Brazil 2014ugm Response Surface Model Predict Flammable Gas Cloud

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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[email protected]

[email protected]

Thank you!

Brazil 2014ugm Response Surface Model Predict Flammable Gas Cloud

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