Effects of Gas Velocity and Solid Hold-Up on the Sub-Grid Behavior of Riser Flows

Two-fluid highly resolved sub-grid simulations (SGS) of riser flows were developed under realistic gas velocities and solid hold-ups, for a solid phase derived from high Stokes number particles. The results showed that both gas velocity and solid hold-up considerably affect the effective hydrodynamics of the solid phase

Solução numérica de problemas bidimensionais de convecção natural em cavidades arbitárias

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-graduação em Engenharia Mecânica

A thermogravimetric analysis of the combustion of a Brazilian mineral coal

Knowledge of coal combustion kinetics is crucial for burner design. This work aims to contribute on this issue by determining the kinetics of a particular Brazilian bituminous coal. Non-isothermal thermogravimetry was applied for determining both the pre-exponential factor and the activation energy. Coal samples of 10 mg and 775 mm mean size were used in synthetic air atmospheres (21 % O2). Heating rates from 10 to 50 ºC/min were applied until the temperature reached 850 ºC, which was kept constant until burnout. The activation energy for the primary and the secondary combustion resulted, respectively, in 135.1 kJ/mol and 85.1 kJ/mol.(FAPESP) São Paulo Research Foundation(CNPq) National Council for Scientific and Technological Developmen

Interpretation of the mechanism diffusion in the gas-solid process of the dessulfurization reaction

The present paper aims to interpret the SO2 diffusion mechanism process for two different limestones: a calcite and a dolomite. In previous study, the apparent activation energies for sulfation reaction were between 3.03 and 4.45 kJ mol-1 for the calcite, and 11.24 kJ mol-1 for the dolomite. Using nitrogen porosimetry it was possible to observe that the dolomite presents mesopores of 0.03 μm, while the calcite presents mesopores of 0.01 μm. The evaluation of limestones porous structure together with their kinetic parameters, allowed concluding that the diffusion mechanism follows Fick law and Knudsen law for dolomite and calcite, respectively.FAPESPCoordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES

Artigo A THERMOGRAVIMETRIC ANALYSIS OF THE COMBUSTION OF A BRAZILIAN MINERAL COAL

Recebido em 8/3/07; aceito em 11/7/07; publicado na web em 19/12/07 Knowledge of coal combustion kinetics is crucial for burner design. This work aims to contribute on this issue by determining the kinetics of a particular Brazilian bituminous coal. Non-isothermal thermogravimetry was applied for determining both the preexponential factor and the activation energy. Coal samples of 10 mg and 775 μm mean size were used in synthetic air atmospheres (21 % O 2 ). Heating rates from 10 to 50 o C/min were applied until the temperature reached 850 o C, which was kept constant until burnout. The activation energy for the primary and the secondary combustion resulted, respectively, in 135.1 kJ/mol and 85.1 kJ/mol

Cluster identification and characterization in the riser of a circulating fluidized bed from numerical simulation results

A methodology of identification and characterization of coherent structures mostly known as clusters is applied to hydrodynamic results of numerical simulation generated for the riser of a circulating fluidized bed. The numerical simulation is performed using the MICEFLOW code, which includes the two-fluids IIT`s hydrodynamic model B. The methodology for cluster characterization that is used is based in the determination of four characteristics, related to average life time, average volumetric fraction of solid, existing time fraction and frequency of occurrence. The identification of clusters is performed by applying a criterion related to the time average value of the volumetric solid fraction. A qualitative rather than quantitative analysis is performed mainly owing to the unavailability of operational data used in the considered experiments. Concerning qualitative analysis, the simulation results are in good agreement with literature. Some quantitative comparisons between predictions and experiment were also presented to emphasize the capability of the modeling procedure regarding the analysis of macroscopic scale coherent structures. (c) 2007 Elsevier Inc. All rights reserved