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Posted by Orville on February 20, 2004 at 15:55:13:
In Reply to: Re: Boiler Rumble posted by Larry on January 13, 2002 at 07:25:55:
: From an article in Control Engineering Online by Kenneth E. Heselton, P.E. & C.E.M., KEH Energy Engineering.
: "Many problems of incomplete combustion are revealed through complaints of flame noise. The condition referred to as "rumbling" is normally due to improper mixing at the burner but subsequent mixing—to form miniature explosive pockets—in other parts of the boiler. Every incident of rumbling I have investigated has included high levels of CO in the stack gases. The condition is not readily fixed because the minute the fuel and air enter the burner, science takes a back seat to art, and the number of combustion "artists" is dwindling.
: Yes, you actually can control incomplete combustion. By installing a continuous CO analyzer on the outlet of a boiler and regulating the air to fuel ratio controls to maintain a constant CO at the outlet you control incomplete combustion. CO control is favored in several installations, especially those where setting leaks, or the like, do not provide an oxygen value at the outlet that is the same as furnace conditions. Air leaking into the equipment can increase the oxygen content of flue gas to prevent accurate control of excess air at the burner. The only effect of air in-leakage on CO measurement is slight dilution.
: CO control also avoids a problem with oxygen trim systems using zirconium oxide analyzers. It is possible for those analyzers to misinterpret CO as oxygen when there is no oxygen present. When controlling excess air at low values an oxygen trim system can automatically swing into a reverse action that produces a lot of incomplete combustion. Many oxygen trim systems also use combustible analysis to detect the problem and alarm or reverse it. A CO analyzer is not capable of misinterpreting anything else as CO."
: Check out the full article - hope this helps.
: : In large, pressurized furnace, utility boilers, what is the definition of "Boiler Rumble" and the causes and cures?
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