The stirrer is one of the key parts of the reaction kettle. According to the physical properties, capacity, and stirring purpose of the different media in the kettle, the appropriate stirrer can be selected to promote the chemical reaction speed and improve the production efficiency.
Mastering the classification of agitators and the applicable occasions will help to choose the appropriate agitator to achieve better response effects.
Application of reactor
The reactor is a pressure vessel that is widely used in petroleum, chemical, rubber, pesticide, dye, medicine, and food to complete the process of vulcanization, nitrification, hydrogenation, alkylation, polymerization, and concentration.
The composition of the reactor
The reaction kettle is composed of a kettle body, a kettle cover, a jacket, a stirrer, a transmission device, a shaft sealing device, and a support.
The role of reactor agitator
Mix the materials uniformly and enhance heat and mass transfer, including homogeneous liquid mixing; liquid-liquid dispersion; gas-liquid dispersion; solid-liquid dispersion; crystallization; solid dissolution; enhanced heat transfer, etc.
The principle of reactor stirring
The agitator is the main component to realize the stirring operation, and its main component is the impeller, which applies mechanical energy to the liquid with the movement of the rotating shaft and promotes the movement of the liquid.
When the agitator rotates, the mechanical energy is transferred to the fluid to form a high-transmission fully mixing zone near the agitator, and a high-speed jet is generated to push the liquid to circulate in the mixing container.
Influencing factors of reactor stirring
The way that the liquid circulates in the equipment is called the “flow model” of the liquid, or “flow pattern” for short.
The flow pattern is divided into: radial flow, axial flow, and tangential flow.
The flow pattern is closely related to the mixing effect and mixing power. The flow pattern depends on the form of the stirrer, the geometric characteristics of the stirring vessel and internal components, as well as the fluid properties, the speed of the stirrer and other factors.
The flow direction of the fluid is parallel to the agitating shaft, and the fluid is pushed by the blades to make the fluid flow downwards, and then turn upwards when encountering the bottom surface of the container, forming an up and down circulation flow.
The fluid flow direction is perpendicular to the stirring shaft and flows in the radial direction. When it encounters the wall of the container, it divides into streams and flows upwards and downwards respectively, and then returns to the tip of the blade without passing through the blades, forming an upper and a lower circulating flow.
In a container without a baffle, the fluid rotates around the axis. When the flow rate is high, the liquid surface will form a vortex. The flow of the fluid from the circumferential direction around the blade to the blade area is small, and the mixing effect is very poor.
The above three flow patterns usually exist simultaneously;
Axial flow and radial flow play a major role in mixing;
Tangential flow should be suppressed. The use of baffles can weaken tangential flow, enhance axial flow and radial flow.
Classification and applicable occasions of reactor agitator
1 paddle agitator
It is composed of blades, keys, collars, and vertical shafts. The blades are generally made of flat steel or stainless steel or non-ferrous metals. The speed of the paddle agitator is low, generally 20~80r/min. The diameter of the paddle agitator is Di/3 ~ 2/3 of the inner diameter of the reactor.
Long, two or more blades are used when the reactor has a large diameter.
The paddle agitator is suitable for liquid materials with high fluidity and low viscosity. It is also suitable for fibrous and crystalline dissolving liquids. When the material layer is deep, several rows of paddles can be installed on the shaft. The folding blade type has less power consumption and lower operating costs than the straight blade type, so the folding blade propeller is more used
Paddle stirrers cannot be used in gas-liquid dispersion operations for the purpose of gas retention and miniaturization. The speed of the paddle agitator is generally 20 ~ 100/min.
2 propeller stirrer
The propeller stirrer can make the material circulate in the reactor during stirring. The main function is volume circulation, the shearing effect is small, and the up and down tumbling effect is good. When a larger flow rate is required, the reactor is equipped with a flow guide.
The standard propeller agitator has three blades, the pitch of which is equal to the diameter d of the paddle. The diameter of the propeller stirrer is about 1/4~1/3 of the inner diameter Di of the reactor, 300~600r/min. The material of the stirrer is usually cast iron and cast steel.
Features of the propeller mixer:
Axial flow agitator;
Large circulation volume and low mixing power;
Simple structure and convenient manufacturing;
Often used in low viscosity fluids.
3 turbo agitator
The turbine agitator speed is relatively high, 300~600r/min. Straight blade and curved blade turbine agitators mainly produce radial flow, and folding turbine agitators mainly produce axial flow.
The main advantage of turbine agitator sahib when the energy consumption is not large, the mixing efficiency is higher, and the mixing produces a strong radial flow. Therefore it is suitable for emulsions, suspensions, etc.
4 anchor stirrer
It is suitable for mixing fluids with a viscosity below 100Pa-s. When the fluid viscosity is 10~100Pa-s, horizontal paddles can be added in the middle of the anchor paddle, which is a frame agitator to increase the mixing in the middle of the container.
Features of anchor agitator:
Simple structure and convenient manufacturing;
Suitable for materials with high viscosity and maximum processing;
It is easy to get a large surface heat transfer coefficient:
It can reduce the occurrence of “wall hanging”.