Q. Explain about Ducts and Flues in steam generators?

All air ducts and gas flues connecting the forced draft fan, fan intake silencer, preheater, and transition piece at the generator outlet shall be supplied.

Ducting shall be of continuous seal welded construction to ensure air tightness, with gasketed / flanged connections for field assembly.

Ducting shall be adequately reinforced and stiffened.

Ducting design shall be based on maximum discharge fan pressure at minimum design temperature. Maximum velocity in intake duct shall be 60 ft/s (18.3 m/s). Maximum velocity in flue gas shall be 90 ft/s (27.5 m/s).

Ducting shall be sized to limit the dynamic head at the point of maximum velocity to no more than ten percent of the burner pressure drop at firing conditions.

Minimum thickness of air ducting shall be 3/16 in (5 mm) for air ducting and 1/4 in (6 mm) for flue gas ducting.