Tank Heat Gain

[DtotheJ]

The refinery I work for has built a storage tank for Isomerate gasoline, which must be maintained below 70°F to abide by EPA emissions regulations.

The tank is a "tank within a tank" with the outer tank serving as the secondary containment. The inner tank has a diameter of 110' and height of 72'. The outer containment diameter is 120' and height is 64'. The outer containment has a shed roof seal welded to the inner tank to prevent rain water from filling the containment annulus.

The tank has an internal floating roof.

I have assumed some green-house effect inside the annulus and estimated a temperature of 120°F inside (on the hottest summer day). I have calculated that the heat gain from conduction/convection at these conditions is about 3MMBtu/hr (assuming all surfaces are wetted, which is conservative). If 4" of insulation are added, this is reduced to 0.35 MMBtu/hr.

It is not realistic to install a chiller for the 3MM case, but insulation is very expensive.

My main question is where would I get the most "bang for my buck". By insulating the inner tank inside the annulus? Or by insulating the roof and tank area above the annulus?

I am aware that the effects of radiation are to the 4th power, but the tank will be painted white, and I just can't see good heat transfer through the vapor space of the gasoline.

Anyone with some experience in this would be very helpful in this discussion! And I will follow up on this thread with operating data once the tank is commissioned. This seems to be a popular and tricky beast for many! Thank you.

Regards,

Dave

 

[IRstuff]

You didn't answer one of the biggest factors, which is HOW LONG do you need to keep it cooled, as well as what temperature does th gas start at? If it's for a few minutes or hours, then perhaps a cheap passive approach is possible, but if its for days on end, then you need to spend some serious money. How is your company even meeting this requirement right now, or should we not talk about that?

Also, using 120°F as the annulus temperature is a bit extreme, since you do not have infinite heat flow through the outer wall. And if you're using air temperature, then you're not really talking about greenhouse effects, which are optical in nature, and you presumably have an opaque tank.

TTFN

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[DtotheJ]

This tank needs to be maintained at 70°F all summer long. It will be getting filled throughout the summer, and the product coming in should be close to 70°F.

The new storage tank is not commissioned yet.

Currently we use a well water cooled hairpin, but the product goes into and out of an intermediate tank at roughly the same rate (so the tank is constantly turned over and does not heat up). Once the "light gasoline" is blended into finished gasoline, the temperature is no longer a problem.

 

[IRstuff]

What temperature does the gas start at?

Also note that at the peak of the summer sun, you're probably looking at about 1.4 MMBTU/hr from solar load

Basically, if there's no latent heat margin, you have to use active cooling. At the very minimum, you would fill the gap with aerogel insulation:

http://thermablok.com/Tech_Support.htm,

or possibly cover the tank with vacuum aerogel, like:

http://www.glacierbay.com/barrierspecs.asp

Some sort of sunshade would also help. But, at the end of the day, you need some sort of active cooling.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[DtotheJ]

The gasoline will enter the tank at approximately 70°F, and needs to be maintained at that temperature. The tank will be filled all summer long to it's capacity of 115,000 BBL.

Does the 1.4 MMBTU/hr you have come up with only account for radiation, or is that convection and conduction as well?

I agree that we will need some active cooling, but I'm wondering if I can put in a smaller chiller (25 ton), if I insulate the whole thing, or maybe just insulate the sides and rely on the white roof paint to reflect most of the radiation load. I am sort of trying to bank on the fact there will be poor heat transfer through the vapor space inside the tank.

 

[IRstuff]

that was strictly solar load on about 1/4 of the surface area of the tank.

vapor space: doubtful, since it's about 5" across. Full natural convection is likely. You might consider filling it with some sort of spray insulation, ala:

http://www.homedepot.com/h_d1/N-5yc...play?langId=-1&storeId=10051&catalogId=10053,

as well as putting it on the outside of the tank.

25-ton seems to be a bit low to me, that's only about 300,000 BTU/hr, but I'm not getting as optimistic numbers as you. With the entire gap filled with 60 mW/m-K insulation, I get about 775,000 BTU/hr.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[DtotheJ]

The annular space around the inner tank is 5 feet thick. I don't think filling it with insulation is an option. We plan on insulating the inner tank with 4" of kaowool insulation.

What I'm debating is whether it will be worth it to insulate the roof also. There will be a large vapor space between the fixed roof and the internal floating roof, and I'm guessing there will be poor heat transfer in this area.

Maybe my logic is wrong and the space will heat up quickly, but I just do see a lot of natural convection with the floating roof being basically 70°F. It would seem that the vapor space (between the fixed and floating roof) would be heated mostly by conduction.

 

[IRstuff]

Oops, my bad, I sort of knew that when I did the initial calculations, but converted it to inches later on...

A 5-ft gap changes things considerably. If you insulate the outside, add the roof shade, and run the A/C into the gap and add circulation fans inside, you should be OK.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[IRstuff]

I re-ran the numbers, and it's much more plausible. The heat load into the gas should only be about 60,000 BTU/hr, which is only about 5 tons of A/C. You could probably run the expander coils directly into the tank, and add a something to stir the gas with.


TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[317069]

what about the 8 feetthe different bewteen the height of the inner tank(72') and the outer tank(64') it make about 10% of the side area?