Modeling of Flammable/Hazardous Gas Release and Dispersion

IOP Conference Series: Materials Science and Engineering

Natural gas is used as fuel in industries, power plants, commercial installations, and households. In its application, natural gas leaks can be considered as a major hazard because of its flammable and explosive nature. In addition to fuel, heat and oxygen sources, fires and explosions can occur if the concentration of natural gas in the air is between Low Flammable Limit (LFL) and Upper Flammable Limit (UFL). If the release of natural gas is not ignited, it will immediately form a Vapor Cloud Explosion (VCE) that can cause an explosion if it meets ignition point. Therefore, a research on dispersion patterns in a particular area or space is needed to minimize hazards and to develop safety procedures and regulations. This research aims to determine the external parameters that affect the dispersion and explosion caused by natural gas by using FLACS software from PT. Gexcon Indonesia. This software can display overpressure graphs of time and 3D visuals of simulations. The external parameters consist of vent size (5.4 m2 and 2.7 m2), wind direction, lighter position (center and back), day and night condition, and the presence of a obstacle (with and without obstacle). From the research results by the simulations, it is obtained that the highest overpressure value when there is an obstacle with a vent size of 2.7 m2; wind direction from the north; night condition, and back ignition point is 0.503 bars at 40,835 s which can cause most buildings to collapse and the death rate to increase.

2013

Integral or phenomenological consequence models are extensively used for explosion and dispersion studies at onshore petrochemical facilities. These models will generally ignore the influence of the geometry of the facility on the ventilation and flow patterns, the generation of flammable gas clouds, and any subsequent explosions. Another significant weakness of these models is the inability to handle dense vapour cloud dispersion in low wind conditions. Risk and consequence studies performed according to API-RP 752 or Seveso-II are mostly referred to as worst-case assessments. In reality these represent some kind of a probabilistic assessment as only “maximum credible” release scenarios are considered. Typically non-conservative gas cloud sizes are predicted, deflagration-to-detonation transitions (DDT) potential is ignored, and the ability to predict the effect of mitigation is limited when using such tools. Computational Fluid Dynamics (CFD), on the other hand, can incorporate th...

Environmental Engineering and Management Journal

The current paper is an overview on previous and ongoing research carried out by the authors concerning the use of Computational Fluid Dynamics for the accurate classification of hazardous Ex areas generated by flammable gases, for the optimization of computational simulation of air-methane mixture explosions by using ANSYS CFX and FLUENT and for calibrating computational simulations of gas explosions using the Schlieren effect. These research works containing analytic studies have led to the observation of basic principles which come to support the benefit of computational approaches for estimating gas dispersion within technological installations in which are handled or stored flammable materials and in which there are likely to occur explosive atmospheres. Preliminary results have led to the idea of developing a computational method for assessing the hazardous area extent in case of gas leak explosions in confined spaces. The computational method intended to be developed has to be validated in the lab using an experimental chamber as domain for analysing accidental flammable gas leaks from transportation installations and for studying the formation, ignition and burning of air-flammable gas mixtures in confined spaces. Results obtained from physical experiments will be used for calibrating the mathematical models. Further, verification and validation of computational simulations carried out based on physical experiments will be performed by a comparative analysis of virtual results with the experimental ones. In the end, the mathematical model will be implemented on a small-scale reproduction of a confined industrial area with explosion hazard.

Journal of Loss Prevention in the Process Industries, 1991

The safety professional in the oil and petrochemical industry is continually involved in decision making in the areas of plant/facility siting, equipment layout and spacing for crosscountry pipelines, isolation and emergency shutdown systems engineering, land use and urban development in the vicinity of existing plants, wells or pipelines, emergency preparedness planning and disaster evacuation procedures. In many instances an effective way to assist in these decisions is to generate quantitative assessments of the risks and hazards associated with each available option. Expressions such as 'rupture exposure radius', 'hazard impact zone', 'risk transect' and 'risk contour plot' are frequently used to convey safety related concerns. Quantitative risk assessment commences by considering an imaginary, but plausible, incident involving accidental loss of containment of a toxic and/or flammable material. A numerical estimate of the unwanted consequences of this incident is then made on the basis of properties of the substance released, rate of release (instantaneous or continuous), rate of vaporization, and transport and dispersion of the vapour under given meteorological conditions. Mathematical modelling of these physical phenomena becomes an essential input to this process. In the aftermath of Bhopal, Mexico City, and Chernobyl, the number of available models has grown. The primary purpose of the paper is to provide background information on the practical uses of gas dispersion models. It does not provide an evaluation of any of the available models.

Journal of Loss Prevention in the Process Industries, 1991

A heavy gas/liquid spill and dispersion modelling system has been developed for estimating the hazard zones due to accidental spills of flammable or toxic chemicals such as propane, butane, chlorine and ammonia. It consists of three basic modules: the spill rate module for estimating the direct source term for an accidental release from refrigerated or pressurized storage; the pool spread and gas generation module for estimating the rate of spread of any liquid spill on a surface and the rate of gas generation (indirect source term) as a result of evaporation or boil-off from the pool; and the heavy gas spread and dispersion module for estimating time dependent downwind concentration distributions and hazard zones. The third module is based on advanced similarity modelling concepts. It incorporates the effects of gravity spread, atmospheric dispersion modified by the presence of the heavy gas cloud, heat transfer from the substrate, diffusion in the x-direction, and cooling and heating of the cloud by physical reaction and phase change of humidity in the air and heavy gas-liquid droplets. The latter effect is particularly important for releases of liquefied gases from pressurized storage where a large part of the spilled material ends up in aerosol form suspended in the gas cloud. The objective of this paper is to describe the basic equations used in the dispersion module in relation to the physical phenomena important in the behaviour of heavy gas clouds released from pressurized liquefied storage. Model comparisons with available field data from Maplin Sands, Thorney Island, China Lake and Frenchman Flats are presented. Results of comparative sensitivity runs are given for various scenarios such as refrigerated versus pressurized storage, diked versus unconfined spills, etc., demonstrating the capabilities of the modelling system and its usefulness in emergency planning and also as a safety design tool.

Journal of Loss Prevention in The Process Industries, 2011

Quantification of spatial and temporal concentration profiles of vapor clouds resulting from accidental loss of containment of toxic and/or flammable substances is of great importance as correct prediction of spatial and temporal profiles can not only help in designing mitigation/prevention equipment such as gas detection alarms and shutdown procedures but also help decide on modifications that may help prevent any escalation of the event.The most commonly used models – SLAB (Ermak, 1990), HEGADAS (Colenbrander, 1980), DEGADIS (Spicer & Havens, 1989), HGSYSTEM (Witlox & McFarlane, 1994), PHAST (DNV, 2007), ALOHA (EPA & NOAA, 2007), SCIPUFF (Sykes, Parker, Henn, & Chowdhury, 2007), TRACE (SAFER Systems, 2009), etc. – for simulation of dense gas dispersion consider the dispersion over a flat featureless plain and are unable to consider the effect of presence of obstacles in the path of dispersing medium. In this context, computational fluid dynamics (CFD) has been recognized as a potent tool for realistic estimation of consequence of accidental loss of containment because of its ability to take into account the effect of complex terrain and obstacles present in the path of dispersing fluid.The key to a successful application of CFD in dispersion simulation lies in the accuracy with which the effect of turbulence generated due to the presence of obstacles is assessed. Hence a correct choice of the most appropriate turbulence model is crucial to a successful implementation of CFD in the modeling and simulation of dispersion of toxic and/or flammable substances.In this paper an attempt has been made to employ CFD in the assessment of heavy gas dispersion in presence of obstacles. For this purpose several turbulence models were studied for simulating the experiments conducted earlier by Health and Safety Executive, (HSE) U.K. at Thorney Island, USA (Lees, 2005). From the various experiments done at that time, the findings of Trial 26 have been used by us to see which turbulence model enables the best fit of the CFD simulation with the actual findings. It is found that the realizable k–ɛ model was the most apt and enabled the closest prediction of the actual findings in terms of spatial and temporal concentration profiles. It was also able to capture the phenomenon of gravity slumping associated with dense gas dispersion.► A new CFD-based method is presented for modeling dense gas dispersion in presence of obstacles. ► The novelty lies in the use of turbulence model and the manner of resolution of domain geometry. ► Excellent fit of theory with experimental findings.

Journal of Hazardous Materials, 2010

Computational fluid dynamics (CFD) tools are increasingly employed for quantifying incident consequences in quantitative risk analysis (QRA) calculations in the process industry. However, these tools must be validated against representative experimental data, involving combined release and ignition scenarios, in order to have a real predictive capability. Forschungszentrum Karlsruhe (FZK) has recently carried out experiments involving vertically upwards hydrogen releases with different release rates and velocities impinging on a plate in two different geometrical configurations. The dispersed cloud was subsequently ignited and resulting explosion overpressures recorded. Blind CFD simulations were carried out prior to the experiments to predict the results. The simulated gas concentrations are found to correlate reasonably well with observations. The overpressures subsequent to ignition obtained in the blind predictions could not be compared directly as the ignition points chosen in the experiments were somewhat different from those used in the blind simulations, but the pressure levels were similar. Simulations carried out subsequently with the same ignition position as those in the experiments compared reasonably well with the observations. This agreement points to the ability of the CFD tool FLACS to model such complex scenarios even with hydrogen as a fuel. Nevertheless, the experimental setup can be considered to be small-scale. Future large-scale data of this type will be valuable to confirm ability to predict large-scale accident scenarios.

Computation, 2018

A hazardous release accident taking place within the complex morphology of an urban setting could cause grave damage both to the population’s safety and to the environment. An unpredicted accident constitutes a complicated physical phenomenon with unanticipated outcomes. This is because, in the event of an unforeseen accident, the dispersion of the hazardous materials exhausted in the environment is determined by unstable parameters such as the wind flow and the complex turbulent diffusion around urban blocks of buildings. Our case study focused on a diesel pool fire accident that occured between an array of nine cubical buildings. The accident was studied with a Large eddy Simulation model based on the Fire Dynamics Simulation method. This model was successfully compared against the nine cubes of the Silsoe experiment. The model’s results were used for the determination of the immediately dangerous to life or health smoke zones of the accident. It was found that the urban geometry ...