ATOFINA - High Pressure Pipeline Rupture (Final)
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Transcript of ATOFINA - High Pressure Pipeline Rupture (Final)
7/30/2019 ATOFINA - High Pressure Pipeline Rupture (Final)
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Simulation of
High Pressure
Pipeline Rupture with
Aspen Dynamics ®
Claudine Boisson
Process Simulation Team
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Simulation of Pipeline Rupture with Aspen Dynamics2
Outline
Introduction
Objective and methodology
Building up the modelTheoretical analysis
Simulation results
Conclusion
1
2
3
4
5
6
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Simulation of Pipeline Rupture with Aspen Dynamics3
1. Introduction: Pipelines
Pipelines are widely used to transporthazardous fluids (crude oil, natural gas,petroleum products, etc.)
Overall length > 750,000 km in North America
> 130,000 km in EuropeGood safety record: pipelines comparefavorably with other transportation methods*
* According to the US National Transportation Safety Board andCONCAWE (the oil companies’ European organization for environment, health and safety)
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Simulation of Pipeline Rupture with Aspen Dynamics4
1. Introduction: Safety issues
But a single pipeline accident can cause acatastrophic disaster and cost millions of dollars.
For both environmental and economic
reasons, companies need to assess thedamage an accident would cause (fire,explosion, toxic release).
For high-pressure pipelines, full rupture is
often the “worst case” scenario. Simulation of pipeline rupture is a key issue
regarding safety and risk assessment.
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Simulation of Pipeline Rupture with Aspen Dynamics5
1. Introduction: Pipeline rupture
What happens when a pipeline carryingliquefied hydrocarbons breaks down?
Inside pressure suddenly decreases in theneighborhood of the opening:
Superheated liquid flashes 2-phase critical flow is established Temperature decreases
A sharp vaporization front propagates within thepipeline, away from the point of failure.
Block valves isolate the ruptured segment.
The remaining fluid is released until P = Pout (effect of gravity on the liquid phase if the pipe isinclined).
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Simulation of Pipeline Rupture with Aspen Dynamics6
1. Introduction: Simulation tools
Simulation of high-pressure pipeline rupture isparticularly difficult (highly transient nature, stiff term, two-phase heat and mass transfer, nonthermal equilibrium, …).
Experimental data are scarce.
Few codes exist (commercial tools are evenscarcer).
To get reasonably accurate results, one has touse complex codes (such as ProFES, META-HEM, BLOWDOWN) - which still sometimesperform poorly.
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Simulation of Pipeline Rupture with Aspen Dynamics7
1. Positioning of Aspen
Dynamics
Aspen Dynamics is an easy-to-use tool for
dynamic simulation of process plants,
Not dedicated to pipeline depressurization
simulation,But has built-in models for pipe, valve and
pipeline.
Is Aspen Dynamics able to simulate a pipelinerupture and accurately predict the released
fluid flowrate and composition?
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Simulation of Pipeline Rupture with Aspen Dynamics8
Outline
Introduction
Objective and methodology
Building up the modelTheoretical analysis
Simulation results
Conclusion
1
2
3
4
5
6
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Simulation of Pipeline Rupture with Aspen Dynamics9
2. Objective and methodology
Objective: ASSESS ASPEN DYNAMICS’ CAPABILITIESTO SIMULATE A HIGH PRESSURE PIPELINERUPTURE
No field data directly available. Basic approach:
Can Aspen Dynamics perform the calculations?
How simplified is the model? How accurate are the results?
(Accuracy estimated through theoretical evaluationof the equations used)
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Simulation of Pipeline Rupture with Aspen Dynamics10
2. Methodology
Choose a test case.
Build up a model with Aspen Dynamics.
Perform the calculations (if the calculations
fail, simplify the model).
Theoretical analysis of:
simplifications
validity of the equations used impact of numerical methods
Evaluation of the accuracy of the results.
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Simulation of Pipeline Rupture with Aspen Dynamics11
2. Test case
Horizontal 8-in diameter pipeline
Supercritical ethylene (100 bar abs/ 15°C/ 100,000 kg/h)
Block valve every 14.5 km
Closes in 40s when P < 65 bar absFull-bore rupture of pipeline in the middle of a 14.5 km
segment
C2H4
14.5km
PC
PT
PC
PT
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Simulation of Pipeline Rupture with Aspen Dynamics12
Outline
Introduction
Objective and methodology
Building up the model Theoretical analysis
Simulation results
Conclusion
1
2
3
4
5
6
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Simulation of Pipeline Rupture with Aspen Dynamics13
3. Building up the model:
Steady-state
110 bar abs
15 °C 93 bar abs,
13 °C Aspen Plus 11.1
Single component: ethylene
Property method: PSRK
2 “Pipe” blocks (8 in , 14.5 and 7.25 km length)
Ball valve (8 in
)Flowrate: 100 t/h
Model exported as a pressure-driven dynamicsimulation
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Simulation of Pipeline Rupture with Aspen Dynamics14
3. Building up the model:
Dynamic
Aspen Dynamics 11.1
Pressure driven model: P1 and P3 fixed.
Simulation of the rupture: outlet pressure (P3) set
from 93 bar abs to 1 bar abs.The valve is closed when P2 < 65 bar abs.
110 bar abs
P1
93 bar abs
1 bar abs
P3 P2
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Simulation of Pipeline Rupture with Aspen Dynamics15
3. Building up the model:
Dynamic
Calculation options
(had to be carefully adjusted to obtain convergence) :
Global property mode : Rigorous
Maximum number of Fortran errors : 500Non linear solver : Newton (max. iterations : 1000)
Integrator : Variable Step Implicit Euler (Gear andRK4 failed)
Discretization interval : 10 segments in the first pipeblock, 50 in the second
Tolerances : 0.0001
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Simulation of Pipeline Rupture with Aspen Dynamics16
3. Restrictions imposed by
the software
Property method:
Calculation failure with BWRS. Had to use PSRK (cubic
equation of state), which is less accurate:- for liquid molar volume and enthalpy
- near the critical region
Number of segments in the pipe block :
systematic run failure with more than 50segments
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Simulation of Pipeline Rupture with Aspen Dynamics17
Outline
Introduction
Objective and methodology
Building up the modelTheoretical analysis
Simulation results
Conclusion
1
2
3
4
5
6
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Simulation of Pipeline Rupture with Aspen Dynamics18
4. Closure relationships
Thermodynamics: Thermal & phase equilibrium: wrong (Tgas Tliquid)
but applicable to long pipelines (>100m)
Cubic equation of state shortcoming near thecritical region
Friction force (momentum equation): Various correlations available
Heat transfer:
Constant fluid-wall heat transfer coefficient:inaccurate (coefficient very different for gas andliquid overall coefficient changes with time)
Interfacial heat transfer: neglected
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Simulation of Pipeline Rupture with Aspen Dynamics19
4. Numerical methods
Pipe model: Finite Difference Method Numerical diffusion
Long CPU time and convergence problems
(Ex : 10 segments in the second pipe : 30 min50 segments in the second pipe : 3h100 segments in the second pipe : no convergence)
Due to :
Fixed grid : discretization into a large number of segments large number of equations
Supercritical property calculations non-linear solver not robust enough (frequent run failures)
Time increment and stiff equations
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Simulation of Pipeline Rupture with Aspen Dynamics20
4. Estimation of results
accuracy
Some good points: No assumption of isentropic or isenthalpic
decompression
Continuous phase change along the pipe length
using rigorous flashes Modeling of two-phase choked flow
Major source of inaccuracy: NumericalMethods
Convergence possible only with a reduced number of segments
Finite Difference Method Numerical diffusion Sharp fronts are smoothed
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Simulation of Pipeline Rupture with Aspen Dynamics21
4. Estimation of results
accuracy
Other inaccuracy factors
PRSK: C2H4 density is ~15% too low (deviation fromNIST* values in the simulated conditions)
Flowrate is underestimated (~5%) and pressuredrop overestimated (up to 10%)
Global heat transfer coefficient : no accurate valueexists. Temperature can be over- or underestimated,depending of the chosen approximation.
Empirical correlations for friction factor dependant onflow regime maps: 2 sources of inaccuracy
* National Institute of Standards and Technology
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Simulation of Pipeline Rupture with Aspen Dynamics22
Outline
Introduction
Objective and methodology
Building up the modelTheoretical analysis
Simulation results
Conclusion
1
2
3
4
5
6
7/30/2019 ATOFINA - High Pressure Pipeline Rupture (Final)
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Simulation of Pipeline Rupture with Aspen Dynamics23
5. Simulation results
Ruptured pipe inlet and outlet pressure
0
20
40
60
80
100
120
0 10 20 30 40 50
Time (min)
P r e s s u r e ( b a r
a b s ) Outlet
InletValve closed
Pipeline rupture
Choked flow
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Simulation of Pipeline Rupture with Aspen Dynamics24
5. Simulation results
Ruptured pipe inlet and outlet flowrate
0
100
200
300
400500
600
700
0 10 20 30 40 50
Time (min)
F l o w r a t e ( t / h
r )
Outlet
InletValve closed
Pipeline rupture
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Simulation of Pipeline Rupture with Aspen Dynamics25
5. Simulation results
Ruptured pipe inlet and outlet temperature
-120
-100
-80
-60
-40
-20
0
20
0 10 20 30 40 50
Time (min)
T e m p e r a t u r e (
° C )
Outlet
Inlet
Valve closed
Pipeline rupture
End of
choking
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Simulation of Pipeline Rupture with Aspen Dynamics26
Outline
Introduction
Objective and methodology
Building up the modelTheoretical analysis
Simulation results
Conclusion
1
2
3
4
5
6
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Simulation of Pipeline Rupture with Aspen Dynamics28
6. Conclusion (cont’d)
Suggested path forward: focus on
numerical methods improvement
Method of Characteristics (curved
characteristics):
Discontinuities are propagated with little
numerical diffusion
Variable grid instead of fixed grid