1 or 2 heat exchangers 1

[mfqd]

Hi,

I'm dealing with a project, where it was designed a heat transfer system between the boiler circuit and the process water, that has 2 heat exchangers instead of just 1. Of course that it has a simple circuit with a pump, to connect both heat exchangers.
I have searched in Holman and found an example that made the economic analisys between both options. In that case, it was better to have just 1 heat axchanger.

Can anyone give me the opinion about this? I would like to know better the reasons behind this option and why in some applications they are used.

Thanks!

 

[Latexman]

More detail please. Are the 2 tube sides in series or parallel? Are the 2 shell sides in series or parallel? Can you attach a sketch or P&ID?

Good luck,
Latexman

 

[TD2K]

Two exchangers in series would be evidence to me of a temperature cross that couldn't be achieved in a single shell and tube exchanger. A temperature cross isn't an issue in a true counter current exchanger like a double pipe but it can be an issue with shell and tube exchangers where the flow is frequently not true counter current.

Two exchangers in parallel could be specified either because a single exchanger was too large for the plant's preferences or to allow one unit to be taken off-line for cleaning/repair while the plant continued at partial rates.

Typically two exchangers providing the same total surface area are more expensive than a single exchanger though that might not be true for all applications with exotic metallurgy, design conditions? I don't know, I don't have the data to say yes or no, just throwing it out as a possibility.

 

[mfqd]

Hi,

thanks for the reply.
I think it might be correct. Maybe the if it was selected just 1 HX, probably it would be too bigger or something...

I attached a simple scheme of the parallel installation.

Thanks

 

[25362]

TD2K has clearly expressed the possible temperature "crossover" reason for a series arrangement. Besides, generally, smaller units in series are more efficient, i.e., need less total surface area that one larger unit for the same duties.

 

[mfqd]

Hi,

Thanks for the reply.

25362,
I understood your point, but can you take a look at the file that i've attached to see this particular case?

Thanks

 

[25362]

I've looked at the sketch. J.P.Holman's Heat Transfer 4th Ed., brings the relevant considerations in point 10-8.

 

[mfqd]

Thanks!

As i said before, i've taken a look in Holman. Maybe that's the same example... I will see closely and after i will reply again commenting what i've learned.