Bell Energy recently completed Fire & Explosion Risk Assessment study for a large Gas Plant in UAE. The explosion assessment was performed adopting Computational Fluid Dynamics (CFD) using GEXCON’s FLACS Software suite.
CFD based explosion studies have several advantages over the usual explosion screening tools that are used in QRA. The main advantage of CFD is its relative accuracy of predicting explosion overpressures in the near and far field. This helps in making more informed decisions about fire or blast protection requirements, which could otherwise lead to unjustified and unreasonable expenditures.
The physical effects and hazards of releases are typically quantified using a simple so-called 2D Analytical approach which is based on semi-empirical equations or broad simplifications of the physics simulated. 3D CFD modelling has been used for design purpose in many applications from process to flow assurance. 3D CFD modelling is now increasingly being used for process safety applications, thanks to the improved performance of computers and algorithms, but also because the use of such models has been extensively validated in the case of the FLACS® application, developed by Gexcon, over the last 30 plus years.
General benefits of 2D modelling include: fast calculations due to approximation with empirical relations, and relative ease of use. But generally they are not accurate in congested areas or near and around the facilities, as they assume the world is flat and empty. Additional limitations in representing the physics involved make such methodology too simplistic, and devoid of real added value. 3D modelling has been on the other hand typically more time consuming since the appropriate fluid dynamics equations have to be resolved in time and space, and require additional input data in order to perform calculations.
In general there are many excellent applications of 3D CFD over 2D modelling e.g. prediction of smoke dispersion, validation of hypothesis on accident investigation, visualisation of the results in three dimensions, location of gas detection, optimized separation between equipment and facilities, specification of passive fire protection, location of safety equipment or HSECEs, etc.
A key advantage of Computational Fluid Dynamics is that it is a very comprehensive, as it can capture accurately the complex physics more realistically, and the tools have powerful visualization capabilities. Engineers can evaluate the performance of a wide range of gas cloud dispersion, fires and vapor cloud explosion configurations in the virtual computer environment without the time, expense, and disruption required to make actual changes onsite. Visualization of 3D videos do improve the understanding of consequences from unwanted gas and liquid releases.
It is a myth that CFD based studies are time consuming and expensive. We were also under the same impression for many years, but after successfully completing several fire, vapour cloud explosion and dust explosion studies for small, medium and large industries, we can confidently challenge this myth. Our aim is to change our client’s perception and encourage the use of CFD techniques in design and engineering of Fire & Explosion protection systems. Our experience has taught us the following:
CFD based Fire & Explosion studies should be used for the following applications:
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