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In this paper we review the current understanding of bubble plumes discharged from subsea sources related to oil and gas production, and show how CFD can be applied for risk assessments. A general introduction to causes and risks is given. This is followed by a discussion of the physics that need to be accounted for before giving a brief review of the different modelling approaches employed today. The empirical and experimental knowledge base is also summarized. An example of how CFD can be applied to study gas releases is given. At the end we outline what is needed to advance current understanding of such releases and model their interaction with the surroundings. The scope of the review is limited to the fate of the gas and the flow induced by the ascending bubble plume in the water column. Atmospheric dispersion of surfacing gas is not considered.

The oxidation of liquid silicon resulting in silica fume has been the subject of previous investigation due to its importance to occupational health in the silicon alloy production industry. Small-scale experiments and industrial measurements have been carried out in order to understand the mechanisms and kinetics of liquid silicon oxidation. Key questions as to the main factors and conditions determining the rate of fume formation in the industry, still remain. In this work the rate of active oxidation of liquid silicon was studied by experimental investigations in a 75 kW induction furnace, where oxidizing gas was introduced via a lance above the liquid silicon surface. The silica formed as a result of the reaction was collected and the silica fuming rate determined as a function of gas composition and gas flow velocity. The system was also modeled using computational fluid dynamics (CFD) and kinetic modeling. The flux of silica increases with increased gas velocity above the liquid surface, and was found to correlate well with mass transfer rates calculated from impinging jet theory. The size of the silica particles was also found to be dependent on the gas flow rate; smaller average particle size was obtained at higher flow rates. It was found that the most important factor for the silicon oxidation reaction rate is the velocity of the gas in vicinity of the silicon surface (i.e. the boundary layer thickness). The velocity is more important than the actual amount of oxygen delivered to the system per unit time, indicating that oxygen ''efficiency'' is not a strong function of oxygen concentration in the gas. Thus, the gas velocity is the rate determining parameter in determining the mass transport of oxygen to the silicon surface. Results from computational fluid dynamics simulations show that the gas flow was laminar in all experiments and that oxidation takes place within 123Oxid Met (2014) 82:395-413 DOI 10.1007/s11085-014-9498-z 0.5 mm from the silicon surface. The results from the experiments and the CFD model were used to suggest a molecular mechanism of the active oxidation of liquid silicon.

During oxidative ladle refining (OLR) of silicon, the metal surface is partly oxidized, resulting in the formation of a condensed silica fume (SiO 2 ). This fugitive emission of silica represents a potential health hazard to the workers in the silicon and ferrosilicon industry. In the current work, industrial measurement campaigns aimed at recording the fume generation during OLR were performed at the Elkem Salten plant in Norway. The measured amounts of silica produced were 2.5-5.1 kg/h, depending on the gas flow rate in the refining process. The rate of silica production correlates with the total flow rate and amount of air in the purge gas, and increases as the flow rate increases. The results of this work suggest that fume generation during OLR primarily results from oxidation of the exposed metal surface, with oxygen transport from the surrounding atmosphere to the metal surface being the limiting factor. Other identified mechanisms of SiO 2 formation were splashing of the metal and/or oxidation of SiO gas carried with the refining purge gas.

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Furnace tapping is a critical operation on pyrometallurgical furnaces known for unpredictable performance in many cases. A reduced order mathematical model capable of predicting tapping rates of both slag and metal is presented. The model accounts for separate liquid phases and particle bed resistance to flow. The model is compared for consistency against results from both a water-model experiment and computational fluid dynamics simulations. The model is applied to study drainage from a typical ferro-manganese furnace. The model results show that particle bed conditions in the immediate vicinity of the tap-hole strongly influence tapping rates and that the slag/metal interface deformation due to suction pressure near to the tap-hole is significant and must be accounted for in such models.

Small scale laboratory experiments on the oxidation of liquid silicon have reproduced important features of the industrial refining of liquid silicon: active oxidation led to the formation of amorphous silica spheres as a reaction product. The boundary condition for active oxidation in terms of maximum oxygen partial pressure in the bulk gas was found to lie between 2Á10 -3 and 5Á10 -3 atm at T = 1,500°C. The active oxidation of liquid silicon had linear kinetics, and the rate was proportional to bulk oxygen partial pressure and the square root of the linear gas flow rate, consistent with viscous flow mass transfer theory. Classical theory for unconstrained flow over a flat plate led to mass transfer rates for SiO (g) which were 2-3 times slower than observed. However, computational fluid dynamic modeling to take into account the effects of reactor tube walls on flow patterns yielded satisfactory agreement with measured volatilization rates.