Corrosion and carburization of superheater materials in oxyfuel combustion

The energy sector is globally the largest CO₂ emitter. Carbon capture and storage (CCS) is a concept to reduce greenhouse gas emissions resulting from the use of fossil fuels in power generation, and integrated oxyfuel combustion concepts, combustion in oxygen-enriched environment to make post-combustion extraction easier, is studied one of the options for CCS. Oxyfuel combustion can be expected to differ from combustion in air by e.g. modified distribution of fireside temperatures, much reduced NO_x but increased levels of fireside CO₂, SO₂ and water levels due to extensive flue gas recirculation. Increased flue gas recirculation may increase the concentration of a number of contaminants in the deposited ash and promote fouling and corrosion. In addition to development of low CO₂ emitting energy generation technologies, improved energy efficiency is essential in order to reach emission reduction targets. Increasing process efficiency requires high in-service temperatures for superheaters and reheaters. In this paper the corrosion performance of two superheater austenitic steels (TP347HFG and Sanicro 25) has been studied in laboratory tests under simulated oxyfuel conditions with and without a synthetic deposits (85 CaCO₃ - 15 wt% CaSO₄, CaSO₄-0.55 wt% KCl) at 650 and 720°C up to 1000 hours.