Chemical Contamination and Heat Transfer

[MW222]

Hi all,

Thanks in advance for any help.

We have a heated water loop that is used as the heat exchange fluid for a kitchen water loop. Currently the heated water loop is treated with a potable chemical treatment chemical even though it never comes into contact with the kitchen water loop water. Hypothetically, if the heat exchanger had an internal leak there could be some contamination between the two loops, which is why the heat exchange fluid is treated with a potable chemical treatment.

My question is: Where can I find the code that requires/describes the requirement for this extra level of protection?

Thanks!

 

[EdStainless]

It depends on where you are. In the US?

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P.E. Metallurgy, Plymouth Tube

 

[MW222]

Hi EdStainless - Yes, we are in the US.

 

[georgeverghese]

In an application like this, you cant afford to penny pinch on materials of construction or the type of HX.

 

[MW222]

georgeverghese- I'm not sure why you would state that, it gives me no useful information to my question.

 

[EdStainless]

There are a few guides for hygienic construction.
I am not sure that a system like yours is regulated, but it is good practice.
There is NSF, STFA, FSIS, EHEDG (Europe) and a scad of others.
I don't where coverage of your application falls. The materials (and maybe chemicals) should all have NFS listing at least, so I would start there.

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

Common failures on heat exchangers that result in migration of fluids from one side to the other are usually due to one or other of the following:

a) Inferior materials of construction that result in corrosion - this can be due to general corrosion or galvanic( dissimilar materials welded or fitted together) or localised pitting corrosion

b)Poor segregation of the fluids on either side - this can be due to simple roller expanded tube to tube sheet joints on a S/T type, or some types of plate frame HX also that can result in cross migration of fluids to to internal mechanical failure.

 

[MW222]

Thanks for the responses!

 

[StoneCold]

Would it not be a lot cheaper to just have an inline electric water heater and forget about the hot water loop???

Regards
StoneCold

 

[MW222]

StoneCold, it actually would not, but good idea, way to think outside the box!

 

[IRstuff]

We had a subcontractor build over 500 units of a system that included a glycol to glycol heat exchanger for a military application. Despite corrosion inhibitors, etc., the number one failure mode was still leakage of coolant.

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[chicopee]

It is interesting to note that that are all sort of regulations by EPA and States about installing backflow preventers on sprinkler systems, boiler feed water lines sewage lines and yet in your application you use a potable chemical treatment. Without researching your detail, my first instinct would be that your are violating the drinking water regulations, however, I don't know that for a fact so check out state, local(board of health) and EPA regulations to confirm compliance.

 

[georgeverghese]

A knee jerk reaction to the minimal information provided so far, if economics indications are that you could spend a little more CAPEX to justify this heat conservation concept, would be to use an all welded plate HX , and use standard duplex SS (22Cr duplex, UNS 31803) as a minimum for all materials of construction. Ask for the wide plate option and also fit a guard strainer on the feed stream inlet on both sides.

Also ask for a nitrogen blanket on the heated water loop expansion drum to keep air - oxygen out.

 

[georgeverghese]

Also, use only demineralised water (not RO quality water) as makeup water in your closed heated water loop. Monitor pH, TDS and oxygen content of the recirc hot water regularly and change out the entire closed loop inventory every few (??) years. Dont think you need to go for superduplex if closed loop hot water temp is less than 80degC or so (from memory).

 

[EdStainless]

2205 is an excellent material option, it is NAF listed for potable water.
But some system to monitor water quality and treatment is needed.

There are a lot of chemicals usable in contact with drinking water, The list is a bit scary.


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P.E. Metallurgy, Plymouth Tube