4 replies to this topic

[Chem_Proc_Eng]

Dear all;
I’m trying to review the design of our TEG dehydration system in the aim to troubleshoot it and to avoid the high TEG loses (daily consumption about 15 gallon). The first problem I faced is the working pressure. It is about 2030 psig (temperature is 120 °F). The GPSA notice at high pressure TEG can also be soluble in natural gas. Can this working pressure be a source of TEG loses?
Can anybody help me to more understand the phenomena and tell me the disadvantages to work in a very high pressure and to provide me with useful reference? (The common working pressure is 600 to 1400 psig)
I’ will be grateful if some can provide me with a rigorous design method?
Thanks in advance ^^

[Zauberberg]

See the article from BRE: http://www.bre.com/p...al Solvents.pdf

[ankur2061]

Chem_Proc_Eng

I understand that what you really mean is solubility of natural gas in TEG (gas solubility in liquid & not the other way around). GPSA indeed has a specific comment on solubility of gas in TEG. I quote verbatim:

TEG will typically absorb about 8.0 (10-3) Sm3 of sweet natural gas per liter of glycol at 6900 kPa (abs) and 38°C. Solubilities will be considerably higher if the gas contains significant amounts of CO2 and H2S.

Regards,
Ankur.

[MrShorty]

Unlike the other two, I'm going to assume that you might mean solubility of TEG in natural gas (certainly, if you meant something other than what we are assuming, please clarify), though I'm not sure I'd call it "solubility". I've heard the term "vapor phase enhancement" used to describe this phenomoneon.

Basically what we see is that the partial pressure of the solvent (TEG) increases as pressure increases. The vapor concentration (y) of TEG may decrease, but the partial pressure of TEG increases. One can kind of see this when you look at a conventional log(k) vs. log(p) plot. As pressure increases, K of the solvent decreases to a minimum, then increases until it reaches 1 where the mixture goes supercritical.

I don't have a reference for VLE data for TEG/CH4, and I can't say off hand if this explains all of the TEG losses -- you'll have to look at all the parameters in your process to see. But I can envision scenarios where the increased partial pressure leads to increased solvent losses.

[Art Montemayor]

Chem Proc Eng:

You state that your basic problem is excessive TEG losses in your natural gas dehydration unit. You should be experiencing approximately 1.0 lb of TEG consumed per 1,000,000 Scf of natural gas (standard conditions of 60 ^oF & 14.696 psia).

You infer that the relatively high pressure is to blame. That is not necessarily true.

You fail to give us any meaningful data to evaluate and comment on – with the exception of the operating pressure and temperature. For example, you don’t give:

• The natural gas capacity of the contactor(s);
• The TEG unit consumption of the unit (lb/MMScf or kg/Sm3) in a listing through its life;
• The designer/fabricator of the unit;
• What type of TEG reboiler do you have – direct fired or electric?
• A description of the Unit’s process (a PFD or sketch);
• The amount of time the unit has operated at the stated conditions;
• The TEG unit consumption of the unit when it was in operation the first year;
• When the TEG unit consumption began to increase – and whether it has fluctuated or how it has behaved with operating time;
• Any consultation from the designer/fabricator;
• If operating conditions have changed from the original design;
• What has been done to date to improve the excessive TEG consumption?
• Where has the “consumed” TEG showed up at – downstream of the contactor? How much have you been able to recover – if any?

If your original process design and fabrication is sound, you should not be having any TEG consumption problems. Excessive TEG make-up is experienced when:

• You have an inherently bad design and fabrication;
• You have bad operations;
• You have a bad maintenance operation.

For example:

• You should be operating the contactor with cool gas and cool TEG.
• You should have efficient vapor- liquid separation ahead of the contactor
• You should have efficient vapor disengagement space and mist elimination at the top of the TEG contactor.
• You should be operating your regeneration unit at optimum conditions and not emitting any TEG out of the Stripper Column.
• You should be achieving your design dewpoint with the rated amount of TEG circulation and with the design Lean TEG concentration.
• You should be controlling your pH level in your TEG.

There are much more points that are involved, but the above suffice for a start.
Await your reply.