Low Pressure TEG Dehydration of Natural Gas

[MIANCH]

Hi,
we have Low pressure TEG dehydrator which was designed for 245 psig and 185 MMSCFD. over the years field declined and production has been reduced to 70 MMSCFD and pressure to 140 psig & temperature is 80 F. gas is bringing very high water say 190 lb/mmscf at these conditions.
Bubble caps are installed in glycol absorber column (16 trays, 4' dia & 44' height. we are facing problem for column efficiency. our target moisture is 18 lb/mmscf. i have calculated glycol circulation rate as per GPSA and superficial velocity. superficial velocity has been also reduced. now i want to see relationship between gas velocity and pressure in absorber performance. can someone explain, is retention time of glycol also changed and its affects on performance.
Best Regards

 

[georgeverghese]

As far as I know, unlike amine columns for CO2, H2S absorption, there is residence time effect in TEG dehydration columns. From memory, all you have to do is to maintain a 10degC water dewpoint temp approach at column top between exit gas and entering lean TEG.
Reverse flow trays are used when glycol circulation rates are very low, but this may most likely not be applicable in your case - there may be an upper limit on glycol circulation rate applicable though. You can use higher permissible gas velocity with structured packing. Higher NTU is also possible with structured packing compared to bubble cap trays for a given net column height.

 

[ChemProcessUser]

Hi Mianch,

Decrease on gas pressure will change its saturation point and gas will hold more water. Therefore, glycol contactor need to remove more water than initial estimated. Things you can possibly check:
1. Increase purity of TEG
2. Increase flow rate of TEG
3. Package internals upgrade (to increase theoretical stages)

 

[georgeverghese]

Error in my previous post : As far as I know, unlike amine columns for CO2, H2S absorption, there is no residence time effect in TEG dehydration columns.
If all revamp possibilities have been investigated and found to be too laborious, then upstream boost compression back to 245 psig may be required.