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Introduction and Features of Bag-in-Bag-out Filters
Introduction and Features of Bag-in-Bag-out FiltersBag-in-bag-out filters appeared in the 1950s and 1960s. They are filters that can be safely replaced using airtight bags. They are currently widely used in various fields with high risks or high isolation requirements, such as chemical and biological (CB) protection, chemical, biological and radiological (CBR) protection, nuclear, biological and chemical (NBC) protection, hospital isolation rooms, pharmaceutical equipment, microelectronic environments, food processing areas, biological research, genetics and biotechnology laboratories, industrial treatment and emission systems, chemical processing equipment, animal disease research laboratories, radioisotope processing equipment, nuclear power plants, strategic nuclear facilities, D.O.E equipment, military bases, etc.The biggest feature of bag-in-bag-out filters is that they are installed, replaced, and tested under the protection of PVC bags (or high-temperature bags). Taking the most commonly used 24-inch × 24-inch (610mm × 610mm) HEPA as an example, its filtration air volume is 1700m³/h at a resistance of 250Pa. When replacing the filter unit, the staff opens the inspection door, puts both hands into the gloves on the PVC bag, loosens the locking device of the filter unit, slides the used filter unit into the PVC bag, and then ties the bag in the middle to cut off the part containing the filter unit, so that the discarded filter unit is removed from the box through the PVC bag. Then put the new filter unit into a new PVC bag, put the new PVC bag on the flange and tie it tightly, remove the remaining bag on the flange, put it into the gloves of the new bag, tie it tightly, and cut it off, then roll up the new bag, close the inspection door and press it, and the whole replacement process is completed. This method makes the filter unit completely out of contact with the outside air, thereby ensuring the safety of personnel and the environment, and the replacement process is convenient and quick. At present, the production of bag-in-bag-out filters in the world is mainly based on the nuclear industry standards of various countries, such as the United States ASME N509 (air purification equipment and components for nuclear power plants), ASME N510 (nuclear air handling system testing), German DIN 25496 (ventilation components for nuclear facilities), etc. The equipment box is generally made of stainless steel and welded. The airtight isolation valve and the box are connected by flanges. The joints are usually sealed with chloroprene sealing gaskets and chloroprene flange gaskets. Under special requirements (such as high-risk and highly pathogenic environments), the equipment can resist earthquakes. The box and the airtight isolation valve use the same sealing standard. When the airtight isolation valve is closed, the US standard requires a pressure decay leakage test under a constant internal and external pressure difference of 2500Pa. The German standard requires a permissible leakage rate of less than 10l/(hm²) under a continuous internal and external pressure difference of 2000Pa. |
