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.
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.
Scenarios of underground gas pipeline failure, crater formation, dispersion of gas, explosion and subsequent fires are investigated with semi-empirical and with CFD (Computational Fluid Dynamics) modelling. In order to strengthen the accident based learning approaches present investigations are performed in the context of recent GAIL (Gas Authority of India Limited) natural gas pipeline incident occurred in India. The foreseeability of damages to lives of people and assets due to explosion overpressure and thermal radiation are assessed. The released gas is considered as slightly dense-than-air i.e. 1.5 times. Depending on the LFL (Lower Flammability Limit) of gas the dispersion diameter and heights are predicted which followed the visual evidences appropriately. The model was furthermore tested with an even denser medium and was found to be worked well there too. The estimated explosion overpressures with the standard methods and also with CFD reproduced the scenario nicely. The effects of congestion VBR (Volume Blockage Ratio) in form of vegetation on stable atmospheric boundary layer flow is analysed and its contribution towards turbulence and hazard enhancement is studied.
It is found that the major source of fatalities was higher thermal radiation emitted by pool fires of methane. The estimated thermal safety distances clearly demonstrate the ignorance/under estimation of likelihood and consequence of such hazardous events. For such incidents CFD demonstrated a strong capability to assess the pre or/and post events foreseeabilities within a reasonable amount of time and with an acceptable level of accuracy meeting the industrial needs for risk analysis.