A refrigerated dryer eliminates the problem by cooling moisture in the air to approximately 37°F, where it condenses and can be removed from the compressor system by way of an automatic drain. Quincy manufactures four main refrigerated dryer product lines: the QPNC non-cycling dryer, the QED cycling dryer, the QPVS variable speed dryer,. The most important points for the correct operation of your dryer are printed in bold type. Introduction Locodryer series is a heatless adsorption air dryer range made for Locomotive air treatment. Rigid and easy to maintain, the dryer is equipped with a pre-filter 0.01 microns at 99.7% filtering efficiency to protect the desiccant from the.
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A desiccant compressed air dryer uses a special material, called desiccant to dry the compressed air.
This desiccant is made of a material that really ‘likes' water, the water sticks to the surface of the desiccant.
Every once in a while, the desiccant needs to be dried, or ‘regenerated', to remove the water again.
Desiccant
To have the largest possible surface, the desiccant is used in the form of thousands of small beads. Types of desiccant that are often used are silica gel and activated alumina.
Activated Alumina. Photo: Atlas Copco
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Autocom 2013.3 keygen v1. Silica Gel. Photo: Atlas Copco
How a desiccant compressed air dryer works
A desiccant dryer usually has two identical towers, filled with desiccant. One tower is used to dry the compressed air, while the other tower is regenerated.
Every once in a while (controlled by a central control unit) the dryer switches towers. The compressed air is now dried by the second tower, while the first tower, filled with wet, saturated desiccant is dried.
Very simple!
On most dryers, there is a small sight-glass. Behind the glass you can see small beads. This is not the drying-desiccant, but an indicator. It will change color when the air the is too wet. Check it every once in a while to make sure that your dryer is
working properly.
Big desiccant compressed air dryer.
Small desiccant dryer. Photo: Atlas Copco
Regeneration or drying of the desiccant
When the desiccant has done its job for some time, it has absorbed all the water from the compressed air and is saturated with water. It cannot hold any more water. In order to re-use the desiccant, we need to get rid of all that water. This is called regeneration.
The regeneration process is done in one of the two towers of the air dryer, the one that is not operational. There are two ways the desiccant can be regenerated: by hot air or by dried compressed air.
With the hot air method, a separate system consisting of a fan with an electric heater is used to blow hot air through the desiccant to dry it. This is just normal air drawn from the compressor room.
Dryer which uses heat from the oil-free compressor for regeneration. Photo: Atlas Copco
There are also special dryers available for use with oil-free screw compressors that used the heat of the compressor to regenerate the desiccant (and thus saving energy and money). This type of dryer consists of 1 rotating drum. 1 quarter is being regenerated, while the rest is drying the compressed air.
A third method of drying the desiccant, is with dry compressed air. This is often used in the smaller dryers and is also not suitable for big dryers.
With this method, part of the compressed air that has just been dried is used to regenerate the desiccant. This means that less compressed air is available for your tools and machinery.
Hidden costs
When buying a desiccant compressed air dryer, keep in mind that there are more costs involved than just the purchase price.
Here is a list of things to consider when buying your desiccant compressed air dryer:
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- Pressure drop. The dryer will create an extra pressure drop. If the pressure drop over your dryer is for example 0.3 bar, and you need 6 bars to operate your tools, it means you need to set your compressor at 6.3 bars. This extra bit of pressure
requires more energy (and money!) to produce. The bigger your compressor, the higher the extra costs. - Regeneration costs: if you buy a hot-air regeneration-type dryer, consider the electricity costs used to heat the regeneration-air. If buying a compressed-air regeneration-type dryer, consider the air lost in the process. A dryer of this type will consume 15 to 20% of your (expensive) dried air!
- Desiccant use: even though the desiccant is regenerated, it will ‘wear down' over time. It has to be replaced after a few years
(check the manual).
Installation
There are a few key things to keep in mind when installing your desiccant compressed air dryer. I have seen so many mistakes with this over the years and it's so easy to do it right and save money in the long run!
Pre-filters: always make sure that the air that enters the dryer is clean and free of oil and water drops. Use a moisture trap, a water-filer and an oil filter to clean up the air before the dryer.
Why a condensate trap and water filter? Any liquid water in the compressed air will quickly saturate all the desiccant, making it unable to do its job properly. Result? Your dryer will not be able to get the desired dew-point. Wet air will pass through your dryer.
Why an oil filter? There will always be some oil from your compressor in the compressed air (this is called ‘oil carry-over'), unless you have an oil-free compressor of course.
If this oil gets to the desiccant it will stick to the surface of it. Result: your desiccant can't do its job anymore, since it's covered in oil.
Wet air will pass through your dryer. Also, you can probably throw the desiccant away and buy new one, which can be quite expensive.
After-filter: It is advisable to install a dust filter after the desiccant compressed air dryer.
The desiccant will always wear down a bit. This means desiccant-dust will exit the dryer together with the compressed air. Use a dust-filter to remove the desiccant dust to protect your equipment.
Outlet filter with dew-point sensor on this
desiccant compressed air dryer.
Photo: Atlas Copco
A refrigerated compressed air dryer is a type of compressed air dryer, used to dry compressed air.
Compressed air always contains water, coming from the air that is sucked in by the compressor.
To protect your piping, tools and equipment, it's best to use a compressed air dryer to dry the air.
Why a refrigerated compressed air dryer?
Refrigerated air dryer
Refrigerated compressed air dryers are one of the most common used types of air dryers (for other types, check out our general page on compressed air dryers). They are simple in design, need very little maintenance and are relatively cheap.
A refrigerated compressed air dryer is the standard choice if you're shopping for a dryer and don't have special requirements, like an ultra-low dewpoint. T
hey don't need much or any special maintenance and
if you buy a quality one, and install it properly, it's basically set-and-forget.
How does it work?
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As the name implies, a refrigerated air dryer works by cooling down the air (like a refrigerator).
The warm wet air enters the dryer, where it is cooled down to about 3 degrees Celsius. All water vapor that was in the air condenses into water.
Much like your window does on a cold day. The liquid water is then removed from the compressed air by a water-trap.
After that, the cold air is re-heated to room temperature. Since a lot of water has condensed into water, the air is now much dryer.
The cooling is done in the same way as your freezer and fridge are cooled. In a separate circuit, liquid refrigerant is evaporated in the evaporator, to cool down the warm compressed air.
The air is cooled, while the refrigerant gets warmer. The refrigerant is compressed by a small compressor and cooled again in the condenser.
Here are two pictures of the inside of an old refrigerated compressed air dryer. You can see the various parts of the refrigerant circuit (with refrigerant compressor and condenser). You can also see the condensate trap with discharge lines.
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The evaporator (where the refrigerant cools down the compressed air) is located at the top of the dryer (the whole area at the top is the insulated evaporator).
In the background you see the refrigerant circuit of a compressed air dryer. In the middle is the condensate trap (with water discharge lines).
At the right the condenser with cooling fan. In the middle you see the refrigerant pipes that go to the evaporator. At the left the condensate trap again.
Types of refrigerated compressed air dryers
There are basically two types of refrigerated compressed air dryers. Cycling and non-cycling. The advantage of the cycling dryer is that it will increase or decrease cooling capacity according to air use. This reduces the energy used and saves you money.
The non-cycling is the most common type and is extremely reliable and have the lowest maintenance
costs.
Example of a refrigerated compressed air dryer. This one is installed after a rotary screw compressor (Atlas Copco GA37, 37 kW compressor). On the control panel you see a start/stop button and the dew-point indicator.
What to look for when buying one?
There are a few key points to keep in mind when shopping for a refrigerated compressed air dryer.
- The maximum pressure. The maximum pressure of the dryer must be the same, or higher than that of your compressor.
- Maximum flow. The maximum air flow that can flow through your dryer (in liters/sec or cfpm) must be higher than what your compressor can deliver.If you choose a too small air dryer, it will result in a big pressure-drop over your dryer (because the air has trouble passing through it). Because of this, you need to set your compressors pressure higher to compensate for the pressure drop. This again will result in a higher energy bill.Secondly, your dryer might not be able to reach the desired dew point.
- Inlet temperature. Air dryers have a maximum specified inlet temperature. If this temperature is exceeded, you can either damage parts of the dryer, or the dryer just doesn't have enough capacity to reach the desired dewpoint.Some compressors have an after-cooler installed, in which case the compressed air will be around
40 degrees Celsius. Without an after-cooler, the air will be around 80 degrees Celsius or higher!Check the temperature of the compressed air leaving your compressor. Is it very hot? There are special ‘high inlet temperature' dryers on the market, which are specifically designed to be able to work with your hot air. - Maximum outside (room) temperature. Will you put your dryer in a hot room? Chances are that the dryer will over-heat and shut itself down. Find out what the maximum temperature is (in summer) in your compressor room and buy a dryer that can handle that.
Maintenance and installation
Always check the manual for guidelines on the installation and maintenance of your refrigerated compressed air dryer. Every make and type has its own specific needs and instructions.
In general however, keep the following things in mind:
Install the dryer in a cool, dust-free room. You will probably also need a drain somewhere to get rid of the water (can be liters of water per day!). Normally you just need a standard 115 (usa) / 230 (Europe) voltage power source.
By far the most common, number 1, breakdown I have seen with compressed air dryer is over-heating. When the condenser of the refrigerant circuits get dirty, or the room is just too hot, the dryer can't get rid of the heat. It will eventually trip on its over-pressure switch.
Maintenance: clean the condenser once in a while. Be careful, the small plates (fins) are sensitive. A good way to remove all the dust is by using a steel-brush and gently scrape off all the dust. There are also special condenser fin combs to clean and straighten the fins.
Another problem I have seen sometimes is that the dryer actually gets too cold!
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If for some reason the dryer dries the air to below 0 degrees Celsius, the water will freeze and the ice will block the pipes. In the end, the dryer will be completely blocked.
Sometimes this happens because somebody just set the setpoint too low, sometimes there is something wrong in the refrigerant circuit (a sensor or valve for example), in which case you will need to get a mechanic to repair it.
