1, batch reactor, or batch reactor.
Its characteristics are flexible operation, easy to adapt to different operating conditions and product varieties, and suitable for small batch, multi-variety and long reaction time product production. The disadvantage of batch reactor is that it needs auxiliary operations such as loading and unloading, and the product quality is unstable. However, in some reaction processes, such as some fermentation reactions and polymerization reactions, it is still difficult to achieve continuous production, and batch reactors are still used.
2. Continuous kettle reactor, or continuous kettle.
Its characteristic is that it can avoid the shortcomings of batch reactor, but the stirring action will cause the back mixing of the fluid in the reactor. When the stirring is intense, the liquid viscosity is low or the average residence time is long, the material flow pattern in the kettle can be regarded as fully mixed flow, and the reaction kettle is correspondingly called fully mixed kettle. When high conversion rate is needed or a series of side reactions exist, back mixing in kettle reactor is unfavorable. At this time, multiple reactors in series can be used to reduce the adverse effects of backmixing, and the reaction conditions can be controlled by separate reactors.
3. Semi-continuous kettle reactor.
Refers to a reactor in which one raw material is added at one time and another raw material is added continuously, and its characteristics are between batch reactor and continuous reactor.
Second, according to the different mixing methods, there are generally anchor, paddle, turbine, propulsion or frame mixing forms.
The stirrer can push the static liquid material to move and maintain the required fluid flow state during the stirring process, so as to achieve the purpose of stirring. The main part of the agitator is the paddle, so the geometry, size, number and speed of the paddle have an important influence on the function and stirring effect of the agitator.
Paddle agitator is suitable for liquid materials with high fluidity and low viscosity, as well as fibrous and crystalline solutions. When the material layer is deep, several rows of blades can be installed on the shaft.
Turbine agitator is divided into disk turbine agitator and open turbine agitator; Impeller can be divided into straight blades and curved blades. The speed of the turbine agitator is relatively high, ranging from 300 to 600 rpm.
The main advantages of turbine agitator are high efficiency and strong radial flow under the condition of low energy consumption. Therefore, it is suitable for emulsion, suspension, etc.
Push agitator can make the materials circulate in the reaction kettle when stirring, and its function is mainly volume circulation, with small shearing effect and good tumbling effect. When a large flow is needed, a draft tube is arranged in the reaction kettle.
The diameter of the pusher agitator is about 1/4 ~ 1/3, and the inner diameter of the reactor is 300 ~ 600 r/min. The agitator is usually made of cast iron and cast steel.
Frame agitator can be regarded as the deformation of paddle agitator, which has a firm structure and a large amount of materials to be stirred. If the bottom of this agitator is similar to the lower head of a reaction kettle, it is usually called an anchor agitator.
The diameter of the frame agitator is relatively large, which is generally 2/3 ~ 9/ 10 and 50 ~ 70r/min of the inner diameter of the reactor. The gap between the frame agitator and the reactor wall is small, which is beneficial to the heat transfer process. When rotating rapidly, the liquid driven by the agitator blades brings the static layer down from the reactor wall. When rotating slowly, the agitator with scraper can produce good heat conduction. This kind of stirrer is often used for heat transfer, crystallization operation and stirring of high viscosity liquid, high concentration slurry and settling slurry.
Ribbon agitator, usually made of flat steel wound into a spiral shape, has a large diameter, and is often made into several long strips close to the inner wall of the kettle, with a small gap with the kettle wall, so it can continuously scrape off the deposits stuck on the kettle wall when stirring. The height of the spiral belt usually takes the height from the bottom of the tank to the liquid level.
The rotating speed of the ribbon agitator and the spiral agitator is relatively low, usually less than 50r/min, which produces a flow dominated by up-and-down circulating flow, and is mainly used for stirring high-viscosity liquids.
The agitator shall be selected in the following form.
Mainly according to the material properties, mixing purposes and the performance characteristics of various mixers.
According to the viscosity of the material.
For low-viscosity liquids, small-diameter high-speed stirrers, such as propeller and turbine, should be selected;
For high-viscosity liquids, choose large-diameter low-speed mixers, such as anchor, frame and paddle.
Choose according to the purpose of mixing.
(1) For low-viscosity homogeneous liquid mixing, the circulating flow rate is mainly considered, and the circulating flow rate of various agitators is arranged in descending order: propulsion type, turbine type and paddle type.
(2) For the heterogeneous liquid-liquid dispersion process, the shearing effect should be considered first, and the circulating flow should be large. The shearing action of various stirrers is arranged in descending order: turbine type, propeller type and paddle type.