How to Remove Moisture from Compressed Air
Moisture in the air will find its way into a compressed air system, and this can cause problems because air needs to be dry for an efficient system to function properly. Finding a solution to these kinds of issues is not always easy, because compressed air has multiple application functions and compressor designs.
If we see moisture in your compressed air lines during a service visit, we will bring this to your attention so your plant can address the issue with the compressed air supplier. Having moisture present in the lines can create havoc for filter pulsing systems as it may deliver moisture into the filter cabinet. Any water or oil in the lines will be pulsed onto the filters which drastically reduces filter life, essentially ruining the filter media and efficacy.
Clean, dry, compressed air is required to ensure a dust collection system runs properly.
The device used to remove moisture in your pressurized air system may be a simple drain valve. Some systems might have far more complicated multi-stage air drying systems.
The type of air compressor that you are using will ultimately determine the best way to remove moisture. While some systems may be able to handle lower moisture content and do not require additional drying needs, many other systems are going to need air dried and moisture released in some form or another.
Drain Your Air Compressor Tank
The mixture of oil and water that collects at the bottom of your air compressor is usually released through the valve found at the bottom. You want to drain the air compressor after every use not only to keep moisture out but also to prevent rust or other damaging elements from amassing in the compressor system.
You can easily modify your drain to make it more easily accessible or automatic. Consider some basic pipe fittings and a ball valve, which can make draining your tank a simple matter of just turning the ball valve a quarter turn. Timed solenoid or automatic no-loss drains can also be valuable items put into the system (for tanks, filter housings, dryers, etc.).
To dry compressed air, the air needs enough time and surface area in the tank to cool such that the water vapor can condense into liquid water that needs to be trapped. Water traps are more common in applications requiring extremely dry air.
Water traps will work with filter regulators such that incoming cool air enters and circulates. Water will collect at the bottom of the trap and drain out while the air exits through a filter element.
Removing Moisture from Compressed Air through Dryers
Filters and separators cannot remove water vapor. They can only remove liquid moisture droplets from the compressed air system.
If you want to remove water vapor, then you will have to use a dryer. Because colder air holds less water, multiple systems are used to cool compressed air and allow water to drop out of the air to be collected and drained.
Refrigerated air dryers are one of the best ways to remove moisture from compressed air through a single unit drying system, but they can be very costly if sized incorrectly.
Your refrigerated air dryer will function much the same as an air conditioning unit. The dryer will be connected to the air compressor and cool the air to a specific temperature. Air is usually cooled to between 35˚F and 50˚F. As a result, the pressure dew point (PDP) should be 33˚F to 39˚F.
Air will be heated and sent through lines for end use after water drops out of the air and is separated. If an application requires a lower PDP, then a desiccant air dryer could be required as condensate freezes at 32˚F. A desiccant air dryer system can purify compressed air and provide air purification from -40°F PDP down to -100°F PDP.
Types of Desiccant Air Dryers
There are essentially four kinds of desiccant air dryers:
- QMOD Heatless Modular Desiccant Dryer — The QMOD is a modular heatless desiccant dryer engineered for optimum space and performance that delivers a -40˚F instrument quality or -100˚F process air for system demands. Its compact footprint saves floor space, so it fits anywhere. It can be installed in either a vertical or horizontal position, NPT connections allow for easy installation and service access, and floor mounting brackets provide stability.
- QHD Heatless Desiccant Dryer — QHD heatless desiccant dryers are designed to provide optimal performance and efficiency in a variety of applications, using a small portion of compressed air to purge and regenerate the off-line tower. The QHD series includes 13 models that deliver between 230 and 3,400 cubic feet per minute (CFM) of clean, dry air.
- QBP Blower Purge Desiccant Dryer — Quality desiccant delivers consistent performance even in harsh conditions, and stainless-steel butterfly valves with actuators ensure a long lifetime. The standard filter package comes with two pre filters and an after filter, while NPT connections allow for easy installation and service access. There are also forklift slots on the frame for easy handling, and wide vessels allow for low airspeeds and longer contact times.
- QHP Heated Purge Desiccant Dryer — An industrial duty heated purge desiccant air dryer capable of removing moisture from compressed air through the process of Heat Assisted Pressure Swing Adsorption, in which saturated compressed air is directed over a bed of desiccant. Moisture adheres to the surface of the desiccant as the saturated compressed air flows up through it and is removed through an exhaust muffler during the regenerating cycle. The dryers are more energy efficient than heatless dryers.
Air Drying Through Piping Systems
Moisture can also be removed from compressed air through the way you plumb your air lines. For example, you can cool air by using longer metal piping lengths in an up and down pattern that allows air to be cooled while the pipes absorb the heat. When this occurs, the water will drop to the bottom of the piping system, possibly into a water trap.
When the air moves through piping in an up and down pattern, the amount of moisture released decreases along the journey such that each leg will have less water than the one before it. When properly constructed, there will be no water left in the final leg. Such methods are one of the cheapest ways to dry compressed air but can be easier said than done, consult further with your local specialist.
Things to Think About When Purchasing a Compressed Air Dryer
You need to take a variety of factors into consideration when determining the best kind of air dryer for your compressed air needs. Know your dew point requirement, the utilities available to you, the type of compressor being used and your ambient air temperature.
You will also want to know your operating pressure, inlet air temperature, and airflow. Some air dryers can be eliminated based only on the water that needs to be removed for an air compressor, and the dew point will generally be the first thing you consider.
The ranges that indicate the best type of dryer for specific dew points are typically deliquescent air dryers for 0˚- 80˚ F, refrigerated air dryers for 0˚- 32˚ F, desiccant air dryers with a silica desiccant for 0˚ - 40˚ F, and desiccant air dryers with activated alumina desiccant for 0˚ - 100˚ F. It is also important to think about the capacity (or CFM rating) and pressure (PSIG) of an air compressor.
Your purchase price is only a partial cost consideration, as you must also keep in mind the cost of energy use as well as maintenance costs. Additionally, there is the cost of the pressure drop that will occur as your compressed air travels through another system. To compensate for the loss of pressure through piping, you will have to run the compressor at a slightly higher pressure with an air dryer (or a second compressor system) to achieve the same pressure for end use.
When you are struggling to drain a tank or properly install a dryer system, do not hesitate to contact Robovent. We can review your system and determine the best possible solutions to help get you functioning properly.
Robovent is ready to talk your compressed air needs with you. Call (888) 298-4214 or contact us online right now to let us help.