Contaminants in the form of dust, rust, carbon, water & oil enter the Compressed Air / Gas System through the atmosphere, Compressor, Aftercooler, Air Receiver, piping etc. Condensate generated during cooling gets added to these contaminants and ultimately you have solid (dust, rust etc.), liquid (oil/water sludge) & vapour (oil & water) in the air. All these are harmful of the system and must be removed. Liquid sludge & solids are removed by Centrifugal Moisture Separator with Demister Pads which allow only fine oil / water liquid aerosols & vapours to escape with the air.

Removal of liquid aerosols is more complex & difficult and is achieved by the principle of coalescence i.e. forcing the aerosol to merge with each other. This is done passing the air through a glass microfibre medium where liquids are collected by the fibres, through the processes of inertial impaction, interception & diffusion. Once collected, the micro liquid particles adhere to the fibre surface and gradually build-up into bigger coalesced droplets which move along the fibres till they attain mass which makes them break away from the fibres. They are driven to the outside of the filter by the air stream, collected at the outer foam barrier and drop out from the filter element at the bottom. The outer foam also does not allow the droplets to re- entrain into the air stream. Two Filters are generally used in series - Prefilter & Microfilter, for removal of larger & smaller aerosols, respectively. Picture shows 3 Nos filter elements being assembled jn a Micro Filter.

In modem machines & equipment, presence of oil / water even at very low level is harmful, particularly where the air is in direct contact with the product e.g. airjet weaving, knitting, etc., use of air as reactant, pneumatic conveying, bag filter operation, Gas Mfg. Plants, etc.

Removal of oil/water is also very important for air used in instrumentation & controls, powder coating / spray painting, sand /grit blasting, high speed production machines, etc.

Air when compressed, collects dust & water from atmosphere, oil from the compressor & rust from the Receiver, Aftercooler, pipelines, etc. This compressed air can be used only after removing these contaminants by installing separators & filters.

The heavier solid & liquid contaminants get separated in the Aftercooler Separator and the Air Receiver. I)1e air now contains light solids and oil &. water (both liquid & solid).

The second stage of separation is done by passing the air through Filters. Earlier, porous ceramic elements were used but these get clogged fast leading to higher pressure drop and had to be cleaned frequently. SPANTECH has now developed a Filter Element fabricated from S.S. screenlwiremesh which gives lower pressure drop & requires only occasional cleaning. These Elements can replace ceramic without any changes required in the existing Filters.