3 replies to this topic

[Graduate process ENG]

Gents:

We are studying whether it is possible to reduce design pressure for glycol dehydration from original design in order to increase the plant capacity as existing glycol dehydration is limited through  4 x 12 reciprocating compressors .

Capacity: 120 MMscfd @ 900 PSI and 110 F

As I stated current glycol dehydration running at low flow 48 MMscfd therefore,  suggestion is  worth to study it.

 

Proposed pressure is 320 psi and flow 100 MMscfd without any change in gas composition and feed gas temperature.

 

My question is if glycol dehydration pressure reduce from 900 psi to 320 psi is such of turndown in the pressure would have any impact on the capacity and dewpoint ? of course , there will be additional requirement on glycol regeneration skid such as pump, heat exchanger etc.  

 

I will appreciate your support and help .

[ColinR33]

I have my doubts you will be able to run at these new conditions.  The first thing you really need to look at is the equilibrium water content data for natural gas as such a large drop in pressure will have a huge effect on the water content of the gas as it will more than double even with all other parameters remaining the same as before, so the amount of glycol you need to circulate will increase accordingly to meet the same dry gas water content.  In addition to this, the amount of dehydration you can achieve is limited by the top tray equilibrium between the dry gas and the incoming lean glycol. Changing the pressure affects this and will increase the number of theoretical stages you will need to achieve the required water removal.  Lastly, dropping the pressure so much increases the specific volume of the gas significantly so your piping and vessels will likely have to be larger to keep velocities/proessure drops down.  This is especially important in the TEG contactor as high velocities will exacerbate foaming and flooding issues unless you have a tower that is oversized or has bubble caps that can be removed and replaced with higher capacity structured packing.

 

I would strongly suggest you search up TEG dehydration design papers and become more familiar with how the system works so you can better understand my comments above.  The GPSA Engineering Data Book has a lot of good information and there are a number of resources on line you can google up.

 

HTH

Colin

Edited by ColinR33, 21 April 2014 - 09:05 AM.

[RockDock]

There are two primary differences:

 

1.  the capacity of the gas to hold water. Higher pressures will drop out more water before the absorber. Lower pressures will hold more water - requiring more glycol to be circulated.

 

2.  you may flood your column

 

There will be some major modifications, I suspect. Model it in ProMax and see how your glycol circulation changes. It will also tell you if you are flooding your column.

[Graduate process ENG]

Thanks you for your feedback ,this will help alot to move forward.