Fluid bed gas RTD: Effect of fines and internals

Lorences, María Jesús; Laviolette, Jean‐Philippe; Patience, Gregory S.; Alonso, Mònica; Dı́ez, Fernando V.

doi:10.1016/j.powtec.2006.06.010

Cited by 28 publications

(18 citation statements)

References 19 publications

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“…The countercurrent flow of the stripping gas and catalysts leads to severe back‐mixing in the strippers. Almost all Peclet numbers in the two strippers are less than 11, which were very comparable to the results of Lorences et al13 who found that the Pe of gas in the gas‐solid bubbling bed was close to 10, and the Pe in the column with internals was higher than in the open column. The Pe of gas in the V‐baffled stripper is about 10, which is 1.1˜2 times of that in the empty cylinder stripper.…”

Section: Resultssupporting

confidence: 88%

“…Smolders and Baeyens12 used axial dispersed model and core/annulus model to describe the RTD curves in gas‐solid circulating fluidized bed. Lorences et al13 characterized the divergence from the plug flow using the axial dispersion and n‐CSTRs in series models via gas RTD experiments in the fixed and bubbling bed regime. Cui et al14 studied the axial gas and solid mixing at different positions of gas‐solid fluid coker stripper with axial dispersion model using helium and treated catalyst as tracers.…”

Section: Introductionmentioning

confidence: 96%

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CFD simulation of gas and solids mixing in FCC strippers

et al. 2011

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The gas and solid mixing in fluid catalytic cracking strippers with and without internals were investigated using computational fluid dynamics simulations. The Eulerian-Eulerian two-fluid model coupled with the modified Gidaspow drag model was used to simulate the gas-solid flow behavior. The grid independency study and the comparison of 2D and 3D simulations were carried out first. The residence time distribution model and axial dispersion model were utilized to obtain the parameters indicating the backmixing degree, such as mean residence time, dimensionless variance and Peclet number of gas and solids. Moreover, the influence of bubble size and gas/solid flow distribution on the mass transfer between the bubble and emulsion phase were also analyzed. The results show that the baffles in the V-baffle stripper can efficiently enhance the gas and solids mixing, reduce the back-mixing degree of gas and solids, strengthen the mass transfer between the bubble and emulsion phase, and hence improve the stripping efficiency.

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Section: Resultssupporting

confidence: 88%

Section: Introductionmentioning

confidence: 96%

CFD simulation of gas and solids mixing in FCC strippers

et al. 2011

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“…4 Heat exchange with vertical tubes is slightly different from horizontal tubes, as explained in the work of Ozawa et al 20 A significant drawback of vertical tubes compared to freely bubbling fluidized beds is their reduction of axial and lateral solids mixing, such that particle segregation is promoted and proper fluidization becomes difficult due to "channeling". 2,5,19 In the literature, only limited research has been published on vertical tubes in fluidized bedsin particular at laboratory scale. While previous studies rather focused on the design and the general advantages of very particular configurations of vertical tubes in fluidized beds, 5,10,17,19 in this paper, the axial distribution of the bubble growth is systematically investigated by means of experiments in a laboratory-scale fluidized bed (D = 0.145 m inner diameter (ID)), as a function of an array of different tube bank configurations.…”

Section: ■ Introductionmentioning

confidence: 99%

Bubble Characterization in a Fluidized Bed with Vertical Tubes

Rüdisüli

Schildhauer

Biollaz

et al. 2012

Ind. Eng. Chem. Res.

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Vertical tubes are commonly used in industrial fluidized beds as heat exchanger tubes. In this study, the influence of vertical tube banks on the axial bubble growth in a 145-mm inner diameter (ID) fluidized bed with Geldart B particles is experimentally investigated by means of pressure fluctuation measurement (PFM) and optical probing (OP). The employed tube bank configurations differ in their tube-to-tube spacing, tube diameter, and tube arrangement (square versus triangular). PFM and OP show that immersed vertical tube banks, irrespective of their configuration, significantly reduce the axial bubble growth. The bubble size reduction is even more significant for higher gas velocities (u 0/u mf > 4.6, where u 0 is the superficial gas velocity and u mf is the minimum fluidization velocity) as well as if the tube-to-tube spacing is narrow and the tube diameter is small. The tube arrangement (square versus triangular), in turn, does not show any significant differences. Depending on the gas velocity, the ratio of the bubble diameter to the tube diameter and the tube-to-tube spacing is changed. This change invokes a different bubble flow pattern between the vertical tubes and different bubble growth mechanism, which defines the effectiveness of vertical tubes to delay slugging and makes the fluidization smoother.

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“…[7] The tanks-in-series model and the dispersion model are roughly equivalent. Indeed, the results are the same for small deviation from plug flow [35] and they are linked by [43] :…”

Section: Open-open Boundary Conditionsmentioning

confidence: 99%

Experimental methods in chemical engineering: Residence time distribution—RTD

2020

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Reactor performance, solids‐(gas)‐mixing, flow through porous media, distillation columns, or through granulators improve as the fluid dynamics approach ideal plug flow. The residence time distribution (RTD) is a diagnostic measure of how close fluid flow approaches ideal conditions. The technique introduces a step change to the inlet concentration—a Dirac‐δ function, Heaviside step function, or a rectangular pulse (bolus)—while high frequency detectors monitor the concentration along the vessel and/or at the exit. The effluent concentration profile spreads due to the variance in the process lines leading to the vessel and at the exit, the detector response, and the system. We quantify how much each of these contributes to the overall variance in a fluidized bed with 9 g of fluid cracking catalyst in 8 mm diameter quartz tubes. The injection variance is lowest for a GC sample loop configuration, compared to a 3‐way valve or 4‐way valve geometry. RTD measurements detect bypassing due to dead zones in vessels and the axial‐dispersion model and continuous stirred‐tank model to characterize deviation from plug flow. However, when the contribution to variance from the ancillary lines and detector is large compared to the system, the uncertainty in the model parameters is high. Research on RTD fundamentals concentrate on boundary conditions while, here, we focus on experimental errors: mechanical, physicochemical mathematical, and instrumental.

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Fluid bed gas RTD: Effect of fines and internals

Cited by 28 publications

References 19 publications

CFD simulation of gas and solids mixing in FCC strippers

CFD simulation of gas and solids mixing in FCC strippers

Bubble Characterization in a Fluidized Bed with Vertical Tubes

Experimental methods in chemical engineering: Residence time distribution—RTD

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