Oil/Water Separators

Oil/Water Separators with integrated activated charcoal filters continuously separate oil containing condensates into oil and water from compressor installations. The residual oil content of the treated water only maintains its level below the limiting value of 20 mg/L over a long period of operation, if the condensate feed is a true mixture of oil and water. Oil/Water Separators are not suitable for the treatment of stable emulsions.

The condensate should be piped to the Oil/Water Separator from the compressed air system via level controlled condensate drains. Automatic drains such as those based on floats or timed solenoid drain valves as sources for feeding the Oil/Water Separator can be used to a limited extent provided that large bores prevent highly turbulent flow and that the oil droplets are not fragmented and dispersed by shearing and impingement.

Oil/Water Separators are most successful with oil/water mixtures which can be separated by gravity only. The polluting ingredients drawn in via the air compression process (e.g. dusts, solvent vapours, pollen, etc.) can exert an unfavourable influence on the separation characteristics between the oil and water phase so that condensate separating systems are capable of separating the oil and water of such condensates to an unsatisfactory degree only.

The feeding of condensate to the oil/water separator takes place under pressure. Pressure release takes place in an expansion and separating chamber (item 1). This causes the surface of the main settlement tank to remain calm.

The condensate passes into a primary settlement chamber 2. Solid particles are trapped by the dirt trap forming the primary settlement chamber. The condensate then passes into the secondary settlement chamber.

The cleaned water from the base of the secondary settlement chamber is fed into the activated charcoal filters, which are configured to flow either singularly or in parallel.

In this way, even the finest oil droplets are retained. Very long dwell times guarantee the particularly high efficiency and the striking effectiveness of oil/water separators. The service life of the activated charcoal depends on the degree of emulsification of the oil in the water.

The oil content of the clean water at the outlet of the Oil/Water Separator should be checked periodically.

As the density of the oil is lower than water, the oil floats on the surface. The oil outlet funnel (item ?), the height of which can be adjusted, is situated 0.5 - 1 cm above the water level. As soon as sufficient oil has settled on the water surface, (approximately 5-10 cm) the oil flows automatically from the Oil/Water Separator into a waste oil container.

Via the water outlet (item 9), the purified water can be channelled directly into the foul drain. The residual oil content of the drained water is less than 10mg/L. The maximum condensate throughput, the residual oil content and the service life of the activated charcoal filters are largely determined by the type of compressor and the lubricating oil used.

As can be seen from below Diagram , condensates from piston compressors are more problematic, because of the higher temperature of compression, than those from rotary or screw compressors. Compressor oils, resulting in the formation of emulsions, only then yield acceptable results if the condensate throughput is considerably reduced.

For Oil/Water Separators operating according to the principle of gravity, the vessel volume and the dwell time resulting from this, form a significant process technological parameter. Equally decisive for the effectiveness of separation is the number of directional diversions within the systems. Both features set a limit to the design size of the oil/water separator. Activated charcoal as a material for oil/water separation, is justified solely for oil/water mixtures which could be separated by the force of gravity only and are capable of removing only the final traces of oil.

When using Oil/Water Separators for emulsions, the oil separation must, be accomplished by activated charcoal filters. Transferring this function from gravity separation to activated charcoal adsorption calls for more frequent changes of activated charcoal filter and consequently additional costs of equipment maintenance, apart from the extremely high costs of responsible disposal.

Figures based on experience confirm that the disposal of 1 tonne of used activated charcoal costs about £690 with, in addition, the issue of the accompanying certificate, the declared analysis and the drawing up of the proof of responsible disposal. The changeover of the principle of oil/water separators to adsorption by activated charcoal for critical condensates cannot be regarded as a solution to these problems.