compressors, oil is used to cool and lubricate in the compression process, and small amounts of oil aerosols and vapours are present in the compressed air output. Although the quantity is limited – less than 3mg/m3

at 20°C, it is still significant

in terms of environmental impact. Oil, in the form of droplets, separated partly in an aftercooler and a water separator, flows through the system with the condensate. This oil/water emulsion is classed officially as waste oil, and therefore must not be drained off into any sewage system or directly into nature. The condensate, as well as its collection,

Andy Lill, business development manager - Quality Air, Atlas Copco, explains the hazards of condensate and suggests ways of managing and removing it from compressed air systems


ot all compressor users are fully aware that the production of

condensate from the air compression process can lead to excessive moisture and contaminants in the compressed air supply. These are by-products that could jeopardise operational equipment and procedures, but which are also subject to stringent environmental laws related to their safe disposal. The main constituent of condensate

released from an oil-injected compressor is water containing minute particles of oil and microscopic contaminants in suspension. The first question is: ‘Where does the water come from?’ Inlet air at atmospheric pressure

contains moisture, but the volume of water produced by an air compressor is largely dependent on the inlet condition, the temperature of the ambient air in a given environment, and the required application pressure. Pressure dew point (PDP) is the

conventional way to measure the water content in compressed air. This is the temperature at which air or gas is saturated with water and begins the process of condensation, or turning into a liquid state − the point at which air is not able to hold any more water vapour. It’s all about compressibility. A

compressor that works with 7 bar(e) overpressure compresses air to seven- eighths of its volume. This also reduces the air’s ability to hold water vapour by seven-eighths. The quantity of water/condensate that is released as a result is surprisingly large − a 100 kW compressor, drawing in ambient air at 20°C and 60% relative humidity, will


produce approximately 85 litres of water during an eight-hour shift. In comparison, hot and humid air will

have a higher moisture content than cold air, and in this type of environment the compressor will produce a correspondingly greater volume of condensate. Managing condensate water involves both removing it from the compressed air system and responsibly from the installation site. There are good reasons for removing

excessive moisture from the system, as it can damage the facility, affect machine and component performance, or introduce contamination risks. In most modern compressors, air passes

through an aftercooler to lower the temperature and reduce the water content. Then, ideally, it passes on through a water separator where about 80–90% of the water can be removed. In most installations, the remaining water flows with the compressed air as water mist into an air receiver. However, compressor condensate is not just about water. In lubricated

The condensate, as well as its collection, can be complex and expensive. A condensate management system is a cost-effective solution to this problem, and involves installing an oil/water separator to produce clean water and separate the oil off into a special receiver

can be complex and expensive. But a cost- effective solution to this problem involves installing an oil/water separator to produce clean water and separate the oil off into a special receiver. With no moving parts, oil water

separators require only minimal maintenance and can handle a range of discharge problems, even with heavily contaminated systems. There are also drain valves, which provide automatic drainage of the condensate that collects at the bottom of an air receiver. Electronically controlled, they monitor condensate build- up and evacuate it only when necessary, to avoid wasting compressed air. Anyone who runs a compressed air

system (using oil-injected technology) must be aware of how to properly dispose of the condensate in a responsible manner, in order to comply with laws governing the handling of environmentally hazardous waste. Not only is incorrect disposal detrimental to the environment, but companies could also incur fines up to £20,000 and damage their reputation. Plant managers are encouraged to make

Electronic condensate drains monitor condensate build-up and evacuate it only when necessary, to avoid wasting compressed air. It’s important to note companies must have a Permit to Discharge or an exemption from the Environment Agency before any disposal procedure takes place

a visual inventory check of their compressor system. A walk-through inspection should reveal the condensate drains at the rear of the compressors, dryers, filters and wet air receivers on the site. Look at where these are piped to – ideally, they should be going to an oil/water separator. If this is the case, the treated condensate can be drained away without damaging the environment or infringing water pollution regulations. If the condensate is going straight from

a drain onto the floor, or just into a plastic container, there is a need for action. Oil/ water separators are very easy to install and operate. But, a note of caution: when it comes to the disposal of condensate, the rules can vary from region to region, so it pays to be fully conversant with specific applications at an individual site.

Atlas Copco


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