Comparative analysis of CFD models of dense gas–solid systems

Wachem, van Bgm Berend; Schouten, JC Jaap; Bleek, van den Cm; Krishna, Rajamani; Sinclair, JL

doi:10.1002/aic.690470510

Cited by 451 publications

(353 citation statements)

References 37 publications

(26 reference statements)

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“…This is a good assumption in dense and slow moving bubbling beds [18] since the local generation (first term on the right), dissipation due to inelastic collisions (third term on the right) [3] and damping by the primary phase (final term) [2] strongly outweigh contributions from convective and diffusive fluxes.…”

Section: The Kinetic Theory Of Granular Flowsmentioning

confidence: 99%

Grid independence behaviour of fluidized bed reactor simulations using the Two Fluid Model: Effect of particle size

2015

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Section: The Kinetic Theory Of Granular Flowsmentioning

confidence: 99%

Grid independence behaviour of fluidized bed reactor simulations using the Two Fluid Model: Effect of particle size

2015

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“…This is a good assumption in dense and slow moving bubbling beds [7] since the local generation (first term on the right), dissipation due to inelastic collisions (third term on the right) [5] and damping by the primary phase (final term) [6] strongly outweigh contributions from convective and diffusive fluxes.…”

Section: The Kinetic Theory Of Granular Flowsmentioning

confidence: 99%

Investigation into the effect of simulating a 3D cylindrical fluidized bed reactor on a 2D plane

2013

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Abstract2D planar simulations of 3D cylindrical fluidized bed reactors are routinely carried out in order to reduce computational costs. The error involved in this simplification is largely unknown, however, and this study was therefore conducted to quantify this error over a wide range of reactor operating conditions. 2D and 3D simulations were carried out over a wide range of flow conditions in the bubbling fluidization regime by changing the fluidization velocity, bed mass, reaction temperature and particle size. Detailed comparisons revealed that 2D simulations qualitatively behaved similarly to 3D simulations, but overpredicted reactor performance (measured by the degree of conversion achieved) by about 45% on average. Large systematic variations of this error were also observed with changes in all four independent variables investigated. These large errors were due to two primary factors; incorrect predictions of the gas residence time by misrepresentations of the bed expansion and incorrect predictions of the mass transfer by misrepresentations of bubble formation and the splash zone at the top of the expanded bed. The mass transfer error was found to be most influential and was also confirmed as the most important factor to be correctly predicted by CFD simulations. 3D predictions of the mass transfer resistance were further analysed to identify the particle size as a very influential variable through which the mass transfer characteristics in fluidized bed reactors can be influenced. IntroductionFluidized bed reactors find application in a wide range of process industries dealing with gas-solid or solid catalysed reactions. The fluid-like behaviour of these reactors results in excellent heat and mass transfer performance which is highly favourable for any reactor process. Fluidized bed reactors can be very challenging to design and scale up, however, and commercialisation of processes utilising such reactors therefore typically consists of a large number of incremental scale-up and demonstration steps. For this reason, there is a great need for modelling tools that can be used to reduce the risk of taking larger scale-up steps.The fundamental flow modelling framework of computational fluid dynamics (CFD) is considered in this work to be a viable methodology for achieving this purpose. CFD inherently accounts for the complex and tightly interconnected non-linear interactions between reactor hydrodynamics, heat transfer, species transfer and reaction kinetics. Because of this fundamental basis, it is reasoned that CFD can provide the generality demanded of a modelling tool used for fluidized bed reactor design, optimization and scale-up.CFD simulations face their own challenges, however. The primary challenge is presented by the mesoscale structure formation characteristic of any fluidized bed reactor process. Small clusters of particles are formed within these beds due to the non-linear drag interaction between the gas and solids and have a very large influence on all physics occurring within the reactor...

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“…This partial differential equation was simplified to an algebraic equation by neglecting the convection and diffusion terms -an often used assumption in dense, slow moving fluidized beds where the local generation and dissipation of granular temperature far outweigh the transport by convection and diffusion [22]. The two final terms in Equation 5 are the collisional dissipation of energy [1] and the interphase exchange between the particle fluctuations and the gas phase [23].…”

Section: Model Equationsmentioning

confidence: 99%

The generality of the standard 2D TFM approach in predicting bubbling fluidized bed hydrodynamics

et al. 2013

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Hydrodynamic simulations of a pseudo-2D bubbling fluidized bed were carried out and compared to experiments conducted over a wide range of flow conditions. The primary purpose of this study was to assess the generality of the standard 2D Two Fluid Model (TFM) closed by the Kinetic Theory of Granular Flows (KTGF) which is regularly used in the literature to simulate bubbling fluidized beds. Comparisons of the bed expansion ratio over wide ranges of fluidization velocity, bed loading and particle size showed systematic differences between simulations and experiments, indicating that the generality of this modelling approach is questionable. More detailed flow velocity measurements collected via Particle Image Velocimetry (PIV) showed that the model greatly over-predicts flow velocities in the bed. Subsequent 3D simulations showed this over-prediction to be the result of 2D simulations neglecting the wall friction at the front and back walls of the pseudo-2D bed.

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Comparative analysis of CFD models of dense gas–solid systems

Abstract: Many gas

Cited by 451 publications

References 37 publications

Grid independence behaviour of fluidized bed reactor simulations using the Two Fluid Model: Effect of particle size

Grid independence behaviour of fluidized bed reactor simulations using the Two Fluid Model: Effect of particle size

Investigation into the effect of simulating a 3D cylindrical fluidized bed reactor on a 2D plane

The generality of the standard 2D TFM approach in predicting bubbling fluidized bed hydrodynamics

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