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Hot Loop

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#1 Guest_chemtreter_*

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Posted 12 April 2012 - 10:06 PM

A client has a 15000 gallon hot loop losing 2000 gallons per day. They won't treat with regular corrosion inhibitors due to cost. I recommended they treat as a cooling tower. My question is will the polymers and other products in a cooling tower product hold up to 180F heat? Or is there another method to treat for scaling/corrosion for this system? Vern Ellis

#2 Guest_dick@richardhouriganinc.com_*

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Posted 14 April 2012 - 12:43 AM

That is fairly hot. The hottest cooling towers I have ever treated with conventional cooling water products, have hot wells that run around 160 degrees Fahrenheit. I assume from your comments that the water is not softened. I would demonstrate to him the difference between the calcium hardness of the water going in and the calcium hardness in the hot loop. Let's say the difference is only 10 ppm. At a loss rate of 2000 gallons per day that would still be 0.1668 pounds of calcium carbonate scale....or 60.882 pounds of calcium carbonate scale per year. This will all go to the hottest part of the system. At the very least he should soften that water BTW: I recommend that for all closed loops since you can seldom be sure that they are truly closed. Also, it should be a twin softener.

If he agrees to that, your problem becomes simpler. Now you only have to treat it for corrosion. If there are no yellow metals in the system, you can use either catalyzed sodium sulfite or erythorbate. I would use both in a blend with enough caustic to keep the pH around 8.5 to 9.0. You need to know how much dissolved iron is in the system water BEFORE raising the pH, since raising the pH can create iron hydroxides which revert to oxides. These could then destroy pump seals and pump impellers. You should also have side stream filtration on this system capable of down to 5 micron filtration capacity. That will be needed during pH elevation, particularly if dissolved iron is currently present.

If he will not soften, then you need to keep the pH to 7.5 to 8.0 to balance the corrosion on iron versus the scaling potential. You need to use some polymers (probably even a good idea if he does soften). I would recommend some terpolymers for iron and some polyacrylate. Probably 5 to 10 ppm of each should do. Phosphontes could be added. I would recommend 5 to 10 ppm as HEDPA. USE ONLY PHOSPHONATES THAT ARE STABLE TO CHLORINE, because at those temperatures you will begin to experience some phosphonate reversion to ortho phosphate. Ortho Phosphate is not a concern in a boiler program, since the high pH will result in hydroxyapatite formation. At this pH tricalcium phosphate will be formed.

If there are yellow metals present you will need to use azoles. This could get tough. High concentrations of 50 to 100 ppm are advisable.

You need to be checking copper and iron in the loop versus the make up water.

PROTECT YOURSELF LEGALLY. It is far from certain that any of this will work. You will need to constantly check for corrosion products and scaling potential, so you can make adjustments in the program. I would strongly urge that you have one of their corporate officers sign a legal document agreeing to hold you harmless, since they are so far away from accepted procedures. Without some sort of hold harmless agreement you may just want to walk away from this one. No point in being sued.

A conventional borate-nitrite treatment could be far cheaper if he would/could close up the system.


Is the 2000 gallon per day loss necessary?

Did anyone treat this before you? What did they do and how did that work?

How is he keeping the expansion tank from filling up with gasses? That should become a major problem at those temperatures and that make up level.

#3 Guest_Timothy Keister_*

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Posted 21 November 2012 - 09:35 PM

Polysilicates work quite nicely as corrosion inhibitors in this temperature range and can be combined with zinc, ortho phosphates, and polyphosphates. As Dick has noted, you must examine all the water quality parameters and materials of construction prior to devising a treatment chemistry. High calcium would require a calcium scale inhibitor and maybe even a silicate scale inhibitor like Lubrizol K798 if magnesium content is significant. With that water loss, you will have to keep the chemistry simple for it to be economic as the dosage will be high to obtain good results.
Tim Keister, CWT

#4 dhourigan


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Posted 24 November 2012 - 04:13 PM

Tim Keister is the owner of Pro Chem Tech. Here is a hyper link to his company's website: http://www.prochemtech.com.

Tim, unlike the Association of Water Technologies (AWT) ListServ, we allow shameless self promotion here. LOL.

BTW: We are also not afraid to host postings from Nalco and GE Water Personnel...unlike the Association that calls itself the "Voice of the Water Treatment Industry".........unless you have over 30 million in sales.

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