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Rigorous Simulation of Divided-wall Columns

Rigorous Simulation of Divided-wall Columns. M. Shamsuzzoha, Maryam Ghadrdan, Ivar J. Halvorsen, Sigurd Skogestad The 15th NPCW'09, Telemark University College, Porsgrunn, Norway January 29-30 2009. Trondheim, Norway. NTNU/SINTEF Trondheim. A. B. ABCD. C. D.

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Rigorous Simulation of Divided-wall Columns

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  1. Rigorous Simulation of Divided-wall Columns M. Shamsuzzoha, Maryam Ghadrdan, Ivar J. Halvorsen, Sigurd Skogestad The 15th NPCW'09, Telemark University College, Porsgrunn, Norway January 29-30 2009

  2. Trondheim, Norway

  3. NTNU/SINTEF Trondheim

  4. A B ABCD C D Minimum Energy for the Four-Product Kaibel Distillation Column Introduction What is Petlyuk columns Experimental setup Assessment by the Vmin diagram Rigorous simulation Summary

  5. 3-product Petlyuk arrangement A AB ABC B BC C A AB B ABCD C CD D BEEDIST (Basic Energy Efficient Distillation Technology) NTNU lab • Founded by the Norwegian Research Council through the GASSMAKS program • SINTEF/NTNU 2008-2012 • Objectives • Study new integrated distillation arrangements • For reduction of capital cost and energy consumption (+ CO2-emission related to the energy). • 20-40% savings in reach. • Evaluate application in natural gas processing and conversion. • Design and operation • Develop laboratory • 2 PhD + post doc 4-product Kaibel-column with a dividing wall

  6. A ABC B C What is a Petlyuk arrengement ? • Integrated distillation column arrangement • Separates a single feed into three separate products • Just a single reboiler and condenser Why? • Saves energy and capital • Distillation consumes 3-5% of the industry energy consumption world-wide=>Need more energy efficient solutions

  7. Industrial DWC/Petlyuk applications German-speaking community dominates • BASF: 40 DWCs in operation. Increasing. G. Kaibel pioner • Monz – main vendor for BASF • Krupp-Uhde • Sulzer • Rashig • Linde Others • MW Kellogg (UK) • UOP (USA) • UK, Japan, Indonesia, South Africa The Kaibel-column 4-product DWC!

  8. A A AB AB Liquid split ABC ABC B B Vapor split BC BC C C Equivalent Petlyuk arrangements Dividing Wall Column (DWC) Classical Petlyuk arrangement Fully thermally coupled sections

  9. A A B ABC ABC AB BC B C C Conventional alternatives for 3-product separation: Sequence of binary columns Indirect split: IS Direct Split: DS

  10. Prefractionator arrangement Alternatives for 3-product separation... A AB ABC B The prefractionator does the simple A/C split while B distributes to both ends B BD C

  11. Conventional Prefractionator arrangementwith a single main column A AB ABC B BC C

  12. Apply full thermal coupling A Petlyuk column AB ABC B BC C

  13. Why consider a Petlyuk arrangement • Large potential energy savings compared to conventional columns (20-30%) • Or – increase production for given energy supply • Capital cost savings due to more compact equipment => smaller footprint and removal of reboiler/condenser units • Usage: • In theory: Anywhere (almost) where distillation is a suitable separation technology and more than 2 products are produced. • In practice: Some cases may be unsuitable due to required temperature/pressure range, height, or if liquid/vapor load in different sections are very different. • Practical variations can be made, e.g. side-strippers/rectifiers • Revamping of existing conventional columns may have significant potential

  14. Critical: How to set the splits • The potential savings are easily lost unless the splits are adjusted properly • Do it right and obtain all the benefits! liquid split (side draw) A liquid split (Rl) D1 A ABC ABC B B V1 vapor split (Rv) vapor split (side draw) C C

  15. A AB B ABCD C CD D Extend to 4-product DWC:The Kaibel column – (1987) Separates 4 products in a single shell! Total reflux section Can save 30-40 %

  16. Minimum energy-Definitions and assumptions • Vapour flow rate (V) generated from all reboilers is used as the energy measure • Ideal Assumptions • Infinite number of stages • Constant relative volatility • Constant molar flow • Constant pressure • No internal heat exchange • Then, exact analytic solution is obtained

  17. Minimum energy (Vapor flow rate V) • Sharp splits: Flat optimum at a line segment (optimality region) • Optimality region depends on feed properties • Rapid increased vapor flow outside optimality region

  18. V/F D/F 1 The Vmin-diagram Operation point f(D/F,V/F) Distillate (D) Binary column –multicomponent feed Feed (F) ABC Vapor rate (V) Feed comp. distribution ? Minimum energy ? Two degrees of freedom – choose D/F,V/F

  19. The Vmin-diagram – 3 component example V/F D F ABC Vminboundary V Preferred A/C split D/F

  20. Characterisitcs of operation

  21. A B ABCD C D Schematic diagram of the experimental setup of 4-product Kaibel-arrangement

  22. Lab installation: Height: 8 meters Atmospheric pressure Vacuum glass sections 4 products Contact: Sigurd Skogestad, or Ivar J. Halvorsen A AB B ABCD C CD D The Kaibel column at NTNU, Trondheim, Norway A B Feed (ABCD) C D

  23. Feed condition for the Kaibel Distillation • Four components: Methanol+Ethanol+1-Propanol+1-Butanol • Flow rate F=1.0 Kgmole/h, q=1 (saturated liquid) • Composition z=[0.25, 0.25, 0.25, 0.25] • EOS Wilson • Pressure Atmospheric • Relative volatility α= [8.27: 4.84: 2.30: 1.0]

  24. UniSim Simulation for Kaibel Column

  25. Steady-State Simulation for Kaibel Column KAIBEL DISTILLATION COLUMN

  26. Minimum Energy – competition

  27. Vmin-diagram for the Kaibel column

  28. Vmin-diagram for the Kaibel column using UniSim • Rigorous calculation confirms ideal shortcut method V/F D/F

  29. A AB B ABCD C CD D Further work • Status: Startup of new PhDs • Directions: • Further studies with Unisim (extended from ideal mixtures) • Further development of Matlab models • Alternative structures like HIDiC, Heat integrated and other energy efficient arrangements • Dynamic studies • Optimizing control • Lab column experiments

  30. How to apply DWC/Petlyuk columns • Make sure to do a reasonable design in terms of placement of the dividing wall/design split. • Important: Make sure to indentify the optimality region for the expected actual feed variations, and thereby clarify the requirements for on-line adjustment of: • None of the split ratios (E.g. in case of quadrangle shaped reg.) • Just the liquid split (In case of a line segment reg.) • Both split ratios (in case of a very short line segment) • Determine the final control strategy based the actual product value/energy cost, and dynamic controllability analysis.

  31. Key issues for full thermal coupling • Liquid and vapour flows in equilibrium avoids irreversible loss due to mixing (Petlyuk 1965) => • Explains why Petlyuk columns beat the other arrangements • Require operation of every internal column at its “preferred split” • Underwood roots “carry over” the coupling (Halvorsen 2001) => • Valid for any operating point • Simple sequential calculation sequence • Extremely simple assessment for n-product Petlyuk arrangement based only on feed properties.

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