Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
(OP)
Facing a new challenge: We have vertical heat exchangers with 1" tubes (SS316)using turbulators. Overheating of our solvent causes coke deposits inside the tubes which we normally can remove by hydro jetting (heat exchangers without turbulators). However, the turbulators stuck inside the tubes and can not be removed mechanically by pulling or trying to knock with hammer. Chemical cleaning (caustic soda, hydrochloic acid etc. does not work either. We now are pulling the bundle to be able to submerge it in any suitable chemical bath or apply other mech. ways to remove turbulators. Any advise on:
1. chemicals that can soften the coke?
2. Mech way like shock cooling with liquid N2 or vibration? Shock cooling might cause unallowable stress in tube sheet as many tubes are totally blocked, others have only loose partice inside and fluid still can pass through tubes.
Pics attached.
Thanks for any advise
1. chemicals that can soften the coke?
2. Mech way like shock cooling with liquid N2 or vibration? Shock cooling might cause unallowable stress in tube sheet as many tubes are totally blocked, others have only loose partice inside and fluid still can pass through tubes.
Pics attached.
Thanks for any advise
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
There are a bunch of solvents that I have seen used, but it really depends on your coke.
There are consultants that work with nothing other than coke (Dr. Coke in Houston) and it sounds like you need to hire one of them.
OR, just rod or drill them out and trash the turbulators, then pressure blast clean.
The only real concern is will you damage tube.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
Do you have any link to Dr. Coke? Cant find it in google.
Thanks in advance
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
We used a low pressure water cleaning (5-6,000 psi) lance to de-coke our heat exchangers (not oil/gas application, but still had coking on HXs). I am not aware of any chemical cleaning solution that will dissolve, or even soften, coke. It seems the only options are mechanical cleaning via pigs (not an option here), water jet cutting (maybe?), and spalling via thermal shock (not great for tube/tubesheet longevity). The only chemical means of removing carbonaceous deposits would be, as others have said, reacting off with oxygen in an oven.
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
I will try using the service of a third party contractor operating High pressure cleaning , let say 1200 bars unit!
Hope this is helping you.
Pierre
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
https://www.atlascopco.com/en-sg/rental/products/s...
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
The removal was extremely difficult due to availability and support here in Batam island. Covid19 did its part by limiting access of equipment and manpower. Anyway, we removed the bundles and heated the tubes up to 350 Deg C in a furnace (electr heated). It took total 2.5 weeks to remove most of the 1282 (2 x 641) pcs. The heating up had the following advantages but still it required other methods:
1. Heating reduced the viscosity of the residue (basically asphalt). The residue became low viscose and ran out of many tubes. However, the turbulators were like cemented into the tubes. Pulling was still impossible- twisted tapes were torn apart.
2. The heat exchanger maufacturer (not experienced in cleaning such tubes - and not the original manufacturer)used air lances to blow the tubes. This resulted in vaporizing the residue but also ignited the coke inside with the negative side effect of sparks flying out and therefore high temperature impact on the tube material. I was worried that we burn the tubes, which at the end did happen. We found 9 leaks and have to plug those. Still the removal was very difficult, we even had to use forklift to pull.
After 2.5 weeks we had all pieces removed with the result of currently 9 leaks and 16 tubes where rests of burned turbulators remain inside (melted and torn apart).
3. We did hydro jetting 15000 psi to remove coke and it works well.
So here is my current challenge, where I would like to get your feedback.
1. These 16 tubes with remaining parts of the melted turbulators might have damaged wall thickness (SS316L 25.4mm x 2 mm). We cannot meassure it as the tubes are not accessible. Hydro test 1.1 x design can only be done when installed in the shell as we do not have any test rings. This is no issue as long there are no new leaks coming up. It would require to remove the bundles again from the structure 30m high etc. Time consuming job under the current situation.
Question: Should we plug these 16 tubes too, where the turbulators were burnt to avoid possible leaks? I learnt that you have to drill a hole into the tubes, which are not leaking but have to be plugged. Drilling is also not possible. The reduced heating surface is not an issue for the capacity. But leaking thermal oil 275 Deg C in our product is something we must avoid.
I have uploaded some pics and videos if someone is interested to see the process of removal. It shows the heating furnace in operation, the pulling of turbulators, heat colours on the tubes, deformed tubes, hydro jetting and some damaged baffle plates due to quality issues during assembly of the heat exchangers)
Download link available until 04/08/20: https://we.tl/t-TqO4X52xvo
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
In the meanwhile, try to get a new HX:
a)Designed and procured with no turbulators
b)Generous tube side fouling factor
c)Low tube side dp in the unfouled design case, which will allow for dp creeping upward when the tubes coke up and still manage to keep hot oil flow at design rate
d)Which has a lower tube ID skin temperature when in operation
e)Much preferably a HX that can operate with lower hot oil feed temperature to reduce coking risk.
f)Mechanical cleaning of the tubeside should be made possible
This will surely be a HX which may most likely need a larger / longer footprint. And also find out what other operational and design improvements need to done to prevent this incident from recurring.
If there is a small tube leak when this damaged HX is returned to service, how will you detect it soon enough to prevent asphalt contamination with hot oil? Low level alarm in the hot oil expansion drum? Is there also a risk of reverse flow of asphalt into hot oil through a leaking tube during some operational upset?
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
Do you have room to go parallel?
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
good luck
luis
RE: Removing turbulators from heat exchanger tubes after overheated solvent formed coke residue inside
It all started with operational issues. Hx was heated but process fluid stopped so the solvent degraded and formed coke. Cleaning was not possible since the turbulator had to be removed which was the major issue and took 3 weeks. So we will no longer use turbulators as the design capacity is still enough. Right now both hx are running well but we will need to replace the bundles.