Heat Exchanger Design aspect

[Falcon03]

What are the differences between a counter-current and co-current exchanger for design aspect point of view?


The main reason for my question is, we are thinking to change the Debutanizer exchanger hot stream side to avoid further corrosion. The current configuration is a counter current and we are thinking to shift to concurrent to help minimize the corrosion rate and hence stop tubes leaking.

 

[Wizard83]

I think you are asking about counter current flow (Flow of each fluid across the heat transfer surface is in opposite direction)

as opposed to Con-current flow (Both flows in same direction).

Counter Current flow is generally MUCH more efficient as there is a larger LMTD (Log Mean Temperature Difference) to work with. This is basically the pressure that drives the heat across the heat transfer surface, i.e. the metal of the plate or tubular heat exchanger.

Con-current flow is less efficeint as the two streams tend to go toward the median together with the LMTD geting less and less as the flow goes through the heat exchanger.

You basically soak the heat out. Performance can be improved by flowing the media faster than the product, but it is going to take more heat transfer surface to do the job, as opposed to counter current flow.

Most all heat exchangers I have worked with in the food industry have been counter current.


Hope this helps.

 

[pmover]

i recommend investigating the source of corrosion and resolving that matter, before changing the exchanger configuration. how will changing the exchanger configuration eliminate the corrosion.

just curious, is the problem corrosion or erosion? have you checked actual process parameters with design parameters (i.e. flow, temp, pressure, fluid properties, etc.)?

something to ponder . . .

good luck!
-pmover

 

[25362]

The light naphtha stream (LN straight run from the crude unit reflux drum, cracked or hydrotreated) may contain corrosives. Have you checked for their presence ?

Where along the tubes is the leakage developing ? What type of exchanger are you referring to ? What temperatures and what metallurgies are in use ?

 

[Montemayor]

Falcon03:

I agree with pmover and 25362's priorities: what type of corrosion is being experienced and what type (TEMA) of exchanger are you contemplating?

I think we all agree (or know) the basic advantages of a concurrent type of heat transfer and the ultimate trade-off it costs: You achieve quick, initial heat transfer with a capability of easily controlling the temperature profile of the process fluid as it progresses through the exchanger. However, you're going to have to relinquish a goodly portion of potential heat exchanger efficiency. But where does the corrosion - errosion? - come into play in the heat transfer arena?

Unless you have a metallurgy (carbon steel?) that is very sensitive to high temperatures with resultant corrosion, I don't believe you will see any corrosion difference between a counter-current model or a concurrent model of heat exchanger. Additionally, I assume that you know that it will be difficult to configure a classical concurrent configuration without it costing you more money than usual. The only way I have succeeded in applying concurrent heat exchange is employing a "double-pipe" configuration - and that is for relatively small flows.

I suspect your corrosion problems are coming in from another direction rather than from the manner in how the heat is transferred. But without sufficient basic data, we can't state more than that.

 

[Falcon03]

Thank you all for your good comments.