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A vapour cloud explosion simply defined as an explosion occurring outdoors is the most dangerous and destructive explosions in the chemical process industries Some examples of vapour cloud explosions are the Fixlborough and Buncefield disasters. A vapour cloud explosion can also be defined as a combustion process, which under appropriate conditions may develop a huge explosion intensity and blast overpressure enough to cause a great amount of damage to the surrounding area. The mechanism of how a vapour cloud explosion occurs and how the initial conditions affect its development and how it can be prevented or mitigated can be understood by studying the phenomenon of combustion from the thermodynamics, kinetics and mass transfer point of view. Thermodynamics describes the equilibrium state of a chemical process and helps in predicting the final temperature and final composition. The final temperature and composition of the system depends on the initial conditions like pressure, temperature and the initial composition of the mixture. When it comes to combustion and vapour cloud explosions it helps in the prediction of the adiabatic flame temperature. The adiabatic flame temperature plays a huge role in the value of the flame speed which the combustion mixture can obtain and this flame speed in the most instances determines whether the flame will propagate or be extinguished or whether an explosion will actually occur. Chemical kinetics helps in determining the rate of the reaction which plays a prominent part in determining the value of flame speed obtained as faster the reaction rate, higher the flame speed and hence higher the probability of an explosion occurring. The important use of chemical kinetics is the help it provides in the determination of the reaction mechanism and exactly how the products are formed from the reactants by the determination of the various elementary reactions. The topic of mass transfer and transport properties helps in understanding why explosions can only occur when the fuel and the oxidiser are sufficiently mixed and hence why premixed combustion can lead to explosions and not non-premixed combustion. It also explains why and how the addition of inerts and inhibitors can successfully mitigate and prevent an explosion from occurring. It also helps in understanding the role turbulence plays when it comes to the occurrence of an explosion. The second part of the thesis is about the simulations performed in the Software Cantera. In the first part of the simulation of Methane combustion is carried out in Cantera for various initial conditions using the GRI Mech 3.0 reaction mechanism and the value of the flame speed and adiabatic flame temperature for these different initial conditions are computed and this gives us an insight into how the various initial conditions affect the flame propagation and contribute to an uncontrolled combustion process and in turn a vapour cloud explosion and how for some conditions the flame ends up being extinguished. In the second part the GRI Mech 3.0 model, modified to include the combustion chemistry for Sodium containing compounds is used for simulations and the results are compared with those of available experiments from literature in order to evaluate the ability of this model and the software Cantera to predict flame propagation and inhibition characteristics of hydrocarbon flames in the presence of Sodium containing compounds as inhibitors.

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The occurrence of dust explosions is an important issue in the processing industries. The development of a model to predict the minimum ignition energy (MIE) could help to better protect installations in these industries to prevent the ignition of such an explosion. Previously developed models are not accurate enough and/or lack a theoretical basis. A new model was developed in this master's thesis with the help of newly defined dimensionless heat transfer equations and numerical simulations, performed in MATLAB. The ignition radius was proposed and approved as a condition for ignition of a dust cloud. The criterion suggested that at least one particle (that lies inside the ignition volume) has to go above its minimum ignition temperature (MIT) after the deposition of a spark energy equal to the MIE. The addition of inert particles was found to increase the critical ignition radius and thus cause an increase of the MIE of a dust cloud. The developed model, the PJDS model, gives a large underestimation, its performance is comparable to Kalkert's model. The theoretical basis is however very solid and can be used for future research. Next to the ignition criterion, a criterion for the propagation of the combustion reaction in the dust cloud is proposed. This criterion takes into account the required dust concentration and heat of combustion for an explosion to occur. Again, the influence of inert particles is noticeable: More inert particles lead to a less likely propagation. The underestimation of the predicted value of the MIE by the PJDS model can be explained through the chemical reaction kinetics. For the development of the model an experimental value of the MIT was used, but it is shown that because of the addition of an energy source, this value becomes unusable and no a priori knowledge of the MIT should be used. Instead, the chemical reaction kinetics should be directly implemented in the development of future models for the prediction of the MIE.

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