What Dryer Do I Need for my Compressor?

How-To Compressed Air Wiki Air Treatment Drying

In previous articles we have covered the potential harmful effects of condensation within a compressed air system. Let’s quickly review why it is important to eliminate condensation out of the compressed air and what option are available to help us accomplish this task.

Why a dryer is necessary in your compressed air system

choosing a dryer for your compressed air system

Moisture creation in a compressor is unavoidable, but if properly treated, it will prevent damage to pneumatic machinery, air motors, valves and any other components, as well as avoid possible contamination of the end products. In order to avoid unnecessary maintenance repairs and potential production shutdown, it is recommended to be proactive and properly implement the necessary steps to keep the compressed air dry, clean and suitable for your operations. Read more on the importance of dryers in compressing air here.

Selecting the proper dryer to treat wet compressed air is largely dependent on the specific requirements and moisture tolerance levels of the machines that utilize compressed air. Most industrial and manufacturing facilities can achieve such requirements with a refrigerated air dryer, while spray paint operations, laboratories and certain printing and pneumatic tool users require a desiccant dryer to supply critically dry air.

Let us take a look at the different types of refrigerated dryers to gain a better understanding of which option is most suitable for your operation.

What is the difference between a non-cycling and cycling refrigerated dryer?

For applications that require dry air, but do not call for a critical dew point, a refrigerated air dryer would be a great option, as it is cost effective and comes in a non-cycling and cycling option dependent on your budget and needs.

Non-Cycling Dryers:
A refrigerated non-cycling dryer is a great start point for anyone looking to improve their compressed air quality while operating on a budget. The term “non-cycling” means that this type of a dryer operates the refrigeration compressor constantly and utilizes hot gas bypass valve to redirect the refrigerant even at less than full load condition. In a refrigerated air dryer, the temperature of compressed air is lowered to 3° Celsius (37° Fahrenheit), which allows for water to drop out from its vapor state, resulting in dry air beneficial for most applications. Non cycling dryers are very simple and reliable machines and come with minimum options in order to simplify the design and operations.

This type of a refrigerated dryer is very affordable as it comes with lowest initial cost of investment, yet provides dry and clean compressed air. The non-cycling dryers are simple to install and easy to operate, making them a market standard in performance, quality and ability to deliver desired outcomes. This type of a dryer is ideally paired with any rotary screw air compressor, while a high temperature version is preferred and recommended for use with any piston air compressors. As the name suggest, “non-cycling” means that the dryer will run constantly, regardless of the compressed air load coming into the dryer.  This means that the energy consumption at full load or no load is nearly the same, therefore making the unit not as energy efficient as other options on the market. If energy savings is not a priority and your facility requires a simple compressed air dryer that provides minimal dew point swings, the non-cycling dryer makes it an attractive option.

Cycling Dryers:
Unlike the non-cycling refrigerated, the cycling uses additional equipment such as thermal mass or frequency controllers, which would allow the dryer to turn on and off based on the compressed air demand coming into the dryer, ultimately making it much more energy efficient. The cycling dryer design comes with a totally customer oriented design, offering performance as well as reliability. The initial cost of the cycling dryer is marginally higher than that of a non-cycling option, but it does provide the lowest, long term solution and lowest life-cycle cost. Cycling dryers are very reliable and offer the convenience of easy installation, small footprint and low noise level. As previously mentioned, cycling dryers offer maximum energy savings and low pressure drops. Due to its advantages, the slightly higher cost of a cycling dryer can be very beneficial to any compressed air system, especially when considering the overall life-cycle cost of the equipment. If your application experiences fluctuating air demand a cycling dryer is most benefecial to you. 

Advantages of integrated dryers

In most facilities, available space comes at a premium, leaving many companies with limited option when it comes to optimizing their compressed air system. When space is limited, but the requirement for dry compressed air exists, some manufacturers offer an integraded refrigerated dryer option on their air compressors. An integrated dryer can effectively remove moisture from your compressed air in an effort to protect your investment. This option not only limits the need for space, but also provides savings on the initial installation costs, while offering a small, quiet and convenient solution for your compressed air needs. A compressed air sales professional should be able to go over all compressed air drying options and help you select the best possible solution for your needs.

What is the difference between a refrigerated dryer and desiccant dryer?

The biggest deciding factor when it comes to compressed air dryers is the need or desired dew point. As previously learned, refrigerated air dryers are capable of providing dew point of 3-5 °Celsius (37-41 °Fahrenheit), which is sufficient for most applications. However, if a process requires compressed air of higher quality, a desiccant dryer would need to be introduced into the system. Regenerative desiccant dryers are capable of achieving up to -70 °C (-100 °F) as standard, providing your compressed air system with clean and dry air. Unlike refrigerated air dryers, regenerative desiccant dryers utilize desiccant beads that adsorb the water vapors out of the compressed air.

During the adsorption process, water vapors adhere to the desiccant bead without changing the composition of the desiccant. Once the desiccant beads get saturated with moisture, a process of regeneration occurs via dry purge air, heat or combination of both application to dry the wet desiccant. This type of a desiccant dryer typically uses a twin tower construction design, in which one tower dries the wet air, while the other tower regenerates and purges the moisture out of the desiccant beads.

Desiccant dryer options

Regenerative desiccant dryers are designed to provide standard dew points of -20 °C (-25° F), -40° C/F or -70 °C (-100 °F), but that comes at a cost of purge air that will need to be utilized and accounted for within a compressed air system. There are various types of regeneration when it comes to desiccant dryers and it all depends on the amount of purge air used during the process. Higher purge will require a larger compressor, therefore resulting in increased power consumption and higher life cycle cost.

Heatless desiccant dryers require 16-25% of purge air and are considered to be most cost effective, but least efficient. When considering a heatless desiccant dryer, make sure to account for the extra purge air when sizing your air compressor. This calculation is required to sufficiently provide the required compressed air for the facility’s needs as well as the purge air necessary for the drying process.

Heated purge air desiccant dryers utilize either internal or external heaters to account for part of the bead drying process. This type of a desiccant dryer reduces the amount of purge air that is required for the tower regeneration process down to less than 10%. Due to its design and ability to cut down the purge air required in the process, this dryer requires a higher initial investment as compared to a heatless desiccant dryer, but offers a significant energy efficiency during its life cycle.

In externally heated desiccant dryers, the external purge air is heated to a higher temperature and introduced to the desiccant beads to aid with the drying and regenerating process. This type of a process utilizes on average 0-4% of purge air, making it one of the more efficient desiccant dryers. In order to eliminate the need for purge air in an externally heated desiccant dryer, a blower can be used, which would circulate the heated air throughout the desiccant bed. Due to its efficiency gains, the blower heat desiccant dryers tend to be most expensive option, but once again offer best return on your investment from the energy consumption standpoint over the lifecycle of the unit.

In conclusion, the need for a refrigerated or desiccant dryer will be mainly dependent on the specific air quality requirements for a given process. Dryers play a vital role in achieving clean and dry air that is less likely to compromise your operations and result in costly shut down or possible contamination of your product. Investing in a proper drying system now can result in substantial savings over the lifetime of the equipment and provide satisfactory products and results for your customers.

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