Enhancing gas-solid fluidized bed dryer performance with horizontal axis rotary agitators: a simulation approach

Modification of kinetic theory of granular flow for frictional spheres, part II: Model validation

Slush nitrogen is a mixture of solid nitrogen particles and liquid nitrogen, and its flow characteristics in a horizontal pipe are investigated experimentally and theoretically in this study. Pressure drop of slush nitrogen is higher than that of subcooled liquid nitrogen due to the viscous and the mechanical frictions, and the dependence of pressure drop on the mean velocity varies under different flow conditions. The solid volume fraction distributions and the velocity throughout the pipe cross‐section of slush nitrogen flow are investigated with the Eulerian–Eulerian multiphase approach incorporated with the kinetic theory of granular flow. The flow patterns of slush nitrogen are determined as the pseudo‐homogeneous flow, the heterogeneous flow and the bedload flow from the experimental and numerical results. The relationship between the friction factor and the Reynolds number for slush nitrogen with various solid volume fractions is obtained by using the slush Reynolds number. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1762–1773, 2013

This paper presents the numerical analysis of fluid flow in a two-dimensional fluidized bed through simulations. The experiment data of Geldart B particles fluidized bed is used to validate the simulation results. Simulations has been conducted using Computational Fluids Dynamics (CFD) method, Eulerian Eulerian two fluid approach with Gidaspow drag model, kinetic theory of granular flow, and two turbulence models. Two different turbulence models of Standard (STD) k-ε and Renormalization Group (RNG) k-ε are used since they are proven applicable for high complexity flows such as in the fluidized bed. Simulations were conducted using the commercial software CFDSOF®. From the experiments obtained that the minimum fluidization velocity is 0.4 m/s and the pressure drop across the bed is around 700 Pa. Both models cannot predict the pressure drop across the bed well below the minimum fluidization velocity, but above it both models give the closer results to the experiment data and the RNG k-ε model predicts closer in comparison to the STD k-ε model. The STD k-ε model predicts the turbulent regime sooner and the static pressure distribution a little bit higher.

Parametric study of particles homogenization in cold-flow riser reactors

CFD modeling of heat transfer and hydrodynamics in a draft tube conical spouted bed reactor under pyrolysis conditions: Impact of wall boundary condition

This work focuses on the numerical modelling and experimental validation of the hydrodynamic behaviour of a novel 50 kWth indirectly heated bubbling fluidized bed steam reformer. The hydrodynamic behaviour of fluidized beds with immersed vertical tubes and complex fluidized bed geometries in general have not been thoroughly investigated in terms of numerical modelling coupled with experimental validation for pilot scale reactors. Therefore, the present study contributes to the fluidized bed hydrodynamics numerical modelling field, while investigating a novel reactor concept. Simulations were performed employing the Two-Fluid Model approach, using the Kinetic Theory of Granular Flows (KTGF) and the adjusted Syamlal O’Brien drag model. The reactor’s hydrodynamic behaviour was simulated successfully, as showcased by a comparison of global hydrodynamic metrics (bed height, pressure drop) between computational and experimental results. Simulations were performed with and without considering an additional nitrogen gas feed on the side of the reactor (feeding system pressurization). Overall, for both cases, for realistic values of the particle restitution coefficient channelling of the gas flow near the reactor walls was observed. Larger bubbles appeared to be forming near the outer wall of the reactor for the no side-flow simulations. The opposite behaviour was encountered for the side-flow simulations due to stream-like behaviour of the side-flow moving up against the reactor’s outer wall. The choice to limit the simulations to a 72° symmetry domain was validated, indicating the possibility of further reduction. Finally, it was argued that increasing the reactor’s diameter could potentially lead to a reduction of the observed channelling of the fluidization media and improve the mixing achieved in the reactor and thus the conversion efficiency of the IHBFBSR during gasification applications.

CFD simulation of an agitated gas-fluidized bed: Effects of particle–particle restitution coefficient on the hydrodynamics

In this work, the business Computational Fluid Dynamics (CFD) is used for the numerical simulations of an air-solid fluidized bed container in the solid phase involving a multi-fluid Eulerian multiphase model and the Kinetic Theory of Granular Flow (KTGF). The height of the fluidized bed setup is 1.5 m while its diameter is 0.2 m. With it, a series of experimentations were obtained using Helium tracer to determine the Residence Time Distribution (RTD) at various normalized velocities, that is, mixing of air-solids at different degrees. 2 and 3 dimensions of the fluidized bed container are simulated. The main purpose of this study is to understand the hydrodynamic behavior of air-solid fluidized bed container through a framework of Eulerian multiphase model and to analyze the hydrodynamic behavior of the air-solids mixing. As a first approach, the CFD model is validated using the experimental results of the residence time study. The numerical results of RTD corresponded well with the experimental findings. This shows that the CFD modeling might be used to indicate the performance of a fluidized bed reactor. Key words: Computational fluid dynamics, fluidized bed, residence time distribution (RTD), gas-solids mixing, turbulence.

An Eulerian-Eulerian granular model was used to simulate the flow and heat transfer through a heatedgassolid fluidised bed. The primary objective of the study was to determine whether the Eulerian-Eulerian granular model adequately predicts the chamber pressure drop, temperature, and bed expansion through the bed. The model predictions were assessed and validated for various flow-regimes, namely the fixed-bed, smooth, bubbling fluidisation, and the maximum fluidisation regimes. This was done on an experimental scale heated gas-solid fluidised bed. However, the results are generalisable for heated gas-solid fluidised beds when the flow is laminar. Numerical models were created using Computational Fluid Dynamics (CFD). The CFD-model predictions were investigated, analysed, and compared to experimental results. Basic experiments were carried out to obtain varying hydrodynamic characteristics. The results showed a slight overprediction of pressure drop and bed expansion, however, the results were still in close agreement with the experiment. In contrast, underprediction of chamber temperatures were obtained. Based on the results of this study, it is recommended that the Eulerian model be used to predict dynamic flow behaviour. Before minimum fluidisation, when in a fixed bed regime, pressure drop in the chamber increases with no increase in bed height. No visible bubbles were present in the fixed bed regime. When fluidisation has been reached, the bed height rises whereas the pressure drop tends to a constant value. Bubble size increases with chamber height and increased superficial velocities. Bubble speed increased with increased chamber height. With increased superficial velocity, the chamber temperatures increase to a maximum temperature of326.65 K with an initial heating element temperature of373.15 K. However, when excessive heat is present in the gas-solid fluidised bed, other methods that sufficiently incorporate particle-particle interactions and bubble-bubble interactions, are recommended. An investigation should be lent to bubble-bubble interactions in the fluidised beds with relation to heat transfer. Additional keywords: Heated fluidised bed, computational fluid dynamics, CFD, Eulerian, granular, fluidisation, gas-solid

Effects of fluidization velocity on solid stack volume in a bubbling fluidized-bed with nozzle-type distributor

The flow behaviour of a lab-scale fluidised bed with a central jet has been simulated. The study has been performed with an in-house computational fluid dynamics (CFD) model named FLOTRACS-MP-3D. The CFD model is based ona multi-fluid Eulerian description of the phases, where the kinetic theory for granular flow forms the basis for turbulence modelling of the solid phases. A two-dimensional Cartesian co-ordinate system is used to describe the geometry. This paper discusses whether bubble formation and bed height are influenced by coefficient of restitution, drag model and number of solid phases. Measurements of the same fluidised bed with a digital video camera are performed. Computational results are compared with the experimental results, and the discrepancies are discussed.

Simulations of flow behavior of particles in a liquid-solid fluidized bed using a second-order moments model

Accurate modeling and simulation of irregular shape sand particle fluidization are challenging as particle shape-resolved simulation is complex and time-consuming. In this study, the coarse-grained discrete element model (CG-DEM)-computational fluid dynamics (CFD) was adopted to improve the computational feasibility of traditional CFD–DEM and simplify the mathematical modeling by lumping a certain amount of physical particles into a numerical parcel. 3D CGDEM–CFD simulated the fluidization behavior of irregular shape sand particles in a fluidized bed, and several key parameters or model settings were assessed to identify critical model factors. Moreover, the impact of the model parameters on hydrodynamics was quantified by comparing the simulation results with the experimental data. The results demonstrate that applying a rolling friction model can increase the simulation accuracy of the fluidization behavior of non-spherical sand particles.

Numerical investigation of ice slurry isothermal flow in various pipes

The methanol to olefins (MTO) process has been successfully commercialized in China and will potentially become an important route for light olefins production. In this work, a modeling approach is presented for MTO fluidized bed reactor design and operation optimization. The two-fluid model (TFM) where the solid phase shear viscosity and solid phase pressure are derived from kinetic theory of granular flow has been used to model the solid–gas two-phase flows. The interphase drag force is calculated by either the traditional Gidaspow model or a recently developed EMMS-bubble model. The simulation study has been performed for a fluidized bed reactor in a 16 kt/a DMTO unit. It has been shown that the Gidaspow model cannot predict a stable dense bed, while the EMMS-bubbling model could simulate the solid fraction distribution in the reactor reasonable well. A reaction model based on the simple MTO reaction kinetics has been implemented to test the effectiveness of the model approach. The simulation results show that the methanol is converted rapidly just above the gas inlet. The selectivity of ethylene and propylene however are underpredicted, while the selectivity of CO2 and other products are overestimated. It is suggested that a further extension of the EMMS model to a turbulent fluidized bed is important in order to get more quantitative results. Also the MTO reaction kinetics for a commercial DMTO catalyst, in which the coke formation kinetics should be included, is highly desired.