Scale build up

[scorer]

Dear All

Can anyone pass on some first hand experience of using descaling solutions to remove build up of rust/scale in reactor jackets or heat exchangers. I know that there are proprietary solutions available, but would also like to hear from people who have used more readily available solutions. Citric acid? Sodium bisulphate?

Guidance on what strength should be used would be appreciated. Are ther any corrosion issues. The solution is to be used on both 304L stainless and CStl equipment.

Thanks.

 

[friartuck]

Have you tried electromagnetic descalers or water conditioners?

go to LIFF, Salamander engineering, Scalewatcher, etc

These affect the scale and turn it into arginite which becomes a flaky deposit rather than a hard scale on the pipe wall

Friar Tuck of Sherwood

 

[EdStainless]

Chemical descaling works, when you pick the right chemicals. You need to do some small tests and make sure that you don't cause more problems.
You need a system to vent off any gases.
You need to be able to circulate the chemicals without flushing them. Often a small pump works for this.
You need to monitor the process so that you know when to add more chemicals and when the job is done.

The two biggest problems to watch out for are corrosion and re-deposition of residues.
Don't worry about how long it takes. Even if hhte process takes a few days it is OK as long as it comes out right.

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

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

 

[imok2]

Calcium Scale Removal
Calcium scales such as calcium sulfate, calcium carbonate and calcium oxalate are insoluble in water. However, all three are soluble in a Sodium Bisulfate acid solution. Calcium scale can be removed with an acid wash using a 5-15% solution of Sodium Bisulfate (SBS). SBS can also be used during a shut down to remove scale by re-circulating it throughout areas of the process where needed. The concentration of SBS solutions and the re-circulation time depend on the amount of scale that needs to be removed. The following chart shows (by weight) the theoretical amount of SBS required to remove one pound of calcium scale. go here for more info:

http://www.jones-hamilton.com/sections/products/sbstg_new-app.html

 

[jamescornford]

You may laugh, but vinegar is excellent to remove scale, not corrosive either.

 

[EdStainless]

You are right James, acetic, citric and phosphoric acids are often used because they are not too aggressive.

I do know of a power plant that used 68 tank trailers of Sulfuric on a descale job. And they still didn't get it done right.

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

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

 

[vpl]

scorer: To arrive at the best answer for your plant, I'd suggest a bit of homework. Start by talking to your plant chemists, then move on to the operators. Things to find out are:[ul][li]Do you know what the scale deposits are formed out of? As imok2 mentioned, calcium deposits react well to mild acidic solutions; however, if you actually have corrosion deposits, an acidic solution might make things much worse.[/li][li]How much scale are you trying to remove? There's a difference between removing a thin "film" and a 1/4" of deposits.[/li][li]Are there any limitations on water chemistry? For example, you mentioned using the descaler in stainless steel pipe. I know you don't use chlorides on stainless.[/li][li]Are there any limitations on discharge? At least in the US, some states have strict limitations on what can be discharged to open waterways. So after you get through descaling, what do you do with the solution?[/li][li]How long is plant management willing to have the component in the "descaling mode" (assuming it can't perform its normal function at the same time) and[/li][li]How much are they willing to spend? There is somewhat of a trade-off between these two - the stronger the descaler, the shorter the time to clean the system and the more it costs.[/li][/ul]

Once you get answers to these questions, and any others you can think of, you'd be better equipped to decide whether to go with an automatic descaler, a strong acidic solution, or a "couple of gallons" of vinegar. :

Patricia Lougheed

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