Compressed air is air kept under a pressure that is greater than atmospheric pressure. It serves many domestic and industrial purposes. In industry, compressed air is so widely used that it is often regarded as the fourth utility, after electricity, natural gas and water. However, compressed air is more expensive than the other three utilities when evaluated on a per unit energy delivered basis.
A compressed air system consists of an air compressor, to raise the pressure of the air, an air receiver, to store the compressed air, a moisture removal system, to remove accumulated moisture and reduce the pressure dew point, and air distibution piping. It may also contain different types of filtration, automatic condensate drains, oil-water separators, pressure regulators, and other devices.
A Dryer can remove moisture from compressed air to a certain degree of dryness and this is referred to as pressure dew point. Different types of dryers can achieve different dew points and, for the most part, the drier air needs to be, the more expensive it is to dry. (The obvious exception to this is the Atlas Copco MD Series heat of compression dryer that uses the energy of a 100 watt light bulb, yet achieves incredibly low pressure dew points.)
And the list goes on. The selection is made on personal preference, the dryness required, and cost, which should include operating and electrical or utility costs.
Compressed air filters, often referred to as line filters, are used to remove contaminates from compressed air after compression has taken place. Air leaving a standard screw or piston compressor will generally have a high water content, as well as a high concentration of oil and other contaminants. There are many different types of filters, suitable for different pneumatics applications.
Unfiltered compressed air frequently contains dust, oil, rust, moisture and other harmful substances, and therefore requires filtration. In the first stage of filtration, the compressed air passes through a tube-shaped mesh filter, which creates a coalescence effect. Here bigger particles are adsorbed on the filter and the water will condense into larger droplets, which can then pass into the separation chamber. The compressed air is slowed down, which makes the particles condense on a honeycomb-like pad, allowing the water droplets to travel to the bottom of the drainage system and through an automatic or electric drain valve to the discharge. In the first filtration stage more than 95% of the water droplets, oil and large particles are removed.
Types of filters
A particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. Particulate compressed air filters are used to remove dust and particles from the air.
Activated carbon filters
Activated carbon filters utilize a composite carbon material to remove gases and odors from the air. They are used in factories where food is produced or for breathing gas.
High oil compressed air coalescing filters remove water and oil aerosols by coalescing the aerosols into droplets. This happens partially because of torturous path and pressure drop. Coalescers remove both water and oil aerosols from the air stream, and are rated at particulate contamination through direct interception. Filtration of oil, water aerosols, dust and dirt particles to 0.01 µm the best achievable in industry.
Cold coalescing filters
Cold coalescing filters are coalescing filters operated at around 35° F (2° C), allowing them to be more effective at removing moisture.
Compressed intake filters
Intake filters are the first line of defense in filtering. These filters can remove contaminates down to 0.3 µm and can remove chemical contaminants.