Preparation and characterization of porous composite filter medium by polytetrafluoroethylene foam coating

High-performance bag filter with a super-hydrophobic microporous polytetrafluoroethylene layer fabricated by air-assisted electrospraying

Reducing PM emissions from industrial sites has become increasingly important as the adverse health effects of particulate matter have been demonstrated by multiple epidemiological and toxicological studies. High-performance bag filters are often used for this purpose. We fabricated polytetrafluoroethylene (PTFE) nanoparticle (NP)-coated high-efficiency bag filters using air-assisted electrospraying (AAES) technology. AAES functionalized with a combination of airflow drag force and an applied electric field facilitates high-throughput without requiring additional purification or preparation process of a PTFE emulsion. PTFE NPs form a unique three-dimensional microporous structure on a foam-filter medium, enhancing mechanical filtration performance (diffusion and interception). Moreover, the surface hydrophobicity was significantly improved as the PTFE NPs covered the bag filter surface. These factors highlight the feasibility of large-scale implementation of PTFE NP-coated bag filters for reducing PM emissions from industrial sources.

Application of powdered activated carbon coating to fabrics in a hybrid filter to enhance mercury removal

Elemental mercury (Hg⁰) is predominant constituent of flue gas emitted from coal-fired power plants. Adsorption has been considered the best available technology for removal of Hg⁰ from flue gas. However, adsorbent injection increases the amount of ash generated. In the present study, powdered activated carbon (PAC) was coated on polytetrafluoroethylene/glass fiber filters to increase Hg⁰ removal while concurrently reducing the amount of ash generated. The optimal PAC coating rate was determined in laboratory experiments to ensure better Hg⁰ removal with low pressure drop. When PAC of particle size less than 45 μm was used, and the areal density was 50 g/m², the pressure drop remained under 30 Pa while the Hg⁰ removal efficiency increased to 15.8% from 4.3%. The Hg⁰ removal efficiency also increased with decrease in filtration velocity. The optimal PAC coating rate was applied on a hybrid filter (HF), which was combined with a bag filter and an electrostatic precipitator in a single chamber. Originally designed to remove fine particulates matter, it was retrofitted to the flue gas control device for simultaneous Hg⁰ removal. By employing the PAC coating, the Hg removal efficiency of the HF increased to 79.79% from 66.35%. Also, a temporary reduction in Hg removal was seen but this was resolved following a cleaning cycle in which the dust layer was removed.

Influence of pleat geometry on filter cleaning in PTFE/glass composite filter

A pleated filter bag is often used to treat exhaust gas in many industrial applications, due to its fairly high dust collection efficiency and relatively low pressure drop. This work deals with the optimum pleating geometries of a pleated filter made with a newly developed PTFE/glass composite filter. It was found that pleating geometries, including pleat height and pleat pitch, directly affect the cleaning efficiency The design index, alpha, which stands for the ratio of pleat height to pleat pitch, is 1.48 for optimum operation. When the alpha value was higher than 1.48, the pressure drop across the pleated filter medium increased, resulting in a decreased cleaning interval due to the difficulty of filter cleaning. Therefore, it is necessary that the optimum pleating geometry should be determined by employing the dimensionless parameter, alpha, in the design of cartridge filters.