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Tank Circulation Heating with Boiler and Heat Exchanger

Tank Circulation Heating with Boiler and Heat Exchanger

Tank Circulation Heating with Boiler and Heat Exchanger

(OP)
Hello,

I am designing a process which requires the heating of a tank holding 20m3 of water using a 500kW diesel powered steam boiler and counter flow shell tube heat exchanger. The volume of the tank will remain constant but will be circulating through the heat exchanger along with the steam from the boiler.

I am trying to calculate the below:
- How long will it take to heat the bath from 4 degrees celsius to 70 degrees celsius?
- What will the outlet temperature of the hot side be returning to the boiler?
- Is the boiler and heat exchanger big enough to achieve this outcome? If not should the boiler or heat exchanger size be increased?

I have attached a basic schematic with assumptions of the process. If any further information is required please let me know. Any assistance would be highly appreciated.

RE: Tank Circulation Heating with Boiler and Heat Exchanger

Some questions:

1) Why do you need the intermediate heat exchanger? Why not heat the tank directly with steam ? This has been done for decades in the petrochemical industry and several companies offer tank heaters. If the steam from the 500 kw boiler is for other additional purposes, fine.... but the system you propose will have long term costs for the circulation pump

2) What is in the tank and what is the liquid specific heat ?

3) What the hell is a "500kW diesel powered steam boiler" and why must the heat exchanger be a "counter flow shell tube " type ... This makes me suspicious (see #6)

4) Ignore the losses through the walls of the tank ? ... Nope

5) "No flow loss through Heat Exchanger"...... DUH !!!!

6) I am beginning to smell a very simple heat balance homework problem .... Tell me my Geezer Spidey Sense is wrong

Come Clean !!!

MJCronin
Sr. Process Engineer

RE: Tank Circulation Heating with Boiler and Heat Exchanger

(OP)
Hi MJCronin,

Apologies if the post was quite vague but we are just trying to get rough calculations. I have answered your questions below.

1)The heat exchanger is being used as we do not want the tank contents to come in contact with the steam directly. In addition, we have the external heat exchangers available so to save on costs we would like to utilise these.

2) The tank content is 10% sulphamic acid solution. I have assumed cp of 4200 J/kg.K. I know this is for water but it is an assumption.

3) A 500 kW powered steam boiler is a boiler that is in a 20ft container which runs off diesel fuel. Basically a portable boiler that runs off diesel not LPG. Again, the heat exchangers is what we have available and would like to use if possible.

4) I know these would occur but for the sake of these initial calcs I am happy to assume negligible for now.

There is a rough sketch attached in the initial post with additional information. My question is mainly based around whether circulation heating will change the time taken to heat up the liquid as opposed to direct heating. Could this time be reduced if we use a larger heat exchanger or do we need a larger boiler to reduce time? Alternatively, if it is sufficient could we use a smaller boiler?

RE: Tank Circulation Heating with Boiler and Heat Exchanger

From your sketch, you have all the necessary information to run this calculation. You can run the total heat transfer in increments on an excel calculation, or you can set up an unsteady state heat transfer differential equation.

This is all basic stuff - Q=m*Cp*dT and Q=U*A*dTlm applied in increments. Your number of U=2000 W/m2k looks very optimistic, though, for a steam-to-liquid heat transfer.

RE: Tank Circulation Heating with Boiler and Heat Exchanger

Quote (TiCl4)

Your number of U=2000 W/m2k looks very optimistic, though, for a steam-to-liquid heat transfer.

Agree! I'd recommend about 850 W/m2k.

Good Luck,
Latexman

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