Method for selecting reactor stirrer

There are many classification methods for agitators, mainly from the following.

1) According to the blade stirring structure, it is divided into flat leaf, inclined (folded) leaf, curved leaf and spiral surface agitator. Both the slurry and the turbine agitator have a flat blade and a slanted blade structure; the propeller, screw and ribbon blades have a spiral surface structure. According to the installation requirements, it can be divided into a whole type and a split type, which is convenient for fixing the agitator directly on the stirring shaft without removing other components such as the coupling.
2) According to the use of the agitator, it is divided into a stirrer for low viscosity fluid and a stirrer for high viscosity fluid. The agitators for low-viscosity fluids include: propulsion, slurry, open turbine, disc turbine, Bruma gold, plate and frame, and three-leaf. The agitators for high viscosity fluids are: anchor, frame, serrated disc, propeller, ribbon and the like.
3) According to the fluid flow pattern, it is divided into an axial flow agitator and a radial flow agitator. In some applications, when the agitator is in operation, the fluid generates an axial flow and a radial flow, which is called a mixed flow agitator. The propeller stirrer is representative of the axial flow type, the straight leaf disc turbine agitator is representative of the radial flow type, and the inclined blade turbine agitator is representative of the mixed flow type.

A good selection method for the reactor stirrer preferably has two conditions. One is that the selection result is reasonable, and the other is that the selection method is simple, and the two points are often difficult to have at the same time.

Since the viscosity of the liquid has a great influence on the stirring state, it is a basic method to select according to the viscosity of the stirring medium. Several typical agitators have different ranges of use depending on the viscosity. The various agitators with increasing viscosity are in the order of propulsion, turbine, slurry, anchor and ribbon. Here, the pusher is finely divided, and low-speed, small-capacity is proposed for large-capacity liquids. Use high speed for liquids. This selection chart does not absolutely stipulate the limitation of using the slurry type. In fact, the usage range of each type of slurry is overlapped. For example, the slurry type has a simple structure, and the baffle can improve the flow pattern, so at a low viscosity It is also more commonly used. The turbine type is almost the most widely used type due to its convective circulation ability, turbulent diffusion and shearing force.

According to the purpose of the agitation process and the flow state caused by the agitator, the slurry type to which the process is applied is judged, which is a relatively suitable method. Because the Soviet type of pulp selection has its own habits, it is not the same as the pulp type commonly used in China.

The recommended slurry type is to divide the slurry into two types: the fast type and the slow type. The former operates in a turbulent state and the latter operates in a laminar flow state. When selecting, the slurry type and the baffle condition are determined according to the purpose of mixing and the flow state, and the flow state is determined by the viscosity of the stirring medium.

The conditions of use are relatively specific, not only for slurry type and mixing purposes, but also recommended medium viscosity range, stirring speed range and tank capacity range.
The proposed selection table is also selected according to the purpose of mixing and the flow state during stirring. It also has the advantage that the use range of the slurry type is divided according to the characteristics of different mixing processes, so that the selection is more specific. Comparing the above table, we can see that the basis and results of the selection are relatively consistent. Here are some more details on some of the main processes.

Low viscosity homogeneous liquid mixing is one of the least difficult mixing processes and is only difficult when the volume is large and the mixing time is short. It is the most suitable because of its strong cycle capability and low power consumption. Turbine type, because of its high power consumption, has high shearing capacity, but it is not necessary for this mixing process. Therefore, if it is used in mixing large-volume liquids, its cycle capacity is insufficient.

For the decentralized operation process, the turbine type is most suitable because of its high shear force and large circulation capacity. In particular, the shearing action of the flat blade turbine is more suitable than the shearing force of the hinged leaf and the curved leaf. The push type and the slurry type are only available in the case where the shearing force is smaller than that of the flat blade turbine type, and the slurry type is rarely used in the dispersion operation. The decentralized operation has baffles to enhance the shearing effect.

The solid suspension operation has the largest range of use in the turbine type, with the turbine type being the best. It has no intermediate disc part, which does not hinder the liquid phase mixing above and below the blade, and the advantage of turning the blade to open the turbine is more prominent. Its discharge is good and the blade is not easy to wear, so it is more suitable for the solid suspension operation. The push type is narrower, and the solid-liquid specific gravity difference is large or the solid-liquid ratio is 50% or more. When using the baffle, care should be taken to prevent the accumulation of solid particles on the corners of the baffle. Generally, when the solid-liquid is relatively low, the baffle is used, and the vane and the propulsion type have axial flow, so the baffle can be omitted.

The gas absorption process is most suitable for a disc type turbine. Its shearing force is strong, and some gas can be stored under the disc to make the gas distribution more stable, and the turbine is not provided with this advantage. The slurry and propulsion type are basically unsuitable for the gas absorption process, and can be applied only when a small amount of gas to be absorbed is required to have a low dispersion.

The crystallization process with agitation is very difficult, especially when strict control of the crystal size is required. Generally, small-diameter rapid agitation, such as turbine type, is suitable for particle crystallization, while large-diameter slow agitation, such as slurry, can be used for crystallization of large crystals.

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