Erosivity of particles from operating fluidized bed combustors

Abstract

The erosion-corrosion (E-C) metal wastage mechanisms and rates that occur in 1018 plain carbon steel used in tubular heat exchangers of fluid bed combustors (FBCs) are discussed. The characteristics of FBC bed material erodent particles such as composition, shape, size and strength were found to have a major effect on the surface degradation mechanisms and rates which occurred. A total of 16 different bed material particles from ten different FBCs were tested. It was determined that when the particles were strong enough not to shatter upon impact, their shape and composition were the most important factors in determining their erosivity. The basic E-C mechanism was the formation of an outer layer of bed material deposit or mixed bed material and iron oxide that was eroded away in a brittle manner by cracking and chipping of a segmented scale. Beneath the outer layer a mixture of varying amounts of iron oxide and bed material occurred, with the iron oxide content increasing as the base metal was approached. The morphology and behavior of the outer layer are closely related to the metal wastage of the tubing steel.