VGO Storage Tank 2

[PAN]

I try to search the related thread about VGO storage tank. The result is only thread483-44469.

Conversion of VGO (70 Deg C) storage cone tank to 140 Deg C VGO tank.
thread483-44469

In my case, we have the existing external floating roof tank for crude storge. There is new requirement to use this tank for VGO storage tank.

- Can we use the FRT tank for VGO storage without any modification?
- Do we need to modify to cone roof with nitrogen blanket?

I understand that the FRT tank has low vapor space above liquid level. The modification should not be necessary. Please comment.

 

[KazakhJeff]

Hello Pan,
I would think that so long as the external pipework is in place, that you should have no problem with this conversion, with no modification. Particularly, VGO should need no blanketing. However before you go forward let me list the things I think you need to look at before you can take the decision/make the change:
- Calculate out that your roof will still float (with required safety margin).
- Look at Pour Point of the VGO (some waxy VGO's have high PP's, and therefore your tank may require internal heating and mixing).
- Look at the wax content of the VGO. If high, then you may require heating/mixing to prevent formation of wax deposits, and even scrapers.
- Check that the pumps can handle VGO in place of crude
- Make sure your tank is properly cleaned before the conversion

 

[PAN]

Thanks KazakhJeff.

Anyone who has experience for the use of FRT for VGO storage. Please advise me.

I intend to use FRT without nitrogen blanketing. However, I do not have any documents for reference. What is the factor to decide that require blanketing (or not)?

 

[JoeTank]

What is VGO?

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[rzrbk]

I would be wary about using an external floating roof tank for storing hot products like vacuum gas oil due to the increased chance for water entry through the seals due to rain, etc. There may be additional complications with the roof due to rubber parts in the seals. Also, insulating the floating roof would probably cause several problems with waterlogging and drainage.

In any case, on the blanketing question, I would propose the following, but am not shure where this would be covered in a code or recommended practice.

-blanketing would only be needed in a cone roof type tank if the product could get above its flash point
-a floating roof would not need blanketing due to the absence of a vapor space

 

[TD2K]

VGO - vacuum gas oil is my guess Steve.

 

[25362]

KazakhJeff notes on probable wax deposition are highly relevant.

Consider all safety aspects, including static electricity buildup and discharges (longer relaxation times). Besides, although VGOs have "per se" very low vapor presures, they may oxidize in storage. For example: VGO films on the tank walls may be prone to oxidation.

Following rzrbk comments, concerning inerting in cone roof tanks, this is the process used on combustible gas mixtures to reduce the concentration of oxygen below the minimum oxygen concentration (MOC). For many gases the MOC is approximately 10%. A commonly used control point is 4% below the MOC.

Good luck.

 

[PAN]

Thanks again for all comments.

SteveBraune,
TD2K is right. (VGO = Vacuum Gas Oil)

25362,
I will use a suction heater at the tank outlet nozzle.
Due to high wax content, I will have steam coil inside the tank and heat tracing for both inlet and outlet lines.

Please advise me the reference paper for further study about MOC.

rzrbk,
Normally, VDU (Vacuum Distillation Unit) will operate at the same time of running HCU (Hydrocracking Unit). The modification of large crude oil tank for VGO storage may not suitable.


I will reconsider to use another existing small cone roof tank to install tank blanketing system.

 

[25362]

PAN, go to thread798-33615.