5 replies to this topic

[Chemico822]

Hello,

Has anybody done any calculations before for a heat transfer from ambient air to a liquid inside the storage tank? let me explain the situation:

 

I have a horizontal vessel of capacity 12.5ft I.D X 40ft length with 5ft of liquid level.

The liquid inside the vessel is about 98% propane and 1.5% ethane and 0.5% butane+ (The composition is mol%).

The pressure inside the vessel is 1.4 psig and the temperature is -45 F. (The liquids are at its bubble point)

I have 3.5" of polyurethane insulation around the vessel.

The design temperature of the vessel is -50 F(Low temperature carbon steel) and the design pressure is 300 psig.

The ambient air is at 100 F and the wind velocity is 20 ft/sec. The heat should transfer through the insulation layer and then through the vessel wall to the liquid inside the vessel. Increase in temperature of liquids inside the tank will raise the pressure. we also have to remember that the vaporization of liquid also bring the liquid level down.

 

I want to know the pressure and temperature profiles inside the tank for every one hour until it comes to a point where the ambient temperature no longer heat the liquids inside the tank.

 

I appreciate your help.

 

Thanks.

 

 

 

[PingPong]

Note that Solar Radiation (and Orientation of the tank towards the sun), and Thickness of the steel tank wall also are of influence.

 

What is the set pressure of the PSV on the tank?

[Chemico822]

Hi Pingpong,

 

yes you are right, we need to include the solar radiation but I won't make it too much complicated by considering that. I forget to mention the vessel wall thickness which is 1.25".

 

The set pressure of the PSV on this tank is 300 psig.

 

Thanks,

Edited by Chemico822, 13 June 2014 - 09:28 AM.

[PingPong]

To calculate what you want is not going to be easy, but if you feel the need to do it anyway, I suggest you start by calculating the following:

 

- Total mass of the steel tank (including heads), and find out what the specific heat and thermal conductivity of the steel is

from -45 ^oF to 100 ^oF

 

- Mass of the liquid in the tank, and find out what the specific heat and thermal conductivity of propane liquid is from -45 ^oF to 100 ^oF

 

- Mass and number of moles of the vapour in the tank, and find out what the specific heat and thermal conductivity of propane vapour is from -45 ^oF to 100 ^oF

 

- Tank wall area (including heads) in contact with the liquid

 

- Tank wall area (including heads) in contact with the vapour

 

- Surface area of the liquid (contact area between vapour and liquid)

 

- Find out what the thermal conductivity of the polyurethane insulation is. I would expect a number in the range

0.025 - 0.035 W/m².K. That depends on the density of the polyurethane foam, which you probably don't know.

 

 

I suspect that the vapour will heat up faster than the liquid. As a result the pressure will rise faster than the vapour pressure of the liquid. It will follow the Gas Law: p.V = n.Z.R.T or p = n.Z.R.T/V

There would then also be heat transfer from the vapour to the liquid, as well as heat transfer through the steel (vertical downward) from the dry wall to the wetted wall.

 

To calculate heat transfer between steel wall and vapour you need to read about Natural Convection. That subject is covered in any decent book on Heat Transfer. If you don't have such book you can freely download one at the MIT website: http://web.mit.edu/l...d/www/ahtt.html

Edited by PingPong, 14 June 2014 - 07:05 AM.

[yasaki]

hello

I am working on my final year project which involves calculating the temperature at different point along a pipeline transporting crude oil. The oil looses heat into the atmosphere as it travels through the distance. The overall heat transfer coefficient per unit area is given as follows if i am correct.

U=1/(1/h_o+dx_w/k+1/h_a)

however, the problem i am facing here is how to get the heat transfer coefficient of the crude oil which is h_o

Edited by yasaki, 17 June 2014 - 03:08 PM.

[Chemico822]

Hi Pingpong,

 

I may not grab your valuable time to do a simple heat transfer calculations. I just want to cross check my calculations. I did not assume the solar radiation in my calculations. I just included the resistances offered by the vessel wall and insulation to calculate the average heat gain from the ambient. I know my calculations are not pretty accurate because of my assumptions, but all i'm looking for is just a ball park number. Is there any way you can just glance at my calculations and let me know if i'm in that ball park range. I have final temperature as an input value in my spread sheet that will tell us how long does it take the liquids to reach that temperature. once it reaches there since this is a closed vessel, the vapor will be in equilibrium with the liquids ands so the pressure inside the tank is the vapor pressure of the liquids.  

 

Again, I did not assume solar radiation, convective heat transfer due to wind velocity, and internal heat transfer from vapor to liquid. I'm Ok even if my calculations are 10-25% off. If you think it is worse than that let me know I will put more efforts on this to get on track.

 

I appreciate your help.

 

Thanks much.

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