Gas dispersion is defined as the production of a suspension of bubbles of gas in an immiscible liquid. A gas dispersion is usually produced in order to enhance mass transfer of a component from the gas to the liquid, but occasionally from the liquid to the gas. Dispersions are produced by high shear mixing devices that impart a high level of turbulent energy to the system. This energy appears as turbulence which breaks up gas pockets into bubbles and disperses these into the mass of liquid. This increases the surface area interface between the gas and the liquid. Generally the gas is introduced close to the bottom of the vessel. However, there are a variety of specialized devices and vessel configurations used for specific gas dispersion applications.
Vessel Design Considerations
These applications almost always require a vertical round vessel. Exceptions may be taken when the viscosity is relatively high, but these are unusual. This is one of the few cases where tall skinny vessels are preferred; some of these have aspect ratios greater than 3.0.
Gas dispersion is almost always a turbulent operation. Round baffled vessels are required. Offset mounting is strongly discouraged because irregular unbalanced hydraulic forces will be very large. This requires costly “oversizing” of the mixer in order to prevent destructive vibration.