Control and operation of dividing-wall columns with vapor split - PowerPoint PPT Presentation

1 Control and operation of dividing-wall columns with vapor split manipulation PhD Defense Presentation Deeptanshu Dwivedi Jan 18 th , 2013 Trondheim Dwivedi, D., PhD Defense Presentation January 18th, 2013

2 Outline • Introduction & Scope • Chapter 3: Control structure selection for three-product Petlyuk (dividing-wall) column • Chapter 4: Steady state and dynamic operation of four-product dividing-wall (Kaibel) columns • Chapter 5: Active vapor split control for dividing-wall columns • Chapter 6: Control structure selection for four-product Petlyuk column • Chapter 7: Conclusions and further work Dwivedi, D., PhD Defense Presentation January 18th, 2013

3 Outline • Introduction & Scope • Chapter 3: Control structure selection for three-product Petlyuk (dividing-wall) column • Chapter 4: Steady state and dynamic operation of four-product dividing-wall (Kaibel) columns • Chapter 5: Active vapor split control for dividing-wall columns • Chapter 6: Control structure selection for four-product Petlyuk column • Chapter 7: Conclusions and further work Dwivedi, D., PhD Defense Presentation January 18th, 2013

4 Introduction & Scope • Conventional distillation is energy intensive process. • Dividing-wall columns for multicomponent separation: – Petlyuk Arrangement for 3 & 4 product separation – Kaibel Arrangement for 4-product separation • Potential Energy Savings up to ~30 % in – Kaibel Arrangement – Petlyuk Arrangements • Proven technology, >100 industrial applications Dwivedi, D., PhD Defense Presentation January 18th, 2013

5 Introduction & Scope.. A AB A/B ABC B/C ABCD C/D B C A D ABCD A/B Conventional Indirect sequence B BCD B/C C CD C/D D Conventional direct sequence Dwivedi, D., PhD Defense Presentation January 18th, 2013

6 Introduction & Scope.. • Petlyuk arrangement for three-product separation A A AB AB A/B ABC ABC B A/C B A/C B/C BC BC C C Up to 30 % energy savings compared to conventional arrangements Capital savings due to fewer reboilers and condensers Dwivedi, D., PhD Defense Presentation January 18th, 2013

7 Introduction & Scope.. • Kaibel arrangement for four-product separation A A A A AB AB A/B A/B AB AB B B B B ABCD ABCD B/C B/C ABCD ABCD B/C B/C B/C B/C C C C C CD CD C/D C/D CD CD D D D D Upto 30 % energy savings compared to conventional arrangements Dwivedi, D., PhD Defense Presentation January 18th, 2013

8 Introduction & Scope.. • Petlyuk arrangement for four-product separation D D AB AB A/B A/B AB AB D D ABC ABC A/C A/C S1 S1 ABC ABC S1 S1 BC BC ABCD ABCD ABCD ABCD A/D A/D B/C B/C BC BC S2 S2 BCD BCD S2 S2 B/D B/D BCD BCD CD CD C/D C/D CD CD B B B B Upto 50 % energy savings compared to conventional arrangements Dwivedi, D., PhD Defense Presentation January 18th, 2013

9 Outline • Introduction & Scope • Chapter 3: Control structure selection for three-product Petlyuk (dividing-wall) column • Chapter 4: Steady state and dynamic operation of four-product dividing-wall (Kaibel) columns • Chapter 5: Active vapor split control for dividing-wall columns • Chapter 6: Control structure selection for four-product Petlyuk column • Chapter 7: Conclusions and further work Dwivedi, D., PhD Defense Presentation January 18th, 2013

10 Control Structures for 3-product Petlyuk* • Degrees of freedom: five L • The control problem: D minimize D1 C21  L 1 J V B R L = L 1 /L S T . . Feed  S in 0.5% C1 impurity top product ABC  in 0.5% light key side product  heavy key in side product 0.5% B1 C22  V 1 impurity in bottom product 0.5% V B R V = V 1 /V B • Constraints above: “optimally active” B • However, the four compositions may not be specified independently, due to presence of “holes” or infeasible states* * Dwivedi et al (2012), **Wolff & Skogestad (1995) Dwivedi, D., PhD Defense Presentation January 18th, 2013

11 Control Structures for 3-product Petlyuk.. • the four product compositions L D may not be specified D1 independently, therefore: C21 – Option I: Control x A S +x C S L 1 R L = L 1 /L – Option II: Over-purify one of the products Feed S C1 • To satisfy option I & II, ABC three DOFs are consumed: D, S & B B1 • Two unconstrained DOF: R L & C22 R V V 1 V B R V = V 1 /V B – We propose, two self optimizing variables, B • x A B1 • x C D1 Dwivedi, D., PhD Defense Presentation January 18th, 2013

12 Control Structures for 3-product Petlyuk.. Setpoint for CVs L D D1 Over-purify: C21 L 1 R L = L 1 /L • the prefractionator products (x A B1 , Feed x C D1 ) to introduce “back-off” S C1 ABC • the main product, where there is B1 C22 excess energy V 1 V B R V = V 1 /V B B Dwivedi, D., PhD Defense Presentation January 18th, 2013

13 Control Structures for 3-product Petlyuk.. • CS1 (R V available): D – control the sum of the x B CC impurities in S (x S A + x S C ) C21 CC x C x A +x C CC Feed C1 S ABC x A CC C22 x B CC B Dwivedi, D., PhD Defense Presentation January 18th, 2013

14 Control Structures for 3-product Petlyuk.. • Closed loop simulations from CS1 Feed +20 % Feed -20 % Feed rate changes may be handled well with CS1 Dwivedi, D., PhD Defense Presentation January 18th, 2013

15 Control Structures for 3-product Petlyuk.. • Closed loop simulations from CS1 – Poor dynamic response for some feed compositions using CS1 z F = [13.3 53.3 33.3 ] z F = [ 33.3 53.3 13.3] Side product flow is a poor MV, as it shows opposite gain for the two keys Dwivedi, D., PhD Defense Presentation January 18th, 2013

16 Control Structures for 3-product Petlyuk.. • CS2 (R V available): D – overpurify one of the products x B CC – Use max selector with boil up C21 CC x C CC x C Feed C1 S ABC x A x A CC > CC C22 x B CC B Dwivedi, D., PhD Defense Presentation January 18th, 2013

17 Control Structures for 3-product Petlyuk.. • Closed loop simulations from CS2 z F = [13.3 53.3 33.3 ] z F = [ 33.3 53.3 13.3] Good performance for feed composition disturbances (and feed rate) Dwivedi, D., PhD Defense Presentation January 18th, 2013

18 Control Structures for 3-product Petlyuk.. • CS3 (R V NOT available)*: D – Light key in side product x B CC and light key in C21 prefractionator bottoms CC remains uncontrolled x C CC x C – Recommended when B/C Feed C1 S is the difficult split ABC C22 x B CC B *Ling and Luyben [2009], Kiss and Rewagad [2011] Dwivedi, D., PhD Defense Presentation January 18th, 2013

19 Control Structures for 3-product Petlyuk.. • Closed loop simulations from CS3 z F = [ 33.3 13.3 53.3] z F = [53.3 13.3 33.3 ] S > 0.5% (Constraint) x A Dwivedi, D., PhD Defense Presentation January 18th, 2013

20 Control Structures for 3-product Petlyuk.. When A/B split becomes more difficult split, CS3 fails!! Dwivedi, D., PhD Defense Presentation January 18th, 2013

21 Control Structures for 3-product Petlyuk.. • CS4 (R V NOT available): D – Use max selector with boil x B CC up C21 – overpurify one/two of the CC products x C CC x C Feed C1 S x A ABC x A CC CC > C22 x B CC B Dwivedi, D., PhD Defense Presentation January 18th, 2013

22 Control Structures for 3-product Petlyuk.. • Closed loop simulations from CS4 z F = [ 33.3 13.3 53.3] z F = [53.3 13.3 33.3 ] Good performance for feed composition disturbances (and feed rate) Dwivedi, D., PhD Defense Presentation January 18th, 2013

23 Control Structures for 3-product Petlyuk.. Summary so far • Decentralized PI control structures with selector switch can give good regulation for 3-Product Petlyuk Column • The over-purification cost little extra energy Dwivedi, D., PhD Defense Presentation January 18th, 2013

24 Outline • Introduction & Scope • Chapter 3: Control structure selection for three-product Petlyuk (dividing-wall) column • Chapter 4: Steady state and dynamic operation of four-product dividing-wall (Kaibel) columns • Chapter 5: Active vapor split control for dividing-wall columns • Chapter 6: Control structure selection for four-product Petlyuk column • Chapter 7: Conclusions and further work Dwivedi, D., PhD Defense Presentation January 18th, 2013

25 Operation of 4-product Kaibel column* A A • Height: 8 meters • Atmospheric pressure • Vacuum glass sections • 4 products B B • Packed Column with 6 mm Raschig Feed Feed Feed rings (ABCD) (ABCD) (ABCD) • Product & liquid split valves are C C solenoid operated • Vapor split valves are motor driven • Labview interface D D *Dwivedi et al (2012) Dwivedi, D., PhD Defense Presentation January 18th, 2013

26 Operation of 4-product Kaibel column.. • 4-point decentralized temperature control – one temperature in prefractionator – three temperatures in main column Dwivedi, D., PhD Defense Presentation January 18th, 2013

27 Operation of 4-product Kaibel column.. • Cold Start-up – Four temperatures are adjusted in closed loop to guide to desired steady state profile Dwivedi, D., PhD Defense Presentation January 18th, 2013