Tank Heat Gain
Tank Heat Gain
(OP)
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
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





RE: Tank Heat Gain
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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RE: Tank Heat Gain
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.
RE: Tank Heat Gain
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
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RE: Tank Heat Gain
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.
RE: Tank Heat Gain
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: ht
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
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RE: Tank Heat Gain
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.
RE: Tank Heat Gain
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
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RE: Tank Heat Gain
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
Chinese prisoner wins Nobel Peace Prize
RE: Tank Heat Gain