Interactions of PbCl2 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 .