The reforms of Peter I gave a significant impetus to the development of the chemical industry in our country, however, the main development took place at the beginning of the twentieth century. With the development of technology, industry more and more needed new materials and substances, which led to the construction of modern chemical plants, the development of new technologies and assemblies.
The fundamental equipment for carrying out chemical and physical processes are apparatuses with mixing devices. They allow for heterogeneous technological processes, such as crystallization, extraction and various homogeneous and heterogeneous chemical reactions.
Mixing is the main way to evenly distribute suspended or dissolved substances, as well as dispersing drops and bubbles in a liquid.
Depending on the necessary processes, properties of the components being mixed, pressure or temperature, a mixing device is selected.
Technologically, the most effective devices can be considered vertical devices with a cylindrical shape. Direct mixing occurs in the capacity of the apparatus. The containers are for the most part cylindrical in shape, but for some types of mixers, it is allowed to use rectangular containers. If it is necessary to heat the mixing medium, the tank is equipped with electric shadows and is thermally insulated. Inside the tank can be equipped with baffles.
The basis of the mixing apparatus is a mixer, the type and design of which directly affects the method and intensity of mixing. All mixers include a drive part and a stirrer. The drive is selected depending on the required power and the required speed of the mixer.
In the existing standards of chemical engineering, GOST 20680-75 is used for 12 standard mixers, in which all applicable standard designs are summarized.
According to the mixing speed, the mixers are divided into two main types. High-speed mixers are used in liquid media for turbulent operation. Slow-moving is used in the laminar mode of movement.
The choice of type, diameter and angular velocity of the mixer is made under the normative and technical documentation.
Mixers are a paddle, three-bladed toothed, turbine, frame, etc. Each type of mixer has a set of its parameters, which are summarized in general tables in the regulatory documentation. More detailed parameters are determined by a hydrodynamic calculation based on the steady-state fluid flow, the stirrer reaching its operating speed and the balance of all applied forces and moments. The purpose of the calculation is to determine the averaged characteristics of mixing speeds, funnel parameters and mixing efficiency.
The most common mixers in the chemical industry arepaddle mixers. The blades of such mixers can be located either perpendicular to the axis of rotation, or at some angle to the plane of rotation.
The blade itself can be either straight or with a pterygoid profile. The impeller (the working part of the mixer) in most of its cases is a support sleeve mounted on a shaft to which the blades are welded.
In the case in which mixing is carried out in an external container, for example, in an Eurocube with a neck smaller than the diameter of the mixer, folding blades are used, which open when rotated and fold at rest.
Propeller mixers in design differ from the blade, only a pterygoid profile.
The other most common type of mixer is theturbine. The impeller of such a mixer is a horizontal disk on a cylindrical sleeve, on the edges of which the blades are evenly spaced. By design, turbine mixers are divided into open and closed.
Frame and anchor mixers
The main low-speed mixers areframe and anchor. Such mixers have found their application in averaging non-Newtonian media and highly viscous fluids, as well as for heat transfer.
Such mixers consist of a support sleeve with two welded profiled blades that repeat the internal profile of the tank. Such agitators are widely used in containers with a conical bottom. The blades of standard low-speed mixers can be located perpendicular or at an angle to the plane of their rotation.
The type of mixers is the working body of the impeller, in which the bowl (transition) in the form of a hollow, truncated cone isconical mixers. Such mixers can be used for work in both high-speed and slow-moving mode.
The last, of the most common types of mixers, aremilling. They are used for mixing both liquid and solid materials. The impeller is a horizontal disk on a cylindrical sleeve, along the edges of the circle of which the teeth are located.
Depending on the mixing conditions, several impellers can be installed on one mixer. And with significant volumes of capacity, such mixers have additional support (thrust bearing) at the base.
In special cases, when more complex mixing is required, special apparatuses are used —dissolvers. Such devices may include several mixing devices of different types and with different parameters. Or, is located on one’s frame, have automation means for controlling the working bodies of the apparatus.