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Eingeladener Vortrag
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Limiting distances for flame merging of multiple n-heptane and di-tert-butyl peroxide pool fires
(2013)
Experiments to determine the limiting distances for flame merging of multiple pool fires are presented. As model substances n-heptane and di-tert-butyl peroxide are used. Laboratory scale tests with a Diameter d = 6 cm and relative distances between the pools of 0.08 ≤ D/d ≤ 4 are described and complemented with field experiments with a diameter d = 1.5 m and relative distances between the pools of 0.17 ≤ D/d ≤ 1.
Three regions for flame merging are observed and limiting distances are determined. A merging Region with the limiting distance Dmerg/d within which all flames merge together over the complete burning time. A transition region with the limiting distance Dtran/d within which some flames merge together while other flames are separated from each other. A separated region within which all flames are completely separated from each other. A correlation against the number of burning pools is presented to predict the limiting distances Dmerg/d und Dtran/d.
Most of the measurements of temperatures in large pool fires are indirect and present a number of complexities due to the interactions of convection, radiation and soot blockage. In the present work these influences for two organic peroxide [tert-butyl peroxybenzoate (TBPB) and tert-butyl peroxy-2-ethylhexanoate (TBPEH)] pool fires are analysed.
Thermocouple measured temperature in the clear flame zone i.e. combustion zone are found to be 250-400 K lower than from the thermographic measurements. The convective and radiative heat flux contributions from the fire on temperature measurements are discussed. CFD (Computational Fluid Dynamics) simulations have been performed for large pool fires and the predicted time averaged flame temperatures were found to be in qualitative agreement with
measurements due to the stoichiometric combustion model used in the present simulations.
The use of energetic materials as a main fuel in high temperature process
industries are not known to the scientific community as such. This paper
highlights some of the features and advantages of using organic peroxides
especially di-tert-butyl peroxide (DTBP) in high temperature process industries.
The feasibility of using DTBP as a main or supporting fuel in process industries
have also been justified with the help of Computational Fluid Dynamics (CFD)
simulations. For peroxides requirement of less fuel and air for the same amount
of heat flux has been shown. The resulted emission from the combustion of
DTBP is also discussed.
Combustion of peroxy-fuels
(2011)
The diffusion flames of organic peroxides exhibit quite different characteristics than hydrocarbons. What makes them interesting to study is their fast burning behaviour. As a result the flame temperature enhances and so does the thermal radiation. Due to all these they demand safe handling during processing. However, they can be utilised at several places in different industries where a fuel with fast burning, high temperature and intense radiation are desired. Some of the possibilities to use them as a main or supporting fuel in a wide range of industrial utilities are the major content of this paper.
A new burner concept (PEROXY-BAM®) for the combustion of liquid organic peroxides (Peroxy-fuels) is presented. As peroxy-fuels are thermally unstable the design of burners for them should be accordingly modified ensuring a safe operation. It is found that 10 to 100 time less amounts of peroxy fuels are required for the same heat flux or output in comparison to hydrocarbons. Correspondingly, the fuel pump power and the volume of combustion chamber (furnace) are also reduced. As a result of less amount of fuel the emissions will also be stepped down and oxygen in the molecule helps to establish conditons like in an oxy-fuel combustion process. The advantages of using peroxy-fuels over hydrocarbons inside a model combustion chamber are also investigated with the help of CFD (Computational Fluid Dynamics) simulations.
new burner concept for peroxy-fuels is proposed. The performance of the proposed peroxy-fuel burner is predicted with the help of Computational Fluid Dynamics (CFD) simulation. It is found that peroxy-fuel burner not only requires considerable less amount of fuel for the same output/power but also at the same time the overall size of the processing unit can be reduced. As peroxy-fuels contain oxygen atoms within the molecule itself a similar to oxy-fuel combustion environment is created without even supplying pure oxygen. CFD simulations also support the above facts and demonstrate the existence of less favorable conditions to form NOx.
The mass burning rate of pool fires of organic peroxides do not vary appreciably with the pool size as have been observed for the hydrocarbons. Instead the decomposition temperature largely controls the same. The dependence of mass burning rate on the decomposition temperatures namely self-accelerating decomposition temperature (SADT) and extrapolated onset temperature measured by differential scanning calorimetry (DSC) for organic peroxide pool fires are identified and correlations are developed.
Industrial fire and explosion hazards due to accidents in fuel storage units have gained a considerable attention in recent years. Both, the regulatory bodies and scientific communities are heavily concerned about the proper safety measures to avoid such calamities in the future. This paper aims to bring some essentials related to the hazards that arose from recent fuel storage fire accidents occurring in Buncefield, UK (2005), Puerto Rico, USA (2009) and Sitapura, India (2009). The potential similarities behind occurrence of these accidents are studied. The applicability of various methods (models) and also computer simulations to estimate the safety distances according to the international standards for both explosion and fire hazard are verified. The overpressures caused by the Vapor Cloud Explosions (VCE) and radiation fluxes emitted by the fires are considered for respective explosion and fire hazard estimations. The prime focus is placed on the regulations laid down by the National Fire Protection Agency of the United States and the European Norms.
An extraordinary deviceless self-sustained oscillatory diffusive burning is observed in tert-butyl peroxybenzoate (TBPB) (technical pure) and hybrid fuel, i.e., TBPB and kerosene (both 50%) flames when burned in form of pool fires. Such oscillations or more precisely self-sustained deviceless control of mass burning (flow) is not reported till date. Generally, devices comprising electronic control system and/or mechanical means (valves) are necessary to produce such oscillatory burning or control of fuel flow. This unique oscillation is strongly recorded for pool diameters of 6 cm ≤ d ≤ 11 cm beyond which the effect was weakened and unseen (hid) visually. The fuel regression (loss) takes place in irregular time steps and is formulated in form of a step function. The variation in fuel mass burning rates, visible flame lengths and radiation heat fluxes with time are measured as respective representatives of oscillations. The periodicity in the strongest oscillations in relative visible flame lengths is investigated and the measured data are found to be best fitted in sinusoidal form. Both, chemical and thermal effects are shown to be possibly responsible for such effects. Furthermore, a theory is offered to characterise similar effect showing fuels.
The flame temperatures T of a multiple n-heptane pool fire d = 6 cm, N = 5, D/d = 0.33 are measured with type S thermocouples and predicted with Large Eddy Simulation (LES) and an assumed pdf-approach containing a detailed kinetic with 112 species and 800 elementary reactions. Multiple pool fires show higher flame temperatures up to ≈ 200 K in comparison to single pool fires. CFD simulation is in good agreement with the experimental results and a validation is performed. It can be shown that multiple fires have an enhanced air-entrainment leading to an increased formation of OH radicals and consequently to the observed higher flame temperatures.
In verfahrenstechnischen Anlagen kann es während des Umgangs, des Transports und der Lagerung durch Freisetzung und anschliesender Zündung von brennbaren Flüssigkeiten zu Lachen-, Pool- oder Tankfeuern kommen. Die sich ausbildenden Feuer konnen große Schäden an benachbarten verfahrenstechnischen Anlagen und Personen verursachen. Im Unterschied zu Einzelfeuern sind multiple Pool- und Tankfeuer aufgrund ihrer Wechselwirkungseffekte sicherheitstechnisch von besonderer Bedeutung. Mit Di-tert-butyl-peroxid (DTBP) und n-Heptan als Leitsubstanzen werden Labor- und Feldexperimente (d ≤ 1.5 m) mit wechselwirkenden Poolflammen (N ≤ 9) in einer Matrixanordnung bei relativen horizontalen Abständen D/d zwischen den Pools im Bereich 0.16 ≤ D/d ≤ 4 durchgeführt.
Die Phänomene der Flammenverschmelzung (Flammenfusion) in Abhängigkeit vom Poolabstand D/d werden experimentell untersucht und modelliert.
Prediction of burning rate of an accidentally released flammable fuel by means of CFD simulation
(2009)
Prediction of burning rate of an accidentally released flammable fuel by means of CFD simulation
(2009)
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.