Problems with compressed air condensation

Water condensation is a natural occurrence and byproduct of compressing air. The amount of water produced by an air compressor is largely dependent on the inlet condition, ambient air quality, and pressure.

In simpler terms, air temperature, humidity, compressor size, and required pressure determine the amount of water coming from a unit. This moisture affects the whole system, including piping. Since hot, humid air has a higher moisture content than cold air, water vapor is created within the compressor.

Consider a 55kW (75HP) rotary screw air compressor operating in a room with a 24 °C (75 °F) ambient temperature and 75% relative humidity. These conditions will produce 280 liters (75 gallons) of water per day. To counteract this, the process of moisture removal within a compressed air system is illustrated below. 

This water can be separated using accessories, including aftercoolers, condensation separators, refrigerant dryers and adsorption dryers. 

A compressor working with 7 bar(e) overpressure compresses air to 7/8 of its volume. This also reduces the air's ability to hold water vapor by 7/8.

The quantity of water released is considerable. The following example further illustrates this point. A 100kW compressor drawing in air at 20 °C and 60% relative humidity gives off around 85 liters of water over 8 hours. Consequently, the amount of water that will be separated depends on the application area of the compressed air. These factors determine which combination of coolers and dryers are suitable.

To further explain compressed air moisture, let's evaluate ambient temperature, flow rate (size of compressor), inlet pressure, inlet temperature, and pressure dew point (PDP).

Flow Rate or Compressor Size. For applications that require higher flow rates (CFM or l/s) will result in greater water content in the system.
Ambient Temperature / Humidity Content. Compressors that operate in higher ambient temperature and humid environment will end up producing larger amounts of water within the compressed air system.
Inlet Temperature. If the inlet temperature going into a dryer is higher, more water content will be present in the compressed air, therefore needing a bigger dryer to treat the air and condense the water out.
Pressure. Unlike flow, temperature or humidity, the pressure works opposite, as higher the pressure, the less water the compressed air contains and easier it is to dry. If you take a sponge filled with water into consideration, the harder you squeeze the sponge, the less water it will contain.
Pressure Dew Point (PDP). Pressure dew point is a common way to measure the water content in compressed air. PDP refers to the temperature point where air or gas is saturated with water and begins the process of condensation or turning into a liquid state. This can also be explained as the point at which air is not able to hold any more water vapor. In order to minimize water content in our compressed air, a lower PDP level is required, while higher PDP values refer to greater amounts of water vapor in the system. The size of the dryer will determine PDP and levels of condensation in compressed air.

Untreated compressed air condensation can damage and cause problems to pneumatic systems, air motors, and valves. In addition, any components or machines connected to the system can be impacted, resulting in potential contamination of the end product.

Here is a list that further explains the adverse effects of moisture:

●     Corrosion of piping system and equipment (i.e. CNC and other manufacturing machines)

●     Damaging of pneumatic controls which can result in expensive shutdowns

●     Rusting and increased wear for production equipment due to washing away of lubricant

●     Quality issues due to risk of discoloration, lowered quality and adherence of paint

●     In cold weather operations, freezing can occur, causing damage to control lines

●     Excessive maintenance to the air compressor and shorter life of equipment

Furthermore, compressed air moisture can have many damaging effects on plant air, instrument air, valves and cylinders, as well as air powered tools. To avoid unnecessary, excessive maintenance costs and potential downtime, it is recommended to be proactive. Properly implementing the necessary steps to keep compressed air dry, clean, and suitable for your application is highly recommended.

Selecting the proper drying method for compressed air largely depends on the specific requirements needed to meet quality control standards for your application.

One of the first steps to remove compressed air moisture inside the compressor. This is important as a moisture separator or aftercooler is capable of removing 40-60% of vaporized water.

After the compressed air leaves the aftercooler it remains saturated with water and can have damaging effects on the overall system if left untreated.

Since an air compressor's tank is much cooler than incoming hot compressed air, utilizing an air receiver can aid in reducing water content. It is important to keep in mind that a wet tank collects excess moisture, and needs to be drained daily. This is important to avoid corrosion and wear.

If your application calls for further moisture removal, it's necessary to introduce an external or internal (integrated) dryer. Depending on the desired dew point, the two dryer options are refrigerated and desiccant air dryers. 

With a refrigerated air dryer, the air temperature is lowered to three degrees Celsius (37 degrees Fahrenheit). This process causes water vapor to condensate out of compressed air. If a refrigerated dryer's dew point is not sufficient, a desiccant air dryer should be used.

A desiccant dryer reduces the dew point to at least -40 degrees Celsuis, resulting in bone dry air. Such levels are essential for spray-painting operations, printing, and other pneumatic tool applications.