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Operational Aspects

Operational Aspects. Typical : Processes are designed & optimized based on given (fixed) data (flowrates, temperatures, pressures, etc.) But : Processes (and Heat Exchanger Networks) are: − often operated “off” design (above/below) − subject to disturbances

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Operational Aspects

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  1. Operational Aspects Typical: Processes are designed & optimized based on given (fixed) data (flowrates, temperatures, pressures, etc.) But: Processes (and Heat Exchanger Networks) are: − often operated “off” design (above/below) − subject to disturbances − to be started up and shut down The Result: The Process Engineer will over-design before the Control Engineer adds new Units for Manipulation Process, Energy and System Various Topics for Heat Exchanger Networks T. Gundersen OPER 01

  2. Various Operational Aspects • Controllability • Property of the Process, not the Control System • Ability to handle operational Variations • Flexibility • Ability to cope with different Operating Conditions • Start-Up and Shut-Down • Starting up from “Cold” Conditions is challenging • “Switchability” • Change Operation from one Condition to another • Environmental Aspects • Safety • Maintenance • “RAMS” • Reliability, Availability, Maintainability, Safety Process, Energy and System Various Topics for Heat Exchanger Networks T. Gundersen OPER 02

  3. Two important Aspects of Operability • Controllability of Processes • “Ability to handle Short Term Variations” • Withstand (unwanted) Disturbances • Stability Issues • Follow (wanted) Set-Point Changes • On-line Optimization • Flexibility of Processes • “Ability to handle Long Term Variations” • Undesirable Variations • Fouling (or Scaling) in Heat Exchangers • Deactivation of Catalysts • Desirable Variations/Changes • New Raw Materials and/or new Products • Changes in Production Volume Process, Energy and System Various Topics for Heat Exchanger Networks T. Gundersen OPER 03

  4. Similarities/Analogies between Synthesis of Processes and Control Systems Process Control • Production Site • Process • Equipment • Choice of Units • Matching • Sequences • Pressures • Temperatures • Flowrates • Optimizing • Advisory • Basic Control • Manipulators • Pairing • Controller Types • Gain • Integral Time • Derivative Time Levels Structure Parameters Process, Energy and System Various Topics for Heat Exchanger Networks T. Gundersen OPER 04

  5. Stream Ts Tt mCp ΔH °C °C kW/°C kW H1 300 100 1.5 300 H2 200 100 5.0 500 C1 50 250 4.0 800 Steam 280 280 (var) Cooling Water 15 20 (var) WS-1: Heat Integration Specification: ΔTmin= 20°C Find: QH,min , QC,min Tpinch , Umin Umin,MER and Network Process, Energy and System Notice: 1) H1 and H2 provide as much heat as C1 needs (800 kW) 2) Ts (C1) < Tt (H1,H2) − 20° and Ts (H1) > Tt (C1) + 20° Heat Integration −Introduction T. Gundersen OPER 05

  6. WS-1: What about Controllability? mCp (kW/°C) 1.5 5.0 4.0 III I 300°C 100°C 200ºC 186.7ºC C H1 130 II 200°C 100°C H2 Process, Energy and System 50°C 250°C 217.5°C 180°C 55°C H C1 130 150 20 500 MER Design with QH = QH,min, QC = QC,min, U = Umin,MER Consider: Disturbance for H1 inlet T, while controlling H2 outlet T Heat Integration −Introduction T. Gundersen OPER 06

  7. mCp 1.0 2.0 3.0 2.0 310° 50° 290° 1 2 H1 450° 280° 285° 3 C H2 10 kW 40° 120° 2 C1 240 kW 115° 290° 280° 1 3 C2 330 kW 20 kW Flexibility in Heat Exchanger Networks Process, Energy and System Various Topics for Heat Exchanger Networks T. Gundersen OPER 07

  8. mCp 1.85 2.0 3.0 2.0 310° 50° 179.7° 1 2 H1 450° 280° 395.5° 3 C H2 231 kW 40° 120° 2 C1 240 kW 115° 290° 169.5° 1 3 C2 241 kW 109 kW Flexibility in Heat Exchanger Networks Process, Energy and System Various Topics for Heat Exchanger Networks T. Gundersen OPER 08

  9. mCp 1.35 2.0 3.0 2.0 310° 227.8° 50° 1 2 H1 450° 280° 330.5° 3 C H2 101 kW 40° 120° 2 C1 240 kW 115° 290° 234.5° 1 3 C2 111 kW 239 kW Flexibility in Heat Exchanger Networks Process, Energy and System Various Topics for Heat Exchanger Networks T. Gundersen OPER 09

  10. Flexibility in Heat Exchanger Networks In Summary: The Network Structure was Flexible (Resilient) for the Cases when mCp was 1.0 and 1.85 for Stream H1, but did not work when mCp was 1.35 even with infinite Heat Transfer Area. The Reason: The Problem is Non-Convex, which happens when: − the Pinch point changes − there is a change in Mass Flowrates Process, Energy and System Various Topics for Heat Exchanger Networks T. Gundersen OPER 10

  11. 4 Exchanger 1 has fouling above 125°C 3 2 4 2 3 H WS-5: Design for Flexibility Q: How to handle Fouling ? U1 (W/m2K) 200° 115° 170° 1 1 155° 90° 120 134° Process, Energy and System 2 20° 175° 84° 81 1 3 20° 175° 138° 73° 6 12 Time (months) 4 Ref.: Kotjabasakisand Linnhoff, Oil & Gas Jl., Sept. 1987 Various Topics for Heat Exchanger Networks T. Gundersen OPER 11

  12. 200° 170° 115° 1 1 4 New Area: 148 m2 Energy Usage: Constant (the same) 155° 90° 134° 2 2 3 20° 175° 84° 1 3 4 20° 175° 138° 4 2 3 H WS-5: Fouling in Heat Exchangers 1: The Traditional Approach Process, Energy and System 73° Various Topics for Heat Exchanger Networks T. Gundersen OPER 12

  13. 4 New Unit: Heater on Stream 3 Energy Usage: From 1850 to 2140 kW 2 3 4 2 3 H WS-5: Fouling in Heat Exchangers 2: An alternative Solution 200° 170° 115° 1 1 Process, Energy and System 155° 90° 134° 2 20° 175° 84° H 1 3 20° 175° 138° 73° 4 Various Topics for Heat Exchanger Networks T. Gundersen OPER 13

  14. 4 New Area: 103 m2 Energy Usage: 15% Reduction !! 2 3 4 2 3 H WS-5: Fouling in Heat Exchangers 3: Use Network Interactions 200° 170° 115° 1 1 Process, Energy and System 155° 90° 134° 2 20° 175° 84° 1 3 20° 175° 138° 73° 4 Various Topics for Heat Exchanger Networks T. Gundersen OPER 14

  15. WS-5: Fouling in Heat Exchangers Summary Process, Energy and System Best Result obtained by using a “Systems Approach” Various Topics for Heat Exchanger Networks T. Gundersen OPER 15

  16. Summary of Operability • Plant Operation is often “Off-Design” • Controllability (Short Term Variations) • Flexibility (Long Term Variations) • A new Design Strategy for Fouling • The importance of Topology (Flowsheet or Network Structure) has been proven • Process Integration has a Focus precisely on the Structural Aspects of Process Plants Process, Energy and System Various Topics for Heat Exchanger Networks T. Gundersen OPER 16

  17. Expansionsof PA & PI • Objectives • from Energy Cost • to Equipment Cost • to Total Annualized Cost • and also Operability, including • Flexibility • Controllability • Switchability • Start-up & Shut-down • New Operating Conditions • and finally Environment, including • Emissions Reduction • Waste Minimization Process, Energy and System Expansions of Process Integration T. Gundersen EXP 01

  18. Expansionsof PA & PI • Scope • from Heat Exchanger Networks • to Separation Systems, especially • Distillation and Evaporation (heat driven) • to Reactor Systems • to Heat & Power, including • Steam & Gas Turbines and Heat Pumps • to Utility Systems, including • Steam Systems, Furnaces, Refrigeration Cycles • to Entire Processes • to Total Sites • to Regions Process, Energy and System Expansions of Process Integration Expansions of Process Integration T. Gundersen EXP 02

  19. Expansionsof PA & PI • Plants • from Continuous • to Batch and Semi-Batch • Projects • from New Design • to Retrofit • to Debottlenecking • Thermodynamics • from Simple 1st Law Considerations • to Various 2nd Law Applications • Exergy in Distillation and Refrigeration Process, Energy and System Expansions of Process Integration Expansions of Process Integration T. Gundersen EXP 03

  20. Expansionsof PA & PI • Methods • Pinch based Methodologies from Analogies • from Heat Pinch for Heat Recovery and CHP in Thermal Energy Systems • to Mass Pinch for Mass Transfer / Mass Exchange Systems • to Water Pinch for Wastewater Minimization and Distributed Effluent Treatment Systems • to Hydrogen Pinch for Hydrogen Management in Oil Refineries • Other Schools of Methods • was discussed on a previous slide Process, Energy and System Expansions of Process Integration Expansions of Process Integration T. Gundersen EXP 04

  21. Expansions in Process Integration Process Integration is much more than Pinch Analysis for Heat Exchanger Networks Strategic Planning Combined Methods Optimization Methods Pinch Analysis Heat Integration Detailed Engineering Conceptual Design Process, Energy and System Expansions of Process Integration T. Gundersen EXP 05

  22. T Heat Pinch Modeling Heat Pinch Q Data Extraction Graphical Diagrams Mass Pinch Analysis Representations and Concepts Water Pinch Design Performance Targets ahead of Design Optimization Hydrogen Pinch Pinch Decomposition Stages and Analogies in Methods Process, Energy and System Expansions of Process Integration Expansions of Process Integration T. Gundersen EXP 06

  23. Wastewater Minimization Topic: Efficient Use of Wastewater Reuse, Regeneration and Recycling - both Targets and Design Methods: Water Pinch (discussed here) Mathematical Programming Process, Energy and System Ref.: Wang and Smith “Wastewater Minimization”, Chem. Engng. Sci., vol. 49, pp 981-1006, 1994 Water Pinch Demonstration T. Gundersen EXP 07

  24. Wastewater Minimization Graphical Representation T C Cpr,in Cout,max mass/heat Process, Energy and System Cpr,out 2 Cin,max analogy 3 1 m H ΔH= mCp ΔT Δm= mH2OΔC Water Pinch Demonstration T. Gundersen EXP 08

  25. Main Results from Pinch Analysis QH,min T C Heat Pinch Water Pinch Process, Energy and System Watermin QC,min H m • The Concept of Composite Curves • Applicable whenever an “Amount” has a “Quality” • Heat & Temperature, Mass & Concentration, etc. • A Two Step Approach: Targets ahead of Design • A fundamentalDecomposition at the Pinch Final Summary T. Gundersen SUM 01

  26. Objectives for using Process Integration • Minimize Total Annual Cost by optimal Trade-off between Energy, Equipment and Raw Material • Within this trade-off: minimize Energy, improve Raw Material usage and minimize Capital Cost • Increase Production Volume by Debottlenecking • Reduce Operating Problems by correct rather than maximum use of Process Integration • Increase Plant Controllability and Flexibility • Minimize undesirable Emissions • Add to the joint Efforts in the Process Industries and Society for a Sustainable Development Process, Energy and System Final Summary T. Gundersen SUM 02

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