Correlations for flame speed and explosion overpressure of dust clouds inside industrial enclosures

Facoltà di Ingegneria, Università degli Studi di Roma “La Sapienza”, Via A. Scarpa 16, 00161 Roma, Italy
Journal of Loss Prevention in the Process Industries (Impact Factor: 1.41). 07/2008; 21(4):374-392. DOI: 10.1016/j.jlp.2008.01.004

ABSTRACT Explosion relief vents on enclosures in powder-handling plants are currently designed according to technical standards that in some situations may overestimate the required vent area significantly. These technical standards sometimes do not take into account the real work conditions of industrial plants (e.g. turbulence intensity) and therefore explosion worst cases are not always foreseeable. The availability of methods either for the evaluation of explosion overpressure or sizing of relief vents, with involvement of the pre-ignition turbulence, could be very useful for a better estimate of these quantities. In this work two empirical correlations are presented: the first one allows the calculation of the flame speed and the burning velocity starting from the explosion indices KSt and Pmax of the standardized 20-l sphere test. The second allows either the calculation of the explosion overpressure or the sizing of relief vents of an enclosure.

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    • "Dust explosions pose a serious hazard to the process industry, as the majority of industrial plants store, handle or manufacture bulk solids and powders that are combustible (Abbasi & Abbasi, 2007; Barton, 2002; Eckhoff, 2003). Although the dust explosion phenomenon has been studied for more than thirty years (Cashdollar, 2000; Eckhoff, 2009; Silvestrini, Genova, & Trujillo, 2008), the frequent occurrence demonstrates that research in this area is still far from that required. From the point of industrial safety, prevention and protection measures are of great important. "
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    ABSTRACT: Ducts are often recommended in the design of dust explosion venting in order to discharge materials to safe locations. However, the maximum reduced overpressure increases in a duct-vented vessel rather than in a simply vented vessel. This needs to be studied further for understanding the duct-venting mechanism. Numerous duct-vented dust explosion experiments were conducted, using a 20 L spherical chamber at elevated static activation overpressures, ranging from 1.8 bar to 6 bar. Duct diameters of 15 mm and 28 mm, and duct lengths of 0 m (simply venting), 1 m and 2 m, were selected. Explosion pressures both in the vessel and in the duct were recorded by pressure sensors, with a frequency of 5 kHz. Flame signals in the duct were also obtained by phototransistors. Results indicate that the secondary explosion occurring in the duct increases the maximum reduced overpressure in the vessel. The secondary explosion is greatly affected by the duct diameter and static activation overpressure, and hence influences the amplification of the maximum reduced overpressure. Larger static activation overpressure decreases the severity of the secondary explosion, and hence decreases the increment in the maximum reduced overpressure. The secondary pressure peak is more obvious as the pressure accumulation is easier in a duct with a smaller diameter. However, the increment of the maximum reduced overpressure is smaller because blockage effect, flame front distortion, and turbulent mixing due to secondary explosion are weaker in a narrow duct. The influence of duct length on the maximum reduced overpressure is small at elevated static activation overpressures, ranging from 1.8 bar to 6 bar at 15 mm and 28 mm duct diameters.
    Journal of Loss Prevention in the Process Industries 11/2014; 32(1). DOI:10.1016/j.jlp.2014.07.016 · 1.41 Impact Factor
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    • "), the flame path distance and the laminar flame speed of the flammable gas (Chen, Qin, Xu, Ju, & Liu, 2007; Pfahl, Ross, Shepherd, Pasamehmetoglu, & Unal, 2000; Silvestrini, Genova, & Trujillo, 2008) which were derived by using the idealized experimental programs' data, the new correlation was deduced with a set of parameters by means of the linear least square method to describe the obstructed region and the fuel properties in the vapor cloud explosion. "
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    ABSTRACT: In this study, we present a newly developed correlation for the estimation of boundary overpressures in and around congested regions subjected to vapor gas explosions. The GAME correlation, which is based on the MERGE, EMERGE experimental programs, shows rather moderate correlation with Computational Fluid Dynamics (CFD) results in homogeneously congested configurations, however, a greater level of inaccuracy is found when it comes to the combination of a number of realistic scenarios. The newly developed model (confinement specific correlation), which consists parameters of volume blockage ration, the density of the gas, the flame path distance, the confinement ratio and the laminar flame speed of the flammable gas is proposed as a non-dimensional alternative and it shows a closer correlation with detailed CFD simulation in general particularly for realistic geometries. A linear least square method is used to achieve the best fitting parameters by applying the validated commercial software FLACS. About 400 CFD cases with homogeneous congestions are modeled using FLACS for the purpose of testing both the GAME correlation and the confinement specific correlation (CSC). In addition to those 400 CFD homogeneous cases, around 700 realistic cases in ten different module scenarios of a Liquefied Natural Gas (LNG) train along with three simplified models are simulated to validate the CSC; it is found that the CSC is applicable to both realistic modules with irregular obstacles and homogeneous artificial modules.
    Journal of Loss Prevention in the Process Industries 09/2014; 31(1). DOI:10.1016/j.jlp.2014.05.013 · 1.41 Impact Factor
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    • "Paul et al. [11] discussed various ways in which the dust explosion hazard can be mitigated to complement the relatively well-established suite of engineering and procedural dust explosion risk-reduction measures . Silvestrini et al. [12] presented two empirical correlations to improve the disadvantages of previous methods. Eckhoff discussed how comprehensive numerical simulation models can promote the development of means for prevention and mitigation of dust explosions in practice [13]. "
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    ABSTRACT: This paper presents the results of experimental investigation on characteristics of methane-coal dust mixture explosion and its mitigation by ultra-fine water mist. Four E12-1-K type fast response thermocouples, two PCB piezotronic pressure transducers were used to obtain the temperature and pressure history of methane-coal dust mixture explosion and its mitigation by ultra-fine water mist, while a GigaView High-speed camera was used to visualize the processes. Different methane concentrations, coal dust concentrations, diameters of coal particles and volumes of ultra-fine water mist were considered for their effects on methane-coal dust mixture explosion. The temperature of explosion flame, the maximum explosion overpressure, the maximum rate of overpressure rise, and the critical volume flux of ultra-fine water mist were experimentally determined. The results show that the characteristics of the methane-coal dust mixture explosion and the mitigating efficiency by ultra-fine water mist are influenced by the methane concentration, the coal dust concentration, the coal dust diameter and the applied volume flux of ultra-fine water mist. For example, both the maximum explosion overpressure and rate of overpressure rise increased with increasing of coal dust concentrations and methane concentrations. All of the test cases indicate that ultra-fine water mist can mitigate the mixture explosion and suppress the flame propagation efficiently from the images record by high speed video camera.
    Journal of Engineering for Gas Turbines and Power 06/2012; 134(6):061401-061406. DOI:10.1115/AJTEC2011-44250 · 0.80 Impact Factor
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