Fired Heaters

Mr. Norman P. Lieberman. Dear Sir, what causes fins in the convective section to break off? This is a big problem for us. I have watched your video on fired heaters, but you did not explain this problem.

--George, Texas


George, when the fins break off, are they rusty or covered with a sticky, gray paste type deposit? The sticky paste is iron sulfates. That’s caused by a combination of high sulfur fuel and low flue gas temperature. Sulfuric acid is formed when sulfur is burned and precipitates out of the flue gas as follows:

• 4% sulfur in fuel oil --------- 450°F
• 100 ppm H₂S in fuel gas ---- 300°F

The acid attacks the fins and forms the sticky iron sulfates.

The rust is caused by afterburn. That is, the fins are burnt-up. The way to avoid this is to add sufficient combustion air to avoid CO, alcohols, ketones, etc. from escaping from the firebox, mixing with convective tramp air leaks, and reigniting. Hope this helps.

--Norm