The hydrodynamic characteristics of dense conical fluidized bed were investigated experimentally and numerically. Experimental studies have been carried out in a bed containing TiO2 particles belonging to A/C boundary of Geldart's classification with a wide particle size distribution. Pressure measurements and an optical fiber technique allowed determining the effect of high bed particles loading on the minimum fluidization velocity, local solid volume fraction and solid velocity. Two-fluid model approach with three different drag models and boundary conditions (BCs) consisting of no-slip, partialslip and free-slip BC is presented for the numerical predictions. In this paper, we show the Gidaspow drag function with k-e turbulent model by applying the partial-slip BC can improve the numerical results at high particle loading.

In the computational fluid dynamics (CFD) modeling of gas-solids two phase flow, the effect of boundary conditions play an important role in predicting the hydrodynamic characteristics of fluidized beds. In this work, the hydrodynamics of conical fluidized bed containing dried TiO2 nano-agglomerates were studied both experimentally and computationally. The pressure drop was obtained by pressure measurements and mean solid velocity in the different axial and radial positions and their experimental values were measured by a parallel 3-fiber optical probe. The Eulerian-Eulerian multiphase model and granular kinetic theory with using Gidaspow (1994) drag function were applied in simulations. The effect of three different types of boundary conditions (BC) including no-slip/friction, free-slip/no-friction and high-slip/small-friction which were developed by Schaeffer (1987) and Johnson and Jackson (1987) were investigated. The results of the model were compared with the experimental data. The numerical simulation using free-slip/no-friction BC agreed reasonably well with the experimental pressure drop measurements. The pressure drops predicted by the simulations were in agreement with the experimental data at superficial gas velocities higher than the minimum fluidization velocity, Umf. The results for simulated mean axial solid velocity showed that the free-slip/no-friction BC was in better agreement with the experimental data compared with other boundary conditions.

In this study, an Eulerian-Eulerian multi-fluid model (MFM) was used to simulate the segregation pattern of a conical fluidized bed containing ternary mixtures of equidensity TiO2 particles. Experimental 'freeze– sieving' method was employed to determine the axial mass fraction profiles of the different-sized particles and validate the simulation results. The profiles of mass fraction for large-, medium-, and small-sized particles along the bed height during the simulation time indicated that the particles’ segregation could be predicted by CFD model. Effect of superficial gas velocity on segregation pattern was also investigated. It was shown that for U0=1. 2Umf, partial segregation of large particles occurred, while for U0=1. 6Umf, small-and medium-sized particles also segregated and full segregation was achieved. By increasing U0 to 2Umf, mixing of different sized particles increased and particles segregation reduced. Therefore, it can be concluded that there was a critical velocity below which particles would segregate while above which their mixing increased.

The size estimating of fluidized Titania agglomerates in a conical fluidized bed was studied by force balance model and fractal scaling analysis. The primary size of titania Nano Particles (NPs) was 21 nm, while for complex agglomerates was in the size range of several hundred micrometers. The formation mechanism of simple-agglomerate and complex-agglomerate structures was studied experimentally. The size distribution and morphology of agglomerates were determined by advanced laser dynamic imaging and scanning electron microscopy. The AFM-nanoindentation test was used to determine the elastic modulus of agglomerates with porous structures. The size distribution of Titania NP agglomerates was estimated by the fractal analysis through the relationship between the number of particles and gyration diameter. The fractal exponent obtained from the power-law scaling of agglomerates and the complex agglomerate sizes were determined experimentally and theoretically. A simple theoretical model was applied to estimate the complex agglomerates' size based on the equilibrium of the separation and cohesion forces. The proposed model showed satisfactory results compared with the experimental data. The results of the present study can help to determine the critical gas velocity in achieving the desired agglomerate size of Titania NPs.

A dynamic model representing the continuous fluidized bed dryer is presented. The model takes into account the presence of the three phases: bubble phase, cloud phase and emulsion phase. The transient analysis for step disturbances in the input variables is obtained. The influence of operating conditions on the dynamics of the dryer is discussed and the results are compared with the experiment. The model can be used for developing a model based on other suitable control strategies.

In present paper, dynamic behavior and control of a fluidized bed reactor for polyethylene production has been considered. A double active sites model for Ziegler-Natta catalysts is used for simulation of polymerization reaction. Hydrodynamic behavior of the bed is modeled using a two phase model including bubble and emulsion phases in which bubble phase has plug flow pattern with differentially variable velocity and size through the bed and emulsion phase has the CSTR flow pattern. The reactor model is validated using industrial data. Conventional PID controllers with anti-windup are considered for control purposes. It has been shown that the control system has satisfactory performances either for set point tracking or load rejection. To improve the performance of the control system for load rejection the cascade control strategy has been considered.