Causes of High Dewpoint Temperatures in Boiler Flue Gases

Abstract

High dewpoint temperature in flue gases in boiler plants causes premature condensation in the cooler gas passages resulting in deposits and corrosion. Evidence is submitted to show that high dewpoint can be caused by the increased temperature of the superheater tubes, the oxide film catalysing the conversion of the sulphur dioxide formed by combustion into sulphur trioxide, thereby increasing the sulphuric acid content of the gases. The trouble is confined chiefly to plants fired by mechanical stokers, pulverized fuel plants generally being unaffected. Coating the catalytic surfaces with lime or fine pulverized fuel ash prevents the action, and it is suggested that these materials sprayed on the tubes at intervals may prevent the formation of acid and its serious consequences.