Onshore and offshore flare systems and their components, pose a number of major accident hazards as well as minor hazards which can and have led to significant losses in the Oil & Gas & Process Industries. Flare systems are present on a wide range of assets and are now being installed in non-traditional industries, such as wastewater treatment plants, distilleries, landfill sites and onshore shale gas exploration sites to minimise releases of unburned hydrocarbons to atmosphere. As such, the effective Process Safety Management (PSM) of these hazards is of increasing relevance and importance to duty holders, designers, and regulators alike as well as community stakeholders.
Objective
The objective of the study is to perform modelling of the flare systems and investigate the effects of igniting flammable gas mixtures during cold venting on entire flare network, thus define the design pressure for the combined Closed Drain/ Flare KO drums on JA platforms.
Methodology
Depending on geometry, mixture composition and turbulence level, in deflagrations, the overpressures reached can be enormous which pose a serious threat to the flare system integrity. The loads or overpressures generated by the combustion process may generate a high-pressure pulse, temperature peaks, shock waves and large pressure gradients which could seriously damage components, and internal walls.
Flame propagation in flare header and drain system, is turbulent premixed flame. Proper model in this study is premixed flame.
Through advancement in the processor of computers, numerical approaches such as Computational Fluid Dynamics (CFD) have become widely applied for the simulation and calculation of turbulent reacting flows. Among different available algorithms within a CFD approach, LES is a robust method capable of providing satisfactory spatial and temporal resolution. Hence, excessive studies have been dedicated to the advance and justification of LES for simulation of premixed flame deflagration.
In premix combustion modelling, the flame development is shown with progress variable.
This analysis for flare system included the following tasks:
- Identification credible condition based on operation scenarios (composition and process conditions provided by Client) and meteorological condition (e.g., Wind direction & speed)
- 3D Model on Flare Header, Flare KO / Closed Drain Drum, to prepare 3D mesh models of pipe and vessels by using the 3D model & the vessels Drawings
- 3D CAD setup: entities that do not affect the flow will be removed, as they will add computational time without adding any additional accuracy to the flow field.
- Set up of operating conditions
- Solve transient analysis to capture evolution of the flow field and propagation of the flame front
- Solve and report, including assumptions, methodologies, and results
Results
Computational Fluid Dynamics Modelling provides valuable information in terms of safety in the dispersion of flammable gas in complex environments, either in outdoor environment such as in urban areas with multiple obstacles and building structures, or indoor environment with complex flow direction. CFD simulations provide not only accurate hazard assessments such as radiation level, overpressure contour, and distribution of toxic cloud, but also detailed information about the spatial and temporal evolution of accidental events.
