Common separators:
1, centrifugal separator
Centrifuges are mainly used to separate solid particles and liquids in suspension; Or separate two immiscible liquids with different densities in the emulsion (such as separating cream from milk); It can also be used to dehumidify liquids in solids, such as washing clothes with a washing machine; The special ultra-fast tube separator can also separate gas mixtures with different densities, such as the concentration and separation of gaseous uranium hexafluoride; Some settling centrifuges can also classify solid particles according to their density or particle size, and the settling speed of solid particles with different density or particle size in liquid is different. Centrifugal separators are widely used in chemical, petroleum, food, pharmaceutical, mineral processing, coal, water treatment and shipping industries.
A centrifugal separator has a cylinder that rotates at high speed around its own axis, called a rotating 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.
① Centrifugal filtration: the centrifugal pressure generated by the suspension under the centrifugal force field acts on the filter medium (filter screen or filter cloth) to make the liquid pass through the filter medium to become filtrate; While solid particles are trapped on the surface of the filter medium to form filter residue, thus realizing liquid-solid separation. There are holes in the circumferential wall of the filter cartridge, and the inner wall is lined with filter media.
② Centrifugal sedimentation: Liquid-solid (or liquid-liquid) separation is realized by using the principle that components with different densities in suspension (or emulsion) quickly settle and stratify in centrifugal field. The circumferential wall of the settling drum has no holes. Figure 3 shows four typical settling tanks. After the suspension (or emulsion) is added to the drum, solid particles (or high-density liquid) settle on the wall of the drum to form sediment (or heavy separation liquid). The liquid with lower density gathers in the center of the drum, flows to the overflow port, and is discharged as separation liquid (or light separation liquid).
Drum is intermittent slag discharge, which is suitable for the separation of suspension or emulsion with small particle size and low solid particle concentration; The drum adopts spiral continuous slag discharge to separate the suspension with high solid particle concentration. In the rotating drum with multi-layer conical disks, the liquid is divided into several thin layers by the disks, which shortens the distance of sedimentation and separation, accelerates the separation and improves the separation effect. When the solid-liquid mixture to be separated enters the high-speed drum from the feed inlet, the mixture is filtered through the filter screen under the action of centrifugal force, and the liquid separation is discharged through the drain pipe, and the solid separation remains in the drum. When the solid separation in the drum meets the requirements specified by the equipment, stop feeding, clean the solid separation and discharge the washing liquid at the same time. After the cleaning meets the requirements, the centrifugal separator runs at a low speed, and the solid separation discharging device (scraper) is driven by AC servo motor to discharge the solid separation and complete a working process.
Step 2: Filter
Filter is a kind of equipment which uses porous filter to realize solid-liquid separation. Filters are used in chemical industry, petroleum, pharmacy, light industry, food, mineral processing, coal and water treatment. The filter is a new type of filtering system, which has the characteristics of novel structure, small volume, simple and flexible operation, high efficiency and closed work, and is a multi-purpose and adaptable filtering equipment. China has used filtration technology in production since ancient times, and paper made of plant fibers has been available since 200 BC. 105, Cai Lun improved the papermaking method. In the process of papermaking, he threw the plant fiber pulp on the dense thin bamboo curtain. Water is filtered through the gap of the bamboo curtain, leaving a thin layer of wet pulp on the surface of the bamboo curtain and drying it into paper.
A simple filter is formed by dividing the container into an upper cavity and a lower cavity with a filter medium. The suspension is added into the upper cavity and enters the lower cavity through the filter medium under pressure to become filtrate, and solid particles are trapped on the surface of the filter medium to form filter residue (or filter cake). In the process of filtration, the filter residue layer accumulated on the surface of filter material gradually thickens, the resistance of liquid passing through the filter residue layer increases, and the filtration speed decreases.
When the filter chamber is full of filter residues or the filter speed is too low, stop filtering, remove filter residues, regenerate filter media and complete a filter cycle. When the liquid passes through the filter residue layer and the filter medium, it must overcome the resistance, so there must be a pressure difference on both sides of the filter medium, which is the driving force to realize filtration. Increasing the pressure difference can accelerate the filtration, but when the pressure difference is large, the compressed deformed particles are easy to block the pores of the filter medium, and the filtration will slow down. There are many industrial chains in China, low production concentration, low R&D capability of high-end products and low manufacturing technology level of filter press industry, and the import and export trade deficit continues to expand. The next few years will be a period of high-speed shock in the filter press industry, and the direct consequence of this high-speed shock is to expand the polarization trend in the brand camp. It is estimated that there will never be so many enterprises that can really survive in the market in the next few years. However, this high-speed shock in the filter press industry will bring great opportunities, and the result of the shock will make the market run more rationally.
The road to localization of high-end electric filter press is extremely bumpy. Basic components have become a short board that restricts the high-end development of China's filter press manufacturing industry. During the "Twelfth Five-Year Plan" period, the government will continue to increase the localization of high-end equipment parts of filter press. With the continuous development of the market, there are three ways of product suspension filtration: residue layer filtration, deep filtration and screen filtration.
① Slag layer filtration: At the initial stage of filtration, the filter medium can only retain larger solid particles, and small particles pass through the filter medium with the filtrate. After the initial filter residue layer is formed, the filter residue layer plays a major role in filtration. At this time, large particles and small particles are trapped, such as the filtration of plate-and-frame filter press.
② Deep filtration: the filter medium is thick, and the suspension contains less solid particles with smaller pores than the filter medium. When filtering, the particles are absorbed in the pores after entering, such as the filtration of porous plastic pipe filters and sand filters.
③ Screen filtration: the solid particles trapped by filtration are larger than the pores of the filter medium, and the solid particles are not adsorbed in the filter medium, such as the coarse impurities in sewage are filtered by the drum screen. In the actual filtering process, the three methods often appear at the same time or successively.