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The use of Computational Fluid Dynamic modelling
(CFD) to optimise safety design in process plantsMarco Pontiggia1, Marco Gattuso2, Hulya Aras3, Giovanni Uguccioni1
(1) D’Appolonia S.p.A. – via Martiri di Cefalonia 2, 20097 – San Donato Milanese (MI) – Italy
(2) D'Appolonia S.p.A. - via Farabola Est 32, 55049 Viareggio (LU) – Italy
(3) D'Appolonia Müh. Tic. Ltd. Şti. Değirmen Sok. Nida Kule İş Merkezi No:18 Kat:9 Kozyatağı 34742 İstanbul-
Türkiye
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Summary
• Introduction
• CFD approach description
• Case #1 – Outdoor Toxic gas dispersion
• Case #2 – Indoor Toxic gas dispersion
• Case #3 – Flammable gas dispersion, mitigation design
• Conclusions
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MumbaiAbu dhabi
Bucharest
Istanbul
Leuvren
Basra
Maputo
Washington DC
Cairo
Saint Petersburg
Beijing
Seoul
Rotterdam
Montevideo
Durban
D’Appolonia
2014 Project Countries
A Company belonging to the RINA Group of Italy providing
engineering and consultancy services to Clients worldwide,
through a network of Project offices and Local companies,
including Turkey (D’Appolonia Müh. Tic. Ltd in Istanbul)
Geosciences
Environment & Permitting
Health, Safety and Loss Prevention
Simulation & Modeling
Concept, Feasibility & Design
Project Management Consulting
Operation and Maintenance
Asset Integrity Management (AIM+)
D’Appolonia Main Services in the Process sector
D’Appolonia Process Safety services
LOSS PREVENTION – QRA - SAFETY CASES - SIL - HAZARDOUS AREAS
CLASSIFICATION - SAFETY CRITICAL ELEMENTS – FIRE PROTECTION STUDIES –
GAS & LIQUID DISPERSION SIMULATION - 3D CONSEQUENCE MODELING –
HUMAN FACTOR ANALYSES
HSE MANAGEMENT - EMERGENCY PLANNING - ACCIDENT INVESTIGATIONS -
HAZOP - HAZID - RELIABILITY STUDIES (RAM) - AVAILABILITY ANALYSES -
BUSINESS CONTINUITY - OCCUPATIONAL HEALTH - TRAINING – AUDITS
Introduction
General
The tool should besuitable for the widestrange of applications
Accurate
The tool should be ableto describe the
phenomena
Economic
The tool should be low time and resources
consuming
CFD Tools
• 3D modelling, • Full 3D meshing• Equivalent
porosity
• Wide application range
• Good accuracy even in geometrically complex environment
• Large computational time
Integral models
• Low resource consuming
• One dimensional modeling
• Roughness height for geometry representation
• Large overestimation of damage distances are possible
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INTRODUCTION
CFD approach
• 3D model import or construction
• Mesh design
Geometry
• Hazardousmaterial
• Source termcharacterization
Scenario• Boundary types
and characterization
• Model tuning
Boundaries
• Most effectivemodel selection
• Convergencecriteria
Calculation• Post processing
tools
• Resultsinterpretation
Results
Open Issues• Lack of data• 3D format compatibility• Data corruption• Level of detail
New methodology• Easy-accessible data• Customizable level of
detail• Fast geometry building
Dose routine implementation
ProbitModified k-ε for
atmospheric turbulence
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CHLORINE RELEASE
(IDLH = 10 PPM)
OPERATIVE CONDITIONS:
3 BARG, 50 °C
HOLE SIZE: 60 MM
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CASE #1
CASE #1 - Problem
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Simple analytical models for consequence assessment provide
very high danger distance s (approx 7 km to IDLH value, 10
ppm and approx 700 m to the 2,5% fatality probability.
Major and costly plant modifications could be required by
Authorities in charge of approving the plant safety report if
this danger distances were confirmed.
A more detailed and realistic modeling was required to
consider the effect on the gas dispersion of local terrain
condition.
CHLORINE RELEASE
(IDLH = 10 PPM)
OPERATIVE CONDITIONS: 3 BARG, 50 °C
HOLE SIZE: 60 MM
CASE #1 SET UP –
Geometry and Release
Earthwork (3m)
Wood (20m)
Plant (5-15m)
Release point
StepDuration
[s]Velocity
[m/s]Mass flowrate
[kg/s]
1 180 286 3.3
2 30 276 2.8
3 45 244 1.9
4 45 129 0.7
5 10 95 0.5
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Case 1
GEOMETRY BUILDING
Shuttle Radar Topography Mission: 90 m resolution cartesian elevation map
Geo-referenced aerial photograph
TERRAIN OBSTACLES
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• Wind speed 2 m/s,
Pasquill class F
• ASsM for atmospheric
profiles tuning
• North-West: minimum
slope, open field
• North: Increasing terrain
elevation, largest
obstacle downwind the
release
• South: Directed towards a
a valley, obstacles upwind
with respect to release
point
CASE #1 SET UP – Wind
Direction
North-West North
South
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Strong recirculation
caused by plant
structures
Shifting in release point
(chlorine release takes
place from the building
wake)
Shifting in plume
direction due to terrain
slope
CASE #1 – Results
Wind to NW
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Strong recirculation caused
by plant structures
Wood weakly influences
chlorine cloud at 10 ppm
Wood strongly influences
Probit values, since they
involves higher chlorine
concentrations
Terrain slope influences
chlorine plume direction
CASE #1– Results
Wind to N
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Strong recirculation caused by plant
structures
Upwind obstacles (wood and terrain
slope) strongly enhance turbulence and
recirculation
The valley further increase chlorine
mixing with fresh air thus reducing IDLH
and Probit distances
CASE #1– Results
Wind to S
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CASE #1 – Results
Wind direction
IDLHVulnerability
0.0035%Vulnerability
0.15%Vulnerability
2.5%
North-West 3480 721 472 309
North 2840 303 267 158
South 2110 289 186 103
AnalyticalModel
6615 1588 1023 646
Wind direction
IDLHVulnerability
(average)
North-West 47% 52%
North 57% 76%
South 68% 82%
Dam
age
dis
tan
ces
Red
uct
ion
in
dam
age
dis
tan
ces
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CASE #1 - Conclusions
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Authorities were satisfied that the reference accidental scenario
was not able to reach the huge distances predicted by analytical
models.
Realistic emergency plans could be developed.
Plant operation was granted.
CASE #2 - Problem
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PSVs of a series of reactors inside a building discharge a
solution of Ammonia (NH3) inside a collection open drain
outside the building.
In case of a release, can ammonia recirculate inside the
building, causing danger to the operators inside?
Shall any design modification or specific operating procedure
be developed to ensure safety or personnel, and if so which
one?
CASE #2 – Description
1 3
2
• Ammonia release following a PSV opening
• Short transient (about 30 seconds)
• Three release points
• Effects of geometry heavilyinfluences release and dispersion
• Target is to identify potentialtoxic risk for people working in the facility
• Toxic effect calculated withprobit approach
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CASE #2 – Geometry
detail
A B
C D
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CASE #2 – Screenshots
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Release Point 1
Release Point 3
CASE #2 – Screenshots
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Level 20 m
20 m
After 30 s
After 45 s
Release Point 1
Level 24 m
CASE #2 - Conclusions
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The three dimensional simulation of the release allowed to
assess the maximum NH3 concentration inside the building
(between 600 and 1200 ppm) and the time behaviour of the
NH3 cloud.
On the basis of these results, operating procedures for the
entrance of personnel at +20 and +24m levels were defined,
to ensure risk to personnel within safe limits.
Acceptability of the PSV and building arrangements was
therefore confirmed.
Case #3 - Description
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For the project of an underground gas storage and
associated pipeline and compressor station in Italy, the
Authorities required to design a shelter around the filtering
and measuring station, to ensure protection to nearby
historical buildings and future industrial buildings in case of
natural gas accidental release from a leak.
The shelter needed not to be enclosed, and the optimum
design of wall height needed to be assessed.
Case #3 - Description
1.1 m
1.1 m
2.2 m 7.0 m Receiving traps
Case 1
Case 2
Wind Wind Wind Wind
• Flammable release fromlaunching trap potentiallyreaching nearby urban areas
• Two release directions
• Two design configurations
• Design mitigation (wall) toreduce damage distances
• Steady-state simulation
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Case #3 - Geometry
Total height: 3m
Above ground: 3m
Total height: 3m
Above ground: 2m
Underground: 1m
A B
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Case #3 - Results
South East
Ab
ove
gro
un
d
1m
be
low
gro
und
26 m
44 m 110 m
146 m
68 m
190 m
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The three dimensional simulation of the
barrier effect allowed to design a
protection system sufficient to ensure
protection of the sensible targets
around.
On the basis of these results, the
Authorities granted building permit to
the plant.
CASE #3 - Conclusions
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CFD Modeling allows to analyze accidental
scenarios in a realistic and accurate way,
avoiding the risks of overdesigning
protection systems and overestimating
accident consequences.
The benefit of a CFD approach, from the
economic and authorization point of view,
are evident.
These tools require skills and competency
to be run, and the time and cost
associated can be significant. There use is
recommended whenever simpler analytical
tools can not provide the detail of results
required by the specific case
Conclusions
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General
The tool shouldbe suitable for
the widest rangeof applications
Accurate
The tool shouldbe able to
describe the phenomena
Economic
The tool shouldbe low time
and resourcesconsuming