Behavior Of Trickle Bed Reactor Research Articles

CFD Simulation of Porosity and Particle Diameter Influence on Wall-to-Bed Heat Transfer in Trickle Bed Reactors

Wall-to-bed (or wall-to-fluid) heat transfer issues in trickle bed reactors (TBR) has an important impact on operation and efficiency in this category of reactors. In this study, the hydrodynamic and thermal behavior of trickle bed reactors was simulated by means of computational fluid dynamics (CFD) technique. The multiphase behavior of trickle bed reactor was studied by the implementation of the Eulerian-Eulerian multiphase approach. Also, bed porosity effect was modeled by porosity function method. In order to study the effect of operating parameters on wall-to-bed heat transfer, the influence of catalyst particle diameter and catalytic bed porosity was investigated on wall-to-bed Nu number. The results showed that the enhancement of catalytic bed porosity from 0.36 to 0.5 decreases the Nu number about 15% due to a reduction of liquid velocity adjacent to the reactor wall. Also, the increase of particle diameter from 4 to 6 millimeter decreases wall-to-bed Nu number about 15% owing to a reduction in liquid phase volume fraction.

Prediction of thermal behavior of trickle bed reactors: The effect of the pellet shape and size

Heat transfer plays an important role in several applications of packed bed reactors with cocurrent downflow of liquid and gas (widely known as trickle-bed reactor – TBR).A literature survey shows that the amount of articles dealing with the prediction of heat transfer rates between a TBR and an external heating or cooling source is limited for spherical catalyst pellets and definitively scarce for other pellet shapes as cylinders and multilobes.Results from an experimental program devoted to study heat transfer between a TBR and an external jacket, employing spherical and cylindrical particles and a commercial trilobe pellet, are presented. A wide range of gas (air) and liquid (water) flow rates were covered corresponding to low and high interaction regime. A two dimensional pseudohomogeneous model was employed to represent the thermal behavior of the packed bed. Values of the effective radial thermal conductivity and the wall heat transfer coefficient were obtained by regression of radial temperature profiles for three different bed lengths. Finally, expressions to estimate both parameters for the different particle shapes were developed, thus providing a useful predictive tool, not available in the literature up to the best of our knowledge.

CFD study and experimental validation of trickle bed hydrodynamics under gas, liquid and gas/liquid alternating cyclic operations

Computational fluid dynamics (CFD) simulations of a trickle bed reactor under gas, liquid, and gas/liquid alternating cyclic operations have been performed by using an unsteady multiple-Euler framework by means of the commercial software FLUENT. Electrical capacitance tomography (ECT) imaging was applied to track the liquid holdup waves along the bed and to validate the CFD simulation results. Comprehensive simulations were conducted to examine the effects of reactor geometry meshing (i.e., one, two, or three-dimensional), domain initialization, numerical schemes (i.e., 1st and 2nd order upwind or 3rd order MUSCL), drag forces, constant coefficients of drag force terms (i.e., Ergun constants), gas and liquid properties and particle size. The important outcome of this work was that a one-dimensional multiple-Euler CFD model with first order numerical scheme was sufficient to accurately capture the non-steady state hydrodynamic behavior of trickle bed reactors under different cyclic operation strategies. This indicates that the alignment of flow and mesh practically eliminates (or minimizes) the numerical diffusion. Moreover, application of uniform bed porosity can predict the hydrodynamics parameters under cyclic operations. The model was able to predict accurately the morphological (i.e., the details of rise and falling or breakthrough and tail as well as plateau) characteristics of a liquid wave inside the bed for all the examined cyclic strategies, including base–peak and ON–OFF modes. In addition, simulation results were in excellent consistency with experimental data in terms of both value and behavior (i.e., fluctuations) of overall bed pressure drop. It was found that the liquid–solid drag force is the main cause of wave attenuation along the bed. The performed case studies with the CFD model revealed the significance of different parameters (e.g., Ergun constants, gas and liquid properties, packing size).

A new model for the design and analysis of trickle bed reactors

A new discrete model was developed for the design and analysis of catalytic trickle bed reactors operating in the low interaction regime based on the local structure of packed beds. By detailed comparisons of model predictions to experimental data the performance of the new model is demonstrated.By means of this model the steady-state behavior of trickle bed reactors can be studied in terms of operating conditions, physical properties of all three phases, transport parameters and isothermal reaction kinetics on a particle as well as on a reactor scale.