Recent Advancements in Vapor Cloud Explosion Modeling for Onshore Installations. Vijay Raghunathan, DNV Energy 25 Oct 2006

Transcription

1 Recent Advancements in Vapor Cloud Explosion Modeling for Onshore Installations Vijay Raghunathan, DNV Energy 25 Oct 2006

2 Introduction Facility Siting Issue Facility Siting Standards- API RP 752, CCPS Confinement and Congestion Ref:Hoorelbelke, P., Izatt, C.;Brewerton, R.W. Vapor Cloud Explosion Analysis of Onshore Petrochmeical Facilities ASSE, Slide 2

3 Vapor Cloud Explosions (VCE) Vapor Cloud Formation - Rapid Release - Mixing - Ignition - Flame propagation Vapor Cloud Explosion - Turbulence - Partial Confinement Ref: Slide 3

4 VCE Incidents Explosion at the Flixborough Plant (1974) Piper Alpha Explosion (1988) Ludwigshaven Rail Car Incident (1943) Texas City Explosion (2005) Slide 4

5 VCE Modeling Empirical Models Empirical models also referred to as quasi-theoritical and are based on limited experimental data and can be considered the most simplified method for estimating the blast effects from vapor cloud explosions. Phenomenological Models Phenomenological models are simplified physical models, which seek to represent only the essential physics of explosions. Computational Fluid Dynamics (CFD) Models Computational Fluid Dynamics (CFD) model solves the partial differential equations governing the explosion process Slide 5

6 Empirical Models TNT Equivalency Method The TNT equivalency method is based on the assumption that explosive power of a vapor cloud explosion can be related to the mass of the TNT that can produce the same explosive power. W TNT = ( W gas ) *( H ( H c gas d TNT ) ) * E W TNT W gas E H d TNT H c gas - Equivalent Mass of TNT, kg - Mass of Gas involved in VCE, kg - Efficiency Factor (dimensionless) - Heat of detonation of TNT, J/kg - Heat of Combustion of Gas, J/kg Slide 6

7 Empirical Models Limitations of TNT Model - Weak Gas Explosions are not well represented - Selection of yield factor - Geometry of vapor cloud is taken into consideration - Blast wave produced by hydrocarbons does not resemble TNT explosion Slide 7

8 Empirical Models TNO Multi Energy Model This model is based on the assumption that vapor cloud explosion can occur only within that portion of a flammable vapor cloud that is partially confined. R = R * ( P E / ) R R P 0 E - Scaled Distance from the charge, (dimensionless) - Distance from the charge, m - Ambient Pressure (Pa) - Charge Combustion Energy, Joules Slide 8

9 Empirical Models Limitations of TNO Model - The selection of the severity factor or charge strength is to be done based on the confinement and little guidance is provided for partial confinement geometries. - Not clear how to deal with several congested regions - Difficult to represent complicated geometries. Slide 9

10 Empirical Models Baker-Strehlow Model The model is quite similar to the TNO model with the premise that a vapor cloud explosion can occur only within that portion of a flammable vapor cloud that is congested. The steps followed in this model are very similar to the TNO model and the only critical difference is the selection of an appropriate flame speed (Mach number) instead of the charge strength. - Model can handle multi ignition points. - Accounts for confinement in the model. - Easy and fast to use - Overpressure results on the conservative side. Slide 10

11 Phenomenological Models SCOPE (Shell Code for Over-pressure Prediction in gas Explosions) - Developed at Shell's Thornton Research Centre, March The model is one-dimensional in nature and is based on the idealized geometry of a vented vessel containing a series of obstacle grids. - SCOPE 3 replaced SCOPE 2 and was improvised to handle mixed scale objects. - SCOPE 3 has been validated against more than 300 experiments. - Future developments include modeling with effect of water deluge. Slide 11

12 Phenomenological Models Limitations of SCOPE Model - Does not provide the great level of geometric detail as the CFD Models. - Can deal with single enclosures only. Slide 12

13 Phenomenological Models CLICHE (Confined LInked CHamber Explosion) - Developed by Advantica Technologies Ltd - CLICHE code represents a generalization of the vented vessel explosion concept to a sequence of interlinked explosion chambers. - Simple combustion model, based on a mixture of some fundamental physics and empirical correlations - Can generate its own input parameters from an obstacle database - Very short model run times Slide 13

14 CFD Models FLACS (FLame ACceleration Simulator) - Originally developed at the Christian Michelsen Research Institute in Norway, now GEXCON. - CFD codes provide great depth of information about flow field. - Uses advance user interface like CASD( Computer Aided Scenario Design) and Flowvis. - Can be applied to congested,but unconfined geometries. - Extensive validation against small, medium and large scale experiments. - Model supports CAD data input Slide 14

15 CFD Models AutoReaGas Couples the features of the REAGAS and BLAST codes developed by TNO and have been integrated into an interactive environment based on the AUTODYN-3D code developed by Century Dynamics Ltd. Advanced CFD Models : REACFLOW, CFX-4 and COBRA produce more accurate results. Slide 15

16 Conclusion Empirical Models: Screening level Phenomenological Models: Good substitute for CFD code CFD Models: Detailed representation of the real scenario Slide 16

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