scholarly journals Effect of Superficial Gas Velocity on Continuous Hydrogen Production by Anabaena sp. in an Internal-loop Airlift Bioreactor

2021 ◽  
Author(s):  
Zahra Zarei ◽  
Peyman Malekshahi ◽  
Mohammad Hossein Morowvat ◽  
Rahbar Rahimi ◽  
Seyyed Vahid Niknezhad
Keyword(s):  
Mass Transfer ◽  
Hydrogen Production ◽  
Light Intensity ◽  
Gas Flow ◽  
Biomass Concentration ◽  
Gas Holdup ◽  
Liquid Circulation ◽  
Airlift Photobioreactor ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity

Abstract Global warming and rising air pollution which has been caused by using too much fossil fuel has led to look for a new clean source, sustainable and eco-friendly of energy like H2, which can be produced by cyanobacteria and microalgae. In this study, Anabaena sp. was used in a continuous operation to achieve biohydrogen production. To this end, an airlift photobioreactor (20 L) was considered. The effects of the gas holdup, liquid circulation velocity, and the amount of dissolved oxygen on hydrogen production were investigated. Gas holdup, liquid circulation velocity, and KLa (mass transfer coefficient) showed an upward trend by increasing the velocity of the inlet gas. Maximum biomass concentration of and maximal H2 production were observed 1.2 g L-1 d-1 and 371 mL h-1 PBR-1, respectively under light intensity of 3500 lux/m2 applying a light-dark cycle in 7 days, at Ad/Ar of 1.25 and 0.185 and 0.542 cm/s. pH, temperature (30+2 °C), light intensity, and inlet gas flow to the bioreactor (containing 98% air and 2% carbon dioxide) were remained steady. Using the airlift photobioreactor with a good mass transfer and light availability to cyanobacteria growth can be a cost-effective and environmentally technology for biological H2 production.

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.

scholarly journals Hydrodynamics of an Airlift Column for Aeration in Molten Sulfur

2021 ◽  
Vol 12 (1) ◽  
pp. 117
Author(s):  
Junjie Wang ◽  
Xiao Xu ◽  
Wei Wang ◽  
Yudong Li ◽  
Shihan Wu ◽  
...  
Keyword(s):  
Bubble Diameter ◽  
Gas Holdup ◽  
Dynamics Simulation ◽  
Column Height ◽  
Gas Velocity ◽  
Liquid Circulation ◽  
Molten Sulfur ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity ◽  
Superficial Gas Velocity

The airlift column is a promising technology for the removal of volatile gas from high-viscosity molten sulfur. However, a detailed analysis is lacking on the hydrodynamic properties inside the column, due to the difficulty in flow behavior detection in the opaque molten sulfur. In this work, we adopted the computational fluid dynamics simulation to understand the hydrodynamic behaviors in an airlift column for molten sulfur aeration. In addition, we analyzed the impacts of the superficial gas velocity (UGr) and column height on the hydrodynamic characteristics, such as gas holdup, average bubble diameter, and liquid circulation velocity (ULr) in the column. The simulation shows that at a constant column height of 15 m, an increase on gas holdup can be obtained with the increase of the superficial gas velocity, while the bubble diameter remains almost constant. Once the superficial gas velocity exceeded 0.333 m/s, the liquid circulation velocity increased slowly. With a variation on the column height from 5 to 25 m, a negligible change on gas holdup, but an obvious increase on liquid circulation velocity and bubble diameter is observed at the given superficial gas velocity of 0.0389 m/s. Furthermore, the simulation shows a similar trend, but with considerably more detailed information, on the relationship between the gas holdup and liquid circulation velocity when compared to the predictions from the Chisti correlation (1988) and an optimized correlation proposed in this work.

Gas holdup and liquid circulation velocity in a draft tube gas-liquid spouted vessel.

1988 ◽  
Vol 14 (5) ◽  
pp. 593-600 ◽  
Author(s):  
Masayuki Toda ◽  
Naoki Mogi ◽  
Shinobu Yoshikawa ◽  
Fumiko Sugano ◽  
Hirotaka Konno
Keyword(s):  
Draft Tube ◽  
Gas Holdup ◽  
Liquid Circulation ◽  
Circulation Velocity ◽  
Liquid Circulation Velocity

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.

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