No description available.

The performance of ebullated bed hydroprocessors depends on the fluids distribution system and liquid recycle pan. Given that bubbles do not readily coalesce in the bed, the original bubble size distribution generated at the bubble cap distributor likely impacts buoyancy-based phase separation at the recycle pan. Gas entrained in the liquid recycle increases bed gas holdup at the expense of liquid holdup and product yield. The aim of this work was to investigate the impact of gas-liquid distribution system on resulting bubble properties and dynamics and incorporate a distributor sub-model into an existing fluid dynamics model of the industrial hydroprocessor. The size of initial bubbles formed in the plenum chamber was found to have negligible impact on phase holdups above the distributor. However, resulting bubble properties were found to depend on distributor geometry, distributor power dissipation and gas-liquid velocity ratio. In addition, a new set of scaling laws for gas-liquid distributors, based on dimensional analysis and similitude, was proposed. Geometric scaling was based on matching distributor fractional open area and ratios of critical dimensions. Dynamic similarity was based on matching three dimensionless groups and bubble coalescence behaviour. A bubble size distribution model was then developed. Both pressure and distributor were found to have an impact on individual bubble drag coefficients, as they both altered bubble size distribution. A novel drag model was thus also developed at industrially relevant conditions. Finally, a new gas-liquid distributor sub-model, including bubble size distribution and drag models previously developed, was incorporated into an overall fluid dynamics model of the hydroprocessor. The bubble size distribution model was also coupled with existing gas-liquid separation sub-model to better predict recycled gas and liquid fractions. A sensitivity analysis performed with the overall model revealed distributor configurations with potential of improving the processing capacity of the hydroprocessor.

No description available.

Hydrogenation of nitrile butadiene rubber (NBR) has been carried out industrially for a number of years, producing a material with exceptional resilience to high temperatures and oxidative conditions. Current processes involve a batch reactor which is difficult to optimize further for larger scale production. A continuous process for this particular process is required in order to provide a large volume of production with consistent qualities. The integration of heat balance could be realized in a continuous process. A novel continuous process for hydrogenation of NBR has been developed in the present work. A multistage agitated contactor (MAC) was proposed as a gas liquid reactor for this process. Comprehensive hydrodynamic data have been acquired under various process conditions. The hydrodynamic behaviour under different operating variables such as stirring speed, liquid flow rate and gas flow rate has been understood through experimental study. It is found that an increase in stirring speed intensifies liquid backmixing while an increase liquid flow rate decreases liquid backmixing. The presence of gas flow helps in reducing liquid back mixing by two coupled effects: liquid entrainment effect due to a cocurrent operation manner and a strengthening effect of liquid flow rate due to its reduction of liquid hold-up. Contradictory conclusions regarding the effect of liquid viscosity on liquid backmixing in a MAC have been resolved through experimental investigation and computational fluid dynamics (CFD) simulations. It is shown that an increase in liquid velocity dampens turbulence which contributes to liquid phase backmixing within the reactor. The established hydrodynamic understanding of MACs in the present work widens its potential application for gas liquid process. Based on comprehensive understanding of the proposed reactor, a bench-scale prototype was designed and constructed in order to demonstrate hydrogenation performance. One more efficient catalyst for NBR hydrogenation, an osmium-based catalyst, was used in the present work. Hydrogenation degree of NBR in the continuous unit was investigated at operating conditions relevant to industrial applications. It is indicated from the experimental results that a desired hydrogenation degree of over 95% in 2.5% and 5% NBR solutions can be achieved at the conditions investigated. It is also shown that both system pressure and catalyst loading increase hydrogenation conversion. Mathematical modeling of the designed process was established by coupling the intrinsic catalytic hydrogenation from batch studies and flow behavior of the reactor. A cascade of stirred tanks with back flow (CTB) model was used to characterize the dynamic hydrogenation performance in a MAC. The comparison of experimental results and numerical prediction indicates that the established model could satisfactorily predict the hydrogenation in the designed process with consideration of approximately 30%-50% catalyst deactivated due to impurities and oxygen contamination in the polymer solution. A revised n CSTRs-in-series model was proposed to predict the hydrogenation degree at steady state and a good agreement was found when comparing the predicted results with the experimental data. A continuous process for hydrogenation at a pilot scale was designed based on the primary results from the bench scale process. A process with a capacity of 50 tons/year was targeted and the hydrogenation efficiency provided by the pilot scale unit has been estimated through the established reactor model.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 167-174).

In turbulent water flows, large quantities of air bubbles are entrained at the free-surfaces. Practical applications of gas-liquid bubbly flows are found in Chemical, Civil, Environmental, Mechanical, Mining and Nuclear Engineering. Air-water flows are observed in small-scale as well as large-scale flow situations. Typical examples include thin circular jets used as mixing devices in chemical plants (Qw = 0.001 L/s, diameter = 1 mm) and spillway flows (Qw larger than 10,000 m3/s, flow thickness over 10 m). In each case, however, the interactions between the entrained air bubbles and the turbulence field are significant. The present manuscript regroups a collection of one book and 43 articles on the study of air bubble entrainment in turbulent flows. The work aims to gain a better understanding of the basic mechanisms of gas entrainment and the nteractions between entrained gas bubbles and the turbulence. It has been the purpose of the research work to assess critically the overall state of this field, to present new analysis and experimental results, to compare these with existing data, and to present new compelling conclusions regarding momentum and void fraction development of air-water gas-liquid bubbly flows. The manuscript presents a comprehensive analysis of the air entrainment processes in free-surface turbulent flows. The air-water flows are investigated as homogeneous mixtures with variable density. The variations of fluid density result from the non-uniform air bubble distributions and the turbulent diffusion process. Several types of air-water free-surface flows are studied : plunging jet flows, open channel flows, and turbulent water jets discharging into air.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 111-121).

Thesis (Ph. D.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains xxiv, 371 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 343-367).

Thesis (M. Sc.)--University of Canterbury, 2007. / Typescript (photocopy). Includes bibliographical references (leaves 76-78). Also available via the World Wide Web.

[pt] O presente trabalho analisa experimentalmente o escoamento estratificado gás-líquido (ar-água) em um duto de seção retangular. Obteve-se uma correlação empírica para a tensão de cisalhamento na interface. Verifica-se que tal tensão, além de ser função dos números de Reynolds de ambos os escoamentos, depende também de características inerentes à fase líquida. Um perfil teórico de velocidade do gás foi comparado com os dados experimentais obtidos por anemometria para a região logarítmica. Foi realizada uma análise de incertezas, que mostrou uma elevada confiabilidade nos resultados obtidos. / [en] Experiments were carried out to analyse a gás-liquid (air-water) stratified flow through a retangular duct. An empirical correlation was ontained for the shear stress at the interface. Such shear stress, that depends on the Reynolds numbers of both flows, is also a function of liquid specific parameters. A theoretical gas velocity profile was compared with experimental data using a hot-wire anemometry with good results in the logaritimic region. The uncertainly abalysis shows that this correlation presents a very low degree of uncertainly.