Interactions of PbCl(2) with Alkali Salts in Ash Deposits and Effects on Boiler Corrosion

A novel temperature gradient laboratory-scale corrosion test method was used to study PbCl(2) migration, interactions with SiO(2), NaCl, Na(2)SO(4), KCl, K(2)SO(4), or NaCl–KCl (50:50 wt %) and corrosion of carbon steel in waste-fired boilers. Two different steel temperatures (200 and 400 °C) were tested. The temperature in the furnace above the deposits was 700–800 °C. Exposure times of 4 and 24 h were used. The deposit cross sections were analyzed using SEM/EDXA. The results show that PbCl(2) vaporized and condensed in the adjacent deposits. PbCl(2) did not interact with SiO(2) but caused severe corrosion. Deposits containing Na(2)SO(4), K(2)SO(4), and/or KCl reacted with the PbCl(2), forming various new compounds (Na(3)Pb(2)(SO(4))(3)Cl, K(3)Pb(2)(SO(4))(3)Cl, and/or K(2)PbCl(4)). In addition, melt formation was observed with all alkali salt deposits. Visibly more Pb was found in deposits where reactions between PbCl(2) and alkali salts were possible, i.e., Pb was observed to be bound to the reaction products. No measurable corrosion was observed with steel temperature at 200 °C, while steel temperature of 400 °C resulted in catastrophic corrosion. PbCl(2) in contact with the steel surface lead to faster corrosion than K(2)PbCl(4).