Filtration performance and charge degradation during particle loading and reusability of charged PTFE needle felt filters

Abstract Electret filter materials have attracted wide attention because of their low pressure drop and high filtration efficiency. Few studies have measured the filtration performance and the charging status of the charged filters during soot particle loading. In this study, the polytetrafluoroethylene (PTFE) needle felt filters were charged by a corona discharge method. The filtration efficiency and surface potential were investigated during the soot particle loading process. The effects of NaCl particles, soot particles and A2 dust on surface potential and filtration efficiency were investigated. The reusability of charged filters and the effect of temperature on surface potential were studied. The results indicated that the initial filtration efficiency of charged PTFE needle felt filters (PNFFs) was greatly improved compared with that of uncharged PNFFs. The attenuation rate of the surface potential at 100 oC was faster than that at room temperature. The surface potential decreased with the start of particle deposition on the filters, correspondingly, the filtration efficiency of the charged PNFFs decreased. The efficiency of charged PNFFs loaded by soot particle decreased first and then increased, with the transition point corresponding to 20 Pa of pressure drop growth. With the same increment of pressure drop, soot particles with higher conductivity caused more efficiency degradation than NaCl particles. The reusability of the charged filters was affected by the effectiveness of dust cake removal and the particle conductivity.