In Manufacturing, What Is Centrifuging?

Centrifugal separator is a machine that uses centrifugal force to separate components of liquid and solid particles or a mixture of liquid and liquid. It is also called a tube centrifuge. Centrifugal separators are mainly used to separate solid particles from liquids in suspensions; or to separate two liquids of different densities in emulsions that are incompatible with each other (such as separating cream, oil, and water from milk); It can also be used to exclude liquids from wet solids

Centrifugal equipment

Centrifugal separator is a machine that uses centrifugal force to separate components of liquid and solid particles or a mixture of liquid and liquid. It is also called a tube centrifuge. Centrifugal separators are mainly used to separate solid particles from liquids in suspensions; or to separate two liquids of different densities in emulsions that are incompatible with each other (such as separating cream, oil, and water from milk); It can also be used to exclude liquids from wet solids

Chinese name

Centrifugal equipment

Time

30 years

Efficiency up to

More than 90

century

20th Century

The more detailed the solid particles in the suspension, the more difficult it is to separate, and the fine particles taken away from the filtrate or separation solution will increase. In this case, the centrifuge needs a higher separation factor to effectively separate; the viscosity of the liquid in the suspension When it is large, the separation speed is slowed down; the density difference of each component of the suspension or emulsion is large, which is favorable for centrifugal sedimentation, and the centrifugal filtration of the suspension does not require the density difference of each component.

In ancient China, people tied one end of a rope to a clay pot, held the other end of the rope, and rotated the pot to generate centrifugal force to squeeze out the honey in the pot. This is the early application of the principle of centrifugal separation.

There are dozens of (50-80) discs of the same shape and size in the drum of the centrifuge. The discs are stacked at a certain distance (0.5-1.2mm) to form a disc group, and each disc leaves the axis. There are several symmetrically distributed circular holes on the circumference of a certain distance. When many such discs are stacked, the corresponding circular holes form a vertical channel. After the mixed liquid of two different heavy liquids enters the centrifugal separator, it enters the gap between the disks through the vertical channels formed by the circular holes on the disks and is rotated at a high speed. Differently, if the heavy liquid has a high centrifugal sedimentation speed, it moves away from the axis, and the light liquid has a small centrifugal sedimentation speed, and then flows toward the axis. In this way, two different heavy liquids are separated during the flow between the discs. Used to filter sediment and other solid impurities in water, the efficiency is up to 90%. A centrifuge has a cylinder, called a rotating drum, that rotates at high speeds about its axis, usually driven by an electric motor. After the suspension (or emulsion) is added to the drum, it is rapidly driven to rotate at the same speed as the drum, and the components are separated and discharged separately under the action of centrifugal force. Generally, the higher the drum speed, the better the separation effect.

A type of separator for experimental analysis can be used for liquid clarification and solid particle enrichment, or liquid-liquid separation. This type of separator has different structural types operating under normal pressure, vacuum, and freezing conditions. The centrifugal separator has two principles: centrifugal filtration and centrifugal sedimentation. Centrifugal filtration is the centrifugal pressure generated by the suspension under the centrifugal force field, which acts on the filter medium, making the liquid pass through the filter medium to become filtrate, and the solid particles are trapped on the surface of the filter medium to achieve liquid-solid separation. The principle of each component with different density of suspension (or emulsion) quickly settles in centrifugal force field to realize liquid-solid separation or liquid-liquid separation. An important index for measuring the separation performance of a centrifugal separator is the separation factor. It indicates the ratio of the centrifugal force and gravity of the material to be separated in the drum. 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 to 20,000, the separation factor of super-speed tube separators can be as high as 62,000, and the separation factors of ultra-speed separators for analysis can be as high as 610,000. Another factor that determines the processing capacity of a centrifugal separator is the working area of the rotating drum, which has a large working area and a large processing capacity.

The centrifugal separator is composed of a fuselage, a transmission device, a rotating drum, a liquid collecting tray, and a liquid inlet bearing seat. The upper part of the rotating drum is a flexible main shaft, and the lower part is a damping floating bearing. The main shaft is connected to the passive wheel by a coupling seat buffer. The motor transmits power to the passive wheel through a conveyor belt and a tensioning wheel, thereby causing the rotating drum to rotate at an excessive speed around its own axis. Form a strong centrifugal force field. The material is injected from the liquid inlet at the bottom. The centrifugal force forces the material liquid to flow upward along the inner wall of the drum, and it is stratified due to the density difference of different components of the material liquid.

1. The impurities and dirt after the emulsion is processed by this machine are easy to clean.

2, carbon powder, glass powder, aluminum powder, stainless steel powder and other particles are easy to remove and separate.

3. No filter material loss.

4. The additives in the solution will not be separated.

5. Suitable for oily and water-soluble cutting fluid.

Centrifugal separation equipment has different models, which can be divided into two types: laboratory and factory.

Centrifuges are widely used in chemical, petroleum, food, pharmaceutical, mineral processing, coal, water treatment and shipbuilding sectors.

1. Sugar industry : sugar distribution

2. Salt industry : Dehalogenation of crystal salt

3. Starch industry : separation of starch and protein

4. Oil industry : refined oil

5. Beer and beverage liquids : clarification

1. Separation equipment should be able to prevent outside microorganisms from mixing into the material being separated.

2. The surface in contact with the separation material will not cause chemical reactions such as adsorption, penetration and oxidative flaking.

3. The inner surface of the centrifuge that is in contact with the material (centrifugal basket drum, shell, etc.) must be polished to the corresponding level, no recessed structure is allowed, and all corners require a circular arc transition. The welding seam must be continuous (ie, no gap welding), the welding point is smooth, and the welding seam needs to be purified after mechanical polishing.

4. The centrifuge should have a CIP function (that is, the equipment can be effectively cleaned without moving or disassembling) to prevent the accumulation of materials and impurities. This is a necessary condition for thorough equipment cleaning. For this, a fully automated CIP cleaning unit from the German GEAWestfalia separator is highly desirable and has been successfully used for cleaning centrifuges, storage tanks, piping systems and other equipment.

5. In order to ensure that all positions inside the centrifuge can be fully inspected, the centrifuge housing cover should be opened in multiple ways, that is, large flip covers, small flip covers, and closed covers.

6. The centrifuge should have the function of preventing static electricity and static electricity accumulation, that is, the inside of the centrifuge should be sealed with nitrogen, and the micro positive pressure in the centrifuge should be maintained by replenishment and emptying, so as to meet the explosion-proof requirements of the whole machine. It also guarantees quality and safety.

7. In some cases, the centrifuge should also have a clean function of in-situ sterilization (SIP). The SIP pressure vessel should be designed with a special spindle seal; as a pressure vessel design body, all contact with the material should be guaranteed The surface of the equipment can be fully sterilized under a certain vapor pressure.

8. For the scraper centrifuge, the selection of the filter is very important. The double-layer lightweight industrial plastic (PP) material filter can prevent any fibers or tiny debris from falling off. Its high temperature resistance and invariant characteristics are prerequisites for SIP high temperature sterilization. It is also necessary to consider the removal of residual filter cake to prevent confusion between batches.

9. It should have auxiliary detection function; the centrifuge is a high-speed rotary machine. Through continuous detection of the vibration amplitude of the equipment, it can pre-alarm when the centrifuge generates harmful vibration and make corresponding protective actions. There are also oxygen detection devices. A centrifugal separator of a patented product of Glacier Metal Co. Ltd. is provided with a check valve and a device capable of reducing noise.

10. Isolation device is used to separate the process area where the centrifuge processes materials from the equipment including transmission and hydraulic systems.

Affected by the promotion of new technologies and the development of related industries, the progress of foreign centrifugal separation technology is mainly reflected in the following aspects:

Strengthen theoretical research and choose the best design solution

The Swedish ALFA-LAVAL company found in the disc runner research that the velocity distribution on the cross section of the disc gap depends on a dimensionless number "", and the "" of industrial centrifuges is usually between 5-28. With the increase of the "" value, the rotation speed of the disc increases and the thin layer decreases, which can increase the Reynolds number and ease the eddy current. By cleverly designing the disc spacers and distribution holes, the feed can be increased by 20%.

In order to choose the best solution, the researchers used the flow field separation method, finite element simulation method, large gradient density step method, inverse modal analysis method, etc. to conduct theoretical research on the working performance and key parts of the centrifuge. For example, Russia's B? Sisjer has derived a series of formulas for analyzing the hydrodynamic problems of centrifuges, and provides a theoretical basis for designing centrifuges with excellent performance. The weir tank depth in the decanter centrifuge with in-band washing was optimized.

Improvement of technical parameters and advent of new models

In order to improve the purity of products and meet the requirements of energy and environmental protection, high parameters have become the development characteristics of foreign models. Because biological engineering needs to separate very fine particles, such as bacteria, enzymes, and insulin, and the smaller the cells, the lower the recovery rate. The German Westfalia company used a SA7-47-476 piston dish machine test and found that the NM (neisseriameningitidis) cell size was 0.8 × 1.0 m and the recovery rate was about 80%, while the TP (treponemaphagedenis) cell size was 0.2 × 10 m. The rate is only about 10%. Therefore, the latest dish-type machine for biological engineering can process 0.1 m particles and has a high speed. For example, the BTAX510 type of the Swedish ALFA-LAVAL company and the CSA160 type of the German Westfalia company have a separation factor of 15,000.

With the improvement of process requirements, new models have been introduced. The BH-46 Merco nozzle disc separator for the starch industry from the American Dorr-Oliver company, the inner diameter of the drum has reached 1.2m, the drum weight is 4.5T and the total weight of the machine is 21T. It is driven by two 220kW motors , The maximum production capacity is twice that of the BH-36 type, that is, 450M3 / h, and the equivalent sedimentation area has reached 250,000m2, which is the highest for a disc separator.

The BTUX510 disc separator for biotechnology from the Swedish company ALFA-LAVAL has an automatically adjusted vortex nozzle. The relationship between the viscosity and concentration of the nozzle feed is used to provide a constant solid-phase emission concentration, regardless of the change in feed rate and solid content. The decanter centrifuge with a separation factor of 10,000 can make up for the shortcomings of the tube separator to some extent. The BTNX3560-A is characterized by an advanced rotary dynamic design. The main bearing is changed to be installed elastically, which can prolong the life of the bearing and greatly reduce the noise when the machine is running. The vibration reduction connection of the gear box and the drum can increase the critical speed of the rotor.

The newly developed SZ type piston pusher centrifuge developed by Germany's Krauss-Maffei company, although small in size, is more effective for solid-liquid separation. There is also a double-cone decanter centrifuge used by the German company Flottweg to handle difficult-to-separate materials.

Strengthen dynamic monitoring and automation

With the development of automatic control and sensing technology, many advanced automatic control methods have been introduced into centrifuges, and various parameters such as temperature, flow, speed, amplitude and noise have been comprehensively performed during the operation of the centrifuge. Measurement. That is, sensors with various performances are installed in the centrifuge, and various information collected is input into the computer. After the system processes, it can understand the changes of various parameters in time to take corresponding measures. This resulted in unmanned disc separators.

Various combination machines and special machines

ALFA-LAVAL company combined screw conveyors on the disc separator, Krauss-Maffei company's piston pusher combined cone drums, etc. In addition, in order to improve the separation performance of centrifuges and seek the best operating conditions, Westfalia has the largest variety of disc separators in the world.

Design progress

With the development of computer technology, CAD technology and modular design have been widely used. The global market is becoming more competitive, and the manufacturing industry is facing a huge challenge to increase customer value. Since the 1990s, "mass customization" has gradually emerged in the manufacturing industry. That is "produce goods and provide services at an efficiency similar to mass production to meet the individual needs of customers." Due to the importance of design in the product life cycle, Design for Mass Customization (DFMC) has become a new trend in design.

In order to improve the performance, strength, rigidity, wear resistance and corrosion resistance of separation machinery, a batch of new materials are constantly emerging. For example, engineering plastics, hard alloys, and wear-resistant and corrosion-resistant stainless steel materials with excellent performance. France has developed a rotor made of hard ceramic materials. The outer layer of the rotor is wound with monofilament to increase the strength of the rotor. The United Kingdom has also developed a continuous fiber composite rotor made of synthetic resin. However, in the disc separator, due to the need for high mechanical strength and a certain degree of corrosion resistance, duplex stainless steel is widely used by manufacturers of separators in Western European countries. Russia has successfully developed a new type of austenite-ferrite dual phase steel 04X25H5M2 (04Cr25Ni5Mo2). Forgings of this steel are used in the manufacture of drums and have sufficient mechanical strength and a certain degree of plasticity.

In order to compensate for the contradiction between the material of corrosion resistance and strength, some advanced manufacturers have generally adopted the self-reinforcing technology of the drum. In addition, German WischnouskiiF and other [developed 16 new materials for separating drums], this centrifugally cast duplex stainless steel has high mechanical strength, good plasticity and good corrosion resistance.

The future development trend of centrifugal separators will be to strengthen the separation performance, develop large-scale centrifugal separators, improve the slag unloading mechanism, add special and combined drum centrifuges, strengthen the study of separation theory and study the optimization control technology of centrifugal separation processes. Chemical separation performance includes increasing the rotating speed of the drum; adding new driving force during centrifugal separation; accelerating the speed of slag pushing; increasing the length of the drum to prolong the time for centrifugal sedimentation and separation. The development of large-scale centrifugal separators is mainly to increase the diameter of the drum and use double-sided drums to increase the processing capacity to reduce equipment investment, energy consumption and maintenance costs for processing unit volume materials.

Theoretical research

It mainly studies the fluid flow condition and filter residue formation mechanism in the drum, and studies the calculation method of minimum resolution and processing capacity.

Centrifugation is the fastest, economical and effective purification method today

Features of centrifugal separation equipment :

Fast: The centrifugal separation speed is more than 5000-10000 times that of the natural sedimentation mode.

Economical: no need to replace the filter element, low running cost. Small footprint and compact

Effective: 1. Simultaneous liquid, liquid and solid three-phase separation. 2. Strong processing ability.

Centrifugation = clean coolant, cleaning solution

Coolant and cleaning fluid are always in a clean state

Advantages of centrifugal separation equipment :

1. Fine particles (below 20) that cannot be removed by ordinary filters, which can be easily removed by the centrifuge (above 1, 99% removed).

2. The oil slick is controlled below 0.5%. The separated oil is pure oil with a purity of 99%.

3. Extend the service life of the working fluid.

4. Cleaning liquid-6 times.

5. Coolant-up to 10 years.

6, less downtime-fewer working fluid changes, more working time.

7. Extending the use of cutting tools is requiredIf the oil content of cutting fluid is reduced from 5% to 0.5%, the life of the cutting tools can be extended by 20%, which is more in line with environmental protection requirements. Environmental protection.