Evolution des méthodes de protection des procédés industriels contre les effets des explosions : le projet DELFINE)

National audienceClassical methods for vent sizing are based on experimental correlations coming from academic test situations, sometime quite different from real industrial conditions. Thus, they do not take into account the variation of turbulence in industrial enclosures, which may alter drastically the explosion violence. The DELFINE installation presently in construction will allow studying dust explosions in real working conditions of a dust collector. Preliminary experiments in an instrumented small size filter are presented, which allow characterizing the turbulence level in every work phase of the system. It appears that the turbulence level is generally lower than in the standard conditions for vent testing, even during reverse jet cleaning. It should offer perspective for optimization of the venting areas for dust collectors. Explosion tests in real conditions on the DELFINE installation will be performed to try to confirm these first observations.Les industries de la chimie, du bois et de l'agroalimentaire concentrent plus de 80% des explosions de poussières recensées en France au cours des 100 dernières années [1]. Pour cette raison il existe aujourd'hui un secteur industriel qui propose des solutions de maîtrise des risques d'explosion de poussière et met sur le marché, qui des technologies de protection, qui des appareils équipés de ces technologies dès la conception. Si des normes relatives à ces stratégies industrielles ont été proposées comme pendant à la Directive ATEX [2], il a été observé qu'elles étaient loin de couvrir la réalité des procédés industriels. Cela est perçu comme un obstacle majeur à l'ingénierie de la sécurité des procédés puisqu'on ne possède pas de " méthodes d'ingénieur " suffisantes. L'objectif du projet DELFINE qui réunit les moyens de FIKE Corp. (producteur de systèmes de protection), de DELTA NEU (producteur de process industriels de filtration) et de l'INERIS (Expert de la phénoménologie de l'explosion) est de promouvoir des méthodes de dimensionnement des systèmes de protection en commençant par la technologie des évents. On présente dans cette communication les résultats obtenus au plan de la modélisation phénoménologique du développement des explosions dans les systèmes industriels (réseaux d'enceintes et de canalisations) et les premiers résultats expérimentaux obtenus à l'échelle réelle au moyen d'une boucle d'essai de dépoussiérage spécialement conçue pour le projet

Are we sure that certified safety systems are really safe ?

CEN bodies produced a significant number of standards explaining how safety devices should be tested so as to be EN certified. However, if the real applications are considered from the physical point of view, it appears sometimes that the prescription of the tests are far from the real situation or that the experimental conditions would not permit to tackle the most dangerous situation. A discussion is proposed and a vision is proposed to try and surpass these limitations

Dynamics of vented hydrogen-air deflagrations

International audienceThe use of hydrogen as an energy carrier is a real perspective for Europe since a number of breakthroughs now enable to envision a deployment at the industrial scale. However some safety issues need to be further addressed but experimental data are still lacking especially about the explosion dynamics in realistic dimensions. A set of hydrogen-air vented explosions were thus performed in two medium scale chambers (1m3 and 10m3). Homogeneous mixtures were used (10% to 30% vol.). The explosion overpressure was measured inside the chamber and outside on the axis of the discharge from the vent. The incidence of the external explosion is clearly seen. All the results in this paper and the predictions from the standards differ greatly meaning that a significant effort is still required. It is the purpose of the French project DIMITRHY to help progressing

Function Testing of Passive Explosion Isolation Flap Valves

Passive isolation flap valves are relatively simple devices that are widely used in the process industries. However, as an explosion mitigation technique, they function only within well-defined conditions and the physics at stake make their definition challenging. INERIS method and findings are presented in the current paper. They concern passive flap valves tested on 1 and 10 m3 vessels with pipes of diameters of 150, 300 and 800 mm. The relatively simple configuration of a flap valve connected to a vented vesselstraight duct arrangement is considered. The initially opened flap valve is triggered by the explosion in the vessel and must close within a delay, short enough to prevent the flame passing. Before valve closure, the flow is accelerated by the explosion and large velocities can be reached in the duct (typically on the order of 200 m/s with a vented vessel, but as much as 800 m/s is possible). Upon valve closing the kinematic energy of the flow is converted into heat and pressure in front (on the explosion side) of the valve while a depressurisation is observed behind it (on the isolated side). Typically, a factor of 4 between the pressure in the vessel and the pressure measured at the valve can be observed. Phenomenological modelling is used in extension to a parametric experimental study to investigate the limits of the valve, its possible installation distances and a practical method for dimensioning is proposed

Influence of vent distribution on the violence of a gas explosion

International audienc

External effect of a vented explosion

International audienceVarious investigators noted that very significant explosions could result from the formation and ignition of a large combustible cloud following from a primary vented explosion. This phenomenon is sometimes referred to as " secondary explosion ". A systematic full scale experimental work (with vessel sizes ranging from 1 m3 to 100 m3 mixture of methane, propane and hydrogen with air) has been performed over a period of several years to understand better the underlying physics. Surprising results were obtained showing for instance that near the vent the maximum overpressure may be lower than further downstream not because the external explosion is developing far downstream but because of the local influence of rarefaction waves produced at the vent. With help of high speed videos the nature and characteristics of the external cloud has been understood and the type of combustion studied. With this knowledge the nature of the interaction with the internal explosion has been clearly identified suggesting models to represent all the phenomenology

Impact of photovoltaic power plants on far-field effects of UVCEs

International audiencePhotovoltaic power stations are developing worldwide as they emit no greenhouse gases while producing electricity. In France, industries such as Total plan to install such stations in fields surrounding their chemical and refining plants. The risk analyses performed for these plants often highlighted Unconfined Vapor Cloud Explosions scenarios, related to heavy gases releases, for which characteristic overpressure effect distances were computed The present work aims at quantifying the impact of the presence of a photovoltaic power station in a potential flammable cloud. It is nevertheless limited to a station geometry provided by Total. The problem is not straightforward as two main physical trends appear: flame acceleration due to panels obstruction and flame extinction when the flame reaches the top of the flammable cloud. It has first to be determined if explosion runaway is possible, this one due to the obstacles repetition on the flame path. Then, characteristic overpressure effects distances can be computed for photovoltaic power plants of any size. To this goal, a CFD-based method is proposed and detailed. The open-source CFD code OpenFoam is used as well as phenomenological considerations for computing characteristic overpressure effects distances

Differentiated routes for the simulation of the consequences of explosions

International audienceThe use of numerical modelling is a "natural" step in today's engineering work, even in safety. Up to a certain extent, solving more or less accurately the basic Navier-Stokes equations has replaced the traditional analytical approximate solutions of the same equations. Doing this, we surely have gained in flexibility, sometimes in accuracy, but we may have lost in expertise and ergonomics. In this paper, different modelling techniques are set in perspective for the specific case of explosions. It is the opinion of the authors that simple physical "modelling" is justified in areas where a consensus is required on "basic" approaches such as standards, that complex numerical modelling is particularly fruitful in research, and that some intermediate "phenomenological" modelling is possible and proves profitable for process safety. Examples of such tools are given and compared to existing data