Influence of Operating Conditions on SO₃ Formation during Air and Oxy-Fuel Combustion

Abstract

Because SO₃ participates in both high- and low-temperature corrosion processes, there is a general concern about the SO₃ formation under oxy-fuel fired conditions. This work has the aim to evaluate the influence of combustion parameters on the formation of SO₃. Experiments were conducted in oxy-fuel and air-fired experiments with propane as fuel and injection of SO₂ in the oxidizer. The SO₃ concentration was measured with a controlled condensation method at the furnace outlet as well as in the flame. The experiments show that the gas-phase is an important contributor to SO₃ formation and that the SO₃ formation is strong during burnout of the fuel. In oxy-fuel combustion with wet flue-gas recycle (FGR), more SO₃ was formed than during dry FGR at similar temperature conditions, which indicates that H₂O enhances SO₃ formation. The experiments also show that the SO₃ formation rises with an increase in furnace temperature. Because temperature and residence time in the furnace increases with reduced FGR ratio, the FGR ratio directly influences the SO₃ formation in oxy-fuel combustion. This was obvious during the experiments, and the SO₃ concentration rose with a reduced FGR ratio