Humidity and condensate in compressed air system

Atmospheric air, containing impurities and water moisture is drawn into a compressor and compressed to a higher pressure.

Compressors mostly require oil for lubrication, sealing and cooling. At the end of compression hot, compressed air flows into an aftercooler to remove the heat of compression. During cooling process compressed air looses the ability to contain large amounts of water and excessive amount of water wapour eliminates in liquid form (it condenses). The air is further cooled in the piping and air dryers, where additional condensation takes place.

Condensate draining equipment is possibly the most ignored component of a compressed air system but nevertheless, a most important part. No matter how much money you wasted on high-quality equipment for compressed air (compressors, dryers, filters), compressed air quality becomes worthless, if the condensate is not discharged from the system. 

Below are some examples of how much litres of condensate produces an 90 kW compressor when operating 24 hours per day. This data is based on an installation with a refrigeration dryer. Pressure dew point is 3°C, compressor pressure is 7,5 BAR and the air flow is 1000Nm3/h. It is listed for South East Asia, Sahara, Central Europe and some cities.

water litres
Data about relative humidity taken from: CRU 0.5 Degree Dataset (New, et al.). The quantity of condensate depends on the quantities of moisture at the inlet of the compressor (temperature, relative humidity), air flow, working pressure, minimal temperture in the system (for example: 3 in the case of refrigeration Dryer).


Condensate in compressed air system can cause large problems:
  • An inconsistent supply of dry air will cause production problems. For example, the moisture will wash away the lubrication from air tools, and cause erratic performance, downtime and maintenance.
  • The presence of water will lead to the formation of rust and scale in the air piping system. This solid contamination will foul equipment.
  • Your air dryers and inline filtration products will not perform if they become overloaded with liquid contamination. Slugs of water due to drain failure can cause major problems in a desiccant dryer.
  • Also, water can back up into the compressor and wreck the machinery.
  • When a drain fails to eject all of the condensate collected, oil and/or water will collect, affecting - filter efficiency – causing carry over into the system – allowing freeze-up in the winter.
  • Drains stuck in the open position due to condensate debris can be a major source of wasted energy in some plants.
  • The condensate transferred to the end user, can lead to irreparable consequences to the final product or process.
The amount of water in compressed air can also be expressed as dew point under pressure. We will not give you extensive information about dew point in this newletter but rather point out that the quality of air is described in ISO 8573-1. In the table below, there is the short representation of the standard.

CLASS 
0
1
2
3
4
5
6
HUMIDITY AND LIQUID WATERPressure dew point°C 
≤ − 70
≤ − 40
≤ − 20
≤ 3
≤ 7
≤ 10
°F 
− 94
− 40
− 4
38
45
50

Knowing the amount of condensate in the system and the final requirements for quality of compressed air makes it easy to choose the correct equipment for your line. The products thus contributing to removing of condensate are refregirant dryers, adsorption dryers, aftercoolers, condensate separators, drains and water oil separators.

  

Drain valves are installed on condensate separators, coalescing filters, air receivers, air dryers and drip legs to remove this condensate from the compressed air system. Take care for timely discharging condensate from the system to prevent damage, rust, wasting energy and ultimately to save final product. Here are some solutions: