Correlations for flame speed and explosion overpressure of dust clouds inside industrial enclosures
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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ABSTRACT: Due to a great lack of knowledge related to the explosion severity of nanopowders, an experimental investigation was carried out on three kinds of nanopowders: carbon black, carbon nanotubes and aluminium. Tests were mainly conducted with a 20 L explosion sphere. Experimental results were then compared with the explosion data obtained for microsized powders. It was shown that the explosion severity of the tested nanopowders, as determined by the 20 L sphere, seems to represent an explosion risk lower than the one of micropowders in spite of the fact it have been thought that nanopowders would be drastically more reactive than micropowders. Consequently, a theoretical investigation was performed in order to evaluate the validity of the 20 L explosion sphere. It was shown that this standard tool should be modified in order to handle nanopowder specificities.
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ABSTRACT: This paper utilises FLUENT software to simulate the spraying and explosion of coal dust in a spherical explosion chamber. The influence of particle size on coal dust spraying is analysed. Explosion easily develops for small particle sizes under the same conditions of coal dust concentration and ignition temperature. For large-size coal dust particles, the speeds of release and transmission reduce dramatically due to lack of oxygen inside. Explosion is very difficult to develop in such conditions. Coal dusts with smaller particle size distribute uniformly in the chamber, whereas larger particles concentrate in parts of the chamber. The influence of coal dust concentration, ignition temperature and particle size on the pressure of coal dust explosion is also studied. The results show that, when ignition temperature is less than a certain value, the maximum pressure increases rapidly with the growth of ignition temperature. As ignition temperature is larger than the value, the change of the maximum pressure is small. The maximum explosion pressure increases first and then decreases with the increase of coal dust concentration. Because the inside of large size particles burn only partially due to lack of oxygen and slow combustion heat release and transfer, the decrease of the maximum explosion pressure is proportional with the increase of particle size.International Journal of Mining Reclamation and Environment 09/2014; 28(5). DOI:10.1080/17480930.2014.964041
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ABSTRACT: Dust explosion venting experiments were performed using a 20-L spherical chamber at elevated static activation overpressures larger than 1 bar. Lycopodium dust samples with mean diameter of 70 um and electric igniters with 0.5 KJ ignition energy were used in experiments. Explosion overpressures in the chamber and flame appearances near the vent were recorded simultaneously. The results indicated that the flame appeared as the underexpanded free jet with shock diamonds, when the overpressure in the chamber was larger than the critical pressure during the venting process. The flame appeared as the normal constant-pressure combustion when the pressure venting process finished. Three types of venting processes were concluded in experiments: no secondary flame and no secondary explosion, secondary flame, secondary explosion. The occurrence of the secondary explosions near the vent was related to the vent diameter and the static activation overpressure. Larger diameters and smaller static activation overpressures were beneficial to the occurrence of the secondary explosions. In current experiments, the secondary explosions only occurred at the following combinations of the vent diameter and the static activation overpressure: 40 mm and 1.2 bar, 60 mm and 1.2 bar, 60 mm and 1.8 bar.Journal of Loss Prevention in the Process Industries 11/2014; 33. DOI:10.1016/j.jlp.2014.11.012