Sintering, Phase Transformations, and Slagging-Fouling Tendencies of Creosote-Treated Railroad Ties

Abstract Disposal of used creosote-treated railroad ties (RT) is environmentally challenging due to the carcinogenic nature of the creosote. Although the US EPA permits using RT as an energy source in certain combustion units, biomass faces issues with slagging and fouling at high temperatures. In this study, the initial sintering temperature (IST) and melting point of RT ash pellets heated between 600 and 900 °C were determined using a compression strength test (CST). The agglomeration and mineral phase changes were analyzed with BET, FTIR, and XRD, while the slagging and fouling potential were assessed using empirical indices such as the bed agglomeration index, base-to-acid ratio, slag viscosity index, silica-aluminum ratio, alkali index, slagging index, fouling index, and a ternary diagram. CST results show that the IST and melting point are approximately 600 °C and 651 °C, respectively. The BET test indicates gradual agglomeration with increasing temperature. FTIR and XRD confirm calcite decomposes into anhydrite at the IST, aiding sintering and agglomeration. At the melting point, calcite, anhydrite, and silicophosphate transform into vitreous Ca-containing aluminosilicate and aluminophosphate phases, reducing the strength of heated RT ash pellets. Moreover, most indices suggest a high potential for slagging and fouling. Thus, thermal conversion of RT should be operated at or below 651 °C to avoid ash-related problems. Otherwise, the use of additives, leaching, and co-utilization must be explored if the conversion process requires higher operating temperatures. Graphical Abstract