16 replies to this topic

[Dmitry]

Hello all,

 

I am process engineer working on producrion facality in Ukraine. We are running standart TEG dehydration unit, which design for gas flow 15 MMSCFD of day at pressure 30 bar and gas temperature +25 deg. C. We are using TEG to get water dew point -15 deg. C.  After few month of running we get problems with water dew point, which is now is +2 deg. C and we found that 50 % of water from glycol sump tank is aromatic hydrocarbons like benzene, toluene, ethylbenzene, and xylene. Total flow from glycol sump tank is 300 lit/day. 50% is water and 50% is of liquid is hydrocarbons (aromatics) with SG 0.816-0.840.  The lean TEG now is 83% by mass so regeneration system does not work properly. This confirms with high water dew point +2 deg. C.

 

Initial gas compositions shows only C6+ components, so we do not know about it content in gas upstream TEG contactor. I want to make full gas analys soon.

 

As I see now we have a two problems:

1. High water dew point of gas +2 deg. C - due to bad quality of lean TEG

2. Condensate (aromatics) flow from sump tank 150 lit/day - due to aromatics in rich TEG.

 

I run model in Hysys and saw that about 50% of aromatics going with rich TEG from TEG contactor to regeneration and then with water vapours going to sump tank. So my model shows the same as real dehydration unit. Ideally it should be water only and very small amount of HC.

 

Please if you have any ideas what we can do with this issue

 

Ideally carbon filter should remove aromatics and glycol flash tank should separate it from TEG. Note that TEG lean flow is 15 lit/min, carbon filter designed for 6 lit/min and glycol flash tank is two phase vessel only. There is only provision for HC outlet and two level gauges.

 

Regards,

Dmitry

[Bobby Strain]

You must realize, too, that benzene is carconegenic. So you must be sure your workers are not unduly exposed. Some companies in the USA offer designs for the situation you have.

 

Bobby

Edited by Bobby Strain, 12 April 2014 - 09:14 AM.

[Zauberberg]

The unit appears to be choked with liquid Hydrocarbons, and some measures need to be taken as soon as possible to re-establish a clean and decontaminated glycol circuit. 83% TEG purity is dramatically low - you should be getting above 99% without stripping.

 

With such a low purity of lean TEG and massive presence of Aromatics, I would suspect very inefficient and contaminated Carbon filters. These should be inspected and probably replaced. Hydrocarbons should be drained (skimmed) from the flash drum, reboiler, and TEG surge drum. Perhaps even the Absorber and Regenerator columns could be fouled with Hydrocarbons or degradation products. Try to apply all possible measures that can be applied for an online Unit, and try to get rid off of as many problems as you can.

 

If the problem with liquid Hydrocarbons persists, there are solutions, as Bobby has mentioned. Combustion chamber can deal quite effectively with this type of problems, or you may consider recovery of Aromatic compounds.

[Dmitry]

You must realize, too, that benzene is carconegenic. So you must be sure your workers are not unduly exposed. Some companies in the USA offer designs for the situation you have.

 

Bobby

Hello,

 

Thanks, could you tell name of company ot type of process required for it? Are you talking about remove BTEX from gas upstream dehydration unit or remove BTEX on TEG regeneration?

 

Dmitry

[Bobby Strain]

Dmitry,

    Start here.  http://www.capp.ca/g...d=105760&DT=PDF

 

Bobby

[Zubair Exclaim]

Do you have a gas sweetening unit upstream .. ... do you have a water wash on top of it ....

is there any filter upstream of it .. if you do then these aromatics should not end up in dehydration unit..

[RockDock]

I don't see any mention of the reboiler duty or Temperature. I also don't see the operating pressure of the column. If you run the column at 0 psig and reboiler at 400 F, you should boil the water off the TEG. The aromatics will go with the water.

 

A full gas analysis is necessary, too. Also be sure to install a 3 phase separator upstream of the regenerator. I suspect you have non-aromatic hydrocarbons in the column. Unlike aromatics, they will build up over time.

[Dmitry]

Do you have a gas sweetening unit upstream .. ... do you have a water wash on top of it ....

is there any filter upstream of it .. if you do then these aromatics should not end up in dehydration unit..

Hello,

 

We have a three phase separator upstream dehydration unit to remove free liquids and integral separator in the bottom of dehydration column. 

 

Dmitry

[Dmitry]

I don't see any mention of the reboiler duty or Temperature. I also don't see the operating pressure of the column. If you run the column at 0 psig and reboiler at 400 F, you should boil the water off the TEG. The aromatics will go with the water.

 

A full gas analysis is necessary, too. Also be sure to install a 3 phase separator upstream of the regenerator. I suspect you have non-aromatic hydrocarbons in the column. Unlike aromatics, they will build up over time.

Thanks, I am waiting for the detail gas and TEG analysis. We have 3 phase flash tank upstream regenerator, but all aromatics going to regenerator so it's saturated with TEG I suppose

[RockDock]

What about the T and P?

[Dmitry]

What about the T and P?

Absorber - T=25 deg. C, P= 30 barg

TEG flsh tank - T=45 deg. C ,P=0,23 barg

TEG Reboiler - T=204 deg. C, P=1-2 psig

[Dmitry]

Dear all,

 

We have a carbon filter (charcoal filter) and solid filter in TEG regeneration skid. The purpose of carbon filter is to absorb trace heavy HC and TEG degradation producs. The design filter capacity is 6 l/min, total TEG design flow rate is 14 l/min. I see that carbon filter desighed for 40 % of full TEG flow and it's can not remove BTEX components from TEG just small amount of organics.

Do we need to pay attention on this filter? Can it absorb aromatics at all?

 

Dmitry

[breizh]

Dmitry ,

I guess you are talking adsorption not absorption ! It means that the filter has to be replaced before saturation or a desorption process should be in place to regenerate your charcoal .

my 2 cents

 

Breizh

[Dmitry]

Dmitry ,

I guess you are talking adsorption not absorption ! It means that the filter has to be replaced before saturation or a desorption process should be in place to regenerate your charcoal .

my 2 cents

 

Breizh

Yes, it's correct!

[narendrasony]

What about the T and P?

Absorber - T=25 deg. C, P= 30 barg
TEG flsh tank - T=45 deg. C ,P=0,23 barg
TEG Reboiler - T=204 deg. C, P=1-2 psig

I think TEG reboiler pressure (1-2 psig or 27-55 in WC) should be reduced to as low as possible to improve reboiler performance. Apart from the charcoal filter performance and HC skimming, TEG temperature to absorber should be checked to avoid further HC build up in TEG.

Regards
Narendra

[RockDock]

Process wise (I am not an expert on filtration), everything sounds okay. My last thought is perhaps the the condenser is running at too low of a temperature, condensing too much water and hydrocarbon.

 

Earlier you mentioned that the hysys model showed 50% of the aromatics went with the rich TEG and then out in the water vapor. You also said that matched your plant data. However, I also understand that from the discussion, the aromatics build up in the TEG, not exiting with the water vapor as expected.  That to me shows the data does not match the simulation. Do you mind posting the H&M balance? I will generate a model, too.

[Dmitry]

Dear!

 

Problem with gas dehydration was solving installation of dew point unit and using MEG for inhibitor. Gas contactor is off line now. Many thanks for your replies.

 

Regards,

Dmitry