vapor recovery in tanks 1

[hianbotech]

I am working in feasibility study.

We want to change the service of two existing tanks in a storage terminal.

The new product to be handled in the existing tanks will be condensate (light naphta), with a maximum RVP of 15. The current tanks are floating roof.

For the new service these ones should be changed to fixed roof, with an additional system to handle the produced gas.

Following the information that we have for the terminal:

Maximum amount of vapor to be produced for both tanks
Rated flow: 0.69 MMSCFHr
(first estimated, based only in the maximum filling rate 110,000 BPH )
Temperature,
Max Storage Temperature: 100°F
Min Storage Temperature: 42 °F (Ambient)
Vapor Molecular Weight: 64, (based on typical molecular weigh of Stock Vapor density for naptha)

We are thinking in a vapor recovery unit or a burning systems. Are We in the righ way?. do you have anothers ideas?.
Regards, Hianbo

 

[ash9144]

I think you would definitely want to look at a vapor recovery unit. Compressor, condenser, chiller or some combo of those. It would be much simpler to operate, cheaper, and there wouldn't be as much to go through for permitting issues.

 

[devaxrayz]

Hienbo, I'm a little bit curious...

what is your method in calculating 0.69 MMSCFHr (16.56 MMSCFD) vapor generated in your storage tank? It seem very high in my opinion for tanks emission(or is there in reality?).

If you calculated it based on outbreathing calculation as like in API 2000 (i assummed because you mention "filling rate" as if you want to calculate vent capacity), volume of vapor should not that higher if your tank level is not changing frequently or level controlled.

Bottom line is in selection of technology, one of major driven is economic. Will you invest more money and get benefit in vapor recovery or save the capital and just burn them all. And economic is really affected by how much you have your waste gas as I questioned earlier. If you vapor rate is proof even lower, you might just need to vent it (if the local environment regulation allowed)

If the rate is right I will prefer the vapor recovery since you may end up with recover thousands of barrel of high API condensate and if you refer to current light oil price you will not think twice...

-rayz-

-rayz-

 

[IFRs]

Why is a floating roof not an option? RVP 15 is not that high. Have you used tanks4 to model your emissions?

 

[hianbotech]

This flow came from the maximum filling rate that you can have in terminal, filling two tanks at the same time. Currently this flow was change for the client to 0.34 MMSCFHr.

Regarding with the type of tanks. I have found several technical information that not recomended floating roof tanks for products with True Vapor pressure
above 13 psia. However we are asking to tanks vendors

 

[IFRs]

In the USA, the EPA limits floating roofs to 11.1 PSIA (76.6 kPa). This is the TVP of the liquid at its storage temperature. Since RVP is at 100 DegF the TVP is often much lower and an IFR can often be used. For example, gasoline has a RVP of upwards of 13 but is most commonly stored in floating roof tanks.

 

[hianbotech]

IFRS thanks for your answer.

Which did EPA regulations mention that pressure limit?

 

[IFRs]

40CFR60 Subpart Kb
Find it at

http://www.epa.gov/EPA-AIR/2003/February/Day-24/a4245.htm

or at

http://www.epa.gov/ttn/chief/ap42/index.html

etc

 

[Unotec]

Are you going to install a gas blanket?

 

[jwysmooth]

I don't know if you got your original question answered, but yes, with a high vapor pressure product like the 15 RVP naphtha, IFR are not appropriate due to the vaporization of the product around the seals. The regulations cited by IFRs are the offical EPA rules that most states abide by.

Are the existing tanks you are looking at have internal floating roofs or external? If they are IFRs, then you can keep the floaters and just seal the fixed roof portion of the tank and pipe the "attic" space vapors from the tank to a vapor combustion or vapor recovery device.

Tank turnovers and vapor concentration will determine whether or not you have enough potential recovered product to economically justify a recovery device over combustion.
Cheers,

 

[hianbotech]

Thanks to all for your answers:

Our Client finally decided:
1. kept the floating roof tank. These tanks have an internal floting roof.
2. Seal the fixed roof portion of the tanks and pipe the vapor from the tank to a vapor combustion system.
3. Added a refrigeration system to reduce the temperature and the losses of product.

Thanks for your support