Centrifuges were born in Europe, for example, in the mid-19th century, there were three legged centrifuges used for textile dehydration and suspended centrifuges used for separating crystalline sugar in sugar factories. These early centrifuges were operated intermittently and manually for slag discharge.
Due to the improvement of slag unloading mechanisms, continuous operation centrifuges emerged in the 1930s, and intermittent operation centrifuges also developed due to the implementation of automatic control.
Centrifuges can be divided into three categories based on their structure and separation requirements: filtration centrifuges, settling centrifuges, and separators.
A centrifuge has a cylinder called a drum that rotates at high speed around its own axis, usually driven by an electric motor. After the suspension (or emulsion) is added to the drum, it is quickly driven to rotate at the same speed as the drum, and under the action of centrifugal force, each component is separated and discharged separately. Usually, the higher the drum speed, the better the separation effect.
The working principles of centrifugal separators include centrifugal filtration and centrifugal settling. Centrifugal filtration is the process of generating centrifugal pressure in a suspension under a centrifugal force field, which acts on the filter medium, causing the liquid to pass through the filter medium and become the filtrate, while solid particles are trapped on the surface of the filter medium, thereby achieving liquid-solid separation; Centrifugal settling is the principle of rapid settling and layering of components with different densities in a suspension (or emulsion) in a centrifugal force field, achieving liquid-solid (or liquid-liquid) separation.
There is also a type of separation machine used for experimental analysis, which can be used for liquid clarification and solid particle enrichment, or liquid-liquid separation. These separation machines have different structural types that can be operated under normal pressure, vacuum, and freezing conditions.
The important indicator for measuring the separation performance of a centrifugal separator is the separation factor. It represents the ratio of the centrifugal force experienced by the separated material in the drum to its gravity. The larger the separation factor, the faster the separation and the better the separation effect. The separation factor of industrial centrifugal separators is generally 100-20000, the separation factor of high-speed tube separators can reach up to 62000, and the separation factor of analytical high-speed separators can reach up to 610000. Another factor that determines the processing capacity of a centrifugal separator is the working area of the drum, and a larger working area also increases the processing capacity.
Filtering centrifuge and settling centrifuge mainly rely on increasing the diameter of the drum to expand the working surface on the circumference of the drum; In addition to the circumferential wall of the drum, the separator also has additional working surfaces, such as the disc of the disc separator and the inner cylinder of the chamber separator, which significantly increase the settling working surface.
In addition, the finer the solid particles in the suspension, the more difficult it is to separate them. The fine particles carried away in the filtrate or separation liquid will increase. In this case, the centrifugal separator needs a high separation factor to effectively separate them; When the viscosity of the liquid in the suspension is high, the separation speed slows down; The density difference between the components of a suspension or emulsion is large, which is beneficial for centrifugal settling, while centrifugal filtration of a suspension does not require a density difference between the components.
The selection of a centrifugal separator should be based on a comprehensive analysis of the size and concentration of solid particles in the suspension (or emulsion), the density difference between solid and liquid (or two liquids), liquid viscosity, the characteristics of the filter residue (or sediment), and the separation requirements. It is necessary to meet the requirements for the moisture content of the filter residue (sediment) and the clarity of the filtrate (separation liquid), and preliminarily choose which type of centrifugal separator to use. Then, based on the processing capacity and automation requirements for the operation, determine the type and specifications of the centrifuge, and verify them through actual experiments.
Usually, for suspensions containing particles with a particle size greater than 0.01 millimeters, a filtration centrifuge can be used; For particles in suspension that are small or compressible, a settling centrifuge should be selected; For suspensions with low solid content, small particles, and high requirements for liquid clarity, a separator should be selected.
The future development trend of centrifugal separators will be to enhance separation performance, develop large-scale centrifugal separators, improve slag discharge mechanisms, increase and combine rotary drum centrifuges, strengthen separation theory research, and study optimization control technology for centrifugal separation processes.
Strengthening separation performance includes increasing the drum speed; Add new driving force during centrifugal separation process; Accelerate the speed of slag pushing; Increasing the length of the drum can prolong the centrifugal settling and separation time. The development of large-scale centrifugal separators mainly involves increasing the diameter of the drum and using double-sided drums to improve processing capacity, thereby reducing equipment investment, energy consumption, and maintenance costs per unit volume of material. In terms of theoretical research, the main focus is on studying the fluid flow conditions inside the drum and the mechanism of filter residue formation, as well as the calculation methods for small separation degree and processing capacity.