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Air filtration and separation technology

2012/4/26 19:00:34
Air filtration and separation technology

In recent years, air filtration technology in media research and development, the research on filtration mechanism and filtration equipment development and application has made great development. This paper mainly introduced the recent years domestic and foreign air filtration technology development status and achievement, put forward air filtration technology research and development and the problems to be solved.

Air filter air filter, refers to air pollution particles close to completely remove. It further than the air purification, air purification applied to many industrial processes of the air pollution of processing requirements are not too strict. [1]. Air filtration technology is nearly a hundred years along with science and technology and the development of modern industry and gradually formed a comprehensive technology, it refers to the application of air purification equipment control of dust pollution or by circulating air filter air suspended particle trapping, to protect environment and human health, it is in the air, ventilation and dust control and other fields has been widely applied.

Filter can be dispersed in the dispersion of solid particles in the fluid is separated from the porous material, diffusion of the fluid can be a gas or liquid. Filter type fiber filter, microporous membrane and membrane filter media. Filter determines the effect and benefit of filtering process, its development determines the air filtration technology development. It is widely used in indoor and outdoor air quality, quality control. In addition, the air conditioning fresh air filtration, air treatment and utilization and environmental protection, machinery, electric power, coal, chemical, ceramics, medicine, light industry, chemical fertilizer, pesticide, food processing, transportation, traffic road and other industries are widely used in synthetic fiber filter material and filter technology.

The rapid development of China's media production. The early nineteen fifties, our country did not have the media production factory, the market also have no special media products;60 time gradually textile fiber as filter medium, is applied to the industrial fields, to meet the needs of different industries, for a variety of different uses of filter material fiber filter cloth with acid and alkali-resistant, high strength smooth, fiber properties;70 time, domestic media208polyester flannel is the birth of filtration technology application to provide a first1 batch filter;80 time according to the Japanese product development729polyester woven filter material, and specifically for the dust filter developed needlepunched filter, improves the bag filter dust filter efficiency;90 time metaphase, scientific and technical personnel in China the successful development of membrane filter media, i.e., using a special process, the polytetrafluoroethylene microporous membrane composite in woven fabrics, nonwoven filter or glass fiber filter, the filter is formed when a layer of dust, realized as surface filtration, high efficiency and low resistance and energy saving provides high quality filter material [2,3].

The current media is the development trend of: (1) by a two-dimensional structure of woven filter cloth to the three-dimensional structure of the nonwoven filter fabric development, by the staple fiber woven filter cloth filter cloth to filament development, by the multifilament yarn twisting cloth filters to filter cloth development; (2) by conventional chemical fiber filter cloth of high performance, multi function, high quality filter cloth development by synthetic fiber filter membrane filter media, to develop [4].

At present, the majority of our synthetic fiber filter material production enterprises finishing and complex equipment is still not perfect, product variety and performance development is limited, some special uses of the media have to rely on imports. The existing filter response after finishing, and the application of composite technology, research and development of new media, to improve the domestic media performance, forming the applicability and products.

Air filter technology is adopted to filter material made of different forms of filter air filter. In order to increase the effective area of filtration performance of filter, optimization, air filter structure has the original single single shape to pleat shape or cylindrical, long cylindrical, stacked disc-shaped and matrix [5]. The earliest domestic high efficiency filter was born in 1964. The early nineteen eighties, foreign filter begins to enter our country, it has promoted the development of domestic filter. In recent years, the domestic research has begun to domestic electret static air filter [6]. The so-called electret refers to the long-term storage charge electrolyte materials, i.e., using some method of making fiber long has a charge, using electrostatic trapping mechanism to improve the filter trap efficiency. At present, domestic production of filters exist production standards and testing standards are not unified, efficiency test methods are not strict, product specifications variety and size is skimble-scamble wait for a problem; at the same time, in microelectronics and precision machinery industry, high efficiency filter purifying effect has been unable to meet the requirements [7], domestic high, ultra-high efficiency filter to be developed. These problems need to adopt and standardize the management and increasing investment in research approach to further improve the solution. The air filter used for residential, office, commercial and industrial buildings in the clean room, HVAC system, laser surgical operation room, air conditioning and other occasions.

The 2.2filter material and filter foreign development status

The new trend of development of foreign filtration materials for: to the nonwoven filter material, filter material composite membrane technology development, to adopt high technology, high performance glass fiber, PTFE, aromatic polyamide fiber, carbon fiber, metal fiber materials development of multi functional filter material development [4].

Foreign research production and application of filter materials, has formed a relatively complete system. Each filter material properties, such as ventilation performance, strength, trapped particle capacity and so on, have a complete set of testing and test tools. The development of new materials of filter increase continuously. In order to reduce the dust resistance, abroad already from weaving class media began to fiber grid filter transition. Fiber grid filter is the long fiber vertical arranged to form a root of the fence, when a layer of palisade filtering effect is not ideal, add another layer of palisade, until it reaches the ideal filter effect. In order to reduce dust leakage, improve the filtering performance, reduce cost, extend the service life, the fine diameter glass fibers and high temperature resistant synthetic fiber complementary advantages, made of composite needled felt filter.

In recent years, along with the hi-tech, new textile material development, foreign filtration technology to medical, new materials and other high-tech fields development of extraction.

Air filter in development, in recent years, electret static air filter is widely used abroad, high performance air filter. Some developed countries such as the United States, Japan and other countries, a few years ago has developed to produce the64MD level above the semiconductor element, air filtration efficiency reaches 99.999999% (0.12 ~0.17 m) above the high efficiency air filter. The domestic enterprises in this aspect and overseas has the very big disparity.

3air filtration theory research and development

Air filtration technology development is inseparable from the air filtration theory research and development. The filtration theory especially the air filter theory in early nineteenth Century has already started, and the air filter research and development only 20years of history, the filtration theory from the early classical filtration theory develops to the modern filtration theory and microporous filtration theory.

For the fine particle motion in the earliest recognized in early nineteenth Century, the botanist Brown observation of fine particles suspended in the liquid movement (i.e. Brown motion ); in 1922, Freundlich development on aerosol filtration rule understanding, proposed in0.1 ~0.2 m radius of maximum permeability of aerosol particles in1931, Albrecht; lead to the airflow through the single cylindrical fiber movement were studied, to establish a theory of Albrecht, then Sell carries on the essential improvement [8].

In 1936, Kaufmann first put Brown motion and inertia sedimentation concepts together are applied to the filtration theory of fiber, deduced the filtering function of mathematical formula; in 1942, Langmuir [9] to continue on the filtration theory, think filtration interception and diffusion collection and filtration fibers of inertial particles in precipitation is negligible.

In 1952, Davies [10] diffusion, interception and inertial3 mechanisms combine and use the formula expressed, so as to establish a new filtration theory -- isolated fiber theory; the 1958 Friedlander and 1967 Yoshioka [11] [12] developed an independent theory of fiber, their large Reynolds number condition, diffusion of particle inertia deposition and gravity effects and filters the blocking phenomenon is studied and summarized; in 1967, Pickaar and Clarenburg tried to present a fiber filter microporous structure of mathematical theory; the 1987 Pich and 1993Brown in his monograph describes the latest development of filtration theory.

The early classical filtration theory focuses on a single fiber model as a basis, think filtration efficiency by3 mechanisms: inertial effect, interception, diffusion effect. The particulate trapping rely on multiple trapping mechanism of joint action.

Modern filtering theory to prove that the inertia sedimentation is correct and the maximum penetration capacity of particles in the presence of filtration efficiency, that is, interception of Brown diffusion effect, the effects of gravity, precipitation effect and pressure effect of sets; the filtering process may exist in the mechanism of interception, inertial impact, diffusion, electrostatic effect, Coulomb attraction exclusion, image force, electrophoretic force and precipitation ( gravity ). Modern filtration theory of representative Davies filtration theory and Kuwarbara flow distribution.

In 1992, Payet, Gougeon and Attoui [14] considered the gas in a single fiber sliding on the classical theory, introducing a correction factor, the theoretical and experimental data to better match. In 1995, Rosnert [12] proposed dispersion in single fiber surface particles with irregular distribution and often forms a dendritic structure is a feature, built the most into improve the theories and particles in a single fiber body on the spatial distribution of. Using this theory, and the calculation program can predict the particle deposition.

In 2001, Thomas [14] of the filter in blocking conditions of air filtration theory and experimental study of the filter are presented, in the presence of filter cake, filtration efficiency and pressure loss calculation model. In recent years, many foreign scholars on the air filter in dust condition efficiency performance and cake formation and mechanism of the experiment and simulation research, obtained certain achievements [15~ 17].

4Conclusion

Filtering theory is not perfect, the relevant domestic research literature rarely filtration mechanism. Different structure filter's collection efficiency and pressure loss calculation, air and polydisperse granular distribution parameters on collection efficiency and pressure loss of effect, filter load characteristics on collection efficiency and pressure loss and the effect of filter structure characteristics on collection efficiency and pressure loss of the impact of the problem, all waits for the research to solve the. Therefore, further study on filtration theory of air filtration technology development is of great significance and practical value.

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