Idicadores intrínsicamente seguros para las explosiones en la industria de procesos

Los parámetros de seguridad de las sustancias inflamables, medidos por procedimientos estandarizados que, generalmente, se han adoptado para la definición de los índices de seguridad inherente, incluso  si las explosiones de gas industrial, de vapor  o de polvo, son motivo de preocupación. Sin embargo, es bien conocido que la naturaleza de los accidentes con explosiones  son más complejos  en la vida real, que los observados  en el laboratorio, bajo un ambiente controlado. Por otro lado, puede haber consecuencias mucho más severas, cuando se tienen  equipos de diseño o   dinámica de fluidos especiales.   Este trabajo propone nuevos indicadores  de seguridad inherentes a las explosiones basadas en los avances recientes en la seguridad de la combustión y  en las metodologías para el análisis de consecuencias

Turbulent Ignition Regimes in 20 L Explosion Vessel: CFD Simulations

The understanding of the ignition process is important for many practical and fundamental applications including safety, chemical conversion, flame stabilization, and internal combustion engines operation. The ignition process can be influenced by many factors, including the pre-ignition turbulence level. Turbulence can generally be generated intentionally by the introduction of gases into the combustion chamber, but it can also occur unintentionally, for example by a sudden release of gases into the atmosphere as a result of an accident. Through the small scale 20 L CFD simulations of the ignition process of a stoichiometric methane-air mixture at different ignition energies and levels of turbulence, the present work aims to create a simple operational map that correlates the ignition energy with the degree of turbulence to understand in which areas flame propagation is successful and in which it is not. Such a tool may be useful both for evaluating the operation of internal combustion engines, where ignition and flame propagation are desired phenomena, and for a preliminary assessment of the risk and probability of ignition. This approach may also be applied in the future to other gaseous (as in the case of hydrogen), liquid, or solid systems

Catalytic Combustion of Waste Streams Coming from the Solvent Recovery Stage of a Packaging Industry

Esters and alcohols are widely used as solvents in the packaging industry. They contribute to the increase of volatile organic compound (VOC) emissions and, as such, represent a serious air pollution problem that must be faced. To this end, two main strategies can be pursued: solvent recovery and/or incineration, the former being of course preferred. Solvent recovery consists of an activated carbon plant, which adsorbs the post-printing exhaust solvents, and a distillation system, which separates the recovered solvent mixture. The waste streams coming from the solvent recovery stage need to be disposed, implying additional costs as well as safety issues. In this work, a low-cost perovskite-based catalyst, doped with a low amount of noble metal (Pt) and supported over a monolithic reactor, was used to run lab-scale combustion tests for waste streams coming from the solvent recovery stage of the packaging industry Icimendue (www.icimen.com). Results of experimental tests support the validity of catalytic combustion of the waste streams as an alternative approach to their disposal

Preliminary Risk Evaluation of Methanol/water Storage in Fuel Cell Integrated Systems for Onboard Applications

In this work, a preliminary risk evaluation of the methanol/water storage in fuel cell integrated systems is performed. The system which couples methanol steam reforming and the fuel cell to generate electricity is considered as a solution in several industrial projects for onboard applications. The challenge of such a system is to control the thermal loads to operate under fully autothermal conditions, recycling the dissipated heat from the fuel cell to preheat and evaporate the reactant mixture. To implement these systems, safety issues must be identified and minimized. Considering the autothermal operating conditions of the methanol steam reforming unit, the water/methanol ratio was set at 3. Under these conditions, the mixture is safer than pure methanol in terms of flammability and toxicity, but not yet inherently safe. Starting from the generation of a hole on the storage tank as initiating event, the consequence analysis as well as some preliminary risk considerations is performed by using empirical models. In this work, the focus was on the effects of a vapour cloud explosion and comparisons were made between a methanol-water solution, pure methanol, and gasoline, used in the conventional internal combustion engine

Large eddy simulation and PIV measurements of unsteady premixed flames accelerated by obstacles

In gas explosions, the unsteady coupling of the propagating flame and the flow field induced by the presence of blockages along the flame path produces vortices of different scales ahead of the flame front. The resulting flame/vortex interaction intensifies the rate of flame propagation and the pressure rise. In this paper, a joint numerical and experimental study of unsteady premixed flame propagation around three sequential obstacles in a small scale vented explosion chamber is presented. The modelling work is carried out utilising Large Eddy Simulation (LES). In the experimental work, previous results [Patel, S.N.D.H., Jarvis, S., Ibrahim, S.S., Hargrave, G.K., Proceedings of the Combustion Institute 29, 1849-1854 (2002)] are extended to include simultaneous flame and Particle Image Velocimetry (PIV) measurements of the flow field within the wake of each obstacle. Comparisons between LES predictions and experimental data show a satisfactory agreement in terms of shape of the propagating flame, flame arrival times, spatial profile of the flame speed, pressure time history and velocity vector fields. Computations through the validated model are also performed to evaluate the effects of both large scale and sub-grid scale (sgs) vortices on the flame propagation. The results obtained demonstrate that the large vortical structures dictate the evolution of the flame in qualitative terms (shape and structure of the flame, succession of the combustion regimes along the path, acceleration-deceleration step around each obstacle, pressure time trend). Conversely, the sgs vortices do not affect the qualitative trends. However, it is essential to model their effects on the combustion rate to achieve quantitative predictions for the flame speed and the pressure peak

Oxidative Methanol Reforming for Hydrogen-fed HT-PEMFC: Applications in the Naval Sector

CO2 emissions from marine transport contributes to about 3% of the overall greenhouse gas (GHG) emissions. International regulations and the Paris agreement require to cut them by 50% by 2050. Moreover, the latest International Maritime Organization (IMO) regulations strongly limits SOx emissions. One of the most promising alternatives to conventional fuels is hydrogen, which can meet the environmental targets set by the international community, if coupled with H2-fed PEM fuel cells (PEMFCs) due to their high efficiency. On-board H2 production starting from a suitable liquid source can be competitive compared to compressed/liquid H2. Methanol (MeOH) is a suitable candidate due to: high H2 content, relatively low reforming temperature, absence of sulfur compounds, and the possibility of being obtained from renewable materials. This work investigates the coupling of autothermal oxidative MeOH steam reforming (OSRM) with high temperature PEMFCs (HT-PEMFCs). The latter outperforms low temperature (LT) PEMFCs, concerning resistance to CO poisoning and high operating temperature, allowing an integrated OSMR reactor – HT-PEMFC and energetically self-sustaining system. The integrated system has also been designed considering also MeOH storage tank and the main auxiliary units, and the dimensions appear very interesting for the installation on board of ships, also in terms of emissions

Intorno al '48: fermenti risorgimentali e resistenze accademiche

La profonda spaccatura tra la produzione accademica (sostenuta dalla politica culturale retorica e attardata dei Borboni e rappresentata da artisti come Tommaso De VIvo e Camillo Guerra) e quella d'avanguardia e foriera di grandi evoluzioni di Domenico Morelli e Saverio Altamura, che contribuirono in seguito in modo rilevante agli esiti della pittura di 'macchia'