Ice formation tempreature 1

[MT47]

I must evaluate ice formation possibility in de-ethanizer tower.Could any one to help me to find ice formation tempreature in 18.7 kg/cm2g.I will be thanks.

 

[Zoobie]

Your question cannot be answered with the information that you have provided. First we need to understand what you mean by 'ice'. Water, hydrocarbons, and low temperatures and high pressures can make ice (solid water phase), hydrates (solid hydrocarbon and water), and even solid CO2 (under the right conditions but I doubt you will see these in a deethanizer).

To evaluate this possibility you will at least need some compositions (and some details around the tower would help). What is the water content? (As an example we have deethanizers that have water dew points in the feed that are -20F and some that are -100F or lower). What is the rest of the stuff? The mix of other materials will tell you what sort of hydrate formation potential you have. In a lot of cases you will form hydrates well before you form actual 'ice'.

 

[MT47]

Zoobie ,Thank you to response me.
My problem related to hydrate formation in low temp.( -12'c top of de-ethanizer tower).The plant feed is wet but two dryers(one work & one regeneration with 12hour cycle) and one moisutre analyzer had considered before tower .but If the dryer couldn't work true, there isn't any methanol injection facility for preventing of hydrate or freezing in top tray of tower .the main problem is :the bottom product of tower is routed to cold box(-45'c).
What could i done in this case?
thank you again.

 

[Zoobie]

I'm having a bit of trouble understanding the problem but I will try to provide as good an answer as I can. If I understand you correctly, you do not have a moisture analyzer currently. This may be cheap insurance depending on what lost production lost to thawing out would cost (or damage to equipment in extreme cases). The hardware for moisture analyzers is not that expensive. Another alternative is to periodically test the beds (still using a moisture analyzer) to make sure you that you have the right cycle time. Most vendors of adsorption media (mole sieve, etc.) should be able to do this testing for you...it might cost you a bit.

I don't think you need any sort of constant methanol injection but its nice to have a spot to put some in if necessary (this can be pumped in by hand if necessary if you got some breakthrough and didn't catch it in time).

If I understand your concern correctly, you are worried about possibly having a dryer bed problem that will freeze your tower. You ask what can you do? Fix the dryer problem. If you now have a hydrate you have two options: inject something or warm-up/depressurize.

I am having difficulty understanding your English so I can't provide much more useful information. Your first post indicated that you wanted to know under what conditions a hydrate would form. Your second post was concerned about what to do when your dryers don't work right.

By the way, what sort of plant is this? What kind of pressures are you operating at? Why are the tower bottoms being cooled?

 

[pmover]

Zoobie

you did a good job of understanding the grammar and hope this may further be of assistance.

i believe MT47 is saying that wet natural gas is entering the gas plant and passes through a set regeneration dryer beds before the demethanizer (1 bed in operation while other is going through a regen cycle of 12 hour duration). a moisture analyzer was considered for installing upstream of regen dryers, but not installed (MT47, please clarify/confirm). the upper tray in demethanizer is where freezing takes place.

i'm a little confused by the product to cold box as well.

will agree that a moisture analyzer might help in determining where the problem is (upstream/downsteam of regen). in fact, i recommend monitoring at both locations.

MT47,
please take a moment and confirm/clarify description.

Zoobie may be correct in that the regen system needs to be evaluated/investigated for proper operation.

good luck!
-pmover

 

[MT47]

Hi zoobie and pmover thank you and i am sorry i couldn't describe my problem.I have two problems.first,Hydrate formation or freezing on tray and second hydrate formation
in cold box.
pmover i confirm you that the wet feed is natural gas but the feed enter to De-ethanizer not De-methanizer.
Please assume that the dryer dosen't work true therefore the moisure analizer alarm has done.in that case what can i do?I don't prefer to plant shut down.
as you know the most of water(if moisture enter to tower)will be in bottom of de-etanizer tower.Whereas the bottom product should be cooled in cold box(Plate fine heat exchanger)and transfer to tie-in of the plant.

thank you

 

[dcasto]

If this is a typical gas plant, then the freezing will occur in the cold box as the gas is chilled feeding the deethanizer, so that is where you'd inject methanol during a dryer problem. By the way, most dryer problems are becuse of switching valve leaks.