Vincenzo Tufano

Numerical simulation of gas explosions in linked vessels

The ability of the CFD code AutoReaGas to simulate a gas explosion in two linked vessels was investigated. These explosions present an anomalous destructive power because both peak pressures and rates of pressure rise are much higher than those generated in single vessel explosions. A fair agreement was observed between the computed results and experimental data taken from literature. Moreover, the computed values of the turbulence intensity at varying diameters of the connecting pipe demonstrate that turbulence induced in both vessels represent a major factor affecting the explosion violence.

Simulation of VCEs by CFD modelling : an analysis of sensitivity

Abstract The AutoReaGas code developed by TNO and Century Dynamics Ltd has been utilized to simulate the occurrence of a Vapour Cloud Explosion in a large fuel storage area. The sensitivity of the results to the main input variables has been investigated, together with the effect of fuel amount and fuel concentration inside the cloud. The marked sensitivity to several adjustable parameters, such as the turbulent modelling constant Ct, shows that the use of Computational Fluid Dynamics codes is not a straightforward task but still requires an adequate skill. From the whole set of computed results, some suggestions are derived, in order to improve the predictive power of the code.

Post-Accident Analysis of Vapour Cloud Explosions in Fuel Storage Areas

A Vapour cloud explosion which occurred in a large fuel storage area close to the harbour of Naples (Italy) was analysed by different methods. Useful ‘experimental data’ were obtained by the post-accident damage analysis (minimum overpressure experienced by different items) and by the seismograms recorded at different stations at the time of explosion (explosion duration and intensity). The analysis of the seismic data allowed a first estimate of the amount of vaporized fuel. A more accurate estimate was obtained by modelling the rate of evaporation of the liquid fuel and the vapour cloud dispersion in the surrounding atmosphere. The dispersion calculation furnished the input data for the CFD gas explosion simulator AutoReagas and constituted the basis for a sensitivity analysis of the results to the amount of fuel involved in the explosion. The results obtained with the different methods above were critically discussed and compared to the results obtained with the Multi-Energy method.

Influence of Solid Phase Thermal Properties on Flame Spread over Polymers

Abstract To determine the influence of solid phase thermal properties on the laminar flame spread over polymer sheets, several experiments were carried out to measure the spreading velocity of polymethyl met-acrylate (PMMA) and polystyrene (PS) samples modified by the addition of copper wires, metallic foils and metallic and inert powders. A mild but not negligible influence of the thermal diffusivity on the spread rate was detected.

Overall Kinetic Parameters and Laminar Burning Velocity from Pressure Measurements in Closed Vessels

Abstract The experimental pressure-time patterns measured during methane-oxygen-nitrogen explosions in a constant-volume bomb were analyzed by means of a lumped-parameter mathematical model. The use in this model of two explicit expressions for the dependence of the laminar burning velocity on pressure, temperature and composition derived from the solutions of the flame equations obtained by asymptotic methods, allowed the evaluation of the kinetic parameters of the overall reaction of combustion, and of the laminar burning velocity. A method of data analysis based on the concepts of non-linear identification was used to increase the accuracy of computations. The computed results, both for the laminar burning velocity and for the overall reaction rate, fairly agree with literature data.

On the design of venting systems against gaseous explosions

Abstract A lumped parameters mathematical model for the venting of gaseous explosions has been used to analyze a wide set of experimental data taken from the literature. The values of a “turbulence factor”, that account for the increase in the laminar burning velocity due to the flow field generated inside the vessel by the effluent gases, have been computed by fitting the model to the experimental maximum explosion pressure. These values have been satisfactorily correlated to the breakout pressure and to the vent area. A diagram, based on this correlation and on the mathematical model, is proposed for the evaluation of the required vent area as a function of the breakout pressure and of the maximum allowable overpressure. This diagram may be used with confidence for hydrocarbon—air mixtures over a wide range of breakout pressures and vent areas.

Analysis and design of venting systems: A simplified approach

Abstract Crescitelli, S., Russo, G. and Tufano, V., 1979. Analysis and design of venting systems: A simplified approach. Journal of Occupational Accidents , 2: 125–133. The use of light vent panels has become common practice for avoiding internal explosions in process vessels. The purpose of such devices is to provide a large venting area to stop any accidental pressure rise reaching a dangerous value. However, the design procedure does not yet seem well established, because the phenomenon which needs to be modelled is a typically unsteady one, and some little-known factors, such as the rate of pressure rise in the vessel, must be taken into account. Moreover, the geometry of the apparatus, mainly the characteristics of the tubes which lead the overpressure outside the protected area, affects the effectiveness of the apparatus design. In this paper, a mathematical model, which takes into account the main features of the phenomenon, is presented for the case in which the pressure rise is due to a deflagration in a combustible gaseous mixture. An attempt is made to establish a reliable design procedure for the venting devices; also the main problems which require more experimental and theoretical work are pointed out.

Modeling runaway reactions in reactors protected with suppression systems

Abstract A mathematical model has been developed for simulating the operation of a system for the protection of chemical reactors against runaway reactions, whi The model has been evaluated with physical and chemical data taken from the literature. The early detection of the runaway and the allowance for a suit In the case examined, which may be considered representative of a large number of real cases, the protection of the reactor appeared possible with reas

The influence of different diluents on the flammability limits of ethylene at high temperatures and pressures

Abstract For the safe design and operation of many chemical processes, it is necessary to know certain flammability limits at high temperatures and pressures. Despite the great importance of such safety problems, few data are available in the literature, and those available are unreliable. This is due to the experimental difficulties involved. In this paper the different methods proposed for such measurements are critically discussed: the double-filling system appears to be the most suitable for avoiding the slow oxidation reactions before ignition. Flammability data up to 250°C amd 20 atm for ethylene-oxygen mixtures with different diluents (nitrogen, carbon dioxide, methane) are presented.

A Model-Based Control Scheme for Chemical Batch Reactors

In this paper, a model-based temperature control scheme for batch chemical reactors is proposed. A controller-observer scheme is designed, where a nonlinear observer is adopted to estimate the heat released by the reaction. The controller is based on the closure of two feedback loops, thus ensuring robustness of the overall scheme, while preserving the simplicity of the control laws. Remarkably, the observer and the controller can be designed and tuned separately. In the case of a poorly known heat-transfer coefficient, both the observer and the controller incorporate a direct adaptive estimation strategy of the coefficient. The performance, in terms of accuracy and robustness, are investigated via computer simulations