Heat losses in a tank

[hianbotech]

We have this problem.
We are designing a tank that will receive 2200 BPD of foamy oil at 80°C. The inlet nozzle will be located at the top of the tank. Inside of the tank the normal liquid level is 5 feet. This equipment is not insulated; only personal protection insulation is needed, because it is not required to maintain the temperature. The Residence Time in the tank is 2 hr. The outlet stream is sent to a oil gathering network though the pumps. The maximum allowable temperature in the network is 50 °C.

We are doing a thermal study in order to know the temperature for the fluid leaving the tank Considering there is no accumulation of the foamy oil), and if an air fan cooler is needed.

Best Regards, Hianbo

 

[hianbotech]

I did not completed the post. The question is:

How can I calculate the temperature in the bottom of the tank?.

Best Regards, Hianbo

 

[corus]

An estimate might be obtained by assuming that you have only radial heat flow (although you'll have heat loss from the bottom and to a lesser extent through the top). I think there's a MathCad sheet you can download that will do transient heat flow in one direction, if you have MathCad.

corus

 

[chicopee]

I dont think that in two hrs. you will be able to drop the temp. of the oil to 50 degree C with natural convection inside and outside the tank unless you are in a cold climate.

 

[MedicineEng]

If you want to cool down the tank, instead of using insulation for personal protection, restrict the area with signs and put some metal bars (eventually build a sort of a cage in the area of potential contact)and like this you will improve your heat loss.

 

[hianbotech]

We also think that it is difficult that the temperature will be reduced until 50°C. However we would like to know how many degrees could be reduced.

The personal protection insulation that we will be installed is metal shields instead insulation, the we will improve our heat loss.

Our Climate is tropical, the range of temperature is between 18 and 35°C. For design we are using 35°C.

Additionally we have a distance between the pumps and the tie-in point in the network of 1600 feets. Is It possible to install in this section a special fin tube??, in order to convert this section in a heat exchanger for natural convection.

thanks for your advice.

 

[Montemayor]

Hianbo:

You are basically working on the correct concept. You are trying to pump out 65 gal/min of crude oil and cooling it down by 40 ^oC. You have the resource of atmospheric air at 35 ^oC and you could use it to effect the required cooling.

Your flow rate calls for a 2” discharge line on the required pump and I would use the pump to take the 90 ^oC crude and pump it through a bank of 2” finned pipes. I would employ electric drive axial fans (similar to those used on cooling water towers) to force atmospheric air across the bank of finned pipes. Since you have to use a pump, this infers you have electricity to drive it and, therefore, electricity to drive the fans. You might be hard pressed to cool the crude within 15 ^oC of its temperature, but it certainly is worth a try since you probably have little or no options.

You probably will require extra horsepower to overcome the inherent pressure drop through the finned pipe header, but this is a price you have to pay. This forced draft atmospheric cooler can be designed by you or you can specify and buy a unit already pre-fabricated from a local designer/fabricator.

This should be an easy and straight-forward project to design and implement. You would be very foolish and naïve to expect natural air convection to be sufficient. If you want to succeed with this application, you will have to invest in forced or induced air convection. I know. I have designed and worked with hot (90 ^oC) Ecuadorean crude in the Amazon jungle as well.

 

[hianbotech]

Finally, as Montemayor said, we will need an air fan cooler in order to get the maximum temperature of 50°C at the outlet.

However we would like to check how many degrees could be
reduced in the system (tank and outlet pipe) without air fan cooler. In the pipe we know how calculated the temperature drop. But, in the tank, We continue investigated how calculated the heat looses.

Regards and thanks to all four your valuable comments.