Comparison of CFD Numerical Approaches for the Simulation of Accidental Gas Release in Energy Applications

Abstract

Oil & Gas plants are risk-relevant complex facilities for the presence of toxic, flammable and pressurized fluids. Risk assessment is mandatory to guarantee plant sustainability and compliance with directives. For offshore plants characterized by congested spaces, semi-empirical models for accident consequence simulation often result in risk overestimation. This could be avoided through Computational Fluid Dynamics (CFD), which guarantees more accurate results. Complex phenomena and geometries, however, entail large computational efforts that force limiting the number of simulations to explore the accident scenarios. This calls for new approaches able to model and simulate complex congested geometries in affordable time, while achieving keeping the required accuracy of the results. In this context, a novel CFD model based on ANSYS Fluent, named SBAM (Source Box Accident Model), has been proposed by the research group of the SEADOG lab in Politecnico di Torino with the aim of simulating complex environments with good accuracy and reduced computational cost. In this work, the results provided by the SBAM model on an accidental high pressure flammable gas release in a platform, are compared with those provided by other tools and models available in the market, and widely used in industrial applications, such as FLACS developed by Gexcon US and KFX developed by DNV-GL.

Quantification of Uncertainty in CFD Simulation of Accidental Gas Release for O & G Quantitative Risk Assessment

“…In FLACS and KFX, the following simulation conditions are set: a 3-D transient solver is used to solve the Reynolds-Averaged N-S equations (in fact KFX allows modeling 3D processes), the Standard k-ε model is employed to model the turbulence of the flow (in fact the k-ε turbulence model is the only turbulence model implemented both in FLACS Energies 2021, 14, 8117 6 of 16 and KFX). More details about the numerical models are given in the previous work [19]. A cartesian grid is built since this is the only one type of grid available in the two software programs.…”

“…This kind of grid is used also in the next test case, although there is a round shape. This is possible since the two software programs use the Porosity Distributed Resistance (PDR) approach; see details in [19].…”

“…In Section 2.2 FLACS, developed by Gexcon US, and KFX, developed by DNV-GL, are also introduced briefly. The interested reader may refer to [19], for further details.…”

“…Since SBAM is a 3-D model, useful for large, congested domains, it is used in Section 4, where the realistic case of the O & G offshore platform is analyzed. The numerical models employed by the three software programs are described in detail in [19].…”

“…Simulations are performed in steady state with an unstructured tetrahedral mesh. The "Species Transport" model is used in order to solve a transport equation without chemical reactions, and the ideal gas law is used to evaluate the density field [19].…”