Hydrodynamics of a Stirred Vessel Equipped with a Gas-Inducing Impeller

A gas-inducing impeller enables efficient recycling of gas from the headspace into the liquid. Historically, these impellers were used for the first time in froth flotation machines. The various designs of gas-inducing impellers (including those used in froth flotation) could be classified into three categories, depending on the flow pattern coming into and leaving the impeller zone. These are denoted as type 11, type 12, and type 22 systems. The critical impeller speed for the onset of gas induction (N CG) is governed by a balance between the velocity head generated by the impeller and the hydrostatic head above the impeller. A number of correlations (for types 11 and 22) are based on this balance (Bernoulli's equation). The rate of gas induction (Q G) for the type 11 system can be accurately determined by equating the pressure difference (between the impeller zone and the headspace) generated by the impeller and the pressure drop required for the flow of gas. For type 22 systems, the correlations for Q G are mainly empirical in nature. Correlations for the power consumption, fractional gas holdup, mass-transfer coefficient, and so forth are also available in the literature, although these studies on are not comprehensive. A process design algorithm has been presented for the design of gas-inducing impellers. The algorithm consists of the determination of the rate-controlling step, selection of geometry and the operating conditions, and an economic analysis to choose the optimum design. Guidelines have been given about the desired geometry of gas-inducing impellers for achieving different design objectives such as heat transfer, mass transfer, mixing, solid suspension, froth flotation, and so forth. It has been shown that the use of a gas-inducing impeller in a conventional stirred vessel can lead to a substantial increase in the productivity. It has been shown that the optimum geometry may not correspond to the maintenance of equal power consumption per unit volume, or equal tip speed on scale-up. Suggestions have been made for future work in this area.

show abstract

“…multiple-impeller and sparger system, different designs of bottom impeller, V G ) 0-29 mm/s Patwardhan and Joshi (1997) Ind. Eng.…”

Section: Classification Of Gas-inducing Impellersmentioning

confidence: 99%

“…Moreover, their work is carried out on small-sized vessels (0.17-m diameter); hence, their results are not expected to be useful for scale-up. Patwardhan and Joshi (1997) have employed a gasinducing impeller in mechanically agitated contactors. They have also presented a rationale for the use of a gas-inducing impeller in MAC.…”

Section: Type 22 Systemsmentioning

confidence: 99%

Design of Gas-Inducing Reactors

Patwardhan

Joshi

1998

Ind. Eng. Chem. Res.

Self Cite

View full text Add to dashboard Cite

show abstract

“…Self-inducing systems include: (i) gas induction through hollow shafts and impellers, also called self-aspirating impellers (Joshi and Sharma, 1977;Rielly et al, 1992;Forrester and Rielly, 1994;Stelmach and Kuncewicz, 2001;Poncin et al, 2002); (ii) self-induction through a rotor-stator device and concentric standpipe (Zundelevich, 1979;Mundale and Joshi, 1995;Saravanan and Joshi, 1996;Patwardhan and Joshi, 1997;Patil and Joshi, 2003); or (iii) "vortex ingesting" vessels (Hsu and Huang, 1996;Hsu et al, 2001;Conway et al, 2002) where the gas phase from the headspace is injected and dispersed into the liquid through suitable surface vortices.…”

Section: Introductionmentioning

confidence: 99%

Mass transfer and hydrodynamic characteristics of a high aspect ratio self-ingesting reactor for gas–liquid operations

Scargiali

Russo

Grisafi

et al. 2007

Chemical Engineering Science

View full text Add to dashboard Cite

“…3), so its pumping capacity is better, and it can push the dispersion further from the mixing system. Saravanan and Joshi [3] and Patwardhan and Joshi [4] have also shown that the combination of a gas-inducing turbine with an up-flow impeller below it increases the fractional gas holdup in the whole tank. The low (see Fig.…”

Section: Bubble Plume Lengthmentioning

confidence: 96%

“…To solve this problem, Saravanan and Joshi [3] and Patwardhan and Joshi [4] have tested several combinations with a gas-inducing turbine closed to the liquid surface and another agitator below it. The best lower impeller to improve the fractional gas holdup is an up-flow agitator (a propeller or a pitched blade turbine).…”

Section: Introductionmentioning

confidence: 99%

Aeration of Large Size Tanks by a Surface Agitator

et al. 2005

View full text Add to dashboard Cite

A new device has been developed in order to achieve urban or industrial wastewater biological treatment. It has been designed specially for lagoon applications to oxygenate and mix with the same apparatus. The goal is both to achieve a high gas flooding rate and to reach a maximal depth with the bubble plume. Mass transfer measurements have allowed us to choose the most appropriate geometry. Considering the application of the device and the possible use of low-pressure O 2 produced on-site, the agitation system is located close to the liquid surface and is composed of a gas-inducing turbine. The role of propellers in addition to the gas-inducing turbine, as well as the use of baffles and a shell, have been experimentally studied. Numerical simulations (CFD) of the whole apparatus in single-phase flow have been used to study the influence of the stator part of the geometry.

show abstract

Hydrodynamics of a Stirred Vessel Equipped with a Gas-Inducing Impeller

Cited by 17 publications

References 12 publications

Design of Gas-Inducing Reactors

Design of Gas-Inducing Reactors

Mass transfer and hydrodynamic characteristics of a high aspect ratio self-ingesting reactor for gas–liquid operations

Aeration of Large Size Tanks by a Surface Agitator

Contact Info

Product

Resources

About