Heat losses in heated tank 2

[jcsantos87]

Hi guys can you help me out

in my plant due to a problema with an heat exchanger, that we are buying a new one right now, we now have to heat up a tank in order to start up the UNIT and we also have to heat it up at least twice a day for an specific operation, I want to calculate the cost of this situation to bump the heat exchanger acquisition to the top of the list.
The two main problems are the heat losses through the Tank Walls and the heat required to heat up the piping to the reactor, so you can imagine the heat losses in piping are huge in a start up if the fluid leaves the tank at 60ºC it gets to the reactor at 30ºC and that's a no go, in the place of the old heat exchanger we have for now a tubular one but it just can't do the job

Fluid: Rapeseed Oil
Temperatures: heated from 15ºC to around 60ºC
Room Temperatura: 10ºC
Tank - Carbon Steel
Tank Height - 6 m
Tank Diameter - 3,8 m

I don't want you to do the job for me, just help me out with the theory
What kind of calculations would you need to do to give a estimate of the heat loss? because we have losses by conduction, convection and radiation (but I think we can discard radiation for simplification purposes) over time, meaning we heat up the tubes and the tank and then it continues to loose heat to the environment

Thanks,
JCSantos

 

[EmmanuelTop]

Do you need to keep the entire tank at a certain temperature, or is it sufficient to provide a heater on the discharge line to the Unit/process (presumably pumped)?

If there is no need to maintain oil temperature in the tank at a certain value, obviously providing pump suction heater is the most effective solution - it is a straightforward decision. Read an interesting discussion at:

http://www.cheresources.com/invision/topic/22536-steam-coil-or-suction-heater/

Dejan IVANOVIC
Process Engineer, MSChE

 

[racookpe1978]

You have desired tank liquid temperature, and tank liquid starting temperature.

But heat losses are dependent on the outside air around the tank. You need that temperature, plus you need to know if it is constant or changing.

Any daylight (sunlight) heating sources?

Are the suction pipes to the pump insulated?

What was the old HX capacity?

 

[chicopee]

Are we dealing with batch or with continuous flow process?

 

[ione]

It seems this subject comes up again and again. I suggest you to trying to put your hands on "Predict storage-tank heat transfer precisely" by Jimmy D. Kumana and Samir P. Kothari (Chemical Engineering March, 22nd 1982). It represents an exhaustive dissertation on this subject with a worked out example.

 

[IRstuff]

Looks like it's available here:

https://www.academia.edu/6434136/Predict_storage-tank_heat_transfer_precisely

TTFN
faq731-376

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[ione]

Well spotted IRstuff, it's exactly the issue I was making reference to.