The gas-solids flow in a CFB riser is simulated applying two-fluid modeling. Two different procedures are used for the calculation of the solids phase pressure and stress tensor: the traditional procedure and an algebraic version of the kinetic theory of granular flows. Three different numerical meshes and two different discretization schemes for the advective terms are used. Results are compared to available experimental data from the literature. The effects of the solids phase modeling procedure, advection discretization scheme, and mesh size are discussed.

Turbulence parameters are derived from results of numerical simulation of gas-solid flow in circulating fluidized bed (CFB). A two fluid model with constant viscosity is applied considering an Eulerian continuum approach for both phases. An analysis is performed using a direct numerical integration of balance equations without an explicit use of any turbulence model for both phases. Even though velocity fluctuations of lower scales are eliminated by the considered computational mesh, fluctuations of larger scales are detected and analyzed. The results show that the Reynolds stresses behave according to the expected for a turbulent flow, and a reasonable agreement is found regarding literature experiment. Following the literature, granular temperature is derived from the Reynolds stresses, and qualitatively matches the expected behavior as described by the kinetic theory of granular flow. Finally, it is seen that solid's phase turbulence is captured using the present approach.

The dynamics of formation, dissipation and breaking of coherent structures in the riser gas-solid flow of a circulating fluidized bed (CFB) are evaluated by numerical simulation. The simulation is performed using the MICEFLOW code, which includes IIT's two-fluid hydrodynamic model B. The methodology for cluster characterization is used from Sharma et al. and is based on determination of four characteristics, average lifetime, average volumetric fraction of solid, existence time fraction and frequency of occurrence. Clusters are identified applying a criterion for the time average value of the volumetric solid fraction. A qualitative analysis of the influence of different drag function correlations on the hydrodynamics of the flow, including the evolution of coherent structures, is performed. The simulation predictions are also compared to experimental results. The results indicate that the choice of a correlation for drag function should be quite judicious. Finally it is shown that the mean clustering criteria of Sharma et al. should be modified to take into account other factors that influence cluster dynamics.

A particulate feeding system based on air flluidization principles was developed at the Thermal and Fluids Engineering Group at EESC-USP. The system is basically formed of a cylindrical chamber comprising two levels of fluid bed distributor plates. The performance of the system was addressed. Repeatability experiments were performed in order to check out for the possibility of solids feeding control through a sphere valve which controls the air feed rate. Silica sand particles of three different size were used, with mean diameters of 152, 287 and 484 µm. Experiments showed that the total particulate discharge depends on the primary air feeding rate, the distance between the exit of the feeding hopper and the primary air distributor plate, and the particulate diameter, but independs on the secondary air feeding rate. The system was observed to be of difficult control and showed poor repeatability. However, the system was found to be an excellent device for distributing the flow of solids throughout several discharge sections. For the operational conditions considered and air volumetric flowrates above 3×10-3 m³/s the deviation on the particulate mass flowrate through a given discharge section related to the average value through the four sections of the injector was always below 5 %.