10 replies to this topic

[gazepdapi1]

We have a TEG unit that we are installing that does not require a thermal oxidizer to burn off the effluet since the BTEX concentration is below the maximum we can vent. Since we can just vent to atmosphere, I was thinking of just having a pipe coming off the still going to atmosphere with a rain cap on it but I'm afraid during cold weather we will have a lot of condensate coming down the side of the still column as that vapor condenses as it's leaving the still column.

 

I was also thinking of just having a slanted pipe with one end pointing up for the vapor and the other end connected to a tank for condensate but I do not like this idea since I have to have a tank, pump, etc.

 

What has been your experience with this? Any help would be appreciated.

[Propacket]

Glycol still column top temperature can be controlled by a manual byapss across the reflux condenser (Between hot glycol to reflux condenser and cold glycol from reflux condenser). If you feel that the overheads temperature is coming down, just bypass hot glycol to send it to the cold glycol stream. This is the simplest option you can have.   

[gazepdapi1]

Yes but my goal is to keep the vapor temperature above 212 so I do not have excess water coming back down into the reboiler. The temperature you speak of is the temperature inside the still column but as soon as the vapor leaves the still, it will begin to drop below 212 and start condensing.

[Propacket]

Why do you think that a LOT of condensate will be coming down into the reboiler during winters. Is it based on calculations or just your guess?
Why do you want to maintain more than 212 degF temperature at top? You fear that, when water rich overheads at 212 degF make contact with colder ambient, water will condense and will come down to reboiler? Its not the way you are thinking.
When still column overhead gas discharges into ambient air, its disperses into air or gets depleted with air. It's dew point will decrease significantly. You can say the water which went out with overhead gas is part of air now. Shall it condense as you think?

[gazepdapi1]

No it's just a guess and I was looking for someone who does have a unit like this operating in cold weather and just venting the effluent to atmosphere. It just seems to be like there would be a lot of condensate (depending on how much water is being removed) coming down on top of the reboiler.

[Propacket]

How much "Cold" you are talking about? The company i am working for has supplied hundreds of TEG Dehy/Regeneration units in Canada where ambient temperature in Winters goes down to as low as -30 degF. These units are operating well and nothing happens like you are assuming.  

[gazepdapi1]

I was talking about -20F but thats good to hear that you don't have this issue. I just want to make sure this unit is designed well and now I have confirmation. Thank you for your help.

 

How do you typically pipe this vent? Just straight up with a rain cap or no?

[Okopo07]

I am new to operating in cold weather conditions. I am having problem with freezing of Glycol in the Surge tank and pipes downstream of the reboiler when the ambient temperature goes below 0F. How can i optimize the reboiler temperature to maintain a 80/20 glycol mix to keep it from freezing? Or do I need to build an housing with a flameless heater around the system to keep the system above 20F? I will take any extreme weather TEG dehydration operating advice!

[ColinR33]

You cannot adjust the reboiler temperature to prevent freezing in downstream equipment, you have to properly insulate the piping/equipment, and heat trace if necessary.  Also, is it an EG injection system or a TEG system?  Typically 80/20 is used for an EG injection/recovery system.

[Okopo07]

Thanks for the response, ColinR33. It is a TEG Dehydration system, and we have all the piping insulated but not heat traced. The major problem we are seeing is in the cold winter during start-up of the TEG unit. After a shut-down of more than 12 hours the lean glycol downstream of the TEG reboiler starts to freeze up in the line leading to issues with recirculation.

 

During shutdown, how do we make the stream downstream of the reboiler capable of handling this winter ambient condition (~ -20F)? Can we heat trace the surge tank and the downstream piping that normally operates at 400F? What can I do to maintain a suitable TEG/water mix that can suppress the freezing point after going through the reboiler at 400F, with the reboiler boiling off most of the water? Or is the complete solution a heated housing around the skid?

[ColinR33]

I recommend either installing a heated shelter around the unit (permanent or even temporary hoarding with portable heaters for the duration of the shutdown) or heat tracing.  The surge tank you don't normally want to insulate and /or heat trace because during normal operation you want to get rid of heat at that point.  I suppose you could heat trace and insulate just the bottom portion of that and hope that thermal current conduct enough heat to keep the unit from freezing.  If possible, keep the TEG pumps running through the startup recirc line.

 

Normally, when we build TEG units for cold climates such as here in Canada we install them inside a heated building.  If it is too large a unit or the end user does not want a building (eg. units we built for Russia) then we will insulate and heat trace.