Fixed tubesheet HX shell side cleaning

[mp662]

I have a fixed tubesheet heat exchanger with massive fouling on the shell side (design was 10 psig drop, now closer to 50 psig). Thermal scans of the exchanger show a large blockage in 2 baffled sections of the exchanger. Tried chemical cleaning it with a non-aggressive solution, but it did not positively affect performance of the flow through the shell. The only chemicals that will clean this material have a good chance of compromising the mechanical integrity of the exchanger.

This exchanger is a BEM configuration with 6 baffled sections spaced 23" apart. The baffles are single segments with 25% baffle cut. The tubes are on a 15/16" triangular pitch. The diameter is 3'-7" and length is 14'. There is a 14" inlet with an impingement plate on the bottom side of the exchanger end. The other side with the outlet is on the top of the exchanger with a 14" nozzle. There are 2x 3/4" bleeds on opposite sides (180 degrees) of the inlet and outlet nozzles on the shell.

Are there any good ways (short of replacing the exchanger) to clean this material out?

 

[sshep]

Hey mp662,

The original project bought the cheapest exchanger (lowest capital) without regard to the future maintainability. They have screwed you. You can cut windows or add nozzles in the shell, but the triangular pitch will make the hydro blasting difficult anyway.

Maybe take another look at your chemical cleaning. Add some velocity, change direction, air rumble, etc. Any improvement is realistically just to buy some time. A new exchanger seems in the cards, so go for something better than BEM- ie a removable bundle. If there is a temperature cross, you might have to go for multiple AEU shells (or long baffle).

What are the solids and the process fluids, including temperatures? There might be a process workaround which can unload the exchanger.

Best wishes,
sshep

 

[Longinthetooth]

Sshep is correct. You are just putting off the evil day. I have been there and we tried everything, to little avail. Ended up replacing the exchanger. We swapped sides, ie. fouling service on the tube side. You have to redesign the exchanger thermaly, but if that works it's a permanent solution. It worked for us.

 

[ash9144]

You tried non aggressive chemical cleaning so I would next try aggressive chemical cleaning. You need to know what the scale is and work with a company that does that work routinely. I've seen success cleaning cooling water scale with weak acid solutions. Of course you lose metal also so it only delays the eventual replacement but could but buy you a year or two.

 

[mp662]

Thank you for all the replies.

Unfortunately this stuff is almost like hard glue. It is a polymer fouling that basically laughs at typical acid washing solutions that we've lab tested.

We are going to try a more aggressive acid solution to wash the exchanger. If that doesn't do it, we may end up installing a bypass line with a valve around the two baffled sections with the most pluggage. Wanted to poll your ideas about that.

Thanks again.

 

[chicopee]

Have a lab test several cleaners with that sample of the polymer and at the same time making sure the concentration of one of those cleaners does not damage the shell or tubes?

 

[cloa]

How about a base or some other type of solvent? Acid might just converting the original gunk into something worse such as catalysing a polymeric reaction.

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[mp662]

We've tried acetone, 20% NaOH, 98% sulfuric, and a few others. 98% sulfuric was the only one that worked, unfortunately we cannot use that due to corrosion, availability, safety, etc. We are going with a 20% sulfuric mixture with corrosion inhibitors. It did OK during a lab test as far as breaking the junk up.

The material is a phenol formaldehyde resin.

 

[ash9144]

98% sulfuric much less corrosive (for steel anyway) than 20%.

Another possibiblity since it is a polymer may be heat. High temp steam through the tubes may melt the polymer. If not there are some companies that will "bake" a heat exchanger.