Oxygen mass transfer characteristics in an internal-loop airlift reactor with preset trumpet-shaped riser

Oxygen transfer and gas holdup in airlift bioreactors assembled with helical flow promoters

Bioreactors can perform biochemical conversions mediated by biocatalysts, such as enzymes, animal cells, plants, and microorganisms. Among several existing models, airlift bioreactors are devices with the low shear environment and good mass transfer with low energy consumption, employed in several biochemical processes. The fluid flow is enabled through air injection by the sparger located at the bioreactor base. Despite its simple geometry compared with the conventional bioreactors, airlift performance can be optimized via geometrical modifications. Therefore, the objective of this work was to evaluate the effects of the addition of helical flow promoters, positioned in the riser and/or downcomer regions of an airlift of concentric tubes measuring the volumetric oxygen coefficient (k_La) and gas holdup. The results obtained by varying the gas flow rate from 1.0 to 4.0 vvm allowed the system evaluation of oxygen transfer and gas holdup. The inclusion of helical flow promoters increased the k_La, reaching up to 23% in oxygen transfer compared to tests without helicoids and up to 14% increase in the gas holdup. The inclusion of helical flow promotors was beneficial for all gas flow rates. Thus, including these flow promoters is an effective strategy to increase the oxygen transfer rate for bioprocess optimization.

Hydrodynamics and mass transfer of concentric-tube internal loop airlift reactors: A review

The concentric-tube internal loop airlift reactor is a typical reactor configuration which has been adopted for a myriad of chemical and biological processes. The reactor hydrodynamics (including mixing) and the mass transfer between the gas and liquid phases remarkably affect the operational conditions and thus are crucial to the overall reactor performance. Hence, this study aims at providing a thorough description of the basic concepts and a comprehensive review of the relevant reported studies on the hydrodynamics and mass transfer of the concentric-tube internal loop airlift reactors, taking microalgae cultivation as an exemplary application. In particular, the reactor characteristics, geometry, CFD modeling, experimental characterization, and scale up considerations are elucidated. The research gaps for future research and development are also identified.

Computational fluid dynamics modeling of carbon dioxide capture from air using biocatalyst in an airlift reactor

In this work, a novel three-phase and three dimensional CFD model based on the Euler-Euler approach developed for modeling the hydrodynamic, mass transfer and CO₂ fixation using microalgae in an internal loop airlift reactor with internal sparger. The main objective of this work was to development of CFD codes in order to simulate the CO₂ biofixation process under different input gas velocity during 11 days of culture time and simulate the unsteady state mass transfer based on Surface-Renewal-Stretch (SRS) model. The CFD results were compared with the our previous experimental work and they showed good agreement with a margin of less than 10%. This paper illustrated the ability of the CFD in complex process simulation such as CO₂ biofixation in the airlift reactor and provided a useful basis for further study.

Advances in airlift reactors: modified design and optimization of operation conditions

Airlift reactor (ALR) is a promising multiphase reactor for industrial applications. Abundant reports about modifications of the conventional ALR and optimization of their operation conditions for the purpose of performance enhancement have been accumulated in literatures, demanding a review paper to summarize the reactor design modifications and operation condition optimization of the ALR. In this review, the published research findings and results have been summarized. The basic concepts including the ALRs’ conventional design, classification, principles of operation, and characteristic parameters have been analyzed and systematically organized. The updated advances in the ALR design modifications have been reported. In particular, the concepts of the “groveled ALR” solving the scaling up problem in wastewater treatment, large-scale application, and the ALR with the cross-shaped geometry modifier stabilizing and strengthening the reactor were considered. Also, new operation modes and optimal conditions for enhancing the performance of the ALR have also been summed up. Except for conventional gas-driven methods, new driven methods for the ALR, such as mixture emission of the gas and the liquid and gas-inducing impeller, have been introduced. Optimization of operation conditions for the ALR includes varying position of the gas spargers, utilizing elevated pressure reactor, and exploring the impact of operation parameters, such as superficial gas velocity, static liquid level, and fluid properties. Comparisons between conventional ALRs and the modified systems are carried out paying attention to analogies, similarities, and differences. Most of the documented research results are obtained for various reactor designs at a laboratory scale; studies at pilot and full scale are still insufficient, which indicates that universal scale up design rules permitting the ALR design with a high confidence are required.