The effect of ash deposition on corrosion behaviour of boiler steels in simulated combustion atmospheres containing carbon dioxide (CORBI PROJECT)

Abstract

AbstractThis study is a part of the FP5 Project entitled “Mitigation of Formation of Chlorine Rich Deposits Affecting Superheater Corrosion under Co‐Combustion Conditions” (CORBI) which is aimed to improve the understanding of corrosion mechanisms in cases of biomass and waste combustion.The laboratory experiments, made at the JRC Plant Simulation Test Laboratory, are focused mainly on common ferritic and austenitic materials (X10, X20, 2.25Cr1Mo, AC66, Sanicro28, Esshette 1250, etc.), which are usually used in energy conversion systems. The experiments were carried out in multi‐sample autoclaves at an isothermal temperature of 535 °C in various simulated combustion atmospheres (22% H2O + 5% O2 + xCO2 + N 2 with different CO2 content varying from 0 to 25 vol.%) on samples with and without filter/cyclone ash deposition. The results obtained show that the corrosion rate of the studied materials increases with increasing CO2 content in the atmosphere. Such behaviour was observed for samples with and without ash deposit.The detailed analysis and thermodynamic calculations of cyclone and filter ash behaviour were performed at MPIE in Duesseldorf. The ashes were exposed to 13% CO2 + 5% O2 + xH2O + y HCl + N2 atmospheres with different H2O content varying from 5–22% and HCl content varying from 0–200 ppm at 535 °C. The results obtained show that in an HCl‐containing atmosphere the alkali chloride formed from alkali carbonate, as well as hydroxides and oxides, can additionally accelerate the oxidation process. In the HCl free atmosphere at increased H2O content, alkali carbonates and hydroxides can form, so enhanced alkali chloride induced oxidation will not occur.