Abstract
Heat exchange surfaces in biomass- and waste-fired boilers are exposed to corrosive species due to the considerable amounts of alkali chlorides and PbCl2 which are released during combustion. The corrosivity of alkali chlorides toward superheater alloys exposed at high temperature has been studied extensively. However, at lower material temperatures, i.e., at waterwall conditions, considerably less research has been performed. In order to investigate the effect of small amounts of KCl and PbCl2 during the initial stages of the corrosion attack, a Fe–2.25Cr–1Mo steel was exposed for 24 h in an atmospheres consisting of O2 + H2O + N2 at 400 °C. Both KCl and PbCl2 resulted in an increased corrosion rate compared to the reference. The aim of the present paper is to investigate the influence of KCl and PbCl2 on the initial oxidation of a Fe–2.25Cr–1Mo steel. The work involves a detailed microstructural investigation as well as thermodynamic equilibrium calculations.
Highlights
The fireside environment in biomass- and waste-fired boilers is characterized by high levels of alkali and HCl, which both are believed to cause elevated corrosion rates
Recent studies have shown that KCl and PbCl2 accelerates the corrosion rate at the relatively moderate temperatures that exist at the waterwalls [10,11,12,13]
In the presence of PbCl2, the mass gain (0.62 mg/cm2) after 24 h is high compared to the reference, but lower than that of the samples exposed in the presence of KCl
Summary
The fireside environment in biomass- and waste-fired boilers is characterized by high levels of alkali and HCl, which both are believed to cause elevated corrosion rates. To increase the power production from biomass- and waste-fired boilers, it is necessary to increase the steam data of these plants. This increase in steam data implies an increase in the material temperature of the superheaters, and an increase in material temperature of the waterwalls. Low-alloyed steels are often used as waterwall material due to its low cost and mechanical properties. These steels form an oxide scale of Fe2O3 and Fe3O4 which offer sufficient protection in mildly corrosive environments at moderate temperatures (\500 °C) [1]. Recent studies have shown that KCl and PbCl2 accelerates the corrosion rate at the relatively moderate temperatures that exist at the waterwalls [10,11,12,13]
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