Coalescence Filters

The mists are liquids and, compared to the separation of the dusts, they have the advantage of not requiring mechanical actions to regenerate the filtering medium, they coalesce and leave the filter automatically, provided that the absence of dusts is guaranteed.

The entrainment of liquids in gases is a recurring phenomenon and can be analyzed considering the size of the drops which, especially in some processes (as in any heat treatment) can reach dimensions well below μm. Such small dimensions are precisely classified as mists, which require a different treatment compared to the classic inertial separators (scrubbers and jet-venturies are the most common). All gaseous flows that have particles smaller than 10 μm are considered mists.

The separation of the mists by filtration is normally carried out using beds of fibers (felts), which differ according to the size of the fibers. The capture mechanism is inertial or diffusive.

The filter fibers used by FIDIA Engineering are cylindrical elements with radial flow, composed of two cylindrical support elements in metallic material (AISI 304), between which the packaging of glass fibers of suitable thickness is arranged.

The candles are hermetically fixed to the top of the container and are equipped with a closure on the bottom which acts as a drain for the liquid held by the fibers, which percolate downwards by gravity.

These separators are successfully used in the separation of oil mists, organic and inorganic impurities from gaseous hydrochloric acid, sulfuric mists, etc.

Mist separators are not suitable for the treatment of dust, as they clog the glass fiber and do not allow the discharge of the liquid from the spark plug. For this reason, only in the case of low dust content, pre-filters are provided upstream of the spark plugs to protect them. It is understood that if sub-chronic dust particles are present, these will in any case go through the pre-filtering stage, clogging the spark plugs which will have to be replaced according to the fouling index.

The air coming from the collector will be introduced into the abatement group by means of the pre-chamber, where a first settling of the particles of higher consistency will take place. The pre-chamber will also have the important function of homogeneously distributing the flow of polluted air inside the filtering section.

For flows containing fats, oils or viscous substances which solidify at room temperature, laboratory tests can be carried out and subsequently tests with a pilot plant, to verify the use of the technology with insulated and heated plants.