First, the internal structure of the agitator must be reasonable;
Second, the internal system of the whole agitator must work together when the agitator is working.
Generally speaking, it is a little difficult for the agitator itself if the two points must be met.
Because the mixing blades in the agitator have a great influence on the mixing state of liquid viscosity when the agitator is working, the selection of mixing blades is a relatively effective method for the internal mixing medium of the agitator.
Several typical agitators have different application ranges according to the viscosity. The order of use of various agitators with increasing viscosity is propulsion type, turbine type, slurry type, anchor type and spiral belt type, among which the propulsion type is divided into smaller ones. It is proposed to use low speed for large capacity liquid and high speed for small capacity liquid. This type selection drawing does not absolutely specify the restrictions on the use of slurry types. In fact, the use scope of various slurry types overlaps. For example, because of its simple structure, the slurry type can improve the flow pattern by using baffles, so it is also widely used at low viscosity. The turbine type is almost the most widely used slurry type due to its strong convection circulation ability, turbulent diffusion and shear force.
Its advantage is that it divides the range of application of the slurry according to the characteristics of different mixing processes, making the selection more specific. Comparing the above table, we can see that the basis and results of agitator selection are relatively consistent. Here are some explanations of the main processes.
1. It is very difficult for the agitator to stir the crystallization process, especially when it is required to strictly control the crystal size. Generally, small diameter fast mixing, such as turbine agitator, is suitable for particle crystallization, while large diameter agitator can be used for crystallization of large crystals at a slow speed, such as paddle agitator, compared with practical application and work.
2. For the decentralized operation process, the agitator is most suitable because of its high shear force and large circulation capacity. In particular, the shear force of the straight blade turbine agitator is greater than that of the bent blade and bent blade agitator, which is more appropriate. Propelled agitators and paddle agitators can only be used when the liquid dispersion is small because their shear force is smaller than that of straight blade turbine agitators, and paddle agitators are rarely used for dispersion operations. There are baffles for decentralized operation to enhance the shearing effect. It is a practical method to judge the slurry type applicable to the mechanical mixing process according to the purpose of the process and the flow state caused by the agitator.
3. For solid suspension operation, the use range of turbine agitator is the largest, and the turbine agitator is the best. It does not have a disc in the middle, which will not hinder the liquid phase mixing up and down the blades. Moreover, the advantages of turning on the turbine with curved blades are more prominent. It has good discharge performance, and the blades are not easy to wear, so it is more suitable for solid suspension operation. It is not applicable to propelling agitators with narrow application scope, large specific gravity difference between solid and liquid or solid to liquid ratio above 50%. When using the baffle, pay attention to prevent solid particles from accumulating on the corner of the baffle. Generally, baffles are only used when the solid-liquid ratio is low, while the turbine with folded blades and the propeller agitator have axial flow, so they can only be used when the liquid dispersion is small, and the slurry type is rarely used for dispersion operation. There are baffles for decentralized operation to enhance the shearing effect.
4. The use conditions of the agitator are specific, including not only the slurry type and mixing purpose of the agitator, but also the recommended viscosity range of the agitator medium, the mixing speed range of the agitator and the capacity range of the tank.
5. The mixing of low viscosity homogeneous liquid in the agitator is the least difficult mixing process. It is difficult only when the volume is large and the mixing time is required to be very short. Because of its strong circulation capacity and less power consumption, the propulsion agitator is most suitable. The turbine agitator has high power consumption and high shear capacity, but it is not necessary for this mixing process. Therefore, if it is used for mixing large volumes of liquid, its circulatory capacity will be insufficient.
6. Propelled agitators divide the slurry type into fast type and slow type. The former operates in turbulent state, and the latter operates in laminar state. The slurry type and baffle conditions are determined according to the mixing purpose and flow state of the agitator. The determination of the flow state is affected by the viscosity of the mixing medium.
7. The disc type turbine agitator is the most suitable for the gas absorption process of the agitator during operation. It has strong shear force and can store some gas under the disc to make the gas distribution more stable. Turning on the turbine agitator does not have this advantage. The slurry type and propulsion type agitators in the internal mixing system of the agitator are basically not suitable for the gas absorption process, and can only be used when a small amount of gas absorbed in the agitator requires low dispersion.