Based On The Values ​​of The Characteristics Of The Industrial Structure Fiber Filter

With the increasingly stringent of controlling the concentration of particle emission and the awareness of the harm of the respirable particle, the national standards for particle emission in some countries and regions are increased to 50mg/m~3, and even below 20mg/m~3. Currently, only the bag filter can meet the requirement. Furthermore, because of its wide adaptability, the character that free from the specific resistance of dust, the bag filter is taken the favor by the public. While the filtration material is the key component of the bag filter, the quality and performance of the filtration material have a significant impact on the operation and application range of the bag filter. Industrial fibrous filtration material has been widely used in the bag filter, and the filtration performance of the fibrous filtration material is good or not will directly influence the using effect of the bag filter. Therefore, the studies for the filtration performance of fibrous filtration material are the domestic and international issues.Numerical simulations were used to analyze the filtration performances of four kinds of fibrous filtration materials, which are 2-D fibrous filtration material with random structure, 3-D fibrous filtration material whose fibers are curved, plain wave fibrous filtration material, and complex gradient fibrous filtration materials whose surface are filmed with ultrafine fiber, respectively, in this study. In addition, the pressure drop and filtration efficiencies for the particles with different particle size under different operating conditions were calculated. Meanwhile, the predicted results based on the simulation were compared with the values of the empirical models in the literature. The following results can be shown:Compared with the values of the empirical models, the predicted values based on computational fluid dynamics (CFD) are more agreement with the experiment values. The results also show that it is feasible and cheap to investigate the filtration performance of the fibrous filtration materials by way of CFD technology.For the pressure drop and filtration efficiencies of fibrous filtration material, the face velocity is a important influencing factor. For small particles (d <0.5μm), the pressure drop is increased with the face velocity linearly, and the filtration efficiency is decreased with the face velocity, and for large particles (d_p >0.5μm), the tendency is just opposite. Additionally, the fiber diameter and the solid volume fraction (SVF) of the fiber are another two important influencing factors, and the filtration efficiency is increased with the SVF, but the pressure drop is also increased. The filtration mechanism is different for different particle sizes, i.e., for small particles, Brownian diffusion plays a significant role in the filtration process, and for large particles, and the inertial impaction becomes an important capture mechanism. Moreover, the filtration efficiency has the least value in the range in which Brownian diffusion and inertial impaction are both relatively weak.The effects of geometry parameters and operating condition including the horizontal distance, the vertical distance and the face velocity on the filtration efficiency and pressure drop of the plain wave fibrous filtration material were studied using response surface methodology (RSM) by means of the statistical software program (Minitab V14) in this study, and two second-order polynomial models were obtained with regard to the effect of the three factors as stated above. Two prediction models can estimate geometry parameters of plain wave fibrous filtration materials and operating condition on the filtration performance of the plain wave fibrous filtration material, which contributes to optimize the design of the plain weave fibrous filtration material.Because the structure of the multi-layer composite filtration material is gradient, i.e., the fiber diameter is increased gradually along the gas flow; it can obtain high filtration efficiency and long running life. In addition, the filtration efficiency can be increased by 13% via covering a layer ultrafine fiber on the surface of the multi-layer composite filtration material, especially for small particles (d_p <0.5μm), the filtration performance is increased markedly, and that the long-running resistance isn't increased obviously.The above results have great significant to understand the filtration performance of different fibrous filtration material further, and consequently can be used to guide the structural design and parameter optimization of the industrial fibrous filtration material.