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Eingeladener Vortrag
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Massenabbrandraten organischer Peroxide unter besonderer Berücksichtigung der thermischen Stabilität
(2013)
Die Flüssigkeitstemperatur Temperatur in der flüssigen Phase unmittelbar im Grenzbereich zur Gasphase während eines Abbrandes organischer Peroxide überschreitet die Onset-Temperatur der beginnenden exothermen Zersetzungsreaktion des Peroxids, so dass diese zu berücksichtigen ist. Für die Peroxide Di-tert-butyl-Peroxid (DTBP) und tert-butyl-peroxybenzoat (TBPB) muss daher bei der Berechnung des Wärmerückstromes ein zusätzlicher Term für die Zersetzung in der Flüssigkeit additiv ergänzt werden. Der Umsatz der Zersetzungsreaktion wird unter den Bedingungen eines CSTR modelliert und erfolgt auf Basis einer Reaktionskinetik 1. Ordnung. Es kann gezeigt werden, dass der Wärmestrom in einem DTBP-Poolfeuer ≈ 40 % und einem TBPB-Poolfeuer ≈ 100 % des Wärmerückstromes durch Wärmestrahlung entspricht. Durch Q-Punkt-d können die vergleichsweise hohen Massenabbrandraten und die relative Unabhängigkeit der Massenabbrandraten vom Pooldurchmesser erklärt werden. Über eine Energiebilanz wird ein Modell basierend auf physikalischen Parametern entwickelt, das die Massenabbrandraten großer Poolfeuer, in sehr guter Übereinstimmung mit den experimentellen Ergebnissen, vorhersagt.
Amuay refinery disaster (2012) is another recent example of Vapor Cloud Explosion (VCE) and fire accidents preceded by Buncefield (2005), Puerto-Rico (2009) and Jaipur (2009), respectively [9]. The incident has left many safety issues behind which must be repeatedly addressed. Unfortunately, the lessons taught by previous similar events are just not understood carefully. It reveals that the proper safety measures for such facilities were either underestimated or were not accounted seriously. Consequently, the resulting overpressures from explosion and the subsequent thermal radiation from tank fires have once again proved to be disastrous to both mankind and infrastructure. This article highlights the aftermaths of Amuay incident and addresses the challenges put forward by it. Furthermore, a comparative study is performed between such incidents to analyze the similarities and how they could have been avoided.
Two-phase CFD (Computational Fluid Dynamics) model for characterising the spill-over/dispersion of peroxy-fuels is presented. The model is independent of type and burning rate of the spilled/dispersed fuel and considers only overflow Reynolds number (Re) to characterise the spill/dispersion behaviour. Additional simulations are performed for LNG (Liquified Natural Gas) dispersion and it is found that the model can be used for different fuels within a defined range of Re. Different scenarios with Re = 100 to 3 × 105 are investigated covering a wide range of mass flow rates, opening sizes and viscosities. Depending on Lower Flammability Limits (LFL) of the fuels spill/dispersion (vapour cloud) diameters (DCFD) and heights (hCFD) are predicted. A generalised correlation between DCFD and Re is established to predict the dispersion occurring at varying scales. The model is validated by: (1) conducting an extensive grid independent study; (2) comparing the results with the existing analytical methods and (3) comparing against the standard field test data on LNG dispersions.
Industrial fire and explosion hazards are most often also associated with the dispersion of toxic substances.
These substances can be gases, liquids, solids or in form of aerosols. The critical toxic exposure limits to People and enviroment from such substances are regulated by the concerned authorities of the countries. In order to comply with the defined regulation estimation of such critical limits must be carried out by different semi-empirical and phenomenological models/methods for risk assessment.
Many of such methods provide a qualitative estimation of time and space dependent extrimities of toxicity. The overwhelm development of computational capacity has made it possible to perform Computational Fluid Dynamics (CFD) simulation by solving the three-dimensional transport equations for mass momentum and species in lower and upper atmosphere, respectively. CFD simulation not only provides a detailed 3D distribution of toxic particulates/gases in the neighbourhood of the plant but also helps to study the worst-case sceanrios. In the past several small- and large-scale accidents occured in oil and gas plants in different parts of the world including the recent one in Rheinland refinery near Cologne in Germany. This work deals with this accident and provides a methodology to predict the critical exposure limits of smoke emitted by a toluene tank fire by means of CFD simulation.
Organic peroxides are energetic substances liable to decompose due to exothermic reactions when exposed to uncontrolled temperature, contamination, confinement and quantity. Their safe storage and transportation are the prime concern and chemical industries and regulating authorities. Their accidental release may and most often lead to shape of a pool. In present study, safety distances from such large pool fires (diameter d = 3.4 m) of organic peroxides are numerically predicted by solving the reactive, 3-D time dependent Navier-Stokes equations with reliable assumptions. The present model is validated against the data on buoyant turbulent diffusion flames. The safety distances predicted by simulation assume three regions in a fully developed fire i.e. hot spot, luminous zone and a flame surface. The time averaged data of temperatures of these regions lead to better estimation of irradiances against the measured data. A developed sphere analogy method (for a special class of organic peroxides) for maximum surface emissive power prediction is also verified.