Air Dryer Location Relative to Receiver
Air Dryer Location Relative to Receiver
(OP)
In a compressed air system that has a compressor, dessicant dryer and air receiver, where is the best location for the dryer?
i.e. should it be upstream or downstream of the receiver.
I've always placed the dryer downstream of the receiver simply based on previous projects our company has performed.
I just recently worked at a plant where the dryer was placed upstream of the receiver. This plant had constant problems with getting water into the air system even though the dryers were supposed to lower the dew point to -40 deg F. Could this problem be due to the dryer/receiver configuration or is it more likely a compressor or dryer malfunction? The air system was fairly new (< 2 years) and apparently has had water problems for most of that time.
i.e. should it be upstream or downstream of the receiver.
I've always placed the dryer downstream of the receiver simply based on previous projects our company has performed.
I just recently worked at a plant where the dryer was placed upstream of the receiver. This plant had constant problems with getting water into the air system even though the dryers were supposed to lower the dew point to -40 deg F. Could this problem be due to the dryer/receiver configuration or is it more likely a compressor or dryer malfunction? The air system was fairly new (< 2 years) and apparently has had water problems for most of that time.





RE: Air Dryer Location Relative to Receiver
Placing the drier upstream of the receiver makes is muct less likely that LIQUID water will form in the receiver. If you go the other way around you are almost guaranteed that you will get liquid in the tank.
RE: Air Dryer Location Relative to Receiver
Few points to consider are,
1. If the compressor and dryer capacity is same and you have less load than compressor discharge, I prefer compressor--->Dryer--->Receiver, because as the compressor is loaded and unloaded based on receiver pressure you can stop dryer whenever the compressor gets unloaded. (for this you need constant dew point system, i.e hot gas bypassing)
2. If you place dryer after receiver, moisture accumulates by coalescing in the receiver and load on dryer decreases.
3. If you don't have a constant dew point dryer (hot gas bypass arrangement) then as the load varies, power consumption by dryer varies (ofcourse, marginally) if you have dryer after receiver.
My preferred choice for tight control of dew point is Compressor----->Receiver---->Dryer (and I did 10 installations this way for pharmaceutical plants)
Regards,
RE: Air Dryer Location Relative to Receiver
RE: Air Dryer Location Relative to Receiver
Rod
RE: Air Dryer Location Relative to Receiver
- act of compression condenses water, a simple 'y' with auto drain discards this.
- reciever allows cooling and further condensate to be removed (along with any bypassing oil). Again an autodrain removes this.
- Dryer can be sized and located for specific demand, rather than whole load, if allowed.
RE: Air Dryer Location Relative to Receiver
What the gents wrote in regards to the location of the receiver is pretty good. However, you mentioned that you still have water in your air. This can be contributed to one of two reasons:
Either your dried air is subjected to cold temperatures that are lower than the dew point of your dry air. A rule of thumb is to design your driers for a dew point at least 10 to 20 degrees below that of the lowest ambient temperature your air will be subjected to.
The other reason is that your driers are not drying the air upto the spec. You should monitor the moisture content on the outlet of each dryer. A very important factor you should check is the flow going into each drier. Make sure it is not exceeding the flow it is designed for. If this happens, you will saturate the desiccant bed with moisture and eventually this will raise the moisture content in your air. Hope this helps
RE: Air Dryer Location Relative to Receiver
Newer (combustion turbine) plants I am familiar with only one receiver have the dryers upstream...
I always assumed that allowing the air to cool off in the receiver reduced the moisture load on the dryer -- we put auto-blowdowns on the receiver drains...
I prefer to have the dryer downstream (if two receivers are used) -- but if given only one receiver, I'd put the dryer in front...
As for your problems, there are a number of items to check: make sure the aftercooler is piped in correctly and you have adequate temperatures and flows to knock a lot of the water out -- check the aftercooler drain pot and piping to make sure it drains properly... also, check the dryers -- are they heating up and cycling properly (I worked at one plant where they never checked this; the dryer had failed and they wondered why their instrument air system froze up ???) check the dryer capacity vs. the air usage -- it may be that the dryer is sized too small to handle the flow quantities...
(what type of compressor are you using?)
RE: Air Dryer Location Relative to Receiver
The receiver is often located between the compressor and the dryers so that it can behave as a water k/o vessel, usually outfitted with an automatic drainer. However, it's best to have an air cooler and a coalescing filter immediately on the discharge of the compressor to knock out most of the water. Also, many air compressors place some oil in the air, so the cooler/coalescer system is very important for removing the oil. Note: a dry filter should be located after the dryer; the dessicant will continuously emit dust which can plug downstream equipment.
Another consideration must be the "shutdown" behavior of the entire system. When shutdown of the compressor occurs you want the air to continue flowing forward through the beds, not backward. Backward flow will usually damage the beds. Therefore, placing the receiver ahead of the dryers helps. Good soft-seat check valves also help.
You should also review the OSHA standards for air compressor systems (www.osha.gov). And, finally, NEVER use air from a system such as this for breathing air. Breathing air systems are further regulated and must be designed according to a totally different set of standards.
RE: Air Dryer Location Relative to Receiver