6 replies to this topic

[Hassen.Gannouni]

Dear all,

First of all, let me thank you for the very helpful content that i discover everytime i visit this website.

As for the topic subject, i really want to share my graduation project progress with experts and people of knowledge like you all. I wish as well to have your opinions and assist concerning some details and methodology that i am following since i am facing many issues.

In fact, firstly, the study includes a modeling of an existing set of two separators: a coalescer vessel and a degasser which role is to get an oil in water content of 30 ppmv for offshore disposal.

Here, i used Ansys Fluent where i made the models, the meshing and inserted the boundary conditions but with no satisfying result. I don't know if the problem is with my software, my laptop or with the manner i put in the data. 

Next, i tried to make a simulation with aspen hysys in order to get an idea of the outlet flow from the coalscer which is the feed of the degasse so i may size it. Unfortunately, when inserting a 3-phase separator it makes a perfect separation with 0 fraction of the light phase within the heavy one. But in reality there must be a quantity that is left to be separated in the second equipment.

In a second part, i have to size new equipments (coalescer+degasser), i am using for this the ShellDEP sizing standards.But, since there is insufficient informations on the coalescer sizing, i subtituted it with a horizental settler with plate packs. The problem here is that i don't have neither the droplet size distribution nor the amount of change in diameter after the plate packs in order to determine which minimal diameter of droplets to be separated to reach the required concentration.

I will stop here talking about my issues hoping that anyone could have any idea or suggestion of any of the cited points above

I thank in advance for giving me of your time to read my topic and to answer

I will give required data if needed.

 

[Bobby Strain]

I'm not sure why you are attempting the project in such detail. These things you mention are usually left to the equipment supplier. They have their own methods to estimate performance. Good luck.

 

Bobby

[Hassen.Gannouni]

Thanks Mr.Bobby for the reply. I really appreciate it.

In fact, that's where i've put myself into since the beginning so i must find a way out as an engineering student.

[thorium90]

Perhaps I didn't understand the question but might I ask a few questions about the original question?

 

Where is this water coming from? Is it some real waste stream or its some hypothetical waste?

Its mentioned that the objective of the process is to get the oi in water content down to 30ppmv for off site disposal. Should we first quantify what is the composition and flow rate coming into the process first before deciding that a coalescer and degasser is the most suitable treatment process? Or is this just a desktop exercise to figure out how to use Hysys to simulate and size a coalescer and a degasser?

Is the objective of all this for a graduate project?

[Hassen.Gannouni]

Dear thorium90,

Thank you for you interest.

 

The water is coming from a product of three gas wells of an offshore concession operated by a platform within the tunisian territory. It is a real waste stream. The mixture is firstly headed to a production separator where gas, condensate and water are separated.

The stream that is of my concern is the heavy liquid outlet stream which is water with some dispersed quantity of oil (condensate) with 2400ppmv as average value.

For the choice of the equipments, there is an existing unit composed of a coalescer and a degasser but which was designed to handle a flow rate of 29m3/h. Actually, the amount of water has increased to 64m3/h which is not suitable for the capacity neither for the separation performance.

And yes the objective is my graduation project of the National Engineering School of Gabes Tunisia.

 

I wish i have treated all of your questions and i thank you again for your time

[Bobby Strain]

One usually begins with an evaluation of the production separator. You can visit my site, bobbystrain.com, and find Mark Bothamley in the links. This might lead you to some interesting articles. Other links might be helpful, too. Still, it is quite unusual for such a project for a student. Condensate/water separation is usually quite easy. In most cases, hydroclones are used in lieu of a coalescer in Gulf of Mexico production. The overflow is sent to a low-pressure separator.

 

Bobby

[Amit J]

Hassen,

HYSYS (steady state)  is meant for ideal separation and hence you won't get any traces of oil in water stream by using separator application.

 

Refer to GPSA (Gas Processors Suppliers Association) Engineering data book. From data available in GPSA handbook, you will be able to build excel calculation sheets, wherein you can do sizing for separator & coalescer. ( you can search on internet, similar sizing sheets are available for same).

 

...Amit