Erosion-Corrosion Effects on Boiler Tube Metals in a Multisolids Fluidized-Bed Coal Combustor

Metal wastage of boiler tube materials has been measured during combustion of coal in a laboratory scale fast fluidized bed. In the multisolids fluidized-bed process, high-sulfur coal and limestone are fed to a conventional bed of selected high specific gravity materials. An entrained bed is superimposed on this dense bed, to act as the heat exchange medium. Erosion-corrosion effects were studied on simulated steam tubes (400–700°F, 204–370°C) oriented either horizontally or vertically in the bed. Results of 50-hr tests showed that the life of heat exchange tubes operating up to 650°F (343°C) in this type of combustor will depend primarily on erosion effects. Erosive wastage was greater in the dense bed than in the entrained bed, with greater losses on horizontal surfaces than on vertical surfaces. Support structures at bed temperature of 1600°F (870°C) were found to be subject to corrosion by oxidation and sulfidation reactions. High-chromium alloy steels proved to be most resistant to the erosive and corrosive effects.