Department of Chemistry
Master of Science
The occurrence of furnace wall and superheater corrosion in fluidized bed combustor systems has caused some operational and economic concerns. It is generally accepted that chlorine and sulfur may play roles in this corrosion. In order to predict the performance of high chlorine or high sulfur coals in these combustion systems, it is necessary to have a better understanding of the different corrosion mechanisms in which chlorine and sulfur may be involved. It is also important to evaluate the critical point of coal chlorine content which may cause initial corrosion. The laboratory-sized atmospheric bed combustor (AFBC) at Western Kentucky University was designed to serve as a flexible research and development facility to gain operating experience, evaluate combustion performance, and estimate the effects of flue gas emissions. Fluidized bed combustion systems are particularly suited to waste fuels because of their ability to burn low grade and variable fuels as well as absorb sulfur oxides through the use of limestone. Our study was mainly designed to evaluate the role coal chloride may play in causing corrosion of boiler components Four different metal alloys [carbon steel CI020 (0.18% C and 0.05% Cr), 304 SS (18.39% Cr and 8.11% Ni), 309 SS (23.28% Cr and 13.41% Ni), and 347 SS (18.03% Cr and 9.79% Ni)] were exposed uncooled in the freeboard at the entrance to the convection pass, where the metal temperature was approximately 900 K. The carbon steel samples were essentially destroyed. However, it was expected that CI020 carbon steel samples would not withstand the high temperatures selected for the testing. A small amount of scale spallation was observed on the other three samples in both test runs. Based on the SEM-EDX mapping results, there was no localized chloride distribution observed on the surface of the coupons, neither in the scale spallation area nor on the rest of the metal part. Some trace amount of chloride was found, but evenly distributed on the surface of the coupons. There is no concentration of chloride on the spot of scale spallation. The scale spallation might be due to the effect of erosion. Further study with higher chlorine (> 0.3%) content coals for more conclusive information is needed.
Xie, Wie, "A Study of High Temperature Corrosion in an AFBC System" (1998). Masters Theses & Specialist Projects. Paper 327.