Interactions of PbCl2 with Alkali Salts in Ash Deposits and Effects on Boiler Corrosion

Jonne Niemi; Hanna Kinnunen; Daniel Lindberg; Sonja Enestam

doi:10.1021/acs.energyfuels.8b01722

Interactions of PbCl₂ with Alkali Salts in Ash Deposits and Effects on Boiler Corrosion

Energy Fuels. 2018 Aug 16;32(8):8519-8529. doi: 10.1021/acs.energyfuels.8b01722. Epub 2018 Jul 8.

Authors

Jonne Niemi¹, Hanna Kinnunen^{1

2}, Daniel Lindberg¹, Sonja Enestam²

Affiliations

¹ Johan Gadolin Process Chemistry Centre, Laboratory of Inorganic Chemistry, Åbo Akademi University, Piispankatu 8, FI-20500 Turku, Finland.
² Valmet Technologies Oy, Lentokentänkatu 11, P.O. Box 109, FI-33101 Tampere, Finland.

Abstract

A novel temperature gradient laboratory-scale corrosion test method was used to study PbCl₂ migration, interactions with SiO₂, NaCl, Na₂SO₄, KCl, K₂SO₄, 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 PbCl₂ vaporized and condensed in the adjacent deposits. PbCl₂ did not interact with SiO₂ but caused severe corrosion. Deposits containing Na₂SO₄, K₂SO₄, and/or KCl reacted with the PbCl₂, forming various new compounds (Na₃Pb₂(SO₄)₃Cl, K₃Pb₂(SO₄)₃Cl, and/or K₂PbCl₄). In addition, melt formation was observed with all alkali salt deposits. Visibly more Pb was found in deposits where reactions between PbCl₂ 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. PbCl₂ in contact with the steel surface lead to faster corrosion than K₂PbCl₄.