Alkali chloride induced corrosion of superheaters under biomass firing conditions: Improved insights from laboratory scale studies

One of the major operational challenges experienced by power plants firing biomass is the high corrosion rate of superheaters. This limits the outlet steam temperature of the superheaters and consequently, the efficiency of the power plants. The high corrosion rates have been attributed to the formation of corrosive deposits (rich in alkali chlorides) on the surfaces of the superheaters. Accordingly, an extensive number of fundamental investigations have been undertaken to understand the basic mechanisms behind the alkali chloride induced high temperature corrosion of superheaters (for example, [1–3]). However, complete understanding of the corrosion mechanism under biomass-firing conditions has not yet been achieved. This is attributed partly to the complex nature of the corrosion process since there are many species produced from fuel combustion which can interact with one another and the steel surface. Many studies have focused on specific parameters such as, deposit composition (KCl, K₂SO₄, K₂CO₃, etc.) or gas species such as HCl, SO₂, H₂O [4–6], however, more research is necessary to understand the interaction of deposits and gas mixtures with each other and metallic superheater materials.