[r.nowshadi]

Hello
what is the specification of activated carbon for glycol purification in natural gas dehydration packages.
Best Regard
r.nowshadi

[eugenedakin]

Hello r.nowshadi,

The specification is actually dependant on the tests you or your service company has.   

You are correct in assuming that activated carbon is different. 

The reasons that there are no common specifications are because the:
1) activated carbon hydrophobic properties depend on the base material in which the activated carbon was created
2) temperature at which the carbon was activated changes it efficiency
3) type of hydrocarbon contamination removed is different for each type of activated carbon
4) time in which the hydrocarbon is exposed to the activated carbon (usually, more time at a slower speed is better)
5) surface and subsurface area of the particles is related to the active longevity of the activated carbon
6) pH of the TEG fluid
7) .. and there may be other factors that I cant determine at the moment.

Its a great question, but unfortunately, the answer is fairly long.

I wish you the best,

Eugene

[Montemayor]

Nowshadi:

The specifications for the Activated Carbon employed in cleaning up impurities in TEG and other glycol streams depends entirely on what it is that you are proposing to adsorb.  Finding out which Activated Carbon type is the correct one is analogous to getting rid of a specific pest in your home.  If you have roaches you want to get rid of, you go to the seller of pest poisons and ask for a roach poison.  You don’t just inquire for a general poison.  There is no such thing.  Any adsorbent depends on van der Waal type of forces to adhere specific molecule diameters to its extended surface.  The degree and type of activation imposed on the adsorbent (Carbon, in this case) depends on a variety of factors – including the source of the original base carbon material.

You didn’t ask the correct question: how does an engineer identify and order the correct type of activated carbon?  The answer is very simply one of requesting the proper type of carbon from your supplier.  Identifying the correct activated carbon is definitely not an analytical problem.  The Unit Operation of Adsorption still lingers in the Empirical World – i.e., the answers to a lot of the problems involving adsorption depend on field or experimental results.  If it works for others out in the field, it will work for you.  And it is the activated carbon manufacturer who has a database for the correct applications of his/her product.  Explain your application in detail to your supplier and you will probably find that several recommendations may be made as to the correct type of carbon.  Sometimes you may wind up doing the field experiment as to the correct carbon for the desired results.  This is the way I have applied a lot of the activated carbon beds I have employed in the past.  I have used activated carbon to clean up glycols, amines, gases, odors, etc., etc..  Barnaby – Cheney is one brand name that I recall as always supplying good, quality product.

If you are employing activated carbon to purify TEG in natural gas dehydration units, then I want to stress one outstanding point related to this application.  The activated carbon employed in glycol dehydration units has never been intended nor expected to adsorb hydrocarbon liquids (or gases) from the glycol being recirculated.  To expect that you could selectively adsorb hydrocarbon liquids entrained in the glycol through the glycol contactor would be to require a huge size of adsorber and this simply is not practical – and much less economically feasible.  If you have problems with accumulated hydrocarbon liquids in your glycol system, then your problem is one of doing serious “housecleaning” and arresting the source of the hydrocarbon liquid entrainment upstream of the TEG contactor.  The way that hydrocarbon liquids are routinely removed from glycol streams in dehydration units is that the glycol Flash Tank is designed and operated as a 3-phase separator (2 liquid phases and 1 gaseous phase) where the hydrocarbon liquid phase is drained (“skimmed”) away.

Rather, the activated carbon is expected to selectively adsorb those corrosive compounds formed by the decomposition of the glycol when it goes through temperature “excursions” in excess of the approximate 410 ^oF decomposition temperature (in the case of TEG).  This is a characteristic need for units using TEG because their reboilers – most of which are direct-fired – are usually operated at 400 ^oF – relatively close to the decomposition temperature.  The presence of oxygen is also detrimental to glycol and causes it to form undesirable compounds.  That’s why all stored TEG and other glycols should always be kept under a dry, inert gas blanket 100% of the time.

If you are going to use activated carbon adsorbers for TEG, then also install a “sock” filter downstream of the adsorber in order to filter and retain the fine carbon dust that is always a by-product of handling activated carbon.  This dust will form a sludge and generally play havoc with your instruments and equipment – especially if you are using plate heat exchangers for the glycol.

I hope this experience helps out.

[chil]

Nowshadi,
I can tell you from practical on the job experience that activated carbon will work in the process of cleaning up a natural gas dehy unit. There are only a few good suppliers of activated carbon used for glycol. Coastal Chemical is a brand that I use which is pelletized therefore greatly reducing the problems with other types of carbon measured in mesh sizes. Because you better believe that it will go down stream and get into your pump. I recently built a glycol reclaimer skid to be used on dehy units employing as one of the processes, activated carbon. The glycol came in black from entrained hydrocarbons and left the unit clear. So, in essence a good supplier can tell you which carbon they make will meet your needs, I prefer bulk pelletized, and carbon will work, but don't try to run more than 1-2 gallons per minute per 30 pounds approx.