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Re: Silica deposits in boiler / testing feedwater

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Posted by Vern on May 30, 2002 at 07:42:37:

In Reply to: Silica deposits in boiler / testing feedwater posted by ROY DE HAAN on May 29, 2002 at 13:19:47:

: How do you test silica levels in feedwater supply?
: How do you filter/remove silica from the feedwater?
: How do you dissolve existing silica deposits inside boiler tubes?

1. To test silica levels, purchase a silica test from 1.Hach, 2. LaMotte, 3. Taylor.
Which test you purchase depends on how accurate you want to be with the results. A colorimetric
type test gives you results in a range of values and can be difficult to determine. Especially if you have trouble
determining shades of color like I do. I use a spectrophotometer from LaMotte because it gives me needle type
readout with a specific number. In boilers, the industry standard for silica is 150 ppm max. I have seen boilers run higher with
no problem.

2.To remove silica is done before your makeup water enters your feedtank. You can use reverse osmosis, or demineralizers.
Either one adds cost to your program. Both have pros and cons, your chemical vendor should be able to
help you with this. Your chemical program will have to change to meet the different probably higher quality
of water you will be sending to your boiler.

3.Removing existing silica deposits is difficult. If you have a large watertube style boiler you may want to mechanically
turbine the deposits out. I have seen good results with company who runs super high pressure water down the tubes to mechanically
scrub them. I have cleaned smaller boilers with a combination of inhibited hydrochloric acid, citric acid, and ammonium bifluoride by
circulating the solution. Acid cleaning is not a job to be undertaken by inexperienced personnel, so be careful if you do this. Feel free
to email me.

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