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2nd Trondheim Gas Technology Conference
Active Vapor Split Adjustment for Energy OptimalControl of Dividing Wall Distillation Columns:
Experimental Studies
Deeptanshu Dwivedi1 Ivar J Halvorsen2 Sigurd Skogestad1
1Department of Chemical Engineering, Norwegian University of Science and Technology,Trondheim, Norway
2Applied Cybernetics, SINTEF, Trondheim, Norway
3 Nov 2011
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 1 / 20
Outline
1 IntroductionConventional DistillationThermally coupled columns
2 Need for active vapor split4–product Kaibel column4–product Kaibel column: Control StructureVmin vs Rv
Summary
3 Experimental setupPilot Plant: 4–Product Kaibel column
4 Experimental ResultsValve behaviourTotal Reflux4–Product Kaibel column
5 Conclusion
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 2 / 20
Introduction Conventional Distillation
Conventional distillation
energy intensive
large mixing losses
at interconnectionsinternal remixing
difficult seperation firstlarge ∆T at exchangers
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 3 / 20
Introduction Thermally coupled columns
Thermally coupled columns
examples: prefractionator arrangementsPetlyuk column
originally proposed for 3 productcan be extended to more than 3 productseasiest separation firstlow mixing lossesenergy saving upto 50 % for 4–component
Kaibel Column
energy saving upto 30 % for 4–component
can be realized by divided–wall columns (DWC)
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 4 / 20
Introduction Thermally coupled columns
Thermally coupled columns
examples: prefractionator arrangementsPetlyuk column
originally proposed for 3 productcan be extended to more than 3 productseasiest separation firstlow mixing lossesenergy saving upto 50 % for 4–component
Kaibel Column
energy saving upto 30 % for 4–component
can be realized by divided–wall columns (DWC)
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 4 / 20
Need for active vapor split 4–product Kaibel column
4–product Kaibel column
A: methanol
B: ethanol
C: propanol
D: butanol
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 5 / 20
Need for active vapor split 4–product Kaibel column
4–product Kaibel column
A: methanol
B: ethanol
C: propanol
D: butanol
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 5 / 20
Need for active vapor split 4–product Kaibel column: Control Structure
4–product Kaibel column: Control Structure
Regulatory layer when V > Vmin
4 point temperature control
inventory control
fixed V & Rv
demonstrated experimentally
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 6 / 20
Need for active vapor split 4–product Kaibel column: Control Structure
4–point control: Experiments
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 7 / 20
Need for active vapor split 4–product Kaibel column: Control Structure
4–product Kaibel column: Control Structure
Regulatory layer when V = Vmin
5 point temperature control
inventory control
also use Rv
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 8 / 20
Need for active vapor split Vmin vs Rv
boilup (Vmin) vs Vapor Split (Rv)
F = 1
zF = equimolar
purity spec: 98%for all products
Figure: Vmin vs Rv
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 9 / 20
Need for active vapor split Vmin vs Rv
boilup (Vmin) vs Vapor Split (Rv) changes with disturbances
Vmin andRv (optimal) maychange with feeddisturbances
Figure: Vmin vs Rv
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 10 / 20
Need for active vapor split Summary
Summary
active vapor split control required
to remain close to optimum Rv and Vmin
to aid to flexibilty in optimal operation for varying disturbances
Problem: Vapor Split may/will be uncertain
Solution: feedback action can remove this uncertainity in input
In four point control
Rl is very precise input: can be used in optimizing layer
Rv is uncertain input: can be used in regulatory layer with feedback
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 11 / 20
Need for active vapor split Summary
Summary
active vapor split control required
to remain close to optimum Rv and Vmin
to aid to flexibilty in optimal operation for varying disturbances
Problem: Vapor Split may/will be uncertain
Solution: feedback action can remove this uncertainity in input
In four point control
Rl is very precise input: can be used in optimizing layer
Rv is uncertain input: can be used in regulatory layer with feedback
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 11 / 20
Need for active vapor split Summary
Summary
active vapor split control required
to remain close to optimum Rv and Vmin
to aid to flexibilty in optimal operation for varying disturbances
Problem: Vapor Split may/will be uncertain
Solution: feedback action can remove this uncertainity in input
In four point control
Rl is very precise input: can be used in optimizing layer
Rv is uncertain input: can be used in regulatory layer with feedback
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 11 / 20
Need for active vapor split Summary
Summary
active vapor split control required
to remain close to optimum Rv and Vmin
to aid to flexibilty in optimal operation for varying disturbances
Problem: Vapor Split may/will be uncertain
Solution: feedback action can remove this uncertainity in input
In four point control
Rl is very precise input: can be used in optimizing layer
Rv is uncertain input: can be used in regulatory layer with feedback
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 11 / 20
Need for active vapor split Summary
Summary
active vapor split control required
to remain close to optimum Rv and Vmin
to aid to flexibilty in optimal operation for varying disturbances
Problem: Vapor Split may/will be uncertain
Solution: feedback action can remove this uncertainity in input
In four point control
Rl is very precise input: can be used in optimizing layer
Rv is uncertain input: can be used in regulatory layer with feedback
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 11 / 20
Need for active vapor split Summary
Summary
active vapor split control required
to remain close to optimum Rv and Vmin
to aid to flexibilty in optimal operation for varying disturbances
Problem: Vapor Split may/will be uncertain
Solution: feedback action can remove this uncertainity in input
In four point control
Rl is very precise input: can be used in optimizing layer
Rv is uncertain input: can be used in regulatory layer with feedback
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 11 / 20
Need for active vapor split Summary
Summary
active vapor split control required
to remain close to optimum Rv and Vmin
to aid to flexibilty in optimal operation for varying disturbances
Problem: Vapor Split may/will be uncertain
Solution: feedback action can remove this uncertainity in input
In four point control
Rl is very precise input: can be used in optimizing layer
Rv is uncertain input: can be used in regulatory layer with feedback
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 11 / 20
Experimental setup Pilot Plant
Pilot Plant
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 12 / 20
Experimental setup Pilot Plant
Vapor Split Valves
stepper motor
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 13 / 20
Experimental setup Pilot Plant
Split range logic
Pulse width modulation
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 14 / 20
Experimental Results Valve behaviour
Vapor valve characterstics- Manual mode
Conclusion: Really bad valve!
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 15 / 20
Experimental Results Valve behaviour
Vapor valve characterstics- Manual mode
Conclusion: Really bad valve!
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 15 / 20
Experimental Results Valve behaviour
Vapor valve characterstics- Manual mode
Conclusion: Really bad valve!
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 15 / 20
Experimental Results Total Reflux
Experiments: total reflux
total reflux conditions
valve control: split range logic
control variable:∆T = T 2 − T 5
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 16 / 20
Experimental Results Total Reflux
Run
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 17 / 20
Experimental Results 4–Product Kaibel column
Experiments: 4–Product Kaibel column
4–point temperature control
1 temperature in prefractionatorcontrolled with Rv in place of Rl
control variable: T 2
3 temperature controlled with L,S1 & S2
control variable: T 3, T 5 &T 6
Rl is very precise input
can be used as optimizinginput
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 18 / 20
Experimental Results 4–Product Kaibel column
Run
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 19 / 20
Conclusion
Conclusions
Active vapor split is feasible
Active vapor split will aid in minimum energy operation
Feedback action can remove uncertainity and drive vapor split ratio toaccurate position
in 5 point control: Rv can be used in regulatory layerin 4 point control: Rv should be used in regulatory layer, Rl can beused for optimization
Further works needed
Superior valve design to operate in low pressure drop applications
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 20 / 20
Conclusion
Conclusions
Active vapor split is feasible
Active vapor split will aid in minimum energy operation
Feedback action can remove uncertainity and drive vapor split ratio toaccurate position
in 5 point control: Rv can be used in regulatory layerin 4 point control: Rv should be used in regulatory layer, Rl can beused for optimization
Further works needed
Superior valve design to operate in low pressure drop applications
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 20 / 20
Conclusion
Conclusions
Active vapor split is feasible
Active vapor split will aid in minimum energy operation
Feedback action can remove uncertainity and drive vapor split ratio toaccurate position
in 5 point control: Rv can be used in regulatory layerin 4 point control: Rv should be used in regulatory layer, Rl can beused for optimization
Further works needed
Superior valve design to operate in low pressure drop applications
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 20 / 20
Conclusion
Conclusions
Active vapor split is feasible
Active vapor split will aid in minimum energy operation
Feedback action can remove uncertainity and drive vapor split ratio toaccurate position
in 5 point control: Rv can be used in regulatory layerin 4 point control: Rv should be used in regulatory layer, Rl can beused for optimization
Further works needed
Superior valve design to operate in low pressure drop applications
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 20 / 20
Conclusion
Conclusions
Active vapor split is feasible
Active vapor split will aid in minimum energy operation
Feedback action can remove uncertainity and drive vapor split ratio toaccurate position
in 5 point control: Rv can be used in regulatory layerin 4 point control: Rv should be used in regulatory layer, Rl can beused for optimization
Further works needed
Superior valve design to operate in low pressure drop applications
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 20 / 20
Conclusion
Conclusions
Active vapor split is feasible
Active vapor split will aid in minimum energy operation
Feedback action can remove uncertainity and drive vapor split ratio toaccurate position
in 5 point control: Rv can be used in regulatory layerin 4 point control: Rv should be used in regulatory layer, Rl can beused for optimization
Further works needed
Superior valve design to operate in low pressure drop applications
Dwivedi et al. (NTNU & SINTEF) Active Vapor Split Adjustment of DWC 3 Nov 2011 20 / 20
