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Rapid transition control of a CO 2 capture plant

Rapid transition control of a CO 2 capture plant. Håkon Dahl-Olsen and Sigurd Skogestad. Control philosophy. Skogestad and Postlethwaite (2005): Multivariable feedback control – analysis and design, Wiley. Maximum gain rule. Optimal control problem:. NCO:. Maximum gain rule.

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Rapid transition control of a CO 2 capture plant

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  1. Rapid transition control of a CO2 capture plant Håkon Dahl-Olsen and Sigurd Skogestad

  2. Control philosophy Skogestad and Postlethwaite (2005): Multivariable feedback control – analysis and design, Wiley

  3. Maximum gain rule Optimal control problem: NCO:

  4. Maximum gain rule Hamiltonian Loss: A second-order approximation yields:

  5. P2P Gains – Simple • Look at step responses for the time-scale that is relevant for economic control:

  6. Cyclic operation of a CO2 removal plant

  7. Lean absorbent L Purified gas yCO2 ≤ 0.005 Column TC Sour gas feed Power plant Rich absorbent, LN 0.02 ≤yCO2 ≤ 0.06 CaCO3 (s), H2O, Ca(OH)2 (aq) PFD

  8. Modeling VLE described by Henry’s law for CO2/water system: Reaction in water phase: Assumed first-order kinetics:

  9. Modeling Variable definitions

  10. Optimal steady-state operation Minimize absorbent usage while maintaining y ≤ 0.5% (active)

  11. Optimal transition paths • Objectives: minimum time and limited absorbent usage • Constraint y < 0.5% at all times • This constraint is active for the transition phase • Constraint not measureable • Can measure dissolved CO2, but threshold on x = 5 ppm

  12. Optimal transition paths

  13. Implementation

  14. Scorecard 1: Direct measurement

  15. Can we use ratio control to limit the span of the CV? • Approximate span propagation by linearization

  16. Loss evaluation(Constant set point policy)

  17. Performance check CO2 comp. Absorbent feed Controlled variable

  18. Discussion

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