A Pilot-Plant Investigation of Factors Affecting Low-Temperature Corrosion in Oil-Fired Boilers

Abstract

Methods for controlling or eliminating low-temperature corrosion are continually being sought to improve boiler availability and thermal efficiency. A small pilot plant was constructed at the authors’ company in which factors that affect low-temperature corrosion could be studied under closely controlled conditions. Results of tests on this unit show that: (a) The corrosion rate on carbon steel increases gradually as metal temperature falls below the acid dewpoint, passing through a peak at a metal temperature about 200 F. The corrosion rate then decreases as metal temperature continues to fall but begins to rise rapidly to extremely high values at temperatures just above the water dewpoint (⋍ 120 F). (b) Low-temperature corrosion of carbon steel can be practically eliminated if a method can be found for reducing the sulfur content of oil to about 0.5 percent. (c) The application of low-excess-air operation has the potential of eliminating low-temperature corrosion in boiler plants firing high-sulfur residual oils. (d) Corrosion of carbon steel above approximately 170 F can be reduced 30 percent or more by recirculating 25 percent of the flue gases to the burner. Future work will include a study of the effect of low-excess-air operation on high-temperature oil-ash corrosion and deposition and on the effect of oil ash on low-temperature corrosion.

Duct injection technology prototype development

“…The ideal environment would be dry unabraded walls with no deposits, or where deposits are continually removed and refreshed; also no temperature cycling and no condensation should be allowed to occur• However, the ideal is difficult to maintain and many duct injection pilot tests have experienced wall wetting and plugging. (4,5) This experience suggests that high corrosion rates will be experienced in localized regions where moisture or deposits can collect. Corrosion in dry scrubber or duct injection environments was initially assumed to be much lower, compared to wet scrubber environments.…”

Plastic heat exchangers: a state-of-the-art review

“…The basic caus.es of low-temperature corrosion are well-known .. 64 Briefly, almost all the sulfur in the fuel is oxidized to S0 2 during combustion and a small part, usually less than 1o/o, is further oxidized to S0 3 • As the flue gases cool in passing through the boiler, the S0 3 reacts with water vapor to form sulfuric acid. Flue gases containing even traces of S0 2 have high acid dew point temperatures, up to about 3 50°F, and liquid that condenses below the dew point contains significant concentrations of sulfuric acid.…”