3 replies to this topic

[Dieguito2]

I'm working at a revamping of an existing TEG dehydration unit, the inlet gas pressure now is about 8 bara, while the original design of the unit was for a pressure of 24.5 bara. The client want to know the theoretical glycol circulation for achieve the original dew point with the new pressure. Here we have two effects: the dew point at lower pressure is lower than the value at higher pressure at the same water content and the temperature raising of the gas in the column become important at low pressure.

 

Anyway, I expect to achieve the same water removal if I compare the column working at the two different pressure keeping constant: the number of theoretical stages, the TEG circulation (kg TEG/kg water removed) and the lean TEG concentration. Instead, simulating the column with hysys, I have very less water removal at 8 bara respect to 24.5 bara. I made a case study at 8, 24.5 and 40 bara with a TEG concentration of 99.99%w and I compared the result with the curve taken from Shell DEP standard (see the enclosed pdf).

 

What are the reason of the less water removal at low pressure? I'm not able to find it, the curves of water removal reported in the literature, e.g. from Shell DEP standard and GPSA, are independant from pressure. Please share your experience.

 

Thank you

 

 

 

 

Attached Files

•  CIRCOLAZIONE -DEW POINT.pdf   27.11KB   45 downloads

Edited by Dieguito2, 05 September 2014 - 02:51 AM.

[himant]

It is simple absorption process which is favorable at higher pressure and lower temperature.

 

At higher pressure and lower temperature, absorption factor will be more and hence, you will need less liquid flowrate for more gas flowrate and vice-versa

[Dieguito2]

It is simple absorption process which is favorable at higher pressure and lower temperature.

 

At higher pressure and lower temperature, absorption factor will be more and hence, you will need less liquid flowrate for more gas flowrate and vice-versa

 

Published equilibrium data, from what I know, for the system gas-water-TEG neglect the effect of pressure and considers only temperature. If you know other sources please share them.

[Bobby Strain]

It is true that one can achieve the same dew point at the lower pressure. But the gas will contain more moisture, of course. If you want to maintain the same moisture content, then you will probably need a stripping gas section to produce leaner glycol.

 

Bobby