Absorption Column - Wet Insulation 1

[fmanzanilla]

Hey guys, I thought I may pick your brains on this sticky issue.

Background: 19 m tall, 2 m ID, insulated trayed column. Operates at a steady -70 degC with rare trips to -10 degC. A couple of months ago ice started forming around several locations of the column and associated piping. This has created a hazard, as we're having chunks of ice falling, plus a slightly increased susceptibility to CUI. Documentation is not too great, and we're not a 100% sure of the insulation material, we believe it to be Polyurethane foam. Everyone pretty much agrees that the insulation got wet somehow, and the ice pattern does suggest that hypothesis (spreading like water would do from the top of the column), although the insulation cladding seems undamaged at the top.

Site is keen on stripping the whole thing and replace all the lagging. For process reasons this requires a plant shutdown, and this would be a very long and costly one.

What I'm suggesting instead is the following:

1) Strip lagging at selected location (accessible from existing platforms) to check for CUI.
2) Remove insulation from the top of the column and
3?) Dry the insulation somehow? Could we pump hot N2 in there and dry it? Does any of you have experience with such a thing? Feasibility?
4) Re-lag, re-seal top of the column.
5) Are there any extra barriers we could install to prevent future water ingress?

Your opinions are greatly appreciated.

-Francisco

 

[EmmanuelTop]

On-line drying of the insulation won't help, in my opinion. It looks like there is continuous ingress of atmospheric air (moisture) and/or migration of cold from the process through the insulation layer. That suggests inconsistent or damaged insulation, or process leaks (not very likely). Furthermore, once the water freezes inside the insulation, it damages the insulation structure as water expands from liquid to solid state. So the problem might get worse by time.

There is no way one can push Nitrogen through polyurethane foam. What you described is commonly applied for full containment tanks and cold boxes in cryogenic service, where continuous Nitrogen purge is employed through Perlite insulation for the same reason. But the expanded Perlite is designed to allow for purging (flakes).

I'm not an expert on insulation but Polyurethane foam doesn't sound like the best solution for cryogenic equipment and piping operating at -70C. I see on some manufacturer's websites that it is not recommended below -22F (-30C), although some others quote working temperatures down to -150C. See

http://www.wbdg.org/design/midg_materials.php#ppgim

and

http://www.insulation.org/articles/article.cfm?id=IO081101

and

http://www.aaamsa.co.za/images/Technical Publications/TIASA/Handbook Chapter1.pdf

You should definitely try to locate damaged sections of the insulation and replace/repair them, to prevent further escalation. On the long run, consult with insulation specialist to see if it is better to use different type of insulation.





Dejan IVANOVIC
Process Engineer, MSChE

 

[StoneCold]

I have seen some problems with a system we used to have that ran at -40C. The insulation was a polyurethane foam. The cells of the foam filled up over time with atmospheric moisture and the insulation became ineffective. The thing about foams is there are open cell and closed cell foams. You want to install closed cell foams as they have much lower ingress of water. Most foams have a water absorption spec on their data sheet. Even with the closed cell it is best if you can seal the outside with a vapor barrier, then lagging over the top. We have had pretty good luck with an insulation called Trymer it is a polyisocyanurate. We experimented with heating the saturated polyurethane foam and trying to dry it out. We did not have any success. Even weeks of the unit being down and just letting it naturally evaporate had very little effect. We eventually abandoned the piping system that it was used on.

Regards
StoneCold

 

[georgeverghese]

Another reason for this ice formation (outside of the lagging) may be some instrumentation tubing compression fitting ( buried in the insulation) that may be leaking?

 

[SJones]

If it's any help, the likelihood of CUI is very low at those continuous operating temperatures. Personally, I have found the most comprehensive insulation specification to be that of the Dutch CINI.

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.

 

[EmmanuelTop]

For that money (1,390 EUR) it better be good

Dejan IVANOVIC
Process Engineer, MSChE

 

[fmanzanilla]

Thanks for the replies. Useful stuff.

* Okay, so it seems that drying the insulation is a long shot - and yes, you've made a good point, even if dried, the insulation would still be damaged, at least where the ice is.

* I'm not too worried about CUI, still have to do my due diligence and inspect it.

* A leak is highly unlikely, this column handles a C1-C2 mix at 4 MPa, if that was the case the ice would 'radiate' from a single point and would creep up. We do have leak sniffing campaigns, I don't know how effective they actually are though.

 

[georgeverghese]

If you remove a small section of insulation for repair while this cold section demethaniser is still running, within minutes a thick layer of solid ice would cover the exposed section.