For the mixing vessel with large ratio of height to diameter, the multi-layer agitator is needed when the single-layer paddle can not obtain good mixing capacity, for example, in the fermentation industry.

In the multi-layer agitator, many types of agitators are often used to obtain high mixing effect, so that the axial circulation capacity and shear dispersion capacity can be comprehensively balanced. For example, some mixing processes need to consider both circulation and shear. At this time, a wide blade wing flow type agitator with strong circulation capacity in the upper two layers is used, and a half tube disc impeller with strong shear capacity is used in the lower layer.

The layer spacing between different agitators has a great influence on the gas dispersion. Increasing the distance between layers can improve the dispersion performance and the average gas holdup of the lower impeller.

New agitator

Now, there are some new developments in gas-liquid reverse stirring system

1) high steam pressure system, such as boiling.

2) high gas velocity behavior (apparent gas velocity 0.08m/s).

3) the expansion of agitator range, including the design of concave propeller and hydroforming of wide blade.

4) correct calculation of the relationship between gas recycling rate and mass transfer driving force.

In order to get a long gas residence time or a good gas flow pattern, some research institutions and companies began to design new agitators.

For example, some reactors add a self-priming stirrer on the liquid surface to make the overflowed gas return to the liquid and increase the residence time of the gas.

Some experts are studying a stirrer that can change the flow pattern of gas, as shown in the figure below. This is a kind of multi-layer paddle, the lower layer is the runoff paddle, the upper two layers are the wing flow paddles that play the role of suction, through which the flow pattern of gas can be forced to improve.

Application of gas-liquid agitation equipment

Gas liquid agitation equipment is mainly used for physical and chemical processes such as hydrogenation, oxidation gas removal, etc. In the process of hydrogenation, oxidation, chlorination and sulfonation, agitators are needed to provide high gas-liquid dispersion capacity and increase gas residence time. In the process of fermentation, it is necessary to use multi-layer combined paddle.