Tube Side Maldistribution

[MIANCH]

Hi Als,
My is regarding maldistribution in tube side of crude oil preheat exchanger and fouling in tubes.
Is this possible for tube side maldistribution and what is the reasons for this?
And what is the relation between maldistribution and fouling in channel side?
Thanks
MIANCH

 

[MortenA]

if all tubes are the same the the flow shall distribute evenly. If - however one gets a different (higher) resistance - then the loss across each tube must be the same - (they start and end the same place) but the resistance is in fact different. So then the flow will distribut unevenly. This will cause the flow in the fouled pipe to drop. This could promote more fouling (lower velocity, longer residence time etc. and thus once out of ballance this could escalate until the tube is blocked.


Best regards

Morten

 

[MIANCH]

Morten,
Could you elaborate more with some examples.
Thanks
MIANCH

 

[MortenA]

Not really - you will have to crack a text book yourself

Best regards

Morten

 

[vpl]

This image was obtained from a google image search on "blocked heat exchanger tube."

There were a number of others, but this one stood out for the clarity and visibility of the biofouling.

I think it's possible they might get some flow on the left side of the finger (there appears to be some opening, though of course I couldn't speak for how much of the total tube is open), but the one directly below appears to be completely blocked, as does the one on the upper far right.

Obviously, the more blockage, the less flow, leading to "flow maldistribution."

Patricia Lougheed

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[racookpe1978]

What I've seen was typical water-side (inside the tubes) fouling on oil coolers. The entire "bottom half" of the tubes in the lower half of the heat exchanger section were plugged with soft sludge/mud/gunk. So the "bottom half" of the tubes had "no" cooling effect and only the upper half tubes each end were "exchanging heat" between tubes and the cooling water.

Design that. Or keep your tubes clean by shutting down your heat exchangers. Water will flow only in clean tubes from a clean HX head.

 

[vpl]

This is an aside to racookpe:

I agree that "typically" I've seen more soft mud/slurry in the bottom tubes such that flow only goes through part of the heat exchanger. The worst case I've seen was a utility that decided to pump "fish puree" through all their heat exchanger tubes -- multiple heat exchangers were packed solid and at one point, the heat transfer was going in the "wrong" direction. I've seen more than a few cases when zebra mussels first hit the midwest where heat exchangers were opened and they resembled the picture above (which did not come from my files.) I also know of a plant that has a continuing problem with calcium carbonate coming out of solution and coating their tubes.

Given the dearth of information from the original poster, the cause of the "maldistribution" in his heat exchanger could range from a "typical" one to one that's completely blocked.

Patricia Lougheed

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[MIANCH]

The tubeside fouling may be not due to maldistribution because you have enough velocity and and angle of erection, blockage of flow may be can create upto some extent this problem due to donwstream fittings and facilities like heaters and exchangers.
The only problem is fouling and my question is,how maldistribution can help in crude oil pre-heat exchangers?
MIANCH

 

[vpl]

Mianch

I am a bit confused by your writeup. The fouling causes the maldistribution of flow through the tubes, not the other way around. As Morten pointed out originally, the flow will enter the tubes equally if they're clean. There's no way that purposeful maldistribution "helps" -- if the fouling isn't removed, it just gets worse.

Looking at your original post, you also mentioned maldistribution and fouling in the channel side. Do you mean the shell side or in the end channels?

I realize there may be a language barrier (though your English is much better than my understanding of any other language). Try writing your problem in your native language, using Google Translate (or other web translator) and then cut-and-pasting it into the forum. Also pictures help.

Patricia Lougheed

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[cloa]

maldistribution can only be bad otherwise it wouldn't be mal-distribution so it can't help anything.

 

[MIANCH]

vpl,
You are right about my writing, I confused to understand, when I study ESDU (Engineering Scientist Data Unit)for fouling in tubes, due to maldistribution in tubes when service is clean. In ESDU mentioned imagine, if maldistribution is there and this can create a fouling.
After reading again ESDU, I confused more how a clean service immediately fouled. my refinery after S/D pre-heat exchanger become fouled with in month and we are facing problem in heater (skin temperature went high).
Again, imagination and practical are close enough but I'm still confused why this is happening and how we can avoid it.
Thanks