4 replies to this topic

[marcocu]

Hello,
i'm a process engineer and i'm designing a firetube for a DEG reboiler .
There is almost no literature about film temperature and heatfluxes
in Dyethilene Glycol Reboilers and this is a big problem for my current work.
Shell DEP and GPSA advice to use a 155°C bath temperature to avoid cooking @ 162°C.
Now i'm sizing the vessel using the TEG data for the heat flux and the film temperatures.
I want to ask to you big community of cCHE if someone know about this problem and can
tell me more precise values for the average flux and the max film Temp.
Thank you.

Marco

[Art Montemayor]

Marco:

Welcome to our Forums.

The answer to how a reboiler (whether TEG or Amine) is designed is found in the GPSA Engineering Databook. If you read through the GPSA, you will find that a reboiler flux rate of 10,000 Btu/hr-ft2 is a recommended design flux for a fired reboiler – or less if you can justify it.

You have failed to tell us what kind of heating medium you are using: is it electric? Direct fired? or hot oil heated?

It has been my practice to use 8,000 Btu/hr-ft2 as the design heat for amine units and TEG dehydrators. What you use depends on your experience and know-how in the field you are designing in. If you are young, I can’t expect you to be very familiar with the correct parameter. This is not a personal or critical observation; it merely is based on my personal experience. I have never had a personal design fail to perform on me.

[marcocu]

First thank you for your answer, but I think i didn't explain well the problem.

The problem is that all the major databook and design guide advice only about MEG and TEG and not about DEG. DEG shows catalytic induced degradation at 162 °C and is much more sensible to peaks in heat flux.

I'm in a company that is designing glycol unit since a long time, but this is a different problem in a different context. I was looking for someone that already knows that problem so maybe i can be less conservative in the design

[Art Montemayor]

Marco:

I think your problem can be resolved very easily.

I recommend you apply a conservative heat flux of approximately 8,000 Btu/hr-ft2 and a reboiler temperature below 162 ^oC – as is recommended by GPSA. Make sure your reboiler heat source is a steady one and that should resolve the problems with peaks in the heat flux.

[marcocu]

THank you again,

i'm using know for a fired heater a 19 kW/m2 flux as Shell DEP advice, so in the range you told me.

Thank you