COMPRESSED AIR
DISPOSING OF COMPRESSED AIR CONDENSATE
N
ot all factories are aware that condensate system – and removing it responsibly from the site. water separator. With no moving parts, oil/water from the air compression process can lead to excessive moisture and contaminants
in a compressed air supply, which can jeopardise equipment and procedures. Condensate is also subject to stringent environmental laws related to safe disposal.
WATER IN THE AIR
The main constituent of condensate from an oil- injected compressor is water, containing particles of oil and microscopic contaminants in suspension. Inlet air at atmospheric pressure contains
moisture, but the volume of water produced by an air compressor depends on the inlet condition, the temperature of the ambient air 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 − the point at which air is not able to hold any more water vapour.
A compressor that works with 7 bar(e)
of water/condensate released is surprising − a 100 SEPERATING OIL & WATER kW compressor, drawing in air at 20°C and 60 per cent 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, and the compressor will produce a greater volume of condensate. For example, a 55 kW rotary screw air compressor, operating in air at 24°C with 75 per cent humidity, will produce 280 litres of water per day. Managing this volume of water involves removing it from the
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
10 O TOBERC 2019 | FA FACTORY&HANDL NGSOLUT ONS ORY&HANDLINGSOLI UTIONSI
PROBLEMS OF EXCESSIVE MOISTURE
Water in compressed air can damage the facility and the effectiveness of operations. Untreated condensation in compressed air can also affect the performance of pneumatic systems, air motors and valves, as well as any components or machines connected to the system. There is also the risk of contaminating the end product of the manufacturing process.
One of the first steps in removing moisture occurs inside most modern compressors where the hot compressed air, at 70–200°C, passes through an aftercooler to lower the temperature and reduce the water content. Then it passes through a water separator, where about 80–90 per cent of the water can be removed.
The remaining water then flows with the
compressed air as mist into an air receiver. This can also reduce water content in compressed air, as the vessel is cooled by the tank’s ambient temperature. However, the wet tank must be drained frequently to avoid corrosion and excessive wear.
In lubricated compressors, oil is used to cool and lubricate, and small amounts of oil aerosols and vapours are present in the air output. Although this is less than 3 mg/m3 at 20°C, it has a significant environmental impact. Oil droplets flow through the system with the condensate. This oil/water emulsion is classed as waste oil, and must not be drained into any sewage system or directly into nature.
A cost-effective solution involves installing an oil/
separators require minimal maintenance and can handle a wide range of discharge problems. There are also drain valves, which provide completely automatic drainage of the condensate that collects at the bottom of an air receiver. They evacuate the condensate only when necessary, to avoid wasting compressed air.
STAYING WITHIN THE LAW Anyone who runs an oil-injected compressed air system must be aware of how to dispose of the condensate to comply with laws. Not only is incorrect disposal detrimental to the environment, but companies could be fined up to £20,000, and damage their reputation.
Plant managers are encouraged to inspect the condensate drains at the rear of the compressors, dryers, filters and wet air receivers. Look at where these are piped to – ideally, to an oil/water separator. If so, the treated condensate can be drained without damaging the environment or infringing water pollution regulations. The treated condensate can be piped into the foul water drain. If the condensate is going straight from a drain onto the floor, or just into a standard plastic container, there is a need for action. Oil/water separators are easy to install and operate. But, a note of caution: when it comes to the disposal of condensate, the rules can vary by region. Companies must have a Permit to Discharge or an exemption from the Environment Agency before any disposal procedure takes place.
For further advice and guidance on condensate management, contact your compressed air system supplier.
Atlas Copco
www.atlascopco.com
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