Canopy Stack Design for Boilers

[ashaari]

Hi all. I noticed that boiler stacks in my plant have an inverted canopy design. But I have also seen boilers in other plants have the 'normal' canopy design. What is the basis of designing the canopy to be inverted? My canopies now experience corrosion which I highly suspect because of water accumulation due to the inverted design. If i were to change the design to 'normal' canopy, will there be any significant impact on the flue gas release to atmosphere? Appreciate your opinion, thanks!