Aftercooler, dryer, filter & Co: How to remove water, oil and dust particles from compressed air

The air becomes hot when compressed. In fact, most of the energy absorbed in a compressor is converted into heat. Only the smaller part is needed by the engine for the mechanical process of compression. This is also the reason why you should provide for heat recovery wherever possible. The compressed air has a temperature between 70 and 200 °C immediately after compression. To reduce this temperature, aftercoolers are used, which also reduce the moisture content of the air. In most cases, the aftercoolers are already installed in the compressor. If this is not the case, the aftercooler should always be installed as close as possible behind the compressor. If the hot compressed air is cooled in the aftercooler, most of the condensate is produced there. This condensate must be removed from the compressed air system as quickly as possible so that it does not enter the compressed air network. An aftercooler can be cooled with either water or air and should always be equipped with a water separator and an automatic drain.

Oil-water separators like the OSC from Atlas Copco separate the condensate separated from the compressed air (by drying) into oil and water components. The condensate then contains so little residual oil that it can be discharged without harming the environment. The oil is collected and can be disposed of. The amount of residual oil to be disposed of is thus considerably reduced. You can also find information on condensate treatment here.

Refrigeration dryers, such as Atlas Copco's FD series units ( https://www.atlascopco.com/de-de/compressors/products/air-dryers/refrigerant-air-dryers)), further cool the compressed air outside the compressor to condense and separate additional water. The units are also available as integrated versions and are already built into Atlas Copco's FF compressor models in this form ("Full Feature", for example GA 75 VSD FF). After cooling and condensing, the dryers reheat the compressed air to room temperature. Since warmer air can absorb more moisture than colder air, condensation in the piping system is prevented. Refrigeration dryers typically cool the compressed air down to a temperature of +3 °C, i.e. the pressure dew point of the subsequently warmer, drier air is then 3 °C. Dew points below 0 °C cannot be achieved with refrigerant dryers, as the condensate would otherwise freeze and the dryer would freeze. For higher demands on compressed air quality, i.e. even lower pressure dew points, adsorption dryers are suitable

With adsorption dryers, pressure dew points of up to -70 °C are achieved. They are suitable for very high demands on compressed air quality or for such construction projects where the pipeline network is partly outdoors - with the risk of moisture contained in the compressed air condensing on the pipe walls at low temperatures in winter. Adsorption dryers work with a desiccant that extracts moisture from the air. It must be regenerated regularly. Adsorption dryers are basically available in double vessel design and as rotary drum dryers for all industrial applications. Atlas Copco offers the units in the AD(+), BD(+), CD(+), MD, MDG and ND series. Adsorption dryers differ in their mode of operation (process), energy consumption and pressure dew point. The desired drying process determines to a large extent which process and which dryer must be selected. Basically, there are cold-regenerating and heat-regenerating adsorption dryers. Cold regenerating adsorption dryers use only compressed air as purge air, i.e. for regeneration. They are suitable for small volume flows and reach pressure dew points of -20 °C. For even lower dew points, larger quantities of purge air are required. 2. heat regenerating dryers regenerate the adsorption material with electrically generated heat or with compression heat and have a better efficiency than cold regenerating dryers The achievable dew points are -40 °C or lower. 3) In the case of compression heat dryers ("Heat of Compression"), the compression heat of the compressors is used for regeneration. These dryers have a drum coated with an adsorption material, which is regenerated in a sector by a hot compressed air stream. This compressed air is then cooled and fed back into the main compressed air stream. In the other, larger sector of the drum, the entire compressed air flow is dried. Due to the slow rotation of the drum, each sector is alternately regenerated and loaded with moisture. The dryer manages without any loss of compressed air. Energy is only required to drive the drum; about 200 watts are sufficient for this. In addition, these dryers do not require any pre-filters or after-filters.