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Arabian Journal for Science and Engineering

, Volume 43, Issue 11, pp 5905–5917 | Cite as

Hydrodynamics and Bubble Size Distribution in a Stirred Reactor

  • Malik Senouci-Bereksi
  • Fairouz Khalida Kies
  • Fatiha Bentahar
Research Article - Chemical Engineering
  • 59 Downloads

Abstract

A study of the hydrodynamics of two-phase stirred tanks is presented. The hydrodynamics in large-scale reactors is shown to be mainly a function of the superficial gas velocity and the stirring in the system. Six configurations for the stirrer have been tested: two single-stage and four two-stage configurations. The three hydrodynamic regimes (short circuit, load and flood) were observed for these configurations. The results show that the gas holdup, measured using the difference in level between aerated and non-aerated states, achieves a maximum value for the mixed two-stage combination. For this configuration, a study of the residence time distribution was carried out by employing the tracer (pulse injection) method, thus allowing the determination of the dead volume and the modeling of the flow in the reactor, corresponding to a perfectly mixed reactor. In stirred tank reactors, the study of the bubble size distribution has a great importance on the flow dynamics, the dimensions of bubbles are measured photographically; this investigation shows the presence of fine bubbles (d < 10 mm) with the experimental bubble size distribution curves exhibiting classical log-normal function traits within ± 3%. The characterization of the hydrodynamics and the flow regimes in the stirred reactor permits to optimize the operating parameters (stirrer type and configuration, stirring speed, gas velocity) within the reactor in order to treat the water contaminated by persistent pollutants.

Keywords

Gas holdup RTD Bubble size distribution Interfacial area Stirred tank Wastewater treatment 

Nomenclature

Symbols

a

Interfacial area (\(\hbox {m}^{2}\,\hbox {m}^{-3}\))

d

Nozzle sparger diameter (mm)

\(d_{\mathrm{i}}\)

Bubble diameter (mm)

ds

Sauter mean diameter (mm)

D

Reactor diameter (mm)

E(t)

Residence time distribution function

\(f_{\mathrm{i}}\)

Number density (%)

H

Aerated state level (mm)

\(H_{0}\)

Non-aerated state level (mm)

\(n_{\mathrm{i}}\)

Number of bubbles of diameter \(d_{\mathrm{i}}\)

N

Stirring speed (rpm)

P

Number of perfectly mixed reactors

\({\bar{t}}\)

Mean residence time (s)

t

Time (s)

\(U_{\mathrm{g}}\)

Gas velocity (\(\hbox {m s}^{-1}\))

\(V_{\mathrm{r}}\)

Reactor’s volume (\(\hbox {m}^{3}\))

\(V_{\mathrm{a}}\)

Accessible volume (\(\hbox {m}^{3}\))

\(V_{\mathrm{m}}\)

Dead volume (\(\hbox {m}^{3}\))

Greek letters

\(\varepsilon _{\mathrm{g}}\)

Gas holdup (%)

\(\theta \)

Reduced time

\(\mu _{\mathrm{N}},\, \mu _{\mathrm{LN}}\)

Normal and log-normal mean deviation, respectively

\(\sigma _{\mathrm{N}},\,\sigma _{\mathrm{LN}}\)

Normal standard deviation and log-normal standard deviation, respectively

\(\tau \)

Passage time (s)

Acronyms

BSD

Bubble size distribution

\(\hbox {Cum}_{\mathrm{N}},\,\,\hbox {Cum}_{\mathrm{LN}}\)

Cumulative normal and log-normal distribution, respectively

FP

Flooding point

LP

Loading point

POP’s

Persistent organic pollutants

RTD

Residence time distribution

TD6

Six blades Rushton turbine

TI6

Six inclined blades turbine

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Copyright information

© King Fahd University of Petroleum & Minerals 2018

Authors and Affiliations

  1. 1.Laboratoire des Phénomènes de Transfert (LPDT), Faculté de Génie Mécanique et de Génie des ProcédésUniversité des Sciences et de la Technologie Houari Boumediène (USTHB)Bab EzzouarAlgeria
  2. 2.Laboratoire de Valorisation des Energies Fossiles (LAVALEF), Département Génie ChimiqueEcole Nationale Polytechnique (ENP)AlgiersAlgeria

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