Contamination of products, disrupted manufacturing processes… physical erosion of your compressed air system. Any of these can reduce the profitability of your plant. A steady supply of ‘commercially dry’ compressed air is vital to keeping quality of products high, maintenance costs as low as possible and preventing lost productivity through downtime.
Within the dryer market there are four categories – Chemical, Refrigerated, Membrane and Regenerative Desiccant.
Regenerative desiccant dryers use adsorbents to take moisture out of the compressed air when at pressure, then once they are full the adsorbent is regenerated at low pressure. Once regenerated the adsorbent media is ready for its next use in the dryer.
This article looks at the four different types of Regenerative Desiccant Dryers, one of the more common types of dryer on the market.
Pressure Swing Regenerative Dryers.
The simplest type of dryer. Pressure swing dryers have multiple vessels where the pressure swings between the different vessels so that while one vessel is being used to dry the air the remaining vessels are regenerating their adsorbent.
No attempt is made to retain the heat of adsorption within the desiccant bed. The dryers work on short cycles of between 5 to 10 minutes before the vessels are switched. The heat adsorbed is used to desorb the moisture in the regeneration phase.
High Pressure Swing Dryers.
At higher pressures air density allows these dryers to dissipate the heat of adsorption before the end of the drying process. In High Pressure Swing Dryers, no attempt is made to retain the heat so it can be used in the regeneration process. These dryers typically operate on a 30 to 60 minute cycle time.
Unheated purge air provides the energy to regenerate the desiccant bed and we see exhaust temperatures as much as 100°F lower than the inlet temperature.
Internally Heated Regenerative Dryers.
Heaters are either clamped to the shells of the desiccant vessels or heating elements are run through the desiccant beds in this class of dryer. These dryers typically operate on four hour cycles. The only problem with internally heated regenerative dryers is desiccant must be changed-out frequently because of the hydro-thermal destruction of the adsorbent at elevated temperatures in moist environments.
Externally Heated Regenerative Dryers.
Externally heated dryers rely on the indirect heating of the wet adsorbent. In this design regeneration can be achieved at either line or atmospheric pressure. Obviously atmospheric pressure is more efficient.
Regenerative desiccant air dryers can be designed and manufactured to almost any service conditions. Before ordering make sure you review the performance of your dryer against your original design spec in partnership with your provider of choice. Nobody wants wet air!
If you need to upgrade your dryer or install a new compressed air system call the team at Pye-Barker on 404-363-6000 or drop us a line email@example.com
I don’t know why this is, but we see a lot of customers underestimate their requirements when they are purchasing an air compressor. They often neglect the volume of air needed and neglect the quality – how dry the air needs to be or how good a filter is required so that rust, debris, slag and water don’t end up in your tools and ruin them.
All of these are opportunities for our competitors to cut the price of their proposal for a new compressor and leave the client with higher ongoing costs…
Sure it looks really cheap on paper… But for the sake of a decent quality filtration system maybe you have to do an extra repair on each of your air tools every 12 months, maybe you knock 25% off of their potential life.
When a client tells us they are looking to replace their air compressor we always like to conduct a thorough needs analysis
Often we try to do an air audit and when we get the chance to do a need analysis or air audit for these clients we find their current air compressor is performing fine and if they would just patch a few leaks in their delivery system they wouldn’t have a problem… but you know, many other vendors out there wouldn’t have told them that.
In the cases where a new compressor is necessary I will say that it is worth spending a little bit more up front to get the system right for your specifications and then reap the rewards of lower maintenance costs, improved up time, and realizing the savings or additional revenues you were looking for.
In your business – you just expect your air compressor to work. And there is nothing more frustrating for your team than endless hours waiting around for the service guy to show up so that your team can start a day’s work, four hours late.
Talk to your team on the floor, trust me it drives them up the wall.
Looking to upgrade or replace your air compressor or just need a second opinion on which air compressor is best suited to your purposes? Give the team at Pye-Barker a call at 404-363-6000 or email us at firstname.lastname@example.org and we’ll conduct a no cost no obligation needs analysis for you so that you can get the right unit to suit your requirements.
Purge air flow on an uncontrolled desiccant dryer is based on the nameplate rating, not the amount of compressed air flowing through the dryer. The purge flow is metered by an orifice or cracked open valve that takes a fixed flow of air from the tower that is regenerating. The cfm of air flowing thru the dryer does not change the purge flow unless there is a dew point or moisture control controlling the dryer.
Example: On a 1000 cfm fixed cycle dryer that is only running at of its rated or 500 cfm, the purge flow will still be 15% of the nameplate rating or 150 cfm, this would mean the real purge flow is 30% of flow.
Purge flows can change often, this is a manual adjustment that is done during a specific part of the dryer cycle, on most dyers the purge flow is controlled by a ball valve based on the pressure reading on a gauge, over time these valves can become misadjusted and purge exhaust ports can become plugged causing back pressure which changes the purge flow.
Dewpoint controls save energy by adjusting the dryer cycle time and purge time, letting the desiccant get fully saturated with moisture before the controls will let the dryer purge.
Southwire has two Gardner-Denver 250HP compressors rated at 1100 CFM each for a total of 2200 CFM, they have a 2700 CFM ZEKS desiccant dyer. The purge flow is 15% of rated flow or 405 CFM. When they have the dryer on-line and working correctly they are putting 2200 CFM into the dryer and the dyer is using 15% of that flow for purge air, so they are losing 405 CFM to purge flow which comes to about 18.5% of their compressor output. Instead of getting 2200 CFM like they need, they are getting 1795 CFM and that means when the dryer is on line the plant does get enough air to run.
International Paper, dealing with another distributor, replaced two Gardner-Denver 75HP compressors and a 650cfm refrigerated dryer with one 150HP Gardner-Denver compressor rated at 620 CFM and a 700cfm Airtek desiccant dryer. They found they could not run their plant because the dryer was using 15% of flow or 105cfm for purge flow; which meant they only had 515cfm of air flow. They had to buy an additional 200HP compressor to have enough air flow for the plant.
What dryer you use in your compressed air system can save energy and saving energy can lower your operating cost.
Let us help you make sure you have all the compressed air you plant needs.
Maybe you need really, really dry air.
Maybe that air is even dryer than -40⁰ F dew point achieved with a typical regenerative desiccant dryer. Maybe you need a -100⁰ F dew point. It’s a rare requirement, but there are applications for it. You would do well to consider Fick’s law before proceeding.
I’ll admit I wasn’t familiar with Adolf Fick, who in 1855 postulated his law of diffusion. I must have missed it in my years of sitting (sleeping) in a classroom. But I was struck by how this law applies to dry air when reading a section of the CAGI Compressed Air and Gas Handbook.
Fick’s Law states that “The rate of diffusion in a given direction is proportional to the negative of the concentration gradient.” Diffusion in this case means the process where two gases intermingle moving from a region of high concentration to a low one. In a compressed air system the law applies to the difference in moisture vapor outside the system to the dry air within the pipe.
When it comes to super dry air, that differential, or gradient, is quite extreme compared to moist ambient air. So any leaks in the piping downstream of a dryer will allow diffusion of atmospheric water vapor to enter the compressed air line. Even if it is at full line pressure.
The clear implication is that proper piping material should be used, and that a vigilant eye be maintained on any leaks in the piping. We have spoken about proper piping material before in our post here: Gardner-Denver Quick-lock Tubing
But here’s a more startling fact mentioned in the CAGI handbook: To purge residual moisture out of a piping system downstream of a dryer takes an extra ordinary amount of dry air. The book states that tests to obtain a 94 deg. F dew point takes a mind-boggling (and expensive) 1,000,000 cubic feet of air dried to that dew point for every 1 cubic foot of piping volume. For reference a cubic foot of 1 inch schedule 40 pipe has a length of 166.7 feet.
What ever your air needs are, if you need extremely dry air then you need to talk with a specialist to make sure you have all your bases covered. Your system might not be able to handle the demand.
Many customers because of a lack of plant floor space or due to safety (noise / heat related) requirements install their compressed air stations outdoors.
If this is you? It is highly recommended you use some type of weather protection to keep blowing rain, snow, ice or dust from entering your air compressor intake. NEMA 4 controls and TEFC motors and sound enclosures can be supplied by the manufacturer but some type of protection such as a lean-too cover or awning is always recommended.
Several customers in my area use a metal canopy or a pitched roof cover on concrete slab next to an exterior building wall and have either fence wall around the area or some will use tarp walls, put up primarily in wintertime, to trap heat from the compressor.
For cold weather operation, I have pasted below an excerpt taken from one of the GARDNER DENVER service manuals:
Figure 2-3 – COLD WEATHER INSTALLATION INSTALLATION FOR COLD WEATHER OPERATION (Figure 2-3) - It is recommended that the unit be installed inside a shelter that will be heated to temperatures above freezing (32 F, 0 C). This will eliminate many of the problems associated with operating units in cold climates where freezing rain, drifting snow, freezing condensate and bitter cold temperatures are encountered.
Refer to Gardner Denver Engineering Data Sheet 13-9-411 for the advantages of using AOL desktop gold customer service the heat recovered from your rotary compressors. This heat recovery could easily pay for an adequate shelter for the unit.
When an outside installation must be made, the precautions required will depend on the severity of the environment. The following are general guidelines for outside installations:
Cold Weather (Down To +10 F, -12 C)
1. Be sure all drains, traps, and control lines, including pressure transducer lines are heated to avoid freezing of condensate. Heat tape with thermostat control is generally satisfactory for this purpose and can be obtained at various local plumbing or hardware outlets at nominal cost.
2. If an air-cooled aftercooler is to be used, provisions to bypass the aftercooler must be made. Since cold air contains very little moisture, successful operation can be achieved without the aftercooler.
3. Provide at least some simple shelter such as a plywood windbreak to protect against drifting snow.
4. Use only Gardner Denver AEON 9000 SP lubricant.
5. Monitor the unit carefully during start-up and operation to be sure it is functioning normally.
6. Specify NEMA 4 enclosure for electrical devices.
Another item to consider when mounting your compressed air station outdoors is your Compressed Air Receivers. If your air receivers are mounted ahead of your system dryers, bulk condensate will collect in bottom of tank and typically an automatic electronic or float drain is needed. Many companies do not run compressors on the weekend and this fluid that is collected in the bottom of tank and possibly in the air lines feeding the tank will freeze during winter conditions.
To protect yourself from future headaches it is recommended to insulate your outside pipe and also the condensate drain used on tank. There are condensate drains available with internal heaters that will also solve this problem.
As far as air filters and air dryers (refrigerated and desiccant) mounted outdoors – please see below excerpt taken from cagi.org (COMPRESSED AIR & GAS INSTITUTE) website regarding the myth of air dryers installed outdoors.
Myth: Any dryer (refrigerated or desiccant) can be installed outdoors.
Fact: All standard dryers are designed for internal installation. However, many are often installed outside, (with a lean-to roof in some cases and without a lean-to roof in some cases). Outside installation is acceptable provided there is lean-to roof with freeze / snow protection, blowing rain protection, and a roof / ceiling high enough to avoid hot air re-circulation. Outside installation of standard dryers with no roof is not recommended.
Low ambient protection such as heat tracing drains and interconnecting piping can be supplied at the time of purchase to solve this problem.
Another problem some of my customers with regenerative dryers encounter is that when the dryers are mounted in a secondary building with outside piping between buildings they have seen poor dew points or shorter desiccant life. Condensation may be formed from outside non-insulated piping or pipe drops and the downstream desiccant dryers see excessive amounts of inlet condensate that will not allow the desiccant to work properly or corrode the desiccant from excessive water.
To potentially protect yourself from this problem, it is HIGHLY recommended to have a secondary air receiver ahead of the dryer that will catch bulk water or condensate and reduce or eliminate the moisture collected on outside piping exposed to varying wintertime and summertime conditions.
It is also true that a secondary air receiver should be included for refrigerated air dryer installations for outside piping for the same downstream moisture problem.
Air receivers are a low cost item compared to downstream instrumentation or precision valves used. In fact, a small air receiver can be as low as $ 200.00.
We frequently receive calls for an air dryer. When pressed for specifics, the customer often has no idea how dry he needs the air to be. He may only need to remove liquid water and contaminants from his line. Or, he could need “instrument quality” air.
The amount of moisture in compressed air is expressed as pressure dew point (PDP), and is given in degrees Fahrenheit. The dew point is the temperature at which the moisture in the compressed air will condense and form a liquid. Since compressed air at 100 PSIG is saturated (100% relative humidity), some form of moisture removal is generally necessary in a compressed air system which means reducing the dew point, condensing the moisture, and removing the liquid water. In most systems, this is done using one or more of the following methods:
Pye-Barker Supply Co. represents several manufacturers of premium quality air drying and cooling equipment. These can be specified to meet most any cooling/drying requirement.