Study On Characteristics Of Fibrous Filter Media For Fine Particulate Matter Removal From Environmental Air With Oil Mist Generation

Fine particulate matters in environmental air are vital contaminants that have a great impact on human health. Using fibrous material for fine particulate matters filtration has become a worldwide research hotspot in the field of environmental protection. For some industrial environments that contain processes producing oil mist flow, it is important to study the properties and optimize the performances of advanced fibrous filter media for oil droplets removal. On the other hand, in the air replenishing processes, purification of solid particles should be taken into account for those solid particles from the ambient air could affect the performance of coalescence filters. Moreover, for those industrial environments which take solid particles as the main object of purification, technical measures of fibrous filter media with high efficiency, low resistance and long service lifetime need to be researched and developed, which is also of great significance for the solid particles removal in other building environments.This dissertation mainly focuses on the following research:(1) Regarding to fine stainless steel fiber media used in gas-oil coalescence filtration, experimental study was conducted on its properties, performances and regeneration. Comparison was made with glass fiber media. The average fiber diameter ranged from 2.0μm~12.0μm. The results showed that the capture efficiency and the quality factor of the media got steady while the media thickness was increased from 2.0mm to 10 mm. the tested stainless steel fiber media had higher porosities and permeabilities than the glass fiber media of same fiber diameter and bulk density, which leads to higher capture efficiency and lower pressure drop. Besides, renewable and reuseable is another advantage of stainless steel fiber media.(2) To evaluate the effects of the saturation of the filter medium on coalescing filter performance, a steady state model for a coalescing filter medium basing on volume averaged continuum equations and single fiber mechanisms was built. The saturation of the medium was assumed to linearly vary with thickness position in the coalescing medium. Data from the coalescence experiments were used to calculate the model. The results show that improving the uniform of the saturation profile as well as decreasing the value of the average saturation can effectively decrease the pressure drop and increase the quality factor of the coalescing filter medium.(3) With the guidance of the theoretical analysis, several vertical drainage channels were established in fibrous filter medium with equal intervals to optimize the coalescence performance. Experiments were conducted on both stainless steel fiber and glass fiber media with and without spacers between the fibrous layers. The results show that isolating thin fiber layers by spacers affects the media performance in gas-liquid coalescence filtration, especially on the pressure drop of the fibrous media. The vertical drainage channels delay the loading of liquid in the subsequent media layers and thus delay the increase of the pressure drop. Besides, the media with steel mesh spacers tended to have higher quality factors.(4) Regarding to the obvious thickness shrinkage phenomenon observed in the coalescence filtration experiments, the shrinkage process and its mechanisms was studied. The shrinkage effect on microfiber media was measured and the extent of the shrinkage is related to a modified Bond number. Moreover, the variations caused by the shrinkage in media properties and coalescence performances were studied. The results indicate that capillary attraction, caused by the inter-molecular attractive forces between oil mists and solid fiber surrounding surfaces, is the cause of the shrinkage. The shrinkage depends upon the fiber diameter, the volume fraction of the liquid and the wetting properties of the fiber surfaces. The effect of shrinkage causes a reduction in filter medium porosity and permeability. Therefore the pressure drop increases more rapidly and the steady state pressure drop becomes higher.(5) In order to avoid solid particles coalescing to oil droplets which could affect the performance of oil droplets removal, for the purification of solid particles with widely size distribution, a filtration measure using composite filter medium with electrets fibrous medium and large dust holding capacity medium was proposed. Experiments were conducted to choose inner and outer layer of the composite medium, and its performance was also studied. The results show that the capture efficiency of the composite filter medium depends upon the efficiency of the inner layer. The pressure drop of the composite medium is a bit higher than the summary of the resistances of the inner and outer layer. However, the resistance of the composite medium is low. Yiren Wu(Heating, Gas Supply, Ventilation & Air-conditioning Engineering)...