查看更多>>摘要：To comprehensively investigate the pressure influence on the flammability limits and explosion pressure of ethane and propane, a high-pressure slender cylindrical vessel with an effective length and diameter of 36.2 cm and 5 cm was used to simulate the explosions occurring in tubing-like space. Coiled tungsten hotwires with high-ignition energy were used as the ignition source during end-wall ignition. The lower flammability limit was assessed for ethane and propane under high pressures up to 15 MPa. A logarithmic dependence of pressure on flammability limits was observed in the examined pressure range. Comparing the lower alkanes data revealed that with rising carbon numbers, the lower flammability limit reduced. The impact of initial pressure on the upper flammability limit of ethane and propane was carried out below 5 MPa and 2.5 MPa, considering the liquefaction of ethane and propane under elevated pressures. For evaluating UEL data for C2H6/C3H8 in the air at high pressure, algebraic equations were developed. Due to the higher combustion heat and adiabatic flame temperature of C2H6 and C3H8, the explosion pressure of them was higher than that of CH4, and propane produced the highest explosion pressure. The explosion pressure varied approximately linearly with the initial pressure. Because of the low concentration of combustible gas at the lower flammability limit, the explosion pressure was lower than that at the upper flammability limit. The underlying mechanism for the pressure dependence of the LFL is correlated to the combustion heat.
Fagundes J.M.Alberton A.L.Gaya de Figueiredo M.A.Antonio Luquetti dos Santos I.J....
24页
查看更多>>摘要：This article presents a methodology for accident analysis developed from the combination of CAST - Causal Analysis based on System Theory, derived from the STAMP (Systems-Theoretic Accident Model and Process) accident causation model and the human error analysis/investigation tool TRACEr (Technique for the Retrospective and Predictive Analysis of Cognitive Errors). This combination was proposed from the perceived need to structure one of the stages of the application of the CAST technique where unsafe control actions, or human errors, that occurred in the course of accidental events are analyzed, for which the application of the TRACEr technique proved extremely useful. From the application of the proposed combination to an accident that occurred in an oil production unit in operation on the coast of southeastern Brazil, it was possible to obtain a deeper understanding of the psychological phenomena that preceded one of the unsafe control actions, as well as the identification of performance shaping factors that contributed to its occurrence. These results demonstrated the conceptual cohesion and mutual complementarity of the associated techniques, which allowed a comprehensive understanding of the accidental event and, consequently, the elaboration of safety recommendations more appropriate to the findings of the analysis, better specified to the aspects of human factors involved.
查看更多>>摘要：Knowledge of the explosion limiting concentration of explosible materials is necessary for the design of explosion protection measures. Currently employed methods of testing the minimum explosible concentration (MEC) of a dust cloud or the lower explosion limit (LEL) of a hybrid mixture are based on arbitrary assumptions and possess technical limitations that often lead to values of MEC/LEL, which are unrealistically low or poorly reproducible. This contribution presents an improved method for the experimental determination of the MEC of a combustible dust cloud or the LEL of a flammable gas or a hybrid mixture. The new set-up operates under laminar conditions and allows a uniform suspension of dust particles in an open top acrylic glass tube. Dust concentration is measured with the help of infrared sensors installed a few centimeters above and below the ignition source. In order to evaluate the dependence of MEC on flow front velocity, MEC of lycopodium was determined at four flow velocities. The results show that the flow field intensity does not significantly influence the MEC of lycopodium for the flow ranges tested in this work. Moreover, LEL of hybrid mixtures of lycopodium and methane was also tested at flow velocities of 4.7 cm/s, 5.8 cm/s, 7 cm/s and 11 cm/s and compared with the values obtained from other sources. The results suggest that the requirement of high energy pyrotechnical igniter may be relinquished, provided that a truly homogeneous suspension of dust particles could be achieved. Moreover, the effect of relative amount of dust and gas, on the course of ignition and flame propagation in hybrid mixtures at their LEL, was studied by the help of high speed videos. For hybrid mixtures of carbonaceous dusts (like lycopodium) at their LEL, ignition occurs in the gas phase, however, flame propagation is only possible through a two-way interaction of dust and gas during the course of combustion.
查看更多>>摘要：The case of a gas explosion occurring in a geometrically simple enclosure, equipped with a vent is considered. It is well known in the gas explosion scientific community that the calculation of the reduced explosion overpressure, determinant in safety studies, is not trivial. Not only there is a strong dependency on the chemical kinetics of the combustible but also on the enclosure geometry, the fluid flow, the vent mechanical behaviour, shape, etc … As a result, the modelling of the physics at stake is challenging, a wide range of models are proposed in the scientific literature and this reference situation is still the object of extensive research. A new simulation approach ignoring a large part of the underlying physics is investigated. It is based on the use of an artificial neural network (ANN). The focus is given on the method of use and results obtained with the ANN rather than on the neural network itself. Our observations are discussed within the scope of industrial safety problems. Calculations performed with the relatively simple ANN proposed in the official TensorFlow tutorial, on a vented explosion database containing 268 tests, led to surprisingly good results considering the ANN implementation efforts. The tool might look promising but is also far from being as trivial as it seems at a first glance: not only the results of simulations obtained with this type of model must be examined with the greatest care but also the initial data base must be very well controlled. Routes are proposed to enhance the initial database and perform relevant analyses of the neural network predictions.
查看更多>>摘要：The effects of vent area on pressure and flame evolution in a 1 m3 vessel with and without obstacles were investigated. Five pressure peaks of Popen, Pout, Pext, Phel, and Pvib, which correspond to vent activation, flame venting, external explosion, Helmholtz oscillation, and the coupling of acoustic waves and flames, respectively, were observed without obstacles when the vent coefficient Kv ≤ 6.25. However, the pressure peaks of Pext and Pout from the external explosion and flame venting disappeared when Kv > 6.25. Moreover, the pressure peaks of Popen and Pvib produced by vent activation and acoustically enhanced combustion become dominant when Kv ≥ 12.5. With the installation of obstacles, the pressure peak Pvib induced by acoustically enhanced combustion disappeared. The other four pressure peaks were observed when Kv < 6.25. The pressure peaks induced by the external explosion and the Helmholtz oscillation disappeared when Kv ≥ 12.5. Nevertheless, the pressure peak resulting from the obstacles was observed and became dominant at Kv ≥ 12.5. It takes less time for the external flame to propagate to the maximum displacement in the tests with obstacles than that without obstacles, and the maximum flame length for the former is smaller than the latter.
查看更多>>摘要：The research is aimed at promoting the suppression of gas explosion accidents. Gas explosion suppression experiments were performed in a 20 L spherical test apparatus with fly ash (FA) and modified fly ash (MFA) as explosion suppressants, and the effect of residual carbon in FA on the gas explosion was explored. The experimental results show that both FA and MFA have a good suppression effect on gas explosions. Under the same conditions, the explosion suppression effect of FA is superior to those of MFA and CaCO3. In addition, the thermal characteristics of FA and MFA were investigated by means of simultaneous thermal analysis. Based on the difference in the composition of FA before and after the explosion, it is found that residual carbon will participate in the explosion reaction, and residual carbon can enhance the explosion suppression effect. The explosion suppression efficiency of FA is at most 4.05 % higher than that of MFA under the same conditions. Finally, the explosion suppression mechanism of FA was expounded.
查看更多>>摘要：Prediction of state of health (SOH) of lithium-ion batteries can extend the service life of the batteries and improve the safe performance of the batteries, which is of great significance to research and development of lithium-ion batteries. Aiming at the problems that the discharge current of electric vehicles constantly changes under actual operating conditions and the number of full charge-discharge cycles is small, a battery health prediction model based on capacity decay rate is proposed. In this paper, the ternary cathode material power lithium-ion battery with a rated capacity of 5Ah is taken as the research subject, and the discharge experiment is conducted under the conditions of ambient temperature of 0 °C, 10 °C, 20 °C, 30 °C, and 40 °C. By fitting the curve of the battery capacity with the number of cycles, the decay rate of the battery capacity with the number of cycles is obtained.
查看更多>>摘要：Computational fluid dynamics (CFD) has been increasingly applied to process safety studies involving scenarios of accidental gas explosions. By offering a deeper understanding of the underlying physics of flame propagation, CFD can improve existing consequence analysis and risk assessment, particularly when confinement or obstructions are present. In the numerical modelling of gas explosions, the reaction rate is a quantity of fundamental importance because it ultimately leads to the values of flame speed and peaks of overpressure. In this work, we investigate the reaction rate models implemented in the CFD tool STOKES, which has been designed for the simulation of gas explosions in complex geometries. STOKES counts on the Bray–Moss–Libby (BML) reaction rate model, where the effects of flame stretch are neglected in its original version, which may lead to an inaccurate representation of the flame behaviour. Also, the length scale of wrinkling is often calculated as a function of the velocity fluctuations via empirical correlations that depend on adjustable constants. In a first approach, we propose an expression for calculating the stretch factor dynamically, based on the local divergence of velocity. In a second approach, a hybrid reaction rate model is presented, incorporating the well-known fractal approach into the BML model. The hybrid approach also counts on the calibration of parameters of the initial laminar burning model. Despite some improvement, the proposed dynamic stretch factor leads to unexpectedly enlarged flame contours. Results using the hybrid approach on the other hand improved agreement with experimental data, particularly in the early stages of flame acceleration when combustion chambers of relatively small sizes are considered. However, applications in real-scale semi-confined geometries indicate that the initial stages of flame development require further work.
查看更多>>摘要：Offshore drilling operations face technological and operational challenges combined with harsh environmental conditions. The well blowouts are the most feared offshore process operational accident. Many methodologies have been proposed to assess the blowout risk. Most of these studies consider the risk factors' independence and focus on a specific drilling life cycle stage. This study presents an integrated methodology that considers the interaction among the drilling risk factors and assesses the blowout risk throughout the deepwater drilling operation's lifecycle. This integrated methodology is developed based on the index-based risk evaluation system, which comprises hazard identification, interaction analysis, indices weights, and risk evaluation. The Decision Making Trial and Evaluation Laboratory method is used to identify and assess risk factors' interaction. The uncertainty associated with the data is addressed using the Z-numbers method. The risk indices are dynamic to capture the hazards during the lifecycle of the drilling operation. The application of the methodology is tested on a deepwater drilling operation. The application demonstrates the methodology's effectiveness in assessing and evaluating blowout risk during the drilling operation lifecycle.
查看更多>>摘要：The control of the risks associated with major hazard events is critical to the safe and continuous operation of the process industry. Over the last decades, the process industry has been successful at establishing and implementing robust Process Safety Management (PSM) systems to prevent and mitigate the consequences of such major hazard events. While there exist some industry guidelines developed relatively recently for events initiated by natural disasters and security-related threats, for initiating events like outbreaks of pathogens and pandemics, there is currently a clear lack of understanding of the impact of the restrictions and disruption caused by a pandemic on the ability of companies operating major hazard facilities to keep controlling the risks associated to their hazardous operations. Moreover, there is no industry guideline on how to account for such an impact in PSM systems for process safety hazards. The recent COVID-19 outbreak caused serious disruptions to normal operations that have challenged industry in their ability to control risks. The objective of this paper is to perform an analysis of the impact of a pandemic situation on the implementation of selected elements of PSM systems related to the identification and evaluation of the risks of a major hazard and their control. The approach chosen involves the analysis of the root causes of the failure of the selected PSM elements using a Fault Tree Analysis method. The findings provide the first steps in the establishment of recommendations for the upgrade of PSM systems to face events such as pandemics.
NSTL
Elsevier