Condensate is an unavoidable by-product of compressed air production. If you take the example of a 30 kW compressor with a free air delivery of 5 m3/min, this would produce around 20 litres of condensate per shift! It is essential that this liquid is removed from the air system via reliable condensate drainage in order to prevent system failures, costly production downtime and corrosion.
Condensate collection & drainage points
Condensate collects at a number of points within every compressed air system. Initially, mechanical elements of the air system serve to collect and drain condensate. 70 to 80% of all the condensate is collected at these points - provided the compressors are fitted with effective after-cooling;
- Centrifugal separator: This is a mechanical separator that separates the condensate from the air by means of centrifugal force. In order to ensure optimum performance, each compressor should be equipped with its own dedicated centrifugal separator.
- Air receivers: As well as its main function as a storage tank, the air receiver separates condensate from the air by gravity. Due to its large heat dissipation surface area, the air receiver additionally cools the air thereby enhancing condensate separation yet further.
- Water-traps in the air line: Defined condensate outlets leading downwards - or 'water traps' - allow condensate to be removed from the main air line. With correct design and an airflow of 2 to 3 m/s a water trap in the wet area of the air system separates condensate just as effectively as an air receiver.
There are additional collecting and drainage points to be found within the compressed air drying process. As an example, when a refrigeration dryer is being used, further condensate is separated in the refrigeration dryers due to the drying effect of cooling the compressed air.
If no central drying system exists, large quantities of condensate will collect at the local separators fitted just upstream from air-consuming equipment. However, these systems are exceptionally maintenance-intensive.
At present, there are three drainage systems which are mainly used;
- Float Drains; one of the oldest drainage systems, the float drain replaced manual drainage, which was both inefficient and highly unreliable. However, even condensate drainage using the float principle has proven to be extremely susceptible to malfunction due to dirt and contaminants in the compressed air.
- Solenoid Valves; time-controlled solenoid valves are more reliable than float drains, but they have to be checked regularly for clogging and contamination. Incorrectly adjusted valve opening periods can cause air losses and increased energy consumption.
- Condensate Drains with level-sensing control; drains equipped with intelligent level-sensing control are predominantly used today. They have the advantage that the float, which is highly susceptible to faults, is replaced by an electronic sensor. This eliminates the faults caused by dirt, or mechanical wear associated with float drains. Furthermore, air losses (which also occur with float valves) are prevented by the automatically controlled valve opening periods. Additional benefits include automatic self-monitoring and the ability to send signals to a central control system.
When it comes to correct installation, a short length of pipe containing a shut-off valve should be fitted between the condensate separating system and the condensate drain. This allows the drain to be isolated during maintenance allowing the compressed air system to remain in operation.