Centrifuges are widely used in chemical industry, petroleum, food, pharmacy, mineral processing, coal, water treatment and shipping.
According to the structure and separation requirements, industrial centrifuges can be divided into three categories: filtering centrifuges, settling centrifuges and separators.
A centrifuge has a cylinder that rotates at a high speed around its own axis, called a drum, and is usually driven by a 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 the components are separated by centrifugal force and discharged separately. Generally speaking, the higher the drum speed, the better the separation effect.
The working principle of centrifugal separator includes centrifugal filtration and centrifugal precipitation. Centrifugal filtration is to make the centrifugal pressure generated by the suspension under the centrifugal force field act on the filter medium, so that the liquid passes through the filter medium to become filtrate, and the solid particles are trapped on the surface of the filter medium to realize liquid-solid separation; Centrifugal sedimentation is to realize liquid-solid (or liquid-liquid) separation by using the principle that components with different densities of suspension (or emulsion) quickly settle and stratify in centrifugal field.
There is also a separator used for experimental analysis, which can be used for liquid clarification and solid particle enrichment, or liquid-liquid separation. This separator has different structural types and can work under normal pressure, vacuum and freezing conditions.
Separation factor is an important index to measure the separation performance of centrifugal separator. It represents the ratio of centrifugal force to gravity of the separated material in the drum. The larger the separation factor, the faster the separation and the better the separation effect. The separation factor of industrial centrifugal separator is generally 100 ~ 20000, the separation factor of ultra-speed tube separator can be as high as 62000, and the separation factor of analytical ultra-speed separator can be as high as 6 10000. Another factor that determines the processing capacity of the centrifugal separator is the working area of the drum. The larger the working area, the greater the processing capacity.
Filtering centrifuge and settling centrifuge mainly enlarge the working surface on the circumference of the drum by increasing the diameter of the drum; In addition to the circumferential wall of the drum, the separator has additional working surfaces, such as the disc of the disc separator and the inner cylinder of the chamber separator, which significantly increases the settling working surface.
In addition, the finer the solid particles in the suspension, the more difficult it is to separate, and the fine particles carried away in the filtrate or separation liquid will also increase. In this case, the centrifugal separator needs a higher separation factor to effectively separate; When the viscosity of the liquid in the suspension is high, the separation speed slows down; The density difference of each component of suspension or emulsion is large, which is beneficial to centrifugal sedimentation, while the centrifugal filtration of suspension does not need the density difference of each component.
The selection of centrifugal separator should be based on the size and concentration of solid particles in suspension (or emulsion), the density difference between solid and liquid (or two liquids), the viscosity of liquid, the characteristics of filter residue (or precipitate) and the separation requirements. In order to meet the requirements of water content of filter residue (sediment) and clarity of filtrate (separation liquid), which centrifugal separator is selected initially. Then, according to the processing capacity and automation requirements of operation, the type and specifications of centrifuges are determined, and finally verified by actual tests.
Generally, for suspensions containing particles with a particle size greater than 0.0 1 mm, a filter centrifuge can be selected; If the particles in the suspension are fine or compressible, a settling centrifuge should be selected. When the suspension contains low solid content, fine particles and requires high liquid transparency, the separator should be selected.
The development trend of centrifugal separator in the future is to strengthen the separation performance, develop large-scale centrifugal separator, improve the slag unloading mechanism, increase special and combined drum centrifuges, strengthen the research on separation theory and study the optimal control technology of centrifugal separation process.
Strengthening separation performance includes increasing the rotating speed of drum; Adding a new driving force in the centrifugal separation process; Speed up the slag pushing speed; Increasing the length of the drum will prolong the time of centrifugal sedimentation and separation. The development of large-scale centrifugal separator is mainly to increase the diameter of drum and improve the processing capacity by using double-sided drum, so as to reduce the equipment investment, energy consumption and maintenance cost for processing unit volume of materials. In theoretical research, the fluid flow in the drum and the formation mechanism of filter residue are mainly studied, and the calculation method of minimum separation degree and treatment capacity is studied.
Centrifuge is mainly used for separating solid particles and liquid in suspension, dissolving in emulsion or two different liquids to remove milk (such as separated milk fat), and it can also be used for liquid elimination, such as washing wet solids with a wet washing machine. Special overspeed tube centrifuge can separate gas mixtures with different densities, and it can also be used for the sedimentation of solid particles in centrifuge, which is suitable for chemical industry, petroleum, food, pharmacy and so on. According to the structure and separation requirements of industrial centrifuges, it can be divided into filtration centrifuges, centrifuges and centrifuges. The centrifuge rotates at high speed around the axis of the cylinder itself, which is called the drum, and is usually driven by a motor. The suspension (or emulsion) is driven after being added to the drum, and the drum rotates at a certain speed under the action of centrifugal force, and is separated from the components. Generally, the higher the rotating speed of the drum, the better the separation effect. The principle of centrifuge is centrifugal filtration and centrifugal precipitation. Centrifugal filter is that the pressure of centrifugal suspension acts on the liquid passing through the filter medium, and solid particles are trapped on the surface of the filter medium as filtrate, thus realizing liquid-solid separation. Centrifugal sedimentation is to realize layered liquid-solid (or liquid-liquid) sedimentation by using the principle that suspensions (or emulsions) with different density components are in the centrifugal field. However, those liquid separators with experimental analysis, centrifuges for clarification and solid concentration, or liquid separation, such as atmospheric pressure and vacuum freeze drying, are carried out under different types of operating conditions. Measuring the separation coefficient of centrifuge is an important index of separation. It represents the centrifugal force of the separated material in the drum, and the ratio of gravity to the separation factor is usually faster, and the separation effect is better. Industrial centrifuges, tubular centrifuges with separation coefficient of 100 ~ 20000, accelerate the analysis of separation coefficient, and the separation coefficient of 6 10000 with centrifugal speed of 62000 ranks first. Another factor that determines the centrifuge is the large working area and strong handling capacity of the drum. Filter centrifuges and settling centrifuges mainly rely on increasing the drum diameter to expand the circumferential surface. In addition to drum machines, there are additional circumferential walls, such as disc separators and chamber disc machines, which greatly increase the mining subsidence. In addition, the more regular the solid particles in the suspension are, the more difficult it is to separate filtrate or separate fine particles. In this case, the centrifuge needs a higher separation factor to effectively separate. When the viscosity of the suspension is high, the separation speed is slow, and the density difference of emulsion or components in the suspension is poor, the centrifugal sedimentation centrifuge does not require the density difference of components in the suspension. The selection of centrifuge should be based on the size and concentration of solid particles in suspension (or emulsion), solid and liquid (or two liquids), viscosity of liquid, density of phosphate-containing residue (or precipitate), and characteristics of separation requirements. In order to separate the water content of filter cake (sediment) from the clarity of filtrate (liquid), which centrifuge to use was initially selected. Then according to the operation ability and automation degree, the type and specification of centrifuge are determined, and finally the actual test is carried out. Usually, for suspensions containing particles with a particle size of 0.065438±0mm or more, filter centrifuges can be selected; for suspensions with small particles or compressed particles, settling centrifuges should be selected; for suspensions with low solid particles, fine particles and liquids require high clarity, separators should be selected. The development trend of centrifuges in the future will be to strengthen and develop large-scale separation, improve the deslagging centrifuges, special and combined mechanisms, strengthen the theoretical research of separation drum centrifuges, and study the optimal control technology of centrifugal separation process. Strengthening the separation characteristics includes increasing the rotating speed of the drum, adding new driving force in the centrifugal separation process, speeding up the slag pushing speed and increasing the length of the drum to prolong the centrifugal separation time. The development of large-scale centrifuges is mainly through improving the diameter of the drum and the capacity of the drum to handle materials per unit volume, that is, reducing the investment, energy consumption and maintenance costs of processing equipment. Theoretically, this paper mainly studies the flow situation in the drum and the formation mechanism of filter cake, and studies the calculation method of minimum separation capacity.