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torque
09-10-2016, 11:02 AM
I have had a ammonia / glycol plate heat exchanger fail internally resulting in the contamination of the full glycol charge. The system has been drained, flushed and a new glycol charge added (approximately 23k ltrs) but due to the allowable system downtime when the new glycol has been charged back into the system and circulated there is still traces of ammonia pressent in the sampled glycol. The system pipe work is stainless steel but the evaporator coils and control valves are copper / brass.

My Questions

Is there anything that can be used to neutralize the affects of NH3 in the water / glycol mix or a recommended allowable level of NH3 in the mix that will not result in the corrosion of the copper and brass that is in the glycol system. Also can anyone recommend a test that can be used to check the NH3 concentration pressent in the water / glycol mix.

hookster
09-10-2016, 09:17 PM
The ammonia will have formed ammonium hydroxide in the glycol water mix, this will be a strong base if there is a lot of ammonia hydroxide. Do a PH test on the glycol solution and either drain and mix or try neutralise the base solution. The ph should be between 7 - 9 and molybdates and nitrites tested for corrosion inhibiting.

I would just get your water treatment company to come draw a sample and advise on result.

Magoo
10-10-2016, 12:35 AM
I agree with Hookster,
the water treatment people will monitor Ph and recommend either a full flush and replacement or a slow constant drain and replacement of glycol charge.
did you establish a reason for plate failure.

torque
10-10-2016, 08:33 PM
Thanks for the replies guys. The PHE issue was the result a gasket failure.

Josip
10-10-2016, 11:07 PM
Hi, torque :)


Thanks for the replies guys. The PHE issue was the result a gasket failure.

I believe it will be much better to use welded PHE .... like....
http://www.vahterus.com/en/applications

Best regards, Josip :)

hookster
12-10-2016, 07:43 AM
Hi Josip
I dont like to disagree but I think Torque comment may be misleading, The PHE on an ammonia pack is usually a welded gasket combination PHE. The ammonia plates are welded together - semi welded PHE.

There is potential for failure on the ring gaskets between plates but these are usually a high grade gasket. Butyl is best but usually Hydrogenated Nitrile (you get what you pay for). This side failure is rare and I have found usually a cause of poor maintenance. Water side usually gets scaled or flow stops resulting in higher pressures and temperatures and premature failure of the gaskets. I have even seen plate welds fail and plates crack due to plate distortion from over temp/pressure.

Semi welded plates have been in operation for a lot of years and usually very reliable and make cleaning the water side far simpler than any shell & tube, sealed PHE.

Josip
12-10-2016, 12:25 PM
Hi, hookster :)

Don't worry ... agree or disagree .... we are here to discuss and if possible to help ... i.e. to solve the problem ...

You're probably right ... Torque info can be misleading ... but I was just thinking out loud ....

There is nothing to last forever ... agree with you ... poor maintenance usually is perfect road to problems ... of course, stresses, due to temp/press changes can cause crack of plate/s ...

... so many variables ;)

Let's hope that Torques solved all problems so far....

Best regards, Josip :)

sandybapat
23-10-2016, 09:46 AM
in semi welded phe, there are two gaskets in series. In case ring gasket fails Ammonia will leak to atmosphere and not on to glycol side. The chance of both ring as well as field gasket failure are rare most. Even then the Ammonia is likely to release to atmosphere.

This must be a case of crack or pin hole developed in the heat transfer area of the plate.