Comparison of CFD Simulation and Simplified Modeling of a Fluidized Bed CO2 Capture Reactor
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Abstract CO 2 capture using solid sorbents in fluidized bed reactors is a promising technology. The multiphase CFD model is increasingly developed to study the reactors, but it is difficult to model all the realistic details and it requires significant computational time. In this study, both the multiphase CFD model (i.e., CFD-DEM model coupled with reaction) and the simplified reactor models (i.e., plug flow model and bubbling two-phase model) are developed for modeling a fluidized bed CO 2 capture reactor. The comparisons are made at different gas velocities from fixed bed to fluidized bed. The DEM based model reveals a detailed view of CO 2 adsorption process with particle flow dynamics, based on which the assumptions in the simplified models can be evaluated. The plug flow model predictions generally show similar trends to the DEM model but there are quantitative differences; thus, it can be used to determine the reactor performance limit. The bubbling two-phase model gives better predictions than the plug flow model because the effect of bubbles on the inter-phase mass transfer and reaction is included. In the future, a closer combination of the multiphase CFD simulation and the simplified reactor models will likely be an efficient design method of CO 2 capture fluidized bed reactors.Keywords:
Plug flow
Multiphase flow
Abstract CO 2 capture using solid sorbents in fluidized bed reactors is a promising technology. The multiphase CFD model is increasingly developed to study the reactors, but it is difficult to model all the realistic details and it requires significant computational time. In this study, both the multiphase CFD model (i.e., CFD-DEM model coupled with reaction) and the simplified reactor models (i.e., plug flow model and bubbling two-phase model) are developed for modeling a fluidized bed CO 2 capture reactor. The comparisons are made at different gas velocities from fixed bed to fluidized bed. The DEM based model reveals a detailed view of CO 2 adsorption process with particle flow dynamics, based on which the assumptions in the simplified models can be evaluated. The plug flow model predictions generally show similar trends to the DEM model but there are quantitative differences; thus, it can be used to determine the reactor performance limit. The bubbling two-phase model gives better predictions than the plug flow model because the effect of bubbles on the inter-phase mass transfer and reaction is included. In the future, a closer combination of the multiphase CFD simulation and the simplified reactor models will likely be an efficient design method of CO 2 capture fluidized bed reactors.
Plug flow
Multiphase flow
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Plug flow
Batch reactor
Process development
Continuous production
Microreactor
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Plug flow
Intensity
Multiphase flow
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This chapter aims to develop low-dimensional representations of chemically reacting flow situations. Specifically these include batch reactors (corresponding to homogeneous mass-action kinetics), plug-flow reactors (PFR) or continuous stirred tank reactor (CSTR), perfectly stirred reactors (PSR), and one-dimensional stagnation flows. Three ideal reactors-the batch reactor, the PFR, and the PSR-are mathematical approximations to corresponding laboratory reactors that are used regularly to study chemical kinetics. The SR may be used as an approximation to conditions with intense turbulent mixing that promotes spatial uniformity. Plug flow can be a useful description of flow with strong mixing in a cross-stream direction but insignificant mixing in the primary flow direction. The plug-flow problem may be formulated with a variable cross-sectional area and heterogeneous chemistry on the channel walls. Although the cross-sectional area varies, a quasi-one-dimensional assumption allows the flow to be represented with only one velocity component, the mean velocity (u).
Plug flow
Chemical reactor
Spark plug
Complete mixing
Continuous reactor
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Plug flow behavior in tubular reactors is often highly desirable in industry, since it can ensure high productivity, good selectivity, and enhanced heat transfer. To achieve this, good radial mixing combined with poor axial mixing is required: these conditions are quite easy to obtain if the flow regime is turbulent, but they are much more challenging to achieve if the flow is laminar. In this work radial mixing and residence time distributions in a side-injected tubular reactor equipped with a series of Sulzer SMX static mixers were investigated using Computational Fluid Dynamics. It was found that even at low values of Reynolds number the reactor can efficiently satisfy the plug flow conditions, and operative diagrams were determined to foresee the reactor behavior.
Residence time distribution
Plug flow
Static mixer
Laminar flow reactor
Complete mixing
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The present paper describes the CFD numerical simulations of liquid-gas flows in the test rig at Nucleo Experimental de Atalaia (NEAT-PETROBRAS). Results for three flow patterns are presented and discussed: plug flow, slug flow, and stratified wavy flow. In addition, flow pattern transitions were determined based on the CFD results. The simulation results provided relevant information about the flow patterns as well as the transitions between them. Except for the annular flow, which presents several difficulties for simulation, the flow pattern predictions in the simulations agree with the predictions made using the Baker flow pattern map. Furthermore, the CFD simulations allowed for reliable, time dependent GVF results, which can be used for direct comparison with the acoustic signals from the multiphase flow meter. The CFD simulations described herein thus provide the necessary means for calibration of the ultrasonic multiphase flow meter being developed.
Ultrasonic flow meter
Multiphase flow
Slug flow
Plug flow
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The performance of a multiphase flow packed-bed reactor was evaluated by a mixing-cell network model in which the cell-scale flow field information was provided by multifluid CFD modeling. Such a sequentially combined modeling approach was able to show the heterogeneity of liquid species conversion in a trickle-bed reactor that has been confirmed by in situ magnetic resonance experiments.1 A conventional plug flow model (PFM) and axial dispersion model (ADM) showed either overpredicted or underpredicted conversion compared with the conversion computed from the CFD-Cell Network model. Preliminary case study has shown the ability of the CFD-Cell Network model in assessing the impact of flow distribution on the trickle-bed reactor performance, which is a great help to trickle-bed reactor design and diagnosis.
Trickle-bed reactor
Plug flow
Multiphase flow
TRICKLE
Network model
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The effect of flow direction on hydrodynamics and mixing in the upflow and downflowcirculating fluidized beds is discussed in details.Similar profiles of gas and solids velocities andsolids concentration are found in both risers and downers.When the flow is in the direction ofgravity(downer),the radial profiles of gas and particle velocity are more uniform than that inthe riser,the solids mixing is very small and the flow pattern approaches plug flow,while theflow is against gravity(riser),the solids backmixing significantly increase and the flow pattern isfar from plug flow.Among many of factors the flow direction has the largest influence onhydrodynamics and axial mixing of gas and solids.
Plug flow
Particle (ecology)
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Flow structure and mixing properties by the baffle shape are numerically studied for a baffled micro combustor. The baffle shape is changed by various fuel and hole sizes. The numerical simulations based on different geometric conditions are performed by using the Reynolds Stress Model. The fuel-air mixing is greatly affected by flow recirculations. The centrally located flow recirculation has an important role for the entire mixing performance. The results show that this feature depends on the baffle configurations, and the baffle with small air holes represents efficient characters.
Baffle
Reynolds stress
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The three-dimension interior flow field of the mixing flow pump of three typical operating conditions was calculated using the amendatory turbulent model of k-e and SIMPLE method of the software CFD,the results of experiment were compared.In the same time,it showed the main flow characteristics of the mixing flow pump by analyzing the distributions of velocity and pressure of the mixing flow pump,catching many important phenomena,such as flow impact and secondary flow,which can be provided for the design of mixing flow pumps,and providing the exact physical message of the capability and improvement of mixing flow pump.
Secondary flow
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