1 reply to this topic

[paatz]

Hello everybody,

if anyone has expierence with TEG regeneration units i would be glad to get some information.

The company i work for plans to install a TEG gas dehydration plant. The Rich TEG is regenerated in the TEG regeneration unit, which should be heated by a fluegas/TEG heat exchanger (not direct fired). 3 of this TEG regeneration units are already installed at this plant. They all use flue gas of the combustion chamber (app. 800-900°C) which is quenched with air to appr. 400°C.
The manufacturer told me that our company is the only one that runs the process this way.

Has anyone experience with this process?
What to you think are the advantages/disadvantages of the use of quenched flue gas??

What i know:

400°C
pro: decomposition of TEG can be reduced
contra: larger heat exchanger area necessary, blower for "quench air" necessary

Thank you in advance.
(Sorry for my broken English)

L

[Art Montemayor]

Paatz:

I’ve had what I consider ample experience with TEG natural gas dehydration units. I’ve designed them, modified them, started them up, and operated them. I’m presently evaluating a 70 MMScfd unit for a major oil company involving the production of <2.5 lb water/MMScfd product gas at 1,800 psig. Those are some of my credentials.

I’ve mostly had to use direct-fired reboiler tube bundles (especially in oil patch units), although I’ve also employed thermal fluid and electric resistance elements to furnish the normal 400 ^oF reboiler temperature. I’ve never had to resort to using flue gas, although I’ve heard of others using it. 400 ^oC seems like a steep temperature to heat the TEG to a maximum of 205 ^oC (400 ^oF). As you probably know, you are pretty close to the acknowledged decomposition temperature of TEG, which is 210 ^oC (410 ^oF) when you operate your reboiler at 205 ^oC. Therefore, you have to be very careful to maintain a reboiler tube skin temperature below the approximately 410 – 415 ^oC limit. I wouldn’t go much higher on the skin temperature. You probably also have to apply a conservative reboiler bundle flux value – such as 8,000 Btu/hr-ft², or less. This probably gets very expensive in capital monies very quickly since flue gas has a notoriously bad convective film heat transfer coefficient. You may have to use a finned surface on the flue gas side to make up for the bad heat transfer there. This all has the tendency to make the reboiler unit very large when compared to an electric heated one, for example. But there is nothing wrong with the design concept – as long as it is the indicated, economic incentive to follow.

I don’t understand your writing in some of the above post. You seem to say that you “know” that 400 ^oC is the decomposition temperature of TEG. This, of course, is wrong.

You also seem to be stating that you can reduce the decomposition of TEG by heating with flue gas. Actually, you can reduce the decomposition of TEG by using a variety of other types of reboilers – including the direct-fired heater type. You do this by a variety of ways – some of which are explained in the GPSA Engineering Databook.

You don’t furnish any essential Basic Data (such as flow rates, product gas water content, TEG contactor pressure and temperature, designer/fabricator of your unit, reboiler bundle flux value, etc.) to make further comments, so this is all I think I can contribute for now.