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Stabilization of Desired Flow Regimes in Pipelines

Stabilization of Desired Flow Regimes in Pipelines. Presented at AIChE Annual meeting in Reno, USA November 9th, 2001 E. Storkaas ,S. Skogestad and V. Alstad Department of Chemical Engineering Norwegian University of Science and Tecnology. Outline. Introduction / Problem description

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Stabilization of Desired Flow Regimes in Pipelines

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  1. Stabilization of Desired Flow Regimes in Pipelines Presented at AIChE Annual meeting in Reno, USA November 9th, 2001 E. Storkaas ,S. Skogestad and V. Alstad Department of Chemical Engineering Norwegian University of Science and Tecnology Trondheim, 2001 Internet: www.ntnu.no/

  2. Outline • Introduction / Problem description • Model description • Previous work • Case descriptions • Simulation results • Controllability analysis • Closed loop example Trondheim, 2001 Internet: www.ntnu.no/

  3. Introduction Trondheim, 2001 Internet: www.ntnu.no/

  4. Slug cycle 1 2 • Liquid blocking • Slug growth/pressure buildup • Liqiud Production • Gas production/Liquid fallback 4 3 Trondheim, 2001 Internet: www.ntnu.no/

  5. Flow regime map: Horizontal flow Trondheim, 2001 Internet: www.ntnu.no/

  6. Flow Regime map: Pipeline-Riser Trondheim, 2001 Internet: www.ntnu.no/

  7. Problem description • Multiphase transport of oil and gas in pipelines and wells with elevation changes can give rise to unstable flow known as slug flow • Causes operational problems for the downstream processing units • Idea: Avoid slug flow by using feedback control to extend the stability region of the desired (non-slug) flow regime • This presentation: Analysis and simulation of simple case study Trondheim, 2001 Internet: www.ntnu.no/

  8. Previous work on avoiding slug flow • Most people in this field regard it as a design problem (e.g. increase pressure, design slug catcher, …) • Use of feedback control to stabilize desired non-slug flow regime: • Hedne and Linga (1990) : Implementation on test rig • Henriot et al. (1999): Simulations with TACITE and (probably) implementation on Dunbar pipleline • Havre et al. (2000): Simulations with OLGA and implementation on Hod-Valhall pipeline. Trondheim, 2001 Internet: www.ntnu.no/

  9. Model description Mass and momentum balance for each phase • Slip through interphase friction • Pure phases; bubbles in liquid and droplet field neglected • Mass transfer neclected • Isothermal • Boundary conditions • Mass flow of each phase into pipe • Multiphase valve with constant pressure downstream Trondheim, 2001 Internet: www.ntnu.no/

  10. Case description • Simple Case • Feed 1 kg/sec • Downstream pressure 20 bar • Exibits severe slugging in OLGA simulations • Mass conservation grid location indicated 1 –13 Trondheim, 2001 Internet: www.ntnu.no/

  11. Open loop simulation 1 Volume fraction liquid 0 Flat section Declining section Inclining sec. Pipe length Trondheim, 2001 Internet: www.ntnu.no/

  12. Open-loop stability – Pressure levels Trondheim, 2001 Internet: www.ntnu.no/

  13. Tool for selecting input and output for stabilization: Pole Vectors • Largest element in pole vector minimizes input usage (H2 and H-norm of KS (Havre et al., 1998) • Output: Use pressure measurement before riser. Trondheim, 2001 Internet: www.ntnu.no/

  14. Reason for problem: RHP-Zeros • RHP-zeros limit achivable bandwith of the system • Bandwith must be higher than 2p (real poles) for stabilization • Thus stabilization is impossible with pressure sensors in the riser (inclining section) Trondheim, 2001 Internet: www.ntnu.no/

  15. Closed loop – Stabilizing the flow • Simple PI-controller • Gain:1 Bar-1 • I : 2000 s • Pressure sensor inbottom of riser Trondheim, 2001 Internet: www.ntnu.no/

  16. Havre et al. (2000): Implementation on Hod-Vallhall pipeline Trondheim, 2001 Internet: www.ntnu.no/

  17. Summary and Conclusion • A ”simple” model for severe slugging has been developed • Simple case study shows severe slugging • Stability properties investigated • Control implications • Break limit cycle; nonlinear aspects important • Keep system stable; Linear controller sufficient Trondheim, 2001 Internet: www.ntnu.no/

  18. References Havre, K., Stornes, K. and Stray, H. Taming Slug Flow in pipelines, ABB Review 4 (2000), p.55-63 Hedne, P. And Linga, H. Supression of terrein slugging with automatic and manual riser choking, riser choking, Advances in Gas-Liquid Flows (1990), p453-469 Henriot, V., Courbot, A., Heintze, E. And Moyeux, L. Simulation of process to control severe slugging: Application to Dunbar pipeline, SPE Annual Conferance and Exibition , Huston, Texas(1999). SPE56461 Trondheim, 2001 Internet: www.ntnu.no/

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