Formation of SO₃ in a Noncatalytic Combustor

The major contributor to corrosion and deposits in boilers and gas turbines has been recognized as the reaction of sulfur oxides, especially SO₃, in the combustion gas with furnace elements. One way to minimize these reactions is to reduce the quantity of SO₃ formed. Factors affecting SO₃ formation have been studied in a noncatalytic laboratory combustor, and results of the investigation show that SO₃ in the combustion gas can be reduced by: (a) Reducing excess air, (b) burning fuel with a lower sulfur content, (c) preventing air leakage into the combustion system, and (d) covering catalytic surfaces, such as superheater tubes, with less catalytic protective coatings. Some experiments showed that iron-oxide coatings, which built up on iron surfaces, were highly catalytic for the production of SO₃ under boiler-furnace-simulated conditions.