Cooling a Tank using plate exchanger

[kunal2603]

I have designed a plate and frame heat exchanger to cool liquid in a tank. The return line from the process to the feed tank running at 20gpm is cooled from 90 to 55 deg F. The cooled liquid is then pumped to the process at 100gpm.

I feel it is economical to cool return line ( 20gpm) to the tank than cooling 100gpm from the pump discharge to the process as it demands for a larger heat exchnager and heavier duty. If the tank volume is 13000 Gal, how do we find the time and energy required to cool the whole tank volume using return line that flows at 20gpm at 55deg F.

Thanks

 

[Montemayor]

Kunal:

You are going to have to explain just exactly what you intend to do in a clear, specific, and accurate engineering manner in order to have your readers understand just what you are thinking and generate a reasonable response.

If you are a professional chemical engineer, you know that unless you state all the facts and data, your listeners can’t be expected to know what you are thinking or what you are assuming we know.

Example: Is your “process” steady state or batch? It makes a BIG difference.

Anyone in this Forum can easily figure out very quickly that if you have a Feed Tank (regardless of size) and you are pumping 100 gpm out of it with only 20 gpm being returned to it, you have an 80 gpm deficiency in any attempted material balance. Sooner or later you are going to drain the Feed Tank dry – regardless of the cooling you do. Perhaps this is a batch Feeding process and you are not telling us. Perhaps this is a school homework problem and you also are not telling us that as well.

Which is it? If it is real-life, then tell us ALL of the basic data and explain the scope of work. Tell us the liquid, the process, the pressures, the temperatures, etc. Otherwise, I doubt if anyone can guess what you are trying to do.

Await your response.

 

[kunal2603]

I am sorry for that. I am a process design engineer. The details are here. It is a batch process. we maintain a minimum of 20% level inventory.

Acetone, used as a solvent in polymerization, is stored in a 13000 gal tank ( 10ftdia X 20ft height). It is pumped at a rate of 60gpm at 30psi to polymerization reactor. The recovered acetone from distillation unit is sent back to the feed tank at 20gpm. Tank overhead is maintained at 20psi. One of the option is to cool the 20gpm acetone from 100 deg F to 55 Deg F before goin in to the tank. how do we find the time and energy required to cool the whole tank volume using return line that flows at 20gpm at 55deg F. I hope my information is clear now.

Thanks

 

[twr]

Kunal,

I'm not familiar with your kind of batching, but my guess is that after the tank is more than 20% full, the polymerization process gets started. The feed tank continues to fill at 100 gpm (?? temp) and a return line has 20 gpm at 55º F. Is the initial acetone temp at 100º F before getting into the tank, or is the 100º F temp increase after the polymerization?

 

[Casimo5]

Okay, let me take a stab at this by making assumptions and you telling me if I'm right or wrong.

Your feed tank starting temperature is 55 deg F.
You are removing material from the tank at 100 gpm at tank temperature.
You are returning material to the tank at 20 gpm at 100 deg F.

You want to maintain 55 deg F leaving the tank but since your return line is at 100 deg F, you are heating up the tank as the process continues.

Does this sound about right?

It seems that if these assumptions are right, the amount of heat you want to remove is the same despite where you place your exchanger.

Cooling a 20 gpm stream down by 45 degrees is the same as cooling a 100 gpm stream down by 9 degrees if the material you are cooling is the same in both cases. I would think that your exchanger would be slightly different due to the pressure and temperature rating, but not that different in price.

So if price is your only concern, then maybe it shouldn't be.