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Problem:
Do you find liquid water downstream of your refrigerated or desiccant air dryer, even downstream of the general-purpose filters you have installed to remove liquid water? Do you want to protect your instrument when the utility room air dryer fails? Do you need a lower dew point than the utility system provides? (back to top)
Solution:
A solution to the age-old problem of water in compressed air lines! CACTUS® membrane air dryers are designed to lower the dew point of the compressed air, so liquid water won't condense even as the compressed air cools. The CACTUS air dryer is an ideal product for OEMs who want to add value to their equipment and offer their customers the benefit of dry air as part of the equipment package. Based on the application, Air Products can customize CACTUS dryers to suit your flow rates and water vapor removal requirements. (back to top)
Benefits:
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Simple. No valves or complex moving parts, no desiccant to replace.
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No liquid water to dispose. No plugging of condensate drains.
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Reliable. Many dryers have been operating in the field for over ten years.
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No dust from desiccant.
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Small, compact units that are easy to install.
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Low maintenance. No periodic cleaning or maintenance required.
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Suitable for hazardous areas.
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Robust. The CACTUS dryer has the highest temperature and pressure ratings in the industry. (back to top)
Example:
Steve Titus, President of the Titus Company, describes his experience with CACTUS membrane dryers.
"The Titus Company has used the CACTUS Membrane for point of use and drying systems since they were introduced in 1987. Air Products led the way in developing membranes for air dehydration and is still advancing the technology today. Membrane technology is the only significant change in air dehydration in the last 50 years and we here at the Titus Company are excited and proud to partner with Air Products to provide this technology to our customers. From our most complicated military systems to the simplest point of use application, the CACTUS membrane is the most advanced and reliable air dehydrator that can be purchased." (back to top)
Performance:
Cactus® Air Dryer Performance at 100 psig (back to top)
Drawings:
(back to top)
Installation Guide:
Membrane Installation Guide (PDF, 222 K) (back to top)
Related Publications:
Murphy, Milton K., Arthur W. Rice, and John J Freeman, US Patent 4,793,830, "Process for Producing High Quality Gas for Instrumentation Applications Using Gas Separation Membranes," Dec. 27, 1988.
Stookey, Donald J., US Patent 4,687,578, "Fluid Separation Membranes," Aug.18, 1987.
Beaver, E.R. and T.E. Graham, "Inert Gas Generation Systems for Offshore Platforms," Energy Progress, Sept. 1986, p.149-154.
Rice, Arthur W., and Milton K. Murphy, US Patent 4,783,201, "Gas Dehydration Membrane Apparatus," Nov. 1988.
Morgan, William H., Lawrence K. Bleikamp, and Dilip G. Kalthod, US Patent 5,525,143, "Hollow Fiber Membrane Dryer with Internal Sweep," June 1996. (back to top)
Frequently Asked Questions:
Is there any liquid to drain from the membrane?
Do the performance tables show atmospheric dew points or pressure dew points?
How does a membrane dryer compare to a refrigerated dryer?
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A refrigerated dryer dehydrates air by cooling it down to condense the water. A refrigerated dryer typically dries your compressed air to a 35°F pressure dew point. The membrane dryer operates on a principle of dew point depression, so the outlet dew point is not limited to 35°F. The refrigerated air dryer also consumes electricity.
Can I replace the fibers in the CACTUS membrane air dryer?
What happens if liquid water gets into the CACTUS membrane air dryer?
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If liquid water enters the membrane dryer, the membrane's drying capability will be reduced; however, the membrane is not damaged by liquid water. Drying out the device by flowing liquid-free compressed air will restore the dryer's performance.
If liquid oil enters the membrane, can I use the same remedy described above?
What are the differences between desiccant dryers and membrane dryers?
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Membrane dryers have a wide range of drying capability, while desiccant dryers dehydrate air by adsorbing water on a solid granular desiccant. Because the desiccant must be regenerated, two desiccant towers are used, and the air to be dried is periodically switched between the two towers. Maintenance is required on the switching valves, and there is the issue of desiccant carryover into the dried air as well as desiccant life.
Are the membrane fibers contained in an ASME shell?
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The shell that encases the membrane fibers is not considered a pressure vessel, since the permeate or sweep gas is vented to atmosphere. The pressure-containing part of the device is the space contained within each endcap. Although designed within ASME guidelines, the volume within each endcap is too small to qualify for ASME certification.
What about purge or sweep gas rates? I have seen membranes advertised with sweep gas rates as low as 8%.
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Look carefully at the reference points for those sweep rates. CAGI standards for inlet conditions are 100 psig and 100°F (saturated) inlet air. Many times, references as low as 60°F inlet dew points will be used instead of 100°F. Also, be aware of references to outlet dew points, and verify they are pressure dew points and not atmospheric dew points.
In what kind of applications have CACTUS membrane air dryers been used?
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A wide variety of applications, including instrument air, spray painting, dental compressors, coordinate measuring machines, process controls, HVAC systems, pneumatic controls, electronics, and many others. Any application which needs dry air at the point of use can benefit from membrane air dryers. (back to top) |
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