONVERSION REACTOR (multiple reactions) – EQUILIBRIUM REACTOR (multiple reactions). ¾ Kinetic: (reactor geometry required) – PLUG FLOW REACTOR (PFR) – CONTINUOUS STIRRED TANK REACTOR (CSTR). ¾ GIBBS: (stoichiometry optional) – Free energy minimization – Kinetics not considered. 14.

(15) PRO/II Training. Optimizer Features ¾ Optimize based on an objective function ¾ Utilizing tag data values ¾ No needs to have a dynamic calculation ¾ Automatic identification of the best design or operating conditions from a collection of alternatives ¾ Frees user from evaluating all possible cases. 15.

(16) PRO/II Training. User-Added Program Features ¾ UAS/PDTS enhancements. – – – – –. additional function calls additional subroutines additional simulation database access full documentation supported in PROVISION. 16.

(17) PRO/II Training. Tag Data Features ¾ Directly access plant historical data ¾ Read tag data from a file ¾ Read tag data from server. – PI – ODBC – @aGlance/IT – AIM ¾ Write tag data back to a file. 17.

(18) PRO/II Training. OLE Features ¾OLE/COM Automation Layer – documented access to simulation database for most data – two way link y simulation data out, design/plant data in. – any OLE compliant application y e.g. MS Office can use VB or VBA. – used for Zyqad or Icarus interface – examples available at www.simsci.com. 18.

(19) PRO/II Training. Spreadsheet Tools. 19.

(20) PRO/II Training. OLE Automation. 20.

(21) PRO/II Training 11. Operator Interface. TURBOEXPANDER PLANT. C1 100 10. 8 E1 2. 1. E2. 2 3X 3. 4 7 5. 6 6 7. 8. 4. 9. Feed Flowrate Pressure Temperature Composition N2 C1 C2 C3 IC4 NC4 IC5 NC5 NC6 NC7. 100 1016700.0000 FT3/HR 587.0000 PSIG 120.0000 F. Range. Products Flowrate Pressure Temperature Composition N2 C1 C2 C3 IC4 NC4 IC5 NC5 NC6 NC7. 7.9100 73.0500 7.6800 5.6900 0.9900 2.4400 0.6900 0.8200 0.4200 0.3100. 9 483.7454 125.0000 24.0874 0.0000 0.0086 0.3633 0.3141 0.0548 0.1351 0.0382 0.0454 0.0233 0.0172. 3. 11 D1 2195.4231 LB-MOL/HR 161.2292 PSIG 5 157.5738 F 0.0965 0.8896 0.0137 0.0002 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000. X1. T1. 10 9. V1. Units X1 adiabatic efficiency X1 outlet pressure C1 adiabatic efficiency C1 work from X1 T1 top pressure T1 C1:C2 ratio bottom E1 HICO Stream 3 temperature. 80.0000 125.0000 75.0000 0.9000 125.0000 0.0150 10.0000 -83.9990. % PSIG %. 0-100 0-100 0-1. PSIG 0-1 F F. Units Reboiler duty E1 duty E2 duty X1 actual work C1 actual work. 2.2889 5.2814 4.9133 392.2247 353.0023. MM BTU/HR MM BTU/HR MM BTU/HR HP HP. Run Simulation. 21.

(22) Introduction. PRO/II Training. Simulation in Seven Steps 2. 1. Check Units of Measur 3 e. Build Flowshe et. 4. 6. Select Therm o 5. Define Compone nts. Suppl y Strea m Data. Provide Process Condition s 7 Run & View Results. 22.

(23) PRO/II Training. Defining the Components.

(24) PRO/II Training. Defining the Components. Component Types ¾ Library component ¾ Petroleum component ¾ User-defined component ¾ Solid component ¾ Polymer component ¾ Ionic component. 24.

(25) PRO/II Training. Defining the Components. Component Selection. 25.

(26) PRO/II Training. Defining the Components. PRO/II Component Library ¾ Composite of several databanks ¾ Databank search order. – – –. PROCESS (default) SIMSCI (default) DIPPR or OLI available as an optional PRO/II add-on. ¾ Component selection by list or access name ¾ Pure component data. – –. Fixed properties Temperature-dependent properties 26.

(27) PRO/II Training. Defining the Components. Adding Library Components. 27.

(28) Defining the Components. PRO/II Training. Component Data Printout ¾ Component name. ¾ Phase type. ¾ Component type. ¾ Nine fixed properties. PROJECT TRAINING PRO/II INPUT PROBLEM COMPONENTS COMPONENT DATA ============================================================================ NO. --1 2 3 4. COMPONENT NAME -------------N2 C1 C2 C3. COMP. TYPE PHASE MOL. WEIGHT SPGR ----------- ----------- ----------- ---------LIBRARY VAP/LIQ 28.013 0.80811 LIBRARY VAP/LIQ 16.043 0.30000 LIBRARY VAP/LIQ 30.070 0.35640 LIBRARY VAP/LIQ 44.097 0.50770. NO. COMPONENT NAME. NBP CRIT. TEMP. CRIT. PRES. CRIT. VOLM. F F PSIG GAL/LB-MOL ----------- ----------- ----------- -----------320.440 -232.420 477.619 10.7963 -258.682 -116.680 652.499 11.8628 -127.534 90.140 693.648 17.7343 -43.726 206.006 601.652 24.3247. --1 2 3 4. -------------N2 C1 C2 C3. NO. COMPONENT NAME --1 2 3 4. -------------N2 C1 C2 C3. ACEN. FACT. HEAT FORM. G FORM. BTU/LB-MOL BTU/LB-MOL ----------- ----------- ----------0.04500 0.00 0.00 0.01040 -32066.21 -21726.14 0.09860 -36120.21 -13810.45 0.15290 -44650.04 -10139.64. 28.

(29) PRO/II Training. Defining the Components. Using DATAPREP ¾ Menu-driven DOS interface ¾ Total access to PRO/II component database ¾ Additional information:. – – – –. Fixed properties Data source Data accuracy Plots and tables. 29.

(30) Defining the Components. PRO/II Training. Enthalpy Curve for Water from DATAPREP (10E+ 2) 320 Ideal Gas Curve. ENTHALPY BTU/lbmol. 240. Sat urat ed Vapor Curve. 160 Heat of Vaporizat ion at NBP. 80 Solid Curve. Heat of Fusion at NMP. Crit ical Point. 0. -80 -500. Sat urat ed Liquid Curve. -250. 0. 250. 500. 750. Temperat ure F. 30.

(31) PRO/II Training. Defining the Components. Petroleum Components ¾ Normal Boiling Point ¾ Gravity ¾ Molecular Weight At least two of three required. 31.

(32) PRO/II Training. Defining the Components. User-defined Components ¾ Component Name ¾ Component Properties. 32.

(33) PRO/II Training. Defining the Components. Component Properties ¾ Fixed properties ¾ Temperature-dependent properties ¾ User Defined and Refinery Inspection properties ¾ Solid properties ¾ Polymer properties ¾ Structure data. 33.

(34) PRO/II Training. Defining the Components. Component Property Window. 34.

(35) PRO/II Training. Selecting the Thermodynamics.

(36) PRO/II Training. Selecting the Thermodynamics. Example: Propane-Propylene Splitter ¾ Choice of Thermo strongly effects results!. Thermodynamic Condenser Reflux/Feed System Duty Ratio Peng-Robinson. -59.6. 13.1. Grayson-Streed. -37.3. 8.2. 36.

(37) PRO/II Training. Selecting the Thermodynamics. Thermodynamic Data ¾ Required for all flowsheets ¾ Thermodynamic Property Methods ¾ Transport Property Methods. –. Required for certain units: y Column. y Dissolver. y Rigorous heat exchanger. y Depressuring unit. y Pipe. y Output tables. 37.

(38) PRO/II Training. Selecting the Thermodynamics. Thermodynamic Properties ¾ K-Values (Mass Balances). ¾ Enthalpies (Heat Balances). ¾ Entropies ¾ Densities. 38.

(39) PRO/II Training. Selecting the Thermodynamics. K-Value Calculation Methods ¾ Ideal ¾ Equation of State ¾ Liquid Activity ¾ Generalized Correlations ¾ Special Packages ¾ Electrolytes ¾ Polymers. 39.

(40) PRO/II Training. Selecting the Thermodynamics. Selecting the Thermodynamic Method. 40.

(41) PRO/II Training. Selecting the Thermodynamics. Enabling VLLE Calculations. Default. 41.

(42) PRO/II Training. Selecting the Thermodynamics. Modifications ¾ Very important to choose the correct thermodynamic method ¾ Even more important to insure that binary interaction parameters are available. 42.

(43) PRO/II Training. Selecting the Thermodynamics. Modifications (Cont.) ¾ Advanced Equations of State. – – – –. Model hydrocarbon behavior Advanced Alpha forms Advanced mixing rules Databank of regressed binary interaction coefficient. 43.

(44) PRO/II Training. Selecting the Thermodynamics. Modifications (Cont.) ¾ Liquid Activity Coefficient methods. – – – –. Model non-ideal behavior Databank of regressed binaries Databank of azeotropes Fill options for binaries. 44.

(45) PRO/II Training. Selecting the Thermodynamics. Modifications (Cont.) ¾ Generalized Correlation. – –. Typically designed for a specific application Do a good job for heavier hydrocarbons. 45.

(46) PRO/II Training. Selecting the Thermodynamics. Modifications (Cont.) ¾ Enthalpy, Entropy and Density. – – – –. Library correlation for enthalpy No Library correlation for entropy Library correlation for density Rackett parameters in Library. 46.

(47) PRO/II Training. Selecting the Thermodynamics. Transport Properties ¾ Viscosities ¾ Thermal conductivities ¾ Surface tension ¾ Liquid diffusivity ¾ 4 methods: Pure, Petroleum, Trapp, User-defined. 47.

(48) Selecting the Thermodynamics. PRO/II Training. Calculation with Two Liquid Phases ¾ Water decant option. ¾ Rigorous VLLE calculations. V. V. L = HC + W. L1 = HC + W. W = pure water. L2 = W + HC 48.

(49) Selecting the Thermodynamics. PRO/II Training. Water Decant Option Vapor VLE K-values. Liquid. Water Vapor Pressure. Pure Water Solubility Water. 49.

(50) PRO/II Training. Selecting the Thermodynamics. Rigorous VLLE Calculations Vapor VLE K-values. Liquid 1. VLE K-values. LLE K-values. Liquid 2. Must enable two-liquid phase calculations. 50.

(51) PRO/II Training. Selecting the Thermodynamics. Hydrocarbon Systems ¾ Refining 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.. 51.

(52) PRO/II Training. Selecting the Thermodynamics. Hydrocarbon Systems ¾ Gas 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. 52.

(53) PRO/II Training. Selecting the Thermodynamics. Online Thermodynamic Help ¾ Reference Manual. –. Detailed technical reference. ¾ Application Guidelines. –. When to use each method. 53.

(54) PRO/II Training. Selecting the Thermodynamics. Chemical Systems: Activity coefficient methods ¾ Non-ideal components. ¾ Low to medium pressures ¾ Rely on binary interaction parameters (if missing will be close to Ideal!) ¾ Missing parameters estimated from structures, azeotrope composition, mutual solubilities etc. ¾ Used with Henry’s Law for non-condensibles ¾ VLLE with some methods 54.

(55) Selecting the Thermodynamics. PRO/II Training. Chemical Systems: Activity coefficient methods. NRTL UNIQUAC WILSON UNIFAC. Two Liquids?. Binary parameters in databank?. Yes. Yes. Yes. Yes. No. No. Yes. Estimates non-ideality from structure. ¾ Other methods - see Reference Manual 55.

(56) PRO/II Training. Selecting the Thermodynamics. Chemical Systems: Equations of State ¾ SRK-SIMSCI, SRKM, and PRM for polar mixtures ¾ SRK-Hexamer for mixtures involving HF ¾ Can model high-pressures ¾ Also rely on binary interaction parameters ¾ Some binary parameters in databanks for above methods. 56.

(57) PRO/II Training. Multicomponent Distillation. 57.

(58) Multicomponent Distillation. PRO/II Training. Tray Model _. Vj yj _. Lj , Vj Liquid, vapor flowrate _. Lj-1 xj-1. VDj. Fj. Feed flowrate. Qj. Heater/cooler duty. _ _. Fj X F. xj , yj Liquid, vapor mole frac. _. Tj Pj. XF. Qj. Feed mole fractions. hj , Hj Liquid, vapor enthalpies LDj _. Vj+1 yj+1. _. Lj xj. Subscript denotes tray number. Tj , Pj Temperature, pressure LDj. Liquid Draw rate. VDj. Vapor Draw rate. Overbar denotes _ component vectors: e.g., x = (x1, x2, ...xNC). 58.

(59) PRO/II Training. Multicomponent Distillation. Tray Numbering ¾ Normally use Theoretical Trays (Stages) ¾ Numbered from top down ¾ Condenser is Stage 1. –. Even for subcooled condenser. ¾ Reboiler is last stage. –. Thermosiphon adds 2 stages. ¾ Convert packing to stages. –. Rule of Thumb: 2 to 3 feet of packing per stage. 59.

(60) Multicomponent Distillation. PRO/II Training. Tray Efficiency ¾ Murphree Efficiency = 75% z. yA 100% efficient: step to equilibrium curve. z. xA. 75% efficient: step 3/4 to equilibrium curve. xA 60.

(61) PRO/II Training. Multicomponent Distillation. Other Tray Efficiency Models ¾ Vaporization. yi = ciKixi. ¾ Equilibrium. K’s adjusted towards 1.0. ¾ Vapor leaving stage not at dew point ¾ Can lead to Mixed Phase Condenser product ¾ Better to use Overall Efficiencies. – – –. Theoretical / Actual trays to carry out separation Use different values in different column zones Tune from experimental data if possible. 61.

(62) Multicomponent Distillation. PRO/II Training. Overall Efficiencies ¾ Efficiency increases as components decrease ¾ Efficiency increases as reflux increases. Reflux. ¾ Results can be very sensitive to number of trays High reflux: number of stages strongly affects results. Low reflux: number of stages is less important. Number of Stages 62.

(63) Multicomponent Distillation. PRO/II Training. Typical Overall Tray Efficiencies SERVICE Simple Absorbers/Strippers Reboiled Absorbers/Strippers Deethanizers Depropanizers Debutanizers Deisobutanizers (Refluxed) Splitters C2, C2C3, C3C4抯or C5抯. PERCENT 20-30 40-50 60-65 65-75 80-90 85-95 85-95 95-100 90-100. 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.. 63.

(64) PRO/II Training. Multicomponent Distillation. All Column Algorithms are Iterative ¾ Want to solve f(x) = 0 ¾ Generate a sequence of estimates of solution: x0, x1, x2, ... xN ¾ Equations are satisfied when x stops changing: | xN - xN-1 | < 0.00001 ¾ xN is regarded as the solution. 64.

(65) Multicomponent Distillation. PRO/II Training. Convergence of Newton’s method ... Good initial guess leads to solution. f(X). x. n +1. ⎡ ∂f = x −⎢ ⎣ ∂x n. −1. ⎤ n f x ( ) ⎥ xn ⎦. Solution. 0 x0 x1. x2. x*. X 65.

(66) PRO/II Training. Multicomponent Distillation. Convergence is not guaranteed! f(x). 0 x*. X 66.

(67) Multicomponent Distillation. PRO/II Training. Convergence is not guaranteed! f(x). Periodic. 0 x*. X 67.

(68) PRO/II Training. Multicomponent Distillation. Convergence is not guaranteed! f(x). Bad guess converges.... But better guess fails!. 0 x*. X 68.

(69) PRO/II Training. Multicomponent Distillation. Available Distillation Algorithms in PRO/II ¾ Inside Out (I/O) ¾ Chemdist ¾ Sure ¾ Liquid-liquid ¾ Enhanced I/O. 69.

(70) PRO/II Training. Multicomponent Distillation. 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. 70.

(71) Multicomponent Distillation. PRO/II Training. I/O Column Features. 1 2 Heater/Cooler. 2 phase condenser + water decant. Side Streams. Heat Source/Sink. Multiple Feeds. Side Columns. Pumparounds N-1. Kettle and Thermosiphon N Reboilers. 71.

(72) PRO/II Training. Multicomponent Distillation. I/O Algorithm Uses Nested Loops ¾ Inner Loop. – – –. Simple thermo model (Fast) Approximate Matrix Inversion (Fast) Converge enthalpy balance and performance specs. ¾ Outer Loop. – – –. Updates, checks thermo using rigorous model (Slow) Checks Bubble Point Criteria If thermo changing or not bubble point, goto Inner Loop. 72.

(73) Multicomponent Distillation. PRO/II Training. I/O Algorithm. Outer Loop. Prepare approximate thermo models for K*(K) and H*L(HL), and H*V(HV).. Approx. Thermo. Model. Iteratively solve the column equations using approximate thermo, K*(T,P) and H*(T,P).. Inner Loop. 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 Done, solution is: x, T, L, V, beginning. Q .... Convergence Check. 73.

(74) Multicomponent Distillation. PRO/II Training. Initial Estimate Generator (IEG) ¾ Generates “good” initial estimates for all column variables P1 P2 PN LN Column Spec’s. IEG. You supply column specs and guesses for a few variables.... x0 y0 T0 P V0 L0 Q0R Q0C. Solver. IEG calculates initial estimates for all column variables.... x* y* T* P V* L* Q*R Q*C. Solver (I/O, Chemdist) converges on solution. 74.

(75) PRO/II Training. Multicomponent Distillation. Four Types of IEG ¾ SIMPLE (default): Simple columns – Only choice for liquid-liquid extraction ¾ CONVENTIONAL: Works well with most columns – Based on shortcut methods – Strongly dependent on your product rate estimates ¾ REFINING: Complex refinery columns (e.g., Crude, Vacuum, FCC main fractionator, Coker) ¾ CHEMICAL: Nonideal thermodynamics (e.g., azeotropic and extractive distillation). Can be slow.. 75.

(76) PRO/II Training. Multicomponent Distillation. Specifications and Variables ¾ Specifications are constraints to be met by the column ¾ Variables are calculated to meet specifications. ¾ Column always balances equations and unknowns ¾ To impose a specification, you must add a variable, otherwise equations and unknowns don’t balance. ¾ Example: Impose two product specifications by declaring reboiler & condenser duties as variables.. 76.

(77) Multicomponent Distillation. PRO/II Training. Column Status at Initialization ¾ Fixed quantities remain at their current values unless you declare them as variables. ¾ If no specs/variables provided, default status used: QUANTITY Overhead and Bottoms Rates Side Draw Rates Duties Feed Rates Tray Temperatures Tray Pressures Vapor and Liquid Rates Product Properties (e.g. Viscosity) Tray Vapor or Liquid Properties. STATUS Calculated Fixed Fixed Fixed Calculated Fixed Calculated Calculated Calculated. 77.

(78) PRO/II Training. Multicomponent Distillation. Improper Specifications ¾ 0% methane in crude column bottoms. –. Infinitely many solutions. ¾ 300 lb-mole/hr propylene in overhead. –. No solutions if column feed only 250 mol/hr propylene. ¾ 98% ethanol product. –. No solutions if Water-Ethanol Azeotrope present. 78.

(79) Multicomponent Distillation. PRO/II Training. What is alpha (α)? ¾ Length of correction:. Xn+1 = Xn + αn δn. 0< |α| < 1. ¾ Decrease α if full step increases error α1 = .7 Unknown 1. α2 = 1. X1 X2. δ3 X3 Solution. Reject: full step increases error. Unknown 2 79.

(80) PRO/II Training. Multicomponent Distillation. You Can Help I/O by Using Damping ¾ Damping reduces iteration step and suppresses oscillation ¾ Conventional columns:. DAMP = 1.0 (default). ¾ Columns with steam:. DAMP = 0.6 - 0.8. –. Crude, Vacuum, FCC Main Fractionator. ¾ Less-ideal:. – –. DAMP = 0.2 - 0.6. Increase number of allowed iterations If oscillations persist, use Chemdist. 80.

(81) PRO/II Training. Multicomponent Distillation. Reboiler Models ¾ Most reboilers can be simulated as:. – – –. Kettle Thermosiphon with Baffles Thermosiphon without Baffles. 81.

(82) Multicomponent Distillation. PRO/II Training. Kettle Reboilers LN-1. Vapor in Equilibrium with Bottoms VN-1. VN. LN-2. N-1 Bottom Tray VN BTMS BTMS. LN-1. N Reboiler. Q. 82.

(83) Multicomponent Distillation. PRO/II Training. Single Pass (Once Through) Thermosiphon. ¾ Equivalent to a Kettle Reboiler because Bottoms is in Equilibrium with VN LN-1. LN-1 VN VN. Bottom Sump BTMS. Bottom Sump Reboiler Sump BTMS. Baffle 83.

(84) Multicomponent Distillation. PRO/II Training. Circulating Thermosiphon Adds 2 Stages ¾ Simulate as TS without Baffles. N-2 Bottom Tray. LN-2. VN-1. VN-1. RV BTMS. RL. Combined Sump BTMS. N-1 Combined Sump RL. RF. LN-2 RV. RF. N Reboiler. Q. 84.

(85) Multicomponent Distillation. PRO/II Training. Circulating Thermosiphon ä Simulate as TS without baffle N-2 Bottom Tray. LN-2 VN-1. RV. VN-1. RL BTMS Bottom Sump. BTMS. Reboiler Sump. N-1 Reboiler Sump RL. RF. LN-2 RV. RF. N Reboiler. Q. 85.

(86) Multicomponent Distillation. PRO/II Training. Preferential Thermosiphon ä Simulate as TS with baffle LN-2. N-2 Bottom Tray. RV. VN-1 RL. VN-1 LO. Bottom Sump Lo. Bottom Sump Reboiler Sump RF. RV N-1 Reboiler Sump RF. BTMS R L BTMS. LN-2. N Reboiler 86. Q.

(87) PRO/II Training. Multicomponent Distillation. Tips... ¾ 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.. ¾ Recovery usually safer than composition specs ¾ Spec reflux ratio and product rate ¾ Spec reflux rate and component recovery. 87.

(88) PRO/II Training. Multicomponent Distillation. Tips... ¾ If Water condenses in column:. – –. Increase temperature estimates to keep water in vapor Reduce steam flow: y 0.1 lb/Gallon bottoms in main column y 0.1--0.2 lb/Gallon sidestripper product. ¾ Pumparounds solve best when you:. –. Fix rate and duty, calculate return temperature. 88.

(89) PRO/II Training. Multicomponent Distillation. Tips... ¾ Excess cooling cause drying above PA return. –. Specify Tray Liquid rate. Remedy: Specify liquid flow above return tray and calculate pumparound duty. Declare Duty as a Variable. ¾ Eliminate loops whenever possible. – –. Break thermal recycles with reference stream Simulate furnace as column tray heater. FZ 89.

(90) PRO/II Training. Multicomponent Distillation. Tips... ¾ 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 trays y Example: Add a stage to column. If results change drastically, then model is very sensitive to this parameter. y Assess if this is physical reality or model defect.. 90.

(91) Multicomponent Distillation. PRO/II Training. Distillation Algorithm Selection Inside/Out (I/O). CHEMDIST. SURE. Unique Features. • Side and main columns solved simultaneously. • Reactive distillation • VLLE on any tray. • Total pumparounds • VLWE on any tray • Water draw any tray. Strengths. • Very fast • Insensitive to initial estimates. • Highly non-ideal systems. • Generality: complex column and thermo. • Thermo non-ideality • NO VLLE capability (VLWE at condenser). • No pumparounds • Side columns solved as recycles. • Slow • Sensitive to initial guesses. • Non-ideal systems • Mechanically simple columns • VLLE within column. • Free water or water draw on trays other than condenser • Total pumparounds or vapor bypass. Limitations. • Hydrocarbons Applicability • EOS & slightly nonideal LACT thermo • Interlinked columns. 91.

(92) Multicomponent Distillation. PRO/II Training. Distillation Algorithm Selection Liquid-Liquid Unique Features. Enhanced I/O. • LLE on each stage. • Total draws and water decants off trays. Strengths. • Perform liquid-liquid extraction. • Converges when zero flowrates on trays. Limitations. • Thermo must be a liquid activity method. • IEG does not work for all cases. • Liquid-liquid extraction columns. • Same as I/O. Applicability. 92.

(93) PRO/II Training. Flowsheet Optimization. 93.

(94) PRO/II Training. Flowsheet Optimization. Optimization allows... ¾ Automatic identification of the best design or operating conditions from a collection of alternatives ¾ Frees you from evaluating all possible cases. 94.

(95) PRO/II Training. Flowsheet Optimization. Setting Up the Optimizer ¾ Objective 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. ¾ Optimization variables. –. A fixed input parameter with defined MIN, MAX values. 95.

(96) PRO/II Training. Flowsheet Optimization. Setting Up the Optimizer ¾ Process constraints (inequality). – –. Limits on flowsheet values which cannot be violated Physical limitations on equipment y Constrain compressor operation to prevent surging y Constrain column tray flows to prevent flooding. ¾ Process specifications (equality). –. Additional criteria imposed on optimum solution y Total cooling water flowrate = 100 y Kerosene product rate = 10000. 96.

(97) Flowsheet Optimization. PRO/II Training. One Variable Optimization ¾ Value of OVHD [$/lb-mole] is proportional to the square of its mole fraction C1 and C2 ¾ What temperature maximizes profit from OVHD? ¾ Objective: maximize. [ OVHD (YC1 + YC2)2 ] OVHD. H2O; C1-C6 -60ºF 900 psia. T=? 30 psia. 97.

(98) Flowsheet Optimization. PRO/II Training. One Variable Optimization 1000. Objective Function Flowrate of C1 and C2 times Purity of C1 and C2. 800 600. Optimal Temperature. 400 200 0 -150. -110. -50. 10. 70. 110. Flash Temperature. Optimization Variable. 98.

(99) Flowsheet Optimization. PRO/II Training. Multivariable Optimization ¾ What temperature and pressure maximize profit from OVHD? ¾ Objective: maximize. [ OVHD (YC1 + YC2)2 ] OVHD. H2O; C1-C6 -60ºF 900 psia. T=? P=?. 99.

(100) Flowsheet Optimization. PRO/II Training. Multivariable Optimization Maximum 1400 1200 1000 800 600 400. 35. 200. 25. 0. Pressure. 90. Tempera ture. 50. 10. 5 -30. -70. 15 -110. -150. Objective Function. 100.

(101) Flowsheet Optimization. PRO/II Training. Optimization with Constraints ¾ Vary temperature and pressure to maximize flowrate of C1 and C2 in OVHD ¾ The OVHD purity must be at least 90% OVHD H2O; C1-C6 -60ºF 900 psia. YC1 + YC2 > 0.9. T=? P=?. 101.

(102) Flowsheet Optimization. PRO/II Training. Optimization with Constraints 35. 0 360 25. Constraint. 650. Flash Pressure. Optimization Variable. 860. 15. 1147. Optimum (1411) 5. -150. -110. -70. -30. 10. 50. 90. Flash Temperature. Optimization Variable 102.

(103) PRO/II Training. Flowsheet Optimization. Analyzing your Results: Shadow Prices ¾ 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. 103.

(104) PRO/II Training. Flowsheet Optimization. Reading the Optimizer Summary ¾ Best results. – –. Objective Function Values of Variables. ¾ Optimizer history at each cycle. – – –. Values for objective function and variables Derivatives (Objective Function/Variable) Shadow Prices. ¾ Convergence plots in output report. 104.

(105) Flowsheet Optimization. PRO/II Training. Optimizer Output ** BEST OBJECTIVE FUNCTION = 1.41158E+03 AT CYCLE NUMBER 6 VARY INDEX ----1 2. --------- VARIABLE ---------INITIAL VALUE OPTIMUM VALUE ------------------------1.00000E+01 -4.12426E+01 3.00000E+01 5.00000E+00. - SHADOW PRICES ---CYCLE 1 ---------- ----------VARY 1 0.0000E+00 VARY 2 0.0000E+00 CNSTR 1 -2.4824E+03. 5 ----------0.0000E+00 -3.1750E+01 -1.4458E+03. BEST - 6 ----------0.0000E+00 -3.1430E+01 -1.4146E+03. 7 ----------0.0000E+00 -3.1428E+01 -1.4149E+03. 8 ----------0.0000E+00 -3.1116E+01 -1.4338E+03. ---- VALUES ---CYCLE 1 ---------- ----------VARY 1 1.0000E+01 VARY 2 3.0000E+01 CNSTR 1 9.2355E-01 REL ERR 0.00E+00 SUM SQ ERR 0.0000E+00 OBJECTIVE 9.5967E+02. 5 -----------3.9238E+01 5.0000E+00 8.9303E-01 -7.74E-03 5.9977E-05 1.4210E+03. BEST - 6 -----------4.1243E+01 5.0000E+00 8.9935E-01 0.00E+00 0.0000E+00 1.4116E+03. 7 -----------4.1439E+01 5.0000E+00 8.9995E-01 0.00E+00 0.0000E+00 1.4106E+03. 8 -----------4.1454E+01 5.0000E+00 9.0000E-01 0.00E+00 0.0000E+00 1.4106E+03. 105.

(106) Flowsheet Optimization. PRO/II Training. Shadow Price Examples 1) Where should you send any extra steam? Stm1. Process. Stm2. Profit. Stm3. 2) Which heat exchanger should you clean first? Gas T=200ºF. 1. 2. 3. 4. Gas T=10ºF. 106.

(107) Flowsheet Optimization. PRO/II Training. Solution Technique: Successive Quadratic Programming (SQP) Initialization Second order method (with derivatives) to determine search direction. Quadratic Programming Sub problem. First order method (no derivatives) to check progress towards the solution. Line Search. Convergence. 107.

(108) PRO/II Training. Flowsheet Optimization. Convergence ¾ Converging loops requires more intervention ¾ Derivative step sizes are very important ¾ Tolerances of units in loops should be lowered. 108.

(109) Flowsheet Optimization. PRO/II Training. Convergence ¾ Specifications and constraints are satisfied and. – – –. -7. Scaled error below tolerance (10 ) or Variables stop changing (tol=0.1%) or Objective function stops changing (tol=0.5%). Objective Function Warning: Optimum is T=100, but any guess between 50 and 150 satisfies objective test. 1005 1000 Tn 995. 50. T (ºC). 100. 150. 109.

(110) Flowsheet Optimization. PRO/II Training. Convergence: Relative Tolerances ¾ Example: want L = 0.99 F ¾ Which specification should you use?. – –. Form 1: Form 2:. F L. L/F = 0.99 V/F = 0.01. ¾ PRO/II converges this to a relative tolerance ε ¾ Form 1:. – –. V. Converges when: | (L/F - 0.99) / 0.99 | < ε so L = 0.99F ± 0.99F ε. 110.

(111) Flowsheet Optimization. PRO/II Training. Convergence: Relative Tolerances ¾ Form 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. ¾ If ε=0.01 (the default) and F=1000. – –. Form 1: Form 2:. L=990 ± 9.9 L=990 ± 0.1. ¾ Form 2 is much more accurate! ¾ To use Form 2, tighten relative tolerance 111.

(112) Flowsheet Optimization. PRO/II Training. Convergence: Compounding of Errors ¾ ¾ ¾ ¾ ¾. Example: specify each flash as Ln = 1/2 Ln-1 Exact solution: LN = (1/2)N L0 If each flash specification relative tolerance = ε Then worst case LN relative error ~ Nε Example: N=5, ε=1%, then L5 = L0/32 ± 5%. L0. 1. L1. 2. L2. 3. L3. LN-1. N. LN. 112.

(113) PRO/II Training. Flowsheet Optimization. Flowsheet Tolerances ¾ Optimization 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 efficient. ¾ Inaccurate flowsheet information may cause optimizer to fail or converge prematurely. 113.

(114) Flowsheet Optimization. PRO/II Training. Finite Difference Derivative dF(xn)/dx = [F(xn +Δx) - F(xn)] / Δx Largest slope. F(x). Smallest slope Error Bar xn. xn+Δx 114.

(115) Flowsheet Optimization. PRO/II Training. Finite Difference Derivative ¾ Smaller step size can worsen derivatives F(x). Calculated slope can be negative!. xn. xn+Δx 115.

(116) Flowsheet Optimization. PRO/II Training. Finite Difference Derivative ¾ Smaller error bars improve derivative calculations F(x). xn. xn+Δx 116.

(117) PRO/II Training. Flowsheet Optimization. Recommendations ¾ Solve base case separately - Check results ¾ Tighten flowsheet tolerances for improved accuracy ¾ Carefully select bounds and constraints to ensure physically well-defined flowsheet ¾ Select appropriate convergence criteria. 117.

(118) PRO/II Training. Questions. Getting Started.

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