Refrigerant Air Dryer vs. Desiccant Dryers

Are you also using coalesing filters prior to the dryers and after? I would try those first in the 1 micron before the dryer, then 0.01 micron after. If you still have problems a desicant might be in order at the end use points.

The short answer is 'Both'

Deploy desiccant dryers after refrigerant to mop up the last dregs. A good refrigerant drier adds to the overall C.O.P. of the system. So no need to lose that gain.

It might be worth checking to see why so much moisture is entering the system. Check the humidity levels at the compressor intake, to ascertain if it is the same as the normal atmospheric humidity. Ducting could solve any problems.

Neither. The air dryer is neither the problem nor the solution.

The existing air dryer is functioning properly. Air dew point is 2 deg C.

A fitting leak may contribute to the problem. But wait. Air pressure forces leaks out not in. Correct. False. When the air is valved out, moist ambient air leaks in.

An underground air line may be leaking. Wait again. This could be the case with Any line that loops down with no drain at the low point.

Slope all lines at least 1" per foot.

Install drains at the low points.

Operating & Maintenance procedures or automatic drains keep the water traps dry. Dry air flow collects and distributes moisture at a low point in a line.

The best of air drying procedures and equipment will not eliminate nor substitute for properly installed air lines and proper O&M procedures.

Well now kmthota First things first, get out the Manual, then get out the WHIP!

Assuming this problem is a recent development, not something that has been bugging the system for years. It may be time for the..... 'Six Year'....'Anual'....Maintanance.

We presume this is a rotary vane compressor, perhaps an Ingersoll Rand? vanes always tend to make more water...Question, "What temperature does the manual say the compressor should normally work at" it might be running hot, for a multitude of reasons.

The oil might be old and if you empty the sump and find a gallon of water, don't be surprised. just fill the kettle with it and tell the culprit that he might have to drink a few cups of tea from it if he does not start cleaning the entire contraption to military specifications. Get the White Gloves out. That is the Military Specification for CLEAN.

An Ingersoll Rand often has a fan assisted cooler on top, if this is clogged up with the dust of ages?.....well it is not going to be very efficient at cooling. Whip needed here!

Follow all the appropriate maintenance procedures to the letter. Then when this gleaming clean machine fires up, let the air blow and probably spit a bit till the air lines are clear of water.

If overheating is due to wear, say on the vanes, then seek advise from the distributor. They may require 'restoration of dimension' but this is an unlikely scenario.

Automatic water traps/filters in the air line are always a good idea. and also a good investment.

Good Luck. Remember White Glove, Whip, No Dust in any coolers/radiators/etc. MAKE CULPRIT DRINK TEA/COFFEE (But don't actually use the sump oil water, just kid him for a laugh)......MAINTANANCE MANUAL....>>>.THE CRUCIAL KIT<<<

SUMMARY:-

Dirty Coolers do not cool efficiently

Dirty Compressors get hot, make more work for inefficient dirty coolers.

Dirty oil is a bad lubricant, bad lubricant makes heat = bad = water in airline.

Solution:- Whip & White Glove & Maintanance Manual.

Dew point of +2 deg C sounds kind of high for instrument (solenoid valve) air. We like to see instrument air dew points of -20 to -40 deg C in our chemical manufacturing plant. May be hard to get that low with refigeration type dryers.

What is your ambient temperature? Good rule of thumb is for the instrument air dew point to be at least 10 deg C below the coldest ambient temperature. This is because the air expands and cools in the solenoid valve or other instrument. The 10 deg C margin allows for this cooling so that the air temperature never drops below the dew point. If it does drop below the dew point, moisture will condense in or just downstream of the instrument.

Supplementary to all previous replies; lets recap and add some pointers:

Cooling the air causes the water vapour to condense. Air leaves the compressor hot and (usually) enters an after-cooler. The air from the after-cooler is (usually) still hotter than the ambient air and thus further cooling takes place throughout the pipework.

Condensation occurs on the walls of the pipe (and equipment) and as fog that makes it's way to every point of use.

A filter/drain in the warm compressed air at source (and 100% efficient and working properly) cab reduce the bulk of the suspended water to zero at the filter, but water vapour (a gas) will pass straight through.

The filter cannot prevent the air from further cooling thus water at the point of use seems to appear from nowhere.

This is where the fridge dryer comes in. Very simply, it takes warm air at source and cools it to a temperature well below ambient. Therefore the outlet air must hence warm up as it passes through the pipework. The air becomes warmer and dryer thus no water appears in the system from then on.

That's the theory.

In practice, a number of problems could arise. Was the dryer sized correctly in the first place? Is 2°C well below your ambient? Is 2°C the true dew point (ie. the air temperature in the chiller) or is it the suction gas temperature (a 5°C difference could exist across the heat-exchanger walls). Is it 2°C because the chiller has been turned down this low ? ( 3°C is the norm).

Do your compressors run too hot (loss of cooling medium, blocked radiators) or (blocked inklet filter, leaking piston-rings or vanes, leaking discharge valves, etc). Similarly the after-cooler can only cool the air by so much (it could suffer from loss of cooling medium, blocked radiators, etc) - thus overloading the fridge dryer. Oily air can also coat the coils/tubes of the chiller to act as a heat insulator. The working dewpoint rises. Thus 'warm' arm leave the dryer - and so does a lot of moisture. Not much in overall bulk, but more than enough to fill up solenoid valves.

On the other hand, you could be running on light load or in cold conditions, thus the condensate is near freezing - where due to the additional cooling effect of rapid expansion to atmosphere, the condensate turns to ice in the drain valve. Condensate does not get dumped - then builds up and carries over to he system. Later in the day, when air flow increases, everything warms up (and if checked) the drains all seems to be working again. You might need a trace heater on the drain to stop it freezing.

The after-filter (if you have one) stops the mist (but not the vapour). The condensate drains to the sump to be dumped (automatically?) Is the drain working? If not the water gets picked up and gets thrown into the system - along with the water vapour that carries over to the system to condense everywhere as it cools.

As a fridge dryer has to cut out at 3°C to prevent it freezing up. A dewpoint below freezing can only be achieved by a desiccant dryer. Even so, you will need to ensure your compressors, after-coolers are running cool.

And, Ladies and Gentleman, this years 'Golden Whip' award for well maintained compressors goes to........ HORACE40.......A big round of applause please.

Great, thorough, and accurate reply Horace40 and thanks for taking the time to respond in a professional manner. Another question to raise is the test point source, method, instrument, calibration, and frequency employed to arrive at the dew point of the subject air and whether or not the measurement was pressure compensated. Specification of ambient is also important.

In a practicle manner, I would suggest walking down the routing of the pneumatic line to determine the location where the document fails to record that the line, or a "tee" off the line has been routed underground. A loose fitting or failed pressure boundary is periodically allowing ambient air to penetrate the pressure boundary thereby negating all the expert and well implemented advise for the major portion of the installation.

If the source of the problem is never resolved, the information alone should merit a promotion for providing an expert path of resolution.

Re Alastair Carnegie Thanks for the compliment and the link. What a lovely little animated demo.

Have you ever come across one that shows how air temperature, pressure, flow and humidity are linked? A sort of family of elevated pressure curves of a psychrometric chart. Now that would be very useful.

The problem most people have with compressed air quality, and water in particular, is that the air behaves like a mini climate/weather system - but with far greater ranges of pressure and temperature than the atmosphere.

With years of historical records, hundreds of experts and £millions of equipment - the Met Office still get it wrong.

It is not surprising the poor old engineer is struggling.

I hope KMTHOTA has enough feedback to help.

.

That sounds like a great idea 'horace40' but with four variables to display, it might be quite a challenge with the display side. That Bernoulli animation shows a graph of the pressure and flow velocity as dimensions change, the little flowing dots could change from red to blue as the humidity changed, ......Well worth thinking about, I got the link surfing wikipedia, so I will endeavour to contact Mr M.Mitchell through the editor, maybe we might see a link to a new version?

The point you raised had not occurred to me, I can just imagine an underground air delivery pipe with a dodgy shut off valve, half or fully submerged in water, a small constriction would 'suck' (pardon the expression) water in without doubt, if it could reach the 'constriction' (i.e. slightly open valve with a worn seal perhaps)

I have this feeling KMTHOTA's plant is going to recover fairly soon. Thanks for sharing your problem with us, we might encounter it ourselves one day.

Alistair - I have no personal knowledge of water being 'sucked' but I suppose it is feasible (in freak conditions?). But the venturi action of compressed air through an orifice creates a vacuum that is a technique used to make air operated vacuum cleaners (such as used for ventillating explosive mixtures from tanks and enclosed spaces) and also for some 'suction' type pneumatic devices - and air movers (blowers).

I hope you find some RH info.

At Red Scar Industrial Coatings, we use a whole load of abrasives and mixtures of abrasives, needless to say we get it into the high pressure air flow no bother at all, well actually the suction (a non scientific term) is often far too high. I was only guessing about a submerged air valve, never having taken one to bits. I can see the danger though.

Oups, sorry, clean the dryer CONDENSER, not the evaporator, my French language translation problem