Dust Filtration

The most effective and economic equipment for filtering particulate material from gas streams is the bag filter. These devices employ an array of fabric sleeves through which dirty gas is passed, to emerge to atmosphere with very low levels of dust remaining - typically a few mg/m3. This often represents a filtration efficiency of 99.9%.

Whilst bag filters offer the best performance for filtering many of the gas streams encountered in iron and steel production, they have limitations with respect to temperature, fire resistance, and their ability to handle abrasive, moist, or sticky dust. These are attributable to the properties of the fabrics available at reasonable cost. A novel device, the KN-Filter, employing metallic mesh screens, offers the possibility of providing bag filter performance levels on some of the gas streams which presently require the use of other, less effective dust removal techniques.

The ability to filter at high temperature (up to 600°C or more) also gives the attractive possibility of heat recovery from filtered gases.

The Environmental Science Department is currently testing this technology at pilot scale.

The principle of operation is based on the belief that in conventional fabric filters the bag performs some filtration but the layer, or cake, of filtered material adhering to the fabric acts as the major filtration medium. Extending this principle, it has been demonstrated that by passing the gas stream through a relatively coarse metallic mesh (typically 60 to 300 mesh), which has gaps many times the size of the particles, a cake can be built which acts as an effective filter. The KN-Filter uses this property.

One chamber of mesh modules undergoes a cake building process whilst one or more chambers which already have an established cake perform the filtration. When the minimum necessary layer has been established in the off-line chamber, this can be brought on-line and one of the others can be isolated and pulse-cleaned, prior to re-establishing a cake.

Initial tests on the off-gas from an Electric Arc Furnace have shown that the test unit can give outlet dust loadings well within those required by the permitting authorities, and at levels very similar to those from fabric filters on similar applications.