Iron in Glycol of Dehydration System 1

[sukitena]

Hi All,
I am looking after an offshore gas platform. We recently drained the entire glycol system (due to solids plugging, suspected carbon from the activated carbon filter). We also took sample of the solids and sent for lab analysis. Analysis found that the main constituent was iron. I did a google search and found website below, which says "The typical contaminant is iron oxide which is formed in the circulating glycol system".

My question is, how could iron formed inside TEG glycol? TEG consists of carbon, hydrogen and oxygen. There could be contaminants such as carbon from activated carbon filter, water (of course), possibly silicon from sand, salt, carbon dioxide from gas. But where does the iron come from? My pipings and vessels which the glycol is contained is made from carbon steel, is it suggesting that there could be iron constituents/atoms leaving these structures and react with glycol? I am not quite sure if this would happen, without the presence of oxygen to form rust.

Can anyone enlighten me how would iron be formed in the TEG?

http://www.pall.com/main/fuels-and-chemicals/glycol-dehydration-5597.page

 

[SNORGY]

My initial suspicion is that the glycol is picking up the iron oxide or mill scale that might be being dislodged and carried by the process gas stream into the dehydrator contactor. Not sure if your contactor is packed or trayed but in any event I would suspect that the contaminant is being entrained by, rather than formed within, the glycol stream, and that the "rust" is forming on the gas side of the process, finally being picked up in the filters.

 

[SJones]

Acid gases will dissolve in the glycol which, as you note, contains water. In addition, the breakdown products of glycol are acidic. It does not then become too hard to see how iron from a carbon steel system ends up in the glycol by reaction with the acids. If inspection results show some metal loss that will also help you to firm up where the iron is coming from.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[SNORGY]

Steve:

Just to enlighten me a bit, since I am not knowledgeable in this area...

If the OP is running a dehydrator with nearly pure TEG, for example, i.e., not a binary solution of TEG + water, will there be water in the glycol? I am thinking that the water, if present, is being picked up by the glycol from the gas stream, and that the corrosion (rust) is on the gas side of the process.

The rationale that the breakdown products of the glycol are acidic, that much I can accept.

 

[SJones]

The system might originate with reasonably pure glycol, but as soon as it starts to do its job, i.e. dehydration, it collects water. That's why it goes to regeneration from the bottom of the contactor: to be continuously recycled. The recycled 'lean' glycol will still retain a small amount of water, so it's never 100%. If the water loaded, 'rich' glycol runs through carbon steel, it will pick up iron that will also circulate.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[SNORGY]

Thanks, Steve.

I was aware that the rich glycol will have water in it. I just had not realized that (or I have not been exposed to processes in which) the service was especially corrosive in a dehydrator.

Probably haven't done enough acid gas dehydrators in my time.

There have been other discussions of this point in these fora similar to the one attached.

thread338-241467