Why H Type Fin Tube Survives Ash Laden Flue Gas

The ash lane

An H type fin is not a continuous disc. Two square halves are welded around the tube with a gap between them, so a straight lane runs the length of the tube.

Fly ash that would bridge between continuous fins falls through that lane instead. The bank keeps its gas side pressure drop for longer, and soot blowing clears what remains.

Why the fins are thick

H type fins run 1.5 mm to 4.0 mm thick - far heavier than the 0.3 mm to 0.5 mm strip used on a wound fin.

That thickness is there for the cleaning cycle, not for heat transfer. Soot blowers erode thin fins until the surface is gone.

Pitch and height

Fin pitch runs 9.0 mm to 30.0 mm. Dirtier gas takes the open end of the range.

Fin height runs 15.0 mm to 45.0 mm, on base tubes from 25 mm to 73 mm with walls of 3.0 mm to 6.0 mm.

The design sequence is: dust loading sets the pitch, then the duty sets the fin height and the bank depth - not the other way round.

When to use HH instead

HH uses a doubled fin arrangement in the same bank geometry, for heavier heat recovery duty where bank depth is limited.

Where the fuel slags rather than simply ashes, move past H type entirely and use stud fin tubes.