CFD Simulation of hold-up and liquid circulation velocity in a membrane airlift reactor

2012 ◽  
Vol 46 (3) ◽  
pp. 266-273 ◽  
Author(s):  
M. K. Moraveji ◽  
B. Sajjadi ◽  
R. Davarnejad
Keyword(s):  
Cfd Simulation ◽  
Airlift Reactor ◽  
Liquid Circulation ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity

scholarly journals Hydrodynamics of an airlift reactor for aeration in molten sulfur

2021 ◽  
Author(s):  
Junjie Wang ◽  
Xiao Xu ◽  
Qiang Yang ◽  
Wei Wang ◽  
Yudong Li ◽  
...  
Keyword(s):  
Bubble Diameter ◽  
Gas Holdup ◽  
Airlift Reactor ◽  
Gas Velocity ◽  
Liquid Circulation ◽  
Molten Sulfur ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity ◽  
Superficial Gas Velocity ◽  
Reactor Height

An industrial-scale internal loop airlift reactor is used to remove volatile gas from high-viscosity molten sulfur. The effects of the superficial gas velocity and reactor height on the hydrodynamic characteristics were studied. The gas holdup, average bubble diameter, and liquid circulation velocity in the reactor under different conditions were analyzed using computational fluid dynamics simulation. The superficial gas velocity was varied from 0.0056 m/s to 0.05 m/s at a constant reactor height of 15 m. The total reactor height was varied from 5 m to 25 m at a superficial gas velocity of 0.0389 m/s.Based on the correlation between the gas holdup and liquid circulation velocity proposed by Chisti (1988), an optimized correlation between the gas holdup and liquid circulation velocity was developed by considering the influence of the bubble diameter. The results obtained using the proposed correlation were compared with those obtained using the Chisti correlation and simulation.

An innovative process for waste water treatment: the circulating floating bed reactor

1996 ◽  
Vol 34 (9) ◽  
pp. 89-99 ◽  
Author(s):  
V. Lazarova ◽  
J. Manem
Keyword(s):  
Water Treatment ◽  
Waste Water Treatment ◽  
Reactor Design ◽  
Effective Control ◽  
Innovative Technology ◽  
Process Stability ◽  
Liquid Circulation ◽  
Three Phase ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity

Increasing volumes of wastewater combined with limited space availability and progressively tightening European standards promote the development of new intensive biotechnologies for water treatment. Fixed biomass processes offer several advantages compared with conventional biological treatments: higher volumetric load, increased process stability and compactness of the reactors. The purpose of this paper is to present a new concept of gas-lift mobile bed, the circulating floating bed reactor (CFBR). The reactor design is simple and does not require any complex technical devices (easier effluent and air-flow distribution, no primary settling, no back-washing). This new process is studied and developed in an industrial-scale prototype. The optimum hydrodynamic characteristics of the CFBR (liquid circulation velocity 0.3-0.4 m s−1, kLa 50-300 h−1, average mixing time 85 s) were not deteriorated by the high solid hold-ups (up to 40% v/v) of the floating media. On the contrary, three-phase operating improves the local gas hold-up in the downcomer. Improved hydrodynamics in the CFBR guarantee high nitrification rates and operation stability either in tertiary (up to 2 kgN m−3 d−1) or secondary (up to 0.6 kgN m−3 d−1) nitrification. The results show that nitrification is the limiting step in simultaneous C+N treatment. The negative effect of the increasing C/N ratio is more pronounced than stepwise decreasing of the temperature. The study of the biofilm composition and activity shows an effective control of the attached biomass growth by the high liquid circulation velocity. It is concluded that this new three-phase bioreactor ensures not only an enhanced process stability and biological reaction rate through an effective biofilm control but also guarantees an excellent synergy between hydrodynamic and biological performances. These advantages are highlighted by the simplicity of the reactor design. Thus, this innovative technology will be an attractive solution for intensive wastewater treatment for nitrogen and carbon removal.

scholarly journals Mixing characteristics of draft tube airlift bioreactor using the electrical resistance tomography

2021 ◽  
Author(s):  
Farouzatu Yakubu-Gumery
Keyword(s):  
Shear Rate ◽  
Xanthan Gum ◽  
Draft Tube ◽  
Mixing Time ◽  
Airlift Bioreactor ◽  
Liquid Circulation ◽  
Mixing Characteristics ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity ◽  
The Cross

In this work, mixing characteristics in terms of mixing time, hydrodynamics (liquid circulation velocity and gas hold up) and shear rate were performed in the downcomer of a draft tube airlift bioreactor with different geometries (i.e., Ad/Ar between 0.38 – 2.31 and bottom clearances between 0.003-0.00 m). Newtonian (water and 34.5% coalescing sugar solution) and on Newtonian (0.2% and 0.5% xanthan gum solutions) with different viscosities were used as the liquid phase. Compressed air was used as the gas phase which was introduced through cross and circular shaped sparger configurations at superficial velocities Ugr = 0.00165-0.00807 m/s. The combined effects of geometric parameters (Ad/Ar, bottom clearances), sparger configuration, and liquid viscosity on mixing characteristics have been presented. Results showed that the increase in superficial gas velocity (Ugr) corresponds to an increase in energy generated, and thus decreases in mixing time. However, the increase in Ugr corresponds to the increase in liquid circulation velocity, gas holdup and shear rate values. Moreover, bottom clearances and draft tube diameters show effects on flow resistance frictional losses which affect results of mixing parameters investigated. The influence of sparger configurations on mixing time and liquid circulation velocity is significant due to their effect on gas distribution. Mixing time decreased to about 40% in air-water media using the cross shaped sparger. Results obtained with cross shaped sparger showed even and uniform distribution of gas, which provided better mixing as compared to the circular shaped sparger configuration. However, the sparger configuration effect on shear rate is not as significant (about 20% reduction in shear rate values using the cross shaped sparger). The effect of fluid viscosity had a significant influence on both mixing times and circulation velocity, especially in the coalescing media of sugar and xanthan gum solutions. Results from this work will help to develop a clear pattern for operation and mixing that can help improving [sic] several industrial processes, especially the ones related to emerging fields of technology such as the biotechnology industry.

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