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Offline chil

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triethylene glycol
« on: August 17, 2007, 04:56:09 PM »
Greetings,
I am needing some information about removing entrained hydrocarbons from glycol used in the dehydration of a natural gas stream. My research has failed to produce answers. Will filtration and activated carbon remove the hydrocarbons and surfactants? What about inadvertently lowering the PH with the carbon? Or is some type of distillation devise needed to remove the hydrocarbons? Thanks for any help.
Chil

Offline eugenedakin

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Re: triethylene glycol
« Reply #1 on: August 19, 2007, 09:44:03 PM »
Hello chil,

Filtration with activated carbon will remove 'some' hydrocarbons from the dehydrator (TEG).  If you are trying to remove more than 0.1% hydrocarbon content from the glycol with activated carbon, your going to be more expensive (and inefficient) than what it would take to remove the current TEG and replenish it with virgin TEG.

Carbon will lower the pH ever so slightly:  Meaning, if you are at a pH of 10, your pH will go down to 9.9.  You should have a high enough concentration of buffers (usually in the form of corrosion inhibitors) to buffer this action.

A very small skimmer in a seperator will usually remove larger amounts of hydrocarbons.  If you have this large of problems with hydrocarbons, this means that 'something' upstream needs to be changed to prevent this contamination from occuring in the first place (aka: knockout drum or earlier in the process).

I hope this helps,

Sincerely,

Eugene
There are 10 kinds of people in this world: Those who understand binary, and those that do not.

Offline JoeWong

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Re: triethylene glycol
« Reply #2 on: August 20, 2007, 05:53:57 AM »
Hi chil,

You may try Solvent Enhanced Stripping method (typically DRIZO technology) to reduce HC in TEG. Also you may think of lower operating pressure in the column couple with dry gas stripping to reduce the HC partial pressure in TEG (make it volatile) and hence remove HC in TEG.

The "carbon" in your earlier post, do you mean "carbon dioxide" ?

HTP

JoeWong :)
Best regards,

JoeWong

Offline chil

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Re: triethylene glycol
« Reply #3 on: August 20, 2007, 09:47:43 AM »
Eugene,
Thanks, at this point the TEG gets so saturated with hydrocarbons that it becomes ineffective and will not absorb water from the gas stream. I am trying to filter out the hydrocarbons using several different filter housings with different cartridges and then go into an activated carbon bed for a final absorption of the remaining hydrocarbons and surfactants. Has sodium chloride build up ever been a problem as well in a TEG system? I have never had a problem but in my research it was mentioned several times. I suppose that I could remove that with a zinc anode. Thanks Joe I look up this DRIZO technology.

Offline eugenedakin

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Re: triethylene glycol
« Reply #4 on: August 20, 2007, 09:28:19 PM »
Hi chil,

Sodium chloride (and any other neutralized inorganic salt) concentrations are an indicator of a very large problem that shows up as a excessive foaming.  Once the inorganic salt concentration achieves a certain level, you can lose your TEG out the top of the contactor due to foaming. 

Foaming doesnt limit itself to the contactor, and can also have nasty effects when removing water at the reboiler.  Similarly, excessive foaming can cause TEG to be lost.

I hope this helps.

Sincerely,

Eugene

There are 10 kinds of people in this world: Those who understand binary, and those that do not.

Offline JoeWong

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Re: triethylene glycol
« Reply #5 on: August 20, 2007, 11:13:42 PM »
Hi Chil,

Salt accumulation is one of nasty problem in reboiler. It formed thick scale and decrease heat transfer drastically. This also caused high skin temperature which probably will degrade the TEG faster.

High concentration of salt may increase corrosion.



JoeWong
Best regards,

JoeWong

Offline chil

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Re: triethylene glycol
« Reply #6 on: August 21, 2007, 03:06:21 PM »
Thanks for the nfo. What are your thoughts on putting a Zinc anode inthe system for cathodic protection?

Offline JoeWong

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Re: triethylene glycol
« Reply #7 on: August 21, 2007, 09:14:11 PM »
chil,
CP is a system for reducing, but not stopping corrosion.

Your proposal of NACl removal "I suppose that I could remove that with a zinc anode.", theoretically it works. From kinetic, cost and installation perspective, might be discourage people doing so. Since you are doing research, might be a topic.

Good luck.

JoeWong

Best regards,

JoeWong

Offline eugenedakin

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Re: triethylene glycol
« Reply #8 on: August 22, 2007, 06:38:27 PM »
Hi chil,

Although I have never seen a zinc anode in a dehydration system in 13 years, Joe Wong has a good point.

Best wishes,

Eugene
There are 10 kinds of people in this world: Those who understand binary, and those that do not.

Offline chil

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Re: triethylene glycol
« Reply #9 on: August 23, 2007, 07:12:46 PM »
Thank you gentlemen for the ideas. Since I am a manufacturer, I will add an anode to the system and see how it works. If anything just to see what happens and let the unit run for a while. Some times field testing is the best way to see working results.
Chil

Offline technologist

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Re: triethylene glycol
« Reply #10 on: August 27, 2007, 06:06:30 AM »
Dear Chil
Can you spell out your process first bcoz sometimes it may be better to change the system rather than solving its problems.
With TEG you have to face many problems - we know this as a manufacturer of MEG / DEG & TEG and other solvents.


Offline chil

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Re: triethylene glycol
« Reply #11 on: August 30, 2007, 12:17:08 PM »
The system is a glycol dehydration unit on a natural gas station (plant). The gas in this particular area is very dirty and it doesn't help that the operators never change the filtration elements like they should.
In designing a filtration unit to clean up the hydrocarbons in the system several of the discussed issues have arisen. What is the opinion on chilling the Glycol to below 100 DEG F to facilitate the removal of hydrocarbons from the TEG.
Thank
Chil

Offline technologist

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Re: triethylene glycol
« Reply #12 on: August 31, 2007, 01:15:51 AM »
Dear Chill,

The selection of a solvent system for dehydration that too any glycol is not on my usual choice list.

I could have considered water wash for salt & dirt removal and then sieve dehydration, which is also a usual practice in this industry. U can refer http://naturalgas.org.

If U still want to use TEG for dehydration, put a washer upstream of absorber for separating out dirt, oil & salts and then use TEG absorption. This will also avoid degradation of TEG & hence its losses (TEG due to degradation) can be reduced.

Also after absorber use some preheating & then flash for removing most of the HC first then go for conventional stripping. This way u can recover HC from flash vessel top and reduce load on stripper.

Ma be U need to reowrk on main system




Offline Montemayor

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Re: Triethylene Glycol
« Reply #13 on: September 01, 2007, 12:13:37 AM »
Chil:

I’ve had what is considered ample experience in the design, modifications, startups, and operations of TEG natural gas dehydrating units.  I’m presently evaluating one such large unit.

What you describe in your original post can be addressed and resolved very simply.  Allow me to address each of your concerns in that first posting:

1. I am needing some information about removing entrained hydrocarbons from glycol used in the dehydration of a natural gas stream.  My research has failed to produce answers.
The resolution to entrained hydrocarbons entering the TEG Contactor (and the rest of the regeneration unit) is simple: entrainment of hydrocarbons is NOT ALLOWED and should be arrested prior to entering the contactor.  This is normally done with a properly designed 2 phase separator.  You cannot allow the hydrocarbons to enter the TEG system for obvious reasons that you are now experiencing.  Why you have allowed this to happen is a good question.  The reason you can’t find any information on how to combat and remove them AFTER you’ve allowed contamination is simple: sucessful operators don’t allow this to happen.  In those cases where you might get some contamination and/or slugs, you should have skimming capabilities within your TEG Flash Vessel – which is upstream of the TEG Stripper/Reboiler.  How to design this Flash Vessel is described in the GPSA Engineering Databook – which I presume you have a copy of.  If you don’t have a copy, you should buy one and study it diligently.

2. Will filtration and activated carbon remove the hydrocarbons and surfactants?
The Activated Carbon Adsorber and the Sock Filter are items that are there to remove trace quantities of impurities in the circulated TEG.  These will not have the capability of removing the quantities that you describe.  Where does the “surfactants” come from and how do they appear in the TEG?  I have always succeeded in running trouble-free TEG units and one of the main reasons for that is that I never, never add anything other than TEG to my circulating absorbent.  When you add inhibitors and/or other little tidbits of other chemicals to the TEG you are asking for trouble – and you usually get it right away, BIG time.

3. What about inadvertently lowering the PH with the carbon?
What about it?  If you are saying that the Activated Carbon lowers the pH of the TEG, then you are absolutely wrong.  You definitely don’t want to run a low pH TEG within the system.  This will start and propagate corrosion problems.  One way to fight this is to use the Activated Carbon adsorbers to remove the acidic compounds formed (usually by oxygen in the system).  Once the pH is lowered, then you are almost forced to add Borax (or something similar) to the TEG and break my “golden rule” of never adding anything else to the TEG.  This is a bad operating situation that you want to avoid and you certainly don’t need.

4. Or is some type of distillation devise needed to remove the hydrocarbons?
No.  The removal of significant liquid hydrocarbons is done by the skimmer compartment within the TEG Flash Vessel.  You mention “dirty” gas, but you don’t quantify or qualify the “dirt” in the gas.  Nor do you explain how and where the gas got “dirty”.  That is the place to start in resolving your operating problems.  Attack and eliminate the SOURCE of the problem – not the effects of the problem.

Additionally, some of the information and ideas you are now throwing out simply do not make good sense.  You should know that the temperature of the Lean TEG entering the contactor should be approximately 10 oF higher than the gas entering the same contactor.  This is to avoid condensing some of the heavier hydrocarbons in the contactor.  Your idea on the cathodic protection is another similar idea that probably won’t work.  You are, once again, avoiding to attack and eliminate the SOURCE of the problem and only attacking the effects. 

You also are asking about salt contamination.  Do you, or do you not have salt contamination.  If you do, then you should apply the universal engineering “K.I.S.S.” rule:  attack and eliminate the source of the problem.  Otherwise you are in for some very bad and costly engineering experiences that won’t look very good in your resume.

Some excellent sources of information and data on the design and operation of TEG units that I recommend is found in the GPSA Engineering Databook, John Campbell’s excellent series on Hydrocarbon processing, and in the papers published by the Laurance Reid Gas Conditioning Conferences at the University of Oklahoma.  These should all be required reading for anyone related to designing or operating a natural gas dehydration unit.  You can obtain the Laurance Reid GCC papers in CD format.

Contrary to what technologist is advising you (“With TEG you have to face many problems”), there are NO extraordinary problems involved in operating a TEG dehydration unit.  Hell, there are probably tens of thousands presently drying natural gas out in the world today.  Most of these units are in totally remote and harsh “Oil Patch” locations and receive little or no attention.  There is a BIG difference between producing TEG and operating successful and effective field TEG dehydration units.  Compared with most other processes, TEG operations are a piece of cake – if designed and maintained properly.  That is well-known engineering fact and not just theory or conjecture.

Basically, your problems (as you describe them) are the result of BAD HOUSEKEEPING.  Clean up your act (& your gas) and you will eliminate practically all your headaches.

I hope this experience helps out.


« Last Edit: September 01, 2007, 09:50:30 AM by Montemayor »

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