100 Most asked questions by Chemical Engineers


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Friday, July 8, 2011

Fired Heaters

Mr. Lieberman – I have read that draft at the top of the firebox should be 0.05 to 0.10 inches of water to minimize tramp air leaks into convective tube banks. We cannot seem to accomplish this. It seems like the draft is too erratic. It jumps around by itself. My boss wants to install auto stack damper controls to stabilize draft. Is this going to help?

--Dan, Wyoming

Dan – Erratic draft is caused by the wind blowing across the top of the stack. Of course draft will also vary with stack temperature, but not very fast. Gusts of wind will create very rapid changes in draft of 0.1” H2O to 0.2” H2O over just a few seconds. I can assure you, based on personal experience, that automated stack dampers will not work.

--Norm

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