Conditioning micro fluidized bed for maximal approach of gas plug flow

Geng, Sulong; Han, Zhennan; Yue, Junrong; Li, Yunjia; Zeng, Xi; Lai, Dengguo; Yu, Jian; Xu, Guangwen

doi:10.1016/j.cej.2018.06.076

Cited by 34 publications

(13 citation statements)

References 40 publications

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“…The average of

U_{mf}

for the microreactor is 125 % higher than the other. The values procured with the larger reactor concord with a recent study with a similar reactor and sand powder . So, wall effects in a microreactor have an important influence on

U_{mf}

.…”

Section: Fluidization Regimessupporting

confidence: 79%

“…Operating micro‐fluidized beds (

D_{t} < 10 mm

) requires at minimum 1 g of solids although more catalyst is better. In reactors, from 5–21 mm in diameter, the gas phase is close to plug flow in shallow beds with an expanded bed height of 20 mm . The riser simulator is a microreator that suspends catalyst and recirculates gas at a high rate to maintain differential conditions in the bed but high overall conversion …”

Section: Uncertaintymentioning

confidence: 99%

“…Tracer studies detect gas bypassing and characterize the overall flow pattern—plug flow and number of continuous stirred tank reactors (

n_{CSTR}

)—but a reactive tracer measures gas‐solids contact efficiency . The convection‐dispersion model assumes at dimensionless time

θ = 0

(

θ = t U_{g} ∕ L

), the concentration of tracer

ρ (0, ξ) = ρ (0, 0)

for

0 < ξ < 1

(

ξ = z ∕ L

\frac{\partial ρ}{\partial θ} + \frac{\partial ρ}{\partial ξ} = \frac{1}{N_{Pe}} \frac{\partial^{2} ρ}{\partial ξ^{2}}

where

N_{Pe} = U_{g} L ∕ scriptD

, the Peclet number (the inverse of which Levenspiel refers to as the dispersion number) and

scriptD

is the dispersion.…”

Section: Gas‐phase Hydrodynamicsmentioning

confidence: 99%

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Experimental methods in chemical engineering: Reactors—fluidized beds

et al. 2019

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Industry relies on fluidized beds to synthesize chemicals (acrylonitrile, maleic anhydride, titanium dioxide, vinyl chloride), combust coal, dry powders, and treat waste. Fluidized bed folklore declares that they are hard to scale‐up and the gas phase is backmixed. Commercial failures that disregard standard design criteria around powder management, gas/solids injection, and mixing reinforce this belief. However, engineers select fluidized beds for processes that are impractical with conventional technologies to achieve economies of scale for highly exothermic, endothermic, or explosive reactions, for catalysts that deactivate in seconds (or minutes), and for chemistry that requires multiple dosing cycles. Failures are more frequent for these challenging applications. For this reason, researchers study reaction kinetics in fixed beds despite internal mass transfer limitations and axial and radial temperature and concentration gradients. Fluidized bed hydrodynamics vary with powder properties (particle diameter, size distribution, density, sphericity), operating conditions (gas density, viscosity, temperature, pressure), reactor geometry (diameter, height, mass, grid geometry). The minimum fluidization velocity (Umf) is a property that identifies the transition from the fixed bed regime to the fluidized bed regime and equals the gas velocity at which the upward drag force equals the weight of the powder. At the experimental scale, fluidized beds operate isothermally, solids are completely backmixed, and the gas phase is close to plug flow (Ug<-0.25em3Umf). Here, we describe the relationship between powder properties and fluidization quality, list experimental techniques, describe recent applications, and gas phase hydrodynamics and uncertainties.

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“…The average of

U_{mf}

U_{mf}

.…”

Section: Fluidization Regimessupporting

confidence: 79%

“…Operating micro‐fluidized beds (

D_{t} < 10 mm

Section: Uncertaintymentioning

confidence: 99%

“…Tracer studies detect gas bypassing and characterize the overall flow pattern—plug flow and number of continuous stirred tank reactors (

n_{CSTR}

)—but a reactive tracer measures gas‐solids contact efficiency . The convection‐dispersion model assumes at dimensionless time

θ = 0

(

θ = t U_{g} ∕ L

), the concentration of tracer

ρ (0, ξ) = ρ (0, 0)

for

0 < ξ < 1

(

ξ = z ∕ L

\frac{\partial ρ}{\partial θ} + \frac{\partial ρ}{\partial ξ} = \frac{1}{N_{Pe}} \frac{\partial^{2} ρ}{\partial ξ^{2}}

where

N_{Pe} = U_{g} L ∕ scriptD

, the Peclet number (the inverse of which Levenspiel refers to as the dispersion number) and

scriptD

is the dispersion.…”

Section: Gas‐phase Hydrodynamicsmentioning

confidence: 99%

See 1 more Smart Citation

Experimental methods in chemical engineering: Reactors—fluidized beds

et al. 2019

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“…Several assumptions limit the validity of the axial dispersion model: the process is continuous or semi‐continuous; the steady state is reached; the inlet and outlet of the system have unidirectional flows (closed‐closed boundary conditions); perfect horizontal mixing; long pipe/tube; non‐viscous materials; the tracer does not affect the system and is distributed evenly in all the system; and the radial diffusion is negligible. …”

Section: Uncertaintymentioning

confidence: 99%

“…Inert, reactive, and absorbing tracers follow the path of the fluid through the system and as they leave the environment, detectors monitor their concentration. Mass spectrometry, infrared, and thermal conductivity detectors are common techniques to follow gas concentration . For liquid phase applications, NaCl and KCl solutions are good tracers particularly with conductivity detectors .…”

Section: Introductionmentioning

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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Acquiring real kinetics of reactions in the inhibitory atmosphere containing product gases using micro fluidized bed

et al. 2021

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This study proposed an isotope‐tagging method to investigate reactions under the atmosphere of product gas. To illustrate this method, the calcination kinetics of calcium carbonate Ca13CO3 in CO2 atmospheres were investigated by monitoring 13CO2 produced using a micro fluidized bed reaction analyzer (MFBRA). The results demonstrated that the presence of CO2 in reaction atmosphere increases the apparent activation energy. The increase in the apparent activation energy is, however, significantly overestimated by the thermogravimetric analyzer (TGA) because of the excessive suppression by stagnated product gas inside the sample crucible. Comparatively, the apparent activation energy increases with CO2 from the MFBRA due primarily to the thermal equilibrium limitation, because the gas diffusion in the MFBRA is essentially eliminated. It is thus concluded that the MFBRA is quite capable of acquiring the real kinetics of reactions in such inhibitory atmospheres.

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Conditioning micro fluidized bed for maximal approach of gas plug flow

Cited by 34 publications

References 40 publications

Experimental methods in chemical engineering: Reactors—fluidized beds

Experimental methods in chemical engineering: Reactors—fluidized beds

Experimental methods in chemical engineering: Residence time distribution—RTD

Acquiring real kinetics of reactions in the inhibitory atmosphere containing product gases using micro fluidized bed

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