Flue gas filtration media
Disclosed is a filter medium useful for flue gas filtering that comprises a non-woven fibrous web having at least 80 weight percent of meta-aramid fibers and from 0.1 to 20 weight percent of meta-aramid fibrids, based on weight of fibers and fibrids. The non-woven fibrous web can have average pore size of 20 to 80 micrometers, maximum pore size of 100 micrometers, dry Mullen burst strength of at least 7 kg/cm 2 , retention of 80% of the dry Mullen burst strength after acid cycling, a filtration efficiency of at least 95% for 2.5 micron particle, and/or a shrinkage of less than 2% after being heated in a dry oven at 205° C. for 2 hours. A method of making the filter medium comprises wet-laying a furnish of the meta-aramid fibers and the meta-aramid fibrids; drying to form the non-woven fibrous web; preferably, calendering; and optionally saturating with binder resin and curing.
1 . A filter medium, the medium comprising a layer of a non-woven fibrous web having a thickness of 0.3 to 3 mm the non-woven fibrous web comprising
at least 80 weight percent of meta-aramid fibers,
from 0.1 to 20 weight percent of meta-aramid fibrids, each based on total amount of fibers and fibrids, and
a binder resin; the filter medium having an air permeability of at least 19.4 cubic feet per minute per square foot according to ASTM D737.
2 . The filter medium of claim 1 wherein the non-woven fibrous web is calendered.
3 . The filter medium of claim 1 , wherein the non-woven fibrous web has a grammage of at least 80 grams per square meter.
4 . The filter medium of claim 1 wherein the non-woven fibrous web has a shrinkage after 2 hours in a dry oven at 205° C. of less than 2% wherein shrinkage is evaluated by measuring a dimension of the non-woven web other than thickness before and after the non-woven fibrous web is placed in the oven for 2 hours.
5 . The filter medium of claim 1 further comprising another material laminated to the non-woven fibrous web.
6 . The filter medium of claim 1 wherein the non-woven fibrous web has a density of at least 0.3 g/cm 3 .
7 . A method for the manufacture of the filter medium of claim 1 , the method comprising:
wet-laying a furnish comprising the meta-aramid fibers and the meta-aramid fibrids to form a mat;
drying the mat to form the layer of the non-woven fibrous web;
saturating the non-woven fibrous web with a binder resin and then curing the binder resin; and optionally
calendering after drying,
to form the layer of the non-woven fibrous web having a thickness of 0.3 to 3 mm.
8 . A flue gas filter assembly, comprising
a flue gas inlet manifold, a flue gas outlet manifold, and a filtering apparatus positioned between the flue gas inlet manifold and the flue gas outlet manifold, wherein the filtration apparatus includes a filter medium comprising a non-woven fibrous web wherein the non-woven comprises at least 85 weight percent of meta-aramid fibers and from 0.1 to 20 weight percent of meta-aramid fibrids, each based on total amount of fibers and fibrids.
9 . The filter medium of claim 1 wherein the binder resin is a phenolic binder resin.
10 . The method of claim 7 wherein the saturating of the non-woven fibrous web with a binder resin occurs after calendaring.
11 . The filter medium of claim 1 wherein the fibrids are present in an amount less than 15%.
12 . A filter medium, the medium comprising a non-woven fibrous web the non-woven fibrous web comprising at least 80 weight percent of meta-aramid fibers and
from 0.1 to 20 weight percent of meta-aramid fibrids, each based on total amount of fibers and fibrids, and
a binder resin,
wherein the non-woven fibrous web has a thickness of 0.772 to 3 mm; and the filter medium having an air permeability of at least 19.4 cubic feet per minute per square foot according to ASTM D737.
13 . The flue gas filter assembly of claim 12 wherein the non-woven fibrous web comprises 0.1 to less than 15 weight percent of meta-aramid fibrids.