Chemistry and melting characteristics of fireside deposits taken from boiler tubes in waste incinerators

Twenty-three tube deposits taken from seven heat-recovery boilers of municipal solid waste incinerators were examined by chemical analyses and X-ray diffraction. These deposits were measured by Differential Scanning Calorimeter (DSC) in N₂ to investigate their melting characteristics. Sixteen deposits were used to evaluate their corrosiveness to carbon steel by high-temperature corrosion test conducted at 400 °C for 20 h in 1500 ppm HCl – 300 ppm SO₂ – 7.5%O₂ – 7.5%CO₂ – 20%H₂O – N₂. Total heat of endothermic reactions of the deposits taking place between 200 and 400 °C can be related to the corrosion rate of carbon steel at 400 °C. Corrosion initiated at temperatures when the deposits started to melt, became severe when fused salt constituents increased, and alleviated when the majority of the deposits became fused. The corrosion can be interpreted as fused salt corrosion caused by chloride and sulfate salts.