Thèses sur le sujet « Oil coalescence »

Dispersed water drops in oils can cause detrimental effects. For example in refining and cracking of crude oil, poisoning of catalysts and equipment corrosion can be major problems due to the presence of water. Therefore there is a need to develop more efficient and cost-effective separators. The work in this thesis covers an investigation of the underlying electrostatic phenomena (i.e. drop-drop and drop-interface coalescence and drop deformation and break-up) leading to the development of compact electrocoalescer-separators. Using novel two-dimensional electrode systems, it is shown here that coalescence readily occurs when the electric field is applied in the same direction as the line joining the centres of the two drops, in line with the previous theoretical prediction of the maximum attractive force induced in this way. An adaptive Finite Element Method, incorporating automatic error and mesh generator programmes, has been used to quantify the electric-induced forces of charged spheres in an insulating medium, for short distances that are much smaller than the drop radius, where analytical solutions are no longer reliable. Moreover, drop-drop attraction can also occur when the angle is 125.3° from the electric field direction. Previous work suggests that pulsed d.c. fields are effective for low-aqueous-content systems, and this has been further investigated here. The applied electric field and pulse frequency can be optimised to achieve the highest coalescence rate. High electric fields (> 3.5 kV/cm) are shown to deform and break up aqueous drops when the electric field-induced stresses overcome the interfacial tension. A critical electrostatic Weber number, corresponding to the onset of drop break-up, has been evaluated to be about 0.49 for several aqueous-oil systems. For the separation of dispersed aqueous drops from an oil phase, it is advantageous to incorporate an aqueous layer to induce drop-interface coalescence. A suitably applied electric field is shown to give efficient drop-interface coalescence. The above investigations have led to the design and development of two compact electrocoalescer-separators. The first separator combines the effects of electrocoalescence and gravitational settling. The second separator, which utilises the electrocoalescence and centrifugal effects, can handle larger throughputs with reasonable separation efficiency. Both devices significantly enhance the separation and are good examples of how the fundamental understanding gained in this studies can be applied to realistic practical situations.

Liquid-liquid coalescers are devices used for increasing the droplet size of the dispersed phase in continuous phase flow, such as oil droplets in water flow. The efficiency of separation technologies is strongly dependent on the droplet size, which is desirable to shift into larger droplet diameters. Theory behind coalescence and its modeling is studied in this Maser’s thesis. Aker Process Systems AS, Division of Advanced Separation Technology, provided the assignment proposal.The scope of this work is a literature study on the coalescence phenomenon and the closely related break-up phenomenon and CFD modeling in general. Further a mathematical model for simulating coalescence of oil droplets in continuous water flow is developed by the use of the commercial CFD-code FLUENT. The basis for the model is a swirl-based coalescer called Compact Tubular Coalescer (CTC), developed by Aker Process Systems AS.The validity of the model is evaluated before different aspects of the performance of the coalescer are studied. Several validation criteria were tested and were acceptable, but some weaknesses regarding lack of test cases were detected. The performance testing showed good performance of the CTC, it was able to increase the Sauter Mean Diameter (SMD) of the droplet with up to 250% for the smallest droplets (20 μm) and highest volume fractions (7%). Remarkable differences of the performance were observed as the physical properties were changed. Higher viscosity and droplet surface tension lead to increased coalescence rate and decreased break-up rate.Future work is recommended to concentrate on improving the present model and to investigate more aspects of the model. An effort should also be made to use a Eulerian approach to model the dispersed phase with the use of population balances, in order to be able to simulate flows with larger dispersed phase volume fractions.

In flotation, the rate with which mineral particles are recovered is governed by the bubbles generated. The smaller the bubbles, the more surface area is available for transport to the froth zone. Surface-active species, known as frothers, are commonly added to help produce small bubbles in flotation. They are believed to act by coalescence prevention and have different characteristics based on their chemical and structural formulas. Many methods have been developed to categorize the classes of frothers, describing different behaviours and material constants. One such method is the critical coalescence concentration (CCC) of a frother which is determined from a plot of Sauter mean bubble size (D32) vs. frother concentration, referred to here as the 'addition' method. Industrial flotation systems can encounter a number of naturally occurring surfactants and salts that also influence bubble size, such as during oil sands extraction. In effect there is a 'system' CCC. The thesis introduces a new dilution method to identify a system CCC. It is shown that the system CCC can be expressed as an equivalent frother concentration to provide context and a means of comparing water samples. Process water samples from the thickener overflow in Shell Albian Sands were tested. The study showed variability in the frother-equivalence of the process waters reaching at most the equivalent of 60 ppm of DF-250, a value that is much higher than the range of frother concentrations commonly employed in the minerals industry. The viability of using gas holdup to provide an estimate of process water D32 is also explored. A gas holdup to D32 correlation was established and used in developing the CCC curve of a sample, the advantage being gas holdup is an easier parameter to measure. It is concluded that the dilution and frother equivalent techniques can be used to help identify system hydrodynamic properties. A longer term ambition is to consider using gas holdup for on-line application to evaluate possible changes in process waters which may impact these hydrodynamic properties.
Dans le procédé de flottation, la vitesse avec laquelle les particules minérales sont récupérés est régie par les bulles générées. Le plus les bulles sont petites, le plus d'aire superficielle disponible pour le transport vers la zone de mousse. Les espèces tensio-actifs, connus comme agents moussants, sont ajoutés pour aider à produire de petites bulles. Ils sont soupçonnés d'agir par la prévention de la coalescence et ont des caractéristiques différentes en fonction de leurs formules chimiques et structurales. De nombreuses méthodes ont été mises au point pour classer les catégories d'agents moussants. Une telle méthode est la concentration de coalescence critique (CCC) d'un agent moussant qui est déterminée à partir d'un graphique de diameter Sauter qui represente la taille moyenne des bulles (D32) contre la concentration d'agent moussant, une méthod dénommé «Addition».Les systèmes de flottation industriels peuvent rencontrer un certain nombre d'agents tensio-actifs d'origine naturelle et les sels qui influencent également la taille des bulles, comme lors de l'extraction des sables bitumineux. En effet, il ya un «système» CCC. La thèse présente une nouvelle méthode de dilution pour identifier un système CCC. Il est démontré que le système CCC peut être exprimée comme une concentration équivalente d'agent moussant, ce qui contribue a fournir un contexte et un moyen de comparer des échantillons d'eau. Les échantillons d'eau de procédé provenant du débordement d'épaississant dans Shell Albian Sands ont été testés. L'étude a révélé une variabilité dans l'équivalence d'agent moussant des eaux de process atteignant tout au plus l'équivalent de 60 ppm de DF-250, une valeur qui est plus élevé que la gamme de concentrations d'agent moussant couramment utilisés dans l'industrie des minéraux.La viabilité de l'utilisation de la rétention de gaz pour fournir une estimation du D32 des échantillons d'eau est aussi explorée. Une corrélation entre la rétention de gaz et D32 a été établie et utilisée dans le développement de la courbe CCC d'un échantillon, l'avantage étant la simplicité de mesurer le retenue de gaz. Il est conclu que la technique de dilution peut être utilisé pour aider à identifier les propriétés hydrodynamiques du système. Une ambition à long terme est d'utiliser la rétention de gaz pour des applications en ligne pour évaluer les changements possibles dans les eaux de procédé qui peuvent influencer ces propriétés hydrodynamiques.

Foam flow in porous media is important for many industrial operations such as enhanced oil recovery, remediation of contaminated aquifers and CO2 sequestration. The application of foam in these processes is due to its unique ability to reduce gas mobility and to divert gas to low permeability zones in porous media which otherwise would not be reached. To achieve optimum success with foam as a displacing fluid in oil recovery and remediation operations, it is essential to understand how different parameters influence foam flow in porous media. In this thesis, a variety of experimental techniques were used to study foam stability, foam rheology as well as the dynamics and patterns of oil displacement by foam under different boundary conditions such as surfactant formulation, oil type, foam quality (gas fraction) and porous media geometry. Bulk scale studies showed that foam stability was surfactant and oil dependant such that decreasing oil carbon number and viscosity decreased the stability of foam. However, no meaningful correlation was found between foam stability at bulk scale and the efficiency of oil displacement in porous media for the various surfactants studied in this work. Additionally, our results show that foams consisting of smaller bubbles do not necessarily correspond to higher apparent viscosity as the foam quality is also crucial. For the same foam quality decreasing bubble size resulted in higher apparent viscosity. Although in theory a higher apparent viscosity (i.e. higher foam quality) would be ideal for displacement purposes, increasing foam quality resulted in less stable foam in porous media due to formation of thin films which were less stable in the presence of oil. The effect of pore geometry on foam generation and oil displacement has also been investigated. Our findings provide new insights about the physics and complex dynamics of foam flow in porous media.

Cilj ove doktorske disertacije je da dâ doprinos u proučavanju nedovoljno poznatih fenomena koalescentne filtracije, kako bi se smanjio obim potrebnih poluindustrijskih istraživanja prilikom projektovnja filtera za neku konkretnu primenu. Svi materijali korišćeni u ovoj doktorskoj disertaciji su otpadni materijali, čija primena kao filtarskog punjenja predstavlja poseban doprinos održivom razvoju. Jedan od ciljeva ove doktorske disertacije je proučavanje istovremenog uticaja promene permeabilnosti sloja i debljine vlakana na osobine sloja, pad pritiska i efikasnost separacije dispergovanog ulja iz kontinualne vodene faze. Uticaj geometrije sloja proučavan je na slojevima homogene i heterogene geometrije po dubini. Realizovano je detaljno ispitivanje izgleda, morfologije vlakana, kao i strukture sloja, izgleda i rasporeda njegovih pora, primenom skening elektronske mikroskopije i optičke mikroskopije. U radu je dat pregled istraživanja primene vlakana različite prirode (slobodnih i međusobno povezanih, krutih i elastičnih, različite debljine te time i različite vijugavosti) i njihovih slojeva. Takođe, dat je doprinos proučavanju istovremenog uticaja promena ulazne koncentracije dispergovane faze i permeabilnosti sloja. U veći deo ostvarenih istraživanja ukjučeno je i proučavanje uticaja prirode uljne faze, pri čemu je neophodno istaći da su sva korišćena ulja mineralnog porekla. Cilj optimizacije rada koalescera bio je da se pronađu uslovi u kojima se postiže maksimalna vrednost kritične brzine uz minimalni pad pritiska.
The aim of this doctoral dissertation is to contribute to the study of insufficiently known phenomena of coalescent filtration, in order to reduce the number of pilot plant experiments required for designing filters for some specific applications. All the used materials are waste materials the use of which as a filter media contributes to sustainable development. One of the goals of this doctoral dissertation is to study the simultaneous effect of changes in bed permeability and fiber thickness on bed properties, pressure drop and the efficiency of the dispersed oil separation from a continuous aqueous phase. The effect of bed geometry was studied by applying the beds of homogeneous and heterogeneous geometry in depth. A detailed examination of the appearance and morphology of the fibers, as well as the structure of the bed and the appearance and arrangement of its pores, was performed by scanning electron microscopy and optical microscopy. The doctoral dissertation gives an overview of the testing of fibers of different nature (free and interconnected, rigid and elastic, of different thickness and thus of different meandering) and their beds. The simultaneous effect of the changes in the input dispersed phase concentration and the bed permeability was also investigated. Much of the conducted research includes the study of the impact of the nature of the oil phase, and it is necessary to point out that all used oils are mineral oils. The goal of optimizing the operation of a coalescer was to find the conditions providing the maximum critical velocity value with a minimum pressure drop.

L'ecoulement d'une dispersion eau-huile a ete analyse experimentalement et theoriquement pour differentes huiles dans le cas d'un ecoulement de couette circulaire. Les mesures locales effectuees ont porte sur le profil radial de concentration des gouttes par imagerie dans le cas ou l'un ou l'autre des deux cylindres est tournant. D'autres mesures globales ont ete faites et portent sur la mesure du diametre de sauter de la population de gouttes par attenuation lumineuse a l'aide d'une sonde optique. Un modele de melange a ete etabli pour la prediction du profil radial de concentration. Ce modele nous a permis de degager une relation empirique de la diffusivite hydrodynamique. D'autre part les mesures du diametre de sauter ont permis d'estimer le taux de coalescence dans une dispersion eau-huile par confrontation des mesures avec une equation de bilan de population

Sub-salt oil and gas formations in deep-water northern Gulf of Mexico are high priority targets. Advances in seismic processing allow for high-resolution, below-salt imaging. Understanding the modes of salt emplacement provide insight into sub-salt traps and potential drilling hazards. A sub-salt sedimentary unit lies in the Keathley Canyon protraction. Autosutures created the transport-parallel lineaments of the upper surface of the unit. In addition, highly variable sediment aggradation rates created ramps, flats, and basal cutoffs along the base of the allochthon as salt and sediment competed for space. Seismic models identify modes of salt emplacement, salt/sediment interactions, and mechanisms responsible for the morphology. Petrophysical assessments highlight an abnormally pressured, dirty salt environment transitioning into a gouge zone. Dirty salt adds an element of difficulty to managing borehole pressures requiring a unique mud-weight plan designed to resist formation pressures without fracturing lithology.

Agitated dispersions of one liquid in another immiscible liquid are widely used in chemical industry in operations such as liquid-liquid extraction, suspension polymerisation, and blending of polymers. When holdup of the dispersed phase is increased, in an effort to increase the productivity, at a critical holdup, the dispersed phase catastrophically becomes the continuous phase and vice versa. This phenomenon is known as phase inversion. Although the inversion phenomenon has been studied off and on over the past few decades, the mechanism of phase inversion (PI) has yet not become clear. These studies have however brought out many interesting aspects of PI, besides unravelling the effect of physical and operational variables on PL Experiments show that oil-in-water (o/w) and water-in-oil (w/o) dispersions behave very differently, e.g water drops in w/o dispersions contain oil droplets in them, but oil drops in o/w dispersions contain none, dispersed phase hold up at which inversion occurs increases with agitation speed for w/o dispersions but decreases for o/w dispersions. A common feature of both types of dispersions however is that as agitation speed is increased to high values, inversion holdups reach a constant value. A further increase in agitation speed does not change inversion hold up. Although this finding was first reported a long time ago, the implications it may have not received any attentions. In fact, the work reported in the literature since then does not even mention it. The present work shows that this finding has profound implications. Starting with the finding that at high agitation speed inversion hold up does not change with agitation speed, the present work shows that inversion hold up also does not change with agitator diameter, type of agitator and vessel diameter. In these experiments, carried out in agitated vessel, energy was introduced as a point source. The experiments carried out with turbulent flow in annular region of two coaxial cylinders, inner one rotating, in which energy is introduced nearly uniformly throughout the system, show that the inversion holdup remains unchanged. These results indicate that constant values of inversion holdups for a given liquid-liquid systems (o/w and w/o) are properties of the liquid-liquid systems alone, independent of geometrical and operational parameters. A new hypothesis is proposed to explain the new findings. Phase inversion is considered to occur as a result of imbalance between breakup and coalescence of drops. Electrolytes, which affect only coalescence of drops, were therefore added to the system to investigate the effect of altering coalescence of drops on phase inversion. The experiments performed in the presence of electrolyte KI at various concentrations indicate that addition of electrolyte increases the inversion holdup for both o/w and w/o dispersions for three types of systems: non polar-water, polar-water and immiscible organic-organic. Higher the concentration of electrolyte used, higher was the holdup required for phase inversion. These findings indicate that while the addition of electrolyte increases coalescence of drops in lean dispersions, it has exactly opposite effect on imbalance of breakage and coalescence of drops at high holdups near phase inversion point. The opposite effect of electrolytes in lean and concentrated dispersions could be explained qualitatively, but only in part in the light of a new theory, involving multi-particle interactions. The phase inversion phenomenon is quantified in a simple manner by testing the breakage and coalescence rate expressions available in literature. It has been found that, equilibrium drop size (where breakage and coalescence events are in dynamic equilibrium) approaches infinity near phase inversion holdup which is not an ex perimentally observed fact. To capture the catastrophic nature of phase inversion, two steady state approach is proposed. The two steady states namely the stable steady state and unstable steady state, are achieved by modifying the expression for coalescence frequency on the basis of (i) shear coalescence mechanism and, (ii) recognising the fact that at high dispersed phase holdup the droplets are already in contact with each other at all times and hence rendering the second order coales cence process to a first order one. Using two steady states approach, catastrophic phase inversion is shown to occur at finite drop size.

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Coalescence enhancement of water droplets in oil emulsions is commonly contemplated for the separation of an aqueous phase dispersed in a dielectric oil phase with a considerably lower dielectric constant than that of the dispersed phase. The characteristics and geometry of the electrode system have a large impact on the performance of an electrostatic coalescer and are actually strictly linked to the type of the applied electric field and the emulsion used. Furthermore, addition of chemicals and heating has also been revealed to further enhance the electrocoalescence of water droplets. In this work, the coalescence of two water drops sinking in a dielectric oil phase at an applied high voltage, pulsed dc electric field, in particular with regards to the effects of pressure and temperature on coalescence performance is investigated. The developed model should help to recognise and prove approaches to electrocoalescence mechanisms, the dispersion flow direction with respect to the applied electric field, as well as the electric field configuration.

PhD thesis research project is focused on kinetics study of olive pastes on malaxation and development of spectroscopic techniques for rapid determination of quality indices for the control of the extra virgin olive oil process. A kinetic time-temperature study during malaxation was carried out to evaluate the coalescence and the extraction yield obtaining an optimization map. Moreover, indices directly related to the biochemical maturation of the drupes have been identified. These indices, quality and legal indices related to extra virgin olive oil were objected to predictive models through rapid determination based on NIR spectroscopy. Il Dottorato ha focalizzato l’attenzione sullo studio cinetico dell’operazione di gramolatura delle paste d’oliva e la messa a punto di tecniche spettroscopiche per la rapida determinazione di indici per il controllo del processo dell’olio extravergine d’oliva. È stato condotto uno studio cinetico tempo-temperatura per valutare la coalescenza e, di conseguenza, la resa d’estrazione ottenendo una carta di ottimizzazione. Inoltre, sono stati identificati indici direttamente correlati alle trasformazioni biochimiche che avvengono durante la maturazione delle olive. Questi indici insieme ai parametri qualitativi e legali dell’olio extravergine d’oliva sono stati oggetto di modelli predittivi mediante determinazione rapida basata sulla spettroscopia nel vicino infrarosso.

Emulsions are advantageous in many applications including healthcare, food science, and detergency due to their ability to disperse one fluid in another, otherwise immiscible fluid. For the same reason, emulsions are also problematic when mixtures of oil and water are undesirable like in industrial wastewater pollution and fuel systems. Whether an emulsion is desirable or not, both benefit from understanding the fundamental relationship of emulsion formation and stability to the physical and chemical properties of the oil-water-surfactant mixture. This work identifies the formation and stability mechanisms of model emulsion systems through the perspective of emulsion prevention for applications in shipboard wastewater (bilge water) treatment. Although experiments in this study were designed to model bilge water systems, their fundamental approach makes them practical for many different applications like food science, pharmaceuticals, and detergency.

The impact of salts on emulsion formation and stability to coalescence were studied to understand how emulsions stabilized by ionic surfactant behave in saltwater environments. Droplet size analysis revealed that emulsion stability to coalescence improved with salt concentration. Through interfacial tension and zeta potential measurements, it was found that the addition of salt promoted close surfactant packing and faster surfactant adsorption kinetics at the oil-water interface. This aided in preventing coalescence and created conditions favorable for the formation of a stable Newton black film. Extended DLVO calculations were used to model the interaction energy between droplets and suggested that hydration forces play an important role in stabilizing these systems. These emulsions were then studied under dynamic ageing conditions to observe the impact of motion on emulsion stability. While statically aged emulsions were stable to coalescence, dynamic ageing induced coalescence (increased droplet size) or emulsified the oil droplets (decreased droplet size) depending on the surfactant concentration and energy input during ageing.

Formation mechanisms and stability of spontaneous emulsion systems were also investigated. Low molecular weight oils (e.g., toluene, xylenes, and cyclohexane) were found to spontaneously emulsify with nonylphenol polyethoxylated (NPE) and sodium dodecylbenzene sulfonate (SDBS). NPE emulsions spontaneously emulsified via diffusion and micelle swelling and displayed limited stability due to Ostwald ripening. SDBS emulsions also spontaneously emulsified with toluene but only in saltwater environments. As the concentration of salt in the aqueous phase increased, the spontaneity of these emulsions also increased. These systems were analyzed using the hydrophilic lipophilic difference (HLD) theory to evaluate its efficacy for predicting the conditions favorable for spontaneous emulsification. Limitations and practicality of using the HLD model for these systems were also explored.