Types of centrifuges in solid state systems
Classification according to working principle
In a solid control system, a filter centrifuge separates solid particles from the fluid by means of a filter medium (e.g. a screen or cloth). When the fluid containing solid particles into the centrifuge drum, under the action of centrifugal force, the liquid through the filter cloth from the small holes in the drum outflow, while the solid particles are retained in the filter cloth to form a cake. This centrifuge is suitable for solid particles large, regular shape and not easy to block the filter media. For example, when dealing with drilling fluids containing large sand particles, the filter centrifuge can effectively separate the sand particles from the drilling fluids and prevent the sand particles from wearing out the drilling equipment. Its advantages are simple structure, convenient operation, high separation efficiency, and the ability to quickly realize solid-liquid separation. However, it also has some limitations, such as poor separation effect for fine particles, easy clogging of the filter media, and the need for regular replacement or cleaning of the filter media.
Sinking centrifuges utilize the difference in settling velocities of solid particles and liquids in the centrifugal force field to achieve separation. In the solid control system, when the mixture enters the centrifuge drum, due to the high speed rotation of the drum to produce a strong centrifugal force, the solid particles with a greater density quickly to the wall of the drum to settle, while the less dense liquid is located in the center of the drum area. The liquid and solid are discharged through special liquid and solid discharge devices. This type of centrifuge is very effective in handling suspensions containing fine particles. For example, in the oil drilling process, when purifying drilling fluids containing fine drill cuttings, the sedimentation centrifuge is able to separate most of the cuttings from the drilling fluids and improve the performance of the drilling fluids. The advantage of the sedimentation centrifuge is that it can deal with solid particles of various sizes, especially the separation of fine particles is better, and it does not need filtering media, avoiding the problem of filtering media clogging. However, its separation precision is relatively low, and the separation effect may not be ideal for substances with small density differences, and the equipment structure is relatively complex and the maintenance cost is high.
Disc centrifuge is more widely used in solid control systems. Its drum is equipped with many disks, and a narrow channel is formed between the disks. When the mixture enters the drum, under the action of centrifugal force, the solid particles with larger density move towards the lower surface of the disks and are deposited on the wall of the drum, while the liquid with smaller density flows upwards along the disks and is discharged through a specific outlet. Disc centrifuges are effective for processing emulsions or complex mixtures containing many components of different densities. They are well used in the separation of fats and oils in food processing, the separation of emulsions in the chemical industry and the separation of complex mixtures containing oil, water and solid particles in some solid control systems. The advantages of disc centrifuges are high separation efficiency, high separation precision, and the ability to simultaneously separate a variety of components with different densities. Its disadvantages are complex structure, high requirements for operation and maintenance, and relatively expensive.
Classification according to rotational speed
In the solid control system, the rotational speed of low-speed centrifuge is generally around 1000 – 3000r/min. It is mainly used for the preliminary separation of larger solids, such as in some simple construction slurry processing, to separate larger soil particles from the slurry. The centrifugal force of the low-speed centrifuge is relatively small, which requires low mechanical strength of the equipment, so the cost of the equipment is also relatively low. It is simple to operate, stable in operation, and suitable for occasions that do not require high separation accuracy.
The rotational speed of high-speed centrifuge is usually between 3000 – 10000r/min. In the solid control system, high-speed centrifuges are able to deal with solid particles of smaller size. For example, in the solid-liquid separation of some chemical materials, when finer solid impurities need to be separated from the liquid, high-speed centrifuges can provide enough centrifugal force to achieve effective separation. The separation efficiency of high-speed centrifuges is higher than that of low-speed centrifuges, but the manufacturing and operating costs of the equipment increase accordingly, and the balance and stability requirements of the equipment are also higher.
Ultra-speed centrifuge speed more than 10000r/min, in the solid control system, mainly used for very fine particles or separation of extremely high precision requirements. For example, in the production process of certain high-end electronic materials, the need for precise solid-liquid separation of solutions containing ultra-fine particles, ultracentrifuge can provide a strong centrifugal pump to separate these very fine particles from the solution. However, the equipment cost of the ultracentrifuge is very high, and the operation and maintenance requirements are extremely strict, requiring specialized technicians to operate and maintain.
Classification according to use
In solid control systems, pre-separation centrifuges are mainly used for preliminary separation of the mixture. Its purpose is to remove most of the large particles of solids in the mixture to reduce the burden of subsequent processing equipment. For example, in the sewage treatment system, the pre-separation centrifuge can first separate the larger sediment, debris, etc. in the sewage, and then send the pre-separated sewage to the subsequent deep treatment equipment, such as settling tanks, biological treatment units, etc.. The pre-separation centrifuge is characterized by large treatment capacity and fast separation speed, but the separation precision is relatively low.
Fine separation centrifuge focuses on further fine separation of materials after pre-separation to achieve higher separation accuracy. In the solid control system of the pharmaceutical industry, fine separation centrifuges can further remove the trace impurities in the raw materials of drugs and improve the purity of drugs. The centrifugal force of fine separation centrifuges is usually larger, and the structure design is more precise, which can effectively separate substances with smaller particle size and smaller density difference, but the processing capacity is relatively small, and the cost of equipment and operation is higher.
The main function of dewatering centrifuge in the solid control system is to remove as much water as possible from the solids in order to get a drier solid product. In sludge treatment, the dewatering centrifuge can reduce the water content in sludge to a certain level, which is convenient for the subsequent treatment of sludge, such as transportation, landfill or incineration. The dewatering centrifuge squeezes out the water in the solid particles through powerful centrifugal force, and its separation effect is closely related to the nature of the solid particles, the rotational speed of the centrifuge, the structure of the drum and other factors.
Selection of centrifuge in solid control system
Selection according to the characteristics of solid particles
If the solid particles are large (e.g., larger than 1 mm in diameter), such as concrete mixing wastewater containing large stones and sand particles handled in the construction industry, filter centrifuges or low-speed centrifuges may be a better choice. Filter centrifuges can intercept these large particles through a simple screen, while low-speed centrifuges are able to separate large particles by rapid sedimentation using relatively small centrifugal forces. For smaller particles (between 1 – 100 μm in diameter), such as some fine powder suspensions in chemical production, high-speed centrifuges or sedimentation centrifuges are more suitable, as they can provide sufficient centrifugal force to settle and separate these fine particles. For very fine particles (diameter less than 1μm), such as solid-liquid separation in the production of some nanomaterials, ultracentrifuges or disc centrifuges may be the only equipment that can achieve effective separation.
Filter centrifuges are more effective when the solid particles have a regular shape, such as spherical or nearly spherical particles. This is because regular shaped particles are less likely to clog the filter media and can pass through the pores of the screen or cloth. For example, when dealing with mixtures of spherical glass beads and liquids, filter centrifuges can efficiently achieve solid-liquid separation. However, for irregularly shaped, angular particles, such as metal scraps with sharp edges and corners from some metalworking processes, a sedimentation centrifuge may be more appropriate. Because these irregular particles tend to clog the filter media, while the sedimentation centrifuge does not need filter media, through the centrifugal force to directly make the particles settle and separate.
If the density difference between solid particles and liquid is large, such as the separation of oil sands from water in oil sands mining, a lower speed centrifuge may achieve better separation. However, if the difference in density is small, such as the separation of microparticles of organic matter in certain organic solutions, a centrifuge with a higher rotational speed, such as a high-speed or ultra-speed centrifuge, is required to provide sufficient centrifugal force to overcome the effect of the small difference in density and to achieve effective separation.
Selection according to liquid characteristics
For low viscosity liquids, such as water or low concentration of aqueous solutions, various types of centrifuges can work better. However, when the liquid viscosity is high, such as highly concentrated syrup or viscous oil, the separation efficiency of the centrifuge will be affected. In this case, with filter centrifuges, the high viscosity liquid slows down the passage of the liquid through the filter media and may even clog the filter media. Therefore, sedimentation or disc centrifuges may be more suitable for solid-liquid separation of high-viscosity liquids. These centrifuges do not rely on filter media, but rather on centrifugal force to settle or separate solid particles in high viscosity liquids.
If it is an ordinary non-emulsion, such as simple solid-liquid suspension, depending on the characteristics of the solid particles can choose filtration, sedimentation or high-speed centrifuges, etc. But if it is an emulsion, such as simple solid-liquid suspension. But if it is an emulsion, such as milk or emulsion in some chemicals, disc centrifuge is the best choice. Disc centrifuge can effectively separate the oil phase, water phase and solid impurities in the emulsion, through the special structure between the discs and the role of centrifugal force, so that the composition of different densities flow to different outlets.
Selection according to the separation precision requirements
If the separation precision requirements are low, such as the preliminary treatment of construction slurry in some construction industries, as long as most of the large solids are removed, low-speed centrifuges or pre-separation centrifuges can meet the requirements. These centrifuges can quickly separate large solids from the liquid, although some small solids may remain, but for the subsequent treatment process has little impact.
When there is a certain requirement for separation accuracy, such as in the production process of some common chemical products, it is necessary to control the solid impurity content within a certain range, high-speed centrifuges or fine separation centrifuges are a better choice. These centrifuges can provide high centrifugal force to separate solid particles of small size, and reduce the solid impurity content to the level that meets the production requirements.
In some high-end manufacturing industries, such as electronic chip manufacturing or high-end pharmaceutical industry, high precision solid-liquid separation of raw materials is required to ensure product quality. In such cases, ultracentrifuges or disc centrifuges are essential. These centrifuges are capable of achieving extremely high separation accuracy and reducing solid impurity content to extremely low levels, meeting the stringent requirements of high-end product production.
Selection based on equipment cost and operating cost
Low-speed centrifuges and simple filter centrifuges have relatively low equipment costs and are suitable for small enterprises with limited budgets or more cost-sensitive application scenarios. For example, some small construction material processing enterprises in the treatment of wastewater, if the separation effect is not very high requirements, you can choose the cheaper low-speed centrifuge. High-speed centrifuges, ultra-speed centrifuges and disc centrifuges have higher equipment costs, especially ultra-speed centrifuges and some high-end disc centrifuges, which may cost several times or even dozens of times as much as low-speed centrifuges. These centrifuges are mainly used in large-scale enterprises or scientific research institutions with high requirements for separation accuracy and processing capacity and sufficient budget.
Running costs include energy consumption, maintenance costs, replacement costs of wearing parts and so on. Generally speaking, low-speed centrifuges have lower energy consumption, simple maintenance and lower replacement cost of wearing parts. While high-speed and ultra-speed centrifuges have higher energy consumption due to high rotational speed, and have higher requirements for balance and lubrication of the equipment, and the maintenance cost increases accordingly. The structure of disc centrifuge is complex, and its internal discs and other parts, if damaged, have a high replacement cost. In the selection of centrifuges, the need to consider the operating costs of the equipment, according to their own economic strength and long-term operational needs to make decisions. For example, in some long-term operation and large processing capacity of the solid control system, if you choose a centrifuge with high operating costs, it may lead to a substantial increase in the operating costs of the enterprise.
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