In order to understand why there is water in your compressor, first we need to know how air compressors work. The most popular type of air compressor in the manufacturing industry is the rotary screw type air compressor. Any factory, plant or mill involved in manufacturing will likely be driven with a screw type compressor.
Screw type compressors have two interlocking helical rotors within its housing. Air from the surroundings is introduced into the compressor through the inlet valve (blue), and is trapped between the two rotors. The screws turn and “compress” the air, reducing the volume while increasing the pressure of the air (red). As the pressure of the compressed air increases, water condensation occurs naturally as the water vapour cannot be compressed.
Screw type air compressor
Several factors affect the rate of water condensation such as the air temperature, humidity, compressor size and required pressure. A compressor that works with 7 bar overpressure will compress air to 7/8 of its volume, reducing the amount ability of air to hold water vapour by 7/8. In Ho Chi Minh’s tropical weather, humidity is generally high with more moisture in the air. This results in more water coming out of compressors located in this region. For example, a 110kW (150HP) rotary screw air compressor which operates in 27 °C temperature with 75% relative humidity (Ho Chi Minh average temperature) will produce 120 liters of water per day. For factories that are located near the ocean, the amount of water produced might be even higher.
Effects of Water in the Compressed Air System
As discussed above, the compressor takes in air from the surroundings and compresses it, increasing its pressure for end-use application. This means that anything else present in the air like water vapour, dirt, or oil is also introduced into the system. As condensation forms, this concentrated mix of “dirty” water, also known as condensate, can cause serious damage to the system, its components and any other equipment connected to the system, and contaminate the end product. Some of the negative effects of condensate such as:
Corrosion of piping system and connected equipment (i.e. CNC lathes, milling machines, and other manufacturing machines)
Damage to compressed air system controls which can result in costly shutdowns
Rusting and increased wear for production equipment due to washing away of lubricant
Quality issues of product due to discolouration, reduced quality and adherence of paint
Excessive maintenance required by the air compressor, shortening lifespan
Removal of Condensate from the System
Now that we know how condensate is formed and what it does to our system, our focus is now on removing condensate. A simple compressed air systems come with the following setup:
Inlet Valve
Compressor
Aftercooler
Water Separator
Condensate Drain
Air Receiver
Dryer
Compressed Air System Schematic
Different compressor manufacturers have different methods of installing their system. Some may have each piece of equipment all connected within one housing, or may have other equipment such as the oil/water separator in the picture above. However, the basic principle is the same.
As the air is compressed, it increases in temperature and needs to be cooled. An aftercooler is a heat exchanger that cools the hot compressed air to precipitate the water that otherwise would condense in the pipe system. The aftercooler can be air-cooled or water-cooled and is usually paired with a water separator where 80-90% of the condensate is formed. Most modern compressors have this built in together by the manufacturer and is one of the biggest issues affecting the dryness of the compressed air.
Keeping the aftercooler well-maintained has a big impact on condensate removal. The cooled air that exits the aftercooler is commonly maintained approximately 10 degrees Celsius above the cooler temperature. A poorly-maintained cooler can see higher temperatures of 15-20 degrees Celsius, which can result in up to 150% more moisture being passed on. An ineffective water separator will also pass on more condensate, by failing to filter out condensate particles above a certain size.
The compressed air along with all this condensate generated is then stored in the air receiver. An inefficient system will result in more condensate being stored in the receiver, reducing its overall capacity to store air. This can limit the air supply during periods of high demand, which in turn leads to compressor overwork. Using the above 120 litres of water generated in one day of operations in HCM, a 1000 litre air receiver would see a 12% reduction in supply! After one day of use!
In order to remove condensate from our system, we turn to the smallest equipment of the entire system, the condensate drain. There are several types of drains that can be used, each with their own advantages and disadvantages. Our recommendation is to go with an automatic drain such as the BEKOMAT.
BEKOMAT automatic drains
The BEKOMAT monitors the condensate produced electronically via a capacitive sensor and purges it automatically once a preset level is reached. They can cater to any compressor size and can be installed at many points along the system (aftercooler, receiver, filter and dryer). By installing BEKOMAT, it removes any worry that comes with condensate build up, or the issues that come with a float or timer drain. A good drain also helps to reduce the load on the dryer, allowing it to work more effectively to ensure your product is of the highest quality.
Conclusion
Water condensation is a natural process that occurs during air compression and there are many factors affecting the amount of water formation. The water formed is usually mixed with contaminants from the environment and has many negative effects on the compressed air system and end product. Here are some tips to reduce the amount of condensate in the system:
Use the cleanest and driest air possible. Try using air that comes from an air-conditioned room. This can help to reduce the relative humidity and hence water in the air.
Clean your aftercooler regularly to ensure optimal performance and check that the temperature of the cooled air. If it is consistently higher than 10 degrees Celsius, maintenance should be performed or a second aftercooler can be installed.
Install effective drains in your system to ensure constant condensate removal. This is often the easiest way for optimizing your system significantly.