Advise in Ammonia quality test 1

[lombardo]

I have a lot of problems related with the ammonia quality for refrigeration compressors, I want to know what kind of analysis I need to do in order to detect the quality of the ammonia.
Thanks

 

[unclesyd]

You might be interested in this. Looks kinda like your problem. I'am looking for my NH3 literature.

http://www.oilanalysis.com/message_...Sludge+in+Ammonia+Compressor&messagenumber=1

 

[BenThayer]

there are typically only two samples done for ammonia and that is water and oil.

i worked at a major ammonia producer and we made effectively two grades:

Agricultural grade (also called Commercial Grade) which had water from 0.2% to 0.5% weight. oil content escapes my memory but was something like less than 3 ppm oil.

Metallurgical grade (sometimes called Refrigeration Grade) was 99.999% ammonia and a maximum of 10 ppm water and 1 ppm oil.

The Metallurgical grade was significantly more costly due to the purity and the cost of equipment needed to store it due to potential stress cracking.

there is no easy field test to determine which you have. i would suggest going to your supplier to find out. we sold ours in railcars and truckloads and so i cannot comment on the cylinder size deliveries or suppliers.

for a refrigeration system, you really should have the high purity or the water could start to accumulate in the evaporator and effect the way the system is behaving.

 

[lombardo]

Thanks a lot Benthayer! very usefull info.

 

[nbucska]

Lombardo:
You may want to contact the manufacturer of the refrigerator to find out what kind of contamination
may cause corrosion or other problem ?

<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

 

[BenThayer]

one other item that i neglected to add is that you may have a low pressure suction side leak contributing to operational problems. if you run a slight vacuum on the suction side, you can be sucking in air. do you have an inerts purger on the system? an easy method for estimating non-condensibles in the system is looking at the condensing temperature vs. the gauge pressure and a table for properties of ammonia. e.g., 100°F condensing and 230 psig pressure suggests ~ 30 psig of non-condensibles.

a crude field test is to take a syringe and sample the vapor from the system (obviously not by filling the syringe directly but by pulling a sample from the gas stream exiting the system via a small purge) and then take a graduated cylinder in a bucket. You invert the cylinder after first letting it fill with water. you then discharge the syringe so the vapor goes into the cylinder. use something like a 100 ml cylinder and 100 ml needle. if the vapor is discharged and 20 ml appears in the cylinder, then the vapor was 80% ammonia and was absorbed by the water and 20% was nitrogen or air, etc. a bent needle or short section of hose or tubing helps to direct the vapor.

i am assuming that you are all well aware of the hazards of handling and sampling ammonia, if not do NOT attempt the above.

my answers are geared to operational issues. good luck and keep us informed.

 

[25362]

Nobody wants contaminants in the anhydrous ammonia (R 717) used for refrigeration. However, I can testify having seen industrial refrigeration plants using for years long commercial or agricultural grades of ammonia with about 2500 ppm water content without suffering any process predicament as a result. Refrigeration grades contain a maximum of 150-200 ppm water.

The aqua-ammonia formed in the chillers gets to the lowest (coldest) points and must be drained off, signifying in a loss of refrigerant. The vaporized ammonia contains much less moisture than the flashed liquid.

This draining operation also allows for some of the entrained compressor-oil to be removed not to impair heat transfer. This being another source of ammonia losses.

Even when working at pressures above atmospheric (see BenThayer's post above) there are cases when air may enter the system as when dissolved in the lube oil used in oil-flooded screw compressors with recurrent replenishments.

There are automatic and manually-operated vents in the market, that function by chilling the vented gas. These are usually located at the condensers' high points. Air, as well as other non-condensables, do not only impair heat transfer in the condensers but oxygen, for example, is also blamed for the appearance of SCC in storage tanks containing anhydrous (less than 0.2% w/w water) ammonia (see nbucska above).

As for the determination of water content, I've been told moisture is usually measured on vaporized ammonia samples.