The earlier parts of this work deals with the individual components of compressed air supply and treatment, dealing with the subject as a whole and focusing on the crucial points.
However, an efficiently functioning compressed air installation is created only by combining all components to form a complete system. A simple compressed air installation consists of a compressor and air consuming equipment connected downstream by interconnecting piping. This simple combination of compressor and air using equipment, cannot be considered suitable as far as compressed air quality is concerned. A ‘compressed air installation’ of this type may be adequate for the simplest works operations but, cannot satisfy the quality requirements of suitable compressed air. If compressed air is dried by cooling only and not by adsorption, a further cooling of the air can occur in long and non-insulated pipes. The formation of condensate will then be the consequence. At temperatures below 0°C, this will lead to freezing of the compressed air lines. If the pipe cross-section is large, layers of ice will, in the first instance, form on the inner pipe walls. These will become progressively thicker and constrict the pipe cross-section. Smaller diameter tubing will freeze completely. As soon as thaw sets in, the layers of ice will become detached and may cause blockages, interrupting the compressed air supply. In contrast to winter, hot summer days may lead to the compressed air being warmed in the piping. Rust particles, previously formed through the condensate, dry out and are conveyed to the air using equipment as fine dust, leading to potential malfunction of equipment. In order to prevent the flooding of the distribution piping by condensate, condensate separators must be installed in the system at suitable points. In winter, additional trace heating of the separators is necessary. The piping must always be installed at a downward gradient towards the drainage points.
Because of high levels of rust and dirt, the separators should not be fitted with automatic draining devices and must be capable of manual operation. Unsuitable drains can cause leakage losses amounting to 5 - 10% of the total compressed air. In addition, this formation of condensate causes air lines to be corroded from the inside. Such problems will not occur, if the compressed air is appropriately dried at the source. The economic advantages of effective compressed air drying are clear. The largest benefit is derived from the elimination of the need for drainage, both in the main and the operational network. Maintenance and servicing costs of the numerous drainage points in the compressed air system are drastically reduced. As a compressed air dewpoint of -25°C can be maintained throughout all seasons, small drying devices for instrument and control air become superfluous. Energy costs for heating the condensate separators during the winter period are also saved. Corrosion within the pipelines, icing up of working machinery and distribution network and malfunctions of the compressed air using equipment are eliminated. If compressed air is used for conveying powder, fine materials or hygroscopic substances, a dryer is essential.
Adsorption dryer installations need little maintenance and have a lower energy consumption compared with other methods of drying air. It is also expedient to subdivide the types of contamination in the compressed air, using separators and dryers installed in accordance with the quality requirements. Purification should therefore be carried out in steps, from coarse to fine. Solids, water and oil in the droplet state, are taken out of the compressed air by means of filters\separators. Oil and water vapour are removed from the compressed air by means of absorbers and dryers respectively. The question of which filters and dryers should be used, can be answered by “as much as necessary and as little as possible”. This generally valid answer is true, as each particular application must be assessed from other specific points of view. However, the ultimate decision as to what quality of compressed air must, be achieved, is that of the operator, who will judge this in relation to the application.
