Simulation of dust explosions in complex geometries with experimental input from standardized tests (original) (raw)
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2008
explosion venting is the most frequently used method for mitigating the effects from accidental dust explosions in the process industry. optimal design of vent systems and credible execution of risk assessments in powder handling plants require practical and reliable ways of predicting the course and consequences of vented dust explosions. The main parameters of interest include flame propagation and pressure build-up inside the vented enclosure, the volume engulfed by the flame, and the magnitude of blast waves outside the enclosure. extensive experimental work forms the empirical foundation for current standards on vent sizing, such as eN 449 and NFpA 68, and various types of software for vent area calculations simply apply correlations from these standards. other models aim at a more realistic description of the geometrical boundary conditions, as well as phenomena such as turbulent compressible particleladen flow and heterogeneous combustion. The latter group include phenomenolo...
Possibilities, limitations, and the way ahead for dust explosion modelling
2006
The purpose of the present paper is threefold. First, a brief review of modelling, main results, and preliminary conclusions from the DESC project are presented; current capabilities and limitations of the DESC code are discussed. Second, it will be demonstrated how a CFD-code for dust explosions can be used as a valuable tool by industry, consultants, researchers or regulatory authorities in order to fulfil more effectively the requirements of the ATEX directives. Third, some thoughts on the way ahead for dust explosion modelling are outlined in the light of both current knowledge about dust explosions, and inherent limitations in modelling capabilities of present CFD-codes.
Biomass dust explosions: CFD simulations and venting experiments in a 1 m3 silo
Process Safety and Environmental Protection, 2023
This study presents CFD simulations of biomass dust explosions in a newly developed experimental 1 m 3 silo apparatus with variable venting, designed and fabricated to operate similarly to the explosivity test standards. The aim of the study is to validate a CFD model under development and investigate its capability to capture the transient effects of a vented explosion. The model is based on OpenFOAM and solves the multiphase (gas-particle) flow using an Eulerian-Lagrangian approach in a two-way regime. It considers the detailed thermochemical conversion of biomass, including moisture evaporation, devolatilization, and char oxidation, along with the homogeneous combustion of gases, turbulence, and radiative heat transfer. The explosion is analyzed in all stages, i.e., dust cloud dispersion, ignition, closed explosion, and vented explosion. The results indicate excellent agreement between the CFD model and experimental tests throughout the sequence. Our findings highlight the critical role of particle size in dust cloud distribution and pre-ignition turbulence, which significantly influences flame dynamics and the explosion itself. This model shows great promise and encourages its application for future investigations of biomass dust explosions in larger-scale geometries, especially in venting situations that fall out of the scope of the NFPA 68 or EN 14491 standards, and to help design effective safety measures to prevent such incidents.
Flame Speed Measurements in Dust Explosions
The main objective of this work was the determination of the near-laminar and turbulent free flame speeds, and explosion enhancement factors of dust-air explosions in fire balls of approximately up to 1 m in diameter. Such information could find immediate application in the more effective design of dust-explosion protection systems in industry. In many respects, this work was a feasibility study and an evaluation of the capability of the proposed measurement techniques in delivering reliable data. Dust-air mixtures were exploded in a 1 m 3 industry standard vessel for the determination of explosion indices of dusts. Maize starch, phenolic resin, pulverised coal, biscuit flour and dried skimmed milk powders were tested. The tests were carried out under turbulent conditions of variable rms turbulent velocity, which was controlled by the ignition delay time from the onset of dust injection. The flame speeds and the K st values were measured at increasing ignition time delays and hence decreasing levels of turbulence, and were extrapolated to their laminar values (limit values at infinite time delay). A methodology was developed for dealing with problem of dust settlement, and other areas where further work is needed (such as the ignition mechanism) were identified. The laminar flame speeds and K st values for 5 dusts tested are reported. Maximum enhancements factors of up to 4 with regard to the laminar K st value were recorded in the ISO vessel, and up to about 6 with regard to the flame speed.
Determination of Fire and Explosion Characteristics of Dust
TRANSACTIONS of the VŠB – Technical University of Ostrava, Safety Engineering Series, 2016
The aim of this paper is to approximate danger of dust clouds normally occur by determining their explosion characteristics. Nowadays, dusty environment is phenomenon in the industry. In general, about 70% of dust produced is explosive. Dust reduction in companies is the main purpose of the national and European legislative. Early identification and characterization of dust in companies may reduce the risk of explosion. It could be used to identify hazards in industrial production where an explosive dust is produced. For this purpose several standards for identification and characterization of explosion characteristics of industrial dust are being used.
MATEC Web of Conferences, 2022
Many industrial processes involving the presence of dust and combustible dust, suspended or accumulated in the form of deposits, have the potential to lead to a fire, explosion or decomposition in the presence of oxygen. As the damage caused by an explosion of dust is generally greater than that caused by explosions of flammable gases and vapours, a special attention must be paid to measures and means of protection and prevention of explosions of dust. A dust explosion can only occur if there is mainly a potentially explosive atmosphere generated by the air / dust mixture and a source of ignition. The level of safety is given by the operational efficiency of the employees and technical equipment involved in the production process to ensure that at least one of the above conditions is eliminated. The probability of a dust explosion is related to the physicochemical properties of the processed materials, together with the nature of the operations performed and the equipment used. This...
Simulating Dust Explosions with the First Version of DESC
Process Safety and Environmental Protection, 2005
ESC is a new CFD-code that is being developed for simulating dust explosions in complex geometries. In the methodology followed, dust-air mixtures are ignited to deflagration in laboratory test vessels to provide information on fundamental flame propagation parameters. These quantities are subsequently used as input for combustion models in the CFD-code. Experiments were performed with maize starch in a 20-litre explosion vessel, the laminar burning velocity was extracted from the experimental pressure-time curve, and subsequently used to predict what might happen if the same mixtures would explode in larger geometries, namely, a vented silo, and, a system involving two interconnected vessels. The results presented in this paper are preliminary and serve as a proof of principle. Uncertainties and gaps in knowledge are identified in the light of this approach, and future challenges discussed.
The influence of air flow on maximum explosion characteristics of dust–air mixtures
Journal of Loss Prevention in the Process Industries, 2013
A standard spherical apparatus for measuring explosion characteristics was modified to give increased and controlled turbulence within a dusteair mixture. This was intended to mimic the local effects which may occur during industrial dust explosions, particularly secondary ones which may develop in ducts or mine galleries where the initial explosion causes an increased air velocity and suspension of further quantities of dust. The results show that there may be a doubling of the maximum explosion pressure and of the rate of pressure rise during the explosion under more turbulent conditions. This is significant for modelling of dust explosions and suggests that explosion relief may be inadequate if this factor is not taken into consideration. The modified apparatus therefore gives a laboratory method for assessing the effect of turbulence in dust explosions.