Flow Mapping and Modeling of Liquid−Solid Risers (original) (raw)
Related papers
Tomographic and Particle Tracking Studies in a Liquid−Solid Riser
Industrial & Engineering Chemistry Research, 1997
ABSTRACT A liquid−solid circulating fluidized bed is a potential reactor of interest in a variety of industrial processes, such as petroleum refining, and in the synthesis of fine chemicals, petrochemicals, and foodstuffs. Rapid deactivation of the solid catalyst in these processes necessitates regeneration and recirculation of the solids into the riser section in which the principal reaction is accomplished. In this study we show that computer-automated radioactive particle tracking (CARPT) can be used to obtain solids velocity patterns in the riser and that backflow of solids exists at the tested liquid velocities. γ-ray computed tomography (CT) reveals slightly higher solids concentrations in the center of the column. This is in contrast to gas−solid riser reactors in which the concentration of solids is higher at the walls.
Solids flow mapping in a gas–solid riser: Mean holdup and velocity fields
Powder Technology, 2006
In this study, solids flow dynamics has been investigated in a 6 in. "cold-flow" circulating fluidized bed riser using non-invasive flow techniques. Gamma ray Computed Tomography (CT) has been used to measure the time-averaged cross-sectional solids holdup distribution. The time-averaged mean and fluctuating solids velocity fields have been quantified using the Computer Automated Radioactive Particle Tracking (CARPT) technique. Details of the experimental techniques, protocol of implementation and data analysis are discussed. The experimental studies examine operating conditions in fast fluidization and dilute phase transport regimes. Comparative and symbiotic analyses of the results obtained from CARPT and CT have been used to develop a coherent picture of the solids flow field. In addition, this work also demonstrates the power of CARPT and CT as flow mapping techniques in studying highly turbulent and opaque multiphase systems.
Experimental investigation of the hydrodynamics in a liquid-solid riser
AIChE Journal, 2005
ABSTRACT Liquid–solid fluid dynamics has been investigated in a 6-in. (0.15 m) “cold-flow” circulating fluidized bed riser using non-invasive flow monitoring methods. Gamma-ray computed tomography (CT) was used to measure the time-averaged cross-sectional solids volume fraction distributions at several elevations. The time-averaged mean and “fluctuating” solids velocity fields were quantified using the computer-automated radioactive particle tracking (CARPT) technique. The experimental equipment, protocol of implementation, and data analysis have been discussed briefly, with particular emphasis on the specific features in the use of these techniques for studying high-density turbulent flows as in a liquid–solid riser. The experimental study examines nine operating conditions, that is, three liquid superficial velocities and three solids flow rates. The solids holdup profile is found to be relatively uniform across the cross section of the riser, with marginal segregation near the walls. The time-averaged solids velocity profiles are found to have a negative component at the walls, indicating significant solids backmixing. Detailed characterization of the solids velocity fields in terms of RMS velocities, kinetic energies, Hurst exponents, residence time distributions, trajectory length distributions, dispersion coefficients, and so forth are presented. Comparative and symbiotic analyses of the results were used to develop a coherent picture of the solids flow field. In addition, the work also serves to demonstrate the power and versatility of these flow-imaging techniques in studying highly turbulent and opaque multiphase systems. © 2005 American Institute of Chemical Engineers AIChE J, 51: 802–835, 2005
Modelling of Gas-Solid Flows in FCC Riser Reactors: Fully Developed Flow
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AIChE Journal, 2015
Comparison of flow development in high density downer and riser reactors is experimentally investigated using fluid catalytic cracking particles with very high solids circulation rate up to 700 kg/m 2 s for the first time. Results show that both axial and radial flow structures are more uniform in downers compared to riser reactors even at very high density conditions, although the solids distribution becomes less uniform in the high density downer. Solids acceleration is much faster in the downer compared to the riser reactor indicating a shorter length of flow development and residence time, which is beneficial to the chemical reactions requiring short contact time and high product selectivity. Slip velocity in risers and downers is also first compared at high density conditions. The slip velocity in the downer is much smaller than in the riser for the same solids holdup indicating less particle aggregation and better gas-solids contacting in the downer reactors.
Industrial & Engineering Chemistry Research, 2007
Circulating fluidized-bed (CFB) risers with Geldart group B particles have found significant application in combustion reactions. The present work attempts to study the solids flow dynamics in a CFB riser that is operated with group B particles, using computational fluid dynamics (CFD) techniques. The key feature in the present study is that the various closure schemes in the CFD model have been evaluated against data from non-invasive experimental techniques: computer automated radioactive particle tracking (CARPT) for solids velocity field and computed tomography (CT) for solids holdup. Since solids flow in a riser is multiscale in character, in addition to the measured averaged solids velocity profiles and solids fraction profiles in the experimental section, mean granular temperature profiles have also been compared. Two flow regimes (viz., fast fluidization and dilute phase transport) have been considered in this study.
Dynamical features of the solid motion in gas–solid risers
International Journal of Multiphase Flow, 2007
The trajectories of a solid tracer with the same characteristics as the circulating solids in the risers of two pilot-scale circulating fluidized beds (CFBs), obtained by the computer automated radioactive particle tracking (CARPT) technique, are examined in detail to get further insights into the complex solids dynamics of these systems. The analysis uses tools from the theory of non-linear dynamics and symbolic dynamics. Distinct features of the solids dynamics within the fast fluidization and the dilute phase transport flow regimes are highlighted and related to the operating conditions. The possibility of downflow cluster existence within the central region of the riser is particularly examined.
Modelling of gas-solid flows in FCC riser reactor: fully developed flow
1999
A two-fluid framework is used with the kinetic theory of granular flows to simulate fully developed gas-solid flows in vertical risers. The computational model was used to simulate the available experimental data over a wide range of operating and design parameters. In addition, several numerical experiments were carried out to understand the influence of riser diameter, particle size, gas and solid flux, solids and gas density on the simulated flow characteristics. The presented results and analysis will be useful for further development of modeling of gas solid flows in riser reactors.
Chemical Engineering and Processing, 2009
Circulating fluidized bed reactor (CFBR) has been widely used for combustion, gasification and cracking. Each reaction has its own characteristics and requires different reactor responses. In this work, novel designs of the riser geometries were studied using a 2D transient Eulerian approach with kinetic theory of granular flow in a commercial simulation package. The new designs were based on the improvement of main factors that have an effect on reaction characteristics. It was found that the tapered-out riser improves the turbulence or mixing while the tapered-in riser enhances particle residence time and gives uniform temperature distribution in the system.
A study of solid behavior in spouted beds using 3-D particle tracking
The Canadian Journal of Chemical Engineering, 1994
A non-invasive y-ray emission system, employing eight NaI detectors, has been developed to follow the motion of a single radioactive particle in a three-dimensional spouted bed reactor. The count-rates measured simultaneously by the detectors are converted into tracer coordinates (x, y, z) using a pre-established calibration model which accounts for every physical and geometrical aspects involved in the spouting facility. Typically four hundred thousands successive coordinates, obtained over 3.5 hours of particle tracking, are used for determining the average particle velocity field and other hydrodynamic quantities such as the cycle time distribution, the spout shape and the solid exchange distribution at the spout boundary, which could not be evaluated accurately using any available techniques.