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Keeping it clean

ems oct nov 18 20Keeping it clean

Compressed air needs to be clean in order to maintain system efficiency. The most effective way to do this is to ensure that each compressor is sited in the best available position and has adequate filtration to remove impurities, as BOGE’s General Manager, Mark Whitmore, explains.

We all prefer to inhale clean air – and the same is true of air compressors. (Read More)

In humans, particulates and other impurities in the air can lead to respiratory problems. In compressors, concentrating these impurities (including hydrocarbons and even bacteria) into a smaller volume magnifies their effect: so, what may have begun as relatively clean air can become much ‘dirtier’ when compressed.

These contaminants – as well as water vapour and aerosols – can cause internal components to wear, while also playing havoc with compressor coolant. This can lead to more frequent breakdowns – requiring costly attention from the service department – and inevitably shorten the life of the compressor. Further down the road, the contaminants could even affect the end product, especially something sensitive such as food or medicine – and nobody wants to sanction a mass product recall. Compressors working in dirty, dusty or contaminated environments are particularly susceptible to damage if they are not looked after properly.

However, these effects can be overcome with scrupulous attention to best practice, particularly regarding filtration and drying. Scrubbing the incoming air to remove as many impurities as possible is critical to the longevity – and ongoing efficient operation – of a compressor.

Air transport

The journey of atmospheric air through the compressor – turning it into clean compressed air – is one of several stages. The specific details will change depending on a multitude of factors, such as the compressor’s location (e.g. indoor or outdoor), ambient temperature, the environment in which it sits (for example, whether there is dust, dirt or noxious gases) and the industry in which it will be used: compressed air for pharmaceuticals or food, for instance, must be far cleaner than that used for metalworking or textiles. All of these factors, and more, will dictate what type of filter or dryer is chosen.

On the water front, a cyclone separator typically removes around 99% of all the water vapour from the air once it has been compressed. This air can then be fed through a dryer, which will normally be one of two main types: refrigerant dryers, which work by lowering the temperature of the air, encouraging the water vapour to condense; and adsorption dryers, where the moist air passes over a chemical desiccant, which takes up the water.

It is worth pointing out that, while many industrial operations correctly choose refrigerant drying, it is not appropriate in every single case: for instance, if pipework passes through ambient temperature zones below 3°C, a desiccant dryer should be used, as it is unaffected by lower temperatures.

Oil-free air is also becoming increasingly important, especially in industries with higher standards of cleanliness. In traditional compressors, oil is injected into the compression cavities. This improves the sealing properties of each air path, reduces pressure drop and dissipates heat during air compression.

However, even well-sealed downstream systems have some degree of leakage. Oil-free compressors do not inject oil into the air paths but still use it to lubricate other moving parts. A further option is to use a compressor such as BOGE’s LPT150, which uses ‘turbo technology’ to dispense with oil altogether.

These can be augmented – if needed – by an increasingly fine series of filters, such as those that use activated carbon to separate the last remaining impurities.

The overall aim is to produce high quality compressed air as cost effectively as possible. However, it is important to draw attention to a common misconception – that reducing system pressure saves cost because it lowers energy consumption. Doing this can actually reduce air quality because filters and dryers that are sized for higher pressures can quickly become inefficient at separating particulates or moisture when operated at below their optimum settings.

In reality, the best way to decrease system cost is to ensure peak efficiency, long lifespan and minimal maintenance, which best practice, and the use of appropriate filters and drying, will help to deliver.

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