Near Field Effects of BLEVE Overpressure Hazard

Near Field Effects of BLEVE Overpressure Hazard Roland Eyssette Department of Mechanical and Materials Engineering, Queen’s University, Kingston, Canada Synopsis The Boiling Liquid Expanding Vapor Explosion (BLEVE) has been a topic of interest for several decades [1]. However, the effect of the shockwave generated by such an explosion on near surrounding structures is still not well defined. Small scale experiments have been set up to create a realistic pressurized vessel failure, aiming to determine the contribution of the vapor expansion and liquid boiling in the shockwave strength. Numerical simulations are run alongside the experiment to give validation and to expand results to cases the experiment can’t model. Introduction A BLEVE is a serious accident occurring in the landscape of industrial risks. Many hazards are associated to this type of event, including fireballs, projection of vessel pieces and blast overpressure [2]. Blast overpressure is critical on the surrounding environment of the vessel, especially structures (buildings, bridges) and potential fatalities. The study of this hazard involves the understanding of the physics of compressed gas expansion, superheated liquid boiling and non-equilibrium phase change that are triggered after failure in and outside of the vessel. CFD and experiments aim to understand the BLEVE physical phenomena. Methods and Results Based on a real scale vessel failure apparatus [3], a small scale apparatus was set up for realistic vessel failure modelling (Figure 1). Overpressure data were obtained using blast gages and high speed imaging to measure the direct impact of the shock on the surrounding (Figure 2). Load cells measure the ground impact (Figure 3). High-speed imaging allows for the observation of the phase change and subsequent timing of the release shock and overpressure [4].These experimental results are compared with numerical models to validate the overpressure and impulse measurements [5]. Maximum overpressure and impulse are comparison criteria for studies involving different compressed gases. Transient simulations were also used to understand the phenomenon at an engineering level through FLUENT. From simple gas explosion models, such as 1D shock tube and open- ended shock tube (Figure 4), to a more complex and realistic model, different phase configurations will be simulated.

Figure 1. Small scale BLEVE experiment Figure 2. Overpressure measurements

Figure 3. Load measurement on small scale experiment Figure 4. Topology of shock diffraction through CFD of OEST Conclusions The current results show that the main contribution of the lead shock is due to vapor expansion. However, the flashing liquid maintains the pressure long enough in the tube to trigger catastrophic failure. CFD reveals that the amount of energy stored in the tube before an explosion does not change the overpressure of the shock, but induces different patterns of propagation, like under-expanded shocks. Modelling the phase change numerically is the next objective for phase contribution understanding. References [1] Reid R. Possible Mechanism for Pressurized-Liquid Tank Explosions or BLEVE’s. Science (1979) [2] Abbasi T. and Abbasi S.A. The BLEVE: Mechanism, consequence assessment, management. Journal of Hazardous Materials (2007) [3] Birk A.M, Davison, C. and Cunningham M. Blast overpressures from medium scale BLEVE tests. Journal of Loss Prevention in the Process Industries (2007) [4] Chen S. Sun J. and Wan W. BLEVE:Experimental research in the evolution of the two- phase flow and over-pressure. Journal of Haardous Materials (2008) [5] Van den Berg A. Blast Chart for Explosive Evaporation of Superheated Liquids, American Institure of Chemical Engineers Process Safety Progress (2008)