Fossil Fired Boiler Fly Ash Erosion vs. Flue Gas Velocity
Fossil Fired Boiler Fly Ash Erosion vs. Flue Gas Velocity
(OP)
B&W's "Steam" offers information on the relationship between fly ash erosion of boiler tubes and flue gas velocity. They state than the metal loss on convection pass tubes is proportional to the total ash quantity passing through the boiler and is an exponential function of flue gas velocty. This is obviously intuitive, However, they offer no additional help on what the exponentional function is or how to determine it. Anyone have any ideas?
Thanks.
Thanks.





RE: Fossil Fired Boiler Fly Ash Erosion vs. Flue Gas Velocity
RE: Fossil Fired Boiler Fly Ash Erosion vs. Flue Gas Velocity
Some techniques to reduce the effect of ash erosion, besides lowering velocity, include anti-laning baffles ( near tube bends at HRA front and rear walls), using inline tube bundles, providing a furnace "nose" and other furnace geometry details to reuce the gas flow unbalance ( to be determined by modeling via numerical models).
To reduce gas velocity , operating at lowest practical excess air helps, and that implies mills are properly maintained for correct fineness and the burner to burner coal flow unbalance must be minmimized.
RE: Fossil Fired Boiler Fly Ash Erosion vs. Flue Gas Velocity
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or google: erosion particle impact
RE: Fossil Fired Boiler Fly Ash Erosion vs. Flue Gas Velocity
The paper confirms the 3.5 exponent, if one recognizes the plots are nomralized as (mg metal loss / kg erodient hitting surface). The rate of erodent hitting the tube surface is proportional to velocity times (lb ash/ lb fluegas), so the 2.5 exponent would be increased to 3.5 if teh erosion rate is not normalized.
Ash particles that are smaller than 25 um do not contribute to erosion of tubes, since they follow the flue gas streamlines , and due to the "law of the wall" such small ash particle will not impact the wall surface except due to brownian motion.
Only ash particles that are harder than steel will cause erosion , and the paper demonstrtes that silica and pyrites that are larger than 25 um diameter are the only significant contributors to ash erosion.