Sizing safety vents for non-tempered systems (organic peroxides): a new tool at lab scale

National audienceThis paper deals with the development of a new experimental “similarity” vent sizing tool for non tempered chemical system combining the advantages of both DIERS method (laboratory scale) and UN similarity method (less overconservative). This tool is an extension of the VSP2 (Vent Sizing Package II) adiabatic calorimeter. The objective of this new vent sizing tool is twofold. The first is to provide the required A/V ratio necessary to assure a safe relief. The second is to provide measurement of mass vented during blow-down. This paper gives a description of this tool and exposes the first promising results obtained. Its main limits are also given

Analyse de l'emballement thermique d'un système chimique hybride non tempéré

National audienceCe travail s'intéresse au “blow-down” (emballement thermique en présence d'un évent de sécurité) d'un système chimique non tempéré (30% CHP) soumis à un incendie. Il utilise une maquette à l'échelle 0,1 l. L'analyse des données post décomposition a montré que la vapeur présente est principalement un produit de la réaction. Toutes les expériences de blow-down ont présenté deux pics de pression, quel que soit le rapport A/V, ce qui est typique des systèmes non tempérés. Nous avons cependant constaté que la température maximale (Tmax) et la vitesse maximale de montée en température ( ) sont sensibles à la taille de l'évent. Nous avons de plus observé une corrélation de type Antoine entre Pmax et Tmax, avec Pmax plus faible que la pression d'équilibre. Cela montre que la cinétique de la décomposition de CHP est sensible à la vaporisation de ses propres produits. Pour le blow-down de CHP 30%, nous avons globalement identifié à la fois des caractéristiques communes avec ce qui se passe pour un système purement gazogène, et des différences importantes dues à l'influence de la vapeur formée

Une recherche partenariale appuyant l'évolution de la réglementation : Un cas délicat de dimensionnement d'évent pour le stockage de peroxydes organiques

National audienceLes dangers présentés par les peroxydes organiques sont très variés, et dans tous les cas, le risque d'emballement thermique, avec explosion pneumatique du contenant est à considérer. Dans le cas étudié, le danger de déflagration ou d'explosion pneumatique éliminé au niveau du stockage mère par l'emploi d'un emballage plastique de 35 litres peu résistant, réapparaît au cœur même de l'unité de polymérisation utilisant le peroxyde, car le concepteur a prévu un stockage tampon en cuve inox d'environ 1 m3 . La préparation de ditertiobutylperoxyde (DTBP) peut donner lieu à une explosion en phase gazeuse même sous azote, induisant éventuellement une déflagration de la phase liquide. Plus classiquement, on doit tenir compte du scénario d'emballement thermique du stockage menant à l'éclatement de la cuve, suite à un incendie extérieur ou à un auto-échauffement. Nous avons réalisé des essais à l'échelle de 0,8 - 10 et 20 litres, en modifiant des méthodes normalisées ou recommandées internationalement ; une évolution de ces méthodes sera proposée dans le futur. Nous avons pu ainsi étudier le couplage entre 'explosion en phase gazeuse et l'emballement thermique de la phase liquide pour le DTBP, et proposer au vu des résultats des recommandations pour réduire dès la conception de l'installation l'apparition de ce phénomène, tout en limitant la violence de l'emballement thermique s'il apparaît. La présente étude a aussi permis de contribuer à mieux comprendre comment établir le projet d'arrêté pour les cas très différents du stockage et de l'usage des peroxydes, dans le contexte de la révision de la nomenclature et les arrêtés relatifs au stockage et à l'utilisation des peroxydes organiques, au titre des Installations Classées pour la Protection de l'Environnement (ICPE)

Vent sizing: Analysis of the blowdown of a hybrid non tempered system

International audienceThe runaway and blowdown of a non tempered hybrid chemical system (30% cumene hydroperoxide) exposed to an external heat input was investigated using a 0.1 l scale tool. The maximum temperature and the maximum temperature rise rate were showed to be sensitive to the vent size. An Antoine type correlation between the maximum temperatures and pressures was observed. These resulted from the presence of vapour, mainly generated by the reaction products. Increasing the initial filling ratio resulted in an earlier vent opening but did not have a significant influence on the blow-down. Three types of mass venting behaviour were observed, when changing the vent area to volume ratio (A/V): * for large A/V, two-phase venting occurred from the vent opening until the end of the second pressure peak; * for medium A/V, two-phase venting occurred before and after the turnaround. The data seem to indicate that gas only venting occurred at turn-around; * for low A/V, two-phase venting was observed only after the second pressure peak. Two-phase venting after the second pressure peak probably results from the boiling of the hot reaction products at low pressure

Developing a Framework for Dynamic Risk Assessment Using Bayesian Networks and Reliability Data

PresentationProcess Safety in the oil and gas industry is managed through a robust Process Safety Management (PSM) system that involves the assessment of the risks associated with a facility in all steps of its life cycle. Risk levels tend to fluctuate throughout the life cycle of many processes due to several time varying risk factors (performances of the safety barriers, equipment conditions, staff competence, incidents history, etc.). While current practices for quantitative risk assessments (e.g. Bow-tie analysis, LOPA, etc.) have brought significant improvements in the management of major hazards, they are static in nature and do not fully take into account the dynamic nature of risk and how it improves risk-based decision making In an attempt to continually enhance the risk management in process facilities, the oil and gas industry has put in very significant efforts over the last decade toward the development of process safety key performance indicators (KPI or parameters to be observed) to continuously measure or gauge the efficiency of safety management systems and reduce the risks of major incidents. This has increased the sources of information that are used to assess risks in real-time. The use of such KPIs has proved to be a major step forward in the improvement of process safety in major hazards facilities. Looking toward the future, there appears to be an opportunity to use the multiple KPIs measured at a process plant to assess the quantitative measure of risk levels at the facility on a time-variant basis. ExxonMobil Research Qatar (EMRQ) has partnered with the Mary Kay O’Connor Process Safety Center – Qatar (MKOPSC-Q) to develop a methodology that establishes a framework for a tool that monitors in real time the potential increases in risk levels as a result of pre-identified risk factors that would include the use of KPIs (leading or lagging) as observations or evidence using Bayesian Belief Networks (BN). In this context, the paper presents a case study of quantitative risk assessment of a process unit using BN. The different steps of the development of the BN are detailed, including: translation of a Bowtie into a skeletal BBN, modification of the skeletal BN to incorporate KPIs (loss of primary containment (LOPC), equipment, management and human related), and testing of the BBN with forward and backward inferences. The outcomes of the dynamic modeling of the BN with real time insertion of evidence are discussed and recommendation for the framework for a dynamic risk assessment tool are made

Sécurité des procédés. Emballement de réaction. Dimensionnement des évents de sécurité pour systèmes gassy ou hybrides non tempérés : outil, expériences et modèle

258 pagesSafety vents allow avoiding explosion of chemical reactors in case of thermal runaway reaction. Vent sizing methods designed by the DIERS often lead to large oversizing for non tempered systems. An alternative method, based on the principle of similarity, was developed within UN for peroxide transportation. It provides more realistic vent areas but is very constraining. This PhD work allowed us to build a new similarity vent sizing tool: the 0,1 litre scale model. This new tool is based on the VSP2 adiabatic calorimeter. It allows for direct determination of the necessary A/V ratio at laboratory scale. It also allows real time measurement of vented mass during the relief. We validated the 0,1 litre scale model (1 x 10-3 m-1 Decomposition of the studied systems looks like that for a non tempered system (2 pressure peaks). However some products of the decompositions are vapour. These latter have a large influence on 2nd pressure peak. They slow the reaction and decrease the maximum reached temperature. One can even observe a correlation Pmax = f(Tmax). This behaviour could concern most decompositions (all ones?). Vented mass measurements allowed us to distinguish three types of behaviour which illustrate the influence of pressure in the vessel on level swell. Comparison with a purely gassy dynamic model showed that the vented mass can be either two-phase venting or an alternation of gas and two-phase venting. It also showed that purely gas venting occurs at turnaround for high pressures and that two phase venting during pressure decrease after the second pressure peak can only be explained by presence of vapour (boiling phenomenon). Finally, we identified the oversizing assumptions of the DIERS method for gassy systems. It appeared that, the main cause of oversizing is assuming that the turnaround is controlled by volume flow equality (volume vented = generated gas volume).Les évents de sécurité protègent de l'explosion les réacteurs chimiques sièges d'un emballement thermique de réaction. Pour les systèmes non tempérés (c'est à dire produisant majoritairement des gaz incondensables), les méthodes de dimensionnement des évents issues des travaux du DIERS sont très surdimensionnantes. Une méthode basée sur le principe de similitude, développée dans le cadre de l'ONU pour la famille des peroxydes, fournit des aires d'évent plus réalistes mais elle est très contraignante. Le présent travail a permis la réalisation d'un nouvel outil de dimensionnement en similitude pour scénario d'incendie : la maquette à 0,1 litre. Il s'agit d'une extension du calorimètre adiabatique VSP2. Cette maquette permet, à l'échelle du laboratoire, la réalisation de blowdowns et la détermination directe du rapport A/V de l'évent nécessaire, mais également le suivi en temps réel de la masse réactionnelle évacuée. Nous avons validé l'utilisation de cette maquette à 0,1 litre (1 x 10-3 m-1 Du point de vue compréhension, nos expériences montrent que, même si la décomposition de notre système ressemble à celle d'un système non tempéré (2 pics de pression), elle génère des vapeurs (produits de la décomposition) qui ont une forte influence sur le 2ème pic : ces vapeurs provoquent un ralentissement de la réaction et l'atténuation des températures maximales atteintes. On constate même une corrélation Pmax = f(Tmax). Ce comportement pourrait concerner la plupart (toutes ?) des décompositions. Les mesures de masse évacuée ont permis de distinguer trois types de comportements qui illustrent l'influence de la pression dans le réacteur sur le « level swell ». La confrontation avec un modèle dynamique purement « gassy » a montré que l'évacuation de masse réactionnelle peut se traduire par une évacuation purement diphasique ou par une alternance gaz/ diphasique, que pour les hautes pressions l'évacuation est purement gazeuse au turnaround et que l'évacuation diphasique lors de la dépressurisation du second pic doit être imputée en grande partie à la présence de vapeur (ébullition). Enfin, nous avons identifié et quantifié la contribution des différentes hypothèses au caractère surdimensionnant de la méthode DIERS appliquée à notre système hybride non tempéré. Parmi les hypothèses surdimensionnantes identifiées, celle qui suppose que le « turnaround » est gouverné par une égalité de débit volumique est de loin celle qui est la cause principale de surdimensionnement

A Medium-Scale Cryogenic Spill Study to Estimate Vapor Formation on Concrete Substrate

PresentationThis paper presents the findings of medium-scale (5 - 15 kg) cryogenic liquid experiments on a concrete substrate which may represent an industrial grade diking material. The temperature varying thermal characteristics, i.e. the conductivity (k) and heat capacity (Cp) of the concrete substrate were measured in the range of -160°C to 50°C using guarded hot plate and DSC, respectively. Vaporization rate of liquid nitrogen (LN2), liquid oxygen (LO2) and a mixture of 80% LN2 and 20% LO2, (i.e. liquid air) were studied on the same concrete substrate. It was found that conductive heat transfer from the concrete substrate has the greatest contribution in the vaporization of cryogenic liquids. The evidence of phase change from film boiling to nucleate boiling was observed during the pool vaporization of LO2. The effect of preferential boiling on the temperature and heat flux profiles inside the concrete substrate was also observed. The change of heat fluxes due to the preferential boiling after each refill of mixture liquids were found to vary from 3% to 15%. Finally, the recorded heat flux during the early and later stages of pool vaporization were 12.4 kW/m2 and 3.7 kW/m2 for LN2 and 12.9 kW/m2 and 2.96 kW/m2 for LO2

Use of a two-parameter Weibull distribution for the description of the particle size effect on dust minimum explosible concentration

Combustible dust explosion properties, like Minimum Explosible Concentration (MEC) and Minimum Ignition Energy (or Temperature), have a strong dependency on the particle surface area to mass ratio which varies with the particle size distribution. Unfortunately, the comparison of the dust explosion properties reported in the literature for a given dust material is often difficult because of the lack of description of the particle size distribution which is usually limited only to scattered information about the median (d50), mean, or one, two, or maximum three percentiles (e.g., d10, d50, and d90). This approach often gives conflicted conclusions or observations of no trend with measured independent parameters. It seems that a different approach is necessary to comprehensively describe the dependency of dust explosion properties on the particle size distribution. Such improvement could be achieved using a continuous probability distribution of which an example is a two-parameter normal distribution. However, the normal probability density function can only represent a symmetrical bell-shaped distribution which does not apply to the dust particle size analysis that often results in a skewed bell-shaped histogram. This study explored the use of a two-parameter (shape and scale) Weibull probability density function to describe a particle size distribution. A series of experimental data on the Minimum Explosible Concentration (MEC) of sulfur and polyethylene dust samples for which the particle distribution is measured were used to estimate the Weibull's scale and shape parameters. Two- and three-dimensional plots were generated to demonstrate the correlations of these parameters with MEC. The results show that as the scale and shape parameters increase, the MEC increases with higher dependence on the scale parameter (b). This is consistent with the initial conclusion where the MEC increases with increasing particle size. The paper discusses the advantages of using such an approach to describe the effect of particle size distribution on dust explosion properties but also shows that using only a median or mean of a particle size distribution to describe MEC may be misleading, especially if a sample represented by d50 as a coarse distribution contains a long tail of fine particles.Other InformationPublished in: Journal of Loss Prevention in the Process IndustriesLicense: http://creativecommons.org/licenses/by/4.0/See article on publisher's website: https://dx.doi.org/10.1016/j.jlp.2024.105269</p