Hydrocarbons in TEG regeneration unit 1

[atayto]

I'm working with glycol dehydration units and we have some problems. This TEG absorber units are installed on oil production platforms. I would like to describe one of this units but there are four another unit with the same problems but operating parameters are slightly different. This unit was designed to handle 320mmscfd of gas and product gas should have water content less than 4lb/mmscf(80ppmw or -12 degrees Celcius at pipeline pressure). Design pressure was 58.5barg and temperature was 35 degrees celcius. Gas temperature is controlled by gas cooler which cools gas from 45 degrees to 35 degrees. In purpose to increase oil production all gas hanling system pressure was reduced to 52.5barg. Gas water content is in spec(there are a lot of debate around reliability of moisture analizers but i thnk that tey are OK). Unit operates at design rate but we experienced one problem. Glycol regeneration unit is just ordinar(standart or simple) unit with stripper after reboiler and performance of this unit is OK. It regenerates glycol to design 99.3% of pure glycol. BUT WE HAVE GOT HYDROCARBONS ALL AROUND GLYCOL REGENERATION UNIT. FOAMING IN FLASH DRUM BECAME VERY EXECIVE. I understand pressure reduction decreased contactor and contactor inlet scubber capacitywhich leads to liquid carry over from inlet scubber to contactor and glycol contamination. Also pressure rediction increased amount heavier hydrocarbons in gas. We tried to reduce temperature to 30 degrees but it didnt helped. Can anybody advise what can I do to prevent foaming and glycol contamination.

 

[dcasto]

As you lower the pressure and temperature, you certainly will increase the liquid hydrocarbons and most likely above the separation equipments ability to remove. Plus at lower pressure and the same standard volume, the velocities increase in the separation equipment.

The most common problem is where the TEG going to the contactor is cooler than the gas. That's an easy check.

More often I see this situation and one of the best fixes is to have a coalessing filter separator ahead of the glycol contactor and just a few feet away from the contactor. In some cases I even recommend cooling the gas to 30 C go through the separation equipment, then heat the gas to 35 C.

 

[atayto]

Glycol temperature entering contactor is 7 degrees higher than the inlet gas temperature(differential temperature control). Dont know about glycol temperature on outlet of contactor. The contactor has skimming bucket. All hydrocarbons is being skimmed from the top of glycol. Only one question why hydrocarbons go with glycol from the bottom of contactor. I assume emultion is being formed in contactor bottom. The lower glycol temperature the higher glycol viscosity and more tendention to form emultion.I would like to increase inlet gas temperature frm 35 to 38 degrees and increase differential temperature from 7 degrees to 9 degrees. this will reduce viscosity of glycol, keep heavier hydrocarbons in gas phaze and alsoreduce solubility of gas in a glycol.

What do you think?

What kind of coalescing filter separator would you advise?Where can i find them? It looks like good idea!

Thanks for your responce. really would like to communicate this issue with more experienced than me person.

 

[tickle]

Do you have a carbon filter on the system? If so does it need recharging?

 

[atayto]

Yes we have carbon filters in a line. Filter elements are changed every 6 month. But it doesnt help.

 

[dcasto]

the fact that you skim HC off in the contactor tells me that you will load up your TEG with hydrocarbons way more than a charcoal system can handle.

I've seen TEG contaminated so badly that upon analysis, it had 15% heavy HC built up in and there was know way to seperate it without vacuum distillation.

You need to remove the liquids before they get to the contactor and keep the gas warmer.

 

[atayto]

Dear Dcasto

One of our ideas was changing char coal filter more frequenly. But differential pressure across this filters never goes too high.It is within normal operating range specified by vendor. and also lean glycol samples doesnt show big concentration of HC.What is from your opinion or experience "normal" HC concentration in lean glycol. I assume even if char coal filters cant remove HC. then all of them will be evaporated in reboiler.

On our units flow through char coal filter varies from 20% to 25%. I assume this depends on pressure at which contactor is operating. But could you please explain it how to determine flow through char coal filter.

I spoke with several experts and didnt get straight away answer and undersood that this problem is quite common for TEG dehydration units. I really apreciate help if some body can share his/her experience around this problem.

Regards
Tarlan

 

[AggieCHEN04]

I recently heard a presentation about a similar operational problem on an offshore platform where the inlet separator had become blocked with sand and all the condensate was carrying over into the contactor. I tend to agree with Dcasto in that you should probably check out your inlet seperation/filtration prior to focusing on the glycol unit.

 

[dcasto]

anything more than say .o5% by weight HC in TEG will be an issue, but not always. I've seen as high as 15% very heavy HC's in TEG. The TEG foamed a lot and they had large losses. They recovered TEG in a filter sep down stream and on the flash gas before the flash gas went to fuel.

Every so offten the operator went offspec on water, but they lived with it instead of fixing the problem in a fashion similar to what I stated here.

Companies like Perry Equipment (PECO) have field representatives that can measure liquids in a mist phase to prove up what I predict. They and other vendors (qbjohnson, peerless, Porous Media) are all good at helping you with your situation.

 

[atayto]

Thanks dcasto

I thought that liquid carri over can be measured only with help on radioactive tracers. WE have a lot of nucleonic level transmitters on pltforms. Thats why i was suspesious about liquid measurement in a gas. But I contacted PECO and was surprised. Thanks again.

Regards
Tarlan