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New results for divided-wall columns

New results for divided-wall columns. Deeptanshu Dwivedi (PhD Candidate, NTNU) Ivar Halvorsen (Senior Scientist, SINTEF) Sigurd Skogestad * (Professor, Department of Chemical Engineering, NTNU, Trondheim). Arctic circle. North Sea. Trondheim. SWEDEN. NORWAY. Oslo. DENMARK. GERMANY. UK.

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New results for divided-wall columns

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  1. New results for divided-wall columns Deeptanshu Dwivedi (PhD Candidate, NTNU) Ivar Halvorsen (Senior Scientist, SINTEF) Sigurd Skogestad * (Professor, Department of Chemical Engineering, NTNU, Trondheim) EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  2. Arctic circle North Sea Trondheim SWEDEN NORWAY Oslo DENMARK GERMANY UK

  3. Outline • Introduction: Divided wall columns for 3- and 4-product separations • Structures • “Vmindiagrams” • Experiments: 4- Product Kaibel Column • Experimental Setup • Control Structure • Experimental Runs- Steady state profiles • Experimental data- model fitting • Experimental Runs- Vapor Split Experiment • Conclusions EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  4. 3-product separation: Conventional “direct split” A/B A ABC B/C B BC C EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  5. Improvement: Prefractionator (Easy split first) A/B A A A/B B/C A/C A/C AB ABC AB ABC Simplification: JOIN B B BC B/C B BC C C EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  6. Simplification: Direct coupling (“Petlyuk”) + single shell (divided wall column) A/B A A AB AB A/C ABC ABC B B A/C B/C BC BC C C Petlyuk column EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  7. Vmin diagram for three components • Vmin | Petlyuk = max (VAB, VBC) = VBC • VPrefractionator = VAC EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  8. D A/B AB AB A/C D ABC S1 ABC B/C A/D S1 BC ABCD ABCD BC B/D S2 BCD S2 BCD C/D CD CD B B 4-product separation: Extended Petlyuk 4-product extended Petlyuk column up to ~50 % energy savings EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  9. A A AB A/B AB B B ABCD ABCD B/C B/C B/C C C CD C/D CD D D 4-product separation: Simplified (“Kaibel column”) 4-product extended Kaibel column up to ~30 % energy savings EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  10. Vmin diagram for four components EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  11. A (Methanol) B (Ethanol) Feed ABCD C (Propanol) D (Butanol) Experimental Set up 8m • 4 products • Packed Column • Magnetic funnel-liquid split & Product valves • Number of theoretical stages (experimentally determined): • Prefractionator: 13 • Main column : 21 EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  12. Experimental Set up (Labview Interface)… EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  13. Control Structure (As used in experiments) • Boilup V=constant • 4 control degrees of freedom: • Liquid split ratio RL1, • Reflux ratio RL2 (top) • Reflux ratio RL3 (middle) • Reflux ratio RL4 (bottom) • Decentralized Control with 4 PI Temperature Controllers: • T2s is adjusted to get large temperature change in the prefractionator • T3s, T5s, T7s is adjusted to get the temperature of product stages close to the boiling points of their main components Rl2 D 3 TC T3S T3 Rl1 T2S 1 4 TC Rl3 S1 5 TC T5S T2 F T5 2 Rl4 S2 6 TC T7S 7 T7 V B EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  14. Start-up Temperatures Reflux ratios • T2s is adjusted to get large temperature change in the prefractionator • T3s,T5s, T7s is adjusted to get the temperature of product stages close to the boiling points of their main components EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  15. TEMPERATURES Reflux ratios Steady Profiles with 4 temperature loops Rl2 D 3 TC T3S T3 Rl1 T2S 1 4 TC Rl3 S1 5 TC T5S T2 F T5 2 Rl4 S2 6 TC T7S 7 T7 V B EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  16. TEMPERATURES Reflux ratios Steady Profiles with 4 temperature loops.. Liquid Split Loop -2 C Rl2 D 3 TC T3S T3 Rl1 T2S 1 4 TC Rl3 S1 5 TC T5S T2 F T5 2 Rl4 S2 6 TC T7S 7 T7 V B EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  17. TEMPERATURES Reflux ratios Steady Profiles with 4 temperature loops.. Distillate Loop ±1 C Rl2 D 3 TC T3S T3 Rl1 T2S 1 4 TC Rl3 S1 5 TC T5S T2 F T5 2 Rl4 S2 6 TC T7S 7 T7 V B EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  18. Steady Profiles with 4 temperature loops.. S1 Loop ±1 C Rl2 D 3 TEMPERATURES Reflux ratios TC T3S T3 Rl1 T2S 1 4 TC Rl3 S1 5 T5S TC T2 F T5 2 Rl4 S2 6 TC T7S 7 T7 V B EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  19. TEMPERATURES Reflux ratios Steady Profiles with 4 temperature loops.. S2 Loop ±1 C Rl2 D 3 TC T3S T3 Rl1 T2S 1 4 TC Rl3 S1 5 TC T5S T2 F T5 2 Rl4 S2 6 TC T7S 7 T7 V B EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  20. Steady Profiles with 4 temperature loops.. All Loops ±1 C Rl2 D 3 TC T3S TEMPERATURES Reflux ratios T3 Rl1 T2S 1 4 TC Rl3 S1 5 TC T5S T2 F T5 2 Rl4 S2 6 TC T7S 7 T7 V B EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  21. Model (lines) and experiments (points) fit well EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  22. Vapor Split • So far: Vapor split (Rv) kept constant • But: Energy usage depends on Rv. • Implement adjustable Rv • But: Difficult to set Rv at desired value • Solution: Use Rv for temperature control (feedback) • The more precise liquid split (Rl) can be preset V/F vs RV for Kaibel column EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  23. Vapor Split Experiment.. Schematic of the vapor split valve From top left: Valve in fully open position Top right: Rack and pinion arrangement EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  24. Vapor Split Experimental run (Kaibel Column) EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  25. Conclusions • Four-Product Kaibel column • Experimentally demonstrated 4-point temperature control for stabilizing and startup operation • Experimentally demonstrated active vapor split control • Experimental data fits well with the model EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  26. Outline • Introduction • 4- Product Kaibel Column • Four-product Kaibel column • Control Structure • Experimental Setup • Experimental Runs- Steady state profiles • Experimental Runs- Vapor Split Experiment • 3- Product Petlyuk Column • Three-product Petlyuk column • The “Vmin diagrams” • Control Structures • Close Loop Results • Conclusions EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  27. Three-product Petlyuk column A/B A A AB AB A/C ABC ABC B B A/C B/C BC BC C C EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  28. CC Control Structure 1 C21 D xB CC • Five degrees of freedom including vapor split • Control key impurities using “close-by” parings • Side product has two side impurities • In CS1, S is paired with heavy key (xC) C1 xC xC CC Feed ABC S xA C22 CC xB CC B EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  29. Closed-loop result from CS1 Fails for feed composition disturbance zf=[5313 33] from nominal equimolar feed EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  30. Why CS1 failed ?? • For nominal equimolar feed, B/C is the most difficult split • For the new feed A/B is more difficult feed and CS1 can not provide sufficient vapor in top section of main column EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  31. CC Control Structure 2 C21 D xB CC • Same as CS1, but boilup now has a maximum select controller with: • light key, xA at S or, • light key, xB at reboiler C1 xC CC xC Feed ABC S xA C22 xA > CC CC xB B EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

  32. Closed loop results from CS2 • Works for all feed composition disturbance from nominal equimolar feed • The purity of bottom product may be over purified for some disturbances EFCE Working Party on Fluid Separations, Bergen, 23-24 May 2012

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