The filter is the main equipment for the low-pressure degassing of the polymer in the polypropylene production process. The polymer from the upper channel I device D301 containing a small amount of propylene monomer enters the bag filter F301, in which the polymer and the monomer are further separated, and the polymer enters the steamer D501 from F301 under the control of the material level. The propylene gas is discharged from the top of the bag filter and then into the low pressure propylene scrubber T302. In the past, the domestic filter bag materials used in the equipment mostly used anti-static polypropylene filter cloth. Later, with the localization of the new filter material stainless fiber sintered felt, the material gradually replaced the polypropylene filter cloth in the F301 bag filter, showing the replacement cycle. Long, good filtering effect, easy to replace and so on.