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Join Date: Feb 2012
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Colloidal Silica

03/20/2012 8:51 AM

Good morning all. Recently we had some silica out brakes in our LP (250 psig) boilers. Although our regular tests did not show Si content close to what we found in the boiler water vs. boiler feed water. We suspect colloidal silica. Does anyone has any experience in this area ?

I guess main question is, how do we battle it? with some chemical additives or just by using blow downs, until the event have passed.

Thank you in advance.

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#1

Re: Colloidal Silica

03/20/2012 11:00 AM

I am not the person to address this, but look at the source of your makeup water and address that.

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#2

Re: Colloidal Silica

03/20/2012 5:43 PM

As 911 posted, confirm your water treatment upstream of the boiler is working correctly, then problem should go away.

But are you sure it is Silica? Have you had this tested, did the tests show any other contaminent? Why do you suspect Colloidal Silica? Please post all the water analysis if you have it. Assuming you are having to clean with Hot Caustic or HF Acid ??

There are specific antiscalant chemicals that can be added to prevent Silica scale or the formation of Metal Silicates (normally Mg, Al, Fe etc - transition metals), but if it is coming into the boiler as colloidal Silica then these won't help. But then wouldn't expect colloidal Silica to be an issue in any case, so I strongly suspect Silica or metal silicate problem in this case.

I can reccommend product called FLOCON 260 by BWA. This is specifically for controlling silica and metal silicate scale formation.

In general the rules of thumb are this will control Silica scale up to 260ppm SiO2 concentration. For metal Silicates, for pH < 7.5, concentration product [SiO2]x[metal] < 220,000, & for pH > 7.5, concentration product [SiO2]x[metal] < 110,000 - with the metal concentation is expessed as CaCO3 equivalanets, SiO2 as mg/L.

Silica and metal silicate scale is an area still very much in need of further research, I've been working in this area lately and the science is really yet to be fully defined as the mechanism for this scale formation is not yet properly understood. This is why Silica and Silcate scale is not covered in any projection software (as many other scales are). They suspect this is because there may be many many different types of scale occuring, depending on the many other chemical species present, and very complex interactions between them. Hence too complex to accurately predict.

But the rules of thumb above do work OK.

Hope this helps,

Anthony

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#3

Re: Colloidal Silica

06/17/2012 1:00 AM

Collidal Silica can be removed in Clarifier and UF

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