8 replies to this topic

[Porcupine]

Hi,

 

I'm chemical process engineering student who's currently doing an internship and I came across the following problem.

 

I have to design a TEG dehydration unit in Aspen HYSYS with the goal of achieving a product stream of dry gas with a water content of max 4 lb/MMSCF.

To accomplish this requirement I had to lower the lean glycol rate first calculated based on GPSA. So I calculated the minimum lean glycol rate that my setup allowed me to use (6.9 m^3/h). With the help of the Adjust feature, the optimal lean glycol rate can be achieved. But the iteration stops at the minimum rate, so this is not enough to the required 4 lb/MMSCF. The purity of the recycled TEG is 99,34 wt%.

 

The used pressure of the feed and the lean glycol are respectively 30 and 31 bar. I was told I should avoid changing them. The only other possibility that comes to mind, is lower the temperature of both the streams. Problem  in an onshore setup, is that to lower the temperature of the feed, a mechanical cooler is required, which is not ideal.

 

Are there any other any other variables I should adjust first? Or is changing the temperature as I do now really my best (and only) choice?

 

 

Thanks in advance.

[Bobby Strain]

I don't believe that there is any optimization to be done; just design.

 

Bobby

[Art Montemayor]

Porcupine:

 

Bravo for Bobby.  It is a false idea that a process design constitutes an "optimization" of a process.  It is very important to fully understand what is the meaning of an "optimization" for a chemical engineer, and that is the reason I mention it here.  That is why I edited your original thread title.

 

To optimize a process is to find out what are the key elements in an operation that determine what characteristics yield the lowest operating cost while costing the lowest capital for its installation - thereby yielding the maximum profit for the project's scope of work.  A process design cannot identify ALL the important keys; it can only identify a few of the key elements, but not all of them.  Other engineering disciplines have to contribute their portion of the final design to produce what can be identified as a possible "optimum" design.  And even then, the product has to be proven in the field, under actual operating conditions.

 

Your initial role in seeking the best and most promising process and making the required process calculations and decisions is very important; but there is a lot of work left to do to reach an acceptable installation.

 

The point here is not semantics, but rather a full understanding as a student of what exactly is the scope of your assignment.

[Porcupine]

And if it's a matter of design and I'm very close to the required water content, what parts are often easily adjusted to meet the required product gas?

[YAH.]

Hello,

 

Have you tried varying the number of stages in the TEG contactor? As this increases the residence time inside the tower and allows greater contact time between the wet gas and TEG.

 

You can also try creating a case study in HYSYS of water dew point versus TEG flow rate , and note when the required dew point is first reached at a certain operating temperature.

 

So, based on the equilibrium dew point required and the TEG concentration you can determine the contactor temperature. Such graph can be found in the GPSA.

 

Hope this would help...

[RockDock]

The number of stages won't have a significant impact once you have any more than 3. Since you have not mentioned the regeneration pressure, I'll go ahead and add that you want to keep the regenerator pressure as close to 0 psig as possible. That will allow you to evaporate more water. Hysys is generally not very accurate with dehydration modeling, so you may want to find a better simulator. I have not come across any reputable design company that uses Hysys for dehydration.

[ADITYA.DUBEY]

Hi team

 

As TEG also absorbs natural gas with it in the contactor during dehydration.

Can anybody do hysys simulation and tell for regeneration package flash drum Hydrocarbon vent gases quantity??

 

Natural Gas Flow in contactor= 55 mmscfd

water content in natural gas = 1000 Kg/mmscm

TEG circulation rate =1600 kg/hr(Lean - 99.3 %,Rich - 96 %)

Rich TEG pressure/contactor pressure = 58 barg and 35 Deg C

flash drum pressure = 5 barg and 30 Deg C

 

I am planning to utilize flash drum vent gases as reboiler fuel.And for that I need to quantify the vent gases.

 

 

Thanks

Aditya

Edited by ADITYA.DUBEY, 20 August 2016 - 09:50 AM.

[YAH.]

Hello,

 

Promax simulation software would be another choice. For TEG contactor designs using HYSYS, the glycol package is recommended.

[lobachemie]

I think that these links can be interesting to know more about chemical products

 http://www.lobachemie.com/

 

http://www.lobachemi...cals.aspx#.aspx

 

Thanks