1. Physical properties of the material being treated
Before choosing a centrifuge, we must first know the chemical composition, pH value of the material to be treated, whether the material is a suspension or an emulsion, and their solid and liquid concentrations, the coarse or fine particles of the material, and the operating temperature. Wait. In industrial production, various forms of suspension are encountered, and in general, the difference in particle diameters in the suspension is large. The viscosity of the suspension increases as the solid material increases.
2. Characteristics and application of centrifuge separation process
Centrifugal separation processes generally include centrifugal filtration, centrifugal sedimentation and high-heart separation. The centrifugal filtration process is commonly used to separate solid-liquid mixtures with large solids and large particles. The separation process can generally be divided into three stages: * Stage, solid particles are deposited on the inner wall of the drum by centrifugal force to form a filter residue layer, and the filtrate is also borrowed. The effect of the centrifugal force is filtered through the mesh of the drum. In the second stage, the filter residue layer is pressed under the action of centrifugal force, and the filter hydraulic pressure contained therein is extruded. In the third stage, the liquid contained in the voids of the filter residue layer is continuously discharged under the action of centrifugal force, so that the filter residue is further dried.
The centrifugal sedimentation process can be used to separate a suspension containing micro-solid forest particles. The separation process can generally be divided into two stages: * Stage, solid particles are deposited on the inner wall of the drum by centrifugal force. In the second stage, the layer of particles deposited on the drum wall is compacted by centrifugal force. When the solid content in the suspension is large, the settled particles are accumulated in a large amount, and the slag layer is quickly thickened, so continuous slag discharge is required. When the solid content in the suspension is small, it can be regarded as the free settlement of a single particle under the action of centrifugal force, and the growth of the slag layer is slow, and the latter can be used as an intermittent slagging method, which is also called a centrifugal clarification process.
In the centrifugal separation process, the emulsion formed by the liquids of different severity is separated by the meter, and the liquid is layered by the gravity difference under the centrifugal force, and then separately extracted.
Centrifugal clarification and centrifugation, because the amount of solid phase separated in the process is small or both are liquid, this high-center machine is easier to carry out the continuous operation of feeding and discharging, but requires a higher separation factor to separate well. This centrifuge is also called a separator.
3. Centrifuge separation factor, classification and model
Let W denote the angular velocity (rad/s) of the drum, R denotes the radius of the drum (m), and w denotes the peripheral speed (m/s) of the drum. The ratio of the centrifugal acceleration to the acceleration of gravity is called the centrifugal separation factor. .
The separation factor indicates the characteristics of the centrifugal force field and is an important factor representing the performance of the centrifuge. The larger the F value, the higher the separation capacity of the centrifuge. Therefore, the more difficult the material is to separate, the more reasonable the centrifuge with a larger separation factor is.
According to the separation factor F classification, it can be divided into ordinary centrifuge F ≤ 3500 (generally 3O0-1200), high-speed centrifuge 5000> F > 3500, ultra-high speed centrifuge F> 5000. .
Ordinary centrifuges are either filtered or decanted. It is suitable for the treatment of particles with equivalent diameter of 0.010-10mm, dewatering of coarse medium-short fiber or block materials. Due to the low rotation speed, the diameter of the drum is generally large.
High-speed centrifuges are usually decanted and separated, suitable for the separation of latex water or thin particles of fine suspension and emulsion. Due to the higher sub-rotation speed, the diameter of the drum is generally smaller and the length is longer.
The ultra-high speed centrifuge is suitable for separating emulsions and colloidal solutions with higher divergence and gas separation of different molecular weights. Due to the high speed, the drum is made into a slender tube.
Classified according to the type of operation process, can be divided into filter centrifuge, decanter centrifuge, clarification and separation centrifuge
Filter centrifuges are more common in industrial production, such as three-legged centrifuges, upper-suspension centrifuges, horizontal scraper discharges, and piston pusher centrifuges. This type of centrifuge can be used for the separation of suspensions with coarser particles or coarser solids and more solids. The separated filter cake layer is also easy to be washed and dehydrated to obtain drier filter residue. However, it is necessary to require the filter residue to have a large compressibility and uniform particles, so as to prevent the filter residue or small particles from passing through or blocking the filter screen, so it is not suitable for materials with high dispersion and amorphous. Since the speed of such a centrifuge is less than 1500 r/min, the separation factor is not large, and it is only suitable for the high fraction of the easy filtrate. Separation of granular materials such as granulated sugar, ammonium sulphate, and ammonium bicarbonate with the mother concentrate is widely used in other industries.
The wall of the drum of the decanter centrifuge has no pores. It uses the difference of the specific gravity of the liquid and the solid in the suspension. When the drum rotates at a high speed, the liquid and the solid act on the drum wall at different speeds by the centrifugal force. . Some sedimentation centrifuge slag is sent out by a screw conveyor, and the filtrate is discharged from the overflow port. The centrifuge is used for separating the drying of the easy-to-filter slurry and the general filter slurry, and the amorphous insoluble material with high dispersion.
The clarification and separation centrifuges have no holes in the drum wall for separating the thin suspension and the emulsion. The centrifuge has a high rotational speed, generally 4000~15000r/min, and the separation factor F>3500.
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