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8/10/2019 Brazil 2014ugm Response Surface Model Predict Flammable Gas Cloud
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A Response Surface Model to PredictFlammable Gas Cloud Volume in Offshore
Modules
Tatiele Dalfior FerreiraSvio Souza Venncio Vianna
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Research Group Overview
University of Campinas (Unicamp)
Founded on October 5, 1966.
Has three campuses and comprises 22 units of
teaching and research
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Research Group Overview
The Faculty of Chemical Engineering (FEQ) was
created in April of 1990 as a Department of
UNICAMP.
Today, it is divided in four departments: DDPP,
DEMBio, DESQ and DEPro.
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Problem Description
Gas explosion safety is a concern in industrial
plants, particulary in oil and gas industry.
The offshore oil installations involve risk of
accidents with a major loss-potential.
Explosion of theoffshore platform
Piper-Alpha located inthe North Sea in 1988.
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Problem Description
Explosion Risk analysishelp risk decisionsto prevent and control accidents:
- Quantify the blast overpressure generate over
distance and time.
- Gas dispersion study.
Three-dimensional analysis using CFD
Mathematical models (in conceptual design)
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Problem Description
The flammable gas cloud size in na offshoremodule:
- Ventilation: wind speed and direction and geometry
of the module.
- Release: leak rate, direction and location and gas
density.
Cleaver et al (1999):
= / 2
/2
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Problem Description
The use Response Surface Methodology
(RSM) to estimate flammable gas cloud size
in offshore modules (Huser and Kevernvold,
2000):
=
1 + 1 + 2
= +
=
=
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Methodology
Geometry and Mesh:
ANSYS
ICEM - 11.0
Unstructured mesh
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Methodology
Release conditions:
- Natural gas composition:
Component Molar Fraction
C1 0.861
C2 0.071
C3 0.030
C4 0.013
C5+ 0.010
CO2 0.005
N2 0.010
Pressurized pipeline
with average pressure
200kgf/cm2
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Methodology
Variables of Interest:
Ventilation and Leak rate: R (Cleaver et al.
(1999) e Huser e Kvernvold (2000))
0.03 < R< 0.3
Wind and Leak directions: (phi)
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Methodology
Wind Directions:
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Methodology
Leak Directions:
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Methodology
Leak and Wind directions: (phi)
= 0
leak and wind inthe same direction
= 180 leak and windin opposite direction
0
45
90
135
180
225
270
315
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Methodology
Leak and Wind direction: (phi)
Quadrant 01= 0, 45e 90
Quadrant 02= 90, 135e 180
Quadrant 03= 180, 225e 270
Quadrant 04= 270, 315e 360
0
45
90
135
180
225
270
315
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Methodology
Design of the Simulations
Design ofExperiments 32
for each quadrant
Scenario Quadrant R
01 01 0 0.03
02 01 45 0.03
03 01 90 0.03
04 01 0 0.1505 01 45 0.15
06 01 90 0.15
07 01 0 0.3
08 01 45 0.3
09 01 90 0.3
10 02 90 0.03
11 02 135 0.03
12 02 180 0.03
13 02 90 0.15
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Methodology
Boundary Conditions and Solver Parameters
ANSYS
CFX -15.0
Region Bondary Condition
Surfaces No slip
Leakage Prescribed mass flow
Ventilation Prescribed velocity
Contour of the Computational Domain Relative Pressure = 0
Parameres Value or type
Reference Pressure 1 atm
Flow Regime Stationary and Incompressible
Turbulence Model k -
Advection Scheme Upwind
Time Scale Automatic (1.0)
Convergence Criterion RSM
Maximum Residual 1x10-5
Mn. and Mx. Number of Iteractions 100 - 1000
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Results
A gas leak
Simulation of an axisymmetric jet:
- Air
- Orifice Diameter = 2,7mm
- Mach Number at the exit = 1
- Air density at the exit = 2,25kg/m3
Birch (1987)
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Results
Simulation of an axisymmetric jet
Comparison between the experimental data and the result of the simulation of an
axisymmetric jet.
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Results
- Air
- Average Pressure =
137,9kPa
- Mass flow rate = 0,15kg/s
Wakes (2002)
Simulation of a high aspect ratio jet
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Results
Simulation of a high aspect ratio jet
Comparison between the experimental data and the result of the simulation of a high
aspect ratio jet.
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Results
Wind Analysis
Superficial atmospheric boundary
layer: =
Hanna (1982)
(01)
= (02)
= 10 (03)
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Results
Values of L , z0e pfor neutral atmospheric and sea
surface
AICHE (2000)
Sea level: 0 m
Platform level: 55 m
Monin-Obukhov lenght (L) (m) > 100
Surface roughness (z0) (m) 1x10-4
Power coefficient (p) 0.15
Wind speed profile tests
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Results
Simulation of the wind speedprofile using equations 01 (a); 02
(b) and 03 (c).
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Results
Example of gas dispersion simulation
R = 0.15
= 135
LFL: 5%
UFL: 15%
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Results
Development of the Response Surfaces
Quadrant 01
Quadrant 03
Quadrant 02
Quadrant 04
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Results
Quadrant 01 Quadrant 02
Quadrant 03 Quadrant 04
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Results
Validation of the Model
Comparison between the CFD results with the values predicted by the
model considering random simulated cases.
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Conclusion and next steps
A Response Surface Model was developed forprediction of flammable gas cloud size in anoffshore module using two main variables: R e ;
The results provided by the model were well fitted
with CFD data within a tolerance of 50%;
The model is a simplified prediction form and can
be applied in early stages of the design when little
is known about the geometry or when thegeometrical model is not available;
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Conclusion and next steps
Through the model every possible release scenariocan be assessed in a risk analysis, which is
infeasible in CFD simulations;
The proposed model can be very useful when
combining with Monte Carlo techniques tocalculate probabilistic cloud sizes.
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Thank you!