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reason for low silica in boiler blow down even CBD is closed 1

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mssengr

Chemical
Apr 6, 2012
2
We are operating four boilers at 105 Kg/Cm2 pressure. Silica in their steam drums is as low as 120 ppb. CBD, IBD and sample coolers valves from their drums are also closed. Moisture in flue gases are also analyzed showing no tube leakages. we fail to understand why silica is so less? BFW being fed to boilers is less than 10 ppb silica and Dissolved Oxygen less than 10 ppb. Eliminox is being dosed as oxygen scavenger. please advise what to check further as we fear that there is some thing going wrong that can led to any failure.
 
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Are you sure all the valves are holding and you don't have an inadertent blowdown occuring? The piping downstream of the should be relatively cool if there really is no flow.
 
You do not add much detail on your boiler system.

What is the silica concentration over time? Has the concentration dropped recently or is it constant?

Do you have significant steam users?

What type of silica is it? Is the silica colloidal?
 
thanks TDK
we removed insulation from IBD lines and CBD lines and checked temperature at upstream and down stream of valves. We found that IBD valve is slightly passing. Problem will be fixed by replacing this valve in coming shut down
 
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