Material Selection on TEG (Glycol) Dehydrators 1

[Shooze]

I am trying to determine what type of material to select for the design of a TEG dehydrator.

The dehy will be used to strip the H20 from the gas stream.

My gas composition is mostly gas (mostly methane) with 20% of the stream being C02. The temperature in my contactor tower is 100 degrees F and the operating at pressure 400 psig

The 20% CO2 worries me. As of now my whole system is design with carbon steel (SA-516-70N). My question are as follows:

1. Will carbon steel be adequate in this enviornment?
2. Should I consider using SS for the tower internals (ie: the contacting tray, bubble cap trays)
3. Will there be any corrosion issue in my glycol reboiler?
4 Is there any specific codes that would make a decision?

Any suggestions would be appreciated.

Thanks!

 

[ash9144]

CS won't survive that environment. Wet CO2 will make weak acid and corrode any CS components.

I wouldn't think there would be enough CO2 at the reboiler to cause issues but check your design to see what the CO2 distribution looks like in the stripper.

As for any codes to make the decision. No that is why they have engineers.

 

[Shooze]

Thanks Ash9144,

I stated question 4 incorrectly.

Should state the following:

4. Is there any codes that I can reference to help in the decision making.

 

[SJones]

No codes - only bitter experience.

1.
CS will only be adequate where lean glycol is predominant. In the contactor, this means above the lower tray or just above the structured packing. Below these limits, many operators have found that cladding with 316L is required probably owing to the high turbulence in the rich glycol at the bottom. The top portion can be in carbon steel with a suitable corrosion allowance.

2.
Most definitely

3.
Oh yes - this is the nastiest place with high temperatures and condensing acids. The still column should be 316L and then one may as well go the whole hog and have the reboiler vessel clad too.

4.
No public domain materials selection code exists for GDUs.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[strider6]

glycol is a "corrosion inhibitor" vs CO2 corrosion, in the Dewaard model there is a factor that account for this effect, but this is used when you have a pipeline or similar equipment.
In the dehydration column is not possibile to account for the inhibition of glycol, and usually the internal surface is clad with SS up to the injection of glycol.

S

Corrosion Prevention & Corrosion Control

 

[dcasto]

I've seen 316 SS TEG reboilers built when the natural gas stream was as low as 5% CO2 and 500 ppm H2S in the treated gas. Normally, a plain carbon steel reboiler is used, but the SS was specified for an off shore system because of the cost to replace the reboiler every 10 to 15 years due to corrosion offshore outweights the up front costs.

 

[tproquip]

I would recommend using stainless thru the flash tank. After this point C.S. should be adequate except for the still column. I would use stainless internals on both the contactor and still. A contactor whose upper section is c.s. may be worth looking into if the contactor is very large in diameter or very high pressure.