Some Aspects of Materials Selection for Condensing Economizers

Abstract The use of a condensing economizer within a biomass combustion system is a potentially attractive heat recovery solution for the pulp and paper industry. Selecting materials from which to construct condensing economizers for installation within utility power boiler units is, however, not trivial considering that aqueous sulphuric acid (H2SO4) condensates are typically formed. The expected corrosiveness of the flue gas condensate derived from pulp and paper biomass fuels is likely higher than that derived from natural gas (lower sulphur and chlorine contents), but lower than that derived from fossil fuels (higher sulphur and chlorine contents). To help guide materials selection, a laboratory corrosion testing program was initiated to evaluate the corrosion resistance of candidate alloys to synthetic acidic flue gas condensates expected to be derived from pulp and paper biomass fuels. The initial work, which is reported here, was focused on evaluating the resistance of carbon steel and stainless steel to dewpoint corrosion in chloride-free aqueous H2SO4 condensates and to stress corrosion cracking in a saturated aqueous ammonium nitrate (NH4NO3) solution.