Chemical Cleaning of Cooling Water system line 2

[devaxrayz]

Hi all,

curently i am studying in posibillity to do a chemical cleaning in cooling water system to remove it scale. When i say cooling water system it means the whole system, incuding all piping and all hot equipment passed by the cooling water.

The cooling water is sweet water downstream clarifier and sand filter.

We planned to do it with sulfuric acid, the concentration around 3%-5%. And part of our idea is how if we do it online (plant is still running).

I still have a lot of doubt, since there is no acid chemical that can really remove all the scale and a lot of diversity material that exposed in this chemical cleaning. I also never heard that anyone ever do it before makes it seems a crazy idea but worthed to studied.

My question :
1.does anyone in this forum ever do this chemical cleaning?what are your opinion?
2.what scale usually occurred in sweet cooling water line? (i supposed it mix of calcium carbonat, silica and dominate with corrosive product scale)
3. What chemical suitable for those scale?
4. Some of the material resistancy data to sulfuric acid can be found in corrosion handbook. but some are not (like tungsten carbon in pump mech seal, and some special metal) where can i find that data?

thanks before....


Devax rayz

 

[cub3bead]

1. I haven't done one but I would be very cautious trying to do the whole system while on line. The rule of unintended consequences will likley come into to play and managment likely wouldn't aprreciate that. If you are going to do it; make sure you plan, plan, plan and be ready for the unexpected.

2. It depends on the water chemistry and materials of construction in the system. You could have the scales you mention or it could be tuberculation. See

http://www.corrosionlab.com/Papers/technical-brief-tuberculation.htm

for more details on this subject.

3. You might consider other chemicals such as sulfamic acid, EDTA, etc. that might be a bit safer to deal with.

4. Have you considered how you will determine that the cleaning is completed?

5. Don't forget to look at the impact of the cleaning agents on the cooling tower materials of construction.

6. Waste disposal will be an issue to address.

7. Have you developed a plan to passivate the surfaces after cleaning?

 

[EdStainless]

Doing the whole system at once may sound easy, but the risk is large. You need to isolate sections based on materials of construction and degree of scaling. Do you even know what all of the materials in the system are? If you do the whole thing at once you may get too much attack in some hot areas and some re-depopsition in cold ones.
You should isolate sections and use a small pump to provide circualtion of the acid.
Sulfamic or phosphoric with EDTA added will be easier on most materials and keep the prodicts in solution.
You will need to monitor the cleaning and determine the end point.
One place to start is

http://www.oakite.com

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[lilliput1]

Is degree of scaling/corrosion is severe, it would be better to replace the piping. You would also have to design a system that would address the scaling issue. onsider using (2) separate water loops with corrossion resistant coated heat exhanger. Consider phenolic coated tubes in shell in tube heat exchanger with the "sweet" water in the shell and the closed loop cooling water (which should be chemically treated) in the tubes. When corrosion barrier is depleted, the tubes should be replaced. Once through water would be difficult & expensive to chemically treat. The recirculated water would be easier to chemically treat, preventing scaling & corrosion in the piping.
No chemical treating company or pipe cleaning company (using rams or pulsed jets of water, which would be a noisy process) would accept liability for any damages resulting from loosened pipe scale/corrosion/debris.

 

[ChrisDerrick]

devaxrayz,

I have done some work with a company called BJ Services doing chemical cleaning on equipment similar to yours. They can provide an evaluation and offer cleaning options. If interested you can call Larry Slabodnic at 909-357-8054.

Hope this helps

Chris Derrick

 

[sshep]

I wouldn't do it online- too much risk. Control of iron content and dumping of the dirty acid will be a problem. You can't nuetralize or passivate directly on top of this dirty chemical cleaning solution. It will need to be diluted down with make-up and blowdown and thereby generate a lot of waste. The same problem will exist to a lesser extent after passivating. You are also dealing with alot of variation in process temperatures which could cause unforseen problems- including some high wall temperatures which caused scaling in the first place.

If you already plan to reduce rates during the cleaning, it is better I think to just shutdown for 5 days and do a good safe job. You can also open the equipment and inspect your work. Hopefully the increased production possible with clean equipment will allow you to make-up for lost production over the subsequent month.

Best of luck, sshep

 

[LeeColl]

I've had some experience in cleaning cooling water systems, either piecemeal components or entire systems during maintenance turnarounds. There are a number of significant considerations should you attempt to clean your facility's entire CWS using chemical cleaning.

The majority of scale species are obviously waterborne deposits, mainly calcium carbonate, iron oxide (usually hematite or goetite), silica scales, and on occasion sulfates if sulfuric acid is used in the plant's pH adjustment process.

There are a variety of solvents that would be effective on the common mix of scales, but I would not use sulfuric acid on these systems. The likelihood of creating calcium sulfate (as a precipitate) will foul your system extensively - as not all of it ends up in the CW basin. You would not want to route the cooling water/solvent mixture back to the CW tower anyway, as once you solubilize or sequester iron, the aeration that occurs can potentially yield a ferric condition, which is extremely corrosive to your equipment.

There are additives and techniques available to design an ideal cleaning process. On-line cleaning to restore your dT across heat exchange equipment is often a simple and effective method that allows the acid or chelant to be injected upstream of the exchanger(s) and a neutralization agent introduced downstream to assure the pH is controlled. Depending on the choice of solvent, nature of scale, and configuration of equipment, the wastes resulting from the on-line cleaning process can usually be captured and contained via filtration of the CW basin or return sump areas, so as not to redistribute any precipitated materials back into the CW supply piping.

If the plant is going to be totally shut down during your outage, sections or segments of the piping and assocated exchangers can be cleaned via circulation of chemicals, high energy flushing, or mechanical (hydrojetting) processes. It is often the case that in the larger diameter piping systems, there is often a lot of solids contamination from airborne dirt, sand, etc. that is slowly pushed around the system. Flushing at high velocities usually motivates this contamination from within the system.

Recommended solvents are:
Inhibited hydroxyacetic/formic acid blends
Inhibited hydrochloric acid with fluoride additives (for silicates)
Inhibited formic acid
Inhibited sulfamic acid
Inhibited EDTA/sulfamic acid blends
Inhibited low-pH EDTA (disodium or diammonium salts)

Convential solvents I would NOT recommend:
Sulfuric acid - due to potential for calcium sulfate precipitation
Citric acid - due to potential for calcium citrate precipitation

HTH

Lee