stabilizing control and controllability n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Stabilizing control and controllability: PowerPoint Presentation
Download Presentation
Stabilizing control and controllability:

Loading in 2 Seconds...

play fullscreen
1 / 27

Stabilizing control and controllability: - PowerPoint PPT Presentation


  • 115 Views
  • Uploaded on

Stabilizing control and controllability:. Control solutions to avoid slug flow in pipeline-riser systems Espen Storkaas Trondheim 7.6.2005. Thesis summary. Introduction Controllability analysis of a two-phase pipeline-riser systems at riser slugging conditions

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Stabilizing control and controllability:' - ian-willis


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
stabilizing control and controllability

Stabilizing control and controllability:

Control solutions to avoid slug flow in pipeline-riser systems

Espen Storkaas

Trondheim 7.6.2005

thesis summary
Thesis summary
  • Introduction
  • Controllability analysis of a two-phase pipeline-riser systems at riser slugging conditions
  • A low-dimensional dynamic model of severe slugging for control design and analysis
  • Implications of input rate limitations on controllability and controller design
  • Stabilization of multiphase flow in pipelines with single-loop and cascade controllers
  • Model-based anti-slug controllers
  • Extended slug control – An industrial application
  • Conclusions and further work
outline
Outline
  • Introduction
  • Slug flow in pipeline-riser systems
  • Modelling of pipeline-riser systems for control applications
  • Controllability analysis
  • Effect of input rate limitations
  • Controller design
  • Extended slug control
  • Conclusions
introduction
Introduction
  • Oil producing wells also produce gas and water
  • Longer multiphase tie-in lines in offshore oil productionfrom increases flow-related challenges
  • Flow assurance technology plays an increasingly important role
    • Hydrates
    • Wax
    • Corrosion
    • Flow regimes
slug flow in pipeline riser systems
Slug flow in pipeline-riser systems
  • Riser slugging
  • Hydrodynamic slugging

.......

  • Terrain slugging
  • Transient slugging

*Pictures from SINTEF Multiphase flow laboratory

riser slugging and control history
Riser slugging and control - History
  • From design challenge to control objective
  • First relevant publication : Schmidt et al (1979)
  • Experimental work by Hedne & Linga (1990)
  • Simulations studies and experimental work from several sources (Total, Shell, ABB, Statoil)
  • First industrial application: Hod-Valhall (Havre et al 2000), more has followed in later years
  • Included in design of new projects (riser slugging potensial at design conditions)
outline1
Outline
  • Introduction
  • Slug flow in pipeline-riser systems
  • Modelling of pipeline-riser systems for control applications
  • Controllability analysis
  • Effect of input rate limitations
  • Controller design
  • Extended slug control
  • Conclusions
main case study
Main case study
  • Test case for riser slugging in OLGA
    • Simplified geometry
    • Two-phase flow
    • Constant feed
    • Constant pressure behind choke
modelling 1 lessons learned from two fluid model
Modelling (1) – Lessons learned from two-fluid model
  • Two-fluid model used to investigate system caracteristics
  • Transition to instability through Hopf bifurbation
  • Complex unstable poles
  • Controllability analysis gives information about measurement selection
  • Simpler model should be used
modelling 2 design specs for simplified model
Modelling (2)- Design specs for simplified model
  • The model must:
    • Describe the dominant dynamic behavior of the system for the time scales for which control is to be effective
  • The model should :
    • be continuous
    • be simple (low state dimension)
    • contain few empirical coefficients
modelling 3 simplified 3 state model
Modelling (3) – Simplified 3-state model

Three dynamical states

From entrainment model

Given by valve equation:

modelling 5 properties of 3 state model
Modelling (5) –Properties of 3-state model
  • Phenomenological model with 3 dynamical states
  • Based on bulk properties
  • Describes both riser slugging and unstable stationary operating points
  • 4 empirical parameters – easy to tune
  • Hopf bifurcation, complex unstable poles
  • Very useful for controllability analysis and controller design
outline2
Outline
  • Introduction
  • Slug flow in pipeline-riser systems
  • Modelling of pipeline-riser systems for control applications
  • Controllability analysis
  • Effect of input rate limitations
  • Controller design
  • Extended slug control
  • Conclusions
controllability analysis

Inverse response

Controllability analysis
  • Investigation into a plants achievable control performance
  • Independent of controller
  • Step in valve opening:
measurement evaluation
Measurement evaluation
  • Achievable performace can be represented by lower bounds on closed-loop transfer functions such as
    • Sensitivity function S
    • Complementary sensitivity function T
    • Input usage KS
  • Bound computed from 3-state model
  • Small numerical value for lower bounds on closed loop transfer functions indicate a good measurement candidate
measurement evaluation1
Measurement evaluation

Unstable system at 30% valve opening pi=0.0007±0.0073

Low steady-state gain

Similar results from two-fluid model

conclusions from controllability analysis
Conclusions from controllability analysis
  • Inlet or riserbase pressure well suited for stabilizing control
    • Time delay may prevent the use of inlet pressure for long pipelines
  • Pressure at top of riser not suitable for stabilizing control due to unstable zero dynamics
  • Flow measurement at riser outlet can be used for stabilization but has lacking low-frequency gain
    • Best used as a secondary measurement in a cascade or in combination with another measurement
outline3
Outline
  • Introduction
  • Slug flow in pipeline-riser systems
  • Modelling of pipeline-riser systems for control applications
  • Controllability analysis
  • Effect of input rate limitations
  • Controller design
  • Extended slug control
  • Conclusions
effect of input rate limitations
Effect of input rate limitations
  • Limitation on input rate can limit performance for control systems
  • Explicit lower bounds on required input rate derived
    • Stabilization
    • Disturbance rejection
  • Controller design with limited input rates
controller design
Controller design
  • Controllers design based on simplified 3-state model
    • Stabilizes both two-fluid model and OLGA model
  • Measurement selection from controllability analysis confirmed
    • Controllers based on upstream pressure measurement robust and effective
    • Controllers based on only a flow measurement tends to drift off
    • A flow measurement combined with another measurement can be used for stabilizing control
single loop controllers
Single-loop controllers

PID controller with measured inlet pressure

H∞controller with measuredinlet pressure

PID controller with measuredriser base pressure

PID controller with measuredoutlet flow

cascade and miso controllers
Cascade and MISO controllers

Cascade controller, y1=PI, y2=Q

H∞-controller, y=[DP Q]

Cascade controller, y1=DP, y2=Q

extended slug control
Extended slug control
  • Anti-slug control combined with functionality to mitigate surge waves and startup slugs
summary
Summary
  • Simplified model of pipeline-riser systems at riser slugging condisons for controllability analysis and controller design
  • Controllability analysis gives clear recommendations for measurement selection for stabilizing control
  • Input rate limitations may be important
  • Controller design
  • Extended control application

Further work

  • Effect of water, different geometries
  • New measurements