Evidence of corrosion on metallic surfaces at 500 C and 560 C by metal-potassium trisulphate formation in oxy-co-combustion

Abstract

This work explores potassium pyrosulphate (K2S2O7) reactivity with iron, chromium and nickel oxides as simulation of the corrosion risk caused by alkaline deposits in the oxy-fuel co-firing of coal with high KCl biomass. TGA studies confirm the formation of metallic trisulphates (K3Fe(SO4)3, K3Cr(SO4)3 and K2Ni2(SO4)3) at 500 C and 560 C. Selected steels and alloys (P91, 409, 304, 347, 310, I800HT and I617) were pre-oxidised in 5% O2/CO2 for 200 h and the oxidation scales were treated with K2S2O7 to study the mechanism of oxide dissolution by Fe, Cr and Ni trisulphates, and inner sulphidation.