Characteristics, Pressure Drop and Capture Efficiency of Heavily Loaded New and Repeatedly Washed HEPA Filters
An extensive literature review revealed few published reports on the wet cleaning and reusing industrial HEPA filters, except for those on metallic and glass fiber filters. Accordingly, the effects of particulate loading effect on pressure drop as well as the capture efficiency of new custom fabricated high-efficiency particulate air (HEPA) filters were determined and the findings were compared with those of the same filters after being wet cleaned and reused multiple times. A set of five samples from three different types of HEPA rated filtration media, made of polypropylene (Puritrate®), Teflon and glass fiber filters, were fabricated in cylindrical shape. Each filter was mounted in a specially designed filter testing unit and gradually loaded with airborne particles of cadmium telluride (CdTe) in 10-gram increments up to a total of 100 grams. During the loading, the face velocity of each filter was kept constant at 17. 8 m/s (3500 ft/min). Four filters (two Puritrate® and two Teflon) were fully loaded 4-10 times and each time they were wet cleaned in dilute (< 4%) nitric acid soaked for 24 hours, rinsed with deionized water and gradually dried at ambient temperature under a laboratory hood until the filter gained its original weight. The glass fiber was used as a reference medium; it was loaded and tested only once and was not wet cleaned or reused. The pressure drop across all filters (new or reused) increased by cubic model expression as the filters were gradually loaded. Baseline pressure drop on new (unused) filters ranged from 45 Pa (Puritrate®) to 115 Pa (Teflon). As the filter-loading progressed, the pressure drop ranged from 146 Pa (Puritrate®) to 306 Pa (Teflon). After each wet cleaning and drying cycle, the filters' pressure drop returned almost to their original baselines. All filters, new or reused, performed well, with particulate capture efficiencies exceeding 99.97% at 0.3 µm. The results suggested that certain custom fabricated HEPA filters can be effectively wet cleaned and reused.
2. Johnson K. How to reuse HEPA filter, 2013. Available at: http://www.ehow.com/ how_7608924_reuse-hepa-filters.html. Accessed 03/24/16.
3. Akbar-Khanzadeh F, Smigielski K. Design and set up of an air filter testing unit to demonstrate characteristics and performance of particulate air filters. J Occup Hyg 2009;1(1):1-8.
4. Bergman W, Larsen G, Lopez R, Wilson IS, Witherell C, McGregor M. Further development of the cleanable steel HEPA filter, cost/benefit analysis, and comparison with competing technologies. Lawrence Livermore National Laboratory, Livermore, CA. 24th Doe/Nrc Nuclear Air Cleaning and Treatment Conference July 15-18; 1996, Portland, Oregon.
5. Oberg E, Jones F, Horton H, Ryffel H, McCauley C. Machinery's Handbook. 29th ed, Engineering, Design & Drafting Store, Toolbox, 2013, Available at http://www.engineersedge.com/filtration/hepa_filter_pressure_drop_considerations.htm Accessed 12/20/17.
6. Recycle Brita Filters, 2012. Available at http://www.preserveproducts.com/ recycling/britafilters.html. Accessed 03/24/16.
7. Baum J. How do electrostatic air filters work? Available at http://www.ehow.com/how-does_4895478_electrostatic-air-filters-work.html Accessed 03/24/16.
8. Ji JH, Bae GN, Kang SH, Hwang J. Effect of particle loading on the collection performance of an electret cabin air filter for submicron aerosols. J Aerosol Sci 2003; 34:1493-1504.
9. Endo Y, Chen D, Pui DYH. Effects of particle polydispersity and shape factor during dust cake loading on air filters. Powder Technol 1998;98(3):241-249.
10. Endo Y, Alonso M. Physical meaning of specific cake resistance and effects of cake properties in compressible cake filtration. Filtr Separat 2001;38(7):42-46.
11. Herman PK, Lehmann MJ, Velu YK. Predicting initial pressure drop of fibrous filter media typical models and recent improvements. J Text Apparel Tech Manag 2006;5(2):1-15.
12. Choi J, Ha S, Bak Y, Park Y. Particle size effect on the filtration drag of fly ash from a coal power plant. Korean J Chem Eng 2002;19(6):1085-1090.
13. Kim SC, Wang J, Shin WG, Scheckman JH, Pui DYH. Structural properties and filter loading characteristics of soot agglomerates. Aerosol Sci Tech 2009;43(10): 1033-1041.
|Issue||Vol 10 No 2 (2018)|
|Recycling HEPA filters Filter pressure drop Filter loading characteristics|
|Rights and permissions|
|This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.|