In power generation from solid fuel such as coal-fired power plants, combustion efficiency can be monitored by the loss on ignition (LOI) of the pulverised fuel. It is the role of the pulveriser-classifier combination to ensure pulverised fuel delivered to the burners is within the specified limits of fineness and mass flow deviation required to keep the LOI at an acceptable level. However, government imposed limits on emissions have spurred the conversion of many coal fired power plants to convert to the use of Low NOx Burners. To maintain good LOI or combustion efficiency, the limits of fineness and mass flow deviation or inter-outlet fuel distribution have become narrower. A lot of existing pulveriser units cannot operate efficiently within these limits hence retrofits of short term solutions such as orifice balancing and classifier maintenance has been applied. The work performed in this thesis relates to an investigation into coal classifier devices that function to control fineness and inter pipe balancing upstream of the burner and downstream of the pulverisers. A cold flow model of a static classifier was developed to investigate the flow characteristics so that design optimisations can be made. Dynamic similarity was achieved by designing a 1/3 scale model with air as the continuous phase and glass cenospheres of a similar size distribution as pulverised fuel, to simulate the coal dust. The rig was operated in positive pressure with air at room temperature and discharge to atmosphere. The Stokes number similarity (0.11-prototype vs. 0.08-model) was the most important dimensionless parameter to conserve as Reynolds number becomes independent of separation efficiency and pressure drop at high industrial values such as 2 x 10 4 Hoffman, 2008). Air-fuel ratio was also compromised and an assumption of dilute flow was made to qualify this. However, the effect of air fuel ratio was ascertained by its inclusion as an experimental variable. Experiments were conducted at air flow rates of 1.41-1.71kg/s and air fuel ratios of 4.8-10 with classifier vane angle adjustment (30°- 60°) and inlet swirl umbers (S) of 0.49 – 1. Radial profiles of tangential, axial and radial velocity were obtained at several cross sections to determine the airflow pattern and establish links with the separation performance and outlet flow balance. Results show a proportional relationship between cone vane angle and cut size or particle fineness. Models can be derived from the data so that reliable predictions of fineness and outlet fuel balance can be used in power stations and replace simplistic and process simulator models that fail to correctly predict performance. It was found that swirl intensity is more significant a parameter in obtaining balanced flow at the classifier outlets than uniform air flow distribution in the mill. However the latter is important in obtaining high grade efficiencies and cut size. The study concludes that the static classifier can be further improved and retrofit-able solutions can be applied to problems of outlet flow imbalance and poor fineness at the mill outlets.

No description available.

Gas lift is a means of enhancing oil recovery from hydrocarbon reservoirs. Gas injected at the production riser base reduces the gravity component of the pressure drop and thereby, increases the supply of oil from the reservoir. Also, gas injection at the base of a riser helps to mitigate slugging and thus, improving the performance of the topside facility. In order to improve the efficiency of the gas lifting technique, a good understanding of the characteristics of gas-liquid multiphase flow in vertical pipes is very important. In this study, experiments of gas/liquid (air/water) two-phase flows, liquid/liquid of oil/water two-phase flows and gas/liquid/liquid (air/oil/water) three-phase flows were conducted in a 10.5 m high 52 mm ID vertical riser. These experiments were performed at liquid and gas superficial velocities ranging from 0.25 to 2 m/s and ~0.1 to ~6.30 m/s, respectively. Dielectric oil and tap water were used as test fluids. Instruments such as Coriolis mass flow meter, single beam gamma densitometer and wire-mesh sensor (WMS) were employed for investigating the flow characteristics. For the experiments of gas/liquid (air/water) two-phase flow, flow patterns of Bubbly, slug, churn flow regimes and transition regions were identified under the experimental conditions. Also, for flow pattern identification and void fraction measurements, the capacitance WMS results are consistent with those obtained simultaneously by the gamma densitometer. Generally, the total pressure gradient along the vertical riser has shown a significant decrease as the injected gas superficial velocity increased. In addition, the rate of decrease in total pressure gradient at the lower injected gas superficial velocities was found to be higher than that for higher gas superficial velocities. The frictional pressure gradient was also found to increase as the injected gas superficial velocity increased. For oil-water experiments, mixture density and total pressure gradient across the riser were found to increase with increasing water cut (ranging between 0 - 100%) and/or mixture superficial velocity. Phase slip between the oil and water was calculated and found to be significant at lower throughputs of 0.25 and 0.5 m/s. The phase inversion point always takes place at a point of input water cut of 42% when the experiments started from pure oil to water, and at an input water cut of 45% when the experiment’s route started from water to pure oil. The phase inversion point was accompanied by a peak increase of pressure gradient, particularly at higher oil-water mixture superficial velocities of 1, 1.5 and 2 m/s. The effects of air injection rates on the fluid flow characteristics were studied by emphasizing the total pressure gradient behaviour and identifying the flow pattern by analysing the output signals from gamma and WMS in air/oil/water experiments. Generally, riser base gas injection does not affect the water cut at the phase inversion point. However, a slight shift forward for the identified phase inversion point was found at highest flow rates of injected gas where the flow patterns were indicated as churn to annular flow. In terms of pressure gradient, the gas lifting efficiency (lowering pressure gradient) shows greater improvement after the phase inversion point (higher water cuts) than before and also at the inversion point. Also, it was found that the measured mean void fraction reaches its lowest value at the phase inversion point. These void fraction results were found to be consistent with previously published results.

Current oil production technologies recover only about one‐third to one‐half of the oil originally present in an oil reservoir. Given current oil prices, even a modest increase in oil recovery efficiency is fiscally attractive. One novel approach to increase oil recovery efficiency is a process called microbial enhanced oil recovery (MEOR), where microorganisms are either used as a clogging agent to redirect flow or to produce biosurfactant that reduces interfacial tension. This dissertation aims to understand the MEOR pore‐scale mechanisms relevant to oil recovery by taking a two‐fold approach where transparent 2‐dimensional micromodel experiments imaged with stereo microscopy and 3‐dimensional column experiments imaged with x‐ray computed microtomography (CMT) are utilized. Micromodel experiments allow for direct visualization of the biological phase (i.e. biofilm), however, only 2‐dimensional information is provided. Conversely, CMT experiments provide 3‐dimensional pore‐scale information, but lack the ability to image the biological phase. With this two‐fold approach, it is possible to distinguish multiple fluid interfaces, quantify fluid phase saturations, measure oil blob size distributions, and visualize the biological phase. Furthermore, a method to measure interfacial curvature from 3‐dimensional images is developed, providing researchers a new perspective from which to study multiphase flow experiments. Overall, the presented research utilizes pore‐scale imaging techniques to study the interfacial interactions occurring during MEOR in an effort to better explain the physics, and thus, increase the efficacy of MEOR. / Graduation date: 2012

Thesis (M.S.)--Ohio University, August, 1995. / Title from PDF t.p.

Thesis (M.S.)--King Fahd University of Petroleum and Minerals, 1989. / Title from document title page. Includes bibliographical references. Available in PDF format via the World Wide Web.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (MSc (Mathematics))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Packed beds are widely used in industry to improve the total contact area between two substances in a multiphase process. The process typically involves forced convection of liquid or gas through either structured or dumped solid packings. Applications of such multiphase processes include mass transfer to catalyst particles forming the packed bed and the adsorption of gases or liquids on the solid packing. An experimental study on the determination of air flow pressure drops over different packingmaterialswas carried out at the Telemark University College in Porsgrunn,Norway. The packed bed consisted of a cylindrical column of diameter 0.072m and height 1.5m, filled with different packingmaterials. Air was pumped vertically upwards through a porous distributor to allow for a uniform inlet pressure. Resulting pressure values were measured at regular height intervals within the bed. Due to the geometric nature of a Raschig ring packing wall effects, namely the combined effects of extra wall shear stress due to the column surface and channelling due to packing adjacent to a solid column surface, were assumed to be negligible. Several mathematical drag models exist for packed beds of granular particles and an important question arises as to whether they can be generalized in a scientific manner to enhance the accuracy of predicting the drag for different kinds of packing materials. Problems with the frequently used Ergun equation, which is based on a tubular model for flow between granules and then being empirically adjusted, will be discussed. Some theoretical models that improve on the Ergun equation and their correlation with experimental work will be discussed. It is shown that a particular pore-scale model, that allows for different geometries and porosities, is superior to the Ergun equation in its predictions. Also important in the advanced models is the fact that it could take into account anomalies such as dead zones where no fluid transport is present and surfaces that do neither contribute to shear stress nor to interstitial form drag. The overall conclusion is that proper modelling of the dynamical situation present in the packing can provide drag models that can be used with confidence in a variety of packed bed applications. / AFRIKAANSE OPSOMMING: Gepakte materiaal strukture word in die industrie gebruik om die kontak area tussen twee stowwe in meervoudige faseprosesse te vergroot. Die proses gaan gewoonlik gepaard met geforseerde konveksie van ’n vloeistof of ’n gas deur gestruktureerde of lukrake soliede gepakte strukture. Toepassings van sulke meervoudige faseprossese sluit onder andere in die massa-oordrag na katalisator partikels wat die gepakte struktuur vorm of die absorpsie van gasse of vloeistowwe op die soliede gepakte elemente. ’n Eksperimentele ondersoek oor die drukval van veskillende gepakte elemente in ’n kolom is gedoen by die Telemark University College in Porsgrunn, Noorweë. Die gepakte struktuur het bestaan uit ’n kolommet ’n diameter van 0.072m en ’n hoogte van 1.5m. Lug is vertikaal opwaarts gepomp deur ’n poreuse plaat wat gesorg het vir ’n benaderde uniforme snelheidsprofiel. Die druk is toe op intervalle deur die poreuse struktuur gemeet. In die studie is die effekte van die eksterne wande, nl. die bydrae van die wand se wrywing en die vorming van kanale langs die kolom wand, as weglaatbaar aanvaar. Daar bestaan baie wiskundige dempingsmodelle vir gepakte strukture wat uit korrels saamgestel is. ’n Belangrike vraag kan dus gevra word, of laasgenoemde modelle veralgemeen kan word op ’n wetenskaplike manier om die demping deur verskillende gepakte strukture akkuraat te kan voorspel. Probleme wat ontstaan het met die wel bekende Ergun vergelyking, wat gebaseer is op ’n kapillêre model en wat toe verder aangepas is deur empiriese resultate van uniforme sfere, sal bespreek word. Teoretiesemodelle wat verbeteringe op die Ergun vergelyking voorstel sal bespreek word en vergelyk word met eksperimentele data. Daar word ook gewys dat ’n spesifieke porie-skaal model, wat aanpasbaar is vir verskillende geometrieë en porositeite, in baie gevalle beter is as die Ergun vergelyking. ’n Ander baie belangrike aspek van gevorderde modelle is die moontlikheid om stagnante gebiede in die gepakte strukture in ag te neem. Laasgenoemde gebiede sal die totale kontak area sowel as die intermediêre vorm demping verlaag. Die gevolgtrekking is dat wanneer deeglike modulering van dinamiese situasies in die industrie gedoen word kan dempings modelle met vertroue op ’n verskeidenheid gepakte strukture toegepas word.

Na região do espectro visível o petróleo é opaco, porém na região do infravermelho o petróleo apresenta translucidez à radiação. Isto permite a detecção óptica e não intrusiva de fenômenos que ocorram com o petróleo e no interior do volume contendo petróleo. É então explorada a região de 8 a 12 μm mostrando resultados que comprovam o potencial da técnica. A detecção óptica baseia-se na Lei de Beer-Lambert: o espectro eletromagnético emitido por fonte óptica, ao atravessar meio absorvedor, sofre decaimento exponencial na intensidade correspondente ao caminho óptico percorrido, à concentração da substância e ao seu coeficiente de absorção. Porém, em certos casos, outros efeitos ópticos, como a reflexão e a refração predominam, gerando resultados que não são compreendidos somente pelo estudo da absorção. Para compreender tais resultados é implementado modelo matemático do escoamento de bolhas de ar em petróleo. Ao utilizar radiação infravermelha para detecção óptica trabalha-se no liminar entre o domínio óptico e o térmico. Para entendimento dos limites de cada efeito é realizado estudo da influência da variação de temperatura na detecção óptica do petróleo. Tendo todo o sistema óptico caracterizado, são realizados testes com o escoamento de bolhas de ar em petróleo e desenvolvido o circuito fechado para o escoamento bifásico envolvendo petróleo e ar. É observado o escoamento de bolhas em cuveta com 12 mm de comprimento de interação. Como os resultados foram obtidos sem a utilização de materiais otimizados para o comprimento de onda de trabalho, conclui-se ser possível transmissão por caminhos mais longos. Como conclusão, é possível detectar de forma não intrusiva o escoamento bifásico envolvendo petróleo e ar empregando técnicas de monitoramento baseadas em radiação infravermelha. Os resultados são promissores e devem resultar no desenvolvimento de instrumentação com potencial para aplicação em campo para a caracterização de escoamento envolvendo petróleo e outras substâncias como água, CO2, H2S, gás natural entre outros. / Petroleum is opaque in the visible region of the electromagnetic spectrum and therefore is normally a common sense that optical techniques cannot be used as a noninvasive tool to monitor any physical or chemical phenomena through a petroleum volume. There is, however, a great opportunity when the infrared region of the petroleum optical absorption spectrum given that it is semitransparent and therefore radiation can propagate through a volume containing petroleum or mixture with petroleum. The optical detection is based on the Beer-Lambert Law: the electromagnetic spectrum emitted by an optical source, crossing through the absorber undergoes exponential decay in intensity corresponding to the optical path, the concentration of the substance and its absorption coefficient. However, in certain cases, other optical effects such as reflection and refraction predominate, leading to light attenuation that is not understood only by the study of absorption. To understand these results it is implemented a mathematical model of the air bubbles flowing inside a petroleum volume. It is worth pointing out that the IR region of the electromagnetic spectrum can be understood via optical as well as thermal phenomena. To understand the limits of each effect a study of the influence of the temperature variation on the optical detection of petroleum is performed. The flow of air bubbles in static petroleum is studied and a flow loop for air and oil is designed and tested and the flow is measured by the IR monitoring system. The flow of bubbles is observed through 12 mm length of petroleum. These results were obtained without using optimized components and it is concluded that transmission through longer paths is possible. In conclusion, it is possible to detect, by a non -intrusive technique, the two-phase flow involving the petroleum and air employing monitoring techniques based on infrared radiation. The results are promising and should result in the development of instrumentation for potential application in the field for characterizing flow involving petroleum and other substances such as water, CO2, H2S, natural gas and others. Keywords (letras minúsculas separadas por vírgulas): infrared, petroleum, CO2, multiphase flow.

L’atomisation assistée est un procédé de formation d’un spray de gouttelettes issu d’une nappe liquide sous l’action d’un courant gazeux à forte vitesse dans un injecteur. Ce procédé est très utilisé dans de nombreuses applications industrielles. Nous étudions la succession d’instabilités hydrodynamiques qui génère les gouttes du spray à l’aide d’une méthode LIF pour mesurer la fréquence des vagues et d’une sonde optique pour la granulométrie des gouttes. Nous validons expérimentalement un nouveau modèle de stabilité linéaire inviscide pour l’instabilité de cisaillement, intégrant un profil de vitesse avec déficit à l’injection. Des simulations numériques et un modèle spatio-temporel de stabilité linéaire sont utilisés pour mettre en avant de nouveaux mécanismes de déstabilisation, de croissance des vagues et de création de gouttes. Les lois d’échelles connues prédictives du diamètre moyen des gouttes en fonction du Weber gaz sont testées pour de nouvelles variables d’étude. / Assisted atomization is a process used to form a spray of droplets. A slow liquid phase is strippedby the action of a strong gas current in order to generate the spray. This process is used in manyindustrial applications. We study the succession of hydrodynamic instabilities generating dropletsby means of a LIF method to measure the frequency and growthrate of waves, and with an opticalprobe to measure drop size and velocity. We validate experimentally a model including an interfacialvelocity deficit in the inviscid stability analysis. Experiments are compared to numerical simulationsand spatiotemporal stability analysis results : the confrontation of these three approaches is used tobring forward new mechanisms of destabilization, growth of waves and creation of drops. We assessthe influence of liquid thickness and dynamic pressure ratio on the dependency of the mean dropletdiameter with the Weber number.