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.

Experiment and CFD Simulation on Gas Holdup Characteristics in an Internal Loop Reactor with External Liquid Circulation

2009 ◽  
Vol 7 (1) ◽  
Author(s):  
Chunxi Lu ◽  
Nana Qi ◽  
Kai Zhang ◽  
Jiaqi Jin ◽  
Hu Zhang
Keyword(s):  
Cfd Simulation ◽  
Gas Holdup ◽  
Gas Velocity ◽  
Loop Reactor ◽  
Internal Loop ◽  
Liquid Circulation ◽  
Liquid Phases ◽  
Ansys Cfx ◽  
Other Information ◽  
Superficial Gas Velocity

An external liquid circulation is introduced into a traditional internal loop reactor in order to improve liquid circulation and increase the interface between gas and liquid phases. The effects of superficial gas velocity and external liquid circulation velocity on local and overall gas holdups are explored experimentally and numerically in the loop section of a combined gas-liquid contactor, which consists of a liquid spray, sieve plates and an internal loop with external liquid circulation. Local gas holdup is measured experimentally by a double-sensor conductivity probe. Numerical simulations are conducted in the platform of a commercial software package, ANSYS CFX 10.0. Gas holdup and other information are obtained by solving the governing equations of mass and momentum balances for gas and liquid phases in a hybrid mesh system. Both measured and simulated results indicate that local, section-averaged, and overall gas holdups increase with an increase of the superficial gas velocity. The downcomer tube for circulating external liquid has a significant influence in the gas-distributor and the downcomer-tube action regions rather than in the upper draft-tube and the gas-liquid separation regions. Good agreement between measured and predicted data suggests that CFD simulation together with experimental investigation can be employed to develop novel gas-liquid contactors with a complex geometrical configuration.

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 The Effect of a Modified Downcomer on the Hydrodynamics in an External Loop Airlift Reactor

2006 ◽  
Author(s):  
Samuel T. Jones ◽  
Theodore J. Heindel
Keyword(s):  
Liquid Velocity ◽  
Bubble Column ◽  
Gas Holdup ◽  
Area Ratio ◽  
Airlift Reactor ◽  
Open Area ◽  
Gas Velocity ◽  
External Loop ◽  
Superficial Gas Velocity ◽  
Superficial Liquid Velocity

Gas holdup and superficial liquid velocity in the downcomer and riser are studied for an external loop airlift reactor with an area ratio of 1:16. Two downcomer configurations are investigated consisting of the downcomer open or closed to the atmosphere. Experiments for these two configurations are carried out over a range of superficial gas velocities from UG = 0.5 to 20 cm/s using three aeration plates with open area ratios of 0.62, 0.99 and 2.22%. These results are compared to a bubble column operated with similar operating conditions. Experimental results show that the gas holdup in the riser does not vary significantly with a change in the downcomer configuration or bubble column operation, while a considerable variation is observed in the downcomer gas holdup. Gas holdup in both the riser and downcomer are found to increase with increasing superficial gas velocity. Test results also show that the maximum gas holdup for the three aerator plates is similar, but the gas holdup trends are different. The superficial liquid velocity is found to vary considerably for the two downcomer configurations. However, for both cases the superficial liquid velocity is a function of the superficial gas velocity and/or the flow condition in the downcomer. These observed variations are independent of the aerator plate open area ratio. When the downcomer vent is open to the atmosphere, the superficial liquid velocity is initially observed to increase with increasing superficial gas velocity until the onset of choking occurs in the downcomer. Increasing the superficial gas velocity beyond the onset of choking increases the effect of choking and decreases the superficial liquid velocity. Once maximum choking is reached, the superficial liquid velocity becomes independent of the superficial gas velocity. When the downcomer vent is closed to the atmosphere, the superficial liquid velocity is initially observed to decrease with increasing superficial gas velocity as choking in the downcomer is immediately present. Once maximum choking occurs, the superficial liquid velocity once again becomes independent of the superficial gas velocity.

scholarly journals Simulation Study on Gas Holdup of Large and Small Bubbles in a High Pressure Gas–Liquid Bubble Column

Processes ◽  
2019 ◽  
Vol 7 (9) ◽  
pp. 594 ◽  
Author(s):  
Fangfang Tao ◽  
Shanglei Ning ◽  
Bo Zhang ◽  
Haibo Jin ◽  
Guangxiang He
Keyword(s):  
Surface Tension ◽  
High Pressure ◽  
Bubble Column ◽  
Bubble Diameter ◽  
Gas Holdup ◽  
Operating Pressure ◽  
Gas Velocity ◽  
Superficial Gas Velocity ◽  
Critical Bubble ◽  
Small Bubbles

The computational fluid dynamics-population balance model (CFD-PBM) has been presented and used to evaluate the bubble behavior in a large-scale high pressure bubble column with an inner diameter of 300 mm and a height of 6600 mm. In the heterogeneous flow regime, bubbles can be divided into “large bubbles” and “small bubbles” by a critical bubble diameter dc. In this study, large and small bubbles were classified according to different slopes in the experiment only by the method of dynamic gas disengagement, the critical bubble diameter was determined to be 7 mm by the experimental results and the simulation values. In addition, the effects of superficial gas velocity, operating pressure, surface tension and viscosity on gas holdup of large and small bubbles in gas–liquid two-phase flow were investigated using a CFD-PBM coupling model. The results show that the gas holdup of small and large bubbles increases rapidly with the increase of superficial gas velocity. With the increase of pressure, the gas holdup of small bubbles increases significantly, and the gas holdup of large bubbles increase slightly. Under the same superficial gas velocity, the gas holdup of large bubbles increases with the decrease of viscosity and the decrease of surface tension, but the gas holdup of small bubbles increases significantly. The simulated values of the coupled model have a good agreement with the experimental values, which can be applied to the parameter estimation of the high pressure bubble column system.

Sign in / Sign up

Export Citation Format

Share Document